E+A galaxies and the formation of early-type galaxies at z ∼ 0

Yujin Yang, Ann I Zabludoff, Dennis F Zaritsky, Tod R. Lauer, J. Christopher Mihos

Research output: Contribution to journalArticle

80 Citations (Scopus)

Abstract

E+A galaxies, whose spectra have deep Balmer absorption lines but no significant [O II] emission, are the best candidates for an evolutionary link between star-forming, gas-rich galaxies and quiescent, gas-poor galaxies. However, their current morphologies are not well known. We present Hubble Space Telescope WFPC2 observations of the five bluest E+A galaxies (z ∼ 0.1) in the sample of Zabludoff and coworkers to study whether their detailed morphologies are consistent with late- to early-type evolution and to determine what drives that evolution. The morphologies of four galaxies are disturbed, indicating that a galaxy-galaxy merger is at least one mechanism that leads to the E+A phase. Two-dimensional image fitting shows that the E+As are generally bulge-dominated systems, even though at least two E+As may have underlying disks. In the fundamental plane, E+As stand apart from the E/S0 galaxies mainly because of their high effective surface brightness. Fading of the young stellar population and the corresponding increase in their effective radii will cause these galaxies to migrate toward the locus of E/S0 galaxies. E+As have profiles qualitatively like those of normal power-law early-type galaxies but have higher surface brightnesses. This result provides the first direct evidence supporting the hypothesis that power-law elliptical galaxies form via gas-rich mergers. In total, at least four E+As are morphologically consistent with early-type galaxies. We detect compact sources, possibly young star clusters, associated with the galaxies. These sources are much brighter (MR ∼ -13) than Galactic globular clusters, have luminosities consistent with the brightest clusters in nearby starburst galaxies, and have blue colors consistent with the ages estimated from the E+A galaxy spectra (several 108 yr). Further study of such young star cluster candidates might provide the elusive chronometer needed to break the age/burst-strength degeneracy for these postmerger galaxies.

Original languageEnglish (US)
Pages (from-to)258-273
Number of pages16
JournalAstrophysical Journal
Volume607
Issue number1 I
DOIs
StatePublished - May 20 2004

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galaxies
merger
power law
gas
young population
star clusters
brightness
gases
young
chronometers
starburst galaxies
elliptical galaxies
fading
loci
globular clusters
Hubble Space Telescope
bursts
luminosity
color
stars

Keywords

  • Galaxies: evolution
  • Galaxies: interactions
  • Galaxies: star clusters
  • Galaxies: starburst
  • Galaxies: stellar content

ASJC Scopus subject areas

  • Space and Planetary Science

Cite this

E+A galaxies and the formation of early-type galaxies at z ∼ 0. / Yang, Yujin; Zabludoff, Ann I; Zaritsky, Dennis F; Lauer, Tod R.; Mihos, J. Christopher.

In: Astrophysical Journal, Vol. 607, No. 1 I, 20.05.2004, p. 258-273.

Research output: Contribution to journalArticle

Yang, Yujin ; Zabludoff, Ann I ; Zaritsky, Dennis F ; Lauer, Tod R. ; Mihos, J. Christopher. / E+A galaxies and the formation of early-type galaxies at z ∼ 0. In: Astrophysical Journal. 2004 ; Vol. 607, No. 1 I. pp. 258-273.
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AB - E+A galaxies, whose spectra have deep Balmer absorption lines but no significant [O II] emission, are the best candidates for an evolutionary link between star-forming, gas-rich galaxies and quiescent, gas-poor galaxies. However, their current morphologies are not well known. We present Hubble Space Telescope WFPC2 observations of the five bluest E+A galaxies (z ∼ 0.1) in the sample of Zabludoff and coworkers to study whether their detailed morphologies are consistent with late- to early-type evolution and to determine what drives that evolution. The morphologies of four galaxies are disturbed, indicating that a galaxy-galaxy merger is at least one mechanism that leads to the E+A phase. Two-dimensional image fitting shows that the E+As are generally bulge-dominated systems, even though at least two E+As may have underlying disks. In the fundamental plane, E+As stand apart from the E/S0 galaxies mainly because of their high effective surface brightness. Fading of the young stellar population and the corresponding increase in their effective radii will cause these galaxies to migrate toward the locus of E/S0 galaxies. E+As have profiles qualitatively like those of normal power-law early-type galaxies but have higher surface brightnesses. This result provides the first direct evidence supporting the hypothesis that power-law elliptical galaxies form via gas-rich mergers. In total, at least four E+As are morphologically consistent with early-type galaxies. We detect compact sources, possibly young star clusters, associated with the galaxies. These sources are much brighter (MR ∼ -13) than Galactic globular clusters, have luminosities consistent with the brightest clusters in nearby starburst galaxies, and have blue colors consistent with the ages estimated from the E+A galaxy spectra (several 108 yr). Further study of such young star cluster candidates might provide the elusive chronometer needed to break the age/burst-strength degeneracy for these postmerger galaxies.

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KW - Galaxies: starburst

KW - Galaxies: stellar content

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