Astrophys. J., 798, L45 (2015/January-2)
Forty-seven Milky Way-sized, extremely diffuse galaxies in the Coma cluster.
VAN DOKKUM P.G., ABRAHAM R., MERRITT A., ZHANG J., GEHA M. and CONROY C.
Abstract (from CDS):
We report the discovery of 47 low surface brightness objects in deep images of a 3°x3° field centered on the Coma cluster, obtained with the Dragonfly Telephoto Array. The objects have central surface brightness µ(g, 0) ranging from 24-26 mag/arcsec2 and effective radii reff= 3''-10'', as measured from archival Canada-France-Hawaii Telescope images. From their spatial distribution we infer that most or all of the objects are galaxies in the Coma cluster. This relatively large distance is surprising as it implies that the galaxies are very large: with reff= 1.5-4.6 kpc their sizes are similar to those of L* galaxies even though their median stellar mass is only ∼6x107 M☉. The galaxies are relatively red and round, with < g - i > = 0.8 and < b/a > = 0.74. One of the 47 galaxies is fortuitously covered by a deep Hubble Space Telescope Advanced Camera for Surveys (ACS) observation. The ACS imaging shows a large spheroidal object with a central surface brightness µ475 = 25.8 mag/arcsec2, a Sérsic index n = 0.6, and an effective radius of 7'', corresponding to 3.4 kpc at the distance of Coma. The galaxy is not resolved into stars, consistent with expectations for a Coma cluster object. We speculate that these "ultra-diffuse galaxies" may have lost their gas supply at early times, possibly resulting in very high dark matter fractions.
galaxies: clusters: individual: Coma - galaxies: evolution - galaxies: structure
Table 1: [VAM2015] DFNN N=47.
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