Jonas Haase

The Hubble Legacy Archive ACS grism data

A public release of slitless spectra, obtained with ACS/WFC and the G800L grism, is presented. Spectra were automatically extracted in a uniform way from 153 archival fields (or “associations”) distributed across the two Galactic caps, covering all observations to 2008. The ACS G800L grism provides a wavelength range of 0.55−1.00 μm, with a dispersion of 40 A/pixel and a resolution of ∼80 A for point-like sources. The ACS G800L images and matched direct images were reduced with an automatic pipeline that handles all steps from archive retrieval, alignment and astrometric calibration, direct image combination, catalogue generation, spectral extraction and collection of metadata. The large number of extracted spectra (73, 581) demanded automatic methods for quality control and an automated classification algorithm was trained on the visual inspection of several thousand spectra. The final sample of quality controlled spectra includes 47 919 datasets (65% of the total number of extracted spectra) for 32 149 unique objects, with a median iAB-band magnitude of 23.7, reaching 26.5 AB for the faintest objects. Each released dataset contains science-ready 1D and 2D spectra, as well as multi-band image cutouts of corresponding sources and a useful preview page summarising the direct and slitless data, astrometric and photometric parameters. This release is part of the continuing effort to enhance the content of the Hubble Legacy Archive (HLA) with highly processed data products which significantly facilitate the scientific exploitation of the Hubble data. In order to characterize the slitless spectra, emission-line flux and equivalent width sensitivity of the ACS data were compared with public ground-based spectra in the GOODS-South field. An example list of emission line galaxies with two or more identified lines is also included, covering the redshift range 0.2−4.6. Almost all redshift determinations outside of the GOODS fields are new. The scope of science projects possible with the ACS slitless release data is large, from studies of Galactic stars to searches for high redshift galaxies.

The End-to-End Pipeline for HST Slitless Spectra PHLAG

The Space Telescope-European Coordinating Facility (ST-ECF) is undertaking a joint project with the Canadian Astronomy Data Centre and the Space Telescope Science Institute to build a Hubble Legacy Archive (HLA) that contains science ready high level data products to be used in the Virtual Observatory (VO). The ST-ECF will provide extracted slitless spectra to the HLA, and for this purpose has developed the Pipeline for Hubble Legacy Archive Grism data (PHLAG). PHLAG is an end-to-end pipeline that performs an unsupervised reduction of slitless data taken with the Advanced Camera for Surveys (ACS) or the Near Infrared Camera and Multi Object Spectrometer (NICMOS) and ingests the VO compatible spectra into the HLA. PHLAG is a modular pipeline, and the various modules and their roles are discussed. In a pilot study, PHLAG is applied to NICMOS data taken with the G141 grism, and the first results of a run on all available data are shown.