Abstract / Description of output
Using long-slit spectroscopy from Moran et al. (2012), we constrain the
radial dependence of the recent star formation histories of nearby
galaxies with stellar masses greater than 1010
M⊙. By fitting stellar population models to the
combination of specific star formation rate, Dn4000 and
HγA, we show that the star formation histories of many
disc galaxies cannot be accurately represented if their star formation
rates declined exponentially with time. Many galaxies have Balmer
absorption line equivalent widths that require recent short-lived
episodes or bursts of star formation.
The fraction of galaxies that have experienced episodic rather than
continuous star formation is highest for `late-type' galaxies with low
stellar masses, low surface densities and low concentrations. In these
systems, bursts occur both in the inner and in the outer regions of the
galaxy. The fraction of stars formed in a single burst episode is
typically around 15 per cent of the total stellar mass in the inner
regions of the galaxy and around 5 per cent of the mass in the outer
regions. When we average over the population, we find that such bursts
contribute around a half of the total mass in stars formed in the last 2
Gyr. In massive galaxies, bursts occur predominantly in the outer disc.
Around a third of all massive, bulge-dominated galaxies have experienced
recent star formation episodes that are fully confined to their outer (R
> 0.7R90) regions. The fraction of stars formed in bursts
is only ˜2-3 per cent of the underlying stellar mass, but when we
average over the population, we find that such bursts contribute nearly
all the stellar mass formed in the last 2 Gyr.
Recent star formation in outer discs is strongly correlated with the
global atomic gas fraction of the galaxy, but not its global molecular
gas fraction. We suggest that outer episodic star formation is triggered
by gas accretion `events'. Episodic star formation in the inner regions
is suppressed in galaxies with large bulge-to-disc ratio. This supports
the idea that inner bursts are linked to instability-driven gas inflows.
Original language | English |
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Pages (from-to) | 2622-2633 |
Journal | Monthly Notices of the Royal Astronomical Society |
Volume | 431 |
Issue number | 3 |
DOIs | |
Publication status | Published - 21 Mar 2013 |
Keywords / Materials (for Non-textual outputs)
- galaxies: evolution
- galaxies: formation