High resolution observations of HCN and HCO⁺J= 3–2 in the disk and outflow of Mrk 231

Abstract

Aims. Our goal is to study molecular gas properties in nuclei and large scale outflows/winds from active galactic nuclei (AGNs) and starburst galaxies. Methods. We obtained high resolution (0. 25 to 0. 90) observations of HCN and HCO + J = 3 → 2 of the ultraluminous QSO galaxy Mrk 231 with the IRAM Plateau de Bure Interferometer (PdBI). Results. We find luminous HCN and HCO + J = 3 → 2 emission in the main disk and we detect compact (r < ∼ 0. 1 (90 pc)) vibrationally excited HCN J = 3 → 2 ν 2 = 1 f emission centred on the nucleus. The velocity field of the vibrationally excited HCN is strongly inclined (position angle PA = 155• ) compared to the east-west rotation of the main disk. The nuclear (r < ∼ 0. 1) molecular mass is estimated to 8 × 10 8 M with an average N(H 2 ) of 1.2 × 10 24 cm −2 . Prominent, spatially extended ( > ∼ 350 pc) line wings are found for HCN J = 3 → 2 with velocities up to ±750 km s −1 . Line ratios indicate that the emission is emerging in dense gas n = 10 4 −5 × 10 5 cm −3 of elevated HCN abundance X(HCN) = 10 −8 −10 −6 . The highest X(HCN) also allows for the emission to originate in gas of more moderate density. We tentatively detect nuclear emission from the reactive ion HOC + with HCO + /HOC + = 10−20. Conclusions. The HCN ν 2 = 1 f line emission is consistent with the notion of a hot, dusty, warped inner disk of Mrk 231 where the ν 2 = 1 f line is excited by bright mid-IR 14 μm continuum. We estimate the vibrational temperature T vib to 200−400 K. Based on relative source sizes we propose that 50% of the main HCN emission may have its excitation affected by the radiation field through IR pumping of the vibrational ground state. The HCN emission in the line wings, however, is more extended and thus likely not strongly affected by IR pumping. Our results reveal that dense clouds survive (and/or are formed) in the AGN outflow on scales of at least several hundred pc before evaporating or collapsing. The elevated HCN abundance in the outflow is consistent with warm chemistry possibly related to shocks and/or X-ray irradiated gas. An upper limit to the mass and momentum flux is 4 × 10 8 M and 12L AGN /c, respectively, and we discuss possible driving mechanisms for the dense outflow.

Molecular Outflows in Local ULIRGs: Energetics from Multitransition OH Analysis

“…In the far-IR, the outflows are also traced by the line wing emission of the [C ii] 158 µm transition (Janssen et al 2016). High-velocity molecular outflows are detected at (sub)millimeter wavelengths in lines of CO, HCN, and HCO + (e.g., Feruglio et al 2010Feruglio et al , 2015Cicone et al 2012Cicone et al , 2014Aalto et al 2012Aalto et al , 2015García-Burillo et al 2015;Lindberg et al 2016). Lower-velocity molecular outflows are also detected in millimeter lines of the above species and in CS (Sakamoto et al 2009;Bolatto et al 2013;Tunnard et al 2015; Alatalo et al 2015;Martín et al 2016).…”

ALMA HCN AND HCO+ J = 3 − 2 OBSERVATIONS OF OPTICAL SEYFERT AND LUMINOUS INFRARED GALAXIES: CONFIRMATION OF ELEVATED HCN-TO-HCO+ FLUX RATIOS IN AGNS

“…These high-spatial-resolution ALMA observations enable us to minimize the contamination from spatially extended starburst activity in host galaxies, and thus provide a clearer view on whether AGNs indeed show enhanced HCN-to-HCO + flux ratios, compared to starburst galaxies. As spatially resolved pre-ALMA HCN and HCO + J=3-2 data for galaxies are still very limited in the literature (Sakamoto et al 2010;Hsieh et al 2012;Aalto et al 2015a), our ALMA Cycle 2 and 3 LIRG data, with various AGN and starburst contributions, are also included so that we can compare the HCN-to-HCO + J=3-2 flux ratios of AGN-dominated nuclei to regions of strong starburst contributions.…”

How Dense Is Your Gas? On the Recoverability of LVG Model Parameters

“…This model is, as ever, a gross simplification of reality, where hot background radiation fields on 10 pc scales are usually due to active-galactic-nucleus-(AGN-) or starburstheated dust, which also emits significantly in the mid-IR, leading to optical pumping of molecular vibrational lines (Aalto et al 2007(Aalto et al , 2015a(Aalto et al , 2015bGonzález-Alfonso et al 2013). Nevertheless, the low T bg SLEDs, where the background temperature of 10 K is reached by the CMB at z=2.3, demonstrate that line ratios indicative of certain behaviors in the local universe are not necessarily applicable in high-redshift galaxies.…”