J/AJ/148/137 Merging galaxies in COSMOS to z∼1 (Lackner+, 2014)
Late-stage galaxy mergers in COSMOS to z∼1.
Lackner C.N., Silverman J.D., Salvato M., Kampczyk P., Kartaltepe J.S.,
Sanders D., Capak P., Civano F., Halliday C., Ilbert O., Jahnke K.,
Koekemoer A.M., Lee N., Le Fevre O., Liu C.T., Scoville N., Sheth K.,
Toft S.
<Astron. J., 148, 137 (2014)>
=2014AJ....148..137L 2014AJ....148..137L
ADC_Keywords: Active gal. nuclei ; X-ray sources ; Redshifts ; Stars, masses ;
Photometry, HST
Keywords: galaxies: active - galaxies: formation - galaxies: interactions -
techniques: image processing
Abstract:
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 to distinguish
two concentrated galaxy nuclei at small separations. This method does
not rely on low surface brightness features to identify mergers, and
is therefore reliable to high redshift. Using mock images, we derive
statistical contamination and incompleteness corrections for the
fraction of late-stage mergers. The mock images show that our method
returns an uncontaminated (<10%) sample of mergers with projected
separations between 2.2 and 8kpc out to z∼1. We apply our new method
to a magnitude-limited (mFW814<23) sample of 44164 galaxies from the
COSMOS HST/ACS catalog. Using a mass-complete sample with log
M*/M☉>10.6 and 0.25<z≤1.00, we find ∼5% of systems are
late-stage mergers. Correcting for incompleteness and contamination,
the fractional merger rate increases strongly with redshift as
Rmerge∝(1+z)3.8±0.9, in agreement both 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 with redshift,
(1+z)4.5±1.3, while the merger rate for quiescent galaxies is
consistent with no evolution, (1+z)1.1±1.2. The merger rate also
becomes steeper with decreasing stellar mass. Limiting our sample to
galaxies with spectroscopic redshifts from zCOSMOS, we find that the
star formation rates and X-ray selected active galactic nucleus (AGN)
activity in likely late-stage mergers are higher by factors of ∼2
relative to those of a control sample. Combining our sample with more
widely separated pairs, we find that 8±5% of star formation and
20±8% of AGN activity are triggered by close encounters (<143kpc) or
mergers, providing additional evidence that major mergers are not the
only channels for star formation and black hole growth.
Description:
In this work, we use two overlapping samples of galaxies, both
selected from the COSMOS Advanced Camera for Surveys (ACS) catalog
(Leauthaud et al., 2007ApJS..172..219L 2007ApJS..172..219L). HST/ACS F814W (I-band)
images are taken as part of the COSMOS project (Koekemoer et al.,
2007ApJS..172..196K 2007ApJS..172..196K; Massey et al., 2010MNRAS.401..371M 2010MNRAS.401..371M).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 63 2112 Late-stage mergers in photo-z + spec-z samples
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See also:
B/hst : HST Archived Exposures Catalog (STScI, 2007)
II/284 : COSMOS Multi-Wavelength Photometry Catalog (Capak+, 2007)
J/A+A/556/A55 : Multi-color photometry of star-forming galaxies
(Ilbert+, 2013)
J/ApJS/201/30 : The Chandra COSMOS survey. III. (Civano+, 2012)
J/ApJ/742/61 : Photometric redshift of AGNs from XMM- and C-COSMOS
(Salvato+ 2011)
J/ApJ/721/98 : Morphology of 70um COSMOS galaxies (Kartaltepe+, 2010)
J/ApJ/716/348 : The XMM-Newton survey of the COSMOS field (Brusa+, 2010)
J/ApJS/184/218 : The zCOSMOS 10k-bright spectroscopic sample (Lilly+, 2009)
J/ApJS/184/158 : Chandra COSMOS survey I. (Elvis+, 2009)
J/ApJS/172/70 : zCOSMOS-bright catalog (Lilly+, 2007)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 9 F9.5 deg RAdeg Right Ascension in decimal degrees (J2000)
11- 17 F7.5 deg DEdeg Declination in decimal degrees (J2000)
19- 22 F4.2 --- zph [0.01/2.83]? Photometric redshift (photo-z) (1)
24- 27 F4.2 --- zsp [0/1.48]? Spectroscopic redshift (spec-z) (2)
29- 33 F5.2 mag Imag HST/ACS F814W (I-band) AB magnitude (3)
35- 39 F5.2 [Msun] logM* ? Log of stellar Mass (4)
41- 44 F4.2 arcsec Psep [0.1/5.5] Peak separation of the pair
46- 49 F4.2 --- PFR [0/1] Peak flux ratio
51- 54 F4.1 [10-7W] logLX1 ? Chandra 0.5-10keV integrated log X-ray
luminosity (in erg/s) (5)
56- 59 F4.1 [10-7W] logLX2 ? XMM 0.5-10keV integrated log X-ray
luminosity (in erg/s) (6)
61- 63 A3 --- f_logLX2 [nan] nan value for logLX2
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Note (1): From Ilbert et al. 2013 (cat. J/A+A/556/A55), except for X-ray sources
then from Salvato et al. 2011 (cat. J/ApJ/742/61).
Note (2): From zCOSMOS (Lilly et al. 2007, cat. J/ApJS/172/70; Lilly et al. 2009
cat. J/ApJS/184/218).
Note (3): From Leauthaud et al. (2007ApJS..172..219L 2007ApJS..172..219L).
Note (4): From Bongiorno et al. (2012MNRAS.427.3103B 2012MNRAS.427.3103B) for XMM sources,
Bolzonella et al. (2010A&A...524A..76B 2010A&A...524A..76B) and Pozzetti et al.
(2010A&A...523A..13P 2010A&A...523A..13P) for sources without a photometric redshift, otherwise
from Ilbert et al. 2013 (cat. J/A+A/556/A55).
Note (5): From Civano et al. 2012 (cat. J/ApJS/201/30).
Note (6): From Brusa et al. 2010 (cat. J/ApJ/716/348).
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Sylvain Guehenneux [CDS] 16-Dec-2014