I'm trying to read and plot a Halpha map from a fits image whose 'info' is the following:
No. Name Ver Type Cards Dimensions Format
0 PRIMARY 1 PrimaryHDU 66 (8640, 4320) float32
And the header is composed of:
"SIMPLE = T / Written by IDL: Sat Jan 25 22:41:24 2003
BITPIX = -32 / Number of bits per data pixel
NAXIS = 2 / Number of data axes
NAXIS1 = 8640 /
NAXIS2 = 4320 /
DATE = '2003-01-26' / Creation UTC (CCCC-MM-DD) date of FITS header
COMMENT FITS (Flexible Image Transport System) format is defined in 'Astronomy
COMMENT and Astrophysics', volume 376, page 359; bibcode 2001A&A...376..359H
CTYPE1 = 'GLON-CAR' /
CRPIX1 = 4320.50 /
CRVAL1 = 0.00000 /
CTYPE2 = 'GLAT-CAR' /
CRPIX2 = 2160.50 /
CRVAL2 = 0.00000 /
CD1_1 = -0.0416666666667 /
CD1_2 = 0.00000000000 /
CD2_1 = 0.00000000000 /
CD2_2 = 0.0416666666667 /
LONPOLE = 180 /
PROJP1 = 0 /
PROJP2 = 0 /
EQUINOX = 2000.00 / "
Therefore, if I understand properly, I can perform directly a conversion from pixels coordinates to world coordinates (in that case, galactic longitude and latitude), using the WCS module. My code is then written as follows:
hdu = fits.open('Halpha_map.fits')
hdr = hdu[0].header
data = hdu[0].data
wcs = WCS(header=hdr, fix = True)
ax = plt.subplot(projection=wcs)
im = ax.imshow(-np.log10(data), cmap = 'gray') #Invert logarithm gray map.
Then I want to restrict the plot to specific galactic longitudes and latitudes, let's say for instance l = [50°,55°] and b = [0°,5°]. When I try this, I obtain the following plot:
https://i.stack.imgur.com/uMo6i.png
So I have a weird grey instead of the proper portion of the Halpha map and the coordinates do not correspond to the part I want to plot. Any idea of the origin of this issue, please?
