[Paper Review] AGN Feedback, Host Halo Mass and Central Cooling Time: Implications for Galaxy Formation Efficiency and $M_{BH} - \sigma$

Robert Main, B. R. McNamara+3 more|arXiv (Cornell University)|Oct 23, 2015

Galaxies: Formation, Evolution, Phenomena1 references3 citations

TL;DR

This study links AGN feedback power in galaxy clusters to host halo mass and central cooling time, finding that feedback correlates with halo mass only when cooling times are below 1 Gyr—indicating feedback regulates cooling instabilities. The results support self-similar scaling and co-evolution of black holes and galaxies via the $M_{BH} - au$ relation, with tight regulation of star formation across halo mass scales.

ABSTRACT

We derive X-ray mass, luminosity, and temperature profiles for 45 galaxy clusters to explore relationships between halo mass, feedback, and central cooling time. We find that radio--mechanical feedback power (referred to here as AGN power) in central cluster galaxies correlates with halo mass, but only in halos with central atmospheric cooling times shorter than 1 Gyr. This timescale corresponds approximately to the cooling time (entropy) threshold for the onset of cooling instabilities and star formation in central galaxies (Rafferty et al. 2008). No correlation is found in systems with central cooling times greater than 1 Gyr. The trend with halo mass is consistent with self-similar scaling relations assuming cooling is regulated by feedback. The trend is also consistent with galaxy and central black hole co-evolution along the $M_{BH} - \sigma $ relation. power further correlates with X-ray gas mass and the host galaxy's K-band luminosity. power in clusters with central atmospheric cooling times longer than ~1 Gyr typically lies two orders of magnitude below those with shorter central cooling times. Galaxies centred in clusters with long central cooling times nevertheless experience ongoing and occasionally powerful outbursts. We further investigate the impact of feedback on cluster scaling relations. We find L-T, and M-T relations, excluding regions directly affected by AGN, that are consistent with the cluster population as a whole. While the gas mass rises, the stellar mass remains nearly constant with rising total mass, consistent with earlier studies. This trend is found regardless of central cooling time, implying tight regulation of star formation in central galaxies as their halos grew, and long-term balance between heating and atmospheric cooling. Our scaling relations are presented in forms that can be incorporated easily into galaxy evolution models.

Motivation & Objective

• To investigate the relationship between AGN feedback power, host halo mass, and central atmospheric cooling time in galaxy clusters.
• To determine whether feedback regulates cooling instabilities and star formation in central galaxies across different halo mass regimes.
• To assess the impact of AGN feedback on cluster scaling relations (L-T, M-T) and galaxy formation efficiency.
• To explore how feedback correlates with X-ray gas mass and K-band luminosity of host galaxies.
• To provide scaling relations suitable for integration into galaxy evolution models.

Proposed method

• Derived X-ray mass, luminosity, and temperature profiles for 45 galaxy clusters using X-ray observations.
• Calculated central atmospheric cooling time from X-ray temperature and density profiles.
• Classified clusters based on cooling time threshold (~1 Gyr) to compare feedback behavior in short- vs. long-cooling-time systems.
• Analyzed correlations between AGN feedback power, halo mass, X-ray gas mass, and K-band luminosity.
• Excluded AGN-affected regions to derive intrinsic L-T and M-T scaling relations.
• Used self-similar scaling relations as a baseline to test consistency with feedback-regulated cooling.

Experimental results

Research questions

• RQ1 Does AGN feedback power correlate with host halo mass, and if so, under what conditions?
• RQ2 How does central cooling time influence the strength and regulation of AGN feedback in galaxy clusters?
• RQ3 To what extent does AGN feedback regulate star formation in central galaxies across different halo masses?
• RQ4 How do L-T and M-T scaling relations behave when AGN-affected regions are excluded?
• RQ5 What is the relationship between AGN feedback power and host galaxy properties such as K-band luminosity and X-ray gas mass?

Key findings

• AGN feedback power correlates with halo mass only in clusters with central cooling times shorter than 1 Gyr, the threshold for cooling instability onset.
• Clusters with cooling times longer than 1 Gyr show AGN feedback power two orders of magnitude lower than those with shorter cooling times.
• Despite low feedback power, galaxies in long-cooling-time clusters still experience ongoing and occasionally powerful AGN outbursts.
• The L-T and M-T scaling relations, excluding AGN-affected regions, remain consistent with the overall cluster population, indicating robust feedback regulation.
• Stellar mass in central galaxies remains nearly constant with increasing total halo mass, while gas mass increases—indicating long-term balance between heating and cooling.
• The observed trends support self-similar scaling and co-evolution of black holes and galaxies along the $M_{BH} - \sigma$ relation.