| 1. |
- Batejat, Fabien, 1979, et al.
(author)
-
Resolution of the Compact Radio Continuum Sources in Arp220
- 2011
-
In: Astrophysical Journal. - 1538-4357 .- 0004-637X. ; 740:2
-
Journal article (peer-reviewed)abstract
- We present 2 cm and 3.6 cm wavelength very long baseline interferometry images of the compact radio continuum sources in the nearby ultra-luminous infrared galaxy Arp220. Based on their radio spectra and variability properties, we confirm these sources to be a mixture of supernovae (SNe) and supernova remnants (SNRs). Of the 17 detected sources we resolve 7 at both wavelengths. The SNe generally only have upper size limits. In contrast all the SNRs are resolved with diameters ≥0.27 pc. This size limit is consistent with them having just entered their Sedov phase while embedded in an interstellar medium (ISM) of density 104 cm–3. These objects lie on the diameter-luminosity correlation for SNRs (and so also on the diameter-surface brightness relation) and extend these correlations to very small sources. The data are consistent with the relation L ∝ D–9/4. Revised equipartition arguments adjusted to a magnetic field to a relativistic particle energy density ratio of 1% combined with a reasonable synchrotron-emitting volume filling factor of 10% give estimated magnetic field strengths in the SNR shells of ∼15-50 mG. The SNR shell magnetic fields are unlikely to come from compression of ambient ISM fields and must instead be internally generated. We set an upper limit of 7 mG for the ISM magnetic field. The estimated energy in relativistic particles, 2%-20% of the explosion kinetic energy, is consistent with estimates from models that fit the IR-radio correlation in compact starburst galaxies.
|
|
| 2. |
- Conway, John, 1963, et al.
(author)
-
Continuum and Spectral Line Radiation from a Random Clumpy Medium
- 2018
-
In: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 865:1
-
Journal article (peer-reviewed)abstract
- The American Astronomical Society. All rights reserved. We present a formalism for continuum and line emission from random clumpy media together with its application to problems of current interest, including CO spectral lines from ensembles of clouds and radio emission from H ii regions, supernovae, and star-forming regions. For line emission, we find that the effects of clump opacity on observed line ratios can be indistinguishable from variations of intrinsic line strengths, adding to the difficulties in determining abundances from line observations. Our formalism is applicable to arbitrary distributions of cloud properties, provided the cloud volume filling factor is small; numerical simulations show it to hold up to filling factors of ∼10%. We show that irrespective of the complexity of the cloud ensemble, the radiative effect of clumpiness can be parameterized at each frequency by a single multiplicative correction to the overall optical depth; this multiplier is derived from appropriate averaging over individual cloud properties. Our main finding is that cloud shapes have only a negligible effect on radiation propagation in clumpy media; the results of calculations employing point-like clouds are practically indistinguishable from those for finite-sized clouds with arbitrary geometrical shapes.
|
|
| 3. |
- Conway, John, 1963, et al.
(author)
-
Modelling OH Megamasers in by Clumpy Starburst Rings
- 2004
-
In: in Proceedings of "The Neutral ISM in Starburst Galaxies", Marstrand, June 2003, eds. Aalto S., Huettemeister S., Pedlar A., Astronomical Society of the Pacific Conf. Series, San Francisco. - 1583811826 ; , s. 191-194
-
Conference paper (peer-reviewed)
|
|
| 4. |
|
|
| 5. |
- Duarte-Cabral, A., et al.
(author)
-
The SEDIGISM survey: Molecular clouds in the inner Galaxy
- 2021
-
In: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 500:3, s. 3027-3049
-
Research review (peer-reviewed)abstract
- We use the 13CO(2-1) emission from the SEDIGISM (Structure, Excitation, and Dynamics of the Inner Galactic InterStellar Medium) high-resolution spectral-line survey of the inner Galaxy, to extract the molecular cloud population with a large dynamic range in spatial scales, using the Spectral Clustering for Interstellar Molecular Emission Segmentation (SCIMES) algorithm. This work compiles a cloud catalogue with a total of 10 663 molecular clouds, 10 300 of which we were able to assign distances and compute physical properties. We study some of the global properties of clouds using a science sample, consisting of 6664 well-resolved sources and for which the distance estimates are reliable. In particular, we compare the scaling relations retrieved from SEDIGISM to those of other surveys, and we explore the properties of clouds with and without high-mass star formation. Our results suggest that there is no single global property of a cloud that determines its ability to form massive stars, although we find combined trends of increasing mass, size, surface density, and velocity dispersion for the sub-sample of clouds with ongoing high-mass star formation. We then isolate the most extreme clouds in the SEDIGISM sample (i.e. clouds in the tails of the distributions) to look at their overall Galactic distribution, in search for hints of environmental effects. We find that, for most properties, the Galactic distribution of the most extreme clouds is only marginally different to that of the global cloud population. The Galactic distribution of the largest clouds, the turbulent clouds and the high-mass star-forming clouds are those that deviate most significantly from the global cloud population. We also find that the least dynamically active clouds (with low velocity dispersion or low virial parameter) are situated further afield, mostly in the least populated areas. However, we suspect that part of these trends may be affected by some observational biases (such as completeness and survey limitations), and thus require further follow up work in order to be confirmed.
|
|
| 6. |
|
|
| 7. |
|
|
| 8. |
- Parra Barraza, Rodrigo, 1974, et al.
(author)
-
COLA. III. RADIO DETECTION OF ACTIVE GALACTIC NUCLEUS IN COMPACT MODERATE LUMINOSITY INFRARED GALAXIES
- 2010
-
In: Astrophysical Journal. - 1538-4357 .- 0004-637X. ; 720:1, s. 555-568
-
Journal article (peer-reviewed)abstract
- We present results from 4.8 GHz Very Large Array (VLA) and global very long baseline interferometry (VLBI) observations of the northern half of the moderate FIR luminosity (median L-IR = 10(11.01) L-circle dot) COLA sample of star-forming galaxies. VLBI sources are detected in a high fraction (20/90) of the galaxies observed. The radio luminosities of these cores (similar to 10(21) W Hz(-1)) are too large to be explained by radio supernovae or supernova remnants and we argue that they are instead powered by active galactic nuclei (AGNs). These sub-parsec scale radio cores are preferentially detected toward galaxies whose VLA maps show bright 100-500 parsec scale nuclear radio components. Since these latter structures tightly follow the FIR to radio-continuum correlation for star formation, we conclude that the AGN-powered VLBI sources are associated with compact nuclear starburst environments. The implications for possible starburst-AGN connections are discussed. The detected VLBI sources have a relatively narrow range of radio luminosity consistent with models in which intense compact Eddington-limited starbursts regulate the gas supply onto a central supermassive black hole. The high incidence of AGN radio cores in compact starbursts suggests little or no delay between the starburst phase and the onset of AGN activity.
|
|
| 9. |
|
|
| 10. |
- Parra Barraza, Rodrigo, 1974, et al.
(author)
-
Multiwavelength radio observations of the compact starburst in Arp 220
- 2006
-
In: Proceedings of Science. - 1824-8039. ; 36
-
Conference paper (peer-reviewed)abstract
- We report the first detection at multiple radio wavelengths (13, 6, and 3.6 cm) of 18 compact sources within both nuclei of the Ultra Luminous Infra-Red Galaxy (ULIRG) Arp 220. In just over half of the sources we find that the observed spectra are consistent with the standard model of powerful Type IIn supernovae interacting with their pre-explosion stellar wind. The rate of appearance of new radio sources ascribed to these supernova events suggests that a large fraction of core-collapse supernovae in Arp 220 are highly luminous, possibly implying a radically different stellar initial mass function (IMF) or stellar evolution compared to galactic disks. A second group of sources, consisting of the brightest and longest monitored sources at 18 cm, do not easily fit the radio supernova model. We propose that these are young supernova remnants that have just begun interacting with their surrounding dense ISM.
|
|
