37 research outputs found
X-ray Absorption and Reflection in Active Galactic Nuclei
X-ray spectroscopy offers an opportunity to study the complex mixture of
emitting and absorbing components in the circumnuclear regions of active
galactic nuclei, and to learn about the accretion process that fuels AGN and
the feedback of material to their host galaxies. We describe the spectral
signatures that may be studied and review the X-ray spectra and spectral
variability of active galaxies, concentrating on progress from recent Chandra,
XMM-Newton and Suzaku data for local type 1 AGN. We describe the evidence for
absorption covering a wide range of column densities, ionization and dynamics,
and discuss the growing evidence for partial-covering absorption from data at
energies > 10 keV. Such absorption can also explain the observed X-ray spectral
curvature and variability in AGN at lower energies and is likely an important
factor in shaping the observed properties of this class of source.
Consideration of self-consistent models for local AGN indicates that X-ray
spectra likely comprise a combination of absorption and reflection effects from
material originating within a few light days of the black hole as well as on
larger scales. It is likely that AGN X-ray spectra may be strongly affected by
the presence of disk-wind outflows that are expected in systems with high
accretion rates, and we describe models that attempt to predict the effects of
radiative transfer through such winds, and discuss the prospects for new data
to test and address these ideas.Comment: Accepted for publication in the Astronomy and Astrophysics Review. 58
pages, 9 figures. V2 has fixed an error in footnote
Dynamics of Disks and Warps
This chapter reviews theoretical work on the stellar dynamics of galaxy
disks. All the known collective global instabilities are identified, and their
mechanisms described in terms of local wave mechanics. A detailed discussion of
warps and other bending waves is also given. The structure of bars in galaxies,
and their effect on galaxy evolution, is now reasonably well understood, but
there is still no convincing explanation for their origin and frequency. Spiral
patterns have long presented a special challenge, and ideas and recent
developments are reviewed. Other topics include scattering of disk stars and
the survival of thin disks.Comment: Chapter accepted to appear in Planets, Stars and Stellar Systems, vol
5, ed G. Gilmore. 32 pages, 17 figures. Includes minor corrections made in
proofs. Uses emulateapj.st
Rapid growth of black holes in massive star-forming galaxies
The tight relationship between the masses of black holes and galaxy spheroids
in nearby galaxies implies a causal connection between the growth of these two
components. Optically luminous quasars host the most prodigious accreting black
holes in the Universe and can account for >30% of the total cosmological
black-hole growth. As typical quasars are not, however, undergoing intense star
formation and already host massive black holes [>10^(8) M(Sun)], there must
have been an earlier pre-quasar phase when these black holes grew [mass range
~10^(6)-10^(8) M(Sun)]. The likely signature of this earlier stage is
simultaneous black-hole growth and star formation in distant (i.e., z>1; >8
billion light years away) luminous galaxies. Here we report ultra-deep X-ray
observations of distant star-forming galaxies that are bright at submillimetre
wavelengths. We find that the black holes in these galaxies are growing almost
continuously throughout periods of intense star formation. This activity
appears to be more tightly associated with these galaxies than any other coeval
galaxy populations. We show that the black-hole growth from these galaxies is
consistent with that expected for the pre-quasar phase.Comment: 5 pages, 2 figures, to appear in Nature on 7th Apri
Air-Ground Interface: Reconstruction of Paleoclimates Using Speleothems
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