Galaxy spectral synthesis. I - Stellar populations in the nuclei of giant ellipticals

Abstract

view Abstract Citations (229) References (86) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Galaxy spiral synthesis. I. Stellar populations in the nuclei of giant ellipticals. O'Connell, R. W. Abstract We develop an automatic spectral synthesis technique based on linear programming and apply it to narrow-band spectrophotometry covering 3300-10800 Angstroms for the nuclei of M31 and three giant elliptical galaxies in Virgo. The mean energy distribution of the gE nuclei (r < 400 pc) is well defined and, within the uncertainty in E(B-V), does not differ significantly from that for M31 (r < 50 pc). The observations are consistent with only a small range of main-sequence turnoffs, which depends on the relative rates of main-sequence and subgiant evolution. Using Iben's (1967) models of stellar interiors, we find the bulk of the stars in gE nuclei formed 8-11 Gyr ago, with star formation possibly continuing at a much reduced level until ~4 Gyr ago. The maximum mean rate of postburst star formation consistent with the data is ~2.9 x [L_v/ 10^11 L_v_sun] M_sun/yr. There is no evidence of a significant Population II component. Na I and Mg I exhibit distinct enhancements with respect to Ca II and the Fe-peak, but the evidence for Fe-peak enrichment is not strong. M giants dominate M dwarfs throughout the spectrum, and M/L_v > 30 (solar units) is excluded if stars with absolute V magnitude > 18 are not important. The best models yield 2 < M/L_v < 15, in agreement with recent dynamical estimates. Infrared spectral features indicate that short-lived, low-gravity phases near the tip of the asymptotic giant branch make significant contributions. There is marginal evidence that the lower main sequence for absolute V magnitude > 11 is enriched, as suggested for M31 by Spinrad and Taylor (1971). Weak [O II] 3727 Angstrom emission is present in two of the gE's, and we find M(H II) < 4 x 10^6 M_sun for the nucleus of NGC 4552. We describe a new method for estimating the H I content of elliptical nuclei, which here yields M(H I) < 5 x 10^6 M_sun. The observations do not exclude a complete recycling into stars of mass shed during stellar evolution at current rates. Aside from marginal evidence for a weak optical nonthermal component in NGC 4552, there are no marked optical peculiarities associated with the radio sources in the gE's, and their general properties are consistent with a model in which the radio energy is produced by supernovae which form in the nucleus following mass loss during stellar evolution. Publication: The Astrophysical Journal Pub Date: June 1976 DOI: 10.1086/154392 Bibcode: 1976ApJ...206..370O Keywords: Astronomical Spectroscopy; Elliptical Galaxies; Galactic Nuclei; Spectral Energy Distribution; Spectrum Analysis; Star Distribution; Abundance; Andromeda Galaxy; Astronomical Models; Data Reduction; Interstellar Extinction; Interstellar Matter; Luminous Intensity; M Stars; Mathematical Models; Metallic Stars; Stellar Evolution; Astrophysics full text sources ADS | data products NED (5) SIMBAD (4) Related Materials (1) Part 2: 1980ApJ...236..430O