SCOTCH Catalogue and Associated Data Files

The Simulated Catalogue of Optical Transients and Correlated Hosts (SCOTCH)

This is a static data release for SCOTCH, a catalogue containing 5 million explosive transients and the properties of their realistically-associated host galaxies. The catalogue consists of 13 transient classes: 3 SN Ia classes (Ia, Iax, Ia 91bg-like), 2 H-rich core-collapse classes (II, IIn), 5 H-poor classes (Ib, Ic, Ic-BL, IIb, SLSN-I), and 3 non-SN classes (AGN, KN, TDE). The parameters available for each transient and host galaxy pair are outlined in SCOTCH_schema.md.

Details on the methodology used to construct these data can be found in Lokken, Gagliano, et al. (2023) and the associated repo for this work is located at https://github.com/LSSTDESC/transient-host-sims. This data release consists of three types of files:

SCOTCH Catalogues (scotch_z3.hdf5, scotch_zlim.hdf5):

1. scotch_Z3.hdf5: This is a catalogue of 5M transients and host properties for 13 transient classes within \(0<z<3\). The relative rates between classes are not realistic. The catalogue consists of two main tables: the Transient Table and the Host Table. The Transient Table contains true, top-of-the-galaxy light curves in Vera Rubin Observatory LSST passbands (ugrizY) for each of the simulated transients. The Host Table contains information about the host galaxies of each transient, including apparent magnitude in LSST passbands, shape, star-formation rate, and stellar mass. The two tables are linked and can be cross-matched by TID, the unique integer ID of a simulated transient; and GID, the unique integer ID of each host galaxy.
2. scotch_ZLIM.hdf5: This catalogue consists of 5M events simulated in SNANA with an upper redshift limit of \(z<0.8\). More events are simulated at lower redshift than SCOTCH_Z3.hdf5, so this catalogue might be more valuable for low-z studies (e.g., of KNe).

The full organization of the catalogue is shown in Figure B1 of our paper, and we provide a list of the schema as Tables 4 and 5. Tutorials for querying the database for specific science cases are available at https://github.com/LSSTDESC/transient-host-sims/blob/main/notebooks/SCOTCH_walkthroughs.ipynb.

If all you want are the data products, then you're done! If you're interested in generating new simulations or are just curious to learn about how we simulated realistic host galaxy correlations, check out the two types of supplemental data files:

HOSTLIBs (*_GHOST.HOSTLIB.gz):

The libraries of candidate CosmoDC2 host galaxies to which simulated transients are matched. These files can be used to rerun SNANA for unique survey strategies (footprint, cadence, etc), and were generated using https://github.com/LSSTDESC/transient-host-sims/blob/main/notebooks/Hostlib_Constructor.ipynb. The transients we've simulated use one of five HOSTLIBs: SNIa, SNIbc, SNII, UNMATCHED, and UNMATCHED_KN. The first three of these HOSTLIBs encode correlations from the GHOST catalogue (Gagliano+2021). The last two contain representative subsets of CosmoDC2 (no explicit host correlations), and the last file contains galaxies whose photometry has been slightly modified to introduce realistic scatter into the color-color distribution of matched KN host galaxies.

The data in these files roughly match the final galaxy properties listed in the SCOTCH catalogue, with one exception: NBR_LIST, the cosmoDC2 IDs of other galaxies in that HOSTLIB within a 10'' radius of a given galaxy. This is useful for calculating the directional light radius (Gupta+2016) to each transient and realistically mis-associating some hosts (as will be done for ELAsTiCC).

WGTMAPs (*_GHOST.WGTMAP.gz):

The Probability Density Functions (PDFs) describing the probability of a class of transient to occur in a galaxy of certain properties. These can be used as input to rerun SNANA, and were generated using the script https://github.com/LSSTDESC/transient-host-sims/blob/main/scripts/weightmap_generator.py. The galaxy properties over which a PDF is defined is variable, and the PDF of each class has been constructed to encode subtler correlations than are captured in GHOST and known correlations with derived properties (star-formation rate, metallicity, and stellar mass, none of which are estimated in GHOST). Host matching in SNANA is done from the HOSTLIB conditioned on the WGTMAP distributions. File schema is

x y z WGT SNMAGSHIFT

Where xyz defines a point along a three-dimensional, uniformly-spaced parameter space of host galaxy properties, WGT defines the weight to assign a galaxy with those properties in matching, and SNMAGSHIFT describes the magnitude offset to attribute to transients matched to a galaxy with these properties (this SNANA functionality is not used). Interpolation is used to determine the weights for HOSTLIB galaxies with properties between grid points.

Questions? Comments? Please reach out to Martine Lokken (mlokken394@gmail.com) or Alex Gagliano (gaglian2@illinois.edu).