Elemental Abundances in M31: Alpha and Iron Element Abundances from Low-resolution Resolved Stellar Spectroscopy in the Stellar Halo

Escala, Ivanna; Kirby, Evan N.; Gilbert, Karoline M.; Cunningham, Emily C.; Wojno, Jennifer

doi:10.3847/1538-4357/ab1eac

Cited by 28 publications

(87 citation statements)

References 92 publications

(183 reference statements)

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“…As was made clear by previous papers in this series (Escala et al 2019(Escala et al , 2020Gilbert et al 2019;Kirby et al 2020), significant progress is being made in determining individual abundances for stars in M31 and its satellite galaxies. However, sample sizes are not yet large enough to provide maximally informative constraints on the SFH of M31.…”

Section: Introductionmentioning

confidence: 91%

“…To determine spectroscopic effective temperature, [Fe/H], and [α/Fe] for individual stars, we adopt the synthetic spectral synthesis method that was outlined in Kirby et al (2008) and further refined in Escala et al (2019) using a Python-based implementation of the method. An in-depth comparison between the results from the two pipelines- Kirby et al (2008), written in IDL, and Escala et al (2019), written in Python-is provided in Appendix A. In Figure 1, we provide a graphical depiction of the pipeline process, both for individual spectra, described in this section, and for coadded spectra, described in Section 4.…”

Section: Individual Abundance Measurementsmentioning

confidence: 99%

“…Here, we outline the pipeline we use to measure [Fe/H] and [α/Fe] for individual stars (Kirby et al 2008;Escala et al 2019), which we modify to measure abundances from coadded spectra as discussed in Section 4.…”

Section: Chemical Abundance Pipelinementioning

confidence: 99%

“…We note that the mask for [α/Fe] is constructed from regions sensitive to the individual alpha elements Mg, Ca, Si, and Ti. In addition to these abundance masks, a general mask is applied to all spectra in order to exclude pixels at the beginning and end of the spectra, pixels near the detector chip gap, regions of bad sky subtraction, and other detector artifacts (Escala et al 2019).…”

Section: Abundance Masksmentioning

confidence: 99%

“…Before the era of large-scale, ground-based spectroscopic surveys, such abundance measurements have been limited to stars within the Milky Way (MW), or MW satellites. It is now possible to push beyond the boundaries of our own Galaxy, and determine spectroscopic metallicities for red giant stars in our nearest neighbor, Andromeda (M31); see Escala et al (2019Escala et al ( , 2020 and Gilbert et al (2019) for the most recent such studies. At a distance of 760 kpc (Tully et al 2013), the Andromeda galaxy is the closest grand-design spiral galaxy to the MW, and provides an opportunity to study in detail the formation history of a massive galaxy external to our own.…”

Section: Introductionmentioning

confidence: 99%

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Elemental Abundances in M31: [Fe/H] and [α/Fe] in M31 Dwarf Galaxies Using Coadded Spectra

Wojno

Gilbert

Kirby

et al. 2020

ApJ

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We present chemical abundances of red giant branch (RGB) stars in the dwarf spheroidal (dSph) satellite system of Andromeda (M31), using spectral synthesis of medium-resolution (R ∼ 6000) spectra obtained with the Keck II telescope and Deep Imaging Multi-Object Spectrometer spectrograph via the Spectroscopic and Photometric Landscape of Andromeda's Stellar Halo survey. We coadd stars according to their similarity in photometric metallicity or effective temperature to obtain a signal-to-noise ratio (S/N) high enough to measure average [Fe/H] and [α/Fe] abundances. We validate our method using high S/N spectra of RGB stars in Milky Way globular clusters, as well as deep observations for a subset of the M31 dSphs in our sample. For this set of validation coadds, we compare the weighted average abundance of the individual stars with the abundance determined from the coadd. We present individual and coadded measurements of [Fe/H] and [α/Fe] for stars in 10 M31 dSphs, including the first [α/Fe] measurements for And IX, XIV, XV, and XVIII. These fainter, less massive dSphs show declining [α/Fe] relative to [Fe/H], implying an extended star formation history (SFH). In addition, these dSphs also follow the same mass-metallicity relation found in other Local Group satellites. The conclusions we infer from coadded spectra agree with those from previous measurements in brighter M31 dSphs with individual abundance measurements, as well as conclusions from photometric studies. These abundances greatly increase the number of spectroscopic measurements of the chemical composition of M31ʼs less massive dwarf satellites, which are crucial to understanding their SFH and interaction with the M31 system.

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Section: Introductionmentioning

confidence: 91%

Section: Individual Abundance Measurementsmentioning

confidence: 99%

Section: Chemical Abundance Pipelinementioning

confidence: 99%

Section: Abundance Masksmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Elemental Abundances in M31: [Fe/H] and [α/Fe] in M31 Dwarf Galaxies Using Coadded Spectra

Wojno

Gilbert

Kirby

et al. 2020

ApJ

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The Prevalence of the α-bimodality: First JWST α-abundance Results in M31

Nidever,

Gilbert,

Tollerud

et al. 2022

Proc. IAU

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We present initial results from our JWST NIRSpec program to study the α-abundances in the M31 disk. The Milky Way has two chemically-defined disks, the low-α and high-α disks, which are closely related to the thin and thick disks, respectively. The origin of the two populations and the α-bimodality between them is not entirely clear, although there are now several models that can reproduce the observed features. To help constrain the models and discern the origin, we have undertaken a study of the chemical abundances of the M31 disk using JWST NIRSpec, in order to determine whether stars in M31’s disk also show an α-abundance bimodality. Approximately 100 stars were observed in our single NIRSpec field at a projected distance of 18 kpc from the M31 center. The 1-D extracted spectra have an average signal-to-noise ratio of 85 leading to statistical metallicity precision of 0.016 dex, α-abundance precision of 0.012 dex, and a radial velocity precision 8 km s-1 (mostly from systematics). The initial results indicate that, in contrast to the Milky Way, there is no α-bimodality in the M31 disk, and no low-α sequence. The entire stellar population falls along a single chemical sequence very similar to the MW’s high-α component which had a high star formation rate. While this is somewhat unexpected, the result is not that surprising based on other studies that found the M31 disk has a larger velocity dispersion than the MW and is dominated by a thick component. M31 has had a more active accretion and merger history than the MW which might explain the chemical differences.

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The chemical composition of globular clusters in the Local Group

Larsen

Eitner

Magg

et al. 2022

A&A

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We present detailed chemical abundance measurements for 45 globular clusters (GCs) associated with galaxies in (and, in one case, beyond) the Local Group. The measurements are based on new high-resolution integrated-light spectra of GCs in the galaxies NGC 185, NGC 205, M 31, M 33, and NGC 2403, combined with reanalysis of previously published observations of GCs in the Fornax dSph, WLM, NGC 147, NGC 6822, and the Milky Way. The GCs cover the range −2.8 < [Fe/H] < −0.1 and we determined abundances for Fe, Na, Mg, Si, Ca, Sc, Ti, Cr, Mn, Ni, Cu, Zn, Zr, Ba, and Eu. Corrections for non local thermodynamic equilibrium effects are included for Na, Mg, Ca, Ti, Mn, Fe, Ni, and Ba, building on a recently developed procedure. For several of the galaxies, our measurements provide the first quantitative constraints on the detailed composition of their metal-poor stellar populations. Overall, the GCs in different galaxies exhibit remarkably uniform abundance patterns of the α, iron-peak, and neutron-capture elements, with a dispersion of less than 0.1 dex in [α/Fe] for the full sample. There is a hint that GCs in dwarf galaxies are slightly less α-enhanced (by ∼0.04 dex on average) than those in larger galaxies. One GC in M 33 (HM33-B) resembles the most metal-rich GCs in the Fornax dSph (Fornax 4) and NGC 6822 (SC7) by having α-element abundances closer to scaled-solar values, possibly hinting at an accretion origin. A principal components analysis shows that the α-element abundances strongly correlate with those of Na, Sc, Ni, and Zn. Several GCs with [Fe/H] < −1.5 are deficient in Mg compared to other α-elements. We find no GCs with strongly enhanced r-process abundances as reported for metal-poor stars in some ultra-faint dwarfs and the Magellanic Clouds. The similarity of the abundance patterns for metal-poor GCs in different environments points to similar early enrichment histories and only allow for minor variations in the initial mass function.

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Elemental Abundances in M31: Alpha and Iron Element Abundances from Low-resolution Resolved Stellar Spectroscopy in the Stellar Halo

Cited by 28 publications

References 92 publications

Elemental Abundances in M31: [Fe/H] and [α/Fe] in M31 Dwarf Galaxies Using Coadded Spectra

Elemental Abundances in M31: [Fe/H] and [α/Fe] in M31 Dwarf Galaxies Using Coadded Spectra

The Prevalence of the α-bimodality: First JWST α-abundance Results in M31

The chemical composition of globular clusters in the Local Group

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