Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Low-redshift evolution of the Lyman-alpha Forest   The low-redshift evolution of the intergalactic medium is investigated using
hydrodynamic cosmological simulations. The assumed cosmological model is a
critical density cold dark matter universe. The imposed uniform background of
ionizing radiation has the amplitude, shape and redshift evolution as computed
from the observed quasar luminosity function by Haardt & Madau. We have
analysed simulated Lyman-alpha spectra using Voigt-profile fitting, mimicking
the procedure with which quasar spectra are analysed. Our simulations reproduce
the observed evolution of the number of Lyman-alpha absorption lines over the
whole observed interval of z=0.5 to z=4. In particular, our simulations show
that the decrease in the rate of evolution of Lyman-alpha absorption lines at
z< 2, as observed by Hubble Space Telescope, can be explained by the steep
decline in the photo-ionizing background resulting from the rapid decline in
quasar numbers at low redshift.

18
The categories of this paper are: econ
37
The categories of this paper are: supr-con
28
The categories of this paper are: alg-geom
9
The categories of this paper are: nlin
20
The categories of this paper are: acc-phys
17
The categories of this paper are: q-fin
24
The categories of this paper are: dg-ga
4
The categories of this paper are: cond-mat
16
The categories of this paper are: stat
23
The categories of this paper are: solv-int
36
The categories of this paper are: cmp-lg
21
The categories of this paper are: adap-org
34
The categories of this paper are: chem-ph
10
The categories of this paper are: q-bio
8
The categories of this paper are: hep-ex
30
The categories of this paper are: q-alg