NGC 0423 – pair alignments

To my knowledge, NGC 0423 has not been discussed as a discordant redshift system before. Figure 1 presents nearby objects that have redshift available. Almost all such objects within 10 arcmin are shown there (only three are little bit outside of the pictured field).

Higher redshift objects 2 and 4 are aligned across NGC 0423. The objects have almost same redshift (object 2 z = 0.106 and object 4 z = 0.105). Their distance from NGC 0423 is somewhat similar (d₄/d₂ = 1.3). Their magnitude is also similar. Alignment is almost exactly across the nucleus of NGC 0423. Field has lot of high redshift objects because it belongs to 2dF coverage area so some alignments are expected. Here we have two of three closest objects aligned almost exactly, and their redshift is the same. However, Object 6 (z = 0.105) also has the same redshift so we are looking at a possible galaxy group in traditional interpretation, and that would increase the odds of having same redshift objects aligned across the main galaxy.

Objects 14 and 17 are aligned across NGC 0423. They have almost same redshift (object 14 z = 0.224 and object 17 z = 0.202) and their angular distance from NGC 0423 is similar (d₁₇/d₁₄ = 1.04). So is their magnitude. There are couple of objects with similar redshift; object 16 has redshift of z = 0.224 and object 21 has redshift of z = 0.219. If we consider these four objects as a galaxy group, there is a problem with large velocity dispersion. When converted to velocity, the redshifts of objects 14 and 17 result in 5200 km/s difference. That seems too large considering that the group doesn’t seem to be very dense (high velocity differences between galaxies are traditionally thought to occur only in dense galaxy clusters). Of course, there is always the possibility that the group is very dense but we only have few redshifts of its members measured, but current knowledge would indicate that objects 14 and 17 don’t belong to same galaxy group. Objects 16 and 21 are situated quite close to each other, as seen in Figure 1, but they too have quite large velocity difference, about 1300 km/s. That is starting to be quite close to what can be traditionally accepted as a velocity difference of physically associated galaxies, but the difference still is suspiciously large.

Objects 11 and 5 are roughly aligned across NGC 0423 but they have very different redshifts and are different kind of objects also (object 5 is a high redshift QSO while object 11 is a galaxy). Object 8 is roughly aligned across NGC 0423 with objects 9 and 10. Redshifts of all objects are quite different, but at least objects 8 and 10 are both QSO’s and their angular distance from NGC 0423 is similar.

Figure 1. Objects with available redshift near NGC 0423. Size of the image is 15 x 15 arcmin. Image is from Digitized Sky Survey (POSS2/UKSTU Blue).

There is a strange situation with object 12 (ESO 412-012); it seems to be quite large object as its apparent size almost matches that of NGC 0423 but it has redshift of z = 0.136 in NED! I checked NED’s redshift data for it, and it seems to have three very different redshift values. The highest one, the 0.136 is from Stromlo-APM Redshift Survey (it is named as “412-003-029″ in the galaxy.dat file), and it has been measured from absorption features. Lowest redshift is from The 2dF Galaxy Redshift Survey, and is also measured from absorption lines. Third redshift is said to be from Arp 1981, but I didn’t find the object in question there. HyperLeda gives the lowest value and doesn’t even list the high value. I assume that the lower redshift is the correct one, as the highest value doesn’t make any sense and the third redshift might not exist at all.

Objects 3 and 16 are aligned across object 12. Their redshifts are of same order and their magnitudes are similar. Objects 6 and 21 are also aligned across object 12 with similar situation on the redshifts and magnitudes. The whole situation with object 12 is that it has two objects on one side with redshift slightly above z = 0.1 and on other side the objects have roughly the z = 0.22. At the same side of z = 0.22 objects there’s also object 20 with z = 0.15.

Objects 9 and 10 are very close to each other but their redshifts are different. Object 9 is a z = 0.17 galaxy and object 10 is a z = 1.8 quasar. There’s no clear signs of interaction between them. See figure 2 for magnified image of them. Objects 13 and 14 both have apparent companion galaxies, but their redshift is not known. They are also shown in figure 2. Object 18 has two objects aligned across it, objects are directly to north (up) and south (down) from object 18, they also don’t have measured redshifts available.

Figure 2. Two sections of zoomed in image of NGC 0423 field. Objects discussed in the text are marked. Image is from Digitized Sky Survey (POSS2/UKSTU Blue) and it has been magnified 4x.

Objects and their data

NBR	NAME	TYPE	REDSHIFT	MAG	SEPARATION
1	NGC 0423	S0/a? pec	0.005344	14.20	0
2	2dFGRS S294Z221	galaxy	0.105538	18.83	2.409
3	2dFGRS S293Z160	galaxy	0.122800	19.36	2.968
4	2dFGRS S294Z229	galaxy	0.104500	18.22	3.142
5	[VCV2001] J011136.5-291318	QSO	2.397000	20.59	3.215
6	2dFGRS S293Z159	galaxy	0.105200	19.09	3.309
7	[VCV2001] J011140.9-291415	QSO	0.960000	20.41	4.081
8	2QZ J011108.6-291654	NELG	0.606400	20.2 (B)	4.101
9	2dFGRS S294Z216	galaxy	0.169287	19.15	4.821
10	2QZ J011140.4-291056	QSO	1.818600	19.9 (B)	5.066
11	2dFGRS S293Z165	galaxy	0.091300	19.02	5.158
12	ESO 412-012	dwarf spiral	0.018000	16.42	6.004
13	2dFGRS S294Z225	galaxy	0.098000	19.14	6.555
14	2dFGRS S294Z230	galaxy	0.223900	19.32	7.279
15	2dFGRS S293Z154	galaxy	0.115653	19.37	7.403
16	2dFGRS S293Z149	galaxy	0.224205	19.13	7.568
17	2dFGRS S293Z157	galaxy	0.202069	19.43	7.593
18	2dFGRS S293Z148	galaxy	0.154600	18.68	7.612
19	2dFGRS S293Z158	galaxy	0.061100	16.95	7.880
20	2dFGRS S293Z150	galaxy	0.154700	19.20	8.110
21	2dFGRS S294Z213	galaxy	0.218600	19.44	9.508

NED objects within 10′ from NGC 0423.

Intrinsic redshift component

Some time ago, I wrote about anomalous redshifts ending that to a mention of intrinsic redshift component. I followed that post by explaining how redshift components are generally calculated. There I gave the basic equation used for that:

1 + z_M = (1 + z_C) * (1 + z_K) [eq. 1]

where z_M is the measured redshift of the object in question, z_C is the cosmological redshift component, and z_K is kinematical redshift component, which is my own term, it is generally called as redshift caused by peculiar velocity of the object.

In discordant redshift systems, the kinematical redshift component tends to be too large to be explained by peculiar velocity in traditional thinking. Too large is rather subjective concept but there is no generally accepted limit for that. 1000 km/s is largely used but in tight galaxy cluster conditions even few thousand km/s might be accepted. When the kinematical redshift component is too large, we need another redshift component, the intrinsic redshift component. The “intrinsic” comes from the assumption that the additional redshift comes from within the object in question. I’m not particularly keen on this term because it assumes a rather specific cause for the additional redshift, but as it is commonly used, I’ll do so too. Here I will deal only with the mechanics of the addition of intrinsic redshift component to the equations described in above mentioned posts, I will not discuss the possible causes of the component.

This additional redshift component is added to the equation 1 like this:

1 + z_M = (1 + z_C) * (1 + z_K)* (1 + z_i) [eq. 2]

where z_i is the intrinsic redshift component. Problem we usually are facing is that we don’t know how large the kinematical redshift component is, so we cannot use this equation as such. As a solution, common method is to assume that there is no kinematical redshift component, so the equation 2 reduces to:

1 + z_M = (1 + z_C) * (1 + z_i) [eq. 3]

Basically it is the same equation as equation 1 but we just call the second redshift component by different name. It is important to remember that the assumption of no kinematical redshift is not necessarily a good assumption. When we are dealing with large redshift differences between objects, then the assumption does not distort our results much, but when the redshift differences are small, the unknown kinematical redshift component introduces a large uncertainty to our calculations, as we shall see later.

Let us now calculate the redshift components of an example system. We’ll use the famous NGC 7603 system. There are four relevant objects in this system; NGC 7603, NGC 7603B, and the two high redshift galaxies ([LG2002] 3 and [LG2002] 2) within the bridge area. Redshift of NGC 7603 (according to NED) is z = 0.029524, redshift of NGC 7603B is z = 0.055742, redshift of [LG2002] 3 is z = 0.391000, and redshift of [LG2002] 2 is z = 0.243000.

Let us now use equation 3 to calculate the intrinsic redshift of NGC 7603B. To calculate that we need to know the cosmological redshift of NGC 7603B. For that, we assume that it is at same physical distance from us than NGC 7603, and we also assume that NGC 7603 itself doesn’t have intrinsic redshift or peculiar velocity (lot of assumptions here). With these assumptions, we can use the redshift of NGC 7603 as cosmological redshift. Before we can calculate the values, we need to solve the equation 3 for intrinsic redshift like this:

1 + z_M = (1 + z_C) * (1 + z_i) | /(1 + z_C)
=> 1 + z_i = (1 + z_M)/(1 + z_C) | -1
=> z_i = (1 + z_M)/(1 + z_C) – 1

Now we can insert the values and calculate:

z_i = (1 + 0.055742)/(1 + 0.029524) – 1 = 0.025466138

Using relativistic Doppler redshift equation to convert that to velocity yields 7537 km/s. We can use exactly the same equation for the other two objects, and we find out that intrinsic redshift of [LG2002] 3 is z_i = 0.35111 (87600 km/s) and intrinsic redshift of [LG2002] 2 is z_i = 0.207354 (55800 km/s).

What if NGC 7603B would have peculiar velocity? Let us assume that it does have a peculiar velocity of 1000 km/s. That corresponds to z_K = 0.00334. Now we have to use equation 2. Solving it for intrinsic redshift gives:

z_i = (1 + z_M)/{(1 + z_C) * (1 + z_K)} – 1

Then we’ll put the numbers in:

z_i = (1 + 0.055742)/{(1 + 0.029524) * (1 + 0.00334)} – 1 = 0.022052

When large peculiar velocity was involved, the intrinsic redshift changed from 0.025466138 to 0.022052, a change of 13 %. From this we can see that high precision studies relating to this are very difficult, remembering also the many assumptions that were needed to come this far. However, because of the large redshift difference between NGC 7603 and [LG2002] 3, a similar peculiar velocity in [LG2002] 3 would change the intrinsic redshift only by 1 %, so this approach can be used to cases that have high redshift difference between the object in question and the main galaxy.

4C +07.04 – tight QSO-galaxy pair

Clarke et al. (1966) associated Parkes catalog radio source PKS 0114+074 (4C +07.04) with a QSO (object 2 in figure 1). Lang et al. (1970) associated the radio source to a “faint red galaxy” (object 1) near the QSO. So did Hunstead & Jauncey (1970), Pauliny-Toth et al. (1972), and Shaffer et al. (1978). Agnew & Arp (1973) gave the redshift of z = 0.861 for the QSO but it had been measured by Bolton in 1970.

Previous studies had shown 4C +07.04 as double radio source, but Akujor (1987) detected three radio sources. The third source coincided with the position of the QSO, while the two previously known coincided with the galaxy. They then suggested that the system consists of either a galaxy + QSO or a galaxy + QSO + unidentified object. In their conclusion they mention:

The QSO and the galaxy are separated by 30 arcsec. If they are physically related, one must assume a noncosmological redshift in order to place a QSO (z = 0.861) and a galaxy with z ~ 0.2 at the same distance.

However, it is unclear where they got the estimate of z ~ 0.2 for the galaxy, but earlier they mentioned assuming a redshift of z = 0.2 for a 18 mag galaxy, so they might have estimated it from the magnitude of the galaxy. Akujor (1989) presented further radio observations of the system, and verified the three radio source structure. Akujor gave a chance projection probability of 10^-3 for the QSO and galaxy, and mentioned that the galaxy has peculiar structure:

Indeed, this may be the first double radio source showing such a wide difference in spectrum between two components, and the first in which one component has a spectrum as flat as 0.45.

Note that here Akujor is talking about the double radio source of the galaxy, not about the radio source related to the QSO.

The redshift of the galaxy was given by Akujor & Jackson (1992). They found it to be z = 0.344. They also found that the spectrum of the galaxy showed a rare occurance of double extended emission line system. The two emission line systems differed from each other by about 400 km/s. They noted that only few cases were known with such wholescale splitting of nuclear emission lines. They discussed rotation as a possible source for emission line splitting but they noted that the usual velocity scale produced by rotation is smaller than 400 km/s observed in 4C +07.04. They also discussed a possibility of a radio jet causing an expanding cylinder of gas:

Because of the velocity field of this expanding cylinder of gas, we see split narrow emission lines as the gas cools. This model can also be applied to the case of 0114+074, although here the splitting occurs in the whole of the nuclear line.

So they didn’t seem very happy with that hypothesis either. Then they suggested a possibility of two active nuclei, but 4C +07.04 didn’t seem to show any double hotspot structure. They also were somewhat puzzled by their observations of the optical extended emission coinciding with radio lobe, and suggested it might be a sign of interaction taking place there.

Figure 1. The objects with measured redshifts near 4C +07.04. Size of the image is 5 x 5 arcmin. Image is from Digitized Sky Survey (POSS2/UKSTU Blue).

Objects and their data

NBR	NAME	TYPE	REDSHIFT	MAG	SEPARATION
1	4C +07.04 NED02	galaxy	0.343000	22.14	0
2	[HB89] 0114+074	QSO	0.858000	18	0.536

NED objects with available redshift within 10′ from 4C +07.04 NED02

References

Agnew & Arp, 1973, PASP, 85, 162, “A List of Quasi-Stellar Radio Sources and Quasi-Stellar Radio Source Candidates from the 3C and 4C Catalogs Between Declination -7° and +40°”

Akujor, 1987, AJ, 94, 867, “PKS 0114+074 – A QSO-galaxy association?”

Akujor, 1989, AJ, 98, 1226, “0114 + 074 – A very asymmetric galaxy in the field of an intermediate-redshift QSO”

Akujor & Jackson, 1992, AJ, 104, 546, “Double emission-line system in the radio galaxy 0114 + 074S”

Clarke et al., 1966, AuJPh, 19, 375, “Identification of extragalactic radio sources between declinations 0° and +20°”

Hunstead & Jauncey, 1970, MNRAS, 149, 91, “Observations of radio sources near 2 f.u. at 408 MHz”

Lang et al., 1970, ApJ, 160, 17, “Additional Occultation Studies of Weak Radio Sources at Arecibo Observatory: lIST 4″

Pauliny-Toth et al., 1972, AJ, 77, 265, “The NRAO 5-GHz radio source survey. II. The 140-ft “strong”, “intermediate”, and “deep” source surveys”

Shaffer et al., 1978, AJ, 83, 209, “Optical identifications of radio sources in the NRAO 5-GHz survey – The ‘S2′ and ‘intermediate’ surveys”

6dF J0406457-124421 – QSO pair at same redshift

Arp (1980) noted this system briefly:

Another pair of obviously related quasars is shown in Figure 6. Search of the Palomar Sky Survey reveals a galaxy just about midway between them.

One point about these two quasars is their similar redshift. The centering galaxy is brightest in the nearby field, according to Arp.

Marr & Spinrad (1985) found a faint galaxy (object 4 in the object table below) near object 3, at redshift of z = 0.568. They said:

The nominal velocity difference between the two objects is only 900 km s^-1 in the quasar’s rest frame, clearly consistent (within the galaxy redshift uncertainty) with a cluster velocity dispersion.

There are some studies of absorption lines in the spectrum of object 3, and their possible correlation with nearby galaxy distribution. Williger et al. (2006) is an example of such study.

Notes

There are lot of objects with available redshift in the field, but only the centering galaxy and the two quasars are shown in Fig. 1. Nearest objects with available redshift to 6dF J0406457-124421 are about at 8 – 10 arcmin angular distance, and as the photographed field in Fig. 1 is only 5 x 5 arcmin, those objects are not shown.

There are 15 objects having redshifts between z = 0.55 and 0.60 within 40 arcmin from 6dF J0406457-124421. The two aligned across 6dF J0406457-124421 are clearly brightest of them.

Figure 1. The field of 6dF J0406457-124421 with the two quasars. Size of the photograph section of the image is 5 x 5 arcmin. Image is from Digitized Sky Survey (POSS2/UKSTU blue).

Objects and their data

NBR	NAME	TYPE	REDSHIFT (cz)	MAG	SEPARATION
1	6dF J0406457-124421	galaxy	0.032621 (9780 km/s)	16.11	0
2	[HB89] 0403-132	QSO, HPQ	0.570550	17.17	29.555
3	[HB89] 0405-123	QSO, blazar, Sy1.2	0.572590	14.82	36.169
4	G1	galaxy	0.568	20	0.22

NED page for object 1
NED page for object 2
NED page for object 3

References

Arp, 1980, ApJ, 236, 63, “Ultraviolet excess objects in the region of a companion galaxy to NGC 2639″

Marr & Spinrad, 1985, PASP, 97, 684, “An emission-line companion galaxy to the quasar PKS 0405-123″

Williger et al., 2006, ApJ, 636, 631, “The Low-Redshift Lyα Forest toward PKS 0405-123″

Edward Fath – early spectroscopy of galaxies

Although I’m concentrating on Fath’s extragalactic work, I’ll mention a paper among his early works as a curiosity; Steppins & Fath (1906), titled “The Use of Astronomical Telescopes in Determining the Speeds of Migrating Birds”.

Fath (1909) measured spectra of spiral galaxies, but he wasn’t able to determine their redshifts. He noted that by that time, general concensus was that spiral galaxies have continuous spectrum and that there were only two studies casting doubt on that. Both of them were inconclusive according to Fath. Fath then discussed the spectra of individual objects. He noted on the Andromeda galaxy (M31):

It contains little more than the spectrum of nucleus, which is not of a stellar character.

Some other objects he measured were NGC 1068 (of which there seemed to be a debate ongoing if it even is a spiral galaxy, or “spiral nebula” as they were called back then), NGC 3031 and NGC 4736. On NGC 5194, he said:

Photographically it is faint. Because of this it is not a promising object for spectrographic analysis, but it seemed best to make an attempt. … The plate showed nothing.

Well, you can’t succeed every time… He summed up his research on the question of the spectrum of spiral galaxies:

No spiral nebula investigated has a truly continuous spectrum.

Fath then proceeded to interesting discussion on the possible explanation for the spectrum of spiral galaxies. He notes that the spectrum usually comes only from the nuclei of spiral galaxies and resembles stellar spectrum, then he says:

The hypothesis that the central portion of a nebula like the famous one in Andromeda is a single star may be rejected at once unless we wish to modify greatly the commonly accepted ideas as to what constitutes a star.

He says that a possible explanation would be a star cluster at the center but asks:

Is it reasonable to assume that in a condensed cluster we should have stars of one spectral type strongly predominating?

He mentioned that there weren’t enough spectral measurements of star clusters to determine the answer to this question, so he proceeded to measure a few star clusters himself. He found out that one spectral type can predominate strongly. He then considered a parallax measurement of Andromeda galaxy and noted that the value of the parallax leads to the impossibly small sizes of hypothesized star cluster members. So, Fath is left with a hypothesis that to his knowledge is only one that can explain the spectrum, but other evidence rather conclusively show that the hypothesis is not likely to be valid.

Fath (1910) discussed some aspects of the distribution of spiral galaxies in the sky. Fath (1911) continued with spiral galaxy spectra. He gave some new spectral information on individual objects, and then suggested a preliminary spectral type division for all nebulae. Fath (1913) was his third paper on the subject, and here he only discussed individual objects.

Although Fath showed that the spectrum of spiral galaxies is not continuous but that it contains spectral lines, he didn’t discuss the possibility of measuring the redshifts of galaxies.

Links

Not much information is available on Edward Fath, but here’s at least something:

A Science Not Earthbound: A Brief History of Astronomy at Carleton College, page 11

References

Fath, 1909, LicOB, 5, 71, “The spectra of some spiral nebulae and globular star clusters”

Fath, 1910, PA, 18, 544, “The Distribution of Nebulae and Globular Star Clusters”

Fath, 1911, ApJ, 33, 58, “The spectra of spiral nebulae and globular star clusters”

Fath, 1913, ApJ, 37, 198, “The spectra of spiral nebulae and globular star clusters”

Stebbins & Fath, 1906, Sci, 24, 49, “The Use of Astronomical Telescopes in Determining the Speeds of Migrating Birds”

53W 080 – QSO triplet

Arp (1999) discussed a quasar triplet (objects 1, 13, and 14 in Figure 1) that was very similar to two previously known Arp/Hazard triplets. He first briefly described the Arp/Hazard triplets, and then said:

Now, in the Her I field, we have another, almost identical triplet configuration. Notice the remarkable close numerical similarity of the redshifts involved in all three of these examples

Numerical similarity here refers to the fact that all three triplets have similar redshift for all three objects: Two old ones have redshifts of 2.15 – 0.51 – 1.72 and 2.12 – 0.54 – 1.61, the new one has redshifts of 2.14 – 0.543 – 1.84. However, in the two old ones the highest redshift quasar was closer (in angular distance) to centering quasar but in this new one it isn’t.

Arp then argued that the centering object is in very active state, and that the oute, higher redshift quasars had been ejected from the centering quasar at opposite direction so that their velocity relative to us would correspond to redshift of z = 0.15, which is similar to the situation with Arp/Hazard triplets. Arp also studied the redshift quantization in new triplet:

If we average their [= the two outer quasars] redshifts to remove the component of ejection velocity, we obtain z = 1.99, very close to the major formula peak of z = 1.96. The central quasar is close to the formula peak of z = 0.60.

I must admit that I find this somewhat odd. Normal procedure has been to convert the redshifts to the reference frame of the parent object, the z = 0.543 quasar in this case. If we use Arp’s averaged value of z = 1.99, we get the intrinsic redshift of:

z_i = (1 + z_M)/(1 + z_C) – 1 = (1 + 1.99)/(1 + 0.543) – 1 = 0.938

Which is close to the Karlsson redshift peak of z = 0.96. Similarily, individual values of the two outer quasars would result in intrinsic redshifts of z_i = 0.84 (z = 1.84 quasar) and z_i = 1.03 (z = 2.14 quasar). First of these is not particularly close to any Karlsson peak, but the latter is quite close to z = 0.96 peak.

Arp also presented a probability calculation for the chance alignment for this quasar triplet. The probability he got is 4 x 10^-8.

Notes

This field has been thoroughly studied redshift-wise, so there’s too much objects to map the entire field covering the quasar triplet in question. Figure 1 presents a few closest objects with available redshifts and the two aligned quasars.

There’s little bit uncertainty about what exactly is the centering object Arp discussed, because there are two objects at z ~ 0.55, objects 1 and 7. But as Arp talks about quasar, the object 1 has been used as the centering object here.

Some rough alignments are seen in the nearby objects. Particularly noteworthy is the pair alignment of objects 4 and 6 across object 5, because objects 4 and 6 have almost the same redshift. Objects 10 and 11 are also aligned across object 5 but don’t have similar redshifts.

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 blue), 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	53W 080	QSO	0.543000	18.3	0
2	HERC-1:[MKK97] 309937	galaxy	0.155500	20.01	1.127
3	HERC-1:[MKK97] 309714	galaxy	0.496300	20.47	1.283
4	HERC-1:[MKK97] 310979	galaxy	0.323700	19.73	1.454
5	LEDA 167151	galaxy	0.155000	19.51	1.633
6	HERC-1:[MKK97] 310632	galaxy	0.323000	20.35	1.922
7	HERC-1:[MKK97] 310248	galaxy	0.545400	21.35	1.924
8	HERC-1:[MKK97] 309838	galaxy	0.087400	19.26	2.085
9	LEDA 167126	galaxy	0.155000	19.18	2.250
10	53W 081	QSO	2.060000	24.84	2.336
11	HERC-1:[MKK97] 310395	galaxy	0.490100	20.67	2.370
12	53W 085	QSO	1.350000	22.57	2.629
13	[HB89] 1719+500	QSO	1.840000	19.3	9.931
14	[HB89] 1721+498	QSO	2.140000	20.3	12.537

NED page for object 1
NED page for object 2
NED page for object 3
NED page for object 4
NED page for object 5
NED page for object 6
NED page for object 7
NED page for object 8
NED page for object 9
NED page for object 10
NED page for object 11
NED page for object 12
NED page for object 13
NED page for object 14

References

Arp, 1999, ApJ, 525, 594, “The Distribution of High-Redshift (z>~2) Quasars near Active Galaxies”

3C 343.1 – radio bridged QSO-galaxy pair

Spinrad et al. (1977) studied the 3C 343.1 system. They gave a (somewhat uncertain) redshift of z = 0.750 for the object they called a “faint galaxy”. They compared the isophotal diameter vs. redshift of 3C 343.1 to that of few other similar objects, and found out that the isophotal diameter of 3C 343.1 matches well with a galaxy of z = 0.75, supporting their redshift determination. They also noted that 3C 343.1 is bluer than similar objects usually are.

Fanti et al. (1985) made radio maps of radio sources, including this system (see their Fig. 11). Two more radio maps of the system was published by van Breugel et al. (1992, see their Fig. 23). Also, de Vries et al. (1997) published radio map and HST image of the system (see their Fig. 2.26). All these radio maps showed two apparently connected radio sources, and HST image also seems to show two objects. Tran et al. (1998) studied this system along with few other systems. They found out something interesting:

A most surprising finding, however, is that the redshift of the absorption lines is radically smaller (z = 0.344) than that of the nuclear AGN emission lines (z = 0.75)!

So they found out that the system has two very different redshift systems. They also noted that the lower redshift system shows some emission lines as well. They showed that lower redshift system is more extended than the higher redshift system, so they concluded that there must be two different objects in a chance alignment. They gave some basic properties for each object, and also discussed the possibility of gravitational lensing.

Arp et al. (2004) reviewed the system, and discussed it as an ejecting system where the QSO would have been ejected from the lower redshift galaxy. They calculated that the probability for the chance projection is 1 x 10^-8 (or, one in a hundred million), and said that it is a conservative estimate. They also calculated the intrinsic redshift of the quasar, if it would be at the distance of the lower redshift galaxy, and found out that it is very close to one of the Karlsson redshift peaks.

Notes

For those who like to check out the presented calculations, there’s a minor mistake in the Arp et al. (2004) equation relating to the intrinsic redshift calculation (see their section 5), a square bracket is missing:

They showed it like this:

(1 + zi) = (1 + zq)/(1 + zg)(1 + zd) ] = 1 + 0.302

But it should be:

(1 + zi) = (1 + zq)/[ (1 + zg)(1 + zd) ] = 1 + 0.302

Figure 1 shows the field of 3C 343.1, but there’s no other objects with available redshifts within 10 arcmin, and 3C 343.1 itself doesn’t show very well in the image. See the referred papers for better images, especially de Vries et al. (1997).

Figure 1. The 3C 343.1 field. 3C 343.1 is at the center, but does not show very well. Size of the image is 5 x 5 arcmin. Image is from Digitized Sky Survey (POSS2/UKSTU Blue).

Objects and their data

NBR	NAME	TYPE	REDSHIFT	MAG	SEPARATION
1	3C 343.1	galaxy	0.344	-	0
2	3C 343.1	NLRG, Sy2	0.750000	20.71	~0.004

NED page for 3C 343.1.

References

Arp et al., 2004, A&A, 414, 37, “The double radio source 3C 343.1: A galaxy-QSO pair with very different redshifts”

de Vries et al., 1997, ApJS, 110, 191, “Hubble Space Telescope Imaging of Compact Steep-Spectrum Radio Sources”

Fanti et al., 1985, A&A, 143, 292, “Compact Steep Spectrum 3CR radio sources – VLBI observations at 18 CM”

Spinrad et al., 1977, ApJ, 216, 87, “Spectroscopy and photometry of the distant radio galaxy 3C 343.1″

Tran et al., 1998, ApJ, 500, 660, “Scattered Radiation from Obscured Quasars in Distant Radio Galaxies”

van Breugel et al., 1992, A&A, 256, 56, “Compact steep-spectrum 3 CR sources – VLA observations at 1.5, 15 and 22.5 GHz”

VV 172 – Chain with one higher redshift object

VV 172 was first introduced in Vorontsov-Velyaminov (1959). Burbidge & Burbidge (1960) gave a brief description of it, and noted some interesting things:

There is a strong presumption that this is a physically connected quintet, although this remains to be proved. … If the galaxies are really arranged spatially in a chain, it seems unlikely that such a configuration could remain stable for a long time. It also seems unlikely that the configuration could be due to a chance orientation effect. … The possibility that this system represents some transient stage in the formation or evolution of small groups of galaxies is intriguing.

First redshifts of the group were given in Burbidge & Burbidge (1960). They measured redshifts of two brightest galaxies in the group. Sargent (1968) gave redshifts for all VV 172 objects, see also excellent image of the system presented there which is a copy of a plate obtained by Arp (1966). Suprising thing in the redshifts of Sargent (1968) was that one of the objects (object 2 in figure 1 here) in the chain had much higher redshift than the rest of the objects. For this, Sargent saw three possible conventional explanations:

(a) a chance coincidence of a background galaxy, (b) gravitation, or (c) a real Doppler shift produced by motion of galaxy B relative to the other four components.

Sargent excluded the gravitational explanation because it would lead to very unlikely configuration of mass in the system. He then calculated the probability of chance projection by two alternative methods and got a probabilities of 1/300 and 1/5000 for the higher redshift galaxy to be found by chance within the group. He noted:

The foregoing probability arguments lend support to, but do not prove, an intuitive belief that the configuration of galaxies in VV 172 is unlikely to be the result of chance superposition.

Sargent noted another interesting feature of the system:

First, we note that there is a systematic trend of redshift with position along the chain for the four galaxies A, C, D, and E. This clearly can be interpreted as a rotation.

Sargent saw this as evidence that system might be stable after all.

Hammer & Nottale (1986) argued that VV 172 system could be explained by gravitational lensing:

Gravitational lensing increases the luminosity, diameter and chance probability of association of background galaxies in such a way that the presently known number of similar associations containing a discrepant redshift is not any more found to be improbable.

Notes

No certain bridges appear between the objects, but it is perhaps noteworthy in this context that the most likely bridge seems to be between objects 1 and 2 (object 2 being the higher redshift object), see right panel of figure 1. Figure 1 has been adjusted so that it shows where the first apparent connection between the objects emerges, and it seems to emerge between objects 1 and 2. However, there’s nothing convincingly bridge-like in the apparent connection.

Figure 1. Left panel: The objects with measured redshifts near of VV 172. Size of the image is 5 x 5 arcmin. Image is from Digitized Sky Survey (POSS2/UKSTU blue). Right panel: same image, 4 x zoomed in and adjusted for brightness and contrast to bring out possible bridges between the objects.

Objects and their data

NBR	NAME	TYPE	REDSHIFT (cz)	MAG	SEPARATION
1	VV 172C	SA0 pec	0.053604 (16070 km/s)	15.93	0
2	VV 172B	S;N galaxy	0.123018	18.03	0.199
3	VV 172D	SBa pec	0.051636 (15480 km/s)	17.43	0.302
4	VV 172A	S0 pec	0.053604 (16070 km/s)	17.63	0.345
5	VV 172E	E pec	0.052336 (15690 km/s)	16.88	0.546

NED objects within 10′ of VV 172C

References

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

Burbidge & Burbidge, 1960, ApJ, 131, 742, “A Chain of Galaxies”

Burbidge et al., 1963, ApJ, 138, 873, “Condensations in the Intergalactic Medium”

Hammer & Nottale, 1986, A&A, 155, 420, “VV 172 – an effect of gravitational amplification by a massive halo?”

Sargent, 1968, ApJ, 153, 135, “The Redshifts of Galaxies in the Remarkable Chain VV 172″

Vorontsov-Velyaminov, 1959, Sternberg Institute, Moscow State University, “Atlas and catalog of interacting galaxies”

3C 212 – radio ejection with matching discordant redshift object

Ridgway & Stockton (1997) studied 3C objects and noticed this system. They first pointed out the unusual clustering of objects around 3C 212 and said:

With the high resolution of the HST image we see that several of these objects have morphologies and locations that make it likely that they are directly associated with the quasar and its radio jet.

They mentioned that there are several objects aligned across the 3C 212. Especially, there are two objects which they have labeled as f and g, in a configuration which looks like a typical well aligned pair alignment. But in this system, there is a surprise relating to these two objects. VLA radio image of 3C 212 superposed on the optical image is presented in their plate 45. They specifically noted the strangeness of the situation with object f:

In fact, its optical image looks very much like a VLA image of a radio lobe: it even has a “hot spot,” barely resolved (FWHM=0″17), near its tip and closely aligned with the three inner knots a, b, and c.

So, what they found is that 3C 212 seems to be ejecting radio material and there are optical objects resembling the radio material, especially the object f’s strange shape is almost duplicated by the radio material. Also the object g has corresponding radio “object”. However, for both objects g and f, the corresponding radio material is clearly closer to 3C 212 than the optical objects.

Next, they proceeded to study the spectra, and it is here where the problem emerges; they found out that object f has discordant redshift compared to 3C 212 (their redshift difference corresponds to velocity difference of 18000 km/s). Note however, that object f has lower redshift than 3C 212. They said:

Note that the fact that we see a blueshift relative to the quasar frame is consistent with the NW radio lobe being the closer to us, as inferred from the radio jet being visible on that side.

They then discussed the possible explanations for the object f (unassociated foreground object, optical synchrotron emission, inverse Compton scattering, jet-induced star formation), but found them unsatisfactory.

Stockton & Ridgway (1998) continued the studies of 3C 212 further. See their figure 1a for a very clear presentation of the system. They published new spectroscopy on the objects mentioned above and some other nearby objects. The spectrum of object f showed stellar absorption lines, of which they said:

Our detection of stellar absorption lines in f, at the same redshift as the emission lines, effectively eliminates any option in which the continuum is dominated by optical synchrotron or inverse Compton radiation. It also eliminates the possibility that we might have been seeing a combination of emission lines from an intervening object superposed by chance on some form of continuum at or near the quasar’s redshift.

They gave redshifts for 66 objects in the field. They found three objects close to the redshift of object f. They said:

This clustering in redshift supports the view that f is simply a projected intervening galaxy and that the morphological suggestions of a connection between the radio and optical structure are fortuitous.

They also found couple of objects at 3C 212 redshift. They then compared the redshift distribution of 3C 212 field galaxies to a comparable field distribution, finding a relatively good match.

Their conclusion is that both 3C 212 and object f are members of loose groups of galaxies, and the morphological evidence for object f’s association to 3C 212 is simply fortuitous.

Notes

Figure 1 presents the 3C 212 field, but only 3C 212 itself is visible at the center of the image. Other objects are too faint to show in the image. See NED’s object list for all objects with redshifts within 10′.

Figure 1. The field around 3C 212, 3C 212 is at the center. Size of the image is 5 x 5 arcmin. Image is from Digitized Sky Survey (POSS2/UKSTU Blue).

Objects and their data

NBR	NAME	TYPE	REDSHIFT (cz)	MAG	SEPARATION
1	3C 212	QSO	1.048000	19.06	0
2	3C 212:[RS97] g	galaxy	1.053000	25.3	0.094
3	3C 212:[RS97] f	galaxy	0.928400	22.6	0.138

NED page for object 1.
NED page for object 2.
NED page for object 3.

References

Ridgway & Stockton, 1997, AJ, 114, 511, “Deep WFPC2 and Ground-Based Imaging of a Complete Sample of 3C Quasars and Galaxies”

Stockton & Ridgway, 1998, AJ, 115, 1340, “Deep Spectroscopy in the Field of 3C 212″

Francis Pease – Dark matters

Francis Pease is known for his work on measuring star diameters, but here I will have a look at his work on spectroscopy of extragalactic objects. Francis Pease’s first extragalactic works were simply publishing measured radial velocities of galaxies and communicating some details on their spectra (Pease, 1915a, 1915b, 1915c, 1916a). Pease (1916b) was closing in on a redshift anomaly, although Pease didn’t seem to notice it then. He reported observations on NGC 4594 (a.k.a. Messier 104) and noted a strange feature:

Light was thus received from points at different distances from the nucleus. An extraordinary feature is that the relation between radial velocity and distance is sensibly linear, thus:
    Velocity = -2.78 x + 1180
in which x is the distance from the center in seconds of arc.

So, it seems that Pease might have published first account here of the flat rotation curves which currently are thought to suggest the presence of dark matter, but the level of detail is so poor in Pease’s paper that it is hard to say for sure. However, in the next paper, Pease (1916c) clearly recognizes that something is not correct there. This paper is basically the same observations reported with plenty more detail. Pease gives a table of his observations, and gives the same equation for the velocity curves. He notes that the equation was obtained from least squares fit, but he also says:

Within the limits of accuracy of the measures the change of rotational velocity is linear, although there may be some variation in individual parts of the nebula.

While interpreting this result, he says:

In any event the results seem to be inconsistent with a system involving planetary motion about a central nucleus, since this would require an increase of linear velocity toward the center of the nebula.

But Pease doesn’t give any comments about possible reasons for this. Pease (1918) studied the rotation curve of the Andromeda Galaxy, M31, and found it to have a linear rotation curve as well. But whether we should start to campaign for Pease as a founder of dark matter instead of Zwicky based on these studies presented here, I’m not so sure.

References

Pease, 1915a, PASP, 27, 133, “The Radial Velocity of the Nebula N. G. C. 1068″

Pease, 1915b, PASP, 27, 134, “Radial Velocity of the Andromedæ Nebula”

Pease, 1915c, PASP, 27, 239, “Radial Velocities of Six Nebulæ”

Pease, 1916a, PASP, 28, 33, “The Spiral Nebula Messier 33″

Pease, 1916b, PASP, 28, 191, “The Rotation and Radial Velocity of the Spiral Nebula N. G. C. C. 4594″

Pease, 1916c, PNAS, 2, 517, “The Rotation and Radial Velocity of the Spiral Nebula N. G. C. 4594″

Pease, 1918, PNAS, 4, 21, “The Rotation and Radial Velocity of the Central Part of the Andromeda nebula”

Links

Wikipedia: Francis Pease