The Millennium Galaxy Catalogue: morphological classification and bimodality in the colour-concentration plane

S. P. Driver, P. D. Allen, Allster W. Graham, E. Cameron, J. Liske, S. C. Ellis, N. J.G. Cross, R. De Propris, S. Phillipps, W. J. Couch

Research output: Contribution to journalReview articleResearchpeer-review

Abstract

Using 10095 galaxies (B < 20 mag) from the Millennium Galaxy Catalogue, we derive B-band luminosity distributions and selected bivariate brightness distributions for the galaxy population subdivided by eyeball morphology; Sérsic index (n); two-degree Field Galaxy Red-shift Survey (2dFGRS) η parameter; rest-(u - r) colour (global and core); MGC continuum shape; half-light radius; (extrapolated) central surface brightness; and inferred stellar mass-to-light ratio. All subdivisions extract highly correlated subsets of the galaxy population which consistently point towards two overlapping distributions: an old, red, inert, predominantly luminous, high central-surface brightness subset; and a young, blue, star forming, intermediate surface brightness subset. A clear bimodality in the observed distribution is seen in both the rest-(u - r) colour and log (n) distributions. Whilst the former bimodality was well established from Sloan Digital Sky Survey data, we show here that the rest-(u - r) colour bimodality becomes more pronounced when using the core colour as opposed to global colour. The two populations are extremely well separated in the colour-log(n) plane. Using our sample of 3314 (B < 19 mag) eyeball classified galaxies, we show that the bulge-dominated, early-type galaxies populate one peak and the bulge-less, late-type galaxies occupy the second. The early- and mid-type spirals sprawl across and between the peaks. This constitutes extremely strong evidence that the fundamental way to divide the luminous galaxy population (M BMGC-5 log h < -16 mag, i.e. dwarfs not included) is into bulges (old red, inert, high concentration) and discs (young, blue, star forming, low concentration) and that the galaxy bimodality reflects the two-component nature of galaxies and not two distinct galaxy classes. We argue that these two components require two independent formation mechanisms/processes and advocate early bulge formation through initial collapse and ongoing disc formation through splashback, infall and merging/accretion. We calculate the B-band luminosity densities and stellar mass densities within each subdivision and estimate that the z ≈ 0 stellar mass content in spheroids, bulges and discs is 35 ± 2,18 ± 7 and 47 ± 7 per cent, respectively.

LanguageEnglish
Pages414-434
Number of pages21
JournalMonthly Notices of the Royal Astronomical Society
Volume368
Issue number1
DOIs
Publication statusPublished - 1 May 2006
Externally publishedYes

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catalogs
galaxies
color
stellar mass
set theory
blue stars
brightness
subdivisions
formation mechanism
accretion
luminosity
distribution
brightness distribution
mass to light ratios
spheroids
red shift
low concentrations
continuums
radii
young

Cite this

Driver, S. P. ; Allen, P. D. ; Graham, Allster W. ; Cameron, E. ; Liske, J. ; Ellis, S. C. ; Cross, N. J.G. ; De Propris, R. ; Phillipps, S. ; Couch, W. J. / The Millennium Galaxy Catalogue : morphological classification and bimodality in the colour-concentration plane. In: Monthly Notices of the Royal Astronomical Society. 2006 ; Vol. 368, No. 1. pp. 414-434.
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abstract = "Using 10095 galaxies (B < 20 mag) from the Millennium Galaxy Catalogue, we derive B-band luminosity distributions and selected bivariate brightness distributions for the galaxy population subdivided by eyeball morphology; S{\'e}rsic index (n); two-degree Field Galaxy Red-shift Survey (2dFGRS) η parameter; rest-(u - r) colour (global and core); MGC continuum shape; half-light radius; (extrapolated) central surface brightness; and inferred stellar mass-to-light ratio. All subdivisions extract highly correlated subsets of the galaxy population which consistently point towards two overlapping distributions: an old, red, inert, predominantly luminous, high central-surface brightness subset; and a young, blue, star forming, intermediate surface brightness subset. A clear bimodality in the observed distribution is seen in both the rest-(u - r) colour and log (n) distributions. Whilst the former bimodality was well established from Sloan Digital Sky Survey data, we show here that the rest-(u - r) colour bimodality becomes more pronounced when using the core colour as opposed to global colour. The two populations are extremely well separated in the colour-log(n) plane. Using our sample of 3314 (B < 19 mag) eyeball classified galaxies, we show that the bulge-dominated, early-type galaxies populate one peak and the bulge-less, late-type galaxies occupy the second. The early- and mid-type spirals sprawl across and between the peaks. This constitutes extremely strong evidence that the fundamental way to divide the luminous galaxy population (M BMGC-5 log h < -16 mag, i.e. dwarfs not included) is into bulges (old red, inert, high concentration) and discs (young, blue, star forming, low concentration) and that the galaxy bimodality reflects the two-component nature of galaxies and not two distinct galaxy classes. We argue that these two components require two independent formation mechanisms/processes and advocate early bulge formation through initial collapse and ongoing disc formation through splashback, infall and merging/accretion. We calculate the B-band luminosity densities and stellar mass densities within each subdivision and estimate that the z ≈ 0 stellar mass content in spheroids, bulges and discs is 35 ± 2,18 ± 7 and 47 ± 7 per cent, respectively.",
keywords = "Galaxies: fundamental parameters, Galaxies: luminosity function, mass function, Galaxies: statistics, Surveys",
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Driver, SP, Allen, PD, Graham, AW, Cameron, E, Liske, J, Ellis, SC, Cross, NJG, De Propris, R, Phillipps, S & Couch, WJ 2006, 'The Millennium Galaxy Catalogue: morphological classification and bimodality in the colour-concentration plane' Monthly Notices of the Royal Astronomical Society, vol. 368, no. 1, pp. 414-434. https://doi.org/10.1111/j.1365-2966.2006.10126.x

The Millennium Galaxy Catalogue : morphological classification and bimodality in the colour-concentration plane. / Driver, S. P.; Allen, P. D.; Graham, Allster W.; Cameron, E.; Liske, J.; Ellis, S. C.; Cross, N. J.G.; De Propris, R.; Phillipps, S.; Couch, W. J.

In: Monthly Notices of the Royal Astronomical Society, Vol. 368, No. 1, 01.05.2006, p. 414-434.

Research output: Contribution to journalReview articleResearchpeer-review

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T2 - Monthly Notices of the Royal Astronomical Society

AU - Driver,S. P.

AU - Allen,P. D.

AU - Graham,Allster W.

AU - Cameron,E.

AU - Liske,J.

AU - Ellis,S. C.

AU - Cross,N. J.G.

AU - De Propris,R.

AU - Phillipps,S.

AU - Couch,W. J.

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N2 - Using 10095 galaxies (B < 20 mag) from the Millennium Galaxy Catalogue, we derive B-band luminosity distributions and selected bivariate brightness distributions for the galaxy population subdivided by eyeball morphology; Sérsic index (n); two-degree Field Galaxy Red-shift Survey (2dFGRS) η parameter; rest-(u - r) colour (global and core); MGC continuum shape; half-light radius; (extrapolated) central surface brightness; and inferred stellar mass-to-light ratio. All subdivisions extract highly correlated subsets of the galaxy population which consistently point towards two overlapping distributions: an old, red, inert, predominantly luminous, high central-surface brightness subset; and a young, blue, star forming, intermediate surface brightness subset. A clear bimodality in the observed distribution is seen in both the rest-(u - r) colour and log (n) distributions. Whilst the former bimodality was well established from Sloan Digital Sky Survey data, we show here that the rest-(u - r) colour bimodality becomes more pronounced when using the core colour as opposed to global colour. The two populations are extremely well separated in the colour-log(n) plane. Using our sample of 3314 (B < 19 mag) eyeball classified galaxies, we show that the bulge-dominated, early-type galaxies populate one peak and the bulge-less, late-type galaxies occupy the second. The early- and mid-type spirals sprawl across and between the peaks. This constitutes extremely strong evidence that the fundamental way to divide the luminous galaxy population (M BMGC-5 log h < -16 mag, i.e. dwarfs not included) is into bulges (old red, inert, high concentration) and discs (young, blue, star forming, low concentration) and that the galaxy bimodality reflects the two-component nature of galaxies and not two distinct galaxy classes. We argue that these two components require two independent formation mechanisms/processes and advocate early bulge formation through initial collapse and ongoing disc formation through splashback, infall and merging/accretion. We calculate the B-band luminosity densities and stellar mass densities within each subdivision and estimate that the z ≈ 0 stellar mass content in spheroids, bulges and discs is 35 ± 2,18 ± 7 and 47 ± 7 per cent, respectively.

AB - Using 10095 galaxies (B < 20 mag) from the Millennium Galaxy Catalogue, we derive B-band luminosity distributions and selected bivariate brightness distributions for the galaxy population subdivided by eyeball morphology; Sérsic index (n); two-degree Field Galaxy Red-shift Survey (2dFGRS) η parameter; rest-(u - r) colour (global and core); MGC continuum shape; half-light radius; (extrapolated) central surface brightness; and inferred stellar mass-to-light ratio. All subdivisions extract highly correlated subsets of the galaxy population which consistently point towards two overlapping distributions: an old, red, inert, predominantly luminous, high central-surface brightness subset; and a young, blue, star forming, intermediate surface brightness subset. A clear bimodality in the observed distribution is seen in both the rest-(u - r) colour and log (n) distributions. Whilst the former bimodality was well established from Sloan Digital Sky Survey data, we show here that the rest-(u - r) colour bimodality becomes more pronounced when using the core colour as opposed to global colour. The two populations are extremely well separated in the colour-log(n) plane. Using our sample of 3314 (B < 19 mag) eyeball classified galaxies, we show that the bulge-dominated, early-type galaxies populate one peak and the bulge-less, late-type galaxies occupy the second. The early- and mid-type spirals sprawl across and between the peaks. This constitutes extremely strong evidence that the fundamental way to divide the luminous galaxy population (M BMGC-5 log h < -16 mag, i.e. dwarfs not included) is into bulges (old red, inert, high concentration) and discs (young, blue, star forming, low concentration) and that the galaxy bimodality reflects the two-component nature of galaxies and not two distinct galaxy classes. We argue that these two components require two independent formation mechanisms/processes and advocate early bulge formation through initial collapse and ongoing disc formation through splashback, infall and merging/accretion. We calculate the B-band luminosity densities and stellar mass densities within each subdivision and estimate that the z ≈ 0 stellar mass content in spheroids, bulges and discs is 35 ± 2,18 ± 7 and 47 ± 7 per cent, respectively.

KW - Galaxies: fundamental parameters

KW - Galaxies: luminosity function, mass function

KW - Galaxies: statistics

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