Inefficient dust production in a massive, metal-rich galaxy at $z=7.13$ uncovered by JWST and ALMA

TL;DR

This study uses joint JWST and ALMA observations of the lensed galaxy A1689-zD1 at z=7.13 to quantify its dust, gas, and metal content. Through SED fitting and nebular/line diagnostics, the authors find a substantial dust mass yet remarkably low DTG and DTM ratios ($DTG\approx5.1\times10^{-4}$ and $DTM\approx6.1\times10^{-2}$) relative to local galaxies with similar metallicity, alongside a high gas mass and HI column density. The results, consistent with a broader trend among other metal-rich z>6 galaxies, imply that dust production or survival mechanisms, or dust emissivity, differ in the early universe. These findings challenge simple extrapolations of local dust evolution models and highlight the need for more JWST+ALMA investigations to map dust lifecycle and its dependencies on metallicity and redshift.

Abstract

Recent observations have revealed a remarkably rapid buildup of cosmic dust in the interstellar medium (ISM) of high redshift galaxies, with complex dust compositions and large abundances already appearing at redshifts $z>6$. Here we present a comprehensive, joint analysis of observations taken with the {\em James Webb Space Telescope} (JWST) and the Atacama Large Millimetre/sub-millimetre Array (ALMA) of the highly magnified, dusty `normal' galaxy, A1689-zD1 at $z=7.13$. We perform detailed spectro-photometric modeling of the rest-frame UV to far-infrared spectral energy distribution (SED) based on archival photometry of the source and report new rest-frame optical strong-line measurements and metallicity estimates from recent JWST/NIRSpec IFU data. We find that despite its substantial dust mass, $M_{\rm dust}\sim 1.5\times 10^{7}\,M_\odot$, A1689-zD1 has remarkably low dust-to-gas and dust-to-metal mass ratios, ${\rm DTG} = (5.1^{+3.0}_{-1.9})\times 10^{-4}$ and ${\rm DTM} = (6.1^{+3.6}_{-2.3})\times 10^{-2}$, respectively, due to its high metallicity $12+\log({\rm O/H}) = 8.36\pm 0.10$ and substantial gas mass, $M_{\rm gas} = (2.8^{+0.2}_{-1.7})\times 10^{10}\,M_\odot$. The DTG and DTM mass ratios are an order of magnitude lower than expected for galaxies in the local universe with similar chemical enrichment. These low relative measurements are also corroborated by the deficit observed in the $A_V/N_{\rm HI}$ ratio of A1689-zD1 in the line-of-sight. We find that this deviation in the DTG and DTM mass ratios appears to be ubiquitous in other metal-rich galaxies at similar redshifts, $z\gtrsim 6$. This suggests that the processes that form and destroy dust at later times, or the dust emissivity itself, are drastically different for galaxies in the early Universe.

Figures (9)

• Figure 1: Overview of the JWST and ALMA imaging and spectroscopic data of A1689-zD1. Panel (a): False-color JWST/NIRCam RGB image cutout (blue: F150W; green: F277W; red: F444W), overlaid with [C ii]-$158\mu$m emission contours showing $3,5,7,10\sigma$ (white solid lines). A scalebar is shown in the image plane. Panel (b): Panchromatic SED modeling of the photometric data of A1689-zD1, fixed to $z_{\rm [CII]}=7.1332$. The derived dust mass corrected for magnification is indicated. Panel (c): Extracted JWST/NIRSpec 1D spectrum (black) and associated $1\sigma$ error spectrum (grey). The best-fit Gaussian models of the most prominent nebular emission lines are shown in red. Panel (d): Extracted ALMA 1D spectrum centered on the [C ii]-$158\mu$m transition in velocity space (zero-point velocity set to $z_{\rm [CII]}=7.1332$). The measured line FWHM is indicated.
• Figure 2: Imaging and SED models. The top panels show the reduced, drizzled images ($3^{\prime \prime} \times 3^{\prime \prime}$) of A1689-zD1 in each of the available JWST/NIRCam filters (labeled above). In the middle panel is shown the best-fit UV to optical SED (grey curve) from BagpipesCarnall18, with the observed (red circles) and model (cyan region) photometric data points overplotted. The bottom panels show the derived posterior distributions, not corrected for magnification, for the stellar mass, $M_\star$, the SFR, the metallicity $Z$, and the visual attenuation, $A_V$, with the median and 16 to 84th percentiles marked.
• Figure 3: FIR dust emission model. The top right panel shows the best-fit modified blackbody (purple) using MercuriusWitstok22 to the derived FIR continuum measurements (black circles). The model is fixed at the spectroscopic redshift, $z=7.1332$. The bottom left cornerplot show the derived posterior distributions, not corrected for magnification, for the main dust emission properties.
• Figure 4: Photometric DLA model. The rest-frame UV to optical intrinsic SED derived from Bagpipes (grey curve) is shown with the best-fit DLA component with $N_{\rm HI}=10^{22.8}$ cm$^{-2}$ that minimizes the $\chi^2$ when compared to the observed photometry (green: HST, blue: JWST). The model photometry for the intrinsic SED (grey squares) and SED+DLA model (orange squares) is shown as well, integrated over the passbands highlighted by the bottom filter transmission curves (green: HST and blue: JWST shaded areas).
• Figure 5: Dust-to-gas versus metallicity relation. The dust-to-gas ratio, $A_V/N_{\rm HI}$, inferred for A1689-zD1 (red star) compared to the Galactic average and the Small and Large Magellanic Clouds Konstantopoulou24 and intermediate redshift $\gamma$-ray burst (GRB) sightlines (circles, color-coded according to their redshift). The black line shows the best-fit GRB and local relation Heintz23_GRB, with the light- and dark-grey shaded regions showing the $1\sigma$ and $2\sigma$ scatter of the relation.