Completeness of the <i>Gaia</i>-verse – IV. The astrometry spread function of <i>Gaia</i> DR2

Everall, Andrew; Boubert, Douglas; Koposov, S. E.; Smith, Leigh C.; Holl, B.

doi:10.1093/mnras/stab041

Cited by 32 publications

(19 citation statements)

References 69 publications

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“…Here the selection effect may be more significant, but it should be possible to model this with publicly available tools (e.g. Boubert et al 2021;Everall et al 2021).…”

Section: Discussionmentioning

confidence: 99%

Gaia Early Data Release 3

Seabroke

Fabricius

Teyssier

et al. 2021

A&A

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Context. Gaia’s Early Third Data Release (EDR3) does not contain new radial velocities because these will be published in Gaia’s full third data release (DR3), expected in the first half of 2022. To maximise the usefulness of EDR3, Gaia’s second data release (DR2) sources (with radial velocities) are matched to EDR3 sources to allow their DR2 radial velocities to also be included in EDR3. This presents two considerations: (i) a list of 70 365 sources with potentially contaminated DR2 radial velocities has been published; and (ii) EDR3 is based on a new astrometric solution and a new source list, which means sources in DR2 may not be in EDR3. Aims. The two aims of this work are: (i) investigate the list in order to improve the DR2 radial velocities being included in EDR3 and to avoid false-positive hypervelocity candidates; and (ii) match the DR2 sources (with radial velocities) to EDR3 sources. Methods. Thetwo methods of this work are: (i) unpublished, preliminary DR3 radial velocities of sources on the list, and high-velocity stars not on the list, are compared with their DR2 radial velocities to identify and remove contaminated DR2 radial velocities from EDR3; and (ii) proper motions and epoch position propagation is used to attempt to match all sources with radial velocities in DR2 to EDR3 sources. The comparison of DR2 and DR3 radial velocities is used to resolve match ambiguities. Results. EDR3 contains 7 209 831 sources with a DR2 radial velocity, which is 99.8% of sources with a radial velocity in DR2 (7 224 631). 14 800 radial velocities from DR2 are not propagated to any EDR3 sources because (i) 3871 from the list are found to either not have a DR3 radial velocity or it differs significantly from its DR2 value, and five high-velocity stars not on the list are confirmed to have contaminated radial velocities, in one case because of contamination from the non-overlapping Radial Velocity Spectrometer windows of a nearby, bright star; and (ii) 10 924 DR2 sources could not be satisfactorily matched to any EDR3 sources, so their DR2 radial velocities are also missing from EDR3. Conclusions. The reliability of radial velocities in EDR3 has improved compared to DR2 because the update removes a small fraction of erroneous radial velocities (0.05% of DR2 radial velocities and 5.5% of the list). Lessons learnt from EDR3 (e.g. bright star contamination) will improve the radial velocities in future Gaia data releases. The main reason for radial velocities from DR2 not propagating to EDR3 is not related to DR2 radial velocity quality. It is because the DR2 astrometry is based on one component of close binary pairs, while EDR3 astrometry is based on the other component, which prevents these sources from being unambiguously matched.

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“…Here the selection effect may be more significant, but it should be possible to model this with publicly available tools (e.g. Boubert et al 2021;Everall et al 2021).…”

Section: Discussionmentioning

confidence: 99%

Gaia Early Data Release 3

Seabroke

Fabricius

Teyssier

et al. 2021

A&A

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“…3 can be derived from first principles, or scaled empirically: for Gaia EDR3 one finds G r ≈ 22. Of course, it is likely, and in the case of Gaia known, that σ , and by extension S/N and G r , vary distinctly with position on the sky (Lindegren et al 2020;Everall et al 2021). In that case, the condition of Eq.…”

Section: Data Quality Cuts As Part Of the Selection Functionmentioning

confidence: 97%

Selection Functions in Astronomical Data Modeling, with the Space Density of White Dwarfs as Worked Example

Rix,

Hogg,

Boubert

et al. 2021

Preprint

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Statistical studies of astronomical data sets, in particular of cataloged properties for discrete objects, are central to astrophysics. One cannot model those objects' population properties or incidences without a quantitative understanding of the conditions under which these objects ended up in a catalog or sample, the sample's selection function. As systematic and didactic introductions to this topic are scarce in the astrophysical literature, we aim to provide one, addressing generically the following questions: What is a selection function? What arguments q should a selection function depend on? Over what domain must a selection function be defined? What approximations and simplifications can be made? And, how is a selection function used in 'modelling' ? We argue that volume-complete samples, with the volume drastically curtailed by the faintest objects, reflect a highly sub-optimal selection function that needlessly reduces the number of bright and usually rare objects in the sample. We illustrate these points by a worked example, deriving the space density of white dwarfs (WD) in the Galactic neighbourhood as a function of their luminosity and Gaia color, Φ 0 (M G , (B − R)) in [mag −2 pc −3 ]. We construct a sample C of 10 5 presumed WDs through straightforward selection cuts on the Gaia EDR3 catalog, in magnitude, color, parallax, and astrometric fidelity, q = (G, (B −R), , p af ). We then combine a simple model for Φ 0 with the effective survey volume derived from this selection function S C (q) to derive a detailed estimate of Φ 0 (M G , (B − R)) is robust against the detailed choices for S C (q). This resulting white dwarf luminosity-color function Φ 0 (M G , (B − R)) differs dramatically from the initial number density distribution in the luminosity-color plane: by orders of magnitude in density and by four magnitudes in density peak location.

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“…Everall (priv. comm., based on a similar method described in Everall et al 2021). For the precision at the end of the nominal 5-year mission, we used the estimated end-of-mission precision as described in Sec.…”

Section: The Astrometric Signalmentioning

confidence: 99%

Uncovering astrometric black hole binaries with massive main-sequence companions with Gaia

Janssens,

Shenar,

Sana

et al. 2021

Preprint

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Context. In the era of gravitational wave astrophysics and precise astrometry of billions of stellar sources, the hunt for compact objects is more alive than ever. Rarely seen massive binaries with a compact object are a crucial phase in the evolution towards compact object mergers. With the upcoming Gaia data release (DR3), the first Gaia astrometric orbital solutions for binary sources will become available, potentially revealing many such binaries. Aims. We investigate how many black holes (BH) with massive main-sequence dwarf companions (OB+BH binaries) are expected to be detected as binaries in Gaia DR3 and at the end of the nominal 5-yr mission. We estimate how many of those are identifiable as OB+BH binaries and we discuss the distributions of the masses of both components as well as of their orbital periods. We also explore how different BH-formation scenarios affect these distributions. Methods. We apply observational constraints to tailored models for the massive star population, which assume a direct collapse and no kick upon BH formation, to estimate the fraction of OB+BH systems that will be detected as binaries by Gaia, and consider these the fiducial results. These OB+BH systems follow a distance distribution according to that of the second Alma Luminous Star catalogue (ALS II). We use a method based on astrometric data to identify binaries with a compact object and investigate how many of the systems detected as binaries are identifiable as OB+BH binaries. Different scenarios for BH natal kicks and supernova mechanisms are explored and compared to the fiducial results. Results. In the fiducial case we conservatively estimate that 77% of the OB+BH binaries in the ALS II catalogue will be detected as binaries in DR3, of which 89% will be unambiguously identifiable as OB+BH binaries. At the end of the nominal 5-yr mission, the detected fraction will increase to 85%, of which 82% will be identifiable. The 99% confidence intervals on these fractions are of the order of a few percent. These fractions become smaller for different BH-formation scenarios. Conclusions. Assuming direct collapse and no natal kick, we expect to find around 190 OB+BH binaries with Gaia in DR3 among the sources in ALS II, which increases the known sample of OB+BH binaries by more than a factor of 20, covering an uncharted parameter space of long-period binaries (10 P 1000 d). Our results further show that the size and properties of the OB+BH population that is identifiable using Gaia DR3 will contain crucial observational constraints to improve our understanding of BH formation. An additional ∼5 OB+BH binaries could be identified at the end of the nominal 5-yr mission, which are expected to have either very short (P 10 d) or long periods (P 1000 d).

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Completeness of the Gaia-verse – IV. The astrometry spread function of Gaia DR2

Cited by 32 publications

References 69 publications

Gaia Early Data Release 3

Gaia Early Data Release 3

Selection Functions in Astronomical Data Modeling, with the Space Density of White Dwarfs as Worked Example

Uncovering astrometric black hole binaries with massive main-sequence companions with Gaia

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