scholarly journals Formaldehyde Abundances in the Dense Molecular Cores DR 21 and W 3(OH)

1987 ◽  
Vol 120 ◽  
pp. 185-186
Author(s):  
H. R. Dickel ◽  
W. M. Goss ◽  
A. H. Rots
Keyword(s):  
Radiative Transfer ◽  
Molecular Hydrogen ◽  
Molecular Clouds ◽  
Hii Regions ◽  
Large Array ◽  
Very Large Array ◽  
Hydrogen Density ◽  
Dense Cores ◽  
Ultracompact Hii

Formaldehyde absorption has been observed with the Very Large Array in both the 6 cm and 2 cm transitions towards a number of ultracompact HII regions which are embedded in the dense cores of molecular clouds. Such data have been compared with the results of radiative transfer calculations to derive the distributions of the molecular hydrogen density and of the abundance of formaldehyde relative to molecular hydrogen. Results are presented for the sources DR 21 and W 3(OH).

scholarly journals Detection of New Ammonia Sources

1980 ◽  
Vol 87 ◽  
pp. 83-84
Author(s):  
G.H. Macdonald ◽  
A.T. Brown ◽  
L.T. Little ◽  
D.N. Matheson ◽  
M. Felli
Keyword(s):  
Hyperfine Structure ◽  
Molecular Hydrogen ◽  
Molecular Clouds ◽  
Column Density ◽  
Rotational Temperature ◽  
Kinetic Temperature ◽  
Excitation Temperature ◽  
Hydrogen Density

Ammonia is a favoured molecule for the study of molecular clouds since several important parameters of the cloud can be deduced from simple observations of the J,K=1,1 and 2,2 inversion doublet transitions and the hyperfine structure in the (1,1) line. With the additional knowledge of the kinetic temperature Tk from observations of CO, for example, it is possible to compute the excitation temperature of the (1,1) line (T11), the rotational temperature between the (1,1) and (2,2) levels (T21), the molecular hydrogen density n(H2) and ammonia column density N(NH3) (see, for example, Martin and Barrett, 1978).

scholarly journals Dense Molecular Gas at High Redshift: First Detection of Emission from HCO+

2006 ◽  
Vol 2 (S235) ◽  
pp. 424-424
Author(s):  
D.A. Riechers ◽  
F. Walter ◽  
C.L. Carilli ◽  
A. Weiss ◽  
F. Bertoldi ◽  
...  
Keyword(s):  
Molecular Hydrogen ◽  
Molecular Clouds ◽  
High Redshift ◽  
Far Infrared ◽  
Hydrogen Gas ◽  
Molecular Gas ◽  
Gas Emission ◽  
Very Large Array ◽  
Star Forming ◽  
Good Tracer

AbstractUsing the Very Large Array (VLA), we have detected the HCO+(1–0) emission line towards the Cloverleaf quasar (z = 2.56; Riechers et al. 2006). This is the first detection of ionized molecular gas emission at high redshift (z>2). HCO+ emission is a star formation indicator similar to HCN, tracing dense molecular hydrogen gas within star-forming molecular clouds. We find a HCO+/CO luminosity ratio of 0.08 and a HCO+/HCN luminosity ratio of 0.8 for the Cloverleaf. These ratios fall within the scatter of the same relationships found for low–z star–forming galaxies. However, a HCO+/HCN luminosity ratio close to unity would not be expected for the Cloverleaf if the recently suggested relation between this ratio and the far–infrared luminosity (Graciá–Carpio et al. 2006) were to hold. We conclude that a ratio between HCO+ and HCN luminosity close to 1 is likely due to the fact that the emission from both lines is optically thick and thermalized and emerges from dense regions of similar volumes. We conclude that HCO+ is potentially a good tracer for dense molecular gas at high redshift.

scholarly journals Gas Feeding Toward the Galactic Center

1994 ◽  
Vol 140 ◽  
pp. 161-165
Author(s):  
P. T. P. Ho
Keyword(s):  
Black Hole ◽  
Gravitational Field ◽  
Molecular Clouds ◽  
Milky Way ◽  
Galactic Center ◽  
Large Array ◽  
Massive Black Hole ◽  
Very Large Array ◽  
Central Gravitational Field

The previous two talks in this session have shown the importance of the nucleus of the Milky Way as the host to a possible massive black hole. SgrA* is apparently surrounded by a circumnuclear ring first seen in the HCN J = l-0 emission (Gusten et al. 1987). Infall from the circumnuclear ring could explain the ionized streamers which appear to orbit SgrA* (Lo and Claussen 1983; Serabyn and Lacy 1985). Recent studies in the NH3 emission using the Nobeyama Millimeter Array (Okumura et al. 1989; 1991) and the Very Large Array (Ho et al. 1991) have suggested that a streamer may feed the Galactic center from the southern cloud M-0.13-0.08. Here we show a second streamer originating from the eastern cloud M-0.02-0.07 as well. In both cases, interactions between the molecular clouds and supernovae seem to be important, and can be seen in position-velocity diagrams. This may be the mechanism by which gas is pushed toward the central gravitational field.

scholarly journals Methanol masers in Galactic center region supernova remnants

2013 ◽  
Vol 9 (S303) ◽  
pp. 156-158
Author(s):  
Y. M. Pihlström ◽  
B. C. McEwen ◽  
L. O. Sjouwerman
Keyword(s):  
Molecular Clouds ◽  
Supernova Remnants ◽  
Galactic Center ◽  
Cosmic Ray ◽  
Large Array ◽  
Very Large Array ◽  
Center Region ◽  
Cosmic Ray Acceleration ◽  
Methanol Masers ◽  
Sgr A

AbstractMethanol masers can be used to constrain densities and estimate kinematical distances to supernova remnants (SNRs), important parameters in cosmic ray acceleration models. With the goal of testing those models both for SNRs inside and outside the Galactic center (GC) region, we have used the Very Large Array to search for 36 GHz and 44 GHz methanol lines in Galactic SNRs. We report on the overall results of the maser search, and in particular the results of the GC SNR G1.4–0.1 in which more than 40 masers were found. They may be due to interactions between the SNR and at least two separate molecular clouds. Methanol masers were also detected in W28 and in Sgr A East.

scholarly journals EXPLORING THE NATURE OF COMPACT RADIO SOURCES ASSOCIATED TO UCHII REGIONS

2021 ◽  
Vol 57 (1) ◽  
pp. 81-89
Author(s):  
J. M. Masqué ◽  
L. F. Rodríguez ◽  
S. A. Dzib ◽  
S. N. Medina ◽  
L. Loinard ◽  
...  
Keyword(s):  
Massive Star ◽  
Thermal Emission ◽  
Hii Regions ◽  
Radio Sources ◽  
Large Array ◽  
Gravitational Radius ◽  
Very Large Array ◽  
Thermal Sources

We present Very Large Array 7 mm continuum observations of four ultracompact (UC) HII regions, observed previously at 1.3 cm, in order to investigate the nature of the compact radio sources associated with these regions. We detect a total of seven compact radio sources, four of them with thermal emission, and two compact radio sources with clear non- thermal emission. The thermal emission is consistent with the presence of an ionized envelope, either static (i.e., trapped in the gravitational radius of an associated massive star) or flowing away (i.e., a photo-evaporative flow). The nature of the non-thermal sources remains unclear and several possibilities are proposed. The possibility that most of these compact radio sources are photo-evaporating objects, and the remaining ones more evolved objects, is consistent with previous studies on UCHII regions.

Water masers associated with compact molecular clouds and ultracompact Hii regions: The extended sample

2008 ◽  
pp. 151-154
Author(s):  
R. Cesaroni ◽  
G. Comoretto ◽  
M. Felli ◽  
F. Palla ◽  
J. Brand ◽  
...  
Keyword(s):  
Molecular Clouds ◽  
Hii Regions ◽  
Water Masers ◽  
Ultracompact Hii

Multiwavelength analysis of OH Megamaser galaxies: The case of IRAS11506-3851

2020 ◽  
Vol 15 (S359) ◽  
pp. 347-349
Author(s):  
Carpes P. Hekatelyne ◽  
Thaisa Storchi-Bergmann
Keyword(s):  
Active Galactic Nuclei ◽  
Hubble Space Telescope ◽  
Galactic Nuclei ◽  
Large Array ◽  
Very Large Array ◽  
Star Forming ◽  
Star Forming Regions ◽  
Field Unit ◽  
Mixed Transition ◽  
Integral Field

AbstractWe present Multi-Object Spectrograph (GMOS) Integral Field Unit (IFU), Hubble Space Telescope (HST) and Very Large Array (VLA) observations of the inner kpc of the OH Megamaser galaxy IRAS 11506-3851. In this work we discuss the kinematics and excitation of the gas as well as its radio emission. The HST images reveal an isolated spiral galaxy and the combination with the GMOS-IFU flux distributions allowed us to identify a partial ring of star-forming regions surrounding the nucleus with a radius of ≍500 pc. The emission-line ratios and excitation map reveal that the region inside the ring present mixed/transition excitation between those of Starbursts and Active Galactic Nuclei (AGN), while regions along the ring are excited by Starbursts. We suggest that we are probing a buried or fading AGN that could be both exciting the gas and originating an outflow.

scholarly journals OH main line masers in the M 82 starburst

2007 ◽  
Vol 3 (S242) ◽  
pp. 427-431
Author(s):  
M. K. Argo ◽  
A. Pedlar ◽  
T. W. B. Muxlow ◽  
R. J. Beswick
Keyword(s):  
Central Region ◽  
Supernova Remnants ◽  
Main Line ◽  
Line Of Sight ◽  
Starburst Galaxy ◽  
Large Array ◽  
Satellite Line ◽  
Very Large Array

AbstractA study of the distribution of OH gas in the central region of the nearby active starburst galaxy M82 has confirmed two previously known bright masers and revealed several new main line masers. Three of these are seen only at 1665 MHz, one is detected only at 1667 MHz, while the rest are detected in both lines. Observations covering both the 1665 and 1667 MHz lines, conducted with both the Very Large Array (VLA) and the Multi-Element Radio Linked Interferometer Network (MERLIN), have been used to accurately measure the positions and velocities of these features. This has allowed a comparison with catalogued continuum features in the starburst such as HII regions and supernova remnants, as well as known water and satellite line OH masers. Most of the main line masers appear to be associated with known HII regions although the two detected only at 1665 MHz are seen along the same line of sight as known supernova remnants.

Bipolar outflow of gas in the spiral galaxy NGC 3079

1986 ◽  
Vol 64 (4) ◽  
pp. 531-535 ◽  
Author(s):  
Nebojsa Duric ◽  
E. R. Seaquist
Keyword(s):  
Spectral Index ◽  
Spiral Galaxy ◽  
Central Region ◽  
Qualitative Description ◽  
Radio Continuum ◽  
Large Array ◽  
Very Large Array ◽  
Bipolar Outflow ◽  
The Galaxy

Very large array, radio-continuum observations of the edge-on spiral galaxy NGC 3079 are presented. The observations reveal that the nucleus has windlike properties and that the central region of the galaxy exhibits an unusual figure-eight morphology that shows evidence of severe depolarization and a flattening spectral index away from the nucleus. A qualitative description of a model is presented to account for the observed radio properties. It is shown that a wind-driven shock propagating away from the nucleus and focused by the ambient disk gas can give rise to the observed morphology.

Sign in / Sign up

Export Citation Format

Share Document