7,023 research outputs found
Cosmic Dawn: Studies of the Earliest Galaxies and Their Role in Cosmic Reionization
I review recent progress and challenges in studies of the earliest galaxies,
seen when the Universe was less than 1 billion years old. Can they be used as
reliable tracers of the physics of cosmic reionization thereby complementing
other, more direct, probes of the evolving neutrality of the intergalactic
medium? Were star-forming galaxies the primary agent in the reionization
process and what are the future prospects for identifying the earliest systems
devoid of chemical enrichment? Ambitious future facilities are under
construction for exploring galaxies and the intergalactic medium in the
redshift range 6 to 20, corresponding to what we now consider the heart of the
reionization era. I review what we can infer about this period from current
observations and in the near-future with existing facilities, and conclude with
a list of key issues where future work is required.Comment: Proceedings of the 26th Solvay Conference on Physics: "Astrophysics
and Cosmology", R. Blandford and A. Sevrin, eds., World Scientifi
Faint Blue Galaxies
The physical properties of the faint blue galaxy population are reviewed in
the context of observational progress made via deep spectroscopic surveys and
Hubble Space Telescope imaging of field galaxies at various limits, and
theoretical models for the integrated star formation history of the Universe.
Notwithstanding uncertainties in the properties of the local population of
galaxies, convincing evidence has emerged from several independent studies for
a rapid decline in the volume-averaged star formation rate of field galaxies
since a redshift z~1. Together with the small angular sizes and modest mean
redshift of the faintest detectable sources, these results can be understood in
hierarchical models where the bulk of the star formation occurred at redshifts
between z~1-2. The physical processes responsible for the subsequent demise of
the faint blue galaxy population remains unclear. Considerable progress will be
possible when the evolutionary trends can be monitored in the context of
independent physical parameters such as the underlying galactic mass.Comment: 42 pages with 10 embedded figures available in gzipped postscript
from ftp://ftp.ast.cam.ac.uk/pub/rse/annrev97.ps.gz To appear in Annual
Reviews Astron. Astrophys. Vol 35, (1997
New Frontiers in Cosmology and Galaxy Formation: Challenges for the Future
(Abridged) Cosmology faces three distinct challenges in the next decade. (1)
The dark sector, both dark matter and dark energy, dominates the Universe. Key
questions include determining the nature of both. Improved observational probes
are crucial. (2) Galaxy formation was initiated at around the epoch of
reionization: we need to understand how and when as well as to develop probes
of earlier epochs. (3) Our simple dark matter-driven picture of galaxy assembly
is seemingly at odds with several observational results, including the presence
of ULIRGS at high z, the `downsizing' signature, chemical signatures of
alpha-element ratios and suggestions that merging may not be important in
defining the Hubble sequence. Understanding the physical implications is a
major challenge for theorists and refiniing the observational uncertainties a
major goal for observers.Comment: To appear in "Structure Formation in the Universe", ed. Chabrier, G.,
Cambridge University Press. High resolution version on
http://www.astro.caltech.edu/~rse/chamonix.pd
- …