scholarly journals HII regions and star formation in the galactic center

1979 ◽  
Vol 84 ◽  
pp. 357-366 ◽  
Author(s):  
P. G. Mezger ◽  
T. Pauls
Keyword(s):  
Thermal Radiation ◽  
High Frequency ◽  
Galactic Center ◽  
Thermal Emission ◽  
Hii Regions ◽  
Radio Continuum ◽  
Line Of Sight ◽  
Low Density ◽  
Recombination Line ◽  
Half Power

The centimeter wavelength continuum radiation seen toward the Galactic center (Figure 1) is a mixture of thermal (free-free) and nonthermal (synchrotron) radiation which originates in the nucleus and along the line-of-sight. In this review we discuss only the thermal emission (also see Mezger 1974 and Oort 1977). High-frequency radio continuum and recombination line observations show that the thermal radiation comes from extend, low-density (ELD) HII, and a number of giant “radio HII regions” (see Mezger 1978 for definitions). The approximate half-power contour of the ELD HII (labelled EI in Fig. 1), probably represents a superposition of evolved and expanded HII regions. Thermal radiation outside EI comes predominantly from along the line-of-sight (see Pauls and Mezger 1975).

scholarly journals A Search for Recombination Line Emission from the Galactic Equator at 408 MHz

1976 ◽  
Vol 29 (5) ◽  
pp. 419 ◽  
Author(s):  
MJ Batty
Keyword(s):  
Surface Brightness ◽  
Thermal Emission ◽  
Line Emission ◽  
Hii Regions ◽  
Line Of Sight ◽  
Recombination Line ◽  
Upper Limits ◽  
Low Surface Brightness ◽  
Lower Limits ◽  
Galactic Longitude

A search for H 2520( recombination line emission was made by scanning the galactic equator region using the Molonglo radio telescope. Upper limits were established over the range of galactic longitude accessible to the instrument. For the region III ;S 40�, estimates of the background thermal continuum brightness temperature were used to derive lower limits of ~ 2000 K for the electron temperature of the gas along the line of sight. Lower limits for the electron density obtained by considering probable non-LTE effects suggest that the thermal emission over this range is due to low surface brightness HII regions. The observed H 2520( upper limit averaged over the range 270� ;S I ;S 320� just admits the line intensity calculated by Shaver (1975) for the cold cloud component of the general interstellar medium.

scholarly journals Radio continuum and radio recombination line observations of the Galactic center lobe

2013 ◽  
Vol 9 (S303) ◽  
pp. 129-131
Author(s):  
Halca Nagoshi ◽  
Kenta Fujisawa ◽  
Yuzo Kubose
Keyword(s):  
Electron Temperature ◽  
Galactic Center ◽  
Thermal Emission ◽  
Radio Continuum ◽  
Continuum Emission ◽  
Recombination Line ◽  
Ionized Gas ◽  
Radio Recombination Line ◽  
Spatial Coverage ◽  
The Continuum

AbstractRadio continuum (cont) and radio recombination line (RRL) observations with the Yamaguchi 32-m radio telescope toward the lower part of the Galactic center lobe (GCL) in the Galactic center region are presented. While two ridges of the GCL were seen in both continuum and RRL images, the spatial coverage of the ridges of the continuum and RRL is not coincident. We distinguish the continuum emission of the GCL into thermal and non-thermal emission by assuming an electron temperature of the ionized gas of 4370 K, estimated based on the line width (14.1 km s−1). The thermal emission was found to be located inside and surrounded by the non-thermal emission.

scholarly journals How far actually is the Galactic Center IRS 13E3 from Sagittarius A*?

2020 ◽  
Vol 72 (3) ◽  
Author(s):  
Masato Tsuboi ◽  
Yoshimi Kitamura ◽  
Takahiro Tsutsumi ◽  
Ryosuke Miyawaki ◽  
Makoto Miyoshi ◽  
...  
Keyword(s):  
Galactic Center ◽  
Three Dimensional ◽  
Line Of Sight ◽  
Recombination Line ◽  
Intermediate Mass ◽  
Ionized Gas ◽  
Sagittarius A ◽  
Projection Distance ◽  
Spectroscopic Information ◽  
Sgr A

Abstract The Galactic Center IRS 13E cluster is a very intriguing infrared object located at ${\sim } 0.13$ pc from Sagittarius A$^\ast$ (Sgr A$^\ast$) in projection distance. There are arguments both for and against the hypothesis that a dark mass like an intermediate mass black hole (IMBH) exists in the cluster. We recently detected the rotating ionized gas ring around IRS 13E3, which belongs to the cluster, in the H30$\alpha$ recombination line using ALMA. The enclosed mass is derived to be $M_{\mathrm{encl.}}\simeq 2\times 10^{4}\, M_\odot$, which agrees with an IMBH and is barely less than the astrometric upper limit mass of an IMBH around Sgr A$^\ast$. Because the limit mass depends on the true three-dimensional (3D) distance from Sgr A$^\ast$, it is very important to determine it observationally. However, the 3D distance is indefinite because it is hard to determine the line-of-sight (LOS) distance by usual methods. We attempt here to estimate the LOS distance from spectroscopic information. The CH$_3$OH molecule is easily destroyed by the cosmic rays around Sgr A$^{\ast }$. However, we detected a highly excited CH$_3$OH emission line in the ionized gas stream associated with IRS 13E3. This indicates that IRS 13E3 is located at $r\gtrsim 0.4$ pc from Sgr A$^{\ast }$.

scholarly journals Radio studies of HII regions and galactic structure

1964 ◽  
Vol 20 ◽  
pp. 116-122
Author(s):  
M. M. Komesaroff ◽  
G. Westerhout
Keyword(s):  
Thermal Emission ◽  
Hii Regions ◽  
Radio Spectrum ◽  
Line Of Sight ◽  
Radio Waves ◽  
Low Frequencies ◽  
High Frequencies ◽  
The Galaxy ◽  
Radio Studies ◽  
Considerable Detail

Radio studies of galactic HII regions are best carried out at the two ends of the radio spectrum. At high frequencies, of hundreds or thousands of megacycles per second, HII regions are seen by virtue of their thermal emission against a weak nonthermal background. Since radio waves are unaffected by the obscuration along the plane, it is possible in principle to see right through the Galaxy, and the high resolution which can be achieved in the thousands of megacycles range enables us to study at least the nearer regions in considerable detail. At low frequencies, below about 20 Mc/s, ionized hydrogen is seen in absorption against a bright nonthermal background. Since quite tenuous regions may be almost opaque at the lower frequencies, the technique provides quite a sensitive method of detecting them. The absorption increases with decreasing frequency so that studies at different frequencies enable us to see to varying depths along the line of sight and could permit the derivation of rough distance estimates.

scholarly journals 158μm [CII] Mapping of the Galactic Center Molecular Clouds

1989 ◽  
Vol 136 ◽  
pp. 151-155
Author(s):  
R. Genzel ◽  
G. J. Stacey ◽  
C. H. Townes ◽  
A. Poglitsch ◽  
N. Geis
Keyword(s):  
Emission Line ◽  
Molecular Clouds ◽  
Galactic Center ◽  
Hii Regions ◽  
Radio Continuum ◽  
Large Intensity ◽  
Sgr A

We have made 55″ resolution maps of the 158 μm [CII] emission line in the region of the curved, thermal filaments and the +20 / +50 kms−1 molecular clouds in Sgr A. The [CII] emission is spatially well correlated with the radio continuum in the filaments. The large intensity of the [CII] radiation excludes shocks as the origin of the ionization and we conclude that the curved filaments are most likely photo-ionized HII regions at the surface of dense molecular clouds. Our [CII] maps of the +20 / +50 kms−1 clouds indicate that the +50 kms−1 cloud is close to (<10pc) Sgr A west while the more massive +20 kms−1 cloud is at a greater distance from the center (>30pc).

scholarly journals Mid-Infrared Observations of the Galactic Center Arc and the Sgr A East HII Region

1989 ◽  
Vol 136 ◽  
pp. 287-292 ◽  
Author(s):  
F. Yusef-Zadeh ◽  
C. M. Telesco ◽  
R. Decher
Keyword(s):  
Galactic Center ◽  
Hii Regions ◽  
Radio Continuum ◽  
Radio Flux ◽  
Ir Camera ◽  
Hii Region ◽  
Sgr A ◽  
5 Ghz ◽  
Almost All ◽  
Ir Emission

We have used the 20-pixel IR camera to observe thermal IR emission from dust associated with the radio continuum Arc near the Galactic center and the cluster of HII regions in the immediate vicinity of Sgr A East. We detected strong 10μm emission from the eastern and western arched filaments (G0.1+0.08), from an unusual pistol-shaped structure known as G0.15–0.05 and from the brightest member of the Sgr A East HII region. Spatial maps of these features at 10μm with a resolution of 4.1″ × 4.2″ are presented and are compared with 5-GHz radio images. We find a general spatial correlation between the ionized gas and the dust distributions. The ratio of IR to radio flux densities is significantly different in the eastern and western arched filaments, which suggests that the source of heating has a softer spectrum along the eastern arched filaments. In addition, the ratio of IR to radio flux densities, which is typically ~10 in normal Galactic HII regions excited by O stars, is at least a factor of two higher than this value in almost all the sources we have observed. This suggests that additional mechanisms other than trapped Lymanαradiation should be present in heating the dust, e.g. stochastic heating of small dust grains by energetic particles associated with the nonthermal filaments.

scholarly journals 4.1. Radio continuum and molecular gas in the Galactic center: large-scale structures

1998 ◽  
Vol 184 ◽  
pp. 161-168
Author(s):  
Yoshiaki Sofue
Keyword(s):  
Radio Emission ◽  
Linear Polarization ◽  
Large Scale ◽  
Galactic Center ◽  
Thermal Emission ◽  
Radio Continuum ◽  
Molecular Gas ◽  
Large Scale Structures ◽  
Almost Everywhere ◽  
Scale Structures

The radio emission from the Galactic Center is a mixture of thermal (free-free) and non-thermal (synchrotron) emissions (Fig. 1a). However, the spectral index in the central 3° region is flat almost everywhere (Sofue 1985), even in regions where strong linear polarization is detected. Therefore, a flat spectrum observed near the galactic center can no longer be taken as an indicator of thermal emission.

scholarly journals Radio Continuum and Recombination Line Studies of the Galactic Center

1974 ◽  
Vol 60 ◽  
pp. 477-489 ◽  
Author(s):  
M. A. Gordon
Keyword(s):  
Galactic Center ◽  
Radio Continuum ◽  
Continuum Emission ◽  
Recombination Line ◽  
Radio Observations ◽  
To Come

This review discusses unsuccessful searches for electromagnetic bursts accompanying gravitational events observed to come from the galactic center, radio observations of continuum emission and recombination lines from the region of the galactic center.

scholarly journals Star Formation in M81

1987 ◽  
Vol 115 ◽  
pp. 626-626
Author(s):  
Frank Bash ◽  
Michele Kaufman
Keyword(s):  
Shock Wave ◽  
Star Formation ◽  
Interstellar Medium ◽  
Thermal Radiation ◽  
Spiral Galaxy ◽  
Density Wave ◽  
Wave Theory ◽  
Hii Regions ◽  
Radio Continuum ◽  
Density Wave Theory

VLA observations of the spiral galaxy M81 in the radio continuum at wavelengths of 6 and 20-cm have been used to check the predictions of the density wave theory. The non-thermal radiation from the arms has been detected and the arms are found to be broader than the predictions of the classical density wave theory. Their width does seem to agree with that predicted by models which take the clumpy nature of the interstellar medium into account. These data are also able to separate giant HII regions from the non-thermal arms. Collaborators have furnished optical Hα data on the HII regions and HI 21-cm data, from the VLA, which will be used to find and measure the location of the HII regions with respect to the spiral shock wave and to measure the visual extinction in the disk of M81.

The Marseille Observatory Hα Survey: Comparisons by CO, 6 CM and IRAS Data

1998 ◽  
Vol 179 ◽  
pp. 186-188
Author(s):  
D. Russeil ◽  
P. Amram ◽  
Y.P. Georgelin ◽  
Y.M. Georgelin ◽  
M. Marcelin ◽  
...  
Keyword(s):  
Molecular Cloud ◽  
Large Scale ◽  
Galactic Plane ◽  
Photon Counting ◽  
Hii Regions ◽  
Radio Continuum ◽  
Line Of Sight ◽  
Ionized Gas ◽  
Hii Region ◽  
Pattern Determination

The Marseille Observatory Hα survey supplies Hα velocities of the ionized hydrogen over large zones of the sky towards the galactic plane. This survey, led at the ESO La Silla, uses a 36 cm telescope equiped with a scanning Fabry-Perot interferometer and a photon counting camera (Le Coarer et al. 1992). About 250 fields (39′×39′) toward the galactic plane have already been covered (see Figure 1) with a spatial resolution of 9″×9″ and a spectral resolution of 5 km s–1. This allows us to observe the discrete HII regions and the diffuse ionized gas widely distributed between them and to separate the distinct layers found along the line of sight. HII regions are often grouped on the molecular cloud surface, then CO, radio continuum and recombination lines surveys of the galactic plane are also essential to distinguish the HII region-molecular cloud complexes met on the line of sight, and in order to take dynamical effects into account, such as the champagne effect, for the kinematic distance determination. Indeed, the spiral structure pattern determination requires avoiding any artificial spread by clearly identifying the giant complexes composed of molecular clouds, HII regions, diffuse ionized hydrogen widely surrounding them, and exciting stars. On the other hand the ionized gas data (Hα and recombination lines) associated with IRAS data help us to study the nature of the young objects constituent of these complexes and to assess their detectability. We present two fields from the Hα survey and parallel large scale investigations.

Sign in / Sign up

Export Citation Format

Share Document