0248+430 – Very close quasar-galaxy pair

Pauliny-Toth et al. (1978) identified object 3 in Fig. 1 as a radio source. Kuhr (1977) suggested that it is a quasar, and near a galaxy (objects 1 & 2). Kuhr (1977) also showed an image of the system. Kuhr (1980) measured the redshift of object 3 as z = 1.316 confirming it a quasar.

Junkkarinen (1987) found absorption lines from the spectrum of 0248+430 at main galaxy’s redshift (absorption redshift z = 0.052). This was followed by Sargent & Steidel (1990), who also found absorption lines from the spectrum of object 3. They found some absorption (z = 0.0519) at the redshift of objects 1 and 2. They also found absorption at redshift z = 0.3940. They said:

These images reveal that the interstellar absorption is produced in a part of a complex tidal tail emanating from G0248+4302, which turns out to be a close double galaxy system.

Unfortunately, the electronic version of their paper doesn’t include the pictures they took of the system. They also suggest that there is a faint background galaxy between the quasar and the main galaxy. Womble et al. (1990) also studied absorption lines in the system, and found two absorption systems at main galaxy’s redshift (z = 0.0515 and z = 0.0523), and two at higher redshifts of z = 0.394 and z = 0.451. They also talk about tidal tail and the double nucleus, so in many ways, this is a confirmation of Sargent & Steidel (1990) who also found the 0.394 absorption system. Womble et al. (1990) also note:

We did not find any galaxies at these absorption redshifts; however, we tentatively identify a galaxy 11″ northeast of the QSO at z = 0.240.

The galaxy they talked about is the object 6 in Fig. 1. They also took spectrum of object 7 in Fig. 1 and found out that it is a probable foreground star. Note also that Womble et al. (1990) did not perform a complete search of the field, so it doesn’t necessarily mean anything that they didn’t find any galaxies at absorption redshifts.

0248_430
Figure 1. The objects with measured redshifts near LEDA 090441. Size of the image is: left panel, 7 x 7 arcmin, right panel, same image but 4 x zoomed in (so roughly 1.75 x 1.5 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.

Borgeest et al. (1991) took new images and spectra of the system. Note how their Fig. 2 seems to show a bridge between the quasar (“Q”) and the galaxy. But let us also remember the tidal tail which is supposedly arising from the merging of the two galaxies, the presence of a tidal tail from such process increases the probability of apparent “bridge” arising to a nearby object. And in this case the “bridge” doesn’t even seem to hit exactly the center of the quasar, which further supports the view that this would be just a background object projected by chance to the direction of the tail. The probability would be roughly 20/360 ~ 0.06, assuming that there’s about 20 degrees out of 360 possible that the tail would point roughly to the quasar. It also should be pointed out that this tail continues far beyond the position of the quasar, see Borgeest et al. fig. 1.

Another interesting thing mentioned by Borgeest et al. was:

Within the positional errors the quasar Q is aligned with A and B.

“A and B” being the merging double nucleus of the main galaxy. Borgeest et al. found absorption line from object 3’s spectrum, the line is at main galaxy’s redshift, supporting previous similar findings. They then analysed the system as gravitational lensing candidate. They first pointed out that this is not exactly a typical system for multiple lensed images because the separation of the quasar and the galaxy is larger than usually in those cases. They discussed the system as macro lensing system (such that the main galaxy as a whole would act as a gravitational lense), but lack of second quasar image makes that scenario improbable.

They also considered micro lensing, in which the stars of the intervening galaxy would cause amplification of the quasar’s brightness when they happen to be between us and the quasar. Difficulty with this scenario is that the amplification events are very brief, so it wouldn’t seem probable that all of our observations would occur at the time of an amplification event. Borgeest et al. argue that with optimistic assumptions it would be possible to detect some lensing variability in this system. They also presented a probability calculation that shows very low probability of the chance projection for this quasar-galaxy association, unless some lensing scenario is at play. But they point out:

However, a strong amplification due to micro-lensing is very unlikely for GC 0248+430, since otherwise the 1950 (POSS) and 1989 magnitudes ought to differ significantly since high amplifications by micro-lensing do not last very long. A large macro-lensing amplification seems also to be very unprobable. From our experience in modelling lens effects we know that highly amplified single images only appear near the centre of the lense.

So, if the lensing is improbable, we are stuck with very low chance projection probability for this system. (But of course, as in all this kind of cases, we need to remember that one cannot do statistics with a single system.)

For other objects in the field, Borgeest et al. noted that object 4 is a F7 star according to their spectrum, and they too think that object 7 is a star. However, they do raise a point about this object; they say that it is possible that it is second gravitational lense image of the quasar (object 3) because of similar color between the two objects, but that there is no signs of emission at correct redshift in object 7’s spectrum for that.

An accompanying paper by same team, Kollatschny et al. (1991), focused on the main galaxy’s double nucleus. They found a redshift for both nuclei (object 1 z = 0.0512 and object 2 z = 0.0507). They also measured galaxy’s rotation curve, which shows disturbances that further advance the merging hypothesis.

Hwang & Chiou (2004) made some observations of the system. Once again we note the bridge-like situation in their fig. 2. Note how the features in the CO-moment map seem to be arising from the main galaxy and focusing to the quasar. Hwang & Chiou found HI absorption at main galaxy’s redshift from the quasar’s HI spectrum. They also pointed out that the absorption derived metal abundances and some other features of the “absorbing cloud” are quite abnormal.

López-Corredoira & Gutiérrez (2006) looked at this system among some other discordant redshift systems, and found that there is another quasar (z = 1.531) further out (object 5 in fig. 1). They said:

The position angle of the first QSO with respect to the major nucleus of the galaxy is -73 [degrees] at a distance of 14.4″ from the major nucleus; and the position angle of the second QSO is -68 [degrees] at a distance of 108″ from the major nucleus. The position angle of the line which joins the two nuclei of the galaxy is -77±18 [degrees] (the error bar is large because both nuclei are very close — 2.7″ — and it was not possible to determine the position of the second centre accurately). Even if we forget the second nucleus and the gas ejection, all in this direction[24], given the low density of expected background quasars, the coincidence of the near-alignment (the difference is 5 degrees) seems unlikely.

Objects and their data

NBR NAME TYPE REDSHIFT MAG SEPARATION
1&2 LEDA 090441 Merger 0.051440 16.11 0
1 AN 0248+43A galaxy 0.051939 16.52 0.075
2 AN 0248+43B galaxy 0.050700 17.36 0.040
3 [HB89] 0248+430 QSO (LPQ) 1.310000 17.45 0.252
4 star F7 probably ~ 0 ~ 0.25
5 quasar quasar 1.531 21.11 (g) 1.8
6 galaxy galaxy 0.240 ~ 0.25
7 star star probably ~ 0 ~ 0.25

NED object list with available redshifts within 10 arcmin.

References

Borgeest et al., 1991, A&A, 249, 93, “GC0248 + 430 – A possibly micro-lensed quasar behind a tidal arm of a merging galaxy system”

Hwang & Chiou, 2004, ApJ, 600, 52, “A New H I 21 Centimeter Absorber Associated with the H I Deficient Interacting Galaxies G0248+430”

Junkkarinen, 1987, BAAS, 19, 953, “A Search for More QSO Absorption Systems Produced by Intervening Galaxies”

Kollatschny et al., 1991, A&A, 249, 57, “An 0248 + 43 – A cold highly luminous FIR-galaxy with two nonthermal nuclei”

Kuhr, 1977, A&AS, 29, 139, “Optical identification of extragalactic radio sources from the NRAO – Bonn 5GHz survey”

Kuhr, 1980, Ph.D. thesis, Bonn, information about this is given in Sargent & Steidel (1990).

López-Corredoira & Gutiérrez, 2006, AIPC, 822, 75, “Research on candidates for non-cosmological redshifts”

Pauliny-Toth et al., 1978, AJ, 83, 451, “The 5 GHz strong source surveys. IV – Survey of the area between declination 35 and 70 degrees and summary of source counts, spectra and optical identifications”

Sargent & Steidel, 1990, ApJ, 359L, 37, “Absorption lines in the spectrum of Q0248 + 4302 due to a foreground tidal tail”

Womble et al., 1990, AJ, 100, 1785, “CA II and NA I absorption in the QSO S4 0248 + 430 due to an intervening galaxy”

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