The effects of gas on morphological transformation in mergers: Implications for bulge and disc demographics

Philip F. Hopkins, Rachel Somerville, Thomas J. Cox, Lars Hernquist, Shardha Jogee, Dusan Kereš, Chung Pei Ma, Brant Robertson, Kyle Stewart

Research output: Contribution to journalArticle

132 Citations (Scopus)

Abstract

Transformation of discs into spheroids via mergers is a well-accepted element of galaxy formation models. However, recent simulations have shown that the bulge formation is suppressed in increasingly gas-rich mergers. We investigate the global implications of these results in a cosmological framework, using independent approaches: empirical halo-occupation models (where galaxies are populated in haloes according to observations) and semi-analytic models. In both, ignoring the effects of gas in mergers leads to the overproduction of spheroids: low- and intermediate-mass galaxies are predicted to be bulge-dominated (B/T ∼ 0.5 at <10 10 M , with almost no 'bulgeless' systems), even if they have avoided major mergers. Including the different physical behaviour of gas in mergers immediately leads to a dramatic change: bulge formation is suppressed in low-mass galaxies, observed to be gas-rich (giving B/T ∼ 0.1 at <10 10 M , with a number of bulgeless galaxies in good agreement with observations). Simulations and analytic models which neglect the similarity-breaking behaviour of gas have difficulty reproducing the strong observed morphology-mass relation. However, the observed dependence of gas fractions on mass, combined with suppression of bulge formation in gas-rich mergers, naturally leads to the observed trends. Discrepancies between observations and models that ignore the role of gas increase with redshift; in models that treat gas properly, galaxies are predicted to be less bulge-dominated at high redshifts, in agreement with the observations. We discuss implications for the global bulge mass density and future observational tests.

Original languageEnglish (US)
Pages (from-to)802-814
Number of pages13
JournalMonthly Notices of the Royal Astronomical Society
Volume397
Issue number2
DOIs
StatePublished - Aug 1 2009

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merger
gases
gas
galaxies
spheroids
halos
effect
galactic evolution
occupation
simulation
retarding
trends

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Keywords

  • Cosmology: theory
  • Galaxies: active
  • Galaxies: evolution
  • Galaxies: formation
  • Galaxies: spiral

Cite this

Hopkins, Philip F. ; Somerville, Rachel ; Cox, Thomas J. ; Hernquist, Lars ; Jogee, Shardha ; Kereš, Dusan ; Ma, Chung Pei ; Robertson, Brant ; Stewart, Kyle. / The effects of gas on morphological transformation in mergers : Implications for bulge and disc demographics. In: Monthly Notices of the Royal Astronomical Society. 2009 ; Vol. 397, No. 2. pp. 802-814.
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abstract = "Transformation of discs into spheroids via mergers is a well-accepted element of galaxy formation models. However, recent simulations have shown that the bulge formation is suppressed in increasingly gas-rich mergers. We investigate the global implications of these results in a cosmological framework, using independent approaches: empirical halo-occupation models (where galaxies are populated in haloes according to observations) and semi-analytic models. In both, ignoring the effects of gas in mergers leads to the overproduction of spheroids: low- and intermediate-mass galaxies are predicted to be bulge-dominated (B/T ∼ 0.5 at <10 10 M ⊙, with almost no 'bulgeless' systems), even if they have avoided major mergers. Including the different physical behaviour of gas in mergers immediately leads to a dramatic change: bulge formation is suppressed in low-mass galaxies, observed to be gas-rich (giving B/T ∼ 0.1 at <10 10 M ⊙, with a number of bulgeless galaxies in good agreement with observations). Simulations and analytic models which neglect the similarity-breaking behaviour of gas have difficulty reproducing the strong observed morphology-mass relation. However, the observed dependence of gas fractions on mass, combined with suppression of bulge formation in gas-rich mergers, naturally leads to the observed trends. Discrepancies between observations and models that ignore the role of gas increase with redshift; in models that treat gas properly, galaxies are predicted to be less bulge-dominated at high redshifts, in agreement with the observations. We discuss implications for the global bulge mass density and future observational tests.",
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The effects of gas on morphological transformation in mergers : Implications for bulge and disc demographics. / Hopkins, Philip F.; Somerville, Rachel; Cox, Thomas J.; Hernquist, Lars; Jogee, Shardha; Kereš, Dusan; Ma, Chung Pei; Robertson, Brant; Stewart, Kyle.

In: Monthly Notices of the Royal Astronomical Society, Vol. 397, No. 2, 01.08.2009, p. 802-814.

Research output: Contribution to journalArticle

TY - JOUR

T1 - The effects of gas on morphological transformation in mergers

T2 - Implications for bulge and disc demographics

AU - Hopkins, Philip F.

AU - Somerville, Rachel

AU - Cox, Thomas J.

AU - Hernquist, Lars

AU - Jogee, Shardha

AU - Kereš, Dusan

AU - Ma, Chung Pei

AU - Robertson, Brant

AU - Stewart, Kyle

PY - 2009/8/1

Y1 - 2009/8/1

N2 - Transformation of discs into spheroids via mergers is a well-accepted element of galaxy formation models. However, recent simulations have shown that the bulge formation is suppressed in increasingly gas-rich mergers. We investigate the global implications of these results in a cosmological framework, using independent approaches: empirical halo-occupation models (where galaxies are populated in haloes according to observations) and semi-analytic models. In both, ignoring the effects of gas in mergers leads to the overproduction of spheroids: low- and intermediate-mass galaxies are predicted to be bulge-dominated (B/T ∼ 0.5 at <10 10 M ⊙, with almost no 'bulgeless' systems), even if they have avoided major mergers. Including the different physical behaviour of gas in mergers immediately leads to a dramatic change: bulge formation is suppressed in low-mass galaxies, observed to be gas-rich (giving B/T ∼ 0.1 at <10 10 M ⊙, with a number of bulgeless galaxies in good agreement with observations). Simulations and analytic models which neglect the similarity-breaking behaviour of gas have difficulty reproducing the strong observed morphology-mass relation. However, the observed dependence of gas fractions on mass, combined with suppression of bulge formation in gas-rich mergers, naturally leads to the observed trends. Discrepancies between observations and models that ignore the role of gas increase with redshift; in models that treat gas properly, galaxies are predicted to be less bulge-dominated at high redshifts, in agreement with the observations. We discuss implications for the global bulge mass density and future observational tests.

AB - Transformation of discs into spheroids via mergers is a well-accepted element of galaxy formation models. However, recent simulations have shown that the bulge formation is suppressed in increasingly gas-rich mergers. We investigate the global implications of these results in a cosmological framework, using independent approaches: empirical halo-occupation models (where galaxies are populated in haloes according to observations) and semi-analytic models. In both, ignoring the effects of gas in mergers leads to the overproduction of spheroids: low- and intermediate-mass galaxies are predicted to be bulge-dominated (B/T ∼ 0.5 at <10 10 M ⊙, with almost no 'bulgeless' systems), even if they have avoided major mergers. Including the different physical behaviour of gas in mergers immediately leads to a dramatic change: bulge formation is suppressed in low-mass galaxies, observed to be gas-rich (giving B/T ∼ 0.1 at <10 10 M ⊙, with a number of bulgeless galaxies in good agreement with observations). Simulations and analytic models which neglect the similarity-breaking behaviour of gas have difficulty reproducing the strong observed morphology-mass relation. However, the observed dependence of gas fractions on mass, combined with suppression of bulge formation in gas-rich mergers, naturally leads to the observed trends. Discrepancies between observations and models that ignore the role of gas increase with redshift; in models that treat gas properly, galaxies are predicted to be less bulge-dominated at high redshifts, in agreement with the observations. We discuss implications for the global bulge mass density and future observational tests.

KW - Cosmology: theory

KW - Galaxies: active

KW - Galaxies: evolution

KW - Galaxies: formation

KW - Galaxies: spiral

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