Journal Article

Enhanced star formation in narrow-line Seyfert 1 active galactic nuclei revealed by <i>Spitzer</i>

E. Sani, D. Lutz, G. Risaliti, H. Netzer, L. C. Gallo, B. Trakhtenbrot, E. Sturm and T. Boller

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 403, issue 3, pages 1246-1260
Published in print April 2010 | ISSN: 0035-8711
Published online April 2010 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2009.16217.x
Enhanced star formation in narrow-line Seyfert 1 active galactic nuclei revealed by Spitzer

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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 active galactic nucleus (AGN) continuum in all and clear polycyclic aromatic hydrocarbon (PAH) emission in 70 per cent of the sources. The 6.2 μm PAH luminosity spans three orders of magnitude, from ∼1039 to ∼1042 erg s−1, providing strong evidence for intense ongoing star formation in the circumnuclear regions of these sources.

Using the Infrared Spectrograph/Spitzer archive, we gathered a large number of additional NLS1s and their broad-line counterparts (BLS1s) and constructed NLS1 and BLS1 subsamples to compare them in various ways. The comparison shows a clear separation according to full width at half-maximum (Hβ) [FWHM(Hβ)] such that objects with narrower broad Hβ 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/LEdd systems indicating that black hole growth and star formation are occurring simultaneously.

Keywords: galaxies: active; galaxies: starburst; infrared: galaxies

Journal Article.  9203 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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