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: interferometric

supernovae: individual: 2008iz

galaxies: star formation

galaxies: starburst

techniques: high angular resolution

galaxies: individual: M82

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 Institute

N. Jackson

University of Manchester

B. Adebahr

Max Planck Institute

Miguel Angel Perez-Torres

Centro de Estudios de Física del Cosmos de Aragón

CSIC - Instituto de Astrofísica de Andalucía (IAA)

University of Zaragoza

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 Institute

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

Universität Hamburg

M. Haverkorn

Leiden University

Radboud 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

Open University

Astronomy and Astrophysics

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

Vol. 574 Art. no. A114- A114

Advanced Radio Astronomy in Europe (RADIONET3)

European Commission (FP7), 2012-01-01 -- 2015-12-31.

Subject Categories

Astronomy, Astrophysics and Cosmology

DOI

10.1051/0004-6361/201425089

More information

Latest update

9/7/2018 1