Quasars and Galaxies: Evidence of Physical Association and Evolution, Notas de estudo de Astronomia

Baixe Quasars and Galaxies: Evidence of Physical Association and Evolution e outras Notas de estudo em PDF para Astronomia, somente na Docsity! J. Astrophys. Astr. (1997) 18, 393–406 Quasar Creation and Evolution into Galaxies Halton Arp, Max-Planck-Institut fuer Astrophysik 85740 Garching, Germany Abstract. Building on evidence starting from 1966, X-ray observations have once again confirmed the association of quasars with low redshift galaxies. Enough examples of quasar-like objects ejected in opposite directions from nearby, active galaxies have accumulated so that an empirical evolutionary sequence can be outlined. The quasars start out with low luminosity and high (z > 2) redshift. As they travel away from their galaxy of origin they grow in size and decay in redshift. The redshifts drop in steps and near the quantized values of z = 0.6, 0.3, and 0.06 the quasars become particularly active, ejecting or breaking up into many objects which evolve finally into groups and clusters of galaxies. The observations massively violate the assumptions of the Big Bang and require continuous, episodic creation in a non expanding universe of indefinitely large size and age. Key words. Quasars—redshifts—galaxies—evolution. 1. Introduction In 1966 it was shown that radio sources ejected from disturbed galaxies in the Atlas of Peculiar Galaxies contained a number of much higher redshift quasars. Later associations of quasars were found with companion galaxies to larger galaxies. The companions tended to be more active and contain a larger component of young stars and the statistical association of quasars with them reached the astonishing level of 16 sigma. (See for review Arp 1987). Fig. 1 shows a pair of radio quasars discovered in 1968 across a disturbed companion where the redshifts later turned out to be, an improbable by accident, z = 0.62 and 0.67. 2. Ejection of quasars from low redshift galaxies With the advent of satellite X-ray telescopes quasars became much easier to discover because they represented the majority of point sources mapped at these high energies. In addition there was a class of galaxies called Seyferts with nuclei which showed the same kind of excited, energetic spectra as quasars and which were also very strong X-ray sources. In the course of observing these Seyfert galaxies, particularly the German X-ray telescope ROSAT built up an archive of observa- tions which encompassed a field of almost one degree radius around each Seyfert. Around this rather complete sample of bright Seyferts it was possible to catalogue an excess of bright X-ray quasar candidates that was visually striking and significant 393 394 Halton Arp Figure 1. The two strongest radio sources in the pictured area fall across the disturbed spiral galaxy IC1767. The redshifts of these radio quasars at z = 0.62 and 0.67 are so close as to insure their physical relation. This pair, published in 1968, established quasars to be in the class of radio sources ejected in opposite directions from active galaxies. at the more than 7.4 sigma level (Radecke 1997). Among this sample of 26 Seyferts more than a dozen had conspicuous pairs of X-ray emitting, blue stellar objects (BSO’s). Among the 53 BSO’s in these pairs a number were already known to be quasars and the rest essentially only await the measurement of their redshifts (Arp 1997). In addition to the statistical proof of physical association there was, of course, the striking pairing of quasars across the active Seyferts, pairs which were too accurately aligned and spaced and with such similarity of properties as to preclude their being accidental projections of background objects. A few examples of such X-ray pairings are shown here in Figs. 2, 3 and 4. Already this tells us that the Seyferts as a class, which are known to be ejecting material, are ejecting these X-ray emitting quasars. Ejection of radio synchrotron emitting material from active galaxies was already an accepted fact from the 1950s and, of course, we had examples of radio quasars ejected from disturbed galaxies from 1966 onward. 3. What do quasars evolve into? Inspection of just the four examples of pairings given so far reveal a pattern which can be substantiated by reference to many other cases. The pattern is that when the quasars are closely spaced across the ejecting galaxy they tend to be fainter Quasar Creation and Evolution into Galaxies 397 Figure 5. A schematic diagram incorporating the empirical data for the low redshift central galaxies and the higher redshift quasars and companions. It is suggested that the most evolved companions have relative intrinsic redshifts of only a few hundred km/sec and have fallen back closer to the parent galaxy. 4. 3C345 – Finally a cluster of quasars Since extragalactic objects are hierarchically distributed astronomers expected to find clusters and groups of quasars. When they did not, they characteristically put this difficulty out of their mind. Actually groups of quasars were found (Arp 1987 p. 64) but they had a wider spread in redshift than could be conventionally accepted. But Fig. 6 shows what happens when we look at the archived X-ray fields centered on 3C345, a bright, strongly variable radio quasar that was among the first to be dis- covered. The brightest X-ray object is naturally 3C345 with an X-ray intensity of 365 counts/kilosec. But forming a conspicuously well aligned pair across it are the next two strongest X-ray sources in the field. Both are catalogued quasars of redshift 398 Halton Arp Figure 6. The bright, violently variable radio quasar, 3C345, is indicated as having the very strong X-ray intensity of 365 cts/ks. Counts for other quasars in the field are marked to the upper right and optical apparent magnitudes directly beneath. The next two brightest X-ray quasars are shown as filled circles and define a conspicuous pair across 3C345. similar to 3C345 as shown in Fig. 7. In this respect 3C345 is just like the examples of paired X-ray quasars shown in the first four figures and referred to in the publications. But what is exceptional in this case is the fact that 3C345 is part of an 8 sq. deg. field which had been optically searched for quasars by Crampton et al. (1988). Part of that uniform search is shown in Fig. 7. It is obvious at a glance that an equal sized adjoining field is bereft of quasars and that almost all of the 14 quasars pictured belong to 3C345! To go back to Fig. 6 for a moment we can point out that the next three, strongest and closest X-ray quasars, fall closely along the ejection line defined by the brightest two. This lowers the probability of accidental alignment with 3C345 from 4 in one hundred thousand to 3 in one hundred million. Obviously they have been ejected from the central object as its active, Seyfert-like spectrum would suggest. In Fig. 7 the central radio quasar is labeled HP signifying that it is highly polarized. In addition to strong radio and X-ray emission this is another characteristic of BL Lac objects. So it is clear that 3C345 is some kind of transition between a quasar and a BL Quasar Creation and Evolution into Galaxies 399 Figure 7. Quasars of redshift 0.5 < z < 1.6 in a homogeneously searched area around 3C345 and an equal area to the west. Redshifts are written to the upper right of each quasar. 3C345 is identified HP (for high polarization) and the Seyfert galaxy is marked S1. Lac object. The importance of this comment lies in the fact that 3C345, as earlier concluded about BL Lacs, appears to be in the process of ejecting and breaking up into smaller entities. In turn this is important because it implies that if this process continues, over time we will develop an increasingly rich cluster of galaxy like objects. 5. The origin of galaxy clusters It is noticeable that three of the quasars NE of 3C345 form a tight group with redshifts z = 0.59, 0.70 and 1.08. This pattern has appeared a number of times in the pairs across Seyferts, i.e. one of the X-ray pairs will be double or triple or the X-ray position will yield two or three BSO quasar candidates (Arp 1997). The preliminary interpretation, consonant with the break up of BL Lac’s discussed previously, is that as the outward travelling quasar evolves its subsequent ejections are sometimes blocked by material in the vicinity and the younger, higher redshift products stay irregularly placed in the vicinity. If this is true it helps us to understand the previous observations that the richest quasar groups found had, at maximum, only about six members and they were all of redshift about z = 1, plus or minus a few tenths (Arp 1987, p. 64). Here we are suggesting that they are on their way to evolving into more populous clusters of low redshift galaxies. Notice in Figs. 6 and 7 that there is a square box representing the Seyfert galaxy NGC6212. At only 4.7 arc min distance from 3C345 it would be unlikely to be a 402 Halton Arp Figure 10. The Arp/Hazard triplets are pictured with the measured redshifts written to the right of each quasar. In the box to the right are written the nearest intrinsic redshift peaks and the velocity components in z which are required to balance the ejections. But with the developments in the understanding of ejection and quantization of intrinsic redshift it is now possible to interpret the triplets more satisfactorily. Notice that the high redshift quasars are within about 0.2z of the strong quantization peak z = 1.96. The side bar in Fig. 10 shows that if these quasars were ejected toward and away from the central quasar with delta z’s of this amount that the observed values of the paired quasars would result (At these z’s a calculation of the ejection velocity would again yield about 0.1c.) As the sidebar also indicates, a modest velocity of the whole system would then enable the central quasars to be at the quantized value of z = 0.60 and the pairs to be ejected symmetrically. The central quasar in each case is quite bright in apparent magnitude, and one is a strong radio source. They are quite like the BL Lac’s which have been found now to eject higher redshift quasars. In this case the ejection appears to be quite recent, the quasars quite young and the intrinsic redshifts quite high. But then the question arises, is there a nearby, lower redshift galaxy from which the two, bright ejecting quasars could have originated? Before we answer that, however, we should consider another extaordinary group of quasars discovered in the same 6 × 6 degree schmidt telescope field by Cyril Hazard. Quasar Creation and Evolution into Galaxies 403 Figure 11. Redshift of all quasars found in rich group by Arp and Hazard on the same objective prism plate as the triplets in Fig 10. Fig. 11 shows Arp/Hazard 1146 + 1112, a group of 6 to 8 quasars which were so conspicuous that theorists tried to explain them as a gravitational lensing phenomenon. When that failed because of the unbelievably large mass required the group was forgotten. But it is the same as a few other groups of quasars known at the time – some brighter quasars at z = 1 or below and a few fainter, higher redshift quasars. The question was whether there was any significance to this group’s occurrence on the same plate as the triplets? The answer is shown in Fig. 12. In the area of sky plotted there is one Catalogued Seyfert galaxy and it falls approximately between the two Arp/Hazard groups. But this is not an ordinary Seyfert galaxy. In an all sky survey of infrared luminous, star burst galaxies which were also strong X-ray sources, 13 galaxies were found to be Seyferts which were exceptionally luminous in X-rays (Moran et al. 1994). NGC3822 was found to be one of these exceptional Seyferts and this is the galaxy that falls between the two extraordinary Arp/Hazard groups in Fig. 12! Only the lower redshift members of the Arp/Hazard groups have been plotted in Fig. 12 and it is instructive to compare the configuration with the quasars emanating from 3C345 in Fig. 7. There is a group of quasars just NE of 3C345 which we concluded was ejected from the active BL Lac like object and was breaking up into redshifts of z = 0.59, 0.70 and 1.08. In Fig. 12 it looks like the eastern group is at intrinsic z = 0.96 with velocity components +/ – 0.1z and a systematic velocity of about +0.05z. The higher z quasars shown in Fig. 11 are further out with slightly higher ejection Z’s. The western triplets can be interpreted as being centered on quasars of intrinsic redshift z = 0.60 with a systematic velocity between –0.75z and –0.03z. 404 Figure 12. The area of the sky in which the very unusual Arp/Hazard group and triplets are found. Only redshifts less than z = 1.6 are plotted. The central identifies one of the 13 most luminous X-ray Seyferts known over the whole sky. Open circles identify members of the NGC3869 group (Nilsen 1973; Uppsala General Catalogue of Galaxies). Figure 13. The strong X-ray galaxy cluster Abell 85. Individual galaxies are plotted as a function of their redshift and distance from the cluster center (Durret et al. 1996).