NGC 0423 – pair alignments

To my knowledge, NGC 0423 has not been discussed as a discordant redshift system before. Figure 1 presents nearby objects that have redshift available. Almost all such objects within 10 arcmin are shown there (only three are little bit outside of the pictured field).

Higher redshift objects 2 and 4 are aligned across NGC 0423. The objects have almost same redshift (object 2 z = 0.106 and object 4 z = 0.105). Their distance from NGC 0423 is somewhat similar (d4/d2 = 1.3). Their magnitude is also similar. Alignment is almost exactly across the nucleus of NGC 0423. Field has lot of high redshift objects because it belongs to 2dF coverage area so some alignments are expected. Here we have two of three closest objects aligned almost exactly, and their redshift is the same. However, Object 6 (z = 0.105) also has the same redshift so we are looking at a possible galaxy group in traditional interpretation, and that would increase the odds of having same redshift objects aligned across the main galaxy.

Objects 14 and 17 are aligned across NGC 0423. They have almost same redshift (object 14 z = 0.224 and object 17 z = 0.202) and their angular distance from NGC 0423 is similar (d17/d14 = 1.04). So is their magnitude. There are couple of objects with similar redshift; object 16 has redshift of z = 0.224 and object 21 has redshift of z = 0.219. If we consider these four objects as a galaxy group, there is a problem with large velocity dispersion. When converted to velocity, the redshifts of objects 14 and 17 result in 5200 km/s difference. That seems too large considering that the group doesn’t seem to be very dense (high velocity differences between galaxies are traditionally thought to occur only in dense galaxy clusters). Of course, there is always the possibility that the group is very dense but we only have few redshifts of its members measured, but current knowledge would indicate that objects 14 and 17 don’t belong to same galaxy group. Objects 16 and 21 are situated quite close to each other, as seen in Figure 1, but they too have quite large velocity difference, about 1300 km/s. That is starting to be quite close to what can be traditionally accepted as a velocity difference of physically associated galaxies, but the difference still is suspiciously large.

Objects 11 and 5 are roughly aligned across NGC 0423 but they have very different redshifts and are different kind of objects also (object 5 is a high redshift QSO while object 11 is a galaxy). Object 8 is roughly aligned across NGC 0423 with objects 9 and 10. Redshifts of all objects are quite different, but at least objects 8 and 10 are both QSO’s and their angular distance from NGC 0423 is similar.

ngc0423_1
Figure 1. Objects with available redshift near NGC 0423. Size of the image is 15 x 15 arcmin. Image is from Digitized Sky Survey (POSS2/UKSTU Blue).

There is a strange situation with object 12 (ESO 412-012); it seems to be quite large object as its apparent size almost matches that of NGC 0423 but it has redshift of z = 0.136 in NED! I checked NED’s redshift data for it, and it seems to have three very different redshift values. The highest one, the 0.136 is from Stromlo-APM Redshift Survey (it is named as “412-003-029” in the galaxy.dat file), and it has been measured from absorption features. Lowest redshift is from The 2dF Galaxy Redshift Survey, and is also measured from absorption lines. Third redshift is said to be from Arp 1981, but I didn’t find the object in question there. HyperLeda gives the lowest value and doesn’t even list the high value. I assume that the lower redshift is the correct one, as the highest value doesn’t make any sense and the third redshift might not exist at all.

Objects 3 and 16 are aligned across object 12. Their redshifts are of same order and their magnitudes are similar. Objects 6 and 21 are also aligned across object 12 with similar situation on the redshifts and magnitudes. The whole situation with object 12 is that it has two objects on one side with redshift slightly above z = 0.1 and on other side the objects have roughly the z = 0.22. At the same side of z = 0.22 objects there’s also object 20 with z = 0.15.

Objects 9 and 10 are very close to each other but their redshifts are different. Object 9 is a z = 0.17 galaxy and object 10 is a z = 1.8 quasar. There’s no clear signs of interaction between them. See figure 2 for magnified image of them. Objects 13 and 14 both have apparent companion galaxies, but their redshift is not known. They are also shown in figure 2. Object 18 has two objects aligned across it, objects are directly to north (up) and south (down) from object 18, they also don’t have measured redshifts available.

ngc0423_2
Figure 2. Two sections of zoomed in image of NGC 0423 field. Objects discussed in the text are marked. Image is from Digitized Sky Survey (POSS2/UKSTU Blue) and it has been magnified 4x.

Objects and their data

NBR NAME TYPE REDSHIFT MAG SEPARATION
1 NGC 0423 S0/a? pec 0.005344 14.20 0
2 2dFGRS S294Z221 galaxy 0.105538 18.83 2.409
3 2dFGRS S293Z160 galaxy 0.122800 19.36 2.968
4 2dFGRS S294Z229 galaxy 0.104500 18.22 3.142
5 [VCV2001] J011136.5-291318 QSO 2.397000 20.59 3.215
6 2dFGRS S293Z159 galaxy 0.105200 19.09 3.309
7 [VCV2001] J011140.9-291415 QSO 0.960000 20.41 4.081
8 2QZ J011108.6-291654 NELG 0.606400 20.2 (B) 4.101
9 2dFGRS S294Z216 galaxy 0.169287 19.15 4.821
10 2QZ J011140.4-291056 QSO 1.818600 19.9 (B) 5.066
11 2dFGRS S293Z165 galaxy 0.091300 19.02 5.158
12 ESO 412-012 dwarf spiral 0.018000 16.42 6.004
13 2dFGRS S294Z225 galaxy 0.098000 19.14 6.555
14 2dFGRS S294Z230 galaxy 0.223900 19.32 7.279
15 2dFGRS S293Z154 galaxy 0.115653 19.37 7.403
16 2dFGRS S293Z149 galaxy 0.224205 19.13 7.568
17 2dFGRS S293Z157 galaxy 0.202069 19.43 7.593
18 2dFGRS S293Z148 galaxy 0.154600 18.68 7.612
19 2dFGRS S293Z158 galaxy 0.061100 16.95 7.880
20 2dFGRS S293Z150 galaxy 0.154700 19.20 8.110
21 2dFGRS S294Z213 galaxy 0.218600 19.44 9.508

NED objects within 10′ from NGC 0423.

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