| 1. |
- Alcolea, J., et al.
(författare)
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HIFISTARS Herschel/HIFI observations of VY Canis Majoris. Molecular-line inventory of the envelope around the largest known star
- 2013
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 559, s. (article nr.) A93-
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Tidskriftsartikel (refereegranskat)abstract
- Aims.The study of the molecular gas in the circumstellar envelopes of evolved stars is normally undertaken by observing lines ofCO (and other species) in the millimetre-wave domain. In general, the excitation requirements of the observed lines are low at thesewavelengths, and therefore these observations predominantly probe the cold outer envelope while studying the warm inner regions ofthe envelopes normally requires sub-millimetre (sub-mm) and far-infrared (FIR) observational data.Methods.To gain insight into the physical conditions and kinematics of the warm (100–1000 K) gas around the red hyper-giantVY CMa, we performed sensitive high spectral resolution observations of molecular lines in the sub-mm/FIR using the HIFI instru-ment of theHerschelSpace Observatory. We observed CO, H2O, and other molecular species, sampling excitation energies from afew tens to a few thousand K. These observations are part of theHerschelguaranteed time key program HIFISTARS.Results.We detected theJ=6–5,J=10–9, andJ=16–15 lines of12CO and13CO at∼100, 300, and 750 K above the groundstate (and the13COJ=9–8 line). These lines are crucial for improving the modelling of the internal layers of the envelope aroundVY CMa. We also detected 27 lines of H2O and its isotopomers, and 96 lines of species such as NH3,SiO,SO,SO2HCN, OH andothers, some of them originating from vibrationally excited levels. Three lines were not unambiguously assigned.Conclusions.Our observations confirm that VY CMa’s envelope must consist of two or more detached components. The molecularexcitation in the outer layers is significantly lower than in the inner ones, resulting in strong self-absorbed profiles in molecular linesthat are optically thick in this outer envelope, for instance, low-lying lines of H2O. Except for the most abundant species, CO and H2O,most of the molecular emission detected at these sub-mm/FIR wavelengths arise from the central parts of the envelope. The spectrumof VY CMa is very prominent in vibrationally excited lines, which are caused by the strong IR pumping present in the central regions.Compared with envelopes of other massive evolved stars, VY CMa’s emission is particularly strong in these vibrationally excitedlines, as well as in the emission from less abundant species such as H13CN, SO, and NH3.
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| 2. |
- Algaba, Juan-Carlos, et al.
(författare)
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Broadband Multi-wavelength Properties of M87 during the 2017 Event Horizon Telescope Campaign
- 2021
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8213 .- 2041-8205. ; 911:1
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Forskningsöversikt (refereegranskat)abstract
- In 2017, the Event Horizon Telescope (EHT) Collaboration succeeded in capturing the first direct image of the center of the M87 galaxy. The asymmetric ring morphology and size are consistent with theoretical expectations for a weakly accreting supermassive black hole of mass ∼6.5 × 109 M o˙. The EHTC also partnered with several international facilities in space and on the ground, to arrange an extensive, quasi-simultaneous multi-wavelength campaign. This Letter presents the results and analysis of this campaign, as well as the multi-wavelength data as a legacy data repository. We captured M87 in a historically low state, and the core flux dominates over HST-1 at high energies, making it possible to combine core flux constraints with the more spatially precise very long baseline interferometry data. We present the most complete simultaneous multi-wavelength spectrum of the active nucleus to date, and discuss the complexity and caveats of combining data from different spatial scales into one broadband spectrum. We apply two heuristic, isotropic leptonic single-zone models to provide insight into the basic source properties, but conclude that a structured jet is necessary to explain M87's spectrum. We can exclude that the simultaneous γ-ray emission is produced via inverse Compton emission in the same region producing the EHT mm-band emission, and further conclude that the γ-rays can only be produced in the inner jets (inward of HST-1) if there are strongly particle-dominated regions. Direct synchrotron emission from accelerated protons and secondaries cannot yet be excluded.
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| 3. |
- Ao, Y., et al.
(författare)
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Deep Submillimeter and Radio Observations in the SSA22 Field. I. Powering Sources and the Ly alpha Escape Fraction of Ly alpha Blobs
- 2017
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 850:2
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Tidskriftsartikel (refereegranskat)abstract
- We study the heating mechanisms and Ly alpha escape fractions of 35 Ly alpha blobs (LABs) at z approximate to 3.1 in the SSA22 field. Dust continuum sources have been identified in 11 of the 35 LABs, all with star formation rates (SFRs) above 100M(circle dot) yr(-1). Likely radio counterparts are detected in 9 out of 29 investigated LABs. The detection of submillimeter dust emission is more linked to the physical size of the Ly alpha emission than to the Ly alpha luminosities of the LABs. A radio excess in the submillimeter/ radio-detected LABs is common, hinting at the presence of active galactic nuclei. Most radio sources without X-ray counterparts are located at the centers of the LABs. However, all X-ray counterparts avoid the central regions. This may be explained by absorption due to exceptionally large column densities along the line-of-sight or by LAB morphologies, which are highly orientation dependent. The median Lya escape fraction is about 3% among the submillimeter-detected LABs, which is lower than a lower limit of 11% for the submillimeter-undetected LABs. We suspect that the large difference is due to the high dust attenuation supported by the large SFRs, the dense large-scale environment as well as large uncertainties in the extinction corrections required to apply when interpreting optical data.
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| 4. |
- Ao, Y., et al.
(författare)
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The thermal state of molecular clouds in the Galactic center: evidence for non-photon-driven heating
- 2014
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Ingår i: Proceedings of the International Astronomical Union. - 1743-9213 .- 1743-9221. ; 9:S303, s. 89-91
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Tidskriftsartikel (refereegranskat)abstract
- We have used the Atacama Pathfinder Experiment (APEX) 12 m telescope at 218 GHz to observe molecular clouds simultaneously in the J_KA,Kc=3_03→2_02,3_22→2_21,and 3_21→2_20 transitions of para-H2CO to determine kinetic temperatures of the dense gas in the central molecular zone of the Galaxy. Gas kinetic temperatures for individual molecular clouds range from 55 to 125 K or even higher. The molecular clouds at high temperatures may be heated by turbulent dissipation and/or cosmic-rays
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| 5. |
- Ao, Y., et al.
(författare)
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The thermal state of molecular clouds in the Galactic center: evidence for non-photon-driven heating
- 2013
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 550
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Tidskriftsartikel (refereegranskat)abstract
- We used the Atacama Pathfinder Experiment (APEX) 12 m telescope to observe the J(KAKc) = 3(03) -> 2(02), 3(22) -> 2(21), and 3(21) -> 2(20) transitions of para-H2CO at 218 GHz simultaneously to determine kinetic temperatures of the dense gas in the central molecular zone (CMZ) of our Galaxy. The map extends over approximately 40' x 8' (similar to 100 x 20 pc(2)) along the Galactic plane with a linear resolution of 1.2 pc. The strongest of the three lines, the H2CO (3(03) -> 2(02)) transition, is found to be widespread, and its emission shows a spatial distribution similar to ammonia. The relative abundance of para-H2CO is 0.5 - 1.2 x 10(-9), which is consistent with results from lower frequency H2CO absorption lines. Derived gas kinetic temperatures for individual molecular clouds range from 50K to values in excess of 100 K. While a systematic trend toward (decreasing) kinetic temperature versus (increasing) angular distance from the Galactic center (GC) is not found, the clouds with highest temperature (T-kin > 100 K) are all located near the nucleus. For the molecular gas outside the dense clouds, the average kinetic temperature is 65 +/- 10 K. The high temperatures of molecular clouds on large scales in the GC region may be driven by turbulent energy dissipation and / or cosmic-rays instead of photons. Such a non-photon-driven thermal state of the molecular gas provides an excellent template for the more distant vigorous starbursts found in ultraluminous infrared galaxies (ULIRGs).
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| 6. |
- Bagdonaite, Julija, et al.
(författare)
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Robust Constraint on a Drifting Proton-to-Electron Mass Ratio at z=0.89 from Methanol Observation at Three Radio Telescopes
- 2013
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Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 111:23, s. 231101-
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Tidskriftsartikel (refereegranskat)abstract
- A limit on a possible cosmological variation of the proton-to-electron mass ratio μ is derived from methanol (CH3OH) absorption lines in the benchmark PKS1830–211 lensing galaxy at redshift z=0.89 observed with the Effelsberg 100-m radio telescope, the Institute de Radio Astronomie Millimétrique 30-m telescope, and the Atacama Large Millimeter/submillimeter Array. Ten different absorption lines of CH3OH covering a wide range of sensitivity coefficients Kμ are used to derive a purely statistical 1σ constraint of Δμ/μ=(1.5±1.5)×10−7 for a lookback time of 7.5 billion years. Systematic effects of chemical segregation, excitation temperature, frequency dependence, and time variability of the background source are quantified. A multidimensional linear regression analysis leads to a robust constraint of Δμ/μ=(−1.0±0.8stat±1.0sys)×10−7.
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| 7. |
- Basu, K., et al.
(författare)
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Non-parametric modeling of the intra-cluster gas using APEX-SZ bolometer imaging data
- 2010
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 519:Article Number: A29
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Tidskriftsartikel (refereegranskat)abstract
- Aims. We aim to demonstrate the usability of mm-wavelength imaging data obtained from the APEX-SZ bolometer array to derive the radial temperature profile of the hot intra-cluster gas out to radius r(500) and beyond. The goal is to study the physical properties of the intra-cluster gas by using a non-parametric de-projection method that is, aside from the assumption of spherical symmetry, free from modeling bias. Methods. We use publicly available X-ray spectroscopic-imaging data in the 0.7-2 keV energy band from the XMM-Newton observatory and our Sunyaev-Zel'dovich Effect (SZE) imaging data from the APEX-SZ experiment at 150 GHz to de-project the density and temperature profiles for a well-studied relaxed cluster, Abell 2204. We derive the gas density, temperature and entropy profiles assuming spherical symmetry, and obtain the total mass profile under the assumption of hydrostatic equilibrium. For comparison with X-ray spectroscopic temperature models, a re-analysis of recent Chandra observation is done with the latest calibration updates. We compare the results with that from an unrelaxed cluster, Abell 2163, to illustrate some differences between relaxed and merging systems. Results. Using the non-parametric modeling, we demonstrate a decrease of gas temperature in the cluster outskirts, and also measure gas entropy profiles, both of which are done for the first time independently of X-ray spectroscopy using the SZE and X-ray imaging data. The gas entropy measurement in the central 100 kpc shows the usability of APEX-SZ data for inferring cluster dynamical states with this method. The contribution of the SZE systematic uncertainties in measuring T-e at large radii is shown to be small compared to XMM-Newton and Chandra systematic spectroscopic errors. The total mass profile obtained using the hydrostatic equilibrium assumption is in agreement with the published X-ray and weak lensing results; the upper limit on M-200 derived from the non-parametric method is consistent with the NFW model prediction from weak lensing analysis.
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| 8. |
- Baudry, A., et al.
(författare)
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ATOMIUM: Probing the inner wind of evolved O-rich stars with new, highly excited H2O and OH lines
- 2023
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Ingår i: Astronomy & Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 674
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Tidskriftsartikel (refereegranskat)abstract
- Context. Water (H2O) and the hydroxyl radical (OH) are major constituents of the envelope of O-rich late-type stars. Transitions involving energy levels that are rotationally or vibrationally highly excited (energies & GSIM;4000 K) have been observed in both H2O and OH. These and more recently discovered transitions can now be observed at a high sensitivity and angular resolution in the inner wind close to the stellar photosphere with the Atacama Large Millimeter/submillimeter Array (ALMA). Aims. Our goals are: (1) to identify and map the emission and absorption of H2O in several vibrational states, and of OH in Lambda-doubling transitions with similar excitation energies; and (2) to determine the physical conditions and kinematics in gas layers close to the extended atmosphere in a sample of asymptotic giant branch stars (AGBs) and red supergiants (RSGs). Methods. Spectra and maps of H2O and OH lines observed in a 27 GHz aggregated bandwidth and with an angular resolution of similar to 0."02-1."0 were obtained at two epochs with the main ALMA array. Additional observations with the Atacama Compact Array (ACA) were used to check for time variability of water transitions. Radiative transfer models of H2O were revisited to characterize masing conditions. Up-to-date chemical models were used for comparison with the observed OH/H2O abundance ratio. Results. Ten rotational transitions of H2O with excitation energies similar to 4000-9000 K were observed in vibrational states up to (& upsilon;(1),& upsilon;(2),& upsilon;(3)) = (0,1,1). All but one are new detections in space, and from these we have derived accurate rest frequencies. Hyperfine split Lambda-doubling transitions in & upsilon; = 0, J = 27/2 and 29/2 levels of the (2)& pi;(3/2) state, as well as J = 33/2 and 35/2 of the (2)& pi;(1/2) state of OH with excitation energies of similar to 4780-8900 K were also observed. Four of these transitions are new detections in space. Combining our measurements with earlier observations of OH, the & upsilon; = 0 and & upsilon; = 1 Lambda-doubling frequencies have been improved. Our H2O maps show compact emission toward the central star and extensions up to twelve stellar radii or more. The 268.149 GHz emission line of water in the & upsilon;(2) = 2 state is time variable, tends to be masing with dominant radiative pumping, and is widely excited in AGBs and RSGs. The widespread but weaker 262.898 GHz water line in the & upsilon;(2) = 1 state also shows signs of maser emission. The OH emission is weak and quasithermally excited. Emission and absorption features of H2O and OH reveal an infall of matter and complex kinematics influenced by binarity. From the OH and H2O column densities derived with nonmasing transitions in a few sources, we obtain OH/H2O abundance ratios of similar to(0.7-2.8) x 10(-2).
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| 9. |
- Bender, A. N., et al.
(författare)
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Galaxy cluster scaling relations measured with APEX-SZ
- 2016
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 460:4, s. 3432-3446
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Tidskriftsartikel (refereegranskat)abstract
- We present thermal Sunyaev-Zel'dovich effect (SZE) measurements for 42 galaxy clusters observed at 150 GHz with the APEX-SZ experiment. For each cluster, we model the pressure profile and calculate the integrated Comptonization Y to estimate the total thermal energy of the intraclustermedium (ICM). We compare the measured Y values to X-ray observables of the ICM from the literature (cluster gas mass M-gas, temperature T-X, and Y-X = MgasTX) that relate to total cluster mass. We measure power-law scaling relations, including an intrinsic scatter, between the SZE and X-ray observables for three subsamples within the set of 42 clusters that have uniform X-ray analysis in the literature. We observe that differences between these X-ray analyses introduce significant variance into the measured scaling relations, particularly affecting the normalization. For all three subsamples, we find results consistent with a selfsimilarmodel of cluster evolution dominated by gravitational effects. Comparing to predictions from numerical simulations, these scaling relations prefer models that include cooling and feedback in the ICM. Lastly, we measure an intrinsic scatter of similar to 28 per cent in the Y - Y-X scaling relation for all three subsamples.
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| 10. |
- Bergman, Per, 1960, et al.
(författare)
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Detection of interstellar hydrogen peroxide
- 2011
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 531, s. L8-
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Tidskriftsartikel (refereegranskat)abstract
- Context. The molecular species hydrogen peroxide, HOOH, is likely to be a key ingredient in the oxygen and water chemistry in the interstellar medium. Aims. Our aim with this investigation is to determine how abundant HOOH is in the cloud core rho Oph A. Methods. By observing several transitions of HOOH in the (sub)millimeter regime we seek to identify the molecule and also to determine the excitation conditions through a multilevel excitation analysis. Results. We have detected three spectral lines toward the SM1 position of rho Oph A at velocity-corrected frequencies that coincide very closely with those measured from laboratory spectroscopy of HOOH. A fourth line was detected at the 4 sigma level. We also found through mapping observations that the HOOH emission extends (about 0.05 pc) over the densest part of the rho Oph A cloud core. We derive an abundance of HOOH relative to that of H(2) in the SM1 core of about 1 x 10(-10). Conclusions. To our knowledge, this is the first reported detection of HOOH in the interstellar medium.
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