The degeneracy between dust colour temperature and spectral index

Juvela, M.; Montillaud, J.; Ysard, N.; Lunttila, T.

doi:10.1051/0004-6361/201220910

Cited by 67 publications

(86 citation statements)

References 35 publications

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“…Potential problems include noise fluctuations and calibration uncertainties, and gradients in density and/or temperature along the line of sight (LOS) that may lead to non-convergence/inconsistent κ-values. Similar would apply to derived β-values, when one assumes that κ(ν) is given by a single power law of index β (e.g., Juvela et al 2013). The accuracy of our results below is limited to twice the statistical error of the intensity I ν at each frequency ν.…”

Section: Extended Dust Emissionmentioning

confidence: 96%

Gas and dust in the star-forming regionρ Oph A

Liseau

Larsson

Lunttila

et al. 2015

A&A

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Aims. We aim at determining the spatial distribution of the gas and dust in star-forming regions and address their relative abundances in quantitative terms. We also examine the dust opacity exponent β for spatial and/or temporal variations. Methods. Using mapping observations of the very dense ρ Oph A core, we examined standard 1D and non-standard 3D methods to analyse data of far-infrared and submillimetre (submm) continuum radiation. The resulting dust surface density distribution can be compared to that of the gas. The latter was derived from the analysis of accompanying molecular line emission, observed with Herschel from space and with APEX from the ground. As a gas tracer we used N 2 H + , which is believed to be much less sensitive to freeze-out than CO and its isotopologues. Radiative transfer modelling of the N 2 H + (J = 3−2) and (J = 6−5) lines with their hyperfine structure explicitly taken into account provides solutions for the spatial distribution of the column density N(H 2 ), hence the surface density distribution of the gas. Results. The gas-to-dust mass ratio is varying across the map, with very low values in the central regions around the core SM 1. The global average, =88, is not far from the canonical value of 100, however. In ρ Oph A, the exponent β of the power-law description for the dust opacity exhibits a clear dependence on time, with high values of 2 for the envelope-dominated emission in starless Class -1 sources to low values close to 0 for the disk-dominated emission in Class III objects. β assumes intermediate values for evolutionary classes in between. Conclusions. Since β is primarily controlled by grain size, grain growth mostly occurs in circumstellar disks. The spatial segregation of gas and dust, seen in projection toward the core centre, probably implies that, like C 18 O, also N 2 H + is frozen onto the grains.

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Section: Extended Dust Emissionmentioning

confidence: 96%

Gas and dust in the star-forming regionρ Oph A

Liseau

Larsson

Lunttila

et al. 2015

A&A

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“…Compared with the χ 2 estimates, the main advantage of the MCMC method is that it maps the full probability distribution of the parameters Juvela et al 2013). This provides a much better picture of the actual uncertainties than the mere 1σ error estimates.…”

Section: Dust Emissivity Spectral Indexmentioning

confidence: 99%

Multiwavelength study of the high-latitude cloud L1642: chain of star formation

Malinen

Juvela

Zahorecz

et al. 2014

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Context. L1642 is one of the two high galactic latitude (|b| > 30 • ) clouds confirmed to have active star formation. Aims. We examine the properties of this cloud, especially the large-scale structure, dust properties, and compact sources at different stages of star formation.Methods. We present high-resolution far-infrared and submillimetre observations with the Herschel and AKARI satellites and millimetre observations with the AzTEC/ASTE telescope, which we combined with archive data from near-and mid-infrared (2MASS, WISE) to millimetre wavelength observations (Planck).Results. The Herschel observations, combined with other data, show a sequence of objects from a cold clump to young stellar objects (YSOs) at different evolutionary stages. Source B-3 (2MASS J04351455-1414468) appears to be a YSO forming inside the L1642 cloud, instead of a foreground brown dwarf, as previously classified. Herschel data reveal striation in the diffuse dust emission around the cloud L1642. The western region shows striation towards the NE and has a steeper column density gradient on its southern side. The densest central region has a bow-shock like structure showing compression from the west and has a filamentary tail extending towards the east. The differences suggest that these may be spatially distinct structures, aligned only in projection. We derive values of the dust emission cross-section per H nucleon of σ e (250 μm) = 0.5−1.5 × 10 −25 cm 2 /H for different regions of the cloud. Modified black-body fits to the spectral energy distribution of Herschel and Planck data give emissivity spectral index β values 1.8-2.0 for the different regions. The compact sources have lower β values and show an anticorrelation between T and β. Conclusions. Markov chain Monte Carlo calculations demonstrate the strong anticorrelation between β and T errors and the importance of millimetre wavelength Planck data in constraining the estimates. L1642 reveals a more complex structure and sequence of star formation than previously known.

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“…Recently, alternative methods for fitting observational data with limited spectral coverage have been proposed, based on Bayesian or hierarchical models (Veneziani et al , 2013Kelly et al 2012;Juvela et al 2013). These new methods were developed specifically to limit the impact of instrumental noise on the estimated parameters.…”

Section: Implementation Of the Sed Fitmentioning

confidence: 99%

Planck2013 results. XI. All-sky model of thermal dust emission

Abergel¹,

Ade²,

Aghanim³

et al. 2014

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This paper presents an all-sky model of dust emission from the Planck 353, 545, and 857 GHz, and IRAS 100 µm data. Using a modified blackbody fit to the data we present all-sky maps of the dust optical depth, temperature, and spectral index over the 353-3000 GHz range. This model is a good representation of the IRAS and Planck data at 5 between 353 and 3000 GHz (850 and 100 µm). It shows variations of the order of 30% compared with the widely-used model of Finkbeiner, Davis, and Schlegel. The Planck data allow us to estimate the dust temperature uniformly over the whole sky, down to an angular resolution of 5 , providing an improved estimate of the dust optical depth compared to previous all-sky dust model, especially in high-contrast molecular regions where the dust temperature varies strongly at small scales in response to dust evolution, extinction, and/or local production of heating photons. An increase of the dust opacity at 353 GHz, τ 353 /N H , from the diffuse to the denser interstellar medium (ISM) is reported. It is associated with a decrease in the observed dust temperature, T obs , that could be due at least in part to the increased dust opacity. We also report an excess of dust emission at H  column densities lower than 10 20 cm −2 that could be the signature of dust in the warm ionized medium. In the diffuse ISM at high Galactic latitude, we report an anticorrelation between τ 353 /N H and T obs while the dust specific luminosity, i.e., the total dust emission integrated over frequency (the radiance) per hydrogen atom, stays about constant, confirming one of the Planck Early Results obtained on selected fields. This effect is compatible with the view that, in the diffuse ISM, T obs responds to spatial variations of the dust opacity, due to variations of dust properties, in addition to (small) variations of the radiation field strength. The implication is that in the diffuse high-latitude ISM τ 353 is not as reliable a tracer of dust column density as we conclude it is in molecular clouds where the correlation of τ 353 with dust extinction estimated using colour excess measurements on stars is strong. To estimate Galactic E(B − V) in extragalactic fields at high latitude we develop a new method based on the thermal dust radiance, instead of the dust optical depth, calibrated to E(B− V) using reddening measurements of quasars deduced from Sloan Digital Sky Survey data.

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The degeneracy between dust colour temperature and spectral index

Cited by 67 publications

References 35 publications

Gas and dust in the star-forming regionρ Oph A

Gas and dust in the star-forming regionρ Oph A

Multiwavelength study of the high-latitude cloud L1642: chain of star formation

Planck2013 results. XI. All-sky model of thermal dust emission

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