The opaque nascent starburst in NGC 1377: Spitzer sings observations

H. Roussel, G. Helou, J.D. D. Smith, B.T. T. Draine, D.J. J. Hollenbach, J. Moustakas, H.W. W. Spoon, R.C. C. Kennicutt, G.H. H. Rieke, F. Walter, L. Armus, D.A. A. Dale, K. Sheth, G.J. J. Bendo, C.W. W. Engelbracht, K.D. D. Gordon, Martin Meyer, M.W. W. Regan, E.J. J. Murphy

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Abstract

We analyze extensive data on NGC 1377 from the Spitzer Infrared Nearby Galaxies Survey (SINGS). Within the category of nascent starbursts that we previously selected as having infrared-to-radio continuum ratios in large excess of the average and containing hot dust, NGC 1377 has the largest infrared excess yet measured. Optical imaging reveals a morphological distortion suggestive of a recent accretion event. Infrared spectroscopy reveals a compact and opaque source dominated by a hot, self-absorbed continuum (t ~ 20 in the 10 µm silicate band). We provide physical evidence against nonstellar activity being the heating source. H II regions are detected through the single [Ne II] line, probing <1% of the ionizing radiation. Not only is the optical depth in different gas and dust phases very high, but >85% of ionizing photons are suppressed by dust. The only other detected emission features are molecular hydrogen lines, arguably excited mainly by shocks, besides photodissociation regions, and weak aromatic bands. The new observations support our interpretation in terms of an extremely young starburst (
Original languageEnglish
Pages (from-to)841-857
Number of pages17
JournalAstrophysical Journal
Volume646
Issue number2 I
DOIs
Publication statusPublished - 2006

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    Roussel, H., Helou, G., Smith, J. D. D., Draine, B. T. T., Hollenbach, D. J. J., Moustakas, J., Spoon, H. W. W., Kennicutt, R. C. C., Rieke, G. H. H., Walter, F., Armus, L., Dale, D. A. A., Sheth, K., Bendo, G. J. J., Engelbracht, C. W. W., Gordon, K. D. D., Meyer, M., Regan, M. W. W., & Murphy, E. J. J. (2006). The opaque nascent starburst in NGC 1377: Spitzer sings observations. Astrophysical Journal, 646(2 I), 841-857. https://doi.org/10.1086/505038