Observational constraints on galaxy formation and evolution
(Jarvis, Stevens, Priddey)
With the discovery that all massive galaxies in the local Universe harbour black-holes with commensurate masses, comes the realisation that black-hole growth and galaxy growth are inherently related. Further proof of this comes from observations which show that the peak of the star-formation activity in the Universe occurred at around the same time as the peak in the AGN activity (i.e. ~3Gyrs after the Big Bang). After this time we observe a decline in both star-formation and AGN activity, however before this time it is still unclear how these fundamental processes in the Universe evolved.
Over a similar timescale it has become apparent, from a theoretical perspective, that one of the fundamental gaps in our knowledge of galaxy formation is that of feedback - the process by which star-formation in galaxies switches off. The most credible candidates to halt the star formation in galaxies are supernovae driven winds and AGN-driven outflows. Both of these processes are able to heat gas so that it cannot cool to form stars, and potentially expel it completely from the galaxy. Thus, it is of both topical and critical importance to investigate how galaxy formation and evolution is affected by, and reliant on, star formation and AGN activity.
We are currently leading large observational programmes using state-of-the-art instrumentation, such as integral-field units and adaptive optics systems on 8-m class telescopes. Coupled with the new survey telescopes such as VISTA, VST and WFCAM and longer wavelength observations from Spitzer, Herschel and LOFAR, our research aims to bring us a step closer to a clear evolutionary picture of the formation and evolution of galaxies in the Universe.
Integral-field surveys of the history of activity in the Universe
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The Ly-alpha emitter luminosity function determined from a 10 hour integration of a ~1.25 square arcmin centred on a radio galaxy at z=2.92. The black stars represent the space density of sources determined from our IFU observations (van Breukelen, Jarvis & Venemans 2005), the other symbols are from separate studies.
The 6400 fibres making up the square arcminute of the VIMOS-IFU on the VLT essentially allows us to probe a volume of 400Mpc^3 and reach twice as deep into the Ly-alpha luminosity function than current narrow-band surveys. The first ever Ly-alpha luminosity function measured in this way was determined by a student and myself (van Breukelen et al. 2005). The benefit of using IFUs to determine the Ly-alpha luminosity function is that all of the galaxies are selected by exactly the same method, regardless of redshift. Thus, it provides a true picture of the evolution in the luminosity function of the particular object under investigating. Furthermore, within this project, we also discovered a radio-quiet type-II (obscured) quasar within the IFU volume (Jarvis et al. 2005), highlighting the advantages that large-area IFU searches have over broad-band imaging selection followed by multi-object spectroscopy, as such an object would never be targeted for spectroscopy in such surveys.
Wide-field surveys and the history of activity in the Universe
Over the next decade the way in which we investigate the diverse properties of the Universe is going to change dramatically. To a certain extent, this has already begun with huge surveys such as the Sloan Digital Sky Survey (SDSS) and the 2df galaxy and quasar surveys. However, in the coming years this will expand from the optical wavebands to the deepest wide-field surveys ever undertaken in the infrared, sub-mm and radio wavebands. The first of the infrared surveys are already underway, the Spitzer satellite is illuminating the obscured Universe at all cosmic epochs through its sensitivity to reprocessed dust emission. This unique facility, coupled with the new UKIRT Infrared Deep Sky Survey (UKIDSS) will provide the necessary information to probe galaxy formation and AGN activity like never before. This will be taken ever further by VISTA in the southern hemisphere, in conjunction with the optical VST surveys that will also be carried out concurrently.
Moreover, long-wavelength astronomy will enter a new era with the onset of infrared satellites such as ASTRO-F and Herschel and radio telescopes such as the Low-Frequency Array (LOFAR), e-MERLIN, e-VLA, ALMA and eventually the Square Kilometre Array (SKA). Below we highlight our position in these projects.
Deep LOFAR surveys
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The number of star-forming galaxies per steradian that will be detected by LOFAR in the planned deep extragalactic surveys. The solid lines represent survey depths of 100muJy and 30muJy at 200 MHz. The dashed lines represent the number of galaxies forming stars at 10, 100 and 1000 solar masses per year. The earliest of these to carry out `all-sky' surveys will be LOFAR, which is due to be fully operational by 2008. LOFAR will be able to detect star-forming galaxies up to the highest redshifts in the planned deep extra-galactic survey, and a galaxy forming stars at 10 solar masses per year would be detected up to z~1 (Jarvis et al. in prep.). This is in addition to much of the accretion activity in the Universe, up to and into the epoch of reionization. We are currently involved in writing the UK science case for LOFAR long baselines with particular emphasis on constraining the evolution of this star-formation and accretion activity over the history of the Universe.
Herschel Open Time Key Project to investigate high-redshift AGN
We lead a Herschel Open Time Key Project to investigate the properties of high-redshift AGN within the Extra-Hot Consortium. The aim of this is to decouple luminosity effects from evolutionary effects in matched samples of radio-loud and radio-quiet quasars, and determine the amount of radiation that is absorbed and reprocessed by the torus, and how this depends on luminosity and orientation.
We have constructed a well-defined sample of radio-quiet quasars from the SDSS, spanning two decades in optical luminosity at a single cosmic epoch, to constrain luminosity dependent effects on the hot dust emission from the obscuring torus, without caveats of luminosity - redshift degeneracies, a fundamental problem in flux-density limited samples.
Crucially, we have also defined a sample of radio-loud quasars selected in exactly the same way as the radio-quiet quasars, allowing us to address what effect radio emission may have on the dust properties of quasars. Finally, by selecting a sample of radio galaxies matched to have the same distribution in radio luminosity as the radio-loud quasars we will determine how orientation influences the near- and mid-IR SEDs, and in particular obtain a firm hold on the geometry of the obscuring torus. Thus, these data will allow us to directly address all facets of AGN unification.
VISTA Public Surveys
We lead one of the public surveys (VIDEO) proposed for VISTA through the ESO. The aim of this public survey will be to probe the Universe from z=1 to 4. The survey will cover 30 square degrees over previously well studied fields, e.g. the southern SWIRE fields. The science goals are wide ranging, as would be expected for a public survey, however the main extragalactic science goals include;
- constraints on galaxy formation and evolution as a function of both epoch and environment.
- determining the evolution in the cluster mass function with the aim of constraining cosmological models
- determine the quasar luminosity function within the epoch of reionization and their contribution to reionization.
This will be the best survey in existence for such studies and will also benefit from multi-wavelength observations over the same fields from XMM-Newton, Chandra, Spitzer, Herschel and LOFAR, in addition to a plethora of optical imaging data which I am also taking a leading role in obtaining.
We are also heavily involved in one of the VISTA Ultra-Deep Survey proposals (VUUDS; PI Dunlop) which aims to stretch the redshift range up to z~5 over the region covered by the UKIDSS UDS with Y and J imaging. Moreover, I am a co-I on the VISTA hemisphere survey (VHS; PI McMahon) and the VISTA Kilo-degree Infrared Galaxy survey (VIKING; PI Sutherland).