Dynamics and X-ray emission of a galactic superwind interacting with disk and halo gas

“The overall morphology is reminiscent of early simulations by Suchkov et al. (1994) of superwind structure, as well as radio observations of Cecil et al. (2001) who studied the coherence of the magnetic field inside similarly trailing lobes.”

“…studies in which blowout has been simulated numerically (Tomisaka & Ikeuchi 1986, 1988 ; Mac Low, McCray, & Norman 1989 ; Tenorio-Tagle, Rozyczka, & Bodenheimer 1990 ; Silich 1992 ; Mineshige, Shibata, & Shapiro 1993 ; Suchkov et al. 1994) have not been followed for long enough evolutionary times.”

“Material evaporated from these clouds could be the source of the mass-loading required to explain the large X-ray surface brightnesses of galactic winds (e.g. Suchkov et al. 1994; Suchkov et al. 1996; Strickland et al. 2002; Martin, Kobulnicky, & Heckman 2002).”

“Column densities to the nucleus for the hot X-rayÈ emitting gas are estimated to be of order 1021 cm~2 in superwinds (e.g., Suchkov et al. 1994 ; Heckman et al. 1999 ; Strickland 1998).”

“The shell may be partly or completely broken up due to RayleighTaylor instabilities (Suchkov et al. 1994).”

“Thin disk models (e.g. Suchkov et al. 1994) have wind opening angles that are too large, θ ∼> 90 ◦.”

“Both fully numerical and semianalytical theoretical modeling (Suchkov et al. 1994; Silich & Tenorio-Tagle 1998; Murakami & Babul 1999) suggest that the properties of the gaseous halos these winds expand into play a major role in determining the fate of the material in superwinds (i.e., escape into…”

“Such a model for building a disk and halo that are in dynamical balance seems to have been initially explored by Suchkov et al. (1994) and a little later in its present form by Matsumoto et al. (1996).”

“The postshock temperatureT2 is within the range favored by numerical models (see, e.g., Suchkov et al. 1994), provided the gas has roughly solar abundances.”

“Simulations of superwinds show that these hot gasses blow new bubbles in the halo, sweeping the ambient halo gas up into new shells (e.g., Tomisaka & Bregman 1993; Suchkov et al. 1994; Strickland & Stevens 2000).”

“…starburst galaxies show outflows of cool emission-line gas with velocities of a few hundred kilometres per second, and models suggest terminal velocities for the hot gas of a few thousand kilometres per second (Heckman et al. 1990; Suchkov et al. 1994; Tenorio-Tagle & MunÄoz TunÄoÂn 1997).”

“The entrained gas, which can easily dominate the wind mass, is accounted for with Λ typically larger than unity (e.g. Suchkov et al. 1994).”

“The hydrodynamical complexity of these outflows (see e.g. (Suchkov et al. 1994); Strickland & Stevens (2000)), and in particular the range of possible physical mechanisms generating X-ray emission in starburst galaxies, has complicated the interpretation of existing X-ray observations of starburst…”

“…X-ray image of the frustum from Strickland et al. (2004b) is first the importance of the opening angle Ω — a naive estimate indicates Ω ∼ 0.01 − 0.05 — and second the potential importance of nonspherical areal divergence as the flow expands on ∼ 0.5− few kpc scales (Suchkov et al. 1994, 1996).”

“If the outÑowing wind consists purely of the thermalized ejecta from supernovae and stellar winds, then the wind Ñuid is hot (D108 K prior to adiabatic cooling) and is so tenuous that it will be an insigniÐcant source of X-ray emission (Chevalier & Clegg 1985 ; Suchkov et al. 1994).”

“Suchkov et al. (1994) performed two-dimensional, axisymmetric simulations of a galactic wind in an isothermal ISM, with varying densities and temperatures.”

“The expansion of a stellar or galactic wind in an inhomogeneous environment will in a natural way lead to the entrainment of cold gas clumps (Smith et al. 1984; Chevalier & Clegg 1985; Hartquist & Dyson 1993; Suchkov et al. 1994; Strickland & Stevens 2000; Marcolini et al. 2005).”

“…the hard X-ray source in NGC 3256 to be comparable to or greater than 7 It is unlikely that the hard X-ray emission of starburst galaxies is dominated by extremely hot gas (see Suchkov et al. 1994) ; moreover, ASCA is not capable of measuring plasma temperatures that lie outside its energy range.”

“H2 Suchkov et al. (1994) and Strickland & Stevens (2000) simulated the appearances at X-ray and optical temperatures of a superbubble at various stages of its winddriven evolution.”

“For any particular model, the column densities and kinematics of the gas vary strongly between di†erent sight lines, due to the structural complexity that arises in twodimensional simulations (see Suchkov et al. 1994 ; Strickland & Stevens 2000).”

“This generally comes at the expense of the number of physical processes included and/or the ability to simulate any galaxy larger than a dwarf galaxy (e.g., Suchkov et al. 1994; Tanner et al. 2016; Emerick et al. 2018; Schneider & Robertson 2018; Smith et al. 2018; Vijayan et al. 2018; Hu 2019).”

“These outflows are driven by the mechanical energy supplied by massive stars in the form of SNe and stellar winds (Tomisaka & Ikeuchi 1988; De Young & Heckman 1994; Suchkov et al. 1994, 1996; MF99; D’Ercole & Brighenti 1999; Silich & Tenorio-Tagle 1998, 2001).”

“These suggest that we are missing much of the outflow energy, in agreement with multi-phase hydrodynamical models (Suchkov et al. 1994; Strickland & Stevens 2000).”

“…the galaxy (Larson 1974; McKee and Ostriker 1977; Dekel and Silk 1986; Efstathiou 2000) or else, as in more recent studies (De Young & Heckman 1994; Suchkov et al 1994; Mac Low and Ferrara 1999; Strickland & Stevens 2000) they are concentrated in a single coeval, cospatial burst of star formation.”

“…high level of sophistication of recent hydrodynamic simulations (see, e.g., Tomisaka 1990 ; Slavin & Cox 1992 ; Mineshige, Shibata, & Shapiro 1993 ; Suchkov et al. 1994 ; Strickland & Stevens 2000) has provided the theoretical basis to interpret our data and to predict the evolution and eventual…”

“The dynamical evolution of a starburst-driven outflow has been extensively discussed (e.g., Chevalier & Clegg 1985; Suchkov et al. 1994; Wang 1995; Tenorio-Tagle & Munoz-Tunon 1998; Strickland & Stevens 2000).”

“This is contrary to the results by Suchkov et al. (1994), who claim that most of the X-ray radiation comes from the shocked ISM.”

“The superwinds have temperatures of 108 K (Suchkov et al. 1994).”

“Some of the works that use this prescription are Chevalier & Clegg 1985; Mac Low, McCray, & Norman 1989; Suchkov et al. 1994; Mac Low & Ferrara 1999; Strickland & Stevens 2000; Cooper et al. 2008; Roy et al. 2013; Recchi & Hensler 2013; Palous̃ et al. 2013.”

“Mach number for the wind M = u/ p gP/r, which satisfies g 1 +2/M2 g+1 (1+g)/[2(1+5g)] 3g+1/M2 1 +3g (1+3g)/(1+5g) = r R (16) for r < R and M2/(g 1) g 21 +2/M2 1 +g (g+1)/[2(g 1)] = r R (17) Galaxies 2018, 6, 1 7 of 47 for r R. The solution of M smoothly transfers from subsonic flow M < 1 for r < R to supersonic…”

“It was in fact an extension to the model developed by Morita (1982), Tomisaka & Ikeuchi (1988), Tomisaka & Bregman (1993) and Suchkov et al. (1994).”

“The powerful winds produced by starburst galaxies have been shown to interact with cool halo clouds, either preexisting clouds, or clouds carried into the halo by the wind itself (Suchkov et al. 1994; Lehnert et al. 1999; Strickland et al. 2002).”

“…a hot bubble is expected not to be radiative because of its rarefied interior, and is indeed rarely observed directly in starburst galaxies (e.g. Suchkov et al. 1994; Strickland & Stevens 2000; Hoopes et al. 2003),2 the temperature of kT ≈ 7 keV implied from the above thermal emission model…”

“One possible reason is that mass loading is occurring in the hot superwind (e.g., Suchkov et al. 1994, 1996).”

“…models of superwinds show that the wind fluid sweeps up and incorporates larger masses of ambient galactic disk and halo interstellar medium (ISM) into the superwind, material which is more easily detected observationally (Chevalier & Clegg 1985; Suchkov et al. 1994; Strickland & Stevens 2000).”

“Yet another possibility is that the dense, relatively cool bubble wall is unstable and moves into the hot wind which fills the bubble (Suchkov et al. 1994).”

“The SSC has likely been the source responsible for expelling the outflowing gas in the last ≈ 10 Myr (e.g., O'Connell et al. 1994; Suchkov et al. 1994; Heckman & Leitherer 1997; Tosi et al. 2001).”

“All these features can be well reproduced by numerical simulations of the superwind in which radiative shock occurs around the expanding hot gas (e.g., Suchkov et al 1994; Strickland & Stevens 2000) (see section 3.3).”

“…1990; Lehnert & Heckman 1996), and are thought to arise when the mechanical energy from massive stars and supernovae in the central starburst is sufficient to drive the dense interstellar medium outward along the minor axis (e.g. Chevalier & Clegg 1985; Joseph & Wright 1985; Suchkov et al. 1994).”

“The need for large-scale mass-loading in the wind of M82 has been inferred ever since the first analytic wind models (Chevalier & Clegg 1985) were compared to X-ray measurements (see also Suchkov et al. 1994).”

“Simulations of a superwind by Suchkov et al. (1994) show the formation of huge bubbles.”

“The diffuse X-ray emission associated with the disks of spi- ral galaxies is believed to arise in gas heated by shocks generat d as a result of supernova explosions and stellar wind interactions (Chevalier & Clegg 1985; Strickland et al. 2000; Suchkov et al. 1994; Grimes et al. 2005).”

“These layers may also be where mass is also stripped and entrained and/or loaded into the wind outflow (Suchkov et al. 1994).”

“…ideas were proposed: (i) bipolar galactic–wind arising in the plane parallel gaseous atmosphere of a galactic disk (e.g., Tomisaka & Ikeuchi 1988; Suchkov et al. 1994, 1996), which is important in the initial phases; and (ii) spherical symmetric galactic–wind for the late phases (e.g., Mathews…”

“…the surrounding intergalactic medium (e.g., Chevalier & Clegg 1985; Schiano 1985; Tenorio-Tagle & Bodenheimer 1988; Tomisaka & Ikeuchi 1988; Suchkov et al. 1994; Heckman, Armus, & Miley 1990; Veilleux et al. 1994; Cecil et al. 2001; Cecil, Bland-Hawthorn, & Veilleux 2002; Veilleux,…”

“Dynamical models (MacLow, McCray, & Norman 1989; Tomisaka & Ikeuchi 1988; Suchkov et al. 1994) of wind-blown bubbles have had success reproducing the range of phenomena observed in radio-lobe spirals (Wehrle & Morris 1988; Wrobel 1994; Veilleux et al. 1994).”

“…¼ 3N n ¼ 2 kpc NMg ii 1014 cm 2 ntot 10 2 cm 3 AMg 3:3 10 5 Z=Z 0:3 fMg ii 0:5 1 : ð2Þ Here N is the total column density of the shell and n is the background number density of the gas to be swept up, where we assume the value for the halo gas density from model A1 by Suchkov et al. (1994).”

“The dynamical evolution of a starburstdriven outflow has been extensively discussed (e.g. Chevalier et al. 1985; Suchkov et al. 1994; Wang 1995; Tenorio-Tagle & Muñoz-Tuñon 1998; Strickland et al. 2000).”

“Shocked gas in the galactic halo and disk (e.g. Suchkov et al. 1994), as well as hot galactic winds (e.g. Strickland & Stevens 2000) are also processes that could yield predominantly soft X-rays.”

“This infall is thought to be necessary to account for the accumulation of the matter detected in these sources (Sanders & Mirabel 1996) and the large rates of star formation (Larson et al. 1987; Suchkov et al. 1994).”

“In galactic winds much of the soft X-ray emission is believed to come from shock-heated clouds caught up in a faster moving, hotter but more tenuous wind (Suchkov et al. 1994).”

“At the final stage of a strong starburst, i.e. type II SN phase (8–60 × 106 yr from the initial burst; Terlevich et al. 1992; Norman & Ikeuchi 1989; Suchkov et al. 1994) giant galactic arcs and extreme Fe II+BAL systems can appear.”

“…the bow shocks and turbulent wakes of galaxies (Balsara et al. 1994) and the presence of jets (Balsara & Norman 1992), galactic superwinds (Suchkov et al. 1994), and cluster formation and mergers (Miniati et al. 2001) could drive turbulence in the intercluster gas, and all these…”

“…model, a hot gas bubble of internally shocked wind material with a temperature of several keV forms in the region of intense star formation (Chevalier & Clegg 1985, Suchkov et al. 1994, Strickland & Heckman 2007); this hot gas eventually flows outward as a high-speed (few 1000 km s−1) wind.”

“It therefore differs from the well known M82 outflow, whose outer regions can be modelled by a supersonic galactic wind (e.g. Suchkov et al. 1994; Shopbell & Bland-Hawthorn 1998; Zirakashvili & Völk 2006).”

“Models with a single source also predict a strong H emission arising from the lateral walls of the disrupted supershell, continuously impacted by the UV radiation arising from the central source (see, for example, Suchkov et al. 1994; Tenorio-Tagle & Muñoz Tuñón 1997, 1998).”

“The two energy bands considered are from 0.1 to 2.2, and from 1.6 to 8.3 keV (X-ray emissivities from Suchkov et al. 1994).”

“Such hot gas is difficult to produce (Suchkov et al. 1994; Strickland & Stevens 2000), but this component is observed in pure starburst galaxies (Pietsch et al. 2001), and a similar model with multitemperature hot components was used by Schurch et al. (2002) to fit the diffuse emission in both…”

“The temperature of 6− 8 keV estimated from the thermal plasma model is rather high compared to those expected from ordinary star-burst activity (∼ 500 eV), and difficult to produce (Suchkov et al. 1994, Strickland & Stevens 2000).”

“Numerical simulations (e.g. Suchkov et al. 1994, 1996; Strickland & Stevens 2000; Fujita et al. 2009; Strickland & Heckman 2009) also implement the initial conditions leading to galactic winds making similar assumptions.”

“This prescription is similar to the set-up of Suchkov et al. (1994).”

“At the final stage of a strong starburst, i.e., type II SN phase ([8-60]×106 yr from the initial burst; Terlevich et al. 1992; Norman & Ikeuchi 1989; Suchkov et al. 1994) giant galactic arcs and extreme Fe ii+BAL systems can appear.”

“…was however not found to correlate with galaxy mass (Heckman et al. 2000; Martin 1999), and it was argued that the supernovae rate increased with SFR and hence the wind velocity might correlate with SFR. Simulations also supported this scenario (Suchkov et al. 1994; Strickland & Stevens 2000).”

“In this case, the gas would be very hot (∼ 108 K prior to adiabatic cooling), but so tenuous that it will be an insignificant source of X-ray emission (Chevalier & Clegg 1985; Suchkov et al 1994).”

“Hydrodynamical simulations with radiative cooling also supported this scenario (Suchkov et al. 1994; Strickland & Stevens 2000; Cooper et al. 2008).”

“Furthermore, the expansion velocity of the GC lobe might be expected to be relatively small, since extragalactic outflows tend to be collimated near the galactic plane (Chevalier & Clegg 1985; Suchkov et al. 1994).”

“Standard models of supernovae driven galactic outflows assume a central region where the SNe energy input is thermalized (e.g., Larson (1974); Chevalier & Clegg (1985); Heckman et al. (1990); Suchkov et al. (1994); Strickland & Heckman (2009); Sharma & Nath (2013)).”

“On the other hand, simulations (Suchkov et al. 1994, Strickland & Stevens 2000) and observations (Heckman et al. 1993, Strickland et al. 2000) suggest that in these systems, most of the X-ray emission is due to small ‘clouds’, shock-heated by a fast (∼ 3000 km s−1), hot (≫ 107 K) wind, produced…”