Galaxies grow their bulges and black holes in diverse ways

Abstract

Galaxies with Milky Way-like stellar masses have a wide range of bulge and black hole masses; in turn, these correlate with other properties such as star formation history. While many processes may drive bulge formation, major and minor mergers are expected to play a crucial role. Stellar halos offer a novel and robust measurement of galactic merger history; cosmologically-motivated models predict that mergers with larger satellites produce more massive, higher metallicity stellar halos, reproducing the recently-observed stellar halo metallicity-mass relation. We quantify the relationship between stellar halo mass and bulge or black hole prominence using a sample of eighteen Milky Way-mass galaxies with newly-available measurements of (or limits on) stellar halo properties. There is an order of magnitude range in bulge mass, and two orders of magnitude in black hole mass, at a given stellar halo mass (or, equivalently, merger history). Galaxies with low mass bulges show a wide range of quiet merger histories, implying formation mechanisms that do not require intense merging activity. Galaxies with massive 'classical' bulges and central black holes also show a wide range of merger histories. While three of these galaxies have massive stellar halos consistent with a merger origin, two do not - merging appears to have had little impact in making these two massive 'classical' bulges. Such galaxies may be ideal laboratories to study massive bulge formation through pathways such as early gas-rich accretion, violent disk instabilities or misaligned infall of gas throughout cosmic time.

Astrophysical Journal Letters, in press. 6 pages, 3 figures, 1 table

References in corpus (12)

• The Dual Origin of Stellar Halos
• The long bar as seen by the VVV survey: I. Colour-magnitude diagrams
• ZFOURGE/CANDELS: On the Evolution of M* Galaxy Progenitors from z=3 to 0.5
• The Dragonfly Nearby Galaxies Survey. I. Substantial variation in the diffuse stellar halos around spiral galaxies
• Diverse Stellar Haloes in Nearby Milky Way-Mass Disc Galaxies
• Early formation of massive, compact, spheroidal galaxies with classical profiles by violent disc instability or mergers
• Global Properties of M31's Stellar Halo from the SPLASH Survey: II. Metallicity Profile
• Tracing the outer halo in a giant elliptical to 25 Reff
• Detection of a distinct metal-poor stellar halo in the early-type galaxy NGC 3115
• Deep Imaging of M51: a New View of the Whirlpool's Extended Tidal Debris
• VLA H53alpha and H92alpha line observations of the central region of NGC 253
• Near-Infrared Structure of Fast and Slow Rotating Disk Galaxies

Cited by in corpus (12)

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• The continuous rise of bulges out of galactic disks
• Study of gravitational fields and globular cluster systems of early-type galaxies
• A correlation between the number of satellites and the baryonic bulge-to-total ratio extending beyond the Local Group
• A New Channel of Bulge Formation via The Destruction of Short Bars
• Ultrafaint Dwarf Galaxy Candidates in the M81 Group: Signatures of Group Accretion
• Collective properties of quasar narrow associated absorption lines
• The role of stochastic and smooth processes in regulating galaxy quenching
• The formation history of the Milky Way disc with high-resolution cosmological simulations
• The "Building Blocks" of Stellar Halos