Enhanced Star Formation in Narrow Line Seyfert 1 AGN revealed by Spitzer

TL;DR

This study uses Spitzer mid-infrared spectroscopy to reveal that Narrow Line Seyfert 1 galaxies exhibit significantly higher star formation activity in their circumnuclear regions compared to broad line Seyfert 1 galaxies, especially in systems with lower black hole mass.

Contribution

It provides the first direct evidence of enhanced star formation in NLS1 galaxies using PAH emission, and compares star formation activity between NLS1s and BLS1s across various parameters.

Findings

NLS1s show strong PAH emission indicating intense star formation.

Star formation activity is higher in NLS1s than in BLS1s of similar luminosity.

Star formation rate correlates with low black hole mass and high L/L_Edd ratios.

Abstract

We present new low resolution Spitzer mid-infrared spectroscopy of a sample of 20 ROSAT selected local Narrow Line Seyfert 1 galaxies (NLS1s). We detect strong AGN continuum in all and clear PAH emission in 70% of the sources. The 6.2 micron PAH luminosity spans three orders of magnitudes, from ~10^(39) erg/s to ~10^(42) erg/s providing strong evidence for intense ongoing star formation in the circumnuclear regions of these sources. Using the IRS/Spitzer archive we gather a large number of additional NLS1s and their broad line counterparts (BLS1s) and constructed NLS1 and BLS1 sub-samples to compare them in various ways. The comparison shows a clear separation according to FWHM(H_beta) such that objects with narrower broad H_beta lines are the strongest PAH emitters. We test this division in various ways trying to remove biases due to luminosity and aperture size. Specifically, we find that star formation activity around NLS1 AGN is larger than around BLS1 of the same AGN luminosity. The above result seems to hold over the entire range of distance and luminosity. Moreover the star formation rate is higher in low black hole mass and high L/L_Edd systems indicating that black hole growth and star formation are occurring simultaneously.