Volume 587, March 2016
|Number of page(s)||21|
|Published online||03 March 2016|
A low-luminosity type-1 QSO sample
IV. Molecular gas contents and conditions of star formation in three nearby Seyfert galaxies
I. Physikalisches Institut, Universität zu Köln,
Zülpicher Str. 77,
2 Institut de Radio Astronomie Millimétrique, 300 rue de la Piscine, Domaine Universitaire, 38406 Saint-Martin d’Hères, France
3 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
4 LERMA (CNRS: UMR 8112), Observatoire de Paris, 61 Av. de l’Observatoire, 75014 Paris, France
5 German Aerospace Center (DLR), Königswinterer Str. 522-524, 53227 Bonn, Germany
6 Göttingen eResearch Alliance, State and University Library Göttingen, Papendiek 14, 37073 Göttingen, Germany
Received: 19 April 2015
Accepted: 15 September 2015
We present a pilot study of ~3′′ resolution observations of low CO transitions with the Submillimeter Array in three nearby Seyfert galaxies, which are part of the low-luminosity quasi-stellar object (LLQSOs) sample consisting of 99 nearby (z = 0.06) type-1 active galactic nuclei (AGN) taken from the Hamburg/ESO quasi-stellar object (QSO) survey. Two sources were observed in 12CO(2–1) and 13CO(2–1) and the third in 12CO(3–2) and HCO+(4–3). None of the sources is detected in continuum emission. More than 80% of the 12CO detected molecular gas is concentrated within a diameter (FWHM) < 1.8 kpc. 13CO is tentatively detected, while HCO+ emission could not be detected. All three objects show indications of a kinematically decoupled central unresolved molecular gas component. The molecular gas masses of the three galaxies are in the range Mmol = (0.7−8.7) × 109M⊙. We give lower limits for the dynamical masses of Mdyn> 1.5 × 109M⊙ and for the dust masses of Mdust> 1.6 × 106M⊙. The R21 = 12CO/13CO(2–1) line luminosity ratios show Galactic values of R21 ~ 5−7 in the outskirts and R21 ≳ 20 in the central region, similar to starbursts and (ultra)luminous infrared galaxies ((U)LIRGs; i.e. LIRGs and ULIRGs), implying higher temperatures and stronger turbulence. All three sources show indications of 12CO(2–1)/12CO(1–0) ratios of ~0.5, suggesting a cold or diffuse gas phase. Strikingly, the 12CO(3–2)/(1–0) ratio of ~1 also indicates a higher excited phase. Since these galaxies have high infrared luminosities of LIR ≥ 1011L⊙ and seem to contain a circumnuclear starburst with minimum surface densities of gas and star formation rate (SFR) around Σmol = 50−550 M⊙pc-2 and ΣSFR = 1.1−3.1 M⊙ kpc-2 yr-1, we conclude that the interstellar medium in the centers of these LIRG Seyferts is strongly affected by violent star formation and better described by the ULIRG mass conversion factor.
Key words: submillimeter: galaxies / radio lines: galaxies / galaxies: ISM / galaxies: active / galaxies: Seyfert / galaxies: kinematics and dynamics
© ESO, 2016
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