Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Heterogeneity of Inverted Calcium II H:K Ratio Cluster Galaxies   The ratio of calcium II H plus H$\epsilon$ to calcium II K inverts as a
galaxy stellar population moves from being dominated by older stars to
possessing more A and B class stars. This ratio - the H:K ratio - can serve as
an indicator of stellar populations younger than 200 Myr. In this work, we
provide a new method to determine H:K, and apply it to spectra taken of cluster
galaxies in Abell~3888. Although H:K is on average systematically lower for the
cluster than for a wider field sample, we show that H:K does not have a simple
relationship with other indices such as the equivalent widths of H$\delta$ and
[OII]. Moreover, strongly inverted galaxies with H:K>1.1 have no preferred
location within the cluster and are only slightly lower in their velocity
dispersions around the cluster compared to strongly emitting [OII] galaxies.
Our results indicate that selecting galaxies on H:K inversion results in a
heterogeneous sample formed via a mixture of pathways that likely includes, but
may not be limited to, merging spiral galaxies, and quiescent galaxies
accreting lower mass, gas rich companions. In concert with other selection
criteria, H:K can provide a means to select a more `pure' passive sample or to
aid in the selection of highly star-forming galaxies, especially where other
spectral line indicators such as H$\alpha$ may not have been observed.

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The categories of this paper are: supr-con
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The categories of this paper are: stat
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The categories of this paper are: chao-dyn
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The categories of this paper are: q-bio
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The categories of this paper are: hep-lat
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The categories of this paper are: eess
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The categories of this paper are: solv-int
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The categories of this paper are: comp-gas
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The categories of this paper are: math-ph
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The categories of this paper are: hep-ph
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The categories of this paper are: cs
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The categories of this paper are: dg-ga
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The categories of this paper are: adap-org
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The categories of this paper are: nucl-th
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The categories of this paper are: gr-qc
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The categories of this paper are: cmp-lg