We present spectra of 5 ultra-diffuse galaxies (UDGs) in the vicinity of the Coma Cluster obtained with the Multi-Object Double Spectrograph on the Large Binocular Telescope. We confirm 4 of these as members of the cluster, quintupling the number of spectroscopically confirmed systems. Like the previously confirmed large (projected half light radius > 4.6 kpc) UDG, DF44, the systems we targeted all have projected half light radii >2.9 kpc. As such, we spectroscopically confirm a population of physically large UDGs in the Coma cluster. The remaining UDG is located in the field, about 45 Mpc behind the cluster. We observe Balmer and Ca II H \& K absorption lines in all of our UDG spectra. By comparing the stacked UDG spectrum against stellar population synthesis models, we conclude that, on average, these UDGs are composed of metal-poor stars ([Fe/H] ≲−1.5). We also discover the first UDG with [OII] and [OIII] emission lines within a clustered environment, demonstrating that not all cluster UDGs are devoid of gas and sources of ionizing radiation.
@article{arxiv.1703.02042,
title = {Spectroscopy of Ultra-diffuse Galaxies in the Coma Cluster},
author = {Jennifer Kadowaki and Dennis Zaritsky and R. L. Donnerstein},
journal= {arXiv preprint arXiv:1703.02042},
year = {2017}
}