Accretion-regulated Type Transitions in Changing-look AGNs: Evidence from Two-epoch Spectral Analysis

Abstract The changing-look active galactic nucleus (CL-AGN), an extraordinary subpopulation of supermassive black holes, has attracted growing attention to understand its nature. We present an analysis of the spectral properties of 203 low-redshift CL-AGNs ( z &lt; 0.35) using two-epoch spectra from Sloan Digital Sky Survey DR16 and DESI DR1 with time baseline ranging from ∼1000 to 8000 days, based on spectral fitting and decomposition. The sample consists of 11.3% type 1.0, 26.6% type 1.2, 43.1% type 1.5, and 19% type 1.8/2.0 AGNs. The total sample is divided into two data sets: Data Set A (110 objects) with minor spectral type variations, likely general AGN variability, and Data Set B (93 objects) showing significant type transitions and characteristic turn-on or turnoff behavior. Our results reveal clear optical continuum and emission-line variability, showing both “bluer-when-brighter” and “redder-when-brighter” trends. A strong correlation between the broad H β /[O iii ] ratio and broad H α luminosity ( L H α ), <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="normal">log</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:mi mathvariant="normal">H</mml:mi> <mml:mi>β</mml:mi> <mml:mo>/</mml:mo> <mml:mo stretchy="false">[</mml:mo> <mml:mi mathvariant="normal">O</mml:mi> <mml:mspace width="0.25em"/> <mml:mi mathvariant="normal">III</mml:mi> <mml:mo stretchy="false">]</mml:mo> <mml:mo stretchy="false">)</mml:mo> <mml:mo>=</mml:mo> </mml:math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo stretchy="false">(</mml:mo> <mml:mn>0.63</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.07</mml:mn> <mml:mo stretchy="false">)</mml:mo> <mml:mi mathvariant="normal">log</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mrow> <mml:mi>L</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">H</mml:mi> <mml:mi>α</mml:mi> </mml:mrow> </mml:msub> <mml:mo stretchy="false">)</mml:mo> <mml:mo>−</mml:mo> </mml:math> (26.49 ± 2.96) ± 0.48 for Data Set B, as well as the correlation between H β /[O iii ] and Eddington ratio ( L bol / L Edd ), <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="normal">log</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:mi mathvariant="normal">H</mml:mi> <mml:mi>β</mml:mi> <mml:mo>/</mml:mo> <mml:mo stretchy="false">[</mml:mo> <mml:mi mathvariant="normal">O</mml:mi> <mml:mspace width="0.25em"/> <mml:mi mathvariant="normal">III</mml:mi> <mml:mo stretchy="false">]</mml:mo> <mml:mo stretchy="false">)</mml:mo> <mml:mo>=</mml:mo> </mml:math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo stretchy="false">(</mml:mo> <mml:mn>0.59</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.08</mml:mn> <mml:mo stretchy="false">)</mml:mo> <mml:mi mathvariant="normal">log</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mrow> <mml:mi>L</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">bol</mml:mi> </mml:mrow> </mml:msub> <mml:mo>/</mml:mo> <mml:msub> <mml:mrow> <mml:mi>L</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">Edd</mml:mi> </mml:mrow> </mml:msub> <mml:mo stretchy="false">)</mml:mo> <mml:mo>+</mml:mo> </mml:math> (1.02 ± 0.15) ± 0.53 for Data Set B, suggests that accretion rate variations drive changes in ionizing flux within the broad-line region, thereby triggering AGN type transitions. These findings underscore the critical role of supermassive black hole accretion processes in refining the AGN unification model. Future work should investigate potential connections between stellar evolution in outer accretion disk and the observed scatter in these correlations.