The Curious Case of Centaurus A II: On the Subject of the Quenched satellites

TL;DR

This work investigates why Cen A's inner satellite system lacks luminous dwarfs by testing several quenching channels within a Galacticus semi-analytic framework. While tidal stripping and tidal destruction struggle to reproduce the observed inner LF, the authors find that heating of the local IGM—driven by Cen A’s AGN and implemented as early suppression of gas accretion for halos with $V_{\rm vir}<V_{\rm quench}$ after $z_{\rm quench}$ (with $V_{\rm quench}\approx80\,\mathrm{km\,s^{-1}}$, $z_{\rm quench}\approx5$)—can reproduce the observed luminosity function within $d<150$\,kpc, including the absence of $M_V \le -15.8$ satellites. They estimate the AGN’s radius of influence using Strömgren-like calculations and find that, depending on the gas-density profile, $R_{\rm influence}$ can range from a few kpc to about $10^3$ kpc, with a plausible value near 1 Mpc when the gas is warm-hot and shock-heated. The results imply that AGN feedback can imprint observable signatures on surrounding dwarf populations and propose using inner-satellite LFs as a diagnostic for past AGN activity in nearby hosts, with future facilities (Roman, Rubin) expanding the statistical power of this approach.

Abstract

The satellite system of Centaurus A presents a curious cosmological puzzle: while the global population is consistent with theoretical expectations, its inner regions (d<150 kpc) exhibit a deficit of luminous satellite galaxies. Using the Galacticus semi-analytic model applied to high-resolution N-body merger trees, we investigate potential quenching mechanisms to explain this trend. Our fiducial models, calibrated to the Milky Way, reproduce the overall Cen A population but overpredict the number of bright inner-halo satellites by a factor of 4 +- 1 at Mv < -15.8. We find that this is not due to statistical variance. Instead, the spatial coincidence of this deficiency with Cen A's massive, kiloparsec-scale radio lobes suggests a powerful environmental driver. We explore a range of physical scenarios, including enhanced tidal disruption, reionization quenching, and suppressed accretion into halos from the surrounding intergalactic medium. Our results indicate that AGN-driven thermal feedback at z < 5 can significantly suppress star formation in satellites, effectively truncating the bright end of the inner luminosity function. Our work suggests that the "Curious Case of Centaurus A" may provide evidence of AGN feedback within the host galaxy that regulates the survival and evolution of its dwarf galaxy satellites.

Figures (16)

• Figure 1: Left panel: Cumulative luminosity functions for Cen A satellites within 2D projected radii in the range $150$--$700\,\mathrm{kpc}$ as indicated by the legend. Green--yellow curves show the median number of satellites within each radius for our Galacticus models from Weerasooriya+2024, while purple--pink lines show the same for the observations. The number of galaxies decreases as the projected radius decreases, due to the reduction in the sky area within that radius. In the observational data, there is a visible lack of luminous satellites with $M_\mathrm{V}<-15.8$ and an excess of fainter satellites $M_\mathrm{V}>-10$ (see the dark purple curve) compared to our model expectations (see the dark green curve). This lack of luminous satellites begins to emerge for luminosity functions within $300\,\mathrm{kpc}$. Right panel: Normalized cumulative luminosity functions for Cen A satellites. The shaded regions show the $1\sigma$ scatter in the number of galaxies in the predicted luminosity function due to anisotropies of the system (see section \ref{['sec:sim']}). The slope of the observed luminosity function begins to steepen as we move inward from $500$--$300\,\mathrm{kpc}$. The normalized cumulative luminosity functions show that models overpredict galaxy counts at all magnitudes, especially within 150 kpc, where observations brighter than $M_\mathrm{V}\leq-10$ are almost 100% complete.
• Figure 2: Cumulative luminosity functions of Cen A satellites within a projected radius of 150 kpc. Observations are shown in purple, while green--yellow lines show results from our models with varying tidal stripping efficiencies from $\beta_\mathrm{tidal}=0.01$ (our default value) through to $1.0$, as indicated in the legend.
• Figure 3: The cumulative luminosity function of Cen A satellites within a projected radius of $150\,\mathrm{kpc}$. Observations are shown by the purple line, with model predictions shown by the green--yellow lines. We present results for several models that include tidal destruction of subhalos across different virial fractions ($f_\mathrm{vir}$). Subhalos that pass within a 3D radius of $f_\mathrm{vir} r_\mathrm{vir}$ of Cen A are assumed to be destroyed due to the tidal field of Cen A.
• Figure 4: Reionization physics: This figure illustrates how quenching of star formation in dwarf galaxies due to reionization is approximated in Galacticus. Halos that accrete gas are shown in blue, while those that do not are shown in red. Gas accretion onto halos is suppressed when $z<z_\mathrm{reion}$ and $V_\mathrm{vir}<V_\mathrm{filter}$ (bottom left panel). We use $V_\mathrm{filter}=30\,\mathrm{km/s}$RicottiGnedin:05 as gas accretion in galaxies with circular velocities $<20$--$30\,\mathrm{km/s}$Bovillricotti2011 is suppressed by reionization.
• Figure 5: Cumulative luminosity functions for Cen A satellites within a projected radius of $150\,\mathrm{kpc}$. Observational data are shown by the purple line, with green--yellow lines showing model results. We show model predictions for three different reionization redshifts as indicated in the legend.