EVIDENCE FOR BLACK HOLE GROWTH IN LOCAL ANALOGS TO LYMAN BREAK GALAXIES

Journal Article · Sun Apr 10 04:00:00 EDT 2011 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/731/1/55· OSTI ID:21574746

Jianjun, Jia; Heckman, Timothy M; LaMassa, Stephanie M ^[1]; Ptak, Andrew; Hornschemeier, Ann ^[2]; Overzier, Roderik A ^[3]

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1. Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218 (United States)
2. Goddard Space Flight Center, Greenbelt, MD 20771 (United States)
3. Max-Planck Institute for Astrophysics, D-85748 Garching (Germany)

We have used XMM-Newton to observe six Lyman break analogs (LBAs): members of the rare population of local galaxies that have properties that are very similar to distant Lyman break galaxies. Our six targets were specifically selected because they have optical emission-line properties that are intermediate between starbursts and Type 2 (obscured) active galactic nuclei (AGNs). Our new X-ray data provide an important diagnostic of the presence of an AGN. We find X-ray luminosities of order 10{sup 42} erg s{sup -1} and ratios of X-ray to far-IR luminosities that are higher than values in pure starburst galaxies by factors ranging from {approx}3 to 30. This strongly suggests the presence of an AGN in at least some of the galaxies. The ratios of the luminosities of the hard (2-10 keV) X-ray to [O III]{lambda}5007 emission line are low by about an order of magnitude compared with Type 1 AGN, but are consistent with the broad range seen in Type 2 AGN. Either the AGN hard X-rays are significantly obscured or the [O III] emission is dominated by the starburst. We searched for an iron emission line at {approx}6.4 keV, which is a key feature of obscured AGNs, but only detected emission at the {approx}2{sigma} level. Finally, we find that the ratios of the mid-infrared (24 {mu}m) continuum to [O III]{lambda}5007 luminosities in these LBAs are higher than the values for Type 2 AGN by an average of 0.8 dex. Combining all these clues, we conclude that an AGN is likely to be present, but that the bolometric luminosity is produced primarily by an intense starburst. If these black holes are radiating at the Eddington limit, their masses would lie in the range of 10{sup 5}-10{sup 6} M{sub sun}. These objects may offer ideal local laboratories to investigate the processes by which black holes grew in the early universe.

• OSTI ID: 21574746
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 731; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
BLACK HOLES
COSMIC RAY SOURCES
COSMIC X-RAY SOURCES
ELECTROMAGNETIC RADIATION
ELEMENTS
EMISSION
GALAXIES
GALAXY NUCLEI
GROWTH
HARD X RADIATION
IONIZING RADIATIONS
IRON
LUMINOSITY
METALS
OPTICAL PROPERTIES
PHYSICAL PROPERTIES
RADIATIONS
TRANSITION ELEMENTS
X RADIATION
X-RAY GALAXIES