arXiv subjects

Stefano Carniani

Publications and source records attributed to Stefano Carniani.

At least 145 records · Page 8Linked to original sources

arXiv2024

GA-NIFS: NIRSpec reveals evidence for non-circular motions and AGN feedback in GN20

We present rest-frame optical data of the z~4 sub-millimeter galaxy GN20 obtained with JWST/NIRSpec in integral field spectroscopy (IFS) mode. The H$α$ emission is asymmetric and clumpy and extends over a projected distance of more than 15 kpc. To first order, the large-scale ionised gas kinematics are consistent with a turbulent ($σ\sim90$ km/s), rotating disc ($v_{\rm rot}\sim500$ km/s), congruent with previous studies of its molecular and ionised gas kinematics. However, we also find clear evidence for non-circular motions in the H$α$ kinematics. We discuss their possible connection with various scenarios, such as external perturbations, accretion or radial flows. In the centre of GN20, we find broad line emission (FWHM $\sim1000-2000$ km/s) in the H$α$+[N II] complex, suggestive of fast, AGN-driven winds or, alternatively, of the broad-line region of an active black hole. Elevated values of [N II]$\lambda6583$/H$α>0.4$ and EW(H$α)>6$ Å, throughout large parts of GN20 suggest that feedback from the active black hole is able to photo-ionise the interstellar medium. Our data corroborates that GN20 offers a unique opportunity to observe key processes in the evolution of the most massive present-day galaxies acting in concert, over 12 billion years ago.

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arXiv2024

GA-NIFS: The core of an extremely massive proto-cluster at the Epoch of Reionization probed with JWST/NIRSpec

The SPT0311-58 system resides in a massive dark matter halo at z ~ 6.9. It hosts two dusty galaxies (E and W) with a combined star formation rate of ~3500 Msun/yr. Its surrounding field exhibits an overdensity of sub-mm sources, making it a candidate proto-cluster. We use spatially-resolved spectroscopy provided by the JWST/NIRSpec Integral Field Unit (IFU) to probe a field of view (FoV) ~ 17 x 17 kpc^2 around this object. These observations have revealed ten new galaxies at z ~ 6.9, characterised by dynamical masses spanning from ~10^9 to 10^10 Msun and a range in radial velocities of ~ 1500 km/s, in addition to the already known E and W galaxies. The implied large number density, and the wide spread in velocities, indicate that SPT0311-58 is at the core of a proto-cluster, immersed in a very massive dark matter halo of ~ 5 x 10^12 Msun. Hence, it represents the most massive proto-cluster ever found at the EoR. We also study the dynamical stage of the system and find that it likely is not fully virialised. The galaxies exhibit a great diversity of properties showing a range of evolutionary stages. We derive their ongoing Ha-based unobscured SFR, and find that its contribution to the total SF varies significantly across the galaxies in the system. Their ionization conditions range from those typical of field galaxies at similar redshift recently studied with JWST to those found in more evolved objects at lower z. The metallicity spans more than 0.8 dex across the FoV, reaching nearly solar values in some cases. The detailed IFU spectroscopy of the E galaxy reveals that it is actively assembling its stellar mass, showing sub-kpc inhomogeneities, and a metallicity gradient that can be explained by accretion of low metallicity gas from the IGM. The kinematic maps indicate departures from regular rotation, high turbulence, and a possible pre-collision minor merger. (Abridged)

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arXiv2024

JWST/NIRSpec WIDE survey: a z=4.6 low-mass star-forming galaxy hosting a jet-driven shock with low ionisation and solar metallicity

We present NIRSpec/MSA observations from the JWST large-area survey WIDE, targeting the rest-frame UV-optical spectrum of Ulema, a radio-AGN host at redshift z=4.6348. The low-resolution prism spectrum displays high equivalent width nebular emission, with remarkably high ratios of low-ionisation species of oxygen, nitrogen and sulphur, relative to hydrogen; auroral O$^+$ emission is clearly detected, possibly also C$^+$. From the high-resolution grating spectrum, we measure a gas velocity dispersion $σ$~400 km s$^{-1}$, broad enough to rule out star-forming gas in equilibrium in the gravitational potential of the galaxy. Emission-line ratio diagnostics suggest that the nebular emission is due to a shock which ran out of pre-shock gas. To infer the physical properties of the system, we model simultaneously the galaxy spectral energy distribution (SED) and shock-driven line emission under a Bayesian framework. We find a relatively low-mass, star-forming system (M* = 1.4$\times$10^{10} M$_\odot$, SFR = 70 M$_\odot$ yr$^{-1}$), where shock-driven emission contributes 50 per cent to the total H$β$ luminosity. The nebular metallicity is near solar - three times higher than that predicted by the mass-metallicity relation at z=4.6, possibly related to fast-paced chemical evolution near the galaxy nucleus. We find no evidence for a recent decline in the SFR of the galaxy, meaning that, already at this early epoch, fast radio-mode AGN feedback was poorly coupled with the bulk of the star-forming gas; therefore, most of the feedback energy must end up in the galaxy halo, setting the stage for future quenching.

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arXiv2024

The Star-forming and Ionizing Properties of Dwarf z~6-9 Galaxies in JADES: Insights on Bursty Star Formation and Ionized Bubble Growth

Reionization is thought to be driven by faint star-forming galaxies, but characterizing this population has long remained very challenging. Here we utilize deep nine-band NIRCam imaging from JADES to study the star-forming and ionizing properties of 756 $z\sim6-9$ galaxies, including hundreds of very UV-faint objects ($M_\mathrm{UV}>-18$). The faintest ($m\sim30$) galaxies in our sample typically have stellar masses of $M_\ast\sim(1-3)\times10^7$ $M_\odot$ and young light-weighted ages ($\sim$50 Myr), though some show strong Balmer breaks implying much older ages ($\sim$500 Myr). We find no evidence for extremely massive galaxies ($>3\times10^{10}$ $M_\odot$). We infer a strong (factor $>$2) decline in the typical [OIII]$+$H$β$ EWs towards very faint $z\sim6-9$ galaxies, yet a weak UV luminosity dependence on the H$α$ EWs at $z\sim6$. We demonstrate that these EW trends can be explained if fainter galaxies have systematically lower metallicities as well as more recently-declining star formation histories relative to the most UV-luminous galaxies in our sample. Our data provide evidence that the brightest galaxies are frequently experiencing a recent strong upturn in SFR. We also discuss how the EW trends may be influenced by a strong correlation between $M_\mathrm{UV}$ and Lyman continuum escape fraction. This alternative explanation has dramatically different implications for the contribution of galaxies along the luminosity function to cosmic reionization. Finally, we quantify the photometric overdensities around two $z>7$ strong Ly$α$ emitters. One Ly$α$ emitter lies close to a strong photometric overdensity while the other shows no significant nearby overdensity, perhaps implying that not all strong $z>7$ Ly$α$ emitters reside in large ionized bubbles.

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arXiv2024

GA-NIFS: the interplay between merger, star formation and chemical enrichment in MACS1149-JD1 at z=9.11 with JWST/NIRSpec

We present JWST/NIRSpec integral-field spectroscopy observations of the z ~ 9.11 lensed galaxy MACS1149-JD1, as part of the GA-NIFS programme. The data was obtained with both the G395H grating (R~ 2700) and the prism (R~ 100). This target shows a main elongated UV-bright clump and a secondary component detected in continuum emission at a projected distance of 2 kpc. The R2700 data trace the ionised-gas morpho-kinematics in between the two components, showing an elongated emission mainly traced by [O III]5007. We spatially resolve [O II]3726,3729, [O III]4959,5007, and [O III]4363, which enable us to map the electron density (ne ~ 1.0 x 103 cm-3), temperature (Te ~ 1.6 x 104 K), and direct-method gas-phase metallicity (-1.2 to -0.7 dex solar). A spatially resolved full-spectrum modelling of the prism indicates a north-south gas metallicity and stellar age gradient between the two components. We found 3-sigma evidence of a spatially resolved anti-correlation of the gas-phase metallicity and the star formation rate density, which is likely driven by gas inflows, enhancing the star formation in JD1. We employ high-z sensitive diagnostic diagrams to rule out the presence of a strong AGN in the main component. These findings show the unambiguous presence of two distinct stellar populations, with the majority of the mass ascribed to an old star formation burst, as suggested by previous works. We disfavour the possibility of a rotating-disc nature for MACS1149-JD1; we favour a merger event that has led to a recent burst of star formation in two separate regions, as supported by high values of [O III]5007/Hbeta, ionised gas velocity dispersion, and gas-phase metallicity.

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arXiv2024

Gas conditions of a star-formation selected sample in the first billion years

We present Atacama Large Millimetre/submillimetre Array (ALMA) observations of the [O$_{\rm III}$] 88 $μ$m emission of a sample of thirteen galaxies at $z$ = 6 to 7.6 selected as [C$_{\rm II}$]-emitting companion sources of quasars. To disentangle the origins of the luminous Oxygen line in the $z$ > 6 Universe, we looked at emission-line galaxies that are selected through an excellent star-formation tracer [C$_{\rm II}$] with star-formation rates between 9 and 162 M$_{\odot}$/yr. Direct observations reveal [O$_{\rm III}$] emission in just a single galaxy (L$_{\rm [O_{\rm III}]}$/L$_{\rm [C_{\rm II}]}$ = 2.3), and a stacked image shows no [O$_{\rm III}$] detection, providing deep upper limits on the L$_{\rm [O_{\rm III}]}$/L$_{\rm [C_{\rm II}]}$ ratios in the $z > 6$ Universe (L$_{\rm [O_{\rm III}]}$/L$_{\rm [C_{\rm II}]}$ < 1.2 at 3$σ$). While the fidelity of this sample is high, no obvious optical/near-infrared counterpart is seen in the JWST imaging available for four galaxies. Additionally accounting for low-redshift CO emitters, line stacking shows that our sample-wide result remains robust: The enhanced L$_{\rm [O_{\rm III}]}$/L$_{\rm [C_{\rm II}]}$ reported in the first billion years of the Universe is likely due to the selection towards bright, blue Lyman-break galaxies with high surface star-formation rates or young stellar populations. The deep upper limit on the rest-frame 90 $μ$m continuum emission (< 141 $μ$Jy at 3$σ$), implies a low average dust temperature (T$_{\rm dust}$ < 30K) and high dust mass (M$_{\rm dust}$ ~ 10$^8$ M$_{\odot}$). As more normal galaxies are explored in the early Universe, synergy between JWST and ALMA is fundamental to further investigate the ISM properties of the a broad range of samples of high-$z$ galaxies.

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arXiv2024

JADES: Physical properties of Ly$α$ and non-Ly$α$ emitters at z ~ 4.8-9.6

We investigate the physical properties of Lyman-alpha emitters (LAEs) and non-Lyman-alpha emitters (non-LAEs) at z$\sim$4.8--9.6 via a stacking analysis of 253 JWST/NIRSpec spectra of galaxies observed as part of the JWST Advanced Deep Extragalactic Survey (JADES). We identify a sample of 42 LAEs with the equivalent width of Ly$α$ $\gtrsim$20Åand a sample of 211 non-LAEs, divide each sample further via the median redshift of the LAEs (z~6.3), and create composite spectra using the low and medium resolution spectra from NIRSpec. We estimate physical quantities such as dust extinction, UV continuum slope $β$, electron temperatures, ionization parameter, escape fraction of Ly$α$ and Lyman Continuum, and the photon production rate for each bin/stack. The existing dust-extinction laws do not appear to be valid at these epochs. The emission line ratio analyses show that active galactic nuclei might dominate all sub-samples, irrespective of Ly$α$ emission. LAEs show much higher [OIII]/[OII] and low [OII]/H$δ$ at z$\lesssim$6.3 compared to non-LAEs, but these line ratios are not sufficient to distinguish the two populations at z$>$6.3. However, the LAEs samples show large EW([OIII]4959, 5007) ($>$1000Å) compared to the non-LAEs sample at all redshifts. CIV/Ly$α$ and CIV/CIII] for LAE population at z$\lesssim$6.3 is $\sim$a factor of 5 larger than that for LAE population at z$>$6.3. The ionizing radiation for LAEs is hard, as revealed from several diagnostics, including CIV detection, high [OIII]/[OII] ($>$8), and large values of $ξ^{\star}_{ion}$.

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arXiv2024

JADES NIRSpec Initial Data Release for the Hubble Ultra Deep Field: Redshifts and Line Fluxes of Distant Galaxies from the Deepest JWST Cycle 1 NIRSpec Multi-Object Spectroscopy

We describe the NIRSpec component of the JWST Deep Extragalactic Survey (JADES), and provide deep spectroscopy of 253 sources targeted with the NIRSpec micro-shutter assembly in the Hubble Ultra Deep Field and surrounding GOODS-South. The multi-object spectra presented here are the deepest so far obtained with JWST, amounting to up to 28 hours in the low-dispersion ($R\sim 30-300$) prism, and up to 7 hours in each of the three medium-resolution $R\approx 1000$ gratings and one high-dispersion grating, G395H ($R\approx2700$). Our low-dispersion and medium-dispersion spectra cover the wavelength range $0.6-5.3μ$m. We describe the selection of the spectroscopic targets, the strategy for the allocation of targets to micro-shutters, and the design of the observations. We present the public release of the reduced 2D and 1D spectra, and a description of the reduction and calibration process. We measure spectroscopic redshifts for 178 of the objects targeted extending up to $z=13.2$. We present a catalog of all emission lines detected at $S/N>5$, and our redshift determinations for the targets. Combined with the first JADES NIRCam data release, these public JADES spectroscopic and imaging datasets provide a new foundation for discoveries of the infrared universe by the worldwide scientific community.

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arXiv2024

Earliest Galaxies in the JADES Origins Field: Luminosity Function and Cosmic Star-Formation Rate Density 300 Myr after the Big Bang

We characterize the earliest galaxy population in the JADES Origins Field (JOF), the deepest imaging field observed with JWST. We make use of the ancillary Hubble optical images (5 filters spanning $0.4-0.9μ\mathrm{m}$) and novel JWST images with 14 filters spanning $0.8-5μ\mathrm{m}$, including 7 medium-band filters, and reaching total exposure times of up to 46 hours per filter. We combine all our data at $>2.3μ\mathrm{m}$ to construct an ultradeep image, reaching as deep as $\approx31.4$ AB mag in the stack and 30.3-31.0 AB mag ($5σ$, $r=0.1"$ circular aperture) in individual filters. We measure photometric redshifts and use robust selection criteria to identify a sample of eight galaxy candidates at redshifts $z=11.5-15$. These objects show compact half-light radii of $R_{1/2}\sim50-200$pc, stellar masses of $M_{\star}\sim10^7-10^8 M_{\odot}$, and star-formation rates of $\mathrm{SFR}\sim0.1-1\,M_{\odot}\,\mathrm{yr}^{-1}$. Our search finds no candidates at $15<z<20$, placing upper limits at these redshifts. We develop a forward modeling approach to infer the properties of the evolving luminosity function without binning in redshift or luminosity that marginalizes over the photometric redshift uncertainty of our candidate galaxies and incorporates the impact of non-detections. We find a $z=12$ luminosity function in good agreement with prior results, and that the luminosity function normalization and UV luminosity density decline by a factor of $\sim2.5$ from $z=12$ to $z=14$. We discuss the possible implications of our results in the context of theoretical models for evolution of the dark matter halo mass function.

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arXiv2024

Multi-phase black-hole feedback and a bright [CII] halo in a Lo-BAL quasar at $z\sim6.6$

Although the mass growth of supermassive black holes during the Epoch of Reionisation is expected to play a role in shaping the concurrent growth of their host-galaxies, observational evidence of feedback at z$\gtrsim$6 is still sparse. We perform the first multi-scale and multi-phase characterisation of black-hole driven outflows in the $z\sim6.6$ quasar J0923+0402 and assess how these winds impact the cold gas reservoir. We employ the SimBAL spectral synthesis to fit broad absorption line (BAL) features and find a powerful ionized outflow on $\lesssim210$ pc scale, with a kinetic power $\sim2-100$\% of the quasar luminosity. ALMA observations of [CII] emission allow us to study the morphology and kinematics of the cold gas. We detect high-velocity [CII] emission, likely associated with a cold neutral outflow at $\sim0.5-2$ kpc scale in the host-galaxy, and a bright extended [CII] halo with a size of $\sim15$ kpc. For the first time at such an early epoch, we accurately constrain the outflow energetics in both the ionized and the atomic neutral gas phases. We find such energetics to be consistent with expectations for an efficient feedback mechanism, and both ejective and preventative feedback modes are likely at play. The scales and energetics of the ionized and atomic outflows suggest that they might be associated with different quasar accretion episodes. The results of this work indicate that strong black hole feedback is occurring in quasars at $z\gtrsim6$ and is likely responsible for shaping the properties of the cold gas reservoir up to circum-galactic scales.

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arXiv2024

JWST-JADES. Possible Population III signatures at z=10.6 in the halo of GN-z11

Finding the first generation of stars formed out of pristine gas in the early Universe, known as Population III (PopIII) stars, is one of the most important goals of modern astrophysics. Recent models have suggested that PopIII stars may form in pockets of pristine gas in the halo of more evolved galaxies. We present NIRSpec integral field spectroscopy and micro-shutter array spectroscopic observations of the region around GN-z11, an exceptionally luminous galaxy at z=10.6, that reveal a greater than 5 sigma detection of a feature consistent with being HeII1640 emission at the redshift of GN-z11. The very high equivalent width of the putative HeII emission in this clump (log(EW_rest(HeII)/A) = 1.79) and a lack of metal lines can be explained in terms of photoionisation by PopIII stars, while photoionisation by PopII stars is inconsistent with the data. The high equivalent width would also indicate that the putative PopIII stars likely have an initial mass function with an upper cutoff reaching at least 500 Msun. The PopIII bolometric luminosity inferred from the HeII line would be 7 x 10^9 Lsun, which would imply a total stellar mass formed in the burst of about 2 x 10^5 Msun. We find that photoionisation by the active galactic nucleus (AGN) in GN-z11 cannot account for the HeII luminosity observed in the clump but can potentially be responsible for an additional HeII emission observed closer to GN-z11. We also consider the possibility of in situ photoionisation by an accreting direct collapse black hole hosted by the HeII clump. We find that this scenario is less favoured, but it remains a possible alternative interpretation. We also report the detection of a Ly-alpha halo stemming out of GN-z11 and extending out to about 2 kpc as well as resolved funnel-shaped CIII emission likely tracing the ionisation cone of the AGN.

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arXiv2024

JADES Data Release 3 -- NIRSpec/MSA spectroscopy for 4,000 galaxies in the GOODS fields

We present the third data release of JADES, the JWST Advanced Deep Extragalactic Survey, providing both imaging and spectroscopy in the two GOODS fields. Spectroscopy consists of medium-depth and deep NIRSpec/MSA spectra of 4,000 targets, covering the spectral range 0.6-5.3 $μ$m and observed with both the low-dispersion prism (R=30-300) and all three medium-resolution gratings (R=500-1,500). We describe the observations, data reduction, sample selection, and target allocation. We measured 2,375 redshifts (2,053 from multiple emission lines); our targets span the range from z=0.5 up to z=13, including 404 at z>5. The data release includes 2-d and 1-d fully reduced spectra, with slit-loss corrections and background subtraction optimized for point sources. We also provide redshifts and S/N>5 emission-line flux catalogs for the prism and grating spectra, and concise guidelines on how to use these data products. Alongside spectroscopy, we are also publishing fully calibrated NIRCam imaging, which enables studying the JADES sample with the combined power of imaging and spectroscopy. Together, these data provide the largest statistical sample to date to characterize the properties of galaxy populations in the first billion years after the Big Bang.

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arXiv2024

JADES: The incidence rate and properties of galactic outflows in low-mass galaxies across 3 < z < 9

We investigate the incidence and properties of ionized gas outflows in a sample of 52 galaxies with stellar mass between $10^7$ M$_{\odot}$ and $10^9$ M$_{\odot}$ observed with ultra-deep JWST/NIRSpec MSA spectroscopy as part of the JWST Advanced Deep Extragalactic Survey (JADES). The high-spectral resolution (R2700) NIRSpec observations allowed us to identify for the first time the signature of outflows in the rest-frame optical nebular lines in low-mass galaxies at $z>3$. The incidence fraction of ionized outflows, traced by broad components, is about 25-40$\%$ depending on the intensity of the emission lines. The low incidence fraction might be due to both the sensitivity limit and the fact that outflows are not isotropic but have a limited opening angle which results in a detection only when this is directed toward our line of sight. Evidence for outflows increases slightly with stellar mass and star-formation rate. The median velocity and mass loading factor (i.e., the ratio between mass outflow rate and star formation rate) of the outflowing ionized gas are 350 km s$^{-1}$ and $η=2.0^{+1.6}_{-1.5}$, respectively. These are 1.5 and 100 times higher, respectively than the typical values observed in local dwarf galaxies. These outflows are able to escape the gravitational potential of the galaxy and enrich the circum-galactic medium and, potentially, the inter-galactic medium. Our results indicate that outflows can significantly impact the star formation activity in low-mass galaxies within the first 2 Gyr of the Universe.

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arXiv2024

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

We present the first statistical investigation of spatially resolved emission-line properties in a sample of 63 low-mass galaxies at $4\leq z<10$, 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]$\lambda5007$/H$β$ and a decreasing one for [NeIII]$\lambda3869$/[OII]$\lambda3727$ (3--4 $σ$ significance). These results are still valid when stacking the sample in two redshift bins (i.e., $4\leq z<5.5$ and $5.5\leq z<10$). The comparison with star-formation photoionization models suggests that the ionization parameter increases by $\sim 0.5$ 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 (7$σ$ 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.

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arXiv2024

GN-z11: The environment of an AGN at $z=$10.603

Recent observations with the \textit{James Webb} Space Telescope (JWST) have further refined the spectroscopic redshift of GN-z11, one of the most distant galaxies identified with the \textit{Hubble} Space Telescope (HST) at $z=10.603$. The presence of extremely dense gas ($>10^{10}$ cm$^{-3}$), the detection of high-ionisation lines and of CII*1335 emission, as well as the presence of an ionisation cone, indicate that GN-z11 also hosts an Active Galactic Nucleus (AGN). Further photometric and spectroscopic follow-up demonstrates that it lies in a large-scale, overdense structure with possible signatures of Population III (PopIII) stars in its halo. Surprisingly, Ly$α$ has also been detected despite the expected largely neutral inter-galactic medium at such a redshift. We exploit recent JWST/NIRSpec IFU observations to demonstrate that the Ly$α$ emission in GN-z11 is part of an extended halo with a minimum size of 0.8--3.2 kpc, depending on the definition used to derive the halo size. The surface brightness of the Ly$α$ halo around GN-z11 appears consistent with Ly$α$ halos observed around $z\sim6$ quasars. At the wavelength of Ly$α$ at $z\sim$10.6, we identify three other emission line candidates within the IFU Field-of-View with no UV rest-frame counterpart visible in deep images from the JWST/NIRCam. If confirmed, this could be the first evidence that the local region of GN-z11 represents a candidate protocluster core, forming just 400 Myr after the Big Bang. We give a first estimate of the dark matter halo mass of this structure ($M_h$=2.96$^{+0.44}_{-0.39} \times$10$^{10}$ M$_{\odot}$), consistent with a Coma-like cluster progenitor.

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arXiv2024

GA-NIFS: Early-stage feedback in a heavily obscured AGN at $z=4.76$

Dust-obscured galaxies are thought to represent an early evolutionary phase of massive galaxies in which the active galactic nucleus (AGN) is still deeply buried in significant amounts of dusty material and its emission is strongly suppressed. The unprecedented sensitivity of the James Webb Space Telescope enables us for the first time to detect the rest-frame optical emission of heavily obscured AGN and unveil the properties of the hidden accreting super-massive black holes (BHs). In this work, we present the JWST/NIRSpec IFS data of ALESS073.1, a massive, dusty, star-forming galaxy at $z = 4.76$ hosting an AGN at its center. The detection of a very broad $H_α$ emission associated with the Broad Line Region (BLR) confirms the presence of a BH ($\log(M_{BH}/M_\odot)>8.7$) accreting at less than 15\% of its Eddington limit and classifies the target as a Type 1 AGN. The rest-frame optical emission lines also reveal a fast ionized gas outflow marginally resolved in the galaxy center. The high sensitivity of NIRSpec allows us to perform the kinematic analysis of the narrow H$α$ component which indicates that the warm ionized gas velocity field is consistent with disk rotation. We also find that, in the innermost nuclear regions ($< 1.5$ kpc), the intrinsic velocity dispersion of the disk reaches $\sim 150$ km/s, $\sim 2-3$ times higher than the velocity dispersion inferred from the [CII] 158$μ$m line tracing mostly cold gas. Since, at large radii, the velocity dispersion of the warm and cold gas are comparable, we conclude that the outflows are injecting turbulence in the warm ionized gas in the central region, but they are not sufficiently powerful to disrupt the dense gas and quench star formation. These findings support the scenario that dust-obscured galaxies represent the evolutionary stage preceding the unobscured quasar when all gas and dust are removed from the host.

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arXiv2024

A recently quenched galaxy 700 million years after the Big Bang

Local and low-redshift ($z$<$3$) galaxies are known to broadly follow a bimodal distribution: actively star forming galaxies with relatively stable star-formation rates, and passive systems. These two populations are connected by galaxies in relatively slow transition. In contrast, theory predicts that star formation was stochastic at early cosmic times and in low-mass systems: these galaxies transitioned rapidly between starburst episodes and phases of suppressed star formation, potentially even causing temporary quiescence -- so-called mini-quenching events. However, the regime of star-formation burstiness is observationally highly unconstrained. Directly observing mini-quenched galaxies in the primordial Universe is therefore of utmost importance to constrain models of galaxy formation and transformation. Early quenched galaxies have been identified out to redshift $z<5$, and these are all found to be massive ($M_{*}>10^{10}~M_{\odot}$) and relatively old. Here we report a (mini-)quenched galaxy at z$=$7.3, when the Universe was only 700~Myr old. The JWST/NIRSpec spectrum is very blue ($U$-$V$$=$0.16$\pm0.03$~mag), but exhibits a Balmer break and no nebular emission lines. The galaxy experienced a short starburst followed by rapid quenching; its stellar mass (4-6$\times 10^8~M_\odot$) falls in a range that is sensitive to various feedback mechanisms, which can result in perhaps only temporary quenching.

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arXiv2024

JADES: The production and escape of ionizing photons from faint Lyman-alpha emitters in the epoch of reionization

We present the properties of 17 faint Ly$α$ emitting galaxies (LAEs) at $z>5.8$ from the JWST Advanced Deep Extragalactic Survey (JADES) in the Hubble Ultra Deep Field/GOODS-S. These LAEs span a redshift range $z\approx5.8-8.0$ and a UV magnitude range $M_{UV}\approx-17$ to $-20.6$, with the Ly$α$ equivalent width (EW) in the range $\approx 25-350$ Å. The detection of other rest-optical emission lines in the spectra of these LAEs enables the determination of accurate systemic redshifts and Lyα velocity offsets, as well as the physical and chemical composition of their stars and interstellar media. These faint LAEs are consistent with metal-poor systems with high ionization parameters, similar to the general galaxy population at $z>6$. We measured an average ionizing photon production efficiency, log($ξ_\rm{ion}$/erg$^{-1}$ Hz) $\approx25.57$ across our LAEs, which does not evolve strongly with redshift. We report an anti-correlation between the Ly$α$ escape fraction (f_\rm{esc}) and the velocity offset from systemic redshift, consistent with model expectations. We further find that the strength and velocity offset of Ly$α$ are neither correlated with galaxy spectroscopic properties nor with $ξ_\rm{ion}$. We find a decrease in $f_\rm{esc}$(Ly$α$) with redshift, indicative of decreasing sizes of ionized bubbles around LAEs at high redshifts. We used a range of galaxy properties to predict Lyman continuum $f_\rm{esc}$ for our LAEs, finding that the ionizing photon output into the intergalactic medium remains roughly constant across the observed Ly$α$ EW, showing a mild increase at fainter M$_{UV}$ and at higher redshifts. We derived correlations between the ionizing photon output from LAEs and $M_{UV}$, Ly$α$ EW and redshifts, which can be used to constrain the ionizing photon contribution of LAEs at $z > 6$ towards cosmic reionization.

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