Spatially-Resolved Recent Star Formation History in NGC 6946

TL;DR

This study uses Hubble Space Telescope UV imaging to map the recent star formation history of NGC 6946 over the last 25 million years, revealing a declining trend in star formation rate and identifying key active regions.

Contribution

It provides the first spatially-resolved star formation history of NGC 6946 over the last 25 Myr using UV CMD modeling from HST data.

Findings

Global SFR (last 25 Myr) = 13.17 M_/yr

SFR decreased from ~23.39 to 5.31 M_/yr over 25 Myr

Two active regions contribute 3% and 5% of recent star formation

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 supernova. We analyze its resolved near-ultraviolet (NUV) stellar photometry measured from images taken with the Hubble Space Telescope's (HST) Wide Field Camera 3 (WFC3) with F275W and F336W filters. We model the color-magnitude diagrams (CMD) of the UV photometry to derive the spatially-resolved star formation history (SFH) of NGC 6946 over the last 25 Myr. From this analysis, we produce maps of the spatial distribution of young stellar populations and measure the total recent star formation rate (SFR) of nearly the entire young stellar disk. We find the global SFR(age$\leq$25 Myr)=$13.17 \substack{+0.91 \\-0.79} M_\odot/\rm yr$. Over this period, the SFR is initially very high ($23.39\substack{+2.43\\-2.11} M_\odot/\rm yr$ between 16-25 Myr ago), then monotonically decreases to a recent SFR of $5.31\substack{+0.19\\-0.17} M_\odot/\rm yr$ in the last 10 Myr. This decrease in global star formation rate 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.