arXiv subjects

Christian Henkel

Publications and source records attributed to Christian Henkel.

At least 55 records · Page 3Linked to original sources

arXiv2022

Deuterated molecules in regions of high-mass star formation

We present the results of our studies of deuterated molecules (DCN, DNC, DCO$^+$, N$_2$D$^+$ and NH$_2$D) in regions of high-mass star formation, which include a survey of such regions with the 20-m Onsala radio telescope and mapping of several objects in various lines with the 30-m IRAM and 100-m MPIfR radio telescopes. The deuteration degree reaches $\sim$10$^{-2}$ in these objects. We discuss its dependencies on the gas temperature and velocity dispersion, as well as spatial distributions of deuterated molecules. We show that the H$^{13}$CN/HN$^{13}$C intensity ratio may be a good indicator of the gas kinetic temperature and estimate densities of the investigated objects.

astro-ph.GA↗

arXiv2022

ALCHEMI finds a "shocking" carbon footprint in the starburst galaxy NGC~253

Centers of starburst galaxies may be characterized by a specific gas and ice chemistry due to their gas dynamics and the presence of various ice desorption mechanisms. This may result in a peculiar observable composition. We analyze abundances of $CO_2$, a reliable tracer of ice chemistry, from data collected as part of the ALMA large program ALCHEMI, a wide-frequency spectral scan toward the starburst galaxy NGC~253 with an angular resolution of 1.6$''$. We constrain the $CO_2$ abundances in the gas phase using its protonated form $HOCO^+$. The distribution of $HOCO^+$ is similar to that of methanol, which suggests that $HOCO^+$ is indeed produced from the protonation of $CO_2$ sublimated from ice. The $HOCO^+$ fractional abundances are found to be $(1-2)\times10^{-9}$ at the outer part of the central molecular zone (CMZ), while they are lower ($\sim10^{-10}$) near the kinematic center. This peak fractional abundance at the outer CMZ is comparable to that in the Milky Way CMZ, and orders of magnitude higher than that in Galactic disk star-forming regions. From the range of $HOCO^+/CO_2$ ratios suggested from chemical models, the gas-phase $CO_2$ fractional abundance is estimated to be $(1-20)\times10^{-7}$ at the outer CMZ, and orders of magnitude lower near the center. We estimate the $CO_2$ ice fractional abundances at the outer CMZ to be $(2-5)\times10^{-6}$ from the literature. A comparison between the ice and gas $CO_2$ abundances suggests an efficient sublimation mechanism. This sublimation is attributed to large-scale shocks at the orbital intersections of the bar and CMZ.

astro-ph.GA↗

arXiv2022

ALMA imaging of the cold molecular and dusty disk in the type 2 active nucleus of the Circinus galaxy

We aim to shed light on the physical properties and kinematics of the molecular material in the nucleus of one of the closest type 2 active galaxies. To this end, we obtained high angular resolution ALMA observations of the nucleus of the Circinus galaxy. The observations map the emission at 350GHz and 690GHz with spatial resolutions of ~3.8pc and ~2.2pc, respectively. The continuum emission traces cold ($T\lesssim100$K) dust in a circumnuclear disk with spiral arms on scales of 25pc, plus a marginally resolved nuclear emission peak. The latter is not extended in polar direction as claimed based on earlier ALMA observations. A significant amount (of the order of 40%) of the 350GHz emission is not related to dust, but most likely free-free emission instead. We detect CO(3-2) and CO(6-5) as well as HCO$^+$(4-3), HCN(4-3), and CS(4-3). The CO emission is extended, showing a spiral pattern, similar to the extended dust emission. Towards the nucleus, CO is excited to higher transitions and its emission is self-absorbed, leading to an apparent hole in the CO(3-2) but not the CO(6-5) emission. On the other hand, the high gas density tracers HCO$^+$, HCN, and CS show a strong, yet unresolved (($\lesssim4$pc) concentration of the emission at the nucleus, pointing at a very small 'torus'. The kinematics are dominated by rotation and point at a geometrically thin disk down to the resolution limit of our observations. In contrast to several other AGNs, no HCN enhancement is found towards the nucleus. The Circinus nucleus is therefore composed of at least two distinct components: (1) an optically thin, warm outflow of ionised gas containing clouds of dust; and (2) a cold molecular and dusty disk. These findings support the most recent radiative transfer calculations of the obscuring structures in AGNs, which find a similar two-component structure. (Abridged)

astro-ph.GA↗

arXiv2022

Energizing Star Formation: The Cosmic Ray Ionization Rate in NGC 253 Derived From ALCHEMI Measurements of H$_3$O$^+$ and SO

The cosmic ray ionization rate (CRIR) is a key parameter in understanding the physical and chemical processes in the interstellar medium. Cosmic rays are a significant source of energy in star formation regions, which impacts the physical and chemical processes which drive the formation of stars. Previous studies of the circum-molecular zone (CMZ) of the starburst galaxy NGC 253 have found evidence for a high CRIR value; $10^3-10^6$ times the average cosmic ray ionization rate within the Milky Way. This is a broad constraint and one goal of this study is to determine this value with much higher precision. We exploit ALMA observations towards the central molecular zone of NGC 253 to measure the CRIR. We first demonstrate that the abundance ratio of H$_3$O$^+$ and SO is strongly sensitive to the CRIR. We then combine chemical and radiative transfer models with nested sampling to infer the gas properties and CRIR of several star-forming regions in NGC 253 due to emission from their transitions. We find that each of the four regions modelled has a CRIR in the range $(1-80)\times10^{-14}$ s$^{-1}$ and that this result adequately fits the abundances of other species that are believed to be sensitive to cosmic rays including C$_2$H, HCO$^+$, HOC$^+$, and CO. From shock and PDR/XDR models, we further find that neither UV/X-ray driven nor shock dominated chemistry are a viable single alternative as none of these processes can adequately fit the abundances of all of these species.

astro-ph.GA↗

arXiv2022

The Interstellar Medium of Dwarf Galaxies

Dwarf galaxies are by far the most numerous galaxies in the Universe, showing properties that are quite different from those of their larger and more luminous cousins. This review focuses on the physical and chemical properties of the interstellar medium of those dwarfs that are known to host significant amounts of gas and dust. The neutral and ionized gas components and the impact of the dust will be discussed, as well as first indications for the existence of active nuclei in these sources. Cosmological implications are also addressed, considering the primordial helium abundance and the similarity of local Green Pea galaxies with young, sometimes proto-galactic sources in the early Universe.

astro-ph.GA↗

arXiv2021

HI mapping of the Leo Triplet: Morphologies and kinematics of tails and bridges

A fully-sampled and hitherto highest resolution and sensitivity observation of neutral hydrogen (HI) in the Leo Triplet (NGC 3628, M 65/NGC 3623, and M 66/NGC 3627) reveals six HI structures beyond the three galaxies. We present detailed results of the morphologies and kinematics of these structures, which can be used for future simulations. In particular, we detect a two-arm structure in the plume of NGC 3628 for the first time, which can be explained by a tidal interaction model. The optical counterpart of the plume is mainly associated with the southern arm. The connecting part (base) of the plume (directed eastwards) with NGC 3628 is located at the blueshifted (western) side of NGC 3628. Two bases appear to be associated with the two arms of the plume. A clump with reversed velocity gradient (relative to the velocity gradient of M 66) and a newly detected tail, i.e. M 66SE, is found in the southeast of M 66. We suspect that M 66SE represents gas from NGC 3628 which was captured by M 66 in the recent interaction between the two galaxies. Meanwhile gas is falling toward M 66, resulting in features already previously observed in the southeastern part of M 66, e.g. large line widths and double peaks. An upside-down `Y'-shaped HI gas component (M 65S) is detected in the south of M 65 which suggests that M 65 may also have been involved in the interaction. We strongly encourage modern hydrodynamical simulations of this interacting group of galaxies to reveal the origin of the gaseous debris surrounding all three galaxies.

astro-ph.GA↗

arXiv2021

Starburst Energy Feedback Seen Through HCO$^+$/HOC$^+$ Emission in NGC 253 from ALCHEMI

Molecular abundances are sensitive to UV-photon flux and cosmic-ray ionization rate. In starburst environments, the effects of high-energy photons and particles are expected to be stronger. We examine these astrochemical signatures through multiple transitions of HCO$^+$ and its metastable isomer HOC$^+$ in the center of the starburst galaxy NGC 253 using data from the ALMA large program ALCHEMI. The distribution of the HOC$^+$(1-0) integrated intensity shows its association with "superbubbles", cavities created either by supernovae or expanding HII regions. The observed HCO$^+$/HOC$^+$ abundance ratios are $\sim 10-150$, and the fractional abundance of HOC$^+$ relative to H$_2$ is $\sim 1.5\times 10^{-11} - 6\times 10^{-10}$, which implies that the HOC$^+$ abundance in the center of NGC 253 is significantly higher than in quiescent spiral-arm dark clouds in the Galaxy and the Galactic center clouds. Comparison with chemical models implies either an interstellar radiation field of $G_0\gtrsim 10^3$ if the maximum visual extinction is $\gtrsim 5$, or a cosmic-ray ionization rate of $ζ\gtrsim 10^{-14}$ s$^{-1}$ (3-4 orders of magnitude higher than that within clouds in the Galactic spiral-arms) to reproduce the observed results. From the difference in formation routes of HOC$^+$, we propose that a low-excitation line of HOC$^+$ traces cosmic-ray dominated regions, while high-excitation lines trace photodissociation regions. Our results suggest that the interstellar medium in the center of NGC 253 is significantly affected by energy input from UV-photons and cosmic rays, sources of energy feedback.

astro-ph.GA↗

arXiv2020

Extended HNCO, SiO, and HC$_{3}$N emission in 43 southern star-forming regions

We have selected 43 southern massive star-forming regions to study the spatial distribution of HNCO 4$_{04}$-3$_{03}$, SiO 2-1 and HC$_{3}$N 10-9 line emission and to investigate their spatial association with the dust emission. The morphology of HNCO 4$_{04}$-3$_{03}$ and HC$_{3}$N 10-9 agrees well with the dust emission. HC$_{3}$N 10-9 tends to originate from more compact regions than HNCO 4$_{04}$-3$_{03}$ and SiO 2-1. We divided our sources into three groups: those in the Central Molecular Zone (CMZ), those associated with bubbles (Bubble), and the remaining sources, which are termed 'normal star forming regions' (NMSFR). These three groups, subdivided into three different categories with respect to line widths, integrated intensities, and column densities, hint at the presence of different physical and chemical processes. We find that the dust temperature $T_{\rm d}$, and the abundance ratios of $N_{\rm HNCO}/N_{\rm SiO}$ and $N_{\rm HNCO}/N_{\rm HC3N}$ show a decreasing trend towards the central dense regions of CMZ sources, while $N_{\rm HC3N}/N_{\rm SiO}$ moves into the opposite direction. Moreover, a better agreement is found between $T_{\rm d}$ and $N_{\rm HC3N}/N_{\rm SiO}$ in Bubble and NMSFR category sources. Both outflow and inflow activities have been found in eight of the sixteen bubble and NMSFR sources. The low outflow detection rate indicates that in these sources the SiO 2-1 line wing emission is either below our sensitivity limit or that the bulk of the SiO emission may be produced by the expansion of an H{\sc\,ii} region or supernova remnant, which has pushed molecular gas away forming a shock and yielding SiO.

astro-ph.GA↗

arXiv2020

Ammonia observations towards the Aquila Rift cloud complex

We surveyed the Aquila Rift complex including the Serpens South and W40 region in the NH$_3$(1,1) and (2,2) transitions making use of the Nanshan 26-m telescope. The kinetic temperatures of the dense gas in the Aquila Rift complex range from 8.9 to 35.0K with an average of 15.3$\pm$6.1K. Low gas temperatures associate with Serpens South ranging from 8.9 to 16.8K with an average 12.3$\pm$1.7K, while dense gas in the W40 region shows higher temperatures ranging from 17.7 to 35.0K with an average of 25.1$\pm$4.9 K. A comparison of kinetic temperatures against HiGal dust temperatures indicates that the gas and dust temperatures are in agreement in the low mass star formation region of Serpens South. In the high mass star formation region W40, the measured gas kinetic temperatures are higher than those of the dust. The turbulent component of the velocity dispersion of NH$_3$(1,1) is found to be positively correlated with the gas kinetic temperature, which indicates that the dense gas may be heated by dissipation of turbulent energy. For the fractional total-NH3 abundance obtained by a comparison with Herschel infrared continuum data representing dust emission we find values from 0.1 to 21$\times 10^{-8}$ with an average of 6.9$(\pm 4.5)\times 10^{-8}$. Serpens South also shows a fractional total-NH3 abundance ranging from 0.2 to 21$\times 10^{-8}$ with an average of 8.6($\pm 3.8)\times 10^{-8}$. In W40, values are lower, between 0.1 and 4.3$\times 10^{-8}$ with an average of 1.6($\pm 1.4)\times 10^{-8}$. Weak velocity gradients demonstrate that the rotational energy is a negligible fraction of the gravitational energy. In W40, gas and dust temperatures are not strongly dependent on the projected distance to the recently formed massive stars. Overall, the morphology of the mapped region is ring-like, with strong emission at lower and weak emission at higher Galactic longitudes.

astro-ph.GA↗

arXiv2020

Evidence for dense gas heated by the explosion in Orion KL

We mapped the kinetic temperature structure of Orion KL in a $\sim$20$''$ ($\sim$8000 AU) sized region with para-H$_{2}$CS $7_{07}-6_{06}$, $7_{26}-6_{25}$, and $7_{25}-6_{24}$ making use of ALMA Band 6 Science Verification data. The kinetic temperatures obtained with a resolution of $1\hbox{$\,.\!\!^{\prime\prime}$}65$$\times$$1\hbox{$\,.\!\!^{\prime\prime}$}14$ ($\sim$550 AU) are deduced by modeling the measured averaged velocity-integrated intensity ratios of para-H$_2$CS $7_{26}-6_{25}/7_{07}-6_{06}$ and $7_{25}-6_{24}/7_{07}-6_{06}$ with a RADEX non-LTE model. The kinetic temperatures of the dense gas, derived from the para-H$_2$CS line ratios at a spatial density of 10$^7$ cm$^{-3}$, are high, ranging from 43 to $>$500 K with an unweighted average of $\sim$170 K. There is no evidence for internal sources playing an important role in the heating of the various structures identified in previous work, namely the elongated ridge, the northwestern clump, and the eastern region of the compact ridge, while the high temperatures in the western region of the compact ridge may be dominated by internal massive star formation. Significant gradients of kinetic temperature along molecular filaments traced by H$_2$CS indicate that the dense gas is heated by the shocks induced by the enigmatic explosive event, which occurred several hundred years ago greatly affecting the energetics of the Orion KL region. Thus, with the notable exception of the western region of the compact ridge, the high temperatures of the dense gas in Orion KL are probably caused by shocks from the explosive event, leading to a dominant component of externally heated dense gas.

astro-ph.GA↗

arXiv2020

Gas and dust cooling along the major axis of M33 (HerM33es) -- Herschel/PACS [CII] and [OI] observations

M33 is a gas rich spiral galaxy of the Local Group. We investigate the relationship between the two major gas cooling lines and the total infrared (TIR) dust continuum. We mapped the emission of gas and dust in M33 using the far-infrared lines of [CII] and [OI](63um) and the TIR. The line maps were observed with Herschel/PACS. These maps have 50pc resolution and form a ~370pc wide stripe along its major axis covering the sites of bright HII regions, but also more quiescent arm and inter-arm regions from the southern arm at 2kpc galacto-centric distance to the south out to 5.7kpc distance to the north. Full-galaxy maps of the continuum emission at 24um from Spitzer/MIPS, and at 70um, 100um, and 160um from PACS were combined to obtain a map of the TIR. TIR and [CII] intensities are correlated over more than two orders of magnitude. The range of TIR translates to a range of far ultraviolet (FUV) emission of G0,obs~2 to 200 in units of the average Galactic radiation field. The binned [CII]/TIR ratio drops with rising TIR, with large, but decreasing scatter. Fits of modified black bodies (MBBs) to the continuum emission were used to estimate dust mass surface densities and total gas column densities. A correction for possible foreground absorption by cold gas was applied to the [OI] data before comparing it with models of photon dominated regions (PDRs). Most of the ratios of [CII]/[OI] and ([CII]+[OI])/TIR are consistent with two model solutions. The median ratios are consistent with one solution at n~2x10^2 cm-3, G0~60, and and a second low-FUV solution at n~10^4 cm-3, G0~1.5. The bulk of the gas along the lines-of-sight is represented by a low-density, high-FUV phase with low beam filling factors ~1. A fraction of the gas may, however, be represented by the second solution.

astro-ph.GA↗

arXiv2020

Optimized Directed Roadmap Graph for Multi-Agent Path Finding Using Stochastic Gradient Descent

We present a novel approach called Optimized Directed Roadmap Graph (ODRM). It is a method to build a directed roadmap graph that allows for collision avoidance in multi-robot navigation. This is a highly relevant problem, for example for industrial autonomous guided vehicles. The core idea of ODRM is, that a directed roadmap can encode inherent properties of the environment which are useful when agents have to avoid each other in that same environment. Like Probabilistic Roadmaps (PRMs), ODRM's first step is generating samples from C-space. In a second step, ODRM optimizes vertex positions and edge directions by Stochastic Gradient Descent (SGD). This leads to emergent properties like edges parallel to walls and patterns similar to two-lane streets or roundabouts. Agents can then navigate on this graph by searching their path independently and solving occurring agent-agent collisions at run-time. Using the graphs generated by ODRM compared to a non-optimized graph significantly fewer agent-agent collisions happen. We evaluate our roadmap with both, centralized and decentralized planners. Our experiments show that with ODRM even a simple centralized planner can solve problems with high numbers of agents that other multi-agent planners can not solve. Additionally, we use simulated robots with decentralized planners and online collision avoidance to show how agents are a lot faster on our roadmap than on standard grid maps.

cs.RO↗

arXiv2020

Evidence for Infalling Gas in a Lyman-$α$ Blob

Lyman-$α$ blobs (LABs) are spatially extended nebulae of emission in the Ly$α$ line of hydrogen, seen at high redshifts$^{1,2}$, and most commonly found in the dense environment of star-forming galaxies$^{3,4}$. The origin of Ly$α$ emission in the LABs is still unclear and under debate$^{5}$. Proposed powering sources generally fall into two categories: (1) photoionization, galactic super-winds/outflows, resonant scattering of Ly$α$ photons from starbursts or active galactic nuclei (AGNs)$^{6,7,8,9,10}$ and (2) cooling radiation from cold streams of gas accreting onto galaxies$^{12}$. Here we analyze the gas kinematics within a LAB providing rare observational evidence for infalling gas. This is consistent with the release of gravitational accretion energy as cold streams radiate Ly$α$ photons. It also provides direct evidence for possible cold streams feeding the central galaxies. The infalling gas is not important by mass but hints at more than one mechanism to explain the origin of the extended Ly$α$ emission around young galaxies. It is also possible that the infalling gas may represent material falling back to the galaxy from where it originated, forming a galactic fountain.

astro-ph.GA↗

arXiv2019

An Optimal Algorithm to Solve the Combined Task Allocation and Path Finding Problem

We consider multi-agent transport task problems where, e.g. in a factory setting, items have to be delivered from a given start to a goal pose while the delivering robots need to avoid collisions with each other on the floor. We introduce a Task Conflict-Based Search (TCBS) Algorithm to solve the combined delivery task allocation and multi-agent path planning problem optimally. The problem is known to be NP-hard and the optimal solver cannot scale. However, we introduce it as a baseline to evaluate the sub-optimality of other approaches. We show experimental results that compare our solver with different sub-optimal ones in terms of regret.

cs.RO↗

arXiv2019

Fire in the Heart: A Characterization of the High Kinetic Temperatures and Heating Sources in the Nucleus of NGC253

The nuclear starburst within the central $\sim 15^{\prime\prime}$ ($\sim 250$ pc; $1^{\prime\prime} \simeq 17$ pc) of NGC253 has been extensively studied as a prototype for the starburst phase in galactic evolution. Atacama Large Millimeter/submillimeter Array (ALMA) imaging within receiver Bands 6 and 7 have been used to investigate the dense gas structure, kinetic temperature, and heating processes which drive the NGC253 starburst. Twenty-nine transitions from fifteen molecular species/isotopologues have been identified and imaged at $1.^{\prime\prime}5$ to $0.^{\prime\prime}4$ resolution, allowing for the identification of five of the previously-studied giant molecular clouds (GMCs) within the central molecular zone (CMZ) of NGC253. Ten transitions from the formaldehyde (H$_2$CO) molecule have been used to derive the kinetic temperature within the $\sim 0.^{\prime\prime}5$ to $5^{\prime\prime}$ dense-gas structures imaged. On $\sim 5^{\prime\prime}$ scales we measure $T_K \gtrsim 50$ K, while on size scales $\lesssim 1^{\prime\prime}$ we measure $T_K \gtrsim 300$ K. These kinetic temperature measurements further delineate the association between potential sources of dense gas heating. We have investigated potential heating sources by comparing our measurements to models which predict the physical conditions associated with dense molecular clouds that possess a variety of heating mechanisms. This comparison has been supplemented with tracers of recently-formed massive stars (Br$γ$) and shocks ([FeII]). Derived molecular column densities point to a radially-decreasing abundance of molecules with sensitivity to cosmic ray and mechanical heating within the NGC253 CMZ. These measurements are consistent with radio spectral index calculations which suggest a higher concentration of cosmic ray producing supernova remnants within the central 10 pc of NGC253.

astro-ph.GA↗

arXiv2018

Search for High-Mass Protostellar Objects in Cold IRAS Sources

We present the results of CS J=2-1 mapping observations towards 39 massive star-forming regions selected from the previous CO line survey of cold IRAS sources with high-velocity CO flows along the Galactic plane (Yang et al. 2002). All sources are detected in CS J=2-1 showing the existence of CS clumps around the IRAS sources. However, one-third of the sources are not deeply embedded in the dense clumps by comparison of the central powering IRAS sources and the morphologies of CS clumps. Physical parameters of the dense molecular clumps are presented. We have identified 12 high-mass protostellar object (HMPO) candidates by checking the association between the dense cores and the IRAS sources, the detection of water maser, and the radio properties towards the IRAS sources. We find that the HMPO sources are characterized by low FIR luminosity to virial mass ratios since they are in very early evolutionary stages when the massive protostars have not reached their full luminosities, which are typical for zero-age main sequence stars. Large turbulent motion in the HMPO sources may be largely due to the large kinetic energy ejected by the central protostars formed in the dense clumps. However, alternative means or undetected outflows may also be responsible for the turbulence in the clumps.

astro-ph.SR↗

arXiv2018

Extended ammonia observations towards the 'Integral-Shaped Filament'

Recent observations suggest a scenario in which filamentary structures in the ISM represent the first step towards clumps/cores and eventually star formation. The densest filaments would then fragment into prestellar cores owing to gravitational instability. We seek to understand the roles filamentary structures play in high-mass star formation. We mapped the integral-shaped filament (ISF) in NH3 (1, 1) and (2, 2). The whole filamentary structure is uniformly and fully sampled. We find that the morphology revealed by the map of velocity-integrated intensity of the NH3 (1, 1) line is closely associated with the dust ridge. We identify 6 "clumps" related to the well known OMC-1 to 5 and 11 "sub-clumps" within the map and they are separated not randomly but in roughly equal intervals along the ISF. The average spacing of clumps is 11.30'$\pm$1.31' (1.36$\pm$0.16 pc ) and the average spacing of sub-clumps is 7.18'$\pm$1.19' (0.86$\pm$0.14 pc). These spacings agree well with the predicted values of the thermal (0.86 pc) and turbulent sausage instability (1.43 pc) by adopting a cylindric geometry of the ISF with an inclination of $60^{\circ}$ with respect to the line of sight. We also find a velocity gradient of about 0.6 km s-1 pc-1 that runs along the ISF which likely arises from an overall rotation of the Orion A molecular cloud. The inferred ratio between rotational and gravitational energy is well below unity. Furthermore, fluctuations are seen in the centroid velocity diagram along the ISF. The OMC-1 to 5 clouds are located close to the local extrema of the fluctuations, which suggests that there exist gas flows associated with these clumps in the ISF. The derived NH3 (1, 1) and (2, 2) rotation temperatures in the OMC-1 are about 30-40 K. In OMC-2, OMC-3, and the northern part of OMC-4, we find higher and lower temperatures at the boundaries and in the interior, respectively.

astro-ph.GA↗

arXiv2018

Investigations of the Class I methanol masers in NGC 4945

We have used the Australia Telescope Compact Array (ATCA) to conduct further observations of the 36.2-GHz ($4_{-1}\rightarrow3_0$E) methanol transition towards the nearby active galaxy NGC 4945. These observations have led to a more accurate determination of the offset between the maser emission and the nucleus of NGC 4945 with a typical synthesised beam of $6^{\prime\prime} \times 4^{\prime\prime}$ ($108\times72$ pc). This corresponds to a factor of 4 improvement with respect to the major-axis of the beam. Other transitions of methanol and lines of other molecular species were obtained alongside the 36.2-GHz methanol emission, with strong detections of HC$_3$N (J = $4 \rightarrow 3$) and CS (J = $1 \rightarrow0$) presented here. We do not detect thermal methanol (5$σ$ upper limit of 5 mJy in a 6 km s$^{-1}$ channel) from the 48.4-GHz ($1_{0}\rightarrow0_0$A$^+$) ground-state transition, nor emission from the 44.1-GHz ($7_{0} \rightarrow 6_1 $A$^+$) class~I maser transition (5$σ$ upper limit of 6 mJy in a 3 km s$^{-1}$ channel). We also present a comparison of the class~I maser emission observed towards NGC 4945 with that from NGC 253 and towards the Galactic giant molecular cloud G 1.6-0.025.

astro-ph.GA↗