The Nearest Ultra Diffuse Galaxy: UGC 2162
We describe the structural, stellar population and gas properties of the nearest ultra diffuse galaxy discovered so far: UGC 2162 (z = 0.00392; R{sub e,g}=1.7(±0.2) kpc; μ{sub g}(0) = 24.4 ± 0.1 mag arcsec{sup −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({sub −1}{sup +2}) × 10{sup 7} M{sub ⊙} and is embedded within a cloud of HI gas ∼10 times more massive: ∼1.9(±0.6) × 10{sup 8} M{sub ⊙}. 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) × 10{sup 9} M{sub ⊙} (i.e., M/L ∼ 200). The estimated virial mass from the cumulative mass curve is ∼8(±2)×10{sup 10} M {sub ⊙}. 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{sub ⊙} yr{sup −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{sub g}(0) ∼ 27 mag arcsec{sup −2} and its size would remain large R{sub 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{sub ⋆} ∼ 10{sup 7} M{sub ⊙} “dark galaxies” in rich environments (depleted of HI gas) waiting to be discovered by current and future ultra-deep surveys.
- OSTI ID:
- 22869319
- Journal Information:
- Astrophysical Journal, Vol. 836, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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