What determines the sizes of bars in spiral galaxies?

Abstract

I use volume-and mass-limited subsamples and recently published data from the Spitzer Survey of Stellar Structure in Galaxies (S 4 G) to investigate how the size of bars depends on galaxy properties. The known correlation between bar semi-major-axis a and galaxy stellar mass (or luminosity) is actually bimodal : for log (M /M ) 10.1, bar size is almost independent of stellar mass (a ∝ M 0.1 ), while it is a strong function for higher masses (a ∝ M 0.6 ). Bar size is a slightly stronger function of galaxy halflight radius R e and (especially) exponential disc scale length h (a ∝ h 0.8 ). Correlations between stellar mass and galaxy size can explain the bar-size-M correlation -but only for galaxies with log (M /M ) 10.1; at higher masses, there is an extra dependence of bar size on M itself. Despite theoretical arguments that the presence of gas can affect bar growth, there is no evidence for any residual dependence of bar size on (present-day) gas mass fraction. The traditional dependence of bar size on Hubble type (longer bars in early-type discs) can be explained as a side-effect of stellar-mass-Hubble-type correlations. Finally, I show that galaxy size (R e or h) can be modeled as a function of stellar mass and both bar presence and bar size: barred galaxies tend to be more extended than unbarred galaxies of the same mass, with larger bars correlated with larger sizes.

Relations among structural parameters in barred galaxies with a direct measurement of bar pattern speed

“…The conclusions from Sheth et al (2008) were subsequently partially questioned. In particular, Erwin (2018Erwin ( , 2019 argued that those conclusions may be affected by a detection problem. SDSS-based studies preferentially miss bars in lower mass, bluer, and gas-rich galaxies due to poor spatial resolution; instead, Erwin found that bars are as common in blue gas-rich galaxies as they are in red gas-poor galaxies using Spitzer data (Erwin 2018).…”

“…By performing a bi-dimensional decomposition on multiband SDSS images of 700 galaxies, Sanchez-Janssen & Gadotti (2013) found that barred discs tend to have fainter central surface brightness, and larger disc scalelengths h than unbarred galaxies of the same stellar mass (M * > 10 10 M ). Barred galaxies appear to be more extended than the unbarred counterparts (Erwin 2019). Consolandi (2016) found that massive spiral galaxies harbour red and dead bars, which become even redder with increasing galaxy mass.…”

“…These conclusions were partially revised with the advent of the S 4 G survey (e.g. Herrera-Endoqui et al 2015;Díaz-García et al 2016a,b;Erwin 2019). Díaz-García et al (2016a) found that bars in LTBGs (T > 5) are unexpectedly long with respect to both R 25 and h, while their physical sizes are small.…”

Bulge formation through disc instability

“…This simplification brushes over the complexity and diversity of galactic morphologies, for example, the distinction between normal and barred spirals (Hubble 1926). Gadotti (2009), Weinzirl et al (2009), Salo et al (2015), and Erwin (2018Erwin ( , 2019 have considered more detailed models that decompose galaxies into three components: a disc, a bulge, and a bar if present. Despite the clear merit of such decompositions, this approach is possible only for relatively small samples of a few thousand nearby galaxies, such as the Spitzer Survey of Stellar Structure in Galaxies (S 4 G; Sheth et al 2010).…”

“…Hence, it is reasonable for us to neglect them in an article that is about stellar discs. 3 We acknowledge that a bar and a bulge are different dynamical entities, and that it is possible to separate in a morphological decomposition (Gadotti 2009;Weinzirl et al 2009;Salo et al 2015;Erwin 2018Erwin , 2019. We merely state that SAMs are not an appropriate tool for such decomposition.…”