2025A&A...698A..11G

Query : 2025A&A...698A..11G

2025A&A...698A..11G - Astronomy and Astrophysics, volume 698A11 (2025/6-1)

The most metal-poor tail of the Galactic halo: Hypothesis for its origin from precise spectral analysis.

GIRIBALDI R.E., MAGRINI L., ROSSI M., AMARSI A.M., ROMANO D. and MASSARI D.

Abstract (from CDS):

Context. The origin of the Galactic halo is one of the fundamental topics linking the study of galaxy formation and evolution to cosmology.
Aims. Our goal is to derive precise and accurate stellar parameters, Mg abundances, and ages for a sample of metal-poor stars with [Fe/H] < - 2 dex from high signal-to-noise and high spectral resolution archival spectra.
Methods. We derived effective temperatures from Hα profiles using three-dimensional non-local thermodynamic equilibrium (3D NLTE) models, and surface gravities and ages from isochrone fitting based on Gaia data. Iron abundances were derived in one-dimensional (1D) NLTE, while Mg abundances were derived in 1D LTE, 1D NLTE, 3D LTE, and 3D NLTE to show the increasing level of accuracy.
Results. The sample stars show a tight trend in the [Mg/Fe] versus [Fe/H] plane with a knee located at [Fe/H] ≈ - 2.8 dex, which indicates a low level of stochasticity at the sampled metallicities in this kind of population. Their location in the Lindblad diagram confirms that they belong to the Galactic halo, but does not show a distinct clustering that might be expected for a merger with a single low-mass galaxy. Comparison with chemical evolution models is also not fully definitive on whether the sample stars were born in situ or in accreted low-mass galaxy mergers.
Conclusions. Overall, we find two plausible explanations for the chemical sequence traced by the stars in the [Mg/Fe] versus [Fe/H] plane. One is that the sample stars originated in the already formed Milky Way, which at that time (12.5 Gyr ago) was already the main galaxy of its Local Group surroundings. Another explanation is that the sample stars originated in several small galaxies with similar properties, which later merged with the Galaxy. Only accurate spectroscopic analysis such as that done here can reveal trustworthy chemical diagrams required to observe the traces of the Galaxy evolution. Increasing the sample size and the analysis of other elements are required to differentiate between the two hypotheses.

Abstract Copyright: © The Authors 2025

Journal keyword(s): stars: abundances - stars: fundamental parameters - Galaxy: abundances - Galaxy: evolution - Galaxy: formation - Galaxy: halo

Simbad objects: 63

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Number of rows : 63
N Identifier Otype ICRS (J2000)
RA 		ICRS (J2000)
DEC 		Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2026 		#notes
1 M 31 AGN 00 42 44.330 +41 16 07.50 4.86 4.36 3.44     ~ 13622 1
2 BPS CS 22953-0003 Pe* 01 02 15.8723379360 -61 43 45.836012208   14.43 13.75 13.339 12.886 KIIvw 78 0
3 HE 0102-1213 Pe* 01 05 27.9559083504 -11 57 30.967736472   14.016 13.574 13.511   CEMP-no 30 0
4 2MASS J01183829-3041026 Pe* 01 18 38.3021768400 -30 41 02.851310832 14.730 14.94 14.6     ~ 27 0
5 BPS CS 29518-0051 Pe* 01 24 10.0049733024 -28 15 21.115362312 13.567 13.62 13.02 12.594 12.162 ~ 35 0
6 BPS CS 22953-0037 Pe* 01 25 06.6508649808 -59 16 00.742176912   14.01 13.64   13.13 CEMP-no 45 0
7 GES J01293652-5020327 * 01 29 36.5170829448 -50 20 32.681630674           ~ 2 0
8 BD-10 388 Pe* 01 50 32.6462570064 -09 21 02.840259744   10.78 10.4     F3 102 0
9 LP 831-70 PM* 03 06 05.4386096664 -22 19 17.828964660   12.043 11.608 11.598   ~ 52 0
10 CD-33 1173 Pe* 03 19 35.3159594880 -32 50 43.157572008   11.272 10.902 10.421 10.152 CEMP 63 0
11 NAME Hubble Ultra Deep Field reg 03 32 39.0 -27 47 29           ~ 1900 0
12 GES J03372526-2724127 * 03 37 25.2613778107 -27 24 12.807013274           ~ 2 0
13 BPS CS 22177-0009 Pe* 04 07 40.6490981040 -25 02 43.970266068   14.67 14.27     ~ 36 0
14 BPS CS 22186-0025 Pe* 04 24 32.7982834272 -37 09 02.518136460   14.99 14.24 13.740 13.269 ~ 40 0
15 BD+03 740 HB* 05 01 16.6226363256 +04 06 37.021736844 9.97 10.17 9.7 9.6   sdF0 182 0
16 BD+24 1676 Pe* 07 30 41.2662525096 +24 05 10.248524088   11.15 10.7 10.4   F 139 0
17 ATO J124.8567-14.0844 EB* 08 19 25.6241770046 -14 05 04.059105743   15.327 14.843 14.627   ~ 5 0
18 HE 0926-0508 Pe* 09 28 55.3529041896 -05 21 40.492169352 12.410 12.34 12.194 11.895 11.617 ~ 26 0
19 UCAC4 398-048552 Pe* 09 47 55.0389374352 -10 27 24.473998980   14.249 13.629 13.516   ~ 5 0
20 UCAC4 243-044523 Pe* 10 09 15.7757862504 -41 27 15.492522775   15.326 14.561 14.452   ~ 3 0
21 UCAC4 246-042607 Pe* 10 14 27.8630059445 -40 52 50.547109489   14.088 13.274 13.145   ~ 5 0
22 UCAC4 372-059586 Pe* 10 58 06.3739178303 -15 42 38.989737203   15.631 14.735 14.504   ~ 3 0
23 BD-13 3442 Pe* 11 46 50.6525751264 -14 06 43.458063768   10.662 10.274     CEMP 117 0
24 UCAC4 225-067876 Pe* 12 55 51.4609200822 -45 07 34.150768267   14.051 13.240 13.125   ~ 6 0
25 UCAC4 232-064708 Pe* 13 30 13.5983879928 -43 46 32.344311504   14.406 13.276 13.063   ~ 7 0
26 Wolf 1492 Pe* 13 40 02.4921849768 -00 02 18.750053436 11.601 11.832 11.451 11.184 10.892 sdF0: 299 0
27 2MASS J14005447+2246423 Pe* 14 00 54.4740571128 +22 46 42.087313956 14.317 14.548 14.2     ~ 26 0
28 HD 122563 Pe* 14 02 31.8455084952 +09 41 09.944391876 7.47 7.10 6.19 5.37 4.79 G8:III:Fe-5 920 0
29 BD+09 2870 Pe* 14 16 29.9462349936 +08 27 52.952766408   10.58 9.70     KIIvw 82 0
30 2MASS J14205624-3701526 Pe* 14 20 56.2485359220 -37 01 52.703252980           ~ 3 0
31 UCAC4 230-075933 Pe* 14 21 48.5959722974 -44 08 39.970223632   15.722 14.681 14.484   ~ 3 0
32 UCAC4 250-068799 Pe* 14 41 00.9152249902 -40 07 41.282574061   14.319 13.356 13.180   ~ 3 0
33 BD+26 2621 Pe* 14 54 10.7123241110 +25 33 48.927279437   11.40 10.9 10.7   F0 52 0
34 BPS BS 16968-0061 Pe* 15 01 06.1171458744 +03 42 45.573411168   13.73 13.22 13.39   ~ 36 0
35 GES J15300154-2005148 * 15 30 01.5415214053 -20 05 14.954516928           ~ 2 0
36 HD 140283 Pe* 15 43 03.0971190219 -10 56 00.595693188 7.508 7.711 7.212 6.63 8.21 F9VkA5mA1 985 0
37 CD-71 1234 Pe* 16 07 44.6410532021 -71 21 01.360284611   10.81 10.44     ~ 44 0
38 NAME Galactic Center reg 17 45 39.60213 -29 00 22.0000           ~ 16269 0
39 SMSS J175433.19-411048.9 Pe* 17 54 33.1884250200 -41 10 48.767894220           ~ 3 0
40 SMSS J175455.52-380339.3 Pe* 17 54 55.5221810808 -38 03 39.386919528           ~ 3 0
41 SMSS J175746.58-384750.0 Pe* 17 57 46.5818041632 -38 47 49.916140224           ~ 4 0
42 GES J18185545-2738118 Pe* 18 18 55.4752119400 -27 38 11.467221268           ~ 3 0
43 UCAC4 280-186369 Pe* 18 21 53.8145872320 -34 10 18.520415004       12.93   ~ 4 0
44 GES J18261627-3154272 * 18 26 16.27 -31 54 27.2           ~ 2 0
45 GES J18265160-3159404 * 18 26 51.5935373994 -31 59 40.440444318           ~ 2 0
46 UCAC4 315-209301 Pe* 18 36 17.3397997440 -27 00 05.323623372       14.11   ~ 4 0
47 GES J18370372-2806385 * 18 37 03.72 -28 06 38.5           ~ 3 0
48 SMSS J183744.90-280831.1 Pe* 18 37 44.8917200088 -28 08 31.058694924           ~ 3 0
49 BPS CS 22891-0209 Pe* 19 42 02.1802427088 -61 03 44.534898612   13.03 12.18     KIIvw 64 0
50 UCAC2 7177623 Pe* 19 42 26.8926894816 -56 58 34.059037980   14.27 13.63     ~ 57 0
51 HD 186478 SB* 19 45 14.1409752672 -17 29 27.071239056   10.116 9.302 8.527 7.961 K2III 166 0
52 BD-18 5550 Pe* 19 58 49.7371417608 -18 12 11.140126164 10.18 10.03 9.35 9.04 8.74 CEMP-no 185 0
53 LP 815-43 Pe* 20 38 13.2998605176 -20 26 10.850795808   11.31 10.72     ~ 82 0
54 CD-35 14849 PM* 21 33 49.7524989129 -35 26 14.228198341   10.95 10.56 10.59   B8 76 0
55 BPS CS 22956-0050 Pe* 21 58 05.8340681280 -65 13 27.160682772   14.95 14.25 13.745 13.211 CEMP-no 42 0
56 BPS BS 17569-0049 Pe* 22 04 58.3605927288 +04 01 32.135832984 14.503 14.263 13.126 13.122 12.259 ~ 40 0
57 GES J22125747-4539203 * 22 12 57.4762064497 -45 39 20.337789241           ~ 2 0
58 UCAC2 20056019 * 22 28 49.8437834664 -28 57 01.569212244   13.86 13.48   12.83 ~ 17 0
59 BPS CS 29491-0053 Pe* 22 36 56.2965716592 -28 31 06.577096368   13.76 12.92 12.380 11.812 ~ 36 0
60 GES J22494718-5001048 * 22 49 47.1770924794 -50 01 04.829663971           ~ 2 0
61 2MASS J23485776-2939228 Pe* 23 48 57.7540034928 -29 39 22.824085392 14.759   14.3   13.512 ~ 38 0
62 NAME Gaia Enceladus-Sausage St* ~ ~           ~ 860 0
63 NAME Local Group GrG ~ ~           ~ 9325 0

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