Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: HI Absorption in High-Frequency Peaker Galaxies   WSRT observations have been used to investigate the presence of neutral
hydrogen in extremely young radio galaxies. These objects were selected from a
sample of High-Frequency Peakers (HFPs). We detect 2 of the 6 observed galaxies
confirming previous detection of HI in these objects. In the case of OQ 208 -
for which discrepant results were available - we confirm the presence of a
broad (~ 1800 km/s), blue-shifted and shallow HI absorption. No significant
changes in the HI profile have been found between the two epochs of the
observations. The intriguing result is that the derived HI column densities and
upper limits obtained for the most compact sources, do not follow the inverse
correlation between the column density and the linear size found for CSS/GPS
sources. This can be explained - assuming the gas is already in a torus/disk
structure - by a combination of the orientation and the extreme compactness of
the sources. In this scenario, our line of sight to the source would intersect
the torus in its inner region with low optical depth due to high spin and
kinetic temperatures. There is no evidence, with the exception of OQ 208, of
unsettled, high column density gas still enshrouding the young radio sources.
This can be due to the low filling factor of such a medium.

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The categories of this paper are: q-fin
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The categories of this paper are: nucl-ex
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The categories of this paper are: patt-sol
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The categories of this paper are: acc-phys
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The categories of this paper are: alg-geom
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The categories of this paper are: bayes-an
5
The categories of this paper are: gr-qc
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The categories of this paper are: math-ph
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The categories of this paper are: eess
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The categories of this paper are: dg-ga
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The categories of this paper are: cond-mat
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The categories of this paper are: plasm-ph
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The categories of this paper are: math
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The categories of this paper are: nlin
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The categories of this paper are: solv-int
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The categories of this paper are: comp-gas