The Effect of Line-of-Sight Temperature Variation and Noise on Dust Continuum Observations

Shetty, Rahul; Kauffmann, Jens; Schnee, Scott; Goodman, Alyssa A.; Ercolano, Barbara

doi:10.1088/0004-637x/696/2/2234

Cited by 192 publications

(246 citation statements)

References 39 publications

(82 reference statements)

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“…Models of Meny et al (2007) modify the dust optical properties to find an effective decrease in the submm emissivity index as the dust temperature increases as suggested by the observations of Dupac et al (2003). However, Shetty et al (2009) express caution in the inverse temperature -β interpretation, showing that flux uncertainties, especially in the Rayleigh-Jeans regime, can affect the results for the SED fits as far as temperature and emissivity are concerned. Although we do not reject the possibility of a modification of the properties of dust with temperature, here we explore the cold dust hypothesis, since it enables us to investigate its consequences on the global properties of the galaxies.…”

Section: Refinement: Adding a Cold Dust Componentmentioning

confidence: 97%

Probing the dust properties of galaxies up to submillimetre wavelengths

Galametz¹,

Madden²,

Galliano³

et al. 2009

A&A

200

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Aims. We study the dust properties of four low metallicity galaxies by modelling their spectral energy distributions. This modelling enables us to constrain the dust properties such as the mass, the temperature or the composition to characterise the global ISM properties in dwarf galaxies. Methods. We present 870 μm images of four low metallicity galaxies (NGC 1705, Haro 11, Mrk 1089 and UM 311) observed with the Large APEX BOlometer CAmera (LABOCA) on the Atacama Pathfinder EXperiment (APEX) telescope. We modeled their spectral energy distributions combining the submm observations of LABOCA, 2MASS, IRAS, Spitzer photometric data, and the IRS data for Haro 11. Results. We found that the PAH mass abundance is very low in these galaxies, 5 to 50 times lower than the PAH mass fraction of our Galaxy. We also found that a significant mass of dust is revealed when using submm constraints compared to that measured with only mid-IR to far-IR observations extending only to 160 μm. For NGC 1705 and Haro 11, an excess in submillimeter wavelengths was detected when we used our standard dust SED model. We rerun our SED procedure adding a cold dust component (10 K) to better describe the high 870 μm flux derived from LABOCA observations, which significantly improves the fit. We found that at least 70% of the dust mass of these two galaxies can reside in a cold dust component. We also showed that the subsequent dust-to-gas mass ratios, considering HI and CO observations, can be strikingly high for Haro 11 in comparison with what is usually expected for these low-metallicity environments. Furthermore, we derived the star formation rate of our galaxies and compared them to the Schmidt law. Haro 11 falls anomalously far from the Schmidt relation. These results may suggest that a reservoir of hidden gas could be present in molecular form not traced by the current CO observations. While there can be a significant cold dust mass found in Haro 11, the SED peaks at exceptionally short wavelengths (36 μm), also highlighting the importance of the much warmer dust component heated by the massive star clusters in Haro 11. We also derived the total IR luminosities derived from our models and compared them with relations that derive this luminosity from Spitzer bands. We found that the Draine & Li (2007) formula compares well to our direct IR determinations.

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Section: Refinement: Adding a Cold Dust Componentmentioning

confidence: 97%

Probing the dust properties of galaxies up to submillimetre wavelengths

Galametz¹,

Madden²,

Galliano³

et al. 2009

A&A

200

View full text Add to dashboard Cite

show abstract

“…A dust colour temperature can be determined by fixing the value of β (see, e.g., Eq. (3) of Shetty et al 2009). The value of β in the OH94 thickice dust model we adopted earlier is about 1.9 over the wavelength range λ ∈ [250, 1300 μm] (see also Shirley et al 2005).…”

Section: Dust Properties Determined From 350 and 870 μM Datamentioning

confidence: 99%

A (sub)millimetre study of dense cores in Orion B9

Miettinen

Harju

Haikala

et al. 2012

A&A

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Context. Studies of dense molecular-cloud cores at (sub)millimetre wavelengths are needed to understand the early stages of star formation. Aims. We aim to further constrain the properties and evolutionary stages of dense cores in Orion B9. The prime objective of this study is to examine the dust emission of the cores near the peak of their spectral energy distributions, and to determine the degrees of CO depletion, deuterium fractionation, and ionisation. Methods. The central part of Orion B9 was mapped at 350 μm with APEX/SABOCA. A sample of nine cores in the region were observed in C 17 O(2−1), H 13 CO + (4−3) (towards 3 sources), DCO + (4−3), N 2 H + (3−2), and N 2 D + (3−2) with APEX/SHFI. These data are used in conjunction with our previous APEX/LABOCA 870-μm dust continuum data. Results. All the LABOCA cores in the region covered by our SABOCA map were detected at 350 μm. The strongest 350 μm emission is seen towards the Class 0 candidate SMM 3. Many of the LABOCA cores show evidence of substructure in the higher-resolution SABOCA image. In particular, we report on the discovery of multiple very low-mass condensations in the prestellar core SMM 6. Based on the 350-to-870 μm flux density ratios, we determine dust temperatures of T dust 7.9−10.8 K, and dust emissivity indices of β ∼ 0.5−1.8. The CO depletion factors are in the range f D ∼ 1.6−10.8. The degree of deuteration in N 2 H + is 0.04−0.99, where the highest value (seen towards the prestellar core SMM 1) is, to our knowledge, the most extreme level of N 2 H + deuteration reported so far. The level of HCO + deuteration is about 1-2%. The fractional ionisation and cosmic-ray ionisation rate of H 2 could be determined only towards two sources with the lower limits of ∼2−6 × 10 −8 and ∼2.6 × 10 −17 −4.8 × 10 −16 s −1 , respectively. We also detected D 2 CO towards two sources. Conclusions. The detected protostellar cores are classified as Class 0 objects, in agreement with our previous SED results. The detection of subcondensations within SMM 6 shows that core fragmentation can already take place during the prestellar phase. The origin of this substructure is likely caused by thermal Jeans fragmentation of the elongated parent core. Varying levels of f D and deuteration among the cores suggest that they are evolving chemically at different rates. A low f D value and the presence of gas-phase D 2 CO in SMM 1 suggest that the core chemistry is affected by the nearby outflow. The very high N 2 H + deuteration in SMM 1 is likely to be remnant of the earlier CO-depleted phase.

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“…However, our methods do not allow the simultaneous fitting of a complex mixture of spectra. Even if the l = 30 • field is potentially characterized by several grain temperatures along the LOS (associated to Sagittarius, Scuttum-Crux and Perseus, as described in Bernard et al 2010), and therefore could induce a spurious T d -β inverse correlation (Masi et al 1995;Shetty et al 2009), the l = 59 • field, less contaminated by various dust mixing effects, still highlights a pronounced behavior in the T d -β parameter space. Both fields, with a different mixture of temperatures, present a T d -β anti-correlation.…”

Section: Variations Of the Emissivity Spectral Index With Temperaturementioning

confidence: 99%

Variations of the spectral index of dust emissivity from Hi-GAL observations of the Galactic plane

Paradis¹,

Veneziani

Noriega-Crespo³

et al. 2010

A&A

103

127

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Context. Variations in the dust emissivity are critical for gas mass determinations derived from far-infrared observations, but also for separating dust foreground emission from the Cosmic Microwave Background (CMB). Hi-GAL observations allow us for the first time to study the dust emissivity variations in the inner regions of the Galactic plane at resolution below 1 • . Aims. We present maps of the emissivity spectral index derived from the combined Herschel PACS 160 μm, SPIRE 250 μm, 350 μm, and 500 μm data, and the IRIS 100 μm data, and we analyze the spatial variations of the spectral index as a function of dust temperature and wavelength in the two science demonstration phase Hi-GAL fields, centered at l = 30 • and l = 59 • . Methods. Applying two different methods, we determine both dust temperature and emissivity spectral index between 100 and 500 μm, at an angular resolution (θ) of 4 . Results. Combining both fields, the results show variations of the emissivity spectral index in the range 1.8-2.6 for temperatures between 14 and 23 K. The median values of the spectral index are similar in both fields, i.e. 2.3 in the range 100-500 μm, while the median dust temperatures are equal to 19.1 K and 16.0 K in the l = 30 • and l = 59 • field, respectively. Statistically, we do not see any significant deviations in the spectra from a power law emissivity between 100 and 500 μm. We confirm the existence of an inverse correlation between the emissivity spectral index and dust temperature, found in previous analyses.

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The Effect of Line-of-Sight Temperature Variation and Noise on Dust Continuum Observations

Cited by 192 publications

References 39 publications

Probing the dust properties of galaxies up to submillimetre wavelengths

Probing the dust properties of galaxies up to submillimetre wavelengths

A (sub)millimetre study of dense cores in Orion B9

Variations of the spectral index of dust emissivity from Hi-GAL observations of the Galactic plane

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