科研之友
微信
新浪微博
Facebook
分享链接
摘要
We report the discovery of 854 ultra-diffuse galaxies (UDGs) in the Coma cluster using deep R band images, with partial B, i, and H alpha band coverage, obtained with the Subaru telescope. Many of them (332) are Milky Way (MW) sized with very large effective radii of r(e) > 1.5 kpc. This study was motivated by the recent discovery of 47 UDGs by Dokkum et al.; our discovery suggests > 1000 UDGs after accounting for the smaller Subaru field (4.1 degree(2); about one-half of Dragonfly). The new Subaru UDGs show a distribution concentrated around the cluster center, strongly suggesting that the great majority are (likely longtime) cluster members. They are a passively evolving population, lying along the red sequence in the color-magnitude diagram with no signature of H alpha emission. Star formation was, therefore, quenched in the past. They have exponential light profiles, effective radii r(e) similar to 800 pc-5 kpc, effective surface brightnesses mu(e) (R) = 25-28 mag arcsec(-2), and stellar masses similar to 1 x 10(7)M(circle dot)-5 x 10(8)M(circle dot). There is also a population of nucleated UDGs. Some MW-sized UDGs appear closer to the cluster center than previously reported; their survival in the strong tidal field, despite their large sizes, possibly indicates a large dark matter fraction protecting the diffuse stellar component. The indicated baryon fraction less than or similar to 1% is less than the cosmic average, and thus the gas must have been removed (from the possibly massive dark halo). The UDG population is elevated in the Coma cluster compared to the field, indicating that the gas removal mechanism is related primarily to the cluster environment.
- 出版日期2015-7-1
- 单位中国科学院国家天文台
