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The optical morphologies of the 2Jy sample of southern radio galaxies

The optical morphologies of the 2Jy sample of southern radio galaxies. Cristina Ramos Almeida & Clive N. Tadhunter University of Sheffield. Introductio n. Triggering of nuclear activity.

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The optical morphologies of the 2Jy sample of southern radio galaxies

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  1. The optical morphologies of the 2Jy sample of southern radio galaxies Cristina Ramos Almeida & Clive N. Tadhunter University of Sheffield

  2. Introduction Triggering of nuclear activity • Galaxy mergers and interactions (Heckman et al. 1986, Smith & Heckman 1989) • Accretion of gas from hot X-ray haloes - Bondi accretion of hot gas (Best et al. 2006, Hardcastle et al. 2007, Balmaverde et al. 2008, Buttiglione et al. 2009) • Galaxy evolution & nuclear activity connection  important to test the models for AGN triggering/fueling. Radio galaxies key in this context – associated with ealy-type hosts  cleaner searches for morphological disturbance. Importance of mergers in triggering of powerful radio galaxies (PRG) activity? Powerful Radio Galaxies: Triggering & Feedback – Leiden – 23rd November

  3. Introduction Mergers in Powerful Radio Galaxies (PRGs) • Ground-based 4m telescopes z < 0.3 PRG (Heckman et al. 1986, Smith & Heckman 1989) “...galaxy interactions/mergers play an important role in the PRG phenomenon” “…in contrast to conventional wisdom, very PRG are not always normal ellipticals.” • HST + WFPC2 (1 orbit) 0.1 < z < 0.25 RG, RQQ, RLQ (Dunlop et al. 2003) “...we demonstrate that the basic properties of these hosts are indistinguishable from those of quiescent, evolved, low-redshift elliptical galaxies of comparable mass.” “…spheroidal hosts become more prevalent with increasing nuclear luminosity.” Powerful Radio Galaxies: Triggering & Feedback – Leiden – 23rd November

  4. Introduction Issues surrounding morphological evidence for mergers / interactions • Surface brightness effects: ground-based and space-based (HST) observations sample structures on different scales, with different surface brightness limits. • Control samples: lack of deep observations of control samples of elliptical galaxies of similar mass, at similar redshifts and within same environments. Powerful Radio Galaxies: Triggering & Feedback – Leiden – 23rd November

  5. Surface brightness effects Evidence for galaxy interactions in QSOs • Deep HST+ACS (5 orbits) observations of quasar hosts (Canalizo et al. 2007, Bennert et al. 2008) • 4/5 low-z QSO host galaxies taken from Dunlop et al. (2003; classified as ellipticals) reveal shells and tidal tails  QSO hosts suffered mergers with accompanying starbursts that likely triggered the QSO activity. Powerful Radio Galaxies: Triggering & Feedback – Leiden – 23rd November

  6. Control samples and Environment Evidence for galaxy interactions in quiescent galaxies • Tidal features in quiescent elliptical galaxies at faint surface brightness levels. van Dokkum et al. (2005) – μ ~ 29 mag/arcsec2 (AB) Malin & Carter (1983) μV ≤ 25.5 mag/arcsec2 Powerful Radio Galaxies: Triggering & Feedback – Leiden – 23rd November

  7. Introduction Our Work • Try to shed some light about importance of mergers/interactions in the triggering of PRG activity by solving previous problems: completeness, environment, control samples, & surface brightness. • Deep GMOS-S / Gemini optical broad-band observations of a complete sample of PRGs. Complete sample Wide range of redshift Deep observations Big sky area covered μV ≤ 26 mag/arcsec2 46 PRG 0.05 < z < 0.7 ~0.8□ Powerful Radio Galaxies: Triggering & Feedback – Leiden – 23rd November

  8. Observations Sample selection • 46 steep-spectrum PRG (S2.7 GHz > 2Jy) with 0.05 < z < 0.7 from Tadhunter et al. (1993). • Sample divided in (according to optical spectroscopy): • broad-line radio galaxies and quasars (BLRG/QSO; 35%) • narrow-line radio galaxies (NLRG; 43%) • weak-line radio galaxies (WLRG; 22%). • In terms of radio morphologies: • 72% of FRII • 13% of FRI • 15% of CSS Powerful Radio Galaxies: Triggering & Feedback – Leiden – 23rd November

  9. Observations GMOS-S data • Broad-band GMOS-S / Gemini data of 46 PRGs. • Galaxies with z ≤ 0.4 observed in the r’-band • Galaxies with z > 0.4 observed in the i’-band • FOV = 5.5’ x 5.5’ - pixel size = 0.146”/ pixel • Offset fields of 5.5’ x 5.5’ also observed for each galaxy • Seeing-limited observations: FWHM < 1.2” • Deep observations μV ≤ 26 mag/arcsec2 ensure detection of faint features. Powerful Radio Galaxies: Triggering & Feedback – Leiden – 23rd November

  10. Observations 5.5’ 0.4” seeing ! PKS1355-41 GMOS-S data Powerful Radio Galaxies: Triggering & Feedback – Leiden – 23rd November

  11. Preliminary Results Evidence for galaxy interactions and mergers in PRGs • 85% of the total sample of PRGs show signs of morphological disturbance (Ramos Almeida et al., in preparation). Powerful Radio Galaxies: Triggering & Feedback – Leiden – 23rd November

  12. Preliminary Results PKS0349-27 Evidence for galaxy interactions and mergers in PRGs • Morphological peculiarities: remnants of a merger event. • Bridges, Tails, Fans, Shells, Dust, Amorphous haloes, Irregular features, Double or multiple nuclei. z = 0.066 Smoothed image (3 pixels) Powerful Radio Galaxies: Triggering & Feedback – Leiden – 23rd November

  13. Preliminary Results Evidence for galaxy interactions and mergers in PRGs • Morphological peculiarities: remnants of a merger event. • Bridges, Tails, Fans, Shells, Dust, Amorphous haloes, Irregular features, Double or multiple nuclei. PKS2314+03 z = 0.220 Smoothed image (3 pixels) Powerful Radio Galaxies: Triggering & Feedback – Leiden – 23rd November

  14. Preliminary Results PKS1934-63 8.9 kpc Evidence for galaxy interactions and mergers in PRGs • Morphological peculiarities: remnants of a merger event. • Bridges, Tails, Fans, Shells, Dust, Amorphous haloes, Irregular features, Double or multiple nuclei. z = 0.183 Smoothed image (3 pixels) Powerful Radio Galaxies: Triggering & Feedback – Leiden – 23rd November

  15. Preliminary Results Evidence for galaxy interactions and mergers in PRGs • Morphological peculiarities: remnants of a merger event. • Bridges, Tails, Fans, Shells, Dust, Amorphous haloes, Irregular features, Double or multiple nuclei. PKS1355-41 z = 0.313 Smoothed image (3 pixels) Powerful Radio Galaxies: Triggering & Feedback – Leiden – 23rd November

  16. Preliminary Results Evidence for galaxy interactions and mergers in PRGs • Division of the sample attending to the different morphologies: • 1) galaxy pair or group in clear tidal interaction (e.g., bridges) – 17% • 2) galaxies presenting morphological disturbance (tails, fans, shells, dust, amorphous haloes, irregular features) – 48% • 3) galaxies with double or multiple nuclei inside 9.6 kpc (Smith & Heckmann 1989) – 20% • 4) galaxies with no sign of interaction – 15% Powerful Radio Galaxies: Triggering & Feedback – Leiden – 23rd November

  17. Preliminary Results Evidence for galaxy interactions and mergers in PRGs • Sample division: • Weak-line Radio Galaxies (WLRG) - 10 objects • Strong-line Radio Galaxies (SLRG) - 36 objects • 50% of WLRG do not show evidence of morphological disturbance versus 6% of the SLRG  different triggering/fueling mechanisms? Different types of mergers? Powerful Radio Galaxies: Triggering & Feedback – Leiden – 23rd November

  18. Preliminary Results Evidence for galaxy interactions and mergers in PRGs • Smith & Heckman (1989)  about 50% of the PRGs with strong optical lines (SLRG) – but only 7% with weak emission lines (WLRG) – exhibit peculiar optical morphologies. • Scenario: • SLRG – merger involving at least one gas-rich, dynamically cold galaxy (disk galaxy). • WLRG (those showing no signs of interaction) • accretion of gas from hot X-ray haloes (Bondi accretion). • merger of ellipticals (gas-poor)  no emission line features and low probability of sharp tidal features (dynamically hot galaxies). Powerful Radio Galaxies: Triggering & Feedback – Leiden – 23rd November

  19. Preliminary Results Evidence for galaxy interactions and mergers in PRGs • Only ~30% of the sample show evidence for significant starburst activity either from optical or mid-IR Spitzer spectroscopy (Dicken et al. 2008; 2009) less than expected considering the evidence for galaxy interactions. • 92% of the starburst sample present peculiar morphologies, following the same trend as the total and the SLRG samples. • See Clive’s talk! Powerful Radio Galaxies: Triggering & Feedback – Leiden – 23rd November

  20. Future Work Ramos Almeida et al., in preparation • Comparison between starburst and non-starburst galaxies in the sample – ages of the stellar populations. • Development of a control sample of quiescent elliptical galaxies using the GMOS-S fields. • Study of the environment properties of our galaxies, relating it with their morphologies. • Multiwavelength analysis of the 2Jy sample using the GMOS-S imaging data + mid- and far-IR data (Dicken et al. 2008; 2009) + optical spectroscopy (Tadhunter et al. 1993). Powerful Radio Galaxies: Triggering & Feedback – Leiden – 23rd November

  21. Conclusions Evidence for galaxy interactions and mergers in PRGs • 85% of the total sample of PRGs show signs of morphological disturbance at relatively high levels of surface brightness. • 17% signs of tidal interaction with companions • 48% signs of morphological disruption (fans, shells, tails, dust, etc.) • 20% show multiple nuclei • 15% do not present signs of interaction. • 50% of WLRG do not show evidence of morphological disturbance versus 6% of the SLRG  two types of PRGs / different accretion mechanisms? • 92% of the starburst galaxies in the sample present peculiar morphologies – same trend as total and SLRG samples. Powerful Radio Galaxies: Triggering & Feedback – Leiden – 23rd November

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