A large population of recently-quenched red-sequence dwarf galaxies in the outskirts of the Coma Cluster

Monthly Notices of the Royal Astronomical Society (Impact Factor: 5.11). 03/2008; 386(1). DOI: 10.1111/j.1745-3933.2008.00469.x
Source: arXiv


We analyse the stellar populations of 75 red-sequence dwarf galaxies in the Coma cluster, based on high signal-to-noise ratio
spectroscopy from the 6.5-m MMT. The sample covers a luminosity range 3–4 mag below M★, in the cluster core and in a field centred 1° to the south-west. We find a strong dependence of the absorption-line strengths
with location in the cluster. Galaxies further from the cluster centre have stronger Balmer lines than inner-field galaxies
of the same luminosity. The magnesium lines are weaker at large radius, while the iron lines are not correlated with radius.
Converting the line strengths into estimates of stellar age, metallicity and abundance ratios, we find the gradients are driven
by variations in age (>6σ significance) and in the iron abundance Fe/H (∼2.7σ significance). The light element (Mg, C, N,
Ca) abundances are almost independent of radius. At radius of times the virial radius), dwarf galaxies have ages ∼3.8 Gyr on average, compared to ∼6 Gyr near the cluster centre. The outer
dwarfs are also ∼50 per cent more iron-enriched, at given luminosity. Our results confirm earlier indications that the ages
of red-sequence galaxies depend on location within clusters, and in Coma in particular. The very strong trends found here
suggest that dwarf galaxies are especially susceptible to environmental ‘quenching’, and/or that the south-west part of Coma
is particularly a clear example of recent quenching in an infalling subcluster.

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Available from: Terry Bridges, Dec 10, 2012
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