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| 2. |
- Batejat, Fabien, 1979, et al.
(författare)
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Resolution of the Compact Radio Continuum Sources in Arp220
- 2011
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Ingår i: Astrophysical Journal. - 1538-4357 .- 0004-637X. ; 740:2
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Tidskriftsartikel (refereegranskat)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.
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| 4. |
- Costagliola, Francesco, 1981, et al.
(författare)
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Molecules as tracers of galaxy evolution: an EMIR survey I. Presentation of the data and first results
- 2011
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 528
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Tidskriftsartikel (refereegranskat)abstract
- Aims. We investigate the molecular gas properties of a sample of 23 galaxies in order to find and test chemical signatures of galaxy evolution and to compare them to IR evolutionary tracers. Methods. Observation at 3 mm wavelengths were obtained with the EMIR broadband receiver, mounted on the IRAM 30 m telescope on Pico Veleta, Spain. We compare the emission of the main molecular species with existing models of chemical evolution by means of line intensity ratios diagrams and principal component analysis. Results. We detect molecular emission in 19 galaxies in two 8 GHz-wide bands centred at 88 and 112 GHz. The main detected molecules are CO, (CO)-C-13, HCN, HNC, HCO+, CN, and C2H. We also detect HC3N J = 10-9 in the galaxies IRAS 17208, IC 860, NGC 4418, NGC 7771, and NGC 1068. The only HC3N detections are in objects with HCO+/HCN 0.8). The brightest HC3N emission is found in IC 860, where we also detect the molecule in its vibrationally excited state. We find low HNC/HCN line ratios (
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| 5. |
- Rottgering, H., et al.
(författare)
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LOFAR and APERTIF Surveys of the Radio Sky: Probing Shocks and Magnetic Fields in Galaxy Clusters
- 2011
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Ingår i: Journal of Astrophysics and Astronomy. - : Springer Science and Business Media LLC. - 0250-6335 .- 0973-7758. ; 32:4, s. 557-566
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Tidskriftsartikel (refereegranskat)abstract
- At very low frequencies, the new pan-European radio telescope LOFAR is opening the last unexplored window of the electromagnetic spectrum for astrophysical studies. The revolutionary APERTIF-phased arrays that are about to be installed on the Westerbork radio telescope (WSRT) will dramatically increase the survey speed for the WSRT. Combined surveys with these two facilities will deeply chart the northern sky over almost two decades in radio frequency from similar to 15 up to 1400 MHz. Here we briefly describe some of the capabilities of these new facilities and what radio surveys are planned to study fun-damental issues related to the formation and evolution of galaxies and clusters of galaxies. In the second part we briefly review some recent observational results directly showing that diffuse radio emission in clusters traces shocks due to cluster mergers. As these diffuse radio sources are relatively bright at low frequencies, LOFAR should be able to detect thousands of such sources up to the epoch of cluster formation. This will allow addressing many question about the origin and evolution of shocks and magnetic fields in clusters. At the end we briefly review some of the first and very preliminary LOFAR results on clusters.
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