When do early-type galaxies form?

Abstract

We have used the Hubble Space Telescope's Advanced Camera for Surveys to measure the mass density function of morphologically selected early-type galaxies in the Gemini Deep Deep Survey fields, over the redshift range 0.9 < z < 1.6. Our imaging data set covers four well-separated sight-lines, and is roughly intermediate (in terms of both depth and area) between the GOODS/GEMS imaging data, and the images obtained in the Hubble Deep Field campaigns. Our images contain 144 galaxies with ultra-deep spectroscopy, and they have been analyzed using a new purpose-written morphological analysis code which improves the reliability of morphological classifications by adopting a 'quasi-petrosian' image thresholding technique. We find that at z = 1 approximately 70% of the stars in massive galaxies reside in early-type systems. This fraction is remarkably similar to that seen in the local Universe. However, we detect very rapid evolution in this fraction over the range 1.0 < z < 1.6, suggesting that in this epoch the strong color-morphology relationship seen in the nearby Universe is beginning to fall into place.

4 pages, 2 figures, Invited talk at IAU Symposium 235, Prague, August 2006

References in corpus (10)

• Lyman Break Galaxies at z>4 and the Evolution of the UV Luminosity Density at High Redshift
• Nearly 5000 Distant Early-Type Galaxies in COMBO-17: a Red Sequence and its Evolution since z~1
• A New Non-Parametric Approach to Galaxy Morphological Classification
• The Luminosity Function of Galaxies in SDSS Commissioning Data
• A New Approach to Galaxy Morphology: I. Analysis of the Sloan Digital Sky Survey Early Data Release
• Old Galaxies in the Young Universe
• The Gemini Deep Deep Survey: III. The abundance of massive galaxies 3-6 billion years after the Big Bang
• The Gemini Deep Deep Survey: I. Introduction to the Survey, Catalogs and Composite Spectra
• Evolved Galaxies at z > 1.5 from the Gemini Deep Deep Survey: The Formation Epoch of Massive Stellar Systems
• Measurement of Star-Formation Rate from H-alpha in field galaxies at z=1