EPoS Contribution
EPoS Contribution
Effect of diffuse background in spatially-resolved star-formation studies

Nimisha Kumari
IoA, Cambridge, GB
The Kennicutt-Schmidt law relating the surface densities of the star-formation rate (SFR) and gas (atomic and molecular) is a widely-accepted star-formation law. However, it is a disk-averaged law smoothing over local variations, and hence may not provide an explanation for the local relationship between SFR and gas density at the sub-galactic scale. To further probe this, various groups have carried out spatially-resolved studies of star-formation in nearby spiral galaxies using different methods. However, most of these studies do not take into account the effect of the spatially varying diffuse background which is potentially present in all star-forming galaxies and affects all the usual SFR tracers (optical, far-ultraviolet and mid-infrared). In this contribution, we present the results from an analysis of nearby spiral galaxies using aperture photometry where the effect of the diffuse background is taken into account. Making use of a novel split of the overall light distribution as a function of spatial scale allows us to subtract the diffuse background in the SFR tracers and determine the current localised SFR density. This is then combined with the gas density estimates (molecular gas from CO(2-1) and atomic gas from HI) to study the relation between SFR and gas density. Our work indicates that accounting for a diffuse background leads to a super-linear slope of the Kennicutt-Schmidt molecular star-formation law.
Caption: NGC 0628: SFR versus H2 before (left) and after (right) subtraction of diffuse background. The dashed black line is the unweighted best-fit line, with coefficients shown in the top of each plot. The errors quoted on each coefficient are the standard best-fit errors and "rms" denotes the root mean square dispersion of the points orthogonal to the best-fit line.
M.J. Irwin, IoA, Cambridge, GB
B.L. James, KICC, Cambridge, GB
R.C. Kennicutt, IoA, Cambridge, GB
Key publication

Suggested Session: From Low- to High-Mass Star Formation