X-RAY EMISSION FROM THE SOMBRERO GALAXY: A GALACTIC-SCALE OUTFLOW

Journal Article · Fri Apr 01 04:00:00 EDT 2011 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/730/2/84· OSTI ID:21574873

Zhiyuan, Li; Jones, Christine; Forman, William R; Kraft, Ralph P; Lal, Dharam V; Di Stefano, Rosanne ^[1]; Spitler, Lee R ^[2]; Tang, Shikui; Wang, Q Daniel ^[3]; Gilfanov, Marat ^[4]; Revnivtsev, Mikhail ^[5]

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1. Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
2. Centre for Astrophysics and Supercomputing, Swinburne University, Hawthorn, VIC 3122 (Australia)
3. Department of Astronomy, University of Massachusetts, 710 North Pleasant Street, Amherst, MA 01003 (United States)
4. Max-Planck-Institut fuer Astrophysik, Karl-Schwarzschild-Str 1, 85741 Garching bei Muenchen (Germany)
5. Excellence Cluster Universe, Technische Universitaet Muenchen, Boltzmannstr.2, 85748 Garching (Germany)

Based on new and archival Chandra observations of the Sombrero galaxy (M 104 = NGC 4594), we study the X-ray emission from its nucleus and the extended X-ray emission in and around its massive stellar bulge. We find that the 0.3-8 keV luminosity of the nucleus appears constant at {approx}2.4 x 10{sup 40} erg s{sup -1}, or {approx}10{sup -7} of its Eddington luminosity, on three epochs between 1999 December and 2008 April, but drops by a factor of two in the 2008 November observation. The 2-6 keV unresolved emission from the bulge region closely follows the K-band starlight and most likely arises from unresolved stellar sources. At lower energies, however, the unresolved emission reaches a galactocentric radius of at least 23 kpc, significantly beyond the extent of the starlight, clearly indicating the presence of diffuse hot gas. We isolate the emission of the gas by properly accounting for the emission from unresolved stellar sources, predominantly cataclysmic variables and coronally active binaries, whose quasi-universal X-ray emissivity was recently established. We find a gas temperature of {approx}0.6 keV with little variation across the field of view, except for a lower temperature of {approx}0.3 keV along the stellar disk. The metal abundance is not well constrained due to the limited counting statistics, but is consistent with metal enrichment by Type Ia supernovae (SNe Ia). We measure a total intrinsic 0.3-2 keV luminosity of {approx}2 x 10{sup 39} erg s{sup -1}, which corresponds to only 1% of the available energy input by SNe Ia in the bulge, but is comparable to the prediction by the latest galaxy formation models for disk galaxies as massive as Sombrero. However, such numerical models do not fully account for internal feedback processes, such as nuclear feedback and stellar feedback, against accretion from the intergalactic medium. On the other hand, we find no evidence for either the nucleus or the very modest star-forming activities in the disk to be a dominant heating source for the diffuse gas. We also show that neither the expected energy released by SNe Ia nor the expected mass returned by evolved stars is recovered by observations. We argue that in Sombrero a galactic-scale subsonic outflow of hot gas continuously removes much of the 'missing' energy and mass input from the bulge region. The observed density and temperature distributions of such an outflow, however, continue to pose challenges to theoretical studies.

• OSTI ID: 21574873
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 730; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
BINARY STARS
COSMIC RAY SOURCES
COSMIC X-RAY SOURCES
ELECTROMAGNETIC RADIATION
EMISSION
ERUPTIVE VARIABLE STARS
GALAXIES
IONIZING RADIATIONS
LUMINOSITY
OPTICAL PROPERTIES
PHYSICAL PROPERTIES
RADIATIONS
STARS
SUPERNOVAE
VARIABLE STARS
X RADIATION
X-RAY GALAXIES