Mathematics – Logic
Scientific paper
Jan 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994phdt........10r&link_type=abstract
PhD Dissertation, Pittsburgh Univ. Pittsburgh, PA United States
Mathematics
Logic
9
Galactic Evolution, Electromagnetic Absorption, Lyman Alpha Radiation, Spiral Galaxies, Cosmic Gases, Density Distribution, Gas Density, Hubble Constant, Statistical Distributions, Time Dependence, Hydrogen, Neutral Gases, Red Shift
Scientific paper
The evolution of the neutral hydrogen content of galaxies as a function of time is an important constraint on processes in galactic evolution. A comprehensive, statistical description of the Hl content and distribution within galaxies at the present epoch is presented and the statistics are compared with the properties of Hl associated with high redshift 'damped Lyman alpha' absorption systems observed in the spectra of QSOs. It is found that spiral galaxies contain 92% of the Hl mass density at the current epoch. The cosmological mass density of H I is estimated to be OmegaHI(z = 0) = (2.4 +/- 0.6) x 10-4/h75, where h75 is the Hubble constant in units of 75 km /s/Mpc. Spirals are also found to offer the largest cross-section to line-of-sight absorption of light from QSOs. A complete sample of 27 large-diameter spirals is used to estimate the number density of absorbers per unit redshift at the present epoch n(z = 0), and the column density distribution of absorbers, f(N). n(z = 0) is found to be 0.015 +/- 0.004, a factor of about 17 smaller than n(z approximately equal to 2.5). f(N) is also shown to have significantly evolved over this redshift interval. The incidence of damped Ly-alpha absorbers in the redshift interval 0 less than z less than 1.65 is investigated with a new method that uses the statistical properties of the well-studied Mg II absorption systems. It is found that nDLy-alpha (z = 0.81) less than or equal to 0.06, which is consistent with the trend at higher z as well as with the number density at the current epoch. The data at z greater than 1.65 combined with the constraint at z = 0 result in nDLy-alpha(z) (0.015 +/- 0.004)(1 + z)2.27 +/- 0.25 for 0 less than z less than 4. The evolution of the cosmological mass density of neutral gas with redshift is also studied. The redshift dependence of the neutral gas density is fitted by a power law given by Omegag(z) = (3.2 +/- 0.8) x 10-4 ((2/3) (1 + z)3/2 + (1/3))1.21 +/- 0.15. It is valid from a redshift of 4 to the present epoch. However, the relation is shown to lead to inconsistencies with the star formation rates observed in nearby galaxies. Processes that can cause changes in the Hl content of galaxies are discussed and simple models are proposed to explain the decline in Omegag with time.
No associations
LandOfFree
The evolution of gas in galaxies 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 The evolution of gas in galaxies, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and The evolution of gas in galaxies will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1684798