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Spatially resolved Spitzer IRS spectroscopy of the central region of M82

Beirão, P. and Brandl, B. R. and Appleton, P. N. and Groves, B. and Armus, L. and Förster Schreiber, N. M. and Smith, J. D. and Charmandaris, V. and Houck, J. R. (2008) Spatially resolved Spitzer IRS spectroscopy of the central region of M82. Astrophysical Journal, 676 (1). pp. 304-316. ISSN 0004-637X. http://resolver.caltech.edu/CaltechAUTHORS:BEIapj08

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Abstract

We present high spatial resolution (~35 pc) 5-38 μm spectra of the central region of M82, taken with the Spitzer Infrared Spectrograph. From these spectra we determined the fluxes and equivalent widths (EWs) of key diagnostic features, such as the [Ne II] 12.8 μm, [Ne III] 15.5 μm, and H2 S(1) 17.03 μm lines, and the broad mid-IR polycyclic aromatic hydrocarbon (PAH) emission features in six representative regions and analyzed the spatial distribution of these lines and their ratios across the central region. We find a good correlation of the dust extinction with the CO 1-0 emission. The PAH emission follows closely the ionization structure along the galactic disk. The observed variations of the diagnostic PAH ratios across M82 can be explained by extinction effects, within systematic uncertainties. The 16-18 μmPAH complex is very prominent, and its EW is enhanced outward from the galactic plane. We interpret this as a consequence of the variation of the UVradiation field. The EWs of the 11.3 μm PAH feature and the H2S(1) line correlate closely, and we conclude that shocks in the outflow regions have no measurable influence on the H2 emission. The [Ne III]/[Ne II] ratio is on average low, at ~0.18, and shows little variations across the plane, indicating that the dominant stellar population is evolved (5-6 Myr) and well distributed. There is a slight increase of the ratio with distance from the galactic plane of M82, which we attribute to a decrease in gas density. Our observations indicate that the star formation rate has decreased significantly in the last 5 Myr. The quantities of dust and molecular gas in the central area of the galaxy argue against starvation and for negative feedback processes, observable through the strong extraplanar outflows.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1086/527343DOIArticle
ORCID:
AuthorORCID
Appleton, P. N.0000-0002-7607-8766
Groves, B.0000-0002-9768-0246
Smith, J. D.0000-0003-1545-5078
Additional Information:© 2008. The American Astronomical Society. Received 2007 February 7; accepted 2007 November 27. We would like to thank L. Snijders for making the Starburst99+ Mappings models available. We would like to thank J. Lacy for providing the mid-infrared maps from IRTF ground-based observations. We also thank the anonymous referee, whose many thoughtful and useful comments greatly improved this paper. This work is based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under NASA contract 1407. Online material: color figures
Group:Infrared Processing and Analysis Center (IPAC)
Funders:
Funding AgencyGrant Number
NASA/JPL/Caltech1407
Subject Keywords:galaxies: individual (M82)—galaxies: starburst—infrared: galaxies
Issue or Number:1
Record Number:CaltechAUTHORS:BEIapj08
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:BEIapj08
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:11485
Collection:CaltechAUTHORS
Deposited By: Marie Noren
Deposited On:09 Oct 2008 15:43
Last Modified:18 Aug 2017 01:35

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