Effect of changes in magnitudes of QSO_s in their redshift distribution

Abstract

Strong emission lines may change the brightness of QSOs and hence their observed magnitudes. Since different lines will affect the magnitudes by entering a particular filter at different redshifts. this effect may alter the number of QSOs at a particular redshift and hence the redshift distribution. The present analysis shows that the influence of the emission lines on the U and B magnitudes are significantly correlated to the redshift distribution. I t is concluded that the changes in observed magnitudes of QSOs caused by the emission lines have significant effects on the present redshift distribution.Starke Emissionslinien konnen die Helligkeit von Quasaren und folglich die beobachtete GroBenklasse verandern. D a die einzelnen Linien sich auf die Helligkeit, je nach dem benutzten Filter und der Rotverschiebung, auswirken werden, kann dies die Zahl der QSO bei bestimmten Rotverschiebungen beeinflussen. Die vorliegende Analyse zeigt, daB der EinfluB von Emissionslinien auf die U-und B-Helligkeiten mit der Rotverschiebungsverteilung signifikant korreliert ist. Daraus wird der SchluD abgeleitet, daB die Veriinderungen in den beobachteten QSO-Helligkeiten, die durch Emissionslinien bedingt sind, signifikante Auswirkungen auf dic gegenwartig zu beobachtende Rotverschiebungsverteilung haben. K q ' words: quasars -redshift distributionThe importance of observational effects on the physical interpretation of the QSO redshift distribution is now well recognized and a number of such effects are already established (ROEDER 1971 ; ROEDER and DYER 1972;BASU 1973BASU , 1975 BASU , 1978BASU , 1983BASU , 1985. However several authors (KJAEGAARD 1978; KODYACHIKH 1979;DEPAQUIT and PECKER 1985;WAMPLER and PONZ 1985) have suggested yet another selection effect, viz., the effect of strong emission lines in changing the brightness of QSOs and hence their observed magnitudes. As different lines will affect the magnitude by entering a particular filter at different redshifts, this effect may alter the number of QSOs observed at a certain redshift and hence the redshift distribution. However, the suggestions referred to above are of purely qualitative nature and no statistical analysis has yet been carried out to test it.It is obvious that any such test must include the effect of the emission lines on all the three filters, viz. U , B and V at which magnitudes are evaluated. MCCREA (1966), KARDASHEV and KOMBERC (19661, SANDAGE (19661, STRITTMATTER and BURBIDCE ( 1967) Considering the importance of the effect mentioned above from cosmological point of view, we were prompted to analyse the present data thoroughly with a view to find out whether the emission lines influence the observed magnitudes of QSOs so as to affect the redshift distribution.We considered the effects of influence of all the emission lines observed in the QSO spectrum, falling within all the three U, B, V filters, with proper "weights", rather than very strong lines only. The "weight" being functions of strength, width and frequency of occurence of a line as report...

Periodicity in quasar redshifts or selection effects?

“…It is associated with the determination of redshift and is completely independant of the way the object is chosen. It is thus not an optical effect (Depaquit et al 1985;Arp et al 1990) that cannot affect redshift measurement of quasars chosen on non-optical basis.A second selection effect also known to influence quasar redshift distribution is the change of observed magnitude and hence brightness of the object as emission lines enter different observing filters resulting in brighter quasars being more easily discovered (Basu, 1987). The effect of emission lines on the U filter is the change in the U magnitude of QSOs (U L ), measured as the number of lines (counted with 'weights' between 0 and 2, values of Basu 1973a), lying in the range of the U-filter, for certain redshift values.We were therefore prompted to investigate whether the periodicity found by Arp et al (1990) is real over the entire redshift domain or have appeared as a result of any of the selection effects mentioned above, at least over some part of the redshift domain.Following Arp et al (1990), we considered z < 1.3 as low redshift domain and z ≥ 1.3 as the high redshift domain.…”

Periodicity in quasar redshifts or selection effects?

“…It is associated with the determination of redshift and is completely independant of the way the object is chosen. It is thus not an optical effect (Depaquit et al 1985;Arp et al 1990) that cannot affect redshift measurement of quasars chosen on non-optical basis.A second selection effect also known to influence quasar redshift distribution is the change of observed magnitude and hence brightness of the object as emission lines enter different observing filters resulting in brighter quasars being more easily discovered (Basu, 1987). The effect of emission lines on the U filter is the change in the U magnitude of QSOs (U L ), measured as the number of lines (counted with 'weights' between 0 and 2, values of Basu 1973a), lying in the range of the U-filter, for certain redshift values.…”

“…A second selection effect also known to influence quasar redshift distribution is the change of observed magnitude and hence brightness of the object as emission lines enter different observing filters resulting in brighter quasars being more easily discovered (Basu, 1987). The effect of emission lines on the U filter is the change in the U magnitude of QSOs (U L ), measured as the number of lines (counted with 'weights' between 0 and 2, values of Basu 1973a), lying in the range of the U-filter, for certain redshift values.…”

“…A, B, (A+B), C, and D also broadly exhibit similar high and low values at same redshift regions as A s and then gradually decline at higher values of redshift. Basu (1987) and the sample X, at the high redshift domain. It may be noted here that the parameter U L is an optical effect, and is applicable to the sample X as the latter is also optically chosen, being "around low-z galaxies".…”