PhD Thesis (PDF) - Department of Astronomy - University of Virginia

the QE degradation in the ACIS detectors. The best-fit emission model for all of the
sources was found to be a bremsstrahlung model with kT = 9.08 keV. This model,
combined with the individual values of NH and distance for each galaxy and the
individual response files for each observation, were used to convert count rates into
unabsorbed X-ray luminosities LX in the 0.3–10.0 keV band.
Due mainly to varying exposure times and distances, the observations of differ-
ent galaxies have differing limiting sensitivities. For each galaxy, we summarize the
number of X-ray detections and the minimum X-ray luminosity for three sample def-
initions in columns 2 and 3 of Table 6.3. The three samples are: all sources with
a positive luminosity (Detected sample); all sources with luminosities determined at
the ≥3σ level (SNR sample); and all sources with LX ≥ 3.2 × 10 38 erg s −1 (Complete
sample). Note that the SNR sample does not include sources that were brighter than
the reported minimum luminosity but not 3σ significant. Since a source with 20 net
counts would be detected at high completeness for most of the galaxies, we defined the
Complete sample by the luminosity that a source in NGC 4649 (the galaxy with the
highest minimum luminosity) with 20 net counts would have. We note that detections
at the centers of the X-ray brightest galaxies (e.g., NGC 4649) may still be incom-
plete due to contamination from bright gaseous emission; however, we have chosen
this luminosity as a compromise between completeness and a reasonable luminosity
limit.
239