Luminous Blue Galaxies at 0.7 < z < 1.7


Photo of Jean-Paul Kneib
Jean-Paul Kneib
École Polytechnique Fédérale de Lausanne


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 bitmasks to learn how to use these values to identify objects in this ancillary target program.

Program (bit name) Bit number Target Description Number of Fibers Number of Unique Primary Objects
ELG 61 Luminous Blue Galaxies 3,661 3,516


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 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 had a limited field of view, and have mostly targeted fainter galaxies.

This dataset has been important in motivating the eBOSS project (PI, J.-P. Kneib), an ongoing survey of the SDSS. The data will also be used to improve the targeting strategy of future projects such as BigBOSS (Schlegel et al. 2011).

Target Selection

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 are discussed in Comparat et al (2013a).

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 are presented in Comparat et al (2013b).


Comparat, J. et al 2013a, MNRAS, 428, 1498

Comparat, J. et al 2013b, 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