Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A z~3 radio galaxy and its protocluster: evidence for a superstructure?   We present spectroscopic follow-up observations of Lyman Break Galaxies
(LBGs) selected in the field surrounding the radio galaxy MRC0316-257 at z~3.13
(0316). Robust spectroscopic redshifts are determined for 20 out of 24 objects.
Three of the spectroscopically confirmed galaxies have 3.12<z<3.13 indicating
that these objects reside in a protocluster structure previously found around
the radio galaxy. An additional 5 objects are found 1600 km/s blue-shifted with
respect to the main protocluster structure. This is in addition to three [OIII]
emitters found at this redshift in a previous study. This is further evidence
that a structure exists directly in front of the 0316 protocluster. We estimate
that the foreground structure is responsible for half of the surface
overdensity of LBGs found in the field as a whole. The foreground structure is
associated with a strong surface density peak 1.4 Mpc to the North-West of the
radio galaxy and a 2D Kolmogorov-Smirnov test indicates that the spatial
distributions of the 0316 and foreground galaxies differ at the 3 sigma level.
In addition, we compare the properties of protocluster, foreground structure
and field galaxies, but we find no significant differences. In terms of the
nature of the two structures, a merger scenario is a possible option. Simple
merger dynamics indicates that the observed relative velocity of 1600 km/s can
be reproduced if the two structures have masses of ~5x10^14 Msun and have
starting separations of around 2.5 to 3 Mpc. It is also possible that the
foreground structure is unrelated to the 0316 protocluster in which case the
two structures will not interact before z=0.

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The categories of this paper are: gr-qc
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The categories of this paper are: q-fin
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The categories of this paper are: eess
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The categories of this paper are: cond-mat
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The categories of this paper are: hep-ph
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The categories of this paper are: funct-an
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The categories of this paper are: adap-org
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The categories of this paper are: nlin
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The categories of this paper are: math-ph
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The categories of this paper are: acc-phys
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The categories of this paper are: supr-con
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The categories of this paper are: cmp-lg
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The categories of this paper are: stat
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The categories of this paper are: nucl-ex
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The categories of this paper are: dg-ga
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The categories of this paper are: cs