MIGHTEE: The dark matter haloes, duty cycle and mechanical feedback from radio-AGN up to $z \sim 2.5$

Abstract

Radio-AGN are observed to be more strongly clustered than non-active galaxies, though it is unclear whether this is simply due to their preference for massive host galaxies, or if they reside in distinct environments beyond this mass dependence. Using data from three fields covered by the MIGHTEE survey, we measure the angular two-point cross-correlation functions with a large, stellar mass-limited population of near-infrared selected galaxies, overcoming limitations of previous single-deep-field studies. By fitting halo occupation distribution models, we infer the galaxy bias parameters, $b$, for radio-AGN in three redshift ranges with median redshifts of $z_{med}=0.76^{+0.17}_{-0.28}$, $1.25^{+0.14}_{-0.17}$ and $1.75^{+0.44}_{-0.18}$, finding $b=1.94^{+0.07}_{-0.07}$, $2.50^{+0.11}_{-0.18}$ and $3.38^{+0.27}_{-0.38}$, respectively. The typical dark matter halo mass decreases with increasing redshift: $\log_{10}(\langle M_{h} \rangle/{M_\odot})=13.44^{+0.08}_{-0.08}$, $13.17^{+0.07}_{-0.06}$ and $13.03^{+0.09}_{-0.10}$, which we attribute to the increased abundance of cold gas required to fuel AGN activity at earlier times. The AGN duty cycle is determined to be $\sim5-9\%$, and we estimate that the total energy radiated by radio-jets over $0<z<2.5$ is $\sim10^{53}$ J per halo, which is sufficient to account for the observed excess heating of gas beyond that of gravitational collapse. Comparing the typical dark matter halo masses to the values obtained for the control sample, we find that the halo masses of radio-AGN are $1.54^{+0.47}_{-0.33}$, $1.11^{+0.25}_{-0.20}$ and $1.82^{+1.04}_{-0.57}$ times greater than those of the stellar mass- and redshift-matched galaxies. This difference could arise because AGN feedback suppresses stellar mass growth while leaving halo mass unchanged, or because radio-AGN preferentially reside in earlier forming haloes which are more strongly clustered.

Figures (9)

• Figure 1: Stellar mass and redshift distribution of NIR-selected galaxies from all three fields (blue points). The banding effect is caused by the discrete redshift bins of LePHARE. The black lines are the 90% stellar mass completeness limits in each field, found by following the method of pozetti2010. The red boxes are our chosen stellar mass and redshift sub-samples.
• Figure 2: Radio luminosity at 1.4 GHz as a function of redshift for classified sources from whittam2022. The black points are the unclassified sources, blue points are those classified as star-forming galaxies or probable star-forming galaxies, and red points are those classified as AGN. The star-forming galaxy points are partially transparent to improve clarity. The solid black line is the radio luminosity threshold, $L_{\rm{AGN}}(z)$, above which 95% of sources are classified as AGN. This same threshold is applied to the DR1 radio catalogue to create the AGN sample. For comparison, the AGN threshold of magliocchetti2014 is denoted by the dashed cyan line.
• Figure 3: The positions of radio sources on the sky after applying the star mask in each field. The transparency of each point reflects the weight assigned to that source, which represents the probability that the source exceeds the AGN luminosity threshold.
• Figure 4: The redshift and stellar mass distributions of galaxies before (solid blue line) and after (dashed blue line) matching to the AGN sample (solid red line), constructed by sampling from the $z$-PDF of each galaxy. The main panel shows the contour plots of these distributions, while the top and right panels display the corresponding normalized histograms for redshift and stellar mass, respectively. The contours are the $10$, $25$, $50$, $68$ and $95\%$ levels.
• Figure 5: The measured angular two-point auto-correlation functions, $\omega(\theta)$, for AGN (red circles) and the stellar mass-matched galaxies sample (blue squares) as functions of angular separation, $\theta$, for each redshift bin. Left to right, these are: $0<z<1$, $1<z<1.5$ and $1.5<z<2.5$. Open markers are negative values. For clarity, the matched galaxy correlations are offset by $+0.1$ dex in $\theta$. The bottom panels give the ratio of the two correlation functions, with the black horizontal line at $\omega_{\rm{AGN}}/\omega_{\rm{mat}}=1$.