Evolution of the stars and gas in galaxies

1980
101 pages
Published in:
  • Fund.Cosmic Phys. 5 (1980) 287
e-Print:
DOI:

Citations per year

198119922003201420250510152025
Abstract: (arXiv)
Essentially everything of astronomical interest is either part of a galaxy, or from a galaxy, or otherwise relevant to the origin or evolution of galaxies. Diverse examples are that the isotropic composition of meteorites provides clues to the history of star formation billions of years ago, and cosmological tests for the deceleration of the Universe are strongly affected by changes in the luminosities of galaxies during the lookback time sampled. The aim of this article is to review some of the vital connections that galaxy evolution makes among many astronomical phenomena.
Note:
  • This paper has been transcribed from a hard copy of Beatrice M. Tinsley's original manuscript into a digital file prepared by Michael J. Greener, a PhD student at the University of Nottingham. If you notice any errors or problems with this transcribed paper, please email Michael at either michael.greener@nottingham.ac.uk or mickgreener@protonmail.com. This version 2 includes a clearer Figure 6
  • 7.2.2 Highly reddened galaxies
    • Some regions of galaxies that are suspected of having intense star formation are extremely dusty, and they show thermal infrared (IR) emission that is interpreted as re-radiation of starlight by the dust. Example of such regions include the centers of M82 and NGC 253, and the dust band around
      • NGC 5128 (e.g. Kleinmann
      • Telesco). Star formation is indicated by early-type spectra and blue colors in unobscured patches (e.g. van den Bergh 1971,), emission from interstellar molecules (e.g. Whiteoak), and the lack of more plausible explanations for the IR emission (e.g. Kleinmann 1977). In NGC 5128, the dust band has an IR luminosity of a few times 1010
      • Lfi (Telesco), which rivals the visual luminosity of the entire elliptical galaxy
      • If the IR luminosity is assumed to represent the bolometric luminosity of buried stars, an SFR can be estimated (StruckMarcell & Tinsley): models like those of Section 7.1 show that any system with a mass-to-luminosity ratio Ms/Lbol < 0.5 is so dominated by young stars that Lbol is almost directly proportional to the SFR
      • with the local IMF, the relation is
        • ψ ' (0.1 - 0.4)
          • Lbol
            • L
              • Mfi Gyr-1
                • (7.1)
                  • An upper limit to the time for which star formation could have continued at this rate is approximately Ms/ψ, so the limiting timescale τs depends only on Ms/Lbol, according to the relation
                    • τs ≡
                      • Ms
                        • ψ
                          • ∼ (3 - 10)
                            • Ms/Lbol
                              • Mfi/L
                                • Gyr. (7.2)
                                  • Some galactic nuclei have such strong IR emission that
                                    • Ms/Lbol is only a few hundredths, so the timescale is only a few times 108 yr. The dust-band region of NGC 5128 is also making stars at a prodigious rate: given a luminosity
                                      • ∼1010
                                        • Lfi, Equation (7.1) leads to an SFR of about 2 Mfi yr-1
                                          • so a respectable disk of stars could be built in just a few times the dynamical timescale of the system. van den Bergh has suggested that NGC 5128 could evolve into an early-type spiral seen edge-on, like the Sombrero galaxy M104