Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The origin of the high-velocity cloud complex C   High-velocity clouds consist of cold gas that appears to be raining down from
the halo to the disc of the Milky Way. Over the past fifty years, two competing
scenarios have attributed their origin either to gas accretion from outside the
Galaxy or to circulation of gas from the Galactic disc powered by supernova
feedback (galactic fountain). Here we show that both mechanisms are
simultaneously at work. We use a new galactic fountain model combined with
high-resolution hydrodynamical simulations. We focus on the prototypical cloud
complex C and show that it was produced by an explosion that occurred in the
Cygnus-Outer spiral arm about 150 million years ago. The ejected material has
triggered the condensation of a large portion of the circumgalactic medium and
caused its subsequent accretion onto the disc. This fountain-driven cooling of
the lower Galactic corona provides the low-metallicity gas required by chemical
evolution models of the Milky Way's disc.

16
The categories of this paper are: stat
18
The categories of this paper are: econ
5
The categories of this paper are: gr-qc
12
The categories of this paper are: nucl-th
11
The categories of this paper are: hep-lat
22
The categories of this paper are: chao-dyn
0
The categories of this paper are: hep-ph
28
The categories of this paper are: alg-geom
24
The categories of this paper are: dg-ga
31
The categories of this paper are: ao-sci
7
The categories of this paper are: hep-th
37
The categories of this paper are: supr-con
17
The categories of this paper are: q-fin
10
The categories of this paper are: q-bio
4
The categories of this paper are: cond-mat
13
The categories of this paper are: quant-ph