290 research outputs found
Proper Motion of Water Masers Associated with IRAS 21391+5802: Bipolar Outflow and an AU-Scale Dusty Circumstellar Shell
We present VLBA observations of water maser emission associated with the
star-forming region IRAS 21391+5802, which is embedded in a bright rimmed
cometary globule in IC1396. The angular resolution of the maps is about 0.8
mas, corresponding to a spatial resolution of about 0.6 AU, at an estimated
distance of 750 pc. Proper motions are derived for 10 maser features identified
consistently over three epochs, which were separated by intervals of about one
month. The masers appear in four groups, which are aligned linearly on the sky,
roughly along a northeast-southwest direction, with a total separation of about
520 AU (about 0.7 arcseconds). The 3-D velocities of the masers have a maximum
value of about 42 km/s (about 9 AU/yr). The average error on the derived proper
motions is about 4 km/s. The overall pattern of proper motions is indicative of
a bipolar outflow. Proper motions of the masers in a central cluster, with a
projected extent of about 20 AU, show systematic deviations from a radial
outflow. However, we find no evidence of Keplerian rotation, as has been
claimed elsewhere. A nearly circular loop of masers lies near the middle of the
cluster. The radius of this loop is 1 AU and the line-of-sight velocities of
the masers in the loop are within 2 km/s of the systemic velocity of the
region. These masers presumably exist at the radial distance where significant
dust condensation occurs in the outflow emanating from the star.Comment: 15 pages, 4 figures. Accepted for publication in the Astrophysical
Journal. Version 2.12.00: Astrometric coordinates of maser revise
A Binary Millisecond Pulsar in Globular Cluster NGC6544
We report the detection of a new 3.06 ms binary pulsar in the globular
cluster NGC6544 using a Fourier-domain ``acceleration'' search. With an implied
companion mass of ~0.01 solar masses and an orbital period of only P_b~1.7
hours, it displays very similar orbital properties to many pulsars which are
eclipsed by their companion winds. The orbital period is the second shortest of
known binary pulsars after 47 Tuc R. The measured flux density of 1.3 +/- 0.4
mJy at 1332 MHz indicates that the pulsar is almost certainly the known
steep-spectrum point source near the core of NGC6544.Comment: Accepted by ApJ Letters on 11 October 2000, 5 page
X-ray Luminosity and Absorption Column Fluctuations in the H2O Maser Galaxy NGC 4258 from Weeks to Years
We report monitoring of the 0.3-10 keV spectrum of NGC4258 with XMM over 1.5
years.We als o report reprocessing of an overlapping series of archival Chandra
observations. By including earlier ASCA and SAX observations, we present a new,
nine-year time series of models fit to the X-ray spectrum of NGC4258. Over the
nine years, the photoelectric absorbing column (~10^23 cm^-2) did not vary
detectably, except for a ~40% drop between two ASCA epochs separated by 3 years
and a ~60% rise between two XMM epochs separated by just 5 months. In contrast,
factor of 2-3 changes are seen in absorbed flux on the timescale of years.
These are uncorrelated with changes in absorbing column and indicative of
central engine variability. The most rapid change in luminosity (5-10 keV) that
we detect is ~30% over 19 days. The warped disk, a known source of H2O maser
emission in NGC4258, is believed to cross the line of sight to the central
engine. We propose that the variations in absorbing column arise from
inhomogeneities sweeping across the line of sight in the rotating disk at the
radius where the disk crosses the line of sight. We estimate that the
inhomogeneities are ~10^15 cm in size at the crossing radius of 0.29 pc,
slightly smaller than the expected scale height of the disk. This result thus
provides strong evidence that the warped accretion disk is the absorber. This
is the first direct confirmation that obscuration in type-2 AGN may, in some
cases, arise in thin, warped accretion disks, rather than in geometrically
thick tori. We do not detect Fe Kalpha line emission in any of our XMM spectra.
We do not observe evidence of absorption lines in the XMM or reprocessed
Chandra data.Comment: 36 pages,14 figures. Accepted for publication in Ap
Concurrent Performances: Reinforcement By Different Doses Of Intravenous Cocaine In Rhesus Monkeys 1
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/96683/1/jeab.1974.22-179.pd
Discovery of Candidate HO Disk Masers in AGN and Estimations of Centripetal Accelerations
Based on spectroscopic signatures, about one-third of known HO maser
sources in active galactic nuclei (AGN) are believed to arise in highly
inclined accretion disks around central engines. These "disk maser candidates"
are of interest primarily because angular structure and rotation curves can be
resolved with interferometers, enabling dynamical study. We identify five new
disk maser candidates in studies with the Green Bank Telescope, bringing the
total number published to 30. We discovered two (NGC1320, NGC17) in a survey of
40 inclined active galaxies (v_{sys}< 20000 kms^{-1}). The remaining three disk
maser candidates were identified in monitoring of known sources: NGC449,
NGC2979, NGC3735. We also confirm a previously marginal case in UGC4203. For
the disk maser candidates reported here, inferred rotation speeds are 130-500
kms^{-1}. Monitoring of three more rapidly rotating candidate disks (CG211,
NGC6264, VV340A) has enabled measurement of likely orbital centripetal
acceleration, and estimation of central masses (2-7x10^7 M_\odot) and mean disk
radii (0.2-0.4pc). Accelerations may ultimately permit estimation of distances
when combined with interferometer data. This is notable because the three AGN
are relatively distant (10000<v_{sys}<15000 kms^{-1}). As signposts of highly
inclined geometries at galactocentric radii of \sim0.1-1pc, disk masers also
provide robust orientation references that allow analysis of (mis)alignment
between AGN and surrounding galactic stellar disks, even without
interferometric mapping. We find no preference among published disk maser
candidates to lie in high-inclination galaxies, providing independent support
for conclusions that central engines and galactic plane orientations are not
correlated. (ABRIDGED)Comment: 7 figures, accepted for publication in ApJ, Dec. 10, 200
Precise Black Hole Masses From Megamaser Disks: Black Hole-Bulge Relations at Low Mass
The black hole (BH)-bulge correlations have greatly influenced the last
decade of effort to understand galaxy evolution. Current knowledge of these
correlations is limited predominantly to high BH masses (M_BH> 10^8 M_sun) that
can be measured using direct stellar, gas, and maser kinematics. These objects,
however, do not represent the demographics of more typical L< L* galaxies. This
study transcends prior limitations to probe BHs that are an order of magnitude
lower in mass, using BH mass measurements derived from the dynamics of H_2O
megamasers in circumnuclear disks. The masers trace the Keplerian rotation of
circumnuclear molecular disks starting at radii of a few tenths of a pc from
the central BH. Modeling of the rotation curves, presented by Kuo et al.
(2010), yields BH masses with exquisite precision. We present stellar velocity
dispersion measurements for a sample of nine megamaser disk galaxies based on
long-slit observations using the B&C spectrograph on the Dupont telescope and
the DIS spectrograph on the 3.5m telescope at Apache Point. We also perform
bulge-to-disk decomposition of a subset of five of these galaxies with SDSS
imaging. The maser galaxies as a group fall below the M_BH-sigma* relation
defined by elliptical galaxies. We show, now with very precise BH mass
measurements, that the low-scatter power-law relation between M_BH and sigma*
seen in elliptical galaxies is not universal. The elliptical galaxy M_BH-sigma*
relation cannot be used to derive the BH mass function at low mass or the
zeropoint for active BH masses. The processes (perhaps BH self-regulation or
minor merging) that operate at higher mass have not effectively established an
M_BH-sigma* relation in this low-mass regime.Comment: 21 pages, 14 figures, accepted for publication in the Astrophysical
Journa
A Wide Field Survey of Satellite Galaxies around the Spiral Galaxy M106
We present a wide field survey of satellite galaxies in M106 (NGC 4258)
covering a 1.7\degr \times 2\degr field around M106 using
Canada-France-Hawaii Telescope/MegaCam. We find 16 satellite galaxy candidates
of M106.
Eight of these galaxies are found to be dwarf galaxies that are much smaller
and fainter than the remaining galaxies. Four of these galaxies are new
findings. Surface brightness profiles of 15 out of 16 satellite galaxies can be
represented well by an exponential disk profile with varying scale length. We
derive the surface number density distribution of these satellite galaxies. The
central number density profile (d kpc) is well fitted by a power-law
with a power index of , similar to the expected power index of
isothermal distribution. The luminosity function of these satellites is
represented well by the Schechter function with a faint end slope of
. Integrated photometric properties (total luminosity,
total colour, and disk scale length) and the spatial distribution of these
satellite galaxies are found to be roughly similar to those of the Milky Way
and M31.Comment: Accepted by MNRA
Dynamical Measurements of Black Hole Masses in Four Brightest Cluster Galaxies at 100 Mpc
We present stellar kinematics and orbit superposition models for the central
regions of four Brightest Cluster Galaxies (BCGs), based upon integral-field
spectroscopy at Gemini, Keck, and McDonald Observatories. Our integral-field
data span radii from < 100 pc to tens of kpc. We report black hole masses,
M_BH, of 2.1 +/- 1.6 x 10^10 M_Sun for NGC 4889, 9.7 + 3.0 - 2.6 x 10^9 M_Sun
for NGC 3842, and 1.3 + 0.5 - 0.4 x 10^9 M_Sun for NGC 7768. For NGC 2832 we
report an upper limit of M_BH < 9 x 10^9 M_Sun. Stellar orbits near the center
of each galaxy are tangentially biased, on comparable spatial scales to the
galaxies' photometric cores. We find possible photometric and kinematic
evidence for an eccentric torus of stars in NGC 4889, with a radius of nearly 1
kpc. We compare our measurements of M_BH to the predicted black hole masses
from various fits to the relations between M_BH and stellar velocity
dispersion, luminosity, or stellar mass. The black holes in NGC 4889 and NGC
3842 are significantly more massive than all dispersion-based predictions and
most luminosity-based predictions. The black hole in NGC 7768 is consistent
with a broader range of predictions.Comment: 24 pages, 18 figures. Accepted for publication in Ap
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A Search for H 2 O Maser Emission in Southern Active Galactic Nuclei and Starâforming Galaxies: Discovery of a Maser in the Edgeâon Galaxy IRAS F01063?8034
We report the cumulative results of five surveys for H2O maser emission at 1.35 cm wavelength in 131 active galactic nuclei (AGNs) and star-forming galaxies, conducted at the Parkes Observatory between 1993 and 1998. We detected one new maser, in the edge-on galaxy IRAS F01063-8034, which exhibits a single, ⌠0.1 Jy spectral feature at 4282 ± 6 km sâ1 (heliocentric) with an unusually large 54 ±16 km sâ1 half-power full width. The centroid velocity of the emission increased to 4319.6 ±0.6 km sâ1 (38 ±2 km sâ1 width) over the 13 days between discovery and confirmation of the detection. A similarly broad linewidth and large change in velocity has been noted for the maser in NGC 1052, wherein jet activity excites the emission. Neither optical spectroscopy, radio-infrared correlations, nor infrared colors provide compelling evidence of unusual activity in the nucleus of IRAS F01063-8034. Since the galaxy appears to be outwardly normal at optical and infrared wavelengths, detection of an H2O maser therein is unique. The maser emission is evidence that the galaxy harbors an AGN that is probably obscured by the edge-on galactic disk. The detection highlights the possibility that undetected AGNs could be hidden in other relatively nearby galaxies. No other maser emission features have been identified at velocities between 3084 km sâ1 and 6181 km sâ1.AstronomyPhysic
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A Warped Accretion Disk and WideâAngle Outflow in the Inner Parsec of the Circinus Galaxy
We present the first VLBI maps of H2O maser emission (λ1.3 cm) in the nucleus of the Circinus Galaxy, constructed from data obtained with the Australia Telescope Long Baseline Array. The maser emission traces a warped, edge-on accretion disk between radii of 0.11 ± 0.02 and ⌠0.40 pc, as well as a wide-angle outflow that extends up to ⌠1 pc from the estimated disk center. The disk rotation is close to Keplerian (v â r â0.5), the maximum detected rotation speed is 260 km sâ1, and the inferred central mass is 1.7 ± 0.3 Ă 106 Mâ. The outflowing masers are irregularly distributed above and below the disk, with relative outflow velocities up to ⌠±160 km sâ1 , projected along the line of sight. The flow probably originates closer than 0.1 pc to the central engine, possibly in an inward extension of the accretion disk, though there is only weak evidence of rotation in the outward moving material. We observe that the warp of the disk appears to collimate the outflow and to fix the extent of the ionization cone observed on larger angular scales. This study provides the first direct evidence (i.e., through imaging) of dusty, high-density, molecular material in a nuclear outflow < 1 pc from the central engine of a Seyfert galaxy, as well as the first graphic evidence that warped accretion disks can channel outflows and illumination patterns in AGN. We speculate that the same arrangement, which in some ways obviates the need for a geometrically thick, dusty torus, may apply to other type-2 AGN.AstronomyPhysic
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