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Spatially resolved Spitzer-IRS spectral maps of the superwind in M82

Beirão, P. and Armus, L. and Lehnert, M. D. and Guillard, P. and Heckman, T. and Draine, B. and Hollenbach, D. and Walter, F. and Sheth, K. and Smith, J. D. and Shopbell, P. and Boulanger, F. and Surace, J. and Hoopes, C. and Engelbracht, C. (2015) Spatially resolved Spitzer-IRS spectral maps of the superwind in M82. Monthly Notices of the Royal Astronomical Society, 451 (3). pp. 2640-2655. ISSN 0035-8711.

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We have mapped the superwind/halo region of the nearby starburst galaxy M82 in the mid-infrared with Spitzer − IRS. The spectral regions covered include the H_2 S(1)–S(3), [Ne II], [Ne III] emission lines and polycyclic aromatic hydrocarbon (PAH) features. We estimate the total warm H2 mass and the kinetic energy of the outflowing warm molecular gas to be between M_(warm) ∼ 5 and 17 × 10^6 M_⊙ and E_K ∼ 6 and 20 × 10^(53) erg. Using the ratios of the 6.2, 7.7 and 11.3 μm PAH features in the IRS spectra, we are able to estimate the average size and ionization state of the small grains in the superwind. There are large variations in the PAH flux ratios throughout the outflow. The 11.3/7.7 and the 6.2/7.7 PAH ratios both vary by more than a factor of 5 across the wind region. The northern part of the wind has a significant population of PAH's with smaller 6.2/7.7 ratios than either the starburst disc or the southern wind, indicating that on average, PAH emitters are larger and more ionized. The warm molecular gas to PAH flux ratios (H_2/PAH) are enhanced in the outflow by factors of 10–100 as compared to the starburst disc. This enhancement in the H_2/PAH ratio does not seem to follow the ionization of the atomic gas (as measured with the [Ne III]/[Ne II] line flux ratio) in the outflow. This suggests that much of the warm H_2 in the outflow is excited by shocks. The observed H_2 line intensities can be reproduced with low-velocity shocks (v < 40 km s^(−1)) driven into moderately dense molecular gas (10^2 < n_H < 10^4 cm^(−3)) entrained in the outflow.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Armus, L.0000-0003-3498-2973
Lehnert, M. D.0000-0003-1939-5885
Guillard, P.0000-0002-2421-1350
Draine, B.0000-0002-0846-936X
Walter, F.0000-0003-4793-7880
Sheth, K.0000-0002-5496-4118
Smith, J. D.0000-0002-1684-1344
Surace, J.0000-0001-7291-0087
Additional Information:© 2015 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2015 May 13. Received 2015 April 24. In original form 2014 July 18. First published online June 13, 2015. We would like to thank an anonymous referee for a number of helpful comments which helped improve the quality of this paper. This work is based on observations made with the Spitzer Space Telescope, which was operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. Support for this work was provided by NASA through an award issued by JPL/Caltech. This work is dedicated to the memory of our friend and colleague, CE.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
Subject Keywords:galaxies: individual: M82; galaxies: starburst; infrared: galaxies
Issue or Number:3
Record Number:CaltechAUTHORS:20151002-103755733
Persistent URL:
Official Citation:P. Beirão, L. Armus, M. D. Lehnert, P. Guillard, T. Heckman, B. Draine, D. Hollenbach, F. Walter, K. Sheth, J. D. Smith, P. Shopbell, F. Boulanger, J. Surace, C. Hoopes, and C. Engelbracht Spatially resolved Spitzer-IRS spectral maps of the superwind in M82 MNRAS (August 11, 2015) Vol. 451 2640-2655 doi:10.1093/mnras/stv1101 First published online June 13, 2015
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:60701
Deposited By: George Porter
Deposited On:02 Oct 2015 18:05
Last Modified:09 Mar 2020 13:19

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