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An ALMA Survey of H₂CO in Protoplanetary Disks

Pegues, Jamila and Öberg, Karin I. and Bergner, Jennifer B. and Loomis, Ryan A. and Qi, Chunhua and Le Gal, Romane and Cleeves, L. Ilsedore and Guzmán, Viviana V. and Huang, Jane and Jørgensen, Jes K. and Andrews, Sean M. and Blake, Geoffrey A. and Carpenter, John M. and Schwarz, Kamber R. and Williams, Jonathan P. and Wilner, David J. (2020) An ALMA Survey of H₂CO in Protoplanetary Disks. Astrophysical Journal, 890 (2). Art. No. 142. ISSN 1538-4357.

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H₂CO is one of the most abundant organic molecules in protoplanetary disks and can serve as a precursor to more complex organic chemistry. We present an Atacama Large Millimeter/submillimeter Array survey of H₂CO toward 15 disks covering a range of stellar spectral types, stellar ages, and dust continuum morphologies. H₂CO is detected toward 13 disks and tentatively detected toward a fourteenth. We find both centrally peaked and centrally depressed emission morphologies, and half of the disks show ring-like structures at or beyond expected CO snowline locations. Together these morphologies suggest that H₂CO in disks is commonly produced through both gas-phase and CO-ice-regulated grain-surface chemistry. We extract disk-averaged and azimuthally-averaged H₂CO excitation temperatures and column densities for four disks with multiple H₂CO line detections. The temperatures are between 20–50 K, with the exception of colder temperatures in the DM Tau disk. These temperatures suggest that H₂CO emission in disks generally emerges from the warm molecular layer, with some contributions from the colder midplane. Applying the same H₂CO excitation temperatures to all disks in the survey, we find that H₂CO column densities span almost three orders of magnitude (~5 × 10¹¹–5 × 10¹⁴ cm⁻²). The column densities appear uncorrelated with disk size and stellar age, but Herbig Ae disks may have less H₂CO compared to T Tauri disks, possibly because of less CO freeze-out. More H₂CO observations toward Herbig Ae disks are needed to confirm this tentative trend, and to better constrain under which disk conditions H₂CO and other oxygen-bearing organics efficiently form during planet formation.

Item Type:Article
Related URLs:
URLURL TypeDescription
Pegues, Jamila0000-0002-6042-1486
Öberg, Karin I.0000-0001-8798-1347
Bergner, Jennifer B.0000-0002-8716-0482
Loomis, Ryan A.0000-0002-8932-1219
Qi, Chunhua0000-0001-8642-1786
Le Gal, Romane0000-0003-1837-3772
Cleeves, L. Ilsedore0000-0003-2076-8001
Guzmán, Viviana V.0000-0003-4784-3040
Huang, Jane0000-0001-6947-6072
Jørgensen, Jes K.0000-0001-9133-8047
Andrews, Sean M.0000-0003-2253-2270
Blake, Geoffrey A.0000-0003-0787-1610
Carpenter, John M.0000-0003-2251-0602
Schwarz, Kamber R.0000-0002-6429-9457
Williams, Jonathan P.0000-0001-5058-695X
Wilner, David J.0000-0003-1526-7587
Additional Information:© 2020 The American Astronomical Society. Received 2019 July 17; revised 2019 December 16; accepted 2019 December 19; published 2020 February 21. This paper has benefited from discussions with Alyssa Goodman and Dimitar Sasselov. J.P. gratefully acknowledges the support of the National Science Foundation (NSF) Graduate Research Fellowship through grant Nos. DGE1144152 and DGE1745303. K.Ö. gratefully acknowledges the support of the Simons Foundation through a Simons Collaboration on the Origins of Life (SCOL) PI grant (No. 321183). J.H. gratefully acknowledges support from the NSF Graduate Research Fellowship under grant No. DGE1144152. G.B. gratefully acknowledges support from the NSF (grant AST-1514918) and NASA (grant NNX16AB48G). J.K.J. gratefully acknowledges support from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme through ERC Consolidator grant "S4F" (grant Agreement No. 646908). K.S., a Sagan Fellow, gratefully acknowledges the support of NASA through Hubble Fellowship Program grant HST-HF2-51419.001, awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555. This paper makes use of the following ALMA data: 1. ADS/JAO.ALMA#2011.0.00629.S 2. ADS/JAO.ALMA#2012.1.00681.S 3. ADS/JAO.ALMA#2013.1.00226.S 4. ADS/JAO.ALMA#2015.1.00657.S 5. ADS/JAO.ALMA#2015.1.00678.S 6. ADS/JAO.ALMA#2015.1.00964.S 7. ADS/JAO.ALMA#2016.1.00627.S. ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada), MOST and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ. This work has made use of data from the European Space Agency (ESA) mission Gaia (, processed by the Gaia Data Processing and Analysis Consortium (DPAC, Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. All computer code used for this research was written in Python (version 2.7). All plots were generated using Python's Matplotlib package (Hunter 2007). This research also made use of Astropy (, a community-developed core Python package for Astronomy, and the NumPy~ (Oliphant 2006) and SciPy~ (Jones et al. 2001) Python packages.
Group:Astronomy Department
Funding AgencyGrant Number
NSF Graduate Research FellowshipDGE-1144152
NSF Graduate Research FellowshipDGE-1745303
Simons Foundation321183
European Research Council (ERC)646908
NASA Hubble FellowshipHST-HF2-51419.001
Gaia Multilateral AgreementUNSPECIFIED
Subject Keywords:Astrochemistry; Protoplanetary disks; Radio interferometry; Interstellar molecules
Issue or Number:2
Classification Code:Unified Astronomy Thesaurus concepts: Astrochemistry (75); Protoplanetary disks (1300); Radio interferometry (1346); Interstellar molecules (849)
Record Number:CaltechAUTHORS:20200221-082104598
Persistent URL:
Official Citation:Jamila Pegues et al 2020 ApJ 890 142
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:101444
Deposited By: Tony Diaz
Deposited On:21 Feb 2020 17:24
Last Modified:20 Apr 2020 08:47

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