Tracing AGN-Galaxy Co-Evolution with UV Line-Selected Obscured AGN

Luigi Barchiesi, Lucia Marchetti, Mattia Vaccari, Cristian Vignali, Francesca Pozzi, Isabella Prandoni, Roberto Gilli, Marco Mignoli, Jose Afonso, Veeresh Singh, Catherine Hale, Ian Heywood, Matt Jarvis, Imogen Whittam

First listed 2025-11-24 | Last updated 2025-11-24

Abstract

Understanding black hole-galaxy co-evolution and the role of AGN feedback requires complete AGN samples, including heavily obscured systems. In this work, we present the first UV line-selected ([Nev]3426 and CIV1549) sample of obscured AGN with full X-ray-to-radio coverage, assembled by combining data from the Chandra COSMOS Legacy survey, the COSMOS2020 catalogue, IR photometry from XID+, and radio observations from the VLA and MIGHTEE surveys. Using CIGALE to perform spectral energy distribution (SED) fitting, we analyse 184 obscured AGN at 0.6 < z < 1.2 and 1.5 < z < 3.1, 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 [NeV]-selected sources are in a pre-quenching stage, while the CIV-selected ones are likely quenched by AGN activity. Our results indicate that [NeV] and CIV selections target galaxies in a transient phase of their co-evolution, characterised by intense, obscured accretion, and pave the way for future extensions with upcoming large area high-z spectroscopic surveys.

Short digest

This paper builds the first UV line–selected ([NeV]3426, CIV1549) sample of obscured AGN with full X-ray–to–radio coverage in COSMOS and models them with CIGALE, totaling 184 sources across z=0.6–1.2 and 1.5–3.1. Including X-ray and radio bands is shown to be crucial for reliable SED constraints, with radio data particularly decisive when X-rays are absent or IR coverage is sparse. Versus matched inactive galaxies and SIMBA, [NeV] systems appear pre-quenching while CIV sources are consistent with AGN-quenched hosts, isolating a transient co-evolution phase. The approach paves the way for robust censuses of heavily obscured accretion with future large-area high-z spectroscopy.

Key figures to inspect

• Figure 1: Check how the [NeV] and CIV selections map onto distinct redshift windows set by VIMOS coverage (z≈0.6–1.2 vs 1.5–3.1), clarifying which cosmic epochs each tracer probes.
• Figure 2: Inspect NH versus intrinsic 2–10 keV luminosity for CIV (blue) and [NeV] (red) sources; note triangles marking NH upper limits from low-count spectra and look for the overall obscuration levels and potential CT candidates.
• Figure 3: Compare real vs mock SED fits to see which parameters are trustworthy—stellar mass is robust while AGN torus optical depth remains poorly constrained with current coverage.
• Figure 4: Examine the [NeV] sample in the SFR–M* plane relative to the Schreiber+15 main sequence; use radio detections (squares) and the 1 μm AGN fraction colors to gauge pre-quenching placement and identify the outlier zCOSMOS 813366 lacking X-ray/radio/IR.