Graziano Coppa M.Mignoli, G.Zamorani, M.Bolzonella, D.Vergani S.Bardelli, E.Zucca & the zCosmos collaboration Università di Bologna - Dipartimento di Astronomia / Osservatorio astronomico di Bologna

May 26th, 2009 – SNAF Bertinoro (FC) Bimodalities for zCOSMOS galaxies: the hunt for Green Valley Redshift survey in the COSMOS field using VIMOS multi-slit spectrograph on VLT (Lilly et al. 2007) Bright: redshifts of 20 thousand galaxies with magnitudes I<22.5 covering 1.7 deg^2 (.1<z<1.2) Deep: redshifts of 10 thousand galaxies selected in colours within central 1 deg^2 (1.4<z<3) Scientific goals: Determine environment Large scale structures maps of few 100 km/s precision; Diagnostics on galaxies themselves (SFRs, stellar population ages, metallicities) Calibration of photometric redshift schemes to be applied to objects with no spectra. The DATA

May 26th, 2009 – SNAF Bertinoro (FC) Bimodalities for zCOSMOS galaxies: the hunt for Green Valley The idea Galaxies show well known bimodal distributions: Colours Spectral features Morphologies Stellar populations... Transition objects exist  “green valley” “Green valley” is defined in many ways, mostly in U-V colour (Brand et al. 2006), but also in other colours (Strateva et al. 2001) Faber et al Can “green valley” be defined as a general property?

The CUBE May 26th, 2009 – SNAF Bertinoro (FC) Bimodalities for zCOSMOS galaxies: the hunt for Green Valley

May 26th, 2009 – SNAF Bertinoro (FC) Bimodalities for zCOSMOS galaxies: the hunt for Green Valley ClassNumberFraction % % % % % % % % The CUBE

May 26th, 2009 – SNAF Bertinoro (FC) Bimodalities for zCOSMOS galaxies: the hunt for Green Valley 4874 sources in redshift range ~0.48<z< ~1.28 Chosen variables: D4000 EW[OII] Δcol (B-z) Gini coefficient M20 clumpiness concentration asymmetry The PCA

May 26th, 2009 – SNAF Bertinoro (FC) Bimodalities for zCOSMOS galaxies: the hunt for Green Valley PC1PC2PC3PC4PC5PC6PC7PC8 SD C.Var The PCA 4874 sources in redshift range ~0.48<z< ~1.28 Chosen variables: D4000 EW[OII] Δcol (B-z) Gini coefficient M20 clumpiness concentration asymmetry

May 26th, 2009 – SNAF Bertinoro (FC) Bimodalities for zCOSMOS galaxies: the hunt for Green Valley The PCA

May 26th, 2009 – SNAF Bertinoro (FC) Bimodalities for zCOSMOS galaxies: the hunt for Green Valley Gath-Geva (GG) algorithm Gath-Geva is able to detect clusters of various sizes, shapes & densities Fuzzy membership – every object is “spread over” various clusters Number of clusters c MUST be known a priori, as well as good priors for cluster centres and initial membership values (FCM or GK algorithms) Cluster analysis

May 26th, 2009 – SNAF Bertinoro (FC) Bimodalities for zCOSMOS galaxies: the hunt for Green Valley Membership threshold = 90% Every object with membership between 10% and 90% belongs neither to “red” cluster nor to “blue” cluster (30%) early types 3035 (62%) late types 426 (8%) intermediate object (“green valley”) “Green valley” objects fall in the low- density region of the PC plane Cluster analysis

May 26th, 2009 – SNAF Bertinoro (FC) Bimodalities for zCOSMOS galaxies: the hunt for Green Valley PCA/clustering vs. CUBE

May 26th, 2009 – SNAF Bertinoro (FC) Bimodalities for zCOSMOS galaxies: the hunt for Green Valley Virtually all of the CUBE-111 objects reside in red cluster & all CUBE-222 in blue cluster Some of the CUBE outliers are pretty well defined within red cluster (211s, 121s) Others are spread over clusters (212s, 122s, 221s) Green valley objects seem to be quite heterogeneous PCA/clustering vs. CUBE

Morpho 2.1s May 26th, 2009 – SNAF Bertinoro (FC) Bimodalities for zCOSMOS galaxies: the hunt for Green Valley CUBE 222s outside the blue cluster are essentially ZEST types 2.1 classified as mophologically 2 due to their color (green dots in plot)

May 26th, 2009 – SNAF Bertinoro (FC) Bimodalities for zCOSMOS galaxies: the hunt for Green Valley Dashed histogram shows distribution in U-B of the whole sample  Bimodality Green histogram shows distribution of the “green valley” sample  peaked around 0.6 Independent parameter! (not included in PCA) Good agreement with literature Green valley…

May 26th, 2009 – SNAF Bertinoro (FC) Bimodalities for zCOSMOS galaxies: the hunt for Green Valley PCA + cluster analysis is a reliable, powerful and flexible way to catalog galaxies “Green valley” objects are interesting, (masses, luminosities, X properties) Conclusions & TBD

May 26th, 2009 – SNAF Bertinoro (FC) Bimodalities for zCOSMOS galaxies: the hunt for Green Valley THANKS The (other) LOC