The Lyman Alpha Reference Sample VII

A&A 587, A78 (2016) Astronomy DOI: 10.1051/0004-6361/201527373 & c ESO 2016 Astrophysics The Lyman alpha reference sample VII. Spatially resolved Hα kinematics?;?? Edmund Christian Herenz1, Pieter Gruyters2, Ivana Orlitova3, Matthew Hayes4, Göran Östlin4, John M. Cannon5, Martin M. Roth1, Arjan Bik4, Stephen Pardy6, Héctor Otí-Floranes7, J. Miguel Mas-Hesse8, Angela Adamo4, Hakim Atek9, Florent Duval4;10, Lucia Guaita4;11, Daniel Kunth12, Peter Laursen13, Jens Melinder4, Johannes Puschnig4, Thøger E. Rivera-Thorsen4, Daniel Schaerer14;15, and Anne Verhamme14 1 Leibniz-Institut far Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany e-mail: [email protected] 2 Lund Observatory, Box 43, 221 00 Lund, Sweden 3 Astronomical Institute, Academy of Sciences of the Czech Republic, Bocníˇ II 1401, 141 00 Prague, Czech Republic 4 Department of Astronomy, Oskar Klein Centre for Cosmoparticle Physics, Stockholm University, AlbaNova University Centre, 106 91 Stockholm, Sweden 5 Department of Physics & Astronomy, Macalester College, 1600 Grand Avenue, Saint Paul, MN 55105, USA 6 Department of Astronomy, University of Wisconsin, 475 North Charter Street, Madison, WI 53706, USA 7 CONACyT research fellow – Instituto de Radioastronomía y Astrofísica, UNAM, Campus Morelia, Michoacán, CP 58089, Mexico 8 Centro de Astrobiología (CSIC–INTA), Departamento de Astrofísica, PO Box 78, 28691 Villanueva de la Cañada, Spain 9 Laboratoire d’Astrophysique, École Polytechnique Fédérale de Lausanne (EPFL), Observatoire, 1290 Sauverny, Switzerland 10 Institute for Cosmic Ray Research, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, 277-8582 Chiba, Japan 11 INAF–Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monteporzio, Italy 12 Institut d’Astrophysique de Paris, UMR 7095 CNRS & UPMC, 98bis Bd Arago, 75014 Paris, France 13 Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen, Denmark 14 Observatoire de Genève, Université de Genève, 51 Ch. des Maillettes, 1290 Versoix, Switzerland 15 CNRS, IRAP, 14 Avenue E. Belin, 31400 Toulouse, France Received 15 September 2015 / Accepted 16 November 2015 ABSTRACT We present integral field spectroscopic observations with the Potsdam Multi-Aperture Spectrophotometer of all 14 galaxies in the z ∼ 0:1 Lyman Alpha Reference Sample (LARS). We produce 2D line-of-sight velocity maps and velocity dispersion maps from the Balmer α (Hα) emission in our data cubes. These maps trace the spectral and spatial properties of the LARS galaxies’ intrinsic Lyα radiation field. We show our kinematic maps that are spatially registered onto the Hubble Space Telescope Hα and Lyman α (Lyα) images. We can conjecture a causal connection between spatially resolved Hα kinematics and Lyα photometry for individual galaxies, however, no general trend can be established for the whole sample. Furthermore, we compute the intrinsic velocity dispersion σ0, the shearing velocity vshear, and the vshear/σ0 ratio from our kinematic maps. In general LARS galaxies are characterised by high intrinsic −1 −1 velocity dispersions (54 km s median) and low shearing velocities (65 km s median). The vshear/σ0 values range from 0.5 to 3.2 with an average of 1.5. It is noteworthy that five galaxies of the sample are dispersion-dominated systems with vshear/σ0 < 1, and are thus kinematically similar to turbulent star-forming galaxies seen at high redshift. When linking our kinematical statistics to the global LARS Lyα properties, we find that dispersion-dominated systems show higher Lyα equivalent widths and higher Lyα escape fractions than systems with vshear/σ0 > 1. Our result indicates that turbulence in actively star-forming systems is causally connected to interstellar medium conditions that favour an escape of Lyα radiation. Key words. galaxies: ISM – galaxies: starburst – cosmology: observations – ultraviolet: galaxies – radiative transfer 1. Introduction equivalent width line provides enough contrast to be effectively singled out in specifically designed observational campaigns. As As already envisioned by Partridge & Peebles(1967), the hydro- of yet, mostly narrowband selection techniques have been em- gen Lyman α (Lyα, λLyα = 1215:67 Å) line has become a promi- ployed (e.g. Hu et al. 1998; Taniguchi et al. 2003; Malhotra nent target in successful systematic searches for galaxies in the & Rhoads 2004; Shimasaku et al. 2006; Tapken et al. 2006; early Universe. Redshifted into the optical, this narrow high Gronwall et al. 2007; Ouchi et al. 2008; Grove et al. 2009; ? Based on observations collected at the Centro Astronómico Shioya et al. 2009; Hayes et al. 2010; Ciardullo et al. 2012; Hispano Alemán (CAHA) at Calar Alto, operated jointly by the Max- Sandberg et al. 2015), but multi-object and integral-field spectro- Planck Institut für Astronomie and the Instituto de Astrofísica de scopic techniques are now also frequently used to deliver large Andalucía (CSIC). Lyman α emitter (LAE) samples (Cassata et al. 2011, 2015; ?? The reduced data cubes (FITS files) are only available at the CDS Adams et al. 2011; Mallery et al. 2012; Bacon et al. 2015). via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via Moreover, all galaxy redshift record holders in the last decade http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/587/A78 Article published by EDP Sciences A78, page 1 of 27 A&A 587, A78 (2016) −1 were spectroscopically confirmed by virtue of their Lyα line (Iye (vexp . 100 km s ) or low neutral hydrogen column densities 19 −2 2011; Ono et al. 2012; Finkelstein et al. 2013; Oesch et al. 2015; NH i . 10 cm , while high expansion velocities (vexp ∼ 150 – Zitrin et al. 2015) and a bright LAE at z = 6:6 is even believed −1 300 km s ) with neutral hydrogen column densities of NH i & to contain a significant amount of stars made exclusively from 1020cm−2 produce the characteristic asymmetric profile with an primordial material (so called Pop-III stars; Sobral et al. 2015). extended red wing (Tapken et al. 2006, 2007; Verhamme et al. As important as Lyα radiation is in successfully unveiling 2008; Schaerer et al. 2011; Gronke & Dijkstra 2014). star formation processes in the early Universe, its correct inter- Further observational constraints on the kinematics of the pretation appears notoriously complicated. Resonant scatterings scattering medium can be obtained by measuring the offset in the interstellar and circum-galactic medium diffuse the intrin- from non-resonant, rest-frame optical emission lines (e.g. Hα sic Lyα radiation field in real and frequency space. These scat- or [O iii]) to low-ionisation state metal absorption lines (e.g. terings increase the path length of Lyα photons within a galaxy O i λ1302 or Si ii λ1304). While the emission lines provide sys- and consequently Lyα is more susceptible to being destroyed temic redshift, some of metal absorption lines in a low ionisa- by dust (see Dijkstra 2014, for a comprehensive review cover- tion state trace the kinematics of the cold neutral gas phase. ing the Lyα radiative transfer fundamentals). Consequently, a Both observables are challenging to obtain for high-z LAEs galaxy’s Lyα observables are influenced by a large number of and require long integration times on 8–10 m class telescopes its physical properties. Understanding these influences is crucial (e.g. Shapley et al. 2003; Tapken et al. 2004) or even additional to correctly interpret high-z LAE samples. In other words, we help from gravitational lenses (e.g. Schaerer & Verhamme 2008; have to answer the question: What differentiates an LAE from Christensen et al. 2012). As the continuum absorption often re- other star-forming galaxies that do not show Lyα in emission? mains undetected, just the offset between the rest-frame optical Regarding Lyα radiation transport in individual galaxies, a lines and the Lyα peaks are measured (e.g. McLinden et al. 2011; large body of theoretical work investigated analytically and nu- Guaita et al. 2013; Erb et al. 2014). Curiously, the observed Lyα merically how within simplified geometries certain parameters profiles also agree well with those predicted by the simple shell (e.g. density, temperature, dust content, kinematics, and clumpi- model, when the measured offsets (typically ∆v ∼ 200 km s−1) ness of the interstellar medium) affect the observed Lyα radi- are associated with shell expansion velocities in the simple shell ation field (e.g. Neufeld 1990; Ahn et al. 2003; Dijkstra et al. model (Verhamme et al. 2008; Hashimoto et al. 2013; Song et al. 2006; Verhamme et al. 2006; Laursen et al. 2013; Gronke & 2014; Hashimoto et al. 2015). Only a few profiles appear incom- Dijkstra 2014; Duval et al. 2014). Commonly a spherical shell patible with the expanding shells (Chonis et al. 2013). These model is adopted. In this model, a thin shell of expanding, con- profiles are characterised by extended wings or bumps in the tracting, or static neutral gas represents the medium responsible blue side of the profile (Martin et al. 2014; Henry et al. 2015). for scattering Lyα photons. As a result, from scattering in the However, given the aforementioned viewing angle dependencies shell complex Lyα line morphologies arise and the expansion in more complex scenarios, this overall success of the simple velocity and the neutral hydrogen column density of the shell shell model appears surprising and is therefore currently under are of pivotal importance in shaping the observable Lyα line. scrutiny (Gronke et al. 2015). Nevertheless, at least qualitatively By introducing deviations from pure spherical symmetry, Zheng the observations demonstrate, in concert with theoretical pre- & Wallace(2014) and Behrens et al.(2014) show that the ob- dictions, that LAEs predominantly have outflow kinematics and served Lyα properties also depend on the viewing angle under that such outflows promote the Lyα escape (see also Kunth et al. which a system is observed. The Behrens et al. result is also 1998; Mas-Hesse et al.

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