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 \sim 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 \pm 0.11 mag ( 773 \pm 40 kpc , or 264 \pm 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 ( r _ { h } ) of 3.24 \pm 0.21 arcmin ( 728 \pm 47 pc ) , ellipticity ( \epsilon ) of 0.44 \pm 0.03 , total magnitude M _ { V } = - 11.4 \pm 0.3 , and central surface brightness \mu _ { V, 0 } = 24.8 \pm 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 M _ { HI } / L _ { V } < 0.06 M _ { \sun } / L _ { \sun } , confirming Lac I as a gas-poor dwarf spheroidal galaxy .
Photometric metallicities derived from Red Giant Branch stars within 2 r _ { h } yield a median [ Fe/H ] of - 1.68 \pm 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 .