Context. The comet Shoemaker-Levy 9 impacted Jupiter in July 1994, leaving its stratosphere with several new species, with water vapor (H2O) among them. Aims. With the aid of a photochemical model, ...H2O can be used as a dynamical tracer in the Jovian stratosphere. In this paper, we aim to constrain the vertical eddy diffusion (Kzz) at levels where H2O is present. Methods. We monitored the H2O disk-averaged emission at 556.936 GHz with the space telescope between 2002 and 2019, covering nearly two decades. We analyzed the data with a combination of 1D photochemical and radiative transfer models to constrain the vertical eddy diffusion in the stratosphere of Jupiter. Results. Odin observations show us that the emission of H2O has an almost linear decrease of about 40% between 2002 and 2019. We can only reproduce our time series if we increase the magnitude of Kzz in the pressure range where H2O diffuses downward from 2002 to 2019, that is, from ~0.2 mbar to ~5 mbar. However, this modified Kzz is incompatible with hydrocarbon observations. We find that even if an allowance is made for the initially large abundances of H2O and CO at the impact latitudes, the photochemical conversion of H2O to CO2 is not sufficient to explain the progressive decline of the H2O line emission, which is suggestive of additional loss mechanisms. Conclusions. The Kzz we derived from the Odin observations of H2O can only be viewed as an upper limit in the ~0.2 mbar to ~5 mbar pressure range. The incompatibility between the interpretations made from H2O and hydrocarbon observations probably results from 1D modeling limitations. Meridional variability of H2O, most probably at auroral latitudes, would need to be assessed and compared with that of hydrocarbons to quantify the role of auroral chemistry in the temporal evolution of the H2O abundance since the SL9 impacts. Modeling the temporal evolution of SL9 species with a 2D model would naturally be the next step in this area of study.
Context. Observations of transitions to the ground-state of a molecule are essential to obtain a complete picture of its excitation and chemistry in the interstellar medium, especially in diffuse ...and/or cold environments. For the important interstellar molecules H2O and NH3, these ground-state transitions are heavily absorbed by the terrestrial atmosphere, hence not observable from the ground. Aims. We attempt to understand the chemistry of nitrogen, oxygen, and their important molecular forms, NH3 and H2O in the interstellar medium of the Galaxy. Methods. We have used the Odin* submillimetre-wave satellite telescope to observe the ground state transitions of ortho-ammonia and ortho-water, including their 15N, 18O, and 17O isotopologues, towards Sgr B2. The extensive simultaneous velocity coverage of the observations, > 500 km s-1, ensures that we can probe the conditions of both the warm, dense gas of the molecular cloud Sgr B2 near the Galactic centre, and the more diffuse gas in the Galactic disk clouds along the line-of-sight. Results. We present ground-state NH3 absorption in seven distinct velocity features along the line-of-sight towards Sgr B2. We find a nearly linear correlation between the column densities of NH3 and CS, and a square-root relation to N2H+. The ammonia abundance in these diffuse Galactic disk clouds is estimated to be about 0.5–1 × 10-8, similar to that observed for diffuse clouds in the outer Galaxy. On the basis of the detection of ${\rm H}_2^{18}{\rm O}$ H 2 18 O absorption in the 3 kpc arm, and the absence of such a feature in the ${\rm H}_2^{17}{\rm O}$ H 2 17 O spectrum, we conclude that the water abundance is around 10-7, compared to ~10-8 for NH3. The Sgr B2 molecular cloud itself is seen in absorption in NH3, 15NH3, H2O, ${\rm H}_2^{18}{\rm O}$ H 2 18 O , and ${\rm H}_2^{17}{\rm O}$ H 2 17 O , with emission superimposed on the absorption in the main isotopologues. The non-LTE excitation of NH3 in the environment of Sgr B2 can be explained without invoking an unusually hot (500 K) molecular layer. A hot layer is similarly not required to explain the line profiles of the 11,0 ← 10,1 transition from H2O and its isotopologues. The relatively weak 15NH3 absorption in the Sgr B2 molecular cloud indicates a high 14N/15N isotopic ratio > 600. The abundance ratio of ${\rm H}_2^{18}{\rm O}$ H 2 18 O and ${\rm H}_2^{17}{\rm O}$H217O is found to be relatively low, 2.5–3. These results together indicate that the dominant nucleosynthesis process in the Galactic centre is CNO hydrogen burning.
Aims. Our aim is to observationally investigate the cosmic Dark Ages in order to constrain star and structure formation models, as well as the chemical evolution in the early Universe. Methods. ...Spectral lines from atoms and molecules in primordial perturbations at high redshifts can give information about the conditions in the early universe before and during the formation of the first stars in addition to the epoch of reionisation. The lines may arise from moving primordial perturbations before the formation of the first stars (resonant scattering lines), or could be thermal absorption or emission lines at lower redshifts. The difficulties in these searches are that the source redshift and evolutionary state, as well as molecular species and transition are unknown, which implies that an observed line can fall within a wide range of frequencies. The lines are also expected to be very weak. Observations from space have the advantages of stability and the lack of atmospheric features which is important in such observations. We have therefore, as a first step in our searches, used the Odin (Odin is a Swedish-led satellite project funded jointly by the Swedish National Space Board (SNSB), the Canadian Space Agency (CSA), the National Technology Agency of Finland (Tekes) and Centre National d'Etudes Spatiales (CNES). The Swedish Space Corporation was the prime contractor and also is responsible for the satellite operation.) satellite to perform two sets of spectral line surveys towards several positions. The first survey covered the band 547–578 GHz towards two positions, and the second one covered the bands 542.0–547.5 GHz and 486.5–492.0 GHz towards six positions selected to test different sizes of the primordial clouds. Two deep searches centred at 543.250 and 543.100 GHz with 1 GHz bandwidth were also performed towards one position. The two lowest rotational transitions of H2 will be redshifted to these frequencies from z ~ 20–30, which is the predicted epoch of the first star formation. Results. No lines are detected at an rms level of 14–90 and 5–35 mK for the two surveys, respectively, and 2–7 mK in the deep searches with a channel spacing of 1–16 MHz. The broad bandwidth covered allows a wide range of redshifts to be explored for a number of atomic and molecular species and transitions. From the theoretical side, our sensitivity analysis show that the largest possible amplitudes of the resonant lines are about 1 mK at frequencies $\la$200 GHz, and a few μK around 500–600 GHz, assuming optically thick lines and no beam-dilution. However, if existing, thermal absorption lines have the potential to be orders of magnitude stronger than the resonant lines. We make a simple estimation of the sizes and masses of the primordial perturbations at their turn-around epochs, which previously has been identified as the most favourable epoch for a detection. This work may be considered as an important pilot study for our forthcoming observations with the Herschel Space Observatory.
Context . The Odin satellite is now into its twentieth year of operation, much surpassing its design life of two years. One of its major astronomical pursuits was the search for and study of water ...vapor in diverse regions of the Solar System and the Milky Way galaxy. The Herschel space observatory was needed to detect water vapor in external galaxies.
Aims . Our goal is to study the distribution and excitation of water vapor and other molecules in the barred spiral galaxy NGC 1365.
Methods . Herschel has observed the central region of NGC 1365 in two positions, and both its SPIRE and PACS observations are available in the Herschel Science Archive. Herschel PACS images have been produced of the 70 and 160 mu m infrared emission from the whole galaxy, and also of the cold dust distribution as obtained from the ratio of the 160 to 70 mu m images. The Herschel SPIRE observations have been used to produce simultaneously observed maps of the 557 GHz o-H2O, 752 GHz p-H2O, 691 GHz CO(6-5), 1037 GHz CO(9-8), 537 GHz CH, 835 GHz CH', and the 1461 GHz N IT lines (efficiently probing the warm ionized medium) in the inner bar and circumnuclear torus region; - however, these observations have no effective velocity resolution. For this reason Odin has recently observed the 557 GHz ortho-H2O ground state line in the central region with high (5 km s(-1)) spectral resolution.
Results . The emission and absorption of H2O at 557 GHz, with a velocity resolution of 5 km s(-1), has been marginally detected in NGC 1365 with Odin . The water vapor is predominantly located in a shocked 15 '' (1.3 kpc) region near some central compact radio sources and hot-spot HIT regions, close to the northeast component of the molecular torus surrounding the nucleus. An analysis of the H2O line intensities and velocities indicates that a shock-region is located here. This is corroborated by a statistical image deconvolution of our SEST CO(3-2) observations, yielding 5 '' resolution, and a study of our Very Large Array HI absorption observations, as well as comparisons with published interferometric CO observations. Additionally, an enticing 20 '' HI ridge is found to extend south-southeast from the nucleus, coinciding in position with the southern edge of an O III outflow cone, emanating from the nucleus. The molecular chemistry of the shocked central region of NGC 1365 is analyzed with special emphasis on the CO, H2O and CH, CH+ results.
Conclusions . The dominating activity near the northeast (NE) torus component may have been triggered by the rapid bar-driven inflow into the circumnuclear torus causing cloud-cloud collisions and shocks, leading to the formation of stellar superclusters and, hence, also to more efficient PDR chemistry, which, here, may also benefit from cosmic ray focusing caused by the observed aligned magnetic field. The very high activity near the NE torus component may reflect the fact that the eastern bar-driven gas inflow into the NE region is much more massive than the corresponding western gas inflow into the southwest region. The H2O and CH+ emissions peak in the NE torus region, but the CO and CH emissions are more evenly distributed across the whole circumnuclear torus. The higher energy CO spectral line energy distribution (SLED) is nicely modeled by a low velocity (10 km s(-1)) shock, which may as well explain the required CH excitation and its high abundance in denser gas. The higher velocity (40 km s(-1)) shock required to model the H2O SLED in the NE torus region, paired with the intense UV radiation from the observed massive young stellar superclusters, may also explain the high abundance of CH+ in this region. The nuclear H I ridge may have been created by the action of outflow-driving X-ray photons colliding with ice-covered dust grains. A precessing nuclear engine, as is suggested by the tilted massive inner gas torus, may be necessary to explain the various nuclear outflows encountered.
The apparition of bright comets C/2012 F6 (Lemmon) and C/2014 Q2 (Lovejoy) in March-April 2013 and January 2015, combined with the improved observational capabilities of submillimeter facilities, ...offered an opportunity to carry out sensitive compositional and isotopic studies of the volatiles in their coma. We observed comet Lovejoy with the IRAM 30 m telescope between 13 and 26 January 2015, and with the Odin submillimeter space observatory on 29 January–3 February 2015. We detected 22 molecules and several isotopologues. The H216O and H218O production rates measured with Odin follow a periodic pattern with a period of 0.94 days and an amplitude of ~25%. The inferred isotope ratios in comet Lovejoy are 16O/18O = 499 ± 24 and D/H = 1.4 ± 0.4 × 10-4 in water, 32S/34S = 24.7 ± 3.5 in CS, all compatible with terrestrial values. The ratio 12C/13C = 109 ± 14 in HCN is marginally higher than terrestrial and 14N/15N = 145 ± 12 in HCN is half the Earth ratio. Several upper limits for D/H or 12C/13C in other molecules are reported. From our observation of HDO in comet C/2014 Q2 (Lovejoy), we report the first D/H ratio in an Oort Cloud comet that is not larger than the terrestrial value. On the other hand, the observation of the same HDO line in the other Oort-cloud comet, C/2012 F6 (Lemmon), suggests a D/H value four times higher. Given the previous measurements of D/H in cometary water, this illustrates that a diversity in the D/H ratio and in the chemical composition, is present even within the same dynamical group of comets, suggesting that current dynamical groups contain comets formed at very different places or times in the early solar system.
Context.
The
Odin
satellite is now into its twentieth year of operation, much surpassing its design life of two years. One of its major astronomical pursuits was the search for and study of water ...vapor in diverse regions of the Solar System and the Milky Way galaxy. The
Herschel
space observatory was needed to detect water vapor in external galaxies.
Aims.
Our goal is to study the distribution and excitation of water vapor and other molecules in the barred spiral galaxy NGC 1365.
Methods.
Herschel
has observed the central region of NGC 1365 in two positions, and both its SPIRE and PACS observations are available in the
Herschel
Science Archive.
Herschel
PACS images have been produced of the 70 and 160
μ
m infrared emission from the whole galaxy, and also of the cold dust distribution as obtained from the ratio of the 160 to 70
μ
m images. The
Herschel
SPIRE observations have been used to produce simultaneously observed maps of the 557 GHz o-H
2
O, 752 GHz p-H
2
O, 691 GHz CO(6−5), 1037 GHz CO(9−8), 537 GHz CH, 835 GHz CH
+
, and the 1461 GHz N
II
lines (efficiently probing the warm ionized medium) in the inner bar and circumnuclear torus region; – however, these observations have no effective velocity resolution. For this reason
Odin
has recently observed the 557 GHz ortho-H
2
O ground state line in the central region with high (5 km s
−1
) spectral resolution.
Results.
The emission and absorption of H
2
O at 557 GHz, with a velocity resolution of 5 km s
−1
, has been marginally detected in NGC 1365 with
Odin
. The water vapor is predominantly located in a shocked 15″ (1.3 kpc) region near some central compact radio sources and hot-spot H
II
regions, close to the northeast component of the molecular torus surrounding the nucleus. An analysis of the H
2
O line intensities and velocities indicates that a shock-region is located here. This is corroborated by a statistical image deconvolution of our SEST CO(3−2) observations, yielding 5″ resolution, and a study of our Very Large Array H
I
absorption observations, as well as comparisons with published interferometric CO observations. Additionally, an enticing 20″ H
I
ridge is found to extend south-southeast from the nucleus, coinciding in position with the southern edge of an O
III
outflow cone, emanating from the nucleus. The molecular chemistry of the shocked central region of NGC 1365 is analyzed with special emphasis on the CO, H
2
O and CH, CH
+
results.
Conclusions.
The dominating activity near the northeast (NE) torus component may have been triggered by the rapid bar-driven inflow into the circumnuclear torus causing cloud-cloud collisions and shocks, leading to the formation of stellar superclusters and, hence, also to more efficient PDR chemistry, which, here, may also benefit from cosmic ray focusing caused by the observed aligned magnetic field. The very high activity near the NE torus component may reflect the fact that the eastern bar-driven gas inflow into the NE region is much more massive than the corresponding western gas inflow into the southwest region. The H
2
O and CH
+
emissions peak in the NE torus region, but the CO and CH emissions are more evenly distributed across the whole circumnuclear torus. The higher energy CO spectral line energy distribution (SLED) is nicely modeled by a low velocity (10 km s
−1
) shock, which may as well explain the required CH excitation and its high abundance in denser gas. The higher velocity (40 km s
−1
) shock required to model the H
2
O SLED in the NE torus region, paired with the intense UV radiation from the observed massive young stellar superclusters, may also explain the high abundance of CH
+
in this region. The nuclear H
I
ridge may have been created by the action of outflow-driving X-ray photons colliding with ice-covered dust grains. A precessing nuclear engine, as is suggested by the tilted massive inner gas torus, may be necessary to explain the various nuclear outflows encountered.
Context. The Odin satellite is now into its twentieth year of operation, much surpassing its design life of two years. One of its major astronomical pursuits was the search for and study of water ...vapor in diverse regions of the Solar System and the Milky Way galaxy. The Herschel space observatory was needed to detect water vapor in external galaxies. Aims. Our goal is to study the distribution and excitation of water vapor and other molecules in the barred spiral galaxy NGC 1365. Methods. Herschel has observed the central region of NGC 1365 in two positions, and both its SPIRE and PACS observations are available in the Herschel Science Archive. Herschel PACS images have been produced of the 70 and 160 μm infrared emission from the whole galaxy, and also of the cold dust distribution as obtained from the ratio of the 160 to 70 μm images. The Herschel SPIRE observations have been used to produce simultaneously observed maps of the 557 GHz o-H2O, 752 GHz p-H2O, 691 GHz CO(6−5), 1037 GHz CO(9−8), 537 GHz CH, 835 GHz CH+, and the 1461 GHz N II lines (efficiently probing the warm ionized medium) in the inner bar and circumnuclear torus region; – however, these observations have no effective velocity resolution. For this reason Odin has recently observed the 557 GHz ortho-H2O ground state line in the central region with high (5 km s−1) spectral resolution. Results. The emission and absorption of H2O at 557 GHz, with a velocity resolution of 5 km s−1, has been marginally detected in NGC 1365 with Odin. The water vapor is predominantly located in a shocked 15″ (1.3 kpc) region near some central compact radio sources and hot-spot H II regions, close to the northeast component of the molecular torus surrounding the nucleus. An analysis of the H2O line intensities and velocities indicates that a shock-region is located here. This is corroborated by a statistical image deconvolution of our SEST CO(3−2) observations, yielding 5″ resolution, and a study of our Very Large Array H I absorption observations, as well as comparisons with published interferometric CO observations. Additionally, an enticing 20″ H I ridge is found to extend south-southeast from the nucleus, coinciding in position with the southern edge of an O III outflow cone, emanating from the nucleus. The molecular chemistry of the shocked central region of NGC 1365 is analyzed with special emphasis on the CO, H2O and CH, CH+ results. Conclusions. The dominating activity near the northeast (NE) torus component may have been triggered by the rapid bar-driven inflow into the circumnuclear torus causing cloud-cloud collisions and shocks, leading to the formation of stellar superclusters and, hence, also to more efficient PDR chemistry, which, here, may also benefit from cosmic ray focusing caused by the observed aligned magnetic field. The very high activity near the NE torus component may reflect the fact that the eastern bar-driven gas inflow into the NE region is much more massive than the corresponding western gas inflow into the southwest region. The H2O and CH+ emissions peak in the NE torus region, but the CO and CH emissions are more evenly distributed across the whole circumnuclear torus. The higher energy CO spectral line energy distribution (SLED) is nicely modeled by a low velocity (10 km s−1) shock, which may as well explain the required CH excitation and its high abundance in denser gas. The higher velocity (40 km s−1) shock required to model the H2O SLED in the NE torus region, paired with the intense UV radiation from the observed massive young stellar superclusters, may also explain the high abundance of CH+ in this region. The nuclear H I ridge may have been created by the action of outflow-driving X-ray photons colliding with ice-covered dust grains. A precessing nuclear engine, as is suggested by the tilted massive inner gas torus, may be necessary to explain the various nuclear outflows encountered.
We present the results of a molecular survey of comet 67P/Churyumov-Gerasimenko undertaken with the Institut de RadioAstronomie Millimétrique (IRAM) 30-m radio telescope in November–December 2021, ...when it had its most favourable apparition in decades. Observations at IRAM 30-m during the 12–16 November period covered 8 GHz bandwidth at 3 mm, 16 GHz at 2 mm, and 60 GHz in the 1 mm window domain. These were completed by snapshots at 1 mm on 12–13 December and a short observation of the H
2
O line at 557 GHz with the Odin sub-millimetre observatory on 17.0 November 2021, and with 18-cm observations of OH with the Nançay radio telescope. Less sensitive observations obtained at a previous perihelion passage on 18–22 September 2015 with IRAM and 9–12 November 2015 with Odin are also presented. The gas outflow velocity, outgassing pattern, and temperature have been accurately constrained by the observations. They are perfectly consistent with those measured in situ with the Rosetta/MIRO sub-millimetre instrument in 2015. In particular, the asymmetry of the line is well represented by a jet concentrating three-quarters of the outgassing in about
π
steradians. We derived abundances relative to water for seven molecules and significant upper limits for approximately five others. The retrieved abundances were compared to those measured in situ at the previous perihelion with Rosetta. While those of HCN, CH
3
OH, and HNCO are comparable, 67P is found to be depleted in H
2
S and relatively normal in CS (H
2
S/CS ≈ 3) in strong contradiction with the Rosetta/ROSINA mass spectrometer measurement of the H
2
S/CS
2
(≈100) abundance ratio. While the formaldehyde total abundance found with IRAM 30-m when assuming it to be mostly produced by a distributed source (Haser parent scale length ≈8000 km) is similar to the one derived by Rosetta/ROSINA, we find that the formaldehyde coming from the nucleus is one order of magnitude less abundant than measured in situ by Rosetta/ROSINA.
Aims. We study the structure and kinematics of the OH-streamer and the +80 km s-1 cloud and their interactions with the circumnuclear disk (CND) and with other molecular clouds in the vicinity of ...the Galactic centre (GC), and we map OH absorption at about 6′′ resolution at R ≤ 10 pc from the GC, with about 9 km s-1 of velocity resolution. Methods. The VLA was used to map OH line absorption at the 1665 and 1667 MHz lambda doublet main lines of the 2Π3/2 state towards the Sagittarius A complex. Results. Strong OH absorption was found in the OH-streamer, the southern streamer (SS), the +20, +50, and +80 km s-1 molecular clouds, the molecular belt, the CND, the expanding molecular ring (EMR), and the high negative velocity gas (HNVG). The OH-streamer was found to comprise three parts, head, mid, and tail, and to interact with the SS/+20, +80 km s-1 clouds and the CND. Optical depths and column densities divided by excitation temperatures have been calculated for the OH-streamer and the +80 km s-1 cloud. Conclusions. The OH-streamer, the SS, the +20 and +80 km s-1 clouds, and the CND are intimately related in position and velocity space. The OH-streamer was found to be a clumpy object stretching in projection from the inner radius of the CND at about 1.8 pc from Sgr A∗towards and partly engulfing Sgr A∗. As a side result of our data, a possible link between the near side of the EMR and the CND’s southwest lobe was found. Additionally, we found OH absorption against all four of the previously known compact H ii regions A−D, located east of Sgr A East, indicating their close association with the +50 km s-1 cloud.
Context.
The comet Shoemaker-Levy 9 impacted Jupiter in July 1994, leaving its stratosphere with several new species, with water vapor (H
2
O) among them.
Aims.
With the aid of a photochemical model, ...H
2
O can be used as a dynamical tracer in the Jovian stratosphere. In this paper, we aim to constrain the vertical eddy diffusion (
K
zz
) at levels where H
2
O is present.
Methods.
We monitored the H
2
O disk-averaged emission at 556.936 GHz with the space telescope between 2002 and 2019, covering nearly two decades. We analyzed the data with a combination of 1D photochemical and radiative transfer models to constrain the vertical eddy diffusion in the stratosphere of Jupiter.
Results. Odin
observations show us that the emission of H
2
O has an almost linear decrease of about 40% between 2002 and 2019. We can only reproduce our time series if we increase the magnitude of
K
zz
in the pressure range where H
2
O diffuses downward from 2002 to 2019, that is, from ~0.2 mbar to ~5 mbar. However, this modified
K
zz
is incompatible with hydrocarbon observations. We find that even if an allowance is made for the initially large abundances of H
2
O and CO at the impact latitudes, the photochemical conversion of H
2
O to CO
2
is not sufficient to explain the progressive decline of the H
2
O line emission, which is suggestive of additional loss mechanisms.
Conclusions.
The
K
zz
we derived from the
Odin
observations of H
2
O can only be viewed as an upper limit in the ~0.2 mbar to ~5 mbar pressure range. The incompatibility between the interpretations made from H
2
O and hydrocarbon observations probably results from 1D modeling limitations. Meridional variability of H
2
O, most probably at auroral latitudes, would need to be assessed and compared with that of hydrocarbons to quantify the role of auroral chemistry in the temporal evolution of the H
2
O abundance since the SL9 impacts. Modeling the temporal evolution of SL9 species with a 2D model would naturally be the next step in this area of study.
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