History Of Galaxy Interactions And Their Impact On Star Formation Over The Last 7 Gyr From GEMS




Jogee, Shardha
Miller, Sarah H.
Penner, Kyle
Skelton, Rosalind E.
Conselice, Christopher J.
Somerville, Rachel S.
Bell, Eric F.
Zheng, Xian Zhong
Rix, Hans-Walter
Robaina, Aday R.

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We perform a comprehensive estimate of the frequency of galaxy mergers and their impact on star formation over z similar to 0.24-0.80 (lookback time T(b) similar to 3-7 Gyr) using similar to 3600 (M >= 1 x 10(9) M(circle dot)) galaxies with GEMS Hubble Space Telescope, COMBO-17, and Spitzer data. Our results are as follows. (1) Among similar to 790 high-mass (M >= 2.5 x 10(10) M(circle dot)) galaxies, the visually based merger fraction over z similar to 0.24-0.80, ranges from 9% +/- 5% to 8% +/- 2%. Lower limits on the major merger and minor merger fraction over this interval range from 1.1% to 3.5%, and 3.6% to 7.5%, respectively. This is the first, albeit approximate, empirical estimate of the frequency of minor mergers over the last 7 Gyr. Assuming a visibility timescale of similar to 0.5 Gyr, it follows that over T(b) similar to 3-7 Gyr, similar to 68% of high-mass systems have undergone a merger of mass ratio > 1/10, with similar to 16%, 45%, and 7% of these corresponding respectively to major, minor, and ambiguous "major or minor" mergers. The average merger rate is similar to a few x 10(-4) galaxies Gyr(-1) Mpc(-3). Among similar to 2840 blue-cloud galaxies of mass M >= 1.0 x 10(9) M(circle dot), similar results hold. (2) We compare the empirical merger fraction and merger rate for high-mass galaxies to three. cold dark matter-based models: halo occupation distribution models, semi-analytic models, and hydrodynamic SPH simulations. We find qualitative agreement between observations and models such that the (major+minor) merger fraction or rate from different models bracket the observations, and show a factor of 5 dispersion. Near-future improvements can now start to rule out certain merger scenarios. (3) Among similar to 3698 M >= 1.0 x 10(9) M(circle dot) galaxies, we find that the mean star formation rate (SFR) of visibly merging systems is only modestly enhanced compared to non-interacting galaxies over z similar to 0.24-0.80. Visibly merging systems only account for a small fraction (< 30%) of the cosmic SFR density over T(b) similar to 3-7 Gyr. This complements the results of Wolf et al. over a shorter time interval of T(b) similar to 6.2-6.8 Gyr, and suggests that the behavior of the cosmic SFR density over the last 7 Gyr is predominantly shaped by non-interacting galaxies.



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Jogee, Shardha, Sarah H. Miller, Kyle Penner, Rosalind E. Skelton, Christopher J. Conselice, Rachel S. Somerville, Eric F. Bell et al. "History of Galaxy Interactions and Their Impact on Star Formation Over the Last 7 Gyr from GEMS." The Astrophysical Journal, Vol. 697, No. 2 (Jun., 2009): 1971.