James Webb Space Telescope Feed Post

Spatially resolved emission lines in galaxies at 4 <= z < 10 from the JADES survey: evidence for enhanced central star formation

3-arcsec false-colour cutouts of all the galaxies with high S/N and with available JWST/NIRCam photometry, sorted by increasing redshift z (targets 4270 and 16745 are reported already in Figs. 1 and 2 and are not repeated here). The nominal location of the shutters is overlaid; the MSA acquisition accuracy is better than one NIRCam pixel (0.03 arcsec). This figure illustrates the key synergy between NIRCam and NIRSpec/MSA; imaging clarifies that for individual galaxies gradients along the slit may result from complex morphologies. However, because the intra-shutter positions are effectively random between different targets, a stacking analysis over a sufficiently large sample may ‘marginalise’ over peculiar morphologies. Abstract: We present the first statistical investigation of spatially resolved emission-line properties in a sample of 63 low-mass galaxies at 4=z<10, using JWST/NIRSpec MSA data from the JWST Advanced Deep Extragalactic (JADES) survey focusing on deep, spatially resolved spectroscopy in the GOODS-S extragalactic field. By performing a stacking of the 2D spectra of the galaxies in our sample, we find an increasing or flat radial trend with increasing radius for [OIII]?5007/Hß and a decreasing one for [NeIII]?3869/[OII]?3727 (3--4 s significance). These results are still valid when stacking the sample in two redshift bins (i.e., 4=z<5.5 and 5.5=z<10). The comparison with star-formation photoionization models suggests that the ionization parameter increases by ~0.5 dex with redshift. We find a tentative metallicity gradient that increases with radius (i.e., 'inverted') in both redshift bins. Moreover, our analysis reveals strong negative gradients for the equivalent width of \Hbeta (7s significance). This trend persists even after removing known AGN candidates, therefore, it is consistent with a radial gradient primarily in stellar age and secondarily in metallicity. Taken all together, our results suggest that the sample is dominated by active central star formation, with possibly inverted metallicity gradients sustained by recent episodes of accretion of pristine gas or strong radial flows. Deeper observations and larger samples are needed to confirm these preliminary results and to validate our interpretation.