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arXiv · 2506.21705

AGN with massive black holes have closer galactic neighbors: k-Nearest-Neighbor statistics of an unbiased sample of AGN at z~0.03

A. Mhatre·M. C. Powell·S. Yuan·S. W. Allen·T. Caglar·M. Koss·I. del Moral-Castro·K. Oh·A. Peca·C. Ricci·F. Ricci·A. Rojas·M. Signorini
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Abstract

The large-scale environments of active galactic nuclei (AGN) reveal important information on the growth and evolution of supermassive black holes (SMBHs). Previous AGN clustering measurements using 2-point correlation functions have hinted that AGN with massive black holes preferentially reside in denser cosmic regions than AGN with less-massive SMBHs. At the same time, little to no dependence on the accretion rate is found. However, the significance of such trends have been limited. Here we present kth-nearest-neighbor (kNN) statistics of 2MASS galaxies around AGN from the Swift/BAT AGN Spectroscopic survey. These statistics have been shown to contribute additional higher-order clustering information on the cosmic density field. By calculating the distances to the nearest 7 galaxy neighbors in angular separation to each AGN within two redshift ranges(0.01 < z < 0.03 and 0.03 < z < 0.06), we compare their cumulative distribution functions to that of a randomly distributed sample to show the sensitivity of this method to the clustering of AGN. We also split the AGN into bins of bolometric luminosity, black hole mass, and Eddington ratio (while controlling for redshift) to search for trends between kNN statistics and fundamental AGN properties. We find that AGN with massive SMBHs have significantly closer neighbors than AGN with less-massive SMBHs (at the 99.98% confidence level), especially in our lower redshift range. We find less significant trends with luminosity or Eddington ratio. By comparing our results to empirical SMBH-galaxy-halo models implemented in N-body simulations, we show that small-scale kNN trends with black hole mass may go beyond stellar mass dependencies. This suggests that massive SMBHs in the local universe reside in more massive dark matter halos and denser regions of the cosmic web, which may indicate that environment is important for the growth of SMBHs.

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A. Mhatre, M. C. Powell, S. Yuan, S. W. Allen, T. Caglar, M. Koss, I. del Moral-Castro, K. Oh, A. Peca, C. Ricci, F. Ricci, A. Rojas, M. Signorini. 2025-06-26. AGN with massive black holes have closer galactic neighbors: k-Nearest-Neighbor statistics of an unbiased sample of AGN at z~0.03. https://doi.org/10.1051/0004-6361%2F202555295

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