THE COSMOLOGICAL SIZE AND VELOCITY DISPERSION EVOLUTION OF MASSIVE EARLY-TYPE GALAXIES

Journal Article · Sun Jan 01 04:00:00 EST 2012 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/744/1/63· OSTI ID:22004301

Oser, Ludwig; Naab, Thorsten ^[1]; Ostriker, Jeremiah P ^[2]

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1. Max-Planck-Institut fuer Astrophysik, 85741 Garching (Germany)
2. Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States)

We analyze 40 cosmological re-simulations of individual massive galaxies with present-day stellar masses of M{sub *} > 6.3 Multiplication-Sign 10{sup 10} M{sub Sun} in order to investigate the physical origin of the observed strong increase in galaxy sizes and the decrease of the stellar velocity dispersions since redshift z Almost-Equal-To 2. At present 25 out of 40 galaxies are quiescent with structural parameters (sizes and velocity dispersions) in agreement with local early-type galaxies. At z = 2 all simulated galaxies with M{sub *} {approx}> 10{sup 11} M{sub Sun} (11 out of 40) at z = 2 are compact with projected half-mass radii of Almost-Equal-To 0.77 ({+-}0.24) kpc and line-of-sight velocity dispersions within the projected half-mass radius of Almost-Equal-To 262 ({+-}28) km s{sup -1} (3 out of 11 are already quiescent). Similar to observed compact early-type galaxies at high redshift, the simulated galaxies are clearly offset from the local mass-size and mass-velocity dispersion relations. Toward redshift zero the sizes increase by a factor of {approx}5-6, following R{sub 1/2}{proportional_to}(1 + z){sup {alpha}} with {alpha} = -1.44 for quiescent galaxies ({alpha} = -1.12 for all galaxies). The velocity dispersions drop by about one-third since z Almost-Equal-To 2, following {sigma}{sub 1/2}{proportional_to}(1 + z){sup {beta}} with {beta} = 0.44 for the quiescent galaxies ({beta} = 0.37 for all galaxies). The simulated size and dispersion evolution is in good agreement with observations and results from the subsequent accretion and merging of stellar systems at z {approx}< 2, which is a natural consequence of the hierarchical structure formation. A significant number of the simulated massive galaxies (7 out of 40) experience no merger more massive than 1:4 (usually considered as major mergers). On average, the dominant accretion mode is stellar minor mergers with a mass-weighted mass ratio of 1:5. We therefore conclude that the evolution of massive early-type galaxies since z Almost-Equal-To 2 and their present-day properties are predominantly determined by frequent 'minor' mergers of moderate mass ratios and not by major mergers alone.

• OSTI ID: 22004301
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 744; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
COMPUTERIZED SIMULATION
DISPERSION RELATIONS
GALACTIC EVOLUTION
GALAXIES
MASS
RED SHIFT