2,115 research outputs found
The largest black holes and the most luminous galaxies
The empirical relationship between the broad line region size and the source
luminosity in active galactic nuclei (AGNs) is used to obtain black holes (BH)
masses for a large number of quasars in three samples. The largests BH masses
found exceed 10^{10} Msun and are correlated, almost linearly, with the source
luminosity. Such BH masses, when converted to galactic bulge mass and
luminosity, indicate masses in excess of 10^{13} Msun and sigma(*) in excess of
700 km/sec. Such massive galaxies have never been observed. The largest BHs
reside, almost exclusively, in high redshift quasars. This, and the deduced BH
masses, suggest that several scenarios of BH and galaxy formation are
inconsistent with the observations. Either the observed size-L relationship in
low luminosity AGNs does not extend to very high luminosity or else the
M(BH)-M_B(bulge)-sigma(*) correlations observed in the local universe do not
reflect the relations of those quantities at the epoch of galaxy formation.Comment: 12 pages, 2 figures, one table, submitted to ApJ
Akn 564: an unusual component in the X-ray spectra of NLSy1 galaxies
We present an ASCA observation of the NLSy1 Ark 564. The X-ray light curve
shows rapid variability, but no evidence for energy-dependence to these
variations, within the 0.6 -- 10 keV bandpass. A strong (EW ~ 70 eV) spectral
feature is observed close to 1 keV. A similar feature has been observed in TON
S180 (another NLSy1) but has not been observed in broad-line Seyfert galaxies.
The feature energy suggests a large contribution from Fe L-shell lines but its
intensity is difficult to explain in terms of emission and/or absorption from
photoionized gas. Models based on gas in thermal equilibrium with kT ~1 keV
provide an alternative parameterization of the soft spectrum. The latter may be
interpreted as the hot intercloud medium, undergoing rapid cooling and
producing strong Fe L-shell recombination lines. In all cases the physical
conditions are rather different from those observed in broad-line Seyferts. The
hard X-ray spectrum shows a broad and asymmetric Fe Kalpha line of large
equivalent width (~550 eV) which can be explained by a neutral disk viewed at ~
60 degrees to the line-of-sight, contrary to the hypothesis that NLSy1s are
viewed pole-on. The large EW of this line, the strong 1 keV emission and the
strong optical Fe emission lines all suggest an extreme Fe abundance in this
and perhaps other NLSy1s.Comment: 15 pages, 5 figures. LaTeX with encapsulated postscript. Accepted for
publication in the Astrophysical Journa
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