The SILCC (SImulating the LifeCycle of molecular Clouds) project – I. Chemical evolution of the supernova-driven ISM

“However, Springel (2005) shows that the worst-case errors, resulting from situations when the target cell is inside the contributing node, can be avoided by introducing an additional criterion that does not allow the target cell lie within a volume of the node increased by a certain factor, ηSB.”

“During the tree walk, the gravitational potential is calculated by the modified Ewald method (Ewald 1921; Klessen 1997).”

“These are (i) the Kennicutt– Schmidt (KS) relation (Kennicutt 1998) with SFR ∝ 1.4H2+H I , as well as (ii) newer results which relate the SFR surface density to the MNRAS 454, 238–268 (2015) molecular gas surface density, H2 , in a galaxy in a linear fashion 3 (Bigiel et al. 2008; Tacconi et al.…”

“It is a Barnes-Hut type octal-spatial tree (Barnes & Hut 1986) described in detail in Wünsch et al., in preparation.”

“2 N U M E R I C A L M E T H O D We use the fully three-dimensional, AMR code FLASH 4 (Fryxell et al. 2000; Dubey et al. 2009, 2012) to simulate representative pieces of galactic discs with dimensions 500 pc × 500 pc × ±5 kpc. FLASH is parallelized via domain decomposition under the Message Passing…”

“…rate is determined self-consistently at all temperatures, allowing us to properly model the non-equilibrium effects that can strongly affect the cooling rate at temperatures close to 104 K (see e.g. Kafatos 1973; Sutherland & Dopita 1993; Micic et al. 2013; Richings, Schaye & Oppenheimer 2014).”

“Following McKee & Ostriker (1977) and Tielens (2005), we can estimate the VFF of the hot phase that we expect for a given SN rate and mean gas density.”

“…are (i) the Kennicutt– Schmidt (KS) relation (Kennicutt 1998) with SFR ∝ 1.4H2+H I , as well as (ii) newer results which relate the SFR surface density to the MNRAS 454, 238–268 (2015) molecular gas surface density, H2 , in a galaxy in a linear fashion 3 (Bigiel et al. 2008; Tacconi et al. 2013).”

“…spiral galaxy evolution on larger spatial and temporal scales at all cosmic epochs (Oppenheimer et al. 2010; Aumer et al. 2013; Hirschmann et al. 2013; Stinson et al. 2013; Brook et al. 2014; Hopkins et al. 2014; Marinacci, Pakmor & Springel 2014; Übler et al. 2014; Murante et al. 2015).”

“In the runs that we perform with our standard SN rate of 15 Myr−1, we use the estimate of Draine (1978) for the strength of the UV radiation field, and set G0 = 1.7.”

“Following McKee & Ostriker (1977) and Tielens (2005), we can estimate the VFF of the hot phase that we expect for a given SN rate and mean gas density.”

“Phys., 230, 3331 Walch S., Naab T., 2015, MNRAS, 451, 2757 Walch S., Wünsch R., Burkert A., Glover S., Whitworth A., 2011, ApJ, 733, 47 Walch S. K., Whitworth A. P., Bisbas T., Wünsch R., Hubber D., 2012, MNRAS, 427, 625 Walch S., Whitworth A. P., Bisbas T. G., Wünsch R., Hubber D. A., 2013, MNRAS, 435, 917 Wetzste…”

“…and the regulation of star formation on galactic scales (see e.g. Stinson et al. 2010; Hopkins, Quataert & Murray 2011, Agertz et al. 2013, and Genel et al. 2014 for a few recent examples), but much of this work considers only large scales and fails to resolve the small-scale processes…”

“…used in the work of Kim, Kim & Ostriker (2011), Shetty & Ostriker (2012), and Kim, Ostriker & Kim (2013), carried out with the ATHENA MHD code (Stone et al. 2008), is different since they correlate SN explosions with dynamically forming, local density maxima, and include shearing box boundary…”

“To account for X-ray heating and ionization, we use the prescription given in appendix A of Wolfire et al. (1995), assuming a fixed absorbing column of hydrogen NH = 1020 cm−2.”

“H2 is assumed to form only on the surface of dust grains, following the prescription given in Hollenbach & McKee (1989), as this dominates over gas-phase formation via the H− or H+2 ions at metallicities close to solar (Glover 2003).”

“This temperature is well above the local minimum in the cooling curve at high temperatures at a few × 105 K (see e.g. Dalgarno & McCray 1972).”

“…& Tielens 1994; Bergin et al. 2004) pe = 1.3 × 10−24 Geffn erg s−1 cm−3, (22) where Geff = G0exp (−2.5AV), and where the photoelectric heating efficiency is given by (Bakes & Tielens 1994; Wolfire et al. 2003) = 0.049 1 + (ψ/963)0.73 + 0.037(T /10 000)0.7 1 + (ψ/2500) , (23) with ψ = GeffT 1/2 ne .”

“To determine fshield,H2 for a particular line of sight, we use the following self-shielding function from Draine & Bertoldi (1996): fshield,H2 = 0.965 (1 + x/b5)2 + 0.035√ 1 + x × exp ( −8.5 × 10−4√1 + x ) , (19) where x = NH2/ ( 5 × 1014 cm−2), b5 = b/(105 cm s−1), and b is the Doppler broadening…”

“For the dust absorption term fdust,CO, we use the expression (van Dishoeck & Black 1988) fdust,CO = exp (−2.5AV) (21) using the same relationship as before between the visual extinction AV and the total hydrogen column density NH,tot.”

“…we do not include at the moment – is potentially important, in particular for gas-rich disc models (Shetty & Ostriker 2012), which resemble the conditions within the Galactic Center or in high-redshift, star-forming galaxies (Förster Schreiber et al. 2011; Genzel et al. 2011; Fisher et al. 2013).”

“…are (i) the Kennicutt– Schmidt (KS) relation (Kennicutt 1998) with SFR ∝ 1.4H2+H I , as well as (ii) newer results which relate the SFR surface density to the MNRAS 454, 238–268 (2015) molecular gas surface density, H2 , in a galaxy in a linear fashion 3 (Bigiel et al. 2008; Tacconi et al. 2013).”

“…forming molecular clouds, i.e. at the peaks in the density distribution; (3) half of the SNe explode randomly, and half of them explode within dense clouds (mixed driving); or (4) the SNe explode in clusters and are therefore correlated in space and time (e.g. Mac Low & McCray 1988; Matzner 2002).”

“…study of stellar feedback and the regulation of star formation on galactic scales (see e.g. Stinson et al. 2010; Hopkins, Quataert & Murray 2011, Agertz et al. 2013, and Genel et al. 2014 for a few recent examples), but much of this work considers only large scales and fails to resolve the…”

“For comparison, we also show the midplane pressure as estimated by Blitz & Rosolowsky (2006): PBR06/kB = GASv √ 2 Gρ /kB = 9965 [K cm−3], (35) where v is the vertical velocity dispersion of the gas, which we set to v = 8 km s−1, following Koyama & Ostriker (2009, green dashed horizontal line).”

“Schruba et al. (2011) use the IRAM HERACLES survey (Leroy et al. 2009) to determine the molecular to atomic gas mass fractions as a function of radius for 33 spiral galaxies.”

“…of galactic winds, which play an important role for regulating spiral galaxy evolution on larger spatial and temporal scales at all cosmic epochs (Oppenheimer et al. 2010; Aumer et al. 2013; Hirschmann et al. 2013; Stinson et al. 2013; Brook et al. 2014; Hopkins et al. 2014; Marinacci, Pakmor &…”

“The heating rate per unit volume due to cosmic ray ionization is then given by cr = 20 ζ Hn eV s−1 cm−3 = 3.2 × 10−11ζ Hn erg s−1 cm−3 (Goldsmith & Langer 1978).”

“…spiral galaxy evolution on larger spatial and temporal scales at all cosmic epochs (Oppenheimer et al. 2010; Aumer et al. 2013; Hirschmann et al. 2013; Stinson et al. 2013; Brook et al. 2014; Hopkins et al. 2014; Marinacci, Pakmor & Springel 2014; Übler et al. 2014; Murante et al. 2015).”

“Schruba et al. (2011) use the IRAM HERACLES survey (Leroy et al. 2009) to determine the molecular to atomic gas mass fractions as a function of radius for 33 spiral galaxies.”

“Previous studies of stratified discs (e.g. Joung & Mac Low 2006; Gent et al. 2013b; Kim & Ostriker 2015), have not employed a chemical network to distinguish between molecular and atomic or ionized gas, and have therefore used temperature cuts to estimate the amount of molecular hydrogen that forms…”

“We use an isothermal sheet, originally proposed by Spitzer (1942), in which the distribution function of stars is Maxwellian.”

“We typically use Minj = 800 M for single SNe, which roughly corresponds to a star formation efficiency of ∼8 per cent for a Chabrier initial stellar mass function (IMF; Chabrier 2001).”

“Runaway OB stars contribute to this ‘random’ SN component (Kimm & Cen 2014).”

“…distribution of H2 is consistent with a broad lognormal shape plus a high-density power-law tail, which is expected to develop due to local gravitational collapse (Klessen, Heitsch & Mac Low 2000; Slyz et al. 2005; Kainulainen et al. 2009; Schneider et al. 2011; Girichidis et al. 2014a).”

“If the mean density becomes too high, i.e. the mean density is n̄ 103 cm−3, then the SN remnants quickly become radiative (Blondin et al. 1998; Gatto et al. 2015; Li et al. MNRAS 454, 238–268 (2015) 2015) and the leftover momentum input (∼3 × 105 M km s−1) is not strong enough to disperse the…”

“…forming molecular clouds, i.e. at the peaks in the density distribution; (3) half of the SNe explode randomly, and half of them explode within dense clouds (mixed driving); or (4) the SNe explode in clusters and are therefore correlated in space and time (e.g. Mac Low & McCray 1988; Matzner 2002).”

“…we do not include at the moment – is potentially important, in particular for gas-rich disc models (Shetty & Ostriker 2012), which resemble the conditions within the Galactic Center or in high-redshift, star-forming galaxies (Förster Schreiber et al. 2011; Genzel et al. 2011; Fisher et al. 2013).”

“A similar basic approach was used in the ZEUSMP MHD code by Glover et al. (2010) and in an earlier version of the FLASH code by Walch et al. (2011) and Micic et al. (2012, 2013).”

“…play an important role for regulating spiral galaxy evolution on larger spatial and temporal scales at all cosmic epochs (Oppenheimer et al. 2010; Aumer et al. 2013; Hirschmann et al. 2013; Stinson et al. 2013; Brook et al. 2014; Hopkins et al. 2014; Marinacci, Pakmor & Springel 2014; Übler et…”

“As the bubble(s) expand and collide (similar to a typical colliding flow scenario, e.g. Banerjee et al. 2009; Heitsch, Naab & Walch 2011) the H2 distribution in case of peak driving is dispersed and becomes very filamentary.”

“…many of these clouds and exert strong feedback on the surrounding gas, in the form of UV radiation (Dale et al. 2005; Dale, Ercolano & Bonnell 2012; Walch et al. 2012, 2013), stellar winds (Toalá & Arthur 2011; Rogers & Pittard 2013), and supernova (SN) explosions (Hill et al. 2012; Gatto et al.…”

“Controlling the code accuracy by setting ap is not as safe as criteria introduced by Salmon & Warren (1994) that allow control of the total error in gravitational acceleration, resulting from contributions of all nodes.”

“The chemical network used in our simulations is based on the network for hydrogen chemistry presented in Glover & Mac Low (2007a,b), supplemented with the simplified model for CO formation introduced by Nelson & Langer (1997).”

“(33) In a high-density environment (n 100 cm−3; see e.g. Walch & Naab 2015) the condition that Rinj ≥ 4 x can typically not be met with Minj = 800 M .”

“Finally, we model the effects of photoelectric heating using a heating rate given by (Bakes & Tielens 1994; Bergin et al. 2004) pe = 1.3 × 10−24 Geffn erg s−1 cm−3, (22) where Geff = G0exp (−2.5AV), and where the photoelectric heating efficiency is given by (Bakes & Tielens 1994; Wolfire et al.…”

“…gas, in the form of UV radiation (Dale et al. 2005; Dale, Ercolano & Bonnell 2012; Walch et al. 2012, 2013), stellar winds (Toalá & Arthur 2011; Rogers & Pittard 2013), and supernova (SN) explosions (Hill et al. 2012; Gatto et al. 2015; Kim & Ostriker 2015; Martizzi, Faucher-Giguère &…”

“…(2015) chemistry of H2 within galactic-scale simulations of the ISM (see e.g. Dobbs et al. 2008; Gnedin, Tassis & Kravtsov 2009; Dobbs, Burkert & Pringle 2011; Christensen et al. 2012), and more recently a couple of studies have also treated CO formation (Pettitt et al. 2014; Smith et al. 2014).”

“Dynamically significant magnetic fields help to guide the gas flows that form and disperse the clouds (e.g. de Avillez & Breitschwerdt 2004, 2005; Banerjee et al. 2009; Heitsch, Stone & Hartmann 2009), and cosmic rays can also play an important role, as they represent a significant fraction of the…”

“Dynamically significant magnetic fields help to guide the gas flows that form and disperse the clouds (e.g. de Avillez & Breitschwerdt 2004, 2005; Banerjee et al. 2009; Heitsch, Stone & Hartmann 2009), and cosmic rays can also play an important role, as they represent a significant fraction of the…”

“Stars E-mail: walch@ph1.uni-koeln.de form in many of these clouds and exert strong feedback on the surrounding gas, in the form of UV radiation (Dale et al. 2005; Dale, Ercolano & Bonnell 2012; Walch et al. 2012, 2013), stellar winds (Toalá & Arthur 2011; Rogers & Pittard 2013), and supernova (SN)…”

“…(2015) chemistry of H2 within galactic-scale simulations of the ISM (see e.g. Dobbs et al. 2008; Gnedin, Tassis & Kravtsov 2009; Dobbs, Burkert & Pringle 2011; Christensen et al. 2012), and more recently a couple of studies have also treated CO formation (Pettitt et al. 2014; Smith et al. 2014).”

“We take the total gas-phase carbon, oxygen and silicon abundances to be xC,tot = 1.41 × 10−4, xO,tot = 3.16 × 10−4 and xSi,tot = 1.5 × 10−5 (Sembach et al. 2000).”

“Other clouds are destroyed by largescale dynamical processes in the disc, such as the strong shear flows around spiral arms (see e.g. Dobbs & Pringle 2013).”

“…et al. 2009; Heitsch, Stone & Hartmann 2009), and cosmic rays can also play an important role, as they represent a significant fraction of the local energy density in the interstellar medium (ISM; e.g. Breitschwerdt 2008; Dorfi & Breitschwerdt 2012; Hanasz et al. 2013; Girichidis et al. 2014b).”

“If the mean density becomes too high, i.e. the mean density is n̄ 103 cm−3, then the SN remnants quickly become radiative (Blondin et al. 1998; Gatto et al. 2015; Li et al. MNRAS 454, 238–268 (2015) 2015) and the leftover momentum input (∼3 × 105 M km s−1) is not strong enough to disperse the…”

“Substantial effort has already been devoted to the study of stellar feedback and the regulation of star formation on galactic scales (see e.g. Stinson et al. 2010; Hopkins, Quataert & Murray 2011, Agertz et al. 2013, and Genel et al. 2014 for a few recent examples), but much of this work considers…”

“In addition, we have improved and optimized the algorithm of Clark et al. (2012) significantly, leading to a speedup of more than a factor of 10 with respect to the original implementation.”

“Full details of our treatment of these processes can be found in Glover & Mac Low (2007a,b) and Glover & Clark (2012b).”

“…distribution of H2 is consistent with a broad lognormal shape plus a high-density power-law tail, which is expected to develop due to local gravitational collapse (Klessen, Heitsch & Mac Low 2000; Slyz et al. 2005; Kainulainen et al. 2009; Schneider et al. 2011; Girichidis et al. 2014a).”

“…spiral galaxy evolution on larger spatial and temporal scales at all cosmic epochs (Oppenheimer et al. 2010; Aumer et al. 2013; Hirschmann et al. 2013; Stinson et al. 2013; Brook et al. 2014; Hopkins et al. 2014; Marinacci, Pakmor & Springel 2014; Übler et al. 2014; Murante et al. 2015).”

“Each cluster has a pre-defined position and a constant lifetime of 40 Myr (Oey & Clarke 1997), and the total number of SNe per cluster, NSNe,clus, are drawn from a truncated power-law distribution f (NSNe,clus) = N−2SNe,clus (Clarke & Oey 2002) with a lower limit of NSNe,clus = 7 and an upper limit…”

“…distribution of H2 is consistent with a broad lognormal shape plus a high-density power-law tail, which is expected to develop due to local gravitational collapse (Klessen, Heitsch & Mac Low 2000; Slyz et al. 2005; Kainulainen et al. 2009; Schneider et al. 2011; Girichidis et al. 2014a).”

“…Dobbs & Smith 2013) even describe shear as one of the main drivers of ISM turbulence (e.g. Piontek & Ostriker 2005; Kevlahan & Pudritz 2009; and see Agertz et al. 2009 for a discussion), although the main role of the spiral arm structure to form and cause collisions between molecular clouds is…”

“…et al. 2009; Heitsch, Stone & Hartmann 2009), and cosmic rays can also play an important role, as they represent a significant fraction of the local energy density in the interstellar medium (ISM; e.g. Breitschwerdt 2008; Dorfi & Breitschwerdt 2012; Hanasz et al. 2013; Girichidis et al. 2014b).”

“Recently, Hennebelle & Iffrig (2014) computed models of low surface density discs with GAS ∼ 3 M pc−2 and galactic SN rates with RAMSES (Teyssier 2002).”

“…scheme that is based on the 5-wave Bouchut MHD solver HLL5R (Bouchut, Klingenberg & Waagan 2007; Klingenberg, Schmidt & Waagan 2007; Waagan 2009; Bouchut, Klingenberg & Waagan 2010; Waagan, Federrath & Klingenberg 2011), which is stable and preserves positivity for high Mach number…”

“In particular, Joung & Mac Low (2006), Hill et al. (2012), Gent et al. (2013a), Gent et al. (2013b), and Creasey, Theuns & Bower (2013) have carried out simulations of stratified discs with the FLASH code (although older releases of it), employing mostly randomly placed or clustered SNe.”

“The role of shear – which we do not include at the moment – is potentially important, in particular for gas-rich disc models (Shetty & Ostriker 2012), which resemble the conditions within the Galactic Center or in high-redshift, star-forming galaxies (Förster Schreiber et al. 2011; Genzel et al.…”

“…pre-defined position and a constant lifetime of 40 Myr (Oey & Clarke 1997), and the total number of SNe per cluster, NSNe,clus, are drawn from a truncated power-law distribution f (NSNe,clus) = N−2SNe,clus (Clarke & Oey 2002) with a lower limit of NSNe,clus = 7 and an upper limit of NSNe,clus = 40.”

“…have been made to account for the non-equilibrium MNRAS 454, 238–268 (2015) chemistry of H2 within galactic-scale simulations of the ISM (see e.g. Dobbs et al. 2008; Gnedin, Tassis & Kravtsov 2009; Dobbs, Burkert & Pringle 2011; Christensen et al. 2012), and more recently a couple of studies…”

“…galactic discs (Dobbs, Pringle & Burkert 2012; Bonnell, Dobbs & Smith 2013) even describe shear as one of the main drivers of ISM turbulence (e.g. Piontek & Ostriker 2005; Kevlahan & Pudritz 2009; and see Agertz et al. 2009 for a discussion), although the main role of the spiral arm structure to…”

“Instead, we assume that at T > 104 K, the helium and the metals are in collisional ionization equilibrium, and determine their contribution to the cooling rate using the ion-by-ion cooling rates given in Gnat & Ferland (2012).”

“…on the surrounding gas, in the form of UV radiation (Dale et al. 2005; Dale, Ercolano & Bonnell 2012; Walch et al. 2012, 2013), stellar winds (Toalá & Arthur 2011; Rogers & Pittard 2013), and supernova (SN) explosions (Hill et al. 2012; Gatto et al. 2015; Kim & Ostriker 2015; Martizzi,…”

“…(temperaturedensity or pressure-density) distributions of the gas are broad due to turbulent heating in dissipative shocks on the one hand, and cooling by expansion on the other hand (Vazquez-Semadeni 2009; Seifried, Schmidt & Niemeyer 2011; Walch et al. 2011; Micic et al. 2013; Saury et al. 2014).”

“…many of these clouds and exert strong feedback on the surrounding gas, in the form of UV radiation (Dale et al. 2005; Dale, Ercolano & Bonnell 2012; Walch et al. 2012, 2013), stellar winds (Toalá & Arthur 2011; Rogers & Pittard 2013), and supernova (SN) explosions (Hill et al. 2012; Gatto et al.…”

“In particular, Joung & Mac Low (2006), Hill et al. (2012), Gent et al. (2013a), Gent et al. (2013b), and Creasey, Theuns & Bower (2013) have carried out simulations of stratified discs with the FLASH code (although older releases of it), employing mostly randomly placed or clustered SNe.”

“…role for regulating spiral galaxy evolution on larger spatial and temporal scales at all cosmic epochs (Oppenheimer et al. 2010; Aumer et al. 2013; Hirschmann et al. 2013; Stinson et al. 2013; Brook et al. 2014; Hopkins et al. 2014; Marinacci, Pakmor & Springel 2014; Übler et al. 2014; Murante…”

“…et al. 2009; Heitsch, Stone & Hartmann 2009), and cosmic rays can also play an important role, as they represent a significant fraction of the local energy density in the interstellar medium (ISM; e.g. Breitschwerdt 2008; Dorfi & Breitschwerdt 2012; Hanasz et al. 2013; Girichidis et al. 2014b).”

“…rate is determined self-consistently at all temperatures, allowing us to properly model the non-equilibrium effects that can strongly affect the cooling rate at temperatures close to 104 K (see e.g. Kafatos 1973; Sutherland & Dopita 1993; Micic et al. 2013; Richings, Schaye & Oppenheimer 2014).”

“…spiral galaxy evolution on larger spatial and temporal scales at all cosmic epochs (Oppenheimer et al. 2010; Aumer et al. 2013; Hirschmann et al. 2013; Stinson et al. 2013; Brook et al. 2014; Hopkins et al. 2014; Marinacci, Pakmor & Springel 2014; Übler et al. 2014; Murante et al. 2015).”

“However, the oct-tree with monopole moments can be constructed in an extremely memory efficient way and consequently, computational costs are spared due to efficient cache usage and faster network communication (Springel 2005; Wetzstein et al. 2009).”

“…(2015) chemistry of H2 within galactic-scale simulations of the ISM (see e.g. Dobbs et al. 2008; Gnedin, Tassis & Kravtsov 2009; Dobbs, Burkert & Pringle 2011; Christensen et al. 2012), and more recently a couple of studies have also treated CO formation (Pettitt et al. 2014; Smith et al. 2014).”

“…spiral galaxy evolution on larger spatial and temporal scales at all cosmic epochs (Oppenheimer et al. 2010; Aumer et al. 2013; Hirschmann et al. 2013; Stinson et al. 2013; Brook et al. 2014; Hopkins et al. 2014; Marinacci, Pakmor & Springel 2014; Übler et al. 2014; Murante et al. 2015).”

“During the tree walk, the gravitational potential is calculated by the modified Ewald method (Ewald 1921; Klessen 1997).”

“A similar basic approach was used in the ZEUSMP MHD code by Glover et al. (2010) and in an earlier version of the FLASH code by Walch et al. (2011) and Micic et al. (2012, 2013).”

“In dense clouds, grain coagulation leads to a slightly different relationship between AV and NH,tot (see e.g. Foster et al. 2013), but we neglect this complication here.”

“A similar basic approach was used in the ZEUSMP MHD code by Glover et al. (2010) and in an earlier version of the FLASH code by Walch et al. (2011) and Micic et al. (2012, 2013).”

“…Pringle & Burkert 2012; Bonnell, Dobbs & Smith 2013) even describe shear as one of the main drivers of ISM turbulence (e.g. Piontek & Ostriker 2005; Kevlahan & Pudritz 2009; and see Agertz et al. 2009 for a discussion), although the main role of the spiral arm structure to form and cause…”

“2 N U M E R I C A L M E T H O D We use the fully three-dimensional, AMR code FLASH 4 (Fryxell et al. 2000; Dubey et al. 2009, 2012) to simulate representative pieces of galactic discs with dimensions 500 pc × 500 pc × ±5 kpc. FLASH is parallelized via domain decomposition under the Message Passing…”

“A similar basic approach was used in the ZEUSMP MHD code by Glover et al. (2010) and in an earlier version of the FLASH code by Walch et al. (2011) and Micic et al. (2012, 2013).”

“…we do not include at the moment – is potentially important, in particular for gas-rich disc models (Shetty & Ostriker 2012), which resemble the conditions within the Galactic Center or in high-redshift, star-forming galaxies (Förster Schreiber et al. 2011; Genzel et al. 2011; Fisher et al. 2013).”

“…et al. 2009; Heitsch, Stone & Hartmann 2009), and cosmic rays can also play an important role, as they represent a significant fraction of the local energy density in the interstellar medium (ISM; e.g. Breitschwerdt 2008; Dorfi & Breitschwerdt 2012; Hanasz et al. 2013; Girichidis et al. 2014b).”

“This is in contradiction to simulations by de Avillez & Breitschwerdt (2004), Joung & Mac Low (2006) and Hill et al. (2012), who find that most of the volume is filled with a pervasive, warm medium (VFF ∼50 per cent) while the VFF of the hot gas component is smaller and where the hot gas is mostly…”

“By creating the hot, X-ray emitting, phase they impact the large-scale multi-phase structure of the ISM (Li et al. 2015, McKee & Ostriker 1977, Walch et al. 2015) and might be important for driving galactic outflows, fountain flows, and galactic winds through hot, low density, chimneys (Chevalier &…”

“…in driving turbulence and shaping the multiphase ISM in galactic disks have been extensively investigated (e.g., Korpi et al. 1999; de Avillez 2000; de Avillez & Breitschwerdt 2004; Joung & Mac Low 2006; Hill et al. 2012; Gent et al. 2013; Walch et al. 2015; Girichidis et al. 2016; Li et al. 2017).”