Quasar catalogue for the astrometric calibration of the forthcoming ILMT survey

TL;DR

This paper presents a catalogue of 6738 quasars with precise coordinates suitable for astrometric calibration of the upcoming ILMT survey, leveraging Gaia-DR2 data to ensure accuracy and facilitate future quasar variability studies.

Contribution

The paper provides the first comprehensive quasar catalogue specifically tailored for ILMT astrometric calibration, with cross-matched Gaia-DR2 data ensuring high positional accuracy.

Findings

Catalogue contains 6738 quasars suitable for ILMT calibration.

Quasars in the ILMT stripe have proper motion < 20 mas/yr.

Quasars have parallax < 10 mas.

Abstract

Quasars are ideal targets to use for astrometric calibration of large scale astronomical surveys as they have negligible proper motion and parallax. The forthcoming 4-m International Liquid Mirror Telescope (ILMT) will survey the sky that covers a width of about 27 arcminute. To carry out astrometric calibration of the ILMT observations, we aimed to compile a list of quasars with accurate equatorial coordinates and falling in the ILMT stripe. Towards this, we cross-correlated all the quasars that are known till the present date with the sources in the Gaia-DR2 catalogue, as the Gaia-DR2 sources have position uncertainties as small as a few milli arcsec (mas). We present here the results of this cross-correlation which is a catalogue of 6738 quasars that is suitable for astrometric calibration of the ILMT fields. In this work, we present this quasar catalogue. This catalogue of quasars can also be used to study quasar variability over diverse time scales when the ILMT starts its observations. While preparing this catalogue, we also confirmed that quasars in the ILMT stripe have proper motion and parallax lesser than 20 mas/yr and 10 mas, respectively.