Antonaldo Diaferio | Turin - Academia.edu (original) (raw)

Papers by Antonaldo Diaferio

We combine the CIRS (Cluster Infall Regions in SDSS) sample of 72 clusters at z<0.1 with the H... more We combine the CIRS (Cluster Infall Regions in SDSS) sample of 72 clusters at z<0.1 with the HeCS (Hectospec Cluster Survey) sample of 74 clusters in the redshift range 0.1-0.3. Both samples are X-ray flux limited. HeCS contains over 20,000 new redshifts obtained with Hectospec on the MMT. We apply the caustic technique to this full sample of 148 clusters to measure M200 directly and to derive the NFW concentration from the fits of the mass profile to each cluster. We derive the correlation between concentration and mass and its spread at fixed mass and compare these measurements with the expected results from numerical simulations. We also tested the conjecture from some weak lensing studies that cluster concentrations substantially exceed model predictions. This work is supported in part by a Cottrell College Science Award from the Research Corporation.

ABSTRACT We describe the first results from a new survey of clusters and their infall regions at ... more ABSTRACT We describe the first results from a new survey of clusters and their infall regions at moderate redshift. The Hectospec multifiber spectrograph on the MMT is an ideal instrument for such a program. We obtained spectra for X-ray selected clusters at z=0.15-0.30. We restrict the sample to clusters within the SDSS DR6 imaging footprint to ensure uniform photometry. Early results show that our observing strategy yields a large number of cluster members throughout the cluster infall regions. HeCS will significantly improve our understanding of cluster infall regions and their evolution. HeCS also offers fresh insights into the evolution of galaxies in clusters. Finally, HeCS should soon yield improved cosmological constraints by extending the cluster mass function to larger masses.

The Astronomical Journal, 2010

We use the Fifth Data Release of the Sloan Digital Sky Survey to study X-ray-selected galaxy grou... more We use the Fifth Data Release of the Sloan Digital Sky Survey to study X-ray-selected galaxy groups and compare their properties to clusters. We search for infall patterns around the groups and use these to measure group mass profiles to large radii. In previous work, we analyzed infall patterns for an X-ray-selected sample of 72 clusters from the ROSAT All-Sky Survey. Here, we extend this approach to a sample of systems with smaller X-ray fluxes selected from the 400 Square Degree serendipitous survey of clusters and groups in ROSAT pointed observations. We identify 16 groups with SDSS DR5 spectroscopy, search for infall patterns, and compute mass profiles out to 2-6 h −1 Mpc from the group centers with the caustic technique. No other mass estimation methods are currently available at such large radii for these low-mass groups, because the virial estimate requires dynamical equilibrium and the gravitational lensing signal is too weak. Despite the small masses of these groups, most display recognizable infall patterns. We use caustic and virial mass estimates to measure the scaling relations between different observables, extending these relations to smaller fluxes and luminosities than many previous surveys. Close inspection reveals that three of the groups are subclusters in the outskirts of larger clusters. A fourth group is apparently undergoing a group-group merger. These four merging groups represent the most extreme outliers in the scaling relations. Excluding these groups, we find L X ∝ σ 3.4±1.6 p , consistent with previous determinations for both clusters and groups. Understanding cluster and group scaling relations is crucial for measuring cosmological parameters from clusters. The complex environments of our group sample reinforce the idea that great care must be taken in determining the properties of low-mass clusters and groups.

The Astrophysical Journal, 2005

There are only two methods for estimating the mass distribution in the outer regions of galaxy cl... more There are only two methods for estimating the mass distribution in the outer regions of galaxy clusters, where virial equilibrium does not hold: weak gravitational lensing and identification of caustics in redshift space. For the first time, we apply both methods to three clusters: A2390, MS1358 and Cl 0024. The two measures are in remarkably good agreement out to ∼ 2h −1 Mpc from the cluster centers. This result demonstrates that the caustic technique is a valuable complement to weak lensing. With a few tens of redshifts per (h −1 Mpc) 2 within the cluster, the caustic method is applicable for any z 0.5.

The Astrophysical Journal, 2007

We present a new determination of the cluster mass function and velocity dispersion function in a... more We present a new determination of the cluster mass function and velocity dispersion function in a volume ∼10 7 h 3 Mpc −3 using data from the Fourth Data Release of the Sloan Digital Sky Survey (SDSS) to determine virial masses. We use the caustic technique to remove foreground and background galaxies. The cluster virial mass function agrees well with recent estimates from both X-ray observations and cluster richnesses. Our determination of the mass function lies between those predicted by the First-Year and Three-Year WMAP data. We constrain the cosmological parameters Ω m and σ 8 and find good agreement with WMAP and constraints from other techniques. With the CIRS mass function alone, we estimate Ω m = 0.24 +0.14 −0.09 and σ 8 = 0.92 +0.24 −0.19 , or σ 8 = 0.84±0.03 when holding Ω m = 0.3 fixed. We also use the WMAP parameters as priors and constrain velocity segregation in clusters. Using the First and Third-Year results, we infer velocity segregation of σ gxy /σ DM ≈0.94±0.05 or 1.28±0.06 respectively. The good agreement of various estimates of the cluster mass function shows that it is a useful independent constraint on estimates of cosmological parameters. We compare the velocity dispersion function of clusters to that of early-type galaxies and conclude that clusters comprise the high-velocity end of the velocity dispersion function of dark matter haloes. Future studies of galaxy groups are needed to study the transition between dark matter haloes containing individiual galaxies and those containing systems of galaxies. The evolution of cluster abundances provides constraints on dark energy models; the mass function presented here offers an important low redshift calibration benchmark.

The Astrophysical Journal, 2012

We use Wide-field Infrared Survey Explorer (WISE) data covering the entire region (∼ 130 deg 2) o... more We use Wide-field Infrared Survey Explorer (WISE) data covering the entire region (∼ 130 deg 2) of the A2199 supercluster at z = 0.03 to study the mid-infrared (MIR) properties of supercluster galaxies. We identify a 'MIR star-forming sequence' in the WISE [3.4] − [12] color-12 µm luminosity diagram, consisting of late-type, star-forming galaxies. At a fixed star formation rate (SFR), the MIR-detected galaxies at 22 µm or 12 µm tend to be more metal rich and to have higher surface brightness than those without MIR detection. Using these MIR-detected galaxies, we construct the IR luminosity function (LF) and investigate its environmental dependence. Both total IR (TIR) and 12 µm LFs are dominated by late-type, star-forming galaxies. The contribution of active galactic nuclei (AGN)-host galaxies increases with both TIR and 12 µm luminosities. The contribution of early-type galaxies to the 12 µm LFs increases with decreasing luminosity. The faint-end slope of the TIR LFs does not change with environment, but the change of faint-end slope in the 12 µm LFs with the environment is significant: there is a steeper faint-end slope in the cluster core than in the cluster outskirts. This steepening results primarily from the increasing contribution of early-type galaxies toward the cluster. These galaxies are passively evolving, and contain old stellar populations with weak MIR emission from the circumstellar dust around asymptotic giant branch stars.

The Astrophysical Journal, 2013

Cluster mass profiles are tests of models of structure formation. Only two current observational ... more Cluster mass profiles are tests of models of structure formation. Only two current observational methods of determining the mass profile, gravitational lensing and the caustic technique, are independent of the assumption of dynamical equilibrium. Both techniques enable determination of the extended mass profile at radii beyond the virial radius. For 19 clusters, we compare the mass profile based on the caustic technique with weak lensing measurements taken from the literature. This comparison offers a test of systematic issues in both techniques. Around the virial radius, the two methods of mass estimation agree to within ∼ 30%, consistent with the expected errors in the individual techniques. At small radii, the caustic technique overestimates the mass as expected from numerical simulations. The ratio between the lensing profile and the caustic mass profile at these radii suggests that the weak lensing profiles are a good representation of the true mass profile. At radii larger than the virial radius, the lensing mass profile exceeds the caustic mass profile possibly as a result of contamination of the lensing profile by large-scale structures within the lensing kernel. We highlight the case of the closely neighboring clusters MS0906+11 and A750 to illustrate the potential seriousness of contamination of the the weak lensing signal by unrelated structures.

The Astrophysical Journal, 2013

The infall regions of galaxy clusters represent the largest gravitationally bound structures in a... more The infall regions of galaxy clusters represent the largest gravitationally bound structures in a ΛCDM universe. Measuring cluster mass profiles into the infall regions provides an estimate of the ultimate mass of these haloes. We use the caustic technique to measure cluster mass profiles from galaxy redshifts obtained with the Hectospec Cluster Survey (HeCS), an extensive spectroscopic survey of galaxy clusters with MMT/Hectospec. We survey 58 clusters selected by X-ray flux at 0.1<z<0.3. The survey includes 22,680 unique MMT/Hectospec redshifts for individual galaxies; 10,145 of these galaxies are cluster members. For each cluster we acquired high signal-to-noise spectra for ∼200 cluster members and a comparable number of foreground/background galaxies. The cluster members trace out infall patterns around the clusters. The members define a very narrow red sequence. We demonstrate that the determination of velocity dispersion is insensitive to the inclusion of bluer members (a small fraction of the cluster population). We apply the caustic technique to define membership and estimate the mass profiles to large radii. The ultimate halo mass of clusters (the mass that remains bound in the far future of a ΛCDM universe) is on average (1.99±0.11)M 200 , a new observational cosmological test in essential agreement with simulations. Summed profiles binned in M 200 and in L X demonstrate that the predicted NFW form of the density profile is a remarkably good representation of the data in agreement with weak lensing results extending to large radius. The concentration of these summed profiles is also consistent with theoretical predictions.

The Astronomical Journal, 2004

CAIRNS (Cluster And Infall Region Nearby Survey) is a spectroscopic survey of the infall regions ... more CAIRNS (Cluster And Infall Region Nearby Survey) is a spectroscopic survey of the infall regions surrounding nine nearby rich clusters of galaxies. In Paper I, we used redshifts within ∼ 10h −1 Mpc of the centers of the clusters to determine the mass profiles of the clusters based on the phase space distribution of the galaxies. Here, we use 2MASS photometry and an additional 515 redshifts to investigate the environmental dependence of near-infrared mass-to-light ratios. In the virial regions, the halo occupation function is non-linear; the number of bright galaxies per halo increases more slowly than the mass of the halo. On larger scales, the light contained in galaxies is less clustered than the mass in rich clusters. Specifically, the mass-to-light ratio inside the virial radius is a factor of 1.8 ± 0.3 larger than that outside the virial radius. This difference could result from changing fractions of baryonic to total matter or from variations in the efficiency of galaxy formation or disruption with environment. The average massto-light ratio M/L K = 53 ± 5h implies Ω m = 0.18 ± 0.03 (statistical) using the luminosity density based on 2dFGRS data. These results are difficult to reconcile with independent methods which suggest higher Ω m. Reconciling these values by invoking bias requires that the typical value of M/L K changes significantly at densities of 3ρ c .

Space Science Reviews, 2008

There are many processes that can transport gas from the galaxies to their environment and enrich... more There are many processes that can transport gas from the galaxies to their environment and enrich the environment in this way with metals. These metal enrichment processes have a large influence on the evolution of both the galaxies and their environment. Various processes can contribute to the gas transfer: ram-pressure stripping, galactic winds, AGN outflows, galaxy-galaxy interactions and others. We review their observational evidence, corresponding simulations, their efficiencies, and their time scales as far as they are known to date. It seems that all processes can contribute to the enrichment. There is not a single process that always dominates the enrichment, because the efficiencies of the processes vary strongly with galaxy and environmental properties.

The Astrophysical Journal, 2010

We present the first comparison of virial masses of galaxy clusters with their Sunyaev-Zel'dovich... more We present the first comparison of virial masses of galaxy clusters with their Sunyaev-Zel'dovich Effect (SZE) signals. We study 15 clusters from the Hectospec Cluster Survey (HeCS) with MMT/Hectospec spectroscopy and published SZE signals. We measure virial masses of these clusters from an average of 90 member redshifts inside the radius r 100. The virial masses of the clusters are strongly correlated with their SZE signals (at the 99% confidence level using a Spearman rank-sum test). This correlation suggests that Y SZ can be used as a measure of virial mass. Simulations predict a powerlaw scaling of Y SZ ∝ M α 200 with α ≈1.6. Observationally, we find α=1.11±0.16, significantly shallower (given the formal uncertainty) than the theoretical prediction. However, the selection function of our sample is unknown and a bias against less massive clusters cannot be excluded (such a selection bias could artificially flatten the slope). Moreover, our sample indicates that the relation between velocity dispersion (or virial mass estimate) and SZE signal has significant intrinsic scatter, comparable to the range of our current sample. More detailed studies of scaling relations are therefore needed to derive a robust determination of the relation between cluster mass and SZE.

Context. We present a spectrophotometric analysis of the galaxy population in the area of the mer... more Context. We present a spectrophotometric analysis of the galaxy population in the area of the merging cluster Abell 3921 at z = 0.093. Aims. We investigate the impact of the complex cluster environment on galaxy properties such as morphology or star formation rate. Methods. We combine multi-object spectroscopy from the two-degree field (2dF) spectrograph with optical imaging taken with the ESO Wide Field Imager. We carried out a redshift analysis and determine cluster velocity dispersions using biweight statistics. Applying a Dressler-Shectman test we sought evidence of cluster substructure. Cluster and field galaxies were investigated with respect to [OII] and Hα equivalent width, star formation rate, and morphological descriptors, such as concentration index and Gini coefficient. We studied these cluster galaxy properties as a function of clustercentric distance and investigated the spatial distribution of various galaxy types. Results. Applying the Dressler-Shectman test, we find a third component (A3921-C) in addition to the two main subclusters (A3921-A and A3921-B) that are already known. The re-determined mass ratio between the main components A and B is ∼2:1. Similar to previous studies of galaxy clusters, we find that a large fraction of the disk galaxies close to the cluster core show no detectable star formation. These are likely systems that are quenched due to ram pressure stripping. Interestingly, we also find quenched spirals at rather large distances of 3−4 Mpc from the cluster core. Conclusions. A3921-C might be a group of galaxies falling onto the main cluster components. We speculate that the unexpected population of quenched spirals at large clustercentric radii in A3921-A and A3921-B might be an effect of the ongoing cluster merger: shocks in the ICM might give rise to enhanced ram pressure stripping and at least in part be the cause for the quenching of star formation. These quenched spirals might be an intermediate stage in the morphological transformation of field spirals into cluster S0s.

Gravity: Where Do We Stand?, 2015

General Relativity is able to describe the dynamics of galaxies and larger cosmic structures only... more General Relativity is able to describe the dynamics of galaxies and larger cosmic structures only if most of the matter in the Universe is dark, namely it does not emit any electromagnetic radiation. Intriguingly, on the scale of galaxies, there is strong observational evidence that the presence of dark matter appears to be necessary only when the gravitational field inferred from the distribution of the luminous matter falls below an acceleration of the order of 10 −10 m s −2. In the standard model, which combines Newtonian gravity with dark matter, the origin of this acceleration scale is challenging and remains unsolved. On the contrary, the full set of observations can be neatly described, and were partly predicted, by a modification of Newtonian dynamics, dubbed MOND, that does not resort to the existence of dark matter. On the scale of galaxy clusters and beyond, however, MOND is not as successful as on the scale of galaxies, and the existence of some dark matter appears unavoidable. A model combining MOND with hot dark matter made of sterile neutrinos seems to be able to describe most of the astrophysical phenomenology, from the power spectrum of the cosmic microwave background anisotropies to the dynamics of dwarf galaxies. Whether there exists a yet unknown covariant theory that contains General Relativity and Newtonian gravity in the weak field limit, and MOND as the ultra-weak field limit is still an open question.

We use a simple analytic model to compute the angular correlation function of clusters identified... more We use a simple analytic model to compute the angular correlation function of clusters identified in upcoming thermal SZ effect surveys. We then compute the expected fraction of close pairs of clusters on the sky that are also close along the line of sight. We show how the expected number of cluster pairs as a function of redshift is sensitive to the assumed biasing relation between the cluster and the mass distribution. We find that, in a ΛCDM model, the fraction of physically associated pairs is 70% for angular separations smaller than 20 arcmin and clusters with specific flux difference larger than 200 mJy at 143 GHz. The agreement of our analytic results with the Hubble volume N-body simulations is satisfactory. These results quantify the feasibility of using SZ surveys to compile catalogues of superclusters at any redshifts.

We present a new Particle-Mesh cosmological N-body code for accurately solving the modified Poiss... more We present a new Particle-Mesh cosmological N-body code for accurately solving the modified Poisson equation of the Quasi Linear formulation of MOND. We generate initial conditions for the Angus (2009) cosmological model, which is identical to ΛCDM except that the cold dark matter is switched for a single species of thermal sterile neutrinos. We set the initial conditions at z = 250 for a (512 M pc/h) 3 box with 256 3 particles and we evolve them down to z = 0. We clearly demonstrate the necessity of MOND for developing the large scale structure in a hot dark matter cosmology and contradict the naive expectation that MOND cannot form galaxy clusters. We find that the correct order of magnitude of X-ray clusters (with T X > 4.5 keV) can be formed, but that we overpredict the number of very rich clusters and seriously underpredict the number of lower mass clusters. The latter is a shortcoming of the resolution of our simulations, whereas we suggest that the over production of very rich clusters might be prevented by incorporating a MOND acceleration constant that varies with redshift and an expansion history that cannot be described by the usual Friedmann models. We present evidence that suggests the density profiles of our simulated clusters are compatible with those of observed X-ray clusters in MOND. It remains to be seen if the low mass end of the cluster mass function can be reproduced and if the high densities of dark matter in the central 20 kpc of groups and clusters of galaxies, measured in the MOND framework, can be achieved. As a last test, we computed the relative velocity between pairs of halos within 10 M pc and find that pairs with velocities larger than 3000 km s −1 , like the bullet cluster, can form without difficulty.

We use numerical simulations of a (480 Mpc/h)^3 volume to show that the distribution of peak heig... more We use numerical simulations of a (480 Mpc/h)^3 volume to show that the distribution of peak heights in maps of the temperature fluctuations from the kinematic and thermal Sunyaev-Zeldovich effects will be highly non-Gaussian, and very different from the peak height distribution of a Gaussian random field. We then show that it is a good approximation to assume that each peak in either SZ effect is associated with one and only one dark matter halo. This allows us to use our knowledge of the properties of haloes to estimate the peak height distributions. At fixed optical depth, the distribution of peak heights due to the kinematic effect is Gaussian, with a width which is approximately proportional to optical depth; the non-Gaussianity comes from summing over a range of optical depths. The optical depth is an increasing function of halo mass, and the distribution of halo speeds is Gaussian, with a dispersion which is approximately independent of halo mass. This means that observations of the kinematic effect can be used to put constraints on how the abundance of massive clusters evolves, and on the evolution of cluster velocities. The non-Gaussianity of the thermal effect, on the other hand, comes primarily from the fact that, on average, the effect is larger in more massive haloes, and the distribution of halo masses is highly non-Gaussian. We also show that because haloes of the same mass may have a range of density and velocity dispersion profiles, the relation between halo mass and the amplitude of the thermal effect is not deterministic, but has some scatter.

Mon Notic Roy Astron Soc, 2004

The fluctuations in the Cosmic Microwave Background (CMB) intensity due to the Sunyaev-Zeldovich ... more The fluctuations in the Cosmic Microwave Background (CMB) intensity due to the Sunyaev-Zeldovich (SZ) effect are the sum of a thermal and a kinetic contribution. Separating the two components to measure the peculiar velocity of galaxy clusters requires radio and microwave observations at three or more frequencies, and knowledge of the temperature T_e of the intracluster medium weighted by the electron number density. To quantify the systematics of this procedure, we extract a sample of 117 massive clusters at redshift z=0 from an N-body hydrodynamical simulation, with 2x480^3 particles, of a cosmological volume 192 Mpc/h on a side of a flat Cold Dark Matter model with Omega_0=0.3 and Lambda=0.7. Our simulation includes radiative cooling, star formation and the effect of feedback and galactic winds from supernovae. We find that (1) our simulated clusters reproduce the observed scaling relations between X-ray and SZ properties; (2) bulk flows internal to the intracluster medium affect the velocity estimate by less than 200 km/s in 93 per cent of the cases; (3) using the X-ray emission weighted temperature, as an estimate of T_e, can overestimate the peculiar velocity by 20-50 per cent, if the microwave observations do not spatially resolve the cluster. For spatially resolved clusters, the assumptions on the spatial distribution of the ICM, required to separate the two SZ components, still produce a velocity overestimate of 10-20 per cent, even with an unbiased measure of T_e. Thanks to the large size of our cluster samples, these results set a robust lower limit of 200 km/s to the systematic errors that will affect upcoming measures of cluster peculiar velocities with the SZ effect.

Mon Notic Roy Astron Soc, 2005

Formation of Dwarf Galaxies During Close Tidal Encounters Michele Kaufman1, Bruce G. Elmegreen2, ... more Formation of Dwarf Galaxies During Close Tidal Encounters Michele Kaufman1, Bruce G. Elmegreen2, and Magnus Thomasson3 1Department of Physics, Ohio State University, Columbus, OH, USA 'IBM-Watson Research Center, Yorktown Heights, NY, USA ...

The Astronomical Journal, 2010

The Astrophysical Journal, 2005

The Astrophysical Journal, 2007

The Astrophysical Journal, 2012

The Astrophysical Journal, 2013

The Astronomical Journal, 2004

Space Science Reviews, 2008

The Astrophysical Journal, 2010

Gravity: Where Do We Stand?, 2015

Mon Notic Roy Astron Soc, 2004

Mon Notic Roy Astron Soc, 2005