| 1. |
- Aalto, Susanne, 1964, et al.
(författare)
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High-resolution HNC 3-2 SMA observations of Arp 220
- 2009
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 493:2, s. 481-487
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Tidskriftsartikel (refereegranskat)abstract
- Aims. We study the properties of the nuclear molecular gas of the ultra luminous merger Arp 220 and effects of the nuclear source on gas excitation and chemistry. Specifically, our aim is to investigate the spatial location of the luminous HNC 3-2 line emission and address the underlying cause of its unusual brightness.Methods. We present high resolution observations of HNC J=3-2 with the submillimeter array (SMA).Results. We find luminous HNC 3-2 line emission in the western part of Arp 220, centred on the western nucleus, while the eastern side of the merger shows relatively faint emission. A bright (36 K at $0\hbox{$.\!\!^{\prime\prime}$ }4$ resolution), narrow (60 ${\rm km~s}^$) emission feature emerges from the western nucleus, superposed on a broader spectral component. A possible explanation is weak maser emission through line-of-sight amplification of the background continuum source. There is also a more extended HNC 3-2 emission feature north and south of the nucleus. This feature resembles the bipolar OH maser morphology around the western nucleus. Substantial HNC abundances are required to explain the bright line emission from this warm environment - even when the high gas column density towards the western nucleus is taken into account. We discuss this briefly in the context of an X-ray affected chemistry and radiative excitation.Conclusions. The luminous and possibly amplified HNC emission of the western nucleus of the Arp 220 merger reflects the unusual, and perhaps transient environment of the starburst/AGN activity there. The faint HNC line emission towards Arp 220-east reveals a real difference in physical conditions between the two merger nuclei.
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| 2. |
- Aalto, Susanne, 1964, et al.
(författare)
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The hidden heart of the luminous infrared galaxy IC 860: I. A molecular inflow feeding opaque, extreme nuclear activity
- 2019
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 627
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Tidskriftsartikel (refereegranskat)abstract
- High-resolution (0.'03-0.'09 (9-26 pc)) ALMA (100-350 GHz (λ3 to 0.8 mm)) and (0.'04 (11 pc)) VLA 45 GHz measurements have been used to image continuum and spectral line emission from the inner (100 pc) region of the nearby infrared luminous galaxy IC 860. We detect compact (r ∼ 10 pc), luminous, 3 to 0.8 mm continuum emission in the core of IC 860, with brightness temperatures TB > 160 K. The 45 GHz continuum is equally compact but significantly fainter in flux. We suggest that the 3 to 0.8 mm continuum emerges from hot dust with radius r ∼ 8 pc and temperature Td ∼ 280 K, and that it is opaque at millimetre wavelengths, implying a very large H2 column density N(H2)≥ 1026 cm-2. Vibrationally excited lines of HCN v2 = 1f J = 4 - 3 and 3-2 (HCN-VIB) are seen in emission and spatially resolved on scales of 40-50 pc. The line-to-continuum ratio drops towards the inner r = 4 pc, resulting in a ring-like morphology. This may be due to high opacities and matching HCN-VIB excitation- and continuum temperatures. The HCN-VIB emission reveals a north-south nuclear velocity gradient with projected rotation velocities of v = 100 km s-1 at r = 10 pc. The brightest emission is oriented perpendicular to the velocity gradient, with a peak HCN-VIB 3-2 TB of 115 K (above the continuum). Vibrational ground-state lines of HCN 3-2 and 4-3, HC15N 4-3, HCO+ 3-2 and 4-3, and CS 7-6 show complex line absorption and emission features towards the dusty nucleus. Redshifted, reversed P-Cygni profiles are seen for HCN and HCO+ consistent with gas inflow with vin ≤ 50 km s-1. Foreground absorption structures outline the flow, and can be traced from the north-east into the nucleus. In contrast, CS 7-6 has blueshifted line profiles with line wings extending out to -180 km s-1. We suggest that a dense and slow outflow is hidden behind a foreground layer of obscuring, inflowing gas. The centre of IC 860 is in a phase of rapid evolution where an inflow is building up a massive nuclear column density of gas and dust that feeds star formation and/or AGN activity. The slow, dense outflow may be signaling the onset of feedback. The inner, r = 10 pc, IR luminosity may be powered by an AGN or a compact starburst, which then would likely require a top-heavy initial mass function.
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| 3. |
- Allen, Ronald J., et al.
(författare)
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Faint extended OH emission from the local interstellar medium in the direction l ≈ 108°, b ≈ 5°
- 2012
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Ingår i: Astronomical Journal. - : American Astronomical Society. - 1538-3881 .- 0004-6256. ; 143:4, s. Article 97, pp. 1-8
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Tidskriftsartikel (refereegranskat)abstract
- We have mapped faint 1667 OH line emission (TA ≈ 20-40 mK in our ≈30' beam) along many lines of sight in the Galaxy covering an area of ≈4° × 4° in the general direction of l ≈ 108°, b ≈ 5°. The OH emission is widespread, similar in extent to the local H I (r lsim 2 kpc) both in space and in velocity. The OH profile amplitudes show a good general correlation with those of H I in spectral channels of ≈1 km s–1; this relation is described by TA (OH) ≈1.50 × 10–4 TB (H I) for values of TB (H I) lsim 60-70 K. Beyond this the H I line appears to "saturate," and few values are recorded above ≈90 K. However, the OH brightness continues to rise, by a further factor ≈3. The OH velocity profiles show multiple features with widths typically 2-3 km s–1, but less than 10% of these features are associated with CO(1-0) emission in existing surveys of the area smoothed to comparable resolution.
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| 4. |
- Becker, Julia K., et al.
(författare)
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Tracing the sources of cosmic rays with molecular ions
- 2011
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Ingår i: Astrophysical Journal Letters. - 2041-8213 .- 2041-8205. ; 739:October 1, s. L43 (5 pages)-
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Tidskriftsartikel (refereegranskat)abstract
- The rate of ionization by cosmic rays (CRs) in interstellar gas directly associated with γ-ray-emitting supernova remnants (SNRs) is for the first time calculated to be several orders of magnitude larger than the Galactic average. Analysis of ionization-induced chemistry yields the first quantitative prediction of the astrophysical H2+ emission line spectrum, which should be detectable together with H3+ lines. The predicted coincident observation of those emission lines and γ-rays will help prove that SNRs are sources of CRs.
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| 5. |
- Bergman, Per, 1960, et al.
(författare)
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Emission from HCN and CH3OH in comets Onsala 20-m observations and radiative transfer modelling
- 2022
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 660
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Tidskriftsartikel (refereegranskat)abstract
- Aims. The aim of this work is to characterise HCN and CH3OH emission from recent comets. Methods. We used the Onsala 20-m telescope to search for millimetre transitions of HCN towards a sample of 11 recent and mostly bright comets in the period from December 2016 to November 2019. Also, CH3OH was searched for in two comets. The HCN sample includes the interstellar comet 2I/Borisov. For the short-period comet 46P/Wirtanen, we were able to monitor the variation of HCN emission over a time-span of about one month. We performed radiative transfer modelling for the observed molecular emission by also including time-dependent effects due to the outgassing of molecules. Results. HCN was detected in six comets. Two of these are short-period comets and four are long-period. Six methanol transitions were detected in 46P/Wirtanen, enabling us to determine the gas kinetic temperature. From the observations, we determined the molecular production rates using time-dependent radiative transfer modelling. For five comets, we were able to determine that the HCN mixing ratios lie near 0.1% using contemporary water production rates, Q(H2O), taken from other studies. This HCN mixing ratio was also found to be typical in our monitoring observations of 46P/Wirtanen but here we notice deviations of up to 0.2% on a daily timescale which could indicate short-time changes in outgassing activity. From our radiative transfer modelling of cometary comae, we find that time-dependent effects on the HCN level populations are of the order of 5-15% when Q(H2O) is around 2 x 10(28) mol s(-1). The effects may be stronger for comets with lower Q(H2O). The exact details of the time-dependent effects depend on the amount of neutral and electron collisions, radiative pumping, and molecular parameters such as the spontaneous rate coefficient.
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| 6. |
- Berné, O., et al.
(författare)
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Formation of the methyl cation by photochemistry in a protoplanetary disk
- 2023
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Ingår i: Nature. - 0028-0836 .- 1476-4687. ; 621:7977, s. 56-59
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Tidskriftsartikel (refereegranskat)abstract
- Forty years ago, it was proposed that gas-phase organic chemistry in the interstellar medium can be initiated by the methyl cation CH3+ (refs. 1–3), but so far it has not been observed outside the Solar System 4,5. Alternative routes involving processes on grain surfaces have been invoked 6,7. Here we report James Webb Space Telescope observations of CH3+ in a protoplanetary disk in the Orion star-forming region. We find that gas-phase organic chemistry is activated by ultraviolet irradiation.
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| 7. |
- Berne, Olivier, et al.
(författare)
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PDRs4All : A JWST Early Release Science Program on Radiative Feedback from Massive Stars
- 2022
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Ingår i: Publications of the Astronomical Society of the Pacific. - : IOP Publishing. - 0004-6280 .- 1538-3873. ; 134:1035
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Tidskriftsartikel (refereegranskat)abstract
- Massive stars disrupt their natal molecular cloud material through radiative and mechanical feedback processes. These processes have profound effects on the evolution of interstellar matter in our Galaxy and throughout the universe, from the era of vigorous star formation at redshifts of 1-3 to the present day. The dominant feedback processes can be probed by observations of the Photo-Dissociation Regions (PDRs) where the far-ultraviolet photons of massive stars create warm regions of gas and dust in the neutral atomic and molecular gas. PDR emission provides a unique tool to study in detail the physical and chemical processes that are relevant for most of the mass in inter- and circumstellar media including diffuse clouds, proto-planetary disks, and molecular cloud surfaces, globules, planetary nebulae, and star-forming regions. PDR emission dominates the infrared (IR) spectra of star-forming galaxies. Most of the Galactic and extragalactic observations obtained with the James Webb Space Telescope (JWST) will therefore arise in PDR emission. In this paper we present an Early Release Science program using the MIRI, NIRSpec, and NIRCam instruments dedicated to the observations of an emblematic and nearby PDR: the Orion Bar. These early JWST observations will provide template data sets designed to identify key PDR characteristics in JWST observations. These data will serve to benchmark PDR models and extend them into the JWST era. We also present the Science-Enabling products that we will provide to the community. These template data sets and Science-Enabling products will guide the preparation of future proposals on star-forming regions in our Galaxy and beyond and will facilitate data analysis and interpretation of forthcoming JWST observations.
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| 8. |
- Bjerkeli, Per, 1977, et al.
(författare)
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Resolving the shocked gas in HH54 with Herschel CO line mapping at high spatial and spectral resolution
- 2014
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 571
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Tidskriftsartikel (refereegranskat)abstract
- Context. The HH 54 shock is a Herbig-Haro object, located in the nearby Chamaeleon II cloud. Observed CO line profiles are due to a complex distribution in density, temperature, velocity, and geometry. Aims. Resolving the HH 54 shock wave in the far-infrared (FIR) cooling lines of CO constrain the kinematics, morphology, and physical conditions of the shocked region. Methods. We used the PACS and SPIRE instruments on board the Herschel space observatory to map the full FIR spectrum in a region covering the HH 54 shock wave. Complementary Herschel-HIFI, APEX, and Spitzer data are used in the analysis as well. The observed features in the line profiles are reproduced using a 3D radiative transfer model of a bow-shock, constructed with the Line Modeling Engine code (LIME). Results. The FIR emission is confined to the HH 54 region and a coherent displacement of the location of the emission maximum of CO with increasing J is observed. The peak positions of the high-J CO lines are shifted upstream from the lower J CO lines and coincide with the position of the spectral feature identified previously in CO(10-9) profiles with HIFI. This indicates a hotter molecular component in the upstream gas with distinct dynamics. The coherent displacement with increasing J for CO is consistent with a scenario where IRAS12500 - 7658 is the exciting source of the flow, and the 180 K bow-shock is accompanied by a hot (800 K) molecular component located upstream from the apex of the shock and blueshifted by -7 km s(-1). The spatial proximity of this knot to the peaks of the atomic fine-structure emission lines observed with Spitzer and PACS ([O I]63, 145 mu m) suggests that it may be associated with the dissociative shock as the jet impacts slower moving gas in the HH 54 bow-shock.
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| 9. |
- Black, John H, 1949
(författare)
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Astrochemistry: an unfinished symphony
- 2009
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Ingår i: Proceedings of the Dalgarno Celebratory Symposium. Contributions to Atomic, Molecular, and Optical Physics, Astrophysics, and Atmospheric Sciences; edited by James F. Babb, Kate Kirby, and Hossein Sadeghpour (London: Imperial College Press). - 9781848164697 ; , s. 117-124
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Alex Dalgarno has introduced many of the themes that define current research in astrochemistry. Variations on these themes will continue to be played out well into the future. Clear and unambiguous tests of theories of formation of interstellar molecules remain elusive; however, the understanding of fluorine chemistry appears to offer one success story. The predicted chemical activity in X-ray dominated regions and in shock waves is being studied with increasingly sensitive observations. Molecules whose chemistry and internal excitation are strongly coupled are especially valuable. In some cases, observations of these reactive species can provide probes of specific chemical rates in interstellar gas. Superthermal OH observed in a shock front appears to offer special diagnostic value. Even cosmologists have recognized that chemistry plays an important role in the early evolution of matter in the Universe around the epoch of recombination. The hydrogen molecule is being used to test cosmological theories of dark matter.
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| 10. |
- Black, John H, 1949
(författare)
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Chemistry and cosmology
- 2006
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Ingår i: Faraday Discussions. - : Royal Society of Chemistry (RSC). - 1359-6640 .- 1364-5498. ; 133, s. 27-32
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Tidskriftsartikel (refereegranskat)abstract
- The simplest elements, hydrogen and helium, offer a remarkably rich chemistry, which has controlled crucial features of the early evolution of the universe. Theoretical models of the origin of structure (stars, galaxies, clusters of galaxies, etc.) now incorporate this chemistry in some detail. In addition to the origin of structure, cosmologists are concerned with observational tests of competing world models. Primordial chemistry may give rise to some of the earliest departures from thermodynamic equilibrium in the universe. These effects may be observable as broad-band spectroscopic distortions of the cosmic background radiation, which otherwise exhibits a nearly perfect blackbody spectrum. The chemical history of the expanding universe is followed through a detailed calculation of the evolution of the abundances of H, H+, H, H2, H+2, H+3, and other minor species. It is shown that continuous absorption by the small concentration of H can produce a distortion in the cosmic background spectrum with a maximum at a frequency near /c = 9 cm1 (wavelength 1.1 mm). The predicted effect lies only a factor of 5 below current limits. Its detection would provide an important test of our understanding of the recombination epoch of the universe.
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