Bar formation as driver of gas inflows in isolated disc galaxies

Abstract

Stellar bars are a common feature in massive disc galaxies. On a theoretical ground, the response of gas to a bar is generally thought to cause nuclear starbursts and, possibly, AGN activity once the perturbed gas reaches the central super-massive black hole. By means of high resolution numerical simulations we detail the purely dynamical effects that a forming bar exerts on the gas of an isolated disc galaxy. The galaxy is initially unstable to the formation of non-axisymmetric structures, and within ∼ 1 Gyr it develops spiral arms that eventually evolve into a central stellar bar on kpc scale. A first major episode of gas inflow occurs during the formation of the spiral arms while at later times, when the stellar bar is establishing, a low density region is carved between the bar co-rotational and inner Lindblad resonance radii. The development of such "dead zone" inhibits further massive gas inflows. Indeed, the gas inflow reaches its maximum during the relatively fast bar formation phase and not, as often assumed, when the bar is fully formed. We conclude that the low efficiency of long-lived, evolved bars in driving gas toward galactic nuclei is the reason why observational studies have failed to establish an indisputable link between bars and AGNs. On the other hand, the high efficiency in driving strong gas inflows of the intrinsically transient process of bar formation suggests that the importance of bars as drivers of AGN activity in disc galaxies has been overlooked so far. We finally prove that our conclusions are robust against different numerical implementations of the hydrodynamics routinely used in galaxy evolution studies.

The buildup of strongly barred galaxies in the TNG100 simulation

“…A general picture is that the gas is torqued by the bar and funnelled into the inner Lindblad Resonance or pushed towards the outer Lindblad Resonance. The gas then will be shocked and will end up in a rapid burst of star formation or feeding the supermassive black hole located at the galaxy centre (Maciejewski 2004;Fanali, et al 2015). Depending on the evolution of the strength and length of the bar, rings or Figure 14.…”

Discovery of an Active Intermediate-mass Black Hole Candidate in the Barred Bulgeless Galaxy NGC 3319

“…The hydrodynamical simulations don't only show that a bar is indeed able to transfer gas to the galactic center and form a central mass concentration, but also suggest that a seed SMBH could be created (e.g., Sellwood & Moore 1999;Fanali et al 2015). Li et al (2017) has revisited the model and argue that a NSC and perhaps a massive BH could form from the concentrated gas of low angular momentum during the bar-driven gas inflow, which will stall at a nuclear ring when the mass of the central object exceeds 1% of the disk mass.…”

Galaxy-scale Bars in Late-type Sloan Digital Sky Survey Galaxies Do Not Influence the Average Accretion Rates of Supermassive Black Holes

“…Secular evolution is expected to be primarily driven through large-scale instabilities, such as dynamic bars (e.g., Shlosman & Noguchi 1993;Courteau et al 1996;Bournaud & Combes 2002;Sheth et al 2005;Cheung et al 2013;Sánchez-Janssen & Gadotti 2013;Sellwood 2014), which may have been induced by an early merger (Noguchi 1987). Through angular momentum exchange, bars generate radial flows that are capable of transporting kiloparsec-scale gas down to approximately parsec scales, close to the galaxy center (e.g., Shlosman et al 1989;Friedli & Benz 1993;Wang et al 2012;Fanali et al 2015). The resulting cool gas reservoir may serve to feed the BH, and hence, bars are proposed as viable mechanisms to trigger AGN activity in spiral galaxies (e.g., Shlosman et al 1990;Wada & Habe 1995;Bournaud & Combes 2002;Athanassoula 2003;Laurikainen et al 2004;Jogee 2006).…”