The existence and shapes of dust lanes in galactic bars

“Despite the fact that the stability is not indicated, one can see from the shape of the characteristics that in the 2D Ferrers bar model in Athanassoula (1992a) the families in the upper part of the 4:1 resonance gap are introduced via tangent bifurcations.”

“Because of orbit crowding, massive star formation occurs predominantly at the apocenters of the x 2 orbits (Athanassoula 1992b), oriented symmetrically on either side of the nucleus.”

“Most of the two components might be interpreted in terms of x1 and x2 orbits. x1 orbits are parallel to the large-scale bar (building up the straight gas lanes), and x2 orbits are perpendicular to the bar (Contopoulos & Grosbol 1989, Athanassoula 1992, van der Laan et al. 2011).”

“For barred spiral galaxies, the ring can be formed inside the large scale galactic spiral structure if the bar pattern speed, Ωb, closely matches the inner Lindblad precession frequency (Ω − κ/2), where Ω is angular velocity and κ is the radial epicyclic frequency (Athanassoula 1992).”

“If a dynamical reso- 1 nance (the so-called inner Lindblad resonance, hereafter ILR; e.g., Contopoulos 1975; Athanassoula 1992) exists, gas will tend to pile up in a ring around the ILR radius (there can be 0, 1, or 2 ILRs, or in the case of a large central mass concentration, even a third ILR; gas…”

“…the response of gaseous or stellar particles to barred, spiral, or lopsided potentials, (e.g., among many articles, Combes & Sanders 1981; Athanassoula 1992; Wada 1994; Sellwood & Binney 2002; Maciejewski 2004; Bournaud et al. 2005; Quillen et al. 2011; Grand et al. 2012; Minchev et al.…”

“In ad- dition, Miwa & Noguchi (1998) claimed that the tidally induced bars end at the Inner Lindblad Resonance, whereas the bars formed in isolation extend up to roughly 80% to 100% of the Corotation Resonance (Athanassoula 1992a,b).”

“A number of theoretical studies suggest various mechanisms of gas and star mixing in barred galaxies (Athanassoula 1992; Sellwood & Binney 2002; Schönrich & Binney 2009; Minchev & Famaey 2010; Di Matteo et al. 2013; Minchev et al. 2013, 2014), which could lead to the flattening of the oxygen…”

“Simulations have shown that a circumnuclear ring connected to the leading-edge lanes on the bar naturally results from the non-axisymmetric gravitational potential (Athanassoula 1992).”

“The bar strength – Theoretical predictions (Athanassoula 1992a,b) suggest that the degree of dust-lane curvature in barred galaxies is inversely proportional to the bar strength, i.e. dust lanes with greater curvature are found in the weaker bars.”

“Fast bars are defined as having 1 1.4, while slow bars have > 1.4 (Debattista & Sellwood 2000); < 1 is not allowed by the orbital structure of barred disks (e.g., Contopoulos 1980; Athanassoula 1992a).”

“The nonaxisymmetric gravitational potential originated by a large-scale bar in the host galaxy has also been suggested as an efficient way to drive the gas to the central region (Shlosman, Begelman, & Frank 1990; Athanassoula 1992).”

“Athanassoula (1992) notes that these dust lanes generally fall in two categories: (i) straight dust lanes which are parallel to each other but make an angle with the bar major axis and (ii) curved dust lanes which are parallel to the bar major axis but offset toward the leading edges and with their…”

“These dust lanes trace the shock front in the gas towards the edges of the bar, predicted by theoretical models (Roberts et al. 1979; Athanassoula 1992).”

“However, there exists another possibility that the NE/SW gas were excited by bar-induced shocks, which can inhibit star formation when the shock and shear is too strong (e.g. Athanassoula 1992; Reynaud & Downes 1998).”

“Using Rcor ∼ (1.2−1.4)×Rbar (Athanassoula 1992), appropriate for fast rotating bars, also gives a similar Rcor ∼ 1 kpc.”

“This may be due to the fact that Epic5 reproduces a weak bar model while the bar in NGC 1097 would easily qualify as a strong bar, and it is expected that dust lanes are more straight as they get stronger (Athanassoula 1992; Knapen et al. 2002; Comerón et al. 2009).”

“…the bar might enhance star formation (hereafter SF) due to a shock, and the enhanced gravitational potential at the tips creates an aggregation of molecular clouds with a higher rate of cloud-cloud collisions than in the restof the galaxy (Athanassoula 1992; Tasker & Tan 2009; Ohishi et al. 2012).”

“Many previous studies based on both observations and simulations have reported that non-circular motion is large in the bar (e.g., Athanassoula 1992, Raynaud & Downes 1998, Watanabe et al. 2011, Fujimoto et al. 2014, Maeda et al. 2018, Sun et al. 2018).”

“According to various studies (Athanassoula 1992; Elmegreen 1996; Aguerri et al. 2003), the expected range for the bar length lies between rbar = rL/1.0 and rbar = rL/1.4.”

“REFERENCES Aguerri J. A. L., Debattista V. P., Corsini E. M., 2003, MNRAS, 338, 465 Athanassoula E., 1992, MNRAS, 259, 345 —, 2003, MNRAS, 341, 1179 —, 2005, MNRAS, 358, 1477 Athanassoula E., Sellwood J. A., 1986, MNRAS, 221, 213 Bland-Hawthorn J., Gerhard O., 2016, ARA&A, 54, 529 Bullock J. S., Dekel A., Kolatt T. S.…”

“…flow in such a strong bar potential can trigger shocks at the leading edge of the bar, appearing as dust lanes following the orbital skeleton (e.g., Athanassoula 1992; Sellwood & Wilkinson 1993; Buta & Combes 1996; Lindblad 1999; Pastras et al. 2022; Sellwood & Masters 2022; see also Figure 1 of…”

“The ratio between the corotation radius of the outer bar and its length is greater than 1 (Table 1, col- c© 2014 RAS, MNRAS 000, 1–5 umn 9), agreeing with simulations by Athanassoula (1992).”

“Much theoretical and modeling work has been done on the formation of circumnuclear rings (e.g. Athanassoula 1992b; Englmaier & Shlosman 2000; Regan & Teuben 2003; Maciejewski 2004).”

“…be explained by the probably unusual interaction history of the galaxy (Balick & Heckman 1981; Mulder & van Driel 1996; Smith et al. 1996; Kregel & Sancisi 2001; Elmegreen et al. 2002), fuelling the ring with accreted neutral gas, as modelled by Athanassoula (1992) and Piner, Stone & Teuben (1995).”

“In other models these three families have disconnected characteristics (see e.g. Contopoulos & Grosbol 1989; Athanassoula 1992a; Patsis & Katsanikas 2014a).”

“The great majority of nuclear rings is believed to form as a result of gas inflow along shocks delineated by dust lanes at the leading edge of the bar (e.g., Athanassoula 1992).”

“We specifically assume RCR=1.2 aB (Athanassoula 1992), where aB = 80 ′′ is the bar length measured by Herrera-Endoqui et al. (2015, see also Figure 1).”

“Some previous studies proposed that GMCs cannot form due to a strong shock and/or shear along the bar (e.g. Tubbs 1982; Athanassoula 1992; Reynaud & Downes 1998).”

“One of the most important mechanisms related to bars is that the non-axisymmetric potential of strong bars exerts torques on the gas, and drives it toward the center of galaxies (Schwarz 1981; Athanassoula 1992b, hereafter A92b; Regan et al. 1999; Sormani et al. 2015; Fragkoudi et al. 2016).”

“…galaxies is understood to be due to the result of bar-driven processes that funnel the gas inwards, which aids in intense nuclear star formation (Athanassoula 1992; Ho et al. 1997a; Sheth et al. 2005; Coelho & Gadotti 2011; Ellison et al. 2011; Oh et al. 2012; Wang et al. 2012; Lin et al. 2020;…”

“As pointed out by Athanassoula (1992), a good indicator of the mean inflow rate is the mass-averaged radial velocity, 〈v r〉.”

“In order to avoid transients in the disc, we introduce the non-axisymmetric potential over a finite period of time, which was found empirically as ∼3 bar rotations, in accordance with previous studies (Athanassoula 1992b; Patsis & Athanassoula 2000).”

“In galaxies with inner rings that form at inner Lindblad resonances, the rings are expected to be elongated perpendicular to the bar, since they form at the family of orbitsx2(Sanders & Huntley 1976 ; Athanassoula 1992 ; Buta & Crocker 1993).”

“In addition, numerical simulations also show that inflows in bars are expected to be 5 km s−1 (e.g., Athanassoula 1992), but not of tens of kilometers per second as observed in most objects.”

“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) and Weiner & Sellwood (1999) to study gas dynamics in bar potentials.”

“In the presence of a bar, gas loses angular momentum and falls toward the centre of the galaxy, where it tends to form an elongated orbit inside the stellar bar (Athanassoula 1992; Combes & Elmegreen 1993; Maciejewski et al. 2002; Martel et al. 2013, hereafter Paper I).”

“In galaxies with inner Lindblad resonances, gas can accumulate on approximately circular orbits near the galactic center (e.g., Buta 1986; Athanassoula 1992; Maciejewski et al. 2002), and this is the case in NGC 1808, where an inner resonance has been found close to the radius of the 500 pc ring…”

“The dividing value at 1.4 between long/fast and short/slow bars is given by consensus (Athanassoula 1992; Debattista & Sellwood 2000) and it does not imply a specific value of the pattern speed.”

“…is consistent with observations (e.g., Kent 1987; Elmegreen 1996; Aguerri et al. 2003) and supported by orbital studies (e.g., Contopoulos 1980; Patsis et al. 1997),N-body simulations (e.g., Sparke & Sellwood 1987; Pfenniger & Friedli 1991), and hydrodynamic simulations (Athanassoula 1992b).”

“Athanassoula (1992) first showed how the orbits in barred galactic potentials lead to gas shocking on the leading edges to form dust lanes with the shocked gas then flowing along the potential to the centre.”

“Athanassoula (1992) has experimented with two-dimensional time-dependent hydrodynamical simulations that produce dust lanes in barred spiral galaxies.”

“…enhancement of nuclear starburst events and the slow buildup of the “pseudo-bulges” in barred galaxies (e.g., Kormendy 1982; Pfenniger & Friedli 1991; Athanassoula 1992; Martin 1995; Ho et al. 1997a; Kormendy & Kennicutt 2004; Sheth et al. 2005; Athanassoula 2005; Ann & Thakur 2005; Coelho &…”

“…of gas at large radii caused by angular momentum loss due to its nonlinear interactions with an underlying stellar bar potential (e.g, Combes & Gerin 1985; Shlosman et al. 1990; Athanassoula 1992; Heller & Shlosman 1994; Knapen et al. 1995; Buta & Combes 1996; Kim et al. 2012b; Kim & Stone 2012).”

“A bar that forms can increase a central mass, for example, by driving gas inflows (e.g., Athanassoula 1992; Buta & Combes 1996; Kim et al. 2012), which in turns weakens or destroys the bar by disturbing bar-supporting x1 orbits (e.g., Pfenniger & Norman 1990; Hasan et al. 1993; Norman et al. 1996;…”

“These are interpreted (Athanassoula 1992) as the signature of gas shocks (e. g., Regan et al. 1997) that result from non-circular forces produced by bars and that result in gas flow toward the center.”

“Theoretical arguments related to the observed morphology of bars indirectly lead to the conclusion that bars must rotate fast (Sanders & Tubbs 1980; Athanassoula 1992).”

“According to Athanassoula (1992), gas density enhancements perpendicular and at the end of the bar are often seen in simulations.”

“Comparisons with Recent Models Previous models have indicated that in order to create and sustain nuclear bars and rings, there must be some form of viscous gas component that can dissipate energy (Combes & Gerin 1985; Athanassoula 1992; Friedli & Martinet 1993; Shaw et al. 1993).”

“This leads to an enhancement in star formation at the nuclear regions of barred galaxies and along the bar itself (Athanassoula 1992; Ho et al. 1997; ? koshyastro@gmail.com Sheth et al. 2005; Coelho & Gadotti 2011; Ellison et al. 2011; Oh et al. 2012).”

“…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 growing bar will also funnel gas to the centre of the galaxy along the arms of the bar (Sorensen et al. 1976; Athanassoula 1992a; Davoust & Contini 2004; Villa-Vargas et al. 2010; Vera et al. 2016; Spinoso et al. 2017; George et al. 2019).”

“As a result, offset shocks form on the leading sides of the bars, which correspond to dust lanes in observed barred spiral galaxies (Athanassoula 1992b).”

“These concentrations are formed by gas dynamical effect by the bar potential (e.g. Athanassoula 1992; Wada & Habe 1992).”

“Several methods have been developed for measuring the pattern speed of bars, including hydrodynamic simulations [201–208] and the shape of dust lanes in the bar regions of some barred galaxies [209, 210].”

“For the interpretation of optical and radio observations of bar galaxies it is important to consider the effect of spraying as predicted from N–body calculations (Athanassoula 1992) and used, for instance, to explain the observations of NGC 1530 (Downes et al. 1996).”

“Galaxy type L S0/a Sa Sab Sb Sbc Sc Scd Sd Sdm Sm Irr Normal 22 3 11 4 16 15 19 23 18 13 2 11 SAB 3 0 1 1 6 7 13 8 4 5 1 2 SB 4 7 4 4 19 7 12 16 13 7 10 3 of star formation (e.g., Roberts et al. 1979; Elmegreen 1988; Athanassoula 1992; Piner et al. 1995).”

“It is known that the orbital motions within the bar induce intense shear (velocity gradient) in the ISM, which could prevent the formation of massive objects (Athanassoula 1992; Hopkins 2012).”

“…nuclear rings, almost exclusively found in barred galaxies (Buta & Combes 1996), are attributed to shock focusing of gas near the location of one or more inner Lindblad resonances (ILRs; Schwarz 1984; Athanassoula 1992; Heller & Shlosman 1996; see also Shlosman 1999; Knapen 2005 for reviews).”

“Bars have often been suggested as a means by which gas may be funneled into the nuclei of galaxies, thus leading to enhanced star formation (Noguchi 1988; Athanassoula 1992; Wada & Habe 1992; Friedli & Benz 1993; Heller & Shlosman 1994; Wada & Habe 1995).”

“It is important to point out that there are substantial differences between the properties of galaxies in most simulations of barred galaxies and in IRAS08 (e.g., Athanassoula 1992; Regan et al. 1997; Maciejewski et al. 2002).”

“In many barred-spiral galaxies, galactic centers host intersections of x1 and x2 orbits 19 (Athanassoula 1992; Seo & Kim 2013; Sormani & Li 2020).”

“Theoretical studies suggest that circumnuclear rings arise due to a bar-driven inflow of gas and dust to an in- ner Lindblad resonance (ILR) or between two ILRs (e.g. Combes & Gerin 1985; Athanassoula 1992; Byrd et al. 1994; Piner et al. 1995).”

“(Athanassoula 1992; Noguchi 1999; Immeli et al. 2004; Debattista et al. 2006; Elmegreen et al. 2009).”

“Based on these experimental results, an OILR is required in order to simulate the nuclear ring and the gas dust lanes, confirming the results obtained by Athanassoula (1992).”

“There they induce the formation of spiral or ring structures (Prendergast 1983; Athanassoula 1992a,b; Englmaier & Shlosman 2000; Maciejewski 2004; Combes 2004).”

“This galaxy exhibits photometric and kinematical evidence of a bar (Cortés et al. 2006) which skews the isovelocity contours parallel to the major axis of the bar (Athanassoula 1992; Vauterin & Dejonghe 1997).”

“Models of orbits in barred, tri-axial potentials indicate that gas in the inner CMZ is likely to be moving on x2 orbits elongated along the minor axis of the bar (Contopoulos & Papayannopoulos 1980; Athanassoula 1992a,b).”

“In fact, some authors have redefined the ILR-radius so that it means the radius with the outermost stable x2orbits (van Albada & Sanders 1982; Athanassoula 1992a; Miwa & Noguchi 1998).”

“…a huge amount of research work has been devoted to understand the orbital structure in barred galaxy models (e.g., Athanassoula et al. 1983; Pfenniger 1984; Combes et al. 1990; Athanassoula 1992; Pfenniger 1996; Kaufmann & Contopoulos 1996; Ollé & Pfenniger 1998; Pichardo, Martos, & Moreno 2004).”

“Athanassoula (1992) studied and modeled the existence and shapes of gas and dust in barred bulges and showed the presence of shocks with velocity jumps and characteristic shapes.”