We have used the Green Bank Telescope to carry out a deep search for redshifted CO J=2-1 line emission from an extended (>17 kpc) Ly-Alpha blob (LAB), "Himiko", at z~6.595. Our non-detection of CO J=2-1 emission places the strong 3-sigma upper limit of L'_CO < 1.8x10^10 x sqrt(dV/250) K km/s pc^2 on the CO line luminosity. This is comparable to the best current limits on the CO line luminosity in LABs at z~3 and lower-luminosity Lyman-Alpha emitters (LAEs) at z>~6.5. High-z LABs appear to have lower CO line luminosities than the host galaxies of luminous quasars and sub-mm galaxies at similar redshifts, despite their high stellar mass. Although the CO-to-H2 conversion factor is uncertain for galaxies in the early Universe, we assume X_CO = 0.8 Msun (K km/s pc^2)^-1 to obtain the limit M(H_2) < 1.4 x 10^10 Msun on Himiko's molecular gas mass; this is a factor of >2.5 lower than the stellar mass in the z~6.595 LAB.
We present results from monitoring observations of the gravitationally lensed quasar RX J1131-1231 performed with the Chandra X-ray Observatory. The X-ray observations were planned with relatively long exposures that allowed a search for energy-dependent microlensing in the soft (0.2-2 keV) and hard (2-10 keV) light curves of the images of RX J1131-1231. We detect significant microlensing in the X-ray light-curves of images A and D, and energy-dependent microlensing of image D. The magnification of the soft band appears to be larger than that in the hard band by a factor of ~ 1.3 when image D becomes more magnified. This can be explained by the difference between a compact, softer-spectrum corona that is producing a more extended, harder spectrum reflection component off the disk. This is supported by the evolution of the fluorescent iron line in image D over three consecutive time-averaged phases of the light curve. In the first period, a Fe line at E = 6.36(-0.16,+0.13) keV is detected (at > 99% confidence). In the second period, two Fe lines are detected, one at E = 5.47(-0.08,+0.06) keV (detected at > 99% confidence) and another at E = 6.02(-0.07,+0.09) keV (marginally detected at > 90% confidence), and in the third period, a broadened Fe line at 6.42(-0.15,+0.19) keV is detected (at > 99% confidence). This evolution of the Fe line profile during the microlensing event is consistent with the line distortion expected when a caustic passes over the inner disk where the shape of the fluorescent Fe line is distorted by General Relativistic and Doppler effects.
X-ray surveys contain sizable numbers of star forming galaxies, beyond the AGN which usually make the majority of detections. Many methods to separate the two populations are used in the literature, based on X-ray and multiwavelength properties. We aim at a detailed test of the classification schemes and to study the X-ray properties of the resulting samples. We build on a sample of galaxies selected at 1.4 GHz in the VLA-COSMOS survey, classified by Smolcic et al. (2008) according to their optical colours and observed with Chandra. A similarly selected control sample of AGN is also used for comparison. We review some X-ray based classification criteria and check how they affect the sample composition. The efficiency of the classification scheme devised by Smolcic et al. (2008) is such that ~30% of composite/misclassified objects are expected because of the higher X-ray brightness of AGN with respect to galaxies. The latter fraction is actually 50% in the X-ray detected sources, while it is expected to be much lower among X-ray undetected sources. Indeed, the analysis of the stacked spectrum of undetected sources shows, consistently, strongly different properties between the AGN and galaxy samples. X-ray based selection criteria are then used to refine both samples. The radio/X-ray luminosity correlation for star forming galaxies is found to hold with the same X-ray/radio ratio valid for nearby galaxies. Some evolution of the ratio may be possible for sources at high redshift or high luminosity, tough it is likely explained by a bias arising from the radio selection. Finally, we discuss the X-ray number counts of star forming galaxies from the VLA- and C-COSMOS surveys according to different selection criteria, and compare them to the similar determination from the Chandra Deep Fields. The classification scheme proposed here may find application in future works and surveys.
We present observational evidence that leakage of ionising photons from star-forming regions can affect the quantification of the star formation rate (SFR) in galaxies. This effect could partially explain the differences between the SFR estimates using the far ultraviolet (FUV) and the Halpha emission. We find that leakage could decrease the SFR(Ha)/SFR(FUV) ratio by up to a 25 per cent. The evidence is based on the observation that the SFR(Ha)/SFR(FUV) ratio is lower for objects showing a shell Halpha structure than for regions exhibiting a much more compact morphology. The study has been performed on three object samples: low luminosity dwarf galaxies from the Local Volume Legacy survey and star-forming regions in the Large Magellanic Cloud and the nearby Local Group galaxy M33. For the three samples we find differences (1.1-1.4sigma) between the SFR(Ha)/SFR(FUV) for compact and shell objects. Although leakage cannot entirely explain the observed trend of SFR(Ha)/SFR(FUV) ratios for systems with low SFR, we show the mechanism can lead to different SFR estimates when using Halpha and FUV luminosities. Therefore, further study is needed to constrain the contribution of leakage to the low SFR(Ha)/SFR(FUV) ratios observed in dwarf galaxies and its impact on the Halpha flux as a SFR indicator in such objects.
We present long slit spectrophotometry of two HII regions: TOL2146-391 and TOL0357-3915. We performed a detailed analysis that involves abundance determinations relaxing the assumption of homogeneous temperature. The temperature inhomogeneities values, t^2, were obtained through two methods: (i) comparing abundances from oxygen recombination lines to abundances from collisionally excited lines and (ii) by using the line intensity ratios of a set of HeI lines together with the HELIO10 program. We find that the HELIO10 program is a good alternative to obtain a t^2 value in photoionized regions where recombination lines of heavy elements are not available. We have plotted 27 high and low metallicity HII regions in an oxygen degree of ionization versus t^2 diagram; we find areas populated by HII regions and areas void of them; the physical characteristics of each area are discussed. In addition, an average t^2 value can be determined for the objects in each area. We propose to use this <t^2> value for the cases where a direct measurement of t^2 cannot be determined
We study the ability of future weak lensing (WL) surveys to constrain primordial non-Gaussianity of the local type. We use a large ensemble of simulated WL maps with survey specifications relevant to Euclid and LSST. The simulations assume Cold Dark Matter cosmologies that vary certain parameters around fiducial values: the non-Gaussianity parameter f_NL, the matter density parameter Omega_m, the amplitude of the matter power spectrum sigma_8, the spectral index of the primordial power spectrum n_s, and the dark-energy equation-of-state parameter w_0. We assess the sensitivity of the cosmic shear correlation functions, the third-order aperture mass statistics, and the abundance of shear peaks to these parameters. We find that each of the considered probes provides unmarginalized constraints of Delta f_NL ~ 20 on f_NL. Marginalized constraints from any individual WL probe are much weaker due to strong correlations between parameters. However, the parameter errors can be substantially reduced by combining information from different WL probes. Combining all WL probes yields the following marginal (68% confidence level) uncertainties: Delta f_NL ~ 50, Delta Omega_m ~ 0.002, Delta sigma_8 ~ 0.004, Delta n_s ~ 0.007, and Delta w_0 ~ 0.03. We examine the bias induced by neglecting f_NL on the constraints on the other parameters. We find sigma_8 and w_0 to be the most affected. Moreover, neglecting non-Gaussianity leads to a severe underestimation of the uncertainties in the other cosmological parameters.
We have performed accurate iron abundance measurements for 44 red giants
(RGs) in the Carina dwarf spheroidal (dSph) galaxy. We used archival,
high-resolution spectra (R~38,000) collected with UVES at ESO/VLT either in
slit mode (5) or in fiber mode (39, FLAMES/GIRAFFE-UVES). The sample is more
than a factor of four larger than any previous spectroscopic investigation of
stars in dSphs based on high-resolution (R>38,000$) spectra. We did not impose
the ionization equilibrium between neutral and singly-ionized iron lines. The
effective temperatures and the surface gravities were estimated by fitting
stellar isochrones in the V, B-V color-magnitude diagram. To measure the iron
abundance of individual lines we applied the LTE spectrum synthesis fitting
method using MARCS model atmospheres of appropriate metallicity. We found
evidence of NLTE effects between neutral and singly-ionized iron abundances.
Assuming that the FeII abundances are minimally affected by NLTE effects, we
corrected the FeI stellar abundances using a linear fit between FeI and FeII
stellar abundance determinations.
We found that the Carina metallicity distribution based on the corrected FeI
abundances (44 RGs) has a weighted mean metallicity of [Fe/H]=-1.80 and a
weighted standard deviation of sigma=0.24 dex. The Carina metallicity
distribution based on the FeII abundances (27 RGs) gives similar estimates
([Fe/H]=-1.72, sigma=0.24 dex). The current weighted mean metallicities are
slightly more metal poor when compared with similar estimates available in the
literature. Furthermore, if we restrict our analysis to stars with the most
accurate iron abundances, ~20 FeI and at least three FeII measurements (15
stars), we found that the range in iron abundances covered by Carina RGs (~1
dex) agrees quite well with similar estimates based on high-resolution spectra.
Using the far-infrared emission, as observed by the Herschel Virgo Cluster Survey (HeViCS), and the integrated HI and CO brightness, we infer the dust and total gas mass for a magnitude limited sample of 35 metal rich spiral galaxies in Virgo. The CO flux correlates tightly and linearly with far-infrared fluxes observed by Herschel. Molecules in these galaxies are more closely related to cold dust rather than to dust heated by star formation or to optical/NIR brightness. We show that dust mass establishes a stronger correlation with the total gas mass than with the atomic or molecular component alone. The dust-to-gas ratio increases as the HI deficiency increases, but in highly HI deficient galaxies it stays constant. Dust is in fact less affected than atomic gas by weak cluster interactions, which remove most of the HI gas from outer and high latitudes regions. Highly disturbed galaxies, in a dense cluster environment, can instead loose a considerable fraction of gas and dust from the inner regions of the disk keeping constant the dust-to-gas ratio. There is evidence that the molecular phase is also quenched. This quencing becomes evident by considering the molecular gas mass per unit stellar mass. Its amplitude, if confirmed by future studies, highlights that molecules are missing in Virgo HI deficient spirals, but to a somewhat lesser extent than dust.
Several models have been proposed to explain the dark energy that is causing universe expansion to accelerate. Here the acceleration predicted by the Holographic Dark Information Energy (HDIE) model is compared to the acceleration that would be produced by a cosmological constant. While identical to a cosmological constant at low redshifts, z<1, the HDIE model results in smaller Hubble parameter values at higher redshifts, z>1, reaching a maximum difference of 2.6\pm0.5% around z \sim 1.7. The next generation of dark energy measurements, both those scheduled to be made in space (ESA's Euclid and NASA's WFIRST missions) and those to be made on the ground (BigBOSS, LSST and Dark Energy Survey), should be capable of determining whether such a difference signature exists or not. The HDIE model is therefore falsifiable.
We report measurements of the carbon monoxide ground state rotational transition (12C16O J = 1--0) with the Zpectrometer ultra-wideband spectrometer on the 100-m diameter Green Bank Telescope. The sample comprises 11 galaxies with redshifts between z = 2.1 and 3.5 from a total sample of 24 targets identified by Herschel-ATLAS photometric colors from the SPIRE instrument. Nine of the CO measurements are new redshift determinations, substantially adding to the number of detections of galaxies with rest-frame peak submillimeter emission near 100um. The CO detections confirm the existence of massive gas reservoirs within these luminous dusty star-forming galaxies (DSFGs). The CO redshift distribution of the 350um-selected galaxies is strikingly similar to the optical redshifts of 850um-selected submillimeter galaxies (SMGs) in 2.1 < z < 3.5. Spectroscopic redshifts break a temperature-redshift degeneracy; optically thin dust models fit to the far-infrared photometry indicate characteristic dust temperatures near 34 K for most of the galaxies we detect in CO. Detections of two warmer galaxies and statistically significant nondetections hint at warmer or molecule-poor DSFGs with redshifts difficult determine from from Herschel-SPIRE photometric colors alone. Many of the galaxies identified by H-ATLAS photometry are expected to be amplified by foreground gravitational lenses. Analysis of CO linewidths and luminosities provides a method for finding approximate gravitational lens magnifications mu from spectroscopic data alone, yielding mu ~ 3--20. Corrected for magnification, most galaxy luminosities are consistent with an ultra-luminous infrared galaxy (ULIRG) classification, but three are candidate hyper-LIRGs with luminosities greater than 10^13 L_sun.
The combination of large size, high stellar density, high metallicity, and Sersic surface brightness profile of the spheroidal component of the Andromeda galaxy (M31) within R_proj ~ 20 kpc suggest that it is unlike any subcomponent of the Milky Way. In this work we capitalize on our proximity to and external view of M31 to probe the kinematical properties of this "inner spheroid." We employ a Markov chain Monte Carlo (MCMC) analysis of resolved stellar kinematics from Keck/DEIMOS spectra of 5651 red giant branch stars to disentangle M31's inner spheroid from its stellar disk. We measure the mean velocity and dispersion of the spheroid in each of five spatial bins after accounting for a locally cold stellar disk as well as the Giant Southern Stream and associated tidal debris. For the first time, we detect significant spheroid rotation (v_rot ~ 50 km/s) beyond R_proj ~ 5 kpc. The velocity dispersion decreases from about 140 km/s at R_proj = 7 kpc to 120 km/s at R_proj = 14 kpc, consistent to 2 sigma with existing measurements and models. We calculate the probability that a given star is a member of the spheroid and find that the spheroid has a significant presence throughout the spatial extent of our sample. Lastly, we show that the flattening of the spheroid is due to velocity anisotropy in addition to rotation. Though this suggests that the inner spheroid of M31 more closely resembles an elliptical galaxy than a typical spiral galaxy bulge, it should be cautioned that our measurements are much farther out (2 - 14 r_eff) than for the comparison samples.
We present the computation of the loop-induced self-annihilation of dark matter particles into two photons in the framework of the NMSSM. This process is a theoretically clean observable with a "smoking-gun" signature but is experimentally very challenging to detect. The rates were computed with the help of the SloopS program, an automatic code initially designed for the evaluation of processes at the one-loop level in the MSSM. We focused on a light neutralino scenario and discuss how the signal can be enhanced in the NMSSM with respect to the MSSM and then compared with the present limits given by the dedicated search of the FERMI-LAT satellite on the monochromatic gamma lines.
We investigate the possibility that the observed rotation of galaxies can be accounted for by invoking a massive baryonic disc with no need for non-baryonic dark matter or a massive halo. There are 5 primary reasons for suggesting this: 1. there are well known disc surface mass density distributions that naturally produce the observed rotation curves of galaxies. 2. there are a number of rotation curve `puzzles' that cannot be explained by a massive dark matter halo i.e. the success of maximum disc fitting, HI gas scaling to the observed rotation, the disc/halo conspiracy and the interpretation of the Tully-Fisher relation. 3. recent 21cm observations show an almost constant HI surface density and a distinct `cut-off' or edge to galactic discs. We explain this constant surface density in terms of either an optical depth effect or the onset of molecular gas formation and hence the possibility of considerably more gas existing in galaxies. We suggest that the HI cut-off does indeed mark the edge of the galactic disc. 4. there have been an increasing number of recent observations that imply that X_CO may be ten times higher in the outer Galaxy. This `dark' gas may provide adequate mass to account for galaxy rotation. 5. we show that the additional baryonic mass required to account for the rotation of galaxies is just that required to reconcile observed baryons with those predicted by big bang nucleosynthesis. Mestel discs can be used to straight forwardly explain the scaling laws of galaxies, particularly the observed relation between rotation velocity and radius and the oft used Tully-Fisher relation. We discuss observations of the baryonic content of galactic discs and where sufficient `hidden' baryons might be found to account for the rotation.
Spherical symmetry for f(R)-gravity is discussed by searching for Noether symmetries. The method consists in selecting conserved quantities in form of currents that reduce dynamics of f(R)-models compatible with symmetries. In this way we get a general method to obtain constants of motion without setting a priori the form of f(R). In this sense, the Noether symmetry results a physical criterium. Relevant cases are discussed.
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In this note we revisit the Fisher information content of cosmological power spectra of Gaussian fields, when based on the assumption of a multivariate Gaussian likelihood for estimators. We discuss that while the assumption of a Gaussian likelihood is motivated by the central limit theorem, it leads if used consistently to a Fisher information content that violates the Cramer-Rao inequality, due to the presence of independent information from the parameter dependent covariance matrix. At any fixed multipole, this term is shown to become dominant in the limit of a large number of correlated fields. While the distribution of the estimators does indeed tend to a Gaussian with a large number of modes, it is shown, however, that its Fisher information content does not, in the sense that the covariance matrix never carries independent information content. The reason why the information content of the spectra is correctly described by the usual formula (i.e. without the covariance term) in this estimator perspective is precisely the fact the the estimators have a chi-squared like distribution, and not a Gaussian distribution. The assumption of a Gaussian estimators likelihood is thus from the point of view of the information neither necessary nor really adequate, and we warn against the use of Gaussian likelihoods with parameter dependent covariance matrices for parameter inference from such spectra.
We present a detailed analysis of redshift-space distortions in the two-point correlation function of the 6dF Galaxy Survey (6dFGS). The K-band selected sub-sample which we employ in this study contains 81971 galaxies distributed over 17000deg^2 with an effective redshift z = 0.067. By modelling the 2D galaxy correlation function, xi(r_p,pi), we measure the parameter combination f(z)sigma_8(z) = 0.423 +/- 0.055. Alternatively, by assuming standard gravity we can break the degeneracy between sigma_8 and the galaxy bias parameter, b. Combining our data with the Hubble constant prior from Riess et al (2011), we measure sigma_8 = 0.76 +/- 0.11 and Omega_m = 0.250 +/- 0.022, consistent with constraints from other galaxy surveys and the Cosmic Microwave Background data from WMAP7. Combining our measurement of fsigma_8 with WMAP7 allows us to test the relationship between matter and gravity on cosmic scales by constraining the growth index of density fluctuations, gamma. Using only 6dFGS and WMAP7 data we find gamma = 0.547 +/- 0.088, consistent with the prediction of General Relativity. We note that because of the low effective redshift of 6dFGS our measurement of the growth rate is independent of the fiducial cosmological model (Alcock-Paczynski effect). We also show that our conclusions are not sensitive to the model adopted for non-linear redshift-space distortions. Using a Fisher matrix analysis we report predictions for constraints on fsigma_8 for the WALLABY survey and the proposed TAIPAN survey. The WALLABY survey will be able to measure fsigma_8 with a precision of 4-10%, depending on the modelling of non-linear structure formation. This is comparable to the predicted precision for the best redshift bins of the Baryon Oscillation Spectroscopic Survey (BOSS), demonstrating that low-redshift surveys have a significant role to play in future tests of dark energy and modified gravity.
The Herschel Reference Survey (HRS) is a guaranteed time Herschel key project aimed at studying the physical properties of the interstellar medium in galaxies of the nearby universe. This volume limited, K-band selected sample is composed of galaxies spanning the whole range of morphological types (from ellipticals to late-type spirals) and environments (from the field to the centre of the Virgo Cluster). We present flux density measurements of the whole sample of 323 galaxies of the HRS in the three bands of the Spectral and Photometric Imaging Receiver (SPIRE), at 250, 350 and 500 microns. Aperture photometry is performed on extended galaxies and point spread function (PSF) fitting on timeline data for unresolved objects; we carefully estimate errors and upper limits. The flux densities are found to be in good agreement with those of the HeViCS and KINGFISH key projects in all SPIRE bands, and of the Planck consortium at 350 and 550 microns, for the galaxies in common. This submillimetre catalogue of nearby galaxies is a benchmark for the study of the dust properties in the local universe, giving the zero redshift reference for any cosmological survey.
We have obtained high-resolution data of the z 2 ring-like, clumpy star-forming galaxy (SFG) ZC406690 using the VLT/SINFONI with AO (in K-band) and in seeing-limited mode (in H- and J-band). Our data includes all of the main strong optical emission lines: [OII], [OIII], Ha, Hb, [NII] and [SII]. We find broad, blueshifted Ha and [OIII] emission line wings in the spectra of the galaxy's massive, star-forming clumps (sigma \sim 85 km s^-1) and even broader wings (up to 70% of the total Ha flux, with sigma \sim 290 km s^-1) in regions spatially offset from the clumps by \sim 2 kpc. The broad emission likely originates from large-scale outflows with mass outflow rates from individual clumps that are 1-8x the SFR of the clumps. Based on emission line ratio diagnostics ([NII]/Ha and [SII]/Ha) and photoionization and shock models, we find that the emission from the clumps is due to a combination of photoionization from the star-forming regions and shocks generated in the outflowing component, with 5-30% of the emission deriving from shocks. In terms of the ionization parameter (6x10^7-10^8 cm/s, based on both the SFR and the O32 ratio), density (local electron densities of 300-1800 cm^-3 in and around the clumps, and ionized gas column densities of 1200-8000 Msol/pc^2), and SFR (10-40 Msol/yr), these clumps more closely resemble nuclear starburst regions of local ULIRGs and dwarf irregulars than HII regions in local galaxies. However, the star-forming clumps are not located in the nucleus as in local starburst galaxies but instead are situated in a ring several kpc from the center of their high-redshift host galaxy, and have an overall disk-like morphology. The two brightest clumps are quite different in terms of their internal properties, energetics and relative ages, and thus we are given a glimpse at two different stages in the formation and evolution of rapidly star-forming giant clumps at high-z.
The blue compact dwarf galaxy I Zw 18 is one of the most metal poor systems known in the local Universe (12 + log(O/H) $=$ 7.17). In this work we study I Zw 18 using data from {\it Spitzer}, {\it Herschel Space Telescope} and IRAM Plateau de Bure Interferometer. Our data set includes the most sensitive maps of I Zw 18, to date, in both, the far infrared and the CO $J=1\rightarrow0$ transition. We use dust emission models to derive a dust mass upper limit of only M$_{dust}\leq1.1\times10^4$ M$_{\odot}$ ($3\sigma$ limit). This upper limit is driven by the non-detection at 160 $\mu$m, and it is a factor of 4-10 times smaller than previous estimates (depending upon the model used). We also estimate an upper limit to the total dust-to-gas mass ratio of M$_{Dust}$/M$_{gas}\leq5.0\times10^{-5}$. If a linear correlation between the dust-to-gas mass ratio and metallicity (measure as O/H) were to hold, we would expect a ratio of 3.9$\times10^{-4}$. We also show that the infrared SED is similar to that of starbursting systems.
In this paper, we revisit generalized Chaplygin gas (GCG) model as a unified dark matter and dark energy model. The energy density of GCG model is given as $\rho_{GCG}/\rho_{GCG0}=[B_{s}+(1-B_{s})a^{-3(1+\alpha)}]^{1/(1+\alpha)}$, where $\alpha$ and $B_s$ are two model parameters which will be constrained by type Ia supernova as standard candles, baryon acoustic oscillation as standard rulers and the seventh year full WMAP data points. In this paper, we will not separate GCG into dark matter and dark energy parts any more as adopted in the literatures. By using Markov Chain Monte Carlo method, we find the result: $\alpha=0.00126_{- 0.00126- 0.00126}^{+ 0.000970+ 0.00268}$ and $B_s= 0.775_{- 0.0161- 0.0338}^{+ 0.0161+ 0.0307}$.
We examine the duty cycle and the history of star formation (SFH) for high-redshift galaxies at z \geq 6 using cosmological hydrodynamic simulations. We find that, even though individual galaxies have bursty SFH, the averaged SFH between z ~ 15 to z = 6 can be characterized well by either an exponentially increasing functional form with characteristic time-scales of 70 Myr to 200 Myr for galaxies with stellar masses Ms \sim 10^6 M\odot to > 10^10 M\odot respectively, or by a simple power-law form which exhibits a similar mass dependent time-scales. Using the SFH of individual galaxies, we measure the duty cycle of star formation (DC_SFH); i.e., the fraction of time a galaxy of a particular mass spends above a star formation rate (SFR) threshold which would make it observable to the Hubble Space Telescope (HST) during a given epoch. We also examine the fraction of galaxies at a given redshift that are brighter than a rest-frame UV magnitude Muv, which is sufficient enough to make them observable (DC_Muv). We find that both DC_SFH and DC_Muv make a sharp transition from zero (for galaxies with Ms \leq 10^7 M\odot) to unity (for Ms > 10^9 M\odot). The measured duty cycle is also manifested in the intrinsic scatter in the Ms-SFR relationship (\sim 1 dex) and Ms-Muv relationship (\Delta Muv \sim \pm 1 mag). We provide analytic fits to the DC as a function of Ms using a sigmoid function, which can be used in semi-analytic models of galaxy formation. We consider the effects of duty cycle to the observational estimate of galaxy stellar mass functions (GSMF) and the star formation rate density (SFRD), and find that it results in a much shallower low-mass end slopes of the GSMF and a reduction of \geq 70% of our intrinsic SFRD, making our simulation results more compatible with observational estimates.
With mid-IR and near-IR long-baseline interferometers, we are now mapping the radial distribution of the dusty accreting material in AGNs at sub-pc scales. We currently focus on Type 1 AGNs, where the innermost region is unobscured and its intrinsic structure can be studied directly. As a first systematic study of Type 1s, we obtained mid-/near-IR data for small samples over ~3-4 orders of magnitudes in UV luminosity L of the central engine. Here we effectively trace the structure by observing dust grains that are radiatively heated by the central engine. Consistent with a naive expectation for such dust grains, the dust sublimation radius R_in is in fact empirically known to be scaling with L^1/2 from the near-IR reverberation measurements, and this is also supported by our near-IR interferometry. Utilizing this empirical relationship, we normalize the radial extent by R_in and eliminate the simple L^1/2 scaling for a direct comparison over the samples. We then find that, in the mid-IR, the overall size in units of R_in seems to become more compact in higher luminosity sources. More specifically, the mid-IR brightness distribution is rather well described by a power-law, and this power-law becomes steeper in higher luminosity objects. The near-IR flux does not seem to be a simple inward extrapolation of the mid-IR power-law component toward shorter wavelengths, but it rather comes from a little distinct brightness concentration at the inner rim region of the dust distribution. Its structure is not well constrained yet, but there is tentative evidence that this inner near-IR-emitting structure has a steeper radial distribution in jet-launching objects. All these should be scrutinized with further observations.
We have computed with a fine time grid the evolution of the elemental abundances of He, C, N and O ejected by a massive (M$=10^{6}$\,\Msun) coeval stellar cluster with a Salpeter initial mass function (IMF) over a range of initial abundances. Our computations incorporate the mass loss from massive stars (M >30 Msun) during their wind phase including the Wolf-Rayet phase plus the ejecta from the supernova events. We find that during the Wolf-Rayet phase (t <5 Myr) the cluster ejecta composition suddenly becomes vastly over-solar in He, C, N and O and for all initial abundances with the C and O abundance in the cluster ejecta reaching over 50 times the solar value.
In this paper we examine the effect of the formation and evolution of the disk galaxy on the distribution of dark halo matter. We have made simulations of isolated dark matter (DM) halo and two component (DM + baryons). N-body technique was used for stellar and DM particles and TVD MUSCL scheme for gas-dynamic simulations. The simulations include the processes of star formation, stellar feedback, heating and cooling of the interstellar medium. The results of numerical experiments with high spatial resolution let us to conclude in two main findings. First, accounting of star formation and supernova feedback resolves the so-called problem of cusp in distribution of dark matter predicted by cosmological simulations. Second, the interaction of dark matter with dynamic substructures of stellar and gaseous galactic disk (e.g., spiral waves, bar) has an impact on the shape of the dark halo. In particular, the in-plane distribution of dark matter is more symmetric in runs, where the baryonic component was taken into account.
Using stacks of Ly-a images of 2128 Ly-a emitters (LAEs) and 24 protocluster UV-selected galaxies (LBGs) at z=3.1, we examine the surface brightness profiles of Ly-a haloes around high-z galaxies as a function of environment and UV luminosity. We find that the slopes of the Ly-a radial profiles become flatter as the Mpc-scale LAE surface densities increase, but they are almost independent of the central UV luminosities. The characteristic exponential scale lengths of the Ly-a haloes appear to be proportional to the square of the LAE surface densities (r(Lya) \propto Sigma(LAE)^2). Including the diffuse, extended Ly-a haloes, the rest-frame Ly-a equivalent width of the LAEs in the densest regions approaches EW_0(Lya) ~ 200 A, the maximum value expected for young (< 10^7 yr) galaxies. This suggests that Ly-a photons formed via shock compression by gas outflows or cooling radiation by gravitational gas inflows may partly contribute to illuminate the Ly-a haloes; however, most of their Ly-a luminosity can be explained by photo-ionisation by ionising photons or scattering of Ly-a photons produced in HII regions in and around the central galaxies. Regardless of the source of Ly-a photons, if the Ly-a haloes trace the overall gaseous structure following the dark matter distributions, it is not surprising that the Ly-a spatial extents depend more strongly on the surrounding Mpc-scale environment than on the activities of the central galaxies.
We study the cosmological information contained in the Minkowski Functionals (MFs) of weak gravitational lensing convergence maps. We show that the MFs provide strong constraints on the local type primordial non-Gaussianity parameter f_NL. We run a set of cosmological N-body simulations and perform ray-tracing simulations of weak lensing, to generate 100 independent convergence maps of 25 deg^2 field-of-view for f_NL = -100, 0 and 100. We perform a Fisher analysis to study the degeneracy among other cosmological parameters such as the dark energy equation of state parameter w and the fluctuation amplitude sigma_8. We use fully nonlinear covariance matrices evaluated from 1000 ray-tracing simulations. For the upcoming wide-field observations such as Subaru Hyper Suprime-Cam survey with the proposed survey area of 1500 deg^2, the primordial non-Gaussianity can be constrained with a level of f_NL ~ 80 and w ~ 0.036 by weak lensing MFs. If simply scaled by the effective survey area, a 20000 deg^2 lensing survey using Large Synoptic Survey Telescope will give constraints of f_NL ~ 25 and w ~ 0.013. We show that these constraints can be further improved by a tomographic method using source galaxies in multiple redshift bins.
The small-scale CMB temperature we observe on the sky is modulated by perturbations that were super-horizon at recombination, giving differential focussing and lensing that generate a non-zero bispectrum even for single-field inflation where local physics is identical. Understanding this signal is important for primordial non-Gaussianity studies and also parameter constraints from the CMB lensing bispectrum signal. Because of cancellations individual effects can appear larger or smaller than they are in total, so a full analysis may be required to avoid biases. I relate angular scales on the sky to physical scales at recombination using the optical equations, and give full-sky results for the large-scale adiabatic temperature bispectrum from Ricci focussing (expansion of the ray bundle), Weyl lensing (convergence and shear), and temperature redshift modulations of small-scale power. The delta N expansion of the beam is described by the constant temperature 3-curvature, and gives a nearly-observable version of the consistency relation prediction from single-field inflation. I give approximate arguments to quantify the likely importance of dynamical effects, and argue that they can be neglected for modulation scales l <~ 100, which is sufficient for lensing studies and also allows robust tests of local primordial non-Gaussianity using only the large-scale modulation modes. For accurate numerical results early and late-time ISW effects must be accounted for, though I confirm that the late-time non-linear Rees-Sciama contribution is negligible compared to other more important complications. The total corresponds to f_NL ~ 7 for Planck-like temperature constraints and f_NL ~ 11 for cosmic-variance limited data to lmax=2000. Temperature lensing bispectrum estimates are affected at the 0.2 sigma level by Ricci focussing, and up to 0.5 sigma with polarization.
By actively distorting the Cosmic Microwave Background (CMB) over our past light cone, cosmic strings are unavoidable sources of non-Gaussianity. Developing optimal estimators able to disambiguate a string signal from the primordial type of non-Gaussianity requires calibration over synthetic full sky CMB maps, which till now had been numerically unachievable at the resolution of modern experiments. In this paper, we provide the first high resolution full sky CMB map of the temperature anisotropies induced by a network of cosmic strings since the recombination. The map has about 200 million sub-arcminute pixels in the healpix format which is the standard in use for CMB analyses (Nside=4096). This premiere required about 800,000 cpu hours; it has been generated by using a massively parallel ray tracing method piercing through a thousands of state of art Nambu-Goto cosmic string numerical simulations which pave the comoving volume between the observer and the last scattering surface. We explicitly show how this map corrects previous results derived in the flat sky approximation, while remaining completely compatible at the smallest scales.
We study the angular bispectrum of local type arising from the (possibly correlated) combination of a primordial adiabatic mode with an isocurvature one. Generically, this bispectrum can be decomposed into six elementary bispectra. We estimate how precisely CMB data, including polarization, can enable us to measure or constrain the six corresponding amplitudes, considering separately the four types of isocurvature modes (CDM, baryon, neutrino density, neutrino velocity). Finally, we discuss how the model-independent constraints on the bispectrum can be combined to get constraints on the parameters of multiple-field inflation models.
We investigate the influence of the initial proto-galaxies over-densities and masses on their evolution, to understand whether the internal properties of the proto-galactic haloes are sufficient to account for the varied properties of the galactic populations. By means of fully hydrodynamical N-body simulations performed with the code EvoL we produce twelve self-similar models of early-type galaxies of different initial masses and over-densities, following their evolution from z \geq 20 down to z \leq 1. The simulations include radiative cooling, star formation, stellar energy feedback, a reionizing photoheating background, and chemical enrichment of the ISM. We find a strong correlation between the initial properties of the proto-haloes and their star formation histories. Massive (10^13M\odot) haloes experience a single, intense burst of star formation (with rates \geq 10^3M\odot/yr) at early epochs, consistently with observations, with a less pronounced dependence on the initial over-density; intermediate mass (10^11M\odot) haloes histories strongly depend on their initial over-density, whereas small (10^9M\odot) haloes always have fragmented histories, resulting in multiple stellar populations, due to the "galactic breathing" phenomenon. The galaxy models have morphological, structural and photometric properties comparable to real galaxies, often closely matching the observed data; even though some disagreement is still there, likely a consequence of some numerical choices. We conclude that internal properties are essentially sufficient to explain many of the observed features of early type galaxies, particularly the complicated and different star formation histories shown by haloes of very different mass. In this picture, nature seems to play the dominant role, whereas nurture has a secondary importance.
From optical spectroscopy of X-ray sources observed as part of ChaMP, we present redshifts and classifications for a total of 1569 Chandra sources from our targeted spectroscopic follow up using the FLWO, SAAO, WIYN, CTIO, KPNO, Magellan, MMT and Gemini telescopes, and from archival SDSS spectroscopy. We classify the optical counterparts as 50% BLAGN, 16% NELG, 14% ALG, and 20% stars. We detect QSOs out to z~5.5 and galaxies out to z~3. We have compiled extensive photometry from X-ray to radio bands. Together with our spectroscopic information, this enables us to derive detailed SEDs for our extragalactic sources. We fit a variety of templates to determine bolometric luminosities, and to constrain AGN and starburst components where both are present. While ~58% of X-ray Seyferts require a starburst event to fit observed photometry only 26% of the X-ray QSO population appear to have some kind of star formation contribution. This is significantly lower than for the Seyferts, especially if we take into account torus contamination at z>1 where the majority of our X-ray QSOs lie. In addition, we observe a rapid drop of the percentage of starburst contribution as X-ray luminosity increases. This is consistent with the quenching of star formation by powerful QSOs, as predicted by the merger model, or with a time lag between the peak of star formation and QSO activity. We have tested the hypothesis that there should be a strong connection between X-ray obscuration and star-formation but we do not find any association between X-ray column density and star formation rate both in the general population or the star-forming X-ray Seyferts. Our large compilation also allows us to report here the identification of 81 XBONG, 78 z>3 X-ray sources and 8 Type-2 QSO candidates. Also we have identified the highest redshift (z=5.4135) X-ray selected QSO with optical spectroscopy.
We reconsider the strength of the electroweak phase transition (EWPT) in the inert doublet dark matter model, using a quantitatively accurate form for the one-loop finite temperature effective potential, taking into account relevant particle physics and dark matter constraints, focusing on a standard model Higgs mass near 126 GeV, and doing a full scan of the space of otherwise unconstrained couplings. We find that there is a significant (although fine-tuned) space of parameters for achieving an EWPT sufficiently strong for baryogenesis while satisfying the Xenon100 constraints from direct detection and obtaining the correct thermal relic density. We predict that the dark matter mass should be in the range 60-67 GeV, and we discuss possible LHC signatures of the charged and CP-odd Higgs bosons, including small suppression of the h -> 2 photon branching ratio.
We show that in imaginary time quantum metric fluctuations of empty space form a self-consistent De Sitter gravitational instanton that can be thought of as describing the tunneling from "nothing" into De Sitter space of real time (no cosmological constant or scalar fields are needed). The first time, this mechanism is activated to give birth to a flat inflationary Universe. The second time, it is turned on to complete cosmological evolution of the Universe after energy density of matter drops below the threshold (energy density of instantons). An accelerated expansion takes over after the scale factor exceeds this threshold, which marks the birth of dark energy at the redshift 1+z=1.44 and provides a possible solution to the "coincidence problem". The number of gravitons which tunneled into the Universe must be of the order of 10^122 to create the observational value of the Hubble constant. This number has nothing to do with vacuum energy, which is a possible solution to the "old cosmological constant problem". The emptying Universe should possibly complete its evolution by tunneling back to "nothing". After that, the entire scenario is repeated, and it can happen endlessly.
A critical challenge in measuring the power spectrum of 21cm emission from cosmic reionization is compensating for the frequency dependence of an interferometer's sampling pattern, which can cause smooth-spectrum foregrounds to appear unsmooth and degrade the separation between foregrounds and the target signal. In this paper, we present an approach to foreground removal that explicitly accounts for this frequency dependence. We apply the delay transformation introduced in Parsons & Backer (2009) to each baseline of an interferometer to concentrate smooth-spectrum foregrounds within the bounds of the maximum geometric delays physically realizable on that baseline. By focusing on delay-modes that correspond to image-domain regions beyond the horizon, we show that it is possible to avoid the bulk of smooth-spectrum foregrounds. We show that delay-modes that are uncorrupted by foregrounds also represent samples of the three-dimensional power spectrum, and can be used to constrain cosmic reionization. Because it uses only spectral smoothness to differentiate foregrounds from the targeted 21cm signature, this per-baseline analysis approach relies on spectrally- and spatially-smooth instrumental responses for foreground removal. For sufficient levels of instrumental smoothness relative to the brightness of interfering foregrounds, this technique substantially reduces the level of calibration previously thought necessary to detect 21cm reionization. As a result, this approach places fewer constraints on antenna configuration within an array, and in particular, facilitates the adoption of configurations that are optimized for power-spectrum sensitivity. Under these assumptions, we demonstrate the potential for the PAPER array to detect 21cm reionization at an amplitude of 10 mK^2 near k~0.2h Mpc^-1 with 128 dipoles in 7 months of observing.
We generalize the previously proposed running vacuum energy model by including a term proportional to \dot{H}, in addition to the existing H^2 term. We show that the added degree of freedom is very constrained if both low redshift and high redshift data are taken into account. Best-fit models are undistinguishable from LCDM at the present time, but could be distinguished in the future with very accurate data at both low and high redshifts. We stress the formal analogy at the phenomenological level of the running vacuum models with recently proposed dark energy models based on the holographic or entropic point of view, where a combination of \dot{H} and H^2 term is also present. However those particular entropic formulations which do not have a constant term in the Friedmann equations are not viable. The presence of this term is necessary in order to allow for a transition from a decelerated to an accelerated expansion. In contrast, the running vacuum models, both the original and the generalized one introduced here contain this constant term in a more natural way. Finally, important conceptual issues common to all these models are emphasized.
We review recent literature on the connection between quantum entanglement and cosmology, with an emphasis on the context of expanding universes. We discuss recent theoretical results reporting on the production of entanglement in quantum fields due to the expansion of the underlying spacetime. We explore how these results are affected by the statistics of the field (bosonic or fermionic), the type of expansion (de Sitter or asymptotically stationary), and the coupling to spacetime curvature (conformal or minimal). We then consider the extraction of entanglement from a quantum field by coupling to local detectors and how this procedure can be used to distinguish curvature from heating by their entanglement signature. We review the role played by quantum fluctuations in the early universe in nucleating the formation of galaxies and other cosmic structures through their conversion into classical density anisotropies during and after inflation. We report on current literature attempting to account for this transition in a rigorous way and discuss the importance of entanglement and decoherence in this process. We conclude with some prospects for further theoretical and experimental research in this area. These include extensions of current theoretical efforts, possible future observational pursuits, and experimental analogues that emulate these cosmic effects in a laboratory setting.
The BLLac object S4 0954+65 is one of the main targets of the Urumqi monitoring program for IntraDay Variable (IDV) sources. Between August 2005 and December 2009, the source was included in 41 observing sessions, carried out at a frequency of 4.8 GHz. The time analysis of the collected light curves, performed through both a structure function analysis and a specifically developed wavelet-based algorithm, disclosed the existence of an annual cycle in the variability timescales, suggesting a fundamental contribution of interstellar scintillation to the IDV pattern of the source. The combined use of the two analysis methods also revealed a dramatic change in the variability characteristics of the source between February and March 2008, at the starting time of a strong outburst phase. The analysis' results suggest that the flaring state of the source coincides with the appearance of multiple timescales in its light curves, indicating that changes in the structure of the relativistically moving emitting region may strongly influence the variability observed on IDV timescales.
We determine the neutrino spectra arising from low-mass (4-10 GeV) dark matter annihilating in the sun. We also determine the low-mass dark matter capture rates (element by element in the sun), assuming dark matter interacts either through elastic contact interactions, elastic long-range interactions, or inelastic contact interactions. These are the non-detector-specific data needed for determining the sensitivity of a neutrino detector to dark matter annihilating in the sun. As an application, we estimate the sensitivity of a one kiloton liquid scintillation neutrino detector (such as KamLAND) and LBNE (LAr-based) to low-mass dark matter with long-range interactions and compare this to the expected CDMS sensitivity. It is found that KamLAND's sensitivity can exceed that obtainable from the current CDMS data set by two orders of magnitude.
Weak-lensing shear estimates show a troublesome dependence on the apparent
brightness of the galaxies used to measure the ellipticity: In several studies,
the amplitude of the inferred shear falls sharply with decreasing source
significance. This dependence limits the overall ability of upcoming large
weak-lensing surveys to constrain cosmological parameters.
We seek to provide a concise overview of the impact of pixel noise on
weak-lensing measurements, covering the entire path from noisy images to shear
estimates. We show that there are at least three distinct layers, where pixel
noise not only obscures but biases the outcome of the measurements: 1) the
propagation of pixel noise to the non-linear observable ellipticity; 2) the
response of the shape-measurement methods to limited amount of information
extractable from noisy images; and 3) the reaction of shear estimation
statistics to the presence of noise and outliers in the measured ellipticities.
We identify and discuss several fundamental problems and show that each of
them is able to introduce biases in the range of a few tenths to a few percent
for galaxies with typical significance levels. Furthermore, all of these biases
do not only depend on the brightness of galaxies but also on their ellipticity,
with more elliptical galaxies often being harder to measure correctly. We also
discuss existing possibilities to mitigate and novel ideas to avoid the biases
induced by pixel noise. We present a new shear estimator that shows a more
robust performance for noisy ellipticity samples. Finally, we release the
open-source python code to predict and efficiently sample from the noisy
ellipticity distribution and the shear estimators used in this work at
https://github.com/pmelchior/epsnoise.
Links to: arXiv, form interface, find, astro-ph, recent, 1204, contact, help (Access key information)
Using spatially-resolved spectra obtained with the Low Resolution Imaging Spectrometer at the Keck I telescope, we investigate the nature of ionizing sources and kinematic properties of emission-line gas in a LINER galaxy SDSS J091628.05+420818.7, which is a nearby (z = 0.0241) and bright (M_r = -20.2) early-type galaxy. After subtracting stellar absorption features using a combination of simple stellar population models, we measure the flux, line-of-sight velocity, and velocity dispersion of four emission lines, i.e., H{\alpha}, H{\beta}, [O III] {\lambda}5007, and [N II] {\lambda}6584, to study radial change of emission-line fluxes and velocities. Compared to the point-spread-function of the observation, the emission-line region is slightly extended but comparable to the seeing size. The central concentration of emission-line gas suggests that ionization is triggered by a nuclear source, excluding old stellar population as ionizing sources. We find that emission-line gas is counter-rotating with respect to stellar component and that the [O III] {\lambda}5007 line is blueshifted compared to other emission lines, possibly due to an outflow.
We develop a method to extract the shape information of line profiles from discrete kinematic data. The Gauss-Hermite expansion, which is widely used to describe the line of sight velocity distributions extracted from absorption spectra of elliptical galaxies, is not readily applicable to samples of discrete stellar velocity measurements, accompanied by individual measurement errors and probabilities of membership. We introduce two parameter families of probability distributions describing symmetric and asymmetric distortions of the line profiles from Gaussianity. These are used as the basis of a maximum likelihood estimator to quantify the shape of the line profiles. Tests show that the method outperforms a Gauss-Hermite expansion for discrete data, with a lower limit for the relative gain of approx 2 for sample sizes N approx 800. To ensure that our methods can give reliable descriptions of the shape, we develop an efficient test to assess the statistical quality of the obtained fit. As an application, we turn our attention to the discrete velocity datasets of the dwarf spheroidals of the Milky Way. In Sculptor, the symmetric deviations are everywhere consistent with velocity distributions more peaked than Gaussian. This may suggest a radially biased orbital structure. In Fornax, there is an evolution in the symmetric deviations of the line profile from a peakier to more flat-topped distribution on moving outwards. This may be an indication of tangential anisotropy in the outer parts. Our methods are sensitive enough to detect evidence for velocity distributions more peaked than Gaussian in Carina and Sextans, which suggest radial anisotropy in the outer parts of these two galaxies. This is all consistent with a picture in which Fornax may have had a different evolutionary history to Sculptor, Carina and Sextans.
We have carefully selected a sample of 60 galaxies that reside in the deepest underdensities of geometrically identified voids within the SDSS. HI imaging of 55 galaxies with the WSRT reveals morphological and kinematic signatures of ongoing interactions and gas accretion. We probe a total volume of 485 Mpc^3 within the voids, with an angular resolution of 8 kpc at an average distance of 85 Mpc. We reach column density sensitivities of 5 x 10^19 cm^-2, corresponding to an HI mass limit of 3 x 10^8 M_sun. We detect HI in 41 galaxies, with total masses ranging from 1.7 x 10^8 to 5.5 x 10^9 M_sun. The upper limits on the 14 non-detections are not inconsistent with their luminosities, given their expected HI mass to light ratios. We find that the void galaxies are generally gas rich, low luminosity, blue disk galaxies, with optical and HI properties that are not unusual for their luminosity and morphology. The sample spans a range of absolute magnitudes (-16.1 > M_r > -20.4) and colors (0.06 < g-r < 0.87), and includes disk and irregular galaxies. We also identify three as early type galaxies, all of which are not detected in HI. All galaxies have stellar masses less than 3 x 10^10 M_sun, and many have kinematic and morphological signs of ongoing gas accretion, suggesting that the void galaxy population is still in the process of assembling. The small scale clustering in the void, within 600 kpc and 200 km/s, is similar to that in higher density regions, and we identify 18 HI rich neighboring galaxies in the voids. Most are within 100 kpc and 100 km/s of the targeted galaxy, and we find no significant population of HI rich low luminosity galaxies filling the voids, contrary to what is predicted by simulations.
We use the Marcario Low Resolution Spectrograph (LRS) at the
Hobby-Eberly-Telescope (HET) to study the kinematics of pseudobulges and
classical bulges in the nearby universe. We present major-axis rotational
velocities, velocity dispersions, and h3 and h4 moments derived from
high-resolution (sigma ~ 39 km/s) spectra for 45 S0 to Sc galaxies; for 27 of
the galaxies we also present minor axis data. We combine our kinematics with
bulge-to-disk decompositions. We demonstrate for the first time that purely
kinematic diagnostics of the bulge dichotomy agree systematically with those
based on S\'ersic index. Low S\'ersic index bulges have both increased
rotational support (higher v/sigma values) and on average lower central
velocity dispersions. Furthermore, we confirm that the same correlation also
holds when visual morphologies are used to diagnose bulge type. The previously
noted trend of photometrically flattened bulges to have shallower velocity
dispersion profiles turns to be significant and systematic if the S\'ersic
index is used to distinguish between pseudobulges and classical bulges. The
correlation between h3 and v/sigma observed in elliptical galaxies is also
observed in intermediate type galaxies, irrespective of bulge type. Finally, we
present evidence for formerly undetected counter rotation in the two systems
NGC 3945 and NGC 4736.
Based on observations obtained with the Hobby-Eberly Telescope, which is a
joint project of the University of Texas at Austin, the Pennsylvania State
University, Stanford University, Ludwig-Maximilians-Universit\"at M\"unchen,
and Georg-August-Universit\"at G\"ottingen.
We report hitherto unnoticed patterns in quasar light curves. We characterize segments of quasars' light curves with the slopes of the straight lines fit through them. These slopes appear to be directly related to the quasars' redshifts. Alternatively, using only global shifts in time and flux, we are able to find significant overlaps between the light curves of different pairs of quasars by fitting the ratio of their redshifts. We are then able to reliably determine the redshift of one quasar from another. This implies that one can use quasars as standard clocks, as we explicitly demonstrate by constructing two independent methods of finding the redshift of a quasar from its light curve.
We examine the rotation rates, sizes, and star formation (SF) efficiencies of a representative population of simulated disc galaxies extracted from the Galaxies-Intergalactic Medium Interaction Calculation (GIMIC) suite of cosmological hydrodynamic simulations. These simulations include efficient, but energetically feasible supernova feedback, but have not been tuned in any way to produce 'realistic' disc galaxies. Yet, they generate a large number of discs, without requiring extremely high resolution. Over the wide galaxy stellar mass range, 9.0 < log10[Mstar (Msun)] < 10.5, the simulations reproduce the observed Tully-Fisher relation, the rotation curves of disc galaxies in bins of stellar mass, the mass-size relation of disc galaxies, and the SF efficiencies of disc galaxies as inferred from stacked weak lensing and stacked satellite kinematics observations. At higher stellar masses, log10[Mstar (Msun)] > 10.6, the simulated galaxies are too concentrated and have too high SF efficiencies. We conjecture that this shortcoming reflects the neglect of feedback from accreting supermassive black holes in these simulations. We conclude that it is possible to generate a realistic and representative population of disc galaxies using standard numerical hydrodynamic techniques and a plausible implementation of the "subgrid" astrophysical processes thought to be relevant to galaxy formation.
Since globular clusters (GCs) are old, low-N systems their dynamics is widely believed to be fully dominated by collisional two-body processes, and their surface brightness profiles are fit by King models. However, for many GCs, especially those with HST-resolved central regions, and `extra-tidal' features, King models provide poor fits. We suggest that this is partly because collisionless dynamics is also important and contribute to shaping the cluster properties. We show using time-scale and length-scale arguments that except for the very centers of clusters, collisionless dynamics should be more important than collisional. We then fit 38 GCs analyzed by Noyola and Gebhardt (2006) with (collisional) King and (collisionless) DARKexp models over the full available radial range, and find that the latter provide a better fit to 29 GCs; for six of these the fit is at least ~5x better in term of rms. DARKexp models are theoretically derived maximum entropy equilibrium states of self-gravitating collisionless systems and have already been shown to fit the results of dark matter N-body simulations. (We do not attempt fits with ad hoc fitting functions.)
Correlations are investigated of the outflow strength of quasars, as measured by the blueshift and asymmetry index (BAI) of the CIV line (Wang et al. 2011), with intensities and ratios of broad emission lines, based on composite quasar spectra built from the Sloan Digital Sky Survey. We find that most of the line ratios of other ions to CIV prominently increases with BAI. These behaviors can be well understood in the context of increasing metallicity with BAI. The strength of dominant coolant, CIV line, decreases and weak collisionally excited lines increase with gas metallicity as a result of the competition between different line coolants. Using SiIV+OIV]/CIV as an indicator of gas metallicity, we present, for the first time, a strong correlation between the metallicitiy and the outflow strength of quasars over a wide range of 1.7 to 6.9 times solar abundance. Our result implies that the metallicity plays an important role in the formation of quasar outflows, likely via affecting outflow acceleration. This effect may have a profound impact on galaxy evolution via momentum feedback and chemical enrichment.
We study the formation of structure in the Universe assuming that dark matter can be described by a scalar field $\tilde{\Phi}$ with a potential $V(\Phi)=-\mathfrak{m}^{2}\tilde{\Phi}^{2}/2+\lambda\tilde{\Phi}^4/4$. We derive the evolution equations of the scalar field in the linear regime of perturbations. We investigate the symmetry breaking and possibly a phase transition of this scalar field in the early Universe. At low temperatures, the scalar perturbations have an oscillating growing mode and therefore, this kind of dark matter could lead to the formation of gravitational structures. In order to study the nonlinear regime, we use the spherical collapse model and show that, in the quadratic potential limit, this kind of dark matter can form virialized structures. The main difference with the traditional Cold Dark Matter paradigm is that the formation of structure in the scalar field model can occur at earlier times. Thus, if the dark matter is of scalar field nature we expect to have large galaxies at high redshifts.
Generalised Teleparallel gravity, also referred to as f(T) gravity, has been recently proposed as an extended theory of gravitation able to give rise to an accelerated expansion in a matter only universe. The cosmic speed up is driven by an effective torsion fluid whose equation of state depend on the f(T) function entering the modified gravity Lagrangian. We focus on two particular choices for f(T) which share the nice property to emulate a phantom divide crossing as suggested by some recent data. We check their viability contrasting the predicted background dynamics to the Hubble diagram as traced by both Type Ia Supernovae (SNeIa) and Gamma Ray Bursts (GRBs), the measurement of the rate expansion H(z), the Baryon Acoustic Oscillations (BAOs) at different redshifts, and the Cosmic Microwave Background Radiation (CMBR) distance priors. Both f(T) models turn out to be in very good agreement with this large dataset so that we also investigate whether it is possible to discriminate among them relying on the different growth factors.
We forecast the constraints on modified theories of gravity from the cosmic microwave background (CMB) anisotropies bispectrum that arises from correlations between lensing and the Integrated Sachs-Wolfe effect. In models of modified gravity the evolution of the metric potentials is generally altered and the contribution to the CMB bispectrum signal can differ significantly from the one expected in the standard cosmological model.We adopt a parametrised approach and focus on three different classes of models: Linder's growth index, Chameleon-type models and f(R) theories. We show that the constraints on the parameters of the models will significantly improve with future CMB bispectrum measurements.
Using a simple two-color selection based on $g$-, $z$-, and $K$-band photometry, we pick out 1609 star-forming galaxies (sgzKs) and 422 passively evolving galaxies (pgzKs) at z\sim2$ from a $K$-band-selected sample ($K_{\rm AB} < 22.0$) in an area of $\sim 0.44$ deg$^{2}$ of the All-wavelength Extended Groth Strip International Survey. The number counts of pgzKs\ in our sample turn over at $K_{\rm AB} \sim 21.0$, and both the number of faint and bright objects (including sgzKs\ and pgzKs) exceed the predictions of a recent semi-analytic model of galaxy formation, a more successful model is need to explain this diversity. We also find that the star formation rate (SFR) and specific SFR (sSFR) of sgzKs\ increases with redshift at all masses, implying that star-forming galaxies were much more active on average in the past. Moreover, the sSFR of massive galaxies is lower at all redshifts, suggesting that star formation contributes more to the mass growth of low-mass galaxies than to high-mass galaxies. From {\it Hubble Space Telescope} Wide Field Camera 3 near-infrared imaging data, we find that morphologies of $z\sim2$ galaxies not only have diffuse structures with lower $G$ and higher $M_{20}$ values, but also have single-object morphologies (higher $G$ and lower $M_{20}$), implying that there are morphological variety and different formation process for these galaxies at $z\sim2$. Finally, we also study the fraction of active galactic nuclei (AGNs) in the gzKs, 82 of 828 gzKs\ with four IRAC bands can be classified as AGNs ($\sim$ 10%). Most of these AGN candidates have $L_{\rm 0.5-10\ keV}>10^{41}\,\rm erg\,s^{-1}$.
A way to probe alternative theories of gravitation is to study if they could account for the structures of the universe. We then modified the well-known Gadget-2 code to probe alternative theories of gravitation through galactic dynamics. As an application, we simulate the evolution of spiral galaxies to probe alternative theories of gravitation whose weak field limits have a Yukawa-like gravitational potential. These simulations show that galactic dynamics can be used to constrain the parameters associated with alternative theories of gravitation. It is worth stressing that the recipe given in the present study can be applied to any other alternative theory of gravitation in which the superposition principle is valid.
We study brightness variations in the double lensed quasar UM673 (Q0142-100) with the aim of measuring the time delay between its two images. In the paper we combine our previously published observational data of UM673 obtained during the 2003 - 2005 seasons at the Maidanak Observatory with archival and recently observed Maidanak and CTIO UM673 data. We analyze the V, R and I-band light curves of the A and B images of UM673, which cover ten observational seasons from August 2001 to November 2010. We also analyze the time evolution of the difference in magnitudes between images A and B of UM673 over more than ten years. We find that the quasar exhibits both short-term (with amplitude of \sim 0.1 mag in the R band) and high-amplitude (\sim 0.3 mag) long-term variability on timescales of about several months and several years, respectively. These brightness variations are used to constrain the time delay between the images of UM673. From cross-correlation analysis of the A and B quasar light curves and error analysis we measure the mean time delay and its error of 89 \pm11 days. Given the input time delay of 88 days, the most probable value of the delay that can be recovered from light curves with the same statistical properties as the observed R-band light curves of UM673 is 95{+5/-16}{+14/-29} days (68 and 95 % confidence intervals). Analysis of the V - I color variations and V, R and I-band magnitude differences of the quasar images does not show clear evidence of the microlensing variations between 1998 and 2010.
We report a list of groups consisting of dwarf galaxies only. The sample contains 126 objects, mainly combined in pairs. The most populated group contains six dwarf galaxies. The majority of systems considered reside in the low-density regions and evolve unaffected by massive galaxies. The characteristic sizes and velocity dispersions of groups are 30 kpc and 11 km/s, respectively. They resemble the associations of dwarf galaxies, but are more compact. On the whole, groups and associations form a continuous sequence. Alike the associations, our groups possess high mass-to-luminosity ratios, what is indicative of a large amount of dark matter present in these systems.
Weakly Interactive Massive Particles are among the most motivated candidates invoked to solve the Dark Matter puzzle. The stability of Dark Matter (DM) typically results from a global protective symmetry. However, the presence of gravitational effects may cause its explicit breaking. We show that this provides a new source of signal for indirect DM searches as well as the embedding of a large class of decaying Dark Matter models into the WIMP paradigm.
It has been known for a long time that the satellite galaxies of the Milky Way (MW) show a significant amount of phase-space correlation, they are distributed in a highly inclined Disc of Satellites (DoS). We have extended the previous studies on the DoS by analysing for the first time the orientations of streams of stars and gas, and the distributions of globular clusters within the halo of the MW. It is shown that the spatial distribution of MW globular clusters classified as young halo clusters (YH GC) is very similar to the DoS, while 7 of the 14 analysed streams align with the DoS. The probability to find the observed clustering of streams is only 0.3 per cent when assuming isotropy. The MW thus is surrounded by a vast polar structure (VPOS) of subsystems (satellite galaxies, globular clusters and streams), spreading from Galactocentric distances as small as 10 kpc out to 250 kpc. These findings demonstrate that a near-isotropic infall of cosmological sub-structure components onto the MW is essentially ruled out because a large number of infalling objects would have had to be highly correlated, to a degree not natural for dark matter sub-structures. The majority of satellites, streams and YH GCs had to be formed as a correlated population. This is possible in tidal tails consisting of material expelled from interacting galaxies. We discuss the tidal scenario for the formation of the VPOS, including successes and possible challenges. The potential consequences of the MW satellites being tidal dwarf galaxies are severe. If all the satellite galaxies and YH GCs have been formed in an encounter between the young MW and another gas-rich galaxy about 10-11 Gyr ago, then the MW does not have any luminous dark-matter substructures and the missing satellites problem becomes a catastrophic failure of the standard cosmological model.
We carry out a time-series analysis of the combined data from three experiments measuring the cosmic muon flux at the Gran Sasso laboratory, at a depth of 3800 m.w.e. These data, taken by the MACRO, LVD and Borexino experiments, span a period of over 20 years, and correspond to muons with a threshold energy, at sea level, of around 1.3 TeV. We compare the best-fit period and phase of the full muon data set with the combined DAMA/NaI and DAMA/LIBRA data, which spans the same time period, as a test of the hypothesis that the cosmic ray muon flux is responsible for the annual modulation detected by DAMA. We find in the muon data a large-amplitude fluctuation with a period of around one year, and a phase that is incompatible with that of the DAMA modulation at 5.2 sigmas. Aside from this annual variation, the muon data also contains a further significant modulation with a period between 10 and 11 years and a power well above the 99.9% C.L threshold for noise, whose phase corresponds well with the solar cycle: a surprising observation for such high energy muons. We see no corresponding long-period oscillation in the stratospheric temperature data.
We study the first Kaluza-Klein excitation of the Higgs boson in universal extra dimensions as a dark matter candidate. The first-level Higgs boson could be the lightest Kaluza-Klein particle, which is stable due to the conservation of Kaluza-Klein parity, in non-minimal models where boundary localized terms modify the mass spectrum. We calculate the relic abundance and find that it agrees with the observed dark matter density if the mass of the first-level Higgs boson is about 2 TeV. We study also the prospects for detection of this dark matter candidate in direct as well as indirect detection experiments. Although the first-level Higgs boson is a typical weakly interacting massive particle, an observation in any of the conventional experiments is very challenging.
Planck scale physics may influence the evolution of cosmological fluctuations in the early stages of cosmological evolution. Because of the quasi-exponential redshifting, which occurs during an inflationary period, the physical wavelengths of comoving scales that correspond to the present large-scale structure of the Universe were smaller than the Planck length in the early stages of the inflationary period. This trans-Planckian effect was studied before using toy models. The Horava-Lifshitz (HL) theory offers the chance to study this problem in a candidate UV complete theory of gravity. In this paper we study the evolution of cosmological perturbations according to HL gravity assuming that matter gives rise to an inflationary background. As is usually done in inflationary cosmology, we assume that the fluctuations originate in their minimum energy state. In the trans-Planckian region the fluctuations obey a non-linear dispersion relation of Corley-Jacobson type. In the "healthy extension" of HL gravity there is an extra degree of freedom which plays an important role in the UV region but decouples in the IR, and which influences the cosmological perturbations. We find that in spite of these important changes compared to the usual description, the overall scale-invariance of the power spectrum of cosmological perturbations is recovered. However, we obtain oscillations in the spectrum as a function of wavenumber with a relative amplitude of order unity and with an effective frequency which scales nonlinearly with wavenumber. Taking the usual inflationary parameters we find that the frequency of the oscillations is so large as to render the effect difficult to observe.
We propose the cosmological model which allows to describe on equal footing the evolution of matter in the universe on the time interval from the inflation till the domination of dark energy. The matter is considered as a two-component perfect fluid imitated by homogeneous scalar fields between which there is energy exchange. Dark energy is represented by the cosmological constant, which is supposed invariable during the whole evolution of the universe. The matter changes its equation of state with time, so that the era of radiation domination in the early universe smoothly passes into the era of a pressureless gas, which then passes into the late-time epoch, when the matter is represented by a gas of low-velocity cosmic strings. The inflationary phase is described as an analytic continuation of the energy density in the very early universe into the region of small negative values of the parameter which characterizes typical time of energy transfer from one matter component to another. The Hubble expansion rate, energy density of the matter, energy density parameter, and deceleration parameter as functions of time are found.
Blue (metal-poor) globular clusters are observed to have half-light radii that are ~20% larger than their red (metal-rich) counterparts. The origin of this enhancement is not clear and differences in either the luminosity function or in the actual size of the clusters have been proposed. I analyze a set of dynamically self-consistent Monte Carlo globular cluster simulations to determine the origin of this enhancement. I find that my simulated blue clusters have larger half-light radii due to differences in the luminosity functions of metal-poor and metal-rich stars. I find that the blue clusters can also be physically larger, but only if they have a substantial number of black holes heating their central regions. In this case the difference between half-light radii is significantly larger than observed. I conclude that the observed difference in half-light radii between red and blue globular clusters is due to differences in their luminosity functions and that half-light radius is not a reliable proxy for cluster size.
This white paper addresses the hypothesis of light sterile neutrinos based on recent anomalies observed in neutrino experiments and the latest astrophysical data.
In this note I respond to Vilenkin's claim that there must have been a beginning.
We used the N-body code of Hernquist and Ostriker (1992) to build a dozen cuspy ({\gamma}\approx 1) triaxial models of stellar systems through dissipationless collapses of initially spherical distributions of 10^6 particles. We chose four sets of initial conditions that resulted in models morphologically resembling E2, E3, E4 and E5 galaxies, respectively. Within each set, three different seed numbers were selected for the random number generator used to create the initial conditions, so that the three models of each set are statistically equivalent. We checked the stability of our models using the values of their central densities and of their moments of inertia, which turned out to be very constant indeed. The changes of those values were all less than 3 per cent over one Hubble time and, moreover, we show that the most likely cause of those changes are relaxation effects in the numerical code. We computed the six Lyapunov exponents of nearly 5,000 orbits in each model in order to recognize regular, partially and fully chaotic orbits. All the models turned out to be highly chaotic, with less than 25 per cent of their orbits being regular. We conclude that it is quite possible to obtain cuspy triaxial stellar models that contain large fractions of chaotic orbits and are highly stable. The difficulty to build such models with the method of Schwarzschild (1979) should be attributed to the method itself and not to physical causes.
While the finite-temperature effective potential in a gauge theory is a gauge-dependent quantity, in several instances a first-order phase transition can be triggered by gauge-independent terms. A particularly interesting case occurs when the potential barrier separating the broken and symmetric vacua of a spontaneously broken symmetry is produced by tree-level terms in the potential. Here, we study this scenario in a simple Abelian Higgs model, for which the gauge-invariant potential is known, augmented with a singlet real scalar. We analyze the possible symmetry breaking patterns in the model, and illustrate in which cases gauge artifacts are expected to manifest themselves most severely. We then show that gauge artifacts can be pronounced even in the presence of a relatively large, tree-level singlet-Higgs cubic interaction. When the transition is strongly first order, these artifacts, while present, are more subtle than in the generic situation.
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We present new detections of the CO(5-4), CO(7-6), [CI](1-0) and [CI](2-1) molecular and atomic line transitions towards the unlensed, obscured quasar AMS12 (z=2.7672), observed with the IRAM PdBI. This is the first unlensed, high redshift source to have both [CI] transitions detected. Continuum measurements between 70 $\mu$m and 3 mm are used to constrain the FIR SED, and we find a best fit FIR luminosity of log[Lfir/Lsol] = 13.5+/-0.1, dust temperature T_d = 88+/-8 K and emissivity index {\beta} = 0.6+/-0.1. The highly-excited molecular gas probed by CO(3-2), (5-4) and (7-6), is modelled with large velocity gradient (LVG) models. The gas kinetic temperature T_g, density n(H2), and the characteristic size r0, are determined using the dust temperature from the FIR SED as a prior for the gas temperature. The best fitting parameters are T_g = 90+/-8 K, n(H2) = 10^(3.9+/-0.1) cm^(-3) and r0 = 0.8+/-0.04 kpc. The ratio of the [CI] lines gives a [CI] excitation temperature of 43+/-10 K, indicating the [CI] and the high-excitation CO are not in thermal equilibrium. The [CI] excitation temperature is below that of T_d and T_g of the high-excitation CO, perhaps because [CI] lies at a larger radius where there may also be a large reservoir of CO at a cooler temperature, perhaps detectable through the CO(1-0). Using the [CI](1-0) line we can estimate the strength of the CO(1-0) line and hence the gas mass. This suggests that a significant fraction (~30%) of the molecular gas is missed from the high-excitation line analysis. The Eddington limited black hole mass is found from the bolometric luminosity to be Mbh >~ 1.5x10^9 Msol. Along with the stellar mass of 3x10^11 Msol, these give a black hole - bulge mass ratio of Mbh/Mbulge >~ 0.005. This is in agreement with studies on the evolution of the Mbh/Mbulge relationship at high redshifts, which find a departure from the local value ~0.002.
In this mini-review we discuss first why we should investigate cosmological models beyond LCDM. We then show how to describe dark energy or modified gravity models in a fluid language with the help of one background and two perturbation quantities. We review a range of dark energy models and study how they fit into the phenomenological framework, including generalizations like phantom crossing, sound speeds different from c and non-zero anisotropic stress, and how these effective quantities are linked to the underlying physical models. We also discuss the limits of what can be measured with cosmological data, and some challenges for the framework.
We review the different frameworks in which Galileon scalar fields have been seen to emerge such an in DGP, New Massive Gravity and Ghost-free massive Gravity and emphasize their relation with the Lovelock invariant in braneworld models. The existence of a non-renormalization theorem for Galileon scalar fields makes them especially attractive candidates for inflation as well as for late-time acceleration. In particular we review the self-accelerating and degravitating branches of solutions present in Galileon models when arising from Massive Gravity and discuss their phenomenology.
The discovery of cosmic acceleration is one of the most important developments in modern cosmology. The observation, thirteen years ago, that type Ia supernovae appear dimmer that they would have been in a decelerating universe followed by a series of independent observations involving galaxies and cluster of galaxies as well as the cosmic microwave background, all point in the same direction: we seem to be living in a flat universe whose expansion is currently undergoing an acceleration phase. In this paper, we review the various observational evidences, most of them gathered in the last decade, and the improvements expected from projects currently collecting data or in preparation.
Assuming the universe is spatially homogeneous on the largest scales lays the foundation for almost all cosmology. This idea is based on the Copernican principle, that we are not at a particularly special place in the universe. Surprisingly, this philosophical assumption has yet to be rigorously demonstrated independently of the standard paradigm. This issue has been brought to light by cosmological models which can potentially explain apparent acceleration by spatial inhomogeneity rather than dark energy. These models replace the temporal fine tuning associated with Lambda with a spatial fine tuning, and so violate the Copernican assumption. While is seems unlikely that such models can really give a realistic solution to the dark energy problem, they do reveal how poorly constrained radial inhomogeneity actually is. So the bigger issue remains: How do we robustly test the Copernican principle independently of dark energy or theory of gravity?
We present for the first time metallicity maps generated using data from the Wide Field Spectrograph (WiFeS) on the ANU 2.3m of 9 Luminous Infrared Galaxies (LIRGs) and discuss the abundance gradients and distribution of metals in these systems. We have carried out optical integral field spectroscopy (IFS) of several several LIRGs in various merger phases to investigate the merger process. In a major merger of two spiral galaxies with preexisting disk abundance gradients, the changing distribution of metals can be used as a tracer of gas flows in the merging system as low metallicity gas is transported from the outskirts of each galaxy to their nuclei. We employ this fact to probe merger properties by using the emission lines in our IFS data to calculate the gas-phase metallicity in each system. We create abundance maps and subsequently derive a metallicity gradient from each map. We compare our measured gradients to merger stage as well as several possible tracers of merger progress and observed nuclear abundances. We discuss our work in the context of previous abundance gradient observations and compare our results to new galaxy merger models which trace metallicity gradient. Our results agree with the observed flattening of metallicity gradients as a merger progresses. We compare our results with new theoretical predictions that include chemical enrichment. Our data show remarkable agreement with these simulations.
A modified Chaplygin gas model (MCG), $\rho_{MCG}/\rho_{MCG0}=[B_{s}+(1-B_{s})a^{-3(1+B)(1+\alpha)}]^{1/(1+\alpha)}$, as a unified dark matter model and dark energy model is constrained by using current available cosmic observational data points which include type Ia supernovae, baryon acoustic oscillation and the seventh year full WMAP data points. As a contrast to the consideration in the literatures, we {\it do not} separate the MCG into two components, i.e. dark mater and dark energy component, but we take it as a whole energy component-a unified dark sector. By using Markov Chain Monte Carlo method, a tight constraint is obtained: $\alpha= 0.000727_{- 0.00140- 0.00234}^{+ 0.00142+ 0.00391}$, $B=0.000777_{- 0.000302- 0.000697}^{+ 0.000201+ 0.000915}$ and $B_s= 0.782_{- 0.0162- 0.0329}^{+ 0.0163+ 0.0307}$ .}
We present an analytic model for the local bias of dark matter halos in a LCDM universe. The model uses the halo mass density instead of the halo number density and is searched for various halo mass cuts, smoothing lengths, and redshift epoches. We find that, when the logarithmic density is used, the second-order polynomial can fit the numerical relation between the halo mass distribution and the underlying matter distribution extremely well. In this model the logarithm of the dark matter density is expanded in terms of log halo mass density to the second order. The model remains excellent for all halo mass cuts (from M_{cut}=3\times10^{11}$ to $3\times10^{12}h^{-1}M_{\odot}$), smoothing scales (from $R=5h^{-1}$Mpc to $50h^{-1}$Mpc), and redshift ranges (from z=0 to 1.0) considered in this study. The stochastic term in the relation is found not entirely random, but a part of the term can be determined by the magnitude of the shear tensor.
Deep, near-infrared JHK-maps were observed for 10 nearby, grand-design,
spiral galaxies using HAWK-I/VLT to study the distribution of young stellar
clusters in them and thereby determine whether strong spiral perturbations can
influence star formation. Complete, magnitude-limited candidate lists of
star-forming complexes were obtained by searching within the K-band maps. The
properties of the complexes were derived from (H-K)-(J-H) diagrams including
the identification of the youngest complexes (i.e. <7 Myr) and the estimation
of their extinction.
Young stellar clusters with ages <7 Myr have significant internal extinction
in the range of Av=3-7m, while older ones typically have Av<1m. The cluster
luminosity function (CLF) is well-fitted by a power law with an exponent of
around -2 and displays no evidence of a high luminosity cut-off. The brightest
cluster complexes in the disk reach luminosities of Mk = -15.5m or estimated
masses of 10^6 Mo. At radii with a strong, two-armed spiral pattern, the star
formation rate in the arms is higher by a factor of 2-5 than in the inter-arm
regions. The CLF in the arms is also shifted towards brighter Mk by at least
0.4m. We also detect clusters with colors compatible with Large Magellanic
Cloud intermediate age clusters and Milky Way globular clusters. The (J-K)-Mk
diagram of several galaxies shows, for the brightest clusters, a clear
separation between young clusters that are highly attenuated by dust and older
ones with low extinction.
The gap in the (J-K)-Mk diagrams implies that there has been a rapid
expulsion of dust at an age around 7 Myr, possibly triggered by supernovae.
Strong spiral perturbations concentrate the formation of clusters in the arm
regions and shifts their CLF towards brighter magnitudes.
We report on sensitive observations of the CO(7-6) and CI(2-1) transitions in the z=2.79 QSO host galaxy RXJ0911.4+0551 using the IRAM Plateau de Bure interferometer (PdBI). Our extremely high signal to noise spectra combined with the narrow CO line width of this source (FWHM = 120 km/s) allows us to estimate sensitive limits on the space-time variations of the fundamental constants using two emission lines. Our observations show that the CI and CO line shapes are in good agreement with each other but that the CI line profile is of order 10% narrower, presumably due to the lower opacity in the latter line. Both lines show faint wings with velocities up to +/-250 km/s, indicative of a molecular outflow. As such the data provide direct evidence for negative feedback in the molecular gas phase at high redshift. Our observations allow us to determine the observed frequencies of both transitions with so far unmatched accuracy at high redshift. The redshift difference between the CO and CI lines is sensitive to variations of dF/F with F=alpha^2/mu where alpha is the fine structure constant and mu the proton-to-electron mass ratio. We find dF/F=6.9 +/-3.7 x 10^-6 at a lookback time of 11.3 Gyr, which within the uncertainties, is consistent with no variations of the fundamental constants.
Observations of neutral hydrogen in spiral galaxies reveal a sharp cutoff in the radial density profile at some distance from the center. Using 22 galaxies with known HI distributions as an example, we discuss the question of whether this effect can be associated exclusively with external ionizing radiation, as is commonly assumed. We show that before the surface density reaches $\sigma_{\textrm{HI}}\le 0.5 {\cal M}_\odot/{\textrm {pc}}^2$(the same for galaxies of different types), it is hard to expect the gas to be fully ionized by background radiation. For two of 13 galaxies with a sharp drop in the HI profile, the "steepening" can actually be caused by ionization. At the same time, for the remaining galaxies, the observed cutoff in the radial HI profile is closer to the center than if it was a consequence of ionization by background radiation and, therefore, it should be caused by other factors.
This is a very informal report that gives further details on the evidence for a bubble universe based on an anomaly in the angular distribution of quasar magnitudes that was presented in a short paper in arXiv:1202.4433. This report addresses some concerns of two reviewers. It is meant to be read in conjunction with 1202.4433. There is very little overlap between the two articles. This extended discussion is, by necessity, somewhat more technical in nature. I am grateful for the reviewers' comments that forced me to understand these issues more thoroughly.
We present a novel approach to modified theories of gravity that consists of adding to the Einstein-Hilbert Lagrangian an f(R) term constructed a la Palatini. Using the respective dynamically equivalent scalar-tensor representation, we show that the theory can pass the Solar System observational constraints even if the scalar field is very light. This implies the existence of a long-range scalar field, which is able to modify the cosmological and galactic dynamics, but leaves the Solar System unaffected. We also verify the absence of instabilities in perturbations and provide explicit models which are consistent with local tests and lead to the late-time cosmic acceleration.
Chameleon fields, which are scalar field dark energy candidates, can evade fifth force constraints by becoming massive in high-density regions. However, this property allows chameleon particles to be trapped inside a vacuum chamber with dense walls. Afterglow experiments constrain photon-coupled chameleon fields by attempting to produce and trap chameleon particles inside such a vacuum chamber, from which they will emit an afterglow as they regenerate photons. Here we discuss several theoretical and systematic effects underlying the design and analysis of the GammeV and CHASE afterglow experiments. We consider chameleon particle interactions with photons, Fermions, and other chameleon particles, as well as with macroscopic magnetic fields and matter. The afterglow signal in each experiment is predicted, and its sensitivity to various properties of the experimental apparatus is studied. Finally, we use CHASE data to exclude a wide range of photon-coupled chameleon dark energy models.
Axino, related to the SUSY transformation of axion, can mix with goldstino in principle. This case is realized when some superfields carrying nonvanishing Peccei-Quinn charges develop both scalar VEVs and F-terms. In this case, we present a proper definition of axion and axino. With this definition, we present the QCD axino mass in the most general framework, including non-minimal K\"ahler potential. The axino mass is known to have a hierarchical mass structure depending on accidental symmetries. If $G_A=0$ where $G=K+M_P^2\ln|W|^2$, we obtain $m_{\tilde a}=(1+ \epsilon^2)m_{3/2}$ with the axino-gravitino mixing parameter $\epsilon$ in the K\"ahler potential. For $G_A\ne 0$, the axino mass depends on the details of the K\"ahler potential. In the gauge mediation scenario, the gaugino mass is the dominant axino mass parameter. Therefore, we can take the theoretical QCD axino mass as a free parameter in the study of its cosmological effects, ranging from eV to multi-TeV scales, without a present knowledge on its ultraviolet completion.
Quantum and thermal fluctuations of an irrotational fluid are studied across the transition regime connecting a protoinflationary phase of decelerated expansion to an accelerated epoch driven by a single inflaton field. The protoinflationary inhomogeneities are suppressed when the transition to the slow roll phase occurs sharply over space-like hypersurfaces of constant energy density. If the transition is delayed, the interaction of the quasi-normal modes related, asymptotically, to fluid phonons and inflaton quanta leads to an enhancement of curvature perturbations. It is shown that the dynamics of the fluctuations across the protoinflationary boundaries is determined by the monotonicity properties of the pump fields controlling the energy transfer between the background geometry and the quasi-normal modes of the fluctuations. After corroborating the analytical arguments with explicit numerical examples, general lessons are drawn on the classification of the protoinflationary transition.
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Theoretical studies of structure formation find an inverse proportionality between the concentration of dark matter haloes and virial mass. This trend has been recently confirmed for virial masses Mvir > ~6e12 Msun by the observation of the X-ray emission from the hot halo gas. We present an alternative approach to this problem, exploring the concentration of dark matter haloes over galaxy scales on a sample of 18 early-type systems. Our c-Mvir relation is consistent with the X-ray analysis, extending towards lower virial masses, covering the range from ~4e11 Msun up to 5e12 Msun. A combination of the lensing analysis along with photometric data allows us to constrain the baryon fraction within a few effective radii, which is compared with prescriptions for adiabatic contraction (AC) of the dark matter haloes. We find that the standard methods for AC are strongly disfavored, requiring additional mechanisms -- such as mass loss during the contraction process -- to play a role during the phases following the collapse of the haloes.
A deep narrow-band survey for Ly-alpha emission carried out on the VLT-FORS2 has revealed 98 Ly-alpha candidates down to a flux limit of 4.e-18 erg/s/cm^2 in a volume of 5500 comoving Mpc^3 at z=2.4 centered on the hyperluminous quasar HE0109-3518. The properties of the detected sources in terms of their i) equivalent width distribution, ii) luminosity function, and iii) the average luminosity versus projected distance from the quasar, all suggest that a large fraction of these objects have been fluorescently "illuminated" by HE0109-3518. This conclusion is supported by comparison with detailed radiative transfer simulations of the effects of the quasar illumination. 18 objects have a rest-frame Equivalent Width (EW0) larger than 240A, the expected limit for Ly-alpha emission powered by Population II star formation and 12 sources among these do not have any continuum counterpart in a deep V-band imaging of the same field. For these, a stacking analysis indicates EW0>800A, effectively ruling out Ly-alpha powered by internal star formation. These sources are thus the best candidates so far for proto-galactic clouds or "dark" galaxies at high-redshift, whose existence has recently been suggested by several theoretical studies. Assuming they are mostly ionized by the quasar radiation, we estimate that their gas masses would be about 10^9 Msun implying that their star formation efficiencies (SFE) are less than 4.e-12 yr^-1 one order of magnitude below the SFE of the most gas-rich dwarf galaxies locally, and five hundred times lower than typical massive star-forming galaxies at z~2. We have also discovered extended, filamentary gas, also likely illuminated by the quasar, around some of the brightest continuum-detected sources with EW0>240A. This emission is compatible with the expectations for circum-galactic cold streams but other origins, including tidal stripping, are also possible.
We investigate where brightest cluster galaxies (BCGs) sit on the fundamental plane of black hole (BH) activity, an established relation between the X-ray luminosity, the radio luminosity and the mass of a BH. Our sample mostly consists of BCGs that lie at the centres of massive, strong cooling flow clusters, therefore requiring extreme mechanical feedback from their central active galactic nucleus (AGN) to offset cooling of the intracluster plasma (L_mech>10^44-45 erg/s). Based on the BH masses derived from the M_BH-sigma and M_BH-M_K correlations, we find that all of our objects are offset from the plane such that they appear to be less massive than predicted from their X-ray and radio luminosities (to more than a 99 per cent confidence level). For these objects to be consistent with the fundamental plane, the M_BH-sigma and M_BH-M_K correlations therefore seem to underestimate the BH masses of BCGs, on average by a factor of 10. Our results suggest that the standard relationships between BH mass and host galaxy properties no longer hold for these extreme galaxies. Furthermore, our results imply that if these BHs follow the fundamental plane, then many of those that lie in massive, strong cool core clusters must be ultramassive with M_BH>10^10M_sun. This exceeds the largest BH masses known and has important ramifications for our understanding of the formation and evolution of BHs.
The Alcock-Paczynski (AP) effect uses the fact that, when analyzed with the correct geometry, we should observe structure that is statistically isotropic in the Universe. For structure undergoing cosmological expansion with the background, this constrains the product of the Hubble parameter and the angular diameter distance. However, the expansion of the Universe is inhomogeneous and local curvature depends on density. We argue that this distorts the AP effect on small scales. After analyzing the dynamics of galaxy pairs in the Millennium simulation, we find an interplay between peculiar velocities, galaxy properties and local density that affects how pairs trace cosmological expansion. We find that only low mass, isolated galaxy pairs trace the average expansion with a minimum "correction" for peculiar velocities. Other pairs require larger, more cosmology and redshift dependent peculiar velocity corrections and, in the small-separation limit of being bound in a collapsed system, do not carry cosmological information.
We develop a new test of local bias, by constructing a locally biased halo density field from sampling the dark matter-halo distribution. Our test differs from conventional tests in that it preserves the full scatter in the bias relation and it does not rely on perturbation theory. We put forward that bias parameters obtained using a smoothing scale R can only be applied to computing the halo power spectrum at scales k ~ 1/R. Our calculations can automatically include the running of bias parameters and give vanishingly small loop corrections at low-k. Our proposal results in much better agreement of the sampling and perturbation theory results with the original simulations. In particular, unlike the standard interpretation of local bias in the literature, our treatment of local bias does not generate a constant power at very large scales, in agreement with our measurements in the simulations of the halo power spectrum at wavenumbers below its turn-over. Using perturbation theory and our non-perturbative sampling technique we also demonstrate that nonlocal bias effects discovered recently in simulations impact the power spectrum only at the few percent level in the weakly nonlinear regime.
We have searched for [OIII] 5007 emission in high resolution spectroscopic data from Flames/Giraffe VLT observations of 174 massive globular clusters (GCs) in NGC4472. No planetary nebulae (PNe) are observed in these clusters, constraining the number of PNe per bolometric luminosity, \alpha<0.8*10^{-7}PN/L_{\odot}. This is significantly lower than the rate predicted from stellar evolution, if all stars produce PNe. Comparing our results to populations of PNe in galaxies, we find most galaxies have a higher \alpha than these GCs (more PNe per bolometric luminosity - though some massive early-type galaxies do have similarly low \alpha). The low \alpha required in these GCs suggests that the number of PNe per bolometric luminosity does not increase strongly with decreasing mass or metallicity of the stellar population. We find no evidence for correlations between the presence of known GC PNe and either the presence of low mass X-ray binaries (LMXBs) or the stellar interaction rates in the GCs. This, and the low \alpha observed, suggests that the formation of PNe may not be enhanced in tight binary systems. These data do identify one [OIII] emission feature, this is the (previously published) broad [OIII] emission from the cluster RZ 2109. This emission is thought to originate from the LMXB in this cluster, which is accreting at super-Eddington rates. The absence of any similar [OIII] emission from the other clusters favors the hypothesis that this source is a black hole LMXB, rather than a neutron star LMXB with significant geometric beaming of its X-ray emission.
Recent cosmological data favour additional relativistic degrees of freedom beyond the three active neutrinos and photons, often referred to as 'dark' radiation. Light sterile neutrinos is one of the prime candidates for such additional radiation. However, constraints on sterile neutrinos based on the current cosmological data have been derived using simplified assumptions about thermalisation of the sterile neutrino at the Big Bang Nucleosynthesis (BBN) epoch. These assumptions are not necessarily justified and here we solve the full quantum kinetic equations in the (1 active + 1 sterile) scenario and derive the number of thermalised species just before BBN begins (T~1MeV) for null (L=0) and large (L=0.01) initial lepton asymmetry and for a range of possible mass-mixing parameters. We find that the full thermalisation assumption during the BBN epoch is justified for initial small lepton asymmetry only. Partial or null thermalisation occurs when the initial lepton asymmetry is large.
Massive AGN-driven outflows are invoked by AGN-galaxy co-evolutionary models to suppress both star formation and black hole accretion. Massive molecular outflows have recently been revealed in some AGN hosts. However, the physical properties and structure of these AGN-driven molecular outflows are still poorly constrained. Here we present new IRAM PdBI observations of Mrk231, the closest quasar known, targeting both the CO(1-0) and CO(2-1) transitions. We detect broad wings in both transitions, tracing a massive molecular outflow with velocities up to 800 km/s. The wings are spatially resolved at high significance level (5-11 sigma), indicating that the molecular outflow extends on the kpc scale. The CO(2-1)/CO(1-0) ratio of the red broad wings is consistent with the ratio observed in the narrow core, while the blue broad wing is less excited than the core. The latter result suggests that quasar driven outflow models invoking shocks (which would predict higher gas excitation) are not appropriate to describe the bulk of the outflow in Mrk231. However, we note that within the central 700 pc the CO(2-1)/CO(1-0) ratio of the red wing is slightly, but significantly, higher than in the line core, suggesting that shocks may play a role in the central region. We also find that the average size of the outflow anticorrelates with the critical density of the transition used as a wind tracer. This indicates that, although diffuse and dense clumps coexist in the outflowing gas, dense outflowing clouds have shorter lifetime and that they evaporate into the diffuse component along the outflow or, more simply, that diffuse clouds are more efficiently accelerated to larger distances by radiation pressure.
The observation that old, massive galaxies have a larger fraction of low-mass stars than their younger, lower-mass counterparts adds to mounting evidence that star formation may have been different in the early Universe.
Any non-gravitational coupling between dark matter and dark energy modifies the cosmological dynamics. Interactions in the dark sector are considered to be relevant to address the coincidence problem. Moreover, in various models the observed accelerated expansion of the Universe is a pure interaction phenomenon. Here we review recent approaches in which a coupling between both dark components is crucial for the evolution of the Universe.
We show how the correlation between the thermal Sunyaev Zel'dovich effect (tSZ) from galaxy clusters and dust emission from cosmic infrared background (CIB) sources can be calculated in a halo model framework. Using recent tSZ and CIB models, we find that the size of the tSZ x CIB cross-correlation is approximately 10 per cent at 150 GHz. The contribution to the total angular power spectrum is of order -1 \mu K^2 at ell=3000, however, this value is uncertain by a factor of two to three, primarily because of CIB source modelling uncertainties. We expect the large uncertainty in this component to degrade upper limits on the kinematic Sunyaev Zel'dovich effect (kSZ), due to similarity in the frequency dependence of the tSZ x CIB and kSZ across the frequency range probed by current Cosmic Microwave Background missions. We also find that the degree of tSZ x CIB correlation is higher for mm x sub-mm spectra than mm x mm, because more of the sub-mm CIB originates at lower redshifts (z<2), where most tSZ clusters are found.
Cold fronts in cluster cool cores should be erased on short timescales by thermal conduction, unless protected by magnetic fields that are "draped" parallel to the front surfaces, suppressing conduction perpendicular to the fronts. We present MHD simulations of cold front formation in the core of a galaxy cluster with anisotropic thermal conduction, exploring a parameter space of conduction strengths parallel and perpendicular to the field lines. Including conduction has a strong effect on the temperature of the core and the cold fronts. Though magnetic field lines are draping parallel to the front surfaces, the temperature jumps across the fronts are nevertheless reduced. The field geometry is such that the cold gas below the front surfaces can be connected to hotter regions outside via field lines along directions perpendicular to the plane of the sloshing motions and along sections of the front which are not perfectly draped. This results in the heating of this gas below the front on a timescale of a Gyr, but the sharpness of the density and temperature jumps may still be preserved. By modifying the density distribution below the front, conduction may indirectly aid in suppressing Kelvin-Helmholtz instabilities. If conduction along the field lines is unsuppressed, we find that the characteristic sharp jumps in X-ray emission seen in observations of clusters do not form. This suggests that the presence of sharp cold fronts in hot clusters could be used to place upper limits on conduction in the {\it bulk} of the ICM. Finally, the combination of sloshing and anisotropic thermal conduction can result in a larger flux of heat to the core than either process in isolation. While still not sufficient to prevent a cooling catastrophe in the very central ($r \sim$ 5 kpc) regions of the cool core, it reduces significantly the mass of cool gas that accumulates outside those radii.
Based on the probability distributions of products of random variables, we propose a simple stringy mechanism that prefers the meta-stable vacua with a small cosmological constant. We state some relevant properties of the probability distributions of functions of random variables. We then illustrate the mechanism within the flux compactification models in Type IIB string theory. As a result of the stringy dynamics, we argue that the generic probability distribution for the meta-stable vacua typically peaks with a divergent behavior at the zero value of the cosmological constant. However, its suppression in the single modulus model studied here is modest.
A search for emission lines in foreground galaxies in quasar spectra (z(gal) < z(QSO)) of the Sloan Digital Sky Survey (SDSS) data release 5 (DR5) reveals 23 examples of quasars shining through low redshift, foreground galaxies at small impact parameters (< 10 kpc). About 74,000 quasar spectra were examined by searching for narrow H{\alpha} emission lines at z < 0.38, at a flux level greater than 5 \times 10^-17 ergs cm^-2 s^-1, then confirming that other expected emission lines of the H II regions in the galaxy are detected. The galaxies were deblended from the quasar images to get colors and morphologies. For cases that allow the galaxy and the quasar to be deblended, the galaxies are blue (0.95 <(u-r)< 1.95). Extinction and reddening through the galaxies is determined from the (g-i) color excesses of the quasars. These reddening values are compared with the flux ratio of H{\alpha} to H{\beta}, which reflect the extinction for an undetermined fraction of the sightline through each galaxy. No trends were found relating E(B-V)_(g-i), impact parameter (b), and (u-r) for the galaxies or between E(B-V) derived from (g-i) and that derived from H{\alpha}/H{\beta}. Comparison with previous studies of quasar absorption systems indicate our sample is more reddened, suggesting disk-dominated absorber galaxies. Measurement or limits on galactic, interstellar Ca II and Na I absorption lines are given from the quasar spectrum. No trends were found relating Ca II equivalent width (W (Ca II)) or Na I equivalent width (W (Na I)) to b, but a correlation of r_s = -0.77 ({\alpha} = 0.05) was found relating W (Ca II) and E(B-V)(g-i) .
We introduce an effective one-fluid description of the interacting dark sector in a spatially flat Friedmann-Robertson-Walker space-time and investigate the stability of the power-law solutions. We find the "source equation" for the total energy density and determine the energy density of each dark component. We study linear and nonlinear interactions which depend on the dark matter and dark energy densities, their first derivatives, the total energy density with its derivatives up to second order and the scale factor. We solve the evolution equations of the dark components for both interactions, examine exhaustively several examples and show cases where the problem of the coincidence is alleviated. We show that a generic nonlinear interaction gives rise to the "relaxed Chaplygin gas model" whose effective equation of state includes the variable modified Chaplygin gas model while some others nonlinear interactions yield de Sitter and power-law scenarios.
We expose a new symmetry for linear perturbations around a solution of non-linear Fierz-Pauli massive gravity plus a bare cosmological constant. The cosmological constant is chosen such that the background metric is flat while the Stuckelberg fields have a non-trivial profile. Around this background, at linear order the new symmetry reduces the propagating degrees of freedom to those of General Relativity, namely the massless helicity 2 modes only. We discuss the physical consequences and possible applications of these findings.
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