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

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 ∼38 kpc2 and extends to ∼3.5 and ∼2 kpc from the center of M33 along the major and semimajor axes, respectively. We divide the PHATTER optical survey into 2005 regions that measure 24 arcsec, ∼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 ± 0.02 M⊙ yr−1. We measure a current SFR (over the last 10 Myr) of 0.20 ± 0.03 M⊙ 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.

The Time-averaged Mass-loss Rates of Red Supergiants as Revealed by Their Luminosity Functions in M31 and M33

“…We have shown that the extinction corrections made by Massey et al (2021b) were a little too high based upon the inferred temperatures for M2-3 I RSGs. Instead, we have recomputed the luminosities by adopting a uniform reddening for each galaxy based on the average values from the M31 PHAT (Dalcanton et al 2012(Dalcanton et al , 2015 and M33 PHATTER (Williams et al 2021;Lazzarini et al 2022) studies. Given that we are using these A V values to compute corrections to K, the differences in luminosities are slight in comparison with Massey et al (2021b), except for the brightest RSGs, where we have argued that Massey et al (2021b) overcorrected the data.…”

“…For M33, the extinctions for multiple regions was measured in a similar manner using the Panchromatic Hubble Andromeda Treasury: Triangulum Extended Region (PHATTER; Williams et al 2021) data set (Lazzarini et al 2022). The average roughly corresponds to a value of A V = 0.8 mag (M. Lazzarini 2022, private communication).…”

“…We are also indebted to Dr. Levesque for providing us with Figure 6, an updated version from the one that appears in the recent text on stellar evolution, Lamers & Levesque (2017), and to Dr. Dorn-Wallenstein for comments on an earlier version of the manuscript. We are also grateful to Dr. Nelson Caldwell for help in eliminating some of the clusters and background galaxies that were in the original sample of M31 RSG candidates, and to Dr. Margaret Lazzarini for calculating the average extinction of star-forming regions in M33 from Lazzarini et al (2022) for us. We are also grateful to Dr. Jacco van Loon for a kind and useful referee report that resulted in multiple improvements in the manuscript.…”

The Masses of Supernova Remnant Progenitors in M33

“…Our larger sample and more homogeneous photometry catalog allow us to compare different fitting methods and quantify the impact these changes have on the age and mass results. Additionally, we compare our custom SNR-centered SFHs to those measured by Lazzarini et al (2022) in grids, allowing us to determine whether grid SFHs are sufficient for inferring a progenitor age and mass. The rest of the paper is outlined as follows: Section 2 details our SNR source catalog, as well as how our SFHs were measured.…”

The Panchromatic Hubble Andromeda Treasury: Triangulum Extended Region (PHATTER). IV. Star Cluster Catalog

“…Overall, this exercise shows that the star formation differences between M31 and M33 are likely significant enough to impact cluster populations. We look forward to using robust star formation history fitting (Lazzarini et al 2022) to inform recent SFR and Σ SFR determinations for M33, and aid future Γ determinations for the PHATTER cluster sample.…”