PHAST

The Panchromatic Hubble Andromeda Southern Treasury (PHAST) is a large 195-orbit Hubble Space Telescope program designed to map roughly 0.45 square degrees of the southern half of M31’s star-forming disk at optical and near-ultraviolet (NUV) wavelengths. The PHAST survey extends the northern coverage of the Panchromatic Hubble Andromeda Treasury (PHAT) down to the southern half of M31, covering out to R~13 kpc along the southern major axis and, in total, roughly 2/3 of M31’s star-forming disk. The PHAST survey covers key diagnostic features that are sensitive to M31’s complex merger history, which were previously unconstrained by the northern disk observations alone. PHAST creates a legacy map with stellar photometry of over 90 million resolved stars using HST’s resolution and sensitivity, enabling a wide range of scientific endeavors.

The PHAST observations build on the techniques developed by the PHAT survey, utilizing a similar but more efficient tiling strategy at the cost of omitting the near-infrared filters that PHAT included. The survey’s fundamental coverage unit uses the larger UVIS footprint and requires only a single orbit per pointing, compared to the 2-orbit PHAT pointings using a smaller WFC3/IR footprint. At each pointing, WFC3/UVIS observations in the F275W and F336W filters, and ACS/WFC observations in the F475W and F814W filters, were taken in parallel within one orbit. All observations were taken at two orientations, separated by 180 degrees, to maximize survey coverage for all cameras and optimize the use of parallel exposures. The PHAST observations are grouped into 13 “bricks”, numbered 24 to 36, following the naming convention used in PHAT, which covered bricks 1 to 23. Each PHAST brick consists of a 3x5 array of WFC3/UVIS pointings, covering an area of 7.5’ x 12.5’ in both UV and optical wavelengths.

Filters: F275W + F336W (WFC3/UVIS), F475W + F814W (ACS/WFC)

Depth: The photometry achieves a 50% completeness-limited depth of m_F475W ~ 27.7, m_F814W ~ 26.2 for ACS data, and m_F275W ~ 24.8, m_F336W ~ 25.4 for UVIS data in the lowest surface density regions in the outer disk, while reaching m_F475W ~ 26.0, m_F814W ~ 24.0, m_F275W ~ 24.6, and m_F336W ~ 25.2 in the most crowded, high surface brightness regions near M31’s bulge. Crowding causes the limiting magnitude to be brighter in the optical bands.

MAST Portal and Astroquery

  All images are available in the MAST Portal and astroquery. Set the 'Provenance Name' filter to PHAST in the Portal Advanced Search to match all observations. The files can be downloaded for each field as a bundle or individually retrieved by selecting the download basket. The observations can also be retrieved programmatically using the astroquery.mast module. The code example below retrieves all the compressed images. Since the image data are larger than 50 GB altogether, we recommend using `curl_flag=True` when downloading with astroquery.

from astroquery.mast import Observations
all_obs = Observations.query_criteria(provenance_name="phast")
data_products = Observations.get_product_list(all_obs)
data_products = Observations.filter_products(data_products, extension="gz")
Observations.download_products(data_products, curl_flag=True)

• MAST Portal

  

  A web-based interface for cross-mission searches of data at MAST or the Virtual Observatory.

  Portal

• MAST Astroquery

  

  Search for and download PHAST data products programmatically in Python.

  MAST Astroquery

Direct Download Links

The image data are large. The file sizes are listed next to the links as (download size, uncompressed size). Because they are so large, we recommend that the compressed versions be downloaded either through the MAST portal, or using the cURL scripts provided here:

Other (non-imaging) data products can be downloaded directly using the links below:

The individual "brick" catalogs are also compressed. This table lists the direct links, followed by the (compressed, uncompressed) file sizes.