@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 {213, title = {{High-resolution imaging of the molecular outflows in two mergers: IRAS 17208-0014 and NGC 1614}}, journal = {Astronomy \& Astrophysics}, volume = {580}, year = {2015}, pages = {A35}, keywords = {galaxies: individual: IRAS 17208-0014, galaxies: individual: NGC1614, galaxies: ISM, galaxies: kinematics and dynamics, galaxies: nuclei, galaxies: starburst}, doi = {10.1051/0004-6361/201526133}, author = {Garcia-Burillo, S. and Combes, F. and Usero, A. and Aalto, S. and Colina, L. and Alonso-Herrero, A. and Hunt, L.~K. and Arribas, S. and Costagliola, F. and Labiano, A. and Neri, R. and Pereira-Santaella, M. and Tacconi, L.~J. and van der Werf, P.~P.} } @article {2015A\&A...574A.114V, title = {{Subarcsecond international LOFAR radio images of the M82 nucleus at 118 MHz and 154 MHz}}, journal = {Astronomy and Astrophysics}, volume = {574}, year = {2015}, month = {feb}, pages = {A114}, abstract = {Context. The nuclear starburst in the nearby galaxy M82 provides an excellent laboratory for understanding the physics of star formation. This galaxy has been extensively observed in the past, revealing tens of radio-bright compact objects embedded in a diffuse free-free absorbing medium. Our understanding of the structure and physics of this medium in M82 can be greatly improved by high-resolution images at low frequencies where the effects of free-free absorption are most prominent.
Aims: The aims of this study are, firstly, to demonstrate imaging using international baselines of the Low Frequency Array (LOFAR), and secondly, to constrain low-frequency spectra of compact and diffuse emission in the central starburst region of M82 via high-resolution radio imaging at low frequencies.
Methods: The international LOFAR telescope was used to observe M82 at 110-126 MHz and 146-162 MHz. Images were obtained using standard techniques from very long baseline interferometry. images were obtained at each frequency range: one only using international baselines, and one only using the longest Dutch (remote) baselines.
Results: The 154 MHz image obtained using international baselines is a new imaging record in terms of combined image resolution (0.3{\textquoteright}{\textquoteright}) and sensitivity ({$\sigma$} = 0.15 mJy/beam) at low frequencies ({\l}t}327 MHz). We detected 16 objects at 154 MHz, six of these also at 118 MHz. Seven objects detected at 154 MHz have not been catalogued previously. For the nine objects previously detected, we obtained spectral indices and emission measures by fitting models to spectra (combining LOFAR with literature data). Four weaker but resolved features are also found: a linear (50 pc) filament and three other resolved objects, of which two show a clear shell structure. We do not detect any emission from either supernova 2008iz or from the radio transient source 43.78+59.3. The images obtained using remote baselines show diffuse emission, associated with the outflow in M82, with reduced brightness in the region of the edge-on star-forming disk.}, keywords = {galaxies: individual: M82, galaxies: star formation, galaxies: starburst, supernovae: individual: 2008iz, techniques: high angular resolution, techniques: interferometric}, doi = {10.1051/0004-6361/201425089}, url = {http://adsabs.harvard.edu/abs/2015A\%26A...574A.114V}, author = {Varenius, E. and Conway, J.~E. and Mart{\'\i}-Vidal, I. and Beswick, R. and Deller, A.~T. and Wucknitz, O. and Jackson, N. and Adebahr, B. and M. A. P{\'e}rez-Torres and Chy{\.z}y, K.~T. and Carozzi, T.~D. and Mold{\'o}n, J. and Aalto, S. and Beck, R. and Best, P. and Dettmar, R.-J. and van Driel, W. and Brunetti, G. and Br{\"u}ggen, M. and Haverkorn, M. and Heald, G. and Horellou, C. and Jarvis, M.~J. and Morabito, L.~K. and Miley, G.~K. and R{\"o}ttgering, H.~J.~A. and Toribio, M.~C. and White, G.~J.} } @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.} } @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 {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 {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...527A.150L, title = {{A survey of HC$_{3}$N in extragalactic sources. Is HC$_{3}$N a tracer of activity in ULIRGs?}}, journal = {Astronomy and Astrophysics}, volume = {527}, year = {2011}, month = {mar}, pages = {A150}, abstract = {Context. HC$_{3}$N is a molecule that is mainly associated with Galactic star-forming regions, but it has also been detected in extragalactic environments.
Aims: To present the first extragalactic survey of HC$_{3}$N, when combining earlier data from the literature with six new single-dish detections, and to compare HC$_{3}$N with other molecular tracers (HCN, HNC), as well as other properties (silicate absorption strength, IR flux density ratios, C ii flux, and megamaser activity).
Methods: We present mm IRAM 30 m, OSO 20 m, and SEST observations of HC$_{3}$N rotational lines (mainly the J = 10-9 transition) and of the J = 1-0 transitions of HCN and HNC. Our combined HC$_{3}$N data account for 13 galaxies (excluding the upper limits reported for the non-detections), while we have HCN and HNC data for more than 20 galaxies.
Results: A preliminary definition {\textquoteright}{\textquoteright}HC$_{3}$N-luminous galaxy{\textquoteright}{\textquoteright} is made based upon the HC$_{3}$N/HCN ratio. Most (\~{}80\%) HC$_{3}$N-luminous galaxies seem to be deeply obscured galaxies and (U)LIRGs. A majority (\~{}60\% or more) of the HC$_{3}$N-luminous galaxies in the sample present OH mega- or strong kilomaser activity. A possible explanation is that both HC$_{3}$N and OH megamasers need warm dust for their excitation. Alternatively, the dust that excites the OH megamaser offers protection against UV destruction of HC$_{3}$N. A high silicate absorption strength is also found in several of the HC$_{3}$N-luminous objects, which may help the HC$_{3}$N to survive. Finally, we find that a high HC$_{3}$N/HCN ratio is related to a high dust temperature and a low C ii flux. Appendix is only available in electronic form at http://www.aanda.org}, keywords = {galaxies: active, galaxies: ISM, galaxies: starburst, ISM: molecules, radio lines: galaxies, radio lines: ISM}, doi = {10.1051/0004-6361/201015565}, url = {http://adsabs.harvard.edu/abs/2011A\%26A...527A.150L}, author = {Lindberg, J.~E. and Aalto, S. and F. Costagliola and P{\'e}rez-Beaupuits, J.-P. and Monje, R. and Muller, S.} } @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.} }