58 research outputs found
Circumnuclear molecular gas in starburst and Seyfert galaxies
In order to investigate circumnuclear molecular gaseous contents and their relation to the nuclear activity, researchers made a search for circumnuclear (12)CO (J=1-0) emission from 28 starburst-nucleus galaxies (SBNs) and 12 Seyfert galaxies with the recession velocities less than 5000 km/s, using the Nobeyama Radio Observatory 45-m telescope. The full half-power beam width of 17 arcsec covers a region of less than about 5 kpc in diameter for the sample galaxies. The circumnuclear CO emission was detected from twelve SBNs (one is marginal) and four Seyfert galaxies. The main results and conclusions are summarized. Researchers derived the circumnuclear surface density of molecular gas which is corrected for inclination of the galaxies. This analysis shows that the surface density spans a wide range over two orders of magnitude. Further, there is no significant difference in the surface densities between types 1 and 2 Seyfert galaxies. Thus, we may conclude that the circumnuclear molecular content is not a key parameter producing the dichotomy of the Seyfert galaxies. It is also shown that there is no significant difference in the circumnuclear surface densities of molecular gas among the Seyfert, starburst, and normal galaxies. This implies that the circumnuclear gaseous content is not a key parameter determining which activity occurs in nuclei. We may conclude that more centrally condensed (i.e., less than 10 - 100 pc in diameter) gas components play an essential role on the occurrence of nuclear activities. Comparing results with the previous ones, researchers deduced radial distribution of surface density of molecular gases. They cannot obtain evidence for strong central concentration of molecular gas in the sample Seyfert galaxies except for NGC 3227. This is consistent with the previous result by Blitz, Mathieu, and Bally (1986). Comparing the CO emission line profiles with the previous ones taken with the larger beams, researchers discovered circumnuclear components of molecular gases. In particular, they found that molecular gas clouds may be absent in the SE of the nucleus of NGC 7469 where the high-excitation emitting region is discovered by Heckman et al. (1986). It is suggested that the nuclear activity (strong radiation and/or wind) may destruct the molecular clouds in that region
Observations of Ammonia in External Galaxies. II. Maffei 2
The ammonia (J,K) = (1,1), (2,2), (3,3), and (4,4) transitions at 23.7 --
24.1 GHz region were searched for in a nearby galaxy Maffei 2 to study relation
between molecular abundances and physical conditions in galaxies. The (1,1),
(2,2), and (3,3) emission lines were clearly detected. The rotational
temperatures and ortho-to-para abundance ratios obtained are about 30 K and
about 2.6, respectively. The abundance of NH3 relative to H2 in Maffei 2 was
found to be the largest among galaxies where NH3 is already detected, and the
abundance in Maffei 2 is more than an order of magnitude larger than the
already reported upper limit in M82. Hence, we further confirmed the
systematically peculiar molecular abundance in the aspect of formation
mechanisms of molecules already reported in M82.Comment: 6 pages, 2 fugure
Water Maser Emission from the Active Nucleus in M51
22 GHz water vapor `kilomaser' emission is reported from the central region
of the Whirlpool galaxy M 51 (NGC 5194). The red-shifted spectral features
(Vlsr ~ 560 km/s), flaring during most of the year 2000, originate from a
spatially unresolved maser spot of size < 30 mas (< 1.5 pc), displaced by < 250
mas from the nucleus. The data provide the first direct evidence for the
association of an H2O kilomaser with an active galactic nucleus (AGN). In early
2001, blue-shifted maser emission (Vlsr ~ 435 km/s) was also detected. Red- and
blue-shifted features bracket the systemic velocity asymmetrically. Within the
standard model of a rotating Keplerian torus, this may either suggest the
presence of a highly eccentric circumnuclear cloud or red- and blue-shifted
`high velocity' emission from a radially extended torus. Most consistent with
the measured H2O position is, however, an association of the red-shifted H2O
emission with the northern part of the bipolar radio jet. In this scenario, the
(weaker) northern jet is receding while the blue-shifted H2O emission is
associated with the approaching southern jet.Comment: 9 pages, 1 figur
High-sensitivity VLBI Observations of the Water Masers in the Seyfert Galaxy NGC 1068
We present observational results of water vapor maser emission with our
high-sensitivity 22 GHz VLBI imaging of the Seyfert galaxy NGC 1068. In this
galaxy, there are the following four nuclear radio sources; NE, C, S1, and S2.
Among them, the S1 component has been identified as the nucleus while the C
component has been considered as attributed to the radio jet. In our VLBI
observation, we find the following two types of the water maser emission at the
S1 component. One is the linearly aligned component that is considered as an
edge-on disk with the inner radius of 0.62 pc. The dynamical mass enclosed
within the inner radius was estimated to be by
assuming the circular Keplerian motion. Note, however, that the best fit
rotation curve shows a sub-Keplerian rotation ().
The other is the water maser emission distributed around the rotating disk
component up to 1.5 pc from the S1 component, suggesting the bipolar outflow
from the S1 component. Further, we detected the water maser emission in the C
component for the first time with VLBI, and discovered a ring-like distribution
of the water maser emission. It is known that a molecular cloud is associated
with the C component (both HCN and HCO emission lines are detected by
ALMA). Therefore, the ring-like maser emission can be explained by the jet
collision to the molecular cloud. However, if these ring-like water masing
clouds constitute a rotating ring around the C component, it is likely that the
C component also has a supermassive black hole with the mass of that could be supplied from a past minor merger of a nucleated
satellite galaxy.Comment: 16 pages, 10 figures, accepted for publication in the PAS
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