Abstract. We present new improved constraints on the Hubble parameter H(z) in the redshift range 0.15 < z < 1.1, obtained from the differential spectroscopic evolution of early-type galaxies as a function of redshift. We extract a large sample of early-type galaxies (∼ 11000) from several spectroscopic surveys, spanning almost 8 billion years of cosmic lookback time (0.15 < z < 1.42). We select the most massive, red elliptical galaxies, passively evolving and without signature of ongoing star formation. Those galaxies can be used as standard cosmic chronometers, as firstly proposed by Jimenez & Loeb (2002), whose differential age evolution as a function of cosmic time directly probesWe analyze the 4000Å break (D4000) as a function of redshift, use stellar population synthesis models to theoretically calibrate the dependence of the differential age evolution on the differential D4000, and estimate the Hubble parameter taking into account both statistical and systematical errors.We provide 8 new measurements of H(z) (see Tab. 4), and determine its change in H(z) to a precision of 5 − 12% mapping homogeneously the redshift range up to z ∼ 1.1; for the first time, we place a constraint on H(z) at z = 0 with a precision comparable with the one achieved for the Hubble constant (about 5-6% at z ∼ 0.2), and covered a redshift range (0.5 < z < 0.8) which is crucial to distinguish many different quintessence cosmologies.These measurements have been tested to best match a ΛCDM model, clearly providing a statistically robust indication that the Universe is undergoing an accelerated expansion. This method shows the potentiality to open a new avenue in constrain a variety of alternative cosmologies, especially when future surveys (e.g. Euclid) will open the possibility to extend it up to z ∼ 2.-1 -

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We report the results of a comprehensive study of the relationship between galaxy size, stellar mass and specific star-formation rate (sSFR) at redshifts 1.3 < z < 1.5. Based on a mass complete (M 6×10 10 M ), spectroscopic sample from the UKIDSS Ultradeep Survey (UDS), with accurate stellar-mass measurements derived from spectrophotometric fitting, we find that at z 1.4 the location of massive galaxies on the sizemass plane is determined primarily by their sSFR. At this epoch we find that massive galaxies which are passive (sSFR 0.1 Gyr −1 ) follow a tight size-mass relation, with half-light radii a factor f g = 2.4 ± 0.2 smaller than their local counterparts. Moreover, amongst the passive sub-sample we find no evidence that the off-set from the local sizemass relation is a function of stellar population age. In contrast, we find that massive star-forming galaxies at this epoch lie closer to the local late-type size-mass relation and are only a factor f g = 1.6 ± 0.2 smaller than observed locally. Based on a subsample with dynamical mass estimates, which consists of both passive and star-forming objects, we also derive an independent estimate of f g = 2.3±0.3 for the typical growth in half-light radius between z 1.4 and the present day. Focusing on the passive subsample, we conclude that to produce the necessary evolution predominantly via major mergers would require an unfeasible number of merger events and over populate the high-mass end of the local stellar mass function. In contrast, we find that a scenario in which mass accretion is dominated by minor mergers can comfortably produce the necessary evolution, whereby an increase in stellar mass of only a factor of 2, accompanied by size growth of a factor of 3.5, is required to reconcile the sizemass relation at z 1.4 with that observed locally. Finally, we note that a significant fraction (44%±12%) of the passive galaxies in our sample have a disk-like morphology, providing additional evidence that separate physical processes are responsible for the quenching of star-formation and morphological transformation in massive galaxies.

We present spectroscopic confirmation of 10 highly luminous (L≥ 2L★) Lyα emitters (LAEs) in the redshift range 6.01 < z < 6.49 (nine galaxies and one active galactic nucleus), initially drawn from a sample of 14 zphot≥ 6 Lyman‐break galaxies (LBGs) selected from an area of 0.25 deg2 within the UK Infrared Deep Sky Survey (UKIDSS) Ultra‐Deep Survey (UDS). Overall, our high rate of spectroscopic confirmation (≥71 per cent) and low rate of contamination provides a strong vindication of the photometric redshift analysis used to define the original sample. By considering star formation rate estimates based on the Lyα and ultraviolet continuum luminosity we conclude that our sample is consistent with a Lyα escape fraction of ≃25 per cent. Moreover, after careful consideration of the potential uncertainties and biases, we find that 40–50 per cent of our sample of L≥ 2L★ galaxies at 6.0 < z < 6.5 display strong Lyα emission (rest‐frame equivalent width ≥25 Å), a fraction which is a factor of ≃2 higher than previously reported for L≤L★ galaxies at z≃ 6. Our results suggest that, as the epoch of reionization is approached, it is plausible that the LAE fraction amongst luminous (L≥ 2L★) LBGs shows a similarly sharp increase to that observed in their lower luminosity (L≤L★) counterparts.

We investigate galactic-scale outflows in the redshift range 0.71 z 1.63, using 413 K-band selected galaxies observed in the spectroscopic follow-up of the UKIDSS Ultra-Deep Survey (UDSz). The galaxies have an average stellar mass of ∼10 9.5 M ⊙ and span a wide range in rest-frame colours, representing typical star-forming galaxies at this epoch. We stack the spectra by various galaxy properties, including stellar mass, [O II] equivalent width, star-formation rate, specific star-formation rate and rest-frame spectral indices. We find that outflows are present in virtually all spectral stacks, with velocities ranging from 100-1000 km s −1 , indicating that large-scale outflowing winds are a common property at these redshifts. The highest velocity outflows (>500 km s −1 ) are found in galaxies with the highest stellar masses and the youngest stellar populations. Our findings suggest that high velocity galactic outflows are mostly driven by star-forming processes rather than AGN, with implied mass outflow rates comparable to the rates of star formation. Such behaviour is consistent with models required to reproduce the high-redshift mass-metallicity relation.