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Large Highly Ionized Nebulae Around Ultra-luminous X-ray Sources

Moon, Dae-Sik and Harrison, Fiona A. and Cenko, S. Bradley and Shariff, Jamil A. (2011) Large Highly Ionized Nebulae Around Ultra-luminous X-ray Sources. Astrophysical Journal Letters, 731 (2). Art. No. L32. ISSN 2041-8205. doi:10.1088/2041-8205/731/2/L32.

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We present the results of deep optical spectroscopic observations using the LRIS spectrograph on the Keck I 10 m telescope of three ultra-luminous X-ray sources (ULXs): Ho IX X-1, M81 X-6, and Ho II X-1. Our observations reveal the existence of large (100-200 pc diameter) highly ionized nebulae, identified by diffuse He II λ4686 emission, surrounding these sources. Our results are the first to find highly ionized nebulae of this extent, and the detection in all three objects indicates this may be a common feature of ULXs. In addition to the extended emission, Ho IX X-1 has an unresolved central component containing about one-third of the total He II flux, with a significant velocity dispersion of ≃370 km s^(–1), suggestive of the existence of a photoionized accretion disk or an extremely hot early-type stellar counterpart. Most of the He II emission appears to be surrounded by significantly more extended Hβ emission, and the intensity ratios between the two lines, which range from 0.12 to 0.33, indicate that photoionization is the origin of the He II emission. Sustaining these extended nebulae requires substantial X-ray emission, in the range ~10^(39)-10^(40) erg s^(–1), comparable to the measured X-ray luminosities of the sources. This favors models where the X-ray emission is isotropic, rather than beamed, which includes the interpretation that ULXs harbor intermediate-mass black holes.

Item Type:Article
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URLURL TypeDescription DOIArticle
Moon, Dae-Sik0000-0003-4200-5064
Harrison, Fiona A.0000-0003-2992-8024
Cenko, S. Bradley0000-0003-1673-970X
Additional Information:© 2011 The American Astronomical Society. Received 2011 January 3; accepted 2011 March 11; published 2011 March 29. D.-S.M. acknowledges the support by NSERC through Discovery program 327277 and S.B.C. acknowledges generous support from Gary and Cynthia Bengier and the Richard and Rhoda Goldman fund. The data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. Facility: Keck:I (LRIS)
Group:Space Radiation Laboratory
Funding AgencyGrant Number
Natural Sciences and Engineering Research Council of Canada (NSERC)327277
Gary and Cynthia BengierUNSPECIFIED
Richard and Rhoda Goldman fundUNSPECIFIED
W. M. Keck FoundationUNSPECIFIED
Subject Keywords:black hole physics; galaxies: individual (Holmberg IX, M81, Holmberg II); ISM: bubbles; ISM: kinematics and dynamics; X-rays: galaxies
Issue or Number:2
Classification Code:PACS: 98.70.Qy; 98.62.Js; 98.52.Wz; 95.85.Kr
Record Number:CaltechAUTHORS:20110816-080612553
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Official Citation:Large Highly Ionized Nebulae Around Ultra-luminous X-ray Sources Dae-Sik Moon et al. 2011 ApJ 731 L32
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:24873
Deposited On:16 Aug 2011 15:27
Last Modified:09 Nov 2021 16:27

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