* Astronomy

Title: Structural and Photometric Properties of the Andromeda Satellite Dwarf Galaxy Lacerta I from Deep Imaging with WIYN pODI
Author: Katherine L. Rhode, Denija Crnojevic, David J. Sand, Steven Janowiecki, Michael D. Young, Kristine Spekkens

We present results from WIYN pODI imaging of Lacerta I (And XXXI), a satellite dwarf galaxy discovered in the outskirts of the Andromeda galaxy (M31) in Pan-STARRS1 survey data. Our deep, wide-field g,i photometry reaches ~3 magnitudes fainter than the photometry in the Pan-STARRS1 discovery paper and allows us to trace the stellar population of Lac I beyond two half-light radii from the galaxy center. We measure a Tip of the Red Giant Branch (TRGB) distance for Lac I of (m-M)0=24.44±0.11 mag (773±40 kpc, or 264±6 kpc from M31), which is consistent with the Pan-STARRS1 distance. We use a maximum-likelihood technique to derive structural properties for the galaxy, and find a half-light radius (rh) of 3.24±0.21 arcmin (728±47 pc), ellipticity () of 0.44±0.03, total magnitude MV = -11.4±0.3, and central surface brightness V,0 = 24.8±0.3 mag arcsec^-2. We find no HI emission in archival data and set a limit on Lac I's neutral gas mass-to-light ratio of MHI/LV < 0.06 Msun/Lsun, confirming Lac I as a gas-poor dwarf spheroidal galaxy. Photometric metallicities derived from Red Giant Branch stars within 2 rh yield a median [Fe/H] of -1.68±0.03, which is more metal-rich than the spectroscopically-derived value from Martin et al. (2014). Combining our measured magnitude with this higher metallicity estimate places Lac I closer to its expected position on the luminosity-metallicity relation for dwarf galaxies.

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