MIRISim Scene Part III

When troubleshooting why my MIRI simulations aren’t working, I decided the problem is with how I am creating the scene (see “MIRISim Troubleshooting Part V”).

When creating the scene, I noted at the time the sources looked strange, but thought it might just have had to do with the way the data was displayed (see MIRISim Scene Part II)

In this post, I am going to revisit this issue.

Stamps

Previous code for adding stamps of each galaxy:

pos = positions[i]
stamp_size = int(np.ceil(radius[i]*3)*oversample) #pixels
stamp_size = max(stamp_size,5)

#Make Stamp
table['r_eff'] = np.array([radius[i]]) * u.arcsec#effective half-light radius
table['n'] = np.array([sersic_index[i]])
table['x_0'] = np.array([stamp_size/2.0]) * u.arcsec
table['y_0'] = np.array([stamp_size/2.0])* u.arcsec
table['ellip'] = np.array([ell[i]])
table['theta'] = np.array([position_angle[i]])
table['amplitude'] = np.array(flux)*u.mJy/A[i]# Surface brightness at r_eff
sersic_stamp = make_model_sources_image((stamp_size,stamp_size), model, table,oversample=oversample)


#Make hdul
myra = ra_list[i]; mydec = dec_list[i]
size_arcsec = stamp_size/oversample # size of stamp in arcsec
mybounds = [myra - size_arcsec/3600/2, myra+ size_arcsec/3600/2, mydec-size_arcsec/3600/2, mydec+size_arcsec/3600/2]
stamp_hdul = create_hdul(mybounds, size_arcsec/stamp_size/3600 )
stamp_hdul[0].data = sersic_stamp.T
stamp_hdul.writeto('teststamp.fits', overwrite=True)

I don’t think that “make_model_sources_image” knows the arcsec/pixel scale, so it wasn’t properly converting the image.

Therefore, I rewrote this to give the size of the galaxy in pixels (I also changed oversample from 10 to 2):

pos = positions[i]
myrad = radius[i]*oversample/pixscale # pixels
stamp_size = max(int(np.ceil(myrad*5)),5)

#Make Stamp
table['r_eff'] = np.array([myrad]) * u.pix #effective half-light radius
table['n'] = np.array([sersic_index[i]])
table['x_0'] = np.array([stamp_size/2.0]) * u.pix
table['y_0'] = np.array([stamp_size/2.0])* u.pix
table['ellip'] = np.array([ell[i]])
table['theta'] = np.array([position_angle[i]]) *u.rad #radians
table['amplitude'] = np.array(flux)*u.mJy/A[i]# Surface brightness at r_eff [mJy/arcsec**2]
sersic_stamp = make_model_sources_image((stamp_size,stamp_size), model, table,oversample=oversample)


#Make hdul
myra = ra_list[i]; mydec = dec_list[i]
size_arcsec = stamp_size/(oversample/pixscale) # size of stamp in arcsec
mybounds = [myra - size_arcsec/3600/2, myra+ size_arcsec/3600/2, mydec-size_arcsec/3600/2, mydec+size_arcsec/3600/2]
stamp_hdul = create_hdul(mybounds, size_arcsec/stamp_size/3600 )
stamp_hdul[0].data = sersic_stamp.T
stamp_hdul.writeto('teststamp.fits', overwrite=True)

Here is an example galaxy in both of these versions:

Note that on the left, the galaxy stamp is 180x180 pixels, and in the right, the stamp is 522x522 pixels. I think that I was therefore mapping the galaxy stamps to the wrong number of pixels.

For this test galaxy, it has a (pixel) half-light radius of 104. Exploring a bit how big I should make the stamp, I have plotted the total flux (i.e. summing up over all pixels in the stamp) as a function of the stamp size.

From this, I decided to make stamps about 10x the half-light radius of the source.

Running all of the (test) galaxies, I find the following:

And looking at the test galaxy, and how big I expect the stamp to be I find:

Now I am fairly positive the locations and sizes of the galaxies are set correctly!

Next Steps

1. Test if this fixes my whole issue
2. Rerun this for the full catalog

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