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J/A+A/430/19         VRI photometry of Abell 3921 galaxies     (Ferrari+, 2005)
Dynamical state and star formation properties of the merging galaxy cluster
Abell 3921.
    Ferrari C., Benoist C., Maurogordato S., Cappi A., Slezak E.
   <Astron. Astrophys. 430, 19 (2005)>
   =2005A&A...430...19F
ADC_Keywords: Clusters, galaxy ; Redshifts ; Photometry, VRI ; Equivalent widths

Keywords: galaxies: clusters: general -
          galaxies: clusters: individual: Abell 3921 -
          galaxies: distances and redshifts - cosmology: observations

Abstract:
    We present the analysis and results of a new VRI photometric and
    spectroscopic survey of the central ∼1.8x1.2Mpc2 region of the
    galaxy cluster A3921 (z=0.094). We detect the presence of two dominant
    clumps of galaxies with a mass ratio of ∼5: a main cluster centred on
    the Brightest Cluster Galaxy (BCG) (A3921-A), and an NW sub-cluster
    (A3921-B) hosting the second brightest cluster galaxy. The distorted
    morphology of the two sub-clusters suggests that they are interacting,
    while the velocity distribution of 104 confirmed cluster members does
    not reveal strong signatures of merging.

Description:
    The optical observations of Abell 3921 were carried out using the Wide
    Field Imager (WFI) mounted at the Cassegrain focus of the MPG/ESO 2.2m
    telescope at La Silla observatory. The data, including photometric
    calibration images, were obtained between August 20th and 23rd, 2001.

    Positions, V, R, I-band magnitudes (AB magnitude system), radial
    velocity measurements, and equivalent widths of [OII]3727Å and
    Hδ lines of 239 objects in the central region of the galaxy
    cluster Abell 3921 are presented.

File Summary:

       FileName      Lrecl  Records   Explanations

ReadMe            80        .   This file
tablea.dat        86      239   Radial velocities and spectral lines for
                             239 galaxies in A3921


Byte-by-byte Description of file: tablea.dat

   Bytes Format Units   Label     Explanations

   1-  3  I3    ---     Seq       Identification number
   5-  6  I2    h       RAh       Right ascension (J2000.0)
   8-  9  I2    min     RAm       Right ascension (J2000.0)
  11- 15  F5.2  s       RAs       Right ascension (J2000.0)
      17  A1    ---     DE-       Declination sign (J2000.0)
  18- 19  I2    deg     DEd       Declination (J2000.0)
  21- 22  I2    arcmin  DEm       Declination (J2000.0)
  24- 28  F5.2  arcsec  DEs       Declination (J2000.0)
  30- 34  F5.2  ---     VmagAB    V-band magnitude (AB system)
  36- 40  F5.2  ---     RmagAB    R-band magnitude (AB system)
  42- 46  F5.2  ---     ImagAB    I-band magnitude (AB system)
  48- 55  F8.1  km/s    cz        ?=999999.9 Radial velocity
  57- 61  F5.1  km/s    e_cz      ?=999.9 Error on radial velocity
      62  A1    ---     n_cz      [*f] Note when no redshift value (1)
  64- 67  I4    ---     Run       Year of observation
      69  I1    ---     q_cz      Quality flag for redshift determination (2)
  71- 75  F5.1  0.1nm  EW([OII])  Equivalent width [OII] (3)
  77- 81  F5.1  0.1nm EW(Hdelta)  Equivalent width Hdelta (3)
  83- 86  A4    ---     MType     Type of galaxy (4)

Note (1): When no value of redshift, this column contains:
      * = star
      f = failed spectrum, no idea of the redshift
Note (2): We have classified the quality of the spectra in the following way:
      1 = good determination (R≥3),
      2 = uncertain determination,
      3 = very poor determination and failed spectra
Note (3): Equivalent-widths have been measured only for spectra with
    good redshift determination (quality flag = 1). Positive (negative)
    equivalent widths correspond to lines detected in absorption
    (emission).
Note (4): Galaxy types are coded as follows:
      k = Spectrum resembling a K-star spectrum
    k+a = Spectrum presenting an intermediate Hδ line in
          absorption, with no detectable [OII] line in emission
   k+a? = Candidate k+a galaxy
   e(a) = Emission-line galaxy, with strong Hδ absorption and
          measurable [OII] emission
   e(b) = Starburst galaxy with very strong [OII] emission
   e(c) = Spiral forming stars at a constant rate, with weak Balmer
          absorption and weak to moderate [OII] emission


Acknowledgements: Chiara Ferrari, Chiara.Ferrari(at)uibk.ac.at

(End)                                      Patricia Vannier [CDS]    13-Jan-2005