Diffuse Ionized Gas in a Sample of Edge‐on Galaxies and Comparisons with Hiand Radio Continuum Emission

2000 ◽  
Vol 536 (2) ◽  
pp. 645-662 ◽  
Author(s):  
Joseph A. Collins ◽  
Richard J. Rand ◽  
Nebojsa Duric ◽  
Rene A. M. Walterbos
Keyword(s):  
Radio Continuum ◽  
Continuum Emission ◽  
Ionized Gas ◽  
Diffuse Ionized Gas

scholarly journals Radio observations of evaporating objects in the Cygnus OB2 region

2019 ◽  
Vol 627 ◽  
pp. A58 ◽  
Author(s):  
N. L. Isequilla ◽  
M. Fernández-López ◽  
P. Benaglia ◽  
C. H. Ishwara-Chandra ◽  
S. del Palacio
Keyword(s):  
Thermal Emission ◽  
Radio Continuum ◽  
Continuum Emission ◽  
Spectral Indices ◽  
Ionized Gas ◽  
Low Frequencies ◽  
Thermal Origin ◽  
Index Maps ◽  
Photoionization Rate ◽  
Gas Component

We present observations of the Cygnus OB2 region obtained with the Giant Metrewave Radio Telescope (GMRT) at frequencies of 325 and 610 MHz. In this contribution we focus on the study of proplyd-like objects (also known as free-floating evaporating gas globules or frEGGs) that typically show an extended cometary morphology. We identify eight objects previously studied at other wavelengths and derive their physical properties by obtaining their optical depth at radio-wavelengths. Using their geometry and the photoionization rate needed to produce their radio-continuum emission, we find that these sources are possibly ionized by a contribution of the stars Cyg OB2 #9 and Cyg OB2 #22. Spectral index maps of the eight frEGGs were constructed, showing a flat spectrum in radio frequencies in general. We interpret these as produced by optically thin ionized gas, although it is possible that a combination of thermal emission, not necessarily optically thin, produced by a diffuse gas component and the instrument response (which detects more diffuse emission at low frequencies) can artificially generate negative spectral indices. In particular, for the case of the Tadpole we suggest that the observed emission is not of non-thermal origin despite the presence of regions with negative spectral indices in our maps.

scholarly journals Multi-Array λ2 and 6cm Radio Continuum Observations of Sgr A West

1989 ◽  
Vol 136 ◽  
pp. 443-451 ◽  
Author(s):  
F. Yusef-Zadeh ◽  
Mark Morris ◽  
Ron Ekers
Keyword(s):  
Spectral Index ◽  
Stellar Wind ◽  
Galactic Center ◽  
Radio Continuum ◽  
Continuum Emission ◽  
Spectral Indices ◽  
Ionized Gas ◽  
Sgr A ◽  
Index Maps ◽  
East West

Sub-arcsecond (down to 0.1″ × 0.2″) radio continuum observations using the VLA2 in a number of configurations have been carried out in order to investigate the fine-scale morphological details of the ionized gas and the distribution of spectral index along the triskelian-shaped figure of Sgr A West. In addition to finding a number of isolated patches of thermally-emitting gas and an absorbing feature at λ6cm within three arcminutes of the Galactic center, we have observed:1) radio continuum emission from IRS-7, implying that the stellar wind from this supergiant is externally ionized. An improved position for this object was obtained.2) the circular mini-cavity located along the east-west bar of Sgr A West. This feature has a diameter of 2-arcseconds and may have been created by a spherical wind, the source of which is yet to be identified; the seemingly most plausible candidate, IRS-16, is offset by 3″ from the center of the cavity.Spectral index maps having a resolution of 0.7″ × 0.3″ were made from scaled array observations at λ2cm and 6cm. They show that the eastern arm has a spectral index near −0.1, while the northern arm and the bar have positive spectral indices, indicating perhaps a partial opacity effect. The spectral index of IRS-7 is +0.6, consistent with that expected from a completely ionized stellar wind.

scholarly journals Diffuse Ionized Gas in Halos of Spiral Galaxies

1997 ◽  
Vol 166 ◽  
pp. 525-538
Author(s):  
Ralf-Jürgen Dettmar
Keyword(s):  
Large Scale ◽  
Spiral Galaxies ◽  
Optical Emission ◽  
Radio Continuum ◽  
Formation Processes ◽  
Ionized Gas ◽  
Ob Stars ◽  
Diffuse Ionized Gas ◽  
Model Predictions ◽  
External Galaxies

AbstractOver the last couple of years Diffuse Ionized Gas (DIG) has been identified as an important constituent of the interstellar medium (ISM) in the halos of spiral galaxies. Imaging in and spectroscopy of optical emission lines allow us to study the distribution and excitation of this gas with a spatial resolution not achievable for other phases of the ISM in external galaxies. Its origin and ionization is under debate and give important constraints for models of the ISM in general and on the large scale exchange of matter between disk and halo in particular. This review summarizes more recent observational results and compares them with model predictions. The data available now demonstrate that the presence of DIG in the disk-halo interface of spiral galaxies is related to star formation processes in the underlying disk. While photoionization by OB stars in the disk seems a viable source for the power required to ionize the DIG, additional processes are needed to explain some of the spectral features. The observed correlation with properties of the non-thermal radio continuum indicate that magnetic fields and cosmic rays could play a role for the physics of this 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 Galactic Worms

1991 ◽  
Vol 144 ◽  
pp. 165-168
Author(s):  
B.C. Koo ◽  
C. Heiles ◽  
W. T. Reach
Keyword(s):  
Filling Factor ◽  
Radio Continuum ◽  
Continuum Emission ◽  
Ionized Gas ◽  
Area Filling

We have found and cataloged over 100 vertical structures in H I, infrared, and radio continuum emission. These correspond to the H I worms detected by Heiles (1984). The infrared and the radio continuum properties of worms suggest that some worms have associated ionized gas. The area filling factor of superbubbles in the inner Galaxy is estimated to be greater than ~0.1.

scholarly journals Radio Continuum Observations of Southern Planetary Nebulae Candidates

1993 ◽  
Vol 155 ◽  
pp. 40-40
Author(s):  
G.C. Van De Steene ◽  
S.R. Pottasch
Keyword(s):  
Point Source ◽  
Planetary Nebulae ◽  
Radio Continuum ◽  
Continuum Emission ◽  
Ionized Gas ◽  
High Brightness ◽  
Brightness Temperatures ◽  
Compact Array

In an attempt to find new Planetary Nebulae we have short radio continuum observations at 6 cm and 3 cm of 90 PN candidates with the Australian Compact Array. We selected the unidentified objects from the IRAS Point Source Catalogue on basis of their PN colors. Detection of radio continuum emission at the IRAS position almost certainly confirms that these objects are PN, because it indicates the presence of ionized gas. Therefore the 18 detected sources are considered new PN. Because of their high brightness temperatures, they are probably young PN.

scholarly journals HCO+and Radio Continuum Emission from the Star Forming Region G75.78+0.34

2014 ◽  
Vol 2014 ◽  
pp. 1-5
Author(s):  
Rogemar A. Riffel ◽  
Everton Lüdke
Keyword(s):  
Massive Star ◽  
Emission Measure ◽  
Radio Continuum ◽  
Continuum Emission ◽  
Ionized Gas ◽  
Very Large Array ◽  
Star Forming ◽  
Molecular Outflows ◽  
H Ii Region ◽  
The Continuum

We present 1.3 and 3.6 cm radio continuum images and a HCO+spectrum of the massive star forming region G75.78+0.34 obtained with the Very Large Array (VLA) and with the Berkley Illinois Maryland Association (BIMA) interferometer. Three structures were detected in the continuum emission: one associated with the well-known cometary H ɪɪ region, plus two more compact structures located at 6′′ east and at 2′′ south of cometary H ɪɪ region. Using the total flux and intensity peak we estimated an electron density of≈1.5 × 104 cm−3, an emission measure of≈6 × 107 cm−6 pc, a mass of ionized gas of≈3 M⊙, and a diameter of 0.05 pc for the cometary H ɪɪ region, being typical values for an ultracompact H ɪɪ region. The HCO+emission probably originates from the molecular outflows previously observed in HCN and CO.

scholarly journals Cool Ionized Gas in Galaxy Thick Disks

1991 ◽  
Vol 144 ◽  
pp. 303-306
Author(s):  
F. P. Israel
Keyword(s):  
Low Temperature ◽  
Spiral Galaxies ◽  
Radio Continuum ◽  
Continuum Emission ◽  
Ionized Gas ◽  
Continuum Spectrum ◽  
Nonthermal Emission ◽  
Thick Disks ◽  
Very Low Temperature

Spiral galaxies whose radio continuum emission is dominated by their disks show a flattening of the radio continuum spectrum at frequencies well below 1 GHz. The effect appears to be stronger for edge-on than for face-on galaxies The most feasible explanation appears to be that the flattening reflects free-free absorption of nonthermal emission by a very low temperature ionized gas. This gas is probably highly clumped, and must be well-mixed with the nonthermally emitting plasma.

scholarly journals Diffuse Ionized Gas in Nearby Galaxies

1991 ◽  
Vol 144 ◽  
pp. 223-232
Author(s):  
R.A.M. Walterbos
Keyword(s):  
Interstellar Medium ◽  
Spectral Characteristics ◽  
High Ratio ◽  
Radio Continuum ◽  
Ionized Gas ◽  
Star Forming ◽  
Star Forming Regions ◽  
Diffuse Ionized Gas ◽  
External Galaxies ◽  
Nearby Galaxies

We discuss the distribution and spectral characteristics of diffuse ionized gas in nearby galaxies. The existence of this elusive component of the interstellar medium (ISM), also referred to as the Warm Ionized Medium, is by now well established from deep imaging and spectroscopic surveys in several emission lines in external galaxies. Diffuse ionized gas is characterized by a relatively high ratio of [SII] over Hα intensities, typically twice as high as for discrete HII regions. The diffuse gas has been mapped in both edge-on and more face-on galaxies providing information on the radial and vertical distribitions. Emission from diffuse ionized gas is strongest around star forming regions. The vertical distribution appears related to the radio continuum thick-disk emission. We also briefly discuss ionization mechanisms, and the connection between star formation characteristics and morphology of the interstellar medium.

scholarly journals Mechanisms for Radio Continuum Emission of Long-Period Variable Stars

1993 ◽  
Vol 155 ◽  
pp. 323-323
Author(s):  
G. M. Rudnitskij
Keyword(s):  
Shock Front ◽  
Stellar Atmosphere ◽  
Variable Stars ◽  
Radio Continuum ◽  
Continuum Emission ◽  
Ionized Gas ◽  
Long Period ◽  
Long Period Variables ◽  
Period Variable ◽  
The Continuum

The radio continuum emission of long-period variables (LPVs) in the continuum is considered. For some LPVs (e.g., R Aql and V Hya) weak emission, observed at centimeter wavelengths, can be explained by thermal free-free radiation of the ionized gas behind the shock front in the stellar atmosphere. The ionized layer behind the shock remains optically thick at the wavelengths as short as 1 cm; the brightness temperature found for R Aql at 2 cm by Drake et al. (1987, AJ, 94, 1280), Tb = 18000 K, is consistent with the expected temperature behind the shock.

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