The Magellanic Mopra Assessment (MAGMA) is a high angular resolution 12CO (J= 1 → 0) mapping survey of giant molecular clouds (GMCs) in the Large Magellanic Cloud (LMC) and Small Magellanic Cloud ...using the Mopra Telescope. Here we report on the basic physical properties of 125 GMCs in the LMC that have been surveyed to date. The observed clouds exhibit scaling relations that are similar to those determined for Galactic GMCs, although LMC clouds have narrower linewidths and lower CO luminosities than Galactic clouds of a similar size. The average mass surface density of the LMC clouds is 50 M⊙ pc−2, approximately half that of GMCs in the inner Milky Way. We compare the properties of GMCs with and without signs of massive star formation, finding that non-star-forming GMCs have lower peak CO brightness than star-forming GMCs. We compare the properties of GMCs with estimates for local interstellar conditions: specifically, we investigate the H i column density, radiation field, stellar mass surface density and the external pressure. Very few cloud properties demonstrate a clear dependence on the environment; the exceptions are significant positive correlations between (i) the H i column density and the GMC velocity dispersion, (ii) the stellar mass surface density and the average peak CO brightness and (iii) the stellar mass surface density and the CO surface brightness. The molecular mass surface density of GMCs without signs of massive star formation shows no dependence on the local radiation field, which is inconsistent with the photoionization-regulated star formation theory proposed by McKee. We find some evidence that the mass surface density of the MAGMA clouds increases with the interstellar pressure, as proposed by Elmegreen, but the detailed predictions of this model are not fulfilled once estimates for the local radiation field, metallicity and GMC envelope mass are taken into account.
Planck 2015 results Adam, R; Ade, P A R; Aghanim, N ...
Astronomy and astrophysics (Berlin),
10/2016, Letnik:
594
Journal Article
Recenzirano
Odprti dostop
The European Space Agency's Planck satellite, which is dedicated to studying the early Universe and its subsequent evolution, was launched on 14 May 2009. It scanned the microwave and submillimetre ...sky continuously between 12 August 2009 and 23 October 2013. In February 2015, ESA and the Planck Collaboration released the second set of cosmology products based ondata from the entire Planck mission, including both temperature and polarization, along with a set of scientific and technical papers and a web-based explanatory supplement. This paper gives an overview of the main characteristics of the data and the data products in the release, as well as the associated cosmological and astrophysical science results and papers. The data products include maps of the cosmic microwave background (CMB), the thermal Sunyaev-Zeldovich effect, diffuse foregrounds in temperature and polarization, catalogues of compact Galactic and extragalactic sources (including separate catalogues of Sunyaev-Zeldovich clusters and Galactic cold clumps), and extensive simulations of signals and noise used in assessing uncertainties and the performance of the analysis methods. The likelihood code used to assess cosmological models against the Planck data is described, along with a CMB lensing likelihood. Scientific results include cosmological parameters derived from CMB power spectra, gravitational lensing, and cluster counts, as well as constraints on inflation, non-Gaussianity, primordial magnetic fields, dark energy, and modified gravity, and new results on low-frequency Galactic foregrounds.
Context.Herschel provides crucial constraints on the IR SEDs of galaxies, allowing unprecedented accuracy on the dust mass estimates. However, these estimates rely on non-linear models and ...poorly-known optical properties. Aims. In this paper, we perform detailed modelling of the Spitzer and Herschel observations of the LMC, in order to: (i) systematically study the uncertainties and biases affecting dust mass estimates; and to (ii) explore the peculiar ISM properties of the LMC. Methods. To achieve these goals, we have modelled the spatially resolved SEDs with two alternate grain compositions, to study the impact of different submillimetre opacities on the dust mass. We have rigorously propagated the observational errors (noise and calibration) through the entire fitting process, in order to derive consistent parameter uncertainties. Results. First, we show that using the integrated SED leads to underestimating the dust mass by ≃50% compared to the value obtained with sufficient spatial resolution, for the region we studied. This might be the case, in general, for unresolved galaxies. Second, we show that Milky Way type grains produce higher gas-to-dust mass ratios than what seems possible according to the element abundances in the LMC. A spatial analysis shows that this dilemma is the result of an exceptional property: the grains of the LMC have on average a larger intrinsic submm opacity (emissivity index β ≃ 1.7 and opacity κabs(160 μm) = 1.6 m2 kg-1) than those of the Galaxy. By studying the spatial distribution of the gas-to-dust mass ratio, we are able to constrain the fraction of unseen gas mass between ≃10, and ≃100% and show that it is not sufficient to explain the gas-to-dust mass ratio obtained with Milky Way type grains. Finally, we confirm the detection of a 500 μm extended emission excess with an average relative amplitude of ≃15%, varying up to 40%. This excess anticorrelates well with the dust mass surface density. Although we do not know the origin of this excess, we show that it is unlikely the result of very cold dust, or CMB fluctuations.
We performed Spitzer Infrared Spectrograph mapping observations covering nearly the entire extent of the Cassiopeia A supernova remnant (SNR), producing mid-infrared (5.5-35 mu m) spectra every 5" ...-10". Gas lines of Ar, Ne, O, Si, S, and Fe, and dust continua were strong for most positions. We identify three distinct ejecta dust populations based on their continuum shapes. The dominant dust continuum shape exhibits a strong peak at 21 mu m. A line-free map of 21 mu m peak dust made from the 19-23 mu m range closely resembles the Ar II, O IV, and Ne II ejecta-line maps, implying that dust is freshly formed in the ejecta. Spectral fitting implies the presence of SiO sub(2), Mg protosilicates, and FeO grains in these regions. The second dust type exhibits a rising continuum up to 21 mu m and then flattens thereafter. This "weak 21 mu m" dust is likely composed of Al sub(2)O sub(3) and C grains. The third dust continuum shape is featureless with a gently rising spectrum and is likely composed of MgSiO sub(3) and either Al sub(2)O sub(3) or Fe grains. Using the least massive composition for each of the three dust classes yields a total mass of 0.020 M unk. Using the most massive composition yields a total mass of 0.054 M unk. The primary uncertainty in the total dust mass stems from the selection of the dust composition necessary for fitting the featureless dust as well as 70 mu m flux. The freshly formed dust mass derived from Cas A is sufficient from SNe to explain the lower limit on the dust masses in high-redshift galaxies.
Abstract
We present the detections of shocked molecular hydrogen (H
2
) gas in near- and mid-infrared and broad CO in millimeter from the mixed-morphology supernova remnant (SNR) HB 3 (G132.7+1.3) ...using the Palomar Wide-field InfraRed Camera, the Spitzer GLIMPSE360 and Wide-field Infrared Survey Explorer (WISE) surveys, and the Heinrich Hertz Submillimeter Telescope. Our near-infrared narrow-band filter H
2
2.12
μ
m images of HB 3 show that both Spitzer Infrared Array Camera and WISE 4.6
μ
m emission originates from shocked H
2
gas. The morphology of H
2
exhibits thin filamentary structures and a large scale of interaction sites between the HB 3 and nearby molecular clouds. Half of HB 3, the southern and eastern shell of the SNR, emits H
2
in a shape of a butterfly or W, indicating the interaction sites between the SNR and dense molecular clouds. Interestingly, the H
2
emitting region in the southeast is also co-spatial to the interacting area between HB 3 and the H
ii
regions of the W3 complex, where we identified star-forming activity. We further explore the interaction between HB 3 and dense molecular clouds with detections of broad CO(3-2) and CO(2-1) molecular lines from the southern and southeastern shell along the H
2
emitting region. The widths of the broad lines are 8–20 km s
−1
; the detection of such broad lines is unambiguous, dynamic evidence of the interactions between the SNR and clouds. The CO broad lines are from two branches of the bright, southern H
2
shell. We apply the Paris–Durham shock model to the CO line profiles, which infer the shock velocities of 20–40 km s
−1
, relatively low densities of 10
3–4
cm
−3
, and strong (>200
μ
G) magnetic fields.
Context. In the past few years, the extinction law has been measured in the infrared wavelengths for various molecular clouds and different laws have been obtained. Aims. In this paper we seek ...variations of the extinction law within the Trifid nebula region. Such variations would demonstrate local dust evolution linked to variation of the environment parameters such as the density or the interstellar radiation field. Methods. The extinction values, Aλ/AV, are obtained using the 2MASS, UKIDSS and Spitzer/GLIMPSE surveys. The technique is to inter-calibrate color-excess maps from different wavelengths to derive the extinction law and to map the extinction in the Trifid region. Results. We measured the extinction law at 3.6, 4.5, and 5.8 μm and we found a transition at AV ≈ 20 mag. Below this threshold the extinction law is as expected from models for RV = 5.5 whereas above 20 mag of visual extinction, it is flatter. Using these results the color-excess maps are converted into a composite extinction map of the Trifid nebula at a spatial resolution of 1 arcmin. A tridimensional analysis along the line-of-sight allowed us to estimate a distance of 2.7 ± 0.5 kpc for the Trifid. The comparison of the extinction with the 1.25 mm emission suggests the millimeter emissivity is enhanced in the dense condensations of the cloud. Conclusions. Our results suggest a dust transition at large extinction which has not been reported so far as well as dust emissivity variations.
A map of surface molecular water was derived from long slit spectroscopy of the south polar region of the Moon using the Faint Object infraRed CAmera for the SOFIA Telescope spectrometer on the ...Stratospheric Observatory for Infrared Astronomy. Mean water abundances detected are about 250 μg/g over that of a mare reference surface at Mare Fecunditatis. Water abundances are locally anticorrelated with temperature. The distribution of water is consistent with derivation of water from pre‐existing hydroxyl subsequently trapped in impact glass, provided hydroxyl increases with latitude as some models and measurements suggest. The detected water cannot be in equilibrium with the exosphere because insufficient water is present in the exosphere to maintain the surface abundance. The data are consistent with a high latitude water‐bearing mineral host that may be a precursor to recently detected high latitude hematite.
Plain Language Summary
If water is present in sufficient quantities on the Moon, it may be an important resource for space exploration as it can be used to make rocket fuel and sustain human presence. Water molecules on the illuminated surface of the Moon can be detected using a unique spectral signature that is obscured from telescopes on Earth's surface by water vapor in the atmosphere. The NASA/DLR Stratospheric Observatory for Infrared Astronomy is a large telescope on a 747 aircraft that operates high in the stratosphere above 99% of the water vapor, and so can detect the infrared thermal emission from water on the Moon's surface. Near the South Pole, we produced a map of water emission that shows water is present at a few hundred parts per million, and is inversely correlated with surface temperature. This is consistent both with the behavior of water free to migrate on the surface, and water bound up in glass from meteorite impacts. However, the amount of water we find probably cannot be freely exchanging with the Moon's tenuous exosphere because it would require much more water in the exosphere than has been measured.
Key Points
Stratospheric Observatory for Infrared Astronomy + Faint Object infraRed CAmera for the SOFIA Telescope confirms the presence of water emission in the South Polar Region of the Moon
Small maps of water emission are presented that begin to enable tests of various hypotheses for water formation and variation
Observations suggest the water cannot migrate and instead is trapped within impact glasses or in a mineral‐based host
•We show results from a Spitzer mid-IR survey of Jupiter-family (JF) comets.•We present 89 new radii and 57 new beaming parameters for the nuclei.•Mean beaming parameter is 1.03±0.11, so ensemble ...thermal inertia is low.•Our independent cumulative size distribution is similar to earlier work.•There are likely low-perihelion, large JF nuclei still undiscovered.
We present results from SEPPCoN, an on-going Survey of the Ensemble Physical Properties of Cometary Nuclei. In this report we discuss mid-infrared measurements of the thermal emission from 89 nuclei of Jupiter-family comets (JFCs). All data were obtained in 2006 and 2007 using imaging capabilities of the Spitzer Space Telescope. The comets were typically 4–5AU from the Sun when observed and most showed only a point-source with little or no extended emission from dust. For those comets showing dust, we used image processing to photometrically extract the nuclei. For all 89 comets, we present new effective radii, and for 57 comets we present beaming parameters. Thus our survey provides the largest compilation of radiometrically-derived physical properties of nuclei to date. We have six main conclusions: (a) The average beaming parameter of the JFC population is 1.03±0.11, consistent with unity; coupled with the large distance of the nuclei from the Sun, this indicates that most nuclei have Tempel 1-like thermal inertia. Only two of the 57 nuclei had outlying values (in a statistical sense) of infrared beaming. (b) The known JFC population is not complete even at 3km radius, and even for comets that approach to ∼2AU from the Sun and so ought to be more discoverable. Several recently-discovered comets in our survey have small perihelia and large (above ∼2km) radii. (c) With our radii, we derive an independent estimate of the JFC nuclear cumulative size distribution (CSD), and we find that it has a power-law slope of around −1.9, with the exact value depending on the bounds in radius. (d) This power-law is close to that derived by others from visible-wavelength observations that assume a fixed geometric albedo, suggesting that there is no strong dependence of geometric albedo with radius. (e) The observed CSD shows a hint of structure with an excess of comets with radii 3–6km. (f) Our CSD is consistent with the idea that the intrinsic size distribution of the JFC population is not a simple power-law and lacks many sub-kilometer objects.
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