PGC 029656 – high redshift galaxy within disk

To my knowledge, PGC 029656 system has not been discussed as discordant redshift system previously. Discordant redshift aspect of this system is the high redshift object (object 2 in Figure 2, z = 0.105) within PGC 029656 (object 1) disk. The object is not just within the disk, but it also is located so that it seems as if the spiral arm of PGC 029656 would lead to this object.

Object 2 is part of a compact galaxy group according to McConnachie et al. (2009). There is indeed one other galaxy nearby (object 3) at same redshift as object 2. Name of the group is SDSSCGB 48128 and it has 4 members. Only two of them (objects 2 and 3, as mentioned above) seem to have redshifts available. Other two members have been marked by “G” in Figure 2.

If we look at the colors of the 4 galaxies in the group, we notice that object 2 has quite different color than others. This might not mean much as galaxies do come in different colors, but it does arise the question of possible reddening of object 2 due to effect of PGC 029656’s disk. Figure 1 shows the magnitudes of the 4 objects in UGRIZ bands as given in SDSS SkyServer.

Figure 1. UGRIZ magnitudes of the objects in galaxy group SDSSCGB 48128. G1 is the closer “G” from PGC 029656.

We see that object 2 stands out here from others. It does seem that U band is dampened in this object more than in other 3 objects (these are apparent magnitudes in which larger value means less bright). But we don’t know if that is what is supposed to happen in such colored objects. I compared object 2’s UGRIZ profile with UGRIZ profile of another similar colored object (the one above and to the left from object 3). The other object also shows dampened U band (also G band is dampened somewhat compared to other objects) but perhaps not as much as object 2. It seems that we don’t get good evidence of reddening from this analysis. But at least we tried.

Object 2 is within PGC 029656 disk so we can assume, if object 2 is behind the material in PGC 029656’s disk, that the material from PGC 029656’s disk also shows up in magnitude measurements of object 2. From Figure 1 we see that object 2 is clearly the brightest (in G, R, I, and Z bands) of the four galaxies in this apparent background group. This probably suggests that the UGRIZ profile of this object is distorted by the presence of PGC 029656’s disk.


– NED says about object 2: “This is part of the galaxy CGCG 064-085”. That of course can’t be so in traditional view because of large redshift difference.

Figure 2. The objects with measured redshifts near PGC 029656. Size of the image is about 3.4 x 3.4 arcmin. Image is from Sloan Digital Sky Survey.

Objects and their data

1 PGC 029656 galaxy 0.027512 (8248 km/s) 15.1 0
2 SDSS J101101.31+095045.1 galaxy 0.104887 16.5 (g) 0.308
3 SDSS J101103.85+095126.8 galaxy 0.104861 18.6 (g) 1.125

NED objects within 10′ from PGC 029656


McConnachie et al., 2009, MNRAS, 395, 255, “Compact groups in theory and practice – III. Compact groups of galaxies in the Sixth Data Release of the Sloan Digital Sky Survey”

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: