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The early-type galaxy population in Abell 2218
We present high signal-to-noise, moderate-resolution spectroscopy of 48early-type members of the rich cluster Abell 2218 at z=0.18, taken withthe LDSS2 spectrograph on the 4.2-m William Herschel Telescope. Thissample both is larger and spans a wider galaxy luminosity range, down toMB*+1, than previous studies. In addition to the relatively large sizeof the sample, we have detailed morphological information from archivalHubble Space Telescope imaging for 20 of the galaxies. We combine themorphological, photometric, kinematic and line-strength information tocompare A2218 with similar samples drawn from local clusters and toidentify evolutionary changes between the samples which have occurredover the last ~3Gyr. The overall picture is one of little or noevolution in nearly all of the galaxy parameters. Zero-point offsets inthe Faber-Jackson, Mgb-σ and Fundamental Planerelations are all consistent with passively evolving stellarpopulations. The slopes of these relations have not changedsignificantly in the 3Gyr between A2218 and today. We do however find asignificant spread in the estimated luminosity-weighted ages of thestellar populations in the galaxies, based on line diagnostic diagrams.This age spread is seen in both the discy early-type galaxies (S0) andalso the ellipticals. We observe both ellipticals with a strongcontribution from a young stellar population and lenticulars dominatedby old stellar populations. On average, we find no evidence forsystematic differences between the populations of ellipticals andlenticulars. In both cases there appears to be little evidence fordifferences between the stellar populations of the two samples. Thispoints to a common formation epoch for the bulk of the stars in most ofthe early-type galaxies in A2218. This result can be reconciled with theclaims of rapid morphological evolution in distant clusters if thesuggested transformation from spirals to lenticulars does not involvesignificant new star formation.
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
| Etude pour chaque champ de l'absorption et de la repartition des vitesses radiales EN fonction de la distance.
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| La mesure des vitesses radiales au prisme objectif. VII - 2e liste de vitesses radiales déterminées au prisme objectif à vision directe
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| Mesures de vitesses radiales au spectrographe C de l'Observatoire de Haute Provence
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| Discussion de la mesure des vitesses radiales au prisme objectif
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Observation and Astrometry data
| Constellation: | Petit Renard |
| Right ascension: | 19h32m56.60s |
| Declination: | +21°27'22.7" |
| Apparent magnitude: | 7.851 |
| Proper motion RA: | 0.3 |
| Proper motion Dec: | -1.9 |
| B-T magnitude: | 9.378 |
| V-T magnitude: | 7.978 |
Catalogs and designations:
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