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تسجيل مستخدم جديدThe nearest ultra diffuse galaxy: UGC2162
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We describe the structural, stellar population and gas properties of the nearest Ultra Diffuse Galaxy (UDG) discovered so far: UGC2162 (z=0.00392; R$_{e,g}$=1.7$(pm$0.2) kpc; $mu_g(0)$=24.4$pm$0.1 mag/arcsec$^2$; g-i=0.33$pm$0.02). This galaxy, located at a distance of 12.3($pm$1.7) Mpc, is a member of the M77 group. UGC2162 has a stellar mass of $sim$2($^{+2}_{-1}$)$times$10$^7$ M$_odot$ and is embedded within a cloud of HI gas $sim$10 times more massive: $sim$1.9($pm$0.6)$times$10$^8$ M$_odot$. Using the width of its HI line as a dynamical proxy, the enclosed mass within the inner R$sim$5 kpc is $sim$4.6($pm$0.8)$times$10$^9$ M$_odot$ (i.e. M/L$sim$200). The estimated virial mass from the cumulative mass curve is $sim$8($pm$2)$times$10$^{10}$ M$_odot$. 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 (SFR) is $sim$0.01 M$_odot$/yr. This SFR would double the stellar mass of the object in $sim$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)$$sim$27 mag/arcsec$^2$ and its size would remain large R$_{e,g}$$sim$ 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}$$sim$10$^7$ M$_odot$ dark galaxies in rich environments (depleted of HI gas) waiting to be discovered by current and future ultra-deep surveys.
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