We analyze rest-frame optical morphologies and gas-phase kinematics as traced by rest-frame far-UV and optical spectra for a sample of 204 star forming galaxies in the redshift range z ~ 2-3 drawn from the Keck Baryonic Structure Survey (KBSS). We find that spectroscopic properties and gas-phase kinematics are closely linked to morphology: compact galaxies with semi-major axis radii r \lesssim 2 kpc are substantially more likely than their larger counterparts to exhibit LyA in emission. Although LyA emission strength varies widely within galaxies of a given morphological type, all twelve galaxies with LyA equivalent width W_LyA > 30 A have small semi-major axes. The velocity structure of absorption lines in the galactic continuum spectra also varies as a function of morphology. Galaxies of all morphological types drive similarly strong outflows (as traced by the blue wing of interstellar absorption line features), but the outflows of larger galaxies are less highly ionized and exhibit larger optical depth at the systemic redshift that may correspond to a decreasing efficiency of feedback in evacuating gas from the galaxy. This v ~ 0 km/s gas is responsible both for shifting the mean absorption line redshift and attenuating W_LyA (via a longer resonant scattering path) in galaxies with larger rest-optical half light radii. In contrast to galaxies at lower redshifts, there is no evidence for a correlation between outflow velocity and inclination, suggesting that outflows from these puffy and irregular systems may be poorly collimated. (Abbrev.)
We present a new method that simultaneously solves for cosmology and galaxy bias on non-linear scales. The method uses the halo model to analytically describe the (non-linear) matter distribution, and the conditional luminosity function (CLF) to specify the halo occupation statistics. For a given choice of cosmological parameters, this model can be used to predict the galaxy luminosity function, as well as the two-point correlation functions of galaxies, and the galaxy-galaxy lensing signal, both as function of scale and luminosity. In this paper, the first in a series, we present the detailed, analytical model, which we test against mock galaxy redshift surveys constructed from high-resolution numerical $N$-body simulations. We demonstrate that our model, which includes scale-dependence of the halo bias and a proper treatment of halo exclusion, reproduces the 3-dimensional galaxy-galaxy correlation and the galaxy-matter cross-correlation (which can be projected to predict the observables) with an accuracy better than 10 (in most cases 5) percent. Ignoring either of these effects, as is often done, results in systematic errors that easily exceed 40 percent on scales of $\sim 1 h^{-1}\Mpc$, where the data is typically most accurate. Finally, since the projected correlation functions of galaxies are never obtained by integrating the redshift space correlation function along the line-of-sight out to infinity, simply because the data only cover a finite volume, they are still affected by residual redshift space distortions (RRSDs). Ignoring these, as done in numerous studies in the past, results in systematic errors that easily exceed 20 perent on large scales ($r_\rmp \gta 10 h^{-1}\Mpc$). We show that it is fairly straightforward to correct for these RRSDs, to an accuracy better than $\sim 2$ percent, using a mildly modified version of the linear Kaiser formalism.
The simple, yet profoundly far-reaching classification scheme based on extended radio morphologies of radio galaxies, the Fanaroff-Riley classification has been a cornerstone in our understanding of radio galaxies. Over the decades since the recognition that there are two basic types of radio galaxy morphologies there have been several findings in different wavebands that have reported properties on different scales. Although it is realized that there may be intrinsic as well external causes an overarching view of how we may understand the two morphological types is missing. With the radio power-absolute magnitude relation (the Owen-Ledlow diagram) as backdrop we review and develop an understanding of the two radio galaxy types in the light of what is known about them. We have for the first time included the dust properties of the two FR classes together with the relative orientations of dust, host major axis and the radio axis to present a qualitative framework within which to understand the conditions under which they form. (Abridged).
We present supernova rate measurements at redshift 0.1-1.0 from the Stockholm VIMOS Supernova Survey (SVISS). The sample contains 16 supernovae in total. The discovered supernovae have been classified as core collapse or type Ia supernovae (9 and 7, respectively) based on their light curves, colour evolution and host galaxy photometric redshift. The rates we find for the core collapse supernovae are 3.29 (-1.78,-1.45)(+3.08,+1.98) x 10^-4 yr^-1 Mpc^-3 h70^3 (with statistical and systematic errors respectively) at <z> =0.39 and 6.40 (-3.12,-2.11)(+5.30,+3.65) x 10^-4 yr^-1 Mpc^-3 h70^3 at <z>=0.73. For the type Ia supernovae we find a rate of 1.29 (-0.57,-0.28)(+0.88,+0.27) x 10^-4 yr^-1 Mpc^-3 h70^3 at <z>=0.62. All of these rate estimates have been corrected for host galaxy extinction, using a method that includes supernovae missed in infrared bright galaxies at high redshift. We use Monte Carlo simulations to make a thorough study of the systematic effects from assumptions made when calculating the rates and find that the most important errors come from misclassification, the assumed mix of faint and bright supernova types and uncertainties in the extinction correction. We compare our rates to other observations and to the predicted rates for core collapse and type Ia supernovae based on the star formation history and different models of the delay time distribution. Overall, our measurements, when taking the effects of extinction into account, agree quite well with the predictions and earlier results. Our results highlight the importance of understanding the role of systematic effects, and dust extinction in particular, when trying to estimate the rates of supernovae at moderate to high redshift.
Here I will outline successes and challenges for finding spectral line sources in large data cubes that are dominated by noise. This is a 3D challenge as the sources we wish to catalog are spread over several spatial pixels and spectral channels. While 2D searches can be applied, e.g., channel by channel, optimal searches take into account the 3-dimensional nature of the sources. In this overview I will focus on HI 21-cm spectral line source detection in extragalactic surveys, in particular HIPASS, the "HI Parkes All-Sky Survey" and WALLABY, the "ASKAP HI All-Sky Survey". I use the original HIPASS data to highlight the diversity of spectral signatures of galaxies and gaseous clouds, both in emission and absorption. Among others, I report the discovery of a 680 km/s wide HI absorption trough in the megamaser galaxy NGC 5793. Issues such as source confusion and baseline ripples, typically encountered in single-dish HI surveys, are much reduced in interferometric HI surveys. Several large HI emission and absorption surveys are planned for the Australian Square Kilometre Array Pathfinder (ASKAP): here we focus on WALLABY, the 21-cm survey of the sky (Dec < +30 degr; z < 0.26) which will take about one year of observing time with ASKAP. Novel phased array feeds ("radio cameras") will provide 30 square degrees instantaneous field-of-view. WALLABY is expected to detect more than 500 000 galaxies, unveil their large-scale structures and cosmological parameters, detect their extended, low-surface brightness disks as well as gas streams and filaments between galaxies. It is a precursor for future HI surveys with SKA Phase I and II, exploring galaxy formation and evolution. The compilation of highly reliable and complete source catalogs will require sophisticated source-finding algorithms as well as accurate source parametrisation.
Simulations of galaxy evolution aim to capture our current understanding as well as to make predictions for testing by future experiments. Simulations and observations are often compared in an indirect fashion: physical quantities are estimated from the data and compared to models. However, many applications can benefit from a more direct approach, where the observing process is also simulated and the models are seen fully from the observer's perspective. To facilitate this, we have developed the Millennium Run Observatory (MRObs), a theoretical virtual observatory which uses virtual telescopes to `observe' semi-analytic galaxy formation models based on the suite of Millennium Run dark matter simulations. The MRObs produces data that can be processed and analyzed using the standard software packages developed for real observations. At present, we produce images in forty filters from the rest-frame UV to IR for two stellar population synthesis models, three different models of IGM absorption, and two cosmologies (WMAP1/7). Galaxy distributions for a large number of mock lightcones can be `observed' using models of major ground- and space-based telescopes. The data include lightcone catalogues linked to structural properties of galaxies, pre-observation model images, mock telescope images, and Source Extractor products that can all be traced back to the higher level dark matter, semi-analytic galaxy, and lightcone catalogues available in the Millennium database. Here, we describe our methods and announce a first public release of simulated observations for SDSS, CFHT-LS Wide/Deep, GOODS, ERS, CANDELS, and HUDF, and an online MRObs browser that facilitates exploration of these simulated data. We demonstrate the benefits of a direct approach through a number of example applications (deep galaxy counts, clusters, galaxy structures, and high-z dropouts).
Known populations of QSOs appear to fall short of producing the ionizing flux required for re-ionizing the universe. The alternative, galaxies as sources of ionizing photons, suffers from the problem that known types of galaxies are almost completely opaque to ionizing photons. For reionization to happen, either large numbers of (largely undiscovered) sources are required, or the known populations of galaxies need to have had a much larger escape fraction for ionizing radiation in the past. We discuss recent discoveries of faint z~3 Lyman alpha emitters with asymmetric, extended Lyman alpha emission regions, which apparently are related to interacting galaxies. The unusually shaped line profiles and the underlying stellar populations of these objects suggest the presence of damaged gaseous halos, infall of gas, tidal or stripped stellar features and young populations of hot stars, that would all be conducive to the release of ionizing radiation. As galaxy interactions and mergers increase with redshift, these effects can only become more important at earlier times, and so these interacting z~3 objects may be late, lower redshift analogues of the sources of reionization.
Elliptical galaxies contain X-ray emitting gas that is subject to continuous ram pressure stripping over timescales comparable to cluster ages. The gas in these galaxies is not in perfect hydrostatic equilibrium. Supernova feedback, stellar winds, or active galactic nuclei (AGN) feedback can significantly perturb the interstellar medium (ISM). Using hydrodynamical simulations, we investigate the effect of subsonic turbulence in the hot ISM on the ram pressure stripping process in early-type galaxies. We find that galaxies with the stronger turbulent ISM produce longer, wider, and more smoothly distributed tails of the stripped ISM than those characterised by weaker ISM turbulence. Our main conclusion is that even very weak internal turbulence, at the level of <15% of the average ISM sound speed in a galaxy, can accelerate the gas removal from the galaxy via ram pressure stripping and remove a significant fraction (~50%) of the preexisting ISM in ~6 Gyr. The magnitude of this effect increases sharply with the strength of the turbulence. As most of the gas stripping takes place near the boundary between the ISM and the intraclustermedium (ICM), the boost in the ISM stripping rate is due to the "random walk" of the ISM from the central regions of the galactic potential well to larger distances, where the ram pressure is able to permanently remove the gas from the galaxy. The ICM can be temporarily trapped inside the galactic potential well due to the mixing of the turbulent ISM with the ICM. The galaxies with more turbulent ISM, yet still characterised by very weak turbulence, can hold larger amounts of the ICM. [Abridged]
The low multipole anomalies of the Cosmic Microwave Background has received much attention during the last few years. It is still not ascertained whether these anomalies are indeed primordial or the result of systematics or foregrounds. An example of a foreground, which could generate some non-Gaussian and statistically anisotropic features at low multipole range, is the very symmetric Kuiper Belt in the outer solar system. In this paper, expanding upon the methods presented by Maris et al. (2011), we investigate the contributions from the Kuiper Belt objects (KBO) to the WMAP ILC 7 map, whereby we can minimize the contrast in power between even and odd multipoles in the CMB, discussed by Kim & Naselsky (2010). We submit our KBO de-correlated CMB signal to several tests, to analyze its validity, and find that incorporation of the KBO emission can resolve the quadrupole-octupole alignment and parity asymmetry problems, provided that the KBO signals has a non-cosmological dipole modulation, associated with the statistical anisotropy of the ILC 7 map. Additionally, we show that the amplitude of the dipole modulation, within a 2 sigma interval, is in agreement with the corresponding amplitudes, discussed by Lew (2008).
The ability to resolve all processes which drive galaxy formation is one of the most fundamental goals in extragalactic astronomy. While star formation rates and the merger history are now being measured with increasingly high certainty, the role of gas accretion from the intergalactic medium in triggering star formation still remains largely unknown. We present in this paper indirect evidence for the accretion of gas into massive galaxies with M_* > 10^{11} M_0 at redshifts 1.5 < z < 3 using results from the GOODS NICMOS Survey (GNS). Our method utilises the observed star formation rates of these massive galaxies based on UV and far-infrared observations, and the amount of stellar and gas mass added due to observed major and minor mergers to calculate the evolution of stellar mass in these systems. We show that the measured gas mass fractions are inconsistent with the observed star formation history for the same galaxy population. We further demonstrate that this additional gas mass cannot be accounted for by cold gas delivered through minor and major mergers. We argue that to sustain star formation at the observed rates there must be additional methods for increasing the cold gas mass, and that the likeliest method for establishing this supply of gas is by accretion from the intergalactic medium. We calculate that the average gas mass accretion rate into these massive galaxies, which is later turned into stars between 1.5 < z < 3.0, is = 83+/-36 M_0/yr. This is similar to what is predicted in detailed simulations of galaxy formation. We show that during this epoch, and for these very massive galaxies, 61+/-21% of stellar assembly is a result of gas accretion, while the remaining ~39% is put into place through mergers. This reveals that for the most massive galaxies at 1.5 < z < 3 gas accretion is the dominant method for instigating galaxy formation.
We present a study of Broad Absorption Line (BAL) quasar outflows that show S IV ?1063 and S IV* ?1073 troughs. The fractional abundance of S IV and C IV peak at similar value of the ionization parameter, implying that they arise from the same physical component of the outflow. Detection of the S IV* troughs will allow us to determine the distance to this gas with higher resolution and higher signal-to-noise spectra, therefore providing the distance and energetics of the ubiquitous C IV BAL outflows. In our bright sample of 156 SDSS quasars 14% show C IV and 1.9% S IV troughs, which is consistent with a fainter magnitude sample with twice as many objects. One object in the fainter sample shows evidence of a broad S IV trough without any significant trough present from the excited state line, which implies that this outflow could be at a distance of several kpc. Given the fractions of C IV and S IV, we establish firm limits on the global covering factor on S IV that ranges from 2.8% to 21% (allowing for the k-correction). Comparison of the expected optical depth for these ions with their detected percentage suggests that these species arise from common outflows with a covering factor closer to the latter.
The explanation of the accelerated expansion of the Universe poses one of the most fundamental questions in physics and cosmology today. If the acceleration is driven by some form of dark energy, one can try to constrain the parameters using a cosmographic approach. Our high-redshift analysis allows us to put constraints on the cosmographic expansion up to the fifth order. It is based on the Union2 Type Ia Supernovae (SNIa) data set, the Hubble diagram constructed from some Gamma Ray Bursts luminosity distance indicators, and gaussian priors on the distance from the Baryon Acoustic Oscillations (BAO), and the Hubble constant h (these priors have been included in order to help break the degeneracies among model parameters). To perform our statistical analysis and to explore the probability distributions of the cosmographic parameters we use the Markov Chain Monte Carlo Method (MCMC). We finally investigate implications of our results for the dark energy, in particular, we focus on the parametrization of the dark energy equation of state (EOS). Actually, a possibility to investigate the nature of dark energy lies in measuring the dark energy equation of state, w, and its time (or redshift) dependence at high accuracy. However, since w(z) is not directly accessible to measurement, reconstruction methods are needed to extract it reliably from observations. Here we investigate different models of dark energy, described through several parametrizations of the equation of state, by comparing the cosmographic and the EOS series.
We estimate the average radio-AGN (mechanical) power deposited into the hot atmospheres of galaxy clusters over more than three quarters of the age of the Universe. Our sample was drawn from eight major X-ray cluster surveys, and includes 685 clusters in the redshift range 0.1<z<0.6 that overlap the area covered by the NVSS. The radio-AGN mechanical power was estimated by scaling the radio luminosity of central NVSS radio sources using the relation between the radio synchrotron luminosities and X-ray cavity power measurements of Cavagnolo et al. (2010). We find only a weak correlation between radio luminosity and cluster X-ray luminosity across the sample. This trend is driven primarily by the most distant clusters, where the detection fraction and average radio powers are higher in the most luminous X-ray clusters at redshifts at or above z=0.3. The average AGN mechanical power of $3\times10^{44}$ erg/s exceeds the X-ray luminosity of 44% of the clusters in our sample, indicating that the accumulation of radio-AGN energy is significant in these clusters. Integrating the AGN mechanical power to redshift z = 2.0, using simple models for its evolution and disregarding the hierarchical growth of clusters, we find that the AGN energy accumulated per particle in low luminosity X-ray clusters exceeds 1.0 keV per particle. This conservative estimate is comparable to the level of energy needed to "preheat" clusters, indicating that continual outbursts from radio-AGN are a significant source of gas energy in hot atmospheres. Our result implies that the supermassive black holes in brightest cluster galaxies that generated this energy did so by accreting an average of 10^9 M_sun over time, which is comparable to the rapid level of growth expected during the quasar era.
The low frequency radio emission of starburst galaxies is informative, but it can be absorbed in several ways. Most importantly, starburst galaxies are home to many H II regions, whose free-free absorption can obscure low frequency radio waves. These H II regions are discrete objects, but most multiwavelength models of starbursts assume a uniform medium of ionized gas, if they include the absorption at all. I calculate the effective absorption coefficient of H II regions in starbursts, which is ultimately a cross section times the density of H II regions. The cross section can be easily calculated by assuming that H II regions are Str\"omgren spheres. The coefficient asymptotes to a constant value at low frequencies, because H II regions partially cover the starburst, and are buried part way into the starburst's synchrotron emitting material. Considering Str\"omgren spheres around both O stars and Super Star Clusters, I apply the calculations to the low frequency radio spectrum of M82. Far from being opaque at low frequencies, I find that M82 mostly transmits its radio flux. I also find that starbursts are transparent down to a few MHz to other possible absorption processes, such as free-free absorption from the diffuse superwind phase, synchrotron self-absorption, and the Razin effect. Hence, starburst galaxies should be observable with new low frequency radio telescopes.
We use the Wilkinson Microwave Anisotropy Probe 7-year data (WMAP7) to further probe point source detection technique in the sky maps of the cosmic microwave background (CMB) radiation. The method by Tegmark et al. for foreground reduced maps and the Kolmogorov parameter as the descriptor are adopted for the analysis of WMAP satellite CMB temperature data. Part of the detected points coincide with point sources already revealed by other methods. However, we have also found 2 source candidates for which still no counterparts are known, and identified 7 point sources listed in Planck Early Release Compact Source Catalogue as high reliability sources.
We present the X-ray point-source catalog produced from the Chandra Advanced CCD Imaging Spectrometer (ACIS-I) observations of the combined \sim3.2 deg2 DEEP2 (XDEEP2) survey fields, which consist of four ~0.7-1.1 deg2 fields. The combined total exposures across all four XDEEP2 fields range from ~10ks-1.1Ms. We detect X-ray point-sources in both the individual ACIS-I observations and the overlapping regions in the merged (stacked) images. We find a total of 2976 unique X-ray sources within the survey area with an expected false-source contamination of ~30 sources (~1%). We present the combined logN-logS distribution of sources detected across the XDEEP2 survey fields and find good agreement with the Extended Chandra Deep Field and Chandra-COSMOS fields to f_{X,0.5-2keV}\sim2x10^{-16} erg/cm^2/s. Given the large survey area of XDEEP2, we additionally place relatively strong constraints on the logN-logS distribution at high fluxes (f_{X,0.5-2keV}\sim3x10^{-14} erg/cm^2/s), and find a small systematic offset (a factor ~1.5) towards lower source numbers in this regime, when compared to smaller area surveys. The number counts observed in XDEEP2 are in close agreement with those predicted by X-ray background synthesis models. Additionally, we present a Bayesian-style method for associating the X-ray sources with optical photometric counterparts in the DEEP2 catalog (complete to R_AB < 25.2) and find that 2126 (~71.4\pm2.8%) of the 2976 X-ray sources presented here have a secure optical counterpart with a <6% contamination fraction. We provide the DEEP2 optical source properties (e.g., magnitude, redshift) as part of the X-ray-optical counterpart catalog.
The 4MOST consortium is currently halfway through a Conceptual Design study for ESO with the aim to develop a wide-field (>3 square degree, goal >5 square degree), high-multiplex (>1500 fibres, goal 3000 fibres) spectroscopic survey facility for an ESO 4m-class telescope (VISTA). 4MOST will run permanently on the telescope to perform a 5 year public survey yielding more than 20 million spectra at resolution R~5000 ({\lambda}=390-1000 nm) and more than 2 million spectra at R~20,000 (395-456.5 nm & 587-673 nm). The 4MOST design is especially intended to complement three key all-sky, space-based observatories of prime European interest: Gaia, eROSITA and Euclid. Initial design and performance estimates for the wide-field corrector concepts are presented. We consider two fibre positioner concepts, a well-known Phi-Theta system and a new R-Theta concept with a large patrol area. The spectrographs are fixed configuration two-arm spectrographs, with dedicated spectrographs for the high- and low-resolution. A full facility simulator is being developed to guide trade-off decisions regarding the optimal field-of-view, number of fibres needed, and the relative fraction of high-to-low resolution fibres. Mock catalogues with template spectra from seven Design Reference Surveys are simulated to verify the science requirements of 4MOST. The 4MOST consortium aims to deliver the full 4MOST facility by the end of 2018 and start delivering high-level data products for both consortium and ESO community targets a year later with yearly increments.
We calculate the polarization of synchrotron radiation produced at the relativistic reconfinement shocks, taking into account globally ordered magnetic field components, in particular toroidal and helical fields. In these shocks, toroidal fields produce high parallel polarization (electric vectors parallel to the projected jet axis), while chaotic fields generate moderate perpendicular polarization. Helical fields result in a non-axisymmetric distribution of the total and polarized brightness. For a diverging downstream velocity field, the Stokes parameter U does not vanish and the average polarization is neither strictly parallel nor perpendicular. A distance at which the downstream flow is changing from diverging to converging can be easily identified on polarization maps as the turning point, at which polarization vectors switch, e.g., from clockwise to counterclockwise.
We present deep photometry in the B,V and I filters from CTIO/MOSAIC for about 270.000 stars in the Fornax dwarf Spheroidal galaxy, out to a radius of r_ell\sim0.8 degrees. By combining the accurately calibrated photometry with the spectroscopic metallicity distributions of individual Red Giant Branch stars we obtain the detailed star formation and chemical evolution history of Fornax. Fornax is dominated by intermediate age (1-10 Gyr) stellar populations, but also includes ancient (10-14 Gyr), and young (<1 Gyr) stars. We show that Fornax displays a radial age gradient, with younger, more metal-rich populations dominating the central region. This confirms results from previous works. Within an elliptical radius of 0.8 degrees, or 1.9 kpc from the centre, a total mass in stars of 4.3x10^7 Msun was formed, from the earliest times until 250 Myr ago. Using the detailed star formation history, age estimates are determined for individual stars on the upper RGB, for which spectroscopic abundances are available, giving an age-metallicity relation of the Fornax dSph from individual stars. This shows that the average metallicity of Fornax went up rapidly from [Fe/H]<-2.5 dex to [Fe/H]=-1.5 dex between 8-12 Gyr ago, after which a more gradual enrichment resulted in a narrow, well-defined sequence which reaches [Fe/H]\sim-0.8 dex, \sim3 Gyr ago. These ages also allow us to measure the build-up of chemical elements as a function of time, and thus determine detailed timescales for the evolution of individual chemical elements. A rapid decrease in [Mg/Fe] is seen for the stars with [Fe/H]>-1.5 dex, with a clear trend in age.
The connection between long GRBs and supernovae is now well established. I briefly review the evidence in favor of this connection and summarise where we are observationally. I also use a few events to exemplify what should be done and what type of data are needed. I also look at what we can learn from looking at SNe not associated with GRBs and see how GRBs fit into the broad picture of stellar explosions.
We generalize the consistency condition for the three-point function in single field inflation to the case of dissipative, multi-field, single-clock models. We use the recently introduced extension of the effective field theory of inflation that accounts for dissipative effects, to provide an explicit proof to leading (non-trivial) order in the generalized slow roll parameters and mixing with gravity scales. Our results illustrate the conditions necessary for the validity of the consistency relation in situations with many degrees of freedom relevant during inflation, namely that there is a preferred clock. Departures from this condition in forthcoming experiments would rule out not only single field but also a large class of multi-field models.
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We present an optical group catalog between 0.1 < z < 1 based on 16,500 high-quality spectroscopic redshifts in the completed zCOSMOS-bright survey. The catalog published herein contains 1498 groups in total and 192 groups with more than five observed members. The catalog includes both group properties and the identification of the member galaxies. Based on mock catalogs, the completeness and purity of groups with three and more members should be both about 83% with respect to all groups that should have been detectable within the survey, and more than 75% of the groups should exhibit a one-to-one correspondence to the "real" groups. Particularly at high redshift, there are apparently more galaxies in groups in the COSMOS field than expected from mock catalogs. We detect clear evidence for the growth of cosmic structure over the last seven billion years in the sense that the fraction of galaxies that are found in groups (in volume-limited samples) increases significantly with cosmic time. In the second part of the paper, we develop a method for associating galaxies that only have photo-z to our spectroscopically identified groups. We show that this leads to improved definition of group centers, improved identification of the most massive galaxies in the groups, and improved identification of central and satellite galaxies, where we define the former to be galaxies at the minimum of the gravitational potential wells. Subsamples of centrals and satellites in the groups can be defined with purities up to 80%, while a straight binary classification of all group and non-group galaxies into centrals and satellites achieves purities of 85% and 75%, respectively, for the spectroscopic sample.
We quantify the accuracy with which the cosmological parameters characterizing the energy density of matter (\Omega_m), the amplitude of the power spectrum of matter fluctuations (\sigma_8), the energy density of neutrinos (\Omega_{\nu}) and the dark energy equation of state (w_0) can be constrained using data from large galaxy redshift surveys. We advocate a joint analysis of the abundance of galaxies, galaxy clustering, and the galaxy-galaxy weak lensing signal in order to simultaneously constrain the halo occupation statistics (i.e., galaxy bias) and the cosmological parameters of interest. We parameterize the halo occupation distribution of galaxies in terms of the conditional luminosity function and use the analytical framework of the halo model described in our companion paper (van den Bosch et al. 2012), to predict the relevant observables. By performing a Fisher matrix analysis, we show that a joint analysis of these observables, even with the precision with which they are currently measured from the Sloan Digital Sky Survey, can be used to obtain tight constraints on the cosmological parameters, fully marginalized over uncertainties in galaxy bias. We demonstrate that the cosmological constraints from such an analysis are nearly uncorrelated with the halo occupation distribution constraints, thus, minimizing the systematic impact of any imperfections in modeling the halo occupation statistics on the cosmological constraints. In fact, we demonstrate that the constraints from such an analysis are both complementary to and competitive with existing constraints on these parameters from a number of other techniques, such as cluster abundances, cosmic shear and/or baryon acoustic oscillations, thus paving the way to test the concordance cosmological model.
We present a group-galaxy cross-correlation analysis using a group catalog produced from the 16,500 spectra from the optical zCOSMOS galaxy survey. Our aim is to perform a consistency test in the redshift range 0.2 \leq z \leq 0.8 between the clustering strength of the groups and mass estimates that are based on the richness of the groups. We measure the linear bias of the groups by means of a group-galaxy cross-correlation analysis and convert it into mass using the bias-mass relation for a given cosmology, checking the systematic errors using realistic group and galaxy mock catalogs. The measured bias for the zCOSMOS groups increases with group richness as expected by the theory of cosmic structure formation and yields masses that are reasonably consistent with the masses estimated from the richness directly, considering the scatter that is obtained from the 24 mock catalogs. An exception are the richest groups at high redshift (estimated to be more massive than 10^13.5 M\odot), for which the measured bias is significantly larger than for any of the 24 mock catalogs (corresponding to a 3{\sigma} effect), which is attributed to the extremely large structure that is present in the COSMOS field at z \sim 0.7. Our results are in general agreement with previous studies that reported unusually strong clustering in the COSMOS field.
Using high resolution cosmological hydrodynamical simulations of Milky Way-massed disk galaxies, we demonstrate that supernovae feedback and tidal stripping lower the central masses of bright (-14 < M_V < -8) satellite galaxies. These simulations resolve high density regions, comparable to giant molecular clouds, where stars form. This resolution allows us to adopt a prescription for H_2 formation and destruction that ties star formation to the presence of shielded, molecular gas. Before infall, supernova feedback from the clumpy, bursty star formation captured by this physically motivated model leads to reduced dark matter (DM) densities and shallower inner density profiles in the massive satellite progenitors (Mvir > 10^9 Msun, Mstar > 10^7 Msun) compared to DM-only simulations. The progenitors of the lower mass satellites are unable to maintain bursty star formation histories, due to both heating at reionization and gas loss from initial star forming events, preserving the steep inner density profile predicted by DM-only simulations. After infall, tidal stripping acts to further reduce the central densities of the luminous satellites, particularly those that enter with cored dark matter halos, increasing the discrepancy in the central masses predicted by baryon+DM and DM-only simulations. We show that DM-only simulations, which neglect the baryonic effects described in this work, produce denser satellites with larger central velocities. We provide a simple correction to the central DM mass predicted for satellites by DM-only simulations. We conclude that DM-only simulations should be used with great caution when interpreting kinematic observations of the Milky Way's dwarf satellites.
The emergence of several large-scale anomalies in the cosmic microwave background (CMB) has pointed to possible deficiencies in the standard model, or perhaps new physics driving the origin of density fluctuations in the early Universe and their evolution into the large-scale structure we see today. In this paper, we focus our attention on the observed absence of angular correlation of the CMB anisotropies at angles larger than ~60 degrees, and consider whether this feature may be understood in the context of the R_h=ct Universe. We find that the significant disparity between the predictions of LCDM and the WMAP sky (at a confidence level of greater than 99.9 percent) may be directly traced to inflation. The classic horizon problem does not exist in the R_h=ct Universe, so a period of exponential growth was not necessary in this cosmology in order to account for the general uniformity of the CMB (save for the aforementioned tiny fluctuations of 1 part in 100,000 in the WMAP relic signal). We show that the R_h=ct Universe without inflation is a significantly better fit to the CMB angular correlation function than LCDM, providing additional motivation for pursuing this cosmology as a viable description of nature.
Galaxies are not distributed randomly in the cosmic web but are instead
arranged in filaments and sheets surrounding cosmic voids. Observationally
there is still no con- vincing evidence of a link between the properties of
galaxies and their host structures. However, by the tidal torque theory (our
understanding of the origin of galaxy angular momentum), such a link should
exist. Using the presently largest spectroscopic galaxy redshift survey (SDSS)
we study the connection between the spin axes of galaxies and the orientation
of their host filaments.
We use a three dimensional field of orientations to describe cosmic
filaments. To restore the inclination angles of galaxies, we use a 3D
photometric model of galaxies that gives these angles more accurately than
traditional 2D models.
We found evidence that the spin axes of bright spiral galaxies have a weak
tendency to be aligned parallel to filaments. For elliptical/S0 galaxies, we
have a statistically significant result that the spin axes of ellipticals are
aligned preferentially perpendic- ular to the host filaments; we show that this
signal practically does not depend on the accuracy of the estimated inclination
angles for elliptical galaxies.
We show how the existence of a relation between the star formation rate and the gas density, i.e. the Kennicutt-Schmidt law, implies a continuous accretion of fresh gas from the environment into the discs of spiral galaxies. We present a method to derive the gas infall rate in a galaxy disc as a function of time and radius, and we apply it to the disc of the Milky Way and 21 galaxies from the THINGS sample. For the Milky Way, we found that the ratio between the past and current star formation rates is about 2-3, averaged over the disc, but it varies substantially with radius. In the other disc galaxies there is a clear dependency of this ratio with galaxy stellar mass and Hubble type, with more constant star formation histories for small galaxies of later type. The gas accretion rate follows very closely the SFR for every galaxy and it dominates the evolution of these systems. The Milky Way has formed two thirds of its stars after z=1, whilst the mass of cold gas in the disc has remained fairly constant with time. In general, all discs have accreted a significant fraction of their gas after z=1. Accretion moves from the inner regions of the disc to the outer parts, and as a consequence star formation moves inside-out as well. At z=0 the peak of gas accretion in the Galaxy is at about 6-7 kpc from the centre.
We consider holographic cosmological models of dark energy in which the infrared cutoff is set by the Hubble's radius. We show that any interacting dark energy model with a matter like term able to alleviate the coincidence problem (i.e., with a positive interaction term, regardless of its detailed form) can be recast as a noninteracting model in which the holographic parameter evolves slowly with time. Two specific cases are analyzed. First, the interacting model presented in [1] is considered, and its corresponding noninteracting version found. Then, a new noninteracting model, with a specific expression of the time-dependent holographic parameter, is proposed and analyzed along with its corresponding interacting version. We constrain the parameters of both models using observational data, and show that they can be told apart at the perturbative level.
We propose to describe the variety of galaxies from SDSS by using only one affine parameter. To this aim, we build the Principal Curve (P-curve) passing through the spine of the data point cloud, considering the eigenspace derived from Principal Component Analysis of morphological, physical and photometric galaxy properties. Thus, galaxies can be labeled, ranked and classified by a single arc length value of the curve, measured at the unique closest projection of the data points on the P-curve. We find that the P-curve has a "W" letter shape with 3 turning points, defining 4 branches that represent distinct galaxy populations. This behavior is controlled mainly by 2 properties, namely u-r and SFR. We further present the variations of several galaxy properties as a function of arc length. Luminosity functions variate from steep Schechter fits at low arc length, to double power law and ending in Log-normal fits at high arc length. Galaxy clustering shows increasing autocorrelation power at large scales as arc length increases. PCA analysis allowed to find peculiar galaxy populations located apart from the main cloud of data points, such as small red galaxies dominated by a disk, of relatively high stellar mass-to-light ratio and surface mass density. The P-curve allows not only dimensionality reduction, but also provides supporting evidence for relevant physical models and scenarios in extragalactic astronomy: 1) Evidence for the hierarchical merging scenario in the formation of a selected group of red massive galaxies. These galaxies present a log-normal r-band luminosity function, which might arise from multiplicative processes involved in this scenario. 2) Connection between the onset of AGN activity and star formation quenching, which appears in green galaxies when transitioning from blue to red populations. (Full abstract in downloadable version)
The identifications of quasars at intermediate redshifts ($2.2<z<3.5$) are inefficient in previous quasar surveys as their optical colors are similar as those of stars.The near-IR K-band excess technique has been suggested to overcome this difficulty. Our recent study also proposed to use the optical/near-IR colors for selecting z$<$4 quasars. To verify the effectiveness of this method, we selected a list of unidentified bright targets with $i\leq18.5$ from the quasar candidates of SDSS DR6 with both SDSS $ugriz$ optical and UKIDSS YJHK near-IR photometric data, which satisfy our proposed Y-K/g-z criterion and have photometric redshifts between 2.2 and 3.5 estimated from the 9-band SDSS-UKIDSS data. 43 of them were observed with the BFOSC instrument on the 2.16m optical telescope at Xinglong station of NAOC in the spring of 2012. 35 of them were spectroscopically identified as quasars with redshifts between 2.1 and 3.4. The high success rate of discovering these missing quasars in the SDSS spectroscopic surveyed area further demonstrates the robustness of both the Y-K/g-z selection criterion and the photometric redshift estimation technique. We also used the above criterion to investigate the possible star contamination rate to the quasar candidates of SDSS DR6, and found that it is much higher in selecting $3<z<3.5$ quasar candidates than the lower redshift ones. The significant improvement in the photometric redshift estimation by using the 9-band SDSS-UKIDSS data than using the 5-band SDSS data is demonstrated and a catalog of 7727 unidentified quasar candidates in SDSS DR6 selected with the optical/near-IR colors and with photometric redshifts between 2.2 and 3.5 is provided. We discuss the implications of our results to the ongoing and upcoming large optical and near-IR sky surveys.
The magnetic field of galaxies is believed to be produced by internal dynamo action, but can be affected by motion of the galaxy through the surrounding medium. Observations of polarized radio emission of galaxies located in galaxy clusters have revealed noticeable features of large-scale magnetic configurations, including displacements of the magnetic structures from the optical images and tails, which are possible imprints of ram pressure effects arising from motion of the galaxies through the intracluster medium. We present a quantitative dynamo model which attempts to describe the above effects. In contrast to the traditional problem of a wind affecting a body with a prescribed magnetic field, we investigate how a non-magnetized wind flow affects a magnetic field that is being self-excited by galactic dynamo action. In order to isolate the leading physical effects we exploit a simple dynamo model that can describe relevant effects. In particular, we use what is known as the 'no-z' approximation for the mean-field dynamo equations. In a suitable parametric range we obtain displacements of the large-scale magnetic field, as well as magnetic tails. However, the specific details of their locations are quite counterintuitive. The direction of displacement is perpendicular to, rather than parallel to, the wind direction. The point at which the tail emerges from the galaxy depends on details of the model. The tail is eventually directed downstream. In the simplest case the magnetic tail begins in the region where the wind decreases the total gas velocity. Any wind that penetrates the galaxy modifies the intrinsic dynamo action. These features are different from those found in ram-pressure models. Any determination of galactic motion through the cluster medium from observational data needs to take the effects of dynamo action into account.
Recently, in [1] we developed a parametric reconstruction method to a homogeneous, isotropic and spatially flat Friedmann-Robertson-Walker (FRW) cosmological model filled of a fluid of dark energy (DE) with constant equation of state (EOS) parameter interacting with dark matter (DM). The reconstruction method is based on expansions of the general interaction term and the relevant cosmological variables in terms of Chebyshev polynomials which form a complete set orthonormal functions. In this article, we reconstruct the interaction function expanding it in terms of only the first four Chebyshev polynomials and obtain the best estimation for the coefficients of the expansion assuming three models: (a) a DE equation of the state parameter w=-1 (an interacting cosmological Lambda), (b) a DE equation of the state parameter w = constant with a dark matter density parameter fixed, (c) a DE equation of the state parameter w = constant with a free constant dark matter density parameter to be estimated. In all the cases, the preliminary reconstruction shows that in the best scenario there exist the possibility of a crossing of the noninteracting line Q=0 in the recent past within the 1-sigma and 2-sigma errors from positive values at early times to negative values at late times. This means that, in this reconstruction, there is an energy transfer from DE to DM at early times and an energy transfer from DM to DE at late times. We conclude that this fact is an indication of the possible existence of a crossing behavior in a general interaction coupling between dark components. Finally, we conclude that in this scenario, the observations put strong constraints on the strength of the interaction so that its magnitude can not solve the coincidence problem or at least alleviate significantly.
In 1988 Bardeen has suggested a pragmatic formulation of cosmological perturbation theory which is powerful in practice to employ various fundamental gauge conditions easily depending on the character of the problem. The perturbation equations are presented without fixing the temporal gauge condition and are arranged so that one can easily impose fundamental gauge conditions by simply setting one of the perturbation variables in the equations equal to zero. In this way one can use the gauge degrees of freedom as an advantage in handling problems. Except for the synchronous gauge condition, all the other fundamental gauge conditions completely fix the gauge mode, and consequently, each variable in such a gauge has a unique gauge invariant counterpart, so that we can identify the variable as the gauge-invariant one. Here, we extend Bardeen's linear formulation to fully nonlinear order in perturbations, with the gauge advantage kept intact. Derived equations are exact, and from these we can easily expand to higher order perturbations in a gauge-ready form. We consider scalar- and vector-type perturbations of an ideal fluid in a flat background; we also present the multiple components of ideal fluid case. As applications we present fully nonlinear density and velocity perturbation equations in Einstein's gravity in the zero-pressure medium, vorticity generation from pure scalar-type perturbation, and fluid formulation of a minimally coupled scalar field, all in the comoving gauge. We also present the equation of gravitational waves generated from pure scalar- and vector-type perturbations.
We study multifield contributions to the scalar power spectrum in an ensemble of six-field inflationary models obtained in string theory. We identify examples in which inflation occurs by chance, near an approximate inflection point, and we compute the primordial perturbations numerically, both exactly and using an array of truncated models. The scalar mass spectrum and the number of fluctuating fields are accurately described by a simple random matrix model. During the approach to the inflection point, bending trajectories and violations of slow roll are commonplace, and 'many-field' effects, in which three or more fields influence the perturbations, are often important. However, in a large fraction of models consistent with constraints on the tilt the signatures of multifield evolution occur on unobservably large scales. Our scenario is a concrete microphysical realization of quasi-single-field inflation, with scalar masses of order $H$, but the cubic and quartic couplings are typically too small to produce detectable non-Gaussianity. We argue that our results are characteristic of a broader class of models arising from multifield potentials that are natural in the Wilsonian sense.
We investigate some of the asymmetries reported in the CMB temperature angular distribution considering the {\Lambda}CDM model in the 3, 5 and 7 year WMAP data. We aim to analyze the 4 quadrants of the ILC CMB maps using 3 Galactic cuts: the WMAP KQ85 mask, a |b|<10 degrees and the WMAP KQ85 mask +|b|<10 degrees Galactic cuts. We used the two-point angular correlation function in the WMAP maps for each of their quadrants. The same procedure was done for 1000 Monte Carlo simulations that were produced using the WMAP team {\Lambda}CDM best-fit power spectrum. We also changed the quadrupole and octopole amplitudes to fit their observable WMAP values in the {\Lambda}CDM model, hereafter M{\Lambda}CDM. Our analysis showed asymmetries between the southeastern quadrant (SEQ) and the other quadrants (southwestern quadrant (SWQ), northeastern quadrant (NEQ) and northwestern quadrant (NWQ)). Over all WMAP maps, the probability for the occurrence of the SEQ-NEQ, SEQ-SWQ and SEQ-NWQ asymmetries varies from 0.1% (SEQ-NEQ) to 8.5% (SEQ-SWQ) using the KQ85 mask and the KQ85 mask + |b|<10 degrees Galactic cut, respectively. We also calculated the probabilities for the M{\Lambda}CDM, finding no significant differences in the results. Moreover, the cold spot region was covered with masks of 5,10 and 15 degrees radius and again the results remained unchanged. This analysis was also repeated for random regions in the SEQ quadrant with a 15-degree mask and the SEQ quadrant still remained asymmetric with respect to the other quadrants of the CMB map. We found an excess of power in the TPCF at scales >100 degrees in the SEQ with respect to the other quadrants that is independent of the Galactic cut used, and found no evidence for its possible relation with the cold spot signal. We could not find any specific region within the SEQ that might be considered responsible for the quadrant asymmetry.
We derive the decoupling limit of Massive Gravity on de Sitter in an arbitrary number of space-time dimensions d. By embedding d-dimensional de Sitter into d+1-dimensional Minkowski, we extract the physical helicity-1 and helicity-0 polarizations of the graviton. The resulting decoupling theory is similar to that obtained around Minkowski. We take great care at exploring the partially massless limit and define the unique fully non-linear candidate theory that is free of the helicity-0 mode in the decoupling limit, and which therefore propagates only four degrees of freedom in four dimensions. In the latter situation, we show that a new Vainshtein mechanism is at work in the limit m^2\to 2 H^2 which decouples the helicity-0 mode when the parameters are different from that of partially massless gravity. As a result, there is no discontinuity between massive gravity and its partially massless limit, just in the same way as there is no discontinuity in the massless limit of massive gravity. The usual bounds on the graviton mass could therefore equivalently well be interpreted as bounds on m^2-2H^2. When dealing with the exact partially massless parameters, on the other hand, the symmetry at m^2=2H^2 imposes a specific constraint on matter. As a result the helicity-0 mode decouples without even the need of any Vainshtein mechanism.
Inspiraling supermassive black hole binary systems with high orbital eccentricity are important sources for space-based gravitational wave (GW) observatories like the Laser Interferometer Space Antenna (LISA). Eccentricity adds orbital harmonics to the Fourier-transform of the GW signal and relativistic pericenter precession leads to a three-way splitting of each harmonic peak. We study the parameter estimation accuracy for such waveforms with different initial eccentricity using the Fisher matrix method and a Monte Carlo sampling of the initial binary orientation. The eccentricity improves the parameter estimation by breaking degeneracies between different parameters. In particular, we find that the source localization precision improves significantly for higher mass binaries due to eccentricity. The typical sky position errors are $\sim1 $deg for a nonspinning, $10^7\,M_{\odot}$ equal mass binary at redshift $z=1$, if the initial eccentricity one year before merger is $e_0\sim 0.6$. Pericenter precession does not affect the source localization accuracy significantly, but it does further improve the mass and eccentricity estimation accuracy systematically by a factor of 3--10 for masses between $10^6$ and $10^7\,M_{\odot}$ for $e_0 \sim 0.3$.
For the last decade, the gravitational lensing in the strong gravitational field has been studied eagerly. It is well known that, for the lensing by a black hole, infinite number of Einstein rings are formed by the light rays which wind around the black hole nearly on the photon sphere, which are called relativistic Einstein rings. This is also the case for the lensing by a wormhole. In this letter, we study the Einstein ring and relativistic Einstein rings for the Schwarzschild black hole and the Ellis wormhole, the latter of which is an example of traversable wormholes of the Morris-Thorne class. Given the configuration of the gravitational lensing and the radii of the Einstein ring and relativistic Einstein rings, we can distinguish between a black hole and a wormhole in the galactic centers because the radius of the relativistic Einstein rings for a wormhole lensing can be observed with the most powerful modern instruments, e.g. the Very Large Telescope Interferometer (VLTI), which have the resolution of $10^{-3}$ arcsecond. We may test some hypotheses of astrophysical wormholes by using the Einstein ring and relativistic Einstein rings in the future.
Cosmology is a field of physics in which the use of General Relativity theory is indispensable. However, a cosmology based on Newtonian gravity theory for gravity is possible in certain circumstances. The applicability of Newtonian theory can be substantially extended if it is modified in such way that pressure has a more active role as source of the gravitational field. This was done in the neo-Newtonian cosmology. The limitation on the construction of a Newtonian cosmology, and the need for a relativistic theory in cosmology are reviewed. The neo-Newtonian proposal is presented, and its consequences for cosmology are discussed.
We study the contribution of spectator massive scalar fields to the inflationary density perturbations through the universal gravitational coupling. We find that such contribution has several remarkable properties: it does not decrease as the mass of the spectator field increases; it has a significant size and cannot be turned off by any adjustable parameters; and it applies to all massive scalars existed during inflation, making the overall effect unexpectedly large. As a result, the primordial density perturbations are anomalously sensitive to the high energy physics.
We calculate the observable signature of a black hole accretion disk with a gap or hole created by a secondary black hole embedded in the disk. We find that for an interesting range of parameters of black hole masses (~10^6 to 10^9 Msun), orbital separation (~1 AU to ~1 pc), and gap width (10--180 disk scale heights), the missing thermal emission from a gap manifests itself in an observable decrement in the spectral energy distribution. We present observational diagnostics in terms of powerlaw forms that can be fit to line-free regions in AGN spectra or in fluxes from sequences of broad filters. Most interestingly, the change in slope in the broken powerlaw is almost entirely dependent on the width of gap in the accretion disk, which in turn is uniquely determined by mass ratio of the black holes, such that it scales roughly as $q^{5/4}$. Thus one can use spectral observations of the continuum of bright active galactic nuclei to infer not only the presence of a closely separated black hole binary but also the mass ratio. When the black hole merger opens a hole in the inner disk, the broad band SED of the AGN or quasar may serve as a diagnostic. Such sources should be especially luminous in optical bands but intrinsically faint in X-rays (i.e., not merely obscured). We briefly note that viable candidates may have already been identified.
Several extensions of the Standard Model predict the existence of Axion-Like Particles (ALPs), very light spin-zero bosons with a two-photon coupling. ALPs can give rise to observable effects in very-high-energy astrophysics. Above roughly 100 GeV the horizon of the observable Universe progressively shrinks as the energy increases, due to scattering of beam photons off background photons in the optical and infrared bands, which produces e+e- pairs. In the presence of large-scale magnetic fields photons emitted by a blazar can oscillate into ALPs on the way to us and back into photons before reaching the Earth. Since ALPs do not interact with background photons, the effective mean free path of beam photons increases, enhancing the photon survival probability. While the absorption probability increases with energy, photon-ALP oscillations are energy-independent, and so the survival probability increases with energy compared to standard expectations. We have performed a systematic analysis of this effect, interpreting the present data on very-high-energy photons from blazars. Our predictions can be tested with presently operating Cherenkov Telescopes like H.E.S.S., MAGIC, VERITAS and CANGAROO III as well as with detectors like ARGO-YBJ and MILAGRO and with the planned Cherenkov Telescope Array and the HAWC-ray observatory. ALPs with the right properties to produce the above effects can possibly be discovered by the GammeV experiment at FERMILAB and surely by the planned photon regeneration experiment ALPS at DESY.
We study the evolution of galactic bars and the link with disk and spheroid formation in a sample of zoom-in cosmological simulations. Our simulation sample focuses on galaxies with present-day stellar masses in the 10^10-10^11 Msun range, in field and loose group environments, with a broad variety of mass growth histories. In our models, bars are almost absent from the progenitors of present-day spirals at z>1.5, and they remain rare and generally too weak to be observable down to z~1. After this characteristic epoch, the fractions of observable and strong bars raise rapidly, bars being present in 80% of spiral galaxies and easily observable in two thirds of these at z<0.5. This is quantitatively consistent with the redshift evolution of the observed bar fraction. Our models predict that the decrease in the bar fraction with increasing redshift should continue with a fraction of observable bars <10-15% in disk galaxies at z>1. Our models also predict later bar formation in lower-mass galaxies, in agreement with existing data. We find that the characteristic epoch of bar formation, namely redshift z~0.8-1, corresponds to the epoch at which today's spirals acquire their disk-dominated morphology. At higher redshift, disks tend to be rapidly destroyed by mergers and gravitational instabilities and rarely develop significant bars. The bar formation epoch corresponds to the transition between an early "violent" phase of spiral galaxy formation at z>1 and a late "secular" phase at z<0.8. In the secular phase, the presence of bars substantially contributes to the growth of the bulge, but the bulge mass budget remains statistically dominated by the contribution of mergers, interactions and disk instabilities at high redshift. Early bars at z>1 are often short-lived, while most of the bars formed at z<1 persist down to z=0, late cosmological gas infall being necessary to maintain some of them.
We surveyed the circumnuclear disk of the Seyfert galaxy NGC1068 between the frequencies 86.2 GHz and 115.6 GHz, and identified 17 different molecules. Using a time and depth dependent chemical model we reproduced the observational results, and show that the column densities of most of the species are better reproduced if the molecular gas is heavily pervaded by a high cosmic ray ionization rate of about 1000 times that of the Milky Way. We discuss how molecules in the NGC1068 nucleus may be influenced by this external radiation, as well as by UV radiation fields.
The no-boundary wave function of quantum gravity tends to assign only very small probability to long periods of inflation. This leads to tension with observations. We study the no-boundary proposal in the context of multi-field inflation to see whether the number of fields changes the situation. For a simple model, we find that indeed the no-boundary wave function can give higher probability for sufficient inflation, but the number of fields involved has to be very high.
We have performed an extensive numerical study of coalescing black-hole binaries to understand the gravitational-wave spectrum of quasi-normal modes excited in the merged black hole. Remarkably, we find that the masses and spins of the progenitor are clearly encoded in the mode spectrum of the ringdown signal. Some of the mode amplitudes carry the signature of the binary's mass ratio, while others depend critically on the spins. Simulations of precessing binaries suggest that our results carry over to generic systems. Using Bayesian inference, we demonstrate that it is possible to accurately measure the mass ratio and individual spins of the progenitor even when the binary itself is invisible to a detector. Our results could have tremendous implications for gravitational astronomy by facilitating novel tests of general relativity using merging black holes.
In generic particle physics models, the inflaton field is coupled to other bosonic and fermionic fields that acquire large masses during inflation and may decay into light degrees of freedom. This leads to dissipative effects that modify the inflationary dynamics and generate a nearly-thermal radiation bath, such that inflation occurs in a warm rather than supercooled environment. In this work, we perform a numerical computation and obtain expressions for the associated dissipation coefficient, focusing on the regime where the radiation temperature is below the heavy mass threshold, while allowing for generic couplings and field multiplicities. We also discuss radiative corrections to particle masses and decay widths and how they may significantly increase the effects of dissipation.
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We present a study using the Karl G. Jansky Very Large Array of 12CO J=1-0 emission in three strongly lensed submillimetre-selected galaxies (SMMJ16359, SMMJ14009 and SMMJ02399) at z=2.5-2.9. These galaxies span L(IR) = 10^11 - 10^13 Lsun, offering an opportunity to compare the interstellar medium of LIRGs and ULIRGs at high redshift. We estimate molecular gas masses in the range (2-40) x 10^9 Msun using a method that assumes canonical underlying brightness temperature ratios for star-forming and non-star-forming gas phases and a maximal star-formation efficiency. A more simplistic method using X(CO) = 0.8 yields gas masses twice as high. The observed CO(3-2)/CO(1-0) brightness temperature ratio for SMMJ14009, r(3-2)/(1-0) = (0.95 \pm 0.12), is indicative of warm star-forming gas, possibly influenced by the central AGN. We search for 12CO(1-0) emission in the Lyman-break galaxy, A2218 #384, located at z=2.517 in the same field as SMMJ16359, and assign a 3-sigma gas mass limit of <6 x 10^8 Msun. We use rest-frame 115-GHz free-free flux densities in SMMJ14009 and SMMJ02399 - measurements tied directly to the photionisation rate of massive stars and made possible by JVLA's bandwidth - to estimate star-formation rates of 400-600 Msun/yr and to estimate the fraction of L(IR) due to the AGN.
Recent work on increasing the effective number of neutrino species (Neff) in the early universe has focussed on introducing extra relativistic species (`dark radiation'). We draw attention to another possibility: a new particle of mass less than 10 MeV that remains in thermal equilibrium with neutrinos until it becomes non-relativistic increases the neutrino temperature relative to the photons. We demonstrate that this leads to a value of Neff that is greater than three and that Neff at CMB formation is larger than at BBN. We investigate the constraints on such particles from the primordial abundance of helium and deuterium created during BBN and from the CMB power spectrum measured by ACT and SPT and find that they are presently relatively unconstrained. We forecast the sensitivity of the Planck satellite to this scenario: in addition to dramatically improving constraints on the particle mass, in some regions of parameter space it can discriminate between the new particle being a real or complex scalar.
We use Luminous Red Galaxies from the Sloan Digital Sky Survey II to test the cosmological structure growth in two alternatives to the standard LCDM+GR cosmological model. We compare observed three-dimensional clustering in SDSS DR7 with theoretical predictions for the standard vanilla LCDM+GR model, Unified Dark Matter cosmologies and the normal branch DGP. In computing the expected correlations in UDM cosmologies, we derive a parameterized formula for the growth factor in these models. For our analysis we apply the methodology tested in Raccanelli et al. 2010 and use the measurements of Samushia et al. 2011, that account for survey geometry, non-linear and wide-angle effects and the distribution of pair orientation. We show that the estimate of the growth rate is potentially degenerate with wide-angle effects, meaning that extremely accurate measurements of the growth rate on large scales will need to take such effects into account. We use measurements of the zeroth and second order moments of the correlation function from SDSS DR7 data and the Large Suite of Dark Matter Simulations, and perform a likelihood analysis to constrain the parameters of the models. Using information on the clustering up to r_max = 120 Mpc/h, and after marginalizing over the bias, we find, for UDM models, a speed of sound < 6.1e-4, and, for the nDGP model, a cross-over scale r_c > 340 Mpc, at 95% confidence level.
We simultaneously constrain cosmology and galaxy bias using measurements of galaxy abundances, galaxy clustering and galaxy-galaxy lensing taken from the Sloan Digital Sky Survey. We use the conditional luminosity function (which describes the halo occupation statistics as function of galaxy luminosity) combined with the halo model (which describes the non-linear matter field in terms of its halo building blocks) to describe the galaxy-dark matter connection. We explicitly account for residual redshift space distortions in the projected galaxy-galaxy correlation functions, and marginalize over uncertainties in the scale dependence of the halo bias and the detailed structure of dark matter haloes. Under the assumption of a spatially flat, vanilla {\Lambda}CDM cosmology, we focus on constraining the matter density, {\Omega}m, and the normalization of the matter power spectrum, {\sigma}8, and we adopt WMAP7 priors for the spectral index, the Hubble parameter, and the baryon density. We obtain that \Omegam = 0.278_{-0.026}^{+0.023} and {\sigma}8 = 0.763_{-0.049}^{+0.064} (95% CL). These results are robust to uncertainties in the radial number density distribution of satellite galaxies, while allowing for non-Poisson satellite occupation distributions results in a slightly lower value for {\sigma}8 (0.744_{-0.047}^{+0.056}). These constraints are in excellent agreement (at the 1{\sigma} level) with the cosmic microwave background constraints from WMAP. This demonstrates that the use of a realistic and accurate model for galaxy bias, down to the smallest non-linear scales currently observed in galaxy surveys, leads to results perfectly consistent with the vanilla {\Lambda}CDM cosmology.
There is sufficient amount of internal evidence in the nature of gravitational theories to indicate that gravity is an emergent phenomenon like, e.g, elasticity. Such an emergent nature is most apparent in the structure of gravitational dynamics. It is, however, possible to go beyond the field equations and study the space itself as emergent in a well-defined manner in (and possibly only in) the context of cosmology. In the first part of this review, I describe various pieces of evidence which show that gravitational field equations are emergent. In the second part, I describe a novel way of studying cosmology in which I interpret the expansion of the universe as equivalent to the emergence of space itself. In such an approach, the dynamics evolves towards a state of holographic equipartition, characterized by the equality of number of bulk and surface degrees of freedom in a region bounded by the Hubble radius. This principle correctly reproduces the standard evolution of a Friedmann universe. Further, (a) it demands the existence of an early inflationary phase as well as late time acceleration for its successful implementation and (b) allows us to link the value of late time cosmological constant to the e-folding factor during inflation.
The search for diffuse non-thermal, inverse Compton (IC) emission from galaxy clusters at hard X-ray energies has been underway for many years, with most detections being either of low significance or controversial. In this work, we investigate 14-195 keV spectra from the Swift Burst Alert Telescope (BAT) all-sky survey for evidence of non-thermal excess emission above the exponentially decreasing tail of thermal emission in the flux-limited HIFLUGCS sample. To account for the thermal contribution at BAT energies, XMM-Newton EPIC spectra are extracted from coincident spatial regions so that both thermal and non-thermal spectral components can be determined simultaneously. We find marginally significant IC components in six clusters, though after closer inspection and consideration of systematic errors we are unable to claim a clear detection in any of them. The spectra of all clusters are also summed to enhance a cumulative non-thermal signal not quite detectable in individual clusters. After constructing a model based on single-temperature fits to the XMM-Newton data alone, we see no significant excess emission above that predicted by the thermal model determined at soft energies. This result also holds for the summed spectra of various subgroups, except for the subsample of clusters with diffuse radio emission. For clusters hosting a diffuse radio halo, a relic, or a mini-halo, non-thermal emission is initially detected at the \sim5-sigma confidence level - driven by clusters with mini-halos - but modeling and systematic uncertainties ultimately degrade this significance. In individual clusters, the non-thermal pressure of relativistic electrons is limited to \sim10% of the thermal electron pressure, with stricter limits for the more massive clusters, indicating that these electrons are likely not dynamically important in the central regions of clusters.
The measurement and characterization of the lensing of the cosmic microwave background (CMB) is a key goal of the current and next generation of CMB experiments. We perform a case study of a three-channel balloon-borne CMB experiment observing the sky at (l,b)=(250deg,-38deg) and attaining a sensitivity of 5.25 muK-arcmin with 8' angular resolution at 150 GHz, in order to assess whether the effect of polarized Galactic dust is expected to be a significant contaminant to the lensing signal reconstructed using the EB quadratic estimator. We find that for our assumed dust model, polarization fractions as low as a few percent may lead to a significant dust bias to the lensing convergence power spectrum. We investigate a parametric component separation method, proposed by Stompor et al. (2009), for mitigating the effect of this dust bias, based on a `profile likelihood' technique for estimating the dust spectral index. We find a dust contrast regime in which the accuracy of the profile likelihood spectral index estimate breaks down, and in which external information on the dust frequency scaling is needed. We propose a criterion for putting a requirement on the accuracy with which the dust spectral index must be estimated or constrained, and demonstrate that if this requirement is met, then the dust bias can be removed.
Deep, high resolution spectroscopic observations have been obtained for six compact, strongly star-forming galaxies at redshift z~0.1-0.3, most of them also known as Green Peas. Remarkably, these galaxies show complex emission-line profiles in the spectral region including H\alpha, [NII]$\lambda\lambda 6548, 6584$ and [SII]$\lambda\lambda 6717, 6731$, consisting of the superposition of different kinematical components on a spatial extent of few kpc: a very broad line emission underlying more than one narrower component. For at least two of the observed galaxies some of these multiple components are resolved spatially in their 2D-spectra, whereas for another one a faint detached H\alpha\ blob lacking stellar continuum is detected at the same recessional velocity ~7 kpc away from the galaxy. The individual narrower H\alpha\ components show high intrinsic velocity dispersion (\sigma ~30-80 km s$^{-1}$), suggesting together with unsharped masking HST images that star formation proceeds in an ensemble of several compact and turbulent clumps, with relative velocities of up to ~500 km s$^{-1}$. The broad underlying H\alpha\ components indicate in all cases large expansion velocities (full width zero intensity FWZI $\ge$ 1000 km s$^{-1}$) and very high luminosities (up to ~10$^{42}$ erg s$^{-1}$), probably showing the imprint of energetic outflows from SNe. These intriguing results underline the importance of Green Peas for studying the assembly of low-mass galaxies near and far.
Making use of HI 21 cm line measurements from the ALFALFA survey (alpha.40) and photometry from the Sloan Digital Sky Survey (SDSS) and GALEX, we investigate the global scaling relations and fundamental planes linking stars and gas for a sample of 9417 common galaxies: the alpha.40-SDSS-GALEX sample. In addition to their HI properties derived from the ALFALFA dataset, stellar masses (M_*) and star formation rates (SFRs) are derived from fitting the UV-optical spectral energy distributions. 96% of the alpha.40-SDSS-GALEX galaxies belong to the blue cloud, with the average gas fraction f_HI = M_HI/M_* ~ 1.5. A transition in SF properties is found whereby below M_* ~ 10^9.5 M_sun, the slope of the star forming sequence changes, the dispersion in the specific star formation rate (SSFR) distribution increases and the star formation efficiency (SFE) mildly increases with M_*. The evolutionary track in the SSFR-M_* diagram, as well as that in the color magnitude diagram are linked to the HI content; below this transition mass, the star formation is regulated strongly by the HI. Comparison of HI- and optically-selected samples over the same restricted volume shows that the HI-selected population is less evolved and has overall higher SFR and SSFR at a given stellar mass, but lower SFE and extinction, suggesting either that a bottleneck exists in the HI to H_2 conversion, or that the process of SF in the very HI-dominated galaxies obeys an unusual, low efficiency star formation law. A trend is found that, for a given stellar mass, high gas fraction galaxies reside preferentially in dark matter halos with high spin parameters. Because it represents a full census of HI-bearing galaxies at z~0, the scaling relations and fundamental planes derived for the ALFALFA population can be used to assess the HI detection rate by future blind HI surveys and intensity mapping experiments at higher redshift.
We investigated gravitational microlensing of AGN dusty tori in the case of lensed quasars in the infrared domain. The dusty torus is modeled as a clumpy two-phase medium. To obtain spectral energy distributions and images of tori at different wavelengths, we used the 3D Monte Carlo radiative transfer code SKIRT. A ray-shooting technique has been used to calculate microlensing magnification maps. We simulated microlensing by the stars in the lens galaxy for different configurations of the lensed system and different values of the torus parameters, in order to estimate (a) amplitudes and timescales of high magnification events, and (b) the influence of geometrical and physical properties of dusty tori on light curves in the infrared domain. We found that, despite their large size, dusty tori could be significantly affected by microlensing in some cases, especially in the near-infrared domain (rest-frame). The very long timescales of such events, in the range from several decades to hundreds of years, are limiting the practical use of this method to study the dusty tori properties. However, our results indicate that, when studying flux ratios between the images in different wavebands of lensed quasars, one should not disregard the possibility that the near and mid-infrared flux ratios could be under the influence of microlensing.
We compute the full bispectra, including cross bispectra, of primordial curvature and tensor perturbations in the most general single-field inflation model whose scalar and gravitational equations of motion are of second order. The formulae in the limits of k-inflation and potential-driven inflation are also given. These expressions are useful for estimating the full bispectra of temperature and polarization anisotropies of the cosmic microwave background radiation.
Stellar shells observed in many giant elliptical and lenticular as well as a few spiral and dwarf galaxies, presumably result from galaxy mergers. Line-of-sight velocity distributions of the shells could, in principle, if measured with a sufficiently high S/N, constitute one of methods to constrain the gravitational potential of the host galaxy. Merrifield & Kuijken (1998) predicted a double-peaked line profile for stationary shells resulting from a nearly radial minor merger. In this paper, we aim at extending their analysis to a more realistic case of expanding shells, inherent to the merging process, in the same type of merger and the same orbital geometry. We use analytical approach as well as test particle simulations to predict the line-of-sight velocity profile across the shell structure. Simulated line profiles are convolved with spectral PSFs to estimate the peak detectability. The resulting line-of-sight velocity distributions are more complex than previously predicted due to non-zero phase velocity of the shells. In principle, each of the Merrifield & Kuijken (1998) peaks splits into two, giving a quadruple-peaked line profile, which allows more precise determination of the potential of the host galaxy and, moreover, contains additional information. We find simple analytical expressions that connect the positions of the four peaks of the line profile and the mass distribution of the galaxy, namely the circular velocity at the given shell radius and the propagation velocity of the shell. The analytical expressions were applied to a test-particle simulation of a radial minor merger and the potential of the simulated host galaxy was successfully recovered. The shell kinematics can thus become an independent tool to determine the content and distribution of the dark matter in shell galaxies, up to ~100 kpc from the center of the host galaxy.
A 2.29 GHz VLBI all-sky survey of ultra-compact radio sources has formed the basis of a number of cosmological investigations, which examine the relationship between angular-size and redshift. Here I use a sample of 468 such sources with 0.5<z<=3.787, to investigate the isotropy of the Universe. The sample is divided into hemispherical sub-samples, over an all-sky 5 degree x 5 degree array, each of which is allowed to determine a value of Omega_m, assuming that we are living in a spatially flat homogeneous isotropic LambdaCDM model. If we regard the latter as a null hypothesis, then it fails the test -- the results show significant anisotropy, the smallest value of Omega_m being towards (l,b)=(253.9,24.1) degrees, the largest in the opposite direction. This is close to the CMB dipole axis, but in the obverse sense. This is interpreted as meaning that the Universe is not spatially homogeneous on the largest scales, and is better represented at late times by a spherically symmetric model with a density enhancement at its centre.
An analysis of the full cosmic microwave background (CMB) sky by the Wilkinson Microwave Anisotropy Probe (WMAP) has revealed that the two lowest cosmologically interesting multipoles, the quadrupole (l=2) and the octopole (l=3) moments of the temperature variations, are unexpectedly aligned with each other. In this paper, we demonstrate that, whereas this alignment constitutes a statistically significant anomaly in the standard model, it is statistically insignificant within the context of the R_h=ct Universe. The key physical ingredient responsible for this difference is the existence in the latter of a maximum fluctuation size at the time of recombination, which is absent in LCDM because of inflation.
We study the evolution of QCD phase transition-generated magnetic fields in freely decaying MHD turbulence of the expanding Universe. We consider a magnetic field generation model that starts from basic non-perturbative QCD theory and predicts stochastic magnetic fields with an amplitude of the order of 0.02 $\mu$G and small magnetic helicity. We employ direct numerical simulations to model the MHD turbulence decay and identify two different regimes: "weakly helical" turbulence regime, when magnetic helicity increases during decay, and "fully helical" turbulence, when maximal magnetic helicity is reached and an inverse cascade develops. The results of our analysis show that in the most optimistic scenario the magnetic correlation length in the comoving frame can reach 10 kpc with the amplitude of the effective magnetic field being 0.007 nG. We demonstrate that the considered model of magneto-genesis can provide the seed magnetic field for galaxies and clusters.
Can the standard cosmological model be questioned on the basis of a single observed extreme galaxy cluster? Usually, the word extreme refers directly to cluster mass, which is not a direct observable and thus subject to substantial uncertainty. Hence, it is desirable to extend studies of extreme clusters to direct observables such as the Einstein radius (ER). We aim to evaluate the occurrence probability of the large observed ER of MACS J0717.5 within the standard LCDM cosmology. In particular, we want to model the distribution function of the single largest ER in a given cosmological volume and to study which underlying assumptions and effects have the strongest impact on the results. We obtain this distribution by a Monte Carlo approach, based on the semi-analytic modelling of the halo population on the past lightcone. After sampling the distribution, we fit the results with the general extreme value (GEV) distribution which we use for the subsequent analysis. We find that the distribution of the maximum ER is particularly sensitive to the precise choice of the halo mass function, lens triaxiality, the inner slope of the halo density profile and the mass-concentration relation. Using the distributions so obtained,we study the occurrence probability of the large ER of MACS J0717.5, finding that this system is not in tension with LCDM. We also find that the GEV distribution can be used to fit very accurately the sampled distributions and that all of them can be described by a Frechet distribution. With a multitude of effects that strongly influence the distribution of the single largest ER, it is more than doubtful that the standard LCDM cosmology can be ruled out on the basis of a single observation. If, despite the large uncertainties in the underlying assumptions, one wanted to do so, a much larger ER (> 100 arcsec) than that of MACS J0717.5 would have to be observed.
The Fermi-LAT collaboration has recently reported the detection of angular power above the photon noise level in the diffuse gamma-ray background between 1 and 50 GeV. Such signal can be used to constrain a possible contribution from Dark-Matter-induced photons. We estimate the intensity and features of the angular power spectrum (APS) of this potential Dark Matter (DM) signal, for both decaying and annihilating DM candidates, by constructing template all-sky gamma-ray maps for the emission produced in the galactic halo and its substructures, as well as in extragalactic (sub)halos. The DM distribution is given by state-of-the-art N-body simulations of cosmic structure formation, namely Millennium-II for extragalactic (sub)halos, and Aquarius for the galactic halo and its subhalos. We use a hybrid method of extrapolation to account for (sub)structures that are below the resolution limit of the simulations, allowing us to estimate the total emission all the way down to the minimal self-bound halo mass. We describe in detail the features appearing in the APS of our template maps and we estimate the effect of various uncertainties such as the value of the minimal halo mass, the fraction of substructures hosted in a halo and the shape of the DM density profile. Our results indicate that the fluctuation APS of the DM-induced emission is of the same order as the Fermi-LAT APS, suggesting that one can constrain this hypothetical emission from the comparison with the measured anisotropy. We also quantify the uncertainties affecting our results, finding "theoretical error bands" spanning more than two orders of magnitude and dominated (for a given particle physics model) by our lack of knowledge of the abundance of low-mass (sub)halos.
We investigate the equation of state (EoS) of the scalar-torsion mode in Poincar\'{e} gauge theory of gravity. We concentrate on two cases with the constant curvature solution and positive kinetic energy, respectively. In the former, we find that the torsion EoS has different values in the various stages of the universe. In particular, it behaves like the radiation (matter) EoS of $w_r=1/3$ ($w_m=0$) in the radiation (matter) dominant epoch, while in the late time the torsion density is supportive for the accelerating universe. In the latter, our numerical analysis shows that in general the EoS has an asymptotic behavior in the high redshift regime, while it could cross the phantom divide line in the low redshift regime.
The pseudoscalar-photon mixing in presence of large scale magnetic field induces polarization in light from distant cosmological sources. We study the effect of these pseudoscalars or axion like particles (ALPs) on Cosmic Microwave Background Radiation (CMBR) and constrain the product of mixing strength $g_{\phi}$ times background magnetic field $B$. The background magnetic field has been assumed to be primordial and we assume large scale correlations with the correlation length of 1Mpc. We use WMAP seven year foreground reduced polarization and temperature data to constrain pseudoscalar-photon mixing parameter. We look for different mass limits of the pseudoscalars and find $g_{\phi}B\le 1.6\times10^{-13} GeV^{-1} nG$ with ALPs of mass $10^{-10} eV$ and $g_{\phi}B\le3.4\times10^{-15} GeV^{-1} nG$ for ultra light ALPs of mass $10^{-15} eV$.
In this paper we conjecture the existence of a new "ground" state in quantum gravity, supplying a wave function for the inflationary Universe. We present its explicit perturbative expression in the connection representation, exhibiting the associated inner product. The state is chiral, dependent on the Immirzi parameter, and is the vacuum of a second quantized theory of graviton particles. We identify the physical and unphysical Hilbert sub-spaces. We then contrast this state with the perturbed Kodama state and explain why the latter can never describe gravitons in a de Sitter background. Instead, it describes self-dual excitations, which are composites of the positive frequencies of the right-handed graviton and the negative frequencies of the left-handed graviton. These excitations are shown to be unphysical under the inner product we have identified. Our rejection of the Kodama state has a moral tale to it: the semi-classical limit of quantum gravity can be the wrong path for making contact with reality (which may sometimes be perturbative but nonetheless fully quantum). Our results point towards a non-perturbative extension, and we present some conjectures on the nature of this hypothetical state.
PHL 1092 is a z~0.4 high-luminosity counterpart of the class of Narrow-Line Seyfert 1 galaxies. In 2008, PHL 1092 was found to be in a remarkably low X-ray flux state during an XMM-Newton observation. Its 2 keV flux density had dropped by a factor of ~260 with respect to a previous observation performed 4.5 yr earlier. The UV flux remained almost constant, resulting in a significant steepening of the optical-to-X-ray slope alpha_ox from -1.57 to -2.51, making PHL 1092 one of the most extreme X-ray weak quasars with no observed broad absorption lines (BALs) in the UV. We have monitored the source since 2008 with three further XMM-Newton observations, producing a simultaneous UV and X-ray database spanning almost 10 yr in total in the activity of the source. Our monitoring program demonstrates that the alpha_ox variability in PHL 1092 is entirely driven by long-term X-ray flux changes. We apply a series of physically-motivated models with the goal of explaining the UV-to-X-ray spectral energy distribution (SED) and the extreme X-ray and alpha_ox variability. We consider three possible models: i) A "breathing corona" scenario in which the size of the X-ray emitting corona is correlated with the X-ray flux. In this case, the lowest X-ray flux states of PHL 1092 are associated with an almost complete collapse of the X-ray corona down to the marginal stable orbit; ii) An absorption scenario in which the X-ray flux variability is entirely due to intervening absorption. If so, PHL 1092 is a quasar with standard X-ray output for its optical luminosity, appearing as X-ray weak at times due to absorption; iii) A disc-reflection-dominated scenario in which the X-ray emitting corona is confined within a few gravitational radii from the black hole at all times. In this case, the intrinsic variability of PHL 1092 only needs to be a factor of ~10 rather than the observed factor of ~260.
Cygnus A harbours the nearest powerful radio jet of an Fanaroff-Riley (FR) class II radio galaxy in a galaxy cluster where the interaction of the jet with the intracluster medium (ICM) can be studied in detail. We use a large set of Chandra archival data, VLA and new LOFAR observations to shed new light on the interaction of the jets with the ICM. We identify an X-ray cavity in the distribution of the X-ray emitting plasma in the region south of the Cyg A nucleus which has lower pressure than the surrounding medium. The LOFAR and VLA radio observations show that the cavity is filled with synchrotron emitting plasma. The spectral age and the buoyancy time of the cavity indicates an age at least as large as the current Cyg A jets and not much larger than twice this time. We suggest that this cavity was created in a previous active phase of Cyg A when the energy output of the Active Galactic Nucleus (AGN) was about two orders of magnitude less than today.
The EAGLE and EVE Phase A studies for instruments for the European Extremely Large Telescope (E-ELT) originated from related top-level scientific questions, but employed different (yet complementary) methods to deliver the required observations. We re-examine the motivations for a multi-object spectrograph (MOS) on the E-ELT and present a unified set of requirements for a versatile instrument. Such a MOS would exploit the excellent spatial resolution in the near-infrared envisaged for EAGLE, combined with aspects of the spectral coverage and large multiplex of EVE. We briefly discuss the top-level systems which could satisfy these requirements in a single instrument at one of the Nasmyth foci of the E-ELT.
Hydrodynamic stability has been a longstanding issue for the cloud model of the broad line region in active galactic nuclei. We argue that the clouds may be gravitationally bound to the supermassive black hole. If true, stabilisation by thermal pressure alone becomes even more difficult. We further argue that if magnetic fields should be present in such clouds at a level that could affect the stability properties, they need to be strong enough to compete with the radiation pressure on the cloud. This would imply magnetic field values of a few Gauss for a sample of Active Galactic Nuclei we draw from the literature. We then investigate the effect of several magnetic configurations on cloud stability in axi-symmetric magnetohydrodynamic simulations. For a purely azimuthal magnetic field which provides the dominant pressure support, the cloud first gets compressed by the opposing radiative and gravitational forces. The pressure inside the cloud then increases, and it expands vertically. Kelvin-Helmholtz and column density instability lead to a filamentary fragmentation of the cloud. This radiative dispersion continues until the cloud is shredded down to the resolution level. For a helical magnetic field configuration, a much more stable cloud core survives with a stationary density histogram which takes the form of a power law. Our simulated clouds develop sub-Alfvenic internal motions on the level of a few hundred km/s.
There is evidence for a 130 GeV gamma-ray line at the Galactic Center in the Fermi Large Area Telescope data. Dark matter candidates that explain this feature should also annihilate to Standard Model particles, resulting in a continuous spectrum of photons. To study this continuum, we analyze the Fermi data down to 5 GeV, restricted to the inner 3 degrees of the Galaxy. We place a strong bound on the ratio of continuum photons to monochromatic line photons that is independent of uncertainties in the dark matter density profile. Neutralino dark matter is excluded by the derived constraints.
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It is a firm prediction of the concordance Cold Dark Matter (CDM) cosmological model that galaxy clusters live at the intersection of large-scale structure filaments. The thread-like structure of this "cosmic web" has been traced by galaxy redshift surveys for decades. More recently the Warm-Hot Intergalactic Medium (WHIM) residing in low redshift filaments has been observed in emission and absorption. However, a reliable direct detection of the underlying Dark Matter skeleton, which should contain more than half of all matter, remained elusive, as earlier candidates for such detections were either falsified or suffered from low signal-to-noise ratios and unphysical misalignements of dark and luminous matter. Here we report the detection of a dark matter filament connecting the two main components of the Abell 222/223 supercluster system from its weak gravitational lensing signal, both in a non-parametric mass reconstruction and in parametric model fits. This filament is coincident with an overdensity of galaxies and diffuse, soft X-ray emission and contributes mass comparable to that of an additional galaxy cluster to the total mass of the supercluster. Combined with X-ray observations, we place an upper limit of 0.09 on the hot gas fraction, the mass of X-ray emitting gas divided by the total mass, in the filament.
Massive black hole binaries at sub-parsec separations may display in their spectra anomalously small flux ratios between the MgII and CIV broad emission lines, i.e. F_MgII/F_CIV <~ 0.1, due to the erosion of the broad line region around the active, secondary black hole, by the tidal field of the primary. In Paper I by Montuori et al. (2011), we focussed on broad lines emitted by gas bound to the lighter accreting member of a binary when the binary is at the center of a hollow density region (the gap) inside a circum-binary disc. The main aim of this new study is at exploring the potential contribution to the broad line emission by the circum-binary disc and by gaseous streams flowing toward the black hole through the gap. We carry out a post-process analysis of data extracted from a SPH simulation of a circum-binary disc around a black hole binary. Our main result is that the MgII to CIV flux ratio can be reduced to ~ 0.1 within an interval of sub-pc binary separations of the order of a ~ (0.01-0.2)(f_Edd/0.1)^(1/2) pc corresponding to orbital periods of ~ (20-200) (f_Edd/0.1)^(3/4) years for a secondary BH mass in the range M_2 ~ 10^7-10^9 M_sun and a binary mass ratio of 0.3. At even closer separations this ratio returns to increase to values that are indistinguishable from the case of a single AGN (typically F_MgII/F_CIV ~ 0.3-0.4) because of the contribution to the MgII line from gas in the circum-binary disc.
A dark matter halo is commonly defined as a spherical overdensity of matter with respect to a reference density, such as the critical density or the mean matter density of the Universe. We show that such definitions lead to a spurious evolution in the halo's mass even if its physical density profile remains constant over time. This pseudo-evolution in mass is caused by the evolution of the reference density with redshift, and has little connection with the actual physical accretion of mass. We compute the pseudo-evolution of halos identified in a large N-body simulation from z=1 to 0, and show that it increases halo masses significantly across a wide range of halo masses and overdensities. Pseudo-evolution accounts for almost the entire mass evolution of halos with M200 smaller or equal 1E12 solar masses, while for larger halos it still accounts for about 50 percent of their overall mass evolution. We estimate the magnitude of the pseudo-evolution assuming that halo density profiles remain static in physical coordinates, and show that this simple model predicts the pseudo-evolution of simulated halos to a few percent accuracy. We discuss the impact of pseudo-evolution on the evolution of the halo mass function. We show that the non-evolution of the low-mass end of the halo mass function is the result of a fortuitous cancellation between pseudo-evolution and the absorption of small halos into larger hosts. We also show that the evolution of the low-mass end of the concentration-mass relation observed in simulations is almost entirely due to the pseudo-evolution of mass. Finally, we discuss the implications of our results for the interpretation of the evolution of various scaling relations between the observable properties of galaxies and galaxy clusters, and their halo masses.
We develop a perturbative approach to redshift space distortions (RSD) using the phase space distribution function approach and apply it to the dark matter redshift space power spectrum and its moments. RSD can be written as a sum over density weighted velocity moments correlators, with the lowest order being density, momentum density and stress energy density. We use standard and extended perturbation theory (PT) to determine their auto and cross correlators, comparing them to N-body simulations. We show which of the terms can be modeled well with the standard PT and which need additional terms that include higher order corrections which cannot be modeled in PT. Most of these additional terms are related to the small scale velocity dispersion effects, the so called finger of god (FoG) effects, which affect some, but not all, of the terms in this expansion, and which can be approximately modeled using a simple physically motivated ansatz such as the halo model. We point out that there are several velocity dispersions that enter into the detailed RSD analysis with very different amplitudes, which can be approximately predicted by the halo model. In contrast to previous models our approach systematically includes all of the terms at a given order in PT and provides a physical interpretation for the small scale dispersion values. We investigate RSD power spectrum as a function of \mu, the cosine of the angle between the Fourier mode and line of sight, focusing on the lowest order powers of \mu and multipole moments which dominate the observable RSD power spectrum. Overall we find considerable success in modeling many, but not all, of the terms in this expansion.
If the radio background is coming from cosmological sources, there should be some amount of clustering due to the large scale structure in the universe. Simple models for the expected clustering combined with the recent measurement by ARCADE-2 of the mean extragalactic temperature lead to predicted clustering levels that are substantially above upper limits from searches for anisotropy on arcminute scales using ATCA and the VLA. The rms temperature variations in the cosmic radio background appear to be more than a factor of 10 smaller (in temperature) than the fluctuations in the cosmic infrared background. It is therefore extremely unlikely that this background comes from galaxies, galaxy clusters, or any sources that trace dark matter halos at z<5, unless typical sources are smooth on arcminute scales, requiring typical sizes of several Mpc.
We develop a numerical statistical method to study linear cosmological fluctuations in inflationary scenarios with multiple fields, and apply it to an ensemble of six-field inflection point models in string theory. The latter are concrete microphysical realizations of quasi-single-field inflation, in which scalar masses are of order the Hubble parameter and an adiabatic limit is reached before the end of inflation. We find that slow-roll violations, bending trajectories and 'many-field' effects are commonplace in realizations yielding more than 60 e-folds of inflation, although models in which these effects are substantial are in tension with observational constraints on the tilt of the scalar power spectrum.
We demonstrate that the space formed by the star-formation rate (SFR), gas-phase metallicity (Z), and stellar mass (M), can be reduced to a plane, as first proposed by Lara-Lopez et al. We study three different approaches to find the best representation of this 3D space, using a principal component analysis, a regression fit, and binning of the data. The PCA shows that this 3D space can be adequately represented in only 2 dimensions, i.e., a plane. We find that the plane that minimises the chi^2 for all variables, and hence provides the best representation of the data, corresponds to a regression fit to the stellar mass as a function of SFR and $Z$, M=f(Z,SFR). We find that the distribution resulting from the median values in bins for our data gives the highest chi^2. We also show that the empirical calibrations to the oxygen abundance used to derive the Fundamental Metallicity Relation (Nagao et al.) have important limitations, which contribute to the apparent inconsistencies. The main problem is that these empirical calibrations do not consider the ionization degree of the gas. Furthermore, the use of the N2 index to estimate oxygen abundances cannot be applied for ~8.8 because of the saturation of the [NII]6584 line in the high-metallicity regime. Finally we provide an update of the Fundamental Plane derived by Lara-Lopez et al.
We present a deep [OII] emission line survey of faint galaxies (22.5<KAB<24) in the Chandra Deep Field South and the FIRES field. With these data we measure the star formation rate (SFR) in galaxies in the stellar mass range 8.85 < log(M*/Msun) < 9.5 at 0.62<z<0.885, to a limit of SFR = 0.1Msun/yr. The presence of a massive cluster (MS1054-03) in the FIRES field, and of significant large scale structure in the CDFS field, allows us to study the environmental dependence of SFRs amongst this population of low-mass galaxies. Comparing our results with more massive galaxies at this epoch, with our previous survey (ROLES) at the higher redshift z=1, and with SDSS Stripe 82 data, we find no significant evolution of the stellar mass function of star-forming galaxies between z=0 and z=1, and no evidence that its shape depends on environment. The correlation between specific star formation rate (sSFR) and stellar mass at z=0.75 has a power-law slope of beta=-0.2, with evidence for a steeper relation at the lowest masses. The normalization of this correlation lies as expected between that corresponding to z=1 and the present day. The global SFR density is consistent with an evolution of the form (1+z)^2 over 0<z<1, with no evidence for a dependence on stellar mass. The sSFR of these star-forming galaxies at z=0.75 does not depend upon the density of their local environment. Considering just high-density environments, the low-mass end of the sSFR-M* relation in our data is steeper than that in Stripe 82 at z=0, and shallower than that measured by ROLES at z=1. Evolution of low-mass galaxies in dense environments appears to be more rapid than in the general field.
Recent N-Body simulations are in favor of the presence of a co-rotating Dark Disk that might contribute significantly (10%-50%) to the local Dark Matter density. Such substructure could have dramatic effect on directional detection. Indeed, in the case of a null lag velocity, one expects an isotropic WIMP velocity distribution arising from the Dark Disk contribution, which might weaken the strong angular signature expected in directional detection. For a wide range of Dark Disk parameters, we evaluate in this Letter the effect of such dark component on the discovery potential of upcoming directional detectors. As a conclusion of our study, using only the angular distribution of nuclear recoils, we show that Dark Disk models as suggested by recent N-Body simulations will not affect significantly the Dark Matter reach of directional detection, even in extreme configurations.
Directional detection is a promising Dark Matter search strategy. Taking advantage on the rotation of the Solar system around the galactic center through the Dark Matter halo, it allows to show a direction dependence of WIMP events that may be a powerful tool to identify genuine WIMP events as such. Directional detection strategy requires the simultaneous measurement of the energy and the 3D track of low energy recoils, which is a common challenge for all current projects of directional detectors.
We consider the possibility that the primordial curvature perturbation was generated through the curvaton mechanism from a scalar field with an electric charge, or precisely the Standard Model U(1) weak hypercharge. This links the dynamics of the very early universe concretely to the Standard Model of particle physics, and because the coupling strength is known, it reduces the number of free parameters in the curvaton model. We show that the model is compatible with CMB observations for Hubble rate $H_* > 10^8 GeV$ and curvaton mass $m > 10^{-2}H_*$. Charge fluctuations generated during inflation are screened by electron-positron pairs, and therefore do not violate observational constraints. The interaction with the gauge field leads to interesting dynamics after inflation, including resonant preheating, with potentially highly non-trivial observational consequences, which should be studied more carefully using numerical field theory simulations.
We investigate the potential to improve optical tracers of cluster mass by exploiting measurements of the magnitude gap, m12, defined as the difference between the r-band absolute magnitude of the two brightest cluster members. We find that in a mock sample of galaxy groups and clusters constructed from the Bolshoi simulation, the scatter about the mass-richness relation decreases by 15-20% when magnitude gap information is included. A similar trend is evident in a volume-limited, spectroscopic sample of galaxy groups observed in the Sloan Digital Sky Survey (SDSS). We find that SDSS groups with small magnitude gaps are richer than large-gap groups at fixed values of the one-dimensional velocity dispersion among group members sigma_v, which we use as a mass proxy. We demonstrate explicitly that m12 contains information about cluster mass that supplements the information provided by group richness and the luminosity of the brightest cluster galaxy, L_bcg. In so doing, we show that the luminosities of the members of a group with richness N are inconsistent with the distribution of luminosities that results from N random draws from the global galaxy luminosity function. As the cosmological constraining power of galaxy clusters is limited by the precision in cluster mass determination, our findings suggest a new way to improve the cosmological constraints derived from galaxy clusters.
In the framework of the recently proposed models of massive gravity, defined with respect to a de Sitter reference metric, we obtain new homogeneous and isotropic solutions for arbitrary cosmological matter and arbitrary spatial curvature. These solutions can be classified into three branches. In the first two, the massive gravity terms behave like a cosmological constant. In the third branch, the massive gravity effects can be described by a time evolving effective fluid with rather remarkable features, including the property to behave as a cosmological constant at late time.
We present a fast likelihood method for including event-level neutrino telescope data in parameter explorations of theories for new physics, and announce its public release as part of DarkSUSY 5.0.6. Our construction includes both angular and spectral information about neutrino events, as well as their total number. We also present a corresponding measure for simple model exclusion, which can be used for single models without reference to the rest of a parameter space. We perform a number of supersymmetric parameter scans with IceCube data to illustrate the utility of the method: example global fits and a signal recovery in the constrained minimal supersymmetric standard model (CMSSM), and a model exclusion exercise in a 7-parameter phenomenological version of the MSSM. The final IceCube detector configuration will probe almost the entire focus-point region of the CMSSM, as well as a number of MSSM-7 models that will not otherwise be accessible to e.g. direct detection. Our method accurately recovers the mock signal, and provides tight constraints on model parameters and derived quantities. We show that the inclusion of spectral information significantly improves the accuracy of the recovery, providing motivation for its use in future IceCube analyses.
We report on a detailed study of the Fe K emission/absorption complex in the nearby, bright Seyfert 1 galaxy Mrk 509. The study is part of an extensive XMM-Newton monitoring consisting of 10 pointings (~60 ks each) about once every four days, and includes also a reanalysis of previous XMM-Newton and Chandra observations. Mrk 509 shows a clear (EW=58 eV) neutral Fe Kalpha emission line that can be decomposed into a narrow (sigma=0.027 keV) component (found in the Chandra HETG data) plus a resolved (sigma=0.22 keV) component. We find the first successful measurement of a linear correlation between the intensity of the resolved line component and the 3-10 keV flux variations on time-scales of years down to a few days. The Fe Kalpha reverberates the hard X-ray continuum without any measurable lag, suggesting that the region producing the resolved Fe Kalpha component is located within a few light days-week (r<~10^3 rg) from the Black Hole (BH). The lack of a redshifted wing in the line poses a lower limit of >40 rg for its distance from the BH. The Fe Kalpha could thus be emitted from the inner regions of the BLR, i.e. within the ~80 light days indicated by the Hbeta line measurements. In addition to these two neutral Fe Kalpha components, we confirm the detection of weak (EW~8-20 eV) ionised Fe K emission. This ionised line can be modeled with either a blend of two narrow FeXXV and FeXXVI emission lines or with a single relativistic line produced, in an ionised disc, down to a few rg from the BH. Finally, we observe a weakening/disappearing of the medium and high velocity high ionisation Fe K wind features found in previous XMM-Newton observations. This campaign has made possible the first reverberation measurement of the resolved component of the Fe Kalpha line, from which we can infer a location for the bulk of its emission at a distance of r~40-1000 rg from the BH.
A survey of the Milky Way disk and the Magellanic System at the wavelengths of the 21-cm atomic hydrogen (HI) line and three 18-cm lines of the OH molecule will be carried out with the Australian Square Kilometre Array Pathfinder telescope. The survey will study the distribution of HI emission and absorption with unprecedented angular and velocity resolution, as well as molecular line thermal emission, absorption, and maser lines. The area to be covered includes the Galactic plane (|b|< 10deg) at all declinations south of delta = +40deg, spanning longitudes 167deg through 360deg to 79deg at b=0deg, plus the entire area of the Magellanic Stream and Clouds, a total of 13,020 square degrees. The brightness temperature sensitivity will be very good, typically sigma_T ~ 1 K at resolution 30arcsec and 1 km/s. The survey has a wide spectrum of scientific goals, from studies of galaxy evolution to star formation, with particular contributions to understanding stellar wind kinematics, the thermal phases of the interstellar medium, the interaction between gas in the disk and halo, and the dynamical and thermal states of gas at various positions along the Magellanic Stream.
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Using multiple tracers of large-scale structure allows to evade the limitations imposed by sampling variance for some parameters of interest in cosmology. We demonstrate the optimal way of carrying out a multitracer analysis in a galaxy redshift survey by considering the principal components of the shot noise matrix from two-point clustering statistics. We show how to construct two tracers that maximize the benefits of sampling variance and shot noise cancellation using optimal weights. On the basis of high-resolution N-body simulations of dark matter halos we apply this technique to the analysis of redshift-space distortions and demonstrate how constraints on the growth rate of structure formation can be substantially improved. The primary limitation are nonlinear effects, which cause significant biases in the method already at scales of k<0.1h/Mpc, suggesting the need to develop nonlinear models of redshift-space distortions in order to extract the maximum information from future redshift surveys.
Cosmic microwave background polarization encodes information not only on the early universe but also dark energy, neutrino mass, and gravity in the late universe through CMB lensing. Ground based surveys such as ACTpol, PolarBear, SPTpol significantly complement cosmological constraints from the Planck satellite, strengthening the CMB dark energy figure of merit and neutrino mass constraints by factors of 3-4. This changes the dark energy probe landscape. We evaluate the state of knowledge in 2017 from ongoing experiments including dark energy surveys (supernovae, weak lensing, galaxy clustering), fitting for dynamical dark energy, neutrino mass, and a modified gravitational growth index. Adding a modest strong lensing time delay survey improves those dark energy constraints by a further 32%, and an enhanced low redshift supernova program improves them by 26%.
Recent studies have shown that the cross-correlation coefficient between galaxies and dark matter is very close to unity on scales outside a few virial radii of galaxy halos, independent of the details of how galaxies populate dark matter halos. This finding makes it possible to determine the dark matter clustering from measurements of galaxy-galaxy weak lensing and galaxy clustering. We present new cosmological parameter constraints based on large-scale measurements of spectroscopic galaxy samples from the Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7). We generalise the approach of Baldauf et al. (2010) to remove small scale information (below 2 and 4 Mpc/h for lensing and clustering measurements, respectively), where the cross-correlation coefficient differs from unity. We derive constraints for three galaxy samples covering 7131 sq. deg., containing 69150, 62150, and 35088 galaxies with mean redshifts of 0.11, 0.28, and 0.40. We clearly detect scale-dependent galaxy bias for the more luminous galaxy samples, at a level consistent with theoretical expectations. When we vary both \sigma_8 and \Omega_m with other cosmological parameters fixed (and marginalise over non-linear galaxy bias), the best-constrained quantity is \sigma_8 (\Omega_m/0.25)^{0.57}=0.80 +/- 0.05 (1-sigma, stat. + sys.), where statistical and systematic errors have comparable contributions. These strong constraints on the dark matter clustering suggest that this method is competitive with cosmic shear in current data, while having very complementary and in some ways less serious systematics. We therefore expect that this method will play a prominent role in future weak lensing surveys. When we combine these data with WMAP7 CMB data, constraints on \sigma_8, \Omega_m, H_0, w_{de} and \sum m_{\nu} become 30--80 per cent tighter than with CMB data alone, since our data break several parameter degeneracies.
We examine a spatially flat Friedmann-Robertson-Walker (FRW) universe filled with interacting dark matter and a modified holographic Ricci dark energy (MHRDE). The interaction term is selected as a significant rational function of the total energy density and its first derivative homogeneous of degree. We show that the effective one-fluid obeys the equation of state of a relaxed Chaplygin gas, then the universe turns to be dominated by pressureless dark matter at early times and undergoes an accelerated expansion in the far future driven by a strong negative pressure. Performing a $\chi^{2}$-statistical analysis with the observational Hubble data and the Union2 compilation of SNe Ia, we place some constraints on cosmological parameters analyzing the feasibleness of the modified holographic Ricci ansatz. It turned that MHRDE gets the accelerated expansion faster than the $\Lambda$CDM model. Finally, a new model with a component that does not exchange energy with the interacting dark sector is presented for studying bounds on the dark energy at early times.
We analyze non-Gaussianity (NG) due to primordial bispectrum and trispectrum using CMB temperature maps of WMAP 7-year data. We first apply the perturbative formulae of Minkowski functionals upto second-order NG derived by Matsubara (2010), which enable us to give limits on the cubic NG parameterized with tau_NL and g_NL as well as various types of quadratic NG parameterized with f_NL. We find no signature of primordial NG in WMAP data, but give constraints on the local-type, equilateral-type, orthogonal-type f_NL: f_NL(loc)=20+-42, f_NL(eq)=-121+-208, f_NL(ort)=-129+-171, and tau_NL/10^4=-7.6+-8.7, and g_NL/10^5=-1.9+-6.4. We also find that these constraints are consistent with the limits from skewness and kurtosis parameters which characterize the perturbative corrections of MFs.
We present the results of a search for red QSOs using a selection based on optical imaging from SDSS and near-infrared imaging from UKIDSS. For a sample of 58 candidates 46 (79%) are confirmed to be QSOs. The QSOs are predominantly dust-reddened except a handul at redshifts z>3.5. The dust is most likely located in the QSO host galaxies. 4 (7%) of the candidates turned out to be late-type stars, and another 4 (7%) are compact galaxies. The remaining 4 objects we could not identify. In terms of their optical spectra the QSOs are similar to the QSOs selected in the FIRST-2MASS red Quasar survey except they are on average fainter, more distant and only two are detected in the FIRST survey. We estimate the amount of extinction using the SDSS QSO template reddened by SMC-like dust. It is possible to get a good match to the observed (restframe ultraviolet) spectra, but for nearly all the reddened QSOs it is not possible to match the near-IR photometry from UKIDSS. The likely reasons are that the SDSS QSO template is too red at optical wavelengths due to contaminating host galaxy light and that the assumed SMC extinction curve is too shallow. Our survey has demonstrated that selection of QSOs based on near-IR photometry is an efficent way to select QSOs, including reddened QSOs, with only small contamination from late-type stars and compact galaxies. This will be useful with ongoing and future wide-field near-IR surveys such as the VISTA and EUCLID surveys. [Abridged]
Group galaxies very often show distinct signs of interaction with both companion galaxies and the intragroup medium. X-ray observations are particularly helpful because they provide information on the temperatures and the densities of the hot gas in galaxies and intergalactic space. This can put important constraints on the nature and timescales of these interactions. We use the XMM-Newton X-ray observations of NGC 3627 in the Leo Triplet galaxy group to explain peculiar features visible in the polarized radio maps. We analyzed soft X-ray (0.2-1 keV) emission from NGC 3627 to study the distribution of the hot gas and its temperature in different areas of the galaxy. Any change throughout the disk can reflect distortions visible in the radio polarized emission. We also studied two bright point sources that are probably tightly linked to the evolution of the galaxy. We find an increase in the temperature of the hot gas in the area of the polarized radio ridge in the western arm of the galaxy. In the eastern part of the disk we find two ultra-luminous X-ray sources. We note a large hot gas temperature difference (by a factor of 2) between the two bar ends. The polarized radio ridge in the western arm of NGC 3627 is most likely formed by ram-pressure effects caused by the movement of the galaxy through the intragroup medium. To explain the distortions visible in the eastern part of the disk in polarized radio maps, the asymmetry of the bar, and the distortion of the eastern arm, we propose a recent collision of NGC 3627 with a dwarf companion galaxy.
Scalar modifications of gravity have an impact on the growth of structure. Baryon and Cold Dark Matter (CDM) perturbations grow anomalously for scales within the Compton wavelength of the scalar field. In the late time Universe when reionisation occurs, the spectrum of the 21cm brightness temperature is thus affected. We study this effect for chameleon-f(R) models, dilatons and symmetrons. Although the f(R) models are more tightly constrained by solar system bounds, and effects on dilaton models are negligible, we find that symmetrons where the phase transition occurs before z_* ~ 2 will be detectable for a scalar field range as low as 5 kpc. For all these models, the detection prospects of modified gravity effects are higher when considering modes parallel to the line of sight where very small scales can be probed. The study of the 21 cm spectrum thus offers a complementary approach to testing modified gravity with large scale structure surveys. Short scales, which would be highly non-linear in the very late time Universe when structure forms and where modified gravity effects are screened, appear in the linear spectrum of 21 cm physics, hence deviating from General Relativity in a maximal way.
The effect of a stochastic background of cosmological perturbations on the luminosity-redshift relation is computed to second order through a recently proposed covariant and gauge-invariant light-cone averaging procedure. The resulting expressions are free from both ultraviolet and infrared divergences, implying that such perturbations cannot mimic a sizable fraction of dark energy. Different averages are estimated and depend on the particular function of the luminosity distance being averaged. The energy flux, being minimally affected by perturbations at large z, is proposed as the best choice for precision estimates of dark-energy parameters. Nonetheless, its irreducible (stochastic) variance induces statistical errors on \Omega_{\Lambda}(z) typically lying in the few-percent range.
Taking advantage of the sensitivity and angular resolution of the Herschel Space Observatory at far-infrared and submm wavelengths, we aim to characterize the physical properties of cold dust within nearby galaxies and study the robustness of the parameters we derive using different modified blackbody models. For a pilot subsample of the KINGFISH program, we perform 2 temperature fits of the Spitzer and Herschel photometric data (24 to 500um), with a warm and a cold component, globally and in each resolution element.At global scales, we observe ranges of values for beta_c(0.8 to 2.5) and Tc(19.1 to 25.1K).We compute maps of our parameters with beta fixed or free to test the robustness of the temperature and dust surface density maps we deduce. When the emissivity is fixed, we observe temperature gradients as a function of radius.When the emissivity is fitted as a free parameter, barred galaxies tend to have uniform fitted emissivities.Gathering resolved elements in a Tc-beta_c diagram underlines an anti-correlation between the two parameters.It remains difficult to assess whether the dominant effect is the physics of dust grains, noise, or mixing along the line of sight and in the beam. We finally observe in both cases that the dust column density peaks in central regions of galaxies and bar ends (coinciding with molecular gas density enhancements usually found in these locations).We also quantify how the total dust mass varies with our assumptions about the emissivity index as well as the influence of the wavelength coverage used in the fits. We show that modified blackbody fits using a shallow emissivity (beta_c < 2.0) lead to significantly lower dust masses compared to the beta_c < 2.0 case, with dust masses lower by up to 50% if beta_c=1.5 for instance.The working resolution affects our total dust mass estimates: masses increase from global fits to spatially-resolved fits.
There is a consensus that Type-Ia supernovae (SNe Ia) arise from the thermonuclear explosion of white dwarf stars that accrete matter from a binary companion. However, direct observation of SN Ia progenitors is lacking, and the precise nature of the binary companion remains uncertain. A temporal series of high-resolution optical spectra of the SN Ia PTF 11kx reveals a complex circumstellar environment that provides an unprecedentedly detailed view of the progenitor system. Multiple shells of circumsteller are detected and the SN ejecta are seen to interact with circumstellar material (CSM) starting 59 days after the explosion. These features are best described by a symbiotic nova progenitor, similar to RS Ophiuchi.
In this paper, we continue to examine the fundamental basis for the Friedmann-Robertson-Walker (FRW) metric and its application to cosmology, specifically addressing the question: What is the proper size of the visible universe? There are several ways of answering the question of size, though often with an incomplete understanding of how far light has actually traveled in reaching us today from the most remote sources. The difficulty usually arises from an inconsistent use of the coordinates, or an over-interpretation of the physical meaning of quantities such as the so-called proper distance R(t)=a(t)r, written in terms of the (unchanging) co-moving radius r and the universal expansion factor a(t). In this paper, we use the five non-trivial FRW metrics with constant spacetime curvature (i.e., the static FRW metrics, but excluding Minkowski) to prove that in static FRW spacetimes in which expansion began from an initial signularity, the visible universe today has a proper size equal to R_h(t_0/2), i.e., the gravitational horizon at half its current age. The exceptions are de Sitter and Lanczos, whose contents had pre-existing positions away from the origin.
We consider the AQUAL theory - a theory of modified gravity capable of resolving the missing mass problem - and study its predictions for micro gravity tests at the gravitational saddle points of the Solar system. We report that the AQUAL model enhances the gravity at the sub-micrometer ranges around the gravitational saddle points in a way that so far had been unnoticed. This enhancement can be measured. We, therefore, call for implementing micrometer gravity tests within the Solar gravitational saddle points.
A generic feature of viable $F(R)$ gravity is investigated: It is demonstrated that during the matter dominated era the large frequency oscillations of the effective dark energy may influence the behavior of higher derivatives of the Hubble parameter with the risk to produce some singular unphysical solutions at high redshift. This behavior is explicitly analyzed for realistic $F(R)$ models, in particular, exponential gravity and a power form model. To stabilize such oscillations, we consider the additional modification of the models via a correction term which does not destroy the viability properties. A detailed analysis on the future evolution of the universe and the evolution history of the growth index of the matter density perturbations are performed. Furthermore, we explore two applications of exponential gravity to the inflationary scenario. We show how it is possible to obtain different numbers of $e$-folds during the early-time acceleration by making different choices of the model parameters in the presence of ultrarelativistic matter, which destabilizes inflation and eventually leads to the exit from the inflationary stage. We execute the numerical analysis of inflation in two viable exponential gravity models. It is proved that at the end of the inflation, the effective energy density and curvature of the universe decrease and thus a unified description between inflation and the $\Lambda$CDM-like dark energy dominated era can be realized.
In this paper, we consider a theory of gravity with a metric-dependent torsion namely the $F(R,T)$ gravity, where $R$ is the curvature scalar and $T$ is the torsion scalar. We study a geometric root of such theory. In particular we give the derivation of the model from the geometrical point of view. Then we present the more general form of $F(R,T)$ gravity with two arbitrary functions and give some of its particular cases. In particular, the usual $F(R)$ and $F(T)$ gravity theories are the particular cases of the $F(R,T)$ gravity. In the cosmological context, we find that our new gravitational theory can describes the accelerated expansion of the universe.
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