Cosmology

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:

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:

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 The rotation velocities of disc galaxies trace dark matter halo structure, providing direct constraints on the galaxy–halo connection. We construct a Bayesian forward model to connect the dark matter halo population predicted by ΛCDM with an observed sample of disc galaxies (SPARC) through their maximum rotation velocities. Our approach combines a subhalo abundance matching scheme (accounting for assembly bias) with a parameterised halo response to galaxy formation. When assuming no correlation between selection in the SPARC survey and halo properties, reproducing the observed velocities requires strong halo expansion, low abundance matching scatter and a halo proxy that strongly suppresses the stellar masses in satellite haloes. This is in clear tension with independent clustering constraints. Allowing for SPARC-like galaxies to preferentially populate low Vmax haloes at fixed virial mass greatly improves the goodness-of-fit and resolves these tensions: the preferred halo response shifts to mild contraction, the abundance matching scatter constraint relaxes to σSHAM < 0.30 dex at 1σ and the proxy becomes consistent with clustering. However, the inferred selection threshold is extreme, implying that SPARC galaxies occupy the lowest ~15 per cent of the Vmax, halo distribution at fixed Mvir. Moreover, even with selection, the inferred scatter remains in statistical disagreement with the low-mass clustering constraints, which are most representative of the SPARC galaxies in our sample. Our analysis highlights the advantage of augmenting clustering-based constraints on the galaxy–halo connection with kinematics and suggests a possible tension using current data.

Abstract:

Map-space E/B decompositions of linear polarization are attractive for foreground and CMB analyses because they separate parity families: B-family patterns directly contaminate primordial tensor searches, while E-family patterns trace coherent Galactic structures. However, the E/B transform is not fully local and can induce apparent spectral complexity even when the underlying sky is spectrally simple in $\underline{P}=Q+iU$. We quantify this effect for synchrotron emission using complex log–Taylor and moment expansions for $\underline{P}$, its spin-preserving projections $\underline{P}_E$ and $\underline{P}_B$, and its more standard scalar projections E and B. We relate the coefficients of these expansions to physical mechanisms such as line-of-sight mixing, synchrotron ageing, and Faraday effects. Using simple sky models, we show how $\underline{P}_E$ and $\underline{P}_B$ reorganize the spectral behaviour of $\underline{P}$ into parity families with a clear geometric meaning. They retain interpretable amplitudes and angles and satisfy the closure relation $\underline{P}=\underline{P}_E+\underline{P}_B$, which extends to all moment orders. By contrast, scalar quantities such as |E| and |B| show larger induced variability of effective spectral parameters and enhanced spectral complexity, while E + iB lacks interpretable polarization amplitude and angle. Finally, we present simple CMB-oriented applications: three-frequency diagnostics to test whether the sky is better described by a power law in P or by separate effective laws in (PE, PB), and idealized ILC and masking examples showing that the preferred map-space field depends on where foreground simplicity and residual contamination reside. This framework provides practical diagnostics for choosing foreground modelling, cleaning, and masking strategies in Galactic and CMB B-mode analyses.