@article {2015A\&A...574A..85A, title = {{High resolution observations of HCN and HCO$^{+}$J = 3-2 in the disk and outflow of Mrk 231. Detection of vibrationally excited HCN in the warped nucleus}}, journal = {Astronomy and Astrophysics}, volume = {574}, year = {2015}, month = {feb}, pages = {A85}, 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.{\#779}25 to 0.{\#779}90) observations of HCN and HCO$^{+}$J = 3 {\rarr} 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 {\rarr} 2 emission in the main disk and we detect compact (r {\l}sim} 0{\textquoteright}{\textquoteright}\&dotbelow;1 (90 pc)) vibrationally excited HCN J = 3 {\rarr} 2{$ν$}$_{2}$ = 1f emission centred on the nucleus. The velocity field of the vibrationally excited HCN is strongly inclined (position angle PA = 155{\deg}) compared to the east-west rotation of the main disk. The nuclear (r {\l}sim} 0.{\#779}1) molecular mass is estimated to 8 {\times} 10$^{8}$ M$_{\&sun;}$ with an average N(H$_{2}$) of 1.2 {\times} 10$^{24}$ cm$^{-2}$. Prominent, spatially extended ({\gsim}350 pc) line wings are found for HCN J = 3 {\rarr} 2 with velocities up to {\plusmn} 750 km s$^{-1}$. Line ratios indicate that the emission is emerging in dense gas n = 10$^{4}$-5 {\times} 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 {$ν$}$_{2}$ = 1f line emission is consistent with the notion of a hot, dusty, warped inner disk of Mrk 231 where the {$ν$}$_{2}$ = 1f line is excited by bright mid-IR 14 {$μ$}m 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 {\times} 10$^{8}$ M$_{\&sun;}$ and 12L$_{AGN}$/c, respectively, and we discuss possible driving mechanisms for the dense outflow. Based on observations carried out with the IRAM Plateau de Bure Interferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain).The reduced data cubes are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/574/A85}, keywords = {galaxies: active, galaxies: evolution, galaxies: individual: Mrk 231, ISM: jets and outflows, ISM: molecules, quasars: general}, doi = {10.1051/0004-6361/201423987}, url = {http://adsabs.harvard.edu/abs/2015A\%26A...574A..85A}, author = {Aalto, S. and S. Garc{\'\i}a-Burillo and Muller, S. and Winters, J.~M. and Gonzalez-Alfonso, E. and van der Werf, P. and Henkel, C. and F. Costagliola and Neri, R.} } @article {221, title = {{High-resolution mm and cm study of the obscured LIRG NGC 4418 . A compact obscured nucleus fed by in-falling gas?}}, journal = {\aap}, volume = {556}, year = {2013}, pages = {A66}, keywords = {galaxies: active, galaxies: individual: NGC 4418, galaxies: ISM, galaxies: kinematics and dynamics, galaxies: starburst}, doi = {10.1051/0004-6361/201220634}, author = {Costagliola, F. and Aalto, S. and Sakamoto, K. and Mart{\'\i}n, S. and Beswick, R. and Muller, S. and Kl{\"o}ckner, H.-R.} } @article {2013A\&A...556A..66C, title = {{High-resolution mm and cm study of the obscured LIRG NGC 4418 . A compact obscured nucleus fed by in-falling gas?}}, journal = {Astronomy and Astrophysics}, volume = {556}, year = {2013}, month = {aug}, pages = {A66}, abstract = {Context. Understanding the nature of the power-source in luminous infrared galaxies (LIRG) is difficult due to their extreme obscuration. Observations at radio and mm wavelengths can penetrate large columns of dust and gas and provide unique insights into the properties of the compact obscured nuclei of LIRGs.
Aims: The aim of this study is to constrain the dynamics, structure, and feeding of the compact nucleus of NGC 4418, and to reveal the nature of the main hidden power-source: starburst or active galactic nucleus (AGN).
Methods: We obtained high spatial resolution observations of NGC 4418 at 1.4 and 5 GHz with MERLIN, and at 230 and 270 GHz with the SMA in very extended configuration. We used the continuum morphology and flux density to estimate the size of the emitting region, the star formation rate, and the dust temperature. Emission lines were used to study kinematics through position-velocity diagrams. Molecular emission was studied with population diagrams and by fitting a local thermal equilibrium (LTE) synthetic spectrum.
Results: We detect bright 1-mm-line emission from CO, HC$_{3}$N, HNC, and C$^{34}$S and 1.4 GHz absorption from HI. The CO 2-1 emission and HI absorption can be fit by two velocity components at 2090 and 2180 km s$^{-1}$. We detect vibrationally excited HC$_{3}$N and HNC, with T$_{vib}$ \~{} 300 K. Molecular excitation is consistent with a layered temperature structure, with three main components at 80, 160, and 300 K. For the hot component we estimate a source size of less than 5 pc. The nuclear molecular gas surface density of 10$^{4}$M$_{\&sun;}$ pc$^{-2}$ is extremely high and similar to that found in the ultra-luminous infrared galaxy (ULIRG) Arp220.
Conclusions: Our observations confirm the presence of a molecular and atomic in-flow, previously suggested by Herschel observations, which is feeding the activity in the center of NGC 4418. Molecular excitation confirms the presence of a very compact, hot dusty core. If a starburst is responsible for the observed IR flux, this has to be at least as extreme as the one in the ULIRG Arp 220, with an age of 3-10 Myr and a star formation rate {\gt}10 M$_{\&sun;}$ yr$^{-1}$. If an AGN is present, it must be extremely Compton-thick. Appendix A is only available in electronic form at http://www.aanda.org}, keywords = {galaxies: active, galaxies: individual: NGC 4418, galaxies: ISM, galaxies: kinematics and dynamics, galaxies: starburst}, doi = {10.1051/0004-6361/201220634}, url = {http://adsabs.harvard.edu/abs/2013A\%26A...556A..66C}, author = {F. Costagliola and Aalto, S. and Sakamoto, K. and Mart{\'\i}n, S. and Beswick, R. and Muller, S. and Kl{\"o}ckner, H.-R.} }