The Multiphase Starburst-Driven Galactic Wind in NGC 5394
Total Page：16
File Type：pdf, Size：1020Kb
MNRAS 000,1{17 (2016) Preprint 3 May 2016 Compiled using MNRAS LATEX style file v3.0 The multiphase starburst-driven galactic wind in NGC 5394 Pablo Mart´ın-Fern´andez,1? Jorge Jim´enez-Vicente,1;2 Almudena Zurita,1;2 Evencio Mediavilla,3;4 and Africa´ Castillo-Morales5 1Dpto. de F´ısica y del Cosmos, Campus de Fuentenueva, Edificio Mecenas, Universidad de Granada, Granada, E-18071, Spain 2Instituto Carlos I de F´ısica Te´orica y Computacional, Facultad de Ciencias, Universidad de Granada, E-18071, Spain 3Instituto de Astrof´ısica de Canarias, V´ıaL´actea, s/n, La Laguna, E-38200, Tenerife, Spain 4Dpto. de Astrof´ısica, Universidad de la Laguna, La Laguna, E-38200, Tenerife, Spain 5Dpto. de Astrof´ısica y C.C. de la Atm´osfera, Universidad Complutense de Madrid, Madrid, E-28040, Spain Accepted XXX. Received YYY; in original form ZZZ ABSTRACT We present a detailed study of the neutral and ionised gas phases in the galactic wind for the nearby starburst galaxy NGC 5394 based on new integral field spectroscopy obtained with the INTEGRAL fibre system at the William Herschel Telescope. The neutral gas phase in the wind is detected via the interstellar Na i D doublet absorption. After a careful removal of the stellar contribution to these lines, a significant amount 7 of neutral gas (∼ 10 M ) is detected in a central region of ∼ 1:75 kpc size. This neutral gas is blueshifted by ∼ 165 km s−1 with respect to the underlying galaxy. The mass outflow of neutral gas is comparable to the star formation rate of the host galaxy. Simultaneously, several emission lines (Hα, [N ii], [S ii]) are also analysed looking for the ionised warm phase counterpart of the wind. A careful kinematic decomposition of the line profiles reveals the presence of a secondary, broader, kinematic component. This component is found roughly in the same region where the Na i D absorption is detected. It presents higher [N ii]/Hα and [S ii]/Hα line ratios than the narrow component at the same locations, indicative of contamination by shock ionization. This secondary component also presents blueshifted velocities, although smaller than those measured for the neutral gas, averaging to ∼ −30 km s−1. The mass and mass outflow rate of the wind is dominated by the neutral gas, of which a small fraction might be able to escape the gravitational potential of the host galaxy. The observations in this system can be readily understood within a bipolar gas flow scenario. Key words: galaxies: evolution { galaxies: individual: NGC 5394 { galaxies: kine- matics and dynamics { ISM: jets and outflows { galaxies: starbursts { galaxies: spiral 1 INTRODUCTION ton 2007). This gas removal can also effectively slow down the star formation rate and even quenching it (e.g. Hopkins arXiv:1605.00407v1 [astro-ph.GA] 2 May 2016 Galactic winds (hereafter GWs) are large scale outflows of et al. 2006; Cazzoli et al. 2014). Nevertheless, in most cases gas from a galaxy. These winds are produced by the energy the majority of the gas will not be able to reach the IGM, input provided by nuclear activity and/or strong starbursts but will fall back to the host galaxy in a so called \galactic (see Veilleux et al. 2005, for a comprehensive review). They fountain" (e.g. Shapiro & Field 1976; Bregman 1980), redis- are able to transport interstellar material against the gravi- tributing heavy elements. tational potential of the host galaxy, even reaching the inter- galactic medium (IGM). As a consequence they have been GWs were more important in earlier stages of the Uni- proposed as a key ingredient in galaxy evolution. Among verse, when starbursts induced by mergers were more fre- their multiple effects are the enrichment of the IGM with quent. Most of the star formation in these epochs (z∼ 1 − 3) heavy elements originated by massive stars in the parent is associated with luminous infrared galaxies (LIRGs, LIR & galaxy (e.g. Garnett 2002; Tremonti et al. 2004; Dalcan- 11 10 L ), in which this phenomenon is ubiquitous (e.g. Mar- tin 2005; Rupke et al. 2005b). At low redshift, LIRGs are less frequent, but more easily accessible observationally than ? E-mail: [email protected] their higher redshift counterparts, and these galaxies have c 2016 The Authors 2 Mart´ın-Fern´andezet al. indeed received most of the attention to study this phe- The structure of the wind is frequently bipolar (Veilleux nomenon (e.g. Heckman et al. 2000; Rupke et al. 2002; Mar- et al. 2005). information, Nevertheless, kinematic informa- tin 2005). Although GWs are not limited to LIRGS (e.g. tion in these cases is very limited because the wind motions Schwartz & Martin 2004; Chen et al. 2010; Krug et al. 2010), take place mainly perpendicular to the line-of-sight. How- galaxies with lower star formation rates have been less stud- ever, observations with high enough spectral resolution may ied and the properties of their associated winds are not so allow discrimination between the wind and the disc emission well known. even for low inclination systems. This way, the kinematics of GWs are a complex phenomenon, in which warm ionised the outflowing gas can be obtained (e.g. Shih & Rupke 2010; and neutral gas from the host galaxy are entrained by a hot Soto et al. 2012; Wood et al. 2015). In this respect, integral flow, originated by an important energy supply from stellar field spectroscopy (IFS), joined to a careful decomposition winds and supernova explosions, or active galactic nuclei of the line profiles, has proved to be a most valuable tech- (Tenorio-Tagle & Mu~noz-Tu~n´on 1998; Veilleux et al. 2005). nique. It permits (provided high enough spatial resolution) Their study therefore requires a multi-wavelength approach to locally separate the low brightness wind emission, from to trace the different involved gas phases. that of the underlying galaxy, which could otherwise remain Absorption-line spectroscopy has proved to be an ef- hidden due to the internal galaxy kinematics (e.g. Sharp & fective method to study GWs through the detection of Bland-Hawthorn 2010; Westmoquette et al. 2012; Rupke & blueshifted absorbing material in front of the galaxy back- Veilleux 2013; Ho et al. 2014; Cazzoli et al. 2014; Arribas ground. Since the starburst-driven winds usually move et al. 2014). nearly perpendicular to the galaxy disc, this technique is Although the measured velocities of the ionised compo- favoured in face-on galaxies. Several absorption features in nent are usually smaller than those of the absorbing neutral the ultraviolet and optical bands can be used to trace differ- gas (Rupke & Veilleux 2013), the maximum velocities of this ent gas phases (e.g. Rupke et al. 2002; Martin 2005; Heck- ionised component seem to follow a similar relation with the man et al. 2015; Wood et al. 2015). At low-z, the Na i SFR (Martin 2005; Arribas et al. 2014). The outflowing com- λλ5890, 5896 doublet (Na i D), are the most frequently used ponent systematically presents larger velocity dispersion and lines to trace neutral gas using ground-based observations. emission-line ratios indicative of shock excitation (Monreal- High blueshifted velocities in the Na i D doublet have Ibero et al. 2006; Sharp & Bland-Hawthorn 2010; Rich et al. been routinely detected in luminous and ultra-luminous in- 2011; Soto et al. 2012; Bellocchi et al. 2013; Arribas et al. 12 frared galaxies (ULIRGs, LIR & 10 L ) (e.g. Heckman 2014). When the kinematics of the neutral and ionised com- et al. 2000; Rupke et al. 2005b; Martin 2005, 2006; Rupke ponents are available for the same galaxy, their maximum & Veilleux 2013; Cazzoli et al. 2014). These objects host the velocities often correlate with each other (Rupke & Veilleux most powerful starbursts, with star formation rates (SFRs) 2013), and most of the outflowing material seems to be con- of up to several hundreds solar masses per year. These kind tained in the neutral phase (Rupke & Veilleux 2013). Never- of techniques have also been applied to non-LIRGs and dwarf theless, Arribas et al.(2014) find similar ionised mass load- starbursts (see e.g. Roche et al. 2015; Jim´enez-Vicente et al. ing factors than the average values available in the literature 2007; Schwartz & Martin 2004; Chen et al. 2010). The spa- for the neutral gas in LIRGs, and even higher in ULIRGs. It tial projected extent of the Na i D absorbers has typical sizes is therefore still unclear the relative importance of the differ- of a few kiloparsecs, and the velocities range from tens to ent gas phases in the winds and any possible dependence on several hundreds of km s−1. Despite a large scatter, the out- the properties of their host galaxies. A better understand- flow velocities seem to increase with the galaxy SFRs (cf. ing of this issue (and other wind properties) would benefit Martin 2005) for (U)LIRGs. However, for SFRs lower than from detailed simultaneous observations and analysis of both −1 ∼ 10 M yr , this result is less clear. While this trend with phases for the same targets. This work aims at supplement- SFR seems to hold for dwarf galaxies (Schwartz & Martin ing the double scarcity of detailed studies of GWs in objects 2004), Chen et al.(2010) do not find any significant trend with moderate star formation, but also of studies simulta- for a large sample of galaxies with SFRs in the range of ∼ 1 neously including the different involved gas phases. In order −1 to 13 M yr . The measured mass outflow rates are com- to do so, we analyse new IFU observations of the nearby parable to their host galaxies global SFR, implying \load- merger galaxy NGC 5394.