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?”

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