1,691 research outputs found
A low-luminosity type-1 QSO sample; III. Optical spectroscopic properties and activity classification
We report on the optical spectroscopic analysis of a sample of 99
low-luminosity quasi-stellar objects (LLQSOs) at base the
Hamburg/ESO QSO survey (HES). The LLQSOs presented here offer the possibility
of studying the faint end of the QSO population at smaller cosmological
distances and, therefore, in greater detail. A small number of our LLQSO
present no broad component. Two sources show double broad components, whereas
six comply with the classic NLS1 requirements. As expected in NLR of broad line
AGNs, the [S{\sc{ii}}]based electron density values range between 100 and
1000 N/cm. Using the optical characteristics of Populations A and
B, we find that 50\% of our sources with H broad emission are consistent
with the radio-quiet sources definition. The remaining sources could be
interpreted as low-luminosity radio-loud quasar. The BPT-based classification
renders an AGN/Seyfert activity between 50 to 60\%. For the remaining sources,
the possible star burst contribution might control the LINER and HII
classification. Finally, we discuss the aperture effect as responsible for the
differences found between data sets, although variability in the BLR could play
a significant role as well.Comment: 22 pages; 5 tables; 17 figures; in press with A&
Adaptive Optics Near-Infrared Spectroscopy of the Sgr A* Cluster
We present K-band ~ 2600 spectroscopy of five stars
(K ~ 14 - 16 mag) within 0.''5 of Sgr A*, the radio source associated with the
compact massive object suspected to be a 2.6 x 10 \msun black hole at the
center of our Galaxy. High spatial resolution of ~ 0.''09, and good strehl
ratios of ~ 0.2 achieved with adaptive optics on the 10-meter Keck telescope
make it possible to measure moderate-resolution spectra of these stars
individually for the first time. Two stars (S0-17 and S0-18) are identified as
late-type stars by the detection of CO bandhead absorption in their spectra.
Their absolute K magnitudes and CO bandhead absorption strengths are consistent
with early K giants. Three stars (S0-1, S0-2, and S0-16), with r
0.0075 pc (~ 0.''2) from Sgr A*, lack CO bandhead absorption, confirming the
results of earlier lower spectral and lower spatial resolution observations
that the majority of the stars in the Sgr A* Cluster are early-type stars. The
absolute K magnitudes of the early-type stars suggest that they are late O -
early B main sequence stars of ages 20 Myr. The presence of young stars in
the Sgr A* Cluster, so close to the central supermassive black hole, poses the
intriguing problem of how these stars could have formed, or could have been
brought, within its strong tidal field.Comment: 19 pages, 8 figures, 2 tables. Accepted for publication in Ap
Line and Continuum Variability in Active Galaxies
We compared optical spectroscopic and photometric data for 18 AGN galaxies
over 2 to 3 epochs, with time intervals of typically 5 to 10 years. We used the
Multi-Object Double Spectrograph (MODS) at the Large Binocular Telescope (LBT)
and compared the spectra to data taken from the SDSS database and the
literature. We find variations in the forbidden oxygen lines as well as in the
hydrogen recombination lines of these sources. For 4 of the sources we find
that, within the calibration uncertainties, the variations in continuum and
line spectra of the sources are very small. We argue that it is mainly the
difference in black hole mass between the samples that is responsible for the
different degree of continuum variability. In addition we find that for an
otherwise constant accretion rate the total line variability (dominated by the
narrow line contributions) reverberates the continuum variability with a
dependency . Since
this dependency is prominently expressed in the narrow line emission it implies
that the luminosity dominating part of the narrow line region must be very
compact with a size of the order of at least 10 light years. A comparison to
literature data shows that these findings describe the variability
characteristics of a total of 61 broad and narrow line sources.Comment: 30 pages including the appendix, 18 figures including the appendix.
Accepted 2015 September 3. Received 2015 August 24; in original form 2015
July 3 in Monthly Notices of the Royal Astronomical Societ
High Proper Motion Stars in the Vicinity of Sgr A*: Evidence for a Supermassive Black Hole at the Center of Our Galaxy
Over a two year period (1995-1997), we have conducted a diffraction-limited
imaging study at 2.2 microns of the inner 6"x6" of the Galaxy's central stellar
cluster using the Keck 10-m telescope. The K band images obtained reveal a
large population of faint stars. We use an unbiased approach for identifying
and selecting stars to be included in this proper motion study, which results
in a sample of 90 stars with brightness ranging from K=9-17 and velocities as
large as 1,400+-100 km/sec. Compared to earlier work (Eckart et al. 1997;
Genzel et al. 1997), the source confusion is reduced by a factor of 9, the
number of stars with proper motion measurement in the central 25 arcsec^2 of
our galaxy is doubled, and the accuracy of the velocity measurements in the
central 1 arcsec^2 is improved by a factor of 4. The peaks of both the stellar
surface density and the velocity dispersion are consistent with the position of
the unusual radio source and blackhole candidate, Sgr A*, suggesting that Sgr
A* is coincident (+-0."1) with the dynamical center of the Galaxy. As a
function of distance from Sgr A*, the velocity dispersion displays a falloff
well fit by Keplerian motion about a central dark mass of 2.6(+-0.2)x10^6 Mo
confined to a volume of at most 10^-6 pc^3, consistent with earlier results.
Although uncertainties in the measurements mathematically allow for the matter
to be distributed over this volume as a cluster, no realistic cluster is
physically tenable. Thus, independent of the presence of Sgr A*, the large
inferred central density of at least 10^12 Mo/pc^3, which exceeds the
volume-averaged mass densities found at the center of any other galaxy, leads
us to the conclusion that our Galaxy harbors a massive central black hole.Comment: 19 pages, 8 figures, accepted for publications in the Astrophysical
Journa
The Molecular Gas in the Circumnuclear Region of Seyfert Galaxies
Sub-arcsecond IRAM Plateau de Bure mm-interferometric observations of the
12CO (2-1) line emission in the Seyfert~1 NGC 3227 and the Seyfert~2 NGC 1068
have revealed complex kinematic systems in the inner 100 pc to 300 pc that are
not consistent with pure circular motion in the host galaxies. Modeling of
these kinematic systems with elliptical orbits in the plane of the host galaxy
(representing gas motion in a bar potential) is a possible solution but does
not reproduce all features observed. A better description of the complex
kinematics is achieved by circular orbits which are tilted out of the plane of
the host galaxy. This could indicate that the thin circumnuclear gas disk is
warped. In the case of NGC 1068 the warp model suggests that at a radius of
about 70 pc, the gas disk is oriented edge-on providing material for the
obscuration of the AGN nucleus. The position-velocity diagrams show rising
rotation curves at r 2
x 10^7 M_solar for NGC 3227 and > 10^8 M_solar for NGC 1068 within the central
25 pc.Comment: 14 pages, Ap.J. letter, accepte
Proximity Effects and Nonequilibrium Superconductivity in Transition-Edge Sensors
We have recently shown that normal-metal/superconductor (N/S) bilayer TESs
(superconducting Transition-Edge Sensors) exhibit weak-link behavior.1 Here we
extend our understanding to include TESs with added noise-mitigating
normal-metal structures (N structures). We find TESs with added Au structures
also exhibit weak-link behavior as evidenced by exponential temperature
dependence of the critical current and Josephson-like oscillations of the
critical current with applied magnetic field. We explain our results in terms
of an effect converse to the longitudinal proximity effect (LoPE)1, the lateral
inverse proximity effect (LaiPE), for which the order parameter in the N/S
bilayer is reduced due to the neighboring N structures. Resistance and critical
current measurements are presented as a function of temperature and magnetic
field taken on square Mo/Au bilayer TESs with lengths ranging from 8 to 130
{\mu}m with and without added N structures. We observe the inverse proximity
effect on the bilayer over in-plane distances many tens of microns and find the
transition shifts to lower temperatures scale approximately as the inverse
square of the in- plane N-structure separation distance, without appreciable
broadening of the transition width. We also present evidence for nonequilbrium
superconductivity and estimate a quasiparticle lifetime of 1.8 \times 10-10 s
for the bilayer. The LoPE model is also used to explain the increased
conductivity at temperatures above the bilayer's steep resistive transition.Comment: 10 pages, 8 figure
Is the physical vacuum a preferred frame ?
It is generally assumed that the physical vacuum of particle physics should
be characterized by an energy momentum tensor in such a way to preserve exact
Lorentz invariance. On the other hand, if the ground state were characterized
by its energy-momentum vector, with zero spatial momentum and a non-zero
energy, the vacuum would represent a preferred frame. Since both theoretical
approaches have their own good motivations, we propose an experimental test to
decide between the two scenarios.Comment: 12 pages, no figure
Observed Limits on Charge Exchange Contributions to the Diffuse X-ray Background
We present a high resolution spectrum of the diffuse X-ray background from
0.1 to 1 keV for a ~1 region of the sky centered at l=90, b=+60 using a
36-pixel array of microcalorimeters flown on a sounding rocket. With an energy
resolution of 11 eV FWHM below 1 keV, the spectrum's observed line ratios help
separate charge exchange contributions originating within the heliosphere from
thermal emission of hot gas in the interstellar medium. The X-ray sensitivity
below 1 keV was reduced by about a factor of four from contamination that
occurred early in the flight, limiting the significance of the results. The
observed centroid of helium-like O VII is 568+2-3 eV at 90% confidence. Since
the centroid expected for thermal emission is 568.4 eV while for charge
exchange is 564.2 eV, thermal emission appears to dominate for this line
complex, consistent with much of the high-latitude O VII emission originating
in 2-3 x 10^6 K gas in the Galactic halo. On the other hand, the observed ratio
of C VI Ly gamma to Ly alpha is 0.3+-0.2. The expected ratios are 0.04 for
thermal emission and 0.24 for charge exchange, indicating that charge exchange
must contribute strongly to this line and therefore potentially to the rest of
the ROSAT R12 band usually associated with 10^6 K emission from the Local Hot
Bubble. The limited statistics of this experiment and systematic uncertainties
due to the contamination require only >32% thermal emission for O VII and >20%
from charge exchange for C VI at the 90% confidence level. An experimental gold
coating on the silicon substrate of the array greatly reduced extraneous
signals induced on nearby pixels from cosmic rays passing through the
substrate, reducing the triggered event rate by a factor of 15 from a previous
flight of the instrument.Comment: 14 pages, 7 figures, to be published in Ap
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