Simulating a slow bar in the low surface brightness galaxy UGC 628

Abstract

We present a disc-halo N-body model of the low surface brightness galaxy UGC 628, one of the few systems that harbours a "slow" bar with a ratio of corotation radius to bar length of R ≡ R c /a b ∼ 2. We select our initial conditions using SDSS DR10 photometry, a physically motivated radially variable mass-to-light ratio profile, and rotation curve data from the literature. A global bar instability grows in our submaximal disc model, and the disc morphology and dynamics agree broadly with the photometry and kinematics of UGC 628 at times between peak bar strength and the onset of buckling. Prior to bar formation, the disc and halo contribute roughly equally to the potential in the galaxy's inner region, giving the disc enough self gravity for bar modes to grow. After bar formation there is significant mass redistribution, creating a baryon dominated inner and dark matter dominated outer disc. This implies that, unlike most other low surface brightness galaxies, UGC 628 is not dark matter dominated everywhere. Our model nonetheless implies that UGC 628 falls on same the relationship between dark matter fraction and rotation velocity found for high surface brightness galaxies, and lends credence to the argument that the disc mass fraction measured at the location where its contribution to the potential peaks is not a reliable indicator of its dynamical importance at all radii.

Characterizing bars in low surface brightness disc galaxies

“…Our bar strength values found for UGC 628, 0.26 and 0.22, are roughly consistent with those found by Chequers et al (2016) at late simulation time, ∼0.30, although our values are somewhat weaker. Based on the behaviour of the relative Fourier amplitudes, our bar strengths are likely indicative of the true strength.…”

“…Finally, we also have selected UGC 628, which has had its bar pattern speed measured via Fabry-Perot kinematics (Chemin & Hernandez 2009) and numerical modeling (Chequers et al 2016).…”

“…While it is very desirable to obtain actual pattern speed measurements, the current number of LSBs with bar pattern speed measurements is only one: UGC 628. The bar pattern speed of this galaxy was measured by applying the TW method to an Hα velocity field (Chemin & Hernandez 2009) as well as with numerical simulations (Chequers et al 2016). The lack of pattern speed measurements for LSBs is due to the large observing time required to obtain high signal to noise spectroscopy for LSBs.…”

“…Mayer & Wadsley (2004) used high resolution simulations of gas dominated discs and found that bars could form if the dark matter halo had a low concentration and the stellar component was higher than typically observed in LSBs. Chequers et al (2016) used hydrodynamical numerical simulations of UGC 628 to estimate the bar pattern speed and found it to suggest the galaxy was not dark matter dominated in the inner bar region. Cervantes Sodi & Sánchez García (2017) observationally found a strong dependance on bar length with disc surface brightness, as well as finding weaker bars in comparison to HSBs.…”

Tidally Induced Bars in Gas-rich Dwarf Galaxies Orbiting the Milky Way

“…Miwa & Noguchi (1998). However, slow bars can be created spontaneously if the disk is dark matter dominated and there is little or no gas (Debattista & Sellwood 2000;Saha & Naab 2013;Athanassoula 2014;Lokas et al 2016;Chequers et al 2016;Pettitt & Wadsley 2018). Our dwarfs were also dominated by dark matter.…”