Spatially Resolved Spitzer-IRS Spectroscopy of the Central Region of M82

Abstract

We present high spatial resolution (~ 35 parsec) 5-38 um spectra of the central region of M82, taken with the Spitzer Infrared Spectrograph. From these spectra we determined the fluxes and equivalent widths of key diagnostic features, such as the [NeII]12.8um, [NeIII]15.5um, and H_2 S(1)17.03um lines, and the broad mid-IR polycyclic aromatic hydrocarbon (PAH) emission features in six representative regions and analysed 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 16-18um PAH complex is very prominent, and its equivalent width is enhanced outwards from the galactic plane. We interpret this as a consequence of the variation of the UV radiation field. The EWs of the 11.3um PAH feature and the H_2 S(1) line correlate closely, and we conclude that shocks in the outflow regions have no measurable influence on the H_2 emission. The [NeIII]/[NeII] 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 extra-planar outflows.

15 pages, 12 figures, 3 tables, ApJ, emulateapj

References in corpus (11)

• Infrared Emission from Interstellar Dust. IV. The Silicate-Graphite-PAH Model in the Post-Spitzer Era
• Dust Masses, PAH Abundances, and Starlight Intensities in the SINGS Galaxy Sample
• Mid-IR Galaxy Classification Based on Silicate Obscuration and PAH Equivalent Width
• Spectral Mapping Reconstruction of Extended Sources
• Extended Mid-Infrared Aromatic Feature Emission in M 82
• Mid-Infrared Spectral Diagnostics of Nuclear and Extra-Nuclear Regions in Nearby Galaxies
• HST/STIS Spectroscopy of Five Super Star Clusters in the Starburst Galaxy M82
• The opaque nascent starburst in NGC 1377: Spitzer SINGS observations
• Mid-infrared diagnostics of starburst galaxies: clumpy, dense structures in star-forming regions in the Antennae (NGC 4038/4039)
• PAH Strength and the Interstellar Radiation Field around the Massive Young Cluster NGC3603
• Spatially Resolved Spitzer Spectroscopy of the Starburst Nucleus in NGC 5253

Cited by in corpus (11)

• Modelling the Pan-Spectral Energy Distribution of Starburst Galaxies: IV The Controlling Parameters of the Starburst SED
• Physical Dust Models for the Extinction toward Supernova 2014J in M82
• The Mid-Infrared [SIV]/[NeII] versus [NeIII]/[NeII] Correlation
• The mid-infrared appearance of the Galactic Mini-Starburst W49A
• Locating the Youngest HII Regions in M82 with 7 mm Continuum Maps
• An optical--near-IR study of a triplet of super star clusters in the starburst core of M82
• JWST Observations of Starbursts: Relations between PAH features and CO clouds in the starburst galaxy M 82
• High-velocity-resolution observations of OH main line lasers in the M82 starburst
• JWST Observations of Starbursts: PAHs Closely Trace the Cool Phase of M82's Galactic Wind
• Variations in the 6.2 $\mu$m polycyclic aromatic hydrocarbon band in Active Galactic Nuclei- and Starburst-dominated galaxies
• JWST Observations of Starbursts: Dust Processing in the M82 Superwind