Warm gas and dust surround the innermost regions of active galactic nuclei (AGN). They provide the material for accretion onto the super-massive black hole and they are held responsible for the orientation-dependent obscuration of the central engine. The AGN-heated dust distributions turn out to be very compact with sizes on scales of about a parsec in the mid-infrared. Only infrared interferometry currently provides the necessary angular resolution to directly study the physical properties of this dust. Size estimates for the dust distributions derived from interferometric observations can be used to construct a size--luminosity relation for the dust distributions. The large scatter about this relation suggests significant differences between the dust tori in the individual galaxies, even for nuclei of the same class of objects and with similar luminosities. This questions the simple picture of the same dusty doughnut in all AGN. The Circinus galaxy is the closest Seyfert 2 galaxy. Because its mid-infrared emission is well resolved interferometrically, it is a prime target for detailed studies of its nuclear dust distribution. An extensive new interferometric data set was obtained for this galaxy. It shows that the dust emission comes from a very dense, disk-like structure which is surrounded by a geometrically thick, similarly warm dust distribution as well as significant amounts of warm dust within the ionisation cone.
Using X-ray stacking analyses we estimate the average amounts of supermassive black hole (SMBH) growth taking place in star-forming galaxies (SFGs) at z~1 and z~2 as a function of galaxy stellar mass (M*). We find the average rate of SMBH growth taking place in SFGs follows remarkably similar trends with both M* and redshift as the average star-formation rates (SFRs) of these galaxies (i.e., dM_BH/dt ~ M*^(0.86+/-0.39) for the z~1 sample and dM_BH/dt ~ M*^(1.05+/-0.36) for the z~2 sample). It follows that the ratio of SMBH growth rate to SFR is (a) flat with respect to galaxy stellar mass (b) not evolving with redshift and (c) close to the ratio required to maintain/establish a SMBH to stellar mass ratio of ~10^(-3) as also inferred from today's M_BH-M_Bulge relationship. We interpret this as evidence that SMBHs have, on average, grown in-step with their host galaxies since at least z~2, irrespective of host galaxy mass and AGN triggering mechanism and that the relative growth rates are more important in establishing inferred M_BH-M* relationships than the seed SMBH masses or merger history. Based on these results we speculate that it is the availability of gas reservoirs that regulates both cosmological SMBH growth and star-formation.
We use the relations between aperture stellar velocity dispersion (\sigma_ap), stellar mass (M_sps), and galaxy size (R_e) for a sample of 150,000 early-type galaxies from SDSS/DR7 to place constraints on the stellar initial mass function (IMF) and dark halo response to galaxy formation. We build LCDM based mass models that reproduce, by construction, the relations between size, light concentration and stellar mass. Reproducing the median \sigma_ap vs M_sps relation is not possible in models that have {\it both} a universal IMF and a universal dark halo response. Significant departures from a universal IMF and/or dark halo response are required. We show that this degeneracy can be broken using the strength of the correlation between residuals of the velocity-mass (\Delta log \sigma_ap) and size-mass (\Delta log R_e) relations. The slope of this correlation, d_vr = \Delta log\sigma_ap/\Delta log R_e, varies systematically with galaxy mass from -0.45 at M_sps \sim 10^{10} M_sun, to -0.15 at M_sps \sim 10^{11.6}M_sun. The virial fundamental plane (FP) has d_vr=-1/2, and thus we find the tilt of the FP is mass dependent. Reproducing this tilt requires {\it both} a non-universal IMF and a non-universal halo response. Our best model has mass-follows-light at low masses (M_sps < 10^{11.2}M_sun) and unmodified NFW haloes at M_sps \sim 10^{11.5}M_sun. The stellar masses imply a mass dependent IMF which is "lighter" than Salpeter at low masses and "heavier" than Salpeter at high masses.
We present the first analysis of the X-ray warm absorber and nuclear obscuration in the Seyfert 1.8 galaxy ESO 113-G010. We used archival data from a 100 ks XMM-Newton observation made in 2005. From high resolution spectroscopy analysis of the RGS data, we detect absorption lines originating from a warm absorber consisting of two distinct phases of ionisation, with log xi ~ 3.2 and 2.3 respectively. The higher-ionised component has a larger column density and outflow velocity (N_H ~ 1.6 x 10^22 cm^-2, v ~ -1100 km/s) than the lower-ionised component (N_H ~ 0.5 x 10^22 cm^-2, v ~ -700 km/s). The shape of the optical-UV continuum and the large Balmer decrement (H_alpha/H_beta ~ 8) indicate significant amount of reddening is taking place in our line of sight in the host galaxy of the AGN; however, the X-ray spectrum is not absorbed by cold neutral gas intrinsic to the source. We discuss different explanations for this discrepancy between the reddening and the X-ray absorption, and suggest that the most likely solution is a dusty warm absorber. We show that dust can exist in the lower-ionised phase of the warm absorber, which causes the observed reddening of the optical-UV emission, whereas the X-rays remain unabsorbed due to lack of cold neutral gas in the ionised warm absorber. Furthermore, we have investigated the uncertainties in the construction of the Spectral Energy Distribution (SED) of this object due to obscuration of the nuclear source and the effects this has on the photoionisation modelling of the warm absorber. We show how the assumed SEDs influence the thermal stability of each phase and whether or not the two absorber phases in ESO 113-G010 can co-exist in pressure equilibrium.
We have vastly increased the CIV statistics at intermediate redshift by surveying the thousands of quasars in the Sloan Digital Sky Survey Data-Release 7. We visually verified over 16,000 CIV systems with 1.46 < z < 4.55---a sample size that renders Poisson error negligible. Detailed Monte Carlo simulations show we are approximately 50% complete down to rest equivalent widths W_r ~ 0.6 \AA. We analyzed the sample as a whole and in ten small redshift bins with approximately 1500 doublets each. The equivalent width frequency distributions f(W_r) were well modeled by an exponential, with little evolution in shape. In contrast with previous studies that modeled the frequency distribution as a single power law, the fitted exponential gives a finite mass density for the CIV ions. The co-moving line density dN_CIV/dX evolved smoothly with redshift, increasing by a factor of 2.36+/-0.08 from z = 4.55 to 1.96, then plateauing at dN_CIV/dX ~ 0.34 for z = 1.96 to 1.46. Comparing our SDSS sample with z < 1 (ultraviolet) and z > 5 (infrared) surveys, we see an approximately ten-fold increase in dN_CIV/dX over z ~ 6 --> 0, for W_r >= 0.6 \AA. This suggests a monotonic and significant increase in the enrichment of gas outside galaxies over the 12 Gyr lifetime of the universe.
We construct a sample of 75,863 star forming galaxies with robust metallicity and star formation rate measurements from the Sloan Digital Sky Survey Data Release 7 (SDSS DR7), from which we select a clean sample of compact group (CG) galaxies. The CGs are defined to be close configurations of at least 4 galaxies that are otherwise apparently isolated. Our selection results in a sample of 112 spectroscopically identified compact group galaxies, which can be further divided into groups that are either embedded within a larger structure, such as a cluster or large group, or truly isolated systems. The compact groups then serve as a probe into the influence of large scale environment on a galaxy's evolution, while keeping the local density fixed at high values. We find that the star formation rates (SFRs) of star forming galaxies in compact groups are significantly different between isolated and embedded systems. Galaxies in isolated systems show significantly enhanced SFR, relative to a control sample matched in mass and redshift, a trend not seen in the embedded systems. Galaxies in isolated systems exhibit a median SFR enhancement at fixed stellar mass of +0.07 \pm 0.03 dex. These dependences on large scale environment are small in magnitude relative to the apparent influence of local scale effects found in previous studies, but the significance of the difference in SFRs between our two samples constrains the effect of large scale environment to be non-zero. We find no significant change in the gas-phase interstellar metallicity for either the isolated or embedded compact group sample relative to their controls. However, simulated samples that include artificial offsets indicate that we are only sensitive to metallicity changes of log O/H >0.13 dex (at 99% confidence), which is considerably larger than the typical metallicity differences seen in previous environmental studies.
We present 3D-HST, a near-infrared spectroscopic Treasury program with the Hubble Space Telescope for studying the processes that shape galaxies in the distant Universe. 3D-HST provides rest-frame optical spectra for a sample of ~7000 galaxies at 1<z<3.5, the epoch when 60% of all star formation took place, the number density of quasars peaked, the first galaxies stopped forming stars, and the structural regularity that we see in galaxies today must have emerged. 3D-HST will cover 3/4 (625 sq.arcmin) of the CANDELS survey area with two orbits of primary WFC3/G141 grism coverage and two to four parallel orbits with the ACS/G800L grism. In the IR these exposure times yield a continuum signal-to-noise of ~5 per resolution element at H~23.1 and a 5sigma emission line sensitivity of 5x10-17 erg/s/cm2 for typical objects, improving by a factor of ~2 for compact sources in images with low sky background levels. The WFC3/G141 spectra provide continuous wavelength coverage from 1.1-1.6 um at a spatial resolution of ~0."13, which, combined with their depth, makes them a unique resource for studying galaxy evolution. We present the preliminary reduction and analysis of the grism observations, including emission line and redshift measurements from combined fits to the extracted grism spectra and photometry from ancillary multi-wavelength catalogs. The present analysis yields redshift estimates with a precision of sigma(z)=0.0034(1+z), or sigma(v)~1000 km/s. We illustrate how the generalized nature of the survey yields near-infrared spectra of remarkable quality for many different types of objects, including a quasar at z=4.7, quiescent galaxies at z~2, and the most distant T-type brown dwarf star known. The CANDELS and 3D-HST surveys combined will provide the definitive imaging and spectroscopic dataset for studies of the 1<z<3.5 Universe until the launch of the James Webb Space Telescope.
Using about 450,000 galaxies in the Deep Lens Survey, we present a detection of the gravitational magnification of z>4 Lyman Break Galaxies by massive foreground galaxies with 0.4<z<1, grouped by redshift. The magnification signal is detected at S/N greater than 20, and rigorous checks confirm that it is not contaminated by any galaxy sample overlap in redshift. The inferred galaxy mass profiles are consistent with earlier lensing analyses at lower redshift. We then explore the tomographic lens magnification signal by splitting our foreground galaxy sample into 7 redshift bins. Combining galaxy-magnification cross-correlations and galaxy angular auto-correlations, we develop a bias-independent estimator of the tomographic signal. As a diagnostic of magnification tomography, the measurement of this estimator rejects a flat dark matter dominated Universe at >9\sigma\ and is found to be consistent with the expected redshift-dependence of the WMAP7 \Lambda CDM cosmology.
An important issue in cosmology is reconstructing the effective dark energy equation of state directly from observations. With few physically motivated models, future dark energy studies cannot only be based on constraining a dark energy parameter space, as the errors found depend strongly on the parameterisation considered. We present a new non-parametric approach to reconstructing the history of the expansion rate and dark energy using Gaussian Processes, which is a fully Bayesian approach for smoothing data. We present a pedagogical introduction to Gaussian Processes, and discuss how it can be used to robustly differentiate data in a suitable way. Using this method we show that the Dark Energy Survey - Supernova Survey (DES) can accurately recover a slowly evolving equation of state to sigma_w = +-0.04 (95% CL) at z=0 and +-0.2 at z=0.7, with a minimum error of +-0.015 at the sweet-spot at z~0.14, provided the other parameters of the model are known. Errors on the expansion history are an order of magnitude smaller, yet make no assumptions about dark energy whatsoever. A code for calculating functions and their first three derivatives using Gaussian processes has been developed and is available for download at this http URL .
Recently, the number of detected galaxy counterparts of z > 2 Damped Lyman-alpha Absorbers in QSO spectra has increased substantially so that we today have a sample of 10 detections. M{\o}ller et al. in 2004 made the prediction, based on a hint of a luminosity-metallicity relation for DLAs, that HI size should increase with increasing metallicity. In this paper we investigate the distribution of impact parameter and metallicity that would result from the correlation between galaxy size and metallicity. We compare our observations with simulated data sets given the relation of size and metallicity. The observed sample presented here supports the metallicity-size prediction: The present sample of DLA galaxies is consistent with the model distribution. Our data also show a strong relation between impact parameter and column density of HI. We furthermore compare the observations with several numerical simulations and demonstrate that the observations support a scenario where the relation between size and metallicity is driven by feedback mechanisms controlling the star-formation efficiency and outflow of enriched gas.
The spectra of several high-redshift (z>6) quasars have shown evidence for a Gunn-Peterson (GP) damping wing, indicating a substantial mean neutral hydrogen fraction (x_HI > 0.03) in the z ~ 6 intergalactic medium (IGM). However, previous analyses assumed that the IGM was uniformly ionized outside of the quasar's HII region. Here we relax this assumption and model patchy reionization scenarios for a range of IGM and quasar parameters. We quantify the impact of these differences on the inferred x_HI, by fitting the spectra of three quasars: SDSS J1148+5251 (z=6.419), J1030+0524 (z=6.308), and J1623+3112 (z=6.247). We find that the best-fit values of x_HI in the patchy models agree well with the uniform case. More importantly, we confirm that the observed spectra favor the presence of a GP damping wing, with peak likelihoods decreasing by factors of > few - 10 when the spectra are modeled without a damping wing. We also find that the Ly alpha absorption spectra, by themselves, cannot distinguish the damping wing in a relatively neutral IGM from a damping wing in a highly ionized IGM, caused either by an isolated neutral patch, or by a damped Ly alpha absorber (DLA). However, neutral patches in a highly ionized universe (x_HI < 0.01), and DLAs with the large required column densities (N_HI > few x 10^{20} cm^{-2}) are both rare. As a result, when we include reasonable prior probabilities for the line of sight (LOS) to intercept either a neutral patch or a DLA at the required distance of ~ 40-60 comoving Mpc away from the quasar, we find strong lower limits on the neutral fraction in the IGM, x_HI > 0.1 (at 95% confidence). This strengthens earlier claims that a substantial global fraction of hydrogen in the z~6 IGM is in neutral form.
Proposed space-based gravitational-wave (GW) detectors such as DECIGO and BBO will detect $\sim10^6$ neutron-star (NS) binaries and determine the luminosity distances to the binaries with high precision. Combining the luminosity distances with cosmologically-induced phase corrections on the GWs, cosmological expansion out to high redshift can be measured without the redshift determinations of host galaxies by electromagnetic observation and can be a unique probe for dark energy. This article is based on the results obtained in [1] where we investigated constraining power of the GW standard siren without redshift information on the equation of state of dark energy with future space-based GW detectors. We also compare the results with those obtained with other instruments and methods.
From the first published z>3 survey of 21-cm absorption within the hosts of radio galaxies and quasars, Curran et al. (2008b) found an apparent dearth of cool neutral gas at high redshift. From a detailed analysis of the photometry, each object is found to have a 1216 Angstrom continuum luminosity in excess of L > 1e23 W/Hz, a critical value above which 21-cm has never been detected at any redshift. For a variety of gas density distributions, we show that by placing a quasar within a galaxy of gas there is always an ultra-violet luminosity above which all of the gas in the galaxy is excited (and most likely ionised). Above this critical luminosity the hydrogen cannot be detected in the absorption of the 21-cm transition (and possibly Lyman-alpha) and while in this state the gas cannot engage in star formation. Applying the mean ionising photon rate of all of the sources searched, we find, using canonical values for the gas density and recombination rate coefficient, that the observed critical luminosity gives a scale-length (3 kpc) similar that of the neutral hydrogen (HI) in the Milky Way, a large spiral galaxy. This demonstrates that these galaxies are truly devoid of star-forming material, rather the non-detection of 21-cm being due to the sensitivity limits of current radio telescopes.
Most theoretical models invoke quasar driven outflows to quench star formation in massive galaxies, this feedback mechanism is required to account for the population of old and passive galaxies observed in the local universe. The discovery of massive, old and passive galaxies at z=2, implies that such quasar feedback onto the host galaxy must have been at work very early on, close to the reionization epoch. We have observed the [CII]158um transition in SDSSJ114816.64+525150.3 that, at z=6.4189, is one of the most distant quasars known. We detect broad wings of the line tracing a quasar-driven massive outflow. This is the most distant massive outflow ever detected and is likely tracing the long sought quasar feedback, already at work in the early Universe. The outflow is marginally resolved on scales of about 16 kpc, implying that the outflow can really affect the whole galaxy, as required by quasar feedback models. The inferred outflow rate, dM/dt > 3500 Msun/yr, is the highest ever found. At this rate the outflow can clean the gas in the host galaxy, and therefore quench star formation, in a few million years.
We present Herschel/SPIRE images at 250, 350, and 500 {\mu}m of NGC 4244, a typical low-mass, disk-only and edge-on spiral galaxy. The dust disk is clumpy and shows signs of truncation at the break radius of the stellar disk. This disk coincides with the densest part of the Hi disk. We compare the Spectral Energy Distribution, including the new SPIRE fluxes, to 3D radiative transfer models; a smooth model disk and a clumpy model with embedded heating. Each model requires a very high value for the dust scale-length (h(dust) = 2 - 5 h(stars)), higher dust masses than previous models of NGC 4244 (Md = 0.47 - 1.39 \times 10e7 Msun) and a face-on optical depth of {\tau}(V) = 0.4 - 1.12, in agreement with previous disk opacity studies. The vertical scales of stars and dust are similar. The clumpy model much better mimics the general morphology in the submm images and the general SED. The inferred gas-to-dust mass ratio is compatible with those of similar low-mass disks. The relatively large radial scale-length of the dust disk points to radial mixing of the dusty ISM within the stellar disk. The large vertical dust scale and the clumpy dust distribution of our SED model are both consistent with a scenario in which the vertical structure of the ISM is dictated by the balance of turbulence and self-gravity.
The presence of a well-defined and narrow dust lane in an edge-on spiral galaxy is the observational signature of a thin and dense molecular disk, in which gravitational collapse has overcome turbulence. Using a sample of galaxies out to z~1 extracted from the COSMOS survey, we identify the fraction of massive disks that display a dust lane. Our goal is to explore the evolution in the stability of the molecular ISM disks in spiral galaxies over a cosmic timescale. We check the reliability of our morphological classifications against changes in restframe wavelength, resolution, and cosmic dimming with (artificially redshifted) images of local galaxies from SDSS. We find that the fraction of L* disks with dust lanes in COSMOS is consistent with the local fraction (~80%) out to z~0.7. At z=0.8, the dust lane fraction is only slightly lower. A somewhat lower dust lane fraction in starbursting galaxies tentatively supports the notion that a high specific star formation rate can efficiently destroy or inhibit a dense molecular disk. A small subsample of higher redshift COSMOS galaxies display low internal reddening (E[B-V]), as well as a low incidence of dust lanes. These may be disks in which the growth of the dusty ISM disk lags behind that of the stellar disk. We note that at z=0.8, the most massive galaxies display a lower dust lane fraction than lower mass galaxies. A small contribution of recent mergers or starbursts to this most massive population may be responsible. The fact that the fraction of galaxies with dust lanes in COSMOS is consistent with little or no evolution implies that models to explain the Spectral Energy Distribution or the host galaxy dust extinction of supernovae based on local galaxies are still applicable to higher redshift spirals. It also suggests that dust lanes are long lived phenomena or can be reformed over very short time-scales.
We monitored the 22 GHz maser line in the lensed quasar MG J0414+0534 at z=2.64 with the 300-m Arecibo telescope for almost two years to detect possible additional maser components and to measure a potential velocity drift of the lines. The main maser line profile is complex and can be resolved into a number of broad features with line widths of 30-160 km/s. A new maser component was tentatively detected in October 2008 at a velocity of +470 km/s. After correcting for the estimated lens magnification, we find that the H2O isotropic luminosity of the maser in MG J0414+0534 is about 26,000 solar luminosities, making this source the most luminous ever discovered. Both the main line peak and continuum flux densities are surprisingly stable throughout the period of the observations. An upper limit on the velocity drift of the main peak of the line has been estimated from our observations and is of the order of 2 km/s per year. We discuss the results of the monitoring in terms of the possible nature of the maser emission, associated with an accretion disk or a radio jet. This is the first time that such a study is performed in a water maser source at high redshift, potentially allowing us to study the parsec-scale environment around a powerful radio source at cosmological distances.
We investigate gravitational lensing in the context of the MOG modified theory of gravity. Using a formulation of the theory with no adjustable or fitted parameters, we present the MOG equations of motion for slow, nonrelativistic test particles and for ultrarelativistic test particles, such as rays of light. We demonstrate how the MOG prediction for the bending of light can be applied to astronomical observations. Our investigation first focuses on a small set of strong lensing observations where the properties of the lensing objects are found to be consistent with the predictions of the theory. We also present an analysis of the colliding clusters 1E0657-558 (known also as the Bullet Cluster) and Abell 520; in both cases, the predictions of the MOG theory are in good agreement with observation.
We discuss a new interacting model for the cosmological dark sector in which the attenuated dilution of cold dark matter scales as $a^{-3}f(a)$, where f(a) is an arbitrary function of the cosmic scale factor $a$. From thermodynamic arguments, we show that f(a) is proportional to entropy source of the particle creation process. In order to investigate the cosmological consequences of this kind of interacting models, we expand f(a) in a power series and viable cosmological solutions are obtained. Finally, we use current observational data to place constraints on the interacting function f(a).
Using SDSS Stripe82 data we have obtained deep radial surface brightness profiles of 7 face-on to intermediate inclined late-type spirals down to \sim 30 mag arcsec^-2 in the r'-band. We do not find any evidence for a sharp cut-off of the light distribution of the disks but a smooth continuation into the stellar halos of galaxies. Stellar halos start to affect the surface brightness profiles of the galaxies at \sim 28 mag arcsec^-2, and at a radial distance of \sim 4-10 inner scale-lengths. We find that the light contribution from the stellar halo could be responsible of previous classification of surface brightness profiles as Type III in late-type galaxies. In order to estimate the contribution of the stellar halo light to the total galaxy light, we carried out a Bulge/Disk/Stellar Halo decomposition by simoultaneously fitting all components. The light contribution of the halo to the total galaxy light varies from ~ 1% to ~ 5%, but in case of ongoing mergers, the halo light fraction can be as high as ~ 10%, independently of the luminosities of the galaxies. We have also explored the integrated (g'-r') color of the stellar halo of our galaxies. We find (g'-r') colors ranging from ~ 0.4 to ~ 1.2. By confronting these colors with model predictions, we encounter problems to fit our very red colors onto stellar population grids with conventional IMFs. Very red halo colors can be attributed to stellar populations dominated by very low mass stars of low to intermediate metallicity produced by bottom-heavy IMFs.
Based on the Veneziano ghost theory of QCD, we estimate the cosmological constant $\Lambda$, which is related to the vacuum energy density, $\rho_{\Lambda}$, by $\Lambda = \frac{8\pi G}{3} \rho_{\Lambda}$. In the current Veneziano ghost theory $\rho_{\Lambda}$ is given by the absolute value of the product of the local quark condensate and quark current mass:$\rho_{\Lambda} = \frac{2N_{f}H}{m_{\eta'}}c |m_{q}<0|:\bar{q}q:|0>|$. By solving Dyson-Schwinger Equations for a dressed quark propagator, we found the local quark condensate $<0|:\bar{q}q:|0> \simeq -(235 MeV)^{3}$, the generally accepted value. The quark current mass, predicted by use of chiral perturbation theory is $m_{q} \simeq 3.29 - 6.15$. This gives the same result for $\rho_{\Lambda}$ as found by previous authors, which is somewhat larger than the observed value. However, when we make use of the nonlocal quark condensate, $<0|:\bar{q}(x)q(0):|0>= g(x)<0|:\bar{q}q:|0>$, with g(x) estimated from our previous work, we find $\Lambda$ is in a good agreement with the observations.
We study the cosmological evolution of an induced gravity model with a scale symmetry breaking potential for the scalar field. The radiation to matter transition, following inflation and reheating, influences the dynamics of such a field through its non minimal coupling. We illustrate how, under certain conditions on the potential, such a dynamics can lead to a suitable amount of dark energy explaining the present accelerated expansion.
In this paper we examine the percentage of type 1 AGN which require the inclusion of a soft excess component and/or significant cold absorption in the modelling of their X-ray spectra obtained by XMM-Newton. We do this by simulating spectra which mimic typical spectral shapes in order to find the maximum detectability expected at different count levels. We then apply a correction to the observed percentages found for the Scott et al. (2011) sample of 761 sources. We estimate the true percentage of AGN with a soft excess component to be 75+/-23%, suggesting that soft excesses are ubiquitous in the X-ray spectra of type 1 AGN. By carrying out joint fits on groups of low count spectra in narrow z bins in which additional spectral components were not originally detected, we show that the soft excess feature is recovered with a mean temperature kT and blackbody to power-law normalisation ratio consistent with those of components detected in individual high count spectra. Cold absorption with nH values broadly consistent with those reported in individual spectra are also recovered. We suggest such intrinsic cold absorption is found in a minimum of ~5% of type 1 AGN and may be present in up to ~10%.
We use a recently-developed analytic model for the ISM structure from scales of GMCs through star-forming cores to explore how the pre-stellar core mass function (CMF) and, by extrapolation, stellar initial mass function (IMF) should depend on both local and galactic properties. If the ISM is supersonically turbulent, the statistical properties of the density field follow from the turbulent velocity spectrum, and the excursion set formalism can be applied to analytically calculate the mass function of collapsing cores on the smallest scales on which they are self-gravitating (non-fragmenting). Two parameters determine the model: the disk-scale Mach number M_h (which sets the shape of the CMF), and the absolute velocity (to assign an absolute scale). For 'normal' variation in disk properties and core gas temperatures in the MW and local galaxies, there is almost no variation in the predicted high-mass behavior of the CMF/IMF. The slope is always close to Salpeter down to <1 M_sun. We predict modest variation in the sub-solar regime, mostly from variation in M_h, but within the observed scatter in sub-solar IMFs in local regions. For fixed galaxy properties, there is little variation in shape or 'upper mass limit' with parent GMC mass. However, in extreme starbursts (e.g. ULIRGs) we predict a bottom-heavy CMF. This agrees with the IMF inferred for the centers of Virgo ellipticals, believed to form in such a nuclear starburst. The CMF is bottom heavy despite the gas temperature being an order of magnitude larger, because M_h is also much larger. Larger M_h values make the 'parent' cloud mass (turbulent Jeans mass) larger, but promote fragmentation to smaller scales; this steepens the slope of the low-mass CMF and shifts the turnover mass. The model may predict a top-heavy CMF for the sub-pc disks around Sgr A*, but the relevant input parameters are uncertain.
The newsletter of the Australian Astronomical Observatory. In this issue: Using 2dF and AAOmega to Harness the Full Power of the Supernova Legacy Survey; Emission Lines in the Near Infrared: Tracing the Violent ISM; Dancing Starbugs: vacuum adhesion, field rotation and other progress; A message of progress from HERMES; Imaging with the 2dF Focal Plane Imager; and all the usual columns and news from the Observatory.
We extend our investigation of soft graviton effects on the microscopic dynamics of matter fields in de Sitter space. We evaluate the quantum equation of motion in generic gauge theories. We find that the Lorentz invariance can be respected and the velocity of light is not renormalized at the one-loop level. The gauge coupling constant is universally screened by soft gravitons and diminishes with time. These features are in common with other four dimensional field theories with dimensionless couplings. In particular the couplings scale with time with definite scaling exponents. Although individual scaling exponents are gauge dependent, we argue that the relative scaling exponents are gauge independent and should be observable. We also mention soft graviton effects on CMB.
The properties of a spherically symmetric static space-time permeated of dark energy are worked out. Dark energy is viewed as the strain energy of an elastically deformable four dimensional manifold. The metric is worked out in the vacuum region around a central spherical mass/defect in the linear approximation. We discuss analogies and differences with the analogue in the de Sitter space time and how these competing scenarios could be differentiated on an observational ground. The comparison with the tests at the solar system scale puts upper limits to the parameters of the theory, consistent with the values obtained applying the classical cosmological tests.
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The fermionic dark matter (DM) phase-space density Q(r) = rho(r)/sigma^3(r) must be smaller than K m^4/\hbar^3 where m is the DM particle mass, sigma(r) is the DM velocity dispersion and K is a pure number of order one which we estimate. This bound follows from the Pauli principle which restricts the phase-space distribution function of fermionic spin-1/2 dark matter (DM) particles to be f(r,p) < 2. Cusped profiles from N-body galaxy simulations produce a divergent Q(r) at r = 0 violating this quantum bound. Combining this quantum bound with the behavior of Q(r) from simulations and with galaxy observational data on Q, implies that classical galaxy dynamics breaks down for fermionic DM at a distance from the centre of at least r_q. For keV scale WDM r_q turns to be in the parsec scale. For cold dark matter (CDM), r_q is between dozens of kilometers and a few meters, astronomically compatible with zero. For fermionic hot dark matter (HDM) r_q is from kpc to Mpc. This quantum bound rules out the presence of galaxy cusps for fermionic WDM. This is in agreement with astronomical observations which show that the DM halos are cored. The formation of cusps would be allowed for bosonic DM for which the Pauli principle does not apply. Hence, bosonic DM is strongly disfavored by the observation of galaxy cores. Quantum dynamical calculations become necessary to compute galaxy structures at kpc scales and below. N-body simulations can be used at scales larger than a kpc and matched with the quantum evolution.The Thomas-Fermi quantum approximation to self-gravitating fermions with masses in the keV scale yields galaxy properties as halo radius, mass and velocity dispersion consistent with the observations. Namely, fermionic WDM treated quantum mechanically, as it must be, reproduces the observed DM cores of galaxies.
The Panchromatic Hubble Andromeda Treasury (PHAT) survey is an on-going Hubble Space Telescope (HST) multi-cycle program to obtain high spatial resolution imaging of one-third of the M31 disk at ultraviolet through near-infrared wavelengths. In this paper, we present the first installment of the PHAT stellar cluster catalog. When completed, the PHAT cluster catalog will be among the largest and most comprehensive surveys of resolved star clusters in any galaxy. The exquisite spatial resolution achieved with HST has allowed us to identify hundreds of new clusters that were previously inaccessible with existing ground-based surveys. We identify 601 clusters in the Year 1 sample, representing more than a factor of four increase over previous catalogs within the current survey area (390 arcmin^2). This work presents results derived from the first \sim25% of the survey data; we estimate that the final sample will include \sim2500 clusters. For the Year 1 objects, we present a catalog with positions, radii, and six-band integrated photometry. Along with a general characterization of the cluster luminosities and colors, we discuss the cluster luminosity function, the cluster size distributions, and highlight a number of individually interesting clusters found in the Year 1 search.
We present the first science results from our Hubble Space Telescope Survey for Lyman limit absorption systems (LLS) using the low dispersion spectroscopic modes of the Advanced Camera for Surveys and the Wide Field Camera 3. Through an analysis of 71 quasars, we determine the incidence frequency of LLS per unit redshift and per unit path length, l(z) and l(x) respectively, over the redshift range 1 < z< 2.6, and find a weighted mean of l(x)=0.29 +/-0.05 for 2.0 < z < 2.5 through a joint analysis of our sample and that of Ribaudo et al. (2011). Through stacked spectrum analysis, we determine a median (mean) value of the mean free path to ionizing radiation at z=2.4 of lambda_mfp = 243(252)h^(-1) Mpc, with an error on the mean value of +/- 43h^(-1) Mpc. We also re-evaluate the estimates of lambda_mfp from Prochaska et al. (2009) and place constraints on the evolution of lambda_mfp with redshift, including an estimate of the "breakthrough" redshift of z = 1.6. Consistent with results at higher z, we find that a significant fraction of the opacity for absorption of ionizing photons comes from systems with N_HI <= 10^{17.5} cm^(-2) with a value for the total Lyman opacity of tau_lyman = 0.40 +/- 0.15. Finally, we determine that at minimum, a 5-parameter (4 power-law) model is needed to describe the column density distribution function f(N_HI, X) at z \sim 2.4, find that f(N_HI,X) undergoes no significant change in shape between z \sim 2.4 and z \sim 3.7, and provide our best fit model for f(N_HI,X).
New data are reported from the operation of a 4.0 kg CF$_{3}$I bubble chamber in the 6800 foot deep SNOLAB underground laboratory. The effectiveness of ultrasound analysis in discriminating alpha decay background events from single nuclear recoils has been confirmed, with a lower bound of $>$99.3% rejection of alpha decay events. Twenty single nuclear recoil event candidates and three multiple bubble events were observed during a total exposure of 553 kg-days distributed over three different bubble nucleation thresholds. The effective exposure for single bubble recoil-like events was 437.4 kg-days. A neutron background internal to the apparatus, of known origin, is estimated to account for five single nuclear recoil events and is consistent with the observed rate of multiple bubble events. This observation provides world best direct detection constraints on WIMP-proton spin-dependent scattering for WIMP masses $>$20 GeV/c$^{2}$ and demonstrates significant sensitivity for spin-independent interactions.
The Elliptical Isolated X-ray (ElIXr) Galaxy Survey is a volume-limited (<110Mpc) study of optically selected, isolated, Lstar elliptical galaxies, to provide an X-ray census of galaxy-scale (virial mass, Mvir < 1e13 Msun) objects, and identify candidates for detailed hydrostatic mass modelling. In this paper, we present a Chandra and XMM study of one such candidate, NGC1521, and constrain its distribution of dark and baryonic matter. We find a morphologically relaxed hot gas halo, extending almost to R500, that is well described by hydrostatic models similar to the benchmark, baryonically closed, Milky Way-mass elliptical galaxy NGC720. We obtain good constraints on the enclosed gravitating mass (M500=3.8e12+/-1e12 Msun, slightly higher than NGC\thin 720), and baryon fraction (fb500=0.13+/-0.03). We confirm at 8.2-sigma the presence of a dark matter (DM) halo consistent with LCDM. Assuming a Navarro-Frenk-White DM profile, our self-consistent, physical model enables meaningful constraints beyond R500, revealing that most of the baryons are in the hot gas. Within the virial radius, fb is consistent with the Cosmic mean, suggesting that the predicted massive, quasi-hydrostatic gas halos may be more common than previously thought. We confirm that the DM and stars conspire to produce an approximately powerlaw total mass profile (rho \propto r^-alpha) that follows the recently discovered scaling relation between alpha and optical effective radius. Our conclusions are insensitive to modest, observationally motivated, deviations from hydrostatic equilibrium. Finally, after correcting for the enclosed gas fraction, the entropy profile is close to the self-similar prediction of gravitational structure formation simulations, as observed in massive galaxy clusters.
We present dynamical and structural scaling relations of quiescent galaxies at z=2, including the dynamical mass-size relation and the first constraints on the fundamental plane (FP). The backbone of the analysis is a new, very deep VLT/X-shooter spectrum of a massive, compact, quiescent galaxy at z=2.0389. We detect the continuum between 3700-22000A and several strong absorption features (Balmer series, Ca H+K, G-band), from which we derive a stellar velocity dispersion of 318 +/- 53 km/s. We perform detailed modeling of the continuum emission and line indices and derive strong simultaneous constraints on the age, metallicity, and stellar mass. The galaxy is a dusty (A_V=0.77 (+0.36,-0.32)) solar metallicity (log(Z/Zsun) = 0.02 (+0.20,-0.41)) post starburst galaxy, with a mean luminosity weighted log(age/yr) of 8.9 +/- 0.1. The galaxy formed the majority of its stars at z>3 and currently has little or no ongoing star formation. We compile a sample of three other z~2 quiescent galaxies with measured velocity dispersions, two of which are also post starburst like. Their dynamical mass-size relation is offset significantly less than the stellar mass-size relation from the local early type relations, which we attribute to a lower central dark matter fraction. Recent cosmological merger simulations qualitatively agree with the data, but can not fully account for the evolution in the dark matter fraction. The z~2 FP requires additional evolution beyond passive stellar aging, to be in agreement with the local FP. The structural evolution predicted by the cosmological simulations is insufficient, suggesting that additional, possibly non-homologous structural evolution is needed.
Being able to measure each merger's sky location, distance, component masses, and conceivably spins, ground-based gravitational-wave detectors will provide a extensive and detailed sample of coalescing compact binaries (CCBs) in the local and, with third-generation detectors, distant universe. These measurements will distinguish between competing progenitor formation models. In this paper we develop practical tools to characterize the amount of experimentally accessible information available, to distinguish between two a priori progenitor models. Using a simple time-independent model, we demonstrate the information content scales strongly with the number of observations. The exact scaling depends on how significantly mass distributions change between similar models. We develop phenomenological diagnostics to estimate how many models can be distinguished, using first-generation and future instruments. Finally, we emphasize that multi-observable distributions can be fully exploited only with very precisely calibrated detectors, search pipelines, parameter estimation, and Bayesian model inference.
Weak gravitational lensing by galaxy clusters on faint higher redshift galaxies has been traditionally used to study the cluster mass distribution and as a tool to identify clusters as peaks in the shear maps. However, it becomes soon clear that peaks statistics can also be used as a way to constrain the underlying cosmological model due to its dependence on both the cosmic expansion rate and the growth rate of structures. This feature makes peak statistics particularly interesting from the point of view of discriminating between General Relativity and modified gravity. Here we consider a general class of f(R) theories and compute the observable mass function based on the aperture mass statistics. We complement our theoretical analysis with a Fisher matrix forecast of the constraints that an Euclid - like survey can impose on the f(R) model parameters. We show that peak statistics alone can in principle discriminate between General Relativity and f(R) models and strongly constrain the f(R) parameters that are sensitive to the non - linear growth of structure. However, we also find a degeneracy between f(R) and dark energy models and the adopted relation between cluster mass and concentration.
Radio and X-ray emission of AGN appears to be correlated. The details of the underlying physical processes, however, are still not fully understood, i.e., to what extent is the X-ray and radio emission originating from the same relativistic particles or from the accretion-disk or corona or both. We study the cm radio emission of an SDSS/ROSAT/FIRST matched sample of 13 X-raying AGN in the redshift range 0.11< z < 0.37 at high angular resolution with the goal of searching for jet structures or diffuse, extended emission on sub-kpc scales. We use MERLIN at 18 cm for all objects and Western EVN at 18 cm for four objects to study the radio emission on scales of ~500 pc and ~40 pc for the MERLIN and EVN observations, respectively. The detected emission is dominated by compact nuclear radio structures. We find no kpc collimated jet structures. The EVN data indicate for compact nuclei on 40 pc scales, with brightness temperatures typical for accretion-disk scenarios. Comparison with FIRST shows that the 18 cm emission is resolved out up to 50% by MERLIN. Star-formation rates based on large aperture SDSS spectra are generally too small to produce considerable contamination of the nuclear radio emission. We can, therefore, assume the 18 cm flux densities to be produced in the nuclei of the AGN. Together with the ROSAT soft X-ray luminosities and black hole mass estimates from the literature, our sample objects follow closely the Merloni et al. (2003) fundamental plane relation, which appears to trace the accretion processes. Detailed X-ray spectral modeling from deeper hard X-ray observations and higher angular resolution at radio wavelengths are required to further proceed in the disentangling of jet and accretion related processes.
We investigate the possibility that the galactic dark matter exists in the phantom field responsible for the dark energy. We obtain the statically and spherically exact solution for this kind of the galaxy system with a supermassive black hole at its center. The solution of the metric functions is satisfied with $g_{tt} = - g_{rr}^{-1}$. Constrained by the observation of the rotational stars moving in circular orbits with nearly constant tangential speed in a spiral galaxy, the background of the phantom field which is spatially inhomogeneous has an exponential potential. The absorption cross section of the low-energy $S$-wave excitations, arising from the phantom dark energy, into the central black hole is shown to be the horizontal area of the central black hole. Because the infalling phantom particles have a total negative energy, the accretion of the phantom energy is companied with the decrease of the black hole mass which is estimated to be much less than a solar mass in the lifetime of the Universe. Using a simple model with the cold dark matters very weakly coupled to the phantom particles which are generated from the background, we show that these two densities can be stable in the galaxy.
We have conducted a statistical analysis of the ultra-luminous X-ray point sources (ULXs; L(X) >= 10^39 erg/s) in a sample of galaxies selected from the Arp Atlas of Peculiar Galaxies. We find a possible enhancement of a factor of ~2-4 in the number of ULXs per blue luminosity for the strongly interacting subset. Such an enhancement would be expected if ULX production is related to star formation, as interacting galaxies tend to have enhanced star formation rates on average. For most of the Arp galaxies in our sample, the total number of ULXs compared to the far-infrared luminosity is consistent with values found earlier for spiral galaxies. This suggests that for these galaxies, ULXs trace recent star formation. However, for the most infrared-luminous galaxies, we find a deficiency of ULXs compared to the infrared luminosity. For these very infrared-luminous galaxies, AGNs may contribute to powering the far-infrared; alternatively, ULXs may be highly obscured in the X-ray in these galaxies and therefore not detected by these Chandra observations. We determined local UV/optical colors within the galaxies in the vicinity of the candidate ULXs using GALEX UV and SDSS optical images. In most cases, the distributions of colors are similar to the global colors of interacting galaxies. However, the u - g and r - i colors at the ULX locations tend to be bluer on average than these global colors, suggesting that ULXs are preferentially found in regions with young stellar populations. In the Arp sample there is a possible enhancement of a factor of ~2 - 5 in the fraction of galactic nuclei that are X-ray bright compared to more normal spirals.
Recent observations of z >~ 7 Ly{\alpha} emitters (LAEs) have derived a variety of Ly{\alpha} luminosity functions (LFs) with contradictory results, evolution or non-evolution from z <~ 6, the epoch after reionization. This could be because most of z >~ 7 LFs comprise photometric candidates and might include some contaminations. We conducted the Subaru Telescope Faint Object Camera And Spectrograph narrowband NB980 ({\lambda}c ~ 9800A, FWHM ~ 100A) imaging and spectroscopy survey of z=7-7.1 LAEs to compare its "contamination-free" result with z >~ 7 photometric Ly{\alpha} LFs previously derived. We imaged the Subaru Deep Field and the sky around a cluster MS 1520.1+3002 and found one LAE candidate, but spectroscopy did not reveal Ly{\alpha} though deep enough to detect it. We calculated the expected number of LAEs in our survey, using five z=7 and three z=7.7 Ly{\alpha} LFs from recent surveys. Seven of them are consistent with null detection (0.1^{+1.8}_{-0.1}-1.1^{+2.2}_{-1.0} LAEs) within errors including Poisson statistics and cosmic variance, but average values (0.7-1.1 LAEs) predicted from one z=7 and two z=7.7 LFs among the seven indicate nearly a single detection. The remaining one z=7 LF predicts 3.0^{+3.2}_{-2.0} LAEs. As to z=7, the discrepancy likely comes from different LAE selection criteria. For z=7.7, there are two possibilities; (1) If z=7.7 LAEs are somehow brighter in Ly{\alpha} luminosity than lower redshift LAEs, z=7.7 LF is observed to be similar to or higher than lower redshift LFs even if attenuated by neutral hydrogen. (2) All/most of the z=7.7 candidates are not LAEs. This supports the decline of LF from z ~ 6 to 7.7 and reionization at z ~ 6-7.7.
We searched for z=7.3 Ly{\alpha} emitters (LAEs) behind two lensing clusters, Abell 2390 and CL 0024, using the Subaru Telescope Suprime-Cam and a narrowband NB1006 ({\lambda}c ~ 1005 nm, FWHM ~ 21 nm). Combination of the fully depleted CCDs of the Suprime-Cam, sensitive to z ~ 7 Ly{\alpha} at ~ 1 {\mu}m, and magnification by the lensing clusters can be potentially a powerful tool to detect faint distant LAEs. Using NB1006 and deep optical-infrared images taken with the Hubble and Spitzer Space Telescopes, we investigated if there exist objects consistent with the color of z=7.3 LAEs behind the clusters. We could not detect any LAEs to the unlensed Ly{\alpha} flux limit F(Ly{\alpha}) ~ 6.9 x 10^{-18} erg s^{-1} cm^{-2}. Comparison with z ~ 7 LAE field searches suggests that a blank field survey covering an area sufficiently larger than lensing clusters is more efficient in finding a large number of z ~ 7 LAEs than both a lensing survey observing many clusters with shallow imaging and a lensing survey imaging one cluster to a deeper luminosity limit, expected from the bright end slope of several z ~ 7 Ly{\alpha} luminosity functions. We also investigated the NB1006 images of the three z ~ 7 z-dropout galaxy candidates previously detected in Abell 2390 and found that none of them are detected in NB1006. Two of them are consistent with predictions from the previous studies that they would be at lower redshifts. The other one has a photometric redshift of z ~ 7.3, and if we assume that it is at z=7.3, the unlensed Ly{\alpha} line flux would be very faint: F(Ly{\alpha}) < 4.4 x 10^{-18} erg s^{-1} cm^{-2} (1 {\sigma} upper limit) or rest frame equivalent width of W(Ly{\alpha}) < 26A. Its Ly{\alpha} emission might be attenuated by neutral hydrogen, as recent studies show that the fraction of Lyman break galaxies displaying strong Ly{\alpha} emission is lower at z ~ 7 than at z <~ 6.
The cosmic string is a useful probe of the early Universe and may give us a clue to physics at high energy scales where any artificial particle accelerators cannot reach. Although one of the most promising tools is the cosmic microwave background, the constraint from gravitational waves is becoming so stringent that one may not hope to detect its signatures in the cosmic microwave background. In this paper, we construct a scenario that contains cosmic strings observable in the cosmic microwave background while evading the constraint imposed by the recent pulsar timing data. We argue that cosmic strings with relatively large tension are allowed by delaying the onset of the scaling regime. We also show that this scenario is naturally realized in the context of chaotic inflation in supergravity, where the phase transition is governed by the Hubble induced mass.
We study the radio - far-infrared (FIR) correlation in a sample of faint dwarf irregular galaxies using NVSS data for 1.4 GHz radio flux, Spitzer MIPS 70 um data for FIR flux, and GALEX FUV data to estimate the star formation rates (SFR). Since our target galaxies are extremely faint, we stack images of many galaxies together to estimate the average radio and FIR fluxes. We find that for a given SFR both 70 um and 1.4 GHz fluxes are low compared to the calibration for large spirals. Nonetheless, the ratio of 70 um to 1.4 GHz flux agrees within errorbars with that seen for large galaxies. The radio-FIR correlation thus appears to be the result of a 'conspiracy'. We use the SFR to estimate the non-thermal fraction of the 1.4 GHz radio emission and find it to be around 50%, much smaller than the 90% typical for spirals. We also estimate the equipartition magnetic field and find it to be ~ 2 microgauss, about five times smaller than that typical for spirals.
Surprisingly little is known about the origin and evolution of the Milky Way's satellite galaxy companions. UV photoionisation, supernova feedback and interactions with the larger host halo are all thought to play a role in shaping the population of satellites that we observe today, but there is still no consensus as to which of these effects, if any, dominates. In this paper, we revisit the issue by re-simulating a Milky Way class dark matter (DM) halo with unprecedented resolution. Our set of cosmological hydrodynamic Adaptive Mesh Refinement (AMR) simulations, called the Nut suite, allows us to investigate the effect of supernova feedback and UV photoionisation at high redshift with sub-parsec resolution. We subsequently follow the effect of interactions with the Milky Way-like halo using a lower spatial resolution (50pc) version of the simulation down to z=0. This latter produces a population of simulated satellites that we compare to the observed satellites of the Milky Way and M31. We find that supernova feedback reduces star formation in the least massive satellites but enhances it in the more massive ones. Photoionisation appears to play a very minor role in suppressing star and galaxy formation in all progenitors of satellite halos. By far the largest effect on the satellite population is found to be the mass of the host and whether gas cooling is included in the simulation or not. Indeed, inclusion of gas cooling dramatically reduces the number of satellites captured at high redshift which survive down to z=0.
We present the growing mode solutions of cosmological perturbations to the second order in the matter dominated era. We also present several gauge-invariant combinations of perturbation variables to the second order in most general fluid context. Based on the solutions we study the Newtonian correspondence of relativistic perturbations to the second order. In addition to the previously known exact relativistic/Newtonian correspondence of density and velocity perturbations to the second order in the comoving gauge, here we show that in the sub-horizon limit we have the correspondences for density, velocity and potential perturbations in the zero-shear gauge and in the uniform-expansion gauge to the second order. Density perturbation in the uniform curvature gauge also shows the correspondence to the second order in the sub-horizon scale. We also identify the relativistic gravitational potential which shows exact correspondence to the Newtonian one to the second order.
A sample of 11 thousand galaxies with radial velocities V_ LG < 3500 km/s is used to study the features of the local distribution of luminous (stellar) and dark matter within a sphere of radius of around 50 Mpc around us. The average density of matter in this volume, Omega_m,loc=0.08+-0.02, turns out to be much lower than the global cosmic density Omega_m,glob=0.28+-0.03. We discuss three possible explanations of this paradox: 1) galaxy groups and clusters are surrounded by extended dark halos, the major part of the mass of which is located outside their virial radii; 2) the considered local volume of the Universe is not representative, being situated inside a giant void; and 3) the bulk of matter in the Universe is not related to clusters and groups, but is rather distributed between them in the form of massive dark clumps. Some arguments in favor of the latter assumption are presented. Besides the two well-known inconsistencies of modern cosmological models with the observational data: the problem of missing satellites of normal galaxies and the problem of missing baryons, there arises another one - the issue of missing dark matter.
By dividing the redshift region under consideration into two bins, we estimate the limitations in determining the equation of state $w_{de}$ of dark energy at high redshift from current and future observational data including supernovae, baryon acoustic oscillation and observational Hubble data. It is found that the constraints of $w_{de}$ from current data are weak (2$\sigma(w_{de})\sim1$) even beyond redshift $z=0.3$. For simulated future observational data, it is shown that $\sim2300$ supernovae data from a SANP-like JDEM survey give $2\sigma(w_{de})\sim1$ beyond $z=0.6$. We consider the effects of the divided point, the number of supernovae data and the error in the distance modulus on constraining $w_{de}$ at high redshift. It is shown that the increase of number of supernovae data seems not efficient on improving the constraints of $w_{de}$ at high redshift, while the improvement of observational error in distance modulus seems to be a better way.
We present a search for the [CII] 158micron fine structure line (a main cooling line of the interstellar medium) and the underlying far-infrared (FIR) continuum in three high-redshift (6.6<z<8.2) star-forming galaxies using the IRAM Plateau de Bure interferometer. We targeted two Lyman-Alpha-selected galaxies (Lyman-Alpha-Emitters, LAEs) with moderate UV-based star formation rates (SFR~20 M_sun/yr; Himiko at z=6.6 and IOK-1 at z=7.0) and a Gamma Ray Burst (GRB) host galaxy (GRB 090423 at z~8.2). Based on our 3 sigma rest-frame FIR continuum limits, previous (rest-frame) UV continuum measurements and spectral energy distribution (SED) fitting, we rule out SED shapes similar to highly obscured galaxies (e.g. Arp220, M82) and less extreme dust-rich nearby spiral galaxies (e.g. M51) for the LAEs. Conservatively assuming a SED shape typical of local spiral galaxies we derive upper limits for the FIR-based star formation rates (SFRs) of ~70 M_sun/yr, ~50 M_sun/yr and ~40 M_sun/yr for Himiko, IOK-1 and GRB 090423, respectively. For the LAEs these limits are only a factor ~3 higher than the published UV-based SFRs (uncorrected for extinction). This indicates that the dust obscuration in the z>6 LAEs studied here is lower by a factor of a few than what has recently been found in some LAEs at lower redshift (2<z<3.5) with similar UV-based SFRs. A low obscuration in our z>6 LAE sample is consistent with recent rest-frame UV studies of z~7 Lyman-Break-Galaxies (LBGs).
We measure the shape of the velocity ellipsoid in two late-type spiral galaxies (Hubble types Sc and Scd) and combine these results with our previous analyses of six early-type spirals (Sa to Sbc) to probe the relation between galaxy morphology and the ratio of the vertical and radial dispersions. We confirm at much higher significance (99.9 percent) our prior detection of a tight correlation between these quantities. We explore the trends of the magnitude and shape of the velocity ellipsoid axes with galaxy properties (colour, gas surface mass density, and spiral arm structure). The observed relationships allow for an observational identification of the radial and vertical disk heating agents in external disk galaxies.
We characterise the primordial perturbations produced due to both inflaton and curvaton fluctuations in models where the curvaton has a quadratic, cosine or hyperbolic potential, and the inflaton potential is characterised by the usual slow-roll parameters. Isocurvature curvaton field perturbations can produce significant non-Gaussianity in the primordial density field, in contrast with adiabatic inflaton field perturbations which produce negligible non-Gaussianity for canonical scalar fields. A non-self-interacting curvaton with quadratic potential produces a local-type non-Gaussianity that is well described by the non-linearity parameter fNL, which may be scale-dependent when the inflaton perturbations dominate the power spectrum. We show how observational bounds on non-linearity parameters and the tensor-scalar ratio can be used to constrain curvaton and inflaton parameters. We find a consistency relation between the bispectrum and trispectrum parameters in a mixed inflaton-curvaton model for a quadratic curvaton potential. Self-interaction terms in the curvaton potential can lead to both a large trispectrum parameter, gNL, and scale-dependence of the non-linearity parameters.
We study the cosmology of quintessence models in an extended theory of gravity in Lyra's geometry. By analyzing the possible interactions between the quintessence scalar and the intrinsic displacement field in Lyra's geometry, we obtain the closed form solutions of the modified Friedmann equations for four classes of quintessence models. Due to the presence of the geometrical displacement field, a late-time cosmic acceleration with the phantom divide crossing in a flat Robertson-Walker background is possible even if in these models there is no dynamical ghost mode involved.
The NGC 1023 group is one of the most studied nearby groups. We want to give an insight into the evolution of its innermost region by means of ultraviolet observations and proper models. We used the FUV and NUV GALEX archival data as well as a large set of SPH simulations with chemo-photometric implementation. From the UV observations we found that several, already known, dwarf galaxies very close to NGC 1023 are also detected in UV and two more objects (with no optical counterpart) can be added to the group. Using these data we construct exhaustive models to account for their formation. We find that the whole SED of NGC 1023 and its global properties are well matched by a simulation which provides a minor merger with a companion system 5 times less massive. The strong interaction phase started 7.7 Gyr ago and the final merger 1.8 Gyr ago.
We investigate the clustering of halos in cosmological models starting with general local-type non-Gaussian primordial fluctuations. We employ multiple Gaussian fields and add local-type non-Gaussian corrections at arbitrary order to cover a class of models described by frequently-discussed f_nl, g_nl and tau_nl parameterization. We derive a general formula for the halo power spectrum based on the peak-background split formalism. The resultant spectrum is characterized by only two parameters responsible for the scale-dependent bias at large scale arising from the primordial non-Gaussianities in addition to the Gaussian bias factor. We introduce a new inequality for testing non-Gaussianities originating from multi fields, which is directly accessible from the observed power spectrum. We show that this inequality is a generalization of the Yamaguchi-Suyama inequality between f_nl and tau_nl to the primordial non-Gaussianities at arbitrary order. We also show that the amplitude of the scale-dependent bias is useful to distinguish the simplest quadratic non-Gaussianities (i.e., f_nl-type) from higher-order ones (g_nl and higher), if one measures it from multiple species of galaxies or clusters of galaxies. We discuss the validity and limitations of our analytic results by comparison with numerical simulations in an accompanying paper.
We study the non-linear gravitational collapse of dark matter into halos through numerical N-body simulations of Lemaitre-Tolman-Bondi void models. We extend the halo mass function formalism to these models in a consistent way. This extension not only compares well with the simulated data at all times and radii, but it also gives interesting clues about the impact of the background shear on the growth of perturbations. Our results give hints about the possibility of constraining the background shear via cluster number counts, which could then give rise to strong constraints on general inhomogeneous models, of any scale.
An unbinned maximum likelihood analysis of CDMS low-energy data reveals a strong preference (5.7 sigma C.L.) for a model containing an exponential excess of events in the nuclear recoil band, when compared to the null hypothesis. We comment on the possible origin of such an excess, establishing a comparison with anomalies in other dark matter experiments. A recent annual modulation search in CDMS data is shown to be insufficiently sensitive to test a dark matter origin for this excess.
The coexistence of Planck and Fermi satellites in orbit has enabled the exploration of the connection between the (sub-)millimeter and gamma-ray emission in a large sample of blazars. We find that the gamma-ray emission and the (sub-)mm luminosities are correlated over five orders of magnitude. However, this correlation is not significant at some frequency bands when simultaneous observations are considered. The most significant statistical correlations, on the other hand, arise when observations are quasi-simultaneous within 2 months. Moreover, we find that sources with an approximate spectral turnover in the middle of the mm-wave regime are more likely to be strong gamma-ray emitters. These results suggest a physical relation between the newly injected plasma components in the jet and the high levels of gamma-ray emission.
We present the stellar population and velocity dispersion gradients for a sample of 24 brightest cluster galaxies (BCGs) in the nearby Universe for which we have obtained high quality long-slit spectra at the Gemini telescopes. With the aim of studying the possible connection between the formation of the BCGs and their host clusters, we explore the relations between the stellar population gradients and properties of the host clusters as well as the possible connections between the stellar population gradients and other properties of the galaxies. We find mean stellar population gradients (negative {\Delta}[Z/H]/log r gradient of -0.285{\pm}0.064; small positive {\Delta}log (age)/log r gradient of 0.069{\pm}0.049; and null {\Delta}[E/Fe]/log r gradient of -0.008{\pm}0.032) that are consistent with those of normal massive elliptical galaxies. However, we find a trend between metallicity gradients and velocity dispersion (with a negative slope of -1.616{\pm}0.539) that is not found for the most massive ellipticals. Furthermore, we find trends between the metallicity gradients and K-band luminosities (with a slope of 0.173{\pm}0.081) as well as the distance from the BCG to the X-ray peak of the host cluster (with a slope of -7.546{\pm}2.752). The latter indicates a possible relation between the formation of the cluster and that of the central galaxy.
We present a clustering analysis of Luminous Red Galaxies (LRGs) in SDSS Stripe 82. We study the angular 2-point correlation function, w(theta), of 130,000 LRG candidates via colour-cut selections in izK with the K band coverage coming from UKIDSS LAS. We have used the cross-correlation technique of Newman (2008) to establish the LRG redshift distribution. Cross-correlating with SDSS QSOs, MegaZ-LRGs and DEEP2 galaxies implies an average LRG redshift of z~1 with space density, n_g~3.2x10^-4 h^3 Mpc^-3. For theta < 10', the LRG w(theta) significantly deviates from a single power-law as noted by previous galaxy clustering studies. A double power-law with a break at r_b~2.4 h^-1 Mpc fits the data better, with scale length, r_0,1=7.63+/-0.27 h^-1Mpc and slope gamma_1=2.01 +/-0.02 at small scales and r_0,2=9.92 +/-0.40 h^-1 Mpc and gamma_2=1.64 +/-0.04 at large scales. Due to the flat slope at large scales, we find that a standard LCDM linear model is accepted only at 2-3sigma, with the best-fit bias factor, b=2.74+/-0.07. We also fitted HOD models and estimate an effective halo mass of Stripe 82 LRGs of M_eff=3.3 +/-0.6x10^13 h^-1 M_sun. But at large scales, the current HOD models did not help explain the power excess in the clustering signal. We then compare the w(theta) results to those of Sawangwit et al. (2011) from 3 samples of photometrically selected LRGs at lower redshifts to measure clustering evolution. We find that a long-lived model may be a poorer fit than at lower redshifts, although this assumes that the Stripe 82 LRGs are luminosity-matched to the AAOmega LRGs. We find stronger evidence for evolution in the form of the z~1 LRG correlation function, with the above flat 2-halo slope maintaining to r>50 h^-1 Mpc. If this result is not caused by systematics, then it may provide evidence for primordial non-Gaussianity in the matter distribution, with f^local_NL=90+/-30.
We present the results of deep, high-resolution, 5 GHz Expanded Very Large Array (EVLA) observations of the nearby, dwarf lenticular galaxy and intermediate mass black hole candidate (M ~4.5 x 10^5 M_sun), NGC 404. For the first time, radio emission at frequencies above 1.4 GHz has been detected in this galaxy. We found a modestly resolved source in the NGC 404 nucleus with a total radio luminosity of 7.6 +/- 0.7 x 10^17 W/Hz at 5 GHz and a spectral index from 5 to 7.45 GHz of alpha = -0.88 +/- 0.30. NGC 404 is only the third central intermediate mass black hole candidate detected in the radio regime with subarcsecond resolution. The position of the radio source is consistent with the optical center of the galaxy and the location of a known, hard X-ray point source (Lx ~1.2 x 10^37 erg/s). The faint radio and X-ray emission could conceivably be produced by an X-ray binary, star formation, a supernova remnant or a low-luminosity AGN powered by an intermediate mass black hole. In light of our new EVLA observations, we find that the most likely scenario is an accreting intermediate mass black hole, with other explanations incompatible with the observed X-ray and/or radio luminosities or statistically unlikely.
Using the planned antenna locations of the 128 antenna buildout of the Murchison Widefield Array (MWA), we accurately calculate its sensitivity to the Epoch of Reionization (EoR) power spectrum of redshifted 21 cm emission. Our calculation takes into account synthesis rotation, chromatic and asymmetrical baseline effects, and excludes modes that will be contaminated by foreground subtraction. With one full season of observation on two fields (900 and 700 hours), the MWA will be capable of a 14$\sigma$ detection of the EoR signal along with slope constraints.
In this paper we propose a mechanism that protects theories violating a holographic bound suggested in arXiv:1203.5467 from developing accelerated expansion. The mechanism builts on work on transplanckian physics, and a non-trivial choice of vacuum states. If correct, it lends further support for detectable signatures in the CMBR signalling new physics.
We successfully detected a molecular outflow with a scale of 370-450 pc in the central region of the starburst galaxy NGC 3628 through deep CO(1-0) observations by using the Nobeyama Millimeter Array (NMA). The mass of the outflowing molecular gas is ~2.8x10^7 M_sun, and the outflow velocity is ~90(+/-10) km s^{-1}. The expansion timescale of the outflow is 3.3-6.8 Myr, and the molecular gas mass flow rate is 4.1-8.5 M_sun yr^{-1}. It requires mechanical energy of (1.8-2.8)x10^{54} erg to create this sub-kpc scale molecular outflow. In order to understand the evolution of the molecular outflow, we compare the physical properties between the molecular outflow observed from our NMA CO(1-0) data and the plasma gas from the soft X-ray emission of the Chandra X-ray Observatory (CXO) archival data. We found that the distribution between the molecular outflow and the strong plasma outflow seems to be in a similar region. In this region, the ram pressure and the thermal pressure of the plasma outflow are 10^{-(8-10)} dyne cm^{-2}, and the thermal pressure of molecular outflow is 10^{-(11-13)} dyne cm^{-2}. This implies the molecular outflow is still expanding outward. The molecular gas consumption timescale is estimated as 17-27 Myr, and the total starburst timescale is 20-34 Myr. The evolutionary parameter is 0.11-0.25, suggesting that the starburst activity in NGC 3628 is still in a young stage.
We find a solution to Einstein field equations for a regular toroidal lattice of size L with equal masses M at the centre of each cell; this solution is exact at order M/L. Such a solution is convenient to study the dynamics of an assembly of galaxy-like objects. We find that the solution is expanding (or contracting) in exactly the same way as the solution of a Friedman-Lema\^itre-Robertson-Walker Universe with dust having the same average density as our model. This points towards the absence of backreaction in a Universe filled with an infinite number of objects, and this validates the fluid approximation, as far as dynamics is concerned.
The hyper luminous X-ray source HLX-1 in the galaxy ESO 243-49, currently the best intermediate mass black hole candidate, displays spectral transitions similar to those observed in Galactic black hole binaries, but with a luminosity 100-1000 times higher. We investigated the X-ray properties of this unique source fitting multi-epoch data collected by Swift, XMM-Newton & Chandra with a disk model computing spectra for a wide range of sub- and super-Eddington accretion rates assuming a non-spinning black hole and a face-on disk (i = 0 deg). Under these assumptions we find that the black hole in HLX-1 is in the intermediate mass range (~2 x 10^4 M_odot) and the accretion flow is in the sub-Eddington regime. The disk radiation efficiency is eta = 0.11 +/-0.03. We also show that the source does follow the L_X ~ T^4 relation for our mass estimate. At the outburst peaks, the source radiates near the Eddington limit. The accretion rate then stays constant around 4 x 10^(-4) M_odot yr^(-1) for several days and then decreases exponentially. Such "plateaus" in the accretion rate could be evidence that enhanced mass transfer rate is the driving outburst mechanism in HLX-1. We also report on the new outburst observed in August 2011 by the Swift-X-ray Telescope. The time of this new outburst further strengthens the ~1 year recurrence timescale.
It has recently been pointed out that a substantial amount of e-folds can occur during the waterfall regime of hybrid inflation. Moreover, Kodama et.al. have derived analytic approximations for the trajectories of the inflaton and of the waterfall fields. Based on these, we derive here the consequences for F- and D-term SUSY hybrid inflation: A substantial amount of e-folds may occur in the waterfall regime, provided kappa << M^2/M_P^2, where kappa is the superpotential coupling, M the scale of symmetry breaking and M_P the reduced Planck mass. When this condition is amply fulfilled, a number of e-folds much larger than N_e\approx60 can occur in the waterfall regime and the scalar spectral index is then given by the expression found by Kodama et.al. n_s=1-4/N_e. This value may be increased up to unity, if only about N_e e-folds occur during the waterfall regime, such that the largest observable scale leaves the horizon close to the critical point of hybrid inflation, what can be achieved for kappa\approx10^(-13) and M\approx5x10^(12) GeV in F-term inflation. Imposing the normalization of the power spectrum leads to a lower bound on the scale of symmetry breaking.
We review progress over the past decade in observations of large-scale star formation, with a focus on the interface between extragalactic and Galactic studies. Methods of measuring gas contents and star formation rates are discussed, and updated prescriptions for calculating star formation rates are provided. We review relations between star formation and gas on scales ranging from entire galaxies to individual molecular clouds.
In thermal equilibrium the ground state of the plasma of Standard Model particles is determined by temperature and exactly conserved combinations of baryon and lepton numbers. We show that at non-zero values of the global charges a translation invariant and homogeneous state of the plasma becomes unstable and the system transits into a new state, containing a large-scale magnetic field. The origin of this effect is the parity-breaking character of weak interactions and chiral anomaly. This situation can occur in the early Universe and may play an important role in its subsequent evolution.
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We present a comprehensive catalog of ultraviolet HST/STIS and FUSE absorbers in the low-redshift IGM at z<0.4. The catalog draws from the extensive literature on IGM absorption, and it reconciles discrepancies among previous catalogs through a critical evaluation of all reported absorption features in light of new HST/COS data. We report on 746 HI absorbers down to a rest-frame equivalent width of 12 milliAngstroms over a maximum redshift path length Deltaz=5.38. We also confirm 111 OVI absorbers, 29 CIV absorbers, and numerous absorption features due to other metal ions. We characterize the distribution of absorber line frequency as a function of column density as a power law, dN/dz \propto N^{-beta}, where beta=2.08+-0.12 for OVI and beta=1.68+-0.03 for HI. Utilizing a more sophisticated accounting technique than past work, the catalog accounts for ~43% of the baryons: 24+-2% in the photoionized Ly-alpha forest and 19+-2% in the WHIM as traced by OVI. We discuss the large systematic effects of various assumed metallicities and ionization states on these calculations, and we implement recent simulation results in our estimates.
We derive general covariant expressions for the six independent observable modes of distortion of ideal standard rulers in a perturbed Friedmann-Robertson-Walker spacetime. Our expressions are gauge-invariant and valid on the full sky. These six modes are most natually classified in terms of their rotational properties on the sphere, yielding two scalars, two vector (spin-1), and two tensor (spin-2) components. One scalar corresponds to the magnification, while the spin-2 components correspond to the shear. The vector components allow for a polar/axial decomposition analogous to the E/B-decomposition for the shear. Scalar modes do not contribute to the axial (B-)vector, opening a new avenue to probing tensor modes. Our results apply, but are not limited to, the distortion of correlation functions (of the CMB, 21cm emission, or galaxies) as well as to weak lensing shear and magnification, all of which can be seen as methods relying on "standard rulers".
We combine recent estimates of dust extinction at z~4-7 with UV luminosity function (LF) determinations to derive star formation rate (SFR) functions at z~4, 5, 6 and 7. SFR functions provide a more physical description of galaxy build-up at high redshift and allow for direct comparisons to other techniques for determining the SFRs at lower redshifts. The present SFR functions are based on well-established z~4-7 UV LFs, UV-continuum slope trends with redshift and luminosity, and IRX-beta relations, and are well-described by Schechter relations. We extend the comparison baseline to z~2 by considering recent determinations of the H{\alpha} and mid-IR luminosity functions. We find that the high-end turnover of the SFR function, log SFR*, increases linearly with cosmic time from ~5 M_sun/yr at z~8, 650 Myr after the Big Bang, to ~100 M_sun/yr at z~2, ~2.5 Gyr later. Recent results at z~10, close to the onset of galaxy formation, are consistent with this trend. These results provide strong evidence that galaxies build up uniformly over the first 3 Gyr of cosmic time. The uniformity of this evolution is even greater than seen in the UV LF over the redshift range z~2-8, providing validation for our dust corrections. The low-end slopes of the SFR functions are flatter than for the UV LFs, \Delta\alpha\sim+0.13, and show no clear evolution with cosmic time (z~0-7).
We study the time variability of five Fe Low ionization Broad Absorption Line (FeLoBAL) QSOs using repeated spectroscopic observations with the 2m telescope at IUCAA Girawali observatory (IGO) spanning an interval of upto 10 years. We report a dramatic variation in Al III and Fe III fine-structure lines in the spectra of SDSS J221511.93-004549.9 (z_em ~ 1.478). However, there is no such strong variability shown by the C IV absorption. This source is known to be unusual with (i) the continuum emission dominated by Fe emission lines, (ii) Fe III absorption being stronger than Fe II and (iii) the apparent ratio of Fe III UV 48 to Fe III UV 34 absorption suggesting an inverted population ratio. This is the first reported detection of time variability in the Fe III fine-structure lines in QSO spectra. There is a strong reduction in the absorption strength of these lines between year 2000 and 2008. Using the template fitting techniques, we show that the apparent inversion of strength of UV lines could be related to the complex spectral energy distribution of this QSO. The observed variability can be related to change in the ionization state of the gas or due to transverse motion of this absorbing gas. The shortest variability timescale of Al III line gives a lower limit on the electron density of the absorbing gas as n_e >= 1.1 x 10^4 cm^-3. The remaining 4 FeLoBALs do not show any changes beyond the measurement uncertainties either in optical depth or in the velocity structure. We present the long-term photometric light curve for all of our sources. Among them only SDSS J221511.93-004549.9 shows significant (>= 0.2 mag) variability.
We derive an accurate mass distribution of the galaxy cluster MACS J1206.2-0847 (z=0.439) from a combined weak-lensing distortion, magnification, and strong-lensing analysis of wide-field Subaru BVRIz' imaging and our recent 16-band Hubble Space Telescope observations taken as part of the Cluster Lensing And Supernova survey with Hubble (CLASH) program. We find good agreement in the regions of overlap between several weak and strong lensing mass reconstructions using a wide variety of modeling methods, ensuring consistency. The Subaru data reveal the presence of a surrounding large scale structure with the major axis running approximately north-west south-east (NW-SE), aligned with the cluster and its brightest galaxy shapes, showing elongation with a \sim 2:1 axis ratio in the plane of the sky. Our full-lensing mass profile exhibits a shallow profile slope dln\Sigma/dlnR\sim -1 at cluster outskirts (R>1Mpc/h), whereas the mass distribution excluding the NW-SE excess regions steepens further out, well described by the Navarro-Frenk-White form. Assuming a spherical halo, we obtain a virial mass M_{vir}=(1.1\pm 0.2\pm 0.1)\times 10^{15} M_{sun}/h and a halo concentration c_{vir} = 6.9\pm 1.0\pm 1.2 (\sim 5.7 when the central 50kpc/h is excluded), which falls in the range 4< <c> <7 of average c(M,z) predictions for relaxed clusters from recent Lambda cold dark matter simulations. Our full lensing results are found to be in agreement with X-ray mass measurements where the data overlap, and when combined with Chandra gas mass measurements, yield a cumulative gas mass fraction of 13.7^{+4.5}_{-3.0}% at 0.7Mpc/h (\approx 1.7r_{2500}), a typical value observed for high mass clusters.
We present constraints on core-collapse supernova progenitors through observations of their environments within host galaxies. This is achieved through 2 routes. Firstly, we investigate the spatial correlation of supernovae with host galaxy star formation using pixel statistics. We find that the main supernova types form a sequence of increasing association to star formation. The most logical interpretation is that this implies an increasing progenitor mass sequence going from the supernova type Ia arising from the lowest mass, through the type II, type Ib, and the supernova type Ic arising from the highest mass progenitors. We find the surprising result that the supernova type IIn show a lower association to star formation than type IIPs, implying lower mass progenitors. Secondly, we use host HII region spectroscopy to investigate differences in environment metallicity between different core-collapse types. We find that supernovae of types Ibc arise in slightly higher metallicity environments than type II events. However, this difference is not significant, implying that progenitor metallicity does not play a dominant role in deciding supernova type.
We present a survey of 2,148 galaxy redshifts from the VLT LBG Redshift Survey (VLRS), a spectroscopic survey of z ~ 3 galaxies in wide fields centred on background QSOs made using the VLT VIMOS instrument. To make a definitive LBG clustering analysis, we have combined the VLRS redshifts with the 813 Keck LBG redshifts of Steidel et al, with the statistical power of VLRS at large scales complementing the accuracy of the Keck sample at small scales. From the semi-projected correlation function for the VLRS and combined surveys, we find that the results are well fit with a single power law model for the real space correlation function with clustering scale lengths of respectively r0 = 3.32 \pm 0.41 and 3.75 \pm 0.24 Mpc/h. We note that the corresponding combined slope is flatter than for local galaxies at {\gamma} = 1.55 \pm 0.09. This flat slope is confirmed by the z-space correlation function and in the range 10 < s < 100 Mpc/h the VLRS shows a 2.5{\sigma} excess over the {\Lambda}CDM linear prediction. This excess may be consistent with recent evidence for non-Gaussianity in clustering results at z \approx 1. We then analyse the LBG z-space distortions using the 2-D correlation function finding for the combined sample a large scale infall parameter of {\beta} = 0.32 \pm 0.20 and a velocity dispersion of 540 \pm 200 km/s. Fixing this velocity dispersion, we fit the 2D clustering for the matter density and infall parameter and break their degeneracy using low-redshift data to find {\Omega}m(z = 0) = 0.30+0.32-0.18. Finally, based on our measured {\beta}, we are able to determine the gravitational growth rate, finding a value of f(z = 3) = 0.83 \pm 0.46, which is the highest redshift measurement of the growth rate via galaxy clustering and is consistent with {\Lambda}CDM.
We present an analysis of the galaxy distribution surrounding 15 of the most luminous (>10^{14} L_sun; M_1450 ~ -30) QSOs in the sky with z~2.7. Our data are drawn from the Keck Baryonic Structure Survey (KBSS). In this work, we use the positions and spectroscopic redshifts of 1558 galaxies that lie within ~3', (4.2 h^{-1} comoving Mpc; cMpc) of the hyperluminous QSO (HLQSO) sightline in one of 15 independent survey fields, together with new measurements of the HLQSO systemic redshifts. We measure the galaxy-HLQSO cross-correlation function, the galaxy-galaxy autocorrelation function, and the characteristic scale of galaxy overdensities surrounding the sites of exceedingly rare, extremely rapid, black hole accretion. On average, the HLQSOs lie within significant galaxy overdensities, characterized by a velocity dispersion sigma_v ~ 200 km s^{-1} and a transverse angular scale of ~25", (~200 physical kpc). We argue that such scales are expected for small groups with log(M_h/M_sun)~13. The galaxy-HLQSO cross-correlation function has a best-fit correlation length r_0_GQ = (7.3 \pm 1.3) h^{-1} cMpc, while the galaxy autocorrelation measured from the spectroscopic galaxy sample in the same fields has r_0_GG = (6.0 \pm 0.5) h^{-1} cMpc. Based on a comparison with simulations evaluated at z ~ 2.6, these values imply that a typical galaxy lives in a host halo with log(M_h/M_sun) = 11.9\pm0.1, while HLQSOs inhabit host halos of log(M_h/M_sun) = 12.3\pm0.5. In spite of the extremely large black hole masses implied by their observed luminosities [log(M_BH/M_sun) > 9.7], it appears that HLQSOs do not require environments very different from their much less luminous QSO counterparts. Evidently, the exceedingly low space density of HLQSOs (< 10^{-9} cMpc^{-3}) results from a one-in-a-million event on scales << 1 Mpc, and not from being hosted by rare dark matter halos.
We report the discovery of 33 Lyman break galaxy (LBG) candidates at z~8 detected in Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) imaging as part of the Brightest of Reionizing Galaxies (BoRG) pure-parallel survey. The ongoing BoRG survey currently has the largest area (274 arcmin^2) with Y_098 (or Y_105), J_125, and H_160 band coverage needed to search for z~8 galaxies, about three times the current CANDELS area, and slightly larger than what will be the final CANDELS wide component with Y_105 data. Our sample of 33 relatively bright Y_098-dropout galaxies have J_125 band magnitudes between 25.5 and 27.4 mag. This is the largest sample of bright (J_125 <~ 27.4) z~8 galaxy candidates presented to date. Combining our dataset with the Hubble Ultra-Deep Field (HUDF09) dataset, we constrain the rest-frame ultraviolet galaxy luminosity function at z~8 over the widest dynamic range currently available. The combined datasets are well fitted by a Schechter function, i.e. \phi(L) = \phi_* (L/L_*)^{\alpha}\ e^{-(L/L_*)}, without evidence for an excess of sources at the bright end. At 68% confidence, we derive \phi_* = (4.3^{+3.5}_{-2.1}) \times 10^{-4} Mpc^{-3}, M_* = -20.26^{+0.29}_{-0.34}, and a very steep faint-end slope \alpha = -1.98^{+0.23}_{-0.22}. While the best-fit parameters still have a strong degeneracy, especially between \phi_* and M_*, our improved coverage at the bright end has reduced the uncertainty of the faint-end power-law slope at z~8 compared to the best previous determination at +/-0.4. With a future expansion of the BoRG survey, combined with planned ultradeep WFC3/IR observations, it will be possible to further reduce this uncertainty and clearly demonstrate the steepening of the faint-end slope compared to measurements at lower redshift, thereby confirming the key role played by small galaxies in the reionization of the universe.
Electromagnetic radiation from superconducting cosmic string loops can reionize neutral hydrogen in the universe at very early epochs, and affect the cosmic microwave background (CMB) temperature and polarization correlation functions at large angular scales. We constrain the string tension and current using WMAP7 data, and compare with earlier constraints that employed CMB spectral distortions. Over a wide range of string tensions, the current on the string has to be less than 10^7 GeV.
Magnetic fields appear wherever plasma and currents can be found. As such, they thread through all scales in Nature. It is natural, therefore, to suppose that magnetic fields might have been formed within the high temperature environments of the big bang. Such a primordial magnetic field (PMF) would be expected to arise from and/or influence a variety of cosmological phenomena such as inflation, cosmic phase transitions, big bang nucleosynthesis, the cosmic microwave background (CMB) temperature and polarization anisotropies, the cosmic gravity wave background, and the formation of large-scale structure. In this review, we summarize the development of theoretical models for analyzing the observational consequences of a PMF. We also summarize the current state of the art in the search for observational evidence of a PMF. In particular we review the framework needed to calculate the effects of a PMF power spectrum on the CMB and the development of large scale structure. We summarize the current constraints on the PMF amplitude $B_\lambda$ and the power spectral index $n_B$ and discuss prospects for better determining these quantities in the near future.
We perform a joint determination of the distance-redshift relation and cosmic expansion rate at redshifts z = 0.44, 0.6 and 0.73 by combining measurements of the baryon acoustic peak and Alcock-Paczynski distortion from galaxy clustering in the WiggleZ Dark Energy Survey, using a large ensemble of mock catalogues to calculate the covariance between the measurements. Further combining our results with other baryon acoustic oscillation and distant supernovae datasets, we use a Monte Carlo Markov Chain technique to determine the evolution of the Hubble parameter H(z) as a stepwise function in 9 redshift bins of width dz = 0.1, also marginalizing over the spatial curvature. Our measurements of H(z), which have precision better than 7% in most redshift bins, are consistent with the expansion history predicted by a cosmological-constant dark-energy model, in which the expansion accelerates at redshift z < 0.7. We also measure the normalized cosmic growth rate at z = 0.44, 0.6 and 0.73, together with its covariance with the expansion history, using redshift-space distortions in the WiggleZ Survey dataset. The measured growth rate is consistent with the same cosmological-constant model that describes the expansion history.
We provide a dynamical mechanism to generate localized features during inflation. The local feature is due to a sharp waterfall phase transition which is coupled to the inflaton field. The key effect is the contributions of waterfall quantum fluctuations which induce a sharp peak on the curvature perturbation which can be as large as the background curvature perturbation from inflaton field. Due to non-Gaussian nature of waterfall quantum fluctuations a large spike non-Gaussianity is produced which is narrowly peaked at modes which leave the Hubble radius at the time of phase transition. The large localized peaks in power spectrum and bispectrum can have interesting consequences on CMB anisotropies.
Several examples of thin, Keplerian, sub-parsec megamaser disks have been discovered in the nuclei of active galaxies and used to precisely determine the mass of their host black holes. We show that there is an empirical linear correlation between the disk radius and black hole mass and that such disks are naturally formed as molecular clouds pass through the galactic nucleus and temporarily engulf the central supermassive black hole. For initial cloud column densities below about 10^{23.5} cm^{-2} the disk is non-self gravitating, but for higher cloud columns the disk would fragment and produce a compact stellar disk similar to that observed around Sgr A* at the galactic centre.
The bispectrum of the cosmic microwave background (CMB) generated by a correlation between a time-dependent gravitational potential and the weak gravitational lensing effect provides a direct measurement of the influence of dark energy on CMB. This bispectrum is also known to yield the most important contamination of the so-called "local-form" primordial bispectrum, which can be used to rule out all single-field inflation models. In this paper, we reexamine the effect of non-linear matter clustering on this bispectrum. We compare three different approaches: the 3rd-order perturbation theory (3PT), and two empirical fitting formulae available in the literature, finding that detailed modeling of non-linearity appears to be not very important, as most of the signal-to-noise comes from the squeezed triangle, for which the correlation in the linear regime dominates. The expected signal-to-noise ratio for an experiment dominated by the cosmic variance up to $l_{\rm max}=1500$ is about 5, which is much smaller than the previous estimates including non-linearity, but agrees with the estimates based on the linear calculation. We find that the difference between the linear and non-linear predictions is undetectable, and does not alter the contamination of the local-form primordial non-Gaussianity.
Narrow absorption line (NAL) outflows are an important yet poorly understood part of the quasar outflow phenomenon. We discuss one particular NAL outflow that has high speeds, time variability, and moderate ionizations like typical BAL flows, at an estimated location just ~5 pc from the quasar. It also has a total column density and line widths (internal velocity dispersions) ~100 times smaller than BALs, with no substantial X-ray absorption. We argue that radiative shielding (in the form of an X-ray/warm absorber) is not critical for the outflow acceleration and that the moderate ionizations occur in dense substructures that have an overall small volume filling factor in the flow. We also present new estimates of the overall incidence of quasar outflow lines; e.g., ~43% of bright quasars have a C IV NAL outflow while ~68% have a C IV outflow line of any variety (NAL, BAL, or mini-BAL).
We measure equivalent widths (EW) - focussing on two unique features (NaI and TiO2) of low-mass stars (\leq 0.3 M\odot) - for luminous red galaxy spectra from the the Sloan Digital Sky Survey (SDSS) and X-Shooter Lens Survey (XLENS) in order to study the low-mass end of the IMF. We compare these EWs to those derived from simple stellar population models computed with different IMFs, ages,[{\alpha}/Fe], and elemental abundances. We find that models are able to simultaneously reproduce the observed NaD {\lambda}5895 and NaI {\lambda}8190 features for the lower-mass (~{\sigma}*) ETGs but deviate increasingly for more massive ETGs, due do strongly mismatching NaD EWs. The TiO2 {\lambda}6230 feature and the NaI {\lambda}8190 feature, may be a powerful IMF diagnostic, with age and metallicity effects orthogonal to the effect of IMF on the feature's strength. We find that both features correlate strongly with galaxy velocity dispersion. The XLENS ETG (SDSSJ0912+0029) and one SDSS ETG (SDSSJ0041-0914) appear to require both an extreme dwarf-rich IMFs and a high sodium enhancement ([Na/Fe]=+0.4). However, lensing constraints on the total mass of the XLENS system within its Einstein radius limit a bottom-heavy IMF with a power-law slope to x \leq 3.0 at the 90% C.L. We conclude that NaI and TiO features, in comparison with state-of-the-art SSP models, suggest a mildly steepening IMF from Salpeter to x~3.0 for ETGs in the range {\sigma}=200-335 km/s.
In this paper we describe the state-of-the art status of multi-frequency detection techniques for compact sources in microwave astronomy. From the simplest cases where the spectral behaviour is well-known (i.e. thermal SZ clusters) to the more complex cases where there is little a priori information (i.e. polarized radio sources) we will review the main advances and the most recent results in the detection problem.
Starlight in the Universe impedes the passage of high energy (e.g. TeV) gamma rays due to positron-electron pair production. The history of this stellar radiation field depends upon observations of star formation rate which themselves can only be interpreted in the context of a particular cosmology. For different equations of state of dark energy, the star formation rate data suggests a different density of stellar photons at a particular redshift and a different probability of arrival of gamma rays from distant sources. In this work we aim to show that this effect can be used to constrain the equation of state of dark energy. The current work is a proof of concept and we outline the steps that would have to be taken to place the method in a rigorous statistical framework which could then be combined with other more mature methods such as fitting supernova luminosity distances.
We show the conclusions claimed in the manuscript arXiv:1202.5309v1 by Cuoco, Komatsu and Siegal-Gaskins (CKS) are not generally valid. The results in CKS are based on a number of simplifying assumptions regarding the source population below the detection threshold and the threshold flux itself, and do not apply to many physical models of the blazar population. Physical blazar population models that match the measured source counts above the observational threshold can account for 60% of the diffuse gamma-ray background intensity between 1-10 GeV, while the assumptions in CKS limit the intensity to <30%. The shortcomings of the model considered in CKS arise from an over-simplified blazar source model. A number of the simplifying assumptions are unjustified, including: first, the adoption of an assumed power-law source-count distribution, dN/dS, to arbitrary low source fluxes, which is not exhibited in physical models of the blazar population; and, second, the lack of blazar spectral information in calculating the anisotropy of unresolved gamma-ray blazar emission. We also show that the calculation of the unresolved blazars' anisotropy is very sensitive to the spectral distribution of the unresolved blazars through the adopted source resolution threshold value, and must be taken into account in an accurate anisotropy calculation.
Tidal debris around galaxies can yield important clues on their evolution. We have identified tidal debris in 11 early type galaxies (T \leq 0) from a sample of 65 early types drawn from the Spitzer Survey of Stellar Structure in Galaxies (S4G). The tidal debris includes features such as shells, ripples and tidal tails. A variety of techniques, including two-dimensional decomposition of galactic structures, was used to quantify the residual tidal features. The tidal debris contributes ~3 - 10% to the total 3.6 {\mu}m luminosity of the host galaxy. Structural parameters of the galaxies were estimated using two-dimensional profile fitting. We investigate the locations of galaxies with tidal debris in the Fundamental Plane and Kormendy relation. We find that galaxies with tidal debris lie within the scatter of early type galaxies without tidal features. Assuming that the tidal debris is indicative of recent gravitational interaction or merger, this suggests that these galaxies have either undergone minor merging events so that the overall structural properties of the galaxies are not significantly altered, or they have undergone a major merging events but already have experienced sufficient relaxation and phase-mixing so that their structural properties become similar to those of the non-interacting early type galaxies.
We explore the implications of a 124-126 GeV CP-even Higgs boson on the fundamental parameter space and sparticle spectroscopy of the minimal gauge mediated supersymmetry breaking (mGMSB) scenario. The above mass for the Higgs boson yields stringent lower bounds on the sparticle masses in this class of models. The lightest neutralino and stau masses lie close to 1.5 TeV and 800 GeV respectively, while the majority of the sparticle masses are in the several to multi-TeV range. We show that with a single pair of 5+\bar{5} SU(5) messenger multiplets, the lower limit on the gravitino mass is \sim 360 eV. This is reduced to about 60 eV if five pairs of 5+\bar{5} messenger fields are introduced. Non-standard cosmology and non-standard gravitino production mechanisms are required in order to satisfy cosmological observations.
If dark matter (DM) is a weakly interacting massive particle (WIMP) that is a thermal relic of the early Universe, then its total self-annihilation cross section is revealed by its present-day mass density. The canonical thermally averaged cross section for a generic WIMP is usually stated as 3*10^-26 cm^3s^-1, with unspecified uncertainty, and taken to be independent of WIMP mass. Recent searches for annihilation products of DM annihilation have just reached the sensitivity to exclude this canonical cross section for 100% branching ratio to certain final states and small WIMP masses. The ultimate goal is to probe all kinematically allowed final states as a function of mass and, if all states are adequately excluded, set a lower limit to the WIMP mass. Probing the low-mass region is further motivated due to recent hints for a light WIMP in direct and indirect searches. We revisit the thermal relic abundance calculation for a generic WIMP and show that the required cross section can calculated precisely. It varies significantly with mass at masses below 10 GeV, reaching a maximum of 5.2*10^-26 cm^3s^-1 at masses around 0.3 GeV, and is 2.2*10^-26 cm^3s^-1 with feeble mass-dependence for masses above 10 GeV. These results, which differ significantly from the canonical value and have not been taken into account in searches for annihilation products from generic WIMPs, have a noticeable impact on the interpretation of present limits from Fermi-LAT and WMAP+ACT.
We analyze the dynamical system defined by a universe filled with a barotropic fluid plus a scalar field with modified kinetic term of the form L = F (X) - V (phi). After a suitable choice of variables that allows us to study the phase space of the system we obtain the critical points and their stability. We find that they reduce to the ones defined for the canonical case when F (X) = X. We also study the field energy conditions to have a nonsingular bounce.
We present 3D models of the Galactic magnetic field including regular and turbulent components, and of the distribution of matter in the Galaxy including relativistic electrons and dust grains. By integrating along the line of sight, we construct maps of the polarized Galactic synchrotron and thermal dust emissions for each of these models. We perform a likelihood analysis to compare the maps of the Ka, Q, V and W bands of the Wilkinson Microwave Anisotropy Probe (Wmap) and the 353 GHz Archeops data to the models obtained by varying the pitch angle of the regular magnetic field, the relative amplitude of the turbulent magnetic field and the extrapolation spectral indices of the synchrotron and thermal dust emissions. The best-fit parameters obtained for the different frequency bands are very similar and globally the data seem to favor a negligible isotropic turbulent magnetic field component at large angular scales (an anisotropic line-of-sight ordered component can not be studied using these data). From this study, we conclude that we are able to propose a consistent model of the polarized diffuse Galac- tic synchrotron and thermal dust emissions in the frequency range from 33 to 353 GHz, where most of the CMB studies are performed and where we expect a mixture of these two main foreground emissions. This model can be very helpful to estimate the contamination by foregrounds of the polarized CMB anisotropies, for experiments like the Planck satellite.
We will investigate the influence of the inhomogeneity of the universe, especially that of the Lema{\^i}tre--Tolman--Bondi (LTB) model, on a gravitationally bound local system such as the solar system. We concentrate on the dynamical perturbation to the planetary motion and derive the leading order effect generated from the LTB model. It will be shown that there appear not only a well-known cosmological effect arisen from the homogeneous and isotropic model, such as the Robertson--Walker (RW) model, but also the additional terms due to the radial inhomogeneity of the LTB model. We will also apply the obtained results to the problem of secular increase in the astronomical unit, reported by Krasinsky and Brumberg (2004), and imply that the inhomogeneity of the universe cannot have a significant effect for explaining the observed $d{\rm AU}/dt = 15 \pm 4 ~{\rm [m/century]}$.
The geometrical structure of a real four-dimensional space-time has been extended via the Conservation group with basic field variable being the orthonormal tetrad. Field equations were obtained from a variational principle which is invariant under the conservation group. Recently, symmetric solutions of the field equations have been developed. In this note, the free-field solution is investigated in terms of the value of the scalar curvature and an expression for the cosmological term is developed. This term, while not a constant, has asymptotic values in the range that match nicely with the current value of $\Lambda$. This may add further support to the conclusion that the theory developed by Pandres unifies the fields.
We reexamine the light deflection by an Ellis wormhole. The bending angle as a function of the ratio between the impact parameter and the throat radius of the wormhole is obtained in terms of a complete elliptic integral of the first kind. This result immediately yields asymptotic expressions in the weak field approximation. It is shown that an expression for the deflection angle derived (and used) in recent papers is valid at the leading order but it breaks down at the next order because of the nontrivial spacetime topology.
Investigation of the cosmic microwave background formation processes is one of the most actual problem at present time. In this paper we analyze the response of the hydrogen atom to the external photon fields. Field characteristics are defined via conditions corresponding to the recombination era of universe. Approximation of three-level atom is used to describe the "atom - fields" interaction. It is found that the phenomena of the electromagnetically induced transparancy takes place in this case. Consideration of EIT phenomena makes it necessary to update astrophysical description of the processes of the cosmic microwave background formation and, in particular, Sobolev escape probability. Additional terms to the optical depth in definition of Sobolev escape probability on the level about 1% are found.
We show that the improper ferroelectric phase transition in the multiferroic hexagonal manganites displays the same symmetry-breaking characteristics as those proposed in early-universe theories. We present an analysis of the Kibble-Zurek theory of topological defect formation applied to the hexagonal manganites, discuss the conditions determining the range of cooling rates in which Kibble-Zurek behavior is expected, and show that recent literature data are consistent with our predictions. We explore experimentally for the first time to our knowledge the cross-over out of the Kibble-Zurek regime and find a surprising "anti-Kibble-Zurek" behavior.
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We have identified and studied a sample of 151 FR IIs found in brightest cluster galaxies (BCGs) in the MaxBCG cluster catalog with data from FIRST and NVSS. We have compared the radio luminosities and projected lengths of these FR IIs to the projected length distribution of a range of mock catalogs generated by an FR II model and estimate the FR II lifetime to be 1.9 x 10^8 yr. The uncertainty in the lifetime calculation is a factor of two, due primarily to uncertainties in the ICM density and the FR II axial ratio. We furthermore measure the jet power distribution of FR IIs in BCGs and find that it is well described by a log-normal distribution with a median power of 1.1 x 10^37 W and a coefficient of variation of 2.2. These jet powers are nearly linearly related to the observed luminosities, and this relation is steeper than many other estimates, although it is dependent on the jet model. We investigate correlations between FR II and cluster properties and find that galaxy luminosity is correlated with jet power. This implies that jet power is also correlated with black hole mass, as the stellar luminosity of a BCG should be a good proxy for its spheroid mass and therefore the black hole mass. Jet power, however, is not correlated with cluster richness, nor is FR II lifetime strongly correlated with any cluster properties. We calculate the enthalpy of the lobes to examine the impact of the FR IIs on the ICM and find that heating due to adiabatic expansion is too small to offset radiative cooling by a factor of at least six. In contrast, the jet power is approximately an order of magnitude larger than required to counteract cooling. We conclude that if feedback from FR IIs offsets cooling of the ICM, then heating must be primarily due to another mechanism associated with FR II expansion.
We present observations of CO J=2-1 line emission in infrared-luminous cluster galaxies at z~1 using the IRAM Plateau de Bure Interferometer. Our two primary targets are optically faint, dust-obscured galaxies (DOGs) found to lie within 2 Mpc of the centers of two massive (>10^14 Msun) galaxy clusters. CO line emission is not detected in either DOG. We calculate 3-sigma upper limits to the CO J=2-1 line luminosities, L'_CO < 6.08x10^9 and < 6.63x10^9 K km/s pc^2. Assuming a CO-to-H_2 conversion factor derived for ultraluminous infrared galaxies in the local Universe, this translates to limits on the cold molecular gas mass of M_H_2 < 4.86x10^9 Msun and M_H_2 < 5.30x10^9 Msun. Both DOGs exhibit mid-infrared continuum emission that follows a power-law, suggesting that an AGN contributes to the dust heating. As such, estimates of the star formation efficiencies in these DOGs are uncertain. A third cluster member with an infrared luminosity, L_IR < 7.4x10^11 Lsun, is serendipitously detected in CO J=2-1 line emission in the field of one of the DOGs located roughly two virial radii away from the cluster center. The optical spectrum of this object suggests that it is likely an obscured AGN, and the measured CO line luminosity is L'_CO = (1.94 +/- 0.35)x10^10 K km/s pc^2, which leads to an estimated cold molecular gas mass M_H_2 = (1.55+/-0.28)x10^10 Msun. A significant reservoir of molecular gas in a z~1 galaxy located away from the cluster center demonstrates that the fuel can exist to drive an increase in star-formation and AGN activity at the outskirts of high-redshift clusters.
The ionizing fluxes from quasars and other active galactic nuclei (AGN) are critical for interpreting the emission-line spectra of AGN and for photoionization and heating of the intergalactic medium (IGM). Using ultraviolet spectra from the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope (HST), we have directly measured the rest-frame ionizing continua and emission lines for 22 AGN. Over the redshift range 0.026 < z < 1.44, COS samples the Lyman continuum and many far-UV emission lines (Lya 1216, C IV 1549, Si IV/OIV] 1400, N V 1240, O VI 1035). Strong EUV emission lines with 14-22 eV excitation energies (Ne VIII 770,780, Ne V 569, O II 834, O III 833, 702, O IV 788,608,554, O V 630, N III 685) suggest the presence of hot gas in the broad emission-line region. The rest-frame continuum, F_nu \sim nu^{alpha_nu}, shows a break at wavelengths below 1000 A, with spectral index alpha_nu = -0.68 +/- 0.14 in the FUV (1200-2000 A) steepening to alpha_nu = -1.41 +/- 0.21 in the EUV (500-1000 A). The COS EUV index is similar to that of radio-quiet AGN in the 2002 HST/FOS survey (alpha_nu = -1.57 +/- 0.17). We see no Lyman edge (tau_HI < 0.03) or He I 584 emission in the AGN composite. Our 22 AGN exhibit a substantial range of FUV/EUV spectral indices and a correlation with AGN luminosity and redshift, likely due to observing below the 1000 A spectral break.
There is ample observational evidence that the star formation rate (SFR) surface density, Sigma_SFR, is closely correlated with the surface density of molecular hydrogen, Sigma_H2. This empirical relation holds both for galaxy-wide averages and for individual >=kpc sized patches of the interstellar medium (ISM), but appears to degrade substantially at a sub-kpc scale. Identifying the physical mechanisms that determine the scale-dependent properties of the observed Sigma_H2-Sigma_SFR relation remains a challenge from a theoretical perspective. To address this question, we analyze the slope and scatter of the Sigma_H2-Sigma_SFR relation using a set of cosmological, galaxy formation simulations with a peak resolution of ~100 pc. These simulations include a chemical network for molecular hydrogen, a model for the CO emission, and a simple, stochastic prescription for star formation that operates on ~100 pc scales. Specifically, star formation is modeled as a Poisson process in which the average SFR is directly proportional to the present mass of H2. The predictions of our numerical model are in good agreement with the observed Kennicutt-Schmidt and Sigma_H2-Sigma_SFR relations. We show that observations based on CO emission are ill suited to reliably measure the slope of the latter relation at low (<20 M_sun pc^-2) H2 surface densities on sub-kpc scales. Our models also predict that the inferred Sigma_H2-Sigma_SFR relation steepens at high H2 surface densities as a result of the surface density dependence of the CO/H2 conversion factor. Finally, we show that on sub-kpc scales most of the scatter in the relation is a consequence of discreteness effects in the star formation process. In contrast, variations of the CO/H2 conversion factor are responsible for most of the scatter measured on super-kpc scales.
We present the results of a cross-correlation of the Planck Early Release Compact Source Catalog (ERCSC) with the catalog of Herschel-ATLAS sources detected in the Phase 1 fields, covering 134.55 deg2. There are 28 ERCSC sources detected by Planck at 857 GHz in this area. As many as 16 of them are probably high Galactic latitude cirrus; 10 additional sources can be clearly identified as bright, low-z galaxies; one further source is resolved by Herschel as two relatively bright sources; and the last is resolved into an unusual condensation of low-flux, probably high-redshift point sources, around a strongly lensed Herschel-ATLAS source at z = 3.26. Our results demonstrate that the higher sensitivity and higher angular resolution H-ATLAS maps provide essential information for the interpretation of candidate sources extracted from Planck sub-mm maps.
We present HST/COS high S/N observations of the z = 0.32566 multi-phase absorber towards 3C263. The COS data shows absorption from H I, O VI, C III, N III, Si III and C II. The Ne VIII in this absorber is detected in the FUSE spectrum. The low and intermediate ions are kinematically aligned with each other and H I and display narrow line widths of 6 km/s. The O VI lines are kinematically offset by 12 km/s from the low ions and are a factor of four broader. All metal ions except O VI and Ne VIII are consistent with an origin in gas photoionized by the extragalactic background radiation. The bulk of the observed H I is also traced by this photoionized medium. The carbon abundance in this gas phase is near-solar. The O VI and Ne VIII favor an origin in collisionally ionized gas at T = 5.2 x 10^5 K. The H I absorption associated with this warm absorber is a BLA marginally detected in the COS spectrum. This warm gas phase has total hydrogen column density of N(H) ~ 3 x 10^19 which is 2 dex higher than what is traced by the photoionized gas. Simultaneous detection of O VI, Ne VIII and BLAs in an absorber can be a strong diagnostic of gas with temperature in the range of 10^5 - 10^6 K corresponding to the warm phase of the WHIM or shock-heated gas in the extended halos of galaxies.
There is an observational indication of extragalactic magnetic fields. No known astrophysical process can explain the origin of such large scale magnetic fields, which motivates us to look for their origin in primordial inflation. By solving the linearized Einstein equations, we study metric perturbations sourced by magnetic fields that are produced during inflation. This leads to a simple but robust bound on the inflation models by requiring that the induced metric perturbation should not exceed the observed value 10^-5. In case of the standard single field inflation model, the bound can be converted into a lower bound on the Hubble parameter during inflation.
We investigate the teleparallel dark energy model with purely non-minimal coupling and without potential. We find the analytic solutions of the scalar field in the radiation, matter, and scalar field (or dark energy) dominated eras, respectively. These solutions indicate the tracker behavior in the radiation and matter dominated eras, while the equation of state $w_{\phi}$ of the teleparallel dark energy is determined by the non-minimal coupling constant $\xi$ but insensitive to the initial condition. In the scalar field dominated era, $w_{\phi}$ monotonically decreases and goes to negative infinity at some finite time when $H$ goes to positive infinity, resulting in a future singularity. We also present the possible evolution patterns and the data fittings in this model.
In this paper, we shall study the dynamical behavior of the universe accelerated by the so called Veneziano ghost dark energy component locally and globally by using the linearization and nullcline method developed in this paper. The energy density is generalized to be proportional to the Hawking temperature defined on the trapping horizon instead of Hubble horizon of the Friedmann-Robertson-Walker (FRW) universe. We also give a prediction of the fate of the universe and present the bifurcation phenomenon of the dynamical system of the universe. It seems that the universe could be dominated by dark energy at present in some region of the parameter space.
In this paper we present results from the Mapping Dark Matter competition that expressed the weak lensing shape measurement task in its simplest form and as a result attracted over 700 submissions in 2 months and a factor of 3 improvement in shape measurement accuracy on high signal to noise galaxies, over previously published results, and a factor 10 improvement over methods tested on constant shear blind simulations. We also review weak lensing shape measurement challenges, including the Shear TEsting Programmes (STEP1 and STEP2) and the GRavitational lEnsing Accuracy Testing competitions (GREAT08 and GREAT10).
Gamma-Ray Bursts are likely associated with a catastrophic energy release in stellar mass objects. Electromagnetic observations provide important, but indirect information on the progenitor. On the other hand, gravitational waves emitted from the central source, carry direct information on its nature. In this context, I give an overview of the multi-messenger study of gamma-ray bursts that can be carried out by using electromagnetic and gravitational wave observations. I also underline the importance of joint optical and gravitational wave searches, in the absence of a gamma-ray trigger. Finally, I discuss how multi-messenger observations may probe alternative gamma-ray burst progenitor models, such as the magnetar scenario.
Process of preheating for supersymmetric hybrid model of inflation is generally analyzed in two different ways known as parametric resonance and tachyonic preheating. In a common frame-work, we study both the processes from the decay or growth of homogeneous inflaton field and inhomogeneous waterfall field. We find that these two processes in SUSY hybrid F-term inflation are not parameter independent; rather one process will be more preferable than the other depending on the values of parameters and Fourier mode of the waterfall field. Parameters of the inflationary potential are constrained from the observed CMB data and these constrains help us to identify the process of preheating responsible for this model.
Radiation, winds and jets from the active nucleus of a massive galaxy can interact with its interstellar medium leading to ejection or heating of the gas. This can terminate star formation in the galaxy and stifle accretion onto the black hole. Such Active Galactic Nucleus (AGN) feedback can account for the observed proportionality between central black hole and host galaxy mass. Direct observational evidence for the radiative or quasar mode of feedback, which occurs when the AGN is very luminous, has been difficult to obtain but is accumulating from a few exceptional objects. Feedback from the kinetic or radio mode, which uses the mechanical energy of radio-emitting jets often seen when the AGN is operating at a lower level, is common in massive elliptical galaxies. This mode is well observed directly through X-ray observations of the central galaxies of cool core clusters in the form of bubbles in the hot surrounding medium. The energy flow, which is roughly continuous, heats the hot intracluster gas and reduces radiative cooling and subsequent star formation by an order of magnitude. Feedback appears to maintain a long-lived heating/cooling balance. Powerful, jetted radio outbursts may represent a further mode of energy feedback which affect the cores of groups and subclusters. New telescopes and instruments from the radio to X-ray bands will come into operation over the next few years and lead to a rapid expansion in observational data on all modes of AGN feedback.
PKS 1749+096 is a BL Lac object showing weak extended jet emission to the northeast of the compact VLBI core on parsec scales. We aim at better understanding the jet kinematics and variability of this source and finding clues that may applicable to other BL Lac objects. The jet was studied with multi-epoch multi-frequency high-resolution VLBI observations. The jet is characterized by a one-sided curved morphology at all epochs and all frequencies. The VLBI core, located at the southern end of the jet, was identified based on its spectral properties. The equipartition magnetic field of the core was investigated, through which we derived a Doppler factor of 5, largely consistent with that derived from kinematics (component C5). The study of the detailed jet kinematics at 22 and 15 GHz, spanning a period of more than 10 years, indicates the possible existence of a bimodal distribution of the jet apparent speed. Ballistic and non-ballistic components are found to coexist in the jet. Superluminal motions in the range of 5--21 c were measured in 11 distinct components. We estimated the physical jet parameters with the minimum Lorentz factor of 10.2 and Doppler factors in the range of 10.2--20.4 (component C5). The coincidence in time of the component's ejection and flares supports the idea that, at least in PKS 1749+096, ejection of new jet components is connected with major outbursts in flux density. For the best-traced component (C5) we found that the flux density decays rapidly as it travels downstream the jet, accompanied by a steepening of its spectra, which argues in favor of a contribution of inverse Compton cooling. These properties make PKS 1749+096 a suitable target for an intensive monitoring to decipher the variability phenomenon of BL Lac objects.
This paper is concerned with string cosmology and the dynamics of multiple scalar fields in potentials that can become negative, and their features as (Early) Dark Energy models. Our point of departure is the "String Axiverse", a scenario that motivates the existence of cosmologically light axion fields as a generic consequence of string theory. We couple such an axion to its corresponding modulus. We give a detailed presentation of the rich cosmology of such a model, ranging from the setting of initial conditions on the fields during inflation, to the asymptotic future. We present some simplifying assumptions based on the fixing of the axion decay constant $f_a$, and on the effective field theory when the modulus trajectory is adiabatic, and find the conditions under which these assumptions break down. As a by-product of our analysis, we find that relaxing the assumption of fixed $f_a$ leads to the appearance of a new meta-stable de-Sitter region for the modulus without the need for uplifting by an additional constant. A dynamical systems analysis reveals the existence of many fixed point attractors, repellers and saddle points, which we analyse in detail. We also provide geometric interpretations of the phase space. The fixed points can be used to bound the couplings in the model. A systematic scan of certain regions of parameter space reveals that the future evolution of the universe in this model can be rich, containing multiple epochs of accelerated expansion.
We demonstrate that three sterile neutrinos can simultaneously explain neutrino oscillations, the observed dark matter and baryon asymmetry of the Universe. We perform the first complete study to identify the range of sterile neutrino properties consistent with these requirements, combining the study of neutrino abundances and lepton asymmetries in the early universe with bounds from nucleosynthesis and direct searches. We find that there is a domain of parameters where all these particles can be found with present day experimental techniques, using upgrades to existing experimental facilities.
In the present work, we reconsider the idea of holographic dark energy. One of its key points is the formation of black hole. And then, we propose the so-called "pilgrim dark energy" based on the speculation that the repulsive force contributed by the phantom-like dark energy ($w<-1$) is strong enough to prevent the formation of black hole. We also consider the cosmological constraints on pilgrim dark energy by using the latest observational data. Of course, one can instead regard pilgrim dark energy as a purely phenomenological model without any physical motivation. We also briefly discuss this issue.
We consider a Hubble expansion law modified in the infra-red by distance-dependent terms, and attempt to enforce homogeneity upon it. As a warm-up, we re-derive the basic kinematics of a Friedman Robertson Walker universe without using standard general relativistic tools: we describe the expansion with a `Hubble velocity field' rather than with a four dimensional metric. Then we extend this analysis to the modified Hubble expansion and impose a transformation for velocities that makes it identical for all comoving observers, and therefore homogeneous. We derive the modified equation for light ray trajectories and other geometrical properties that are incompatible with the general relativistic description. We speculate that this extended framework could help addressing cosmological problems which are normally explained with accelerating expansions.
We have recently suggested [1,2] that Inflation could have started in a local minimum of the Higgs potential at field values of about $10^{15}-10^{17}$ GeV, which exists for a narrow band of values of the top quark and Higgs masses and thus gives rise to a prediction on the Higgs mass to be in the range 123-129 GeV, together with a prediction on the the top mass and the cosmological tensor-to-scalar ratio $r$. Inflation can be achieved provided there is an additional degree of freedom which allows the transition to a radiation era. In [1] we had proposed such field to be a Brans-Dicke scalar. Here we present an alternative possibility with an additional subdominant scalar very weakly coupled to the Higgs, realizing an (inverted) hybrid Inflation scenario. Interestingly, we show that such model has an additional constraint $m_H<125.3 \pm 3_{th}$, where $3_{th}$ is the present theoretical uncertainty on the Standard Model RGEs. The tensor-to-scalar ratio has to be within the narrow range $10^{-4}\lesssim r<0.007$, and values of the scalar spectral index compatible with the observed range can be obtained. Moreover, if we impose the model to have subplanckian field excursion, this selects a narrower range $10^{-4} \lesssim r<0.001$ and an upper bound on the Higgs mass of about $m_H <124 \pm 3_{th}$.
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Recent studies have found a dramatic difference between the observed number density evolution of low mass galaxies and that predicted by semi-analytic models. Whilst models accurately predict the z=0 number density, they require that the evolution occurs rapidly at early times, which is incompatible with the strong late evolution found in observational results. We report here the same discrepancy in two state-of-the-art cosmological hydrodynamical simulations, which is evidence that the problem is fundamental. We search for the underlying cause of this problem using two complementary methods. Firstly, we try to find evidence for the evolutionary history of today's low mass galaxies being different in models and observations. We find that the exclusion of satellite galaxies from the analysis brings the median ages and star formation rates of galaxies into good agreement. However, the models yield too few young, strongly star-forming galaxies. Secondly, we construct a toy model to link the observed evolution of specific star formation rates and the galaxy stellar mass function. We infer from this model that a key cause of the discrepancy is the presence of a positive correlation between specific star formation rate and stellar mass in both semi-analytical and hydrodynamical models. A similar positive correlation is found between the specific dark matter accretion rate and the halo mass, indicating that model galaxies are growing in a way that follows the growth of their host haloes too closely. It therefore appears necessary to find a mechanism that decouples the growth of low mass galaxies, which occurs at late times, from the growth of their host haloes, which occurs at early times. We argue that the current form of star-formation driven feedback implemented in most galaxy formation models is unlikely to achieve this goal, owing to its fundamental dependence on host halo mass and time.
We present a study on Spectral Energy Distributions, Morphologies, and star formation for an IRAC-selected extremely red object sample in the GOODS Chandra Deep Field-South. This work was enabled by new HST/WFC3 near-IR imaging from the CANDELS survey as well as the deepest available X-ray data from Chandra 4 Ms observations. This sample consists of 133 objects with the 3.6um limiting magnitude of [3.6] = 21.5, and is approximately complete for galaxies with M >10^{11}M_sun at 1.5 < z < 2.5. We classify this sample into two types, quiescent and star-forming galaxies, in the observed infrared color-color ([3.6]-[24] vs K-[3.6]) diagram. The further morphological study of this sample show a consistent result with the observed color classification. The classified quiescent galaxies are bulge dominated and star-forming galaxies in the sample have disk or irregular morphologies. Our observed infrared color classification is also consistent with the rest-frame color (U-V vs V-J) classification. We also found that quiescent and star-forming galaxies are well separated in the nonparametric morphology parameter (Gini vs M_{20}) diagram measuring their concentration and clumpiness: quiescent galaxies have Gini coefficient higher than 0.58 and star forming galaxies have Gini coefficient lower that 0.58. We argue that the star formation quenching process must lead to or be accompanied by the increasing galaxy concentration. One prominent morphological feature of this sample is that disks are commonly seen in this massive galaxy sample at 1.5 < z < 2.5: 30% of quiescent galaxies and 70% of star forming galaxies with M >10^{11}M_sun have disks in their rest-frame optical morphologies. The prevalence of these extended, relatively undisturbed disks challenges the merging scenario as the main mode of massive galaxy formation.
The discovery of a relationship between supermassive black hole (SMBH) mass and spiral arm pitch angle (P) is evidence that SMBHs are tied to the overall secular evolution of a galaxy. The discovery of SMBHs in late-type galaxies with little or no bulge suggests that an underlying correlation between the dark matter halo concentration and SMBH mass (MBH) exists, rather than between the bulge mass and MBH. In this paper we measure P using a two-dimensional fast fourier transform and estimate the bar pattern speeds of 40 barred spiral galaxies from the Carnegie-Irvine Galaxy Survey. The pattern speeds were derived by estimating the gravitational potentials of our galaxies from Ks-band images and using them to produce dynamical simulation models. The pattern speeds allow us to identify those galaxies with low central dark halo densities, or fast rotating bars, while P provides an estimate of MBH. We find that a wide range of MBH exists in galaxies with low central dark matter halo densities, which appears to support other theoretical results. We also find that galaxies with low central dark halo densities appear to follow more predictable trends in P versus de Vaucouleurs morphological type (T) and bar strength versus T than barred galaxies in general. The empirical relationship between MBH and total gravitational mass of a galaxy (Mtot) allows us to predict the minimum Mtot that will be observationally measured of our fast bar galaxies. These predictions will be investigated in a subsequent paper.
We study the evolution of the galactic spin using data of high redshift galaxies in the fields of the Great Observatories Origins Deep Survey (GOODS). Through simple dynamical considerations we estimate the spin for the disc galaxies in our sample and find that its distribution is consistent with that found for nearby galaxies. Defining a dimensionless angular momentum parameter for the disc component of the galaxies ($\lambda_{d}$), we do not find signs of evolution in the redshift range $0.4 \leq z \leq 1.2$. We find that the mass and environmental dependence of the spin of our high redshift galaxies are similar to that of low-$z$ galaxies; showing a strong dependence on mass, in the sense that low-mass systems present higher $\lambda_{d}$ values than high-mass galaxies, with no significant dependence on the environmental density. These results lead us to conclude that, although individual disc galaxies might occasionally suffer from strong evolution, they evolve in such a way that the overall spin distribution of the galactic population remains constant from $z\sim1$ to the present epoch.
(Abridged) We investigate the phenomenological consequences of a modification of the initial state of a single inflationary field. While single-field inflation with the standard Bunch-Davies initial vacuum state does not generally produce a measurable three-point function (bispectrum) in the squeezed configuration, allowing for a non-standard initial state produces an exception. Here, we calculate the signature of an initial state modification in single-field slow-roll inflation in both the scale-dependent bias of the large-scale structure (LSS) and mu-type distortion in the black-body spectrum of the cosmic microwave background (CMB). We parametrize the initial state modifications and identify certain choices of parameters as natural, though we also note some fine-tuned choices that can yield a larger bispectrum. In both cases, we observe a distinctive k^-3 signature in LSS (as opposed to k^-2 for the local-form). As a non-zero bispectrum in the squeezed configuration correlates a long-wavelength mode with two short-wavelength modes, it induces a correlation between the CMB temperature anisotropy on large scales with the temperature-anisotropy-squared on very small scales; this correlation persists as the small-scale anisotropy-squared is processed into mu-type distortions. While the local-form mu-distortion turns out to be too small to detect in the near future, a modified initial vacuum state enhances the signal by a large factor owing to an extra factor of k_1/k. For example, a proposed absolutely-calibrated experiment, PIXIE, is expected to detect this correlation with a signal-to-noise ratio greater than 10, for an occupation number of about 0.5 in the observable modes. Relatively calibrated experiments such as Planck and LiteBIRD should also be able to measure this effect, provided that the relative calibration between different frequencies meets the required precision.
[Abriged] Supermassive black holes (SMBH) lurk in the nuclei of most massive galaxies, perhaps in all of them. The tight observed scaling relations between SMBH masses and structural properties of their host spheroids likely indicate that the processes fostering the growth of both components are physically linked, despite the many orders of magnitude difference in their physical size. This chapter discusses how we constrain the evolution of SMBH, probed by their actively growing phases, when they shine as active galactic nuclei (AGN) with luminosities often in excess of that of the entire stellar population of their host galaxies. Following loosely the chronological developments of the field, we begin by discussing early evolutionary studies, when AGN represented beacons of light probing the most distant reaches of the universe and were used as tracers of the large scale structure. This early study turned into AGN "Demography", once it was realized that the strong evolution (in luminosity, number density) of the AGN population hindered any attempt to derive cosmological parameters from AGN observations directly. Following a discussion of the state of the art in the study of AGN luminosity functions, we move on to discuss the "modern" view of AGN evolution, one in which a bigger emphasis is given to the physical relationships between the population of growing black holes and their environment. This includes observational and theoretical efforts aimed at constraining and understanding the evolution of scaling relations, as well as the resulting limits on the evolution of the SMBH mass function. Physical models of AGN feedback and the ongoing efforts to isolate them observationally are discussed next. Finally, we touch upon the problem of when and how the first black holes formed and the role of black holes in the high-redshift universe.
The aperture mass statistic is a common tool used in weak lensing studies. By convolving lensing maps with a filter function of a specific scale, chosen to be larger than the scale on which the noise is dominant, the lensing signal may be boosted with respect to the noise. This allows for detection of structures at increased fidelity. Furthermore, higher-order statistics of the aperture mass (such as its skewness or kurtosis), or counting of the peaks seen in the resulting aperture mass maps, provide a convenient and effective method to constrain the cosmological parameters. In this paper, we more fully explore the formalism underlying the aperture mass statistic. We demonstrate that the aperture mass statistic is formally identical to a wavelet transform at a specific scale. Further, we show that the filter functions most frequently used in aperture mass studies are not ideal, being non-local in both real and Fourier space. In contrast, the wavelet formalism offers a number of wavelet functions that are localized both in real and Fourier space, yet similar to the 'optimal' aperture mass filters commonly adopted. Additionally, for a number of wavelet functions, such as the starlet wavelet, very fast algorithms exist to compute the wavelet transform. This offers significant advantages over the usual aperture mass algorithm when it comes to image processing time, demonstrating speed-up factors of ~ 5 - 1200 for aperture radii in the range 2 to 64 pixels on an image of 1024 x 1024 pixels.
Galileon gravity offers a robust theoretical alternative to general relativity with a cosmological constant for explaining cosmic acceleration, protected by a shift symmetry and having second order field equations. The predictions for the combination of cosmic expansion and growth history are distinct from \Lambda CDM, and we demonstrate that approaching \Lambda CDM in one causes deviations in the other. This tension allows us to severely disfavor the entire class of minimally coupled standard Galileon gravity through current observational constraints.
We present a new efficient diagnostic method, based on mid-infrared and X-ray data, to select local (z<0.1) Compton-thick (CT) AGN with the aim of estimating their surface and space density. We define a region in the X-ray/IR vs. HR plane associated to CT AGN, i.e. F(2-12keV)/F25nu25<0.02 and HR>-0.2. We build up a sample of 43 CT AGN candidates using data from IRAS-PSC and 2XMM catalogue. In order to test the efficiency of the proposed method in selecting CT AGN we use the results of the X-ray spectral analysis performed on all the sources of our sample. After taking into account the different selection effects, we have estimated the number of CT in the local Universe and their density down to the IRAS flux limit of F25=0.5Jy. We find that the diagnostic plot proposed here is an efficient method to select Compton-thick AGN in the nearby Universe since ~84% of the sources populating the proposed CT region are actually CT AGN. Twenty percent are newly-discovered CT AGN. We then estimate the surface density of CT AGN down to the IRAS PSC catalogue flux limit (F25=0.5Jy) that turns out to be ~3e-3 src deg-2. After estimating an equivalent IR-hard X-ray limiting flux, we compare our result with those found with SWIFT-BAT. We find that the surface density derived here is a factor 4 above the density computed in the hard X-ray surveys. This difference is ascribed, at least in part, to a significant contribution (~60-90%) of the star-forming activity to the total 25 mic emission for the sources in our sample. By considering only the 25 mic AGN emission, we estimate a surface density of CT AGN which is consistent with the results found by hard X-ray surveys. Finally, we estimated the co-moving space density of CT AGN with intrinsic LX>1e43 erg s-1 (0.004<z<0.06): ~3.5e-6 Mpc-3. The prediction for CT AGN based on the synthesis model of XRB in Gilli et al.(2007) is consistent with this value.
The reported spatial variation in the fine-structure constant at high redshift, if physical, could be due to the presence of dilatonic domains, and one or more domain walls inside our horizon. An absorption spectrum of an object in a different domain from our own would be characterized by a different value of alpha. We show that while a single wall solution is statically comparable to a dipole fit, and is a big improvement over a weighted mean (despite adding 3 parameters), a two-wall solution is a far better fit (despite adding 3 parameters over the single wall solution). We derive a simple model accounting for the two-domain wall solution. The goodness of these fits is however dependent on the extra random error which was argued to account for the large scatter in most of the data. When this error is omitted, all the above solutions are poor fits to the data. When included, the solutions that exhibit a spatial dependence agree with the data much more significantly than the Standard Model; however, the Standard Model itself is not a terrible fit to the data, having a p-value of ~ 20 %.
Several non-threshold reactions which may be used to detect the cosmic neutrino background are presented. The corresponding cross sections are calculated analytically within the Standard Model. These reactions are sensitive not only to the electron neutrinos but also to the muon and tau neutrinos. Some possibilities of experimental observation of the neutrino background are indicated.
We calculate Large Scale Structure observables for non-Gaussianity arising from non-Bunch-Davies initial states in single field inflation. These scenarios can have substantial primordial non-Gaussianity from squeezed (but observable) momentum configurations. They generate a term in the halo bias that may be more strongly scale-dependent than the contribution from the local ansatz. We also discuss theoretical considerations required to generate an observable signature.
We present the results of an extended narrow-band H{\alpha} study of the massive galaxy cluster XMMU J2235.3-2557 at z = 1.39. This paper represents a follow up study to our previous investigation of star-formation in the cluster centre, extending our analysis out to a projected cluster radius of 1.5 Mpc. Using the Near InfraRed Imager and Spectrograph (NIRI) on Gemini North we obtained deep H narrow-band imaging corresponding to the rest-frame wavelength of H{\alpha} at the cluster's redshift. We identify a total of 163 potential cluster members in both pointings, excluding stars based on their near-IR colours derived from VLT/HAWK-I imaging. Of these 163 objects 14 are spectroscopically confirmed cluster members, and 20% are excess line-emitters. We find no evidence of star formation activity within a radius of 200 kpc of the brightest cluster galaxy in the cluster core. Dust-corrected star formation rates (SFR) of excess emitters outside this cluster quenching radius, RQ \sim 200 kpc, are on average <SFR> = 2.7 \pm 1.0 M\odot yr-1, but do not show evidence of increasing star-formation rates toward the extreme 1.5 Mpc radius of the cluster. No individual cluster galaxy exceeds an SFR of 6 M\odot yr-1 . Massive galaxies (log M\ast /M\odot > 10.75) all have low specific SFRs (SSFRs, i.e. SFR per unit stellar mass). At fixed stellar mass, galaxies in the cluster centre have lower SSFRs than the rest of the cluster galaxies, which in turn have lower SSFRs than field galaxies at the same redshift by a factor of a few to 10. For the first time we can demonstrate through measurements of individual SFRs that already at very early epochs (at an age of the Universe of \sim4.5 Gyr) the suppression of star-formation is an effect of the cluster environment which persists at fixed galaxy stellar mass.
A list of galaxies with inner regions revealing polar (or strongly inclined to the main galactic plane) disks and rings is compiled from the literature data. The list contains 47 galaxies of all morphological types, from E to Irr. We consider the statistics of the parameters of polar structures known from observations. The radii of the majority of them do not exceed 1.5 kpc. The polar structures are equally common in barred and unbarred galaxies. At the same time, if a galaxy has a bar (or a triaxial bulge), this leads to the polar disk stabilization - its axis of rotation usually coincides with the major axis of the bar. More than two thirds of all considered galaxies reveal one or another sign of recent interaction or merging. This fact indicates a direct relation between the external environment and the presence of an inner polar structure.
The present paper extends to clusters of galaxies the study of Del Popolo (2012), concerning how the baryon-dark matter (DM) interplay shapes the density profile of dwarf galaxies. Cluster density profiles are determined taking into account dynamical friction, random and ordered angular momentum and the response of dark matter halos to condensation of baryons. We find that halos containing only DM are characterized by Einasto's profiles, and that the profile flattens with increasing content of baryons, and increasing values of random angular momentum. The analytical results obtained in the first part of the paper were applied to well studied clusters whose inner profiles have slopes flatter than NFW predictions (A611, A383) or are characterized by profiles in agreement with the NFW model (MACS J1423.8+2404, RXJ1133). By using independently-measured baryonic fraction, a typical spin parameter value $\lambda \simeq 0.03$, and adjusting the random angular momentum, we re-obtain the mass and density profiles of the quoted clusters. Finally, we show that the baryonic mass inside $\simeq 10$ kpc, $M_{b,in}$ is correlated with the total mass of the clusters, %finding a correlation among the two quantities, as $M_{b,in} \propto M_{500}^{0.4}$.
Using a sample of 28 HII regions from the literature with measured temperature inhomogeneity parameter, t^2, we present a statistical correction to the chemical abundances determined with the direct method. We used the t^2 values to correct the oxygen gaseous abundances and consider the oxygen depletion into dust to calculate the total abundances for these objects. This correction is used to obtain a new calibration of Pagel's strong-line method to determine oxygen abundances in HII regions. Our new calibration simultaneously considers the temperature structure, the ionization structure, and the fraction of oxygen depleted into dust grains. Previous calibrations in the literature have included one or two of these factors; this is the first time all three are taken into account. This recalibration conciliates the systematic differences among the temperatures found from different methods. We find that the total correction due to thermal inhomogeneities and dust depletion amounts to an increase in the O/H ratio of HII regions by factors of 1.7 to 2.2 (or 0.22 to 0.35 dex). This result has important implications in various areas of astrophysics such as the study of the higher end of the initial mass function, the star formation rate, and the mass-metallicity relation of galaxies, among others.
Chameleon scalar fields are dark energy candidates which suppress fifth forces in high density regions of the universe by becoming massive. We consider chameleon models as effective field theories and estimate quantum corrections to their potentials. Requiring that quantum corrections be small, so as to allow reliable predictions of fifth forces, leads to an upper bound $m < 0.0073 (\rho / 10 {\rm g\, cm}^{-3})^{1/3}$eV for gravitational strength coupling whereas fifth force experiments place a lower bound of $m>0.0042$\,eV. An improvement of less than a factor of two in the range of fifth force experiments could test all classical chameleon field theories whose quantum corrections are well-controlled and couple to matter with nearly gravitational strength regardless of the specific form of the chameleon potential.
In general, when gas accretes on to a supermassive black hole binary it is likely to have no prior knowledge of the binary angular momentum. Therefore a circumbinary disc forms with a random inclination angle, theta, to the binary. It is known that for theta < 90 degrees the disc will coalign wrt the binary. If theta > 90 degrees the disc wholly counteraligns if it satisfies cos(theta) < -J_d/2J_b, where J_d and J_b are the magnitudes of the disc and binary angular momentum vectors respectively. If however theta > 90 degrees and this criterion is not satisfied the same disc may counteralign its inner regions and, on longer timescales, coalign its outer regions. I show that for typical disc parameters, describing an accretion event on to a supermassive black hole binary, a misaligned circumbinary disc is likely to wholly co-- or counter--align with the binary plane. This is because the binary angular momentum dominates the disc angular momentum. However with extreme parameters (binary mass ratio M_2/M_1 << 1 or binary eccentricity e ~ 1) the same disc may simultaneously co- and counter-align. It is known that coplanar prograde circumbinary discs are stable. I show that coplanar retrograde circumbinary discs are also stable. A chaotic accretion event on to an SMBH binary will therefore result in a coplanar circumbinary disc that is either prograde or retrograde with respect to the binary plane.
We review observational evidence for a matter-antimatter asymmetry in the early universe, which leads to the remnant matter density we observe today. We also discuss observational bounds on the presence of antimatter in the present day universe, including the possibility of a large lepton asymmetry in the cosmic neutrino background. We briefly review the theoretical framework within which baryogenesis, the dynamical generation of a matter-antimatter asymmetry, can occur. As an example, we discuss a testable minimal model that simultaneously explains the baryon asymmetry of the universe, neutrino oscillations and dark matter.
Soft limits of inflationary correlation functions are both observationally relevant and theoretically robust. Various theorems can be proven about them that are insensitive to detailed model-building assumptions. In this paper, we re-derive several of these theorems in a universal way. Our method makes manifest why soft limits are such an interesting probe of the spectrum of additional light fields during inflation. We illustrate these abstract results with a detailed case study of the soft limits of quasi-single-field inflation.
During the process of core-collapse of a massive star, the iron core evolves into an inner central core and an outer envelope, generating a cavity in between. The dynamics of this cavity, filled with plasma and magnetic field by the rapidly rotating pulsar (spun-down magnetar) at the center, is believed to be very relevant to account for supernovae and gamma-ray bursts \citep{uzdensky2007}. The interactions of the pressurized conducting plasma and the magnetic field could generate some spatial distributions of plasma and magnetic field within the cavity. In an effort to better understand the spatial distributions, a set of time-dependent magnetohydrodynamic (MHD) equations is used to model this cavity system. Homologous solutions in Lagrangian representation are obtained to account for the spatial structures. Under this self-similar description, the magnetic flux function is governed by an eigenvalue equation with the eigenvalue being the poloidal plasma $\beta$, which is the ratio of plasma pressure to poloidal magnetic pressure. In terms of the flux function, the magnetic fields are structured in the cavity with a set of axisymmetric lobes (magnetic vortices). Because of a geometric singularity, the magnetic lobe energy tends to collimate onto the polar axis, as a function of increasing plasma pressure in the cavity. Since this model indicates $\beta\gg 1$, plasma pressure stored in the cavity is the primary motor for supernova, not the magnetic field. At very high plasma pressure and high magnetic fields, the collimation is confined to a very small cone along the axis with a sequence of magnetic lobes, generating a configuration appropriate for gamma-ray burst with multiple fireballs.
The Swift Burst Alert Telescope (BAT) is discovering interesting new objects while monitoring the sky in the 14-195 keV band. Here we present the X-ray properties and spectral energy distributions for two unusual AGN sources. Both NVSS 193013+341047 and IRAS 05218-1212 are absorbed, Compton-thin, but heavily obscured (NH \sim 10^23 cm-2), X-ray sources at redshifts < 0.1. The spectral energy distributions reveal these galaxies to be very red, with high extinction in the optical and UV. A similar SED is seen for the extremely red objects (EROs) detected in the higher redshift universe. This suggests that these unusual BAT-detected sources are a low- redshift (z << 1) analog to EROs, which recent evidence suggests are a class of the elusive type II quasars. Studying the multi-wavelength properties of these sources may reveal the properties of their high redshift counterparts.
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