Subarcsecond international LOFAR radio images of the M82 nucleus at 118 MHz and 154 MHz
Journal article, 2015
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.
techniques: high angular resolution
supernovae: individual: 2008iz
galaxies: star formation
techniques: interferometric
galaxies: individual: M82
galaxies: starburst
Author
Eskil Varenius
Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics
John Conway
Chalmers, Earth and Space Sciences, Onsala Space Observatory
Ivan Marti-Vidal
Chalmers, Earth and Space Sciences, Onsala Space Observatory
R. Beswick
University of Manchester
A. T. Deller
Netherlands Institute for Radio Astronomy (ASTRON)
O. Wucknitz
Max Planck Society
N. Jackson
University of Manchester
B. Adebahr
Max Planck Society
Miguel Angel Perez-Torres
Spanish National Research Council (CSIC)
University of Zaragoza
CEFCA
K.T. Chyz̊y
Jagiellonian University in Kraków
Tobia Carozzi
Chalmers, Earth and Space Sciences, Onsala Space Observatory
J. Moldon
Netherlands Institute for Radio Astronomy (ASTRON)
Susanne Aalto
Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics
R. Beck
Max Planck Society
P. Best
Royal Observatory
R. J. Dettmar
Ruhr-Universität Bochum
W. van Driel
Centre national de la recherche scientifique (CNRS)
G. Brunetti
Istituto di Radioastronomia
M. Brüggen
University of Hamburg
M. Haverkorn
Radboud University
Leiden University
G. Heald
Netherlands Institute for Radio Astronomy (ASTRON)
University of Groningen
Cathy Horellou
Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics
M. J. Jarvis
University of the Western Cape
University of Oxford
L. K. Morabito
Leiden University
G. K. Miley
Leiden University
H. Rottgering
Leiden University
M. C. Toribio
Netherlands Institute for Radio Astronomy (ASTRON)
G. J. White
RAL Space/STFC
The Open University
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 574 Art. no. A114- A114Advanced Radio Astronomy in Europe (RADIONET3)
European Commission (EC) (EC/FP7/283393), 2012-01-01 -- 2015-12-31.
Subject Categories (SSIF 2011)
Astronomy, Astrophysics and Cosmology
DOI
10.1051/0004-6361/201425089