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International audience; We report on results from the analysis of a stellar mass-selected (log (M-*/M-circle dot) \textgreater= 9.0) sample of 1644 galaxies at 0.65 \textless z \textless 1.1 with ultradeep (m(AB) \textless 26.5) optical medium-band (R similar to 50) photometry from the Survey for High-z Absorption Red and Dead Sources (SHARDS). The spectral resolution of SHARDS allows us to consistently measure the strength of the 4000 A spectral break [D-n(4000), an excellent age indicator for the stellar populations of quiescent galaxies] for all galaxies at z similar to 0.9 down to log (M-*/M-circle dot) similar to 9. The D-n(4000) index cannot be resolved from broad-band photometry, and measurements from optical spectroscopic surveys are typically limited to galaxies at least 10 times more massive. When combined with the rest-frame U - V colour, (U - V)(r), D-n(4000) provides a powerful diagnostic of the extinction affecting the stellar population that is relatively insensitive to degeneracies with age, metallicity or star formation history. We use this novel approach to estimate de-reddened colours and light-weighted stellar ages for individual sources. We explore the relationships linking stellar mass, (U - V)(r), and D-n(4000) for the sources in the sample, and compare them to those found in local galaxies. The main results are: (a) both D-n(4000) and (U - V)(r) correlate with M-*. The dispersion in D-n(4000) values at a given M-* increases with M-*, while the dispersion for (U - V)(r) decreases due to the higher average extinction prevalent in massive star-forming galaxies. (b) For massive galaxies, we find a smooth transition between the blue cloud and red sequence in the intrinsic U - V colour, in contrast with other recent results. (c) At a fixed stellar age, we find a positive correlation between extinction and stellar mass. (d) The fraction of sources with declining or halted star formation increases steeply with the stellar mass, from similar to 5 per cent at log (M-*/M-circle dot) = 9.0-9.5 to similar to 80 per cent at log (M-*/M-circle dot) \textgreater 11, in agreement with downsizing scenarios.

Pérez-González et al., We present the Survey for High-z Absorption Red and Dead Sources (SHARDS), an ESO/GTC Large Program carried out using the OSIRIS instrument on the 10.4 m Gran Telescopio Canarias (GTC). SHARDS is an ultra-deep optical spectro-photometric survey of the GOODS-N field covering 130 arcmin2 at wavelengths between 500 and 950 nm with 24 contiguous medium-band filters (providing a spectral resolution R ∿ 50). The data reach an AB magnitude of 26.5 (at least at a 3σ level) with sub-arcsec seeing in all bands. SHARDS' main goal is to obtain accurate physical properties of intermediate- and high-z galaxies using well-sampled optical spectral energy distributions (SEDs) with sufficient spectral resolution to measure absorption and emission features, whose analysis will provide reliable stellar population and active galactic nucleus (AGN) parameters. Among the different populations of high-z galaxies, SHARDS' principal targets are massive quiescent galaxies at z > 1, whose existence is one of the major challenges facing current hierarchical models of galaxy formation. In this paper, we outline the observational strategy and include a detailed discussion of the special reduction and calibration procedures which should be applied to the GTC/OSIRIS data. An assessment of the SHARDS data quality is also performed. We present science demonstration results on the detection and study of emission-line galaxies (star-forming objects and AGNs) at z = 0-5. We also analyze the SEDs for a sample of 27 quiescent massive galaxies with spectroscopic redshifts in the range 1.0 < z ≲ 1.4. We discuss the improvements introduced by the SHARDS data set in the analysis of their star formation history and stellar properties. We discuss the systematics arising from the use of different stellar population libraries, typical in this kind of study. Averaging the results from the different libraries, we find that the UV-to-MIR SEDs of the massive quiescent galaxies at z = 1.0-1.4 are well described by an exponentially decaying star formation history with scale Ï„ = 100-200 Myr, age around 1.5-2.0 Gyr, solar or slightly sub-solar metallicity, and moderate extinction, A(V) ∿ 0.5 mag. We also find that galaxies with masses above M* are typically older than lighter galaxies, as expected in a downsizing scenario of galaxy formation. This trend is, however, model dependent, i.e., it is significantly more evident in the results obtained with some stellar population synthesis libraries, and almost absent in others. © 2013. The American Astronomical Society. All rights reserved., We acknowledge support from the Spanish Programa Nacional de Astronomía y Astrofísica under grants AYA2009-07723-E and AYA2009-10368. SHARDS has been funded by the Spanish MICINN/MINECO under the Consolider-Ingenio 2010 Program grant CSD2006-00070: First Science with the GTC. O.G.-M., C.M.-T., J.M.R.-E., and J.R.-Z. wish to acknowledge support from grant AYA2010-21887-C04-04. A.A.-H. and A.H.-C. acknowledge financial support from the Universidad de Cantabria through the Augusto G. Linares Program.