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Superdense and normal early-type galaxies at 1<z<2

Superdense and normal early-type galaxies at 1<z<2. P. Saracco 1 M. Longhetti 1 , A. Gargiulo 1 1 INAF – Osservatorio Astronomico di Brera, Milano Italy. Outline of the talk. Introduction: first evidence of compact ETGs at z>1 A study of a sample of 65 ETGs at 0.9<z spec <2

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Superdense and normal early-type galaxies at 1<z<2

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  1. Superdense andnormalearly-typegalaxies at 1<z<2 P. Saracco1 M. Longhetti1, A. Gargiulo1 1 INAF – Osservatorio Astronomico di Brera, Milano Italy Galaxy Evolution and Environment - Bologna, November 2009

  2. Outlineof the talk • Introduction: first evidence of compact ETGs at z>1 • A study of a sample of 65 ETGs at 0.9<zspec<2 • Scaling relations of ETGs at z>1 • Color gradients in high-z ETGs (an ongoing work) • Key observing follow-up • Conclusions and the key open question Galaxy Evolution and Environment - Bologna, November 2009

  3. Compact ETGs at z>1: first evidence Trujillo et al. (2006) Daddi et al. (2005) HST-ACS - F850W, λrest<3000 Ǻ Hubble UDF - 7 ETGs z>1.4 Re [Kpc] Mass 10 ETGs z>1.2 Near-IR ground based observations FWHM~1.0 arcsec Galaxy Evolution and Environment - Bologna, November 2009

  4. HST-NICMOS (0.075”/pix) observations of 10 ETGs at 1.2<zspec<1.5 (Longhetti, Saracco, et al. 2007) Kormendy relation in the R band The SB exceeds by ~1mag the one expected in the case of PLE for constant Re, i.e. luminosity evolution does not account for the observed SB of ETGs at high-z. 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. Galaxy Evolution and Environment - Bologna, November 2009

  5. High-zETGs are more compact thanlocalETGs Manyindependentconfirmations • Trujillo et al. (2007) • Cimatti et al. (2008) • Damjanov et al. (2008) • van Dokkum et al. (2008) • McGrath et al. (2008) • Buitrago et al. (2008) • etc. Based on small sample (≤10 ETGs) and/or on photometric z. Galaxy Evolution and Environment - Bologna, November 2009

  6. Large sample of z>1 ETGsneeded • Literature and HST archiveresearch • Aim – collecting a large (larger than 10…!) sample of ETGs at z>1 with • spectroscopic confirmation of redshift and spectral type; • HST observations (NICMOS and/or ACS) F160W or F850LP filter; • multiwavelength coverage (optical + near-IR + mid-IR) 65 early-type galaxies 0.9<zspec<2 U,B,V,R,I,z,J,H,K,3.6,4.5,5.8,8.0 µm 30 ETGs 1<z<2, 17.0<K<20, HST-NICMOS observations F160W (Saracco et al. 2009) 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) 1 ETGs z=1.55 53W091 (Dunlop et al. 1996; Waddington et al. 2002) 35 ETGs 1<z<2, 17.0<K<20, HST-ACS observations F850LP, F606W (GOODS-South) 9 ETGs 1.4<z<2 from GMASS (Cimatti et al. 2008) 12 ETGs 0.9<z<1.2 from van derWel et al. (2005) and Rettura et al. (2006) 5 ETGs 0.9<z<1.2 from K20 (diSerego Alighieri et al. 2005) 9 New ETGs 0.9<z<1.9 from the GOODS-South survey Galaxy Evolution and Environment - Bologna, November 2009

  7. Size-Mass (S-M) relation 34 ETGs (~50%) are smallerthanlocalETGswithequal stellar mass. 31 ETGs (~50%) agreewith the local S-M relation. Compact ETGs 2.5-3timessmallerthanlocalETGs and than NormalETGs Compact ETGs :15-30 timesdenser! Galaxy Evolution and Environment - Bologna, November 2009

  8. Size-Luminosity (S-L) relation Normal ETGs follow the local S-L relation Compact ETGs 2.5-3 times smaller than local ETGs Galaxy Evolution and Environment - Bologna, November 2009

  9. The Kormendy relation in the R-band z=0 z~1.5 The ETGs at z~1.5 are placed on the [<µ>e,Re] plane according to the KR. z~1.5 ETGs follow the KR at z=0 with a different zero-point. ~50% of the sample occupies the KR at z=0. ~50% doesnot match the local KR, their SB exceedsby1-1.5 mag the one at z=0. Galaxy Evolution and Environment - Bologna, November 2009

  10. Superdenseand Normal ETGs coexist at 1<z<2 • Normal ETGs • They follow the local S-M relation. • Luminosity evolution brings them onto the local Kormendy • and S-L relations. • No effective radius evolution required. • Compact ETGs • They do not follow the local scaling relations. • They are 2.5-3 times smaller than their local and high-z • counterparts with comparable mass, SB and luminosity. • Effective radius evolution required. • What does it make the difference ? • Different assembly histories ? Galaxy Evolution and Environment - Bologna, November 2009

  11. Compactness vs z Compactness vs zform Re: effective radius of the galaxy Re,z=0: effective radius of a galaxy of equal mass at z=0 derived from the local S-M relation Normal Compact At high zonly compact ETGs form. Galaxy Evolution and Environment - Bologna, November 2009

  12. Stellar mass vs z Stellar mass vs zform Normal Compact “downsizing” At high zonly compact and high-mass ETGs form Galaxy Evolution and Environment - Bologna, November 2009

  13. Normal and Compact ETGs:different assembly histories • Normal ETGs: Low-z dry-merger products ? • Last episode of star formation occurred at zform<2.5. • Dissipation-less (gas poor) mergers of small sub-units at low z  efficient mechanism to produce large ETGs. • (e.g. Boylan-Koclhin et al. 2006, ’08, Ciotti et al. 2007) • Compact ETGs:High-z gas-rich merger/collapse products ? • Last episode of star formation occurred at 2<zform<10. • Gas-rich merger/collapse  high fraction of stars forms in situ through a violent starburst  highly compact and massive ETGs. • (e.g. Khochfar et al. 2008; Naab et al. 2007, Ciotti et al. 2007) • What does it rout ETGs in the different assembly histories ? • Environment …? Galaxy Evolution and Environment - Bologna, November 2009

  14. Tracing the evolution of Compact ETGs at z<2 They must increase their size by 2.5-3 times to match the local scaling relations. Dissipation-less “dry” merging: the size increases according to the relation Boylan-Kolchin et al. 2006-08 Khochfar and Silk 2006 Nipoti et al. 2002, 2009 Ciotti et al. 2007 Too many high-mass ETGs Galaxy Evolution and Environment - Bologna, November 2009

  15. Are compact ETGs the progenitors of the BCGs ? Tracing the evolution of Compact ETGs at z<2 They must increase their size by 2.5-3 times to match the local scaling relations. Dissipation-less “dry” merging: the size increases according to the relation Boylan-Kolchin et al. 2006-08 Khochfar and Silk 2006 Nipoti et al. 2002, 2009 Ciotti et al. 2007 Too many high-mass ETGs Galaxy Evolution and Environment - Bologna, November 2009

  16. Surface brightness profiles: obs vs fitting FWHM~0.1” F850LP F606W Galaxy Evolution and Environment - Bologna, November 2009

  17. Color gradients in ETGs at z>1 • Simulationstocheckforeachgalaxy • the reliabilityof the measuredgradient; • the uncertainty and the significanceof the measuredgradient. • Are color gradientsmainlypresent in Normal or in Superdense ETGs ? FWHM~0.1” Galaxy Evolution and Environment - Bologna, November 2009

  18. Key observations 1. Compact vs Normal ETGs: two formation scenarios ? Near-IR/optical color gradients: HST high resolution (≤0.1”) near-IR and optical imaging. 2. Were compact ETGs really denser in the past ? Spectroscopic observations to measure the velocity dispersion: at fixed mass the smaller the size, the higher the density and, consequently, the velocity dispersion. Awaiting for the ESO-OPC (P85) and LBT TACs’ verdict. VLT ISAAC σv=410±…km/s Saracco et al. 2005; Longhetti et al. 2005) Galaxy Evolution and Environment - Bologna, November 2009

  19. Normal and superdense ETGs coexist at z>1. Their different physical properties imply that they follow two distinct formation and evolutionary paths. Has the environment the X-Factor ? Thank you ! Galaxy Evolution and Environment - Bologna, November 2009

  20. Best-fittingtemplateto the observed SED at zspec Charlot & Bruzual ’08 models: IMF: Chabrier 0≤Av≤0.6 mag SFH: 0.1, 0.3, 0.4, 0.6 Gyr Z=0.2 Zסּ, Zסּ, 2 Zסּ Best fitting values: Av<0.4 mag (85%) SFH< 0.3 Gyr (90%) Z=Zסּ(90%) Galaxy Evolution and Environment - Bologna, November 2009

  21. Best-fittingtemplateto the observed SED at zspec Charlot & Bruzual ’08 models: IMF: Chabrier 0≤Av≤0.6 mag SFH: 0.1, 0.3, 0.4, 0.6 Gyr Z=0.2 Zסּ, Zסּ, 2 Zסּ Best fitting values: Av<0.4 mag (85%) SFH< 0.3 Gyr (90%) Z=Zסּ(90%) Galaxy Evolution and Environment - Bologna, November 2009

  22. HST-NICMOS observations of 10 ETGs at 1.2<z<1.7. (Longhetti et al. 2007) 0.075 “/pixel • Effective radius re (arcsec) and mean surface brightness (SB) <>e withinre from Sersicprofile fitting • n=4de Vaucouleurs profile • n=1exponential profile • galfit(Peng et al. 2002) to perform the fitting after the convolution with the NIC2 PSFs. Data sampling the rest-frame R-band (λrest~6500 Ǻ) at z~1.4, at a spatial resolution <0.8 kpc (FWHM~0.12 “) NIC2 images models residuals z=1.34 z=1.40 z=1.7 n=3.2 n=4.5 n=2.7 Galaxy Evolution and Environment - Bologna, November 2009

  23. Av vs Age Galaxy Evolution and Environment - Bologna, November 2009

  24. Re(F850LP) vs Re(F606W) Galaxy Evolution and Environment - Bologna, November 2009

  25. The Kormendy relation in the R-band z=0 z~1.5 The ETGs at z~1.5 are placed on the [<µ>e,Re] plane according to the KR. z~1.5 ETGs follow the KR at z=0 with a different zero-point. ~50% of the sample occupies the KR at z=0. ~50% doesnot match the local KR, their SB exceedsby1-1.5 mag the one at z=0. Galaxy Evolution and Environment - Bologna, November 2009

  26. Compactness vs stellar mass 5% Stellar mass Galaxy Evolution and Environment - Bologna, November 2009

  27. Mean age vs stellar mass 5% Stellar mass Galaxy Evolution and Environment - Bologna, November 2009

  28. Mass density vs vs stellar mass 5% Stellar mass Galaxy Evolution and Environment - Bologna, November 2009

  29. Our sample Luminosity evolution SFH tau=0.6 Gyr, solar metallicity, Chabrier IMF Luminosity evolution + Evolution of Re 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. Longhetti et al. 2007 Galaxy Evolution and Environment - Bologna, November 2009

  30. Luminosity evolution of Young and Old ETGs Galaxy Evolution and Environment - Bologna, November 2009 Saracco et al. 2008

  31. Simulations To assess the robustness of the results we applied the same fitting procedure to a set of simulated galaxies Real galaxies Simulated De Vaucouleurs profile • 100 simulated galaxies • magnitudes F160W and reassigned randomly in the ranges 19<F160W<21 and 0.1< re <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 Galaxy Evolution and Environment - Bologna, November 2009

  32. Absolute magnitudes Galaxy Evolution and Environment - Bologna, November 2009

  33. Size-Luminosity/Mass relations SDSS Shen et al. (2003) Size-Luminosity Size- Mass Galaxy Evolution and Environment - Bologna, November 2009

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