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: ISM

galaxies: Seyfert

galaxies: kinematics and dynamics

galaxies: active

radio lines: galaxies

submillimeter: galaxies

Author

Lydia Moser

Max Planck Inst Radioaston

University of Cologne

Melanie Krips

Domaine Universitaire

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

Andreas Eckart

Max Planck Inst Radioaston

University of Cologne

Semir Smajic

Max Planck Inst Radioaston

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

12/3/2021