1. Bologna 22.01.2009 The size evolution of early-type galaxies since z=2 P. Saracco 1, M. Longhetti 1, with the contribution of S. Andreon 1, A. Mignano 1, G. Feulner 2, N. Drory 2, U. Hopp 2, R. Bender 2 1 INAF – Osservatorio Astronomico di Brera, Milano 2 Max Planck Institute and University of Munchen

2. Bologna 22.01.2009 Outline of the talk Small/compact Early-Type Galaxies (ETGs) at z>1: first evidence A morphologycal study of a sample of 10 ETGs at 1.2<z<1.7: size evolution of ETGs required The population of ETGs at 1<z<2: new clues on their formation and evolution ? Summary and conclusions

3. Small Small size, high-density ETGs: first evidence Daddi et al. (2005) Hubble UDF - 7 ETGs z>1.4 HST-ACS obs., FWHM~0.12”, F850W filter, λ rest <3000 Ǻ Bologna 22.01.2009

4. Cassata et al. (2005) K20 + GOODS data HST-ACS observations, F850W λ rest <3000 Ǻ Further evidence Bologna 22.01.2009 Trujillo et al. (2006) IR ground based observations FWHM~1.0 arcsec redshift Re [Kpc] MassRe [Kpc]

5. Are ETGs at z>1 really more compact/denser than local counterparts ? These results were based on HST optical observations sampling the blue and UV rest-frame of the galaxies sensitive to k-correction and star formation and/or HST optical observations sampling the blue and UV rest-frame of the galaxies sensitive to k-correction and star formation and/or seeing limited ground-based observations seeing limited ground-based observations Doubts on the reliability of the estimate of R e Doubts on the reliability of the comparison high-z vs low-z High-resolution near-IR obs. sampling λ rest ~6500 Ǻ for a reliable comparison between high-z and low-z ETGs. Bologna 22.01.2009

6. Effective radius r e (arcsec) and mean surface brightness (SB) e within r e from Sersic profile fitting n=4 de Vaucouleurs profile n=1 exponential profile galfit (Peng et al. 2002) to perform the fitting after the convolution with the NIC2 PSFs. 0.075 “/pixel NIC2 images models residuals z=1.34 z=1.40 z=1.7 n=3.2 n=4.5 n=2.7 Bologna 22.01.2009 HST-NICMOS observations in the F160W (λ~1.6 µm) filter of a sample of 10 ETGs at 1.2<z<1.7. (Longhetti et al. 2007) Data sampling the rest-frame R-band (λ rest ~6500 Ǻ) at z~1.4, at a spatial resolution <0.8 kpc (FWHM~0.12 “)

7. It is a scaling relation between the effective radius R e [Kpc] and the mean SB e [mag/arcsec 2 ] Any deviation from the KR at z=0 should reflects the evolution of e due luminosity evolution. The ETGs follow this tight relation with  ~3 up to z~1.  is found to vary reflecting the luminosity evolution. Expected KR at z=1.5 passive luminosity evolution (maximum evolution expected for early-types). Observed KR at z=0. Expected locus for z<1.5 early-type galaxies in case of luminosity evolution. The Kormendy relation in the R-band Bologna 22.01.2009

8. It is a scaling relation between the effective radius R e [Kpc] and the mean SB e [mag/arcsec 2 ] The ETGs follow this tight relation with  ~3 up to z~1.  is found to vary reflecting the luminosity evolution. Expected KR at z=1.5 passive luminosity evolution (maximum evolution expected for early-types). Observed KR at z=0. Expected locus for z<1.5 early-type galaxies in case of luminosity evolution. The Kormendy relation in the R-band The SB exceeds by ~1 mag the one expected in the case of PLE for constant R e, i.e. luminosity evolution does not account for the observed SB of ETGs at high-z. luminosity evolution does not account for the observed SB of ETGs at high-z. (Longhetti et al. 2007) Bologna 22.01.2009

9. Are ETGs at z>1 really more compact/denser than local counterparts ? These results are based on HST near-IR observations sampling the red rest-frame of the galaxies NOT sensitive to k-correction and star formation and/or NO seeing limited ground-based observations NO doubts on the reliability of the estimate of R e High-z ETGs (at least some of them) are more compact then their local counterparts. (Longhetti et al. 2007) Bologna 22.01.2009

10. GMASS sample 13 ETGs 1.4<z<2 Spectroscopic data Morphology based on HST-ACS obs. F850W (λ rest ~3000 Ǻ) (Cimatti et al. 2008) The Kormendy relation in the B-band Bologna 22.01.2009

11. Literature and HST archive research Aim – to collect a large (larger than 10…!) sample of ETGs at z>1 with spectroscopic confimation of the spectral type; HST-NICMOS observations in the F160W filter; multiwavelength coverage (optical + near-IR) in order to study the population of ETGs at 1<z<2 from an homogeneous set of data and a uniform analysis covering a larger interval in luminosity; defining the scaling relations at z~1.5 (Kormendy, size-luminosity/mass relations) Sample 10 ETGs 1.2<z<1.7 from TESIS (Saracco et al. 2005; Longhetti et al. 2005) + 10 ETGs 1.4<z<1.9 from GDDS (Abraham et al. 2004; McCarthy et al. 2005) + 6 ETGs z~1.27 from RDCS 0848+4453 (Stanford et al.1997; van Dokkum et al. 2003 + 3 ETGs 1<z<1.8 from HDF-N (Stanford et al. 2004) + 2 ETGs z=1.4,1.9 from GMASS H-UDF (Daddi et al. 2005; Cimatti et al. 2008) + 1 ETGs z=1.55 53W091 (Dunlop et al. 1996; Waddington et al. 2002) = 32 ETGs 1<z<2, 17.0<K<20, HST-NICMOS observations F160W NIC2 (0.075 ”/pixel) for 14 galaxies NIC3 (0.2 “/pixel) for 18 galaxies FWHM ~ 0.12 arcsec Bologna 22.01.2009

12. Physical properties of ETGs Morphological parameters effective radius and surface brightness derived as in Longhetti et al. (2007); Simulations done also for NIC3 images 0.16 and 0.32 kpc at z~1.5 Absolute magnitudes, stellar masses, ages Fit to the observed SEDs (BVRIzJHK F160W) at fixed z Charlot and Bruzual models (2007, CB07) IMF=Chabrier SFHs τ=0.1,0.3,0.6 Gyr (best-fit τ<0.3 Gyr for 28 out of 32) Metallicity Z ☼,0.4 Z ☼ (best-fit Z ☼ ) A V <0.6 mag (best-fit A V <0.3 for 24 out of 32 ) Bologna 22.01.2009

13. The Kormendy relation in the R-band z=0 z~1.5 The ETGs at z~1.5 are placed on the [ e,R e ] plane according to the KR. z~1.5 ETGs follow the same KR of ETGs at z=0 but with a different zero-point. Saracco et al. 2008 Bologna 22.01.2009

14. Luminosity evolution Only 40% (13 gal) of the sample occupies the KR at z=0. The remaining 60% (19 gal) does not match the local KR, the SB exceeds by 1-1.5 mag the one expected. Two distinct populations ? Each ETG evolves from z=z gal to z=0 according to its own SFH. Saracco et al. 2008 Bologna 22.01.2009

15. Two distinct populations ?Two distinct populations ! Saracco et al. 2008

16. Bologna 22.01.2009 Two distinct populations of ETGs at 1<z<2 Old ETGs, ~3.5 Gyr, =1.5  z f >5 Their stellar population formed in the early universe. Pure luminosity evolution does not account for their high SB. The evolution of their size must be invoked. Young ETGs, ~1.2 Gyr, ~1.5  z f ~2.5 Their stellar population formed much later than the stellar population of Old ETGs. Pure luminosity evolution from z gal to z=0 brings them onto the local KR.

17. Bologna 22.01.2009 Size-Luminosity/Mass relations SDSS Shen et al. (2003) Size-LuminositySize- Mass

18. Bologna 22.01.2009 Size-Luminosity (S-L) relation Saracco et al. 2008 Young Old R e of oETGs is 2.5-3 times smaller than - the local ETGs and - the yETGs with comparable luminosity.

19. Bologna 22.01.2009 Size-Mass (S-M) relation Saracco et al. 2008 R e of Old ETGs is 2.5-3 times smaller than - the local ETGs and - the yETGs with comparable stellar mass. Old ETGs are 15-30 times denser ! Young - 9 out of 13 (70%) follow the S-M relation Old - 4 out of 19 (20%) follow the S-M relation

20. Constraining the formation and the evolution of ETGs Bologna 22.01.2009 Two distinct populations of ETGs at z~1-2 1.How did these two populations evolve from z~2 to z=0 to match the properties of the local ETGs ? 2.Which assembly history did they follow to have the properties shown at z~1.5-2 ?

21. Tracing the evolution at z<2 Bologna 22.01.2009 oETGs Luminosity evolution DOES NOT bring them onto the local Kormendy and S-L relations. They DO NOT match the local S-M relation. They are 2.6(±0.5) times smaller than their local counterparts. They must change their structure. Size evolution from z~2 to z=0 is required to move them onto the local scaling relations.

22. Tracing the evolution at z<2 Bologna 22.01.2009 oETGs Size evolution often used to advocate the merging processes the ETGs should experience in the hierarchical paradigm of galaxy formation. Dissipation-less (“dry”) merging is the most obvious and efficient mechanism to increase the size of galaxies. The size of ETGs increases according to the relation Boylan-Kolchin et al. 2006-08 Khochfar and Silk 2006 Nipoti et al. 2002 Ciotti et al. 2007

23. Tracing the evolution at z<2 Bologna 22.01.2009 oETGs - Merging would produce too much ETGs with M>10 11 M sun : we should observe 3 times more ETGs with M>4-5x10 11 M sun. - Why α=1.3 ? Merging cannot be the mechanism with which oETGs increase their size at z<2. Alternative mechanism(s) leaving nearly unchanged the mass and relaxing the system: 1.interactions between galaxies (e.g. close encounters) 2.minor or “satellite” merging (Naab et al. 2007): M 1 :M 2 = 0.1:1 Efficiency can be constrained from simulations.

24. Tracing the evolution at z<2 Bologna 22.01.2009 yETGs Luminosity evolution brings them on the local Kormendy and S-L relations. They match the local S-M relation. No size evolution is required. To move them along the S-M, α~0.6  M f ~5M i No evidence of merging at z<2. The build-up of yETGs was already completed at z~2.

25. Constraining the path at z>2 - Toward the formation of ETGs Bologna 22.01.2009 oETGs ~3.5 Gyr, =1.5  z f >5 (Age Univ. 4.2 Gyr at z=1.5)  To build-up 10 11 M sun SFR>>100 M sun /yr Size 2.5-3 times smaller  mechanism(s) acting at z>2 must be capable to produce galaxies 5-10 times more compact (15-30 times denser) than local ones Gas-rich merging with high fraction of stars formed during the merger in a violent starburst can produce highly compact ETGs (Khochfar et al. 2008; Naab et al. 2007). BUT t merger >3 Gyr

26. Constraining the path at z>2 - Toward the formation of ETGs Bologna 22.01.2009 yETGs ~1.2 Gyr, ~1.5  z f >2.5 Constraints on the mechanism(s) acting at z>2 less stringent: They can increase their mass and enlarge their size by subsequent mergers (major and minor/satellite) and through starburts till z~2.5 (contrary to oETGs). Different progenitors oETGs: we should see them as they are (younger) till z~3-3.5 yETGs: in the phase of merging, or star forming and interacting with other galaxies at z>2.5

27. Bologna 22.01.2009 Two distinct populations of ETGs at z~1-2 whose stellar populations differ in age by about 2 Gyr Young ETGs: No size/mass evolution is required. Old ETGs: Strong size evolution is required at z<2. The system must relaxes from high to low redshift  oETGs must show higher central velocity dispersion than local ETGs and than yETGs. Key observational test: measuring the velocity dispersion of oETGs. ESO-P82 VLT-FORS2: spectra of 10 oETGs, 10 hrs/spec Observations started in November 2008…we shall see! Summary and conclusions

28. Bologna 22.01.2009 Mean age vs stellar mass 5% Stellar mass

29. The evolution of the zero point α Zero point α of the KR derived from various samples at different redshifts. The curves show the expected evolution of α for different formation redshift zf. Luminosity evolution + Evolution of R e Our sample Luminosity evolution SFH tau=0.6 Gyr, solar metallicity, Chabrier IMF Longhetti et al. 2007 Bologna 22.01.2009

30. Luminosity evolution of Young and Old ETGs Saracco et al. 2008

31. Absolute magnitudes Bologna 22.01.2009

32. Morphological study of a sample of 10 ETGs at 1.2<z<1.7 based on HST-NICMOS observations in the F160W (λ~1.6 µm) filter (Longhetti et al. 2007) NICMOS data - NIC2 camera (0.075 “/pixel) sampling the rest-frame R- band (λ rest ~6500 Ǻ) at z~1.4, at a resolution <0.8 kpc (FWHM~0.12 arcsec) Sample - K<18.5, spectroscopic confirmation of the spectral type from TESIS ( TNG EROs Spectroscopic Identification Survey; Saracco et al. 2003, 2005; Longhetti et al. 2005 ). Bologna 22.01.2009

33. Estimating the mean age of the stellar population 5% Stellar mass0.5 Gyr old 95% stellar mass, 4 Gyr old B V R I z J H K

34. Bologna 22.01.2009 Size-density and mass-density relations Saracco et al. 2008

35. 100 simulated galaxies magnitudes F160W and r e assigned randomly in the ranges 19<F160W<21 and 0.1< r e <0.5 arcsec (1-5 Kpc at z~1.4); axial ratio b/a and position angle PA in the ranges 0.4<b/a<1 and 0<PA<180 Bologna 22.01.2009 Simulations Real galaxies Simulated De Vaucouleurs profile To assess the robustness of the results we applied the same fitting procedure to a set of simulated galaxies

36. NIC3 images (0.2 “/pixel) GDDS sample. z=1.65 z=1.73 z=1.85 NIC3 images (0.2 “/pixel) HDFS-NICMOS z=1.55 z phot =1.94 Bologna 22.01.2009