Subarcsecond international LOFAR radio images of the M82 nucleus at 118 MHz and 154 MHz
Artikel i vetenskaplig tidskrift, 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.

galaxies: star formation

techniques: interferometric

galaxies: starburst

supernovae: individual: 2008iz

galaxies: individual: M82

techniques: high angular resolution

Författare

Eskil Varenius

Chalmers, Rymd- och geovetenskap, Radioastronomi och astrofysik

John Conway

Chalmers, Rymd- och geovetenskap, Onsala rymdobservatorium

Ivan Marti-Vidal

Chalmers, Rymd- och geovetenskap, Onsala rymdobservatorium

R. Beswick

University of Manchester

A. T. Deller

Netherlands Institute for Radio Astronomy (ASTRON)

O. Wucknitz

Max Planck-institutet

N. Jackson

University of Manchester

B. Adebahr

Max Planck-institutet

Miguel Angel Perez-Torres

Universidad de Zaragoza

Centro de Estudios de la Física Del Cosmos de Aragón

CSIC - Instituto de Astrof&amp;iacute;sica de Andaluc&amp;iacute;a (IAA)

K.T. Chyz̊y

Uniwersytet Jagiellonski w Krakowie

Tobia Carozzi

Chalmers, Rymd- och geovetenskap, Onsala rymdobservatorium

J. Moldon

Netherlands Institute for Radio Astronomy (ASTRON)

Susanne Aalto

Chalmers, Rymd- och geovetenskap, Radioastronomi och astrofysik

R. Beck

Max Planck-institutet

P. Best

Royal Observatory

R. J. Dettmar

Ruhr-Universität Bochum

W. van Driel

CNRS Centre National de la Recherche Scientifique

G. Brunetti

Istituto di Radioastronomia

M. Brüggen

Universität Hamburg

M. Haverkorn

Universiteit Leiden

Radboud Universiteit

G. Heald

Netherlands Institute for Radio Astronomy (ASTRON)

Rijksuniversiteit Groningen

Cathy Horellou

Chalmers, Rymd- och geovetenskap, Radioastronomi och astrofysik

M. J. Jarvis

University of the Western Cape

University of Oxford

L. K. Morabito

Universiteit Leiden

G. K. Miley

Universiteit Leiden

H. Rottgering

Universiteit Leiden

M. C. Toribio

Netherlands Institute for Radio Astronomy (ASTRON)

G. J. White

Open University

RAL Space/STFC

Astronomy and Astrophysics

0004-6361 (ISSN) 1432-0746 (eISSN)

Vol. 574 Art. no. A114- A114

Ämneskategorier

Astronomi, astrofysik och kosmologi

DOI

10.1051/0004-6361/201425089