The Nearest Ultra Diffuse Galaxy: UGC 2162

Trujillo, I.; Roman, J.; Filho, M.; Sánchez Almeida, J.
Bibliographical reference

The Astrophysical Journal, Volume 836, Issue 2, article id. 191, 6 pp. (2017).

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2
2017
Number of authors
4
IAC number of authors
4
Citations
81
Refereed citations
76
Description
We describe the structural, stellar population and gas properties of the nearest ultra diffuse galaxy discovered so far: UGC 2162 (z = 0.00392 {R}e,g=1.7(+/- 0.2) kpc; {μ }g(0) = 24.4 ± 0.1 mag arcsec‑2 g-i = 0.33 ± 0.02). This galaxy, located at a distance of 12.3(±1.7) Mpc, is a member of the M77 group. UGC 2162 has a stellar mass of ∼ 2{(}-1+2) × 107 {M}ȯ and is embedded within a cloud of HI gas ∼10 times more massive: ∼1.9(±0.6) × 108 {M}ȯ . Using the width of its HI line as a dynamical proxy, the enclosed mass within the inner R ∼ 5 kpc is ∼4.6(±0.8) × 109 {M}ȯ (i.e., M/L ∼ 200). The estimated virial mass from the cumulative mass curve is ∼8(±2)×1010 M ⊙. Ultra-deep imaging from the IAC Stripe82 Legacy Project show that the galaxy is irregular and has many star-forming knots, with a gas-phase metallicity around one-third of the solar value. Its estimated star-formation rate is ∼0.01 {M}ȯ yr‑1. This SFR would double the stellar mass of the object in ∼2 Gyr. If the object were to stop forming stars at this moment, after a passive evolution, its surface brightness would become extremely faint: {μ }g(0) ∼ 27 mag arcsec‑2 and its size would remain large {R}e,g ∼ 1.8 kpc. Such faintness would make it almost undetectable to most present-day surveys. This suggests that there could be an important population of {M}\star ∼ 107 {M}ȯ “dark galaxies” in rich environments (depleted of HI gas) waiting to be discovered by current and future ultra-deep surveys.
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