Public Data Access Overview / Discussion Forum

In the API Cookbook you show (e.g. Task 2) an example of a search_query string with boolean expression: [search_query = "?massgt=" + str(mass_min) + "&masslt=" + str(mass_max)]. My question is: which is the syntax used to construct these queries? For instance, which is the syntax one should use to query by the Barro et al. (2013) compactness criterion:
search_query = "?(mass_stars1e10/0.704)/(halfmassrad_stars/((z+1)0.704))^1.5gt=" + str(barro13) + "&mass_starsgt=" + str(mass_min) NOTE that this "search_query" does not work... it is just a reference for the kind of operations needed. Many thanks in advance Ignacio

Hi Ignacio,

This is described at the API documentation under "Search and cutout requests".

But, this will not cover such a "diagonal" search that you were after. Best option, is to simply download the group catalog (for the redshift and simulation you want), then e.g.

gc = il.groupcat.loadSubhalos(basePath, snapNum, fields=['SubhaloMassType','SubhaloHalfmassRadType'])

mass_stars = gc['SubhaloMassType'][:,4] * 1e10 / little_h # Msun
rad_stars = gc['SubhaloHalfmassRadType'][:,4] / (1+z) / little_h # pkpc

w = np.where( (mass_stars/rad_stars**1.5 > barro13) & (mass_stars > mass_min) )

Or, if you really want to do this on the web API, you could (i) pick a small bin of stellar mass, (ii) calculate the restriction on halfmassrad_stars as a single scalar number appropriate for that bin and redshift, (iii) do a search of e.g. &halfmassrad_stars__gt=value&mass_stars__gt=minmass&mass_stars__lte=maxmass. You could do this in a loop over mass bins and combine the result.

Also you might want to look at Wellons+ (2015), probably you have seen already, Sec 3.1 describes a Barro selection on Illustris and some details of relevance.

Thanks a lot, Dylan. That's what I needed. Very efficient service!