VSOP-2 Survey of a complete sample of nearby sources selected at low frequency

Transcription

1 VSOP-2 Survey of a complete sample of nearby sources selected at low frequency Gabriele Giovannini Dipartimento di Astronomia, Bologna University Istituto di Radioastronomia - INAF In collaboration with: M. Giroletti, L. Feretti, T. Venturi, Liuzzo et al. (IRA) G.B. Taylor (UNM) W.B. Cotton (NRAO)

2 The Bologna Complete Sample B2 and 3CR radio sources with z < 0.1 B2: S(408) > 0.25 Jy 3CR: S(178) > 10 Jy Declination greater than 10 degree Galactic latitude b larger than 15 degree Being selected at low frequency it is not affected by observational biases related to orientation effects. Nearby sources: good linear resolution; high + low power z= mas = 1.8 pc VLBI data are available now for 78/95 sources (core > 5 mjy) Giovannini et al. ApJ 552, 508; ApJ 618, 635; Liuzzo et al. in preparation

3 The large scale morphology of observed sources is: 50 FR I (+15 to be observed soon) 15 FR II (+1) 12 compact sources: Bl-Lacs, CSO, CSS, flat spectrum, 1 Spiral (+1 small double) Summary Statistical properties Fr I Fr II Compact Two-sided Limb-brightened Restarted Peculiar Why a VSOP-2 survey?

4 Two-sided sources on the pc scale are 30 % in our sample to be compared with 11% in PR sample and 4.6 % in the Caltech-Jodrell Bank survey -Consistent with a j/cj ratio R 5 if jet velocity = c -In all sources pc scale jets move at high velocity. No correlation has been found with core or total radio power - All FR II two-sided are NLRG. -Two-sided sources show low power radio cores. - In most sources there is a good agreement between the pc-kpc scale jet orientation

5 FR I FR I sources 0.7pc 3C 31 3C66B 90 mjy 150 mjy 2pc 3C272.1 M84 0.4pc Opt. + IR jet 125mJy

6 A2634 merging cluster: 3C 465 (Venturi et al. 1995) 3pc 20kpc 220 mjy

7 FR II 2 pc 3C382 3C33 30mJy 130mJy 10pc

8 10 pc 5pc 3C 452 a NL FR II radio galaxy Peak: 20mJy/b 3C 338 a FR I radio galaxy Two-sided

9 6kpc pc Compact 110 mjy 0.25kpc 10 pc 120 mjy

10 C236 The largest radio galaxy (more than 4 Mpc) 5pc 30mJy Restarted 10pc 40mJy

11 Giant radio galaxy, core dominated at z = pc counterjet flat spectrum core main jet

12 NGC 4278 Nearby large dusty elliptical Direct distance measure = 14.9 Mpc (Jensen et al. 2003) 1mas = pc S 1.4 GHz =300 mjy, P= W Hz -1 : LLAGN Ionized nuclear gas typical of a LINER (Goudfrooj et al. 1994) HST observations reveal a central point source and a large distribution of dust N-NW of the core (Carollo et al 1997)

13 NGC 4278, images 1 pc 10 3 R S 5 GHz 8.4 GHz Correlated flux % total VLA flux density

14 VSOP-2 Feasibility 8 GHz: 7sigma detection with a VLBA telescope: 23 mjy large telescope 5 mjy angular resolution 0.2 mas 0.36 pc at z = pc for NGC4278 About 40% sources detected without observations in phase reference mode with one or more large telescope (but phase reference useful) 22 GHz: 7sigma detection with a VLBA telescope: 50 mjy large telescope 12 mjy angular resolution 0.08 mas 0.15 pc at z = pc for NGC4278 Most sources will need observations in phase reference mode 8 GHz preferred (sensitivity, steep spectrum structures) VLBA data for all the sample it is possible to select a sub-sample A few sources well studied elsewhere (M87, MRK501, MRK421..) a subsample also at 22 GHz???? Spectral index + Faraday Rotation

15 Possible results from VSOP-2 survey * Two sided jets: - possible gap in between the jet starting points - Bulk velocity estimate from surface brightness comparison - symmetric or not sub-structures: knots, bendings, - Comparison between FR I and FR II * One-side jets: - possible short counter-jets (test for accelerating jets) - Velocity substructures (limb-brightened) in polarization too - Comparison with two-sided: orientation only effects or the ambient (e.g. cooling flow clusters) is important? * Restarted sources: - new components? Life cycle - Comparison with normal FR I and FR II (binary SMBHs?) * Comparison with high power higher redshift sources

16 * core dominance at high resolution: if visible jets are relatively slowly moving close to the core, the high resolution core prominence should be different with respect to the well known arcsecond core dominance * binary SMBH? linear resolution is in agreement with present models * Spectral index and comparison with available ground-only observations at higher frequency * Statistical considerations: comparison between FR I and FR II, different ambient is important?, and more * Polarization Note: scientific aims, and observing strategy very preliminary. Open discussion and more contributions are necessary to improve this project

17 Thanks