3C 303 – a nearby QSO with possible radio bridge

Kronberg (1976) studied the radio structure of 3C 303 field. Kronberg noted:

Also visible is a low brightness extension of the western component toward the southwest. This extension is approximately superposed on a ~19.5 mag object at ([alpha] = 14h41m22s68, [sigma] = 52[degrees]14’18″0) which is clearly visible in Figure 1 and which we shall call object C.

At that time, object C (object 2 in figure 1) wasn’t yet identified, but there were some spectral knowledge from Burbidge indicating it was not a star or a normal radio galaxy nucleus. Kronberg also showed that there were two other objects very close to object C and that all three objects showed ultraviolet excess. Object that Kronberg called G was best positioned with the end of the radio extension (or rather the second component of the double radio source). Kronberg et al. (1977) published further radio observations and spectra observations. They said on the radio extension:

The existence of the faint features between the two main radio components strongly suggests that the latter are physically connected and are not just a chance superposition of unrelated radio systems (Kronberg 1976).

Kronberg et al. (1977) measured the spectrum of the object C. It turned out to be a quasar with redshift of z = 1.57. They then discussed the possible explanations of the system, one question being if the object C was in the background. They calculated the probability for the chance projection of object C to be about 0.001. Their analysis showed that there were no satisfactory explanation with the information available at that point.

Lonsdale et al. (1983) produced new radio maps of the field. The maps didn’t show much association between the radio sources and the quasar, but they showed that Kronberg’s object G was likely to be associated with the other radio component (commonly referred to as a radio hotspot). Arp (1987) mentioned this system as an example of a possible bridge between lower and higher redshift objects.

Meisenheimer et al. (1997) studied the system in infrared. They detected the bridge between the two radio sources. They weren’t able to determine if the object G was the one associated with the radio hotspot but it seemed very probable as the object G showed the similar structure as the radio hotspot. They concluded that the radio hotspot candidate was not actual radio hotspot, but just a bright knot in the jet of 3C 303. Lähteenmäki & Valtaoja (1999) made some observations that showed that the object G is indeed the optical object that corresponds to the radio hotspot. They didn’t find any connection with the quasar (object C).

Kataoka et al. (2003) studied the system in X-rays. They first showed a radio image of the system where the quasar seems to lie within the general radio feature of the system. Their X-ray image shows the quasar to be “in touch” with the radio hotspot (which in turn is clearly bridged to 3C 303 in radio image) but it is impossible to say that the apparent connection would be anything else than an overlapping effect.


Objects 4 (cz = 26791 km/s) and 9 (cz = 26806 km/s) have lower redshift than 3C 303. They also have similar redshift to each other, and there’s one more object (SDSS J144314.14+515610.0, cz = 26823 km/s) little outside the pictured field in figure 1 that has similar redshift. They form a probable galaxy group with mean redshift of cz = 26807 km/s. Group’s redshift dispersion is very small, maximum dispersion is only 16 km/s. Object 9 has almost exactly the mean redshift and is brightest of the three, so it would be natural main galaxy candidate for the group. On the other hand, object 4 has largest major diameter (0.33 against 0.25 and 0.12 of objects 9 and the one outside the field respectively). If object 4 would be the main galaxy, the other group members would have slightly higher redshift than the redshift of the main galaxy.

There are three objects that have similar redshift as 3C 303 (cz = 42327 km/s): object 3 (cz = 42049 km/s), object 5 (cz = 42931 km/s), and object 7 (cz = 42574 km/s). They form a probable galaxy group with mean redshift of cz = 42470 km/s. Group’s redshift dispersion is 461 km/s at maximum. There are two good main galaxy candidates; 3C 303 is brightest and object 7 has largest major diameter. Both of these objects are closest to the mean redshift of the group (object 7 being the closest to the mean). Object 3 is smallest and faintest but has lowest redshift.

There is a line of four objects; object 6 (z = 0.43), 3C 303 (z = 0.14), object 3 (z = 0.14), and object 5 (z = 0.14). Line is very straight and one of the objects has discordant redshift (object 6). There is a similar situation with objects 9 (z = 0.09), 4 (z = 0.09), and 8 (z = 0.16), but there object 8 is slightly off the line.

Figure 1. The field around 3C 303. Size of the image is 10 x 10 arcmin. Image is from Digitized Sky Survey (POSS2/UKSTU Blue) and it has been adjusted for brightness and contrast to bring out faint objects.

Objects and their data

1 3C 303 N galaxy, BLRG 0.141186 17.6 (G) 0
2 3C 303C QSO 1.570000 19.97 0.275
3 SDSS J144301.15+520153.9 galaxy 0.140261 19.6 (G) 0.373
4 SDSS J144317.79+520209.5 galaxy 0.089365 17.6 (G) 2.374
5 SDSS J144251.74+520321.6 galaxy 0.143201 17.9 (G) 2.429
6 SDSS J144313.85+515946.6 galaxy 0.433745 21.2 (G) 2.512
7 SDSS J144313.09+520356.4 galaxy 0.142013 17.9 (G) 2.811
8 SDSS J144307.10+520440.0 galaxy 0.157260 18.6 (G) 3.119
9 SDSS J144326.46+515953.4 galaxy 0.089415 17.3 (G) 4.038

NED objects within 10′ from 3C 303 with redshifts available.

SDSS image of 3C 303 system.


Arp, 1987, IAUS, 124, 479, “Observations requiring a non-standard approach”

Kataoka et al., 2003, A&A, 399, 91, “Chandra detection of hotspot and knots of 3C 303”

Kronberg, 1976, ApJ, 203, 47, “3C 303: a source with unusual radio and optical properties”

Kronberg et al., 1977, ApJ, 218, 8, “The radio structure and optical field of 3C 303”

Lonsdale et al., 1983, MNRAS, 202, 1, “The radio structure of 3C303 at 408 MHz”

Lähteenmäki & Valtaoja, 1999, AJ, 117, 1168, “Optical Polarization and Imaging of Hot Spots in Radio Galaxies”

Meisenheimer et al., 1997, A&A, 325, 57, “The synchrotron spectra of radio hot spots. II. Infrared imaging”

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