A Lower Bound on the Cosmic Baryon Density

Astronomy and Astrophysics – Astrophysics

Scientific paper

Rate now

  [ 0.00 ] – not rated yet Voters 0   Comments 0

Details

AASlatex, 15 pages w/ 1 embedded ps figure. Submitted to ApJ

Scientific paper

10.1086/304893

We derive analytic lower bounds on the cosmic baryon density by requiring that the high-redshift IGM contain enough neutral hydrogen to produce the observed \lya absorption in quasar spectra. The key theoretical assumption is that absorbing structures are no more extended in redshift space than in real space. This assumption might not hold if \lya clouds are highly overdense and thermally broadened, but it is likely to hold in the gravitational instability picture for the \lya forest suggested by cosmological simulations, independently of the details of the cosmological model. The other ingredients in these bounds are an estimate of the UV background from quasars, a temperature $T~10^4K$ for the "warm" photoionized IGM that produces most of the \lya absorption, a value of the Hubble constant, and observational estimates of the mean \lya flux decrement $\Dbar$ or, for a more restrictive bound, the distribution function $P(\tau)$ of \lya optical depths. With plausible parameter values, the mean decrement bound implies a baryon density parameter $\Omb \ga 0.0125/h^2$. With conservative values, the bound weakens to $\Omb \ga 0.005/h^2$, but the required clustering of the IGM is then incompatible with other properties of quasar spectra. A recent observational determination of $P(\tau)$ implies $\Omb \ga 0.0125/h^2$ even for a conservative estimate of the UV background, and $\Omb \ga 0.018/h^2$ for a more reasonable estimate. These bounds are consistent with recent low estimates of the primordial deuterium-to-hydrogen ratio $\dtoh$, which imply $\Omb \approx 0.025/h^2$, but the $P(\tau)$ bound can only be reconciled with high $\dtoh$ estimates by abandoning standard big bang nucleosynthesis or the gravitational instability picture for the origin of the \lya forest. (Shortened abstract.)

No associations

LandOfFree

Say what you really think

Search LandOfFree.com for scientists and scientific papers. Rate them and share your experience with other people.

Rating

A Lower Bound on the Cosmic Baryon Density does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with A Lower Bound on the Cosmic Baryon Density, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and A Lower Bound on the Cosmic Baryon Density will most certainly appreciate the feedback.

Rate now

     

Profile ID: LFWR-SCP-O-306803

  Search
All data on this website is collected from public sources. Our data reflects the most accurate information available at the time of publication.