Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Redshifted 21cm Observations of High Redshift Quasar Proximity Zones   The introduction of low-frequency radio arrays is expected to revolutionize
the study of the reionization epoch. Observation of the contrast in redshifted
21cm emission between a large HII region and the surrounding neutral
inter-galactic medium (IGM) will be the simplest and most easily interpreted
signature. However the highest redshift quasars known are thought to reside in
an ionized IGM. Using a semi-analytic model we describe the redshifted 21cm
signal from the IGM surrounding quasars discovered using the i-drop out
technique (i.e. quasars at z~6). We argue that while quasars at z<6.5 seem to
reside in the post overlap IGM, they will still provide valuable probes of the
late stages of the overlap era because the light-travel time across a quasar
proximity zone should be comparable to the duration of overlap. For redshifted
21cm observations within a 32MHz bandpass, we find that the subtraction of a
spectrally smooth foreground will not remove spectral features due to the
proximity zone. These features could be used to measure the neutral hydrogen
content of the IGM during the late stages of reionization. The density of
quasars at z~6 is now well constrained. We use the measured quasar luminosity
function to estimate the prospects for discovery of high redshift quasars in
fields that will be observed by the Murchison Widefield Array.

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The categories of this paper are: math
30
The categories of this paper are: q-alg
29
The categories of this paper are: funct-an
4
The categories of this paper are: cond-mat
25
The categories of this paper are: patt-sol
19
The categories of this paper are: eess
37
The categories of this paper are: supr-con
26
The categories of this paper are: bayes-an
8
The categories of this paper are: hep-ex
34
The categories of this paper are: chem-ph
31
The categories of this paper are: ao-sci
3
The categories of this paper are: physics
35
The categories of this paper are: mtrl-th
11
The categories of this paper are: hep-lat
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The categories of this paper are: cs
0
The categories of this paper are: hep-ph