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Title: Pavo: Discovery of a Star-forming Dwarf Galaxy Just Outside the Local Group*

We report the discovery of Pavo, a faint (MV= −10.0), star-forming, irregular, and extremely isolated dwarf galaxy atD≈ 2 Mpc. Pavo was identified in Dark Energy Camera Legacy Survey imaging via a novel approach that combines low surface brightness galaxy search algorithms and machine-learning candidate classifications. Follow-up imaging with the Inamori-Magellan Areal Camera and Spectrograph on the 6.5 m Magellan Baade telescope revealed a color–magnitude diagram (CMD) with an old stellar population, in addition to the young population that dominates the integrated light, and a tip of the red giant branch distance estimate of1.990.22+0.20Mpc. The blue population of stars in the CMD is consistent with the youngest stars having formed no later than 150 Myr ago. We also detected no Hαemission with SOAR telescope imaging, suggesting that we may be witnessing a temporary low in Pavo’s star formation. We estimate the total stellar mass of Pavo to belogM*/M=5.6±0.2and measure an upper limit on its Higas mass of 1.0 × 106Mbased on the HIPASS survey. Given these properties, Pavo’s closest analog is Leo P (D= 1.6 Mpc), previously the only known isolated, star-forming, Local Volume dwarf galaxy in this mass range. However, Pavo appears to be even more isolated, with no other known galaxy residing within over 600 kpc. As surveys and search techniques continue to improve, we anticipate an entire population of analogous objects being detected just outside the Local Group.

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Author(s) / Creator(s):
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Publisher / Repository:
DOI PREFIX: 10.3847
Date Published:
Journal Name:
The Astrophysical Journal Letters
Medium: X Size: Article No. L5
["Article No. L5"]
Sponsoring Org:
National Science Foundation
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