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Subarcsecond international LOFAR radio images of the M82 nucleus at 118 MHz and 154 MHz

Eskil Varenius (Institutionen för rymd- och geovetenskap, Radioastronomi och astrofysik) ; John Conway (Institutionen för rymd- och geovetenskap, Onsala rymdobservatorium) ; Ivan Marti-Vidal (Institutionen för rymd- och geovetenskap, Onsala rymdobservatorium) ; R. Beswick ; A. T. Deller ; O. Wucknitz ; N. Jackson ; B. Adebahr ; M. A. Perez-Torres ; K. T. Chyzy ; Tobia Carozzi (Institutionen för rymd- och geovetenskap, Onsala rymdobservatorium) ; J. Moldon ; Susanne Aalto (Institutionen för rymd- och geovetenskap, Radioastronomi och astrofysik) ; R. Beck ; P. Best ; R. J. Dettmar ; W. van Driel ; G. Brunetti ; M. Bruggen ; M. Haverkorn ; G. Heald ; Cathy Horellou (Institutionen för rymd- och geovetenskap, Radioastronomi och astrofysik) ; M. J. Jarvis ; L. K. Morabito ; G. K. Miley ; H. J. A. Rottgering ; M. C. Toribio ; G. J. White
Astronomy and Astrophysics (0004-6361). Vol. 574 (2015), p. Art. no. A114.
[Artikel, refereegranskad vetenskaplig]

Context. The nuclear starburst in the nearby galaxy M82 provides an excellent laboratory for understanding the physics of star formation. This galaxy has been extensively observed in the past, revealing tens of radio bright compact objects embedded in a diffuse free-free absorbing medium. Our understanding of the structure and physics of this medium in M82 can be greatly improved by high-resolution images at tow frequencies where the effects of free-free absorption are most prominent.

Aims. The aims of this study are, firstly, to demonstrate imaging using international baselines of the Low Frequency Array (LOFAR), and secondly, to constrain low frequency spectra of compact and diffuse emission in the central starburst region of M82 via high resolution radio imaging at low frequencies.

Methods. The international LOFAR telescope was used to observe M82 at 110-126 MHz and 146-1621\4Hz. Images were obtained using standard techniques from very long baseline interferometry. images were obtained at each frequency range: one only using international baselines, and one only using the longest Dutch (remote) baselines.

Results. The 154 MHz image obtained using international baselines is a new imaging record in terms of combined image resolution (0.3") and sensitivity (sigma = 0.15 mIy/beath) at low frequencies (<327 MHz). We detected 16 objects at 154 MHz, six of these also at 118 MHz. Seven objects detected at 154 MHz have not been catalogued previously. For the nine objects previously detected, we obtained spectral indices and emission measures by fitting models to spectra (combining LOFAR with literature data). Four weaker but resolved features are also found: a linear (50 pc) filament and three other resolved objects, of which two show a clear shell structure. We do not detect any emission from either supernova 2008iz or from the radio transient source 43.78+59.3. The images obtained using remote baselines show diffuse emission associated with the outflow in M82, with reduced brightness in the region of the edge on star forming disk.

Nyckelord: techniques: interferometric, techniques: high angular resolution, supernovae: individual: 2008iz; galaxies: starburst; galaxies: individual: M82; galaxies: star formation



Denna post skapades 2015-03-31. Senast ändrad 2015-07-07.
CPL Pubid: 214607

 

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Projekt

Denna publikation är ett resultat av följande projekt:


Advanced Radio Astronomy in Europe (RADIONET3) (EC/FP7/283393)