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On the Spectral Index-Flux Density Relation for Large Samples of Radio Sources
Zhang Xizhen1; Reich W2; Reich P2; Wielebinski R2
2003
Source PublicationChinese Journal of Astronomy and Astrophysics
ISSN1009-9271
Volume3Issue:4Pages:347
AbstractWe present new statistical results on the spectral index-flux density relation for large samples of radio sources using archival data of the most sensitive surveys, such as 6C, Miyun, WENSS, B3, NVSS, GB87. Instrumental selection effects and the completeness of the catalogs are discussed. Based on the spectral indices calculated for about 200000 sources from the WENSS (327 MHz) and NVSS (1.4 GHz) catalogs, we obtained (1) The median spectral index increases from alpha(med) similar to -0-9 to alpha(med) similar to -0.8 (S-nu proportional to nu(alpha)), while S-327 flux densities decrease from 0.1 Jy down to 25 mJy. The median spectral indices nearly show no variation within the error bars when the flux density is larger than 0.1 Jy. (2) A dependence. of the fraction of ultra-steep spectrum sources (USS, -1.5 less than or equal to alpha less than or equal to -1.0), steep spectrum sources (SSS, -1.0 less than or equal to alpha less than or equal to -0.5) and flat spectrum sources (FSS, -0.5 less than or equal to alpha less than or equal to 0.0) is partly responsible for the spectral flattening. Another contribution to the spectral flattening comes from the variation of alpha(med) of steep spectrum sources (alpha < -0.5) themselves which increases with decreasing flux densities. (3) The spectral flattening for faint sources (down to S-327 similar to 20 mJy) with steep spectra (alpha < -0.5) suggests' that alphamed is correlated with luminosity rather than redshift according to the Condon' model. (4) A strong spectral selection effect occurs when spectral indices are calculated from samples with a large frequency separation.
Language英语
Document Type期刊论文
Identifierhttp://ir.bao.ac.cn/handle/114a11/49174
Collection中国科学院国家天文台
Affiliation1.中国科学院国家天文台
2.德国马普学会射电天文学研究所
First Author AffilicationNational Astronomical Observatories, Chinese Academy of Sciences
Recommended Citation
GB/T 7714
Zhang Xizhen,Reich W,Reich P,et al. On the Spectral Index-Flux Density Relation for Large Samples of Radio Sources[J]. Chinese Journal of Astronomy and Astrophysics,2003,3(4):347.
APA Zhang Xizhen,Reich W,Reich P,&Wielebinski R.(2003).On the Spectral Index-Flux Density Relation for Large Samples of Radio Sources.Chinese Journal of Astronomy and Astrophysics,3(4),347.
MLA Zhang Xizhen,et al."On the Spectral Index-Flux Density Relation for Large Samples of Radio Sources".Chinese Journal of Astronomy and Astrophysics 3.4(2003):347.
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