scholarly journals The formation of the Milky Way halo and its dwarf satellites; a NLTE-1D abundance analysis

2017 ◽  
Vol 608 ◽  
pp. A89 ◽  
Author(s):  
L. Mashonkina ◽  
P. Jablonka ◽  
T. Sitnova ◽  
Yu. Pakhomov ◽  
P. North
Keyword(s):  
Milky Way ◽  
Dwarf Galaxy ◽  
Chemical Species ◽  
Dwarf Spheroidal Galaxies ◽  
Massive Galaxies ◽  
Type Ia ◽  
Ursa Minor ◽  
R Process ◽  
Ia Supernovae ◽  
Process Elements

We present the non-local thermodynamic equilibrium (NLTE) abundances of up to 10 chemical species in a sample of 59 very metal-poor (VMP, −4 ≤ [Fe/H] ≾−2) stars in seven dwarf spheroidal galaxies (dSphs) and in the Milky Way (MW) halo. Our results are based on high-resolution spectroscopic datasets and homogeneous and accurate atmospheric parameters determined in Paper I. We show that once the NLTE effects are properly taken into account, all massive galaxies in our sample, that is, the MW halo and the classical dSphs Sculptor, Ursa Minor, Sextans, and Fornax, reveal a similar plateau at [α/Fe] ≃ 0.3 for each of the α-process elements: Mg, Ca, and Ti. We put on a firm ground the evidence for a decline in α/Fe with increasing metallicity in the Boötes I ultra-faint dwarf galaxy (UFD), that is most probably due to the ejecta of type Ia supernovae. For Na/Fe, Na/Mg, and Al/Mg, the MW halo and all dSphs reveal indistinguishable trends with metallicity, suggesting that the processes of Na and Al synthesis are identical in all systems, independent of their mass. The dichotomy in the [Sr/Ba] versus [Ba/H] diagram is observed in the classical dSphs, similarly to the MW halo, calling for two different nucleosynthesis channels for Sr. We show that Sr in the massive galaxies is well correlated with Mg suggesting a strong link to massive stars and that its origin is essentially independent of Ba, for most of the [Ba/H] range. Our three UFDs, that is Boötes I, UMa II, and Leo IV, are depleted in Sr and Ba relative to Fe and Mg, with very similar ratios of [Sr/Mg] ≃−1.3 and [Ba/Mg] ≃−1 on the entire range of their Mg abundances. The subsolar Sr/Ba ratios of Boötes I and UMa II indicate a common r-process origin of their neutron-capture elements. Sculptor remains the classical dSph, in which the evidence for inhomogeneous mixing in the early evolution stage, at [Fe/H] <−2, is the strongest.

Early chemical enrichment of the Milky Way dwarf satellites from high-resolution and NLTE analysis of VMP stars

2018 ◽  
Vol 14 (S344) ◽  
pp. 103-104
Author(s):  
Lyudmila Mashonkina ◽  
Pascale Jablonka ◽  
Tatyana Sitnova ◽  
Yuri Pakhomov ◽  
Pierre North ◽  
...  
Keyword(s):  
High Resolution ◽  
Milky Way ◽  
Chemical Species ◽  
Chemical Enrichment ◽  
Ursa Minor ◽  
R Process ◽  
Milky Way Halo

AbstractWe present the NLTE abundances of 10 chemical species in 65 very metal-poor stars in eight dSphs and the Milky Way halo. The classical dSphs Sculptor, Ursa Minor, Sextans, and Fornax reveal a similar plateau at [α/Fe] = 0.3 for each of Mg, Ca, and Ti, similarly to the MW halo. We provide the evidence for a decline in α/Fe in the Boötes I UFD, that is probably due to the ejecta of SNeIa. The dichotomy in the [Sr/Ba] versus [Ba/H] diagram is observed in the classical dSphs, similarly to the MW halo, calling for two different nucleosynthesis channels for Sr. The Boötes I and UMa II UFDs reveal very similar ratios of [Sr/Mg] = −1.3 and [Ba/Mg] = –1. The stars in the Coma Berenices and Leo IV UFDs are even poorer in Sr and Ba. The subsolar Sr/Ba ratios of Boötes I and UMa II indicate a common r-process origin of their n-capture elements.

scholarly journals The chemical connection between damped Lyman-α systems and Local Group dwarf galaxies

2018 ◽  
Vol 615 ◽  
pp. A137 ◽  
Author(s):  
Á. Skúladóttir ◽  
S. Salvadori ◽  
M. Pettini ◽  
E. Tolstoy ◽  
V. Hill
Keyword(s):  
Milky Way ◽  
Local Group ◽  
Dwarf Galaxies ◽  
Type Ia Supernovae ◽  
Volatile Elements ◽  
Dwarf Spheroidal Galaxies ◽  
Type Ia ◽  
Low Metallicity ◽  
Ia Supernovae ◽  
Star Formation Histories

Abundances of the volatile elements S and Zn have now been measured in around 80 individual stars in the Sculptor dwarf spheroidal galaxy, covering the metallicity range − 2.4 ≤ [Fe/H] ≤−0.9. These two elements are of particular interest as they are not depleted onto dust in gas, and their ratio, [S/Zn], has thus commonly been used as a proxy for [α/Fe] in Damped Lyman-α systems (DLAs). The S abundances in Sculptor are similar to other α-elements in this galaxy, consistent with S being mainly created in core-collapse supernovae, but also having some contribution from type Ia supernovae. However, our results show that Zn and Fe do not trace all the same nucleosynthetic production channels. In particular, (contrary to Fe) Zn is not significantly produced by type Ia supernovae. Thus, [S/Zn] cannot be reliably used as a proxy for [α/Fe]. We propose [O/S] as a function of [S/H] as a possible alternative. At higher metallicities, the values of [S/Zn] measured in DLAs are inconsistent with those in local dwarf galaxies, and are more compatible with the Milky Way disk. Low-metallicity DLAs are, however, consistent with the most metal-poor stars in Local Group dwarf spheroidal galaxies. Assuming that the dust depletions of S and Zn are negligible, our comparison indicates that the star formation histories of DLAs are on average different from both the Milky Way and the Sculptor dwarf spheroidal galaxy.

scholarly journals Chemical evolution of r-process elements in the Draco dwarf spheroidal galaxy

2015 ◽  
Vol 11 (S317) ◽  
pp. 310-311
Author(s):  
M. N. Ishigaki ◽  
T. Tsujimoto ◽  
T. Shigeyama ◽  
W. Aoki
Keyword(s):  
Neutron Star ◽  
High Resolution ◽  
Neutron Capture ◽  
Milky Way ◽  
Origin And Evolution ◽  
Dwarf Spheroidal Galaxies ◽  
Giant Stars ◽  
Upper Limits ◽  
R Process ◽  
Process Elements

AbstractA dominant astrophysical site for r-process, which is responsible for producing heavy neutron-capture elements, is unknown. Dwarf spheroidal galaxies around the Milky Way halo provide ideal laboratories to investigate the origin and evolution of r-process elements. We carried out high-resolution spectroscopic observations of three giant stars in the Draco dwarf spheroidal galaxy to estimate their europium abundances. We found that the upper-limits of [Eu/H] are very low in the range [Fe/H] < −2, while this ratio is nearly constant at higher metallicities. This trend is not well reproduced with models which assume that Eu is produced together with Fe by SNe, and may suggest the contribution from other objects such as neutron-star mergers.

scholarly journals The AMBRE Project: r-process elements in the Milky Way thin and thick discs

2018 ◽  
Vol 619 ◽  
pp. A143 ◽  
Author(s):  
G. Guiglion ◽  
P. de Laverny ◽  
A. Recio-Blanco ◽  
N. Prantzos
Keyword(s):  
Chemical Evolution ◽  
Milky Way ◽  
Element Abundances ◽  
Thick Disc ◽  
Thin Disc ◽  
Solar Metallicity ◽  
R Process ◽  
Process Elements ◽  
Process Element ◽  
The Eu

Context. The chemical evolution of neutron capture elements in the Milky Way disc is still a matter of debate. There is a lack of statistically significant catalogues of such element abundances, especially those of the r-process. Aims. We aim to understand the chemical evolution of r-process elements in Milky Way disc. We focus on three pure r-process elements Eu, Gd, and Dy. We also consider a pure s-process element, Ba, in order to disentangle the different nucleosynthesis processes. Methods. We take advantage of high-resolution FEROS, HARPS, and UVES spectra from the ESO archive in order to perform a homogeneous analysis on 6500 FGK Milky Way stars. The chemical analysis is performed thanks to the automatic optimization pipeline GAUGUIN. We present abundances of Ba (5057 stars), Eu (6268 stars), Gd (5431 stars), and Dy (5479 stars). Based on the [α/Fe] ratio determined previously by the AMBRE Project, we chemically characterize the thin and the thick discs, and a metal-rich α-rich population. Results. First, we find that the [Eu/Fe] ratio follows a continuous sequence from the thin disc to the thick disc as a function of the metallicity. Second, in thick disc stars, the [Eu/Ba] ratio is found to be constant, while the [Gd/Ba] and [Dy/Ba] ratios decrease as a function of the metallicity. These observations clearly indicate a different nucleosynthesis history in the thick disc between Eu and Gd–Dy. The [r/Fe] ratio in the thin disc is roughly around +0.1 dex at solar metallicity, which is not the case for Ba. We also find that the α-rich metal-rich stars are also enriched in r-process elements (like thick disc stars), but their [Ba/Fe] is very different from thick disc stars. Finally, we find that the [r/α] ratio tends to decrease with metallicity, indicating that supernovae of different properties probably contribute differently to the synthesis of r-process elements and α-elements. Conclusions. We provide average abundance trends for [Ba/Fe] and [Eu/Fe] with rather small dispersions, and for the first time for [Gd/Fe] and [Dy/Fe]. This data may help to constrain chemical evolution models of Milky Way r- and s-process elements and the yields of massive stars. We emphasize that including yields of neutron-star or black hole mergers is now crucial if we want to quantitatively compare observations to Galactic chemical evolution models.

scholarly journals The failure of stellar feedback, magnetic fields, conduction, and morphological quenching in maintaining red galaxies

2019 ◽  
Vol 487 (3) ◽  
pp. 4393-4408 ◽  
Author(s):  
Kung-Yi Su ◽  
Philip F Hopkins ◽  
Christopher C Hayward ◽  
Xiangcheng Ma ◽  
Claude-André Faucher-Giguère ◽  
...  
Keyword(s):  
Cosmic Rays ◽  
Magnetic Fields ◽  
Mass Range ◽  
Massive Galaxies ◽  
Cooling Flows ◽  
Stellar Feedback ◽  
Type Ia ◽  
Saturation Effects ◽  
Red Galaxies ◽  
Ia Supernovae

ABSTRACT The quenching ‘maintenance’ and related ‘cooling flow’ problems are important in galaxies from Milky Way mass through clusters. We investigate this in haloes with masses ∼$10^{12}\!-\!10^{14}\, {\rm M}_{\odot }$, using non-cosmological high-resolution hydrodynamic simulations with the FIRE-2 (Feedback In Realistic Environments) stellar feedback model. We specifically focus on physics present without AGN, and show that various proposed ‘non-AGN’ solution mechanisms in the literature, including Type Ia supernovae, shocked AGB winds, other forms of stellar feedback (e.g. cosmic rays), magnetic fields, Spitzer–Braginskii conduction, or ‘morphological quenching’ do not halt or substantially reduce cooling flows nor maintain ‘quenched’ galaxies in this mass range. We show that stellar feedback (including cosmic rays from SNe) alters the balance of cold/warm gas and the rate at which the cooled gas within the galaxy turns into stars, but not the net baryonic inflow. If anything, outflowing metals and dense gas promote additional cooling. Conduction is important only in the most massive haloes, as expected, but even at ∼$10^{14}\, {\rm M}_{\odot }$ reduces inflow only by a factor ∼2 (owing to saturation effects and anisotropic suppression). Changing the morphology of the galaxies only slightly alters their Toomre-Q parameter, and has no effect on cooling (as expected), so has essentially no effect on cooling flows or maintaining quenching. This all supports the idea that additional physics, e.g. AGN feedback, must be important in massive galaxies.

scholarly journals Dynamical and Chemical Evolution of IZw18

2004 ◽  
Vol 21 (2) ◽  
pp. 157-160
Author(s):  
Simone Recchi
Keyword(s):  
Star Formation ◽  
Chemical Evolution ◽  
Dwarf Galaxy ◽  
Star Formation History ◽  
Intermediate Mass ◽  
Intermediate Mass Stars ◽  
Formation History ◽  
Type Ia ◽  
Ia Supernovae ◽  
Detailed Chemical

AbstractWe study the effect of different star formation regimes on the dynamical and chemical evolution of IZw18, the most metal-poor dwarf galaxy locally known. To do that we adopt a two-dimensional hydrocode coupled with detailed chemical yields originating from Type II and Type Ia supernovae and from intermediate-mass stars. Particular emphasis is devoted to the problem of mixing of metals. We conclude that, under particular conditions, cooling of metals occurs with a timescale of the order of 10 Myr, thus confirming the hypothesis of instantaneous mixing adopted in chemical evolution models. We try to draw conclusions about the star formation history and the age of the last burst in IZw18.

scholarly journals Evidence for Light-weight Local Group Dwarf Spheroidal Galaxies

2004 ◽  
Vol 220 ◽  
pp. 365-366
Author(s):  
J. R. Kuhn ◽  
D. Kocevski
Keyword(s):  
Dark Matter ◽  
Milky Way ◽  
Local Group ◽  
Light Weight ◽  
Natural Explanation ◽  
Dwarf Spheroidal Galaxies ◽  
Ursa Minor ◽  
Matter Component ◽  
Morphological State ◽  
Spheroidal Galaxies

A simple and natural explanation for the dynamics and morphology of the Local Group Dwarf Spheroidal galaxies, Draco (Dra) and Ursa Minor (UMi), is that they are weakly unbound stellar systems with no significant dark matter component. A gentle, but persistent, Milky Way (MW) tide has left them in their current kinematic and morphological state (the “parametric tidal excitation”). A new test of a dark matter dominated dS potential follows from a careful observation of the “clumpiness” of the dS stellar surface density.

scholarly journals Too big to fail in light of Gaia

2019 ◽  
Vol 490 (1) ◽  
pp. 231-242 ◽  
Author(s):  
Manoj Kaplinghat ◽  
Mauro Valli ◽  
Hai-Bo Yu
Keyword(s):  
Dark Matter ◽  
Milky Way ◽  
Large Scatter ◽  
Too Big To Fail ◽  
Dwarf Spheroidal Galaxies ◽  
Ursa Minor ◽  
Spheroidal Galaxies

ABSTRACT We point out an anticorrelation between the central dark matter (DM) densities of the bright Milky Way dwarf spheroidal galaxies (dSphs) and their orbital pericenter distances inferred from Gaia data. The dSphs that have not come close to the Milky Way centre (like Fornax, Carina and Sextans) are less dense in DM than those that have come closer (like Draco and Ursa Minor). The same anticorrelation cannot be inferred for the ultrafaint dSphs due to large scatter, while a trend that dSphs with more extended stellar distributions tend to have lower DM densities emerges with ultrafaints. We discuss how these inferences constrain proposed solutions to the Milky Way’s too-big-to-fail problem and provide new clues to decipher the nature of DM.

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