UGC 10806 – a line of galaxies with two different redshifts

Preprint of Melnyk et al. (2009) was just inserted to arXiv. One of the objects in their study is UGC 10806. See their figure 2, which shows UGC 10806 field. Four most obvious galaxies in the pictured field form a line, but the objects in the line have discordant redshifts. Two galaxies are at cz ~ 1000 km/s and two are at cz ~ 7500 km/s. Melnyk et al. (2009) say:

The two faint ”companions” to the west of UGC10806 have radial velocities of +7354 and +7569 km/s; that is, they are objects in the distant background.

The line alignment is somewhat off-center of UGC 10806, but besides UGC 10806, the alignment is very exact.

Melnyk et al. (2009) fig. 2 shows the field of 15′ x 8′. Let us look full 15′ x 15′ field. It is presented here in Fig. 1. There we see the four objects described by Melnyk et al. (2009), the UGC 10806 (object 1) and its three nearby galaxies (objects 2, 3, and 4). However, we note that there are couple of other obvious galaxies in the wider field (for some reason Melnyk et al. have not included them into their sample). Objects 5 and 6 have even higher redshift than objects 3 and 4. Objects 5 and 6 also have similar redshift to each other, so they are probably a physical pair of galaxies. The presence of these two galaxies makes the probability bigger for the apparent line alignment (more objects – bigger probability for any alignments to occur).

ugc10806_1
Figure 1. The biggest galaxies near UGC 10806. Size of the image is 15 x 15 arcmin. Image is from Digitized Sky Survey (POSS2/UKSTU Blue).

Let us also look at all objects with available redshifts near UGC 10806. They are shown in Fig. 2. This area has been covered by the Kitt Peak Galaxy Redshift Survey, so there’s quite many objects with redshifts. There are no remarkable alignments. Objects 12 and 14 are roughly aligned across the main galaxy. Redshift of object 4 is quite accurately twice the redshift of object 12 (z14/z12 = 2.029).

Objects 11, 13, and 14 have very similar redshifts, their redshift velocity (calculated from relativistic Doppler redshift line of sight equation) is within 300 km/s, so they could be part of a background galaxy group. Object 14 seems to be situated quite far away from other two, though.

Redshifts of objects 9 and 10 are close to each other, and they are also situated near each other. However, their redshift velocity differs by 1250 km/s, which is rather large for a physical galaxy pair, unless they are in a galaxy cluster.

ugc10806_2
Figure 2. The objects with available redshifts near UGC 10806. Size of the image is 7 x 7 arcmin. Image is from Digitized Sky Survey (POSS2/UKSTU Blue).

Objects and their data

NBR NAME TYPE REDSHIFT (cz) MAG SEPARATION
1 UGC 10806 SBdm 0.003109 (932 km/s) 13.73 0
2 LEDA 167108 galaxy 0.003400 (1019 km/s) 16.88 3.126
3 LEDA 167103 galaxy 0.024000 (7195 km/s) 16.27 3.273
4 171812.0+495615 galaxy (7569 km/s) 7.7
5 UGC 10816 Scd 0.033046 (9907 km/s) 15.6 6.396
6 2MASX J17191363+4958366 galaxy 0.033200 (9953 km/s) 15.55 6.608
7 HERC-1:[MKK97] 308890 PofG? 0.003000 (899 km/s) 12.58 0.757
8 HS 1717+4955 PofG? 0.003466 (1039 km/s) 17.7 0.891
9 HERC-1:[MKK97] 308000 galaxy 0.384400 20.05 1.699
10 HERC-1:[MKK97] 307733 galaxy 0.390800 19.65 2.142
11 HERC-1:[MKK97] 307422 galaxy 0.312400 19.46 2.758
12 LEDA 167145 galaxy 0.153900 17.92 2.965
13 HERC-1:[MKK97] 307244 galaxy 0.311200 18.85 3.119
14 HERC-1:[MKK97] 309090 galaxy 0.312200 18.57 3.340

NED nearby objects search for UGC 10806.

References

Melnyk et al., 2009, arXiv, 0906.1493, “Search For Companions Of Nearby Isolated Galaxies”

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