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Abstract:

Understanding black hole–galaxy co-evolution and the role of active galactic nucleus (AGN) feedback requires complete AGN samples, including heavily obscured systems. Such sources are key to constraining the black hole accretion rate density over cosmic time, yet they are challenging to identify and characterize across most wavelengths. In this work, we present the first ultraviolet (UV) line-selected ([Ne v] Å and C iv Å) sample of obscured AGN with full X-ray-to-radio coverage, assembled by combining data from the Chandra COSMOS Legacy survey, the COSMOS2020 UV–NIR catalogue, mid- and far-IR photometry from XID+, and radio observations from the Very Large Array and MeerKAT International GHz Tiered Extragalactic Exploration Survey (MIGHTEE) surveys. Using cigale to perform spectral energy distribution (SED) fitting, we analyse 184 obscured AGNs at and , enabling detailed measurements of AGN and host-galaxy properties, and direct comparison with simba hydrodynamical simulations. We find that X-ray and radio data are essential for accurate SED fits, with the radio band proving critical when X-ray detections are missing or in cases of poor IR coverage. Comparisons with matched non-active galaxies and simulations suggest that the [Ne v]-selected sources are in a pre-quenching stage, while the C iv-selected ones are likely quenched by AGN activity. Our results indicate that [Ne v] and C iv selections target galaxies in a transient phase of their co-evolution, characterized by intense, obscured accretion, and pave the way for future extensions with upcoming large area high-z spectroscopic surveys.

Abstract:

Stellar and planetary magnetic fields play a crucial role in the habitability of a planet and the integrity of its atmosphere. The detection of methane and carbon dioxide, along with a tentative identification of the potential biosignature dimethyl sulfide/disulfide, in the atmosphere of K2-18 b, a sub-Neptune orbiting an M dwarf star, presents an intriguing question regarding the stellar magnetic environment and the resistance of the planet’s magnetosphere (if it exists) to erosion by magnetic activity from the host. To probe for radio emission from the system, we have conducted observations using the Karl G. Jansky Very Large Array at S, C, and X bands (2–4, 5.5–7.5, and 8–10 GHz, respectively) to search for coherent and incoherent radio emission. We detect no radio emission associated with incoherent emission mechanisms. We report Stokes I upper limits of at S band, at C band, and at X band and an upper limit of the ratio of the radio to the total bolometric luminosity of . We have also searched for short duration bursts associated with coherent emission mechanisms at C and X bands. No signals above a significance threshold are detected. Although no signals are detected, our radio observations offer constraints, albeit limited, on the stellar magnetic environment 91̽»¨ing recent X-ray observations indicating that K2-18 is a very faint emitter. Our results also contextualize any planetary transmission spectra by providing constraints on the activity level of the host.

Abstract:

We present a systematic statistical analysis of an informal astrophysical phenomenon known as Renzo’s rule (or Sancisi’s law), which states that ‘for any feature in a galaxy’s luminosity profile, there is a corresponding feature in the rotation curve, and vice versa’. This is often posed as a challenge for the standard Λ cold dark matter (CDM) model while 91̽»¨ing alternative theories such as modified Newtonian dynamics (MOND). Indeed, we identify clear features in the dwarf spiral NGC 1560 – a prime example for Renzo’s rule – and find correlation statistics which 91̽»¨ Renzo’s rule with a slight preference for MOND over CDM halo fits. However, a broader analysis on galaxies in the Spitzer Photometry & Accurate Rotation Curves (SPARC) data base reveals an excess of features in rotation curves that lack clear baryonic counterparts, with correlation statistics deviating up to on average from that predicted by both MOND and CDM haloes, challenging the validity of Renzo’s rule. Thus we do not find clear evidence for Renzo’s rule in present galaxy data overall. We additionally perform mock tests, which show that a definitive test of Renzo’s rule is primarily limited by the lack of clearly resolved baryonic features in current galaxy data.