244 research outputs found
The Discovery of Water Maser Emission from Eight Nearby Galaxies
Using the Green Bank Telescope, we conducted a ``snapshot'' survey for water
maser emission toward the nuclei of 611 galaxies and detected eight new
sources. The sample consisted of nearby (v < 5000 km/s) and luminous (M_B <
-19.5) galaxies, some with known nuclear activity but most not previously known
to host AGNs. Our detections include both megamasers associated with AGNs and
relatively low luminosity masers probably associated with star formation. The
detection in UGC 3789 is particularly intriguing because the spectrum shows
both systemic and high-velocity lines indicative of emission from an AGN
accretion disk seen edge-on. Based on six months of monitoring, we detected
accelerations among the systemic features ranging from 2 to 8 km/s/yr, the
larger values belonging to the most redshifted systemic components.
High-velocity maser lines in UGC 3789 show no detectable drift over the same
period. Although UGC 3789 was not known to be an AGN prior to this survey, the
presence of a disk maser is strong evidence for nuclear activity, and an
optical spectrum obtained later has confirmed it. With follow up observations,
it may be possible to measure a geometric distance to UGC 3789.Comment: to appear in Astrophysical Journal, 1 May 200
Magnetic Fields in the Center of the Perseus Cluster
We present Very Long Baseline Array (VLBA) observations of the nucleus of NGC
1275, the central, dominant galaxy in the Perseus cluster of galaxies. These
are the first observations to resolve the linearly polarized emission from
3C84, and from them we determine a Faraday rotation measure (RM) ranging from
6500 to 7500 rad/m^2 across the tip of the bright southern jet component. At 22
GHz some polarization is also detected from the central parsec of 3C84,
indicating the presence of even more extreme RMs that depolarize the core at
lower frequencies. The nature of the Faraday screen is most consistent with
being produced by magnetic fields associated with the optical filaments of
ionized gas in the Perseus Cluster.Comment: Accepted for publication in MNRA
Polarimetry of Compact Symmetric Objects
We present multi-frequency VLBA observations of two polarized Compact
Symmetric Objects (CSOs), J0000+4054 and J1826+1831, and a polarized CSO
candidate, J1915+6548. Using the wavelength-squared dependence of Faraday
rotation, we obtained rotation measures (RMs) of -180 \pm 10 rad m^-2 and 1540
\pm 7 rad m^-2 for the latter two sources. These are lower than what is
expected of CSOs (several 1000 rad m^-2) and, depending on the path length of
the Faraday screens, require magnetic fields from 0.03 to 6 \mu G. These CSOs
may be more heavily affected by Doppler boosting than their unpolarized
counterparts, suggesting that a jet-axis orientation more inclined towards the
line of sight is necessary to detect any polarization. This allows for low RMs
if the polarized components are oriented away from the depolarizing
circumnuclear torus. These observations also add a fourth epoch to the proper
motion studies of J0000+4054 and J1826+1831, constraining their kinematic age
estimates to >610 yrs and 2600 \pm 490 yrs, respectively. The morphology,
spectrum, and component motions of J1915+6548 are discussed in light of its new
classification as a CSO candidate, and its angle to the line of sight (~50\deg)
is determined from relativistic beaming arguments.Comment: 29 pages, including 9 figures; Accepted by Astrophysical Journal, 16
Feb 0
Dating COINS: Kinematic Ages for Compact Symmetric Objects
We present multi-epoch VLBA observations of Compact Symmetric Objects (CSOs)
from the COINS sample (CSOs Observed In the Northern Sky). These observations
allow us to make estimates of, or place limits on, the kinematic ages for those
sources with well-identified hot spots. This study significantly increases the
number of CSOs with well-determined ages or limits. The age distribution is
found to be sharply peaked under 500 years, suggesting that many CSOs die
young, or are episodic in nature, and very few survive to evolve into FR II
sources like Cygnus A. Jet components are found to have higher velocities than
hot spots which is consistent with their movement down cleared channels. We
also report on the first detections of significant polarization in two CSOs,
J0000+4054 (2.1%) and J1826+1831 (8.8%). In both cases the polarized emission
is found in jet components on the stronger side of the center of activity.Comment: 34 pages including 7 figures, Accepted to ApJ on Dec 7, 200
J16021+3326: New Multi-Frequency Observations of a Complex Source
We present multifrequency Very Long Baseline Array (VLBA) observations of
J16021+3326. These observations, along with variability data obtained from the
Owens Valley Radio Observatory (OVRO) candidate gamma-ray blazar monitoring
program, clearly indicate this source is a blazar. The peculiar characteristic
of this blazar, which daunted previous classification attempts, is that we
appear to be observing down a precessing jet, the mean orientation of which is
aligned with us almost exactly.Comment: 16 pages, 7 Figures, 2 Tables, accepted to Ap
A survey of Low Luminosity Compact sources and its implication for evolution of radio-loud AGNs. I. Radio data
We present a new sample of Compact Steep Spectrum (CSS) sources with radio
luminosity below 10^26 W/Hz at 1.4 GHz called the low luminosity compact (LLC)
objects. The sources have been selected from FIRST survey and observed with
MERLIN at L-band and C-band. The main criterion used for selection was
luminosity of the objects and approximately one third of the CSS sources from
the new sample have a value of radio luminosity comparable to FRIs. About 80%
of the sources have been resolved and about 30% of them have weak extended
emission and disturbed structures when compared with the observations of higher
luminosity CSS sources. We studied correlation between radio power and linear
size, and redshift with a larger sample that included also published samples of
compact objects and large scale FRIIs and FRIs. The low luminosity compact
objects occupy the space in radio power versus linear size diagram below the
main evolutionary path of radio objects. We suggest that many of them might be
short-lived objects, and their radio emission may be disrupted several times
before becoming FRIIs. We conclude that there exists a large population of
short-lived low luminosity compact objects unexplored so far and part of them
can be precursors of large scale FRIs.Comment: 19 pages, 5 figures, 3 tables, MNRAS in pres
Atomic hydrogen in the one-sided "compact double" radio galaxy 2050+364
European VLBI Network spectral imaging of the "compact double" radio source
2050+364 in the UHF band at 1049 MHz has resolved the HI absorbing region, and
has shown a faint continuum component to the North (N), in addition to the
well-known East-West double (E, W). Re-examination of VLBI continuum images at
multiple frequencies suggests that 2050+364 may well be a one-sided core-jet
source, which appears as a double over a limited frequency range. One of the
dominant features, W, would then be the innermost visible portion of the jet,
and could be at or adjacent to the canonical radio core. The other, E, is
probably related to shocks at a sudden bend of the jet, towards extended
steep-spectrum region N. A remarkably deep and narrow HI absorption line
component extends over the entire projected extent of 2050+364. It coincides in
velocity with the [OIII] optical doublet lines to within 10 km/s. This HI
absorption could arise in the atomic cores of NLR clouds, and the motion in the
NLR is then remarkably coherent both along the line-of-sight and across a
projected distance of > 300 pc on the plane of the sky. Broader, shallower HI
absorption at lower velocities covers only the plausible core area W. This
absorption could be due to gas which is either being entrained by the inner jet
or is flowing out from the accretion region; it could be related to the BLR.Comment: 10 pages, 7 figures. Accepted in A&
Compact symmetric objects and supermassive binary black holes in the VLBA Imaging and Polarimetry Survey
We present multifrequency Very Long Baseline Array (VLBA) follow-up observations of VLBA Imaging and Polarimetry Survey sources identified as likely compact symmetric objects (CSOs) or supermassive binary black holes (SBBHs). We also present new spectroscopic redshifts for 11 sources observed with the Hobby-Eberly Telescope. While no new SBBHs can be confirmed from these observations, we have identified 24 CSOs in the sample, 15 of which are newly designated, and refuted 52 candidates leaving 33 unconfirmed candidates. This is the first large uniform sample of CSOs which can be used to elicit some of the general properties of these sources, including morphological evolution and environmental interaction. We have detected polarized emission from two of these CSOs the properties of which are consistent with active galactic nuclei unification schemes
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