arXiv subjects

A. Pallottini

Publications and source records attributed to A. Pallottini.

At least 19 recordsLinked to original sources

arXiv2025

The ALPINE-CRISTAL-JWST Survey: JWST/IFU Optical Observations for 18 Main-Sequence Galaxies at z=4-6

To fully characterize the formation and evolution of galaxies, we need to observe their stars, gas, and dust on resolved spatial scales. We present the ALPINE-CRISTAL-JWST survey, which combines kpc-resolved imaging and spectroscopy from HST, JWST, and ALMA for 18 representative main-sequence galaxies at z=4-6 and log(M/$M_\odot$) > 9.5 to study their star formation, chemical properties, and extended gas reservoirs. The co-spatial measurements resolving the ionized gas, molecular gas, stars, and dust on 1-2 kpc scales make this a unique benchmark sample for the study of galaxy formation and evolution at $z\sim5$, connecting the Epoch of Reionization with the cosmic noon. In this paper, we outline the survey goals and sample selection, and present a summary of the available data for the 18 galaxies. In addition, we measure spatially integrated quantities (such as global gas metallicity), test different star formation rate indicators, and quantify the presence of H$α$ halos. Our targeted galaxies are relatively metal rich (10-70% solar), complementary to JWST samples at lower stellar mass, and there is broad agreement between different star formation indicators. One galaxy has the signature of an active galactic nuclei (AGN) based on its emission line ratios. Six show broad H$α$~emission suggesting type 1 AGN candidates. We conclude with an outlook on the exciting science that will be pursued with this unique sample in forthcoming papers.

astro-ph.GA↗

arXiv2025

Tentative rotation in a galaxy at z$\sim$14 with ALMA

We re-analysed ALMA observations of the [OIII]$λ$88$μ$m emission line in JADES-GS-z14.0, so far the most distant spectroscopically confirmed galaxy at z=14.18. Our analysis shows a tentative detection of a velocity gradient of [OIII]$λ$88$μ$m using three independent tests: 1) construction of moment maps; 2) extraction of integrated spectra from a grid of apertures; and 3) spectro-astrometry in both the image and uv planes. We performed kinematical fitting using the KinMS code and estimated a dynamical mass of log$_{10}$(M$_{\rm dyn}$/$\rm M_\odot$)= 9.4$^{+0.8}_{-0.4}$, with the bulk of the uncertainties due to the degeneracy between dynamical mass and inclination. We measure an upper limit on the velocity dispersion ($σ_{v}$) of $<40~$ km/s~which results in an estimate of V$_{\rm rot}/σ>$ 2.5. This result, if confirmed with higher-resolution observations, would imply that kinematically cold discs are already in place at $z\sim14$. Comparison with mock observations from the SERRA cosmological simulations confirms that even low-resolution observations are capable of detecting a velocity gradient in $z>10$ galaxies as compact as JADES-GS-z14.0. This work shows that deeper ALMA or JWST/NIRSpec IFS observations with high spatial resolution will be able to estimate an accurate dynamical mass for JADES-GS-z14.0, providing an upper limit to the stellar mass of this over-luminous galaxy.

astro-ph.GA↗

arXiv2025

Unveiling the trends between dust attenuation and galaxy properties at z ~ 2 - 12 with the James Webb Space Telescope

A variety of dust attenuation/extinction curves have been observed in high-redshift galaxies, with mixed results regarding their correlations with global galaxy properties. These variations are likely driven by factors such as intrinsic dust properties, total dust content, and the dust-star geometry. In this work, we explore how the shape of dust attenuation curves-quantified by the UV-optical slope (S) and UV bump strength (B)-correlates with galaxy properties. Our goal is to identify the key physical mechanisms shaping attenuation curves through cosmic time. We build on arXiv:2402.05996, analyzing 173 dusty galaxies at z ~ 2-11.5, with attenuation curves inferred via SED fitting of JWST data using a modified version of BAGPIPES (arXiv:2304.11178). We investigate trends between S, B, and properties inferred from SED fitting: AV, SFR, stellar mass (M*), specific SFR (sSFR), mass-weighted stellar age (a*), ionization parameter (U), and metallicity (Z). For a subset, we also consider oxygen abundance (12 + log(O/H)), derived via Te-based methods. We find that lower AV galaxies tend to have steeper slopes and stronger UV bumps, consistent with radiative transfer predictions involving dust geometry and content. S also correlates with a* and sSFR, suggesting that strong radiation fields in young, bursty galaxies may destroy small grains, flattening the slope. B correlates with 12 + log(O/H), possibly due to metallicity-driven dust composition changes. Overall, attenuation curve shapes appear most strongly linked to: (1) redshift (dust evolution), (2) AV (RT effects), (3) a* or sSFR (radiation field), and (4) oxygen abundance (dust composition). Disentangling these effects requires spatially resolved data and theoretical models including dust evolution.

astro-ph.GA↗

arXiv2025

Neutral hydrogen in and around galaxies during the Epoch of Reionization

JWST spectra revealing Lyman-$α$ (Ly$α$) absorption in $z\sim 5-14$ galaxies offer a unique probe of reionization's earliest stages. However, disentangling absorption by the increasingly neutral intergalactic medium (IGM) from that in galaxies' interstellar and circumgalactic medium (ISM, CGM) remains challenging due to the poorly constrained nature of neutral hydrogen (HI) in and around galaxies at these redshifts. We use the SERRA high-resolution cosmological zoom-in simulations to characterize the HI distribution and its evolution along sightlines to star-forming regions during reionization, to interpret the contribution of local HI (ISM+CGM) to Ly$α$ absorption in $z>5$ spectra. We analyze $\sim 100$ $z=6-9.5$ galaxies, generating mock sightlines from each galaxy's star formation peak. We study the sightline distribution of HI column densities ($N_{\rm HI}$) and its variation with radius, halo mass and redshift. We find broad sightline variation in $N_{\rm HI}$ (0.5-1.5dex) due to complex ISM morphology driven by bursty star formation, with median $\log(N_{\rm HI}/{\rm cm}^{-2}) \simeq 21-22$. Dense ISM gas is the dominant origin of damped Ly$α$ absorption (DLA) systems along sightlines towards star-forming regions, outweighing gas in the CGM, filaments and proximate absorbers. Median $N_{\rm HI}$ increases with halo mass, scaling roughly with the virial radius, as expected due to larger potentials and more extended CGM, but shows negligible redshift evolution at fixed halo mass. This suggests post-reionization $N_{\rm HI}$ distributions may provide useful priors to interpret IGM damping wings at higher redshifts. To interpret strong $z>5$ DLA candidates found by JWST, we investigate $N_{\rm HI}>10^{22}{\rm cm}^{-2}$ sightlines. These trace dense, metal-enriched ISM within <1 kpc of massive halos, a scenario testable with higher-resolution spectroscopy.

astro-ph.GA↗

arXiv2025

Dust attenuation evolution in $z \sim 2$-$12$ JWST galaxies

A sizable fraction of the heavy elements synthesized by stars in galaxies condenses into sub-micron-sized solid-state particles, known as dust grains. Dust produces a wavelength-dependent attenuation, $A_λ$, of the galaxy emission, thereby significantly altering its observed properties. Locally, $A_λ$ is in general the sum of a power-law and a UV feature ('bump') produced by small, carbon-based grains. However, scant information exists regarding its evolution across cosmic time. Here, leveraging data from 173 galaxies observed by the James Webb Space Telescope in the redshift range z = 2 - 12, we report the most distant detection of the UV bump in a z ~ 7.55 galaxy (when the Universe was only ~ 700 Myr old), and show for the first time that the power-law slope and the bump strength decrease towards high redshifts. We propose that the flat $A_λ$ shape at early epochs is produced by large grains newly formed in supernova ejecta, which act as the main dust factories at such early epochs. Importantly, these grains have undergone minimal reprocessing in the interstellar medium due to the limited available cosmic time. This discovery opens new perspectives in the study of cosmic dust origin and evolution.

astro-ph.GA↗

arXiv2025

The ALMA REBELS survey: [OIII]$_{88μ\text{m}}$ line scans of UV-bright $z \gtrsim 7.6$ galaxies

We present the [OIII]$_{88μ\text{m}}$ spectral scan results from the ALMA Large Program REBELS (Reionization Era Bright Emission Line Survey). The generally high luminosity of [OIII]$_{88μ\text{m}}$ and ALMA's Band 7 efficiency motivated its use for line scans of REBELS targets at $z>8$. Spectral scans of four sources covered 326.4-373.0 GHz ($z=8.10$-9.39), reaching [OIII]$_{88μ\text{m}}$ luminosities of $\mathrm{\sim7.6\times10^8\ L_{\odot}}$ ($5σ$) for a FWHM of 400 km s$^{-1}$. No credible lines are detected for the four targets. For REBELS-04, the non-detection is unexpected given the $\geq92\%$ coverage of the redshift likelihood distribution and its estimated SFR of 40 $\text{M}_{\odot}\ \text{yr}^{-1}$. Possible explanations for the faint [OIII]$_{88μ\text{m}}$ emission (assuming a FWHM of 100 km s$^{-1}$) include high ISM densities ($>n_{\text{crit}} \approx 510\ \text{cm}^{-3}$) and low ionization parameters ($\mathrm{log_{10}\ U_{ion}\lesssim -2.5}$). For REBELS-37, a subsequent detection of [CII]$_{158μ\text{m}}$ ($z=7.643$) confirmed it lay outside our scan range. For REBELS-11 and REBELS-13, it remains unclear if the non-detection is due to the depth of the line scan or redshift coverage. REBELS-04 and REBELS-37 show significant ($\geq3.8σ$) dust continuum emission in Band 7. If the photometric redshift of REBELS-04 is accurate, i.e., $z_{\mathrm{phot}}=8.57^{+0.10}_{-0.09}$ or $z_{\mathrm{phot}}=8.43^{+0.10}_{-0.10}$ accounting for additional neutral hydrogen in the circumgalactic medium, REBELS-04 would constitute the most distant dust-detected galaxy identified with ALMA to date. Additional Band 6 dust observations of REBELS-37 constrain the shape of the far-IR SED, ruling out cold dust temperatures ($\lesssim28$ K) at $3σ$. Further insight into these galaxies will require spectroscopic redshifts and deeper multi-band dust observations.

astro-ph.GA↗

arXiv2025

Spatially resolved [CII]-gas conversion factor in early galaxies

Determining how efficiently gas collapses into stars at high-redshift is key to understanding galaxy evolution in the Epoch of Reionization (EoR). Globally, this process is quantified by the gas depletion time ($t_{dep}$); on resolved scales, by the slope and normalization of the Kennicutt-Schmidt (KS) relation. This work explores the global ($α_{[CII]}$) and spatially resolved ($W_{[CII]}$) [CII]-to-gas conversion factors at high-$z$ and their role in inferring reliable gas masses, surface densities, and $t_{dep}$ in the EoR. We select galaxies at 4<z<9 from the SERRA cosmological zoom-in simulation, that features on-the-fly radiative transfer and resolves interstellar medium properties down to $\approx$30 pc. The [CII] emission modelling from photodissociation regions allow us to derive global $α_{ [CII]}$, and maps of $W_{[CII]}$. We study their dependence on gas metallicity (Z), density (n), Mach number (M), and burstiness parameter ($k_s$), and provide best fit relations. The $α_{[CII]}$ decreases with increasing $Z$ and galaxy compactness, while the resolved $W_{[CII]}$ shows two regimes: at $Z< 0.2 Z_\odot$, it anticorrelates with n and Z, but not with $k_s$; above this threshold, it also depends on $k_s$, with more bursty regions showing lower conversion factors. This implies $W_{[CII]}\propto Σ_{[CII]}^{-0.5}$, as dense, metal-rich, and bursty regions exhibit higher [CII] surface brightness. Applying a constant $α_{[CII]}$ overestimates $Σ_{gas}$ in bright $Σ_{[CII]}$ patches, thus flattening the KS slope and overestimating $t_{dep}$ by a factor of $\approx$4.

astro-ph.GA↗

arXiv2025

The mass-metallicity relation as a ruler for galaxy evolution: insights from the James Webb Space Telescope

Galaxy evolution emerges from the balance between cosmic gas accretion, fueling star formation, and supernova (SN) feedback, regulating the metal enrichment. Hence, the stellar mass ($M_*$) - gas metallicity relation (MZR) is key to understanding the physics of galaxies. High-quality JWST data enable accurate measurements of the MZR up to redshift z=10. Our aims are to understand the observed MZR, its connection with the star formation rate (SFR), the role played by SFR stochasticity, and how it is regulated by SN feedback. We compare the MZR from the JADES, CEERS, and UNCOVER surveys, which comprise about 180 galaxies at $z=3-10$ with $10^6<M_*/M_\odot<10^{10}$, with 200 galaxies from the SERRA cosmological simulations. To interpret the MZR, we develop a minimal model for galaxy evolution that includes: cosmic accretion modulated with an amplitude $A_{100}$ on 100 Myr; a time delay $t_d$ between SFR and SN; SN-driven outflows with a varying mass loading factor $ε_{SN}$. Using our minimal model, we find the observed mean MZR is reproduced by weak outflows ($ε_{SN}=1/4$), in line with findings from JADES. Matching the observed MZR dispersion requires $t_d=20$ Myr and a $A_{100}=1/3$ modulation of the accretion rate. Successful models have low stochasticity ($σ_{SFR}=0.2$), yielding a MZR dispersion of $σ_{Z}=0.2$. Such values are close but lower than SERRA predictions ($σ_{SFR}=0.24$, $σ_{Z}=0.3$), clarifying why SERRA shows flatter trend and some tension with the observations. As the MZR is very sensitive to SFR stochasticity, models predicting high r.m.s. values ($σ_{SFR}=0.5$) result in a ``chemical chaos'' (i.e. $σ_{Z}=1.4$), virtually destroying the MZR. As a consequence, invoking a highly stochastic SFR ($σ_{SFR}=0.8$) to explain the overabundance of bright, super-early galaxies leads to inconsistencies with the observed MZR.

astro-ph.GA↗

arXiv2025

Primordial Rotating Disk Composed of $\geq$15 Dense Star-Forming Clumps at Cosmic Dawn

Early galaxy formation, initiated by the dark matter and gas assembly, evolves through frequent mergers and feedback processes into dynamically hot, chaotic structures. In contrast, dynamically cold, smooth rotating disks have been observed in massive evolved galaxies merely 1.4 billion years after the Big Bang, suggesting rapid morphological and dynamical evolution in the early Universe. Probing this evolution mechanism necessitates studies of young galaxies, yet efforts have been hindered by observational limitations in both sensitivity and spatial resolution. Here we report high-resolution observations of a strongly lensed and quintuply imaged, low-luminosity, young galaxy at $z=6.072$ (dubbed the Cosmic Grapes), 930 million years after the Big Bang. Magnified by gravitational lensing, the galaxy is resolved into at least 15 individual star-forming clumps with effective radii of $r_{\rm e}\simeq$ 10--60 parsec (pc), which dominate $\simeq$ 70\% of the galaxy's total flux. The cool gas emission unveils a smooth, underlying rotating disk characterized by a high rotational-to-random motion ratio and a gravitationally unstable state (Toomre $Q \simeq$ 0.2--0.3), with high surface gas densities comparable to local dusty starbursts with $\simeq10^{3-5}$ $M_{\odot}$/pc$^{2}$. These gas properties suggest that the numerous star-forming clumps are formed through disk instabilities with weak feedback effects. The clumpiness of the Cosmic Grapes significantly exceeds that of galaxies at later epochs and the predictions from current simulations for early galaxies. Our findings shed new light on internal galaxy substructures and their relation to the underlying dynamics and feedback mechanisms at play during their early formation phases, potentially explaining the high abundance of bright galaxies observed in the early Universe and the dark matter core-cusp problem.

astro-ph.GA↗

arXiv2024

Blue Monsters at $z>10$. Where has all their dust gone?

The properties of luminous, blue (a.k.a. Blue Monsters), super-early galaxies at redshift $z>10$ have been successfully explained by the attenuation-free model (AFM) in which dust is pushed to kpc-scales by radiation-driven outflows. As an alternative to AFM, here we assess whether *attenuation-free* conditions can be replaced by a *dust-free* scenario in which dust is produced in very limited amounts and/or later destroyed in the interstellar medium. To this aim we compare the predicted values of the dust-to-stellar mass ratio, $ξ_d$, with those measured in 15 galaxies at $z>10$ from JWST spectra, when outflows are not included. Our model constrains $ξ_d$ as a function of several parameters by allowing wide variations in the IMF, dust/metal production, and dust destruction for a set of SN progenitor models and explosion energies. We find $\log ξ_d \approx -2.2$ for all systems, indicative of the dominant role of SN dust production over destruction in these early galaxies. Such value is strikingly different from the data, which instead indicate $\log ξ_d < -4$. We conclude that dust destruction alone can hardly explain the transparency of Blue Monsters. Other mechanisms, such as outflows, might be required.

astro-ph.GA↗

arXiv2024

Gas-phase metallicity gradients in galaxies at $z \sim 6-8$

The study of gas-phase metallicity and its spatial distribution at high redshift is crucial to understand the processes that shaped the growth and evolution of galaxies in the early Universe. Here we study the spatially resolved metallicity in three systems at $z\sim6-8$, namely A2744-YD4, BDF-3299, and COSMOS24108, with JWST NIRSpec IFU low-resolution ($R\sim100$) spectroscopic observations. These are among the highest-$z$ sources in which metallicity gradients have been probed so far. Each of these systems hosts several spatial components in the process of merging within a few kpc, identified from the rest-frame UV and optical stellar continuum and ionised gas emission line maps. The sources have heterogeneous properties, with stellar masses log($M_*/M_\odot) \sim 7.6-9.3$, star formation rates (SFRs) $\sim1-15$ $M_\odot$ yr$^{-1}$, and gas-phase metallicities 12+log(O/H) $\sim 7.7-8.3$, which exhibit a large scatter within each system. Their properties are generally consistent with those of the highest-$z$ samples to date ($z\sim3-10$), though the sources in A2744-YD4 and COSMOS24108 are at the high end of the mass-metallicity relation (MZR) defined by the $z\sim3-10$ sources. Moreover, the targets in this work follow the predicted slope of the MZR at $z\sim 6-8$ from most cosmological simulations. The gas-phase metallicity gradients are consistent with being flat in the main sources of each system. Flat metallicity gradients are thought to arise from gas mixing processes on galaxy scales, such as mergers or galactic outflows and SN winds driven by intense stellar feedback, which wash out any gradient formed in the galaxy. The existence of flat gradients at $z\sim6-8$ sets also important constraints on cosmological simulations and chemical evolution models, whose predictions on the cosmic evolution of metallicity gradients differ significantly, but are mostly limited to $z<3$ so far.

astro-ph.GA↗

arXiv2024

Unveiling [CII] clumps in a lensed star-forming galaxy at z ~ 3.4

Observations at UV and optical wavelengths have revealed that galaxies at z~1-4 host star-forming regions, dubbed "clumps", which are believed to form due to the fragmentation of gravitationally unstable, gas-rich disks. However, the detection of the parent molecular clouds that give birth to such clumps is still possible only in a minority of galaxies, mostly at z~1. We investigated the [CII] and dust morphology of a z~3.4 lensed galaxy hosting four clumps detected in the UV continuum. We aimed to observe the [CII] emission of individual clumps that, unlike the UV, is not affected by dust extinction, to probe their nature and cold gas content. We conducted ALMA observations probing scales down to ~300 pc and detected three [CII] clumps. One (dubbed "NE") coincides with the brightest UV clump, while the other two ("SW" and "C") are not detected in the UV continuum. We do not detect the dust continuum. We converted the [CII] luminosity of individual clumps into molecular gas mass and found Mmol~10^8 Msun. By complementing it with the star formation rate (SFR) estimate from the UV continuum, we estimated the gas depletion time (tdep) of clumps and investigated their location in the Schmidt-Kennicutt plane. While the NE clump has a short tdep=0.16 Gyr, comparable with high-redshift starbursts, the SW and C clumps instead have longer tdep>0.65 Gyr and are likely probing the initial phases of star formation. The lack of dust continuum detection is consistent with the blue UV continuum slope estimated for this galaxy (beta~-2.5) and it indicates that dust inhomogeneities do not significantly affect the detection of UV clumps in this target. We pushed the observation of the cold gas content of individual clumps up to z~3.4 and showed that the [C II] line emission is a promising tracer of molecular clouds at high redshift, allowing the detection of clumps with a large range of depletion times.

astro-ph.GA↗

arXiv2024

Time evolution of the galactic $B- ρ$ relation: the impact of the magnetic field morphology

One of the most frequently used indicators to characterize the magnetic field's influence on star formation is the relation between magnetic field strength and gas density ($B-ρ$ relation), usually expressed as $B \propto ρ^κ$. The value of $κ$ is an indication of the dynamical importance of the magnetic field during gas compression. Investigating the global magnetic field's impact on this relation and its evolution, we conduct MHD simulations of Milky-Way-like galaxies including gravity, star formation, and supernova feedback along with non-equilibrium chemistry up to $H_2$ formation fueling star formation. Two initial magnetic field morphologies are studied: one completely ordered (toroidal) and the other completely random. In these models, we study the dynamical importance of the magnetic field through the plasma $β$ and the $B-ρ$ relation. For both magnetic morphologies, low-density regions are thermally supported, while high-density regions are magnetically dominated. Equipartition is reached earlier and at lower densities in the toroidal model. However, the $B-ρ$ relation is not unique even within the same galaxy, as it consistently includes two different branches for a given density, with $κ$ ranging from about 0.2 to 0.8. The mean value of $κ$ for each model also displays significant variations over time, which supersede the differences between the two models. While our findings suggest that the magnetic field morphology does influence the galactic $B-ρ$ relation, its impact is transient, since time-averaged differences between the models fall within the large temporal scatter. The context and time-dependent nature of the $B-ρ$ relation underscore the need for comprehensive research and observations to understand the intricate role of magnetic fields in star formation processes across diverse galactic environments.

astro-ph.GA↗

arXiv2024

CONCERTO: Extracting the power spectrum of the [C II ] emission line

CONCERTO is the first experiment to perform a [CII] line intensity mapping survey to target $z>5.2$. Measuring the [CII] power spectrum allows us to study the role of dusty star-forming galaxies in the star formation history during the Reionization and post-Reionization. The main obstacle to this measurement is the contamination by bright foregrounds. We evaluate our ability to retrieve the [CII] signal in mock observations using the Simulated Infrared Dusty Extragalactic Sky. We compared two methods for dealing with the dust continuum emission from galaxies: the standard PCA and the arPLS method. For line interlopers, the strategy relies on masking low-redshift galaxies using external catalogues. As we do not have observations of CO or classical CO proxies ,we relied on the COSMOS stellar mass catalogue. To measure the power spectrum of masked data, we adapted the P of K EstimatoR and discuss its use on LIM data. The arPLS method achieves a reduction of the continuum background to a sub-dominant level of the [CII] at z=7 by a factor of>70. When using PCA, this factor is only 0.7. The masking lowers the power amplitude of line contamination down to $2 \times 10^2 Jy^2/sr$ This residual level is dominated by faint undetected sources. For our [CII] model, this results in a detection at z = 5.2 with a power ratio [CII]/(residual interlopers) = $62 \pm 32$ for a 22 % area survey loss. However, at z = 7, [C II ] / (residual interlopers)$=2.0 \pm 1.4$. Thanks to the large area covered by SIDES-Uchuu, we show that the power amplitude of line residuals varies by 12-15% for z=5.2-7. We present an end-to-end simulation of the extragalactic foreground removal that we ran to detect the [CII] at high redshift via its power spectrum. We show that dust continuum emission are not a limiting foreground for [CII] LIM. Residual CO and [CI] limits our ability to measure the [CII] power spectrum at z>7.

astro-ph.CO↗

arXiv2023

The ALMA Reionization Era Bright Emission Line Survey (REBELS): The molecular gas content of galaxies at z~7

A key to understanding the formation of the first galaxies is to quantify the content of the molecular gas as the fuel for star formation activity through the epoch of reionization. In this paper, we use the 158$μ$m [CII] fine-structure emission line as a tracer of the molecular gas in the interstellar medium (ISM) in a sample of $z=6.5-7.5$ galaxies recently unveiled by the Reionization Era Bright Line Emission Survey, REBELS, with the Atacama Large Millimeter/submillimeter Array. We find substantial amounts of molecular gas ($\sim10^{10.5}\ M_\odot$) comparable to those found in lower redshift galaxies for similar stellar masses ($\sim10^{10}\ M_\odot$). The REBELS galaxies appear to follow the standard scaling relations of molecular gas to stellar mass ratio ($μ_{\rm mol}$) and gas depletion timescale ($t_{\rm dep}$) with distance to the star-forming main-sequence expected from extrapolations of $z\sim1-4$ observations. We find median values at $z\sim7$ of $μ_{\rm mol}=2.6_{-1.4}^{4.1}$ and $t_{\rm dep}=0.5_{-0.14}^{+0.26}$ Gyr, indicating that the baryonic content of these galaxies is gas-phase dominated and little evolution from $z\sim7$ to 4. Our measurements of the cosmic density of molecular gas, log$(ρ_{\rm mol}/(M_\odot {\rm Mpc}^{-3}))=6.34^{+0.34}_{-0.31}$, indicate a steady increase by an order of magnitude from $z\sim7$ to 4.

astro-ph.GA↗

arXiv2023

Stochastic star formation in early galaxies: JWST implications

The star formation rate (SFR) in high redshift galaxies is expected to be time-variable due to competing physical processes. Such stochastic variability might boost the luminosity of galaxies, possibly explaining the over-abundance seen at $z\gtrsim 10$ by JWST. We aim at quantifying the amplitude and timescales of such variability, and identifying the key driving physical processes. We select 245 $z=7.7$ galaxies with stellar mass $5\times 10^{6}\lesssim M_\star/{\rm M}_\odot\lesssim 5\times 10^{10}$ from SERRA, a suite of high-resolution, radiation-hydrodynamic cosmological simulations. After fitting the average SFR trend, $\langle {\rm SFR} \rangle$, we quantify the time-dependent variation, $δ(t) \equiv \log [\rm SFR/\langle {\rm SFR} \rangle]$ for each system, and perform a periodogram analysis to search for periodicity modulations. We find that $δ(t)$ is distributed as a zero-mean Gaussian, with standard deviation $σ_δ\simeq 0.24$ (corresponding to a UV magnitude s.d. $σ_{\rm UV} \simeq 0.61$) that is independent of $M_\star$. However, the modulation timescale increases with stellar mass: $t_δ\sim (9, 50, 100)\, \rm Myr$ for $M_\star \sim (0.1, 1, 5)\times 10^9\, {\rm M}_\odot$, respectively. These timescales are imprinted on the SFR by different processes: (i) photoevaporation, (ii) supernova explosions, and (iii) cosmological accretion/merging dominating in low, intermediate, and high mass systems, respectively. The predicted SFR variations cannot account for the required $z\gtrsim 10$ UV luminosity function boost. Other processes, such as radiation-driven outflows clearing the dust, must then be invoked to explain the enhanced luminosity of super-early systems.

astro-ph.GA↗

arXiv2023

XQR-30: the ultimate XSHOOTER quasar sample at the reionization epoch

The final phase of the reionization process can be probed by rest-frame UV absorption spectra of quasars at z>6, shedding light on the properties of the diffuse intergalactic medium within the first Gyr of the Universe. The ESO Large Programme "XQR-30: the ultimate XSHOOTER legacy survey of quasars at z~5.8-6.6" dedicated ~250 hours of observations at the VLT to create a homogeneous and high-quality sample of spectra of 30 luminous quasars at z~6, covering the rest wavelength range from the Lyman limit to beyond the MgII emission. Twelve quasar spectra of similar quality from the XSHOOTER archive were added to form the enlarged XQR-30 sample, corresponding to a total of ~350 hours of on-source exposure time. The median effective resolving power of the 42 spectra is R~11400 and 9800 in the VIS and NIR arm, respectively. The signal-to-noise ratio per 10 km/s pixel ranges from ~11 to 114 at $λ\simeq 1285$ Årest frame, with a median value of ~29. We describe the observations, data reduction and analysis of the spectra, together with some first results based on the E-XQR-30 sample. New photometry in the H and K bands are provided for the XQR-30 quasars, together with composite spectra whose characteristics reflect the large absolute magnitudes of the sample. The composite and the reduced spectra are released to the community through a public repository, and will enable a range of studies addressing outstanding questions regarding the first Gyr of the Universe.

astro-ph.GA↗

arXiv2023

Dust attenuation law in JWST galaxies at z = 7-8

Attenuation curves in galaxies depend on dust chemical composition, content, and grain size distribution. Such parameters are related to intrinsic galaxy properties such as metallicity, star formation rate, and stellar age. Due to the lack of observational constraints at high redshift, dust empirical curves measured in the local Universe (e.g. Calzetti and SMC curves) have been employed to describe the dust attenuation at early epochs. We exploit the high sensitivity and spectral resolution of the JWST to constrain the dust attenuation curves in high-z galaxies. Our goals are to check whether dust attenuation curves evolve with redshift and quantify the dependence of the inferred galaxy properties on the assumed dust attenuation law. We develop a modified version of the SED fitting code BAGPIPES by including a detailed dust attenuation curve parametrization. Dust parameters are derived, along with galaxy properties, from the fit to the data from FUV to mm bands. Once applied to three star-forming galaxies at z = 7-8, we find that their attenuation curves differ from local templates. One out of three galaxies shows a characteristic MW bump, typically associated to the presence of small carbonaceous dust grains such as PAHs. This is one of the first evidences suggesting the presence of PAHs in early galaxies. Galaxy properties such as stellar mass and SFR inferred from SED fitting are strongly affected by the assumed attenuation curve, though the adopted star formation history also plays a major role. Our results highlight the importance of accounting for the potential diversity of dust attenuation laws when analyzing the properties of galaxies at the EoR, whose dust properties are still poorly understood. The application of our method to a larger sample of galaxies observed with JWST can provide us important insights into the properties of dust and galaxies in the early universe.

astro-ph.GA↗