The Stellar Content of Galaxy Halos: A Comparison between LambdaCDM Models and Observations of M31

Abstract

Recent observations have revealed that high surface-brightness, metal-rich debris is present over large regions of the Andromeda (M31) stellar halo. We use a set of numerical models to determine whether extended metal-rich debris is expected to exist in galaxy halos formed in a hierarchical LambdaCDM universe. We identify tidal debris in the simulations according to the current best surface brightness detection limits in M31 and demonstrate that bright features in the outer halo regions usually originate from single satellites, with very little contamination from other sources due to the low probability of tidal streams from two overlapping accretion events. In contrast, high-surface brightness features in the inner halo often originate from multiple progenitors. We also compare the age and metallicity distribution of the debris with the well-mixed stellar halos in which they reside. We find that high-surface brightness tidal debris is produced almost exclusively by relatively high mass progenitors (Mstar ~ 10^7- 10^9 Msun) and thus is expected to be of moderate- to high-metallicity. Similarly, in our models the smooth inner halo is expected to be metal-rich as this region has been built up mainly from massive satellites. Our results imply that the stellar populations of substructure observed around external galaxies with current techniques should not resemble old and metal-poor dwarf spheroidal satellites, nor the underlying component of the stellar halo.

12 pages, 8 figures (accepted to ApJ)

References in corpus (7)

• The Haunted Halos of Andromeda and Triangulum: A panorama of galaxy formation in action
• High-resolution spectroscopy of RGB stars in the Sagittarius Streams. I. Radial velocities and chemical abundances
• Stellar Kinematics in the Complicated Inner Spheroid of M31: Discovery of Substructure Along the Southeastern Minor Axis and its Relationship to the Giant Southern Stream
• Detection of a population gradient in the Sagittarius Stream
• The Extended Star Formation History of the Andromeda Spheroid at Twenty One Kiloparsecs on the Minor Axis
• Probing the Nature of the G1 Clump Stellar Overdensity in the Outskirts of M31
• Discovery of an extended halo of metal-poor stars in the Andromeda spiral galaxy

Cited by in corpus (5)

• Tracing Galaxy Formation with Stellar Halos II: Relating Substructure in Phase- and Abundance-Space to Accretion Histories
• Metallicity and Alpha-Element Abundance Measurement in Red Giant Stars from Medium Resolution Spectra
• The Nature and Origin of Substructure in the Outskirts of M31. I. Surveying the Stellar Content with HST/ACS
• The Once and Future Andromeda Stream
• An HST/ACS investigation of the spatial and chemical structure and sub-structure of NGC 891, a Milky Way analogue