Draft version May 26, 2020 Typeset using LATEX twocolumn style in AASTeX63 PHANGS CO kinematics: disk orientations and rotation curves at 150 pc resolution Philipp Lang,1 Sharon E. Meidt,2 Erik Rosolowsky,3 Joseph Nofech,3 Eva Schinnerer,1 Adam K. Leroy,4 Eric Emsellem,5, 6 Ismael Pessa,1 Simon C. O. Glover,7 Brent Groves,8, 9 Annie Hughes,10, 11 J. M. Diederik Kruijssen,12 Miguel Querejeta,13 Andreas Schruba,14 Frank Bigiel,15 Guillermo A. Blanc,16, 17 Melanie´ Chevance,12 Dario Colombo,18 Christopher Faesi,1 Jonathan D. Henshaw,1 Cinthya N. Herrera,19 Daizhong Liu,1 Jer´ ome^ Pety,19, 20 Johannes Puschnig,15 Toshiki Saito,1 Jiayi Sun,4 and Antonio Usero13 1Max-Planck-Institut f¨urAstronomie, K¨onigstuhl17 D-69117 Heidelberg, Germany 2Sterrenkundig Observatorium, Universiteit Gent, Krijgslaan 281 S9, B-9000 Gent, Belgium 3Department of Physics, University of Alberta, Edmonton, AB, Canada 4Department of Astronomy, The Ohio State University, 140 West 18th Avenue, Columbus, Ohio 43210, USA 5European Southern Observatory, Karl-Schwarzschild Straße 2, D-85748 Garching bei M¨unchen,Germany 6Univ Lyon, Univ Lyon1, ENS de Lyon, CNRS, Centre de Recherche Astrophysique de Lyon UMR5574, F-69230 Saint-Genis-Laval France 7Instit¨utf¨urTheoretische Astrophysik, Zentrum f¨urAstronomie der Universit¨atHeidelberg, Albert-Ueberle-Strasse 2, 69120 Heidelberg, Germany 8Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT 2611, Australia 9International Centre for Radio Astronomy Research, The University of Western Australia, Crawley, WA 6009 Australia 10Universit´ede Toulouse, UPS-OMP, 31028 Toulouse, France 11CNRS, IRAP, Av. du Colonel Roche BP 44346, 31028 Toulouse cedex 4, France 12Astronomisches Rechen-Institut, Zentrum f¨urAstronomie der Universit¨atHeidelberg, M¨onchhofstraße 12-14, 69120 Heidelberg, Germany 13Observatorio Astron´omico Nacional (IGN), C/Alfonso XII 3, Madrid E-28014, Spain 14Max-Planck-Institut f¨urExtraterrestrische Physik, Giessenbachstraße 1, D-85748 Garching bei M¨unchen,Germany 15Argelander-Institut f¨urAstronomie, Universit¨atBonn, Auf dem H¨ugel71, 53121 Bonn, Germany 16The Observatories of the Carnegie Institution for Science, 813 Santa Barbara St., Pasadena, CA, 91101 17Departamento de Astronom´ıa,Universidad de Chile, Camino del Observatorio 1515, Las Condes, Santiago, Chile 18Max-Planck-Institut f¨urRadioastronomie, Auf dem H¨ugel9, D-53121 Bonn, Germany 19Institut de Radioastronomie Millim´etrique, 300 rue de la Piscine, 38406 Saint-Martin-d'H`eres Cedex 20Sorbonne Universit´e,Observatoire de Paris, Universit´ePSL, CNRS, LERMA, 75014, Paris, France ABSTRACT We present kinematic orientations and high resolution (150 pc) rotation curves for 67 main sequence star-forming galaxies surveyed in CO (2-1) emission by PHANGS-ALMA. Our measurements are based on the application of a new fitting method tailored to CO velocity fields. Our approach identifies an optimal global orientation as a way to reduce the impact of non-axisymmetric (bar and spiral) features and the uneven spatial sampling characteristic of CO emission in the inner regions of nearby galaxies. The method performs especially well when applied to the large number of independent lines-of-sight contained in the PHANGS CO velocity fields mapped at 100 resolution. The high resolution rotation curves fitted to these data are sensitive probes of mass distribution in the inner regions of these galaxies. We use the inner slope as well as the amplitude of our fitted rotation curves to demonstrate that CO arXiv:2005.11709v1 [astro-ph.GA] 24 May 2020 is a reliable global dynamical mass tracer. From the consistency between photometric orientations from the literature and kinematic orientations determined with our method, we infer that the shapes of stellar disks in the mass range of log(M?(M ))=9.0-10.9 probed by our sample are very close to circular and have uniform thickness. Keywords: galaxies: ISM | ISM: kinematics and dynamics | ISM: clouds 1. INTRODUCTION high completeness across large areas (e.g., Schinnerer et Modern extragalactic CO surveys measure the prop- al. 2013; Freeman et al. 2017; Leroy et al. 2017; Sun et erties of molecular gas at cloud (50−100 pc) scales with al. 2018). This makes it possible to place cloud-scale molecular gas properties in the context of the global 2 kinematic response to the galactic potential, offering a ognizable deviations from their true values. In these view of the factors that influence the organization of the cases, rotational velocities also reflect the added contri- molecular gas and the star formation that occurs within bution from non-circular motions, leading to systematic it. One of the strengths of this approach is the ability to offsets in the inferred rotation curve (e.g., Fathi et al. use one data set to characterize the density distribution, 2005; van de Ven & Fathi 2010; Chemin et al. 2015, the local gas motions, and the galaxy dynamical mass 2016). for any single galaxy over a range of spatial scales. In this paper, we present global disk orientations and There are several factors that make the cold molecular rotation curves from ∼ 100 PHANGS-ALMA1 CO data phase of the interstellar medium (ISM) a good tracer of extending on average out to ∼ 0:7 R25 for 67 local star- the global dynamics of a galaxy. For nearby galaxies, in- forming galaxies. This is the largest such compilation of formation about the molecular gas kinematics can typi- CO rotation curves to date (c.f., Sofue & Rubin 2001) cally be obtained out to the edge of the optical disk (e.g., and complements the rich kinematics constraints offered Schruba et al. 2011, report extents in the range ∼ 0:3 by a growing number of stellar and multi-phase gas kine- to 1.3 R25). They reveal a projection of motion that matics surveys in the local universe (de Blok et al. 2008; can be used to infer the orientation of the galaxy with Epinat et al. 2008; Chung et al. 2009; Lelli et al. 2016; respect to the line-of-sight, as well as the speed at which Kalinova et al. 2017; Levy et al. 2018; Korsaga et al. material orbits around the galaxy center. The projected 2018). velocities in this case are an almost direct probe of the We use an approach that is optimized for kinematic galaxy's underlying mass distribution given the dissipa- tracers with low spatial filling factor that probe the cen- tive nature of molecular gas, which results in character- tral regions of galaxies at high spatial resolution. This istically low velocity dispersions (1−20 km s−1) in the makes it ideally suited for the wide-field CO data now disks of typical nearby galaxies (e.g., Combes & Bec- regularly produced by ALMA and NOEMA. Our tech- quaert 1997; Helfer et al. 2003; Colombo et al. 2014; nique incorporates many of the same elements imple- Sun et al. 2018; Boizelle et al. 2019). This feature has mented in the wealth of existing algorithms that fit 2D prompted the use of high resolution kinematic maps of and 3D kinematic data (van Albada et al. 1985; Bege- the inner portions of CO disks observed with the At- man 1987; Schoenmakers 1999; Simon et al. 2003; Kra- acama Large Millimeter/submillimeter Array (ALMA) jnovi´cet al. 2006; J´ozsaet al. 2007; Spekkens & Sellwood to reconstruct the masses of supermassive black holes in 2007; Bouche et al. 2015; Di Teodoro & Fraternali 2015; the centers of nearby galaxies (e.g., Davis & McDermid Kamphuis et al. 2015; Peters et al. 2017; Oh et al. 2018). 2017; Onishi et al. 2017; Davis et al. 2018). To overcome the complications of fitting CO velocity The dissipative quality of the gas also leads to a dis- fields, we introduce a new element that involves fitting tinctly strong response to underlying non-axisymmetric orientations to all lines-of-sight at once. This maximizes components in the gravitational potential (e.g., Roberts constraints from regions that provide an unbiased probe & Stewart 1987; Kim & Ostriker 2006; Dobbs & Pringle of circular motion. 2009). Bar and spiral arm features yield recognizable This paper is structured as follows: We discuss the deviations from circular motions in velocity field maps observational data used as well as our sample selection that provide powerful constraints on the structure of the in Section2. This is followed by a description of our ISM and its organization by the local galactic environ- fitting technique in Section3. Our results are presented ment. in Section4, followed by a discussion of our findings in Yet, as a global dynamics tracer, molecular gas kine- Section5. Finally, we present our conclusions in Sec- matics are confronted with issues that become more ob- tion6. vious at high spatial resolutions: Because the molecular phase traces the material at densities where gas begins 2. OBSERVATIONS AND SAMPLE to decouple from the background potential, thus forming 2.1. ALMA CO (2-1) observations and sample weakly self-gravitating clouds (e.g., Meidt et al. 2018), selection molecular gas emission is primarily confined to spiral arms, bars, or collections of individual clouds. The gas This work exploits observations of the PHANGS- in these regions reveals a strong contribution from non- ALMA sample of nearby galaxies with CO (2-1) emis- 00 circular streaming motions, more evident at higher spa- sion mapped with ALMA at high (∼ 1 ) angular res- tial resolution (e.g., Meidt et al. 2013; Colombo et al. olution. Details of the sample selection, ALMA obser- 2014). Without additional modelling, measurements of disk orientation based on velocity maps thus exhibit rec- 1 www.phangs.org 3 vations, and data processing are described in detail by tion of the pixels for each spectrum, iteratively rejecting A. K. Leroy et al. (in prep). In short, PHANGS-ALMA positive outliers associated with signal. We then smooth is designed to target 74 massive (log (M?=M ) > 9:75), the spatial noise estimate over ∼ 3 beam FWHM.