@article {2015ApJ...799...11X, title = {{ALMA Observations of Warm Dense Gas in NGC 1614 - Breaking of the Star Formation Law in the Central Kiloparsec}}, journal = {The Astrophysical Journal}, volume = {799}, year = {2015}, month = {jan}, pages = {11}, abstract = {We present ALMA Cycle-0 observations of the CO (6-5) line emission and of the 435 {$μ$}m dust continuum emission in the central kiloparsec of NGC 1614, a local luminous infrared galaxy at a distance of 67.8 Mpc (1$\{$$^{\prime \prime }$$\}$= 329 pc). The CO emission is well resolved by the ALMA beam (0.{\textquoteright}{\textquoteright}26 {\times} 0.{\textquoteright}{\textquoteright}20) into a circumnuclear ring, with an integrated flux of f $_{ CO(6-5)}$ = 898 ({\plusmn} 153) Jy km s$^{-1}$, which is 63({\plusmn} 12)\% of the total CO (6-5) flux measured by Herschel. The molecular ring, located between 100 pc {\l}t} r {\l}t} 350 pc from the nucleus, looks clumpy and includes seven unresolved (or marginally resolved) knots with median velocity dispersion of \~{}40 km s$^{-1}$. These knots are associated with strong star formation regions with {$Σ$}$_{SFR}$ \~{} 100 M $_{\&sun;}$ yr$^{-1}$ kpc$^{-2}$ and {$Σ$} $_{Gas}${\tilde} 10$^{4}$ $\{$M$\}$\_{\sun} pc$^{-2}$. The non-detections of the nucleus in both the CO (6-5) line emission and the 435 {$μ$}m continuum rule out, with relatively high confidence, a Compton-thick active galactic nucleus in NGC 1614. Comparisons with radio continuum emission show a strong deviation from an expected local correlation between {$Σ$}$_{Gas}$ and {$Σ$}$_{SFR}$, indicating a breakdown of the Kennicutt-Schmidt law on the linear scale of \~{}100 pc. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.}, keywords = {galaxies: active, galaxies: evolution, galaxies: general, galaxies: interactions, galaxies: ISM, galaxies: magnetic fields, galaxies: nuclei, galaxies: starburst, submillimeter: galaxies}, doi = {10.1088/0004-637X/799/1/11}, url = {http://adsabs.harvard.edu/abs/2015ApJ...799...11X}, author = {Xu, C.~K. and Cao, C. and Lu, N. and Gao, Y. and Diaz-Santos, T. and R. Herrero-Illana and Meijerink, R. and Privon, G. and Zhao, Y.-H. and Evans, A.~S. and K{\"o}nig, S. and Mazzarella, J.~M. and Aalto, S. and Appleton, P. and Armus, L. and Charmandaris, V. and Chu, J. and Haan, S. and Inami, H. and Murphy, E.~J. and Sanders, D.~B. and Schulz, B. and van der Werf, P.} } @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 {2013MNRAS.434..978V, title = {{Molecular gas in type 2 quasars at z {\tilde} 0.2-0.3}}, journal = {Monthly Notices of the Royal Astronomical Society}, volume = {434}, year = {2013}, month = {sep}, pages = {978-991}, abstract = {{We present results of CO(1-0) spectroscopic observations of 10 Sloan Digital Sky Survey type 2 quasars (QSO2) at z {\tilde} 0.2-0.3 observed with the 30-m IRAM radio telescope and the Australia Telescope Compact Array. We report five new confirmed CO(1-0) detections and one tentative detection. They have L\^{}{\textquoteright} $\}$\_CO {\tilde} several {\times} 10$^{9}$ K km s$^{-1}$ pc$^{2}$, while upper limits for the non-detections are L\^{}{\textquoteright} $\}, keywords = {galaxies: evolution, galaxies: interactions, quasars: general}, author = {Villar-Mart{\'\i}n, M. and M. Rodr{\'\i}guez and Drouart, G. and Emonts, B. and Colina, L. and Humphrey, A. and S. Garc{\'\i}a-Burillo and Graci{\'a} Carpio, J. and Planesas, P. and P{\'e}rez Torres, M. and Arribas, S.} } @article {190, title = {{SDSS J002531.46-104022.2 at z = 0.30: a candidate for the (ultra)luminous infrared galaxy to optical quasar transition}}, journal = {MNRAS}, volume = {432}, year = {2013}, pages = {2104-2111}, keywords = {galaxies: evolution, galaxies: interactions, quasars: individual: SDSS J002531.46-104022.2}, doi = {10.1093/mnras/stt538}, url = {http://adsabs.harvard.edu/abs/2013MNRAS.432.2104V}, author = {Villar-Mart{\'\i}n, M. and Emonts, B. and M. Rodr{\'\i}guez and Torres, M.~P. and Drouart, G.} } @article {2013ApJ...764...42S, title = {{Submillimeter Interferometry of the Luminous Infrared Galaxy NGC 4418: A Hidden Hot Nucleus with an Inflow and an Outflow}}, journal = {The Astrophysical Journal}, volume = {764}, year = {2013}, month = {feb}, pages = {42}, abstract = {We have observed the nucleus of the nearby luminous infrared galaxy NGC 4418 with subarcsec resolution at 860 and 450 {$μ$}m for the first time to characterize its hidden power source. A \~{}20 pc (0.{\textquoteright}{\textquoteright}1) hot dusty core was found inside a 100 pc scale concentration of molecular gas at the galactic center. The 860 {$μ$}m continuum core has a deconvolved (peak) brightness temperature of 120-210 K. The CO(3-2) peak brightness temperature there is as high as 90 K at 50 pc resolution. The core has a bolometric luminosity of about 10$^{11}$ L $_{\&sun;}$, which accounts for most of the galaxy luminosity. It is Compton thick (N $_{H}$ {\gt}\~{} 10$^{25}$ cm$^{-2}$) and has a high luminosity-to-mass ratio (L/M) \~{} 500 L $_{\&sun;}$ M $_{\&sun;}$ $^{-1}$ as well as a high luminosity surface density 10$^{8.5 {\textpm} 0.5}$ L $_{\&sun;}$ pc$^{-2}$. These parameters are consistent with an active galactic nucleus to be the main luminosity source (with an Eddington ratio about 0.3), while they can be also due to a young starburst near its maximum L/M. We also found an optical color (reddening) feature that we attribute to an outflow cone emanating from the nucleus. The hidden hot nucleus thus shows evidence of both an inflow, previously seen with absorption lines, and the new outflow reported here in a different direction. The nucleus must be rapidly evolving with these gas flows.}, keywords = {galaxies: active, galaxies: evolution, galaxies: individual: NGC 4418, galaxies: ISM}, doi = {10.1088/0004-637X/764/1/42}, url = {http://adsabs.harvard.edu/abs/2013ApJ...764...42S}, author = {Sakamoto, K. and Aalto, S. and F. Costagliola and Mart{\'\i}n, S. and Ohyama, Y. and Wiedner, M.~C. and Wilner, D.~J.} } @article {2012A\&A...537A..44A, title = {{Detection of HCN, HCO$^{+}$, and HNC in the Mrk 231 molecular outflow. Dense molecular gas in the AGN wind}}, journal = {Astronomy and Astrophysics}, volume = {537}, year = {2012}, month = {jan}, pages = {A44}, abstract = {
Aims: Our goal is to study gas properties in large-scale molecular outflows and winds from active galactic nuclei (AGNs) and starburst galaxies.
Methods: We obtained high-resolution (1.{\textquoteright}{\textquoteright}55 {\times} 1.{\textquoteright}{\textquoteright}28) observations of HCN, HCO$^{+}$, HNC 1-0 and HC$_{3}$N 10-9 of the ultraluminous galaxy (ULIRG) Mrk 231 with the IRAM Plateau de Bure Interferometer.
Results: We detect luminous emission from HCN, HCO$^{+}$ and HNC 1-0 in the QSO ULIRG Mrk 231. All three lines show broad line wings - which are particularly prominent for HCN. Velocities are found to be similar ( {\ap} {\plusmn} 750 km s$^{-1}$) to those found for CO 1-0. This is the first time bright HCN, HCO$^{+}$ and HNC emission has been detected in a large-scale galactic outflow. We find that both the blue- and red-shifted line wings are spatially extended by at least 0.{\textquoteright}{\textquoteright}75 ({\gt}700 pc) in a north-south direction. The line wings are brighter (relative to the line center intensity) in HCN than in CO 1-0 and line ratios suggest that the molecular outflow consists of dense (n {\gt} 10$^{4}$ cm$^{-3}$) and clumpy gas with a high HCN abundance X(HCN) {\gt} 10$^{-8}$. These properties are consistent with the molecular gas being compressed and fragmented by shocks in the outflow. Alternatively, HCN is instead pumped by mid-IR continuum, but we propose that this effect is not strong for the spatially extended outflowing gas. In addition, we find that the rotation of the main disk, in east-west direction, is also evident in the HCN, HCO$^{+}$ and HNC line emission. An unexpectedly bright HC$_{3}$N 10-9 line is detected inside the central 400 pc of Mrk 231. This HC$_{3}$N emission may emerge from a shielded, dust-enshrouded region within the inner 40-50 pc where the gas is heated to high temperatures (200-300 K) by the AGN. Based on observations carried out with the IRAM Plateau de Bure Interferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain).}, keywords = {galaxies: active, galaxies: evolution, galaxies: individual: Mrk 231, ISM: molecules, quasars: general, radio lines: ISM}, doi = {10.1051/0004-6361/201117919}, url = {http://adsabs.harvard.edu/abs/2012A\%26A...537A..44A}, author = {Aalto, S. and S. Garc{\'\i}a-Burillo and Muller, S. and Winters, J.~M. and van der Werf, P. and Henkel, C. and F. Costagliola and Neri, R.} } @article {2012A\&A...546A..68A, title = {{Winds of change - a molecular outflow in NGC 1377?. The anatomy of an extreme FIR-excess galaxy}}, journal = {Astronomy and Astrophysics}, volume = {546}, year = {2012}, month = {oct}, pages = {A68}, abstract = {
Aims: Our goal was to investigate the molecular gas distribution and kinematics in the extreme far-infrared (FIR) excess galaxy NGC 1377 and to address the nature and evolutionary status of the buried source.
Methods: We used high- (0{\textquoteright}{\textquoteright}65 {\times} 0{\textquoteright}{\textquoteright}52, (65 {\times} 52 pc)) and low- (4{\textquoteright}{\textquoteright}88 {\times} 2{\textquoteright}{\textquoteright}93) resolution SubMillimeter Array (SMA) observations to image the $^{12}$CO and $^{13}$CO 2-1 line emission.
Results: We find bright, complex $^{12}$CO 2-1 line emission in the inner 400 pc of NGC 1377. The $^{12}$CO 2-1 line has wings that are tracing a kinematical component that appears to be perpendicular to the component traced by the line core. Together with an intriguing X-shape of the integrated intensity and dispersion maps, this suggests that the molecular emission of NGC 1377 consists of a disk-outflow system. Lower limits to the molecular mass and outflow rate are M$_{out}$(H$_{2}$) {\gt} 1 {\times} 10$^{7}$ M$_{\&sun;}$ and {\.M} {\gt} 8 M$_{\&sun;}$ yr$^{-1}$. The age of the proposed outflow is estimated to be 1.4 Myr, the extent to be 200 pc and the outflow speed to be V$_{out}$ = 140 km s$^{-1}$. The total molecular mass in the SMA map is estimated to M$_{tot}$(H$_{2}$) = 1.5 {\times} 10$^{8}$ M$_{\&sun;}$ (on a scale of 400 pc) while in the inner r = 29 pc the molecular mass is M$_{core}$(H$_{2}$) = 1.7 {\times} 10$^{7}$ M$_{\&sun;}$ with a corresponding H$_{2}$ column density of N(H$_{2}$) = 3.4 {\times} 10$^{23}$ cm$^{-2}$ and an average $^{12}$CO 2-1 brightness temperature of 19 K. $^{13}$CO 2-1 emission is found at a factor 10 fainter than $^{12}$CO in the low-resolution map while C$^{18}$O 2-1 remains undetected. We find weak 1 mm continuum emission of 2.4 mJy with spatial extent less than 400 pc.
Conclusions: Observing the molecular properties of the FIR-excess galaxy NGC 1377 allows us to probe the early stages of nuclear activity and the onset of feedback in active galaxies. The age of the outflow supports the notion that the current nuclear activity is young - a few Myr. The outflow may be powered by radiation pressure from a compact, dust enshrouded nucleus, but other driving mechanisms are possible. The buried source may be an active galactic nucleus (AGN) or an extremely young (1 Myr) compact starburst. Limitations on size and mass lead us to favor the AGN scenario, but additional studies are required to settle this question. In either case, the wind with its implied mass outflow rate will quench the nuclear power source within the very short time of 5-25 Myr. It is possible, however, that the gas is unable to escape the galaxy and may eventually fall back onto NGC 1377 again.}, keywords = {galaxies: active, galaxies: evolution, galaxies: individual: NGC 1377, galaxies: starburst, ISM: molecules, radio lines: ISM}, doi = {10.1051/0004-6361/201118052}, url = {http://adsabs.harvard.edu/abs/2012A\%26A...546A..68A}, author = {Aalto, S. and Muller, S. and Sakamoto, K. and Gallagher, J.~S. and Mart{\'\i}n, S. and F. Costagliola} } @article {2011MNRAS.410.2556D, title = {{Extragalactic background light inferred from AEGIS galaxy-SED-type fractions}}, journal = {Monthly Notices of the Royal Astronomical Society}, volume = {410}, year = {2011}, month = {feb}, pages = {2556-2578}, abstract = {The extragalactic background light (EBL) is of fundamental importance both for understanding the entire process of galaxy evolution and for {$\gamma$}-ray astronomy, but the overall spectrum of the EBL between 0.1 and 1000 {$μ$}m has never been determined directly from galaxy spectral energy distribution (SED) observations over a wide redshift range. The evolving, overall spectrum of the EBL is derived here utilizing a novel method based on observations only. This is achieved from the observed evolution of the rest-frame K-band galaxy luminosity function up to redshift 4, combined with a determination of galaxy-SED-type fractions. These are based on fitting Spitzer Wide-Area Infrared Extragalactic Survey (SWIRE) templates to a multiwavelength sample of about 6000 galaxies in the redshift range from 0.2 to 1 from the All-wavelength Extended Groth Strip International Survey (AEGIS). The changing fractions of quiescent galaxies, star-forming galaxies, starburst galaxies and active galactic nucleus (AGN) galaxies in that redshift range are estimated, and two alternative extrapolations of SED types to higher redshifts are considered. This allows calculation of the evolution of the luminosity densities from the ultraviolet (UV) to the infrared (IR), the evolving star formation rate density of the Universe, the evolving contribution to the bolometric EBL from the different galaxy populations including AGN galaxies and the buildup of the EBL. Our EBL calculations are compared with those from a semi-analytic model, another observationally based model and observational data. The EBL uncertainties in our modelling based directly on the data are quantified, and their consequences for attenuation of very-high-energy {$\gamma$}-rays due to pair production on the EBL are discussed. It is concluded that the EBL is well constrained from the UV to the mid-IR, but independent efforts from IR and {$\gamma$}-ray astronomy are needed in order to reduce the uncertainties in the far-IR.}, keywords = {cosmology: observations, diffuse radiation, galaxies: evolution, galaxies: formation, infrared: diffuse background}, doi = {10.1111/j.1365-2966.2010.17631.x}, url = {http://adsabs.harvard.edu/abs/2011MNRAS.410.2556D}, author = {Dom{\'\i}nguez, A. and Primack, J.~R. and Rosario, D.~J. and Prada, F. and Gilmore, R.~C. and Faber, S.~M. and Koo, D.~C. and Somerville, R.~S. and M. A. P{\'e}rez-Torres and P. P{\'e}rez-Gonz{\'a}lez and Huang, J.-S. and Davis, M. and Guhathakurta, P. and Barmby, P. and Conselice, C.~J. and Lozano, M. and Newman, J.~A. and Cooper, M.~C.} } @article {2011A\&A...527A..69A, title = {{H$_{3}$O$^{+}$ line emission from starbursts and AGNs}}, journal = {Astronomy and Astrophysics}, volume = {527}, year = {2011}, month = {mar}, pages = {A69}, abstract = {Context. The H$_{3}$O$^{+}$ molecule probes the chemistry and the ionization rate of dense circumnuclear gas in galaxies.
Aims: We use the H$_{3}$O$^{+}$ molecule to investigate the impact of starburst and AGN activity on the chemistry of the molecular interstellar medium.
Methods: Using the JCMT, we have observed the 3$_{2}$$^{+}$ - 2$_{2}$$^{+}$ 364 GHz line of p-H$_{3}$O$^{+}$ towards the centres of seven active galaxies.
Results: We have detected p-H$_{3}$O$^{+}$ towards IC 342, NGC 253, NGC 1068, NGC 4418, and NGC 6240. Upper limits were obtained for IRAS 15250 and Arp 299. We find large H$_{3}$O$^{+}$ abundances (N(H$_{3}$O$^{+}$)/N(H$_{2}$) {\gsim} 10$^{-8}$) in all detected galaxies apart from in IC 342 where it is about one order of magnitude lower. We note, however, that uncertainties in N(H$_{3}$O$^{+}$) may be significant due to lack of definite information on source size and excitation. We furthermore compare the derived N(H$_{3}$O$^{+}$) with N(HCO$^{+}$) and find that the H$_{3}$O$^{+}$ to HCO$^{+}$ column density ratio is large in NGC 1068 (24), moderate in NGC 4418 and NGC 253 (4-5), slightly less than unity in NGC 6240 (0.7) and lowest in IC 342 (0.2-0.6). We compare our results with models of X-ray and photon dominated regions (XDRs and PDRs).
Conclusions: For IC 342 we find that a starburst PDR chemistry can explain the observed H$_{3}$O$^{+}$ abundance. For the other galaxies, the large H$_{3}$O$^{+}$ columns are generally consistent with XDR models. In particular for NGC 1068 the elevated N(H$_{3}$O$^{+}$)/N(HCO$^{+}$) ratio suggests a low column density XDR. For NGC 4418 however, large HC$_{3}$N abundances are inconsistent with the XDR interpretation. An alternative possibility is that H$_{3}$O$^{+}$ forms through H$_{2}$O evaporating off dust grains and reacting with HCO$^{+}$ in warm, dense gas. This scenario could also potentially fit the results for NGC 253. Further studies of the excitation and distribution of H$_{3}$O$^{+}$ - as well as Herschel observations of water abundances - will help to further constrain the models.}, keywords = {galaxies: active, galaxies: evolution, galaxies: starburst, ISM: molecules, radio lines: galaxies}, doi = {10.1051/0004-6361/201015878}, url = {http://adsabs.harvard.edu/abs/2011A\%26A...527A..69A}, author = {Aalto, S. and F. Costagliola and van der Tak, F. and Meijerink, R.} } @article {2011A\&A...528A..30C, title = {{Molecules as tracers of galaxy evolution: an EMIR survey. I. Presentation of the data and first results}}, journal = {Astronomy and Astrophysics}, volume = {528}, year = {2011}, month = {apr}, pages = {A30}, abstract = {
Aims: We investigate the molecular gas properties of a sample of 23 galaxies in order to find and test chemical signatures of galaxy evolution and to compare them to IR evolutionary tracers.
Methods: Observation at 3 mm wavelengths were obtained with the EMIR broadband receiver, mounted on the IRAM 30 m telescope on Pico Veleta, Spain. We compare the emission of the main molecular species with existing models of chemical evolution by means of line intensity ratios diagrams and principal component analysis.
Results: We detect molecular emission in 19 galaxies in two 8 GHz-wide bands centred at 88 and 112 GHz. The main detected molecules are CO, $^{13}$CO, HCN, HNC, HCO$^{+}$, CN, and C$_{2}$H. We also detect HC$_{3}$N J = 10-9 in the galaxies IRAS 17208, IC 860, NGC 4418, NGC 7771, and NGC 1068. The only HC$_{3}$N detections are in objects with HCO$^{+}$/HCN {\l}t} 1. Galaxies with the highest HC$_{3}$N/HCN ratios have warm IRAS colours (60/100 {$μ$}m {\gt} 0.8). The brightest HC$_{3}$N emission is found in IC 860, where we also detect the molecule in its vibrationally excited state. We find low HNC/HCN line ratios ({\l}t}0.5), that cannot be explained by existing PDR or XDR chemical models. The intensities of HCO+ and HNC appear anti-correlated. No correlation is found between the HNC/HCN line ratio and dust temperature. All HNC-bright objects are either luminous IR galaxies (LIRG) or Seyferts. Galaxies with bright polycyclic aromatic hydrocarbons (PAH) emission show low HNC/HCO$^{+}$ ratios. The CO/$^{13}$CO ratio is positively correlated with the dust temperature and is generally higher than in our galaxy. The emission of CN and C$^{18}$O is correlated.
Conclusions: Bright HC$_{3}$N emission in HCO$^{+}$-faint objects may imply that these are not dominated by X-ray chemistry. Thus the HCN/HCO$^{+}$ line ratio is not, by itself, a reliable tracer of XDRs. Bright HC$_{3}$N and faint HCO$^{+}$ could be signatures of embedded star-formation, instead of AGN activity. Mechanical heating caused by supernova explosions may be responsible for the low HNC/HCN and high HCO$^{+}$/HCN ratios in some starbursts. We cannot exclude, however, that the discussed trends are largely caused by optical depth effects or excitation. Chemical models alone cannot explain all properties of the observed molecular emission. Better constraints to the gas spacial distribution and excitation are needed to distinguish abundance and excitation effects. Appendices are only available in electronic form http://www.aanda.org}, keywords = {evolution, galaxies: active, galaxies: evolution, galaxies: ISM, ISM: molecules}, doi = {10.1051/0004-6361/201015628}, url = {http://adsabs.harvard.edu/abs/2011A\%26A...528A..30C}, author = {F. Costagliola and Aalto, S. and M. Rodr{\'\i}guez and Muller, S. and Spoon, H.~W.~W. and Mart{\'\i}n, S. and M. A. P{\'e}rez-Torres and Alberdi, A. and Lindberg, J.~E. and Batejat, F. and J{\"u}tte, E. and van der Werf, P. and Lahuis, F.} } @article {2010A\&A...515A..71C, title = {{Vibrationally excited HC$_{3}$N in NGC 4418}}, journal = {Astronomy and Astrophysics}, volume = {515}, year = {2010}, month = {jun}, pages = {A71}, abstract = {
Aims: We investigate the molecular gas properties of the deeply obscured luminous infrared galaxy NGC 4418. We address the excitation of the complex molecule HC$_{3}$N to determine whether its unusually luminous emission is related to the nature of the buried nuclear source.
Methods: We use IRAM 30 m and JCMT observations of rotational and vibrational lines of HC$_{3}$N to model the excitation of the molecule by means of rotational diagrams.
Results: We report the first confirmed extragalactic detection of vibrational lines of HC$_{3}$N. We detect 6 different rotational transitions ranging from J = 10-9 to J = 30-29 in the ground vibrational state and obtain a tentative detection of the J = 38-37 line. We also detect 7 rotational transitions of the vibrationally excited states v$_{6}$ and v$_{7}$, with angular momenta ranging from J = 10-9 to 28-27. The energies of the upper states of the observed transitions range from 20 to 850 K. In the optically thin regime, we find that the rotational transitions of the vibrational ground state can be fitted for two temperatures, 30 K and 260 K, while the vibrationally excited levels can be fitted for a rotational temperature of 90 K and a vibrational temperature of 500 K. In the inner 300 pc of NGC 4418, we estimate a high HC$_{3}$N abundance, of the order of 10$^{-7}$.
Conclusions: The excitation of the HC$_{3}$N molecule responds strongly to the intense radiation field and the presence of warm, dense gas and dust at the center of NGC 4418. The intense HC$_{3}$N line emission is a result of both high abundances and excitation. The properties of the HC$_{3}$N emitting gas are similar to those found for hot cores in Sgr B2, which implies that the nucleus ({\l}t}300 pc) of NGC 4418 is reminiscent of a hot core. The potential presence of a compact, hot component (T = 500 K) is also discussed.}, keywords = {galaxies: active, galaxies: evolution, galaxies: starburst, globular clusters: individual: NGC 4418, ISM: molecules, radio lines: ISM}, doi = {10.1051/0004-6361/200913370}, url = {http://adsabs.harvard.edu/abs/2010A\%26A...515A..71C}, author = {F. Costagliola and Aalto, S.} }