Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The X-ray Emission in Post-Merger Ellipticals   The evolution in X-ray properties of early-type galaxies is largely
unconstrained. In particular, little is known about how, and if, remnants of
mergers generate hot gas halos. Here we examine the relationship between X-ray
luminosity and galaxy age for a sample of early-type galaxies. Comparing
normalized X-ray luminosity to three different age indicators we find that
L_X/L_B increases with age, suggesting an increase in X-ray halo mass with time
after a galaxy's last major star-formation episode. The long-term nature of
this trend, which appears to continue across the full age range of our sample,
poses a challenge for many models of hot halo formation. We conclude that
models involving a declining rate of type Ia supernovae, and a transition from
outflow to inflow of the gas originally lost by galactic stars, offers the most
promising explanation for the observed evolution in X-ray luminosity.

12
The categories of this paper are: nucl-th
15
The categories of this paper are: nucl-ex
35
The categories of this paper are: mtrl-th
23
The categories of this paper are: solv-int
4
The categories of this paper are: cond-mat
25
The categories of this paper are: patt-sol
19
The categories of this paper are: eess
1
The categories of this paper are: cs
14
The categories of this paper are: math-ph
7
The categories of this paper are: hep-th
10
The categories of this paper are: q-bio
5
The categories of this paper are: gr-qc
32
The categories of this paper are: atom-ph
27
The categories of this paper are: comp-gas
8
The categories of this paper are: hep-ex
30
The categories of this paper are: q-alg