The existence and shapes of dust lanes in galactic bars

“3) very different from the typical straight dust lanes found in stronger barred galaxies such as NGC 1300, and also different from the curved dust shapes in weak bars as in NGC 1433 (Athanassoula 1992).”

“In this exchange, the angular momentum lost by the gas is transferred to the bar, letting the gas inside the co-rotation radius to fall to the central region and preventing the inflow of gas from external regions (Athanassoula 1992; Heller & Shlosman 1994; Knapen et al. 1995; Sheth et al. 2005).”

“This general conclusion has since been supported in diverse publications, both theoretical and observational (Athanassoula 1992; Valenzuela & Klypin 2003; Rautiainen et al. 2008; Buta & Zhang 2009; Font et al. 2014a; Aguerri et al. 2015).”

“Bars with R < 1.0 corresponds to an unphysical regime for the x1 orbits (Contopoulos 1981; Athanassoula 1992; Vasiliev & Athanassoula 2015) and are called ultrafast (Buta & Zhang 2009; Aguerri et al. 2015, hereafter Paper I).”

“…mechanism for funneling gas and dust to the centers of galaxies: gas clouds orbiting in the disk lose angular momentum as they encounter the bar, thereby sinking toward the galaxy’s center (Binney & Tremaine 1987; Athanassoula 1992; Piner et al. 1995; Regan et al. 1997; Maciejewski et al. 2002).”

“In this way, the gas circulates to the center slowly, taking 3 or more rotations relative to the bar to decrease its radius by a factor of 2 (in their Figure 26b; see also Athanassoula 1992).”

“Athanassoula (1992) found that the presence of typical dust lanes in the leading side requires that the bar has an ILR and that it extends near the corotation resonance: the shape of the shock is related to change from x1 orbits to x2 orbits.”

“Numerical simulations of the gas dynamics (Athanassoula 1992; Fux 1999) show that the gas in the center tends to follow nearly circular x2 orbits creating a nuclear ring (the GCR).”

“At their apocentres they often have cusps or loops (see Athanassoula 1992a for a study of their morphology).”

“The average value of this ratio, when all galaxies listed in Table 7 are taken into account, is found to be 1.35±0.36, which is in agreement with the dynamical simulations of Athanassoula (1992), who predicted a value for ! of 1.2±0.2.”

“…also affect the mass redistributions in the inner parts and are responsible for the formation of various gaseous substructures such as dust lanes and nuclear rings (e.g., Sanders & Huntley 1976; Athanassoula 1992; Heller & Shlosman 1994; Piner et al. 1995; Buta & Combes 1996; Kim et al. 2012a).”

“There have been a number of numerical simulations to discuss the effect of a bar and spiral arms on the kinematics of interstellar gas and stars (e.g., Athanassoula 1992; Wada and Habe 1995).”

“(i) As we stated before, the strong shear and parallel shocks limit the formation of stars (e.g., Athanassoula 1992; Reynaud & Downes 1998; Zurita et al. 2004), because the giant molecular clouds can be pulled apart (Downes et al. 1996; Schinnerer et al. 2002).”

“…radius of Rbar = 20′′ (800 pc) based on ellipse fitting, which implies a ratio of RCR,bar/Rbar ≈ 1.1, in agreement with expectations for fast bars (e.g. Athanassoula 1992a), and also well compatible with the values measured by Rautiainen et al. (2008) for galaxies of similar morphological type…”

“Simulation models predict that this process increases the disk size (e.g. Hohl 1971) and causes secular evolution of bulges (e.g. Athanassoula 1992a; Wada & Habe 1992; Friedli & Benz 1993) after the bar-funneled cold gas is transformed into stars, and also as a result of old stars being driven…”

“…as dynamical transients (Sellwood & Carlberg 1984; Elmegreen & Thomasson 1993), can be created by bar rotation (Contopoulos & Papayannopoulos 1980; Athanassoula 1992), tidal interactions (Toomre & Toomre 1972; Elmegreen et al. 1991) and rotations of non-axisymmetric dark matter haloes (Dubinski &…”

“The latter mechanism is theorized to occur in galaxies hosting bars; the bar funnels gas to the centre of the galaxy (Athanassoula 1992a), where gas is exhausted by star formation effectively quenching the galaxy (Zurita et al. 2004; Sheth et al. 2005).”

“In their study, they also found that the leading edges of bars are favorable for converging gas flows and large-scale shocks (see also Athanassoula 1992).”

“…involving the transfer of angularmomentum to the outer parts of the galaxy and resulting in an accumulation of gas in the central regions (e.g., Athanassoula 1992a, 1992b; Friedli & Benz 1993, 1995; Sakamoto et al. 1999a, 1999b), sweeping large-scale chemical abundance gradients (Martin & Roy…”

“The formation of new stars out of molecular clouds along the bars is expected to be regulated by the effect of shear, which can be controlled by orbits making up the bar (e.g., Athanassoula 1992a).”

“Athanassoula (1992) argued that the shapes and locations of dust lanes in bars also seem to suggest that R ≃ 1.2.”

“In the extended ILR region of the CND it is expected that the gas flow would trace the gradual transition from thex1 orbits of the nuclear bar (between corotation and the outer ILR) to the x2 orbits (between the ILRs) (e.g., Athanassoula 1992; Buta & Combes 1996).”

“Clouds move in a dynamical time-scale from the x1- to the inner x2-orbits mainly as a result of losing angular momentum to the stellar bar after piling up behind the shock that forms along two of the nearly straight line segments of the cusped orbit (Athanassoula 1992).”

“11 of Athanassoula 1992), very close to what was predicted by Roberts (1969) and what is shown in Fig.”

“…indicate that in barred galaxies, gas falls into the nuclear ring through a pair of dust lanes located on the leading side of a bar (e.g., Athanassoula 1992; Benedict et al. 1996; Regan et al. 1997, 1999; Laine et al. 1999; Schinnerer et al. 2002; Kim et al. 2012; Sormani et al. 2015;…”

“The increase in bar fraction at NIR wavelengths has been attributed to a higher c© 2015 RAS prevalence of weak (AB) bars, which are obscured by dust and star forming regions in the optical (Athanassoula 1992; Marinova et al. 2009a).”

“…& Dottori , 1997; Aguerri et al. , 1998; Buta & Zhang , 2009); detecting the offset and shape of dust lanes (see, e.g., van Albada & Sanders , 1982; Athanassoula , 1992); locating colour and star formation changes outside the bar region (Cepa & Beckman , 1990; Aguerri et al. , 2000); or…”

“This is not surprising, as inflow velocities in bars are expected to be much lower than 111 km s−1 (Athanassoula 1992; Regan & Teuben 2004).”

“The bar can effectively funnel gas toward the galaxy center to induce the build-up of the central stellar concentration or pseudobulge (Combes & Gerin 1985; Athanassoula 1992; Regan & Elmegreen 1997; Sakamoto et al. 1999; Sheth et al. 2000; Kormendy & Kennicutt 2004).”

“The overall shape and kinematics of the CO spiral arms are reminiscent of models for gas flows in a weakly barred potential (e.g. Athanassoula 1992).”

“Athanassoula (1992) used hydrodynamic simulations to show that, in order for the shock loci in the bar tohave the same shape as the observed dust lanes, the pattern speed must be such as to fulfilRCR = (1.2± 0.2)Lb .”

“…& Hernquist, 1992) or formed by gravitational disk instabilities, are thought to be an efficient mechanism for transporting galactic material into the central regions of galaxies (Larson, 1994; Wada & Habe, 1995), and for dissipating angular momentum via shocks in the bar (Athanassoula, 1992b).”

“Numerical models (e.g. Athanassoula 1992; Sellwood & Wilkinson 1993) have demonstrated that large-scale stellar bars are especially efficient in moving gas into the central kpc.”

“Additionally, there is evidence showing that through funnelling gas towards the centre, bars may be the cause of morphological quenching (Athanassoula 1992; Sheth et al. 2005; Masters et al. 2012; Cheung et al. 2013; Vera, Alonso & Coldwell 2016).”

“Nuclear gas bars are relatively common but appear to be associated with x 2 orbits embedded within the bar-supporting x 1 orbit families ( Athanassoula 1992 ) .”

“This gas becomes compressed, loses angular momentum and energy, and falls towards the centre of the galaxy (Athanassoula 1992; Heller & Shlosman 1994; Knapen et al. 1995; Sheth et al. 2005), which explains the higher central gas concentrations observed in barred galaxies compared to unbarred…”

“Bars have been proposed as an effective mechanism for radial migration (e.g.,Athanassoula 1992; Sellwood & Binney 2002b).”

“Both observations (e.g. Sakamoto et al. 1999; Sheth et al. 2005) and theoretical models (e.g. Athanassoula 1992; Friedli & Benz 1993) have demonstrated that bars drive gas into the centres of spiral galaxies.”

“We model the intrinsic gas orbits as nonintersecting, inclined elliptical annuli that conserve angular momentum (so there are no hydrodynamic shocks or gas Ñows near the corotation radius or in the bar ; Athanassoula 1992 ; Piner et al. 1995).”

“Barred galaxies with an inner Lindblad resonance (ILR) tend to have two long and symmetric dust spirals near the resonance that are a continuation of the leading-edge dust lanes in the bar (Athanassoula 1992).”

“This behaviour is unexpected, as ionised gas is commonly observed tracing the often present dust lanes seen along the main bar major axis (e.g., Athanassoula 1992; Patsis & Athanassoula 2000).”

“…have helped to understand barred galaxies, their orbital structures and their influence on different galaxy properties (e.g. Combes & Sanders 1981; Athanassoula 1992a,b; Debattista & Sellwood 2000; Athanassoula 2003; Bureau & Athanassoula 2005; Martinez-Valpuesta, Shlosman & Heller 2006; Minchev…”

“The inner near-circular spiral, which extends from the inner minor axis of the " " bar ÏÏ to a smaller radius, twisting 90¡ along the way, would be the ILR shock feature.”

“Little and Carlberg 1991a, Little and Carlberg 1991b, Hernquist and Weinberg 1992, Athanassoula 1996, Debattista and Sellwood 2000, Valenzuela and Klypin 2003), but considerably less than that predicted by Weinberg (1985). Weinberg (2004) stressed that the derivation of the formulae of Lynden-Bell and Kalnajs assumes…”

“The non-axisymmetric potential of a bar induces large scale streaming motions in stars and gas into the central part of the galaxy (e.g., Athanassoula 1992a,b; Sellwood & Wilkinson 1993).”

“A strong triaxial potential can lead to significant gas inflow in large-scale bars (Athanassoula 1992) and if similar gas flow occurs in nuclear stellar bars, they may have associated dust lanes.”

“Bars have long been considered an efficient mechanism for transporting gas to the sub-kpc regions of a galaxy, and hence, an AGN (e.g., Athanassoula 1992 ; Shlosman & Noguchi 1993).”

“Alternatively, Ωp can be estimated by matching observations to models as suggested by Athanassoula (1992) and successfully applied by Salo et al. (1999).”

“These include clump migration in violently unstable discs (Noguchi 1999), bar-induced gas inflows (Athanassoula 1992), gas-rich minor mergers (Barnes & Hernquist 1996), angular momentum loss due to the reorientation of the disc rotation axis (Aumer & White 2013; Okamoto 2013) and the infall of gas…”

“This bar may be responsible for driving gas into the central region of the galaxy, forming a ring of gas near the Inner Lindblad Resonance, triggering the formation of massive star clusters (e.g. Athanassoula 1992).”

“…then encountering another shock at the opposite region and repeating the pattern, which makes bars important agents for the gas in spiral galaxies to lose part of its angular momentum and form substantial gas concentrations in their central regions (e.g. Athanassoula 1992; Sakamoto et al. 1999).”

“…of barred galaxies is shaped by the orbital structure of the underlying barred gravitational potential and typically forms two bar lanes along the leading sides of the bar that generally curve at smaller galactocentric radii (right panels of Figure 1; see seminal paper by Athanassoula 1992).”

“In weak bars, the dust lanes are curved because of weaker shocks (Athanassoula 1992).”

“Many theoretical studies and numerical simulations have shown that these motions pile up the gas along the leading side of the bar and induce shock waves and/or shear motion (e.g. Roberts, Huntley & van Albada 1979; Athanassoula 1992).”

“The starburst possibly was triggered through cannibalization of a small irregular galaxy in the past 108 yr (Balick & Heckman 1981; and modeled by Athanassoula 1992 and Piner, Stone, & Teuben 1995).”

“…potential of a bar is able to exert torques which result in radial gaseous inflows toward the galactic center, leading to high central concentrations of molecular gas and nuclear star formation (Athanassoula 1992; Martin 1995; Sakamoto et al. 1999; Regan et al. 1999; Sheth et al. 2005).”

“In simulations that lack gas, angular-momentum loss to the dark halo and disc causes the bar to strengthen and slow down (Athanassoula, 1992).”

“In isolated galaxies, hydro-dynamical simulations predict that the bars may produce a falling of gas into the central regions (Athanassoula 1992; Friedli et al. 1994) which have been confirmed by observational studies (Zaritsky et al. 1994; Martin & Roy 1994).”

“…the inner disc is explained by invoking some level of star formation happening in the inner disc (as well as in the outer regions) after the inner bar was already assembled (as it has actually been seen in simulations and observations; Athanassoula 1992; Emsellem et al. 2015; Romeo & Fathi 2016).”

“The limiting value 1.4 was set by numerical simulations (Athanassoula 1992; Debattista & Sellwood 2000) and it does not imply any specific range for Ωbar.”

“Presumably, the deficit of stars affects only the near-plane regions, where the disc material can be swept up due to the motion of the in-plane bar (Athanassoula 1992, L01).”

“In a strong barred perturbation of the gravitational potential, shocks develop along the rotation-leading side of the bar and are associated with strong shear, as shown by Athanassoula (1992) and references therein (also Friedli & Benz 1993).”

“The gravitational torque ex- pei-ying.hsieh@alma.cl erted on the gas by a stellar bar has often been invoked to drive the inflows onto a kilo-pc and hundred-pc disk or ring (e.g., Athanassoula 1992; Sakamoto et al. 1999; Hsieh et al. 2011; Lin et al. 2013; Sormani & Barnes 2019; Tress et al. 2020).”

“These characteristic profiles are produced by the shape and orientation of the stellar orbits of the bar (see Contopoulos & Grosbol 1989; Athanassoula 1992).”

“The non-axisymmetric gravitational potential created by a bar can produce important kinematic effects on the gas which have been studied by hydrodynamical (e.g Lindblad et al. 1996; Kim et al. 2012; Athanassoula 1992) and/or N-body simulations (e.g. Sellwood 1981; Emsellem et al. 2001a).”

“This is in accordance with results from both Contopoulos & Grosbol (1989) and Athanassoula (1992a), the latter of which showed that there are a number of model parameters which can affect this distance.”

“Minor offsets between the gas and stars, like the one we find here, have been seen before in spiral arms created during encounters with lower-mass companions (Pettitt et al. 2016) and along the leading edges of strong central bars (Prendergast 1983; Athanassoula 1992; Sheth et al. 2002).”

“This is possible through the inflow of gas from the outer disk to the central region which results in an enhanced nuclear/central star formation observed in barred spiral galaxies (Athanassoula 1992; Ho et al. 1997; Sheth et al. 2005; Coelho & Gadotti 2011; Ellison et al. 2011; Oh et al. 2012).”

“Theoretical arguments by Contopoulos (1980) have shown that this value should be a little larger than 1, and measurements of in simulation (Athanassoula 1992; Debattista & Sellwood 2000) and in observation (e.g., Merrifield & Kuijken 1995; Gerssen et al. 1999; Font et al. 2017) have shown < <1 1.4.”

“The bar ends happen to be the apocentres of the orbits that are elongated parallel to the bar, as the gas flows on these orbits near the bar ends (Athanassoula 1992).”

“…related not to the gravitational potential (as inferred by Mast et al. 2006 and Dı́az et al. 2006) but to localeffects of the dust lane (see, e.g., Athanassoula 1992 for a detailed discussion of how shocks occur near dust lanes in bars, and Zurita et al. 2004 for an example of how this can be…”

“3) and radio maps (k6 cm; Telesco 1988), which, in addition to their tidal shape, would not show a continuity of their features with the bar dust lanes (marking the main bar streaming regions; Athanassoula 1992).”

“This is qualitatively consistent with observations of bluer galaxies, typically late-type spirals, which generally host weaker, smaller bars (i.e. Athanassoula 1992; Hoyle et al. 2011).”

“Thus, in practice the bar ends inside corotation in accordance with empirical requirement (see, e.g., Athanassoula 1992).”

“The waves excited at the OILR carry negative angular momentum which will be deposited over the annular region covered by the waves during propagation.”