In this work we combine spectroscopic information from the extit{SkyMapper survey for Extremely Metal-Poor stars} and astrometry from Gaia DR2 to investigate the kinematics of a sample of 475 stars with a metallicity range of $ -6.5 leq m [Fe/H] leq -2.05$ dex. Exploiting the action map, we identify 16 and 40 stars dynamically consistent with the extit{Gaia Sausage} and extit{Gaia Sequoia} accretion events, respectively. The most metal-poor of these candidates have metallicities of $ m [Fe/H]=-3.31$ and $ m [Fe/H]=-3.74$, respectively, helping to define the low-metallicity tail of the progenitors involved in the accretion events. We also find, consistent with other studies, that $sim$21% of the sample have orbits that remain confined to within 3~kpc of the Galactic plane, i.e., |Z$_{max}$| $leq$ 3~kpc. Of particular interest is a sub-sample ($sim$11% of the total) of low |Z$_{max}$| stars with low eccentricities and prograde motions. The lowest metallicity of these stars has [Fe/H] = --4.30 and the sub-sample is best interpreted as the very low-metallicity tail of the metal-weak thick disk population. The low |Z$_{max}$|, low eccentricity stars with retrograde orbits are likely accreted, while the low |Z$_{max}$|, high eccentricity pro- and retrograde stars are plausibly associated with the extit{Gaia Sausage} system. We find that a small fraction of our sample ($sim$4% of the total) is likely escaping from the Galaxy, and postulate that these stars have gained energy from gravitational interactions that occur when infalling dwarf galaxies are tidally disrupted.

Exploring the Galaxy's halo and very metal-weak thick disk with SkyMapper and Gaia DR2

G. Cordoni
;
A. F. Marino;A. P. Milone
2021

Abstract

In this work we combine spectroscopic information from the extit{SkyMapper survey for Extremely Metal-Poor stars} and astrometry from Gaia DR2 to investigate the kinematics of a sample of 475 stars with a metallicity range of $ -6.5 leq m [Fe/H] leq -2.05$ dex. Exploiting the action map, we identify 16 and 40 stars dynamically consistent with the extit{Gaia Sausage} and extit{Gaia Sequoia} accretion events, respectively. The most metal-poor of these candidates have metallicities of $ m [Fe/H]=-3.31$ and $ m [Fe/H]=-3.74$, respectively, helping to define the low-metallicity tail of the progenitors involved in the accretion events. We also find, consistent with other studies, that $sim$21% of the sample have orbits that remain confined to within 3~kpc of the Galactic plane, i.e., |Z$_{max}$| $leq$ 3~kpc. Of particular interest is a sub-sample ($sim$11% of the total) of low |Z$_{max}$| stars with low eccentricities and prograde motions. The lowest metallicity of these stars has [Fe/H] = --4.30 and the sub-sample is best interpreted as the very low-metallicity tail of the metal-weak thick disk population. The low |Z$_{max}$|, low eccentricity stars with retrograde orbits are likely accreted, while the low |Z$_{max}$|, high eccentricity pro- and retrograde stars are plausibly associated with the extit{Gaia Sausage} system. We find that a small fraction of our sample ($sim$4% of the total) is likely escaping from the Galaxy, and postulate that these stars have gained energy from gravitational interactions that occur when infalling dwarf galaxies are tidally disrupted.
File in questo prodotto:
File Dimensione Formato  
EMP.ms.1.gc.pdf

accesso aperto

Tipologia: Preprint (submitted version)
Licenza: Accesso gratuito
Dimensione 3 MB
Formato Adobe PDF
3 MB Adobe PDF Visualizza/Apri
Pubblicazioni consigliate

Caricamento pubblicazioni consigliate

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11577/3400340
Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus ND
  • ???jsp.display-item.citation.isi??? ND
social impact