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

kindly provided by Alexey Vikhlinin and Jonathon McDowell. The spectra were fit-
ted using XSPEC. 4 Since launch, the ACIS quantum efficiency (QE) has undergone
continuous degradation. 5 We used the XSPEC ACISABS model to correct X-ray
spectra for this effect.
2.3 X-ray Image
The X-ray images of NGC 4365 and NGC 4382 show both resolved point sources
and diffuse emission. To best image this combination, we adaptively smoothed the
Chandra S3 image using a minimum signal–to–noise ratio (S/N) per smoothing beam
of 3. After correcting for exposure and background, we removed regions of less than
20 ks to avoid artifacts at the chip’s edge. Figure 2.1 displays gray-scale images with
a logarithmic surface brightness scale ranging between 1.56 × 10 −6 and 3.3 × 10 −4
counts pixel −1 s −1 . In both galaxies, the majority of the X-ray luminosity emission
has been resolved into point sources.
In Figure 2.2, we show the Digital Sky Survey (DSS) optical images centered on
NGC 4365 and NGC 4382 using a logarithmic gray scale. The overlaid circles indicate
the positions of the X-ray point sources listed in Tables 2.1 and 2.2. Only a small
fraction of the weaker point sources are not evident in Figure 2.1. In NGC 4365,
the diffuse emission qualitatively has the same ellipticity and position angle (P.A.) as
the optical emission. On the other hand, the X-ray emission in NGC 4382 appears
rounder than the optical emission.
4 See http://heasarc.gsfc.nasa.gov/docs/software/lheasoft/.
5 See http://cxc.harvard.edu/cal/Acis/Cal prods/qeDeg/.
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