1998/09/11 by E. J. M. Colbert, R. F. Mushotzky
Physics and Astronomy · #Active galactic nucleus #Astronomy #Astrophysical Phenomena and Observations #Astrophysics #Astrophysics and Cosmic Phenomena #Black hole (networking) #Elliptical galaxy #Galaxies: Formation, Evolution, Phenomena #Galaxy #Lenticular galaxy #Luminosity #Physics #ROSAT #Spiral galaxy #Supernova #astro-ph
paper · pdf · doi:10.1016/s0273-1177(99)00231-8
4 pages, TeX, two postscript figures, to be published in proceedings of 32nd COSPAR Session E1.2 (1998 July 15-17 Nagoya) "The AGN-Normal Galaxy Connection"
arxiv created 1998/09/11 · openalex publication_date 1999/01/01 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
We have found compact, near-nuclear X-ray sources in 21 (54%) of a complete sample of 39 nearby face-on spiral and elliptical galaxies with available ROSAT HRI data. ROSAT X-ray luminosities (0.2 - 2.4 keV) of these compact X-ray sources are ∼1037-1040 erg~s-1. The mean displacement between the location of the compact X-ray source and the optical photometric center of the galaxy is ∼390 pc. ASCA spectra of six of the 21 galaxies show the presence of a hard component with relatively steep (Γ≈ 2.5) spectral slope. A multicolor disk blackbody plus power-law model fits the data from the spiral galaxies well, suggesting that the X-ray objects in these galaxies may be similar to a black hole candidate (BHC) in its soft (high) state. ASCA data from the elliptical galaxies indicate that hot (kT ≈ 0.7 keV) gas dominates the emission. The fact that the spectral slope of the spiral galaxy sources is steeper than in normal type 1 active galactic nuclei (AGNs) and that relatively low absorbing columns (NH ≈ 1021 cm-2) were found to the power-law component indicates that these objects are somehow geometrically and/or physically different from AGNs in normal active galaxies. The X-ray sources in the spiral galaxies may be BHCs, low-luminosity AGNs, or possibly X-ray luminous supernovae. We estimate the black hole masses of the X-ray sources in the spiral galaxies (if they are BHCs or AGNs) to be ∼102-103 M_\odot. The X-ray sources in the elliptical galaxies may be BHCs, AGNs or young X-ray supernova also.