The Panchromatic Hubble Andromeda Treasury. VI. The reliability of far-ultraviolet flux as a star formation tracer on sub-kpc scales

Abstract

We have used optical observations of resolved stars from the Panchromatic Hubble Andromeda Treasury (PHAT) to measure the recent (< 500 Myr) star formation histories (SFHs) of 33 FUV-bright regions in M31. The region areas ranged from ~$10^4$ to $10^6$ pc${}^2$, which allowed us to test the reliability of FUV flux as a tracer of recent star formation on sub-kpc scales. The star formation rates (SFRs) derived from the extinction-corrected observed FUV fluxes were, on average, consistent with the 100-Myr mean SFRs of the SFHs to within the 1$\sigma$ scatter. Overall, the scatter was larger than the uncertainties in the SFRs and particularly evident among the smallest regions. The scatter was consistent with an even combination of discrete sampling of the initial mass function and high variability in the SFHs. This result demonstrates the importance of satisfying both the full-IMF and the constant-SFR assumptions for obtaining precise SFR estimates from FUV flux. Assuming a robust FUV extinction correction, we estimate that a factor of 2.5 uncertainty can be expected in FUV-based SFRs for regions smaller than $10^5$ pc${}^2$, or a few hundred pc. We also examined ages and masses derived from UV flux under the common assumption that the regions are simple stellar populations (SSPs). The SFHs showed that most of the regions are not SSPs, and the age and mass estimates were correspondingly discrepant from the SFHs. For those regions with SSP-like SFHs, we found mean discrepancies of 10 Myr in age and a factor of 3 to 4 in mass. It was not possible to distinguish the SSP-like regions from the others based on integrated FUV flux.

arXiv commentAccepted for publication in The Astrophysical Journal

References in corpus (29)

• Astropy: A Community Python Package for Astronomy
• On the variation of the Initial Mass Function
• Star Formation in Galaxies Along the Hubble Sequence
• PARSEC: stellar tracks and isochrones with the PAdova and TRieste Stellar Evolution Code
• Starburst99: Synthesis Models for Galaxies with Active Star Formation
• Star Formation in the Milky Way and Nearby Galaxies
• 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 propagation of uncertainties in stellar population synthesis modeling III: model calibration, comparison, and evaluation
• WFPC2 Stellar Photometry with HSTphot
• Calibrating Extinction-Free Star Formation Rate Diagnostics with 33GHz Free-Free Emission in NGC6946
• An Analysis of the Shapes of Interstellar Extinction Curves. V. The IR-Through-UV Curve Morphology
• Star counts in the Galaxy. Simulating from very deep to very shallow photometric surveys with the TRILEGAL code
• Dust-Corrected Star Formation Rates of Galaxies. II. Combinations of Ultraviolet and Infrared Tracers
• Numerical Methods of Star Formation History Measurement and Applications to Seven Dwarf Spheroidals
• The ACS Nearby Galaxy Survey Treasury
• The Panchromatic Hubble Andromeda Treasury
• M31 Globular Clusters: Colors and Metallicities
• The ACS Nearby Galaxy Survey Treasury IX. Constraining asymptotic giant branch evolution with old metal-poor galaxies
• Estimating the Star Formation Rate at 1 kpc Scales in Nearby Galaxies
• Modeling CO Emission: I. CO as a Column Density Tracer and the X-Factor in Molecular Clouds
• Gravity or turbulence? II. Evolving column density PDFs in molecular clouds
• The Turbulent Warm Ionized Medium: Emission Measure Distribution and MHD Simulations
• On the Estimation of Random Uncertainties of Star Formation Histories
• Density probability distribution functions of diffuse gas in the Milky Way
• Measuring Galaxy Star Formation Rates From Integrated Photometry: Insights from Color-Magnitude Diagrams of Resolved Stars
• An Ultraviolet Study of Star-Forming Regions in M31
• The ACS Nearby Galaxy Survey Treasury II. Young Stars and their Relation to Halpha and UV Emission Timescales in the M81 Outer Disk
• Star Formation Histories of Local Group Dwarf Galaxies
• The Recent Star Formation in NGC 6822: an Ultraviolet Study

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• The Panchromatic Hubble Andromeda Treasury XVII. Examining Obscured Star Formation with Synthetic Ultraviolet Flux Maps in M31
• On recent SFR calibrations and the constant SFR approximation
• The Panchromatic Hubble Andromeda Treasury. Progression of Large-Scale Star Formation across Space and Time in M31
• The Local Ultraviolet to Infrared Treasury I. Survey Overview of the Broadband Imaging
• Models of Late-Type Disk Galaxies: 1-D Versus 2-D
• The Panchromatic Hubble Andromeda Southern Treasury (PHAST). II. The Spatially Resolved Recent Star Formation History in M31