An Ionizing Photon Rate Map of NGC 6946
Abstract
Significant progress in our understanding of star formation and galaxy evolution depends on ability to obtain precise measurements of the star formation rate on scales from individual regions to large samples of galaxies. In order to do so we need to benchmark star formation rate estimators available for large samples and over wide areas (e.g., Halpha+IR, UV+IR) against high quality, spatially resolved "ground-truth" measurements. This has been done in groundbreaking studies for indivdiual regions, but has yet to be done carefully using maps covering whole area of nearby galaxies. The Paschen beta line is ideal for this purpose: it tracks star formation by tracing ionizing photons the can be cleanly associated with young stars and it is 3x less affected by extinction than the commonly used Halpha line. Most important WFC3 has the demonstrate ability to map Paschen beta at high resolution and excellent sensitivity over the whole area of nearby galaxies. We propose to use this capability to map the active area of active star formation in NGC6946, making only the second deeply sensitive map of Paschen beta across a whole nearby star-forming galaxy. We will use this to (1) inter-compare proposed ground-truth tracers (free-free, optical Balmer decrement, Paschen beta + Halpha) and (2) to improve the calibration of empirical star formation rate estimators by measuring them for individual regions, across large parts of galaxies, and comparing galaxies. Only HST can provide this new and important measurement of an extinction robust tracer of ionizing photon rates at high sensitivity and resolution across a whole galaxy.
- Publication:
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HST Proposal
- Pub Date:
- November 2015
- Bibcode:
- 2015hst..prop14156L