Astrometry with the Wide-Field InfraRed Space Telescope

The Wide-Field InfraRed Space Telescope (WFIRST) will be capable of delivering precise astrometry for faint sources over the enormous field of view of its main camera, the Wide-Field Imager (WFI). This unprecedented combination will be transformative for the many scientific questions that require precise positions, distances, and velocities of stars. We describe the expectations for the astrometric precision of the WFIRST WFI in different scenarios, illustrate how a broad range of science cases will see significant advances with such data, and identify aspects of WFIRST's design where small adjustments could greatly improve its power as an astrometric instrument.Comment: version accepted to JATI

VVVX-Gaia Discovery of a Low Luminosity Globular Cluster in the Milky Way Disk

© 2020 ESOMilky Way globular clusters (MW GCs) are difficult to identify at low Galactic latitudes because of high differential extinction and heavy star crowding. The new deep near-IR images and photometry from the VISTA Variables in the Via L\'actea Extended Survey (VVVX) allow us to chart previously unexplored regions. Our long term aim is to complete the census of MW GCs. The immediate goals are to estimate the astrophysical parameters, measuring their reddenings, extinctions, distances, total luminosities, proper motions, sizes, metallicities and ages. We use the near-IR VVVX survey database, in combination with Gaia DR2 optical photometry, and with the Two Micron All Sky Survey (2MASS) photometry. We report the detection of a heretofore unknown Galactic Globular Cluster at RA = 14:09:00.0; DEC=-65:37:12 (J2000). We calculate a reddening of E(J-K_s)=(0.3 +/- 0.03) mag and an extinction of A_Ks=(0.15 +/- 0.01) mag for this new GC. Its distance modulus and corresponding distance were measured as (m-M)=(15.93 +/- 0.03) mag and D=(15.5 +/- 1.0) kpc, respectively. We estimate the metallicity and age by comparison with known GCs and by fitting PARSEC and Dartmouth isochrones, finding $[Fe/H]=(-0.70\pm0.2)$ dex and t=(11.0 +/- 1.0) Gyr. The mean GC PMs from Gaia are mu_alpha^(star)=(-4.68 +/- 0.47) mas yr^(-1) and mu_delta=(-1.34 \pm 0.45) mas yr^(-1). The total luminosity of our cluster is estimated to be M_Ks=(-7.76 +/- 0.5) mag. We have found a new low-luminosity, old and metal-rich globular cluster, situated in the far side of the Galactic disk, at R_G=11.2 kpc from the Galactic centre, and at z=1.0 kpc below the plane. Interestingly, the location, metallicity and age of this globular cluster are coincident with the Monoceros Ring (MRi) structure.Peer reviewe

Uncovering CDM halo substructure with tidal streams

Models for the formation and growth of structure in a cold dark matter dominated universe predict that galaxy halos should contain significant substructure. Studies of the Milky Way, however, have yet to identify the expected few hundred sub-halos with masses greater than about 10^6 Msun. Here we propose a test for the presence of sub-halos in the halos of galaxies. We show that the structure of the tidal tails of ancient globular clusters is very sensitive to heating by repeated close encounters with the massive dark sub-halos. We discuss the detection of such an effect in the context of the next generation of astrometric missions, and conclude that it should be easily detectable with the GAIA dataset. The finding of a single extended cold stellar stream from a globular cluster would support alternative theories, such as self-interacting dark matter, that give rise to smoother halos.Comment: 7 pages, 7 figures, submitted to MNRA