CO in Protostars (COPS): $ Herschel $-SPIRE Spectroscopy of Embedded
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Draft version May 15, 2018 Typeset using LATEX twocolumn style in AASTeX61 CO IN PROTOSTARS (COPS): HERSCHEL-SPIRE SPECTROSCOPY OF EMBEDDED PROTOSTARS ∗ Yao-Lun Yang,1 Joel D. Green,2, 1 Neal J. Evans II,1, 3, 4 Jeong-Eun Lee,5 Jes K. Jørgensen,6 Lars E. Kristensen,6 Joseph C. Mottram,7 Gregory Herczeg,8 Agata Karska,9 Odysseas Dionatos,10 Edwin A. Bergin,11 Jeroen Bouwman,7 Ewine F. van Dishoeck,12, 13 Tim A. van Kempen,14, 12 Rebecca L. Larson,1 and Umut A. Yıldız15 1The University of Texas at Austin, Department of Astronomy, 2515 Speedway, Stop C1400, Austin, TX 78712, USA 2Space Telescope Science Institute, 3700 San Martin Dr., Baltimore, MD 02138, USA 3Korea Astronomy and Space Science Institute, 776 Daedeokdae-ro, Yuseong-gu, Daejeon 34055, Korea 4Humanitas College, Global Campus, Kyung Hee University, Yongin-shi 17104, Korea 5Department of Astronomy & Space Science, Kyung Hee University, Gyeonggi 446-701, Korea School of Space Research, Kyung Hee University, Yongin-shi, Kyungki-do 449-701, Korea 6Centre for Star and Planet Formation, Niels Bohr Institute and Natural History Museum of Denmark, University of Copenhagen, Øster Voldgade 5-7, DK-1350 Copenhagen K., Denmark 7Max Planck Institute for Astronomy, K¨onigstuhl17, 69117 Heidelberg, Germany 8Kavli Institute for Astronomy and Astrophysics, Peking University, Yi He Yuan Lu 5, Haidian Qu, 100871 Beijing, China 9Centre for Astronomy, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University, Grudziadzka 5, 87-100 Torun, Poland 10Department of Astrophysics, University of Vienna, Tuerkenschanzstrasse 17, 1180 Vienna, Austria 11Department of Astronomy, University of Michigan, 1085 S. University Avenue, Ann Arbor, MI 48109, USA 12Leiden Observatory, Leiden University, Netherlands 13Max Planck Institute for Extraterrestrial Physics, Garching, Germany 14SRON Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, Netherlands 15Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA ABSTRACT We present full spectral scans from 200{670 µm of 26 Class 0+I protostellar sources, obtained with Herschel-SPIRE, as part of the "COPS-SPIRE" Open Time program, complementary to the DIGIT and WISH Key programs. Based on our nearly continuous, line-free spectra from 200{670 µm, the calculated bolometric luminosities (Lbol) increase by 50% on average, and the bolometric temperatures (Tbol) decrease by 10% on average, in comparison with the measurements without Herschel. Fifteen protostars have the same Class using Tbol and Lbol/Lsmm. We identify 13 + rotational transitions of CO lines from J = 4 ! 3 to J = 13 ! 12, along with emission lines of CO, HCO ,H2O, 12 13 12 and [C I]. The ratios of CO to CO indicate that CO emission remains optically thick for Jup < 13. We fit up to four components of temperature from the rotational diagram with flexible break points to separate the components. The distribution of rotational temperatures shows a primary population around 100 K with a secondary population at ∼350 K. We quantify the correlations of each line pair found in our dataset, and find the strength of correlation arXiv:1805.00957v2 [astro-ph.GA] 11 May 2018 of CO lines decreases as the difference between J-level between two CO lines increases. The multiple origins of CO emission previously revealed by velocity-resolved profiles are consistent with this smooth distribution if each physical component contributes to a wide range of CO lines with significant overlap in the CO ladder. We investigate the spatial extent of CO emission and find that the morphology is more centrally peaked and less bipolar at high-J lines. We find the CO emission observed with SPIRE related to outflows, which consists two components, the entrained gas and shocked gas, as revealed by our rotational diagram analysis as well as the studies with velocity-resolved CO emission. Corresponding author: Yao-Lun Yang [email protected] ∗ Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. 2 Yang et al. 1. INTRODUCTION PACS and SPIRE spectra was also presented for specific Large samples of protostars in relatively nearby (d ≤ sources (e.g. Serpens SMM1, Goicoechea et al. 2012). 300 pc) clouds have been developed through recent sur- The full Herschel bands contain numerous pure rota- veys with the Spitzer Space Telescope (e.g. Evans et al. tional transitions of CO, as well as lines of H2O, OH, + 2009a; Dunham et al. 2015) as well as the Herschel HCO , and atomic lines ([C I], [C II], [N II], and [O I]), Space Observatory (e.g. Andr´eet al. 2010; van Dishoeck all potential tracers of gas content and properties. Her- et al. 2011; Kirk et al. 2013; Green et al. 2013b; Manoj schel enabled access to the CO ladder toward higher et al. 2016; Mottram et al. 2017), along with ground- energy levels (Jup=4{48), providing an opportunity to based surveys (e.g. Jørgensen et al. 2009). Over recent constrain the origin of CO emission entirely. At least decades, infrared and submillimeter studies of such sam- two rotational temperatures are typically found with the ples have allowed significant advances in our understand- PACS spectra toward embedded protostars (e.g. Green ing of the properties, structure and evolution of such et al. 2013b; Manoj et al. 2013; Karska et al. 2013). protostars. The SPIRE spectra reveal the colder CO component, ISO/LWS spanned the 20{200 µm spectral region and which has a different physical origin than the one for was well-suited to study the warm (T > 100 K) region the higher-J CO lines, suggested from velocity-resolved of protostellar envelopes, distinguishable from the am- observations (see Kristensen et al. 2017b). Visser et al. bient cloud typically probed in ground-based millimeter (2012) argued that C-type shocks dominate the high-J CO lines at embedded sources with the the velocity- studies. ISO-LWS detected gas phase H2O, high-J CO rotational transitions, and fine structure emission lines unresolved PACS data, while Yıldız et al. (2012) found toward protostars and related structures (e.g., Loren- the signature of shocked gas in the broad line profiles in zetti et al. 1999; Giannini et al. 1999; Ceccarelli et al. the CO J = 6 ! 5 line, suggesting a different origin for 1999; Lorenzetti et al. 2000; Giannini et al. 2001; Nisini the higher-J CO lines compared to the CO lines that et al. 2002). These lines were considered to originate are typically accessed from the ground (Jup ≤ 3). Kris- from the outflows (Giannini et al. 1999, 2001; Nisini tensen et al. (2017b), who have a similar source list, et al. 2002), or the inner envelope (Ceccarelli et al. 1999); showed that the CO J = 16 ! 15 line contains a broad however, recent observations of Herschel Space Obser- component at the source velocity and a narrow compo- vatory clearly show that these lines are dominated by nent offsetting from the source velocity. outflow activity (Kristensen et al. 2010, 2012; Mottram The emission of water has a similar line profile to et al. 2014). the broad component found in CO J = 3 ! 2 and Herschel was an European Space Agency (ESA) J = 10 ! 9 lines (Kristensen et al. 2012; Mottram et al. space-based far-infrared/submillimeter telescope with 2014, 2017). Both the line profiles and spatial extent a 3.5-meter primary mirror (Pilbratt et al. 2010). For of water emission suggest its close relation to outflows the first time, Herschel-SPIRE (Spectral and Photo- (Santangelo et al. 2012; Vasta et al. 2012; Kristensen metric Imaging REceiver, 194{670 µm; Griffin et al. et al. 2012; Mottram et al. 2014, 2017). Detailed mod- 2010) enabled low resolution spectroscopy of the entire elings of water emission indicate a similar shock origin submillimeter domain. These wavelengths are sensitive to the high-J CO lines (Karska et al. 2014; Manoj et al. to dust continuum, and provide access to the full suite 2013, Karska et al. to be accepted) Thus, these lines + 13 make excellent diagnostics of opacity, density, temper- of mid-J CO, HCO , CO and several H2O emission lines. ature, and shock velocities (e.g., Kaufman & Neufeld In the previous analysis with data from the Dust, 1996; Flower & Pineau Des For^ets 2010; Neufeld 2012) Gas, and Ice In Time Herschel Key Program (DIGIT), of the gas surrounding these systems (Kristensen et al. we used the PACS spectrograph (50{200 µm, Poglitsch 2013; Mottram et al. 2014). et al. 2010) to characterize a sample of well-studied pro- In this work, we present Herschel-SPIRE observations tostars, selected from the c2d sample, including both from the \CO in Protostars-SPIRE" (COPS-SPIRE) Class 0 and Class I objects (Green et al. 2013b). Sim- survey (PI: J. Green), of 27 protostars taken from the ilar studies also used PACS data to characterize the \DIGIT" and \WISH" samples. In Section 2, we de- properties of protostars in different regions with data scribe the sample, and provide an archive of 1{1000 µm from the Water in Star-forming Regions with Herschel spectral energy distributions (SEDs), combining the (WISH) Key Program (Karska et al. 2013) and the Spitzer-IRS, PACS, and SPIRE spectra, along with the Herschel Orion Protostar Survey (HOPS) Key Program description of the data processing pipeline. In Section 3, (Manoj et al. 2013, 2016). The analysis of the combined we present the SEDs and the line fitting results, as well as the effect of emission lines on photometry. We charac- COPS-SPIRE 3 terize the molecular and atomic lines with a customized The data processing pipeline is based on the method line fitting pipeline previously optimized for Herschel described in (Green et al.