J/MNRAS/503/2539 Galaxy halo Extremely Metal-Poor stars (Cordoni+, 2021)
Exploring the Galaxy's halo and very metal-weak thick disc with SkyMapper and
Gaia DR2.
Cordoni G., Da Costa G.S., Yong D., Mackey A.D., Marino A.F., Monty S.,
Nordlander T., Norris J.E., Asplund M., Bessell M.S., Casey A.R.,
Frebel A., Lind K., Murphy S.J., Schmidt B.P., Gao X.D.,
Xylakis-Dornbusch T., Amarsi A.M., Milone A.P.
<Mon. Not. R. Astron. Soc., 503, 2539-2561 (2021)>
=2021MNRAS.503.2539C 2021MNRAS.503.2539C (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; Stars, metal-deficient ; Stars, distances ;
Space velocities
Keywords: stars: kinematics and dynamics - Galaxy: disc - Galaxy: formation -
Galaxy: halo - Galaxy: kinematics and dynamics - Galaxy: structure
Abstract:
In this work, we combine spectroscopic information from the 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≤[Fe/H]≤-2.05dex. Exploiting the action map, we
identify 16 and 40 stars dynamically consistent with the Gaia Sausage
and Gaia Sequoia accretion events, respectively. The most metal poor
of these candidates have metallicities of [Fe/H]=-3.31 and -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 ∼21 per cent of the sample have orbits that
remain confined to within 3kpc of the Galactic plane, that is,
|Zmax|≤3kpc. Of particular interest is a subsample (∼11 per cent of
the total) of low |Zmax| stars with low eccentricities and prograde
motions. The lowest metallicity of these stars has [Fe/H]=-4.30 and
the subsample is best interpreted as the very low-metallicity tail of
the metal-weak thick disc population. The low |Zmax|, low
eccentricity stars with retrograde orbits are likely accreted, while
the low |Zmax|, high eccentricity pro- and retrograde stars are
plausibly associated with the Gaia Sausage system. We find that a
small fraction of our sample (∼4 per cent 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.
Description:
We have analysed a sample of 475 very metal-poor giant stars, most of
which have originated from the SkyMapper search for the most
metal-poor stars in our Galaxy (Da Costa et al., 2019MNRAS.489.5900D 2019MNRAS.489.5900D,
Cat. J/MNRAS/489/5900). The data set covers a metallicity range of
almost five dex (-6.5<[Fe/H]≤-2), and together with the relatively
large number of stars, makes it ideal to investigate the kinematics,
and ultimately the origin, of these very rare and important objects
together with the implications for the formation of the MW.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 390 475 Observed properties
table2.dat 658 475 Derived orbital properties
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See also:
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
II/358 : SkyMapper Southern Sky Survey. DR1.1 (Wolf+, 2018)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- Index Index
5- 23 I19 --- GaiaDR2 GaiaDR2 source_id
25- 43 A19 --- SMSSJ SkyMapper SMSS identifier
(HHMMSS.ss+DDMMSS.s)
45- 65 F21.17 deg RAdeg Right ascension (J2000)
67- 88 F22.18 deg DEdeg Declination (J2000)
90-112 F23.20 mas plx Parallax
114-133 F20.18 mas e_plx Parallax error
135-154 F20.17 kpc Dist Distance
156-176 F21.18 kpc e_Dist Distance error
178 I1 --- flag [0/1]
180-202 F23.19 mas/yr pmRA Proper motion along RA, pmRA*cosDE
204-225 E22.18 mas/yr pmDE Proper motion along DE
227-246 F20.18 mas/yr e_pmRA Proper motion along RA error
248-267 F20.18 mas/yr e_pmDE Proper motion along DE error
269-289 F21.16 km/s RV Radial velocity
291-310 F20.17 km/s e_RV Radial velocity error
312-329 F18.16 [K] logTeff Effective temperature
331-351 F21.19 [K] e_logTeff Effective temperature error
353-357 F5.2 --- [Fe/H] Metallicity
359-378 F20.18 mag E(B-V) B-V colour excess
380-390 A11 --- DatasetId Dataset
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- Index Index
5- 14 F10.8 --- ecc Eccentricity
16- 36 F21.19 --- e_ecc Eccentricity error (lower value)
38- 58 F21.19 --- E_ecc Eccentricity error (upper value)
60- 70 F11.6 kpc apo Apo-galacticon distance
72- 94 F23.19 kpc e_apo Apo-galacticon distance (lower value)
96-117 F22.18 kpc E_apo Apo-galacticon distance (upper value)
119-129 F11.8 kpc peri Peri-galacticon distance
131-151 F21.18 kpc e_peri Peri-galacticon distance (lower value)
153-173 F21.18 kpc E_peri Peri-galacticon distance (upper value)
175-186 F12.7 kpc zmax Maximun height above the plane
188-209 F22.18 kpc e_zmax Maximun height above the plane
(lower value)
211-233 F23.19 kpc E_zmax Maximun height above the plane
(upper value)
235-250 F16.7 kpc.km/s Jr Orbital action Jr
252-276 F25.16 kpc.km/s e_Jr Orbital action Jr (lower value)
278-302 F25.16 kpc.km/s E_Jr Orbital action Jr (upper value)
304-315 F12.6 kpc.km/s Jp Orbital action Jp
317-337 F21.16 kpc.km/s e_Jp Orbital action Jp (lower value)
339-359 F21.15 kpc.km/s E_Jp Orbital action Jp (upper value)
361-373 F13.7 kpc.km/s Jz Orbital action Jz
375-396 F22.17 kpc.km/s e_Jz Orbital action Jz (lower value)
398-420 F23.17 kpc.km/s E_Jz Orbital action Jz (upper value)
422-432 F11.3 kpc.km2/s2 Energy Orbital energy
434-454 F21.14 kpc.km2/s2 e_Energy Orbital energy (lower value)
456-476 F21.14 kpc.km2/s2 E_Energy Orbital energy (upper value)
478-489 F12.7 km/s U U velocity
491-511 F21.17 km/s e_U U velocity (lower value)
513-532 F20.16 km/s E_U U velocity (upper value)
534-546 F13.7 km/s V V velocity
548-567 F20.16 km/s e_V V velocity (lower value)
569-588 F20.16 km/s E_V V velocity (upper value)
590-601 F12.7 km/s W W velocity
603-623 F21.17 km/s e_W W velocity (lower value)
625-645 F21.17 km/s E_W W velocity (upper value)
647-658 A12 --- OrbitType Orbit type
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 17-Jan-2024