Requirements for Twinkles

We are still in the process of planning the Simulation inputs for SN in TWINKLES 3. We are interested in keeping things somewhat realistic, but this is to be able to evaluate questions we want to in situations which are expected to arise (kind of like you would want to have support in regions of parameter space that are important if you plan on correcting things using importance sampling). We will have a set of galaxies (we can get stellar, halo masses, morphology in terms of sersic indices of 1 and 4 (ie., disk or bulge) in catsim, along with measures of size (half light radius, angle of axis.

We want to populate some of these galaxies with SN with known input parameters. These input parameters are:

matching of galactic hosts. Ie. Given a large set of galaxies at different redshifts, positions and other parameters, which of them are likely to host more SN? Don't know if this is coming out of EmpericiSN, if not we can use rates (or our own ideas of how many we want to do this). Then, given a set of galaxies and SN, can we match them up?
positional (redshift, ie. must match host, ra, dec must be relative to host and match orientation)
SALT parameters t0 (uniform), x0, x1, c, z

There are different levels at which we can use EmpericiSN It is possible to take the positional parameters (which are relatively more important here, and supply other parameters from external distributions) or do both for EmpericiSN.

In order to make progress, here are the steps I think we need:

[ ] Decide what are the smallest set of galaxy parameters for which EmpericiSN can make good predictions for SN. Which SN parameters ? Only positional, only SALT, both?
[ ] Let us say we do only positional parameters: What we need is to take the galaxy parameters as input (Here is the relevant schema) and return a distribution (or rather samples) of SN positions. Notice that this has a bulge (disk) ra, dec, and bulge (disk) semi-major axis. along with sersic indices of both the components and position angle of the disk. Given these parameters, we get a surface brightness of the galaxy. Can you output a set of SN sample positions for each of these? Can you output the probability of a SN to occupy these hosts during a fixed time interval? This will mean outputting a radius (which I think you already have) and an angle.
[ ] Plot a comparison of the positions obtained this way to positions obtained by sampling the ellipse. Again, I think this comparison is important to demonstrate what EmpericiSN can do, and I would expect to see such (or some variation of this plot) in a paper trying to do what EmpericiSN is doing.

It might be ok even if we feel that the distribution is not terribly realistic (I don't know what the most realistic thing here is), what I want to know is what the distribution is like, and whether we have to add SN in some region to provide samples of SN in those kinds of areas.

The model is currently using the 10 permutations of ugriz colors, the position of the SN in the galaxy (in units of log(R/Re)), the redshift, and the local surface brightness at the location of the SN, which is calculated from either a deVaucouleurs profile or an exponential profile using the radius, the half-light radius, and the model flux from the SDSS host photometry. (It chooses whether to use an exponential or a deVaucouleurs profile based on which has a higher likelihood from the r-band model fit.) If catsim can give the fluxes and magnitudes in each band, an effective radius, a redshift, and either an exponential or de Vaucouleurs designation, empiriciSN should be able to calculate SN parameters for that galaxy now.

Sampling a likely SN is done in two stages: First, use the redshift and galaxy colors to extract a likely position, then calculate the local surface brightness at that location. Then use all the parameters to condition the model and sample x0, x1, and c. So in the end, it will provide the 3 SALT2 parameters and an angular separation from the host nucleus for a given host.

I was discussing with Phil, and I think these 4 things are what we want empiriciSN to provide to the user. Once the user (e.g., Twinkles, or someone else) has the SALT2 parameters and a separation, they can simulate a light curve. As far as placing it in the galaxy is concerned (vis-a-vis position angle, placing it in a disk vs. bulge, etc.), we are thinking this should fall on the user. We can still help to get this figured out for Twinkes, I just think that including the angles and axis ratios and such in EmpiriciSN will complicate things, and I want it to be easy to calculate the SN parameters.

As far as which galaxies are more likely to host SNe and things like that, we designed empiriciSN from the beginning not to be concerned with that. The idea here is that the user can say "I have this galaxy, with these parameters" and empiriciSN can give the user likely SN parameters for that galaxy, using the XDGMM model that's been fit to the SDSS and SNLS data. So we didn't want to incorporate things like looking at a galaxy catalog and selecting likely hosts based on some rate model, or anything like that.

I guess the primary question would be, can catsim provide the parameters discussed in my first paragraph above? If so, I don't think too much additional work is needed on empiriciSN itself, though some additional work may be required to build it into Twinkles. Otherwise, we may need to change the datasets being used to train the model, since the SDSS photometry doesn't provide things like bulge-disk decompositions.

Oh also, what is the timeframe needed to incorporate this into TWINKLES 3? The amount of time we have may decide the scope of what we want to do.

One tiny follow-up: I have in mind that if you get the radial separation of the SN from empiriciSN, you could plausibly treat it as a circularized radius, which you then convert to an actual (R,phi) position in polar coordinates taking the axis ratio and orientation of the target host into account.

In practice I would draw a uniform random deviate in the range 0 to 2pi and assign that to phi, the azimuthal angle between the SN position relative to the host center measured counter-clockwise from the host major axis. Then I would use the host's axis ratio q = b/a to stretch one cartesian axis and squash the other to give the radial coordinate R that corresponds to the circularized radial position r that empiriSN provides. I think this means that we want R such that

(R * cos(phi) / a)**2  + (R * sin(phi) / b)**2 = 1

for an elliptically symmetric galaxy, where

a * b = r**2

and

q = b / a

There might be a better way of making the correspondence between r**2 and a and b. Re-arranging this, though, I get

R = r / sqrt( q * cos(phi)**2 + sin(phi)**2 / q)

So if phi is zero, the SN is on the major axis and R is bigger than r by a factor of 1/sqrt(q), and when phi is pi/2, the SN is on the minor axis and R is smaller than r by a factor of sqrt(q).

On Sun, Sep 18, 2016 at 9:18 PM, Tom Holoien notifications@github.com wrote:

Oh also, what is the timeframe needed to incorporate this into TWINKLES 3? The amount of time we have may decide the scope of what we want to do.

— You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub https://github.com/tholoien/empiriciSN/issues/22#issuecomment-247908988, or mute the thread https://github.com/notifications/unsubscribe-auth/AArY95rV-KmGGizrIgNyVfaN-DgT79lnks5qrg0HgaJpZM4KAEU5 .

tholoien / empiriciSN

Requirements for Twinkles #22