arXiv subjects

Andrea Ferrara

Publications and source records attributed to Andrea Ferrara.

At least 55 records · Page 3Linked to original sources

arXiv2025

Can primordial black holes explain the overabundance of bright super-early galaxies?

JWST is detecting an excess of high-redshift ($z\gtrsim 10$), bright galaxies challenging most theoretical predictions. To address this issue, we investigate the impact of Primordial Black Holes (PBHs) on the halo mass function and UV luminosity function (LF) of super-early galaxies. We explore two key effects: (i) the enhancement of massive halos abundance due to the compact nature and spatial distribution of PBHs, and (ii) the luminosity boost, characterized by the Eddington ratio $λ_E$, due to Active Galactic Nuclei (AGN) powered by matter accretion onto PBHs. We build an effective model, calibrated using data at lower redshifts ($z\approx 4-9$), to derive the evolution of the LF including the additional PBH contribution. Via Bayesian analysis, we find that: (a) Although a small fraction ($\log f_{\rm PBH} \approx -5.42$) of massive ($\log M_{\rm PBH} / {\rm M_{\odot}} \approx 8.37$), non-emitting ($λ_E=0$) PBHs can explain the galaxy excess via the halo abundance enhancement, this solution is excluded by CMB $μ$-distortion constraints on monochromatic PBHs. (b) If PBHs power an AGN emitting at super-Eddington luminosity ($λ_E \approx 10$), the observed LF can be reproduced by a PBH population with characteristic mass $\log M_{\rm PBH} / {\rm M_{\odot}} \approx 3.69$ constituting a tiny ($\log f_{\rm PBH} \approx -8.16$) fraction of the cosmic dark matter content. In the AGN scenario, about 75% of the observed galaxies with ${\rm M_{UV}}=-21$ at $z=11$ should host a PBH-powered AGN and typically reside in low mass halos, $M_h = 10^{8-9} {\rm M_{\odot}}$. These predictions can be tested with available and forthcoming JWST spectroscopic data. We note that our analysis considers a lognormal PBH mass function and compares its parameters with monochromatic limits on PBH abundance. Further work is required to relax such limitations.

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arXiv2025

Bridging Theory and Observations: Insights into Star Formation Efficiency and Dust Attenuation in $z > 5$ Galaxies

We investigate early galaxy evolution by modeling self-consistently their radially-resolved evolution of gas, stars, heavy elements, and dust content. Our model successfully reproduces various observed properties of JWST-identified galaxies at $z > 5$, including sizes, stellar masses, star formation rates (SFR), metallicities, and dust-to-stellar mass ratios. We show that the star formation efficiency (SFE), $f_\ast \equiv {\rm SFR}/(f_{\rm b} \dot{M}_{\rm h})$, is regulated by the global equilibrium between cosmological gas inflows, star formation, and gas outflows. Our model predicts $f_\ast \lesssim 20~\%$ for galaxies with halo masses of $M_{\rm h} \sim 10^{11-12}\, M_\odot$ down to $z = 5$, allowing them to reach intrinsic UV magnitudes of $M_{\rm UV} \lesssim -22~{\rm mag}$; when dust attenuation is ignored, the predicted UV luminosity function (LF) at $z \sim 12$ agrees well with observations. However, our model also suggests that these galaxies would be heavily obscured by dust, with high optical depths at 1500~Å~of $τ_{1500} \gtrsim 10$, causing the dust-attenuated UV LF to fall significantly below the observed one. This discrepancy highlights the need for mechanisms that mitigate strong dust attenuation, such as dust evacuation from star-forming regions and/or preferential production of large dust grains. Further exploration of these processes is essential for understanding the early stages of galaxy evolution.

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arXiv2025

Deep Constraints on [CII]158$μ$m in JADES-GS-z14-0: Further Evidence for a Galaxy with Low Gas Content at z=14.2

We present deep ALMA observations targeting the [CII]$_{158μm}\,$ line in JADES-GS-z14-0, the most distant known galaxy at z=14.1793. We do not detect the [CII]$_{158μm}\,$ line in our deep observations, implying a luminosity of $<$6$\times10^7$ L$_{\odot}$ (3$σ$) for the target. Comparing this with the detected [OIII]$_{88μm}\,$ line, we constrain the [OIII]/[CII] ratio to be $>$3.5, significantly improving our probe of the ionization parameter $U$. The observed ratio is higher than analogues in the local universe, but consistent with galaxies at $z\approx6$-9. Through ISM modeling, we infer extreme ionizing conditions with log(U)$>-$2.0, likely requiring a young stellar population. Our modeling also indicates a relatively low gas density ($51_{-32}^{+116}$ cm$^{-3}$), significantly lower than expected from lower redshift trends. We infer a relatively high gas-phase metallicity (16$\pm$6\% solar) consistent with previous results and implying a rapid build-up of metals. Finally, using [CII]$_{158μm}\,$ as a molecular/cold gas mass tracer, we infer a low gas fraction ($f_\mathrm{gas} < 0.77$), consistent with previous estimates of the dynamical mass from [OIII]$_{88μm}\,$. Combined with the low observed gas density, lack of dust and high ionization parameter, this suggests strong feedback processes are playing an important role in the evolution of this galaxy. Our observations show that JADES-GS-z14-0 is a rapidly evolving galaxy with extreme ISM conditions, shedding light on the earliest phases of galaxy formation.

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arXiv2025

Temporarily quiescent galaxies at cosmic dawn: probing bursty star formation

The bursty, time-variable nature of star formation in the first billion years, as revealed by JWST, drives phases of temporary quiescence in low-mass galaxies that quench after starbursts. These galaxies provide unique probes of the burstiness of early star formation and its underlying physical processes. Using the SERRA cosmological zoom-in simulations, we analyze over 200 galaxies with $M_\star<10^{9.5}\rm M_\odot$ at $z\sim 6-8$, finding that most experience quiescent phases driven by stellar feedback, with minimal influence from environmental effects. The fraction of temporarily quiescent galaxies increases with decreasing mass and luminosity, representing the dominant population at $M_\star<10^8\rm M_\odot$ and $M_{UV}>-17$. By forward modeling their spectral energy distributions, we show that they are faint ($\langle M_{UV}\rangle = -15.6$ for $M_\star=10^{8}\rm M_\odot$), have strong Balmer breaks ($> 0.5$) and no emission lines. Comparing our predicted fractions with JWST results, we find similar luminosity-dependent trends; however, the observed fractions of temporarily quiescent galaxies at $M_{UV}\sim-20$ to $-19$ are higher, suggesting that stronger feedback or additional mechanisms beyond supernovae may be at play. We propose searching for F200W drop-outs and satellites in the proximity ($<5^{\prime\prime}$) of massive ($>10^{10}\rm M_\odot$) galaxies as effective strategies to uncover the hidden majority of faint ($M_{UV}>-17$), temporarily quiescent systems, crucial for constraining early feedback processes in low-mass galaxies.

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arXiv2025

The ALMA-CRISTAL Survey: Spatial extent of [CII] line emission in star-forming galaxies at $z=4-6$

We investigate the spatial extent and structure of the [CII] line emission in a sample of 34 galaxies at $z=4-6$ from the ALMA-CRISTAL Survey. By modeling the [CII] line emission in the interferometric visibility, we derive the effective radius of [CII] line emission assuming an exponential profile. The [CII] line radius ranges from 0.5 to 3.5 kpc with an average value of $\langle R_{e,[CII]}\rangle=1.90$ kpc. We compare the [CII] sizes with the sizes of rest-frame UV and FIR continua, which were measured from the HST F160W images and ALMA Band-7 continuum images, respectively. We confirm that the [CII] line emission is more spatially extended than the continuum emission, with average size ratios of $\langle R_{e,[CII]}/R_{e,UV}\rangle=2.90$ and $\langle R_{e,[CII]}/R_{e,FIR}\rangle=1.54$, although about half of the FIR-detected sample show comparable spatial extent between [CII] line and FIR continuum emission. The residual visibility of the best-fit model do not show statistical evidence of flux excess, indicating that the [CII] line emission in star-forming galaxies can be characterized by an extended exponential profile. Overall, our results suggest that the spatial extent of [CII] line emission can primarily be explained by PDRs associated with star formation activity, while the contribution from diffuse neutral medium (atomic gas) and the effects of past merger events may further expand the [CII] line distributions, causing their variations. Finally, we report the negative correlation between $Σ_{[CII]}$ and EW$_{Lyα}$, and possible negative correlation between $R_{e,[CII]}/R_{e,UV}$ and EW$_{Lyα}$, which may be in line with the scenario that atomic gas largely contributes to the extended [CII] line emission. Future 3-D analysis of Ly$α$ and H$α$ lines will shed light on the association of the extended [CII] line emission with atomic gas and outflows.

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arXiv2025

REBELS-IFU: Dust attenuation curves of 12 massive galaxies at $z\simeq7$

We present measurements of the dust attenuation curves of 12 massive ($9~<~\log$($M_{\star}/{M}_{\odot})$ $<~10$) Lyman-break galaxies at $z=6.5-7.7$ derived from James Webb Space Telescope (JWST) NIRSpec integral field unit (IFU) spectroscopy. The galaxies are drawn from the Atacama Large Millimeter/submillimeter Array (ALMA) Reionization Era Bright Emission Line Survey (REBELS) large program. The dust attenuation curves were obtained by fitting spectral energy distribution (SED) models with a flexible dust law to the full galaxy spectra over observed wavelengths $0.6-5.3$ $μ$m. These attenuation curves show a range of recovered slopes ($-0.39\leqδ\leq0.08$) that are on average slightly flatter than seen in local sources of the same stellar masses, with none exhibiting very steep slopes. Three galaxies exhibit evidence for a 2175 Å dust bump ($>4σ$) and we find SED fitting excluding the bump can overestimate derived stellar masses by up to $0.4$ dex. Correcting for the dust attenuation with our best-fit attenuation curves we recover a range of intrinsic UV-slopes ($-2.5\leqβ_0\leq-2.2$). The galaxies show moderate reddening ($A_V~=~0.1-0.6$ mag) and the $A_V$ to stellar mass relation is consistent with local sources. The attenuation law slope is found to correlate with $A_V$, while we see no strong correlation with stellar mass, ${M_{\rm UV}}$, or gas-phase metallicity. Overall, our results show little evolution in dust properties in the REBELS sources compared to the local Universe. Comparing our recovered trends to empirical models suggests that the most important factor driving the variation in the attenuation curves in our sample is the dust-star geometry, not the properties of the dust grains themselves.

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arXiv2025

REBELS-IFU: Evidence for metal-rich massive galaxies at z~6-8

Metallicity is a crucial tracer of galaxy evolution, providing insights into gas accretion, star formation, and feedback. At high redshift, these processes reveal how early galaxies assembled and enriched their interstellar medium. In this work, we present rest-frame optical spectroscopy of 12 massive ($\log(M_*/\mathrm{M_{\odot}})>9$) galaxies at $z\sim 6$-$8$ from the REBELS ALMA large program, observed with JWST NIRSpec/IFU in the prism mode. These observations span emission lines from [OII]$λ$3727,9 to [SII]$λ$6716,31, providing key information on nebular dust attenuation, ionisation states, and chemical abundances. We find lower O32 ratios (average $\sim3.7$) and [OIII]$λ$5007 equivalent widths (average ${EW_{[OIII]}}\sim390$Å) than are generally found in existing large spectroscopic surveys at $z>6$, indicating less extreme ionising conditions. Strong-line diagnostics suggest that these systems are some of the most metal-rich galaxies observed at $z>6$ (average $Z_{\mathrm{gas}}\sim 0.4 Z_{\odot}$), including sources with near-solar oxygen abundances, in line with their high stellar masses (average $\log{M_*/\mathrm{M_{\odot}}}\sim9.5$). Supplementing with literature sources at lower masses, we investigate the mass-metallicity and fundamental metallicity relations (MZR and FMR, respectively) over a 4 dex stellar mass range at $6 3$ studies.

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arXiv2024

Physically motivated modeling of LyC escape fraction during reionization

Aims: We present an analysis of the Lyman continuum (LyC) escape fraction of high redshift galaxies using an analytic post-processing approach. Methods: We apply the model to 600,000 galaxies of the Illustris TNG50 simulation in the redshift range z = 5.2 - 20. Results: Our study reveals a bimodal nature of LyC escape, which is associated either to (a) high metallicity (1e-3.5 < Z < 1e-2), low mass (Mstar < 1e7Msun) galaxies which due to their efficient cooling exhibiting extended star formation, with photons escaping primarily from the outer regions of the galactic plane (ext-mode), or (b) low metallicity (Z < 1e-3), moderately massive galaxies (Mstar < 1e8Msun) in which star-formation can only take place in small high density regions with localized LyC escape originating from these regions (loc-mode). While the loc-mode is present at all redshifts under investigation, the ext-mode becomes prominent in small galaxies at later cosmic times, once sufficient metal enrichment has occurred. Building on these findings, we develop an analytical fitting formula to determine the escape fraction of galaxies based on their stellar and gas mass, as well as redshift, providing a valuable subgrid modelling tool for future studies.

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arXiv2024

Primordial black holes as supermassive black holes seeds

The presence of supermassive black holes (SMBHs, $M_{\bullet}\sim 10^{6-10}~M_{\odot}$) in the first cosmic Gyr ($z\gtrsim 6$) challenges current models of BH formation and evolution. We propose a novel mechanism for the formation of early SMBH seeds based on primordial black holes (PBHs). We assume a non-Gaussian primordial power spectrum as expected in inflationary models; these scenarios predict that PBHs are initially clustered and preferentially formed in the high-$σ$ fluctuations of the large-scale density field, out of which dark matter (DM) halos are originated. Our model accounts for (i) PBH accretion and feedback, (ii) DM halo growth, and (iii) gas dynamical friction. PBHs lose angular momentum due to gas dynamical friction, sink into a dense core, where BH binaries form and undergo a runaway merger, eventually leading to the formation of a single, massive seed. This mechanism starts at $z\sim 20-40$ in rare halos ($M_h\sim 10^7\ M_\odot$ corresponding to $\sim 5-7σ$ fluctuations), and provides massive ($\sim 10^{4-5}~ M_{\odot}$) seeds by $z\sim 10-30$. We derive a physically-motivated seeding prescription that provides the mass of the seed, $ M_{\rm seed}(z)=3.1\times 10^{5}\ { M_{\odot}}[(1+z)/10]^{-1.2}$, and seeded halo, $ M_{h}(z)=2\times 10^{9}\ {M_{\odot}}[(1+z)/10]^{-2}e^{-0.05z}$ as a function of redshift. This seeding mechanism requires that only a small fraction of DM is constituted by PBHs, namely $f_{\rm PBH}\sim 3 \times 10^{-6}$. We find that $z\sim 6-7$ quasars can be explained with $6\times 10^4 M_{\rm \odot}$ seeds planted at $z\sim 32$, and growing at sub-Eddington rates, $\langleλ_{\rm E}\rangle\sim 0.55$. The same scenario reproduces the BH mass of GNz11 at $z=10.6$, while UHZ1 ($z=10.1$) and GHZ9 ($z=10$) data favour instead slightly later ($z\sim 20-25$), more massive ($10^5~M_{\rm \odot}$) seeds. [Abridged]

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arXiv2024

Rapid Dust Formation in the Early Universe

Interstellar dust links the formation of the first stars to the rocky planet we inhabit by playing a pivotal role in the cooling and fragmentation of molecular clouds, and catalyzing the formation of water and organic molecules. Despite its central role, the origin of dust and its formation timescale remain unknown. Some models favor rapid production in supernova ejecta as the primary origin of dust, while others invoke slower production by evolved asymptotic giant branch stars or grain growth in the interstellar medium (ISM). The dust content of young early-universe galaxies is highly sensitive to the dust formation timescales. Here, we evaluate the dust content of 631 galaxies at $3 < z_{\rm spec} < 14$ based on rest-UV to optical spectroscopy obtained with JWST NIRSpec. We find that dust appears rapidly. Attenuation immediately follows star formation on timescales shorter than $\sim 30$ Myr, favoring dust production by supernovae. The degree of attenuation is $\sim 30$ times lower than expected if the entire supernova dust yield were preserved in the ISM, and had Milky Way-like grain properties. This can be reconciled if the early-universe dust is composed mostly of silicate or grains much larger than those in the Milky Way, and if significant dust destruction or ejection by outflows takes place.

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arXiv2024

The ALMA-CRISTAL Survey: Spatially-resolved Star Formation Activity and Dust Content in 4 < z < 6 Star-forming Galaxies

Using a combination of HST, JWST, and ALMA data, we perform spatially resolved spectral energy distributions (SED) fitting of fourteen 4<z<6 UV-selected main-sequence galaxies targeted by the [CII] Resolved ISM in Star-forming Galaxies with ALMA (CRISTAL) Large Program. We consistently model the emission from stars and dust in ~0.5-1kpc spatial bins to obtain maps of their physical properties. We find no offsets between the stellar masses (M*) and star formation rates (SFRs) derived from their global emission and those from adding up the values in our spatial bins, suggesting there is no bias of outshining by young stars on the derived global properties. We show that ALMA observations are important to derive robust parameter maps because they reduce the uncertainties in Ldust (hence Av and SFR). Using these maps we explore the resolved star-forming main sequence for z~5 galaxies, finding that this relation persists in typical star-forming galaxies in the early Universe. We find less obscured star formation where the M* (and SFR) surface densities are highest, typically in the central regions, contrary to the global relation between these parameters. We speculate this could be caused by feedback driving gas and dust out of these regions. However, more observations of infrared luminosities with ALMA are needed to verify this. Finally, we test empirical SFR prescriptions based on the UV+IR and [CII] line luminosity, finding they work well at the scales probed (~kpc). Our work demonstrates the usefulness of joint HST, JWST, and ALMA resolved SED modeling analyses at high redshift.

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arXiv2024

An optically-dark merging system at z~6 detected by JWST

Near- to mid-Infrared observations (from Spitzer and JWST) have revealed a hidden population of galaxies at redshift z=3-6, called optically-dark objects, which are believed to be massive and dusty star-formers. While optically-dark sources are widely recognized as a significant component of the stellar mass function, the history of their stellar mass assembly remains unexplored. However, they are thought to be the progenitors of the more massive early-type galaxies found in present-day groups and clusters. It is thus important to examine the possible connection between dark sources and merging events, in order to understand the environment in which they live. Here, we report our search for close companions in a sample of 19 optically-dark objects identified in the SMACS0723 JWST deep field. They were selected in the NIRCam F444W band and undetected below 2mu. We restrict our analysis to the reddest (i.e. F277W-F444W> 1.3) and brightest (F444W< 26 mag) objects. We have identified an optically-dark source showing a very close companion (<0.5"). The spatially resolved SED fitting procedure indicates that all components lying within 1.5" from the dark source are indeed at z~5.7. Tidal features (leading to a whale shaped morphology) corroborate the hypothesis that the dark source is the most massive (log(M/Msun)>10.3) and dusty (Av~3 at the core) system of an ongoing merger with a mass ratio of ~10. Similar merging systems are identified in the SERRA simulations, allowing us to reconstruct their stellar mass assembly history and predict their molecular gas properties The discovery of mergers within dark galaxies at the end of the Epoch of Reionization underscores the importance of conducting a statistical search for additional candidates in deep NIRCam fields. Such research will aid in understanding the role of merging processes during the obscured phase of stellar mass accumulation.

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arXiv2024

Accurate Simultaneous Constraints on the Dust Mass, Temperature and Emissivity Index of a Galaxy at Redshift 7.31

We present new multi-frequency ALMA continuum observations of the massive [$\log_{10}(M_\star/M_\odot) = 10.3_{-0.2}^{+0.1}$], UV-luminous [$M_\mathrm{UV} = -21.7 \pm 0.2$] $z=7.31$ galaxy REBELS-25 in Bands 3, 4, 5, and 9. Combining the new observations with previously-taken data in Bands 6 and 8, we cover the dust continuum emission of the galaxy in six distinct bands -- spanning rest-frame $50-350\,μ$m -- enabling simultaneous constraints on its dust mass ($M_\mathrm{dust}$), temperature ($T_\mathrm{dust}$) and emissivity index ($β_\mathrm{IR}$) via modified blackbody fitting. Given a fiducial model of optically thin emission, we infer a cold dust temperature of $T_\mathrm{dust} = 32_{-6}^{+9}\,$K and a high dust mass of $\log_{10}(M_\mathrm{dust}/M_\odot) = 8.2_{-0.4}^{+0.6}$, and moderately optically thick dust does not significantly alter these estimates. If we assume dust production is solely through supernovae (SNe), the inferred dust yield would be high, $y = 0.7_{-0.4}^{+2.3}\,M_\odot$ per SN. Consequently, we argue grain growth in the interstellar medium of REBELS-25 also contributes to its dust build-up. This is supported by the steep dust emissivity index $β_\mathrm{IR} = 2.5 \pm 0.4$ we measure for REBELS-25, as well as by its high stellar mass, dense interstellar medium, and metal-rich nature. Our results suggest that constraining the dust emissivity indices of high-redshift galaxies is important not only to mitigate systematic uncertainties in their dust masses and obscured star formation rates, but also to assess if dust properties evolve across cosmic time. We present an efficient observing setup to do so with ALMA, combining observations of the peak and Rayleigh-Jeans tail of the dust emission.

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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

Evidence of Pop~III stars' chemical signature in neutral gas at z~6. A study based on the E-XQR-30 spectroscopic sample

This study explores the metal enrichment signatures attributed to the first generation of stars (PopIII) in the Universe, focusing on the E-XQR-30 sample. We aim to identify traces of Pop III metal enrichment by analyzing neutral gas in the interstellar medium of primordial galaxies and their satellite clumps, detected in absorption. To chase the chemical signature of PopIII stars, we studied metal absorption systems in the E-XQR-30 sample, selected through the detection of the OI absorption line at 1302A. The OI line is a reliable tracer of HI and allowed us to overcome the challenges posed by the Lyman-$α$ forest's increasing saturation at redshifts above $\sim5$ to identify Damped Lyman-$α$ systems (DLA). We detected and analyzed 29 OI systems at $z\geq5.4$, differentiating between proximate DLAs (PDLA) and intervening DLAs. Voigt function fits were applied to obtain ionic column densities, and relative chemical abundances were determined for 28 systems. These were then compared with the predictions of theoretical models. Our findings expand the study of OI systems at $z\geq5.4$ fourfold. No systematic differences were observed in the average chemical abundances between PDLAs and intervening DLAs. The chemical abundances in our sample align with literature systems at $z>4.5$, suggesting a similar enrichment pattern for this class of absorption systems. A comparison between these DLA-analogues at $4.5<z<6.5$ with a sample of very metal-poor DLAs at $2<z<4.5$ shows in general similar average values for the relative abundances, with the exception of [C/O], [Si/Fe] and [Si/O] which are significantly larger for the high-$z$ sample. Furthermore, the dispersion of the measurements significantly increases in the high-redshift bin. This increase is predicted by the theoretical models and indicates a potential retention of PopIII signatures in the probed gas. (Abridged)

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arXiv2024

The First Billion Years, According to JWST

With stunning clarity, JWST has revealed the Universe's first billion years. The scientific community is analyzing a wealth of JWST imaging and spectroscopic data from that era, and is in the process of rewriting the astronomy textbooks. Here, 1.5 years into the JWST science mission, we provide a snapshot of the great progress made towards understanding the initial chapters of our cosmic history. We highlight discoveries and breakthroughs, topics and issues that are not yet understood, and questions that will be addressed in the coming years, as JWST continues its revolutionary observations of the Early Universe. While this compendium is written by a small number of authors, invited to ISSI Bern in March 2024 as part of the 2024 ISSI Breakthrough Workshop, we acknowledge the work of a large community that is advancing our collective understanding of the evolution of the Early Universe.

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arXiv2024

The eventful life of GS-z14-0, the most distant galaxy at redshift $z=14.32$

We developed a model for the star formation history (SFH) of super-early galaxies and applied it to GS-z14-0, the most distant galaxy known, located at $z=14.32$ (294 million years after the Big Bang). The SFH, starting at $z=26.7$, is complex. Initially ($z>18$), the galaxy experiences feedback-regulated phases that are bursty, relatively faint (reaching $M_{\rm UV}=-18.4$), and unattenuated. When dust shielding allows for a smooth star formation rate (SFR), the galaxy quickly becomes heavily obscured. During this obscured phase, which lasts for approximately 20% of the total star-forming time, 70% of the observed stars are formed. Super-early galaxies in this phase should be detectable by ALMA. Twenty-six million years before observation, as the galaxy becomes super-Eddington, a powerful radiation-driven outflow clears most of the dust and significantly reduces the SFR by a factor of seven, from $100 \to 15\ M_\odot \rm yr^{-1}$. The galaxy transitions into a "blue monster" dominating the bright end of the UV luminosity function. When the outflow ceases due to decreased dust opacity, the galaxy relaxes into a post-starburst phase, in which it is currently observed. Our model accurately reproduces all the observed and inferred properties of the galaxy. The analysis of this extreme system opens exciting opportunities for studying the beginnings of the luminous Universe.

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arXiv2024

REBELS-25: Discovery of a dynamically cold disc galaxy at z = 7.31

We present high resolution ($\sim0.14$" = 710 pc) ALMA [CII] 158$μ$m and dust continuum follow-up observations of REBELS-25, a [CII]-luminous ($L_{\mathrm{[CII]}}=(1.7\pm0.2)\times 10^9 \mathrm{L_{\odot}}$) galaxy at redshift $z=7.3065\pm0.0001$. These high resolution, high signal-to-noise observations allow us to study the sub-kpc morphology and kinematics of this massive ($M_* = 8^{+4}_{-2} \times 10^9 \mathrm{M_{\odot}}$) star-forming (SFR$_{\mathrm{UV+IR}} = 199^{+101}_{-63} \mathrm{M_{\odot}} \mathrm{yr}^{-1}$) galaxy in the Epoch of Reionisation. By modelling the kinematics with $^{\mathrm{3D}}$BAROLO, we find it has a low velocity dispersion ($\barσ = 33 \pm 9$ km s$^{-1}$) and a high ratio of ordered-to-random motion ($V_{\mathrm{rot, ~max}}/\barσ = 11 ^{+8}_{-4}$), indicating that REBELS-25 is a dynamically cold disc. Additionally, we find that the [CII] distribution is well fit by a near-exponential disc model, with a Sérsic index, $n$, of $1.3 \pm 0.2$, and we see tentative evidence of more complex non-axisymmetric structures suggestive of a bar in the [CII] and dust continuum emission. By comparing to other high spatial resolution cold gas kinematic studies, we find that dynamically cold discs seem to be more common in the high redshift Universe than expected based on prevailing galaxy formation theories, which typically predict more turbulent and dispersion-dominated galaxies in the early Universe as an outcome of merger activity, gas accretion and more intense feedback. This higher degree of rotational support seems instead to be consistent with recent cosmological simulations that have highlighted the contrast between cold and warm ionised gas tracers, particularly for massive galaxies. We therefore show that dynamically settled disc galaxies can form as early as 700 Myr after the Big Bang.

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