Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Optical to mid-IR observations of Lyman-alpha galaxies at redshift 5 in
  the HUDF: a young and low mass population   High redshift galaxies selected on the basis of their strong Lyman-alpha
emission tend to be young ages and small physical sizes. We show this by
analyzing the spectral energy distribution (SED) of 9 Lyman-alpha emitting
(LAE) galaxies at 4.0 < z < 5.7 n the Hubble Ultra Deep Field (HUDF).
Rest-frame UV to optical 700A < lambda < 7500A luminosities, or upper limits,
are used to constrain old stellar populations. We derive best fit, as well as
maximally massive and maximally old, properties of all 9 objects. We show that
these faint and distant objects are all very young, being most likely only a
few millions years old, and not massive, the mass in stars being ~10^6-10^8
M_sun. Deep Spitzer Infrared Array Camera (IRAC) observations of these objects,
even in cases where objects were not detected, were crucial in constraining the
masses of these objects. The space density of these objects, ~1.25x10^-4 Mpc^-3
is comparable to previously reported space density of LAEs at moderate to high
redshifts. These Lyman-alpha galaxies show modest star formation rates of ~8
M_sun yr^-1, which is nevertheless strong enough to have allowed these galaxies
to assemble their stellar mass in less than a few x10^6 years. These sources
appear to have small physical sizes, usually smaller than 1 Kpc, and are also
rather concentrated. They are likely to be some of the least massive and
youngest high redshift galaxies observed to date.

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The categories of this paper are: quant-ph
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The categories of this paper are: mtrl-th
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The categories of this paper are: patt-sol
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The categories of this paper are: nucl-ex
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The categories of this paper are: q-bio
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The categories of this paper are: ao-sci
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The categories of this paper are: funct-an
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The categories of this paper are: hep-ex
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The categories of this paper are: comp-gas
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The categories of this paper are: plasm-ph
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The categories of this paper are: stat
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The categories of this paper are: solv-int
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The categories of this paper are: eess
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The categories of this paper are: hep-lat
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The categories of this paper are: math-ph
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The categories of this paper are: econ