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J/ApJ/470/724       Abell 576 galaxies magnitude and velocities (Mohr+ 1996)
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An optical and X-ray study of Abell 576, a galaxy cluster with a cold core.
     Mohr J.J., Geller M.J., Fabricant D.G., Wegner G., Thorstensen J.,
     Richstone D.O.
    <Astrophys. J. 470, 724 (1996)>
    =1996ApJ...470..724M      (SIMBAD/NED BibCode)
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ADC_Keywords: Clusters, galaxy ; Magnitudes ; Spectroscopy
Keywords: galaxies: clusters: individual (A576) -
          galaxies: distances and redshifts -
          galaxies: luminosity function, mass function - galaxies: photometry -
          X-rays: galaxies

Abstract:
    We analyse the galaxy population and dynamics of the galaxy cluster
    A576; the observational constraints include 281 redshifts (230 new),
    R-band CCD galaxy photometry over a 2h^-1^Mpcx2h^-1^Mpc region
    centered on the cluster, an Einstein IPC X-ray image, and an Einstein
    MPC X-ray spectrum. We focus on an 86% complete magnitude-limited
    sample (R_23.5_<17) of 169 cluster galaxies. The cluster galaxies with
    emission lines in their spectra have a larger velocity dispersion and
    are significantly less clustered on this 2h^-1^Mpc scale than galaxies
    without emission lines. We show that excluding the emission-line
    galaxies from the cluster sample decreases the velocity dispersion by
    18% and the virial mass estimate by a factor of 2. The central cluster
    region contains a non-emission galaxy population and an intracluster
    medium which is significantly cooler
    ({sigma}_core_=387^+250^_-105_km/s and T_X_=1.6-0.3/+0.4keV at 90%
    confidence) than the global populations ({sigma}=977^+124^_-96_km/s
    for the non-emission population and T_X_>4keV at 90% confidence).
    Because (1) the low-dispersion galaxy population is no more luminous
    than the global population and (2) the evidence for a cooling flow is
    weak, we suggest that the core of A576 may contain the remnants of a
    lower mass subcluster. We examine the cluster mass, baryon fraction,
    and luminosity function. The cluster virial mass varies significantly
    depending on the galaxy sample used. Consistency between the
    hydrostatic and virial estimators can be achieved if (1) the gas
    temperature at r~1h^-1^Mpc is T_X_~8keV (the best-fit value) and
    (2) several velocity outliers are excluded from the virial calculation.
    Although the best-fit Schechter function parameters and the ratio of
    galaxy to gas mass in A576 are typical of other clusters, the baryon
    fraction is relatively low. Using the consistent cluster binding mass,
    we show that the gas mass fraction is ~3h^-3/2^% and the baryon
    fraction is ~4%.

File Summary:
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  FileName        Lrecl  Records   Explanations
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ReadMe             80        .   This file
table1.dat         53      281   Galaxy velocities and photometry
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Byte-by-byte Description of file: table1.dat
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   Bytes Format Units   Label     Explanations
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       1  I1    h       RAh       [7] Right ascension (1950)
   3-  4  I2    min     RAm       Right ascension (1950)
   6- 10  F5.2  s       RAs       Right ascension (1950)
      12  A1    ---     DE-       Declination sign
  13- 14  I2    deg     DEd       [55/56] Declination (1950)
  16- 17  I2    arcmin  DEm       Declination (1950)
  19- 22  F4.1  arcsec  DEs       Declination (1950)
  24- 28  F5.2  mag     R23.5     Isophotal R=23.5mag/arcsec^2^  magnitude
      29  A1    ---   n_R23.5     Note on R23.5 (1)
  31- 35  F5.3  mag   e_R23.5     rms uncertainty on R23.5
  37- 41  I5    km/s    Vel       Line-of-sight velocity
      42  A1    ---   n_Vel       Note on velocity (1)
  44- 46  I3    km/s  e_Vel       rms uncertainty on Vel
      48  A1    ---     Type      [NE] E: emission; N: non-emission
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Note (1): #: POSS digitized scan photometry
          +: Hintzen et al., 1982AJ.....87.1656H
          *: Marzke & Huchra 1996, in prep.
          x: Hill et al., 1980ApJ...242L..69H
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History: Prepared via OCR at CDS.
  * 30-Sep-1998: 4 OCR errors detected by H. Andernach and corrected
    (heinz@astro.ugto.mx)
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(End)                         James Marcout,   Patricia Bauer [CDS]  30-Sep-1997