Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: "GiGa": the Billion Galaxy HI Survey -- Tracing Galaxy Assembly from
  Reionization to the Present   In this paper, we review the Billion Galaxy Survey that will be carried out
at radio--optical wavelengths to micro--nanoJansky levels with the telescopes
of the next decades. These are the Low-Frequency Array, the Square Kilometer
Array and the Large Synoptic Survey Telescope as survey telescopes, and the
Thirty Meter class Telescopes for high spectral resolution+AO, and the James
Webb Space Telescope (JWST) for high spatial resolution near--mid IR follow-up.
With these facilities, we will be addressing fundamental questions like how
galaxies assemble with super-massive black-holes inside from the epoch of First
Light until the present, how these objects started and finished the
reionization of the universe, and how the processes of star-formation, stellar
evolution, and metal enrichment of the IGM proceeded over cosmic time. We also
summarize the high-resolution science that has been done thus far on high
redshift galaxies with the Hubble Space Telescope (HST). Faint galaxies have
steadily decreasing sizes at fainter fluxes and higher redshifts, reflecting
the hierarchical formation of galaxies over cosmic time. HST has imaged this
process in great structural detail to z<~6. We show that ultradeep
radio-optical surveys may slowly approach the natural confusion limit, where
objects start to unavoidably overlap because of their own sizes, which only SKA
can remedy with HI redshifts for individual sub-clumps. Finally, we summarize
how the 6.5 meter James Webb Space Telescope (JWST) will measure first light,
reionization, and galaxy assembly in the near--mid-IR.

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The categories of this paper are: supr-con
20
The categories of this paper are: acc-phys
3
The categories of this paper are: physics
21
The categories of this paper are: adap-org
23
The categories of this paper are: solv-int
19
The categories of this paper are: eess
0
The categories of this paper are: hep-ph
5
The categories of this paper are: gr-qc
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The categories of this paper are: atom-ph
28
The categories of this paper are: alg-geom
1
The categories of this paper are: cs
33
The categories of this paper are: plasm-ph
12
The categories of this paper are: nucl-th
16
The categories of this paper are: stat
15
The categories of this paper are: nucl-ex
24
The categories of this paper are: dg-ga