The Relation Between Dynamics and Star Formation in Barred Galaxies

Abstract

We analyze optical and near-infrared data of a sample of 11 barred spiral galaxies, in order to establish a connection between star formation and bar/spiral dynamics. We find that 22 regions located in the bars, and 20 regions in the spiral arms beyond the end of the bar present azimuthal color/age gradients that may be attributed to star formation triggering. Assuming a circular motion dynamic model, we compare the observed age gradient candidates with stellar populations synthesis models. A link can then be established with the disk dynamics that allows us to obtain parameters like the pattern speed of the bar or spiral, as well as the positions of resonance radii. We subsequently compare the derived pattern speeds with those expected from theoretical and observational results in the literature (e.g., bars ending near corotation). We find a tendency to overestimate bar pattern speeds derived from color gradients in the bar at small radii, away from corotation; this trend can be attributed to non-circular motions of the young stars born in the bar region. In spiral regions, we find that ∼ 50% of the color gradient candidates are "inverse", i.e., with the direction of stellar aging contrary to that of rotation. The other half of the gradients found in spiral arms have stellar ages that increase in the same sense as rotation. Of the 9 objects with gradients in both bars and spirals, 6 (67%) appear to have a bar and a spiral with similar Ω p , while 3 (33%) do not.

Signatures of Long-Lived Spiral Patterns

“…For NGC 6951 (type SAB in the RC3) and NGC 6907 (type SB in the RC3), the CR radius may lie around R arm end ∼ 0.8. This is possibly an indication of color gradients within the bar region, as already found in Martínez-García & González-Lópezlira (2011).…”

“…All galaxy types are taken from the Third Reference Catalogue of Bright Galaxies (RC3, de Vaucouleurs et al 1991). ibrated with the same standard procedures used in Martínez-García et al (2009a), and Martínez-García & González-Lópezlira (2011). The optical (g, r, and i) calibration was done in the Thuan-Gunn system (Thuan & Gunn 1976;Wade et al 1979).…”

Star Formation in Nuclear Rings of Barred Galaxies

“…While star formation is concentrated in nuclear rings in our models, observations indicate that star formation in some galaxies occurs not only in nuclear rings but also in the bar region including dust lanes (e.g., Martin & Friedli 1997;Zurita & Pérez 2008;Elmegreen et al 2009;Martínez-García & González-Lópezlira 2011). While dust lanes themselves are known hostile to star formation due to strong velocity shear (e.g., Athanassoula 1992;Kim et al 2012a), proposed that stars form in interbar dust spurs in filamentary shape that impact the dust lanes from the trailing side of the bar (see also Sheth et al 2002;Zurita & Pérez 2008).…”

EMBEDDED STAR FORMATION IN S4G GALAXY DUST LANES

“…Early proposals for triggering involved shock compression of incoming clouds (Woodward 1976), diffuse cloud formation in a phase transition driven by thermal instabilities (Shu et al 1973), diffuse cloud formation in the magnetic instability of Parker (1966;Mouschovias et al 1974), cloud-cloud collisions (Vogel et al 1988;Koda & Sofue 2006), and giant cloud formation by gravitational instabilities in the shocked gas (Elmegreen 1979;. Color and age gradients downstream from the shock suggest star formation triggering (Sheth et al 2002;Tamburro et al 2008;Martínez-García et al 2009;Egusa et al 2009;Martínez-García & González-Lópezlira 2011;Sánchez-Gil et al 2011), but differential compression of old stars and gas (Elmegreen 1987) and between H i and CO gas phases (Louie 20 European Space Agency Research Fellow. et al 2013) can produce structures that mimic age gradients.…”