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; Re.g= 1.7(+/- 0.2) kpc; mu(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 similar to 2 ((+2)(-1)) x 10(7) M-circle dot and is embedded within a cloud of HI gas similar to 10 times more massive: similar to 1.9(+/- 0.6) x 10(8) M-circle dot. Using the width of its HI line as a dynamical proxy, the enclosed mass within the inner R similar to 5 kpc is similar to 4.6 (+/- 0.8) x 10(9) M-circle dot (i.e., M/L similar to 200). The estimated virial mass from the cumulative mass curve is similar to 8(+/- 2) x10(10) M-circle dot. Ultra-deep imaging from the IAC Stripe82 Legacy Project show that the galaxy is irregular and has many starforming knots, with a gas-phase metallicity around one-third of the solar value. Its estimated star-formation rate is similar to 0.01 M(circle dot)yr(-1). This SFR would double the stellar mass of the object in similar to 2 Gyr. If the object were to stop forming stars at this moment, after a passive evolution, its surface brightness would become extremely faint: mu(g)(0) similar to 27 mag arcsec(-2) and its size would remain large R-e.g similar to 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 similar to 10(7) M-circle dot dark galaxies in rich environments (depleted of HI gas) waiting to be discovered by current and future ultra-deep surveys.