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Departmental Colloquium


Galaxy Formation in the Redshift Desert: The Gemini Deep Deep Survey

Roberto Abraham
Department of Astronomy and Astrophysics, University of Toronto

Time
 
Wed. March 2, 2005     12:30 PM     Stirling A

Abstract
 
I will summarize some of the key results obtained from the Gemini Deep Deep Survey (GDDS). The GDDS is the deepest spectroscopic redshift survey ever undertaken. It preferentially targets galaxies in the redshift range 0.8 < z <2, spanning the predicted peak in the Universe's galaxy building activity. The primary goal of the GDDS is to make the first direct measurement of the evolving stellar mass function over 0.8 < z < 2. This observable is a key component in models for galaxy formation. We find that ~15% of the local stellar mass density is already in place by z = 1.8, rising to 40 - 50% by z = 1. Nearly half the stellar mass density at z = 1.8 is in massive `red-and-dead' galaxies. These numbers are inconsistent with existing hierarchical models, although the models are improving rapidly in order to incorporate our data. Almost all of the high-redshift red-and-dead galaxies in the GDDS exhibit early-type morphologies, although around 20% of these show tidal distortions consistent with recent (dry?) merger activity. A decomposition of the star-formation history of the Universe into the sum of individual histories for mass-segregated galaxy populations reveals strong evidence for the `down-sizing' paradigm (espoused by Cowie et al. 1997) in which the most massive galaxies form early in the history of the Universe and galaxy formation proceeds from larger to smaller mass scales.

All are welcome! Refreshments will be available after the talk.

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