Age patterns in a sample of spiral galaxies

Abstract

We present the burst ages for young stellar populations in a sample of six nearby (<10 Mpc) spiral galaxies using a differential pixel‐based analysis of the ionized gas emission. We explore this as an alternative approach for connecting large‐scale dynamical mechanisms with star formation processes in disc galaxies, based on burst ages derived from the Hα to far‐UV (FUV) flux ratio. Images of each galaxy in Hα were taken with Taurus Tunable Filter and matched to FUV imaging from GALEX. The resulting flux ratio provides a robust measure of relative age across the disc which we discuss in terms of the large‐scale dynamical motions. Systematic effects such as a variable initial mass function, non‐solar metallicities, variable star formation histories (SFHs) and dust attenuation have been used to derive estimates of the systematic uncertainty. The resulting age maps show a wide range of patterns outside of those galaxies with the strongest spiral structure, confirming the idea that star formation is driven one by several processes, largely determined by the individual circumstances of the galaxy. Generally, grand design spirals such as M74, M100 and M51 exhibit age gradients across the main spiral arms, with the youngest star formation regions along the central and inner edges. Likewise, in the dominant star‐forming complex of IC 2574 or the ring of M94, the most recent star formation is centrally confined to the regions of star formation activity. In M63 and M74 galaxy‐wide trends emerge, contrary to the spiral structure in these galaxies, suggesting that spiral density waves are not the dominant driver in some cases. We argue that despite appearances, galaxy morphology is not an absolute discriminator of the SFH of an individual galaxy, nor of the processes triggering it. We conclude that Hα‐to‐FUV flux ratios are a relatively direct way to probe burst ages across galaxies and infer something of their dynamical histories, provided that sources of systematics are properly taken into account.

The relation between surface star formation rate density and spiral arms in NGC 5236 (M 83)

“…Previous works have tried to relate the spiral arms with the star formation (see e.g. Ivanov 1985;Allen et al 1986;Tilanus & Allen 1993;Stedman & Knapen 2001;Knapen et al 2010;Sánchez-Gil et al 2011). These studies have shown the relation between the star formation and the spiral structure using different gas components over different parts of a large set of galaxies (e.g.…”

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.…”

ENHANCED NITROGEN IN MORPHOLOGICALLY DISTURBED BLUE COMPACT GALAXIES AT 0.20 < z < 0.35: PROBING GALAXY MERGING FEATURES

“…On the other hand, the UV flux traces less massive stars with timescales of a few hundred Myr (Kennicutt 1998;Iglesias-Paramo et al 2004). The Hα luminosity declines more rapidly than the UV continuum luminosity, which leads to a decrease in the Hα to UV SFR ratio with increasing starburst age (Sánchez-Gil et al 2011). Thus, the Hα to UV SFR ratio carries important information about the SFH and the duration of the SF episode of a galaxy.…”