On the variation in stellar $\alpha$-enhancements of star-forming galaxies in the EAGLE simulation

Abstract

The ratio of $\alpha$-elements to iron in galaxies holds valuable information about the star formation history since their enrichment occurs on different timescales. The fossil record of stars in galaxies has mostly been excavated for passive galaxies, since the light of star-forming galaxies is dominated by young stars which have much weaker atmospheric absorption features. Here we use the largest reference cosmological simulation of the EAGLE project to investigate the origin of variations in stellar $\alpha$-enhancement among star-forming galaxies at $z=0$, and their impact on integrated spectra. The definition of $\alpha$-enhancement in a composite stellar population is ambiguous. We elucidate two definitions - termed `mean' and `galactic' $\alpha$-enhancement - in more detail. While a star-forming galaxy has a high `mean' $\alpha$-enhancement when its stars formed rapidly, a galaxy with a large `galactic' $\alpha$-enhancement generally had a delayed star formation history. We find that absorption-line strengths of Mg and Fe correlate with variations in $\alpha$-enhancement. These correlations are strongest for the `galactic' $\alpha$-enhancement. However, we show that these are mostly caused by other effects which are cross-correlated with $\alpha$-enhancement, such as variations in the light-weighted age. This severely complicates the retrieval of $\alpha$-enhancements in star-forming galaxies. The ambiguity is not severe for passive galaxies and we confirm that spectral variations in these galaxies are caused by measurable variations in $\alpha$-enhancements. We suggest that this more complex coupling between $\alpha$-enhancement and star formation histories can guide the interpretation of new observations of star-forming galaxies.

arXiv comment21 pages, 12 figures, 4 tables. Accepted to ApJ

References in corpus (88)

• SciPy 1.0--Fundamental Algorithms for Scientific Computing in Python
• The NumPy array: a structure for efficient numerical computation
• Planck 2015 results. XIII. Cosmological parameters
• Galactic Stellar and Substellar Initial Mass Function
• Planck 2013 results. XVI. Cosmological parameters
• The cosmological simulation code GADGET-2
• The Global Schmidt Law in Star Forming Galaxies
• The EAGLE project: Simulating the evolution and assembly of galaxies and their environments
• Populating a cluster of galaxies - I. Results at z=0
• Parametric Recovery of Line-of-Sight Velocity Distributions from Absorption-Line Spectra of Galaxies via Penalized Likelihood
• The Apache Point Observatory Galactic Evolution Experiment (APOGEE)
• The epochs of early-type galaxy formation as a function of environment
• The EAGLE simulations of galaxy formation: calibration of subgrid physics and model variations
• The New Galaxy: Signatures of its Formation
• Substructures in hydrodynamical cluster simulations
• Modeling the Panchromatic Spectral Energy Distributions of Galaxies
• The effect of photo-ionization on the cooling rates of enriched, astrophysical plasmas
• The Chemical Evolution of the Galaxy: the two-infall model
• Cosmological simulations of the growth of supermassive black holes and feedback from active galactic nuclei: method and tests
• The GALAH Survey: Scientific Motivation
• Stellar population models of Lick indices with variable element abundance ratios
• Stellar Chemical Signatures And Hierarchical Galaxy Formation
• Old Stellar Populations. VI. Absorption-Line Spectra of Galaxy Nuclei and Globular Clusters
• Chemical enrichment in cosmological, smoothed particle hydrodynamics simulations
• The Stellar Population Histories of Local Early-Type Galaxies. I. Population Parameters
• On the relation between the Schmidt and Kennicutt-Schmidt star formation laws and its implications for numerical simulations
• Chemical Cartography with APOGEE: Metallicity Distribution Functions and the Chemical Structure of the Milky Way Disk
• How to Measure Galaxy Star Formation Histories II: Nonparametric Models
• Simulating galactic outflows with thermal supernova feedback
• The EAGLE simulations of galaxy formation: public release of halo and galaxy catalogues
• The Atlas3D Project - XXX. Star formation histories and stellar population scaling relations of early-type galaxies
• Chemical yields from low- and intermediate-mass stars: model predictions and basic observational constraints
• Evolution of galaxy stellar masses and star formation rates in the EAGLE simulations
• Evidence from the H3 Survey that the Stellar Halo is Entirely Comprised of Substructure
• Evolutionary stellar population synthesis with MILES - II. Scaled-solar and α-enhanced models
• Environment and self-regulation in galaxy formation
• On the typical timescale for the chemical enrichment from SNeIa in Galaxies
• Early-Type Galaxy Archeology: Ages, Abundance Ratios, and Effective Temperatures from Full-Spectrum Fitting
• The star formation main sequence and stellar mass assembly of galaxies in the Illustris simulation
• An Older, More Quiescent Universe from Panchromatic SED Fitting of the 3D-HST Survey
• The GALAH Survey: Observational Overview and Gaia DR1 companion
• STEllar Content and Kinematics from high resolution galactic spectra via Maximum A Posteriori
• Optical colours and spectral indices of $z=0.1$ EAGLE galaxies with 3D dust radiative transfer code SKIRT
• Galactic Archaeology with asteroseismic ages: evidence for delayed gas infall in the formation of the Milky Way disc
• Inflow, Outflow, Yields, and Stellar Population Mixing in Chemical Evolution Models
• VINTERGATAN I: The origins of chemically, kinematically and structurally distinct discs in a simulated Milky Way-mass galaxy
• ProSpect: Generating Spectral Energy Distributions with Complex Star Formation and Metallicity Histories
• Non-parametric Star Formation History Reconstruction with Gaussian Processes I: Counting Major Episodes of Star Formation
• On the function describing the stellar initial mass function
• Galaxy metallicity scaling relations in the EAGLE simulations
• Stochastic modelling of star-formation histories II: star-formation variability from molecular clouds and gas inflow
• The IMACS Cluster Building Survey: IV. The Log-normal Star Formation History of Galaxies
• Far-infrared and dust properties of present-day galaxies in the EAGLE simulations
• The origin of scatter in the star formation rate - stellar mass relation
• Chemical element ratios of SDSS early-type galaxies
• The AMBRE Project: chemical evolution models for the Milky Way thick and thin discs
• Equilibrium and Sudden Events in Chemical Evolution
• The Diversity and Variability of Star Formation Histories in Models of Galaxy Evolution
• Chemical Enrichment and Radial Migration in the Galactic Disk -- the origin of the [$\alpha /\mathrm{Fe}]$ Double Sequence
• The origin of diverse $\alpha$-element abundances in galaxy discs
• Galactic chemical evolution in hierarchical formation models - I. Early-type galaxies in the local Universe
• The Ages, Metallicities and Alpha Element Enhancements of Globular Clusters in the Elliptical NGC 5128: A Homogeneous Spectroscopic Study with Gemini/GMOS
• The Fornax 3D project: unveiling the thick disk origin in FCC 170: signs of accretion?
• APOGEE DR16: a multi-zone chemical evolution model for the Galactic disc based on MCMC methods
• The link between the Star Formation History and [alpha/Fe]
• Differential stellar population models: how to reliably measure [Fe/H] and [alpha/Fe] in galaxies
• The rise and fall of the star formation histories of blue galaxies at redshifts 0.2<z<1.4
• Log-normal star formation histories in simulated and observed galaxies
• Galaxy evolution across environments as probed by the ages, stellar metallicities and [alpha/Fe] of central and satellite galaxies
• Variations of the initial mass function in semi-analytical models: implications for the mass assembly and the chemical enrichment of galaxies in the GAEA model
• Probing recent star formation with absorption-line strengths in hierarchical models and observations
• Deriving the Metallicity Distribution Function of Galactic Systems
• Stellar Metallicities and Elemental Abundance Ratios of z~1.4 Massive Quiescent Galaxies
• The origin of the $\alpha$-enhancement of massive galaxies
• Age-chemical abundance structure of the Galaxy I: Evidence for a late accretion event in the outer disc at z ~ 0.6
• Timing the evolution of quiescent and star-forming local galaxies
• Stellar populations across galaxy bars in the MUSE TIMER project
• Reproducing the Universe: a comparison between the EAGLE simulations and the nearby DustPedia galaxy sample
• The Milky Way's bulge star formation history as constrained from its bimodal chemical abundance distribution
• The [α/Fe]-[Fe/H] relation in the E-MOSAICS simulations: its connection to the birth place of globular clusters and the fraction of globular cluster field stars in the bulge
• How Unusual is the Milky Way's Assembly History?
• The distribution of [$\alpha$/Fe] in the Milky Way disc
• Galaxy properties as revealed by MaNGA. III. Kinematic profiles and stellar population gradients in S0s
• Star-forming galaxies are predicted to lie on a fundamental plane of mass, star formation rate and α-enhancement
• The effects of the IMF on the chemical evolution of elliptical galaxies
• sMILES: A Library of Semi-Empirical MILES Stellar Spectra with Variable [$\alpha$/Fe] Abundances
• How well can we determine ages and chemical abundances from spectral fitting of integrated light spectra?
• Calibrated, cosmological hydrodynamical simulations with variable IMFs II: Correlations between the IMF and global galaxy properties

Cited by in corpus (4)

• A Tale of Two Disks: Mapping the Milky Way with the Final Data Release of APOGEE
• Revisiting equilibrium condensation and rocky planet compositions: Introducing the ECCOplanets code
• A Galactic Self-Portrait: Density Structure and Integrated Properties of the Milky Way Disk
• The Stellar Chemical Abundances of Simulated Massive Galaxies at $z=2$