scholarly journals Completeness of the Gaia verse II: what are the odds that a star is missing from Gaia DR2?

2020 ◽  
Vol 497 (4) ◽  
pp. 4246-4261 ◽  
Author(s):  
Douglas Boubert ◽  
Andrew Everall
Keyword(s):  
Milky Way ◽  
Magellanic Clouds ◽  
Probability Of Detection ◽  
Easy Access ◽  
Selection Function ◽  
G 21 ◽  
Data Release ◽  
Many Sources ◽  
Gaia Dr2 ◽  
Python Package

ABSTRACT The second data release of the Gaia mission contained astrometry and photometry for an incredible 1692 919 135 sources, but how many sources did Gaiamiss and where do they lie on the sky? The answer to this question will be crucial for any astronomer attempting to map the Milky Way with Gaia DR2. We infer the completeness of Gaia DR2 by exploiting the fact that it only contains sources with at least five astrometric detections. The odds that a source achieves those five detections depends on both the number of observations and the probability that an observation of that source results in a detection. We predict the number of times that each source was observed by Gaia and assume that the probability of detection is either a function of magnitude or a distribution as a function of magnitude. We fit both these models to the 1.7 billion stars of Gaia DR2, and thus are able to robustly predict the completeness of Gaia across the sky as a function of magnitude. We extend our selection function to account for crowding in dense regions of the sky, and show that this is vitally important, particularly in the Galactic bulge and the Large and Small Magellanic Clouds. We find that the magnitude limit at which Gaiais still 99 per cent complete varies over the sky from G = 18.9 to fainter than G = 21. We have created a new python package selectionfunctions (https://github.com/gaiaverse/selectionfunctions) which provides easy access to our selection functions.

scholarly journals Characterizing the Gaia radial velocity sample selection function in its native photometry

2020 ◽  
Vol 500 (1) ◽  
pp. 397-409
Author(s):  
Jan Rybizki ◽  
Hans-Walter Rix ◽  
Markus Demleitner ◽  
Coryn A L Bailer-Jones ◽  
William J Cooper
Keyword(s):  
Radial Velocity ◽  
Milky Way ◽  
Sample Selection ◽  
Small Scale ◽  
Apparent Magnitude ◽  
Selection Function ◽  
Source Density ◽  
Dimensional Phase Space ◽  
Data Release ◽  
Gaia Dr2

ABSTRACT The Gaia Data Release 2 (DR2) radial velocity sample (GDR2RVS), which provides six-dimensional phase-space information on 7.2 million stars, is of great value for inferring properties of the Milky Way. Yet a quantitative and accurate modelling of this sample is hindered without knowledge and inclusion of a well-characterized selection function. Here we derive the selection function through estimates of the internal completeness, i.e. the ratio of GDR2RVS sources compared to all Gaia DR2 sources (GDR2all). We show that this selection function or ‘completeness’ depends on basic observables, in particular the apparent magnitude GRVS and colour G − GRP, but also on the surrounding source density and on sky position, where the completeness exhibits distinct small-scale structure. We identify a region of magnitude and colour that has high completeness, providing an approximate but simple way of implementing the selection function. For a more rigorous and detailed description we provide python code to query our selection function, as well as tools and adql queries that produce custom selection functions with additional quality cuts.

scholarly journals seestar: Selection functions for spectroscopic surveys of the Milky Way

2020 ◽  
Vol 493 (2) ◽  
pp. 2042-2058 ◽  
Author(s):  
Andrew Everall ◽  
Payel Das
Keyword(s):  
Milky Way ◽  
Estimation Method ◽  
Likelihood Estimation ◽  
Bayesian Framework ◽  
Apparent Magnitude ◽  
Selection Function ◽  
Data Release

ABSTRACT Selection functions are vital for understanding the observational biases of spectroscopic surveys. With the wide variety of multiobject spectrographs currently in operation and becoming available soon, we require easily generalizable methods for determining the selection functions of these surveys. Previous work, however, has largely been focused on generating individual, tailored selection functions for every data release of each survey. Moreover, no methods for combining these selection functions to be used for joint catalogues have been developed. We have developed a Poisson likelihood estimation method for calculating selection functions in a Bayesian framework, which can be generalized to any multiobject spectrograph. We include a robust treatment of overlapping fields within a survey as well as selection functions for combined samples with overlapping footprints. We also provide a method for transforming the selection function that depends on the sky positions, colour, and apparent magnitude of a star to one that depends on the galactic location, metallicity, mass, and age of a star. This ‘intrinsic’ selection function is invaluable for chemodynamical models of the Milky Way. We demonstrate that our method is successful at recreating synthetic spectroscopic samples selected from a mock galaxy catalogue.

scholarly journals The Pisces Plume and the Magellanic wake

2019 ◽  
Vol 488 (1) ◽  
pp. L47-L52 ◽  
Author(s):  
Vasily Belokurov ◽  
Alis J Deason ◽  
Denis Erkal ◽  
Sergey E Koposov ◽  
Julio A Carballo-Bello ◽  
...  
Keyword(s):  
Milky Way ◽  
Galactic Halo ◽  
Magellanic Clouds ◽  
Line Of Sight ◽  
Rr Lyrae Stars ◽  
Rr Lyrae ◽  
Data Release ◽  
Magellanic Stream ◽  
Lyrae Stars

ABSTRACT Using RR Lyrae stars in the Gaia Data Release 2 and Pan-STARRS1 we study the properties of the Pisces overdensity, a diffuse substructure in the outer halo of the Milky Way. We show that along the line of sight, Pisces appears as a broad and long plume of stars stretching from 40 to 110 kpc with a steep distance gradient. On the sky Pisces’s elongated shape is aligned with the Magellanic Stream. Using follow-up VLT FORS2 spectroscopy, we have measured the velocity distribution of the Pisces candidate member stars and have shown it to be as broad as that of the Galactic halo but offset to negative velocities. Using a suite of numerical simulations, we demonstrate that the structure has many properties in common with the predicted behaviour of the Magellanic wake, i.e. the Galactic halo overdensity induced by the infall of the Magellanic Clouds.

scholarly journals THE MASS DISTRIBUTION AND ASSEMBLY OF THE MILKY WAY FROM THE PROPERTIES OF THE MAGELLANIC CLOUDS

2011 ◽  
Vol 743 (1) ◽  
pp. 40 ◽  
Author(s):  
Michael T. Busha ◽  
Philip J. Marshall ◽  
Risa H. Wechsler ◽  
Anatoly Klypin ◽  
Joel Primack
Keyword(s):  
Mass Distribution ◽  
Milky Way ◽  
Magellanic Clouds

scholarly journals VVV DR1: The first data release of the Milky Way bulge and southern plane from the near-infrared ESO public survey VISTA variables in the Vía Láctea

2012 ◽  
Vol 537 ◽  
pp. A107 ◽  
Author(s):  
R. K. Saito ◽  
M. Hempel ◽  
D. Minniti ◽  
P. W. Lucas ◽  
M. Rejkuba ◽  
...  
Keyword(s):  
Near Infrared ◽  
Milky Way ◽  
Public Survey ◽  
Data Release

scholarly journals Local disc model in view of Gaia DR1 and RAVE data

2018 ◽  
Vol 620 ◽  
pp. A71 ◽  
Author(s):  
K. Sysoliatina ◽  
A. Just ◽  
I. Koutsouridou ◽  
E. K. Grebel ◽  
G. Kordopatis ◽  
...  
Keyword(s):  
Main Sequence ◽  
Galactic Plane ◽  
Formation Rate ◽  
Velocity Distribution Function ◽  
Initial Mass Function ◽  
Selection Function ◽  
Thin Disc ◽  
Disc Model ◽  
Starting Point ◽  
Data Release

Aims. We test the performance of the semi-analytic self-consistent Just-Jahreiß disc model (JJ model) with the astrometric data from the Tycho-Gaia Astrometric Solution (TGAS) sub-catalogue of the first Gaia data release (Gaia DR1), as well as the radial velocities from the fifth data release of the Radial Velocity Experiment survey (RAVE DR5). Methods. We used a sample of 19 746 thin-disc stars from the TGAS×RAVE cross-match selected in a local solar cylinder of 300 pc radius and 1 kpc height below the Galactic plane. Based on the JJ model, we simulated this sample via the forward modelling technique. First, we converted the predicted vertical density laws of the thin-disc populations into a mock sample. For this we used the Modules and Experiments in Stellar Astrophysics (MESA) Isochrones and Stellar Tracks (MIST), a star formation rate (SFR) that decreased after a peak at 10 Gyr ago, and a three-slope broken power-law initial mass function (IMF). Then the obtained mock populations were reddened with a 3D dust map and were subjected to the selection criteria corresponding to the RAVE and TGAS observational limitations as well as to additional cuts applied to the data sample. We calculated the quantities of interest separately at different heights above the Galactic plane, taking the distance error effects in horizontal and vertical directions into account separately. Results. The simulated vertical number density profile agrees well with the data. An underestimation of the stellar numbers begins at ∼800 pc from the Galactic plane, which is expected as the possible influence of populations from |z| > 1 kpc is ignored during the modelling. The lower main sequence (LMS) is found to be thinner and under-populated by 3.6% relative to the observations. The corresponding deficits for the upper main sequence (UMS) and red giant branch (RGB) are 6% and 34.7%, respectively. However, the intrinsic uncertainty related to the choice of stellar isochrones is ∼10% in the total stellar number. The vertical velocity distribution function f(|W|) simulated for the whole cylinder agrees to within 1σ with the data. This marginal agreement arises because the dynamically cold populations at heights < 200 pc from the Galactic plane are underestimated. We also find that the model gives a fully realistic representation of the vertical gradient in stellar populations when studying the Hess diagrams for different horizontal slices. We also checked and confirm the consistency of our results with the newly available second Gaia data release (DR2). Conclusions. Based on these results and considering the uncertainties in the data selection as well as the sensitivity of the simulations to the sample selection function, we conclude that the fiducial JJ model confidently reproduces the vertical trends in the thin-disc stellar population properties. Thus, it can serve as a starting point for the future extension of the JJ model to other Galactocentric distances.

scholarly journals A Gaia DR2 view of the open cluster population in the Milky Way

2018 ◽  
Vol 618 ◽  
pp. A93 ◽  
Author(s):  
T. Cantat-Gaudin ◽  
C. Jordi ◽  
A. Vallenari ◽  
A. Bragaglia ◽  
L. Balaguer-Núñez ◽  
...  
Keyword(s):  
Stellar Evolution ◽  
Milky Way ◽  
Galactic Plane ◽  
Galactic Disk ◽  
Open Cluster ◽  
Open Clusters ◽  
Number Of Clusters ◽  
History Of ◽  
Gaia Dr2

Context. Open clusters are convenient probes of the structure and history of the Galactic disk. They are also fundamental to stellar evolution studies. The second Gaia data release contains precise astrometry at the submilliarcsecond level and homogeneous photometry at the mmag level, that can be used to characterise a large number of clusters over the entire sky. Aims. In this study we aim to establish a list of members and derive mean parameters, in particular distances, for as many clusters as possible, making use of Gaia data alone. Methods. We compiled a list of thousands of known or putative clusters from the literature. We then applied an unsupervised membership assignment code, UPMASK, to the Gaia DR2 data contained within the fields of those clusters. Results. We obtained a list of members and cluster parameters for 1229 clusters. As expected, the youngest clusters are seen to be tightly distributed near the Galactic plane and to trace the spiral arms of the Milky Way, while older objects are more uniformly distributed, deviate further from the plane, and tend to be located at larger Galactocentric distances. Thanks to the quality of Gaia DR2 astrometry, the fully homogeneous parameters derived in this study are the most precise to date. Furthermore, we report on the serendipitous discovery of 60 new open clusters in the fields analysed during this study.

scholarly journals Gaia DR2 proper motions of dwarf galaxies within 420 kpc

2018 ◽  
Vol 619 ◽  
pp. A103 ◽  
Author(s):  
T. K. Fritz ◽  
G. Battaglia ◽  
M. S. Pawlowski ◽  
N. Kallivayalil ◽  
R. van der Marel ◽  
...  
Keyword(s):  
Milky Way ◽  
Dwarf Galaxies ◽  
High Mass ◽  
Proper Motions ◽  
Proper Understanding ◽  
Satellite Problem ◽  
Cosmological Context ◽  
Good Consistency ◽  
Gaia Dr2 ◽  
Limited Accuracy

A proper understanding of the Milky Way (MW) dwarf galaxies in a cosmological context requires knowledge of their 3D velocities and orbits. However, proper motion (PM) measurements have generally been of limited accuracy and are available only for more massive dwarfs. We therefore present a new study of the kinematics of the MW dwarf galaxies. We use the Gaia DR2 for those dwarfs that have been spectroscopically observed in the literature. We derive systemic PMs for 39 galaxies and galaxy candidates out to 420 kpc, and generally find good consistency for the subset with measurements available from other studies. We derive the implied Galactocentric velocities, and calculate orbits in canonical MW halo potentials of low (0.8 × 1012 M⊙) and high mass (1.6 × 1012 M⊙). Comparison of the distributions of orbital apocenters and 3D velocities to the halo virial radius and escape velocity, respectively, suggests that the satellite kinematics are best explained in the high-mass halo. Tuc III, Crater II, and additional candidates have orbital pericenters small enough to imply significant tidal influences. Relevant to the missing satellite problem, the fact that fewer galaxies are observed to be near apocenter than near pericenter implies that there must be a population of distant dwarf galaxies yet to be discovered. Of the 39 dwarfs: 12 have orbital poles that do not align with the MW plane of satellites (given reasonable assumptions about its intrinsic thickness); 10 have insufficient PM accuracy to establish whether they align; and 17 satellites align, of which 11 are co-orbiting and (somewhat surprisingly, in view of prior knowledge) 6 are counter-orbiting. Group infall might have contributed to this, but no definitive association is found for the members of the Crater-Leo group.

scholarly journals Effects of the selection function on metallicity trends in spectroscopic surveys of the Milky Way

2017 ◽  
Vol 606 ◽  
pp. A97 ◽  
Author(s):  
G. Nandakumar ◽  
M. Schultheis ◽  
M. Hayden ◽  
A. Rojas-Arriagada ◽  
G. Kordopatis ◽  
...  
Keyword(s):  
Stellar Population ◽  
Milky Way ◽  
Target Selection ◽  
Selection Function ◽  
Population Synthesis ◽  
Sample Distribution ◽  
Stellar Population Synthesis ◽  
Source Sample ◽  
Correction Terms ◽  
Metallicity Distribution

Context. Large spectroscopic Galactic surveys imply a selection function in the way they performed their target selection. Aims. We investigate here the effect of the selection function on the metallicity distribution function (MDF) and on the vertical metallicity gradient by studying similar lines of sight using four different spectroscopic surveys (APOGEE, LAMOST, RAVE, and Gaia-ESO), which have different targeting strategies and therefore different selection functions. Methods. We use common fields between the spectroscopic surveys of APOGEE, LAMOST, RAVE (ALR) and APOGEE, RAVE, Gaia-ESO (AGR) and use two stellar population synthesis models, GALAXIA and TRILEGAL, to create mock fields for each survey. We apply the selection function in the form of colour and magnitude cuts of the respective survey to the mock fields to replicate the observed source sample. We make a basic comparison between the models to check which best reproduces the observed sample distribution. We carry out a quantitative comparison between the synthetic MDF from the mock catalogues using both models to understand the effect of the selection function on the MDF and on the vertical metallicity gradient. Results. Using both models, we find a negligible effect of the selection function on the MDF for APOGEE, LAMOST, and RAVE. We find a negligible selection function effect on the vertical metallicity gradients as well, though GALAXIA and TRILEGAL have steeper and shallower slopes, respectively, than the observed gradient. After applying correction terms on the metallicities of RAVE and LAMOST with respect to our reference APOGEE sample, our observed vertical metallicity gradients between the four surveys are consistent within 1σ. We also find consistent gradient for the combined sample of all surveys in ALR and AGR. We estimated a mean vertical metallicity gradient of − 0.241 ± 0.028 dex kpc-1. There is a significant scatter in the estimated gradients in the literature, but our estimates are within their ranges. Conclusions. We have shown that there is a negligible selection function effect on the MDF and the vertical metallicity gradients for APOGEE, RAVE, and LAMOST using two stellar population synthesis models. Therefore, it is indeed possible to combine common fields of different surveys in studies using MDF and metallicity gradients provided their metallicities are brought to the same scale.

scholarly journals Life Cycle of Dust in the Magellanic Clouds and the Milky Way

2014 ◽  
Author(s):  
Svitlana Zhukovska ◽  
Thomas Henning
Keyword(s):  
Life Cycle ◽  
Milky Way ◽  
Magellanic Clouds
Sign in / Sign up

Export Citation Format

Share Document