Spatially Resolved Recent Star Formation History in NGC 6946

Abstract

The nearby face-on star-forming spiral galaxy NGC 6946 is known as the Fireworks Galaxy due to its hosting an unusually large number of supernovae. We analyze its resolved near-ultraviolet stellar photometry measured from images taken with the Hubble Space Telescope’s Wide Field Camera 3 with the F275W and F336W filters. We model the color–magnitude diagrams of the UV photometry to derive the spatially resolved star formation history of NGC 6946 over the last 25 Myr. From this analysis, we produce maps of the spatial distribution of the young stellar population and measure the total recent star formation rate (SFR) of nearly the entire young stellar disk. We find the global SFR(age ≤25 Myr) = ${13.17}_{-0.79}^{+0.91}{M}_{\odot }\,{\mathrm{yr}}^{-1}$ . Over this period, the SFR is initially very high ( ${23.39}_{-2.11}^{+2.43}{M}_{\odot }\,{\mathrm{yr}}^{-1}$ 16–25 Myr ago), then monotonically decreases to ${5.31}_{-0.17}^{+0.19}{M}_{\odot }\,{\mathrm{yr}}^{-1}$ in the last 10 Myr. This decrease in global SFR over the last 25 Myr is consistent with measurements made with other SFR indicators. We discuss in detail two of the most active regions of the galaxy, which we find are responsible for 3% and 5% of the total star formation over the past 6.3 Myr.

Keywords

• Star formation
• Spiral galaxies
• Galaxy evolution
• Stellar populations