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

Abstract

We present results from the analysis of WIYN pODI imaging of 23 ultra-compact high-velocity clouds (UCHVCs), which were identified in the ALFALFA Hi survey as possible dwarf galaxies in or near the Local Group. To search for a resolved stellar population associated with the Hi 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. (2015) and Janesh et al. (2017); 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 Hi masses from 2 × 10 4 −3 × 10 6 M , M V from −1.4−−7.1, and stellar masses from 4 × 10 2 −4 × 10 5 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 ultra faint 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 testbed for theories regarding the baryonic feedback processes that impact star formation and galaxy evolution in this low-mass regime.

The Star Formation History of Eridanus II: On the Role of Supernova Feedback in the Quenching of Ultrafaint Dwarf Galaxies*

“…2012;Weisz et al 2012; F. Surot et al, 2021 in preparation; other gas-rich UFDs are discussed byMcQuinn et al 2015 andJanesh et al 2019). The available SFHs of Leo T all agree on a low early SFR, ∼10 −5 M e yr −1 , around two orders or magnitude lower than the one we have inferred for Eri II, that would not have been able to quench it by SN feedback.…”

The ALFALFA Almost-Dark Galaxy AGC~229101: A Two Billion Solar Mass HI Cloud with a Very Low Surface Brightness Optical Counterpart

“…The remaining objects fall into two main categories. The first is Ultra-Compact High-Velocity Clouds (e.g., Giovanelli et al 2010;Adams et al 2013;Janesh et al 2019), which have velocities and other properties (e.g., HI sizes, masses) that make them good candidates for as-yet unidentified gas-rich dwarf galaxies located in and around the Local Group. The second category is "Almost Dark galaxies" (e.g., Cannon et al 2015;Janowiecki et al 2015), which also lack an unambiguous optical counterpart (although some do show faint optical emission nearby that may or may not be associated with the H i source) but have a much wider range of masses and distances than the UCHVCs.…”

Boltzmann hierarchies for self-interacting warm dark matter scenarios

“…However, it has been noted that in this paradigm it is challenging to describe some observables on smaller scales, such as the "missing" dark matter sub-halos or the so called core-cusp discrepancy [21]. High resolution cosmological simulations of average-sized halos in ΛCDM predicts [22] an overproduction of small-scale structures, significantly larger that the observed number of small satellite galaxies in the Local Group [23,24]. Moreover, N-body simulations of CDM-only predict a singular density profile for virialized halos [25,26], while observational evidence points to dwarf spheroidal galaxies (dSphs) having smooth cores in their central regions [27,28].…”