Ultraviolet and X-ray Properties of Coma's Ultra-Diffuse Galaxies

Abstract

Many ultra-diffuse galaxies (UDGs) have been discovered in the Coma cluster, and there is evidence that some, notably Dragonfly 44, have Milky Way-like dynamical masses despite dwarf-like stellar masses. We used X-ray, UV, and optical data to investigate the star formation and nuclear activity in the Coma UDGs, and we obtained deep UV and X-ray data (Swift and XMM-Newton) for Dragonfly 44 to search for low-level star formation, hot circumgalactic gas, and the integrated emission from X-ray binaries. Among the Coma UDGs, we find UV luminosities consistent with quiescence but NUV$-r$ colors indicating star formation in the past Gyr. This indicates that the UDGs were recently quenched. The $r$-band luminosity declines with projected distance from the Coma core. The Dragonfly 44 UV luminosity is also consistent with quiescence, with SFR$<6\times 10^{-4}{M}_{\odot }$ yr${}^{-1}$, and no X-rays are detected down to a sensitivity of $10^{38}$ erg s${}^{-1}$. This rules out a hot corona with a $M>10^8{M}_{\odot }$ within the virial radius, which would normally be expected for a dynamically massive galaxy. The absence of bright, low mass X-ray binaries is consistent with the expectation from the galaxy total stellar mass, but it is unlikely if most low-mass X-ray binaries form in globular clusters, as Dragonfly 44 has a very large population. Based on the UV and X-ray analysis, the Coma UDGs are consistent with quenched dwarf galaxies, although we cannot rule out a dynamically massive population.

12 pages, 5 tables, 7 figures. Accepted for publication in MNRAS

References in corpus (7)

• Some Aspects of Measurement Error in Linear Regression of Astronomical Data
• Forty-Seven Milky Way-Sized, Extremely Diffuse Galaxies in the Coma Cluster
• A High Stellar Velocity Dispersion and ~100 Globular Clusters for the Ultra Diffuse Galaxy Dragonfly 44
• Constraining the Milky Way's Hot Gas Halo with OVII and OVII Emission Lines
• Extensive Globular Cluster Systems Associated with Ultra Diffuse Galaxies in the Coma Cluster
• Constraining the dark matter halo mass of isolated low-surface-brightness galaxies
• Sub-Eddington super-massive black hole activity in Fornax early type galaxies

Cited by in corpus (4)

• Implications for Galaxy Formation Models from Observations of Globular Clusters around Ultra-Diffuse Galaxies
• Still at Odds with Conventional Galaxy Evolution: The Star Formation History of Ultra-Diffuse Galaxy Dragonfly 44
• The Archetypal Ultra-Diffuse Galaxy, Dragonfly 44, is not a Dark Milky Way
• Probing ultra-diffuse galaxies out to the virial radius of the Coma cluster with XMM-Newton