Draft version July 27, 2017 Preprint typeset using LATEX style emulateapj v. 01/23/15 ALIGNMENT BETWEEN PROTOSTELLAR OUTFLOWS AND FILAMENTARY STRUCTURE Ian W. Stephens1, Michael M. Dunham2,1, Philip C. Myers1, Riwaj Pokhrel1,3, Sarah I. Sadavoy1, Eduard I. Vorobyov4,5,6, John J. Tobin7,8, Jaime E. Pineda9, Stella S. R. Offner3, Katherine I. Lee1, Lars E. Kristensen10, Jes K. Jørgensen11, Alyssa A. Goodman1, Tyler L. Bourke12,Hector´ G. Arce13, Adele L. Plunkett14 Draft version July 27, 2017 ABSTRACT We present new Submillimeter Array (SMA) observations of CO(2{1) outflows toward young, em- bedded protostars in the Perseus molecular cloud as part of the Mass Assembly of Stellar Systems and their Evolution with the SMA (MASSES) survey. For 57 Perseus protostars, we characterize the orientation of the outflow angles and compare them with the orientation of the local filaments as derived from Herschel observations. We find that the relative angles between outflows and filaments are inconsistent with purely parallel or purely perpendicular distributions. Instead, the observed dis- tribution of outflow-filament angles are more consistent with either randomly aligned angles or a mix of projected parallel and perpendicular angles. A mix of parallel and perpendicular angles requires perpendicular alignment to be more common by a factor of ∼3. Our results show that the observed distributions probably hold regardless of the protostar's multiplicity, age, or the host core's opacity. These observations indicate that the angular momentum axis of a protostar may be independent of the large-scale structure. We discuss the significance of independent protostellar rotation axes in the general picture of filament-based star formation. Keywords: stars: formation { galaxies: star formation { stars: protostars { ISM: jets and outflows { ISM: clouds { ISM: structure 1. INTRODUCTION be hierarchically transferred from molecular clouds to Many stars form in filamentary structures with widths cores to protostars (e.g., Bodenheimer 1995). For a star- of order 0.1 pc (e.g., Arzoumanian et al. 2011). While forming filament, large-scale flows are probably either the exact shape of filaments is debated, e.g., cylinders onto the short axes of the filament from its cloud (either versus ribbons (Auddy et al. 2016), filaments are de- via accretion from the cloud or accretion via a collision) fined by a long axis and two much shorter axes. Dense or along the long filamentary axis. In a simplistic, non- cores (∼0.1 pc scale) either form within the filaments or turbulent scenario where one of the flows about the three form simultaneously with the filaments (Chen & Ostriker filamentary axes dominates, a core will likely rotate pri- 2015). Inhomogeneous flow or shear from colliding flows marily parallel or perpendicular to the parent filament. can torque cores (e.g., Fogerty et al. 2016; Clarke et al. If the angular momentum direction at the protostellar 2017). Classically, angular momentum is expected to scale is inherited from this core scale, the rotation axes of newly formed protostars will also be preferentially par- 1 Harvard-Smithsonian Center for Astrophysics, 60 Garden allel or perpendicular to the filaments. Street, Cambridge, MA, USA [email protected] One way to empirically test the alignment between a 2 Department of Physics, State University of New York at Fre- protostar's spin and its filamentary structure is to ob- donia, 280 Central Ave, Fredonia, NY 14063, USA 3 Department of Astronomy, University of Massachusetts, serve a protostar's outflow direction and compare it to Amherst, MA 01003, USA the filamentary structure as probed by dust emission. 4 Institute of Fluid Mechanics and Heat Transfer, TU Wien, Vi- By using this method across five nearby star-forming re- enna, 1060, Austria gions, Anathpindika & Whitworth(2008) found sugges- 5 Research Institute of Physics, Southern Federal University, Stachki Ave. 194, Rostov-on-Don, 344090, Russia tive evidence that outflows (as traced by scattered light) 6 University of Vienna, Department of Astrophysics, Vienna, tend to be preferentially perpendicular to filaments. On 1180, Austria the other hand, Davis et al.(2009) found that in Orion, arXiv:1707.08122v1 [astro-ph.GA] 25 Jul 2017 7 Homer L. Dodge Department of Physics and Astronomy, Uni- the orientation between outflows (as traced by H ) and versity of Oklahoma, 440 W. Brooks Street, Norman, OK 73019, 2 USA filaments appear random. A well-focused study that an- 8 Leiden Observatory, Leiden University, P.O. Box 9513, 2300- alyzes the outflow-filament angles is needed to reconcile RA Leiden, The Netherlands this disagreement. 9 Max-Planck-Institut f¨ur extraterrestrische Physik, D-85748 The rotation axis of a protostar, or even the parent Garching, Germany 10 Centre for Star and Planet Formation, Niels Bohr Institute protostellar core, could also be independent of its na- and Natural History Museum of Denmark, University of Copen- tal filamentary structure. Some observations have shown hagen, Øster Voldgade 5-7, DK-1350 Copenhagen K, Denmark that the angular momentum vectors of cores themselves 11 Niels Bohr Institute and Center for Star and Planet Forma- may be randomly distributed about the sky, regardless tion, Copenhagen University, DK-1350 Copenhagen K., Denmark 12 SKA Organization, Jodrell Bank Observatory, Lower With- of the cloud, core, or filamentary structure (Heyer 1988; ington, Macclesfield, Cheshire SK11 9DL, UK Myers et al. 1991; Goodman et al. 1993; Tatematsu et al. 13 Department of Astronomy, Yale University, New Haven, CT 2016). Multiplicity could also affect rotation axes. In the 06520, USA 14 European Southern Observatory, Av. Alonso de Cordova Submillimeter Array (SMA, Ho et al. 2004) large project 3107, Vitacura, Santiago de Chile, Chile called the Mass Assembly of Stellar Systems and their 2 Evolution with the SMA (MASSES; co-PIs: Michael data published in Lee et al. 2015, 2016) since these ob- Dunham and Ian Stephens), Lee et al.(2016) found that servations were either better quality and/or at higher outflows of wide-binary pairs (i.e., binary pairs sepa- resolution. These published PAs each came from obser- rated by 1000 AU and 10,000 AU) are typically randomly vations of one of three different J rotational transitions aligned or perpendicular (but not parallel) to each other. of CO: CO(1{0), CO(2{1), and CO(3{2). The rest fre- Radiation-magnetohydrodynamic simulations by Offner quencies for these three spectral lines are 115.27120 GHz, et al.(2016) of slightly magnetically-supercritical turbu- 230.53796 GHz, and 345.79599 GHz, respectively. lent cores found the same results for wide-binary pairs. 2.2. Herschel-derived Optical Depth Maps These simulations suggest that the direction of the proto- stellar spin axis can evolve significantly during formation, Herschel is well-suited for finding filaments in Perseus indicating that, at least for wide-binaries, the rotation given its resolution and wavelength range. The resolu- axes are independent of the large-scale structure. tion at the longest Herschel wavelength (500 µm) is 3600 In this paper, we aim to observationally test whether or ∼0.04 pc at the distance of Perseus (235 pc, Hirota or not a preferential alignment exists between the local et al. 2008). Star-forming filaments have temperatures filamentary elongation and the angular momentum axis of ∼10 to 20 K, and thus the dust continuum will peak as traced by outflows. To test such alignment, we use within the Herschel bands (70 µm to 500 µm). These new CO observations from the MASSES survey to trace wavebands can be used to approximate the optical depth the molecular outflows in the Perseus molecular cloud. and the column density of Perseus filaments. Indeed, Along with ancillary data, we determine accurate pro- several studies have already created optical depth or col- jected outflow position angles (PAs) for 57 Class 0 and I umn density maps of the Perseus molecular cloud using protostars. The MASSES survey provides uniform spa- Herschel observations, including Sadavoy et al.(2014), tial coverage of the same molecular line tracers in a single Zari et al.(2016), and Abreu-Vicente et al.(2016). All cloud, and only focuses on young sources { Class 0 and I three of the aforementioned studies assumed a modified protostars. Since these protostars are young, their par- blackbody with a specific intensity of ent filamentary structure has had less time to change in I = B (T )(1 − e−τν ) ≈ B (T )τ ; (1) morphology since the birth of the stars. These outflow ν ν ν ν observations can then be compared to the filamentary where Bν is the blackbody function at temperature T structure as observed by the Herschel Gould Belt sur- and τν is the optical depth. τν is assumed to follow a β vey (e.g., Andr´eet al. 2010). power-law function of the form τν / ν , where β is the We describe the observations used in Section2 and the dust emissivity index. The dust column density, Ndust, outflow/filament PA extraction techniques in Section3. can be calculated assuming τν = Ndustκν , where κν is We present the results in Section4 and discuss their pos- the dust opacity. Each study assumed τν and T to be sible implications in Section5. Finally, we summarize the free parameters. main results in Section6. While these studies varied slightly, e.g., on their as- sumption for β, the resulting maps are very similar. We choose to use the 353 GHz optical depth (τ353 GHz) map 2. OBSERVATIONS from Zari et al.(2016) since this map has been made 2.1. Outflow and Continuum Data publicly available. Zari et al.(2016) assumed a value For the Perseus protostellar outflows studied in this pa- of β = 2, and they did not convert the τ353 GHz maps per, we introduce new, unpublished MASSES CO(2{1) to column density.