46 research outputs found
Evidence of a large scale positive rotation-metallicity correlation in the Galactic thick disk
This study is based on high quality astrometric and spectroscopic data from
the most recent releases by Gaia and APOGEE. We select thin and thick
disk red giants, in the Galactocentric (cylindrical) distance range ~kpc and within ~kpc, for which full chemo-kinematical information
is available. Radial chemical gradients, , and rotational velocity-metallicity correlations, , are re-derived firmly uncovering that the thick disk
velocity-metallicity correlation maintains its positiveness over the ~kpc
range explored. This observational result is important as it sets experimental
constraints on recent theoretical studies on the formation and evolution of the
Milky Way disk and on cosmological models of Galaxy formation.Comment: Accepted for publication in Monthly Notices of the Royal Astronomical
Societ
New Signatures of the Milky Way Formation in the Local Halo and Inner Halo Streamers in the Era of Gaia
We explore the vicinity of the Milky Way through the use of
spectro-photometric data from the Sloan Digital Sky Survey and high-quality
proper motions derived from multi-epoch positions extracted from the Guide Star
Catalogue II database. In order to identify and characterise streams as relics
of the Milky Way formation, we start with classifying, select, and study
subdwarfs with up to kpc away from the Sun as tracers
of the local halo system. Then, through phase-space analysis, we find
statistical evidence of five discrete kinematic overdensities among of the
fastest-moving stars, and compare them to high-resolution N-body simulations of
the interaction between a Milky-Way like galaxy and orbiting dwarf galaxies
with four representative cases of merging histories. The observed overdensities
can be interpreted as fossil substructures consisting of streamers torn from
their progenitors, such progenitors appear to be satellites on prograde and
retrograde orbits on different inclinations. In particular, of the five
detected overdensities, two appear to be associated, yelding twenty-one
additional main-sequence members, with the stream of Helmi et al. (1999) that
our analysis confirms on a high inclination prograde orbit. The three newly
identified kinematic groups could be associated with the retrograde streams
detected by Dinescu (2002) and Kepley et al. (2007), whatever their origin, the
progenitor(s) would be on retrograde orbit(s) and inclination(s) within the
range . Finally, we use our simulations to
investigate the impact of observational errors and compare the current picture
to the promising prospect of highly improved data expected from the Gaia
mission.Comment: 16 pages, 10 figures, 6 Tables. Accepted for publication in The
Astronomical Journa
Icarus: A Flat and Fast Prograde Stellar Stream in the Milky Way Disk
We explore the local volume of the Milky Way via chemical and kinematical measurements from high-quality astrometric and spectroscopic data recently released by the Gaia, APOGEE, and GALAH programs. We chemically select 1137 stars up to 2.5 kpc of the Sun and [Fe/H] ≤ −1.0 dex, and find evidence of statistically significant substructures. Clustering analysis in velocity space classifies 163 objects into eight kinematical groups, whose origin is further investigated with high-resolution N-body numerical simulations of single merging events. The two retrograde groups appear associated with Gaia-Sausage-Enceladus (GSE), while the slightly prograde group could be connected to GSE or possibly Wukong. We find evidence of a new 44-member-strong prograde stream that we name Icarus; to our knowledge, Icarus is the fast-rotating stream closest to the Galactic disk to date (, 〈V + V LSR〉 sime 231 km s−1). Its peculiar chemical (〈[Fe/H]〉 sime −1.45, 〈[Mg/Fe]〉 sime −0.02) and dynamical (mean eccentricity sime 0.11) properties are consistent with the accretion of debris from a dwarf galaxy progenitor with a stellar mass of ~109 M ☉ on an initial prograde low-inclination orbit, ~10°. The remaining prograde groups are either streams previously released by the same progenitor of Icarus (or Nyx), or remnants from different satellites accreted on initial orbits at higher inclination
Relics of the Formation of the Galactic Halo from Gaia and APOGEE
The solar neighborhood potentially contains a very large number of kinematic groups which are related to the various building blocks of the stellar halo. We explore the vicinity of the Milky Way through the use of high quality astrometric and spectroscopic data from the most recent releases by Gaia and APOGEE. We chemically select 663 halo stars and analyse their kinematics and orbital properties in order to investigate and characterise the possibly detectable signatures that remain in phase-space. We find evidence of statistically significant substructures among 177 stars, with velocity difference less than 20 km/s, that are classified in 15-25 kinematic groups and compared to the high velocity streamers by Re Fiorentin et al. 2015. The signal is even stronger among the stars with [Mg/Fe] < 0.2 dex, that more likely have been accreted; preliminary results are shown. The chemical properties of the kinematically selected moving groups are going to be analysed to reconstruct the accretion history of the stellar halo
The Overdensity in Virgo, Sagittarius Debris, and the Asymmetric Spheroid
We investigate the relationship between several previously identified
Galactic halo stellar structures in the direction of Virgo using imaging and
spectroscopic observations of F turnoff stars and blue horizontal branch stars
from the Sloan Digital Sky Survey (SDSS) and the Sloan Extension for Galactic
Understanding and Exploration (SEGUE). We show that the Sagittarius dwarf
leading tidal tail does not pass through the solar neighborhood; it misses the
Sun by more than 15 kpc, passing through the Galactic plane outside the Solar
Circle. It also is not spatially coincident with the large stellar overdensity
S297+63-20.5 in the Virgo constellation. S297+63-20.5 has a distinct turnoff
color and kinematics. Faint (g ~ 20.3) turnoff stars in S297+63-20.5 have
line-of-sight, Galactic standard of rest velocities V(GSR)= 130 +/- 10 km/s,
opposite in sign to infalling Sgr tail stars. The path of the Sgr leading tidal
tail is also inconsistent with the positions of some of the nearer stars with
which it has been associated, and whose velocities have favored models with
prolate Milky Way potentials. We additionally show that the number densities of
brighter (g ~ 19.8) F turnoff stars are not symmetric about the Galactic
center, and that this discrepancy is not primarily due to the S297+63-20.5
moving group. Either the spheroid is asymmetric about the Galactic center, or
there are additional substructures that conspire to be on the same side of the
Galaxy as S297+63-20.5. The S297+63-20.5 overdensity in Virgo is likely
associated with two other previously identified Virgo substructures: the Virgo
Stellar Stream (VSS) and the Virgo Overdensity (VOD). However, the velocity
difference between the VSS and S297+63-20.5 and the difference in distance
estimates between the VOD and S297+63-20.5 must be reconciled.Comment: 10 figures, ApJ in pres
The formation history of the Milky Way disc with high-resolution cosmological simulations
We analyse from an observational perspective the formation history and kinematics of a Milky Way-like galaxy from a high- resolution zoom-in cosmological simulation that we compare to those of our Galaxy as seen by Gaia DR2 to better understand the origin and evolution of the Galactic thin and thick discs. The cosmological simulation was carried out with the GADGET-3 TreePM+SPH code using the MUlti-Phase Particle Integrator (MUPPI) model. We disentangle the complex overlapping of stellar generations that rises from the top-down and inside-out formation of the galactic disc. We investigate cosmological signatures in the phase-space of mono-age populations and highlight features stemming from past and recent dynamical perturbations. In the simulation, we identify a satellite with a stellar mass of 1.2 × 109 M⊙, i.e. stellar mass ratio ∼ 5.5 per cent at the time, accreted at z ∼ 1.6, which resembles the major merger Gaia–Sausage–Enceladus that produced the Galactic thick disc, i.e. ∼ 6 per cent. We found at z ∼ 0.5–0.4 two merging satellites with a stellar mass of 8.8 × 108 M⊙ and 5.1 × 108 M⊙ that are associated to a strong starburst in the star formation history, which appears fairly similar to that recently found in the solar neighbourhood. Our findings highlight that detailed studies of coeval stellar populations kinematics, which are made available by current and future Gaia data releases and in synergy with simulations, are fundamental to unravel the formation and evolution of the Milky Way discs
The Gaia mission: the dawn of Astrometric Cosmology? Status and prospects after 14 months of science operations
The concept of precisely gauging a gravity-dominated Universe like ours through the individual observations of its fundamental constituents, the stars, immediately calls astrometry, the oldest quantitative specialty of astronomy, into play. Today, thanks to the launch of the Gaia satellite, astrometry has reached such levels to become a key player in the field of local cosmology and experimental gravitation. Updates on the status of the mission, orbiting in L2 since January 2014 and in nominal observation mode since July 2014, are presented. We also discuss how the astrometric observations from within the gravitational fields of the Solar System can uniquely probe possible deviations from General Relativity and how accurate absolute kinematics at the scale of the Milky Way can, for the first time in situ, account for the predictions of the CDM model for the formation of the Galactic halo
The thick disk rotation-metallicity correlation, comparison with Galactic cosmological simulations
Although the existence of a thick disc in the Milky Way was revealed 35 years ago and its spatial, kinematic, and chemical properties are today better defined, its origin is still matter of debate. Proposed scenarios include the heating of a pre-existing thin disc through a minor merger, accretion of dwarf galaxies stars from disrupted satellites, or stars formed in situ from gas-rich mergers at high redshift.In order to better understand these processes, we have investigated the chemo-dynamical evolution of a Milky Way-like disk galaxy, as produced by the recent cosmological simulations, integrating a sub-resolution ISM model, published by Murante et al. (2015). In particular, we evidence a global inside-out and top-down disk evolution.Recently, Re Fiorentin, Lattanzi & Spagna (2019) analysed a new chemo-kinematic catalogue based on Gaia DR2 and APOGEE DR14 and showed evidence that the thick disk rotation-metallicity correlation is persistently positive from R=5 kpc to 13 kpc, in spite of a quasi-flat metallicity gradient.Our simulation at redshift z=0 shows very similar properties when we look at the "thick disk" stellar particles at 1 kpc 2) with a negative rotation-metallicity correlation associated with a negative radial metallicity gradient (cfr. also Schoenrich & McMillan 2017; Kawata et al. 2018)
Chemo-dynamical signatures in simulated Milky Way-like galaxies
We have investigated the chemo-dynamical evolution of a Milky Way-like disk galaxy, AqC4, produced by a cosmological simulation integrating a sub-resolution ISM model. We evidence a global inside-out and upside-down disk evolution, that is consistent with a scenario where the ``thin disk'' stars are formed from the accreted gas close to the galactic plane, while the older ``thick disk'' stars are originated in situ at higher heights. Also, the bar appears the most effective heating mechanism in the inner disk. Finally, no significant metallicity-rotation correlation has been observed, in spite of the presence of a negative [Fe/H] radial gradient
Euclid FGS Input Star Catalogue Verification Test Report
This document is applicable to the FGS Star Catalogue in the frame of the EUCLID Program in the Pre-CD phase and CD phases.The objective of the verification testing is to assess to what degree the delivered third version of the ISC (ISC.R3) satisfy the requirements defined by the Requirement Specifications (EUCL-TAST-RS-2-056). This document presents the results of the executed verification test cases, described in the ISC Verification Test Specifications
(VTS), as part of the requirement verification phase described in the DDVP