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 Classification of Supernova Remnants and HII Regions from their Recombination Line Emission

1972 ◽  
Vol 25 (5) ◽  
pp. 539 ◽  
Author(s):  
JR Dickel ◽  
DK Milne
Keyword(s):  
Electron Temperature ◽  
Supernova Remnants ◽  
Line Emission ◽  
Hii Regions ◽  
Radio Sources ◽  
Recombination Line ◽  
Line Frequency ◽  
Upper Limits ◽  
Galactic Radio

H109a, recombination line observations are used in an attempt to classify 46 galactic radio sources as either supernova remnants or HII regions. Long integrations at the H109a line frequency on two well-known supernova remnants (IC 443 and 3C 391) provide improved upper limits on the line emission from these objects. From these results the electron temperature in IC 443 is estimated to be in excess of 1�6 � 104 K.

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).

Variation of the amount of hydrogen along the galactic ridge

1967 ◽  
Vol 31 ◽  
pp. 171-172
Author(s):  
Th. Schmidt-Kaler
Keyword(s):  
Surface Brightness ◽  
Milky Way ◽  
Neutral Hydrogen ◽  
Line Of Sight ◽  
Optical Surface ◽  
Hydrogen Density ◽  
Continuous Radiation ◽  
Galactic Longitude

The integralNHof neutral-hydrogen density along the line of sight is determined from the Kootwijk and Sydney surveys. The run ofNHwith galactic longitude agrees well with that of thermal continuous radiation and that of the optical surface brightness of the Milky Way.

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.

Optical spectroscopy of radio jets in 3C 31, 3C 75, 3C 83.1B, and 3C 465

1986 ◽  
Vol 64 (4) ◽  
pp. 369-372 ◽  
Author(s):  
Christopher P. O'Dea ◽  
Frazer N. Owen ◽  
William C. Keel
Keyword(s):  
Optical Spectroscopy ◽  
External Medium ◽  
Line Emission ◽  
Radio Sources ◽  
Ionized Gas ◽  
Radio Jets ◽  
Upper Limits ◽  
The Galaxy ◽  
Lower Limits ◽  
Total Velocity

We present preliminary results of optical spectroscopy of four radio galaxies with jets (3C 75, 3C 465, 3C 31, and 3C 83. 1B (NGC 1265)). We examined selected regions in and around the radio jets for evidence of the interaction of the jets with their external medium (e.g., entrainment or bending through collision with clouds). We searched for the emission lines expected from ionized gas at a temperature of T ~ 104 K (e.g., Hα and [NII]) as well as those expected at higher temperatures (T ~ 106 K, Fe X (λ6374) and Fe XIV (λ5303)).We found no extranuclear emission in the regions searched in 3C 75, 3C 465, and 3C 83.1B. Assuming values for the pressure in the environment of the radio sources, we found the upper limits to the line emission correspond to model-dependent lower limits to the temperature in the range T ≥ 1.5–3 × 106 K and upper limits to the electron density in the range ne ≤ 5 × 10−2−5 × 10−3 cm−3.In 3C 31, we detected extended Hα and [NII] emission that is peaked on the nucleus and exhibits a velocity gradient. The [NII] emission has a total velocity width of ~800 km∙s−1. It is not yet clear whether any of this emission is associated with the jet (e.g., entrained gas) or whether it is associated with a known dust lane in the galaxy NGC 383.

scholarly journals The Structure of the Multi-Phase ISM in Low Surface Brightness Galaxies

1999 ◽  
Vol 171 ◽  
pp. 237-244 ◽  
Author(s):  
M. Spaans
Keyword(s):  
Carbon Monoxide ◽  
Galaxy Evolution ◽  
Molecular Hydrogen ◽  
Surface Brightness ◽  
Ambient Pressure ◽  
Upper Limits ◽  
Low Surface Brightness ◽  
Multi Phase ◽  
Low Surface Brightness Galaxies ◽  
Formation Efficiency

AbstractThe multi-phase structure of the interstellar medium in low surface brightness galaxies is investigated and compared to observations. It is found that the ambient pressure and metallicity very strongly influence the abundances of molecular hydrogen and carbon monoxide. The emissivity of the latter is computed and found to agree naturally with the upper limits measured for low surface brightness galaxies. The implications for star formation efficiency and galaxy evolution are discussed.

The Velocities of 6cm Recombination Line Emission originating near the Galactic Nucleus

1977 ◽  
Vol 3 (2) ◽  
pp. 150-152 ◽  
Author(s):  
F. F. Gardner ◽  
J. B. Whiteoak
Keyword(s):  
Radio Source ◽  
Strong Evidence ◽  
Line Emission ◽  
Hii Regions ◽  
Galactic Centre ◽  
Recombination Line ◽  
The Galaxy ◽  
Centre Region ◽  
Sgr A

Although it is well known that HII regions are present in the innermost regions of the Galaxy their kinematics are still not fully understood. In one study Pauls et al. (1976) surveyed with a beamwidth of 3′ arc the 10 GHz recombination line emission in directions within 15′ arc of the nuclear radio source Sgr A. They found that the emission velocities varied from position to position within the range -50 to + 50 km s-1but appeared to lack any overall pattern. In contrast, we have recently observed the recombination line emission from the galactic centre region with a beamwidth of 4′.5 arc, and find strong evidence of ordered motions near the galactic nucleus.

scholarly journals Corrigendum: Classification of Supernova Remnants and HII Regions from their Recombination Line Emission

1973 ◽  
Vol 26 (2) ◽  
pp. 267 ◽  
Author(s):  
JR Dickel ◽  
DK Milne
Keyword(s):  
Supernova Remnants ◽  
Supernova Remnant ◽  
Line Emission ◽  
Hii Regions ◽  
Recombination Line ◽  
Hii Region ◽  
Galactic Source ◽  
Source Number

The galactic source number designations G35'6-0'4 and G35�5-0�0 in Table 1 should be interchanged. Thus G35'6-0'4 is the supernova remnant and G35�5 -0�0 appears to be an HII region. The authors thank Dr. T Velusamy for calling this error to their attention.

scholarly journals 12CO(J=3→2) detections in bulges of low surface brightness galaxies with APEX

2007 ◽  
Vol 3 (S245) ◽  
pp. 191-192
Author(s):  
Gaspar Galaz ◽  
Paulo Cortes ◽  
Leonardo Bronfman ◽  
Monica Rubio
Keyword(s):  
Surface Brightness ◽  
High Surface ◽  
Rotational Transition ◽  
Main Beam ◽  
Molecular Gas ◽  
Gas Temperature ◽  
Upper Limits ◽  
Low Surface Brightness ◽  
Low Surface Brightness Galaxies ◽  
First Time

AbstractUsing the APEX sub-millimeter telescope we have detected for the first time the CO rotational transition 12CO(J=3→2) in two of five low surface brightness galaxies. For galaxies with positive detection, the emission is detected in their bulges, with measured gas velocity dispersion of about 80 km/s and observed main-beam brightness temperature TM B ~ 10 mK. Using a standard CO to H2 conversion factor, we are able to estimate molecular gas masses for LSBs with positive detections, and upper limits for those LSBs with negative detections. Assuming a higher gas temperature for the generation of the 12CO(J=3→2) line compared to that for the 12CO(J=1→0) one, results suggest that a warm molecular gas component is present in bulges, indicating a radiation field preventing the formation of large cooler amounts of molecular gas, compared to high surface brightness galaxies with higher metallicity and likely more dust.

Sign in / Sign up

Export Citation Format

Share Document