Five Gas-rich Ultrafaint Dwarf Galaxy Candidates Discovered in WIYN Imaging of ALFALFA Sources

William Janesh,Martha P Haynes,Steven Janowiecki,John M Cannon,Katherine L Rhode,Elizabeth A K Adams,John J Salzer,Riccardo Giovanelli

doi:10.3847/1538-3881/ab12d3

Abstract

Abstract We present results from the analysis of WIYN pODI imaging of 23 ultracompact high-velocity clouds (UCHVCs), which were identified in the ALFALFA H i survey as possible dwarf galaxies in or near the Local Group. To search for a resolved stellar population associated with the H i gas in these objects, we carried out a series of steps designed to identify stellar overdensities in our optical images. We identify five objects that are likely stellar counterparts to the UCHVCs, at distances of ∼350 kpc to ∼1.6 Mpc. Two of the counterparts were already described in Janesh et al.; the estimated distance and detection significance for one of them changed in the final analysis of the full pODI data set. At their estimated distances, the detected objects have H i masses from 2 × 104 to 3 × 106 M ⊙, M V from −1.4 to −7.1, and stellar masses from 4 × 102 to 4 × 105 M ⊙. None of the objects shows evidence of a young stellar population. Their properties would make the UCHVCs some of the most extreme objects in and around the Local Group, comparable to ultrafaint dwarf galaxies in their stellar populations, but with significant gas content. Such objects probe the extreme end of the galaxy mass function and provide a test bed for theories regarding the baryonic feedback processes that impact star formation and galaxy evolution in this low-mass regime.

Highlights

We have undertaken a campaign to obtain deep, wide-field optical imaging of specific sources detected by the ALFALFA blind neutral hydrogen survey (Giovanelli et al 2005; Haynes et al 2011) called ultracompact high-velocity clouds, or UCHVCs (Giovanelli et al 2010; Adams et al 2013)
We have been observing a subsample of the UCHVCs with the WIYN 3.5 m telescope9 in order to search for detectable stellar populations and investigate the exact nature of these objects
Ξ, of the overdensities we find by performing a Monte-Carlo-style test, generating 25,000 random, uniformly spatially distributed sets of points, with the number of points set equal to the number of stars that are selected by the color–magnitude diagrams (CMDs) filter

Summary

Introduction

We have undertaken a campaign to obtain deep, wide-field optical imaging of specific sources detected by the ALFALFA blind neutral hydrogen survey (Giovanelli et al 2005; Haynes et al 2011) called ultracompact high-velocity clouds, or UCHVCs (Giovanelli et al 2010; Adams et al 2013). Its H I-to-stellar mass ratio was large, but with a wide possible range (between 9 and 144, depending on how the optical magnitude was estimated) Though this object has no clearly associated neighbors, the most likely neighbor is the faint irregular galaxy UGC 9128, which has a distance of 2.3 Mpc (Tully et al 2013) and is

The Sample of UCHVCs Observed with WIYN pODI

Results

Corner and Edge Overdensities

Comparison to Known Galaxies

Incidence Rate of Stellar Counterparts

Implications for Galaxy Formation Scenarios