Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Physical State of the Intergalactic Medium or Can We Measure Y?   We present an argument for a {\it lower limit} to the Compton-$y$ parameter
describing spectral distortions of the cosmic microwave background (CMB). The
absence of a detectable Gunn-Peterson signal in the spectra of high redshift
quasars demands a high ionization state of the intergalactic medium (IGM).
Given an ionizing flux at the lower end of the range indicated by the proximity
effect, an IGM representing a significant fraction of the
nucleosynthesis-predicted baryon density must be heated by sources other than
the photon flux to a temperature $\go {\rm few} \times 10^5\, K$. Such a gas at
the redshift of the highest observed quasars, $z\sim 5$, will produce a $y\go
10^{-6}$. This lower limit on $y$ rises if the Universe is open, if there is a
cosmological constant, or if one adopts an IGM with a density larger than the
prediction of standard Big Bang nucleosynthesis.

11
The categories of this paper are: hep-lat
4
The categories of this paper are: cond-mat
24
The categories of this paper are: dg-ga
0
The categories of this paper are: hep-ph
25
The categories of this paper are: patt-sol
22
The categories of this paper are: chao-dyn
17
The categories of this paper are: q-fin
13
The categories of this paper are: quant-ph
35
The categories of this paper are: mtrl-th
20
The categories of this paper are: acc-phys
30
The categories of this paper are: q-alg
1
The categories of this paper are: cs
12
The categories of this paper are: nucl-th
14
The categories of this paper are: math-ph
36
The categories of this paper are: cmp-lg
3
The categories of this paper are: physics