Probing the evolution of early-type galaxies using multicolour number counts and redshift distributions

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By this: publisher
In this Subject: Astronomy
By this author: Nakata F. ;&nbsp; Shimasaku K. ;&nbsp; Doi M. ;&nbsp; Kashikawa N. ;&nbsp; Kawasaki W. ;&nbsp; Komiyama Y. ;&nbsp; Okamura S. ;&nbsp; Sekiguchi M. ;&nbsp; Yagi M. ;&nbsp; Yasuda N.

Authors: Nakata F.; Shimasaku K.; Doi M.; Kashikawa N.; Kawasaki W.; Komiyama Y.; Okamura S.; Sekiguchi M.; Yagi M.; Yasuda N.

Source: Monthly Notices of the Royal Astronomical Society, Volume 309, Number 4, November 1999 , pp. L25-L29(5)

Publisher: Wiley-Blackwell

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Abstract:

We investigate pure luminosity evolution models for early-type (elliptical and S0) galaxies (i.e. no number density change or morphological transition), and examine whether these models are consistent with observed number counts in the B, I and K bands, and redshift distributions of two samples of faint galaxies selected in the I and K bands. The models are characterized by the star formation time-scale _SF and the time t_gw when the galactic wind starts to blow, in addition to several other conventional parameters. We find that the single-burst model (_SF=0.1 Gyr and t_gw=0.353 Gyr), which is known to reproduce the photometric properties of early-type galaxies in clusters, is inconsistent with the redshift distributions of early-type galaxies in the field environment, owing to overpredictions of the number of galaxies at z gsim 1.4 even with strong extinction which is at work until t_gw. In order for dust extinction to be more effective, we treat _SF and t_gw as free parameters, and find that models with _SF gsim 0.5 Gyr and t_gw>1.0 Gyr can be made consistent with both the observed redshift distributions and the number counts, if we introduce strong extinction [E(B-V)1 as a peak value]. These results suggest that early-type galaxies in the field environment do not have the same evolutionary history as described by the single-burst model.