The First Hour of Extragalactic Data of the Sloan Digital Sky Survey Spectroscopic Commissioning: The Coma Cluster

On 26 May 1999, one of the Sloan Digital Sky Survey (SDSS) fiber-fedspectrographs saw astronomical first light. This was followed by the firstspectroscopic commissioning run during the dark period of June 1999. We presenthere the first hour of extra-galactic spectroscopy taken during these earlycommissioning stages: an observation of the Coma cluster of galaxies. Our datasamples the Southern part of this cluster, out to a radius of 1.5degrees andthus fully covers the NGC 4839 group. We outline in this paper the maincharacteristics of the SDSS spectroscopic systems and provide redshifts andspectral classifications for 196 Coma galaxies, of which 45 redshifts are new.For the 151 galaxies in common with the literature, we find excellent agreementbetween our redshift determinations and the published values. As part of ouranalysis, we have investigated four different spectral classificationalgorithms: spectral line strengths, a principal component decomposition, awavelet analysis and the fitting of spectral synthesis models to the data. Wefind that a significant fraction (25%) of our observed Coma galaxies show signsof recent star-formation activity and that the velocity dispersion of theseactive galaxies (emission-line and post-starburst galaxies) is 30% larger thanthe absorption-line galaxies. We also find no active galaxies within thecentral (projected) 200 h-1 Kpc of the cluster. The spatial distribution of ourComa active galaxies is consistent with that found at higher redshift for theCNOC1 cluster survey. Beyond the core region, the fraction of bright activegalaxies appears to rise slowly out to the virial radius and are randomlydistributed within the cluster with no apparent correlation with the potentialmerger of the NGC 4839 group. [ABRIDGED]Comment: Accepted in AJ, 65 pages, 20 figures, 5 table