Hostname: page-component-cd9895bd7-gxg78 Total loading time: 0 Render date: 2024-12-26T03:58:07.384Z Has data issue: false hasContentIssue false
  • English
  • Français

Unified Schemes for Extragalactic Radio Sources

Published online by Cambridge University Press:  25 May 2016

Gopal Krishna
Gopal Krishna*
Affiliation:
NCRA-TIFR, Poona University Campus, PUNE-411007, India

Extract

Core share and HTML view are not available for this content. However, as you have access to this content, a full PDF is available via the ‘Save PDF’ action button.

The most widely discussed class of unified schemes for radio-loud extragalactic sources attempts to interpret their seemingly disparate types as the same objects seen from different directions. The orientation dependence is attributed to relativistic beaming of the nonthermal jet and, possibly, anisotropic obscuration/re-radiation of the nuclear emission by a circum-nuclear distribution of dusty material with polar openings, possibly a torus. Although alternative approaches have been mooted for unifying radio galaxies (RGs) and quasars (QSRs) by incorporating a strong jet-environment interaction, or temporally decaying nuclear prominence, the orientation based unified scheme, thanks to its rich predictive potential, has been subjected to a multitude of observational tests and its pros and cons have been discussed extensively in recent reviews. Here we briefly address some recent developments, including the claim that the radio size measurements of powerful RGs and QSRs are incompatible with orientation being the primary distinction between them. On balance, it seems that while the basic orientation picture can broadly explain the bulk of the observations, its viability could be much enhanced by taking into consideration the (inevitable) temporal evolution of radio sources.

Type
Unification Issues
Information
Symposium - International Astronomical Union , Volume 175: Extragalactic Radio Sources , 1996 , pp. 373 - 378
Copyright
Copyright © Kluwer 1996 

References

1. Antonucci, R. 1993, ARAA , 31, 473.Google Scholar
2. Norman, C., and Miley, G. 1984, A&A , 141, 85.Google Scholar
3. Hutchings, J.B., Price, R., and Gower, A.C. 1988, ApJ , 329, 122.Google Scholar
4. Barthel, P.D. 1994, in The Physics of Active Galaxies, Bicknell, G., Dopita, M. and Quinn, P., eds. (ASP, San Francisco), Vol. 54, p.175.Google Scholar
5. Gopal-Krishna, 1995, in Quasars and AGN: High Resolution Imaging, Kellermann, K.I. and Cohen, M.H., eds. (Nat. Acad. Sci., Washington), in press.Google Scholar
6. Singal, A.K. 1995, in Quasars and AGN: High Resolution Imaging, Kellermann, K.I. and Cohen, M.H., eds., (Nat. Acad. Sci., Washington), in press.Google Scholar
7. Urry, C.M., and Padovani, P. 1995, PASP , 107, 803.Google Scholar
8. Browne, I.W.A., and Jackson, N. 1992, in Physics of AGN, Duschl, W.J. and Wagner, S.J., eds. (Springer-Verlag), p.618.Google Scholar
9. Blandford, R.D., and Rees, M.J. 1978, in Pittsberg Conf. on BL Lacs, Wolfe, A.M., ed., Pittsberg Univ. Press, p.328.Google Scholar
10. Giovannini, G., et al., these proceedings. Google Scholar
11. Venturi, T. et al. 1995, ApJ, in press (Bologna preprint: BAP06-1995-029-IRA).Google Scholar
12. Parma, P., these proceedings. Google Scholar
13. Smith, E.P., O'Dea, C.P., and Baum, S.A. 1995, ApJ , 441, 113.Google Scholar
14. Pesce, J.E., Falomo, R., and Treves, A. 1995, AJ , 110, 1554.Google Scholar
15. Owen, F.N., Ledlow, M.J., and Keel, W.C. 1995, in preparation.Google Scholar
16. Wurtz, R., Stocke, J., and Yec, H.K.C., 1995, ApJ (Suppl.), in press.Google Scholar
17. Morris, S.L., Stocke, J.T., Gioia, I.M., Schild, R.E., Wolter, A., Maccacaro, T., and Della Ceca, R. 1991, ApJ , 380, 49.Google Scholar
18. Urry, C.M., Padovani, P., and Stickel, M. 1991, ApJ , 382, 501.Google Scholar
19. Padovani, P., and Giommi, P. 1995, ApJ , 444, 567.Google Scholar
20. Kukula, M.J. et al., these proceedings. Google Scholar
21. Heckman, T.M., O'Dea, C.P., Baum, S.A., and Laurikainen, E. 1994, ApJ , 428, 65.Google Scholar
22. Hes, R., Barthel, P.D., and Hoekstra, H. 1995, A&A , 303, 8.Google Scholar
23. Antonucci, R., Hurt, T., and Kinney, A. 1994, Nature , 371, 313.Google Scholar
24. Harris, D.E., these proceedings. Google Scholar
25. Terasranta, H., and Valtaoja, E. 1994, A&A , 283, 51.Google Scholar
26. Vermeulen, R., these proceedings. Google Scholar
27. Antonucci, R., Barvainis, R., and Alloin, D. 1990, ApJ , 353, 416.Google Scholar
28. Gopal-Krishna, , and Steppe, H., 1991, in Variability of AGN, Miller, H.R. and Wiita, P.J., eds. (CUP), p.194.Google Scholar
29. Athreya, R., Kapahi, V.K., McCarthy, P.J., and van Breugel, W., these proceedings. Google Scholar
30. Garrington, S.T., Holmes, G.F., and Saikia, D.J., these proceedings. Google Scholar
31. Best, P.N., Bailer, D.M., Longair, M.S., and Riley, J.M. 1995, MNRAS , 275, 1171.Google Scholar
32. Lister, M.L., Hutchings, J.B., and Gower, A.C. 1994, ApJ , 427, 125.Google Scholar
33. Oppenheimer, B.R., and Biretta, J.A. 1994, AJ , 107, 892.Google Scholar
34. Saikia, D.J., Jeyakumar, S., Wiita, P., Sanghera, H.S., and Spencer, R. 1995, MNRAS , 276, 1215.Google Scholar
35. Barthel, P.D., 1989, ApJ , 336, 606.Google Scholar
36. Kapahi, V.K., Athreya, R.M., Subrahmanya, C.R., Hunstead, R.W., Baker, J.C., McCarthy, P.J., and van Breugel, W. 1995, JAA (Suppl.) , 16, 125.Google Scholar
37. Kapahi, V.K., Athreya, R.M., Subrahmanya, C.R., McCarthy, P.J., van Breugel, W., Baker, J.C., and Hunstead, R.W., these proceedings. Google Scholar
38. Blundell, K. et al., these proceedings. Google Scholar
39. Alexander, P., and Leahy, J.P. 1987, MNRAS , 225, 1.Google Scholar
40. Fanti, C., Fanti, R., Dallacasa, D., Schilizzi, R.T., and Stanghellini, C. 1995, in Quasars and AGN: High Resolution Imaging, Kellermann, K.I. and Cohen, M.H., eds., (Nat. Acad. Sci., Washington), in press.Google Scholar
41. Readhead, A.C.S., Taylor, G.B., Pearson, T.J., and Wilkinson, P.N. 1995, in Quasars and AGN: High Resolution Imaging, Kellermann, K.I. and Cohen, M.H., eds., (Nat. Acad. Sci., Washington), in press.Google Scholar
42. Falcke, H., Gopal-Krishna, , and Biermann, P.L. 1995, A&A , 298, 395.Google Scholar
43. Lawrence, A. 1991, MNRAS , 252, 586.Google Scholar
44. Gopal-Krishna, , Kulkarni, V.K., and Wiita, P.J. 1995, submitted.Google Scholar
45. Gopal-Krishna, , 1995, JAA (Suppl.) , 16, 153.Google Scholar
46. Baker, J.C., and Hunstead, R.W. 1995, ApJ , 452, L95.Google Scholar
47. Maraschi, L., and Rovetti, F. 1994, ApJ , 436, 79.Google Scholar
48. Vagnetti, F., and Spera, R. 1994, ApJ , 436, 611.Google Scholar
49. Vagnetti, F., these proceedings. Google Scholar
50. Corbin, M.R., and Francis, P.J. 1994, AJ , 108, 2016.Google Scholar
51. Wills, B.J. et al. 1995, ApJ , 447, 139.Google Scholar
52. Laing, R.A., Jenkins, C.R., Wall, J.V., and Unger, S.W., 1994, in The Physics of Active Galaxies, Bicknell, G., Dopita, M. and Quinn, P., eds. (ASP, San Francisco), Vol. 54, p.227.Google Scholar
53. Hine, R.G., and Longair, M.S. 1979, MNRAS , 188, 111.Google Scholar
54. Morganti, R., Osterloo, T., Fosbury, R., and Tadhunter, C. 1995, MNRAS , 274, 393.Google Scholar
55. Baum, S.A., Zirbel, E.L., and O'Dea, C.P., 1995, ApJ , 451, 88.Google Scholar