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Luminous Blue Galaxies


Spectra of a sample of luminous blue galaxies at 0.7 < z < 1.7 in a 143-square-degree subset of the BOSS survey area

Finding Targets

An object whose ANCILLARY_TARGET1 value includes one or more of the bitmasks in the following table was targeted for spectroscopy as part of this ancillary target program. See SDSS-III bitmasks to learn how to use these values to identify objects in this ancillary target program.

Program (bit name) Bit Target Description Target density
ELG 61 Luminous Blue Galaxies 22

Primary contact

Jean-Paul Kneib
Laboratoire d'Astrophysique de Marseille
jean-paul.kneib -at-

Other contacts

Johan Comparat, Sébastien Heinis, Anne Ealet, Stéphanie Escoffier, David Schlegel, Martin White, Nick Mostek, Alexie Leauthaud, Eric Huff, Will Percival, Jeffrey Newman


Studies from the second Deep Extragalactic Evolutionary Probe (DEEP2; Davis et al. 2003) reveal that the most luminous, most star-forming blue galaxies at z ~ 1 appear to be a population that evolves into massive red galaxies at lower redshifts (Cooper et al. 2008). Sampling 2,000 color-selected galaxies from either SDSS Stripe 82 or the CFHT-LS Wide fields (W1, W3, and W4) allows a measure of the clustering of the rarest, most luminous of these blue galaxies on large scales. Such a measurement has not yet been conducted, as prior galaxy-evolution motivated surveys have a limited field of view and mostly target fainter galaxies.

Target Selection Details

The galaxy targets were color-selected based on the CFHT-LS photometric-redshift catalog (Coupon et al. 2009). Different color selections were explored using either the (uPSF - gPSF , gPSF - rPSF ) color-color diagram down to gPSF < 22.5 or the (gPSF - rPSF , rPSF -iPSF) color-color diagram down to iPSF < 21.3. Detailed description of the color selection and redshift measurements will be discussed in Comparat et al (2012a, to be submitted). Using this dataset, photometric redshifts can be re-calibrated in the CFHT-LS W3 field, thereby reducing biases in redshift estimates at z > 1. Measurement of the galaxy bias of these luminous blue galaxies will be presented in Comparat et al (in preparation).

This dataset has been important in motivating the "extended-BOSS" project (PI, J.-P. Kneib), a survey that is proposed to begin in Fall 2014 as part of the successor to SDSS-III. The data will also be used to improve the targeting strategy of future projects such as BigBOSS (Schlegel et al. 2011).


Comparat, J. et al 2013, MNRAS, 428, 1498
Comparat, J. et al 2013, MNRAS, 433, 1146
Cooper, M. C., et al. 2008, MNRAS, 383, 1058
Coupon, J., et al. 2009, A&A, 500, 981
Davis, M., et al. 2003, in Discoveries and Research Prospects from 6- to 10-Meter-Class Telescopes II. Edited by Guhathakurta, Puragra. Proceedings of the SPIE, Volume 4834, 161-172
Schlegel, D., et al. 2011, ArXiv 1106.1706