Appendix A. Chandra Galaxy Atlas Data Products

 

For those who want to take a quick look at the hot gas distribution and the thermal structure, the figures posted in the CGA website can be useful.

The following downloadable data products are made available in two packages. The main package (package 1) consists of the high-level data products, e.g., point source removed and filled, exposure corrected images (jpg/png and FITS format) in multiple energy bands to best illustrate the diffuse hot gas distribution, derived T-maps (jpg/png and FITS format) in various adaptive binning methods to show the hot gas thermal structure. They can be used directly to get an overview, to obtain the necessary hot gas quantities and to compare them with data at other wavelengths with no additional X-ray data reduction.

For those who intend to perform their own analyses, e.g., to extract and fit X-ray spectra from user-specified regions, we provide all the necessary data in the supplementary package (package 2), e.g., event files per obsid and per ccd.

Those with red bold letters below are in the main package and the others are in the supplementary package. Those with faint orange letters are not in the package, due to the large number of files and their size. They can be available upon individual requests.

 

Merged data (see section 3.1)

·      ${gmv}_evt.fits – a single event file containing the entire observations of a given galaxy. Here g, m and v in ${gmv} indicate galaxy name, merge id (mid) and version, respectively. ${gmv} looks like N1234_90201_v01.

·      ${gmve}_img.fits – a full-resolution image for a given energy band. 1 pixel corresponds to 0.492 arcsec. Here e in ${gmve} indicates an energy band (a short name in Table 3). ${gmve} looks like N1234_90201_v01_G.

·      ${gmve}_exp.fits – a matching exposure map for a given energy band in unit of cm² s (= effective area x exposure time). Due to the energy dependent effective area, the exposure map was made at the effective energy for each energy band given in Table 3.

·      ${gmv}_frame.reg – an ASCII region file of the full field-of-view. It contains one polygon per obsid in a physical pixel coordinate.

·      ${gmv}_frame_fk5.reg - same as the above but in fk5 (in sexagesimal). 

 

Point source list (see section 3.2)

·      ${gmve}_src.fits – a source list (FITS table) for each energy band. They were detected by wavdetect on the merged image file.

·      ${gmv}_src_psfsize.fits – an fits list of sources which are to be removed. To avoid false sources to be excluded, we limit sources with net counts > 10 and significance > 3 s. As described in section 3.2, the sources are determined in the C band detections by default, but when the diffuse emission is strong in the central region of gas-rich galaxies, the sources are determined in the H band detections, instead. The source sizes (used to remove them) are set by MARX PSF with variable encircled energy fractions depending on the source strength.

·      ${gmv}_src_psfsize.dat – the same as the above, but an ASCII list file with additional information about ra, dec, and net counts.

 

Event and image files after point sources removed (not filled)

·      ${gmv}_psrem.evt – an event file containing all data for all obsids and all ccds. All detected point sources were removed, but not filled.

·      ${gmv}_C_psrem.img – an image file containing data for all obsids and all ccds for C energy band. All detected point sources were removed, but not filled. This image file is the one used in the 2D adaptive binning (section 3.3).

·      ${gmv}_${oc}_psrem_evt.fits -  a FITS event file for each obsid for each ccd. They are used for spectral extraction of each binned region. (section 3.4)

·      ${gmv}_${oc}_psrem_bevt.fits – corresponding background FITS event file for each obsid for each ccd. They were made appropriate for each obsid from the blank sky data (section 3.4).

 

Diffuse images after point sources removed and filled (see section 3.2)

·      ${gmve}_diff_img.fits – a diffuse image for a given energy band. This image was made after point sources removed and filled by surrounding pixels.

·      ${gmve}_diff_flux.fits – an exposure-corrected, flux diffuse image for a given energy band. It was made from a diffuse image divided by a corresponding exposure map.

·      ${gmve}_sm_diff_img.fits – a smoothed diffuse image for a given energy band by the 2D Gaussian smoothing with a 5σ kernel (7 pixels per σ) was applied. 

·      ${gmve}_sm_diff_flux.fits – a smoothed, exposure-corrected flux diffuse image for a given energy band. The same smoothing was applied as in the above.

 

JPEG/PNG figures of the above images

·      ${gmve}_img_${z}.jpg – a ds9 jpg file for an X-ray image, ${gmve}_img. Here ${z} indicates a zoom factor (z1 = unzoomed, z05 = zoomed out by a factor of 1/2).

·      ${gmve}_exp_${z}.jpg – a ds9 jpg file for an exposure map, ${gmve}_exp.

·      ${gmve}_flux_${z}.jpg – a ds9 jpg file for a flux image, ${gmve}_flux.

·      ${gmv}_rgb.png - three color images to visualize the 2D spectral variation (including point sources). The energybands used in rgb are 0.5-1.2, 1.2-2 and 2-7 keV, respectively.

·      ${gm}_OX.png – a ds9 jpg file to compare the X-ray (${gmve}.img where e=B band) and optical (DSS POSS2 Red) images. The D₂₅ ellipse (from RC3) and the fov (${gmv}_frame.reg) are overlaid.

·      ${gmve}_diff_img_${z}.jpg – a ds9 jpg file for a diffuse image, ${gmve}_diff.img.

·      ${gmve}_diff_flux_${z}.jpg – a ds9 jpg file for a diffuse flux image, ${gmve}_diff.flux.

·      ${gmve}_sm_diff_img_${z}.jpg – a ds9 jpg file for a smoothed diffuse image, ${gmve}_sm_diff.img.

·      ${gmve}_sm_diff_flux_${z}.jpg – a ds9 jpg file for a smoothed diffuse flux image, ${gmve}_sm_diff.flux.

 

Adaptively binned spatial regions and images (see section 3.3)

·      ${gmvb}_Imap.fits – a FITS image with pixel value = relative intensity in each bin. Here b in in the filename indicates one of four binning methods (AB, WB, CB, HB). ${gmvb} is like N1234_90201_v01_WB.

·      ${gmvbn}.reg – an ASCII region file for the n-th bin. Here n in in the file name is a 5-digit bin number. ${gmvbn} is like N1234_90201_v01_WB_00012.

·      ${gmvb}_binno.fits – an FIT image file with pixel value = bin number

·      ${gmvb}_binrad.fits – a FITS image file with pixel value = radius of bin (only for HB). Due to the nature of the HB method, the spectral extraction region is different from the bin and the extraction circle is generally overlapping and bigger than the bin size given by the square grid.

 

Spectra, arf and rmf for each bin (see section 3.4)

·      ${gmvbn}.pi – A type I PHA file for the source spectrum for the n-th bin, extracted from individual event files for each obsid and for each ccd, then combined into a single file (see section 3.4)

·      ${gmvbn}_bkg.pi – same as the above but for the background spectrum. The same extraction region is used as in the source spectrum.

·      ${gmvbn}_src.arf – an ancilliary response file (ARF) for the n-th bin, made for each obsid and for each ccd, then combined into a single file.

·      ${gmvbn}_src.rmf – an response matrix file (RMF) for the n-th bin, made for each obsid and for each ccd, then combined into a single file.

 

Fitting results (see section 3.4)

·      ${gmvb}_sum.dat– an ASCII table containing (total and net) counts, galacto-centric distance (arcmin),  area (number of pixels), reduced c² and T (best-fit and error) for each bin. The distance is determined by photon weighted mean distance from the galaxy center.

·      ${gmvbns}.log – an ASCII log file for SHERPA spectral fitting. Here, s in ${gmvbns}indicates spectral models (e.g., APEC, APECnPL = APEC + Power-law). ${gmvbns} looks like N1234_90201_v01_WB_00012_APECnPL.

 

Spectral maps (see section 3.4)

·      ${gmvbsp}map.fits -  A FITS image with pixel value = spectral parameter map. Here p in the file name indicate the spectral parameters used in the map (T=temperarure, N=norm of the ASPEC component/area, P=projected pseudo pressure and K=projected pseudo entropy). ${gmvbsp} is like N1234_90201_v01_WB_APECnPL_T.

·      ${gmvbsp}map_lo.fits – same as the above but with pixel value = lower limit of a given parameter

·      ${gmvbsp}map_up.fits - same as the above but with pixel value = upper limit of a given parameter

·      ${gmvbsp}map_30pc.fits – same as ${gmvbsp}.map, but the bins with a large error (> 30% in T) are masked out. Here ${gmvbrsp} looks like

N1234_90201_v01_WB_sn20_APECnPL_T.                                                        

·      ${gmvbs}_Cmap_30pc.fits - A FITS image with pixel value = reduced chi2

 

PNG figures

·      ${gmbr}_Imap.png – a png file of the binned intensity map, ${gmvb}_Imap.fits.

·      ${gmbrsp}map_30pc.png – a png file of the masked (by 30% T error) spectral parameter maps, ${gmvbsp}map_30pc.fits.