* Astronomy

Title: Two Local Volume Dwarf Galaxies Discovered in 21 cm Emission: Pisces A and B
Author: Erik J. Tollerud, Marla C. Geha, Jana Grcevich, Mary E. Putman, Daniel Stern

We report the discovery of two dwarf galaxies, Pisces A and B, from a blind 21 cm HI search. These were the only two galaxies found via optical imaging and spectroscopy of 22 HI clouds identified in the GALFA-HI survey as dwarf galaxy candidates. They have properties consistent with being in the Local Volume (<10 Mpc), and one has resolved stellar populations such that it may be on the outer edge of the Local Group (~1Mpc from M31). While the distance uncertainty makes interpretation ambiguous, these may be among the faintest starforming galaxies known. Additionally, rough estimates comparing these galaxies to \Lambda CDM dark matter simulations suggest consistency in number density, implying that dark matter halos likely to host these galaxies are primarily HI-rich. The galaxies may thus be indicative of a large population of dwarfs at the limit of detectability that are comparable to the faint satellites of the Local Group. Because they are outside the influence of a large dark matter halo to alter their evolution, these galaxies can provide critical anchors to dwarf galaxy formation models.

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