Circumnuclear regions in barred spiral galaxies -- II. Relations to host galaxies

Abstract

We present optical broad‐ and narrow‐band imaging of a sample of a dozen barred galaxies. These images are analysed in conjunction with our previously published near‐infrared imaging of their central regions and with literature values for, e.g. bar strengths and the total star formation activity of the galaxies. We present B, I and Hα images, and radial profiles derived from these, to infer geometric and dynamical parameters of the structural components of the galaxies, such as bar lengths, bar ellipticities, and location of star formation and dust. We find that the more centrally concentrated the Hα emission in a galaxy is, i.e. the higher the fraction of star formation originating in the circumnuclear region, the higher the overall star formation rate, as measured from far‐infrared flux ratios. Stronger bars host smaller nuclear rings, but the strength of the bar does not correlate with either the intrinsic ellipticity of the ring or the offset between the position angles of the bar and the ring. We interpret these results in comparison with modelling of gas inflow in the circumnuclear region, and show that they were theoretically expected. We confirm observationally, and for the first time, the anticorrelation predicted from theory and modelling between the degree of curvature of the bar dust lanes and the strength of the bar, where stronger bars have straighter dust lanes.

On the morphology of dust lanes in galactic bars

“…A methodology similar to the one presented here, is used by Knapen et al (2002) and Comerón et al (2009) on real galaxies. These works also developed a way to quantify the curvature of dust lanes using real galaxies.…”

“…These works also developed a way to quantify the curvature of dust lanes using real galaxies. Their method is based on measurements of the change in the angle of the tangent to the curved dust lanes in the range where the curvature is constant, Knapen et al (2002) expressing the result in units of degrees per kpc and Comerón et al (2009) multiplying that angle by the angular radius at which the torque is maximal, to take into account the size of the host bars. This method has the advantage of being simple and rather straightforward, but it also presents a number of drawbacks.…”

“…There have been a few attempts to observationally find this relation between dust lane curvature and bar strength (Knapen et al 2002;Comerón et al 2009), but without taking into account the bar pattern speed. Even though Knapen et al (2002) confirmed a correlation between bar strength and dust lane curvature, Comerón et al (2009), using a larger sample and improving the number statistics from Knapen et al (2002), showed a large spread in the data and concluded that, though bar strength set an upper limit to the dust lane curvature allowed, this parameter by itself did not determine the dust lane curvature.…”

Molecular Gas in NUclei of GAlaxies (NUGA)

“…This implies that the strong accretion phase is a fraction 0.3/N of the characteristic galaxy dynamical time (∼10 8 yr). Although large-scale bars can produce gas inflow (e.g., Combes & Gerin 1985;Sakamoto et al 1999) and in some cases also drive powerful starbursts (e.g., Knapen et al 2002;Jogee et al 2005), a correlation between large-scale bars and nuclear activity has not yet been verified (e.g., Mulchaey & Regan 1997). This lack of correlation is probably related to the different timescales for bar-induced gas inflow ( 300 Myr, Jogee et al 2005), AGN duty cycles (∼10 7 yr), and intermittent active accretion every ∼10 8 yr (Ferrarese et al 2001;Marecki et al 2003;Janiuk et al 2004;Hopkins & Hernquist 2006;King & Pringle 2007).…”

Molecular gas in NUclei of GAlaxies (NUGA) XIII. The interacting Seyfert 2/LINER galaxy NGC 5953

“…Large-scale bars can transport gas inward efficiently (e.g., Combes & Gerin 1985;Sakamoto et al 1999), and it appears that they can also drive powerful starbursts (e.g., Knapen et al 2002;Jogee et al 2005). Nevertheless, a clear correlation between large-scale bars and nuclear activity has not yet been found (e.g., Mulchaey & Regan 1997), probably because the timescales for bar-induced gas inflow and AGN duty cycles are very different.…”