Abell 85 – galaxy sheets or quantized redshifts?

Beers et al. (1991) measured some new redshifts for Abell 85 (among few other clusters). They first noted that the velocity spread for the Abell 85 is very large. Then they noted that there are five galaxies at lower redshift so that there is a clear gap between regular Abell 85 radial velocity distribution and radial velocities of the five galaxies (between 13000 and 14500 km/s), so they suggested that the five galaxies belong to a foreground group. Even after the deletion of the five galaxies from the Abell 85 sample, the Abell 85 distribution didn’t show gaussian profile which lead them to hypothesize that Abell 85 might have further substructure. They noted that there had been similar results reported by Kriss et al. (1989) but that was a conference presentation and doesn’t even have abstract available in ADS. However, Malumuth et al. (1992) has Kriss as one of the Authors, so perhaps it is the same study reported in Kriss et al. (1989).

Malumuth et al. (1992) also presented new redshifts for Abell 85 (also with some other clusters). They also found the lower redshift foreground group but in their sample there was 8 galaxies in that group. Four of those were same galaxies as in Beers et al. sample. The fifth foreground galaxy in Beers et al. were measured to have higher redshift by Malumuth et al.. Malumuth et al. also noted the deviation from Gaussian distribution and they noted that there is a second peak in the cluster radial velocity distribution at about 15000-15250 km/s. They also calculated that the deviation probability to be random is 0.09 so they suggested that there is another foreground group of galaxies.

Durret et al. (1996) studied the field of Abell 85 photometrically and spectroscopically. They showed an interesting graph that had redshift on Y-axis and distance from cluster centre in X-axis. The graph has been recreated here in Figure 1 from current data in NED. Durret et al. noted the banded structure of the graph, and said:

We can see from this figure that there is indeed a “sheet” of galaxies with velocities of about 6000 km/s, as mentioned by previous authors. Behind the cluster, there is a large number of galaxies following a velocity distribution suggestive of a certain periodicity that could correspond to voids and sheets of galaxies and could therefore be used as an indicator of large scale structures in this direction.


Figure 1. The redshifts of objects near Abell 85 (within 60 arcmin) as a function of distance from the cluster centre. Object data has been taken from NED.

Arp (1997) presented the same graph that Durret et al. presented. Arp argued:

The discretely larger redshifts of the galaxies in this cluster cannot be attributed to background sheets and filaments of galaxies because the galaxies are concentrated toward the center of the cluster.

Arp also made another note:

It is also impressive to note that the cluster Abell 85 is a very strong X-ray emitter and at z = 0.055, essentially at the first quantized quasar redshift peak of z = 0.06. This would conform to the expectation of an X-ray strong group of quasars at the quantized value of z = 0.30 breaking up and evolving to the next lower step at z = 0.06.

However, there were no mention of z = 0.30 objects in the field. Arp (1998) also noted the situation briefly:

Stunning support for this process has been available with the first measures of a large number of redshifts in the X-ray cluster Abell 85 (Durret et al. 1996) : there are a number of quantized levels of redshift in the cluster!

Durret et al. (1998) published new redshift measurements of the cluster, and they provided a catalogue of all available velocities of the cluster. In another paper, Durret et al. (1998b) used velocity density profiles to study the velocity distributions (among other issues) in a larger field near Abell 85. They detected several clusters and/or galaxy groups in the field and they largely concentrated on the other clusters nearby. They also presented some maps showing how different clusters are situated spatially and noted that Abell 85 is elongated towards Abell 87, a neighbouring galaxy cluster. Durret et al. (1999) continued the studies on Abell 85. They studied the distribution of emission line galaxies (among other things) in the cluster and found that they are concentrated to the main cluster and suggested that it is because the merging of other clusters to the main cluster is triggering star formation which shows as emission line galaxies.

Kempner et al. (2002) studied the merger situation in Abell 85 and found a bow shock. Based on the bow shock compression they estimated a mach number of 1.4 which would correspond to a merger velocity of 2150 km/s and from that they derived an infall velocity of 2520 km/s between the main cluster and the merging subcluster.

Bravo-Alfaro et al. (2009) revisited the velocity distribution in the cluster and made some statistical tests on the positions of galaxies. They were able to confirm the presence of several subclusters.

Notes

Arp noted that the redshift of Abell 85 (z ~ 0.055) is close to the Karlsson peak of z = 0.06. However, from figure 1 it can be seen that the redshift levels don’t match Karlsson peaks. Above z = 0.06, next Karlsson peak would be z = 0.3. Here is a table of rough redshift levels present in the field:

Velocity (km/s) Redshift Difference to previous (km/s)
6000 0.020
11000 0.037 5000
17000 0.057 6000
20000 0.067 3000
23000 0.077 3000
29000 0.097 6000
34000 0.113 5000
39000 0.130 5000

Note that the values in the above table are just estimated from the Figure 1 and are very rough estimates. It can be seen that there are many apparent redshift levels between the Karlsson peaks of z = 0.06 and 0.30, so it seems that Karlsson peaks are not the answer here. It is interesting to note that without the 20000 km/s redshift level (which is very weakly present anyway), the redshift levels seem to be very accurately at 6000 km/s intervals below cz ~ 30000 km/s and quite close to that even above it. However, the banded appearance seems to break down above cz ~ 40000 km/s or at least it becomes unclear (there are some signs of bands but it is difficult to determine).

One interesting feature in Figure 1 is the apparent gap between about cz = 75000 and cz = 85000.

Whatever is the reason for the redshift distribution in this field – whether it’s normal large scale structure of the universe or some kind of unexpected redshift trick – it is nevertheless very interesting distribution.

Figure 2 shows the field around Abell 85 central region. However, presented field is only a small part of the discussed region (presenting whole region here would not be practical due to its large size and numerous objects), so it is not very relevant to the above discussion, but I’ll make some notes on it anyway.

Objects 21 and 22 seem to have possible bridge between them but their velocity difference is very large (about 1700 km/s). However, this is a center of a massive galaxy cluster, so the velocity difference might not be too big. It is also interesting to note that objects 18 and 24 are somewhat aligned across object 21, and objects 18 and 24 have exactly the same redshift. Note, however, that their redshift is not discordant to object 21.

Objects 4 and 6 are side by side but their velocity difference is very large (about 2850 km/s). It’s difficult to say if the difference is too big. We also need to remember that it is known that there are several overlapping galaxy clusters in the area, so close projections by chance are expected to occur.


Figure 2. The field around Abell 85 central region. Size of the image is 7.5 x 7.5 arcmin. Image is from Digitized Sky Survey (POSS2/UKSTU Blue) and it has been adjusted for brightness and contrast to bring out faint objects.

SDSS image centered to object 6.

Objects and their data

NBR NAME TYPE REDSHIFT (cz) MAG SEPARATION
1 ABELL 0085 GClstr 0.055061 (16507 km/s) 15.7 0
2 APMUKS(BJ) B003902.91-093727.4 galaxy 0.057900 (17358 km/s) 17.75 0.880
3 LEDA 093204 galaxy 0.054607 (16371 km/s) 17.3 (G) 1.119
4 SDSS J004134.94-092138.4 galaxy 0.057051 (17103 km/s) 18.1 (G) 1.297
5 SDSS J004142.47-092125.9 galaxy 0.049156 (14737 km/s) 18.5 (G) 1.449
6 LEDA 093200 galaxy 0.047486 (14236 km/s) 16.59 1.481
7 LEDA 093196 galaxy 0.046013 (13794 km/s) 16.3 (G) 1.522
8 LEDA 093217 galaxy 0.046418 (13916 km/s) 17.9 (G) 1.745
9 LEDA 093213 galaxy 0.047643 (14283 km/s) 16.5 (G) 1.818
10 APMUKS(BJ) B003904.46-093502.4 galaxy 0.052089 (15616 km/s) 19.55 2.003
11 LEDA 093191 galaxy 0.054589 (16365 km/s) 17.7 (G) 2.064
12 APMUKS(BJ) B003902.82-093910.0 galaxy 0.059374 (17800 km/s) 19.31 2.302
13 LEDA 093209 galaxy 0.056122 (16825 km/s) 17.45 2.368
14 LEDA 093193 galaxy 0.057062 (17107 km/s) 18.3 (G) 3.142
15 LEDA 138211 galaxy 0.059478 (17831 km/s) 18.6 (G) 3.236
16 APMUKS(BJ) B003916.15-093919.6 galaxy 0.057426 (17216 km/s) 19.58 3.409
17 LEDA 093220 galaxy 0.058916 (17663 km/s) 17.0 (G) 3.464
18 ABELL 0085:[DFL98] 241 galaxy 0.055158 (16536 km/s) 17.0 (G) 3.562
19 LEDA 093229 galaxy 0.061126 (18325 km/s) 17.8 (G) 3.829
20 SDSS J004127.86-092329.6 galaxy 0.049486 (14836 km/s) 18.1 (G) 3.831
21 MCG -02-02-086 cD 0.055672 (16690 km/s) 14.7 (B) 3.918
22 SDSS J004149.62-091743.1 galaxy 0.050018 (14995 km/s) 16.01 4.064
23 APMUKS(BJ) B003853.69-094001.2 galaxy 0.056696 (16997 km/s) 18.71 4.269
24 [BFH91] 0039-0935B galaxy 0.055158 (16536 km/s) 18.19 4.310
25 LEDA 093224 galaxy 0.052938 (15870 km/s) 16.3 (G) 4.342
26 LEDA 138212 galaxy 0.060108 (18020 km/s) 19.32 4.660

NED objects within 10′ from Abell 85 with redshifts available.

SDSS image of ABELL 85 system.

References

Arp, 1997, JApA, 18, 393, “Quasar Creation and Evolution into Galaxies”

Arp, 1998, ApJ, 496, 661, “The Origin of Companion Galaxies”

Beers et al., 1991, AJ, 102, 1581, “A dynamical analysis of twelve clusters of galaxies”

Bravo-Alfaro et al., 2009, A&A, 495, 379, “Galaxy evolution in Abell 85. I. Cluster substructure and environmental effects on the blue galaxy population”

Durret et al., 1996, Msngr, 84, 20, “Redshift and photometric survey of the X-ray cluster of galaxies Abell 85”

Durret et al., 1998, A&AS, 129, 281, “A catalogue of velocities in the cluster of galaxies Abell 85”

Durret et al., 1998b, A&A, 335, 41, “The rich cluster of galaxies ABCG 85. III. Analyzing the ABCG 85/87/89 complex”

Durret et al., 1999, A&A, 343, 760, “The rich cluster of galaxies ABCG 85. IV. Emission line galaxies, luminosity function and dynamical properties”

Kempner et al., 2002, ApJ, 579, 236, “Chandra Observations of A85: Merger of the South Subcluster”

Malumuth et al., 1992, AJ, 104, 495, “Dynamics of clusters of galaxies with central dominant galaxies. I – Galaxy redshifts”

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