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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 origin of the complex orbital structure of young massive stars at the Galactic centre remains an open question. If these stars formed in a single episode from a gaseous accretion disc, they may initially have constituted a single, coherently rotating stellar disc. We investigate whether perturbations from an unseen intermediate-mass black hole (IMBH) could fragment and/or disrupt such a disc into the multiple orbital components observed today. First, we derive a theoretical criterion for when and where the IMBH’s torque overcomes the disc’s self-torque and tears it apart. We then test this picture with direct N-body simulations of a stellar disc interacting with an inclined IMBH around a central supermassive black hole. We find that the outcome depends strongly on the IMBH’s orbit and mass. A prograde IMBH rapidly aligns with the stellar disc, while a massive retrograde IMBH (m• ≃ 0.67 Md) anti-aligns relative to the radially overlapping stars and efficiently fragments the original disc into three components in angular-momentum space: an inner disc, a misaligned overlapping region, and an unperturbed outer disc. The IMBH also excites eccentricities in the overlapping region, driving stars away from initially circular orbits. These features emerge for an IMBH mass of 2000 ⊙ and a disc mass of 3000 ⊙ within 10–20 Myr, a timescale comparable to the age of the young Galactic centre stellar population, and provide a plausible explanation for the observed multiple orbital planes, warped geometry, and broad eccentricity distribution.

Abstract:

We systematically search for galaxy overdensities using 20 independent fields with a minimum of six filters (F090W, F115W, F150W, F277W, F356W, and F444W) from BEACON, the JWST Cycle 2 NIRCam pure-parallel imaging survey. We apply an adaptive kernel-density estimation method that incorporates the full photometric redshift probability distribution function of each galaxy to map galaxy overdensities, and identify 207 significant (>4σ) overdensities at 1.5 < z < 5. We measure the quenched galaxy fraction, the average specific star formation rate (sSFR), the total dark matter mass, and the local galaxy density of each system. By investigating the correlation among these observables, we find that galaxy quenching proceeds in two paths. (i) Overdensities within more massive halos exhibit higher quenched fractions and lower averaged sSFRs. This trend weakens at z ≳ 2, consistent with cold gas streams penetrating shock-heated massive halos and sustaining star formation activity at early times. (ii) We also find a dependence of the same parameters on local densities at z < 2, where the quenched fraction increases and the sSFR decreases toward higher densities. The environmental trend in sSFR weakens at z ∼ 2–3 and shows tentative evidence for a reversal at z > 3, potentially due to a larger cold gas supply in earlier times. Our study reveals a complex interplay between individual galaxies and large-scale environmental properties, marking the onset of environmental effects on galaxy quenching in massive halos at cosmic noon.