The ALPINE-CRISTAL-JWST Survey: Gas-phase abundance gradients of main sequence star-forming galaxies and their kinematics at $4 < z < 6$

Abstract

We present gas-phase radial metallicity profiles for 20 main-sequence galaxies at $4<z<6$, primarily based on JWST NIRSpec IFU observations obtained as part of the JWST-ALPINE-CRISTAL programme. Our study aims to connect the metallicity gradients of these galaxies with their kinematic properties from [CII]158$μ$m ALMA observations. We map the radial profiles of oxygen abundance using the strong-line method leveraging the rich set of rest-frame optical emission lines. Linear fits to the annular-binned radial profiles show that, on average, the metallicity gradients are slightly positive with a median of $+0.039 \pm 0.010{\rm dexkpc^{-1}}$. There are no substantial systematic offsets in gradients when using different line diagnostics. However, only three galaxies show a gradient $>0.05{\rm dexkpc^{-1}}$ at $1σ$, and none have a significant negative gradient. We investigate the correlation between the metallicity gradients and the intrinsic gas velocity dispersion $σ_0$, as well as the ratio $V_{\rm rot}/σ_0$ of the disks. Combining our sample with mass-matched literature samples at $3<z<7$, we find a negative shallow correlation between $V_{\rm rot}/σ_0$ and the metallicity gradients, but no strong relationships with $σ_0$. As $V_{\rm rot}/σ_0$ increases towards later cosmic times, the observed negative trend with $V_{\rm rot}/σ_0$ is consistent with the overall cosmic evolution of metallicity gradients from high to low redshifts. This suggests that disk maturity plays a crucial role in shaping the radial metallicity gradients. [Abridged abstract]

Figures (15)

• Figure 1: Example spectral fit of CRISTAL-11 ($z=4.439$) for each annulus (left). The fitting procedure of the spectra is described in Sect. \ref{['sec:emission_line_fitting']}. The radius of the corresponding annulus is indicated in physical units on the right. The lines used for inferring metallicity in Sect. \ref{['sec:strong_line_method']} are annotated at the top. The shape of the annuli are shown in the right panel, overlaid on the line flux map of H${\alpha}$. The PSF after PSF homogenisation is shown at the bottom left.
• Figure 2: Radial profiles of metallicities and their best-fit linear models (black lines). For each galaxy, the left panel shows the azimuthally-averaged profiles, where dark green pentagons with black outlines represent the metallicities derived by combining the listed line diagnostics using a Bayesian approach (Method I). The translucent grey lines are 300 random draws from the posterior distribution of the model parameters. The outermost radius at which each diagnostic is used is annotated at the corresponding location on the profile. The fainter coloured diamonds represent the metallicities obtained from individual diagnostics via Method II, while the lines in the corresponding colours show the best-fit models for each diagnostic. Similarly, the right panel shows the pixel-based metallicity profile with each data point coloured coded by its (absolute) acute azimuthal angle difference from the major axis. Line diagnostics of which only two annuli are available are shown (coloured diamonds) but not fitted.
• Figure 3: (Continued.)
• Figure 4: (Continued.)
• Figure 5: Distributions of metallicity gradients, $\nabla_r \log({Z})$, as a function of the velocity dispersion, $\sigma_0$ (left), and the ratio of rotational velocity to velocity dispersion, $V_{\rm rot}/\sigma_0$ (right), for the CRISTAL disk galaxies (green hexagons). We also show $M_{\star}$-matched literature samples at $3$$\lesssim$$z$$\lesssim7$ as red hexagons, and $z$$<$$3$ as grey crosses. The references for these literature samples are listed in Table \ref{['tab:literature_sample']}. The Kendall's $\tau$ correlation coefficients and the $p$-values are annotated in the top left in each panel. Histograms of the distributions of the $3$$\lesssim$$z$$\lesssim7$ and $z$$<$$3$ samples are shown along the $x$- and $y$-axes in red and grey, respectively. The combined CRISTAL and literature sample exhibits a shallow negative correlation between $\nabla_r \log({Z})$ and $V_{\rm rot}/\sigma_0$, as indicated by the Kendall's $\tau$ value. The yellow dot-dashed line is the Theil–Sen median-slope regression Sen1968, included solely to guide the eye; it is not used in any statistical tests. In contrast, the Kendall's correlation test reveals no significant correlation with $\sigma_0$, which could be due to the inherently shallow trend and the large scatter. However, the overall distribution of the two populations at $z<3$ (grey histogram) and $z\geqslant3$ (red histogram), a clearer distinction emerges between the $z<3$ and $z\geqslant3$ populations. Specifically, the $z\geqslant3$ population tends to have higher $\sigma_0$ values and more positive metallicity gradients, whereas the $z<3$ population has lower $\sigma_0$ values and, on average, lower metallicity gradients. This distinction is supported by the significant 2D K-S test statistics, which gives a nearly 3-$\sigma$ significance level (annotated at the bottom left of each panel). The predicted trends from cosmological simulations are shown, including FIRE at $z$$=$$2$ from Ma2017 (purple contour), FIRE2 at $z$$=$$3$ from Sun2025 (right, open purple pentagons), and TNG50 at $z=3$ from Hemler2021 (right, orange dashed line). While the simulations capture the slight positive and negative relationships between $\nabla_r \log({Z})$ and $\sigma_0$ and $V_{\rm rot}/\sigma_0$, respectively, the normalisation and steepness of these relationships differ from the observations.