scholarly journals Linear Size Evolution and Luminosity Selection Effects in Quasars

1997 ◽  
Vol 50 (5) ◽  
pp. 967
Author(s):  
A. A. Ubachukwu
Keyword(s):  
Linear Size ◽  
Selection Effects ◽  
Large Sample ◽  
Size Evolution

We have quantitatively estimated the amount of luminosity selection effects present in the observed linear size-redshift data for a large sample of extended steep spectrum quasars. We show that ~90% of the observed dependence of sizes of quasars on redshift can be interpreted in terms of luminosity selection effects alone. This gives quantitative support to earlier results which show that little or no intrinsic linear size evolution appears to be occurring among quasars.

scholarly journals Implications of a Nonzero Cosmological Constant and Luminosity Selection Effects on Cosmological Tests

1998 ◽  
Vol 51 (3) ◽  
pp. 585 ◽  
Author(s):  
A. A. Ubachukwu
Keyword(s):  
Cosmological Constant ◽  
The Other ◽  
Linear Size ◽  
Low Density ◽  
Selection Effects ◽  
Flat Universe ◽  
Size Evolution ◽  
Significant Difference ◽  
Cosmological Tests ◽  
The Universe

This paper examines the implications of a nonzero cosmological constant Λ 0 on the amount of linear size evolution and the luminosity selection effects usually required in the interpretation of the angular diameter–redshift (θ–z) test. This is based on three typical cases chosen on various plausible assumptions which can be made concerning the contribution of Λ 0 to the density of the universe (parametrised by ?0). The results show that a fairly strong linear size evolution will be required to interpret the θ–z data of extended steep spectrum quasars for all three cases, if luminosity effects are neglected. However, this evolution is significantly steeper in a matter-dominated universe with ?M = ?0 = 1 than in both the flat universe with ?Λ = 0·8, ?M = 0·2 and an open universe with ?M = 0·2, Λ = 0. Furthermore, when the luminosity selection effects present in the sample are considered, a milder size evolution is obtained for the ?M = 1, ?Λ = 0 model while little or no size evolution is found for the other two cases. There is therefore no significant difference in our results for an open low density universe with ?Λ = 0 and a flat universe dominated by ?Λ predicted by inflation. The present results therefore imply that an open low density universe with ?M = 0·2 and ?Λ = 0 is compatible with an inflationary model of the universe with ?M = 0·2 and ?Λ = 0 · 8. This leads to a contradiction since the universe cannot be open and spatially closed at the same time (the existence of one should preclude the other).

scholarly journals Luminosity Selection Effects and Linear Size Evolution in the Quasar/Galaxy Unification Scheme

1998 ◽  
Vol 51 (1) ◽  
pp. 143
Author(s):  
A. A. Ubachukwu ◽  
J. N. Ogwo
Keyword(s):  
High Redshift ◽  
Radio Galaxies ◽  
Linear Size ◽  
Selection Effects ◽  
Size Evolution

The implications of linear size evolution and luminosity selection effects in the quasar/galaxy unification scheme have been investigated. We show that both radio galaxies and quasars undergo similar size evolution above some low redshift cut-off zc = 0·2–0·3. However, this evolution can be attributed largely to the strong luminosity selection effects present in the sample. We also observe that there is a marked difference in the luminosity–redshift slope between low and high redshift sources, which may be responsible for the conflicting results in the literature as to whether or not radio galaxies and quasars have similar linear size versus luminosity/redshift relationships. Our present result seems consistent with the quasar/galaxy unification scheme in which the two classes of object are expected to have similar linear size versus luminosity/redshift relationships.

scholarly journals The Angular Size Distribution of Radio Sources at Low Flux Densities

1982 ◽  
Vol 97 ◽  
pp. 393-400
Author(s):  
Ann Downes
Keyword(s):  
Size Distribution ◽  
Flux Density ◽  
Angular Size ◽  
Linear Size ◽  
Radio Sources ◽  
High Flux ◽  
Extragalactic Radio Sources ◽  
Size Evolution

Observations of complete samples of extragalactic radio sources at low and intermediate flux densities are described. Many types of source are found. The angular sizes form a smooth extrapolation from higher flux densities, and can be predicted from the known properties of samples at high flux density either with linear size evolution (for Ω = 1 or Ω = 0 Universes) or without linear size evolution (for Ω = 0). The question of whether such evolution is required therefore remains open.

scholarly journals Measuring Cosmological Parameters with Very Long Baseline Interferometry

1999 ◽  
Vol 183 ◽  
pp. 67-67 ◽  
Author(s):  
L.I. Gurvits ◽  
K.I. Kellermann ◽  
S. Frey
Keyword(s):  
Cosmological Model ◽  
Very Long Baseline Interferometry ◽  
Cosmological Parameters ◽  
Angular Size ◽  
Linear Size ◽  
Radio Sources ◽  
Selection Effects ◽  
Extended Source ◽  
Long Baseline ◽  
5 Ghz

Very Long Baseline Interferometry (VLBI) allows us to study a core of AGN with a sub-parsec resolution. We analyze the dependencies “apparent angular size – redshift” and “apparent motion – redshift” which contain an imprint of the source's properties and cosmology. We present data on the “angular size – redshift” relation obtained with VLBI at 5 GHz on a sample of 300 AGN distributed over the widest available range of redshifts 0.016 ≤ z ≤ 4.5. The sample exceeds those used in similar studies earlier by Kellermann (1993, 79 sources) and Wilkinson et al. (1997, 160 sources). Unlike extended source, the angular size-redshift for compact radio sources appears consistent with the predictions of standard Friedmann world models with qo ≃ 0.5 without taking into account evolutionary effects or selection effects due to a “linear size – luminosity” or “linear size – spectral index” dependences. We discuss different approaches allowing us to disentangle intrinsic evolutionary properties of sources and parameters of the cosmological model. Recent estimates of parameters of the cosmological model are given. We also discuss a perspective of conclusive cosmological tests using the VLBI technique.

A direct determination of linear-size evolution of elliptical radio galaxies

Nature ◽  
1987 ◽  
Vol 328 (6130) ◽  
pp. 500-501 ◽  
Author(s):  
M. J. A. Oort ◽  
P. Katgert ◽  
R. A. Windhorst
Keyword(s):  
Direct Determination ◽  
Radio Galaxies ◽  
Linear Size ◽  
Size Evolution

scholarly journals The APM QSO Survey: Description and Status Report

1989 ◽  
Vol 134 ◽  
pp. 25-30
Author(s):  
Craig B. Foltz ◽  
Frederic H. Chaffee ◽  
Paul C. Hewett ◽  
Brenda Frye ◽  
Ray J. Weymann ◽  
...  
Keyword(s):  
Preliminary Analysis ◽  
Selection Criteria ◽  
Status Report ◽  
Selection Effects ◽  
Schmidt Telescope ◽  
Large Sample ◽  
Quantitative Survey ◽  
Objective Prism

The APM QSO survey is a quantitative survey aimed at finding a large sample (∼ 1000) of QSOs using broadly-based selection criteria applied to machine-scanned UK Schmidt Telescope direct and objective-prism plates. The survey is currently entering its third year and, as of August 1988, the sample consists of ∼ 700 QSOs with mJ ≥ 18.75 in the range 0.2 ≤ z ≤ 3.3. Preliminary analysis suggests that the sample is relatively free of the selection effects endemic to most QSO surveys based on slitless spectroscopy.

scholarly journals Galactic habitability re-examined: indications of bimodality

2019 ◽  
Vol 490 (1) ◽  
pp. 408-416 ◽  
Author(s):  
N Stojković ◽  
B Vukotić ◽  
N Martinović ◽  
M M Ćirković ◽  
M Micic
Keyword(s):  
Selection Effects ◽  
Large Sample ◽  
Habitable Zones ◽  
Second Mode ◽  
Tentative Evidence ◽  
Observation Selection

ABSTRACT The problem of the extent of habitable zones in different kinds of galaxies is one of the outstanding challenges for contemporary astrobiology. In the present study, we investigate habitability in a large sample of simulated galaxies from the illustris Project in order to at least roughly quantify the hospitality to life of different galactic types. The pioneering study of Dayal et al. is critically examined and some of its results are amended. In particular, we find a tentative evidence for a second mode of galactic habitability comprising metal-rich dwarfs similar to IC 225, LMC, or M32. The role of the galactic environment and the observation-selection effects is briefly discussed and prospects for further research on the topic outlined.

scholarly journals Galaxy Size Evolution at High Redshift and Surface Brightness Selection Effects: Constraints from the Hubble Ultra Deep Field

2004 ◽  
Vol 611 (1) ◽  
pp. L1-L4 ◽  
Author(s):  
R. J. Bouwens ◽  
G. D. Illingworth ◽  
J. P. Blakeslee ◽  
T. J. Broadhurst ◽  
M. Franx
Keyword(s):  
Surface Brightness ◽  
High Redshift ◽  
Selection Effects ◽  
Size Evolution ◽  
Hubble Ultra Deep Field

scholarly journals SELECTION EFFECTS AND STRUCTURAL SYMMETRIES IN THE ORIENTATION BASED UNIFIED SCHEME

2019 ◽  
Vol 55 (1) ◽  
pp. 105-116
Author(s):  
C. C. Onuchukwu ◽  
A. A. Ubachukwu
Keyword(s):  
Linear Size ◽  
Radio Sources ◽  
Selection Effects ◽  
Orientation Parameter ◽  
Regression Analyses ◽  
Asymmetry Parameters ◽  
Q Values

Using the projected linear size, (D) as an orientation parameter, the armlength ratio, (Q) and the lobe-luminosity ratio, (R) as asymmetry parameters, we test the FR-II galaxies (Gs) and radio-loud quasar (Qs) unification scheme. Using the median values of our binned sample, our results, generally indicate that the D of the radio sources are smaller at higher redshifts z and at larger Q values, with the D of Qs smaller than those of Gs across all Q, z and R bins. Also, the D of Gs appear smaller for lower values of Q, if R ≤ 1.0 but become larger at higher values of Q if R > 1.0. For Qs, the D decreases with increasing Q, R and z. These results imply that the beaming effect is more important in Qs than in Gs. The D − R regression analyses for different Q and z subsamples suggest the importance of factors other than beaming and orientation in the interpretation of the evolution of these radio sources.

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