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ABSTRACT We present results from the NIRVANDELS survey on the gas-phase metallicity (Zg, tracing O/H) and stellar metallicity (Z⋆, tracing Fe/H) of 33 star-forming galaxies at redshifts 2.95 < z < 3.80. Based on a combined analysis of deep optical and near-IR spectra, tracing the rest-frame far-ultraviolet (FUV; 1200–2000 Å) and rest-frame optical (3400–5500 Å), respectively, we present the first simultaneous determination of the stellar and gas-phase mass–metallicity relationships (MZRs) at z ≃ 3.4. In both cases, we find that metallicity increases with increasing stellar mass (M⋆) and that the power-law slope at M⋆ ≲ 1010M⊙ of both MZRs scales as $$Z \propto M_{\star }^{0.3}$$. Comparing the stellar and gas-phase MZRs, we present direct evidence for super-solar O/Fe ratios (i.e. α-enhancement) at z > 3, finding (O/Fe) = 2.54 ± 0.38 × (O/Fe)⊙, with no clear dependence on M⋆. 

ABSTRACT We discovered a strongly lensed (μ ≳ 40) Ly α emission at z = 6.629 (S/N ≃ 18) in the MUSE Deep Lensed Field (MDLF) targeting the Hubble Frontier Field (HFF) galaxy cluster MACS J0416. Dedicated lensing simulations imply that the Ly α emitting region necessarily crosses the caustic. The arc-like shape of the Ly α extends 3 arcsec on the observed plane and is the result of two merged multiple images, each one with a de-lensed Ly α luminosity L ≲ 2.8 × 1040 erg s−1 arising from a confined region (≲150 pc effective radius). A spatially unresolved Hubble Space Telescope(HST) counterpart is barely detected at S/N ≃ 2 after stacking the near-infrared bands, corresponding to an observed (intrinsic) magnitude m1500 ≳ 30.8 (≳35.0). The inferred rest-frame Ly α equivalent width is EW0 > 1120 if the IGM transmission is TIGM < 0.5. The low luminosities and the extremely large Ly α EW0 match the case of a Population III (Pop III) star complex made of several dozens stars (∼104 M⊙) that irradiate an H ii region crossing the caustic. While the Ly α and stellar continuum are among the faintest ever observed at this redshift, the continuum and the Ly α emissions could be affected by differential magnification, possibly biasing the EW0 estimate. The aforementioned tentative HST detection tends to favour a large EW0, making such a faint Pop III candidate a key target for the James Webb Space Telescope and Extremely Large Telescopes. 

We report the discovery of a complete Einstein ring around the elliptical galaxy NGC 6505, atz = 0.042. This is the first strong gravitational lens discovered inEuclidand the first in an NGC object from any survey. The combination of the low redshift of the lens galaxy, the brightness of the source galaxy (I_E = 18.1 lensed,I_E = 21.3 unlensed), and the completeness of the ring make this an exceptionally rare strong lens, unidentified until its observation byEuclid. We present deep imaging data of the lens from theEuclidVisible Camera (VIS) and Near-Infrared Spectrometer and Photometer (NISP) instruments, as well as resolved spectroscopy from theKeckCosmic Web Imager (KCWI). TheEuclidimaging in particular presents one of the highest signal-to-noise ratio optical/near-infrared observations of a strong gravitational lens to date. From the KCWI data we measure a source redshift ofz = 0.406. Using data from the Dark Energy Spectroscopic Instrument (DESI) we measure a velocity dispersion for the lens galaxy ofσ_⋆ = 303 ± 15 km s⁻¹. We model the lens galaxy light in detail, revealing angular structure that varies inside the Einstein ring. After subtracting this light model from the VIS observation, we model the strongly lensed images, finding an Einstein radius of 2.″5, corresponding to 2.1 kpc at the redshift of the lens. This is small compared to the effective radius of the galaxy,R_eff ∼ 12.″3. Combining the strong lensing measurements with analysis of the spectroscopic data we estimate a dark matter fraction inside the Einstein radius off_DM = (11.1_−3.5^+5.4)% and a stellar initial mass-function (IMF) mismatch parameter ofα_IMF = 1.26_−0.08^+0.05, indicating a heavier-than-Chabrier IMF in the centre of the galaxy. 

Abstract We constrain the distribution of spatially offset Lyman-alpha emission (Ly α) relative to rest-frame ultraviolet emission in ∼300 high redshift (3 < z < 5.5) Lyman-break galaxies (LBGs) exhibiting Ly α emission from VANDELS, a VLT/VIMOS slit-spectroscopic survey of the CANDELS Ultra Deep Survey and Chandra Deep Field South fields (≃0.2 deg2 total). Because slit spectroscopy only provides one spatial dimension, we use Bayesian inference to recover the underlying two-dimensional Ly α spatial offset distribution. We model the distribution using a two-dimensional circular Gaussian, defined by a single parameter σr,Ly α, the standard deviation expressed in polar coordinates. Over the entire redshift range of our sample (3 < z < 5.5), we find $$\sigma _{r,\mathrm{Ly}\,\alpha }=1.70^{+0.09}_{-0.08}$$ kpc ($$68\hbox{ per cent}$$ conf.), corresponding to ∼0$${^{\prime\prime}_{.}}$$25 at 〈z〉 = 4.5. We also find that σr,Ly α decreases significantly with redshift. Because Ly α spatial offsets can cause slit losses, the decrease in σr,Ly α with redshift can partially explain the increase in the fraction of Ly α emitters observed in the literature over this same interval, although uncertainties are still too large to reach a strong conclusion. If σr,Ly α continues to decrease into the reionization epoch, then the decrease in Ly α transmission from galaxies observed during this epoch might require an even higher neutral hydrogen fraction than what is currently inferred. Conversely, if spatial offsets increase with the increasing opacity of the intergalactic medium, slit losses may explain some of the drop in Ly α transmission observed at z > 6. Spatially resolved observations of Ly α and UV continuum at 6 < z < 8 are needed to settle the issue.