Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userInferring the Galactic potential with Gaia and friends: synergies with other surveys
60
0
0.0
(
0
)
Authors
Robyn E. Sanderson
Ask ChatGPT about the research
No Arabic abstract
In the coming decade the Gaia satellite will precisely measure the positions and velocities of millions of stars in the Galactic halo, including stars in many tidal streams. These streams, the products of hierarchical accretion of satellite galaxies by the Milky Way (MW), can be used to infer the Galactic gravitational potential thanks to their initial compactness in phase space. Plans for observations to extend Gaias radial velocity (RV) measurements to faint stars, and to determine precise distances to RR Lyrae (RRLe) in streams, would further extend the power of Gaias kinematic catalog to characterize the MWs potential at large Galactocentric distances. In this work I explore the impact of these extra data on the ability to fit the potential using the method of action clustering, which statistically maximizes the information content (clumpiness) of the action space of tidal streams, eliminating the need to determine stream membership for individual stars. Using a mock halo in a toy spherical potential, updated post-launch error models for Gaia, and estimates for RV and distance errors for the tracers to be followed up, I show that combining either form of additional information with the Gaia catalog greatly reduces the bias in determining the scale radius and total mass of the Galaxy, compared to the use of Gaia data alone.
rate research
Read More
The era of high-precision astrometry has dawned upon us. The potential of Gaia $mu$as-level precision in positional measurements is about to be unleashed in the field of extrasolar planetary systems. The Gaia data hold the promise for much improved global characterization of planetary systems around stars of all types, ages, and chemical composition, particularly when synergistically combined with other indirect and direct planet detection and characterization programs.
Studies of stellar populations, understood to mean collections of stars with common spatial, kinematic, chemical, and/or age distributions, have been reinvigorated during the last decade by the advent of large-area sky surveys such as SDSS, 2MASS, RAVE, and others. We review recent analyses of these data that, together with theoretical and modeling advances, are revolutionizing our understanding of the nature of the Milky Way, and galaxy formation and evolution in general. The formation of galaxies like the Milky Way was long thought to be a steady process leading to a smooth distribution of stars. However, the abundance of substructure in the multi-dimensional space of various observables, such as position, kinematics, and metallicity, is by now proven beyond doubt, and demonstrates the importance of mergers in the growth of galaxies. Unlike smooth models that involve simple components, the new data reviewed here clearly show many irregular structures, such as the Sagittarius dwarf tidal stream and the Virgo and Pisces overdensities in the halo, and the Monoceros stream closer to the Galactic plane. These recent developments have made it clear that the Milky Way is a complex and dynamical structure, one that is still being shaped by the merging of neighboring smaller galaxies. We also briefly discuss the next generation of wide-field sky surveys, such as SkyMapper, Pan-STARRS, Gaia and LSST, which will improve measurement precision manyfold, and comprise billions of individual stars. The ultimate goal, development of a coherent and detailed story of the assembly and evolutionary history of the Milky Way and other large spirals like it, now appears well within reach.
The ongoing Gaia mission of ESA will provide accurate spatial and kinematical information for a large fraction of stars in the Galaxy. Interstellar extinction and line absorption studies toward a large number of stars at different distances and directions can give a 3-dimensional distribution map of interstellar absorbers, and thus reach a similar spatial perfection. Under certain morphologies (e.g. geometrically thin absorption curtains) one can infer a complete velocity vector from its radial velocity component and so obtain a dynamical information comparable to stars. But observations of a large number of stars at different distances are needed to determine the location of the absorption pockets. Therefore, techniques to measure interstellar absorptions towards (abundant) cool stars are needed. A complex mix of colliding absorption clouds is found in the Galactic plane. Thus, one would wish to start with deep observations to detect the weak, but simpler interstellar absorptions at high Galactic latitudes. Finally, interstellar atomic line absorption studies toward cool stars in the optical are largely limited to Sodium and Potassium doublets, not covered by many surveys, including Gaia. Diffuse interstellar bands can give the same type of information as interstellar atomic absorption lines. A combination of both may also point to differences in dynamics of different components of the interstellar medium. In particular, the Gaia DIB at 862 nm can be used to build absorption maps, as already demonstrated by RAVE. Additionally, several ground-based surveys (e.g APOGEE, Gaia-ESO and Galah) are upgrading this approach. The use of this new information can change our understanding in many areas (e.g. determination of membership of stars in clusters, studies of a few Myr old supernova remnants and investigations of Galactic fountains).
We characterize the kinematic and chemical properties of 589 Galactic Anticenter Substructure Stars (GASS) with K-/M- giants in Integrals-of-Motion space. These stars likely include members of previously identified substructures such as Monoceros, A13, and the Triangulum-Andromeda cloud (TriAnd). We show that these stars are on nearly circular orbits on both sides of the Galactic plane. We can see velocity($V_{Z}$) gradient along Y-axis especially for the south GASS members. Our GASS members have similar energy and angular momentum distributions to thin disk stars. Their location in [$alpha$/M] vs. [M/H] space is more metal poor than typical thin disk stars, with [$alpha$/M] textbf{lower} than the thick disk. We infer that our GASS members are part of the outer metal-poor disk stars, and the outer-disk extends to 30 kpc. Considering the distance range and $alpha$-abundance features, GASS could be formed after the thick disk was formed due to the molecular cloud density decreased in the outer disk where the SFR might be less efficient than the inner disk.
We revisit the stellar velocity distribution in the Galactic bulge/bar region with APOGEE DR16 and {it Gaia} DR2, focusing in particular on the possible high-velocity (HV) peaks and their physical origin. We fit the velocity distributions with two different models, namely with Gauss-Hermite polynomial and Gaussian mixture model (GMM). The result of the fit using Gauss-Hermite polynomials reveals a positive correlation between the mean velocity ($bar{V}$) and the skewness ($h_{3}$) of the velocity distribution, possibly caused by the Galactic bar. The $n=2$ GMM fitting reveals a symmetric longitudinal trend of $|mu_{2}|$ and $sigma_{2}$ (the mean velocity and the standard deviation of the secondary component), which is inconsistent to the $x_{2}$ orbital family predictions. Cold secondary peaks could be seen at $|l|sim6^circ$. However, with the additional tangential information from {it Gaia}, we find that the HV stars in the bulge show similar patterns in the radial-tangential velocity distribution ($V_{rm R}-V_{rm T}$), regardless of the existence of a distinct cold HV peak. The observed $V_{rm R}-V_{rm T}$ (or $V_{rm GSR}-mu_{l}$) distributions are consistent with the predictions of a simple MW bar model. The chemical abundances and ages inferred from ASPCAP and CANNON suggest that the HV stars in the bulge/bar are generally as old as, if not older than, the other stars in the bulge/bar region.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
