GAS-RICH MERGERS IN LCDM: DISK SURVIVABILITY AND THE BARYONIC ASSEMBLY OF GALAXIES

Journal Article · Tue Sep 01 04:00:00 EDT 2009 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/702/1/307; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA)· OSTI ID:21333853

Stewart, Kyle R; Bullock, James S ^[1]; Wechsler, Risa H ^[2]; Maller, Ariyeh H ^[3]

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1. Center for Cosmology, Department of Physics and Astronomy, The University of California at Irvine, Irvine, CA, 92697 (United States)
2. Kavli Institute for Particle Astrophysics and Cosmology, Physics Department and Stanford Linear Accelerator Center, Stanford University, Stanford, CA 94305 (United States)
3. Department of Physics, New York City College of Technology, 300 Jay St., Brooklyn, NY 11201 (United States)

We use N-body simulations and observationally normalized relations between dark matter halo mass, stellar mass, and cold gas mass to derive robust expectations about the baryonic content of major mergers out to redshift z {approx} 2. First, we find that the majority of major mergers (m/M>0.3) experienced by the Milky Way size dark matter halos should have been gas-rich, and that gas-rich mergers are increasingly common at high redshifts. Though the frequency of major mergers into galaxy halos in our simulations greatly exceeds the observed early-type galaxy fraction, the frequency of gas-poor major mergers is consistent with the observed fraction of bulge-dominated galaxies across the halo mass range M{sub DM} {approx} 10{sup 11}-10{sup 13} M{sub sun}. These results lend support to the conjecture that mergers with high-baryonic gas fractions play an important role in building and/or preserving disk galaxies in the universe. Second, we find that there is a transition mass below which a galaxy's past major mergers were primarily gas-rich and above which they were gas-poor. The associated stellar mass scale corresponds closely to that marking the observed bimodal division between blue, star-forming, disk-dominated systems and red, bulge-dominated systems with old populations. Finally, we find that the overall fraction of a galaxy's cold baryons deposited directly via major mergers is significant. Approximately {approx}20%-30% of the cold baryonic material in M{sub star} {approx} 10{sup 10.5} M{sub sun} (M{sub DM} {approx} 10{sup 12} M{sub sun}) galaxies is accreted as cold gas or stars via major mergers since z = 2, with most of this accretion in the form of cold gas. For more massive galaxies with M{sub star} {approx} 10{sup 11} M{sub sun} (M {sub DM} {approx} 10{sup 13} M{sub sun}), the fraction of baryons amassed in mergers since z = 2 is even higher, {approx}40%, but most of these accreted baryons are delivered directly in the form of stars. This baryonic mass deposition is almost unavoidable, and provides a limit on the fraction of a galaxy's cold baryons that can originate in cold flows or from hot halo cooling.

• OSTI ID: 21333853
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 702; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
BARYONS
COSMOLOGY
MASS
MILKY WAY
NONLUMINOUS MATTER
RED SHIFT
SIMULATION
STARS
UNIVERSE