The bright Lyα line is regularly used to identify high-redshift star-forming galaxies known as Lyα emitters (LAEs). However, Lyα is affected by resonant scattering and dust absorption making interpretation of its brightness challenging without additional observations. We use SCUBA-2, PACS and SPIRE data to investigate the far-infrared emission, Lyα escape fraction (fesc(Lyα)) and infrared excess (IRX=LIR/LUV) in ∼4000 LAEs at z=2.2-6 from SC4K. Five LAEs, all hosting AGN, are individually detected with fluxes S_850 = 3.7-5.5 mJy at 850μm. Stacking is used to probe the average emission from all individually undetected LAEs, though the stacks are undetected at all wavelengths (e.g. S_850 < 0.09 mJy; 3σ). We group the sample into bins of redshift, stellar mass, Lyα luminosity and AGN status. Most subsets are undetected but LAEs containing AGN and that have high stellar masses (M_⋆ = 10^10 - 10^12 M_⊙; including and excluding AGN) are detected at most wavelengths, suggesting that stellar mass and AGN heating may be enhancing the dust visibility. Individually detected LAEs and detected stacks have fesc(Lyα)=1-7

We aim to characterise the mass-metallicity relation (MZR) and the 3D correlation between the stellar mass, metallicity, and star formation rate (SFR) known as the fundamental metallicity relation (FMR) for galaxies at 5 < z < 7. Using ∼800 [O III] selected galaxies from deep NIRCam grism surveys, we present our stacked measurements of direct-Te metallicities, which we used to test recent strong-line metallicity calibrations. Our measured direct-Te metallicities (0.1–0.2 Z⊙ for M★ ≈ 5 × 107 − 9 M⊙, respectively) match recent JWST/NIRSpec-based results. However, there are significant inconsistencies between observations and hydrodynamical simulations. We observe a flatter MZR slope than the SPHINX20 and FLARES simulations, which cannot be attributed to selection effects. With simple models, we show that the effect of an [O III] flux-limited sample on the observed shape of the MZR is strongly dependent on the FMR. If the FMR is similar to the one in the local Universe, the intrinsic high-redshift MZR should be even flatter than is observed. In turn, a 3D relation where SFR correlates positively with metallicity at fixed mass would imply an intrinsically steeper MZR. Our measurements indicate that metallicity variations at fixed mass show little dependence on the SFR, suggesting a flat intrinsic MZR. This could indicate that the low-mass galaxies at these redshifts are out of equilibrium and that metal enrichment occurs rapidly in low-mass galaxies. However, being limited by our stacking analysis, we are yet to probe the scatter in the MZR and its dependence on SFR. Large carefully selected samples of galaxies with robust metallicity measurements can put tight constraints on the high-redshift FMR and help us to understand the interplay between gas flows, star formation, and feedback in early galaxies.

We introduce J-HERTz (J-PLUS Heritage Exploration of Radio Targets at z < 5), a new multiwavelength catalog that combines optical narrowband photometry from J-PLUS, infrared observations from the Wide-field Infrared Survey Explorer, and deep low-frequency radio data from LoTSS for nearly 0.5 million sources across 2100 deg ^2 of the northern sky. Key innovations of J-HERTz include Bayesian neural network classifications for 390,000 galaxies, 31,000 quasars, and 20,000 stars, along with significantly improved photometric redshifts for 235,000 galaxies compared to previous J-PLUS DR3 and LoTSS DR2 estimates. We identify 831 candidate Galactic radio stars, which, if confirmed, would constitute a significant addition to the number of radio-emitting stars identified to date. Among radio-loud galaxies with spectroscopic observations, ≳20% lack Seyfert or LINER signatures, indicating a substantial population of optically quiescent radio galaxies, in agreement with previous works. Spectral energy distribution fitting of their host galaxies using J-PLUS photospectra reveals systematically low specific star formation rates, consistent with quenched stellar populations. J-HERTz thus provides a powerful data set to exploit radio-optical synergies, enabling studies that span from the origin of stellar radio emission to the active galactic nucleus life cycle and the role of jet activity in shaping host galaxy evolution.

Context: Narrowband JWST/NIRCam selection isolates star-forming galaxies in well-defined redshift slices, while ALMA and archival far-IR/submm data reveal obscured growth. We combine these to measure Paschen-line SFRs, infer nebular extinction from EAZY Av, and probe FIR-to-submm emission via weighted-median stacking, to constrain galaxy growth at cosmic noon. Aims: We characterize stellar, nebular, and FIR properties of Paschen-selected galaxies in COSMOS, in two ensembles at z 1.50 (Pa-alpha) and z 2.65 (Pa-beta), quantifying short- vs long-timescale SF and dust attenuation, and constraining obscured SFR and gas masses. Methods: We select robust narrowband-excess samples from the JELS F466N/F470N mosaic (Pa-alpha: 77, Pa-beta: 31 sources), remove AGN via X-ray/radio matching, and assemble multiwavelength photometry (JWST, HST, Spitzer, Herschel, SCUBA-2, AzTEC, ALMA). Photo-z/stellar properties come from EAZY/STARDUST; line SFRs use recent Paschen calibrations, with nebular extinction from EAZY Av. Results: EAZY fits show stellar masses log(Mstar/Msun) 7.4-10.3 and modest SFRs (0.1-27 Msun/yr). Line SFRs are 0.1-22.0 and 0.7-47.9 Msun/yr for Pa-alpha/beta. Most sources show short-term bursts (line SFRs exceed SED SFRs), weakly decreasing with mass. Nebular attenuation correlates with mass and SFR. Stacking gives no >3sigma detections beyond MIRI. The weighted-median SED gives SFR_UV,med = 0.48+-0.11 and 3.92+-0.47 Msun/yr for Pa-alpha/beta. ALMA Band 4 gives the tightest constraints: median 3-sigma limits SFR_IR<53 (Pa-alpha) and <44 Msun/yr (Pa-beta); gas mass <10^11.2 (Pa-alpha) and <10^10.6 Msun (Pa-beta). Conclusions: Paschen-selected samples show widespread short-timescale star formation, but FIR/sub-mm data give only upper limits on obscured SFR/ISM mass. Deeper spectroscopy and ALMA continuum data are needed to constrain obscured SF and gas reservoirs.

The physical processes that led to the formation of billion-solar-mass black holes within the first 700 million years of cosmic time, a period known as cosmic dawn, remain a puzzle1. Several theoretical scenarios have been proposed to seed and rapidly grow black holes2-4, but direct observations of these mechanisms remain elusive. Here we present a source 660 million years after the Big Bang that exhibits singular properties: among the largest hydrogen Balmer breaks reported at any redshift, broad multi-peaked Hβ emission, and Balmer line absorption in several transitions. We model this source as an enshrouded black hole in which the Balmer break and absorption features are a result of extremely dense, turbulent gas forming a dust-free envelope around a supermassive black hole5,6. This source may provide evidence of an early black hole embedded in dense gas-a theoretical configuration proposed to rapidly grow black holes by super-Eddington accretion7,8. Radiation from the black hole seems to dominate almost all observed light, leaving limited room for contribution from its host galaxy. If the source merged with its brighter neighbour, it would resemble the recently discovered 'little red dots' with perplexing spectral energy distributions9-11. The redness of the black hole is due to gas, not dust12,13, and scattering, not kinematics, gives rise to the complex line shapes and luminosities-black hole masses of these sources may therefore be overestimated by orders of magnitude.

We aim to characterise the mass-metallicity relation (MZR) and the 3D correlation between the stellar mass, metallicity, and star formation rate (SFR) known as the fundamental metallicity relation (FMR) for galaxies at 5 < z < 7. Using ∼800 [O III] selected galaxies from deep NIRCam grism surveys, we present our stacked measurements of direct-Te metallicities, which we used to test recent strong-line metallicity calibrations. Our measured direct-Te metallicities (0.1–0.2 Z⊙ for M★ ≈ 5 × 107 − 9 M⊙, respectively) match recent JWST/NIRSpec-based results. However, there are significant inconsistencies between observations and hydrodynamical simulations. We observe a flatter MZR slope than the SPHINX20 and FLARES simulations, which cannot be attributed to selection effects. With simple models, we show that the effect of an [O III] flux-limited sample on the observed shape of the MZR is strongly dependent on the FMR. If the FMR is similar to the one in the local Universe, the intrinsic high-redshift MZR should be even flatter than is observed. In turn, a 3D relation where SFR correlates positively with metallicity at fixed mass would imply an intrinsically steeper MZR. Our measurements indicate that metallicity variations at fixed mass show little dependence on the SFR, suggesting a flat intrinsic MZR. This could indicate that the low-mass galaxies at these redshifts are out of equilibrium and that metal enrichment occurs rapidly in low-mass galaxies. However, being limited by our stacking analysis, we are yet to probe the scatter in the MZR and its dependence on SFR. Large carefully selected samples of galaxies with robust metallicity measurements can put tight constraints on the high-redshift FMR and help us to understand the interplay between gas flows, star formation, and feedback in early galaxies.

We present the JWST Emission-Line Survey (JELS), a JWS7 imaging programme exploiting the wavelength coverage and sensitivity of the Near-Infrared Camera (NIRCam) to extend narrow-band rest-optical emission-line selection into the Epoch of Reionization (EoR) for the first time, and to enable unique studies of the resolved ionized gas morphology in individual galaxies across cosmic history. The primary JELS observations comprise similar to 4.7 mu m narrow-band imaging over similar to 63 arcmin(2) designed to enable selection of H alpha emitters at z similar to 6.1 and a host of novel emission-line samples, including [OIII] (z similar to 8.3) and Paschen alpha/beta (z similar to 1.5/2.8). For the F466N/F470N narrow-band observations, the emission-line sensitivities achieved are up to similar to 2x more sensitive than current slitless spectroscopy surveys (5 sigma limits of 0.8-1.2 x 10(-18) erg s(-1)cm(-2)), corresponding to unobscured H alpha star formation rates (SFRs) of 0.9-1.3 M-circle dot yr(-1) at z similar to 6.1, extending emission-line selections in the EoR to fainter populations. Simultaneously, JELS also adds F200W broad-band and F212N narrow-band imaging (H alpha at z similar to 2.23) that probes SFRS greater than or similar to 5x fainter than previous ground-based narrow-band studies (similar to 0.2 M-circle dot yr(-1)), offering an unprecedented resolved view of star formation at cosmic noon. We present the detailed JELS design, key data processing steps specific to the survey observations, and demonstrate the exceptional data quality and imaging sensitivity achieved. We then summarize the key scientific goals of JELS, demonstrate the precision and accuracy of the expected redshift and measured emission-line recovery through detailed simulations, and present examples of spectroscopically confirmed H alpha and [O III] emitters discovered by JELS that illustrate the novel parameter space probed.

We present a dedicated automated pipeline to construct spatially resolved emission Hα+ NII maps and to derive the spectral energy distributions (SEDs) in 12 optical filters (five broad and seven narrow and medium) of Hα emission line regions in nearby galaxies (z $<$ 0.0165) observed by the Javalambre Photometric Local Universe Survey (J-PLUS). We used the J0660 filter of $140$ Å width centered at $6600$ Å to trace Hα + NII emission, and r and i broad bands were used to estimate the stellar continuum. We created pure emission line images after the continnum subtraction, where the Hα emission line regions were detected. This method was also applied to integral field unit (IFU) spectroscopic data from PHANGS-MUSE, CALIFA, and MaNGA surveys by building synthetic narrow bands based on J-PLUS filters. The studied sample includes the cross-matched catalog of these IFU surveys with the J-PLUS third data release (DR3), amounting to two PHANGS-MUSE, $78$ CALIFA, and $78$ MaNGA galaxies at z < 0.0165, respectively. We compared the Hα+ NII radial profiles from J-PLUS and the IFU surveys, finding good agreement within the expected uncertainties. We also compared the SEDs from the emission line regions detected in J-PLUS images, reproducing the main spectral features present in the spectroscopic data. Finally, we compared the emission fluxes from the J-PLUS and IFU surveys accounting for scale differences, finding a difference of only 2% with a dispersion of 7% in the measurements. The J-PLUS data provide reliable spatially resolved Hα+ NII emission maps for nearby galaxies. We provide the J-PLUS DR3 catalog for the $158$ galaxies with IFU data, including emission maps, SEDs of star-forming clumps, and radial profiles.

We present the first results of the JWST Emission Line Survey (JELS). Utilizing the first NIRCam narrow-band imaging at 4.7 mu m, over 63 arcmin2 in the PRIMER/COSMOS field, we have identified 609 emission line galaxy candidates. From these, we robustly selected 35 H alpha star-forming galaxies at z <^> 6 . 1, with H alpha star-formation rates (SFRH alpha) of <^> 0 . 9-15 Mo yr(-1) . Combining our unique H alpha sample with the exquisite panchromatic data in the field, we explored their physical properties and star-formation histories, and compared these to a broad-band selected sample at z <^> 6 which has offered vital new insights into the nature of high-redshift galaxies. UV-continuum slopes ( 3) were considerably redder for our H alpha sample ( ( 3) <^> -1.92) compared to the broad-band sample ( ( 3) <^> -2.35). This was not due to dust attenuation as our H alpha sample was relatively dust-poor (median AV = 0 . 23); instead, we argue that the reddened slopes could be due to nebular continuum. We compared SFRH alpha and the UV-continuum-derived SFRUV to SED-fitted measurements averaged over canonical time-scales of 10 and 100 Myr (SFR10 and SFR100). We found an increase in recent SFR for our sample of H alpha emitters, particularly at lower stellar masses (< 10( 9) M-o). We also found that SFRH alpha strongly traces SFR averaged over 10 Myr time-scales, whereas the UV-continuum overpredicts SFR on 100 Myr time-scales at low stellar masses. These results point to our H alpha sample undergoing 'bursty' star formation. Our F356W z <^> 6 sample showed a larger scatter in SFR10 /SFR100 across all stellar masses, which has highlighted how narrow-band photometric selections of H alpha emitters are key to quantifying the burstiness of star-formation activity.

The physical processes that led to the formation of billion solar mass black holes within the first 700 million years of cosmic time remain a puzzle. Several theoretical scenarios have been proposed to seed and rapidly grow black holes, but direct observations of these mechanisms remain elusive. Here we present a source 660 million years after the Big Bang that displays singular properties: among the largest Hydrogen Balmer breaks reported at any redshift, broad multi-peaked Hβ emission, and Balmer line absorption in multiple transitions. We model this source as a "black hole star" (BH*) where the Balmer break and absorption features are a result of extremely dense, turbulent gas forming a dust-free "atmosphere" around a supermassive black hole. This source may provide evidence of an early black hole embedded in dense gas – a theoretical configuration proposed to rapidly grow black holes via super-Eddington accretion. Radiation from the BH* appears to dominate almost all observed light, leaving limited room for contribution from its host galaxy. We demonstrate that the recently discovered "Little Red Dots" (LRDs) with perplexing spectral energy distributions can be explained as BH*s embedded in relatively brighter host galaxies. This source provides evidence that black hole masses in the LRDs may be over-estimated by orders of magnitude – the BH* is effectively dust-free contrary to the steep dust corrections applied while modeling LRDs, and the physics that gives rise to the complex line shapes and luminosities may deviate from assumptions underlying standard scaling relations.

Submillimetre galaxies (SMGs) are some of the most extreme star-forming systems in the Universe, whose place in the framework of galaxy evolution is as yet uncertain. It has been hypothesized that SMGs are progenitors of local early-type galaxies, requiring that SMGs generally reside in galaxy cluster progenitors at high redshift. We test this hypothesis and explore SMG environments using a narrow-band VLT/HAWK-I+GRAAL study of H alpha and [OIII] emitters around an unbiased sample of three ALMA-identified and spectroscopically confirmed SMGs at z similar to 2.3 and similar to 3.3, where these SMGs were selected solely on spectroscopic redshift. Comparing with blank-field observations at similar epochs, we find that one of the three SMGs lies in an overdensity of emission-line sources on the similar to 4 Mpc scale of the HAWK-I field of view, with overdensity parameter delta(g)=2.6(-1.2)(+1.4). A second SMG is significantly overdense only on less than or similar to 1.6 Mpc scales and the final SMG is consistent with residing in a blank field environment. The total masses of the two overdensities are estimated to be log(M-h/M-circle dot)= 12.1-14.4, leading to present-day masses of log(M-h,M-z=0/M-circle dot)= 12.9-15.9. These results imply that SMGs occupy a range of environments, from overdense protoclusters or protogroups to the blank field, suggesting that while some SMGs are strong candidates for the progenitors of massive elliptical galaxies in clusters, this may not be their only possible evolutionary pathway.

Past studies have investigated the evolution in specific star formation rate (sSFR) and its observational proxy (H alpha equivalent width; EW) up to z similar to 6; however, such measurements may overestimate the typical sSFR/EW at a given redshift due to selection effects. We investigate the 'intrinsic' (selection and observational effects corrected) H alpha EW distributions of z similar to 0.4-2.2 narrowband-selected H alpha samples from High-z Emission Line Survey (HiZELS) and Deep and Wide Narrowband survey (DAWN) using a forward modelling approach where we assume an 'intrinsic' exponential EW distribution, apply selection and filter effects, and compare with observed H alpha EW distributions. We find an 'intrinsic' EW-stellar mass anticorrelation, EW0 proportional to M gamma, with steepening slopes gamma=-0.18 +/- 0.03 to -0.24(-0.08)(+0.06 )at z similar to 0.4 and z similar to 2.2, respectively. At 1010 M-circle dot, we find EW0 proportional to(1+z)1.78(-0.23)(+0.22) and a steeper evolution with decreasing stellar mass highlighting the high EW nature of low-mass, high-z systems. We model this redshift evolving EW-stellar mass anticorrelation, W0(M,z), and find it produces H alpha luminosity and SFR functions strongly consistent with observations. Our W0(M,z) model suggests EW0>200 & Aring; emitters contribute similar to 40 per cent to overall cosmic SF at z similar to 1.5(-2), consistent with sSFR >10(-8.5) yr(-1) (makes up similar to 45-55 per cent of cosmic SF at z similar to 2) and highlights the importance of high EW systems at high-z. Our W0(M,z) model also reproduces the cosmic sSFR evolution found in both simulations and observations (including selection limits), such that selection effects in observations may explain the disagreement. Lastly, we forecast Roman and Euclid grism surveys using our W-0(M,z) model including limiting resolution and observational efficiency effects. We predict similar to 24000 and similar to 300000.55x10(-17 )erg s(-1) cm(-2) including 107.2-8 M-circle dot galaxies at z>1 with EW0>1000 & Aring;. Both Roman and Euclid will observe some of the most bursty/high EW, low-mass star-forming galaxies near cosmic noon in unprecedented detail.

We present a detailed exploration of the most optically-luminous Little Red Dot (L_Hα=10^44erg/s, L_V=10^45erg/s, F444W=22AB) found to date. Located in the Abell 2744 field, source A744-45924 was observed by NIRSpec/PRISM with ultradeep spectroscopy reaching SNR∼100pix^-1, high-resolution 3-4 micron NIRCam/Grism spectroscopy, and NIRCam Medium Band imaging. The NIRCam spectra reveal high rest-frame EW W_Hα,0,broad>800Å, broad Hα emission (FWHM∼4500 km/s), on top of narrow, complex absorption. NIRSpec data show exceptionally strong rest-frame UV to NIR Fe II emission (W_FeII-UV,0∼340Å), N IV]λλ1483,1486 and N III]λ1750, and broad NIR O I λ8446 emission. The spectra unambiguously demonstrate a broad-line region associated with an inferred M_BH∼10^9M_⊙ supermassive black hole embedded in dense gas, which might explain a non-detection in ultradeep Chandra X-ray data (>10× underluminous relative to broad L_Hα). Strong UV Nitrogen lines suggest supersolar N/O ratios due to rapid star formation or intense radiation near the AGN. The continuum shows a clear Balmer break at rest-frame 3650Å, which cannot be accounted for by an AGN power-law alone. A stellar population model produces an excellent fit with a reddened Balmer break and implying a massive (M_*∼8×10^10M_⊙), old ∼500 Myr, compact stellar core, among the densest stellar systems known (ρ∼3×10^6M_⊙/pc^2 for R_e,opt=70±10 pc), and AGN emission with extreme intrinsic EW W_Hα,0≫1000Å. However, although high M_* and M_BH are supported by evidence of an overdensity containing 40 galaxies at z=4.41-4.51, deep high-resolution spectroscopy is required to confirm stellar absorption and rule out that dense gas around the AGN causes the Balmer break instead.

The increasingly neutral intergalactic gas at z > 6 impacts the Lyman-alpha (Ly alpha) flux observed from galaxies. One luminous galaxy, COLA1, stands out because of its unique double-peaked Ly alpha line at z = 6.6, unseen in any simulation of reionization. Here, we present JWST/NIRCam wide-field slitless spectroscopy in a 21 arcmin(2) field centered on COLA1. We find 141 galaxies spectroscopically selected through the [O III] doublet at 5.35 < z < 6.95, with 40 of these sources showing H beta. For COLA1, we additionally detect [O III](4363) as well as H gamma. We measure a systemic redshift of z = 6.5917 for COLA1, confirming the classical double-peak nature of the Ly alpha profile. This implies that it resides in a highly ionized bubble and that it is leaking ionizing photons with a high escape fraction of f(esc)(LyC) = 20-50%, making it a prime laboratory to study Lyman continuum escape in the Epoch of Reionization. COLA1 shows all the signs of a prolific ionizer with a Ly alpha escape fraction of 81 +/- 5%, Balmer decrement indicating no dust, a steep UV slope (beta(UV) = -3.2 +/- 0.4), and a star-formation surface density greater than or similar to 10x that of typical galaxies at similar redshift. We detect five galaxies in COLA1's close environment (Delta z < 0.02). Exploiting the high spectroscopic completeness inherent to grism surveys, and using mock simulations that fully mimic the selection function, we show that the number of detected companions is very typical for a normal similarly UV-bright (M-UV similar to -21.3) galaxy - that is, the ionized bubble around COLA1 is unlikely to be due to an excessively large over-density. Instead, the measured ionizing properties suggest that COLA1 by itself might be powering the bubble required to explain its double-peaked Ly alpha profile (R-ion approximate to 0.7 pMpc), with only minor contributions from detected neighbors (-19.5 less than or similar to M-UV less than or similar to -17.5).

We investigate the `intrinsic' H$\alpha$ EW distributions of $z \sim 0.4 - 2.2$ narrowband-selected H$\alpha$ samples from HiZELS and DAWN using a forward modeling approach. We find an EW - stellar mass anti-correlation with steepening slopes $-0.18\pm0.03$ to $-0.24^{+0.06}_{-0.08}$ at $z \sim 0.4$ and $z\sim 2.2$, respectively. Typical EW increases as $(1+z)^{1.78^{+0.22}_{-0.23}}$ for a $10^{10}$ M$_\odot$ emitter from $15^{+2.4}_{-2.3}$\r{A} ($z \sim 0.4$) to $67.7^{+10.4}_{-10.0}$\r{A} ($z \sim 2.2$) and is steeper with decreasing stellar mass highlighting the high EW nature of low-mass high-$z$ systems. We model this redshift evolving anti-correlation, $W_0(M,z)$, and find it produces H$\alpha$ luminosity and SFR functions strongly consistent with observations validating the model and allowing us to use $W_0(M,z)$ to investigate the relative contribution of H$\alpha$ emitters towards cosmic SF. We find EW$_0 > 200$ \r{A} emitters contribute significantly to cosmic SF activity at $z \sim 1.5 - 2$ making up $\sim 40$% of total SF consistent with sSFR $> 10^{-8.5}$ yr$^{-1}$ ($\sim 45 - 55$%). Overall, this highlights the importance of high EW systems at high-$z$. Our $W_0(M,z)$ model also reproduces the cosmic sSFR evolution found in simulations and observations and show that tension between the two can simply arise from selection effects in observations. Lastly, we forecast Roman and Euclid grism surveys using $W_0(M,z)$ including observational efficiency and limiting resolution effects where we predict $\sim 24000$ and $\sim 30000$ $0.5 < z < 1.9$ H$\alpha$ emitters per deg$^{-2}$, respectively, down to $>5\times10^{-17}$ erg s$^{-1}$ cm$^{-2}$ including $10^{7.2 - 8}$ M$_\odot$ galaxies at $z > 1$ with EW$_0 >1000$\r{A}. Both Roman and Euclid will enable us to observe with unprecedented detail some of the most bursty/high EW, low-mass star-forming galaxies near cosmic noon.

Dwarf galaxies hold the key to crucial frontiers of astrophysics, however, their faintness renders spectroscopy challenging. Here we present the JWST Cycle 2 survey, All the Little Things (ALT, PID 3516), which is designed to seek late-forming Pop III stars and the drivers of reionization at z∼6-7. ALT has acquired the deepest NIRCam grism spectroscopy yet (7-27 hr), at JWST's most sensitive wavelengths (3-4 μm), covering the powerful lensing cluster Abell 2744. Over the same 30 arcmin^2, ALT's ultra-deep F070W+F090W imaging (∼30 mag) enables selection of very faint sources at z>6. We demonstrate the success of ALT's novel “butterfly" mosaic to solve spectral confusion and contamination, and introduce the “Allegro" method for emission line identification. By collecting spectra for every source in the field of view, ALT has measured precise (R∼1600) redshifts for 1630 sources at z=0.2-8.5. This includes one of the largest samples of distant dwarf galaxies: [1015, 475, 50] sources less massive than the SMC, Fornax, and Sculptor with log(M_*/M_⊙)<[8.5, 7.5, 6.5]. We showcase ALT's discovery space with: (i) spatially resolved spectra of lensed clumps in galaxies as faint as M_UV∼-15; (ii) large-scale clustering – overdensities at z=[2.50, 2.58, 3.97, 4.30, 5.66, 5.77, 6.33] hosting massive galaxies with striking Balmer breaks; (iii) small-scale clustering – a system of satellites around a Milky Way analog at z∼6; (iv) spectroscopically confirmed multiple images that help constrain the lensing model underlying all science in this legacy field; (v) sensitive star-formation maps based on dust-insensitive tracers such as Paα; (vi) direct spectroscopic discovery of rare sources such as AGN with ionized outflows. These results provide a powerful proof of concept for how grism surveys maximize the potential of strong lensing fields.

We use multi-object near-infrared (NIR) spectroscopy with VLT/KMOS to investigate the role of the environment in the evolution of the ionized gas properties of narrow-band selected H$\alpha$ emitters (HAEs) in the Spiderweb protocluster at $z=2.16$. Based on rest-frame optical emission lines, H$\alpha$ and [NII]$\lambda$6584, we confirm the cluster membership of 39 of our targets (i.e. 93% success rate), and measure their star-formation rates (SFR), gas-phase oxygen abundances and effective radius. We parametrize the environment where our targets reside by using local and global density indicators based on previous samples of spectroscopic and narrow-band cluster members. We find that star-forming galaxies embedded in the Spiderweb protocluster display SFRs compatible with those of the main sequence and morphologies comparable to those of late-type galaxies at $z=2.2$ in the field. We also report a mild gas-phase metallicity enhancement ($0.6\pm0.3$ dex) at intermediate stellar masses. Furthermore, we identify two UVJ-selected quiescent galaxies with residual H$\alpha$-based star formation and find signs of extreme dust obscuration in a small sample of SMGs based on their FIR and H$\alpha$ emission. Interestingly, the spatial distribution of these objects differs from the rest of HAEs, avoiding the protocluster core. Finally, we explore the gas fraction-gas metallicity diagram for 7 galaxies with molecular gas masses measured by ATCA using CO(1-0). In the context of the gas-regulator model, our objects are consistent with relatively low mass-loading factors, suggesting lower outflow activity than field samples at the cosmic noon and thus, hinting at the onset of environmental effects in this massive protocluster.

Galaxy evolution is driven by a variety of physical processes that are predicted to proceed at different rates for different dark matter haloes and environments across cosmic times. A record of this evolution is preserved in galaxy stellar populations, which we can access using absorption-line spectroscopy. Here we explore the large LEGA-C survey (DR3) to investigate the role of the environment and stellar mass on stellar populations at z ∼ 0.6–1 in the COSMOS field. Leveraging the statistical power and depth of LEGA-C, we reveal significant gradients in D n 4000 and H δ equivalent widths (EWs) distributions over the stellar mass versus environment 2D spaces for the massive galaxy population ( M > 10 10 M ⊙ ) at z ∼ 0.6–1.0. D n 4000 and H δ EWs primarily depend on stellar mass, but they also depend on environment at fixed stellar mass. By splitting the sample into centrals and satellites, and in terms of star-forming galaxies and quiescent galaxies, we reveal that the significant environmental trends of D n 4000 and H δ EW, when controlling for stellar mass, are driven by quiescent galaxies. Regardless of being centrals or satellites, star-forming galaxies reveal D n 4000 and H δ EWs, which depend strongly on their stellar mass and are completely independent of the environment at 0.6 < z < 1.0. The environmental trends seen for satellite galaxies are fully driven by the trends that hold only for quiescent galaxies, combined with the strong environmental dependency of the quiescent fraction at fixed stellar mass. Our results are consistent with recent predictions from simulations that point toward massive galaxies forming first in overdensities or the most compact dark matter haloes.

The Javalambre-Physics of the Accelerating Universe Astrophysical Survey (J-PAS) is expected to map thousands of square degrees of the northern sky with 56 narrowband filters (spectral resolution of R ∼ 60) in the upcoming years. This resolution allows us to study emission line galaxies (ELGs) with a minimum equivalent width of 10 Å in the H α emission line for a median signal-to-noise ratio (S/N) of 5. This will make J-PAS a very competitive and unbiased emission line survey compared to spectroscopic or narrowband surveys with fewer filters. The miniJPAS survey covered 1 deg 2 , and it used the same photometric system as J-PAS, but the observations were carried out with the pathfinder J-PAS camera. In this work, we identify and characterize the sample of ELGs from miniJPAS with a redshift lower than 0.35, which is the limit to which the H α line can be observed with the J-PAS filter system. Using a method based on artificial neural networks, we detect the ELG population and measure the equivalent width and flux of the H α , H β , [O III ], and [N II ] emission lines. We explore the ionization mechanism using the diagrams [OIII]/H β versus [NII]/H α (BPT) and EW(H α ) versus [NII]/H α (WHAN). We identify 1787 ELGs (83%) from the parent sample (2154 galaxies) in the AEGIS field. For the galaxies with reliable EW values that can be placed in the WHAN diagram (2000 galaxies in total), we obtained that 72.8 ± 0.4%, 17.7 ± 0.4%, and 9.4 ± 0.2% are star-forming (SF), active galactic nucleus (Seyfert), and quiescent galaxies, respectively. The distribution of EW(H α ) is well correlated with the bimodal color distribution of galaxies. Based on the rest-frame ( u − r )–stellar mass diagram, 94% of the blue galaxies are SF galaxies, and 97% of the red galaxies are LINERs or passive galaxies. The nebular extinction and star formation rate (SFR) were computed from the H α and H β fluxes. We find that the star formation main sequence is described as log SFR [ M ⊙ yr −1 ] = 0.90 −0.02 +0.02 log M ⋆ [ M ⊙ ]−8.85 −0.20 +0.19 and has an intrinsic scatter of 0.20 −0.01 +0.01 . The cosmic evolution of the SFR density ( ρ SFR ) is derived at three redshift bins: 0 < z ≤ 0.15, 0.15 < z ≤ 0.25, and 0.25 < z ≤ 0.35, which agrees with previous results that were based on measurements of the H α emission line. However, we find an offset with respect to other estimates that were based on the star formation history obtained from fitting the spectral energy distribution of the stellar continuum. We discuss the origin of this discrepancy, which is probably a combination of several factors: the escape of ionizing photons, the SFR tracers, and dust attenuation, among others.

ABSTRACT The cosmic ionizing emissivity from star-forming galaxies has long been anchored to UV luminosity functions. Here, we introduce an emissivity framework based on Lyα emitters (LAEs), which naturally hones in on the subset of galaxies responsible for the ionizing background due to the intimate connection between production and escape of Lyα and LyC photons. Using constraints on the escape fractions of bright LAEs (LLyα > 0.2L*) at z ≈ 2 obtained from resolved Lyα profiles, and arguing for their redshift-invariance, we show that: (i) quasars and LAEs together reproduce the relatively flat emissivity at z ≈ 2–6, which is non-trivial given the strong evolution in both the star formation density and quasar number density at these epochs and (ii) LAEs produce late and rapid reionization between z ≈ 6−9 under plausible assumptions. Within this framework, the >10 × rise in the UV population-averaged fesc between z ≈ 3–7 naturally arises due to the same phenomena that drive the growing LAE fraction with redshift. Generally, a LAE dominated emissivity yields a peak in the distribution of the ionizing budget with UV luminosity as reported in latest simulations. Using our adopted parameters ($f_{\rm {esc}}=50{{\ \rm per\ cent}}$, ξion = 1025.9 Hz erg−1 for half the bright LAEs), a highly ionizing minority of galaxies with MUV < −17 accounts for the entire ionizing budget from star-forming galaxies. Rapid flashes of LyC from such rare galaxies produce a ‘disco’ ionizing background. We conclude proposing tests to further develop our suggested Lyα-anchored formalism.