Unearthing Foundations of a Cosmic Cathedral: Searching the Stars for M33's Halo

Abstract

We use data from the Pan-Andromeda Archaeological Survey (PAndAS) to search for evidence of an extended halo component belonging to M33 (the Triangulum Galaxy). We identify a population of red giant branch (RGB) stars at large radii from M33's disk whose connection to the recently discovered extended "disk substructure" is ambiguous, and which may represent a "bona-fide" halo component. After first correcting for contamination from the Milky Way foreground population and misidentified background galaxies, we average the radial density of RGB candidate stars over circular annuli centered on the galaxy and away from the disk substructure. We find evidence of a low-luminosity, centrally concentrated component that is everywhere in our data fainter than mu_V ~ 33 mag arcsec^(-2). The scale length of this feature is not well constrained by our data, but it appears to be of order r_exp ~ 20 kpc; there is weak evidence to suggest it is not azimuthally symmetric. Inspection of the overall CMD for this region that specifically clips out the disk substructure reveals that this residual RGB population is consistent with an old population with a photometric metallicity of around [Fe/H] ~ -2 dex, but some residual contamination from the disk substructure appears to remain. We discuss the likelihood that our findings represent a bona-fide halo in M33, rather than extended emission from the disk substructure. We interpret our findings in terms of an upper limit to M33's halo that is a few percent of its total luminosity, although its actual luminosity is likely much less.

57 pages, 13 figures, 2 tables. Accepted by the Monthly Notices of the Royal Astronomical Society

References in corpus (25)

• The Dartmouth Stellar Evolution Database
• Two Stellar Components in the Halo of the Milky Way
• The accretion origin of the Milky Way's stellar halo
• The Haunted Halos of Andromeda and Triangulum: A panorama of galaxy formation in action
• The Dual Origin of Stellar Halos
• An Orphan in the "Field of Streams"
• Detection of a 60 Degree-Long Dwarf Galaxy Debris Stream
• The Metal-Poor Halo of the Andromeda Spiral Galaxy (M31)
• The Hercules-Aquila Cloud
• A kinematically selected, metal-poor stellar halo in the outskirts of M31
• Discovery of a New, Polar-Orbiting Debris Stream in the Milky Way Stellar Halo
• RR Lyrae Variables in M33. I. Evidence For a Field Halo Population
• Unravelling the mystery of the M31 bar
• Evidence for Distinct Components of the Galactic Stellar Halo from 838 RR Lyrae Stars Discovered in the LONEOS-I Survey
• Stellar populations across the NGC4244 truncated galactic disk
• The stellar halo and outer disk of M33
• Galactic halo stellar structures in the Triangulum-Andromeda region
• The total mass and dark halo properties of the Small Magellanic Cloud
• The Stellar Populations of M33's Outer Regions IV: Inflow History and Chemical Evolution
• The Stellar Populations of M33's Outer Regions III: Star Formation History
• AGB stars as tracers of metallicity and mean age across M33
• The Stellar Populations of M33's Outer Regions II: Deep ACS Imaging
• Point spread function tails and the measurements of diffuse stellar halo light around edge-on disc galaxies
• The asymmetric structure of the Galactic halo
• On the Origin of the Kinematical Differences Between the Stellar Halo and the Old Globular Cluster System in the Large Magellanic Cloud

Cited by in corpus (6)

• Stellar halos from The Dragonfly Edge-on Galaxies Survey
• The TREX Survey: Kinematical Complexity Throughout M33's Stellar Disk and Evidence for a Stellar Halo
• Triangulum galaxy viewed by Planck
• The elusive stellar halo of the Triangulum Galaxy
• The outskirts of M33: Tidally induced distortions versus signatures of gas accretion
• Simulations of the accreted stellar halos of low-mass field galaxies