Evidence for a sizable age spread among galaxies from the ultraviolet-upturn phenomenon in early-type systems

Jang Hyun Park, Young-Wook Lee

Research output: Contribution to journalArticle

54 Citations (Scopus)

Abstract

The suggestion of Lee that the age spread among galaxies is responsible for the systematic variation of the ultraviolet upturn among early-type systems is examined here with detailed population synthesis models. Our models differ from previous ones by including (1) the effect of metallicity spreads and (2) detailed modeling of the variations in H-R diagram morphology (including the helium-burning phase) with age and metallicity. Our models suggest that the far-UV radiation of these systems is dominated by a minority population of metal-poor, hot horizontal-branch (HB) stars and their post-HB progeny, with some contribution from metal-rich post-asymptotic giant branch stars, while the optical radiation is dominated by a metal-rich population. The systematic variation of the UV upturn depends on the contribution from metal-poor, hot HB stars and their post-HB progeny, which in turn depends on the ages of old stellar populations in galaxies. Our result implies a prolonged epoch of galaxy formation, in the sense that more massive galaxies (in denser environments) formed first. With the assumption that the UV-upturn phenomenon is solely due to the age variations among galaxies, we estimate the difference in age between the giant elliptical galaxies and the spiral bulges of the Local Group to be ∼3 Gyr. This suggests that the best estimate for the lower limit of the age of the universe is ∼19 Gyr, which of course would be in conflict with the current estimate of H0, together with the standard cosmological models with zero cosmological constant.

Original languageEnglish
Pages (from-to)28-39
Number of pages12
JournalAstrophysical Journal
Volume476
Issue number1 PART I
DOIs
Publication statusPublished - 1997 Jan 1

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galaxies
horizontal branch stars
progeny
hot stars
metals
metallicity
estimates
metal
asymptotic giant branch stars
elliptical galaxies
galactic evolution
radiation
minorities
suggestion
universe
helium
diagrams
time measurement
synthesis
diagram

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

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abstract = "The suggestion of Lee that the age spread among galaxies is responsible for the systematic variation of the ultraviolet upturn among early-type systems is examined here with detailed population synthesis models. Our models differ from previous ones by including (1) the effect of metallicity spreads and (2) detailed modeling of the variations in H-R diagram morphology (including the helium-burning phase) with age and metallicity. Our models suggest that the far-UV radiation of these systems is dominated by a minority population of metal-poor, hot horizontal-branch (HB) stars and their post-HB progeny, with some contribution from metal-rich post-asymptotic giant branch stars, while the optical radiation is dominated by a metal-rich population. The systematic variation of the UV upturn depends on the contribution from metal-poor, hot HB stars and their post-HB progeny, which in turn depends on the ages of old stellar populations in galaxies. Our result implies a prolonged epoch of galaxy formation, in the sense that more massive galaxies (in denser environments) formed first. With the assumption that the UV-upturn phenomenon is solely due to the age variations among galaxies, we estimate the difference in age between the giant elliptical galaxies and the spiral bulges of the Local Group to be ∼3 Gyr. This suggests that the best estimate for the lower limit of the age of the universe is ∼19 Gyr, which of course would be in conflict with the current estimate of H0, together with the standard cosmological models with zero cosmological constant.",
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Evidence for a sizable age spread among galaxies from the ultraviolet-upturn phenomenon in early-type systems. / Park, Jang Hyun; Lee, Young-Wook.

In: Astrophysical Journal, Vol. 476, No. 1 PART I, 01.01.1997, p. 28-39.

Research output: Contribution to journalArticle

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