16,342 research outputs found
Intermediate-mass Black Holes in Galactic Nuclei
We present the first homogeneous sample of intermediate-mass black hole
candidates in active galactic nuclei. Starting with broad-line active nuclei
from the Sloan Digital Sky Survey, we use the linewidth-luminosity-mass scaling
relation to select a sample of 19 galaxies in the mass range M_BH ~ 8 x 10^4 -
10^6 solar masses. In contrast to the local active galaxy population, the host
galaxies are ~1 mag fainter than M* and thus are probably late-type systems.
The active nuclei are also faint, with M_g ~ -15 to -18 mag, while the
bolometric luminosities are close to the Eddington limit. The spectral
properties of the sample are compared to the related class of objects known as
narrow-line Seyfert 1 galaxies. We discuss the importance of our sample as
observational analogues of primordial black holes, contributors to the
integrated signal for future gravitational wave experiments, and as a valuable
tool in the calibration of the M-sigma relation.Comment: 4 pages, 4 figures. To appear in "The Interplay among Black Holes,
Stars and ISM in Galactic Nuclei," Proc. IAU 222 (Gramado, Brazil), eds Th.
Storchi Bergmann, L.C. Ho, H.R. Schmit
TOPEX orbital radiation study
The space radiation environment of the TOPEX spacecraft is investigated. A single trajectory was considered. The external (surface incident) charged particle radiation, predicted for the satellite, is determined by orbital flux integration for the specified trajectory. The latest standard models of the environment are used in the calculations. The evaluation is performed for solar maximum conditions. The spacecraft exposure to cosmic rays of galactic origin is evaluated over its flight path through the magnetosphere in terms of geomagnetic shielding effects, both for surface incident heavy ions and for particles emerging behind different material thickness. Limited shielding and dose evaluations are performed for simple infinite slab and spherical geometries. Results, given in graphical and tabular form, are analyzed, explained, and discussed. Conclusions are presented and commented on
SOFIP: A Short Orbital Flux Integration Program
A computer code was developed to evaluate the space radiation environment encountered by geocentric satellites. The Short Orbital Flux Integration Program (SOFIP) is a compact routine of modular compositions, designed mostly with structured programming techniques in order to provide core and time economy and ease of use. The program in its simplest form produces for a given input trajectory a composite integral orbital spectrum of either protons or electrons. Additional features are available separately or in combination with the inclusion of the corresponding (optional) modules. The code is described in detail, and the function and usage of the various modules are explained. A program listing and sample outputs are attached
A Case of Autoimmune Hepatitis Treated with Rituximab
Autoimmune hepatitis (AIH) is a form of chronic hepatitis of unknown etiology. It was first described in the 1950s as a form of chronic hepatitis noted in younger women. It was later termed lupoid hepatitis due to its association with autoantibodies before being named AIH in 1965. Corticosteroids and azathioprine have been the standard therapy for AIH, but due to treatment failures and toxicities from these medications, new medications are being investigated as possible treatment options. Rituximab has been used in various autoimmune disorders with good success. We report the case of a 34-year-old Caucasian woman with a history of B cell lymphoma and concurrent AIH treated with rituximab. The diagnosis of AIH was made by classic serological and histological features. The patient was initially treated with steroids but had a progression of her disease as well as suffering toxicities from the steroids. She was then given eight weeks of rituximab with good improvement in both laboratory and histological findings
Physical Properties of the Narrow-Line Region of Low-Mass Active Galaxies
We present spectroscopic observations of 27 active galactic nuclei (AGN) with
some of the lowest black hole (BH) masses known. We use the high spectral
resolution and small aperture of our Keck data, taken with the Echellette
Spectrograph and Imager, to isolate the narrow-line regions (NLRs) of these
low-mass BHs. We investigate their emission-line properties and compare them
with those of AGN with higher-mass black holes. While we are unable to
determine absolute metallicities, some of our objects plausibly represent
examples of the low-metallicity AGN described by Groves et al. (2006), based on
their [N II]/H_alpha ratios and their consistency with the Kewley & Ellison
(2008) mass-metallicity relation. We find tentative evidence for steeper far-UV
spectral slopes in lower-mass systems. Overall, NLR emission lines in these
low-mass AGN exhibit trends similar to those seen in AGN with higher-mass BHs,
such as increasing blueshifts and broadening with increasing ionization
potential. Additionally, we see evidence of an intermediate line region whose
intensity correlates with L/L_Edd, as seen in higher-mass AGN. We highlight the
interesting trend that, at least in these low-mass AGN, the [O III] equivalent
width (EW) is highest in symmetric NLR lines with no blue wing. This trend of
increasing [O III] EW with line symmetry could be explained by a high covering
factor of lower ionization gas in the NLR. In general, low-mass AGN preserve
many well-known trends in the structure of the NLR, while exhibiting steeper
ionizing continuum slopes and somewhat lower gas-phase metallicities.Comment: 46 pages, 14 figures, 7 table
Feedback In Luminous Obscured Quasars
We use spatially resolved long-slit spectroscopy from Magellan to investigate the extent, kinematics, and ionization structure in the narrow-line regions of 15 luminous, obscured quasars with z < 0.5. Increasing the dynamic range in luminosity by an order of magnitude, as well as improving the depth of existing observations by a similar factor, we revisit relations between narrow-line region size and the luminosity and linewidth of the narrow emission lines. We find a slope of 0.22 +/- 0.04 for the power-law relationship between size and luminosity, suggesting that the nebulae are limited by availability of gas to ionize at these luminosities. In fact, we find that the active galactic nucleus is effectively ionizing the interstellar medium over the full extent of the host galaxy. Broad (similar to 300-1000 km s(-1)) linewidths across the galaxies reveal that the gas is kinematically disturbed. Furthermore, the rotation curves and velocity dispersions of the ionized gas remain constant out to large distances, in striking contrast to normal and starburst galaxies. We argue that the gas in the entire host galaxy is significantly disturbed by the central active galactic nucleus. While only similar to 10(7)-10(8) M-circle dot worth of gas are directly observed to be leaving the host galaxies at or above their escape velocities, these estimates are likely lower limits because of the biases in both mass and outflow velocity measurements and may in fact be in accord with expectations of recent feedback models. Additionally, we report the discovery of two dual obscured quasars, one of which is blowing a large-scale (similar to 10 kpc) bubble of ionized gas into the intergalactic medium.NSF AST-0548198Astronom
A Stellar Dynamical Mass Measurement of the Black Hole in NGC 3998 from Keck Adaptive Optics Observations
We present a new stellar dynamical mass measurement of the black hole in the
nearby, S0 galaxy NGC 3998. By combining laser guide star adaptive optics
observations obtained with the OH-Suppressing Infrared Imaging Spectrograph on
the Keck II telescope with long-slit spectroscopy from the Hubble Space
Telescope and the Keck I telescope, we map out the stellar kinematics on both
small spatial scales, well within the black hole sphere of influence, and on
large scales. We find that the galaxy is rapidly rotating and exhibits a sharp
central peak in the velocity dispersion. Using the kinematics and the stellar
luminosity density derived from imaging observations, we construct
three-integral, orbit-based, triaxial stellar dynamical models. We find the
black hole has a mass of M_BH = (8.1_{-1.9}^{+2.0}) x 10^8 M_sun, with an
I-band stellar mass-to-light ratio of M/L = 5.0_{-0.4}^{+0.3} M_sun/L_sun
(3-sigma uncertainties), and that the intrinsic shape of the galaxy is very
round, but oblate. With the work presented here, NGC 3998 is now one of a very
small number of galaxies for which both stellar and gas dynamical modeling have
been used to measure the mass of the black hole. The stellar dynamical mass is
nearly a factor of four larger than the previous gas dynamical black hole mass
measurement. Given that this cross-check has so far only been attempted on a
few galaxies with mixed results, carrying out similar studies in other objects
is essential for quantifying the magnitude and distribution of the cosmic
scatter in the black hole mass - host galaxy relations.Comment: 19 pages, 15 figures, accepted for publication in Ap
- …