Mass Profile of the Infall Region of the Abell 2199 Supercluster

Using a redshift survey of 1323 galaxies (1092 new or remeasured) in a region of 95 square degrees centered on the nearby galaxy cluster Abell 2199, we analyze the supercluster containing A2199, A2197, and an X-ray group. The caustic technique accurately reproduces the true mass profiles of simulated simple superclusters (i.e., superclusters where the virial mass of one cluster is 2-10 times the virial mass of all other clusters in the supercluster). We calculate the masses of the two main components of A2197 (A2197W and A2197E) using archival X-ray observations and demonstrate that the A2199 supercluster is simple and thus that the caustic technique should yield an accurate mass profile. The mass profile is uncertain by ~30% within 3 Mpc/h and by a factor of two within 8 Mpc/h and is one of only a few for a supercluster on such large scales. Independent X-ray mass estimates agree with our results at all radii where they overlap. The mass profile strongly disagrees with an isothermal sphere profile but agrees with profiles suggested by simulations. We discuss the interplay of the supercluster dynamics and the dynamics of the bound subclusters. The agreement between the infall mass profile and other techniques shows that the caustic technique is surprisingly robust for simple superclusters (abridged).Comment: 49 pages, 20 figures, to appear in The Astronomical Journal, version containing high-resolution figures available at http://cfa-www.harvard.edu/~krines/a2199mp.p

Dark Energy Constraints from Galaxy Cluster Peculiar Velocities

Future multifrequency microwave background experiments with arcminute resolution and micro-Kelvin temperature sensitivity will be able to detect the kinetic Sunyaev-Zeldovich (kSZ) effect, providing a way to measure radial peculiar velocities of massive galaxy clusters. We show that cluster peculiar velocities have the potential to constrain several dark energy parameters. We compare three velocity statistics (the distribution of radial velocities, the mean pairwise streaming velocity, and the velocity correlation function) and analyze the relative merits of these statistics in constraining dark energy parameters. Of the three statistics, mean pairwise streaming velocity provides constraints that are least sensitive to velocity errors: the constraints on parameters degrades only by a factor of two when the random error is increased from 100 to 500 km/s. We also compare cluster velocities with other dark energy probes proposed in the Dark Energy Task Force report. For cluster velocity measurements with realistic priors, the eventual constraints on the dark energy density, the dark energy equation of state and its evolution are comparable to constraints from supernovae measurements, and better than cluster counts and baryon acoustic oscillations; adding velocity to other dark energy probes improves constraints on the figure of merit by more than a factor of two. For upcoming Sunyaev-Zeldovich galaxy cluster surveys, even velocity measurements with errors as large as 1000 km/s will substantially improve the cosmological constraints compared to using the cluster number density alone.Comment: 25 pages, 10 figures. Results and conclusions unchanged. Minor changes to match the accepted version in Physical Review

Mass accretion rates of clusters of galaxies: CIRS and HeCS

We use a new spherical accretion recipe tested on N-body simulations to measure the observed mass accretion rate (MAR) of 129 clusters in the Cluster Infall Regions in the Sloan Digital Sky Survey (CIRS) and in the Hectospec Cluster Survey (HeCS). The observed clusters cover the redshift range of $0.01<z<0.30$ and the mass range of $\sim 10^{14}-10^{15} {h^{-1}~\rm{M_\odot}}$. Based on three-dimensional mass profiles of simulated clusters reaching beyond the virial radius, our recipe returns MARs that agree with MARs based on merger trees. We adopt this recipe to estimate the MAR of real clusters based on measurements of the mass profile out to $\sim 3R_{200}$. We use the caustic method to measure the mass profiles to these large radii. We demonstrate the validity of our estimates by applying the same approach to a set of mock redshift surveys of a sample of 2000 simulated clusters with a median mass of $M_{200}= 10^{14} {h^{-1}~\rm{M_{\odot}}}$ as well as a sample of 50 simulated clusters with a median mass of $M_{200}= 10^{15} {h^{-1}~\rm{M_{\odot}}}$: the median MARs based on the caustic mass profiles of the simulated clusters are unbiased and agree within $19\%$ with the median MARs based on the real mass profile of the clusters. The MAR of the CIRS and HeCS clusters increases with the mass and the redshift of the accreting cluster, which is in excellent agreement with the growth of clusters in the $\Lambda$CDM model.Comment: 25 pages, 19 figures, 7 table

The Infall Region of Abell 576: Independent Mass and Light Profiles

We describe observations of the nearby cluster of galaxies A576 beyond the virial radius and into the infall region. Using 1057 redshifts, we use the infall pattern in redshift space to determine the mass profile of A576 to a radius of ~4 Mpc/h. This mass estimation technique makes no assumptions about the equilibrium state of the cluster. Within 1 Mpc/h, the mass profile we derive exceeds that determined from X-ray observations by a factor of 2.5. At \~2.5 Mpc/h, however, the mass profile agrees with virial mass estimates. Our mass profile is consistent with a NFW or Hernquist profile, but it is inconsistent with an isothermal sphere. R-band images of a $3^\circ x 3^\circ$ region centered on the cluster allow an independent determination of the cluster light profile. We calculate the integrated mass-to-light ratio as a function of cluster radius; it decreases smoothly from the core to ~4 Mpc/h. The differential dM/dL_R profile decreases more steeply; we find M/L_R ~100 h at ~4 Mpc/h, in good agreement with the mass-to-light ratios of individual galaxies. This value implies $\Omega_m \lesssim 0.4$ at 95% confidence. For a Hernquist model, the best-fit mass profiles differ from the observed surface number density of galaxies; the galaxies have a larger scale radius than the mass. This result is consistent with the centrally peaked $M/L_R$ profile. Similarly, the scale radius of the light profile is larger than that of the mass profile. We discuss some potential systematic effects; none can easily reconcile our results with a constant mass-to-light ratio. (abstract edited)Comment: 54 pages, 25 figures, to appear in Astronomical Journal November 200

X-ray Emitting Groups in the Infall Region of Abell 2199

Using a large redshift survey covering 95 square degrees, we demonstrate that the infall region of Abell 2199 contains Abell 2197, one or two X-ray emitting groups, and up to five additional groups identified in redshift surveys. Our survey shows that the X-ray emitting systems, located at projected radii of $1.^\circ4, 1.^\circ9$, and $5.^\circ1$ (2.2, 3.1, and $8.0 h^{-1}$Mpc), are connected kinematically to A2199. A2197 is itself an optically rich cluster; its weak X-ray emission suggests that it is much less massive than A2199. The absence of a sharp peak in the infall pattern at the position of A2197 supports this hypothesis. The outermost group is well outside the virial region of A2199 and it distorts the infall pattern in redshift space. The two X-ray emitting groups are roughly colinear, suggesting the existence of an extended ($8.0 h^{-1}$Mpc) filament. The identification of these infalling groups provides direct support of hierarchical structure formation; studies of these systems will provide insights into structure evolution. Groups in the infall regions of nearby clusters may offer a unique probe of the physics of the warm/hot ionized medium (WHIM) which is difficult to observe directly with current instruments

Constraining q_0 with Cluster Gas Mass Fractions: A Feasibility Study

As the largest gravitationally bound objects in the universe, clusters of galaxies may contain a fair sample of the baryonic mass fraction of the universe. Since the gas mass fraction from the hot ICM is believed to be constant in time, the value of the cosmological deceleration parameter $q_0$ can be determined by comparing the calculated gas mass fraction in nearby and distant clusters (Pen 1997). To test the potential of this method, we compare the gas fractions derived for a sample of luminous ($L_X > 10^{45}$erg s$^{-1}$), nearby clusters with those calculated for eight luminous, distant ($0.3 < z < 0.6$) clusters using ASCA and ROSAT observations. For consistency, we evaluate the gas mass fraction at a fixed physical radius of 1 $h_{50}^{-1}$ Mpc (assuming $q_0=0.0$). We find a best fit value of $q_0 = 0.07$ with -0.47 < q_0 < 0.67 at 95% confidence. We also determine the gas fraction using the method of Evrard, Metzler, & Navarro (1997) to find the total mass within $r_{500}$, the radius where the mean overdensity of matter is 500 times the critical density. In simulations, this method reduces the scatter in the determination of gravitational mass without biasing the mean. We find that it also reduces the scatter in actual observations for nearby clusters, but not as much as simulations suggest. Using this method, the best fit value is $q_0 = 0.04$ with -0.50 < q_0 < 0.64. The excellent agreement between these two methods suggests that this may be a useful technique for determining $q_0$. The constraints on $q_0$ should improve as more distant clusters are studied and precise temperature profiles are measured to large radii.Comment: 8 pages, 4 figures, uses emulateapj.sty, onecolfloat.st

Detailed Study of the Ursa Major Supercluster of Galaxies Using the 2MASS and SDSS Catalogs

We study the infrared (K_s band) properties of clusters of galaxies in the Ursa Major supercluster using data from 2MASS (Two-Micron All-Sky Survey) and SDSS (Sloan Digital Sky Survey). We identified three large filaments with mean redshifts of z = 0.051, 0.060, and 0.071. All clusters of the supercluster are located in these filaments. We determined the total K_s-band luminosities and masses for 11 clusters of galaxies within comparable physical regions (within a radius R_200 close to the virial radius) using a homogeneous method. We constructed a combined luminosity function for the supercluster in this region, which can be described by the Schechter function with the following parameters: M*_K = -24^m.50 and \alpha = -0.98. The infrared luminosities of the clusters of galaxies correlate with their masses; the M/L_K ratios of the systems increase with their masses (luminosities), with most of the Ursa Major clusters of galaxies (particularly the richer ones) closely following the relations derived previously for a large sample of clusters and groups of galaxies. The total mass-to-infrared-luminosity ratio is 52 M_{\odot}/L_{\odot} for six Abell clusters and 49 M_{\odot}/L_{\odot} for all of the clusters, except Anon2.Comment: 16 pages, 5 figure

Halo mass - concentration relation from weak lensing

We perform a statistical weak lensing analysis of dark matter profiles around tracers of halo mass from galactic- to cluster-size halos. In this analysis we use 170,640 isolated ~L* galaxies split into ellipticals and spirals, 38,236 groups traced by isolated spectroscopic Luminous Red Galaxies (LRGs) and 13,823 MaxBCG clusters from the Sloan Digital Sky Survey (SDSS) covering a wide range of richness. Together these three samples allow a determination of the density profiles of dark matter halos over three orders of magnitude in mass, from 10^{12} M_{sun} to 10^{15} M_{sun}. The resulting lensing signal is consistent with an NFW or Einasto profile on scales outside the central region. We find that the NFW concentration parameter c_{200b} decreases with halo mass, from around 10 for galactic halos to 4 for cluster halos. Assuming its dependence on halo mass in the form of c_{200b} = c_0 [M/(10^{14}M_{sun}/h)]^{\beta}, we find c_0=4.6 +/- 0.7 (at z=0.22) and \beta=0.13 +/- 0.07, with very similar results for the Einasto profile. The slope (\beta) is in agreement with theoretical predictions, while the amplitude is about two standard deviations below the predictions for this mass and redshift, but we note that the published values in the literature differ at a level of 10-20% and that for a proper comparison our analysis should be repeated in simulations. We discuss the implications of our results for the baryonic effects on the shear power spectrum: since these are expected to increase the halo concentration, the fact that we see no evidence of high concentrations on scales above 20% of the virial radius suggests that baryonic effects are limited to small scales, and are not a significant source of uncertainty for the current weak lensing measurements of the dark matter power spectrum. [ABRIDGED]Comment: 17 pages, 5 figures, accepted to JCAP pending minor revisions that are included in v2 here on arXi