THE NUCLEAR X-RAY EMISSION OF NEARBY EARLY-TYPE GALAXIES

Journal Article · Sat Jul 10 00:00:00 EDT 2010 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/717/2/640· OSTI ID:21455229

Pellegrini, S ^[1]

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1. Astronomy Department, University of Bologna, via Ranzani 1, 40127 Bologna (Italy)

Nuclear hard X-ray luminosities (L{sub X,nuc}) for a sample of 112 early-type galaxies within a distance of 67 Mpc are used to investigate their relationship with the central galactic black hole mass M{sub BH} (coming from direct dynamical studies or the M{sub BH}-{sigma} relation), the inner galactic structure (using the parameters describing its cuspiness), the hot gas content, and the core radio luminosity. For this sample, L {sub X,nuc} ranges from 10{sup 38} to 10{sup 42} erg s{sup -1}, and the Eddington ratio L{sub X,nuc}/L {sub Edd} from 10{sup -9} to 10{sup -4}, with the largest values belonging to four Seyfert galaxies. Together with a trend for L{sub X,nuc} to increase on average with the galactic luminosity L{sub B} and M{sub BH}, there is a wide variation of L{sub X,nuc} (and L{sub X,nuc}/L {sub Edd}), by up to 4 orders of magnitude, at any fixed L{sub B} > 6 x 10{sup 9} L{sub B,sun} or M{sub BH} > 10{sup 7} M{sub sun}. This large observed range should reflect a large variation of the mass accretion rate M-dot{sub BH}, and possible reasons for this difference are searched for. On the circumnuclear scale, in a scenario where accretion is (quasi) steady, M-dot{sub BH} at fixed L{sub B} (or M{sub BH}) could vary due to differences in the fuel production rate from stellar mass return linked to the inner galactic structure; a trend of L {sub X,nuc} with cuspiness is not observed, though, while a tendency for L{sub X,nuc}/L {sub Edd} to be larger in cuspier galaxies is present. In fact, M-dot {sub BH} is predicted to vary with cuspiness by a factor exceeding a few only in hot gas-poor galaxies and for large differences in the core radius; for a subsample with these characteristics the expected effect seems to be present in the observed L{sub X,nuc} values. L{sub X,nuc} does not show a dependence on the age of the stellar population in the central galactic region, for ages >3 Gyr; less luminous nuclei, though, are found among the youngest galaxies or galaxies with a younger stellar component. On the global galactic scale, L{sub X,nuc} shows a trend with the total galactic hot gas cooling rate (L{sub X,ISM}): it is detected both in gas-poor and gas-rich galaxies, and on average increases with L{sub X,ISM}, but again with a large scatter. The observed lack of a tight relationship between L{sub X,nuc} and the circumnuclear and total gas content can be explained if accretion is regulated by factors overcoming the importance of fuel availability, as (1) the gas is heated by black hole feedback and M-dot {sub BH} varies due to an activity cycle, and (2) the mass effectively accreted by the black hole can be largely reduced with respect to that entering the circumnuclear region, as in radiatively inefficient accretion with winds/outflows. Finally, differently from L{sub X,nuc}, the central 5 GHz VLA luminosity shows a clear trend with the inner galactic structure that is similar to that shown by the total soft X-ray emission; therefore, it is suggested that they could both be produced by the hot gas.

• OSTI ID: 21455229
• Journal Information: Astrophysical Journal, Vol. 717, Issue 2; Other Information: DOI: 10.1088/0004-637X/717/2/640; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
BLACK HOLES
GALAXY NUCLEI
GAS COOLING
HARD X RADIATION
LUMINOSITY
MASS
SEYFERT GALAXIES
SOFT X RADIATION
X-RAY GALAXIES
COOLING
COSMIC RAY SOURCES
COSMIC X-RAY SOURCES
ELECTROMAGNETIC RADIATION
GALAXIES
IONIZING RADIATIONS
OPTICAL PROPERTIES
PHYSICAL PROPERTIES
RADIATIONS
X RADIATION