Structural and Photometric Properties of the Andromeda Satellite Dwarf Galaxy Lacerta I from Deep Imaging with WIYN pODI

Abstract

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.

Accepted for publication in The Astrophysical Journal

References in corpus (14)

• The Dartmouth Stellar Evolution Database
• The Kinematics of the Ultra-Faint Milky Way Satellites: Solving the Missing Satellite Problem
• Cats and Dogs, Hair and A Hero: A Quintet of New Milky Way Companions
• Beasts of the Southern Wild: Discovery of nine Ultra Faint satellites in the vicinity of the Magellanic Clouds
• A Vast Thin Plane of Co-rotating Dwarf Galaxies Orbiting the Andromeda Galaxy
• Discovery and analysis of three faint dwarf galaxies and a globular cluster in the outer halo of the Andromeda galaxy
• Tip of the Red Giant Branch Distances. I. Optimization of a Maximum Likelihood Algorithm
• A trio of new Local Group galaxies with extreme properties
• The Dearth of Neutral Hydrogen in Galactic Dwarf Spheroidal Galaxies
• A Hero's Dark Horse: Discovery of an Ultra-Faint Milky Way Satellite in Pegasus
• A Catalog of Ultra-compact High Velocity Clouds from the ALFALFA Survey: Local Group Galaxy Candidates?
• Infrared Tip of the Red Giant Branch and Distances to the Maffei/IC 342 Group
• A PAndAS view of M31 dwarf elliptical satellites: NGC147 and NGC185
• Spectroscopy of the three distant Andromedan satellites Cassiopeia III, Lacerta I, and Perseus I