[Paper Review] Difference of $\alpha$-disks between Seyfert 1 galaxies and Quasars

Wei‐Hao Bian, Yinghe Zhao|arXiv (Cornell University)|Sep 25, 2003

Galaxies: Formation, Evolution, Phenomena1 references4 citations

TL;DR

This study re-evaluates accretion disk parameters in 20 Seyfert 1 galaxies and 17 PG quasars by using nuclear B-band magnitudes instead of total magnitudes to minimize host galaxy contamination. It finds that Seyfert 1 galaxies require a lower $α$-viscosity parameter in their $α$-disk models compared to quasars, suggesting intrinsic differences in disk physics, with most objects accreting below the Eddington limit when using nuclear luminosities.

ABSTRACT

In a previous paper (Bian & Zhao 2002), it was suggested that contamination to the luminosity of galactic nucleus from the host galaxies play an important role in determining parameters of the standard $\alpha$ disk for AGNs. Using the nuclear absolute B band magnitude instead of the total absolute B band magnitude, the central black hole masses, the accretion rates and the disk inclinations to the line of sight for 20 Seyfert 1 galaxies and 17 Palomar-Green (PG) quasars were recalculated. It was found that small value of $\alpha$ is needed in the accretion disk for Seyfert 1 galaxies compared with PG quasars. The difference of $\alpha$ maybe lead to the different properties between Seyfert 1 galaxies and Quasars. Furthermore, we found most of the objects in this sample are not accreting at super-Eddington rates when we adopted the nuclear optical luminosity in our calculation.

Motivation & Objective

• To reduce host galaxy contamination in luminosity measurements by using nuclear B-band magnitudes instead of total magnitudes.
• To re-calculate black hole masses, accretion rates, and disk inclinations for 20 Seyfert 1 galaxies and 17 PG quasars with improved luminosity estimates.
• To investigate whether differences in the $α$-viscosity parameter between Seyfert 1 galaxies and quasars could explain their distinct observational properties.
• To assess whether the accretion rates in these objects are consistent with super-Eddington accretion when using nuclear optical luminosities.

Proposed method

• Replaced total absolute B-band magnitude with nuclear absolute B-band magnitude to isolate the AGN contribution and minimize host galaxy contamination.
• Applied standard $α$-disk model equations to derive black hole masses and accretion rates using the revised luminosity estimates.
• Used the $α$-disk model to infer the viscosity parameter $α$ by fitting observed luminosities and inferred masses.
• Calculated Eddington ratios using the nuclear optical luminosity to assess accretion efficiency and determine if super-Eddington accretion occurs.
• Compared the derived $α$ values between Seyfert 1 galaxies and PG quasars to identify systematic differences.
• Assessed disk inclination by comparing model predictions with observed flux and spectral energy distributions.

Experimental results

Research questions

• RQ1 Does using nuclear B-band magnitudes instead of total magnitudes lead to different estimates of black hole mass and accretion rate in AGNs?
• RQ2 Are the $α$-viscosity parameters derived for Seyfert 1 galaxies significantly different from those of PG quasars when host galaxy contamination is minimized?
• RQ3 Do the recalculated accretion rates indicate that most Seyfert 1 galaxies and PG quasars are accreting below the Eddington limit?
• RQ4 Can differences in $α$-disk parameters explain the observed differences in spectral and luminosity properties between Seyfert 1 galaxies and quasars?

Key findings

• The $α$-viscosity parameter is smaller for Seyfert 1 galaxies than for PG quasars when nuclear luminosities are used, indicating a potential intrinsic difference in disk physics.
• Most objects in the sample are found to be accreting below the Eddington limit when nuclear optical luminosities are used in the calculations.
• The recalculated black hole masses and accretion rates are more accurate due to reduced host galaxy contamination from using nuclear magnitudes.
• The difference in $α$ values suggests that the accretion disk structure or efficiency may differ between Seyfert 1 galaxies and quasars.
• The results support that the observed differences between Seyfert 1 galaxies and quasars may stem from intrinsic disk properties rather than observational biases from host galaxy light.