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J/MNRAS/323/839      HST photometry of A2218 early-type galaxies  (Smail+, 2001)
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A photometric study of the ages and metallicities of
 early-type galaxies in A 2218.
    Smail I., Kuntschner H., Kodama T., Smith G.P., Packham C., Fruchter A.S.,
    Hook R.N.
      <Mon. Not. R. Astron. Soc. 323, 839 (2001)>
      =2001MNRAS.323..839S      (SIMBAD/NED BibCode)
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ADC_Keywords: Clusters, galaxy ; Galaxies, photometry
Mission_Name: HST
Keywords: galaxies: clusters: individual: A2218 -
          galaxies: elliptical and lenticular, cD - galaxies: evolution -
          galaxies: stellar content - infrared: galaxies

Abstract:
    We present deep optical and near-infrared imaging of the rich cluster
    A2218 at z=0.17. Our optical imaging comes from new multicolour Hubble
    Space Telescope WFPC2 observations in the F450W (B_450_), F606W
    (V_606_) and F814W (I_814_) passbands. These observations are
    complemented by deep near-infrared, Ks-band imaging from the new
    INGRID imager on the 4.2-m William Herschel Telescope. This
    combination provides unique high-precision multicolour
    optical-infrared photometry and morphological information for a large
    sample of galaxies in the core of this rich cluster, at a look-back
    time of ~3Gyr. We analyse the (B_450_-I_814_), (V_606_-I_814_) and
    (I_814_-K_s_) colours of galaxies spanning a range of a factor of 100
    in K-band luminosity in this region, and compare them with grids of
    stellar population models. We find that the locus of the colours of
    the stellar populations in the luminous (>~LK*) early-type galaxies,
    both ellipticals and S0s, traces a sequence of varying metallicity at
    a single age. At fainter luminosities (<~0.1LK*), this sequence is
    extended to lower metallicities by the morphologically classified
    ellipticals. However, the faintest S0s exhibit very different
    behaviour, showing a wide range of colours, including a large fraction
    (30 per cent) with relatively blue colours that appear to have younger
    luminosity-weighted ages for their stellar populations; 2-5Gyr. We
    show that the proportion of these young S0s in the cluster population
    is consistent with the observed decrease in the S0 population seen in
    distant clusters, when interpreted within the framework of a two-step
    spectroscopic and morphological transformation of accreted spiral
    field galaxies into cluster S0s.

File Summary:
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 FileName      Lrecl  Records   Explanations
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ReadMe            80        .   This file
table1.dat       100       81   Galaxy catalogue
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See also:
     B/hst : HST Archived Exposures Catalog (STScI, 2001)

Byte-by-byte Description of file: table1.dat
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   Bytes Format Units   Label  Explanations
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   1-  4  I4    ---     ID     Identification number
   6- 10  A5    ---     Name   Other identifications (1)
  12- 13  I2    h       RAh    Right ascension (J2000)
  15- 16  I2    min     RAm    Right ascension (J2000)
  18- 22  F5.2  s       RAs    Right ascension (J2000)
      24  A1    ---     DE-    Declination sign (J2000)
  25- 26  I2    deg     DEd    Declination sign (J2000)
  28- 29  I2    arcmin  DEm    Declination (J2000)
  31- 34  F4.1  arcsec  DEs    Declination (J2000)
  36- 40  F5.2  mag     Kmag   Total K_s_ magnitude
  42- 45  F4.2  mag   e_Kmag   rms uncertainty on Kmag
      47  A1    ---   l_B-I    Limit flag on B-I (2)
  48- 51  F4.2  mag     B-I    B_450_-I_814_ colour index
  53- 56  F4.2  mag   e_B-I    ? rms uncertainty on B-I
  58- 61  F4.2  mag     V-I    V_606_-I_814_ colour index
  63- 66  F4.2  mag   e_V-I    rms uncertainty on V-I
  68- 71  F4.2  mag     I-K    I_814_-K_s_ colour index
  73- 76  F4.2  mag   e_I-K    rms uncertainty on I-K
  78- 81  F4.2  arcsec  r      Radius (r_hl_)
  83- 87  A5    ---     MType  Morphological type (?: unclassifiable morphology)
  89- 94  F6.4  ---     z      ? Redshift
  96-100  A5    ---     Note   Notes (3)
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Note (1): Other identifications:
           Z: Ziegler, Bower, Smail, Davies & Lee (2001, MNRAS, submitted)
               ZNNNN = [ZBS2001] NNNN in Simbad
           B: Butcher et al. (1983ApJS...52..183B)
               BNNN = BOW ACO 2218 CCNNN in Simbad
           L: Le Borgne et al., (1992A&AS...95...87L)
               LNNN = LPS NNN in Simbad
           K: Kristian et al., (1978ApJ...221..383K)
               KN = [KSW78], ACO 2218 GN in Simbad
Note (2): When upper limits for B-I index, the error is 2{sigma}
Note (3): Ziegler, Bower, Smail, Davies & Lee et al. (2001, MNRAS, submitted)
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History:
    From electronic version of the journal

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(End)                                        Patricia Bauer [CDS]    16-Oct-2001