High-z Galaxies Research Articles

Bursty star formation and galaxy–galaxy interactions in low-mass galaxies 1 Gyr after the Big Bang

ABSTRACT We use CANUCS JWST/NIRCam imaging of galaxies behind the gravitationally-lensing cluster MACS J0417.5-1154 to investigate star formation burstiness in low-mass (M⋆ ∼ 108 M⊙) galaxies at z ∼ 4.7–6.5. Our sample of 123 galaxies is selected using the Lyman break selection and photometric emission-line excess methods. Sixty per cent of the 123 galaxies in this sample have Hα-to-UV flux ratios that deviate significantly from the range of Hα-to-UV ratio values consistent with smooth and steady star formation histories. This large fraction indicates that the majority of low-mass galaxies is experiencing bursty star formation histories at high redshift. We also searched for interacting galaxies in our sample and found that they are remarkably common ($\sim 40~{{\ \rm per\ cent}}$ of the sample). Compared to non-interacting galaxies, interacting galaxies are more likely to have very low Hα-to-UV ratios, suggesting that galaxy–galaxy interactions enhance star formation burstiness and enable faster quenching (with time-scales of ≲100 Myr) that follows the rapid rise of star formation activity. Given the high frequency of galaxy–galaxy interactions and the rapid SFR fluctuations they appear to cause, we conclude that galaxy–galaxy interactions could be a leading cause of bursty star formation in low-mass, high-z galaxies. They could thus play a significant role in the evolution of the galaxy population at early cosmological times.

Implications of the Stellar Mass Density of High-z Massive Galaxies from JWST on Warm Dark Matter

A significant excess of the stellar mass density at high redshift has been discovered from the early data release of James Webb Space Telescope (JWST), and it may require a high star formation efficiency. However, this will lead to large number density of ionizing photons in the epoch of reionization (EoR), so that the reionization history will be changed, which can arise tension with the current EoR observations. Warm dark matter (WDM), via the free streaming effect, can suppress the formation of small-scale structure as well as low-mass galaxies. This provides an effective way to decrease the ionizing photons when considering a large star formation efficiency in high-z massive galaxies without altering the cosmic reionization history. On the other hand, the constraints on the properties of WDM can be derived from the JWST observations. In this work, we study WDM as a possible solution to reconcile the JWST stellar mass density of high-z massive galaxies and reionization history. We find that, the JWST high-z comoving cumulative stellar mass density alone has no significant preference for either CDM or WDM model. But using the observational data of other stellar mass density measurements and reionization history, we obtain that the WDM particle mass with keV and star formation efficiency parameter in 2σ confidence level can match both the JWST high-z comoving cumulative stellar mass density and the reionization history.

Validating Posteriors Obtained by an Emulator When Jointly Fitting Mock Data of the Global 21 cm Signal and High-z Galaxy UV Luminosity Function

Although neural-network-based emulators enable efficient parameter estimation in 21 cm cosmology, the accuracy of such constraints is poorly understood. We employ nested sampling to fit mock data of the global 21 cm signal and high-z galaxy ultraviolet luminosity function (UVLF) and compare for the first time the emulated posteriors obtained using the global signal emulator globalemu to the “true” posteriors obtained using the full model on which the emulator is trained using ARES. Of the eight model parameters we employ, four control the star formation efficiency (SFE) and thus can be constrained by UVLF data, while the remaining four control UV and X-ray photon production and the minimum virial temperature of star-forming halos () and thus are uniquely probed by reionization and 21 cm measurements. For noise levels of 50 and 250 mK in the 21 cm data being jointly fit, the emulated and “true” posteriors are consistent to within 1σ. However, at lower noise levels of 10 and 25 mK, globalemu overpredicts and underpredicts γ lo, an SFE parameter, by ≈3σ–4σ, while the “true” ARES posteriors capture their fiducial values within 1σ. We find that jointly fitting the mock UVLF and 21 cm data significantly improves constraints on the SFE parameters by breaking degeneracies in the ARES parameter space. Our results demonstrate the astrophysical constraints that can be expected for global 21 cm experiments for a range of noise levels from pessimistic to optimistic, as well as the potential for probing redshift evolution of SFE parameters by including UVLF data.

LIMpy: A Semianalytic Approach to Simulating Multiline Intensity Maps at Millimeter Wavelengths

Mapping of multiple lines such as the fine-structure emission from [C ii] (157.7 μm), [O iii] (52 and 88.4 μm), and rotational emission lines from CO are of particular interest for upcoming line intensity mapping (LIM) experiments at millimeter wavelengths, due to their brightness features. Several upcoming experiments aim to cover a broad range of scientific goals, from detecting signatures of the epoch of reionization to the physics of star formation and its role in galaxy evolution. In this paper, we develop a semianalytic approach to modeling line strengths as functions of the star formation rate (SFR) or infrared luminosity based on observations of local and high-z galaxies. This package, LIMpy (Line Intensity Mapping in Python), estimates the intensity and power spectra of [C ii], [O iii], and CO rotational transition lines up to the J levels (1–0) to (13–12) based both on analytic formalism and on simulations. We develop a relation among halo mass, SFR, and multiline intensities that permits us to construct a generic formula for the evolution of several line strengths up to z ∼ 10. We implement a variety of star formation models and multiline luminosity relations to estimate the astrophysical uncertainties on the intensity power spectrum of these lines. As a demonstration, we predict the signal-to-noise ratio of [C ii] detection for an EoR-Spec-like instrument on the Fred Young Submillimeter Telescope. Furthermore, the ability to use any halo catalog allows the LIMpy code to be easily integrated into existing simulation pipelines, providing a flexible tool to study intensity mapping in the context of complex galaxy formation physics.

Redshift Evolution of Electron Density in the Interstellar Medium at z ∼ 0–9 Uncovered with JWST/NIRSpec Spectra and Line-spread Function Determinations

We present electron densities n e in the interstellar medium (ISM) of star-forming galaxies at z = 4–9 observed by the JWST/NIRSpec GLASS, Early Release Observations, and CEERS programs. We carefully evaluate the line-spread functions of the NIRSpec instrument as a function of wavelength with the calibration data of a planetary nebula taken on board, and obtain secure [O ii] λ λ3726, 3729 doublet fluxes for 14 galaxies at z = 4.02–8.68 falling on the star formation main sequence with the NIRSpec high- and medium-resolution spectra. We thus derive the electron densities of singly ionized oxygen nebulae with the standard n e indicator of the [O ii] doublet, and find that the electron densities of the z = 4–9 galaxies are n e ≳ 300 cm−3 significantly higher than those of low-z galaxies at a given stellar mass, star formation rate (SFR), and specific SFR. Interestingly, the typical electron densities of the singly ionized nebulae increase from z = 0 to z = 1−3 and z = 4–9, which is approximated by the evolutionary relation of n e ∝ (1 + z) p with p ∼ 1–2. Although it is not obvious that the ISM property of n e is influenced by global galaxy properties, these results may suggest that the nebula densities of high-z galaxies are generally high due to the compact morphologies of high-z galaxies evolving by (r vir ∝ (1 + z)−1) for a given stellar (halo) mass whose inverse square corresponds to the p ∼ 2 evolutionary relation. The p ∼ 1−2 evolutionary relation can be explained by a combination of the compact morphology and the reduction of n e due to the high electron temperature of high-z metal-poor nebulae.

Dark energy in light of the early JWST observations: case for a negative cosmological constant?

Early data from the James Webb Space Telescope (JWST) has uncovered the existence of a surprisingly abundant population of very massive galaxies at extremely high redshift, which are hard to accommodate within the standard ΛCDM cosmology. We explore whether the JWST observations may be pointing towards more complex dynamics in the dark energy (DE) sector. Motivated by the ubiquity of anti-de Sitter vacua in string theory, we consider a string-inspired scenario where the DE sector consists of a negative cosmological constant (nCC) and a evolving component with positive energy density on top, whose equation of state is allowed to cross the phantom divide. We show that such a scenario can drastically alter the growth of structure compared to ΛCDM, and accommodate the otherwise puzzling JWST observations if the dynamical component evolves from the quintessence-like regime in the past to the phantom regime today: in particular, we demonstrate that the presence of a nCC (which requires a higher density for the evolving component) plays a crucial role in enhancing the predicted cumulative comoving stellar mass density. Our work reinforces the enormous potential held by observations of the abundance of high-z galaxies in probing cosmological models and new fundamental physics, including string-inspired ingredients.

Gauging the mass of metals in the gas phase of galaxies from the Local Universe to the Epoch of Reionization

The chemical enrichment of dust and metals are vital processes in constraining the star formation history of the universe. These are important ingredients in the formation and evolution of galaxies overall. Previously, the dust masses of high-redshift star-forming galaxies have been determined through their far-infrared continuum, however, equivalent, and potentially simpler, approaches to determining the metal masses have yet to be explored at z ≳ 2. Here, we present a new method of inferring the metal mass in the interstellar medium (ISM) of galaxies out to z ≈ 8, using the far-infrared [C II]−158 μm emission line as a proxy. We calibrated the [C II]-to-MZ, ISM conversion factor based on a benchmark observational sample at z ≈ 0, in addition to gamma-ray burst sightlines at z > 2 and cosmological hydrodynamical simulations of galaxies at z ≈ 0 and z ≈ 6. We found a universal scaling across redshifts of log(MZ, ISM/M⊙) = log(L[CII]/L⊙)−0.45, with a 0.4 dex scatter, which is constant over more than two orders of magnitude in metallicity. We applied this scaling to recent surveys for [C II] in galaxies at z ≳ 2 and compared their inferred MZ, ISM to their stellar mass (M⋆). In particular, we determined the fraction of metals retained in the gas-phase ISM, MZ, ISM/M⋆, as a function of redshift and we showed that an increasing fraction of metals reside in the ISM of galaxies at higher redshifts. We place further constraints on the cosmic metal mass density in the ISM (ΩZ, ISM) at z ≈ 5 and ≈7 based on recent estimates of the [C II]−158 μm luminosity functions at these epochs, yielding ΩZ,ISM = 6.6−4.3+13 × 10−7 M⊙ Mpc−3 (z ≈ 5) and ΩZ,ISM = 2.0−1.3+3.5 × 10−7 M⊙ Mpc−3 (z ≈ 7), respectively. These results are consistent with the expected metal yields from the integrated star formation history at the respective redshifts. This suggests that the majority of metals produced at z ≳ 5 are confined to the ISM, with strong implications that disfavor efficient outflow processes at these redshifts. Instead, these results suggest that the extended [C II] halos predominantly trace the extended neutral gas reservoirs of high-z galaxies.

The IR Compactness of Dusty Galaxies Sets Star Formation and Dust Properties at z ∼ 0–2

The surface densities of gas, dust, and stars provide a window into the physics of star formation that, until the advent of high-resolution far-IR/submillimeter observations, has been historically difficult to assess among dusty galaxies. To study the link between IR surface densities and dust properties, we leverage the Atacama Large Millimetre/Submillimetre Array archive to measure the extent of cold dust emission in 15 z ∼ 2 IR-selected galaxies selected on the basis of having available mid-IR spectroscopy from Spitzer. We use the mid-IR spectra to constrain the relative balance between dust heating from star formation and active galactic nuclei (AGNs), and to measure emission from polycylic aromatic hydrocarbons (PAHs), small dust grains that play a key role in the photoelectric heating of gas. In general, we find that dust-obscured star formation at high IR surface densities exhibits similar properties at low and high redshift, namely, local luminous IR galaxies (LIRGs) have comparable PAH luminosity to total dust mass ratios as high-z galaxies, and star formation at z ∼ 0–2 is more efficient at high IR surface densities despite the fact that our sample of high-z galaxies is closer to the main sequence than local LIRGs. High star formation efficiencies are coincident with a decline in the PAH-to-IR luminosity ratio reminiscent of the deficit observed in far-IR fine-structure lines. Changes in the gas and dust conditions arising from high star formation surface densities might help drive the star formation efficiency up. This could help explain the high efficiencies needed to reconcile star formation and gas volume densities in dusty galaxies at cosmic noon.

Massive dark matter haloes at high redshift: implications for observations in the JWST era

ABSTRACT The presence of massive galaxies at high z as recently observed by JWST appears to contradict the current ΛCDM cosmology. Here, we aim to alleviate this tension by incorporating uncertainties from three sources in counting galaxies: cosmic variance, error in stellar mass estimation, and backsplash enhancement. Each of these factors significantly increases the cumulative stellar mass density ρ*(>M*) at the high-mass end, and their combined effect can boost the density by more than one order of magnitude. Assuming a star formation efficiency of ϵ* ∼ 0.5, cosmic variance alone reduces the tension to a 2σ level, except for the most massive galaxy at z = 8. Additionally, incorporating a 0.3 dex lognormal dispersion in the stellar mass estimation brings the observed ρ*(>M*) at z ∼ 7–10 within 2σ. The tension is completely eliminated when we account for the gas stripped from backsplash haloes. These results highlight the importance of fully modelling uncertainties when interpreting observational data of rare objects. We use the constrained simulation, ELUCID, to investigate the descendants of high-z massive galaxies. Our findings reveal that a significant portion of these galaxies ultimately resides in massive haloes at z = 0 with $M_{\rm halo} \gt 10^{13}\, h^{-1}{\rm M_\odot }$. Moreover, a large fraction of local central galaxies in $M_{\rm halo} \geqslant 10^{14.5} \, h^{-1}{\rm M_\odot }$ haloes are predicted to contain substantial amounts of ancient stars formed in massive galaxies at z ∼ 8. This prediction can be tested by studying the structure and stellar population of central galaxies in present-day massive clusters.

Crossing the Rubicon of Reionization with z ∼ 5 QSOs

One of the key open questions in cosmology is the nature of sources that completed cosmological hydrogen reionization at z ∼ 5.2. High-z primeval galaxies have been long considered the main drivers of reionization, with a minor role played by high-z active galactic nuclei (AGN). However, in order to confirm this scenario, it is fundamental to measure the photoionization rate produced by active SMBHs close to the Epoch of Reionization. Given the pivotal role played by spectroscopically complete observations of high-z QSOs, in this paper we present the first results of the RUBICON (Reionizing the Universe with Bright Cosmological Nuclei) survey. It consists of a color-selected sample of bona fide z ∼ 5 QSO candidates from the Hyper Suprime-Cam Subaru Strategic Survey. Our QSO candidates have been validated both by photometric redshifts based on spectral energy distribution fitting and by spectroscopic redshifts, confirming that they lie at 4.5 < z spec < 5.2. A relatively high space density of QSOs (Φ ∼ 1.4 × 10−8 c Mpc−3) is thus confirmed at z ∼ 5 and M 1450 ∼ −27, consistent with a pure density evolution of the AGN luminosity function from z = 4 to z = 5, with a mild density evolution rate of 0.25 dex. This indicates that AGN could play a nonnegligible role in cosmic reionization. The Rubicon of reionization has been crossed.

The UV luminosity functions of bright z &amp;gt; 8 galaxies: determination from ∼0.41 deg2 of HST observations along ∼300 independent sightlines

ABSTRACT We determine the bright end of the rest-frame UV luminosity function (UVLF) at z = 8–10 by selecting bright z ≳ 8 photometric candidates from the largest systematic compilation of HST (pure-)parallel observations to date, the Super-Brightest-of-Reionizing-Galaxies (SuperBoRG) data set. The data set includes ∼300 independent sightlines from WFC3 observations, totalling 800–1300 arcmin2 (depending on redshift). We identify 31 z ≳ 8 candidates via colour selection and photo-z analysis with observed magnitude (24.1 &amp;lt; H160 &amp;lt; 26.6) and 1σ range probability of $58\!-\!95~{{\ \rm per\ cent}}$ of being true high-z galaxies. Following detailed completeness and source recovery simulations, as well as modelling of interloper contamination, we derive rest-frame UVLFs at z = 8–10 down to MUV ≃ −23. We find that the bright end of the galaxy luminosity function can be described both by a Schechter and by a double power-law function, with our space-based large area determination showing some tentative discrepancies with the luminosity functions derived from ground-based observations at the same redshifts. We identify two possible explanations. The first is that the UVLF includes a substantial contribution from AGNs at magnitudes MUV &amp;lt; −22. The UVLF we derive at z = 8 is consistent with no evolution of the bright end from z = 6–7 UVLFs that include AGNs. An alternative (and non-exclusive) possibility is that the dust content of the observed galaxies decreases with redshift, thereby countering the naturally expected decrease in the UV luminosity functions because of a decreased star-formation rate with increasing redshift. Both scenarios raise interesting prospects to further understand galaxy formation in extreme objects during the epoch of reionization.

CO Survey of High-z Radio Galaxies, Revisited with the Atacama Large Millimeter/submillimeter Array: Jet–Cloud Alignments and Synchrotron Brightening by Molecular Gas in the Circumgalactic Environment

Powerful radio sources associated with supermassive black holes are among the most luminous objects in the universe, and are frequently recognized both as cosmological probes and active constituents in the evolution of galaxies. We present alignments between radio jets and cold molecular gas in the environment of distant radio galaxies, and show that the brightness of the radio synchrotron source can be enhanced by its interplay with the molecular gas. Our work is based on CO J > 1 observations with the Atacama Large Millimeter/submillimeter Array (ALMA) of three radio galaxies with redshifts in the range 1.4 < z < 2.1, namely MRC 0114-211 (z = 1.41), MRC 0156-252 (z = 2.02), and MRC 2048-272 (z = 2.05). These ALMA observations support previous work that found molecular gas out to 50 kpc in the circumgalactic environment, based on a CO(1–0) survey performed with the Australia Telescope Compact Array. The CO emission is found along the radio axes but beyond the main radio lobes. When compared to a large sample of high-z radio galaxies from the literature, we find that the presence of this cold molecular medium correlates with an increased flux-density ratio of the main versus counter-lobe. This suggest that the radio lobe brightens when encountering cold molecular gas in the environment. While part of the molecular gas is likely related to the interstellar medium from either the host or a companion galaxy, a significant fraction of the molecular gas in these systems shows very low excitation, with r 2−1/1−0 and r 3−2/1−0 values ≲0.2. This could be part of the circumgalactic medium.

Lyman α emitters in ionized bubbles: constraining the environment and ionized fraction

ABSTRACT Lyman α emitters (LAEs) are excellent probes of the reionization process, as they must be surrounded by large ionized bubbles in order to be visible during the reionization era. Large ionized regions are thought to correspond to overdense regions and may be protoclusters, making them interesting test-beds for early massive structures. Close associations containing several LAEs are often assumed to mark overdense, ionized bubbles. Here, we develop the first framework to quantify the ionization and density fields of high-z galaxy associations. We explore the interplay between (i) the large-scale density of a survey field, (ii) Poisson noise due to the small number density of bright sources at high redshifts (z ∼ 7), and (iii) the effects of the ionized fraction on the observation of LAEs. We use Bayesian statistics, a simple model of reionization, and a Monte Carlo simulation to construct a more comprehensive method for calculating the large-scale density of LAE regions than previous works. We find that Poisson noise has a strong effect on the inferred density of a region and show how the ionized fraction can be inferred. We then apply our framework to the strongest association yet identified: Hu et al. found 14 LAEs in a volume of ∼50 000 cMpc3 inside the COSMOS field at z ∼ 7. We show that this is most likely a 2.4σ overdensity inside of an ionized or nearly ionized bubble. We also show that this LAE association implies that the global ionized fraction is $\bar{Q} = 0.59^{+0.10}_{-0.11}$, within the context of a simple reionization model.

EMPRESS. XI. SDSS and JWST Search for Local and z ∼4–5 Extremely Metal-poor Galaxies (EMPGs): Clustering and Chemical Properties of Local EMPGs

We search for local extremely metal-poor galaxies (EMPGs), selecting photometric candidates by broadband color excess and machine-learning techniques with the SDSS photometric data. After removing stellar contaminants by shallow spectroscopy with Seimei and Nayuta telescopes, we confirm that three candidates are EMPGs with 0.05–0.1 Z ⊙ by deep Magellan/MagE spectroscopy for faint [Oiii] λ4363 lines. Using a statistical sample consisting of 105 spectroscopically confirmed EMPGs taken from our study and the literature, we calculate the cross-correlation function (CCF) of the EMPGs and all SDSS galaxies to quantify environments of EMPGs. Comparing another CCF of all SDSS galaxies and comparison of SDSS galaxies in the same stellar-mass range (107.0–108.4 M ⊙), we find no significant (>1σ) difference between these two CCFs. We also compare mass–metallicity relations (MZRs) of the EMPGs and those of galaxies at z ∼ 0–4 with a steady chemical evolution model and find that the EMPG MZR is comparable with the model prediction on average. These clustering and chemical properties of EMPGs are explained by a scenario of stochastic metal-poor gas accretion on metal-rich galaxies showing metal-poor star formation. Extending the broadband color excess technique to a high-z EMPG search, we select 17 candidates of z ∼ 4–5 EMPGs with the deep (≃30 mag) near-infrared JWST/NIRCam images obtained by ERO and ERS programs. We find galaxy candidates with negligible [Oiii] λ λ 4959,5007 emission weaker than the local EMPGs and known high-z galaxies, suggesting that some of these candidates may fall in the range of 0–0.01 Z ⊙, which potentially breaks the lowest metallicity limit known to date.

The Dragonfly Galaxy. III. Jet Brightening of a High-redshift Radio Source Caught in a Violent Merger of Disk Galaxies

The Dragonfly galaxy (MRC 0152-209), the most infrared-luminous radio galaxy at redshift z ∼ 2, is a merger system containing a powerful radio source and large displacements of gas. We present kiloparsec-resolution data from the Atacama Large Millimeter/submillimeter Array and the Very Large Array of carbon monoxide (6−5), dust, and synchrotron continuum, combined with Keck integral field spectroscopy. We find that the Dragonfly consists of two galaxies with rotating disks that are in the early phase of merging. The radio jet originates from the northern galaxy and brightens when it hits the disk of the southern galaxy. The Dragonfly galaxy therefore likely appears as a powerful radio galaxy because its flux is boosted into the regime of high-z radio galaxies by the jet–disk interaction. We also find a molecular outflow of (1100 ± 550) M ⊙ yr−1 associated with the radio host galaxy, but not with the radio hot spot or southern galaxy, which is the galaxy that hosts the bulk of the star formation. Gravitational effects of the merger drive a slower and longer-lived mass displacement at a rate of (170 ± 40) M ⊙ yr−1, but this tidal debris contains at least as much molecular gas mass as the much faster outflow, namely M H2 = (3 ± 1) × 109 (α CO/0.8) M ⊙. This suggests that both the active-galactic-nucleus-driven outflow and mass transfer due to tidal effects are important in the evolution of the Dragonfly system. The Keck data show Lyα emission spread across 100 kpc, and C iv and He ii emission across 35 kpc, confirming the presence of a metal-rich and extended circumgalactic medium previously detected in CO(1–0).

Spectroscopic Confirmation of CEERS NIRCam-selected Galaxies at z ≃ 8–10

We present JWST/NIRSpec prism spectroscopy of seven galaxies selected from Cosmic Evolution Early Release Science (CEERS) survey NIRCam imaging with photometric redshifts z phot > 8. We measure emission line redshifts of z = 7.65 and 8.64 for two galaxies. For two other sources without securely detected emission lines we measure and by fitting model spectral templates to the prism data, from which we detect continuum breaks consistent with Lyα opacity from a mostly neutral intergalactic medium. The presence of strong breaks and the absence of strong emission lines give high confidence that these two galaxies have redshifts z > 9.6, but the redshift values derived from the breaks alone have large uncertainties given the low spectral resolution and relatively low S/N of the CEERS NIRSpec prism data. The two z ∼ 10 sources observed are relatively luminous (M UV < −20), with blue continua (−2.3 ≲ β ≲ −1.9) and low dust attenuation (); and at least one of them has a high stellar mass for a galaxy at that redshift (). Considered together with spectroscopic observations of other CEERS NIRCam-selected high-z galaxy candidates in the literature, we find a high rate of redshift confirmation and low rate of confirmed interlopers (8%). Ten out of 35 z > 8 candidates with CEERS NIRSpec spectroscopy do not have secure redshifts, but the absence of emission lines in their spectra is consistent with redshifts z > 9.6. We find that z > 8 photometric redshifts are generally in agreement (within their uncertainties) with the spectroscopic values, but also that the photometric redshifts tend to be slightly overestimated (〈Δz〉 = 0.45 ± 0.11), suggesting that current templates do not fully describe the spectra of very-high-z sources. Overall, the spectroscopy solidifies photometric redshift evidence for a high spatial density of bright galaxies at z > 8 compared to theoretical model predictions, and further disfavors an accelerated decline in the integrated UV luminosity density at z > 8.

High-z galaxies with JWST and local analogues – it is not only star formation

ABSTRACT I present an analysis of the JWST NIRSpec data of SMACS 0723 released as Early Release Observations. As part of this three new redshifts are provided, bringing the total of reliable redshifts to 14. I propose a modification to the direct abundance determination method that reduces sensitivity to flux calibration uncertainties by a factor of ∼3 and show that the resulting abundances are in good agreement with Bayesian photoionization models of the rest-frame optical spectrum. I also show that 6355 is most likely a narrow-line active galactic nucleus (AGN) with $M_*\lt 10^9\, \mathrm{M}_\odot$ at z = 7.66 and argue that 10 612 might also have an AGN contribution to its flux through comparison to photoionization models and low-redshift analogues. Under the assumption that the lines come from star formation, I find that the galaxies have gas depletion times of ∼107 yr, comparable to similar galaxies locally. I also identify a population of possibly shock-dominated galaxies at z &amp;lt; 3, whose near-IR emission lines plausibly come nearly all from shocks and discuss their implications. I close with a discussion of the potential for biases in the determination of the mass–metallicity relation using samples defined by detected [O iii]4363 and show using low-z galaxies that this can lead to biases of up to 0.5 dex with a systematic trend with mass.

Neutral outflows in high-z QSOs

The OH+(11 − 10) absorption line is a powerful tracer of inflowing and outflowing gas in the predominantly atomic diffuse and turbulent halo surrounding galaxies. In this Letter, we present observations of OH+(11 − 10), CO(9-8) and the underlying dust continuum in five strongly lensed z ∼ 2 − 4 quasi-stellar objects (QSOs), using the Atacama Large Millimeter/submillimeter Array (ALMA) to detect outflowing neutral gas. Blue-shifted OH+(11 − 10) absorption is detected in three out of five QSOs and tentatively detected in a fourth. Absorption at systemic velocities is also detected in one source also displaying blue-shifted absorption. OH+(11 − 10) emission is observed in three out of five QSOs at systemic velocities and the OH+(21 − 10) transition is also detected in one source. CO(9-8) is detected in all five QSOs at high S/N, providing information on the dense molecular gas within the host galaxy. We compare our sample to high-z far-infrared (FIR) luminous star-forming and active galaxies from the literature. We find no difference in OH+ absorption line properties between active and star-forming galaxies with both samples roughly following the same optical depth-dust temperature relation. This suggests that these observables are driven by the same mechanism in both samples. Similarly, star-forming and active galaxies both follow the same OH+ emission–FIR relation. Obscured QSOs display broader (&gt; 800 km s−1) emission than the unobscured QSOs and all but one of the high-z star-forming galaxies (likely caused by the warm molecular gas reservoir obscuring the accreting nucleus). Broader CO(9-8) emission (&gt; 500 km s−1) is found in obscured versus unobscured QSOs, but overall they cover a similar range in line widths as the star-forming galaxies and follow the CO(9-8)–FIR luminosity relation found in low-z galaxies. We find that outflows traced by OH+ are only detected in extreme star-forming galaxies (indicated by broad CO(9-8) emission) and in both types of QSOs, which, in turn, display no red-shifted absorption. This suggests that diffuse neutral outflows in galaxy halos may be associated with the most energetic evolutionary phases leading up to and following the obscured QSO phase.

ALMA hints at the presence of turbulent disk galaxies at z &gt; 5

Context. High-redshift galaxies are expected to be more turbulent than local galaxies because of their smaller size and higher star formation and thus stronger feedback from star formation, frequent mergers events, and gravitational instabilities. However, this scenario has recently been questioned by the observational evidence of a few galaxies at z ∼ 4 − 5 with a gas velocity dispersion similar to what is observed in the local population. Aims. Our goal is to determine whether galaxies in the first billion years of the Universe have already formed a dynamically cold rotating disk similar to the local counterparts. Methods. We studied the gas kinematic of 22 main-sequence star-forming galaxies at z &gt; 5 and determined their dynamical state by estimating the ratio of the rotational velocity and of the gas velocity dispersion. We mined the ALMA public archive and exploited the [C II] and [O III] observations to perform a kinematic analysis of the cold and warm gas of z &gt; 5 main-sequence galaxies. We compared our results with what was found in the local and distant Universe and investigated the evolution of the gas velocity dispersion with redshift. We also compared the observations with theoretical expectations to assess the main driver of the gas turbulence at z &gt; 5. Results. The gas kinematics of the high-z galaxy population observed with ALMA is consistent within the errors with rotating but turbulent disks. We indeed infer a velocity dispersion that is systematically higher by 4–5 times than the local galaxy population and the z ∼ 5 dust-obscured galaxies reported in the literature. The difference between our results and those reported at similar redshift can be ascribed to the systematic difference in the galaxy properties in the two samples: the disks of massive dusty galaxies are dynamically colder than the disks of dust-poor galaxies. The comparison with the theoretical predictions suggests that the main driver of the velocity dispersion in high-redshift galaxies is the gravitational energy that is released by the transport of mass within the disk. Finally, we stress that future deeper ALMA high-angular resolution observations are crucial to constrain the kinematic properties of high-z galaxies and to distinguish rotating disks from kiloparsec-scale mergers.

Gravitational lensing modification of the high-redshift galaxy luminosity function

ABSTRACT The bright end of the rest-frame ultraviolet luminosity function (UVLF) of high-redshift galaxies is modified by gravitational lensing magnification bias. Motivated by recent discoveries of very high-z galaxies with JWST, we study the dependence of magnification bias on the finite size of sources at 6 &amp;lt; z &amp;lt; 14. We calculate the magnification probability distributions and use these to calculate the magnification bias assuming a rest-frame Schechter UVLF for galaxies at redshift 6 &amp;lt; z &amp;lt; 14. We find that the finite size of bright high-redshift galaxies together with lens ellipticity significantly suppresses magnification bias, producing an observed bright end which declines more sharply than the power law resulting from assumption of point sources. By assuming a luminosity–size relation for the source population and comparing with the observed z = 6 galaxy luminosity function from Harikane et al. (2022), we show that the UVLF can be used to set mild constraints on the galaxies intrinsic size, favouring smaller galaxies compared to the fiducial luminosity–size relation. In the future, wide surveys using Euclid and Roman Space Telescope will place stronger constraints. We also tabulate the maximum magnification possible as a function of source size and lens ellipticity.