• D. Basu

      Articles written in Journal of Astrophysics and Astronomy

    • Ejections of quasars at relativistic speeds from nearby galaxies: Ejection mechanism and selection effects

      M. J. Valtonen D. Basu

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      It has become part of the conventional wisdom of quasar research that quasars cannot be objects ejected from nearby galaxies. The reasons are summarized in Burbidge & Burbidge (1967) and they include: (1) in quasar spectra only redshifts, and no blueshifts, are observed, contrary to expectation in a local Doppler interpretation of quasar line shifts; (2) the energy requirements for relativistically moving quasars seem excessive and the ejection mechanism is unknown. In. this work we show that the first problem could be explained via some powerful selection effects, and that the second problem does not exist in the relativistic slingshot process of ejecting black holes. Consequently one cannot exclude the possibility that at least some of the quasar-galaxy associations of large redshift differentials discussed by Arp and Sulentic are real and that the redshift differences are due to high speeds of ejected quasars

    • Ejections of population III objects seen as blueshifted QSOs?

      Shirin Haque-Copilah D. Basu M. Valtonen

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      We discuss the origin of the optical jets and the apparently associated cloud of QSOs in NGC 1097. There is a simple explanation for the jets in terms of ejection trails of supermassive black holes. In this interpretation, the trails provide the first direct evidence for the non-conservation of linear momentum in a two black hole collision. The cluster of quasars at the end of the jets is then naturally associated with objects which have been ejected by the merging pair of black holes. It is possible to interpret the spectral lines of these QSOs such that half of them are blueshifted relative to NGC 1097 while the other half is redshifted. We infer that the objects in the QSO cluster are not real QSOs but probably collapsed objects of lower mass. We argue that these objects are likely to represent the hypothetical population III black holes of Carretal.

    • Variability of extragalactic objects in relation to redshift, color, radio spectral index and absorption lines

      D. Basu

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      Optical variability of extragalactic objects, viz., QSOs, BL Lacs and Seyfert galaxies has been monitored systematically over an appreciable period of time and a large amount of data have accumulated. The present work reports results of investigations involving statistical analysis of updated data on relationships between variability and various observed properties of the objects, viz., redshift, color indices, radio spectral index and absorption lines. It is found that at high frequencies (rest frame) radio spectral index does not change significantly with the degree of variability. However, the degree of variability depends on redshifts. On the other hand, presence or absence of absorption lines is significantly associated with variability for QSOs with larger redshifts (z > 1.0), while no such relationship exists for QSOs at smaller redshifts (z < 1.0) or other objects. Correlation between color indices and redshifts depends on the degree of variability and the sample chosen for the color index.

    • The Hubble relation for a comprehensive sample of QSOs

      D. Basu

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      A correlation between redshifts (z) and apparent magnitudes (V) (Hubble relation) of Quasi Stellar Objects (QSOs) has long been sought. Such a correlation exists for galaxies whose redshifts are of cosmological origin. However, a plot of the two quantities representing the Hubble diagram for QSOs exhibits, in general, a wild scatter. This raises the question whether redshifts of QSOs are cosmological. On the other hand, most luminous QSOs in groups, and subsamples with particular properties, have been reported to show the Hubble relation. In the present paper, we analyse all optically non-variable QSOs in a comprehensive sample. In our analysis we grouped the objects into certain intervals of apparent magnitudes. Correlations obtained between redshifts and magnitudes are all statistically robust. Also, the Hubble relation in the usual formV = 5 logz +C is obeyed very convincingly for QSOs withV < 19.5.

    • QSO pairsacross active galaxies: Evidence of blueshifts?

      D. Basu

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      Several QSO pairs have been reported and their redshifts determined, where the two objects in each pair are locatedacross an active galaxy. The usually accepted explanation of such occurrences is that the pair is ejected from the parent galaxy. Currently interpreted redshifted spectra for both the QSOs imply that both the objects are receding from the observer. However, ejection can occur towards and away from the observer with equal probability. We argue that for a system with two QSOs lyingacross the parent galaxy, ejection should have occurred in opposite directions, whereby one object will be approaching us and the other will be receding from us. The former would exhibit a blueshifted spectrum. We analyse here a sample of four such pairs and show that the observed spectrum of one QSO in each pair can be interpreted as blueshifted. The other exhibits the usual redshifted spectrum. A scenario based on the ‘sling-shot’ mechanism of ejection is presented to explain the occurrences of the pairs in opposite sides of the active galaxies moving in opposite directions.

    • Close Separation Triple System QSO 1009-0252 with Discordant Redshifts: Is the Spectrum of One Component Blueshifted?

      D. Basu

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      1009-0252 is a Quasi Stellar Object (QSO) with three components A, B, C. A, B are thought to be the result of gravitational lensing of one object, and A, C constitute a close pair with redshifts 2.74 and 1.62 respectively. Close separation pairs of QSOs with discordant redshifts have received special attention in recent years, probably because of the possibility that they may be physically associated, implying non-cosmological redshifts. Attempts have been made to explain their occurrences due to the effect of gravitational lensing. However, gravitational lensing has not offered a completely satisfactory explanation for this triplet. Furthermore, examination revealed some inadequacies and inconsistencies in the redshift identification of the observed lines in the component A. Observational results of 1009-0252 therefore remain puzzling.We propose an alternative explanation by suggesting that A, B actually constitute a close pair and C is an unrelated object in the field. We show that the observed spectrum of A can be interpreted as blueshifted. This implies that A, B are two separate objects, one (A) approaching us and the other (B) receding from us, and are not the result of gravitational lensing of a single object. The oppositely directed pair A, B may have been ejected due to the merger of two galaxies.

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    • Continuous Article Publication

      Posted on January 27, 2016

      Since January 2016, the Journal of Astrophysics and Astronomy has moved to Continuous Article Publishing (CAP) mode. This means that each accepted article is being published immediately online with DOI and article citation ID with starting page number 1. Articles are also visible in Web of Science immediately. All these have helped shorten the publication time and have improved the visibility of the articles.

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