3C 343.1 – radio bridged QSO-galaxy pair

Spinrad et al. (1977) studied the 3C 343.1 system. They gave a (somewhat uncertain) redshift of z = 0.750 for the object they called a “faint galaxy”. They compared the isophotal diameter vs. redshift of 3C 343.1 to that of few other similar objects, and found out that the isophotal diameter of 3C 343.1 matches well with a galaxy of z = 0.75, supporting their redshift determination. They also noted that 3C 343.1 is bluer than similar objects usually are.

Fanti et al. (1985) made radio maps of radio sources, including this system (see their Fig. 11). Two more radio maps of the system was published by van Breugel et al. (1992, see their Fig. 23). Also, de Vries et al. (1997) published radio map and HST image of the system (see their Fig. 2.26). All these radio maps showed two apparently connected radio sources, and HST image also seems to show two objects. Tran et al. (1998) studied this system along with few other systems. They found out something interesting:

A most surprising finding, however, is that the redshift of the absorption lines is radically smaller (z = 0.344) than that of the nuclear AGN emission lines (z = 0.75)!

So they found out that the system has two very different redshift systems. They also noted that the lower redshift system shows some emission lines as well. They showed that lower redshift system is more extended than the higher redshift system, so they concluded that there must be two different objects in a chance alignment. They gave some basic properties for each object, and also discussed the possibility of gravitational lensing.

Arp et al. (2004) reviewed the system, and discussed it as an ejecting system where the QSO would have been ejected from the lower redshift galaxy. They calculated that the probability for the chance projection is 1 x 10-8 (or, one in a hundred million), and said that it is a conservative estimate. They also calculated the intrinsic redshift of the quasar, if it would be at the distance of the lower redshift galaxy, and found out that it is very close to one of the Karlsson redshift peaks.


For those who like to check out the presented calculations, there’s a minor mistake in the Arp et al. (2004) equation relating to the intrinsic redshift calculation (see their section 5), a square bracket is missing:

They showed it like this:

(1 + zi) = (1 + zq)/(1 + zg)(1 + zd) ] = 1 + 0.302

But it should be:

(1 + zi) = (1 + zq)/[ (1 + zg)(1 + zd) ] = 1 + 0.302

Figure 1 shows the field of 3C 343.1, but there’s no other objects with available redshifts within 10 arcmin, and 3C 343.1 itself doesn’t show very well in the image. See the referred papers for better images, especially de Vries et al. (1997).

Figure 1. The 3C 343.1 field. 3C 343.1 is at the center, but does not show very well. Size of the image is 5 x 5 arcmin. Image is from Digitized Sky Survey (POSS2/UKSTU Blue).

Objects and their data

1 3C 343.1 galaxy 0.344 0
2 3C 343.1 NLRG, Sy2 0.750000 20.71 ~0.004

NED page for 3C 343.1.


Arp et al., 2004, A&A, 414, 37, “The double radio source 3C 343.1: A galaxy-QSO pair with very different redshifts”

de Vries et al., 1997, ApJS, 110, 191, “Hubble Space Telescope Imaging of Compact Steep-Spectrum Radio Sources”

Fanti et al., 1985, A&A, 143, 292, “Compact Steep Spectrum 3CR radio sources – VLBI observations at 18 CM”

Spinrad et al., 1977, ApJ, 216, 87, “Spectroscopy and photometry of the distant radio galaxy 3C 343.1”

Tran et al., 1998, ApJ, 500, 660, “Scattered Radiation from Obscured Quasars in Distant Radio Galaxies”

van Breugel et al., 1992, A&A, 256, 56, “Compact steep-spectrum 3 CR sources – VLA observations at 1.5, 15 and 22.5 GHz”


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