The Panchromatic Hubble Andromeda Southern Treasury (PHAST). II. The Spatially Resolved Recent Star Formation History in M31

Abstract

We use Hubble Space Telescope optical imaging from the Panchromatic Hubble Andromeda Southern Treasury (PHAST) to measure the spatially resolved recent star formation history (SFH) across the southern disk of M31. We fit color-magnitude diagrams (CMDs) of over 6500 individual 0.01 kpc${}^2$ regions to measure SFHs over the last $\sim$500 Myr. The resulting maps show coherent structure that traces the ringed morphology of the disk. We find a clear global decline in the recent SFR, with a pronounced drop in the last $\sim$40 Myr that is most evident in the region closest to M32. Combining PHAST and PHAT measurements, we now cover two thirds of M31's star-forming disk with homogeneous SFHs, yielding the highest-resolution spatially resolved SFHs of M31. Inside the joint footprint, we measure mean SFRs of $0.445\pm 0.006$ M${}_{\odot }$ yr${}^{-1}$ over the last 100 Myr and $0.285\pm 0.014$ M${}_{\odot }$ yr${}^{-1}$ over the last 20 Myr, implying total disk SFRs of $\sim$0.67 and $\sim$0.43 M${}_{\odot }$ yr${}^{-1}$, respectively. The observed decline is interpreted as the late stage of a multi-Gyr wind-down from a previously more active state. Because recent star formation in M31 is concentrated primarily in the rings, the global decline is driven mainly by decreasing activity within those features. We also compare the CMD-based SFR surface densities to those inferred from FUV+24 $\mu$m prescriptions and find that the FUV-based calibration underestimates the CMD-based 100 Myr average by a factor of $\sim$2.1. However, the PHAST SFHs produce a synthetic GALEX FUV image that agrees well with observations, indicating that the CMD-derived SFHs provide an accurate description of recent star formation. The mismatch with the FUV+24 $\mu$m estimates underscores that tracers implicitly averaged over $\sim$100 Myr are not reliable when the recent SFR is evolving.

Accepted to ApJ. 38 Pages, 15 figures, and 1 table. 2 Animations are available with the journal version

References in corpus (37)

• Array Programming with NumPy
• The Astropy Project: Sustaining and Growing a Community-oriented Open-source Project and the Latest Major Release (v5.0) of the Core Package
• The propagation of uncertainties in stellar population synthesis modeling I: The relevance of uncertain aspects of stellar evolution and the IMF to the derived physical properties of galaxies
• The Star Formation Histories of Local Group Dwarf Galaxies I. Hubble Space Telescope / Wide Field Planetary Camera 2 Observations
• The Haunted Halos of Andromeda and Triangulum: A panorama of galaxy formation in action
• The ACS Nearby Galaxy Survey Treasury IX. Constraining asymptotic giant branch evolution with old metal-poor galaxies
• The Panchromatic Hubble Andromeda Treasury X. Ultraviolet to Infrared Photometry of 117 Million Equidistant Stars
• The Recent Star Formation Histories of M81 Group Dwarf Irregular Galaxies
• An almost head-on collision as the origin of two off-centre rings in the Andromeda galaxy
• The Panchromatic Hubble Andromeda Treasury XI: The Spatially-Resolved Recent Star Formation History of M31
• The ACS Nearby Galaxy Survey Treasury V. Radial Star Formation History of NGC 300
• Quiescence correlates strongly with directly-measured black hole mass in central galaxies
• Star Formation Laws and Efficiencies across 80 Nearby Galaxies
• Galaxy bulges and their black holes: a requirement for the quenching of star formation
• Supermassive black holes as the regulators of star formation in central galaxies
• On the duration of the embedded phase of star formation
• The Herschel Exploitation of Local Galaxy Andromeda (HELGA) VII: A SKIRT radiative transfer model and insights on dust heating
• The Panchromatic Hubble Andromeda Treasury: Triangulum Extended Region (PHATTER) I. Ultraviolet to Infrared Photometry of 22 Million Stars in M33
• The Extended Star Formation History of the Andromeda Spheroid at 35 Kpc on the Minor Axis
• The Extended Star Formation History of the Andromeda Spheroid at Twenty One Kiloparsecs on the Minor Axis
• An Ultraviolet Study of Star-Forming Regions in M31
• Signatures of the M31-M32 Galactic Collision
• A Global Star Forming Episode in M31 2-4 Gyr Ago
• Star Formation and Molecular Gas Diagnostics with Mid- and Far-Infrared Emission
• The Panchromatic Hubble Andromeda Treasury: Triangulum Extended Region (PHATTER). III. The Mass Function of Young Star Clusters in M33
• X-Rays Beware: The Deepest Chandra Catalogue of Point Sources in M31
• Multiwavelength Characterization of the High Mass X-ray Binary Population of M31
• The Panchromatic Hubble Andromeda Treasury XVII. Examining Obscured Star Formation with Synthetic Ultraviolet Flux Maps in M31
• The Panchromatic Hubble Andromeda Treasury. VI. The reliability of far-ultraviolet flux as a star formation tracer on sub-kpc scales
• XMM-Newton RGS spectroscopy of the M31 bulge. I: Evidences for a past AGN half a million years ago
• The Karl G. Jansky Very Large Array Local Group L-band Survey (LGLBS)
• The Timescales of Embedded Star Formation as Observed in STARFORGE
• Dark matter fraction derived from the M31 rotation curve
• Dust around massive stars is agnostic to galactic environment: New insights from PHAT/BEAST
• Assessing the accuracy of the star formation rate measurements by direct star count in molecular clouds
• Searching for Radio Outflows from M31* with VLBI Observations
• The ALMaQUEST Survey XVII: Unveiling Multiple Quenching Pathways in Green Valley Galaxies via Molecular Gas and Quenching Timescale Analyses