Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Counter Arc to MS1512-cB58 and a Companion Galaxy   We present near-infrared spectra of ``A2'', the primary counter arc to the
gravitationally lensed galaxy MS1512-cB58. The spectra showredshifted H-alpha,
[NII], [OIII], and H-beta at z=2.728 +/- 0.001. We observe the same
H-alpha/[OIII] ratio as cB58, which together with the redshift confirms that A2
is indeed another image of a single background galaxy. Published lensing
reconstruction reports that A2 is a magnification of the entire source, while
cB58 is an image of only a part. At marginal significance, A2 shows higher line
to continuum ratios than cB58 (by a factor of about 2), suggesting a
non-uniform ratio of young to old stars across the galaxy. We observe a second
emission line source in the slit. This object, ``W5'', is predicted to be a
lensed image of another galaxy at a redshift similar to cB58. W5 is blueshifted
from cB58 by about 400 km/s and has a significantly lower H-alpha/[OIII] ratio,
confirming that it is an image of a different background galaxy in a group with
cB58. The H-alpha emission line in W5 implies a star formation rate of 6
Msun/yr (H_0 = 70 km/s/Mpc, Omega_M=0.3, Omega_L=0.7), after correcting for
lensing magnification.

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The categories of this paper are: chao-dyn
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The categories of this paper are: solv-int
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The categories of this paper are: econ
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The categories of this paper are: hep-th
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The categories of this paper are: hep-ph
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The categories of this paper are: atom-ph
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The categories of this paper are: acc-phys
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The categories of this paper are: comp-gas
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The categories of this paper are: dg-ga
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The categories of this paper are: hep-lat
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The categories of this paper are: stat
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The categories of this paper are: quant-ph
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The categories of this paper are: ao-sci
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The categories of this paper are: supr-con
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The categories of this paper are: cond-mat
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The categories of this paper are: bayes-an