Star-Forming Radio Galaxies


Photo of Guinevere Kauffmann
Guinevere Kauffmann
MPA Garching


A search for star-forming galaxies in SDSS DR7 imaging that are also radio sources from FIRST

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
BLUE_RADIO 56 SDSS photometric galaxy with blue colors cross-matched to a radio source from FIRST 2,938 2,781


Joint analysis of SDSS, FIRST, and the NRAO VLA Sky Survey (NVSS; Condon et al. 1998) has shown that low-redshift radio AGNs play an essential role in regulating the growth of massive galaxies (e.g. Best et al. 2005, Best et al. 2007).

However, much less is known about the detailed interplay of gas cooling and radio feedback in more luminous radio galaxies at higher redshifts. Current samples are incomplete, in particular for radio galaxies with significant ongoing star formation.

Target Selection

This ancillary program selects radio galaxies with blue colors at z > 0.3 that would otherwise be missed from the LOWZ and CMASS samples. Galaxy targets were selected from DR7 photometry according to the following criteria:

  • extended morphology in SDSS photometry
  • clean ugriz model photometry and 17 < i < 19.9
  • ifib2 < 21.7
  • [(g – r) > 1.45] OR [(u – g) < 1.14 * (g – r)], where photometry is determined from model magnitudes

The last criterion is designed to color-select objects at z > 0.3. We cross-matched this sample with the FIRST catalog (July 2008 version) and selected all objects within 3″ of FIRST sources with fluxes > 3.5 mJy. Most targets were within 1.5″. Finally, we rejected objects spectroscopically observed by SDSS-I/II, and objects meeting the target selection criterion for the galaxy samples. In total there were 4,610 targets; we randomly sampled these to produce a final list of 4,170 ancillary targets.


Best, P. N., Kauffmann, G., Heckman, T. M., Brinchmann, J., Charlot, S., Ivezić, Ž., & White, S. D. M. 2005 (Abstract from ADS), MNRAS, 362, 25, doi:10.1111/j.1365-2966.2005.09192.x

Best, P. N., von der Linden, A., Kauffmann, G., Heckman, T. M., & Kaiser, C. R. 2007 (Abstract from ADS), MNRAS, 379, 894, doi:10.1111/j.1365-2966.2007.11937.x

Condon, J. J.; Cotton, W. D.; Greisen, E. W.; Yin, Q. F.; Perley, R. A.; Taylor, G. B.; Broderick, J. J. 1998 (Abstract from ADS), AJ, 115, 1693, doi:10.1086/300337