Subarcsecond international LOFAR radio images of Arp 220 at 150 MHz: A kpc-scale star forming disk surrounding nuclei with shocked outflows
Artikel i vetenskaplig tidskrift, 2016

Context. Arp 220 is the prototypical ultra luminous infrared galaxy (ULIRG). Despite extensive studies, the structure at MHz-frequencies has remained unknown because of limits in spatial resolution. Aims: This work aims to constrain the flux and shape of radio emission from Arp 220 at MHz frequencies. Methods: We analyse new observations with the International Low Frequency Array (LOFAR) telescope, and archival data from the Multi-Element Radio Linked Interferometer Network (MERLIN) and the Karl G. Jansky Very Large Array (VLA). We model the spatially resolved radio spectrum of Arp 220 from 150 MHz to 33 GHz. Results: We present an image of Arp 220 at 150 MHz with resolution 0.̋65 × 0.̋35, sensitivity 0.15 mJy beam-1, and integrated flux density 394 ± 59 mJy. More than 80% of the detected flux comes from extended (6''≈ 2.2 kpc) steep spectrum (α = -0.7) emission, likely from star formation in the molecular disk surrounding the two nuclei. We find elongated features extending 0.3'' (110 pc) and 0.9'' (330 pc) from the eastern and western nucleus respectively, which we interpret as evidence for outflows. The extent of radio emission requires acceleration of cosmic rays far outside the nuclei. We find that a simple three component model can explain most of the observed radio spectrum of the galaxy. When accounting for absorption at 1.4 GHz, Arp 220 follows the FIR/radio correlation with q = 2.36, and we estimate a star formation rate of 220 M⊙ yr-1. We derive thermal fractions at 1 GHz of less than 1% for the nuclei, which indicates that a major part of the UV-photons are absorbed by dust. Conclusions: International LOFAR observations shows great promise to detect steep spectrum outflows and probe regions of thermal absorption. However, in LIRGs the emission detected at 150 MHz does not necessarily come from the main regions of star formation. This implies that high spatial resolution is crucial for accurate estimates of star formation rates for such galaxies at 150 MHz.

galaxies: individual: Arp 220

galaxies: starburst

ISM: structure

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

Susanne Aalto

Chalmers, Rymd- och geovetenskap, Radioastronomi och astrofysik

Loreto Barcos-Munoz

University of Virginia

Sabine König

Chalmers, Rymd- och geovetenskap, Radioastronomi och astrofysik

Miguel Angel Perez-Torres

Universidad de Zaragoza

CSIC - Instituto de Astrofísica de Andalucía (IAA)

A. Deller

Netherlands Institute for Radio Astronomy (ASTRON)

J. Moldon

University of Manchester

J. S. Gallagher III

University of Wisconsin Madison

Tova M. Yoast-Hull

University of Wisconsin Madison

Cathy Horellou

Chalmers, Rymd- och geovetenskap, Radioastronomi och astrofysik

L. K. Morabito

Universiteit Leiden

Antxon Alberdi

CSIC - Instituto de Astrofísica de Andalucía (IAA)

N. Jackson

University of Manchester

R. J. Beswick

University of Manchester

Tobia Carozzi

Chalmers, Rymd- och geovetenskap, Onsala rymdobservatorium

O. Wucknitz

Max Planck-institutet

Naim Ramirez-Olivencia

CSIC - Instituto de Astrofísica de Andalucía (IAA)

Astronomy and Astrophysics

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

Vol. 593 A86- A86

Advanced Radio Astronomy in Europe (RADIONET3)

Europeiska kommissionen (FP7), 2012-01-01 -- 2015-12-31.

Ämneskategorier

Astronomi, astrofysik och kosmologi

Fundament

Grundläggande vetenskaper

DOI

10.1051/0004-6361/201628702

Mer information

Senast uppdaterat

2018-06-14