A study of purely astrometric selection of extragalactic point sources with Gaia

Abstract

Selection of extragalactic point sources, e.g. QSOs, is often hampered by significant selection effects causing existing samples to have rather complex selection functions. We explore whether a purely astrometric selection of extragalactic point sources, e.g. QSOs, is feasible with the ongoing Gaia mission. Such a selection would be interesting as it would be unbiased in terms of colours of the targets and hence would allow selection also with colours in the stellar sequence. We have analyzed a total of 18 representative regions of the sky by using GUMS, the simulator prepared for ESAs Gaia mission, both in the range of $12\le G\le 20$ mag and $12\le G\le 18$ mag. For each region we determine the density of apparently stationary stellar sources, i.e. sources for which Gaia cannot measure a significant proper motion. The density is contrasted with the density of extragalactic point sources, e.g. QSOs, in order to establish in which celestial directions a pure astrometric selection is feasible. When targeting regions at galactic latitude $|b|\ge 30^{\mathrm{o}}$ the ratio of QSOs to apparently stationary stars is above 50\% and when observing towards the poles the fraction of QSOs goes up to about $\sim 80$\%. We show that the proper motions from the proposed Gaia successor mission in about 20 years would dramatically improve these results at all latitudes. Detection of QSOs solely from zero proper motion, unbiased by any assumptions on spectra, might lead to the discovery of new types of QSOs or new classes of extragalactic point sources.

arXiv comment4 pages, 4 figures, sent in and accepted for publishing to A&A

References in corpus (10)

• Science performance of Gaia, ESA's space-astrometry mission
• The Sloan Digital Sky Survey quasar catalog: ninth data release
• Efficient Photometric Selection of Quasars from the Sloan Digital Sky Survey: 100,000 z<3 Quasars from Data Release One
• Gaia Universe Model Snapshot : A statistical analysis of the expected contents of the Gaia catalogue
• A synthetic view on structure and evolution of the Milky Way
• VLBI measurement of the secular aberration drift
• Mining for Dust in Type 1 Quasars
• Optical/near-infrared selection of red QSOs: Evidence for steep extinction curves towards galactic centers?
• Overview and stellar statistics of the expected Gaia Catalogue using the Gaia Object Generator
• The High A(V) Quasar Survey: Reddened quasi-stellar objects selected from optical/near-infrared photometry - II

Cited by in corpus (11)

• Gaia Data Release 3: The extragalactic content
• A quasar reddened by a sub-parsec sized, metal-rich and dusty cloud in a damped Lyman-alpha absorber at z=2.13
• The extended High A(V) Quasar Survey: Searching for dusty absorbers toward mid-infrared selected quasars
• Unidentified quasars among stationary objects from Gaia DR2
• A quasar hiding behind two dusty absorbers. Quantifying the selection bias of metal-rich, damped Lyman-alpha absorption systems
• Gaia-assisted selection of a quasar reddened by dust in an extremely-strong Damped Lyman-α Absorber at z=2.226
• Spectroscopic classification of a complete sample of astrometrically-selected quasar candidates using Gaia DR2
• Determining the fraction of reddened quasars in COSMOS with multiple selection techniques from X-ray to radio wavelengths
• Gaia-assisted discovery of a detached low-ionisation BAL quasar with very large ejection velocities
• Search for Quasar Pairs with $Gaia$ Astrometric Data. I. Method and Candidates
• On the Dusty Proximate Damped Lyman-α System toward Q2310-3358 at z = 2.40