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Sample records for galaxy cluster velocities

  1. Galaxy Cluster Bulk Flows and Collision Velocities in QUMOND

    NASA Astrophysics Data System (ADS)

    Katz, Harley; McGaugh, Stacy; Teuben, Peter; Angus, G. W.

    2013-07-01

    We examine the formation of clusters of galaxies in numerical simulations of a QUMOND cosmogony with massive sterile neutrinos. Clusters formed in these exploratory simulations develop higher velocities than those found in ΛCDM simulations. The bulk motions of clusters attain ~1000 km s-1 by low redshift, comparable to observations whereas ΛCDM simulated clusters tend to fall short. Similarly, high pairwise velocities are common in cluster-cluster collisions like the Bullet Cluster. There is also a propensity for the most massive clusters to be larger in QUMOND and to appear earlier than in ΛCDM, potentially providing an explanation for "pink elephants" like El Gordo. However, it is not obvious that the cluster mass function can be recovered.

  2. GALAXY CLUSTER BULK FLOWS AND COLLISION VELOCITIES IN QUMOND

    SciTech Connect

    Katz, Harley; McGaugh, Stacy; Teuben, Peter; Angus, G. W. E-mail: stacy.mcgaugh@case.edu E-mail: angus.gz@gmail.com

    2013-07-20

    We examine the formation of clusters of galaxies in numerical simulations of a QUMOND cosmogony with massive sterile neutrinos. Clusters formed in these exploratory simulations develop higher velocities than those found in {Lambda}CDM simulations. The bulk motions of clusters attain {approx}1000 km s{sup -1} by low redshift, comparable to observations whereas {Lambda}CDM simulated clusters tend to fall short. Similarly, high pairwise velocities are common in cluster-cluster collisions like the Bullet Cluster. There is also a propensity for the most massive clusters to be larger in QUMOND and to appear earlier than in {Lambda}CDM, potentially providing an explanation for ''pink elephants'' like El Gordo. However, it is not obvious that the cluster mass function can be recovered.

  3. New measurements of radial velocities in clusters of galaxies. II

    NASA Astrophysics Data System (ADS)

    Proust, D.; Mazure, A.; Sodre, L.; Capelato, H.; Lund, G.

    1988-03-01

    Heliocentric radial velocities are determined for 100 galaxies in five clusters, on the basis of 380-518-nm observations obtained using a CCD detector coupled by optical fibers to the OCTOPUS multiobject spectrograph at the Cassegrain focus of the 3.6-m telescope at ESO La Silla. The data-reduction procedures and error estimates are discussed, and the results are presented in tables and graphs and briefly characterized.

  4. Dwarf galaxies in the Coma cluster - I. Velocity dispersion measurements

    NASA Astrophysics Data System (ADS)

    Kourkchi, E.; Khosroshahi, H. G.; Carter, D.; Karick, A. M.; Mármol-Queraltó, E.; Chiboucas, K.; Tully, R. B.; Mobasher, B.; Guzmán, R.; Matković, A.; Gruel, N.

    2012-03-01

    We present the study of a large sample of early-type dwarf galaxies in the Coma cluster observed with DEIMOS on the Keck II to determine their internal velocity dispersion. We focus on a subsample of 41 member dwarf elliptical galaxies for which the velocity dispersion can be reliably measured, 26 of which were studied for the first time. The magnitude range of our sample is -21 < MR < -15 mag. This paper (Paper I) focuses on the measurement of the velocity dispersion and their error estimates. The measurements were performed using penalized pixel fitting (PPXF) and using the calcium triplet absorption lines. We use Monte Carlo bootstrapping to study various sources of uncertainty in our measurements, namely statistical uncertainty, template mismatch and other systematics. We find that the main source of uncertainty is the template mismatch effect which is reduced by using templates with a range of spectral types. Combining our measurements with those from the literature, we study the Faber-Jackson relation (L∝σα) and find that the slope of the relation is α= 1.99 ± 0.14 for galaxies brighter than MR≃-16 mag. A comprehensive analysis of the results combined with the photometric properties of these galaxies is reported in Paper II.

  5. GLOBULAR CLUSTERS AND DARK SATELLITE GALAXIES THROUGH THE STREAM VELOCITY

    SciTech Connect

    Naoz, Smadar; Narayan, Ramesh

    2014-08-10

    The formation of purely baryonic globular clusters with no gravitationally bound dark matter is still a theoretical challenge. We show that these objects might form naturally whenever there is a relative stream velocity between baryons and dark matter. The stream velocity causes a phase shift between linear modes of baryonic and dark matter perturbations, which translates to a spatial offset between the two components when they collapse. For a 2σ (3σ) density fluctuation, baryonic clumps with masses in the range 10{sup 5}-2.5 × 10{sup 6} M {sub ☉} (10{sup 5}-4 × 10{sup 6} M {sub ☉}) collapse outside the virial radii of their counterpart dark matter halos. These objects could survive as long-lived, dark-matter-free objects and might conceivably become globular clusters. In addition, their dark matter counterparts, which were deprived of gas, might become dark satellite galaxies.

  6. Galaxy Transformation as probed by Morphology and Velocity Fields of Distant Cluster Galaxies

    NASA Astrophysics Data System (ADS)

    Ziegler, Bodo

    2005-07-01

    We seek to obtain ACS imaging of four distant {0.3clusters of galaxies within a 6'x6' field covered by a 2x2 mosaic to determine morphological and structural parameters of late-type galaxies. We specifically concentrate on peculiarities indicative of past or ongoing interaction processes. The 90 target galaxies have been {Period74} or will be {P75} observed with 3D-spectroscopy at ESO-VLT yielding 2D-velocity fields with unprecedented spatial coverage and sampling. The good spatial resolution of the ground-based data will be further enhanced by a deconvolution method based on the proposed ACS images. The velocity field and the morphology in restframe-UV light will reveal possible transformation mechanisms affecting not only the stellar populations but also the mass distribution of the galaxies. Additionally, it will be possible to pin down the nature of the interaction {e.g. tidally or ram-pressure induced}. This assessment gets supported by our N-body/SPH simulations {including star formation} of different interaction processes that allow the direct comparison of structural and kinematical characteristics at each time step with the observations on an individual basis taking into account all observational constraints for a given galaxy. All together, we will be able to explore the relative efficiency of the various proposed transformation phenomena. In the case of non-disturbed spirals, a rotation curve can be extracted from the full 2D velocity field with unprecedented quality, from which the maximum rotation speed can be derived with high confidence. In combination with accurate size and luminosity determinations from the ACS images, we will be able to establish the Tully-Fisher and Fundamental Plane relations of cluster spiral members at cosmological epochs. At these distances cluster assembly is predicted to peak and we can probe the galaxies' luminosity, size and mass evolution with robust methods. Together with our already existing sample of 200

  7. Optical spectroscopy and velocity dispersions of galaxy clusters from the SPT-SZ survey

    SciTech Connect

    Ruel, J.; Bayliss, M.; Bazin, G.; Bocquet, S.; Brodwin, M.; Foley, R. J.; Stalder, B.; Ashby, M. L. N.; Aird, K. A.; Armstrong, R.; Bautz, M.; Benson, B. A.; Bleem, L. E.; Carlstrom, J. E.; Chang, C. L.; Crawford, T. M.; Crites, A. T.; Chapman, S. C.; Cho, H. M.; Clocchiatti, A.; and others

    2014-09-01

    We present optical spectroscopy of galaxies in clusters detected through the Sunyaev-Zel'dovich (SZ) effect with the South Pole Telescope (SPT). We report our own measurements of 61 spectroscopic cluster redshifts, and 48 velocity dispersions each calculated with more than 15 member galaxies. This catalog also includes 19 dispersions of SPT-observed clusters previously reported in the literature. The majority of the clusters in this paper are SPT-discovered; of these, most have been previously reported in other SPT cluster catalogs, and five are reported here as SPT discoveries for the first time. By performing a resampling analysis of galaxy velocities, we find that unbiased velocity dispersions can be obtained from a relatively small number of member galaxies (≲ 30), but with increased systematic scatter. We use this analysis to determine statistical confidence intervals that include the effect of membership selection. We fit scaling relations between the observed cluster velocity dispersions and mass estimates from SZ and X-ray observables. In both cases, the results are consistent with the scaling relation between velocity dispersion and mass expected from dark-matter simulations. We measure a ∼30% log-normal scatter in dispersion at fixed mass, and a ∼10% offset in the normalization of the dispersion-mass relation when compared to the expectation from simulations, which is within the expected level of systematic uncertainty.

  8. Redshift and velocity dispersion of the cluster of galaxies around NGC 326

    NASA Astrophysics Data System (ADS)

    Werner, P. N.; Worrall, D. M.; Birkinshaw, M.

    1999-08-01

    Redshifts of several galaxies thought to be associated with NGC 326 are determined. The results confirm the presence of a cluster and find a mean redshift of z=0.0477+/-0.0007 and a line-of-sight velocity dispersion sigma_z=599 (+230,-110)kms^-1. The velocity dispersion and previously measured X-ray gas temperature of kT~=1.9keV are consistent with the cluster sigma_zkT relation, and NGC 326 is seen to be a slowly moving member of the cluster.

  9. Velocity bias from the small-scale clustering of SDSS-III BOSS galaxies

    NASA Astrophysics Data System (ADS)

    Guo, Hong; Zheng, Zheng; Zehavi, Idit; Dawson, Kyle; Skibba, Ramin A.; Tinker, Jeremy L.; Weinberg, David H.; White, Martin; Schneider, Donald P.

    2015-01-01

    We present the measurements and modelling of the projected and redshift-space clustering of CMASS galaxies in the Sloan Digital Sky Survey-III Baryon Oscillation Spectroscopic Survey Data Release 11. For a volume-limited luminous red galaxy sample in the redshift range of 0.48 < z < 0.55, we perform halo occupation distribution modelling of the small- and intermediate-scale (0.1-60 h-1 Mpc) projected and redshift-space two-point correlation functions, with an accurate model built on high-resolution N-body simulations. To interpret the measured redshift-space distortions, the distribution of galaxy velocities must differ from that of the dark matter inside haloes of ˜1013-1014 h-1 M⊙, i.e. the data require the existence of galaxy velocity bias. Most notably, central galaxies on average are not at rest with respect to the core of their host haloes, but rather move around it with a 1D velocity dispersion of 0.22^{+0.03}_{-0.04} times that of the dark matter, implying a spatial offset from the centre at the level of ≲1 per cent of the halo virial radius. The luminous satellite galaxies move more slowly than the dark matter, with velocities 0.86^{+0.08}_{-0.03} times those of the dark matter, which suggests that the velocity and spatial distributions of these satellites cannot both be unbiased. The constraints mainly arise from the Fingers-of-God effect at non-linear scales and the smoothing to the Kaiser effect in the translinear regime; the robustness of the results is demonstrated by a variety of tests. We discuss the implications of the existence of galaxy velocity bias for investigations of galaxy formation and cosmology.

  10. Alignments of the galaxies in and around the Virgo cluster with the local velocity shear

    SciTech Connect

    Lee, Jounghun; Rey, Soo Chang; Kim, Suk

    2014-08-10

    Observational evidence is presented for the alignment between the cosmic sheet and the principal axis of the velocity shear field at the position of the Virgo cluster. The galaxies in and around the Virgo cluster from the Extended Virgo Cluster Catalog that was recently constructed by Kim et al. are used to determine the direction of the local sheet. The peculiar velocity field reconstructed from the Sloan Digital Sky Survey Data Release 7 is analyzed to estimate the local velocity shear tensor at the Virgo center. Showing first that the minor principal axis of the local velocity shear tensor is almost parallel to the direction of the line of sight, we detect a clear signal of alignment between the positions of the Virgo satellites and the intermediate principal axis of the local velocity shear projected onto the plane of the sky. Furthermore, the dwarf satellites are found to appear more strongly aligned than their normal counterparts, which is interpreted as an indication of the following. (1) The normal satellites and the dwarf satellites fall in the Virgo cluster preferentially along the local filament and the local sheet, respectively. (2) The local filament is aligned with the minor principal axis of the local velocity shear while the local sheet is parallel to the plane spanned by the minor and intermediate principal axes. Our result is consistent with the recent numerical claim that the velocity shear is a good tracer of the cosmic web.

  11. The Mean and Scatter of the Velocity Dispersion-Optical Richness Relation for MaxBCG Galaxy Clusters

    SciTech Connect

    Becker, M.R.; McKay, T.A.; Koester, B.; Wechsler, R.H.; Rozo, E.; Evrard, A.; Johnston, D.; Sheldon, E.; Annis, J.; Lau, E.; Nichol, R.; Miller, C.; /Michigan U.

    2007-06-05

    The distribution of galaxies in position and velocity around the centers of galaxy clusters encodes important information about cluster mass and structure. Using the maxBCG galaxy cluster catalog identified from imaging data obtained in the Sloan Digital Sky Survey, we study the BCG--galaxy velocity correlation function. By modeling its non-Gaussianity, we measure the mean and scatter in velocity dispersion at fixed richness. The mean velocity dispersion increases from 202 {+-} 10 km s{sup -1} for small groups to more than 854 {+-} 102 km s{sup -1} for large clusters. We show the scatter to be at most 40.5{+-}3.5%, declining to 14.9{+-}9.4% in the richest bins. We test our methods in the C4 cluster catalog, a spectroscopic cluster catalog produced from the Sloan Digital Sky Survey DR2 spectroscopic sample, and in mock galaxy catalogs constructed from N-body simulations. Our methods are robust, measuring the scatter to well within one-sigma of the true value, and the mean to within 10%, in the mock catalogs. By convolving the scatter in velocity dispersion at fixed richness with the observed richness space density function, we measure the velocity dispersion function of the maxBCG galaxy clusters. Although velocity dispersion and richness do not form a true mass--observable relation, the relationship between velocity dispersion and mass is theoretically well characterized and has low scatter. Thus our results provide a key link between theory and observations up to the velocity bias between dark matter and galaxies.

  12. The Luminosities, Sizes, and Velocity Dispersions of Brightest Cluster Galaxies: Implications for Formation History

    NASA Astrophysics Data System (ADS)

    Bernardi, Mariangela; Hyde, Joseph B.; Sheth, Ravi K.; Miller, Chris J.; Nichol, Robert C.

    2007-04-01

    The size-luminosity relation of early-type brightest cluster galaxies (BCGs), Re ~ L0.88, is steeper than that for the bulk of the early-type galaxy population, for which Re ~ L0.68. This is true if quantities derived from either de Vaucouleurs or Sérsic fits to the surface brightness profiles are used. Contamination from an intracluster light component centered on the BCG, with parameters similar to what has been seen in some recent studies, is not able to account for this difference. In addition, although BCGs are hardly offset from the fundamental plane defined by the bulk of the early-type population, they show considerably smaller scatter. The larger than expected sizes of BCGs, and the increased homogeneity, are qualitatively consistent with models that seek to explain the colors of the most massive galaxies by invoking dry dissipationless mergers, since dissipation tends to reduce the sizes of galaxies, and wet mergers that result in star formation would tend to increase the scatter in luminosity at a fixed size and velocity dispersion. Furthermore, BCGs define the same g - r color-magnitude relation as the bulk of the early-type population. If BCGs formed from dry mergers, then BCG progenitors must have been red for their magnitudes, suggesting that they hosted older stellar populations than is typical for their luminosities. Our findings have two other consequences. First, the Re-L relation of the early-type galaxy population as a whole (i.e., normal plus BCG) exhibits some curvature: the most luminous galaxies tend to have larger sizes than is expected from the Re ~ L0.68 scaling—some of this curvature must be a consequence of the fact that an increasing fraction of the most luminous galaxies are BCGs. The second consequence is suggested by the fact that, despite following a steeper size-luminosity relation, BCGs tend to define a tight relation between dynamical mass Reσ2/G and luminosity. Although this relation is slightly different than that defined

  13. Galaxy Clusters

    NASA Astrophysics Data System (ADS)

    Miller, Christopher J. Miller

    2012-03-01

    There are many examples of clustering in astronomy. Stars in our own galaxy are often seen as being gravitationally bound into tight globular or open clusters. The Solar System's Trojan asteroids cluster at the gravitational Langrangian in front of Jupiter’s orbit. On the largest of scales, we find gravitationally bound clusters of galaxies, the Virgo cluster (in the constellation of Virgo at a distance of ˜50 million light years) being a prime nearby example. The Virgo cluster subtends an angle of nearly 8◦ on the sky and is known to contain over a thousand member galaxies. Galaxy clusters play an important role in our understanding of theUniverse. Clusters exist at peaks in the three-dimensional large-scale matter density field. Their sky (2D) locations are easy to detect in astronomical imaging data and their mean galaxy redshifts (redshift is related to the third spatial dimension: distance) are often better (spectroscopically) and cheaper (photometrically) when compared with the entire galaxy population in large sky surveys. Photometric redshift (z) [Photometric techniques use the broad band filter magnitudes of a galaxy to estimate the redshift. Spectroscopic techniques use the galaxy spectra and emission/absorption line features to measure the redshift] determinations of galaxies within clusters are accurate to better than delta_z = 0.05 [7] and when studied as a cluster population, the central galaxies form a line in color-magnitude space (called the the E/S0 ridgeline and visible in Figure 16.3) that contains galaxies with similar stellar populations [15]. The shape of this E/S0 ridgeline enables astronomers to measure the cluster redshift to within delta_z = 0.01 [23]. The most accurate cluster redshift determinations come from spectroscopy of the member galaxies, where only a fraction of the members need to be spectroscopically observed [25,42] to get an accurate redshift to the whole system. If light traces mass in the Universe, then the locations

  14. A Measurement of Large-Scale Peculiar Velocities of Clusters of Galaxies: Results and Cosmological Implications

    NASA Astrophysics Data System (ADS)

    Kashlinsky, A.; Atrio-Barandela, F.; Kocevski, D.; Ebeling, H.

    2008-10-01

    Peculiar velocities of clusters of galaxies can be measured by studying the fluctuations in the cosmic microwave background (CMB) generated by the scattering of the microwave photons by the hot X-ray-emitting gas inside clusters. While for individual clusters such measurements result in large errors, a large statistical sample of clusters allows one to study cumulative quantities dominated by the overall bulk flow of the sample with the statistical errors integrating down. We present results from such a measurement using the largest all-sky X-ray cluster catalog combined to date and the 3 yr WMAP CMB data. We find a strong and coherent bulk flow on scales out to at least gsim300 h-1 Mpc, the limit of our catalog. This flow is difficult to explain by gravitational evolution within the framework of the concordance ΛCDM model and may be indicative of the tilt exerted across the entire current horizon by far-away pre-inflationary inhomogeneities.

  15. Radial velocities of galaxies in the cluster Klemola 22 from observations with OPTOPUS, the ESO multiple object spectroscopy facility

    NASA Astrophysics Data System (ADS)

    Cristiani, S.; D'Odorico, S.; de Souza, R.; Lund, G.; Quintana, H.

    1987-06-01

    This paper presents the first results obtained with the ESO multiple fiber spectroscopic facility (OPTOPUS). Radial velocities and magnitudes are given for 44 galaxies in the cluster Klemola 22. The average redshift is 16160 km s-1 and the velocity dispersion 742 km s-1. The galaxy Kle 22/17 shows strong emission lines of [O III], with a FWHM of 850 km s-1, and is classified as a type 2 Seyfert. From these observations, the average efficiency of OPTOPUS, including telescope, spectrograph and detector, is computed as 1 detected photoelectron Å-1s-1 for an object of 15 B magnitude.

  16. A High Stellar Velocity Dispersion and ~100 Globular Clusters for the Ultra-diffuse Galaxy Dragonfly 44

    NASA Astrophysics Data System (ADS)

    van Dokkum, Pieter; Abraham, Roberto; Brodie, Jean; Conroy, Charlie; Danieli, Shany; Merritt, Allison; Mowla, Lamiya; Romanowsky, Aaron; Zhang, Jielai

    2016-09-01

    Recently a population of large, very low surface brightness, spheroidal galaxies was identified in the Coma cluster. The apparent survival of these ultra-diffuse galaxies (UDGs) in a rich cluster suggests that they have very high masses. Here, we present the stellar kinematics of Dragonfly 44, one of the largest Coma UDGs, using a 33.5 hr integration with DEIMOS on the Keck II telescope. We find a velocity dispersion of σ ={47}-6+8 {km} {{{s}}}-1, which implies a dynamical mass of {M}{dyn}(\\lt {r}1/2)={0.7}-0.2+0.3× {10}10 {M}ȯ within its deprojected half-light radius of {r}1/2=4.6+/- 0.2 {kpc}. The mass-to-light ratio is M/{L}I(\\lt {r}1/2)={48}-14+21 {M}ȯ /{L}ȯ , and the dark matter fraction is 98% within {r}1/2. The high mass of Dragonfly 44 is accompanied by a large globular cluster population. From deep Gemini imaging taken in 0\\buildrel{\\prime\\prime}\\over{.} 4 seeing we infer that Dragonfly 44 has {94}-20+25 globular clusters, similar to the counts for other galaxies in this mass range. Our results add to other recent evidence that many UDGs are “failed” galaxies, with the sizes, dark matter content, and globular cluster systems of much more luminous objects. We estimate the total dark halo mass of Dragonfly 44 by comparing the amount of dark matter within r=4.6 {kpc} to enclosed mass profiles of NFW halos. The enclosed mass suggests a total mass of ˜ {10}12 {M}ȯ , similar to the mass of the Milky Way. The existence of nearly dark objects with this mass is unexpected, as galaxy formation is thought to be maximally efficient in this regime.

  17. A High Stellar Velocity Dispersion and ~100 Globular Clusters for the Ultra-diffuse Galaxy Dragonfly 44

    NASA Astrophysics Data System (ADS)

    van Dokkum, Pieter; Abraham, Roberto; Brodie, Jean; Conroy, Charlie; Danieli, Shany; Merritt, Allison; Mowla, Lamiya; Romanowsky, Aaron; Zhang, Jielai

    2016-09-01

    Recently a population of large, very low surface brightness, spheroidal galaxies was identified in the Coma cluster. The apparent survival of these ultra-diffuse galaxies (UDGs) in a rich cluster suggests that they have very high masses. Here, we present the stellar kinematics of Dragonfly 44, one of the largest Coma UDGs, using a 33.5 hr integration with DEIMOS on the Keck II telescope. We find a velocity dispersion of σ ={47}-6+8 {km} {{{s}}}-1, which implies a dynamical mass of {M}{dyn}(\\lt {r}1/2)={0.7}-0.2+0.3× {10}10 {M}ȯ within its deprojected half-light radius of {r}1/2=4.6+/- 0.2 {kpc}. The mass-to-light ratio is M/{L}I(\\lt {r}1/2)={48}-14+21 {M}ȯ /{L}ȯ , and the dark matter fraction is 98% within {r}1/2. The high mass of Dragonfly 44 is accompanied by a large globular cluster population. From deep Gemini imaging taken in 0\\buildrel{\\prime\\prime}\\over{.} 4 seeing we infer that Dragonfly 44 has {94}-20+25 globular clusters, similar to the counts for other galaxies in this mass range. Our results add to other recent evidence that many UDGs are “failed” galaxies, with the sizes, dark matter content, and globular cluster systems of much more luminous objects. We estimate the total dark halo mass of Dragonfly 44 by comparing the amount of dark matter within r=4.6 {kpc} to enclosed mass profiles of NFW halos. The enclosed mass suggests a total mass of ∼ {10}12 {M}ȯ , similar to the mass of the Milky Way. The existence of nearly dark objects with this mass is unexpected, as galaxy formation is thought to be maximally efficient in this regime.

  18. THE RELATION BETWEEN GAS DENSITY AND VELOCITY POWER SPECTRA IN GALAXY CLUSTERS: QUALITATIVE TREATMENT AND COSMOLOGICAL SIMULATIONS

    SciTech Connect

    Zhuravleva, I.; Allen, S. W.; Churazov, E. M.; Gaspari, M.; Schekochihin, A. A.; Lau, E. T.; Nagai, D.; Nelson, K.; Parrish, I. J.

    2014-06-10

    We address the problem of evaluating the power spectrum of the velocity field of the intracluster medium using only information on the plasma density fluctuations, which can be measured today by Chandra and XMM-Newton observatories. We argue that for relaxed clusters there is a linear relation between the rms density and velocity fluctuations across a range of scales, from the largest ones, where motions are dominated by buoyancy, down to small, turbulent scales: (δρ{sub k}/ρ){sup 2}=η{sub 1}{sup 2}(V{sub 1,k}/c{sub s}){sup 2}, where δρ {sub k}/ρ is the spectral amplitude of the density perturbations at wavenumber k, V{sub 1,k}{sup 2}=V{sub k}{sup 2}/3 is the mean square component of the velocity field, c{sub s} is the sound speed, and η{sub 1} is a dimensionless constant of the order of unity. Using cosmological simulations of relaxed galaxy clusters, we calibrate this relation and find η{sub 1} ≈ 1 ± 0.3. We argue that this value is set at large scales by buoyancy physics, while at small scales the density and velocity power spectra are proportional because the former are a passive scalar advected by the latter. This opens an interesting possibility to use gas density power spectra as a proxy for the velocity power spectra in relaxed clusters across a wide range of scales.

  19. The Rotation of Galaxy Clusters

    NASA Astrophysics Data System (ADS)

    Tovmassian, H. M.

    2015-09-01

    The method for detection of the galaxy cluster rotation based on the study of distribution of member galaxies with velocities lower and higher than the cluster mean velocity over the cluster image is proposed. The search for rotation is made for flat clusters with a/b > 1.8 and BMI type clusters which are expected to be rotating. For comparison there were studied also round clusters and clusters of NBMI type, the second by brightness galaxy, which does not differ significantly from the cluster cD galaxy. Seventeen out of studied 65 clusters are found to be rotating. It was found that the detection rate is sufficiently high for flat clusters, over 60%, and clusters of BMI type with dominant cD galaxy, ≈ 35% . The obtained results show that clusters were formed from the huge primordial gas clouds and preserved the rotation of the primordial clouds, unless they did not experience mergings with other clusters and groups of galaxies, as a result of which the rotation was prevented.

  20. PROSPECTS FOR MEASURING THE RELATIVE VELOCITIES OF GALAXY CLUSTERS IN PHOTOMETRIC SURVEYS USING THE KINETIC SUNYAEV-ZEL'DOVICH EFFECT

    SciTech Connect

    Keisler, Ryan; Schmidt, Fabian E-mail: fabians@astro.princeton.edu

    2013-03-10

    We consider the prospects for measuring the pairwise kinetic Sunyaev-Zel'dovich (kSZ) signal from galaxy clusters discovered in large photometric surveys such as the Dark Energy Survey (DES). We project that the DES cluster sample will, in conjunction with existing mm-wave data from the South Pole Telescope (SPT), yield a detection of the pairwise kSZ signal at the 8{sigma}-13{sigma} level, with sensitivity peaking for clusters separated by {approx}100 Mpc distances. A next-generation version of SPT would allow for a 18{sigma}-30{sigma} detection and would be limited by variance from the kSZ signal itself and the residual thermal Sunyaev-Zel'dovich (tSZ) signal. Throughout our analysis, we assume photometric redshift errors that wash out the signal for clusters separated by {approx}<50 Mpc; a spectroscopic survey of the DES sample would recover this signal and allow for a 26{sigma}-43{sigma} detection, and would again be limited by kSZ/tSZ variance. Assuming a standard model of structure formation, these high-precision measurements of the pairwise kSZ signal will yield detailed information on the gas content of the galaxy clusters. Alternatively, if the gas can be sufficiently characterized by other means (e.g., using tSZ, X-ray, or weak lensing), then the relative velocities of the galaxy clusters can be isolated, thereby providing a precision measurement of gravity on 100 Mpc scales. We briefly consider the utility of these measurements for constraining theories of modified gravity.

  1. Velocity width measurements of the coolest X-ray emitting material in the cores of clusters, groups and elliptical galaxies

    NASA Astrophysics Data System (ADS)

    Sanders, J. S.; Fabian, A. C.

    2013-03-01

    We examine the velocity width of cool X-ray emitting material using XMM-Newton Reflection Grating Spectrometer (RGS) spectra of a sample of clusters and group of galaxies and elliptical galaxies. Improving on our previous analyses, we apply a spectral model which accounts for broadening due to the spatial extent of the source. With both conventional and Markov Chain Monte Carlo approaches we obtain limits, or in a few cases measurements, of the velocity broadening of the coolest X-ray material. In our sample, we include new observations targeting objects with compact, bright, line-rich cores. One of these, MACS J2229.7-2755, gives a velocity limit of 280 km s^{-1} at the 90 per cent confidence level. Other systems with limits close to 300 km s^{-1} include A 1835, NGC 4261 and NGC 4472. For more than a third of the targets we find limits better than 500 km s^{-1} . HCG 62, NGC 1399 and A 3112 show evidence for {˜ } 400 km s^{-1} velocity broadening. For a smaller sample of objects, we use continuum-subtracted emission line surface brightness profiles to account for the spatial broadening. Although there are significant systematic errors associated with the technique ({˜ } 150 km s^{-1} ), we find broadening at the level of 280 to 500 km s^{-1} in A 3112, NGC 1399 and NGC 4636.

  2. THE ORIENTATION OF GALAXIES IN GALAXY CLUSTERS

    SciTech Connect

    Godlowski, Wlodzimierz; Piwowarska, Paulina; Panko, Elena; Flin, Piotr E-mail: paoletta@interia.p E-mail: sfflin@cyf-kr.edu.p

    2010-11-10

    We present an analysis of the spatial orientations of galaxies in 247 optically selected rich Abell clusters which have at least 100 members in the considered area. We investigated the relation between angles that give information about galaxy angular momenta and the number of members in each structure. The position angles of the galaxies' major axes, as well as two angles describing the spatial orientation of the galaxy plane, were tested for isotropy by applying three different statistical tests. It is found that the values of the statistics increase with the amount of the galaxies' members, which is equivalent to the existence of a relation between anisotropy and the number of galaxies in a cluster. The search for connection between the galaxies' alignments and Bautz-Morgan (BM) morphological types of examined clusters showed a weak dependence. A statistically marginal relation between velocity dispersion and cluster richness was observed. In addition, it was found that the velocity dispersion decreases with BM type at almost 3{sigma} level. These results show the dependence of alignments with respect to clusters' richness, which can be regarded as an environmental effect.

  3. Galaxies in ΛCDM with Halo Abundance Matching: Luminosity-Velocity Relation, Baryonic Mass-Velocity Relation, Velocity Function, and Clustering

    NASA Astrophysics Data System (ADS)

    Trujillo-Gomez, Sebastian; Klypin, Anatoly; Primack, Joel; Romanowsky, Aaron J.

    2011-11-01

    It has long been regarded as difficult if not impossible for a cosmological model to account simultaneously for the galaxy luminosity, mass, and velocity distributions. We revisit this issue using a modern compilation of observational data along with the best available large-scale cosmological simulation of dark matter (DM). We find that the standard cosmological model, used in conjunction with halo abundance matching (HAM) and simple dynamical corrections, fits—at least on average—all basic statistics of galaxies with circular velocities V circ > 80 km s-1 calculated at a radius of ~10 kpc. Our primary observational constraint is the luminosity-velocity (LV) relation—which generalizes the Tully-Fisher and Faber-Jackson relations in allowing all types of galaxies to be included, and provides a fundamental benchmark to be reproduced by any theory of galaxy formation. We have compiled data for a variety of galaxies ranging from dwarf irregulars to giant ellipticals. The data present a clear monotonic LV relation from ~50 km s-1 to ~500 km s-1, with a bend below ~80 km s-1 and a systematic offset between late- and early-type galaxies. For comparison to theory, we employ our new ΛCDM "Bolshoi" simulation of DM, which has unprecedented mass and force resolution over a large cosmological volume, while using an up-to-date set of cosmological parameters. We use HAM to assign rank-ordered galaxy luminosities to the DM halos, a procedure that automatically fits the empirical luminosity function and provides a predicted LV relation that can be checked against observations. The adiabatic contraction of DM halos in response to the infall of the baryons is included as an optional model ingredient. The resulting predictions for the LV relation are in excellent agreement with the available data on both early-type and late-type galaxies for the luminosity range from Mr = -14 to Mr = -22. We also compare our predictions for the "cold" baryon mass (i.e., stars and cold gas) of

  4. Constraints on turbulent velocity broadening for a sample of clusters, groups and elliptical galaxies using XMM-Newton

    NASA Astrophysics Data System (ADS)

    Sanders, J. S.; Fabian, A. C.; Smith, R. K.

    2011-01-01

    Using the width of emission lines in XMM-Newton Reflection Grating Spectrometer spectra, we place direct constraints on the turbulent velocities of the X-ray emitting medium in the cores of 62 galaxy clusters, groups and elliptical galaxies. We find five objects where we can place an upper limit on the line-of-sight broadening of 500 km s-1 (90 per cent confidence level), using a single thermal component model. Two other objects are lower than this limit when two thermal components are used. Half of the objects examined have an upper limit on the velocity broadening of less than 700 km s-1. To look for objects which have significant turbulent broadening, we use Chandra spectral maps to compute the expected broadening caused by the spatial extent of the source. Comparing these with our observed results, we find that Klemola 44 has extra broadening at the level of 1500 km s-1. RX J1347.5-1145 shows weak evidence for turbulent velocities at 800 km s-1. In addition we obtain limits on turbulence for Zw 3146, Abell 496, Abell 1795, Abell 2204 and HCG 62 of less than 200 km s-1. After subtraction of the spatial contribution and including a 50 km s-1 systematic uncertainty, we find at least 15 sources with less than 20 per cent of the thermal energy density in turbulence.

  5. VizieR Online Data Catalog: Velocity distributions in galaxy clusters (Sampaio+, 2014)

    NASA Astrophysics Data System (ADS)

    Sampaio, F. S.; Ribeiro, A. L. B.

    2015-03-01

    We study 416 galaxy systems selected from the 2MASS (Two Micron All Sky Survey Extended Source Catalog - Crook et al. (2007, Cat. J/ApJ/655/790)). We used just groups with more than 7 members to avoid severe sample size effects (1 data file).

  6. Brightest Cluster Galaxy Identification

    NASA Astrophysics Data System (ADS)

    Leisman, Luke; Haarsma, D. B.; Sebald, D. A.; ACCEPT Team

    2011-01-01

    Brightest cluster galaxies (BCGs) play an important role in several fields of astronomical research. The literature includes many different methods and criteria for identifying the BCG in the cluster, such as choosing the brightest galaxy, the galaxy nearest the X-ray peak, or the galaxy with the most extended profile. Here we examine a sample of 75 clusters from the Archive of Chandra Cluster Entropy Profile Tables (ACCEPT) and the Sloan Digital Sky Survey (SDSS), measuring masked magnitudes and profiles for BCG candidates in each cluster. We first identified galaxies by hand; in 15% of clusters at least one team member selected a different galaxy than the others.We also applied 6 other identification methods to the ACCEPT sample; in 30% of clusters at least one of these methods selected a different galaxy than the other methods. We then developed an algorithm that weighs brightness, profile, and proximity to the X-ray peak and centroid. This algorithm incorporates the advantages of by-hand identification (weighing multiple properties) and automated selection (repeatable and consistent). The BCG population chosen by the algorithm is more uniform in its properties than populations selected by other methods, particularly in the relation between absolute magnitude (a proxy for galaxy mass) and average gas temperature (a proxy for cluster mass). This work supported by a Barry M. Goldwater Scholarship and a Sid Jansma Summer Research Fellowship.

  7. Nature of multiple-nucleus cluster galaxies

    SciTech Connect

    Merritt, D.

    1984-05-01

    In models for the evolution of galaxy clusters which include dynamical friction with the dark binding matter, the distribution of galaxies becomes more concentrated to the cluster center with time. In a cluster like Coma, this evolution could increase by a factor of approximately 3 the probability of finding a galaxy very close to the cluster center, without decreasing the typical velocity of such a galaxy significantly below the cluster mean. Such an enhancement is roughly what is needed to explain the large number of first-ranked cluster galaxies which are observed to have extra ''nuclei''; it is also consistent with the high velocities typically measured for these ''nuclei.'' Unlike the cannibalism model, this model predicts that the majority of multiple-nucleus systems are transient phenomena, and not galaxies in the process of merging.

  8. Seven poor clusters of galaxies

    NASA Astrophysics Data System (ADS)

    Beers, T. C.; Geller, M. J.; Huchra, J. P.; Latham, D. W.; Davis, R. J.

    1984-08-01

    The authors have measured 83 new redshifts for galaxies in the region of seven of the poor clusters of galaxies identified by Morgan, Kayser, and White and Albert, White, and Morgan. For three systems (MKW 1s, AWM 1, and AWM 7) complete redshift samples were obtained for galaxies brighter than mB(0) = 15.7 within 1° of the D or cD galaxy. The authors estimate masses for the clusters by applying both the virial theorem and the projected mass method. For the two clusters with the highest X-ray luminosities, the line-of-sight velocity dispersions are ≡700 km s-1, and mass-to-light ratios M/LB(0) ⪆ 400 M_sun;/L_sun;. For the five other clusters the velocity dispersions are ⪉370 km s-1, and four of the five have mass-to-light ratios ⪉250 M_sun;/L_sun;. The D or cD galaxy in each poor cluster is at the kinematic center of the system.

  9. The Origin of the Brightest Cluster Galaxies

    NASA Astrophysics Data System (ADS)

    Dubinski, John

    1998-07-01

    Most clusters and groups of galaxies contain a giant elliptical galaxy in their centers that far outshines and outweighs normal ellipticals. The origin of these brightest cluster galaxies is intimately related to the collapse and formation of the cluster. Using an N-body simulation of a cluster of galaxies in a hierarchical cosmological model, we show that galaxy merging naturally produces a massive central galaxy with surface brightness and velocity dispersion profiles similar to those of observed BCGs. To enhance the resolution of the simulation, 100 dark halos at z = 2 are replaced with self-consistent disk + bulge + halo galaxy models following a Tully-Fisher relation using 100,000 particles for the 20 largest galaxies and 10,000 particles for the remaining ones. This technique allows us to analyze the stellar and dark-matter components independently. The central galaxy forms through the merger of several massive galaxies along a filament early in the cluster's history. Galactic cannibalism of smaller galaxies through dynamical friction over a Hubble time only accounts for a small fraction of the accreted mass. The galaxy is a flattened, triaxial object whose long axis aligns with the primordial filament and the long axis of the cluster galaxy distribution, agreeing with observed trends for galaxy cluster alignment.

  10. THE HIGH-VELOCITY SYSTEM: INFALL OF A GIANT LOW-SURFACE-BRIGHTNESS GALAXY TOWARD THE CENTER OF THE PERSEUS CLUSTER

    SciTech Connect

    Yu, Alice P.-Y.; Lim, Jeremy; Chan, Jeffrey C.-C.; Ohyama, Youichi; Broadhurst, T.

    2015-12-01

    The high-velocity system (HVS) lies just north-west of the center and is moving at a speed of 3000 km s{sup −1} toward NGC 1275, the central giant elliptical galaxy in the Perseus cluster. We report imaging spectroscopy of the HVS in Hα and [N ii] that resolves both the nature of this galaxy and its physical relationship with NGC 1275. The HVS exhibits a distorted disk having a projected rotational velocity that rises steadily to ∼200 km s{sup −1} at a radius of ∼12 kpc, the same maximal extent detectable in neutral gas and dust. We discover highly blueshifted emission at relative velocities of up to ∼800 km s{sup −1} distributed throughout and confined almost entirely within the projected area of the disk, tracing gas stripped by ram pressure. The distribution of the stripped gas implies that the HVS is moving essentially along our sightline closely toward the center of NGC 1275. We show that the speed of the HVS is consistent with it having fallen from rest at the virial radius of the Perseus cluster and reached ∼100 kpc from the cluster center. Despite having an overall metallicity (inferred from [N ii]/Hα) significantly lower than that of star-forming disk galaxies, the HVS exhibits a current star formation rate of ∼3.6 M{sub ⊙} yr{sup −1} and numerous young star clusters projected against giant H ii regions. The evidence assembled implicates a progenitor giant low-surface-brightness galaxy that, because of galaxy harassment and/or the cluster tidal field, has developed two prominent spiral arms along which star formation is strongly elevated.

  11. THE STRUCTURE OF 2MASS GALAXY CLUSTERS

    SciTech Connect

    Blackburne, Jeffrey A.; Kochanek, Christopher S.

    2012-01-01

    We use a sample of galaxies from the Two Micron All Sky Survey Extended Source Catalog to refine a matched filter method of finding galaxy clusters that takes into account each galaxy's position, magnitude, and redshift if available. The matched filter postulates a radial density profile, luminosity function, and line-of-sight velocity distribution for cluster galaxies. We use this method to search for clusters in the galaxy catalog, which is complete to an extinction-corrected K-band magnitude of 13.25 and has spectroscopic redshifts for roughly 40% of the galaxies, including nearly all brighter than K = 11.25. We then use a stacking analysis to determine the average luminosity function, radial distribution, and velocity distribution of cluster galaxies in several richness classes, and use the results to update the parameters of the matched filter before repeating the cluster search. We also investigate the correlations between a cluster's richness and its velocity dispersion and core radius using these relations to refine priors that are applied during the cluster search process. After the second cluster search iteration, we repeat the stacking analysis. We find a cluster galaxy luminosity function that fits a Schechter form, with parameters M{sub K*} - 5log h = -23.64 {+-} 0.04 and {alpha} = -1.07 {+-} 0.03. We can achieve a slightly better fit to our luminosity function by adding a Gaussian component on the bright end to represent the brightest cluster galaxy population. The radial number density profile of galaxies closely matches a projected Navarro-Frenk-White profile at intermediate radii, with deviations at small radii due to well-known cluster centering issues and outside the virial radius due to correlated structure. The velocity distributions are Gaussian in shape, with velocity dispersions that correlate strongly with richness.

  12. Clusters of galaxies

    NASA Astrophysics Data System (ADS)

    Vikhlinin, A. A.; Kravtsov, A. V.; Markevich, M. L.; Sunyaev, R. A.; Churazov, E. M.

    2014-04-01

    Galaxy clusters are formed via nonlinear growth of primordial density fluctuations and are the most massive gravitationally bound objects in the present Universe. Their number density at different epochs and their properties depend strongly on the properties of dark matter and dark energy, making clusters a powerful tool for observational cosmology. Observations of the hot gas filling the gravitational potential well of a cluster allows studying gasdynamic and plasma effects and the effect of supermassive black holes on the heating and cooling of gas on cluster scales. The work of Yakov Borisovich Zeldovich has had a profound impact on virtually all cosmological and astrophysical studies of galaxy clusters, introducing concepts such as the Harrison-Zeldovich spectrum, the Zeldovich approximation, baryon acoustic peaks, and the Sunyaev-Zeldovich effect. Here, we review the most basic properties of clusters and their role in modern astrophysics and cosmology.

  13. On the Dynamics of Galaxy Clustering.

    NASA Astrophysics Data System (ADS)

    Rivolo, Arthur Rex

    The galaxies of the Revised Shapley-Ames (RSA) redshift catalog, which is complete to B(TURN)13 are used to conduct a statistical search for binary galaxies, and to determine the dynamical parameters of galaxy pairs. By analyzing the velocity differences of neighboring pairs of galaxies, the velocity dispersion per galaxy is determined as a function of isolation. This velocity dispersion is found to be constant in pairs of galaxies irrespective of how isolated they are, and whether or not they are each other's nearest neighbors. The interpretation of isolated galaxy pairs as binaries, whose dynamics is dominated by the two-body force, is therefore questioned. The velocity dispersion of the general galaxy field within 4000 kms(' -1)/H(,0) of the Sun is also determined. Various implications of the derived velocity dispersion are discussed, with particular attention given to its significance in the virialization process occurring in the cores of the great clusters of galaxies. A model for the evolutionary dynamics of superclusters is presented incorporating the velocity dispersion of galaxies as boundary conditions in time and space. The model is evolved numerically using an N-body spherically symmetric algorithm, from the epoch at which density perturbations were of order unity to the present. It is shown that the effects of velocity dispersion during adiabatic collapse are: (1) to halt the collapse by virialization of a core, through orbital phase mixing, (2) to give rise to power -law density profiles with indices between -2 and -3, and (3) to generate one-dimensional velocity dispersion of (TURN)1000 kms('-1) in the cores of great clusters. In the context of Virial theorem analyses, projection factors at various stages of cluster evolution are discussed as a function of cylindrical sampling. It is shown that projection factors may be routinely over-estimated by factors of 1.5-2, resulting in a proportionate over-estimate for virial mass/light in the great clusters.

  14. Evidence for Tides and Interactions in Galaxy Clusters

    NASA Astrophysics Data System (ADS)

    Conselice, C. J.; Gallagher, J. S.

    1997-12-01

    We present preliminary results of a search for tidally distorted, or interacting galaxies in the galaxy clusters: Abell 2199, AWM 5, AWM 3, the Coma and Perseus clusters. This is part of a large study to determine the nature of small-scale structure in galaxy clusters of various morphologies. Our B and R band observations were made with the CCD imager on the WIYN 3.5-m telescope, and typically have an angular resolution of 1 arcsec or better. We are able to classify all of the observed structures into seven different types. These include: Galaxy Interactions, Multiple Galaxies, Tailed Galaxies, Dwarf Galaxy Groups, Galaxy Aggregates, Distorted Galaxies, and Line Galaxies. We present examples of objects in these categories and conclude that interactions that perturb individual galaxies are common in clusters of galaxies, despite the high relative random velocities between cluster members.

  15. The environments of poor clusters of galaxies

    NASA Astrophysics Data System (ADS)

    Bliton, Mark Alan

    , combined with the lower velocity dispersions, create significant tidal interactions, which may generate enhanced star formation activity. Therefore star formation efficiency may be reduced in richer clusters via ram-pressure stripping, and is enhanced in poorer clusters due to galaxy interactions. (Abstract shortened by UMI.)

  16. Understanding Galaxy Cluster MKW10

    NASA Astrophysics Data System (ADS)

    Sanders, Tim; Henry, Swain; Coble, Kimberly A.; Rosenberg, Jessica L.; Koopmann, Rebecca A.

    2015-01-01

    As part of the Undergraduate ALFALFA Team (UAT), we are studying the galaxy cluster MKW 10 (RA = 175.454, Dec = 10.306, z ~ 0.02), a poor cluster with a compact core in which tidal interactions have occurred. This cluster has been observed in HI and Hα. We used SDSS and NED to search for optical counterparts. By comparing data at multiple wavelengths, we hope to understand the structure, environment, and star formation history of this cluster. Following the techniques of others involved in the groups project and using the program TOPCAT to manipulate the data, we explored both the spatial and velocity distributions to determine cluster membership. We have determined that this cluster consists of 11 galaxies, mostly spiral in shape. Chicago State University is new the UAT and we began our work after taking part in the winter workshop at Arecibo.This work was supported by: Undergraduate ALFALFA Team NSF Grant AST-1211005 and the Illinois Space Grant Consortium.

  17. Cosmology with galaxy clusters

    NASA Astrophysics Data System (ADS)

    Sartoris, Barbara

    2015-08-01

    Clusters of galaxies are powerful probes to constrain parameters that describe the cosmological models and to distinguish among different models. Since, the evolution of the cluster mass function and large-scale clustering contain the informations about the linear growth rate of perturbations and the expansion history of the Universe, clusters have played an important role in establishing the current cosmological paradigm. It is crucial to know how to determine the cluster mass from observational quantities when using clusters as cosmological tools. For this, numerical simulations are helpful to define and study robust cluster mass proxies that have minimal and well understood scatter across the mass and redshift ranges of interest. Additionally, the bias in cluster mass determination can be constrained via observations of the strong and weak lensing effect, X-ray emission, the Sunyaev- Zel’dovic effect, and the dynamics of galaxies.A major advantage of X-ray surveys is that the observable-mass relation is tight. Moreover, clusters can be easily identified in X-ray as continuous, extended sources. As of today, interesting cosmological constraints have been obtained from relatively small cluster samples (~102), X-ray selected by the ROSAT satellite over a wide redshift range (0clusters, the ROSAT All-Sky Survey.The next generation of X-ray telescopes will enhance the statistics of detected clusters and enlarge their redshift coverage. In particular, eROSITA will produce a catalog of >105 clusters with photometric redshifts from multi-band optical surveys (e.g. PanSTARRS, DES, and LSST). This will vastly improve upon current cosmological constraints, especially by the synergy with other cluster surveys that

  18. The origin of galaxies and clusters of galaxies.

    PubMed

    Peebles, P J

    1984-06-29

    Debate on how galaxies and clusters of galaxies formed has reached an interesting stage at which one can find arguments for quite different scenarios. The galaxy distribution has a complex "frothy" character that could be the fossil of a network of protoclusters or pancakes that produced galaxies. However, there are galaxies like our own that seem never to have been in a protocluster but are physically similar to the galaxies in dense clusters. Some clues to be assessed in resolving this dilemma are the possible existence of galaxy filaments, the relative ages of galaxies and clusters of galaxies, and the continuity between cluster and field galaxies and between galaxies and clusters of galaxies.

  19. The relation between gas density and velocity power spectra in galaxy clusters: High-resolution hydrodynamic simulations and the role of conduction

    NASA Astrophysics Data System (ADS)

    Gaspari, M.; Churazov, E.; Nagai, D.; Lau, E. T.; Zhuravleva, I.

    2014-09-01

    Exploring the power spectrum of fluctuations and velocities in the intracluster medium (ICM) can help us to probe the gas physics of galaxy clusters. Using high-resolution 3D plasma simulations, we study the statistics of the velocity field and its intimate relation with the ICM thermodynamic perturbations. The normalization of the ICM spectrum (related to density, entropy, or pressure fluctuations) is linearly tied to the level of large-scale motions, which excite both gravity and sound waves due to stratification. For a low 3D Mach number M ~ 0.25, gravity waves mainly drive entropy perturbations, which are traced by preferentially tangential turbulence. For M> 0.5, sound waves start to significantly contribute and pass the leading role to compressive pressure fluctuations, which are associated with isotropic (or slightly radial) turbulence. Density and temperature fluctuations are then characterized by the dominant process: isobaric (low M), adiabatic (high M), or isothermal (strong conduction). Most clusters reside in the intermediate regime, showing a mixture of gravity and sound waves, hence drifting toward isotropic velocities. Remarkably, regardless of the regime, the variance of density perturbations is comparable to the 1D Mach number, M1D ~ δρ/ρ. This linear relation allows us to easily convert between gas motions and ICM perturbations (δρ/ρ< 1), which can be exploited by the available Chandra, XMM data and by the forthcoming Astro-H mission. At intermediate and small scales (10-100 kpc), the turbulent velocities develop a tight Kolmogorov cascade. The thermodynamic perturbations (which can be generally described by log-normal distributions) act as effective tracers of the velocity field, in broad agreement with the Kolmogorov-Obukhov-Corrsin advection theory. The cluster radial gradients and compressive features induce a flattening in the cascade of the perturbations. Thermal conduction, on the other hand, acts to damp the thermodynamic

  20. The circular velocity function of group galaxies

    SciTech Connect

    Abramson, Louis E.; Williams, Rik J.; Benson, Andrew J.; Kollmeier, Juna A.; Mulchaey, John S.

    2014-09-20

    A robust prediction of ΛCDM cosmology is the halo circular velocity function (CVF), a dynamical cousin of the halo mass function. The correspondence between theoretical and observed CVFs is uncertain, however: cluster galaxies are reported to exhibit a power-law CVF consistent with N-body simulations, but that of the field is distinctly Schechter-like, flattened compared to ΛCDM expectations at circular velocities v {sub c} ≲ 200 km s{sup –1}. Groups offer a powerful probe of the role environment plays in this discrepancy as they bridge the field and clusters. Here, we construct the CVF for a large, mass- and multiplicity-complete sample of group galaxies from the Sloan Digital Sky Survey. Using independent photometric v {sub c} estimators, we find no transition from field to ΛCDM-shaped CVF above v {sub c} = 50 km s{sup –1} as a function of group halo mass. All groups with 12.4 ≲ log M {sub halo}/M {sub ☉} ≲ 15.1 (Local Group analogs to rich clusters) display similar Schechter-like CVFs marginally suppressed at low v {sub c} compared to that of the field. Conversely, some agreement with N-body results emerges for samples saturated with late-type galaxies, with isolated late-types displaying a CVF similar in shape to ΛCDM predictions. We conclude that the flattening of the low-v {sub c} slope in groups is due to their depressed late-type fractions—environment affecting the CVF only to the extent that it correlates with this quantity—and that previous cluster analyses may suffer from interloper contamination. These results serve as useful benchmarks for cosmological simulations of galaxy formation.

  1. The spiral density-wave structure of our own Galaxy as traced by open clusters: Least-squares analysis of line-of-sight velocities

    NASA Astrophysics Data System (ADS)

    Griv, Evgeny; Lin, Chien-Cheng; Ngeow, Chow-Choong; Jiang, Ing-Guey

    2014-05-01

    The rotation about the Galactic center of open clusters belonging to the thin component of the Milky Way Galaxy is studied on the basis of line-of-sight velocities and positions for 169 nearby objects taken from the literature. The minor second-order effects caused by the Lin-Shu-type density waves are taken into account by using the least-squares numerical method. Even preliminary, the physical interpretation of the results obtained in this manner shows that (i) among several Fourier modes of collective oscillations developing in the solar neighborhood the one-armed m=1 spiral mode is the main one; the Galaxy has thus significant lopsidedness in the stellar distribution at large radii, (ii) the Sun is located between the major trailing spiral-arm segments in Carina-Sagittarius and Perseus, closer to the outer Perseus one, (iii) the local Cygnus-Orion segment is not a part of the dominant spiral arm but is a minor one, which is due to a secondary Fourier harmonic of the Galaxy’s oscillations, (iv) the pitch angle of the dominant density-wave pattern in the solar vicinity seems to be relatively small, of the order of 7°, and the wavelength (the radial distance between spiral arms) of the m=1 pattern is about 6 kpc, (v) the Galactocentric distance where the velocities of disk rotation and of the spiral density wave (the corotation radius) coincide is located outside of the solar circle; thus, a pattern angular speed lower than the local angular rotation velocity, and finally (vi) the spiral arms of the Galaxy do not represent small deviations of the surface density and gravitational potential from a basic distribution that is axisymmetric in the mean.

  2. The Assembly of Galaxy Clusters

    SciTech Connect

    Berrier, Joel C.; Stewart, Kyle R.; Bullock, James S.; Purcell, Chris W.; Barton, Elizabeth J.; Wechsler, Risa H.

    2008-05-16

    We study the formation of fifty-three galaxy cluster-size dark matter halos (M = 10{sup 14.0-14.76} M{sub {circle_dot}}) formed within a pair of cosmological {Lambda}CDM N-body simulations, and track the accretion histories of cluster subhalos with masses large enough to host {approx} 0.1L{sub *} galaxies. By associating subhalos with cluster galaxies, we find the majority of galaxies in clusters experience no 'pre-processing' in the group environment prior to their accretion into the cluster. On average, {approx} 70% of cluster galaxies fall into the cluster potential directly from the field, with no luminous companions in their host halos at the time of accretion; and less than {approx} 12% are accreted as members of groups with five or more galaxies. Moreover, we find that cluster galaxies are significantly less likely to have experienced a merger in the recent past ({approx}< 6 Gyr) than a field halo of the same mass. These results suggest that local, cluster processes like ram-pressure stripping, galaxy harassment, or strangulation play the dominant role in explaining the difference between cluster and field populations at a fixed stellar mass; and that pre-evolution or past merging in the group environment is of secondary importance for setting cluster galaxy properties for most clusters. The accretion times for z = 0 cluster members are quite extended, with {approx} 20% incorporated into the cluster halo more than 7 Gyr ago and {approx} 20% within the last 2 Gyr. By comparing the observed morphological fractions in cluster and field populations, we estimate an approximate time-scale for late-type to early-type transformation within the cluster environment to be {approx} 6 Gyr.

  3. The Dynamical Equilibrium of Galaxy Clusters

    NASA Astrophysics Data System (ADS)

    Carlberg, R. G.; Yee, H. K. C.; Ellingson, E.; Morris, S. L.; Abraham, R.; Gravel, P.; Pritchet, C. J.; Smecker-Hane, T.; Hartwick, F. D. A.; Hesser, J. E.; Hutchings, J. B.; Oke, J. B.

    1997-02-01

    If a galaxy cluster is effectively in dynamical equilibrium, then all galaxy populations within the cluster must have distributions in velocity and position that individually reflect the same underlying mass distribution, although the derived virial masses can be quite different. Specifically, within the Canadian Network for Observational Cosmology cluster sample, the virial radius of the red galaxy population is, on the average, a factor of 2.05 +/- 0.34 smaller than that of the blue population. The red galaxies also have a smaller rms velocity dispersion, a factor of 1.31 +/- 0.13 within our sample. Consequently, the virial mass calculated from the blue galaxies is 3.5 +/- 1.3 times larger than from the red galaxies. However, applying the Jeans equation of stellar hydrodynamic equilibrium to the red and blue subsamples separately gives statistically identical cluster mass profiles. This is strong evidence that these clusters are effectively equilibrium systems and therefore demonstrates empirically that the masses in the virialized region are reliably estimated using dynamical techniques.

  4. High velocity gas in external galaxies

    NASA Technical Reports Server (NTRS)

    Kamphuis, J.; Vanderhulst, J. M.; Sancisi, R.

    1990-01-01

    Two nearby, nearly face-on spiral galaxies, M 101 and NGC 6946, observed in the HI with the Westerbork Synthesis Radio Telescope (WSRT) as part of a program to search for high velocity gas in other galaxies, are used to illustrate the range of properties of high velocity gas in other galaxies found thusfar.

  5. Massive star clusters in galaxies.

    PubMed

    Harris, William E

    2010-02-28

    The ensemble of all star clusters in a galaxy constitutes its star cluster system. In this review, the focus of the discussion is on the ability of star clusters, particularly the systems of old massive globular clusters (GCs), to mark the early evolutionary history of galaxies. I review current themes and key findings in GC research, and highlight some of the outstanding questions that are emerging from recent work.

  6. Mass calibration and cosmological analysis of the SPT-SZ galaxy cluster sample using velocity dispersion σ v and x-ray Y X measurements

    DOE PAGES

    Bocquet, S.; Saro, A.; Mohr, J. J.; Aird, K. A.; Ashby, M. L. N.; Bautz, M.; Bayliss, M.; Bazin, G.; Benson, B. A.; Bleem, L. E.; et al

    2015-01-30

    Here, we present a velocity-dispersion-based mass calibration of the South Pole Telescope Sunyaev-Zel'dovich effect survey (SPT-SZ) galaxy cluster sample. Using a homogeneously selected sample of 100 cluster candidates from 720 deg2 of the survey along with 63 velocity dispersion (σv) and 16 X-ray YX measurements of sample clusters, we simultaneously calibrate the mass-observable relation and constrain cosmological parameters. Our method accounts for cluster selection, cosmological sensitivity, and uncertainties in the mass calibrators. The calibrations using σv and YX are consistent at the 0.6σ level, with the σ v calibration preferring ~16% higher masses. We use the full SPTCL data setmore » (SZ clusters+σv+YX) to measure σ8(Ωm/0.27)0.3 = 0.809 ± 0.036 within a flat ΛCDM model. The SPT cluster abundance is lower than preferred by either the WMAP9 or Planck+WMAP9 polarization (WP) data, but assuming that the sum of the neutrino masses is mν = 0.06 eV, we find the data sets to be consistent at the 1.0σ level for WMAP9 and 1.5σ for Planck+WP. Allowing for larger Σmν further reconciles the results. When we combine the SPTCL and Planck+WP data sets with information from baryon acoustic oscillations and Type Ia supernovae, the preferred cluster masses are 1.9σ higher than the YX calibration and 0.8σ higher than the σ v calibration. Given the scale of these shifts (~44% and ~23% in mass, respectively), we execute a goodness-of-fit test; it reveals no tension, indicating that the best-fit model provides an adequate description of the data. Using the multi-probe data set, we measure Ωm = 0.299 ± 0.009 and σ8 = 0.829 ± 0.011. Within a νCDM model we find Σmν = 0.148 ± 0.081 eV. We present a consistency test of the cosmic growth rate using SPT clusters. Allowing both the growth index γ and the dark energy equation-of-state parameter w to vary, we find γ = 0.73 ± 0.28 and w = –1.007 ± 0.065, demonstrating that the eΣxpansion and the growth

  7. Heating and Turbulence Driving by Galaxy Motions in Galaxy Clusters

    NASA Astrophysics Data System (ADS)

    Kim, Woong-Tae

    2007-09-01

    Using three-dimensional hydrodynamic simulations, we investigate heating and turbulence driving in an intracluster medium (ICM) by orbital motions of galaxies in a galaxy cluster. We consider Ng member galaxies on isothermal and isotropic orbits through an ICM typical of rich clusters. An introduction of the galaxies immediately produces gravitational wakes, providing perturbations that can potentially grow via resonant interaction with the background gas. When N1/2gM11<~100, where M11 is each galaxy mass in units of 1011 Msolar, the perturbations are in the linear regime and the resonant excitation of gravity waves is efficient in generating kinetic energy in the ICM, resulting in the velocity dispersion σv~2.2N1/2gM11 km s-1. When N1/2gM11>~100, on the other hand, nonlinear fluctuations of the background ICM destroy galaxy wakes and thus render resonant excitation weak or absent. In this case, the kinetic energy saturates at the level corresponding to σv~220 km s-1. The angle-averaged velocity power spectra of turbulence driven in our models have slopes in the range of -3.7 to -4.3. With the nonlinear saturation of resonant excitation, none of the cooling models considered are able to halt the cooling catastrophe, suggesting that the galaxy motions alone are unlikely to solve the cooling flow problem.

  8. Searching for FUV line emission from 107 K gas in massive elliptical galaxies and galaxy clusters as a tracer of turbulent velocities

    NASA Astrophysics Data System (ADS)

    Anderson, Michael E.; Sunyaev, Rashid

    2016-07-01

    Non-thermal pressure from turbulence and bulk flows is a fundamental ingredient in hot gaseous haloes, and in the intracluster medium, it will be measured through emission line kinematics with calorimeters on future X-ray spacecraft. In this paper, we present a complementary method for measuring these effects, using forbidden FUV emission lines of highly ionized Iron which trace 107 K gas. The brightest of these is [Fe XXI] λ1354.1. We search for these lines in archival Hubble Space Telescope (HST)-Cosmic Origins Spectrograph (COS) spectra from the well-known elliptical galaxies M87 and NGC4696, which harbor large reservoirs of 107 K gas. We report a 2.2σ feature which we attribute to [Fe XXI] from a filament in M87, and positive residuals in the nuclei of M87 and NGC4696, for which the 90 per cent upper limits on the line flux are close to the predicted fluxes based on X-ray observations. In a newer reduction of the data from the Hubble Spectroscopic Legacy Archive, these limits become tighter and the [Fe XXI] feature reaches a formal significance of 5.3σ, neglecting uncertainty in fitting the continuum. Using our constraints, we perform emission measure analysis, constraining the characteristic path length and column density of the ˜107 K gas. We also examine several sightlines towards filaments or cooling flows in other galaxy clusters, for which the fraction of gas at 107 K is unknown, and place upper limits on its emission measure in each case. A medium-resolution HST-COS observation of the M87 filament for ˜10 orbits would confirm our detection of [Fe XXI] and measure its width.

  9. Analysis of radial velocities in the Antlia cluster

    NASA Astrophysics Data System (ADS)

    Faifer, F. R.; Smith Castelli, A. V.; Calderón, J. P.; Caso, J. P.; Bassino, L. P.; Cellone, S. A.; Richtler, T.

    We present preliminary results of a radial velocity survey in the central re- gion of the Antlia cluster. These velocities have been measured on spec- tra obtained, in the 2008A and 2009A semesters, with GMOS (GEMINI South). In this way, several dwarf galaxies that had no previous radial ve- locities, have been confirmed as cluster members. Our work is based on the Ferguson & Sandage (1990) catalogue, in which originally only 6% of the catalogued galaxies (375) had radial velocities. Thanks to the newly determined radial velocities we are able to begin to disentangle the cluster internal structure. FULL TEXT IN SPANISH

  10. Astrophysics of galaxy clusters

    NASA Astrophysics Data System (ADS)

    Ettori, Stefano

    2016-07-01

    As the nodes of the cosmic web, clusters of galaxies trace the large-scale distribution of matter in the Universe. They are thus privileged sites in which to investigate the complex physics of structure formation. However, the complete story of how these structures grow, and how they dissipate the gravitational and non-thermal components of their energy budget over cosmic time, is still beyond our grasp. Most of the baryons gravitationally bound to the cluster's halo is in the form of a diffuse, hot, metal-enriched plasma that radiates primarily in the X-ray band. X-ray observations of the evolving cluster population provide a unique opportunity to address such fundamental open questions as: How do hot diffuse baryons accrete and dynamically evolve in dark matter potentials? How and when was the energy that we observe in the ICM generated and distributed? Where and when are heavy elements produced and how are they circulated? We will present the ongoing activities to define the strategy on how an X-ray observatory with large collecting area and an unprecedented combination of high spectral and angular resolution, such as Athena, can address these questions.

  11. Spatial and kinematic distributions of transition populations in intermediate redshift galaxy clusters

    SciTech Connect

    Crawford, Steven M.; Wirth, Gregory D.; Bershady, Matthew A. E-mail: wirth@keck.hawaii.edu

    2014-05-01

    We analyze the spatial and velocity distributions of confirmed members in five massive clusters of galaxies at intermediate redshift (0.5 < z < 0.9) to investigate the physical processes driving galaxy evolution. Based on spectral classifications derived from broad- and narrow-band photometry, we define four distinct galaxy populations representing different evolutionary stages: red sequence (RS) galaxies, blue cloud (BC) galaxies, green valley (GV) galaxies, and luminous compact blue galaxies (LCBGs). For each galaxy class, we derive the projected spatial and velocity distribution and characterize the degree of subclustering. We find that RS, BC, and GV galaxies in these clusters have similar velocity distributions, but that BC and GV galaxies tend to avoid the core of the two z ≈ 0.55 clusters. GV galaxies exhibit subclustering properties similar to RS galaxies, but their radial velocity distribution is significantly platykurtic compared to the RS galaxies. The absence of GV galaxies in the cluster cores may explain their somewhat prolonged star-formation history. The LCBGs appear to have recently fallen into the cluster based on their larger velocity dispersion, absence from the cores of the clusters, and different radial velocity distribution than the RS galaxies. Both LCBG and BC galaxies show a high degree of subclustering on the smallest scales, leading us to conclude that star formation is likely triggered by galaxy-galaxy interactions during infall into the cluster.

  12. Luminosity function for galaxy clusters

    NASA Astrophysics Data System (ADS)

    Bajan, K.; Biernacka, M.; Flin, P.; Godłowski, W.; Panko, E.; Popiela, J.

    2016-10-01

    We constructed and studied the luminosity function of 6188 galaxyclusters. This was performed by counting brightness of galaxiesbelonging to clusters in the PF catalogue, taking galaxy data fromMRSS. Our result shows that the investigated structures arecharacterized by a luminosity function different from that ofoptical galaxies and radiogalaxies (Machalski & Godłowski2000). The implications of this result for theoriesof galaxy formation are briefly discussed.

  13. Is the velocity-distance relation for galaxies linear?

    PubMed

    van den Bergh, S

    1993-06-01

    Diameters of ScI galaxies, the luminosities of supernovae of type Ia at maximum light, and the brightness of central galaxies in rich clusters are examined as potential yardsticks or standard candles for study of the velocity-distance relationship. Both supergiant ScI galaxies and supernovae Ia (which have luminosities that differ by up to a factor of approximately 10) are found to be unsuitable for such a study. The remarkably small luminosity dispersion of first-ranked cluster galaxies (which is not yet understood physically) suggests that deviations from a linear velocity-distance relationship are less, approximately 20% out to red shifts of approximately 40,000 km.s-1. PMID:11607389

  14. Is the velocity-distance relation for galaxies linear?

    PubMed Central

    van den Bergh, S

    1993-01-01

    Diameters of ScI galaxies, the luminosities of supernovae of type Ia at maximum light, and the brightness of central galaxies in rich clusters are examined as potential yardsticks or standard candles for study of the velocity-distance relationship. Both supergiant ScI galaxies and supernovae Ia (which have luminosities that differ by up to a factor of approximately 10) are found to be unsuitable for such a study. The remarkably small luminosity dispersion of first-ranked cluster galaxies (which is not yet understood physically) suggests that deviations from a linear velocity-distance relationship are less, approximately 20% out to red shifts of approximately 40,000 km.s-1. Images Fig. 1 PMID:11607389

  15. MASS CALIBRATION AND COSMOLOGICAL ANALYSIS OF THE SPT-SZ GALAXY CLUSTER SAMPLE USING VELOCITY DISPERSION σ {sub v} AND X-RAY Y {sub X} MEASUREMENTS

    SciTech Connect

    Bocquet, S.; Saro, A.; Mohr, J. J.; Bazin, G.; Chiu, I.; Desai, S.; Aird, K. A.; Ashby, M. L. N.; Bayliss, M.; Bautz, M.; Benson, B. A.; Bleem, L. E.; Carlstrom, J. E.; Chang, C. L.; Crawford, T. M.; Crites, A. T.; Brodwin, M.; Cho, H. M.; Clocchiatti, A.; De Haan, T.; and others

    2015-02-01

    We present a velocity-dispersion-based mass calibration of the South Pole Telescope Sunyaev-Zel'dovich effect survey (SPT-SZ) galaxy cluster sample. Using a homogeneously selected sample of 100 cluster candidates from 720 deg{sup 2} of the survey along with 63 velocity dispersion (σ {sub v}) and 16 X-ray Y {sub X} measurements of sample clusters, we simultaneously calibrate the mass-observable relation and constrain cosmological parameters. Our method accounts for cluster selection, cosmological sensitivity, and uncertainties in the mass calibrators. The calibrations using σ {sub v} and Y {sub X} are consistent at the 0.6σ level, with the σ {sub v} calibration preferring ∼16% higher masses. We use the full SPT{sub CL} data set (SZ clusters+σ {sub v}+Y {sub X}) to measure σ{sub 8}(Ω{sub m}/0.27){sup 0.3} = 0.809 ± 0.036 within a flat ΛCDM model. The SPT cluster abundance is lower than preferred by either the WMAP9 or Planck+WMAP9 polarization (WP) data, but assuming that the sum of the neutrino masses is ∑m {sub ν} = 0.06 eV, we find the data sets to be consistent at the 1.0σ level for WMAP9 and 1.5σ for Planck+WP. Allowing for larger ∑m {sub ν} further reconciles the results. When we combine the SPT{sub CL} and Planck+WP data sets with information from baryon acoustic oscillations and Type Ia supernovae, the preferred cluster masses are 1.9σ higher than the Y {sub X} calibration and 0.8σ higher than the σ {sub v} calibration. Given the scale of these shifts (∼44% and ∼23% in mass, respectively), we execute a goodness-of-fit test; it reveals no tension, indicating that the best-fit model provides an adequate description of the data. Using the multi-probe data set, we measure Ω{sub m} = 0.299 ± 0.009 and σ{sub 8} = 0.829 ± 0.011. Within a νCDM model we find ∑m {sub ν} = 0.148 ± 0.081 eV. We present a consistency test of the cosmic growth rate using SPT clusters. Allowing both the growth index γ and the dark energy equation

  16. A Multivariate Analysis of Galaxy Cluster Properties

    NASA Astrophysics Data System (ADS)

    Ogle, P. M.; Djorgovski, S.

    1993-05-01

    We have assembled from the literature a data base on on 394 clusters of galaxies, with up to 16 parameters per cluster. They include optical and x-ray luminosities, x-ray temperatures, galaxy velocity dispersions, central galaxy and particle densities, optical and x-ray core radii and ellipticities, etc. In addition, derived quantities, such as the mass-to-light ratios and x-ray gas masses are included. Doubtful measurements have been identified, and deleted from the data base. Our goal is to explore the correlations between these parameters, and interpret them in the framework of our understanding of evolution of clusters and large-scale structure, such as the Gott-Rees scaling hierarchy. Among the simple, monovariate correlations we found, the most significant include those between the optical and x-ray luminosities, x-ray temperatures, cluster velocity dispersions, and central galaxy densities, in various mutual combinations. While some of these correlations have been discussed previously in the literature, generally smaller samples of objects have been used. We will also present the results of a multivariate statistical analysis of the data, including a principal component analysis (PCA). Such an approach has not been used previously for studies of cluster properties, even though it is much more powerful and complete than the simple monovariate techniques which are commonly employed. The observed correlations may lead to powerful constraints for theoretical models of formation and evolution of galaxy clusters. P.M.O. was supported by a Caltech graduate fellowship. S.D. acknowledges a partial support from the NASA contract NAS5-31348 and the NSF PYI award AST-9157412.

  17. SPATIAL ANISOTROPY OF GALAXY KINEMATICS IN SLOAN DIGITAL SKY SURVEY GALAXY CLUSTERS

    SciTech Connect

    Skielboe, Andreas; Wojtak, Radoslaw; Pedersen, Kristian; Rozo, Eduardo; Rykoff, Eli S.

    2012-10-10

    Measurements of galaxy cluster kinematics are important in understanding the dynamical state and evolution of clusters of galaxies, as well as constraining cosmological models. While it is well established that clusters exhibit non-spherical geometries, evident in the distribution of galaxies on the sky, azimuthal variations of galaxy kinematics within clusters have yet to be observed. Here we measure the azimuthal dependence of the line-of-sight velocity dispersion profile in a stacked sample of 1743 galaxy clusters from the Sloan Digital Sky Survey (SDSS). The clusters are drawn from the SDSS DR8 redMaPPer catalog. We find that the line-of-sight velocity dispersion of galaxies lying along the major axis of the central galaxy is larger than those that lie along the minor axis. This is the first observational detection of anisotropic kinematics of galaxies in clusters. We show that the result is consistent with predictions from numerical simulations. Furthermore, we find that the degree of projected anisotropy is strongly dependent on the line-of-sight orientation of the galaxy cluster, opening new possibilities for assessing systematics in optical cluster finding.

  18. The Cluster of Galaxies Surrounding Cygnus A

    NASA Astrophysics Data System (ADS)

    Owen, Frazer N.; Ledlow, Michael J.; Morrison, Glenn E.; Hill, John M.

    1997-10-01

    We report optical imaging and spectroscopy of 41 galaxies in a 22' square region surrounding Cygnus A. The results show that there is an extensive rich cluster associated with Cyg A of Abell richness of at least 1 and possibly as high as 4. The velocity histogram has two peaks, one centered on Cyg A and a more significant peak redshifted by about 2060 km s-1 from the velocity of Cyg A. The dynamical centroid of the spatial distribution is also shifted somewhat to the northwest. However, statistical tests show only weak evidence that there are two distinct clusters. The entire system has a velocity dispersion of 1581 km s-1, which is slightly larger than other, well-studied examples of rich clusters.

  19. Stormy weather in galaxy clusters

    PubMed

    Burns

    1998-04-17

    Recent x-ray, optical, and radio observations coupled with particle and gas dynamics numerical simulations reveal an unexpectedly complex environment within clusters of galaxies, driven by ongoing accretion of matter from large-scale supercluster filaments. Mergers between clusters and continuous infall of dark matter and baryons from the cluster periphery produce long-lived "stormy weather" within the gaseous cluster atmosphere-shocks, turbulence, and winds of more than 1000 kilometers per second. This weather may be responsible for shaping a rich variety of extended radio sources, which in turn act as "barometers" and "anemometers" of cluster weather.

  20. Stormy weather in galaxy clusters

    PubMed

    Burns

    1998-04-17

    Recent x-ray, optical, and radio observations coupled with particle and gas dynamics numerical simulations reveal an unexpectedly complex environment within clusters of galaxies, driven by ongoing accretion of matter from large-scale supercluster filaments. Mergers between clusters and continuous infall of dark matter and baryons from the cluster periphery produce long-lived "stormy weather" within the gaseous cluster atmosphere-shocks, turbulence, and winds of more than 1000 kilometers per second. This weather may be responsible for shaping a rich variety of extended radio sources, which in turn act as "barometers" and "anemometers" of cluster weather. PMID:9545210

  1. Combining Galaxy-Galaxy Lensing and Galaxy Clustering

    SciTech Connect

    Park, Youngsoo; Krause, Elisabeth; Dodelson, Scott; Jain, Bhuvnesh; Amara, Adam; Becker, Matt; Bridle, Sarah; Clampitt, Joseph; Crocce, Martin; Honscheid, Klaus; Gaztanaga, Enrique; Sanchez, Carles; Wechsler, Risa

    2015-01-01

    Combining galaxy-galaxy lensing and galaxy clustering is a promising method for inferring the growth rate of large scale structure, a quantity that will shed light on the mechanism driving the acceleration of the Universe. The Dark Energy Survey (DES) is a prime candidate for such an analysis, with its measurements of both the distribution of galaxies on the sky and the tangential shears of background galaxies induced by these foreground lenses. By constructing an end-to-end analysis that combines large-scale galaxy clustering and small-scale galaxy-galaxy lensing, we also forecast the potential of a combined probes analysis on DES datasets. In particular, we develop a practical approach to a DES combined probes analysis by jointly modeling the assumptions and systematics affecting the different components of the data vector, employing a shared halo model, HOD parametrization, photometric redshift errors, and shear measurement errors. Furthermore, we study the effect of external priors on different subsets of these parameters. We conclude that DES data will provide powerful constraints on the evolution of structure growth in the universe, conservatively/ optimistically constraining the growth function to 8%/4.9% with its first-year data covering 1000 square degrees, and to 4%/2.3% with its full five-year data covering 5000 square degrees.

  2. DISTANT CLUSTER OF GALAXIES [left

    NASA Technical Reports Server (NTRS)

    2002-01-01

    One of the deepest images to date of the universe, taken with NASA's Hubble Space Telescope (HST), reveals thousands of faint galaxies at the detection limit of present day telescopes. Peering across a large volume of the observable cosmos, Hubble resolves thousands of galaxies from five to twelve billion light-years away. The light from these remote objects has taken billions of years to cross the expanding universe, making these distant galaxies fossil evidence' of events that happened when the universe was one-third its present age. A fraction of the galaxies in this image belong to a cluster located nine billion light-years away. Though the field of view (at the cluster's distance) is only two million light-years across, it contains a multitude of fragmentary objects. (By comparison, the two million light-years between our Milky Way galaxy and its nearest large companion galaxy, in the constellation Andromeda, is essentially empty space!) Very few of the cluster's members are recognizable as normal spiral galaxies (like our Milky Way), although some elongated members might be edge-on disks. Among this zoo of odd galaxies are ``tadpole-like'' objects, disturbed and apparently merging systems dubbed 'train-wrecks,' and a multitude of faint, tiny shards and fragments, dwarf galaxies or possibly an unknown population of objects. However, the cluster also contains red galaxies that resemble mature examples of today's elliptical galaxies. Their red color comes from older stars that must have formed shortly after the Big Bang. The image is the full field view of the Wide Field and Planetary Camera-2. The picture was taken in intervals between May 11 and June 15, 1994 and required an 18-hour long exposure, over 32 orbits of HST, to reveal objects down to 29th magnitude. [bottom right] A close up view of the peculiar radio galaxy 3C324 used to locate the cluster. The galaxy is nine billion light-years away as measured by its spectral redshift (z=1.2), and located in the

  3. BRIGHTEST CLUSTER GALAXIES AT THE PRESENT EPOCH

    SciTech Connect

    Lauer, Tod R.; Postman, Marc; Strauss, Michael A.; Graves, Genevieve J.; Chisari, Nora E.

    2014-12-20

    We have obtained photometry and spectroscopy of 433 z ≤ 0.08 brightest cluster galaxies (BCGs) in a full-sky survey of Abell clusters to construct a BCG sample suitable for probing deviations from the local Hubble flow. The BCG Hubble diagram over 0 < z < 0.08 is consistent to within 2% of the Hubble relation specified by a Ω {sub m} = 0.3, Λ = 0.7 cosmology. This sample allows us to explore the structural and photometric properties of BCGs at the present epoch, their location in their hosting galaxy clusters, and the effects of the cluster environment on their structure and evolution. We revisit the L{sub m} -α relation for BCGs, which uses α, the log-slope of the BCG photometric curve of growth, to predict the metric luminosity in an aperture with 14.3 kpc radius, L{sub m} , for use as a distance indicator. Residuals in the relation are 0.27 mag rms. We measure central stellar velocity dispersions, σ, of the BCGs, finding the Faber-Jackson relation to flatten as the metric aperture grows to include an increasing fraction of the total BCG luminosity. A three-parameter ''metric plane'' relation using α and σ together gives the best prediction of L{sub m} , with 0.21 mag residuals. The distribution of projected spatial offsets, r{sub x} of BCGs from the X-ray-defined cluster center is a steep γ = –2.33 power law over 1 < r{sub x} < 10{sup 3} kpc. The median offset is ∼10 kpc, but ∼15% of the BCGs have r{sub x} > 100 kpc. The absolute cluster-dispersion normalized BCG peculiar velocity |ΔV {sub 1}|/σ {sub c} follows an exponential distribution with scale length 0.39 ± 0.03. Both L{sub m} and α increase with σ {sub c}. The α parameter is further moderated by both the spatial and velocity offset from the cluster center, with larger α correlated with the proximity of the BCG to the cluster mean velocity or potential center. At the same time, position in the cluster has little effect on L{sub m} . Likewise, residuals from the metric plane

  4. Percolation technique for galaxy clustering

    NASA Technical Reports Server (NTRS)

    Klypin, Anatoly; Shandarin, Sergei F.

    1993-01-01

    We study percolation in mass and galaxy distributions obtained in 3D simulations of the CDM, C + HDM, and the power law (n = -1) models in the Omega = 1 universe. Percolation statistics is used here as a quantitative measure of the degree to which a mass or galaxy distribution is of a filamentary or cellular type. The very fast code used calculates the statistics of clusters along with the direct detection of percolation. We found that the two parameters mu(infinity), characterizing the size of the largest cluster, and mu-squared, characterizing the weighted mean size of all clusters excluding the largest one, are extremely useful for evaluating the percolation threshold. An advantage of using these parameters is their low sensitivity to boundary effects. We show that both the CDM and the C + HDM models are extremely filamentary both in mass and galaxy distribution. The percolation thresholds for the mass distributions are determined.

  5. STAR CLUSTERS, GALAXIES, AND THE FUNDAMENTAL MANIFOLD

    SciTech Connect

    Zaritsky, Dennis; Zabludoff, Ann I.; Gonzalez, Anthony H. E-mail: azabludoff@as.arizona.edu

    2011-02-01

    We explore whether global observed properties, specifically half-light radii, mean surface brightness, and integrated stellar kinematics, suffice to unambiguously differentiate galaxies from star clusters, which presumably formed differently and lack dark matter halos. We find that star clusters lie on the galaxy scaling relationship referred to as the fundamental manifold (FM), on the extension of a sequence of compact galaxies, and so conclude that there is no simple way to differentiate star clusters from ultracompact galaxies. By extending the validity of the FM over a larger range of parameter space and a wider set of objects, we demonstrate that the physics that constrains the resulting baryon and dark matter distributions in stellar systems is more general than previously appreciated. The generality of the FM implies (1) that the stellar spatial distribution and kinematics of one type of stellar system do not arise solely from a process particular to that set of systems, such as violent relaxation for elliptical galaxies, but are instead the result of an interplay of all processes responsible for the generic settling of baryons in gravitational potential wells, (2) that the physics of how baryons settle is independent of whether the system is embedded within a dark matter halo, and (3) that peculiar initial conditions at formation or stochastic events during evolution do not ultimately disturb the overall regularity of baryonic settling. We also utilize the relatively simple nature of star clusters to relate deviations from the FM to the age of the stellar population and find that stellar population models systematically and significantly overpredict the mass-to-light ratios of old, metal-rich clusters. We present an empirical calibration of stellar population mass-to-light ratios with age and color. Finally, we use the FM to estimate velocity dispersions for the low surface brightness, outer halo clusters that lack such measurements.

  6. Galaxy Cluster Smashes Distance Record

    NASA Astrophysics Data System (ADS)

    2009-10-01

    he most distant galaxy cluster yet has been discovered by combining data from NASA's Chandra X-ray Observatory and optical and infrared telescopes. The cluster is located about 10.2 billion light years away, and is observed as it was when the Universe was only about a quarter of its present age. The galaxy cluster, known as JKCS041, beats the previous record holder by about a billion light years. Galaxy clusters are the largest gravitationally bound objects in the Universe. Finding such a large structure at this very early epoch can reveal important information about how the Universe evolved at this crucial stage. JKCS041 is found at the cusp of when scientists think galaxy clusters can exist in the early Universe based on how long it should take for them to assemble. Therefore, studying its characteristics - such as composition, mass, and temperature - will reveal more about how the Universe took shape. "This object is close to the distance limit expected for a galaxy cluster," said Stefano Andreon of the National Institute for Astrophysics (INAF) in Milan, Italy. "We don't think gravity can work fast enough to make galaxy clusters much earlier." Distant galaxy clusters are often detected first with optical and infrared observations that reveal their component galaxies dominated by old, red stars. JKCS041 was originally detected in 2006 in a survey from the United Kingdom Infrared Telescope (UKIRT). The distance to the cluster was then determined from optical and infrared observations from UKIRT, the Canada-France-Hawaii telescope in Hawaii and NASA's Spitzer Space Telescope. Infrared observations are important because the optical light from the galaxies at large distances is shifted into infrared wavelengths because of the expansion of the universe. The Chandra data were the final - but crucial - piece of evidence as they showed that JKCS041 was, indeed, a genuine galaxy cluster. The extended X-ray emission seen by Chandra shows that hot gas has been detected

  7. Combining cluster number counts and galaxy clustering

    NASA Astrophysics Data System (ADS)

    Lacasa, Fabien; Rosenfeld, Rogerio

    2016-08-01

    The abundance of clusters and the clustering of galaxies are two of the important cosmological probes for current and future large scale surveys of galaxies, such as the Dark Energy Survey. In order to combine them one has to account for the fact that they are not independent quantities, since they probe the same density field. It is important to develop a good understanding of their correlation in order to extract parameter constraints. We present a detailed modelling of the joint covariance matrix between cluster number counts and the galaxy angular power spectrum. We employ the framework of the halo model complemented by a Halo Occupation Distribution model (HOD). We demonstrate the importance of accounting for non-Gaussianity to produce accurate covariance predictions. Indeed, we show that the non-Gaussian covariance becomes dominant at small scales, low redshifts or high cluster masses. We discuss in particular the case of the super-sample covariance (SSC), including the effects of galaxy shot-noise, halo second order bias and non-local bias. We demonstrate that the SSC obeys mathematical inequalities and positivity. Using the joint covariance matrix and a Fisher matrix methodology, we examine the prospects of combining these two probes to constrain cosmological and HOD parameters. We find that the combination indeed results in noticeably better constraints, with improvements of order 20% on cosmological parameters compared to the best single probe, and even greater improvement on HOD parameters, with reduction of error bars by a factor 1.4-4.8. This happens in particular because the cross-covariance introduces a synergy between the probes on small scales. We conclude that accounting for non-Gaussian effects is required for the joint analysis of these observables in galaxy surveys.

  8. Velocity anisotropy in tidally limited star clusters

    NASA Astrophysics Data System (ADS)

    Tiongco, Maria A.; Vesperini, Enrico; Varri, Anna Lisa

    2016-02-01

    We explore the long-term evolution of the anisotropy in the velocity space of star clusters starting with different structural and kinematical properties. We show that the evolution of the radial anisotropy strength and its radial variation within a cluster contain distinct imprints of the cluster initial structural properties, dynamical history, and of the external tidal field of its host galaxy. Initially isotropic and compact clusters with small initial values of the ratio of the half-mass to Jacobi radius, rh/rJ, develop a strong radial anisotropy during their long-term dynamical evolution. Many clusters, if formed with small values of rh/rJ, should now be characterized by a significant radial anisotropy increasing with the distance from the cluster centre, reaching its maximum at a distance between 0.2 rJ and 0.4 rJ, and then becoming more isotropic or mildly tangentially anisotropic in the outermost regions. A similar radial variation of the anisotropy can also result from an early violent relaxation phase. In both cases, as a cluster continues its evolution and loses mass, the anisotropy eventually starts to decrease and the system evolves towards an isotropic velocity distribution. However, in order to completely erase the strong anisotropy developed by these compact systems during their evolution, they must be in the advanced stages of their evolution and lose a large fraction of their initial mass. Clusters that are initially isotropic and characterized by larger initial values of rh/rJ, on the other hand, never develop a significant radial anisotropy.

  9. Galaxy luminosity functions in WINGS clusters

    NASA Astrophysics Data System (ADS)

    Moretti, A.; Bettoni, D.; Poggianti, B. M.; Fasano, G.; Varela, J.; D'Onofrio, M.; Vulcani, B.; Cava, A.; Fritz, J.; Couch, W. J.; Moles, M.; Kjærgaard, P.

    2015-09-01

    Aims: Using V band photometry of the WINGS survey, we derive galaxy luminosity functions (LF) in nearby clusters. This sample is complete down to MV = -15.15, and it is homogeneous, thus facilitating the study of an unbiased sample of clusters with different characteristics. Methods: We constructed the photometric LF for 72 out of the original 76 WINGS clusters, excluding only those without a velocity dispersion estimate. For each cluster we obtained the LF for galaxies in a region of radius = 0.5 × r200, and fitted them with single and double Schechter's functions. We also derive the composite LF for the entire sample, and those pertaining to different morphological classes. Finally, we derive the spectroscopic cumulative LF for 2009 galaxies that are cluster members. Results: The double Schechter fit parameters are correlated neither with the cluster velocity dispersion nor with the X-ray luminosity. Our median values of the Schechter's fit slope are, on average, in agreement with measurements of nearby clusters, but are less steep that those derived from large surveys, such as the SDSS. Early-type galaxies out number late-types at all magnitudes, but both early and late types contribute equally to the faint end of the LF. Finally, the spectroscopic LF is in excellent agreement with the one derived for A2199, A85 and Virgo, and with the photometric LF at the bright magnitudes (where both are available). Conclusions: There is a large spread in the LF of different clusters, however, this spread is not caused by correlation of the LF shape with cluster characteristics such as X-ray luminosity or velocity dispersions. The faint end is flatter than previously derived (αf = -1.7), which is at odds with that predicted from numerical simulations. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile. Progs. ID 67.A-0030, 68.A-0139, and 69.A-0119.Table 1 and full Fig. 1 (Fig. A.1) are available in

  10. Kinematics and evolution of poor clusters of galaxies

    NASA Astrophysics Data System (ADS)

    Koranyi, Daniel Mark

    2000-11-01

    The AWM and MKW poor clusters form a complete nearby sample of poor clusters that span a range of velocity dispersions and populations; they were selected on the basis of a cD-like galaxy at their centers. I describe a photometric and kinematic study of AWM 7, the richest cluster in the sample, and extend the galaxy sample to perform a detailed analysis of the mass profile of this cluster. I assess the performance of the virial mass estimator under a variety of assumptions about the orbital anisotropy profile. I then describe an extensive kinematic analysis of 17 AWM and MKW clusters, investigating velocity distributions, spectral segregation, velocity dispersion profiles, and X-ray properties. This section establishes a robust observational baseline for comparison to simulations. The AWM and MKW clusters are as varied in their properties as their richer counterparts, and are globally no different from poor clusters without cD galaxies. This similarity suggests that the formation of the cD in such clusters is governed by local physics, independent of the global cluster properties. Finally, I describe and analyze high-resolution N-body simulations of poor clusters that are a good match to the AWM and MKW clusters in mass, galaxy population, and velocity dispersion. The simulations consist of ~10 million particles, of which typically 2 million constitute the final virialized region. The simulations track galaxies and dark matter separately, permitting an analysis of the morphological evolution of the galaxy population. I summarize the kinematic properties of the simulated clusters and their evolution with redshift, I compare them to the observed sample of AWM and MKW clusters, and test the accuracy with which the standard virial mass estimator recovers the true underlying mass profile. The virial estimator recovers the total mass accurately on average, but systematically overestimates the mass profile interior to the virial radius.

  11. Galaxy Populations and Evolution in Clusters IV Deep H 1 Observations of Dwarf Elliptical Galaxies in the Virgo Cluster

    NASA Technical Reports Server (NTRS)

    Conselice, Christopher J.; ONeil, Karen; Gallagher, John S.; Wyse, Rosemary F. G.

    2003-01-01

    In this paper we present deep Arecibo H I and WIYN optical observations of Virgo Cluster dwarf elliptical galaxies. Based on this data we argue that a significant fraction of low-mass galaxies in the Virgo Cluster recently underwent evolution. Our new observations consist of H I 21 cm line observations for 22 classified dE galaxies with optical radial velocities consistent with membership in the Virgo Cluster. Cluster members VCC 390 and VCC 1713 are detected with H 1 masses M H1= 6 x 10 sup 7 and 8 x 10 sup 7 M , respectively, while MH I values in the remaining 20 dE galaxies have upper limits as low as about 5 x 1O sup 5 M. We combine our results with those for 26 other Virgo Cluster dE galaxies with H 1 observations in the literature, seven of which have H I detection claims.

  12. Decaying neutrinos in galaxy clusters

    NASA Technical Reports Server (NTRS)

    Melott, Adrian L.; Splinter, Randall J.; Persic, Massimo; Salucci, Paolo

    1994-01-01

    Davidsen et al. (1991) have argued that the failure to detect UV photons from the dark matter (DM) in cluster A665 excludes the decaying neutrino hypothesis. Sciama et al. (1993) argued that because of high central concentration the DM in that cluster must be baryonic. We study the DM profile in clusters of galaxies simulated using the Harrison-Zel'dovich spectrum of density fluctuations, and an amplitude previously derived from numerical simulations (Melott 1984b; Anninos et al. 1991) and in agreement with microwave background fluctuations (Smoot et al. 1992). We find that with this amplitude normalization cluster neutrino DM densities are comparable to observed cluster DM values. We conclude that given this normalization, the cluster DM should be at least largely composed of neutrinos. The constraint of Davidsen et al. can be somewhat weakened by the presence of baryonic DM; but it cannot be eliminated given our assumptions.

  13. Radial velocities of remote globular clusters - stalking the missing mass

    SciTech Connect

    Peterson, R.C.

    1985-10-01

    Measurements good to 25 km/s are presented of radial velocities of five remote galactic globular clusters, based on aperture-plate spectra of individual stars at 3.0 A resolution. Velocities with respect to the galactic rest-frame of two individual systems, Eridanus and Palomar 14, are large enough to suggest a total mass for the Galaxy of 1 trillion solar masses. A similar mass is inferred from the average of the galactocentric distance times velocity squared. 36 references.

  14. MASSIVE BLACK HOLES IN CENTRAL CLUSTER GALAXIES

    SciTech Connect

    Volonteri, Marta; Ciotti, Luca

    2013-05-01

    We explore how the co-evolution of massive black holes (MBHs) and galaxies is affected by environmental effects, addressing in particular MBHs hosted in the central cluster galaxies (we will refer to these galaxies in general as ''CCGs''). Recently, the sample of MBHs in CCGs with dynamically measured masses has increased, and it has been suggested that these MBH masses (M{sub BH}) deviate from the expected correlations with velocity dispersion ({sigma}) and mass of the bulge (M{sub bulge}) of the host galaxy: MBHs in CCGs appear to be ''overmassive''. This discrepancy is more pronounced when considering the M{sub BH}-{sigma} relation than the M{sub BH}-M{sub bulge} one. We show that this behavior stems from a combination of two natural factors: (1) CCGs experience more mergers involving spheroidal galaxies and their MBHs and (2) such mergers are preferentially gas poor. We use a combination of analytical and semi-analytical models to investigate the MBH-galaxy co-evolution in different environments and find that the combination of these two factors is in accordance with the trends observed in current data sets.

  15. Clusters of Galaxies: Setting the Stage

    NASA Astrophysics Data System (ADS)

    Diaferio, A.; Schindler, S.; Dolag, K.

    2008-02-01

    Clusters of galaxies are self-gravitating systems of mass ˜1014 1015 h -1 M⊙ and size ˜1 3 h -1 Mpc. Their mass budget consists of dark matter (˜80%, on average), hot diffuse intracluster plasma (≲20%) and a small fraction of stars, dust, and cold gas, mostly locked in galaxies. In most clusters, scaling relations between their properties, like mass, galaxy velocity dispersion, X-ray luminosity and temperature, testify that the cluster components are in approximate dynamical equilibrium within the cluster gravitational potential well. However, spatially inhomogeneous thermal and non-thermal emission of the intracluster medium (ICM), observed in some clusters in the X-ray and radio bands, and the kinematic and morphological segregation of galaxies are a signature of non-gravitational processes, ongoing cluster merging and interactions. Both the fraction of clusters with these features, and the correlation between the dynamical and morphological properties of irregular clusters and the surrounding large-scale structure increase with redshift. In the current bottom-up scenario for the formation of cosmic structure, where tiny fluctuations of the otherwise homogeneous primordial density field are amplified by gravity, clusters are the most massive nodes of the filamentary large-scale structure of the cosmic web and form by anisotropic and episodic accretion of mass, in agreement with most of the observational evidence. In this model of the universe dominated by cold dark matter, at the present time most baryons are expected to be in a diffuse component rather than in stars and galaxies; moreover, ˜50% of this diffuse component has temperature ˜0.01 1 keV and permeates the filamentary distribution of the dark matter. The temperature of this Warm-Hot Intergalactic Medium (WHIM) increases with the local density and its search in the outer regions of clusters and lower density regions has been the quest of much recent observational effort. Over the last thirty

  16. Galaxy clustering on large scales.

    PubMed

    Efstathiou, G

    1993-06-01

    I describe some recent observations of large-scale structure in the galaxy distribution. The best constraints come from two-dimensional galaxy surveys and studies of angular correlation functions. Results from galaxy redshift surveys are much less precise but are consistent with the angular correlations, provided the distortions in mapping between real-space and redshift-space are relatively weak. The galaxy two-point correlation function, rich-cluster two-point correlation function, and galaxy-cluster cross-correlation function are all well described on large scales ( greater, similar 20h-1 Mpc, where the Hubble constant, H0 = 100h km.s-1.Mpc; 1 pc = 3.09 x 10(16) m) by the power spectrum of an initially scale-invariant, adiabatic, cold-dark-matter Universe with Gamma = Omegah approximately 0.2. I discuss how this fits in with the Cosmic Background Explorer (COBE) satellite detection of large-scale anisotropies in the microwave background radiation and other measures of large-scale structure in the Universe.

  17. Abundances in Spiral Galaxies of the Pegasus I Cluster

    NASA Astrophysics Data System (ADS)

    Robertson, Paul; Shields, G. A.; Blanc, G. A.

    2011-01-01

    We present a study of abundances in spiral galaxies of the Pegasus I cluster (cz = 4000 km/s), motivated by evidence for high interstellar abundances in the spirals of the Virgo cluster. Spectra of H II regions in six galaxies with a range of H I deficiency were obtained with the VIRUS-P integral field spectrograph on the 2.7-meter telescope at McDonald Observatory. The results suggest a pattern of higher abundances in more hydrogen deficient galaxies. This resembles the case for Virgo, despite the lower velocity dispersion and higher spiral fraction in the Pegasus cluster.

  18. THE ACCRETION OF DWARF GALAXIES AND THEIR GLOBULAR CLUSTER SYSTEMS

    SciTech Connect

    Masters, Craig E.; Ashman, Keith M. E-mail: ashmank@umkc.ed

    2010-12-10

    The question of where the low-metallicity globular clusters in early-type galaxies came from has profound implications for the formation of those galaxies. Our work supports the idea that the metal-poor globular cluster systems of giant early-type galaxies formed in dwarf galaxies that have been subsumed by the giants. To support this hypothesis, two linear relations, one involving globular cluster metallicity versus host galaxy luminosity and one involving metallicity versus velocity dispersion were studied. Tentatively, these relations show that the bright ellipticals do not obey the same trend as the dwarfs, suggesting that the low-metallicity globular clusters did not form within their parent bright ellipticals.

  19. Multiple object redshift determinations in clusters of galaxies using OCTOPUS

    NASA Astrophysics Data System (ADS)

    Mazure, A.; Proust, D.; Sodre, L.; Lund, G.; Capelato, H.

    1987-03-01

    The ESO multiobject facility, Octopus, was used to observe a sample of galaxy clusters such as SC2008-565 in an attempt to collect a large set of individual radial velocities. A dispersion of 114 A/mm was used, providing spectral coverage from 3800 to 5180 A. Octopus was found to be a well-adapted instrument for the rapid and simultaneous determination of redshifts in cataloged galaxy clusters.

  20. Multiple object redshift determinations in clusters of galaxies using OCTOPUS

    NASA Astrophysics Data System (ADS)

    Mazure, A.; Proust, D.; Sodre, L.; Capelato, H. V.; Lund, G.

    1988-04-01

    The ESO multiobject facility, Octopus, was used to observe a sample of galaxy clusters such as SC2008-565 in an attempt to collect a large set of individual radial velocities. A dispersion of 114 A/mm was used, providing spectral coverage from 3800 to 5180 A. Octopus was found to be a well-adapted instrument for the rapid and simultaneous determination of redshifts in cataloged galaxy clusters.

  1. Decaying neutrinos in galaxy clusters

    NASA Technical Reports Server (NTRS)

    Melott, Adrian L.; Splinter, Randall J.; Persic, Massimo; Salucci, Paolo

    1993-01-01

    The DM profile in clusters of galaxies was studied and simulated using the Harrison-Zel'dovich spectrum of density fluctuations, and an amplitude previously derived from numerical simulations and in agreement with microwave background fluctuations. Neutrino DM densities, with this amplitude normalization cluster, are comparable to observed cluster DM values. It was concluded that given this normalization, the cluster DM should be al least largely composed of neutrinos. The constraint of Davidson et al., who argued that the failure to detect uv photons from the dark matter (DM) in cluster A665 excludes the decaying neutrino hypothesis, could be somewhat weakened by the presence of baryonic DM; but it cannot be eliminated given our assumptions.

  2. Dynamical Mass Measurements of Contaminated Galaxy Clusters Using Machine Learning

    NASA Astrophysics Data System (ADS)

    Ntampaka, Michelle; Trac, Hy; Sutherland, Dougal; Fromenteau, Sebastien; Poczos, Barnabas; Schneider, Jeff

    2016-01-01

    Galaxy clusters are a rich source of information for examining fundamental astrophysical processes and cosmological parameters, however, employing clusters as cosmological probes requires accurate mass measurements derived from cluster observables. We study dynamical mass measurements of galaxy clusters contaminated by interlopers, and show that a modern machine learning (ML) algorithm can predict masses by better than a factor of two compared to a standard scaling relation approach. We create a mock catalog from Multidark's publicly-available N-body MDPL1 simulation where a simple cylindrical cut around the cluster center allows interlopers to contaminate the clusters. In the standard approach, we use a power law scaling relation to infer cluster mass from galaxy line of sight (LOS) velocity dispersion. The presence of interlopers in the catalog produces a wide, flat fractional mass error distribution, with width = 2.13. We employ the Support Distribution Machine (SDM) class of algorithms to learn from distributions of data to predict single values. Applied to distributions of galaxy observables such as LOS velocity and projected distance from the cluster center, SDM yields better than a factor-of-two improvement (width = 0.67). Remarkably, SDM applied to contaminated clusters is better able to recover masses than even a scaling relation approach applied to uncontaminated clusters. We show that the SDM method more accurately reproduces the cluster mass function, making it a valuable tool for employing cluster observations to evaluate cosmological models.

  3. Kinematic evidence of satellite galaxy populations in the potential wells of first-ranked cluster galaxies

    SciTech Connect

    Cowie, L.L.; Hu, E.M.

    1986-06-01

    The velocities of 38 centrally positioned galaxies (r much less than 100 kpc) were measured relative to the velocity of the first-ranked galaxy in 14 rich clusters. Analysis of the velocity distribution function of this sample and of previous data shows that the population cannot be fit by a single Gaussian. An adequate fit is obtained if 60 percent of the objects lie in a Gaussian with sigma = 250 km/s and the remainder in a population with sigma = 1400 km/s. All previous data sets are individually consistent with this conclusion. This suggests that there is a bound population of galaxies in the potential well of the central galaxy in addition to the normal population of the cluster core. This is taken as supporting evidence for the galactic cannibalism model of cD galaxy formation. 14 references.

  4. Kinematic evidence of satellite galaxy populations in the potential wells of first-ranked cluster galaxies

    NASA Technical Reports Server (NTRS)

    Cowie, L. L.; Hu, E. M.

    1986-01-01

    The velocities of 38 centrally positioned galaxies (r much less than 100 kpc) were measured relative to the velocity of the first-ranked galaxy in 14 rich clusters. Analysis of the velocity distribution function of this sample and of previous data shows that the population cannot be fit by a single Gaussian. An adequate fit is obtained if 60 percent of the objects lie in a Gaussian with sigma = 250 km/s and the remainder in a population with sigma = 1400 km/s. All previous data sets are individually consistent with this conclusion. This suggests that there is a bound population of galaxies in the potential well of the central galaxy in addition to the normal population of the cluster core. This is taken as supporting evidence for the galactic cannibalism model of cD galaxy formation.

  5. Color and magnitude dependence of galaxy clustering

    NASA Astrophysics Data System (ADS)

    Müller, Volker

    2016-10-01

    A quantitative study of the clustering properties of galaxies in the cosmic web as a function of absolute magnitude and colour is presented using the SDSS Data Release 7 galaxy redshift survey. We compare our results with mock galaxy samples obtained with four different semi-analytical models of galaxy formation imposed on the merger trees of the Millenium simulation.

  6. On the formation of cD galaxies and their parent clusters

    NASA Astrophysics Data System (ADS)

    Tovmassian, Hrant M.; Andernach, Heinz

    2012-12-01

    In order to study the mechanism of the formation of cD galaxies, we search for possible dependencies between the K-band luminosity of cD galaxies and the parameters of their host clusters which we select to have a dominant cD galaxy, corresponding to a cluster morphology of Bautz-Morgan type I (BM I). As a comparison sample we use cD galaxies in clusters where they are not dominant, which we define here as non-BM I (NBMI) type clusters. We find that for 71 BM I clusters the absolute K-band luminosity of cD galaxies depends on the cluster richness, but less strongly on the cluster velocity dispersion. Meanwhile, for 35 NBMI clusters the correlation between cD luminosity and cluster richness is weaker, and is absent between cD luminosity and velocity dispersion. In addition, we find that the luminosity of the cD galaxy hosted in BM I clusters tends to increase with the cD's peculiar velocity with respect to the cluster mean velocity. In contrast, for NBMI clusters the cD luminosity decreases with increasing peculiar velocity. Also, the X-ray luminosity of BM I clusters depends on the cluster velocity dispersion, while in NBMI clusters such a correlation is absent. These findings favour the cannibalism scenario for the formation of cD galaxies. We suggest that cD galaxies in clusters of BM I type were formed and evolved preferentially in one and the same cluster. In contrast, cD galaxies in NBMI-type clusters were either originally formed in clusters that later merged with groups or clusters to form the current cluster, or are now in the process of merging.

  7. Kinematics of cD Clusters of Galaxies

    NASA Astrophysics Data System (ADS)

    Hill, J. M.; Oegerle, W. R.

    1992-12-01

    In order to determine the distribution and frequency of peculiar velocities of cD galaxies and the nature of their parent clusters, we have begun a survey of a statistically complete sample of cD clusters with the MX multifiber spectrometer at Steward Observatory. If ``speeding'' cDs are common, then their existence must be taken into account by formation models, which usually assume that cDs lie at rest in the bottom of the cluster potential well (ie. the cannibalism model). Our sample is the subset of the Hoessel, Gunn & Thuan (1980) Abell cluster sample satisfying the following constraints: (1) the cluster must be of Rood-Sastry type cD, (2) have redshift <0.08, and (3) have declination >-10(deg) . This provides a statistically complete, unbiased sample of cD clusters. There are 24 Abell clusters in this sample, and we present data for 10 clusters. The goal of the survey is to collect ~ 60 redshifts per cluster, in order that peculiar velocities of 250\\ km\\ s(-1) or higher can be verified at a >2.5sigma level of significance. In the current sample of clusters, 7 cD galaxies have no statistically significant peculiar velocities (A399, 401, 1749, 1809, 2063, 2124, 2589). Three other clusters (A1795, 2107, and 2634) have peculiar or marginally peculiar velocities, but show evidence for subclustering or non-Gaussian velocity distributions. Based on the data taken so far, ~ 25% of all cD galaxies appear to have statistically significant peculiar velocities with respect to their parent clusters. Evidence is now beginning to mount that these peculiar velocities are due to subclustering, as first suggested by Sharples etal (1988) & Hill etal (1988).

  8. Lopsidedness of cluster galaxies in modified gravity

    SciTech Connect

    Wu, Xufen; Zhao, HongSheng; Famaey, Benoit E-mail: hz4@st-andrews.ac.uk

    2010-06-01

    We point out an interesting theoretical prediction for elliptical galaxies residing inside galaxy clusters in the framework of modified Newtonian dynamics (MOND), that could be used to test this paradigm. Apart from the central brightest cluster galaxy, other galaxies close enough to the centre experience a strong gravitational influence from the other galaxies of the cluster. This influence manifests itself only as tides in standard Newtonian gravity, meaning that the systematic acceleration of the centre of mass of the galaxy has no consequence. However, in the context of MOND, a consequence of the breaking of the strong equivalence principle is that the systematic acceleration changes the own self-gravity of the galaxy. We show here that, in this framework, initially axisymmetric elliptical galaxies become lopsided along the external field's direction, and that the centroid of the galaxy, defined by the outer density contours, is shifted by a few hundreds parsecs with respect to the densest point.

  9. Galaxy and Mass Assembly (GAMA): galaxy pairwise velocity dispersion

    NASA Astrophysics Data System (ADS)

    Loveday, Jon; Christodoulou, Leonidas

    2016-10-01

    We describe preliminary measurements of the pairwise velocity dispersion (PVD) of galaxies in the Galaxy and Mass Assembly (GAMA) survey as a function of projected separation and galaxy luminosity. Due to the faint magnitude limit (r < 19.8) and highly-complete spectroscopic sampling of the GAMA survey, we are able to measure the PVD to smaller scales and for lower-luminosity galaxies than previous SDSS-based work. We see no strong scale-dependence at most luminosities in the quasi-linear regime. We observe an apparent drop in PVD towards very small scales (below ~ 0.1h -1 Mpc), but this could in part be due to a restriction of the streaming model employed. At intermediate scales, the PVD is highest (~ 500 km/s) at intermediate luminosities, dropping at both fainter and brighter luminosities.

  10. Dynamical Mass Measurements of Contaminated Galaxy Clusters Using Machine Learning

    NASA Astrophysics Data System (ADS)

    Ntampaka, M.; Trac, H.; Sutherland, D. J.; Fromenteau, S.; Póczos, B.; Schneider, J.

    2016-11-01

    We study dynamical mass measurements of galaxy clusters contaminated by interlopers and show that a modern machine learning algorithm can predict masses by better than a factor of two compared to a standard scaling relation approach. We create two mock catalogs from Multidark’s publicly available N-body MDPL1 simulation, one with perfect galaxy cluster membership information and the other where a simple cylindrical cut around the cluster center allows interlopers to contaminate the clusters. In the standard approach, we use a power-law scaling relation to infer cluster mass from galaxy line-of-sight (LOS) velocity dispersion. Assuming perfect membership knowledge, this unrealistic case produces a wide fractional mass error distribution, with a width of {{Δ }}ε ≈ 0.87. Interlopers introduce additional scatter, significantly widening the error distribution further ({{Δ }}ε ≈ 2.13). We employ the support distribution machine (SDM) class of algorithms to learn from distributions of data to predict single values. Applied to distributions of galaxy observables such as LOS velocity and projected distance from the cluster center, SDM yields better than a factor-of-two improvement ({{Δ }}ε ≈ 0.67) for the contaminated case. Remarkably, SDM applied to contaminated clusters is better able to recover masses than even the scaling relation approach applied to uncontaminated clusters. We show that the SDM method more accurately reproduces the cluster mass function, making it a valuable tool for employing cluster observations to evaluate cosmological models.

  11. Galaxy Evolution in Clusters Since z ~ 1

    NASA Astrophysics Data System (ADS)

    Aragón-Salamanca, A.

    Galaxy clusters provide some of the most extreme environments in which galaxies evolve, making them excellent laboratories to study the age old question of "nature" vs. "nurture" in galaxy evolution. Here I review some of the key observational results obtained during the last decade on the evolution of the morphology, structure, dynamics, star-formation history and stellar populations of cluster galaxies since the time when the Universe was half its present age. Many of the results presented here have been obtained within the ESO Distant Cluster Survey (EDisCS) and Space Telescope A901/02 Galaxy Evolution Survey (STAGES) collaborations.

  12. Galaxy evolution in clusters since z~1

    NASA Astrophysics Data System (ADS)

    Aragon-Salamanca, Alfonso

    2010-09-01

    Galaxy clusters provide some of the most extreme environments in which galaxies evolve, making them excellent laboratories to study the age old question of "nature" vs. "nurture" in galaxy evolution. Here I review some of the key observational results obtained during the last decade on the evolution of the morphology, structure, dynamics, star-formation history and stellar populations of cluster galaxies since the time when the universe was half its present age. Many of the results presented here have been obtained within the ESO Distant Cluster Survey (EDisCS) and Space Telescope A901/02 Galaxy Evolution Survey (STAGES) collaborations.

  13. Hot outflows in galaxy clusters

    NASA Astrophysics Data System (ADS)

    Kirkpatrick, C. C.; McNamara, B. R.

    2015-10-01

    The gas-phase metallicity distribution has been analysed for the hot atmospheres of 29 galaxy clusters using Chandra X-ray Observatory observations. All host brightest cluster galaxies (BCGs) with X-ray cavity systems produced by radio AGN. We find high elemental abundances projected preferentially along the cavities of 16 clusters. The metal-rich plasma was apparently lifted out of the BCGs with the rising X-ray cavities (bubbles) to altitudes between twenty and several hundred kiloparsecs. A relationship between the maximum projected altitude of the uplifted gas (the `iron radius') and jet power is found with the form R_Fe ∝ P_jet^{0.45}. The estimated outflow rates are typically tens of solar masses per year but exceed 100 M⊙ yr- 1 in the most powerful AGN. The outflow rates are 10-20 per cent of the cooling rates, and thus alone are unable to offset a cooling inflow. Nevertheless, hot outflows effectively redistribute the cooling gas and may play a significant role at regulating star formation and AGN activity in BCGs and presumably in giant elliptical galaxies. The metallicity distribution overall can be complex, perhaps due to metal-rich gas returning in circulation flows or being blown around in the hot atmospheres. Roughly 15 per cent of the work done by the cavities is expended lifting the metal-enriched gas, implying their nuclear black holes have increased in mass by at least ˜107-109 M⊙. Finally, we show that hot outflows can account for the broad, gas-phase metallicity distribution compared to the stellar light profiles of BCGs, and we consider a possible connection between hot outflows and cold molecular gas flows discovered in recent Atacama Large Millimeter Array observations.

  14. PECULIAR VELOCITIES OF GALAXIES IN THE LEO SPUR

    SciTech Connect

    Karachentsev, Igor D.; Makarova, Lidia N.; Makarov, Dmitry I.; Tully, R. Brent; Rizzi, Luca

    2015-06-01

    The Hubble Space Telescope Advanced Camera for Surveys has been used to determine accurate distances for the spiral galaxy NGC 2683 and 12 other galaxies in a zone of the “local velocity anomaly” from luminosity measurements of the brightest red giant branch stars. These galaxies lie in the Leo Spur, the nearest filament beyond our Local Sheet. The new accurate distance measurements confirm that galaxies along the Leo Spur are more distant than expected from uniform cosmic expansion, and hence have large and peculiar velocities toward us. The motions are generally explained by a previously published model that posits that the Local Sheet is descending at 259 km s{sup −1} toward the south supergalactic pole due to expansion of the Local Void and is being attracted toward the Virgo Cluster at 185 km s{sup −1}. With the standard ΛCDM cosmology, an empty void expands at 16 km s{sup −1} Mpc{sup −1}, so a motion of 259 km s{sup −1} requires the Local Void to be impressively large and empty. Small residuals from the published model can be attributed to an upward push toward the north supergalactic pole by the expansion of the Gemini–Leo Void below the Leo Spur. The Leo Spur is sparsely populated, but among its constituents there are two associations that contain only dwarf galaxies.

  15. ROSAT Discovers Unique, Distant Cluster of Galaxies

    NASA Astrophysics Data System (ADS)

    1995-06-01

    Brightest X-ray Cluster Acts as Strong Gravitational Lens Based on exciting new data obtained with the ROSAT X-ray satellite and a ground-based telescope at the ESO La Silla Observatory, a team of European astronomers [2] has just discovered a very distant cluster of galaxies with unique properties. It emits the strongest X-ray emission of any cluster ever observed by ROSAT and is accompanied by two extraordinarily luminous arcs that represent the gravitationally deflected images of even more distant objects. The combination of these unusual characteristics makes this cluster, now known as RXJ1347.5-1145, a most interesting object for further cosmological studies. DISCOVERY AND FOLLOW-UP OBSERVATIONS This strange cluster of galaxies was discovered during the All Sky Survey with the ROSAT X-ray satellite as a moderately intense X-ray source in the constellation of Virgo. It could not be identified with any already known object and additional ground-based observations were therefore soon after performed with the Max-Planck-Society/ESO 2.2-metre telescope at the La Silla observatory in Chile. These observations took place within a large--scale redshift survey of X-ray clusters of galaxies detected by the ROSAT All Sky Survey, a so-called ``ESO Key Programme'' led by astronomers from the Max-Planck-Institut fur Extraterrestrische Physik and the Osservatorio Astronomico di Brera. The main aim of this programme is to identify cluster X-ray sources, to determine the distance to the X-ray emitting clusters and to investigate their overall properties. These observations permitted to measure the redshift of the RXJ1347.5-1145 cluster as z = 0.45, i.e. it moves away from us with a velocity (about 106,000 km/sec) equal to about one-third of the velocity of light. This is an effect of the general expansion of the universe and it allows to determine the distance as about 5,000 million light-years (assuming a Hubble constant of 75 km/sec/Mpc). In other words, we see these

  16. Galaxy cluster mass estimation from stacked spectroscopic analysis

    NASA Astrophysics Data System (ADS)

    Farahi, Arya; Evrard, August E.; Rozo, Eduardo; Rykoff, Eli S.; Wechsler, Risa H.

    2016-08-01

    We use simulated galaxy surveys to study: (i) how galaxy membership in redMaPPer clusters maps to the underlying halo population, and (ii) the accuracy of a mean dynamical cluster mass, Mσ(λ), derived from stacked pairwise spectroscopy of clusters with richness λ. Using ˜130 000 galaxy pairs patterned after the Sloan Digital Sky Survey (SDSS) redMaPPer cluster sample study of Rozo et al., we show that the pairwise velocity probability density function of central-satellite pairs with mi < 19 in the simulation matches the form seen in Rozo et al. Through joint membership matching, we deconstruct the main Gaussian velocity component into its halo contributions, finding that the top-ranked halo contributes ˜60 per cent of the stacked signal. The halo mass scale inferred by applying the virial scaling of Evrard et al. to the velocity normalization matches, to within a few per cent, the log-mean halo mass derived through galaxy membership matching. We apply this approach, along with miscentring and galaxy velocity bias corrections, to estimate the log-mean matched halo mass at z = 0.2 of SDSS redMaPPer clusters. Employing the velocity bias constraints of Guo et al., we find = ln (M30) + αm ln (λ/30) with M30 = 1.56 ± 0.35 × 1014 M⊙ and αm = 1.31 ± 0.06stat ± 0.13sys. Systematic uncertainty in the velocity bias of satellite galaxies overwhelmingly dominates the error budget.

  17. Selection effects and binary galaxy velocity differences

    NASA Technical Reports Server (NTRS)

    Schneider, Stephen E.; Salpeter, Edwin E.

    1990-01-01

    Measurements of the velocity differences (delta v's) in pairs of galaxies from large statistical samples have often been used to estimate the average masses of binary galaxies. A basic prediction of these models is that the delta v distribution ought to decline monotonically. However, some peculiar aspects of the kinematics have been uncovered, with an anomalous preference for delta v approx. equal to 72 km s(sup-1) appearing to be present in the data. The authors examine a large sample of binary galaxies with accurate redshift measurements and confirm that the distribution of delta v's appears to be non-monotonic with peaks at 0 and approx. 72 km s (exp -1). The authors suggest that the non-zero peak results from the isolation criteria employed in defining samples of binaries and that it indicates there are two populations of binary orbits contributing to the observed delta v distribution.

  18. Investigations of Galaxy Clusters Using Gravitational Lensing

    SciTech Connect

    Wiesner, Matthew P.

    2014-08-01

    In this dissertation, we discuss the properties of galaxy clusters that have been determined using strong and weak gravitational lensing. A galaxy cluster is a collection of galaxies that are bound together by the force of gravity, while gravitational lensing is the bending of light by gravity. Strong lensing is the formation of arcs or rings of light surrounding clusters and weak lensing is a change in the apparent shapes of many galaxies. In this work we examine the properties of several samples of galaxy clusters using gravitational lensing. In Chapter 1 we introduce astrophysical theory of galaxy clusters and gravitational lensing. In Chapter 2 we examine evidence from our data that galaxy clusters are more concentrated than cosmology would predict. In Chapter 3 we investigate whether our assumptions about the number of galaxies in our clusters was valid by examining new data. In Chapter 4 we describe a determination of a relationship between mass and number of galaxies in a cluster at higher redshift than has been found before. In Chapter 5 we describe a model of the mass distribution in one of the ten lensing systems discovered by our group at Fermilab. Finally in Chapter 6 we summarize our conclusions.

  19. VizieR Online Data Catalog: Mark III Catalog of Galaxy Peculiar Velocities (Willick+ 1997)

    NASA Astrophysics Data System (ADS)

    Willick, J. A.; Courteau, S.; Faber, S. M.; Burstein, D.; Dekel, A.; Kolatt, T.

    1996-08-01

    The Mark III Catalog of Galaxy Peculiar Velocities comprises five different types of data files. 1. Basic Observational and Catalog Data 2. Individual Galaxy TF and Dn-sigma Distances 3. Grouped Spiral Galaxy TF Distances 4. Elliptical Galaxy Distances as in the Mark II 5. Comparison of Spiral Galaxy Distances 1. The Basic Data files are: a. Aaronson et al. Field, (359 galaxies; a82): a82file1.dat, a82file2.dat, a82file3.dat b. Mathewson et al. 1992 (1355 galaxies; mat): matfile1.dat, matfile2.dat, matfile3.dat c. Willick 1991, Perseus-Pisces sample (383 galaxies; w91pp): d. Willick 1991, Cluster galaxy sample (156 galaxies; w91cl): The basic data for all 539 objects in the w91 sample are given in the following files: w91file1.dat, w91file2.dat, w91file3.dat Some galaxies are duplicates; see below for details. e. Courteau-Faber 1993 (326 galaxies; cf): cffile1.dat, cffile2.dat, cffile3.dat f. Han-Mould et al. 1992+, Cluster galaxy sample (433 galaxies; hmcl): The basic data for all 433 galaxies the the hm sample are given in the following files: hmfile1.dat, hmfile3.dat, hmfile2.dat Some galaxies are duplicates; see below for details. 2. The Individual Spiral Galaxy Distances Files are: (See notes for detailed descriptions of how the w91pp, w91cl, hmcl and cf distance files correspond to the galaxies in the w91file*, hmfile*, and cffile* Basic Data files.) a. Aaronson et al. Field, (359 galaxies; a82): a82_s b. Mathewson et al. 1992 (1355 galaxies; mat): mat_s c. Willick 1991, Perseus-Pisces sample (326 galaxies; w91pp): w91pp_s.dat d. Willick 1991, Cluster galaxy sample (156 galaxies; w91cl): w91cl_s.dat e. Courteau-Faber 1993 (321 galaxies; cf): cf_s.dat f. Han-Mould et al. 1992+, all cluster galaxies (427 galaxies; hmcl): hmcl_s.dat 3. The Grouped Spiral Galaxy Distance Files are: (Note: Group numbers in the wcf group (merged w91pp and cf) data file correspond to those in the w91pp and cf individual galaxy files. The hmw group file (merged w91cl and hmcl, 10

  20. The Radio Properties of Brightest Cluster Galaxies

    NASA Astrophysics Data System (ADS)

    Hogan, M. T.

    2014-09-01

    Energetic feedback from the Active Galactic Nucleus (AGN) of the Brightest Cluster Galaxy (BCG) is required to prevent catastrophic cooling of the intra-cluster medium (ICM) in galaxy clusters. Evidence for this is seen through the inflation of cavities in the ICM by AGN-launched, radio-emitting jets, and understanding this process is an active area of research. Radio observations play an integral role in this, as they trace the active stages of the feedback cycle. Understanding the radio properties of BCGs is therefore paramount for understanding both galaxy clusters and AGN feedback processes globally. Within this thesis, the BCGs in a large (>700) sample of X-ray selected clusters are studied. We observe these BCGs with a wide variety of facilities, building a census of their radio properties across a range of frequencies, timescales and angular resolutions. Radio spectral energy distributions (SEDs) are built for over 200 BCGs, and then decomposed into two components; a core, attributable to ongoing nuclear activity, and a non-core, attributable to historical accretion. Both components are not only more common, but also significantly more powerful in cool-core (CC) clusters than non-cool core (NCC) clusters. However, it is the presence of an active core that shows BCGs in CC clusters are constantly `on' - explaining how they regulate their environments over gigayear timescales. We observe 35 currently active BCGs at high (15-353 GHz) radio frequencies, and monitor their variability. Self-absorbed, active components are found to be common at high frequency. Little variability is seen on < year timescales, although longer term variation of ~10% annually over few-decade timescales is observed. Evidence is presented for a hitherto unseen component in BCG spectra that may be attributable to a naked Advection Dominated Accretion Flow (ADAF). The milli-arcsecond scale radio properties of 59 sources are studied, with a large range of morphologies recovered although no

  1. Weighing galaxy clusters with gas. II. On the origin of hydrostatic mass bias in ΛCDM galaxy clusters

    SciTech Connect

    Nelson, Kaylea; Nagai, Daisuke; Yu, Liang; Lau, Erwin T.; Rudd, Douglas H.

    2014-02-20

    The use of galaxy clusters as cosmological probes hinges on our ability to measure their masses accurately and with high precision. Hydrostatic mass is one of the most common methods for estimating the masses of individual galaxy clusters, which suffer from biases due to departures from hydrostatic equilibrium. Using a large, mass-limited sample of massive galaxy clusters from a high-resolution hydrodynamical cosmological simulation, in this work we show that in addition to turbulent and bulk gas velocities, acceleration of gas introduces biases in the hydrostatic mass estimate of galaxy clusters. In unrelaxed clusters, the acceleration bias is comparable to the bias due to non-thermal pressure associated with merger-induced turbulent and bulk gas motions. In relaxed clusters, the mean mass bias due to acceleration is small (≲ 3%), but the scatter in the mass bias can be reduced by accounting for gas acceleration. Additionally, this acceleration bias is greater in the outskirts of higher redshift clusters where mergers are more frequent and clusters are accreting more rapidly. Since gas acceleration cannot be observed directly, it introduces an irreducible bias for hydrostatic mass estimates. This acceleration bias places limits on how well we can recover cluster masses from future X-ray and microwave observations. We discuss implications for cluster mass estimates based on X-ray, Sunyaev-Zel'dovich effect, and gravitational lensing observations and their impact on cluster cosmology.

  2. Redshifts for galaxies in three Yerkes poor clusters

    NASA Astrophysics Data System (ADS)

    Stauffer, J.; Spinrad, H.

    1980-01-01

    Redshifts have been obtained for 11 galaxies in the Yerkes poor cluster AWM 7, five galaxies in AWM 5, and two galaxies in AWM 1. In contrast to the result for AWM 4 previously noted by Stauffer and Spinrad, both AWM 5 and AWM 7 are real clusters with apparent line-of-sight velocity dispersions of 400 km/s and 600 km/s respectively. Surface photometry of the cD galaxy in AWM 7, obtained with the Berkeley PDS from a Crossley plate of the cluster, indicates that it is quite luminous, with an absolute magnitude to r about 30 kpc of M(v) about -23.5. A rough dynamical estimate of the AWM 7 cD mass from the spectroscopic data gives M(cD) about 2.0 x 10 to the 13th solar masses.

  3. Photometric Properties of Galaxies in Poor Clusters

    NASA Astrophysics Data System (ADS)

    Sharma, M.; Prabhu, T.

    We study several statistical properties of galaxies in four poor clusters of galaxies using optical photometry. We select these poor clusters as luminous, extended X-ray sources identified with poor galaxy systems in the EMSS catalogue of clusters of galaxies. The clusters are at moderate redshifts (0.08galaxy populations are clearly evolved, as traced by the tightness of their color--magnitude relations and accordance of the latter with those of the Virgo Cluster. The fraction of blue galaxies is similar to those of low-redshift richness 0 clusters and higher than those of richer clusters at similar redshifts. The luminosity functions (LFs) of the individual clusters are not significantly different from each other. Using these, we construct composite LFs in B, V , and R bands (to MV=-18). The faint-end of these LFs are flat, like the V-band LF of other (e.g., MKW/AWM) poor clusters, but steeper than the field LF in the R-band. In terms of the statistical properties of their member galaxies, poor clusters appear to be lower-mass extensions of their rich counterparts.

  4. STAR CLUSTERS IN PSEUDOBULGES OF SPIRAL GALAXIES

    SciTech Connect

    Di Nino, Daiana; Trenti, Michele; Stiavelli, Massimo; Carollo, C. Marcella; Scarlata, Claudia; Wyse, Rosemary F. G.

    2009-11-15

    We present a study of the properties of the star-cluster systems around pseudobulges of late-type spiral galaxies using a sample of 11 galaxies with distances from 17 Mpc to 37 Mpc. Star clusters are identified from multiband Hubble Space Telescope ACS and WFPC2 imaging data by combining detections in three bands (F435W and F814W with ACS and F606W with WFPC2). The photometric data are then compared to population synthesis models to infer the masses and ages of the star clusters. Photometric errors and completeness are estimated by means of artificial source Monte Carlo simulations. Dust extinction is estimated by considering F160W NICMOS observations of the central regions of the galaxies, augmenting our wavelength coverage. In all galaxies we identify star clusters with a wide range of ages, from young (age {approx}< 8 Myr) blue clusters, with typical mass of 10{sup 3} M {sub sun} to older (age >100-250 Myr), more massive, red clusters. Some of the latter might likely evolve into objects similar to the Milky Way's globular clusters. We compute the specific frequencies for the older clusters with respect to the galaxy and bulge luminosities. Specific frequencies relative to the galaxy light appear consistent with the globular cluster specific frequencies of early-type spirals. We compare the specific frequencies relative to the bulge light with the globular cluster specific frequencies of dwarf galaxies, which have a surface brightness profile that is similar to that of the pseudobulges in our sample. The specific frequencies we derive for our sample galaxies are higher than those of the dwarf galaxies, supporting an evolutionary scenario in which some of the dwarf galaxies might be the remnants of harassed late-type spiral galaxies that hosted a pseudobulge.

  5. Galaxy and mass assembly (GAMA): projected galaxy clustering

    NASA Astrophysics Data System (ADS)

    Farrow, D. J.; Cole, Shaun; Norberg, Peder; Metcalfe, N.; Baldry, I.; Bland-Hawthorn, Joss; Brown, Michael J. I.; Hopkins, A. M.; Lacey, Cedric G.; Liske, J.; Loveday, Jon; Palamara, David P.; Robotham, A. S. G.; Sridhar, Srivatsan

    2015-12-01

    We measure the projected two-point correlation function of galaxies in the 180 deg2 equatorial regions of the GAMA II survey, for four different redshift slices between z = 0.0 and 0.5. To do this, we further develop the Cole method of producing suitable random catalogues for the calculation of correlation functions. We find that more r-band luminous, more massive and redder galaxies are more clustered. We also find that red galaxies have stronger clustering on scales less than ˜3 h-1 Mpc. We compare to two different versions of the GALFORM galaxy formation model, Lacey et al. (in preparation) and Gonzalez-Perez et al., and find that the models reproduce the trend of stronger clustering for more massive galaxies. However, the models underpredict the clustering of blue galaxies, can incorrectly predict the correlation function on small scales and underpredict the clustering in our sample of galaxies with {˜ } 3 Lr^*. We suggest possible avenues to explore to improve these clustering predictions. The measurements presented in this paper can be used to test other galaxy formation models, and we make the measurements available online to facilitate this.

  6. Clustering of galaxies in brane world models

    NASA Astrophysics Data System (ADS)

    Hameeda, Mir; Faizal, Mir; Ali, Ahmed Farag

    2016-04-01

    In this paper, we analyze the clustering of galaxies using a modified Newtonian potential. This modification of the Newtonian potential occurs due to the existence of extra dimensions in brane world models. We will analyze a system of galaxies interacting with each other through this modified Newtonian potential. The partition function for this system of galaxies will be calculated, and this partition function will be used to calculate the free energy of this system of galaxies. The entropy and the chemical potential for this system will also be calculated. We will derive explicit expression for the clustering parameter for this system. This parameter will determine the behavior of this system, and we will be able to express various thermodynamic quantities using this clustering parameter. Thus, we will be able to explicitly analyze the effect that modifying the Newtonian potential can have on the clustering of galaxies. We also analyse the effect of extra dimensions on the two-point functions between galaxies.

  7. Star formation and substructure in galaxy clusters

    SciTech Connect

    Cohen, Seth A.; Hickox, Ryan C.; Wegner, Gary A.; Einasto, Maret; Vennik, Jaan

    2014-03-10

    We investigate the relationship between star formation (SF) and substructure in a sample of 107 nearby galaxy clusters using data from the Sloan Digital Sky Survey. Several past studies of individual galaxy clusters have suggested that cluster mergers enhance cluster SF, while others find no such relationship. The SF fraction in multi-component clusters (0.228 ± 0.007) is higher than that in single-component clusters (0.175 ± 0.016) for galaxies with M{sub r}{sup 0.1}<−20.5. In both single- and multi-component clusters, the fraction of star-forming galaxies increases with clustercentric distance and decreases with local galaxy number density, and multi-component clusters show a higher SF fraction than single-component clusters at almost all clustercentric distances and local densities. Comparing the SF fraction in individual clusters to several statistical measures of substructure, we find weak, but in most cases significant at greater than 2σ, correlations between substructure and SF fraction. These results could indicate that cluster mergers may cause weak but significant SF enhancement in clusters, or unrelaxed clusters exhibit slightly stronger SF due to their less evolved states relative to relaxed clusters.

  8. Brightest cluster galaxies as standard candles

    NASA Technical Reports Server (NTRS)

    Postman, Marc; Lauer, Tod R.

    1995-01-01

    We investigate the use of brightest cluster galaxies (BCGs) as standard candles for measuring galaxy peculiar velocities on large scales. We have obtained precise large-format CCD surface photometry and redshifts for an all-sky, volume-limited (z less than or = 0.05) sample of 199 BCG. We reinvestigate the Hoessel (1980) relationship between the metric luminosity, L(sub m), within the central 10 kpc/h of the BCGs and the logarithmic slope of the surface brightness profile, alpha. The L(sub m)-alpha relationship reduces the cosmic scatter in L(sub m) from 0.327 mag to 0.244 mag, yielding a typical distance accuracy of 17% per BCG. Residuals about the L(sub m)-alpha relationship are independent of BCG luminosity, BCG B - R(sub c) color, BCG location within the host cluster, and richness of the host cluster. The metric luminosity is independent of cluster richness even before correcting for its dependence on alpha, which provides further evidence for the unique nature of the BCG luminosity function. Indeed, the BCG luminosity function, both before and after application of the alpha-correction, is consistent with a single Gaussian distribution. Half the BCGs in the sample show some evidence of small color gradients as a function of radius within their central 50 kpc/h regions but with almost equal numbers becoming redder as becoming bluer. However, with the central 10 kpc/h the colors are remarkably constant -- the mean B - R(sub c) color is 1.51 with a dispersion of only 0.06 mag. The narrow photometric and color distributions of the BCGs, the lack of 'second-parameter' effects, as well as the unique rich cluster environment of BCGs, argue that BCGs are the most homogeneous distance indicators presently available for large-scale structure research.

  9. ORIENTATION OF BRIGHTER GALAXIES IN NEARBY GALAXY CLUSTERS

    SciTech Connect

    Panko, E.; Juszczyk, T.; Flin, P. E-mail: sfflin@cyf-kr.edu.pl

    2009-12-15

    A sample of 6188 nearby galaxy structures, complete to r{sub F} = 18fm3 and containing at least 10 members each, was the observational basis for an investigation of the alignment of bright galaxies with the major axes for the parent clusters. The distribution of position angles for galaxies within the clusters, specifically the brightest, the second brightest, the third, and the tenth brightest galaxies was tested for isotropy. Galaxy position angles appear to be distributed isotropically, as are the distributions of underlying cluster structure position angles. The characterization of galaxy structures according to richness class also appears to be isotropic. Characterization according to BM types, which are known for 1056 clusters, is more interesting. Only in the case of clusters of BM type I is there an alignment of the brightest cluster member with the major axis of the parent cluster. The effect is observed at the 2 significance level. In other investigated cases the distributions are isotropic. The results confirm the special role of cD galaxies in the origin/evolution of large-scale structures.

  10. Spiral Galaxies in MKW/AWM Clusters

    NASA Astrophysics Data System (ADS)

    Williams, Barbara A.

    1997-03-01

    Observations have been made of the neutral hydrogen content of more than 170 galaxies within MKW 4, MKW 7, MKW 8, MKW 9, MKW 11, AWM 1, AWM 3, AWM 4, and AWM 5. This sample of nine clusters is representative of the general class of poor clusters identified by MKW and AWM in that they all contain D-- or cD--like dominant galaxies at their dynamical centers. We examine the neutral hydrogen (HI) content of the spiral members in these systems as a function of the local and global properties of the cluster, i.e., galaxy density, x-ray intra cluster gas pressure, x-ray and optical luminosities, and compare our findings with the HI properties of similar galaxies in rich clusters and loose groups of galaxies.

  11. Observing dynamical friction in galaxy clusters

    NASA Astrophysics Data System (ADS)

    Adhikari, Susmita; Dalal, Neal; Clampitt, Joseph

    2016-07-01

    We present a novel method to detect the effects of dynamical friction in observed galaxy clusters. Following accretion into clusters, massive satellite galaxies will backsplash to systematically smaller radii than less massive satellites, an effect that may be detected by stacking the number density profiles of galaxies around clusters. We show that this effect may be understood using a simple toy model which reproduces the trends with halo properties observed in simulations. We search for this effect using SDSS redMaPPer clusters with richness 10 < λ < 20, and find that bright (Mi < ‑21.5) satellites have smaller splashback radii than fainter (Mi > ‑20) satellites at 99% confidence.

  12. Star-forming galaxies in low-redshift clusters: comparison of integrated properties of cluster and field galaxies

    NASA Astrophysics Data System (ADS)

    Bretherton, C. F.; James, P. A.; Moss, C.; Whittle, M.

    2010-12-01

    Aims: We investigate the effect of the cluster environment on the star formation properties of galaxies in 8 nearby Abell clusters. Methods: Star formation properties are determined for individual galaxies using the equivalent width of Hα+[Nii] line emission from narrow-band imaging. Equivalent width distributions are derived for each galaxy type in each of 3 environments - cluster, supercluster (outside the cluster virial radius) and field. The effects of morphological disturbance on star formation are also investigated. Results: We identify a population of early-type disk galaxies in the cluster population with enhanced star formation compared to their field counterparts. The enhanced cluster galaxies frequently show evidence of disturbance, and the disturbed galaxies show marginal evidence for a higher velocity dispersion, possibly indicative of an infalling population. Based on observations made with the Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias; and with the Jacobus Kapteyn Telescope, which was operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias.

  13. On Escaping a Galaxy Cluster in an Accelerating Universe

    NASA Astrophysics Data System (ADS)

    Stark, Alejo; Miller, Christopher J.; Gifford, Daniel

    2016-10-01

    We derive the escape velocity profile for an Einasto density field in an accelerating universe and demonstrate its physical viability by comparing theoretical expectations to both light-cone data generated from N-body simulations and archival data on 20 galaxy clusters. We demonstrate that the projection function (g(β )) is deemed physically viable only for the theoretical expectation that includes a cosmology-dependent term. Using simulations, we show that the inferred velocity anisotropy is more than 6σ away from the expected value for the theoretical profile that ignores the acceleration of the universe. In the archival data, we constrain the average velocity anisotropy parameter of a sample of 20 clusters to be β ={0.248}-0.360+0.164 at the 68% confidence level. Lastly, we briefly discuss how our analytic model may be used as a novel cosmological probe based on galaxy clusters.

  14. N-Body Simulations of Galaxies in the Cluster Environment

    NASA Astrophysics Data System (ADS)

    Humphrey, Nicholas; Berrington, R. C.

    2010-01-01

    We present numerous N-body simulations of galaxy clusters consisting of up to 600,000 total particles and 50 galaxies each to characterize the evolution of galaxies in the cluster environment. These simulations were run on the Ball State University (BSU) College of Science and Humanities (CSH) 64-node Beowulf Cluster. Because the velocity dispersion (σ) is a tracer of a galaxies’ potential well and therefore its mass, we will use it to examine the mass evolution of the galaxies in the simulations by fitting a function to the σ of the galaxies. The strength of this function is its direct comparison to observational data. We further investigate the evolution of the galaxy structure parameters through the use of projected mass radii and line-of-sight (LOS) σ. Additionally, we discuss the use of alternate orbital parameters such as Vesc to investigate the potential wells of the galaxies. Our goal is to isolate the mass and luminosity evolution from the environmental effects on the evolution of elliptical galaxies. This project is a subset of a continuing study whose intent is to combine observational data with numerical techniques to study the effects of a galaxies’ environment on its mass evolution and internal dynamics.

  15. Record-breaking ancient galaxy clusters

    NASA Astrophysics Data System (ADS)

    2003-12-01

    A tale of two record-breaking clusters hi-res Size hi-res: 768 kb Credits: for RDCS1252: NASA, ESA, J.Blakeslee (Johns Hopkins Univ.), M.Postman (Space Telescope Science Inst.) and P.Rosati, Chris Lidman & Ricardo Demarco (European Southern Observ.) for TNJ1338: NASA, ESA, G.Miley (Leiden Observ.) and R.Overzier (Leiden Obs) A tale of two record-breaking clusters Looking back in time to when the universe was in its formative youth, the Advanced Camera for Surveys (ACS) aboard the NASA/ESA Hubble Space Telescope captured these revealing images of two galaxy clusters. The image at left, which is made with an additional infrared exposure taken with the European Southern Observatory’s Very Large Telescope, shows mature galaxies in a massive cluster that existed when the cosmos was 5000 million years old. The cluster, called RDCS1252.9-2927, is as massive as ‘300 trillion’ suns and is the most massive known cluster for its epoch. The image reveals the core of the cluster and is part of a much larger mosaic of the entire cluster. Dominating the core are a pair of large, reddish elliptical galaxies [near centre of image]. Their red colour indicates an older population of stars. Most of the stars are at least 1000 million years old. The two galaxies appear to be interacting and may eventually merge to form a larger galaxy that is comparable to the brightest galaxies seen in present-day clusters. The red galaxies surrounding the central pair are also cluster members. The cluster probably contains many thousands of galaxies, but only about 50 can be seen in this image. The full mosaic (heic0313d) reveals several hundred cluster members. Many of the other galaxies in the image, including several of the blue galaxies, are foreground or background galaxies. The colour-composite image was assembled from two observations (through i and z filters) taken between May and June 2002 by the ACS Wide Field Camera, and one image with the ISAAC instrument on the VLT taken in 2002

  16. Reconstructing galaxy histories from globular clusters

    NASA Astrophysics Data System (ADS)

    West, Michael J.; Côté, Patrick; Marzke, Ronald O.; Jordán, Andrés

    2004-01-01

    Nearly a century after the true nature of galaxies as distant `island universes' was established, their origin and evolution remain great unsolved problems of modern astrophysics. One of the most promising ways to investigate galaxy formation is to study the ubiquitous globular star clusters that surround most galaxies. Globular clusters are compact groups of up to a few million stars. They generally formed early in the history of the Universe, but have survived the interactions and mergers that alter substantially their parent galaxies. Recent advances in our understanding of the globular cluster systems of the Milky Way and other galaxies point to a complex picture of galaxy genesis driven by cannibalism, collisions, bursts of star formation and other tumultuous events.

  17. Reconstructing galaxy histories from globular clusters.

    PubMed

    West, Michael J; Côté, Patrick; Marzke, Ronald O; Jordán, Andrés

    2004-01-01

    Nearly a century after the true nature of galaxies as distant 'island universes' was established, their origin and evolution remain great unsolved problems of modern astrophysics. One of the most promising ways to investigate galaxy formation is to study the ubiquitous globular star clusters that surround most galaxies. Globular clusters are compact groups of up to a few million stars. They generally formed early in the history of the Universe, but have survived the interactions and mergers that alter substantially their parent galaxies. Recent advances in our understanding of the globular cluster systems of the Milky Way and other galaxies point to a complex picture of galaxy genesis driven by cannibalism, collisions, bursts of star formation and other tumultuous events. PMID:14702077

  18. Reconstructing galaxy histories from globular clusters.

    PubMed

    West, Michael J; Côté, Patrick; Marzke, Ronald O; Jordán, Andrés

    2004-01-01

    Nearly a century after the true nature of galaxies as distant 'island universes' was established, their origin and evolution remain great unsolved problems of modern astrophysics. One of the most promising ways to investigate galaxy formation is to study the ubiquitous globular star clusters that surround most galaxies. Globular clusters are compact groups of up to a few million stars. They generally formed early in the history of the Universe, but have survived the interactions and mergers that alter substantially their parent galaxies. Recent advances in our understanding of the globular cluster systems of the Milky Way and other galaxies point to a complex picture of galaxy genesis driven by cannibalism, collisions, bursts of star formation and other tumultuous events.

  19. Galaxy evolution in clusters since z=1

    NASA Astrophysics Data System (ADS)

    Aragón-Salamanca, A.

    2011-11-01

    It is now 30 years since Alan Dressler published his seminal paper onthe morphology-density relation. Although there is still much to learnon the effect of the environment on galaxy evolution, extensive progress has been made since then both observationally and theoretically.Galaxy clusters provide some of the most extreme environments in which galaxies evolve, making them excellent laboratories to study the age old question of "nature'' vs. "nurture'' in galaxy evolution. Here I review some of the key observational results obtained during the last decade on the evolution of the morphology, structure, dynamics, star-formation history and stellar populations of cluster galaxies since the time when the universe was half its present age.Many of the results presented here have been obtainedwithin the ESO Distant Cluster Survey (EDisCS) and Space Telescope A901/02 Galaxy Evolution Survey (STAGES) collaborations.

  20. High velocity clouds in nearby disk galaxies

    NASA Technical Reports Server (NTRS)

    Schulman, Eric; Bregman, Joel N.; Roberts, Morton S.; Brinks, Elias

    1993-01-01

    Clouds of neutral hydrogen in our galaxy with the absolute value of v greater than 100 km/s cover approximately 10 percent of the sky to a limiting column density of 1 x 10(exp 18) cm(exp -2). These high velocity clouds (HVCs) may dominate the kinetic energy of neutral hydrogen in non-circular motion, and are an important though poorly understood component of galactic gas. It has been suggested that the HVCs can be reproduced by a combination of three phenomena: a galactic fountain driven by disk supernovae which would account for most of the HVCs, material tidally torn from the Magellanic Clouds, and an outer arm complex which is associated with the large scale structure of the warped galactic disk. We sought to detect HVCs in external galaxies in order to test the galactic fountain model.

  1. Galaxy Clustering Around Nearby Luminous Quasars

    NASA Technical Reports Server (NTRS)

    Fisher, Karl B.; Bahcall, John N.; Kirhakos, Sofia; Schneider, Donald P.

    1996-01-01

    We examine the clustering of galaxies around a sample of 20 luminous low redshift (z approx. less than 0.30) quasars observed with the Wide Field Camera-2 on the Hubble Space Telescope (HST). The HST resolution makes possible galaxy identification brighter than V = 24.5 and as close as 1 min or 2 min to the quasar. We find a significant enhancement of galaxies within a projected separation of approx. less than 100 1/h kpc of the quasars. If we model the QSO/galaxy correlation function as a power law with a slope given by the galaxy/galaxy correlation function, we find that the ratio of the QSO/galaxy to galaxy/galaxy correlation functions is 3.8 +/- 0.8. The galaxy counts within r less than 15 1/h kpc of the quasars are too high for the density profile to have an appreciable core radius (approx. greater than 100 1/h kpc). Our results reinforce the idea that low redshift quasars are located preferentially in groups of 10-20 galaxies rather than in rich clusters. We see no significant difference in the clustering amplitudes derived from radio-loud and radio-quiet subsamples.

  2. Peculiar velocities of cD galaxies - MX spectroscopy of Abell 1795

    NASA Astrophysics Data System (ADS)

    Hill, John M.; Hintzen, Paul; Oegerle, W. R.; Romanishin, W.; Lesser, M. P.; Eisenhamer, J. D.; Batuski, D. J.

    1988-09-01

    Spectroscopic observations of galaxies in the Abell 1795 field have been obtained using the MX multiple-object spectrograph on the Steward Observatory 2.3 m telescope. Redshifts are presented for 46 galaxies, including 41 cluster members. It is found that the A1795 cD galaxy is not at rest in the cluster gravitational potential well; it has a peculiar radial velocity, cz, of 365 km/s, and the hypothesis that the mean cluster velocity is as large as the cD's velocity can be rejected at the 99.5 percent confidence level. This conclusion is supported by spectroscopic data for the 'cooling flow' gas found in the central region of the cluster; this gas, except for the portion coincident with the cD nucleus, lies at the velocity derived for the cluster mean. It is suggested that current models of the formation of cD galaxies are unlikely to account for the large peculiar velocities of the cD galaxies in A1795 and A2670 unless substantial subclustering is still present. However, the available data show no evidence for velocity subclustering in either A1795 or A2670.

  3. Photometric Properties of Poor Cluster Galaxies

    NASA Astrophysics Data System (ADS)

    Sharma, M.; Prabhu, T. P.

    2002-12-01

    We study several statistical properties of galaxies in four poor clusters of galaxies using multi-color optical photometry obtained at the Vainu Bappu Telescope, India. The clusters, selected from the EMSS Catalog, are at moderate redshifts (0.08 < z < 0.25), of equivalent Abell richness R=0, and appear to be dynamically young. The early-type galaxy populations are clearly evolved, as traced by the tightness of the color-magnitude relations and the accordance of the latter with those of the Virgo cluster. The blue galaxy fractions are similar to those of R=0 clusters and higher than those of richer clusters at similar redshifts. The composite luminosity functions (LFs) in B, V, and R bands are flat at the faint end, similar to the V-band LF derived by Yamagata & Maehara for other (MKW/AWM) poor clusters but steeper than the R-band field LF derived by Lin et al. In terms of the statistical properties of their member galaxies, poor clusters appear to be lower-mass extensions of their rich counterparts. The brightest galaxies of three of these poor clusters appear to be luminous ellipticals with no incontrovertible signatures of a halo. It is likely that they were formed from multiple mergers early in the history of the clusters.

  4. The velocity-distance relation for galaxies on a bubble

    NASA Technical Reports Server (NTRS)

    Bothun, Gregory D.; Geller, Margaret J.; Kurtz, Michael J.; Huchra, John P.; Schild, Rudolph E.

    1992-01-01

    The characteristic diameter of the most prominent void in the redshift survey of de Lapparent et al. (1986) is measured. Distances and peculiar velocities to individual galaxies are derived, and it is shown that the void is approximately a 'Hubble Bubble' in which the near and far edges are separating with the general expansion of the universe. At the 3 sigma level, infall toward the Coma cluster is detected for a portion of the bubble wall. Limits on the net outflow from the void and infall into Coma are used to estimate Omega.

  5. A simple recipe for estimating masses of elliptical galaxies and clusters of galaxies

    NASA Astrophysics Data System (ADS)

    Lyskova, N.

    2013-04-01

    We discuss a simple and robust procedure to evaluate the mass/circular velocity of massive elliptical galaxies and clusters of galaxies. It relies only on the surface density and the projected velocity dispersion profiles of tracer particles and therefore can be applied even in case of poor or noisy observational data. Stars, globular clusters or planetary nebulae can be used as tracers for mass determination of elliptical galaxies. For clusters the galaxies themselves can be used as tracer particles. The key element of the proposed procedure is the selection of a ``sweet'' radius R_sweet, where the sensitivity to the unknown anisotropy of the tracers' orbits is minimal. At this radius the surface density of tracers declines approximately as I(R)∝ R-2, thus placing R_sweet not far from the half-light radius of the tracers R_eff. The procedure was tested on a sample of cosmological simulations of individual galaxies and galaxy clusters and then applied to real observational data. Independently the total mass profile was derived from the hydrostatic equilibrium equation for the gaseous atmosphere. Mismatch in mass profiles obtained from optical and X-ray data is used to estimate the non-thermal contribution to the gas pressure and/or to constrain the distribution of tracers' orbits.

  6. Testing gravity with the stacked phase space around galaxy clusters.

    PubMed

    Lam, Tsz Yan; Nishimichi, Takahiro; Schmidt, Fabian; Takada, Masahiro

    2012-08-01

    In general relativity, the average velocity field of dark matter around galaxy clusters is uniquely determined by the mass profile. The latter can be measured through weak lensing. We propose a new method of measuring the velocity field (phase space density) by stacking redshifts of surrounding galaxies from a spectroscopic sample. In combination with lensing, this yields a direct test of gravity on scales of 1-30 Mpc. Using N-body simulations, we show that this method can improve upon current constraints on f(R) and Dvali-Gabadadze-Porrati model parameters by several orders of magnitude when applied to upcoming imaging and redshift surveys. PMID:23006162

  7. Modelling galaxy clustering: halo occupation distribution versus subhalo matching

    NASA Astrophysics Data System (ADS)

    Guo, Hong; Zheng, Zheng; Behroozi, Peter S.; Zehavi, Idit; Chuang, Chia-Hsun; Comparat, Johan; Favole, Ginevra; Gottloeber, Stefan; Klypin, Anatoly; Prada, Francisco; Rodríguez-Torres, Sergio A.; Weinberg, David H.; Yepes, Gustavo

    2016-07-01

    We model the luminosity-dependent projected and redshift-space two-point correlation functions (2PCFs) of the Sloan Digital Sky Survey (SDSS) Data Release 7 Main galaxy sample, using the halo occupation distribution (HOD) model and the subhalo abundance matching (SHAM) model and its extension. All the models are built on the same high-resolution N-body simulations. We find that the HOD model generally provides the best performance in reproducing the clustering measurements in both projected and redshift spaces. The SHAM model with the same halo-galaxy relation for central and satellite galaxies (or distinct haloes and subhaloes), when including scatters, has a best-fitting χ2/dof around 2-3. We therefore extend the SHAM model to the subhalo clustering and abundance matching (SCAM) by allowing the central and satellite galaxies to have different galaxy-halo relations. We infer the corresponding halo/subhalo parameters by jointly fitting the galaxy 2PCFs and abundances and consider subhaloes selected based on three properties, the mass Macc at the time of accretion, the maximum circular velocity Vacc at the time of accretion, and the peak maximum circular velocity Vpeak over the history of the subhaloes. The three subhalo models work well for luminous galaxy samples (with luminosity above L*). For low-luminosity samples, the Vacc model stands out in reproducing the data, with the Vpeak model slightly worse, while the Macc model fails to fit the data. We discuss the implications of the modelling results.

  8. THE VELOCITY FIELD AROUND GROUPS OF GALAXIES

    SciTech Connect

    Hartwick, F. D. A.

    2011-06-15

    A statistical method is presented for determining the velocity field in the immediate vicinity of groups of galaxies using only positional and redshift information with the goal of studying the perturbation of the Hubble flow around groups more distant than the Local Group. The velocities are assumed to obey a Hubble-like expansion law, i.e., V = H{sub exp} R, where the expansion rate H{sub exp} is to be determined. The method is applied to a large, representative group catalog and evidence is found for a sub-Hubble expansion rate within two well-defined radii beyond the virial radii of the groups. This result is consistent with that of Teerikorpi et al. who found a similar expansion law around three nearby groups and extends it to a more representative volume of space.

  9. Globular Clusters and Spur Clusters in NGC 4921, the Brightest Spiral Galaxy in the Coma Cluster

    NASA Astrophysics Data System (ADS)

    Lee, Myung Gyoon; Jang, In Sung

    2016-03-01

    We resolve a significant fraction of globular clusters (GCs) in NGC 4921, the brightest spiral galaxy in the Coma cluster. We also find a number of extended bright star clusters (star complexes) in the spur region of the arms. The latter are much brighter and bluer than those in the normal star-forming region, being as massive as 3 × 105 M⊙. The color distribution of the GCs in this galaxy is found to be bimodal. The turnover magnitudes of the luminosity functions of the blue (metal-poor) GCs (0.70 < (V - I) ≤ 1.05) in the halo are estimated V(max) = 27.11 ± 0.09 mag and I(max) = 26.21 ± 0.11 mag. We obtain similar values for NGC 4923, a companion S0 galaxy, and two Coma cD galaxies (NGC 4874 and NGC 4889). The mean value for the turnover magnitudes of these four galaxies is I(max) = 26.25 ± 0.03 mag. Adopting MI (max) = -8.56 ± 0.09 mag for the metal-poor GCs, we determine the mean distance to the four Coma galaxies to be 91 ± 4 Mpc. Combining this with the Coma radial velocity, we derive a value of the Hubble constant, H0 = 77.9 ± 3.6 km s-1 Mpc-1. We estimate the GC specific frequency of NGC 4921 to be SN = 1.29 ± 0.25, close to the values for early-type galaxies. This indicates that NGC 4921 is in the transition phase to S0s.

  10. On the clustering of faint red galaxies

    NASA Astrophysics Data System (ADS)

    Xu, Haojie; Zheng, Zheng; Guo, Hong; Zhu, Ju; Zehavi, Idit

    2016-08-01

    Faint red galaxies in the Sloan Digital Sky Survey show a puzzling clustering pattern in previous measurements. In the two-point correlation function (2PCF), they appear to be strongly clustered on small scales, indicating a tendency to reside in massive haloes as satellite galaxies. However, their weak clustering on large scales suggests that they are more likely to be found in low-mass haloes. The interpretation of the clustering pattern suffers from the large sample variance in the 2PCF measurements, given the small volume of the volume-limited sample of such faint galaxies. We present improved clustering measurements of faint galaxies by making a full use of a flux-limited sample to obtain volume-limited measurements with an increased effective volume. In the improved 2PCF measurements, the fractional uncertainties on large scales drop by more than 40 per cent, and the strong contrast between small-scale and large-scale clustering amplitudes seen in previous work is no longer prominent. From halo occupation distribution modelling of the measurements, we find that a considerable fraction of faint red galaxies to be satellites in massive haloes, a scenario supported by the strong covariance of small-scale 2PCF measurements and the relative spatial distribution of faint red galaxies and luminous galaxies. However, the satellite fraction is found to be degenerate with the slope of the distribution profile of satellites in inner haloes. We compare the modelling results with semi-analytic model predictions and discuss the implications.

  11. The C4 clustering algorithm: Clusters of galaxies in the Sloan Digital Sky Survey

    SciTech Connect

    Miller, Christopher J.; Nichol, Robert; Reichart, Dan; Wechsler, Risa H.; Evrard, August; Annis, James; McKay, Timothy; Bahcall, Neta; Bernardi, Mariangela; Boehringer, Hans; Connolly, Andrew; Goto, Tomo; Kniazev, Alexie; Lamb, Donald; Postman, Marc; Schneider, Donald; Sheth, Ravi; Voges, Wolfgang; /Cerro-Tololo InterAmerican Obs. /Portsmouth U., ICG /North Carolina U. /Chicago U., Astron. Astrophys. Ctr. /Chicago U., EFI /Michigan U. /Fermilab /Princeton U. Observ. /Garching, Max Planck Inst., MPE /Pittsburgh U. /Tokyo U., ICRR /Baltimore, Space Telescope Sci. /Penn State U. /Chicago U. /Stavropol, Astrophys. Observ. /Heidelberg, Max Planck Inst. Astron. /INI, SAO

    2005-03-01

    We present the ''C4 Cluster Catalog'', a new sample of 748 clusters of galaxies identified in the spectroscopic sample of the Second Data Release (DR2) of the Sloan Digital Sky Survey (SDSS). The C4 cluster-finding algorithm identifies clusters as overdensities in a seven-dimensional position and color space, thus minimizing projection effects that have plagued previous optical cluster selection. The present C4 catalog covers {approx}2600 square degrees of sky and ranges in redshift from z = 0.02 to z = 0.17. The mean cluster membership is 36 galaxies (with redshifts) brighter than r = 17.7, but the catalog includes a range of systems, from groups containing 10 members to massive clusters with over 200 cluster members with redshifts. The catalog provides a large number of measured cluster properties including sky location, mean redshift, galaxy membership, summed r-band optical luminosity (L{sub r}), velocity dispersion, as well as quantitative measures of substructure and the surrounding large-scale environment. We use new, multi-color mock SDSS galaxy catalogs, empirically constructed from the {Lambda}CDM Hubble Volume (HV) Sky Survey output, to investigate the sensitivity of the C4 catalog to the various algorithm parameters (detection threshold, choice of passbands and search aperture), as well as to quantify the purity and completeness of the C4 cluster catalog. These mock catalogs indicate that the C4 catalog is {approx_equal}90% complete and 95% pure above M{sub 200} = 1 x 10{sup 14} h{sup -1}M{sub {circle_dot}} and within 0.03 {le} z {le} 0.12. Using the SDSS DR2 data, we show that the C4 algorithm finds 98% of X-ray identified clusters and 90% of Abell clusters within 0.03 {le} z {le} 0.12. Using the mock galaxy catalogs and the full HV dark matter simulations, we show that the L{sub r} of a cluster is a more robust estimator of the halo mass (M{sub 200}) than the galaxy line-of-sight velocity dispersion or the richness of the cluster. However, if we

  12. The dwarf galaxy population of nearby galaxy clusters

    NASA Astrophysics Data System (ADS)

    Lisker, Thorsten; Wittmann, Carolin; Pak, Mina; Janz, Joachim; Bialas, Daniel; Peletier, Reynier; Grebel, Eva; Falcon Barroso, Jesus; Toloba, Elisa; Smakced Collaboration, Focus Collaboration

    2015-01-01

    The Fornax, Virgo, Ursa Major and Perseus galaxy clusters all have very different characteristics, in terms of their density, mass, and large-scale environment. We can regard these clusters as laboratories for studying environmental influence on galaxy evolution, using the sensitive low-mass galaxies as probes for external mechanisms. Here we report on recent and ongoing observational studies of the said clusters with imaging and spectroscopy, as well as on the interpretation of present-day cluster galaxy populations with the aid of cosmological simulations.Multicolor imaging data allow us to identify residual star formation in otherwise red early-type dwarf galaxies, which hold clues to the strength of gas stripping processes. Major-axis spectra and 2D kinematical maps provide insight regarding the amount of rotational support and how much dynamical heating a dwarf galaxy may have experienced. To this end, dedicated N-body simulations that follow the evolution of galaxies since early epochs reveal their path through parameter space, and can be compared to observations in order to understand the time-integrated effect of environmental influence.

  13. The Mass Accretion Rate of Galaxy Clusters: A Measurable Quantity

    NASA Astrophysics Data System (ADS)

    De Boni, C.; Serra, A. L.; Diaferio, A.; Giocoli, C.; Baldi, M.

    2016-02-01

    We explore the possibility of measuring the mass accretion rate (MAR) of galaxy clusters from their mass profiles beyond the virial radius R200. We derive the accretion rate from the mass of a spherical shell whose inner radius is 2R200, whose thickness changes with redshift, and whose infall velocity is assumed to be equal to the mean infall velocity of the spherical shells of dark matter halos extracted from N-body simulations. This approximation is rather crude in hierarchical clustering scenarios where both smooth accretion and aggregation of smaller dark matter halos contribute to the mass accretion of clusters. Nevertheless, in the redshift range z = [0, 2], our prescription returns an average MAR within 20%-40% of the average rate derived from the merger trees of dark matter halos extracted from N-body simulations. The MAR of galaxy clusters has been the topic of numerous detailed numerical and theoretical investigations, but so far it has remained inaccessible to measurements in the real universe. Since the measurement of the mass profile of clusters beyond their virial radius can be performed with the caustic technique applied to dense redshift surveys of the cluster outer regions, our result suggests that measuring the mean MAR of a sample of galaxy clusters is actually feasible. We thus provide a new potential observational test of the cosmological and structure formation models.

  14. Globular clusters as tracers of the halo assembly of nearby central cluster galaxies

    NASA Astrophysics Data System (ADS)

    Hilker, Michael; Richtler, Tom

    2016-08-01

    The properties of globular cluster systems (GCSs) in the core of the nearby galaxy clusters Fornax and Hydra I are presented. In the Fornax cluster we have gathered the largest radial velocity sample of a GCS system so far, which enables us to identify photometric and kinematic sub-populations around the central galaxy NGC 1399. Moreover, ages, metallicities and [α/Fe] abundances of a sub-sample of 60 bright globular clusters (GCs) with high S/N spectroscopy show a multi-modal distribution in the correlation space of these three parameters, confirming heterogeneous stellar populations in the halo of NGC 1399. In the Hydra I cluster very blue GCs were identified. They are not uniformly distributed around the central galaxies. 3-color photometry including the U-band reveals that some of them are of intermediate age. Their location coincides with a group of dwarf galaxies under disruption. This is evidence of a structurally young stellar halo ``still in formation'', which is also supported by kinematic measurements of the halo light that point to a kinematically disturbed system. The most massive GCs divide into generally more extended ultra-compact dwarf galaxies (UCDs) and genuine compact GCs. In both clusters, the spatial distribution and kinematics of UCDs are different from those of genuine GCs. Assuming that some UCDs represent nuclei of stripped galaxies, the properties of those UCDs can be used to trace the assembly of nucleated dwarf galaxies into the halos of central cluster galaxies. We show via semi-analytical approaches within a cosmological simulation that only the most massive UCDs in Fornax-like clusters can be explained by stripped nuclei, whereas the majority of lower mass UCDs belong to the star cluster family.

  15. Extragalactic Globular Clusters: Tracers of Galaxy Evolution

    NASA Astrophysics Data System (ADS)

    Bassino, Lilia P.

    2008-09-01

    The study of globular cluster systems provides clues about different topics related to galaxy evolution. In the past years we have been investigating the globular cluster systems of galaxies in the Fornax and Antlia clusters, particularly those associated to the cluster-dominant galaxies. We present here the main results related to these systems. All of them have bimodal color distributions, even those around low-luminosity galaxies, that correspond to the metal-poor (``blue'') and metal-rich (``red'') globular cluster subpopulations. The radial and azimuthal projected areal distributions of the globular clusters are also analyzed. Total globular cluster populations are estimated through the luminosity functions. We stress on the properties of the globular cluster systems that allow us to trace possible interaction processes between the galaxies, like tidal stripping of globular clusters. The observational material consists of CCD images obtained with the wide-field MOSAIC Imager of the CTIO 4-m telescope (La Serena, Chile), and the FORS1 camera at the VLT ``Antu'' 8-m telescope (Cerro Paranal, Chile).

  16. Dynamics of cD Clusters of Galaxies. 4; Conclusion of a Survey of 25 Abell Clusters

    NASA Technical Reports Server (NTRS)

    Oegerle, William R.; Hill, John M.; Fisher, Richard R. (Technical Monitor)

    2001-01-01

    We present the final results of a spectroscopic study of a sample of cD galaxy clusters. The goal of this program has been to study the dynamics of the clusters, with emphasis on determining the nature and frequency of cD galaxies with peculiar velocities. Redshifts measured with the MX Spectrometer have been combined with those obtained from the literature to obtain typically 50 - 150 observed velocities in each of 25 galaxy clusters containing a central cD galaxy. We present a dynamical analysis of the final 11 clusters to be observed in this sample. All 25 clusters are analyzed in a uniform manner to test for the presence of substructure, and to determine peculiar velocities and their statistical significance for the central cD galaxy. These peculiar velocities were used to determine whether or not the central cD galaxy is at rest in the cluster potential well. We find that 30 - 50% of the clusters in our sample possess significant subclustering (depending on the cluster radius used in the analysis), which is in agreement with other studies of non-cD clusters. Hence, the dynamical state of cD clusters is not different than other present-day clusters. After careful study, four of the clusters appear to have a cD galaxy with a significant peculiar velocity. Dressler-Shectman tests indicate that three of these four clusters have statistically significant substructure within 1.5/h(sub 75) Mpc of the cluster center. The dispersion 75 of the cD peculiar velocities is 164 +41/-34 km/s around the mean cluster velocity. This represents a significant detection of peculiar cD velocities, but at a level which is far below the mean velocity dispersion for this sample of clusters. The picture that emerges is one in which cD galaxies are nearly at rest with respect to the cluster potential well, but have small residual velocities due to subcluster mergers.

  17. The rate of gravitational galaxy clustering

    NASA Astrophysics Data System (ADS)

    Saslaw, William C.

    1992-06-01

    The rate of gravitational galaxy clustering is considered within the framework of the simple but fundamental case when the initial distribution of galaxy positions is close to Poisson and most of the matter is closely associated with the galaxies. Simple gravitational clustering in an expanding universe is found to evolve along an adiabat of the equation of state which includes gravitational interactions. The faster the universe expands relative to its gravitational clustering time scale, the better this adiabatic approximation becomes. This generalizes the well-known result that a homogeneous unclustered perfect gas in an expanding universe evolves along an adiabat of the perfect gas equation of state. The evolving clustering is characterized. There is a critical value of 0.8604 at which clustering dominates the equation of state and the specific heat at constant volume becomes negative. Subsequent growth of clustering slows appreciably. Numerical N-body experiments are consistent with these properties.

  18. Enhanced Abundances in Spiral Galaxies of the Pegasus I Cluster

    NASA Astrophysics Data System (ADS)

    Robertson, Paul; Shields, Gregory A.; Blanc, Guillermo A.

    2012-03-01

    We study the influence of cluster environment on the chemical evolution of spiral galaxies in the Pegasus I cluster. We determine the gas-phase heavy element abundances of six galaxies in Pegasus derived from H II region spectra obtained from integral-field spectroscopy. These abundances are analyzed in the context of Virgo, whose spirals are known to show increasing interstellar metallicity as a function of H I deficiency. The galaxies in the Pegasus cluster, despite its lower density and velocity dispersion, also display gas loss due to interstellar-medium-intracluster-medium interaction, albeit to a lesser degree. Based on the abundances of three H I deficient spirals and two H I normal spirals, we observe a heavy element abundance offset of +0.13 ± 0.07 dex for the H I deficient galaxies. This abundance differential is consistent with the differential observed in Virgo for galaxies with a similar H I deficiency, and we observe a correlation between log (O/H) and the H I deficiency parameter DEF for the two clusters analyzed together. Our results suggest that similar environmental mechanisms are driving the heavy element enhancement in both clusters.

  19. Radio luminosity function of brightest cluster galaxies

    NASA Astrophysics Data System (ADS)

    Yuan, Z. S.; Han, J. L.; Wen, Z. L.

    2016-08-01

    By cross-matching the currently largest optical catalogue of galaxy clusters and the NVSS radio survey data base, we obtain a large complete sample of brightest cluster galaxies (BCGs) in the redshift range of 0.05 < z ≤ 0.45, which have radio emission and redshift information. We confirm that more powerful radio BCGs tend to be these optically very bright galaxies located in more relaxed clusters. We derived the radio luminosity functions of the largest sample of radio BCGs, and find that the functions depend on the optical luminosity of BCGs and the dynamic state of galaxy clusters. However, the radio luminosity function does not show significant evolution with redshift.

  20. The Formation of Galaxies and Clusters.

    ERIC Educational Resources Information Center

    Gregory, Stephen; Morrison, Nancy D.

    1985-01-01

    Summarizes recent research on the formation of galaxies and clusters, focusing on research examining how the materials in galaxies seen today separated from the universal expansion and collapsed into stable bodies. A list of six nontechnical books and articles for readers with less background is included. (JN)

  1. A catalog of isolated galaxy pairs with accurate radial velocities

    NASA Astrophysics Data System (ADS)

    Chamaraux, P.; Nottale, L.

    2016-07-01

    The present paper is devoted to the construction of a catalog of isolated galaxy pairs from the Uppsala Galaxy Catalog (UGC), using accurate radial velocities. The UGC lists 12 921 galaxies to δ > -2°30' and is complete to an apparent diameter of 1'. The criteria used to define the isolated galaxy pairs are based on velocity, interdistance, reciprocity and isolation information. A peculiar investigation has allowed to gather very accurate radial velocities for pair members, from high quality HI and optical measurements (median uncertainty on velocity differences 10 kms-1). Our final catalog contains 1005 galaxy pairs with ρ > 2.5, of which 509 have ρ > 5 (50% of the pairs, i.e. 8%of the UGC galaxies) and 273 are highly isolated with ρ > 10 (27% of the pairs, i.e. 4% of the UGC galaxies). Some global properties of the pair catalog are given.

  2. On the dust content of galaxy clusters

    NASA Astrophysics Data System (ADS)

    Gutiérrez, C. M.; López-Corredoira, M.

    2014-11-01

    Context. Most of the contribution to dust emission in clusters of galaxies comes from late-type galaxies. However, several ejection processes of material from these galaxies could introduce dust in the intracluster media. Even a relatively low abundance of this dust could act as an efficient cooling agent and have a relevant role in the evolution of clusters. Aims: We present a study to estimate the dust content in galaxy clusters. Methods: This was done by using one the most complete existing catalogues of galaxy clusters based on Sloan Digital Sky Survey (SDSS) data and following two methods: the first one compares the colours of samples of galaxies in the background of clusters with those of galaxies in the field. Using this method, we have explored clustercentric distances up to 6 Mpc; this covers at least 2 × R200 for all the clusters in the sample. The galaxies used in this first method were selected from the SDSS-DR9, among those having reliable photometry and accurate estimation of photometric redshifts. Using the colours of background galaxies, we analyzed several regions at galactic latitudes | b | > 20° and >50°. The results are largely independent of the galactic cut applied. At | b | > 20°, the sample contains 56 985 clusters in the redshift range 0.05 galaxies. The second method computes the contribution of dust in clusters of galaxies to the far infrared sky. That is estimated indirectly by measuring the effect of clusters in the E(B - V) extinction map. Results: Using the first method, we did not find any dependence with clustercentric distance in the colours of background galaxies. As representative of the whole results, the surface integral of the excess of colour g - i in three rings centred in the clusters and with radius 0-1, 0-2, and 0-3 Mpc is -3.7 ± 3.5, + 3.2 ± 6.8, and -4.5 ± 10.1 milimag Mpc2, respectively. This allows us to constrain the mass of dust in the intracluster media

  3. The kinematics and dynamics of the rich cluster of galaxies Abell 539

    NASA Technical Reports Server (NTRS)

    Ostriker, Eve C.; Huchra, John P.; Geller, Margaret J.; Kurtz, Michael J.

    1988-01-01

    A sample of 289 redshifts within 10 deg of the center of the cluster A539 have been obtained in order to investigate the cluster kinematics and dynamics. Within 1 Mpc of the center, the physical parameters of A539 are found to be typical of those of rich clusters. It is shown that early-type galaxies are more concentrated toward the cluster center and that the velocity distributions of early-type and late-type galaxies differ marginally.

  4. Cooling Flow Spectra in Ginga Galaxy Clusters

    NASA Technical Reports Server (NTRS)

    White, Raymond E., III

    1997-01-01

    The primary focus of this research project has been a joint analysis of Ginga LAC and Einstein SSS X-ray spectra of the hot gas in galaxy clusters with cooling flows is reported. We studied four clusters (A496, A1795, A2142 & A2199) and found their central temperatures to be cooler than in the exterior, which is expected from their having cooling flows. More interestingly, we found central metal abundance enhancements in two of the clusters, A496 and A2142. We have been assessing whether the abundance gradients (or lack thereof) in intracluster gas is correlated with galaxy morphological gradients in the host clusters. In rich, dense galaxy clusters, elliptical and SO galaxies are generally found in the cluster cores, while spiral galaxies are found in the outskirts. If the metals observed in clusters came from proto-ellipticals and proto-S0s blowing winds, then the metal distribution in intracluster gas may still reflect the distribution of their former host galaxies. In a research project which was inspired by the success of the Ginga LAC/Einstein SSS work, we analyzed X-ray spectra from the HEAO-A2 MED and the Einstein SSS to look for temperature gradients in cluster gas. The HEAO-A2 MED was also a non-imaging detector with a large field of view compared to the SSS, so we used the differing fields of view of the two instruments to extract spatial information. We found some evidence of cool gas in the outskirts of clusters, which may indicate that the nominally isothermal mass density distributions in these clusters are steepening in the outer parts of these clusters.

  5. New Fast Lane towards Discoveries of Clusters of Galaxies Inaugurated

    NASA Astrophysics Data System (ADS)

    2003-07-01

    Space and Ground-Based Telescopes Cooperate to Gain Deep Cosmological Insights Summary Using the ESA XMM-Newton satellite, a team of European and Chilean astronomers [2] has obtained the world's deepest "wide-field" X-ray image of the cosmos to date. This penetrating view, when complemented with observations by some of the largest and most efficient ground-based optical telescopes, including the ESO Very Large Telescope (VLT), has resulted in the discovery of several large clusters of galaxies. These early results from an ambitious research programme are extremely promising and pave the way for a very comprehensive and thorough census of clusters of galaxies at various epochs. Relying on the foremost astronomical technology and with an unequalled observational efficiency, this project is set to provide new insights into the structure and evolution of the distant Universe. PR Photo 19a/03: First image from the XMM-LSS survey. PR Photo 19b/03: Zoom-in on PR Photo 19b/03. PR Photo 19c/03: XMM-Newton contour map of the probable extent of a cluster of galaxies, superimposed upon a CHFT I-band image. PR Photo 19d/03: Velocity distribution in the cluster field shown in PR Photo 19c/03. The universal web Unlike grains of sand on a beach, matter is not uniformly spread throughout the Universe. Instead, it is concentrated into galaxies which themselves congregate into clusters (and even clusters of clusters). These clusters are "strung" throughout the Universe in a web-like structure, cf. ESO PR 11/01. Our Galaxy, the Milky Way, for example, belongs to the so-called Local Group which also comprises "Messier 31", the Andromeda Galaxy. The Local Group contains about 30 galaxies and measures a few million light-years across. Other clusters are much larger. The Coma cluster contains thousands of galaxies and measures more than 20 million light-years. Another well known example is the Virgo cluster, covering no less than 10 degrees on the sky ! Clusters of galaxies are the most

  6. SUPERDENSE MASSIVE GALAXIES IN WINGS LOCAL CLUSTERS

    SciTech Connect

    Valentinuzzi, T.; D'Onofrio, M.; Fritz, J.; Poggianti, B. M.; Bettoni, D.; Fasano, G.; Moretti, A.; Omizzolo, A.; Varela, J.; Cava, A.; Couch, W. J.; Dressler, A.; Moles, M.; Kjaergaard, P.; Vanzella, E.

    2010-03-20

    Massive quiescent galaxies at z > 1 have been found to have small physical sizes, and hence to be superdense. Several mechanisms, including minor mergers, have been proposed for increasing galaxy sizes from high- to low-z. We search for superdense massive galaxies in the WIde-field Nearby Galaxy-cluster Survey (WINGS) of X-ray selected galaxy clusters at 0.04 < z < 0.07. We discover a significant population of superdense massive galaxies with masses and sizes comparable to those observed at high redshift. They approximately represent 22% of all cluster galaxies more massive than 3 x 10{sup 10} M{sub sun}, are mostly S0 galaxies, have a median effective radius (R{sub e} ) = 1.61 +- 0.29 kpc, a median Sersic index (n) = 3.0 +- 0.6, and very old stellar populations with a median mass-weighted age of 12.1 +- 1.3 Gyr. We calculate a number density of 2.9 x 10{sup -2} Mpc{sup -3} for superdense galaxies in local clusters, and a hard lower limit of 1.3 x 10{sup -5} Mpc{sup -3} in the whole comoving volume between z = 0.04 and z = 0.07. We find a relation between mass, effective radius, and luminosity-weighted age in our cluster galaxies, which can mimic the claimed evolution of the radius with redshift, if not properly taken into account. We compare our data with spectroscopic high-z surveys and find that-when stellar masses are considered-there is consistency with the local WINGS galaxy sizes out to z {approx} 2, while a discrepancy of a factor of 3 exists with the only spectroscopic z > 2 study. In contrast, there is strong evidence for a large evolution in radius for the most massive galaxies with M{sub *} > 4 x 10{sup 11} M{sub sun} compared to similarly massive galaxies in WINGS, i.e., the brightest cluster galaxies.

  7. On the interrelation between the surface photometric parameters and the internal velocities of galaxies

    SciTech Connect

    Kodaira, K. )

    1989-07-01

    The interrelations between the surface photometric parameters and the internal velocities are explored by means of the principal component analysis and the regression line analysis of homogeneous data for 18 elliptical and 28 spiral galaxies of moderate inclinations in the Virgo Cluster. Extremely tight correlations are found both for ellipticals and spirals, between the visual magnitude and a combined parameter involving the internal velocity and the isophotal diameter of galaxies. The physical meaning of the parameter is inferred to be a sort of phase-space density related to the basic structure of galaxies, and its empirical behavior in the diameter versus surface brightness diagram is briefly described. 26 refs.

  8. AGN feedback in galaxy clusters and groups

    NASA Astrophysics Data System (ADS)

    Hardcastle, Martin

    2016-07-01

    Mechanical feedback via Active Galactic Nuclei (AGN) jets in the centres of galaxy groups and clusters is a crucial ingredient in current models of galaxy formation and cluster evolution. Jet feedback is believed to regulate gas cooling and thus star formation in the most massive galaxies, but a robust physical understanding of this feedback mode is currently lacking. Athena will provide (1) the first kinematic measurements on relevant spatial scales of the hot gas in galaxy, group and cluster haloes as it absorbs the impact of AGN jets, and (2) vastly improved ability to map thermodynamic conditions on scales well-matched to the jets, lobes and gas disturbances produced by them. I will present new predictions of Athena's ability to measure the energetic impact of powerful jets based on our most recent set of numerical models.

  9. Massive Star Clusters in Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    Larsen, Soeren

    2015-08-01

    Dwarf galaxies are often characterized by very high globular cluster specific frequencies, in some cases exceeding that of the Milky Way by a factor of 100 or more. Moreover, the GCs are typically much more metal-poor than the bulk of the field stars, so that a substantial fraction (up to 20-25% or more) of all metal-poor stars in some dwarf galaxies are associated with GCs. The metal-poor components of these galaxies thus represent an extreme case of the "specific frequency problem". In this talk I will review the current status of our understanding of GC systems in dwarf galaxies. Particular emphasis will be placed on the implications of the high GC specific frequencies for the amount of mass loss the clusters could have experienced and the constraints this provides on theories for the origin of multiple populations in globular clusters.

  10. Low X-Ray Luminosity Galaxy Clusters: Main Goals, Sample Selection, Photometric and Spectroscopic Observations

    NASA Astrophysics Data System (ADS)

    Nilo Castellón, José Luis; Alonso, M. Victoria; García Lambas, Diego; Valotto, Carlos; O'Mill, Ana Laura; Cuevas, Héctor; Carrasco, Eleazar R.; Ramírez, Amelia; Astudillo, José M.; Ramos, Felipe; Jaque Arancibia, Marcelo; Ulloa, Natalie; Órdenes, Yasna

    2016-06-01

    We present our study of 19 low X-ray luminosity galaxy clusters (L{}X ˜ 0.5-45 × 1043 erg s-1), selected from the ROSAT Position Sensitive Proportional Counters Pointed Observations and the revised version of Mullis et al. in the redshift range of 0.16-0.7. This is the introductory paper of a series presenting the sample selection, photometric and spectroscopic observations, and data reduction. Photometric data in different passbands were taken for eight galaxy clusters at Las Campanas Observatory; three clusters at Cerro Tololo Interamerican Observatory; and eight clusters at the Gemini Observatory. Spectroscopic data were collected for only four galaxy clusters using Gemini telescopes. Using the photometry, the galaxies were defined based on the star-galaxy separation taking into account photometric parameters. For each galaxy cluster, the catalogs contain the point-spread function and aperture magnitudes of galaxies within the 90% completeness limit. They are used together with structural parameters to study the galaxy morphology and to estimate photometric redshifts. With the spectroscopy, the derived galaxy velocity dispersion of our clusters ranged from 507 km s-1 for [VMF98]022 to 775 km s-1 for [VMF98]097 with signs of substructure. Cluster membership has been extensively discussed taking into account spectroscopic and photometric redshift estimates. In this sense, members are the galaxies within a projected radius of 0.75 Mpc from the X-ray emission peak and with clustercentric velocities smaller than the cluster velocity dispersion or 6000 km s-1, respectively. These results will be used in forthcoming papers to study, among the main topics, the red cluster sequence, blue cloud and green populations, the galaxy luminosity function, and cluster dynamics.

  11. SUBMILLIMETER GALAXY NUMBER COUNTS AND MAGNIFICATION BY GALAXY CLUSTERS

    SciTech Connect

    Lima, Marcos; Jain, Bhuvnesh; Devlin, Mark; Aguirre, James

    2010-07-01

    We present an analytical model that reproduces measured galaxy number counts from surveys in the wavelength range of 500 {mu}m-2 mm. The model involves a single high-redshift galaxy population with a Schechter luminosity function that has been gravitationally lensed by galaxy clusters in the mass range 10{sup 13}-10{sup 15} M{sub sun}. This simple model reproduces both the low-flux and the high-flux end of the number counts reported by the BLAST, SCUBA, AzTEC, and South Pole Telescope (SPT) surveys. In particular, our model accounts for the most luminous galaxies detected by SPT as the result of high magnifications by galaxy clusters (magnification factors of 10-30). This interpretation implies that submillimeter (submm) and millimeter surveys of this population may prove to be a useful addition to ongoing cluster detection surveys. The model also implies that the bulk of submm galaxies detected at wavelengths larger than 500 {mu}m lie at redshifts greater than 2.

  12. ON THE BARYON FRACTIONS IN CLUSTERS AND GROUPS OF GALAXIES

    SciTech Connect

    Dai Xinyu; Bregman, Joel N.; Kochanek, Christopher S.; Rasia, Elena

    2010-08-10

    We present the baryon fractions of 2MASS groups and clusters as a function of cluster richness using total and gas masses measured from stacked ROSAT X-ray data and stellar masses estimated from the infrared galaxy catalogs. We detect X-ray emission even in the outskirts of clusters, beyond r {sub 200} for richness classes with X-ray temperatures above 1 keV. This enables us to more accurately determine the total gas mass in these groups and clusters. We find that the optically selected groups and clusters have flatter temperature profiles and higher stellar-to-gas mass ratios than the individually studied, X-ray bright clusters. We also find that the stellar mass in poor groups with temperatures below 1 keV is comparable to the gas mass in these systems. Combining these results with individual measurements for clusters, groups, and galaxies from the literature, we find a break in the baryon fraction at {approx}1 keV. Above this temperature, the baryon fraction scales with temperature as f{sub b} {proportional_to} T {sup 0.20{+-}0.03}. We see significantly smaller baryon fractions below this temperature and the baryon fraction of poor groups joins smoothly onto that of systems with still shallower potential wells such as normal and dwarf galaxies where the baryon fraction scales with the inferred velocity dispersion as f{sub b} {proportional_to} {sigma}{sup 1.6}. The small scatter in the baryon fraction at any given potential well depth favors a universal baryon loss mechanism and a preheating model for the baryon loss. The scatter is, however, larger for less massive systems. Finally, we note that although the broken power-law relation can be inferred from data points in the literature alone, the consistency between the baryon fractions for poor groups and massive galaxies inspires us to fit the two categories of objects (galaxies and clusters) with one relation.

  13. Studying Dark Energy with Galaxy Cluster Surveys

    NASA Astrophysics Data System (ADS)

    Mohr, J.; Majumdar, S.

    2003-05-01

    Galaxy cluster surveys provide a powerful means of studying the amount and nature of the dark energy. Cluster surveys are complementary to studies using supernova distance estimates, because the cosmological parameter degeneracies are quite different. The redshift distribution of detected clusters in a deep, large solid angle survey is very sensitive to the dark energy equation of state, but robust constraints require mass--observable relations that connect cluster halo mass to observables such as the X-ray luminosity, Sunyaev-Zel'dovich effect distortion, galaxy light or weak lensing shear. Observed regularity in the cluster population and the application of multiple, independent mass estimators provide evidence that these scaling relations exist in the local and intermediate redshift universe. Large cluster surveys contain enough information to study the dark energy and solve for these scaling relations and their evolution with redshift. This self--calibrating nature of galaxy cluster surveys provides a level of robustness that is extremely attractive. Cosmological constraints from a survey can be improved by including more than just the redshift distribution. Limited followup of as few as 1% of the surveyed clusters to make detailed mass measurements improves the cosmological constraints. Including constraints on the mass function at each redshift provides additional power in solving for the evolution of the mass--observable relation. An analysis of the clustering of the surveyed clusters provides additional cosmological discriminating power. There are several planned or proposed cluster surveys that will take place over the next decade. Observational challenges include estimating cluster redshifts and understanding the survey completeness. These challenges vary with wavelength regime, suggesting that multiwavelength surveys provide the most promising avenue for precise galaxy cluster studies of the dark energy. This work is supported in part by the NASA Long

  14. Major Cluster Mergers and the Location of the Brightest Cluster Galaxy

    NASA Astrophysics Data System (ADS)

    Martel, Hugo; Robichaud, Fidèle; Barai, Paramita

    2014-05-01

    Using a large N-body cosmological simulation combined with a subgrid treatment of galaxy formation, merging, and tidal destruction, we study the formation and evolution of the galaxy and cluster population in a comoving volume (100 Mpc)3 in a ΛCDM universe. At z = 0, our computational volume contains 1788 clusters with mass M cl > 1.1 × 1012 M ⊙, including 18 massive clusters with M cl > 1014 M ⊙. It also contains 1, 088, 797 galaxies with mass M gal >= 2 × 109 M ⊙ and luminosity L > 9.5 × 105 L ⊙. For each cluster, we identified the brightest cluster galaxy (BCG). We then computed two separate statistics: the fraction f BNC of clusters in which the BCG is not the closest galaxy to the center of the cluster in projection, and the ratio Δv/σ, where Δv is the difference in radial velocity between the BCG and the whole cluster and σ is the radial velocity dispersion of the cluster. We found that f BNC increases from 0.05 for low-mass clusters (M cl ~ 1012 M ⊙) to 0.5 for high-mass clusters (M cl > 1014 M ⊙) with very little dependence on cluster redshift. Most of this result turns out to be a projection effect and when we consider three-dimensional distances instead of projected distances, f BNC increases only to 0.2 at high-cluster mass. The values of Δv/σ vary from 0 to 1.8, with median values in the range 0.03-0.15 when considering all clusters, and 0.12-0.31 when considering only massive clusters. These results are consistent with previous observational studies and indicate that the central galaxy paradigm, which states that the BCG should be at rest at the center of the cluster, is usually valid, but exceptions are too common to be ignored. We built merger trees for the 18 most massive clusters in the simulation. Analysis of these trees reveal that 16 of these clusters have experienced 1 or several major or semi-major mergers in the past. These mergers leave each cluster in a non-equilibrium state, but eventually the cluster settles into an

  15. Major cluster mergers and the location of the brightest cluster galaxy

    SciTech Connect

    Martel, Hugo; Robichaud, Fidèle; Barai, Paramita

    2014-05-10

    Using a large N-body cosmological simulation combined with a subgrid treatment of galaxy formation, merging, and tidal destruction, we study the formation and evolution of the galaxy and cluster population in a comoving volume (100 Mpc){sup 3} in a ΛCDM universe. At z = 0, our computational volume contains 1788 clusters with mass M {sub cl} > 1.1 × 10{sup 12} M {sub ☉}, including 18 massive clusters with M {sub cl} > 10{sup 14} M {sub ☉}. It also contains 1, 088, 797 galaxies with mass M {sub gal} ≥ 2 × 10{sup 9} M {sub ☉} and luminosity L > 9.5 × 10{sup 5} L {sub ☉}. For each cluster, we identified the brightest cluster galaxy (BCG). We then computed two separate statistics: the fraction f {sub BNC} of clusters in which the BCG is not the closest galaxy to the center of the cluster in projection, and the ratio Δv/σ, where Δv is the difference in radial velocity between the BCG and the whole cluster and σ is the radial velocity dispersion of the cluster. We found that f {sub BNC} increases from 0.05 for low-mass clusters (M {sub cl} ∼ 10{sup 12} M {sub ☉}) to 0.5 for high-mass clusters (M {sub cl} > 10{sup 14} M {sub ☉}) with very little dependence on cluster redshift. Most of this result turns out to be a projection effect and when we consider three-dimensional distances instead of projected distances, f {sub BNC} increases only to 0.2 at high-cluster mass. The values of Δv/σ vary from 0 to 1.8, with median values in the range 0.03-0.15 when considering all clusters, and 0.12-0.31 when considering only massive clusters. These results are consistent with previous observational studies and indicate that the central galaxy paradigm, which states that the BCG should be at rest at the center of the cluster, is usually valid, but exceptions are too common to be ignored. We built merger trees for the 18 most massive clusters in the simulation. Analysis of these trees reveal that 16 of these clusters have experienced 1 or several major or semi

  16. The Virgo Cluster of Galaxies in the Making

    NASA Astrophysics Data System (ADS)

    2004-10-01

    VLT Observations of Planetary Nebulae Confirm the Dynamical Youth of Virgo [1] Summary An international team of astronomers [2] has succeeded in measuring with high precision the velocities of a large number of planetary nebulae [3] in the intergalactic space within the Virgo Cluster of galaxies. For this they used the highly efficient FLAMES spectrograph [4] on the ESO Very Large Telescope at the Paranal Observatory (Chile). These planetary nebulae stars free floating in the otherwise seemingly empty space between the galaxies of large clusters can be used as "probes" of the gravitational forces acting within these clusters. They trace the masses, visible as well as invisible, within these regions. This, in turn, allows astronomers to study the formation history of these large bound structures in the universe. The accurate velocity measurements of 40 of these stars confirm the view that Virgo is a highly non-uniform galaxy cluster, consisting of several subunits that have not yet had time to come to equilibrium. These new data clearly show that the Virgo Cluster of galaxies is still in its making. They also prove for the first time that one of the bright galaxies in the region scrutinized, Messier 87, has a very extended halo of stars, reaching out to at least 65 kpc. This is more than twice the size of our own galaxy, the Milky Way. PR Photo 29a/04: Velocity Measurements of Forty Intracluster Planetary Nebulae (FLAMES/VLT) PR Photo 29b/04: Intracluster Planetary Nebulae in the SUC field in the Virgo Cluster (Digital Sky Survey) A young cluster At a distance of approximately 50 million light-years, the Virgo Cluster is the nearest galaxy cluster. It is located in the zodiacal constellation Virgo (The Virgin) and contains many hundreds of galaxies, ranging from giant and massive elliptical galaxies and spirals like our own Milky Way, to dwarf galaxies, hundreds of times smaller than their big brethren. French astronomer Charles Messier entered 16 members of the

  17. Chandra Observation of Abell 1142: A Cool-core Cluster Lacking a Central Brightest Cluster Galaxy?

    NASA Astrophysics Data System (ADS)

    Su, Yuanyuan; Buote, David A.; Gastaldello, Fabio; van Weeren, Reinout

    2016-04-01

    Abell 1142 is a low-mass galaxy cluster at low redshift containing two comparable brightest cluster galaxies (BCGs) resembling a scaled-down version of the Coma Cluster. Our Chandra analysis reveals an X-ray emission peak, roughly 100 kpc away from either BCG, which we identify as the cluster center. The emission center manifests itself as a second beta-model surface brightness component distinct from that of the cluster on larger scales. The center is also substantially cooler and more metal-rich than the surrounding intracluster medium (ICM), which makes Abell 1142 appear to be a cool-core cluster. The redshift distribution of its member galaxies indicates that Abell 1142 may contain two subclusters, each of which contain one BCG. The BCGs are merging at a relative velocity of ≈1200 km s-1. This ongoing merger may have shock-heated the ICM from ≈2 keV to above 3 keV, which would explain the anomalous LX-TX scaling relation for this system. This merger may have displaced the metal-enriched “cool core” of either of the subclusters from the BCG. The southern BCG consists of three individual galaxies residing within a radius of 5 kpc in projection. These galaxies should rapidly sink into the subcluster center due to the dynamical friction of a cuspy cold dark matter halo.

  18. Chandra Observation of Abell 1142: A Cool-core Cluster Lacking a Central Brightest Cluster Galaxy?

    NASA Astrophysics Data System (ADS)

    Su, Yuanyuan; Buote, David A.; Gastaldello, Fabio; van Weeren, Reinout

    2016-04-01

    Abell 1142 is a low-mass galaxy cluster at low redshift containing two comparable brightest cluster galaxies (BCGs) resembling a scaled-down version of the Coma Cluster. Our Chandra analysis reveals an X-ray emission peak, roughly 100 kpc away from either BCG, which we identify as the cluster center. The emission center manifests itself as a second beta-model surface brightness component distinct from that of the cluster on larger scales. The center is also substantially cooler and more metal-rich than the surrounding intracluster medium (ICM), which makes Abell 1142 appear to be a cool-core cluster. The redshift distribution of its member galaxies indicates that Abell 1142 may contain two subclusters, each of which contain one BCG. The BCGs are merging at a relative velocity of ≈1200 km s‑1. This ongoing merger may have shock-heated the ICM from ≈2 keV to above 3 keV, which would explain the anomalous LX–TX scaling relation for this system. This merger may have displaced the metal-enriched “cool core” of either of the subclusters from the BCG. The southern BCG consists of three individual galaxies residing within a radius of 5 kpc in projection. These galaxies should rapidly sink into the subcluster center due to the dynamical friction of a cuspy cold dark matter halo.

  19. A combined optical/X-ray study of the Galaxy cluster Abell 2256

    NASA Technical Reports Server (NTRS)

    Fabricant, Daniel G.; Kent, Stephen M.; Kurtz, Michael J.

    1989-01-01

    The dynamics of Abell 2256 is investigated by combining X-ray observations of the intracluster gas with optical observations of the galaxy distribution and kinematics. Magnitudes and positions are presented for 172 galaxies and new redshifts for 75. Abell 2256 is similar to the Coma Cluster in its X-ray luminosity, mass, and galaxy density. Both the X-ray surface brightness and the galaxy surface density distributions exhibit an elliptical morphology. The radial galaxy distribution is steeper than the density profile of the X-ray-emitting gas, yet the galaxy velocity dispersion is higher than the equivalent value for the gas. Under the simplest assumptions that the galaxy velocity distribution is isotropic and the gas is isothermal, the galaxies and gas cannot be in hydrostatic equilibrium in a common gravitational potential. Models consistent with available data have mass-to-light ratios which increase with radius and galaxy orbits that are anisotropic with a radial bias.

  20. The Evolving Shape of Galaxy Clusters

    NASA Astrophysics Data System (ADS)

    Just, Dennis W.; Yee, H. K. C.; Muzzin, Adam; Wilson, Gillian; Gilbank, David G.; Gladders, Michael

    2016-10-01

    We present the first measurement of the evolution of the apparent projected shape of galaxy clusters from 0.2<~ z<~2. We measure the ellipticities (ɛcl) of homogeneously selected galaxy clusters over this wide redshift range. We confirm the predictions of N-body simulations that clusters are more elongated at higher redshift, finding the mean projected ellipticity changes linearly from 0.36+/-0.01 to 0.25+/-0.01 over that range. The fraction of relaxed clusters (defined as having ɛ cl <0.2) is 9+5-3% at z~1.8, steadily increasing to 42+7-6% by z~0.3. Because more spherical clusters have a higher degree of virialization, our result shows significant evolution in the degree of cluster virialization over cosmic time.

  1. A Cluster and a Sea of Galaxies

    NASA Astrophysics Data System (ADS)

    2010-05-01

    A new wide-field image released today by ESO displays many thousands of distant galaxies, and more particularly a large group belonging to the massive galaxy cluster known as Abell 315. As crowded as it may appear, this assembly of galaxies is only the proverbial "tip of the iceberg", as Abell 315 - like most galaxy clusters - is dominated by dark matter. The huge mass of this cluster deflects light from background galaxies, distorting their observed shapes slightly. When looking at the sky with the unaided eye, we mostly only see stars within our Milky Way galaxy and some of its closest neighbours. More distant galaxies are just too faint to be perceived by the human eye, but if we could see them, they would literally cover the sky. This new image released by ESO is both a wide-field and long-exposure one, and reveals thousands of galaxies crowding an area on the sky roughly as large as the full Moon. These galaxies span a vast range of distances from us. Some are relatively close, as it is possible to distinguish their spiral arms or elliptical halos, especially in the upper part of the image. The more distant appear just like the faintest of blobs - their light has travelled through the Universe for eight billion years or more before reaching Earth. Beginning in the centre of the image and extending below and to the left, a concentration of about a hundred yellowish galaxies identifies a massive galaxy cluster, designated with the number 315 in the catalogue compiled by the American astronomer George Abell in 1958 [1]. The cluster is located between the faint, red and blue galaxies and the Earth, about two billion light-years away from us. It lies in the constellation of Cetus (the Whale). Galaxy clusters are some of the largest structures in the Universe held together by gravity. But there is more in these structures than the many galaxies we can see. Galaxies in these giants contribute to only ten percent of the mass, with hot gas in between galaxies

  2. Dynamics & Morphology of Coma Cluster Galaxies

    NASA Astrophysics Data System (ADS)

    Beijersbergen, M.; van der Hulst, J. M.

    The principal aim of this project is to explore the link between the cluster and its environment, and to study the effects that changes in environment have on the properties of galaxies. Coma, the richest of the nearby clusters, appears to be a close equivalent to clusters at higher redshift. The most remarkable similarity is the presence of blue disk galaxies and galaxies with E+A type spectra, making Coma the perfect link between nearby and distant clusters. Despite numerous observations, many aspects of both the dynamics of the Coma cluster and of its galaxy populations remain unexplained. One of the most notable pieces of information that is as yet unavailable, is a proper, unbiased HI survey of the entire Coma area. The few pointed observations that have been done show a variety in HI properties: stripped disks, blue disk galaxies with quite a range in HI content and galaxies with low surface brightness companions. We have used the Westerbork Synthesis Radio Telescope (WSRT) to perform a blind survey of galaxies in Coma in the redshifted HI line. We have covered an area of 4.6 square degrees with 17 MHz bandwidth in 432 hours of total integration time. This allows us to study the HI properties as function of environment and assess the importance of merging and stripping. The HI observations will be used in combination with optical data from the wide field camera on the Isaac Newton Telescope (INT) to address a large number of interesting problems. Our data sets are unrivalled by what is available for any other cluster and will greatly enhance the ability to study the structure and dynamics of Coma. Here, I will discuss the data and the status of this ongoing project.

  3. Tidally Induced Bars of Galaxies in Clusters

    NASA Astrophysics Data System (ADS)

    Łokas, Ewa L.; Ebrová, Ivana; del Pino, Andrés; Sybilska, Agnieszka; Athanassoula, E.; Semczuk, Marcin; Gajda, Grzegorz; Fouquet, Sylvain

    2016-08-01

    Using N-body simulations, we study the formation and evolution of tidally induced bars in disky galaxies in clusters. Our progenitor is a massive, late-type galaxy similar to the Milky Way, composed of an exponential disk and a Navarro-Frenk-White dark matter halo. We place the galaxy on four different orbits in a Virgo-like cluster and evolve it for 10 Gyr. As a reference case, we also evolve the same model in isolation. Tidally induced bars form on all orbits soon after the first pericenter passage and survive until the end of the evolution. They appear earlier, are stronger and longer, and have lower pattern speeds for tighter orbits. Only for the tightest orbit are the properties of the bar controlled by the orientation of the tidal torque from the cluster at pericenter. The mechanism behind the formation of the bars is the angular momentum transfer from the galaxy stellar component to its halo. All of the bars undergo extended periods of buckling instability that occur earlier and lead to more pronounced boxy/peanut shapes when the tidal forces are stronger. Using all simulation outputs of galaxies at different evolutionary stages, we construct a toy model of the galaxy population in the cluster and measure the average bar strength and bar fraction as a function of clustercentric radius. Both are found to be mildly decreasing functions of radius. We conclude that tidal forces can trigger bar formation in cluster cores, but not in the outskirts, and thus can cause larger concentrations of barred galaxies toward the cluster center.

  4. Quenching star formation in cluster galaxies

    NASA Astrophysics Data System (ADS)

    Taranu, Dan S.; Hudson, Michael J.; Balogh, Michael L.; Smith, Russell J.; Power, Chris; Oman, Kyle A.; Krane, Brad

    2014-05-01

    In order to understand the processes that quench star formation in cluster galaxies, we construct a library of subhalo orbits drawn from Λ cold dark matter cosmological N-body simulations of four rich clusters. We combine these orbits with models of star formation followed by environmental quenching, comparing model predictions with observed bulge and disc colours and stellar absorption line-strength indices of luminous cluster galaxies. Models in which the bulge stellar populations depend only on the galaxy subhalo mass while the disc is quenched upon infall are acceptable fits to the data. An exponential disc quenching time-scale of 3-3.5 Gyr is preferred. Quenching in lower mass groups prior to infall (`pre-processing') provides better fits, with similar quenching time-scales. Models with short (≲1 Gyr) quenching time-scales yield excessively steep cluster-centric gradients in disc colours and Balmer line indices, even if quenching is delayed for several Gyr. The data slightly prefer models where quenching occurs only for galaxies falling within ˜0.5r200. These results imply that the environments of rich clusters must impact star formation rates of infalling galaxies on relatively long time-scales, indicative of gentler quenching mechanisms such as slow `strangulation' over more rapid ram-pressure stripping.

  5. HUBBLE SPIES GLOBULAR CLUSTER IN NEIGHBORING GALAXY

    NASA Technical Reports Server (NTRS)

    2002-01-01

    Hubble Space Telescope has captured a view of a globular cluster called G1, a large, bright ball of light in the center of the photograph consisting of at least 300,000 old stars. G1, also known as Mayall II, orbits the Andromeda galaxy (M31), the nearest major spiral galaxy to our Milky Way. Located 130,000 light-years from Andromeda's nucleus, G1 is the brightest globular cluster in the Local Group of galaxies. The Local Group consists of about 20 nearby galaxies, including the Milky Way. The crisp image is comparable to ground-based telescope views of similar clusters orbiting the Milky Way. The Andromeda cluster, however, is nearly 100 times farther away. A glimpse into the cluster's finer details allow astronomers to see its fainter helium-burning stars whose temperatures and brightnesses show that this cluster in Andromeda and the oldest Milky Way clusters have approximately the same age. These clusters probably were formed shortly after the beginning of the universe, providing astronomers with a record of the earliest era of galaxy formation. During the next two years, astronomers will use Hubble to study about 20 more globular clusters in Andromeda. The color picture was assembled from separate images taken in visible and near-infrared wavelengths taken in July of 1994. CREDIT: Michael Rich, Kenneth Mighell, and James D. Neill (Columbia University), and Wendy Freedman (Carnegie Observatories), and NASA Image files in GIF and JPEG format and captions may be accessed on Internet via anonymous ftp from oposite.stsci.edu in /pubinfo.

  6. Brightest Cluster Galaxies and Dry Mergers

    NASA Astrophysics Data System (ADS)

    Deng, Z. G.; Liu, F. S.; Xia, X. Y.; Mao, S.

    2008-01-01

    Photometric properties of the early type Brightest Cluster Galaxies (BCGs) has been investigated for a sample of 85 BCGs with redshifts less than 0.1 selected from the C4 cluster catalogue. The results are compared to those obtained from a sample of elliptical galaxies chosen with similar apparent magnitude and redshift ranges. We find that BCGs have steeper size-luminosity (R~Lα) and Faber-Jackson (L~σβ) relations than the bulk of early type galaxies. The differences in the scaling relations suggest that the dynamical structure and formation route of BCGs may be different from the bulk of early type galaxies, in particular dry (dissipationless) mergers may play a more important role in their formation.

  7. Far-infrared properties of cluster galaxies

    NASA Technical Reports Server (NTRS)

    Bicay, M. D.; Giovanelli, R.

    1987-01-01

    Far-infrared properties are derived for a sample of over 200 galaxies in seven clusters: A262, Cancer, A1367, A1656 (Coma), A2147, A2151 (Hercules), and Pegasus. The IR-selected sample consists almost entirely of IR normal galaxies, with Log of L(FIR) = 9.79 solar luminosities, Log of L(FIR)/L(B) = 0,79, and Log of S(100 microns)/S(60 microns) = 0.42. None of the sample galaxies has Log of L(FIR) greater than 11.0 solar luminosities, and only one has a FIR-to-blue luminosity ratio greater than 10. No significant differences are found in the FIR properties of HI-deficient and HI-normal cluster galaxies.

  8. The peculiar velocities of rich clusters in the hot and cold dark matter scenarios

    NASA Technical Reports Server (NTRS)

    Rhee, George F.; West, Michael J.; Villumsen, Jens V.

    1993-01-01

    We present the results of a study of the peculiar velocities of rich clusters of galaxies. The peculiar motion of rich clusters in various cosmological scenarios is of interest for a number of reasons. Observationally, one can measure the peculiar motion of clusters to greater distances than galaxies because cluster peculiar motions can be determined to greater accuracy. One can also test the slope of distance indicator relations using clusters to see if galaxy properties vary with environment. We have used N-body simulations to measure the amplitude and rms cluster peculiar velocity as a function of bias parameter in the hot and cold dark matter scenarios. In addition to measuring the mean and rms peculiar velocity of clusters in the two models, we determined whether the peculiar velocity vector of a given cluster is well aligned with the gravity vector due to all the particles in the simulation and the gravity vector due to the particles present only in the clusters. We have investigated the peculiar velocities of rich clusters of galaxies in the cold dark matter and hot dark matter galaxy formation scenarios. We have derived peculiar velocities and associated errors for the scenarios using four values of the bias parameter ranging from b = 1 to b = 2.5. The growth of the mean peculiar velocity with scale factor has been determined and compared to that predicted by linear theory. In addition, we have compared the orientation of force and velocity in these simulations to see if a program such as that proposed by Bertschinger and Dekel (1989) for elliptical galaxy peculiar motions can be applied to clusters. The method they describe enables one to recover the density field from large scale redshift distance samples. The method makes it possible to do this when only radial velocities are known by assuming that the velocity field is curl free. Our analysis suggests that this program if applied to clusters is only realizable for models with a low value of the bias

  9. Hydrodynamic simulation of non-thermal pressure profiles of galaxy clusters

    SciTech Connect

    Nelson, Kaylea; Nagai, Daisuke; Lau, Erwin T.

    2014-09-01

    Cosmological constraints from X-ray and microwave observations of galaxy clusters are subjected to systematic uncertainties. Non-thermal pressure support due to internal gas motions in galaxy clusters is one of the major sources of astrophysical uncertainties. Using a mass-limited sample of galaxy clusters from a high-resolution hydrodynamical cosmological simulation, we characterize the non-thermal pressure fraction profile and study its dependence on redshift, mass, and mass accretion rate. We find that the non-thermal pressure fraction profile is universal across redshift when galaxy cluster radii are defined with respect to the mean matter density of the universe instead of the commonly used critical density. We also find that the non-thermal pressure is predominantly radial, and the gas velocity anisotropy profile exhibits strong universality when galaxy cluster radii are defined with respect to the mean matter density of the universe. However, we find that the non-thermal pressure fraction is strongly dependent on the mass accretion rate of the galaxy cluster. We provide fitting formulae for the universal non-thermal pressure fraction and velocity anisotropy profiles of gas in galaxy clusters, which should be useful in modeling astrophysical uncertainties pertinent to using galaxy clusters as cosmological probes.

  10. Testing Cosmological Models with Clusters of Galaxies

    NASA Astrophysics Data System (ADS)

    Böhringer, Hans; Schuecker, Peter

    2003-05-01

    Galaxy clusters are ideal probes for the large-scale structure of the Universe and for the tests of cosmological models. We use, REFLEX, the currently largest and best defined cluster X-ray survey to illustrate this application of galaxy cluster studies. Based on this survey of X-ray selected clusters of galaxies we determine statistical properties of the galaxy cluster population, their spatial correlation, and the density fluctuation power spectrum of the cosmic matter distribution on large scales up to about 1 Gpc. Comparing these results with predictions of cosmological models we obtain tight constrains for the matter density parameter of the Universe, consistent with the combined results from observations of the microwave background anisotropies and distant type Ia supernovae. The only difference between the present results and the ``concordance model'' is a low value for the σ8-normalization. Exploring the parameter space of the cosmic matter density and the equation of state parameter of dark energy most favoured by the combined observations of REFLEX clusters and distant type Ia supernovae we find that the conventional cosmological constant model is best consistent with the observational data.

  11. Clusters of galaxies: a cosmological probe.

    PubMed

    Mushotzky, Richard

    2002-09-15

    The constraints on cosmological parameters presently obtained and those that can be obtained from X-ray cluster surveys are presented. Extremely strong bounds on the values of Omega, Lambda, sigma(8) and the power spectrum of fluctuations, as well as constraints on the equation of state of dark energy, can be determined. Recent Advanced Satellite for Cosmology and Astrophysics and XMM results on the chemical composition of clusters show that the Fe abundance is not universal, but is correlated with cluster mass and central gas density. The Si, S and Fe abundances do not resemble those seen in Milky Way Halo stars or those in the Lyman-limit galaxies. The XMM RGS abundances for gas in elliptical galaxies are subsolar and the abundance pattern is not alpha-element rich, in contradiction with all models of elliptical-galaxy gas abundances. PMID:12804244

  12. Clusters of galaxies: a cosmological probe.

    PubMed

    Mushotzky, Richard

    2002-09-15

    The constraints on cosmological parameters presently obtained and those that can be obtained from X-ray cluster surveys are presented. Extremely strong bounds on the values of Omega, Lambda, sigma(8) and the power spectrum of fluctuations, as well as constraints on the equation of state of dark energy, can be determined. Recent Advanced Satellite for Cosmology and Astrophysics and XMM results on the chemical composition of clusters show that the Fe abundance is not universal, but is correlated with cluster mass and central gas density. The Si, S and Fe abundances do not resemble those seen in Milky Way Halo stars or those in the Lyman-limit galaxies. The XMM RGS abundances for gas in elliptical galaxies are subsolar and the abundance pattern is not alpha-element rich, in contradiction with all models of elliptical-galaxy gas abundances.

  13. Large-scale peculiar velocities through the galaxy luminosity function at z ~ 0.1

    NASA Astrophysics Data System (ADS)

    Feix, Martin; Nusser, Adi; Branchini, Enzo

    2016-10-01

    Peculiar motion introduces systematic variations in the observed luminosity distribution of galaxies. This allows one to constrain the cosmic peculiar velocity field from large galaxy redshift surveys. Using around half a million galaxies from the SDSS Data Release 7 at z ~ 0.1, we demonstrate the applicability of this approach to large datasets and obtain bounds on peculiar velocity moments and σ8, the amplitude of the linear matter power spectrum. Our results are in good agreement with the ΛCDM model and consistent with the previously reported ~ 1% zero-point tilt in the SDSS photometry. Finally, we discuss the prospects of constraining the growth rate of density perturbations by reconstructing the full linear velocity field from the observed galaxy clustering in redshift space.

  14. A Cluster and a Sea of Galaxies

    NASA Astrophysics Data System (ADS)

    2010-05-01

    A new wide-field image released today by ESO displays many thousands of distant galaxies, and more particularly a large group belonging to the massive galaxy cluster known as Abell 315. As crowded as it may appear, this assembly of galaxies is only the proverbial "tip of the iceberg", as Abell 315 - like most galaxy clusters - is dominated by dark matter. The huge mass of this cluster deflects light from background galaxies, distorting their observed shapes slightly. When looking at the sky with the unaided eye, we mostly only see stars within our Milky Way galaxy and some of its closest neighbours. More distant galaxies are just too faint to be perceived by the human eye, but if we could see them, they would literally cover the sky. This new image released by ESO is both a wide-field and long-exposure one, and reveals thousands of galaxies crowding an area on the sky roughly as large as the full Moon. These galaxies span a vast range of distances from us. Some are relatively close, as it is possible to distinguish their spiral arms or elliptical halos, especially in the upper part of the image. The more distant appear just like the faintest of blobs - their light has travelled through the Universe for eight billion years or more before reaching Earth. Beginning in the centre of the image and extending below and to the left, a concentration of about a hundred yellowish galaxies identifies a massive galaxy cluster, designated with the number 315 in the catalogue compiled by the American astronomer George Abell in 1958 [1]. The cluster is located between the faint, red and blue galaxies and the Earth, about two billion light-years away from us. It lies in the constellation of Cetus (the Whale). Galaxy clusters are some of the largest structures in the Universe held together by gravity. But there is more in these structures than the many galaxies we can see. Galaxies in these giants contribute to only ten percent of the mass, with hot gas in between galaxies

  15. Cluster galaxy evolution with the Las Campanas Distant Cluster Survey

    NASA Astrophysics Data System (ADS)

    Nelson, Amy Elizabeth

    Understanding the formation and evolution of galaxies is a principal goal of modern cosmology. In this thesis, we place constraints on galaxy evolution models using the largest sample of high redshift clusters to date. Our sample consists of 63 clusters at 0.3 ≲ z ≲ 0.9 drawn from the Las Campanas Distant Cluster Survey (LCDCS). This survey differs from traditional optical surveys in that we detect clusters as regions of excess surface brightness relative to the background sky rather than selecting overdensities of resolved galaxies. Therefore, not only does this sample result in a significant increase in the number of known clusters at these redshifts, but because our cluster identification criteria is independent of those utilized in previous surveys, this catalog provides an independent, well-defined sample with which to compare the results of more traditional surveys. In this work, we take a two-pronged approach to studying galaxy evolution. First, we examine the luminosity and color evolution of the bright cluster galaxies as a class. Specifically, we measure the evolution of: (1) M*I , the characteristic luminosity of cluster galaxies, (2) the location of the red envelope in V--I and I--K', and (3) the fraction of blue galaxies (i.e. the Butcher-Oemler effect; Butcher & Oemler 1984). Our data suggest that luminous early type galaxies (or the progenitors of current day early type galaxies) form the bulk of their stellar populations at high redshifts ( ≲ 5) and that many of these galaxies, if not all, experience a short term episode of star formation at lower redshifts (1.5 < z < 2). Second, we narrow the focus and study a single type of cluster galaxy, the brightest cluster galaxy (BCG). We constrain the amount of luminosity and color evolution of BCGs, particularly in the context of recent claims in the literature of significant mass accretion since z ˜ 1 (Aragon-Salamanca 1998; Burke, Collins, & Mann 2000). Consistent with previous results (Burke

  16. Recent Galaxy Mergers and Residual Star Formation of Red Sequence Galaxies in Galaxy Clusters

    NASA Astrophysics Data System (ADS)

    Sheen, Yun-Kyeong; Yi, Sukyoung K.; Ree, Chang H.; Jaffé, Yara; Demarco, Ricardo; Treister, Ezequiel

    2016-08-01

    This study explored the Galaxy Evolution Explorer ultraviolet (UV) properties of optical red sequence galaxies in four rich Abell clusters at z≤slant 0.1. In particular, we tried to find a hint of merger-induced recent star formation (RSF) in red sequence galaxies. Using the NUV - r\\prime colors of the galaxies, RSF fractions were derived based on various criteria for post-merger galaxies and normal galaxies. Following k-correction, about 36% of the post-merger galaxies were classified as RSF galaxies with a conservative criterion (NUV - r\\prime ≤slant 5), and that number was doubled (˜72%) when using a generous criterion (NUV - r\\prime ≤slant 5.4). The trend was the same when we restricted the sample to galaxies within 0.5 × R 200. Post-merger galaxies with strong UV emission showed more violent, asymmetric features in the deep optical images. The RSF fractions did not show any trend along the clustocentric distance within R 200. We performed a Dressler–Shectman test to check whether the RSF galaxies had any correlation with the substructures in the galaxy clusters. Within R 200 of each cluster, the RSF galaxies did not appear to be preferentially related to the clusters’ substructures. Our results suggested that only 30% of RSF red sequence galaxies show morphological hints of recent galaxy mergers. This implies that internal processes (e.g., stellar mass loss or hot gas cooling) for the supply of cold gas to early-type galaxies may play a significant role in the residual star formation of early-type galaxies at a recent epoch.

  17. Recent Galaxy Mergers and Residual Star Formation of Red Sequence Galaxies in Galaxy Clusters

    NASA Astrophysics Data System (ADS)

    Sheen, Yun-Kyeong; Yi, Sukyoung K.; Ree, Chang H.; Jaffé, Yara; Demarco, Ricardo; Treister, Ezequiel

    2016-08-01

    This study explored the Galaxy Evolution Explorer ultraviolet (UV) properties of optical red sequence galaxies in four rich Abell clusters at z≤slant 0.1. In particular, we tried to find a hint of merger-induced recent star formation (RSF) in red sequence galaxies. Using the NUV - r\\prime colors of the galaxies, RSF fractions were derived based on various criteria for post-merger galaxies and normal galaxies. Following k-correction, about 36% of the post-merger galaxies were classified as RSF galaxies with a conservative criterion (NUV - r\\prime ≤slant 5), and that number was doubled (˜72%) when using a generous criterion (NUV - r\\prime ≤slant 5.4). The trend was the same when we restricted the sample to galaxies within 0.5 × R 200. Post-merger galaxies with strong UV emission showed more violent, asymmetric features in the deep optical images. The RSF fractions did not show any trend along the clustocentric distance within R 200. We performed a Dressler-Shectman test to check whether the RSF galaxies had any correlation with the substructures in the galaxy clusters. Within R 200 of each cluster, the RSF galaxies did not appear to be preferentially related to the clusters’ substructures. Our results suggested that only 30% of RSF red sequence galaxies show morphological hints of recent galaxy mergers. This implies that internal processes (e.g., stellar mass loss or hot gas cooling) for the supply of cold gas to early-type galaxies may play a significant role in the residual star formation of early-type galaxies at a recent epoch.

  18. Galaxy Luminosity Function of the Dynamically Young Abell 119 Cluster: Probing the Cluster Assembly

    NASA Astrophysics Data System (ADS)

    Lee, Youngdae; Rey, Soo-Chang; Hilker, Michael; Sheen, Yun-Kyeong; Yi, Sukyoung K.

    2016-05-01

    We present the galaxy luminosity function (LF) of the Abell 119 cluster down to {M}r˜ -14 mag based on deep images in the u, g, and r bands taken by using MOSAIC II CCD mounted on the Blanco 4 m telescope at the CTIO. The cluster membership was accurately determined based on the radial velocity information and on the color-magnitude relation for bright galaxies and the scaling relation for faint galaxies. The overall LF exhibits a bimodal behavior with a distinct dip at r˜ 18.5 mag ({M}r˜ -17.8 mag), which is more appropriately described by a two-component function. The shape of the LF strongly depends on the clustercentric distance and on the local galaxy density. The LF of galaxies in the outer, low-density region exhibits a steeper slope and more prominent dip compared with that of counterparts in the inner, high-density region. We found evidence for a substructure in the projected galaxy distribution in which several overdense regions in the Abell 119 cluster appear to be closely associated with the surrounding, possible filamentary structure. The combined LF of the overdense regions exhibits a two-component function with a distinct dip, while the LF of the central region is well described by a single Schechter function. We suggest that, in the context of the hierarchical cluster formation scenario, the observed overdense regions are the relics of galaxy groups, retaining their two-component LFs with a dip, which acquired their shapes through a galaxy merging process in group environments, before they fall into a cluster.

  19. Properties of The Brightest Cluster Galaxy and Its Host Cluster

    NASA Astrophysics Data System (ADS)

    Katayama, H.; Hayashida, K.; Takahara, F.

    2001-09-01

    We investigate the relation between the brightest cluster galaxy (BCG) and its host cluster. A BCG is a bright and massive elliptical galaxy in a cluster of galaxies. The luminosity of a BCG is 10 times larger than that of normal field galaxy and the mass of a BCG is about 1013Msolar which corresponds to that of galaxy group. In order to explain the origin of BCGs, the following three models are proposed: (1) star formation from cooling flow. In this model, intracluster gas gradually condenses at the center of the cluster and forms the BCG. (2) ``Galactic cannibalism'' or the accretion of smaller galaxies. In this model, dynamical friction accounts for the formation of the BCG. These two models predict the BCG evolves with the evolution of cluster. (3) Galaxy merging in the early history of the formation of the cluster. In this model, the property of BCGs is determined no later than cluster collapse. In any model, the formation of BCGs is related to the collapse and formation of its host cluster. The relation between the BCG and its host cluster was studied by Edge (1991). Edge (1991) found that the optical luminosity of the BCG is positively correlated with the X-ray luminosity and temperature of its host cluster. Edge (1991) concludes that these correlations indicate that the BCG responds to the overall cluster properties. In order to investigate the other relation between the BCG and its host cluster, we analyzed ROSAT archival data and compared the displacement between the X-ray peak and the BCG with the Z parameter of the fundamental relation found by Fujita and Takahara (1999). It is found that the displacement is larger with decreasing Z. Furthermore, the large Z clusters tend to have a regular X-ray profile, which implies a relaxed system. The fundamental parameter Z depends mainly on the virial density ρvir, and is considered to be related to the formation epoch of the cluster, i.e., large Z clusters are old clusters and small Z clusters are young

  20. Mass calibration and cosmological analysis of the SPT-SZ galaxy cluster sample using velocity dispersion σ v and x-ray Y X measurements

    SciTech Connect

    Bocquet, S.; Saro, A.; Mohr, J. J.; Aird, K. A.; Ashby, M. L. N.; Bautz, M.; Bayliss, M.; Bazin, G.; Benson, B. A.; Bleem, L. E.; Brodwin, M.; Carlstrom, J. E.; Chang, C. L.; Chiu, I.; Cho, H. M.; Clocchiatti, A.; Crawford, T. M.; Crites, A. T.; Desai, S.; de Haan, T.; Dietrich, J. P.; Dobbs, M. A.; Foley, R. J.; Forman, W. R.; Gangkofner, D.; George, E. M.; Gladders, M. D.; Gonzalez, A. H.; Halverson, N. W.; Hennig, C.; Hlavacek-Larrondo, J.; Holder, G. P.; Holzapfel, W. L.; Hrubes, J. D.; Jones, C.; Keisler, R.; Knox, L.; Lee, A. T.; Leitch, E. M.; Liu, J.; Lueker, M.; Luong-Van, D.; Marrone, D. P.; McDonald, M.; McMahon, J. J.; Meyer, S. S.; Mocanu, L.; Murray, S. S.; Padin, S.; Pryke, C.; Reichardt, C. L.; Rest, A.; Ruel, J.; Ruhl, J. E.; Saliwanchik, B. R.; Sayre, J. T.; Schaffer, K. K.; Shirokoff, E.; Spieler, H. G.; Stalder, B.; Stanford, S. A.; Staniszewski, Z.; Stark, A. A.; Story, K.; Stubbs, C. W.; Vanderlinde, K.; Vieira, J. D.; Vikhlinin, A.; Williamson, R.; Zahn, O.; Zenteno, A.

    2015-01-30

    Here, we present a velocity-dispersion-based mass calibration of the South Pole Telescope Sunyaev-Zel'dovich effect survey (SPT-SZ) galaxy cluster sample. Using a homogeneously selected sample of 100 cluster candidates from 720 deg2 of the survey along with 63 velocity dispersion (σv) and 16 X-ray YX measurements of sample clusters, we simultaneously calibrate the mass-observable relation and constrain cosmological parameters. Our method accounts for cluster selection, cosmological sensitivity, and uncertainties in the mass calibrators. The calibrations using σv and YX are consistent at the 0.6σ level, with the σ v calibration preferring ~16% higher masses. We use the full SPTCL data set (SZ clustersv+YX) to measure σ8(Ωm/0.27)0.3 = 0.809 ± 0.036 within a flat ΛCDM model. The SPT cluster abundance is lower than preferred by either the WMAP9 or Planck+WMAP9 polarization (WP) data, but assuming that the sum of the neutrino masses is mν = 0.06 eV, we find the data sets to be consistent at the 1.0σ level for WMAP9 and 1.5σ for Planck+WP. Allowing for larger Σmν further reconciles the results. When we combine the SPTCL and Planck+WP data sets with information from baryon acoustic oscillations and Type Ia supernovae, the preferred cluster masses are 1.9σ higher than the YX calibration and 0.8σ higher than the σ v calibration. Given the scale of these shifts (~44% and ~23% in mass, respectively), we execute a goodness-of-fit test; it reveals no tension, indicating that the best-fit model provides an adequate description of the data. Using the multi-probe data set, we measure Ωm = 0.299 ± 0.009 and σ8 = 0.829 ± 0.011. Within a νCDM model we find Σmν = 0.148 ± 0.081 eV. We present a consistency test of the cosmic growth rate using SPT clusters. Allowing both the growth index γ and the

  1. When clusters collide - A numerical Hydro/N-body simulation of merging galaxy clusters

    NASA Technical Reports Server (NTRS)

    Roettiger, Kurt; Burns, Jack; Loken, Chris

    1993-01-01

    A 3D numerical simulation of two merging clusters of galaxies, using a hybrid Hydro/N-body code, is presented. The hydrodynamics of the code is solved by an Eulerian finite difference method. Initial results disclose that the X-ray emission of the dominant cluster becomes elongated and broadened; heating occurs at the core of the dominant cluster as a result of multiple shocks, and high velocity gas motions within the intracluster medium. It is predicted that clusters which have undergone recent mergers and do not have cooling flows will have high peculiar gas velocities and that the shocks and turbulence generated during the merger may power cluster-wide radio halos. Prolonged high-velocity gas motions through the dominant cluster core possibly play a major role in the formation and shaping of wide-angle tailed radio sources associated with central dominant galaxies. The N-body component of the simulation reveals the subcluster to be dispersed as it passes through the dominant cluster.

  2. Intracluster Light in Galaxy Groups and Clusters

    NASA Astrophysics Data System (ADS)

    DeMaio, Tahlia; Gonzalez, Anthony; Zabludoff, Ann I.; Zaritsky, Dennis F.

    2016-01-01

    We present recent results from our study on the origin and assembly history of the intracluster starlight (ICL) for a sample of 29 galaxy groups and clusters with 3x1013clusters show clear negative color gradients. Such negative colour (and equivalently, metallicity) gradients can arise from tidal stripping of L* galaxies and/or the disruption of dwarf galaxies, but not major mergers with the brightest cluster galaxy (BCG). We also find ICL luminosities of 3-9 L* in the range 10 < r < 110 kpc for these clusters. Dwarf disruption alone cannot explain the total luminosity of the ICL and remain consistent with the observed evolution in the faint-end slope of the luminosity function. The results of our study are suggestive of a formation history in which the ICL is built-up by a combination of stripping of L* galaxies and/or dwarf disruption and disfavor significant contribution by major mergers with the BCG.This sample of groups and clusters is the largest with HST/WFC3 data for ICL analysis that spans two orders of magnitude in halo mass at redshifts >0.3. Because of this we can investigate how the ICL color profile changes as a function of cluster mass for the first time, as well as expand previous studies of the changing fraction of cluster luminosity that is contained in the BCG+ICL as a function of halo mass. We present our preliminary results and describe our next steps using this sample to investigate the intracluster light in massive halos.

  3. Two populations of open star clusters in the Galaxy

    NASA Astrophysics Data System (ADS)

    Gozha, M. L.; Koval', V. V.; Marsakov, V. A.

    2012-08-01

    Based on our compiled catalogue of fundamental astrophysical parameters for 593 open clusters, we analyze the relations between the chemical composition, spatial positions, Galactic orbital elements, age, and other physical parameters of open star clusters. We show that the population of open clusters is heterogeneous and is divided into two groups differing by their mean parameters, properties, and origin. One group includes the Galactic clusters formed mainly from the interstellar matter of the thin disk with nearly solarmetallicities ([Fe/H] > -0.2) and having almost circular orbits a short distance away from the Galactic plane, i.e., typical of the field stars of the Galactic thin disk. The second group includes the peculiar clusters formed through the interaction of extragalactic objects (such as high-velocity clouds, globular clusters, or dwarf galaxies) with the interstellar matter of the thin disk, which, as a result, derived abnormally low (for field thin-disk stars) metallicities and/or Galactic orbits typical of objects of the older Galactic subsystems. About 70% of the clusters older than 1Gyr have been found to be peculiar, suggesting a slower disruption of clusters with noncircular high orbits. Analysis of orbital elements has shown that the bulk of the clusters from both groups were formed within a Galactocentric radius of ≈10.5 kpc and closer than ≈180 pc from the Galactic plane, but owing to their high initial velocities, the peculiar clusters gradually took up the volumes occupied by the objects of the thick disk, the halo, and even the accreted halo of the Galaxy. Analysis of the relative abundances of magnesium (a representative of the α-elements) in clusters that, according to their kinematical parameters, belong to different Galactic subsystems has shown that all clusters are composed of matter incorporating the interstellar matter of a single protogalactic cloud in different proportions, i.e., reprocessed in genetically related stars of

  4. SPECTRAL IMAGING OF GALAXY CLUSTERS WITH PLANCK

    SciTech Connect

    Bourdin, H.; Mazzotta, P.; Rasia, E.

    2015-12-20

    The Sunyaev–Zeldovich (SZ) effect is a promising tool for detecting the presence of hot gas out to the galaxy cluster peripheries. We developed a spectral imaging algorithm dedicated to the SZ observations of nearby galaxy clusters with Planck, with the aim of revealing gas density anisotropies related to the filamentary accretion of materials, or pressure discontinuities induced by the propagation of shock fronts. To optimize an unavoidable trade-off between angular resolution and precision of the SZ flux measurements, the algorithm performs a multi-scale analysis of the SZ maps as well as of other extended components, such as the cosmic microwave background (CMB) anisotropies and the Galactic thermal dust. The demixing of the SZ signal is tackled through kernel-weighted likelihood maximizations. The CMB anisotropies are further analyzed through a wavelet analysis, while the Galactic foregrounds and SZ maps are analyzed via a curvelet analysis that best preserves their anisotropic details. The algorithm performance has been tested against mock observations of galaxy clusters obtained by simulating the Planck High Frequency Instrument and by pointing at a few characteristic positions in the sky. These tests suggest that Planck should easily allow us to detect filaments in the cluster peripheries and detect large-scale shocks in colliding galaxy clusters that feature favorable geometry.

  5. Watching the Birth of a Galaxy Cluster?

    NASA Astrophysics Data System (ADS)

    1999-07-01

    First Visiting Astronomers to VLT ANTU Observe the Early Universe When the first 8.2-m VLT Unit Telescope (ANTU) was "handed over" to the scientists on April 1, 1999, the first "visiting astronomers" at Paranal were George Miley and Huub Rottgering from the Leiden Observatory (The Netherlands) [1]. They obtained unique pictures of a distant exploding galaxy known as 1138 - 262 . These images provide new information about how massive galaxies and clusters of galaxies may have formed in the early Universe. Formation of clusters of galaxies An intriguing question in modern astronomy is how the first galaxies and groupings or clusters of galaxies emerged from the primeval gas produced in the Big Bang. Some theories predict that giant galaxies, often found at the centres of rich galaxy clusters, are built up through a step-wise process. Clumps develop in this gas and stars condense out of those clumps to form small galaxies. Finally these small galaxies merge together to form larger units. An enigmatic class of objects important for investigating such scenarios are galaxies which emit intense radio emission from explosions that occur deep in their nuclei. The explosions are believed to be triggered when material from the merging swarm of smaller galaxies is fed into a rotating black hole located in the central regions. There is strong evidence that these distant radio galaxies are amongst the oldest and most massive galaxies in the early Universe and are often located at the heart of rich clusters of galaxies. They can therefore help pinpoint regions of the Universe in which large galaxies and clusters of galaxies are being formed. The radio galaxy 1138-262 The first visiting astronomers pointed ANTU towards a particularly important radio galaxy named 1138-262 . It is located in the southern constellation Hydra (The Water Snake). This galaxy was discovered some years ago using ESO's 3.5-m New Technology Telescope (NTT) at La Silla. Because 1138-262 is at a distance of

  6. UNCLOAKING GLOBULAR CLUSTERS IN THE INNER GALAXY

    SciTech Connect

    Alonso-Garcia, Javier; Catelan, Marcio; Minniti, Dante; Mateo, Mario; Sen, Bodhisattva; Banerjee, Moulinath; Von Braun, Kaspar E-mail: mcatelan@astro.puc.cl E-mail: mmateo@umich.edu E-mail: moulib@umich.edu

    2012-03-15

    Extensive photometric studies of the globular clusters located toward the center of the Milky Way have been historically neglected. The presence of patchy differential reddening in front of these clusters has proven to be a significant obstacle to their detailed study. We present here a well defined and reasonably homogeneous photometric database for 25 of the brightest Galactic globular clusters located in the direction of the inner Galaxy. These data were obtained in the B, V, and I bands using the Magellan 6.5 m Telescope and the Hubble Space Telescope. A new technique is extensively used in this paper to map the differential reddening in the individual cluster fields, and to produce cleaner, dereddened color-magnitude diagrams for all the clusters in the database. Subsequent papers will detail the astrophysical analysis of the cluster populations, and the properties of the obscuring material along the clusters' lines of sight.

  7. Kinematics of the Globular Cluster System of the Sombrero Galaxy

    NASA Astrophysics Data System (ADS)

    Windschitl, Jessica L.; Rhode, K. L.; Bridges, T. J.; Zepf, S. E.; Gebhardt, K.; Freeman, K. C.

    2013-06-01

    Using spectra from the Hydra spectrograph on the 3.5m WIYN telescope and from the AAOmega spectrograph on the 3.9m Anglo-Australian Telescope, we have measured heliocentric radial velocities for >50 globular clusters in the Sombrero Galaxy (M104). We combine these new measurements with those from previous studies to construct and analyze a total sample of >360 globular cluster velocities in M104. We use the line-of-sight velocity dispersion to determine the mass and mass-to-light ratio profiles for the galaxy using a spherical, isotropic Jeans mass model. In addition to the increased sample size, our data provide a significant expansion in radial coverage compared to previous spectroscopic studies. This allows us to reliably compute the mass profile of M104 out to ~43 kpc, nearly 14 kpc farther into the halo than previous work. We find that the mass-to-light ratio profile increases from the center to a value of ~20 at 43 kpc. We also look for the presence of rotation in the globular cluster system as a whole and within the red and blue subpopulations. Despite the large number of clusters and better radial sampling, we do not find strong evidence of rotation.

  8. New Frontiers in Galaxy Clusters with ASTRO-H

    NASA Astrophysics Data System (ADS)

    Miller, Eric D.; Kitayama, Tetsu; Akamatsu, Hiroki; Allen, Steven W.; Bautz, Mark W.; de Plaa, Jelle; Galeazzi, Massimiliano; Kawaharada, Madoka; Madejski, Grzegorz Maria; Markevitch, Maxim L.; Matsushita, Kyoko; McNamara, Brian R.; Nakazawa, Kazuhiro; Ota, Naomi; Russell, Helen; Sato, Kosuke; Sekiya, Norio; Simionescu, Aurora; Tamura, Takayuki; Uchida, Yuusuke; Ursino, Eugenio; Werner, Norbert; Zhuravleva, Irina; Zuhone, John A.; ASTRO-H Team

    2015-01-01

    The next generation X-ray observatory ASTRO-H will open up a new dimension in the study of galaxy clusters. For the first time, the focal plane calorimeter aboard ASTRO-H will achieve the spectral resolution required to measure velocities of the intracluster plasma. At the same time, the Hard X-ray Imager (HXI) will extend the simultaneous spectral coverage to energies well above 10 keV, critical for studying both thermal and non-thermal gas in clusters. We present an overview of the capabilities of ASTRO-H for exploring gas motions in galaxy clusters, including their cosmological implications, the physics of AGN feedback, the dynamics of cluster mergers and associated high-energy processes, the chemical enrichment of the intracluster medium, and the nature of missing baryons and unidentified dark matter. By demonstrating these capabilities explicitly on representative galaxy clusters, we hope to aid and encourage the broader astrophysical community in developing ASTRO-H science.

  9. New Frontiers in Galaxy Clusters with ASTRO-H

    NASA Astrophysics Data System (ADS)

    Miller, Eric D.; Kitayama, Tetsu; Bautz, Marshall; Markevitch, Maxim; Matsushita, Kyoko; Allen, Steven; Kawaharada, Madoka; McNamara, Brian; Ota, Naomi; Akamatsu, Hiroki; de Plaa, Jelle; Galeazzi, Massimiliano; Madejski, Grzegorz; Nakazawa, Kazuhiro; Russell, Helen; Sato, Kosuke; Sekiya, Norio; Simionescu, Aurora; Tamura, Takayuki; Uchida, Yuusuke; Ursino, Eugenio; Werner, Norbert; Zhuravleva, Irina; ZuHone, John; ASTRO-H Team

    2015-08-01

    The next generation X-ray observatory ASTRO-H will open up a new dimension in the study of galaxy clusters. For the first time, the focal plane calorimeter aboard ASTRO-H will achieve the spectral resolution required to measure velocities of the intracluster plasma. At the same time, the Hard X-ray Imager (HXI) will extend the simultaneous spectral coverage to energies well above 10 keV, critical for studying both thermal and non-thermal gas in clusters. We present an overview of the capabilities of ASTRO-H for exploring gas motions in galaxy clusters, including their cosmological implications, the physics of AGN feedback, the dynamics of cluster mergers and associated high-energy processes, the chemical enrichment of the intracluster medium, and the nature of missing baryons and unidentified dark matter. By demonstrating these capabilities explicitly on representative galaxy clusters, we hope to aid and encourage the broader astrophysical community in developing ASTRO-H science.

  10. Spectroscopy for E and S0 galaxies in nine clusters

    NASA Astrophysics Data System (ADS)

    Jorgensen, Inger; Franx, Marijn; Kjaergaard, Per

    1995-10-01

    Central velocity dispersions, Mg_2 line indices and radial velocities for 220 E and S0 galaxies are derived on the basis of intermediate resolution spectroscopy. Galaxies in the following clusters have been observed: Abell 194, Abell 539, Abell 3381, Abell 3574, S639, S753, Doradus, HydraI (Abell 1060) and Grm 15. For 151 of the galaxies, the velocity dispersion has not previously been measured. 134 of the Mg_2 determinations are for galaxies with no previous measurement. The spectra cover either 500 or 1000A, centred on the magnesium triplet at 5177A. The observations were obtained with the Boller & Chivens spectrograph at the ESO 1.5-m telescope and with the OPTOPUS, a multi-object fibre-fed B&C spectrograph, at the ESO 3.6-m telescope. The data are part of our ongoing study of the large-scale motions in the Universe and the physical background for the Fundamental Plane. The Fourier fitting method was used to derive the velocity dispersions and radial velocities. The velocity dispersions have been corrected for the effect of the size of the aperture. The correction was established on the basis of velocity dispersion profiles available in the literature. A comparison with results from Davies et al. shows that the derived central velocity dispersions have an rms error of 0.036 in logsigma. There is no offset relative to the velocity dispersions from Davies et al. The offset relative to data from Lucey & Carter is -0.017+/-0.011 in logsigma, with our velocity dispersions being the smallest. The velocity dispersions derived from the B&C and the OPTOPUS observations, as well as the velocity dispersions published by Davies et al., Dressler, Lucey & Carter and Lucey et al., can be brought on a system consistent within 3 per cent. The Mg_2 line indices have been corrected for the size of the apertures, transformed to the Lick system, and corrected for the effect of the velocity dispersion. From comparison with data from Davies et al. and from Faber, we find that the rms

  11. Dark Hearts in the Perseus Cluster Galaxies: A Study of Dust Absorption Features

    NASA Astrophysics Data System (ADS)

    Hooper, Eric Jon; Wojtaszek, M.; Gallagher, J. S.

    2013-01-01

    Indicators of a cool interstellar medium, such as dust features and HI emission, are more prevalent in early type galaxies than once thought. Yet it is still difficult to understand their presence in the cores of massive clusters. The hot intracluster medium can strip low-density gas from infalling galaxies via ram pressure or can heat the gas past its escape velocity. Nevertheless, galaxies with cool ISM in the form of dust do exist in the Coma Cluster. Here we report on several such systems observed near the core of the Perseus Cluster, the nearest massive cluster of galaxies (D = 70 Mpc). Perseus is an optically unrelaxed cluster with an extensive hot ICM. It also contains several high-velocity galaxies, including a system infalling towards NGC 1275 at a relative speed of ~3000 km/sec, which suggests a continued accretion of systems from the cluster's surroundings. We detect dust features in early-type galaxies through the presence of optical absorption, visible in the form of very circular rings, dark spiral arms and disk systems, or both. These features range in size from 50 to 1700 parsecs. We suggest that these components may be remnants of evolutionary pre-processing in groups that occurs as objects fall into the Perseus cluster. We also discuss their existence in terms of survival time scales for cold ISM in the early-type members of a rich galaxy cluster.

  12. Cosmology and astrophysics with galaxy clusters

    SciTech Connect

    Nagai, Daisuke

    2014-11-20

    Galaxy clusters are the largest gravitationally bound objects in the universe, whose formation is driven by dark energy and dark matter. The majority of the baryonic mass in clusters resides in the hot X-ray emitting plasma, which also leaves imprints in the cosmic microwave background radiation. Recent X-ray and microwave observations have revealed detailed thermodynamic structure of the hot X-ray emitting plasma from their cores to the virial radii, making comparisons of baryonic component in simulations to observations a strong cosmological probe. However, the statistical power of these future surveys can only be exploited for cosmology if and only if we are able to measure the cluster mass with a very high precision. I will discuss recent progress and future challenges for the use of galaxy clusters as precise cosmological probes, with highlights on (1) the importance of understanding thermodynamics and plasma physics in the outskirts of galaxy clusters and (2) prospects for improving the power of cluster-based cosmological measurements using numerical simulations and multi-wavelength observations.

  13. GALAXY CLUSTERS AT HIGH REDSHIFT AND EVOLUTION OF BRIGHTEST CLUSTER GALAXIES

    SciTech Connect

    Wen, Z. L.; Han, J. L.

    2011-06-10

    Identification of high-redshift clusters is important for studies of cosmology and cluster evolution. Using photometric redshifts of galaxies, we identify 631 clusters from the Canada-France-Hawaii Telescope (CFHT) wide field, 202 clusters from the CFHT deep field, 187 clusters from the Cosmic Evolution Survey (COSMOS) field, and 737 clusters from the Spitzer Wide-area InfraRed Extragalactic Survey (SWIRE) field. The redshifts of these clusters are in the range 0.1 {approx}< z {approx}< 1.6. Merging these cluster samples gives 1644 clusters in the four survey fields, of which 1088 are newly identified and more than half are from the large SWIRE field. Among 228 clusters of z {>=} 1, 191 clusters are newly identified, and most of them from the SWIRE field. With this large sample of high-redshift clusters, we study the color evolution of the brightest cluster galaxies (BCGs). The r' - z' and r{sup +} - m{sub 3.6{mu}m} colors of the BCGs are consistent with a stellar population synthesis model in which the BCGs are formed at redshift z{sub f} {>=} 2 and evolved passively. The g' - z' and B - m{sub 3.6{mu}m} colors of the BCGs at redshifts z > 0.8 are systematically bluer than the passive evolution model for galaxies formed at z{sub f} {approx} 2, indicating star formation in high-redshift BCGs.

  14. Interpreting the Clustering of Distant Red Galaxies

    SciTech Connect

    Tinker, Jeremy L.; Wechsler, Risa H.; Zheng, Zheng; /Princeton, Inst. Advanced Study

    2009-08-03

    We analyze the angular clustering of z {approx} 2.3 distant red galaxies (DRGs) measured by Quadri et al. (2008). We find that, with robust estimates of the measurement errors and realistic halo occupation distribution modeling, the measured clustering can be well fit within standard halo occupation models, in contrast to previous results. However, in order to fit the strong break in w({theta}) at {theta} = 10{double_prime}, nearly all satellite galaxies in the DRG luminosity range are required to be DRGs. Within this luminosity-threshold sample, the fraction of galaxies that are DRGs is {approx} 44%, implying that the formation of DRGs is more efficient for satellite galaxies than for central galaxies. Despite the evolved stellar populations contained within DRGs at z = 2.3, 90% of satellite galaxies in the DRG luminosity range have been accreted within 500 Myr. Thus, satellite DRGs must have known they would become satellites well before the time of their accretion. This implies that the formation of DRGs correlates with large-scale environment at fixed halo mass, although the large-scale bias of DRGs can be well fit without such assumptions. Further data are required to resolve this issue. Using the observational estimate that {approx} 30% of DRGs have no ongoing star formation, we infer a timescale for star formation quenching for satellite galaxies of 450 Myr, although the uncertainty on this number is large. However, unless all non-star forming satellite DRGs were quenched before accretion, the quenching timescale is significantly shorter than z {approx} 0 estimates. Down to the completeness limit of the Quadri et al sample, we find that the halo masses of central DRGs are {approx} 50% higher than non-DRGs in the same luminosity range, but at the highest halo masses the central galaxies are DRGs only {approx} 2/3 of the time.

  15. Diffuse optical light in galaxy clusters

    NASA Astrophysics Data System (ADS)

    Krick, Jessica E.

    We have measured the flux, profile, color, and substructure in the diffuse intracluster light (ICL) in a sample of ten galaxy clusters that have varying mass, morphology, redshift, and density. Deep, wide-field observations for this project were made in two bands at the one meter Swope and 2.5 meter du Pont telescope at Las Campanas Observatory. Careful attention in reduction and analysis was paid to the illumination correction, background subtraction, point spread function determination, galaxy subtraction, and ICL flux determination. ICL flux is detected in both r - and either B - or V - band in all ten clusters ranging from 7.6 × 10 10 to 7.0 × 10 11 [Special characters omitted.] in r - and 1.4 × 10 10 to 1.2 × 10 11 [Special characters omitted.] in the B -band. These fluxes account for 6 to 22% of the total cluster light within one quarter of the virial radius in r - and 4 to 21% in the B - band. ICL B - r colors range from 1.49 to 2.75 when k and evolution corrected to the present epoch. ICL profiles extend to 28-29 mag arcsec -2 and radii up to 600 [Special characters omitted.] kpc, and are well fit by exponential, deVaucouleurs, and Hubble Reynolds profiles (substitute for an NFW density profile). Low surface brightness features are present in the clusters as evidence of ongoing tidal interactions. We find that the ICL forms in group environments and remains with those groups as they are in-falling into the cluster environment. Our sample, having been selected from the Abell sample, is incomplete. The sample does not include high redshift clusters with low density, low flux, or low mass, and it does not include low redshift clusters with high flux, mass, or density. Given this selection bias between ICL properties and cluster properties we do find that the presence of a cD galaxy corresponds to both centrally concentrated galaxy profiles and centrally concentrated ICL profiles. This is consistent with ICL either forming from galaxy interactions at the

  16. INTEGRAL-FIELD STELLAR AND IONIZED GAS KINEMATICS OF PECULIAR VIRGO CLUSTER SPIRAL GALAXIES

    SciTech Connect

    Cortés, Juan R.; Hardy, Eduardo; Kenney, Jeffrey D. P. E-mail: ehardy@nrao.cl

    2015-01-01

    We present the stellar and ionized gas kinematics of 13 bright peculiar Virgo cluster galaxies observed with the DensePak Integral Field Unit at the WIYN 3.5 m telescope in order to look for kinematic evidence that these galaxies have experienced gravitational interactions or gas stripping. Two-dimensional maps of the stellar velocity V, stellar velocity dispersion σ, and the ionized gas velocity (Hβ and/or [O III]) are presented for the galaxies in the sample. The stellar rotation curves and velocity dispersion profiles are determined for 13 galaxies, and the ionized gas rotation curves are determined for 6 galaxies. Misalignments between the optical and kinematical major axes are found in several galaxies. While in some cases this is due to a bar, in other cases it seems to be associated with gravitational interaction or ongoing ram pressure stripping. Non-circular gas motions are found in nine galaxies, with various causes including bars, nuclear outflows, or gravitational disturbances. Several galaxies have signatures of kinematically distinct stellar components, which are likely signatures of accretion or mergers. For all of our galaxies, we compute the angular momentum parameter λ {sub R}. An evaluation of the galaxies in the λ {sub R} ellipticity plane shows that all but two of the galaxies have significant support from random stellar motions, and have likely experienced gravitational interactions. This includes some galaxies with very small bulges and truncated/compact Hα morphologies, indicating that such galaxies cannot be fully explained by simple ram pressure stripping, but must have had significant gravitational encounters. Most of the sample galaxies show evidence for ICM-ISM stripping as well as gravitational interactions, indicating that the evolution of a significant fraction of cluster galaxies is likely strongly impacted by both effects.

  17. PROFILES OF DARK MATTER VELOCITY ANISOTROPY IN SIMULATED CLUSTERS

    SciTech Connect

    Lemze, Doron; Ford, Holland; Wagner, Rick; Norman, Michael L.; Rephaeli, Yoel; Sadeh, Sharon; Barkana, Rennan; Broadhurst, Tom

    2012-06-20

    We report statistical results for dark matter (DM) velocity anisotropy, {beta}, from a sample of some 6000 cluster-size halos (at redshift zero) identified in a {Lambda}CDM hydrodynamical adaptive mesh refinement simulation performed with the ENZO code. These include profiles of {beta} in clusters with different masses, relaxation states, and at several redshifts, modeled both as spherical and triaxial DM configurations. Specifically, although we find a large scatter in the DM velocity anisotropy profiles of different halos (across elliptical shells extending to at least {approx}1.5r{sub vir}), universal patterns are found when these are averaged over halo mass, redshift, and relaxation stage. These are characterized by a very small velocity anisotropy at the halo center, increasing outward to {approx}0.27 and leveling off at {approx}0.2r{sub vir}. Indirect measurements of the DM velocity anisotropy fall on the upper end of the theoretically expected range. Though measured indirectly, the estimations are derived by using two different surrogate measurements-X-ray and galaxy dynamics. Current estimates of the DM velocity anisotropy are based on a very small cluster sample. Increasing this sample will allow theoretical predictions to be tested, including the speculation that the decay of DM particles results in a large velocity boost. We also find, in accord with previous works, that halos are triaxial and likely to be more prolate when unrelaxed, whereas relaxed halos are more likely to be oblate. Our analysis does not indicate that there is significant correlation (found in some previous studies) between the radial density slope, {gamma}, and {beta} at large radii, 0.3 r{sub vir} < r < r{sub vir}.

  18. The evolution of galaxy groups and clusters

    NASA Astrophysics Data System (ADS)

    Mazzotta, Pasquale

    2016-07-01

    The Athena mission will implement the Hot and Energetic Universe science theme which poses the question of How does ordinary matter assemble into the large-scale structures we see today?. Groups and Galaxy clusters are key laboratories to understand the role of the various physical processes governing the baryonic matter from the kilo-parsec scale of super-massive black holes to the mega-parsec one of the clusters outskirts on assembling and evolving large scale structures. We will focus on the study of the galaxy groups and clusters evolution with the Athen a mission. We will review the status of current constraints in light of the newest results obtained from state of the art cosmological simulations and will discuss the perspectives out to the mission launch time in 2028.

  19. VLA Discovers Giant Rings Around Galaxy Cluster

    NASA Astrophysics Data System (ADS)

    2006-11-01

    Astronomers using the National Science Foundation's Very Large Array (VLA) radio telescope have discovered giant, ring-like structures around a cluster of galaxies. The discovery provides tantalizing new information about how such galaxy clusters are assembled, about magnetic fields in the vast spaces between galaxy clusters, and possibly about the origin of cosmic rays. Radio-Optical Image of Cluster Galaxy Cluster Abell 3376 (Radio/Optical) CREDIT: Joydeep Bagchi, IUCAA, NRAO/AUI/NSF Above, a combined radio/optical image shows the galaxy cluster Abell 3376 in visible light (blue) and radio (red) images. The giant radio arcs surrounding the cluster were discovered using the Very Large Array. The visible-light image is from the Digitized Sky survey. Below, an X-ray image of Abell 3376 made using the European Space Agency's XMM-Newton telescope shows a spectacular, bullet-shaped region of X-rays coming from gas heated to 60 million degrees Kelvin. The bullet shape results from the supersonic collision of a smaller smaller galaxy subcluster with the main body of the larger cluster. Click on images for larger version. X-Ray Image of Cluster Galaxy Cluster Abell 3376 (X-Ray) CREDIT: Joydeep Bagchi, IUCAA, ESA "These giant, radio-emitting rings probably are the result of shock waves caused by violent collisions of smaller groups of galaxies within the cluster," said Joydeep Bagchi, of the Inter-University Centre for Astronomy and Astrophysics in Pune, India, who led an international research team. The scientists reported their findings in the November 3 edition of the journal Science. The newly-discovered ring segments, some 6 million light-years across, surround a galaxy cluster called Abell 3376, more than 600 million light-years from Earth. They were revealed because fast-moving electrons emitted radio waves as they spiraled around magnetic field lines in intergalactic space. "Even from this large distance, the feeble radio waves were easily picked up by the VLA

  20. Properties of the Brightest Cluster Galaxy and Its Host Cluster

    NASA Astrophysics Data System (ADS)

    Katayama, Haruyoshi; Hayashida, Kiyoshi; Takahara, Fumio; Fujita, Yutaka

    2003-03-01

    We investigate the relation between the properties of brightest cluster galaxies (BCGs) and those of their host clusters. To quantify the properties of cluster hot gas, we employ the parameter Z of the fundamental plane of X-ray clusters. It is found that the offset of the BCG from the peak of cluster X-ray emission is larger for smaller Z clusters. The parameter Z (not the redshift z), which depends mainly on virial density ρvir, is considered to represent the formation epoch of a cluster. We thus consider that the offset of the BCG is correlated with the dynamical equilibrium state of its host cluster. On the contrary, no significant correlation is found between the absolute optical magnitude of the BCG and the parameter Z. If the extreme brightness of the BCG is acquired mainly in the course of cluster evolution by environmental effect, BCGs are expected to be brighter in large Z clusters. Our result is not consistent with this simplified view. On the contrary, it is possible that the extreme brightness of the BCG is likely to be determined in the early history of cluster collapse.

  1. ChaMP Serendipitous Galaxy Cluster Survey

    SciTech Connect

    Barkhouse, Wayne A.; Green, P.J.; Vikhlinin, A.; Kim, D.-W.; Perley, D.; Cameron, R.; Silverman, J.; Mossman, A.; Burenin, R.; Jannuzi, B.T.; Kim, M.; Smith, M.G.; Smith, R.C.; Tananbaum, H.; Wilkes, B.J.; /Harvard-Smithsonian Ctr. Astrophys. /UC, Berkeley, Astron. Dept. /SLAC /Garching, Max Planck Inst., MPE /Moscow, Space Res. Inst. /NOAO, Tucson /Cerro-Tololo InterAmerican Obs.

    2006-04-03

    We present a survey of serendipitous extended X-ray sources and optical cluster candidates from the Chandra Multi-wavelength Project (ChaMP). Our main goal is to make an unbiased comparison of X-ray and optical cluster detection methods. In 130 archival Chandra pointings covering 13 square degrees, we use a wavelet decomposition technique to detect 55 extended sources, of which 6 are nearby single galaxies. Our X-ray cluster catalog reaches a typical flux limit of about {approx} 10{sup -14} erg s{sup -1} cm{sup -2}, with a median cluster core radius of 21''. For 56 of the 130 X-ray fields, we use the ChaMP's deep NOAO/4m MOSAIC g', r', and i' imaging to independently detect cluster candidates using a Voronoi tessellation and percolation (VTP) method. Red-sequence filtering decreases the galaxy fore/background contamination and provides photometric redshifts to z {approx} 0.7. From the overlapping 6.1 square degree X-ray/optical imaging, we find 115 optical clusters (of which 11% are in the X-ray catalog) and 28 X-ray clusters (of which 46% are in the optical VTP catalog). The median redshift of the 13 X-ray/optical clusters is 0.41, and their median X-ray luminosity (0.5-2 keV) is L{sub X} = (2.65 {+-} 0.19) x 10{sup 43} ergs s{sup -1}. The clusters in our sample that are only detected in our optical data are poorer on average ({approx} 4{sigma}) than the X-ray/optically matched clusters, which may partially explain the difference in the detection fractions.

  2. The 3-Dimensional Structure of Galaxy Clusters

    NASA Astrophysics Data System (ADS)

    King, Lindsay

    NASA's Hubble Space Telescope Multi-Cycle Treasury Program CLASH (PI Postman) has provided the community with the most detailed views ever of the central regions of massive galaxy clusters. These galaxy clusters have also been observed with NASA's Chandra X-Ray Observatory, with the ground-based Subaru telescope, and with other ground- and space-based facilities, resulting in unprecedented multi-wavelength data sets of the most massive bound structures in the universe. Fitting 3-Dimensional mass models is crucial to understanding how mass is distributed in individual clusters, investigating the properties of dark matter, and testing our cosmological model. With the exquisite data available, the time is now ideal to undertake this analysis. We propose to use algorithms that we have developed and obtain mass models for the clusters from the CLASH sample. The project would use archival gravitational lensing data, X-ray data of the cluster's hot gas and additional constraints from Sunyaev-Zel'dovich (SZ) data. Specifically, we would model the 23 clusters for which both HST and Subaru data (or in one case WFI data) are publicly available, since the exquisite imaging of HST in the clusters' central regions is beautifully augmented by the wide field coverage of Subaru imaging. If the true 3-D shapes of clusters are not properly accounted for when analysing data, this can lead to inaccuracies in the mass density profiles of individual clusters - up to 50% bias in mass for the most highly triaxial systems. Our proposed project represents an independent analysis of the CLASH sample, complementary to that of the CLASH team, probing the triaxial shapes and orientations of the cluster dark matter halos and hot gas. Our findings will be relevant to the analysis of data from future missions such as JWST and Euclid, and also to ground-based surveys to be made with telescopes such as LSST.

  3. Evolution of brightest cluster galaxies in X-ray clusters

    NASA Astrophysics Data System (ADS)

    Brough, S.; Collins, C. A.; Burke, D. J.; Mann, R. G.; Lynam, P. D.

    2002-01-01

    A recent paper presents the analysis of the K-band Hubble diagram of 76 brightest cluster galaxies (BCGs) in X-ray clusters and shows that the properties of BCGs depend on the X-ray luminosity (LX) of their host clusters. Unfortunately, the low numbers of nearby clusters in this sample makes it difficult to constrain evolutionary trends. In this letter we extend the Hubble diagram of Burke, Collins & Mann to a total of 155 clusters using new data on 79 BCGs at z<=0.1 from the 2MASS extended source catalogue. We show that the major division between BCGs in high- and low-LX clusters disappears at z<=0.1, with BCGs having similar absolute magnitudes independent of the X-ray luminosity of their host clusters. At larger redshifts, the K-band light of BCGs in high-LX systems is consistent with little or no merging back to z~0.8, whereas BCGs in the low-LX systems have a different evolutionary history, with many increasing their mass by a factor >=4 since z~=1. This provides direct evidence of hierarchical merging in a galaxy population.

  4. SUPERMODEL ANALYSIS OF GALAXY CLUSTERS

    SciTech Connect

    Fusco-Femiano, R.; Cavaliere, A.; Lapi, A.

    2009-11-01

    We present the analysis of the X-ray brightness and temperature profiles for six clusters belonging to both the Cool Core (CC) and Non Cool Core (NCC) classes, in terms of the Supermodel (SM) developed by Cavaliere et al. Based on the gravitational wells set by the dark matter (DM) halos, the SM straightforwardly expresses the equilibrium of the intracluster plasma (ICP) modulated by the entropy deposited at the boundary by standing shocks from gravitational accretion, and injected at the center by outgoing blast waves from mergers or from outbursts of active galactic nuclei. The cluster set analyzed here highlights not only how simply the SM represents the main dichotomy CC versus NCC clusters in terms of a few ICP parameters governing the radial entropy run, but also how accurately it fits even complex brightness and temperature profiles. For CC clusters like A2199 and A2597, the SM with a low level of central entropy straightforwardly yields the characteristic peaked profile of the temperature marked by a decline toward the center, without requiring currently strong radiative cooling and high mass deposition rates. NCC clusters like A1656 require instead a central entropy floor of a substantial level, and some like A2256 and even more A644 feature structured temperature profiles that also call for a definite floor extension; in such conditions the SM accurately fits the observations, and suggests that in these clusters the ICP has been just remolded by a merger event, in the way of a remnant cool core. The SM also predicts that DM halos with high concentration should correlate with flatter entropy profiles and steeper brightness in the outskirts; this is indeed the case with A1689, for which from X-rays we find concentration values c approx 10, the hallmark of an early halo formation. Thus, we show the SM to constitute a fast tool not only to provide wide libraries of accurate fits to X-ray temperature and density profiles, but also to retrieve from the ICP

  5. Brightest Cluster Galaxies and Core Gas Density in REXCESS Clusters

    NASA Astrophysics Data System (ADS)

    Haarsma, Deborah B.; Leisman, Luke; Donahue, Megan; Bruch, Seth; Böhringer, Hans; Croston, Judith H.; Pratt, Gabriel W.; Voit, G. Mark; Arnaud, Monique; Pierini, Daniele

    2010-04-01

    We investigate the relationship between brightest cluster galaxies (BCGs) and their host clusters using a sample of nearby galaxy clusters from the Representative XMM-Newton Cluster Structure Survey. The sample was imaged with the Southern Observatory for Astrophysical Research in R band to investigate the mass of the old stellar population. Using a metric radius of 12 h -1 kpc, we found that the BCG luminosity depends weakly on overall cluster mass as L BCG vprop M 0.18±0.07 cl, consistent with previous work. We found that 90% of the BCGs are located within 0.035 r 500 of the peak of the X-ray emission, including all of the cool core (CC) clusters. We also found an unexpected correlation between the BCG metric luminosity and the core gas density for non-cool-core (non-CC) clusters, following a power law of ne vprop L 2.7±0.4 BCG (where ne is measured at 0.008 r 500). The correlation is not easily explained by star formation (which is weak in non-CC clusters) or overall cluster mass (which is not correlated with core gas density). The trend persists even when the BCG is not located near the peak of the X-ray emission, so proximity is not necessary. We suggest that, for non-CC clusters, this correlation implies that the same process that sets the central entropy of the cluster gas also determines the central stellar density of the BCG, and that this underlying physical process is likely to be mergers.

  6. Nearby Spiral Galaxy Globular Cluster Systems. II. Globular Cluster Metallicities in NGC 300

    NASA Astrophysics Data System (ADS)

    Nantais, Julie B.; Huchra, John P.; Barmby, Pauline; Olsen, Knut A. G.

    2010-03-01

    We present new metallicity estimates for globular cluster (GC) candidates in the Sd spiral NGC 300, one of the nearest spiral galaxies outside the Local Group. We have obtained optical spectroscopy for 44 Sculptor Group GC candidates with the Boller and Chivens (B&C) spectrograph on the Baade Telescope at Las Campanas Observatory. There are two GCs in NGC 253 and 12 objects in NGC 300 with globular-cluster-like spectral features, nine of which have radial velocities above 0 km s-1. The remaining three, due to their radial velocities being below the expected 95% confidence limit for velocities of NGC 300 halo objects, are flagged as possible foreground stars. The non-cluster-like candidates included 13 stars, 15 galaxies, and an H II region. One GC, four galaxies, two stars, and the H II region from our sample were identified in archival Hubble Space Telescope images. For the GCs, we measure spectral indices and estimate metallicities using an empirical calibration based on Milky Way GCs. The GCs of NGC 300 appear similar to those of the Milky Way. Excluding possible stars and including clusters from the literature, the GC system (GCS) has a velocity dispersion of 68 km s-1 and has no clear evidence of rotation. The mean metallicity for our full cluster sample plus one literature object is [Fe/H] = -0.94, lying above the relationship between mean GC metallicity and overall galaxy luminosity. Excluding the three low-velocity candidates, we obtain a mean [Fe/H] = -0.98, still higher than expected, raising the possibility of significant foreground star contamination even in this sample. Visual confirmation of genuine GCs using high-resolution space-based imagery could greatly reduce the potential problem of interlopers in small samples of GCSs in low-radial-velocity galaxies. Data for this project were obtained at the Baade 6.5 m telescope, Las Campanas Observatory, Chile. This publication makes use of data products from the Two Micron All Sky Survey, which is a joint

  7. When galaxy clusters collide: the impact of merger shocks on cluster gas and galaxy evolution

    NASA Astrophysics Data System (ADS)

    Stroe, A.

    2015-09-01

    Galaxy clusters mainly grow through mergers with other clusters and groups. Major mergers give rise to cluster-wide traveling shocks, which can be detected at radio wavelengths as relics: elongated, diffuse synchrotron emitting areas located at the periphery of merging clusters. The 'Sausage' cluster hosts an extraordinary Mpc-wide relic, which enables us to study to study particle acceleration and the effects of shocks on cluster galaxies. We derive shock properties and the magnetic field structure for the relic. Our results indicate that particles are shock-accelerated, but turbulent re-acceleration or unusually efficient transport of particles in the downstream area are important effects. We demonstrate the feasibility of high-frequency observations of radio relics, by presenting a 16 GHz detection of the 'Sausage' relic. Halpha mapping of the cluster provides the first direct test as to whether the shock drives or prohibits star formation. We find numerous galaxies in! close proximity to the radio relic which are extremely massive, metal-rich, star-forming with evidence for gas mass loss though outflows. We speculate that the complex interaction between the merger, the shock wave and gas is a fundamental driver in the evolution of cluster galaxies from gas rich spirals to gas-poor ellipticals.

  8. Clusters of Galaxies in the last 5 Billion Years: from the Brightest Cluster Galaxy to the Intra-Cluster Light

    NASA Astrophysics Data System (ADS)

    Pillepich, Annalisa

    2014-10-01

    Understanding the physical processes which shape the galaxy population in the high density environment of galaxy clusters as a function of cosmic time is a central open question in galaxy evolution studies. With the Frontier Field Initiative, HST will provide an ultra-deep view and an unprecedented multi-wavelength dataset to study the galaxy population in and around galaxy clusters at intermediate redshift. With our study, we aim at providing the first self-consistent theoretical framework based on cosmological hydrodynamical simulations to understand the evolution of cluster galaxies: our analysis is designed to complement and aid the interpretation of the wealth of observational data within the LCDM Cosmology. In particular, we plan an in-depth analysis of a sample of 15 haloes with masses between 7x10^13 and 2x10^15 Msun at z=0, simulated with the gravity+hydrodynamics code Arepo. The numerical scheme and the galaxy formation model adopted in this study have already been successfully tested against a series of global measurements: they will allow us to follow the fate, within each cluster, of hundreds of well-resolved galaxies with stellar masses above 5x10^9 Msun. Our analysis will include the assembly properties of the central brightest galaxies as well as the demographics of the satellite populations and their cluster-centric gradients of colors, morphologies and star formation rates. Our setup is suitable to quantify the effects of environment on star formation, stripping, and quenching across an unprecedented range of galaxy masses, cluster masses and spatial scales, in addition to providing valuable clues about the diffuse intra-cluster light.

  9. Merging Galaxy Cluster A2255 in Mid-infrared

    NASA Astrophysics Data System (ADS)

    Shim, Hyunjin; Im, Myungshin; Lee, Hyung Mok; Lee, Myung Gyoon; Kim, Seong Jin; Hwang, Ho Seong; Hwang, Narae; Ko, Jongwan; Lee, Jong Chul; Lim, Sungsoon; Matsuhara, Hideo; Seo, Hyunjong; Wada, Takehiko; Goto, Tomotsugu

    2011-01-01

    We present the mid-infrared (MIR) observation of a nearby galaxy cluster, A2255, by the AKARI space telescope. Using AKARI's continuous wavelength coverage between 3 and 24 μm and the wide field of view, we investigate the properties of cluster member galaxies to see how the infall of the galaxies, the cluster substructures, and the cluster-cluster merger influence their evolution. We show that the excess of MIR (~11 μm) flux is a good indicator for discriminating galaxies at different evolutionary stages and for dividing galaxies into three classes accordingly: strong MIR-excess (N3 - S11>0.2) galaxies that include both unobscured and obscured star-forming galaxies; weak MIR-excess (-2.0 < N3 - S11 < -1.2) galaxies that are quiescent, old (>5 Gyr) galaxies where the MIR emission arises mainly from the circumstellar dust around AGB stars; and intermediate MIR-excess (-1.2 < N3 - S11 < 0.2) galaxies in between the two classes that are less than a few Gyr old past the prime star formation activity. With the MIR-excess diagnostics, we investigate how local and cluster-scale environments affect the individual galaxies. We derive the total star formation rate (SFR) and the specific SFR of A2255 using the strong MIR-excess galaxies. The dust-free, total SFR of A2255 is ~130 M sun yr-1, which is consistent with the SFRs of other clusters of galaxies at similar redshifts and with similar masses. We find no strong evidence that supports enhanced star formation either inside the cluster or in the substructure region, suggesting that the infall or the cluster merging activities tend to suppress star formation. The intermediate MIR-excess galaxies, representing galaxies in transition from star-forming galaxies to quiescent galaxies, are located preferentially at the medium density region or cluster substructures with higher surface density of galaxies. Our findings suggest that galaxies are being transformed from star-forming galaxies into red, quiescent galaxies from the

  10. Two confirmed compact elliptical galaxies in the Antlia cluster

    NASA Astrophysics Data System (ADS)

    Smith Castelli, A. V.; Faifer, F. R.; Bassino, L. P.; Romero, G. A.; Cellone, S. A.; Richtler, T.

    We confirm the existence of two compact elliptical (cE) galaxies in the cen- tral region of the Antlia cluster through MAGELLAN-MIKE and GEMINI- GMOS spectra. Only about a dozen galaxies of this rare type are known today up to a distance of 100 Mpc. With this finding, Antlia becomes the nearest galaxy cluster harbouring more than one cE galaxy among its galaxy population. One of these galaxies shows evidence of interaction with one of the giant ellipticals that dominate the central region of the cluster.

  11. The galaxy cluster outskirts probed by Chandra

    NASA Astrophysics Data System (ADS)

    Morandi, Andrea; Sun, Ming; Forman, William; Jones, Christine

    2015-08-01

    Exploring the virialization region of galaxy clusters has recently raised the attention of the scientific community, offering a direct view of structure formation. In this talk, I will present recent results on the physical properties of the intracluster medium in the outer volumes of a sample of 320 clusters (0.056 3 keV) in the Chandra archive, with a total integration time of ~20 Ms. We stacked the emission measure profiles of the clusters to detect a signal out to R_{100}. We then measured the average emission measure, gas density and gas fraction, which scale according to the self-similar model of cluster formation. We observe a steepening of the density profiles beyond R_{500} with slope beta ~ 0.68 at R_{500} and beta ~ 1 at R_{200} and beyond. By tracking the direction of the cosmic filaments where the clusters are embedded, we report that galaxy clusters deviate from spherical symmetry. We also did not find evolution of the gas density with redshift, confirming the self-similar evolution of the gas density. The value of the baryon fraction reaches the cosmic value at R_{200}: however, systematics due to non-thermal pressure support and clumpiness might enhance the measured gas fraction, leading to an actual deficit of the baryon budget with respect to the primordial value). This novel method, the stacking the X-ray signal of cluster outskirts, has the capacity to provide a generational leap forward in our understanding of cluster physics and formation, and the use of clusters as cosmological probes.

  12. The Effect of Cluster Environment on Galaxy Evolution in the Core Pegasus I Cluster.

    NASA Astrophysics Data System (ADS)

    Levy, L.; Rose, J. A.; van Gorkom, J. H.

    2004-12-01

    We present HI observations of 28 galaxies which complete the sample of spiral galaxies within 1 RA of the core Pegasus I cluster. The observations include single dish neutral Hydrogen measurements, obtained with the Arecibo telescope for all 28 galaxies in the sample, as well as HI spatial distribution maps, obtained with the VLA. The HI morphology of some galaxies shows that the HI is smaller than the optical disk and slightly offset from the stars. This could indicate an ICM-ISM interaction. This would be very surprising since the Pegasus cluster has a virtually undetectable level of X-ray emission, and a very low velocity dispersion. The low velocity dispersion, coupled with the lack of a dense hot ICM indicate that ram pressure stripping should not play a significant role in this environment. Nonetheless, we find evidence of some galaxies with HI deficiencies of up to a factor of 2 and with displaced HI. Also, two of the galaxies, NGC7604 and NGC7648, are morphologically peculiar. Their peculiarities indicate contradictory scenarios of what is triggering their unusual star formation. Hα imaging, along with long-slit spectroscopy of NGC7648 reveal morphological features which point to a recent tidal interaction. On the other hand, Hα imaging of NGC7604 reveals a strong episode of star formation concentrated into an symmetric arc, preferentially located on one side of the galaxy. VLA HI mapping shows the HI also highly concentrated into that region, suggestive of a ram pressure event. Our data hint at the possibility that ram pressure stripping may play a role in a wider variety of environments than previously considered.

  13. Galaxy Cluster Takes It to the Extreme

    NASA Astrophysics Data System (ADS)

    2007-05-01

    Evidence for an awesome upheaval in a massive galaxy cluster was discovered in an image made by NASA's Chandra X-ray Observatory. The origin of a bright arc of ferociously hot gas extending over two million light years requires one of the most energetic events ever detected. The cluster of galaxies is filled with tenuous gas at 170 million degree Celsius that is bound by the mass equivalent of a quadrillion, or 1,000 trillion, suns. The temperature and mass make this cluster a giant among giants. VLA Radio Image of 3C438 VLA Radio Image of 3C438 "The huge feature detected in the cluster, combined with the high temperature, points to an exceptionally dramatic event in the nearby Universe," said Ralph Kraft of the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Mass., and leader of a team of astronomers involved in this research. "While we're not sure what caused it, we've narrowed it down to a couple of exciting possibilities." The favored explanation for the bright X-ray arc is that two massive galaxy clusters are undergoing a collision at about 4 million miles per hour. Shock waves generated by the violent encounter of the clusters' hot gas clouds could produce a sharp change in pressure along the boundary where the collision is occurring, giving rise to the observed arc-shaped structure which resembles a titanic weather front. "Although this would be an extreme collision, one of the most powerful ever seen, we think this may be what is going on," said team member Martin Hardcastle, of the University of Hertfordshire, United Kingdom. Images of 3C438 and Surrounding Galaxy Cluster Images of 3C438 and Surrounding Galaxy Cluster A problem with the collision theory is that only one peak in the X-ray emission is seen, whereas two are expected. Longer observations with Chandra and the XMM-Newton X-ray observatories should help determine how serious this problem is for the collision hypothesis. Another possible explanation is that the disturbance was

  14. The Adopted Morphological Types of 247 Rich PF Galaxy Clusters

    NASA Astrophysics Data System (ADS)

    Panko, Elena; Bajan, Katarzyna; Flin, Piotr; Gotsulyak, Alla

    2016-10-01

    Morphological types were determined for 247 rich galaxy clusters from the PF Catalogue of Galaxy Clusters and Groups. The adopted types are based on classical morphological schemes and consider concentration to the cluster center, the signs of preferential direction or plane in the cluster, and the positions of the brightest galaxies. It is shown that both concentration and preferential plane are significant and independent morphological criteria.

  15. Dynamical evolution of globular-cluster systems in clusters of galaxies

    SciTech Connect

    Muzzio, J.C.

    1987-04-01

    The dynamical processes that affect globular-cluster systems in clusters of galaxies are analyzed. Two-body and impulsive approximations are utilized to study dynamical friction, drag force, tidal stripping, tidal radii, globular-cluster swapping, tidal accretion, and galactic cannibalism. The evolution of galaxies and the collision of galaxies are simulated numerically; the steps involved in the simulation are described. The simulated data are compared with observations. Consideration is given to the number of galaxies, halo extension, location of the galaxies, distribution of the missing mass, nonequilibrium initial conditions, mass dependence, massive central galaxies, globular-cluster distribution, and lost globular clusters. 116 references.

  16. Not a galaxy: IRAS 04186+5143, a new young stellar cluster in the outer Galaxy

    NASA Astrophysics Data System (ADS)

    Yun, J. L.; Elia, Davide; Djupvik, A. A.; Torrelles, J. M.; Molinari, S.

    2015-09-01

    We report the discovery of a new young stellar cluster in the outer Galaxy located at the position of an IRAS Point Source Catalog source that has been previously misidentified as an external galaxy. The cluster is seen in our near-infrared imaging towards IRAS 04186+5143 and in archive Spitzer images confirming the young stellar nature of the sources detected. There is also evidence of subclustering seen in the spatial distributions of young stars and of gas and dust. Near- and mid-infrared photometry indicates that the stars exhibit colours compatible with reddening by interstellar and circumstellar dust and are likely to be low- and intermediate-mass young stellar objects (YSOs) with a large proportion of Class I YSOs. Ammonia and CO lines were detected, with the CO emission well centred near the position of the richest part of the cluster. The velocity of the CO and NH3 lines indicates that the gas is Galactic and located at a distance of about 5.5 kpc, in the outer Galaxy. Herschel data of this region characterize the dust environment of this molecular cloud core where the young cluster is embedded. We derive masses, luminosities, and temperatures of the molecular clumps where the young stars reside and discuss their evolutionary stages.

  17. A systematic survey for distant galaxy clusters

    NASA Technical Reports Server (NTRS)

    Gunn, J. E.; Hoessel, J. G.; Oke, J. B.

    1986-01-01

    A photographic survey for faint clusters of galaxies has been carried out with fine-grained photographic emulsions using the 1.2 m Schmidt and 5 m Hale telescopes, as well as the 4 m Mayall telescope. A total of 418 clusters have been found with redshifts mostly in the range from 0.15 to 0.92. The survey was planned to minimize distance-dependent selection effects in the resulting catalog. In areas of sky where the deepest search was made, the sample is complete to about z = 0.50; there are 11 clusters per square degree at this limit. At a redshift of 1.0 there should be 63 or 45 clusters per square degree depending on whether q0 is 0.0 or 0.5, provided there is no evolution.

  18. PREDICTING MERGER-INDUCED GAS MOTIONS IN ΛCDM GALAXY CLUSTERS

    SciTech Connect

    Nagai, Daisuke; Lau, Erwin T.; Avestruz, Camille; Rudd, Douglas H.; Nelson, Kaylea

    2013-11-10

    In the hierarchical structure formation model, clusters of galaxies form through a sequence of mergers and continuous mass accretion, which generate significant random gas motions especially in their outskirts where material is actively accreting. Non-thermal pressure provided by the internal gas motions affects the thermodynamic structure of the X-ray emitting intracluster plasma and introduces biases in the physical interpretation of X-ray and Sunyaev-Zeldovich effect observations. However, we know very little about the nature of gas motions in galaxy clusters. The ASTRO-H X-ray mission, scheduled to launch in 2015, will have a calorimeter capable of measuring gas motions in galaxy clusters at the level of ∼< 100 km s{sup –1}. In this work, we predict the level of merger-induced gas motions expected in the ΛCDM model using hydrodynamical simulations of galaxy cluster formation. We show that the gas velocity dispersion is larger in more massive clusters, but exhibits a large scatter. We show that systems with large gas motions are morphologically disturbed, while early forming, relaxed groups show a smaller level of gas motions. By analyzing mock ASTRO-H observations of simulated clusters, we show that such observations can accurately measure the gas velocity dispersion out to the outskirts of nearby relaxed galaxy clusters. ASTRO-H analysis of merging clusters, on the other hand, requires multi-component spectral fitting and enables unique studies of substructures in galaxy clusters by measuring both the peculiar velocities and the velocity dispersion of gas within individual sub-clusters.

  19. The tau of galaxy clusters

    NASA Astrophysics Data System (ADS)

    Battaglia, N.

    2016-08-01

    The recent emergence of detections of the kinetic Sunyeav-Zel'dovich (kSZ) effect through cross-correlation techniques is encouraging for the prospects of future cosmic microwave background (CMB) experiments. Extracting information on the large-scale velocity fields and constraining cosmological parameters from such kSZ measurements requires an understanding of the optical depth to CMB photons through halos. Using cosmological hydrodynamic simulations we find that there exists a low-scatter relation between the optical depth and thermal Sunyeav-Zel'dovich (tSZ) signal of halos within a physical aperture. We propose that such a relation can be used to break the degeneracy between optical depth and line-of-sight velocity in kSZ measurements. The limiting factors in our proposal are systematic uncertainties associated with the sub-grid physics models in the simulations, which we calculate to be less than 10 percent. We discuss future observational measurements that could potentially be used to mitigate the systematic uncertainties in this scaling relation.

  20. Dark Matter in Galaxy Clusters: Shape, Projection, and Environment

    NASA Astrophysics Data System (ADS)

    Groener, Austen M.

    We explore the intrinsic distribution of dark matter within galaxy clusters, by combining insights from the largest N-body simulations as well as the largest observational dataset of its kind. Firstly, we study the intrinsic shape and alignment of isodensities of galaxy cluster halos extracted from the MultiDark MDR1 cosmological simulation. We find that the simulated halos are extremely prolate on small scales and increasingly spherical on larger ones. Due to this trend, analytical projection along the line of sight produces an overestimate of the concentration index as a decreasing function of radius, which we quantify by using both the intrinsic distribution of 3D concentrations (c200) and isodensity shape on weak and strong lensing scales. We find this difference to be ˜ 18% (˜ 9%) for low (medium) mass cluster halos with intrinsically low concentrations (c200=1- 3), while we find virtually no difference for halos with intrinsically high concentrations. Isodensities are found to be fairly well-aligned throughout the entirety of the radial scale of each halo population. However, major axes of individual halos have been found to deviate by as much as ˜ 30°. We also present a value-added catalog of our analysis results, which we have made publicly available to download. Following that, we then turn to observational measurements galaxy clusters. Scaling relations of clusters have made them particularly important cosmological probes of structure formation. In this work, we present a comprehensive study of the relation between two profile observables, concentration (cvir ) and mass (Mvir). We have collected the largest known sample of measurements from the literature which make use of one or more of the following reconstruction techniques: Weak gravitational lensing (WL), strong gravitational lensing (SL), Weak+Strong Lensing (WL+SL), the Caustic Method (CM), Line-of-sight Velocity Dispersion (LOSVD), and X-ray. We find that the concentration-mass (c-M) relation

  1. Impact of High Velocity Interactions on Galaxy Evolution in Galaxy Groups

    NASA Astrophysics Data System (ADS)

    Machacek, Marie E.; Jones, C.; Forman, W. R.; Kraft, R. P.; Ashby, M. L.; Hardcastle, M. J.

    2007-05-01

    Galaxy interactions in cool groups dominate galaxy evolution at high redshift. Observations of galaxies interacting in nearby galaxy groups, where the same dynamical processes that transform galaxies at high redshift can be studied in detail, are critical to our understanding of galaxy and group evolution. X-ray observations of hot gas features, e.g. surface brightness edges and wakes, reveal that high velocity interactions play a significant role in the transformation of galaxies in groups, yet, because these encounters are difficult to identify in other wavebands, few have been studied. We present two case studies of high velocity galaxy-galaxy and galaxy-gas interactions in galaxy groups: NGC4782(3C278) and NGC4783 in LGG316, and NGC6872 and NGC6876 in the Pavo group. From Chandra and XMM-Newton X-ray data, we measure the hot gas temperature, density and metal abundance in the galaxies and the intragroup medium (IGM) to characterize the thermodynamic state of the group, constrain 3D motions of the galaxies through the IGM, and determine the dominant processes transferring matter and energy between the galaxy and group gas. We compare these results with VLA observations of NGC4782/3 and Spitzer IRAC observations of NGC6872 and NGC6876 to study the impact of these interactions on nuclear activity, radio jet evolution, and star formation in these galaxies, and on the heating and enrichment of the IGM. This work was supported in part by the Smithsonian Institution, the Chandra Science Center, NASA contracts AR5-6011X, GO6-7068X, NNX06AG34G, JPL1279244 and the Royal Society.

  2. Study of bright globular clusters and Ultra-Compact Dwarf galaxies in the Antlia cluster.

    NASA Astrophysics Data System (ADS)

    Caso, J. P.; Bassino, L. P.; Richtler, T.; Smith Castelli, A. V.; Faifer, F. R.; Calderón, J. P.

    A sample of confirmed Ultra-Compact Dwarf galaxies and globular clusters around the giant galaxy NGC 3268 in the Antlia cluster is presented, including their Washington photometry. For the Antlia objects discovered so far, the reliability of a common origin with the globular clusters of the galaxies NGC 3258 and NGC 3268 is analyzed.

  3. Galaxy populations in the Antlia cluster - I. Photometric properties of early-type galaxies

    NASA Astrophysics Data System (ADS)

    Smith Castelli, Analía V.; Bassino, Lilia P.; Richtler, Tom; Cellone, Sergio A.; Aruta, Cristian; Infante, Leopoldo

    2008-06-01

    We present the first colour-magnitude relation (CMR) of early-type galaxies in the central region of the Antlia cluster, obtained from CCD wide-field photometry in the Washington photometric system. Integrated (C - T1) colours, T1 magnitudes, and effective radii have been measured for 93 galaxies (i.e. the largest galaxies sample in the Washington system till now) from the FS90 Antlia Group catalogue. Membership of 37 objects can be confirmed through new radial velocities and data collected from the literature. The resulting colour-magnitude diagram shows that early-type FS90 galaxies that are spectroscopically confirmed Antlia members or that were considered as definite members by FS90, follow a well-defined CMR that spans 9 mag in brightness with no apparent change of slope. This relation is very tight for the whole magnitude range but S0 galaxies show a larger dispersion, apparently due to a separation of ellipticals and S0s. Antlia displays a slope of -13.6 in a T1 versus (C - T1) diagram, in agreement with results for clusters like Fornax, Virgo, Coma and Perseus, which are dynamically different to Antlia. This fact might indicate that the build-up of the CMR in cluster of galaxies is more related to galaxies internal processes than to the influence of the environment. Interpreting the CMR as a luminosity-metallicity relation of old stellar systems, the metallicities of the Antlia galaxies define a global relation down to MV ~ -13. We also find, for early-type dwarfs, no clear relation between luminosity and effective radius, indicating a nearly constant mean effective radius of ~1 kpc. This value is also found in several samples of dwarf galaxies in Virgo and Coma. This paper is based on data obtained with the 4-m telescope at CTIO, Chile, with the 6.5-m Magellan telescopes at Las Campanas Observatory, Chile, and at CASLEO, operated under agreement between CONICET and the Universities of La Plata, Córdoba and San Juan, Argentina. E-mail: asmith

  4. Chandra View of Galaxy Cluster Abell 2554

    NASA Astrophysics Data System (ADS)

    kıyami Erdim, Muhammed; Hudaverdi, Murat

    2016-07-01

    We study the structure of the galaxy cluster Abell 2554 at z = 0.11, which is a member of Aquarius Super cluster using the Chandra archival data. The X-ray peak coincides with a bright elliptical cD galaxy. Slightly elongated X-ray plasma has an average temperature and metal abundance values of ˜6 keV and 0.28 solar, respectively. We observe small-scale temperature variations in the ICM. There is a significantly hot wall-like structure with 9 keV at the SE and also radio-lope locates at the tip of this hot region. A2554 is also part of a trio-cluster. Its close neighbors A2550 (at SW) and A2556 (at SE) have only 2 Mpc and 1.5 Mpc separations with A2554. Considering the temperature fluctuations and the dynamical environment of super cluster, we examine the possible ongoing merger scenarios within A2554.

  5. A CATALOG OF GLOBULAR CLUSTER SYSTEMS: WHAT DETERMINES THE SIZE OF A GALAXY'S GLOBULAR CLUSTER POPULATION?

    SciTech Connect

    Harris, William E.; Alessi, Matthew; Harris, Gretchen L. H. E-mail: alessimj@mcmaster.ca

    2013-08-01

    We present a catalog of 422 galaxies with published measurements of their globular cluster (GC) populations. Of these, 248 are E galaxies, 93 are S0 galaxies, and 81 are spirals or irregulars. Among various correlations of the total number of GCs with other global galaxy properties, we find that N{sub GC} correlates well though nonlinearly with the dynamical mass of the galaxy bulge M{sub dyn}= 4{sigma}{sub e}{sup 2} R{sub e} /G, where {sigma}{sub e} is the central velocity dispersion and R{sub e} the effective radius of the galaxy light profile. We also present updated versions of the GC specific frequency S{sub N} and specific mass S{sub M} versus host galaxy luminosity and baryonic mass. These graphs exhibit the previously known U-shape: highest S{sub N} or S{sub M} values occur for either dwarfs or supergiants, but in the midrange of galaxy size (10{sup 9}-10{sup 10} L{sub Sun }) the GC numbers fall along a well-defined baseline value of S{sub N} {approx_equal} 1 or S{sub M} = 0.1, similar among all galaxy types. Along with other recent discussions, we suggest that this trend may represent the effects of feedback, which systematically inhibited early star formation at either very low or very high galaxy mass, but which had its minimum effect for intermediate masses. Our results strongly reinforce recent proposals that GC formation efficiency appears to be most nearly proportional to the galaxy halo mass M{sub halo}. The mean 'absolute' efficiency ratio for GC formation that we derive from the catalog data is M{sub GCS}/M{sub halo} = 6 Multiplication-Sign 10{sup -5}. We suggest that the galaxy-to-galaxy scatter around this mean value may arise in part because of differences in the relative timing of GC formation versus field-star formation. Finally, we find that an excellent empirical predictor of total GC population for galaxies of all luminosities is N{sub GC} {approx} (R{sub e} {sigma}{sub e}){sup 1.3}, a result consistent with fundamental plane scaling

  6. A GMBCG Galaxy Cluster Catalog of 55,424 Rich Clusters from SDSS DR7

    SciTech Connect

    Hao, Jiangang; McKay, Timothy A.; Koester, Benjamin P.; Rykoff, Eli S.; Rozo, Eduardo; Annis, James; Wechsler, Risa H.; Evrard, August; Siegel, Seth R.; Becker, Matthew; Busha, Michael; Gerdes, David; Johnston, David E.; Sheldon, Erin; /Brookhaven

    2011-08-22

    We present a large catalog of optically selected galaxy clusters from the application of a new Gaussian Mixture Brightest Cluster Galaxy (GMBCG) algorithm to SDSS Data Release 7 data. The algorithm detects clusters by identifying the red sequence plus Brightest Cluster Galaxy (BCG) feature, which is unique for galaxy clusters and does not exist among field galaxies. Red sequence clustering in color space is detected using an Error Corrected Gaussian Mixture Model. We run GMBCG on 8240 square degrees of photometric data from SDSS DR7 to assemble the largest ever optical galaxy cluster catalog, consisting of over 55,000 rich clusters across the redshift range from 0.1 < z < 0.55. We present Monte Carlo tests of completeness and purity and perform cross-matching with X-ray clusters and with the maxBCG sample at low redshift. These tests indicate high completeness and purity across the full redshift range for clusters with 15 or more members.

  7. A GMBCG galaxy cluster catalog of 55,880 rich clusters from SDSS DR7

    SciTech Connect

    Hao, Jiangang; McKay, Timothy A.; Koester, Benjamin P.; Rykoff, Eli S.; Rozo, Eduardo; Annis, James; Wechsler, Risa H.; Evrard, August; Siegel, Seth R.; Becker, Matthew; Busha, Michael; /Fermilab /Michigan U. /Chicago U., Astron. Astrophys. Ctr. /UC, Santa Barbara /KICP, Chicago /KIPAC, Menlo Park /SLAC /Caltech /Brookhaven

    2010-08-01

    We present a large catalog of optically selected galaxy clusters from the application of a new Gaussian Mixture Brightest Cluster Galaxy (GMBCG) algorithm to SDSS Data Release 7 data. The algorithm detects clusters by identifying the red sequence plus Brightest Cluster Galaxy (BCG) feature, which is unique for galaxy clusters and does not exist among field galaxies. Red sequence clustering in color space is detected using an Error Corrected Gaussian Mixture Model. We run GMBCG on 8240 square degrees of photometric data from SDSS DR7 to assemble the largest ever optical galaxy cluster catalog, consisting of over 55,000 rich clusters across the redshift range from 0.1 < z < 0.55. We present Monte Carlo tests of completeness and purity and perform cross-matching with X-ray clusters and with the maxBCG sample at low redshift. These tests indicate high completeness and purity across the full redshift range for clusters with 15 or more members.

  8. Cosmology with velocity dispersion counts: an alternative to measuring cluster halo masses

    NASA Astrophysics Data System (ADS)

    Caldwell, C. E.; McCarthy, I. G.; Baldry, I. K.; Collins, C. A.; Schaye, J.; Bird, S.

    2016-11-01

    The evolution of galaxy cluster counts is a powerful probe of several fundamental cosmological parameters. A number of recent studies using this probe have claimed tension with the cosmology preferred by the analysis of the Planck primary cosmic microwave background (CMB) data, in the sense that there are fewer clusters observed than predicted based on the primary CMB cosmology. One possible resolution to this problem is systematic errors in the absolute halo mass calibration in cluster studies, which is required to convert the standard theoretical prediction (the halo mass function) into counts as a function of the observable (e.g. X-ray luminosity, Sunyaev-Zel'dovich flux, and optical richness). Here we propose an alternative strategy, which is to directly compare predicted and observed cluster counts as a function of the one-dimensional velocity dispersion of the cluster galaxies. We argue that the velocity dispersion of groups/clusters can be theoretically predicted as robustly as mass but, unlike mass, it can also be directly observed, thus circumventing the main systematic bias in traditional cluster counts studies. With the aid of the BAHAMAS suite of cosmological hydrodynamical simulations, we demonstrate the potential of the velocity dispersion counts for discriminating even similar Λ cold dark matter models. These predictions can be compared with the results from existing redshift surveys such as the highly complete Galaxy And Mass Assembly survey, and upcoming wide-field spectroscopic surveys such as the Wide Area Vista Extragalactic Survey and the Dark Energy Survey Instrument.

  9. STUDYING INTERCLUSTER GALAXY FILAMENTS THROUGH STACKING gmBCG GALAXY CLUSTER PAIRS

    SciTech Connect

    Zhang Yuanyuan; Dietrich, Joerg P.; McKay, Timothy A.; Nguyen, Alex T. Q.; Sheldon, Erin S.

    2013-08-20

    We present a method to study the photometric properties of galaxies in filaments by stacking the galaxy populations between pairs of galaxy clusters. Using Sloan Digital Sky Survey data, this method can detect the intercluster filament galaxy overdensity with a significance of {approx}5{sigma} out to z = 0.40. Using this approach, we study the g - r color and luminosity distribution of filament galaxies as a function of redshift. Consistent with expectation, filament galaxies are bimodal in their color distribution and contain a larger blue galaxy population than clusters. Filament galaxies are also generally fainter than cluster galaxies. More interestingly, the observed filament population seems to show redshift evolution at 0.12 < z < 0.40: the blue galaxy fraction has a trend to increase at higher redshift; such evolution is parallel to the ''Butcher-Oemler effect'' of galaxy clusters. We test the dependence of the observed filament density on the richness of the cluster pair: richer clusters are connected by higher density filaments. We also test the spatial dependence of filament galaxy overdensity: this quantity decreases when moving away from the intercluster axis between a cluster pair. This method provides an economical way to probe the photometric properties of filament galaxies and should prove useful for upcoming projects like the Dark Energy Survey.

  10. Studying Intercluster Galaxy Filaments through Stacking gmBCG Galaxy Cluster Pairs

    NASA Astrophysics Data System (ADS)

    Zhang, Yuanyuan; Dietrich, Jörg P.; McKay, Timothy A.; Sheldon, Erin S.; Nguyen, Alex T. Q.

    2013-08-01

    We present a method to study the photometric properties of galaxies in filaments by stacking the galaxy populations between pairs of galaxy clusters. Using Sloan Digital Sky Survey data, this method can detect the intercluster filament galaxy overdensity with a significance of ~5σ out to z = 0.40. Using this approach, we study the g - r color and luminosity distribution of filament galaxies as a function of redshift. Consistent with expectation, filament galaxies are bimodal in their color distribution and contain a larger blue galaxy population than clusters. Filament galaxies are also generally fainter than cluster galaxies. More interestingly, the observed filament population seems to show redshift evolution at 0.12 < z < 0.40: the blue galaxy fraction has a trend to increase at higher redshift; such evolution is parallel to the "Butcher-Oemler effect" of galaxy clusters. We test the dependence of the observed filament density on the richness of the cluster pair: richer clusters are connected by higher density filaments. We also test the spatial dependence of filament galaxy overdensity: this quantity decreases when moving away from the intercluster axis between a cluster pair. This method provides an economical way to probe the photometric properties of filament galaxies and should prove useful for upcoming projects like the Dark Energy Survey.

  11. The ESO nearby Abell cluster survey. VII. Galaxy density profiles of rich clusters of galaxies

    NASA Astrophysics Data System (ADS)

    Adami, C.; Mazure, A.; Katgert, P.; Biviano, A.

    1998-08-01

    We have analyzed the projected galaxy distributions in a subset of the ENACS cluster sample, viz. in those 77 clusters that have z < 0.1 and R_ACO >= 1 and for which ENACS and COSMOS data are available. For 20 % of these, the distribution of galaxies in the COSMOS catalogue does not allow a reliable centre position to be determined. For the other 62 clusters, we first determined the centre and elongation of the galaxy distribution. Subsequently, we made Maximum-Likelihood fits to the distribution of COSMOS galaxies for 4 theoretical profiles, two with `cores' (generalized King- and Hubble-profiles) and two with `cusps' (generalized Navarro, Frenk and White, or NFW, and de Vaucouleurs profiles). We obtain average core radii (or characteristic radii for the profiles without core) of 128, 189, 292 and 1582 kpc for fits with King, Hubble, NFW and de Vaucouleurs profiles respectively, with dispersions around these average values of 88, 116, 191 and 771 kpc. The surface density of background galaxies is about 4 10(-5) gals arcsec(-2) (with a spread of about 2 10(-5) ), and there is very good agreement between the values found for the 4 profiles. There is also very good agreement on the outer logarithmic slope of the projected galaxy distribution, which is that for the non-generalized King- and Hubble-profile (i.e. beta_ {King} = beta_ {Hubble} = 1, with the corresponding values for the two other model-profiles). We use the Likelihood ratio to investigate whether the observations are significantly better described by profiles with cusps or by profiles with cores. Taking the King and NFW profiles as `model' of either class, we find that about 75 % of the clusters are better fit by the King profile than by the NFW profile. However, for the individual clusters the preference for the King profile is rarely significant at a confidence level of more than 90 %. When we limit ourselves to the central regions it appears that the signifance increases drastically, with 65 % of the

  12. ON THE CLUSTERING OF SUBMILLIMETER GALAXIES

    SciTech Connect

    Williams, Christina C.; Giavalisco, Mauro; Yun, Min S.; Pope, Alexandra; Wilson, Grant W.; Cybulski, Ryan; Schloerb, F. Peter; Porciani, Cristiano; Scott, Kimberly S.; Austermann, Jason E.; Aretxaga, Itziar; Hughes, David H.; Hatsukade, Bunyo; Kawabe, Ryo; Lee, Kyoung-Soo; Kohno, Kotaro; Perera, Thushara

    2011-06-01

    We measure the angular two-point correlation function of submillimeter galaxies (SMGs) from 1.1 mm imaging of the COSMOS field with the AzTEC camera and ASTE 10 m telescope. These data yield one of the largest contiguous samples of SMGs to date, covering an area of 0.72 deg{sup 2} down to a 1.26 mJy beam{sup -1} (1{sigma}) limit, including 189 (328) sources with S/N {>=}3.5 (3). We can only set upper limits to the correlation length r{sub 0}, modeling the correlation function as a power law with pre-assigned slope. Assuming existing redshift distributions, we derive 68.3% confidence level upper limits of r{sub 0} {approx}< 6-8h{sup -1} Mpc at 3.7 mJy and r{sub 0} {approx}< 11-12 h{sup -1} Mpc at 4.2 mJy. Although consistent with most previous estimates, these upper limits imply that the real r{sub 0} is likely smaller. This casts doubts on the robustness of claims that SMGs are characterized by significantly stronger spatial clustering (and thus larger mass) than differently selected galaxies at high redshift. Using Monte Carlo simulations we show that even strongly clustered distributions of galaxies can appear unclustered when sampled with limited sensitivity and coarse angular resolution common to current submillimeter surveys. The simulations, however, also show that unclustered distributions can appear strongly clustered under these circumstances. From the simulations, we predict that at our survey depth, a mapped area of 2 deg{sup 2} is needed to reconstruct the correlation function, assuming smaller beam sizes of future surveys (e.g., the Large Millimeter Telescope's 6'' beam size). At present, robust measures of the clustering strength of bright SMGs appear to be below the reach of most observations.

  13. A COMPARISON OF THE CLUSTERING PROPERTIES BETWEEN GALAXIES AND GROUPS OF GALAXIES

    SciTech Connect

    Deng Xinfa

    2013-03-01

    In this study, I apply cluster analysis and perform comparative studies of clustering properties between galaxies and groups of galaxies. It is found that the number of objects N{sub max} of the richest system and the maximal length D{sub max} of the largest system for groups in all samples are apparently larger than ones for galaxies, and that galaxies preferentially form isolated, paired, and small systems, while groups preferentially form grouped and clustered systems. These results show that groups are more strongly clustered than galaxies, which is consistent with statistical results of the correlation function.

  14. Dynamical Analyses of Galaxy Clusters With Large Redshift Samples

    NASA Astrophysics Data System (ADS)

    Mohr, J. J.; Richstone, D. O.; Wegner, G.

    1998-12-01

    We construct equilibrium models of galaxy orbits in five nearby galaxy clusters to study the distribution of binding mass, the nature of galaxy orbits and the kinematic differences between cluster populations of emission-line and non emission-line galaxies. We avail ourselves of 1718 galaxy redshifts (and 1203 cluster member redshifts) in this Jeans analysis; most of these redshifts are new, coming from multifiber spectroscopic runs on the MDM 2.4m with the Decaspec and queue observing on WIYN with Hydra. In addition to the spectroscopic data we have V and R band CCD mosaics (obtained with the MDM 1.3m) of the Abell region in each of these clusters. Our scientific goals include: (i) a quantitative estimate of the range of binding masses M500 consistent with the optical and X-ray data, (ii) an estimate of the typical galaxy oribital anisotropies required to make the galaxy data consistent with the NFW expectation for the cluster potential, (iii) a better understanding of the systematics inherent in the process of rescaling and ``stacking'' galaxy cluster observations, (iv) a reexamination of the recent CNOC results implying that emission-line (blue) galaxies are an equilibrium population with a more extended radial distribution than their non emission-line (red) galaxy counterparts and (v) a measure of the galaxy contribution to the cluster mass of baryons.

  15. SPIDER - IX. Classifying galaxy groups according to their velocity distribution

    NASA Astrophysics Data System (ADS)

    Ribeiro, A. L. B.; de Carvalho, R. R.; Trevisan, M.; Capelato, H. V.; La Barbera, F.; Lopes, P. A. A.; Schilling, A. C.

    2013-09-01

    We introduce a new method to study the velocity distribution of galaxy systems, the Hellinger Distance (HD), designed for detecting departures from a Gaussian velocity distribution. Testing different approaches to measure normality of a distribution, we conclude that HD is the least vulnerable method to type I and II statistical errors. We define a relaxed galactic system as the one with unimodal velocity distribution and a normality deviation below a critical value (HD < 0.05). In this work, we study the Gaussian nature of the velocity distribution of the Berlind group sample, and of the FoF groups from the Millennium simulation. For the Berlind group sample (z < 0.1), 67 per cent of the systems are classified as relaxed, while for the Millennium sample we find 63 per cent (z = 0). We verify that in multi-modal groups the average mass of modes in high-multiplicity (N ≥ 20) systems are significantly larger than in low-multiplicity ones (N < 20), suggesting that groups experience a mass growth at an increasing virialization rate towards z = 0, with larger systems accreting more massive subunits. We also investigate the connection between galaxy properties ([Fe/H], Age, eClass, g - r, Rpetro and <μpetro>) and the Gaussianity of the velocity distribution of the groups. Bright galaxies (Mr ≤ -20.7) residing in the inner and outer regions of groups do not show significant differences in the listed quantities regardless if the group has a Gaussian (G) or a Non-Gaussian (NG) velocity distribution. However, the situation is significantly different when we examine the faint galaxies (-20.7 < Mr ≤ -17.9). In G groups, there is a remarkable difference between the galaxy properties of the inner and outer galaxy populations, testifying how the environment is affecting the galaxies. Instead, in NG groups there is no segregation between the properties of galaxies in the inner and outer regions, showing that the properties of these galaxies still reflect the physical

  16. Statistical Issues in Galaxy Cluster Cosmology

    NASA Technical Reports Server (NTRS)

    Mantz, Adam

    2013-01-01

    The number and growth of massive galaxy clusters are sensitive probes of cosmological structure formation. Surveys at various wavelengths can detect clusters to high redshift, but the fact that cluster mass is not directly observable complicates matters, requiring us to simultaneously constrain scaling relations of observable signals with mass. The problem can be cast as one of regression, in which the data set is truncated, the (cosmology-dependent) underlying population must be modeled, and strong, complex correlations between measurements often exist. Simulations of cosmological structure formation provide a robust prediction for the number of clusters in the Universe as a function of mass and redshift (the mass function), but they cannot reliably predict the observables used to detect clusters in sky surveys (e.g. X-ray luminosity). Consequently, observers must constrain observable-mass scaling relations using additional data, and use the scaling relation model in conjunction with the mass function to predict the number of clusters as a function of redshift and luminosity.

  17. Tangential Velocity of the Dark Matter in the Bullet Cluster from Precise Lensed Image Redshifts

    NASA Astrophysics Data System (ADS)

    Molnar, Sandor M.; Broadhurst, Tom; Umetsu, Keiichi; Zitrin, Adi; Rephaeli, Yoel; Shimon, Meir

    2013-09-01

    We show that the fast-moving component of the "Bullet Cluster" (1E0657-56) can induce potentially resolvable redshift differences between multiply lensed images of background galaxies. This moving cluster effect, due to the tangential peculiar velocity of the lens, can be expressed as the scalar product of the lensing deflection angle with the tangential velocity of the mass components; the effect is maximal for clusters colliding in the plane of the sky with velocities boosted by their mutual gravity. The Bullet Cluster is likely to be the best candidate for the first measurement of this effect due to the large collision velocity and because the lensing deflection and the cluster fields can be calculated in advance. We derive the deflection field using multiply lensed background galaxies detected with the Hubble Space Telescope. The velocity field is modeled using self-consistent N-body/hydrodynamical simulations constrained by the observed X-ray and gravitational lensing features of this system. We predict that the triply lensed images of systems "G" and "H" straddling the critical curve of the bullet component will show the largest frequency shifts up to ~0.5 km s-1. These shifts are within the range of the Atacama Large Millimeter/Submillimeter Array for molecular emission, and are near the resolution limit of the new generation high-throughput optical-IR spectrographs. The detection of this effect measures the tangential motion of the subclusters directly, thereby clarifying the tension with ΛCDM, which is inferred from the gas motion less directly. This method may be extended to smaller redshift differences using the Lyα forest toward QSOs lensed by more typical clusters of galaxies. More generally, the tangential component of the peculiar velocities of clusters derived by our method complements the radial component determined by the kinematic Sunyaev-Zel'dovich effect, providing a full three-dimensional description of velocities.

  18. TANGENTIAL VELOCITY OF THE DARK MATTER IN THE BULLET CLUSTER FROM PRECISE LENSED IMAGE REDSHIFTS

    SciTech Connect

    Molnar, Sandor M.; Broadhurst, Tom; Zitrin, Adi; Rephaeli, Yoel; Shimon, Meir

    2013-09-01

    We show that the fast-moving component of the ''Bullet Cluster'' (1E0657-56) can induce potentially resolvable redshift differences between multiply lensed images of background galaxies. This moving cluster effect, due to the tangential peculiar velocity of the lens, can be expressed as the scalar product of the lensing deflection angle with the tangential velocity of the mass components; the effect is maximal for clusters colliding in the plane of the sky with velocities boosted by their mutual gravity. The Bullet Cluster is likely to be the best candidate for the first measurement of this effect due to the large collision velocity and because the lensing deflection and the cluster fields can be calculated in advance. We derive the deflection field using multiply lensed background galaxies detected with the Hubble Space Telescope. The velocity field is modeled using self-consistent N-body/hydrodynamical simulations constrained by the observed X-ray and gravitational lensing features of this system. We predict that the triply lensed images of systems ''G'' and ''H'' straddling the critical curve of the bullet component will show the largest frequency shifts up to {approx}0.5 km s{sup -1}. These shifts are within the range of the Atacama Large Millimeter/Submillimeter Array for molecular emission, and are near the resolution limit of the new generation high-throughput optical-IR spectrographs. The detection of this effect measures the tangential motion of the subclusters directly, thereby clarifying the tension with {Lambda}CDM, which is inferred from the gas motion less directly. This method may be extended to smaller redshift differences using the Ly{alpha} forest toward QSOs lensed by more typical clusters of galaxies. More generally, the tangential component of the peculiar velocities of clusters derived by our method complements the radial component determined by the kinematic Sunyaev-Zel'dovich effect, providing a full three-dimensional description of

  19. The galaxy velocity field and CDM models

    NASA Technical Reports Server (NTRS)

    Tormen, Giuseppe; Moscardini, Lauro; Lucchin, Francesco; Matarrese, Sabino

    1993-01-01

    It is generally accepted that some kind of non-baryonic dark matter accounts for most of the mass density of the universe. Considering such a component has become, in the last decade, a key ingredient in current theories of structure formation. In particular, the Cold Dark Matter (CDM) scenario has proven to be quite successful in explaining most of the observed properties of galaxies and of their large-scale distribution. The standard CDM model is characterized by a primordial Zel'dovich spectrum, of random-phase adiabatic perturbations in a universe with density parameter omega sub 0 = 1 and vanishing cosmological constant. This poster paper presents an analysis of observational data on peculiar motion of optical galaxies in comparison to the predictions of CDM models where the assumptions of the standard scenario: omega sub 0 = 1, n = 1, and bias parameter b = 1 are relaxed. In particular, CDM models with 0 less than n less than 1 and 0.4 less than omega sub 0 less than 1 are considered.

  20. Cosmological Constraints from Galaxy Clustering and the Mass-to-number Ratio of Galaxy Clusters

    NASA Astrophysics Data System (ADS)

    Tinker, Jeremy L.; Sheldon, Erin S.; Wechsler, Risa H.; Becker, Matthew R.; Rozo, Eduardo; Zu, Ying; Weinberg, David H.; Zehavi, Idit; Blanton, Michael R.; Busha, Michael T.; Koester, Benjamin P.

    2012-01-01

    We place constraints on the average density (Ω m ) and clustering amplitude (σ8) of matter using a combination of two measurements from the Sloan Digital Sky Survey: the galaxy two-point correlation function, wp (rp ), and the mass-to-galaxy-number ratio within galaxy clusters, M/N, analogous to cluster M/L ratios. Our wp (rp ) measurements are obtained from DR7 while the sample of clusters is the maxBCG sample, with cluster masses derived from weak gravitational lensing. We construct nonlinear galaxy bias models using the Halo Occupation Distribution (HOD) to fit both wp (rp ) and M/N for different cosmological parameters. HOD models that match the same two-point clustering predict different numbers of galaxies in massive halos when Ω m or σ8 is varied, thereby breaking the degeneracy between cosmology and bias. We demonstrate that this technique yields constraints that are consistent and competitive with current results from cluster abundance studies, without the use of abundance information. Using wp (rp ) and M/N alone, we find Ω0.5 m σ8 = 0.465 ± 0.026, with individual constraints of Ω m = 0.29 ± 0.03 and σ8 = 0.85 ± 0.06. Combined with current cosmic microwave background data, these constraints are Ω m = 0.290 ± 0.016 and σ8 = 0.826 ± 0.020. All errors are 1σ. The systematic uncertainties that the M/N technique are most sensitive to are the amplitude of the bias function of dark matter halos and the possibility of redshift evolution between the SDSS Main sample and the maxBCG cluster sample. Our derived constraints are insensitive to the current level of uncertainties in the halo mass function and in the mass-richness relation of clusters and its scatter, making the M/N technique complementary to cluster abundances as a method for constraining cosmology with future galaxy surveys.

  1. Gas loss in simulated galaxies as they fall into clusters.

    PubMed

    Cen, Renyue; Pop, Ana Roxana; Bahcall, Neta A

    2014-06-01

    We use high-resolution cosmological hydrodynamic galaxy formation simulations to gain insights into how galaxies lose their cold gas at low redshift as they migrate from the field to the high-density regions of clusters of galaxies. We find that beyond three cluster virial radii, the fraction of gas-rich galaxies is constant, representing the field. Within three cluster-centric radii, the fraction of gas-rich galaxies declines steadily with decreasing radius, reaching <10% near the cluster center. Our results suggest galaxies start to feel the effect of the cluster environment on their gas content well beyond the cluster virial radius. We show that almost all gas-rich galaxies at the cluster virial radius are falling in for the first time at nearly radial orbits. Furthermore, we find that almost no galaxy moving outward at the cluster virial radius is gas-rich (with a gas-to-baryon ratio greater than 1%). These results suggest that galaxies that fall into clusters lose their cold gas within a single radial round-trip.

  2. Gas loss in simulated galaxies as they fall into clusters.

    PubMed

    Cen, Renyue; Pop, Ana Roxana; Bahcall, Neta A

    2014-06-01

    We use high-resolution cosmological hydrodynamic galaxy formation simulations to gain insights into how galaxies lose their cold gas at low redshift as they migrate from the field to the high-density regions of clusters of galaxies. We find that beyond three cluster virial radii, the fraction of gas-rich galaxies is constant, representing the field. Within three cluster-centric radii, the fraction of gas-rich galaxies declines steadily with decreasing radius, reaching <10% near the cluster center. Our results suggest galaxies start to feel the effect of the cluster environment on their gas content well beyond the cluster virial radius. We show that almost all gas-rich galaxies at the cluster virial radius are falling in for the first time at nearly radial orbits. Furthermore, we find that almost no galaxy moving outward at the cluster virial radius is gas-rich (with a gas-to-baryon ratio greater than 1%). These results suggest that galaxies that fall into clusters lose their cold gas within a single radial round-trip. PMID:24843167

  3. Gas loss in simulated galaxies as they fall into clusters

    PubMed Central

    Cen, Renyue; Pop, Ana Roxana; Bahcall, Neta A.

    2014-01-01

    We use high-resolution cosmological hydrodynamic galaxy formation simulations to gain insights into how galaxies lose their cold gas at low redshift as they migrate from the field to the high-density regions of clusters of galaxies. We find that beyond three cluster virial radii, the fraction of gas-rich galaxies is constant, representing the field. Within three cluster-centric radii, the fraction of gas-rich galaxies declines steadily with decreasing radius, reaching <10% near the cluster center. Our results suggest galaxies start to feel the effect of the cluster environment on their gas content well beyond the cluster virial radius. We show that almost all gas-rich galaxies at the cluster virial radius are falling in for the first time at nearly radial orbits. Furthermore, we find that almost no galaxy moving outward at the cluster virial radius is gas-rich (with a gas-to-baryon ratio greater than 1%). These results suggest that galaxies that fall into clusters lose their cold gas within a single radial round-trip. PMID:24843167

  4. The Criteria for Morphological Classification of PF Galaxy Clusters

    NASA Astrophysics Data System (ADS)

    Panko, E. A.

    The morphological types of galaxy clusters resulting from their out ward appearance is physically related to the clusters and their member galaxies. Presented here is an adopted system of morphological types of galaxy clusters based on the Zwicky, Boutz&Morgan, Rood&Sastry, and L'opez-Cruz systems. The adopted types are suitable for automated classification of galaxy clusters from The Catalogue of Galaxy Clusters and Groups (Panko& Flin 2006). Numerical criteria describing 6 main types were distinguished: Concentrated C, Intermediate I, Open O, Line L, Flat F, and cD. The types correspond to the base divisions from regular to irregular clusters, but also note the presence of preferential direction orplane in each cluster.

  5. Cosmological parameter constraints from galaxy-galaxy lensing and galaxy clustering with the SDSS DR7

    NASA Astrophysics Data System (ADS)

    Mandelbaum, Rachel; Slosar, Anže; Baldauf, Tobias; Seljak, Uroš; Hirata, Christopher M.; Nakajima, Reiko; Reyes, Reinabelle; Smith, Robert E.

    2013-06-01

    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 haloes, independent of the details of how galaxies populate dark matter haloes. 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. We generalize the approach of Baldauf et al. to remove small-scale information (below 2 and 4 h-1 Mpc for lensing and clustering measurements, respectively), where the cross-correlation coefficient differs from unity. We derive constraints for three galaxy samples covering 7131 deg2, containing 69 150, 62 150 and 35 088 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 σ8 and Ωm (and marginalize over non-linear galaxy bias) in a flat Λ cold dark matter model, the best-constrained quantity is σ8(Ωm/0.25)0.57 = 0.80 ± 0.05 (1σ, stat. + sys.), where statistical and systematic errors (photometric redshift and shear calibration) have comparable contributions, and we have fixed ns = 0.96 and h = 0.7. These strong constraints on the 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 Wilkinson Microwave Anisotropy Probe 7-year (WMAP7) cosmic microwave background (CMB) data, constraints on σ8, Ωm, H0, wde and ∑mν become 30-80 per cent tighter than with CMB data alone, since our data break several parameter

  6. Joint Analysis of Galaxy-Galaxy Lensing and Galaxy Clustering: Methodology and Forecasts for DES

    SciTech Connect

    Park, Y.

    2015-07-19

    The joint analysis of galaxy-galaxy lensing and galaxy clustering is a promising method for inferring the growth function of large scale structure. Our analysis will be carried out on data from the Dark Energy Survey (DES), with its measurements of both the distribution of galaxies and the tangential shears of background galaxies induced by these foreground lenses. We develop a practical approach to modeling the assumptions and systematic effects affecting small scale lensing, which provides halo masses, and large scale galaxy clustering. Introducing parameters that characterize the halo occupation distribution (HOD), photometric redshift uncertainties, and shear measurement errors, we study how external priors on different subsets of these parameters affect our growth constraints. Degeneracies within the HOD model, as well as between the HOD and the growth function, are identified as the dominant source of complication, with other systematic effects sub-dominant. The impact of HOD parameters and their degeneracies necessitate the detailed joint modeling of the galaxy sample that we employ. Finally, we conclude that DES data will provide powerful constraints on the evolution of structure growth in the universe, conservatively/optimistically constraining the growth function to 7.9%/4.8% with its first-year data that covered over 1000 square degrees, and to 3.9%/2.3% with its full five-year data that will survey 5000 square degrees, including both statistical and systematic uncertainties.

  7. Understanding the Toothbrush Merging Galaxy Cluster to Constrain Dark Matter

    NASA Astrophysics Data System (ADS)

    Dawson, William; Brüggen, M.; Van Weeren, R. J.; Wittman, D. M.

    2014-01-01

    Merging galaxy clusters have proven to be one of the most important probes of dark matter self-interaction properties. If their full dark matter constraining power is to be realized though, we must accurately quantify the properties of these dissociative mergers. Some properties such as mass and relative line of sight velocity can be directly measured and sufficiently constrained, but there remains considerable uncertainty on indirect properties of the mergers. Indirect properties such as the angle of the merger axis with the plane of the sky and collision velocity are crucial to translating the gravitational lensing measurements of the mass, X-ray measurements of the cluster gas and optical measurements of the galaxies into constraints on the dark matter properties. By utilizing multi-wavelength measurements (X-ray to radio), of the Toothbrush radio relic dissociative merger (1RXS J0603+4212) we show that we can improve the constraints on the indirect parameters of the merger by up to an order of magnitude vs. traditional approaches. By utilizing multi-wavelength measurements (X-ray to radio), of the Toothbrush radio relic dissociative merger we show that we can improve the constraints on the indirect parameters of the merger by up to an order of magnitude vs. traditional approaches.

  8. Alignments of the Dominant Galaxies in Poor Clusters

    NASA Astrophysics Data System (ADS)

    Fuller, Todd M.; West, Michael J.; Bridges, Terry J.

    1999-07-01

    We have examined the orientations of brightest cluster galaxies (BCGs) in poor MKW (Morgan, Kayser, and White) and AWM (Albert, White, and Morgan) clusters and find that, like their counterparts in richer Abell clusters, poor cluster BCGs exhibit a strong propensity to be aligned with the principal axes of their host clusters as well as the surrounding distribution of nearby (<=20 h-1 Mpc) Abell clusters. The processes responsible for dominant galaxy alignments are therefore independent of cluster richness. We argue that these alignments most likely arise from anisotropic infall of material into clusters along large-scale filaments.

  9. Major axis alignments of poor cluster dominant galaxies

    NASA Astrophysics Data System (ADS)

    Fuller, T.; West, M.; Bridges, T.

    1996-12-01

    The MKW and AWM poor clusters are very different environments from rich Abell clusters. We obtained images with the Jacobus Kapteyn Telescope of 21 brightest cluster members (BCM) of the MKW/AWM clusters and determined that the major axis of the BCMs exhibits alignments similar to those in rich cluster dominant galaxies. Specifically, the major axes of the poor cluster BCMs point to nearby (< 20 Mpc) Abell clusters. Using the Kolmolgorov-Smirnov test, we reject the hypothesis that the position angles are randomly distributed at the 97% confidence level. The processes responsible for dominant galaxy alignments are therefore independent of cluster richness.

  10. On the distribution of galaxy ellipticity in clusters

    NASA Astrophysics Data System (ADS)

    D'Eugenio, F.; Houghton, R. C. W.; Davies, R. L.; Dalla Bontà, E.

    2015-07-01

    We study the distribution of projected ellipticity n(ɛ) for galaxies in a sample of 20 rich (Richness ≥ 2) nearby (z < 0.1) clusters of galaxies. We find no evidence of differences in n(ɛ), although the nearest cluster in the sample (the Coma Cluster) is the largest outlier (P(same) < 0.05). We then study n(ɛ) within the clusters, and find that ɛ increases with projected cluster-centric radius R (hereafter the ɛ-R relation). This trend is preserved at fixed magnitude, showing that this relation exists over and above the trend of more luminous galaxies to be both rounder and more common in the centres of clusters. The ɛ-R relation is particularly strong in the subsample of intrinsically flattened galaxies (ɛ > 0.4), therefore it is not a consequence of the increasing fraction of round slow rotator galaxies near cluster centers. Furthermore, the ɛ-R relation persists for just smooth flattened galaxies and for galaxies with de Vaucouleurs-like light profiles, suggesting that the variation of the spiral fraction with radius is not the underlying cause of the trend. We interpret our findings in light of the classification of early type galaxies (ETGs) as fast and slow rotators. We conclude that the observed trend of decreasing ɛ towards the centres of clusters is evidence for physical effects in clusters causing fast rotator ETGs to have a lower average intrinsic ellipticity near the centres of rich clusters.

  11. GEMINI/GMOS SPECTROSCOPY OF 26 STRONG-LENSING-SELECTED GALAXY CLUSTER CORES

    SciTech Connect

    Bayliss, Matthew B.; Gladders, Michael D.; Koester, Benjamin P.; Hennawi, Joseph F.; Sharon, Keren; Dahle, Haakon; Oguri, Masamune

    2011-03-15

    We present results from a spectroscopic program targeting 26 strong-lensing cluster cores that were visually identified in the Sloan Digital Sky Survey (SDSS) and the Second Red-Sequence Cluster Survey (RCS-2). The 26 galaxy cluster lenses span a redshift range of 0.2 < z < 0.65, and our spectroscopy reveals 69 unique background sources with redshifts as high as z = 5.200. We also identify redshifts for 262 cluster member galaxies and measure the velocity dispersions and dynamical masses for 18 clusters where we have redshifts for N {>=} 10 cluster member galaxies. We account for the expected biases in dynamical masses of strong-lensing-selected clusters as predicted by results from numerical simulations and discuss possible sources of bias in our observations. The median dynamical mass of the 18 clusters with N {>=} 10 spectroscopic cluster members is M {sub Vir} = 7.84 x 10{sup 14} M {sub sun} h {sup -1} {sub 0.7}, which is somewhat higher than predictions for strong-lensing-selected clusters in simulations. The disagreement is not significant considering the large uncertainty in our dynamical data, systematic uncertainties in the velocity dispersion calibration, and limitations of the theoretical modeling. Nevertheless our study represents an important first step toward characterizing large samples of clusters that are identified in a systematic way as systems exhibiting dramatic strong-lensing features.

  12. Gas and iron content of galaxy clusters

    NASA Astrophysics Data System (ADS)

    Chiosi, C.

    2000-12-01

    Up to now, many theoretical studies aimed at reproducing the total amount of iron and gas in the intra-cluster medium meet the embarrassing situation, in which if the iron content is reproduced, the gas is not. More precisely, at given iron mass, too little gas and too high Fe abundance in turn are obtained as compared to the observational data. Large dilution by primordial gas is then invoked to get rid of the difficulty. In this paper we present a new approach to this problem. Basic ingredients of the present analysis are: (i) The adoption of multi-zone models of elliptical galaxies in the framework of the super-nova driven galactic wind scheme. They yield a more realistic description of the galactic ejecta in which the effects of gradients in star formation and chemical enrichment are taken into account. (ii) The stellar initial mass function is let vary with the physical conditions of the star forming medium. More precisely, the typical mass scale of the initial mass function increases with the gas temperature. Since no cooling process exists decreasing the temperature of a galaxy's gas below the limit set by the current value of the cosmic background radiation, it immediately follows that the stellar initial mass function of proto-galaxies whose stellar activity began at high red-shift (when the CBR temperature was higher than the present-day mean temperature of molecular clouds) is different from the one in galaxies which did the same but at lower red-shift. Because of this, at given galaxy mass the ejecta are expected to depend on the red-shift. (iii) Finally, the basic assumption is made that at any time (red-shift) the mass distribution of proto-galaxies follows the Press-Schechter law holding for Dark Matter, however with masses comprised between suitable minimum and maximum values, M_Lmin and M_L*, respectively, that are also varying with time and/or red-shift. This is equivalent to assume a sort of continuously varying mass function for galaxies as well

  13. QUASAR-GALAXY CLUSTERING THROUGH PROJECTED GALAXY COUNTS AT z = 0.6-1.2

    SciTech Connect

    Zhang Shaohua; Zhou Hongyan; Wang Tinggui; Wang Huiyuan E-mail: twang@ustc.edu.cn

    2013-08-20

    We investigate the spatial clustering of galaxies around quasars at z = 0.6-1.2 using photometric data from Sloan Digital Sky Survey Stripe 82. The quasar and galaxy cross-correlation functions are measured through the projected galaxy number density n(r{sub p} ) on scales of 0.05 < r{sub p} < 20 h {sup -1} Mpc around quasars for a sample of 2300 quasars from Schneider et al. We detect strong clustering signals at all redshifts and find that the clustering amplitude increases significantly with redshift. We examine the dependence of quasar-galaxy clustering on quasar and galaxy properties and find that the clustering amplitude is significantly larger for quasars with more massive black holes or with bluer colors, while there is no dependence on quasar luminosity. We also show that quasars have a stronger correlation amplitude with blue galaxies than with red galaxies. We finally discuss the implications of our findings.

  14. H I absorption toward cooling flows in clusters of galaxies

    NASA Technical Reports Server (NTRS)

    Mcnamara, Brian R.; O'Connell, Robert W.; Bregman, Joel N.

    1990-01-01

    An H I survey of 14 cooling flow clusters and two noncooling flow clusters was conducted, and H I absorption features were detected against the nuclear radio continuum sources of two cooling flow dominant (CFD) galaxies, 2A 0335 + 096 and MKW3s. The absorption features are broad and redshifted with respect to the stellar absorption-line velocity of the CFDs by 90-225 km/s. This indicates that the H I is falling onto, and is probably gravitationally bound to, the CFDs. The kinematics of the H I clouds suggest a possible kinematic link between the warm and cold phases of the intracluster medium. The clouds are orders of magnitude smaller in radius and mass and larger in density than Galactic H I clouds. The detected CFDs have mass-accretion rates that are about 2.5 times larger than the CFDs that were not detected.

  15. GALAXY CLUSTERS IN THE LINE OF SIGHT TO BACKGROUND QUASARS. III. MULTI-OBJECT SPECTROSCOPY

    SciTech Connect

    Andrews, H.; Barrientos, L. F.; Padilla, N.; Lacerna, I.; Lopez, S.; Lira, P.; Maureira, M. J.; Gilbank, D. G.; Ellingson, E.; Gladders, M. D.; Yee, H. K. C.

    2013-09-01

    We present Gemini/GMOS-S multi-object spectroscopy of 31 galaxy cluster candidates at redshifts between 0.2 and 1.0 and centered on QSO sight lines taken from Lopez et al. The targets were selected based on the presence of an intervening Mg II absorption system at a similar redshift to that of a galaxy cluster candidate lying at a projected distance <2 h{sub 71}{sup -1} Mpc from the QSO sight line (a {sup p}hotometric hit{sup )}. The absorption systems span rest-frame equivalent widths between 0.015 and 2.028 A. Our aim was three-fold: (1) to identify the absorbing galaxies and determine their impact parameters, (2) to confirm the galaxy cluster candidates in the vicinity of each quasar sightline, and (3) to determine whether the absorbing galaxies reside in galaxy clusters. In this way, we are able to characterize the absorption systems associated with cluster members. Our main findings are as follows. (1) We identified 10 out of 24 absorbing galaxies with redshifts between 0.2509 {<=} z{sub gal} {<=} 1.0955, up to an impact parameter of 142 h{sub 71}{sup -1} kpc and a maximum velocity difference of 280 km s{sup -1}. (2) We spectroscopically confirmed 20 out of 31 cluster/group candidates, with most of the confirmed clusters/groups at z < 0.7. This relatively low efficiency results from the fact that we centered our observations on the QSO location, and thus occasionally some of the cluster centers were outside the instrument field of view. (3) Following from the results above, we spectroscopically confirmed of 10 out of 14 photometric hits within {approx}650 km s{sup -1} from galaxy clusters/groups, in addition to two new ones related to galaxy group environments. These numbers imply efficiencies of 71% in finding such systems with MOS spectroscopy. This is a remarkable result since we defined a photometric hit as those cluster-absorber pairs having a redshift difference {Delta}z = 0.1. The general population of our confirmed absorbing galaxies have luminosities

  16. Tides, Interactions, and Fine-Scale Substructures in Galaxy Clusters

    NASA Astrophysics Data System (ADS)

    Conselice, Christopher J.; Gallagher, John S., III

    1999-01-01

    We present the results of a study on galaxy interactions, tides, and other processes that produce luminous fine-scale substructures in the galaxy clusters: Coma, Perseus, Abell 2199, AWM 3, and AWM 5. All unusual structures in these clusters can be categorized into seven morphologies: interacting galaxies, multiple galaxies (noninteracting), distorted galaxies, tailed galaxies, line galaxies, dwarf galaxy groups, and galaxy aggregates. The various morphologies are described, and a catalog is presented, of 248 objects in these five clusters along with color, and positional information obtained from CCD images taken with the WIYN 3.5 m telescope in broadband B and R filters. Distorted, interacting, and fine-scale substructures have a range of colors extending from blue objects with B-R~0 to redder colors at B-R~2.5. We also find that the structures with the most disturbed morphology have the bluest colors. In addition, the relative number distributions of these structures suggest that two separate classes of galaxy clusters exist: one dominated by distorted structures and the other dominated by galaxy associations. The Coma and Perseus clusters, respectively, are proposed as models for these types of clusters. These structures avoid the deep potentials of the dominant D or cD galaxies in the Coma and Perseus clusters, and tend to clump together. Possible mechanisms for the production of fine-scale substructure are reviewed and compared with observations of z~0.4 Butcher-Oemler clusters. We conclude, based on color, positional, and statistical data, that the most likely mechanism for the creation of these structures is through an interaction with the gravitational potential of the cluster, possibly coupled with effects of weak interactions with cluster ellipticals.

  17. Galaxy Cluster Studies with the Hobby Eberly Telescope Dark Energy Experiment

    NASA Astrophysics Data System (ADS)

    Boada, Steven A.; Papovich, Casey J.; Wechsler, Risa H.; Rozo, Eduardo; Rykoff, Eli S.; Gebhardt, Karl

    2016-01-01

    The study of clusters of galaxies has been argued to be a very effective way to measure cosmological parameters, including measuring dark energy and testing models of gravity. The Hobby Eberly Telescope Dark Energy Experiment (HETDEX) will observe many hundreds of square degrees, covering a large sample of galaxy clusters out to z = 0.5 based on their optical spectra (3500-5500 Å). The spectra will provide important measures of the clusters dynamics and may enable constraints on cosmological parameters, but only if the measurements provide accurate estimates of the total cluster masses. We have carried out a study to investigate the ability of HETDEX to recover accurate galaxy cluster masses over a wide range of masses and redshifts. We used a detailed mock galaxy catalog and present mock observations of two different scenarios: (1) We targeted individual galaxy clusters to investigate the recovery of parameters with such observations. (2) We created and evaluated a HETDEX-like selection "function'' of galaxies over a similarly sized portion of the sky and use well adopted techniques to recover the dynamical properties, such as velocity dispersion and mass. Using both observing strategies, we produce cluster mass probability density functions P(X|M,z), which can be used to determine the probability that a galaxy cluster of given mass (M), located at redshift (z) determined using observable parameter (X). We then applied these probability functions to ten galaxy clusters selected from the Sloan Digital Sky Survey DR8 and the Chandra-XMM X-ray Cluster Survey at z=0.2-0.3, and observed by the HETDEX spectrograph prototype instrument (VIRUS-p). We measured spectroscopic redshifts and line-of-sight velocities of the galaxies in and around each cluster, derived a line-of-sight velocity dispersion, and inferred a dynamical mass for each cluster which ranges from (0.4-24) x 1014 M⊙ (M200c). Using the mass probability density functions described above, we updated these

  18. Detection of CO emission in Hydra 1 cluster galaxies

    NASA Technical Reports Server (NTRS)

    Huchtmeier, W. K.

    1990-01-01

    A survey of bright Hydra cluster spiral galaxies for the CO(1-0) transition at 115 GHz was performed with the 15m Swedish-ESO submillimeter telescope (SEST). Five out of 15 galaxies observed have been detected in the CO(1-0) line. The largest spiral galaxy in the cluster, NGC 3312, got more CO than any spiral of the Virgo cluster. This Sa-type galaxy is optically largely distorted and disrupted on one side. It is a good candidate for ram pressure stripping while passing through the cluster's central region. A comparison with global CO properties of Virgo cluster spirals shows a relatively good agreement with the detected Hydra cluster galaxies.

  19. Supermassive black holes and central star clusters: Connection with the host galaxy kinematics and color

    NASA Astrophysics Data System (ADS)

    Zasov, A. V.; Cherepashchuk, A. M.

    2013-11-01

    The relationship between the masses of the central, supermassive black holes ( M bh) and of the nuclear star clusters ( M nc) of disk galaxies with various parameters galaxies are considered: the rotational velocity at R = 2 kpc V (2), the maximum rotational velocity V max, the indicative dynamical mass M 25, the integrated mass of the stellar population M *, and the integrated color index B-V. The rotational velocities andmasses of the central objects were taken from the literature. Themass M nc correlatesmore closely with the kinematic parameters and the disk mass than M bh, including with the velocity V max, which is closely related to the virial mass of the dark halo. On average, lenticular galaxies are characterized by higher masses M bh compared to other types of galaxies with similar characteristics. The dependence of the blackhole mass on the color index is bimodal: galaxies of the red group (red-sequence) with B-V >0.6-0.7 which are mostly early-type galaxies with weak star formation, differ appreciably from blue galaxies, which have higher values of M nc and M bh. At the dependences we consider between the masses of the central objects and the parameters of the host galaxies (except for the dependence of M bh on the central velocity dispersion), the red-group galaxies have systematically higher M bh values, even when the host-galaxy parameters are similar. In contrast, in the case of nuclear star clusters, the blue and red galaxies form unified sequences. The results agree with scenarios in which most red-group galaxies form as a result of the partial or complete loss of interstellar gas in a stage of high nuclear activity in galaxies whose central black-hole masses exceed 106-107 M ⊙ (depending on the mass of the galaxy itself). The bulk of disk galaxies with M bh > 107 M ⊙ are lenticular galaxies (types S0, E/S0) whose disks are practically devoid of gas.

  20. The dynamics of z ~ 1 clusters of galaxies from the GCLASS survey

    NASA Astrophysics Data System (ADS)

    Biviano, A.; van der Burg, R. F. J.; Muzzin, A.; Sartoris, B.; Wilson, G.; Yee, H. K. C.

    2016-10-01

    Context. The dynamics of clusters of galaxies and its evolution provide information on their formation and growth, on the nature of dark matter and on the evolution of the baryonic components. Poor observational constraints exist so far on the dynamics of clusters at redshift z > 0.8. Aims: We aim to constrain the internal dynamics of clusters of galaxies at redshift z ~ 1, namely their mass profile M(r), velocity anisotropy profile β(r), and pseudo-phase-space density profiles Q(r) and Qr(r), obtained from the ratio between the mass density profile and the third power of the (total and, respectively, radial) velocity dispersion profiles of cluster galaxies. Methods: We used the spectroscopic and photometric data-set of 10 clusters at 0.87 < z < 1.34 from the Gemini Cluster Astrophysics Spectroscopic Survey (GCLASS). We determined the individual cluster masses from their velocity dispersions, then stack the clusters in projected phase-space. We investigated the internal dynamics of this stack cluster, using the spatial and velocity distribution of its member galaxies. We determined the stack cluster M(r) using the MAMPOSSt method, and its β(r) by direct inversion of the Jeans equation. The procedures used to determine the two aforementioned profiles also allowed us to determine Q(r) and Qr(r). Results: Several M(r) models are statistically acceptable for the stack cluster (Burkert, Einasto, Hernquist, NFW). The stack cluster total mass concentration, c ≡ r200/r-2 = 4.0-0.6+1.0, is in agreement with theoretical expectations. The total mass distribution is less concentrated than both the cluster stellar-mass and the cluster galaxies distributions. The stack cluster β(r) indicates that galaxy orbits are isotropic near the cluster center and become increasingly radially elongated with increasing cluster-centric distance. Passive and star-forming galaxies have similar β(r). The observed β(r) is similar to that of dark matter particles in simulated cosmological

  1. A Statistical Approach to Galaxy Cluster Gas Inhomogeneity: Chandra Observations of Nearby Galaxy Clusters

    NASA Astrophysics Data System (ADS)

    Reese, Erik D.; Kawahara, H.; Kitayama, T.; Sasaki, S.; Suto, Y.

    2009-01-01

    Motivated by cosmological hydrodynamic simulations, the intracluster medium (ICM) inhomogeneity of galaxy clusters is modeled statistically with a lognormal model for density inhomogeneity. Through mock observations of synthetic clusters the relationship between density inhomogeneities and that of the X-ray surface brightness has been developed. This enables one to infer the statistical properties of the fluctuations of the underlying three-dimensional density distribution of real galaxy clusters from X-ray observations. We explore inhomogeneity in the intracluster medium by applying the above methodology to Chandra observations of a sample of nearby galaxy clusters. We also consider extensions of the model, including Poissonian effects and compare this hybrid lognormal-Poisson model to the nearby cluster Chandra data. EDR gratefully acknowledges support from JSPS (Japan Society for the Promotion of Science) Postdoctoral Fellowhip for Foreign Researchers award P07030. HK is supported by Grands-in-Aid for JSPS of Science Fellows. This work is also supported by Grant-in-Aid for Scientific research of Japanese Ministry of Education, Culture, Sports, Science and Technology (Nos. 20.10466, 19.07030, 16340053, 20340041, and 20540235) and by JSPS Core-to-Core Program "International Research Network for Dark Energy".

  2. A partial list of southern clusters of galaxies

    NASA Technical Reports Server (NTRS)

    Quintana, H.; White, R. A.

    1990-01-01

    An inspection of 34 SRC/ESO J southern sky fields is the basis of the present list of clusters of galaxies and their approximate classifications in terms of cluster concentration, defined independently of richness and shape-symmetry. Where possible, an estimate of the cluster morphological population is provided. The Bautz-Morgan classification was applied using a strict comparison with clusters on the Palomar Sky Survey. Magnitudes were estimated on the basis of galaxies with photoelectric or photographic magnitudes.

  3. Luminosity dependence of the spatial and velocity distributions of galaxies: semi-analytic models versus the Sloan Digital Sky Survey

    NASA Astrophysics Data System (ADS)

    Li, Cheng; Jing, Y. P.; Kauffmann, Guinevere; Börner, Gerhard; Kang, Xi; Wang, Lan

    2007-04-01

    By comparing semi-analytic galaxy catalogues with data from the Sloan Digital Sky Survey (SDSS), we show that current galaxy formation models reproduce qualitatively the dependence of galaxy clustering and pairwise peculiar velocities on luminosity, but some subtle discrepancies with the data still remain. The comparisons are carried out by constructing a large set of mock galaxy redshift surveys that have the same selection function as the SDSS Data Release Four (DR4). The mock surveys are based on two sets of semi-analytic catalogues presented by Croton et al. and Kang et al. From the mock catalogues, we measure the redshift-space projected two-point correlation function wp(rp), the power spectrum P(k) and the pairwise velocity dispersion (PVD) in Fourier space σ12(k) and in configuration space σ12(rp), for galaxies in different luminosity intervals. We then compare these theoretical predictions with the measurements derived from the SDSS DR4. On large scales and for galaxies brighter than L*, both sets of mock catalogues agree well with the data. For fainter galaxies, however, both models predict stronger clustering and higher pairwise velocities than observed. We demonstrate that this problem can be resolved if the fraction of faint satellite galaxies in massive haloes is reduced by ~30 per cent compared to the model predictions. A direct look into the model galaxy catalogues reveals that a significant fraction (15 per cent) of faint galaxies (-18 < M0.1r - 5 log10h < -17) reside in haloes with Mvir > 1013 Msolar, and this population is predominantly red in colour. These faint red galaxies are responsible for the high PVD values of low-luminosity galaxies on small scales.

  4. THE GALAXY POPULATION OF LOW-REDSHIFT ABELL CLUSTERS

    SciTech Connect

    Barkhouse, Wayne A.; Yee, H. K. C.; Lopez-Cruz, Omar E-mail: hyee@astro.utoronto.c

    2009-10-01

    We present a study of the luminosity and color properties of galaxies selected from a sample of 57 low-redshift Abell clusters. We utilize the non-parametric dwarf-to-giant ratio (DGR) and the blue galaxy fraction (f{sub b} ) to investigate the clustercentric radial-dependent changes in the cluster galaxy population. Composite cluster samples are combined by scaling the counting radius by r {sub 200} to minimize radius selection bias. The separation of galaxies into a red and blue population was achieved by selecting galaxies relative to the cluster color-magnitude relation. The DGR of the red and blue galaxies is found to be independent of cluster richness (B {sub gc}), although the DGR is larger for the blue population at all measured radii. A decrease in the DGR for the red and red+blue galaxies is detected in the cluster core region, while the blue galaxy DGR is nearly independent of radius. The f{sub b} is found not to correlate with B {sub gc}; however, a steady decline toward the inner-cluster region is observed for the giant galaxies. The dwarf galaxy f{sub b} is approximately constant with clustercentric radius except for the inner-cluster core region where f{sub b} decreases. The clustercentric radial dependence of the DGR and the galaxy blue fraction indicates that it is unlikely that a simple scenario based on either pure disruption or pure fading/reddening can describe the evolution of infalling dwarf galaxies; both outcomes are produced by the cluster environment.

  5. Internal dynamics of the galaxy cluster Abell 545. The ideal case where to study the simultaneous formation of a galaxy system and its brightest galaxy

    NASA Astrophysics Data System (ADS)

    Barrena, R.; Girardi, M.; Boschin, W.; de Grandi, S.; Eckert, D.; Rossetti, M.

    2011-05-01

    Context. The mechanisms giving rise to diffuse radio emission in galaxy clusters, and in particular their connection with cluster mergers, are still debated. Aims: We seek to explore the internal dynamics of the cluster Abell 545, which has been shown to host a radio halo. Abell 545 is also peculiar for hosting in its center a very bright, red, diffuse intracluster light due to an old, presumably metal-rich stellar population, so bright to be named as "star pile". Methods: Our analysis is mainly based on redshift data for 110 galaxies acquired at the Telescopio Nazionale Galileo. We identify 95 cluster members and analyze the cluster internal dynamics by combining galaxy velocities and positions. We also use both multiband photometric data acquired at the Isaac Newton Telescope and X-ray data from the XMM-Newton Science Archive. Results: We estimate the cluster redshift, ⟨ z ⟩ = 0.1580, a large line-of-sight (LOS) velocity dispersion σV ~ 1200 km s-1, and ICM temperature kTX ~ 8 keV. Our optical and X-ray analyses detect substructures. Optical data reveal three main galaxy clumps (one at the center hosting the peak of X-ray emission; one at NNW, and one at NE); and possibly a fourth clump at South. There is not a dominant galaxy and the four brightest galaxies avoid the cluster core - ≳ 0.4 h70-1 Mpcdistant from the cluster center - and are ≳ 1500 km s-1far from the mean cluster velocity. Two of these brightest galaxies are located in the NNW and NE clumps. The analysis of the X-ray surface brightness distribution provides us evidence of a disturbed dynamical phase: the strong NNW-SSE elongation, a western excess, and a sharp discontinuity in the northern region which is the likely signature of a shock. Located in the star pile region there is the brightest galaxy of the cluster core (CBCG) and a very compact elliptical galaxy, likely a M32-like dwarf. We show that the star pile, which has a previously determined redshift, has a similar redshift to that of

  6. The Formation of Cluster Populations Through Direct Galaxy Collisions

    NASA Astrophysics Data System (ADS)

    Peterson, Bradley W.; Smith, Beverly J.; Struck, Curtis

    2016-01-01

    Much progress has been made on the question of how globular clusters form. In particular, the study of extragalactic populations of young, high-mass clusters ("super star clusters") has revealed a class of objects can evolve into globular clusters. The process by which these clusters form, and how many survive long enough to become globular clusters, is not wholly understood. Here, we use new data on the colliding galaxy system Arp 261 to investigate the possibility that young, massive clusters form in greater numbers during direct galaxy collisions, compared to less direct tidal collisions.

  7. Galaxy populations in the Antlia cluster - II. Compact elliptical galaxy candidates

    NASA Astrophysics Data System (ADS)

    Smith Castelli, Analía V.; Faifer, Favio R.; Richtler, Tom; Bassino, Lilia P.

    2008-12-01

    Continuing our study of galaxy populations in the Antlia cluster, we present a photometric analysis of four galaxies classified as compact elliptical (cE) galaxies in the 1990 Antlia Group catalogue of Ferguson and Sandage. Until now, there have been only six known members of this rare type of galaxy. Using data from various photometric systems (Washington C, Kron-Cousins R, Bessel V and I, Hubble Space Telesecope F814W and F435W), we measured the brightness and colour profiles, as well as the structural parameters. By comparing these with those of other galaxies in the Antlia cluster, as well as with confirmed cE galaxies from the literature, we found that two of the cE candidates, although spectroscopically confirmed Antlia members, are not cE galaxies. However, one of these objects presents strong ellipticity and position angle variations that resemble those already reported for M32, leading us to speculate about this type of object being a progenitor of a cE galaxy. The other two cE candidates, for which radial velocities are not available, match some features typical of cE galaxies, such as being close in projection to a larger galaxy, displaying flat colour profiles, and having a high degree of compactness. Only one of the remaining cE candidates shows a high central surface brightness, two components in its brightness profile and distinct changes in ellipticity and position angle where the outer component begins to dominate. It seems to follow the same trend as other confirmed cE galaxies in a luminosity versus mean effective surface brightness diagram. Moreover, it shows a distorted inner structure with similar characteristics to those found by simulations of interacting galaxies. Also, an extremely faint structure, which seems to link this object with one of the Antlia dominant galaxies, has been detected in images from the Cerro Tololo Inter-American Observatory MOSAIC, the Very Large Telescope FORS1 and the Hubble Space Telescope Advanced Camera for

  8. Cosmology with EMSS Clusters of Galaxies

    NASA Technical Reports Server (NTRS)

    Donahue, Megan; Voit, G. Mark

    1999-01-01

    We use ASCA observations of the Extended Medium Sensitivity Survey sample of clusters of galaxies to construct the first z = 0.5 - 0.8 cluster temperature function. This distant cluster temperature function, when compared to local z approximately 0 and to a similar moderate redshift (z = 0.3 - 0.4) temperature function strongly constrains the matter density of the universe. Best fits to the distributions of temperatures and redshifts of these cluster samples results in Omega(sub M) = 0.45 +/- 0.1 if Lambda = 0 and Omega = 0.27 +/- 0.1 if Lambda + Omega(sub M) = 1. The uncertainties are 1sigma statistical. We examine the systematics of our approach and find that systematics, stemming mainly from model assumptions and not measurement errors, are about the same size as the statistical uncertainty +/- 0.1. In this poster proceedings, we clarify the issue of a8 as reported in our paper Donahue & Voit (1999), since this was a matter of discussion at the meeting.

  9. Mass-Luminosity Relationship of Galaxy Clusters

    NASA Astrophysics Data System (ADS)

    Stanek, Rebecca; Evrard, August

    2004-04-01

    Deriving cosmological parameters from counts of galaxy clusters requires a clear understanding of the relationship between cluster observables and their underlying mass. While previous work has assumed pure power-law forms for these relationships, we explore here a power-law model with log-normal scatter and apply it to describing the REFLEX X-ray cluster luminosity function within a ΛCDM universe. We assume a space density calibrated from Hubble Volume simulations (the ``Jenkins mass function'' dn(M)/d ln M) and compute a luminosity function dn(L)/d ln L by assuming a conditional probability p(M|L) described by a Gaussian of fixed log-normal width ΔM and mean relation L = L_15 M^p. Because of the flux-limited nature of the REFLEX catalog, the space density of clusters at different luminosities is effectively sampling the mass function at different redshifts. We explore different corrections for this effect, and derive maximum-likelihood estimates for the three model parameters, L_15, p and Δ_M. The most likely model requires large scatter ΔM ˜ 1, but the allowed region in parameter space is fairly broad. We discuss the role that independent observables such as gas temperature and lensing mass will have in helping to break the model degeneracy.

  10. EXTERNAL MASS ACCUMULATION ONTO CORE POTENTIALS: IMPLICATIONS FOR STAR CLUSTERS, GALAXIES, AND GALAXY CLUSTERS

    SciTech Connect

    Naiman, J. P.; Ramirez-Ruiz, E.; Lin, D. N. C.

    2011-07-01

    Accretion studies have been focused on the flow around bodies with point mass gravitational potentials, but few general results are available for non-point mass distributions. Here, we study the accretion flow onto non-divergent, core potentials moving through a background medium. We use Plummer and Hernquist potentials as examples to study gas accretion onto star clusters, dwarf and large galaxy halos, and galaxy clusters in a variety of astrophysical environments. The general conditions required for a core potential to collectively accrete large quantities of gas from the external medium are derived using both simulations and analytic results. The consequences of large mass accumulation in galaxy nuclei, dwarf galaxies, and star clusters are twofold. First, if the gas cools effectively star formation can be triggered, generating new stellar members in the system. Second, if the collective potential of the system is able to alter the ambient gas properties before the gas is accreted onto the individual core members, the augmented mass supply rates could significantly alter the state of the various accreting stellar populations and result in an enhanced central black hole accretion luminosity.

  11. Two high-velocity encounters of elliptical galaxies

    NASA Technical Reports Server (NTRS)

    Balcells, Marc; Borne, Kirk D.; Hoessel, John G.

    1989-01-01

    This paper describes results obtained on a simulation of two high-velocity encounters of NGC 4782/4783 and NGC 2672/2673 binary elliptical galaxies which differ substantially in mass ratio (about 1 for the first pair, and about 10 for the second). CCD images and velocities obtained from digital spectra were used to constrain simulations of the galaxy collisions. The binary orbital elements, the orientation of the orbit in the sky, the time since pericenter, and the dynamical mass of the pair were derived. Results suggested that the dumb-bell galaxy NGC 4782/4783 is not a supermassive galaxy, as was claimed earlier on the basis of the high relative velocity and high central dispersion, but has a moderate mass to luminosity ratio M/L(B) of about 10. It was concluded that its trajectory changed from hyperbolic to elliptical as a result of energy lost during the collision. It was found that the NGC 2672/2673 also has a moderate M/L(B) of about 7.

  12. The galaxy population of the z= 1 cluster of galaxies MG2016+112

    NASA Astrophysics Data System (ADS)

    Toft, S.; Soucail, G.; Hjorth, J.

    2003-09-01

    A photometric redshift analysis of galaxies in the field of the wide-separation gravitational lens MG2016+112 reveals a population of 69 galaxies with photometric redshifts consistent with being in a cluster at the redshift of the giant elliptical lensing galaxy z= 1.00. The Ks-band luminosity function of the cluster galaxies is well represented by the Schechter function with a characteristic magnitude K*s= 18.90+0.45-0.57 and faint-end slope α=-0.60+0.39-0.33, consistent with what is expected for a passively evolving population of galaxies formed at high redshift, zf > 2. From the total Ks-band flux of the cluster galaxies and a dynamical estimate of the total mass of the cluster, the rest-frame Ks-band mass-to-light ratio of the cluster is derived to be M/LKs= 27+64-17h50(M/LKs)solar, in agreement with the upper limit derived earlier from Chandra X-ray observations and the value derived locally in the Coma cluster. The cluster galaxies span a red sequence with a considerable scatter in the colour-magnitude diagrams, suggesting that they contain young stellar populations in addition to the old populations of main-sequence stars that dominate the Ks-band luminosity function. This is in agreement with spectroscopic observations which show that 5 out of the 6 galaxies in the field confirmed to be at the redshift of the lensing galaxy have emission lines. The projected spatial distribution of the cluster galaxies is filamentary-like rather than centrally concentrated around the lensing galaxy, and shows no apparent luminosity segregation. A handful of the cluster galaxies show evidence of merging/interaction. The results presented in this paper suggest that a young cluster of galaxies is assembling around MG2016+112.

  13. Do Disk Galaxies Have Different Central Velocity Dispersions At A Given Rotation Velocity?

    NASA Astrophysics Data System (ADS)

    Danilovich, Taissa; Jones, H.; Mould, J.; Taylor, E.; Tonini, C.; Webster, R.

    2011-05-01

    Hubble's classification of spiral galaxies was one dimensional. Actually it was 1.5 dimensional, as he distinguished barred spirals. Van den Bergh's was two dimensional: spirals had luminosity classes too. Other schemes are summarized at http://www.daviddarling.info/encyclopedia/G/galaxyclassification.html A more quantitative approach is to classify spiral galaxies by rotation velocity. Their central velocity dispersion (bulge) tends to be roughly one half of their rotation velocity (disk). There is a trend from σ/W = 0.8 to σ/W = 0.2 as one goes from W = 100 to 500 km/s, where W is twice the rotation velocity. But some fraction of spirals have a velocity dispersion up to a factor of two larger than that. In hierarchical galaxy formation models, the relative contributions of σ and W depend on the mass accretion history of the galaxy, which determines the mass distribution of the dynamical components such as disk, bulge and dark matter halo. The wide variety of histories that originate in the hierarchical mass assembly produce at any value of W a wide range of σ/W, that reaches high values in more bulge- dominated systems. In a sense the two classifiers were both right: spirals are mostly one dimensional, but σ/W (bulge to disk ratio) is often larger than average. Is this a signature of merger history?

  14. High-Velocity Clouds and Superbubbles in Nearby Disk Galaxies

    NASA Astrophysics Data System (ADS)

    Schulman, Eric

    1996-05-01

    The galactic fountain model predicts that energetic stellar winds and supernovae in OB associations produce superbubbles containing hot gas that breaks out of the Galactic disk, cools radiatively as it rises upward, and recombines and returns to the disk ballistically. The hot (T ~ 10^6 K) gas can be observed with X-ray telescopes, while the cool returning neutral hydrogen (H I) is detectable as 21 cm emission from high-velocity clouds (HVCs). In the Milky Way Galaxy, a combination of infalling material tidally torn from the Magellanic Clouds and a galactic fountain can explain the high-velocity clouds that cover about 10% of the sky down to a column density of 2 to 3 X 10^18 cm^-2. Sensitive H I observations of nearby disk galaxies were performed with the Arecibo 305 m radio telescope to search for and measure the mass of HVCs in other galaxies. Ten of 14 galaxies have high-velocity wings that can be modeled as arising from a component of galactic gas with a velocity dispersion of 30 or 50 km s^-1. The HVC mass for the 10 galaxies ranges from 6 X 10^7 solar mass to 4 X 10^9 solar mass, which corresponds to 4 to 14% of the total H I in the galaxies. This is the first survey to search for HVCs in more than a few galaxies, and the results imply that Galactic HVCs are a disk-wide phenomenon with a characteristic distance of 10 to 20 kpc, containing a substantial fraction (~10%) of the neutral hydrogen in the Galaxy and much of the random kinetic energy in neutral gas. 21 cm synthesis imaging of UGC 12732 and NGC 5668, performed with the Very Large Array, confirmed the Arecibo results that the former does not have high-velocity gas while the latter does. Two components of high-velocity gas are present in NGC~5668; one may be from an accretion event, while the other is visible due to the increased H I velocity dispersion throughout the optical disk and may be galactic fountain gas. Neither of these components are visible in the observations of UGC 12732, and this galaxy

  15. A Comparison of the Galaxy Populations in the Coma and Distant Clusters: The Evolution of k+a Galaxies and the Role of the Intracluster Medium

    NASA Astrophysics Data System (ADS)

    Poggianti, Bianca M.; Bridges, Terry J.; Komiyama, Y.; Yagi, M.; Carter, Dave; Mobasher, Bahram; Okamura, S.; Kashikawa, N.

    2004-01-01

    The spectroscopic properties of galaxies in the Coma Cluster are compared with those of galaxies in rich clusters at z~0.5, to investigate the evolution of the star formation history in clusters. Luminous galaxies with MV<=-20 and poststarburst/post-star-forming (k+a) spectra that constitute a significant fraction of galaxies in distant cluster samples are absent in Coma, where spectacular cases of k+a spectra are found instead at MV>-18.5 and represent a significant proportion of the cluster dwarf galaxy population. A simple inspection of their positions on the sky indicates that this type of galaxy does not show a preferential location within the cluster, but the bluest and strongest lined group of k+a galaxies lie in projection toward the central 1.4 Mpc of Coma and have radial velocities significantly higher than the cluster mean. We find a striking correlation between the positions of these young and strong poststarburst galaxies and substructure in the hot intracluster medium (ICM) identified from XMM-Newton data, with these galaxies lying close to the edges of two infalling substructures. This result strongly suggests that the interaction with the dense ICM could be responsible for the quenching of the star formation (thus creating the k+a spectrum) and, possibly, for any previous starburst. The evolution with redshift of the luminosity distribution of k+a galaxies can be explained by a ``downsizing effect,'' with the maximum luminosity/mass of actively star-forming galaxies infalling onto clusters decreasing at lower redshift. We discuss the possible physical origin of this downsizing effect and the implications of our results for current scenarios of environmental effects on the star formation in galaxies. Based on observations made with the William Herschel Telescope operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias.

  16. The Effect of Mergers on Galaxy Cluster Mass Estimates

    NASA Astrophysics Data System (ADS)

    Johnson, Ryan E.; Zuhone, John A.; Thorsen, Tessa; Hinds, Andre

    2015-08-01

    At vertices within the filamentary structure that describes the universal matter distribution, clusters of galaxies grow hierarchically through merging with other clusters. As such, the most massive galaxy clusters should have experienced many such mergers in their histories. Though we cannot see them evolve over time, these mergers leave lasting, measurable effects in the cluster galaxies' phase space. By simulating several different galaxy cluster mergers here, we examine how the cluster galaxies kinematics are altered as a result of these mergers. Further, we also examine the effect of our line of sight viewing angle with respect to the merger axis. In projecting the 6-dimensional galaxy phase space onto a 3-dimensional plane, we are able to simulate how these clusters might actually appear to optical redshift surveys. We find that for those optical cluster statistics which are most often used as a proxy for the cluster mass (variants of σv), the uncertainty due to an inprecise or unknown line of sight may alter the derived cluster masses moreso than the kinematic disturbance of the merger itself. Finally, by examining these, and several other clustering statistics, we find that significant events (such as pericentric crossings) are identifiable over a range of merger initial conditions and from many different lines of sight.

  17. Dissecting simulated disc galaxies - II. The age-velocity relation

    NASA Astrophysics Data System (ADS)

    Martig, Marie; Minchev, Ivan; Flynn, Chris

    2014-09-01

    We study the relation between stellar ages and vertical velocity dispersion (the age-velocity relation, or AVR) in a sample of seven simulated disc galaxies. In our simulations, the shape of the AVR for stars younger than 9 Gyr depends strongly on the merger history at low redshift, with even 1:10-1:15 mergers being able to create jumps in the AVR (although these jumps might not be detectable if the errors on stellar ages are of the order of 30 per cent). For galaxies with a quiescent history at low redshift, we find that the vertical velocity dispersion rises smoothly for ages up to 8-9 Gyr, following a power law with a slope of ˜0.5, similar to what is observed in the solar neighbourhood by the Geneva-Copenhagen Survey. For these galaxies, we show that the slope of the AVR is not imprinted at birth, but is the result of subsequent heating. By contrast, in all our simulations, the oldest stars form a significantly different population, with a high velocity dispersion. These stars are usually born kinematically hot in a turbulent phase of intense mergers at high redshift, and also include some stars accreted from satellites. This maximum in σz is strongly decreased when age errors are included, suggesting that observations can easily miss such a jump with the current accuracy of age measurements.

  18. Investigation of dwarf galaxies in the Virgo cluster

    SciTech Connect

    Bothun, G.D.; Mould, J.R.; Wirth, A.; Caldwell, N.

    1985-05-01

    We have obtained 21-cm H I observations of a sample of 32 dwarf irregular (dI) and 12 dwarf elliptical (dE) galaxies that are located in the Virgo cluster. Altogether, 18 of 32 DIs were detected in H I, but none of the dEs were detected at a sensitivity level of M/sub Htsi/ = 2--3 x 10/sup 6/ M/sub sun/. The detected dIs have M/sub Htsi/>3 x 10/sup 7/ M/sub sun/. This disparity in H I content between dIs and dEs effectively dispels the possibility that the dEs are presently in a stage of quiescence (hibernation), between bursts of star formation. In order to supplement the 21-cm data, we have acquired optical spectroscopy, CCD images, and infrared photometry for a limited subsample of these dwarfs. The most significant result provided by this additional data is that the dEs, although very H I poor, nevertheless have observed (J-K) colors which indicate somewhat high metallicity, implying some degree of enrichment due to multiple generations of star formation. In contrast, most of the dIs are quite H I rich (with some having fractional H I contents that exceed 30% by mass), yet they are apparently in a quiescent phase, judging by their low central surface brightnesses (<10% of sky) and lack of resolution into obvious regions of star formation. A small gas-poor contingent of dIs have been found but there is no apparent correlation between dI gas content and either their velocity with respect to the Virgo ICM or their position in the cluster. In general, the velocity distribution of the dIs is flat with only a weak peak that corresponds to the mean velocity of the brighter galaxies in Virgo.

  19. Spectroscopy of clusters in the ESO distant cluster survey (EDisCS). II.. Redshifts, velocity dispersions, and substructure for clusters in the last 15 fields

    NASA Astrophysics Data System (ADS)

    Milvang-Jensen, B.; Noll, S.; Halliday, C.; Poggianti, B. M.; Jablonka, P.; Aragón-Salamanca, A.; Saglia, R. P.; Nowak, N.; von der Linden, A.; De Lucia, G.; Pelló, R.; Moustakas, J.; Poirier, S.; Bamford, S. P.; Clowe, D. I.; Dalcanton, J. J.; Rudnick, G. H.; Simard, L.; White, S. D. M.; Zaritsky, D.

    2008-05-01

    Aims: We present spectroscopic observations of galaxies in 15 survey fields as part of the ESO Distant Cluster Survey (EDisCS). We determine the redshifts and velocity dispersions of the galaxy clusters located in these fields, and we test for possible substructure in the clusters. Methods: We obtained multi-object mask spectroscopy using the FORS2 instrument at the VLT. We reduced the data with particular attention to the sky subtraction. We implemented the method of Kelson for performing sky subtraction prior to any rebinning/interpolation of the data. From the measured galaxy redshifts, we determine cluster velocity dispersions using the biweight estimator and test for possible substructure in the clusters using the Dressler-Shectman test. Results: The method of subtracting the sky prior to any rebinning/interpolation of the data delivers photon-noise-limited results, whereas the traditional method of subtracting the sky after the data have been rebinned/interpolated results in substantially larger noise for spectra from tilted slits. Redshifts for individual galaxies are presented and redshifts and velocity dispersions are presented for 21 galaxy clusters. For the 9 clusters with at least 20 spectroscopically confirmed members, we present the statistical significance of the presence of substructure obtained from the Dressler-Shectman test, and substructure is detected in two of the clusters. Conclusions: Together with data from our previous paper, spectroscopy and spectroscopic velocity dispersions are now available for 26 EDisCS clusters with redshifts in the range 0.40-0.96 and velocity dispersions in the range 166 km s-1-1080 km s-1. Based on observations collected at the European Southern Observatory, Chile, as part of large programme 166.A-0162 (the ESO Distant Cluster Survey). Full Table 4 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/482/419

  20. Chemical Enrichment in the Third Closest Galaxy Cluster

    NASA Astrophysics Data System (ADS)

    Million, Evan

    2011-10-01

    We propose a 180 ks XMM-Newton observation of the Antlia Cluster, the third closest galaxy cluster in the sky. We will determine the central temperature, Si and Fe abundance structure of the cluster to constrain detailed chemical enrichment processes in the nearest cluster without a strong cool core. The detailed abundance structure of the cluster will be resolved at the best physical resolution of any non-cool core cluster to date.

  1. Constraining Dark Matter Through the Study of Merging Galaxy Clusters

    NASA Astrophysics Data System (ADS)

    Dawson, William Anthony

    2013-03-01

    Context: The majority (~85%) of the matter in the universe is composed of dark matter, a mysterious particle that does not interact via the electromagnetic force yet does interact with all other matter via the gravitational force. Many direct detection experiments have been devoted to finding interactions of dark matter with baryonic matter via the weak force. It is still possible that dark matter interacts with itself via a strong scale force and has a self-scattering cross-section of ~0.5 cm2g -1. In fact such a strong scale scattering force could resolve several outstanding astronomical mysteries: a discrepancy between the cuspy density profiles seen in ΛCDM simulations and the cored density profiles observed in low surface brightness galaxies, dwarf spheroidal galaxies, and galaxy clusters, as well as the discrepancy between the significant number of massive Milky Way dwarf spheroidal halos predicted by ΛCDM and the dearth of observed Milky Way dwarf spheroidal halos. Need: While such observations are in conflict with ΛCDM and suggest that dark matter may self-scatter, each suffers from a baryonic degeneracy, where the observations might be explained by various baryonic processes (e.g., AGN or supernove feedback, stellar winds, etc.) rather than self-interacting dark matter (SIDM). If dark matter lags behind the effectively collisionless galaxies then this is clear evidence that dark matter self-interacts. The expected galaxy-dark matter offset is typically >25 kpc (for cross-sections that would explain the other aforementioned issues with ΛCDM), this is larger than the scales of that are plagued by the baryonic degeneracies. Task: To test whether dark matter self-interacts we have carried out a comprehensive survey of the dissociative merging galaxy cluster DLSCL J0916.2+2951 (also known as the Musket Ball Cluster). This survey includes photometric and spectroscopic observations to quantify the position and velocity of the cluster galaxies, weak

  2. The nature and evolution of infrared galaxies in clusters

    NASA Astrophysics Data System (ADS)

    Farahmandi, Alireza

    In chapter 1, I present a spectroscopic and photometric study of 105 Spitzer-MIPS 24 micron detected galaxies in the fields of candidate clusters from the SpARCS survey. I spectroscopically both confirm nine clusters of galaxies at 0.07 < z < 0.49 and investigate the nature of the cluster members and field galaxies to compare their optical and infrared star formation activities. Spectroscopic classifications reveal different populations of galaxies in clusters and in the field. Most 24 micron sources are star forming galaxies which are mostly dusty starbursts. I conclude that specific star formation rates of star forming galaxies in clusters are not dependent upon clustercentric radius, but, rather, dependent upon stellar mass. In chapter 2, I present the results of an infrared study of 250 galaxy clusters at 0.2 < z < 1 from the SpARCS survey. My sample spans a cluster mass range 14 < log M_sun < 15 with an average about 2x10. 14 M_sun overthe redshift. Assuming a star forming galaxy template, I statistically count the number of infrared luminous galaxies in clusters above a fixed inferred infrared luminosity of 6x10. 11 L_sun per unit cluster mass and find it increaseswith redshift. Fitting a simple power law, I measure an evolution of (1 + z ). (5.2+/-0.5) within R_200 and (1 + z ). (9.6+/-1.6) within R =2Mpc from the cluster center over the redshift range of this sample. By accounting for the evolution of infrared galaxies in the field, I show that this observed evolution in clusters is due to new infalling field galaxies. Also, I estimate the total star formation rate per unit cluster mass (SigmaSFR/M_cluster) and find a similar evolution of (1+z). (5.6+/-0.5) within R_(200) and(1+z). (8.6+/-1.5) within R = 2Mpc from the cluster center. The surfacedensity of the infrared luminous galaxies seems to decrease as the distance from cluster center increases. Finally, I show that the accretion rate of infalling infrared galaxies from the field into clusters increases

  3. Looking Wider and Further: The Evolution of Galaxies Inside Galaxy Clusters

    SciTech Connect

    Zhang, Yuanyuan

    2016-01-01

    Galaxy clusters are rare objects in the universe, but on-going wide field optical surveys are identifying many thousands of them to redshift 1.0 and beyond. Using early data from the Dark Energy Survey (DES) and publicly released data from the Sloan Digital Sky Survey (SDSS), this dissertation explores the evolution of cluster galaxies in the redshift range from 0 to 1.0. As it is common for deep wide field sky surveys like DES to struggle with galaxy detection efficiency at cluster core, the first component of this dissertation describes an efficient package that helps resolving the issue. The second part focuses on the formation of cluster galaxies. The study quantifies the growth of cluster bright central galaxies (BCGs), and argues for the importance of merging and intra-cluster light production during BCG evolution. An analysis of cluster red sequence galaxy luminosity function is also performed, demonstrating that the abundance of these galaxies is mildly dependent on cluster mass and redshift. The last component of the dissertation characterizes the properties of galaxy filaments to help understanding cluster environments

  4. Discovery of a Galaxy Cluster with a Violently Starbursting Core at z = 2.506

    NASA Astrophysics Data System (ADS)

    Wang, Tao; Elbaz, David; Daddi, Emanuele; Finoguenov, Alexis; Liu, Daizhong; Schreiber, Corentin; Martín, Sergio; Strazzullo, Veronica; Valentino, Francesco; van der Burg, Remco; Zanella, Anita; Ciesla, Laure; Gobat, Raphael; Le Brun, Amandine; Pannella, Maurilio; Sargent, Mark; Shu, Xinwen; Tan, Qinghua; Cappelluti, Nico; Li, Yanxia

    2016-09-01

    We report the discovery of a remarkable concentration of massive galaxies with extended X-ray emission at z spec = 2.506, which contains 11 massive (M * ≳ 1011 M ⊙) galaxies in the central 80 kpc region (11.6σ overdensity). We have spectroscopically confirmed 17 member galaxies with 11 from CO and the remaining ones from Hα. The X-ray luminosity, stellar mass content, and velocity dispersion all point to a collapsed, cluster-sized dark matter halo with mass M 200c = 1013.9±0.2 M ⊙, making it the most distant X-ray-detected cluster known to date. Unlike other clusters discovered so far, this structure is dominated by star-forming galaxies (SFGs) in the core with only 2 out of the 11 massive galaxies classified as quiescent. The star formation rate (SFR) in the 80 kpc core reaches ˜3400 M ⊙ yr-1 with a gas depletion time of ˜200 Myr, suggesting that we caught this cluster in rapid build-up of a dense core. The high SFR is driven by both a high abundance of SFGs and a higher starburst fraction (˜25%, compared to 3%-5% in the field). The presence of both a collapsed, cluster-sized halo and a predominant population of massive SFGs suggests that this structure could represent an important transition phase between protoclusters and mature clusters. It provides evidence that the main phase of massive galaxy passivization will take place after galaxies accrete onto the cluster, providing new insights into massive cluster formation at early epochs. The large integrated stellar mass at such high redshift challenges our understanding of massive cluster formation.

  5. Hα star formation rates of z > 1 galaxy clusters in the IRAC shallow cluster survey

    SciTech Connect

    Zeimann, Gregory R.; Stanford, S. A.; Brodwin, Mark; Gonzalez, Anthony H.; Mancone, Conor; Snyder, Gregory F.; Stern, Daniel; Eisenhardt, Peter; Dey, Arjun; Moustakas, John

    2013-12-20

    We present Hubble Space Telescope near-IR spectroscopy for 18 galaxy clusters at 1.0 Cluster Survey. We use Wide Field Camera 3 grism data to spectroscopically identify Hα emitters in both the cores of galaxy clusters as well as in field galaxies. We find a large cluster-to-cluster scatter in the star formation rates within a projected radius of 500 kpc, and many of our clusters (∼60%) have significant levels of star formation within a projected radius of 200 kpc. A stacking analysis reveals that dust reddening in these star-forming galaxies is positively correlated with stellar mass and may be higher in the field than the cluster at a fixed stellar mass. This may indicate a lower amount of gas in star-forming cluster galaxies than in the field population. Also, Hα equivalent widths of star-forming galaxies in the cluster environment are still suppressed below the level of the field. This suppression is most significant for lower mass galaxies (log M {sub *} < 10.0 M {sub ☉}). We therefore conclude that environmental effects are still important at 1.0 galaxies in galaxy clusters with log M {sub *} ≲ 10.0 M {sub ☉}.

  6. Radio Galaxy NGC 1265 Unveils the Accretion Shock Onto the Perseus Galaxy Cluster

    NASA Astrophysics Data System (ADS)

    Pfrommer, C.; Jones, T. W.

    2011-03-01

    We present a consistent three-dimensional model for the head-tail radio galaxy NGC 1265 that explains the complex radio morphology and spectrum by a past passage of the galaxy and radio bubble through a shock wave. Using analytical solutions to the full Riemann problem and hydrodynamical simulations, we study how this passage transformed the plasma bubble into a toroidal vortex ring. Adiabatic compression of the aged electron population causes it to be energized and to emit low surface brightness and steep-spectrum radio emission. The large infall velocity of NGC 1265—which is barely gravitationally bound to the Perseus cluster at its current position—and the low Faraday rotation measure values and variance of the jet strongly argue that this transformation was due to the accretion shock onto Perseus situated roughly at R 200. Estimating the volume change of the radio bubble enables inferring a shock Mach number of M≃ 4.2_{-1.2}^{+0.8}, a density jump of 3.4+0.2 -0.4, a temperature jump of 6.3+2.5 -2.7, and a pressure jump of 21.5 ± 10.5 while allowing for uncertainties in the equation of state of the radio plasma and volume of the torus. Extrapolating X-ray profiles, we obtain upper limits on the gas temperature and density in the infalling warm-hot intergalactic medium of kT <~ 0.4 keV and n <~ 5 × 10-5 cm-3. The orientation of the ellipsoidally shaped radio torus in combination with the direction of the galaxy's head and tail in the plane of the sky is impossible to reconcile with projection effects. Instead, this argues for post-shock shear flows that have been caused by curvature in the shock surface with a characteristic radius of 850 kpc. The energy density of the shear flow corresponds to a turbulent-to-thermal energy density of 14%—consistent with cosmological simulations. The shock-injected vorticity might be important in generating and amplifying magnetic fields in galaxy clusters. We suggest that future polarized radio observations by, e

  7. Multicolor photometry of the merging galaxy cluster A2319: Dynamics and star formation properties

    SciTech Connect

    Yan, Peng-Fei; Yuan, Qi-Rong; Zhang, Li; Zhou, Xu E-mail: yuanqirong@njnu.edu.cn

    2014-05-01

    Asymmetric X-ray emission and a powerful cluster-scale radio halo indicate that A2319 is a merging cluster of galaxies. This paper presents our multicolor photometry for A2319 with 15 optical intermediate filters in the Beijing-Arizona-Taiwan-Connecticut (BATC) system. There are 142 galaxies with known spectroscopic redshifts within the viewing field of 58' × 58' centered on this rich cluster, including 128 member galaxies (called sample I). A large velocity dispersion in the rest frame, 1622{sub −70}{sup +91} km s{sup –1}, suggests merger dynamics in A2319. The contour map of projected density and localized velocity structure confirm the so-called A2319B substructure, at ∼10' northwest to the main concentration A2319A. The spectral energy distributions (SEDs) of more than 30,000 sources are obtained in our BATC photometry down to V ∼ 20 mag. A u-band (∼3551 Å) image with better seeing and spatial resolution, obtained with the Bok 2.3 m telescope at Kitt Peak, is taken to make star-galaxy separation and distinguish the overlapping contamination in the BATC aperture photometry. With color-color diagrams and photometric redshift technique, 233 galaxies brighter than h {sub BATC} = 19.0 are newly selected as member candidates after an exclusion of false candidates with contaminated BATC SEDs by eyeball-checking the u-band Bok image. The early-type galaxies are found to follow a tight color-magnitude correlation. Based on sample I and the enlarged sample of member galaxies (called sample II), subcluster A2319B is confirmed. The star formation properties of cluster galaxies are derived with the evolutionary synthesis model, PEGASE, assuming a Salpeter initial mass function and an exponentially decreasing star formation rate (SFR). A strong environmental effect on star formation histories is found in the manner that galaxies in the sparse regions have various star formation histories, while galaxies in the dense regions are found to have shorter SFR time

  8. Comparisons of the galaxy age, stellar velocity dispersion and K-band luminosity distributions between grouped galaxies and isolated ones

    NASA Astrophysics Data System (ADS)

    Wu, Ping; Deng, Xin-Fa

    2016-02-01

    In two volume-limited Main galaxy samples of the Sloan Digital Sky Survey Data Release 10 (SDSS DR10), we compare the age, stellar velocity dispersion and K-band luminosity distributions of grouped galaxies with those of isolated galaxies, to explore the environmental dependence of these properties of galaxies. It is found that grouped galaxies have preferentially larger stellar velocity dispersions and are preferentially older than isolated galaxies. We also note apparent difference of K-band luminosity distribution at both extremes of density in the luminous volume-limited Main galaxy sample: grouped galaxies are preferentially more luminous than isolated galaxies, while this difference in the faint volume-limited Main galaxy sample is very small.

  9. Simulations of clusters of galaxies with massive cores.

    NASA Astrophysics Data System (ADS)

    Saarinen, S.; Valtonen, M. J.

    Clusters of galaxies with strong concentration of mass in their cores can be very far from dynamical equilibrium during their early evolution. Then a straightforward application of the virial theorem can lead to a totally wrong idea of the mass distribution of the cluster, hiding away the very central mass concentration. Numerical simulations have been carried out of clusters of galaxies which separate out of the Hubble flow and collapse on their massive cores.

  10. Understanding the physical processes driving galaxy evolution in clusters : a case study of two z~0.5 galaxy clusters

    NASA Astrophysics Data System (ADS)

    Moran, Sean M.

    Clusters of galaxies represent the largest laboratories in the universe for testing the incredibly chaotic physics governing the collapse of baryons into the stars, galaxies, groups, and diffuse clouds that we see today. Within the cluster environment, there are a wide variety of physical processes that may be acting to transform galaxies.In this thesis, we combine extensive Keck spectroscopy with wide-field HST imaging to perform a detailed case study of two intermediate redshift galaxy clusters, Cl 0024+1654 (z=0.395) and MS 0451-03 (z=0.540). Leveraging a comprehensive multiwavelength data set that spans the X-ray to infrared, and with spectral-line measurements serving as the key to revealing both the recent star-formation histories and kinematics of infalling galaxies, we aim to shed light on the environmental processes that could be acting to transform galaxies in clusters.We adopt a strategy to make maximal use of our HST-based morphologies by splitting our sample of cluster galaxies according to morphological type, characterizing signs of recent evolution in spirals and early types separately. This approach proves to be powerful in identifying galaxies that are currently being altered by an environmental interaction: early-type galaxies that have either been newly transformed or prodded back into an active phase, and spiral galaxies where star formation is being suppressed or enhanced all stand out in our sample.We begin by using variations in the early-type galaxy population as indicators of recent activity. Because ellipticals and S0s form such a homogeneous class in the local universe, we are sensitive to even very subtle signatures of recent and current environmental interactions. This study has yielded two key results: By constructing the Fundamental Plane (FP) of Cl 0024, we observe that elliptical and S0 galaxies exhibit a high scatter in their FP residuals, which occurs only among galaxies in the cluster core, suggesting a turbulent assembly history

  11. Jellyfish: Observational Properties of Extreme Ram-Pressure Stripping Events in Massive Galaxy Clusters

    NASA Astrophysics Data System (ADS)

    Conor, McPartland; Ebeling, Harald; Roediger, Elke

    2015-08-01

    We investigate the physical origin and observational signatures of extreme ram-pressure stripping (RPS) in 63 massive galaxy clusters at z=0.3-0.7, based on data in the F606W passband obtained with the Advanced Camera for Surveys aboard the Hubble Space Telescope. Using a training set of a dozen ``jellyfish" galaxies identified earlier in the same imaging data, we define quantitative morphological criteria to select candidate galaxies which are similar to known cases of RPS. Considering a sample of 16 ``jellyfish" galaxies (10 of which we present for the first time), we visually derive estimates of the projected direction of motion based on dynamical features such as apparent compression shocks and debris trails. Our findings suggest that the observed events occur primarily at large distances from the cluster core and involve infall trajectories featuring high impact parameters. Simple models of cluster growth show that such trajectories are consistent with two scenarios: 1) galaxy infall along filaments; and 2) infall at high velocities (≥1000 km/s) characteristic of cluster mergers. The observed distribution of events is best described by timescales of ˜few Myr in agreement with recent numerical simulations of RPS. The broader areal coverage of the Hubble Frontier Fields should provide an even larger sample of RPS events to determine the relative contributions of infall and cluster mergers. Prompted by the discovery of several jellyfish galaxies whose brightness in the F606W passband rivals or exceeds that of the respective brightest cluster galaxy, we attempt to constrain the luminosity function of galaxies undergoing RPS. The observed significant excess at the bright end compared to the luminosity functions of blue cluster members strongly suggests enhanced star formation, thus challenging theoretical and numerical studies according to which RPS merely displaces existing star-forming regions. In-depth studies of individual objects will help test our

  12. The Clustering of Massive Galaxies in the Early Universe

    NASA Astrophysics Data System (ADS)

    Quadri, Ryan

    2009-01-01

    Until recently it was thought that the early universe was dominated by low-mass galaxies undergoing rapid star formation. But deep near-infrared (NIR) surveys have uncovered a population of red, massive galaxies at z=2-3 with a wide range of star formation rates. This talk is concerned with the identification and analysis of red galaxies at these redshifts, and particularly with their clustering properties. First, we present deep NIR imaging from the Multiwavelength Survey by Yale-Chile (MUSYC). These data are used to assess differences between several sets of selection criteria that are commonly used to identify distant galaxies, including the J-K>2.3 criterion for distant red galaxies (DRGs). Next, we present MUSYC results for galaxy clustering at z 2.5. While the broad population of NIR-selected galaxies clusters similarly to the low-mass, star-forming galaxies found in previous surveys, the reddest galaxies have much higher correlation lengths. This suggests that a color-density relationship was in place at these redshifts. We use the clustering results to estimate the mass of the dark matter halos that host NIR-selected galaxies. We find that the reddest galaxies, which include DRGs, significantly outnumber the halos that are massive enough to host them. This suggests that the observations may be incompatible with the models. To test whether this discrepancy is an artifact due to limited field size, we also investigate the clustering of DRGs in the larger UKIDSS Ultra-Deep Survey, but the models remain inconsistent with the observations. The disagreement could be due to inaccurate photometric redshifts or to incorrect models. An explanation for this disagreement will result in a more complete understanding of the relationship between different galaxy populations, and of the relationship between galaxy evolution and dark matter.

  13. A new giant luminous arc gravitational lens associated with a z = 0.62 galaxy cluster, and the environments of distant radio galaxies

    NASA Technical Reports Server (NTRS)

    Dickinson, Mark

    1993-01-01

    In the course of a survey investigating the cluster environments of distant 3CR radio galaxies, I have identified a previously unknown 'giant luminous arc' gravitational lens. The lensing cluster is associated with the radio galaxy 3C 220.1 at z = 0.62 and is the most distant cluster now known to produce such arcs. I present imaging and spectroscopic observations of the cluster and the arc, and discuss the implications for the cluster mass. At z greater than 0.6 the cluster velocity dispersions implied by such giant arcs may provide an interesting constraint on theories of large scale structure formation. The parent investigation in which this arc was identified concerns galaxy clusters and radio galaxy environments at 0.35 less than z less than 0.8. At the present epoch, powerful FR 2 radio galaxies tend to be found in environments of poor or average galaxy density. In contrast, at the higher redshifts investigated here, richer group and cluster environments are common. I present additional data on other clusters from this survey, and discuss its extension to z greater than 1 through a program of near-infrared and optical imaging.

  14. Central Dominant Galaxies and the evolution of their host Clusters

    NASA Astrophysics Data System (ADS)

    Caretta, C. A.; Andernach, H.; Trejo-Alonso, J. J.; De Anda-Suárez, J.; Santoyo-Ruiz, H.; Muñiz-Torres, M. A.; Hernández-Aguayo, C.

    2014-10-01

    We have studied a sample of 50 galaxy clusters, all with more than 100 spectroscopically confirmed member galaxies, from all Bautz-Morgan types, in order to determine the importance of the brightest cluster members (BCMs) and their relation to the structure and dynamical state of their host clusters. Strict tests for membership and for the presence of substructures were applied. Near-infrared data were used for photometry and astrometry, which allowed us to rank the member galaxies in order of their stellar mass content. The large spectroscopic sampling, the broad range of morphologies, masses and intra-cluster medium properties, beyond the improved analyses for membership and substructuring, make this sample an especially suitable reference of nearby optical clusters (0.005 < z < 0.150) for the study of cluster evolution and environment effects on member galaxies. Only 35% of the clusters revealed to be unimodal, 50% to be substructured and other 15% to be multi-modal. Also, for about 20% of the sample, the Central Dominant Galaxy (CDG) of the main structure is not the first-ranked BCM, but the CDG of a substructure. More massive clusters present more than one dominant galaxy, while the less massive ones present only one, if any. This correlation goes in the sense that most of the evolution of CDGs occurs in groups that are doomed to merge and form clusters.

  15. Optical signatures of high-redshift galaxy clusters

    NASA Technical Reports Server (NTRS)

    Evrard, August E.; Charlot, Stephane

    1994-01-01

    We combine an N-body and gasdynamic simulation of structure formation with an updated population synthesis code to explore the expected optical characteristics of a high-redshift cluster of galaxies. We examine a poor (2 keV) cluster formed in a biased, cold dark matter cosmology and employ simple, but plausible, threshold criteria to convert gas into stars. At z = 2, the forming cluster appears as a linear chain of very blue (g-r approximately equals 0) galaxies, with 15 objects brighter than r = 25 within a 1 square arcmin field of view. After 2 Gyr of evolution, the cluster viewed at z = 1 displays both freshly infalling blue galaxies and red galaxies robbed of recent accretion by interaction with the hot intracluster medium. The range in G-R colors is approximately 3 mag at z = 1, with the reddest objects lying at sites of highest galaxy density. We suggest that red, high-redshift galaxies lie in the cores of forming clusters and that their existence indicates the presence of a hot intracluster medium at redshifts z approximately equals 2. The simulated cluster viewed at z = 2 has several characteristics similar to the collection of faint, blue objects identified by Dressler et al. in a deep Hubble Space Telescope observation. The similarities provide some support for the interpretation of this collection as a high-redshift cluster of galaxies.

  16. Probing Globular Cluster Formation in Low Metallicity Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    Johnson, Kelsey E.; Hunt, Leslie K.; Reines, Amy E.

    2008-12-01

    The ubiquitous presence of globular clusters around massive galaxies today suggests that these extreme star clusters must have been formed prolifically in the earlier universe in low-metallicity galaxies. Numerous adolescent and massive star clusters are already known to be present in a variety of galaxies in the local universe; however most of these systems have metallicities of 12 + log(O/H) > 8, and are thus not representative of the galaxies in which today's ancient globular clusters were formed. In order to better understand the formation and evolution of these massive clusters in environments with few heavy elements, we have targeted several low-metallicity dwarf galaxies with radio observations, searching for newly-formed massive star clusters still embedded in their birth material. The galaxies in this initial study are HS 0822+3542, UGC 4483, Pox 186, and SBS 0335-052, all of which have metallicities of 12 + log(O/H) < 7.75. While no thermal radio sources, indicative of natal massive star clusters, are found in three of the four galaxies, SBS 0335-052 hosts two such objects, which are incredibly luminous. The radio spectral energy distributions of these intense star-forming regions in SBS 0335-052 suggest the presence of ~12,000 equivalent O-type stars, and the implied star formation rate is nearing the maximum starburst intensity limit.

  17. Star Clusters in Intermediate-Age Galaxy Merger Remnants

    NASA Astrophysics Data System (ADS)

    Miller, Bryan W.; Trancho, G.; Schweizer, F.

    2011-01-01

    Studies of globular cluster systems play a critical role in our understanding of galaxy formation. Star clusters are useful tracers of major star-formation events in galaxies since they are compact, relatively easy to detect, and have properties well described by simple-stellar-population models. Imaging with the Hubble Space Telescope has revealed that young compact star clusters are formed copiously during galaxy mergers, strengthening theories in which giant elliptical galaxies are formed through mergers of spirals. However, the formation and evolution of globular cluster systems is still not well understood. We should be able to observe how cluster systems evolve from the very young systems with power-law luminosity functions to old systems with log-normal luminosity functions like those observed in old elliptical galaxies. Finding intermediate-age cluster systems would constrain theories of cluster formation and destruction (evaporation, shocking, dynamical friction) as well as show the significance of merger events in the histories of galaxies. We present results of combining HST optical photometry with ground-based K-band photometry from NIRI and Flamingos-I on Gemini to study the star cluster systems of five intermediate-age merger remnants. The galaxies were chosen based on blue colors and fine structure such as shells and ripples that are indicative of past interactions. We find evidence for star clusters with ages consistent with the estimated merger ages. The properties of the star clusters systems and implications for galaxy and star cluster formation will be discussed. Based on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the Particle Physics and Astronomy Research Council (United Kingdom), the National Research Council (Canada

  18. Completing the survey of the most massive southern galaxy clusters

    NASA Astrophysics Data System (ADS)

    Boehringer, Hans

    2014-09-01

    With the recently completed REFLEX II galaxy cluster survey we obtained a new sample of the most X-ray luminous and most massive galaxy clusters comprising a total of 45 galaxy clusters (Lx>=6e44 erg/s) at z>=0.3 in the southern sky. The majority of these prominent clusters have been detected in various surveys and have been well studied in X-rays before, except for 8 clusters in our new sample. These clusters are the most interesting objects of this kind since they are prominent gravitational lensing objects, easily detected through the Sunyaev-Zeldovich effect, and important cosmological probes. To complete this sample of massive clusters, we propose Chandra observations with a total of 220 ks exposure to well characterize their global parameters and explore their morphology.

  19. Redshift and Optical Properties for S Statistically Complete Sample of Poor Galaxy Clusters

    NASA Astrophysics Data System (ADS)

    Ledlow, Michael J.; Loken, Chris; Burns, Jack O.; Hill, John M.; White, Richard A.

    1996-08-01

    From the poor cluster catalog of White et al. (1996), we define a sample of 71 optically-selected poor galaxy clusters. The surface-density enhancement we require for our clusters falls between that of the loose associations of Turner & Gott [AJ, 91,204(1976)] and the Hickson compact groups [Hickson, ApJ, 255, 382(1982)]. We review the selection biases and determine the statistical completeness of the sample. For this sample, we report new velocity measurements made with the ARC 3.5-m Dual-Imaging spectrograph and the 2.3-m Steward Observatory MX fiber spectrograph. Combining our own measurements with those from the literature, we examine the velocity distributions, velocity dispersions, and ID velocity substructure for our poor cluster sample, and compare our results to other poor cluster samples. We find that approximately half of the sample may have significant ID velocity substructure. The optical morphology, large-scale environment, and velocity field of many of these clusters are indicative of young, dynamically evolving systems. In future papers, we will use this sample to derive the poor cluster x-ray luminosity function and gas mass function, and will examine the optical/x-ray properties of the clusters in more detail.

  20. Cold Fronts in Clusters of Galaxies: Observations and Modeling

    NASA Technical Reports Server (NTRS)

    Markevitch, Maxim

    2012-01-01

    Mergers of galaxy clusters -- some of the most energetic events in the Universe -- produce disturbances in hot intracluster medium, such as shocks and cold fronts, that can be used as tools to study the physics of galaxy clusters. Cold fronts may constrain viscosity and the structure and strength of the cluster magnetic fields. Combined with radio data, these observations also shed light on the production of ultrarelativistic particles that are known to coexist with the cluster thermal plasma. This talk will summarize the current X-ray observations of cluster mergers, as well as some recent radio data and high resolution hydrodynamic simulations.

  1. LENSING NOISE IN MILLIMETER-WAVE GALAXY CLUSTER SURVEYS

    SciTech Connect

    Hezaveh, Yashar; Vanderlinde, Keith; Holder, Gilbert; De Haan, Tijmen

    2013-08-01

    We study the effects of gravitational lensing by galaxy clusters of the background of dusty star-forming galaxies (DSFGs) and the cosmic microwave background (CMB), and examine the implications for Sunyaev-Zel'dovich-based (SZ) galaxy cluster surveys. At the locations of galaxy clusters, gravitational lensing modifies the probability distribution of the background flux of the DSFGs as well as the CMB. We find that, in the case of a single-frequency 150 GHz survey, lensing of DSFGs leads both to a slight increase ({approx}10%) in detected cluster number counts (due to a {approx}50% increase in the variance of the DSFG background, and hence an increased Eddington bias) and a rare (occurring in {approx}2% of clusters) 'filling-in' of SZ cluster signals by bright strongly lensed background sources. Lensing of the CMB leads to a {approx}55% reduction in CMB power at the location of massive galaxy clusters in a spatially matched single-frequency filter, leading to a net decrease in detected cluster number counts. We find that the increase in DSFG power and decrease in CMB power due to lensing at cluster locations largely cancel, such that the net effect on cluster number counts for current SZ surveys is subdominant to Poisson errors.

  2. Brightest cluster galaxies in the extended GMRT radio halo cluster sample. Radio properties and cluster dynamics

    NASA Astrophysics Data System (ADS)

    Kale, R.; Venturi, T.; Cassano, R.; Giacintucci, S.; Bardelli, S.; Dallacasa, D.; Zucca, E.

    2015-09-01

    Aims: First-ranked galaxies in clusters, usually referred to as brightest cluster galaxies (BCGs), show exceptional properties over the whole electromagnetic spectrum. They are the most massive elliptical galaxies and show the highest probability to be radio loud. Moreover, their special location at the centres of galaxy clusters raises the question of the role of the environment in shaping their radio properties. In the attempt to separate the effect of the galaxy mass and of the environment on their statistical radio properties, we investigate the possible dependence of the occurrence of radio loudness and of the fractional radio luminosity function on the dynamical state of the hosting cluster. Methods: We studied the radio properties of the BCGs in the Extended GMRT Radio Halo Survey (EGRHS), which consists of 65 clusters in the redshift range 0.2-0.4, with X-ray luminosity LX ≥ 5 × 1044 erg s-1, and quantitative information on their dynamical state from high-quality Chandra imaging. We obtained a statistical sample of 59 BCGs, which we divided into two classes, depending on whether the dynamical state of the host cluster was merging (M) or relaxed (R). Results: Of the 59 BCGs, 28 are radio loud and 31 are radio quiet. The radio-loud sources are favourably located in relaxed clusters (71%), while the reverse is true for the radio-quiet BCGs, which are mostly located in merging systems (81%). The fractional radio luminosity function for the BCGs in merging and relaxed clusters is different, and it is considerably higher for BCGs in relaxed clusters, where the total fraction of radio loudness reaches almost 90%, to be compared to the ~30% in merging clusters. For relaxed clusters, we found a positive correlation between the radio power of the BCGs and the strength of the cool core, consistent with previous studies on local samples. Conclusions: Our study suggests that the radio loudness of the BCGs strongly depends on the cluster dynamics; their fraction is

  3. Determination of hydrogen cluster velocities and comparison with numerical calculations.

    PubMed

    Täschner, A; Köhler, E; Ortjohann, H-W; Khoukaz, A

    2013-12-21

    The use of powerful hydrogen cluster jet targets in storage ring experiments led to the need of precise data on the mean cluster velocity as function of the stagnation temperature and pressure for the determination of the volume density of the target beams. For this purpose a large data set of hydrogen cluster velocity distributions and mean velocities was measured at a high density hydrogen cluster jet target using a trumpet shaped nozzle. The measurements have been performed at pressures above and below the critical pressure and for a broad range of temperatures relevant for target operation, e.g., at storage ring experiments. The used experimental method is described which allows for the velocity measurement of single clusters using a time-of-flight technique. Since this method is rather time-consuming and these measurements are typically interfering negatively with storage ring experiments, a method for a precise calculation of these mean velocities was needed. For this, the determined mean cluster velocities are compared with model calculations based on an isentropic one-dimensional van der Waals gas. Based on the obtained data and the presented numerical calculations, a new method has been developed which allows to predict the mean cluster velocities with an accuracy of about 5%. For this two cut-off parameters defining positions inside the nozzle are introduced, which can be determined for a given nozzle by only two velocity measurements. PMID:24359372

  4. CO deficiency in galaxies of the Fornax cluster?

    NASA Technical Reports Server (NTRS)

    Horellou, Cathy; Casoli, Fabienne; Dupraz, Christophe

    1993-01-01

    There is ample observational evidence that cluster galaxies are different from those in the field. Interaction with the hot intracluster medium affects the morphology of the galaxies, their gaseous content and possibly their star-formation activity. Tidal encounters between galaxies also play an important role. The atomic component has been investigated in detail for several clusters, among them our neighbor Virgo. With the Swedish-ESO 15 m telescope, we have observed in the 12CO(1-0) transition the 23 brightest spirals and lenticulars of the Formax cluster.

  5. THE LUMINOSITY PROFILES OF BRIGHTEST CLUSTER GALAXIES

    SciTech Connect

    Donzelli, C. J.; Muriel, H.; Madrid, J. P.

    2011-08-01

    We have derived detailed R-band luminosity profiles and structural parameters for a total of 430 brightest cluster galaxies (BCGs), down to a limiting surface brightness of 24.5 mag arcsec{sup -2}. Light profiles were initially fitted with a Sersic's R {sup 1/n} model, but we found that 205 ({approx}48%) BCGs require a double component model to accurately match their light profiles. The best fit for these 205 galaxies is an inner Sersic model, with indices n {approx} 1-7, plus an outer exponential component. Thus, we establish the existence of two categories of the BCG luminosity profiles: single and double component profiles. We found that double profile BCGs are brighter ({approx}0.2 mag) than single profile BCGs. In fact, the Kolmogorov-Smirnov test applied to these subsamples indicates that they have different total magnitude distributions, with mean values M{sub R} = -23.8 {+-} 0.6 mag for single profile BCGs and M{sub R} = -24.0 {+-} 0.5 mag for double profile BCGs. We find that partial luminosities for both subsamples are indistinguishable up to r = 15 kpc, while for r > 20 kpc the luminosities we obtain are on average 0.2 mag brighter for double profile BCGs. This result indicates that extra-light for double profile BCGs does not come from the inner region but from the outer regions of these galaxies. The best-fit slope of the Kormendy relation for the whole sample is a = 3.13 {+-} 0.04. However, when fitted separately, single and double profile BCGs show different slopes: a{sub single} = 3.29 {+-} 0.06 and a{sub double} = 2.79 {+-} 0.08. Also, the logarithmic slope of the metric luminosity {alpha} is higher in double profile BCGs ({alpha}{sub double} = 0.65 {+-} 0.12) than in single profile BCGs ({alpha}{sub single} = 0.59 {+-} 0.14). The mean isophote outer ellipticity (calculated at {mu} {approx} 24 mag arcsec{sup -2}) is higher in double profile BCGs (e{sub double} = 0.30 {+-} 0.10) than in single profile BCGs (e{sub single} = 0.26 {+-} 0.11). Similarly

  6. Weak lensing mass reconstruction of the galaxy cluster Abell 209

    NASA Astrophysics Data System (ADS)

    Paulin-Henriksson, S.; Antonuccio-Delogu, V.; Haines, C. P.; Radovich, M.; Mercurio, A.; Becciani, U.

    2007-05-01

    Context: Weak lensing applied to deep optical images of clusters of galaxies provides a powerful tool to reconstruct the distribution of the gravitating mass associated to these structures. Aims: We use the shear signal extracted by an analysis of deep exposures of a region centered around the galaxy cluster ABCG 209, at redshift z˜ 0.2, to derive both a map of the projected mass distribution and an estimate of the total mass within a characteristic radius. Methods: We use a series of deep archival R-band images from CFHT-12k, covering an area of 0.3 deg^2. We determine the shear of background galaxy images using a new implementation of the modified Kaiser-Squires-Broadhurst KSB+ pipeline for shear determination, which we has been tested against the "Shear TEsting Program 1 and 2'' simulations. We use mass aperture statistics to produce maps of the 2 dimensional density distribution, and parametric fits using both Navarro-Frenk-White and singular-isothermal-sphere profiles to constrain the total mass. Results: The projected mass distribution shows a pronounced asymmetry, with an elongated structure extending from the SE to the NW. This is in general agreement with the optical distribution previously found by other authors. A similar elongation was previously detected in the X-ray emission map, and in the distribution of galaxy colours. The circular NFW mass profile fit gives a total mass of M200 = 7.7+4.3-2.7× 1014 {M}_⊙ inside the virial radius r200 = 1.8± 0.3 Mpc. Conclusions: The weak lensing profile reinforces the evidence for an elongated structure of ABCG 209, as previously suggested by studies of the galaxy distribution and velocities. This project has been partly supported by a Marie Curie Transfer of Knowledge Fellowship of the European Community's Sixth Framework Programme, under contract: MTKD-CT-002995 COSMOCT. Based on observations obtained at the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council of Canada

  7. Evolutionary Effects on Brightest Cluster Galaxy (BCG) Detections in the CFHTLS-Deep Fields

    NASA Astrophysics Data System (ADS)

    Alis, S.

    2009-09-01

    Brightest cluster galaxies (BCGs) are the most massive and most luminous galaxies in the universe. These galaxies dominate galaxy clusters and lie at the top of the potential well of clusters. Investigating these galaxies can improve our understandings on galaxy cluster evolution. In this work, evolutionary effects on BCG detections are emphasized. For detecting BCGs, CFHTLS (Canada-France-Hawaii Telescope Legacy Survey) galaxy clusters, detected by Olsen et al. (2007) were used. To make a proper BCG detection, modeled galaxy colors should be evolved according to redshift. In this work, it is shown how unevolved galaxy colors can effect BCG detection.

  8. GAMMA RAYS FROM STAR FORMATION IN CLUSTERS OF GALAXIES

    SciTech Connect

    Storm, Emma M.; Jeltema, Tesla E.; Profumo, Stefano

    2012-08-20

    Star formation in galaxies is observed to be associated with gamma-ray emission, presumably from non-thermal processes connected to the acceleration of cosmic-ray nuclei and electrons. The detection of gamma rays from starburst galaxies by the Fermi Large Area Telescope (LAT) has allowed the determination of a functional relationship between star formation rate and gamma-ray luminosity. Since star formation is known to scale with total infrared (8-1000 {mu}m) and radio (1.4 GHz) luminosity, the observed infrared and radio emission from a star-forming galaxy can be used to quantitatively infer the galaxy's gamma-ray luminosity. Similarly, star-forming galaxies within galaxy clusters allow us to derive lower limits on the gamma-ray emission from clusters, which have not yet been conclusively detected in gamma rays. In this study, we apply the functional relationships between gamma-ray luminosity and radio and IR luminosities of galaxies derived by the Fermi Collaboration to a sample of the best candidate galaxy clusters for detection in gamma rays in order to place lower limits on the gamma-ray emission associated with star formation in galaxy clusters. We find that several clusters have predicted gamma-ray emission from star formation that are within an order of magnitude of the upper limits derived in Ackermann et al. based on non-detection by Fermi-LAT. Given the current gamma-ray limits, star formation likely plays a significant role in the gamma-ray emission in some clusters, especially those with cool cores. We predict that both Fermi-LAT over the course of its lifetime and the future Cerenkov Telescope Array will be able to detect gamma-ray emission from star-forming galaxies in clusters.

  9. Probing dark energy via galaxy cluster outskirts

    NASA Astrophysics Data System (ADS)

    Morandi, Andrea; Sun, Ming

    2016-04-01

    We present a Bayesian approach to combine Planck data and the X-ray physical properties of the intracluster medium in the virialization region of a sample of 320 galaxy clusters (0.056 < z < 1.24, kT ≳ 3 keV) observed with Chandra. We exploited the high level of similarity of the emission measure in the cluster outskirts as cosmology proxy. The cosmological parameters are thus constrained assuming that the emission measure profiles at different redshift are weakly self-similar, that is their shape is universal, explicitly allowing for temperature and redshift dependence of the gas fraction. This cosmological test, in combination with Planck+SNIa data, allows us to put a tight constraint on the dark energy models. For a constant-w model, we have w = -1.010 ± 0.030 and Ωm = 0.311 ± 0.014, while for a time-evolving equation of state of dark energy w(z) we have Ωm = 0.308 ± 0.017, w0 = -0.993 ± 0.046 and wa = -0.123 ± 0.400. Constraints on the cosmology are further improved by adding priors on the gas fraction evolution from hydrodynamic simulations. Current data favour the cosmological constant with w ≡ -1, with no evidence for dynamic dark energy. We checked that our method is robust towards different sources of systematics, including background modelling, outlier measurements, selection effects, inhomogeneities of the gas distribution and cosmic filaments. We also provided for the first time constraints on which definition of cluster boundary radius is more tenable, namely based on a fixed overdensity with respect to the critical density of the Universe. This novel cosmological test has the capacity to provide a generational leap forward in our understanding of the equation of state of dark energy.

  10. The Most Massive Ultra-compact Dwarf Galaxy in the Virgo Cluster

    NASA Astrophysics Data System (ADS)

    Liu, Chengze; Peng, Eric W.; Toloba, Elisa; Mihos, J. Christopher; Ferrarese, Laura; Alamo-Martínez, Karla; Zhang, Hong-Xin; Côté, Patrick; Cuillandre, Jean-Charles; Cunningham, Emily C.; Guhathakurta, Puragra; Gwyn, Stephen; Herczeg, Gregory; Lim, Sungsoon; Puzia, Thomas H.; Roediger, Joel; Sánchez-Janssen, Rubén; Yin, Jun

    2015-10-01

    We report on the properties of the most massive ultra-compact dwarf galaxy (UCD) in the nearby Virgo Cluster of galaxies using imaging from the Next Generation Virgo Cluster Survey and spectroscopy from Keck/DEIMOS. This object (M59-UCD3) appears to be associated with the massive Virgo galaxy M59 (NGC 4621), has an integrated velocity dispersion of 78 {km} {{{s}}}-1, a dynamical mass of 3.7× {10}8{M}⊙ , and an effective radius (Re) of 25 pc. With an effective surface mass density of 9.4× {10}10{M}⊙ {{kpc}}-2, it is the densest galaxy in the local universe discovered to date, surpassing the density of the luminous Virgo UCD, M60-UCD1. M59-UCD3 has a total luminosity of {M}{g\\prime }=-14.2 mag, and a spectral energy distribution consistent with an old (14 Gyr) stellar population with [Fe/H] = 0.0 and [α /{Fe}]=+0.2. We also examine deep imaging around M59 and find a broad low surface brightness stream pointing toward M59-UCD3, which may represent a tidal remnant of the UCD progenitor. This UCD, along with similar objects like M60-UCD1 and M59cO, likely represents an extreme population of tidally stripped galaxies more akin to larger and more massive compact early-type galaxies than to nuclear star clusters in present-day dwarf galaxies.

  11. The Most Massive Ultra-compact Dwarf Galaxy in the Virgo Cluster

    NASA Astrophysics Data System (ADS)

    Liu, Chengze; Peng, Eric W.; Toloba, Elisa; Mihos, J. Christopher; Ferrarese, Laura; Alamo-Martínez, Karla; Zhang, Hong-Xin; Côté, Patrick; Cuillandre, Jean-Charles; Cunningham, Emily C.; Guhathakurta, Puragra; Gwyn, Stephen; Herczeg, Gregory; Lim, Sungsoon; Puzia, Thomas H.; Roediger, Joel; Sánchez-Janssen, Rubén; Yin, Jun

    2015-10-01

    We report on the properties of the most massive ultra-compact dwarf galaxy (UCD) in the nearby Virgo Cluster of galaxies using imaging from the Next Generation Virgo Cluster Survey and spectroscopy from Keck/DEIMOS. This object (M59-UCD3) appears to be associated with the massive Virgo galaxy M59 (NGC 4621), has an integrated velocity dispersion of 78 {km} {{{s}}}-1, a dynamical mass of 3.7× {10}8{M}ȯ , and an effective radius (Re) of 25 pc. With an effective surface mass density of 9.4× {10}10{M}ȯ {{kpc}}-2, it is the densest galaxy in the local universe discovered to date, surpassing the density of the luminous Virgo UCD, M60-UCD1. M59-UCD3 has a total luminosity of {M}{g\\prime }=-14.2 mag, and a spectral energy distribution consistent with an old (14 Gyr) stellar population with [Fe/H] = 0.0 and [α /{Fe}]=+0.2. We also examine deep imaging around M59 and find a broad low surface brightness stream pointing toward M59-UCD3, which may represent a tidal remnant of the UCD progenitor. This UCD, along with similar objects like M60-UCD1 and M59cO, likely represents an extreme population of tidally stripped galaxies more akin to larger and more massive compact early-type galaxies than to nuclear star clusters in present-day dwarf galaxies.

  12. Redshift-Distance Survey of Early-Type Galaxies. I. The ENEARc Cluster Sample

    NASA Astrophysics Data System (ADS)

    Bernardi, M.; Alonso, M. V.; da Costa, L. N.; Willmer, C. N. A.; Wegner, G.; Pellegrini, P. S.; Rité, C.; Maia, M. A. G.

    2002-06-01

    This paper presents data on the ENEARc subsample of the larger ENEAR survey of nearby early-type galaxies. The ENEARc galaxies belong to clusters and were specifically chosen to be used for the construction of a Dn-σ template. The ENEARc sample includes new measurements of spectroscopic and photometric parameters (redshift, velocity dispersion, line index Mg2, and the angular diameter dn), as well as data from the literature. New spectroscopic data are given for 229 cluster early-type galaxies, and new photometry is presented for 348 objects. Repeat and overlap observations with external data sets are used to construct a final merged catalog consisting of 640 early-type galaxies in 28 clusters. Objective criteria, based on catalogs of groups of galaxies derived from complete redshift surveys of the nearby universe, are used to assign galaxies to clusters. In a companion paper, these data are used to construct the template Dn-σ distance relation for early-type galaxies, which has been used to estimate galaxy distances and derive peculiar velocities for the ENEAR all-sky sample. Based on observations at Complejo Astronomico El Leoncito, operated under agreement between the Consejo Nacional de Investigaciones Científicas de la República Argentina and the National Universities of La Plata, Córdoba, and San Juan; Cerro Tololo Inter-American Observatory, National Optical Astronomical Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under cooperative agreement with the National Science Foundation; the European Southern Observatory (ESO), partially under the ESO-ON agreement; the Fred Lawrence Whipple Observatory; the Observatório do Pico dos Dias, operated by the Laboratório Nacional de Astrofísica and the MDM Observatory at Kitt Peak.

  13. Galaxy Infall by Interacting with Its Environment: A Comprehensive Study of 340 Galaxy Clusters

    NASA Astrophysics Data System (ADS)

    Gu, Liyi; Wen, Zhonglue; Gandhi, Poshak; Inada, Naohisa; Kawaharada, Madoka; Kodama, Tadayuki; Konami, Saori; Nakazawa, Kazuhiro; Xu, Haiguang; Makishima, Kazuo

    2016-07-01

    To study systematically the evolution of the angular extents of the galaxy, intracluster medium (ICM), and dark matter components in galaxy clusters, we compiled the optical and X-ray properties of a sample of 340 clusters with redshifts <0.5, based on all the available data from the Sloan Digital Sky Survey and Chandra/XMM-Newton. For each cluster, the member galaxies were determined primarily with photometric redshift measurements. The radial ICM mass distribution, as well as the total gravitational mass distribution, was derived from a spatially resolved spectral analysis of the X-ray data. When normalizing the radial profile of galaxy number to that of the ICM mass, the relative curve was found to depend significantly on the cluster redshift; it drops more steeply toward the outside in lower-redshift subsamples. The same evolution is found in the galaxy-to-total mass profile, while the ICM-to-total mass profile varies in an opposite way. The behavior of the galaxy-to-ICM distribution does not depend on the cluster mass, suggesting that the detected redshift dependence is not due to mass-related effects, such as sample selection bias. Also, it cannot be ascribed to various redshift-dependent systematic errors. We interpret that the galaxies, the ICM, and the dark matter components had similar angular distributions when a cluster was formed, while the galaxies traveling in the interior of the cluster have continuously fallen toward the center relative to the other components, and the ICM has slightly expanded relative to the dark matter although it suffers strong radiative loss. This cosmological galaxy infall, accompanied by an ICM expansion, can be explained by considering that the galaxies interact strongly with the ICM while they are moving through it. The interaction is considered to create a large energy flow of 1044‑45 erg s‑1 per cluster from the member galaxies to their environment, which is expected to continue over cosmological timescales.

  14. Galaxy Infall by Interacting with Its Environment: A Comprehensive Study of 340 Galaxy Clusters

    NASA Astrophysics Data System (ADS)

    Gu, Liyi; Wen, Zhonglue; Gandhi, Poshak; Inada, Naohisa; Kawaharada, Madoka; Kodama, Tadayuki; Konami, Saori; Nakazawa, Kazuhiro; Xu, Haiguang; Makishima, Kazuo

    2016-07-01

    To study systematically the evolution of the angular extents of the galaxy, intracluster medium (ICM), and dark matter components in galaxy clusters, we compiled the optical and X-ray properties of a sample of 340 clusters with redshifts <0.5, based on all the available data from the Sloan Digital Sky Survey and Chandra/XMM-Newton. For each cluster, the member galaxies were determined primarily with photometric redshift measurements. The radial ICM mass distribution, as well as the total gravitational mass distribution, was derived from a spatially resolved spectral analysis of the X-ray data. When normalizing the radial profile of galaxy number to that of the ICM mass, the relative curve was found to depend significantly on the cluster redshift; it drops more steeply toward the outside in lower-redshift subsamples. The same evolution is found in the galaxy-to-total mass profile, while the ICM-to-total mass profile varies in an opposite way. The behavior of the galaxy-to-ICM distribution does not depend on the cluster mass, suggesting that the detected redshift dependence is not due to mass-related effects, such as sample selection bias. Also, it cannot be ascribed to various redshift-dependent systematic errors. We interpret that the galaxies, the ICM, and the dark matter components had similar angular distributions when a cluster was formed, while the galaxies traveling in the interior of the cluster have continuously fallen toward the center relative to the other components, and the ICM has slightly expanded relative to the dark matter although it suffers strong radiative loss. This cosmological galaxy infall, accompanied by an ICM expansion, can be explained by considering that the galaxies interact strongly with the ICM while they are moving through it. The interaction is considered to create a large energy flow of 1044-45 erg s-1 per cluster from the member galaxies to their environment, which is expected to continue over cosmological timescales.

  15. Old Star Clusters in Spiral Galaxies: M101 as a Case Study

    NASA Astrophysics Data System (ADS)

    Simanton, Lesley Ann

    2015-01-01

    Most stars form in groups and clusters, at least a small fraction of which can be extremely long-lived. However, many details of how star clusters form and how they disrupt are still unclear. We present and examine a catalog of old star clusters in the nearby spiral galaxy M101, and compare with the known properties of old star clusters in other spiral galaxies. Data include multi-band Hubble Space Telescope images and Gemini-GMOS spectra. Among the properties examined are luminosity distributions, colors, sizes, spatial distributions, and velocities. We highlight the somewhat surprising result of a population of old, disk clusters in M101, which are unlike populations found in the Milky Way and M31.

  16. The impact of galaxy geometry and mass evolution on the survival of star clusters

    SciTech Connect

    Madrid, Juan P.; Hurley, Jarrod R.; Martig, Marie

    2014-04-01

    Direct N-body simulations of globular clusters in a realistic Milky-Way-like potential are carried out using the code NBODY6 to determine the impact of the host galaxy disk mass and geometry on the survival of star clusters. A relation between disk mass and star-cluster dissolution timescale is derived. These N-body models show that doubling the mass of the disk from 5 × 10{sup 10} M {sub ☉} to 10 × 10{sup 10} M {sub ☉} halves the dissolution time of a satellite star cluster orbiting the host galaxy at 6 kpc from the galactic center. Different geometries in a disk of identical mass can determine either the survival or dissolution of a star cluster orbiting within the inner 6 kpc of the galactic center. Furthermore, disk geometry has measurable effects on the mass loss of star clusters up to 15 kpc from the galactic center. N-body simulations performed with a fine output time step show that at each disk crossing the outer layers of star clusters experiences an increase in velocity dispersion of ∼5% of the average velocity dispersion in the outer section of star clusters. This leads to an enhancement of mass loss—a clearly discernable effect of disk shocking. By running models with different inclinations, we determine that star clusters with an orbit that is perpendicular to the Galactic plane have larger mass loss rates than do clusters that evolve in the Galactic plane or in an inclined orbit.

  17. UV TO FAR-IR CATALOG OF A GALAXY SAMPLE IN NEARBY CLUSTERS: SPECTRAL ENERGY DISTRIBUTIONS AND ENVIRONMENTAL TRENDS

    SciTech Connect

    Hernandez-Fernandez, Jonathan D.; Iglesias-Paramo, J.; Vilchez, J. M.

    2012-03-01

    In this paper, we present a sample of cluster galaxies devoted to study the environmental influence on the star formation activity. This sample of galaxies inhabits in clusters showing a rich variety in their characteristics and have been observed by the SDSS-DR6 down to M{sub B} {approx} -18, and by the Galaxy Evolution Explorer AIS throughout sky regions corresponding to several megaparsecs. We assign the broadband and emission-line fluxes from ultraviolet to far-infrared to each galaxy performing an accurate spectral energy distribution for spectral fitting analysis. The clusters follow the general X-ray luminosity versus velocity dispersion trend of L{sub X} {proportional_to} {sigma}{sup 4.4}{sub c}. The analysis of the distributions of galaxy density counting up to the 5th nearest neighbor {Sigma}{sub 5} shows: (1) the virial regions and the cluster outskirts share a common range in the high density part of the distribution. This can be attributed to the presence of massive galaxy structures in the surroundings of virial regions. (2) The virial regions of massive clusters ({sigma}{sub c} > 550 km s{sup -1}) present a {Sigma}{sub 5} distribution statistically distinguishable ({approx}96%) from the corresponding distribution of low-mass clusters ({sigma}{sub c} < 550 km s{sup -1}). Both massive and low-mass clusters follow a similar density-radius trend, but the low-mass clusters avoid the high density extreme. We illustrate, with ABELL 1185, the environmental trends of galaxy populations. Maps of sky projected galaxy density show how low-luminosity star-forming galaxies appear distributed along more spread structures than their giant counterparts, whereas low-luminosity passive galaxies avoid the low-density environment. Giant passive and star-forming galaxies share rather similar sky regions with passive galaxies exhibiting more concentrated distributions.

  18. Velocity dispersions in galaxies. IV - The nucleus of NGC 1068

    NASA Technical Reports Server (NTRS)

    Richstone, D. O.; Morton, D. C.

    1975-01-01

    A high-resolution spectrum of the Seyfert galaxy NGC 1068, obtained with an integrating television system, is compared with the spectrum of a KO III star (delta Tau) to derive the line-of-sight velocity dispersion of the stars in the galactic nucleus. An Fe I absorption line observed at 4059.7 A yields a velocity dispersion of 150 (plus or minus 50) km/sec. An upper limit for the nuclear mass is derived in terms of this velocity dispersion, an estimated nuclear radius of 136 pc, and a Hubble constant of 50 km/sec per Mpc. The results, 14 (+10, -8) by 10 to the 8th power solar masses, is shown to be consistent with a number of quasar models scaled down in luminosity to provide the energy source for a Seyfert nucleus. Strong H and K interstellar absorption lines superposed on the spectrum of NGC 1068 are analyzed.-

  19. H ii REGIONS WITHIN A COMPACT HIGH VELOCITY CLOUD. A NEARLY STARLESS DWARF GALAXY?

    SciTech Connect

    Bellazzini, M.; Magrini, L.; Mucciarelli, A.; Fraternali, F.; Ibata, R.; Martin, N.; Battaglia, G.; Testa, V.; Fumana, M.; Marchetti, A.; Correnti, M.

    2015-02-10

    Within the SECCO survey we identified a candidate stellar counterpart to the Ultra Compact High Velocity Cloud (UCHVC) HVC274.68+74.70-123 that was suggested by Adams et al. to be a possible mini halo within the Local Group of galaxies. The spectroscopic follow-up of the brightest sources within the candidate reveals the presence of two H ii regions whose radial velocity is compatible with a physical association with the UVHVC. The available data do not allow us to give a definite answer on the nature of the newly identified system. A few alternative hypotheses are discussed. However, the most likely possibility is that we have found a new faint dwarf galaxy residing in the Virgo cluster of galaxies, which we name SECCO 1. Independently of its actual distance, SECCO 1 displays a ratio of neutral hydrogen mass to V luminosity of M{sub H} {sub I}/L{sub V}≳20, by far the largest among local dwarfs. Hence, it appears to be a nearly starless galaxy and it may be an example of the missing links between normal dwarfs and the dark mini halos that are predicted to exist in large numbers according to the currently accepted cosmological model.

  20. Optical-to-virial velocity ratios of local disc galaxies from combined kinematics and galaxy-galaxy lensing

    NASA Astrophysics Data System (ADS)

    Reyes, R.; Mandelbaum, R.; Gunn, J. E.; Nakajima, R.; Seljak, U.; Hirata, C. M.

    2012-10-01

    In this paper, we measure the optical-to-virial velocity ratios Vopt/V200c of disc galaxies in the Sloan Digital Sky Survey (SDSS) at a mean redshift of = 0.07 and with stellar masses 109 < M* < 1011 M⊙. Vopt/V200c, the ratio of the circular velocity measured at the optical radius of the disc (˜10 kpc) to that at the virial radius of the dark matter halo (˜150 kpc), is a powerful observational constraint on disc galaxy formation. It links galaxies to their dark matter haloes dynamically and constrains the total mass profile of disc galaxies over an order of magnitude in length scale. For this measurement, we combine Vopt derived from the Tully-Fisher relation (TFR) from Reyes et al. with V200c derived from halo masses measured with galaxy-galaxy lensing. In anticipation of this combination, we use similarly selected galaxy samples for both the TFR and lensing analysis. For three M* bins with lensing-weighted mean stellar masses of 0.6, 2.7 and 6.5 × 1010 M⊙, we find halo-to-stellar mass ratios M200c/M* = 41, 23 and 26, with 1σ statistical uncertainties of around 0.1 dex, and Vopt/V200c = 1.27 ± 0.08, 1.39 ± 0.06 and 1.27 ± 0.08 (1σ), respectively. Our results suggest that the dark matter and baryonic contributions to the mass within the optical radius are comparable, if the dark matter halo profile has not been significantly modified by baryons. The results obtained in this work will serve as inputs to and constraints on disc galaxy formation models, which will be explored in future work. Finally, we note that this paper presents a new and improved galaxy shape catalogue for weak lensing that covers the full SDSS Data Release 7 footprint.

  1. Tracing galaxy evolution through resolved stellar populations and star clusters

    NASA Astrophysics Data System (ADS)

    Silva-Villa, E.

    2011-09-01

    Field stars and star clusters contain a big part of the galaxy’s history. To understand galaxy formation and evolution we need then to understand the parts of which galaxies are composed. It has commonly been assumed that most stars formed in clusters. However, the connection between these two systems is not clear, and the fraction of actual star formation happening in clusters is still uncertain. Through this thesis, we aim to use field stars and star clusters to attack different problems regarding galaxy formation and evolution, named: 1. the cluster formation efficiency and its (co-)relation with environment (i.e. the host galaxy), 2. the star formation rate in the arms and inter-arm regions of spiral galaxies, and 3. the indications of a possible interaction between two galaxies observed through their resolved stellar populations. We performed a systematic and homogeneous study over the galaxies NGC45, NGC1313, NGC4395, NGC5236 and NGC7793, where star clusters and field stars are analyze separately. For this aim, we used Hubble Space Telescope observations in the optical bands U, B, V and I, using the Advanced Camera for Surveys and the Wide Field Planetary Camera 2. Standard photometric procedures are use to study the properties of these two main parts of the galaxies. However, incompleteness constrains our results to ages younger than 100 Myr. Following the synthetic CMD method we recovered the star formation history for the last 100 Myr over the five galaxies. Comparing observed clusters properties with simple stellar population models, we estimate ages and masses of star clusters. We observe that the galaxies NGC5236 and NGC1313 show higher star and cluster formation rates, while NGC45, NGC4395 and NGC7793 show lower values. We found that the actual fraction of star formation happening in clusters presents low values (< 10%), contrary to common assumptions, however in agreement with studies in other galaxies. Observations of the surface star formation

  2. Thermal conduction and reduced cooling flows in galaxy clusters

    NASA Astrophysics Data System (ADS)

    Voigt, L. M.; Fabian, A. C.

    2004-02-01

    Conduction may play an important role in reducing cooling flows in galaxy clusters. We analyse a sample of 16 objects using Chandra data and find that a balance between electron conduction and cooling can exist in the hotter clusters (T>~ 5 keV), provided that the plasma conductivity is close to the unhindered Spitzer value. In the absence of any additional heat sources, a reduced mass inflow must then develop in the cooler objects in the sample. We fit cooling flow models to deprojected spectra and compare the spectral mass deposition rates found to the values required to account for the excess luminosity, assuming Spitzer-rate heat transfer over the observed temperature gradients. The measured mass inflow rates are insufficient to maintain energy balance in at least five clusters. However, emission from cooling gas may be partially absorbed. We also compute the flux supplied by turbulent heat transport and find conductivity profiles that follow a strikingly similar temperature dependence to the conductivity values required to prevent cooling. The larger-scale turbulent motions implied by this process are required to have velocities of between 10 and 50 per cent of the speed of sound in the local intracluster gas.

  3. VizieR Online Data Catalog: Galaxies and Clusters of Galaxies (CGCG) (Zwicky, 1968)

    NASA Astrophysics Data System (ADS)

    Zwicky, F.; et al.

    1995-10-01

    This document describes a machine-readable version of a portion of the "Catalogue of Galaxies and Clusters of Galaxies" (Zwicky, et al.). The published catalogue covers 560 Palomar Sky Survey fields, and for each field it lists both individual galaxies and clusters of galaxies. Its limiting magnitude for galaxies is approximately +15.5 apparent photographic magnitude. The present machine-readable version includes only the individual galaxies. It consists of two files, the first of which lists the galaxies (data file) and the second of which enumerates the fields covered (headers file). Note: the abbreviation ADC used in this document refers to the Astronomical Data Center, NASA/Goddard Space Flight Center. (2 data files).

  4. A High-Velocity Collision With Our Galaxy's Disk

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2016-08-01

    What caused the newly discovered supershell in the outskirts of our galaxy? A new study finds evidence that a high-velocity cloud may have smashed into the Milky Ways disk millions of years ago.Mysterious Gas ShellsA single velocity-channel map of the supershell GS040.2+00.670, with red contours marking the high-velocity cloud at its center. [Adapted from Park et al. 2016]The neutral hydrogen gas that fills interstellar space is organized into structures like filaments, loops, and shells. Supershells are enormous shells of hydrogen gas that can have radii of a thousand light-years or more; weve spotted about 20 of these in our own galaxy, and more in nearby dwarfs and spiral galaxies.How do these structures form? One theory is that they result from several supernovae explosions occurring in the same area. But the energy needed to create a supershell is more than 3 x 1052 erg, which corresponds to over 30 supernovae quite a lot to have exploding in the same region.Theres an interesting alternative scenario: the supershells might instead be caused by the impacts of high-velocity clouds that fall into the galactic disk.Velocity data for the compact high-velocity cloud CHVC040. The cloud is moving fast enough to create the supershell observed. [Adapted from Park et al. 2016]The Milky Ways Speeding CloudsHigh-velocity clouds are clouds of mostly hydrogen that speed through the Milky Way with radial velocities that are very different from the material in the galactic disk. The origins of these clouds are unknown, but its proposed that they come from outside the galaxy they might be fragments of a nearby, disrupting galaxy, or they might have originated from flows of accreting gas in the space in between galaxies.Though high-velocity clouds have long been on the list of things that might cause supershells, weve yet to find conclusive evidence of this. But that might have just changed, with a recent discovery by a team of scientists led by Geumsook Park (Seoul National

  5. Dwarf Galaxies in the Antlia Cluster: First Results

    NASA Astrophysics Data System (ADS)

    Smith Castelli, A. V.; Bassino, L. P.; Cellone, S. A.; Richtler, T.; Dirsch, B.; Infante, L.; Aruta, C.; Gómez, M.

    The Antlia cluster (l = 273°, b = 19°) is the third nearest galaxy cluster (d = 35 Mpc) after Virgo and Fornax. In spite of its proximity, it has been poorly investigated. Its population is dominated by early type galaxies, with dwarf ellipticals being the most abundant galaxy type [1]. Here we present the first results of a project aimed to study the galaxy population of the Antlia cluster. Our results correspond to the identification and classification of dwarf galaxies in the central cluster region, extending the list of \\cite{FS90} (FS90 catalogue), a photographic survey that is complete only up to B_T ≃ 18 mag (M_B ≃ -14.7 mag at the Antlia cluster distance). The final aim of our project is to study the luminosity function, morphology and structural parameters of dwarf galaxies in the Antlia cluster with a more complete sample. We also intend to investigate the kinematics of the cluster (50 spectra have been already obtained).

  6. 60 micron luminosity evolution of rich clusters of galaxies

    SciTech Connect

    Kelly, D.M.; Rieke, G.H. )

    1990-10-01

    The average 60-micron flux has been determined for a collection of optically selected galaxy clusters at redshifts ranging from 0.30 to 0.92. The result, 26 mJy per cluster, represents the faintest flux determination known of using the IRAS data base. The flux from this set of clusters has been compared to the 60-micron flux from a sample of nearby galaxy clusters. It is found that the far-infrared luminosity evolution in cluster galaxies can be no more than a factor of 1.7 from z = 0.4 to the present epoch. This upper limit is close to the evolution predicted for simple aging of the stellar populations. Additional processes such as mergers, cannibalism, or enhanced rates of starbursts appear to occur at a low enough level that they have little influence on the far-infrared emission from clusters over this redshift range. 38 refs.

  7. 60 micron luminosity evolution of rich clusters of galaxies

    NASA Technical Reports Server (NTRS)

    Kelly, Douglas M.; Rieke, George H.

    1990-01-01

    The average 60-micron flux has been determined for a collection of optically selected galaxy clusters at redshifts ranging from 0.30 to 0.92. The result, 26 mJy per cluster, represents the faintest flux determination known of using the IRAS data base. The flux from this set of clusters has been compared to the 60-micron flux from a sample of nearby galaxy clusters. It is found that the far-infrared luminosity evolution in cluster galaxies can be no more than a factor of 1.7 from z = 0.4 to the present epoch. This upper limit is close to the evolution predicted for simple aging of the stellar populations. Additional processes such as mergers, cannibalism, or enhanced rates of starbursts appear to occur at a low enough level that they have little influence on the far-infrared emission from clusters over this redshift range.

  8. Structures and Components in Galaxy Clusters: Observations and Models

    NASA Astrophysics Data System (ADS)

    Bykov, A. M.; Churazov, E. M.; Ferrari, C.; Forman, W. R.; Kaastra, J. S.; Klein, U.; Markevitch, M.; de Plaa, J.

    2015-05-01

    Clusters of galaxies are the largest gravitationally bounded structures in the Universe dominated by dark matter. We review the observational appearance and physical models of plasma structures in clusters of galaxies. Bubbles of relativistic plasma which are inflated by supermassive black holes of AGNs, cooling and heating of the gas, large scale plasma shocks, cold fronts, non-thermal halos and relics are observed in clusters. These constituents are reflecting both the formation history and the dynamical properties of clusters of galaxies. We discuss X-ray spectroscopy as a tool to study the metal enrichment in clusters and fine spectroscopy of Fe X-ray lines as a powerful diagnostics of both the turbulent plasma motions and the energetics of the non-thermal electron populations. The knowledge of the complex dynamical and feedback processes is necessary to understand the energy and matter balance as well as to constrain the role of the non-thermal components of clusters.

  9. WITNESSING THE FORMATION OF A BRIGHTEST CLUSTER GALAXY IN A NEARBY X-RAY CLUSTER

    SciTech Connect

    Rasmussen, Jesper; Mulchaey, John S.; Bai, Lei; Ponman, Trevor J.; Raychaudhury, Somak; Dariush, Ali

    2010-07-10

    The central dominant galaxies in galaxy clusters constitute the most massive and luminous galaxies in the universe. Despite this, the formation of these brightest cluster galaxies (BCGs) and the impact of this on the surrounding cluster environment remain poorly understood. Here we present multiwavelength observations of the nearby poor X-ray cluster MZ 10451, in which both processes can be studied in unprecedented detail. Chandra observations of the intracluster medium (ICM) in the cluster core, which harbors two optically bright early-type galaxies in the process of merging, show that the system has retained a cool core and a central metal excess. This suggests that any merger-induced ICM heating and mixing remain modest at this stage. Tidally stripped stars seen around either galaxy likely represent an emerging intracluster light component, and the central ICM abundance enhancement may have a prominent contribution from in situ enrichment provided by these stars. The smaller of the merging galaxies shows evidence for having retained a hot gas halo, along with tentative evidence for some obscured star formation, suggesting that not all BCG major mergers at low redshift are completely dissipationless. Both galaxies are slightly offset from the peak of the ICM emission, with all three lying on an axis that roughly coincides with the large-scale elongation of the ICM. Our data are consistent with a picture in which central BCGs are built up by mergers close to the cluster core, by galaxies infalling on radial orbits aligned with the cosmological filaments feeding the cluster.

  10. The dynamics and evolution of clusters of galaxies

    NASA Technical Reports Server (NTRS)

    Geller, Margaret; Huchra, John P.

    1987-01-01

    Research was undertaken to produce a coherent picture of the formation and evolution of large-scale structures in the universe. The program is divided into projects which examine four areas: the relationship between individual galaxies and their environment; the structure and evolution of individual rich clusters of galaxies; the nature of superclusters; and the large-scale distribution of individual galaxies. A brief review of results in each area is provided.

  11. STAR-FORMING GALAXY EVOLUTION IN NEARBY RICH CLUSTERS

    SciTech Connect

    Tyler, K. D.; Rieke, G. H.; Bai, L.

    2013-08-20

    Dense environments are known to quench star formation in galaxies, but it is still unknown what mechanism(s) are directly responsible. In this paper, we study the star formation of galaxies in A2029 and compare it to that of Coma, combining indicators at 24 {mu}m, H{alpha}, and UV down to rates of 0.03 M{sub Sun} yr{sup -1}. We show that A2029's star-forming galaxies follow the same mass-SFR relation as the field. The Coma cluster, on the other hand, has a population of galaxies with star formation rates (SFRs) significantly lower than the field mass-SFR relation, indicative of galaxies in the process of being quenched. Over half of these galaxies also host active galactic nuclei. Ram-pressure stripping and starvation/strangulation are the most likely mechanisms for suppressing the star formation in these galaxies, but we are unable to disentangle which is dominating. The differences we see between the two clusters' populations of star-forming galaxies may be related to their accretion histories, with A2029 having accreted its star-forming galaxies more recently than Coma. Additionally, many early-type galaxies in A2029 are detected at 24 {mu}m and/or in the far-UV, but this emission is not directly related to star formation. Similar galaxies have probably been classified as star forming in previous studies of dense clusters, possibly obscuring some of the effects of the cluster environment on true star-forming galaxies.

  12. Evolution of the early-type galaxy fraction in clusters since z = 0.8

    NASA Astrophysics Data System (ADS)

    Simard, L.; Clowe, D.; Desai, V.; Dalcanton, J. J.; von der Linden, A.; Poggianti, B. M.; White, S. D. M.; Aragón-Salamanca, A.; De Lucia, G.; Halliday, C.; Jablonka, P.; Milvang-Jensen, B.; Saglia, R. P.; Pelló, R.; Rudnick, G. H.; Zaritsky, D.

    2009-12-01

    We study the morphological content of a large sample of high-redshift clusters to determine its dependence on cluster mass and redshift. Quantitative morphologies are based on PSF-convolved, 2D bulge+disk decompositions of cluster and field galaxies on deep Very Large Telescope FORS2 images of eighteen, optically-selected galaxy clusters at 0.45 < z < 0.80 observed as part of the ESO Distant Cluster Survey (“EDisCS”). Morphological content is characterized by the early-type galaxy fraction f_et, and early-type galaxies are objectively selected based on their bulge fraction and image smoothness. This quantitative selection is equivalent to selecting galaxies visually classified as E or S0. Changes in early-type fractions as a function of cluster velocity dispersion, redshift and star-formation activity are studied. A set of 158 clusters extracted from the Sloan Digital Sky Survey is analyzed exactly as the distant EDisCS sample to provide a robust local comparison. We also compare our results to a set of clusters from the Millennium Simulation. Our main results are: (1) the early-type fractions of the SDSS and EDisCS clusters exhibit no clear trend as a function of cluster velocity dispersion. (2) Mid-z EDisCS clusters around σ = 500 km s-1 have f_et ≃ 0.5 whereas high-z EDisCS clusters have f_et ≃ 0.4. This represents a ~25% increase over a time interval of 2 Gyr. (3) There is a marked difference in the morphological content of EDisCS and SDSS clusters. None of the EDisCS clusters have early-type galaxy fractions greater than 0.6 whereas half of the SDSS clusters lie above this value. This difference is seen in clusters of all velocity dispersions. (4) There is a strong and clear correlation between morphology and star formation activity in SDSS and EDisCS clusters in the sense that decreasing fractions of [OII] emitters are tracked by increasing early-type fractions. This correlation holds independent of cluster velocity dispersion and redshift even

  13. Galaxy clusters as probes for cosmology and dark matter

    NASA Astrophysics Data System (ADS)

    Battistelli, Elia S.; Burigana, Carlo; de Bernardis, Paolo; Kirillov, Alexander A.; Neto, Gastao B. Lima; Masi, Silvia; Norgaard-Nielsen, Hans U.; Ostermann, Peter; Roman, Matthieu; Rosati, Piero; Rossetti, Mariachiara

    2016-07-01

    In recent years, significant progress has been made in building new galaxy clusters samples, at low and high redshifts, from wide-area surveys, particularly exploiting the Sunyaev-Zel’dovich (SZ) effect. A large effort is underway to identify and characterize these new systems with optical/NIR and X-ray facilities, thus opening new avenues to constraint cosmological models using structure growth and geometrical tests. A census of galaxy clusters sets constraints on reionization mechanisms and epochs, which need to be reconciled with recent limits on the reionization optical depth from cosmic microwave background (CMB) experiments. Future advances in SZ effect measurements will include the possibility to (unambiguously) measure directly the kinematic SZ effect, to build an even larger catalogue of galaxy clusters able to study the high redshift universe, and to make (spatially-)resolved galaxy cluster maps with even spectral capability to (spectrally-)resolve the relativistic corrections of the SZ effect.

  14. THE GALAXY CONTENT OF SDSS CLUSTERS AND GROUPS

    SciTech Connect

    Hansen, Sarah M.; Wechsler, Risa H.; Koester, Benjamin P.

    2009-07-10

    Imaging data from the Sloan Digital Sky Survey are used to characterize the population of galaxies in groups and clusters detected with the MaxBCG algorithm. We investigate the dependence of brightest cluster galaxy (BCG) luminosity, and the distributions of satellite galaxy luminosity and satellite color, on cluster properties over the redshift range 0.1 {<=} z {<=} 0.3. The size of the data set allows us to make measurements in many bins of cluster richness, radius and redshift. We find that, within r {sub 200} of clusters with mass above 3 x 10{sup 13} h {sup -1} M {sub sun}, the luminosity function (LF) of both red and blue satellites is only weakly dependent on richness. We further find that the shape of the satellite LF does not depend on cluster-centric distance for magnitudes brighter than {sup 0.25} M{sub i} - 5log{sub 10} h =-19. However, the mix of faint red and blue galaxies changes dramatically. The satellite red fraction is dependent on cluster-centric distance, galaxy luminosity, and cluster mass, and also increases by {approx}5% between redshifts 0.28 and 0.2, independent of richness. We find that BCG luminosity is tightly correlated with cluster richness, scaling as L {sub BCG} {approx} M {sup 0.3} {sub 200}, and has a Gaussian distribution at fixed richness, with {sigma}{sub logL} {approx} 0.17 for massive clusters. The ratios of BCG luminosity to total cluster luminosity and characteristic satellite luminosity scale strongly with cluster richness: in richer systems, BCGs contribute a smaller fraction of the total light, but are brighter compared to typical satellites. This study demonstrates the power of cross-correlation techniques for measuring galaxy populations in purely photometric data.

  15. The Galaxy Content of SDSS Clusters And Groups

    SciTech Connect

    Hansen, Sarah M.; Sheldon, Erin S.; Wechsler, Risa H.; Koester, Benjamin P.; /Chicago U., Astron. Astrophys. Ctr.

    2007-11-09

    Imaging data from the Sloan Digital Sky Survey are used to characterize the population of galaxies in groups and clusters detected with the MaxBCG algorithm. We investigate the dependence of Brightest Cluster Galaxy (BCG) luminosity, and the distributions of satellite galaxy luminosity and satellite color, on cluster properties over the redshift range 0.1 {le} z {le} 0.3. The size of the dataset allows us to make measurements in many bins of cluster richness, radius and redshift. We find that, within r200 of clusters with mass above 3x10{sup 13}h{sup -1}M{sub {circle_dot}}, the luminosity function of both red and blue satellites is only weakly dependent on richness. We further find that the shape of the satellite luminosity function does not depend on cluster-centric distance for magnitudes brighter than {sup 0.25}M{sub i} - 5log{sub 10}h = -19. However, the mix of faint red and blue galaxies changes dramatically. The satellite red fraction is dependent on cluster-centric distance, galaxy luminosity and cluster mass, and also increases by {approx}5% between redshifts 0.28 and 0.2, independent of richness. We find that BCG luminosity is tightly correlated with cluster richness, scaling as L{sub BCG} {approx} M{sup 0.3}{sub 200}, and has a Gaussian distribution at fixed richness, with {sigma}{sub log}L {approx} 0.17 for massive clusters. The ratios of BCG luminosity to total cluster luminosity and characteristic satellite luminosity scale strongly with cluster richness: in richer systems, BCGs contribute a smaller fraction of the total light, but are brighter compared to typical satellites. This study demonstrates the power of cross-correlation techniques for measuring galaxy populations in purely photometric data.

  16. A study of cooling flows in poor clusters of galaxies

    NASA Technical Reports Server (NTRS)

    Kriss, Gerard A.; Dillingham, Stephen

    1995-01-01

    We observed three poor clusters with central dominant galaxies (AWM 4, MKW 4, and MKW 3's) using the Position Sensitive Proportional Counter on the ROSAT X-ray satellite. The images reveal smooth, symmetrical X-ray emission filling the cluster with a sharp peak on each central galaxy. The cluster surface brightness profiles can be decomposed using superposed King models for the central galaxy and the intracluster medium. The King model parameters for the cluster portions are consistent with previous observations of these clusters. The newly measured King model parameters for the central galaxies are typical of the X-ray surface brightness distributions of isolated elliptical galaxies. Spatially resolved temperature measurements in annular rings throughout the clusters show a nearly isothermal profile. Temperatures are consistent with previously measured values, but are much better determined. There is no significant drop in temperature noted in the innermost bins where cooling flows are likely to be present, nor is any excess absorption by cold gas required. All cold gas columns are consistent with galactic foreground absorption. We derive mass profiles for the clusters assuming both isothermal temperature profiles and cooling flow models with constant mass flow rates. Our results are consistent with previous Einstein IPC observations by Kriss, Cioffi, & Canizares, but extend the mass profiles out to 1 Mpc in these poor clusters.

  17. A study of cooling flows in poor clusters of galaxies

    NASA Astrophysics Data System (ADS)

    Kriss, Gerard A.; Dillingham, Stephen

    1995-08-01

    We observed three poor clusters with central dominant galaxies (AWM 4, MKW 4, and MKW 3's) using the Position Sensitive Proportional Counter on the ROSAT X-ray satellite. The images reveal smooth, symmetrical X-ray emission filling the cluster with a sharp peak on each central galaxy. The cluster surface brightness profiles can be decomposed using superposed King models for the central galaxy and the intracluster medium. The King model parameters for the cluster portions are consistent with previous observations of these clusters. The newly measured King model parameters for the central galaxies are typical of the X-ray surface brightness distributions of isolated elliptical galaxies. Spatially resolved temperature measurements in annular rings throughout the clusters show a nearly isothermal profile. Temperatures are consistent with previously measured values, but are much better determined. There is no significant drop in temperature noted in the innermost bins where cooling flows are likely to be present, nor is any excess absorption by cold gas required. All cold gas columns are consistent with galactic foreground absorption. We derive mass profiles for the clusters assuming both isothermal temperature profiles and cooling flow models with constant mass flow rates. Our results are consistent with previous Einstein IPC observations by Kriss, Cioffi, & Canizares, but extend the mass profiles out to 1 Mpc in these poor clusters.

  18. A 1400-MHz survey of 1478 Abell clusters of galaxies

    NASA Technical Reports Server (NTRS)

    Owen, F. N.; White, R. A.; Hilldrup, K. C.; Hanisch, R. J.

    1982-01-01

    Observations of 1478 Abell clusters of galaxies with the NRAO 91-m telescope at 1400 MHz are reported. The measured beam shape was deconvolved from the measured source Gaussian fits in order to estimate the source size and position angle. All detected sources within 0.5 corrected Abell cluster radii are listed, including the cluster number, richness class, distance class, magnitude of the tenth brightest galaxy, redshift estimate, corrected cluster radius in arcmin, right ascension and error, declination and error, total flux density and error, and angular structure for each source.

  19. Disentangling Structures in the Cluster of Galaxies Abell 133

    NASA Technical Reports Server (NTRS)

    Way, Michael J.; DeVincenzi, Donald (Technical Monitor)

    2002-01-01

    A dynamical analysis of the structure of the cluster of galaxies Abell 133 will be presented using multi-wavelength data combined from multiple space and earth based observations. New and familiar statistical clustering techniques are used in combination in an attempt to gain a fully consistent picture of this interesting nearby cluster of galaxies. The type of analysis presented should be typical of cluster studies in the future, especially those to come from the surveys like the Sloan Digital Sky Survey and the 2DF.

  20. Line-of-Sight Velocity Distributions of Elliptical Galaxies

    NASA Astrophysics Data System (ADS)

    Bender, R.; Saglia, R. P.; Gerhard, O. E.

    1994-08-01

    The line-of-sight velocity distributions (LOSVDs) have been measured to > R_e_/2 along the major axes of 44 elliptical galaxies (more than 80 per cent of all ellipticals north of δ = -10^deg^ and brighter than B_T_ = 12.0), together with stellar rotational velocity and velocity dispersion profiles. For 19 of these 44 objects, minor axis profiles are also given. Monte Carlo simulations have been used to estimate errors. LOSVDs are found to deviate from Gaussians by no more than ~10 per cent. If rotation is present, LOSVDs are asymmetric with the prograde wings being always steeper than the retrograde wings. The degree of asymmetry (measured by the H_3_ Gauss-Hermite coefficient) correlates with ν/σ. Round and boxy ellipticals have lower asymmetries than flat and discy ones. On the whole, both types must have intrinsically asymmetric velocity distributions. Symmetric deviations (measured by the H_4_ Gauss-Hermite coefficient) are generally smaller than asymmetric ones. On the basis of the observed LOSVD shapes, the validity of two- integral models can be ruled out for most of the non-discy objects observed here (discy ellipticals require detailed modelling before similar conclusions can be drawn). Discy ellipticals have H_3_ and H_4_ major and minor axis profiles which appear consistent with a bulge+disc superposition. The observed H_4_ profile in M87 argues for radially anisotropic spherical or oblate models. Velocity dispersion profiles show significant individuality, but typically become flat outside R_e_/4. Major and minor axis slopes are mostly correlated one to one. We confirm that, with increasing luminosity, ellipticals become more anisotropic and that discy ellipticals have more rotational support. The Fundamental Plane of elliptical galaxies is tighter if total kinetic energy is used instead of central velocity dispersion. Both the small scatter about the Fundamental Plane and the homogenous and systematic properties of the LOSVDs imply that only a small

  1. cluster-lensing: Tools for calculating properties and weak lensing profiles of galaxy clusters

    NASA Astrophysics Data System (ADS)

    Ford, Jes

    2016-05-01

    The cluster-lensing package calculates properties and weak lensing profiles of galaxy clusters. Implemented in Python, it includes cluster mass-richness and mass-concentration scaling relations, and NFW halo profiles for weak lensing shear, the differential surface mass density ΔΣ(r), and for magnification, Σ(r). Optionally the calculation will include the effects of cluster miscentering offsets.

  2. Radio Galaxy Zoo: discovery of a poor cluster through a giant wide-angle tail radio galaxy

    NASA Astrophysics Data System (ADS)

    Banfield, J. K.; Andernach, H.; Kapińska, A. D.; Rudnick, L.; Hardcastle, M. J.; Cotter, G.; Vaughan, S.; Jones, T. W.; Heywood, I.; Wing, J. D.; Wong, O. I.; Matorny, T.; Terentev, I. A.; López-Sánchez, Á. R.; Norris, R. P.; Seymour, N.; Shabala, S. S.; Willett, K. W.

    2016-08-01

    We have discovered a previously unreported poor cluster of galaxies (RGZ-CL J0823.2+0333) through an unusual giant wide-angle tail radio galaxy found in the Radio Galaxy Zoo project. We obtained a spectroscopic redshift of z = 0.0897 for the E0-type host galaxy, 2MASX J08231289+0333016, leading to Mr = -22.6 and a 1.4 GHz radio luminosity density of L1.4 = 5.5 × 1024 W Hz-1. These radio and optical luminosities are typical for wide-angle tailed radio galaxies near the borderline between Fanaroff-Riley classes I and II. The projected largest angular size of ≈8 arcmin corresponds to 800 kpc and the full length of the source along the curved jets/trails is 1.1 Mpc in projection. X-ray data from the XMM-Newton archive yield an upper limit on the X-ray luminosity of the thermal emission surrounding RGZ J082312.9+033301 at 1.2-2.6 × 1043 erg s-1 for assumed intracluster medium temperatures of 1.0-5.0 keV. Our analysis of the environment surrounding RGZ J082312.9+033301 indicates that RGZ J082312.9+033301 lies within a poor cluster. The observed radio morphology suggests that (a) the host galaxy is moving at a significant velocity with respect to an ambient medium like that of at least a poor cluster, and that (b) the source may have had two ignition events of the active galactic nucleus with 107 yr in between. This reinforces the idea that an association between RGZ J082312.9+033301 and the newly discovered poor cluster exists.

  3. Galaxy Halo Truncation and Giant Arc Surface Brightness Reconstruction in the Cluster MACSJ1206.2-0847

    NASA Astrophysics Data System (ADS)

    Eichner, Thomas; Seitz, Stella; Suyu, Sherry H.; Halkola, Aleksi; Umetsu, Keiichi; Zitrin, Adi; Coe, Dan; Monna, Anna; Rosati, Piero; Grillo, Claudio; Balestra, Italo; Postman, Marc; Koekemoer, Anton; Zheng, Wei; Høst, Ole; Lemze, Doron; Broadhurst, Tom; Moustakas, Leonidas; Bradley, Larry; Molino, Alberto; Nonino, Mario; Mercurio, Amata; Scodeggio, Marco; Bartelmann, Matthias; Benitez, Narciso; Bouwens, Rychard; Donahue, Megan; Infante, Leopoldo; Jouvel, Stephanie; Kelson, Daniel; Lahav, Ofer; Medezinski, Elinor; Melchior, Peter; Merten, Julian; Riess, Adam

    2013-09-01

    In this work, we analyze the mass distribution of MACSJ1206.2-0847, particularly focusing on the halo properties of its cluster members. The cluster appears relaxed in its X-ray emission, but has a significant amount of intracluster light that is not centrally concentrated, suggesting that galaxy-scale interactions are still ongoing despite the overall relaxed state. The cluster lenses 12 background galaxies into multiple images and one galaxy at z = 1.033 into a giant arc and its counterimage. The multiple image positions and the surface brightness (SFB) distribution of the arc, which is bent around several cluster members, are sensitive to the cluster galaxy halo properties. We model the cluster mass distribution with a Navarro-Frenk-White profile and the galaxy halos with two parameters for the mass normalization and the extent of a reference halo assuming scalings with their observed near-infrared light. We match the multiple image positions at an rms level of 0.''85 and can reconstruct the SFB distribution of the arc in several filters to a remarkable accuracy based on this cluster model. The length scale where the enclosed galaxy halo mass is best constrained is about 5 effective radii—a scale in between those accessible to dynamical and field strong-lensing mass estimates on the one hand and galaxy-galaxy weak-lensing results on the other hand. The velocity dispersion and halo size of a galaxy with m 160W, AB = 19.2 and M B, Vega = -20.7 are σ = 150 km s-1 and r ≈ 26 ± 6 kpc, respectively, indicating that the halos of the cluster galaxies are tidally stripped. We also reconstruct the unlensed source, which is smaller by a factor of ~5.8 in area, demonstrating the increase in morphological information due to lensing. We conclude that this galaxy likely has star-forming spiral arms with a red (older) central component.

  4. N-body experiments and missing mass in clusters of galaxies

    NASA Technical Reports Server (NTRS)

    Smith, H.; Hintzen, P.; Sofia, S.; Oegerle, W.; Scott, J.; Holman, G.

    1979-01-01

    It is commonly assumed that the distributions of surface density and radial-velocity dispersion in clusters of galaxies are sensitive tracers of the underlying distribution of any unseen mass. N-body experiments have been used to test this assumption. Calculations with equal-mass systems indicate that the effects of the underlying mass distribution cannot be detected by observations of the surface-density or radial-velocity distributions, and the existence of an extended binding mass in all well-studied clusters would be consistent with available observations.

  5. Small-scale Conformity of the Virgo Cluster Galaxies

    NASA Astrophysics Data System (ADS)

    Lee, Hye-Ran; Lee, Joon Hyeop; Jeong, Hyunjin; Park, Byeong-Gon

    2016-06-01

    We investigate the small-scale conformity in color between bright galaxies and their faint companions in the Virgo Cluster. Cluster member galaxies are spectroscopically determined using the Extended Virgo Cluster Catalog and the Sloan Digital Sky Survey Data Release 12. We find that the luminosity-weighted mean color of faint galaxies depends on the color of adjacent bright galaxy as well as on the cluster-scale environment (gravitational potential index). From this result for the entire area of the Virgo Cluster, it is not distinguishable whether the small-scale conformity is genuine or if it is artificially produced due to cluster-scale variation of galaxy color. To disentangle this degeneracy, we divide the Virgo Cluster area into three sub-areas so that the cluster-scale environmental dependence is minimized: A1 (central), A2 (intermediate), and A3 (outermost). We find conformity in color between bright galaxies and their faint companions (color-color slope significance S ˜ 2.73σ and correlation coefficient {cc}˜ 0.50) in A2, where the cluster-scale environmental dependence is almost negligible. On the other hand, the conformity is not significant or very marginal (S ˜ 1.75σ and {cc}˜ 0.27) in A1. The conformity is not significant either in A3 (S ˜ 1.59σ and {cc}˜ 0.44), but the sample size is too small in this area. These results are consistent with a scenario in which the small-scale conformity in a cluster is a vestige of infallen groups and these groups lose conformity as they come closer to the cluster center.

  6. Small-scale Conformity of the Virgo Cluster Galaxies

    NASA Astrophysics Data System (ADS)

    Lee, Hye-Ran; Lee, Joon Hyeop; Jeong, Hyunjin; Park, Byeong-Gon

    2016-06-01

    We investigate the small-scale conformity in color between bright galaxies and their faint companions in the Virgo Cluster. Cluster member galaxies are spectroscopically determined using the Extended Virgo Cluster Catalog and the Sloan Digital Sky Survey Data Release 12. We find that the luminosity-weighted mean color of faint galaxies depends on the color of adjacent bright galaxy as well as on the cluster-scale environment (gravitational potential index). From this result for the entire area of the Virgo Cluster, it is not distinguishable whether the small-scale conformity is genuine or if it is artificially produced due to cluster-scale variation of galaxy color. To disentangle this degeneracy, we divide the Virgo Cluster area into three sub-areas so that the cluster-scale environmental dependence is minimized: A1 (central), A2 (intermediate), and A3 (outermost). We find conformity in color between bright galaxies and their faint companions (color–color slope significance S ˜ 2.73σ and correlation coefficient {cc}˜ 0.50) in A2, where the cluster-scale environmental dependence is almost negligible. On the other hand, the conformity is not significant or very marginal (S ˜ 1.75σ and {cc}˜ 0.27) in A1. The conformity is not significant either in A3 (S ˜ 1.59σ and {cc}˜ 0.44), but the sample size is too small in this area. These results are consistent with a scenario in which the small-scale conformity in a cluster is a vestige of infallen groups and these groups lose conformity as they come closer to the cluster center.

  7. Detailed modeling of cluster galaxies in free-form lenses

    NASA Astrophysics Data System (ADS)

    Lam, Daniel

    2015-08-01

    The main goal of the Frontier Fields is to characterize the population of high redshift galaxies that are gravitationally lensed and magnified by foreground massive galaxy clusters. The magnification received by lensed images has to be accurately quantified in order to derive the correct science results. The magnification is in turn computed from lens models, which are constructed from various constraints, most commonly the positions and redshifts of multiply-lensed galaxies.The locations and magnification of multiple images that appear near cluster galaxies are very sensitive to the mass distribution of those individual galaxies. In current free-form lens models, they are at best crudely approximated by arbitrary mass halos and are usually being completely neglected. Given sufficient free parameters and iterations, such models may be highly consistent but their predictive power would be rather limited. This shortcoming is particularly pronounced in light of the recent discovery of the first multiply-lensed supernova in the Frontier Fields cluster MACSJ1149. The proximity of its images to cluster galaxies mandates detailed modeling on galaxy-scales, where free-form methods solely based on grid solutions simply fail.We present a hybrid free-form lens model of Abell 2744, which for the first time incorporates a detailed mass component modeled by GALFIT that accurately captures the stellar light distribution of the hundred brightest cluster galaxies. The model better reproduces the image positions than a previous version, which modeled cluster galaxies with simplistic NFW halos. Curiously, this improvement is found in all but system 2, which has two radial images appearing around the BCG. Despite its complex light profile is being captured by GALFIT, the persistent discrepancies suggest considering mass distributions that may be largely offset from the stellar light distribution.

  8. The Atacama Cosmology Telescope: dynamical masses for 44 SZ-selected galaxy clusters over 755 square degrees

    NASA Astrophysics Data System (ADS)

    Sifón, Cristóbal; Battaglia, Nick; Hasselfield, Matthew; Menanteau, Felipe; Barrientos, L. Felipe; Bond, J. Richard; Crichton, Devin; Devlin, Mark J.; Dünner, Rolando; Hilton, Matt; Hincks, Adam D.; Hlozek, Renée; Huffenberger, Kevin M.; Hughes, John P.; Infante, Leopoldo; Kosowsky, Arthur; Marsden, Danica; Marriage, Tobias A.; Moodley, Kavilan; Niemack, Michael D.; Page, Lyman A.; Spergel, David N.; Staggs, Suzanne T.; Trac, Hy; Wollack, Edward J.

    2016-09-01

    We present galaxy velocity dispersions and dynamical mass estimates for 44 galaxy clusters selected via the Sunyaev-Zel'dovich (SZ) effect by the Atacama Cosmology Telescope. Dynamical masses for 18 clusters are reported here for the first time. Using N-body simulations, we model the different observing strategies used to measure the velocity dispersions and account for systematic effects resulting from these strategies. We find that the galaxy velocity distributions may be treated as isotropic, and that an aperture correction of up to 7 per cent in the velocity dispersion is required if the spectroscopic galaxy sample is sufficiently concentrated towards the cluster centre. Accounting for the radial profile of the velocity dispersion in simulations enables consistent dynamical mass estimates regardless of the observing strategy. Cluster masses M200 are in the range (1-15) × 1014 M⊙. Comparing with masses estimated from the SZ distortion assuming a gas pressure profile derived from X-ray observations gives a mean SZ-to-dynamical mass ratio of 1.10 ± 0.13, but there is an additional 0.14 systematic uncertainty due to the unknown velocity bias; the statistical uncertainty is dominated by the scatter in the mass-velocity dispersion scaling relation. This ratio is consistent with previous determinations at these mass scales.

  9. The Atacama Cosmology Telescope: Dynamical Masses for 44 SZ-Selected Galaxy Clusters over 755 Square Degrees

    NASA Technical Reports Server (NTRS)

    Sifon, Cristobal; Battaglia, Nick; Hasselfield, Matthew; Menanteau, Felipe; Barrientos, L. Felipe; Bond, J. Richard; Crichton, Devin; Devlin, Mark J.; Dunner, Rolando; Hilton, Matt; Wollack, Edward J.

    2016-01-01

    We present galaxy velocity dispersions and dynamical mass estimates for 44 galaxy clusters selected via the Sunyaev-Zeldovich (SZ) effect by the Atacama Cosmology Telescope. Dynamical masses for 18 clusters are reported here for the first time. Using N-body simulations, we model the different observing strategies used to measure the velocity dispersions and account for systematic effects resulting from these strategies. We find that the galaxy velocity distributions may be treated as isotropic, and that an aperture correction of up to 7 per cent in the velocity dispersion is required if the spectroscopic galaxy sample is sufficiently concentrated towards the cluster centre. Accounting for the radial profile of the velocity dispersion in simulations enables consistent dynamical mass estimates regardless of the observing strategy. Cluster masses M200 are in the range (1 - 15) times 10 (sup 14) Solar Masses. Comparing with masses estimated from the SZ distortion assuming a gas pressure profile derived from X-ray observations gives a mean SZ-to-dynamical mass ratio of 1:10 plus or minus 0:13, but there is an additional 0.14 systematic uncertainty due to the unknown velocity bias; the statistical uncertainty is dominated by the scatter in the mass-velocity dispersion scaling relation. This ratio is consistent with previous determinations at these mass scales.

  10. Using cluster analysis to organize and explore regional GPS velocities

    USGS Publications Warehouse

    Simpson, Robert W.; Thatcher, Wayne; Savage, James C.

    2012-01-01

    Cluster analysis offers a simple visual exploratory tool for the initial investigation of regional Global Positioning System (GPS) velocity observations, which are providing increasingly precise mappings of actively deforming continental lithosphere. The deformation fields from dense regional GPS networks can often be concisely described in terms of relatively coherent blocks bounded by active faults, although the choice of blocks, their number and size, can be subjective and is often guided by the distribution of known faults. To illustrate our method, we apply cluster analysis to GPS velocities from the San Francisco Bay Region, California, to search for spatially coherent patterns of deformation, including evidence of block-like behavior. The clustering process identifies four robust groupings of velocities that we identify with four crustal blocks. Although the analysis uses no prior geologic information other than the GPS velocities, the cluster/block boundaries track three major faults, both locked and creeping.

  11. Effects of Cosmological Constant on Clustering of Galaxies

    NASA Astrophysics Data System (ADS)

    Hameeda, Mir; Upadhyay, Sudhaker; Faizal, Mir; Ali, Ahmed Farag

    2016-09-01

    In this paper, we analyse the effect of the expansion of the universe on the clustering of galaxies. We evaluate the configurational integral for interacting system of galaxies in an expanding universe by including effects produced by the cosmological constant. The gravitational partition function is obtained using this configuration integral. Thermodynamic quantities, specifically, Helmholtz free energy, entropy, internal energy, pressure and chemical potential are also derived for this system. It is observed that they depend on the modified clustering parameter for this system of galaxies. It is also demonstrated that these thermodynamical quantities get corrected because of the cosmological constant.

  12. Luminosity-velocity diagrams for Virgo Cluster spirals. I - Inner rotation curves

    NASA Technical Reports Server (NTRS)

    Woods, David; Fahlman, Gregory G.; Madore, Barry F.

    1990-01-01

    Optical rotation curves are presented for the innermost portions of nine spiral galaxies in the Virgo Cluster. The emission-line (H-alpha and forbidden N II) velocity data are to be used in combination with new CCD photometry to construct luminosity-velocity diagrams, in a continuing investigation of an apparent initial linear branch and its potential as a distance indicator. Compared to recent H I data, the present optical rotation curves generally show systematically steeper inner gradients. This effect is ascribed to the poorer resolution of the H I data and/or to holes in the gas distribution.

  13. Luminosity-velocity diagrams for Virgo Cluster spirals. I. Inner rotation curves

    SciTech Connect

    Woods, D.; Fahlman, G.G.; Madore, B.F. California Institute of Technology, Pasadena )

    1990-04-01

    Optical rotation curves are presented for the innermost portions of nine spiral galaxies in the Virgo Cluster. The emission-line (H-alpha and forbidden N II) velocity data are to be used in combination with new CCD photometry to construct luminosity-velocity diagrams, in a continuing investigation of an apparent initial linear branch and its potential as a distance indicator. Compared to recent H I data, the present optical rotation curves generally show systematically steeper inner gradients. This effect is ascribed to the poorer resolution of the H I data and/or to holes in the gas distribution. 28 refs.

  14. Three Gravitational Lenses for the Price of One: Enhanced Strong Lensing Through Galaxy Clustering

    SciTech Connect

    Fassnacht, Chris D.; McKean, J.P.; Koopmans, L.V.E.; Treu, T.; Blandford, R.D.; Auger, M.W.; Jeltema, T.E.; Lubin, L.M.; Margoniner, V.E.; Wittman, D.; /UC, Davis /Kapteyn Astron. Inst., Groningen /UC, Santa Barbara /KIPAC, Menlo Park /Carnegie Inst. Observ.

    2006-04-03

    We report the serendipitous discovery of two strong gravitational lens candidates (ACS J160919+6532 and ACS J160910+6532) in deep images obtained with the Advanced Camera for Surveys on the Hubble Space Telescope, each less than 40'' from the previously known gravitational lens system CLASS B1608+656. The redshifts of both lens galaxies have been measured with Keck and Gemini: one is a member of a small galaxy group at z {approx} 0.63, which also includes the lensing galaxy in the B1608+656 system, and the second is a member of a foreground group at z {approx} 0.43. By measuring the effective radii and surface brightnesses of the two lens galaxies, we infer their velocity dispersions based on the passively evolving Fundamental Plane (FP) relation. Elliptical isothermal lens mass models are able to explain their image configurations within the lens hypothesis, with a velocity dispersion compatible with that estimated from the FP for a reasonable source-redshift range. Based on the large number of massive early-type galaxies in the field and the number-density of faint blue galaxies, the presence of two additional lens systems around CLASS B1608+656 is not unlikely in hindsight. Gravitational lens galaxies are predominantly early-type galaxies, which are clustered, and the lensed quasar host galaxies are also clustered. Therefore, obtaining deep high-resolution images of the fields around known strong lens systems is an excellent method of enhancing the probability of finding additional strong gravitational lens systems.

  15. Infall of nearby galaxies into the Virgo cluster as traced with Hubble space telescope

    SciTech Connect

    Karachentsev, Igor D.; Tully, R. Brent; Wu, Po-Feng; Shaya, Edward J.; Dolphin, Andrew E.

    2014-02-10

    We measured the tip of the red giant branch distances to nine galaxies in the direction to the Virgo cluster using the Advanced Camera for Surveys on the Hubble Space Telescope. These distances put seven galaxies (GR 34, UGC 7512, NGC 4517, IC 3583, NGC 4600, VCC 2037, and KDG 215) in front of Virgo and two galaxies (IC 3023 and KDG 177) likely inside the cluster. Distances and radial velocities of the galaxies situated between us and the Virgo core clearly exhibit the infall phenomenon toward the cluster. In the case of spherically symmetric radial infall, we estimate the radius of the 'zero-velocity surface' to be (7.2 ± 0.7) Mpc, which yields a total mass of the Virgo cluster of (8.0 ± 2.3) × 10{sup 14} M {sub ☉}, in good agreement with its virial mass estimates. We conclude that the Virgo outskirts do not contain significant amounts of dark matter beyond their virial radius.

  16. MODELING THE ALIGNMENT PROFILE OF SATELLITE GALAXIES IN CLUSTERS

    SciTech Connect

    Song, Hyunmi; Lee, Jounghun E-mail: jounghun@astro.snu.ac.kr

    2012-04-01

    Analyzing the halo and galaxy catalogs from the Millennium Simulations at redshifts z = 0, 0.5, 1, we determine the alignment profiles of cluster galaxies by measuring the average alignments between the major axes of the pseudo inertia tensors from all satellites within a cluster's virial radius and from only those satellites within some smaller radius as a function of the top-hat scale difference. The alignment profiles quantify how well the satellite galaxies retain the memory of the external tidal fields after merging into their host clusters and how fast they lose the initial alignment tendency as the cluster's relaxation proceeds. It is found that the alignment profile drops faster at higher redshifts and on smaller mass scales. This result is consistent with the picture that the faster merging of the satellites and earlier onset of the nonlinear effect inside clusters tend to break the preferential alignments of the satellites with the external tidal fields. Modeling the alignment profile of cluster galaxies as a power law of the density correlation coefficient that is independent of the power spectrum normalization ({sigma}{sub 8}) and demonstrating that the density correlation coefficient varies sensitively with the density parameter ({Omega}{sub m}) and neutrino mass fraction (f{sub {nu}}), we suggest that the alignment profile of cluster galaxies might be useful for breaking the {Omega}{sub m}-{sigma}{sub 8} and f{sub {nu}}-{sigma}{sub 8} degeneracies.

  17. A GMBCG GALAXY CLUSTER CATALOG OF 55,424 RICH CLUSTERS FROM SDSS DR7

    SciTech Connect

    Hao Jiangang; Annis, James; Johnston, David E.; McKay, Timothy A.; Evrard, August; Siegel, Seth R.; Gerdes, David; Koester, Benjamin P.; Rykoff, Eli S.; Rozo, Eduardo; Wechsler, Risa H.; Busha, Michael; Becker, Matthew; Sheldon, Erin

    2010-12-15

    We present a large catalog of optically selected galaxy clusters from the application of a new Gaussian Mixture Brightest Cluster Galaxy (GMBCG) algorithm to SDSS Data Release 7 data. The algorithm detects clusters by identifying the red-sequence plus brightest cluster galaxy (BCG) feature, which is unique for galaxy clusters and does not exist among field galaxies. Red-sequence clustering in color space is detected using an Error Corrected Gaussian Mixture Model. We run GMBCG on 8240 deg{sup 2} of photometric data from SDSS DR7 to assemble the largest ever optical galaxy cluster catalog, consisting of over 55,000 rich clusters across the redshift range from 0.1 < z < 0.55. We present Monte Carlo tests of completeness and purity and perform cross-matching with X-ray clusters and with the maxBCG sample at low redshift. These tests indicate high completeness and purity across the full redshift range for clusters with 15 or more members.

  18. Obscured starbursts in galaxy clusters: a MIPS survey of z=0.5 clusters

    NASA Astrophysics Data System (ADS)

    Smail, Ian; Ebeling, Harald; Edge, Alastair; Geach, Jim; Ma, Cheng-Jiun; Wardlow, Julie

    2008-03-01

    We propose panoramic MIPS 24um imaging of four intermediate redshift (z~0.5) clusters selected from the MACS X-ray Survey. We will combine these with observations of four clusters at the same epoch from our pilot study (which span a broader range in mass) to parameterize the evolutionary sequence of infalling field galaxies in terms of the cluster global structure. This analysis will distinguish between the role of global and local environment in determining the star formation histories of starburst galaxies entering the cluster potential from the low-density field. Our previous successful MIPS project has yielded some exciting results - in particular the existence of large populations of starburst galaxies in z~0.5 clusters with strong PAH emission - which have been completely overlooked by previous optical/near-IR surveys of these well-studied systems. These are potentially the missing link between distant spirals and the local passive S0 galaxies which are the dominant population in local clusters. Our initial results point to a strong dependence of star formation on specific cluster properties - either the dynamical state or the cluster mass (or equivalently temperature of the ICM). By specifically targeting four clusters with a narrow range in mass, but a wide range of structures, we aim to determine the key drivers of the variation in the starburst population within clusters. This will provide vital clues as to the physics of environmental transformations of galaxies: an important ingredient of current galaxy evolution models.

  19. FAR-FLUNG GALAXY CLUSTERS MAY REVEAL FATE OF UNIVERSE

    NASA Technical Reports Server (NTRS)

    2002-01-01

    A selection of NASA Hubble Space Telescope snapshots of huge galaxy clusters that lie far away and far back in time. These are selected from a catalog of 92 new clusters uncovered during a six-year Hubble observing program known as the Medium Deep Survey. If the distances and masses of the clusters are confirmed by ground based telescopes, the survey may hold clues to how galaxies quickly formed into massive large-scale structures after the big bang, and what that may mean for the eventual fate of the expanding universe. The images are each a combination of two exposures in yellow and deep red taken with Hubble's Wide Field and Planetary Camera 2. Each cluster's distance is inferred from the reddening of the starlight, which is due to the expansion of space. Astronomers assume these clusters all formed early in the history of the universe. HST133617-00529 (left) This collection of spiral and elliptical galaxies lies an estimated 4 to 6 billion light-years away. It is in the constellation of Virgo not far from the 3rd magnitude star Zeta Virginis. The brighter galaxies in this cluster have red magnitudes between 20 and 22 near the limit of the Palomar Sky Survey. The bright blue galaxy (upper left) is probably a foreground galaxy, and not a cluster member. The larger of the galaxies in the cluster are probably about the size of our Milky Way Galaxy. The diagonal line at lower right is an artificial satellite trail. HST002013+28366 (upper right) This cluster of galaxies lies in the constellation of Andromeda a few degrees from the star Alpheratz in the northeast corner of the constellation Pegasus. It is at an estimated distance of 4 billion light-years, which means the light we are seeing from the cluster is as it appeared when the universe was roughly 2/3 of its present age. HST035528+09435 (lower right) At an estimated distance of about 7 to 10 billion light-years (z=1), this is one of the farthest clusters in the Hubble sample. The cluster lies in the

  20. Weakly damped modes in star clusters and galaxies

    NASA Technical Reports Server (NTRS)

    Weinberg, Martin D.

    1994-01-01

    A perturber may excite a coherent mode in a star cluster or galaxy. If the stellar system is stable, it is commonly assumed that such a mode will be strongly damped and therefore of little practical consequence other than redistributing momentum and energy deposited by the perturber. This paper demonstrates that this assumption is false; weakly damped modes exist and may persist long enough to have observable consequences. To do this, a method for investigating the dispersion relation for spherical stellar systems and for locating weakly damped modes in particular is developed and applied to King models of varying concentration. This leads to a following remarkable result: King models exhibit very weakly damped m = 1 modes over a wide range of concentration (0.67 less than or equal to c less than or equal to 1.5 have been examined). The predicted damping time is tens of hundreds of crossing times. This mode causes the peak density to shift from and slowly revolve about the initial center. The existence of the mode is supported by n-body simulation. Higher order modes and possible astronomical consequences are discussed. Weakly damped modes, for example, may provide a neutral explanation for observed discrepancies between density and kinematic centers in galaxies, off-center nuclei, the location of velocity cusps due to massive black holes, and both m = 1 and barlike disturbances of disks enbedded in massive halos or spheroids. Gravitational shocking may excite the m = 1 mode in globular clusters, which could modify their subsequent evolution and displace the positions of exotic remnants.

  1. High-energy Neutrinos from Sources in Clusters of Galaxies

    NASA Astrophysics Data System (ADS)

    Fang, Ke; Olinto, Angela V.

    2016-09-01

    High-energy cosmic rays can be accelerated in clusters of galaxies, by mega-parsec scale shocks induced by the accretion of gas during the formation of large-scale structures, or by powerful sources harbored in clusters. Once accelerated, the highest energy particles leave the cluster via almost rectilinear trajectories, while lower energy ones can be confined by the cluster magnetic field up to cosmological time and interact with the intracluster gas. Using a realistic model of the baryon distribution and the turbulent magnetic field in clusters, we studied the propagation and hadronic interaction of high-energy protons in the intracluster medium. We report the cumulative cosmic-ray and neutrino spectra generated by galaxy clusters, including embedded sources, and demonstrate that clusters can contribute a significant fraction of the observed IceCube neutrinos above 30 TeV while remaining undetected in high-energy cosmic rays and γ rays for reasonable choices of parameters and source scenarios.

  2. A WISE VIEW OF STAR FORMATION IN LOCAL GALAXY CLUSTERS

    SciTech Connect

    Chung, Sun Mi; Gonzalez, Anthony H.; Eisenhardt, Peter R.; Stern, Daniel; Stanford, Spencer A.; Brodwin, Mark; Jarrett, Thomas

    2011-12-10

    We present results from a systematic study of star formation in local galaxy clusters using 22 {mu}m data from the Wide-field Infrared Survey Explorer (WISE). The 69 systems in our sample are drawn from the Cluster Infall Regions Survey, and all have robust mass determinations. The all-sky WISE data enable us to quantify the amount of star formation, as traced by 22 {mu}m, as a function of radius well beyond R{sub 200}, and investigate the dependence of total star formation rate upon cluster mass. We find that the fraction of star-forming galaxies increases with cluster radius but remains below the field value even at 3R{sub 200}. We also find that there is no strong correlation between the mass-normalized total specific star formation rate and cluster mass, indicating that the mass of the host cluster does not strongly influence the total star formation rate of cluster members.

  3. The Globular Cluster System of the Virgo Dwarf Elliptical Galaxy VCC 1087

    NASA Astrophysics Data System (ADS)

    Beasley, Michael A.; Strader, Jay; Brodie, Jean P.; Cenarro, A. Javier; Geha, M.

    2006-02-01

    We present an analysis of the globular cluster (GC) system of the nucleated dwarf elliptical galaxy VCC 1087 in the Virgo Cluster based on Keck LRIS spectroscopy and archival Hubble Space Telescope Advanced Camera for Surveys imaging. We estimate that VCC 1087 hosts a total population of 77+/-19 GCs, which corresponds to a relatively high V-band specific frequency of 5.8+/-1.4. The g475-z850 color distribution of the GCs shows a blue (metal-poor) peak with a tail of redder (metal-rich) clusters similar in color to those seen in luminous elliptical galaxies. The luminosity function of the GCs is lognormal and peaks at MTOg475=-7.2+/-0.3, MTOz850=-8.1+/-0.2. These peak positions are consistent with those found for luminous Virgo elliptical galaxies, suggesting either the lack of or, surprisingly similarly, the dynamical destruction processes of GCs among dwarf and giant galaxies. Spectroscopy of a subsample of 12 GCs suggests that the GC system is old and coeval (>~10 Gyr), with a fairly broad metallicity distribution (-1.8<~[M/H]<~-0.8). In contrast, an integrated spectrum of the underlying galaxy starlight reveals that its optical luminosity is dominated by metal-rich, intermediate-age stars. The radial velocities of the GCs suggest rotation close to the major axis of the galaxy, and this rotation is dynamically significant with (vrot/σlos)*>1. A compilation of the kinematics of the GC systems of nine early-type galaxies shows surprising diversity in the (vrot/σlos) parameter for GC systems. In this context, the GC system of VCC 1087 exhibits the most significant rotation-to-velocity dispersion signature. Dynamical mass modeling of the velocity dispersion profile of the GCs and galaxy stars suggests fairly constant mass-to-light ratios of ~3 out to 6.5 kpc. The present observations can entertain both baryonic and nonbaryonic solutions, and GC velocities at larger radii would be most valuable with regard to this issue. Finally, we discuss the evolution of VCC 1087

  4. Super Star Cluster Nebula in the Starburst Galaxy NGC 660

    NASA Astrophysics Data System (ADS)

    Naiman, J. P.; Turner, J. L.; Tsai, C.-W.; Beck, S. C.; Ho, P. T. P.

    2004-12-01

    We have mapped the starburst galaxy NGC 660 at 100mas resolution at K band (1.3 cm) with the NRAO Very Large Array. A peculiar galaxy at a distance of 13 Mpc, NGC 660 contains concentrated central star formation of power ˜ 2 x 1010 Lsun. Our 1.3 cm continuum image reveals a bright, compact source of less than 10 pc extent with a rising spectral index. We infer that this is optically thick free-free emission from a super star cluster nebula. The nebula is less than 10 pc in size, comparable in luminosity to the ``supernebula" in the dwarf galaxy, NGC 5253. We estimate that there are a few thousand O stars contained in this single young cluster. There are a number of other weaker continuum sources, either slightly smaller or more evolved clusters of similar size within the central 300 parsecs of the galaxy. This work is supported in part by the National Science Foundation.

  5. Violent galaxy evolution in the Frontier Fields clusters

    NASA Astrophysics Data System (ADS)

    Ebeling, Harald; McPartland, Conor; Blumenthal, Kelly; Roediger, Elke

    2015-08-01

    In a recent study we used customized morphological selection criteria to identify potential ram-pressure stripping events in shallow HST images of MACS clusters at z=0.3-0.7 and found tantalising evidence of such violent evolution (a) being at least partly triggered by galaxy mergers and (b) causing extensive star formation and thus brightening of the affected galaxies. Due to the limited depth of the HST data used, our project focused (by design and necessity) on the brightest galaxies. We here present results of a similar survey for “jellyfish” galaxies conducted using the much deeper, multi-passband imaging data of the Frontier Fields clusters that allow us to probe much farther into the luminosity function of ram-pressure stripping in some of the most massive and most dynamically disturbed clusters known.

  6. Intermediate-age globular clusters in four galaxy merger remnants

    SciTech Connect

    Trancho, Gelys; Miller, Bryan W.; Schweizer, François; Burdett, Daniel P.; Palamara, David

    2014-08-01

    We present the results of combining Hubble Space Telescope optical photometry with ground-based K{sub s} -band photometry from the Gemini imagers NIRI and FLAMINGOS-I to study the globular cluster (GC) populations in four early-type galaxies that are candidate remnants of recent mergers (NGC 1700, NGC 2865, NGC 4382, and NGC 7727). These galaxies were chosen based on their blue colors and fine structure, such as shells and ripples that are indicative of past interactions. We fit the combined VIK{sub s} GC data with simple toy models of mixed cluster populations that contain three subpopulations of different age and metallicity. The fits, done via chi-squared mapping of the parameter space, yield clear evidence for the presence of intermediate-age clusters in each galaxy. We find that the ages of ∼1-2 Gyr for these GC subpopulations are consistent with the previously estimated merger ages for the host galaxies.

  7. Intermediate-age Globular Clusters in Four Galaxy Merger Remnants

    NASA Astrophysics Data System (ADS)

    Trancho, Gelys; Miller, Bryan W.; Schweizer, François; Burdett, Daniel P.; Palamara, David

    2014-08-01

    We present the results of combining Hubble Space Telescope optical photometry with ground-based Ks -band photometry from the Gemini imagers NIRI and FLAMINGOS-I to study the globular cluster (GC) populations in four early-type galaxies that are candidate remnants of recent mergers (NGC 1700, NGC 2865, NGC 4382, and NGC 7727). These galaxies were chosen based on their blue colors and fine structure, such as shells and ripples that are indicative of past interactions. We fit the combined VIKs GC data with simple toy models of mixed cluster populations that contain three subpopulations of different age and metallicity. The fits, done via chi-squared mapping of the parameter space, yield clear evidence for the presence of intermediate-age clusters in each galaxy. We find that the ages of ~1-2 Gyr for these GC subpopulations are consistent with the previously estimated merger ages for the host galaxies.

  8. BUDHIES II: a phase-space view of H I gas stripping and star formation quenching in cluster galaxies

    NASA Astrophysics Data System (ADS)

    Jaffé, Yara L.; Smith, Rory; Candlish, Graeme N.; Poggianti, Bianca M.; Sheen, Yun-Kyeong; Verheijen, Marc A. W.

    2015-04-01

    We investigate the effect of ram-pressure from the intracluster medium on the stripping of H I gas in galaxies in a massive, relaxed, X-ray bright, galaxy cluster at z = 0.2 from the Blind Ultra Deep H I Environmental Survey (BUDHIES). We use cosmological simulations, and velocity versus position phase-space diagrams to infer the orbital histories of the cluster galaxies. In particular, we embed a simple analytical description of ram-pressure stripping in the simulations to identify the regions in phase-space where galaxies are more likely to have been sufficiently stripped of their H I gas to fall below the detection limit of our survey. We find a striking agreement between the model predictions and the observed location of H I-detected and non-detected blue (late-type) galaxies in phase-space, strongly implying that ram-pressure plays a key role in the gas removal from galaxies, and that this can happen during their first infall into the cluster. However, we also find a significant number of gas-poor, red (early-type) galaxies in the infall region of the cluster that cannot easily be explained with our model of ram-pressure stripping alone. We discuss different possible additional mechanisms that could be at play, including the pre-processing of galaxies in their previous environment. Our results are strengthened by the distribution of galaxy colours (optical and UV) in phase-space, that suggests that after a (gas-rich) field galaxy falls into the cluster, it will lose its gas via ram-pressure stripping, and as it settles into the cluster, its star formation will decay until it is completely quenched. Finally, this work demonstrates the utility of phase-space diagrams to analyse the physical processes driving the evolution of cluster galaxies, in particular H I gas stripping.

  9. The Evolution of the Globular Cluster System in a Triaxial Galaxy: Can a Galactic Nucleus Form by Globular Cluster Capture?

    NASA Astrophysics Data System (ADS)

    Capuzzo-Dolcetta, Roberto

    1993-10-01

    Among the possible phenomena inducing evolution of the globular cluster system in an elliptical galaxy, dynamical friction due to field stars and tidal disruption caused by a central nucleus is of crucial importance. The aim of this paper is the study of the evolution of the globular cluster system in a triaxial galaxy in the presence of these phenomena. In particular, the possibility is examined that some galactic nuclei have been formed by frictionally decayed globular clusters moving in a triaxial potential. We find that the initial rapid growth of the nucleus, due mainly to massive clusters on box orbits falling in a short time scale into the galactic center, is later slowed by tidal disruption induced by the nucleus itself on less massive clusters in the way described by Ostriker, Binney, and Saha. The efficiency of dynamical friction is such to carry to the center of the galaxy enough globular cluster mass available to form a compact nucleus, but the actual modes and results of cluster-cluster encounters in the central potential well are complicated phenomena which remains to be investigated. The mass of the resulting nucleus is determined by the mutual feedback of the described processes, together with the initial spatial, velocity, and mass distributions of the globular cluster family. The effect on the system mass function is studied, showing the development of a low- and high-mass turnover even with an initially flat mass function. Moreover, in this paper is discussed the possibility that the globular cluster fall to the galactic center has been a cause of primordial violent galactic activity. An application of the model to M31 is presented.

  10. Galaxies as Clocks: the Radius -- Velocity Relationship of HI Rich Galaxies

    NASA Astrophysics Data System (ADS)

    Meurer, Gerhardt; Obreschkow, D.; Hanish, D.; Wong, O.; Zheng, Z.; de Blok, E.; Thilker, D. A.; SINGG Team; SUNGG Team

    2014-01-01

    We show that the outskirts of HI rich galaxies obey a linear radius (R) versus rotational velocity (Vrot) relationship. This means they behave like clocks: they have the same orbital time of ~800 Myr. The relationship is valid over the full range for which we have data - a factor of 30 from dwarf galaxies with R ~ 1 kpc and Vrot ~ 10 km/s to giant spirals with R = 30 kpc and Vrot = 300 km/s with an intrinsic scatter smaller than 40%. A linear R -- Vrot relationship is expected for Cold Dark Matter (CDM) dominated halos. The fact that the collapsed baryons of disk galaxies obey this relationship can be readily understood within the CDM paradigm. We show what is required for the situation to occur. The mean density within the outer radius is 3e-3 Msun/pc^3, requiring that the baryonic component of disk galaxies to have collapsed by a factor of ~40. We outline the practical uses of the relationship and the implications for galaxy evolution.

  11. Internal dynamics of Abell 1240: a galaxy cluster with symmetric double radio relics

    NASA Astrophysics Data System (ADS)

    Barrena, R.; Girardi, M.; Boschin, W.; Dasí, M.

    2009-08-01

    Context: The mechanisms giving rise to diffuse radio emission in galaxy clusters, and in particular their connection with cluster mergers, are still debated. Aims: We aim to obtain new insights into the internal dynamics of the cluster Abell 1240, which appears to contain two roughly symmetric radio relics, separated by ~2 h_70-1 Mpc. Methods: Our analysis is based mainly on redshift data for 145 galaxies mostly acquired at the Telescopio Nazionale Galileo and on new photometric data acquired at the Isaac Newton Telescope. We also use X-ray data from the Chandra archive and photometric data from the Sloan Digital Sky Survey (Data Release 7). We combine galaxy velocities and positions to select 89 cluster galaxies and analyze the internal dynamics of the Abell 1237 + Abell 1240 cluster complex, Abell 1237 being a close companion of Abell 1240 in its southern direction. Results: We estimate similar redshifts for Abell 1237 and Abell 1240, < z > = 0.1935 and < z > = 0.1948, respectively. For Abell 1237, we estimate a line-of-sight (LOS) velocity dispersion of σV ~ 740 km s-1and a mass of M ~ 6 × 1014 h_70-1 M⊙. For Abell 1240, we estimate a LOS σV ~ 870 km s-1and a mass in the range M ~ 0.9-1.9 × 1015 h_70-1 M⊙, which takes account of its complex dynamics. Abell 1240 is shown to have a bimodal structure with two galaxy clumps roughly aligned along its N-S direction, the same as defined by the elongation of its X-ray surface brightness and the axis of symmetry of the relics. The two brightest galaxies of Abell 1240, associated with the northern and southern clumps, are separated by a LOS rest-frame velocity difference Vrf ~ 400 km s-1and a projected distance D ~ 1.2 h_70-1 Mpc. The two-body model agrees with the hypothesis that we are looking at a cluster merger that occurred largely in the plane of the sky, the two galaxy clumps being separated by a rest-frame velocity difference Vrf ~ 2000 km s-1at a time of 0.3 Gyr after the crossing core, while Abell 1237

  12. Gas Poor Galaxies in MKW/AWM Clusters

    NASA Astrophysics Data System (ADS)

    Williams, B. A.

    1995-03-01

    Follow-up observations were made of the neutral hydrogen content of 129 galaxies near the cores of MKW 4, MKW 8, MKW 11, AWM 4, and AWM 5. The neutral hydrogen content of these galaxies appears to be lower than that of galaxies of similar type in the field or in loose groups and are more consistent with those of galaxies in the richer Abell clusters. Of the 14 galaxies that appear to be spirals in MKW 4, only one was detected above a sensitivity limit of ~ 10(5) Msun /Mpc(2) . The low detection rate of galaxies in MKW 4 suggest that its core is truly deficient in neutral hydrogen gas.

  13. The environment of x ray selected BL Lacs: Host galaxies and galaxy clustering

    NASA Technical Reports Server (NTRS)

    Wurtz, Ron; Stocke, John T.; Ellingson, Erica; Yee, Howard K. C.

    1993-01-01

    Using the Canada-France-Hawaii Telescope, we have imaged a complete, flux-limited sample of Einstein Medium Sensitivity Survey BL Lacertae objects in order to study the properties of BL Lac host galaxies and to use quantitative methods to determine the richness of their galaxy cluster environments.

  14. Red sequence modal colour gradients across intermediate X-ray luminosity galaxy clusters

    NASA Astrophysics Data System (ADS)

    Jensen, Peter C.; Pimbblet, Kevin A.

    2012-06-01

    We assemble a sample of 45 intermediate X-ray luminosity galaxy clusters (? erg s-1) at low redshifts (0.03 < z < 0.16) using Sloan Digital Sky Survey (SDSS) data to conduct a comprehensive investigation into the photometric variation of red sequence modal galaxy colours with environment. The clusters span a range of Bautz-Morgan types and evolutionary stages and are shown to be representative of the global underlying intermediate LX cluster sample. We define cluster membership using SDSS spectroscopic data and characterize the clusters by deriving new recession velocities, velocity dispersions and other parameters for each. We construct colour-magnitude diagrams for each of these clusters and obtain the position of the red sequence using a robust line fitting algorithm with a Lorentzian merit function. In doing so, we describe a population of discordant points on the colour-magnitude plane which are the result of photometric blending, dust and other causes. By fitting the clusters with Schechter functions to derive M★ values in each SDSS passband, we combine the red sequence of the galaxy clusters together to form a composite sample. We detail how the modal colour value of the red sequence varies with radius from the centre of this composite cluster and local galaxy density for all SDSS colours. In agreement with previous studies, these colours are shown to systematically move blueward with increasing distance from the cluster centres, or equivalently lower local galaxy density, whilst the width of the red sequence increases. This supports the idea that the galaxies at the outskirts of these clusters have younger luminosity-weighted ages than those at the core indicating that their star formation has been quenched more recently than in the core. A comparison of our derived gradients in (g-r) (explicitly, ? and d(g-r)/dlog (Σ) = 0.012 ± 0.002) with earlier works tentatively suggests that these gradients vary redshift which would reflect the hierarchical build

  15. The Influence of Cluster Mergers on Galaxy Evolution

    NASA Astrophysics Data System (ADS)

    Rawle, T. D.; Altieri, B.; Bouy, H.; Egami, E.; Pérez-González, P. G.; Richard, J.; Valtchanov, I.; Walth, G.

    2016-06-01

    The rich environment of galaxy clusters is understood to have a profound effect on the evolution of constituent galaxies. However, even clusters of a similar mass and at fixed redshift are not homogeneous, displaying a range in structural complexity. Here we concentrate on the effect of cluster merging, the most massive dynamic process in the Universe. Two spectacular cluster mergers at z~0.3 are explored: the archetypal Bullet cluster (1E0657-558; Rawle et al. 2012), and the HST Frontier Field, Pandora's cluster (Abell 2744; Rawle et al. 2014, 2016). We present detailed analysis of their total star formation, derived from multi-wavelength observations of both dusty and unobscured activity from Herschel, Spitzer, WISE and GALEX. Examination of the morphologies of individual cluster galaxies reveals striking evidence for transformation and enhanced star formation, triggered by the merger-induced shock front. This includes several galaxies identified as having "jellyfish" morphologies caused by the passing shock. We discuss the implications, and preview future work exploring a large sample of clusters covering a range of dynamic states and redshifts.

  16. Physics of Galaxy Clusters and How it Affects Cosmological Tests

    NASA Technical Reports Server (NTRS)

    Vikhlinin, Alexey; Oliversen, Ronald J. (Technical Monitor)

    2002-01-01

    We have worked on the analysis of the Chandra observations of the nearby and distant clusters of galaxies, and on the expansion of the sample of distant X-ray clusters based on the archival ROSAT PSPC data. Some of the scientific results are discussed.

  17. Minimization of biases in galaxy peculiar velocity catalogues

    NASA Astrophysics Data System (ADS)

    Sorce, Jenny G.

    2015-07-01

    Galaxy distances and derived radial peculiar velocity catalogues constitute valuable data sets to study the dynamics of the Local Universe. However, such catalogues suffer from biases whose effects increase with the distance. Malmquist biases and lognormal error distribution affect the catalogues. Velocity fields of the Local Universe reconstructed with these catalogues present a spurious overall infall on to the Local Volume if they are not corrected for biases. Such an infall is observed in the reconstructed velocity field obtained when applying the Bayesian Wiener-Filter technique to the raw second radial peculiar velocity catalogue of the Cosmicflows project. In this paper, an iterative method to reduce spurious non-Gaussianities in the radial peculiar velocity distribution, to retroactively derive overall better distance estimates resulting in a minimization of the effects of biases, is presented. This method is tested with mock catalogues. To control the cosmic variance, mocks are built out of different cosmological constrained simulations which resemble the Local Universe. To realistically reproduce the effects of biases, the mocks are constructed to be lookalikes of the second data release of the Cosmicflows project, with respect to the size, distribution of data and distribution of errors. Using a suite of mock catalogues, the outcome of the correction is verified to be affected neither by the added error realization, nor by the data point selection, nor by the constrained simulation. Results are similar for the different tested mocks. After correction, the general infall is satisfactorily suppressed. The method allows us to obtain catalogues which together with the Wiener-Filter technique give reconstructions approximating non-biased velocity fields at 100-150 km s-1 (2-3 h-1 Mpc in terms of linear displacement), the linear theory threshold.

  18. The Morphologies and Alignments of Gas, Mass, and the Central Galaxies of CLASH Clusters of Galaxies

    NASA Astrophysics Data System (ADS)

    Donahue, Megan; Ettori, Stefano; Rasia, Elena; Sayers, Jack; Zitrin, Adi; Meneghetti, Massimo; Voit, G. Mark; Golwala, Sunil; Czakon, Nicole; Yepes, Gustavo; Baldi, Alessandro; Koekemoer, Anton; Postman, Marc

    2016-03-01

    Morphology is often used to infer the state of relaxation of galaxy clusters. The regularity, symmetry, and degree to which a cluster is centrally concentrated inform quantitative measures of cluster morphology. The Cluster Lensing and Supernova survey with Hubble Space Telescope (CLASH) used weak and strong lensing to measure the distribution of matter within a sample of 25 clusters, 20 of which were deemed to be “relaxed” based on their X-ray morphology and alignment of the X-ray emission with the Brightest Cluster Galaxy. Toward a quantitative characterization of this important sample of clusters, we present uniformly estimated X-ray morphological statistics for all 25 CLASH clusters. We compare X-ray morphologies of CLASH clusters with those identically measured for a large sample of simulated clusters from the MUSIC-2 simulations, selected by mass. We confirm a threshold in X-ray surface brightness concentration of C ≳ 0.4 for cool-core clusters, where C is the ratio of X-ray emission inside 100 h70-1 kpc compared to inside 500 {h}70-1 kpc. We report and compare morphologies of these clusters inferred from Sunyaev-Zeldovich Effect (SZE) maps of the hot gas and in from projected mass maps based on strong and weak lensing. We find a strong agreement in alignments of the orientation of major axes for the lensing, X-ray, and SZE maps of nearly all of the CLASH clusters at radii of 500 kpc (approximately 1/2 R500 for these clusters). We also find a striking alignment of clusters shapes at the 500 kpc scale, as measured with X-ray, SZE, and lensing, with that of the near-infrared stellar light at 10 kpc scales for the 20 “relaxed” clusters. This strong alignment indicates a powerful coupling between the cluster- and galaxy-scale galaxy formation processes.

  19. Determining the Role of Merging in the Growth of the Galaxy Cluster Population in the Massive and Distant Clusters of WISE Survey

    NASA Astrophysics Data System (ADS)

    Brodwin, Mark; Decker, Bandon; Gonzalez, Anthony; Stanford, Adam; Eisenhardt, Peter; Stern, Daniel; Wylezalek, Dominika; Marrone, Daniel; Stalder, Brian; Mantz, Adam; Galametz, Audrey

    2015-10-01

    We propose to obtain deep Spitzer/IRAC imaging of 14 distant (z ~ 1), stellar mass-selected galaxy clusters from the Massive and Distant Clusters of WISE Survey (MaDCoWS) for which robust Sunyaev-Zel'dovich (SZ)-based masses spanning ~2-10 x 10^14 Msun have been measured. These proposed IRAC data, along with joint HST imaging, will allow us to directly test key predictions of current models of cluster formation. These models posit that galaxy-galaxy merging drives the bursts of star formation and AGN activity seen in high redshift Spitzer studies of low-mass clusters, and predict the rate of such activity should be a function of total cluster mass. As clusters grow in mass (and hence velocity dispersion), the merging efficiency drops and the growth of the galaxy population, via both mergers and star formation, should cease. By measuring the cluster stellar mass function, as a function of both mass and morphological type, we will directly confirm or refute this model. We will also identify, on the basis of IRAC colors and HST morphologies, the AGN content in these clusters. We will thus test the prediction that the incidence of AGN should be higher in the lower mass clusters. Finally, we will measure the stellar mass fraction as a function of total mass, a crucial quantity in calibrating numerical cluster simulations that are key for cluster abundance cosmology.

  20. Open Cluster Radial Velocity determination from observations at Observatório Pico Dos Dias

    NASA Astrophysics Data System (ADS)

    Faria, M. A. F.; Monteiro, H.; Dias, W. S.; Lépine, J. R. D.

    2014-10-01

    In studies of the dynamics of the Galactic disk, such as the determination of the speed of the spiral pattern and the permanence of stars in the spiral arms, it is crucial to know orbits obtained from proper motions, radial velocities and the potential of the Galaxy. Aiming to improve the statistics of our catalog of open clusters, maintained by our research group, we determined the radial velocity of stars belonging to a group of open clusters using spectra with a resolution of 4000, obtained at the Pico dos Dias Observatory (LNA) with the 1.60 m telescope and the Coudé spectrograph. We observed the open cluster's member stars and calculated their radial speeds using standard techniques. The stars were selected from our own database based on relevant information concerning the clusters, obtained by statistical analysis of their proper motions and/or their position in the HR's diagram. In this work, we present the detailed analysis of the data reduction and radial velocity determination using synthetic spectra from different libraries. Finally we present the open cluster's radial (and spacial) velocities.

  1. Gaussian covariance matrices for anisotropic galaxy clustering measurements

    NASA Astrophysics Data System (ADS)

    Grieb, Jan Niklas; Sánchez, Ariel G.; Salazar-Albornoz, Salvador; Dalla Vecchia, Claudio

    2016-04-01

    Measurements of the redshift-space galaxy clustering have been a prolific source of cosmological information in recent years. Accurate covariance estimates are an essential step for the validation of galaxy clustering models of the redshift-space two-point statistics. Usually, only a limited set of accurate N-body simulations is available. Thus, assessing the data covariance is not possible or only leads to a noisy estimate. Further, relying on simulated realizations of the survey data means that tests of the cosmology dependence of the covariance are expensive. With these points in mind, this work presents a simple theoretical model for the linear covariance of anisotropic galaxy clustering observations with synthetic catalogues. Considering the Legendre moments (`multipoles') of the two-point statistics and projections into wide bins of the line-of-sight parameter (`clustering wedges'), we describe the modelling of the covariance for these anisotropic clustering measurements for galaxy samples with a trivial geometry in the case of a Gaussian approximation of the clustering likelihood. As main result of this paper, we give the explicit formulae for Fourier and configuration space covariance matrices. To validate our model, we create synthetic halo occupation distribution galaxy catalogues by populating the haloes of an ensemble of large-volume N-body simulations. Using linear and non-linear input power spectra, we find very good agreement between the model predictions and the measurements on the synthetic catalogues in the quasi-linear regime.

  2. STAR CLUSTER DISRUPTION IN THE STARBURST GALAXY MESSIER 82

    SciTech Connect

    Li, Shuo; Li, Chengyuan; De Grijs, Richard; Anders, Peter

    2015-01-01

    Using high-resolution, multiple-passband Hubble Space Telescope images spanning the entire optical/near-infrared wavelength range, we obtained a statistically complete U-band-selected sample of 846 extended star clusters across the disk of the nearby starburst galaxy M82. Based on a careful analysis of the clusters' spectral energy distributions, we determined their galaxy-wide age and mass distributions. The M82 clusters exhibit three clear peaks in their age distribution, thus defining relatively young, log (t yr{sup –1}) ≤ 7.5, intermediate-age, log (t yr{sup –1}) in [7.5, 8.5], and old samples, log (t yr{sup –1}) ≥ 8.5. Comparison of the completeness-corrected mass distributions offers a firm handle on the galaxy's star cluster disruption history. The most massive star clusters in the young and old samples are (almost) all concentrated in the most densely populated central region, while the intermediate-age sample's most massive clusters are more spatially dispersed, which may reflect the distribution of the highest-density gas throughout the galaxy's evolutionary history, combined with the solid-body nature of the galaxy's central region.

  3. Radio Selected Clusters of Galaxies at High Redshift

    NASA Astrophysics Data System (ADS)

    Wing, Joshua; Blanton, Elizabeth

    2010-08-01

    Previous studies have shown that three-component radio sources exhibiting some degree of bending between components are likely to be found in galaxy clusters. Often this radio emission is associated with a cD type galaxy at the center of a cluster. We have cross-correlated the Sloan Digital Sky Survey (SDSS) with samples selected from the Faint Images of the Radio Sky at Twenty Centimeters (FIRST) catalog and measured the richness of the cluster environments surrounding three- component sources exhibiting both bent and straight lobes. This has lead to the discovery and classification of a large number of galaxy clusters out to a redshift of z ~ 0.5. For both bent- and straight- lobed sources without an optical counterpart it is likely that the radio emission is associated with a galaxy fainter than m_r=22 (the limiting magnitude of the SDSS) and at a redshift higher than z~0.8. We propose to observe a small sub-sample of these sources with the FLAMINGOS instrument on the Mayall 4-m telescope in an attempt to discover if these sources are located in high redshift (z≳0.8) galaxy clusters. In our visually-selected bent radio source sample, 78% of sources with counterparts in the SDSS are associated with clusters.

  4. Constraining gravity at the largest scales through CMB lensing and galaxy velocities

    NASA Astrophysics Data System (ADS)

    Pullen, Anthony R.; Alam, Shadab; He, Siyu; Ho, Shirley

    2016-08-01

    We demonstrate a new method to constrain gravity on the largest cosmological scales by combining measurements of cosmic microwave background (CMB) lensing and the galaxy velocity field. EG is a statistic, constructed from a gravitational lensing tracer and a measure of velocities such as redshift-space distortions (RSD), that can discriminate between gravity models while being independent of clustering bias and σ8. While traditionally, the lensing field for EG has been probed through galaxy lensing, CMB lensing has been proposed as a more robust tracer of the lensing field for EG at higher redshifts while avoiding intrinsic alignments. We perform the largest-scale measurement of EG ever, up to 150 Mpc h-1, by cross-correlating the Planck CMB lensing map with the Sloan Digital Sky Survey III (SDSS-III) CMASS galaxy sample and combining this with our measurement of the CMASS auto-power spectrum and the RSD parameter β. We report EG(z = 0.57) = 0.243 ± 0.060 (stat) ± 0.013 (sys), a measurement in tension with the general relativity (GR) prediction at a level of 2.6σ. Note that our EG measurement deviates from GR only at scales greater than 80 Mpc h-1, scales which have not been probed by previous EG tests. Upcoming surveys, which will provide an order-of-magnitude reduction in statistical errors, can significantly constrain alternative gravity models when combined with better control of systematics.

  5. Active galactic nucleus feedback in clusters of galaxies

    PubMed Central

    Blanton, Elizabeth L.; Clarke, T. E.; Sarazin, Craig L.; Randall, Scott W.; McNamara, Brian R.

    2010-01-01

    Observations made during the last ten years with the Chandra X-ray Observatory have shed much light on the cooling gas in the centers of clusters of galaxies and the role of active galactic nucleus (AGN) heating. Cooling of the hot intracluster medium in cluster centers can feed the supermassive black holes found in the nuclei of the dominant cluster galaxies leading to AGN outbursts which can reheat the gas, suppressing cooling and large amounts of star formation. AGN heating can come in the form of shocks, buoyantly rising bubbles that have been inflated by radio lobes, and the dissipation of sound waves. PMID:20351250

  6. Low-Frequency Radio Observations of Galaxy Cluster Merger Shocks

    NASA Astrophysics Data System (ADS)

    van Weeren, Reinout

    2014-10-01

    In a few dozen merging galaxy clusters diffuse extended radio emission has been found, implying the presence of relativistic particles and magnetic fields in the intracluster medium. A major question is how these particles are accelerated up to such extreme energies. In this talk I will present LOFAR and JVLA radio observations of the Toothbrush galaxy cluster. The Toothbrush cluster hosts diffuse 2 Mpc extended radio emission in the form of a radio relic and halo. Our deep LOFAR and JVLA observations allow a radio spectral study to test the shock origin of the relic and underlying particle acceleration mechanisms.

  7. The Spiderweb Galaxy: A Forming Massive Cluster Galaxy at z ~ 2

    NASA Astrophysics Data System (ADS)

    Miley, George K.; Overzier, Roderik A.; Zirm, Andrew W.; Ford, Holland C.; Kurk, Jaron; Pentericci, Laura; Blakeslee, John P.; Franx, Marijn; Illingworth, Garth D.; Postman, Marc; Rosati, Piero; Röttgering, Huub J. A.; Venemans, Bram P.; Helder, Eveline

    2006-10-01

    We present a deep image of the radio galaxy MRC 1138-262 taken with the Hubble Space Telescope (HST) at a redshift of z=2.2. The galaxy is known to have properties of a cD galaxy progenitor and be surrounded by a 3 Mpc-sized structure, identified with a protocluster. The morphology shown on the new deep HST ACS image is reminiscent of a spider's web. More than 10 individual clumpy features are observed, apparently star-forming satellite galaxies in the process of merging with the progenitor of a dominant cluster galaxy 11 Gyr ago. There is an extended emission component, implying that star formation was occurring over a 50×40 kpc region at a rate of more than 100 Msolar yr-1. A striking feature of the newly named ``Spiderweb galaxy'' is the presence of several faint linear galaxies within the merging structure. The dense environments and fast galaxy motions at the centers of protoclusters may stimulate the formation of these structures, which dominate the faint resolved galaxy populations in the Hubble Ultra Deep Field. The new image provides a unique testbed for simulations of forming dominant cluster galaxies.

  8. Star clusters in the interacting galaxy system Arp 284

    NASA Astrophysics Data System (ADS)

    Peterson, Bradley W.; Struck, Curtis; Smith, Beverly J.; Hancock, Mark

    2009-12-01

    We present results from a study of protoglobular cluster candidates in the interacting galaxy system Arp 284 (NGC 7714/5) using data from the Hubble Space Telescope (HST). Previous studies of the Antennae and M51 have suggested that the majority of young massive star clusters dissolve within 20 Myr due to mass loss. We use the evolutionary synthesis code STARBURST99 to estimate ages and extinctions for approximately 175 clusters visible with HST. We also use lower resolution Galaxy Evolution Explorer and ground-based Hα data to estimate the ages of the giant HII regions in which these clusters are found, and compare the Spitzer colours of these HII regions to those of star-forming regions in other interacting systems. The ages are also used to aid in the interpretation of Chandra X-ray data. Clusters in the tidal tails of NGC 7714 are generally found to have ages less than 20 Myr, though observational limits make the significance of this result uncertain. Older clusters, though not numerous, have nearly the same spatial distribution within the imaged portion of NGC 7714 as young clusters. The cluster population in the bridge connecting the two galaxies appears to be older, but the data in this part of the system are too limited to draw firm conclusions. The ages of the giant HII regions in NGC 7714 are generally older than those of their constituent clusters, possibly indicating that the young clusters we detect are surrounded by their dispersed predecessors.

  9. Galaxy cluster thermal x-ray spectra constrain axionlike particles

    NASA Astrophysics Data System (ADS)

    Conlon, Joseph P.; Powell, Andrew J.; Marsh, M. C. David

    2016-06-01

    Axionlike particles (ALPs) and photons interconvert in the presence of a magnetic field. At keV energies in the environment of galaxy clusters, the conversion probability can become unsuppressed for light ALPs. Conversion of thermal x-ray photons into ALPs can introduce a steplike feature into the cluster thermal bremsstrahlung spectrum, and we argue that existing x-ray data on galaxy clusters should be sufficient to extend bounds on ALPs in the low-mass region ma≲1 ×10-12 eV down to M ˜7 ×1011 GeV , and that for 1011 GeV galaxy clusters.

  10. Interpretation of the Stephan Quintet Galaxy Cluster using Hydro-Gravitational-Dynamics: Viscosity and Fragmentation

    NASA Astrophysics Data System (ADS)

    Gibson, Carl H.; Schild, Rudolph E.

    2011-10-01

    Stephan's Quintet (SQ) is a compact group of galaxies that has been well studied since its discovery in 1877 but is mysterious using cold dark mat- ter hierarchical clustering cosmology (CDMHCC). Anomalous red shifts z = (0.0027, 0.019, 0.022, 0.022, 0.022) among galaxies in SQ either reduce it to a Trio with two highly improbable intruders from CDMHCC or support the Arp (1973) hypothesis that its red shifts are intrinsic. An alternative is provided by the Gib- son 1996-2006 hydro-gravitational-dynamics (HGD) theory where superclusters, clusters and galaxies all originate by gravitational fragmentation in the super- viscous plasma epoch and at planetary and star cluster mass scales in the pri- mordial gas of the expanding universe. By this fluid-mechanical cosmology, the SQ galaxies gently separate and remain precisely along a line of sight because of perspective and the small transverse velocities permitted by their sticky viscous- gravitational beginnings. Star and gas bridges and young-globular-star-cluster (YGC) trails observed by the Hubble Space Telescope are triggered as SQ galax- ies separate through viscous baryonic-dark-matter halos of dark proto-globular- cluster (PGC) clumps of frozen Earth-mass primordial-fog-particles (PFPs).

  11. Jellyfish: the origin and distribution of extreme ram-pressure stripping events in massive galaxy clusters

    NASA Astrophysics Data System (ADS)

    McPartland, Conor; Ebeling, Harald; Roediger, Elke; Blumenthal, Kelly

    2016-01-01

    We investigate the observational signatures and physical origin of ram-pressure stripping (RPS) in 63 massive galaxy clusters at z = 0.3-0.7, based on images obtained with the Hubble Space Telescope. Using a training set of a dozen `jellyfish' galaxies identified earlier in the same imaging data, we define morphological criteria to select 211 additional, less obvious cases of RPS. Spectroscopic follow-up observations of 124 candidates so far confirmed 53 as cluster members. For the brightest and most favourably aligned systems, we visually derive estimates of the projected direction of motion based on the orientation of apparent compression shocks and debris trails. Our findings suggest that the onset of these events occurs primarily at large distances from the cluster core (>400 kpc), and that the trajectories of the affected galaxies feature high-impact parameters. Simple models show that such trajectories are highly improbable for galaxy infall along filaments but common for infall at high velocities, even after observational biases are accounted for, provided the duration of the resulting RPS events is ≲500 Myr. We thus tentatively conclude that extreme RPS events are preferentially triggered by cluster mergers, an interpretation that is supported by the disturbed dynamical state of many of the host clusters. This hypothesis implies that extreme RPS might occur also near the cores of merging poor clusters or even merging groups of galaxies. Finally, we present nine additional `jellyfish" galaxies at z > 0.3 discovered by us, thereby doubling the number of such systems known at intermediate redshift.

  12. THE MASSIVE DISTANT CLUSTERS OF WISE SURVEY: THE FIRST DISTANT GALAXY CLUSTER DISCOVERED BY WISE

    SciTech Connect

    Gettings, Daniel P.; Gonzalez, Anthony H.; Mancone, Conor; Stanford, S. Adam; Eisenhardt, Peter R. M.; Stern, Daniel; Brodwin, Mark; Zeimann, Gregory R.; Masci, Frank J.; Papovich, Casey; Tanaka, Ichi; Wright, Edward L.

    2012-11-01

    We present spectroscopic confirmation of a z = 0.99 galaxy cluster discovered using data from the Wide-field Infrared Survey Explorer (WISE). This is the first z {approx} 1 cluster candidate from the Massive Distant Clusters of WISE Survey to be confirmed. It was selected as an overdensity of probable z {approx}> 1 sources using a combination of WISE and Sloan Digital Sky Survey DR8 photometric catalogs. Deeper follow-up imaging data from Subaru and WIYN reveal the cluster to be a rich system of galaxies, and multi-object spectroscopic observations from Keck confirm five cluster members at z = 0.99. The detection and confirmation of this cluster represents a first step toward constructing a uniformly selected sample of distant, high-mass galaxy clusters over the full extragalactic sky using WISE data.

  13. X-ray morphological study of galaxy cluster catalogues

    NASA Astrophysics Data System (ADS)

    Democles, Jessica; Pierre, Marguerite; Arnaud, Monique

    2016-07-01

    Context : The intra-cluster medium distribution as probed by X-ray morphology based analysis gives good indication of the system dynamical state. In the race for the determination of precise scaling relations and understanding their scatter, the dynamical state offers valuable information. Method : We develop the analysis of the centroid-shift so that it can be applied to characterize galaxy cluster surveys such as the XXL survey or high redshift cluster samples. We use it together with the surface brightness concentration parameter and the offset between X-ray peak and brightest cluster galaxy in the context of the XXL bright cluster sample (Pacaud et al 2015) and a set of high redshift massive clusters detected by Planck and SPT and observed by both XMM-Newton and Chandra observatories. Results : Using the wide redshift coverage of the XXL sample, we see no trend between the dynamical state of the systems with the redshift.

  14. Constraints on the alignment of galaxies in galaxy clusters from ~14 000 spectroscopic members

    NASA Astrophysics Data System (ADS)

    Sifón, Cristóbal; Hoekstra, Henk; Cacciato, Marcello; Viola, Massimo; Köhlinger, Fabian; van der Burg, Remco F. J.; Sand, David J.; Graham, Melissa L.

    2015-03-01

    Torques acting on galaxies lead to physical alignments, but the resulting ellipticity correlations are difficult to predict. As they constitute a major contaminant for cosmic shear studies, it is important to constrain the intrinsic alignment signal observationally. We measured the alignments of satellite galaxies within 90 massive galaxy clusters in the redshift range 0.05 galaxies with spectroscopic redshifts with high-quality data from the Canada-France-Hawaii Telescope. We used phase-space information to select 14 576 cluster members, 14 250 of which have shape measurements and measured three different types of alignment: the radial alignment of satellite galaxies toward the brightest cluster galaxies (BCGs), the common orientations of satellite galaxies and BCGs, and the radial alignments of satellites with each other. Residual systematic effects are much smaller than the statistical uncertainties. We detect no galaxy alignment of any kind out to at least 3r200. The signal is consistent with zero for both blue and red galaxies, bright and faint ones, and also for subsamples of clusters based on redshift, dynamical mass, and dynamical state. These conclusions are unchanged if we expand the sample with bright cluster members from the red sequence. We augment our constraints with those from the literature to estimate the importance of the intrinsic alignments of satellites compared to those of central galaxies, for which the alignments are described by the linear alignment model. Comparison of the alignment signals to the expected uncertainties of current surveys such as the Kilo-Degree Survey suggests that the linear alignment model is an adequate treatment of intrinsic alignments, but it is not clear whether this will be the case for larger surveys. Table is available in electronic form at

  15. Featured Image: A Galaxy Plunges Into a Cluster Core

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2015-10-01

    The galaxy that takes up most of the frame in this stunning image (click for the full view!) is NGC 1427A. This is a dwarf irregular galaxy (unlike the fortuitously-located background spiral galaxy in the lower right corner of the image), and its currently in the process of plunging into the center of the Fornax galaxy cluster. Marcelo Mora (Pontifical Catholic University of Chile) and collaborators have analyzed observations of this galaxy made by both the Very Large Telescope in Chile and the Hubble Advanced Camera for Surveys, which produced the image shown here as a color composite in three channels. The team worked to characterize the clusters of star formation within NGC 1427A identifiable in the image as bright knots within the galaxy and determine how the interactions of this galaxy with its cluster environment affect the star formation within it. For more information and the original image, see the paper below.Citation:Marcelo D. Mora et al 2015 AJ 150 93. doi:10.1088/0004-6256/150/3/93

  16. Cosmological Constraints from Galaxy Clusters and Clustering in the Sloan Digital Sky Survey

    NASA Astrophysics Data System (ADS)

    Tinker, Jeremy

    2009-01-01

    I will present constraints on cosmological parameters from a combination of cluster mass to galaxy number ratios combined with halo occupation analysis of the galaxy autocorrelation function. In two-point clustering, cosmology an bias are degenerate; good fits to the correlation function can be obtained for a wide variety of comologies. However, in order to match the observed level of clustering, each cosmology predicts a different number of galaxies per unit mass at the cluster mass scale. A combination of DR7 galaxy clustering results and M/N data from the weak lensing analysis of the maxBCG catalog break the degeneracy between cosmology and bias, leading to constraints on \\Omega_m and \\sigma_8 that are competitive with current CMB results.

  17. HUBBLE CAPTURES VIEW OF SUPERNOVA BLAST IN REMOTE GALAXY CLUSTER

    NASA Technical Reports Server (NTRS)

    2002-01-01

    In March 1996, the Hubble Space Telescope's Wide Field and Planetary Camera 2 just happened to be pointed at the faraway galaxy cluster MS1054-0321 when it captured the light from an exploding star, called supernova 1996CL. The cluster is 8 billion light-years from Earth. The Hubble telescope can clearly distinguish the supernova light from the glow of its parent galaxy. The larger image on the left shows the entire cluster of galaxies. The galaxy where the supernova was discovered is located in the boxed area. The bright knot of light from the supernova and the fainter glow from the parent galaxy are shown in the inset image on the right. The arrow points to the light from the supernova explosion. The supernova was discovered by members of the Supernova Cosmology Project, led by Saul Perlmutter of Lawrence Berkeley Laboratory in California. Perlmutter and his team made this discovery using images from the Hubble telescope and ground-based observatories. The Hubble data were furnished by Megan Donahue of the Space Telescope Science Institute. Donahue was using the Hubble telescope to study galaxy cluster MS1054-0321. Members of the Supernova Project use ground-based telescopes to search for distant supernovae, such as 1996CL, by comparing multiple, wide-field images of galaxies and clusters of galaxies taken at different times. Supernovae are named for the year and the order in which they are found. Supernova 1996CL is a Type Ia supernova. Exploding stars of this type are particularly useful for cosmology because they share a standard maximum brightness. By measuring this brightness, astronomers can determine a Type Ia's distance from Earth. Astronomers use this information to measure the expansion rate of the universe.

  18. DISENTANGLING THE ROLE OF ENVIRONMENTAL PROCESSES IN GALAXY CLUSTERS

    SciTech Connect

    Hernandez-Fernandez, Jonathan D.; Vilchez, J. M.; Iglesias-Paramo, J.

    2012-05-20

    In this work, we present the results of a novel approach devoted to disentangling the role of the environmental processes affecting galaxies in clusters. This is based on the analysis of the near-UV (NUV) - r' distributions of a large sample of star-forming galaxies in clusters spanning more than four absolute magnitudes. The galaxies inhabit three distinct environmental regions: virial regions, cluster infall regions, and field environment. We have applied rigorous statistical tests to analyze both the complete NUV - r' distributions and their averages for three different bins of the r'-band galaxy luminosity down to M{sub r{sup '}}{approx}-18, throughout the three environmental regions considered. We have identified the environmental processes that significantly affect the star-forming galaxies in a given luminosity bin by using criteria based on the characteristics of these processes: their typical timescales, the regions where they operate, and the galaxy luminosity range for which their effects are more intense. We have found that the high-luminosity (M{sub r{sup '}}{<=}-20) star-forming galaxies do not show significant signs in their star formation activity of being affected by: (1) the environment in the last {approx}10{sup 8} yr, or (2) a sudden quenching in the last 1.5 Gyr. The intermediate-luminosity (-20< M{sub r{sup '}}{<=}-19) star-forming galaxies appear to be affected by starvation in the virial regions and by the harassment in the virial and infall regions. Low-luminosity (-19galaxies seem to be affected by the same environmental processes as intermediate-luminosity star-forming galaxies in a stronger way, which would be expected for their lower luminosities.

  19. Globular clusters kinematics and dynamical models of the massive early-type galaxy NGC 1399

    NASA Astrophysics Data System (ADS)

    Samurović, S.

    2016-06-01

    We analyze the dynamical models of the massive early-type galaxy NGC 1399, the central galaxy of the Fornax cluster. We use the sample of 790 globular clusters as tracers of gravitational potential and we first extract the kinematics, which is then dynamically modeled. We find that the velocity dispersion remains high and approximately constant throughout the whole galaxy and that the departures from the Gaussian distribution of the orbits are not large. We use the spherical Jeans equation in both Newtonian and MOND approaches, assuming three cases of orbital anisotropies: we study isotropic, tangentially and radially anisotropic models in order to establish the best-fitting values of the mass-to-light ratios. We found that in the Newtonian approximation a significant amount of dark matter is needed and that Navarro-Frenk-White (NFW) model with a dark halo provides a satisfactory description of the kinematics of NGC 1399. We tested three MOND models (standard, simple and toy) and found that none of them can provide a fit of the velocity dispersion profile without the inclusion of dark matter. Finally, using our findings, we placed the galaxy NGC 1399 within the context of other observed early-type galaxies and discuss its location among them.

  20. Baryon content and dynamic state of galaxy clusters

    NASA Astrophysics Data System (ADS)

    Wang, D.

    2016-06-01

    We are carrying out a panchromatic observing program to study the baryon content and dynamic state of galaxy clusters. In this talk, I will present results primarily from XMM-Newton observations of optically-selected clusters in the redshift range of 0.1-0.4. These clusters are selected because of their fortuitous alignment with background far-UV-bright QSOs, which thus allows for Ly-alpha and O VI absorption line spectroscopy with HST/COS, probing physical processes of the evolving intracluster medium, freshly accreted from the intergalactic medium and/or stripped out of individual galaxies, as well as the gaseous halos of individual cluster galaxies. Interestingly, such clusters tend to be dynamically young and often consist of merging subcluster pairs at similar redshifts. These subclusters themselves typically show substantial substructures, including strongly distorted radio lobes, as well as large position offsets between the diffuse X-ray centroids and the brightest galaxies. A comparison of the hot gas and stellar masses of each cluster with the expected cosmological baryonic mass fraction indicates a significant room for other gas components. I will also briefly examine the limitations of both optically and X-ray selected clusters, as well as how they may be used in a complementary fashion.

  1. Radial velocities of three poorly studied clusters and the kinematics of open clusters

    SciTech Connect

    Hayes, Christian R.; Friel, Eileen D. E-mail: efriel@indiana.edu

    2014-04-01

    We present radial velocities for stars in the field of the open star clusters Berkeley 44, Berkeley 81, and NGC 6802 from spectra obtained using the Wisconsin-Indiana-Yale-NOAO (WIYN) 3.5 m telescope. These clusters are of intermediate age (1-3 Gyr), located within the solar Galactocentric radius, and have no previous radial velocity measurements. We find mean radial velocities of –9.6 ± 3.0 km s{sup –1}, 48.1 ± 2.0 km s{sup –1}, and 12.4 ± 2.8 km s{sup –1} for Be 44, Be 81, and NGC 6802, respectively. We present an analysis of radial velocities of 134 open clusters of a wide range of ages using data obtained in this study and the literature. Assuming the system of clusters rotates about the Galactic center with a constant velocity, we find older clusters exhibit a slower rotation and larger line-of-sight (LOS) velocity dispersion than younger clusters. The gradual decrease in rotational velocity of the cluster system with age is accompanied by a smooth increase in LOS velocity dispersion, which we interpret as the effect of heating on the open cluster system over time.

  2. Chandra Finds Surprising Black Hole Activity In Galaxy Cluster

    NASA Astrophysics Data System (ADS)

    2002-09-01

    Scientists at the Carnegie Observatories in Pasadena, California, have uncovered six times the expected number of active, supermassive black holes in a single viewing of a cluster of galaxies, a finding that has profound implications for theories as to how old galaxies fuel the growth of their central black holes. The finding suggests that voracious, central black holes might be as common in old, red galaxies as they are in younger, blue galaxies, a surprise to many astronomers. The team made this discovery with NASA'S Chandra X-ray Observatory. They also used Carnegie's 6.5-meter Walter Baade Telescope at the Las Campanas Observatory in Chile for follow-up optical observations. "This changes our view of galaxy clusters as the retirement homes for old and quiet black holes," said Dr. Paul Martini, lead author on a paper describing the results that appears in the September 10 issue of The Astrophysical Journal Letters. "The question now is, how do these black holes produce bright X-ray sources, similar to what we see from much younger galaxies?" Typical of the black hole phenomenon, the cores of these active galaxies are luminous in X-ray radiation. Yet, they are obscured, and thus essentially undetectable in the radio, infrared and optical wavebands. "X rays can penetrate obscuring gas and dust as easily as they penetrate the soft tissue of the human body to look for broken bones," said co-author Dr. Dan Kelson. "So, with Chandra, we can peer through the dust and we have found that even ancient galaxies with 10-billion-year-old stars can have central black holes still actively pulling in copious amounts of interstellar gas. This activity has simply been hidden from us all this time. This means these galaxies aren't over the hill after all and our theories need to be revised." Scientists say that supermassive black holes -- having the mass of millions to billions of suns squeezed into a region about the size of our Solar System -- are the engines in the cores of

  3. cluster-lensing: a new Python package for galaxy clusters & lensing

    NASA Astrophysics Data System (ADS)

    Ford, Jes

    2016-03-01

    Short demo and links to a newly released pure Python package called cluster- lensing. This package contains tools to calculate galaxy cluster halo properties and weak lensing shear and magnification profiles. The model can easily include the effects of possible cluster miscentering offsets, which would otherwise lead to biased mass or concentration estimates.

  4. Hubble tracks down a galaxy cluster's dark matter

    NASA Astrophysics Data System (ADS)

    2003-07-01

    Unique mass map hi-res Size hi-res: 495 kb Credits: European Space Agency, NASA and Jean-Paul Kneib (Observatoire Midi-Pyrénées, France/Caltech, USA) Unique mass map This is a mass map of galaxy cluster Cl0024+1654 derived from an extensive Hubble Space Telescope campaign. The colour image is made from two images: a dark-matter map (the blue part of the image) and a 'luminous-matter' map determined from the galaxies in the cluster (the red part of the image). They were constructed by feeding Hubble and ground-based observations into advanced mathematical mass-mapping models. The map shows that dark matter is present where the galaxies clump together. The mass of the galaxies is shown in red, the mass of the dark matter in blue. The dark matter behaves like a 'glue', holding the cluster together. The dark-matter distribution in the cluster is not spherical. A secondary concentration of dark-matter mass is shown in blue to the upper right of the main concentration. Sky around galaxy cluster Cl0024+1654 hi-res Size hi-res: 3742 kb Credits: European Space Agency, NASA and Jean-Paul Kneib (Observatoire Midi-Pyrénées, France/Caltech, USA) Sky around galaxy cluster Cl0024+1654 This is a 2.5-degree field around galaxy cluster Cl0024+1654. The cluster galaxies are visible in the centre of the image in yellow. The image is a colour composite constructed from three Digitized Sky Survey 2 images: Blue (shown in blue), Red (shown in green), and Infrared (shown in red). HST observes shapes of more than 7000 faint background galaxies hi-res Size hi-res: 5593 kb Credits: European Space Agency, NASA and Jean-Paul Kneib (Observatoire Midi-Pyrénées, France/Caltech, USA) Hubble observes shapes of more than 7000 faint background galaxies Five days of observations produced the altogether 39 Hubble Wide Field and Planetary Camera 2 (WFPC2) images required to map the mass of the galaxy cluster Cl0024+1654. Each WFPC2 image has a size of about 1/150 the diameter of the full Moon. In

  5. Sommerfeld enhancement of invisible dark matter annihilation in galaxies and galaxy clusters

    NASA Astrophysics Data System (ADS)

    Chan, Man Ho

    2016-07-01

    Recent observations indicate that core-like dark matter structures exist in many galaxies, while numerical simulations reveal a singular dark matter density profile at the center. In this article, I show that if the annihilation of dark matter particles gives invisible sterile neutrinos, the Sommerfeld enhancement of the annihilation cross-section can give a sufficiently large annihilation rate to solve the core-cusp problem. The resultant core density, core radius, and their scaling relation generally agree with recent empirical fits from observations. Also, this model predicts that the resultant core-like structures in dwarf galaxies can be easily observed, but not for large normal galaxies and galaxy clusters.

  6. Constraining Self-Interacting Dark Matter: Insights from Equal Mass Mergers of Galaxy Clusters

    NASA Astrophysics Data System (ADS)

    Yeonchi Kim, Stacy; Peter, Annika

    2016-01-01

    While the ΛCDM model has been wildly successful at explaining structure on large scales, it fails to do so on small scales---dark matter halos of scales comparable to that of galaxy clusters and smaller are more cored and less numerous than ΛCDM predicts. One potential solution challenges the canonical assumption that dark matter is collisionless and instead assumes that it is collisional, or self-interacting. The most stringent upper limits on the dark matter self-interaction cross section have come from observations of merging galaxy clusters. Self-interactions cause the merging dark matter halos to evolve differently from the galaxies, which are effectively collisionless. It has been hypothesized that this leads to an spatial offset between the peaks in the dark matter and galaxy distributions. We show that in equal mass mergers offsets do not develop except under a narrow range of merger conditions. Mergers with observable offsets have an infall velocity comparable to the escape velocity from a halo---promoting the explusion of significant mass and the formation of tails---and is head-on. We discuss other observable signatures of self-interactions that may better constrain the dark matter self-interaction cross-section in equal mass cluster mergers.

  7. STAR FORMATION AND RELAXATION IN 379 NEARBY GALAXY CLUSTERS

    SciTech Connect

    Cohen, Seth A.; Hickox, Ryan C.; Wegner, Gary A.

    2015-06-10

    We investigate the relationship between star formation (SF) and level of relaxation in a sample of 379 galaxy clusters at z < 0.2. We use data from the Sloan Digital Sky Survey to measure cluster membership and level of relaxation, and to select star-forming galaxies based on mid-infrared emission detected with the Wide-Field Infrared Survey Explorer. For galaxies with absolute magnitudes M{sub r} < −19.5, we find an inverse correlation between SF fraction and cluster relaxation: as a cluster becomes less relaxed, its SF fraction increases. Furthermore, in general, the subtracted SF fraction in all unrelaxed clusters (0.117 ± 0.003) is higher than that in all relaxed clusters (0.097 ± 0.005). We verify the validity of our SF calculation methods and membership criteria through analysis of previous work. Our results agree with previous findings that a weak correlation exists between cluster SF and dynamical state, possibly because unrelaxed clusters are less evolved relative to relaxed clusters.

  8. Galaxy Clustering in the Dark Energy Survey Science Verification Data

    NASA Astrophysics Data System (ADS)

    Ross, Ashley; Crocce, Martin; Dark Energy Survey Large Scale Structure Working Group Collaboration

    2015-04-01

    I present the results of a study of galaxy clustering in a flux-limited sample (iAB < 22 . 5) selected from the photometric Science Verification (SV) data of the Dark Energy Survey (DES), conducted by the DES large scale structure working group. The SV data provides science-quality images for more than 250 deg2 at the nominal DES depth (iAB ? 24). I will present the clustering analysis of this data, performed over five tomographic bins, with photometric redshifts, z, in the range 0.2 < z < 1.2. I will describe our work to identify and ameliorate systematics in the data set, which has allowed us to robustly measure the clustering amplitude of the galaxies in each tomographic bin. We test the relationship between the clustering of the galaxies and analytic predictions of the clustering of the dark matter, known as the bias relationship and determine the regime where it is described by a linear model I will present these results and compare them against a similar sample from the (previously) state-of-the-art CFHTLS, with which we find very good agreement. These results pave the way for exciting cosmological measurements to be made with future (larger) DES data sets and by combining the results with other probes such as CMB lensing and galaxy-galaxy lensing.

  9. Clustering of Dust-Obscured Galaxies at z ~ 2

    NASA Astrophysics Data System (ADS)

    Brodwin, Mark; Dey, Arjun; Brown, Michael J. I.; Pope, Alexandra; Armus, Lee; Bussmann, Shane; Desai, Vandana; Jannuzi, Buell T.; Le Floc'h, Emeric

    2008-11-01

    We present the angular autocorrelation function of 2603 dust-obscured galaxies (DOGs) in the Boötes field of the NOAO Deep Wide-Field Survey. DOGs are red, obscured galaxies, defined as having R - [ 24] >= 14 (F24/FRgtrsim 1000). Spectroscopy indicates that they are located at 1.5 lesssim z lesssim 2.5. We find strong clustering, with r0 = 7.40-0.84+1.27 h-1 Mpc for the full F24 > 0.3 mJy sample. The clustering and space density of the DOGs are consistent with those of submillimeter galaxies, suggestive of a connection between these populations. We find evidence for luminosity-dependent clustering, with the correlation length increasing to r0 = 12.97-2.64+4.26 h-1 Mpc for brighter (F24 > 0.6 mJy) DOGs. Bright DOGs also reside in richer environments than fainter ones, suggesting these subsamples may not be drawn from the same parent population. The clustering amplitudes imply average halo masses of log M = 12.2-0.2+0.3 M⊙ for the full DOG sample, rising to log M = 13.0-0.3+0.4 M⊙ for brighter DOGs. In a biased structure formation scenario, the full DOG sample will, on average, evolve into ~3L* present-day galaxies, whereas the most luminous DOGs may evolve into brightest cluster galaxies.

  10. Search for gas bulk motions in eight nearby clusters of galaxies with Suzaku

    NASA Astrophysics Data System (ADS)

    Ota, Naomi; Yoshida, Hiroko

    2016-06-01

    To search for bulk motions of the intracluster medium, we analyzed X-ray spectra taken with the Suzaku satellite, and measured the Doppler shift of the Fe-K line emission from eight nearby clusters of galaxies with various X-ray morphologies. In the cores of the Centaurus and Perseus clusters, the gas bulk velocity does not exceed the sound velocity, which confirms the results of previous researchs. For the Cen 45 subcluster, we found that the radial velocity relative to the Centaurus core, <780 km s-1, is significantly smaller than that reported in the optical band at the 3.9 σ level, which suggests an offset between the gas and galaxy distributions along the line of sight due to the subcluster merger. In A 2199, A 2142, A 3667, and A 133, no significant bulk motion was detected, indicating an upper limit on the radial velocity of 3000-4000 km s-1. A sign of large bulk velocity in excess of the instrumental calibration uncertainty was found near the center of the cool-core cluster A 2029 and in a subcluster of the merging cluster A 2255, suggesting that the nonthermal pressure support is not negligible in estimating the total gravitational mass of not only merging clusters, but also relaxed clusters, as predicted by numerical simulations. To improve the significance of the detection, however, a further examination by follow-up observations is required. The present study provides a pilot survey prior to future high-resolution spectroscopy with ASTRO-H, which is expected to play a critical role in revealing the dynamical evolutions of clusters.

  11. Cosmological simulations of isotropic conduction in galaxy clusters

    SciTech Connect

    Smith, Britton; O'Shea, Brian W.; Voit, G. Mark; Ventimiglia, David; Skillman, Samuel W.

    2013-12-01

    Simulations of galaxy clusters have a difficult time reproducing the radial gas-property gradients and red central galaxies observed to exist in the cores of galaxy clusters. Thermal conduction has been suggested as a mechanism that can help bring simulations of cluster cores into better alignment with observations by stabilizing the feedback processes that regulate gas cooling, but this idea has not yet been well tested with cosmological numerical simulations. Here we present cosmological simulations of 10 galaxy clusters performed with five different levels of isotropic Spitzer conduction, which alters both the cores and outskirts of clusters, though not dramatically. In the cores, conduction flattens central temperature gradients, making them nearly isothermal and slightly lowering the central density, but failing to prevent a cooling catastrophe there. Conduction has little effect on temperature gradients outside of cluster cores because outward conductive heat flow tends to inflate the outer parts of the intracluster medium (ICM), instead of raising its temperature. In general, conduction tends reduce temperature inhomogeneity in the ICM, but our simulations indicate that those homogenizing effects would be extremely difficult to observe in ∼5 keV clusters. Outside the virial radius, our conduction implementation lowers the gas densities and temperatures because it reduces the Mach numbers of accretion shocks. We conclude that, despite the numerous small ways in which conduction alters the structure of galaxy clusters, none of these effects are significant enough to make the efficiency of conduction easily measurable, unless its effects are more pronounced in clusters hotter than those we have simulated.

  12. Star Formation in Galaxy Clusters Over the Past 10 Billion Years

    NASA Astrophysics Data System (ADS)

    Tran, Kim-Vy

    2012-01-01

    Galaxy clusters are the largest gravitationally bound systems in the universe and include the most massive galaxies in the universe; this makes galaxy clusters ideal laboratories for disentangling the nature versus nurture aspect of how galaxies evolve. Understanding how galaxies form and evolve in clusters continues to be a fundamental question in astronomy. The ages and assembly histories of galaxies in rich clusters test both stellar population models and hierarchical formation scenarios. Is star formation in cluster galaxies simply accelerated relative to their counterparts in the lower density field, or do cluster galaxies assemble their stars in a fundamentally different manner? To answer this question, I review multi-wavelength results on star formation in galaxy clusters from Coma to the most distant clusters yet discovered at look-back times of 10 billion years (z 2).

  13. Dark matter fraction of low-mass cluster members probed by galaxy-scale strong lensing

    NASA Astrophysics Data System (ADS)

    Parry, W. G.; Grillo, C.; Mercurio, A.; Balestra, I.; Rosati, P.; Christensen, L.; Lombardi, M.; Caminha, G. B.; Nonino, M.; Koekemoer, A. M.; Umetsu, K.

    2016-05-01

    We present a strong lensing system, composed of four multiple images of a source at z = 2.387, created by two lens galaxies, G1 and G2, belonging to the galaxy cluster MACS J1115.9+0129 at z = 0.353. We use observations taken as part of the Cluster Lensing and Supernova survey with Hubble, and its spectroscopic follow-up programme at the Very Large Telescope, to estimate the total mass distributions of the two galaxies and the cluster through strong gravitational lensing models. We find that the total projected mass values within the half-light radii, Re, of the two lens galaxies are MT,G1(velocity dispersion values of G1 and G2 are (122 ± 7) km s-1 and (137 ± 27) km s-1, respectively. We remark that these values are relatively low when compared to those of ≈200-300 km s-1, typical of lens galaxies found in the field by previous surveys. By fitting the spectral energy distributions of G1 and G2, we measure projected luminous over total mass fractions within Re of 0.11 ± 0.03, for G1, and 0.73 ± 0.32, for G2. The fact that the less massive galaxy, G1, is dark matter-dominated in its inner regions raises the question of whether the dark matter fraction in the core of early-type galaxies depends on their mass. Further investigating strong lensing systems will help us understand the influence that dark matter has on the structure and evolution of the inner regions of galaxies.

  14. Dynamical Models of Elliptical Galaxies in z = 0.5 Clusters. I. Data-Model Comparison and Evolution of Galaxy Rotation

    NASA Astrophysics Data System (ADS)

    van der Marel, Roeland P.; van Dokkum, Pieter G.

    2007-10-01

    We present spatially resolved stellar rotation velocity and velocity dispersion profiles from Keck/LRIS absorption-line spectra for 25 galaxies, mostly visually classified ellipticals, in three clusters at z~0.5. We interpret the kinematical data and HST photometry using oblate axisymmetric two-integral f(E,Lz) dynamical models based on the Jeans equations. This yields good fits, provided that the seeing and observational characteristics are carefully modeled. The fits yield for each galaxy the dynamical mass-to-light ratio (M/L) and a measure of the galaxy rotation rate. Paper II addresses the implied M/L evolution. Here we study the rotation-rate evolution by comparison to a sample of local elliptical galaxies of similar present-day luminosity. The brightest galaxies in the sample all rotate too slowly to account for their flattening, as is also observed at z=0. But the average rotation rate is higher at z~0.5 than locally. This may be due to a higher fraction of misclassified S0 galaxies (although this effect is insufficient to explain the observed strong evolution of the cluster S0 fraction with redshift). Alternatively, dry mergers between early-type galaxies may have decreased the average rotation rate over time. It is unclear whether such mergers are numerous enough in clusters to explain the observed trend quantitatively. Disk-disk mergers may affect the comparison through the so-called ``progenitor bias,'' but this cannot explain the direction of the observed rotation-rate evolution. Additional samples are needed to constrain possible environmental dependencies and cosmic variance in galaxy rotation rates. Either way, studies of the internal stellar dynamics of distant galaxies provide a valuable new approach for exploring galaxy evolution.

  15. TELESCOPES UNVEIL VIEW OF REMOTE, MASSIVE GALAXY CLUSTER

    NASA Technical Reports Server (NTRS)

    2002-01-01

    hese images, taken by three different telescopes, show the distant, hefty galaxy cluster MS1054-0321, containing thousands of galaxies and trillions of stars. Weighing the equivalent of several thousand of our Milky Ways, the cluster is 8 billion light-years from Earth. The image on the left is a color composite taken by ground-based and X-ray observatories showing the entire galaxy cluster surrounded by background and foreground galaxies. The blue color in the center of the image represents the huge amount of hot gas that fills the space between the galaxies in the cluster. This gas - colored blue - cannot be seen in visible light, but glows in X-ray frequencies. Astronomers have measured its temperature at 300 million degrees Fahrenheit. The X-ray information was used to estimate the cluster's total mass. The boxed area in the center of the image pinpoints the Hubble telescope's field of view. The image on the right, taken by the Wide Field and Planetary Camera 2, shows a clearer view of the galaxies in the heart of the cluster. The width of this massive cluster is a few million light-years. The ground-based image was taken between May 1992 and November 1993 by the 88-inch telescope at the University of Hawaii. Astronomers Isabella Gioia and Gerry Luppino of the University of Hawaii made this four-hour exposure with a near-infrared filter (8,000 angstroms). The X-ray image was taken in 1996 by astronomer Megan Donahue of the Space Telescope Science Institute with the High Resolution Imager aboard the Rosat satellite. The exposure time was 34 hours. Donahue used a near-infrared filter (F814W) to take the Hubble telescope image in 1996. The exposure time was four hours.

  16. Redshift space clustering of galaxies and cold dark matter model

    NASA Technical Reports Server (NTRS)

    Bahcall, Neta A.; Cen, Renyue; Gramann, Mirt

    1993-01-01

    The distorting effect of peculiar velocities on the power speturm and correlation function of IRAS and optical galaxies is studied. The observed redshift space power spectra and correlation functions of IRAS and optical the galaxies over the entire range of scales are directly compared with the corresponding redshift space distributions using large-scale computer simulations of cold dark matter (CDM) models in order to study the distortion effect of peculiar velocities on the power spectrum and correlation function of the galaxies. It is found that the observed power spectrum of IRAS and optical galaxies is consistent with the spectrum of an Omega = 1 CDM model. The problems that such a model currently faces may be related more to the high value of Omega in the model than to the shape of the spectrum. A low-density CDM model is also investigated and found to be consistent with the data.

  17. On the influence of ram-pressure stripping on interacting galaxies in clusters

    NASA Astrophysics Data System (ADS)

    Kapferer, W.; Kronberger, T.; Ferrari, C.; Riser, T.; Schindler, S.

    2008-09-01

    We investigate the influence of ram pressure on the star-formation rate and the distribution of gas and stellar matter in interacting model galaxies in clusters. To simulate the baryonic and non-baryonic components of interacting disc galaxies moving through a hot, thin medium, we use a combined N-body/hydrodynamic code GADGET2 with a description for star formation based on density thresholds. Two identical model spiral galaxies on a collision trajectory with three different configurations were investigated in detail. In the first configuration, the galaxies collide without the presence of an ambient medium. In the second configurations, the ram pressure acts face-on on the interacting galaxies and in the third configuration the ram pressure acts edge-on. The ambient medium is thin (10-28gcm-3), hot (3keV ~ 3.6 × 107 K) and has a relative velocity of 1000kms-1, to mimic an average low ram pressure in the outskirts of galaxy clusters. The interaction velocities are comparable to galaxy interactions in groups, falling along filaments into galaxy clusters. The global star-formation rate of the interacting system is enhanced in the presence of ram pressure by a factor of 3 in comparison to the same interaction without the presence of an ambient medium. The tidal tails and the gaseous bridge of the interacting system are almost completely destroyed by the ram pressure. The amount of gas in the wake of the interacting system is ~50 per cent of the total gas of the colliding galaxies after 500Myr the galaxies start to feel the ram pressure. Nearly ~10-15 per cent in mass of all newly formed stars are formed in the wake of the interacting system at distances larger than 20 kpc behind the stellar discs. As the tidal tails and the gaseous bridge between the interacting systems feel the ram pressure, knots of cold gas (T < 1 × 105 K) start to form. These irregular structures contain several 106Msolar of cold gas and newly formed stars and, as the ram pressure acts on them

  18. Isolated elliptical galaxies, their globular cluster systems, and LCDM

    NASA Astrophysics Data System (ADS)

    Lane, Richard; Salinas, Ricardo; Richtler, Tom

    2015-08-01

    The globular cluster (GC) systems of isolated elliptical galaxies (IEs) have only recently begun to be studied in detail, and may exhibit morphological connections to the evolutionary histories of their hosts. In fact evidence is mounting that the GC systems of massive galaxies in clusters are largely assembled by infall/accretion processes. IEs are their counterparts in low density environments and a comparison of their GC systems should directly highlight environmental effects. Are GCs the answer to unlocking the evolution of isolated galaxies? In addition, the GC systems of reasonably nearby galaxies are detectable out to large radii, making them useful tracers for producing dynamical models of their hosts. How much dark matter is contained within IEs? Very little it seems, at least in some cases. GCs are, therefore, also one of the most important tools we have for testing Lambda CDM models observationally.

  19. Hubble tracks down a galaxy cluster's dark matter

    NASA Astrophysics Data System (ADS)

    2003-07-01

    Unique mass map hi-res Size hi-res: 495 kb Credits: European Space Agency, NASA and Jean-Paul Kneib (Observatoire Midi-Pyrénées, France/Caltech, USA) Unique mass map This is a mass map of galaxy cluster Cl0024+1654 derived from an extensive Hubble Space Telescope campaign. The colour image is made from two images: a dark-matter map (the blue part of the image) and a 'luminous-matter' map determined from the galaxies in the cluster (the red part of the image). They were constructed by feeding Hubble and ground-based observations into advanced mathematical mass-mapping models. The map shows that dark matter is present where the galaxies clump together. The mass of the galaxies is shown in red, the mass of the dark matter in blue. The dark matter behaves like a 'glue', holding the cluster together. The dark-matter distribution in the cluster is not spherical. A secondary concentration of dark-matter mass is shown in blue to the upper right of the main concentration. Sky around galaxy cluster Cl0024+1654 hi-res Size hi-res: 3742 kb Credits: European Space Agency, NASA and Jean-Paul Kneib (Observatoire Midi-Pyrénées, France/Caltech, USA) Sky around galaxy cluster Cl0024+1654 This is a 2.5-degree field around galaxy cluster Cl0024+1654. The cluster galaxies are visible in the centre of the image in yellow. The image is a colour composite constructed from three Digitized Sky Survey 2 images: Blue (shown in blue), Red (shown in green), and Infrared (shown in red). HST observes shapes of more than 7000 faint background galaxies hi-res Size hi-res: 5593 kb Credits: European Space Agency, NASA and Jean-Paul Kneib (Observatoire Midi-Pyrénées, France/Caltech, USA) Hubble observes shapes of more than 7000 faint background galaxies Five days of observations produced the altogether 39 Hubble Wide Field and Planetary Camera 2 (WFPC2) images required to map the mass of the galaxy cluster Cl0024+1654. Each WFPC2 image has a size of about 1/150 the diameter of the full Moon. In

  20. Cosmological constraints from galaxy clustering and the mass-to-number ratio of galaxy clusters: marginalizing over the physics of galaxy formation

    SciTech Connect

    Reddick, Rachel M.; Wechsler, Risa H.; Lu, Yu; Tinker, Jeremy L. E-mail: rwechsler@stanford.edu

    2014-03-10

    Many approaches to obtaining cosmological constraints rely on the connection between galaxies and dark matter. However, the distribution of galaxies is dependent on their formation and evolution as well as on the cosmological model, and galaxy formation is still not a well-constrained process. Thus, methods that probe cosmology using galaxies as tracers for dark matter must be able to accurately estimate the cosmological parameters. This can be done without knowing details of galaxy formation a priori as long as the galaxies are well represented by a halo occupation distribution (HOD). We apply this reasoning to the method of obtaining Ω {sub m} and σ{sub 8} from galaxy clustering combined with the mass-to-number ratio of galaxy clusters. To test the sensitivity of this method to variations due to galaxy formation, we consider several different models applied to the same cosmological dark matter simulation. The cosmological parameters are then estimated using the observables in each model, marginalizing over the parameters of the HOD. We find that for models where the galaxies can be well represented by a parameterized HOD, this method can successfully extract the desired cosmological parameters for a wide range of galaxy formation prescriptions.

  1. Galaxy Clusters in the Line of Sight to Background Quasars. III. Multi-object Spectroscopy

    NASA Astrophysics Data System (ADS)

    Andrews, H.; Barrientos, L. F.; López, S.; Lira, P.; Padilla, N.; Gilbank, D. G.; Lacerna, I.; Maureira, M. J.; Ellingson, E.; Gladders, M. D.; Yee, H. K. C.

    2013-09-01

    We present Gemini/GMOS-S multi-object spectroscopy of 31 galaxy cluster candidates at redshifts between 0.2 and 1.0 and centered on QSO sight lines taken from López et al. The targets were selected based on the presence of an intervening Mg II absorption system at a similar redshift to that of a galaxy cluster candidate lying at a projected distance <2 h_{71}^{-1} Mpc from the QSO sight line (a "photometric hit"). The absorption systems span rest-frame equivalent widths between 0.015 and 2.028 Å. Our aim was three-fold: (1) to identify the absorbing galaxies and determine their impact parameters, (2) to confirm the galaxy cluster candidates in the vicinity of each quasar sightline, and (3) to determine whether the absorbing galaxies reside in galaxy clusters. In this way, we are able to characterize the absorption systems associated with cluster members. Our main findings are as follows. (1) We identified 10 out of 24 absorbing galaxies with redshifts between 0.2509 <= z gal <= 1.0955, up to an impact parameter of 142\\ h_{71}^{-1} kpc and a maximum velocity difference of 280 km s-1. (2) We spectroscopically confirmed 20 out of 31 cluster/group candidates, with most of the confirmed clusters/groups at z < 0.7. This relatively low efficiency results from the fact that we centered our observations on the QSO location, and thus occasionally some of the cluster centers were outside the instrument field of view. (3) Following from the results above, we spectroscopically confirmed of 10 out of 14 photometric hits within ~650 km s-1 from galaxy clusters/groups, in addition to two new ones related to galaxy group environments. These numbers imply efficiencies of 71% in finding such systems with MOS spectroscopy. This is a remarkable result since we defined a photometric hit as those cluster-absorber pairs having a redshift difference Δz = 0.1. The general population of our confirmed absorbing galaxies have luminosities L_{B} \\sim L_{B}^{\\ast } and mean rest

  2. Properties of the galaxy population in hydrodynamical simulations of clusters

    NASA Astrophysics Data System (ADS)

    Saro, A.; Borgani, S.; Tornatore, L.; Dolag, K.; Murante, G.; Biviano, A.; Calura, F.; Charlot, S.

    2006-11-01

    We present a study of the galaxy population predicted by hydrodynamical simulations of galaxy clusters. These simulations, which are based on the GADGET-2 TREE + SPH code, include gas cooling, star formation, a detailed treatment of stellar evolution and chemical enrichment, as well as supernova energy feedback in the form of galactic winds. As such, they can be used to extract the spectrophotometric properties of the simulated galaxies, which are identified as clumps in the distribution of star particles. Simulations have been carried out for a representative set of 19 cluster-sized haloes, having mass M200 in the range 5 × 1013-1.8 × 1015h-1Msolar. All simulations have been performed for two choices of the stellar initial mass function (IMF), namely using a standard Salpeter IMF with power-law index x = 1.35, and a top-heavy IMF with x = 0.95. In general, we find that several of the observational properties of the galaxy population in nearby clusters are reproduced fairly well by simulations. A Salpeter IMF is successful in accounting for the slope and the normalization of the colour-magnitude relation for the bulk of the galaxy population. In contrast, the top-heavy IMF produces too red galaxies, as a consequence of their exceedingly large metallicity. Simulated clusters have a relation between mass and optical luminosity, which generally agrees with observations, both in normalization and in slope. Also in keeping with observational results, galaxies are generally bluer, younger and more star forming in the cluster outskirts. However, we find that our simulated clusters have a total number of galaxies which is significantly smaller than the observed one, falling short by about a factor of 2-3. We have verified that this problem does not have an obvious numerical origin, such as lack of mass and force resolution. Finally, the brightest cluster galaxies are always predicted to be too massive and too blue, when compared to observations. This is due to gas

  3. Stellar velocity dispersion in dissipative galaxy mergers with star formation

    SciTech Connect

    Stickley, Nathaniel R.; Canalizo, Gabriela

    2014-05-01

    In order to better understand stellar dynamics in merging systems, such as NGC 6240, we examine the evolution of central stellar velocity dispersion (σ{sub *}) in dissipative galaxy mergers using a suite of binary disk merger simulations that include feedback from stellar formation and active galactic nuclei (AGNs). We find that σ{sub *} undergoes the same general stages of evolution that were observed in our previous dissipationless simulations: coherent oscillation, then phase mixing, followed by dynamical equilibrium. We also find that measurements of σ{sub *} that are based only upon the youngest stars in simulations consistently yield lower values than measurements based upon the total stellar population. This finding appears to be consistent with the so-called 'σ{sub *} discrepancy', observed in real galaxies. We note that quasar-level AGN activity is much more likely to occur when σ{sub *} is near its equilibrium value rather than during periods of extreme σ{sub *}. Finally, we provide estimates of the scatter inherent in measuring σ{sub *} in ongoing mergers.

  4. Optical bias and hierarchical clustering. [Of galaxies

    SciTech Connect

    Bonometto, S.A.; Lucchin, F.; Matarrese, S.

    1987-12-01

    The present transfer of statistical results for biased theories of galaxy origin to a direct analysis of the celestial sphere's luminosity field notes that magnitude-limited galaxy catalogs are interpretable as sets of luminosity peaks bypassing suitable luminosity limits. The relationship between this view and that based on the Limber equation is discussed, and a tentative explanation is proposed for peculiarities arising in observed spatial correlations. Zwicky catalog data appear to confirm the validity of the concepts presented. 30 references.

  5. A simulation of the intracluster medium with feedback from cluster galaxies

    NASA Technical Reports Server (NTRS)

    Metzler, Christopher A.; Evrard, August E.

    1994-01-01

    We detail method and report first results from a three-dimensional hydrodynamical and N-body simulation of the formation and evolution of a Coma-sized cluster of galaxies, with the intent of studying the history of the hot, X-ray emitting intracluster medium. Cluster gas, galaxies, and dark matter are included in the model. The galaxies and dark matter fell gravitational forces; the cluster gas also undergoes hydrodynamical effects such as shock heating and PdV work. For the first time in three dimensions, we include modeling of ejection of processed gas from the simulated galaxies by winds, including heating and heavy element enrichment. For comparison, we employ a `pure infall' simulation using the same initial conditions but with no galaxies or winds. We employ an extreme ejection history for galactic feedback in order to define the boundary of likely models. As expected, feedback raises the entropy of the intracluster gas, preventing it from collapsing to densities as high as those attained in the infall model. The effect is more pronounced in subclusters formed at high redshift. The cluster with feedback is always less X-ray luminous, but experiences more rapid luminosity evolution, than the pure infall cluster. Even employing an extreme ejection model, the final gas temperature is only approximately 15% larger than in the infall model. The radial temperature profile is very nearly isothermal within 1.5 Mpc. The cluster galaxies in the feedback model have a velocity dispersion approximately 15% lower than the dark matter. This results in the true ratio of specific energies in galaxies to gas being less than one, beta(sub spec) approximately 0.7. The infall model predicts beta(sub spec) approximately 1.2. Large excursions in these values occur over time, following the complex dynamical history of the cluster. The morphology of the X-ray emission is little affected by feedback. The emission profiles of both clusters are well described by the standard beta

  6. THE IMACS CLUSTER BUILDING SURVEY. II. SPECTRAL EVOLUTION OF GALAXIES IN THE EPOCH OF CLUSTER ASSEMBLY

    SciTech Connect

    Dressler, Alan; Oemler, Augustus Jr.; Poggianti, Bianca M.; Vulcani, Benedetta; Gladders, Michael D.; Abramson, Louis

    2013-06-10

    The IMACS Cluster Building Survey (ICBS) provides spectra of {approx}2200 galaxies 0.31 < z < 0.54 in five rich clusters (R {approx}< 5 Mpc) and the field. Infalling, dynamically cold groups with tens of members account for approximately half of the supercluster population, contributing to a growth in cluster mass of {approx}100% by the present day. The ICBS spectra distinguish non-star-forming (PAS) and poststarburst (PSB) from star-forming galaxies-continuously star-forming (CSF) or starbursts (SBH or SBO), identified by anomalously strong H{delta} absorption or [O II] emission. For the infalling cluster groups and similar field groups, we find a correlation between PAS+PSB fraction and group mass, indicating substantial ''preprocessing'' through quenching mechanisms that can turn star-forming galaxies into passive galaxies without the unique environment of rich clusters. SBH + SBO starburst galaxies are common, and they maintain an approximately constant ratio (SBH+SBO)/CSF Almost-Equal-To 25% in all environments-from field, to groups, to rich clusters. Similarly, while PSB galaxies strongly favor denser environments, PSB/PAS Almost-Equal-To 10%-20% for all environments. This result, and their timescale {tau} {approx} 500 Myr, indicates that starbursts are not signatures of a quenching mechanism that produces the majority of passive galaxies. We suggest instead that starbursts and poststarbursts signal minor mergers and accretions, in star-forming and passive galaxies, respectively, and that the principal mechanisms for producing passive systems are (1) early major mergers, for elliptical galaxies, and (2) later, less violent processes-such as starvation and tidal stripping, for S0 galaxies.

  7. INTRINSIC ALIGNMENT OF CLUSTER GALAXIES: THE REDSHIFT EVOLUTION

    SciTech Connect

    Hao Jiangang; Kubo, Jeffrey M.; Feldmann, Robert; Annis, James; Johnston, David E.; Lin Huan; McKay, Timothy A.

    2011-10-10

    We present measurements of two types of cluster galaxy alignments based on a volume limited and highly pure ({>=}90%) sample of clusters from the GMBCG catalog derived from Data Release 7 of the Sloan Digital Sky Survey (SDSS DR7). We detect a clear brightest cluster galaxy (BCG) alignment (the alignment of major axis of the BCG toward the distribution of cluster satellite galaxies). We find that the BCG alignment signal becomes stronger as the redshift and BCG absolute magnitude decrease and becomes weaker as BCG stellar mass decreases. No dependence of the BCG alignment on cluster richness is found. We can detect a statistically significant ({>=}3{sigma}) satellite alignment (the alignment of the major axes of the cluster satellite galaxies toward the BCG) only when we use the isophotal fit position angles (P.A.s), and the satellite alignment depends on the apparent magnitudes rather than the absolute magnitudes of the BCGs. This suggests that the detected satellite alignment based on isophotal P.A.s from the SDSS pipeline is possibly due to the contamination from the diffuse light of nearby BCGs. We caution that this should not be simply interpreted as non-existence of the satellite alignment, but rather that we cannot detect them with our current photometric SDSS data. We perform our measurements on both SDSS r-band and i-band data, but do not observe a passband dependence of the alignments.

  8. Constructing mock catalogues for the REFLEX II galaxy cluster sample

    NASA Astrophysics Data System (ADS)

    Balaguera-Antolínez, A.; Sánchez, Ariel G.; Böhringer, H.; Collins, C.

    2012-09-01

    We describe the construction of a suite of galaxy cluster mock catalogues from N-body simulations, based on the properties of the new ROSAT-ESO Flux Limited X-Ray (REFLEX II) galaxy cluster catalogue. Our procedure is based on the measurements of the cluster abundance, and involves the calibration of the underlying scaling relation linking the mass of dark matter haloes to the cluster X-ray luminosity determined in the ROSAT energy band 0.1-2.4 keV. In order to reproduce the observed abundance in the luminosity range probed by the REFLEX II X-ray luminosity function [0.01 < LX/(1044 erg s-1 h-2) < 10], a mass-X-ray luminosity relation deviating from a simple power law is required. We discuss the dependence of the calibration of this scaling relation on the X-ray luminosity and the definition of halo masses and analyse the one- and two-point statistical properties of the mock catalogues. Our set of mock catalogues provides samples with self-calibrated scaling relations of galaxy clusters together with inherent properties of flux-limited surveys. This makes them a useful tool to explore different systematic effects and statistical methods involved in constraining both astrophysical and cosmological information from present and future galaxy cluster surveys.

  9. Galaxy clustering with photometric surveys using PDF redshift information

    NASA Astrophysics Data System (ADS)

    Asorey, J.; Carrasco Kind, M.; Sevilla-Noarbe, I.; Brunner, R. J.; Thaler, J.

    2016-06-01

    Photometric surveys produce large-area maps of the galaxy distribution, but with less accurate redshift information than is obtained from spectroscopic methods. Modern photometric redshift (photo-z) algorithms use galaxy magnitudes, or colours, that are obtained through multiband imaging to produce a probability density function (PDF) for each galaxy in the map. We used simulated data to study the effect of using different photo-z estimators to assign galaxies to redshift bins in order to compare their effects on angular clustering and galaxy bias measurements. We found that if we use the entire PDF, rather than a single-point (mean or mode) estimate, the deviations are less biased, especially when using narrow redshift bins. When the redshift bin widths are Δz = 0.1, the use of the entire PDF reduces the typical measurement bias from 5 per cent, when using single point estimates, to 3 per cent.

  10. Galaxy clustering with photometric surveys using PDF redshift information

    DOE PAGES

    Asorey, J.; Carrasco Kind, M.; Sevilla-Noarbe, I.; Brunner, R. J.; Thaler, J.

    2016-03-28

    Here, photometric surveys produce large-area maps of the galaxy distribution, but with less accurate redshift information than is obtained from spectroscopic methods. Modern photometric redshift (photo-z) algorithms use galaxy magnitudes, or colors, that are obtained through multi-band imaging to produce a probability density function (PDF) for each galaxy in the map. We used simulated data to study the effect of using different photo-z estimators to assign galaxies to redshift bins in order to compare their effects on angular clustering and galaxy bias measurements. We found that if we use the entire PDF, rather than a single-point (mean or mode) estimate, the deviations are less biased, especially when using narrow redshift bins. When the redshift bin widths aremore » $$\\Delta z=0.1$$, the use of the entire PDF reduces the typical measurement bias from 5%, when using single point estimates, to 3%.« less

  11. Clustering of very luminous infrared galaxies and their environment

    NASA Technical Reports Server (NTRS)

    Gao, YU

    1993-01-01

    The IRAS survey reveals a class of ultraluminous infrared (IR) galaxies (ULIRG's) with IR luminosities comparable to the bolometric luminosities of quasars. The nature, origin, and evolution of ULIRG's are attracting more and more attention recently. Since galaxy morphology is certainly a function of environment, morphological observations show that ULIRG's are interacting/merging galaxies, and some ULIRG's might be the dust-enshrouded quasars (S88) or giant ellipticals, the study of ULIRG's environment and large scale clustering effects should be worthwhile. ULIRG's and very luminous IR galaxies have been selected from the 2Jy IRAS redshift survey. Meanwhile, a catalog of IRAS groups of galaxies has been constructed using a percolation-like algorithm. Therefore, whether ULIRG's and/or VLIRG's have a group environment can be checked immediately. Other aspects of the survey are discussed.

  12. The Celestial Buffet: multiple populations and globular cluster formation in dwarf galaxies

    NASA Astrophysics Data System (ADS)

    Maxwell, Aaron J.; Wadsley, James; Couchman, H. M. P.; Sills, Alison

    2014-04-01

    We present a framework that explains the commonly observed variation in light element abundances in globular clusters. If globular clusters form in the centres of dwarf galaxies, they will be pumped on to larger orbits as star formation progresses. The potential well will only retain the moderate velocity asymptotic giant branch (AGB) ejecta, the expected source of enrichment, but not supernova ejecta. There is no need to increase the initial cluster mass, a requirement of self-enrichment scenarios, as all the stars within the dwarf can contribute. As the clusters move through the dwarf centre they sweep up a mix of AGB ejecta and in-falling pristine gas to form a second generation of stars. The specific mix will vary in time and is thus able to explain the spread in second generation abundances observed in different clusters. The globular clusters will survive to the present day or be stripped as part of the hierarchical merging process of larger galaxies. We illustrate how this process may operate using a high-resolution simulation of a dwarf galaxy at high redshift.

  13. Chandra Finds Most Distant X-ray Galaxy Cluster

    NASA Astrophysics Data System (ADS)

    2001-02-01

    The most distant X-ray cluster of galaxies yet has been found by astronomers using NASA’s Chandra X-ray Observatory. Approximately 10 billion light years from Earth, the cluster 3C294 is 40 percent farther than the next most distant X-ray galaxy cluster. The existence of such a distant galaxy cluster is important for understanding how the universe evolved. "Distant objects like 3C294 provide snapshots to how these galaxy clusters looked billions of years ago," said Andrew Fabian of the Institute of Astronomy, Cambridge, England and lead author of the paper accepted for publication in the Monthly Notices of Britain’s Royal Astronomical Society. "These latest results help us better understand what the universe was like when it was only 20 percent of its current age." Chandra’s image reveals an hourglass-shaped region of X-ray emission centered on the previously known central radio source. This X-ray emission extends outward from the central galaxy for at least 300,000 light years and shows that the known radio source is in the central galaxy of a massive cluster. Scientists have long suspected that distant radio-emitting galaxies like 3C294 are part of larger groups of galaxies known as "clusters." However, radio data provides astronomers with only a partial picture of these distant objects. Confirmation of the existence of clusters at great distances - and, hence, at early stages of the universe - requires information from other wavelengths. Optical observations can be used to pinpoint individual galaxies, but X-ray data are needed to detect the hot gas that fills the space within the cluster. "Galaxy clusters are the largest gravitationally bound structures in the universe," said Fabian. "We do not expect to find many massive objects, such as the 3C294 cluster, in early times because structure is thought to grow from small scales to large scales." The vast clouds of hot gas that envelope galaxies in clusters are thought to be heated by collapse toward the

  14. On the Diffuse Non-thermal Emission from Galaxy Clusters

    NASA Astrophysics Data System (ADS)

    Donnert, J.

    2011-07-01

    A number of galaxy clusters show complex radio emission not associable with optical counterparts. These objects are commonly classified as radio relics, radio mini halos and giant radio halos. The latter are diffuse Mpc-sized objects centred on the intra-cluster medium (ICM) and are commonly observed in merging clusters. In this work we investigate the formation of radio halos by means of astrophysical numerical simulations. Radio halos (RH) are observed in the GHz regime and show a complex broken power-law emission spectrum. This points to a population of relativistic electrons (CRe) interacting with the magnetic field present in the intra-cluster medium and emitting radio synchrotron radiation. Furthermore RH are transient phenomena, as inferred from the bimodal distribution of radio bright and radio quiet clusters found early on. Their scaling relations with thermal cluster observables breaks the self-similar model established from X-ray observations. In general, relativistic particles are injected strongly localised by shocks and galactic outflows into the ICM with a power-law spectrum. They are then subject to energy losses via inverse Compton, synchrotron, bremsstrahlung and Coulomb processes. This results in a limited lifetime of cosmic-ray electrons at synchrotron bright energies in the intra-cluster medium of ≈ 10^8 yrs. However, due to their interaction with the complex magnetic field of the ICM, it can be shown that cosmic-ray electrons have their effective diffusion speed limited to the Alven velocity in the thermal plasma. This poses a problem on the formation of radio halos, because it is unclear how the cluster-wide synchrotron bright population of CRe, necessary to make a radio halo, can be maintained under these conditions. Currently two competing models are heavily discussed to solve this problem. Hadronic (secondary) models consider the hadronic interaction of relativistic protons (CRp) with the thermal gas of the ICM. In contrast to CR

  15. Imaging the Sunyaev-Zeldovich Effect in Clusters of Galaxies

    NASA Technical Reports Server (NTRS)

    Joy, Marshall K.; Rose, M. Franklin (Technical Monitor)

    2000-01-01

    Sunyaev-Zeldovich Effect imaging capabilities have recently advanced to the point that high signal-to-noise measurements are available for numerous clusters of galaxies. We discuss the results of these S-Z observations, including determination of the pressure distribution of the hot intracluster medium and the cluster gas mass; total cluster masses can also be inferred via x-ray measurements of the gas temperature, resulting in a significant constraint on the cosmological mass density parameter. S-Z Effect measurements have been further combined with x-ray imaging data, including high resolution data recently obtained with the Chandra X-ray Observatory, to estimate cluster distances and to place independent constraints on the expansion rate of the universe. We also discuss future S-Z Effect survey instruments, which will provide powerful probes of cosmology by measuring the abundance of galaxy clusters at intermediate and high redshift.

  16. The Alignment effect of brightest cluster galaxies in the SDSS

    SciTech Connect

    Kim, R. S. J.; Annis, J.; Strauss, M. A.; Lupton, R. H.; Bahcall, N. A.; Gunn, J. E.; Kepner, J. V.; Postman, M.

    2001-10-01

    One of the most vital observational clues for unraveling the origin of Brightest Cluster Galaxies (BCG) is the observed alignment of the BCGs with their host cluster and its surroundings. We have examined the BCG-cluster alignment effect, using clusters of galaxies detected from the Sloan Digital Sky Survey (SDSS). We find that the BCGs are preferentially aligned with the principal axis of their hosts, to a much higher redshift (z >~ 0.3) than probed by previous studies (z <~ 0.1). The alignment effect strongly depends on the magnitude difference of the BCG and the second and third brightest cluster members: we find a strong alignment effect for the dominant BCGs, while less dominant BCGs do not show any departure from random alignment with respect to the cluster. We therefore claim that the alignment process originates from the same process that makes the BCG grow dominant, be it direct mergers in the early stage of cluster formation, or a later process that resembles the galactic cannibalism scenario. We do not find strong evidence for (or against) redshift evolution between 0clusters). However, we have developed a framework by which we can examine many more clusters in an automated fashion for the upcoming SDSS cluster catalogs, which will provide us with better statistics for systematic investigations of the alignment with redshift, richness and morphology of both the cluster and the BCG.

  17. MULTIWAVELENGTH OBSERVATIONS OF MASSIVE STELLAR CLUSTER CANDIDATES IN THE GALAXY

    SciTech Connect

    Richards, Emily E.; Lang, Cornelia C.; Trombley, Christine; Figer, Donald F. E-mail: er7@indiana.edu

    2012-09-01

    The Galaxy appears to be richer in young, massive stellar clusters than previously known, due to advances in infrared surveys that have uncovered deeply embedded regions of star formation. Young, massive clusters can significantly impact the surrounding interstellar medium (ISM) and hence radio observations can also be an important tracer of their activity. Several hundred cluster candidates are now known by examining survey data. Here, we report on multiwavelength observations of six of these candidates in the Galaxy. We carried out 4.9 and 8.5 GHz Very Large Array observations of the radio emission associated with these clusters to obtain the physical characteristics of the surrounding gas, including the Lyman continuum photon flux and ionized gas mass. Spitzer Infrared Array Camera observations were also made of these regions, and provide details on the stellar population as well as the dust continuum and polycyclic aromatic hydrocarbon emission. When compared to the known young, massive clusters in the Galaxy, the six cluster candidates have less powerful Lyman ionizing fluxes and ionize less of the H II mass in the surrounding ISM. Therefore, these cluster candidates appear to be more consistent with intermediate-mass clusters (10{sup 3}-10{sup 4} M{sub Sun }).

  18. Globular Cluster Populations in Four Early-Type Poststarburst Galaxies

    NASA Astrophysics Data System (ADS)

    Maybhate, Aparna; Goudfrooij, Paul; Schweizer, François; Puzia, Thomas H.; Carter, David

    2009-01-01

    We present a study of the globular cluster (GC) systems of four early-type poststarburst galaxies using deep g- and I-band images from the Advanced Camera for Surveys aboard the Hubble Space Telescope. All the galaxies feature shells distributed around their main bodies and are thus likely merger remnants. The color distribution of the GCs in all four galaxies shows a broad peak centered on g - I ≈ 1.4, while PGC 6240 and PGC 42871 show a significant number of GCs with g - I ≈ 1.0. The latter GCs are interpreted as being of age ~500 Myr and likely having been formed in the merger. The color of the redder peak is consistent with that expected for an old metal-poor population that is very commonly found around normal galaxies. However, all galaxies except PGC 10922 contain several GCs that are significantly brighter than the maximum luminosity expected of a single old metal-poor population. To test for multiple-age populations of overlapping g - I color, we model the luminosity functions of the GCs as composites of an old metal-poor subpopulation with a range of plausible specific frequencies and an intermediate-age subpopulation of solar metallicity. We find that three of the four sample galaxies show evidence for the presence of an intermediate-age (~1 Gyr) GC population, in addition to the old metal-poor GC population seen in normal early-type galaxies. None of the galaxies show a significant population of clusters consistent with an old, metal-rich red cluster population that is typically seen in early-type galaxies. The presence of a substantial number of intermediate-age clusters and the absence of old, metal-rich clusters indicate that the progenitor galaxies which formed the resulting shell galaxy were gas rich and did not host significant bulges. Late-type spirals seem to be the most plausible progenitors. These results lend credence to the "merger scenario" in which the red, metal-rich GCs observed in normal ellipticals are formed during a dissipative

  19. Galaxies at the Extremes: Ultra-diffuse Galaxies in the Virgo Cluster

    NASA Astrophysics Data System (ADS)

    Mihos, J. Christopher; Durrell, Patrick R.; Ferrarese, Laura; Feldmeier, John J.; Côté, Patrick; Peng, Eric W.; Harding, Paul; Liu, Chengze; Gwyn, Stephen; Cuillandre, Jean-Charles

    2015-08-01

    We report the discovery of three large ({R}29 ≳ 1‧) extremely low surface brightness (LSB; {μ }V,0≈ 27.0) galaxies identified using our deep, wide-field imaging of the Virgo Cluster from the Burrell Schmidt telescope. Complementary data from the Next Generation Virgo Cluster Survey do not resolve red giant branch stars in these objects down to i = 24, yielding a lower distance limit of 2.5 Mpc. At the Virgo distance, these objects have half-light radii 3-10 kpc and luminosities {L}{{V}} = 2-9 × 107 {L}⊙ . These galaxies are comparable in size but lower in surface brightness than the large ultradiffuse LSB galaxies recently identified in the Coma cluster, and are located well within Virgo’s virial radius; two are projected directly on the cluster core. One object appears to be a nucleated LSB in the process of being tidally stripped to form a new Virgo ultracompact dwarf galaxy. The others show no sign of tidal disruption, despite the fact that such objects should be most vulnerable to tidal destruction in the cluster environment. The relative proximity of Virgo makes these objects amenable to detailed studies of their structural properties and resolved stellar populations. They thus provide an important new window onto the connection between cluster environment and galaxy evolution at the extremes.

  20. DUST-OBSCURED STAR FORMATION IN INTERMEDIATE REDSHIFT GALAXY CLUSTERS

    SciTech Connect

    Finn, Rose A.; Desai, Vandana; Rudnick, Gregory; Poggianti, Bianca; Bell, Eric F.; Hinz, Joannah; Zaritsky, Dennis; Jablonka, Pascale; Milvang-Jensen, Bo; Moustakas, John; Rines, Kenneth E-mail: jmoustakas@ucsd.ed

    2010-09-01

    We present Spitzer MIPS 24 {mu}m observations of sixteen 0.4 < z < 0.8 galaxy clusters drawn from the ESO Distant Cluster Survey. This is the first large 24 {mu}m survey of clusters at intermediate redshift. The depth of our imaging corresponds to a total IR luminosity of 8 x 10{sup 10} L{sub sun}, just below the luminosity of luminous infrared galaxies (LIRGs), and 6{sup +1}{sub -1}% of M{sub V} < -19 cluster members show 24 {mu}m emission at or above this level. We compare with a large sample of coeval field galaxies and find that while the fraction of cluster LIRGs lies significantly below that of the field, the IR luminosities of the field and cluster galaxies are consistent. However, the stellar masses of the EDisCS LIRGs are systematically higher than those of the field LIRGs. A comparison with optical data reveals that {approx}80% of cluster LIRGs are blue and the remaining 20% lie on the red sequence. Of LIRGs with optical spectra, 88{sup +4} {sub -5}% show [O II] emission with EW([O II]) > 5 A, and {approx}75% exhibit optical signatures of dusty starbursts. On average, the fraction of cluster LIRGs increases with projected clustercentric radius but remains systematically lower than the field fraction over the area probed (<1.5x R {sub 200}). The amount of obscured star formation declines significantly over the 2.4 Gyr interval spanned by the EDisCS sample, and the rate of decline is the same for the cluster and field populations. Our results are consistent with an exponentially declining LIRG fraction, with the decline in the field delayed by {approx}1 Gyr relative to the clusters.

  1. H II Regions Within a Compact High Velocity Cloud. A Nearly Starless Dwarf Galaxy?

    NASA Astrophysics Data System (ADS)

    Bellazzini, M.; Magrini, L.; Mucciarelli, A.; Beccari, G.; Ibata, R.; Battaglia, G.; Martin, N.; Testa, V.; Fumana, M.; Marchetti, A.; Correnti, M.; Fraternali, F.

    2015-02-01

    Within the SECCO survey we identified a candidate stellar counterpart to the Ultra Compact High Velocity Cloud (UCHVC) HVC274.68+74.70-123 that was suggested by Adams et al. to be a possible mini halo within the Local Group of galaxies. The spectroscopic follow-up of the brightest sources within the candidate reveals the presence of two H ii regions whose radial velocity is compatible with a physical association with the UVHVC. The available data do not allow us to give a definite answer on the nature of the newly identified system. A few alternative hypotheses are discussed. However, the most likely possibility is that we have found a new faint dwarf galaxy residing in the Virgo cluster of galaxies, which we name SECCO 1. Independently of its actual distance, SECCO 1 displays a ratio of neutral hydrogen mass to V luminosity of {{M}H I}/{{L}V}≳ 20, by far the largest among local dwarfs. Hence, it appears to be a nearly starless galaxy and it may be an example of the missing links between normal dwarfs and the dark mini halos that are predicted to exist in large numbers according to the currently accepted cosmological model. Based on data acquired using the Large Binocular Telescope (LBT). The LBT is an international collaboration among institutions in the United States, Italy, and Germany. LBT Corporation partners are The University of Arizona on behalf of the Arizona university system; Istituto Nazionale di Astrofisica, Italy; LBT Beteiligungsgesellschaft, Germany, representing the Max-Planck Society, the Astrophysical Institute Potsdam, and Heidelberg University; The Ohio State University; and The Research Corporation, on behalf of The University of Notre Dame, University of Minnesota, and University of Virginia.

  2. DARK MATTER HALOS IN GALAXIES AND GLOBULAR CLUSTER POPULATIONS

    SciTech Connect

    Hudson, Michael J.; Harris, Gretchen L.; Harris, William E.

    2014-05-20

    We combine a new, comprehensive database for globular cluster populations in all types of galaxies with a new calibration of galaxy halo masses based entirely on weak lensing. Correlating these two sets of data, we find that the mass ratio η ≡ M {sub GCS}/M {sub h} (total mass in globular clusters, divided by halo mass) is essentially constant at (η) ∼ 4 × 10{sup –5}, strongly confirming earlier suggestions in the literature. Globular clusters are the only known stellar population that formed in essentially direct proportion to host galaxy halo mass. The intrinsic scatter in η appears to be at most 0.2 dex; we argue that some of this scatter is due to differing degrees of tidal stripping of the globular cluster systems between central and satellite galaxies. We suggest that this correlation can be understood if most globular clusters form at very early stages in galaxy evolution, largely avoiding the feedback processes that inhibited the bulk of field-star formation in their host galaxies. The actual mean value of η also suggests that about one-fourth of the initial gas mass present in protogalaxies collected into giant molecular clouds large enough to form massive, dense star clusters. Finally, our calibration of (η) indicates that the halo masses of the Milky Way and M31 are (1.2 ± 0.5) × 10{sup 12} M {sub ☉} and (3.9 ± 1.8) × 10{sup 12} M {sub ☉}, respectively.

  3. Small Stellar Systems in Antlia: Globular Clusters and Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    Bassino, L. P.; Smith Castelli, A. V.; Richtler, T.; Cellone, S.; Gómez, M.; Infante, L.; Aruta, C.; Dirsch, B.

    2009-05-01

    We present the combined results of two investigations of the Antlia galaxy cluster: (1) A study of the globular cluster (GC) systems around NGC 3258 and NGC 3268 (Bassino et al. 2008, MNRAS, 386, 1145), on the basis of V, I photometry perform