ACTIVE GALACTIC NUCLEI AND THE TRUNCATION OF STAR FORMATION IN K+A GALAXIES

Journal Article · Sun Sep 20 04:00:00 EDT 2009 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/703/1/150· OSTI ID:21372018

Brown, Michael J. I.; Palamara, David ^[1]; Moustakas, John ^[2]; Caldwell, Nelson ^[3]; Cool, Richard J; Zaritsky, Dennis ^[4]; Dey, Arjun; Jannuzi, Buell T ^[5]; Hickox, Ryan C

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1. School of Physics, Monash University, Clayton, Victoria 3800 (Australia)
2. Center for Astrophysics and Space Sciences, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA, 92093-0424 (United States)
3. Smithsonian Astrophysical Observatory, 60 Garden Street, Cambridge, MA 02138 (United States)
4. Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States)
5. National Optical Astronomy Observatory, Tucson, AZ 85726-6732 (United States)

We have searched for active galactic nuclei (AGNs) in K+A galaxies, using multiwavelength imaging and spectroscopy in the Booetes field of the NOAO Deep Wide-Field Survey. The K+A galaxies, which have had their star formation rapidly truncated, are selected via their strong Balmer absorption lines and weak Halpha emission. Our sample consists of 24 K+A galaxies selected from 6594 0.10 < z < 0.35 galaxies brighter than I = 20 with optical spectroscopy from the AGN and Galaxy Evolution Survey. Two thirds of the K+A galaxies are likely ongoing galaxy mergers, with nearby companion galaxies or tidal tails. Galaxy mergers may be responsible for the truncation of star formation, or we are observing the aftermath of merger triggered starbursts. As expected, the optical colors of K+A galaxies largely fall between blue galaxies with ongoing star formation and red passive galaxies. However, only 1% of the galaxies with colors between the red and blue populations are K+A galaxies, and we conclude that the truncation of star formation in K+A galaxies must have been unusually abrupt ({approx}<100 Myr). We examined the AGN content of K+A galaxies with both optical emission-line ratios (BPT diagrams) and Chandra X-ray imaging. At least half of all K+A galaxies display the optical emission-line ratios of AGNs, and a third of M{sub R} < -22 K+A galaxies host AGNs with X-ray luminosities of {approx}10{sup 42} erg s{sup -1}. The faintest K+A galaxies do not show clear evidence for hosting AGNs, having emission-line ratios consistent with photoionization by massive stars and few X-ray detections. We speculate that two mechanisms may be responsible for the truncation of star formation in K+A galaxies, with AGN feedback only playing a role in M{sub R} {approx}< -20.5 galaxies.

• OSTI ID: 21372018
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 703; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ABSORPTION
COSMIC RAY SOURCES
COSMIC X-RAY SOURCES
DETECTION
EMISSION
GALAXIES
GALAXY NUCLEI
IONIZATION
LUMINOSITY
OPTICAL PROPERTIES
PHOTOIONIZATION
PHYSICAL PROPERTIES
RADIATION DETECTION
SORPTION
SPECTROSCOPY
STARS
X-RAY DETECTION
X-RAY GALAXIES