Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The disappearance of Lyman alpha blobs: a GALEX search at z=0.8   Lyman alpha blobs - luminous, spatially extended emission-line nebulae, often
lacking bright continuum counterparts - are common in dense environments at
high redshift. Until recently, atmospheric absorption and filter technology
have limited our knowledge of any similar objects at z<2. We use GALEX slitless
spectroscopy to search for similar objects in the rich environments of two
known cluster and supercluster fields at z=0.8, where the instrumental
sensitivity peaks. The regions around Cl 1054-0321 and Cl 0023+0423 were each
observed in slitless-spectrum mode for 10-19 ksec, with accompanying direct
images of 3-6 ksec to assist in recognizing continuum sources. Using several
detection techniques, we find no resolved Lyman alpha emitters to a flux limit
of(1.5-9) x 10^{-15} erg/ cm^2 s, on size scales of 5-30 arcseconds. This
corresponds to line luminosities of (0.5-3) x 10^43 erg/s for linear scales
35-200 kpc. Comparison with both blind and targeted surveys at higher redshifts
indicates that the population must have evolved in comoving density at least as
strongly as (1+z)^3. These results suggest that the population of Lyman alpha
blobs is specific to the the high-redshift Universe.

19
The categories of this paper are: eess
25
The categories of this paper are: patt-sol
4
The categories of this paper are: cond-mat
3
The categories of this paper are: physics
1
The categories of this paper are: cs
7
The categories of this paper are: hep-th
36
The categories of this paper are: cmp-lg
32
The categories of this paper are: atom-ph
26
The categories of this paper are: bayes-an
9
The categories of this paper are: nlin
33
The categories of this paper are: plasm-ph
27
The categories of this paper are: comp-gas
13
The categories of this paper are: quant-ph
20
The categories of this paper are: acc-phys
23
The categories of this paper are: solv-int
11
The categories of this paper are: hep-lat