Unveiling the Cosmic Chemistry II: "Direct" $T_e$-based metallicity of galaxies at 3 $< z <$ 10 with JWST/NIRSpec

Abstract

We report the detection of the [O III] auroral line in 42 galaxies within the redshift range of $3 < z < 10$. These galaxies were selected from publicly available JWST data releases, including the JADES and PRIMALsurveys, and observed using both the low-resolution PRISM/CLEAR configuration and medium-resolution gratings. The measured electron temperatures in the high-ionization regions of these galaxies range from $T_e$([O III]) = 12,000 to 24,000 K, consistent with temperatures observed in local metal-poor galaxies and previous JWST studies. In 10 galaxies, we also detect the [O II] auroral line, allowing us to determine electron temperatures in the low-ionization regions, which range between $T_e$([O II]) = 10,830 and 20,000 K. The direct-$T_e$-based metallicities of our sample span from 12 + log(O/H) = 7.2 to 8.4, indicating these high-redshift galaxies are relatively metal-poor. By combining our sample with 25 galaxies from the literature, we expand the dataset to a total of 67 galaxies within $3 < z < 10$, effectively more than doubling the previous sample size for direct-$T_e$ based metallicity studies. This larger dataset allow us to derive empirical metallicity calibration relations based exclusively on high-redshift galaxies, using six key line ratios: R3, R2, R23, Ne3O2, O32, and O3N2. Notably, we derive a novel metallicity calibration relation for the first time using high-redshift $T_e$-based metallicities: $\hat{R}$ = 0.18log $R2$ + 0.98log $R3$. This new calibration significantly reduces the scatter in high-redshift galaxies compared to the $\hat{R}$ relation previously calibrated for low-redshift galaxies.

Figures (10)

• Figure 1: Left-top: Redshift distribution ($3 < z < 10$) of galaxies used in our study that exhibit the auroral [$\hbox{\rm O {\sc iii}}$]$\lambda4363$ line. The green histogram represents galaxies from GOODS-N and GOODS-S Data Release 3 2024arXiv240406531D, while the orange histogram shows galaxies from the PRIMAL survey 2024arXiv240402211H. The grey histogram captures JWST-detected galaxies from existing literature within $3 < z < 10$ that also display the [$\hbox{\rm O {\sc iii}}$]$\lambda4363$ line 2024ApJ...962...24S. Left-bottom: The stellar mass distribution of galaxies used in our study is shown, using the same color-coding as above. Right-top: The Mass-Excitation (MEx) diagram for our complete sample, illustrating the relationship between log([$\hbox{\rm O {\sc iii}}$]$\lambda$5007/H$\beta$) and the stellar mass. This diagnostic, based on 2024ApJ...960L..13H and MEx curves from 2015ApJ...801...35C, shows probable AGN regions with likelihoods of $\sim$0.3 (red) and $\sim$0.8 (blue). We find no evidence of significant AGN contamination in our sample. Right-bottom: [$\hbox{\rm O {\sc iii}}$]/H$\beta$ vs. [$\hbox{\rm N {\sc ii}}$]/H$\alpha$ BPT diagram for our sample of galaxies. The green dotted curve represents the $z\sim0$ demarcation line between star-forming galaxies and AGNs from 2003MNRAS.346.1055K. The blue solid and red dashed curves indicate the predicted upper limits for star-forming galaxies at $z\sim2.3$, as proposed by 2013ApJ...774L..10K and the theoretical model from 2014MNRAS.443.1358M, respectively.
• Figure 2: The 1D spectra of six galaxies in our sample illustrate the detected [$\hbox{\rm O {\sc iii}}$]$\lambda$4363 and H$\gamma$ emission lines, representing galaxies across various redshifts. The x-axes are converted to rest-frame wavelengths using the best-fit redshifts. The red curve shows the best-fit continuum along with the [$\hbox{\rm O {\sc iii}}$]$\lambda$4363 and H$\gamma$ emission line profiles. The black dashed line marks the rest-frame wavelengths of [$\hbox{\rm O {\sc iii}}$]$\lambda$4363 and H$\gamma$.
• Figure 3: The 1D spectra of 10 galaxies in our sample show the detected [$\hbox{\rm O {\sc ii}}$]$\lambda\lambda7322, 7332$ doublet. The x-axes are converted to rest-frame wavelengths using the best-fit redshifts. The grey represents the observed data, while the red curve displays the best-fit continuum along with the emission line profiles for [$\hbox{\rm O {\sc ii}}$]$\lambda7322$ and [$\hbox{\rm O {\sc ii}}$]$\lambda7332$. Vertical black dashed lines indicate the rest-frame wavelengths of these lines.
• Figure 4: The relation between the electron temperatures, $T_e$([$\hbox{\rm O {\sc ii}}$]) and $T_e$([$\hbox{\rm O {\sc iii}}$]), is shown for the 10 galaxies in our sample with detected $[\hbox{\rm O {\sc ii}}]\lambda\lambda 7322, 7332$ auroral lines. Black filled circles represent our sample, while the gray triangle indicates the one galaxy from 2024ApJ...962...24S at $z$ = 3.302. The red curve shows the best-fit linear regression line with $1\sigma$ uncertainties. Blue, violet, and green dashed lines display $T_e$([$\hbox{\rm O {\sc ii}}$]) vs. $T_e$([$\hbox{\rm O {\sc iii}}$]) relations for local galaxies from 1986MNRAS.223..811C, 2009MNRAS.398..485P, and 1992MNRAS.255..325P. The orange dashed and dotted curves, adapted from 2006AA...448..955I, represent metallicities $12 + \log(\text{O/H}) = 7.2$ and $8.2$, respectively.
• Figure 5: The relationship between $T_e$-based metallicity and strong-line ratios (R3, R2, R23, O32, Ne3O2, and O3N2) is shown for a sample of 67 individual galaxies within the redshift range $3 < z < 10$. Purple and green data points represent galaxies from the GOODS-N and GOODS-S fields, respectively, based on the JADES data release 3 2024arXiv240406531D. Orange data points correspond to galaxies from the PRIMAL survey 2024arXiv240402211H, while gray data points indicate JWST-detected galaxies compiled from the literature 2024ApJ...962...24S. Large red data points denote the metallicity-averaged line ratios. Blue curves represent our best-fit polynomials with $1\sigma$ uncertainties for each diagnostic.