scholarly journals Observations of radio continuum emission from M31

1970 ◽  
Vol 38 ◽  
pp. 72-72
Author(s):  
G. G. Pooley
Keyword(s):  
Radio Emission ◽  
Major Axis ◽  
Radio Continuum ◽  
Continuum Emission ◽  
H Ii Regions ◽  
Nuclear Region ◽  
Spiral Arms ◽  
Compact Source ◽  
M 31 ◽  
Sgr A

Observations of continuum emission from M 31 have been made with the Cambridge One-mile radio telescope (Pooley, 1969). Two observing frequencies were used; maps of the whole of the visible nebula were obtained at 408 MHz, and spectral data for the central region at 1407 MHz. The results show that the radiation from the disc is confined to the nucleus and to the population I spiral arms.The nuclear region may be described in terms of two spherical radio components, with diameters of 200 pc and 1 kpc. Any more compact source at the nucleus has a luminosity less than 1/20 of that of the source Sgr A in our Galaxy.The intensity of the radio emission from the spiral arms is closely correlated with the number of H ii regions visible. The main spiral arms, corresponding to Baade's arms 4 and 5, cross the major axis at about 8 and 12.5 kpc from the nucleus. The spectrum of the radiation shows that it is non-thermal in origin; the spectral index is 0.8. The intensity is less than that which would be observed from our own Galaxy at the same distance.

scholarly journals Radio Continuum Emission from the Nuclei of Normal Galaxies

1980 ◽  
Vol 5 ◽  
pp. 177-184 ◽  
Author(s):  
J. M. van der Hulst
Keyword(s):  
Radio Emission ◽  
Galactic Center ◽  
Galactic Nuclei ◽  
Radio Continuum ◽  
Continuum Emission ◽  
Thermal Source ◽  
Very Large Array ◽  
Normal Galaxies ◽  
The Galaxy ◽  
Sgr A

During the last few years detailed and sensitive observations of the radio emission from the nuclei of many normal spiral galaxies has become available. Observations from the Very Large Array (VLA) of the National Radio Astronomy Observatory (NRAO1), in particular, enable us to distinguish details on a scale of ≤100 pc for galaxies at distances less than 21 Mpc. The best studied nucleus, however, still is the center of our own Galaxy (see Oort 1977 and references therein). Its radio structure is complex. It consists of an extended non-thermal component 200 × 70 pc in size, with embedded therein several giant HII regions and the central source Sgr A (˜9 pc in size). Sgr A itself consists of a thermal source, Sgr A West, located at the center of the Galaxy, and a weaker, non-thermal source, Sgr A East. Sgr A West moreover contains a weak, extremely compact (≤10 AU) source. The radio morphology of several other galactic nuclei is quite similar to that of the Galactic Center, as will be discussed in section 2. Recent reviews of the radio properties of the nuclei of normal galaxies have been given by Ekers (1978a,b) and De Bruyn (1978). The latter author, however, concentrates on galaxies with either active nuclei or an unusual radio morphology. In this paper I will describe recent results from the Westerbork Synthesis Radio Telescope (WSRT, Hummel 1979), the NRAO 3-element interferometer (Carlson, 1977; Condon and Dressel 1978), and the VLA (Heckman et al., 1979; Van der Hulst et al., 1979). I will discuss the nuclear radio morphology in section 2, the luminosities in section 3, and the spectra in section 4. In section 5 I will briefly comment upon the possible implications for the physical processes in the nuclei that are responsible for the radio 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.

Radio Continuum Emission from Sculptor Galaxies

1986 ◽  
Vol 6 (3) ◽  
pp. 325-329 ◽  
Author(s):  
J . I. Harnet
Keyword(s):  
Radio Emission ◽  
Blue Light ◽  
Hii Regions ◽  
Radio Continuum ◽  
Radial Dependence ◽  
Continuum Emission ◽  
Upper Limits ◽  
Peak Flux

AbstractThe five major members of the Sculptor Group of galaxies and NGC 45 have been observed with the Molonglo observatory synthesis telescope. NGC 247 and NGC 300 were not detected and upper limits to their 843 MHz flux densities are given. Radio emission from NGC 7793 is discussed with particular attention to its morphology, radial dependence compared with that of the blue light and possible coincidences between HII regions and 843 MHz peak flux densities.

scholarly journals A closer look at the deep radio sky: Multi-component radio sources at 3 GHz VLA-COSMOS

2019 ◽  
Vol 627 ◽  
pp. A142
Author(s):  
E. Vardoulaki ◽  
E. F. Jiménez Andrade ◽  
A. Karim ◽  
M. Novak ◽  
S. K. Leslie ◽  
...  
Keyword(s):  
Radio Emission ◽  
Radio Continuum ◽  
Continuum Emission ◽  
High Angular Resolution ◽  
Radio Sources ◽  
Source Population ◽  
Data Set ◽  
Star Forming ◽  
Large Project ◽  
Automatic Code

Context. Given the unprecedented depth achieved in current large radio surveys, we are starting to probe populations of radio sources that have not been studied in the past. However, identifying and categorising these objects, differing in size, shape and physical properties, is becoming a more difficult task. Aims. In this data paper we present and characterise the multi-component radio sources identified in the VLA-COSMOS Large Project at 3 GHz (0.75 arcsec resolution, 2.3 μJy beam−1 rms), i.e. the radio sources which are composed of two or more radio blobs. Methods. The classification of objects into multi-components was done by visual inspection of 351 of the brightest and most extended blobs from a sample of 10,899 blobs identified by the automatic code BLOBCAT. For that purpose we used multi-wavelength information of the field, such as the 1.4 GHz VLA-COSMOS data and the Ultra Deep Survey with the VISTA telescope (UltraVISTA) stacked mosaic available for COSMOS. Results. We have identified 67 multi-component radio sources at 3 GHz: 58 sources with active galactic nucleus (AGN) powered radio emission and nine star-forming galaxies. We report eight new detections that were not observed by the VLA-COSMOS Large Project at 1.4 GHz, due to the slightly larger area coverage at 3 GHz. The increased spatial resolution of 0.75 arcsec has allowed us to resolve (and isolate) multiple emission peaks of 28 extended radio sources not identified in the 1.4 GHz VLA-COSMOS map. We report the multi-frequency flux densities (324 MHz, 325 MHz, 1.4 GHz & 3 GHz), star formation rates, and stellar masses of these objects. We find that multi-component objects at 3 GHz VLA-COSMOS inhabit mainly massive galaxies (> 1010.5 M⊙). The majority of the multi-component AGN lie below the main sequence of star-forming galaxies (SFGs), in the green valley and the quiescent region. Furthermore, we provide detailed descriptions of the objects and find that amongst the AGN there are two head-tail, ten core-lobe, nine wide-angle-tail (WAT), eight double-double or Z-/X-shaped, three bent-tail radio sources, and 26 symmetric sources, while amongst the SFGs we find the only star-forming ring seen in radio emission in COSMOS. Additionally, we report a large number (32 out of 58) of disturbed/bent multi-component AGN, 18 of which do not lie within X-ray groups in COSMOS (redshift range 0.08 ≤ z <  1.53). Conclusion. The high angular resolution and sensitivity of the 3 GHz VLA-COSMOS data set give us the opportunity to identify peculiar radio structures and sub-structures of multi-component objects, and relate them to physical phenomena such as AGN or star-forming galaxies. This study illustrates the complexity of the μJy radio-source population; at the sensitivity and resolution of 3 GHz VLA-COSMOS, the radio structures of AGN and SFG both emitting radio continuum emission, become comparable in the absence of clear, symmetrical jets. Thus, disentangling the AGN and SFG contributions using solely radio observations can be misleading in a number of cases. This has implications for future surveys, such as those done by square kilometre array (SKA) and precursors, which will identify hundreds of thousands of multi-component objects.

scholarly journals Maser Sources in H ii Regions

1974 ◽  
Vol 60 ◽  
pp. 267-273 ◽  
Author(s):  
B. F. Burke
Keyword(s):  
Background Radiation ◽  
Formation Rate ◽  
Infrared Emission ◽  
Radio Continuum ◽  
H Ii Regions ◽  
Line Radiation ◽  
Compact Source ◽  
Stellar Formation ◽  
Exciting Star ◽  
Compact Sources

When OH and H2O sources are found in Hii regions, a compact source of radio continuum and infrared emission is usually, perhaps always, found nearby, < 1017 cm away (approximately the conjectured size of a prestellar condensation). Whether the masers are self-excited, are amplifying the background radiation, or are themselves associated with an exciting star is clearly model-dependent, and observations have not yet given the answer. H2O masers occur less frequently than OH masers. When they occur together they appear as a cluster of compact sources of line radiation, exhibiting the same range of radial velocities, The OH sources nearly always are strongly polarized, while the H2O maser is not. Both classes of maser are probably saturated, and some care is needed in inferring the maser geometry from the observations. The period of stability of neither OH nor H2O can be much more than 103 yr, and this fact can be used as an estimator of stellar formation rate.

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.

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 (&lt;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 Spectra of Planetary Nebulae

Galaxies ◽  
2018 ◽  
Vol 7 (1) ◽  
pp. 6
Author(s):  
Marcin Hajduk ◽  
Peter van Hoof ◽  
Karolina Sniadkowska ◽  
Andrzej Krankowski ◽  
Leszek Błaszkiewicz ◽  
...  
Keyword(s):  
Radio Emission ◽  
Planetary Nebulae ◽  
Radio Continuum ◽  
Continuum Emission ◽  
Physical Parameters ◽  
Spectral Indices ◽  
Homogeneous Sphere ◽  
Spherical Morphology ◽  
Competing Models ◽  
Source Of Information

Radio continuum emission of planetary nebulae is a rich source of information about their structure and physical parameters. Although radio emission is well studied, planetary nebulae show higher spectral indices than expected for homogeneous sphere. A few competing models exist in the literature to explain this discrepancy. We propose that it is related to non-spherical morphology of most of planetary nebulae.

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.

Sign in / Sign up

Export Citation Format

Share Document