THE EVOLUTION OF METALLICITY AND METALLICITY GRADIENTS FROM z = 2.7 TO 0.6 WITH KMOS^3D

Abstract

We present measurements of the [N II]/Hα ratio as a probe of gas-phase oxygen abundance for a sample of 419 star-forming galaxies at z = 0.6 − 2.7 from the KMOS 3D near-IR multi-IFU survey. The mass-metallicity relation (MZR) is determined consistently with the same sample selection, metallicity tracer, and methodology over the wide redshift range probed by the survey. We find good agreement with long-slit surveys in the literature, except for the low-mass slope of the relation at z ∼ 2.3, where this sample is less biased than previous samples based on optical spectroscopic redshifts. In this regime we measure a steeper slope than some literature results. Excluding the AGN contribution from the MZR reduces sensitivity at the high mass end, but produces otherwise consistent results. There is no significant dependence of the [N II]/Hα ratio on SFR or environment at fixed redshift and stellar mass. The IFU data allow spatially resolved measurements of [N II]/Hα, from which we can infer abundance gradients for 180 galaxies, thus tripling the current sample in the literature. The observed gradients are on average flat, with only 15 gradients statistically offset from zero at > 3σ. We have modelled the effect of beam-smearing, assuming a smooth intrinsic radial gradient and known seeing, inclination and effective radius for each galaxy. Our seeing-limited observations can recover up to 70% of the intrinsic gradient for the largest, face-on disks, but only 30% for the smaller, more inclined galaxies. We do not find significant trends between observed or corrected gradients and any stellar population, dynamical or structural galaxy parameters, mostly in agreement with existing studies with much smaller sample sizes. In cosmological simulations, strong feedback is generally required to produce flat gradients at high redshift.

What the Milky Way bulge reveals about the initial metallicity gradients in the disc

“…Our findings suggest that the stellar populations that make up the inner MW arose from an ISM that was well mixed and turbulent and whose radial metallicity gradients were mostly flat (Haywood et al 2013;Nidever et al 2014;Feng & Krumholz 2014;Di Matteo et al 2015;Haywood et al 2015;Wuyts et al 2016;Di Matteo 2016), with stars first forming in a geometrically thick layer and then in thinner layers in an upsidedown fashion (e.g. Bird et al 2013).…”

“…Discs D2 and D3 are assigned a flat radial metallicity gradient, since we assume that the interstellar medium (ISM) was well mixed at the time the young and old thick disc formed (z > 1) owing to a high star formation rate (> 10 M /yr), meaning that the galaxy was likely in a bursty and turbulent state (Lehnert et al 2014;Wuyts et al 2016;Ma et al 2017, but see also Pilkington et al 2012). The thin disc (D1) is associated with the final more quiescent phase of the MW in the last ∼7-8 Gyr (see Snaith et al 2014;Haywood et al 2016b).…”

Survival of Massive Star-forming Galaxies in Cluster Cores Drives Gas-phase Metallicity Gradients: The Effects of Ram Pressure Stripping

“…Observations of local field galaxies show that all isolated spiral galaxies have the same internal metallicity gradient within ±0.14 dex/R 25 (Ho et al 2015;Sánchez et al 2016). However, the internal metallicity gradient of spiral galaxies evolves with redshift (Yuan et al 2013;Jones et al 2013;Wuyts et al 2016). In our simulation, we redshift the CALIFA galaxies from an average redshift of z = 0.01 to z cl = 0.35.…”

Galaxy metallicity scaling relations in the EAGLE simulations

“…In the following, we summarize briefly the different observational data used here (for more details, the reader is referred to the corresponding papers): de los Reyes et al (2015) (medians and scatter at z ≈ 0.8), Hunt et al (2016) (medians with 75 per cent and 25 per cent quantile levels at 0.4 < z ≤ 0.7, 0.9 < z ≤ 1.8, 1.8 < z ≤ 2.8 and 2.8 < z ≤ 3.8), Ly et al (2016) (medians with the 16th and 84th percentiles at z = 0.5-1.0), Stott et al (2013) (median values and standard errors at z ≈ 0.84-1.47), Yabe et al (2014) (medians and bootstrap errors at z ≈ 1.4), Zahid et al (2014b) (fitted metallicities and observational uncertainties at z ≈ 1.6), Wuyts et al (2016) (mean values and standard errors at z ≈ 0.9 and z ≈ 2.3), Sanders et al (2015) (mean values and uncertainties at z ≈ 2.3), Cullen et al (2014) (fitted metallicities with uncertainties at z 2), Troncoso et al (2014) (individual measurements and their uncertainties at z ≈ 3.4) and Onodera et al (2016) (results from stacking analysis at z ≈ 3.3). Dotted lines in the large four panels indicate the fits to observations at different z given by Maiolino et al (2008).…”