* Astronomy

Title: Lacerta I and Cassiopeia III: Two luminous and distant Andromeda satellite dwarf galaxies found in the 3 Pan-STARRS1 survey
Authors: Nicolas F. Martin, Colin T. Slater, Edward F. Schlafly, Eric Morganson, Hans-Walter Rix, Eric F. Bell, Benjamin P. M. Laevens, Edouard J. Bernard, Annette M. N. Ferguson, Douglas P. Finkbeiner, William S. Burgett, Kenneth C. Chambers, Klaus W. Hodapp, Nicholas Kaiser, Rolf-Peter Kudritzki, Eugene A. Magnier, Jeffrey S. Morgan, Paul A. Price, John L. Tonry, Richard J. Wainscoat

We report the discovery of two new dwarf galaxies, Lacerta I/Andromeda XXXI (Lac I/And XXXI) and Cassiopeia III/Andromeda XXXII (Cas III/And XXXII), in stacked Pan-STARRS1 r_P1- and i_P1-band imaging data. Both are luminous systems (M_V ~ -12) located at projected distances of 20.3° and 10.5° from M31. Lac I and Cas III are likely satellites of the Andromeda galaxy with heliocentric distances of 756^{+44}_{-28} kpc and 772^{+61}_{-56} kpc, respectively, and corresponding M31-centric distances of 275±7 kpc and 144^{+6}_{-4} kpc . The brightest of recent Local Group member discoveries, these two new dwarf galaxies owe their late discovery to their large sizes (r_h = 4.2^{+0.4}_{-0.5} arcmin or 912^{+124}_{-93} pc for Lac I; r_h = 6.5^{+1.2}_{-1.0} arcmin or 1456±267 pc for Cas III), and consequently low surface brightness (µ_0 ~ 26.0 mag/arcsec²), as well as to the lack of a systematic survey of regions at large radii from M31, close to the Galactic plane. This latter limitation is now alleviated by the 3{\pi} Pan-STARRS1 survey, which could lead to the discovery of other distant Andromeda satellite dwarf galaxies.

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