Periodic Reporting for period 1 - EMMY (Evolutionary Mechanisms in the Milky waY: the Gaia Data Release 3 revolution)
Okres sprawozdawczy: 2022-09-01 do 2024-08-31
Our home Galaxy, the Milky Way, can be used as an enormous laboratory to study the laws of physics in extreme conditions. The EMMY project is focused on the exploration of the complexity of the physical processes driving the evolution of the Galactic disc. The EMMY project aims to study the co-existence of both internal (such as the influence of the bar or spiral arms) and external (such as accretions of satellite galaxies) physical mechanisms, based on the properties of the stars that can be observed today (e.g. their spatial distributions, their motions, their chemical abundances).
The Gaia satellite is currently mapping the Milky Way by measuring positions and motions for more than one billion stars with strong accuracy and unprecedented detail. Taking advantage of the unprecedented wealth of chemo-dynamical data published in Gaia Data Release 3 (DR3), it is possible to obtain an unparalleled view of our Galaxy.
In the Milky Way disc, the stars in the inner parts are more rich in metals than those in the outer stars. This property is known as the "large-scale metallicity gradient" of the disc, and it is thought to be the result of how our Galaxy formed (inside-out formation).
Using Gaia DR3, we mapped the chemical composition of several groups of stars throughout the Galactic disc, in a radius of 13 000 light-years (4 Kpc) around the Sun. We found that the stars not only have a radial metallicity gradient, but also chemical azimuthal variations (i.e. for a given radius, the metallicity varies with Galactic azimuthal angle). We also found that the observed azimuthal variations change depending on the typical age of the consireded stars.
The young stars show interesting chemical features, apparent as chemical undulations, on top of the radial metallicity gradient. We also found an important correlation between the observed chemical maps and the position of the spiral arms in the Galaxy. Specifically, young stars located in the spiral arms of the Galaxy are typically richer in metals than those out of them.The important statistical correlations between density (i.e. spiral arm segments) and metallicity (i.e. chemical undulations) in the young stars indicate that the spiral arms of the Milky Way might be at the origin of the detected chemical inhomogeneities.
On the other hand, the old stars exhibit a relatively smooth radial metallicity gradient, whose slope (inclination) gradually changes with azimuthal angle. Possible explanations for the observed azimuthal variations in the old populations do not only include the spiral arms, but also radial migration induced by the bar, and/or the interaction with a satellite Galaxy (e.g. the Sagittarius dwarf galaxy).
Using the three-dimensional kinematics of stars in the Galactic, we detected a large-scale wave on top of the Galactic warp, with a vertical height of 150 pc, a radial half-amplitude of about 1 kpc and a total length of at least 10 kpc. The stars in the wave exhibit both radial and vertical systematic motions, consistent with a vertical wave propagating towards the outer parts of the Galactic disk. The observed wave might be a signature of the interaction with a satellite galaxy.
The Gaia satellite is currently mapping the Milky Way by measuring positions and motions for more than one billion stars with strong accuracy and unprecedented detail. Taking advantage of the unprecedented wealth of chemo-dynamical data published in Gaia Data Release 3 (DR3), it is possible to obtain an unparalleled view of our Galaxy.
In the Milky Way disc, the stars in the inner parts are more rich in metals than those in the outer stars. This property is known as the "large-scale metallicity gradient" of the disc, and it is thought to be the result of how our Galaxy formed (inside-out formation).
Using Gaia DR3, we mapped the chemical composition of several groups of stars throughout the Galactic disc, in a radius of 13 000 light-years (4 Kpc) around the Sun. We found that the stars not only have a radial metallicity gradient, but also chemical azimuthal variations (i.e. for a given radius, the metallicity varies with Galactic azimuthal angle). We also found that the observed azimuthal variations change depending on the typical age of the consireded stars.
The young stars show interesting chemical features, apparent as chemical undulations, on top of the radial metallicity gradient. We also found an important correlation between the observed chemical maps and the position of the spiral arms in the Galaxy. Specifically, young stars located in the spiral arms of the Galaxy are typically richer in metals than those out of them.The important statistical correlations between density (i.e. spiral arm segments) and metallicity (i.e. chemical undulations) in the young stars indicate that the spiral arms of the Milky Way might be at the origin of the detected chemical inhomogeneities.
On the other hand, the old stars exhibit a relatively smooth radial metallicity gradient, whose slope (inclination) gradually changes with azimuthal angle. Possible explanations for the observed azimuthal variations in the old populations do not only include the spiral arms, but also radial migration induced by the bar, and/or the interaction with a satellite Galaxy (e.g. the Sagittarius dwarf galaxy).
Using the three-dimensional kinematics of stars in the Galactic, we detected a large-scale wave on top of the Galactic warp, with a vertical height of 150 pc, a radial half-amplitude of about 1 kpc and a total length of at least 10 kpc. The stars in the wave exhibit both radial and vertical systematic motions, consistent with a vertical wave propagating towards the outer parts of the Galactic disk. The observed wave might be a signature of the interaction with a satellite galaxy.
We developed specific criteria to select three catalogs of stars of different typical age, based on stellar effective temperatures and surface gravities from the Gaia GSP-Spec catalog.
We obtained three catalogs, called Sample A, B and C (which respectively contain young, intermediate and old stars). The outcomes are three calalogs, which are publicly available on cds at the link: http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/666/L4(odnośnik otworzy się w nowym oknie)
Using the above-selected datasets, we constructed maps of the mean stellar metallicity in the Galactic disc, as well as metallicity excess maps (to map whether a specific location in the Galactic disc is more metal-rich or metal-poor than the average metallicity of stars on a large-scale region). This technique has been developed ad hoc, to study the variations of metallicity in the Galactic disc (on top of the well-known metallicity gradient).
We also analysed the statistical correlation between the observed chemical inhomogeneities for the young sample (which had the strongest signal) and the position of the spiral arms in density.
The chemical inhomogeneities exhibit a strong statistical correlation with the spiral arms, which suggests that the spiral arms of the Milky Way are at the origin of the observed chemical substructures in the young stars.
We also analysed the three dimensional structure and kinematics of a sample of young giants selected from the XGboost catalog (Andrae et al. 2023), containing about 20000 stars. We inferred the three-dimensional shape and kinematics of the Galactic warp, in agreement with previous works. We found a new feature, apparent as a large-scale corrugation on top of the Galactic warp, which is propagating outwards in the Galactic disc.
We obtained three catalogs, called Sample A, B and C (which respectively contain young, intermediate and old stars). The outcomes are three calalogs, which are publicly available on cds at the link: http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/666/L4(odnośnik otworzy się w nowym oknie)
Using the above-selected datasets, we constructed maps of the mean stellar metallicity in the Galactic disc, as well as metallicity excess maps (to map whether a specific location in the Galactic disc is more metal-rich or metal-poor than the average metallicity of stars on a large-scale region). This technique has been developed ad hoc, to study the variations of metallicity in the Galactic disc (on top of the well-known metallicity gradient).
We also analysed the statistical correlation between the observed chemical inhomogeneities for the young sample (which had the strongest signal) and the position of the spiral arms in density.
The chemical inhomogeneities exhibit a strong statistical correlation with the spiral arms, which suggests that the spiral arms of the Milky Way are at the origin of the observed chemical substructures in the young stars.
We also analysed the three dimensional structure and kinematics of a sample of young giants selected from the XGboost catalog (Andrae et al. 2023), containing about 20000 stars. We inferred the three-dimensional shape and kinematics of the Galactic warp, in agreement with previous works. We found a new feature, apparent as a large-scale corrugation on top of the Galactic warp, which is propagating outwards in the Galactic disc.
The results obtained in this project indicate that the Galactic disc does not only have a large-scale metallicity radial metallicity gradient (as already indicated by several works in the past elements), but has a new important dimension to explore: Galactic azimuth. For a given position in the Galactic disc, chemical inhomogeneities are present and statistically significant.
An additional result of this project is that azimuthal variations depend on the typical age of the considered stars. In the young stars, the chemical inhomogeneities exhibit a strong statistical correlation with the spiral arms, which suggests that the spiral arms of the Milky Way are at the origin of the observed chemical substructures in the young stars. This implies an important new feature of the Galactic disc: the chemical signature of the Galactic spiral arms.
For the old stars, a new feature has also been observed: the azimuthal dependency of the radial metallicity gradient (i.e. its slope gradually changes with azimuthal angle).
Finally, using the three-dimensional spatial and kinematic data of young giants in the Galactic disc, we detected a new large-scale wave on top of the Galactic warp. The stars in the wave have systematic vertical and radial velocities consistent with a large-scale wave (at least 10 kpc in length) propagating towards the outer parts of the disc.
With the new data from Gaia (Gaia Data Release 4) and ground based survey, we plan to expand these results, taking advantage of the largest spatial coverage of the Galactic disc, as well as improved astrometric quality. We are also planning to expand the chemical analysis performed here in this work using other chemical elements (e.g. alpha elements) to put new observational constrains on the mechanisms regulating the evolution of the Galactic disc.
An additional result of this project is that azimuthal variations depend on the typical age of the considered stars. In the young stars, the chemical inhomogeneities exhibit a strong statistical correlation with the spiral arms, which suggests that the spiral arms of the Milky Way are at the origin of the observed chemical substructures in the young stars. This implies an important new feature of the Galactic disc: the chemical signature of the Galactic spiral arms.
For the old stars, a new feature has also been observed: the azimuthal dependency of the radial metallicity gradient (i.e. its slope gradually changes with azimuthal angle).
Finally, using the three-dimensional spatial and kinematic data of young giants in the Galactic disc, we detected a new large-scale wave on top of the Galactic warp. The stars in the wave have systematic vertical and radial velocities consistent with a large-scale wave (at least 10 kpc in length) propagating towards the outer parts of the disc.
With the new data from Gaia (Gaia Data Release 4) and ground based survey, we plan to expand these results, taking advantage of the largest spatial coverage of the Galactic disc, as well as improved astrometric quality. We are also planning to expand the chemical analysis performed here in this work using other chemical elements (e.g. alpha elements) to put new observational constrains on the mechanisms regulating the evolution of the Galactic disc.