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 mag 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 distance for Lac I of (m - M)0 = 24.44 ± 0.11mag (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 μV,0 = 24.8 ± 0.3 mag arcsec-2. We find no H I emission in archival data and set a limit on Lac I's neutral gas mass-to-light ratio of MH I/LV < 0.06 M⊙/L⊙, 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. 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.
- Local Group Supporting material: machine-readable table
- galaxies: dwarf
- galaxies: individual (Lac I, and XXXI)
- galaxies: photometry
ASJC Scopus subject areas
- Astronomy and Astrophysics
- Space and Planetary Science