arXiv subjects

Rolf Güsten

Publications and source records attributed to Rolf Güsten.

At least 19 recordsLinked to original sources

arXiv2026

Oxygen in the protostellar clump OMC-2 FIR4

Atomic oxygen (OI), OH, H2O, and CO are the main carriers of oxygen in dense interstellar gas and important coolants of shocks associated with protostellar outflows. We determine the relative abundances of these species in the warm inner parts of the protostellar clump OMC-2 FIR4 in Orion A. The clump contains several young stellar objects. The upGREAT receiver including the High Frequency Array (HFA, operating at 4.74 THz, 63 micron) onboard the Stratospheric Observatory for Far-Infrared Astronomy (SOFIA) was used to observe OMC-2 FIR4 in the lines of OI, OH, OD, HDO, and CO. Additional HDO lines were observed with the Atacama Pathfinder Experiment (APEX). Archival H2O and CO spectra observed by the Herschel satellite were included in the analysis. The observed lines were reasonably well reproduced by an expanding spherical shell model. The OI spectrum at 63 micron towards OMC-2 FIR4 is dominated by a broad line component, on top of which medium-wide and narrow line components can be discerned. The same components are present in the OH, H2O, and high-J CO spectra towards this source. We find that OI is more abundant than H2O in the shocked gas. In the broad line component, the following abundance ratios are derived: OI/H2O ~ 700, OI/OH ~ 300, OI/CO ~ 4. The high relative abundance of atomic oxygen there suggests an origin in dissociative J-shocks that are associated with strong ultraviolet radiation. The OI/CO ratio decreases below unity in the components with a smaller velocity dispersion, and these components also have higher abundances of H2O than the broad line component, although remaining below that of CO. The HDO/H2O ratio in the low-velocity components corresponds to the average ratio in the icy mantles of dust grains, and the presence of water there could also be understood in terms of sublimation without invoking high-temperature chemistry.

astro-ph.GA↗

arXiv2025

SOFIA FEEDBACK Survey: The Eagle Nebula in [C II] and Molecular Lines

We characterize the physical conditions and energy budget of the M16 H II region using SOFIA FEEDBACK observations of the [C II] 158 $μ$m line. The O stars in the $\sim 10^{4}~{\rm M}_{\odot}$ NGC 6611 cluster powering this H II region have blown at least 2 cavities into the giant molecular cloud: the large M16 cavity and the small N19 bubble. We detect the spectroscopic signature of an expanding photodissociation region shell towards N19, and traces of a thin, fragmented expanding shell towards M16. Our [C II] observations are resolved to 0.5 km s$^{-1}$ and 15.5$^{\prime\prime}$ and analyzed alongside similarly resolved CO J=3$-$2 observations as well as archival data ranging from the radio to X-ray tracing a variety of gas phases spanning dense $\sim$10 K molecular gas, $10^{4}$ K photoionized gas, and million-K collisionally ionized plasma. With this dataset, we evaluate the coupling of energetic feedback from NGC 6611 and the O9 V star within N19 to the surrounding gas. Winds from NGC 6611 have blown a 20 pc radius cavity constrained in size along the major axis of the natal giant molecular filament, and much of the mechanical wind energy ($>$90%) has escaped through breaches in the $\lesssim 10^{4}~{\rm M}_{\odot}$ shell. Reservoirs of dense gas remain within a few parsecs of the cluster. N19, younger than M16 by $\gtrsim 10^6$ yr, is driven by a combination of mechanical wind energy and thermal pressure from photoionized gas and has swept up $\sim 10^{3}~{\rm M}_{\odot}$ into neutral atomic and molecular shells.

astro-ph.GA↗

arXiv2025

[C II]-deficit caused by self-absorption in an ionized carbon-filled bubble in RCW79

Recent spectroscopic observations of the [C II] 158$\,\mathrm{μm}$ fine-structure line of ionized carbon (C$^+$), using the Stratospheric Observatory for Infrared Astronomy (SOFIA), have revealed expanding [C II] shells in Galactic H II regions. We report the discovery of a bubble-shaped source (S144 in RCW79), associated with a compact H II region, excited by a single O7.5--9.5V/III star, which is consistent with a scenario that the bubble is still mostly ``filled'' with C$^+$. This indicates most likely a very early evolutionary state, in which the stellar wind has not yet blown material away, as it is the case for more evolved H II regions. Using the SimLine non-LTE radiative transfer code, the [C II] emission can be modeled to originate from three regions. First, a central H II region with little C$^+$ in the fully ionized phase, followed by two layers with gas density around $2500\,\mathrm{cm^{-3}}$ of partially photo-dissociated gas. The second layer is a slowly expanding [C II] shell with an expansion velocity of $\sim\,$$2.6\,\mathrm{km\,s^{-1}}$. The outermost layer exhibits a temperature and velocity gradient that produces the observed self-absorption features in the optically thick [C II] line ($τ\sim 4$) leading to an apparent deficit in [C II] emission and a low ratio of [C II] to total far-infrared (FIR) emission. We developed a procedure to approximate the missing [C II] flux and find a linear correlation between [C II] and FIR without a [C II]-deficit. This demonstrates that at least some of the [C II]-deficit found in Galactic H II bubbles can be attributed to self-absorption.

astro-ph.GA↗

arXiv2024

SOFIA/upGREAT far-infrared spectroscopy of bright rimmed pillars in IC 1848

Using the upGREAT instrument on SOFIA, we have imaged the [C II] 158 μm fine structure line emission in bright-rimmed pillars located at the southern edge of the IC1848 H II region, and carried out pointed observations of the [O I] 63 and 145 μm fine structure lines toward selected positions. The observations are used to characterize the morphology, velocity field, and the physical conditions in the G1 - G3 filaments. The velocity-resolved [C II] spectra show evidence of a velocity shift at the head of the brightest G1 filament, possibly caused by radiation pressure from the impinging UV photons or the rocket effect of the evaporating gas. Archival Herschel PACS and SPIRE data imply H2 column densities in the range 10^{21} - 10^{22} cm^{-2}, corresponding to maximum visual extinction AV = 10 mag, and average H2 volume density of about 4500 cm^{-3} in the filaments. The [C II] emission traces ~ 17% of the total H2 column density, as derived from dust SED fits. PDR models are unable to explain the observed line intensities of the two [O I] fine structure lines in IC1848, with the observed [O I] 145 μm line being too strong compared to the model predictions. The [O I] lines in IC1848 are overall weak and the signal-to-noise ratio is limited. However, our observations suggest that the [O I] 63/145 μm intensity ratio is a sensitive probe of the physical conditions in photon dominated regions such as IC1848. These lines are thus excellent targets for future high-altitude balloon instruments, less affected by telluric absorption.

astro-ph.GA↗

arXiv2024

Bright-rimmed clouds in IC 1396 I. Dynamics

We investigate the dynamical and physical structures of bright-rimmed clouds (BRCs) in a nearby HII region. We focused on carbon- and oxygen-bearing species that trace photon-dominated regions (PDRs) and warm molecular cloud surfaces in order to understand the effect of UV radiation from the exciting stars on the cloud structure. We mapped four regions around the most prominent BRCs at scales of 4--10 arcmin in the HII region IC 1396 in [CII] 158 micron with (up)GREAT on board SOFIA. IC 1396 is predominantly excited by an O6.5V star. Toward IC 1396A, we also observed [OI] 63 micron and 145 micron. We combined these observations with JCMT archive data, which provide the low-J transitions of CO, $^{13}$CO, and C$^{18}$O. All spectra are velocity-resolved. The line profiles show a variety of velocity structures, which we investigated in detail for all observed emission lines. We find no clear sign of photoevaporating flows in the [CII] spectra, although the uncertainty in the location of the BRCs along the line of sight makes this interpretation inconclusive. Our analysis of the [$^{13}$CII] emission in IC 1396A suggests that the [CII] is likely mostly optically thin. The heating efficiency, measured by the ([CII]+[OI] 63 micron)/far-infrared intensity ratio, is higher in the northern part of IC 1396A than in the southern part, which may indicate a difference in the dust properties of the two areas. The complex velocity structures identified in the BRCs of IC 1396, which is apparently a relatively simple HII region, highlight the importance of velocity-resolved data for disentangling different components along the line of sight and thus facilitating a detailed study of the dynamics of the cloud. We also demonstrate that the optically thin [$^{13}$CII] and [OI] 145 micron emission lines are essential for a conclusive interpretation of the [CII] 158 micron and [OI] 63 micron line profiles.

astro-ph.GA↗

arXiv2023

Observing the LMC with APEX: Signatures of Large-scale Feedback in the Molecular Clouds of 30 Doradus

Stellar feedback plays a crucial role in star formation and the life cycle of molecular clouds. The intense star formation region 30 Doradus, which is located in the Large Magellanic Cloud (LMC), is a unique target for detailed investigation of stellar feedback owing to the proximity of the hosting galaxy and modern observational capabilities that together allow us to resolve individual molecular clouds $-$ nurseries of star formation. We study the impact of large-scale feedback on the molecular gas using the new observational data in the $^{12}$CO(3$-$2) line obtained with the APEX telescope. Our data cover an unprecedented area of 13.8 sq. deg. of the LMC disc with a spatial resolution of 5 pc and provide an unbiased view of the molecular clouds in the galaxy. Using this data, we located molecular clouds in the disc of the galaxy, estimated their properties, such as the areal number density, relative velocity and separation, width of the line profile, CO line luminosity, size, and virial mass, and compared these properties of the clouds of 30 Doradus with those in the rest of the LMC disc. We find that, compared with the rest of the observed molecular clouds in the LMC disc, those in 30 Doradus show the highest areal number density; they are spatially more clustered, they move faster with respect to each other, and they feature larger linewidths. In parallel, we do not find statistically significant differences in such properties as the CO line luminosity, size, and virial mass between the clouds of 30 Doradus and the rest of the observed field. We interpret our results as signatures of gas dispersal and fragmentation due to high-energy large-scale feedback.

astro-ph.GA↗

arXiv2023

SOFIA FEEDBACK Survey: The Pillars of Creation in [C II] and Molecular Lines

We investigate the physical structure and conditions of photodissociation regions (PDRs) and molecular gas within the Pillars of Creation in the Eagle Nebula using SOFIA FEEDBACK observations of the [C II] 158 micron line. These observations are velocity resolved to 0.5 km s$^{-1}$ and are analyzed alongside a collection of complimentary data with similar spatial and spectral resolution: the [O I] 63 micron line, also observed with SOFIA, and rotational lines of CO, HCN, HCO$^{+}$, CS, and N$_2$H$^{+}$. Using the superb spectral resolution of SOFIA, APEX, CARMA, and BIMA, we reveal the relationships between the warm PDR and cool molecular gas layers in context of the Pillars' kinematic structure. We assemble a geometric picture of the Pillars and their surroundings informed by illumination patterns and kinematic relationships and derive physical conditions in the PDRs associated with the Pillars. We estimate an average molecular gas density $n_{{\rm H}_2} \sim 1.3 \times 10^5$ cm$^{-3}$ and an average atomic gas density $n_{\rm H} \sim 1.8 \times 10^4$ cm$^{-3}$ and infer that the ionized, atomic, and molecular phases are in pressure equilibrium if the atomic gas is magnetically supported. We find pillar masses of 103, 78, 103, and 18 solar masses for P1a, P1b, P2, and P3 respectively, and evaporation times of $\sim$1-2 Myr. The dense clumps at the tops of the pillars are currently supported by the magnetic field. Our analysis suggests that ambipolar diffusion is rapid and these clumps are likely to collapse within their photoevaporation timescales.

astro-ph.GA↗

arXiv2023

Physics and Chemistry of Radiation Driven Cloud Evolution. [C II] Kinematics of IC 59 and IC 63

We used high-resolution [C II] 158 $μ$m mapping of two nebulae IC 59 and IC 63 from SOFIA/upGREAT in conjunction with ancillary data on the gas, dust, and polarization to probe the kinematics, structure, and magnetic properties of their photo-dissociation regions (PDRs). The nebulae are part of the Sh 2-185 H II region illuminated by the B0 IVe star $γ$ Cas. The velocity structure of each PDR changes with distance from $γ$ Cas, consistent with driving by the radiation. Based on previous FUV flux measurements of, and the known distance to $γ$ Cas along with the predictions of 3D distances to the clouds, we estimated the FUV radiation field strength (G0) at the clouds. Assuming negligible extinction between the star and clouds, we find their 3D distances from $γ$ Cas. For IC 63, our results are consistent with earlier estimates of distance from Andersson et al. (2013), locating the cloud at 2 pc from $γ$ Cas, at an angle of 58 to the plane of the sky, behind the star. For IC 59, we derive a distance of 4.5 pc at an angle of 70 in front of the star. We do not detect any significant correlation between the orientation of the magnetic field (Soam et al. 2017) and the velocity gradients of [C II] gas, indicating a moderate magnetic field strength. The kinetic energy in IC 63 is estimated to be order of ten higher than the magnetic energies. This suggests that kinetic pressure in this nebula is dominant.

astro-ph.GA↗

arXiv2023

Atomic oxygen abundance toward Sagittarius B2

A substantial fraction of oxygen in diffuse clouds is unaccounted for by observations and is postulated to be in an unknown refractory form, referred to as unidentified depleted oxygen (UDO), which, depending on the local gas density, may contribute up to 50% of the total oxygen content. Previous Infrared Space Observatory (ISO) observations suggest that a significant fraction of oxygen in even denser, translucent clouds may be in atomic form. We have analyzed velocity-resolved archival SOFIA observations of the 63 $μ$m fine-structure [O I] transition toward the high-mass star-forming region Sgr B2(M) in the Central Molecular Zone. The foreground spiral-arm clouds as well as the extended Sgr B2 envelope between the Sun and the background dust continuum source produce multiple [O i] absorption components, spectrally separated in velocity space. The gas-phase atomic oxygen column density in foreground clouds toward Sgr B2 is well correlated with the total hydrogen column density, with an average atomic oxygen abundance of $(2.51 \pm 0.69) \times 10^{-4}$ with respect to hydrogen nuclei. This value is in good agreement with the earlier ISO measurements on the same line of sight, and is about 35% lower than the total interstellar medium oxygen abundance in the low-density warm gas, as measured in the UV. We find no evidence that a significant fraction of the oxygen on the line of sight toward Sagittarius B2 is in the form of UDO.

astro-ph.GA↗

arXiv2023

An APEX study of molecular outflows in FUor-type stars

FU Orionis-type objects (FUors) are low-mass pre-main-sequence objects which go through a short-lived phase (~100 years) of increased mass accretion rate (from 10^-8 to 10^-4 M_sun yr^-1). These eruptive young stars are in the early stages of stellar evolution and, thus, still deeply embedded in a massive envelope that feeds material to the circumstellar disk that is then accreted onto the star. Some FUors drive molecular outflows, i.e. low-velocity wide-angle magneto-hydrodynamical winds, that inject energy and momentum back to the surrounding envelopes, and help clear the material surrounding the young star. Here we present a 12CO (3--2), 13CO (3--2) and 12CO (4--3) survey of 20 FUor-type eruptive young stars observed with APEX. We use our 13CO (3--2) observations to measure the masses of the envelopes surrounding each FUor and find an agreement with the FUor evolutionary trend found from the 10um silicate feature. We find outflows in 11 FUors, calculate their masses and other kinematic properties, and compare these with those of outflows found around quiescent young stellar objects gathered from the literature. This comparison indicates that outflows in FUors are more massive than outflows in quiescent sources, and that FUor outflows have a higher ratio outflow mass with respect to the envelope than the quiescent sample, indicating that the eruptive young stars have lower star-forming efficiencies. Finally, we found that the outflow forces in FUors are similar to those of quiescent young stellar objects, indicating that their accretion histories are similar or that the FUor outflows have lower velocities.

astro-ph.SR↗

arXiv2022

Living on the edge of the Central Molecular Zone: G1.3 is the more likely candidate for gas accretion into the CMZ

The 1.3deg (G1.3) and 1.6deg (G1.6) cloud complexes in the Central Molecular Zone (CMZ) of our Galaxy have been proposed to possibly reside at the intersection region of the X1 and X2 orbits for several reasons. This includes the detection of co-spatial low- and high-velocity clouds, high velocity dispersion, high fractional molecular abundances of shock-tracing molecules, and kinetic temperatures that are higher than for usual CMZ clouds. We mapped both cloud complexes in molecular lines in the frequency range from 85 to 475GHz with the IRAM 30m and the APEX 12m telescopes. The kinematic structure of G1.3 reveals an `emission bridge' at intermediate velocities (~150km/s) connecting low-velocity (~100km/s) and high-velocity (~180km/s) gas and an overall fluffy shell-like structure. These may represent observational evidence of cloud-cloud interactions. Low- and high-velocity gas components in G1.6 do not show such evidence of interaction, suggesting that they are spatially separated. We selected three positions in each cloud complex for further analysis. Based on non-LTE modelling of an ensemble of CH3CN lines, we derived kinetic temperatures of 60-100K and H2 volume densities of 10$^4$-10$^5$cm-3 in both complexes. Molecular abundances relative to H2 suggest a similar chemistry of the two clouds, which is moreover similar to that of other GC clouds. We conclude that G1.3 may indeed exhibit signs of cloud-cloud interactions. We propose an interaction of gas that is accreted from the near-side dust lane to the CMZ, with gas pre-existing at this location. Low- and high-velocity components in G1.6 are rather coincidentally observed along the same line of sight. They may be associated with either overshot decelerated gas from the far-side dust line or actual CMZ gas and high-velocity gas moving on a dust lane. These scenarios would be in agreement with numerical simulations.

astro-ph.GA↗

arXiv2022

An Interferometric View of H-MM1. I. Direct Observation of NH3 Depletion

Spectral lines of ammonia, NH$_3$, are useful probes of the physical conditions in dense molecular cloud cores. In addition to advantages in spectroscopy, ammonia has also been suggested to be resistant to freezing onto grain surfaces, which should make it a superior tool for studying the interior parts of cold, dense cores. Here we present high-resolution NH$_3$ observations with the Very Large Array (VLA) and Green Bank Telescope (GBT) towards a prestellar core. These observations show an outer region with a fractional NH$_3$ abundance of X(NH$_3$) = (1.975$\pm$0.005)$\times 10^{-8}$ ($\pm 10\%$ systematic), but it also reveals that after all, the X(NH$_3$) starts to decrease above a H$_2$ column density of $\approx 2.6 \times 10^{22}$ cm$^{-2}$. We derive a density model for the core and find that the break-point in the fractional abundance occurs at the density n(H$_2$) $\sim 2\times10^5$ cm$^{-3}$, and beyond this point the fractional abundance decreases with increasing density, following the power law $n^{-1.1}$. This power-law behavior is well reproduced by chemical models where adsorption onto grains dominates the removal of ammonia and related species from the gas at high densities. We suggest that the break-point density changes from core to core depending on the temperature and the grain properties, but that the depletion power law is anyway likely to be close to $n^{-1}$ owing to the dominance of accretion in the central parts of starless cores.

astro-ph.GA↗

arXiv2021

The chemistry of chlorine-bearing species in the diffuse interstellar medium, and new SOFIA/GREAT observations of HCl$^+$

We have revisited the chemistry of chlorine-bearing species in the diffuse interstellar medium with new observations of the HCl$^+$ molecular ion and new astrochemical models. Using the GREAT instrument on board SOFIA, we observed the $^2Π_{3/2}\, J = 5/2 - 3/2$ transition of HCl$^+$ near 1444 GHz toward the bright THz continuum source W49N. We detected absorption by diffuse foreground gas unassociated with the background source, and were able to thereby measure the distribution of HCl$^+$ along the sight-line. We interpreted the observational data using an updated version of an astrochemical model used previously in a theoretical study of Cl-bearing interstellar molecules. The abundance of HCl$^+$ was found to be almost constant relative to the related H$_2$Cl$^+$ ion, but the observed $n({\rm H_2Cl^+})/n({\rm HCl^+})$ abundance ratio exceeds the predictions of our astrochemical model by an order-of-magnitude. This discrepancy suggests that the rate of the primary destruction process for ${\rm H_2Cl^+}$, dissociative recombination, has been significantly overestimated. For HCl$^+$, the model predictions can provide a satisfactory fit to the observed column densities along the W49N sight-line while simultaneously accounting for the ${\rm OH^+}$ and ${\rm H_2O^+}$ column densities.

astro-ph.GA↗

arXiv2021

Observations and analysis of CH$^+$ vibrational emissions from the young, carbon-rich planetary nebula NGC 7027: a textbook example of chemical pumping

We discuss the detection of 14 rovibrational lines of CH$^+$, obtained with the iSHELL spectrograph on NASA's Infrared Telescope Facility (IRTF) on Maunakea. Our observations in the 3.49 - 4.13 $μ$m spectral region, obtained with a 0.375" slit width that provided a spectral resolving power $λ/Δλ\sim 80,000$, have resulted in the unequivocal detection of the $R(0) - R(3)$ and $P(1)-P(10)$ transitions within the $v=1-0$ band of CH$^+$. The $R$-branch transitions are anomalously weak relative to the $P$-branch transitions, a behavior that is explained accurately by rovibronic calculations of the transition dipole moment reported in a companion paper (Changala et al. 2021). Nine infrared transitions of H$_2$ were also detected in these observations, comprising the $S(8)$, $S(9)$, $S(13)$ and $S(15)$ pure rotational lines; the $v=1-0$ $O(4) - O(7)$ lines, and the $v=2-1$ $O(5)$ line. We present a photodissociation region model, constrained by the CH$^+$ and H$_2$ line fluxes that we measured, that includes a detailed treatment of the excitation of CH$^+$ by inelastic collisions, optical pumping, and chemical ("formation") pumping. The latter process is found to dominate the excitation of the observed rovibrational lines of CH$^+$, and the model is remarkably successful in explaining both the absolute and relative strengths of the CH$^+$ and H$_2$ lines.

astro-ph.GA↗

arXiv2021

Stellar feedback and triggered star formation in the prototypical bubble RCW 120

Radiative and mechanical feedback of massive stars regulates star formation and galaxy evolution. Positive feedback triggers the creation of new stars by collecting dense shells of gas, while negative feedback disrupts star formation by shredding molecular clouds. Although key to understanding star formation, their relative importance is unknown. Here, we report velocity-resolved observations from the SOFIA (Stratospheric Observatory for Infrared Astronomy) legacy program FEEDBACK of the massive star-forming region RCW 120 in the [CII] 1.9-THz fine-structure line, revealing a gas shell expanding at 15 km/s. Complementary APEX (Atacama Pathfinder Experiment) CO J=3-2 345-GHz observations exhibit a ring structure of molecular gas, fragmented into clumps that are actively forming stars. Our observations demonstrate that triggered star formation can occur on much shorter time scales than hitherto thought (<0.15 million years), suggesting that positive feedback operates on short time periods.

astro-ph.GA↗

arXiv2020

4GREAT -- a four-color receiver for high-resolution airborne terahertz spectroscopy

4GREAT is an extension of the German Receiver for Astronomy at Terahertz frequencies (GREAT) operated aboard the Stratospheric Observatory for Infrared Astronomy (SOFIA). The spectrometer comprises four different detector bands and their associated subsystems for simultaneous and fully independent science operation. All detector beams are co-aligned on the sky. The frequency bands of 4GREAT cover 491-635, 890-1090, 1240-1525 and 2490-2590 GHz, respectively. This paper presents the design and characterization of the instrument, and its in-flight performance. 4GREAT saw first light in June 2018, and has been offered to the interested SOFIA communities starting with observing cycle 6.

astro-ph.IM↗

arXiv2020

Terahertz Water Masers: II. Further SOFIA/GREAT Detections toward Circumstellar Outflows, and a Multitransition Analysis

Following up on our discovery of terahertz water masers, reported in 2017, we report two further detections of water maser emission at frequencies above 1 THz. Using the GREAT instrument on SOFIA, we have detected emission in the 1.296411 THz $8_{27}-7_{34}$ transition of water toward two additional oxygen-rich evolved stars, omicron Ceti (Mira) and R Crateris, and obtained an upper limit on the 1.296 THz line emission from U Orionis. Toward these three sources, and toward the red supergiant star VY Canis Majorae from which 1.296 THz line emission was reported previously, we have also observed several lower-frequency (sub)millimeter water maser transitions using the APEX 12-m telescope along with the 22 GHz transition using the Effelsberg 100-m telescope. We have used a simple model to analyse the multi-transition data thereby obtained. Adopting, as a prior, independent literature estimates of the mass-loss-rates in these four sources and in W Hydrae, we infer water abundances in a remarkably narrow range: $n({\rm H_2O})/n({\rm H_2}) = 1.4 - 2.5 \times 10^{-4}$. For o Cet, VY CMa, and W Hya, the model is successful in predicting the maser line fluxes to within a typical factor $\sim 1.6 - 3$. For R Crt and U Ori, the model is less successful, with typical line flux predictions lying an order of magnitude above or below the observations; such discrepancies are perhaps unsurprising given the exponential nature of maser amplification.

astro-ph.GA↗

arXiv2020

The multi-phase ISM in the nearby composite AGN-SB galaxy NGC 4945: large (parsecs) scale mechanical heating

We aim at carrying out a comprehensive study of the nearby composite AGN-SB galaxy, NGC 4945, using spectroscopic and photometric data from the Herschel satellite. In particular, we want to characterize the thermal structure in this galaxy by a multi-transitions analysis of the spatial distribution of the 12^CO emission at different spatial scales using HIFI, PACS, SPIRE as well as APEX data. We combined the 12^CO/IR flux ratios and the LTE analysis of the 12^CO images to derive the thermal structure of the Interstellar Medium (ISM) for spatial scales raging from <200 pc to 2 kpc. From the 12^CO analysis we found clear trend in the distribution of the derived temperatures and the 12^CO/IR ratios. It is remarkable that at intermediate scales (360 pc-1 kpc) we see large temperatures in the direction of the X-ray outflow while at smaller scales (<200 pc-360 pc), the highest temperature, derived from the high-J lines, is not found toward the nucleus, but toward the galaxy plane. The thermal structure derived from the 12CO multi-transition analysis suggests that mechanical heating, like shocks or turbulence, dominates the heating of the ISM in the nucleus of NGC 4945 located beyond 100 pc from the center of the galaxy. This result is further supported by the Kazandjian et al. 2015 models, which are able to reproduce the emission observed at high-J (PACS) 12^CO transitions when mechanical heating mechanisms are included. Shocks and/or turbulence are likely produced by the barred potential and the outflow, observed in X-rays.

astro-ph.GA↗