The Gaia hybrid catalog: a leverage to find Galactic structures

Abstract

The ongoing Gaia mission will undertake an astrometric, photometric and spectroscopic survey of the Galaxy. The Gaia consortium will use Gaia-only data to classify objects and to estimate their individual astrophysical parameters. However, one can achieve more reliable estimates of stellar parameters by combining Gaia data with data from other spectroscopic and photometric surveys.

The Gaia “hybrid catalog” project will provide an exquisite value-added catalogs of astrophysical parameters for Gaia targets by taking into account the “obvious” non-Gaia data (e.g., SDSS, WISE, Pan-STARRS, APOGEE, PPMXL, SDSS, 2MASS, Tycho). By including spectroscopic indicators of metallicity when available, or infrared photometry, we can reduce the degeneracies between extinction and temperature and improve the estimation of metallicity and surface gravity.

However, the creation of such catalogs comes with significant challenges. First the cross-matching of catalogs with various selection functions, or photometric depths. Second, we must optimize the data analysis to produce the most accurate information given a specific science goal. Finally, the construction of such catalogs will require significant computation power. The current plan is to do this using the local resources at the Max-Planck-Institut für Astronomie, and then each catalog will go through validation and integration processes to finally be released as part of the value-added Gaia data products. From these challenges, it is clear that hybrid catalogs will not be a copy of the Gaia catalog but must be adapted to support very specific science questions.

In the poster we presented, we details in particular two applicationsof the Gaia hybrid catalogs. First, we considered the addition of WISEdata to the Gaia information. The WISE data enable us to constrainnot only the amount of extinction through the addition of infrareddata, but also allow us to better classify certain spectral types. Forinstance, from the addition of the WISE filters, one can select theOxygen-rich Asymptotic Giant Branch (AGBs) stars to find spatialsubstructures with particular interstellar medium properties. Breaking through the distance-extinction degeneracies will also help finding largescale structures in the disk such as streams or spiral arms, especiallywhen combined with age or metallicity selections for instance.

Second, we presented one aspect of the hybrid catalogs dedicatedto support the analysis of star clusters. Star clusters are not onlycalibrators of stellar evolution models but also references to study starformation in general. We presented one future outcome of the hybridcatalogs, in which we provide for known star clusters, an assessment ofstellar memberships based on a combination of phase-space, and colormagnitudedistribution fitting. In this application, the assumption thata cluster is a “simple” population provides a significant advantage whenderiving individual star properties. Eventually one can imagine thisapplication can be extended to stellar streams.

Hybrid catalogs are meant to be provided along with the Gaia datareleases, and will offer a tremendous source of validation for the GaiaData Processing.