Late-stage galaxy mergers in COSMOS to z~1
| Autor: | Lackner, C. N., Silverman, J. D., Salvato, M., Kampczyk, P., Kartaltepe, J. S., Sanders, D., Capak, P., Civano, F., Ilbert, O., Jahnke, K., Koekemoer, A. M., Lee, N., Fevre, O. Le, Liu, C. T., Scoville, N., Sheth, K., Toft, S. |
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| Rok vydání: | 2014 |
| Předmět: | |
| Druh dokumentu: | Working Paper |
| DOI: | 10.1088/0004-6256/148/6/137 |
| Popis: | The role of major mergers in galaxy and black hole formation is not well constrained. To help address this, we develop an automated method to identify late-stage galaxy mergers before coalescence of the galactic cores. The resulting sample of mergers is distinct from those obtained using pair-finding and morphological indicators. Our method relies on median-filtering of high-resolution images in order to distinguish two concentrated galaxy nuclei at small separations. Using mock images, we derive statistical contamination and incompleteness corrections for the fraction of late-stage mergers. We apply our new method to a magnitude-limited (I < 23) sample of 44,164 galaxies from the COSMOS HST/ACS catalog. Using a mass-complete sample with $\log M_*/M_\odot > 10.6$ and $0.25 < z \leq 1.00$, we find ~5% of systems are late-stage mergers with separations between 2.2 and 8 kpc. Correcting for incompleteness and contamination, the fractional merger rate increases strongly with redshift as $(1+z)^{3.8\pm0.9}$, in agreement with earlier studies and with dark matter halo merger rates. Separating the sample into star-forming and quiescent galaxies shows that the merger rate for star-forming galaxies increases strongly redshift, $(1+z)^{4.5\pm1.3}$, while the merger rate for quiescent galaxies is consistent with no evolution, $(1+z)^{1.1\pm1.2}$. Limiting our sample to galaxies with spectroscopic redshifts from zCOSMOS, we find that the star formation rates and X-ray selected AGN activity in likely late-stage mergers are enhanced by factors of ~2 relative to a control sample. Combining our sample with more widely separated pairs, we find that $8\pm5\%$ of star formation and $20\pm8\%$ of AGN activity is triggered by close encounters (<143 kpc) or mergers, once more suggesting that major mergers are not the only channels for star formation and black hole growth. (abridged) Comment: 28 pages, 24 figures, submitted to AJ |
| Databáze: | arXiv |
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