We present colour-colour diagrams of detected sources in the Herschel-ATLAS science demonstration field from 100 to 500 μm using both PACS and SPIRE. We fit isothermal modified black bodies to the spectral energy distribution (SED) to extract the dust temperature of sources with counterparts in Galaxy And Mass Assembly (GAMA) or SDSS surveys with either a spectroscopic or a photometric redshift. For a subsample of 330 sources detected in at least three FIR bands with a significance greater than 3σ, we find an average dust temperature of (28 ± 8) K. For sources with no known redshift, we populate the colour-colour diagram with a large number of SEDs generated with a broad range of dust temperatures and emissivity parameters, and compare to colours of observed sources to establish the redshift distribution of this sample. For another subsample of 1686 sources with fluxes above 35 mJy at 350 μm and detected at 250 and 500 μm with a significance greater than 3σ, we find an average redshift of 2.2 ± 0.6.

Aims. The Herschel-ATLAS survey (H-ATLAS) will be the largest area survey to be undertaken by the Herschel Space Observatory. It will cover 550 sq. deg. of extragalactic sky at wavelengths of 100, 160, 250, 350 and 500µm when completed, reaching flux limits (5σ) from 32 to 145mJy. We here present galaxy number counts obtained for SPIRE observations of the first ∼14 sq. deg. observed at 250, 350 and 500µm. Methods. Number counts are a fundamental tool in constraining models of galaxy evolution. We use source catalogs extracted from the H-ATLAS maps as the basis for such an analysis. Correction factors for completeness and flux boosting are derived by applying our extraction method to model catalogs and then applied to the raw observational counts. Results. We find a steep rise in the number counts at flux levels of 100-200mJy in all three SPIRE bands, consistent with results from BLAST. The counts are compared to a range of galaxy evolution models. None of the current models is an ideal fit to the data but all ascribe the steep rise to a population of luminous, rapidly evolving dusty galaxies at moderate to high redshift.

We present a self-consistent, semi-analytical cold dark matter ( CDM) model of star formation and reionization. For the cosmological parameters favoured by the Wilkinson Microwave Anisotropy Probe (WMAP) data, our models consistently reproduce the electron scattering optical depth to reionization, redshift of reionization and the observed luminosity functions (LF) and hence the star formation rate (SFR) density at 3 z 6 for a reasonable range of model parameters. While simple photoionization feedback produces the correct shape of LF at z = 6, for z = 3 we need additional feedback that suppresses star formation activities in haloes with 10 10 (M/M ) 10 11 . Models with prolonged continuous star formation activities are preferred over those with short bursts as they are consistent with the existence of a Balmer break in considerable fraction of observed galaxies even at z ∼ 6. The halo number density evolution from the standard CDM structure formation model that fits LF up to z = 6 is consistent with the upper limits on z 7 LF and source counts at 8 z 12 obtained from the Hubble Ultra Deep Field (HUDF) observations without requiring any dramatic change in the nature of star formation. However, to reproduce the observed LF at 6 z 10, obtained from the near-IR observations around strong lensing clusters, we need a strong evolution in the initial mass function, reddening correction and the mode of star formation at z 8. We show that low-mass molecular cooled haloes, which may be important for reionizing the universe, are not detectable in the present deep field observations even if a considerable fraction of its baryonic mass goes through a star burst phase. However, their presence and contribution to reionization can be inferred indirectly from the redshift evolution of the LF in the redshift range 6 z 12. In our model calculations, the contribution of low-mass haloes to global SFR density prior to reionization reveals itself in the form of second peak at z 6. However, this peak will not be visible in the observed SFR density as a function of z as most of these galaxies have luminosity below the detection threshold of various ongoing deep field surveys. Accurately measuring the LF at high redshifts can be used to understand the nature of star formation in the dark ages and probe the history of reionization.

We study winds in high-redshift galaxies driven by a relativistic cosmic ray (proton) component in addition to the hot thermal gas component. Cosmic rays (CRs) are likely to be efficiently generated in supernova shocks inside galaxies. We obtain solutions of such CR-driven free winds in a gravitational potential of the Navarro-Frenk-White form, relevant to galaxies. CRs naturally provide the extra energy and/or momentum input to the system, needed for a transonic wind solution in a gas with adiabatic index γ = 5/3. We show that CRs can effectively drive winds even when the thermal energy of the gas is lost due to radiative cooling. These wind solutions predict an asymptotic wind speed closely related to the circular velocity of the galaxy. Furthermore, the mass outflow rate per unit star formation rate (η w ) is predicted to be ∼0.2-0.5 for massive galaxies, with masses M ∼ 10 11 -10 12 M . We show η w to be inversely proportional to the square of the circular velocity. Magnetic fields at the μG levels are also required in these galaxies to have a significant mass loss. A large η w for small mass galaxies implies that CR-driven outflows could provide a strong negative feedback to the star formation in dwarf galaxies. Further, our results will also have important implications to the metal enrichment of the intergalactic medium. These conclusions are applicable to the class of free wind models where the source region is confined to be within the sonic point.

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