LACOS

This collection consists of data from HST observations of 42 low-redshift (z~0.3) compact, star-forming galaxies, 22 of which are Lyman Continuum Emitters. Most of the data were observed as part of HST program GO 17069, with three galaxies having additional data from programs GO 14131, 14466 and 11107. The galaxies were imaged in five filters, sampling the rest-frame optical and UV emission with instruments WFC3/UVIS, ACS/SBC and ACS/WFC. This collection provides reduced images in each filter, Lyman-α line and continuum maps produced from SBC images and COS spectra, and a table containing properties for the sample. All images are corrected for Milky Way extinction and PSF-matched. 

This release (v1.0) of the data collection contains, for each galaxy: 

• Seven files of Multi-Extension FITS (MEF) per target with each FITS containing 2 frames each in total, split between science frames and standard deviation maps.
• One FITS table containing general properties and photometric measurements. 
• One PNG file with preview RGB optical composite

LACOS uses calibrated frames from MAST (`_flt` files) for ACS/SBC and calibrated, CTE-corrected frames from MAST (`_flc` files) for WFC3/UVIS and ACS/WFC. Additional cosmic ray rejection for is performed on UVIS and WFC data using a custom script. Dark current and sky subtraction is performed on SBC data. Images were pre-aligned using custom image alignment tool CROCOA. The images were then drizzled to a common scale of 0.04 arcsec/pix and aligned to a common coordinate frame. If necessary, the drizzled frames were background-subtracted. The SBC weight maps were recalculated to take into account the correlation of noise across pixels resulting from drizzling. The images were corrected for Milky Way dust extinction using the Fitzpatrick1999 law, and the images were PSF-matched.  

At the redshift of the LACOS galaxies, F150LP images contain contributions from both the Lyα line and UV continuum, while the F165LP image only samples the UV continuum. To produce the Lyα and UV continuum images, the SBC F150LP and F165LP data were subtracted, scaled by a normalization factor. This normalization factor was calculated to match the Lyα equivalent width values obtained from HST/COS spectra, within a 2.5" vignetted aperture centered on the brightest F165LP pixel. 

MAST Portal and Astroquery

The LACOS image data products are available in the MAST Search Portal (web-based, cross-mission search interface) and Astroquery (Python package to search for and download files from Python scripts you write). The catalog of photometric properties can be downloaded through the download link below.

• In the MAST Search Portal, set the Provenance Name filter to "LACOS" in an Advanced Search to find these data. The user guide for how to search and download products using the MAST Portal is available here.
• For Astroquery, the following example code demonstrates how to search for and download these products. This code assumes that you want to download all products from this HLSP, so you may want to consider narrowing down your search for large HLSPs (> 10 GB) or those with many individual files (> 10k). You can find more astroquery.mast tutorials here.

from astroquery.mast import Observations
# Search for all <HLSP-NAME> products
all_obs = Observations.query_criteria(provenance_name="lacos")
data_products = Observations.get_product_list(all_obs)
# Print the number of data products that would be downloaded
print(len(data_products))
# Download data
Observations.download_products(data_products)

• 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 data products for this HLSP programmatically in Python.

  MAST Astroquery

Direct download