0846+51W1 – A Cosmic Coincidence With Surprises

0846+51W1 (SBS 0846+513, object 2 in Figure 1) is a high redshift quasar that is positioned very close to a low redshift galaxy (object 1) at the end of a chain of five galaxies. Arp et al. (1979) described the system. They first discussed the general properties of 0846+51W1. It is an interesting object because it brightened considerably during a month in 1975. They classified 0846+51W1 as a BL Lacertae object (although they later pointed out some features that suggested it to be a transitional object between quasars and BL Lacertae objects). Then they mentioned the situation with the galaxies:

Figures 1 and 2 also conspicuously show that the eruptive object 0846+51W1 is extremely close to one of a pair of interacting spiral galaxies (12″ south of the southernmost of the pair). Actually, the configuration north of 0846+51W1 is even rarer than an interacting pair. The five brightest galaxies in this general area form a chain stretching north and slightly west with 0846+51W1 being a sixth object aligned closely in this same direction.

Then they presented their research of the light curve of 0846+51W1. Their discussion on the color of 0846+51W1 brings out an interesting detail that might be relevant to the discordant redshift issue of the system:

It is clear that 0846+51W1 is much redder than normal quasars. It is known that BL Lacertae objects tend to be redder than quasars (for a review, see Stein, O’Dell, and Strittmatter 1976). But 0846+51W1 at minimum is redder than most BL Lacertae objects.

Later they returned to the discussion of the color of 0846+51W1:

To what is the redness of 0846+51W1 due? The normal explanation of the redness of BL Lacertae objects involves an underlying galaxy. But at a redshift of z = 1.86 for the object 0846+51W1, any normal galaxy would be much too faint in apparent magnitude to make any contribution to the observed light. So the nature of this high-redshift, BL Lacertae object – Quasar remains a mystery.

Next they discussed the energy curve, radio observations, and the optical spectrum of 0846+51W1. They measured a redshift of z = 1.86 for 0846+51W1, which they noted to be rather high for a BL Lacertae object. From spectral features, they suggested a hypothesis about 0846+51W1:

However, the most attractive among a poor choice of hypotheses may still be that the slit is observing a central blue stellar object embedded in a slightly resolved redder object.

They measured an emission line that didn’t fit to the redshift of z = 1.86. They questioned the reality of the line but also mentioned that if the line were real, it likely had a redshift of z = 0.747. They also noted a presence of a small nebulosity very close to 0846+51W1, and suggested that the nebulosity actually is a normal red galaxy that might be a part of a loose galaxy cluster or associated with 0846+51W1.

They calculated the probability for the chance projection of 0846+51W1 close to the small nebulosity/galaxy, and found out that it is quite possibly a chance projection with that object. They also calculated the chance projection probability for 0846+51W1’s association with the nearby interacting pair of galaxies, and find that the association is quite rare.

0846+51W1 was included in the sample of Arp (1981). Sitko et al. (1984) studied the polarimetry of 0846+51W1 and concluded it to be highly polarized, highly variable quasar.

A gravitational lens?

Nottale (1986) suggested that 0846+51W1 is a gravitational lens:

The aim of this paper is to suggest that all these characteristics may be accounted for in a simple model where most of the variability is not intrinsic to the object, but instead due to the gravitational amplification by a star lying in the intervening galaxy at z = 0.072.

They then continued to show in detail how the different features of 0846+51W1 can be explained by gravitational lens hypothesis. Barnothy & Barnothy (1986) also suggested the gravitational lens hypothesis, although they also invoked a hypothesis of a supernova going off in the object of the lens to explain some of the observed features. Additionally, they noted that 0846+51W1 is positioned so close to the galaxy that the sight line to it passes through the halo of the galaxy. Crampton et al. (1989) published a new image on the system, and also suggested gravitational amplification.

Stickel et al. (1989) presented new imaging of the system and noticed that 0846+51W1 was elongated towards the north (in which direction also the object 1 lies by the way), which they found to be due to an intervening galaxy almost exactly positioned on the line of sight to the 0846+51W1. Their images show that the luminous areas of 0846+51W1 and object 1 apparently connect, but there’s no evidence of any bridge-like feature, just two objects overlapping slightly. From the images, they suggested:

Due to the high redshift (z = 1.86), this northern elongation is not attributable to the BL Lac host galaxy, but more likely to an intervening galaxy with considerably smaller redshift lying nearly on the line of sight.

They even utilized a decomposition technique to show each object separately in the images. That way they were also able to show the small nebulosity/galaxy Arp et al. (1979) had noted. Stickel et al. (1989) noted that it also lies on the line of sight to 0846+51W1, and they called that galaxy a “southern companion galaxy”, because they assumed that it is a companion to the intervening galaxy (and hence should have about the same redshift). They also took a new spectrum of 0846+51W1 confirming the redshift of z = 1.86. They also determined the redshift of the intervening galaxy (z = 0.235), but that was done based on energy distribution of standard elliptical galaxy, not from spectral lines.

Additionally, they noted that their spectral measurements recorded an emission line from a galaxy they named “G1” (object 9 in figure 1). They gave most likely redshift for it as z = 0.249. From this they went on to suggest that as there are lot of apparently similar objects nearby, there might be a group or cluster at z ~ 0.24.

New spectral information

Zhou et al. (2005) discussed the SDSS spectrum of 0846+51W1:

However, the narrow wavelength coverage of Arp et al. and Stickel et al. led 0846+51W1 be taken as a high redshift BL Lacs (z=1.86) by these authors whereas the SDSS spectrum clearly shows that its true redshift is z = 0.5835.

They note that they see no signs of any intervening galaxies in the SDSS spectrum, but they suggest that the spectrum is a composite of three basic features:

Its optical spectrum can be well decomposed into three components, a power law component from the relativistic jet, a stellar component from the host galaxy, and a component from a typical NLS1 nucleus.

Here NLS1 stands for narrow line Seyfert 1. They suggest further that:

In 0846+51W1 and SDSS J0948+0022 we are very likely observing the innermost part of the jet pointing toward us and the fact that all of the radio sources in NLS1s are compact can be understood according to this interpretation.

Zhou et al. (2005) practically turned the situation upside down; redshift was all wrong and there’s no intervening objects to support the gravitational amplification hypothesis. However, as the redshift of 0846+51W1 got much smaller, there’s less need for amplification to explain the object. Unfortunately, Zhou et al. didn’t address this issue explicitly. So, we still have a high redshift object very close to a low redshift galaxy, and the high redshift object is elongated towards the low redshift object, and even a visible “connection” is a possibility (although there’s no signs of any connections in Digitized Sky Survey images). There’s also the line of objects 1, 2, 3, 4 mentioned by Arp et al. (1979) (and the two additional ones they mentioned which are quite far outside the field shown in Fig. 1), and there’s also additional object that falls to this line (object 6 in Fig. 1).

0846_51W1
Figure 1. The objects with measured redshifts near SDSS J084957.48+510842.3. 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 SDSS J084957.48+510842.3 galaxy 0.073485 (22030 km/s) 16.8 (g) 0
2 SBS 0846+513 QSO FSRQ 0.583715 18.8 (g) 0.235
3 SDSS J084956.70+510927.1 galaxy 0.073379 (21998 km/s) 17.4 (g) 0.757
4 SDSS J084953.16+511151.6 galaxy 0.056646 (16982) 17.3 (g) 3.227
5 SDSS J084949.11+510538.0 galaxy 0.044816 (13436 km/s) 16.4 (g) 3.341
6 SDSS J085003.35+510524.8 galaxy 0.267347 19.5 (g) 3.418
7 small nebulosity/galaxy galaxy 19.6 ~0.04 from obj. 2
8 intervening galaxy galaxy 0.235 19.2 ~0.005 from obj. 2
9 G1 galaxy 0.249 ~ 1

Objects in NED within 10 arcmin from SDSS J084957.48+510842.3

References

Arp et al., 1979, ApJ, 230, 68, “An eruptive BL Lacertae object with a high redshift, 0846 + 51 W1”

Arp, 1981, ApJ, 250, 31, “Quasars near companion galaxies”

Barnothy & Barnothy, 1986, AJ, 91, 755, “Morphological aberration in gravitational-lens images”

Crampton et al., 1989, AJ, 98, 1188, “A search for closely spaced gravitational lenses”

Nottale, 1986, A&A, 157, 383, “The eruptive BL Lac object 0846 + 51W1 – A gravitationally lensed QSO?”

Sitko et al., 1984, PASP, 96, 402, “Optical and radio polarimetry of the quasar 0846 + 513”

Stickel et al., 1989, A&A, 224, 27, “The gravitational lens hypothesis for 0846 + 51W1 supported by new observations”

Zhou et al., 2005, ChJAA, 5, 41, “The Hybrid Nature of 0846+51W1: a BL Lac Object with a Narrow Line Seyfert 1 Nucleus”

MCG -01-02-034 – A typical QSO-galaxy pair

Arp (1981) made a case about quasars being generally near to companion galaxies (i.e. to galaxies that are near to some other, usually bigger galaxy). One of the cases included in that study was MCG -01-02-034, a companion galaxy to NGC 0157 (which has an angular distance of 29.65 arcmin from MCG -01-02-034). The Figure 1 of Arp (1981) shows the whole system including the NGC 0157. Nothing interesting in discordant redshift sense about this system specifically is noted in Arp (1981), just that there is a quasar ([HB89] 0032-086) positioned near MCG -01-02-034.

There is one piece of information in addition to things mentioned in Arp’s study; MCG -01-02-034 has discordant redshift compared to NGC 0157. Redshift of MCG -01-02-034 was not known at the time of Arp’s study.

In addition to the quasar, there aren’t any other objects with measured redshifts within 10 arcmin from MCG -01-02-034. NED shows the [HB89] 0032-086 in slightly different position than Arp (1981). Figure 1 shows it in the position Arp (1981) gives (as there doesn’t seem to be visible objects in the position NED gives).

mcg034
Figure 1. The objects with measured redshifts near MCG -01-02-034. 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 MCG -01-02-034 galaxy 0.017919 (5372 km/s) 13.92 0
2 [HB89] 0032-086 QSO 0.756000 19 2.541
3 NGC 0157 SABbc 0.005510 (1652 km/s) 11.00 29.650

References

Arp, 1981, ApJ, 250, 31, “Quasars near companion galaxies”

ARP 175 – A tale of a tail

ARP 175 is a system where two galaxies at similar redshifts are seemingly interacting, and an interaction tail from those two is emerging and apparently connecting to a third galaxy. This third galaxy has much lower redshift than the two other galaxies, so in traditional view the apparent connection should be just a chance projection. This is one of the oldest discordant redshift systems known, most of the relevant things about this system were already discussed by Zwicky (1956).

Zwicky (1956) said:

These widely separated galaxies which were the first ones to be found interconnected by long luminous filaments of intergalactic matter also turned out to be some of the most remarkable in the sense of presenting astrophysics with some unsuspected and very puzzling problems.

Then he mentioned about magnitudes:

From the near equality of their apparent magnitudes and of their angular diameters one would off hand conclude that the two galaxies IC 3481 and IC 3483 are roughly at the same distance.

Magnitude is of course only very rough distance indicator, but, as Zwicky stated:

This first evaluation is of course greatly strengthened because of the apparent connection of the two galaxies with the smaller and fainter central nebula by faintly luminous bands of intergalactic matter.

See the plate II of Zwicky (1956) for an image of the connecting material. He also said that the apparent bridge seemed to be an extension of one of IC 3483’s spiral arms (see Fig. 1 of Zwicky, 1956). He then described the spectral measurements of the system and started by stating the initial attitude:

From the features discussed in the preceding, the writer and his colleagues felt certain that the three galaxies form a physical triple system and that within narrow limits they are located at the same distance. Under these circumstances the results of the spectral studies which Drs. R. MINKOWSKI and M. L. HUMASON undertook at the request of the writer came as a complete surprise.

The resulting redshifts were: IC 3481 cz = 7304 km/s, IC 3481A (which was called “Anon” by Zwicky) cz = 7278, and IC 3483 cz = 108 km/s. He noted that the redshift of the apparent bridge couldn’t be obtained.

Zwicky then stated three possible explanations for the situation:

1. IC 3483 is a foreground galaxy.
2. IC 3483 is at the same distance as the two other galaxies and its low value of Vs indicates a real radial velocity of about 7000 km/sec relative to two other members of the triple system.
3. IC 3483 is at the same distance as the two other galaxies, but the large value of Vs between IC 3481 and IC 3483 is caused by some differential effect on the frequency of light quanta travelling cosmic distances. The gravitational drag of light which was discussed by the writer (23) long ago as a possibility of explaining the universal redshift of light in a non-expanding universe would in some cases produce large differential shifts in the spectra of little separated galaxies.

He then proceeded to present some arguments relating to these options. He discussed the properties of IC 3483 if it would be a foreground galaxy. Based on the redshift, it would be part of Virgo cluster. However, Zwicky noted based on the properties of IC 3483:

If a member of the Virgo cluster, it therefore follows that IC 3483 is a most unusual dwarf nebula of distinct spiral structure and with a central surface brightness comparable to that of the giant spirals.

He then emphasized the situation with the apparent luminous connection, and noted that the measured amount of reddening of IC 3483 implies greater distance than Virgo cluster. He also mentioned that the situation with IC 3481 and IC 3481A would also be exceptional if IC 3483 would be foreground object:

Finally, if IC 3483 were a foreground nebula, the remaining systems of IC 3481 and Anon would be left as one of the most unusual interconnected galaxies in the sense that among thousands of similar double galaxies not a single one can be found where the “countertide”, as we propose to call it, does not constitute the exact tangential continuation of the bridge between the two nebulae in question.

Zwicky then cited a few examples where there are quite large velocity differences between objects, but not as large as in this system. So it didn’t seem very probable that all three would be at same distance and just having large velocities causing the redshift difference. Zwicky still considered it to be possible though. However, he noted a complication for that hypothesis:

On this interpretation there nevertheless arises another great difficulty. It is well known from astrophysical theory that two stellar systems devoid of gas and dust passing through each other in the process of a head-on collision hardly disturb each other, unless their relative velocity is very low.

This argument would suggest that the connecting luminous bridge would not form if the redshift differences were due velocity differences in an interacting system. Zwicky then concluded that the third possibility should not be discarded lightly:

It will in this case be quite possible that the redshift is not a function of the distance alone but depends also on the particular constellations of matter surrounding any individual cosmic trajectory of a quantum of light.

Other studies

ARP 175 (VV 043) system was included in a study by Humason et al. (1956). They noted briefly:

Zwicky believes IC3483 also connected with this pair. The discrepancy in the velocities, however, indicates that 3483 is a member of the Virgo Cl and not physically connected with this pair.

Vorontsov-Velyaminov (1959) included the system in his catalog (as #43), and published the image of the system shown in Figure 1.


Figure 1. Image of ARP 175 system from Vorontsov-Velyaminov (1959). Image is linked from NED.

Burbidge & Burbidge (1961) noted about this system:

However, Zwicky (1958 and earlier references given there) has argued that all three galaxies are connected by luminous bridges and must therefore be a physical group (IC 3481 and 3483 also are of about the same luminosity and diameter). The presence of many galaxies nearby, since the system lies in the field of the Virgo Cluster increases the probability that in this case IC 3483 is not a member of the small group.

In another paper, Burbidge & Burbidge (1961b) mentioned that sometimes there are long extensions from interacting galaxies ending to empty space, so in this case that might be a possibility.

The system was briefly mentioned by Vorontsov-Velyaminov (1962). Arp (1966) included the system in his Atlas of Peculiar Galaxies (as #175), and published the image of the system shown in Figure 2.


Figure 2. Image of ARP 175 system from Arp (1966). Image is linked from NED.

Toomre & Toomre (1972) commented on ARP 175 system:

…the Zwicky triplet (= ARP 175) has often been cited (e.g., Hoyle and Narlikar 1971; Arp 1971b) as a possible example of a bridge connecting galaxies with very disparate redshifts. Yet now even the shape of that “bridge” warns of an impostor: Such a long, broad, curving crescent seems much more characteristic of a tail emanating from the anonymous galaxy [= IC 3481A] solely as the result of an encounter with IC 3481. This makes IC 3483 presumably just a foreground galaxy.

I haven’t read the mentioned Hoyle & Narlikar (1971) and Arp (1971) because I don’t have access to them, but I’ll give links to them in the reference section anyway in case some readers with access wish to read them. The system was also briefly discussed in Jaakkola (1973) and in Burbidge (1973).

Katsiyannis et al. (1998) published new images in the system. They noted that the halo of the foreground star near IC 3483 (the object right above object 1 in Figure 3) hides the details of the connection of the tail to IC 3483. They conclude that visually IC 3483 appears to be interacting with IC 3481/IC 3481A, but that according to redshift IC 3483 is a foreground galaxy. By the way, Katsiyannis et al. say that Arp (1966) was the first to note the possible interaction between the three galaxies in this system, but as we have seen above, that’s not true. Katsiyannis et al. (2001) gives the same images of the system, and the discussion there is also the same.

Pérez Grana et al. (2009) discuss the interaction between OC 3481 and IC 3481A, but I don’t know what they say about IC 3483 because I don’t have access to the paper.

arp175
Figure 3. The objects with measured redshifts near IC 3483. Size of the image is 15 x 15 arcmin. Image is from Digitized Sky Survey (POSS2/UKSTU Blue).

Few notes

There’s a higher redshift galaxy, SDSS J123301.88+112301.9 (object 4 in Figure 3) between IC 3481A (object 3) and IC 3483 (object 1). It appears to coincide with the bulge of the bridge seen at the center in the image of the system published in Vorontsov-Velyaminov (1959), as shown in Figure 1.

SDSS has quite good image of the system. Playing with brightness and contrast of the image suggests that the tail from IC 3481/IC 3481A is not particularly well associated to IC 3483, it just seems that it happens to point generally to that direction, but I see no clear signs of any interaction between the tail and IC 3483. There also are not any clear signs of interaction between the tail and the above mentioned SDSS galaxy (object 4).

There are 5 objects in Figure 3 that have similar redshift as IC 3481 (object 2): Objects 3, 5, 7, 8, 9. IC 3481 is clearly the biggest of them, and hence the probable main galaxy of the group. IC 3481 also has lowest redshift of the group, so all the known nearby companions for IC 3481 have higher redshift than the redshift of IC 3481.

Objects 4 and 6 have almost same redshift. Objects 1, 2, 3, and 10 are aligned in a very straight line. Object 10 is the only object in Figure 3 that has non-discordant redshift to IC 3483, so object 10 is possible companion for IC 3483, IC 3483 seems to be bigger of the two. Redshift velocity of object 10 is about 600 km/s bigger than the redshift velocity of IC 3483.

Objects and their data

NBR NAME TYPE REDSHIFT MAG SEPARATION
1 IC 3483 SABb, pec 0.000430 15.7 0
2 IC 3481 SAB0, pec 0.023636 14.2 (g) 5.5
3 IC 3481A E, pec 0.024457 15.9 (g) 4.1
4 SDSS J123301.88+112301.9 galaxy 0.148379 18.4 (g) 3.0
5 SDSS J123320.91+112108.2 galaxy 0.024139 18.7 (g) 3.0
6 SDSS J123250.81+111910.3 galaxy 0.148931 18.1 (g) 5.0
7 SDSS J123244.54+111920.3 galaxy 0.024603 18.1 (g) 6.4
8 SDSS J123245.24+112313.8 galaxy 0.023796 18.6 (g) 6.5
9 SDSS J123241.40+112220.4 galaxy 0.025866 18.5 (g) 7.2
10 PGC 041723 S0? 0.002542 15.73 7.9

SDSS image centered on object 4.

References

Arp, 1966, ApJS, 14, 1, “Atlas of Peculiar Galaxies”

Arp, 1971, Sci, 174, 1189, “Observational Paradoxes in Extragalactic Astronomy”

Burbidge & Burbidge, 1961, ApJ, 134, 244, “A Further Investigation of Stephan’s Quintet”

Burbidge & Burbidge, 1961b, AJ, 66, 541, “Recent investigations of groups and clusters of galaxies”

Burbidge, 1973, MitAG, 34, 19, “The Riddle of the Redshifts”

Hoyle & Narlikar, 1971, Nature, 233, 41, “On the Nature of Mass”

Humason et al., 1956, AJ, 61, 97, “Redshifts and magnitudes of extragalactic nebulae”

Jaakkola, 1973, A&A, 27, 449, “The Relation between Redshift and Surface Brightness for Normal Galaxies in Systems of Galaxies”

Katsiyannis et al., 1998, A&AS, 132, 387, “Results of the digital co-addition of thirteen Schmidt films of the Virgo cluster of galaxies”

Katsiyannis et al., 2001, Ap&SS, 276, 733, “Faint Features of Interacting Galaxies Revealed by the Digital Coaddition of 13 Tech-Pan Films of the Virgo Cluster”

Pérez Grana et al., 2009, NewA, 14, 556, “The unusual interacting pair of galaxies IC 3481 and IC 3481A: An optical-NIR photometric and spectroscopic analysis”

Vorontsov-Velyaminov, 1959, Sternberg Institute, Moscow: Moscow State University, “Atlas and Catalog of Interacting Galaxies”

Vorontsov-Velyaminov, 1962, SvA, 6, 131, “Extragalactic Astronomy and Cosmogony at the 1961 Conferences in California. A Survey of the Outstanding Problems in 1961”

Zwicky, 1956, ErNW, 29, 344, “Multiple Galaxies”

NGC 0101 – connection to high-z object

I haven’t found any previous mentions of this system as a discordant redshift system. Very close to NGC 0101 (object 1 in Figure 1 and 3) there is a higher redshift object (object 2). Figure 2 shows DSS image of the situation with these two objects. Image has been zoomed in (4x) and adjusted for brightness and contrast in order to bring out faint features. Between objects 1 and 2 there is an obvious apparent luminous connection. It should be noted that NGC 0101 has lot of arms and filaments around it, so it doesn’t seem surprising if some nearby object would happen to be positioned so that it would appear to be connected. It would be very interesting to see a better image of this system. Redshift difference between NGC 0101 and object 2 is so large that it doesn’t seem possible to explain the situation with redshift difference being caused by real peculiar velocities.

ngc0101close
Figure 1. Close-up image of NGC 0101. Image is from Digitized Sky Survey (POSS2/UKSTU Red), and it has been zoomed in (4x) and adjusted for brightness and contrast to bring out the faint features in the field.

Objects 7 and 9 (see Figure 3) are very close to each other but have different redshifts. I tried to adjust the brightness and contrast of the DSS image but I couldn’t bring out any signs of bridge between them. My image is presented in Figure 2. However, the image in NED suggest that there is a possibility of a bridge between them (save the NED image and then adjust it for brightness and contrast, there seems to be a quite strong apparent bridge which doesn’t seem to be a noise artifact).

ngc0101_7_9
Figure 2. Close-up image of a field near NGC 0101. Image is from Digitized Sky Survey (POSS2/UKSTU Red), and it has been zoomed in (4x) and adjusted for brightness and contrast to bring out the faint features in the field. Object 7 is at the center, and object 9 is right beside it.

Objects 14 and 18 are quite well aligned across NGC 0101. Their redshifts are quite different, but their angular distance from NGC 0101 is somewhat similar. Other possibility is that objects 14 and 7 are aligned across NGC 0101. In that case the objects would have quite similar redshifts. However, for object 7, more interesting pair is object 4, because they have almost the same redshift (cz difference is only 140 km/s) and are still aligned quite well. Their angular distance from NGC 0101 is also quite similar. Object 10 also has the same redshift than objects 4 and 7. Object 10 is located near object 7, so they are an apparent galaxy pair.

There are quite a lot of objects with measured redshifts within this field. That is because the field belongs to 2dF coverage area. However, the distribution of objects with measured redshifts in the field is quite one-sided. It might be that 2dF coverage area ends there or has a hole there.

ngc0101
Figure 3. The objects with measured redshifts near of NGC 0101. Size of the image is 15 x 15 arcmin. Image is from Digitized Sky Survey (POSS2/UKSTU Red), and it has been adjusted for brightness and contrast to bring out the faint objects in the field.

Objects and their data

NBR NAME TYPE REDSHIFT (cz) MAG SEPARATION
1 NGC 0101 SABc 0.011284 (3383 km/s) 13.46 0
2 2dFGRS S438Z082 galaxy 0.162700 18.88 1.087
3 2dFGRS S438Z084 galaxy 0.134500 19.10 2.828
4 2dFGRS S438Z078 galaxy 0.051500 19.48 3.163
5 2dFGRS S498Z148 galaxy 0.250800 19.11 3.455
6 2dFGRS S438Z071 galaxy 0.138800 19.27 3.803
7 2dFGRS S438Z089 galaxy 0.051300 18.36 3.835
8 2dFGRS S438Z073 galaxy 0.171100 19.35 3.971
9 2dFGRS S498Z153 galaxy 0.184700 19.09 4.023
10 2dFGRS S498Z154 galaxy 0.051500 17.64 4.621
11 2dFGRS S438Z075 galaxy 0.111600 18.07 5.043
12 2dFGRS S438Z076 galaxy 0.194200 19.41 5.751
13 2dFGRS S498Z152 galaxy 0.251300 19.35 5.799
14 2dFGRS S438Z072 galaxy 0.041000 18.14 6.399
15 2dFGRS S498Z135 galaxy 0.124000 17.52 6.511
16 2dFGRS S438Z081 galaxy 0.266200 19.44 7.156
17 2dFGRS S438Z079 galaxy 0.111700 18.94 7.188
18 2dFGRS S498Z157 galaxy 0.107500 18.49 7.259

NGC 0007 – nearby quasars and alignments

This system hasn’t been discussed as a discordant redshift system before, at least to my knowledge.

Objects 3 (see Figure 1) and 4 form a pair alignment across NGC 0007. Their separations from NGC 0007 are similar, but their redshifts are not similar. The alignment with these two is not exactly across the nucleus of NGC 0007. Another option for pair alignment would be objects 3 and 6. Their separations from NGC 0007 is not similar, but redshifts are closer to each other than in 3 – 4 pair, and both objects are QSO’s. Alignment across the nucleus of NGC 0007 in this case is almost exact.

There’s another, very rough pair alignment across NGC 0007. It’s with objects 7 and 11. Although the alignment is very rough, the interesting thing here is that redshifts of the two are very close to each other (0.1390 and 0.1395). However, it has to be noted that also object 8 has similar redshift (0.1389), so there is a possibility of a background group of galaxies.

Objects 3 and 5 have very similar redshift (2.062 and 2.041). The nominal redshift difference is little large for physical pair, the nominal velocity difference is 2070 km/s. However, if we consider the given error bars for the redshift measurements, the velocity difference might be only 1080 km/s. But even that is still rather high for a physical pair, but perhaps acceptable. It is also interesting to note that the field has three quasars, all of which are positioned near NGC 0007. The field has been covered by 2dF quasar search, so one would expect roughly homogenous distribution of quasars. In that light, the presence of the three quasars near NGC 0007 would suggest either a deviation from homogeneity of 2dF quasar search for some reason, or some kind of association between NGC 0007 and the three quasars. But, chance projection can never be ruled out in these cases either.

Object 10 seems to be a real companion candidate to NGC 0007 because it has similar redshift (the redshift velocity difference between the two is less than 150 km/s).

ngc0007
Figure 1. The objects with measured redshifts near of NGC 0007. Size of the image is 15 x 15 arcmin. Image is from Digitized Sky Survey (POSS2/UKSTU Red), and it has been adjusted for brightness and contrast to bring out the faint objects in the field.

Objects and their data

NBR NAME TYPE REDSHIFT (cz) MAG SEPARATION
1 NGC 0007 SBc? 0.004987 (1495 km/s) 13.47 0
2 6dF J0008227-295413 PofG 0.005325 (1596 km/s) 15.5 (R) 0.782
3 [VCV2001] J000827.5-295422 QSO 2.062000 19.53 1.513
4 2dFGRS S359Z113 galaxy 0.124839 19.18 1.947
5 [VCV2001] J000826.5-295749 QSO BAL 2.041000 20.74 3.177
6 [VCV2001] J000802.7-295631 QSO BAL 1.591000 20.23 4.269
7 2dFGRS S360Z141 galaxy 0.139000 18.83 6.162
8 2dFGRS S359Z094 galaxy 0.138856 18.53 6.764
9 2dFGRS S359Z122 galaxy 0.061288 18.48 7.911
10 2dFGRS S359Z100 galaxy 0.005437 (1630 km/s) 17.12 8.304
11 2dFGRS S278Z243 galaxy 0.139495 18.39 8.712

NED object list with available redshifts within 10 arcmin.