Tuesday

Spiral arms are commonly observed features in low-redshift galaxies, with as many as two-thirds of galaxies displaying spiral arms. These arms are sites of increased density of gas and dust, meaning they are the primary regions where new stars form in galaxies. However, it is not well understood what mechanisms are responsible for observed spiral structure and how they influence star formation. Of principal concern is that the processes via which arms form varies from galaxy to galaxy: two-arm, grand design spiral arms are usually associated with density waves, bars or tidal interactions, whereas more patchy, flocculent structure is more likely due to gravitational instabilities in galaxy discs. In this talk, I will compare the star formation demographics of spiral galaxies with respect to arm number using a sample of 6,000 SDSS galaxies, reliably classified in Galaxy Zoo 2. I will show that different spiral patterns do little to influence the overall star formation rates or efficiencies in their galaxies, but that a greater fraction of the the star formation occurs in heavily dust obscured regions in two-arm galaxies. This implies that the mechanisms that lead to the presence of strong two-armed structures in galaxy discs lead to star-forming molecular clouds being denser, larger and/or more clustered than those in many-armed galaxies.