Prof Gavin Dalton

Abstract:

We compare Hα, ultraviolet (UV) and infrared (IR) indicators of star formation rate (SFR) for a well-defined sample of z = 0.84 emission-line galaxies from the High-. z Emission Line Survey (HiZELS). Using emission-line, optical, IR, radio and X-ray diagnostics, we estimate that 5-11 per cent of Hα emitters at this redshift are active galactic nuclei. We detect 35 per cent of the Hα emitters individually at 24 μm, and stack the locations of star-forming emitters on deep 24-μm Spitzer Space Telescope images in order to calculate the typical SFRs of our Hα-emitting galaxies. These are compared to the observed Hα line fluxes in order to estimate the extinction at z = 0.84, and we find a significant increase in dust extinction for galaxies with higher SFRs. We demonstrate that the relationship between SFR and extinction found in the local Universe is also suitable for our high-redshift galaxies, and attribute the overall increase in the typical dust extinction for z = 0.84 galaxies to an increase in the average SFR, rather than to a change in dust properties at higher redshift. We calculate the UV extinction, and find a similar dependence on SFR to the Hα results, but no evidence for a 2175 Å UV bump in the dust attenuation law for high-redshift star-forming galaxies. By comparing Hα and UV indicators, we calculate the conversion between the dust attenuation of nebular and stellar radiation, γ, and show that γ = 0.50 ± 0.14. The extinction/SFR relationship is shown to be applicable to galaxies with a range of morphologies and bulge-to-disc ratios, to both merging and non-merging galaxies, and to galaxies within high- and low-density environments, implying that it is a fundamental property of star-forming regions. In order to allow future studies to easily correct for a SFR-dependent amount of dust extinction, we present an equation to predict the extinction of a galaxy, based solely on its observed Hα luminosity, and use this to recalculate the Hα luminosity function and SFR density at z = 0.84. © 2009 The Authors. Journal compilation © 2009 RAS.

Abstract:

The clustering properties of a well-defined sample of 734 Hα emitters at z= 0.845 ± 0.015, obtained as part of the Hi-z Emission Line Survey, are investigated. The spatial correlation function of these Hα emitters is very well described by the power-law ξ = (r/r0)-1.8, with a real-space correlation, r0, of 2.7 ± 0.3 h-1 Mpc. The correlation length r0 increases strongly with Hα luminosity (LHα), from r0 ∼ 2 h-1 Mpc for the most quiescent galaxies [star formation rates (SFRs) of ∼4 M⊙ yr-1] up to r0 > 5 h-1 Mpc for the brightest galaxies in Hα. The correlation length also increases with increasing rest-frame K-band (MK) luminosity, but the r0-LHα correlation maintains its full statistical significance at fixed MK. At z = 0.84, star-forming galaxies classified as irregulars or mergers are much more clustered than discs and non-mergers, respectively; however, once the samples are matched in LHα and MK, the differences vanish, implying that the clustering is independent of morphological type at z ∼ 1 just as in the local Universe. The typical Hα emitters found at z = 0.84 reside in dark matter haloes of ≈1012 M⊙, but those with the highest SFRs reside in more massive haloes of ≈1013 M⊙. The results are compared with those of Hα surveys at different redshifts: although the break of the Hα luminosity function L*Hα evolves by a factor of ∼30 from z= 0.24 to 2.23, if the Hα luminosities at each redshift are scaled by L*Hα(z) then the correlation lengths indicate that, independently of cosmic time, galaxies with the same (LHα)/L*Hα(z) are found in dark matter haloes of similar masses. This not only confirms that the star formation efficiency in high redshift haloes is higher than locally but also suggests a fundamental connection between the strong negative evolution of L*Hα since z = 2.23 and the quenching of star formation in galaxies residing within dark matter haloes significantly more massive than 1012 M⊙ at any given epoch. © 2010 The Authors. Journal compilation © 2010 RAS.

Abstract:

The Herschel ATLAS is the largest open-time key project that will be carried out on the Herschel Space Observatory. It will survey 570 deg 2 of the extragalactic sky, 4 times larger than all the other Herschel extragalactic surveys combined, in five far-infrared and submillimeter bands. We describe the survey, the complementary multiwavelength data sets that will be combined with the Herschel data, and the six major science programs we are undertaking. Using new models based on a previous submillimeter survey of galaxies, we present predictions of the properties of the ATLAS sources in other wave bands. © 2010. The Astronomical Society of the Pacific. All rights reserved.