301 research outputs found
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
Chandra and XMM Observations of the ADC Source 0921-630
We analyze observations of the low mass X-ray binary 2S0921-63 obtained with
the gratings and CCDs on Chandra and XMM. This object is a high inclination
system showing evidence for an accretion disk corona (ADC). Such a corona has
the potential to constrain the properties of the heated accretion disk in this
system, and other LMXBs by extension. We find evidence for line emission which
is generally consistent with that found by previous experiments, although we
are able to detect more lines. For the first time in this source, we find that
the iron K line has multiple components. We set limits on the line widths and
velocity offsets, and we fit the spectra to photoionization models and discuss
the implications for accretion disk corona models. For the first time in any
ADC source we use these fits, together with density constraints based on the O
VII line ratio, in order to constrain the flux in the medium-ionization region
of the ADC. Under various assumptions about the source luminosity this
constrains the location of the emitting region. These estimates, together with
estimates for the emission measure, favor a scenario in which the intrinsic
luminosity of the source is comparable to what we observe.Comment: 40 pages, 11 figures submitted to Ap.
Extended emission-line regions in low-redshift quasars: Dependence on nuclear spectral properties
We searched for the presence of extended emission-line regions (EELRs) around
low-redshift QSOs. We observed a sample of 20 mainly radio-quiet low-redshift
quasars (z<0.3) by means of integral field spectroscopy. After decomposing the
extended and nuclear emission components, we constructed [OIII] 5007
narrow-band images of the EELR to measure the total flux. From the same data we
obtained high S/N (>50) nuclear spectra to measure properties such as
[OIII]/Hbeta flux ratios, FeII equivalent widths and Hbeta line widths. A
significant fraction of the quasars (8/20) show a luminous EELR, with detected
linear sizes of several kpc. Whether or not a QSO has a luminous EELR is
strongly related with nuclear properties, in the sense that an EELR was
detected in objects with low FeII equivalent width and large Hbeta FWHM. The
EELRs were detected preferentially in QSOs with larger black hole masses. There
is no discernible relation, however, between EELR detection and QSO luminosity
and Eddington ratio.Comment: 4 pages, 4 figures, accepted for publication in A&
The Black Hole Mass - Galaxy Bulge Relationship for QSOs in the SDSS DR3
We investigate the relationship between black hole mass and host galaxy
velocity dispersion for QSOs in Data Release 3 of the Sloan Digital Sky Survey.
We derive black hole mass from the broad Hbeta line width and continuum
luminosity, and the bulge stellar velocity dispersion from the [OIII] narrow
line width. At higher redshifts, we use MgII and [OII] in place of Hbeta and
[OIII]. For redshifts z < 0.5, our results agree with the black hole mass -
bulge velocity dispersion relationship for nearby galaxies. For 0.5 < z < 1.2,
this relationship appears to show evolution with redshift in the sense that the
bulges are too small for their black holes. However, we find that part of this
apparent trend can be attributed to observational biases, including a Malmquist
bias involving the QSO luminosity. Accounting for these biases, we find ~0.2
dex evolution in the black hole mass-bulge velocity dispersion relationship
between now and redshift z ~ 1.Comment: Accepted by ApJ, 15 pages, 9 figure
Ultraviolet observations of the X-ray photoionized wind of Cygnus X-1 during X-ray soft/high state
(Shortened) Ultraviolet observations of the black hole X-ray binary Cygnus
X-1 were obtained using the STIS on HSTubble. We detect P Cygni line features
show strong, broad absorption components when the X-ray source is behind the
companion star and noticeably weaker absorption when the X-ray source is
between us and the companion star. We fit the P Cygni profiles using the SEI
method applied to a spherically symmetric stellar wind subject to X-ray
photoionization from the black hole. The Si IV doublet provides the most
reliable estimates of the parameters of the wind and X-ray illumination. The
velocity increases with radius according to
, with and
km s.The microturbulent velocity was
km s. Our fit implies a ratio of X-ray luminosity to wind mass-loss rate
of L, measured at = 4.8. Our
models determine parameters that may be used to estimate the accretion rate
onto the black hole and independently predict the X-ray luminosity. Our
predicted L matches that determined by contemporaneous RXTE ASM remarkably
well, but is a factor of 3 lower than the rate according to
Bondi-Hoyle-Littleton spherical wind accretion. We suggest that some of the
energy of accretion may go into powering a jet.Comment: 34 pages, 21 figures, 4 tables, accepted for publication in Ap
Enhanced Star Formation in Narrow Line Seyfert 1 AGN revealed by Spitzer
We present new low resolution Spitzer mid-infrared spectroscopy of a sample
of 20 ROSAT selected local Narrow Line Seyfert 1 galaxies (NLS1s). We detect
strong AGN continuum in all and clear PAH emission in 70% of the sources. The
6.2 micron PAH luminosity spans three orders of magnitudes, from ~10^(39) erg/s
to ~10^(42) erg/s providing strong evidence for intense ongoing star formation
in the circumnuclear regions of these sources. Using the IRS/Spitzer archive we
gather a large number of additional NLS1s and their broad line counterparts
(BLS1s) and constructed NLS1 and BLS1 sub-samples to compare them in various
ways. The comparison shows a clear separation according to FWHM(H_beta) such
that objects with narrower broad H_beta lines are the strongest PAH emitters.
We test this division in various ways trying to remove biases due to luminosity
and aperture size. Specifically, we find that star formation activity around
NLS1 AGN is larger than around BLS1 of the same AGN luminosity. The above
result seems to hold over the entire range of distance and luminosity. Moreover
the star formation rate is higher in low black hole mass and high L/L_Edd
systems indicating that black hole growth and star formation are occurring
simultaneously.Comment: 30 pages, 11 figures, 4 tables. Now accepted in MNRA
X-Ray Spectral Study of AGN Sources Content in Some Deep Extragalactic XMM-Newton Fields
We undertake a spectral study of a sample of bright X-ray sources taken from
six XMM-Newton fields at high galactic latitudes, where AGN are the most
populous class. These six fields were chosen such that the observation had an
exposure time more than 60 ksec, had data from the EPIC-pn detector in the
full-Frame mode and lying at high galactic latitude . The analysis
started by fitting the spectra of all sources with an absorbed power-law model,
and then we fitted all the spectra with an absorbed power-law with a low energy
black-body component model.The sources for which we added a black body gave an
F-test probability of 0.01 or less (i.e. at 99% confidence level), were
recognized as sources that display soft excess. We perform a comparative
analysis of soft excess spectral parameters with respect to the underlying
power-law one for sources that satisfy this criterion. Those sources, that do
not show evidence for a soft excess, based on the F-test probability at a 99%
confidence level, were also fitted with the absorbed power-law with a low
energy black-body component model with the black-body temperature fixed at 0.1
and 0.2 keV. We establish upper limits on the soft excess flux for those
sources at these two temperatures. Finally we have made use of Aladdin
interactive sky atlas and matching with NASA/IPAC Extragalactic Database (NED)
to identify the X-ray sources in our sample. For those sources which are
identified in the NED catalogue, we make a comparative study of the soft excess
phenomenon for different types of systems
Identification of an Extended Accretion Disk Corona in the Hercules X-1 Low State: Moderate Optical Depth, Precise Density Determination, and Verification of CNO Abundances
We identify an accretion disk atmosphere and corona from the high resolution
X-ray spectrum of Hercules X-1, and we determine its detailed physical
properties. More than two dozen recombination emission lines (from Fe XXVI at
1.78 A to N VI at 29.08 A) and Fe K-alpha, K-beta fluorescence lines were
detected in a 50 ks observation with the Chandra High-Energy Transmission
Grating Spectrometer (HETGS). They allow us to measure the density,
temperature, spatial distribution, elemental composition, and kinematics of the
plasma. We exclude HZ Her as the source of the recombination emission. We
compare accretion disk model atmospheres with the observed spectrum in order to
constrain the stratification of density and ionization, disk atmosphere area,
elemental composition, and energetics. The atmospheric spectrum observed during
the low state is photoionized by the main-on X-ray continuum, indicating that
the disk is observed edge-on during the low state. We infer the mean number of
scatterings N of Ly-alpha and Ly-beta line photons from H-like ions. We derive
N < 69 for O VIII Ly_alpha_1, which rules out the presence of a mechanism
modeled by Sako (2003) to enhance N VII emission via a line overlap with O
VIII. The line optical depth diagnostics are consistent with a flattened
atmosphere. Our spectral analysis, the disk atmosphere model, and the presence
of intense N VII and N VI lines (plus N V in the UV), confirm the
over-abundance of nitrogen relative to other metals, which was shown to be
indicative of CNO cycle processing in a massive progenitor.Comment: 38 pages, 14 figures, accepted for publication in Ap
The UV Properties of the Narrow Line Quasar I Zwicky 1
I Zw 1 is the prototype narrow line quasar. We report here the results of our
study of the UV emission of I Zw 1 using a high S/N (50-120) spectrum obtained
with the HST FOS. The following main new results are obtained: 1. The Mg II and
Al III doublets are partially/fully resolved. The measured doublet ratios
verify theoretical predictions that the lines are thermalized in the BLR. 2. A
weak associated UV absorption system is detected in N~V, and possibly also in C
IV and Lya, suggesting an outflow with a velocity of 1870 km/s and velocity
dispersion <300 km/s. 3. Lines from ions of increasing ionization level show
increasing excess blue wing flux, and an increasing line peak velocity shift,
reaching a maximum blueshift of about 2000 km/s for He II 1640. This may
indicate an out-flowing component in the BLR, where the ionization level
increases with velocity, and which is visible only in the approaching
direction. The highest velocity part of this outflow may produce the associated
UV absorption system. 4. The small C III] 1909 EW, and the small C III]
1909/Lya and C III] 1909/Si III] 1892 flux ratios indicate a typical BLR
density of 10^11, i.e. about an order of magnitude larger than implied by C
III] 1909 in most quasars. A BLR component of a higher density is implied by
the EW and doublet ratio of the Al III 1857 doublet. 5. Prominent Fe II UV 191
emission is seen, together with weaker line emission at 1294 and 1871 A. These
three features have been proposed as evidence for significant Lya pumping of
the 8-10 eV levels of Fe II. 6. Significant Fe III emission is present. The Fe
III UV 34 and UV 48 multiplets are clearly resolved, and Fe III UV 1, UV 47, UV
50, and UV 68 may also be present. (Shortened version)Comment: 28 pages, 1 table and 7 figures included. Uses aas2pp4.sty. Scheduled
for the Astrophysical Journal November 10, 1997 issue, Vol. 48
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