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- 2019
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Journal article (peer-reviewed)
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| 2. |
- Goicoechea, J.R., et al.
(author)
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VELOCITY-RESOLVED [C II] EMISSION AND [C II]/FIR MAPPING ALONG ORION WITH HERSCHEL
- 2015
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In: Astrophysical Journal. - 1538-4357 .- 0004-637X. ; 812:1, s. 75-
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Journal article (peer-reviewed)abstract
- We present the first ~7.′5 × 11.′5 velocity-resolved (~0.2 km/s) map of the [C II] 158 μm line toward the Orion molecular cloud1 (OMC1) taken with the Herschel/HIFI instrument. In combination with far-IR (FIR) photometric images and velocity-resolved maps of the H41α hydrogen recombination and CO J = 2–1 lines, this data set provides an unprecedented view of the intricate small-scale kinematics of the ionized/photodissociation region (PDR)/molecular gas interfaces and of the radiative feedback from massive stars. The main contribution to the [C II] luminosity (~85%) is from the extended, FUV-illuminated face of the cloud (G0 > 500, nH > 5 × 10^3 cm^−3) and from dense PDRs (G0>~10^4, nH>~10^5 cm^−3) at the interface between OMC 1 and the H II region surrounding the Trapezium cluster. Around ~15% of the [C II] emission arises from a different gas component without a CO counterpart. The [C II] excitation, PDR gas turbulence, line opacity (from [13C II]), and role of the geometry of the illuminating stars with respect to the cloud are investigated. We construct maps of the L[CII]/LFIR and LFIR/MGas ratios and show that L[CII]/LFIR decreases from the extended cloud component (~10^−2–10^−3) to the more opaque star-forming cores (~10^-3-10−4). The lowest values are reminiscent of the “[C II] deficit” seen in local ultraluminous IR galaxies hosting vigorous star formation. Spatial correlation analysis shows that the decreasing L[C II]/LFIR ratio correlates better with the column density of dust through the molecular cloud than with LFIR/MGas. We conclude that the [C II]-emitting column relative to the total dust column along each line of sight is responsible for the observed L[C II]/LFIR variations through the cloud.
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| 3. |
- Indriolo, N., et al.
(author)
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Herschel Survey of Galactic OH+, H2O+, and H3O+: Probing the Molecular Hydrogen Fraction and Cosmic-Ray Ionization Rate
- 2015
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In: Astrophysical Journal. - 1538-4357 .- 0004-637X. ; 800:1, s. 40-
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Journal article (peer-reviewed)abstract
- In diffuse interstellar clouds the chemistry that leads to the formation of the oxygen-bearing ions OH+, H2O+, and H3O+ begins with the ionization of atomic hydrogen by cosmic rays, and continues through subsequent hydrogen abstraction reactions involving H2. Given these reaction pathways, the observed abundances of these molecules are useful in constraining both the total cosmic-ray ionization rate of atomic hydrogen (ζH) and molecular hydrogen fraction (f_H_2). We present observations targeting transitions of OH+, H2O+, and H3O+ made with the Herschel Space Observatory along 20 Galactic sight lines toward bright submillimeter continuum sources. Both OH+ and H2O+ are detected in absorption in multiple velocity components along every sight line, but H3O+ is only detected along 7 sight lines. From the molecular abundances we compute f_H_2 in multiple distinct components along each line of sight, and find a Gaussian distribution with mean and standard deviation 0.042 ± 0.018. This confirms previous findings that OH+ and H2O+ primarily reside in gas with low H2 fractions. We also infer ζH throughout our sample, and find a lognormal distribution with mean log (ζH) = –15.75 (ζH = 1.78 × 10–16 s–1) and standard deviation 0.29 for gas within the Galactic disk, but outside of the Galactic center. This is in good agreement with the mean and distribution of cosmic-ray ionization rates previously inferred from H_3^+ observations. Ionization rates in the Galactic center tend to be 10-100 times larger than found in the Galactic disk, also in accord with prior studies.
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| 4. |
- Muller, Holger, et al.
(author)
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Detection of extragalactic argonium, ArH+, toward PKS 1830-211
- 2015
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 582, s. 4-
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Journal article (peer-reviewed)abstract
- Context. Argonium has recently been detected as a ubiquitous molecule in our Galaxy. Model calculations indicate that its abundance peaks at molecular fractions in the range of 10-4 to 10-3 and that the observed column densities require high values of the cosmic ray ionization rate. Therefore, this molecular cation may serve as an excellent tracer of the very diffuse interstellar medium (ISM), as well as an indicator of the cosmic ray ionization rate.Aims. We attempted to detect ArH+ in extragalactic sources to evaluate its diagnostic power as a tracer of the almost purely atomic ISM in distant galaxies.Methods. We obtained ALMA observations of a foreground galaxy at z = 0.89 in the direction of the lensed blazar PKS 1830−211.Results. Two isotopologs of argonium, 36ArH+ and 38ArH+, were detected in absorption along two different lines of sight toward PKS 1830−211, known as the SW and NE images of the background blazar. The argonium absorption is clearly enhanced on the more diffuse line of sight (NE) compared to other molecular species. The isotopic ratio 36Ar/38Ar is 3.46 ± 0.16 toward the SW image, i.e., significantly lower than the solar value of 5.5.Conclusions. Our results demonstrate the suitability of argonium as a tracer of the almost purely atomic, diffuse ISM in high-redshift sources. The evolution of the isotopic ratio with redshift may help to constrain nucleosynthetic scenarios in the early Universe.
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| 5. |
- Neufeld, D.A., et al.
(author)
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HERSCHEL OBSERVATIONS of INTERSTELLAR CHLORONIUM. II. DETECTIONS TOWARD G29.96-0.02, W49N, W51, and W3(OH), and DETERMINATIONS of the ORTHO-TO-PARA and 35Cl/37Cl ISOTOPIC RATIOS
- 2015
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In: Astrophysical Journal. - 1538-4357 .- 0004-637X. ; 807:1
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Journal article (peer-reviewed)abstract
- We report additional detections of the chloronium molecular ion, H2Cl+, toward four bright submillimeter continuum sources: G29.96-0.02, W49N, W51, and W3(OH). With the use of the HIFI instrument on board the Herschel Space Observatory, we observed the 212-101 transition of ortho-H235Cl+ at 781.627 GHz in absorption toward all four sources. Much of the detected absorption arises in diffuse foreground clouds that are unassociated with the background continuum sources and in which our best estimates of the N(H2Cl+)/N(H) ratio lie in the range (0.9-4.8)× 10-9. These chloronium abundances relative to atomic hydrogen can exceed the predictions of current astrochemical models by up to a factor of 5. Toward W49N, we have also detected the 212-101 transition of ortho-H237Cl+ at 780.053 GHz and the 111-000 transition of para-H235Cl+ at 485.418 GHz. These observations imply H235Cl+/H237Cl+ column density ratios that are consistent with the solar system 35Cl/37Cl isotopic ratio of 3.1, and chloronium ortho-to-para ratios consistent with 3, the ratio of spin statistical weights.
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| 6. |
- Morris, P. W., et al.
(author)
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Eta Carinae's Dusty Homunculus Nebula from Near-infrared to Submillimeter Wavelengths: Mass, Composition, and Evidence for Fading Opacity
- 2017
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In: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 842:2, s. Article no. 79 -
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Journal article (peer-reviewed)abstract
- Infrared observations of the dusty, massive Homunculus Nebula around the luminous blue variable eta Carinae are crucial to characterize the mass-loss history and help constrain the mechanisms leading to the great eruption. We present the 2.4-670 mu m spectral energy distribution, constructed from legacy Infrared Space Observatory observations and new spectroscopy obtained with the Herschel Space Observatory. Using radiative transfer modeling, we find that the two best-fit dust models yield compositions that are consistent with CNO-processed material, with iron, pyroxene and other metal-rich silicates, corundum, and magnesium-iron sulfide in common. Spherical corundum grains are supported by the good match to a narrow 20.2 mu m feature. Our preferred model contains nitrides AlN and Si3N4 in low abundances. Dust masses range from 0.25 to 0.44 M-circle dot, but M-tot. 45M(circle dot) in both cases, due to an expected high Fe gas-to-dust ratio. The bulk of dust is within a 5 '' x 7 '' central region. An additional compact feature is detected at 390 mu m. We obtain L-IR = 2.96 x 10(6) L-circle dot, a 25% decline from an average of mid-IR photometric levels observed in 1971-1977. This indicates a reduction in circumstellar extinction in conjunction with an increase in visual brightness, allowing 25%-40% of optical and UV radiation to escape from the central source. We also present an analysis of (CO)-C-12 and (CO)-C-13 J = 5-4 through 9-8 lines, showing that the abundances are consistent with expectations for CNO-processed material. The [C-12 II] line is detected in absorption, which we suspect originates in foreground material at very low excitation temperatures.
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| 7. |
- Motta, V., et al.
(author)
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The "Cosmic Seagull": A Highly Magnified Disk-like Galaxy at z ≃ 2.8 behind the Bullet Cluster
- 2018
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In: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8213 .- 2041-8205. ; 863:2
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Journal article (peer-reviewed)abstract
- We present Atacama Large Millimeter/submillimeter Array measurements of the "Cosmic Seagull," a strongly magnified galaxy at z = 2.7779 behind the Bullet Cluster. We report CO(3-2) and continuum 344 μm (rest-frame) data at one of the highest differential magnifications ever recorded at submillimeter wavelengths (μ up to ∼50), facilitating a characterization of the kinematics of a rotational curve in great detail (at ∼620 pc resolution in the source plane). We find no evidence for a decreasing rotation curve, from which we derive a dynamical mass of (6.3 ± 0.7) × 1010Mowithin r = 2.6 ± 0.1 kpc. The discovery of a third, unpredicted, image provides key information for a future improvement of the lensing modeling of the Bullet Cluster and allows a measure of the stellar mass, , unaffected by strong differential magnification. The baryonic mass is expected to be dominated by the molecular gas content (fgas≤ 80 ± 20%) based on an mass estimated from the difference between dynamical and stellar masses. The star formation rate (SFR) is estimated via the spectral energy distribution (SFR = 190 ± 10 Moyr-1), implying a molecular gas depletion time of 0.25 ± 0.08 Gyr.
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| 8. |
- Persson, Carina, 1964, et al.
(author)
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Ortho-to-para ratio of NH2. Herschel-HIFI observations of ortho- and para-NH2 rotational transitions towards W31C, W49N, W51 and G34.3+0.1
- 2016
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 586, s. Art Nr. A128-
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Journal article (peer-reviewed)abstract
- We have used the Herschel-HIFI instrument to observe both nuclear spin symmetries of amidogen (NH2) towards the high-mass star-forming regions W31C (G10.6-0.4), W49N (G43.2-0.1), W51 (G49.5-0.4) and G34.3+0.1. The aim is to investigate the ratio of nuclear spin types, the ortho-to-para ratio (OPR), of NH2. The excited NH2 transitions are used to construct radiative transfer models of the hot cores and surrounding envelopes in order to investigate the excitation and possible emission of the ground state rotational transitions of ortho-NH2 N_(K_a,K_c} J=1_(1,1) 3/2 - 0_(0,0) 1/2 and para-NH2 2_(1,2) 5/2 - 1_(0,1) 3/2$ used in the OPR calculations. Our best estimate of the average OPR in the envelopes lie above the high temperature limit of three for W49N, specifically 3.5 with formal errors of \pm0.1, but for W31C, W51, and G34.3+0.1 we find lower values of 2.5\pm0.1, 2.7\pm0.1, and 2.3\pm0.1, respectively. Such low values are strictly forbidden in thermodynamical equilibrium since the OPR is expected to increase above three at low temperatures. In the translucent interstellar gas towards W31C, where the excitation effects are low, we find similar values between 2.2\pm0.2 and 2.9\pm0.2. In contrast, we find an OPR of 3.4\pm0.1 in the dense and cold filament connected to W51, and also two lower limits of >4.2 and >5.0 in two other translucent gas components towards W31C and W49N. At low temperatures (T \lesssim 50 K) the OPR of H2 is 20-25 K, depending on time, and values above three at lower temperatures.
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| 9. |
- Wallström, Sofia, 1988, et al.
(author)
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ALMA Compact Array observations of the Fried Egg nebula: Evidence for large-scale asymmetric mass-loss from the yellow hypergiant IRAS 17163-3907
- 2017
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 597, s. A99, pp. 1-10
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Journal article (peer-reviewed)abstract
- Yellow hypergiants are rare and represent a fast evolutionary stage of massive evolved stars. That evolutionary phase is characterised by a very intense mass loss, the understanding of which is still very limited. Here we report ALMA Compact Array observations of a 50??-mosaic toward the Fried Egg nebula, around one of the few Galactic yellow hypergiants IRAS 17163-3907. The emission from the 12CO J = 2-1 line, H30? recombination line, and continuum is imaged at a resolution of ~8??, revealing the morphology of the molecular environment around the star. The continuum emission is unresolved and peaks at the position of the star. The radio recombination line H30? shows unresolved emission at the star, with an approximately Gaussian spectrum centered on a velocity of 21 ± 3km s-1 with a width of 57 ± 6km s-1. In contrast, the CO 2-1 emission is complex and decomposes into several components beyond the contamination from interstellar gas in the line of sight. The CO spectrum toward the star is a broad plateau, centered at the systemic velocity of +18 km s-1 and with an expansion velocity of 100 ± 10km s-1. Assuming isotropic and constant mass-loss, we estimate a mass-loss rate of 8 ± 1.5 × 10-5M? yr-1. At a radius of 25?? from the star, we detect CO emission associated with the dust ring previously imaged by Herschel. The kinematics of this ring, however, is not consistent with an expanding shell, but show a velocity gradient of vsys ± 20km s-1. In addition, we find a puzzling bright feature radially connecting the star to the CO ring, at a velocity of +40 km s-1 relative to the star. This spur feature may trace a unidirectional ejection event from the star. Our ACA observations reveal the complex morphology around IRAS 17163 and illustrate the breakthroughs that ALMA will bring to the field of massive stellar evolution.
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| 10. |
- Wallström, Sofia, 1988, et al.
(author)
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Investigating the nature of the Fried Egg nebula: CO mm-line and optical spectroscopy of IRAS 17163–3907
- 2015
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 574:A139
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Journal article (peer-reviewed)abstract
- Through CO mm-line and optical spectroscopy, we investigate the properties of the Fried Egg nebula IRAS 17163–3907, which has recently been proposed to be one of the rare members of the yellow hypergiant class. The CO J = 2−1 and J = 3−2 emission arises from a region within 20'' of the star and is clearly associated with the circumstellar material. The CO lines show a multi-component asymmetrical profile, and an unexpected velocity gradient is resolved in the east-west direction, suggesting a bipolar outflow. This is in contrast with the apparent symmetry of the dust envelope as observed in the infrared. The optical spectrum of IRAS 17163–3907 between 5100 and 9000 Å was compared with that of the archetypal yellow hypergiant IRC+10420 and was found to be very similar. These results build on previous evidence that IRAS 17163–3907 is a yellow hypergiant.
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