FAUST

Astronomy and Astrophysics, vol. 700, pp. A188

Abstract

Context. The (sub-)millimetre dust opacity spectral index (β) is a critical observable for constraining dust properties, such as the maximum grain size of an observed dust population. It has been widely measured at Galactic scales and down to protoplanetary disks. Because of observational and analytical challenges, however, quite a gap exists in following the evolution of dust in the interstellar medium (ISM): we lack measures of the dust properties in the envelopes that feed newborn protostars and their disks. Aims. To fill this gap, we used sensitive dust continuum emission data at 1.2 and 3.1 mm from the ALMA FAUST Large Program and constrained the spectral index of the submillimetre dust opacity for a sample of protostars. Methods. Our high-resolution data, along with a method that was more refined than the methods in previous efforts, allowed us to distinguish the contributions from the disk and envelope in the uv-plane, and thus, to measure spectral indices for the envelopes that are not contaminated by the optically thick emission of the inner disk regions. Results. The FAUST sources (n = 13) include a variety of morphologies in continuum emission: compact young disks, extended collapsing envelopes, and dusty outflow cavity walls. Firstly, we found that the young disks in our sample are small (down to < 9 au) and optically thick. Secondly, we measured the dust opacity spectral index β at envelope scales for n = 11 sources: The β of n = 9 of these sources were not constrained before. We effectively doubled the number of sources for which the dust opacity spectral index β has been measured at these scales. Thirdly, by combining the available literature measurements with our own (a total n = 18), we showed the distribution of the envelope spectral indices between ISM-like and disk-like values. This bridges the gap in the inferred dust evolution. Finally, we statistically confirmed a significant correlation between β and the mass of protostellar envelopes, as previously suggested in the literature. Conclusions. Our findings indicate that the optical dust properties smoothly vary from the ISM (≫ 0.1 parsec) through envelopes (∼ 500–2000 au) to protoplanetary disks (< 200 au). Multi-wavelength surveys including longer wavelengths and in controlled starforming regions are needed to further this study and make more general claims about the dust evolution in its pathway from the cloud to disks.

Authors 16

1. Luca Cacciapuoti

   European Southern Observatory

   Affiliation as printed

   European Southern Observatory, Alonso de Cordova 3107, Vitacura, Region Metropolitana de Santiago, Chile

2. L. Testi

   University of Bologna

   Affiliation as printed

   Dipartimento di Fisica e Astronomia "Augusto Righi" Viale Berti Pichat 6/2, Bologna, Italy

3. Anaëlle J. Maury

   Centre National de la Recherche Scientifique · Université Paris Cité · Commissariat à l'Énergie Atomique et aux Énergies Alternatives · Université Paris-Saclay · Astrophysique, Instrumentation et Modélisation · Institut d'Estudis Espacials de Catalunya

   Affiliation as printed

   Institut d'Estudis Espacials de Catalunya (IEEC), c/Gran Capita 24, 08034 Barcelona, Catalonia, Spain

   Université Paris-Saclay, Université Paris Cité, CEA, CNRS, AIM, 91191 Gif-sur-Yvette, France

4. C. J. Chandler

   National Radio Astronomy Observatory

   Affiliation as printed

   National Radio Astronomy Observatory, PO Box O, Socorro, NM 87801, USA

5. Nami Sakai

   RIKEN

   Affiliation as printed

   RIKEN Cluster for Pioneering Research, 2-1, Hirosawa, Wako-shi, Saitama 351-0198, Japan

6. C. Ceccarelli

   Centre National de la Recherche Scientifique · Institut de Planétologie et d'Astrophysique de Grenoble · Université Grenoble Alpes

   Affiliation as printed

   Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France

7. C. Codella

   Arcetri Astrophysical Observatory · National Institute for Astrophysics

   Affiliation as printed

   INAF, Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy

8. M. De Simone

   European Southern Observatory

   Affiliation as printed

   European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei Munchen, Germany

9. Enrique Macías

   European Southern Observatory

   Affiliation as printed

   European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei Munchen, Germany

10. Claudia Toci

    European Southern Observatory

    Affiliation as printed

    European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei Munchen, Germany

11. Yancy L. Shirley

    University of Arizona

    Affiliation as printed

    Steward Observatory, 933 N Cherry Avenue, Tucson, AZ 85721, USA

12. Satoshi Ohashi

    National Astronomical Observatory of Japan

    Affiliation as printed

    National Astronomical Observatory of Japan, Osawa 2-21-1, Mitakashi, Tokyo 181-8588, Japan

13. F. Fontani

    Arcetri Astrophysical Observatory · National Institute for Astrophysics

    Affiliation as printed

    INAF, Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy

14. Yuan Zhang

    Shanghai Jiao Tong University

    Affiliation as printed

    Department of Astronomy, Shanghai Jiao Tong University, 800 Dongchuan Road, Minhang, Shanghai 200240, PR China

15. P. Hennebelle

    Centre National de la Recherche Scientifique · Université Paris Cité · Commissariat à l'Énergie Atomique et aux Énergies Alternatives · Université Paris-Saclay · Astrophysique, Instrumentation et Modélisation

    Affiliation as printed

    Université Paris-Saclay, Université Paris Cité, CEA, CNRS, AIM, 91191 Gif-sur-Yvette, France

16. S. Yamamoto

    The Graduate University for Advanced Studies, SOKENDAI

    Affiliation as printed

    SOKENDAI, Shonan Village, Hayama, Kanagawa 240-0193, Japan