Internal dark matter structure of the most massive galaxy clusters since redshift 1
Amandine M. C. Le Brun, Romain Teyssier
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Published in Proceedings of mmUniverse at NIKA2 - Observing the mm Universe with the NIKA2 camera, Rome (Italy), June 2021 7 pages, 3 figures This proceeding is entirely based upon arXiv:1709.07457 by the same first author
We investigate the evolution of the dark matter density profiles of the most massive galaxy clusters in the Universe. Using a `zoom-in' procedure on a large suite of cosmological simulations of total comoving volume of $3\,(h^{-1}\,\rm Gpc)^3$, we study the 25 most massive clusters in four redshift slices from $z\sim 1$ to the present. The minimum mass is $M_{500} > 5.5 \times 10^{14}$ M$_{\odot}$ at $z=1$. Each system has more than two million particles within $r_{500}$. Once scaled to the critical density at each redshift, the dark matter profiles within $r_{500}$ are strikingly similar from $z\sim1$ to the present day, exhibiting a low dispersion of 0.15 dex, and showing little evolution with redshift in the radial logarithmic slope and scatter. They have the running power law shape typical of the NFW-type profiles, and their inner structure, resolved to $3.8\,h^{-1}$ comoving kpc at $z=1$, shows no signs of converging to an asymptotic slope. Our results suggest that this type of profile is already in place at $z>1$ in the highest-mass haloes in the Universe, and that it remains exceptionally robust to merging activity.
Modified gravity and massive neutrino cosmologies are two of the most interesting scenarios that have been recently explored to account for possible observational deviations from the concordance $Λ$-cold dark matter ($Λ$CDM) model. In this context, we investigated the large-scale structure of the Universe by exploiting the \dustp simulations that implement, simultaneously, the effects of $f(R)$ gravity and massive neutrinos. To study the possibility of breaking the degeneracy between these two effects, we analysed the redshift-space distortions in the clustering of dark matter haloes at differ…
The amplitude of weak lensing should increase with source distance, rising steeply behind a lens and saturating at high redshift, providing a model-independent means of measuring cosmic geometry. We measure the amplitude of weak lensing with redshift for three massive clusters, A370 (z=0.375), ZwCl0024+17 (z=0.395) and RXJ1347-11 (z=0.451), using deep, three-colour Subaru imaging. We define the depth of lensed populations with reference to the COSMOS and GOODS fields, providing a consistency check of photo-z estimates over a wide range of redshift and magnitude. The predicted distance-redshift…
Mass and concentration of clusters of galaxies are related and evolving with redshift. We study the properties of a sample of 31 massive galaxy clusters at high redshift, 0.8 < z < 1.5, using weak and strong lensing observations. Concentration is a steep function of mass, c_{200} ~M_{200}^{-0.83 +-0.39}, with higher-redshift clusters being less concentrated. Mass and concentration from the stacked analysis, M_{200}=(4.1+-0.4)x10^{14}M_Sun/h and c_{200}=2.3+-0.2, are in line with theoretical results extrapolated from the local universe. Clusters with signs of dynamical activity preferentially f…
Massive compact galaxies seem to be more common at high redshift than in the local universe, especially in denser environments. To investigate the fate of such massive galaxies identified at z~2 we analyse the evolution of their properties in three cosmological hydrodynamical simulations that form virialised galaxy groups of mass ~10^13 Msun hosting a central massive elliptical/S0 galaxy by redshift zero. We find that at redshift ~2 the population of galaxies with M_*> 2 10^10 Msun is diverse in terms of mass, velocity dispersion, star formation and effective radius, containing both very compa…
We place firm upper limits on the global accretion history of massive black holes at z>5 from the recently measured unresolved fraction of the cosmic X-ray background. The maximum allowed unresolved intensity observed at 1.5 keV implies a maximum accreted-mass density onto massive black holes of rho_acc < 1.4E4 M_sun Mpc^{-3} for z>5. Considering the contribution of lower-z AGNs, the value reduces to rho_acc < 0.66E4 M_sun Mpc^{-3}. The tension between the need for the efficient and rapid accretion required by the observation of massive black holes already in place at z>7 and the strict upper …
The {\rm HI} 21-cm intensity mapping signal experiences redshift space distortions due to the motion of the galaxies which contain the {\rm HI} as well as the motions of the {\rm HI} gas within the galaxies. A detailed modelling is essential if this signal is to be used for precision cosmology. Considering dark matter only simulations where the {\rm HI} is assumed to reside in galaxies which are associated with haloes, in this work we introduce a technique to incorporate the {\rm HI} motions within the galaxies. This is achieved through a line profile which accounts for both the rotational and…
We performed an internal-consistency test of the KiDS+VIKING-450 (KV450) cosmic shear analysis with a colour-based split of source galaxies. Utilising the same measurements and calibrations for both sub-samples, we inspected the characteristics of the shear measurements and the performance of the calibration pipelines. On the modelling side, we examined the observational nuisance parameters, specifically those for the redshift calibration and intrinsic alignments, using a Bayesian analysis with dedicated test parameters. We verified that the current nuisance parameters are sufficient for the K…
In this work we present an application of general extreme value statistics (GEV) to very massive single clusters at high and low redshifts. After introducing the formalism, we apply this statistics to four very massive high redshift clusters. Those clusters comprise ACT-CL J0102-4915 with a mass of M_200m=(2.16+/-0.32)x10^{15} M_sun at a redshift of z=0.87, SPT-CL J2106-5844 with a mass of M_200m=(1.27+/-0.21)x10^{15} M_sun at z=1.132 and two clusters found by the XMM-Newton Distant Cluster Project survey: XMMU J2235.32557 with a mass of M_200c= (7.3+/-1.3)x10^{14} M_sun located at a redshift …
Galactic nuclei host central massive objects either in the form of supermassive black holes or nuclear stellar clusters. Recent investigations have shown that both components co-exist in at least a few galaxies. In this paper we explore the possibility of a connection between nuclear star clusters and black holes that establishes at the moment of their formation. We here model the evolution of high redshift discs, hosted in dark matter halos with virial temperatures 10^4 K, whose gas has been polluted with metals just above the critical metallicity for fragmentation. A nuclear cluster forms as…
From a search of a portion of the sky covered by the SDSS and UKIDSS databases, we have located 2 galaxies at z~0.5 that have properties similar to those of the luminous passive compact galaxies found at z~2.5. From Keck moderate-resolution spectroscopy and laser-guided adaptive-optics imaging of these galaxies, we can begin to put together a more detailed picture of what their high-redshift counterparts might be like. Spectral-synthesis models that fit the u to K photometry also seem to give good fits to the spectral features. From these models, we estimate masses in the range of 3-4 10^11 M_…
Massive clusters of galaxies have been found as early as 3.9 Billion years (z=1.62) after the Big Bang containing stars that formed at even earlier epochs. Cosmological simulations using the current cold dark matter paradigm predict these systems should descend from "proto-clusters" - early over-densities of massive galaxies that merge hierarchically to form a cluster. These proto-cluster regions themselves are built-up hierarchically and so are expected to contain extremely massive galaxies which can be observed as luminous quasars and starbursts. However, observational evidence for this scen…
Massive present-day early-type (elliptical and lenticular) galaxies probably gained the bulk of their stellar mass and heavy elements through intense, dust-enshrouded starbursts - that is, increased rates of star formation - in the most massive dark matter halos at early epochs. However, it remains unknown how soon after the Big Bang such massive starburst progenitors exist. The measured redshift distribution of dusty, massive starbursts has long been suspected to be biased low in redshift owing to selection effects, as confirmed by recent findings of systems out to redshift z~5. Here we repor…
Luminous high-redshift QSOs are thought to exist within the most massive dark matter haloes in the young Universe. As a consequence they are likely to be markers for biased, over-dense regions where early galaxies cluster, regions that eventually grow into the groups and clusters seen in the lower redshift universe. In this paper we explore the clustering of galaxies around z ~ 5 QSOs as traced by Lyman Break Galaxies (LBGs). We target the fields of three QSOs using the same optical imaging and spectroscopy techniques used in the ESO Remote Galaxy Survey (ERGS, Douglas et al. 2009, 2010), whic…
The Dark Energy Survey (DES) will be unprecedented in its ability to probe exceptionally large cosmic volumes to relatively faint optical limits. Primarily designed for the study of comparatively low redshift (z<2) galaxies with the aim of constraining dark energy, an intriguing byproduct of the survey will be the identification of massive (>10^(12.0) M_sun) galaxies at z>~4. This will greatly improve our understanding of how galaxies form and evolve. By both passively evolving the low redshift mass function and extrapolating the observed high redshift mass function, we find that such galaxies…
Large-scale structure surveys in the coming years will measure the redshift-space power spectrum to unprecedented accuracy, allowing for powerful new tests of the LambdaCDM picture as well as measurements of particle physics parameters such as the neutrino masses. We extend the Time-RG perturbative framework to redshift space, computing the power spectrum P_s(k,mu) in massive neutrino cosmologies with time-dependent dark energy equations of state w(z). Time-RG is uniquely capable of incorporating scale-dependent growth into the P_s(k,mu) computation, which is important for massive neutrinos as…
We present Gran-Telescopio-Canarias/OSIRIS optical spectra of 4 of the most compact and massive early-type galaxies in the Groth Strip Survey at redshift z~1, with effective radii Reff=0.5-2.4 kpc and photometric stellar masses Mstar=1.2-4x10^11 Msun. We find these galaxies have velocity dispersions sigma=156-236 km/s. The spectra are well fitted by single stellar population models with approximately 1 Gyr of age and solar metallicity. We find that: i) the dynamical masses of these galaxies are systematically smaller by a factor of ~6 than the published stellar masses using BRIJK photometry; i…
There are observations of 15 high-redshift massive galaxy clusters, which have an extremely small probability with a purely Gaussian initial curvature perturbation. Here we revisit the estimation of the contribution of non-Gaussianities to the cluster mass function and point out serious problems that have resulted in the application of the mass function out of the range of its validity. We remedy the situation and show that the values of f_NL previously claimed to completely reconcile (i.e. at ~100% confidence) the existence of the clusters with LambdaCDM are unphysically small. However, for W…
We present a study of galaxy populations in the central region of the IRAC-selected, X-ray detected galaxy cluster Cl J1449+0856 at z=2. Based on a sample of spectroscopic and photometric cluster members, we investigate stellar populations and morphological structure of cluster galaxies over an area of ~0.7Mpc^2 around the cluster core. The cluster stands out as a clear overdensity both in redshift space, and in the spatial distribution of galaxies close to the center of the extended X-ray emission. The cluster core region (r<200 kpc) shows a clearly enhanced passive fraction with respect to f…
Gaussian-Process Emulation of the Redshift-Space Halo Power Spectrum Monopole in Cosmologies with Massive Neutrinos
National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）；School of Astronomy and Space Science, University of Chinese Academy of Sciences（中国科学院大学天文与空间科学学院）；Institute for Frontiers in Astronomy and Astrophysics, Beijing Normal University（北京师范大学天文与前沿科学研究院）；Chinese Academy of Sciences South America Center for Astronomy (CASSACA), National Astronomical Observatories, Chinese Academy of Sciences（中国科学院南美天文中心）
The stellar mass-halo mass relation is a key constraint in all semi-analytic, numerical, and semi-empirical models of galaxy formation and evolution. However, its exact shape and redshift dependence remain debated. Several recent works support a relation in the local Universe steeper than previously thought. Based on the comparisons with a variety of data on massive central galaxies, we show that this steepening holds up to z~1, for stellar masses Mstar>2e11 Msun. Specifically, we find significant evidence for a high-mass end slope of β>0.35-0.70, instead of the usual β~0.20-0.30 reported by a…
In this work we propose a novel method for testing the validity of the fiducial LCDM cosmology by measuring the cumulative distribution function of the most massive haloes in a sample of subvolumes of identical size tiled on the sky at a fixed redshift. The fact that the most massive clusters probe the high-mass tail of the mass function, where the difference between LCDM and alternative cosmological models is strongest, makes our method particularly interesting as a cosmological probe. We utilise general extreme value statistics (GEV) to obtain a cumulative distribution function of the most m…
We critically investigate current statistical tests applied to high redshift clusters of galaxies in order to test the standard cosmological model and describe their range of validity. We carefully compare a sample of high-redshift, massive, galaxy clusters with realistic Poisson sample simulations of the theoretical mass function, which include the effect of Eddington bias. We compare the observations and simulations using the following statistical tests: the distributions of ensemble and individual existence probabilities (in the >M,>z sense), the redshift distributions, and the 2d Kolmogoro…
Massive galaxy clusters are interesting astrophysical and cosmological study objects, but are relatively rare. In the redshift range z = 0.25 to 0.5 which is, for example, a favourable region for gravitational lensing studies, about 100 such systems are known. Most of them have been studied in X-rays. In this paper we study the six remaining massive clusters in this redshift interval in the highly complete CLASSIX survey which have so far not been observed with sufficiently deep exposures in X-rays. With data from our new XMM-Newton observations we characterise their structures, derive X-ray p…
Galaxy formation models invoke the presence of strong feedback mechanisms that regulate the growth of massive galaxies at high redshifts. In this paper we aim to: (1) confirm spectroscopically the redshifts of a sample of massive galaxies selected with photometric redshifts z > 2.5; (2) investigate the properties of their stellar and interstellar media; (3) detect the presence of outflows, and measure their velocities. To achieve this, we analysed deep, high-resolution (R~2000) FORS2 rest-frame UV spectra for 11 targets. We confirmed that 9 out of 11 have spectroscopic redshifts z > 2.5. We al…
We identify a sample of 1959 massive clusters of galaxies in the redshift range of 0.7<z<1.0 from the survey data of Sloan Digital Sky Survey (SDSS) and Wide-field Infrared Survey Explorer (WISE). These clusters are recognized as the overdensity regions around the SDSS luminous red galaxies, having a richness greater than 15 or an equivalent mass M_{500} \ge 2.5*10^{14}M_{\odot}. Among them, 1505 clusters are identified for the first time, which significantly enlarge the number of high-redshift clusters of z>0.75. By comparing them with clusters at lower redshifts, we confirm that richer clust…
Aims. We present a determination of the intrinsic colors and ages of galaxies at very high redshift, in particular old galaxies (OGs) within extremely red objects (EROs). To date, the definition of EROs has been restricted to objects with z<2.5, however, here consider objects with the same properties but shifted to higher redshifts (z>2.5). We therefore, refer to these objects as very high-redshift EROs (Z-EROS, herein). Methods. We analyze 63,550 galaxies selected in the XMM-LSS field. To obtain a reasonably sized sample of EROs, it is essential to consider a very wide area surveys. We identi…
(Abridged) We trace the interaction processes of galaxies at intermediate redshift by measuring the irregularity of their ionized gas kinematics, and investigate these irregularities as a function of the environment (cluster versus field) and of morphological type (spiral versus irregular). Our sample consists of 92 distant galaxies. 16 cluster (z~0.3 and z~0.5) and 29 field galaxies (mean z=0.44) of these have velocity fields with sufficient signal to be analyzed. We find that the fraction of galaxies that have irregular gas kinematics is remarkably similar in galaxy clusters and in the field…
We aim to determine the mass, velocity anisotropy, and pseudo phase-space density profiles (M(r), beta(r), and Q(r), respectively) of clusters of galaxies at the highest redshifts investigated in detail so far. We combine the GOGREEN and GCLASS spectroscopic data-sets for 14 clusters with mass M200 > 10^14 Msolar at redshifts 0.9 < z < 1.4. We stack these 14 clusters into an ensemble cluster of 581 member galaxies with stellar mass > 10^9.5 M_solar. We use the MAMPOSSt method and the inversion of the Jeans equation technique to determine M(r) and beta(r). We then combine the results of the M(r…
The abundance of the most massive objects in the Universe at different epochs is a very sensitive probe of the cosmic background evolution and of the growth history of density perturbations, and could provide a powerful tool to distinguish between a cosmological constant and a dynamical dark energy field. In particular, the recent detection of very massive clusters of galaxies at high redshifts has attracted significant interest as a possible indication of a failure of the standard LCDM model. Several attempts have been made in order to explain such detections in the context of non-Gaussian sc…
Tracking the evolution of high redshift seed black hole masses to late times, we examine the observable signatures today. These massive initial black hole seeds form at extremely high redshifts from the direct collapse of pre-galactic gas discs. Populating dark matter halos with seeds formed in this fashion, we follow the mass assembly history of these black holes to the present time using a Monte-Carlo merger tree approach. Utilizing this formalism, we predict the black hole mass function at high redshifts and at the present time; the integrated mass density of black holes in the Universe; th…
We investigate the accuracy of Eulerian perturbation theory for describing the matter and galaxy power spectra in real and redshift space in light of future observational probes for precision cosmology. Comparing the analytical results with a large suite of N-body simulations (160 independent boxes of 13.8 (Gpc/h)^3 volume each, which are publicly available), we find that re-summing terms in the standard perturbative approach predicts the real-space matter power spectrum with an accuracy of < 2% for k < 0.20 h/Mpc at redshifts z < 1.5. This is obtained following the widespread technique of wri…
We present composite 3.6 and 4.5 micron luminosity functions for cluster galaxies measured from the Spitzer Deep, Wide-Field Survey (SDWFS) for 0.3<z<2. We compare the evolution of m* for these luminosity functions to models for passively evolving stellar populations to constrain the primary epoch of star formation in massive cluster galaxies. At low redshifts (z < 1.3) our results agree well with models with no mass assembly and passively evolving stellar populations with a luminosity-weighted mean formation redshift zf=2.4 assuming a Kroupa initial mass function (IMF). We conduct a thorough …
El Gordo (ACT-CL J0102-4915) is an extremely massive galaxy cluster ($M_{200} \approx 3 \times 10^{15}$ $M_{\odot}$) at redshift $z = 0.87 $ composed of two subclusters with mass ratio 3.6 merging at speed $V_{infall} \approx 2500$ km/s. Such a fast collision between individually rare massive clusters is unexpected in Lambda cold dark matter ($Λ$CDM) cosmology at such high $z$. However, this is required for non-cosmological hydrodynamical simulations of the merger to match its observed properties (Zhang et al. 2015). Here, we determine the probability of finding a similar object in a $Λ$CDM co…
We use high-resolution K-band VLT/HAWK-I imaging over 0.25 square degrees to study the structural evolution of massive early-type galaxies since z~1. Mass-selected samples, complete down to log(M/M_sun)~10.7 such that `typical' L* galaxies are included at all redshifts, are drawn from pre-existing photometric redshift surveys. We then separated the samples into different redshift slices and classify them as late- or early-type galaxies on the basis of their specific star-formation rate. Axis-ratio measurements for the ~400 early-type galaxies in the redshift range 0.6<z<1.8 are accurate to 0.1…
We present MMT spectroscopic observations of two massive galaxy cluster candidates at redshift $z\sim0.07$ that show extended and diffuse X-ray emission in the ROSAT All Sky Survey (RASS) images. The targets were selected from a previous catalog of 303 newly-identified cluster candidates with the similar properties using the intra-cluster medium emission. Using the new MMT Hectospec data and SDSS archival spectra, we identify a number of member galaxies for the two targets and confirm that they are galaxy clusters at $z=0.079$ and 0.067, respectively. The size of the two clusters, calculated f…
Several bright and massive galaxy candidates at high redshifts have been recently observed by the James Webb Space Telescope. Such early massive galaxies seem difficult to reconcile with standard $Λ$ Cold Dark Matter model predictions. We discuss under which circumstances such observed massive galaxy candidates can be explained by introducing primordial non-Gaussianity in the initial conditions of the cosmological perturbations.
The presence of massive black holes (BHs) with masses of order $10^9\rm\, M_\odot$, powering bright quasars when the Universe was less than 1 Gyr old, poses strong constraints on their formation mechanism. Several scenarios have been proposed to date to explain massive BH formation, from the low-mass seed BH remnants of the first generation of stars to the massive seed BHs resulting from the rapid collapse of massive gas clouds. However, the plausibility of some of these scenarios to occur within the progenitors of high-z quasars has not yet been thoroughly explored. In this work, we investiga…
Using data drawn from the DEEP2 and DEEP3 Galaxy Redshift Surveys, we investigate the relationship between the environment and the structure of galaxies residing on the red sequence at intermediate redshift. Within the massive (10 < log(M*/Msun) < 11) early-type population at 0.4 < z <1.2, we find a significant correlation between local galaxy overdensity (or environment) and galaxy size, such that early-type systems in higher-density regions tend to have larger effective radii (by ~0.5 kpc or 25% larger) than their counterparts of equal stellar mass and Sersic index in lower-density environme…
Recent deep Hubble Space Telescope WFC3 imaging suggests that a majority of compact quiescent massive galaxies at z~2 may contain disks. To investigate this claim, we have compared the ellipticity distribution of 31 carefully selected high-redshift massive quiescent compact galaxies to a set of mass-selected ellipticity and Sersic index distributions obtained from 2D structural fits to ~40,000$ nearby galaxies from the Sloan Digital Sky Survey. A Kolmogorov-Smirnov test shows that the distribution of ellipticities for the high-redshift galaxies is consistent with the ellipticity distribution o…
The recent detection (Jee etal 2009) of the massive cluster XMMU J2235.3-2557 at a redshift z = 1.4, with an estimated mass M = 6.4 +- 1.2 X 10^14 M_sol, has been claimed to be a possible challenge to the standard LCDM cosmological model. More specifically, the probability to detect such a cluster has been estimated to be 0.005 if a LCDM model with gaussian initial conditions is assumed, resulting in a 3 sigma discrepancy from the standard cosmological model. In this paper we propose to use high redshift clusters as the one detected in Jee etal 2009 to compare the cosmological constant scenari…
Quasars represent the brightest Active Galactic Nuclei (AGN) in the Universe and are thought to indicate the location of prodigiously growing Black Holes (BHs), with luminosities as high as 10^48 erg/sec. It is often expected though that such an extremely energetic process will take place in the most massive bound structures in the dark matter (DM) distribution. We show that in contrast to this expectation, in a galaxy formation model which includes AGN feedback, quasars are predicted to live in average DM halo environments with typical masses of a few times 10^12 Msun. This fundamental predic…
We present the characterisation of the massive cluster ClG-J$104803.7+313843$ at $z=0.76$ performed using a serendipitous XMM-Newton observation. High redshift and massive objects represent an ideal laboratory to benchmark our understanding of how cluster form and assembly formation driven mainly by gravity.Leveraging the high throughput of XMM-Newton we were firstly able to determine the redshift of the object, shedding light on ambiguous photometric redshift associations. We investigated the morphology of this cluster which shows signs of merging activities in the outskirts and a flat core. …
We present the development of a photometrically selected massive galaxy catalog, targeting Luminous Red Galaxies (LRGs) and massive blue galaxies at redshifts $z\geq 0.55$. Massive galaxy candidates are selected using infrared/optical color-color cuts, with optical data from Sloan Digital Sky Survey (SDSS) and infrared data from "unWISE" forced photometry derived from the Wide-field Infrared Survey Explorer (WISE). The selection method is based on previously developed techniques to select LRGs with $z>0.5$, and is optimized using receiver operating characteristic (ROC) curves. The catalog cont…
We examine the relation between surface brightness, velocity dispersion and size$-$the fundamental plane$-$for quiescent galaxies at intermediate redshifts in the COSMOS field. The COSMOS sample consists of $\sim150$ massive quiescent galaxies with an average velocity dispersion $σ\sim 250$ km s$^{-1}$ and redshifts between $0.2<z<0.8$. More than half of the galaxies in the sample are compact. The COSMOS galaxies exhibit a tight relation ($\sim0.1$ dex scatter) between surface brightness, velocity dispersion and size. At a fixed combination of velocity dispersion and size, the COSMOS galaxies …
We study the effect of magnetic braking due to a primordial magnetic field in the context of the formation of massive ($\gtrsim 10^{4} M_\odot$) direct collapse black holes (DCBHs) at high redshifts. Under the assumption of axial symmetry, we analytically compute the effect of magnetic braking on the angular momentum of gas collapsing into the potential well of massive dark matter haloes ($\simeq 10^{7-9} M_\odot$) which are spun up by gravitational tidal torques. We find that a primordial magnetic field of strength $B_0\simeq 0.1$~nG (comoving) can remove the initial angular momentum gained b…
We use a dense redshift survey in the foreground of the Subaru GTO2deg^2 weak lensing field (centered at $α_{2000}$ = 16$^h04^m44^s$;$δ_{2000}$ =43^\circ11^{\prime}24^{\prime\prime}$) to assess the completeness and comment on the purity of massive halo identification in the weak lensing map. The redshift survey (published here) includes 4541 galaxies; 4405 are new redshifts measured with the Hectospec on the MMT. Among the weak lensing peaks with a signal-to-noise greater that 4.25, 2/3 correspond to individual massive systems; this result is essentially identical to the Geller et al. (2010) t…
Using cosmological, radiation-hydrodynamic simulations targeting a rare $\approx \, 2 \times 10^{12} \, \rm M_\odot$ halo at $z \, = \, 6$, we show that the number counts and internal properties of satellite galaxies within the massive halo are sensitively regulated by a combination of local stellar radiative feedback and strong tidal forces. Radiative feedback operates before the first supernova explosions erupt and results in less tightly-bound galaxies. Satellites are therefore more vulnerable to tidal stripping when they accrete onto the main progenitor and are tidally disrupted on a signi…
We present measurements of the stellar mass fractions ($f_\star$) for a sample of high-redshift ($0.93 \le z \le 1.32$) infrared-selected galaxy clusters from the Massive and Distant Clusters of WISE Survey (MaDCoWS) and compare them to the stellar mass fractions of Sunyaev-Zel'dovich (SZ) effect-selected clusters in a similar mass and redshift range from the South Pole Telescope (SPT)-SZ Survey. We do not find a significant difference in mean $f_\star$ between the two selection methods, though we do find an unexpectedly large range in $f_\star$ for the SZ-selected clusters. In addition, we me…
Massive black hole binaries are the primary source of gravitational waves (GW) for the future eLISA observatory. The detection and parameter estimation of these sources to high redshift would provide invaluable information on the formation mechanisms of seed black holes, and on the evolution of massive black holes and their host galaxies through cosmic time. The Fisher information matrix has been the standard tool for GW parameter estimation in the last two decades. However, recent studies have questioned the validity of using the Fisher matrix approach. For example, the Fisher matrix approach…
There is a well known degeneracy between the enhancement of the growth of large-scale structure produced by modified gravity models and the suppression due to the free-streaming of massive neutrinos at late times. This makes the matter power-spectrum alone a poor probe to distinguish between modified gravity and the concordance $Λ$CDM model when neutrino masses are not strongly constrained. In this work, we investigate the potential of using redshift-space distortions (RSD) to break this degeneracy when the modification to gravity is scale-dependent in the form of Hu-Sawicki $f(R)$. We find th…
If the Universe is dominated by cold dark matter and dark energy as in the currently popular LCDM cosmology, it is expected that large scale structures form gradually, with galaxy clusters of mass M > ~10^14 Msun appearing at around 6 Gyrs after the Big Bang (z ~ 1). Here, we report the discovery of 59 massive structures of galaxies with masses greater than a few x 10^13 Msun at redshifts between z=0.6 and 4.5 in the Great Observatories Origins Deep Survey fields. The massive structures are identified by running top-hat filters on the two dimensional spatial distribution of magnitude-limited s…
The formation of thick stellar disks in spiral galaxies is studied. Simulations of gas-rich young galaxies show formation of internal clumps by gravitational instabilities, clump coalescence into a bulge, and disk thickening by strong stellar scattering. The bulge and thick disks of modern galaxies may form this way. Simulations of minor mergers make thick disks too, but there is an important difference. Thick disks made by internal processes have a constant scale height with galactocentric radius, but thick disks made by mergers flare. The difference arises because in the first case, perpendi…
We study the prospects of using the low-redshift and high-redshift black hole shadows as new cosmological standard rulers for measuring cosmological parameters. We show that, using the low-redshift observation of the black hole shadow of M87$^\star$, the Hubble constant can be independently determined with a precision of about $13\%$ as $H_0=70\pm 9$ km s$^{-1}$ Mpc$^{-1}$. The high-redshift observations of super-massive black hole shadows may accurately determine a combination of parameters $H_0$ and ${Ω_{\rm m}}$, and we show by a simple simulation that combining them with the type Ia supern…
