The Spitzer/IRS ATLAS project

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Presentation

The ATLAS project is a compilation of spectroscopic and photometric data from extragalactic sources, in particular star-forming and active galaxies, that have been observed with the Infrared Spectrograph (IRS) of the Spitzer Space Telescope.

The core of the project is a sample of around 750 spectra of low, intermediate and high redshift galaxies, and a database of mid-infrared spectral properties measured from them, as well as ancillary data (optical, infrared and radio photometry, redshifts, etc). Source types include seyferts, quasars, radiogalaxies, starburst galaxies, ULIRGs, submillimeter galaxies and others.

The aim of the project is double: to provide astronomers with a handy library of real MIR spectra they can use to benchmark their models, and to facilitate data miners in their quest for sources with specific properties, by providing an array of spectral measurements they can use to identify the best targets to be retrieved from the Spitzer Archive.

ATLAS sources are spread over the whole sky, but their density is higher in high galactic latitudes, in particular in several regions of low far-infrared diffuse galactic emission, where most extragalactic infrared surveys are carried out. Our selection does not put constraints on redshift, not even the existence of a consistent redshift estimate is required, but individual subsamples usually target certain redshift range, or indirectly bias the selection through flux or colour constraints.

Distribution of ATLAS sources in the sky: each white dot represents one ATLAS galaxy. The background image is the Planck one year all sky survey. Copyright ESA, HFI and LFI consortia.

The ATLAS sample is drawn from papers in the recent literature presenting Spitzer/IRS spectroscopy of active and star-forming galaxies (see the list of references here). Spitzer/IRS data include observations with both the Low-Resolution (R~100) and High-Resolution (R~600) IRS modules, most of them performed in staring mode.

The ATLAS spectra are extracted from postscript figures uploaded to the astro-ph preprint service by their authors, and thus do not contain all the information available in a fully reduced IRS observation. In particular, quality flags and flux uncertainties are missing (even if we have managed to at least partially overcome this), and many authors smooth or truncate the spectra in their plots. Because of this, researchers who require precise measurement of spectral properties or an accurate estimate of uncertainties are encouraged to use our database to find suitable candidates, and then obtain the latest version of the BCD data from the Spitzer Archive and perform a proper data reduction.