Evidence of a Fast Evolution of the UV Luminosity Function of LBGs beyond z=6 from a wide and deep HAWK-I Survey Andrea Grazian INAF - Osservatorio Astronomico di Roma M. Castellano, A. Fontana, K. Boutsia, R. Bouwens, S. Cristiani, M. Dickinson, F. Fiore, E. Giallongo, M. Giavalisco, A. Koekemoer, R, Maiolino, A. Moorwood, N. Menci, M. Nonino, L. Pentericci, A. Renzini, P. Rosati, S. Salimbeni, P. Santini, E. Vanzella

Goals: “exploration” of the Universe: observing galaxies, AGNs and structures up to the earliest phases of the Universe; to reconstruct the history of fundamental physical quantites: Star Formation Rate, Stellar Mass, dust content, morphology, metallicity etc. To Understand the physics involved. Develop and constrain theoretical models. Pb#1: How can we derive “physical quantities” from a handful of photons? Pb#2: We have to select complete galaxy samples by physical properties and not (only) by photometric criteria.

Motivation of our ESO HAWK-I Large Program: z=7 is fashionable; availability of HAWK-I. COMPLEMENTARY to deep pencil beam surveys with WFC3 Beat the cosmic variance: wide area survey. Possibility to spectroscopically confirm our z=7 relatively bright candidates ESO LP 181.A.0717 (P.I. A. Fontana)

HAWK-I is a newly-installed wide-field imager at the Nasmyth A focus of the 8 meter UT4 telescope (ESO, Paranal). It is provided with four 2048x2048 pixels detectors for a total field of view of 7.5'x7.5'. The pixel scale is 0.106". It has 10 observing filters: 4 broad band filters (Y, J, H & K) and 6 narrow band filters (Bracket gamma, CH4, H2, μm, μm & μm).

Hawk-I Science Verification + ESO LP (HAWK-I+FORS2): (PI A. Fontana) Deep IR Survey with Hawk-I & WFC3 GOODS-S BDF4 NTTDF WFC3 Early Science Release + Illingworth’s UDF data

ACS - ZHawk-I - Y WFC3- 1.5hrHawk-I 15hr Hawk-I is a powerful survey machine, even in WFC3 era. Yband WFC3 4.7 sq. arcmin Hawk-I 56.3 sq. arcmin

Hawk-I Y 15hr WFC3-J 22hr

z=6.8 z=7 Z bandY band Lyα UV continuum Lyman Break Galaxies at z=7

An unexpected, large population of contaminants To clean the sample: “aggressive” requirement of non-detection in the UBVRI bands (ALL <2σ; 4 bands <1σ) Z I R V B Y

Castellano et al arxiv: z ∼ 7 candidates in Hawk-I GOODS-S observations

Castellano et al arxiv: Stacking of z ∼ 7 candidates in Hawk-I GOODS-S

z ∼ 7 candidates in Hawk-I BDF4 and NTTDF field Y Y

B+V+IZYJ+H+K Hawk-I candidates are consistent with WFC3 observations done so far. IZY 105 J 125 UDF Hawk-I

Extract expected galaxies in your field (L UV, z) Compute Magnitudes (A V, Lyα) Place them at random position in the image Perform multicolor extraction Retain the fraction selected with your favoured criterion For each set of LF param (α,L*, φ ) Repe at N times For GOODS-S, about 10 4 simulations for 10 6 galaxies.. “Counting” is not enough... need to evaluate systematics

Castellano et al arxiv: Hawk-I: bright &rare ERS: intermediate HUDF: faint & numerous Clear evidence of a fast evolution of the LF from z=6 to z=7

Bunker +09 arxiv: Oesch+ 09 arxiv: Yan+ 09 arxiv: McLure+ 09 arxiv z ≈ 7 in the WFC3

The SFRD(z): impact of the uncertainties of WFC3 data. Bouwens+09, arxiv: Yan+09, arxiv:

Summary & Conclusions Galaxies at z=7 and 8 are reliably detected with new generation IR imagers - Hawk-I and WFC3 are complementary at Y= beyond WFC3 wins. Data interpretation is complex -requires careful evaluation of instrumental and selection effects. 60 hours of FORS2 already awarded for spectroscopy!! Clear evidence for a fast evolution from z=6 to z=7. beyond is controversial Castellano et al (A&A in press) arXiv: