arXiv subjects

A. M. Read

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

At least 73 records · Page 4Linked to original sources

arXiv2004

The XMM Large Scale Structure (XMM-LSS) Survey: X-ray analysis and first results

Thanks to its unprecedented sensitivity and large field of view, XMM occupies a leading position as a survey instrument. The XMM-LSS survey is a medium-deep large-area X-ray survey, and greatly extends the cosmological tests attempted using earlier studies. While a wealth of complementary multiwavelength studies are taking place, I concentrate here on the XMM-EPIC data, describing aspects of the X-ray pipeline and analysis, and selected first results, including the deepest wide-angle X-ray image of the cosmos to date.

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arXiv2003

An XMM-Newton observation of the galaxy group MKW 4

We present an X-ray study of the galaxy group or poor cluster MKW 4. Working with XMM data we examine the distribution and properties of the hot gas which makes up the group halo. The inner halo shows some signs of structure, with circular or elliptical beta models providing a poor fit to the surface brightness profile. This may be evidence of large scale motion in the inner halo, but we do not find evidence of sharp fronts or edges in the emission. The temperature of the halo declines in the core, with deprojected spectral fits showing a central temperature of ~1.3 keV compared to ~3 keV at 100 kpc. In the central ~30 kpc of the group multi-temperature spectral models are required to fit the data, but they indicate a lack of gas at low temperatures. Steady state cooling flow models provide poor fits to the inner regions of the group and the estimated cooling time of the gas is long except within the central dominant galaxy, NGC 4073. Abundance profiles show a sharp increase in the core of the group, with mean abundance rising by a factor of two in the centre of NGC 4073. Fitting individual elements shows the same trend, with high values of Fe, Si and S in the core. We estimate that ~50% of the Fe in the central 40 kpc was injected by SNIa, in agreement with previous ASCA studies. Using our best fitting surface brightness and temperature models, we calculate the mass, gas fraction, entropy and mass-to-light ratio of the group. At 100 kpc (~0.1 virial radii) the total mass and gas entropy of the system (~2x10^13 Msol and ~300 keV cm^2) are quite comparable to those of other systems of similar temperature, but the gas fraction is rather low (~1%). We conclude that MKW 4 is a fairly relaxed group, which has developed a strong central temperature gradient but not a large-scale cooling flow.

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arXiv2003

Chandra Observations of the Mice

Presented here are high spatial and spectral resolution Chandra X-ray observations of the famous interacting galaxy pair, the Mice, a system similar to, though less evolved than, the well-known Antennae galaxies. Previously unpublished ROSAT HRI data of the system are also presented. Starburst-driven galactic winds outflowing along the minor axis of both galaxies (but particularly the northern) are observed, and spectral and spatial properties, and energetics are presented. That such a phenomenon can occur in such a rapidly-evolving and turbulent system is surprising, and this is the first time that the very beginning - the onset, of starburst-driven hot gaseous outflow in a full-blown disk-disk merger has been seen. Point source emission is seen at the galaxy nuclei, and within the interaction-induced tidal tails. Further point source emission is associated with the galactic bar in the southern system. A comparison of the source X-ray luminosity function and of the diffuse emission properties is made with the Antennae and other galaxies, and evidence of a more rapid evolution of the source population than the diffuse component is found. No evidence for variability is found between the Chandra and previous observations.

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arXiv2002

Analysis of the XMM-Newton EPIC Background: Production of Background Maps and Event Files

XMM-Newton background maps for the 3 EPIC instruments in their different instrument/mode/filter combinations and in several energy bands have been constructed using a superposition of many pointed observations. Event datasets for the different instrument/mode/filter combinations have also been constructed, with longer exposure times than previously created files. This document describes the construction of the background maps and event files, and their usage. Further details on how to obtain these background products, together with related software and these explanatory notes can be found at http://www.sr.bham.ac.uk/xmm3/BGproducts.html

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arXiv2002

An X-ray view of the active nucleus in NGC 4258

XMM-Newton observed the Seyfert 1.9 galaxy NGC 4258 in December 2000. At energies above 2 keV a hard nuclear point source is resolved that can be fitted by a highly absorbed power-law spectrum (NH = (8.0+-0.4)x10^22 cm^-2, photon index 1.64+-0.08) with an unabsorbed luminosity of 7.5x10^40erg/s in the 2-10 keV band. No narrow iron Kalpha emission line is detected (90% upper limit of equivalent width EW ~40 eV). The nuclear emission flux was observed to remain constant over the observation. A short archival Chandra observation taken in March 2000 further constrains the hard emission to a point source coincident with the radio nucleus. A point source ~3" southwest of the nucleus does not contribute significantly. Spectral results of the Chandra nuclear source are comparable (within the limited statistics) to the XMM-Newton parameters. The comparison of our iron line upper limit with reported detections indicates variability of the line EW. These results can be explained by the relatively low nuclear absorption of NGC 4258 (which is in the range expected for its intermediate Seyfert type) and some variability of the absorbing material. Reflection components as proposed to explain the large iron line EW of highly absorbed Seyfert 2 galaxies and/or variations in the accretion disk are however imposed by the time variability of the iron line flux.

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arXiv2001

The central region of M31 observed with XMM-Newton. II. Variability of the individual sources

We present the results of a study of the variability of X-ray sources in the central 30' of the nearby Andromeda Galaxy (M31) based on XMM Performance Verification observations. Two observations of this field, with a total exposure time of about 50 ks, were performed in June and December of 2000. We found 116 sources brighter than a limiting luminosity of 6 x 10(35) erg/s (0.3--12 keV, d=760 kpc). For the ~60 brightest sources, we searched for periodic and non-periodic variability; at least 15% of these sources appear to be variable on a time scale of several months. We discovered a new bright transient source ~2.9' from the nucleus in the June observation; this source faded significantly and was no longer detected in December. The behaviour of the object is similar to a handful of Galactic LMXB transients, most of which are supposed to harbor black holes. We detected pulsations with a period of \~865 s from a source with a supersoft spectrum. The flux of this source decreased significantly between the two XMM observations. The detected period is unusually short and points to a rapidly spinning magnetized white dwarf. The high luminosity and transient nature of the source suggest its possible identification with classical or symbiotic nova, some of which were observed earlier as supersoft sources.

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arXiv2001

ROSAT PSPC observations of nearby spiral galaxies - II. Statistical properties

We present a statistical analysis of the largest X-ray survey of nearby spiral galaxies in which diffuse emission has been separated from discrete source contributions. Regression and rank-order correlation analyses are used to compare X-ray properties such as total, source and diffuse luminosities, and diffuse emission temperature, with a variety of physical and multi-wavelength properties, such as galaxy mass, type and activity, and optical and infrared luminosity. The results are discussed in terms of the way in which hot gas and discrete X-ray sources scale with the mass and activity of galaxies, and with the star formation rate. We find that the X-ray properties of starburst galaxies are dependent primarily on their star-forming activity, whilst for more quiescent galaxies, galaxy mass is the more important parameter. One of the most intriguing results is the tight linear scaling between far-infrared and diffuse X-ray luminosity across the sample, even though the hot gas changes from a hydrostatic corona to a free wind across the activity range sampled here.

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arXiv2001

X-ray emission from the Sculptor galaxy NGC 300

We report here the results of a full analysis of all the ROSAT PSPC spectral imaging observations and all the ROSAT HRI high resolution imaging observations of the very nearby (D=2.1 Mpc) Sculptor galaxy, NGC 300. Many point sources are detected within the field, several of them showing evidence for variability, and we present full source lists detailing their X-ray properties, and attempt to classify them on the basis of their temporal, spectral and multi-wavelength characteristics. A black hole X-ray binary candidate, a supersoft source and several supernova remnants and HII regions are detected in X-rays, as is unresolved, possibly diffuse emission, accounting for perhaps 20% of the total NGC 300 X-ray (0.1-2.4 keV) luminosity (5.8 10e38 erg/s). We compare the X-ray source luminosity distribution of NGC 300 with that of other nearby galaxies, and we also compare NGC 300 with its Sculptor neighbours, concluding that it is a quite an unremarkable system, showing no unusual X-ray (or other multi-wavelength) properties. It may be one of the best examples of a completely typical normal quiescent late-type spiral galaxy.

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arXiv2001

The second ROSAT PSPC survey of M31 and the complete ROSAT PSPC source list

This paper reports the results of the analysis of the second ROSAT PSPC survey of M31 performed in summer 1992. We compare our results with those of the first survey. Within the ~10.7 deg^2 field of view, 396 individual X-ray sources are detected in the second survey data, of which 164 are new detections. When combined with the first survey, this result in a total of 560 X-ray sources in the field of M31. Their (0.1 keV - 2.0 keV) fluxes range from 7 x 10^-15 to 7.6 x 10^-12 erg cm^-2 s^-1, and of these 560 sources, 55 are tentatively identified with foreground stars, 33 with globular clusters, 16 with supernova remnants, and 10 with radio sources and galaxies (including M32). A comparison with the results of the Einstein M31 survey reveals 491 newly detected sources, 11 long term variable sources, and 7 possible transient sources. Comparing the two ROSAT surveys, we come up with 34 long term variable sources and 8 transient candidates. For the M31 sources, the observed luminosities range from 4 x 10^35 to 4 x 10^38 erg s^-1. The total (0.1 keV - 2.0 keV) luminosity of M31 is (3.4+-0.3) x 10^39 erg s^-1, distributed approximately equally between the bulge and disk. Within the bulge region, the luminosity of a possible diffuse component combined with faint sources below the detection threshold is (2.0+-0.5) x 10^38 erg s^-1. An explanation in terms of hot gaseous emission leads to a maximum total gas mass of (1.0+-0.3) x 10^6 M_sun.

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arXiv2001

Radio jets and diffuse X-ray emission around the peculiar galaxy pair ESO 295-IG022

We report Australia Telescope Compact Array (ATCA) radio-continuum and ROSAT PSPC X-ray observations of the region surrounding the peculiar galaxy pair ESO 295-IG022, lying at the centre of the poor cluster Abell S0102. We identify a radio galaxy coincident with the galaxy pair, with bipolar, bent radio jets appearing centred on the southern galaxy, and extending both to the south, for about 95 arcseconds (approximately 100 kpc at the distance of ESO 295-IG022), and to the north, for approximately 80 arcseconds, encompassing the northern galaxy. We discuss also the idea of an additional single jet structure from the northern galaxy contributing to the emission. We estimate lower limit jet velocities of at least 1000 km/s, and a relative proper velocity for the southern galaxy through the cluster of around 200 km/s. Diffuse (kT=2.2 keV) X-ray emission consistent with group or poor cluster emission is seen centred on the southern galaxy surrounding the galaxy pair and the associated radio jets. Structure within the radio jets and the X-ray emission is very suggestive of there being some channeling of the radio emission with the surrounding intragroup medium. Another bipolar jet radio galaxy, discovered close by, is likely to be a background object, the optical counterpart having a magnitude greater than m=22.

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arXiv2000

The Extended X-ray Halo of the Crab-like SNR G21.5-0.9

Recent XMM-Newton observations reveal an extended (150") low-surface brightness X-ray halo in the supernova remnant G21.5-0.9. The near circular symmetry, the lack of any limb brightening and the non-thermal spectral form, all favour an interpretation of this outer halo as an extension of the central synchrotron nebula rather than as a shell formed by the supernova blast wave and ejecta. The X-ray spectrum of the nebula exhibits a marked spectral softening with radius, with the power-law spectral index varying from Gamma = 1.63 +/- 0.04 in the core to Gamma = 2.45 +/- 0.06 at the edge of the halo. Similar spectral trends are seen in other Crab-like remnants and reflect the impact of the synchrotron radiation losses on very high energy electrons as they diffuse out from the inner nebula. A preliminary timing analysis provides no evidence for any pulsed X-ray emission from the core of G21.5-0.9.

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arXiv2000

The central region of M31 observed with XMM-Newton (I. Group properties and diffuse emission)

We present the results of a study based on an XMM-Newton Performance Verification observation of the central 30 arcmin of the nearby spiral galaxy M31. In the 34-ks European Photon Imaging Camera (EPIC) exposure, we detect 116 sources down to a limiting luminosity of 6 x 10^35 erg/s (0.3--12 keV, d = 760 kpc). The luminosity distribution of the sources detected with XMM-Newton flattens at luminosities below ~ 2.5 x 10^37 erg/s. We make use of hardness ratios for the detected sources in order to distinguish between classes of objects such as super-soft sources and intrinsically hard or highly absorbed sources. We demonstrate that the spectrum of the unresolved emission in the bulge of M31 contains a soft excess which can be fitted with a ~ 0.35-keV optically-thin thermal-plasma component clearly distinct from the composite point-source spectrum. We suggest that this may represent diffuse gas in the centre of M31, and we illustrate its extent in a wavelet-deconvolved image.

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arXiv2000

XMM-Newton survey of the low-metallicity open cluster NGC 2516

We present the first results of an XMM-Newton EPIC survey of NGC 2516, a southern low-metallicity open cluster with an age close to the Pleiades. The attained limiting sensitivity is of ~ 2.4 10^-15 erg sec^-1} cm^-2 in the 0.1--4.0 keV bandpass. This has been achieved by summing the data of the MOS and PN cameras of two distinct observations for a total exposure time of ~ 33 ks and by analyzing the summed data set with the wavelet detection algorithm developed at Osservatorio Astronomico di Palermo (OAPA) that has yielded over 200 X-ray detections. Using data just from a single exposure or from a single camera would have reduced by a factor 2--4 our limiting sensitivity and would have resulted in 25--40% less X-ray detections. To date, 129 detections have as counterparts one or more of the 540 photometrically selected cluster members in the surveyed region, for a total of 147 likely detected members, with unique identification in 112 cases. We derive the X-ray luminosity functions (XLF) of NGC 2516 members of different spectral types and compare them with those of the more metal rich, approximately coeval Pleiades cluster, finding the NGC 2516 photometrically selected dG and dK stars less luminous than the Pleiades. The XLFs of the NGC 2516 and of the Pleiades dM stars are indistinguishable. We compare the XMM-Newton results with those recently obtained with Chandra.

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arXiv2000

XMM-Newton observations of NGC 253: Resolving the emission components in the disk and nuclear area

The high XMM-Newton throughput allows a detailed investigation of the spatial, spectral and variability properties of the extended and point source emission of the starburst galaxy NGC 253 simultaneously. We characterize the brightest sources by their hardness ratios, detect a bright X-ray transient, and show the spectrum and light curve of the brightest point source, most likely a black-hole X-ray binary. The unresolved emission of two disk regions can be modeled by two thin thermal plasma components of 0.13 and 0.4 keV plus residual harder emission, with the lower temperature component originating from above the disk, the nuclear spectrum by a three temperature plasma (~0.6, 0.9, and 6 keV) with the higher temperatures increasingly absorbed. The high temperature component most likely originates from the starburst nucleus. No non-thermal component, that would point at a significant contribution from an active nucleus (AGN), is needed. Assuming that type IIa supernova remnants (SNRs) are mostly responsible for the E>4 keV emission, the detection with EPIC of the 6.7 keV line allows us to estimate a supernova rate within the nuclear starburst of 0.2 yr^-1. RGS spectra and EPIC images reveal that the limb-brightening of the plume is mostly seen in higher ionization emission lines, while in the lower ionization lines, and below 0.5 keV, the plume is more homogeneously structured. (abridged)

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arXiv1998

ROSAT observations of the Sculptor galaxy NGC7793

We report here the results of spectral imaging observations with the ROSAT PSPC of the field surrounding the very nearby (D=3.38 Mpc) Sculptor galaxy, NGC7793. Many point sources are detected within the field, several of them showing evidence for variability. Seven sources are seen to lie within the optical confines of the system, the brightest (Lx ~ 9x10e38 erg/s), lying to the southern edge of NGC7793. This source, also observed to be variable, is seen now, not to be associated with a z=0.071 redshift QSO, as was previously thought. A number of the other sources within the NGC7793 disc are likely to be due to X-ray binaries, supernova remnants or superbubbles within the galaxy itself. Other sources may be associated with background AGN. In addition to the point source emission, rather uniform unresolved emission is detected in and around NGC7793 extending to a radius of perhaps 4 kpc. This emission is likely to be contaminated to some degree by unresolved point sources, as its temperature (kT~1 keV) is rather hotter than is seen for the diffuse gas components in other nearby spiral galaxies. Comparing the X-ray properties of NGC7793 with those of the remaining Sculptor group members, suggests that it may, in terms of activity, lie somewhere between its quiescent and starburst neighbours.

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arXiv1998

ROSAT observations of the IC4329A galaxy group

We report here the results of high-resolution and spectral imaging X-ray observations, with both the ROSAT HRI and PSPC, of the field surrounding the nearby Seyfert galaxy IC4329A. Many point sources are detected, the brightest being associated with IC4329A itself, having an extremely bright Lx of 6x10e43erg/s, and spectral properties compatible with a single power-law model, with a spectral break at 0.7keV. Two other bright sources are detected associated with the companion galaxy IC4329, and a likely quasar 14' to the south-west. We have also established, through optical observations, that three further X-ray point sources, intriguingly positioned with respect to IC4329A, are in fact nothing to do with the system. In addition to point source emission, residual, unresolved emission is detected surrounding the IC4329A/IC4329 pair, extending for some 200kpc. This emission appears markedly two-component, comprising of a spectrally hard and smooth component, circularly-distributed about the central galaxy pair, and a spectrally soft, more clumpy component, positioned almost entirely to the south-east of IC4329A. The hard component of the residual emission itself appears two-component, one component being due to the `wings' of the intensely bright IC4329A source, the other, apparently due to hot (~1.5keV) gas, likely associated with the galaxy group of which IC4329A and IC4329 are members. The soft component of the residual emission may be a larger version of the superwinds seen around some ultraluminous far-infrared galaxies, or may even represent a `stripped wake' of intragroup gas. Evidence for shocked gas due to the central IC4329A/IC4329 interaction is also found between the two central galaxies.

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arXiv1998

The X-ray Evolution of Merging Galaxies

We present here the first study of the X-ray properties of an evolutionary sample of merging galaxies. Both ROSAT PSPC and HRI data are presented for a sample of eight interacting galaxy systems, each believed to involve a similar encounter between two spiral discs of approximately equal size. The mergers span a large range in age, from completely detached to fully merged systems. A great deal of interesting X-ray structure is seen, and the X-ray properties of each individual system are discussed in detail. Along the merging sequence, several trends are evident: in the case of several of the infrared bright systems, the diffuse emission is very extended, and appears to arise from material ejected from the galaxies. The onset of this process seems to occur very soon after the galaxies first encounter one another, and these ejections soon evolve into distorted flows. More massive extensions (perhaps involving up to 1e10 solar masses of hot gas) are seen at the `ultraluminous' peak of the interaction, as the galactic nuclei coalesce. The amplitude of the evolution of the X-ray emission through a merger is markedly different from that of the infrared and radio emission however, and this, we believe, may well be linked with the large extensions of hot gas observed. The late, relaxed remnants, appear relatively devoid of gas, and possess an X-ray halo very different from that of typical ellipticals, a problem for the `merger hypothesis', whereby the merger of two disc galaxies results in an elliptical galaxy. However, these systems are still relatively young in terms of total merger lifetime, and they may still have a few Gyr of evolution to go through, before they resemble typical elliptical galaxies.

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arXiv1995

EUV Emission from Normal Galaxies

Using data from the ROSAT Wide Field Camera all-sky survey, we have established upper limits to the extreme ultraviolet (EUV) flux from a sample of 30 bright, nearby, non-active spiral galaxies. These galaxies were chosen to be those most likely to be detected in the EUV on the basis of (i) low interstellar absorption within our own galaxy, (ii) brightness in other wavebands, (iii) high star formation activity, and (iv) proximity. The derived EUV upper limits are restrictive, and establish that the EUV flux escaping from galaxies does not contribute a major component of their bolometric luminosity, and in particular that it is very unlikely to be the sink for the energy injected into the interstellar medium by supernova explosions, as had been suggested following the failure to detect this power in the X-ray band.

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