Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: H-alpha Photometry of Abell 2390   We present the results of a search for strong H-alpha emission line galaxies
(rest frame equivalent widths greater than 50 A) in the z=0.23 cluster Abell
2390. The survey contains 1189 galaxies over 270 square arcminutes, and is 50%
complete at M_r=-17.5+5 log h. The fraction of galaxies in which H-alpha is
detected at the 2sigma level rises from 0.0 in the central regions (excluding
the cD galaxy) to 12.5+/-8% at R200. For 165 of the galaxies in our catalogue,
we compare the H-alpha equivalent widths with their [OII] equivalent widths,
from the CNOC1 spectra. The fraction of strong H-alpha emission line galaxies
is consistent with the fraction of strong [OII] emission galaxies in the CNOC1
sample: only 2+/-1% have no detectable [OII] emission and yet significant
(>2sigma) H-alpha equivalent widths. Dust obscuration, non-thermal ionization,
and aperture effects are all likely to contribute to this non-correspondence of
emission lines. We identify six spectroscopically 'secure' k+a galaxies
(W(OII)<5 A and W(Hdelta)>5 A); at least two of these show strong signs in
H-alpha of star formation in regions that are covered by the slit from which
the spectra were obtained. Thus, some fraction of galaxies classified k+a based
on spectra shortward of 6000 A are likely to be undergoing significant star
formation. These results are consistent with a 'strangulation' model for
cluster galaxy evolution, in which star formation in cluster galaxies is
gradually decreased, and is neither enhanced nor abruptly terminated by the
cluster environment.

3
The categories of this paper are: physics
26
The categories of this paper are: bayes-an
2
The categories of this paper are: math
10
The categories of this paper are: q-bio
36
The categories of this paper are: cmp-lg
14
The categories of this paper are: math-ph
15
The categories of this paper are: nucl-ex
13
The categories of this paper are: quant-ph
1
The categories of this paper are: cs
0
The categories of this paper are: hep-ph
21
The categories of this paper are: adap-org
31
The categories of this paper are: ao-sci
27
The categories of this paper are: comp-gas
4
The categories of this paper are: cond-mat
7
The categories of this paper are: hep-th
16
The categories of this paper are: stat