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arXiv · astro-ph/0305046

Nascent starbursts in synchrotron-deficient galaxies with hot dust

H. Roussel·G. Helou·R. Beck·J. J. Condon·A. Bosma·K. Matthews·T. H. Jarrett
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Abstract

Three nearby galaxies which have abnormally high infrared to radio continuum ratios, NGC 1377, IC 1953 and NGC 4491, are investigated with a view to understanding the physical origin of their peculiarity. We review the existing data and present new radio continuum measurements along with near-infrared integral-field spectroscopy and molecular gas observations. The three galaxies have low luminosities but starburst-like infrared colors; in NGC 1377, no synchrotron emission is detected at any wavelength; in IC 1953, the observed synchrotron component is attributable to the spiral disk alone, and is lacking in the central regions; the radio spectrum of NGC 4491 is unusually flat. We also compare and contrast them with NGC 4418, a heavily extinguished galaxy which shares some attributes with them. After examining various scenarios, we conclude that these galaxies are most likely observed within a few Myr of the onset of an intense star formation episode after being quiescent for at least ~ 100 Myr. This starburst, while heating the dust, has not produced optical signatures nor a normal amount of cosmic rays yet. We briefly discuss the statistics of such galaxies and what they imply for star formation surveys.

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H. Roussel, G. Helou, R. Beck, J. J. Condon, A. Bosma, K. Matthews, T. H. Jarrett. 2003-05-04. Nascent starbursts in synchrotron-deficient galaxies with hot dust. https://doi.org/10.1086/379247

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