J. P. D. Mittaz

The XMM-Newton optical/UV monitor telescope

The XMM-OM instrument extends the spec- tral coverage of the XMM-Newton observatory into the ul- traviolet and optical range. It provides imaging and time- resolved data on targets simultaneously with observations in the EPIC and RGS. It also has the ability to track stars in its field of view, thus providing an improved post- facto aspect solution for the spacecraft. An overview of the XMM-OM and its operation is given, together with cur- rent information on the performance of the instrument.

The XMM-Newton serendipitous survey - IV. Optical identification of the XMM-Newton medium sensitivity survey (XMS)

Aims. X-ray sources at intermediate fluxes (a few x 10(-14) erg cm(-2) s(-1)) with a sky density of similar to 100 deg(-2) are responsible for a significant fraction of the cosmic X-ray background at various energies below 10 keV. The aim of this paper is to provide an unbiased and quantitative description of the X-ray source population at these fluxes and in various X-ray energy bands. Methods. We present the XMM-Newton Medium sensitivity Survey (XMS), including a total of 318 X-ray sources found among the serendipitous content of 25 XMM-Newton target fields. The XMS comprises four largely overlapping source samples selected at soft (0.5-2 keV), intermediate (0.5-4.5 keV), hard (2-10 keV) and ultra-hard (4.5-7.5 keV) bands, the first three of them being flux-limited. Results. We report on the optical identification of the XMS samples, complete to 85-95%. At the flux levels sampled by the XMS we find that the X-ray sky is largely dominated by Active Galactic Nuclei. The fraction of stars in soft X-ray selected samples is below 10%, and only a few per cent for hard selected samples. We find that the fraction of optically obscured objects in the AGN population stays constant at around 15-20% for soft and intermediate band selected X-ray sources, over 2 decades of flux. The fraction of obscured objects amongst the AGN population is larger (similar to 35-45%) in the hard or ultra-hard selected samples, and constant across a similarly wide flux range. The distribution in X-ray-to-optical flux ratio is a strong function of the selection band, with a larger fraction of sources with high values in hard selected samples. Sources with X-ray-to-optical flux ratios in excess of 10 are dominated by obscured AGN, but with a significant contribution from unobscured AGN.

The XMM-Newton Serendipitous Survey - I. The role of XMM-Newton Survey Science Centre

This paper describes the performance of XMM-Newton for serendipitous surveys and summarises the scope and potential of the XMM-Newton Serendipitous Survey. The role of the Survey Science Centre (SSC) in the XMM-Newton project is outlined. The SSCs follow-up and identification programme for the XMM-Newton serendipitous survey is described together with the presentation of some of the first results.

Submillimeter Evidence for the Coeval Growth of Massive Black Holes and Galaxy Bulges

The correlation, found in nearby galaxies, between black hole mass and stellar bulge mass implies that the formation of these two components must be related. Here we report submillimeter photometry of eight x-ray–absorbed active galactic nuclei that have luminosities and redshifts characteristic of the sources that produce the bulk of the accretion luminosity in the universe. The four sources with the highest redshifts are detected at 850 micrometers, with flux densities between 5.9 and 10.1 millijanskies, and hence are ultraluminous infrared galaxies. If the emission is from dust heated by starbursts, then the majority of stars in spheroids were formed at the same time as their central black holes built up most of their mass by accretion. This would account for the observed demography of massive black holes in the local universe. The skewed rate of submillimeter detection with redshift is consistent with a high redshift epoch of star formation in radio-quiet active galactic nuclei, similar to that seen in radio galaxies.

A survey of hard spectrum ROSAT sources – II. Optical identification of hard sources

We have surveyed 188 ROSAT PSPC fields for X–ray sources with hard spectra (� 1) identified hard sources have broad lines.

The luminosity function evolution of soft X-ray-selected active galactic nuclei in the RIXOS survey

A sample of 198 soft X-ray-selected active galactic nuclei (AGN) from the ROSAT International X-ray Optical Survey (RIXOS) is used to investigate the X-ray luminosity function and its evolution. RIXOS, with a flux limit of 3 x 10(-14) erg s(-1) cm(-2) (0.5 to 2.0 keV), samples a broad range in redshift over 20 deg(2) of sky, and is almost completely identified; it is used in combination wtih the Einstein Extended Medium Sensitivity Survey (EMSS) to give a total sample of over 600 AGN. We find the evolution of AGN with redshift to be consistent with pure luminosity evolution (PLE) models in which the evolution slows markedly or stops at high redshifts (z > 1.8). We find that this result is not affected by the inclusion, or exclusion, of narrow-emission-line galaxies at low redshift in the RIXOS and EMSS samples, and is insensitive to uncertainties in the conversion between flux values measured with ROSAT and Einstein. We confirm, using a model-independent [V-e/V-a] test, that our survey is consistent with no evolution at high redshifts.

UV observations of the galaxy cluster Abell 1795 with the optical monitor on XMM-Newton

We present the results of an analysis of broad band UV observations of the central regions of Abell 1795 observed with the optical monitor on XMM-Newton. As have been found with other UV observations of the central regions of clusters of galaxies, we find evidence for star formation. However, we also find evidence for absorption in the cD galaxy on a more extended scale than has been seen with optical imaging. We also report the first UV observation of part of the filamentary structure seen in H-alpha, X-rays and very deep U band imaging. The part of the filament we see is very blue with UV colours consistent with a very early (O/B) stellar population. This is the first direct evidence of a dominant population of early type stars at the centre of Abell 1795 and implies very recent star formation. The relationship of this emission to emission at other wavebands is discussed.

A survey of hard spectrum ROSAT sources – I. X‐ray source catalogue

We present a catalogue of 147 serendipitous X-ray sources selected to have hard spectra (alpha 10(-14) erg cm(-2) s(-1). If their N(S) continues to fainter fluxes, the hard sources will comprise similar to 40 per cent of sources with 5x10(-15)<S < 10(-14) erg cm(-2) s(-1). The population of hard sources can therefore account for the harder average spectra of ROSAT sources with S < 10(-14) erg cm(-2) s(-1). They probably make a strong contribution to the X-ray background at faint fluxes and could be the solution to the X-ray background spectral paradox.

Soft X-ray spectral variations of the narrow-line Seyfert 1 galaxy Markarian 766

The X-ray variability of the narrow-line Seyfert 1 galaxy Markarian 766 is studied using nine ROSAT PSPC data sets. The spectrum is well described by a power law combined with a blackbody (kT ∼ 70 eV) soft excess. Examination of flux ratio changes and variability amplitude in three X-ray bands shows that the power-law component varies continuously on time-scales of ∼ 5000 s and is steeper when it is brighter. In contrast, variability of the soft excess is not detected. Spectral modelling of 31 spectra from different observations and at a range of count rates is also consistent with a picture in which the power law is steeper when it is brighter, and in which the soft-excess component does not vary. The power-law variability can be explained if the power law is produced by variable thermal or non-thermal Comptonization of soft photons. This behaviour is similar to that of Galactic black hole candidates in the low state. The X-ray and multiwavelength properties of Markarian 766 are shown to be very similar to those of other narrow-line Seyfert 1s. This may mean that the rapid X-ray variability seen in other narrow-line Seyfert 1s may also not originate in their strong soft-excess components.

XMM-Newton spectra of hard spectrum Rosat AGN: X-ray absorption and optical reddening

We present the XMM-Newton spectra of three low-redshift intermediate Seyferts (one S y1.5, and two Sy1.8), from our survey of hard spectrum Rosat sources. The three AGN are well fitted by absorbed powerlaws, with intrinsic nuclear photo- electric absorption from column densities between 1.3 and 4.0×10 21 cm −2 . In the brightest object the X-ray spectrum is good enough to show that the absorber is not significantly ionized . For all three objects the powerlaw slopes appear to be somewhat flatter ( ∼ 1.3− 1.6) than those found in typical unabsorbed Seyferts. The constraints from optical and X-ray emission lines imply that all three objects are Compton-thin. For the two fainter objects, the reddening deduced from the optical broad emis- sion lines in one of them, and the optical continuum in the other, are similar to those expected from the X-ray absorption, if we assume a Galactic gas-to-dust ratio and reddening curve. The broad line region Balmer decrement of our brightest object is larger than expected from its X-ray absorption, which can be explained either by an intrinsic Balmer decrement with standard gas-to-dust ratio, or by a>Galactic gas-to-dust ratio. These≥ Galactic ratios of extinction to photoelectric absorption cannot ex- tend to the high redshift, high luminosity, broad line AGN in our sample, because they have column densities> 10 22 cm −2 , and so their broad line regions would be totally obscured. This means that some effect (e.g., luminosity dependence, or evolution) needs to be present in order to explain the whole population of absorbed AGN.