Browsing by Author "Hewett, PC"

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    Luminous early-type field galaxies at z ∼ 0.4 -: I.: Observations and redshift catalogue of 581 galaxies
    (2001) Willis, JP; Hewett, PC; Warren, SJ
    We have compiled a sample of similar to 9600 bright, i less than or equal to 18.95, red, b(J) - r > 2, candidate galaxies in an area of 220 deg(2). These are luminous, L > L*, field early-type galaxies with redshifts 0.3 less than or similar to z less than or similar to 0.6. We present a redshift catalogue of a subsample of 581 targets. The galaxies were selected according to their broad-band b(J)ri colours from United Kingdom Schmidt Telescope plates, and have a surface density on the sky of only similar to 50 deg(-2). Such luminous field galaxies are virtually absent from published redshift surveys and the catalogue provides a large sample of the most luminous normal galaxies, at cosmological distances. The statistical properties of the galaxy spectra, including absorption-line and emission-line measures, are presented and a composite spectrum constructed. The nature of the sample, combined with the relatively bright apparent magnitudes, makes the galaxies suitable targets for several key investigations in galaxy evolution and cosmology.
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    Luminous early-type field galaxies at z∼0.4 -: II.: Star formation history and space density
    (2002) Willis, JP; Hewett, PC; Warren, SJ; Lewis, GF
    We present a combined photometric and spectroscopic analysis of the star formation history and space density of a sample of 485 luminous, M-V - 5 log h < -20.5, field early-type galaxies at redshifts 0.3 ≲ z ≲ 0.6. The observed b(J)ori colours as a function of redshift, mean absorption-line strengths and [O II] λ3727 emission properties are used to constrain the star formation history of the galaxies. The mean star formation history of the early-type galaxy sample is consistent with an old (z(f) > 1), passively evolving luminosity-weighted stellar population. 21 per cent of the sample possess detectable [O II] lambda3727 emission consistent with a low level (less than or similar to1 M-circle dot yr(-1)) of on-going star formation. Parametric and non-parametric estimates of the space density of the sample are derived. The integrated luminosity density at z similar or equal to 0.4, allowing only for passive luminosity evolution, is in excellent agreement with the local, ((z) = 0.1), luminosity density of early-type galaxies. Overall, the sample properties are consistent with a galaxy formation scenario in which the majority of luminous field early-type galaxies formed at redshifts z > 1 and have largely evolved passively since the formation epoch.