The Stellar Content of M82

Author: O'Connell, Robert West

Year: 1970

Degree: Dissertation (Ph.D.)

Advisors: Sargent, Wallace L. W.; Oke, J. Beverley

Committee Member: Unknown, Unknown

Option: Astronomy; Physics

DOI: 10.7907/AEZK-3E15

Abstract

The stellar contents of two regions on the peculiar galaxy M82 are investigated by spectral synthesis. One of the regions is identified as the nucleus of the galaxy on the basis of its surface brightness and inferred mass density; the other is spectrally representative of the disk of M82. Narrow-band spectrophotometry for both regions can be satisfactorily interpreted in terms of ordinary kinds of stars and dust prevalent in the solar neighborhood if 10³ M⊙ of dust is mixed with the stars in the nucleus. There is no evidence for stellar abundance anomalies or the presence of significant amounts of non-stellar radiation except for gaseous emission between 3400 and 11000 Å. Approximately 50% of the observed Na I λ5892 absorption feature originates in the interstellar medium of M82. The deduced main sequence luminosity functions for both regions resemble that for the galactic disk in the solar vicinity except that an excess of massive stars (Mv < -3) exists in the nucleus and a deficiency, in the disk. Sufficient numbers of hot stars are present in the nucleus to maintain the observed level of nuclear interstellar ionization. The absence of massive stars in the disk is corroborated by photographic and spectroscopic evidence and may be the result of a suppression of star formation by a nuclear disturbance. The mass density inferred from the synthesis for the small disk region observed is much higher than found in typical late-type galaxies.

The results of extensive absorption feature index photometry of common galactic stars are also described.

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