GBT25B-014

Dark galaxy or circumgalactic cloud(s)? A deep investigation

Abstract

Our deep GBT observations of the circumgalactic medium (CGM) of NGC891 at unprecedented sensitivity of 10^16 cm^-2 have serendipitously revealed HI at unexpectedly high column density and anomalous velocity at one pointing (J0223+4250) 100 kpc away from the disk of NGC891. There is no nearby optical counterpart down to mu_V=26.5 mag/arcsec^2. To pinpoint the location of the HI emitter and distinguish between a new ultra-diffuse galaxy or a dwarf galaxy with unusually low M*/MHI ratio or high-velocity cloud(s), we propose to obtain deep spectra at five pointings one GBT beam away from J0223+4250. This unique data set will represent the emission from small-scale and large-scale HI in the CGM of NGC891 and provide an alternative to look for gas-rich satellite galaxies that are otherwise missed by optical surveys.

Investigators

Name	Institution
Sanskriti Das *	Stanford University

* indicates the PI