LVG Model Research Articles

The methanol emission in the J1– J0 A−+ line series as a tracer of specific physical conditions in high-mass star-forming regions

ABSTRACT We present results of the investigations of the properties of the methanol J1 –J0 A−+ line series motivated by the recent serendipitous detection of the maser emission in the 141 – 140 A−+ line at 349 GHz in S255IR-SMA1 soon after the accretion burst. The study includes further observations of several lines of this series in S255IR with the SMA, a mini-survey of methanol lines in the 0.8-mm range towards a sample of bright 6.7-GHz methanol maser sources with the IRAM 30-m telescope, and theoretical modelling. We found that the maser component of the 141 – 140 A−+ line in S255IR decayed by more than order of magnitude in comparison with that in 2016. No clear sign of maser emission is observed in other lines of this series in the SMA observations except the 71 – 70 A−+ line where an additional bright component is detected at the velocity of the maser emission observed earlier in the 141 – 140 A−+ line. Our LVG model constrains the ranges of the physical parameters that match the observed emission intensities. No obvious maser emission in the J1 – J0 A−+ lines was detected in the mini-survey of the 6.7-GHz methanol maser sources, though one component in NGC 7538 may represent a weak maser. In general, the maser effect in the J1 – J0 A−+ lines may serve as a tracer of rather hot environments and in particular luminosity flaring events during high-mass star formation.

Observations of [OI]63 μm line emission in main-sequence galaxies at z ∼ 1.5

ABSTRACT We present Herschel–PACS spectroscopy of four main-sequence star-forming galaxies at z ∼ 1.5. We detect [OI]63 μm line emission in BzK-21000 at z = 1.5213, and measure a line luminosity, $L_{\rm [O\, {\small I}]63\, \mu m} = (3.9\pm 0.7)\times 10^9$ L⊙. Our PDR modelling of the interstellar medium in BzK-21000 suggests a UV radiation field strength, G ∼ 320G0, and gas density, n ∼ 1800 cm−3, consistent with previous LVG modelling of the molecular CO line excitation. The other three targets in our sample are individually undetected in these data, and we perform a spectral stacking analysis which yields a detection of their average emission and an [O i]63 μm line luminosity, $L_{\rm [O\, {\small I}]63\, \mu m} = (1.1\pm 0.2)\times 10^9$ L⊙. We find that the implied luminosity ratio, $L_{\rm [O\, {\small I}]63\, \mu m}/L_{\rm IR}$, of the undetected BzK-selected star-forming galaxies broadly agrees with that of low-redshift star-forming galaxies, while BzK-21000 has a similar ratio to that of a dusty star-forming galaxy at z ∼ 6. The high [O i]63 μm line luminosities observed in BzK-21000 and the z ∼ 1−3 dusty and sub-mm luminous star-forming galaxies may be associated with extended reservoirs of low density, cool neutral gas.

Detection of a turbulent gas component associated with a starless core with subthermal turbulence in the Orion A cloud

We report the detection of a wing component in NH$_3$ emission toward the starless core TUKH122 with subthermal turbulence in the Orion A cloud. This NH$_3$ core is suggested to be on the verge of star formation because the turbulence inside the NH$_3$ core is almost completely dissipated, and also because it is surrounded by CCS, which resembles the prestellar core L1544 in Taurus showing infall motions. Observations were carried out with the Nobeyama 45 m telescope at 0.05 km s$^{-1}$ velocity resolution. We find that the NH$_3$ line profile consists of two components. The quiescent main component has a small linewidth of 0.3 km s$^{-1}$ dominated by thermal motions, and the red-shifted wing component has a large linewidth of 1.36 km s$^{-1}$ representing turbulent motions. These components show kinetic temperatures of 11 K and $<$ 30 K, respectively. Furthermore, there is a clear velocity offset between the NH$_3$ quiescent gas ($VLSR=3.7$ km s$^{-1}$) and the turbulent gas ($VLSR=4.4$ km s$^{-1}$). The centroid velocity of the turbulent gas corresponds to that of the surrounding gas traced by the $^{13}$CO ($J=1-0$) and CS ($J=2-1$) lines. LVG model calculations for CS and CO show that the turbulent gas has a temperature of $8-13$ K and an H$_2$ density of ~ $10^4$ cm$^{-3}$, suggesting that the temperature of the turbulent component is also ~ 10 K. The detections of both NH$_3$ quiescent and wing components may indicate a sharp transition from the turbulent parent cloud to the quiescent dense core.

Extended warm gas in Orion KL as probed by methyl cyanide

In order to study the temperature distribution of the extended gas within the Orion Kleinmann-Low nebula, we have mapped the emission by methyl cyanide (CH3CN) in its J=6_K-5_K, J=12_K-11_K, J=13_K-12_K, and J=14_K-13_K transitions at an average angular resolution of ~10 arcsec (22 arcsec for the 6_K-5_K lines), as part of a new 2D line survey of this region using the IRAM 30m telescope. These fully sampled maps show extended emission from warm gas to the northeast of IRc2 and the distinct kinematic signatures of the hot core and compact ridge source components. We have constructed population diagrams for the four sets of K-ladder emission lines at each position in the maps and have derived rotational excitation temperatures and total beam-averaged column densities from the fitted slopes. In addition, we have fitted LVG model spectra to the observations to determine best-fit physical parameters at each map position, yielding the distribution of kinetic temperatures across the region. The resulting temperature maps reveal a region of hot (T > 350 K) material surrounding the northeastern edge of the hot core, whereas the column density distribution is more uniform and peaks near the position of IRc2. We attribute this region of hot gas to shock heating caused by the impact of outflowing material from active star formation in the region, as indicated by the presence of broad CH3CN lines. This scenario is consistent with predictions from C-shock chemical models that suggest that gas-phase methyl cyanide survives in the post-shock gas and can be somewhat enhanced due to sputtering of grain mantles in the passing shock front.

13 CO and C18O emission from a dense gas disc at z = 2.3: abundance variations, cosmic rays and the initial conditions for star formation

We analyse the SLEDs of 13CO and C18O for the J=1-0 up to J=7-6 transitions in the gravitationally lensed ultraluminous infrared galaxy SMMJ2135-0102 at z=2.3. This is the first detection of 13CO and C18O in a high-redshift star-forming galaxy. These data comprise observations of six transitions taken with PdBI and we combine these with 33GHz JVLA data and our previous 12CO and continuum emission information to better constrain the properties of the ISM within this system. We study both the velocity-integrated and kinematically decomposed properties of the galaxy and coupled with an LVG model we find that the star-forming regions in the system vary in their cold gas properties. We find strong C18O emission both in the velocity-integrated emission and in the two kinematic components at the periphery of the system, where the C18O line flux is equivalent to or higher than the 13CO. We derive an average velocity-integrated flux ratio of 13CO/C18O~1 suggesting a [13CO]/[C18O] abundance ratio at least 7x lower than that in the Milky Way. This may suggest enhanced C18O abundance, perhaps indicating star formation preferentially biased to high-mass stars. We estimate the relative contribution to the ISM heating from cosmic rays and UV of (30-3300)x10^(-25)erg/s and 45x10^(-25)erg/s per H2 molecule respectively and both are comparable to the total cooling rate of (0.8-20)x10^(-25)erg/s from the CO. However, our LVG models indicate high (>100K) temperatures and densities (>10^(3))cm^(-3) in the ISM which may suggest that cosmic rays play a more important role than UV heating in this system. If cosmic rays dominate the heating of the ISM, the increased temperature in the star forming regions may favour the formation of massive stars and so explain the enhanced C18O abundance. This is a potentially important result for a system which may evolve into a local elliptical galaxy.

L1448-MM OBSERVATIONS BY THE HERSCHEL KEY PROGRAM, “DUST, ICE, AND GAS IN TIME” (DIGIT)

We present Herschel/PACS observations of L1448-MM, a Class 0 protostar with a prominent outflow. Numerous emission lines are detected at 55 < lambda < 210 micrometer including CO, OH, H2O, and [O I]. We investigate the spatial distribution of each transition to find that lines from low energy levels tend to distribute along the outflow direction while lines from high energy levels peak at the central spatial pixel. Spatial maps reveal that OH emission lines are formed in a relatively small area, while [O I] emission is extended. According to the rotational diagram analysis, the CO emission can be fitted by two (warm and hot) temperature components. For H2O, the ortho-to-para ratio is close to 3. The non-LTE LVG calculations suggest that CO and H2O lines could instead be formed in a high kinetic temperature (T > 1000 K) environment, indicative of a shock origin. For OH, IR-pumping processes play an important role in the level population. The molecular emission in L1448-MM is better explained with a C-shock model, but the atomic emission of PACS [O I] and Spitzer/IRS [Si II] emission is not consistent with C-shocks, suggesting multiple shocks in this region. Water is the major line coolant of L1448-MM in the PACS wavelength range, and the best-fit LVG models predict that H2O and CO emit (50-80)% of their line luminosity in the PACS wavelength range.

74 MHz Nonthermal Emission from Molecular Clouds: Evidence for a Cosmic Ray Dominated Region at the Galactic Center

We present 74 MHz radio continuum observations of the Galactic center region. These measurements show nonthermal radio emission arising from molecular clouds that is unaffected by free–free absorption along the line of sight. We focus on one cloud, G0.13-0.13, representative of the population of molecular clouds that are spatially correlated with steep spectrum (α(327MHz)(74MHz) = 1.3 ± 0.3) nonthermal emission from the Galactic center region. This cloud lies adjacent to the nonthermal radio filaments of the Arc near l 0.2° and is a strong source of 74 MHz continuum, SiO (2-1), and Fe I Kα 6.4 keV line emission. This three-way correlation provides the most compelling evidence yet that relativistic electrons, here traced by 74 MHz emission, are physically associated with the G0.13-0.13 molecular cloud and that low-energy cosmic ray electrons are responsible for the Fe I Kα line emission. The high cosmic ray ionization rate 10(–1)3 s(–1) H(–1) is responsible for heating the molecular gas to high temperatures and allows the disturbed gas to maintain a high-velocity dispersion. Large velocity gradient (LVG) modeling of multitransition SiO observations of this cloud implies H2 densities 10(4–5) cm(–3) and high temperatures. The lower limit to the temperature of G0.13-0.13 is 100 K, whereas the upper limit is as high as 1000 K. Lastly, we used a time-dependent chemical model in which cosmic rays drive the chemistry of the gas to investigate for molecular line diagnostics of cosmic ray heating. When the cloud reaches chemical equilibrium, the abundance ratios of HCN/HNC and N2H+/HCO+ are consistent with measured values. In addition, significant abundance of SiO is predicted in the cosmic ray dominated region of the Galactic center. We discuss different possibilities to account for the origin of widespread SiO emission detected from Galactic center molecular clouds.

ALMA OBSERVATIONS OF THE GALACTIC CENTER: SiO OUTFLOWS AND HIGH-MASS STAR FORMATION NEAR Sgr A*

ALMA observations of the Galactic center with spatial resolution $2.61"\times0.97"$ resulted in the detection of 11 SiO (5-4) clumps of molecular gas within 0.6pc (15$"$) of Sgr A*, interior to the 2-pc circumnuclear molecular ring. The three SiO (5-4) clumps closest to Sgr A* show the largest central velocities, $\sim150$ \kms, and broadest asymmetric linewidths with full width zero intensity (FWZI) $\sim110-147$ \kms. The remaining clumps, distributed mainly to the NE of the ionized mini-spiral, have narrow FWZI ($\sim18-56$ \kms). Using CARMA SiO (2-1) data, LVG modeling of the the SiO line ratios for the broad velocity clumps, constrains the column density N(SiO) $\sim10^{14}$ cm$^{-2}$, and the H$_2$ gas density n$_{\rm H_2}=(3-9)\times10^5$ cm$^{-3}$ for an assumed kinetic temperature 100-200K. The SiO clumps are interpreted as highly embedded protostellar outflows, signifying an early stage of massive star formation near Sgr A* in the last $10^4-10^5$ years. Support for this interpretation is provided by the SiO (5-4) line luminosities and velocity widths which lie in the range measured for protostellar outflows in star forming regions in the Galaxy. Furthermore, SED modeling of stellar sources shows two YSO candidates near SiO clumps, supporting in-situ star formation near Sgr A*. We discuss the nature of star formation where the gravitational potential of the black hole dominates. In particular, we suggest that external radiative pressure exerted on self-shielded molecular clouds enhances the gas density, before the gas cloud become gravitationally unstable near Sgr A*. Alternatively, collisions between clumps in the ring may trigger gravitational collapse.

SUBMILLIMETER LINE SPECTRUM OF THE SEYFERT GALAXY NGC 1068 FROM THEHERSCHEL-SPIRE FOURIER TRANSFORM SPECTROMETER

The first complete submillimetre spectrum (190-670um) of the Seyfert 2 galaxy NGC1068 has been observed with the SPIRE Fourier Transform Spectrometer onboard the {\it Herschel} Space Observatory. The sequence of CO lines (Jup=4-13), lines from water, the fundamental rotational transition of HF, two o-H_2O+ lines and one line each from CH+ and OH+ have been detected, together with the two [CI] lines and the [NII]205um line. The observations in both single pointing mode with sparse image sampling and in mapping mode with full image sampling allow us to disentangle two molecular emission components, one due to the compact circum-nuclear disk (CND) and one from the extended region encompassing the star forming ring (SF-ring). Radiative transfer models show that the two CO components are characterized by density of n(H_2)=10^4.5 and 10^2.9 cm^-3 and temperature of T=100K and 127K, respectively. The comparison of the CO line intensities with photodissociation region (PDR) and X-ray dominated region (XDR) models, together with other observational constraints, such as the observed CO surface brightness and the radiation field, indicate that the best explanation for the CO excitation of the CND is an XDR with density of n(H_2) 10^4 cm^-3 and X-ray flux of 9 erg s^-1 cm^-2, consistent with illumination by the active galactic nucleus, while the CO lines in the SF-ring are better modeled by a PDR. The detected water transitions, together with those observed with the \her \sim PACS Spectrometer, can be modeled by an LVG model with low temperature (T_kin \sim 40K) and high density (n(H_2) in the range 10^6.7-10^7.9 cm^-3).

Rotational excitation of simple polar molecules by H2and electrons in diffuse clouds

[This is truncated to suit the whims of the archivers ...] Parameter studies in LVG models are used to show how the low-lying rotational transitions of common polar molecules HCO+, HCN and CS vary with number density, column density and electron fraction; with molecular properties such as the charge state and permanent dipole moment; and with observational details such as the transition that is observed. Physically-based models are used to check the parameter studies and provide a basis for relating the few extant observations. The parameter studies of LVG radiative transfer models show that lines of polar molecules are uniformly brighter for ions, for lower J-values and for higher dipole moments. Excitation by electrons is more important for J=1-0 lines and contributes rather less to the brightness of CS J=2-1 lines. If abundances are like those seen in absorption, the HCO+ J=1-0 line will be the brightest line after CO, followed by HCN (1-0) and CS (2-1). Because of the very weak rotational excitation in diffuse clouds, emission brightnesses and molecular column densities retain a nearly-linear proportionality under fixed physical conditions, even when transitions are quite optically thick; this implies that changes in relative intensities among different species can be used to infer changes in their relative abundances.

KINEMATICS AND PHYSICAL CONDITIONS OF THE INNERMOST ENVELOPE IN B335

We made C18O (2-1) and CS (7-6) images of the protostellar envelope around B335 with a high spatial dynamic range from ~10000 to ~400 AU, by combining the Submillimeter Array and single-dish data. The C18O emission shows an extended (~10000 AU) structure as well as a compact (~1500 AU) component concentrated at the protostellar position. The CS emission shows a compact (~900 AU) component surrounding the protostar, plus a halo-like (~3000 AU) structure elongated along the east-west direction. At higher velocities (|dV| >~0.3 km s^-1), the CS emission is stronger and more extended than the C18O emission. Physical conditions of the envelope were examined through an LVG model. At |dV| >~0.3 km s^-1, the gas temperature is higher (>40 K) than that at |dV| <~0.3 km s^-1, whereas the gas density is lower (<10^6 cm^-3). We consider that the higher-temperature and lower-density gas at |dV| >~0.3 km s^-1 is related to the associated outflow, while the lower-temperature and higher-density gas at |dV| <~0.3 km s^-1 is the envelope component. From the inspection of the positional offsets in the velocity channel maps, the radial profile of the specific angular momentum of the envelope rotation in B335 was revealed at radii from ~10^4 down to ~10^2 AU. The specific angular momentum decreases down to the radius of ~370 AU, and then appears to be conserved within that radius. A possible scenario of the evolution of envelope rotation is discussed.

DISCOVERY OF WATER VAPOR IN THE HIGH-REDSHIFT QUASAR APM 08279+5255 AT z = 3.91

We report a detection of the excited 220-211 rotational transition of para-H2O in APM 08279+5255 using the IRAM Plateau de Bure interferometer. At z = 3.91, this is the highest-redshift detection of interstellar water to date. From LVG modeling, we conclude that this transition is predominantly radiatively pumped and on its own does not provide a good estimate of the water abundance. However, additional water transitions are predicted to be detectable in this source, which would lead to an improved excitation model. We also present a sensitive upper limit for the HF J = 1 - 0 absorption toward APM 08279+5255. While the face-on geometry of this source is not favorable for absorption studies, the lack of HF absorption is still puzzling and may be indicative of a lower fluorine abundance at z = 3.91 compared with the Galactic ISM.

High-resolution mapping of the physical conditions in two nearby active galaxies based on12CO(1–0), (2–1), and (3–2) lines

We present a detailed analysis of high resolution observations of the three lowest CO transitions in two nearby active galaxies, NGC4569 and NGC4826. The CO(1-0) and (2-1) lines were observed with the Plateau de Bure Interferometer and the CO(3-2) line with the Submillimeter Array. Combining these data allows us to compare the emission in the three lines and to map the line ratios, R21=I_{CO(2-1)}/I_{CO(1-0)} and R32=I_{CO(3-2)}/I_{CO(1-0)} at a resolution of ~2", i.e., a linear resolution of 160 pc for NGC4569 and 40 pc for NGC4826. In both galaxies the emission in the three lines is similarly distributed spatially and in velocity, and CO is less excited (R32<0.6) than in the Galactic Center or the centers of other active galaxies studied so far. According to a pseudo-LTE model the molecular gas in NGC4569 is cold and mainly optically thick in the CO(1-0) and (2-1) lines; less than 50% of the gas is optically thin in the CO(3-2) line. LVG modeling suggests the presence of an elongated ring of cold and dense gas coinciding with the ILR of the stellar bar. More excited gas is resolved in the circumnuclear disk of NGC4826. According to our pseudo-LTE model this corresponds to warmer gas with a ~50% of the CO(3-2) emission being optically thin. LVG modeling indicates the presence of a semicircular arc of dense and cold gas centered on the dynamical center and ~70 pc in radius. The gas temperature increases and its density decreases toward the center. A near side/far side asymmetry noticeable in the CO, R32 and Pa-alpha maps suggests that opacity effects play a role. Examining published CO maps of nearby active galaxies we find similar asymmetries suggesting that this could be a common phenomenon in active galaxies. These mainly qualitative results open new perspectives for the study of active galaxies with the future Atacama Large Millimeter/submillimeter Array.

Rare CO Isotope Observations of M51a (NGC5194)

Abstract We present observations of the central regions of M51a (NGC5194) in the $J=$ 1-0 rotational transitions of $^{13}$CO, C$^{18}$O, and C$^{17}$O. The last two are the first detections reported for this object. We have combined these data with published HCN and CO($J=$ 1-0) observations with the same telescope to carry out some LVG modeling (single-cloud and two-cloud mixtures) of the line ratios. The results are compatible with the presence of a region emitting most of the HCN and another component at lower temperatures and densities emitting most of the rest of the molecular emission. The observed high C$^{18}$O$/$C$^{17}$O ratio, together with our models, suggest that this is caused by an underabundance of [C$^{17}$O] (compared with Galactic values). This can be explained by different evolutionary histories. The C$^{18}$O emission line has a clearly asymmetric profile, implying the presence of significant excitation differences within the observed region. Finally, there is an indication that the CO(1-0) is overestimating the molecular gas mass in the central kpc of this galaxy. This is similar to what is found in the Milky Way at similar spatial scales, and possibly associated with a change in the conversion factor due to the average cloud properties in the central regions of this object.

SiO line emission from interstellar jets and outflows: silicon-containing mantles and non-stationary shock waves

Context. We study the production and emission of SiO and H 2 in the gas phase of molecular outflows, extending previous work in which we considered steady-state C-type shock waves and assumed the silicon to be present only in the cores of silicate grains. Aims. We place constraints on the physical parameters of the pre-shock region, using recent observations of SiO and observations of molecular hydrogen. We show the effects of introducing SiO-containing mantles and of varying the age of the shock wave. We consider simultaneously the emission of SiO and H 2 from the young L1157 outflow. Methods. The molecular outflows are studied by means of a code that can generate stationary C- and J-type shock models and approximate non-stationary solutions, which combine these two types of shock wave. The emission of molecular hydrogen is computed by this code, whereas the SiO emission is computed by means of a separate LVG model, which uses the calculated physical and chemical profiles. A grid of models has been computed, with shock speeds in the range 10 ≤ u s < 35 km s -1 and pre-shock gas densities 10 4 ≤ n H ≤ 10 6 cm -3 . A wide range of magnetic field strengths has been investigated, from 45 pG to about 600 pG. Results. We illustrate our results by means of observational data obtained on the blue lobe of the L1157 outflow. Given the combinations of pre-shock densities and shock velocities necessary to fit the H 2 observations, we find that the erosion only of the silicate material in the grains cores cannot account for the observed SiO line intensities. We investigate the possiblity that a fraction of the SiO is present initially in the grain mantles, and we succeed in constraining this fraction. Introducing even a few percent of the silicon (as SiO) into the mantles is sufficient to increase the SiO line widths and fluxes by an order of magnitude. With this assumption, it is possible to find a non-stationary shock model that provides a reasonable fit of the observations of both H 2 and SiO. Conclusions. With a few percent of the silicon present initially in the grain mantles, good agreement is obtained with recent observations of SiO line integrated line intensities for a pre-shock density n H = 10 4 cm - and a shock speed v s = 20 km s -1 . The magnetic field strength and the shock age are not well constrained by the observations of either H 2 or SiO. We show that CO observations (in particular, with the Herschel satellite) could provide further discrimination between the models.

First detection of extragalactic13CO(6-5) line emission

We report the first detection of a mid-J isotopic CO line from an external galaxy. We detected the 13CO (6-5) line from the starburst nucleus of NGC 253. The line is suprisingly bright with an integrated intensity 7% of the 12CO (6-5) line, indicating optical depth in the 12CO line. Our LVG modeling shows that a single warm (T ~ 120 K), dense (n ~ 104 cm-3) component emits most of the 12CO and 13CO line emission from J = 2-1 through J = 7-6. The CO(1-0) line comes from an additional lower excitation envelope. About 60% of the total molecular gas mass within 70 pc of the nucleus is in the warm, dense component. We show that stellar far-UV photons or X-ray photons from a nuclear source are unlikely to be the primary sources of the gas heating. The most likely sources of heat are cosmic rays from the nuclear starburst or microturbulence within molecular clouds.

CI] 370 µm and CO (7-6) and (6-5) Observations of ULIRGs with ZEUS

We have begun a survey of the [CI] 370 μ m fine structure line and of mid-J CO line emission from ULIRGs and starburst galaxies using our grating spectrometer ZEUS on the CSO. Here we present observations from six ULIRGs: Mrk 231, Zw 049.057, NGC 6240, Arp 299, Arp 220, and IRAS 17208. The CO (6-5)/FIR ratio in ULIRGs appears to be lower for ULIRGs than for LIRGs. Comparing the CO SEDs of the ULIRGs shows the necessity of obtaining CO rotational transitions up to at least J = 7 to properly constrain LVG models.

The physical conditions in the BHR71 outflows

Highly-collimated outflows are believed to be the earliest stage in outflow evolution, so their study is essential for understanding the processes driving outflows. The BHR71 Bok globule is known to harbour such a highly-collimated outflow, which is powered by a protostar belonging to a protobinary system. Using the APEX telescope on Chajnantor, we mapped the BHR71 highly-collimated outflow in CO(3-2), and observed several bright points of the outflow in the molecular transitions CO(4-3), CO(7-6), 13CO(3-2), C18O(3-2), CH3OH(7-6) and H2CO(4-3). We use an LVG code to characterise the temperature enhancements in these regions. These observations are particularly interesting for investigating the interaction of collimated outflows with the ambient molecular cloud. In our CO(3-2) map, the second outflow driven by IRS2, which is the second source of the binary system, is completely revealed and shown to be bipolar. We also measure temperature enhancements in the lobes. The CO and methanol LVG modelling points to temperatures between 30 and 50 K in the two lobes. The methanol emission in the southern lobe bright knot is barely resolved with the APEX single-dish. ALMA will thus be a central tool to study the shock chemistry in these regions.

Arcsecond-resolution $^\mathsf{{12}}$CO mapping of the yellow hypergiants IRC +10420 and AFGL 2343

IRC +10420 and AFGL 2343 are the unique, known yellow hypergiants (YHGs) presenting a heavy circumstellar envelope (CSE). We aim to study the morphology, exceptional kinematics, and excitation conditions of their CSEs, and the implications for mass-loss processes. We have mapped the 12CO J=2-1 and 1-0 emission in these YHGs with the IRAM Plateau de Bure interferometer and the 30m telescope. We developed LVG models in order to analyze their circumstellar characteristics. The maps show that the overall shape of both CSEs is approximately spherical, although they also reveal several aspherical features. The CSE around IRC +10420 shows a rounded extended halo surrounding a bright inner region, with both components presenting aspherical characteristics. It presents a brightness minimum at the center. The envelope around AFGL 2343 is a detached shell, showing spherical symmetry and clumpiness at a level of about 15% of the maximum brightness. The envelopes expand isotropically at about 35 km/s, about two or three times faster than typical CSEs around AGB stars. High temperatures (~ 200 K) are derived for the innermost regions in IRC +10420, while denser and cooler (~ 30 K) gas is found in AFGL 2343. The mass-loss processes in these YHGs have been found to be similar. The deduced mass-loss rates (~ 10E-4 - 10E-3 Msun/yr) are much higher than those obtained in AGB stars, and they present significant variations on time scales of ~ 1000 yr.

Star Formation Feedback on the ISM Properties

We observed nearby (D < 10 Mpc) galaxies (Henize 2-10, IC 10, IC 342, M 83, NGC 253 and NGC 6946) in the rotational lines of carbon monoxide CO and in the fine-structure transitions of atomic carbon [CI] with the Caltech Submillimeter Observatory (CSO). Using our new data, those from the literature and the LVG and PDR models, we derived the physical properties of the warm and dense molecular gas (kinetic temperature, UV radiation field, gas density...) in each nucleus. We predicted lines intensities for the 12CO(5-4), 12CO(7-6) and 12CO(8-7) lines which are, even now, still difficult or impossible to detect from the ground but will become available in few years with ALMA and HIFI or PACS, on board the Herschel satellite. Studying the ISM of nearby galaxies, we provide a first step in the understanding of the ISM processes in more distant galaxies.