Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Detecting First Star Lyman-$\alpha$ Spheres through Gravitational
  Telescopes   Lyman-$\alpha$ spheres, i.e. regions around the first stars which are
illuminated by Lyman-$\alpha$ photons and show 21cm absorption feature against
the CMB, are smoking guns at the dawn of the reionization epoch. Though
overwhelming radio foreground makes their detections extremely difficult, we
pointed out that, strong gravitational lensing can significantly improve their
observational feasibility. Since Lyman-$\alpha$ spheres have ~10" sizes,
comparable to the caustic size of galaxy clusters, individual images of each
strongly lensed Lyman-$\alpha$ sphere often merge together and form single
structures in the 21cm sky with irregular shapes. Using high-resolution N-body
LCDM simulations, we found that the lensing probability to have magnification
bigger than 10 is ~10^{-5}. This results in $\ga 10^6$ strongly lensed
Lyman-$\alpha$ spheres across the sky, which should be the primary targets for
first detections of Lyman-$\alpha$ spheres. Although the required total radio
array collecting area for their detection is large (~100 km^2), the design of
long fixed cylindrical reflectors can significantly reduce the total cost of
such array to the level of the square kilometer array (SKA) and makes the
detection of these very first objects feasible.

12
The categories of this paper are: nucl-th
5
The categories of this paper are: gr-qc
8
The categories of this paper are: hep-ex
36
The categories of this paper are: cmp-lg
37
The categories of this paper are: supr-con
0
The categories of this paper are: hep-ph
1
The categories of this paper are: cs
33
The categories of this paper are: plasm-ph
3
The categories of this paper are: physics
21
The categories of this paper are: adap-org
10
The categories of this paper are: q-bio
27
The categories of this paper are: comp-gas
35
The categories of this paper are: mtrl-th
28
The categories of this paper are: alg-geom
25
The categories of this paper are: patt-sol
29
The categories of this paper are: funct-an