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Abstract:

We report the detection of a previously unknown object with a single emission line within the Hubble Ultra Deep Field, using a new JWST NIRSpec technique called Multiobject Coronagraphy for Slitless Spectroscopy (MOCSS) with the G140M/F100LP observing mode. The MOCSS technique involves opening almost all the shutters on the NIRSpec microshutter array, while simultaneously closing the shutters that lie on top of known low-redshift objects, facilitating a wide-field slitless spectroscopic search without contamination from bright objects. This observational technique has enabled the detection of a strong emission line in four different dither positions and in two position angles, and thus cannot be artificial. This line is detected at 1.60 μm with a line flux of [2.5 ± 0.3] × 10−18 erg s−1cm−2 and an FWHM of 13.2 ± 2.0 Å, and does not correspond to any known source with some of the deepest Hubble Space Telescope and JWST imaging in existence. Based upon the absence of imaging detection, we place a lower limit on the observed frame equivalent width (EW) of 7620 Å on this object, which strongly limits the number of possible lines that this line can be. Given the wavelength, an EW limit that is near the ceiling of expectation, and the lack of other lines in the bandpass, this line cannot be easily explained by [O ii] at z = 3.29, [O iii] at z = 2.20, Hα at z = 1.44, and Lyα at z = 12.16. We discuss possible active galactic nucleus and transient phenomena that could explain the finding.

Abstract:

Abstract Dust attenuation is a major source of systematic uncertainty in both spectral energy distribution (SED) fitting and forward modeling of galaxy populations, yet the functional form used to parameterize attenuation curves has received surprisingly little systematic scrutiny. Particular unanswered questions include: how many free parameters are genuinely needed, and which analytic expression best captures the full diversity of attenuation curve shapes in galaxies across cosmic time? Using a large library of synthetic attenuation curves from TNG50 and TNG100 galaxies post-processed with the skirt radiative transfer code using three dust mixtures (Milky Way, SMC, and stellar dust), we show via Information-Ordered Bottleneck analysis that exactly four parameters are needed to capture the diversity of attenuation curves. Guided by this result, we use symbolic regression to derive a new, interpretable four-parameter attenuation model that outperforms existing parameterizations in recovering both attenuation curves and emergent fluxes across all dust mixtures explored. The four parameters of this model have clear physical interpretations: UV bump strength, far-ultraviolet slope, UV-bump transition curvature, and large-scale optical slope. Their correlations with galaxy properties are primarily regulated by star formation rate surface density, metallicity, and stellar–dust geometry, and are largely preserved across dust mixtures—except for the bump-sensitive parameters, which retain a stronger dependence on grain composition. We further provide symbolic-regression scaling relations linking all four parameters to quasi-observable galaxy properties, offering a physically motivated route to assign realistic attenuation curves in SED fitting and forward modeling without radiative-transfer calculations.

Abstract:

Over the last year, kinematic Sunyaev–Zel'dovich (kSZ) velocity reconstruction — the measurement of the large-scale velocity field using the anisotropic statistics of the small-scale kSZ-galaxy overdensity correlation — has emerged as a statistically significant probe of the large-scale Universe. In this work, we perform a 2-dimensional tomographic reconstruction using ACT DR6 CMB data and photometric DESI legacy luminous red galaxies (LRGs). We measure the cross-correlation of the kSZ-reconstructed velocity v kSZ with the velocity inferred from the continuity equation applied to the photometric DESI LRG sample v cont at the ∼10σ level, detecting the signal with an amplitude with respect to our theory of bv = 0.339 ± 0.034. We fit a scale-dependent galaxy bias model to our measurement in order to constrain local primordial non-Gaussianity f NL loc, finding f NL loc =- 180+61 -86 at 67% confidence, with f NL loc consistent with zero at 95% confidence. We also measure an auto spectrum at 2.1σ significance which provides a constraint on bv of bv = 0.26-0.05 +0.11, which is consistent with the measurement from the cross spectrum. Our combined measurement is bv = 0.33 ± 0.03, an 11σ measurement. We find a good fit of our model to the data in all cases. Finally, we use different ACT frequency combinations to explore foreground contamination, finding no evidence for foreground contamination in our velocity cross correlation. We compare to a similar measurement where v kSZ is directly cross correlated with the large-scale galaxy field, and find signs of foreground contamination which is contained in the equal-redshift spectra.

Abstract:

Context . Ly α emitters (LAEs) are galaxies with strong Ly α emission, tracing early star formation and ionizing radiation. Their connection to active galactic nuclei (AGNs) is key to understanding the mechanisms behind (extended) Ly α emission. Aims . For this study, we measured the fraction of LAEs identified as radio-emitting AGNs ( f AGN,radio ) and the fraction of radio sources that exhibit Ly α emission ( f Ly α ) to investigate the connection of radio AGN activity to Ly α emission at 1.88 < z < 3.52. Methods . We identified 928 sources that were detected in both the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) and the LOw Frequency ARray (LOFAR) surveys. These matches were drawn from 55 109 spectroscopically confirmed LAEs and 27 625 radio sources. Results . After applying completeness corrections, we obtain f AGN,radio = 1.77 ± 0.04% and f Ly α = 18.15 ± 0.14% (for Ly α fluxes above 3×10 −17 erg s −1 cm −2 and radio flux densities above 0.1 mJy at 144 MHz). The fraction f AGN,radio increases from 0.4 ± 0.1% at log 10 L Lyα,ergs −1 ≈ 42.6 to 9.7 ± 1.3% at log 10 L Lyα,ergs −1 ≈ 44.5. The fraction f Lyα rises from 0.7 ± 0.1% at log 10 L 150,WHz −1 ≈ 24.6 to 55.8 ± 14.5% for log 10 L 150,WHz −1 ≈ 28.3. ‘LAEs with radio AGNs’ and ‘optical AGNs with Ly α emission’ exhibit similar radio luminosity distributions above the AGN threshold ( L 150MHz > 10 23.9 W Hz −1 ), though optical AGNs show systematically higher Ly α luminosities. We find no statistically significant correlations of Ly α luminosity with both radio luminosity and a low-frequency spectral index, suggesting that Ly α emission is regulated by gas properties rather than jet power alone. We also find a positive correlation between the full width at half maximum (FWHM) and luminosity of the Ly α line, suggesting that more luminous sources have broader lines, potentially due to enhanced outflows or velocity dispersions. However, we find no correlation between FWHM and radio size, indicating minimal direct jet-gas interaction in these systems. Conclusions . Our results show that most Ly α emission at 1.88 < z < 3.52 is powered by star formation, with radio AGN activity confined to a small luminous subset (1.77 ± 0.04%). While luminous systems preferentially host radio AGNs, the lack of correlation between Ly α and radio luminosities in individual sources indicates that Ly α emission is governed primarily by host galaxy gas properties rather than direct AGN jet coupling.

Abstract:

Abstract We present nitrogen abundance measurements based on the low-ionisation [N ii] λ6583 emission line for 588 galaxies between 1.5 < z < 7.0 from the JWST Advanced Deep Extragalactic Survey (JADES). We detect the temperature-sensitive [O iii] λ4363 auroral line in 40 galaxies in our sample, affording Te-based abundances for this subset. We find that the average N/O abundance ratio in this Te −based low-metallicity sample is at least 0.1 dex higher than z ~ 0 samples. In particular, we find significant scatter toward high N/O, with five galaxies being identified with enhanced nitrogen abundances (log (N/O) > −1.1) at low-metallicity (12 + log (O/H) < 8.0) from Te-based measurements. Meanwhile, applying strong-line abundance measurements to the remainder of our sample reveals a further 14 candidate galaxies passing these abundance cuts, implying that around 13 % of 12 + log (O/H) < 8.0 galaxies at these redshifts are nitrogen-enhanced at this level. We find that N/O abundance in low-metallicity systems correlates with SFR, ΣSFR, and $\Sigma _{M_*}$at high redshift, while only in high-metallicity systems does a correlation with M* emerge. Despite healthy representation of these ‘moderately nitrogen-enhanced’ galaxies (−1.1 < log (N/O) ≤ −0.6), no galaxies in our low-metallicity [N ii]-based sample are identified as having log (N/O) > −0.6, abundances that are typical of high-redshift N iii]- and N iv]-emitters. This demonstrates that the extreme nitrogen enhancements seen in some N iii]- and N iv]-emitters are only attained during the most extreme starbursts. This suggests that these elevated abundances are caused by enrichment from young massive stars in extreme environments and that the impact of this enrichment pathway is milder, though still important, for high-redshift systems on the star-forming main sequence.