The Panchromatic Hubble Andromeda Treasury: Triangulum Extended Region (PHATTER) II. The Spatially Resolved Recent Star Formation History of M33

TL;DR

This study uses Hubble Space Telescope data to map the recent star formation history of M33 with high spatial resolution, revealing fluctuations, structural features, and star formation rates over the past 630 million years.

Contribution

It provides the first detailed spatially resolved recent star formation history of M33, highlighting small-scale fluctuations and structural features like spiral arms and a central bar.

Findings

Significant fluctuations in star formation history on small and galaxy-wide scales.

Younger stellar populations show a flocculent spiral structure, older populations are dominated by two spiral arms.

The mean star formation rate over the last 100 Myr is 0.32 M$_{ ext{sun}}$ yr$^{-1}$, with a current rate of 0.20 M$_{ ext{sun}}$ yr$^{-1}$.

Abstract

We measure the spatially resolved recent star formation history (SFH) of M33 using optical images taken with the Hubble Space Telescope as part of the Panchromatic Hubble Andromeda Treasury: Triangulum Extended Region (PHATTER) survey. The area covered by the observations used in this analysis covers a de-projected area of $\sim$38 kpc$^{2}$ and extends to $\sim$3.5 and $\sim$2 kpc from the center of M33 along the major and semi-major axes, respectively. We divide the PHATTER optical survey into 2005 regions that measure 24 arcsec, $\sim$100 pc, on a side and fit color magnitude diagrams for each region individually to measure the spatially resolved SFH of M33 within the PHATTER footprint. There are significant fluctuations in the SFH on small spatial scales and also galaxy-wide scales that we measure back to about 630 Myr ago. We observe a more flocculent spiral structure in stellar populations younger than about 80 Myr, while the structure of the older stellar populations is dominated by two spiral arms. We also observe a bar in the center of M33, which dominates at ages older than about 80 Myr. Finally, we find that the mean star formation rate (SFR) over the last 100 Myr within the PHATTER footprint is 0.32$\pm$0.02 M$_{\odot}$ yr$^{-1}$. We measure a current SFR (over the last 10 Myr) of 0.20$\pm$0.03 M$_{\odot}$ yr$^{-1}$. This SFR is slightly higher than previous measurements from broadband estimates, when scaled to account for the fraction of the D25 area covered by the PHATTER survey footprint.