A low-luminosity type-1 QSO sample. IV. Molecular gas contents and conditions of star formation in three nearby Seyfert galaxies
Journal article, 2016

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.

galaxies: kinematics and dynamics

radio lines: galaxies

galaxies: ISM

submillimeter: galaxies

galaxies: Seyfert

galaxies: active

Author

Lydia Moser

Max-Planck Institute for Radio Astronomy

University of Cologne

Melanie Krips

Domaine universitaire de Grenoble

Gerold Busch

University of Cologne

Julia Scharwächter

LERMA - Laboratoire d'Etudes du Rayonnement et de la Matiere en Astrophysique et Atmospheres

Sabine König

Domaine universitaire de Grenoble

Andreas Eckart

Max-Planck Institute for Radio Astronomy

University of Cologne

Semir Smajic

Max-Planck Institute for Radio Astronomy

University of Cologne

Macarena Garcia-Marin

University of Cologne

Monica Valencia-S.

University of Cologne

Sebastian Fischer

German Aerospace Center (DLR)

Jens Dierkes

University of Göttingen

Astronomy and Astrophysics

0004-6361 (ISSN) 1432-0746 (eISSN)

Vol. 587 A137-

Subject Categories

Astronomy, Astrophysics and Cosmology

Roots

Basic sciences

DOI

10.1051/0004-6361/201526358

More information

Latest update

5/11/2022