Absorption line redshift distribution of QSOs

A gap in a distribution is the interval between two consecutive values. Analysis of gaps in the absorption line redshift distribution (241 values) of QSOs shows a definite trend in the distribution of gaps. The trend indicates that the absorption line distribution is not random, but does not suggest any periodicity.     

Gaps in the emission line redshift distribution of QSOs

A gap in a distribution is the interval between two consecutive values. Gaps in the emission line redshift distribution of QSOs are analysed using up-to-date data comprising 371 objects. It is found that the distribution of gaps is not random, but follows a definite trend, depending on the mean value of the redshift in the region.     

Periodicity versus selection effects in the redshift distribution of QSOs

Periodicities and selection effects in the redshift (z) distribution of QSOs have been debated for a long time in the literature. Here we show that peaks and troughs in the redshift distribution of three new samples, claimed to demonstrate the existence of a periodicity, can be interpreted in terms of known selection effects. This analysis confirms earlier findings that the presence of such selection effects seriously weakens any suggestion for periodicity of the form Δl n (1 + z) = constant.     

A trend in the gaps in redshift distribution of QSOs

Analysis of gaps in the emission line redshift distribution of 537 QSOs shows a single definite trend in the distribution of the gaps. The trend is similar for radio-quiet objects, radio sources and all QSO's taken together. However, the trend does not suggest any periodicity in redshifts in any of the three cases.     

Effect of changes in magnitudes of QSOs in their redshift distribution

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. It is concluded that the changes in observed magnitudes of QSOs caused by the emission lines have significant effects on the present redshift distribution.     

Correlation between the Lyman alpha absorption line density and the emission line redshift of QSOs

A statistical analysis of the absorption line density N(z_abs) in the Lαforest of 16 high-redshift quasars shows that the line density is clearly dependent on the emission redshift of the quasar, z_em. Not only is the mean density of all the Lα absorption lines larger for larger z_em, but more importantly, for each given absorption redshift interval, N(z_abs) is also positively correlated with z_em. A two-factor variance analysis, with ejection velocity as the second factor, shows that the line density in the Lα forest depends sensitively on z_em but not on the ejection velocity. These results are difficult to interpret by either the intervening or the ejecting hypothesis and are unlikely to be due to the selection effects suggested by Carswell et al. [13].     

Effect of search lines on emission and absorption redshift distribution of QSOs

Search lines used for identification of observed spectral lines in QSO_s and hence for determination of redshifts have significant effects on the peaks and valleys in the emission and absorption redshift distributions of the present sample of QSO_s, including ‘the 1.95 peak’.     

Magnitude and redshift distributions of QSOs

The peak in the distribution of apparent magnitude (V) of QSOs at 18.0 can be explained by loss of QSOs forV<-18.0 arising out of selection effects due to the availability of search lines necessary for the determination of redshifts and due to the misidentification of QSOs as Main-Sequence stars. ForV>18.0, the number of objects seem to fall off as they become progressively fainter and detection efficiency goes down. The present analysis also shows that a strong correlation exists between apparent magnitude and redshift of QSOs indicating redshifts are of cosmological origin.     

Correlation between colors and redshift of optically violent QSOs

In this Letter we report the findings of a statistically significant relation between the continuum color indices and redshift of optically violent variable QSOs. No such correlation is found to exist for non-variable and moderately variable QSOs.     

The effects of emission line identification on the redshift distribution of QSO's

We use the QSO's in the catalog compiled by Hewitt and Burbidge (1980) as the sample to analyse for the selection effects in the redshift identification. The results show that the redshift distribution caused mainly by the selection effects has almost same global feature as those given by the observations. The analysis leads us to conclude that the observational redshift distribution of QSO's should be heavily affected by these selection effects, and that attention should be paid to them in the investigations of the redshift distribution, the origion of redshift, and the evolutionary properties of QSO's.     

Distribution of gaps in emission line redshifts of QSOs

A gap in the distribution of a parameter is simply the absence of the parameter for the values corresponding to the gap. The gap in the emission line redshift (z) of QSOs thus represents absence of QSOs with emission line redshift values corresponding to the gap region. Gaps in emission line redshifts of QSOs have been analysed statistically with updated data consisting of 1549 values. The study indicates: (i) There is a critical redshiftz _c =2.4, which separates two distinct phases in the creation of QSOs. Forz>z _c , the creation appears to have been a slow process. Atz?z _c there was a triggering action which produced a burst of QSOs simultaneously. Forz _c , the rate of production of QSOs have been fast. (ii) The distribution of gaps atz _c ; appear to be consequence of periodicities, provided the periodicities involved are perfect and the redshift values are accurate. (iii) The distribution of gaps atz>z _c are not random, but follow a definite trend.     

Absorption line redshifts of QSOs in relation to their emission line redshifts

Analysis of the recent data indicate that absorption line redshifts of QSOs are significantly correlated to their emission line redshifts. It is concluded that the absorption lines originate in materials intrinsic to the QSOs.     

Periodic redshift distribution of quasars associated with low — redshift galaxies

We applied power spectral analysis to the redshift distribution of the quasars associated with low-redshift galaxies. Periodicity is confirmed at a level of confidence >99%, with a period of Δln(1+z) = 0.206. This result is exactly the same as previously found for different quasar samples. The periodicity is not caused by any selection effect in the emission lines. The two phenomena, the periodicity in the redhsift distribution and the association of quasars with low-redhsift galaxies can both be rather well explained by a multiply-connected model of the universe.     

The redshift distribution law of quasars revisited

Can observational selection effects, tied with the existence of strong lines, explain the observed log (1 + z) periodicity of the quasar's histogram, as sometimes claimed? A first approach shows that one must distinguish radio from optical quasars. In the former case spectroscopic selection due to strong lines is investigated from the study of homogeneous samples. Then, the role played by pairs of strong lines in the redshift's determination is evaluated and it shows that teh spectroscopic selection cannot explain the observed periodicity of the radio quasar's histogram. The study of the complete sample confirms this conslusion.     

UV Emission and bust properties of high redshift galaxies

The number density of the high-redshift (z >2) galaxies discoveredover the last few years with the Lyman-break technique is only afactor of a few lower than the number density of galaxies in the LocalUniverse. Thus, understanding the properties and the nature of thesehigh-redshift systems is instrumental to our understanding of thecosmic evolution of galaxies and their stellar content. I brieflyreview the observed characteristics of the Lyman-break galaxies,relate these galaxies to their most likely low-redshift counterparts,and discuss the implications of dust obscuration on the globalproperties of the Lyman-break population. Finally, the observationalproperties of the high-redshift population are set in the framework ofa simple evolutionary model for the stellar, metal and dust content ofgalaxies, to derive the intrinsic star formation history of theUniverse.     

Quasar redshift distribution and selection effects

With the Hewitt-Burbidge catalogue of quasars as our sample, separately for 3 sets of respectively 7, 11, and 13 spectral lines as the “key lines” in the identification of quasar redshifts, we derive the redshift distribution arising from the identification of the lines. A comparison between the calculated and observed distributions shows that 1) the two are clearly correlated, with a correlation coefficient of 0.56. 2) Similar peaks are present in both in the z-intervals 0.2 – 0.4, 0.8 – 0.9, 1.4 – 1.5, and particularly around 1.95, as well similar valleys at 0.1 and 1.5 – 1.8. 3) Both rise or fall together at z = 0.2, 0.3, 0.4, 0.8, 1.9, 1.4, 1.5, 1.6 and 1.7. It thus appears that selection effects play an important role in the redshift distribution of the quasars.     

An absorption line study of galaxies at high redshift

Complex velocity structure is revealed in several absorption systems in the spectrum of 0215+015 (z=1.715) at resolutions of 20–30 km s^–1 FWHM. Striking differences are found in the relative strengths of low to high ions among the components, reinforcing our interpretation of these systems as intervening galaxies.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984.     

Open issues with the gamma-ray burst redshift distribution

Cosmological gamma ray bursts (GRBs) are the brightest explosions in the Universe. Satellite detectors, such as Beppo-SAX, HETE2 and more recently Swift, have provided a wealth of data, including the localization and redshifts of subsets of GRBs. The redshift distribution has been utilized in several studies in attempts to constrain the evolving star formation rate and to probe GRB rate evolution in the high-redshift Universe. These studies find that the GRB luminosity function and/or the rate density evolve with redshift. We present a short review of the problems of constraining GRB rate evolution in the context of the complex mix of biases inherent in the redshift measurements. To disentangle GRB rate evolution from the biases prevalent in the redshift distribution will require accounting for the incompleteness of the observed redshift sample. We highlight the importance of formulating a ‘complete GRB selection function’ to account for the main sources of bias.