396 research outputs found
Observational Similarities and Potential Connections Between Luminous Ultrasoft NLS1s and BALQSOs
Luminous ultrasoft NLS1s and low-ionization BALQSOs share many properties,
and they both represent important extremes of the active galaxy phenomenon. We
briefly discuss their observational similarities as well as potential physical
connections between them, concentrating on the X-ray point of view. We present
several ways by which potential connections might be further tested.Comment: Invited talk presented at the Joint MPE,AIP,ESO workshop on NLS1s,
Bad Honnef, Dec. 1999, to appear in New Astronomy Reviews; also available at
http://wave.xray.mpe.mpg.de/conferences/nls1-worksho
Deep Extragalactic X-ray Surveys
Deep surveys of the cosmic X-ray background are reviewed in the context of
observational progress enabled by the Chandra X-ray Observatory and the X-ray
Multi-Mirror Mission-Newton. The sources found by deep surveys are described
along with their redshift and luminosity distributions, and the effectiveness
of such surveys at selecting active galactic nuclei (AGN) is assessed. Some key
results from deep surveys are highlighted including (1) measurements of AGN
evolution and the growth of supermassive black holes, (2) constraints on the
demography and physics of high-redshift AGN, (3) the X-ray AGN content of
infrared and submillimeter galaxies, and (4) X-ray emission from distant
starburst and normal galaxies. We also describe some outstanding problems and
future prospects for deep extragalactic X-ray surveys.Comment: 32 pages; Annu. Rev. Astron. Astrophys., Volume 43 (2005); updated to
match accepted versio
Sequence of the cysteine-containing portion of histone F2al from the sea urchin Parechinus angulosus
1H0419-577: a two-state Seyfert Galaxy?
The preliminary results of the BeppoSAX observation of the radio-quiet AGN
1H0419-577 are presented. Despite its broad line optical spectrum, the
intermediate X-ray spectrum (i.e. 2--10 keV) is flatter than typically observed
in Seyfert 1s and no iron line is significantly detected. Even more
intriguingly, a 1992 ROSAT pointed observation suggests a dramatic (~ 1) change
in the spectral shape for E < 2 keV. Such behavior is briefly discussed in the
framework of our current understanding of Comptonization scenarios in the
nuclear regions of radio-quiet AGN.Comment: 4 pages, Latex, 4 Postscript figures, `espcrc2.sty included, to
appear in the Proceedigns of the Workshop "The active X-ray sky: results from
Beppo-SAX and RXTE
Probing Broad Absorption Line Quasar Outflows: X-ray Insights
Energetic outflows appear to occur in conjunction with active mass accretion
onto supermassive black holes. These outflows are most readily observed in the
approximately 10% of quasars with broad absorption lines, where the observer's
line of sight passes through the wind. Until fairly recently, the paucity of
X-ray data from these objects was notable, but now sensitive hard-band missions
such as Chandra and XMM-Newton are routinely detecting broad absorption line
quasars. The X-ray regime offers qualitatively new information for the
understanding of these objects, and these new results must be taken into
account in theoretical modeling of quasar winds.Comment: Submitted to Advances in Space Research for New X-ray Results from
Clusters of Galaxies and Black Holes (Oct 2002; Houston, TX), eds. C. Done,
E.M. Puchnarewicz, M.J. Ward. Requires cospar.sty (6 pgs, 5 figs
Restless Quasar Activity: From BeppoSAX to Chandra and XMM-Newton
We briefly review some of the progress made in the last decade in the study
of the X-ray properties of the quasar population from the luminous, local
objects observed by BeppoSAX to the large, rapidly increasing population of z>4
quasars detected by Chandra and XMM-Newton in recent years.Comment: 4 pages, 4 figures. To appear in the Proceedings of the Symposium
"The Restless High-Energy Universe", 5-8 May 2003, Amsterdam, The
Netherlands, E.P.J. van den Heuvel, J.J.M. in 't Zand, and R.A.M.J. Wijers
Ed
X-ray Surveys and Wide-Field Optical/Near-Infrared Imaging with the Joint Dark Energy Mission
I briefly describe a few important scientific issues that could be addressed
effectively via the combination of data from JDEM and X-ray missions. The
topics covered are largely focused on active galactic nuclei (AGN) and include
(1) the selection of AGN via X-ray emission and optical variability, (2)
nuclear outbursts in galaxies due to transient fueling of their supermassive
black holes, (3) moderate-luminosity AGN at high redshift (z > 4) found via
application of "dropout" techniques to X-ray sources, and (4) the host-galaxy
morphologies of X-ray selected AGN. I also describe the substantial challenges
to obtaining wide-field X-ray data with sufficient sensitivity to complement
JDEM properly.Comment: 9 pages, 3 color figures, latex. To appear in the conference
proceedings of "Wide Field Imaging from Space" published in New Astronomy
Reviews, ed. T. McKay, A. Fruchter, & E. Linde
The UV spectra of NLS1s - Implications for their broad line regions
We study the UV spectra of NLS1 galaxies and compare them with typical
Seyfert 1 galaxies and quasars. The NLS1 spectra show narrower UV lines as well
as weaker CIV lambda 1549 and CIII] lambda 1909 emission. We show that these
line properties are due to a lower ionization parameter and somewhat higher BLR
cloud densities. These modified conditions can be explained by the hotter big
blue bumps observed in NLS1s, which are in turn due to higher L/L_Edd ratios,
as shown by our accretion disk and corona modeling of the NLS1 continua. We
also present evidence that the Boroson & Green eigenvector 1, which is
correlated with the optical and UV emission-line properties, is not driven by
orientation and hence NLS1s, which have extreme eigenvector 1 values, are not
viewed from an extreme viewing angle.Comment: Contributed talk presented at the Joint MPE,AIP,ESO workshop on
NLS1s, Bad Honnef, Dec. 1999, to appear in New Astronomy Reviews; also
available at http://wave.xray.mpe.mpg.de/conferences/nls1-worksho
The cosmic history of hot gas cooling and radio active galactic nucleus activity in massive early-type galaxies
We study the X-ray properties of 393 optically selected early-type galaxies (ETGs) over the redshift range of zâ 0.0â1.2 in the Chandra Deep Fields (CDFs). To measure the average X-ray properties of the ETG population, we use X-ray stacking analyses with a subset of 158 passive ETGs (148 of which were individually undetected in X-ray). This ETG subset was constructed to span the redshift ranges of z= 0.1â1.2 in the â4âMs CDF-South and â2âMs CDF-North and z= 0.1â0.6 in the â250âks Extended-CDF-South where the contribution from individually undetected active galactic nuclei (AGN) is expected to be negligible in our stacking. We find that 55 of the ETGs are detected individually in X-ray, and 12 of these galaxies have properties consistent with being passive hot-gas-dominated systems (i.e. systems not dominated by an X-ray bright AGN). On the basis of our analyses, we find little evolution in the mean 0.5â2âkeV to B-band luminosity ratio (LX/LBâ [1 +z]1.2) since zâ 1.2, implying that some heating mechanism prevents the gas from cooling in these systems. We consider that feedback from radio-mode AGN activity could be responsible for heating the gas. We select radio AGN in the ETG population using their far-infrared/radio flux ratio. Our radio observations allow us to constrain the duty cycle history of radio AGN activity in our ETG sample. We estimate that if scaling relations between radio and mechanical power hold out to zâ 1.2 for the ETG population being studied here, the average mechanical power from AGN activity is a factor of â1.4â2.6 times larger than the average radiative cooling power from hot gas over the redshift range zâ 0â1.2. The excess of inferred AGN mechanical power from these ETGs is consistent with that found in the local Universe for similar types of galaxies
Probing the extremes of Seyfert activity: BeppoSAX observations of Narrow-Line Seyfert 1 galaxies
Results are presented for the first year of observations of a selected sample
of Narrow-Line Seyfert 1 galaxies (Ton S 180, RE J1034+396, Ark 564) obtained
with the imaging instruments onboard BeppoSAX. These are the first simultaneous
broad band (0.1--10 keV) spectra so far obtained for this class of objects.Comment: Contributed Talk, to appear in : The Active X-ray Sky: Results from
BeppoSAX and Rossi-XTE, Nuclear Physics B Proceedings Supplements, L. Scarsi,
H. Bradt, P. Giommi and F. Fiore (eds.), Elsevier Science B.V. 6 pages LateX
and 8 ps figures, using espcrc2 and epsfi
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