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

2. 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) Introduction Triggering of nuclear activity Powerful Radio Galaxies: Triggering & Feedback – Leiden – 23rd November 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?

3. 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.” Introduction Mergers in Powerful Radio Galaxies (PRGs) Powerful Radio Galaxies: Triggering & Feedback – Leiden – 23rd November

4. 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. Introduction Issues surrounding morphological evidence for mergers / interactions 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) Powerful Radio Galaxies: Triggering & Feedback – Leiden – 23rd November 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.

6. Control samples and Environment Evidence for galaxy interactions in quiescent galaxies Tidal features in quiescent elliptical galaxies at faint surface brightness levels. Powerful Radio Galaxies: Triggering & Feedback – Leiden – 23rd November Malin & Carter (1983) μ V ≤ 25.5 mag/arcsec 2 van Dokkum et al. (2005) – μ ~ 29 mag/arcsec 2 (AB)

7. 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. Introduction Our Work Complete sample Wide range of redshift Deep observations Big sky area covered 46 PRG0.05 < z < 0.7~0.8 □ Powerful Radio Galaxies: Triggering & Feedback – Leiden – 23rd November μ V ≤ 26 mag/arcsec 2

8. Sample selection Observations 46 steep-spectrum PRG (S 2.7 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. GMOS-S data Observations 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 μ V ≤ 26 mag/arcsec 2  ensure detection of faint features. Powerful Radio Galaxies: Triggering & Feedback – Leiden – 23rd November

10. GMOS-S data Observations 5.5’ PKS1355-41 0.4” seeing !

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

12. 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. PKS0349-27 Smoothed image (3 pixels) Powerful Radio Galaxies: Triggering & Feedback – Leiden – 23rd November z = 0.066

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. Smoothed image (3 pixels) PKS2314+03 Powerful Radio Galaxies: Triggering & Feedback – Leiden – 23rd November z = 0.220

14. 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. Smoothed image (3 pixels) PKS1934-63 8.9 kpc Powerful Radio Galaxies: Triggering & Feedback – Leiden – 23rd November z = 0.183

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. Smoothed image (3 pixels) PKS1355-41 Powerful Radio Galaxies: Triggering & Feedback – Leiden – 23rd November z = 0.313

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% MORPHOLOGICAL GROUP TOTAL SAMPLE 46 GALAXIES WLRG SUBSAMPLE 10 GALAXIES SLRG SUBSAMPLE 36 GALAXIES STAR-FORMING GALAXIES 13 GALAXIES BRIDGES8 galaxies (17%)1 galaxy (10%)7 galaxies (19%)3 galaxies (23%) MORPHOLOGICAL DISTURBANCE 22 galaxies (48%)3 galaxies (30%)19 galaxies (53%)6 galaxies (46%) MULTIPLE NUCLEI9 galaxies (20%)1 galaxy (10%)8 galaxies (22%)3 galaxies (23%) NO INTERACTION7 galaxies (15%)5 galaxies (50%)2 galaxies (6%)1 galaxy (8%) 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? MORPHOLOGICAL GROUP TOTAL SAMPLE 46 GALAXIES WLRG SUBSAMPLE 10 GALAXIES SLRG SUBSAMPLE 36 GALAXIES STAR-FORMING GALAXIES 13 GALAXIES BRIDGES8 galaxies (17%)1 galaxy (10%)7 galaxies (19%)3 galaxies (23%) MORPHOLOGICAL DISTURBANCE 22 galaxies (48%)3 galaxies (30%)19 galaxies (53%)6 galaxies (46%) MULTIPLE NUCLEI9 galaxies (20%)1 galaxy (10%)8 galaxies (22%)3 galaxies (23%) NO INTERACTION7 galaxies (15%)5 galaxies (50%)2 galaxies (6%)1 galaxy (8%) 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! MORPHOLOGICAL GROUP TOTAL SAMPLE 46 GALAXIES WLRG SUBSAMPLE 10 GALAXIES SLRG SUBSAMPLE 36 GALAXIES STAR-FORMING GALAXIES 13 GALAXIES BRIDGES8 galaxies (17%)1 galaxy (10%)7 galaxies (19%)3 galaxies (23%) MORPHOLOGICAL DISTURBANCE 22 galaxies (48%)3 galaxies (30%)19 galaxies (53%)6 galaxies (46%) MULTIPLE NUCLEI9 galaxies (20%)1 galaxy (10%)8 galaxies (22%)3 galaxies (23%) NO INTERACTION7 galaxies (15%)5 galaxies (50%)2 galaxies (6%)1 galaxy (8%) 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