The Panchromatic Hubble Andromeda Treasury: Triangulum Extended Region (PHATTER). I. Ultraviolet to Infrared Photometry of 22 Million Stars in M33
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We present panchromatic resolved stellar photometry for 22 million stars in the Local Group dwarf spiral Triangulum (M33), derived from Hubble Space Telescope observations with the Advanced Camera for Surveys in the optical (F475W, F814W), and the Wide Field Camera 3 in the near-ultraviolet (F275W, F336W) and near-infrared (F110W, F160W) bands. The large, contiguous survey area covers ∼14 square kpc and extends to 3.5 kpc (14′, or 1.5–2 scale lengths) from the center of M33. The PHATTER observing strategy and photometry technique closely mimics that of Panchromatic Hubble Andromeda Treasury, but with updated photometry techniques that take full advantage of all overlapping pointings (aligned to within <5–10 milliarcseconds) and improved treatment of spatially varying point-spread functions. The photometry reaches a completeness-limited depth of F475W∼28.5 in the lowest surface density regions observed in M33 and F475W∼26.5 in the most crowded regions found near the center of M33. We find the young populations trace several relatively tight arms, while the old populations show a clear, looser two-armed structure. We present extensive analysis of the data quality, including artificial star tests to quantify completeness, photometric uncertainties, and flux biases. This stellar catalog is the largest ever produced for M33, and is publicly available for download by the community.
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PHAST builds upon the strategy of the PHAT and PHATTER surveys, providing contiguous four-band coverage in the F275W, F336W, F475W, and F814W filters using single-orbit observations from ACS/WFC and WFC3/UVIS.
“PHAST builds upon the strategy of the PHAT (Dalcanton et al. 2012) and PHATTER (Williams et al. 2021) surveys, providing contiguous four-band coverage in the F275W, F336W, F475W, and F814W filters using single-orbit observations from ACS/WFC and WFC3/UVIS.”
From The Panchromatic Hubble Andromeda Southern Treasury (PHAST). II. The Spatially Resolved Recent Star Formation History in M31 (2026) · cites this paper as Williams et al. 2021
A standard way to characterize photometric uncertainties, completeness, and bias due to crowding, is to use artificial star tests (ASTs) inserted throughout the survey area.
“A standard way to characterize photometric uncertainties, completeness, and bias due to crowding, is to use artificial star tests (ASTs) inserted throughout the survey area (Dolphin 2002; Dalcanton et al. 2012; Williams et al. 2021; Chen et al. 2025).”
From The Panchromatic Hubble Andromeda Southern Treasury (PHAST). II. The Spatially Resolved Recent Star Formation History in M31 (2026) · cites this paper as Williams et al. 2021
Cites
Harris, C. R., Millman, K. J., van der Walt, S. J., Gommers, R., Virtanen, P., Cournapeau, D., Wieser, E., Taylor, J., Berg, S., Smith, N. J., et al. (2020) · Nature · doi:10.1038/s41586-020-2649-2 · Cited by 23,826 · see citing works
Lewis, A. R., Dolphin, A. E., Dalcanton, J. J., Weisz, D. R., Williams, B. F., Bell, E. F., Seth, A. C., Simones, J. E., Skillman, E. D., Choi, Y., et al. (2015) · The Astrophysical Journal · doi:10.1088/0004-637x/805/2/183 · Cited by 132 · see citing works
Self-citationLewis, A. R., Simones, J. E., Johnson, B. D., Dalcanton, J. J., Skillman, E. D., Weisz, D. R., Dolphin, A. E., Williams, B. F., Bell, E. F., Fouesneau, M., et al. (2017) · The Astrophysical Journal · doi:10.3847/1538-4357/834/1/70 · Cited by 16 · see citing works
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Lazzarini, M., Williams, B. F., Durbin, M. J., Dalcanton, J. J., Smercina, A., Bell, E. F., Choi, Y., Dolphin, A., Gilbert, K., Guhathakurta, P., et al. (2022) · The Astrophysical Journal · doi:10.3847/1538-4357/ac7568 · Cited by 28 · see citing works
Self-citationWainer, T. M., Williams, B. F., Chen, Z., Lazzarini, M., Dalcanton, J. J., Bell, E. F., Goold, K., Dolphin, A., Durbin, M. J., Dubón, S. L. F., et al. (2026) · The Astrophysical Journal · doi:10.3847/1538-4357/ae6db9
“A standard way to characterize photometric uncertainties, completeness, and bias due to crowding, is to use artificial star tests (ASTs) inserted throughout the survey area (Dol-phin 2002; Dalcanton et al. 2012; Williams et al. 2021; Chen et al. 2025).”
InfluentialSelf-citation
- Authors
- Williams, B. F., Durbin, M. J., Dalcanton, J. J., Lang, D., Girardi, L., Smercina, A., Dolphin, A., Weisz, D. R., Choi, Y., Bell, E. F., Rosolowsky, E., Skillman, E., Koch, E. W., Lindberg, C. W., Hagen, L., Gordon, K. D., Seth, A., Gilbert, K., Guhathakurta, P., Lauer, T., & Bianchi, L.
- ORCID
- Williams, Benjamin F.
- Durbin, Meredith J.
- Dalcanton, Julianne J.
- Lang, Dustin
- Girardi, Leo
- Smercina, Adam
- Dolphin, Andrew
- Weisz, Daniel R.
- Choi, Yumi
- Bell, Eric F.
- Rosolowsky, Erik
- Skillman, Evan
- Koch, Eric W.
- Lindberg, Christina W.
- Hagen, Lea
- Gordon, Karl D.
- Seth, Anil
- Gilbert, Karoline
- Guhathakurta, Puragra
- Lauer, Tod
- Bianchi, Luciana
- Venue
- The Astrophysical Journal Supplement Series
- Publisher
- American Astronomical Society
- Published
- 2021-04-01
- Volume
- 253
- Issue
- 2
- Pages
- 53
- ISSN
- 0067-0049 (ISSN-L)
- 1538-4365
- OpenAlex
- W3120457523
- Cited by
- 78
- References
- 3
- Citations by year
- 2026: 10 · 2025: 20 · 2024: 19 · 2023: 14 · 2022: 12 · 2021: 3
- FWCI
- 6.34
- Type
- journal article
- Language
- en
- Open access
- green
- arxiv.org
- Licence
- Locations
- The Astrophysical Journal Supplement Series (publishedVersion)
- UA Campus Repository (The University of Arizona) (acceptedVersion)
- arXiv (Cornell University) (submittedVersion)
- arXiv (Cornell University) (cc-by)
- Funders
- Space Telescope Science Institute (GO-14610)
- Topics
- Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Galaxies: Formation, Evolution, Phenomena
- Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Stellar, planetary, and galactic studies
- Physical Sciences › Physics and Astronomy › Instrumentation › Astronomy and Astrophysical Research
- Keywords
- M33, resolved stellar photometry, star catalogues, ultraviolet photometry, near-infrared photometry, young stellar populations, old stellar populations, spiral arms, point spread function, photometric completeness
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