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ABSTRACT We present a new semi-analytical formalism for modelling metal absorption lines that emerge from a clumpy galactic environment, ALPACA. We predict the “down-the-barrel” (DTB) metal absorption line profiles and the equivalent width (EW) of absorption at different impact parameters (b) as a function of the clump properties, including clump kinematics, clump volume filling factor, clump number density profile, and clump ion column densities. With ALPACA, we jointly model the stacked DTB C ii λ1334 spectrum of a sample of z ∼ 3 Lyman break galaxies and the EW versus b profile of a sample of z ∼ 2 star-forming galaxy–galaxy pairs. ALPACA successfully reproduced two data sets simultaneously, and the best fit prefers a low clump volume filling factor (∼3 × 10−3). The radial velocities of the clumps are a superposition of a rapidly accelerated outflow with a maximum velocity of $$\sim 400 \, {\mathrm{km}\, \mathrm{s}^{-1}}$$ and a velocity dispersion of $$\sigma \sim 120 \, {\mathrm{km}\, \mathrm{s}^{-1}}$$. The joint modelling reveals a physical scenario where the absorption observed at a particular velocity is contributed by the clumps distributed over a fairly broad range of radii. We also find that the commonly adopted Sobolev approximation is at best only applicable within a narrow range of radii where the clumps are undergoing rapid acceleration in a non-volume-filling clumpy medium. Lastly, we find that the clump radial velocity profile may not be fully constrained by the joint modelling and spatially resolved Ly α emission modelling may help break the degeneracy. 

ABSTRACT We report the detection of cold dust in an apparently quiescent massive galaxy (log (M⋆/M⊙) ≈ 11) at z ∼ 2 (G4). The source is identified as a serendipitous 2 mm continuum source in a deep ALMA observation within the field of Q2343-BX610, a z = 2.21 massive star-forming disc galaxy. Available multiband photometry of G4 suggests redshift of z ∼ 2 and a low specific star formation rate (sSFR), log (SFR/M⋆)[yr−1] ≈ −10.2, corresponding to ≈1.2 dex below the z = 2 main sequence (MS). G4 appears to be a peculiar dust-rich quiescent galaxy for its stellar mass (log (Mdust/M⋆) = −2.71 ± 0.26), with its estimated mass-weighted age (∼1–2 Gyr). We compile z ≳ 1 quiescent galaxies in the literature and discuss their age–ΔMS and log (Mdust/M⋆)–age relations to investigate passive evolution and dust depletion scale. A long dust depletion time and its morphology suggest morphological quenching along with less efficient feedback that could have acted on G4. The estimated dust yield for G4 further supports this idea, requiring efficient survival of dust and/or grain growth, and rejuvenation (or additional accretion). Follow-up observations probing the stellar light and cold dust peak are necessary to understand the implication of these findings in the broader context of galaxy evolutionary studies and quenching in the early universe. 

Abstract We present the first results from Chemical Evolution Constrained Using Ionized Lines in Interstellar Aurorae (CECILIA), a Cycle 1 JWST NIRSpec/MSA program that uses ultra-deep ∼30 hr G235M/F170LP observations to target multiple electron temperature-sensitive auroral lines in the spectra of 33 galaxies atz∼ 1–3. Using a subset of 23 galaxies, we construct two ∼600 object-hour composite spectra, both with and without the stellar continuum, and use these to investigate the characteristic rest-optical (λ_rest≈ 5700–8500 Å) spectrum of star-forming galaxies at the peak epoch of cosmic star formation. Emission lines of eight different elements (H, He, N, O, Si, S, Ar, and Ni) are detected, with most of these features observed to be ≲3% the strength of Hα. We report the characteristic strength of three auroral features ([Nii]λ5756, [Siii]λ6313, and [Oii]λλ7322, 7332), as well as other semi-strong and faint emission lines, including forbidden [Niii]λλ7380, 7414 and permitted Oiλ8449, some of which have never before been observed outside of the local Universe. Using these measurements, we findT_e[Nii] = 13,630 ± 2540 K, representing the first measurement of electron temperature using [Nii] in the high-redshift Universe. We also see evidence for broad line emission with a FWHM of ${536}_{-167}^{+45}$km s⁻¹; the broad component of Hαis 6.01%–28.31% the strength of the narrow component and likely arises from star-formation-driven outflows. Finally, we briefly comment on the feasibility of obtaining large samples of faint emission lines using JWST in the future. 

ABSTRACT The connection between the escape fraction of ionizing radiation (fesc) and the properties of galaxies, such as stellar mass ($$\rm M_{\rm *}$$), age, star-formation rate (SFR), and dust content, are key inputs for reionization models, but many of these relationships remain untested at high redshift. We present an analysis of a sample of 96 $$z$$ ∼ 3 galaxies from the Keck Lyman Continuum Spectroscopic Survey (KLCS). These galaxies have both sensitive Keck/LRIS spectroscopic measurements of the Lyman continuum (LyC) region, and multiband photometry that places constraints on stellar population parameters. We construct composite spectra from subsamples binned as a function of galaxy property and quantify the ionizing-photon escape for each composite. We find a significant anti-correlation between fesc and $$\rm M_{\rm *}$$, consistent with predictions from cosmological zoom-in simulations. We also find significant anti-correlation between fesc and E(B−V), encoding the underlying physics of LyC escape in our sample. We also find no significant correlation between fesc and either stellar age or specific SFR (= SFR/$$\rm M_{\rm *}$$), challenging interpretations that synchronize recent star formation and favorable conditions for ionizing escape. The galaxy properties now shown to correlate with fesc in the KLCS are Lyα equivalent width, UV Luminosity, $$\rm M_{\rm *}$$, SFR, and E(B−V), but not age or sSFR. This comprehensive analysis of galaxy properties and LyC escape at high redshift will be used to guide future models and observations of the reionization epoch. 

Abstract Dwarf galaxies located in extremely underdense cosmic voids are excellent test beds for disentangling the effects of large-scale environments on galaxy formation and evolution. We present the first results of the Dwarfs in Void Environments Survey, which has obtained integral field spectroscopy for low-mass galaxies (M_⋆= 10⁷–10⁹M_⊙) located inside (N= 21) and outside (N= 9) cosmic voids using the Keck Cosmic Web Imager. Using measurements of stellar line-of-sight rotational velocityv_rotand velocity dispersionσ_⋆, we test the tidal stirring hypothesis, which posits that dwarf spheroidal galaxies are formed through tidal interactions with more massive host galaxies. We measure low values ofv_rot/σ_⋆≲ 2 for our sample of isolated dwarf galaxies, and we find no trend betweenv_rot/σ_⋆and the distance from a massive galaxy $d_{L^{\star }}$out to $d_{L^{\star }}\sim 10$Mpc. These suggest that dwarf galaxies can become dispersion-supported, “puffy” systems even in the absence of environmental effects like tidal interactions. We also find indications of an upward trend betweenv_rot/σ_⋆and galaxy stellar mass, perhaps implying that stellar disk formation depends on mass rather than environment. Although some of our conclusions may be slightly modified by systematic effects, our main result still holds: that isolated low-mass galaxies may form and remain as puffy systems rather than the dynamically cold disks predicted by classical galaxy formation theory. 

Abstract Gravitational lenses can magnify distant galaxies, allowing us to discover and characterize the stellar populations of intrinsically faint, quiescent galaxies that are otherwise extremely difficult to directly observe at high redshift from ground-based telescopes. Here, we present the spectral analysis of two lensed, quiescent galaxies atz≳ 1 discovered by theASTRO 3D Galaxy Evolution with Lensessurvey:AGEL1323 (M_*∼ 10^11.1M_⊙,z= 1.016,μ∼ 14.6) andAGEL0014 (M_*∼ 10^11.5M_⊙,z= 1.374,μ∼ 4.3). We measured the age, [Fe/H], and [Mg/Fe] of the two lensed galaxies using deep, rest-frame-optical spectra (S/N ≳40 Å⁻¹) obtained on the Keck I telescope. The ages ofAGEL1323 andAGEL0014 are ${5.6}_{-0.8}^{+0.8}$Gyr and ${3.1}_{-0.3}^{+0.8}$Gyr, respectively, indicating that most of the stars in the galaxies were formed less than 2 Gyr after the Big Bang. Compared to nearby quiescent galaxies of similar masses, the lensed galaxies have lower [Fe/H] and [Mg/H]. Surprisingly, the two galaxies have comparable [Mg/Fe] to similar-mass galaxies at lower redshifts, despite their old ages. Using a simple analytic chemical evolution model connecting the instantaneously recycled element Mg with the mass-loading factors of outflows averaged over the entire star formation history, we found that the lensed galaxies may have experienced enhanced outflows during their star formation compared to lower-redshift galaxies, which may explain why they quenched early. 

ABSTRACT We present new spectroscopic observations of Ly α (Ly α) Blob 2 (z ∼ 3.1). We observed extended Ly α emission in three distinct regions, where the highest Ly α surface brightness (SB) centre is far away from the known continuum sources. We searched through the MOSFIRE slits that cover the high Ly α SB regions, but were unable to detect any significant nebular emission near the highest SB centre. We further mapped the flux ratio of the blue peak to the red peak and found it is anticorrelated with Ly α SB with a power-law index of ∼ –0.4. We used radiative transfer models with both multiphase, clumpy, and shell geometries and successfully reproduced the diverse Ly α morphologies. We found that most spectra suggest outflow-dominated kinematics, while 4/15 spectra imply inflows. A significant correlation exists between parameter pairs, and the multiphase, clumpy model may alleviate previously reported discrepancies. We also modelled Ly α spectra at different positions simultaneously and found that the variation of the inferred clump outflow velocities can be approximately explained by line-of-sight projection effects. Our results support the ‘central powering  + scattering’ scenario, i.e. the Ly α photons are generated by a central powering source and then scatter with outflowing, multiphase H  i gas while propagating outwards. The infalling of cool gas near the blob outskirts shapes the observed blue-dominated Ly α profiles, but its energy contribution to the total Ly α luminosity is less than 10 per cent, i.e. minor compared to the photoionization by star-forming galaxies and/or AGNs. 

ABSTRACT The combination of the MOSDEF and KBSS-MOSFIRE surveys represents the largest joint investment of Keck/MOSFIRE time to date, with ∼3000 galaxies at 1.4 ≲ z ≲ 3.8, roughly half of which are at z ∼ 2. MOSDEF is photometric- and spectroscopic-redshift selected with a rest-optical magnitude limit, while KBSS-MOSFIRE is primarily selected based on rest-UV colours and a rest-UV magnitude limit. Analysing both surveys in a uniform manner with consistent spectral-energy-distribution (SED) models, we find that the MOSDEF z ∼ 2 targeted sample has higher median M* and redder rest U−V colour than the KBSS-MOSFIRE z ∼ 2 targeted sample, and smaller median SED-based SFR and sSFR (SFR(SED) and sSFR(SED)). Specifically, MOSDEF targeted a larger population of red galaxies with U−V and V−J ≥1.25, while KBSS-MOSFIRE contains more young galaxies with intense star formation. Despite these differences in the z ∼ 2 targeted samples, the subsets of the surveys with multiple emission lines detected and analysed in previous work are much more similar. All median host-galaxy properties with the exception of stellar population age – i.e. M*, SFR(SED), sSFR(SED), AV, and UVJ colours – agree within the uncertainties. Additionally, when uniform emission-line fitting and stellar Balmer absorption correction techniques are applied, there is no significant offset between both samples in the [O iii]λ5008/H β versus [N ii]λ6585/H α diagnostic diagram, in contrast to previously reported discrepancies. We can now combine the MOSDEF and KBSS-MOSFIRE surveys to form the largest z ∼ 2 sample with moderate-resolution rest-optical spectra and construct the fundamental scaling relations of star-forming galaxies during this important epoch. 

ABSTRACT The discovery of giant quasar Ly α nebulae at z > 2 has opened up the possibility to directly study in emission the Circumgalactic and Intergalactic Medium (CGM/IGM). However, the resonant nature of the Ly α line and its different emission mechanisms hamper the ability to constrain both the kinematics and physical properties of the CGM/IGM. Here, we present results of a pilot project aiming at the detection of CGM H α emission, a line which does not suffer from these limitations. To this end, we first used KCWI to detect Ly α emission around three bright quasars with 2.25 < z < 2.27, a range which is free from bright IR sky lines for H α, and then selected the most extended nebula for H α follow-up with MOSFIRE. Within the MOSFIRE slit, we detected H α emission extending up to 20 physical kpc with a total H α flux of FH α = (9.5 ± 0.9) × 10$$^{-18}~\mathrm{erg\, s^{-1}\, cm^{-2}}$$. Considering the Ly α flux in the same region, we found FLy α/FH α = 3.7 ± 0.3 consistent with that obtained for the Slug Nebula at z = 2.275 and with recombination radiation. This implies high densities or a very broad density distribution within the CGM of high-redshift quasars. Moreover, the H α line profile suggests the presence of multiple emitting components overlapping along our line of sight and relatively quiescent kinematics, which seems incompatible with either quasar outflows capable of escaping the potential well of the host halo or disc-like rotation in a massive halo (>1012 M⊙). 

ABSTRACT The connection between the escape fraction of ionizing photons (fesc) and star formation rate surface density (ΣSFR) is a key input for reionization models, but remains untested at high redshift. We analyse 35 z ∼ 3 galaxies from the Keck Lyman Continuum Survey (KLCS) covered by deep, rest far-UV spectra of the Lyman continuum (LyC) and high-resolution HST V606 imaging, enabling estimates of both fesc and rest-UV sizes. Using Sérsic profile fits to HST images and spectral-energy distribution fits to multiband photometry, we measure effective sizes and SFRs for the galaxies in our sample, and separate the sample into two bins of ΣSFR. Based on composite spectra, we estimate 〈fesc〉 for both ΣSFR subsamples, finding no significant difference in 〈fesc〉 between the two. To test the representativeness of the KLCS HST sample and robustness of this result, we attempt to recover the well-established correlation between fesc and Lyα equivalent width. This correlation is not significant within the KLCS HST sample, indicating that the sample is insufficient for correlating fesc and galaxy properties such as ΣSFR. We perform stacking simulations using the KLCS parent sample to determine the optimal sample size for robust probes of the fesc-ΣSFR connection to inform future observing programs. For a program with a selection independent of ionizing properties, ≥90 objects are required; for one preferentially observing strongly-leaking LyC sources, ≥58 objects are required. More generally, measuring the connection between fesc and ΣSFR requires a larger, representative sample spanning a wide dynamic range in galaxies properties such as ΣSFR.