Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Reconstructing three-dimensional densities from two-dimensional
  observations of molecular gas   Star formation has long been known to be an inefficient process, in the sense
that only a small fraction $\epsilon_{\rm ff}$ of the mass of any given gas
cloud is converted to stars per cloud free-fall time. However, developing a
successful theory of star formation will require measurements of both the mean
value of $\epsilon_{\rm ff}$ and its scatter from one molecular cloud to
another. Because $\epsilon_{\rm ff}$ is measured relative to the free-fall
time, such measurements require accurate determinations of cloud volume
densities. Efforts to measure the volume density from two-dimensional projected
data, however, have thus far relied on treating molecular clouds as simple
uniform spheres, while their real shapes are likely filamentary and their
density distributions far from uniform. The resulting uncertainty in the true
volume density is likely one of the major sources of error in observational
estimates of $\epsilon_{\rm ff}$. In this paper, we use a suite of simulations
of turbulent, magnetized, radiative, self-gravitating star-forming clouds to
examine whether it is possible to obtain more accurate volume density estimates
and thereby reduce this error. We create mock observations from simulations,
and show that current analysis methods relying on the spherical assumption
likely yield ~ 0.26 dex underestimations and ~ 0.51 dex errors in volume
density estimates, corresponding to a ~ 0.13 dex overestimation and a ~ 0.25
dex scatter in $\epsilon_{\rm ff}$, comparable to the scatter in observed cloud
samples. We build a predictive model that uses information accessible in
two-dimensional measurements -- most significantly the Gini coefficient of the
surface density distribution -- to estimate volume density with ~ 0.3 dex less
scatter. We test our method on a recent observation of the Ophiuchus cloud, and
show that it successfully reduces the $\epsilon_{\rm ff}$ scatter.

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The categories of this paper are: hep-th
17
The categories of this paper are: q-fin
20
The categories of this paper are: acc-phys
35
The categories of this paper are: mtrl-th
23
The categories of this paper are: solv-int
2
The categories of this paper are: math
24
The categories of this paper are: dg-ga
29
The categories of this paper are: funct-an
1
The categories of this paper are: cs
15
The categories of this paper are: nucl-ex
0
The categories of this paper are: hep-ph
37
The categories of this paper are: supr-con
11
The categories of this paper are: hep-lat
5
The categories of this paper are: gr-qc
34
The categories of this paper are: chem-ph
28
The categories of this paper are: alg-geom