arXiv subjects

M. J. Page

Publications and source records attributed to M. J. Page.

At least 199 records · Page 11Linked to original sources

arXiv2006

The XMM-Newton RGS spectrum of the high luminosity Seyfert 1 galaxy Markarian 509

We present a detailed analysis of the soft X-ray spectrum of the Seyfert 1 galaxy Markarian 509 taken with the XMM-Newton Reflection Grating Spectrometer. An underlying power-law continuum and three warm absorber phases provide a good fit to the data along with a number of broad and narrow emission lines. Our three warm absorber phases each have different ionization parameters and column densities. We identify a low ionization, log xi=0.89, high outflow velocity phase producing an Fe M-shell UTA feature along with absorption from O VI and N VI. There is an intermediate phase, log xi=2.14, showing absorption from H-like carbon and nitrogen and He-like neon and oxygen. The third, high ionization, log xi=3.26, low outflow velocity phase contains absorption from O VIII, Ne X and highly ionized iron. All phases are blueshifted with respect to the systemic velocity with flow velocities ranging from -60km/s to -510km/s. The observed broad emission features have an RMS velocity of ~8000km/s for the C VI and O VII lines.

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arXiv2006

Optical, Infrared, and Ultraviolet Observations of the X-Ray Flash GRB 050416A

We present ultraviolet, optical, and infrared photometry of the afterglow of the X-ray flash XRF 050416A taken between approximately 100 seconds and 36 days after the burst. We find an intrinsic spectral slope between 1930 and 22,200 Angstrom of beta = -1.14 +/- 0.20 and a decay rate of alpha = -0.86 +/- 0.15. There is no evidence for a change in the decay rate between approximately 0.7 and 4.7 days after the burst. Our data implies that there is no spectral break between the optical and X-ray bands between 0.7 and 4.7 days after the burst, and is consistent with the cooling break being redward of the K_s band (22,200 Angstrom) at 0.7 days. The combined ultraviolet/optical/infrared spectral energy distribution shows no evidence for a significant amount of extinction in the host galaxy along the line of sight to XRF 050416A. Our data suggest that the extragalactic extinction along the line of sight to the burst is only approximately A_V = 0.2 mag, which is significantly less than the extinction expected from the hydrogen column density inferred from $X$-ray observations of XRF 050416A assuming a dust-to-gas ratio similar to what is found for the Milky Way. The observed extinction, however, is consistent with the dust-to-gas ratio seen in the Small Magellanic Cloud. We suggest that XRF 050416A may have a two-component jet similar to what has been proposed for GRB 030329. If this is the case the lack of an observed jet break between 0.7 and 42 days is an illusion due to emission from the wide jet dominating the afterglow after approximately 1.5 days.

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arXiv2006

The SCUBA HAlf Degree Extragalactic Survey (SHADES) -- II. Submillimetre maps, catalogue and number counts

We present the maps, source catalogue and number counts of the largest, most complete and unbiased extragalactic submillimetre survey ever undertaken: the 850-micron SCUBA HAlf Degree Extragalactic Survey (SHADES). Using the Submillimetre Common-User Bolometer Array (SCUBA) on the James Clerk Maxwell Telescope (JCMT), SHADES mapped two separate regions of sky: the Subaru/XMM-Newton Deep Field (SXDF) and the Lockman Hole East (LH). These SCUBA maps cover 720 square arcmin with an RMS noise level of about 2 mJy and have uncovered >100 submillimetre galaxies. In order to ensure the utmost robustness of the resulting source catalogue, data reduction was independently carried out by four sub-groups drawn within the SHADES team, providing an unprecedented degree of reliability with respect to other SCUBA catalogues available from the literature. Individual source lists from the four groups were combined to produce a robust 120-object SHADES catalogue; an invaluable resource for follow-up campaigns aiming to study the properties of a complete and consistent sample of submillimetre galaxies. We present differential and integral source number counts of submillimetre galaxies and find that the differential counts are better fit with a broken power-law or a Schechter function than with a single power-law; the SHADES data alone significantly show that a break is required at several mJy, although the precise position of the break is not well constrained. We also find that an 850-micron survey complete down to 2 mJy would resolve 20-30 per cent of the Far-IR background into point sources. [abridged]

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arXiv2006

Galaxy clusters at 0.6 < z < 1.4 in the UKIDSS Ultra Deep Survey Early Data Release

We present the first cluster catalogue extracted from the UKIRT Infrared Deep Sky Survey Early Data Release. The catalogue is created using UKIDSS Ultra Deep Survey infrared J and K data combined with 3.6 micro-m and 4.5 micro-m Spitzer bands and optical BVRi'z' imaging from the Subaru Telescope over 0.5 square degrees in the Subaru XMM-Newton Deep Field. We have created a new cluster-detection algorithm, based on the Friends-Of-Friends and Voronoi Tessellation methods, which utilises probability distribution functions derived from a photometric redshift analysis. We employ mock catalogues to understand the selection effects and contamination associated with the algorithm. The cluster catalogue contains 13 clusters at redshifts 0.61 <= z <= 1.39 with luminosities 10 L* <~ L_tot <~ 50 L*, corresponding to masses 5 x 10^13 M_sun <~ M_cluster <~ 3 x 10^14 M_sun for (M/M_sun) / (L/L_sun) = 75h. The measured sky surface density of ~ 10 deg^-2 for high-redshift (z=0.5-1.5), massive (>10^14 M_sun) clusters is precisely in line with theoretical predictions presented by Kneissl et al. (2001).

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arXiv2006

The distribution of absorption in AGN detected in the XMM-Newton observations of the CDFS

We have used very deep XMM-Newton observations of the Chandra Deep Field-South to examine the spectral properties of the faint active galactic nucleus (AGN) population. Crucially, redshift measurements are available for 84% (259/309) of the XMM-Newton sample. We have calculated the absorption and intrinsic luminosities of the sample using an extensive Monte Carlo technique incorporating the specifics of the XMM-Newton observations. Twenty-three sources are found to have substantial absorption and intrinsic X-ray luminosities greater than 10^44 erg/s, putting them in the "type-2" QSO regime. We compare the redshift, luminosity and absorption distributions of our sample to the predictions of a range of AGN population models. In contrast to recent findings from ultra-deep Chandra surveys, we find that there is little evidence that the absorption distribution is dependent on either redshift or intrinsic X-ray luminosity. The pattern of absorption in our sample is best reproduced by models in which ~75% of the AGN population is heavily absorbed at all luminosities and redshifts.

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arXiv2006

The discovery of a significant sample of massive galaxies at redshifts 5 < z < 6 in the UKIDSS Ultra Deep Survey Early Data Release

We have exploited the large area coverage of the combined UKIDSS Ultra Deep Survey (UDS) and Subaru/XMM-Newton Deep Survey (SXDS) to search for bright Lyman-break galaxies (LBGs) at z >= 5. Using the available optical+near-infrared photometry to efficiently exclude low-redshift contaminants, we identify nine z >= 5 LBG candidates brighter than z'=25(AB) within the 0.6 square degree overlap region between the UDS early data release (EDR) and the optical coverage of the SXDS. Accounting for selection incompleteness, we estimate the corresponding surface density of z >= 5 LBGs with z'<=25(AB) to be 0.005+/-0.002 per square arcmin. Modelling of the optical+near-infrared photometry constrains the candidates' redshifts to lie in the range 5.1 < z < 5.9, and provides estimates for their stellar masses. Although the stellar mass estimates are individually uncertain, a stacking analysis suggests that the typical stellar mass of the LBG candidates is >~5x10^10 Msun which, if confirmed, places them amongst the most massive galaxies currently known at z >= 5. It is found that Lambda CDM structure formation can produce sufficient numbers of dark matter halos at z >= 5 to accommodate our estimated number density of massive LBGs for plausible values of sigma_8 and the ratio of stellar to dark matter. Moreover, it is found that recent galaxy formation models can also account for the existence of such massive galaxies at z >= 5. Finally, no evidence is found for the existence of LBGs with stellar masses in excess of ~3x10^11 Msun at this epoch, despite the large co-moving volume surveyed.

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arXiv2006

Anatomy of A Dark Burst - The Afterglow of GRB 060108

We report the first detection of an optical afterglow of a GRB (060108) that would have been classified as 'dark' in the absence of deep, rapid ground-based optical imaging with the 2-m robotic Faulkes Telesscope (FTN). Our multiwavelength analysis reveals an X-ray light curve typical of many Swift long GRBs (3-segments plus flare). Its optical afterglow, however, was already fainter than the detection limit of the UVOT within 100s of the burst. Optical imaging in BVRi' filters with the FTN began 2.75 minutes after the burst and resulted in the detection of the optical afterglow at 5.3 minutes, with a UKIRT K-band identification at ~45 mins. R and i'-band light curves are consistent with a single power law decay in flux, F(t) prop t^-a where a=0.43+/-0.08, or a 2-segment light curve with a steep decay a_1 <0.88, flattening to a_2 ~ 0.31, with evidence for rebrightening at i' band. Deep VLT R-band imaging at ~12 days reveals a faint, extended object (R ~23.5 mag) at the location of the afterglow. Although the brightness is compatible with the extrapolation of the a_2 slow decay, significant flux is likely due to a host galaxy. This implies that the optical light curve had a break before 12 days, akin to what observed in the X-rays. We derive a maximum photometric redshift z<3.2 for GRB 060108 and a best-fitting optical-to-X-ray SED at 1000 s after the burst consistent with a power law with index beta_OX = 0.54 and a small amount of extinction. The unambiguous detection at B-band and the derived photometric redshift rule out a high redshift as the reason for the optical faintness of GRB 060108. Instead, the hard opt/X-ray spectral index confirms it as one of the optically-darkest bursts detected and with modest host extinction explains the UVOT non-detection (abridged).

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arXiv2006

Swift observations of GRB050712

We present the results of X-ray and optical observations of GRB050712 performed by Swift. The X-ray lightcurve of this burst exhibits episodes of flares in the first 1000s, the same epoch at which the UVOT detected an optical counterpart. A shallow X-ray decay, with a decay slope of -0.73, followed and lasted ~70ks. This behaviour can be explained in terms of activity of GRB 'inner engine', with the possibility of that the last flare is caused by the interaction of the ejecta with the surrounding medium. We also find interesting spectral parameters for the X-ray emission. In particular, data suggest the presence of an intrinsic absorption in the first 1000s, which can be explained if circumbust medium clouds lie along the line of sight.

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arXiv2006

X-ray spectra of sources in the 13H XMM-Newton / Chandra deep field

We present the X-ray spectra of 86 optically-identified sources in the 13H XMM-Newton/Chandra deep field which have >70 X-ray counts. The sample consists of 50 broad line AGN, 25 narrow emission line galaxies, 6 absorption line galaxies, and 5 Galactic stars. The majority (42/50) of the broad line AGN have X-ray spectra which are consistent with a power law shape. They have a mean photon index of Gamma = 2.0 +- 0.1 and an intrinsic dispersion sigma = 0.4 +- 0.1. Five BLAGN show a deficit of soft X-rays, indicating absorption. Significant absorption is more common in the narrow emission line galaxies (13/25) and absorption line galaxies (2/6) than in the broad line AGN (5/50), but is not universal in any of these classes of object. The majority of the 20 absorbed sources have X-ray spectra consistent with a simple cold photoelectric absorber, but 6/20 require more complex models with either an additional component of soft X-ray emitting plasma, or an ionised absorber. Of the 16 galaxies which do not show evidence for X-ray absorption, only 2 objects are likely to be powered by star formation, and both have 2-10 keV X-ray luminosities of <= 10^40 cgs. The X-ray emission in the other 14 unabsorbed NELGs and galaxies is most likely powered by AGN, which are not detected in the optical because they are outshone by their luminous host galaxies. The Galactic stars show multi-temperature thermal spectra which peak between 0.5 and 1 keV. Star/AGN discrimination is possible for 4 of the 5 stars solely from their X-ray spectra.

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arXiv2006

Swift-UVOT Observations of the X-Ray Flash 050406

We present Swift-UVOT data on the optical afterglow of the X-ray flash of 2005 April 6 (XRF 050406) from 88s to \sim 10^5s after the initial prompt gamma-ray emission. Our observations in the V, B and U bands are the earliest that have been taken of an XRF optical counterpart. Combining the early -time optical temporal and spectral properties with γ- and simultaneous X-ray data taken with the BAT and XRT telescopes on-board Swift, we are able to constrain possible origins of the XRF. The prompt emission had a FRED profile (fast-rise, exponential decay) with a duration of T_90 = 5.7\pm 0.2s, putting it at the short end of the long-burst duration distribution. The absence of photoelectric absorption red-ward of 4000 Åin the UV/optical spectrum provides a firm upper limit of z\leq 3.1 on the redshift, thus excluding a high redshift as the sole reason for the soft spectrum. The optical light curve is consistent with a power-law decay with slope alpha = -0.75\pm 0.26 (F_ν\propto t^α), and a maximum occurring in the first 200s after the initial gamma-ray emission. The softness of the prompt emission is well described by an off-axis structured jet model, which is able to account for the early peak flux and shallow decay observed in the optical and X-ray bands.

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arXiv2006

An X-ray bright ERO hosting a type 2 QSO

We present the XMM-Newton and the optical-VLT spectra along with the optical and the near-infrared photometric data of one of the brightest X-ray (F(2-10 keV)~1e-13 erg/s cm^2) extremely red objects (R-K>=5) discovered so far. The source, XBSJ0216-0435, belongs to the XMM-Newton Bright Serendipitous Survey and it has extreme X-ray-to-optical (~220) and X-ray-to-near-infrared (~60) flux ratios. Thanks to its brightness, the X-ray statistics are good enough for an accurate spectral analysis by which the presence of an X-ray obscured (NH>1e22 cm^-2) QSO (L(2-10 keV)=4e45 erg/s) is determined. A statistically significant (~99%) excess around 2 keV in the observed-frame suggests the presence of an emission line. By assuming that this feature corresponds to the iron Kalpha line at 6.4 keV, a first estimate of the redshift of the source is derived (z_x~2). The presence of a high redshift QSO2 has been finally confirmed through dedicated VLT optical spectroscopic observations (z_o=1.985+/-0.002). This result yields to an optical validation of a new X-ray Line Emitting Object (XLEO) for which the redshift has been firstly derived from the X-ray data. XBSJ0216-0435 can be considered one of the few examples of X-ray obscured QSO2 at high redshift for which a detailed X-ray and optical spectral analysis has been possible. The spectral energy distribution from radio to X-rays is also presented. Finally from the near-infrared data the luminosity and the stellar mass of the host galaxy has been estimated finding a new example of the coexistence at high-z between massive galaxies and powerful QSOs.

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arXiv2005

The nature of X-ray absorbed starburst QSOs and the QSO evolutionary scheme

In contradiction to the simple AGN unification schemes, there exists a significant population of broad line, z~2 QSOs which have heavily absorbed X-ray spectra. These objects have luminosities and redshifts characteristic of the sources that produce the bulk of the QSO luminosity in the universe. Our follow up observations in the submillimetre show that these QSOs are embedded in ultraluminous starburst galaxies, unlike most unabsorbed QSOs at the same redshifts and luminosities. The radically different star formation properties between the absorbed and unabsorbed QSOs implies that the X-ray absorption is unrelated to the torus invoked in AGN unification schemes. The most puzzling question about these objects is the nature of the X-ray absorber. We present our study of the X-ray absorbers based on deep (50-100ks) XMM-Newton spectroscopy. The hypothesis of a normal QSO continuum, coupled with a neutral absorber is strongly rejected. We consider the alternative hypotheses for the absorber, originating either in the QSO or in the surrounding starburst. Finally we discuss the implications for QSO/host galaxy formation, in terms of an evolutionary sequence of star formation and black hole growth. We propose that both processes occur simultaneously in the gas-and-dust-rich heavily obscured centres of young galaxies, and that absorbed QSOs form a transitional stage, between the main obscured growth phase, and the luminous QSO.

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arXiv2005

XMM-Newton observations of the Seyfert 1 AGN H0557-385

We present XMM-Newton observations of the Seyfert 1 AGN H0557-385. We have conducted a study into the warm absorber present in this source, and using high-resolution RGS data we find that the absorption can be characterised by two phases: a phase with log ionisation parameter xi of 0.50 (where xi is in units of ergs cm/s) and a column of 0.2e21 cm^-2, and a phase with log xi of 1.62 and a column of 1.3e22 cm^-2. An iron K alpha line is detected. Neutral absorption is also present in the source, and we discuss possible origins for this. On the assumption that the ionised absorbers originate as an outflow from the inner edge of the torus, we use a new method for finding the volume filling factor. Both phases of H0557-385 have small volume filling factors (< 1%). We also derive the volume filling factors for a sample of 23 AGN using this assumption and for the absorbers with log xi > 0.7 we find reasonable agreement with the filling factors obtained through the alternative method of equating the momentum flow of the absorbers to the momentum loss of the radiation field. By comparing the filling factors obtained by the two methods, we infer that some absorbers with log xi < 0.7 occur at significantly larger distances from the nucleus than the inner edge of the torus.

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arXiv2005

Prompt optical observations of GRB050319 with the Swift UVOT

The UVOT telescope on the Swift observatory has detected optical afterglow emission from GRB 050319. The flux declines with a power law slope of alpha = -0.57 between the start of observations some 230 seconds after the burst onset (90s after the burst trigger) until it faded below the sensitivity threshold of the instrument after ~5 x 10^4s. There is no evidence for the rapidly declining component in the early light curve that is seen at the same time in the X-ray band. The afterglow is not detected in UVOT shortward of the B-band, suggesting a redshift of about 3.5. The optical V-band emission lies on the extension of the X-ray spectrum, with an optical to X-ray slope of beta = -0.8. The relatively flat decay rate of the burst suggests that the central engine continues to inject energy into the fireball for as long as a few x 10^4s after the burst.

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arXiv2005

Principal component analysis of the X-ray variability in NGC 7469

We apply Principal Component Analysis (PCA) to study the variability of the X-ray continuum in the Seyfert 1 galaxy NGC 7469. The PCA technique is used to separate out linear components contributing to variability between multiple datasets; the technique is often used in analysis of optical spectra, but has rarely been applied to AGN X-ray spectroscopy. Running a PCA algorithm on 0.3-10 keV EPIC data from a 150 ks XMM-Newton observation of NGC 7469, we describe the spectral components extracted and evaluate the usefulness of the PCA technique for understanding the X-ray continuum in AGN.

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arXiv2005

High spatial resolution mapping of extinction in the SMC with the Swift-UVOT

The wide range of UV extinction properties in the Small Magellanic Cloud (SMC) probably traces the effects of star formation on interstellar dust. The Swift UVOT, with its three UV filters (centred at 1800, 2200 and 2500 A respectively) and three optical filters, is an ideal instrument to map this extinction. We present preliminary results of six-band photometry in a ~ 3.3 arcminute square field in the SMC. Fitting the resulting optical/UV spectral distributions with a dust model, we estimate the depths of extinction for 53 stars and use this to map the distribution of dust in the observed field. We briefly discuss the relevance of this study for star forming galaxies, including the hosts of Gamma-Ray Bursts.

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arXiv2005

Probing the birth of the first quasars with the future far infrared mission

It is now widely recognised that massive black holes must have had a fundamental influence on the formation of galaxies and vice versa. With current and imminent missions we aim to unravel much of this relationship for the last 10 Gyr of cosmic history, while the quasar population waned and star formation died down. The picture at earlier times will be more difficult to reconstruct, but will likely be even more exciting: when the first stars shone, the first dust was formed, and quasars were a vigorously rising population. One of the primary goals of XEUS is to allow us to find and study the earliest quasars, however deeply buried in gas and dust they may be. But to understand fully the astrophysical context of these objects, their significance in the grand picture, we must learn how they relate to their environments and their host galaxies. The ESA future Far-InfraRed Mission (FIRM) will provide much of the data we require, revealing the dust heated by star formation in the host galaxy, the relative evolutionary stages of spheroid and black hole, and the total energy budgets posessed by these first quasars. FIRM will reveal star formation in the immediate proto-cluster environment of the quasar and so tell us how the formation of the first galaxies and quasars coupled to the earliest large scale structures.

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arXiv2005

XMM-Newton 13H Deep field - I. X-ray sources

We present the results of a deep X-ray survey conducted with XMM-Newton, centred on the UK ROSAT 13H deep field area. This region covers 0.18 deg^2 and is the first of two areas covered with XMM-Newton as part of an extensive multi-wavelength survey designed to study the nature and evolution of the faint X-ray source population. We have produced detailed Monte-Carlo simulations to obtain a quantitative characterisation of the source detection procedure and to assess the reliability of the resultant sourcelist. We use the simulations to establish a likelihood threshold above which we expect less than 7 (3%) of our sources to be spurious. We present the final catalogue of 225 sources. Within the central 9 arcmin, 68 per cent of source positions are accurate to 2 arcsec, making optical follow-up relatively straightforward. We construct the N(>S) relation in four energy bands: 0.2-0.5 keV, 0.5-2 keV, 2-5 keV and 5-10 keV. In all but our highest energy band we find that the source counts can be represented by a double powerlaw with a bright end slope consistent with the Euclidean case and a break around 10^-14 cgs. Below this flux the counts exhibit a flattening. Our source counts reach densities of 700, 1300, 900 and 300 deg^-2 at fluxes of 4.1x10^-16, 4.5x10^-16, 1.1x10^-15 and 5.3x10^-15 cgs in the 0.2-0.5, 0.5-2, 2-5 and 5-10 keV energy bands respectively. We have compared our source counts with those in the two Chandra deep fields and Lockman hole and find our source counts to be amongst the highest of these fields in all energy bands. We resolve >51% (>50%) of the X-ray background emission in the 1-2 keV (2-5 keV) energy bands.

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