Prevalence of radio Active Galactic Nuclei in galaxy groups since z=3.5 in the COSMOS-Web field

arXiv:2610.10719 · astro-ph.GA · Submitted 2026-10-07 · Read on arXiv

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Introduction to the show: ident: Astrophysics Radio. Generated commentary on the latest astrophysics papers.

Vera: Today's paper: "Prevalence of radio Active Galactic Nuclei in galaxy groups since z=3.5 in the COSMOS-Web field".

Jocelyn: The gist The radio AGN luminosity function in galaxy groups is systematically higher than in the field in the range 0.1 ≤ z < 3.5 and this enhancement persists out…

Vera: First, who's behind it and why it matters.

Paper summary: Vera: What this paper claims is that there's a systematic difference between radio AGN activity in galaxy groups compared to the field, and that this difference stays significant from redshift zero point one all the way out to three point five.

Jocelyn: It claims that the radio AGN luminosity function in galaxy groups is systematically higher than it is in the field across that entire range of redshift.

Subrahmanyan: This enhancement persists out to at least z=three point five, which is a significant cosmic time period for these processes <ref:2610.10719#pg1>.

Vera: The authors then provide a new parametric description for how radio AGN fractions depend on the environment, stellar mass, radio luminosity, and redshift.

Jocelyn: They confirm what we already knew: that the radio AGN fraction increases with host stellar mass in both groups and in the field.

Subrahmanyan: But more importantly, they find that when you compare groups to the field at a fixed stellar mass, the activation of a radio AGN in groups is enhanced relative to the field by a factor of three to thirty in space density and by two in radio AGN fraction.

Vera: That enhancement isn't constant either; it's shown to be dependent on stellar mass, radio luminosity, and redshift.

Jocelyn: They also found that in all redshift bins they looked at, the radio AGN fractions peak within a radius of zero point two times the virial radius, or r less than or equal to zero point two R200 <ref:2610.10719#pg2>.

Subrahmanyan: So, dense environments definitely enhance radio AGN triggering out to at least z=three point five, and this enhancement is linked to where the activity is happening spatially within those groups <ref:2610.10719#pg1>.

Conclusion: Vera: Looking at the title, "Prevalence of radio Active Galactic Nuclei in galaxy groups since z=three point five in the COSMOS-Web field," it really tells you the focus is on linking these radio AGN to their immediate surroundings and how that connection evolves with cosmic history <ref:2610.10719#pg1,Prevalence of radio Active Galactic Nuclei in galaxy groups since z=3>.

Jocelyn: The authors are F. Ubertosi and collaborators, and what they show us is that the environment matters significantly more than just having a big black hole or a lot of stars in terms of when this feedback kicks in.

Subrahmanyan: What this means for the bigger picture is that dense environments aren't just places where radio AGN happen; they actively boost their triggering rate by a factor of three to thirty compared to the field at the same stellar mass.

Vera: And it suggests there might be a shift happening around redshift one point five, because they found that the radio AGN fraction in groups actually has a minimum at that redshift, while its space density peaks around that time.

Jocelyn: So, if you're thinking about how these black holes feed their host galaxies and affect the surrounding gas—the kinetic feedback—this paper points toward a transition in how those processes are dominant at different cosmic epochs.

Subrahmanyan: It suggests that lower redshift, around one point five z, might be characterized by the intragroup medium providing that fueling reservoir, whereas earlier times might be dominated by merger and structure growth.

Vera: That’s a very concrete way of putting it—the environment dictates the timing of the feedback mechanism.

Jocelyn: It gives us a clearer picture of how we should interpret those radio observations when we try to model cosmic evolution.

F. Ubertosi, I. Delvecchio, I. Prandoni, G. Toni, G. Zamorani, E. Daddi, M. Gitti, M. Sargent

Dipartimento di Fisica e Astronomia, Università di Bologna · Istituto Nazionale di Astrofisica - Istituto di Radioastronomia (IRA) · Zentrum für Astronomie, Universität Heidelberg · Université Paris-Saclay, Université Paris Cité, CEA, CNRS · Institute of Physics, Laboratory of Astrophysics, École Polytechnique Fédérale de Lausanne · Department of Physics, University of Zagreb · Department of Computer Science, Aalto University · Centre for Astrophysics Research Department of Physics Astronomy and Mathematics University of Hertfordshire · Space Telescope Science Institute

astro-ph.GA

Submitted: 2026-10-07

Updated: 2026-10-07

Comments: Under review for Astronomy & Astrophysics (referee report received)

License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/

Importance score: 78/100

The gist: The gist The radio AGN luminosity function in galaxy groups is systematically higher than in the field in the range 0.1 ≤ z < 3.5 and this enhancement persists out to at least z ∼ 3.5.

Key concepts

Radio Active Galactic Nuclei (AGN)
These are extremely luminous centers of galaxies powered by supermassive black holes actively accreting matter. They produce powerful jets that emit radio waves, making them key tracers of kinetic feedback from these black holes.
Radio Luminosity Function (RLF)
The RLF describes the distribution of radio AGN based on their luminosity across different environments. The study compares the RLF in galaxy groups to that in the field to quantify how many radio sources exist at different brightness levels in each setting.
Host Stellar Mass ($M_{ ext{ast}}$)
This refers to the total mass of stars within a host galaxy, measured on a logarithmic scale. The paper examines how the prevalence and triggering of radio AGN change as the host galaxy's stellar mass increases, showing correlations in both group and field settings.
Kinetic Luminosity Density (KLD)
The KLD measures the total mechanical energy output from radio AGN within a given volume. The study found that radio AGN in dense groups release significantly more mechanical energy than those in the field, peaking at lower redshifts.

Terminology

Summary

The gist The radio AGN luminosity function in galaxy groups is systematically higher than in the field in the range 0.1 ≤ z < 3.5 and this enhancement persists out to at least z ∼ 3.5.

How it works

The study investigates the role of the large-scale environment in triggering radio AGN activity by combining VLA-COSMOS 3 GHz Large Project data with COSMOS-Web galaxy and group catalogs to select radio-excess AGN and build radio luminosity functions (RLF) and radio AGN fractions separately for sources in galaxy groups (124) and in the field (405). The analysis examines the dependence of these properties on host stellar mass (10 ≤ log M∗ [M⊙] ≤ 11.4), radio luminosity (22 ≤ log L1.4 [W Hz−1] ≤ 26), and redshift (0.1 ≤ z ≤ 3.5).

Key Findings on Environmental Enhancement

The results confirm a positive correlation of the radio AGN fraction with host stellar mass in both galaxy groups and in the field but find that the activation of a radio AGN in galaxy groups is enhanced relative to the field by a factor of ≃3–30 in space density and of ≃2 in radio AGN fraction at fixed stellar mass (space density and fraction enhancement). This enhancement is also a function of M∗, L1.4, and z. Furthermore, in all redshift bins, the radio AGN fractions peak within r ≤ 0.2R200 (radial dependence). Dense environments enhance radio AGN triggering out to at least z ∼ 3.5.

Evolution of Radio AGN Fractions and Luminosity Functions

The RLF of radio AGN in galaxy groups is systematically higher than in the field across the redshift range 0.1 ≤ z < 3.5 and this difference is quantified by a ratio δg ≈ 3–30 in space density. The best-fit PDE parameters indicate a steeper cosmic evolution for radio AGN in groups than in the field, consistent with the observed decrease in δg with z (cosmic evolution). The radio AGN fraction is globally higher than in the field at all redshifts (0.1 ≤ z ≤ 3.5), by a factor ≃ 2.

Dependence on Stellar Mass and Radio Luminosity

The radio AGN fraction increases with stellar mass in both environments, and the dependence on L1.4 is flat in groups and mildly negative in the field, although the two slopes are consistent at ∼1.4σ. In the field, the radio AGN fraction increases monotonically with z (redshift dependence), while in galaxy groups, the fraction has a minimum at z ∼ 1.3 and an increase at both lower and higher redshifts (redshift evolution).

Radial Distribution within Groups

The radio AGN fraction decreases with increasing group-centric distance expressed as a fraction of R200, especially for z ≤ 1.4. At earlier cosmic times, the trend appears to change and there seems to be a flattening out to r ∼ 3 R200 (radial distribution).

Feedback Output

The kinetic luminosity density (KLD) of radio AGN in groups seems to exceed that of radio AGN in the field by an order of magnitude (assuming the same fW), and peaks at 1 ≲ z ≲ 1.5, compared to z ∼ 2 for the field population. This suggests that radio AGN in dense environments release the majority of their mechanical energy at later cosmic times than sources in the field (KLD evolution).

Conclusion

The study presents a multi-parametric analysis showing that dense environments enhance radio AGN triggering over a wide range of cosmic time. The results suggest that 1 ≲ z ≤ 1.5 represents a characteristic epoch in the co-evolution of radio AGN and their host structures.

How it works

The paper presents a multi-parametric study of radio AGN triggering in the COSMOS field, combining the VLA-COSMOS 3 GHz Large Project with the COSMOS-Web galaxy and group catalogs to investigate the role of the large-scale environment in the redshift range 0.1 ≤ z ≤ 3.5. The analysis quantifies the role of the large-scale environment – in terms of membership to a group or to the field, and in terms of projected distance from the center of the group – in promoting the activation of a radio AGN (environmental role).

Key Findings on Environmental Influence

The analysis shows that the radio AGN fraction increases with stellar mass at all redshifts and radio luminosities (stellar mass dependence), and the dependence on L1.4 is flat in groups and mildly negative in the field, although the two slopes are consistent at ∼1.4σ (luminosity dependence). The environmental enhancement of the radio AGN fraction persists out to z ∼ 3.5.

Radial Distribution within Groups

The analysis of radial distribution shows that the radio AGN fraction decreases with increasing group-centric distance expressed as a fraction of R200, especially for z ≤ 1.4 (radial distribution). At earlier cosmic times, we observe a relative increase in the radio AGN fraction in the outskirts of the galaxy groups, for 1 R200 ≤ r ≤ 3 R200 (outskirts enhancement).

Feedback Output

The kinetic luminosity density (KLD) of radio AGN in groups seems to exceed that of radio AGN in the field by an order of magnitude (assuming the same fW), and peaks at 1 ≲ z ≲ 1.5, compared to z ∼ 2 for the field. This suggests that radio AGN in dense environments release the majority of their mechanical energy at later cosmic times than sources in the field (KLD evolution).

Conclusion

Overall, we find that at 1 ≲ z ≤ 1.5 the radio AGN fraction in groups has a minimum and the radial distribution of radio AGN in groups changes. Notably, over the same redshift range radio AGN in groups also reach their peak space density. This may suggest that 1 ≲ z ≤ 1.5 represents a characteristic epoch in the co-evolution of radio AGN and their host structures.

How it works

The authors present a new parametric form to fit the fractions of radio AGN, assuming the radio AGN fraction can be described as the combination of power-laws in the log-log space for M∗ and L1.4, and a redshift-dependent evolutionary term (parametric form). This model is fitted to observed data in both environments.

Key Findings on Parametric Trends

The best fit parametric form for radio AGN in the field is fAGN(M∗, L1.4,z field) = 0.0026 M∗/M⊙!1.19 L1.4/W Hz−1 −0.26 (1 + z)(1.31−0.13z) and for radio AGN in galaxy groups is fAGN(M∗, L1.4,z group) = 0.017 M∗/M⊙!0.95 L1.4/W Hz−1 −0.05 (1 + z)(-1.52+0.46z). The best-fit model for the field shows that the radio AGN fraction seems to decrease with increasing L1.4 (luminosity dependence), while in galaxy groups the dependence is consistent with being flat (luminosity dependence).

How it works

The authors derive the cumulative kinetic luminosity density (KLD) by integrating their best-fit RLFs separately for radio AGN in groups and in the field, using scaling relations from literature. The KLD is defined as omegakin(z) = Z Pkin(L1.4) × Φ(L1.4,z) d(log L1.4).

Key Findings on Feedback Output

The KLD evolution of radio AGN in groups is peaked at lower redshifts than that of radio AGN in the field. In particular, "it appears that the evolution of the radio AGN in groups population reaches its maximum at 1 ≤ z ≤ 1.

Improvements for AI systems

  1. Improved environmental triggering prediction for radio AGN: The system can predict whether an AGN is more likely to be triggered in a galaxy group versus a field by using a new parametric description of the radio AGN fractions as a function of environment, M∗, L1.4, and z (Abstract), specifically noting that the activation of a radio AGN in galaxy groups is enhanced relative to the field by a factor of ≃3–30 in space density and of ≃2 in radio AGN fraction at fixed stellar mass (Results).

  2. Enhanced luminosity function modeling: The AI can fit the Radio Luminosity Function (RLF) using "a multi-parametric approach to simultaneously investigate the dependence of the radio AGN fraction on the environment, on redshift (0.1 ≤ z ≤ 3.5), on stellar mass (10 ≤ log M∗ [M⊙] ≤ 11.4), and on radio luminosity (22 ≤ log L1.4 [W Hz−1] ≤ 26) to derive a new parametric description of the radio AGN fractions as a function of environment, M∗, L1.4, and z" (Methods).

  3. Radial distribution analysis for feedback: The system can map how the radio AGN fraction varies with distance from group centers by identifying that at z ≲ 1.4, we observe an increase in the radio AGN fraction toward the group centers, with an enhancement within r ≤ 0.2 R200 of up to a factor of ∼ 4 with respect to r ≥ R200 (Section 4.3).

  4. Kinetic luminosity density estimation: The system can estimate the kinetic luminosity density (KLD) of radio AGN in groups and the field, finding that the KLD evolution derived for radio AGN in galaxy groups is peaked at lower redshifts than that of radio AGN in field, which suggests radio AGN in dense environments release the majority of their mechanical energy at later cosmic times than sources in the field (Fig. 8).

  5. Parametric modeling for fraction prediction: The AI can use a complex parametric form, such as fAGN(M∗, L1.4,z group) = 10const. M∗10log(M/M)1!α L1.410log(L1.4/W Hz−1)2β (1 + z) (γ+δz) to model the dependence of the radio AGN fraction across all variables, allowing for a more complex, but also more flexible, description of the observed trends (Appendix D).

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