The existence and shapes of dust lanes in galactic bars

“The existence of the ILR implied by the EVC peaks requires only a concentrated mass within that radius, so our conclusion is little a†ected by the details of the density proÐle.”

“This is seen in both theoretical and observational work (see, e.g., Combes & Gerin 1985; Athanassoula 1992; Sellwood & Wilkinson 1993; Piner et al. 1995; Sakamoto et al. 1999; Rautiainen & Salo 2000; Regan & Teuben 2003, 2004; Athanassoula 2005; Sheth et al. 2005; Wozniak 2007; Knapen 2007; Gadotti…”

“Numerical simulations based on gas dynamics give a clue to bar-induced fueling in disk galaxies (Sanders & Huntley 1976; Combes & Gerin 1985; Shlosman, Frank, & Begelman 1989; Athanassoula 1992; Friedli, Benz, & Kennicutt 1994; Englmaier & Gerhard 1997; Ann & Thakur 2005).”

“…& 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…”

“Athanassoula (1992) observed this gas response of centered shocks when no ILR(s) were present in the model.”

“The effect of large-scale bars has been studied in detail by simulations which have successfully shown that bars are very efficient for transporting the gas towards the center (e.g. Sparke & Sellwood 1987; Athanassoula 1992; Shlosman & Noguchi 1993; Heller & Shlosman 1994; Athanassoula 2003).”

“The distance from the center at which the flow stalls depends both on where the quadrupole field of the bar weakens and whether an inner Lindblad resonance (ILR) exists to halt the flow (Athanassoula 1992).”

“We know that bars often have strong dust lanes running along the leading edges of the bar (e.g. Athanassoula 1992), so in principle offset spurs could be the result of extinction along the bar leading edges.”

“…of star formation rings being the consequence of gas responding to a bar-shaped potential is generally accepted, and is nicely illustrated e.g. in Athanassoula (1992): dynamical resonances associated with the non-axisymmetric rotating bar potential cause the orbiting gas to lose angular momentum…”

“It also mimics numerically simulated distributions of materials orbiting in a barred potential (see, e.g., Athanassoula 1992).”

“Extensive hydrodynamic modeling of the galaxy has been done by Huntley (1978) and Athanassoula (1992b).”

“An additional term is introduced in the continuity equation to implement the recycling law of Athanassoula (1992).”

“As for the stars, the inward move- ment of the gas particles lying in the inner zones is due to thebar (Roberts et al. (1979); Athanassoula (1992)); this gas fallto the innermost regions following orbits with an important radial component.”

“…particle hydrodynamics (SPH) technique (e.g., Englmaier & Gerhard 1997; Patsis & Athanassoula 2000; Ann & Thakur 2005; Thakur et al. 2009) and (2) those using a grid-based algorithm (e.g., Athanassoula 1992b; Piner et al. 1995; Maciejewski et al. 2002; Maciejewski 2004b; Regan & Teuben 2003, 2004).”

“The analysis is novel because previous studies (Tubbs 1982 ; Athanassoula 1992b ; Reynaud & Downes 1998) have only sought to explain the lack of bar star formation.”

“…of gas in a bar potential is complex, depending on the local environment of the interstellar medium (ISM) and how the bar evolves (see e.g., Athanassoula 1992; Piner et al. 1995; Englmaier & Shlosman 2000; Wada & Koda 2001; Maciejewski et al. 2002; Regan & Teuben 2004; Fragkoudi et al.…”

“Because the characteristic offset dust lanes delineating shocks exist only in a narrow range of a fast bar parameters (e.g., Athanassoula 1992), we do not expect them to exist or, at least, to have their usual shape, during ∼ 1 Gyr of the buckling and some time thereafter, when the bar is a slow…”

“The simulations are not self-consistent and we do not consider the self-gravity of the gas ; the Ñow is calculated using the potential described in Paper I (see also Athanassoula 1992a, hereafter A92a).”

“Given that IR photometry suggests a bar length Rb of about 0.45R0, this implies a ratio RCR/Rb of about 1.25 ± 0.2, in agreement with the few estimates for external galaxies (Merrifield & Kuijken 1995; Lindblad et al. 1996; Gerssen et al. 1999) and simulations (Athanassoula 1992).”

“…et al. 2013), and orbital changes from the disruptive (mergers; e.g., Darg et al. 2010a,b; Lotz et al. 2008a,b) to the relatively subtle (e.g., bars, Athanassoula 1992; Sellwood & Wilkinson 1993; Athanassoula 2005; Athanassoula et al. 2013, and for studies of visually-identified bars at z > 0…”

“In order to avoid transients, we introduce the bar gradually, as is common practice in simulations of gas flow in barred potentials (e.g. Athanassoula 1992).”

“The inflow could be measured if density-weighted galactic radial velocities could be found at all azimuth angles, assuming steady state flow (Athanassoula 1992, hereafter A92).”

“In concordance with Athanassoula (1992), we model Rb(t) such as to keep the ratio against the co-rotation radius constant b ≡ Rb(t) RCR(t) = const.”

“According to gas dynamical simulations by Athanassoula (1992), the existence of leading offset dust lanes in the bars tells us two things: that there is an ILR and that R = 1.2 ± 0.2.”

“One piece of evidence for the formation was already provided by Athanassoula (1992b), who showed that the existence of offset bar dust lanes is related to the existence of stable stellar bar orbits whose major axis is perpendicular to the major axis of the bar (x2 orbits in the nomenclature of…”

“…being able to drive strong inflows of gas towards the central galactic regions (e.g. Sanders & Huntley 1976; Roberts, Huntley & van Albada 1979; Athanassoula 1992) and triggering nuclear star-bursts (e.g. Ho, Filippenko & Sargent 1997; Martinet & Friedli 1997; Hunt & Malkan 1999; Laurikainen,…”

“A bar needs to be fast for the shocks to remain curved with their concave sides towards the bar major axis, as is usually observed (van Albada & Sanders 1982; Athanassoula 1992).”

“As x2 orbits cannot extend past the bar edges, more elongated bars will tend to have 6 We point out that, with all things being equal, more eccentric bars will have smaller nuclear discs, since the extent of the x2 orbits is then shorter (see Athanassoula 1992).”

“The rationale for a relatively constant PA is that the main x1 family of barsupporting orbits can be modeled by concentric ellipses with a fairly constant PA as a function of semimajor axis in the bar region (Athanassoula 1992b).”

“Various compelling theoretical arguments indicate that bars in galaxies are indeed an efficient mechanism for channeling gas from the outer to the nuclear regions of spirals (Shlosman, Begelmann, & Frank 1990, Athanassoula 1992, Buta & Combes 1996).”

“For this reason, we will discuss here first the relevant observational results and then present simulated PVDs of the gas component in a strongly barred galaxy model from Athanassoula (1992a).”

“Kinematical studies have shown that bars should be fast even in late-type galaxies (e.g. due to dust lane placement Athanassoula 1992, and hydrodynamical simulations Weiner et al. 2001).”

“As gas crosses these shocks, it loses angular momentum resulting in inflow towards the centre (e.g. Athanassoula 1992; Maciejewski et al. 2002).”

“…is agreed that the presence of a galactic bar can have significant influence on angular momentum and redistribution of gas, including inflow toward the central regions (e.g., Combes & Gerin 1985; Athanassoula 1992, 2000; Knapen et al. 1995a; Heller & Shlosman 1996; Maciejewski et al. 2002).”

“In particular, Athanassoula (1992a) studied orbits in analytic potentials of barred galaxies and showed that generalized ellipses are a good representation of the main barsupporting stellar orbits.”

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

“Numerical studies of gas dynamics find that stellar bars remove a steady fraction fbar of the local gas mass per rotation; 0.01 ∼< fbar ∼< 0.1 (Athanassoula 1992; Wada & Habe 1992; Friedli & Benz 1993; Heller & Shlosman 1994; Athanassoula 1994).”

“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).”

“These dust lanes, often observed offset toward the leading edges of the bar structure in barred spirals, have been identified as tracers of shocks (e.g., Roberts et al. 1979; Athanassoula 1992b).”

“Dust lanes along the leading edges of the bar are expected from theoretical work (Athanassoula 1992), and in the case of NCG 1433 end at the inner disc (see also Sormani et al. 2018).”

“The usual convention is that a slow bar is one that has a ratio R ≡ RCR/Rb > 1.4 and a fast bar is one with 1.0 R 1.4 (e.g., Athanassoula 1992).”

“Those are known to extend to their corotation (Athanassoula 1992).”

“To minimize the number of free parameters characterizing our models, we followed Athanassoula (1992a) in adopting analytical forms for the various potential components.”

“An efficient way to drag significant amount of mass in the central regions would be the presence of a large scale bar in the host galaxy, which could initiate strong inflows of gas (e.g. Athanassoula 1992; Friedli & Benz 1993).”

“In fact, this has been observed in a number of nearby galaxies (Athanassoula 1992c; Puerari et al 2000).”

“…lanes are located at the leading sides of the bar and the southwestern part of the galaxy is the near side, indicating that the deviations associated with the dust lanes seen in Figure 14 could be radial inÑowing motion along the bar, as predicted by theory (Robert et al. 1979 ; Athanassoula 1992).”

“Some of the gas will reach the center and produce a disclike bulge (Athanassoula 1992, 2005).”

“• Theoretical studies show that, in the frame of the bar, the velocity of the gas is approximately parallel to the dust lanes, and that the gas plunges along the dust lanes directly from Galactocentric distances of R ∼ 3kpc down to the CMZ (e.g. Athanassoula 1992; Sormani et al. 2015a, 2018).”

“These bars have been shown both theoretically (Athanassoula 1992, 2000) and observationally to drive gas inflows and nuclear starbursts (Jogee et al. 1999, 2002, 2005; Petitpas & Wilson 2002, 2003).”

“Models predict shocks predominantly at the leading edges of such bars (cf. Athanassoula 1992, 1992).”

“The main premise of this understanding is that the asymmetric potential outlined by the bar extracts angular momentum from the gas, which flows inwards as a result (Prendergast 1983; Shlosman, Begelman & Frank 1990; Athanassoula 1992).”

“The transition happens through the mediation of large-scale shocks, which correspond to observed dust lanes in external barred galaxies (Athanassoula 1992).”

“When 1 < R < 1.4, the bar is classified as ‘fast’ (Athanassoula 1992; Debattista & Sellwood 2000; Athanassoula 2014).”

“11 in Athanassoula 1992).”

“We expect star formation to occur as gas falls into the spiral-arm potential (Wada et al. 2011; Athanassoula 1992).”

“…studied using numerical simulations on hydrodynamical models (e.g. Sanders & Huntley 1976; Roberts et al. 1979; van Albada & Roberts 1981; Athanassoula 1992b; Piner et al. 1995; Englmaier & Gerhard 1997; Patsis & Athanassoula 2000; Maciejewski et al. 2002; Maciejewski 2004a,b; Regan &…”

“The structure of these dust-lanes, which are not curved inward toward the center, suggests that there is no ILR in this galaxy (Athanassoula 1992a,b).”

“Such results have also been established in hydrodynamical mod- els (Prendergast 1983; Athanassoula 1992; Piner et al. 1995) which also showed that gas concentration on the leading side corresponds to shocks.”

“…but metalpoor companion galaxy, which subsequently fragmented as a result of the encounter (BH81, Schweizer & Seitzer 1988, MvDB95, MvD96, Smith et al. 1996, hereafter S96; modeled by Athanassoula 1992 and Piner, Stone & Teuben 1995), or perhaps we are currently seeing a newly-formed disc.”

“Theoretical models of gas dynamics in barred galaxies suggest that gas flow produces arms of gas/du t density enhancement that extend from the leading side of the bar (Athanassoula 1992).”

“More precisely, stars in the nuclear disc or nuclear ring form in-situ from gas that has been A65, page 11 of 29 funnelled to the centre by the bar (see e.g. Athanassoula 1992b,a; Piner et al. 1995; but also Kormendy & Kennicutt 2004 for a review).”

“Figure 4 in Athanassoula (1992) shows a model simulation that could be like part of NGC 2366.”

“This result suggests that we need a relatively massive and concentrated bulge to support the formation ofx2-type rings, which is consistent with previous simulation results (e.g., Athanassoula 1992b; Regan & Teuben 2003).”

“…Canzian & Allen 1997; Puerari & Dottori 1997; Aguerri et al. 1998; Buta & Zhang 2009), the offset and shape of dust lanes (van Albada & Sanders 1982; Athanassoula 1992), or the morphology of the residual gas velocity field after rotation velocity subtraction (Sempere et al. 1995b; Font et al.…”

“…bars greatly influence evolution of gas in disks by exerting a non-axisymmetric gravitational torque and by creating gaseous substructures such as dust lanes and nuclear rings (e.g., Sanders & Huntley 1976; Athanassoula 1992; Buta & Combes 1996; Martini et al. 2003a, 2003b; Kim et al. 2012a).”

“…galaxies, it is commonly accepted that the effect of the bar is to transport gas from the inner disk to the galaxy’s centre – see for example the observational studies of M100 (Allard et al. 2006) and NGC1365 (Zánmar Sánchez et al. 2008), as well as numerical work (e.g. Athanassoula 1992).”

“A common way of exploring the orbital structure of such systems has been by studying closed periodic orbits (CPO’s) in a frame of reference co-rotating with the bar (e.g. Contopoulos 1980; Athanassoula 1992a; Dehnen 2000; Patsis et al. 2002; Sormani et al. 2015a; Fragkoudi et al. 2015).”

“Furthermore, bars cause gas to shock (see Athanassoula, 1992, for a detailed analysis; the concept was first proposedby Prendergast, unpublished c1962), resulting in additional inflow.”

“…hydrodynamical simulations in such barred potentials emphasize the importance of the orbital resonance (Inner/Outer Lindblad Resonance:ILR/OLR) in promoting both central gas inflow (e.g. Athanassoula 1992b; Sellwood & Wilkinson 1993; Byrd et al. 1994) and radial outflow (Buta & Combes 1996).”

“The reason for this behavior is the smaller region where orbits exist.x2Indeed, sometimes the inner Lindblad resonance is redeÐned as the radius inside which these orbits are stable (van Albada & Sanders 1982 ; Athanassoula 1992a).”

“…(R ≤ 4 kpc), we see a typical gas flow driven by the bar, with a pair of off-axis shocks (corresponding to the dust-lanes) and a circum-nuclear ring, which is commonly observed in nearby barred galaxies (e.g., Sanders & Huntley 1976; Athanassoula 1992; Buta & Combes 1996; Martini et al. 2003).”

“Assuming the standard corotation radius to bar length ratio rCR/rb = 1.2 for early-type barred galaxies (e.g., Athanassoula 1992; Gerssen, Kuijken & Merrifield 2003 and references therein), rCR ≈ 30 ′′.”

“In theoretical calculations, the high shear and/or diverging streamlines (caused by changing orbits) present at the location of the gas lanes along the stellar bar either prevent clouds from forming or tears them apart before star formation can happen (e.g. Athanassoula 1992; Regan et al. 1997).”

“Self-consistent Bars Orbital calculations in barred-disk potentials show that bars should end at or inside their corotation radii (see, e.g., Contopoulos 1980 ; Athanassoula 1992a ; for a review, see Contopoulos & 1989).”

“For the purpose of this work, we adopt a radial inflow velocity profile induced by a bar of current size RB = 3. kpc, having a corotation radius at RC = 1.2 RB, which is a typical relation between bar length and corotation radius (e.g. Athanassoula 1992).”

“Pseudobulge and ring are results of bar-induced gas flows as discussed e.g. in Athanassoula (1992).”

“The curvature of the dust lanes has theoretically been related to the strength of the bar, in the sense that weak bars are associated with curved dust lanes, whereas strong bars have straight dust lanes (Athanassoula 1992b).”

“According to numerical modelling of gas in a bar potential (Athanassoula 1992), the flow velocity of gas and magnetic fields is faster than the pattern speed of the bar and enters the bar from the receding side.”

“For instance, torques from bars are well-know to drive gas infall towards the galactic centre (Roberts et al. 1979; Athanassoula 1992; Garćıa-Burillo et al. 2014; Emsellem et al. 2015).”