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Superluminal sources
1Owens Valley Radio Observatory, California Institute of Technology, Pasadena, CA 91125, USA.
Summary
This study analyzes apparent velocity statistics in radio jet sources, finding no evidence for distinct populations. The distribution suggests a skewed Lorentz factor distribution, impacting cosmological models.
Area of Science:
- Astrophysics
- Cosmology
- Radio Astronomy
Background:
- Apparent velocity statistics of extragalactic radio sources are crucial for understanding jet physics and cosmology.
- Beaming models predict specific velocity distributions, which need observational validation.
Purpose of the Study:
- To present predictions for apparent velocity statistics under simple beaming models.
- To compare these predictions with observational data from a large, homogeneous survey.
- To discuss applications for testing unification models and for cosmological measurements (Hubble constant, deceleration parameter).
Main Methods:
- Comparison of theoretical predictions from simple beaming models with observed apparent velocity statistics.
- Analysis of data from a large, homogeneous survey of radio sources.
- Examination of the relationship between apparent velocity and observed luminosity.
Main Results:
- The data do not provide compelling evidence for intrinsically different populations of galaxies, BL Lacertae objects, or quasars.
- Apparent velocities (βapp) in the range 1-5 h⁻¹ (where h = H₀/100 km s⁻¹ Mpc⁻¹) occur with roughly equal frequency.
- Higher βapp values (up to 10 h⁻¹) are scarcer than previously reported, suggesting earlier studies focused on non-representative sources.
- The βapp distribution indicates a skewed distribution of Lorentz factors (γb), peaking around 2 h⁻¹ and extending to at least 10 h⁻¹.
- A rising upper envelope in the βapp distribution is observed as a function of 5-GHz luminosity.
Conclusions:
- The observed apparent velocity statistics are consistent with simple beaming models and suggest a skewed distribution of Lorentz factors.
- The findings challenge the notion of intrinsically different source populations and highlight the importance of representative samples.
- Combined analysis of source counts and apparent velocity statistics in larger samples can offer significant insights into radio jet source properties and cosmological parameters.