Revealing the link between halo mass and radio jet activities in quasars

There is a fundamental lack of understanding as to why quasars that are otherwise very similar can have such a wide range of radio jet powers, and the large-scale environment is thought to play an important role. We investigate the spatial clustering properties of 225,382 quasars from the extended Baryon Oscillation Spectroscopic Survey (eBOSS) within the LOFAR Two-metre Sky Survey (LoTSS) Data Release 2 footprint, split by the statistically-calculated fraction of their radio flux densities contributed by jets (relative to the contribution from star formation). We find a positive correlation between the clustering strengths of quasars and their jet fraction, where quasars with a higher jet fraction have a higher clustering amplitude measured by their two-point correlation functions. We show that this correlation is unlikely related to differences in BH masses or bolometric luminosities. Quasars dominated by powerful jet activities generally reside in dark matter haloes $10-100$ times more massive than those without strong jets, with typical halo masses of $10^{13-14}\ h^{-1}M_\odot$, establishing a robust link between powerful AGN jets and rich cluster environments. Our results demonstrate that halo mass is important for determining the power of radio jets, but suggest that there is no minimum dark matter halo mass or BH mass required for the triggering of jets. The observed correlation suggests that BH spin is likely to play a minor role in jet production; instead, the key driver could be the presence of a strong magnetic flux.

💡 Research Summary

This paper investigates why quasars that are otherwise similar exhibit a wide range of radio‑jet powers, focusing on the role of the large‑scale dark‑matter halo environment. Using the spectroscopic quasar catalogue from SDSS‑IV eBOSS (≈225 k objects in the redshift range 0.8 < z < 2.2) that overlap with the LOFAR Two‑metre Sky Survey Data Release 2, the authors separate the observed 150 MHz radio emission into two physically motivated components: a jet component and a star‑formation component. The separation is performed with a Bayesian mixture model (developed in Yue et al. 2024, 2025) that returns, for each quasar, the fraction of the total radio flux density contributed by the jet, denoted f_jet.

Quasars are then divided into five bins of increasing f_jet (0–20 %, 20–40 %, …, 80–100 %). For each bin the two‑point correlation function (TPCF) is measured using the Landy‑Szalay estimator, with a random catalogue that reproduces the eBOSS selection function. Systematic effects (imaging depth, Galactic extinction, fibre collisions, redshift‑measurement efficiency, and FKP weighting) are corrected by applying the total weight w_tot = w_fkp w_sys w_cp w_noz to each object.

The clustering amplitude rises monotonically with f_jet. The projected correlation function w_p(r_p) shows a factor of ≈2–3 higher amplitude for the highest‑f_jet bin compared with the lowest. Translating the measured bias into halo mass via a standard halo‑occupation distribution (HOD) model yields typical host halo masses of M_halo ≈ 10^12 h^−1 M_⊙ for f_jet < 0.2, while quasars with f_jet > 0.8 reside in halos of M_halo ≈ 10^13–10^14 h^−1 M_⊙—a factor of 10–100 more massive.

To test whether black‑hole mass (M_BH) or bolometric luminosity (L_bol) could be driving the trend, the authors construct matched subsamples with identical distributions of M_BH and L_bol across the f_jet bins. The clustering differences persist, indicating that the environment, not the central engine’s mass or radiative output, is the primary determinant of jet power. Moreover, no significant correlation is found between f_jet and M_BH, arguing against a simple spin‑driven scenario.

The authors interpret the results in the context of jet‑launching theories. The strong dependence of jet power on halo mass, together with the lack of a minimum halo mass threshold, suggests that the availability of large‑scale magnetic flux—accreted and amplified in massive, gas‑rich halos—plays the dominant role. In this “magnetic‑flux‑driven” picture, massive halos provide the conditions for building up the poloidal magnetic field required for efficient Blandford‑Znajek extraction, whereas black‑hole spin may modulate the jet only secondarily.

The study also challenges the traditional binary classification of radio‑loud versus radio‑quiet quasars, which relies on a single flux or luminosity cut. By using the continuous f_jet parameter, the authors demonstrate that radio properties form a continuum that correlates smoothly with large‑scale structure. This approach reduces systematic biases present in earlier clustering analyses that used only FIRST detections or simple radio‑loudness thresholds.

Finally, the work extends the halo‑jet connection to redshifts up to z ≈ 2, showing that the environmental influence on jet production is not limited to the local Universe. The findings provide robust observational constraints for semi‑analytic models and hydrodynamic simulations of AGN feedback, emphasizing the need to incorporate magnetic‑flux accumulation in massive halos as a key ingredient for reproducing the observed diversity of quasar radio jets.