Overview of Gaia EDR3 and looking forward to DR4

Anthony Brown (Leiden)

A brief overview of EDR3 and the known issues will be presented, followed by a look ahead at the contents of Gaia DR3 and DR4.

Gaia Discovery Engine

Maarten Breddels

The Gaia Discovery Engine is a system based on the Python Vaex library designed to enable extremely fast exploratory data analysis with a heavily cross-matched EDR3 from Sergey Koposov. The idea is that a user, with many different interface options, can make a 1, 2, or many-dimensional histogram with real or synthetic data columns from the database and get a result in a few seconds. We propose to provide this system, along with a short presentation, training, and support to the whole of the EDR3 sprint team.

Gaia operations status and tips for data access

Jos de Bruijne (ESA)

Gaia’s latest data release, Gaia EDR3 launched on 3 December 2020, is in heavy use by astronomers worldwide to study a wide range of topics, from unravelling galactic structure to unveiling details of stellar evolution. Meanwhile, the spacecraft is in good health and continues to collect unique science data to be included in a forthcoming data release, following calibration by the data processing and analysis consortium DPAC. This presentation provides an update of the spacecraft operations and mission status. Moreover, it provides an overview of the various data products and how and where to access these.

The EDR3 astrometric solution from a user perspective

Lennart Lindegren (Lund)

In addition to formal uncertainties, the EDR3 astrometry contains a lot of quality indicators that could be used for filtering the data, but their meaning and relevance are not always obvious. Moreover, in the months since the data became public there have appeared a number of investigations attempting to characterize the solution, including biases, correlations, and inflation factors for the uncertainties. In this talk I try to summarize the main conclusions and recommendations relevant to the user.

Completeness of the Gaia-verse

Douglas Boubert (Oxford) & Andy Everall (Cambridge)

What are the odds that Gaia would have seen a given star? If Gaia did see the star, then what are the odds it measured the parallax, proper motion or radial velocity? If Gaia did measure the parallax or proper motion, then what would the uncertainty be on those quantities? Being able to answer these questions is crucial when modelling the enormous stellar population revealed by Gaia. We will begin by arguing the importance of Gaia's scanning law to answering these questions. We will then introduce you to our Completeness of the Gaia-verse project, with a focus on how you can access our results. We will carry out a live demo of our selection functions and scanning law Python packages, which together allow you to calculate the odds of a star being in Gaia DR2 and to predict both when it was observed by Gaia and what the astrometric uncertainty should have been if the star was a point source. We'll end by giving you a glimpse of on-going work to infer the Gaia EDR3 selection function and the selection function of the subsets with astrometry and radial velocities.

A classifier for spurious astrometric solutions in Gaia EDR3

Jan Rybizki (MPIA)

For a small fraction of Gaia sources the astrometric solutions are poor. This means that their reported values and uncertainties may not apply, which is due to a break-down of the measurement model assumptions (e.g. binarity of the source). We looked for signatures of those poor solutions in the Gaia astrometric parameters by training a classifier on examples of good and bad solutions. The classifier shows a high purity of 99.7% and completeness of 97.6% as validated on our test data. We released the training/validation-notebook and a catalogue of these classifications which can be queried via the Virtual Observatory.

The detection of 800pc long tidal tails of Hyades: New ways of constraining the MW potential with EDR3

Tereza Jerabkova (ESTEC)

The tidal tails of stellar clusters provide an important tool for studying their birth conditions, their evolution, coupling, and interaction with the Galactic potential. Up until recently only the tidal tails of a few distant globular clusters have been observed. This is because the stars in the tidal tails are in the process of becoming part of the Galactic field stellar population and, for a nearby star cluster, the tails can be spread all over the sky. In this talk I will present the results of N-body simulations of a Hyades-like star cluster, showing how the cluster and its tidal tail look like in the eyes of the Gaia space telescope. I will use these results to locate the Hyades star cluster and its tails in the newest Gaia Data Release. With this I will explain how to search for co-moving but extended stellar structures using astrometric measurements by using the new compact convergent point method. The main results include the extraction of the full extent of the Hyades tidal tail spanning over 1kpc in length from tip to tip, and showing a puzzling asymmetry as well as the first detection of epicyclic over-densities in the tail of an open star cluster that provide constraints on the potential of Milky Way. I will discuss if the puzzling asymmetry can be explained through an interaction of the Hyades with a massive Galactic lump.

Open clusters and Gaia: perspectives and early science from EDR3

Tristan Cantat-Gaudin (IEEC-UB) and Alfred Castro-Ginard (IEEC-UB)

Gaia has had a tremendous impact on the cluster census in the Milky Way, allowing us to identify the faint members of known clusters and to detect hundreds of new objects. The improved parallaxes and especially proper motions of the EDR3 astrometry represent a step forward in detecting and characterizing clusters. In this talk, we will present our procedure to blind search for open clusters in the Galactic disc and its application to EDR3 up to magnitude G = 18. We will review recent results concerning the Galactic structure, and show how DR3 improves our knowledge of cluster membership for distant clusters.

Precision Galactic archaeology: Revealing the Milky Way's engines through the statistical alignment of stars

Yuan-Sen Ting (IAS)

The unprecedented precise astrometry of Gaia eDR3 has revealed a larger number of pairs of stars with coherent motions. However, most studies thus far have focused on the bound “wide binaries” with separation < 1pc. The study for their much wider separation counterparts with separations of 1-100 pc remains scant, and the nature of these comoving stars has remained a mystery. Are they co-natal stars but drifted apart? Are they chance alignments? Or are they “chance captured” by their companion. To study the nature of these comoving pairs, I have led a program to observe a complete sample (with G < 10.5) of wide binaries with extremely high-resolution spectra (R > 45,000) and SNR (150-250). Our pilot study showed that comoving stars, even with separation of ~30 pc, 30 times wider than the widest known wide binaries, are mostly co-natal. We further quantify the conatal fraction of stars as a function of their spatial and velocity separations. Our results have important implications of using this much larger sample of comoving stars as a way to study planet engulfment, calibration stellar evolution models, and quantifying ISM mixing. Finally, I will also discuss how we could optimize the selection of co-natal stars from their phase space information.

Synergies between Gaia and asteroseismology in EDR3 and beyond

Oliver Hall (ESTEC)

The Gaia mission has provided us with the largest catalogue of stellar distances to date, but it’s not the only mission capable of measuring distance. By studying the internal vibrations of stars, asteroseismology with the Kepler, K2 and TESS missions can also measure distance through the stellar radius. Gaia has quantity and precision, whereas asteroseismology has accuracy (albeit a little model-dependent). Because of this, these two techniques complement one another excellently. In this talk, I’ll talk through past and present synergies of asteroseismology and Gaia parallaxes. First, we’ll look at how asteroseismology has been used to calibrate Gaia distances, and whether doing so will remain relevant as Gaia data releases become more accurate and precise. Second we’ll look at how Gaia luminosities have improved (and continue to improve) asteroseismic models and results, with a look on the future of DR3 and DR4. Finally, we'll look at how Gaia data more generally is improving studies of stellar variability as it improves our benchmark understanding of the Milky Way.

Multi-band RR Lyrae PL relations from Gaia DR2 to Gaia EDR3

Rachael Beaton (Princeton)

RR Lyrae are evolved, low-mass, pulsating stars. In some photometric bands, their period-luminosity-metallicity relationships have the ability to probe distances at the few-percent level for individual stars. This has powerful implications for tracing Galactic structure and the distribution of galaxies in the very nearby Universe. Trigonometric parallaxes measured by Gaia are at the precision level to now directly calibrate the period-luminosity-relationships using nearby field stars. Using our sample of 55 RR Lyrae with photometry in 10 photometric bands, we have explored the period-luminosity-metallicity relationships for RR Lyrae type variables with Gaia DR2 (Neeley et al. 2019) and found that the parallaxes were systematics limited. In this talk, I will share updates to this work using Gaia eDR3. Our preliminary analysis indicates that the parallax systematics are no longer the limiting factor in constraining the Period-Luminosity relationships!

Cosmic distances calibrated to 1% precision with Gaia EDR3 Cepheid parallaxes

Adam Riess (JHU)

We present an expanded sample of 75 Milky Way Cepheids with Hubble Space Telescope (HST) photometry and Gaia EDR3 parallaxes, which we use to recalibrate the extragalactic distance ladder and refine the determination of the Hubble constant. We use new Gaia EDR3 parallaxes, greatly improved since DR2, and the period-luminosity (P-L) relation of these Cepheids to simultaneously calibrate the extragalactic distance ladder and to refine the determination of the Gaia EDR3 parallax offset. The resulting geometric calibration of Cepheid luminosities has 1.0% precision, better than any alternative geometric anchor in good agreement with conclusions based on earlier Gaia data releases. We also find the slope of the Cepheid P-L relation in the Milky Way, and the metallicity dependence of its zero-point, to be in good agreement with the mean values derived from other galaxies. In combination with the best complementary sources of Cepheid calibration, we reach 1.8% precision and find H0 = 73.2 ± 1.3 km s-1 Mpc-1, a 4.2σ difference with the prediction from Planck CMB observations under ΛCDM, a furtherance of the widely-called “Hubble Tension” between the Early and Late Universe.

Searching for dwarf galaxies in Gaia DR2 and EDR3 using wavelet transforms

Elise Darragh-Ford (Stanford)

Searching for dwarf galaxies in the Milky Way has previously focused on spatial and color information from large photometric surveys like DES and Pan-STARRS. However, the kinematic information from Gaia offers a unique opportunity to search for dwarf galaxies in 4D position-proper motion space. I will present a wavelet-based algorithm that takes advantage of the special properties of the wavelet transform to perform exactly this 4D search. The algorithm was optimized by searching for mock dwarfs injected into Gaia DR2 data and for known Milky Way satellite galaxies. Based on the results of the optimization and careful modeling of the expected dwarf population in the Milky Way, we predict that our search is expected to discover 5 +/- 2 new satellite galaxies. I will present the updated candidate list from the most recent run of the algorithm on the EDR3 dataset as well as follow-up efforts currently being undertaken to verify candidates in our list.

Internal rotation of MW dSph satellites with Gaia EDR3

Alberto Manuel Martínez García (IAC)

Dwarf galaxies are key in the domain of the formation and evolution of galaxies. The Local Group (LG) offers a unique opportunity for their study, since it contains a sizable amount of dwarfs with resolved populations. Nevertheless, dwarfs internal kinematics remain mostly unknown. Gaia has provided proper motions (PMs) of thousands of stars of Milky Way (MW) satellites, opening a new window for their analysis. This has allowed us to study the kinematics of fourteen MW satellites. We have derived their systemic 3D motion using line-of-sight velocities from the literature and PMs from the Gaia EDR3. For Carina, Draco, Fornax, Sculptor, Sextans, and Ursa Minor dwarf spheroidal galaxies (dSphs) we have studied their internal kinematics. We projected the stellar PMs into radial and tangential velocity components referred to the centre-of-mass, finding significant clockwise rotation in Carina, Fornax and Sculptor. In addition to Sagittarius dSph, these are the first measurements of rotation in the plane of the sky in the MW classical dSphs. Carina is the only galaxy in our sample with larger rotation than its velocity dispersion. We find that slower rotators tend to show larger projected ellipticities and tend to be located at smaller Galactocentric distances, nevertheless these trends are not statistically significant. This indicates that rotation does not play a key role shaping these galaxies, and that either tidal stirring had a weak impact on their evolution or these systems have been similarly perturbed independently of their current distance to the MW.

The Radcliffe Wave and the new Local Galactic Neighborhood

João Alves (University of Vienna)

For the past 150 years, the local interstellar medium's prevailing view has been based on a peculiarity known as the Gould Belt, an expanding ring of young stars, gas and dust, tilted about 20 degrees to the Galactic plane. However, the physical relationship between local gas clouds has remained unknown because the accuracy in distance measurements to such clouds is of the same order as, or larger than, their sizes. With the advent of large photometric surveys and the astrometric survey, in particular ESA Gaia, this situation has changed. In this talk, I will present the three-dimensional structure of all local cloud complexes. We find a narrow and coherent 2.7-kiloparsec arrangement of dense gas in the solar neighborhood that contains many of the clouds thought to be associated with the Gould Belt. This finding is inconsistent with the notion that these clouds are part of a ring, bringing the Gould Belt model into question. The structure comprises the majority of nearby star-forming regions, has an aspect ratio of about 1:20, and contains about three million solar masses of gas. Remarkably, this structure appears to be undulating, and its three-dimensional shape is well described by a damped sinusoidal wave on the plane of the Milky Way.

Galactic spiral structure revealed by Gaia EDR3

Eloisa Poggio (Observatoire de la Côte d'Azur, France; INAF-Osservatorio Astrofisico di Torino, Italy)

Using the astrometry and integrated photometry from the Gaia Early Data Release 3 (EDR3), we map the density variations in the distribution of young Upper Main Sequence (UMS) stars, open clusters and classical Cepheids in the Galactic disk within several kiloparsecs of the Sun. Maps of relative over/under-dense regions for UMS stars in the Galactic disk are derived, using both bivariate kernel density estimators and wavelet transformations. The resulting overdensity maps exhibit large-scale arches, that extend in a clumpy but coherent way over the entire sampled volume, indicating the location of the spiral arms segments in the vicinity of the Sun. Peaks in the UMS overdensity are well-matched by the distribution of young and intrinsically bright open clusters. By applying a wavelet transformation to a sample of classical Cepheids, we find that their overdensities possibly extend the spiral arm segments on a larger scale (~10 kpc from the Sun). While the resulting map based on the UMS sample is generally consistent with previous models of the Sagittarius-Carina spiral arm, the geometry of the arms in the III quadrant (galactic longitudes 180 deg >l>270 deg ) differs significantly from many previous models. In particular we find that our maps favor a larger pitch angle for the Perseus arm, and that the Local Arm extends into the III quadrant at least 4 kpc past the Sun's position, giving it a total length of at least 8 kpc.