arXiv subjects

Andrea Pallottini

Publications and source records attributed to Andrea Pallottini.

At least 37 records · Page 2Linked to original sources

arXiv2025

Lessons Learned from Studying H$α$ Galaxy Kinematics with Mock JWST/NIRSpec IFU Observations at $z > 6$

Galaxies with a disk morphology have been established at $z > 9$ with the James Webb Space Telescope (JWST). However, confirming their disky nature requires studying their gas kinematics, which can be challenging when relying solely on the warm gas observed by JWST. Unlike the cold gas traced by the Atacama Large Millimetre/Submillimetre Array (ALMA), warm gas is sensitive to outflows, complicating the interpretation of the disk dynamics. This elicits the question of how to compare information obtained from varied tracers, as well as how to physically interpret the low angular and spectral resolution observations generally available at high redshift. We address these challenges through comparative kinematic analysis of idealised and realistic NIRSpec/IFU mock observations derived from two galaxies in the SERRA suite of cosmological zoom-in simulations. With these synthetic data, we determine the robustness of dynamical information recovered from typical IFU observations, and test widely-used criteria for identifying disks and gaseous outflows at high redshift. We find that at the typical NIRSpec/IFU spectral and angular resolution ($\sim$ 0.05"/pixel), non-circular motions due to inflows or outflows can mimic the smooth velocity gradient indicative of a disk, and bias measured velocity dispersion upwards by a factor of $2-3\times$. As a result, the level of rotational support may be underestimated in the NIRSpec/IFU observations. However, the recovered dynamical mass appears to be relatively robust despite biases in $v_\text{rot}$ and $σ$.

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arXiv2025

Beyond the first galaxies primordial black holes shine

The presence of nine candidate galaxies at $z=17$ and $z=25$ discovered by the James Webb Space Telescope in relatively small sky areas, if confirmed, is virtually impossible to reconcile with the predictions of the current galaxy formation model. We show here that the implied UV luminosity density can be produced by a population of primordial black holes (PBHs) of mass $M_{\rm PBH} = 10^{4-5} \, M_{\odot}$ residing in low-mass halos ($M_h \approx 10^{7} \, M_{\odot}$), and accreting at a moderate fraction of the Eddington luminosity, $λ_E \simeq 0.36$. These sources precede the first significant episodes of cosmic star formation. At later times, as star formation is ignited, PBH emission becomes comparable to, or subdominant with respect to, the galactic emission. This PBH+galaxy scenario reconciles the evolution of the UV luminosity function (LF) from $z=25$ to $z=11$. If ultra-early sources are powered purely by accretion, this strongly disfavours seed production mechanisms requiring the presence of stars (massive stars, Pop III stars, or clusters), or their UV radiation (direct collapse BHs), leaving PBHs as the only alternative solution available so far. Alternative explanations, such as isolated, large clusters ($\approx 10^7 \,M_{\odot}$) of massive ($m_\star =10^3 M_{\odot}$) Pop III stars are marginally viable, but require extreme and unlikely conditions that can be probed via UV and far-infrared (FIR) emission lines or gravitational waves.

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arXiv2025

ALMA Observations of [OI]145um and [NII]205um Emission lines from Star-Forming Galaxies at $z\sim7$

We present results of new observations of [OI]145um and [NII]205um emission lines from four star-forming galaxies at redshifts between $z=6.58$ and $7.68$ that have previous detections of \Ciium\ and dust continua. Using ALMA, we successfully detect [OI]145um emission from all targets at $>4\,σ$ significance. However, [NII]205um emission is undetected in all galaxies (SNR $<3.5\,σ$) except for a tentative detection from A1689-zD1. From the observed high [CII]/[NII] emission line ratios ($\gtrsim20 - 80$), we find that most of the [CII]158um emission arise from neutral gas regions ($3\,σ$ lower limits of $\gtrsim 74 - 96\%$). From [OI]145um, [CII]158um lines, and infrared luminosities, we estimate the neutral gas densities of $n_{\rm H}=10^{3.5}$ - $10^6\,{\rm cm^{-3}}$ and the far-ultraviolet (FUV) radiation strengths of $G_0\sim10^{2.5}$-$10^{3}$. While the neutral gas densities are similar to those of high-redshift starburst galaxies, the FUV strengths are lower compared to both local and high-redshift starbursts. Finally, we estimate atomic hydrogen masses using [OI]145um emission lines and the oxygen abundances measured from recent JWST observations. We find gas mass ratios of $f_{\rm gas}\sim0.3$ - $0.8$, which are similar to earlier studies using [CII]158um. Starting from this pilot observation, future large [OI]145um emission line surveys will provide us with currently little-known neutral gas properties of star-forming galaxies in the early Universe.

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arXiv2025

Strong nebular HeII emission induced by He$^+$ ionizing photons escaping through the clumpy winds of massive stars

The origin of nebular HeII-emission in both local and high-redshift galaxies remains an unsolved problem. Various theories have been proposed to explain it, including HeII-ionization by high mass X-ray binaries, ultra-luminous X-ray sources, or "stripped" He stars, shock ionization, and hidden AGNs. All these theories have shortcomings, however, leaving the cause of nebular HeII emission unclear. We investigate the hypothesis that the photons responsible for driving nebular HeII emissions are produced by the evolution of single massive stars and/or WR stars. We combine models of stellar evolution with population synthesis and nebular models to identify the most favorable scenarios for producing nebular HeII via this channel. We find that, if WR winds are clumpy enough to become close to optically thin, stellar populations with a wide range of metallicities and rotation rates can produce HeII ionizing photons at rates sufficient to explain the observed nebular $I(HeII)/I(\mathrm{H}β)$ ratio $\sim 0.004-0.07$ found in HeII-emitting galaxies. Metal-poor, rapidly rotating stellar populations ($[\mathrm{Fe}/\mathrm{H}]=-2.0$, $v/v_\mathrm{crit}=0.4$) also reach these levels of HeII production even for partially clumpy winds. These scenarios also yield HeII, H$β$, and "Blue-Bump" line equivalent widths comparable to those observed in HeII emitters. Only for laminar, non-clumpy winds, do we fail to find combinations of metallicity and stellar rotation rate that yield $I(HeII)/I(\mathrm{H}β)$ values as high as those observed in HeII-emitters. Contrary to previous findings, we conclude that single WR stars can be a strong source for nebular HeII emission if their winds are sufficiently clumpy allowing significant escape of hard ionizing photons.

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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

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

Stellar halos tracing the assembly of ultra-faint dwarf galaxies

[Abridged]Ultra-faint dwarfs (UFDs) are expected to be the relics of the earliest galaxies forming in the Universe. Observations show the presence of a stellar halo around them, which can give precious insights into the evolution of UFDs. This work investigates how merger properties impact the formation of stellar halos around UFDs, focusing on Tucana II, the most promising UFD assembled through mergers. We develop N-body simulations of isolated mergers between two UFDs with $1M_\odot$ stellar resolution. We build a suite of simulations by varying: i) the merger mass ratio, $M_1/M_2$, the specific ii) kinetic energy, $k$, and iii) angular momentum, $l$, iv) the dark-to-stellar mass ratio, $M_{DM}/M_*$, of the progenitors and iv) their stellar size, $R_{1/2}$. We use a neural network to explore the parameter space, emulating the properties of the "post-merger" UFD by quantifying the half-mass radius ($R_*$) and the fraction of stars at radii $>5R_*$ ($f_5$). Our principal component analysis clearly shows that $f_5$ ($R_*$) is primarily determined by $M_1/M_2$ ($R_{1/2}$), with $R_{1/2}$ ($M_1/M_2$) playing a secondary role. Both $f_5$ and $R_*$ show almost no dependence on $k$, $l$, and $M_{DM}/M_*$ in the explored range. Using our emulator, we find that to form the stellar halo observed in Tucana II, i.e. $f_5=10\pm5\%$ and $R_*=120\pm30$pc, we need $M_1/M_2=8_{-3}^{+4}$ and $R_{1/2}=97^{+25}_{-18}$pc. Such findings are corroborated by the consistency ($χ^2=0.5-2$) between the stellar density profile observed and those of simulations having $M_1/M_2$ and $R_{1/2}$ close to the emulator's predictions. Ongoing and planned spectroscopic surveys will greatly increase the statistics of observed stars and thus stellar halos in UFDs. By interpreting such observations with our model, we will provide new insights into the assembly history of UFDs and thus on the early galaxy formation process.

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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

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

Investigating the ultraviolet and infrared radiation through the turbulent life of molecular clouds

Context. Molecular Clouds (MCs) are the place where stars are formed and their feedback starts to take place, regulating the evolution of galaxies. Therefore, MCs represent the critical scale at which to study how ultra-violet (UV) photons emitted by young stars are reprocessed in the far-infrared (FIR) by interaction with dust grains, thereby determining the multi-wavelength continuum emission of galaxies. Aims. Our goal is to analyze the UV and IR emission of a MC at different stages of its evolution and relate its absorption and emission properties with its morphology and star formation rate. Such a study is fundamental to determine how the properties of MCs shape the emission from entire galaxies. Method. We consider a radiation-hydrodynamic simulation of a MC with self-consistent chemistry treatment. The MC has a mass $M_{\rm MC} = 10^5 ~ M_\odot$, is resolved down to a scale of $0.06\, \rm pc$, and evolves for $\simeq 2.4$~Myr after the onset of star formation. We post-process the simulation via Monte Carlo radiative transfer calculations to compute the detailed UV-to-FIR emission of the MC. Such results are compared with data from physically-motivated analytical models, other simulations, and observations. Results. We find that the simulated MC is globally UV-optically thick, but optically-thin channels allow for photon escape ($0.1\%-10\%$), feature which is not well-captured in the analytical models. Dust temperature spans a wide range ($T_{\rm dust} \sim 20-300$~K) depending on the dust-to-stellar geometry, which is reproduced reasonably well by analytical models. However, the complexity of the dust temperature distribution is not captured in the analytical models, as evidenced by the 10 K (20 K) difference in the mass (luminosity) average temperature. Indeed, the total IR luminosity is the same in all the models, but the IR emission -abridged

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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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arXiv2024

Emulating the interstellar medium chemistry with neural operators

Galaxy formation and evolution critically depend on understanding the complex photo-chemical processes that govern the evolution and thermodynamics of the InterStellar Medium (ISM). Computationally, solving chemistry is among the most heavy tasks in cosmological and astrophysical simulations. The evolution of such non-equilibrium photo-chemical network relies on implicit, precise, computationally costly, ordinary differential equations (ODE) solvers. Here, we aim at substituting such procedural solvers with fast, pre-trained, emulators based on neural operators. We emulate a non-equilibrium chemical network up to H$_2$ formation (9 species, 52 reactions) by adopting the DeepONet formalism, i.e. by splitting the ODE solver operator that maps the initial conditions and time evolution into a tensor product of two neural networks. We use $\texttt{KROME}$ to generate a training set spanning $-2\leq \log(n/\mathrm{cm}^{-3}) \leq 3.5$, $\log(20) \leq\log(T/\mathrm{K}) \leq 5.5$, $-6 \leq \log(n_i/n) < 0$, and by adopting an incident radiation field $\textbf{F}$ sampled in 10 energy bins with a continuity prior. We separately train the solver for $T$ and each $n_i$ for $\simeq 4.34\,\rm GPUhrs$. Compared with the reference solutions obtained by $\texttt{KROME}$ for single zone models, the typical precision obtained is of order $10^{-2}$, i.e. the $10 \times$ better with a training that is $40 \times$ less costly with respect to previous emulators which however considered only a fixed $\mathbf{F}$. The present model achieves a speed-up of a factor of $128 \times$ with respect to stiff ODE solvers. Our neural emulator represents a significant leap forward in the modeling of ISM chemistry, offering a good balance of precision, versatility, and computational efficiency.

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arXiv2023

Dynamically cold disks in the early Universe: myth or reality?

Theoretical models struggle to reproduce dynamically cold disks with significant rotation-to-dispersion support($V_{\rm{rot}}/σ$) observed in star-forming galaxies in the early Universe, at redshift $z>4$. We aim to explore the possible emergence of dynamically cold disks in cosmological simulations and to understand if different kinematic tracers can help reconcile the tension between theory and observations. We use 3218 galaxies from the SERRA suite of zoom-in simulations, with $8<\log(M_*/M_{\odot})<10.3$ and SFR$<128\,M_{\odot}{yr}^{-1}$, within $4 10^9\,M_{\odot}$ galaxies, for which $σ_{Hα}>2σ_{CII}$ for a significant fraction of the sample. Regardless of the tracer, our predictions suggest the existence of massive ($M_*>10^{10}M_{\odot}$) galaxies with $V_{rot}/σ>10$ at $z>4$, maintaining cold disks for >10 orbital periods (200Myr). Furthermore, we do not find any significant redshift dependence for $V_{rot}/σ$ ratio in our sample. Our simulations predict the existence of dynamically cold disks in the early Universe. However, different tracers are sensitive to different kinematic properties. While [CII] effectively traces the thin, gaseous disk of galaxies, H$α$ includes the contribution from ionized gas beyond the disk, characterized by prevalent vertical or radial motions that may be associated with outflows. The presence of H$α$ halos could be a signature of such galactic outflows. This emphasizes the importance of combining ALMA and JWST/NIRspec studies of high-z galaxies.

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arXiv2023

Can supernovae quench star formation in high-$z$ galaxies?

JWST is providing the unique opportunity to directly study feedback processes regulating star formation (SF) in early galaxies. The two $z>5$ quiescent systems (JADES-GS-z7-01-QU and MACS0417-z5BBG) detected so far show a recent starburst after which SF is suppressed. To clarify whether such quenching is due to supernova (SN) feedback, we have developed a minimal physical model. We derive a condition on the minimum star formation rate, $\rm SFR_{min}$, lasting for a time interval $Δt_{b}$, required to quench SF in a galaxy at redshift $z$, with gas metallicity $Z$, and hosted by a halo of mass $M_h$. We find that lower $(z, Z, M_h)$ systems are more easily quenched. We then apply the condition to JADES-GS-z7-01-QU ($z=7.3$, $M_\star=10^{8.6} M_\odot$) and MACS0417-z5BBG ($z=5.2$, $M_\star=10^{7.6} M_\odot$), and find that SN feedback largely fails to reproduce the observed quenched SF history. Alternatively, we suggest that SF is rapidly suppressed by radiation-driven dusty outflows sustained by the high specific SFR (43 and 25 Gyr$^{-1}$, respectively) of the two galaxies. Our model provides a simple tool to interpret the SF histories of post-starburst galaxies, and unravel quenching mechanisms from incoming JWST data.

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arXiv2023

Spatially resolved Kennicutt-Schmidt relation at z~7 and its connection with the interstellar medium properties

We exploit moderately resolved [OIII], [CII] and dust continuum ALMA observations to derive the gas density ($n$), the gas-phase metallicity ($Z$) and the deviation from the Kennicutt-Schmidt (KS) relation ($κ_s$) on ~sub-kpc scales in the interstellar medium (ISM) of five bright Lyman Break Galaxies at the Epoch of Reionization ($z\approx 7$). To do so, we use GLAM, a state-of-art, physically motivated Bayesian model that links the [CII] and [OIII] surface brightness ($Σ_{\rm [CII]}$, $Σ_{\rm [OIII]}$) and the SFR surface density ($Σ_{\rm SFR}$) to $n$, $κ_s$, and $Z$. All five sources are characterized by a central starbursting region, where the $Σ_{\rm gas}$ vs $Σ_{\rm SFR}$ align ~10x above the KS relation ($κ_s\approx10$). This translates into gas depletion times in the range $t_{\rm dep}\approx 80-250$ Myr. The inner starbursting centers are characterized by higher gas density ($\log (n/{\rm cm^{-3}}) \approx 2.5-3.0$) and higher metallicity ($\log (Z/Z_{\odot}) \approx -0.5$) than the galaxy outskirts. We derive marginally negative radial metallicity gradients ($\nabla \log Z \approx -0.03 \pm 0.07$dex/kpc), and a dust temperature ($T_d\approx$32-38 K) that anticorrelates with the gas depletion time.

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arXiv2023

Quiescent low-mass galaxies observed by JWST in the Epoch of Reionization

The surprising JWST discovery of a quiescent, low-mass ($M_\star=10^{8.7} \rm M_\odot$) galaxy at redshift $z=7.3$ (JADES-GS-z7-01-QU) represents a unique opportunity to study the imprint of feedback processes on early galaxy evolution. We build a sample of 130 low-mass ($M_\star\lesssim 10^{9.5} \rm M_\odot$) galaxies from the SERRA cosmological zoom-in simulations, which show a feedback-regulated, bursty star formation history (SFH). The fraction of time spent in an active phase increases with the stellar mass from $f_{duty}\approx 0.6$ at $M_\star\approx 10^{7.5} \rm M_\odot$ to $\approx 0.99$ at $M_\star\geq 10^{9} \rm M_\odot$, and it is in agreement with the value $f_{duty}\approx 0.75$ estimated for JADES-GS-z7-01-QU. On average, 30% of the galaxies are quiescent in the range $6 < z < 8.4$; they become the dominant population at $M_\star\lesssim 10^{8.3} \rm M_\odot$. However, none of these quiescent systems matches the Spectral Energy Distribution of JADES-GS-z7-01-QU, unless their SFH is artificially truncated a few Myr after the main star formation peak. As supernova feedback can only act on a longer timescale ($\gtrsim 30 \rm \, Myr$), this implies that the observed abrupt quenching must be caused by a faster physical mechanism, such as radiation-driven winds.

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