I am trying to extract the kinematics from the elliptical galaxy NGC 4697 using the Fourier Correlation Quotient (FCQ) algorithm described by Bender (http://adsabs.harvard.edu/full/1990A%26A...229..441B). I am working with the stellar spectrum of the K3-III star hd132345 as template and the galaxy spectra along the major axis of NGC 4697. Both spectra were taken by a long slit spectrograph. I have implemented a first version of the FCQ algorithm, my current problem is that I am not completely certain how to extract the galaxy spectra for different radii (I am new to working with astrophysical spectra in fits format). Underneath I will show my first lines of code for the data acquisition.
file_temp = dir + '/hd132345.fits' # template spectra: star hd132345 (K3-IIICN 2 B) file_gal = dir + '/ngc_4697_major_axis.fits' # galaxy spectra along major axis from ngc 4697` hdu_temp = fits.open(file_temp) hdu_gal = fits.open(file_gal) hdr_temp = hdu_temp.header hdr_gal = hdu_gal.header data_gal = hdu_gal.data data_temp = hdu_temp.data # extract wavelength array and flux flux_gal = data_gal flux_temp = data_temp w_gal = WCS(hdr_gal, naxis=1, relax=False, fix=False) loglam_gal = w_gal.wcs_pix2world(np.arange(len(flux_gal)), 0) w_temp = WCS(hdr_temp, naxis=1, relax=False, fix=False) loglam_temp = w_temp.wcs_pix2world(np.arange(len(flux_temp)), 0)`
Plotted flux_gal over loglam_gal and flux_temp over loglam_temp looks as follows (spectra are rebinned in loglam). The redshift has not been removed yet. I was wondering why the absorbtion lines of the template are broader then those of the galaxy, since it actually should be the other way arround.
The header of my galaxy fits file:
I understand that the keywords CRVAL1 and CRVAL2 describe the initial values for ln lambda in A and the radius in arcseconds. While CDELT1 and CDELT2 describe the increments ln lambda and the radius. So I should have a spectrum for my galaxy every 0.2 arcseconds. I am unsure how to extract those from my input fits files and would be very happy about a respond. Do I have to shift my galaxy spectra for all radii to the rest-wavelength frame, or can I somehow do it all in advance, since the redshift for all radii should be the same. I would be pleased about any tips or comments on this issue.
Thanks to Peter Erwin's comment, the results now look as follows. The entire 2D-image spectral image of NGC-4697 along the major axis (displayed with SAOImage):
The spectrum of the galaxy center taken at row 597. (flux_gal_center = data_gal(597,:)):