arXiv:0906.0358 [ps, pdf, other]
    Title: How the extinction of extragalactic background light
    affects surface photometry of galaxies, groups and clusters
    Authors: E. Zackrisson, G. Micheva, G. Ostlin
    Comments: 15 pages, 10 figures, accepted for publication in MNRAS
    Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

    The faint regions of galaxies, groups and clusters hold important
    clues about how these objects formed, and surface photometry at
    optical and near-infrared wavelengths represents a powerful tool
    for studying such structures. Here, we identify a hitherto
    unrecognized problem with this technique, related to how the night
    sky flux is typically measured and subtracted from astronomical
    images. While most of the sky flux comes from regions between the
    observer and the target object, a small fraction - the
    extragalactic background light (EBL) - comes from behind. We argue
    that since this part of the sky flux can be subject to extinction
    by dust present in the galaxy/group/cluster studied, standard
    reduction procedures may lead to a systematic oversubtraction of
    the EBL. Even very small amounts of extinction can lead to
    spurious features in radial surface surface brightness profiles
    and colour maps of extended objects. We assess the likely impact
    of this effect on a number of topics in extragalactic astronomy
    where very deep surface photometry is currently attempted,
    including studies of stellar halos, starburst host galaxies, disc
    truncations and diffuse intragroup/intracluster light. We argue
    that EBL extinction may provide at least a partial explanation for
    the anomalously red colours reported for the halos of disc
    galaxies and the hosts of local starburst galaxies. EBL extinction
    effects also mimic truncations in discs with unusually high dust
    opacities, but are unlikely to be the cause of such features in
    general. Failure to account for EBL extinction can also give rise
    to a non-negligible underestimate of intragroup and intracluster
    light at the faintest surface brightness levels currently
    probed. (Abridged)


 arXiv:0906.0424 [ps, pdf, other]
    Title: Reconstructing galaxy fundamental distributions and scaling
    relations from photometric redshift surveys. Applications to the
    SDSS early-type sample
    Authors: Graziano Rossi, Ravi K. Sheth, Changbom Park
    Comments: 12 pages, 12 figures, submitted to MNRAS
    Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO);
    Galaxy Astrophysics (astro-ph.GA)

    Noisy distance estimates associated with photometric rather than
    spectroscopic redshifts lead to a mis-estimate of the
    luminosities, and produce a correlated mis-estimate of the
    sizes. We consider a sample of early-type galaxies from the SDSS
    DR6 for which both spectroscopic and photometric information is
    available, and apply the generalization of the V_max method to
    correct for these biases. We show that our technique recovers the
    true redshift, magnitude and size distributions, as well as the
    true size-luminosity relation. We find that using only 10% of the
    spectroscopic information randomly spaced in our catalog is
    sufficient for the reconstructions to be accurate within about 3%,
    when the photometric redshift error is dz = 0.038. We then address
    the problem of extending our method to deep redshift catalogs,
    where only photometric information is available. In addition to
    the specific applications outlined here, our technique impacts a
    broader range of studies, when at least one distance-dependent
    quantity is involved. It is particularly relevant for the next
    generation of surveys, some of which will only have photometric
    information.


1]  arXiv:0906.0573 [ps, pdf, other]
    Title: Moderate Steepening of Galaxy Cluster Dark Matter Profiles
    by Baryonic Pinching
    Authors: Jesper Sommer-Larsen (1,2), Marceau Limousin (3,1) ((1)
    Dark Cosmology Centre, NBI, Copenhagen;(2) Excellence Cluster
    Universe, TUM, Munich; (3) Laboratoire d'Astrophysique, Marseille,
    France)
    Comments: 11 Pages, 8 Figures, submitted to MNRAS, printing in
    colour recommended
    Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

    To assess the effect of baryonic ``pinching'' of galaxy cluster
    dark matter (DM) haloes, cosmological (LCDM) TreeSPH simulations
    of the formation and evolution of two galaxy clusters have been
    performed, with and without baryons included.
    The simulations with baryons invoke star formation, chemical
    evolution with non-instantaneous recycling, metallicity dependent
    radiative cooling, strong star-burst, driven galactic super-winds
    and the effects of a meta-galactic UV field, including simplified
    radiative transfer. The two clusters have T_X~3 and 6 keV,
    respectively, and, at z~0, both host a prominent, central cD
    galaxy.
    Comparing the simulations without and with baryons, it is found
    for the latter that the inner DM density profiles, r<50-100 kpc,
    steepen considerably: Delta(alpha)~0.5-0.6, where -alpha is the
    logarithmic DM density gradient. This is mainly due to the central
    stellar cDs becoming very massive, as a consequence of the onset
    of late time cooling flows and related star formation. Once these
    spurious cooling flows have been corrected for, and the cluster
    gravitational potentials dynamically adjusted, much smaller
    pinching effects are found: Delta(alpha)~0.1. Including the
    effects of baryonic pinching, central slopes of alpha~1.0 and 1.2
    are found for the DM in the two clusters, interestingly close to
    recent observational findings.
    For the simulations with baryons, the inner density profile of
    DM+ICM gas combined is found to be only very marginally steeper
    than that of the DM, Delta(alpha)<0.05. However, the total matter
    inner density profiles are found to be Delta(alpha)~0.5 steeper
    than the inner profiles in the dark matter only simulations.


8]  arXiv:0906.0585 [ps, pdf, other]
    Title: The velocity function in the local environment from LCDM
    and LWDM constrained simulations
    Authors: J. Zavala, Y. P. Jing, A. Faltenbacher, G. Yepes,
    Y. Hoffman, S. Gottlober, B. Catinella
    Comments: 24 pages, 14 figures, 1 table, accepted for publication
    in ApJ
    Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

    Using constrained simulations of the local Universe for generic
    cold dark matter and for 1keV warm dark matter, we investigate the
    difference in the abundance of dark matter halos in the local
    environment. We find that the mass function within 20 Mpc/h of the
    Local Group is ~2 times larger than the universal mass function in
    the 10^9-10^13 M_odot/h mass range. Imposing the field of view of
    the on-going HI blind survey ALFALFA in our simulations, we
    predict that the velocity function in the Virgo-direction region
    exceeds the universal velocity function by a factor of
    3. Furthermore, employing a scheme to translate the halo velocity
    function into a galaxy velocity function, we compare the
    simulation results with a sample of galaxies from the early
    catalog release of ALFALFA. We find that our simulations are able
    to reproduce the velocity function in the 80-300 km/s velocity
    range, having a value ~10 times larger than the universal velocity
    function in the Virgo-direction region. In the low velocity
    regime, 35-80 km/s, the warm dark matter simulation reproduces the
    observed flattening of the velocity function. On the contrary, the
    simulation with cold dark matter predicts a steep rise in the
    velocity function towards lower velocities; for V_max=35 km/s, it
    forecasts ~10 times more sources than the ones observed. If
    confirmed by the complete ALFALFA survey, our results indicate a
    potential problem for the cold dark matter paradigm or for the
    conventional 


arXiv:0906.0803 [ps, pdf, other]
    Title: Galaxy clusters identified from the SDSS DR6 and their
    properties
    Authors: Z. L. Wen, J. L. Han, F. S. Liu
    Comments: 18 pages, 27 figures, 2 tables; accepted for publication
    in ApJS
    Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

    Clusters of galaxies in most previous catalogs have redshifts
    z<0.3. Using the photometric redshifts of galaxies from the Sloan
    Digital Sky Survey Data Release 6 (SDSS DR6), we identify 39,716
    clusters in the redshift range 0.05< z <0.6 with more than 8
    luminous (M_r<-21) member galaxies. Cluster redshifts are
    estimated accurately with an uncertainty less than 0.022. The
    contamination rate of member galaxies is found to be roughly 20%,
    and the completeness of member galaxy detection reaches to
    ~90%. Monte Carlo simulations show that the cluster detection rate
    is more than 90% for massive (M_{200}>2\times10^{14} M_{\odot})
    clusters of z<0.42. The false detection rate is ~5%. We obtain the
    richness, the summed luminosity and the gross galaxy number within
    the determined radius for identified clusters. They are tightly
    related to the X-ray luminosity and temperature of
    clusters. Cluster mass is related to the richness and summed
    luminosity with M_{200}\propto R^{1.90\pm0.04} and M_{200}\propto
    L_r^{1.64\pm0.03}, respectively. In addition, 790 new candidates
    of X-ray clusters are found by cross-identification of our
    clusters with the source list of the ROSAT X-ray survey.
[