CHEMICAL ABUNDANCES OF THE MILKY WAY THICK DISK AND STELLAR HALO. I. IMPLICATIONS OF [α/Fe] FOR STAR FORMATION HISTORIES IN THEIR PROGENITORS

Ishigaki, Miho N.; Chiba, Masashi; Aoki, Wako

doi:10.1088/0004-637x/753/1/64

Cited by 107 publications

(150 citation statements)

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“…Previous studies have also reported the detection of α-element abundance differences in metal-poor stars, with some making selections specifically in Mg, as performed here (Nissen & Schuster 2010;Navarro et al 2011;Ishigaki et al 2012;Sheffield et al 2012;Jackson-Jones et al 2014;Hawkins et al 2015), albeit with fewer stars. The advantage of our study is that we rely on a large sample of stars that have homogeneously determined abundances for many chemical species.…”

Section: Discussionmentioning

confidence: 80%

“…A commonly used strategy is to rely on kinematical definitions to separate stars into populations (Venn et al 2004;Reddy et al 2006;Ruchti et al 2011;Ishigaki et al 2012Ishigaki et al , 2013. Unfortunately, this is fraught with several difficulties, not least that it requires that the necessary kinematical data are in hand and of sufficient quality to provide meaningful discrimination.…”

Section: Introductionmentioning

confidence: 99%

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Disentangling the Galactic Halo with APOGEE. I. Chemical and Kinematical Investigation of Distinct Metal-poor Populations

Hayes

Majewski

Shetrone

et al. 2018

ApJ

158

122

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We find two chemically distinct populations separated relatively cleanly in the [Fe/H]-[Mg/Fe] plane, but also distinguished in other chemical planes, among metal-poor stars (primarily with metallicities < -[ ] Fe H 0.9) observed by the Apache Point Observatory Galactic Evolution Experiment (APOGEE) and analyzed for Data Release 13 (DR13) of the Sloan Digital Sky Survey. These two stellar populations show the most significant differences in their [X/Fe] ratios for the α-elements, C+N, Al, and Ni. In addition to these populations having differing chemistry, the low metallicity high-Mg population (which we denote "the HMg population") exhibits a significant net Galactic rotation, whereas the low-Mg population (or "the LMg population") has halo-like kinematics with little to no net rotation. Based on its properties, the origin of the LMg population is likely an accreted population of stars. The HMg population shows chemistry (and to an extent kinematics) similar to the thick disk, and is likely associated with in situ formation. The distinction between the LMg and HMg populations mimics the differences between the populations of low-and high-α halo stars found in previous studies, suggesting that these are samples of the same two populations.

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Section: Discussionmentioning

confidence: 80%

Section: Introductionmentioning

confidence: 99%

Disentangling the Galactic Halo with APOGEE. I. Chemical and Kinematical Investigation of Distinct Metal-poor Populations

Hayes

Majewski

Shetrone

et al. 2018

ApJ

158

122

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“…Among the different proposed processes that could produce this abundance flattening, we wish to mention: (i) large-scale processes of angular momentum transport that produce a mix of gas abundances, including radial gas flows (e.g., Lacey & Fall 1985;Goetz & Koeppen 1992;Portinari & Chiosi 2000;Schönrich & Binney 2009;Spitoni & Matteucci 2011), resonance scattering with transient spiral density waves (Sellwood & Binney 2002), and the overlap of spiral and bar resonances (Minchev et al 2011); (ii) minor mergers and captures of or perturbations by satellite galaxies that increase the metal content in the outer regions (Quillen et al 2009;Bird et al 2012); (iii) a nonlinear Schmidt-Kennicutt law that is able to trigger a highly efficient star formation process at these distances (e.g., Esteban et al 2013); (iv) a spatial association of the flatter area with gas located in the thick disk, which is known to have different metallicity patterns (e.g., Neves et al 2009;Ishigaki et al 2012); (v) a plateau of the gas abundance in the intergalactic medium due to the cosmological evolution of galaxies; and the subsequent pollution of metals (Sánchez et al, in prep. ); Stellar radial migration has also been proposed as a possible cause for the flattening of the metallicity gradients for stellar populations in spiral galaxies (e.g., Roškar et al 2008b,a).…”

Section: The Flattening Of the Abundance Gradient In The Outer Regionsmentioning

confidence: 99%

A characteristic oxygen abundance gradient in galaxy disks unveiled with CALIFA

Sánchez

Rosales-Ortega

Iglésias-Páramo

et al. 2014

A&A

427

289

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We present the largest and most homogeneous catalog of H ii regions and associations compiled so far. The catalog comprises more than 7000 ionized regions, extracted from 306 galaxies observed by the CALIFA survey. We describe the procedures used to detect, select, and analyze the spectroscopic properties of these ionized regions. In the current study we focus on characterizing of the radial gradient of the oxygen abundance in the ionized gas, based on the study of the deprojected distribution of H ii regions. We found that all galaxies without clear evidence of an interaction present a common gradient in the oxygen abundance, with a characteristic slope of α O/H = −0.1 dex/r e between 0.3 and 2 disk effective radii (r e ), and a scatter compatible with random fluctuations around this value, when the gradient is normalized to the disk effective radius. The slope is independent of morphology, the incidence of bars, absolute magnitude, or mass. Only those galaxies with evidence of interactions and/or clear merging systems present a significantly shallower gradient, consistent with previous results. The majority of the 94 galaxies with H ii regions detected beyond two disk effective radii present a flattening in the oxygen abundance. The flattening is statistically significant. We cannot provide a conclusive answer regarding the origin of this flattening. However, our results indicate that its origin is most probably related to the secular evolution of galaxies. Finally, we find a drop/truncation of the oxygen abundance in the inner regions for 26 of the galaxies. All of them are non-interacting, mostly unbarred Sb/Sbc galaxies. This feature is associated with a central star-forming ring, which suggests that both features are produced by radial gas flows induced by resonance processes. Our result suggests that galaxy disks grow inside-out, with metal enrichment driven by the local star formation history and with a small variation galaxy-by-galaxy. At a certain galactocentric distance, the oxygen abundance seems to be correlated well with the stellar mass density and total stellar mass of the galaxies, independently of other properties of the galaxies. Other processes, such as radial mixing and inflows/outflows seem to have a limited effect on shaping of the radial distribution of oxygen abundances, although they are not ruled out.

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“…Figure 8 compares mean abundances of the Boötes I stars and field halo stars in the metallicity range of −3.0 < [Fe/H] < −2.0. To minimize systematic errors in the abundance comparison, eight halo giants (T eff < 5000 K and log g < 3.0, including one of the comparison stars HD 85773) from Ishigaki et al (2012Ishigaki et al ( , 2013 are only considered for the field halo sample. In their work, the adopted 1D-LTE abundance analysis technique and the line list are the same as in this work.…”

Section: Comparison With the Field Mw Halomentioning

confidence: 99%

Chemical compositions of six metal-poor stars in the ultra-faint dwarf spheroidal galaxy Boötes I

Ishigaki

Aoki

Arimoto

et al. 2014

A&A

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Context. Ultra-faint dwarf galaxies recently discovered around the Milky Way (MW) contain extremely metal-poor stars, and might represent the building blocks of low-metallicity components of the MW. Among them, the Boötes I dwarf spheroidal galaxy is of particular interest because of its exclusively old stellar population. Detailed chemical compositions of individual stars in this galaxy are a key to understanding formation and chemical evolution in the oldest galaxies in the Universe and their roles in building up the MW halo. Aims. Previous studies of the chemical abundances of Boötes I show discrepancies in elemental abundances between different authors, and thus a consistent picture of its chemical enrichment history has not yet been established. In the present work, we independently determine chemical compositions of six red giant stars in Boötes I, some of which overlap with those analyzed in the previous studies. Based on the derived abundances, we re-examine trends and scatters in elemental abundances and make comparisons with MW field halo stars and other dwarf spheroidal galaxies in the MW. Methods. High-resolution spectra of a sample of stars were obtained with the High Dispersion Spectrograph mounted on the Subaru Telescope. Abundances of 12 elements, including C, Na, α, Fe-peak, and neutron capture elements, were determined for the sample stars. The abundance results were compared to those in field MW halo stars previously obtained using an abundance analysis technique similar to the present study. Conclusions. Our results of small scatter in the [X/Fe] ratios for elements lighter than zinc suggest that these abundances were homogeneous among the ejecta of prior generation(s) of stars in this galaxy. The lower mean [Mg/Fe] and [Ca/Fe] ratios relative to the field halo stars and the similarity in these abundance ratios with some of the more luminous dwarf spheroidal galaxies at metallicities [Fe/H] < −2 can be interpreted as star formation in Boötes I having lasted at least until Type Ia supernovae started to contribute to the chemical enrichment in this galaxy.

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CHEMICAL ABUNDANCES OF THE MILKY WAY THICK DISK AND STELLAR HALO. I. IMPLICATIONS OF [α/Fe] FOR STAR FORMATION HISTORIES IN THEIR PROGENITORS

Cited by 107 publications

References 113 publications

Disentangling the Galactic Halo with APOGEE. I. Chemical and Kinematical Investigation of Distinct Metal-poor Populations

Disentangling the Galactic Halo with APOGEE. I. Chemical and Kinematical Investigation of Distinct Metal-poor Populations

A characteristic oxygen abundance gradient in galaxy disks unveiled with CALIFA

Chemical compositions of six metal-poor stars in the ultra-faint dwarf spheroidal galaxy Boötes I

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