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2006MNRAS.370...74R - Mon. Not. R. Astron. Soc., 370, 74-90 (2006/July-3)
Deep GMOS spectroscopy of extremely red galaxies in GOODS-South: ellipticals, mergers and red spirals at 1 < z < 2.
ROCHE N.D., DUNLOP J., CAPUTI K.I., McLURE R., WILLOTT C.J. and CRAMPTON D.
Abstract (from CDS):
We examine the morphologies of these ERGs on Hubble Space Telescope Advanced Camera for Surveys (HST-ACS) images and fit radii and Sersic indices. We find three broad classes: (i) spheroidals; (ii) mergers at a variety of stages (some are spheroidal-disc pairs, some have tidal tails), often with a high surface brightness and (iii) red spirals (which may have star forming regions in their outer discs).
We perform an age-dating analysis by fitting the spectra and nine-band photometry (BVIZJHK, plus 3.6/4.5-µm fluxes from Spitzer) of the ERGs with two-component models, consisting of passively evolving, old stellar populations combined with a younger, continuously star forming component, for which the age and dust extinction are allowed to vary from 10 to 800Myr and E(B - V) = 0.0 to 0.5mag. For only one ERG is the best-fitting model purely passive, for the others the best fit is obtained by including a star forming component, which typically forms a few (0.26-13.5) per cent of the stellar mass, and is subject to dust reddening averaging E(B - V) ≃ 0.35. The ages of the star forming components tend to be youngest (10-40Myr) in the merging ERGs, and older (200-800Myr) in spiral ERGs, with mixed ages for the spheroidals.
The best-fitting mean ages for the old stellar populations range from 0.6 to 4.5Gyr, averaging 2.1Gyr, with masses from 3x1010 to 2x1011M☉. The mean stellar formation redshifts of ERGs are spread from ∼0.5Gyr before the epoch of observation out to z ∼ 5. We propose that most ERGs are galaxies, or mergers of galaxies, formed some Gyr earlier, in an early (z ∼ 5) phase of massive galaxy formation, which since then have experienced a wide variety of merger and star formation (SF) histories, accounting for the wide range of observed stellar ages.
Finally, we examine the clustering of the ERGs on this field, as a function of the photometric redshifts estimated by Caputi et al. The comoving correlation radius is r0≃ 13h–1Mpc for the full sample and, dividing by redshift, is constant or increasing with redshift, thus favouring comoving (ε = -1.2) evolution over a stable (ε = 0) clustering model.
Abstract Copyright: 2006 The Authors. Journal compilation © 2006 RAS
Journal keyword(s): galaxies: distances and redshifts - galaxies: evolution - galaxies: high-redshift
Simbad objects: 7
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