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The RINGS Survey III: Medium-Resolution Halpha Fabry

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The RINGS Survey III: Medium-Resolution Halpha Fabry Revised version submitted to AJ on January 23, 2018 A Preprint typeset using LTEX style emulateapj v. 12/16/11 THE RINGS SURVEY III: MEDIUM-RESOLUTION Hα FABRY-PEROT´ KINEMATIC DATASET Carl J. Mitchell Department of Physics and Astronomy, Rutgers, the State University of New Jersey, 136 Frelinghuysen Rd., Piscataway, NJ 08854 J. A. Sellwood1 Department of Physics and Astronomy, Rutgers, the State University of New Jersey, 136 Frelinghuysen Rd., Piscataway, NJ 08854 and 1 Current address: Steward Observatory, 933 N Cherry Ave, Tucson, AZ 85721 T. B. Williams South African Astronomical Observatory, Observatory, Cape Town 7925, South Africa Astronomy Department, University of Cape Town, Rondebosch 7700, South Africa and Department of Physics and Astronomy, Rutgers, the State University of New Jersey, 136 Frelinghuysen Rd., Piscataway, NJ 08854 Kristine Spekkens Department of Physics, Royal Military College of Canada, P.O. Box 17000, Station Forces, Kingston, Ontario K7K 7B4, Canada Rachel Kuzio de Naray Department of Physics and Astronomy, Georgia State University, Atlanta, GA 30302 Alex Bixel Department of Astronomy and Steward Observatory, The University of Arizona, 933 North Cherry Ave, Tucson, AZ 85721 (Dated: September 23, 2018) Revised version submitted to AJ on January 23, 2018 ABSTRACT The distributions of stars, gas, and dark matter in disk galaxies provide important constraints on galaxy formation models, particularly on small spatial scales (<1 kpc). We have designed the RSS Imaging spectroscopy Nearby Galaxy Survey (RINGS) to target a sample of 19 nearby spiral galaxies. For each of these galaxies, we are obtaining and modeling Hα and H I 21 cm spectroscopic data as well as multi-band photometric data. We intend to use these models to explore the underlying structure and evolution of these galaxies in a cosmological context, as well as whether the predictions of ΛCDM are consistent with the mass distributions of these galaxies. In this paper, we present spectroscopic imaging data for 14 of the RINGS galaxies observed with the medium spectral resolution Fabry- P´erot etalon on the Southern African Large Telescope. From these observations, we derive high spatial resolution line of sight velocity fields of the Hα line of excited hydrogen, as well as maps and azimuthally averaged profiles of the integrated Hα and [N II] emission and oxygen abundances. We then model these kinematic maps with axisymmetric models, from which we extract rotation curves and projection geometries for these galaxies. We show that our derived rotation curves agree well with other determinations and the similarity of the projection angles with those derived from our photometric images argues against these galaxies having intrinsically oval disks. arXiv:1801.07750v1 [astro-ph.GA] 23 Jan 2018 Keywords: galaxies, galaxies: spiral, galaxies: individual, galaxies: kinematics and dynamics 1. INTRODUCTION it remains somewhat unclear whether the internal struc- The standard cosmological paradigm of Cold Dark tures of simulated galaxies formed in a ΛCDM framework Matter with the addition of a cosmological constant are consistent with observations of real galaxies. (ΛCDM) has been successful at interpreting astrophysi- In spiral galaxies, the structure of dark matter halos cal phenomena on a wide range of scales, from the large can be constrained using galaxy rotation curves (e.g. scale structure of the Universe to the formation of in- Bosma 1978). Typically, the observed rotation curve dividual galaxies (Somerville & Dav´e2015). However, is decomposed into contributions from stars and gas and any remaining velocity is attributed to dark mat- ter. In cosmological simulations of dark matter structure [email protected] [email protected] growth, dark matter halos have been observed to follow a [email protected] broken power law form (e.g. Einasto 1965; Navarro et al. [email protected] 1996, 2004; Gao et al. 2008). To account for the addi- [email protected] tional gravitational pull provided by baryons, modifica- [email protected] 2 Mitchell et al. tions can be applied to theoretical halo density profiles to A number of previous surveys have obtained two- increase their densities at small radii (e.g. Gnedin et al. dimensional Hα velocity fields of galaxies with similar 2004; Sellwood & McGaugh 2005). Applying these mod- goals to RINGS, e.g. BHαBAR (Hernandez et al. 2005), ified halo models to observed rotation curves produces GHASP (Epinat et al. 2008), GHαFaS (Hernandez et al. dark matter halos which are underdense relative to 2008), DiskMass (Bershady et al. 2010), and CALIFA the predictions of ΛCDM simulations (Papastergis et al. (S´anchez et al. 2012). Compared to these surveys, our 2015). data are deeper and more extended thanks to SALT’s Numerical simulations which incorporate stellar feed- large primary mirror and large angular field-of-view. The back in galaxies have partially eased this ten- typical angular resolution of the RINGS data is similar to sion by showing that feedback from baryonic pro- that of the DiskMass and CALIFA surveys and somewhat cesses can redistribute dark matter within a galaxy worse than that of GHαFaS. However, the RINGS galax- (Governato et al. 2010; Pontzen & Governato 2012; ies are typically more nearby than the galaxies in those Teyssier et al. 2013). These effects are stronger in galax- surveys, and our physical resolutions are comparable to ies with lower masses (e.g. Oh et al. 2011; Brook et al. those of GHαFaS and higher than those of DiskMass 2011; Pontzen & Governato 2014). Recent simulations and CALIFA. The typical spectral resolution of our data have shown that the ability of a galaxy to redistribute (R ∼ 1300) is similar to that of CALIFA (R ∼ 1000) and dark matter through stellar feedback depends on the ra- lower than that of DiskMass (R ∼ 8000) and GHαFaS tio of its stellar mass to its halo mass (e.g. Di Cintio et al. (R ∼ 15000). Our target selection criteria also differ 2014; Brook 2015). These M∗/Mhalo-dependent density from these surveys in choosing a representative sample profiles have been shown by Katz et al. (2017) to be more of partially inclined galaxies across a wide range of Hub- consistent with the photometry and rotation curves of ble classifications, masses, and luminosities. real galaxies than traditional NFW profiles. In Paper I (Mitchell et al. 2015), we presented our The relationship between dark matter halos and first Hα and H I kinematic data and modelling for the observed rotation curves is not a trivial one, as galaxy NGC 2280. In Paper II (Kuzio de Naray et al. measurements of rotation curves can be biased by in prep.), we presented our photometric sample and mod- non-circular motions, projection effects, and halo elling. In this paper, we present kinematic maps and triaxiality (e.g. Rhee et al. 2004; Hayashi & Navarro axisymmetric models of 14 of the 19 RINGS galax- 2006; Valenzuela et al. 2007). Measurements of one- ies. The maps are derived from data taken using the dimensional rotation curves are therefore insufficient to medium-resolution etalon of SALT’s Fabry-P´erot sys- constrain the three-dimensional mass distributions. All tem. The typical angular resolution of our resulting of these mechanisms for potential bias in rotation curves Hα velocity fields is ∼ 2.5′′, corresponding to a typi- leave kinematic signatures in the full three-dimensional cal spatial resolution of ∼ 250 pc at the source loca- velocity distributions of galaxy disks. For example, gas tions. We then model the kinematic data using the streaming along bars and spiral arms has both circular DiskFit software package (Spekkens & Sellwood 2007; and radial components to its velocity, and therefore will Sellwood & Z´anmar S´anchez 2010) and show that the affect the line of sight velocities along the major and mi- derived rotation curves generally agree well with others nor axes differently (Sellwood & Z´anmar S´anchez 2010). in the literature. We also compare the fitted projection Measurements of the velocity field of the entire parameters with those obtained from our I-band images. disk at high spatial resolution are required to extract Finally, we present azimuthally-averaged Hα and [N II] these kinematic signatures. For example, to separate profiles for these galaxies, which we use to derive oxygen bar-like flows in spiral galaxies from their rotation abundance gradients. In future papers in this series, we curves, < 200 pc spatial resolution is required (e.g. will use our velocity maps in order to better understand Marinova & Jogee 2007; Sellwood & Z´anmar S´anchez these galaxies’ mass distributions. 2010; Barrera-Ballesteros et al. 2014; Holmes et al. 2. DATA ACQUISITION AND REDUCTION 2015). In recent years, the state of the art in numerical sim- We obtained data on 14 nearby late-type galaxies with ulations has moved to smaller and smaller spatial scales. the medium-resolution mode of the Fabry-P´erot inter- However, comparisons of these simulations to observed ferometer on the RSS of SALT. Our data were acquired galaxies have been lacking, partially due to a lack of ve- over a total exposure time of 19 hours during the period locity fields of sufficiently high resolution for comparison. 11 Nov 2011 to 8 Sept 2015. A typical single observation We have designed the RSS Imaging spectroscopy consists of ∼ 25 exposures, each of length ∼ 70 seconds. Nearby Galaxy Survey (RINGS) to obtain the high- The medium-resolution etalon has a spectral full width resolution kinematic data necessary to probe these open at half maximum (FWHM) at Hα of ∼ 5 A.˚ For each ex- questions of galaxy structure. Our survey targets 19 posure taken in an observation, we offset the wavelength nearby, late-type spiral galaxies over a wide range of of the etalon’s peak transmission by ∼ 2 A˚ from the pre- −1 −1 masses (67 km s < Vflat < 275 km s ) and lumi- vious exposure.
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