480 research outputs found
Blueshifted [O III] Emission: Indications of a Dynamic NLR
The [O III] 5007 line is commonly used as an indicator of the systemic
redshift of AGNs. Also, recent studies have used the width of this emission
line as a proxy for the stellar velocity dispersion in the host galaxy. This
paper calls both of these assumptions into question by analyzing a sample of
approximately 400 AGN spectra from the first data release of the Sloan Digital
Sky Survey. These spectra show that the low-ionization forbidden lines ([O II],
[N II], [S II]) define a consistent redshift, but that the peak of the [O III]
line is blueshifted in approximately half of the AGNs with respect to that
redshift. For the sample studied here, the average shift is 40 km/s, with the
largest shift being over 400 km/s. The magnitude of this shift is found to be
correlated with a number of properties, including the width of the [O III] line
and the Eddington ratio (L/L), derived from the luminosity and width of
H-beta.Comment: 17 pages, 4 figures, accepted for publication in the Astronomical
Journa
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 Lunar Laser Communication Demonstration: NASA’s First Step Toward Very High Data Rate Support of Science and Exploration Missions
Future NASA missions for both Science and Exploration will have needs for much higher data rates than are presently available, even with NASA’s highly-capable Space- and Deep-Space Networks. As a first step towards this end, for one month in late 2013, NASA’s Lunar Laser Communication Demonstration (LLCD) successfully demonstrated for the first time high-rate duplex laser communications between a satellite in lunar orbit, the Lunar Atmosphere and Dust Environment Explorer (LADEE), and multiple ground stations on the Earth. It constituted the longest-range laser communication link ever built and demonstrated the highest communication data rates ever achieved to or from the Moon.
This report will summarize the main achievements of LLCD and put them in context of the near-term and long-term communications goals of NASA space missions.United States. National Aeronautics and Space Administration (Air Force Contract #FA8721-05-C-0002
PPM demodulation: On approaching fundamental limits of optical communications
We consider the problem of demodulating M-ary optical PPM (pulse-position
modulation) waveforms, and propose a structured receiver whose mean probability
of symbol error is smaller than all known receivers, and approaches the quantum
limit. The receiver uses photodetection coupled with optimized phase-coherent
optical feedback control and a phase-sensitive parametric amplifier. We present
a general framework of optical receivers known as the conditional pulse nulling
receiver, and present new results on ultimate limits and achievable regions of
spectral versus photon efficiency tradeoffs for the single-spatial-mode
pure-loss optical communication channel.Comment: 5 pages, 6 figures, IEEE ISIT, Austin, TX (2010
A Candidate Sub-Parsec Supermassive Binary Black Hole System
We identify SDSS J153636.22+044127.0, a QSO discovered in the Sloan Digital
Sky Survey, as a promising candidate for a binary black hole system. This QSO
has two broad-line emission systems separated by 3500 km/sec. The redder system
at z=0.3889 also has a typical set of narrow forbidden lines. The bluer system
(z=0.3727) shows only broad Balmer lines and UV Fe II emission, making it
highly unusual in its lack of narrow lines. A third system, which includes only
unresolved absorption lines, is seen at a redshift, z=0.3878, intermediate
between the two emission-line systems. While the observational signatures of
binary nuclear black holes remain unclear, J1536+0441 is unique among all QSOs
known in having two broad-line regions, indicative of two separate black holes
presently accreting gas. The interpretation of this as a bound binary system of
two black holes having masses of 10^8.9 and 10^7.3 solar masses, yields a
separation of ~ 0.1 parsec and an orbital period of ~100 years. The separation
implies that the two black holes are orbiting within a single narrow-line
region, consistent with the characteristics of the spectrum. This object was
identified as an extreme outlier of a Karhunen-Loeve Transform of 17,500 z <
0.7 QSO spectra from the SDSS. The probability of the spectrum resulting from a
chance superposition of two QSOs with similar redshifts is estimated at
2X10^-7, leading to the expectation of 0.003 such objects in the sample
studied; however, even in this case, the spectrum of the lower redshift QSO
remains highly unusual.Comment: 8 pages, 2 figures, Nature in pres
H-beta Line Width and the UV-X-ray Spectra of Luminous AGN
The width of the broad H-beta emission line is the primary defining
characteristic of the NLS1 class. This parameter is also an important component
of Boroson and Green's optical Eigenvector 1 (EV1), which links steeper soft
X-ray spectra with narrower H-beta emission, stronger H-beta blue wing,
stronger optical Fe II emission, and weaker [O III] lambda 5007. Potentially,
EV1 represents a fundamental physical process linking the dynamics of fueling
and outflow with the accretion rate. We attempted to understand these
relationships by extending the optical spectra into the UV for a sample of 22
QSOs with high quality soft-X-ray spectra, and discovered a whole new set of UV
relationships that suggest that high accretion rates are linked to dense gas
and perhaps nuclear starbursts. While it has been argued that narrow (BLR)
H-beta means low Black Hole mass in luminous NLS1s, the C IV, lambda 1549 and
Ly alpha emission lines are broader, perhaps the result of outflows driven by
their high Eddington accretion rates. We present some new trends of optical-UV
with X-ray spectral energy distributions. Steeper X-ray spectra appear
associated with stronger UV relative to optical continua, but the presence of
strong UV absorption lines is associated with depressed soft X-rays and redder
optical-UV continua.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
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
Testing Hydrodynamic Models of LMC X-4 with UV and X-ray Spectra
We compare the predictions of hydrodynamic models of the LMC X-4 X-ray binary
system with observations of UV P Cygni lines with the GHRS and STIS
spectrographs on the Hubble Space Telescope. The hydrodynamic model determines
density and velocity fields of the stellar wind, wind-compressed disk,
accretion stream, Keplerian accretion disk, and accretion disk wind. We use a
Monte Carlo code to determine the UV P Cygni line profiles by simulating the
radiative transfer of UV photons that originate on the star and are scattered
in the wind. The qualitative orbital variation predicted is similar to that
observed, although the model fails to reproduce the strong orbital asymmetry
(the observed absorption is strongest for phi>0.5). The model predicts a
mid-eclipse X-ray spectrum, due almost entirely to Compton scattering, with a
factor 4 less flux than observed with ASCA. We discuss how the model may need
to be altered to explain the spectral variability of the system.Comment: 11 figures, accepted by Ap
On-axis spectroscopy of the z=0.144 radio-loud quasar HE 1434-1600: an elliptical host with a highly ionized ISM
VLT on-axis optical spectroscopy of the z=0.144 radio-loud quasar HE
1434-1600 is presented. The spatially resolved spectra of the host galaxy are
deconvolved and separated from those of the central quasar in order to study
the dynamics of the stars and gas as well as the physical conditions of the
ISM. We find that the host of HE 1434-1600 is an elliptical galaxy that resides
in a group of at least 5 member galaxies, and that most likely experienced a
recent collision with its nearest companion. Compared with other quasar host
galaxies, HE 1434-1600 has a highly ionized ISM. The ionization state
corresponds to that of typical Seyferts, but the ionized regions are not
distributed in a homogeneous way around the QSO, and are located preferentially
several kiloparsecs away from it. While the stellar absorption lines do not
show any significant velocity field, the gas emission lines do. The observed
gas velocity field is hard to reconcile with dynamical models involving
rotating disk, modified Hubble laws or power laws, that all require extreme
central masses (M > 10^9 M_sun) to provide only poor fit to the data. Power law
models, which best fit the data, provide a total mass of M(< 10 kpc)=9.2 10^10
M_sun. We conclude that the recent interaction between HE 1434-1600 and its
closest companion has strongly affected the gas velocity and ionization state,
from the center of the galaxy to its most external parts.Comment: 11 pages, 14 figures, accepted for publication in Astronomy &
Astrophysic
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