High Redshift Research at Oxford


Star-formation and SMBH play critical roles in galaxy formation as both provide feedback mechanisms to regulate the growth of observable structures like galaxies and clusters of galaxies. Reliable measurements of both the history of star formation and the growth of SMBH needed the development of sensitive IR (and mm) instrumentation because of the effects of redshift and dust. Our programme is thus now focussed on surveys selected at NIR or longer wavelengths, and on wide-field NIR spectroscopic follow-up, with Dr Gavin Dalton’s leadership roles in VISTA and FMOS placing Oxford at the centre of crucial imaging and redshift surveys.


We have played a central role in the redshift surveys that now provide benchmark z ∼ 0 information. Dalton was central to the 2dFGRS (Colless et al., 2001), and Dr. Tom Mauch to the 6dF Galaxy Redshift Survey which now covers ∼ 20, 000 deg to z ∼ 0.1 (Jones et al., 2009; Mahony et al., 2009). Mauch has led definitive studies of the ∼ 20% of 6dF galaxies that are radio sources either because they are starbursts or AGN, and measured their space density, clustering and accretion properties (Mauch, 2006; Mauch & Sadler, 2007; Mauch et al., in prep.; Murphy et al., 2007). In the future we will use 6dFGRS spectra (Fig. 8) either directly, as templates, or as a ‘training set’ for principal component analyses or more sophisticated treatments.


We have also made studies of SMBH growth and feedback yielding the following: evidence that most SMBH growth is obscured by dust and (Compton-thick) gas (Martínez-Sansigre, Rawlings et al., 2005, 2006a,b, 2007; Martínez-Sansigre et al., 2008; Bonfield et al., 2009); evidence that the principal effects of jet feed- back switches from, at high-z (z>∼1.5), rare powerful events capable of influencing the evolution of galaxies throughout systems like clusters (Rawlings & Jarvis, 2004) to common, weaker feedback events at low z (Vardoulaki et al., 2008, 2009); the first small samples of distant (z ∼ 1 − 1.5) near-IR-selected clusters (van Breukelen et al., 2006, 2007; van Breukelen & Clewley, 2009) and evidence that AGN activity is strongly linked to a cluster’s dynamical status (van Breukelen et al., 2009). Through Mauch, we now routinely incorporate such results into two flavours, ’semi-empirical’ [S-SEX] Wilman et al. (2008) and ’semi-analytic’ [S-SAX] Obreschkow et al. (2009a), of simulated sky surveys


Mauch has also been pioneering a new approach to classifying objects, and hence selecting targets for the FMOS GTO. It uses each pixel in multi-waveband data stacks, together with a Bayesian ’multi-atom’ Markov- Chain Monte-Carlo (MCMC) (eg. BayeSys; Skilling, 2004) approach, to deliver posterior probabilities for the number of sources of some low-spatial-resolution emission (e.g. IR or radio), and their redshifts; it also automates the detection of possible gravitational lenses (Fig. 9).

With the successful launch of Herschel, Oxford is in a privileged position to help maximise its scientific output. By combining two unique datasets, GMRT radio data  and, PACS/SPIRE H-ATLAS FIR data, and exploiting (at intermediate z) optical redshift surveys like GAMA, and (at high z) FMOS, we will be the first to make robust studies of cosmic evolution in the FIR-radio correlation. Oxford also aims to lead exploration of the major cooling lines of the ISM via Herschel spectroscopy of a variety of galaxies sampling a wide parameter space of luminosity and metallicity.


The FMOS GTO programme is coordinated in the UK by Dalton; it will use around 30 nights of FMOS/Subaru time in 2010/2011, taking spectra of ∼ 25000 galaxies in a few well studied sky patches (e.g. SXDS, COSMOS, Lockman Hole and Elias-N1, ∼ 3 deg in total). The Mauch MCMC code will be critical for optimizing the FMOS GTO by placing fibres on ’all’ the quasars (24µm- and X-ray- selected), ’all’ the radio-AGN (from GMRT surveys), alongside the general galaxy population in the ’Sloan at z ∼ 1.5’ survey. Repeat exposures will be needed for the absorption-line objects (to build up s:n), whereas emission-line objects will need only one exposure; the Mauch MCMC code will be used to separate these and pinpoint objects requiring special attention (e.g. IFU or KMOS follow-up) rather than a single FMOS fibre.


We are involved in the Herschel-ATLAS survey, a wide (600 deg) area covered at two PACS and three SPIRE bands down to twice the confusion limit. Rigopoulou’s involvement with the SPIRE/ICC (Instrument Control Centre) allows access to further surveys within the SPIRE-GTO programs. Within the H-ATLAS collaboration we are uniquely placed to probe the FIR-radio correlation out to high z. With Jarvis (Herts), we are leading a large ongoing 327-MHz GMRT programme, and test fields have already been successfully processed through the Oxford GMRT pipeline; we have also have contributed, along with many other UK groups, to a large archive of 1-GHz and 610-MHz GMRT datasets in other fields to be targetted by Herschel (including Oxford-led 610-MHz surveys of the equatorial VIDEO fields).


To go beyond the standard interpretations of the FIR-radio correlation we are:


  1. •Exploring the evolution of the FIR-radio correlation as a function z which is currently highly uncertain (Ibar et al., 2008): as the sizes of high-z galaxies are smaller, significant changes in the magnetic field structures should strongly influence the synchrotron component of the radio emission, as will the (1 + z) scaling of CMB intensity with z. At z<∼0.5, the FIR-radio correlation can be studied over wide sky areas using GAMA optical spectroscopy, and at higher redshifts (z<∼2), over smaller sky areas using FMOS.

  2. •In probing the FIR-radio correlation for extremely luminous objects, it will be critical to assess the separate contributions of AGN and star formation. In the case of FIR, this will be done via modelling, meaning our studies will be confined to areas with archival Spitzer data, allowing adequate probing of both hot and dust components. In the case of radio this will require the use of eMERLIN Legacy Survey data.


We are involved in the FIR Spectroscopic Surveys (primarily with PACS) of both local and distant luminous infrared objects (PDRA Verma). The FIR fine structure lines [CII], [OI], [OIII] and [NII], important coolants of the neutral interstellar gas and HII regions, will be used to infer the physical conditions of the gas. The line ratios will be compared to theoretical predictions for photodissociation regions (PDRs; Kaufman et al. (1999)). ISO barely touched the ’tip of the iceberg’ in this area (Fischer et al., 1999), by observing these important FIR indicators in a handful of nearby luminous infrared galaxies, and the Herschel-PACS GTO spectroscopy program (SHINING) will revolutionize the subject. Our goals here are:


  1. •To investigate the properties of the gas and the underlying ionizing sources in infrared luminous galaxies. using extinction-insensitive fine-structure as diagnostics.

  2. •To use a sample of low-metallicity galaxies (from SHINING) to investigate the role of metallicity in star- forming galaxies that will allow us to better understand earlier-Universe environments. Having established the template Herschel spectroscopic sample, to lead PACS/SPIRE-FTS spectroscopy of the extremely luminous, highest-z objects in Herschel surveys to probe the state of their ionised media and PDRs using the diagnostic lines; modelling with advanced PDR models will allow the separation of UV-excited (starburst) and X-ray excited (AGN) components.


In the future, through ALMA observation of the CO rotational ladder of Herschel-selected objects, it will be possible to study molecular gas as a function of the physical quantities probed by Herschel. At the highest redshifts (z > 7), within the EoR, the CO lines observable by ALMA will not be excited in typical objects (Obreschkow et al., 2009b) so the [CII] line is likely to be the brightest detectable emission line.

 

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