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Radio sources in the 2dF Galaxy Redshift Survey (2dFGRS)

Radio sources in the 2dF Galaxy Redshift Survey (2dFGRS). With Russell Cannon (AAO), Carole Jackson (ANU), Vince McIntyre (ATNF) and the 2DFGRS team (PIs Matthew Colless & John Peacock)

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Radio sources in the 2dF Galaxy Redshift Survey (2dFGRS)

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  1. Radio sources in the 2dF Galaxy Redshift Survey (2dFGRS) • With Russell Cannon (AAO), Carole Jackson (ANU), Vince McIntyre (ATNF) and the 2DFGRS team (PIs Matthew Colless & John Peacock) • Cross-match the 2dF Galaxy Redshift Survey (spectra of 250,000 galaxies to bJ=19.4 mag) with large-area radio continuum surveys (NVSS at 1.4 GHz, SUMSS at 843 MHz) • When 2dFGRS complete, will have good-quality spectra of ~4000 radio-emitting galaxies to z=0.3. Currently analysed ~900 galaxies (20%). • Goal: Accurate study of local radio source populations as benchmark for work at higher z

  2. Main themes of this talk: • Radio telescopes are highly efficient machines for probing the distant universe and measuring the cosmic evolution of galaxies. • Developing a proper physical understanding of galaxy formation and evolution requires data sets much larger than those available in the past. • “The astronomy of the 21st century will be dominated by computer-based manipulation of huge homogeneous surveys of various types of astronomical objects.’’Van den Bergh (2000), PASP 112, 4.

  3. Optical and radio views of the sky DSS B band SUMSS 843 MHz Optical - Galactic stars and a few nearby galaxies Radio - distant galaxies with median z~1

  4. A brief history of the Universe

  5. Redshift and lookback time for a universe withHo=50 km/s/Mpc, W=1 Redshift Time Since Big Bang Fraction of . z (in Gyr=109 yr) current age 1400 250,000 yr 0.0019% . 20 0.1 Gyr 1.0 % . 10 0.3 2.7 % . 5 0.9 6.8 % . 3 1.6 13 % . 2 2.5 19 % . 1 4.6 35 % . 0.5 7.1 54 % . 0.3 8.8 67 % . 0.2 9 .9 76 % . 0.1 11.3 87 % . 0 13.0 100 % COBE Peak of Galaxy formation? .2dF

  6. Nearby galaxies: Hubble type is related to star-formation history Galaxy classification scheme first proposed by Hubble (1936)

  7. The Milky Way Galaxy in far-IR(COBE) Much of what we currently know about galaxy formation comes from studies of the stellar populations in our own Milky Way

  8. Galactic archaeology: Stellar populations in nearby galaxies • Techniques: Spectroscopy of resolved stars/clusters line-strength gradients, colour gradients. • Spiral galaxies: Wide range in stellar ages (0 to 13 Gyr) and metalliciies. 10% (Sc) to 90%(Sa) of available gas now converted to stars. Star formation continues to present day. • Elliptical galaxies: Age/metallicitydegeneracy, but stellar population all old (?). ‘Assembled’ from merger of subsystems, but Mg/Fe ratio implies rapid formation (<1Gyr). Kinematics, metallicity, luminosity etc. closely linked (fundamental plane).

  9. Radio galaxies in the local universe Radio galaxy PKS 2356-61 (ATCA image, radio emission shown in red, optical light in blue) Radio synchrotron emission, collimated radio jets powered by accretion disk around supermassive black hole (Blandford & Rees 1978)

  10. Unified model for Active Galactic Nuclei (AGN) (Urry & Padovani) • Ingredients of a model AGN: • Black hole • Accretion disk • Collimated jets

  11. M87 - a nearby radio galaxy with a central supermassive black hole (Harms et al. 1994)

  12. Correlation between bulge mass and black hole mass (Kormendy & Richstone 1995) Black hole mass-bulge mass correlation implies that formation of galaxy and central black hole (AGN) are closely coupled (i.e. in mergers, black holes also merge?) Explains how AGN ‘know’ what kind of galaxy they live in.

  13. Galactic time machines: Direct observations at high redshift (z=0.1 to 5) • Techniques: Selection of candidates by colour or other criteria, spectroscopy with large optical/IR telescopes. • Elliptical galaxies: Ellipticals at z~1 (lookback time 8-9 Gyr) still look ‘old’, main epoch of formation probably earlier than z=3. • Cosmic evolution: Powerful radio galaxies much more common at high redshifts - energy output implies supermassive black holes (~109 solar masses) in nuclei of many ellipticals. Beyond z~2, radio galaxies have ‘disturbed’ optical morphology (Miley et al.), possibly implying that black hole formation precedes star formation?

  14. Galaxies in the Hubble Deep Field Our deepest view of the Universe in optical light: Median redshift of z~1 implies galaxies typically appear as they were when the Universe was a third of its current age.

  15. The star formation history of the Universe (Baugh et al. 1998)

  16. The rise and fall of quasars - evidence for an AGN/starburst link? (Keel 2000)

  17. High-redshift radio galaxies - ancestors of present day ellipticals? Steep radio spectra efficiently select high-z galaxies. Infrared K magnitude can be used as initial redshift estimator. (Keel 2000)

  18. The K-band Hubble diagram (van Breughel et al. 1999) Finding high-z galaxies: 1) Radio filter (e.g. spectral index) 2) IR (K-band) imaging - estimate z 3) Optical/IR spectra (8m-class telescopes)

  19. Cosmic evolution of active galaxies - interpreting radio data • First need to disentangle the following: • Orientation effects:Relativistic beaming for sources oriented near line of sight. Differences in observed emission-line widths, projected source sizes. • Source lifetime:Typical AGN lifetime ~108 years, expect correlation between age and source size and/or luminosity. Onset of active phase may be related to interaction/merger. • Host galaxy luminosity:On average, bigger galaxies have more massive BHs, stronger radio sources. • Therefore need a large sample of nearbyobjects.

  20. How large a sample of active galaxies do we need at z~0? • Need: At least 50 galaxies/bin for <15% error bars • Radio power: At least 10 bins to cover full range observed (at least 1021 to 1026 W/Hz). • Host galaxy luminosity:At least 4 bins to cover full range in optical luminosity. Plus, for sample as a whole: • Orientation effects:Say 5 bins to cover full range in orientation. • Source lifetime:Say 5 bins to cover full age range and investigate AGN/starburst connection. • i.e. Need spectra of 5,000-10,000 galaxies as local benchmark for studies of cosmic evolution.

  21. The 2dF Galaxy Redshift Survey Goal: 250,000 galaxy spectra in 1700 deg2 of sky (completion end 2001)

  22. 2dF corrector, robot positioner and fibre-fed spectrographs on the AAT

  23. Typical 2dFGRS radio-source spectra (Sadler et al. 1999) • Star-forming galaxy, z=0.14 (40%) • Emission-line AGN, z=0.15 (10%) • Absorption-line AGN, z=0.14 (50%) Ha Hb [OIII]

  24. 2dFGRS radio sources - progress so far • Have analysed data taken up to May 1999 (58,454 spectra, 20% of final 2dFGRS data set) • 757 confirmed radio-source IDs - 1.5% of 2dFGRS galaxies • Spectra classified by eye (60% AGN, 40% star-forming galaxies) • Cross-matching with far-infrared (IRAS) and X-ray (ROSAT) catalogues • 2dFGRS spectra cover the closest 5% of NVSS/SUMSS radio sources (flux limit 2-3 mJy)

  25. Redshift distribution of 2dFGRS radio sources (and all galaxies) (Colless 2001)

  26. Spatially-resolved 2dFGRS radio sources Around 25% of 2dFGRS radio sources are spatially resolved by the 45 arcsec radio beam, allowing us to measure their projected linear sizes. In star-forming galaxies, radio emission is usually confined to the galactic disk (scales of a few tens of kpc). In active galaxies, sources are often several hundred kpc in size. 3 GRGs

  27. Local radio luminosity function (RLF) for 2dFGRS radio sources (Sadler et al. 2001) RLF measures space density of radio sources as a function of luminosity. To account for greater survey depth for luminous sources, use V/Vmax method (Schmidt 1968) Mixture of AGN and SF galaxies

  28. Radio emission from star-forming galaxies UGC 09057 NGC 5257/5258 NGC 7252z=0.0054 z=0.0223 z=0.0161 Derived star formation rate: 1.8 Msun/yr 120 Msun/yr 32 Msun/yr (Radio emission is dominated by synchrotron radiation from electrons accelerated by supernova remnants)

  29. Far-infrared - radio correlation for 2dFGRS galaxies In star-forming galaxies, far-IR and radio emission are tightly correlated. Above 1023 W/Hz (i.e. implied star formation rates of ~100 Msun/yr), many star-forming galaxies also have active nuclei. Signs are Seyfert-like emission-line ratios and (sometimes) excess radio emission * AGN spectrum o SF spectrum Normalgalaxy line

  30. Local RLF for star-forming galaxies RLF derived from 2dFGRS data fits onto values for nearby bright (RSA) galaxies (Condon 1989). Star formation rates derived from radio data are typically 10-100 Msun/yr (vs ~1 Msun/yr for Milky Way). RSA 2dFGRS NVSS radio limit (3mJy) biases towards high SFR

  31. Local star-formation density from radio and Hadata Local star formation density (zero-point of Madau diagram) in Msun/yr/Mpc3: Ha: 0.013 +/-0.006(Gallego et al. 1995) Radio: 0.022 +/-0.004(Sadler et al. 2001) Radio data show more galaxies with very high SFR (> 30 Msun/yr), otherwise very good agreement. Ha Radio

  32. What are the “high SFR” galaxies? • Radio LF for star-forming galaxies implies that galaxies with SFR > 30 Msun/yr are far more common than Ha surveys suggest, and may account for up to 40% of the local star-formation density. • Dust obscuration in star-forming regions could lead to under-estimate of Ha line strength. • Deep VLA studies of clusters at z~0.4 (Smail et al. 1999) and local (z <0.5) “post-starburst” galaxies (Miller & Owen 2001) also suggest that star-forming regions can be hidden by dust. • Important to study the 2dFGRS “high-SFR” galaxies in more detail (high-res. radio images, IR spectra...) - are the high star-formation rates real?

  33. Radio emission from active galaxies TGN284Z051 TGN348Z183 TGS153Z214z=0.1065 z=0.1790 z=0.2079 1.4 GHz radio power and projected linear size:1024.3W/Hz 1025.0 W/Hz 1024.8W/Hz 327 kpc 475 kpc 471 kpc

  34. Local radio LF for active galaxies RLF derived from 2dFGRS data fits onto values for nearby bright E/S0 galaxies derived by Sadler et al. (1989). RLF must turn over not far below 1020 W/Hz to avoid exceeding the space density of early-type galaxies. Power-law F(P)a P-0.62

  35. Black hole mass spectrum for active galaxies in the local universe Can use radio LF for AGN to estimate the local mass density of black holes (>3x107 Msun) following relation from Franchescini et al. (1998;ADAF model) . Total min. BH density rBH=1.6x105 Msun/Mpc3 agrees with Choksi & Turner QSO estimate (rBH=1.4-2.2 x105 Msun/Mpc3). No turnover in BH density yet!

  36. Local radio luminosity function of active and star-forming galaxies Below 1025 W/Hz, the local radio source population is always a mixture of AGN and star-forming galaxies. i.e. There is probably no observational regime where radio surveys detect only star-forming galaxies. Low-lum AGN are hard to find

  37. Summary: Results so far • The local radio source population is a mixture of star-forming galaxies and AGN, but 2dFGRS spectra usually allow us to distinguish them unambiguously. • The local star-formation density derived from the radio continuum is higher than the value measured from Ha because we find more galaxies with SFR > 30-50 Msun/yr (possibly dust-obscured in optical light). • The black-hole mass density in AGN agrees with the value derived for QSOs in the early Universe, suggesting that local radio galaxies are the direct descendants of high-z QSOs.

  38. The next steps... • With the full 2dFGRS data set: Evolution of the AGN and SF luminosity functions to z~0.3, split by radio spectral index. • With the 6dF Galaxy Survey: From mid-2001, expect ~12,000 radio-source spectra to z~0.1 (16% detection rate!), define faint end of RLF, starburst/AGN connection, (Tom Mauch thesis). • Going deeper: Deep 2dF spectroscopy to z~0.5, photometric redshifts to z~1, steep-spectrum sources + k-band imaging/8m spectroscopy to z>3.

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