A deep radio and optical survey near the North Galactic Pole - V. JHKobservations of a sample of 5C 12 optical identifications.
Abstract
Infrared JHK photometry is reported for 26 candidate optical identifications of faint radio sources (S_0.4 GHz_ > 14 mJy) from the 5C 12 survey. All object observed were detected with K < 18. The measurements show that the classes of object suggested as present among the 5C 12 identifications are distinct, particularly on the b-r, v-K plane, confirming both photographic photometry and star-galaxy separation techniques. The stellar objects coinsident with the radio sources have infrared excesses, typical of QSOs, and most have bvrJHK colours consistent with power laws Fnu_ is proportional to νalpha^, -1.5 < α <-0.5. Of the two bluest extended images observed, one has optical/infrared colours consistent with a power law (Fnu_ is proportional to νalpha^, α~-1) and may be a QSO confused by a close neighbouring image, while the other has colours similar to those predicted for a spiral galaxy - in fact, it is probably a misidentification with a foreground galaxy. The red extended images have apparent magnitudes and infrared and optical-infrared colours consistent with those expected for non-evolving giant elliptical galaxies at redshifts z < 0.6, and similar to those of 3CR radio galaxies. The lack of dependence of optical luminosity on radio luminosity for 10^24.5 < P_0.4GHz_ < 10^27.5^ W Hz^-1^ is thereby confirmed. Redshifts for these red galaxies have been estimated independently on the basis of apparent magnitudes and on the basis of colours. There is good agreement between the two estimates (rms difference: σ_z_~0.04 for z < 0.6), and a combination of the two techniques may provide an accurate estimate of redshift for low- to medium-redshift radio galaxies, although spectroscopic redshifts are needed to confirm this.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- November 1988
- DOI:
- 10.1093/mnras/235.2.465
- Bibcode:
- 1988MNRAS.235..465B
- Keywords:
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- Astronomical Spectroscopy;
- Faint Objects;
- Infrared Photometry;
- Radio Sources (Astronomy);
- Sky Surveys (Astronomy);
- Deep Space;
- Elliptical Galaxies;
- Flux Density;
- Luminosity;
- Quasars;
- Red Shift;
- Spiral Galaxies;
- Astronomy