Introduction to anomalous redshifts

It is very difficult to determine the exact meaning of the term “redshift anomaly”. It can be lot of things. It can be said that redshift is anomalous if it doesn’t somehow fit in our current descriptions of the things in the universe. Basically any strange thing studied by redshifts is a redshift anomaly. Redshift anomalies could be found within one object, or within a group of objects, or then a group of objects could exhibit a redshift anomaly as a whole.

In traditional view, redshift of an object is composed of three components; kinematical, gravitational, and cosmological. Local and nearby objects don’t have any cosmological redshift, and gravitational redshift is so small that it can usually be ignored (although in the context of redshift anomalies, gravitational redshift is often mentioned, and sometimes with a good reason), so in those objects we are generally only interested in kinematical redshift, which is caused by peculiar velocity differences between the source of light and the receiving end. On the other hand, objects that are far away have so large cosmological redshift that all other redshift components can be ignored. Generally an extragalactic object has cosmological redshift component that is proportional to its distance from us, and kinematical redshift component which usually is considered to be smaller than cz ~ 1000 km/s (although in some extreme cases even 3000 km/s has been accepted, NGC 1275 system is an example of that). In some cases there are also other redshift components from scattering processes (Compton scattering for example), but they are not usually considered in average extragalactic objects. If there are some redshift observations that don’t fit to this traditional view, then those redshifts are anomalous.

Through the history of spectroscopy there has been redshift anomaly candidates. There is an apparent solar limb effect, where the redshifts at the limb of the Sun don’t quite match the expected values (Mikhail et al., 2002, and references therein). Within Milky Way, there is so called K-effect, where certain types of stars have a small excess redshift component (Arp, 1992). Outside Milky Way lot of redshift anomaly candidates have been found. Companion galaxies might have an excess redshift component (Arp, 1994). Some higher redshift objects might be associated with lower redshift objects, as suggested by their apparent nearness, or by their geometrical alignment, or by apparent connecting bridges (Lopez-Corredoira, 2009). Supporting these, some strange coincidences in redshift values have been cited, such as redshifts of higher redshift objects decreasing when their location being further out from the lower redshift object (Arp, 1999), or redshift values clustering around certain values (Tifft, 1995). Redshift anomalies relating to associations of objects with differing redshifts are usually called discordant redshifts.

Other type of redshift anomaly candidates are already mentioned redshift clustering around certain values (which is known as redshift quantization or periodic redshifts), excess redshift in certain galaxy types, unexpected redshift behaviour across galaxy disks (Jaakkola et al., 1975), and multitude of other suggested anomalous redshift issues (Pioneer anomalies, blueshifted quasars, etc.).

Solutions for redshift anomalies are usually sought from observational problems and from traditional science. Often it is the case that traditional physics are performing some unexpected tricks, and we see them as redshift anomalies. Those occasions give us an opportunity to extend our knowledge and polish our theories. Such seems to be the case with the solar limb effect, which has been a problem for a long time, and now seems to be getting solved mainly by gravitational redshift component revision (Mikhail et al., 2002). Another example of redshift anomaly that got solved, and is now part of mainstream science is the redshift anomaly found in 1920’s that most galaxies seemed to have “velocity shift” towards the red color in the spectrum. This was solved by Hubble (1929) by showing that there is a redshift-luminosity relation in galaxies which was interpreted as redshift-distance relation.

One interesting aspect of anomalous redshifts is the possibility to find something remarkably unexpected, perhaps something that doesn’t fit to our current theories at all. A whole new redshift component, perhaps intrinsic to the object itself (as has been suggested in many papers dealing with some redshift anomaly candidate)? We’ll see…

References

Arp, 1992, MNRAS, 258, 800, “Redshifts of high-luminosity stars – The K effect, the Trumpler effect and mass-loss corrections”

Arp, 1994, ApJ, 430, 74, “Companion galaxies: A test of the assumption that velocities can be inferred from redshifts”

Arp, 1999, A&A, 341L, 5, “A QSO 2.4 arcsec from a dwarf galaxy – the rest of the story”

Hubble, 1929, PNAS, 15, 168, “A Relation between Distance and Radial Velocity among Extra-Galactic Nebulae”

Jaakkola et al., 1975, A&A, 40, 257, “On possible systematic redshifts across the disks of galaxies”

Lopez-Corredoira, 2009, arXiv, 0901.4534, “Apparent discordant redshift QSO-galaxy associations”

Mikhail et al., 2002, Ap&SS, 280, 223, “Application of Theorems on Null-Geodesics on The Solar Limb Effect”

Russell, 2005, Ap&SS, 298, 577, “Evidence for Intrinsic Redshifts in Normal Spiral Galaxies”

Tifft, 1995, Ap&SS, 227, 25, “Redshift Quantization – A Review”

NGC 1073 – The Quasar Magnet

Condon & Dressler (1978) found that there is a radio source within NGC 1073 disk very close to NGC 1073’s spiral arm. But based on the features of the object (PKS 0241+011, object 2 in Figure 1) they said:

Since 0241+011 is so unlike any known spiral-arm radio source, we tentatively count it as a QSO…

Then they calculated the statistics of close QSO-galaxy pairs, especially for this pair, and they arrive to following result:

The expected number of BSOs in this area is 1.1; the number discovered is one – the probable QSO 0241+011.

Note, however, that they are not talking only about NGC 1073 area, but their whole survey area. It’s also interesting to note that according to Condon & Dressler (1978), NGC 1073 doesn’t show a spiral structure in neutral hydrogen. They also make a prediction about this case:

The cosmological interpretation of 0241+011 requires that it lie well behind the spiral arm of U02210, and a deep 21 cm neutral hydrogen absorption line should be present in its spectrum.

As we shall see later, this was confirmed by England & Gottesman (1990). Good work there by Condon & Dressler.

It’s a quasar – and two more

Arp & Sulentic (1979) confirmed spectroscopically that 0241+011 is a quasar, and searched the field for other similar blue stellar objects. They found two more, which also turned out to be quasars. They measured following redshifts for the three quasars: 0.601 (Fig. 1 obj. 5), 1.941 (obj. 4), and 1.400 (obj. 2). Based on average quasar density and surface areas relating to the proximity of quasars, they calculated that the chance projection probability for the two additional quasars, in addition to 0241+011, is at best about one chance in a thousand. López-Corredoira & Gutiérrez (2006) also arrived to similar result in their calculation. Arp & Sulentic (1979) also mentioned some possible signs of interaction with the quasars and NGC 1073, such as arms splitting just before the quasar positions. One suggestion in the paper was that there might be a tendency of Scd-Sd type galaxies to have quasars very near them, and as another example they mentioned the quasar at the edge of the disk of NGC 4395.

Burbidge et al. (1979) measured following redshifts for the three quasars: 0.599 (obj. 5), 1.945 (obj. 4), and 1.411 (obj. 2), confirming Arp & Sulentic (1979) redshifts. They noted on the redshift values:

It is interesting to note that the redshifts of these three objects, z = 1.945, 0.599, and 1.411, fall in three peaks of the redshift distribution, at z = 0.60, 1.41, and 1.96, discussed by Burbidge (1978).

They also reported a possible absorption line in the spectrum of the object 4. Arp (1987) noted one additional on NGC 1073’s association to the three quasars:

Three clumps of hydrogen in the disk, if rotated forward by ~20 degrees, correspond to the positions of the three quasars.

ngc1073
Figure 1. The objects with measured redshifts near NGC 1073. Size of the image is 7 x 7 arcmin. Image is from Digitized Sky Survey (POSS2/UKSTU Blue).

Studies continue

England et al. (1990) noted a symmetry that could be caused by interaction:

The excellent circular symmetry is not maintained in the northwest quadrant. Here the gas density has a steep gradient… This effect could be caused by interaction between NGC 1073 and another nearby galaxy or other object. … No evidence was found for objects likely to interact with NGC 1073 and produce the steep density gradient seen in the northwest quadrant.

So, there’s signs of interaction, but no candidate objects. Are you thinking that perhaps the quasars are causing the interaction signs? If you are, hold your horses, England et al. (1990) also note this:

An inspection of the gas distribution does not appear to show any anomalous effects at the positions of these quasars.

So it appears that the interaction feature is not caused by the three quasars, although this is not definite proof about it.

England & Gottesman (1990) looked at the spectrum of PKS 0241+011, and found neutral hydrogen absorption, just as predicted by Condon & Dressler (1978):

The absorption feature in the quasar spectrum is centered at a heliocentric velocity of 1172 +/- 5 km/s.

NGC 1073’s redshift in NED is 1208 km/s, so the absorption redshift is is a good fit to that. England & Gottesman (1990) conclude that PKS 0241+011 is further from us than NGC 1073.

Nilsson & Lehto (1997) see if two other strong radio sources in the field are related to the radio source of PKS 0241+011, and they find out that they aren’t. Other one of those two radio sources is possibly a quasar or a foreground star in our own galaxy. According to them, the other one of the two is a faint optical galaxy.

Arp et al. (2004) studied ultraluminous X-ray sources, and found that one such object in NGC 1073 (object 3 in Fig. 1) is a probable HII region roughly at NGC 1073’s redshift. Liu & Bregman (2005) note that object 3’s:

…luminosities increased by more than 50% between two observations separated by half a year.

Kaaret (2005) studied the position of object 3 and tried to find an optical counterpart to it by HST observations. Two candidate objects were found, and Kaaret (2005) suggested that the object is a X-ray binary in either case.

Couple of notes

In addition to the three known quasars, next quasar in NED is of 10.8 arcmin distance from NGC 1073 (distance of the furthest of the three quasars is 2 arcmin).

The semi-circular object near object 3 is an interesting one. It seems to be somewhat separate entity from other NGC 1073 parts. Could it be some sort of irregular companion galaxy?

NED lists a quasar ([AGL2004] J024339.5+012220) almost at the nucleus of NGC 1073. This is same quasar as [HB89] 0240+011 NED02, but there’s an error in the positional data of Arp et al. (2004), and that’s why there’s an extra entry in NED.

Objects and their data

NBR NAME TYPE REDSHIFT MAG SEPARATION
1 NGC 1073 SBc 0.004030 11.47 0
2 PKS 0241+011 BLLAC 1.400000 20 1.4
3 IXO 05 HII (?) 0.003700 1.7
4 [HB89] 0240+011 NED02 QSO 1.945000 19.8 1.8
5 [HB89] 0240+011 NED01 QSO [HB89] 0240+011 NED01 18.8 2.0

Object descriptions in NED: object 1, object 2, object 3,
object 4, object 5.

References

Arp & Sulentic, 1979, ApJ, 229, 496, “Three quasars near the spiral arms of NGC 1073”

Arp, 1987, IAUS, 124, 479, “Observations requiring a non-standard approach”

Arp et al., 2004, A&A, 418, 877, “New optical spectra and general discussion on the nature of ULXs”

Burbidge et al., 1979, ApJ, 233, 97, “Observations of three QSOs lying in the spiral arms of NGC 1073”

Condon & Dressler, 1978, ApJ, 221, 456, “Compact radio sources in and near bright galaxies”

England et al., 1990, ApJ, 348, 456, “High-resolution observations, kinematics, and dynamics of the barred spiral NGC 1073”

England & Gottesman, 1990, AJ, 100, 96, “Neutral hydrogen absorption in the radio spectrum of PKS 0241 + 011”

Kaaret, 2005, ApJ, 629, 233, “Optical Sources near the Bright X-Ray Source in NGC 1073”

Liu & Bregman, 2005, ApJS, 157, 59, “Ultraluminous X-Ray Sources in Nearby Galaxies from ROSAT High Resolution Imager Observations I. Data Analysis”

López-Corredoira & Gutiérrez, 2006, A&A, 454, 77, “Toward a clean sample of ultra-luminous X-ray sources”

Nilsson & Lehto, 1997, A&A, 328, 526, “PKS 0241+011: The largest quasar?”

NGC 5001 – Nice pair alignment

NGC 5001 is a galaxy that haven’t been studied much. It mainly has just been part of a sample in some large surveys. The NGC 5001 field has been covered by SDSS, so there are some objects that have measured redshifts within the field. There are not many discordant redshift issues here, but there is one pair alignment worth mentioning.

Figure 1 presents all objects within 7 arcmin from NGC 5001 that have measured redshifts. Of those objects, there are only two that are outside NGC 5001 (object 2 seems to be a part of NGC 5001), and those two objects are aligned across NGC 5001. They both have considerable higher redshifts (z = 0.13 and 0.18) than NGC 5001 (z = 0.03), and their redshifts are roughly similar. They have almost the same separation from NGC 5001, and have comparable magnitudes. Based on the object coordinates in NED, the alignment deviates from straight line by 11 degrees.

ngc5001
Figure 1. The objects with measured redshifts near NGC 5001. 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 MAG SEPARATION
1 NGC 5001 SB 0.030311 14.6 0
2 SDSS J130933.51+532934.4 PofG 0.029874 19.1 (g) 0.1
3 SDSS J130917.12+533123.4 galaxy(?) 0.179216 18.8 (g) 2.9
4 SDSS J130947.16+532724.7 galaxy(?) 0.126274 18.3 (g) 3.1

Links to object descriptions in NED: Object 1, Object 2, Object 3, Object 4.

Links to object descriptions in SDSS SkyServer: Object 1, Object 2, Object 3, Object 4.

LINKS

Objects within 10 arcmin from NED

SDSS SkyServer image of the system, click zoom out once to see objects 3 and 4.

NGC 4698 – Line of X-ray sources

It was found by Foschini et al. (2002a) that there is an ultraluminous X-ray source (ULX) (Object 2 in Figure 1) within the disk of NGC 4698. They have in that paper a note added in proof that says:

After acceptance of this manuscript, we obtained the VLT–FORS1 spectrum of NGC 4698–ULX1, that allowed us to identify this source as a background BL Lac object at z = 0.43, thus rejecting the classification of that source as a ULX (see Foschini et al., in preparation).

That spectral identification is discussed in Foschini et al. (2002b), and the situation is also noted in Foschini et al. (2002c). Foschini et al. (2002b) also mention another X-ray source in the field. It is shown in Foschini et al. (2002b) Figure 1 marked as “1RXS J124828.1+083103”. They say:

The three X-ray sources identified to date, however, have three redshifts: XMMU J124825.9+083020 has z = 0.43, NGC 4698 has z = 0.0033, and the ROSAT source 1RXS J124828.1+083103 has been recently identified with a Seyfert nucleus at z = 0.12 (Xu et al. 2001). Therefore, these three sources are not members of a single cluster.

So, what we have here is a straight line of three objects; the nucleus of NGC 4698 (z = 0.003), object 2 (z = 0.43), object 3 (z = 0.12). Foschini et al. (2002a) Figure 2 shows the X-ray contours drawn over an optical image of NGC 4698. NGC 4698 nucleus is an X-ray source, and then there is another X-ray source marked as “ULX 1”, it’s the object 2. Further out you can see stronger X-ray source, it’s the object 3. Notice how straight the alignment is between these three X-ray sources.

Burbidge et al. (2003) also briefly discuss the ULX in NGC 4698. Check out this nice image of this system. The field is quite crowded with apparent background galaxies. Notice how the object 2 seems clearly reddened (compare the small objects within the NGC 4698 area and outside of it, there’s a general difference in coloring of the objects), so it might very well be a background object.

Objects near NGC 4698
Figure 1. The objects with measured redshifts near NGC 4698. 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 MAG SEPARATION
1 NGC 4698 SAab, Sy2 0.00334 11.46 0
2 XMMU J124825.9+083020 BLLAC 0.43000 20.5 1.3
3 RXJ1248.4+0831 Sy 0.12000 18.0 (g) 2.4

NED object descriptions: Object 1, Object 2, Object 3

SDSS SkyServer object descriptions: Object 1, Object 3

SDSS SkyServer image of the system

References

Burbidge et al., 2003, A&A, 400, 17, “The nature of the ultraluminous X-ray sources inside galaxies and their relation to local QSOs”

Foschini et al., 2002a, A&A, 392, 817, “XMM-Newton observations of ultraluminous X-ray sources in nearby galaxies”

Foschini et al., 2002b, A&A, 396, 787, “BL Lac identification for the ultraluminous X-ray source observed in the direction of NGC 4698”

Foschini et al., 2002c, iorb. conf, 88, “Search for ultraluminous X-ray sources in nearby galaxies”

May 23, 2009 – Updated: I fought with HTML-tables, and finally won. 🙂

Hello world!

Hi!

Some of you might have seen my website. I started this blog in order to discuss matters relating to discordant redshift systems (DRS), which has been one of the main themes of my website. It is my goal to move everything from my DRS database to this blog. I will do it so that I will write a blog entry for each system containing all the issues mentioned in my website entry for the system in question. I will also make some new comments on the systems. I’m doing this mainly because I was too lazy to update my website frequently, and updates are easier to manage in a blog environment. It will also allow the readers to comment on the systems. I will also include images of the systems, which is something I didn’t do in my website version.

I am also thinking of including some more general writings whenever I have something to say, so this will not be limited strictly to the details of DRS. I will also add some new systems, there’s some waiting in my back pocket already…

I hope you have a nice time here! 🙂

Ari Jokimäki