M82: The saga continues

K. K. Mcleod, George H. Rieke, Marcia J Rieke, D. M. Kelly

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Abstract

We present new near-infrared observations of the starburst galaxy M82, including high-resolution J, H, and K imagery, 1-5 μm spectrophotometry and photometry, and 1.05-1.35 μm spectroscopy. These measurements are used to examine the stellar population in the galaxy and conditions in the interstellar medium. We combine our observations with results from the literature to derive a new set of constraints for starburst models, which are presented in a companion paper. Our measurements of Paschen line fluxes in combination with the strengths of other recombination lines allow study of the reddening in M82. We find that a uniform foreground screen model for the dust geometry cannot explain the relative line strengths. A variety of other models can fit the data reasonably well, such as a nonuniform foreground screen or a homogeneous mix of dust and gas. The derived properties of the galaxy are not strongly dependent on which of these models is selected; we derive an ionizing flux of ≈1054 s-1 and an absolute magnitude of the starburst region of MK < -22.5. Depending on the reddening model, the visual extinction to the nucleus lies between AV = 12 and AV = 27; we show that the nucleus does not coincide with any feature that is bright at visual wavelengths. The stellar H2O index in the nuclear region is less than 0.06 and the CO index is ≈0.21; contamination of the CO band by emission by hot dust must be small. We use several lines in the 1.3 μm region to derive a lower limit to the electron density of ne > 104.5 cm-3 in the [Fe II] emission region. The [Fe II] line fluxes are consistent with excitation by fast shocks incident on dense gas. We report the tentative detection of several lines of H2, which, if confirmed, implicate UV fluorescence as the excitation mechanism.

Original languageEnglish (US)
Pages (from-to)111-126
Number of pages16
JournalAstrophysical Journal
Volume412
Issue number1
Publication statusPublished - Jul 20 1993

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Keywords

  • Dust, extinction
  • Galaxies: individual (M82)
  • Galaxies: ISM
  • Galaxies: photometry
  • Galaxies: starburst
  • Infrared: galaxies
  • ISM: molecules

ASJC Scopus subject areas

  • Space and Planetary Science

Cite this

Mcleod, K. K., Rieke, G. H., Rieke, M. J., & Kelly, D. M. (1993). M82: The saga continues. Astrophysical Journal, 412(1), 111-126.