We accurately determine a new Cepheid distance to M101 (NGC 5457) using archival HST/ACS V and I time series photometry of two fields within the galaxy. We make a slight modification to the ISIS image subtraction package to obtain optimal differential light curves from HST data. We discovered 827 Cepheids with periods between 3 and 80 days, the largest extragalactic sample of Cepheids observed with HST by a factor of 2. With this large Cepheid sample we find that the relative distance of M101 from the LMC is delta {\mu}LMC = 10.63 \pm 0.04 (random) \pm 0.07 (systematic) mag. If we use the geometrically determined maser distance to NGC 4258 as our distance anchor, the distance modulus of M101 is {\mu}0 = 29.04 \pm 0.05 (random) \pm 0.18 (systematic) mag or D = 6.4 \pm 0.2 (random) \pm 0.5 (systematic) Mpc. The uncertainty is dominated by the maser distance estimate (\pm 0.15 mag), which should improve over the next few years. We determine a steep metallicity dependence, gamma, for our Cepheid sample through two methods, yielding gamma = -0.84 \pm 0.22 (random) \pm 0.07 (systematic) mag dex-1 and gamma = -0.72+0.20 -0.22 (random) \pm 0.06 (systematic) mag dex-1. We see marginal evidence for variations in the Wesenheit P-L relation slope as a function of deprojected galactocentric radius. We also use the TRGB method to independently determine the distance modulus to M101 of {\mu}0 = 29.05 \pm 0.06 (random) \pm 0.12 (systematic) mag.
High resolution, multi-wavelength maps of a sizeable set of nearby galaxies have made it possible to study how the surface densities of HI, H2 and star formation rate (Sigma_HI, Sigma_H2, Sigma_SFR) relate on scales of a few hundred parsecs. At these scales, individual galaxy disks are comfortably resolved, making it possible to assess gas-SFR relations with respect to environment within galaxies. Sigma_H2, traced by CO intensity, shows a strong correlation with Sigma_SFR and the ratio between these two quantities, the molecular gas depletion time, appears to be constant at about 2Gyr in large spiral galaxies. Within the star-forming disks of galaxies, Sigma_SFR shows almost no correlation with Sigma_HI. In the outer parts of galaxies, however, Sigma_SFR does scale with Sigma_HI, though with large scatter. Combining data from these different environments yields a distribution with multiple regimes in Sigma_gas - Sigma_SFR space. If the underlying assumptions to convert observables to physical quantities are matched, even combined datasets based on different SFR tracers, methodologies and spatial scales occupy a well define locus in Sigma_gas - Sigma_SFR space.
We build a model for the density and integrated Sachs-Wolfe (ISW) profile of supervoid and supercluster structures. Our model assumes that fluctuations evolve linearly from an initial Gaussian random field. We find these assumptions capable of describing N-body simulations and simulated ISW maps remarkably well on large scales. We construct an ISW map based on locations of superstructures identified previously in the SDSS Luminous Red Galaxy sample. A matched filter analysis of the cosmic microwave background confirms a signal at the $3.2-\sigma$ confidence level and estimates the radius of the underlying structures to be $55 \pm 28 ~h^{-1}$Mpc. The amplitude of the signal, however, is $2-\sigma$ higher than $\Lambda$CDM predictions.
We present a catalogue of galaxy photometric redshifts and k-corrections for the Sloan Digital Sky Survey Seven Data Release (SDSS-DR7), available on the World Wide Web. The photometric redshifts were estimated with an artificial neural network using five ugriz bands, concentration indices and Petrosian radii in the g and r bands. We have explored our redshift estimates with different training set concluding that the best choice to improve redshift accuracy comprises the Main Galaxies Sample (MGS), the Luminous Red Galaxies, and galaxies of active galactic nuclei covering the redshift range 0<z<0.3. For the MGS, the photometric redshift estimates agree with the spectroscopic values within rms=0.0227. The derived distribution of photometric redshifts in the range 0<zphot<0.6 agrees well with the model predictions. k-corrections were derived by calibration of the k-correct-v4.2 code results for the MGS with the reference frame (z=0.1) (g-r) colours. We adopt a linear dependence of k corrections on redshift and (g-r) colours that provide suitable distributions of luminosity and colours for galaxies up to redshift zphot=0.6 comparable to the results in the literature. Thus, our k-correction estimate procedure is a powerful, low computational time algorithm capable of reproducing suitable results that can be used for testing galaxy properties at intermediate redshifts using the large SDSS database.
We present the first aperture synthesis unbiased spectral line survey toward an extragalactic object. The survey covered the 40 GHz frequency range between 202 and 242 GHz of the 1.3 mm atmospheric window. We find that 80% of the observed band shows molecular emission, with 73 features identified from 15 molecular species and 6 isotopologues. The 13C isotopic substitutions of HC3N and transitions from H2(18)O, 29SiO, and CH2CO are detected for the first time outside the Galaxy. Within the broad observed band, we estimate that 28% of the total measured flux is due to the molecular line contribution, with CO only contributing 9% to the overall flux. We present maps of the CO emission at a resolution of 2.9"x1.9" which, though not enough to resolve the two nuclei, recover all the single-dish flux. The 40 GHz spectral scan has been modelled assuming LTE conditions and abundances are derived for all identified species. The chemical composition of Arp 220 shows no clear evidence of an AGN impact on the molecular emission but seems indicative of a purely starburst-heated ISM. The overabundance of H2S and the low isotopic ratios observed suggest a chemically enriched environment by consecutive bursts of star formation, with an ongoing burst at an early evolutionary stage. The large abundance of water (~10^-5), derived from the isotopologue H2(18)O, as well as the vibrationally excited emission from HC3N and CH3CN are claimed to be evidence of massive star forming regions within Arp 220. Moreover, the observations put strong constraints on the compactness of the starburst event in Arp 220. We estimate that such emission would require ~2-8x10^6 hot cores, similar to those found in the Sgr B2 region in the Galactic center, concentrated within the central 700 pc of Arp 220.
We present a detailed study of the dwarf galaxy VV124, recently recognized as a isolated member of the Local Group. We have obtained deep (r=26.5) wide-field g,r photometry of individual stars with the LBT under sub-arcsec seeing conditions. The Color-Magnitude Diagram suggests that the stellar content of the galaxy is dominated by an old, metal-poor population, with a significant metallicity spread. A very clean detection of the RGB tip allows us to derive an accurate distance of D=1.3 +/- 0.1 Mpc. Combining surface photometry with star counts, we are able to trace the surface brightness profile of VV124 out to ~ 5' = 1.9 kpc radius (where mu_r=30 mag/arcsec^2), showing that it is much more extended than previously believed. Moreover, the surface density map reveals the presence of two symmetric flattened wings emanating from the central elongated spheroid and aligned with its major axis, resembling a stellar disk seen nearly edge-on. We also present HI observations obtained with the WSRT, the first ever of this object. A total amount of 10^6 M_sun of HI gas is detected in VV124. Compared to the total luminosity, this gives a value of M_HI/L_V=0.11, which is particularly low for isolated Local Group dwarfs. The spatial distribution of the gas does not correlate with the observed stellar wings. The systemic velocity of the HI in the region superposed to the stellar main body of the galaxy is V_h=-25 km/s. The velocity field shows substructures typical of galaxies of this size but no sign of rotation. The HI spectra indicates the presence of a two-phase interstellar medium, again typical of many dwarf galaxies.
We present an analysis of the properties of the lowest Halpha-luminosity galaxies (L_Halpha<4x10^32 W; SFR<0.02 Msun/yr) in the Galaxy And Mass Assembly (GAMA) survey. These galaxies make up the the rise above a Schechter function in the number density of systems seen at the faint end of the Halpha luminosity function. Above our flux limit we find that these galaxies are principally composed of intrinsically low stellar mass systems (median stellar mass =2.5x10^8 Msun) with only 5/90 having stellar masses M>10^10 Msun. The low SFR systems are found to exist predominantly in the lowest density environments (median density ~0.02 galaxy Mpc^-2 with none in environments more dense than ~1.5 galaxy Mpc^-2). Their current specific star formation rates (SSFR; -8.5 < log(SSFR[yr^-1])<-12.) are consistent with their having had a variety of star formation histories. The low density environments of these galaxies demonstrates that such low-mass, star-forming systems can only remain as low-mass and forming stars if they reside sufficiently far from other galaxies to avoid being accreted, dispersed through tidal effects or having their gas reservoirs rendered ineffective through external processes.
Cosmological analysis based on currently available observations are unable to rule out a sizeable coupling between dark energy and dark matter. However, the signature of the coupling is not easy to grasp, since the coupling is degenerate with other cosmological parameters, such as the dark energy equation of state and the dark matter abundance. We discuss the possible ways to break such degeneracy. Based on the perturbation formalism, we carry out the global fitting by using latest observational data and get a tight constraint on the interaction between dark sectors. We find that the appropriate interaction can alleviate the coincidence problem.
The determination of dark matter constraints from liquid xenon direct detection experiments depends upon the amount of scintillation light produced by nuclear recoils in the detector, a quantity that is characterized by the scintillation efficiency factor Leff. We examine how uncertainties in the measurements of Leff and the extrapolated behavior of Leff at low recoil energies (where measurements do not exist) affect the constraints from experiments such as XENON10 and XENON100, particularly in the light WIMP regions of interest for the DAMA and CoGeNT experimental results.
We investigate cosmological consequences of a class of exponential $f(R)$ gravity in the Palatini formalism. By using the current largest type Ia Supernova sample along with determinations of the cosmic expansion at intermediary and high-$z$ we impose tight constraints on the model parameters. Differently from other $f(R)$ models, we find solutions of transient acceleration, in which the large-scale modification of gravity will drive the Universe to a new decelerated era in the future. We also show that a viable cosmological history with the usual matter-dominated era followed by an accelerating phase is predicted for some intervals of model parameters.
Directional detection is a promising Dark Matter search strategy. Indeed, WIMP-induced recoils would present a direction dependence toward the Cygnus constellation, while background-induced recoils exhibit an isotropic distribution in the galactic rest frame. Taking advantage on theses characteristic features and even in the presence of a sizeable background, it has recently been shown that data of forthcoming directional detectors could lead either to a competitive exclusion or to a conclusive discovery, depending on the value of the WIMP-nucleon cross section. However, it is possible to further exploit these upcoming data by using the strong dependence of the WIMP signal with : the WIMP mass and the WIMP velocity distribution. Within the framework of a model independent method and by using a Markov Chain Monte Carlo analysis of recoil events, we show the possibility to constrain the unknown WIMP parameters, both from particle physics (mass and cross section) and galactic halo (velocity dispersion along the three axis), leading to an identification of non-baryonic Dark Matter.
In general, for single field, the scale invariant spectrum of curvature perturbation can be given by either its constant mode or its increasing mode. We show that during slowly expanding or contracting, the spectrum of curvature perturbation given by its increasing mode can be scale invariance. The perturbation mode can be naturally extended out of horizon, and the amplitude of perturbation is consistent with the observations. We briefly discuss the implement of this scenario.
The channeling of the recoiling nucleus in crystalline detectors after a WIMP collision would produce a larger scintillation or ionization signal in direct detection experiments than otherwise expected. I present estimates of the importance of this effect in NaI, Si and Ge crystals, using analytic models developed from the 1960's onwards to describe channeling and blocking effects.
We study the impact on the primordial abundances of light elements created by a variation of the quark masses at the time of Big Bang nucleosynthesis (BBN). In order to navigate through the particle and nuclear physics required to connect quark masses to binding energies and reaction rates in a model-independent way, we use lattice QCD data and a hierarchy of effective field theories. We find that the measured Helium-4 abundances put a bound of -1 % <~ d m_q/m_q <~ 0.7 % on a possible variation of quark masses. The effect of quark mass variations on the deuterium abundances can be largely compensated by changes of the baryon-to-photon ratio eta. Including bounds on the variation of eta coming from WMAP results and adding some additional assumptions further narrows the range of allowed values of d m_q/m_q.
Interferometric millimeter observations of the cosmic microwave background and clusters of galaxies with arcmin resolutions require antenna arrays with short spacings. Having all antennas co-mounted on a single steerable platform sets limits to the overall weight. A 25 kg lightweight novel carbon-fiber design for a 1.2 m diameter Cassegrain antenna is presented. The finite element analysis predicts excellent structural behavior under gravity, wind and thermal load. The primary and secondary mirror surfaces are aluminum coated with a thin TiO$_2$ top layer for protection. A low beam sidelobe level is achieved with a Gaussian feed illumination pattern with edge taper, designed based on feedhorn antenna simulations and verified in a far field beam pattern measurement. A shielding baffle reduces inter-antenna coupling to below $\sim$ -135 dB. The overall antenna efficiency, including a series of efficiency factors, is estimated to be around 60%, with major losses coming from the feed spillover and secondary blocking. With this new antenna, a detection rate of about 50 clusters per year is anticipated in a 13-element array operation.
Context. Absorption line indices are widely used to determine the stellar population parameters such as age and metallicity of galaxies, but it is not easy to obtain the line indices of some distant galaxies that have colours available. Aims. This paper investigates the correlations between absorption line indices and colours. Methods. A few statistical fitting methods are mainly used, via both the observational data of Sloan Digital Sky Survey and a widely used theoretical stellar population model. Results. Some correlations between widely used absorption line indices and ugriz colours are found from both observational data of early-type galaxies and a theoretical simple stellar population model. In particular, good correlations between colours and widely used absorption line indices such as Dn(4000), HgammaA, HgammaF, Hdelta?A, Mg1, Mg2, and Mgb, are shown in this paper. Conclusions. Some important absorption line indices of early-type galaxies can be estimated from their colours using correlations between absorption line indices and colours. For example, age-sensitive absorption line indices can be estimated from (u-r) or (g-r) colours and metallicity-sensitive ones from (u - z) or (g - z). This is useful for studying the stellar populations of distant galaxies, especially for statistical investigations.
The Dark Matter Time Projection Chamber (DMTPC) experiment uses CF_4 gas at low pressure (0.1 atm) to search for the directional signature of Galactic WIMP dark matter. We describe the DMTPC apparatus and summarize recent results from a 35.7 g-day exposure surface run at MIT. After nuclear recoil cuts are applied to the data, we find 105 candidate events in the energy range 80 - 200 keV, which is consistent with the expected cosmogenic neutron background. Using this data, we obtain a limit on the spin-dependent WIMP-proton cross-section of 2.0 \times 10^{-33} cm^2 at a WIMP mass of 115 GeV/c^2. This detector is currently deployed underground at the Waste Isolation Pilot Plant in New Mexico.
Since the evidence for an accelerated universe and the gap of 70% in the total energy, collected by WMAP, search for alternatives for the general relativity is an important issue, for this theory is not suited for these new phenomena. A particular alternative is the Brans-Dicke theory which has being allowing inspiring results, for example, concerning k-essence type fields in 4 dimensions. However, this theory is almost unexplored in the context of the dimensional reduction of the theory in 3 dimensions. In this work, we address some problems in this dimensional reduction, namely, evaluation of the deceleration parameter of the universe described by the 3 dimensional Brans-Dicke with and without matter. In both cases, we see that it is not possible to consider the theory as a model of k-essence descrybing the dark energy, but it can be considered as descrybing the dark matter.
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We study the effect of shear on the cosmological backreaction in the context of matching voids and walls together using the exact inhomogeneous Lemaitre-Tolman-Bondi solution. Generalizing JCAP 1010 (2010) 021, we allow the size of the voids to be arbitrary and the densities of the voids and walls to vary in the range 0 < Omega_v < Omega_w < 1. We derive the exact analytic result for the backreaction and consider its series expansion in powers of the ratio of the void size to the horizon size, r_0/t_0. In addition, we deduce a very simple fitting formula for the backreaction with error less than 1% for voids up to sizes r_0 = t_0. We also construct an exact solution for a network of voids with different sizes and densities, leading to a non-zero relative variance of the expansion rate between the voids. While the leading order term of the backreaction for a single void-wall pair is of order (r_0/t_0)^2, the relative variance between the different voids in the network is found to be of order (r_0/t_0)^4 and thus very small for voids of the observed size. Furthermore, we show that even for very large voids, the backreaction is suppressed by an order of magnitude relative to the estimate obtained by treating the walls and voids as disjoint Friedmann solutions. Whether the suppression of the backreaction due to the shear is just a consequence of the restrictions of the used exact models, or a generic feature, has to be addressed with more sophisticated solutions.
We present the results of an optical spectroscopic study of 12 GALEX-discovered star-forming Lyman alpha emitting galaxies (LAEs) at z ~ 0.3. We measure the emission line fluxes from these galaxies by fitting their observed spectra to stellar population models in order to correct for underlying stellar absorption. We revisit earlier stellar population model fitting results, finding that excluding now-known AGNs lowers the typical stellar population age and stellar mass of this sample to ~ 300 Myr and ~ 4 x 10^9 Msol, respectively. We calculate their dust extinction using the Balmer decrement, and find a typical visual attenuation of Av ~ 0.3 mag, similar to that seen in many high-redshift LAEs. Comparing the ratio of Lyalpha/Halpha and the Lyman alpha equivalent widths to the measured dust extinction, we find that the ISMs in these objects appear to be neither enhancing nor seriously attenuating the Lyman alpha equivalent widths, as would be the case in a quasi-clumpy ISM. Lastly, we perform a detailed analysis of the gas-phase metallicities of these galaxies, and we find that most galaxies in our sample have Z < 0.4 Zsol. We find that at a fixed stellar mass, these low-redshift LAE analogs are offset by ~ 0.6 dex lower in metallicity from the general galaxy population at similar redshifts based on the local mass-metallicity relationship. This implies that galaxies with Lyman alpha in emission may be systematically more metal poor than star-forming galaxies at the same stellar mass and redshift, similar to preliminary results at z ~ 2.
We present the first results of the spectroscopy of distant, obscured AGN as obtained with the ultra-deep (~3.3 Ms) XMM-Newton survey in the Chandra Deep Field South (CDFS). One of the primary goals of the project is to characterize the X-ray spectral properties of obscured and heavily obscured Compton-thick AGN over the range of redhifts and luminosities that are relevant in terms of their contribution to the X-ray background. The ultra-deep exposure, coupled with the XMM detector's spectral throughput, allowed us to accumulate good quality X-ray spectra for a large number of X-ray sources and, in particular, for heavily obscured AGN at cosmological redshifts. Specifically we present the X-ray spectral properties of two high-redshift - z= 1.53 and z=3.70 - sources. The XMM spectra of both are very hard, with a strong iron Kalpha line at a rest-frame energy of 6.4 keV. A reflection-dominated continuum provides the best description of the X-ray spectrum of the z=1.53 source, while the intrinsic continuum of the z=3.70 AGN is obscured by a large column N_H ~ 10^24 cm-2 of cold gas. Compton-thick absorption, or close to it, is unambiguously detected in both sources. Interestingly, these sources would not be selected as candidate Compton thick AGN by some multiwavelength selection criteria based on the mid-infrared to optical and X-ray to optical flux ratios.
We present results of Hubble Space Telescope NICMOS H-band imaging of 73 of most luminous (i.e., log[L_IR/L_0]>11.4) Infrared Galaxies (LIRGs) in the Great Observatories All-sky LIRG Survey (GOALS). This dataset combines multi-wavelength imaging and spectroscopic data from space (Spitzer, HST, GALEX, and Chandra) and ground-based telescopes. In this paper we use the high-resolution near-infrared data to recover nuclear structure that is obscured by dust at optical wavelengths and measure the evolution in this structure along the merger sequence. A large fraction of all galaxies in our sample possess double nuclei (~63%) or show evidence for triple nuclei (~6%). Half of these double nuclei are not visible in the HST B-band images due to dust obscuration. The majority of interacting LIRGs have remaining merger timescales of 0.3 to 1.3 Gyrs, based on the projected nuclear separations and the mass ratio of nuclei. We find that the bulge luminosity surface density increases significantly along the merger sequence (primarily due to a decrease of the bulge radius), while the bulge luminosity shows a small increase towards late merger stages. No significant increase of the bulge Sersic index is found. LIRGs that show no interaction features have on average a significantly larger bulge luminosity, suggesting that non merging LIRGs have larger bulge masses than merging LIRGs. This may be related to the flux limited nature of the sample and the fact that mergers can significantly boost the IR luminosity of otherwise low luminosity galaxies. We find that the projected nuclear separation is significantly smaller for ULIRGs (median value of 1.2 kpc) than for LIRGs (mean value of 6.7 kpc), suggesting that the LIRG phase appears earlier in mergers than the ULIRG phase.
We investigate the column density distribution function of neutral hydrogen at redshift z = 3 using a cosmological simulation of galaxy formation from the OverWhelmingly Large Simulations (OWLS) project. The base simulation includes gravity, hydrodynamics, star formation, supernovae feedback, stellar winds, chemodynamics, and element-by-element cooling in the presence of a uniform UV background. Self-shielding and formation of molecular hydrogen are treated in post-processing, without introducing any free parameters, using an accurate reverse ray-tracing algorithm and an empirical relation between gas pressure and molecular mass fraction. The simulation reproduces the observed z = 3 abundance of Ly-A forest, Lyman Limit and Damped Ly-A HI absorption systems probed by quasar sight lines over ten orders of magnitude in column density. Self-shielding flattens the column density distribution for NHI > 10^18 cm-2, while the conversion to fully neutral gas and conversion of HI to H2 steepen it around column densities of NHI = 10^20.3 cm-2 and NHI = 10^21.5 cm-2, respectively.
Clusters of galaxies are known to be dynamically active systems, yet X-ray studies of the low redshift population exhibit tight scaling laws. In this work, we extend previous studies of this apparent paradox using numerical simulations of two extreme merger cases, one is a high Mach number (above 2.5) satellite merger similar to the "bullet cluster" and the other a merger of nearly equal mass progenitors. Creating X-ray images densely sampled in time, we construct TX, Mgas, and YX measures within R500 and compare to the calibrations of Kravtsov et al. (2006). We find that these extreme merger cases respect the scaling relations, for both intrinsic measures and for measures derived from appropriately masked, synthetic Chandra X-ray images. The masking procedure plays a critical role in the X-ray temperature calculation while it is irrelevant in the X-ray gas mass derivation. Mis-centering up to 100 kpc does not influence the result. The observationally determined radius R500 might conduce to systematic shifts in Mgas, and YX which increase the total mass scatter.
We present spectroscopic follow-up observations of 70{\mu}m selected galaxies from the SWIRE XMMLSS and Lockman Hole fields. We have measured spectroscopic redshifts for 293 new sources down to a 70{\mu}m flux limit of 9mJy and R < 22. The redshift distribution peaks at z ~ 0.3 and has a high redshift tail out to z = 3.5. We perform emission line diagnostics for 91 sources where [OIII], H{\beta}, [NII], H{\alpha} and [SII] emission lines are available to determine their power source. We find in our sample 13 QSOs, 1 Seyfert II galaxy, 33 star forming galaxies, 30 composite galaxies, 5 LINERs and 21 ambiguous galaxies. We fit single temperature dust spectral energy distributions (SEDs) to 81 70{\mu}m sources with 160{\mu}m photometry to estimate dust temperatures and masses. Assuming the dust emissivity factor ({\beta}) as 1.5, we determine temperatures in the range ~ 20-60K and dust masses with a range of 10{^6}-10{^9} M{_\odot}. Plotting these objects in the luminosity-temperature diagram suggests that these objects have lower dust temperatures than local IR luminous galaxies. The Herschel Space Observatory will be crucial in understanding the nature of these sources and to accurately determining the shape of the Rayleigh-Jeans tail of the dust SED. We then model SEDs from optical to far-IR for each source using a set of galaxy and quasar templates in the optical and near-IR (NIR) and with a set of dust emission templates (cirrus, M82 starburst, Arp 220 starburst and AGN dust torus) in the mid-IR (MIR) to far-IR (FIR). The number of objects fit with each dust template are: 57 Arp 220, 127 M82, 9 cirrus, 1 AGN dust torus, 70 M82 and cirrus, 26 M82 and AGN dust torus and 3 Arp 220 and AGN dust torus. We determine the total IR luminosity (LIR) in range 10{^8}-10{^{15}} L{_\odot} by integrating the SED models from 8 to 1000{\mu}m.
We present a catalog of over 130,000 quasars candidates with NIR photometric properties, with an areal coverage of approximately 1,200~deg^2. This is achieved by matching the Sloan Digital Sky Survey (SDSS) in the optical ugriz bands, to the UKIRT Infrared Digital Sky Survey (UKIDSS) Large Area Survey (LAS) in the near-infrared YJHK bands. We match the ~1 million SDSS DR6 Photometric Quasar catalog to Data Release 3 of the UKIDSS LAS (ULAS), and produce a catalog with 130,827 objects with detections in one or more NIR bands, of which 74,351 objects have optical and K-band detections and 42,133 objects have the full 9-band photometry. The majority ~85 of the SDSS objects were not matched simply because there were not covered by the ULAS. Our matched catalog has a surface density of ~53 deg^-2 for K >18.27 objects; tests using our matched catalog, along with data from the UKIDSS DXS, implies that our limiting magnitude is i ~ 20.6. Color-redshift diagrams, for the optical and NIR, show the close agreement between our matched catalog and recent quasar color models at redshift z > 2.0, while at higher redshifts, the models generally appear to be bluer than the mean observed quasar colors. The gJK and giK color-spaces are used to examine methods of differentiating between stars and (mid-redshift) quasars, key to currently ongoing quasar surveys. Finally, we report on the NIR photometric properties of high, z>4.6, and very high, z>5.7, redshift previously discovered quasars.
A new class of inflation models within the context of G-inflation is proposed, in which the standard model Higgs boson can act as an inflaton thanks to Galileon-like non-linear derivative interaction. The generated primordial density perturbation is shown to be consistent with the present observational data. We also make a general discussion on potential-driven G-inflation models, and find a new consistency relation between the tensor-to-scalar ratio $r$ and the tensor spectral index $n_T$, $r = -32 \sqrt{6}n_T / 9$, which is crucial in discriminating the present models from standard inflation with a canonical kinetic term.
We use the secondary infall model described in Del Popolo (2009), which takes into account the effect of dynamical friction, ordered and random angular momentum, baryons adiabatic contraction and dark matter baryons interplay, to study how in- ner slopes of relaxed LCDM dark matter (DM) halos with and without baryons (baryons+DM, and pure DM) depend on redshift and on halo mass. We apply the quoted method to structures on galactic scales and clusters of galaxies scales. We find that the inner logarithmic density slope, of dark matter halos with baryons has a significant dependence on halo mass and redshift with slopes ranging from 0 for dwarf galaxies to 0.4 for objects of M = 10^13M_solar and 0.94 for M = 10^15M_solar clusters of galaxies. Structures slopes increase with increasing redshift and this trend reduces going from galaxies to clusters. In the case of density profiles constituted just of dark matter the mass and redshift dependence of slope is very slight. In this last case, we used the Merrit et al. (2006) analysis who compared N-body density profiles with various parametric models finding systematic variation in profile shape with halo mass. This last analysis suggests that the galaxy-sized halos obtained with our model have a different shape parameter, i.e. a different mass distribution, than the cluster-sized halos, obtained with the same model. The results of the present paper argue against universality of density profiles constituted by dark matter and baryons and confirm claims of a systematic variation in profile shape with halo mass, for dark matter halos.
We present a study of the extended radio emission in a sample of 8434 low redshift (z < 0.35) broad line active galactic nuclei (AGN) from the Sloan Digital Sky Survey (SDSS). To calculate the jet and lobe contributions to the total radio luminosity, we have taken the 846 radio core sources detected in our previous study of this sample and performed a systematic search in the Faint Images of the Radio Sky at Twenty-centimeters (FIRST) database for extended radio emission that is likely associated with the optical counterparts. We found 51 out of 846 radio core sources have extended emission (> 4" from the optical AGN) that is positively associated with the AGN, and we have identified an additional 12 AGN with extended radio emission but no detectable radio core emission. Among these 63 AGN, we found 6 giant radio galaxies (GRGs), with projected emission exceeding 750 kpc in length, and several other AGN with unusual radio morphologies also seen in higher redshift surveys. The optical spectra of many of the extended sources are similar to that of typical broad line radio galaxy spectra, having broad H$\alpha$ emission lines with boxy profiles and large M_BH. With extended emission taken into account, we find strong evidence for a bimodal distribution in the radio-loudness parameter R, where the lower radio luminosity core-only sources appear as a population separate from the extended sources, with a dividing line at log(R) $\approx 1.75$. This dividing line ensures that these are indeed the most radio-loud AGN, which may have different or extreme physical conditions in their central engines when compared to the more numerous radio quiet AGN.
Hawking and Carr showed that the proper size of a spherical overdense region surrounded by a flat FRW universe cannot be arbitrarily large as otherwise the region would close up on itself and become a separate universe. From this result they derived a condition connecting size and density of the overdense region ensuring that it is part of our universe. Carr used this condition to obtain a maximum density fluctuation amplitude with the property that for smaller amplitudes the formation of a primordial black hole is possible, while larger ones indicate a separate universe. In contrast, we find that the appearance of a maximum is not a consequence of avoiding separate universes but arises naturally from the geometry of the chosen slicing and the Hamiltonian constraint. Using instead of density a volume fluctuation variable reveals that a fluctuation is a separate universe iff this variable diverges on superhorizon scales. Hence density fluctuations can never form or be separate universes and Hawking's and Carr's condition does not pose a physical constraint on density fluctuations. Primordial black hole formation with an initial fluctuation amplitude larger than the one corresponding to the maximum density fluctuation amplitude was previously not considered and so we compare it to the well known case where the amplitude is smaller by presenting embedding and conformal diagrams of both types in dust spacetimes.
We use the W_Ha versus [NII]/Ha (WHAN) diagram to provide a comprehensive emission-line classification of SDSS galaxies. This classification is able to cope with the large population of weak line galaxies that do not appear in traditional diagrams due to a lack of some of the diagnostic lines. A further advantage of the WHAN diagram is to allow the differentiation between two very distinct classes that overlap in the LINER region of traditional diagnostic diagrams. These are galaxies hosting a weakly active nucleus (wAGN) and "retired galaxies" (RGs), i.e. galaxies that have stopped forming stars and are ionized by their hot evolved low-mass stars. A useful criterion to distinguish true from fake AGN (i.e. the RGs) is the ratio (\xi) of the extinction-corrected L_Ha with respect to the Ha luminosity expected from photoionization by stellar populations older than 100 Myr. This ratio follows a markedly bimodal distribution, with a \xi >> 1 population composed by systems undergoing star-formation and/or nuclear activity, and a peak at \xi ~ 1 corresponding to the prediction of the RG model. We base our classification scheme on the equivalent width of Ha, an excellent observational proxy for \xi. Based on the bimodal distribution of W_Ha, we set the division between wAGN and RGs at W_Ha = 3 A. Five classes of galaxies are identified within the WHAN diagram: (a) Pure star forming galaxies: log [NII]/Ha < -0.4 and W_Ha > 3 A. (b) Strong AGN (i.e., Seyferts): log [NII]/Ha > -0.4 and W_Ha > 6 A. (c) Weak AGN: log [NII]/Ha > -0.4 and W_Ha between 3 and 6 A. (d) RGs: W_Ha < 3 A. (e) Passive galaxies (actually, line-less galaxies): W_Ha and W_[NII] < 0.5 A. A comparative analysis of star formation histories and of other properties in these different classes of galaxies corroborates our proposed differentiation between RGs and weak AGN in the LINER-like family. (Abridged)
We study the pseudo equivalent width of the Si II 4000 feature of Type Ia supernovae in the redshift range 0.0024 < z < 0.634. We find that this spectral indicator correlates with the lightcurve color excess (SALT2 c) as well as previously defined spectroscopic subclasses (Branch types) and the evolution of the Si II 6150 velocity, i.e., the so called velocity gradient. Based on our study of 55 objects from different surveys, we find indications that the Si II 4000 spectral indicator could provide important information to improve cosmological distance measurements with Type Ia supernovae.
We present an interesting Sunyaev-Zel'dovich (SZ) detection in the first of the Arcminute Microkelvin Imager (AMI) `blind', degree-square fields to have been observed down to our target sensitivity of 100 microJy/beam. In follow-up deep pointed observations the SZ effect is detected with a maximum peak decrement greater than 8 times the thermal noise. No corresponding emission is visible in the ROSAT all-sky X-ray survey and no cluster is evident in the Palomar all-sky optical survey. Compared with existing SZ images of distant clusters, the extent is large (approximately 10') and complex; our analysis favours a model containing two clusters rather than a single cluster. Our Bayesian analysis is currently limited to modelling each cluster with an ellipsoidal (or spherical) beta-model, which does not do justice to this decrement. Fitting an ellipsoid to the deeper candidate we find the following: (a) Assuming that the Evrard et al. (2002) approximation to Press & Schechter (1974) correctly gives the number density of clusters as a function of mass and redshift, then, in the search area, the probability ratio of the AMI detection of this cluster is 7.9 x 10^4:1; alternatively assuming Jenkins et al. (2001) as the true prior, the probability ratio of detection is 2.1 x 10^5:1. (b) The cluster mass is M200= 5.5 x 10^14 h70^-1Msun. (c) Finally, abandoning modelling the cluster physically, and instead simply modelling the SZ decrement using a beta-model, we find a central SZ temperature decrement of -295microK after allowing for CMB primary anisotropies, receiver noise and sources. We are unsure if the cluster system we observe is a merging system or two separate clusters.
We explore the model-independent constraints from cosmology on a dark-matter particle with no prominent standard model interactions that interacts and thermalizes with other particles in a hidden sector. Without specifying detailed hidden-sector particle physics, we characterize the relevant physics by the annihilation cross section, mass, and temperature ratio of the hidden to visible sectors. While encompassing the standard cold WIMP scenario, we do not require the freeze-out process to be nonrelativistic. Rather, freeze-out may also occur when dark matter particles are semirelativistic or relativistic. We solve the Boltzmann equation to find the conditions that hidden-sector dark matter accounts for the observed dark-matter density, satisfies the Tremaine-Gunn bound on dark-matter phase space density, and has a free-streaming length consistent with cosmological constraints on the matter power spectrum. We show that for masses <1.4 keV no region of parameter space satisfies all these constraints. This is a gravitationally-mediated lower bound on the dark-matter mass for any model in which the primary component of dark matter once had efficient interactions -- even if it has never been in equilibrium with the standard model.
We model the cosmological substratum by a viscous fluid that is supposed to provide a unified description of the dark sector and pressureless baryonic matter. In the homogeneous and isotropic background the \textit{total} energy density of this mixture behaves as a generalized Chaplygin gas. The perturbations of this energy density are intrinsically non-adiabatic and source relative entropy perturbations. The resulting baryonic matter power spectrum is shown to be compatible with the 2dFGRS and SDSS (DR7) data. A joint statistical analysis, using also Hubble-function and supernovae Ia data, shows that, different from other studies, there exists a maximum in the probability distribution for a negative present value $q_{0} \approx - 0.53$ of the deceleration parameter. Moreover, different from other approaches, the unified model presented here favors a matter content that is of the order of the baryonic matter abundance suggested by big-bang nucleosynthesis.
A monochromatic gamma ray line results when dark matter particles in the galactic halo annihilate to produce a two body final state which includes a photon. Such a signal is very distinctive from astrophysical backgrounds, and thus represents an incisive probe of theories of dark matter. We compare the recent null results of searches for gamma ray lines in the galactic center and other regions of the sky with the predictions of effective theories describing the interactions of dark matter particles with the Standard Model. We find that the null results of these searches provide constraints on the nature of dark matter interactions with ordinary matter which are complementary to constraints from other observables, and stronger than collider constraints in some cases.
We discover that some unstable vacua have long memory. By that we mean that even in the theories containing only massive particles, there are correllators and expectation values which grow with time. We examine the cases of instabilities caused by the constant electric fields, expanding and contracting universes and, most importantly, the global de Sitter space. In the last case the interaction leads to a remarkable UV/IR mixing and to a large back reaction. This gives reasons to believe that the cosmological constant problem could be resolved by the infrared physics.
We study a cosmological model in 1+D+d dimensions where D dimensions are associated with the usual Friedman-Robertson-Walker type metric with radio a(t) and d dimensions corresponds to an additional homogeneous space with radio b(t). We make a general analysis of the field equations and then we obtain solutions involving the two cosmological radii, a(t) and b(t). The particular case D=3, d=1 is studied in some detail.
We analyze the relation between teleparallelism and local Lorentz invariance. We show that generic modifications of the teleparallel equivalent to general relativity will not respect local Lorentz symmetry. We clarify the reasons for this and explain why the situation is different in general relativity. We give a prescription for constructing teleparallel equivalents for known theories. We also explicitly consider a recently proposed class of generalized teleparallel theories, called f(T) theories of gravity, and show why restoring local Lorentz symmetry in such theories cannot lead to sensible dynamics, even if one gives up teleparallelism.
We present a catalog of compact sources derived from the QUaD Galactic Plane Survey. The survey covers ~800 square degrees of the inner galaxy (|b|<4 degrees) in Stokes I, Q and U parameters at 100 and 150 GHz, with angular resolution 5 and 3.5 arcminutes. 505 unique sources are identified in I, of which 239 are spatially matched between frequency bands, with 50 (216) detected at 100 (150) GHz alone; 182 sources are identified as ultracompact HII (UCHII) regions. Approximating the distribution of total intensity source fluxes as a power-law, we find a slope of $\gamma_{S,100}=-1.8\pm0.4$ at 100 GHz, and $\gamma_{S,150}=-2.2\pm0.4$ at 150 GHz. Similarly, the power-law index of the source two-point angular correlation function is $\gamma_{\theta,100}=-1.21\pm0.04$ and $\gamma_{\theta,150}=-1.25\pm0.04$. The total intensity spectral index distribution peaks at $\alpha_{I}\sim0.25$, indicating that dust emission is not the only source of radiation produced by these objects between 100 and 150 GHz; free-free radiation is likely significant in the 100 GHz band. Four sources are detected in polarized intensity P, of which three have matching counterparts in I. Three of the polarized sources lie close to the galactic center, Sagittarius A*, Sagittarius B2 and the Galactic Radio Arc, while the fourth is RCW 49, a bright HII region. An extended polarized source, undetected by the source extraction algorithm on account of its $\sim0.5^{\circ}$ size, is identified visually, and is an isolated example of large-scale polarized emission oriented distinctly from the bulk galactic dust polarization.
(Abridged) We present a comprehensive analysis of the spatially resolved
stellar population properties of 26 early-type dwarf (dE) galaxies in the Virgo
cluster. Using Lick/IDS absorption line indices we derive simple stellar
population(SSP)-equivalent age, metallicity and [$\alpha$/Fe] abundance ratio.
In particular, we focus on the comparison of the stellar populations between
the central nucleus and the surrounding galactic main body. The stellar
populations of the nuclei are, for most dEs, significantly younger than those
of the respective galactic main bodies, with an average difference of 3.5 Gyr.
We find only five dEs with significantly older nuclei than their galactic main
bodies. Furthermore, we observe most dE nuclei to be more metal rich compared
to their host galaxies. These age and metallicity behaviours are shown by
almost all dEs brighter than M$_{\it r}$ = -17 mag.
We also examine the presence of radial gradients in the SSP parameters for a
subset of 13 dEs (up to 1.2 kpc or 15 arcsec radius). We notice two different
types of gradients, namely smooth profiles that include the nucleus, and
profiles where a break occurs between the nucleus and the rest of the galaxy.
Nevertheless, an overall trend of increasing age and decreasing metallicity
with radius exists, consistent with earlier studies.
Within the context of space-time (D-particle) foam in string/brane-theory it is demonstrated that it is possible to generate non-extensive statistics. The D-particle foam model involves point-like brane defects (D-particles), which provide the topologically non-trivial foamy structures of space-time. The D-particles can capture and emit stringy matter and this leads to a recoil of D-particles. It is indicated how one effect of such a recoil of D-particles is a back reaction on the space-time metric of Finsler type which is stochastic. We show that such a type of stochastic space-time foam can lead to cosmological effects similar to those induced by modifications of particle distributions within the framework of Tsallis entropies. The restrictions placed on the free parameters of the Finsler type metric are obtained from solving the Boltzmann equation in this background for relic abundances of a Lightest Supersymmetric Particle (LSP) dark matter candidate. It is demonstrated that the D-foam acts as a source for particle production in the Boltzmann equation, thereby leading to enhanced thermal LSP relic abundances relative to those in the Standard Lambda CDM Cosmology. For D-particle masses of order TeV, such effects may be relevant for dark matter searches at colliders. The latter constraints complement those coming from high energy gamma-ray astronomy on the induced vacuum refractive index that D-foam models entail.
We present a new approach to the sky subtraction for long-slit spectra suitable for low-surface brightness objects based on the controlled reconstruction of the night sky spectrum in the Fourier space using twilight or arc-line frames as references. It can be easily adopted for FLAMINGOS-type multi-slit data. Compared to existing sky subtraction algorithms, our technique is taking into account variations of the spectral line spread along the slit thus qualitatively improving the sky subtraction quality for extended targets. As an example, we show how the stellar metallicity and stellar velocity dispersion profiles in the outer disc of the spiral galaxy NGC 5440 are affected by the sky subtraction quality. Our technique is used in the survey of early-type galaxies carried out at the Russian 6-m telescope, and it strongly increases the scientific potential of large amounts of long-slit data for nearby galaxies available in major data archives.
We report the results of a successful 7 hour 1.4 GHz VLBI experiment using two new stations, ASKAP-29 located in Western Australia and WARK12M located on the North Island of New Zealand. This was the first geodetic VLBI observing session with the participation of these new stations. We have determined the positions of ASKAP-29 and WARK12M. Random errors on position estimates are 150-200 mm for the vertical component and 40-50 mm for the horizontal component. Systematic errors caused by the unmodeled ionosphere path delay may reach 1.3 m for the vertical component and 0.1 m for the horizontal component.
We analyzed the electron neutrino data of the Gallium radioactive source experiments and the electron antineutrino data of the reactor Bugey and Chooz experiments in terms of neutrino oscillations. We found a hint of a CPT-violating asymmetry of the effective neutrino and antineutrino mixing angles.
While moving down the potential on its classical slow roll trajectory, the inflaton field is subject to quantum jumps, which take it up or down the potential at random. In "stochastic inflation", the impact of these quantum jumps is modeled by smoothing out the field over (at least) Hubble-patch sized domains and treating fluctuations on smaller scales as noise. The inflaton thus becomes a stochastic process whose values at a given time are calculated using its probability distribution. We generalize this approach for non-canonic kinetic terms of Dirac Born Infeld (DBI) type and investigate the resulting modifications of the field's trajectory. Since models of DBI inflation arise from string-inspired scenarios in which the scalar field has a geometric interpretation, we insist that field value restrictions imposed by the model's string origin must be respected at the quantum level.
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We reexamine the age distribution of star clusters in the Antennae in the context of N-body+hydrodynamical simulations of these interacting galaxies. All of the simulations that account for the observed morphology and other properties of the Antennae have star formation rates that vary relatively slowly with time, by less than a factor of 3 over the past ~10^8 yr. In contrast, the observed age distribution of the clusters declines by more than a factor of 30 over the same period. These two facts can only be reconciled if the clusters are disrupted more or less continually for at least 10^8 yr and possibly 10^9 yr. In quiescent (non-interacting) galaxies, such as the Milky Way and the Magellanic Clouds, the observed age distribution declines approximately as a power-law, dN/dt \propto t^{gamma} with -1.0 \la gamma \la -0.7, which we interpret primarily as a consequence of disruption. When we combine this disruption rate with the formation rates in the simulations, we find excellent agreement with the observed age distribution of clusters in the Antennae. This result demonstrates that the disruption history of star clusters in at least this one prototypical interacting galaxy is essentially the same as that in quiescent galaxies.
The hypothesis of a tiny fraction of the cosmic inventory evolving cosmologically as a degenerate Fermi gas test fluid at some dominant cosmological background is investigated. Our analytical results allow for performing preliminary computations to the evolution of perturbations for relativistic and non-relativistic test fluids. The density fluctuation, $\delta$, the fluid velocity divergence, $\theta$, and an explicit expression for the dynamics of the shear stress, $\sigma$, are obtained for a degenerate Fermi gas in the background regime of radiation. Extensions to the dominance of matter and to the $\Lambda$CDM cosmological background are also investigated and lessons concerning the formation of large structures of degenerate Fermi gas are depicted.
The redshift-luminosity distributions for well-defined galaxies and quasars in the Sloan Digital Sky Survey (SDSS) are compared for the two redshift-distance relations of a Hubble redshift and a de Sitter redshift. Assuming a Hubble redshift, SDSS data can be interpreted as luminosity evolution following the Big Bang. In contrast, given a de Sitter redshift, the intrinsic brightness of objects at all redshifts is roughly the same. In a de Sitter universe, 95 per cent of SDSS galaxies and quasars fall into a magnitude range of only 2.8, and 99.7 per cent are within 5.4 mag. The comparable Hubble luminosity ranges are much larger: 95 per cent within 6.9, and 99.7 per cent within 11.5 mag. De Sitter space is now widely discussed, but the de Sitter redshift is hardly mentioned.
The multifrequency radio continuum and 21cm HI observations of five blue compact dwarf (BCD) galaxies, Mrk 104, Mrk 108, Mrk 1039, Mrk 1069 and I Zw 97 using the Giant Meterwave Radio Telescope (GMRT) are presented here. Radio continuum emission at 610 MHz and 325 MHz is detected from all the observed galaxies whereas only a few are detected at 240 MHz. In our sample, three galaxies are members of groups and two galaxies (Mrk 1069 and I Zw 97) are isolated galaxies. The radio emission from Mrk 104 and Mrk 108 is seen to encompass the entire optical galaxy whereas the radio emission from Mrk 1039, Mrk 1069, I Zw 97 is confined to massive HII regions. This, we suggest, indicates that the star formation in the latter group of galaxies has recently been triggered and that the environment in which the galaxy is evolving plays a role. Star formation rates (SFR) calculated from 610 MHz emission is in the range 0.01-0.1 M_sun/yr; this is similar to the SFR obtained for individual star forming regions in BCDs. The integrated radio spectra of four galaxies are modelled over the frequency range where data is available. We find that two of the galaxies Mrk 1069 and Mrk 1039, show a turnover at low frequencies which is well fitted by free-free absorption whereas the other two galaxies, Mrk 104 and Mrk 108, show a power law at the lowest GMRT frequencies. The flatter spectrum, localized star formation and radio continuum in isolated galaxies lend support to stochastic self-propagating star formation (SSPSF). The HI observations of four galaxies Mrk 104, Mrk 108, Mrk 1039 and Mrk 1069 show extended disks as large as ~1.1-6 times the optical size. All the observed BCDs (except Mrk 104) show rotating disk with a half power width of ~50-124 km/s. Solid body rotation is common in our sample. We note that the tidal dwarf (TD) origin is possible for two of the BCDs in our sample.
We investigated the instability of advective accretion flow as a consequence of angular momentum transfer in one-dimensional, quasi-spherical transonic accretion flow around a non-rotating black hole. The code is designed to include the effects of viscosity; the hydrodynamics component preserves angular momentum strictly with Lagrangian and remap method in absence of viscosity, while the viscosity component updates viscous angular momentum transfer through the implicit method. We performed two tests to demonstrate the suitability of the code for accretion study. First, we simulated the inviscid, low angular momentum, transonic accretion flow with shocks around a black hole, and then the subsonic, self-similar ADAF solution around a Newtonian object. Both simulations fitted the corresponding analytical curves extremely well. We then simulated a rotating, viscous, transonic fluid with shocks. We showed that for low viscosity parameter, stable shocks at larger distance are possible. For higher viscosity parameter, more efficient angular momentum transfer in the post-shock disk makes the shock structure oscillatory. Moreover, as the shock drifts to larger distances, a secondary inner shock develops. We showed that the inner shock is the direct consequence of expansion of the outer shock, as well as creation of regions with $\partial l / \partial r < 0$ due to more efficient angular momentum transfer near the inner sonic point. We showed that all disk parameters, including emissivity, oscillate with the same period as that of the shock oscillation. Our simulation may have implication for low frequency QPOs, e.g., GRO J1655-40 and XTE J1550-564.
We study the cosmological evolution of domain walls bounded by strings which arise naturally in axion models. If we introduce a bias in the potential, walls become metastable and finally disappear. We perform two dimensional lattice simulations of domain wall networks and estimate the decay rate of domain walls. By using the numerical results, we give a constraint for the bias parameter and the Peccei-Quinn scale. We also discuss the possibility to probe axion models by direct detection of gravitational waves produced by domain walls.
Current semi-analytic models (SAMs) of galaxy formation over-predict the fraction of passive small late-type satellite galaxies in dense environments by a factor of two to three. We hypothesize that this is due to inaccurate prescriptions on cold gas evolution. In the hope of solving this problem we apply detailed prescriptions on the evolution of diffuse hot gases in satellites and on stellar mass loss, both of which are critical to model cold gas evolution. We replace the conventional shock-heating motivated instant stripping with a realistic gradual prescription based on ram pressure and tidal stripping. We also carefully consider stellar mass loss in our model. When both mechanisms are included, the fraction of passive late types matches the data much more closely. The satellite over-quenching problem is still present in small galaxies in massive haloes, however. In terms of the detectable residual star formation rates, gradual diffuse gas stripping appears to be much more important than stellar mass loss in our model. The implications of these results and other possibilities, such as redshift-dependent merging geometry and tidal disruption, are also discussed.
A contribution $\zeta_\chi$ to the curvature perturbation will be generated during the waterfall that ends hybrid inflation, that may be significant on small scales. In particular, it may lead to excessive black hole formation. We consider only standard hybrid inflation, with the tachyonic mass of the waterfall field much bigger than the Hubble parameter. We calculate $\zeta_\chi$ under some assumptions, and we see how the calculation will go if these assumptions are relaxed. Earlier attempts to calculate $\zeta_\chi$ are seen to be incorrect.
We study the g-essence model with Yukawa interactions between a scalar field and a Dirac field. For the homogeneous, isotropic and flat Friedmann-Robertson-Walker universe filled with the such g-essence, the exact solution of the model is found. Moreover, we reconstruct the corresponding scalar and fermionic potentials which describe the coupled dynamics of the scalar and fermionic fields.
We perform a consistent calculation of primordial black hole (PBH) mass spectrum and second-order induced gravitational wave (GW) background produced from primordial scalar perturbations in radiation era of the early Universe. It is shown that the maximal amplitudes of the second order GW spectrum that can be approached without conflicting with the PBH data do not depend significantly on the shape of primordial perturbation spectrum. The constraints on the GW background obtained in previous works are extended to a wider GW frequency range. We discuss the applicability of the currently available pulsar timing limits for obtaining the constraints on scalar power spectrum and PBH abundance and show that they can be used for strongly constraining the PBH number density in the PBH mass range $\sim (0.03 - 10) M_{\odot}$.
It has been proposed that the radio spectra of radio-quiet quasars is produced by free-free emission in the optically thin part of an accretion disc wind. An important observational constraint on this model is the observed X-ray luminosity. We investigate this constraint using a sample of PG radio-quiet quasars for which XMM-Newton EPIC spectra are available. Comparing the predicted and measured luminosities for 0.5, 2 and 5 keV, we conclude that all of the studied PG quasars require a large hydrogen column density absorber, requiring these quasars to be close to or Compton-thick. Such a large column density can be directly excluded for PG 0050+124, for which a high-resolution RGS spectrum exists. Further constraint on the column density for a further 19 out of the 21 studied PG quasars comes from the EPIC spectrum characteristics such as hard X-ray power-law photon index and the equivalent width of the Fe Kalpha line; and the small equivalent width of the C IV absorber present in UV spectra. For 2 sources: PG 1001+054 and PG 1411+442 we cannot exclude that they are indeed Compton-thick, and the radio and X-ray luminosity are due to a wind originating close to the super-massive black hole. We conclude that for 20 out of 22 PG quasars studied free-free emission from a wind emanating from the accretion disc cannot mutually explain the observed radio and X-ray luminosity.
We present partial results from our monitoring of the nuclear region of the starburst galaxy IC 694 (=Arp 299-A) at radio wavelengths, aimed at discovering recently exploded CCSNe, as well as to determine their rate of explosion, which carries crucial information on star formation rates and starburst scenarios at work. Two epochs of eEVN observations at 5.0 GHz, taken in 2008, revealed the presence of a rich cluster of compact radio emitting sources in the central 150 pc of the nuclear starburst in Arp 299A. The large brightness temperatures observed for the compact sources indicate a non-thermal origin for the observed radio emission, implying that most, if not all, of those sources were young radio supernovae (RSNe) and supernova remnants (SNRs). More recently, contemporaneous EVN observations at 1.7 and 5.0 GHz taken in 2009 have allowed us to shed light on the compact radio emission of the parsec-scale structure in the nucleus of Arp 299-A. Namely, our EVN observations have shown that one of the compact VLBI sources, A1, previously detected at 5.0 GHz, has a flat spectrum between 1.7 and 5.0 GHz and is the brightest source at both frequencies. The morphology, radio luminosity, spectral index and ratio of radio-to-X-ray emission of the A1-A5 region allowed us to identify A1-A5 with long-sought AGN in Arp 299-A. This finding may suggest that both starburst and AGN are frequently associated phenomena in mergers. Finally, we also note that component A0, identified as a young RSN, exploded at the mere distance of two parsecs from the putative AGN in Arp 299-A, which makes this supernova one of the closest to a central supermassive black hole ever detected.
We report measurements of the cosmic microwave background (CMB) power spectrum from the complete 2008 South Pole Telescope (SPT) data set. We analyze twice as much data as the first SPT power spectrum analysis, using an improved cosmological parameter estimator which fits multi-frequency models to the SPT $150$ and $220\,$GHz bandpowers. We find an excellent fit to the measured bandpowers with a model that includes lensed primary CMB anisotropy, secondary thermal (tSZ) and kinetic (kSZ) Sunyaev-Zel'dovich anisotropies, unclustered synchrotron point sources, and clustered dusty point sources. In addition to measuring the power spectrum of dusty galaxies at high signal-to-noise, the data primarily constrain a linear combination of the kSZ and tSZ anisotropy contributions at $150\,$GHz and $\ell=3000$: $D^{tSZ}_{3000} + 0.5\,D^{kSZ}_{3000} = 4.5\pm 1.0 \,\mu{\rm K}^2$. The $95%$ confidence upper limits on secondary anisotropy power are $D^{tSZ}_{3000} < 5.3\,\mu{\rm K}^2$ and $D^{kSZ}_{3000} < 6.5\,\mu{\rm K}^2$. We also consider the potential correlation of dusty and tSZ sources, and find it incapable of relaxing the tSZ upper limit. These results increase the significance of the lower than expected tSZ amplitude previously determined from SPT power spectrum measurements. We find that models including non-thermal pressure support in groups and clusters predict tSZ power in better agreement with the SPT data. Combining the tSZ power measurement with primary CMB data halves the statistical uncertainty on $\sigma_8$. However, the preferred value of $\sigma_8$ varies significantly between tSZ models. Improved constraints on cosmological parameters from tSZ power spectrum measurements require continued progress in the modeling of the tSZ power.
We investigate the possibility of using the X-ray telescope (XRT) on board the Swift satellite to improve the current accuracy of the ICM temperature measurements in the region close to the virial radius of nearby clusters. We present the spectral analysis of the Swift XRT observations of 6 galaxy clusters and their temperature profiles in the regions within 0.2-0.6 r200. Four of them are nearby famous and very well studied objects (Coma, Abell 1795, Abell 2029 and PKS0745-19). The remaining two, SWJ1557+35 and SWJ0847+13, at redshift z=0.16 and z=0.36, were serendipitously observed by Swift-XRT. We accurately quantify the temperature uncertainties, with particular focus on the impact of the background scatter (both instrumental and cosmic). We extrapolate these results and simulate a deep observation of the external region of Abell 1795 which is assumed here as a case study. In particular we calculate the expected uncertainties in the temperature measurement as far as r200. We find that, with a fairly deep observation (300 ks), the Swift XRT would be able to measure the ICM temperature profiles in the external regions as far as the virial radius, significantly improving the best accuracy among the previous measurements. This can be achieved thanks to the unprecedented combination of good PSF over the full field of view and very accurate control of the instrumental background. Somehow unexpectedly we conclude that, among currently operating telescope, the Swift-XRT is the only potentially able to improve the current accuracy in plasma temperature measurement at the edges of the cluster potential. This will be true until a newgeneration of low-background and large field of view telescopes, aimed to the study of galaxy clusters, will operate. These observations would be of great importance in developing the observing strategy for suchmissions.
Cosmic magnetic fields may be generated during early cosmic phase transition, such as the QCD- or electroweak- transitions. The magnitude of the remainder of such fields at the present epoch crucially depends on the exponent $n$ of their (initially super-Hubble) large-scale tail, i.e. B(lambda) ~ lambda^(-n). It has been claimed that causality requires n=5/2, contrary to much earlier claims of n=3/2. Here we analyze this question in detail. First, we note that contrary to current belief, the large-scale magnetic field tail is not established at the phase transition itself, but rather continuoulsy evolves up to the present epoch. Neglecting turbulent flows we find n=7/2, i.e. very strongly suppressed large-scale fields. However, in the inevitable presence of turbulent flows we find that the large-scale magnetic field tail has sufficient time to evolve to that of the fluid turbulence. For white noise fluid turbulence this yields n=3/2 up to a certain scale and n=5/2 beyond for the magnetic field spectrum. This picture is also not changed when primordial viscosity and fluid flow dissipation is taken into account. Appreciable primordial magnetic fields originating from cosmic phase transitions seem thus possible.
Tidal stellar disruptions have traditionally been discussed as a probe of the single, massive black holes (MBHs) that are dormant in the nuclei of galaxies. In Chen et al. (2009), we used numerical scattering experiments to show that three-body interactions between bound stars in a stellar cusp and a non-evolving "hard" MBH binary will also produce a burst of tidal disruptions, caused by a combination of the secular "Kozai effect" and by close resonant encounters with the secondary hole. Here we derive basic analytical scalings of the stellar disruption rates with the system parameters, assess the relative importance of the Kozai and resonant encounter mechanisms as a function of time, discuss the impact of general relativistic (GR) and extended stellar cusp effects, and develop a hybrid model to self-consistently follow the shrinking of an MBH binary in a stellar background, including slingshot ejections and tidal disruptions. In the case of a fiducial binary with primary hole mass M_1=10^7\msun and mass ratio q=M_2/M_1=1/81, embedded in an isothermal cusp, we derive a stellar disruption rate \dot{N_*} ~ 0.2\,yr^{-1} lasting ~ 3X10^5 yr. This rate is 3 orders of magnitude larger than the corresponding value for a single MBH fed by two-body relaxation, confirming our previous findings. For q<<0.01, the Kozai/chaotic effect could be quenched due to GR/cusp effects by an order of magnitude, but even in this case the stellar-disruption rate is still two orders of magnitude larger than that given by standard relaxation processes around a single MBH. Our results suggest that >10% of the tidal-disruption events may originate in MBH binaries.
Annihilation of different dark matter (DM) candidates into Standard Model (SM) particles could be detected through their contribution to the gamma ray fluxes that are measured on the Earth. The magnitude of such contributions depends on the particular DM candidate, but certain imprints of produced photon spectra may be analyzed in a model-independent fashion. In this work we provide the fitting formulae for the photon spectra generated by WIMP annihilation into quarks, leptons and gauge bosons channels in a wide range of WIMP masses.
I present the theoretical evidence which suggests that gravity is an emergent phenomenon like gas dynamics or elasticity with the gravitational field equations having the same status as, say, the equations of fluid dynamics/elasticity. This paradigm views a wide class of gravitational theories - including Einstein's theory - as describing the thermodynamic limit of the statistical mechanics of "atoms of spacetime". The evidence for this paradigm is hidden in several classical features of the gravitational theories and depends on just one quantum mechanical input, viz. the existence of Davies-Unruh temperature of horizons. I discuss several conceptual ingredients of this approach.
The MPF mission will provide a statistical census of exoplanets with masses greater than 0.1 Earth-masses and orbital separations ranging from 0.5AU to infinity. This includes analogs to all the Solar System's planets except for Mercury, as well as most types of planets predicted by planet formation theories. Such a survey will provide results on the frequency of planets around all types of stars except those with short lifetimes. Close-in planets with separations < 0.5 AU are invisible to a space-based microlensing survey, but these can be found by Kepler. Other methods, including ground-based microlensing, cannot approach the comprehensive statistics on the mass and semi-major axis distribution of extrasolar planets that a space-based microlensing survey will provide. The terrestrial planet sensitivity of a ground-based microlensing survey is limited to the vicinity of the Einstein radius at 2-3 AU, and space-based imaging is needed to identify and determine the mass of the planetary host stars for the vast majority of planets discovered by microlensing. Thus, a space-based microlensing survey is likely to be the only way to gain a comprehensive understanding of the architecture of planetary systems, which is needed to understand planet formation and habitability. MPF can accomplish these objectives with proven technology and a cost of $333 million (excluding launch vehicle).
We provide ingredients and recipes for computing signals of TeV-scale Dark Matter annihilations and decays in the Galaxy and beyond. For each DM channel, we present the energy spectra of electrons and positrons, antiprotons, antideuterons, gamma rays, neutrinos and antineutrinos e, mu, tau at production, computed by high-statistics simulations. We estimate the Monte Carlo uncertainty by comparing the results yielded by the Pythia and Herwig event generators. We then provide the propagation functions for charged particles in the Galaxy, for several DM distribution profiles and sets of propagation parameters. Propagation of electrons and positrons is performed with an improved semi-analytic method that takes into account position-dependent energy losses in the Milky Way. Using such propagation functions, we compute the energy spectra of electrons and positrons, antiprotons and antideuterons at the location of the Earth. We then present the gamma ray fluxes, both from prompt emission and from Inverse Compton scattering in the galactic halo. Finally, we provide the spectra of extragalactic gamma rays. All results are available in numerical form and ready to be consumed.
We present a statistic for the detection of stochastic gravitational-wave backgrounds (SGWBs) using radiometry with a network of multiple baselines. We also quantitatively compare the sensitivities of existing baselines, and their network, to SGWBs. We assess how the measurement accuracy of signal parameters, e.g., the sky position of a localized source, can improve when using a network of baselines as compared to any of the single participating baselines. The search statistic itself is derived from the likelihood ratio of the cross-correlation of the data across all possible baselines in a detector network, and is optimal in Gaussian noise. Specifically, it is the likelihood-ratio maximized over the strength of the SGWB, and is called the maximized likelihood ratio (MLR). One of the main advantages of using the MLR over past search strategies for inferring the presence or absence of a signal is that the former does not require the deconvolution of the cross-correlation statistic. Therefore, it does not suffer from errors inherent to the deconvolution procedure and is, especially, useful for detecting weak sources. In the limit of a single baseline, it reduces to the detection statistic studied by Ballmer [Class. Quant. Grav. 23, S179 (2006)] and Mitra et al. [Phys. Rev. D 77, 042002 (2008)]. Unlike past studies, here the MLR statistic enables us to compare quantitatively the performances of a variety of baselines searching for a SGWB signal in (simulated) data. Although we use simulated noise and SGWB signals for making these comparisons, our method can be straightforwardly applied on real data.
From the particle physics point of view, the most peculiar property of the dark matter particle is its stability on cosmological time scales. We briefly review the possible origins of this characteristic feature for candidates whose relic density results from the thermal freeze-out of their annihilation. We emphasize that each stabilization mechanism implies an all specific phenomenology. The models reviewed include supersymmetric and non-supersymmetric models where the stability is a consequence of grand-unification, models where stability is due to an unbroken gauge group and models where the DM stability is accidental. The latter possibility includes minimal dark matter, hidden vector dark matter and composite DM models.
At the present work, it is studied the extension of F (R) gravities to the new recently proposed theory of gravity, the so-called Horava-Lifshitz gravity, which provides a way to make the theory power counting renormalizable by breaking Lorentz invariance. It is showed that dark energy can be well explained in the frame of this extension, just in terms of gravity. It is also explored the possibility to unify inflation and late-time acceleration under the same mechanism, providing a natural explanation the accelerated expansion.
We study the prospects of observing the presence of a relatively light Elko particle as a possible dark matter candidate, being produced at the LHC, with center of mass energy of 7 TeV and total luminosity from $1 fb^{-1}$ to $10 fb^{-1}$. It is analyzed an specific high order process and the result indicates that even in this case the number of events, considering the previous luminosity, is large enough to motivate a detailed analysis of such particle at high energy experiments.
We model the expected X-ray polarisation induced by complex reprocessing in the active nucleus of the Seyfert-2 galaxy NGC 1068. Recent analysis of infrared interferometry observations suggests that the ionised outflows ejected by the central engine are not aligned with the symmetry axis of the obscuring torus. This conclusion was obtained by extrapolating the apparent orientation of the narrow line region to the inner parts of the ionisation cones. We show that future measurements of the soft X-ray polarisation vector unambiguously determine the orientation of the ionisation cones. Furthermore, X-ray polarimetry across a broad photon energy range is going to independently verify the misalignment between the ionisation cones and the axis of the torus. To determine the expected polarisation percentage and position angle, we apply the radiative transfer code STOKES. Reprocessing of the primary X-ray radiation takes place in the accretion disc, the surrounding equatorial torus and the inclined, ionised outflows. Radiative coupling between these different components is computed coherently. The resulting polarisation properties depend on the optical depth of the reprocessing regions and on the viewing angle of the observer. We show that even under not favourable conditions the misalignment of the outflows with respect to the torus axis can be determined from a rotation of the polarisation position angle between softer and harder X-rays. The presence of an equatorial scattering region located between the accretion disk and the inner boundary of the torus leads to a more prominent difference in the polarisation vector. A measurement of the rotation is going to be possible with the latest generation of X-ray imaging polarimeters, such as proposed for the New Hard X-ray Mission.
Whereas preheating after chaotic and hybrid inflation models has been abundantly studied in the literature, preheating in small field inflation models, where the curvature of the inflaton potential is negative during inflation, remains less explored. In these models, a tachyonic instability at the end of inflation leads to a succession of exponentially large increases and \emph{decreases} of the inflaton fluctuations as the inflaton condensate oscillates around the minimum of its potential. The net effect is a competition between low-momentum modes which grow and decrease significantly, and modes with higher momenta which grow less but also decrease less. We develop an analytical description of this process, which is analogous to the quantum mechanical problem of tunneling through a volcano-shaped potential. Depending on the parameters, preheating may be so efficient that it completes in less than one oscillation of the inflaton condensate. Preheating after small field inflation may also be followed by a long matter-dominated stage before the universe thermalizes, depending on the energy scale of inflation and the details of the inflaton interactions. Finally, another feature of these models is that the spectrum of the inflaton fluctuations at the end of preheating may be peaked around the Hubble scale. In fact, because preheating starts when the second slow-roll parameter $|\eta|$ becomes of order unity while the first slow-roll parameter $\epsilon$ is still much smaller than one, the universe is still inflating during preheating and the modes amplified by the initial tachyonic instability leave the Hubble radius. This may lead to an abundant production of primordial black holes and gravitational waves with frequencies today which are naturally small enough to fall into the range accessible by high-sensitivity interferometric experiments.
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We use archival data of NASA's Chandra X-ray telescope to compile an X-ray light curve of all four images of the quadruply lensed quasar Q2237+0305 (z=1.695) from January 2006 to January 2007. We fit simulated point spread functions to the four individual quasar images using Cash's C-statistic to account for the Poisson nature of the X-ray signal. The quasar images display strong flux variations up to a factor of ~4 within one month. We can disentangle the intrinsic quasar variability from flux variations due to gravitational microlensing by looking at the flux ratios of the individual quasar images. Doing this, we find evidence for microlensing in image A. In particular, the time-sequence of the flux ratio A/B in the X-ray regime correlates with the corresponding sequence in the optical monitoring by OGLE in the V-band. The amplitudes in the X-ray light curve are larger. For the most prominent peak, the increase of the X-ray ratio A/B is larger by a factor ~1.6 compared to the signal in the optical. In agreement with theory and other observations of multiply imaged quasars, this suggests that the X-ray emission region of this quasar is significantly smaller than the optical emission region.
A new approach is given for the implementation of boundary conditions used in solving the Mukhanov-Sasaki equation in the context of inflation. The familiar quantization procedure is reviewed, along with a discussion of where one might expect deviations from the standard approach to arise. The proposed method introduces a (model dependent) fitting function for the z"/z and a"/a terms in the Mukhanov-Sasaki equation for scalar and tensor modes, as well as imposes the boundary conditions at a finite conformal time. As an example, we employ a fitting function, and compute the spectral index, along with its running, for a specific inflationary model which possesses background equations that are analytically solvable. The observational upper bound on the tensor to scalar ratio is used to constrain the parameters of the boundary conditions in the tensor sector as well. An overview on the generalization of this method is also discussed.
The luminosity gap between the two brightest members of galaxy groups and clusters is thought to offer a strong test for the models of galaxy formation and evolution. This study focuses on the statistics of the luminosity gap in galaxy groups, in particular fossil groups, e.g. large luminosity gap, in an analogy with the same in a cosmological simulation. We use spectroscopic legacy data of seventh data release (DR7) of SDSS, to extract a volume limited sample of galaxy groups utilizing modified friends-of-friends (mFoF) algorithm. Attention is paid to galaxy groups with the brightest group galaxy (BGG) more luminous than \Mr = -22. An initial sample of 620 groups in which 109 optical fossil groups, where the luminosity gap exceeds 2 magnitude, were identified. We compare the statistics of the luminosity gap in galaxy groups at low mass range from the SDSS with the same in the Millennium simulations where galaxies are modeled semi-analytically. We show that the BGGs residing in galaxy groups with large luminosity gap, i.e. fossil groups, are on average brighter and live in lower mass halos with respect to their counter parts in non-fossil systems. Although low mass galaxy groups are thought to have recently formed, we show that in galaxy groups with 15 galaxies brighter than $M_r\ge -19.5$, evolutionary process are most likely to be responsible for the large luminosity gap. We also examine a new probe of finding fossil group. In addition we extend the recently introduced observational probe based on the luminosity gap, the butterfly diagram, to galaxy groups and study the probe as a function of halo mass. This probe can, in conjunction with the luminosity function, help to fine tune the semi-analytic models of galaxies employed in the cosmological simulations.
We address the issue of the cosmological bias between matter and galaxy distributions, looking at dark-matter haloes as a first step to characterize galaxy clustering. Starting from the linear density field at high redshift, we follow the centre of mass trajectory of the material that will form each halo at late times (proto-halo). We adopt a fluid-like description for the evolution of perturbations in the proto-halo distribution, which is coupled to the matter density field via gravity. We present analytical solutions for the density and velocity fields, in the context of renormalized perturbation theory. We start from the linear solution, then compute one-loop corrections for the propagator and the power spectrum. Finally we analytically resum the propagator and we use a suitable extension of the time-renormalization-group method (Pietroni 2008) to resum the power spectrum. For halo masses M<10^{14} Msol/h our results at z=0 are in good agreement with N-body simulations. Our model is able to predict the halo-matter cross spectrum with an accuracy of 5 per cent up to k = 0.1 h/Mpc approaching the requirements of future galaxy redshift surveys.
We present a pilot narrow-band survey of H-alpha emitters at z=2.2 in the Great Observatories Origins Deep Survey North (GOODS-N) field with MOIRCS instrument on the Subaru telescope. The survey reached a 3 sigma limiting magnitude of 23.6 (NB209) which corresponds to a 3 sigma limiting line flux of 2.5 x 10^-17 erg s^-1 cm^-2 over a 56 arcmnin^2 contiguous area (excluding a shallower area). From this survey, we have identified 11 H-alpha emitters and one AGN at z=2.2 on the basis of narrow-band excesses and photometric redshifts. We obtained spectra for seven new objects among them, including one AGN, and an emission line above 3 sigma is detected from all of them. We have estimated star formation rates (SFR) and stellar masses (M_star) for individual galaxies. The average SFR and M_star is 27.8M_solar yr^-1 and 4.0 x 10^10M_solar, respectivly. Their specific star formation rates are inversely correlated with their stellar masses. Fitting to a Schechter function yields the H-alpha luminosity function with log L = 42.82, log phi = -2.78 and alpha = -1.37. The average star formation rate density in the survey volume is estimated to be 0.31M_solar yr^-1Mpc^-3 according to the Kennicutt relation between H-alpha luminosity and star formation rate. We compare our H-alpha emitters at z=2.2 in GOODS-N with narrow-band line emitters in other field and clusters to see their time evolution and environmental dependence. We find that the star formation activity is reduced rapidly from z=2.5 to z=0.8 in the cluster environment, while it is only moderately changed in the field environment. This result suggests that the timescale of galaxy formation is different among different environments, and the star forming activities in high density regions eventually overtake those in lower density regions as a consequence of "galaxy formation bias" at high redshifts.
In order to test the possible interaction between dark energy and dark matter, we investigate observational constraints on a phenomenological scenario, in which the ratio between the dark energy and matter energy densities is proportional to the pow law case of the scale factor, $r\equiv (\rho_X/\rho_m)\propto a^{\xi}$. With the newly revised $H(z)$ data, as well as the cosmic microwave background (CMB) observation from the 7-year Wilkinson Microwave Anisotropy Probe (WMAP7) results, the baryonic acoustic oscillation (BAO) observation from the spectroscopic Sloan Digital Sky Survey (SDSS) Data Release and the type Ia supernovae (SNe Ia) from Union2 set, by using the Markov Chain Monte Carlo (MCMC) method, we obtain $\Omega_{m0}=0.253_{-0.018}^{+0.020}$ and $\xi=3.07_{-0.11}^{+0.12}$ for the phenomenological $\Lambda$CDM scenario; and $\Omega_{m0}=0.276_{-0.028}^{+0.028}$, $\xi=3.41_{-0.52}^{+0.61}$, and $w_X=-1.07_{-0.13}^{+0.12}$ for the phenomenological $w$CDM scenario with a constant EoS of dark energy. These results show that the standard $\Lambda$CDM model without any interaction remains a good fit to the recent observational data; however, the interaction that the energy transferring from dark matter to dark energy is slightly favored over the interaction from dark energy to dark matter. It is also shown that the $H(z)$ data can provide strong constraints on the phenomenological interacting scenario when combined with CMB and BAO observations, and the confidence regions of $H(z)$+BAO+CMB, SNe Ia+BAO+CMB, and SNe Ia+$H(z)$+BAO+CMB combinations are consistent with each other.
We study non-Gaussianity generated by adiabatic and isocurvature primordial perturbations. We first obtain, in a very general setting, the non-linear perturbations, up to third order, for an arbitrary number of cosmological fluids, going through one or several decay transitions. We then apply this formalism to the mixed curvaton and inflaton model, allowing for several decay channels. We compute the various contributions to the bispectrum and trispectrum resulting from adiabatic and isocurvature perturbations, which are correlated in general. By investigating some hybrid decay scenario, we show that significant non-Gaussianity of adiabatic and isocurvature types can be generated without conflicting with the present isocurvature constraints from the power spectrum. In particular, we find cases where non-Gaussianity of isocurvature origin can dominate its adiabatic counterpart, both in the bispectrum and in the trispectrum.
We present a short (and necessarily incomplete) review of the evidence for the accelerated expansion of the Universe. The most direct probe of acceleration relies on the detailed study of supernovae (SN) of type Ia. Assuming that these are standardizable candles and that they fairly sample a homogeneous and isotropic Universe, the evidence for acceleration can be tested in a model- and calibration-independent way. Various light-curve fitting procedures have been proposed and tested. While several fitters give consistent results for the so-called Constitution set, they lead to inconsistent results for the recently released SDSS SN. Adopting the SALT fitter and relying on the Union set, cosmic acceleration is detected by a purely kinematic test at 7 sigma when spatial flatness is assumed and at 4 sigma without assumption on the spatial geometry. A weak point of the described method is the local set of SN (at z < 0.2), as these SN are essential to anchor the Hubble diagram. These SN are drawn from a volume much smaller than the Hubble volume and could be affected by local structure. Without the assumption of homogeneity, there is no evidence for acceleration, as the effects of acceleration are degenerate with the effects of inhomogeneities. Unless we sit in the centre of the Universe, such inhomogeneities can be constrained by SN observations by means of tests of the isotropy of the Hubble flow.
The metal-poor Cepheids in the dwarf galaxies IC 1613, WLM, Pegasus, Sextans A and B, and Leo A are compared with the about equally metal-poor Cepheids of SMC. The period-color (P-C) and period-luminosity (P-L) relations - extended to the shortest periods and for overtone pulsators - of the six galaxies are undistinguishable, but are distinctly different from those in LMC and the solar neighborhood. Adopting (m-M)^{0}_{SMC}=18.93 from independent evidence, one can determine reliable distance moduli for the other dwarf galaxies: (m-M)^{0} = 24.36+/-0.02, 24.81+/-0.04, 24.86+/-0.06, 25.62+/-0.04, and 24.63+/-0.04, respectively. They are in good agreement with independent moduli from RR Lyrae stars and the tip of the red-giant branch (TRGB).
Significant historic cosmic evolution for the formation rate of stellar black holes is inferred from current theoretical models of the evolution of massive stars, the multiple observations of compact stellar remnants in the near and distant universe, and the cosmic chemical evolution. The mean mass of stellar black holes, the fraction of black holes/neutron stars, and the fraction of black hole high mass X-ray binaries (BH-HMXBs)/solitary black holes increase with redshift. The energetic feedback from large populations of BH-HMXBs form in the first generations of star burst galaxies has been overlooked in most cosmological models of the reionization epoch of the universe. The powerful radiation, jets, and winds from BH-HMXBs heat the intergalactic medium over large volumes of space and keep it ionized until AGN take over. It is concluded that stellar black holes constrained the properties of the faintest galaxies at high redshifts. I present here the theoretical and observational grounds for the historic cosmic evolution of stellar black holes. Detailed calculations on their cosmic impact are presented elsewhere (Mirabel, Dijkstra, Laurent, Loeb, Pritchard, 2011).
We consider a holographic cosmological model in which the infrared cutoff is fixed by the Ricci's length and dark matter and dark energy do not evolve separately but interact non-gravitationally with one another. This substantially alleviates the cosmic coincidence problem as the ratio between both components remains finite throughout the expansion. We constrain the model with observational data from supernovae, cosmic background radiation, baryon acoustic oscillations, gas mass fraction in galaxy clusters, the history of the Hubble function, and the growth function. The model shows consistency with observation.
Current studies of the Sunyaev-Zel'dovich (SZ) effect are based on parameterized models of galaxy clusters. Investigating the effects of different parameterizations and the assumptions made within any parameterized model are,therefore, crucial in extracting cluster physical properties in a robust way. In this paper, we study three different parameterizations of the well-studied isothermal beta-model applied to a simulated Arcminute Microkelvin Imager observation of a galaxy cluster through its SZ effect. We propose a method for generating simulated SZ data that leads to consistent values of cluster physical properties upon employing different parameterization methods. The results of our study clearly reveal different biases and constraints induced by each parameterization. We also find that the way in which conventional assumptions on the dynamical state of the gas and dark matter are applied to a parameterized cluster model play a significant role in both determining degeneracies and deriving apparent constraints. By comparing different parameterizations, we confirm the model parameters that cannot be constrained by SZ data alone. We also find that the assumption of isothermality when the cluster hot gas is in hydrostatic equilibrium with its total gravitational potential introduces clear biases in the posterior probability distributions of the cluster parameters, as the temperature gradient is eliminated from the analysis. However, our results show that by employing a scaling relation to link cluster total mass internal to the virial radius with mean temperature, we are able to obtain reliable results for extracting physical cluster parametes compared to the corresponding true input values in the simulation .
We study the cosmic microwave background temperature and polarisation spectra sourced by multi-tension cosmic superstring networks. First we obtain solutions for the characteristic length scales and velocities associated with the evolution of a network of F-D strings, allowing for the formation of junctions between strings of different tensions. We find two distinct regimes describing the resulting scaling distributions for the relative densities of the different types of strings, depending on the magnitude of the fundamental string coupling g_s. In one of them, corresponding to the value of the coupling being of order unity, the network's stress-energy power spectrum is dominated by populous light F and D strings, while the other regime, at smaller values of g_s, has the spectrum dominated by rare heavy D strings. These regimes are seen in the CMB anisotropies associated with the network. We focus on the dependence of the shape of the B-mode polarisation spectrum on g_s and show that measuring the peak position of the B-mode spectrum can point to a particular value of the string coupling. Finally, we assess how this result, along with pulsar bounds on the production of gravitational waves from strings, can be used to constrain a combination of g_s and the fundamental string tension mu_F. Since CMB and pulsar bounds constrain different combinations of the string tensions and densities, they result in distinct shapes of bounding contours in the (mu_F, g_s) parameter plane, thus providing complementary constraints on the properties of cosmic superstrings.
If Dark Energy introduces an acceleration in the universal expansion then large scale gravitational potential wells should be shrinking, causing a blueshift in the CMB photons that cross such structures (Integrated Sachs-Wolfe effect, [ISW]). Galaxy clusters are known to probe those potential wells. In these objects, CMB photons also experience inverse Compton scattering off the hot electrons of the intra-cluster medium, and this results in a distortion with a characteristic spectral signature of the CMB spectrum (the so-called thermal Sunyaev-Zel'dovich effect, [tSZ]). Since both the ISW and the tSZ effects take place in the same potential wells, they must be spatially correlated. We present how this cross ISW-tSZ signal can be detected in a CMB-data contained way by using the frequency dependence of the tSZ effect in multi frequency CMB experiments like {\it Planck}, {\em without} requiring the use of external large scale structure tracers data. We find that by masking low redshift clusters, the shot noise level decreases significantly, boosting the signal to noise ratio of the ISW--tSZ cross correlation. We also find that galactic and extragalactic dust residuals must be kept at or below the level of ~0.04 muK^2 at l=10, a limit that is a factor of a few below {\it Planck}'s expectations for foreground subtraction. If this is achieved, CMB observations of the ISW-tSZ cross correlation should also provide an independent probe for the existence of Dark Energy and the amplitude of density perturbations.
Recently, de Roany & Pacheco (2010) performed a Newtonian analysis on the evolution of perturbations for a class of relativistic cosmological models with Creation of Cold Dark Matter (CCDM) proposed by the present authors. In this note we demonstrate that the basic equations adopted in their work do not recover the specific (unperturbed) CCDM model. Unlike to what happens in the original CCDM cosmology, their basic conclusions refer to a decelerating cosmological model in which there is no transition from a decelerating to an accelerating regime as required by SNe type Ia and complementary observations.
Results are presented from a reanalysis of the entire five-tower data set acquired with the Cryogenic Dark Matter Search (CDMS II) experiment at the Soudan Underground Laboratory, with an exposure of 969 kg-days. The analysis window was extended to a recoil energy of 150 keV, and an improved surface-event background-rejection cut was defined to increase the sensitivity of the experiment to the inelastic dark matter (IDM) model. Three dark matter candidates were found between 25 keV and 150 keV. The probability to observe three or more background events in this energy range is 11%. Due to the occurrence of these events the constraints on the IDM parameter space are slightly less stringent than those from our previous analysis, which used a narrower energy window of 10-100 keV.
We examine the rest-frame far-infrared emission from powerful radio sources with 1.4GHz luminosity densities of 25<=log(L_1.4/WHz^-1)<=26.5 in the extragalactic Spitzer First Look Survey field. We combine Herschel/SPIRE flux densities with Spitzer/IRAC and MIPS infrared data to obtain total (8-1000um) infrared luminosities for these radio sources. We separate our sources into a moderate, 0.4<z<0.9, and a high, 1.2<z<3.0, redshift sub-sample and we use Spitzer observations of a z<0.1 3CRR sample as a local comparison. By comparison to numbers from the SKA Simulated Skies we find that our moderate redshift sample is complete and our high redshift sample is 14per cent complete. We constrain the ranges of mean star formation rates (SFRs) to be 3.4-4.2, 18-41 and 80-581Msun/yr for the local, moderate and high redshift samples respectively. Hence, we observe an increase in the mean SFR with increasing redshift which we can parameterise as ~(1+z)^Q, where Q=4.2+/-0.8. However we observe no trends of mean SFR with radio luminosity within the moderate or high redshift bins. We estimate that radio-loud AGN in the high redshift sample contribute 0.1-0.5per cent to the total SFR density at that epoch. Hence, if all luminous starbursts host radio-loud AGN we infer a radio-loud phase duty cycle of 0.001-0.005.
We present the details of a method for conducting a targeted, coherent search for compact binary coalescences. The search is tailored to be used as a followup to electromagnetic transients such as Gamma Ray Bursts. We derive the coherent search statistic for Gaussian detector noise and discuss the benefits of a coherent, multi-detector search over coincidence methods. To mitigate the effects of non-stationary data, we introduce a number of signal consistency tests, including the null SNR, amplitude consistency and several $\chi^{2}$ tests. We demonstrate the search performance on Gaussian noise and on data from LIGO's fourth science run and verify that the signal consistency tests are capable of removing the majority of noise transients and the search gives an efficiency comparable to that achieved in Gaussian noise.
In order to precisely determine temperature and density of molecular gas in the Large Magellanic Cloud, we made observations of optically thin $^{13}$CO($J=3-2$) transition by using the ASTE 10m telescope toward 9 peaks where $^{12}$CO($J=3-2$) clumps were previously detected with the same telescope. The molecular clumps include those in giant molecular cloud (GMC) Types I (with no signs of massive star formation), II (with HII regions only), and III (with HII regions and young star clusters). We detected $^{13}$CO($J=3-2$) emission toward all the peaks and found that their intensities are 3 -- 12 times lower than those of $^{12}$CO($J=3-2$). We determined the intensity ratios of $^{12}$CO($J=3-2$) to $^{13}$CO($J=3-2$), $R^{12/13}_{3-2}$, and $^{13}$CO($J=3-2$) to $^{13}$CO($J=1-0$), $R^{13}_{3-2/1-0}$, at 45$\arcsec$ resolution. These ratios were used for radiative transfer calculations in order to estimate temperature and density of the clumps. The parameters of these clumps range kinetic temperature $T\mathrm{_{kin}}$ = 15 -- 200 K, and molecular hydrogen gas density $n(\mathrm{H_2})$ = 8$\times 10^2$ -- 7$\times 10^3$ cm$^{-3}$. We confirmed that the higher density clumps show higher kinetic temperature and that the lower density clumps lower kinetic temperature at a better accuracy than in the previous work. The kinetic temperature and density increase generally from a Type I GMC to a Type III GMC. We interpret that this difference reflects an evolutionary trend of star formation in molecular clumps. The $R^{13}_{3-2/1-0}$ and kinetic temperature of the clumps are well correlated with H$\alpha$ flux, suggesting that the heating of molecular gas $n(\mathrm{H_2})$ = $10^3$ -- $10^4$ cm$^{-3}$ can be explained by stellar FUV photons.
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We show how to estimate the enclosed mass from the observed motions of an ensemble of test particles. Traditionally, this problem has been attacked through virial or projected mass estimators. Here, we examine and extend these systematically, and show how to construct an optimal estimator for any given assumption as to the potential. The estimators do not explicitly depend on any properties of the density of the test objects, which is desirable as in practice such information is dominated by selection effects. As particular examples, we also develop estimators tailored for the problem of estimating the mass of the Hernquist or NFW dark matter haloes from the projected positions and velocities of stars.
We present the first direct and unbiased measurement of the evolution of the dust mass function of galaxies over the past 5 billion years of cosmic history using data from the Science Demonstration Phase of the Herschel-ATLAS. The sample consists of galaxies selected at 250um which have reliable counterparts from SDSS at z<0.5, and contains 1867 sources. Dust masses are calculated through fitting the spectral energy distributions of the galaxies and are shown to be dominated by cold dust at 15-25 K. The dust temperature shows no trend with redshift. Splitting the sample into bins of redshift reveals a strong evolution in the dust properties of the most massive galaxies. At z=0.4-0.5, massive galaxies had dust masses about five times larger than in the local Universe. At the same time, the dust-to-stellar mass ratio was about 3-4 times larger, and the optical depth derived from fitting the UV-sub-mm data with an energy balance model was also higher. This increase in the dust content of massive galaxies at high redshift is difficult to explain using standard dust evolution models and requires a rapid gas consumption timescale together with either a more top-heavy IMF, efficient mantle growth, less dust destruction or combinations of all three. This evolution in dust mass can also be associated with a change in overall ISM mass, and points to an enhanced supply of fuel for star formation at earlier cosmic epochs.
The new VISual and Infrared Telescope for Astronomy (VISTA) has started operations. Over its first five years it will be collecting data for six public surveys, one of these is the near-infrared YJKsVISTA survey of the Magellanic Clouds system (VMC). This survey comprises the LMC, the SMC, the Bridge connecting the two galaxies and two fields in the Stream. This paper provides an overview of the VMC survey strategy and presents first science results. The main goals of the VMC survey are the determination of the spatially resolved SFH and 3D structure of the Magellanic system. Therefore, the VMC survey is designed to reach stars as faint as the oldest main sequence turn-off point and to constrain the mean magnitude of pulsating variable stars such as RR Lyrae stars and Cepheids. This paper focuses on observations of VMC fields in the LMC obtained between November 2009 and March 2010. These observations correspond to a 7% completeness of the LMC fields. The VMC observations consist of multi-epoch measurements organised following a specific structure. The data were reduced using the VISTA Data Flow System pipeline whose source catalogues were produced and made available via the VISTA Science Archive. The analysis of the data shows that the sensitivity in each wave band agrees with expectations. Uncertainties and completeness of the data are also derived. The first science results, aimed at assessing the science quality of the VMC data, include an overview of the distribution of stars in colour-magnitude and colour-colour diagrams, the detection of planetary nebulae and of stellar clusters, and the Ks band light-curve of variable stars. The VMC survey represents a tremendous improvement, in spatial resolution and sensitivity, on previous panoramic observations of the Magellanic system in the near-infrared and complements nicely the deep observations at other wavelengths. (Abridged)
This lecture is a sketch of the physics of the cosmic microwave background. The observed anisotropy can be divided into four main contributions: variations in the temperature and gravitational potential of the primordial plasma, Doppler effect from its motion, and a net red/blueshift the photons accumulate from traveling through evolving gravitational potentials on their way from the primordial plasma to here. These variations are due to primordial perturbations, probably caused by quantum fluctuations in the very early universe. The ongoing Planck satellite mission to observe the cosmic microwave background is also described.
Galaxy interactions and mergers play a significant, but still debated and poorly understood role in the star formation history of galaxies. Numerical and theoretical models cannot yet explain the main properties of merger-induced starbursts, including their intensity and their spatial extent. Usually, the mechanism invoked in merger-induced starbursts is a global inflow of gas towards the central kpc, resulting in a nuclear starburst. We show here, using high-resolution AMR simulations and comparing to observations of the gas component in mergers, that the triggering of starbursts also results from increased ISM turbulence and velocity dispersions in interacting systems. This forms cold gas that are denser and more massive than in quiescent disk galaxies. The fraction of dense cold gas largely increases, modifying the global density distribution of these systems, and efficient star formation results. Because the starbursting activity is not just from a global compacting of the gas to higher average surface densities, but also from higher turbulence and fragmentation into massive and dense clouds, merging systems can enter a different regime of star formation compared to quiescent disk galaxies. This is in quantitative agreement with recent observations suggesting that disk galaxies and starbursting systems are not the low-activity end and high-activity end of a single regime, but actually follow different scaling relations for their star formation.
We study the effect of inhomogeneities on light propagation. The Sachs equations are solved numerically in the Swiss-Cheese models with inhomogeneities modelled by the Lemaitre-Tolman solutions. Our results imply that, within the models we study, inhomogeneities may partially mimic the accelerated expansion of the Universe, but the effect is small.
We investigate the nonlinear power spectra of density perturbations and acoustic oscillations in growing neutrino quintessence. In this scenario, the neutrino mass has a strong dependence on the quintessence field. The induced coupling stops the evolution of the field when the neutrinos become nonrelativistic, and triggers the transition to the accelerating phase of the cosmological expansion. At redshifts around five, the neutrino fluctuations are still linear and acoustic oscillations are present in the neutrino power spectrum, induced by the acoustic oscillations in the baryonic and dark-matter sectors. The neutrino perturbations become nonlinear at redshifts around three. The mode coupling generated by the nonlinearities erases the oscillations in the neutrino spectrum at some redshift above two. There is a potential danger that at later times the influence of the gravitational potentials induced by the neutrino inhomogeneities could erase the oscillations from the baryonic and dark-matter spectra, making the scenario incompatible with observations. For the scenario to be viable, the neutrino-induced gravitational potentials in the range of baryonic acoustic oscillations should not grow to average values much larger than 10^{-4}. The magnitude of the expected potentials is still not known reliably, as the process of structure formation is poorly understood in growing neutrino quintessence.
We describe a novel approach to accelerating Monte Carlo Markov Chains. Our focus is cosmological parameter estimation, but the algorithm is applicable to any problem for which the likelihood surface is a smooth function of the free parameters and computationally expensive to evaluate. We generate a high-order interpolating polynomial for the log-likelihood using the first points gathered by the Markov chains as a training set. This polynomial then accurately computes the majority of the likelihoods needed in the latter parts of the chains. We implement a simple version of this algorithm as a patch (InterpMC) to CosmoMC and show that it accelerates parameter estimatation by a factor of between two and four for well-converged chains. The current code is primarily intended as a "proof of concept", and we argue that there is considerable room for further performance gains. Unlike other approaches to accelerating parameter fits, we make no use of precomputed training sets or special choices of variables, and InterpMC is almost entirely transparent to the user.
Chameleons are scalar fields that couple directly to ordinary matter with gravitational strength, but which nevertheless evade the stringent constraints on tests of gravity because of properties they acquire in the presence of high ambient matter density. Chameleon theories were originally constructed in a bottom-up, phenomenological fashion, with potentials and matter couplings designed to hide the scalar from experiments. In this paper, we attempt to embed the chameleon scenario within string compactifications, thus UV completing the scenario. We look for stabilized potentials that can realize a screening mechanism, and we find that the volume modulus rather generically works as a chameleon, and in fact the supersymmetric potential used by Kachru, Kallosh, Linde and Trivedi (KKLT) is an example of this type. We consider all constraints from tests of gravity, allowing us to put experimental constraints on the KKLT parameters.
It is well known that global symmetries protect local supersymmetry and a zero value for the cosmological constant in no--scale supergravity. The breakdown of these symmetries, which ensure the vanishing of the vacuum energy density, results in a set of degenerate vacua with broken and unbroken supersymmetry leading to the natural realisation of the multiple point principle (MPP). Assuming the degeneracy of vacua with broken and unbroken SUSY in the hidden sector we estimate the value of the cosmological constant. We argue that the observed value of the dark energy density can be reproduced in the split-SUSY scenario if the SUSY breaking scale is of the order of 10^{10} GeV.
We study the collision of two particles with the different rest masses moving in the equatorial plane of a Kerr-Taub-NUT black hole and get the center-of-mass (CM) energy for the particles. We find that the CM energy depends not only on the rotation parameter of the black hole, $a$, but also on the NUT charge of the black hole, $n$. Especially, for the extremal black hole, an unlimited CM energy can be approached if the parameter $a$ is in the range $[1,\sqrt{2}]$, which is different from that of the Kerr and Kerr-Newman black holes.
We present chemodynamical simulations of a Milky Way-type galaxy using a self-consistent hydrodynamical code that includes supernova feedback and chemical enrichment, and predict the spatial distribution of elements from Oxygen to Zinc. In the simulated galaxy, the kinematical and chemical properties of the bulge, disk, and halo are consistent with the observations. The bulge formed from the assembly of subgalaxies at z>3, and has higher [alpha/Fe] ratios because of the small contribution from Type Ia Supernovae. The disk formed with a constant star formation over 13 Gyr, and shows a decreasing trend of [alpha/Fe] and increasing trends of [(Na,Al,Cu,Mn)/Fe] against [Fe/H]. However, the thick disk stars tend to have higher [alpha/Fe] and lower [Mn/Fe] than thin disk stars. We also predict the frequency distribution of elemental abundance ratios as functions of time and location, which can be directly compared with galactic archeology projects such as HERMES.
In order to assess the role of ghosts in cosmology, we study the evolution of linear cosmological perturbations during inflation when a Weyl term is added to the action. Our main result is that vector perturbations can no longer be ignored and that scalar modes diverge in the newtonian gauge but remain bounded in the comoving slicing.
We define a family of spacetimes representing isolated black holes exhibiting remarkable universal properties which are natural generalizations from stationary space-times. They admit a well defined notion of surface gravity k_H. This generalized surface gravity mediates an exponential relation between a regular null coordinate $w$ near the horizon and an asymptotic Bondi null coordinate $u$ defined in the vicinity of future null infinity. Our construction provides a framework for the study of gravitational collapse of an isolated system in its late stage of evolution.
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