Search

Sulphur-bearing species are detected in various environments within Galactic star-forming regions and are particularly abundant in the gas phase of outflows and shocks, and photo-dissociation regions. In this work, we aim to investigate the nature of the emission from the most common sulphur-bearing species observable at millimetre wavelengths towards the nuclear starburst of the galaxy NGC 253. We intend to understand which type of regions are probed by sulphur-bearing species and which process(es) dominate(s) the release of sulphur into the gas phase. We used the high-angular resolution (1.6" or 27 pc) observations from the ALCHEMI ALMA Large Program to image several sulphur-bearing species towards the central molecular zone (CMZ) of NGC 253. We performed local thermodynamic equilibrium (LTE) and non-LTE large velocity gradient (LVG) analyses to derive the physical conditions of the gas in which S-bearing species are emitted, and their abundance ratios across the CMZ. Finally, we compared our results with previous ALCHEMI studies and a few selected Galactic environments. We found that not all sulphur-bearing species trace the same type of gas: strong evidence indicates that H2S and part of the emission of OCS, H2CS, and SO, are tracing shocks whilst part of SO and CS emission rather trace the dense molecular gas. For some species, such as CCS and SO2, we could not firmly conclude on their origin of emission. The present analysis indicates that the emission from most sulphur-bearing species throughout the CMZ is likely dominated by shocks associated with ongoing star formation. In the inner part of the CMZ where the presence of super star clusters was previously indicated, we could not distinguish between shocks or thermal evaporation as the main process releasing the S-bearing species., Comment: 44 pages, 20 figures, Accepted for publication in A&A

Determining the evolution of the CNO isotopes in the interstellar medium (ISM) of starburst galaxies can yield important constraints on the ages of superstar clusters (SSCs), or on other aspects and contributing factors of their evolution. Due to the time-dependent nature of the abundances of isotopes within the ISM as they are supplied from processes such as nucleosynthesis or chemical fractionation, this provides the possible opportunity to probe the ability of isotopes ratios to trace the ages of high star forming regions, such as SSCs. The goal of this study is to investigate whether the isotopic variations in SSC regions within NGC253 are correlated with their different ages as derived from stellar population modelling. We have measured abundance ratios of CO, HCN and HCO$^+$ isotopologues in six regions containing SSCs within NGC253 using high spatial resolution (1.6",$\sim 28$pc) data from the ALCHEMI (ALma Comprehensive High-resolution Extragalactic Molecular Inventory) ALMA Large program. We have then analysed these ratios using RADEX radiative transfer modelling, with the parameter space sampled using the nested sampling Monte Carlo algorithm MLFriends. These abundance ratios were then compared to ages predicted in each region via the fitting of observed star formation tracers (such as Br$\gamma$) to starburst stellar population evolution models. We do not find any significant trend with age for the CO and HCN isotopologue ratios on the timescales for the ages of the SSC* regions observed. The driving factors of these ratios within SSCs could be the Initial Mass Function as well as possibly fractionation effects. To further probe these effects in SSCs over time a larger sample of SSCs must be observed spanning a larger age range., Comment: 44 pages, 43 Figures, Accepted for Publication to A&A

HNCO and SiO are well known shock tracers and have been observed in nearby galaxies, including the nearby (D=3.5 Mpc) starburst galaxy NGC 253. The simultaneous detection of these two species in regions where the star formation rate is high may be used to study the shock history of the gas. We perform a multi-line molecular study using these two shock tracers (SiO and HNCO) with the aim of characterizing the gas properties. We also explore the possibility of reconstructing the shock history in NGC 253's Central Molecular Zone (CMZ). Six SiO transitions and eleven HNCO transitions were imaged at high resolution $1''.6$ (28 pc) with the Atacama Large Millimeter/submillimeter Array (ALMA) as part of the ALCHEMI Large Programme. Both non-LTE radiative transfer analysis and chemical modelling were performed in order to characterize the gas properties, and to investigate the chemical origin of the emission. The non-LTE radiative transfer analysis coupled with Bayesian inference shows clear evidence that the gas traced by SiO has different densities and temperatures than that traced by HNCO, with an indication that shocks are needed to produce both species. Chemical modelling further confirms such a scenario and suggests that fast and slow shocks are responsible for SiO and HNCO production, respectively, in most GMCs. We are also able to infer the physical characteristics of the shocks traced by SiO and HNCO for each GMC. Radiative transfer and chemical analysis of the SiO and HNCO in the CMZ of NGC 253 reveal a complex picture whereby most of the GMCs are subjected to shocks. We speculate on the possible shock scenarios responsible for the observed emission and provide potential history and timescales for each shock scenario. Higher spatial resolution observations of these two species are required in order to quantitatively differentiate between scenarios.

Context: Methanol masers of Class I (collisionally-pumped) and Class II (radiatively-pumped) have been studied in great detail in our Galaxy in a variety of astrophysical environments such as shocks and star-forming regions and are helpful to analyze the properties of the dense interstellar medium. However, the study of methanol masers in external galaxies is still in its infancy. Aims: Our main goal is to search for methanol masers in the central molecular zone (CMZ; inner 500 pc) of the nearby starburst galaxy NGC 253. Methods: Covering a frequency range between 84 and 373 GHz ($\lambda$ = 3.6 to 0.8 mm) at high angular (1.6"$\sim$27 pc) and spectral ($\sim$8--9 km s$^{-1}$) resolution with the ALMA large program ALCHEMI, we have probed different regions across the CMZ of NGC 253. In order to look for methanol maser candidates, we employed the rotation diagram method and a set of radiative transfer models. Results: We detect for the first time masers above 84 GHz in NGC 253, covering an ample portion of the $J_{-1}\rightarrow(J-$ 1)$_{0}-E$ line series (at 84, 132, 229, and 278 GHz) and the $J_{0}\rightarrow(J-$ 1)$_{1}-A$ series (at 95, 146, and 198 GHz). This confirms the presence of the Class I maser line at 84 GHz, already reported but now being detected in more than one location. For the $J_{-1}\rightarrow(J-$ 1)$_{0}-E$ line series, we observe a lack of Class I maser candidates in the central star-forming disk. Conclusions: The physical conditions for maser excitation in the $J_{-1}\rightarrow(J-$ 1)$_{0}-E$ line series can be weak shocks and cloud-cloud collisions as suggested by shock tracers (SiO and HNCO) in bi-symmetric shock/active regions located in the outskirts of the CMZ. On the other hand, the presence of photodissociation regions due to a high star-formation rate would be needed to explain the lack of Class I masers in the very central regions., Comment: Accepted for publication in A&A. 29 pages, 17 figures (4 in Appendix)

Phosphorus (P) is a crucial element for life given its central role in several biomolecules. P-bearing molecules have been discovered in different regions of the Milky Way, but not yet towards an extragalactic environment. We have searched for P-bearing molecules towards the nearby starburst Galaxy NGC 253. Using observations from the ALMA Comprehensive High-resolution Extragalactic Molecular Inventory (ALCHEMI) project, we used the MADCUBA package to model the emission of P-bearing molecules assuming Local Thermodynamic Equilibrium (LTE) conditions. We have also performed a non-LTE analysis using SpectralRadex. We report the detection of a P-bearing molecule, phosphorus nitride (PN), for the first time in an extragalactic environment, towards two giant molecular clouds (GMCs) of NGC 253. The LTE analysis yields total PN beam-averaged column densities $N$=(1.20$\pm$0.09)$\times$10$^{13}$ cm$^{-2}$ and $N$=(6.5$\pm$1.6)$\times$10$^{12}$ cm$^{-2}$, which translate into abundances with respect to H$_2$ of $\chi$=(8.0$\pm$1.0)$\times$10$^{-12}$ and $\chi$=(4.4$\pm$1.2)$\times$10$^{-12}$. We derived a low excitation temperature of $T_{\rm ex}$=(4.4$\pm$1.3) K towards the GMC with the brightest PN emission, which indicates that PN is sub-thermally excited. The non-LTE analysis results in column densities consistent with the LTE values. We have also searched for other P-bearing molecules (PO, PH$_{3}$, CP and CCP), and upper limits were derived. The derived PO/PN ratios are $<$1.3 and $<$1.7. The abundance ratio between PN and the shock-tracer SiO derived towards NGC 253 follows the same trend previously found towards Galactic sources. Comparison of the observations with chemical models indicates that the derived molecular abundances of PN in NGC 253 can be explained by shock-driven chemistry followed by cosmic-ray-driven photochemistry., Comment: 14 pages, 14 figures, 4 tables. Accepted for publication in A&A

We used the Atacama Large Millimeter/submillimeter Array (ALMA), covering a nearly contiguous 289 GHz frequency range between 84.2 and 373.2 GHz, to image the continuum and spectral line emission at 1.6\arcsec ($\sim 28$ pc) resolution down to a sensitivity of $30-50$ mK. This article describes the ALMA Comprehensive High-resolution Extragalactic Molecular Inventory (ALCHEMI) Large Program. We focus on the analysis of the spectra extracted from the $15''$ ($\sim255$ pc) resolution ALMA Compact Array data. We model the molecular emission assuming local thermodynamic equilibrium with 78 species detected. Additionally, multiple hydrogen and helium recombination lines are identified. Spectral lines contribute 5 to 36\% of the total emission in frequency bins of 50 GHz. We report the first extragalactic detections of C$_2$H$_5$OH, HOCN, HC$_3$HO, and several rare isotopologues. Isotopic ratios of carbon, oxygen, sulfur, nitrogen and silicon were measure with multiple species. Infrared pumped vibrationaly excited HCN, HNC, and HC$_3$N emission, originating in massive star formation locations, is clearly detected at low resolution, while we do not detect it for HCO$^+$. We suggest high temperature conditions in these regions driving a seemingly "carbon-rich" chemistry which may also explain the observed high abundance of organic species close to those in Galactic hot cores. The $L_{vib}/L_{IR}$ ratio is used as a proxy to estimate a $3\%$ contribution from proto super star cluster to the global infrared emission. Measured isotopic ratios with high dipole moment species agree with those within the central kiloparsec of the Galaxy, while those derived from $\rm^{13}C^{18}O$ are a factor of 5 larger, confirming the existence of multiple ISM components within NGC 253 with different degrees of nucleosynthesis enrichment. ALCHEMI provides a template for early Universe galaxies., Comment: 60 pages, 32 figures, 15 tables, Accepted for publication at A&A

Observations of chemical species can provide an insight into the physical conditions of the emitting gas but it is important to understand how their abundances and excitation vary within different heating environments. C$_2$H is a molecule typically found in PDR regions of our own Galaxy but there is evidence to suggest it also traces other regions undergoing energetic processing in extragalactic environments. As part of the ALCHEMI ALMA large program, the emission of C$_2$H in the central molecular zone of the nearby starburst galaxy NGC 253 was mapped at 1.6 " (28 pc) resolution and characterized to understand its chemical origins. Spectral modelling of the N=1-0 through N=4-3 rotational transitions of C$_2$H was used to derive the C$_2$H column densities towards the dense clouds in NGC 253. Chemical modelling, including PDR, dense cloud, and shock models were then used to investigate the chemical processes and physical conditions that are producing the molecular emission. We find high C$_2$H column densities of $\sim 10^{15} cm^{-3}$ detected towards the dense regions of NGC 253. We further find that these column densities cannot be reproduced by assuming that the emission arises from the PDR regions at the edge of the clouds. Instead, we find that the C$_2$H abundance remains high even in the high visual extinction interior of these clouds and that this is most likely caused by a high cosmic-ray ionization rate., Comment: 18 pages, 13 figures, accepted for publication in A&A

Some luminous and ultraluminous infrared galaxies (LIRGs and ULIRGs) host extremely compact and dusty nuclei. The intense infrared radiation arising from warm dust in these sources is prone to excite vibrational levels of molecules such as HCN. This results in emission from the rotational transitions of vibrationally excited HCN (HCN-vib), with the brightest emission found in compact obscured nuclei (CONs). We aim to establish how common CONs are in the local Universe, and whether their prevalence depends on the luminosity or other properties of the host galaxy. We have conducted an Atacama Large Millimeter/submillimeter Array (ALMA) survey of the rotational J=3-2 transition of HCN-vib in a sample of 46 far-infrared luminous galaxies. Compact obscured nuclei are identified in 38 percent of ULIRGs, 21 percent of LIRGs, and 0 percent of lower luminosity galaxies. We find no dependence on the inclination of the host galaxy, but strong evidence of lower IRAS 25 to 60 {\mu}m flux density ratios (f25/f60) in CONs compared to the rest of the sample. Furthermore, we find that CONs have stronger silicate features (s9.7{\mu}m) but similar PAH equivalent widths (EQW6.2{\mu}m) compared to other galaxies. In the local Universe, CONs are primarily found in (U)LIRGs. High resolution continuum observations of the individual nuclei are required to determine if the CON phenomenon is related to the inclinations of the nuclear disks. The lower f25/f60 ratios in CONs as well as the results for the mid-infrared diagnostics investigated are consistent with large dust columns shifting the nuclear radiation to longer wavelengths, making the mid- and far-infrared "photospheres" significantly cooler than the interior regions. To assess the importance of CONs in the context of galaxy evolution, it is necessary to extend this study to higher redshifts where (U)LIRGs are more common., Comment: 16 pages, 11 figures, Accepted for publication in Astronomy and Astrophysics

Submillimetre and millimetre observations are important in probing the properties of the molecular gas and dust around obscured active galactic nuclei (AGNs) and their feedback. With very high-resolution (0."02x0."03 (2x3 pc)) ALMA 345 GHz observations of CO 3-2, HCO$^+$ 4-3, HCN 4-3 $\nu_2$=1$f$, and continuum we have studied the molecular outflow and nucleus of the extremely radio-quiet lenticular galaxy NGC1377. The outflow is resolved, revealing a 150 pc long, clumpy, high-velocity, collimated molecular jet. The molecular emission is emerging from the spine of the jet with an average diameter of 3-7 pc. A narrow-angle, rotating molecular wind surrounds the jet and is enveloped by a larger-scale, slower CO-emitting structure. The jet and narrow wind are turbulent ($\sigma>$40 kms$^{-1}$) and have steep radial gas excitation gradients. The jet shows velocity reversals that we propose are caused by precession, or episodic directional changes. We suggest that an important process powering the outflow is magneto-centrifugal driving. In contrast, the large-scale CO-envelope may be a slow wind, or cocoon that stems from jet-wind interactions. An asymmetric, nuclear r$\sim$2 pc and hot (>180 K) dust structure with a high molecular column density, N(H$_2$)$\sim1.8 \times 10^{24}$ cm$^{-2}$, is detected in continuum and vibrationally excited HCN. Its luminosity is likely powered by a buried AGN. The mass of the supermassive black hole (SMBH) is estimated to $\sim9\times10^6$ M$_\odot$ and the SMBH of NGC1377 appears to be at the end of an intense phase of accretion. The nuclear growth may be fuelled by low-angular momentum gas inflowing from gas ejected in the molecular jet and wind. Such a feedback-loop of cyclic accretion and outflows would be an effective process in growing the nuclear SMBH. This result invites new questions as to SMBH growth processes in obscured, dusty galaxies., Comment: 16 pages, 12 figures, accepted for publication in Astronomy and Astrophysics. Updated affiliations, added reference

We present spatial variations of the CO J=2-1/1-0 line ratio in M83 using Total Power array data from ALMA. While the intensities of these two lines correlate tightly, the ratio varies over the disk, with a disk average ratio of 0.69, and shows the galactic center and a two-arm spiral pattern. It is high (>0.7) in regions of high molecular gas surface density, but ranges from low to high ratios in regions of low surface density. The ratio correlates well with the spatial distributions and intensities of FUV and IR emissions, with FUV being the best correlated. It also correlates better with the ratio of IR intensities (70/350mic), a proxy for dust temperature, than with the IR intensities. Taken together, these results suggest either a direct or indirect link between the dust heating by the interstellar radiation field and the condition of GMCs, even though no efficient mechanism is known for a thermal coupling of dust and bulk gas in GMCs., Comment: Accepted for ApJ Letters

We investigate neutralization processes (especially thermal surface neutralization), which are required for the magneto-optical trapping of radioactive atoms. A variety of neutralization methods are first summarized: neutral beam injection for fusion reactors, neutral atom implantation in semiconductor processing, and the production of radioactive neutral atoms in accelerators. We focus on thermal surface neutralization, which produces neutral atoms in the thermal energy range for laser cooling. The experiments were carried out with yttrium, gadolinium, and zirconium foils to neutralize francium and rubidium ions for magneto-optical trapping. The results reconfirm that yttrium foil is a good neutralizer (i.e., it has a neutral release efficiency $>65\%$). In addition, the release fraction when using yttrium foil exceeds 75\% at 1350 K, which is greater than the release fraction for the other foils. This reconfirmation is important because few previous studies have focused on thermal surface neutralization. Moreover, the results show that the neutralization efficiency is strongly influenced by the experimental process itself.

High-resolution (0."03 - 0."09) (9 - 26 pc)) ALMA (100 - 350 GHz (3 - 0.8 mm)) and VLA 45 GHz measurements have been used to image continuum and spectral line emission from the inner region of the nearby infrared luminous galaxy IC 860. We detect compact (r=8-10 pc), luminous, mm continuum emission in the core of IC 860, with brightness temperatures $T_{\rm B}>$ 280 K. The 45 GHz continuum is equally compact, but fainter in flux. We suggest that the 3 to 0.8 mm continuum is opaque at mm-wavelengths, implying a very large H$_2$ column density $N$(H$_2$) of 1e26 cm-2, and that it emerges from hot dust with temperature $T_{\rm d} \sim 280$ K. Vibrationally excited lines of HCN $\nu_2$=1f J=4-3 and 3-2 (HCN-VIB) are seen in emission and resolved on scales of 40-50 pc. The HCN-VIB emission reveals a north-south nuclear velocity gradient with projected rotation velocities of v=100 kms$^{-1}$ at r=10 pc. The brightest HCN-VIB emission is oriented perpendicular to the velocity gradient. Ground state lines of HCN 3-2, 4-3, HC$^{15}$N 4-3, HCO$^+$ 3-2, 4-3 and CS 7-6, show complex line absorption and emission features. HCN and HCO$^+$ have red-shifted, reversed P-Cygni profiles consistent with gas inflows of $\sim$50 kms$^{-1}$. The absorption features can be traced from the north-east into the nucleus. In contrast, CS 7-6 shows blue-shifted line wings extending to -180 kms$^{-1}$. We suggest that a dense and slow outflow is hidden behind a foreground layer of inflowing gas. It appears that the centre of IC 860 is in a phase of rapid evolution where an inflow is building up the nuclear column density of gas. A slow, dense outflow may be signalling the onset of feedback. The inner, r=10 pc, IR luminosity can be powered by an accreting black hole and/or a compact starburst with a top-heavy initial mass function., Comment: 13 pages, 9 figures, Accepted for publication in Astronomy and Astrophysics; Language edited

The layered van der Waals antiferromagnet MnBi$_2$Te$_4$ has been predicted to combine the band ordering of archetypical topological insulators such as Bi$_2$Te$_3$ with the magnetism of Mn, making this material a viable candidate for the realization of various magnetic topological states. We have systematically investigated the surface electronic structure of MnBi$_2$Te$_4$(0001) single crystals by use of spin- and angle-resolved photoelectron spectroscopy experiments. In line with theoretical predictions, the results reveal a surface state in the bulk band gap and they provide evidence for the influence of exchange interaction and spin-orbit coupling on the surface electronic structure., Comment: Revised version

To trace chemical evolution in a prototypical starburst environment, we spatially resolve the carbon and oxygen isotope ratios across the central molecular zone (full size ~$\sim 600$ pc) in the nearby starburst galaxy NGC 253. We imaged the emission of the optically thin isotopologues $^{13}$CO, C$^{18}$O, C$^{17}$O, $^{13}$C$^{18}$O at a spatial resolution $\sim50$ pc, comparable to the typical size of giant molecular associations. Optical depth effects and contamination of $^{13}$C$^{18}$O by C$_4$H is discussed and accounted for to derive column densities. This is the first extragalactic detection of the double isotopologue $^{13}$C$^{18}$O. Derived isotopic ratios $^{12}$C/$^{13}$C$\sim21\pm6$, $^{16}$O/$^{18}$O$\sim130\pm40$, and $^{18}$O/$^{17}$O$\sim4.5\pm0.8$ differ from the generally adopted values in the nuclei of galaxies. The molecular clouds in the central region of NGC 253 show similar rare isotope enrichment to those within the central molecular zone of the Milky way. This enrichment is attributed to stellar nucleosynthesis. Measured isotopic ratios suggest an enhancement of $^{18}$O as compared to our Galactic center, which we attribute to an extra $^{18}$O injection from massive stars. Our observations show evidence for mixing of distinct gas components with different degrees of processing. We observe an extra molecular component of highly processed gas on top of the already proposed less processed gas being transported to the central region of NGC 253. Such multicomponent nature and optical depth effects may hinder the use of isotopic ratios based on spatially unresolved line to infer the star formation history and/or initial stellar mass function properties in the nuclei of galaxies., Comment: 14 pages, 9 figures, Accepted for publication in A&A

Understanding the nuclear growth and feedback processes in galaxies requires investigating their often obscured central regions. One way to do this is to use (sub)millimeter line emission from vibrationally excited HCN (HCN-vib). It has been suggested that the most intense HCN-vib emission from a galaxy is connected to a phase of nuclear growth that occurs before the nuclear feedback processes have been fully developed. We aim to investigate if there is a connection between the presence of strong HCN-vib emission and the development of feedback in (U)LIRGs. We collected literature and archival data to compare the luminosities of rotational lines of HCN-vib, normalized to the total infrared luminosity, to the median velocities of 119 {\mu}m OH absorption lines, potentially indicating outflows, in a total of 17 (U)LIRGs. The most HCN-vib luminous systems all lack signatures of significant molecular outflows in the far-infrared OH absorption lines. However, at least some of the systems with bright HCN-vib emission do have fast and collimated outflows that can be seen in spectral lines at longer wavelengths. We conclude that the galaxy nuclei with the highest L(HCN-vib)/L(IR) do not drive wide-angle outflows detectable using the median velocities of far-infrared OH absorption lines. It is possible that this is due to an orientation effect where sources which are oriented in such a way that their outflows are not along our line of sight also radiate a smaller proportion of their infrared luminosity in our direction. It could also be that massive wide-angle outflows destroy the deeply embedded regions responsible for bright HCN-vib emission, so that the two phenomena cannot coexist. This would strengthen the idea that vibrationally excited HCN traces a heavily obscured stage of evolution before nuclear feedback mechanisms are fully developed., Comment: 10 pages, 4 figures, Accepted for publication in Astronomy and Astrophysics

We report ALMA observations of CO(3-2) emission in a sample of 7 Seyfert/LINER galaxies at the unprecedented spatial resolution of 0.1'' = 4-9 pc. Our aim is to explore the close environment of AGN, and the dynamical structures leading to its fueling. The selected galaxies host low-luminosity AGN, and have a wide range of activity types, and barred or ringed morphologies. The observed maps reveal the existence of circum-nuclear disk structures, defined by their morphology and decoupled kinematics. We call these structures "molecular tori", even though they appear often as disks, without holes in the center. They have varied orientations, unaligned with their host galaxy. The radius of the tori ranges from 6 to 27 pc, and their mass from 0.7 10$^7$ to 3.9 10$^7$ Msun. At larger scale, the gas is always piled up in a few 100~pc scale resonant rings, that play the role of a reservoir to fuel the nucleus. In some cases, a trailing spiral is observed inside the ring, providing evidence for feeding processes. Most frequently, the torus and the AGN are slightly off-centered, with respect to the bar-resonant ring position, implying that the black hole is wandering by a few 10~pc amplitude around the center of mass of the galaxy. Our spatial resolution allows us to measure gas velocities inside the sphere of influence of the central black holes. By fitting the observations with different simulated cubes, varying the torus inclination and the black hole mass, it is possible to estimate the mass of the central black hole, which is in general difficult for such late-type galaxies, with only a pseudo-bulge., Comment: 20 pages, 21 figures, accepted in Astron. and Astrophys

Feedback in the form of mass outflows driven by star formation or active galactic nuclei is a key component of galaxy evolution. The luminous infrared galaxy Zw 049.057 harbours a compact obscured nucleus with a possible far-IR signature of outflowing molecular gas. Due to the high optical depths at far-IR wavelengths, the interpretation of the outflow signature is uncertain. At mm and radio wavelengths, the radiation is better able to penetrate the large columns of gas and dust. We used high resolution observations from the SMA, ALMA, and the VLA to image the CO 2-1 and 6-5 emission, the 690 GHz continuum, the radio cm continuum, and absorptions by rotationally excited OH. The CO line profiles exhibit wings extending 300 km/s beyond the systemic velocity. At cm wavelengths, we find a compact (40 pc) continuum component in the nucleus, with weaker emission extending several 100 pc approximately along the major and minor axes of the galaxy. In the OH absorption lines toward the compact continuum, wings extending to a similar velocity as for the CO are seen on the blue side of the profile. The weak cm continuum emission along the minor axis is aligned with a highly collimated, jet-like dust feature previously seen in near-IR images of the galaxy. Comparison of the apparent optical depths in the OH lines indicate that the excitation conditions in Zw 049.057 differ from those in other OH megamaser galaxies. We interpret the wings in the spectral lines as signatures of a molecular outflow. A relation between this outflow and the minor axis radio feature is possible, although further studies are required to investigate this possible association and understand the connection between the outflow and the nuclear activity. Finally, we suggest that the differing OH excitation conditions are further evidence that Zw 049.057 is in a transition phase between megamaser and kilomaser activity., Comment: 12 pages, 12 figures, Accepted for publication in Astronomy and Astrophysics

High resolution submm observations are important in probing the morphology, column density and dynamics of obscured active galactic nuclei (AGNs). With high resolution (0.06 x 0.05) ALMA 690 GHz observations we have found bright (TB >80 K) and compact (FWHM 10x7 pc) CO 6-5 line emission in the nucleus of the extremely radio-quiet galaxy NGC1377. The integrated CO 6-5 intensity is aligned with the previously discovered jet/outflow of NGC1377 and is tracing the dense (n>1e4 cm-3), hot gas at the base of the outflow. The velocity structure is complex and shifts across the jet/outflow are discussed in terms of jet-rotation or separate, overlapping kinematical components. High velocity gas (deltaV +-145 km/s) is detected inside r<2-3 pc and we suggest that it is emerging from an inclined rotating disk or torus of position angle PA=140+-20 deg with a dynamical mass of approx 3e6 Msun. This mass is consistent with that of a supermassive black hole (SMBH), as inferred from the M-sigma relation. The gas mass of the proposed disk/torus constitutes <3% of the nuclear dynamical mass. In contrast to the intense CO 6-5 line emission, we do not detect dust continuum with an upper limit of S(690GHz)<2mJy. The corresponding, 5 pc, H2 column density is estimated to N(H2)<3e23 cm-2, which is inconsistent with a Compton Thick (CT) source. We discuss the possibility that CT obscuration may be occuring on small (subparsec) or larger scales. From SED fitting we suggest that half of the IR emission of NGC1377 is nuclear and the rest (mostly the far-infrared (FIR)) is more extended. The extreme radio quietness, and the lack of emission from other star formation tracers, raise questions on the origin of the FIR emission. We discuss the possibility that it is arising from the dissipation of shocks in the molecular jet/outflow or from irradiation by the nuclear source along the poles., Comment: 7 pages, 5 figures, submitted to Astronomy and Astrophysics

Extragalactic observations of water emission can provide valuable insights into the excitation of the interstellar medium. In addition, extragalactic megamasers are powerful probes of kinematics close to active nuclei. Therefore, it is paramount to determine the true origin of the water emission, whether it is excited by processes close to an AGN or in star-forming regions. We use ALMA Band 5 science verification observations to analyse the emission of the 183 GHz water line in Arp 220 on sub-arcsecond scales, in conjunction with new ALMA Band 7 data at 325 GHz. Specifically, the nature of the process leading to the excitation of emission at these water lines is studied in this context. Supplementary 22 GHz VLA observations are used to better constrain the parameter space in the excitation modelling of the water lines. We detect 183 GHz H2O and 325 GHz water emission towards the two compact nuclei at the center of Arp 220, being brighter in Arp 220 West. The emission at these two frequencies is compared to previous single-dish data and does not show evidence of variability. The 183 and 325 GHz lines show similar spectra and kinematics, but the 22 GHz profile is significantly different in both nuclei due to a blend with an NH3 absorption line. Our findings suggest that the most likely scenario to cause the observed water emission in Arp 220 is a large number of independent masers originating from numerous star-forming regions., Comment: 10 pages, 7 figures, 3 tables, accepted for publication in A&A

We present new ALMA Band 7 ($\sim340$ GHz) observations of the dense gas tracers HCN, HCO$^+$, and CS in the local, single-nucleus, ultraluminous infrared galaxy IRAS 13120-5453. We find centrally enhanced HCN (4-3) emission, relative to HCO$^+$ (4-3), but do not find evidence for radiative pumping of HCN. Considering the size of the starburst (0.5 kpc) and the estimated supernovae rate of $\sim1.2$ yr$^{-1}$, the high HCN/HCO$^+$ ratio can be explained by an enhanced HCN abundance as a result of mechanical heating by the supernovae, though the active galactic nucleus and winds may also contribute additional mechanical heating. The starburst size implies a high $\Sigma_{IR}$ of $4.7\times10^{12}$ $L_{\odot}$ kpc$^{-2}$, slightly below predictions of radiation-pressure limited starbursts. The HCN line profile has low-level wings, which we tentatively interpret as evidence for outflowing dense molecular gas. However, the dense molecular outflow seen in the HCN line wings is unlikely to escape the galaxy and is destined to return to the nucleus and fuel future star formation. We also present modeling of Herschel observations of the H$_2$O lines and find a nuclear dust temperature of $\sim40$ K. IRAS 13120-5453 has a lower dust temperature and $\Sigma_{IR}$ than is inferred for the systems termed "compact obscured nuclei" (such as Arp 220 and Mrk 231). If IRAS 13120-5453 has undergone a compact obscured nucleus phase, we are likely witnessing it at a time when the feedback has already inflated the nuclear ISM and diluted star formation in the starburst/AGN core., Comment: accepted for publication in ApJ, 21 pages, 11 figures

The classical Johnson-Mehl-Avrami-Kolmogorov approach for nucleation and growth models of diffusive phase transitions is revisited and applied to model the growth of ferrite in multiphase steels. For the prediction of mechanical properties of such steels, a deeper knowledge of the grain structure is essential. To this end, a Fokker-Planck evolution law for the volume distribution of ferrite grains is developed and shown to exhibit a log-normally distributed solution. Numerical parameter studies are given and confirm expected properties qualitatively. As a preparation for future work on parameter identification, a strategy is presented for the comparison of volume distributions with area distributions experimentally gained from polished micrograph sections., Comment: 16 pages, 19 figures

We demonstrated a frequency offset locking between two laser sources using a waveguide-type electro-optic modulator (EOM) with 10th-order sidebands for magneto-optical trapping of Fr atoms. The frequency locking error signal was successfully obtained by performing delayed self-homodyne detection of the beat signal between the repumping frequency and the 10th-order sideband component of the trapping light. Sweeping the trapping-light and repumping-light frequencies with keeping its frequency difference of 46 GHz was confirmed over 1 GHz by monitoring the Doppler absorption profile of I2. This technique enables us to search for a resonance frequency of magneto-optical trapping of Fr., Comment: 6 pages, 6 figures

We explore the potential of imaging vibrationally excited molecular emission at high angular resolution to better understand the morphology and physical structure of the dense gas in Arp~220 and to gain insight into the nature of the nuclear powering sources. Vibrationally excited emission of HCN is detected in both nuclei with a very high ratio relative to the total $L_{FIR}$, higher than in any other observed galaxy and well above what is observed in Galactic hot cores. HCN $v_2=1f$ is observed to be marginally resolved in $\sim60\times50$~pc regions inside the dusty $\sim100$~pc sized nuclear cores. Its emission is centered on our derived individual nuclear velocities based on HCO$^+$ emission ($V_{WN}=5342\pm4$ and $V_{EN}=5454\pm8$~\kms, for the western and eastern nucleus, respectively). With virial masses within $r\sim25-30$~pc based on the HCN~$v_2=1f$ line widths, we estimate gas surface densities (gas fraction $f_g=0.1$) of $3\pm0.3\times10^4~M_\odot~\rm pc^{-2}$ (WN) and $1.1\pm0.1\times10^4~M_\odot~\rm pc^{-2}$ (EN). The $4-3/3-2$ flux density ratio could be consistent with optically thick emission, which would further constrain the size of the emitting region to $>15$~pc (EN) and $>22$~pc (WN). The absorption systems that may hide up to $70\%$ of the HCN and HCO$^+$ emission are found at velocities of $-50$~\kms~(EN) and $6$, $-140$, and $-575$~\kms (WN) relative to velocities of the nuclei. Blueshifted absorptions are the evidence of outflowing motions from both nuclei. The bright vibrational emission implies the existence of a hot dust region radiatively pumping these transitions. We find evidence of a strong temperature gradient that would be responsible for both the HCN $v_2$ pumping and the absorbed profiles from the vibrational ground state as a result of both continuum and self-absorption by cooler foreground gas., Comment: 14 pages accepted for publication in A&A

With high resolution (0."25 x 0."18) ALMA CO 3-2 observations of the nearby (D=21 Mpc, 1"=102 pc), extremely radio-quiet galaxy NGC1377, we have discovered a high-velocity, very collimated nuclear outflow which we interpret as a molecular jet with a projected length of +-150 pc. Along the jet axis we find strong velocity reversals where the projected velocity swings from -150 km/s to +150 km/s. A simple model of a molecular jet precessing around an axis close to the plane of the sky can reproduce the observations. The velocity of the outflowing gas is difficult to constrain due to the velocity reversals but we estimate it to be between 240 and 850 km/s and the jet to precess with a period P=0.3-1.1 Myr. The CO emission is clumpy along the jet and the total molecular mass in the high-velocity (+-(60 to 150 km/s)) gas lies between 2e6 Msun (light jet) and 2e7 Msun (massive jet). There is also CO emission extending along the minor axis of NGC1377. It holds >40% of the flux in NGC1377 and may be a slower, wide-angle molecular outflow which is partially entrained by the molecular jet. We discuss the driving mechanism of the molecular jet and suggest that it is either powered by a very faint radio jet or by an accretion disk-wind similar to those found towards protostars. The nucleus of NGC1377 harbours intense embedded activity and we detect emission from vibrationally excited HCN J=4-3 v_2=1f which is consistent with hot gas and dust. We find large columns of H2 in the centre of NGC1377 which may be a sign of a high rate of recent gas infall. The dynamical age of the molecular jet is short (<1 Myr), which could imply that it is young and consistent with the notion that NGC1377 is caught in a transient phase of its evolution. However, further studies are required to determine the age of the molecular jet, its mass and the role it is playing in the growth of the nucleus of NGC1377., Comment: This is a revised and expanded version of a previous submission which now has 13 pages, 6 figures (+ 4 in the Appendix) and is accepted for publication in Astronomy & Astrophysics

We obtained an ALMA Cycle 0 spectral scan of the dusty LIRG NGC 4418, spanning a total of 70.7 GHz in bands 3, 6, and 7. We use a combined local thermal equilibrium (LTE) and non-LTE (NLTE) fit of the spectrum in order to identify the molecular species and derive column densities and excitation temperatures. We derive molecular abundances and compare them with other Galactic and extragalactic sources by means of a principal component analysis. We detect 317 emission lines from a total of 45 molecular species, including 15 isotopic substitutions and six vibrationally excited variants. Our LTE/NLTE fit find kinetic temperatures from 20 to 350 K, and densities between 10$^5$ and 10$^7$ cm$^{-3}$. The spectrum is dominated by vibrationally excited HC$_3$N, HCN, and HNC, with vibrational temperatures from 300 to 450 K. We find high abundances of HC$_3$N, SiO, H$_2$S, and c-HCCCH and a low CH$_3$OH abundance. A principal component analysis shows that NGC 4418 and Arp 220 share very similar molecular abundances and excitation, which clearly set them apart from other Galactic and extragalactic environments. The similar molecular abundances observed towards NCG 4418 and Arp 220 are consistent with a hot gas-phase chemistry, with the relative abundances of SiO and CH$_3$OH being regulated by shocks and X-ray driven dissociation. The bright emission from vibrationally excited species confirms the presence of a compact IR source, with an effective diameter $<$5 pc and brightness temperatures $>$350 K. The molecular abundances and the vibrationally excited spectrum are consistent with a young AGN/starburst system. We suggest that NGC 4418 may be a template for a new kind of chemistry and excitation, typical of compact obscured nuclei (CON). Because of the narrow line widths and bright molecular emission, NGC 4418 is the ideal target for further studies of the chemistry in CONs., Comment: accepted by A&A on 29/06/2015

We present high resolution (0."4) IRAM PdBI and ALMA mm and submm observations of the (ultra) luminous infrared galaxies ((U)LIRGs) IRAS17208-0014, Arp220, IC860 and Zw049.057 that reveal intense line emission from vibrationally excited ($\nu_2$=1) J=3-2 and 4-3 HCN. The emission is emerging from buried, compact (r<17-70 pc) nuclei that have very high implied mid-infrared surface brightness $>$$5\times 10^{13}$ L$_{\odot}$ kpc$^{-2}$. These nuclei are likely powered by accreting supermassive black holes (SMBHs) and/or hot (>200 K) extreme starbursts. Vibrational, $\nu_2$=1, lines of HCN are excited by intense 14 micron mid-infrared emission and are excellent probes of the dynamics, masses, and physical conditions of (U)LIRG nuclei when H$_2$ column densities exceed $10^{24}$ cm$^{-2}$. It is clear that these lines open up a new interesting avenue to gain access to the most obscured AGNs and starbursts. Vibrationally excited HCN acts as a proxy for the absorbed mid-infrared emission from the embedded nuclei, which allows for reconstruction of the intrinsic, hotter dust SED. In contrast, we show strong evidence that the ground vibrational state ($\nu$=0), J=3-2 and 4-3 rotational lines of HCN and HCO$^+$ fail to probe the highly enshrouded, compact nuclear regions owing to strong self- and continuum absorption. The HCN and HCO$^+$ line profiles are double-peaked because of the absorption and show evidence of non-circular motions - possibly in the form of in- or outflows. Detections of vibrationally excited HCN in external galaxies are so far limited to ULIRGs and early-type spiral LIRGs, and we discuss possible causes for this. We tentatively suggest that the peak of vibrationally excited HCN emission is connected to a rapid stage of nuclear growth, before the phase of strong feedback., Comment: 13 pages, 7 figures, accepted for publication in Astronomy and Astrophysics

The aim of this study is to constrain the dynamics, structure and feeding of the compact nucleous of NGC4418, and to reveal the nature of the main hidden power source: starburst or AGN. We obtained high spatial resolution observations of NGC4418 at 1.4 and 5 GHz with MERLIN, and at 230 and 270 GHz with the SMA very extended configuration. We use the continuum morphology and flux density to estimate the size of the emitting region, the star formation rate and the dust temperature. Emission lines are used to study the kinematics through position-velocity diagrams. Molecular emission is studied with population diagrams and by fitting an LTE synthetic spectrum. We detect bright 1mm line emission from CO, HC3N, HNC and C34S, 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 HC3N and HNC, with Tvib 300K. 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 1e4 Msun pc-2 is extremely high, and similar to that found in the ultra-luminous infrared galaxy (ULIRG) Arp220. Our observations confirm the the presence of a molecular and atomic in-flow, previously suggested by Herschel observations, which is feeding the activity in the center of NGC4418. 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 Arp220, with an age of 3-10 Myr and a star formation rate >10 Msun yr-1. If an AGN is present, it must be extremely Compton-thick., Comment: 18 pages, 11 figures, Accepted for publication by A&A on 10/6/2013

We use high (0."65 x 0."52,(65x52pc)) resolution SubMillimeter Array (SMA) observations to image the CO and 13CO 2-1 line emission of the extreme FIR-excess galaxy NGC 1377. We find bright, complex CO 2-1 line emission in the inner 400 pc of the galaxy. The CO 2-1 line has wings that are tracing a kinematical component which appears perpendicular to that of 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(H2)>1e7 Msun and dM/dt>8 Msun/yr. The age of the proposed outflow is estimated to 1.4Myrs, the extent to 200pc and the outflow speed to 140 km/s. The total molecular mass in the SMA map is estimated to M_tot(H2)=1.5e8 Msun (on a scale of 400 pc) while in the inner r=29 pc the molecular mass is M_core(H2)=1.7e7 Msun with a corresponding H2 column density of N(H2)=3.4e23 cm-2 and an average CO 2-1 brightness temperature of 19K. 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 Myrs. 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 AGN or an extremely young (1Myr) compact starburst. Limitations on size and mass lead us to favour the AGN scenario, but further studies are required to settle the issue. In either case, the wind with its implied mass outflow rate will quench the nuclear power source within a very short time of 5-25 Myrs. It is however possible that the gas is unable to escape the galaxy and may eventually fall back onto NGC 1377 again., Comment: 10 pages, 7 figures, accepted for publication in Astronomy & Astrophysics

We report on atomic gas (HI) and molecular gas (as traced by CO(2-1)) redshifted absorption features toward the nuclear regions of the closest powerful radio galaxy, Centaurus A (NGC 5128). Our HI observations using the Very Long Baseline Array allow us to discern with unprecedented sub-parsec resolution HI absorption profiles toward different positions along the 21 cm continuum jet emission in the inner 0."3 (or 5.4 pc). In addition, our CO(2-1) data obtained with the Submillimeter Array probe the bulk of the absorbing molecular gas with little contamination by emission, not possible with previous CO single-dish observations. We shed light with these data on the physical properties of the gas in the line of sight, emphasizing the still open debate about the nature of the gas that produces the broad absorption line (~55 km/s). First, the broad H I line is more prominent toward the central and brightest 21 cm continuum component than toward a region along the jet at a distance ~ 20 mas (or 0.4 pc) further from it. This suggests that the broad absorption line arises from gas located close to the nucleus, rather than from diffuse and more distant gas. Second, the different velocity components detected in the CO(2-1) absorption spectrum match well other molecular lines, such as those of HCO+(1-0), except the broad absorption line that is detected in HCO+(1-0) (and most likely related to that of the H I). Dissociation of molecular hydrogen due to the AGN seems to be efficient at distances <= 10 pc, which might contribute to the depth of the broad H I and molecular lines., Comment: 17 pages, 9 figures, accepted for publication in ApJ