Size and Luminosity

Our observations of NVSS 2146+82 clearly show that it is an unusually large FR II radio galaxy. Its angular distance from the north lobe to the south lobe gives an unusually large extent of . For our assumed cosmology and our measured redshift of z=0.145, the linear extent of the radio structure is 4h₅₀^-1 Mpc, placing it in the Giant Radio Galaxy (GRG) class, which we define as sources larger than 2h₅₀^-1 Mpc. NVSS 2146+82 is therefore the second largest FR II known, surpassed only by 3C236 which is ~6h₅₀^-1 Mpc in extent. FR II galaxies of this size are extremely rare; a literature search by [Nilsson et al. (1993)] of 540 FR IIs contains only 27 objects with sizes greater than 1h₅₀^-1 Mpc. Of this sample of 27 large FR IIs, only 5 are larger than 2h₅₀^-1 Mpc. For comparison, the other known giant radio sources are shown in Table 6. The log radio luminosity of NVSS 2146+82 at 1.4 GHz is 25.69, in the middle of the range for giant radio sources.

 

 

Table 6: Giant Radio Galaxies

(arcsec) (h₅₀^-2 W Hz^-1 ) (h₅₀^-1 Mpc)

2146+82 NVSS 2146+82 0.1450 1175 25.69 3.91

0821+695 8C 0821+695 0.5380 402 26.30 2.94

1637+826 NGC6251 0.0230 4500 24.73 2.89

0319-454 0.0633 1644 25.83 2.72

1549+202 3C326 0.0885 1206 26.08 2.67

1358+305 B2 1358+305 0.2060 612 25.93 2.64

1029+570 HB13 0.0450 2100 24.57 2.54

0503-286 0.0380 2400 25.23 2.48

1452-517 MRC 1452-517 0.08 1218 25.66 2.48

0114-476 PKS 0114-476 0.1460 702 26.51 2.36

1127-130 PKS 1127-130 0.6337 297 27.53 2.30

0707-359 PKS 0707-359 0.2182 492 26.71 2.21

1910-800 0.3460 366 26.65 2.18

0745+560 DA240 0.0350 2164 25.39 2.07

0313+683 WENSS 0313+683 0.0902 894 25.64 2.01

It remains unclear if there are fundamental differences between GRGs and "normal'' radio galaxies. The relative paucity of known GRGs may be in part due to observational selection effects in past radio surveys. An alternative reason for the rarity of giant radio galaxies may be that the physical conditions necessary for the creation of a GRG are uncommon in the universe. Although the similarity between NVSS 2146+82 and other FR IIs suggests that it is a typical FR II radio galaxy at the extreme end of the size distribution, a study of a complete sample of radio galaxies that includes GRGs will have to be made to determine if GRGs are part of a continuous distribution in size of normal radio galaxies or if there are fundamental differences between GRGs and smaller FR IIs.