DISCOVERY OF AN ACTIVE SUPERMASSIVE BLACK HOLE IN THE BULGELESS GALAXY NGC 4561
- Department of Astronomy, Ohio State University, 140 West 18th Avenue, Columbus, OH 43210 (United States)
- CNRS/CEA-Saclay, F-91911 Gif-sur-Yvette (France)
- Osservatorio Astronomico di Roma, Via Frascati 33, I-100040 Monteporzio Catone (Italy)
We present XMM-Newton observations of the Chandra-detected nuclear X-ray source in NGC 4561. The hard X-ray spectrum can be described by a model composed of an absorbed power law with {Gamma} = 2.5{sup +0.4}{sub -0.3} and column density N{sub H} = 1.9{sup +0.1}{sub -0.2} Multiplication-Sign 10{sup 22} atoms cm{sup -2}. The absorption-corrected luminosity of the source is L(0.2-10.0 keV) =2.5 Multiplication-Sign 10{sup 41} erg s{sup -1}, with bolometric luminosity over 3 Multiplication-Sign 10{sup 42} erg s{sup -1}. Based on the spectrum and the luminosity, we identify the nuclear X-ray source in NGC 4561 to be an active galactic nucleus (AGN), with a black hole (BH) of mass M{sub BH} >2 Multiplication-Sign 10{sup 4} M{sub Sun }. The presence of a supermassive black hole at the center of this bulgeless galaxy shows that BH masses are not necessarily related to bulge properties, contrary to general belief. Observations such as these call into question several theoretical models of BH-galaxy coevolution that are based on merger-driven BH growth; secular processes clearly play an important role. Several emission lines are detected in the soft X-ray spectrum of the source which can be well parameterized by an absorbed diffuse thermal plasma with non-solar abundances of some heavy elements. Similar soft X-ray emission is observed in spectra of Seyfert 2 galaxies and low-luminosity AGNs, suggesting an origin in the circumnuclear plasma.
- OSTI ID:
- 22092140
- Journal Information:
- Astrophysical Journal, Vol. 757, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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