H2O Emission Research Articles

THE DEPLETION OF WATER DURING DISPERSAL OF PLANET-FORMING DISK REGIONS

ABSTRACT We present a new velocity-resolved survey of 2.9 μm spectra of hot H2O and OH gas emission from protoplanetary disks, obtained with the Cryogenic Infrared Echelle Spectrometer at the VLT (R ∼ 96,000). With the addition of archival Spitzer-IRS spectra, this is the most comprehensive spectral data set of water vapor emission from disks ever assembled. We provide line fluxes at 2.9–33 μm that probe from the dust sublimation radius at ∼0.05 au out to the region of the water snow line. With a combined data set for 55 disks, we find a new correlation between H2O line fluxes and the radius of CO gas emission, as measured in velocity-resolved 4.7 μm spectra (R ), which probes molecular gaps in inner disks. We find that H2O emission disappears from 2.9 μm (hotter water) to 33 μm (colder water) as increases and expands out to the snow line radius. These results suggest that the infrared water spectrum is a tracer of inside-out water depletion within the snow line. It also helps clarify an unsolved discrepancy between water observations and models by finding that disks around stars of generally have inner gaps with depleted molecular gas content. We measure radial trends in H2O, OH, and CO line fluxes that can be used as benchmarks for models to study the chemical composition and evolution of planet-forming disk regions at 0.05–20 au. We propose that JWST spectroscopy of molecular gas may be used as a probe of inner disk gas depletion, complementary to the larger gaps and holes detected by direct imaging and by ALMA.

Variability of the OH and H2O maser emission toward AS 501

The results of observations of OH (λ = 18 cm) and H2O (λ = 1.35 cm) masers toward AS 501 obtained with the Nancay Observatory Radio Telescope (France) and the 22-m radio telescope of the Pushchino Radio Astronomy Observatory (Russia), respectively, are presented. Nine cycles of H2O maser activity ranging from 2.8 to 6.0 years were detected, identifying AS 501 as an irregular variable star. Zeeman splitting was found only in the 1612-MHz satellite line at −59.2 km/s. The splitting is 0.11 km/s, corresponding to a line-of-sight magnetic field strength of 0.48 mG. The field is directed toward the observer. The detected radial-velocity drift of the H2O emission features can be explained in a model with elongated filaments with radial-velocity gradients.

An insight into the roles of exogenous potassium salts on the thermal degradation of flue-cured tobacco

The effects of exogenous potassium salts on the thermal degradation of flue-cured tobacco were investigated using thermogravimetric analysis (TGA), surface area/porosity measurements (SAPM), real-time fourier transform infrared (RT-FTIR), and thermogravimetric/Fourier transform infrared spectrometry (TG-FTIR), respectively. TGA analysis showed that potassium salts accelerated tobacco’s degradation at around 150–350°C, but improved the thermal stability of char residue at high temperature range. The porous texture analysis displayed that potassium salts reduced the pore volume and surface area of tobacco pyrolysis residues. Further study using RT-FTIR illustrated that there was a positive catalysis of potassium salts with CO, OH and CO bonds at different temperature ranges, but a protective effect was given to CH bond, CC bond and aromatic moieties except for the accelerating degradation of CH by the oxidation effect of KNO3. The evolution comparison of their gaseous products manifested that potassium salts cut down the emission of CO2, H2O, CO, aldehydes and alkanes, but enhanced the release of carbonyl compounds, anhydrides and alcohols at around 150–350°C. Above 350°C, the potassium salt-containing samples exhibited a gentle escape process for both the oxygen-bearing molecules (CO2, H2O and CO) and oxygen-free species (alkanes, methane and unsaturated compounds) in comparison with their quick emission for the virgin samples.

Submillimeter H2O and H2O+emission in lensed ultra- and hyper-luminous infrared galaxies atz ~ 2–4

(abridged) We report rest-frame submillimeter H2O emission line observations of 11 HyLIRGs/ULIRGs at z~2-4 selected among the brightest lensed galaxies discovered in the Herschel-ATLAS. Using the IRAM NOEMA, we have detected 14 new H2O emission lines. The apparent luminosities of the H2O emission lines are $\mu L_{\rm{H_2O}} \sim 6-21 \times 10^8 L_\odot$, with velocity-integrated line fluxes ranging from 4-15 Jy km s$^{-1}$. We have also observed CO emission lines using EMIR on the IRAM 30m telescope in seven sources. The velocity widths for CO and H2O lines are found to be similar. With almost comparable integrated flux densities to those of the high-J CO line, H2O is found to be among the strongest molecular emitters in high-z Hy/ULIRGs. We also confirm our previously found correlation between luminosity of H2O ($L_{\rm{H_2O}}$) and infrared ($L_{\rm{IR}}$) that $L_{\rm{H_2O}} \sim L_{\rm{IR}}^{1.1-1.2}$, with our new detections. This correlation could be explained by a dominant role of far-infrared (FIR) pumping in the H2O excitation. Modelling reveals the FIR radiation fields have warm dust temperature $T_\rm{warm}$~45-75 K, H2O column density per unit velocity interval $N_{\rm{H_2O}}/\Delta V \gtrsim 0.3 \times 10^{15}$ cm$^{-2}$ km$^{-1}$ s and 100 $\mu$m continuum opacity $\tau_{100} > 1$ (optically thick), indicating that H2O is likely to trace highly obscured warm dense gas. However, further observations of $J\geq4$ H2O lines are needed to better constrain the continuum optical depth and other physical conditions of the molecular gas and dust. We have also detected H2O+ emission in three sources. A tight correlation between $L_{\rm{H_2O}}$ and $L_{\rm{H_2O^+}}$ has been found in galaxies from low to high redshift. The velocity-integrated flux density ratio between H2O+ and H2O suggests that cosmic rays generated by strong star formation are possibly driving the H2O+ formation.

Long-term monitoring and interpretation of flares in the H2O maser emission of IRAS 16293–2422

The results of a study of the H2O and OH maser emission from the cool IR source IRAS 16293−2422 are presented. The observations analyzed were obtained in H2O lines with the 22-m telescope of the Pushchino Radio Astronomy Observatory during 1999–2015 and in OH lines with the Nanc¸ ay radio telescope (France). A large number of very strong flares of the H2O maser were detected, reaching fluxes of tens of thousands of Jansky. Individual features can form organized structures resembling chains ∼2 AU in length with a radial-velocity gradient along them. The observed drift of the H2O emission (2003–2004) in space and velocity (from 4.3 to 5.3 km/s) is not due solely to proper motion of the features. The other origin of the drift is a drift of the emission maximum during a flare as the shock consecutively excites spatially separated features in the structure in the form of a chain. The OH-line observations at 18 cm show that the emission remains unpolarized and thermal, with a line width of 0.7 km/s, which corresponds to a cloud temperature of ∼30 K.

ALMA finds dew drops in the dusty spider’s web

We present 0."5 resolution ALMA detections of the observed 246GHz continuum, [CI]^3P_2-^3P_1 fine structure line ([CI]2-1), CO(7-6) and H2O lines in the z=2.161 radio galaxy MRC1138-262, the 'Spiderweb Galaxy'. We detect strong [CI]2-1 emission both at the position of the radio core, and in a second component ~4kpc away from it. The 1100km/s broad [CI]2-1 line in this latter component, combined with its H2 mass of 1.6x10^10Msun implies this emission must come from a compact region <60pc, possibly containing a second AGN. The combined H2 mass derived for both objects using the [CI]2-1 emission is 3.3x10^10Msun. The total CO(7-6)/[CI]2-1 line flux ratio of 0.2 suggests a low excitation molecular gas reservoir and/or enhanced atomic carbon in cosmic-ray dominated regions. We detect spatially-resolved H2O 2_{11}-2_{02} emission - for the first time in a high-z un-lensed galaxy - near the outer radio lobe to the east, and near the bend of the radio jet to the west of the radio galaxy. No underlying 246GHz continuum emission is seen at either position. We suggest that the H2O emission is excited in the cooling region behind slow (10-40km/s) shocks in dense molecular gas (10^{3-5} cm^-3). The extended water emission is likely evidence of the radio jet's impact in cooling and forming molecules in the post-shocked gas in the halo and inter-cluster gas similar to what is seen in low-z clusters and other high-z radio galaxies. These observations imply that the passage of the radio jet in the interstellar and inter-cluster medium not only heats gas to high temperatures as is commonly assumed or found in simulations, but also induces cooling and dissipation which can lead to substantial amounts of cold dense molecular gas. The formation of molecules and strong dissipation in the halo gas of MRC1138-262 may explain both the extended diffuse molecular gas and young stars observed around MRC1138-262.

Observations of Extended Green Objects in the 1.35-cm H2O Line on the 22-m Pushchino Radio Telescope

Observations of H2O maser sources at 1.35 cm associated with extended regions of 4.5-µm emission (indicated as “green” on Spitzer survey maps—so-called Extended Green Objects, EGOs) are reported. EGOs are considered as characteristic signposts of regions of formation of massive stars, which host high-velocity outflows, as well as methanol, water, and hydroxyl masers. The observations were carried out in January–May 2015 on the 22-meter radio telescope of the Pushchino Radio Astronomy Observatory. The sample studied includes 24 EGOs north of declination -29° taken from the Spitzer GLIMPSE survey, together with one of the brightest Class I methanol masers G6.05-1.45 (M8E) and the Class I methanol maser in an IRDC G359.94+0.17. H2O maser emission was detected toward 11 of the EGOs: G11.94-0.62, G14.33-0.64, G16.59-0.06, G23.01-0.41, G24.943+0.074, G28.83-0.25, G34.3+0.2, G34.403+0.233, G35.20-0.74, G45.47+0.07, and G49.267-0.337. These including the well known H2O maser in the W44 region, G34.3+0.2. H2O emission from G28.83-0.25 was detected for the first time, at 77.6 km/s, with a flux density of 19 Jy in January and 16 Jy in February 2015. The source was probably caught at an early stage of the propagation of a shock wave. The Class I methanol masers G359.94+0.17 and G6.05-1.45 (M8E) and 13 of the EGOs were not detected in the H2O line, with 3s upper limits of ~6-7 Jy. Spectra and maser-emission parameters are given for the detected H2Omasers, for some of which strong variability of the H2O maser emission was observed. The detected H2Omasers, together with the Class I methanol masers and extended 4.5-µm emission, are associated with a very early stage in the development of young stellar objects in the regions of the EGOs. However, this sample of EGOs is not uniform. The presence of 44-GHz Class I methanol masers together with EGOs cannot be considered the only sign of early stages of star formation.

Cerebral Functional Response during Eyelid Opening/Closing with Bell's Phenomenon and Volitional Vertical Eye Movements in Humans.

Bell's phenomenon is a physiological phenomenon wherein the eye ball involuntarily rolls upward during eyelid closing. Although this phenomenon occurs in healthy individuals, the neural mechanism related to Bell's phenomenon has not yet been identified. We aimed to investigate the brain regions relevant to Bell's phenomenon and volitional eye movement using [15O] H2O and positron emission tomography (PET). We measured regional cerebral blood flow (rCBF) in 8 normal subjects under 3 conditions: at rest with eyes closed, during opening and closing of the eyelids in response to sound stimuli (lid opening/closing), and during vertical movement of the eyes with lids closed in response to sound stimuli (volitional eye movement). The supplementary motor area (SMA) proper, right superior temporal gyrus, right insular cortex and left angular gyrus were activated during lid opening/closing. The right frontal eye field (FEF), pre-SMA, left primary motor area, right angular gyrus, and SMA proper were activated during volitional eye movement. The SMA proper was active during both tasks, while the FEF and pre-SMA were active during volitional eye movement, but not during eyelid opening/closing. A comparison of activation during volitional eye movements and lid opening/closing tasks revealed a relative increase in rCBF in the FEF. There were no areas that are activated in relation to Bell's phenomenon. In conclusion, activation in the FEF mainly occurs during volitional eye movement. Since Bell's phenomenon is a reflexive eye movement, the FEF is scarcely concerned in Bell's phenomenon.

Molecule survival in magnetized protostellar disk winds

We investigate whether the broad wings of H2O emission identified with Herschel towards low-mass Class 0 and Class 1 protostars may be consistent with an origin in a dusty MHD disk wind, and the constraints it would set on the underlying disk properties. We present synthetic H2O line profiles predictions for a typical MHD disk wind solution with various values of disk accretion rate, stellar mass, extension of the launching area, and view angle. We compare them in terms of line shapes and intensities with the HIFI profiles observed by the WISH Key Program. We find that a dusty MHD disk wind launched from 0.2--0.6 AU AU to 3--25 AU can reproduce to a remarkable degree the observed shapes and intensities of the broad H2O component, both in the fundamental 557 GHz line and in more excited lines. Such a model also readily reproduces the observed correlation of 557 GHz line luminosity with envelope density, if the infall rate at 1000 AU is 1--3 times the disk accretion rate in the wind ejection region. It is also compatible with the typical disk size and bolometric luminosity in the observed targets. However, the narrower line profiles in Class 1 sources suggest that MHD disk winds in these sources, if present, would have to be slower and/or less water rich than in Class 0 sources. In conclusion, MHD disk winds appear as a valid (though not unique) option to consider for the origin of the broad H2O component in low-mass protostars. ALMA appears ideally suited to further test this model by searching for resolved signatures of the warm and slow wide-angle molecular wind that would be predicted.

The influence of initial pressure on the characteristics of conical bubble sonoluminescence

Based on a conical bubble U-tube, conical bubble sonoluminescence was investigated by using pure water as the working medium. Intense cavitation luminescence can be obtained. With the decrease in initial pressure inside the bubble, the intensity and duration of light emission increased. The spectrum is mainly composed of the spectral bands of H2O at the initial pressure of 1000 Pa. With the decrease in initial pressure, a broad continuum background spectrum that is well fitted by blackbody radiation can be detected, on which several spectral bands emitted by water molecules are superimposed. A higher temperature inside the bubble can be obtained with the decrease in initial pressure. Moreover, the intensity of the continuum background spectrum becomes more dominant compared with that of H2O emission bands. Finally, we conclude that blackbody radiation and molecular emission contribute to luminescence of conical bubble cavitation. Moreover, the initial pressure inside the conical bubble significantly affects the emission mechanism of conical bubble sonoluminescence.

Lyman series emission of valence and inner-shell excited gaseous H2O

SynopsisWe present emission cross section functions for Lyman series fluorescence emission after photoexcitation of water molecules with monochromatized synchrotron radiation as function of the exciting-photon energy. Both the valence and inner-shell excitation energy range of the water molecule are covered. The results are compared to literature and contribute to complete the model of dissociative relaxation dynamics of excited small molecules.

THE 2014 ALMA LONG BASELINE CAMPAIGN: OBSERVATIONS OF THE STRONGLY LENSED SUBMILLIMETER GALAXY HATLAS J090311.6+003906 AT z = 3.042

We present initial results of very high resolution Atacama Large Millimeter/submillimeter Array (ALMA) observations of the $z$=3.042 gravitationally lensed galaxy HATLAS J090311.6+003906 (SDP.81). These observations were carried out using a very extended configuration as part of Science Verification for the 2014 ALMA Long Baseline Campaign, with baselines of up to 15 km. We present continuum imaging at 151, 236 and 290 GHz, at unprecedented angular resolutions as fine as 23 milliarcseconds (mas), corresponding to an un-magnified spatial scale of ~180 pc at z=3.042. The ALMA images clearly show two main gravitational arc components of an Einstein ring, with emission tracing a radius of ~1.5". We also present imaging of CO(10-9), CO(8-7), CO(5-4) and H2O line emission. The CO emission, at an angular resolution of ~170 mas, is found to broadly trace the gravitational arc structures but with differing morphologies between the CO transitions and compared to the dust continuum. Our detection of H2O line emission, using only the shortest baselines, provides the most resolved detection to date of thermal H2O emission in an extragalactic source. The ALMA continuum and spectral line fluxes are consistent with previous Plateau de Bure Interferometer and Submillimeter Array observations despite the impressive increase in angular resolution. Finally, we detect weak unresolved continuum emission from a position that is spatially coincident with the center of the lens, with a spectral index that is consistent with emission from the core of the foreground lensing galaxy.

Contribution of CO2 and H2S emitted to the atmosphere by plume and diffuse degassing from volcanoes: the Etna volcano case study

Active subaerial volcanoes often discharge large amounts of CO2 and H2S to the atmosphere, not only during eruptions but also during periods of quiescence. These gases are discharged through focused (plumes, fumaroles, etc.) and diffuse emissions. Several studies have been carried out to estimate the global contribution of CO2 and H2S emitted to the atmosphere by subaerial volcanism, but additional volcanic degassing studies will help to improve the current estimates of both CO2 and H2S discharges. In October 2008, a wide-scale survey was carried out at Mt. Etna volcano, one the world’s most actively degassing volcanoes on Earth, for the assessment of the total budget of volcanic/hydrothermal discharges of CO2 and H2S, both from plume and diffuse emissions. Surface CO2 and H2S effluxes were measured by means of the accumulation chamber method at 4075 sites, covering an area of about 972.5 km2. Concurrently, plume SO2 emission at Mt. Etna was remotely measured by a car-borne Differential Optical Absorption Spectrometry (DOAS) instrument. Crater emissions of H2O, CO2 and H2S were estimated by multiplying the plume SO2 emission times the H2O/SO2, CO2/SO2 and H2S/SO2 gas plume mass ratios measured in situ using a portable multisensor. The total output of diffuse CO2 emission from Mt. Etna was estimated to be 20,000 ± 400 t day−1 with 4520 t day−1 of deep-seated CO2. Diffuse H2S output was estimated to be 400 ± 20 kg day−1, covering an area of 9.1 km2 around the summit craters of the volcano. Diffuse H2S emission on the volcano flanks was either negligible or null, probably due to scrubbing of this gas before reaching the surface. During this study, the average crater SO2 emission rate was ~2100 t day−1. Based on measured SO2 emission rates, the estimated H2O, CO2 and H2S emission rates from Etna’s crater degassing were 220,000 ± 100,000, 35,000 ± 16,000 and 510 ± 240 t day−1, respectively. These high values are explained in terms of intense volcanic activity at the time of this survey. The diffuse/plume CO2 emission mass ratio at Mt. Etna was ~0.57, that is typical of erupting volcanoes (mass ratio <1). The average CO2/SO2 molar ratio measured in the plume was 11.5, which is typical of magmatic degassing at great depth beneath the volcano, and the CO2/H2S mass ratio in total diffuse gas emissions was much higher (~11,000) than in plume gas emissions (~68). These results will provide important implications for estimates of volcanic total carbon and sulfur budget from subaerial volcanoes.

OH and H2O maser variations in W33B

The active star-forming region W33B is a source of OH and H2O maser emission located in distinct zones around the central object. The aim was to obtain the complete Stokes pattern of polarised OH maser emission, to trace its variability and to investigate flares and long-term variability of the H2O maser and evolution of individual emission features. Observations in the OH lines at a wavelength of 18 cm were carried out on the Nan\c{c}ay radio telescope (France) at a number of epochs in 2008--2014; H2O line observations (long-term monitoring) at a wavelength of 1.35 cm were performed on the 22-metre radio telescope of the Pushchino Radio Astronomy Observatory (Russia) between 1981 and 2014. We have observed strong variability of the emission features in the main 1665- and 1667-MHz OH lines as well as in the 1612-MHz satellite line. Zeeman splitting has been detected in the 1665-MHz OH line at 62 km/s and in the 1667-MHz line at 62 and 64 km/s. The magnetic field intensity was estimated to be from 2 to 3 mG. The H2O emission features form filaments, chains with radial-velocity gradients, or more complicated structures including large-scale ones. Long-term observations of the hydroxyl maser in the W33B region have revealed narrowband polarised emission in the 1612-MHz line with a double-peak profile characteristic of Type IIb circumstellar masers. The 30-year monitoring of the water-vapour maser in W33B showed several strong flares of the H2O line. The observed radial-velocity drift of the H2O emission features suggests propagation of an excitation wave in the masering medium with a gradient of radial velocities. In OH and H2O masers some turbulent motions of material are inferred.

HERSCHELFAR-INFRARED SPECTRAL-MAPPING OF ORION BN/KL OUTFLOWS: SPATIAL DISTRIBUTION OF EXCITED CO, H2O, OH, O, AND C+IN SHOCKED GAS

We present ~2'x2' spectral-maps of Orion BN/KL outflows taken with Herschel at ~12'' resolution. For the first time in the far-IR domain, we spatially resolve the emission associated with the bright H2 shocked regions "Peak 1" and "Peak 2" from that of the Hot Core and ambient cloud. We analyze the ~54-310um spectra taken with the PACS and SPIRE spectrometers. More than 100 lines are detected, most of them rotationally excited lines of 12CO (up to J=48-47), H2O, OH, 13CO, and HCN. Peaks 1/2 are characterized by a very high L(CO)/L(FIR)~5x10^{-3} ratio and a plethora of far-IR H2O emission lines. The high-J CO and OH lines are a factor ~2 brighter toward Peak 1 whereas several excited H2O lines are ~50% brighter toward Peak 2. A simplified non-LTE model allowed us to constrain the dominant gas temperature components. Most of the CO column density arises from Tk~200-500 K gas that we associate with low-velocity shocks that fail to sputter grain ice mantles and show a maximum gas-phase H2O/CO~10^{-2} abundance ratio. In addition, the very excited CO (J>35) and H2O lines reveal a hotter gas component (Tk~2500 K) from faster (v_S>25 km/s) shocks that are able to sputter the frozen-out H2O and lead to high H2O/CO>~1 abundance ratios. The H2O and OH luminosities cannot be reproduced by shock models that assume high (undepleted) abundances of atomic oxygen in the preshock gas and/or neglect the presence of UV radiation in the postshock gas. Although massive outflows are a common feature in other massive star-forming cores, Orion BN/KL seems more peculiar because of its higher molecular luminosities and strong outflows caused by a recent explosive event.

Water distribution in shocked regions of the NGC 1333-IRAS 4A protostellar outflow

We present the study of the H2O spatial distribution at two bright shocked regions along IRAS4A, one of the strongest H2O emitters among the Class 0 outflows. We obtained Herschel-PACS maps of the IRAS4A outflow and HIFI observations of two shocked positions. The largest HIFI beam of 38 arcsec at 557 GHz was mapped in several key water lines with different upper energy levels, to reveal possible spatial variations of the line profiles. We detect four H2O lines and CO (16-15) at the two selected positions. In addition, transitions from related outflow and envelope tracers are detected. Different gas components associated with the shock are identified in the H2O emission. In particular, at the head of the red lobe of the outflow, two distinct gas components with different excitation conditions are distinguished in the HIFI emission maps: a compact component, detected in the ground-state water lines, and a more extended one. Assuming that these two components correspond to two different temperature components observed in previous H2O and CO studies, the excitation analysis of the H2O emission suggests that the compact (about 3 arcsec) component is associated with a hot (T~1000 K) gas with densities ~(1-4)x10^5 cm^{-3}, whereas the extended one (10-17 arcsec) traces a warm (T~300-500 K) and dense gas (~(3-5)x10^7 cm^{-3}). Finally, using the CO (16-15) emission observed at R2, we estimate the H2O/H2 abundance of the warm and hot components to be (7-10)x10^{-7} and (3-7)x10^{-5}. Our data allowed us, for the first time, to resolve spatially the two temperature components previously observed with HIFI and PACS. We propose that the compact hot component may be associated with the jet that impacts the surrounding material, whereas the warm, dense, and extended component originates from the compression of the ambient gas by the propagating flow.

Modeling the H2O submillimeter emission in extragalactic sources

Recent observational studies have shown that H2O emission at (rest) submillimeter wavelengths is ubiquitous in infrared galaxies, both in the local and in the early Universe, suggestive of far-infrared pumping of H2O by dust in warm regions. In this work, models are presented that show that (i) the highest-lying H2O lines (E_{upper}>400 K) are formed in very warm (T_{dust}>~90 K) regions and require high H2O columns (N_{H2O}>~3x10^{17} cm^{-2}), while lower lying lines can be efficiently excited with T_{dust}~45-75 K and N_{H2O}~(0.5-2)x10^{17} cm^{-2}; (ii) significant collisional excitation of the lowest lying (E_{upper}<200 K) levels, which enhances the overall L_{H2O}-L_{IR} ratios, is identified in sources where the ground-state para-H2O 1_{11}-0_{00} line is detected in emission; (iii) the H2O-to-infrared (8-1000 um) luminosity ratio is expected to decrease with increasing T_{dust} for all lines with E_{upper}<~300 K, as has recently been reported in a sample of LIRGs, but increases with T_{dust} for the highest lying H2O lines (E_{upper}>400 K); (iv) we find theoretical upper limits for L_{H2O}/L_{IR} in warm environments, owing to H2O line saturation; (v) individual models are presented for two very different prototypical galaxies, the Seyfert 2 galaxy NGC 1068 and the nearest ultraluminous infrared galaxy Arp 220, showing that the excited submillimeter H2O emission is dominated by far-infrared pumping in both cases; (vi) the L_{H2O}-L_{IR} correlation previously reported in observational studies indicates depletion or exhaustion time scales, t_{dep}=Sigma_{gas}/Sigma_{SFR}, of <~12 Myr for star-forming sources where lines up to E_{upper}=300 K are detected, in agreement with the values previously found for (U)LIRGs from HCN millimeter emission...

Warm gas towards young stellar objects in Corona Australis

The effects of external irradiation on the chemistry and physics in the protostellar envelope around low-mass young stellar objects are poorly understood. The Corona Australis star-forming region contains the R CrA dark cloud, comprising several low-mass protostellar cores irradiated by an intermediate-mass young star. We study the effects on the warm gas and dust in a group of low-mass young stellar objects from the irradiation by the young luminous Herbig Be star R CrA. Herschel/PACS far-infrared datacubes of two low-mass star-forming regions in the R CrA dark cloud are presented. The distribution of CO, OH, H2O, [C II], [O I], and continuum emission is investigated. We have developed a deconvolution algorithm which we use to deconvolve the maps, separating the point-source emission from the extended emission. We also construct rotational diagrams of the molecular species. By deconvolution of the Herschel data, we find large-scale (several thousand AU) dust continuum and spectral line emission not associated with the point sources. Similar rotational temperatures are found for the warm CO ($282\pm4$ K), hot CO ($890\pm84$ K), OH ($79\pm4$ K), and H2O ($197\pm7$ K) emission, respectively, in the point sources and the extended emission. The rotational temperatures are also similar to what is found in other more isolated cores. The extended dust continuum emission is found in two ridges similar in extent and temperature to molecular mm emission, indicative of external heating from the Herbig Be star R CrA. Our results show that a nearby luminous star does not increase the molecular excitation temperatures in the warm gas around a young stellar object (YSO). However, the emission from photodissociation products of H2O, such as OH and O, is enhanced in the warm gas associated with these protostars and their surroundings compared to similar objects not suffering from external irradiation.

Water emission from the high-mass star-forming region IRAS 17233-3606

We investigate the physical and chemical processes at work during the formation of a massive protostar based on the observation of water in an outflow from a very young object previously detected in H2 and SiO in the IRAS 17233-3606 region. We estimated the abundance of water to understand its chemistry, and to constrain the mass of the emitting outflow. We present new observations of shocked water obtained with the HIFI receiver onboard Herschel. We detected water at high velocities in a range similar to SiO. We self-consistently fitted these observations along with previous SiO data through a state-of-the-art, one-dimensional, stationary C-shock model. We found that a single model can explain the SiO and H2O emission in the red and blue wings of the spectra. Remarkably, one common area, similar to that found for H2 emission, fits both the SiO and H2O emission regions. This shock model subsequently allowed us to assess the shocked water column density, N(H2O)=1.2x10^{18} cm^{-2}, mass, M(H2O)=12.5 M_earth, and its maximum fractional abundance with respect to the total density, x(H2O)=1.4x10^{-4}. The corresponding water abundance in fractional column density units ranges between 2.5x10^{-5} and 1.2x10^{-5}, in agreement with recent results obtained in outflows from low- and high-mass young stellar objects.

Water and methanol in low-mass protostellar outflows: gas-phase synthesis, ice sputtering and destruction

Water in outflows from protostars originates either as a result of gas-phase synthesis from atomic oxygen at T > 200 K, or from sputtered ice mantles containing water ice. We aim to quantify the contribution of the two mechanisms that lead to water in outflows, by comparing observations of gas-phase water to methanol (a grain surface product) towards three low-mass protostars in NGC1333. In doing so, we also quantify the amount of methanol destroyed in outflows. To do this, we make use of JCMT and Herschel-HIFI data of H2O, CH3OH and CO emission lines and compare them to RADEX non-LTE excitation simulations. We find up to one order of magnitude decrease in the column density ratio of CH3OH over H2O as the velocity increases in the line wings up to ~15 km/s. An independent decrease in X(CH3OH) with respect to CO of up to one order of magnitude is also found in these objects. We conclude that gas-phase formation of H2O must be active at high velocities (above 10 km/s, relative to the source velocity) to re-form the water destroyed during sputtering. In addition, the transition from sputtered water at low velocities to formed water at high velocities must be gradual. We place an upper limit of two orders of magnitude on the destruction of methanol by sputtering effects.