140 research outputs found
Chemical Composition of the Early Universe
A prediction of standard inflationary cosmology is that the elemental
composition of the medium out of which the earliest stars and galaxies
condensed consisted primarily of hydrogen and helium 4He with small admixtures
of deuterium, lithium 7Li, and 3He. The most red-shifted quasars, galaxies, and
Ly-alpha absorbers currently observed, however, all exhibit at least some
admixture of heavier elements, as do the most ancient stars in the Galaxy. Here
we examine ways in which the abundance of these same elements, if present
before the epoch of population III formation, might be observationally
established or ruled out.Comment: Accepted by the Astrophysical Journa
Models for High-Redshift Lyman Alpha Emitters
We present models for dusty high-redshift Lyman alpha emitting galaxies by
combining the Press-Schechter formalism with a treatment of inhomogeneous dust
distribution inside galaxies. These models reproduce the surface density of
emitters inferred from recent observations, and also agree with previous
non-detections. Although a detailed determination of the individual model
parameters is precluded by uncertainties, we find that (i) the dust content of
primordial galaxies builds up in no more than 5x10^8 years, (ii) the galactic
HII regions are inhomogeneous with a cloud covering factor of order unity, and
(iii) the overall star formation efficiency is at least 5 percent. Future
observations should be able to detect Lyman alpha galaxies upto redshifts of
about z=8. If the universe is reionized at z(reion)<8, the corresponding
decline in the number of Lyman alpha emitters at z>z(reion) could prove to be a
useful probe of the reionization epoch.Comment: 4 pages, poster contribution to Proc. of 9th Annual October
Astrophysics Conference in Maryland, "After the Dark Ages: When Galaxies Were
Young (the Universe at 2 < z < 5", College Park, October 199
The Polytropic Equation of State of Interstellar Gas Clouds
Models are presented for the polytropic equation of state of
self-gravitating, quiescent interstellar gas clouds. A detailed analysis,
including chemistry, thermal balance, and radiative transfer, is performed for
the physical state of the gas as a function of density, metallicity, velocity
field, and background radiation field. It is found that the stiffness of the
equation of state strongly depends on all these physical parameters, and the
adiabatic index varies between 0.2-1.4. The implications for star formation, in
particular at high redshift and in starburst galaxies, and the initial stellar
mass function are discussed.Comment: Accepted by Ap
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