Low dust emissivities and radial variations in the envelopes of Class 0 protostars: possible signature of early grain growth

Galametz, M.; Maury, A.; Valdivia, Valeska; Testi, L.; Беллоче, А.; André, P.

doi:10.1051/0004-6361/201936342

Cited by 70 publications

(100 citation statements)

References 105 publications

(121 reference statements)

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“…Values with ( * ) are calculated via the relation from Dunham et al (2008) using fluxes from archival data of Herschel PACS at 70 µm. Galametz et al (2019) for Serpens Emb 8. Yang et al (2017) for BHR 71.…”

Section: Discussionmentioning

confidence: 99%

“…Sadavoy et al (2014) and Karska et al (2018) for L1448 IRS2. Karska et al (2018) and Galametz et al (2019) for IRAS4A. Chini et al (1997) and Manoj et al (2016) for OMC3 MMS6.…”

Section: Discussionmentioning

confidence: 99%

“…Furthermore, observations have revealed that radiation, presumably caused by accretion processes near the central protostar, causes enhanced polarized emission along the cavity walls of bipolar outflows (Hull et al 2017b(Hull et al , 2020Maury et al 2018;Le Gouellec et al 2019). Finally, indications of larger dust grain size with respect to the ISM dust grain population have been found in embedded objects (Miotello et al 2014;Valdivia et al 2019;Galametz et al 2019;Hull et al 2020;Le Gouellec et al 2019). This suggests that, in the context of the RAT alignment mechanism, these phenomena may counterbalance one another, thus precluding a significant variation of alignment efficiency as a function of column density.…”

Section: The Effects Of Environmental Conditions On Dust Grain Alignmmentioning

confidence: 99%

“…Radiative transfer studies assuming dust grains aligned by RATs of simulations of low-mass A11, page 15 of 32 A&A 644, A11 2020collapsing cores have shown that the typical amount of polarization detected in observations can be reproduced by simulations if the implemented maximum dust grain size exceeds 10 µm (Valdivia et al 2019). In addition, indications of such large grains have been found in multiwavelength observations of protostellar envelopes in studies analyzing dust grain emissivities (Miotello et al 2014;Galametz et al 2019). Finally, while the typical elongation of dust grains in star-forming environments is unconstrained observationally, grain alignment may strongly depend on this parameter; further efforts that use dust models to produce predictive observational tests would help further constrain the effect of grain elongation.…”

Section: Different Dust Grain Propertiesmentioning

confidence: 99%

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A statistical analysis of dust polarization properties in ALMA observations of Class 0 protostellar cores

Gouellec

Maury

Guillet

et al. 2020

A&A

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Context. Recent observational progress has challenged the dust grain-alignment theories used to explain the polarized dust emission routinely observed in star-forming cores. Aims. In an effort to improve our understanding of the dust grain alignment mechanism(s), we have gathered a dozen ALMA maps of (sub)millimeter-wavelength polarized dust emission from Class 0 protostars and carried out a comprehensive statistical analysis of dust polarization quantities. Methods. We analyze the statistical properties of the polarization fraction Pfrac and the dispersion of polarization position angles S. More specifically, we investigate the relationship between S and Pfrac as well as the evolution of the product S × Pfrac as a function of the column density of the gas in the protostellar envelopes. We compare the observed trends with those found in polarization observations of dust in the interstellar medium and in synthetic observations of non-ideal magneto-hydrodynamic (MHD) simulations of protostellar cores. Results. We find a significant S ∝ Pfrac−0.79 correlation in the polarized dust emission from protostellar envelopes seen with ALMA; the power-law index significantly differs from the one observed by Planck in star-forming clouds. The product S × Pfrac, which is sensitive to the dust grain alignment efficiency, is approximately constant across three orders of magnitude in envelope column density (from NH2 = 1022 cm−2 to NH2 = 1025 cm−2), with a mean value of 0.36−0.17+0.10. This suggests that the grain alignment mechanism producing the bulk of the polarized dust emission in star-forming cores may not systematically depend on the local conditions such as the local gas density. However, in the lowest-luminosity sources in our sample, we find a hint of less efficient dust grain alignment with increasing column density. Our observations and their comparison with synthetic observations of MHD models suggest that the total intensity versus the polarized dust are distributed at different intrinsic spatial scales, which can affect the statistics from the ALMA observations, for example, by producing artificially high Pfrac. Finally, synthetic observations of MHD models implementing radiative alignment torques (RATs) show that the statistical estimator S × Pfrac is sensitive to the strength of the radiation field in the core. Moreover, we find that the simulations with a uniform perfect alignment (PA) of dust grains yield, on average, much higher S × Pfrac values than those implementing RATs; the ALMA values lie among those predicted by PA, and they are significantly higher than the ones obtained with RATs, especially at large column densities. Conclusions. Ultimately, our results suggest that dust alignment mechanism(s) are efficient at producing dust polarized emission in the various local conditions typical of Class 0 protostars. The grain alignment efficiency found in these objects seems to be higher than the efficiency produced by the standard RAT alignment of paramagnetic grains. Further studies will be needed to understand how more efficient grain alignment via, for example, different irradiation conditions, dust grain characteristics, or additional grain alignment mechanisms can reproduce the observations.

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Section: Discussionmentioning

confidence: 99%

“…Sadavoy et al (2014) and Karska et al (2018) for L1448 IRS2. Karska et al (2018) and Galametz et al (2019) for IRAS4A. Chini et al (1997) and Manoj et al (2016) for OMC3 MMS6.…”

Section: Discussionmentioning

confidence: 99%

Section: The Effects Of Environmental Conditions On Dust Grain Alignmmentioning

confidence: 99%

Section: Different Dust Grain Propertiesmentioning

confidence: 99%

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A statistical analysis of dust polarization properties in ALMA observations of Class 0 protostellar cores

Gouellec

Maury

Guillet

et al. 2020

A&A

Self Cite

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“…A major observational bias could be caused by the dust opacity, which could be very high in Class 0/I sources, due to their high densities and, consequently, column densities (e.g., Miotello et al 2014;Galván-Madrid et al 2018;Galametz et al 2019). If the effect of dust absorption is not negligible, there are three major consequences: (1) hot corinos may be difficult to detect in the millimeter (also) because of the high dust absorption of the iCOMs lines; (2) the molecular complexity diversity observed in binary system objects may reflect a difference in the front dust column density rather than a real chemical difference of the two objects; (3) the iCOM abundances in hot corinos could have been underestimated so far.…”

Section: Introductionmentioning

confidence: 99%

Hot Corinos Chemical Diversity: Myth or Reality?

Simone

Ceccarelli

Codella

et al. 2020

ApJL

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After almost 20 years of hunting, only about a dozen hot corinos, hot regions enriched in interstellar complex organic molecules (iCOMs), are known. Of them, many are binary systems with the two components showing drastically different molecular spectra. Two obvious questions arise. Why are hot corinos so difficult to find and why do their binary components seem chemically different? The answer to both questions could be a high dust opacity that would hide the molecular lines. To test this hypothesis, we observed methanol lines at centimeter wavelengths, where dust opacity is negligible, using the Very Large Array interferometer. We targeted the NGC 1333 IRAS 4A binary system, for which one of the two components, 4A1, has a spectrum deprived of iCOMs lines when observed at millimeter wavelengths, while the other component, 4A2, is very rich in iCOMs. We found that centimeter methanol lines are similarly bright toward 4A1 and 4A2. Their non-LTE analysis indicates gas density and temperature (2 10 6 cm −3 and 100-190 K), methanol column density (∼10 19 cm −2), and extent (∼35 au in radius) similar in 4A1 and 4A2, proving that both are hot corinos. Furthermore, the comparison with previous methanol line millimeter observations allows us to estimate the optical depth of the dust in front of 4A1 and 4A2, respectively. The obtained values explain the absence of iCOMs line emission toward 4A1 at millimeter wavelengths and indicate that the abundances toward 4A2 are underestimated by ∼30%. Therefore, centimeter observations are crucial for the correct study of hot corinos, their census, and their molecular abundances.

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Limitations of the modified blackbody fit method for determining molecular cloud properties

Zielinski,

Wolf

2024

Astron Nachr

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Achieving a comprehensive understanding of the star and planet formation process is one of the fundamental tasks of astrophysics, requiring detailed knowledge of the physical conditions during the different phases of this process. During the earliest stages, that is, concerning physical processes in molecular clouds and filaments, the column density N(H2), dust temperature and dust emissivity index of these objects can be derived by adopting a modified blackbody fit of the far‐infrared (FIR) to (sub‐)millimeter spectral energy distributions (SEDs). However, this often applied method is based on various assumptions. In addition, the observational basis and required, but only assumed cloud properties, such as a limited wavelength‐coverage of the SED and dust properties, respectively, may differ between different studies. We review the basic limitations of this method and evaluate their impact on the derived physical properties of the objects of interest, that is, molecular clouds and filaments. We find that the highest uncertainty when applying this method is introduced by the often poorly constrained dust properties. Therefore, we propose to first derive the optical depth and subsequently the column density with the help of a suitable dust model as the optical depth can be obtained with high accuracy, especially at longer wavelengths. The method provides reliable results up to the high densities and corresponding optical depths observed in molecular clouds. Considering typically used observational data, that is, measurements obtained with FIR instruments like Herschel/PACS, JCMT/SCUBA‐2 and SOFIA/HAWC+, data at four wavelengths are sufficient to obtain accurate results. Furthermore, we find that the dust emissivity index derived from this method is not suitable as an indicator of dust grain size.

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Low dust emissivities and radial variations in the envelopes of Class 0 protostars: possible signature of early grain growth

Cited by 70 publications

References 105 publications

A statistical analysis of dust polarization properties in ALMA observations of Class 0 protostellar cores

A statistical analysis of dust polarization properties in ALMA observations of Class 0 protostellar cores

Hot Corinos Chemical Diversity: Myth or Reality?

Limitations of the modified blackbody fit method for determining molecular cloud properties

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