Metallicity Structure across the Galactic Disk: Radio Observations of H ii Regions

2017 ◽  
Vol 13 (S334) ◽  
pp. 275-276
Author(s):  
Dana S. Balser ◽  
Trey V. Wenger ◽  
T. M. Bania ◽  
L. D. Anderson
Keyword(s):  
Electron Temperature ◽  
Massive Star ◽  
Galactic Disk ◽  
Radio Continuum ◽  
Continuum Emission ◽  
H Ii Regions ◽  
Thermal Electron ◽  
Radio Recombination Line ◽  
Nuclear Processing ◽  
Metallicity Distribution

AbstractHii regions are the sites of massive star formation and are the archetypal tracers of spiral arms. Because of their short lifetimes (<10 Myr) their abundances provide a measure of the nuclear processing of many stellar generations. Here we review our ongoing efforts to explore the metallicity structure of the Galactic disk by observing radio recombination line (RRL) and thermal radio continuum emission toward Hii regions. The RRL-to-continuum ratio provides an accurate measure of the electron temperature which is used as a proxy for metallicity. Since collisionally excited lines from metals (e.g., O, C) are the main coolant in Hii regions, the thermal electron temperature is well correlated with metallicity (e.g., [O/H]). We determine Hii region distances from maser parallax measurements when possible; otherwise we use kinematic distances. Such radio diagnostics of Hii regions yield an extinction free tracer to map the metallicity distribution across the entire Galactic disk.

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.

The diagnostic power of radio spectra from star-forming galaxies

2019 ◽  
Vol 15 (S341) ◽  
pp. 177-186
Author(s):  
Eric J. Murphy
Keyword(s):  
Star Formation ◽  
Dust Emission ◽  
Cosmic Ray ◽  
Microwave Emission ◽  
Radio Continuum ◽  
Continuum Emission ◽  
H Ii Regions ◽  
Synchrotron Emission ◽  
Very Large Array ◽  
Star Forming

AbstractRadio continuum emission from galaxies is powered by a combination of distinct physical processes, each providing unique diagnostic information. Over frequencies spanning ∼ 1–120 GHz, radio spectra of star-forming galaxies are primarily comprised of: (1) non-thermal synchrotron emission powered by accelerated cosmic-ray electrons/positrons; (2) free-free emission from young massive star-forming (H ii) regions; (3) anomalous microwave emission, which is a dominant, but completely unconstrained, foreground in cosmic microwave background experiments; and (4) cold, thermal dust emission that accounts for most of the dust and total mass content in the interstellar medium in galaxies. In this proceeding, we discuss these key energetic processes that contribute to the radio emission from star-forming galaxies, with an emphasis on frequencies ≳30 GHz, where current investigations of star formation within nearby galaxies show that the free-free emission begins to dominate over non-thermal synchrotron emission. We also discuss how planned radio facilities that will access these frequencies, such as a next-generation Very Large Array (ngVLA), will be transformative to our understanding of the star formation process in galaxies.

Millimetre Continuum Observations of AGNs and IRAS Galaxies

1996 ◽  
Vol 13 (2) ◽  
pp. 182-182
Author(s):  
Ray Norris
Keyword(s):  
Active Galactic Nucleus ◽  
Black Body ◽  
Active Galaxies ◽  
Radio Continuum ◽  
Continuum Emission ◽  
Starburst Galaxy ◽  
H Ii Regions ◽  
Synchrotron Emission ◽  
Compact Array ◽  
Three Components

The 3 mm radio continuum emission from active galaxies consists of three components: (1)Synchrotron emission from the active galactic nucleus (AGN), which is over 1 Jy in 3C273 but which is not significant in most of the types of galaxy considered here.(2)Free–free emission from H II regions. The flux of this in a starburst galaxy is typically of the order of 10 mJy and could be imaged with a 3 mm-capable Australia Telescope Compact Array (ATCA).(3)Emission from the tail of the 50–100 K black-body spectrum of the dust. For example, the dust in Arp 220 (redshift of 0·02) at a temperature of 50 K has a flux of 30 mJy at 3 mm. Interestingly, this flux does not decrease substantially with redshift, as the decrease in brightness is compensated for by the redshifting of the steep edge of the blackbody curve, and so infrared-bright galaxies can be studied up to high redshifts with existing instruments.

The infrared and radio-continuum emission of the galactic disk

Nature ◽  
1987 ◽  
Vol 327 (6119) ◽  
pp. 211-214 ◽  
Author(s):  
C. G. T. Haslam ◽  
J. L. Osborne
Keyword(s):  
Galactic Disk ◽  
Radio Continuum ◽  
Continuum Emission

scholarly journals VLA Search for Optically Thick H II Regions in Luminous Embedded Infrared Sources

1987 ◽  
Vol 115 ◽  
pp. 185-186
Author(s):  
Paul T.P. Ho ◽  
T. N. Rengarajan
Keyword(s):  
High Resolution ◽  
Radio Emission ◽  
High Sensitivity ◽  
Radio Continuum ◽  
Continuum Emission ◽  
H Ii Regions ◽  
Upper Limit ◽  
Infrared Sources ◽  
Sensitivity Maps

We have searched for radio continuum emission at 15 GHz from a number of deeply embedded protostar like infrared objects, using the B configuration of the VLA. The aim was to get high resolution (1″) and high sensitivity maps. For 10 objects (NGC 7538-IRS 3, GL 989, GL 4029-IRS 1, GL 437N, GL 2789, NGC 1333-IRS 13, S235B, GL 4029-IRS 2, R Mon and OMC2-IRS 3) we did not detect radio emission, the 3 upper limit being 0.3 – 0.5 mJy. Positive detections were made for W33A, 0MC2-IRS 4, S 235-IRS 1 and NGC 6334V-IRS 4. The cleaned maps for these objects are shown in Figures 1-4.

scholarly journals A 12.2 GHz Methanol Maser Survey toward the 6.7 GHz Counterparts Associated with/without UC H ii Regions

2022 ◽  
Vol 258 (1) ◽  
pp. 19
Author(s):  
Shi-Min Song ◽  
Xi Chen ◽  
Zhi-Qiang Shen ◽  
Bin Li ◽  
Kai Yang ◽  
...  
Keyword(s):  
Detection Rate ◽  
Radio Continuum ◽  
Young Stellar Objects ◽  
High Mass ◽  
Continuum Emission ◽  
H Ii Regions ◽  
Stellar Objects ◽  
Methanol Maser ◽  
Physical Environments ◽  
Methanol Masers

Abstract We report a new survey of the 12.2 GHz Class II methanol masers toward a sample of 367 sources with the 6.7 GHz methanol masers conducted with the Shanghai 65 m Tianma Radio Telescope. This sample has been previously made with observations of the radio continuum emission of UC H ii regions by the VLA. A total of 176 sources were detected with the 12.2 GHz methanol maser, with a detection rate of 48%, including 8 new detections. A lower detection rate (<10%) was determined toward the sources in the Galactic longitude ranges of 60°–180°, revealing that the physical environments from those sources in the Local arm or the tails of Galactic arms do not easily excite the 12.2 GHz masers. In addition, two detections of highly excited-state OH masers at the 13.4 GHz transition were made, one of which is a new detection. Compared to previous surveys, one-third of the detected 12.2 GHz masers show considerable flux variations, implying the possible changes of their physical environments associated with variable radiation fields from their host high-mass young stellar objects. A positive log–log correlation is found between the luminosities of the 6.7 and 12.2 GHz masers in our observed sample, suggesting that both the transition masers have similar excitation conditions. The statistical analysis for the relationships between the methanol maser luminosity and UC H ii region spatial size indicates that the maser luminosities of both the 6.7 and 12.2 GHz transitions have a decreasing trend with the spatial sizes of the associated UC H ii regions, indicating that the Class II methanol masers might fade away with the H ii region evolution.

scholarly journals ALMA observations of PSR B1259−63/LS 2883 in an inactive period: Variable circumstellar disk?

2020 ◽  
Vol 72 (5) ◽  
Author(s):  
Yutaka Fujita ◽  
Hiroshi Nagai ◽  
Takuya Akahori ◽  
Akiko Kawachi ◽  
Atsuo T Okazaki
Keyword(s):  
Binary System ◽  
Massive Star ◽  
Gamma Ray ◽  
Thermal Emission ◽  
Radio Continuum ◽  
Continuum Emission ◽  
Circumstellar Disk ◽  
Inactive Period ◽  
Period Variable ◽  
Pulsar Winds

Abstract We report Atacama Large Millimeter/submillimeter Array (ALMA) observations of the gamma-ray binary system containing the pulsar PSR B1259−63 orbiting around a massive star LS 2883 in an inactive period between the 2017 and 2021 periastron passages. We detected radio continuum emission from the binary system at 97 GHz (Band 3) and 343 GHz (Band 7). Compared with our previous ALMA observations performed soon after the 2017 periastron passage, the fluxes have decreased by a factor of six at 97 GHz and of two at 343 GHz. The flux at 343 GHz is large relative to that at 97 GHz and appears to be thermal emission from the circumstellar disk around LS 2883. The decrease of the 343 GHz flux may indicate that the disk has expanded and become partially optically thin since the disk is no longer affected by pulsar winds. The flux at 97 GHz is consistent with that expected from the pulsed emission from the pulsar, which indicates that the unpulsed emission that had been produced through pulsar-disk or pulsar-stellar wind interaction has disappeared. The image of the system is consistent with a point source and shows no sign of ejecta.

Preliminary Results of a Survey of Ultracompact H II Regions

1995 ◽  
Vol 12 (2) ◽  
pp. 186-189 ◽  
Author(s):  
A. J. Walsh ◽  
A. R. Hyland ◽  
G. Robinson ◽  
T. L. Bourke ◽  
S. D. James
Keyword(s):  
Star Formation ◽  
Molecular Clouds ◽  
Radio Continuum ◽  
High Mass ◽  
Continuum Emission ◽  
H Ii Regions ◽  
Mass Star ◽  
Methanol Maser ◽  
Preliminary Results ◽  
Selection Of

AbstractUltracompact H II regions are small, dense regions of ionised gas surrounding high-mass stars which are still embedded in their natal molecular clouds. A survey of such regions has been commenced in an attempt to improve our understanding of the processes of high-mass star formation. The initial stages of the survey have involved selection of likely candidates from the IRAS Point Source Catalogue, correlation with radio continuum emission at 4·85 GHz and subsequent observations of methanol maser emission at 6·668 GHz. Preliminary results of the methanol maser survey are given.

scholarly journals A Detailed Model of the Distribution of Synchrotron Emission in the Galactic Disk

1990 ◽  
Vol 140 ◽  
pp. 61-61
Author(s):  
A. Broadbent ◽  
C.G.T. Haslam ◽  
J.L. Osborne
Keyword(s):  
Magnetic Field ◽  
Galactic Plane ◽  
Galactic Disk ◽  
Cosmic Ray ◽  
Radio Continuum ◽  
Continuum Emission ◽  
Field Variation ◽  
Detailed Model ◽  
Spiral Arm ◽  
Scale Length

A technique for separating the radio continuum emission of the Galaxy into its thermal and nonthermal components has been recently developed by Broadbent, Haslam and Osborne (1989). In this the thermal component is identified by its detailed correlation with the 60 μm infrared emission as observed by IRAS after the subtraction of zodiacal light and the HI-associated dust emission. This technique has been applied to the 408 MHz allsky survey of Haslam et al. (1982). A model of the distribution of synchrotron emissivity in the galactic disk has then been derived including information on the other tracers of spiral structure (HI, CO and giant HII regions) in order to account in detail for the observed nonthermal emission. The spiral arm pattern has two pairs of arms emanating from a central ellipse. The function describing the underlying variation of synchrotron emissivity with galactocentric radius is zero at the centre, rises to a sharp peak and then falls off slowly beyond 3 kpc. Using a scale length of the variation of cosmic ray electron density derived from γ-ray observations, we find that the scale length of the magnetic field variation must be as long as 22 kpc. This agrees with the scale length derived assuming equipartition between energy densities of magnetic field and cosmic rays. The variation of emissivity with height above the plane deduced by Phillipps et al. (1981) when included in our model gives good fits to the observed cuts across the plane. We have modelled the variation of the galactic magnetic field across a spiral arm as a gaussian. In order to fit the peaks in the galactic plane profile σ=0.2 kpc and a maximum compression of the field in the arm of 3.5:1 is required. These parameters are compatible with the results of N-body simulations of spiral arm formation which treat gas clouds as the unit particles. A detailed description of the model is about to be submitted for publication.

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.

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