Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Foregrounds for 21cm Observations of Neutral Gas at High Redshift   We investigate a number of potential foregrounds for an ambitious goal of
future radio telescopes such as the Square Kilometer Array (SKA) and Low
Frequency Array (LOFAR): spatial tomography of neutral gas at high redshift in
21cm emission. While the expected temperature fluctuations due to unresolved
radio point sources is highly uncertain, we point out that free-free emission
from the ionizing halos that reionized the universe should define a minimal
bound. This emission is likely to swamp the expected brightness temperature
fluctuations, making proposed detections of the angular patchwork of 21cm
emission across the sky unlikely to be viable. An alternative approach is to
discern the topology of reionization from spectral features due to 21cm
emission along a pencil-beam slice. This requires tight control of the
frequency-dependence of the beam in order to prevent foreground sources from
contributing excessive variance. We also investigate potential contamination by
galactic and extragalactic radio recombination lines (RRLs). These are unlikely
to be show-stoppers, although little is known about the distribution of RRLs
away from the Galactic plane. The mini-halo emission signal is always less than
that of the IGM, making mini-halos unlikely to be detectable. If they are seen,
it will be only in the very earliest stages of structure formation at high
redshift, when the spin temperature of the IGM has not yet decoupled from the
CMB.

4
The categories of this paper are: cond-mat
12
The categories of this paper are: nucl-th
28
The categories of this paper are: alg-geom
29
The categories of this paper are: funct-an
8
The categories of this paper are: hep-ex
17
The categories of this paper are: q-fin
31
The categories of this paper are: ao-sci
11
The categories of this paper are: hep-lat
1
The categories of this paper are: cs
10
The categories of this paper are: q-bio
25
The categories of this paper are: patt-sol
21
The categories of this paper are: adap-org
9
The categories of this paper are: nlin
37
The categories of this paper are: supr-con
32
The categories of this paper are: atom-ph
33
The categories of this paper are: plasm-ph