ar X iv : a st ro - p h / 98 05 26 2 v 1 2 0 M ay 1 99 8 Does the Number Density of Elliptical Galaxies Change at z < 1 ?
نویسندگان
چکیده
We have performed a detailed V/Vmax test for a sample of the Canada-France Redshift Survey (CFRS) for the purpose of examining whether the comoving number density of field galaxies changes significantly at redshifts of z < 1. Taking into account the luminosity evolution of galaxies which depends on their morphological type through different history of star formation, we obtain 〈V/Vmax〉 ≈ 0.5 in the range of 0.3 < z < 0.8, where reliable redshifts were secured by spectroscopy of either absorption or emission lines for the CFRS sample. This indicates that a picture of mild evolution of field galaxies without significant mergers is consistent with the CFRS data. Early-type galaxies, selected by their (V − I)AB color, become unnaturally deficient in number at z > 0.8 due to the selection bias, thereby causing a fictitious decrease of 〈V/Vmax〉 . We therefore conclude that a reasonable choice of upper bound of redshift z ∼ 0.8 in the V/Vmax test saves the picture of passive evolution for field ellipticals in the CFRS sample, which was rejected by Kauffman, Charlot, & White (1996) without confining the redshift range. However, about 10% of the CFRS sample consists of galaxies having colors much bluer than predicted for irregular galaxies, and their 〈V/Vmax〉 is significantly larger than 0.5. We discuss this population of extremely blue galaxies in terms of starburst that has just turned on at their observed redshifts. Subject headings: galaxies: elliptical and lenticular, cD — galaxies: evolution — galaxies: formation
منابع مشابه
ar X iv : a st ro - p h / 98 05 10 0 v 1 8 M ay 1 99 8 Dwarfmology
We address two important cosmological questions relating to dwarf galaxies: (1) What is their contribution to the field galaxy baryon budget; and (2) what is their contribution to the faint blue galaxy problem. Both of these are addressed empirically from a complete photometric redshift catalogue[1][2] derived from the Hubble Deep Field[3]. The answer to the first question is: very little (< 1%...
متن کاملar X iv : a st ro - p h / 93 05 00 2 v 1 6 M ay 1 99 3 Visibility of Gravitational Lenses and the Cosmological Constant Problem
Recent observations suggest appreciable star formation activity in early-type galaxies down to redshift z ∼ 0.5. If so, there is likely to be dust in these galaxies. We consider the possibility that obscuration by dust can reconcile the observed frequency of gravitational lensing of quasar images with the considerably larger rate predicted in a low density cosmologically flat universe dominated...
متن کاملar X iv : a st ro - p h / 98 05 16 7 v 1 1 3 M ay 1 99 8 Issues for the Next Generation of Galaxy Surveys
I argue that the weight of the available evidence favours the conclusions that galaxies are unbiased tracers of mass, the mean mass density (excluding a cosmological constant or its equivalent) is less than the critical Einstein-de Sitter value, and an isocurvature model for structure formation offers a viable and arguably attractive model for the early assembly of galaxies. If valid these conc...
متن کاملar X iv : a st ro - p h / 98 05 07 7 v 1 6 M ay 1 99 8 Long - Term X - ray Variability in GX 354 – 0
We report for the first time the detection of long-term X-ray variability in the bright bulge source GX 354–0 (=4U 1728–34) observed with the All Sky Monitor (ASM) on board the Rossi X-Ray Timing Explorer (RXTE). The 2-year RXTE ASM database reveals significant power at ∼ 72 days. Similar behaviour was seen in the 6-year Ariel 5 ASM database, but at a period of ∼ 63 days. The timescales and lig...
متن کامل