AM 0058-402 – bridged discordant redshift objects

Arp (1980) reported three new discordant redshift cases. One of the reported systems was AM 0058-402. This system has main galaxy (object 1) connected to an apparent companion (object 2) galaxy with a spiral arm-like bridge. Problem is that main galaxy has radial velocity cz = 6773 km/s while the companion has radial velocity 16415 km/s, so the difference in these velocities is too large for them to be physically connected in traditional view. Arp says this about the bridge:

On this latter higher-resolution photograph, it is seen that the connecting filament is in the nature of a spiral arm emerging from the larger galaxy. But the arm is much longer than any of the other arms in the galaxy, emerges orthogonally rather than tangentially from the main body, and terminates directly at the center of the companion.

Notes

Figure 1 shows nearest objects with measured redshifts in AM 0058-402 field.

– The bridged object, object 2, seems to belong to a group of galaxies at about 16500 km/s. Object 19 (which is just outside the pictured field) is brightest and seemingly largest of the galaxies in this group, and might be the main galaxy of the group. Objects in the group (within this field) are 2, 6, 7, 8, 11, 16, and 19.

– There seems to be another group at redshift z = 0.177. This group seems to be overlapping with the 16500 km/s group described above. Objects in this group are 9, 10, 13, 14, and 17.

– Objects 12 and 15 are roughly aligned across object 1. Object 3 also falls to their alignment line.

AM0058_402
Figure 2. The objects with measured redshifts near AM 0058-402. Size of the image is about 15 x 15 arcmin. Image is from Digitized Sky Survey. Click for larger version of the image.

Objects and their data

NBR NAME TYPE REDSHIFT MAG SEPARATION
1 MCG -07-03-005 spiral 0.022592 (6773 km/s) 14.5 0
2 PGC 003633 galaxy 0.054755 (16415 km/s) 15.6 (I) 0.426
3 ESP 40160 galaxy 0.105483 18.60 0.948
4 ESP 38602 galaxy 0.223564 19.21 2.551
5 ESP 38632 galaxy 0.115486 19.13 3.021
6 ESP 38526 galaxy 0.055215 (16553 km/s) 19.18 3.706
7 ESP 40626 galaxy 0.053981 (16183 km/s) 17.33 4.657
8 ESP 40625 galaxy 0.054845 (16442 km/s) 17.86 6.093
9 ESP 40187 galaxy 0.179334 18.29 6.479
10 ESP 40161 galaxy 0.177549 18.65 6.733
11 ESP 38528 galaxy 0.055582 (16663 km/s) 18.84 6.858
12 ESP 38482 galaxy 0.188030 19.38 6.875
13 ESP 38605 galaxy 0.176455 18.94 6.912
14 ESP 38669 galaxy 0.177936 18.99 7.119
15 ESP 38704 galaxy 0.107267 19.03 7.224
16 ESP 38529 galaxy 0.054858 (16446 km/s) 18.84 7.258
17 ESP 40188 galaxy 0.179994 18.72 7.799
18 [VCV2001] J010031.5-401351 QSO 0.610000 17.90 7.958
19 LEDA 101141 E 0.054948 (16473 km/s) 16.17 7.961
20 ESP 38483 galaxy 0.159123 18.95 8.449

NED objects within 10′ from AM 0058-402

References

Arp, H. 1980, Astrophysical Journal, Part 1, vol. 239, July 15, 1980, p. 469-471, 473, 474, “Three new cases of galaxies with large discrepant redshifts”

NGC 4460 – high redshift object within disk

It seems that NGC 4460 system hasn’t been discussed as discordant redshift system before. NGC 4460 has a high redshift object (object 2, z = 0.173) within its disk. NED says this about object 2: “This is part of the galaxy NGC 4460. Either z or Dxd is incorrect.” Quite confident statement considering that object 2’s appearance is not something you would expect to see in NGC 4460’s disk, and fits rather well with a background galaxy shining through NGC 4460’s disk.

Object 3 also has discordant redshift compared to NGC 4460, and it is very close to NGC 4460. There’s nothing apparent to suggest interaction in the system, so this seems to be genuine background object (also the appearance of object 3 suggests background galaxy in my opinion).

Notes

Only two additional redshifts are available in the field despite it being within SDSS coverage area. Object 4 has similar redshift to NGC 4460, so apparently it is an object of NGC 4460’s disk. Additionally there’s one star in the field. Both of these redshifts are in SDSS DR9 and they are not yet available in NED.

NGC4460
Figure 1. The objects with measured redshifts near NGC 4460. Size of the image is about 6.8 x 6.8 arcmin. Image is from Sloan Digital Sky Survey. Click for larger version of the image.

Objects and their data

NBR NAME TYPE REDSHIFT MAG SEPARATION
1 NGC 4460 SB(s)0+? sp 0.001634 (490 km/s) 12.26 0
2 SDSS J122848.76+445208.7 galaxy 0.172950 15.2 (g) 0.638
3 SDSS J122842.63+445230.3 galaxy 0.066883 (20051 km/s) 18.0 (g) 0.833
4 SDSS J122841.41+445054.9 part of galaxy (544 km/s) 20.92 (g) 1.188

NED objects with measured redshifts within 10′ from NGC 4460

2dFGRS N379Z082 – another case of high redshift galaxy within disk

Apparently 2dFGRS N379Z082 system has not been discussed as discordant redshift system before. The main galaxy (2dFGRS N379Z082, object 1) has redshift of z = 0.08 (cz ~ 24000 km/s). Within its disk there is object 2 that has redshift of z = 0.163. These redshifts suggest, if interpreted traditionally, that object 2 is a background object that has been accidentally positioned behind the main galaxy and shining through the main galaxy disk.


Figure 1. Closeup of 2dFGRS N379Z082 system. Image is from Sloan Digital Sky Survey.

There are lot of galaxies in the universe so we would expect to see some of them to fall close to same lines of sight, so we can’t really say if the position of the high redshift object within the main galaxy disk is unexpected. However, Figure 2 below shows that the field near this system has lot of objects at the redshift of main galaxy (cz ~ 24000 km/s) and at the redshift of object 2 (cz ~ 49000 km/s). In fact, it seems that if you would have to get two of all these objects shown very close together (such as the situation with objects 1 and 2), you would be most likely to succeed in that with objects having radial velocities of 24000 and 49000 km/s, because there seems to be most objects at those two radial velocities (i.e. redshifts). So, the presence of groups at the redshifts of both objects increases the probability of chance projection.


Figure 2. Objects with redshift available in NED within 20 arcmin from 2dFGRS N379Z082. X axis is angular separation from 2dFGRS N379Z082 and Y axis is the redshift (shown as radial velocity, cz) of the object. Excluded are objects with redshift quality problems and galaxy group entries.

One curious coincidence here is that the redshift of the higher redshift group is very closely twice the redshift of the lower redshift group. Figure 2 also shows a banded structure so that at some radial velocity ranges there are lot of objects and some radial velocity ranges don’t have any objects.

The question always presented with these kind of systems is that should the background galaxy show so well through the disk of the main galaxy? To this I don’t have answer, but object 2 is somewhat at the outskirts of the main galaxy disk, so seeing through the disk might be more probable there.

Notes

Figure 3 below shows the field near 2dFGRS N379Z082 and object data is presented below that. Some notes on the field:

– There are some stars in the field marked by their radial velocity (ones that have number followed by “km/s”). These are given in SDSS DR9 (NED only gives objects to SDSS DR6 level currently).

– Although there are many objects with redshifts in the field, there are no good alignments across lower redshift galaxies. However, field has a possibly interesting alignment. Object C seems to be a galaxy that has two blue stellar appearing objects (D and E) aligned across it. It would be interesting to know the redshifts for these three objects.

– Object 10 has another redshift measurement within its disk (z = 0.080900, 24253 km/s).

– Object 10 has two very close objects (A and B). object A has redshift close to object 10 in NED but its quality is marked as “FoF”, which I don’t know what it means, but usually these redshift quality flags indicate uncertain redshift.

2dFGRS_N379Z082
Figure 3. The objects with measured redshifts near 2dFGRS N379Z082. Size of the image is about 6.7 x 6.7 arcmin. Image is from Sloan Digital Sky Survey. Click for larger version of the image.

Objects and their data

NBR NAME TYPE REDSHIFT MAG SEPARATION
1 2dFGRS N379Z082 galaxy 0.080021 (23990 km/s) 17.0 (g) 0
2 SDSS J120040.27-000800.1 galaxy 0.163021 19.3 (g) 0.104
3 SDSS J120041.61-000923.3 galaxy 0.49599 (DR9) 22.1 (g) 1.389
4 SDSS J120044.69-000922.4 galaxy 0.165374 18.1 (g) 1.769
5 2dFGRS N380Z131 galaxy 0.164100 18.4 (g) 1.825
6 2dFGRS N379Z077 galaxy 0.165720 17.6 (g) 1.834
7 2dFGRS N379Z078 galaxy 0.163164 18.2 (g) 2.191
8 SDSS J120046.64-000620.1 galaxy 0.166192 18.9 (g) 2.408
9 2QZ J120047.5-000939 galaxy 0.206 20.7 2.470
10 SDSS J120028.87-000724.8 galaxy 0.081336 (24384 km/s) 16.1 (g) 2.843
11 SDSS J120029.52-000943.3 galaxy 0.43266 (DR9) 22.2 (g) 3.086
12 2dFGRS N379Z088 galaxy 0.177200 19.39 3.298
13 SDSS J120028.47-000619.1 galaxy 0.257866 20.6 (g) 3.356
14 SDSS J120026.81-000611.1 galaxy 0.257464 21.0 (g) 3.781
15 2dFGRS N379Z087 galaxy 0.200016 18.8 (g) 4.373

NED objects within 10′ from 2dFGRS N379Z082