I'm a research astronomer in the X-ray and Observational Astronomy Group at Leicester, working in particular on the XID ground-based identification program of the XMM X-ray Serendipitous Survey, led by Prof Mike Watson here at Leicester on behalf of the European Space Agency community of astronomers. This work is wide-ranging and includes analysis of large samples of XMM X-ray data for use in the 2XMMi catalogue and unique astronomical research subsamples such as XWAS: the XMM-2dF Wide Angle Serendipitous Survey. XWAS makes use of optical multi-fibre spectroscopic identification of optically selected but serendipitously detected XMM sources using 2dF on the Anglo Australian Telescope in the Southern Hemisphere and has achieved the XID Medium Sensitivity Sample target of over 1000 identified X-ray sources brighter than F(0.5-4.5keV) > 10-14 erg/cm2/s. This will allow us to definitively characterise the bulk of objects contributing to the X-ray background (which peaks at fluxes ~10-14 erg/cm2/s). Uniquely, the wide area coverage of our survey together with the high throughput and sensitivity of XMM yield X-ray rare objects, e.g. at high redshifts Broad Absorption Line Quasars of a kind not found serendipitously in narrow deep field surveys such as HDF or the smaller field of view NASA Chandra X-ray telescope.
Co-authored work includes the newly published 2XMM serendipitous source catalogue paper (Watson et al. 2009) and results of the XMM Serendipitous Survey Bright Sample (Della Ceca et al. 2004) with optical identifications (Caccianigi et al. 2008) and cosmological properties of AGN in hard X-ray bright sample (Della Ceca et al. 2008). An XID Medium Sample (XMS-AXIS) X-ray source counts and angular clustering paper (Carrera et al. 2007) is based on the XMS catalogue paper (Barcons et al. 2007), which complements XWAS in the Northern hemisphere. Recent papers based on the medium sensitivity survey include a study of the average Fe K alpha emission from distant AGN (Corral et al. 2008), studies of an X-ray hard, optically bright sample (Page et al. 2007), X-ray absorption in distant type II QSOs (Krumpe et al. 2008). See also a detailed X-ray spectral analysis of the AXIS sample (Mateos et al. 2005). Forthcoming papers include a Galactic Plane sample paper (Motch et al.), in preparation, while an important new paper describes high precision X-ray logN-logS distributions and their implications for the obscured AGN population (Mateos et al. 2008), based on all fields included in the 2XMM catalogue. Further papers are also available from the XID and XMM Serendipitous Survey Bright Sample webpages. XWAS derived optical spectra are used in a study of optical vs. X-ray classifications of AGN and the unified scheme (Garcet et al. 2007) and to investigate quasar selection in the XMM-LSS field via the KX technique (Nakos et al. 2009). Long term work to obtain multiband optical imaging data and photometric redshifts for large numbers of XMM fields is near completion using the INT 4m class telescope with the Wide Field Camera (Northern hemisphere) and the ESO 2.2m telescope with the Wide Field Imager camera (Southern Hemisphere). I am coordinating with XMM-Newton SSC colleagues the collation of all of these datasets and correlated catalogues into a new database to be hosted at Strasbourg in 2009.
The complexity of the large and diverse multi wavelength datasets collected in such an international European collaboration is in itself challenging and requires the implementation of complex database systems to support such a programme, supported by the LEicester Database and Archive Service (LEDAS). Ultimately, we would like to train algorithms to statistically identify X-ray sources routinely and explore unforeseen parameter space in the underlying astrophysics. Together with other UK AstroGrid colleagues we are leading international efforts to build the Virtual Observatory tools and infrastructure needed to mine the ever growing multi wavelength astronomical datasets in this way. In a nutshell, instead of having to mine each archive separately and stitch the results back together later, astronomers need to access and correlate multiple mission datasets simultaneously from one entry point. They then need tools that can analyse and explore any of these, all requiring the development of common international standards. AstroGrid plays a crucial role in the European Virtual Observatory (Euro VO) for which I was the UK representative on the Internal Science Team of the Euro VO Data Centre Alliance, an EU funded FP6 project which enables European and other data centres to publish their archives to the Virtual Observatory. This work now continues through the FP7 AIDA project.
Try the AstroGrid VO Desktop which provides a suite of interoperating java based tools and interfaces with full documentation and helpdesk. Listen to an interview with me for the Jodcast describing AstroGrid and the Virtual Observatory at the 2008 UK National Astronomy Meeting. An easy place to start is the positional search and visualisation tool AstroScope which can access any archive of catalogues, images or spectra and go on to pass them into interoperating exploration and analysis tools. Go on to automate your searches for lists of object positions using a new Multi Query interface or for more advanced cases use python scripting. I describe the latest 2009 release of the AstroGrid VO Desktop and it's application to science use in an invited review paper for a conference on Multi Wavelength Astronomy and the VO at the European Space Agency.
I am also still involved in research into dynamical
interactions in star forming regions and the study of interstellar molecular hydrogen, a crucial building block in the Universe as described further below. In XMM work on determining positional accuracy of XMM X-ray sources we have been able to use cross-correlation with optical catalogues to accurately pinpoint e.g. Gamma Ray Bursts and associate the afterglow of these bursts with observations at other energies, often with spectacular results!
Dr Jonathan A. Tedds,
XMM-Newton Survey Science Centre, AstroGrid Scientist and EuroVO Data Centre Alliance
X-ray and Observational Astronomy (XROA) group,
Department of Physics & Astronomy,
University of Leicester,
Leicester LE1 7RH, UK
Tel: +44 (0)116 252 3502
Fax: +44 (0)116 252 3311
Email: jat at star.le.ac.uk
Last updated: 17 June 2009
The 2XMMi catalogue provides an effective dataset for generating large, well-defined samples of various types of astrophysical object, notably active galaxies (AGN), clusters of galaxies, interacting compact binaries and active stellar coronae, using the power of X-ray selection. The large sky area covered by the serendipitous survey also means that 2XMMi is a rich resource for exploring the variety of the X-ray source populations and identifying rare source types.
The catalogue contains source detections drawn from 4117 XMM-Newton EPIC observations made between February 2000 and March 2008; all datasets were publicly available by May 2008 but not all public observations are included in this catalogue. The catalogue contains 289083 X-ray source detections which relate to 221012 unique X-ray sources (covering an energy interval from 0.2 keV to 12 keV).
|XMM-Newton's EPIC X-ray cameras show the expanding rings caused by a flash of X-rays from a distant galaxy scattered by dust in our own Galaxy. The X-rays were produced by a powerful gamma-ray burst that took place on 3 December 2003. The slowly fading afterglow of the GRB is at the centre of the rings. Other, unrelated, X-ray sources can also be seen (the XID program described above seeks to identify samples of such serendipitously found objects!) The time since the burst is shown. At its largest, the inner ring is about one fifth the size of the full moon. Credit: ESA, S. Vaughan et al. (University of Leicester)|
The scientific paper describing this discovery was published in the Astrophysical Journal while a second scientific paper by us presents an analysis of the X-ray afterglow of GRB 031203, which is itself very unusual. The GRB is shown to actually be a so-called 'X-ray Flash', that is a GRB with more X-rays than gamma-rays. Because the object is so close (the apparent host is a small galaxy at a redshift of 0.1, ie about a billion light-years away, making it the second closest GRB known), the burst and afterglow are much less luminous than typical GRBs, and appear to provide a link between normal GRBs and the nearby and very under-luminous GRB 980425 associated with supernova 1998bw.
The nature of such molecular shocks, which play an important role in the processes of momentum and energy transfer within star forming molecular clouds, is still uncertain. Recently, significant increases in the spatial and spectral resolution of near-infrared spectrometers such as CGS4 at UKIRT has been achieved together with the ongoing development of integral field IR spectrometers like 3D (see below), mid-IR spectrometers (Michelle) and adaptive optics imaging techniques (Adonis). The aim of the current work is to make the decisive measurements of the velocity structure, relative intensities and resolved cooling lengths of a range of shocked H2 transitions that must provide constraints so tight that it should be possible to reject most (or even all!) of the steady state shock models. Ongoing observations will extend this work to study clump ablation and dynamical interactions in planetary nebulae, HII regions and circumstellar disks.
This is a narrowband JHK colour montage of the Orion Bullets and wakes was taken using IRIS at the Anglo Australian Telescope (AAT) with 0.26" pixel scale and featured in Nature (Allen & Burton 1993). Fe+ bullets (green) are seen at the tips of H2 wakes (red). It is proposed that knots of gas have been ejected explosively or have condensed in situ due to instabilities which might be caused by differential velocity and density gradients in the outflowing and ambient molecular gas. Once launched, the bullets drive bow shocks into the surrounding molecular gas seen as hot shocked H2. These images provide an ideal opportunity to study molecular shock physics in the brightest H2 source. Although Fe+ bullet emission is well explained by bow shock models, it is very difficult to reconcile our new measurements of H2 dynamics and excitation in the wakes with steady state molecular bow shock models suggesting that the role of instabilities may be important. Note that the brightest (and fastest) bullets have no clearly associated H2 wakes which is consistent with high shock velocities sufficient to dissociate H2.
A lower resolution (0.6" pixel scale) IRIS image from Allen & Burton (1993) is shown above which includes the hot, young Trapezium stars at lower centre and the Orion bar ionization feature at bottom left.
I was the UK "Friend" for the MPE-3D near-IR imaging spectrometer. This instrument uniquely combined state of the art near-IR spectroscopy with precise spatial contiguity enabling detailed spectral mapping of a 16x16 pixel field of view at 0.4" spatial resolution. I used 3D to make a higher resolution map of the H2 excitation in the best defined of the Orion Bullets (see below). We also used 3D to similarly map the H2 excitation around the head of an individual cometary knot within the Helix planetary nebula in an effort to determine the underlying mechanisms involved in clump ablation which plays an important role in the star formation process. The instrument was last mounted on the AAT during Semester 98B/99A and then moved to the Calar Alto 3.5m telescope for testing laser guide star adaptive optics systems that enable diffraction-limited spectroscopic observations in new generation instruments for the ESO VLT telescopes such as SINFONI as well as influencing the design of the latest IFU near-IR spectrometers such as UIST on UKIRT.
Tracing Shock Evolution in YSO Jets
J.A. Tedds (Leicester), M.D. Smith (Armagh), A.J.L. Fernandes (Porto) & C.J. Davis (JACH)
We have undertaken new observations tracing the evolution of shocks along the best resolved examples of protostellar jets by means of high resolution, deep K band spectroscopy at UKIRT and NTT. In this paper we analyse trends in H2 excitation within the well collimated jet of HH212, comprising multiple bows along each flow axis. The aim of our survey is to better understand the origin of the sequence of knots observed along many jets by directly comparing to theoretical models including flow velocity variability and Kelvin-Helmholtz (KH) instabilities. We also investigate any evolution in shock excitation from C-type near the jet source, where ionisation fractions may be low and B-field strengths high, to J-type further downstream where ambient densities decrease. We will establish whether fluorescent excitation becomes significant for knots closer to the source in each system. Using these results we can now go on to directly compare our results to model predictions, e.g. knot luminosity, separation and excitation in pulsating jet models (Smith et al 97).
Integral Field 3D Spectroscopy in Outflows
J.A. Tedds (Leeds), P.W.J.L. Brand (Edinburgh) & M.G. Burton (UNSW)
We describe the new capability provided by integral field spectroscopy for simultaneously mapping a wide range of shocked emission lines across outflows at high spatial resolution. We have used the MPE-3D near-IR integral field spectrometer on the AAT to carry out a detailed observational study of the physics of shocked H2 and [FeII] excitation within individual bow shocks. Simultaneous measurement of line ratio variations with position across and along bow shocks will strongly constrain shock models in a number of outflow sources. In Orion, where broad H2 line widths had previously implied magnetically moderated C shocks, our echelle observations of the H2 velocity profiles in two of the bullets (Tedds et al. 1999) contradict any steady-state molecular bow shock models. This suggests that instabilities or supersonic turbulence may be important in this case. 3D measurements of the corresponding H2 level populations will address this.
Shocked H2 and Fe+ Dynamics in the Orion Bullets
J.A. Tedds (Leeds), P.W.J.L. Brand (Edinburgh) & M.G. Burton (UNSW)
Observations of H2 velocity profiles in the two most clearly defined Orion bullets are extremely difficult to reconcile with existing steady-state shock models. We have observed [FeII] velocity profiles of selected bullets and H2 1-0 S(1) velocity profiles for a series of positions along and across the corresponding bow-shaped shock fronts driven into the surrounding molecular cloud. Integrated [FeII] velocity profiles of the brightest bullets are consistent with theoretical bow shock predictions. However, observations of broad, singly-peaked H2 1-0 S(1) profiles at a range of positions within the most clearly resolved bullet wakes are not consistent with molecular shock modelling. A uniform, collisionally broadened background component which pervades the region in both tracers is inconsistent with fluorescence due to the ionizing radiation of the Trapezium stars alone.
Accepted by Monthly Notices of the Royal Astronomical Society - Vol 307, 337 (Aug 1st 1999 issue).
Shocked H2 Excitation in the Orion Bullets
J.A. Tedds (Leeds), P.W.J.L. Brand (Edinburgh), M.G. Burton (UNSW) & A.J.L. Fernandes (Porto)
This paper summarises the first results of a detailed observational study of the physics of shocked H2 excitation and dynamics in the Orion ``bullets'' (Tedds 1996; PhD Thesis, University of Edinburgh) using the recently upgraded CGS4 near-IR spectrometer at UKIRT. It is very difficult to reconcile any steady-state molecular bow shock model with these observations. We have identified an additional uniform but collisionally broadened background component pervading the region in both Fe+ and H2 which is inconsistent with a fluorescent component due to the ionizing radiation of the Trapezium stars alone.
Published in Low Mass Star Formation - From Infall to Outflow, Proceedings of IAU Symposium 182, eds F. Malbet &. A. Castets (1997).
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