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1
A FULLY EMPIRICAL APPROACH TO GALAXY EVOLUTION

Renzini, Alvio The Korean Astronomical Society 2010 天文學論叢 Vol.25 No.3
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  ScienceON
  
  코리아스칼라
Observations of large samples of galaxies from low to high redshifts are composing a picture of remarkable simplicity: (1) The star formation rate (SFR) of starforming galaxies scales almost linearly with mass, strongly decline with cosmic time, and exhibits very small scatter around the average relation. (2) Due to the high observed SFRs the mass of galaxies at high redshifts must increase very rapidly, and yet the mass function of star forming galaxies evolves only very slightly with redshift. (3) At all redshifts the fraction of quenched (passively evolving) galaxies increases with galactic stellar mass and with local overdensity, with the remarkable property that the relative efficiency of "mass quenching" is independent of environment, and that of "environment quenching" is independent of mass. In a recent paper by the zCOSMOS collaboration, Peng et al. (2010) demonstrate that these three empirical facts suffice to account for the observed evolution of the galaxy mass function and naturally generate the "double-Schechter" mass function for quenched galaxies.
2
METAL DEFICIENCY IN CLUSTER STAR-FORMING GALAXIES ATZ= 2

Valentino, F.,Daddi, E.,Strazzullo, V.,Gobat, R.,Onodera, M.,Bournaud, F.,Juneau, S.,Renzini, A.,Arimoto, N.,Carollo, M.,Zanella, A. IOP Publishing 2015 The Astrophysical journal Vol.801 No.2
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We investigate the environmental effect on the metal enrichment of star-forming galaxies (SFGs) in the farthest spectroscopically confirmed and X-ray-detected cluster, CL J1449+0856 at z = 1.99. We combined Hubble Space Telescope/WFC3 G141 slitless spectroscopic data, our thirteen-band photometry, and a recent Subaru/Multi-object InfraRed Camera and Spectrograph (MOIRCS) near-infrared spectroscopic follow-up to constrain the physical properties of SFGs in CL J1449+0856 and in a mass-matched field sample. After a conservative removal of active galactic nuclei, stacking individual MOIRCS spectra of 6 (31) sources in the cluster (field) in the mass range 10 <= log(M/M-circle dot) <= 11, we find a similar to 4 sigma. lower [N II]/H alpha ratio in the cluster than in the field. Stacking a subsample of 16 field galaxies with H beta and [O III] in the observed range, we measure an [O III]/H beta ratio fully compatible with the cluster value. Converting these ratios into metallicities, we find that the cluster SFGs are up to 0.25 dex poorer in metals than their field counterparts, depending on the adopted calibration. The low metallicity in cluster sources is confirmed using alternative indicators. Furthermore, we observe a significantly higher H alpha luminosity and equivalent width in the average cluster spectrum than in the field. This is likely due to the enhanced specific star formation rate; even if lower dust reddening and/or an uncertain environmental dependence on. the continuum-to-nebular emission differential reddening may play a role. Our findings might be explained by the accretion of pristine gas around galaxies at z = 2 and from cluster-scale reservoirs, possibly connected with a phase of rapid halo mass assembly at z > 2 and of a high galaxy merging rate.
3
A GIANT LYαNEBULA IN THE CORE OF AN X-RAY CLUSTER ATZ= 1.99: IMPLICATIONS FOR EARLY ENERGY INJECTION

Valentino, Francesco,Daddi, Emanuele,Finoguenov, Alexis,Strazzullo, Veronica,Brun, Amandine Le,Vignali, Cristian,Bournaud, Fré,dé,ric,Dickinson, Mark,Renzini, Alvio,Bé,thermin, Matth American Astronomical Society 2016 The Astrophysical journal Vol.829 No.1
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We present the discovery of a giant >= 100 kpc Ly alpha nebula detected in the core of the X-ray emitting cluster CL J1449 +0856 at z = 1.99 through Keck/LRIS narrow-band imaging. This detection extends the known relation between Lya nebulae and overdense regions of the universe to the dense core of a 5-7 x 10(13) M-circle dot cluster. The most plausible candidates to power the nebula are two Chandra-detected AGN host cluster members, while cooling from the X-ray phase and cosmological cold flows are disfavored primarily because of the high Ly alpha to X-ray luminosity ratio (L-Ly alpha/L-X approximate to 0.3, greater than or similar to 10-1000 times. higher than in local cool-core clusters) and by current modeling. Given the physical conditions of the Ly alpha-emitting gas and the possible interplay with the X-ray phase, we argue that the Ly alpha nebula would be short-lived (less than or similar to 10 Myr) if not continuously replenished with cold gas at a rate of greater than or similar to 1000 M-circle dot yr(-1). We investigate the possibility that cluster galaxies supply the required gas through outflows and we show that their total mass outflow rate matches the replenishment necessary to sustain the nebula. This scenario directly implies the extraction of energy from galaxies and its deposition in the surrounding intracluster medium (ICM), as required to explain the thermodynamic properties of local clusters. We estimate an energy injection of the order of approximate to 2 keV per particle in the ICM over a 2 Gyr interval. In our baseline calculation, AGNs provide up to 85% of the injected energy and two-thirds. of the mass, while the rest is supplied by supernovae-driven winds.