The Progenitor of the Peculiar Galaxy NGC3077

Abstract

We present a study of the structural properties and metallicity distribution of the nearby peculiar galaxy NGC3077. Using data from our survey of the M81 Group with the Hyper Suprime-Cam on the Subaru Telescope, we construct deep color-magnitude diagrams that are used to probe the old red giant branch population of NGC3077. We map these stars out to and beyond the nominal tidal radius, which allows us to derive the structural properties and stellar content of the peripheral regions. We show that NGC3077 has an extended stellar halo and pronounced ``S-shaped" tidal tails that diverge from the radial profile of the inner region. The average metallicity of the old population in NGC3077 is estimated from individual RGBs to be $[M/H]=-0.98\pm 0.26$, which decreases with the distance from the galaxy center as $[M/H]=-0.17$ dex ${{\mathrm{R}}_{\mathrm{h}}}^{-1}$. The metallicity of the S-shaped structure is similar to that of the regions lying at $r\sim 4\times {\mathrm{R}}_{\mathrm{h}}(\sim 30$~kpc), indicating that the stellar constituents of the tidal tails have come from the outer envelope of NGC3077. These results suggest that this peculiar galaxy was probably a rather normal dwarf elliptical galaxy before the tidal interaction with M81 and M82. We also examine the evidence in our dataset for the six recently-reported ultra-faint dwarf candidates around NGC3077. We recover a spatial overdensity of sources coinciding with only one of these.

13 pages, 10 figures, Accepted for publication in ApJ

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