Implement color dependent galaxy shapes

[dkirkby]

The catalog bulge/disk/AGN normalizations are specified at a one wavelength but multiply different SEDs, so this issue is to combine the normalization parameters (fluxnorm_bulge/disk/agn) with the appropriate SEDs (sedname_bulge/disk/agn) to calculate correct bulge/disk/agn proportions in each band.

As a cross check, try to reproduce the extinction corrected AB apparent magnitudes in the input catalog, which will require using the av_b/d, rv_b/d and ext_model_b/d catalog params (@danielsf why no corresponding AGN params?).

@jmeyers314 I remember you saying you had already done a similar check. How good was the agreement? Did you check the catalog magnitudes, colors or both?

The galaxy input catalog schema is documented here (@danielsf is this still current?)

[danielsf]

Yes. That schema is still current.

As to why there are no dust parameters for the AGN: I'm not sure. These tables were constructed before my time. I will ask around. It is possible that we decided it did not matter since literally every AGN in our catalog has the same SED (or, put another way, we only have one AGN SED in our SED library), so whatever we do isn't going to be very realistic anyway. I will get back to you.

[danielsf]

Apparently, we matched our AGN distribution to the distribution in this reference

Y. Q. Xue, B. Luo, W. N. Brandt, F. E. Bauer, B. D. Lehmer, P. S. Broos, D. P. Schneider, D. M.
Alexander, M. Brusa, A. Comastri, A. C. Fabian, R. Gilli, G. Hasinger, A. E. Hornschemeier,
A. Koekemoer, T. Liu, V. Mainieri, M. Paolillo, D. A. Rafferty, P. Rosati, O. Shemmer, J. D.
Silverman, I. Smail, P. Tozzi, and C. Vignali. The Chandra Deep Field-South Survey: 4 Ms
Source Catalogs. Astrophysical Journal Supplemental, 195:10, July 2011. doi: 10.1088/0067-
0049/195/1/10.

The AGN SED is taken from vandenBerg (let me know if that doesn't make any sense to you and I can try to find a more detailed citation). The normalization of the SED (which does vary from AGN to AGN) was done to try to empirically match observed magnitudes (so there ought to be some dust implicitly folded in there). The variability parameters were also tuned to the observed distribution.

Does this help?

[dkirkby]

Thanks @danielsf ! How literally should I take the schema descriptions, e.g. for fluxnorm_bulge:

Multiplicative scaling factor to apply to the bulge SED

Do I really just multiply the raw SED (from here?) by this scaling factor? I guess the result is then in erg/cm2/s/A, based on the comment line in the individual SED files?

[danielsf]

Yes, you can just multiply by the fluxnorm factor appropriate to the component.

Note: the LSST bandpass throughputs have evolved since the database was created. In order to get near exact agreement with the catalog, you will have to use the throughputs as they exist in commit 3ed95bd of this github repository

https://github.com/lsst/throughputs

[danielsf]

Also note that the [u,g,r,i,z,y]_ab magnitudes in the database neglect the AGN contribution (this is just based on a similar validation I did last week)

[jmeyers314]

I looked at reproducing the CatSim magnitudes from the SEDs/extinction/normalizations a few years ago. The agreement at the time is in the following figure:

Pretty good, but not exact. At the time I chalked this up to evolution of the bandpasses since the catalog was created.

However, I seem to remember an earlier offline conversation with @dkirkby that the SEDs library may have also evolved (at least for stars) since I last queried CatSim.

[danielsf]

Stars have evolved (mostly we changed the wavelength grid at which we keep the SEDs). Galaxies should not have been touched the last two or three years.

[danielsf]

@dkirkby Am I correct that you ultimately want a catalog of galaxies with individual bulge, disk, and agn magnitudes in each of the LSST bands?

[dkirkby]

That's the near-term goal, yes, to improve on my current assumption that the bulge/disk/agn proportions are the same in all bands. However, I ultimately want to be able to calculate magnitudes of all components in arbitrary bands, e.g., WFIRST. I already have the SED to magnitude part under control (using specsim) so I just need to be able to calculate SEDs for each component.

[dkirkby]

On the topic of extinction, the schema says for, e.g. ext_model_b:

Extinction model identifier ('ccm')

I guess ccm refers to Cardelli, Clayton & Mathis (ApJ, 345, 245, 1989), but this appears to be Milky Way (not host galaxy) extinction, so shouldn't it depend on the (ra,dec) of an observation, which isn't fixed for a catalog object because of the tiling?

[danielsf]

Okay. We already have many tools in CatSim for querying our database, loading the SEDs, integrating them over bandpasses (Bryce Kalmbach recently added WFIRST, Hipparcos, and PanStarrs filters to our throughputs repository). If you'd rather not deal with the trouble of querying our database and parsing its contents "by hand," let me know, and I can show you how to do all of this in the CatSim framework.

[danielsf]

The rv_d, rv_b etc. parameters are for defining a dust extinction model (that is CCM-like) inside the host galaxy. If you want to further apply Milky Way extinction on top of that, you need to calculated the relevant dust parameters based on the galaxy's RA, Dec

[dkirkby]

I am using a preprocessed 1 sq.deg. of CatSim to insulate users entirely from the database layer, but
I am willing to try out the CatSim framework if you think it is ready for wider distribution. What dependencies would that pull in? Where should I start in the docs? Will you be in Tucson next week?

[danielsf]

I will be in Tucson.

The tools I describe exist entirely in the code that you get when you install the LSST Simulations stack.

https://confluence.lsstcorp.org/display/SIM/Catalogs+and+MAF

The best tutorial on how CatSim works is here

https://github.com/uwssg/LSST-Tutorials/blob/master/CatSim/CatSimTutorial_SimulationsAHM_1503.ipynb

I will draw up an iPython notebook explaining how to do what you want and send it to you tomorrow.

[dkirkby]

That's 28 packages, including boost, just to read the SED text files in sims_sed_library ! I'm interested to learn how to do this, but not sure I want to pass this on to users.

I think my next step should be to replace the current dbquery script with equivalent code using the LSST Sims Stack, since users do not normally run this.