Star formation history of barred disc galaxies

Abstract

We present the first results of a pilot study aimed at understanding the influence of bars on the evolution of galaxy discs through the study of their stellar content. We examine here the kinematics, star formation history, mass-weighted, luminosity-weighted, and single stellar population (SSP) equivalent ages and metallicities for four galaxies ranging from lenticulars to late-type spirals. The data employed extends to 2-3 disc scalelengths, with S/N(A)>50. Several techniques are explored to derive star formation histories and SSP-equivalent parameters, each of which are shown to be compatible. We demostrate that the age-metallicity degeneracy is highly reduced by using spectral fitting techniques --instead of indices-- to derive these parameters. We found that the majority of the stellar mass in our sample is composed of old (~10 Gyr) stars. This is true in the bulge and the disc region, even beyond two disc scalelengths. In the bulge region, we find that the young, dynamically cold, structures produced by the presence of the bar (e.g., nuclear discs or rings) are responsible for shaping the bulges' age and metallicity gradients. In the disc region, a larger fraction of young stars is present in the external parts of the disc compared with the inner disc. The disc growth is, therefore, compatible with a moderate inside-out formation scenario, where the luminosity weighted age changes from ~10 Gyrs in the centre, to ~4 Gyrs at two disc scalelengths, depending upon the galaxy. For two galaxies, we compare the metallicity and age gradients of the disc major axis with that of the bar, finding very important differences. In particular, the stellar population of the bar is more similar to the bulge than to the disc, indicating that, at least in those two galaxies, bars formed long ago and have survived to the present day. (abridged)Comment: 24 pages, 23 figures, accepted for publication in MNRA

Study of the stellar population properties in the discs of ten spiral galaxies

“…Yoachim & Dalcanton (2008) and MacArthur et al (2009) detected the presence of an old stellar population (8-10 Gyrs) in the disc-dominated region of 9 edge-on and 8 low inclined spirals, respectively. This result was confirmed by Sánchez-Blázquez et al (2011) andSánchez-Blázquez et al (2014) who studied 62 nearly face-on spirals without finding any significant difference between the discs of unbarred and barred galaxies. Discs are characterised by a large spread in metallicity spanning values between [Z/H]=0 and [Z/H]=-0.2 (Yoachim & Dalcanton 2008).…”

“…Discs are characterised by a large spread in metallicity spanning values between [Z/H]=0 and [Z/H]=-0.2 (Yoachim & Dalcanton 2008). The age and metallicity radial profiles derived by MacArthur et al (2009), Sánchez-Blázquez et al (2011), and Sánchez-Blázquez et al (2014 display shallow or negative metallicity gradients. The [α/Fe] enhancement was only measured by Yoachim & Dalcanton (2008).…”

firefly (Fitting IteRativEly For Likelihood analYsis): a full spectral fitting code

“…However, the effect on metallicity is much more pronounced, with no clear stable region of correct metallicity recovery and instead a ∼ 0.1 dex displacement for every 30 km/s offset from the true input value. This effect on metallicity was also found in Koleva et al (2008) and Sánchez-Blázquez et al (2011), where it was described as the 'metallicity-velocity dispersion degeneracy'.…”

The mass dependence of star formation histories in barred spiral galaxies

“…Metallicities and gas content have also yielded conflicting results, with wide variations in radial abundance profiles in both gas (Edmunds & Roy 1993;Oey & Kennicutt 1993;Zaritsky et al 1994;Considère et al 2000) and stars (Pérez et al 2009;Sánchez-Blázquez et al 2011;Seidel et al 2016). Comparison between barred and unbarred galaxies show that the former can have higher central metallicities (Ellison et al 2011), no significant variations (Cacho et al 2014;Sánchez-Blázquez et al 2014), or even lower metallicities than the latter (Dutil & Roy 1999;Considère et al 2000).…”