Dalcanton, Julianne J. and Melbourne, Jason L. (2012) The Panchromatic Hubble Andromeda Treasury. Astrophysical Journal Supplement Series, 200 (2). Art. No. 18. ISSN 0067-0049 http://resolver.caltech.edu/CaltechAUTHORS:20120712-093320878
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The Panchromatic Hubble Andromeda Treasury is an ongoing Hubble Space Telescope Multi-Cycle Treasury program to image ~1/3 of M31's star-forming disk in six filters, spanning from the ultraviolet (UV) to the near-infrared (NIR). We use the Wide Field Camera 3 (WFC3) and Advanced Camera for Surveys (ACS) to resolve the galaxy into millions of individual stars with projected radii from 0 to 20 kpc. The full survey will cover a contiguous 0.5 deg^(2)area in 828 orbits. Imaging is being obtained in the F275W and F336W filters on the WFC3/UVIS camera, F475W and F814W on ACS/WFC, and F110W and F160W on WFC3/IR. The resulting wavelength coverage gives excellent constraints on stellar temperature, bolometric luminosity, and extinction for most spectral types. The data produce photometry with a signal-to-noise ratio of 4 at m F_(275W) = 25.1, m_(F336W) = 24.9, m_(F475W) = 27.9, m_(F814W) = 27.1, m_(F110W) = 25.5, and m_(F160W) = 24.6 for single pointings in the uncrowded outer disk; in the inner disk, however, the optical and NIR data are crowding limited, and the deepest reliable magnitudes are up to 5 mag brighter. Observations are carried out in two orbits per pointing, split between WFC3/UVIS and WFC3/IR cameras in primary mode, with ACS/WFC run in parallel. All pointings are dithered to produce Nyquist-sampled images in F475W, F814W, and F160W. We describe the observing strategy, photometry, astrometry, and data products available for the survey, along with extensive testing of photometric stability, crowding errors, spatially dependent photometric biases, and telescope pointing control. We also report on initial fits to the structure of M31's disk, derived from the density of red giant branch stars, in a way that is independent of assumed mass-to-light ratios and is robust to variations in dust extinction. These fits also show that the 10 kpc ring is not just a region of enhanced recent star formation, but is instead a dynamical structure containing a significant overdensity of stars with ages >1 Gyr.
|Additional Information:||© 2012 American Astronomical Society. Received 2012 February 17; accepted 2012 March 29; published 2012 May 31. The authors are very happy to acknowledge discussions with Jay Anderson, Tom Brown, Suzanne Hawley, and Alesandro Bressan. We are grateful to Stefano Casertano for sharing the code to produce the exposure time maps in Figure 5, Alesandro Bressan for providing the tracks plotted in Figure 24, Jean-Charles Cuillandre for allowing us to use his CFHT imaging to tie our data to a global astrometric frame, to Pauline Barmby for providing us the Spitzer IRAC images, and the anonymous referee for an extremely knowledgeable and prompt report. The project has received superb support from personnel at the Space Telescope Science Institute, including Alison Vick, Ken Sembach, Neill Reid, and the ACS and WFC3 instrument teams. Zolt Levay is particularly thanked for the beautiful visualizations found in Figure 6, which far surpassed anything we were able to generate on our own. Stan Vlcek, Sarah Garner, and Pat Taylor at UW have been instrumental in helping with logistics for the project. This work was supported by the Space Telescope Science Institute through GO-12055. L.G. acknowledges support from contract ASI-INAF I/009/10/0.|
|Subject Keywords:||individual (M31); galaxies: stellar content; stars: general; stars: imaging|
|Official Citation:||The Panchromatic Hubble Andromeda Treasury Julianne J. Dalcanton et al. 2012 ApJS 200 18|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Jason Perez|
|Deposited On:||12 Jul 2012 18:29|
|Last Modified:||26 Dec 2012 15:30|
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