arXiv subjects

A. M. Read

Publications and source records attributed to A. M. Read.

At least 55 records · Page 3Linked to original sources

arXiv2007

Low-power radio galaxy environments in the Subaru/XMM-Newton Deep Field at z~0.5

We present multi-object spectroscopy of galaxies in the immediate (Mpc-scale) environments of four low-power (L_1.4 GHz < 10^25 W/Hz) radio galaxies at z~0.5, selected from the Subaru/XMM-Newton Deep Field. We use the spectra to calculate velocity dispersions and central redshifts of the groups the radio galaxies inhabit, and combined with XMM-Newton (0.3-10 keV) X-ray observations investigate the L_X--sigma_v and T_X--sigma_v scaling relationships. All the radio galaxies reside in moderately rich groups -- intermediate environments between poor groups and rich clusters, with remarkably similar X-ray properties. We concentrate our discussion on our best statistical example that we interpret as a low-power (FRI) source triggered within a sub-group, which in turn is interacting with a nearby group of galaxies, containing the bulk of the X-ray emission for the system -- a basic scenario which can be compared to more powerful radio sources at both high (z>4) and low (z<0.1) redshifts. This suggests that galaxy-galaxy interactions triggered by group mergers may play an important role in the life-cycle of radio galaxies at all epochs and luminosities.

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arXiv2007

The Chandra View of Galaxy Mergers

From a Chandra survey of nine interacting galaxy systems the evolution of X-ray emission during the merger process has been investigated. It is found that the X-ray luminosity peaks ~300 Myr before nuclear coalescence, and then dips, even though we know that rapid and increasing activity is still taking place at this time. It is likely that this drop in X-ray luminosity is a consequence of outflows breaking out of the galactic discs of these systems. In this work it is also shown that, for the systems close to the point of nuclear coalescence, Lfir becomes massively enhanced compared to the X-ray luminosity of these systems. We suggest that this enhancement may indicate a `top heavy' IMF, with an enhanced fraction of massive stars. At a time ~1 Gyr after coalescence, the merger-remnants in our sample are X-ray faint when compared to typical mature elliptical galaxies. However, we do see evidence that these systems will start to resemble typical elliptical galaxies at a greater dynamical age, given the properties of the 3 Gyr system within our sample, supporting the idea that halo regeneration will take place within low Lx merger-remnants. Also as a part of this survey, detailed Chandra observations for the double nucleus merger system Mkn 266 and the merger-remnant Arp 222 are presented for the first time.

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arXiv2007

An XMM-Newton view of M101 - III. Diffuse X-ray emission

We present a study of the X-ray properties of the nearby face-on Scd spiral galaxy M101 based on recent XMM-Newton observations. In this third and final paper in the present series, we focus on the spatial and spectral properties of the residual emission, after excluding bright X-ray sources with L(X) > 10^37 erg/s. Within a central region of radius 10 arcmins (21 kpc), the X-ray emission broadly traces the pattern of the spiral arms, establishing a strong link with recent star formation, but it also exhibits a radial scale length of \~2.6 arcmins (5.4 kpc) consistent with optical data. We estimate the soft X-ray luminosity within the central 5 arcmins (10.5 kpc) region to be L(X) ~2.1 x 10^39 erg/s (0.5-2 keV), the bulk of which appears to originate as diffuse emission. We find a two-temperature thermal model best fits the spectral data with derived temperatures of 0.20 +/- 0.01 keV and 0.68^(+0.06)_(-0.04) keV which are very typical of the diffuse components seen in other normal and starburst galaxies. More detailed investigation of the X-ray morphology reveals a strong correlation with images recorded in the far-UV through to V band, with the best match being with the U band. We interpret these results in terms of a clumpy thin-disk component which traces the spiral arms of M101 plus an extended lower-halo component with large filling factor.

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arXiv2007

The XMM-Newton EPIC Background and the production of Background Blank Sky Event Files

We describe in detail the nature of XMM-Newton EPIC background and its various complex components, summarising the new findings of the XMM-Newton EPIC background working group, and provide XMM-Newton background blank sky event files for use in the data analysis of diffuse and extended sources. Blank sky event file data sets are produced from the stacking of data, taken from 189 observations resulting from the Second XMM-Newton Serendipitous Source Catalogue (2XMMp) reprocessing. The data underwent several filtering steps, using a revised and improved method over previous work, which we describe in detail. We investigate several properties of the final blank sky data sets. The user is directed to the location of the final data sets. There is a final data set for each EPIC instrument-filter-mode combination.

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arXiv2006

Candidate tidal disruption events from the XMM-Newton Slew Survey

In recent years, giant amplitude X-ray flares have been observed from a handful of non-active galaxies. The most plausible scenario of these unusual phenomena is tidal disruption of a star by a quiescent supermassive black hole at the centre of the galaxy. Comparing the XMM-Newton Slew Survey Source Catalogue with the ROSAT PSPC All-Sky Survey five galaxies have been detected a factor of up to 88 brighter in XMM-Newton with respect to ROSAT PSPC upper limits and presenting a soft X-ray colour. X-ray luminosities of these sources derived from slew observations have been found in the range 10^41-10^44 erg s^-1, fully consistent with the tidal disruption model. This model predicts that during the peak of the outburst, flares reach X-ray luminosities up to 10^45 erg s^-1, which is close to the Eddington luminosity of the black hole, and afterwards a decay of the flux on a time scale of months to years is expected. Multi-wavelength follow-up observations have been performed on these highly variable objects in order to disentangle their nature and to investigate their dynamical evolution. Here we present sources coming from the XMM-Newton Slew Survey that could fit in the paradigm of tidal disruption events. X-ray and optical observations revealed that two of these objects are in full agreement with that scenario and three other sources that, showing signs of optical activity, need further investigation within the transient galactic nuclei phenomena.

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arXiv2006

The XMM Large Scale Structure survey: The X-ray pipeline and survey selection function

We present the X-ray pipeline developed for the purpose of the cluster search in the XMM-LSS survey. It is based on a two-stage procedure via a dedicated handling of the Poisson nature of the signal: (1) source detection on multi-resolution wavelet filtered images; (2) source analysis by means of a maximum likelihood fit to the photon images. The source detection efficiency and characterisation are studied through extensive Monte-Carlo simulations. This led us to define two samples of extended sources: the C1 class that is uncontaminated, and the less restrictive C2 class that allows for 50% contamination. The resulting predicted selection function is presented and the comparison to the current XMM-LSS confirmed cluster sample shows very good agreement. We arrive at average predicted source densities of about 7 C1 and 12 C2 per deg2, which is higher than any available wide field X-ray survey. We finally notice a substantial deviation of the predicted redshift distribution for our samples from the one obtained using the usual assumption of a flux limited sample.

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arXiv2005

The XMM-Newton Slew Survey: a wide-angle survey in the 0.2 - 12 keV band

The scientific data collected during slews of the XMM-Newton satellite are used to construct a slew survey catalogue. This comprises of the order of 4000 sources detected in the EPIC-pn 0.2-12 keV band with exposures of less than 15s and a sky coverage of about 6300 square degrees (source density ~0.65 per square degree). Below 2 keV the sensitivity limit is comparable to the ROSAT PSPC All-Sky Survey and the XMM-Newton slew survey offers long-term variablity studies. Above 2 keV the survey will be a factor of 10 more sensitive than all previous all-sky X-ray surveys. The slew survey is almost complementary to the serendipitous survey compiled from pointed XMM-Newton observations. It is aimed to release the first source catalogue by the end of 2005. Later slew observations and detections will continuously be added. This paper discusses the XMM-Newton slew survey also in a historical context.

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arXiv2005

The XMM-Newton Slew Survey: towards the XMMSL1 catalogue

The XMM-Newton satellite is the most sensitive X-ray observatory flown to date due to the great collecting area of its mirrors coupled with the high quantum efficiency of the EPIC detectors. It performs slewing manoeuvers between observation targets tracking almost circular orbits through the ecliptic poles due to the Sun constraint. Slews are made with the EPIC cameras open and the other instruments closed, operating with the observing mode set to the one of the previous pointed observation and the medium filter in place. Slew observations from the EPIC-pn camera in FF, eFF and LW modes provide data, resulting in a maximum of 15 seconds of on-source time. These data can be used to give a uniform survey of the X-ray sky, at great sensitivity in the hard band compared with other X-ray all-sky surveys.

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arXiv2005

Status of the XMM-Newton cross-calibration with SASv6.5.0

Further achievements of the XMM-Newton cross-calibration - XMM internal as well as with other X-ray missions - are presented. We explain the major changes in the new version SASv6.5 of the XMM-Newton science analysis system. The current status of the cross-calibration of the three EPIC cameras is shown. Using a large sample of blazars, the pn energy redistribution at low energy could be further calibrated, correcting the overestimation of fluxes in the lowest energy regime. In the central CCDs of the MOSs, patches were identified at the bore-sight positions, leading to an underestimation of the low energy fluxes. The further improvement in the understanding of the cameras resulted in a good agreement of the EPIC instruments down to lowest energies. The latest release of the SAS software package already includes corrections for both effects as shown in several examples of different types of sources. Finally the XMM internal cross-calibration is completed by the presentation of the current cross-calibration status between EPIC and RGS instruments. Major efforts have been made in cross-calibrations with other X-ray missions, most importantly with Chandra, of course, but also with currently observing satellites like Swift.

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arXiv2005

Extended sources in the XMM-Newton slew survey

The low background, good spatial resolution and great sensitivity of the EPIC-pn camera on XMM-Newton give useful limits for the detection of extended sources even during the short exposures made during slewing maneouvers. In this paper we attempt to illustrate the potential of the XMM-Newton slew survey as a tool for analysing flux-limited samples of clusters of galaxies and other sources of spatially extended X-ray emission.

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arXiv2005

The X-ray Evolution of Merging Galaxies

From a Chandra survey of nine interacting galaxy systems the evolution of X-ray emission during the merger process has been investigated. From comparing Lx/Lk and Lfir/Lb it is found that the X-ray luminosity peaks around 300 Myr before nuclear coalescence, even though we know that rapid and increasing star formation is still taking place at this time. It is likely that this drop in X-ray luminosity is a consequence of outflows breaking out of the galactic discs of these systems. At a time around 1 Gyr after coalescence, the merger-remnants in our sample are X-ray dim when compared to typical X-ray luminosities of mature elliptical galaxies. However, we do see evidence that these systems will start to resemble typical elliptical galaxies at a greater dynamical age, given the properties of the 3 Gyr system within our sample, indicating that halo regeneration will take place within low Lx merger-remnants.

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arXiv2005

The XMM-Newton Slew Survey

XMM-Newton, with the huge collecting area of its mirrors and the high quantum efficiency of its EPIC detectors, is the most sensitive X-ray observatory ever flown. This is strikingly evident during slew exposures, which, while yielding only at most 14 seconds of on-source exposure time, actually constitute a 2-10 keV survey ten times deeper than all other "all-sky" surveys. The current (April 2005) XMM archive contains 374 slew exposures which give a uniform coverage over around 10,000 square degrees (approx. 25% of the sky). Here we describe the results of pilot studies, the current status of the XMM-Newton Slew Survey, up-to-date results and our progress towards constructing a catalogue of slew detections in the full 0.2-12 keV energy band.

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arXiv2005

Chandra Observations of the Interacting Galaxies NGC 3395/3396 (Arp 270)

In this paper we present the results of a 20 ks high resolution Chandra X-ray observation of the peculiar galaxy pair NGC 3395/3396, a system at a very early stage of merging, and less evolved than the famous Antennae and Mice merging systems. Previously unpublished ROSAT HRI data are also presented. The point source population and the hot diffuse gas in this system are investigated, and compared with other merging galaxy pairs. 16 X-ray point sources are detected in Arp 270, 7 of which are classified as ULXs (Lx > 10^39 erg/s). From spectral fits and the age of the system it seems likely that these are predominantly high mass X-ray binaries. The diffuse gas emits at a global temperature of ~0.5 keV, consistent with temperatures observed in other interacting systems, and we see no evidence of the starburst-driven hot gaseous outflows seen in more evolved systems such as The Mice and The Antennae. It is likely that these features are absent from Arp 270 as the gas has had insufficient time to break out of the galaxy disks. 32% of the luminosity of Arp 270 arises from the diffuse gas in the system, this is low when compared to later stage merging systems and gives further credence that this is an early stage merger. Comparing the ULX population of Arp 270 to other merging systems, we derive a relationship between the star formation rate of the system, indicated by Lfir, and the number (N(ULX)) and luminosity (Lulx) of its ULX population. We find Nulx proportional to Lfir^0.18 and Lulx proportional to Lfir^0.54. These relationships, coupled with the relation of the point source X-ray luminosity (Lxp) to Lk and Lfir+uv (Colbert et al. 2003), indicate that the ULX sources in an interacting system have contributions from both the old and young stellar populations.

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arXiv2005

A Chandra View of the Anomalous Half-Merger NGC520

(abridged) High spatial and spectral resolution Chandra X-ray observations of the anomalous merging galaxy NGC520, a similarly-evolved system to the well-known Antennae galaxies, are presented here. Of great interest is the fact that NGC520, on account of it being due to the result of an encounter between one gas-rich disk and one gas-poor disk, appears in X-rays to be only 'half a merger'; Whereas a ULX lies at the primary (SE), more-massive nucleus, no sources are seen at the secondary nucleus. Whereas what appears to be a starburst-driven galactic wind is seen outflowing perpendicular to the molecular disk surrounding the primary nucleus, no such diffuse structure is seen anywhere near the secondary nucleus. Comparing the X-ray properties with those of other merging galaxies, one sees that, relative to its SFR, the number of ULXs seen within the system is rather small. Similarly the total X-ray luminosity and the fraction of this emission that appears diffuse are both a factor ~2 less than that expected based on NGC520's evolutionary merger stage. 15 X-ray sources are detected within the system, including a small number of bright ULXs that flatten the source XLF to a level similar to that of the Antennae and other mergers. Lastly, to see what appears to be a starburst-driven diffuse galactic wind, with a spectrum entirely consistent with that of other known galactic winds, though unusually, emanating from only one of the nuclei, is a surprise, given that one might have expected such structures to have distorted very quickly in such a rapidly evolving environment. The wind is larger and more massive than features seen in evolutionarily earlier systems (eg the Mice), but smaller and less massive than as seen in later systems (eg the Antennae), or classic starbursts.

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arXiv2004

The XMM-LSS survey. Survey design and first results

We have designed a medium deep large area X-ray survey with XMM - the XMM Large Scale Structure survey, XMM-LSS - with the scope of extending the cosmological tests attempted using ROSAT cluster samples to two redshift bins between 0<z<1 while maintaining the precision of earlier studies. Two main goals have constrained the survey design: the evolutionary study of the cluster-cluster correlation function and of the cluster number density. The results are promising and, so far, in accordance with our predictions as to the survey sensitivity and cluster number density. The feasibility of the programme is demonstrated and further X-ray coverage is awaited in order to proceed with a truly significant statistical analysis. (Abridged)

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arXiv2004

XMM-Newton (cross)-calibration

ESA's large X-ray space observatory XMM-Newton is in its fifth year of operations. We give a general overview of the status of calibration of the five X-ray instruments and the Optical Monitor. A main point of interest in the last year became the cross-calibration between the instruments. A cross-calibration campaign started at the XMM-Newton Science Operation Centre at the European Space Astronomy Centre in collaboration with the Instrument Principle Investigators provides a first systematic comparison of the X-ray instruments EPIC and RGS for various kind of sources making also an initial assessment in cross calibration with other X-ray observatories.

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arXiv2004

XMM-Newton observations of the late-stage merger-remnant galaxies NGC 3921 and NGC 7252

Using the high sensitivity of XMM, we have studied the X-ray emission of the two proto-typical late-stage merger remnants, NGC 3921 and NGC 7252. In the case of NGC 7252, this is complemented by archival Chandra data. We investigate the nature of the discrete X-ray point source populations and the hot diffuse gas components in these two galaxies, and compare them in the light of their different merger ages and histories. We detect 3 candidate ultra-luminous X-ray point sources in NGC 3921 and at least 6 in NGC 7252, for which we have high spatial resolution Chandra data. These have luminosities ranging from \~1.4x10^39-10^40 erg s^-1 (for H_0= 75 km s-1 Mpc^-1). We expect these ULXs to be high mass X-ray binaries, associated with the recent star formation in these two galaxies. Extended hot gas is observed in both galaxies. We have sufficient counts in the XMM data to fit two-component hot plasma models to their X-ray spectra and estimate the X-ray luminosities of the hot diffuse gas components to be 2.75x10^40 erg s^-1 and 2.09x10^40 erg s^-1 in NGC 3921 and NGC 7252, respectively. These luminosities are low compared with the luminosities observed in typical mature elliptical galaxies LX ~10^(41-42) erg s^-1), into which these merger remnants are expected to evolve. We do not see evidence that the X-ray halos of these galaxies are currently being regenerated to the masses and luminosities seen in typical elliptical galaxies. The mass of atomic gas available to fall back into the main bodies of these galaxies and shock-heat to X-ray temperatures is insufficient for this to be the sole halo regeneration mechanism. We conclude that halo regeneration is most likely a long-term (>10 Gyr) process, occurring predominantly via mass loss from evolving stars, in a sub-sonic outflow stage commencing ~2 Gyr after the merging event.

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arXiv2004

X-ray flares from the ultra-luminous X-ray source in NGC 5408

We have studied an ultra-luminous X-ray source (ULX) in the dwarf galaxy NGC 5408 with a series of XMM-Newton observations, between 2001 July and 2003 January. We find that its X-ray spectrum is best fitted with a power law of photon index Gamma ~ 2.6--2.9 and a thermal component with blackbody temperature kT_bb ~ 0.12--0.14 keV. These spectral features, and the inferred luminosity ~ 10^{40} erg/s in the 0.3--12 keV band, are typical of bright ULXs in nearby dwarf galaxies. The blackbody plus power-law model is a significantly better fit than either a simple power law or a broken power law (although the latter model is also acceptable at some epochs). Doppler-boosted emission from a relativistic jet is not required, although we cannot rule out this scenario. Our preliminary timing analysis shows flaring behaviour which we interpret as variability in the power-law component, on timescales of ~ 10^2 s. The hard component is suppressed during the dips, while the soft thermal component is consistent with being constant. The power density spectrum is flat at low frequencies, has a break at f_b ~ 2.5 mHz, and has a slope ~ -1 at higher frequencies. A comparison with the power spectra of Cyg X-1 and of a sample of other BH candidates and AGN suggests a mass of ~ 10^2 M_sun. It is also possible that the BH is at the upper end of the stellar-mass class (M ~ 50 M_sun), in a phase of moderately super-Eddington accretion. The formation of such a massive BH via normal stellar evolution may have been favoured by the very metal-poor environment of NGC 5408.

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