CLASSY

Far-UV spectra are fundamental to our understanding of star-forming galaxies, providing a unique window on massive stellar populations, chemical evolution, feedback processes, and reionization. The launch of the James Webb Space Telescope (JWST) and construction of the extremely large telescopes (ELTs) will soon usher in a new era, pushing the UV spectroscopic frontier to z~15-20. The success of these future endeavors hinges on a comprehensive understanding of the massive star populations and interstellar medium (ISM) gas conditions that power the observed UV spectral features. This requires the level of detail that is only possible in local galaxies.  

The COS Legacy Spectroscopic SurveY (CLASSY) is a treasury survey that builds on the Hubble Space Telescope (HST) archive to construct the first high-quality, high-resolution far-ultraviolet (far-UV) spectral database of 45 nearby star-forming galaxies. The survey combines 177 orbits of archival observations with 135 new orbits (312 total orbits) of HST observations, or more than 600 total spectral images taken with the Cosmic Origins Spectrograph (COS). The CLASSY Treasury sample contains 45 star-forming galaxies selected to span similar properties as seen at high redshift, with a large range of masses, metallicities, ionization parameters, and densities, but enhanced star formation rates. The CLASSY spectral atlas contains a suite of emission and absorption features that enable investigations of the massive stellar population properties, the physical properties of large-scale outflows that regulate star formation, and the chemical abundance patterns of the gas and stars. Further, CLASSY will improve the diagnostic power of the rest-frame UV lines for use by future JWST/ELT surveys, providing a long-lasting legacy to the astronomical community for decades to come.

The main objective of CLASSY is to use FUV spectra to unify stellar and gas-phase physics, allowing a holistic understanding of massive stars as the drivers of the gaseous evolution of star-forming galaxies. Naturally, the pursuit of this goal will produce a number of additional HLSPs beyond the coadded spectra that will be useful to the astronomical community. Therefore, the enduring value and utility of CLASSY will reside in these state-of-the-art HLSPs products. 

Summary of Planned CLASSY Deliverables:

• CLASSY spectral atlas 

• Compiled ancillary data 

• CLASSY stellar continuum fits

• Database of emission and absorption feature properties

• Database of Lyα emission profile fits

• Database of tailored photoionization models

• Database of nebular properties

• UV Diagnostic Tools

• Database of tailored chemical evolution models

• Database of feedback properties

• Predictive tools of inferred LyC escape fractions %of ionizing photons

• Improved stellar models and prescriptions

• User-friendly CLASSY tutorials on interacting with and utilizing the HLSPs

• CLASSY Target Properties

  

  Target properties of the 45 CLASSY targets, including RA, Dec, redshift, stellar mass, star formation rate.

• CLASSY Observation Details

  

  View details on COS observations of CLASSY targets, including dataset names, exposure times, grating, wavelength coverage, and more.

• Download CLASSY Data

  

  MAST tool to download CLASSY data, including subset selection based on target properties, observation parameters, or file type.

HST/COS NUV acquisition images for the CLASSY sample are shown in blue, overlaid on top of the red-yellow SDSS r-band images (when available, see Berg+2021 for exceptions). The 2.5” COS aperture used for the UV spectra are shown as blue circles, closely matching the SDSS 3” optical aperture in orange.

CLASSY data products are available to download below. To download a tarball of HLSPs use the ‘Download All CLASSY data’ button. To download a subset of CLASSY products based on target properties, observation parameters, or file type, click the ‘MAST Query Tool’ button.

• Missions Search

  

  A web-based interface for searching by mission-specific metadata. Also available through astroquery.mast.

  CLASSY Mission Search

• Download All CLASSY Data

  

  Download tarball of CLASSY HLSPs

  Download File

Interactive HST/COS CLASSY spectra, combining archival and new FUV G130M+G160M+G185M observations. Note that chip gaps are indicated by blank spaces and that Milky Way absorption features and geocoronal lines are still present. By zooming in on different regions of the spectrum, you will see different stellar, ISM, and nebular features. Some of the common features are marked by colored bands and are labeled when you hover. You can click on the different types of spectral features in the legend to turn them on and off.

We extend our gratitude to the Lorentz Center for useful discussions during the “Characterizing Galaxies with Spectroscopy with a view for JWST” 2017 workshop that led to the formation of the CLASSY collaboration and survey.

We are sincerely grateful to the MAST team at STScI and their expertise in developing the MAST Search Tool for use with CLASSY data.