We explore the kinematic gas properties of six \(5.5<z<7.4\) galaxies in the JWST Advanced Deep Extragalactic Survey (JADES), using high-resolution JWST/NIRSpec multi-object spectroscopy of the ...rest-frame optical emission lines OIII and H\(\alpha\). The objects are small and of low stellar mass (\(\sim 1\,\)kpc; \(M_*\sim10^{7-9}\,{\rm M_\odot}\)), less massive than any galaxy studied kinematically at \(z>1\) thus far. The cold gas masses implied by the observed star formation rates are \(\sim 10\times\) larger than the stellar masses. We find that their ionised gas is spatially resolved by JWST, with evidence for broadened lines and spatial velocity gradients. Using a simple thin-disc model, we fit these data with a novel forward modelling software that accounts for the complex geometry, point spread function, and pixellation of the NIRSpec instrument. We find the sample to include both rotation- and dispersion-dominated structures, as we detect velocity gradients of \(v(r_{\rm e})\approx100-150\,{\rm km\,s^{-1}}\), and find velocity dispersions of \(\sigma_0\approx 30-70\,{\rm km\,s^{-1}}\) that are comparable to those at cosmic noon. The dynamical masses implied by these models (\(M_{\rm dyn}\sim10^{9-10}\,{\rm M_\odot}\)) are larger than the stellar masses by up to a factor 40, and larger than the total baryonic mass (gas + stars) by a factor of \(\sim 3\). Qualitatively, this result is robust even if the observed velocity gradients reflect ongoing mergers rather than rotating discs. Unless the observed emission line kinematics is dominated by outflows, this implies that the centres of these galaxies are dark-matter dominated or that star formation is \(3\times\) less efficient, leading to higher inferred gas masses.
We present a study of the environments of 17 Lyman-\(\alpha\) (Ly\(\alpha\)) emitting galaxies (LAEs) in the reionisation era (\(5.8 < z < 8\)) identified by JWST/NIRSpec as part of the JWST Advanced ...Deep Extragalactic Survey (JADES). Unless situated in sufficiently (re)ionised regions, Ly\(\alpha\) emission from these galaxies would be strongly absorbed by neutral gas in the intergalactic medium (IGM). We conservatively estimate sizes of the ionised regions required to reconcile the relatively low Ly\(\alpha\) velocity offsets (\(\Delta v_\text{Ly\)\alpha\(}<300\,\mathrm{km\,s^{-1}}\)) with moderately high Ly\(\alpha\) escape fractions (\(f_\mathrm{esc,\,Ly\alpha}>5\%\)) observed in our sample of LAEs, suggesting the presence of ionised hydrogen along the line of sight towards at least eight out of 17 LAEs. We find minimum physical `bubble' sizes of the order of \(R_\text{ion}\sim0.1\)-\(1\,\mathrm{pMpc}\) are required in a patchy reionisation scenario where ionised bubbles containing the LAEs are embedded in a fully neutral IGM. Around half of the LAEs in our sample are found to coincide with large-scale galaxy overdensities seen in FRESCO at \(z \sim 5.8\)-\(5.9\) and \(z\sim7.3\), suggesting Ly\(\alpha\) transmission is strongly enhanced in such overdense regions, and underlining the importance of LAEs as tracers of the first large-scale ionised bubbles. Considering only spectroscopically confirmed galaxies, we find our sample of UV-faint LAEs (\(M_\text{UV}\gtrsim-20\,\mathrm{mag}\)) and their direct neighbours are generally not able to produce the required ionised regions based on the Ly\(\alpha\) transmission properties, suggesting lower-luminosity sources likely play an important role in carving out these bubbles. These observations demonstrate the combined power of JWST multi-object and slitless spectroscopy in acquiring a unique view of the early Universe during cosmic reionisation via the most distant LAEs.
Recent JWST/NIRCam imaging taken for the ultra-deep UNCOVER program reveals a very red dropout object at \(z_{\mathrm{phot}}\simeq7.6\), triply imaged by the galaxy cluster Abell 2744 ...(\(z_{\mathrm{d}}=0.308\)). All three images are very compact, i.e. unresolved, with a de-lensed size upper-limit of \(r_{e}\lesssim35\) pc. The images have apparent magnitudes of \(m_{\mathrm{F444W}}\sim25-26\) AB, and the magnification-corrected absolute UV magnitude of the source is \(M_{\mathrm{UV},1450}=-16.81\pm0.09\). From the sum of observed fluxes and from a spectral energy distribution (SED) analysis, we obtain estimates of the bolometric luminosities of the source of \(L_{\mathrm{bol}}\gtrsim10^{43} \frac{\mathrm{erg}}{\mathrm{s}}\) and \(L_{\mathrm{bol}}\sim10^{44}-10^{46} \frac{\mathrm{erg}}{\mathrm{s}}\), respectively. Based on its compact, point-like appearance, its position in color-color space and the SED analysis, we tentatively conclude that this object is a UV-faint dust-obscured quasar-like object, i.e. an active galactic nucleus (AGN) at high redshift. We also discuss other alternative origins for the object's emission features, including a massive star cluster, Population III, supermassive, or dark stars, or a direct-collapse black hole. Although populations of red galaxies at similar photometric redshifts have been detected with JWST, this object is unique in that its high-redshift nature is corroborated geometrically by lensing, that it is unresolved despite being magnified -- and thus intrinsically even more compact -- and that it occupies notably distinct regions in both size-luminosity and color-color space. Planned UNCOVER JWST/NIRSpec observations, scheduled in Cycle 1, will enable a more detailed analysis of this object.
We present emission line ratios from a sample of 26 Lyman break galaxies from \(z\sim5.5-9.5\) with \(-17.0<M_{1500}<-20.4\), measured from ultra-deep JWST/NIRSpec MSA spectroscopy from JADES. We use ...28 hour deep PRISM/CLEAR and 7 hour deep G395M/F290LP observations to measure, or place strong constraints on, ratios of widely studied rest-frame optical emission lines including H\(\alpha\), H\(\beta\), OII \(\lambda\lambda\)3726,3729, NeIII \(\lambda\)3869, OIII \(\lambda\)4959, OIII \(\lambda\)5007, OI \(\lambda\)6300, NII \(\lambda\)6583, and SII \(\lambda\lambda\)6716,6731 in individual \(z>5.5\) spectra. We find that the emission line ratios exhibited by these \(z\sim5.5-9.5\) galaxies occupy clearly distinct regions of line-ratio space compared to typical z~0-3 galaxies, instead being more consistent with extreme populations of lower-redshift galaxies. This is best illustrated by the OIII/OII ratio, tracing interstellar medium (ISM) ionisation, in which we observe more than half of our sample to have OIII/OII>10. Our high signal-to-noise spectra reveal more than an order of magnitude of scatter in line ratios such as OII/H\(\beta\) and OIII/OII, indicating significant diversity in the ISM conditions within the sample. We find no convincing detections of NII in our sample, either in individual galaxies, or a stack of all G395M/F290LP spectra. The emission line ratios observed in our sample are generally consistent with galaxies with extremely high ionisation parameters (log \(U\sim-1.5\)), and a range of metallicities spanning from \(\sim0.1\times Z_\odot\) to higher than \(\sim0.3\times Z_\odot\), suggesting we are probing low-metallicity systems undergoing periods of rapid star-formation, driving strong radiation fields. These results highlight the value of deep observations in constraining the properties of individual galaxies, and hence probing diversity within galaxy population.
We report the discovery of a triply imaged active galactic nucleus (AGN), lensed by the galaxy cluster MACS J0035.4-2015 (\(z_{\mathrm{d}}=0.352\)). The object is detected in Hubble Space Telescope ...imaging taken for the RELICS program. It appears to have a quasi-stellar nucleus consistent with a point-source, with a de-magnified radius of \(r_e\lesssim100\) pc. The object is spectroscopically confirmed to be an AGN at \(z_{\mathrm{spec}}=2.063\pm0.005\) showing broad rest-frame UV emission lines, and is detected in both X-ray observations with Chandra and in ALCS ALMA band 6 (1.2 mm) imaging. It has a relatively faint rest-frame UV luminosity for a quasar-like object, \(M_{\mathrm{UV},1450}=-19.7\pm0.2\). The object adds to just a few quasars or other X-ray sources known to be multiply lensed by a galaxy cluster. Some diffuse emission from the host galaxy is faintly seen around the nucleus and there is a faint object nearby sharing the same multiple-imaging symmetry and geometric redshift, possibly an interacting galaxy or a star-forming knot in the host. We present an accompanying lens model, calculate the magnifications and time delays, and infer physical properties for the source. We find the rest-frame UV continuum and emission lines to be dominated by the AGN, and the optical emission to be dominated by the host galaxy of modest stellar mass \(M_{\star}\simeq10^{9.2} \mathrm{M}_{\odot}\). We also observe some variation in the AGN emission with time, which may suggest that the AGN used to be more active. This object adds a low-redshift counterpart to several relatively faint AGN recently uncovered at high redshifts with HST and JWST.
We present JADES JWST/NIRSpec spectroscopy of GN-z11, the most luminous candidate \(z>10\) Lyman break galaxy in the GOODS-North field with \(M_{UV}=-21.5\). We derive a redshift of \(z=10.603\) ...(lower than previous determinations) based on multiple emission lines in our low and medium resolution spectra over \(0.8-5.3 \mu\)m. We significantly detect the continuum and measure a blue rest-UV spectral slope of \(\beta=-2.4\). Remarkably, we see spatially-extended Lyman-\(\alpha\) in emission (despite the highly-neutral IGM expected at this early epoch), offset 555 km s\(^{-1}\) redward of the systemic redshift. From our measurements of collisionally-excited lines of both low- and high-ionization (including O II\(\lambda3727\), Ne III\(\lambda 3869\) and C III\(\lambda1909\)) we infer a high ionization parameter (\(\log U\sim -2\)). We detect the rarely-seen N IV\(\lambda1486\) and N III\(\lambda1748\) lines in both our low and medium resolution spectra, with other high ionization lines seen in the low resolution spectrum such as He II (blended with O III) and C IV (with a possible P-Cygni profile). Based on the observed rest-UV line ratios, we cannot conclusively rule out photoionization from AGN, although the high C III/He II and N III/He II ratios are compatible with a star-formation explanation. If the observed emission lines are powered by star formation, then the strong N III\(\lambda1748\) observed may imply an unusually high \(N/O\) abundance. Balmer emission lines (H\(\gamma\), H\(\delta\)) are also detected, and if powered by star formation rather than an AGN we infer a star formation rate of \(\sim 20-30 M_{\odot} yr^{-1}\) (depending on the IMF) and low dust attenuation. Our NIRSpec spectroscopy confirms that GN-z11 is a remarkable galaxy with extreme properties seen 430 Myr after the Big Bang.
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