The existence and shapes of dust lanes in galactic bars

“Well studied examples are galactic-scale stellar bars (e.g. Sanders & Huntley 1976; Roberts et al. 1979; Athanassoula 1992).”

“The same conclusion was reached by Athanassoula (1992) for simulations of gas moving in a rigid barred potential.”

“However taking the latter into account we can interpret the observations in terms of a resonance model of the type illustrated in Downes et al. (1996) to interpret their measurements in CO, based on models incorporating an ILR to a main galactic bar by Athanassoula (1992).”

“This is an excellent fit considering that hydrodynamic effects (e.g., strong shocks along the bar; Athanassoula 1992; Piner, Stone, & Teuben 1995) are ignored in our simple kinematic model.”

“1Gyrs; see, e.g., Athanassoula 1992; Seo et al. 2019; Baba & Kawata 2020).”

“Bars are ubiquitous in numerical simulations; detailed studies by many authors show that the quasistatic gas response agrees well with observed morphology (e.g., Athanassoula 1992).”

“However, numerical simulations show that areas in front of galactic bars are locations where clouds sporadically agglomerate (e.g. Athanassoula 1992; Wozniak 2007; Renaud et al. 2013).”

“Gas and dust usually accumulates in the downstream region of bars (Athanassoula 1992).”

“Numerical simulations (Athanassoula 1992; Friedli & Benz 1993; Shlosman & Noguchi 1993) showed that the presence of a non-axisymmetric potential from a bar can drive important amounts of gas inwards of corotation (CR) fuelling star formation in the galactic nucleus, while at the same time gas is…”

“It is presumably caused by the bar, which sweeps gas inside its corotation radius from the bar region towards the galaxy center, as seen in fluid-dynamical simulations (e.g. Athanassoula 1992b; Piner et al. 1995; Weiner & Sellwood 1999; Paper II).”

“The bar is able to push gas to the centre quickly (on a typical time scale of ∼108 yr, Athanassoula 1992a; Emsellem et al. 2015, see also Huang & Kauffmann 2015; Gavazzi et al. 2015), and the subsequent formation of the inner disc and nuclear ring and other nuclear disclike structures might very…”

“It is important to point out, as numerical simulations show, that a in ow speed as high as this is consistent with the predictions of galaxy mergers (Mihos & Hernquist 1994a,b) and not with that of a bar perturbation in an isolated galaxy (Athanassoula 1992, 1-6 km/sec).”

“Evidence that bars are fast comes mostly from simulations of the hydrodynamics of gas in the bar region (e.g., Athanassoula 1992; Lindblad, Lindblad, & Athanassoula 1996).”

“…the bar has the ability to channel gas from the disc towards the nucleus (e.g. Huntley, Sanders & Roberts 1978; Sanders & Tubbs 1980; Simkin, Su & Schwarz 1980; van Albada & Roberts 1981; Schwarz 1984; Combes & Gerin 1985; Shlosman, Begelman & Frank 1990; Athanassoula 1992; Knapen et al. 1995a,b).”

“…bars exert torques that accumulate gas and dust at the leading end of the bar where they get shocked, lose angular momentum, and fall inward the central regions of the galaxy (Athanassoula 1992b; Knapen et al. 1995; Regan et al. 1999; Maciejewski et al. 2002; Sheth et al. 2002; Kim et al. 2012).”

“The non-axisymmetric potential of a bar is predicted to funnel interstellar gas into the central kpc (Athanassoula 1992) – which has been confirmed by multiple observational works (Regan, Vogel & Teuben 1995; Regan, Sheth & Vogel 1999; Sakamoto et al. 1999; Sheth et al. 2000, 2002, 2005; Zurita et…”

“Theoretical calculations (e.g. Athanassoula 1992a) predict that gas at the leading side of the bar is shocked and compressed, favoring the formation of stars there.”

“The often prominent dust lanes along the leading edges of bars in galaxies are associated with shocks in the gas streaming along the length of the bar (e.g. Athanassoula 1992), which in turn lead to velocity jumps across the dust lanes (e.g. Mundell & Shone 1999).”

“Simulations have shown that the growth of a bar causes gas to either form a ring structure or fall inwards and trigger central star formation (Athanassoula 1992; Athanassoula et al. 2013).”

“This is a typical gas flow pattern in a rotating barred potential (e.g., Athanassoula 1992; Kim et al. 2012; Li et al. 2015; Sormani et al. 2015a).”

“This is not suitable for M100-type bars and gives erroneous positions for the ILRs, which require non-linear orbit analysis (Athanassoula 1992; Knapen et al. 1995b).”

“Hydrodynamical simulations can therefore recover Ωp; these find fast bars (e.g. van Albada & Sanders 1982; Athanassoula 1992; Lindblad & Kristen ⋆ email: debattis@phys.ethz.ch 1996; Lindblad et al. 1996; Weiner et al. 2001).”

“NGC 1097 has a bar axial ratio of ∼2.6 (Menéndez-Delmestre et al. 2007), which indicates the maximum velocity jump is ∼ 70 km s−1 (Figure 12; Athanassoula 1992b) .”

“Circular motions in gaseous disks are expected as a result of the dissipative nature of the gas; however, anisotropies in the stellar potential rapidly lead to noncircular streaming (e.g., Athanassoula 1992).”

“…Combes & Gerin 1985; Pfenniger & Friedli 1991; Heller & Shlosman 1994; Bournaud & Combes 2002; Athanassoula 2003; Jogee 2006), as demonstrated by a number of numerical simulations (e.g., Roberts et al. 1979; Athanassoula 1992; Friedli & Benz 1993; Maciejewski et al. 2002; Regan & Teuben 2004).”

“A large number of simulations show that non-axisymetries are able to rearrange disk gas such that the central gas density increases (Simkin et al. 1980; Combes & Sanders 1981; Pfenniger & Norman 1990; Athanassoula 1992; Zhang 1999).”

“The effectiveness of bars in modifying the dynamics of gas has been recognized since decades (e.g. Sanders & Huntley 1976; Roberts, Huntley & van Albada 1979; Athanassoula 1992).”

“The transfer of material (inflow or outflow) may be linked to the pattern speed (Athanassoula 1992b).”

“Namely, in strong bars which exhibit almost straight offset dust lanes believed to trace strong shocks, the strong shear in the postshock flow can inhibit SF (e.g., Athanassoula 1992; Tubbs 1982).”

“2 of Athanassoula 1992; hereafter A92; see Section 5).”

“The shape of dust lanes inside the bar, coinciding with the location of shocks in the gasflow, reveals information about the internal dynamics of the bar and disc (Athanassoula 1992b).”

“…automatic 8 Note that in some papers on bars, a family of orbits that lie close to the 4th and 5th Lagrange points of the bar are also referred to as “banana” (Athanassoula 1992) but is not a member of this resonant family. classification code is unable to distinguish between banana and…”

“Since the properties of periodic orbits in barred galaxies are tightly related to the gas flows (Athanassoula 1992a,b), this already hinted at the effect that b/ps would have on the gas inflow.”

“We use a grid-based, Eulerian code based on the second-order flux-splitting scheme developed by van Albada et al. (1982) and later used by Athanassoula (1992), Weiner & Sellwood (1999) and others to study gas dynamics in barred potentials.”

“…et al. 1997; Martinet & Friedli 1997; Hunt & Malkan 1999; Laurikainen et al. 2004; Jogee et al. 2005), as well as diffuse gas (e.g. Sanders & Huntley 1976; Roberts et al. 1979; Athanassoula 1992; Cheung et al. 2013; Fanali et al. 2015; Hakobyan et al. 2016) and dust (e.g. Consolandi et al. 2017).”

“There is general consensus that gas flow in a barred potential can produce a depression in the gas surface density in the regions of the bar (e.g. Athanassoula 1992).”

“This region therefore favours star formation, unlike the inner bar where the high-velocity shocks are likely to prevent it (Tubbs 1982; Athanassoula 1992; Reynaud & Downes 1998).”

“This is interpreted as star formation occurring at the leading edge of spiral arms, due to shocks in the compressed ISM.”

“9), with a corotation to bar radius ratio of about 1.6, slightly higher than expected and typically observed in barred disc galaxies (1.2 for fast bars; see e.g. Athanassoula 1992; Aguerri, Debattista & Corsini 2003; Gerssen, Kuijken & Merrifield 2003).”

“Hydrodynamical simulations of gas in barred potentials by Athanassoula (1992) show that shocks on the leading edge of bars cause this angular momentum loss.”

“In the upper panels, dotted curves draw the outermost x1-orbit that cuts the x- and y-axes at xc = 3.6 and yc = 4.7 kpc, respectively, and has a Jacobi energy of EJ = −1.24 × 105 (km s−1)2 under our adopted external potential (e.g., Athanassoula 1992a).”

“Bars that extend to the vicinity of the CR, have a narrow range of Rb/RCR ∼ 1.2 ± 0.2, so-called fast bars, while those that fall short of CR are slow bars (e.g., Teuben & Sanders 1985; Athanassoula 1992b).”

“Theoretical studies and modeling of observations suggest that bars end somewhat inside their corotation radius (Contopoulos et al. 1989; Athanassoula 1992; Laine, Shlosman, & Heller 1998).”

“An inverse process might be responsible too, where a strong bar forms first and this causes the bulge to grow through accretion (e.g., Athanassoula 1992, 2003).”

“Indirect evidence comes from the location of dust lanes (Athanassoula 1992) and rings (Buta & Combes 1996).”

“…vicinity of inner Lindblad resonances set up by a non-axisymmetry in the gravitational potential, due to, e.g., a bar or an interaction (see, e.g., Athanassoula 1992; Knapen et al. 1995b; Buta & Combes 1996; Heller & Shlosman 1996; Knapen et al. 2004b), it is instructive to scrutinise the four…”

“The same is true in barred potentials too (Athanassoula 1992).”

“Such features, accompanied by shocks, have been observed by other authors (Athanassoula 1992; Athanassoula & Bureau 1999) in full hydrodynamical simulations.”

“In terms of bar orbit structure, this result can be interpreted as an indication that there are stable stellar orbits whose major axis is perpendicular to the bar major axis (x2 orbits, e.g., Athanassoula 1992; Buta & Combes 1996; Regan & Teuben 2003).”

“…drives the gas in the diskeither outward to form aring-like structure in the outskirtor inward to trigger star formation in the central region (e.g., Athanassoula 1992; Sellwood & Wilkinson 1993; Piner et al. 1995; Knapen et al. 2000; Sheth et al. 2002; Regan & Teuben 2004; Zurita & Pérez 2008).”

“Our work is complementary to studies that focused on large-scale gasdynamics in barred galaxies and, due to the limitations of the numerical schemes, did not resolve the central regions discussed here (e.g., Athanassoula 1992).”

“Similarly, some studies (e.g. Athanassoula 1992; Friedli et al. 1994; Friedli & Benz 1995) from numerical simulations found such trends, showing that bar strength is related to the efficiency and quantity of gas inflow, and therefore with the star formation activity and metallicity gradients.”

“Theory predicts this parameter has values in the range ofR = 1.2±0.2 (Athanassoula 1992; Debattista & Sellwood 2000).”

“…of barred galaxies have shown that the torque of bars induces gas inflow towards the galactic centre and results in the formation of a nuclear gas disc in the central sub-kpc of the barred galaxies (e.g. Athanassoula 1992; Friedli & Benz 1993; Athanassoula 2005; Kim et al. 2011; Seo et al. 2019).”

“The ratio of corotation to bar radii (RCR/Rbar) is expected to lie in the range of 1.2±0.2 as found empirically by Athanassoula (1992).”

“Besides, Athanassoula (1992) explained that flat bars could have roughly rectangular orbits around the end of bar through the stellar orbit calculation.”

“As a matter of fact, it is the barlike structure to drag the gas and the molecular clouds from the inner disk into the nuclear bulge (Athanassoula 1992; Kim et al. 2011).”

“Some studies have been devoted to explore galaxy models with bar–induced spiral structure (Contopoulos & Papayannopoulos 1980) and spiral features explained by a manifold (Contopoulos & Papayannopoulos 1980; Athanassoula 1992).”

“According to bar models by Athanassoula (1992), weak bars promote the inflow of gas toward the inner Lindblad resonance (ILR), and forms a nuclear ring.”

“There is now growing evidence that nuclear discs and nuclear rings are built from gas that was funnelled to the centre by the bar (see e.g. Athanassoula 1992, Kim et al. 2011, Fragkoudi et al. 2016).”

“Athanassoula 1992b;Wills et al. 2000).”

“Their morphological components are subjected to mutual gravitational torques that, in addition to external factors, provide an efficient mechanism for driving their internal evolution (e.g., Weinberg 1985; Athanassoula 1992; Heller & Shlosman 1994; Sellwood 2006).”

“These shocks have been detected by the dust lanes, whose shape is constrained by the ratio of corotation-to-bar-radii, 1.2 ± 0.2, as found empirically by Athanassoula (1992).”

“Fueling the Active Nucleus As discussed in Athanassoula (1992) and Regan et al. (1997), probably only a small fraction of the streaming gas does actually result in an inÑow (10%È30%).”

“Wada & Habe find that the presence of an ILR is essential, but Athanassoula (1992) and Piner, Stone & Teuben (1995) find that more generic mass transport always occurs, even preferentially in systems without ILR.”

“The same correlation between bar strength and size of the ring is expected in out theory, but for a different reason: a stronger bar changes the orbital structure of the potential, which results in smaller x2 orbits (e.g. Contopoulos & Grosbol 1989; Athanassoula 1992a).”

“These observations bear a striking resemblance to the theoretical predictions of gas behaviour in a weak barred potential (Athanassoula 1992b), also shown in Fig.”

“Athanassoula (1992) also proposed that the strength of SF near the dust lanes depends on the strength of the bar.”

“The 1 kpc ring in NGC 3310, is the scale sized predicted for such a ringed star formation effect (e.g. Athanassoula 1992; Piner et al. 1995).”

“…may play an important role in galaxy evolution : they may generate gas inÑow (see, e.g., & NelsonMatsuda might drive spiral structure (e.g.,1977 ; Athanassoula 1992), & Huntley & Sellwood andSanders 1976 ; James 1978), could Ñatten the radial abundance gradient & Roy(Martin They may also be…”

“Indeed, for the ILRs, Athanassoula (1992a) has computed the spatial extension of the x2 and x3 families associated with the existence of these resonances.”

“…is inconsistent with the results from early analytical calculations (Contopoulos & Grosbol 1989), which show that corotation occurs just outside the end of the bar, and also larger than results from numerical SPH simulations (Athanassoula 1992), which suggest a distance to the CR of 1.2±0.2 R bar .”

“In the latter case, the ratio is inside the range determined by hydrodynamic simulations rL/a = 1.2 ± 0.2 (Athanassoula 1992), while in the former, it is outside it.”

“…ballistic models in which the gas is represented by colliding clouds on ballistic orbits (Combes & Gerin 1985; Byrd et al. 1994), and hydrodynamic models in which the gas is assumed to be a continuous dissipative medium (Athanassoula 1992; Piner et al. 1995; Wada & Habe 1995; Friedli & Benz 1993).”

“(26) Here I fixed σ 0 and R0 to the values set by Athanassoula (1992), when she originally proposed this form of the potential.”

“This empirical result is consistent with numerical models (e.g. Athanassoula 1992; Friedli et al. 1994; Ann & Thakur 2005) in which the presence of a bar enhances large-scale mixing over the galaxy’s disc, damping radial abundance variations.”

“Large-scale shocks driven by density waves have been long predicted by numerical simulations of spiral/barred galaxies, made following either hydrodynamical schemes (Roberts 1969; Athanassoula 1992) or ballistic ones (Casoli & Combes 1982; Combes & Gerin 1985).”