Pixel Color Magnitude Diagrams for Semi-Resolved Stellar Populations: The Star Formation History of Regions within the Disk and Bulge of M31

Abstract

The analysis of stellar populations has, by and large, been developed for two limiting cases: spatially-resolved stellar populations in the color-magnitude diagram, and integrated light observations of distant systems. In between these two extremes lies the semi-resolved regime, which encompasses a rich and relatively unexplored realm of observational phenomena. Here we develop the concept of pixel color magnitude diagrams (pCMDs) as a powerful technique for analyzing stellar populations in the semi-resolved regime. pCMDs show the distribution of imaging data in the plane of pixel luminosity vs. pixel color. A key feature of pCMDs is that they are sensitive to all stars, including both the evolved giants and the unevolved main sequence stars. An important variable in this regime is the mean number of stars per pixel, $N_{\mathrm{pix}}$. Simulated pCMDs demonstrate a strong sensitivity to the star formation history (SFH) and allow one to break degeneracies between age, metallicity and dust based on two filter data for values of $N_{\mathrm{pix}}$ up to at least $10^4$. We extract pCMDs from Hubble Space Telescope (HST) optical imaging of M31 and derive non-parametric SFHs from $10^6$ yr to $10^{10}$ yr for both the crowded disk and bulge regions (where $N_{\mathrm{pix}}\approx 30-10^3$). From analyzing a small region of the disk we find a non-parametric SFH that is smooth and consistent with an exponential decay timescale of 4 Gyr. The bulge SFH is also smooth and consistent with a 2 Gyr decay timescale. pCMDs will likely play an important role in maximizing the science returns from next generation ground and space-based facilities.

11 pages, 9 figures, submitted to ApJ

References in corpus (7)

• MESA Isochrones and Stellar Tracks (MIST) 0: Methods for the construction of stellar isochrones
• The Star Formation Histories of Local Group Dwarf Galaxies I. Hubble Space Telescope / Wide Field Planetary Camera 2 Observations
• The Panchromatic Hubble Andromeda Treasury X. Ultraviolet to Infrared Photometry of 117 Million Equidistant Stars
• The Panchromatic Hubble Andromeda Treasury XI: The Spatially-Resolved Recent Star Formation History of M31
• The Metallicity Distribution of Intracluster Stars in Virgo
• A Global Star Forming Episode in M31 2-4 Gyr Ago
• Fluctuation Spectroscopy: A New Probe of Old Stellar Populations

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