437 research outputs found
Internal Motion of 6.7-GHz Methanol Masers in H II Region S269
We present the first internal motion measurement of the 6.7-GHz methanol
maser within S269, a small HII region in the outer Galaxy, which was carried
out in 2006 and 2011 using the Japanese VLBI Network (JVN). Several maser
groups and weak isolated spots were detected in an area spanning by ~200 mas
(1000 AU). Three remarkable maser groups are aligned at a position angle of 80
degree. Two of three maser groups were also detected by a previous observation
in 1998, which allowed us to study a long-term position variation of maser
spots from 1998 to 2011. The angular separation between the two groups
increased ~10 mas, which corresponds to an expansion velocity of ~10 km s^{-1}.
Some velocity gradient (~10^{-2} km s^{-1} mas^{-1}) in the overall
distribution was found. The internal motion between the maser groups support
the hypothesis that the methanol masers in S269 could trace a bipolar outflow.Comment: 8 pages, 6 figures, accepted for publication in PAS
The Dense Plasma Torus Around the Nucleus of an Active Galaxy NGC 1052
A subparsec-scale dense plasma torus around an active galactic nucleus (AGN)
is unveiled. We report on very-long-baseline interferometry (VLBI) observations
at 2.3, 8.4, and 15.4 GHz towards the active galaxy NGC 1052. The convex
spectra of the double-sided jets and the nucleus imply that synchrotron
emission is obscured through free--free absorption (FFA) by the foreground cold
dense plasma. A trichromatic image was produced to illustrate the distribution
of the FFA opacity. We found a central condensation of the plasma which covers
about 0.1 pc and 0.7 pc of the approaching and receding jets, respectively. A
simple explanation for the asymmetric distribution is the existence of a thick
plasma torus perpendicular to the jets. We also found an ambient FFA absorber,
whose density profile can be ascribed to a spherical distribution of the
isothermal King model. The coexistence of torus-like and spherical
distributions of the plasma suggests a transition from radial accretion to
rotational accretion around the nucleus.Comment: 10 pages, to appear in Publ. Astron. Soc. Japan, vol.53, No.2 (2001
Preliminary experimental results of gas recycling subsystems except carbon dioxide concentration
Oxygen concentration and separation is an essential factor for air recycling in a controlled ecological life support system (CELSS). Furthermore, if the value of the plant assimilatory quotient is not coincident with that of the animal respiratory quotient, the recovery of oxygen from the concentrated CO2 through chemical methods will become necessary to balance the gas contents in a CELSS. Therefore, oxygen concentration and separation equipment using Salcomine and O2 recovery equipment, such as Sabatier and Bosch reactors, were experimentally developed and tested
Very Long Baseline Interferometry imaging of H2O maser emission in the nearby radio galaxy NGC 4261
We report dual-frequency very long baseline interferometry (VLBI)
observations at 22 and 43 GHz toward the nucleus of a nearby radio galaxy NGC
4261. In particular, we present a VLBI image of the 22 GHz H2O maser line and
its location in the circumnuclear region of NGC 4261. H2O maser emission is
marginally detected above the three times the rms level within a velocity range
of approximately 2250-2450 km/s, slightly red-shifted with respect to the
systemic velocity. H2O maser emission is located approximately 1 milliarcsecond
(mas) east of the brightest continuum component at 22 GHz, where the continuum
spectrum is optically thick, that is at the free-free absorbed receding jet by
ionized gas. A positional coincidence between H2O maser emission and an ionized
gas disk implies that the H2O maser emission arises from the near side of the
disk, amplifying continuum emission from the background receding jet. If the
disk axis is oriented 64 degree relative to the line of sight, the H2O maser
emission is expected to be at a mean radius of 0.3 pc in the disk. The broad
line width of the H2O maser emission can be attributed to complex kinematics in
the immediate vicinity of the supermassive black hole (SMBH), including ongoing
gas infall onto the SMBH, turbulence, and outflow. This is analogous to the
multi-phase circumnuclear torus model in the nearest radio-loud H2O megamaser
source NGC 1052. An alternative explanation for H2O maser association is the
shock region between the jet and the ambient molecular clouds. However, this
explanation fails to describe the explicit association of H2O maser emission
only with the free-free absorbed receding jet.Comment: 10 pages, 5 figures, submitted to PAS
ALMA Detection of 321 GHz water maser emission in the radio galaxy NGC 1052
The Atacama Large Millimeter/submillimeter Array (ALMA) serendipitously
detected HO emission at 321 GHz in NGC
1052. This is the first submillimeter maser detection in a radio galaxy and the
most luminous 321-GHz HO maser known to date with the isotropic luminosity
of 1090 . The line profile consists of a broad velocity component
with FWHM km s straddling the systemic velocity and a
narrow component with FWHM km s blueshifted by 160 km
s. The profile is significantly different from the known 22-GHz maser which shows a broad profile redshifted by 193 km s. The
submillimeter maser is spatially unresolved with a synthesized beam of
and coincides with the
continuum core position within 12 pc. These results indicate amplification of
the continuum emission through high-temperature ( K) and dense ( cm) molecular gas in front of the coreComment: 3 figures, Accepted for publication in Publications of Astronomical
Society of Japa
Sub-parsec-scale Accleration of the Radio Jet in the Powerful Radio Galaxy NGC 6251
In order to investigate the genesis of powerful radio jet, we have mapped the
central 10 pc region of the nearby radio galaxy NGC 6251 with a 0.2 pc
resolution using Very Long Baseline Interferometer (VLBI) at two radio
frequencies, 5 GHz and 15 GHz, we have found the sub-parsec-scale counterjet
for the first time in this radio galaxy. This discovery allows us to
investigate the jet acceleration based on the relativistic beaming model.Comment: 7 pages with 7 figures. To appear in PASJ, 52, No. 5, Oct. 25, 200
VLBI imaging of OH absorption: The puzzle of the nuclear region of NGC 3079
Broad hydroxyl (OH) absorption-lines in the 1667 MHz and 1665 MHz transition
towards the central region of NGC 3079 have been observed at high resolution
with the European VLBI Network (EVN). Velocity fields of two OH absorption
components were resolved across the unresolved nuclear radio continuum of ~10
parsecs. The velocity field of the OH absorption close to the systemic velocity
shows rotation in nearly the same sense as the edge-on galactic-scale molecular
disk probed by CO(1-0) emission. The velocity field of the blue-shifted OH
absorption displays a gradient in almost the opposite direction. The
blue-shifted velocity field represents a non-rotational component, which may
trace an outflow from the nucleus, or material driven and shocked by the
kiloparsec-scale superbubble. This OH absorption component traces a structure
that does not support a counter-rotating disk suggested on the basis of the
neutral hydrogen absorption.Comment: 9 pages, 10 figures, submitted to MNRAS (03/12/2003
Free-Free Absorption and the Unified Scheme
We report Very-Long-Baseline Array (VLBA) observations at 2.3, 8.4, and 15.4
GHz towards nine GHz-Peaked Spectrum (GPS) sources. One Seyfert 1 galaxy, one
Seyfert 2 galaxy, three radio galaxies, and four quasars were included in our
survey. We obtained spatial distributions of the Free-Free Absorption (FFA)
opacity with milliarcsec resolutions for all sources. It is found that type-1
(Seyfert 1 and quasars) and type-2 (Seyfert 2 and radio galaxies) sources
showed different distributions of the FFA opacities. The type-1 sources tend to
show more asymmetric opacity distributions towards a double lobe, while those
of the type-2 sources are rather symmetric. Our results imply that the
different viewing angle of the jet causes the difference of FFA opacity along
the external absorber. This idea supports the unified scheme between quasars
and radio galaxies, proposed by Barthel (1989).Comment: 17 pages, including 8 figures. Proceedings of the 3rd Compact Steep
Spectrum and GHz Peaked Spectrum Sources, 2002, Greece. Submitted to the
Publications of Astronomical Society of Australi
Dense Plasma Torus in the GPS Galaxy NGC 1052
We report results from nearly simultaneous pentachromatic VLBI observations
towa rds a nearby GPS galaxy NGC 1052. The observations at 1.6 and 4.8 GHz with
VSOP, and at 2.3, 8.4, and 15.4 GHz wit h VLBA, provide linear resolutions of
pc. Convex spectra of a double-sided jet imply that synchrotron
emission is obscured through foreground cold dense plasma, in terms of
free--free absorption (FFA). We found a central condensation of the plasma
which covers about 0.1 pc and 1 pc of the approaching and receding jets,
respectively. A simple model with a geometrically thick plasma torus
perpendicular to the jets is established to explain the asymmetric distribution
of FFA opacities.Comment: 9 pages, 4 figures, other comment
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