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The History of the M31 Disk from Resolved Stellar Populations as seen by PHAT

The History of the M31 Disk from Resolved Stellar Populations as seen by PHAT. Alexia Lewis University of Washington The Structure and Dynamics of Disk Galaxies 12 August 2013. Julianne Dalcanton (UW) Ben Williams (UW) Dan Weisz (UW, UCSC) Adam Leroy (NRAO) Andy Dolphin (Raytheon).

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The History of the M31 Disk from Resolved Stellar Populations as seen by PHAT

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  1. The History of the M31 Disk from Resolved Stellar Populations as seen by PHAT Alexia Lewis University of Washington The Structure and Dynamics of Disk Galaxies 12 August 2013 Julianne Dalcanton (UW) Ben Williams (UW) Dan Weisz (UW, UCSC) Adam Leroy (NRAO) Andy Dolphin (Raytheon)

  2. Panchromatic Hubble Andromeda Treasury (PHAT) • HST multi-cycle program: 828 orbits • Data collection: 2009-2013 • >100 million stars • Total area: 0.5 deg2 24 μm 24 μm Dalcanton+ 2012 Dalcanton+ 2012 12 August 2013

  3. B15 F336W + F475W + F814W + F160W Dalcanton+ 2012 approx. 1.5 x 3 kpc 12 August 2013

  4. Optical Color-Magnitude Diagram MATCH Brighter RHeBs BHeBs MS Ingredients IMF Binary Fraction Stellar Models Filter Convolution Bin the CMD AGB RGB SGB Oldest MSTO Lower MS Dolphin 2002 12 August 2013

  5. Adjust SFH, Extinction until Model = Data F475W Ingredients IMF Binary Fraction Stellar Models Filter Convolution Bin the CMD Observational Errors Extinction Differential Extinction F475W – F814W Model CMD = Linear combination of SSPs 12 August 2013

  6. Recovering SFHs “Observed” CMD Model CMD observed density in bin i: ni model density in bin i: mi Maximize likelihood to find most likely SFH 12 August 2013

  7. Recent SFH of the 10-kpc Ring Survey Area: 0.5 deg2 Each brick: ~1.5 x 3 kpc (12’ x 6’.5) 12 August 2013

  8. Recent SFHs F475W F475W – F814W F475W – F814W Lewis+ (in prep) Old stars = excluded region 12 August 2013

  9. Recent SFH of the 10-kpc Ring 100 pc (~26”) pixels 500 pc There are a wide variety of SFHs on small scales Lewis+ (in prep) 12 August 2013

  10. Recent SFH of the 10-kpc Ring • Good spatial correspondence • Mean age of stellar populations contributing to emission (Kennicutt & Evans 2012) : • FUV: 10 Myr • Hα: 3 Myr 500 pc Lewis+ (in prep) 12 August 2013

  11. Lewis+ (in prep) 12 August 2013

  12. Recent SFHs: Applications • Correlations between SFHs and gas and SFR tracers • Examine Kennicutt-Schmidt relation on small scales • No assumptions about constant SFR • Evolution of SF-ing events and the timescales on which they occur log ΣSFR log Σgas Bigiel+ 2008 12 August 2013

  13. Ancient SFHs • Recover SFH on larger spatial scales (500 pc) • Extend ancient SFH studies from outer disk (Bernard+ 2012, Brown+ 2006,2007,2008) to inner disk • But dust is a problem MS F475W RGB Red Clump F475W – F814W 12 August 2013

  14. Summary • Recent SFHs at 100pc resolution • Stability of 10-kpc star-forming ring over ~200 Myr • Extend to more bricks • Propagation of SFing events, interplay between gas and SF on small scales • Ancient SFHs • Model extinction distributions of young and old populations • Look for radial trends in age, metallicity, SF, etc • PHAT publically available: http://archive.stsci.edu/prepds/phat/ 12 August 2013

  15. 12 August 2013

  16. B21 F336W + F475W + F814W + F160W Dalcanton+ 2012 12 August 2013

  17. Measuring SFHs “Observed” CMD Model CMD observed density in bin i: ni model density in bin i: mi Maximize to find most likely SFH Dolphin 2002

  18. Padova Models: Marigo 2008 with AGB updates in Girardi 2010 • IMF: Salpeter • Binary Fraction: 0.35 • 50% completeness limit characterized by ASTs 12 August 2013

  19. Star Formation in UV-Bright Regions Jake Simones (University of Minnesota) PHAT B15 UV bright regions from Kang+ 2009 catalog Simones+ (submitted) 12 August 2013

  20. Star Formation in UV-Bright Regions • UV flux-determined SFRs assume SSP or constant SFR • Not a good assumption • Purple line: SFR from FUV flux • Blue line: <SFR> over 100 Myr • Green line: <SFR> over 500 Myr • Single Age, Single SFR not good approximations • Caveat: Region sizes are small (< 100 pc) 50 150 100 0 200 Age (Myr) Simones+ (submitted) 12 August 2013

  21. Star Formation in UV-Bright Regions Masses differ up to 2 orders of magnitude Integrated FUV flux over-predicts mean SFR from CMD-based SFH by a factor of 3- 5 Simones+ (submitted) 12 August 2013

  22. B15 Dalcanton+ 2012 12 August 2013

  23. Ancient SFHs PRELIMINARY B15F01 B15F04 Most mass forms between 10 and 6 Gyr ago. 12 August 2013

  24. Summary • Recent SFHs at 100pc resolution • Stability of 10-kpc star-forming ring over ~200 Myr • Extend to more bricks • Propagation of SFing events, interplay between gas and SF on small scales • SFH of UV-Bright Regions • UV-based estimates over-predict SFR, show mass discrepancy compared to SFH based quantities • Expand to larger regions • Ancient SFHs • Look for radial trends in age, metallicity, SF, etc • PHAT publically available: http://archive.stsci.edu/prepds/phat/ 12 August 2013

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