XMM-Newton Observation of the Lockman Hole

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Performance Verification. The X-ray data reduction and The dataset, the cleaning procedure used, the source analysis (restricted to sources within a 10 arcmin radius) detection and the astrometric corrections are described in was reported in Paper I where it was demonstrated that details in Paper I. the different populations of X-ray sources are well sep- In this work, we use a sample of 192 sources with a arated in X-ray spectral diagnostics based on hardness likelihood value > 10 (corresponding to ∼ 4σ; see Paper ratios. The extensive optical follow-up programs of this I), and extend the analysis to the whole Lockman Hole field (Lehmann et al. 2001a, and references therein) pro- field of view (in Paper I only sources with off-axis angle vide an understanding of the physical nature of the X-ray < 10′ were considered). The flux limits of this sample in sources. The point sources detected in the soft band by the [0.5-2], [2-10] and [5-10] keV bands are 0.31, 1.4 and ROSAT are predominantly unobscured (in both optical 2.4 × 10−15 erg cm−2 s−1, respectively. We have used only and X-ray bands) AGN spanning a wide redshift range. EPIC-pn data in this work. We restrict the X-ray spec- In the XMM-Newton sample, there is a significant frac- tral analysis to sources with more than 70 counts in the tion of sources with hard spectra. This new population is [0.5-7] keV band after background subtraction, for which most probably dominated by intrinsically absorbed AGN. a reasonable parameter fit can be obtained. This defines This assumption can be tested using the available optical a sample of 98 sources, of which 76 within an off-axis an- spectra and, more efficently, by X-ray spectral study. gle of 10′. The full sample includes 38 Type-1 AGN, 15 To this aim, we have performed an X-ray spectral anal- Type-2 AGN, 34 unidentified sources (mostly newly de- ysis of the sources in the Lockman Hole to understand tected XMM-Newton sources), four extended sources, two their physical nature combining the X-ray data with the normal galaxies and five stars. optical/near IR information. We also use the subsample with redshift identification to check the validity of our 2.2. The X-ray source catalogue conclusions concerning the specific properties of the obscured AGN population. Preliminary results of this work The catalogue of the 98 X-ray sources studied here is were reported by Mainieri et al. (2002). given in Table 2. We report in the first two columns In the following we will refer to Type-1 (broad and narrow the source number and the ROSAT number (if any); emission lines) and Type-2 AGN (high ionization narrow in the third column the classification scheme (see emission lines) using the optical spectroscopic classifica- Schmidt et al. 1998): 1=Type-1 AGN, 2=Type-2 AGN, tion. 3=galaxy, 4=group/cluster of galaxies, 5=star, 9=uniden- The observations are presented in Sect. 2. The results tified source; in columns 4 and 5 the X-ray source coordi- of the spectral analysis are described in Sect. 3, in partic- nates (J2000). Off-axis angles and observed counts in the ular the range of the X-ray spectral index, the observed [0.5-7] keV band are reported in columns 6 and 7. The NH distribution and colour-colour diagnostics diagrams. X-ray flux is given in three different bands : [0.5-2], [2-10] The optical/near IR properties are discussed in Sect. 4 and [5-10] keV (see Table 2 in Paper I for the energy con- together with a comparison with QSO and galaxy evolu- version factors in the different bands). Cols. 11, 12 and ′ ′ tionary tracks. The search for relations between X-ray and 13 give the R and K magnitudes, and R−K colour re- optical/near IR fluxes is presented in Sect. 5. The effect spectively. In column 14, we give the redshift based on of the absorbing column density on the X-ray luminos- low-resolution Keck spectra. The column density, log(NH) ity and the Type-2 QSO candidates are discussed in Sect. (in excess to the galactic ones), and the spectral index Γ 6. Representative spectra of the different classes of X-ray as measured from spectral fitting are reported in columns sources are given in Sect. 7. Finally, our conclusions are 15 and 16. The errors correspond to 90% confidence level outlined in Sect. 8. for one interesting parameter (∆χ2 =2.706). The last two columns give the absorbed X-ray luminosities, which are derived from the X-ray spectra in the rest-frame bands: [0.5-2] and [2-10] keV. We assume a critical density uni- −1 −1 2. X-ray observations verse with H0 =50 km s Mpc and Λ = 0. 2.1. Sample definition

The X-ray results reported in this paper are obtained from 3. Spectral analysis the XMM observation of the Lockman Hole field, centered 3.1. Spectra extraction on the sky position RA 10:52:43, DEC +57:28:48 (J2000). This is a region of extremely low Galactic Hydrogen col- The purpose of this work is to perform an X-ray spec- 19 −2 umn density, NH =5.7×10 cm (Lockman et al. 1986). tral analysis of the sources in the Lockman Hole field, The observation was performed in five separate revolutions taking advantage of the large collecting area of the XMM- (70, 71, 73, 74 and 81) during the period April 27-May 19, Newton satellite. This represent a step forward respect to 2000 for a total exposure time of 190 ksec. Due to peri- the hardness ratios diagnostic diagrams and stacking tech- ods of high background and flares, the good time intervals niques (Tozzi et al. 2001; Alexander et al. 2001a) in which added up to approximately 100 ksec. the range of source redshifts will smear out the signature V. Mainieri et al.: XMM-Newton observation of the Lockman Hole 3

Fig. 1. The power-law photon index (Γ) versus log(NH). Fig. 2. Intrinsic NH distribution for sources inside an off- Filled circles show the Type-1 AGN spectroscopically axis angle of 10′ with more than 70 counts in the [0.5-7] identified in the ROSAT ultradeep HRI survey (Lehmann keV band. The shaded part indicates the sources without et al. 2001a) and in the on-going optical follow-up of redshift, for which the measured NH value represents a the newly detected XMM-Newton sources (PI: Maarten lower limit. Schmidt), open circles are Type-2 AGN, crosses are three still unidentified objects for which we have photometric 3.2. Spectral parameters redshift estimations (Lehmann et al. 2001a). The his- togram shows the spectral index distribution (shaded We use XSPEC (v11.1) for the spectral fitting analysis. As area). For both parameters, error bars correspond to 90% a first approximation, a powerlaw model with an intrin- confidence level for one interesting parameter (∆χ2 = sic absorption (wabs or zwabs if the redshift is known) is 2.706). used. An additional photoelectric absorption component (wabs) fixed to the Galactic column density is also in- cluded in the model. This fit yields the power-law photon index Γ, the of absorption and other X-ray spectral features (e.g., the intrinsic column density N , and the X-ray luminos- iron Kα line). H ity in the [0.5-2] and [2-10] keV rest-frame bands. A We use an automated procedure to extract the X-ray clear soft excess is present in several sources (especially spectra of the 98 sources. Firstly, a source catalog is con- the absorbed ones). In order to reproduce this feature structed using the SAS detection algorithm (see Paper I we add two separate components to the baseline model for details on the detection process). We then perform (wabs∗zwabs∗powerlaw): a blackbody or an extra power- the source detection using SExtractor (Bertin et al. 1996) law. Extra parameters measured from this composite fit on the same image ([0.5-7] keV band). SExtractor yields (second power-law index or blackbody temperature) are shape elliptical parameters for each source (the semi- not reported in Table 21. major/minor axes and the orientation angle) which are In Fig. 1, we plot Γ versus the column density NH for added to the main SAS catalog by cross-correlating the the sources with known redshifts. This diagram suggests two source lists. that the intrinsic slope of the X-ray spectrum is the same Elliptical parameters for each source are used to define for all the objects whatever the absorption levels, with the appropriate region for the extraction of the spectrum, hΓi ≃ 2. Therefore the increasing hardness of the source thus taking into account the broadening of the PSF at spectra at fainter fluxes observed in the Chandra deep increasing off-axis angles. The background region is de- fields (Giacconi et al. 2001; Tozzi et al. 2001; Brandt et fined as an annulus around the source, after masking out al. 2001) is probably due to intrinsic absorption and not nearby sources. The XSELECT tool is used to extract the to an intrinsically hard power law. Several teams (Della spectrum, and the GRPPHA tool is used to bin the data Ceca et al. 1999b; Akiyama et al. 2000; Fiore et al. 2001; so as to have at least 20 counts per bin. In this process, Maiolino et al. 2001a; Page et al. 2001; Reeves et al. 2000; the background count rate is rescaled with the ratio of the Risaliti et al. 2001) reported the existence of AGN opti- source and background areas. 1 In Sect. 7, we present six spectra and best fit models representative of different classes of objects. 4 V. Mainieri et al.: XMM-Newton observation of the Lockman Hole

Fig. 3. X-ray diagnostic diagrams based on hardness ratios. Filled circles show the Type-1 AGN spectroscopically identified in the ROSAT ultradeep HRI survey (Lehmann et al. 2001a) and in the on-going optical follow-up of the newly detected XMM-Newton sources (PI: Maarten Schmidt). Type-2 AGN are marked with open circles and unidentified sources with crosses. The large filled circles are EROs (R−K′ ≥ 5). The sources inside a box are those with an intrinsic log(NH) > 21.5. For clarity, only sources with hardness ratio errors less than 0.1 are plotted. The source #50 is indicated, see Sect. 7.3 for more details. cally classified as Type-1 but with an indication of ab- distribution representative of the overal AGN population sorption in their X-ray spectra. In our sample, there are at the afore mentioned flux limit. seven objects with an intrinsic absorption between 1021 and 1022 cm−2 which are optically classified as Type-1 AGN. Moreover, the source #96 (ROSAT #39) shows a 3.4. X-ray colour-colour diagrams +5 22 −2 high intrinsic absorption of 5−3 × 10 cm while it was optically classified as an unabsorbed QSO at a redshift of A useful method to constrain the nature of X-ray sources, 3.279. In these cases the optical classification is de-coupled in particular when the signal-to-noise ratio is not high from the X-ray classification. This could be due to a gas- enough for spectral analysis, is to use X-ray colour-colour to-dust ratio and/or a chemical composition different from diagrams (e.g. Della Ceca et al. 1999a; Paper I). In Fig. 3 those in Galactic interstellar gas (Akiyama et al. 2000; we present two of these diagrams. We have used the en- Maiolino et al. 2001b). The three sources with photomet- ergy bands : 0.2-0.5 keV (US), 0.5-2 keV (S), 2-4.5 keV ric redshifts have an absorption greater than 1021.5 cm−2 (M) and 4.5-10 keV (H) to define three different hard- which, combined with the R−K′ colours, suggest that they ness ratios: HR1=(S-US)/(S+US), HR2=(M-S)/(M+S), are probably obscured AGN (Lehmann et al. 2001a). HR3=(H-M)/(H+M). We use different symbols to indicate Type-1 AGN, Type-2 AGN and unidentified sources. The sources with log(NH) > 21.5 have special labels (square box); when the redshift is unknown, the derived 3.3. Observed NH distribution column densities are only lower limits. We also highlight the sources with R−K′ ≥ 5, usually called Extremely Red Objects (see Sect. 4.2 for a discussion of the properties of The NH distribution and its cosmological evolution are key ingredients in the XRB synthesis models (Comastri et this class of objects). al. 1995; Gilli et al. 2001). In Fig. 2 we show the NH dis- In both diagrams, Type-1 AGN are confined in a tribution for the 38 sources with an off-axis angle < 10′. small region, as opposed to Type-2 AGN and unidenti- In this central region where the exposure time is approxi- fied sources which are spread over a much broader area mately constant, our threshold of 70 counts in the [0.5-7] with high hardness ratios (see also Paper I). Moreover, us- keV band corresponds to a flux of 1.6 × 10−15 erg cm−2 ing the additional information on the measured intrinsic s−1. The surface density of sources down to this flux limit, absorption column density, it is now clear that the hard- ∼1700 deg−2, is in very good agreement with that derived ening of non-Type-1 sources is mainly due to the pres- from the logN-logS relation given in Paper I. Therefore ence of intrinsic absorption with log(NH) > 21.5 superim- our sample can be regarded complete and the derived NH posed on relatively soft spectra (see Fig. 1), rather than V. Mainieri et al.: XMM-Newton observation of the Lockman Hole 5

absorption and optical colour. For comparison, we also plot the evolutionary tracks of an early, late and irregular galaxy type using the template library of Coleman et al. (1980), whose spectral energy distributions (SEDs) were extended to the near-IR and far UV using Bruzual & Charlot (1993) models as updated in 2000 (private com- munication). Magnitudes are normalized to the measured local value K∗ = 10.8, and no dust extinction is assumed. The QSO evolutionary track is derived from the empiri- cal template from the Sloan Digital Sky Survey (Vanden Berk et al. 2001), together with the models of Granato et ∗ al. (1997), normalized to MB = −22.4 (for brighter objects the curve should be shifted to the left), for the extension in the near IR. In the R−K′ versus K′ diagram, shown in Fig. 4b, there is no evident trend between R−K′ colour and near-IR flux. Moreover, the range of K′ magnitudes covered by the Type-2 AGN and unidentified sources is almost the same as that of the Type-1 AGN population. This is likely due to a combination of a less pronounced absorption effect in Fig. 5. Optical/near-infrared colours as a function of red- ′ the K band, a different K-correction for AGN-type spec- shift for a sample of ROSAT and XMM-Newton sources tra (small) and star-like galaxy spectra (large), as well as in the Lockman Hole with optical spectroscopy. Symbols an increased contribution of the host galaxy light in the are as in Fig. 3. The evolutionary tracks shown are the ′ K band relative to that of the AGN. Consequently the same as in Fig. 4. Type-1 AGN have the typical blue difference in the observed magnitudes between absorbed colour of a QSO and are unabsorbed, Type-2 AGN fol- and unabsorbed sources is smaller than in the R band. low much redder optical colour tracks expected for their ′ The R−K versus redshift diagram is shown in Fig. host galaxy - because the optical nucleus is obscured - and 5 for the subsample with optical identification (redshift are intrinsically absorbed. There are, however, two high- and AGN type) and X-ray spectral fit (see also Fig. 7 in redshift Type-1 QSOs whith strong X-ray absorption (see Lehmann et al. 2001a). The correlation between optical Sect. 7.4). classification, optical/near IR colour and X-ray absorption is even clearer than in Fig. 4. Most of Type-2 AGN, intrinsically hard spectra (this is also consistent with the whose optical colours are dominated by the host galaxy, fact that Type-1 and Type-2 AGN span similar range in are also significantly absorbed (log NH > 21.5), whereas HR3). These diagrams also suggest that a large fraction Type-1 AGN are unobscured and the emission from the of the unidentified sources (mainly newly detected XMM- central AGN is contributing significantly to their optical Newton sources) are X-ray obscured AGN. colours. There are two exceptions, high redshift Type-1 QSOs, which are optically unobscured but absorbed in the X-ray band (see Sect. 7.4): this could indicate a variation 4. Optical properties in the gas-to-dust ratio (Granato et al. 1997; Maiolino et 4.1. Optical-to-near-IR colours al. 2001a; Maiolino et al. 2001b). The colours of the three sources with photometric redshifts appear to be domi- A deep broad-band K′ (1.92-2.29 µm) survey of the nated by the light from their host galaxies. Lockman Hole region was carried out with the Omega- The spectroscopic identification is still in progress and, Prime camera (Bizenberger et al. 1998) at the Calar Alto to date, we have 24 new XMM-Newton sources with mea- 3.5m telescope in 1997 and 1998. This survey covers ap- sured redshift using LRIS at the Keck II telescope in proximately half the Lockman Hole field. March 2001 (PI: Maarten Schmidt). There is an increas- Several X-ray surveys (Hasinger et al. 1999; Giacconi ing fraction of Type-2 AGN among these fainter X-ray et al. 2001; Lehmann et al. 2001a; Alexander et al. 2001a) sources, and almost all the identified Type-2 AGN are have shown that the R−K′ colour of the optical coun- at z < 1. The derived but still preliminary redshift dis- terparts of X-ray sources increases with the optical faint- tribution seems to be in clear disagreement with predic- ness, and this in a more pronounced way than for the tions from X-ray background models (e.g. Gilli et al. 2001) field sources (Rosati et al. 2002). This trend is also ev- based on the integrated emission of Type-1 and Type-2 ident in the colour-magnitude diagram R−K′ versus R AGN and constrained by deep ROSAT surveys (see also shown in Fig. 4a. We note that the still unidentified ob- Hasinger 2002; Rosati et al. 2002). This calls for a revision jects are significantly redder than the bulk of the identi- of the evolutionary parameters of these models for both fied sources. Using the X-ray information on NH, we also the space density of Type-1 and Type-2 AGN and the ob- find that there is a strong correlation between the X-ray scuration fraction (Type-1/Type-2 ratio) as a function of 6 V. Mainieri et al.: XMM-Newton observation of the Lockman Hole

Fig. 4. Color-magnitude diagram, R−K′ versus R (a) and R−K′ versus K′ (b), of Lockman Hole sources. Symbols are as in Fig. 3, while ﬁeld sources are marked with small dots. The four evolutionary tracks correspond to an unreddened ∗ ∗ QSO with L = LB and z= 0 ÷ 6 (solid line), and to an unreddened elliptical, Sbc and irregular L galaxies (z= 0 ÷ 3) from the Coleman, Wu & Weedman (1980) template library (dashed lines).

Table 1. X-ray detected EROs tremely red colours has signiﬁcantly increased when com- pared to the ﬁrst examples of EROs found in ROSAT sur-

a b c d veys (Lehmann et al. 2001a). Ty-1 Ty-2 Unid. Abs ′ In the subsample of 66 X-ray sources with measured R − K ≥ 3 12 (24%) 14 (28%) 21 (43%) 20 (41%) ′ ′ R − K colour, we find 18 (or 27%) EROs. Two of them R − K ≥ 4 2 ( 6%) 10 (30%) 19 (57%) 16 (48%) are Type-2 AGN, one is classified as a normal galaxy, one R − K′ ≥ 5 0 ( 0%) 2 (11%) 14 (78%) 12 (67%) ′ is an extended source and 14 are unidentified sources; no R − K ≥ 6 0(0%) 0(0%) 6(100%) 4(67%) Type-1 AGN are found. From Table 1, we infer that the a fraction of Type-1 AGN decreases with increasing values Type-1 AGN of R − K′, whereas the fraction of unidentified sources and b Type-2 AGN c intrinsically absorbed (log(N ) > 21.5) sources increases. Unidentified sources H d Moreover, all the X-ray detected EROs have an X-ray-to- Sources with log(NH) > 21.5 − fX[2 10keV] > optical flux ratio log( fR ) 1 (see Fig. 6b) and they sample the hardest part of X-ray colour-colour diagrams (see Fig. 3). The X-ray luminosities in the [0.5- the redshift. The latter is directly related to assumptions 10] keV rest-frame energy band of the seven EROs with in the unified AGN scheme. known spectroscopic and/or photometric redshift are in the range 2.6 × 1042 − 8 × 1044 erg s−1. We thus conclude that our X-ray selected sample of EROs is heavily domi- 4.2. X-ray detected Extremely Red Objects nated by sources with strong AGN activity and absorbed In recent years, much efforts have been devoted to under- X-ray spectra (twelve, or 67%, have log(NH) > 21.5). stand the nature of Extremely Red Objects (EROs here- In the 1 Msec observation of the Chandra Deep Field ′ after). We define EROs as objects with R − K ≥ 52. South (Tozzi et al. 2001; Rosati et al. 2002) about 5% of In a recent wide-area survey, Cimatti et al. (2002) have the optically selected EROs are detected at X-ray energies, spectroscopically identified a sizeble sample of field EROs and their stacked spectrum is consistent with absorbed with K< 19.2 and found them to be almost equally divided objects. In that field 19% of the X-ray sources are EROs, between old passively evolving ellipticals and dusty star- down only to the flux limits of our complete sample in the forming galaxies at 0.7

2 Other selection criteria have also been used, such as X-ray-to-optical ﬂux ratios can yield important informa- R − K ≥ 5.3 or I − K ≥ 4. tion on the nature of X-ray sources (Maccacaro et al. V. Mainieri et al.: XMM-Newton observation of the Lockman Hole 7

Fig. 6. X-ray ﬂux in the [0.5-2.0] (a) and [2.0-10.] (b) keV bands versus optical R magnitudes for those sources in the Lockman Hole with available R band photometry. Symbols are as in Fig. 3. The dashed lines are X-ray-to-optical ﬂux ratio log( fX ) of −1, 0 and 1 fR

Fig. 7. X-ray ﬂux in the [0.5-2.0] (a) and [2.0-10.] (b) keV bands versus optical K′ magnitudes for those sources in the Lockman Hole with available K′ band photometry. Symbols are as in Fig. 3.

1988). A value of −1 < log( fX ) < 1 is a clear sign of sources is almost the same as that of the Type-1 AGN fR AGN activity since normal galaxies and stars have usu- sample. We also note that 32% of the sources are confined − ally lower X-ray-to-optical flux ratios, log( fX ) < −2. In in a region with log( fX [2 10] ) > 1. Among the sources fR fR Fig. 6, we plot the X-ray flux in [0.5-2.0] (a) and [2.0-10] with a high X-ray-to-optical flux ratio, ∼ 85% are heavily (b) keV bands as a function of the R magnitude for the 98 absorbed (log(NH) > 21.5) and ∼ 60% are EROs. Their sources of the sample. A large fraction of the sources spans optical classification is still largely incomplete due to their the typical X-ray-to-optical flux ratio of AGN. While in faintness: two are Type-1 AGN, four are Type-2 AGN, one the soft band (Fig. 6a) the Type-2 AGN and the unidenti- is an extended source and 13 are unidentified. fied sources are confined at the lower fluxes of our sample, At the current flux limit of our complete sample, in the hard band (Fig. 6b), where the effect of the ab- the population of objects with very low X-ray-to-optical sorption is weaker, the range of fluxes covered by these flux ratio is largely missing. Such a population was un- 8 V. Mainieri et al.: XMM-Newton observation of the Lockman Hole

Fig. 8. X-ray luminosity in the [0.5-2] (a) and [0.5-10] (b) keV rest-frame band versus the logarithm of the column density NH. Symbols are as in Fig. 3. Arrows show luminosities corrected for intrinsic absorption. The dashed lines in panel b define the “Type-2 QSO region”. veiled by the Chandra deep surveys (Giacconi et al. 2001; 6. X-ray luminosity and Type-2 QSO candidates Hornschemeier et al. 2001) and found to comprise normal 42 −1 galaxies and low-luminosity AGN (with LX < 10 erg s We have redshifts (and luminosities) for 61 objects or ∼ in the [0.5-10] keV energy band). 62% of the sample with X-ray spectral analysis. In Fig. 8, we plot X-ray luminosity in the [0.5-2] (a) and [0.5-10] There are examples in the literature of “X-ray bright” (b) keV rest-frame bands as a function of the log(N ). objects (L [2-10] > 1041 erg s−1) but without any ob- H X Type-1 AGN (objects without soft absorption) cover a vious signature of nuclear activity in the optical spectra − − range between 1 × 1041 erg s 1 and 9 × 1044 erg s 1 in (Griffiths et al. 1995; Comastri et al. 2002 and references the [0.5-2] keV band; whereas absorbed Type-2 AGN have therein). A heavily obscured AGN is among the most likely − luminosities in the range 1×1041 -2×1043 erg s 1. In the explanations. In our sample there are two sources (#60 total band (Fig. 8b) the effect of absorption is less evident and #92) optically classified as normal galaxies (their so that the range of luminosity of Type-1 (1×1042 -2×1045 optical spectra show emission lines that declare them − − erg s 1) and Type-2 AGN (1 × 1042 - 2 × 1044 erg s 1) is as star-forming galaxies) which are however X-ray lumi- comparable. We have derived the unabsorbed luminosities nous: L [2-10]= 3.7 × 1041 and L [2-10]= 1.9 × 1042 erg X X for objects with log(N ) > 21.5 and reported them in Fig. s−1 respectively. Their X-ray spectra are clearly absorbed H 8 as arrows. In the soft band (Fig. 8a), where the effect of (N = 2+2.8 × 1023 and N = 9+3.2 × 1020 cm−2) rein- H −1.6 H −1.4 absorption is stronger, luminosities increase substantially forcing the evidence that they contain an obscured AGN. and the range of intrinsic luminosities of Type-2 AGN fall More examples of this class of objects are expected at the in the same range as that of Type-1’s (see also Gilli et completion of the optical identification of the newly de- al., in preparation). In Fig. 8b, we have highlighted the tected XMM-Newton sources. 44 −1 region where LX[0.5-10]> 10 erg s and log(NH) > 22 In Fig. 7, we plot the X-ray flux in [0.5-2.0] (a) and cm−2, i.e. the “Type-2 QSO region”. Six objects fall inside ′ [2.0-10] (b) keV bands as a function of K magnitudes. In this area: one is optically classified as a Type-1 AGN (see these diagrams, there is a strong overlap between Type-2 Sect. 7.4 for more details), two are Type-2 AGN. For the AGN and unidentified sources and the Type-1 AGN pop- remaining three, we derived photometric redshifts and due ulation, more prounonced in Fig. 7b. The overlap in mag- to their X-ray absorption and optical/near-IR colours are nitudes is likely due mainly to a K-correction effect (see likely Type-2 AGN. Four of them are also EROs. We argue also Fig. 4b), whereas in the X-ray hard band the effect that these six sources are reliable Type-2 QSO candidates. of the absorption is weaker (see also Fig. 6b). All of them are within an off-axis angle of 10′ where the Finally, in the soft band (Fig. 6a and 7a) the fraction sample is complete (see Sect. 3.3) and we thus derive a of absorbed objects increases significantly as the flux de- density of ∼69 objects of this class per square degree. creases. This inevitably leads, in a flux limited sample, to In Fig. 9, we show the X-ray luminosity as a function a bias in the NH distribution at high value of NH (see Fig. of redshift, using the observed hard band luminosity which 2). is relatively unaffected by absorption. V. Mainieri et al.: XMM-Newton observation of the Lockman Hole 9

Fig. 9. X-ray luminosity in the [2-10] keV rest-frame band versus redshift. Symbols are as in Fig. 2. The dashed line shows the current limit in the X-ray ﬂux of our sample.

7. High S/N spectra 7.2. Absorbed sources Source #25 (ROSAT #84): this object was part of the In Fig. 10 we show six X-ray spectra representative of ROSAT ultradeep HRI survey (Hasinger et al., 1998). the different classes of objects in our sample. The source Lehmann et al. (2001a) give a photometric redshift +0.29 numbers refer to the catalogue presented in this work, zphot = 2.71−0.41. The spectrum extracted from the for reference we give also the ROSAT catalogue numbers EPIC-pn data (332 counts in the [0.5-7] keV band) is well 2 (Hasinger et al., 1998). The redshift of the sources are re- fitted (χν = 1.09) by a wabs ∗ zwabs(powerlaw) model, +1 23 −2 ported in Lehmann et al. (2001a). Sources with interesting with an intrinsic absorption of NH = 3−1 × 10 cm line features will be reported in a future work (Hasinger +0.3 and Γ=2.3−0.3; the unabsorbed rest-frame luminosity in 45 −1 et al. 2002, in preparation). the [0.5-10] keV band is LX =5.49 × 10 erg s . Source #26 (ROSAT #117): was observed by ROSAT (Schmidt et al. 1998) and optically classified as a Type-2 7.1. Unabsorbed sources AGN at z = 0.780. From the fit of the X-ray spectra we +1 22 −2 +0.4 get the values, NH = 2−1 × 10 cm and Γ = 1.5−0.3. The unabsorbed X-ray luminosity in the [0.5-10] keV 43 −1 Source #4 (ROSAT #29): this source was already rest-frame band is LX =4 × 10 erg s . observed by ROSAT (Lehmann et al. 2000) and optically classified as a Type-1 AGN at z = 0.784. This is one of the brightest sources in our sample (3164 EPIC-pn counts in the [0.5-7] keV band). This source is very well 7.3. Multi component spectra 2 fitted (χν = 1.03) by a simple power law model with +0.04 Source #50 (ROSAT #901): this source was classified as Γ=2.02−0.04 and NH consistent with the Galactic value a Type-2 AGN at z=0.204 by Lehmann et al. (2001a). 19 −2 44 −1 (5.7 × 10 cm ). We measure LX = 4.2 × 10 erg s As noted in Paper I, a very soft component superim- in the [0.5-10] keV rest-frame band, and log( fx )=0.6. fR posed on a heavy absorbed power law, is likely present Source #6 (ROSAT #16): it was observed by ROSAT in this source as suggested by the unusually large value (Schmidt et al.1998) and classified as a Type-1 AGN of the hardness ratio HR3. The XMM-Newton spectrum at z = 0.586. This source (1537 EPIC-pn counts in clearly shows such a feature. By fitting a double power law 2 the [0.5-7] keV band) is well fitted (χν = 1.15) by a wabs zwabs powerlaw powerlaw +0.08 model ( ( ( )+ )), we obtain: simple power law model with Γ = 2.47− and N +2.5 23 −2 +1 0.03 H N =4− ×10 cm ,Γ=3− for the hard component 19 −2 H 1.5 1 consistent with the Galactic value (5.7 × 10 cm ). It +0.4 2 44 −1 and Γ = 3.3−0.5 for the soft component (χν = 1.2). We has LX =1.2 × 10 erg s in the [0.5-10] keV rest-frame 43 also find an unabsorbed X-ray luminosty LX =5.7 × 10 band. − erg s 1 in the [0.5-10] keV rest-frame band and a ratio fx . log( fR )= −2 4, unusually low for an AGN, which is probably due to the strong intrinsic absorption. 10 V. Mainieri et al.: XMM-Newton observation of the Lockman Hole

7.4. Type-1 QSO with X-ray absorption is an optically classified Type-1 QSO (source #96 see Sect. 7.4), two are Type-2 AGN and the remaining three have Source #96 (ROSAT #39): this object is optically clas- a photometric redshift and due to their X-ray absorption sified as a Type-1 QSO at z = 3.279 (Lehmann et al., and optical/near-IR colours likely Type-2 AGN. Four of 2001a). A clear absorption is present in the X-ray spec- ′ them are also EROs (R − K ≥ 5). These are likely to be trum and the fit yields N =5+5 × 1022 cm−2. As already H −3 Type-2 QSO candidates and we derive a density of ∼ 69 argued in Sect. 3.2, this mismatch between the optical objects of this class per square degree at a flux limit in and X-ray classifications could be due to a gas-to-dust ra- − − − the [0.5-7] keV band of 1.6 × 10 15 erg cm 2 s 1. tio or a chemical composition different from that of the Our analysis of the unidentified sources (mostly newly Galactic interstellar gas (Akiyama et al. 2000; Maiolino et detected XMM sources) shows that the majority of these al. 2001b). sources have absorbed X-ray spectra and are consequently located in the harder part of the diagnostic X-ray colour- 8. Conclusions colour diagrams. They are also optically fainter (∼ 80% of them have R> 24) and their optical-to-near-IR colours We have discussed the X-ray spectral properties of a sam- are redder (∼ 90% have R−K′ ≥ 4) than already ple of 98 sources found in the 100 ksec XMM-Newton identified sources. Their X-ray-to-optical flux ratios are − observation of the Lockman Hole, using data from the log( fX [2 10] ) > 1. From these properties, we argue that fR EPIC-pn detector. The large throughput and the unprece- the majority of these sources are Type-2 AGN. This is con- dented sensitivity at high energies of the X-ray telescope firmed by our on-going optical spectroscopic survey which and detectors allow us, for the first time, to measure sep- is showing that the bulk of these sources is at z < 1. Two aretely the intrinsic absorption and the slope of the power X-ray bright optically “normal” galaxies are present in law emission spectrum for the faint source population. We our sample. Their X-ray spectra are clearly absorbed sug- have derived the spectral index (Γ) and the column den- gesting the presence of an obscured AGN. We expect this sity (NH) for sources with more than 70 counts in the class of objects to increase from the optical identification [0.5-7] keV band. We find that the value of Γ is indepen- of the newly detected XMM-Newton sources. dent of the absorption level with < Γ >≈ 2. Thus, we infer that the progressive hardening of the X-ray spectra Acknowledgements. We thank Andrea Comastri, Roberto of faint sources observed in Chandra deep fields (Giacconi Gilli, Giorgio Matt and Paolo Tozzi for useful comments et al. 2001; Tozzi et al. 2001; Brandt et al. 2001) is mainly and discussions. We thank the referee, X. Barcons, for help- due to the increasing level of intrinsic absorption rather ful comments that improved the manuscript. RDC acknowl- than intrinsically flat spectra. edge financial support from the Italian Space Agency, ASI ′ We confirm that the R − K colours of X-ray counter- (I/R/037/01), under the project ”Cosmologia Osservativa con parts get redder towards fainter R magnitudes. Such a XMM-Newton”. ′ trend is not present between R − K and the K′ magnitude; this is likely due to a combination of a less pro- References nounced absorption effect in this band, a different K- correction for AGN-type spectra (small) and star-like Akiyama, M., Ohta, K., Yamada, T., et al. 2000, ApJ, 532, 700 galaxy spectra (large), as well as an increased contribu- Alexander, D.M., Brandt, W.N., Hornschemeier, A.E., et al. tion of the host galaxy light in the K′ band relative to 2001a, AJ, 122, 2156 Alexander, D.M., Vignali, C., Bauer, F.E., et al. 2001b, AJ, that of the AGN. ′ 123, 1149 Comparing the R − K colours of the X-ray sources Barger, A.J., Cowie, L.L., Mushotzky, R.F., & Richards, E.A. with evolutionary tracks of various galaxy-types as a func- 2001, AJ, 121, 662 tion of redshift, we find that Type-2 AGN have colours Bertin, E., & Arnouts, S. 1996, A&A Supplement, 117, 393 dominated by the host galaxy and are also significantly Bizenberger, P., McCaughrean, M.J., Birk, C., et al. 1998, in absorbed (log NH > 21.5). On the other hand, for Type- Omega Prime: the wide-field near-infrared camera for the 1 AGN, the large majority of which are unabsorbed, the 3.5 m telescope of the Calar Alto Observatory, ed. A.M. nuclear component is significantly contributing to their Fowler, Infrared astronomical instrumentation, SPIE 3354, optical colours. In addition, there is a strong correlation 825 ′ between the R − K colour and the amount of intrinsic Brandt, W.N., Alexander, D.M., Hornschemeier, A.E., et al. X-ray absorption. 2001, AJ, 122, 2810 We have also defined an X-ray selected sample of 18 Brusa, M., Comastri, A., Daddi, E., et al. 2002, Proceedings of ′ the Workshop ‘X-ray spectroscopy of AGN with Chandra EROs (R − K ≥ 5) and found that it mainly comprises and XMM-Newton’, MPE report, ed. Th. Boller, in press, X-ray absorbed objects with a strong correlation between astro-ph/0204251 colour and intrinsic column density. Bruzual, G.A., & Charlot S. 1993, ApJ, 405, 538 We have derived the unabsorbed rest-frame luminosi- Cimatti, A., Daddi, E., Mignoli, M., et al. 2002, A&A, 381, ties of the sources with strong intrinsic absorption. There L68 are six absorbed, bright X-ray objects in our sample with Comastri, A., Setti, G, Zamorani, & G., Hasinger, G. 1995, 44 −1 22 −2 LX[0.5−10] > 10 erg s and log(NH) > 10 cm : one A&A, 296, 1 V. Mainieri et al.: XMM-Newton observation of the Lockman Hole 11

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Fig. 10. XMM EPIC-pn CCD spectra and best fit models. Top: source #4 (ROSAT #29) and source #6 (ROSAT #16); middle: source #25 (ROSAT #84) and source #26 (ROSAT #117); bottom: source #50 (ROSAT #901) and source #96 (ROSAT #39). V. Mainieri et al.: XMM-Newton observation of the Lockman Hole 13 I oa Type Rosat XID 2. Table 02 05 05+73 01.01804 .000 ...... 0.00 0.00 0.43 178 11.90 40 30 +57 10.5 54 10 5 20 40 9091 40. 5 03 37 7 .400 .0...... 0.00 0.00 0.44 179 13.72 36 20 +57 04.5 54 10 9 0 39 8021 20. 5 92 .21701 .403 181. . 0. 4.3 17.5 21.8 0.34 0.84 0.15 187 4.92 24 29 +57 06.6 52 10 2 0 38 74691 24. 5 80 .91101 .403 441. 5.3 19.1 24.4 0.34 0.44 0.19 191 0.79 00 28 +57 43.2 52 10 9 486 37 68411 24. 5 12 .51903 .900 051. 1.5 19.0 20.5 0.00 0.29 0.30 199 7.45 21 21 +57 45.2 52 10 1 814 36 51621 23. 5 10 .02602 .703 091. 4.8 16.1 20.9 0.32 0.47 0.26 206 2.40 05 31 +57 37.5 52 10 2 116 35 48 05 46+72 778 0 .004 .02. 92203 2.0 19.2 21.2 0.00 0.45 0.30 207 7.87 07 28 +57 44.6 51 10 1 80 34 31391 12. 5 73 01 0 .612 .02. 003. 20.0 23.6 0.60 1.24 0.16 209 10.11 37 27 +57 28.3 51 10 9 123 33 24191 22. 5 55 .92601 .204 461. 6.3 18.3 24.6 0.49 0.72 0.16 216 3.79 50 25 +57 25.3 52 10 9 491 32 11421 24. 5 65 .52402 .104 88...... 18.8 0.49 0.81 0.28 224 8.05 50 36 +57 41.3 52 10 2 104 31 05 05 34+71 51.42005 .600 ...... 0.00 0.46 0.57 250 13.04 45 15 +57 43.4 52 10 1 52 30 91 05 31+73 253 7 .905 .02. 95251 2.5 19.5 22.0 0.00 0.50 0.39 277 5.36 22 32 +57 13.1 52 10 1 13 29 82 05 46+73 028 8 .506 .02. 80441 4.4 18.0 22.4 0.00 0.64 0.35 286 2.83 10 30 +57 24.6 52 10 1 23 28 74 05 92+71 21.62704 .200 12...... 21.2 0.00 0.52 0.47 287 11.06 52 18 +57 19.2 53 10 2 45 27 58 05 70+72 792 3 .215 .52. 93622 6.2 19.3 25.5 0.75 1.51 0.32 332 9.21 17 20 +57 17.0 52 10 9 84 25 61721 34. 5 03 .93103 .710 291. 3.4 19.5 22.9 1.02 1.27 0.34 321 8.99 35 30 +57 48.6 53 10 2 117 26 4021 23. 5 32 .23201 .316 261. . 0. 5.1 17.5 22.6 1.61 2.03 0.17 352 4.62 22 33 +57 37.8 52 10 2 0 24 33 05 73+72 641 6 .107 .02. 80311 3.1 18.0 21.1 0.00 0.72 0.61 368 4.16 06 25 +57 57.3 52 10 1 30 23 2511 30. 5 75 .33706 .604 101. . 1. 2.7 18.3 21.0 0.48 1.06 0.63 387 9.53 57 37 +57 02.5 53 10 1 5 22 12 05 15+72 493 1 .508 .62. 86221 2.2 18.6 20.8 0.56 0.89 0.65 412 9.37 04 27 +57 51.5 53 10 1 27 21 01011 30. 5 82 .74605 .504 041. 2.7 17.7 20.4 0.45 0.75 0.54 426 3.57 21 28 +57 09.3 53 10 1 120 20 91 05 22+73 831 2 .612 .42. 96541 5.4 19.6 25.0 0.64 1.28 0.46 427 3.18 58 31 +57 42.2 52 10 9 14 19 84611 30. 5 92 .74307 .100 201. 4.5 17.5 22.0 0.00 0.81 0.76 443 2.87 24 29 +57 03.8 53 10 1 426 18 7091 40. 5 52 30 1 .514 .3...... 0.63 1.44 1.35 511 13.09 27 35 +57 07.1 54 10 9 0 17 67 05 91+73 927 1 .211 .02. 88331 3.3 18.8 22.1 0.70 1.15 0.62 516 2.75 29 30 +57 59.1 52 10 1 77 16 51 05 86+73 783 7 .132 .72. 80490 4.9 18.0 22.9 2.17 3.29 0.41 570 8.32 47 32 +57 48.6 51 10 2 12 15 4211 23. 5 91 05 9 .415 .8...... 0.48 1.55 1.14 599 10.57 13 39 +57 30.1 52 10 1 2 14 33 05 81+72 775 1 .107 .42. 73280 2.8 17.3 20.1 0.34 0.77 1.11 612 7.54 17 21 +57 48.1 52 10 1 37 13 25311 25. 5 34 .26108 .306 231. 4.0 18.3 22.3 0.62 1.33 0.86 681 5.32 42 23 +57 54.4 52 10 1 513 12 1911 15. 5 43 .47412 .007 121. . 0. 2.9 18.3 21.2 0.74 1.60 1.24 744 8.74 36 34 +57 54.3 51 10 1 9 11 02 05 49+72 183 4 .716 .02. 80281 2.8 18.0 20.8 0.50 1.69 1.17 746 8.33 41 28 +57 44.9 53 10 1 25 10 821 42. 5 54 35 011.62.193 ...... 9.30 20.31 11.06 6071 13.58 43 25 +57 21.3 54 10 2 28 1 211 23. 5 43 .844 .760 .71. 61181 1.8 16.1 17.9 2.97 6.02 5.87 4440 4.28 32 24 +57 39.6 52 10 1 32 2 05 68+73 284 5059 .038 881. . 1. 2.2 16.6 18.8 3.86 8.60 5.90 3590 8.40 52 35 +57 16.8 53 10 1 6 3 911 33. 5 54 .536 .364 .21. 72230 2.3 17.2 19.5 2.62 6.45 4.73 3164 7.65 43 25 +57 35.1 53 10 1 29 4 611 33. 5 10 .513 .631 .31. 63310 3.1 .... 16.3 .... 19.4 .... 1.33 0.00 3.15 0.65 3.16 4.66 1537 1958 7.95 11.30 05 31 +57 39 34 +57 39.7 53 10 30.9 51 10 1 5 16 8 6 5 111 33. 5 45 .410 .422 .62. 77281 2.8 .... 17.7 .... 20.5 .... 1.16 0.00 2.21 0.00 1.84 3.58 1208 1271 7.64 13.58 56 24 +57 10 42 +57 31.9 53 10 00.5 53 10 1 5 31 0 8 7 3 05 63+73 11.79224 .000 ...... 0.00 0.00 2.42 962 11.67 01 38 +57 36.3 53 10 5 232 9 -a catalogue X-ray a ADcO-xscut Flux counts Off-axis Dec RA angle f 057 052 21][5-10] [2-10] [0.5-2] [0.5-7] b Flux b Flux b K R ′ R-K . .0 21.29 0.205 ... .. 22.15 ..... 6 ...... 3 22.26 0.137 . .4 .02.29 0.00 2.144 . .1 20.32 0.711 ...... ′ 1.21 .71 .94 .3 .02.12 0.00 2.832 .0 20.99 0.708 .8 22.27 0.780 .6 .02.12 0.00 1.568 .8 20.79 0.788 .3 21.03 1.437 .6 .01.75 0.00 0.761 .. .02.74 0.00 ...... 22.04 ...... 02.29 0.00 ...... 4921.08 .409 8220.73 .872 0920.94 .009 5700 2.35 0.00 .527 7000 1.66 0.00 .720 6600 1.56 0.00 .676 9023.50 .990 4700 2.81 0.00 .467 1300 2.49 0.00 .113 7400 2.02 0.00 .784 5600 2.50 0.00 .586 9600 1.93 0.00 .956 8600 1.89 0.00 .816 0 21.93 708 0 23.01 707 8 .01.94 0.00 881 7 20.20 877 0 .01.91 0.00 204 log(N z phot. g phot. g phot. g 22.02 23.51 22.59 21 22 21 22 19 21 19 22 21 22 21 22 21 22 19 21 19 21 19 20 22 22 23 23 22 23 22 22 19 20 23 23 20 21 19 20 21 21 H ...... ) 23 31 72 29 76 41 76 11 83 40 73 30 60 29 76 11 76 32 76 48 06 53 37 63 70 18 39 77 76 90 29 74 30 36 76 30 26 32 c 1.47 1.49 1.50 1.75 1.90 2.17 1.95 1.81 1.95 1.77 1.50 2.27 1.63 1.67 2.14 2.02 2.03 2.18 1.89 Γ d 3 2 1 0 1 1 2 1 1 1 2 1 2 1 2 1 2 1 2 1 2 2 2 1 2 1 1 1 2 1 1 1 2 2 2 1 1 1 2 1 1 1 2 1 2 2 1 1 2 1 2 1 2 2 1 1 2 2 1 1 1 1 2 2 1 1 2 1 2 2 1 1 ...... 00 57 83 97 59 16 32 88 75 27 06 53 34 30 89 52 25 31 07 63 48 15 33 65 01 59 90 20 64 92 87 40 50 21 11 79 76 56 28 98 97 41 38 91 38 20 71 45 80 61 12 89 91 72 88 65 35 06 91 80 93 85 53 45 94 87 06 98 56 45 99 86 28543.879 42.855 43544.524 44.335 27943.304 42.789 12941.862 41.209 45544.552 44.555 32843.485 43.248 30843.284 43.018 23743.572 42.327 23243.711 42.362 42944.185 44.239 41944.383 44.169 42844.634 44.258 41244.307 44.192 38544.644 43.825 32243.288 43.202 41044.528 44.100 29244.239 42.922 41744.352 44.127 33042.905 43.310 33543.631 43.365 38343.837 43.833 44444.708 44.484 33643.715 43.356 49144.745 44.911 47344.964 44.783 42644.366 44.276 38043.663 43.880 48245.088 44.882 052 [2-10] [0.5-2] L ...... 43.072 ...... 44.958 ...... 44.230 ...... 44.903 ...... X e L X e 14 V. Mainieri et al.: XMM-Newton observation of the Lockman Hole I oa Type Rosat XID 2. Table 1021 30. 5 81 .81600 .811 311. . 0. 5.3 17.8 23.1 1.15 0.88 0.00 176 3.08 10 28 +57 05.4 53 10 2 0 41 28111 32. 5 85 .61002 .600 271. 4.0 18.7 22.7 0.00 0.26 0.25 170 5.26 52 28 +57 22.1 53 10 1 821 42 44711 30. 5 42 .91902 .600 031. 1.9 18.4 20.3 0.00 0.26 0.22 159 6.39 25 34 +57 05.6 53 10 1 477 44 37 05 53+73 81.21102 .305 931. 1.7 17.6 19.3 0.57 0.33 0.27 161 10.62 48 30 +57 25.3 51 10 1 75 43 54091 31. 5 63 .11801 .400 431. 5.3 19.0 24.3 0.00 0.64 0.14 158 4.91 30 26 +57 15.3 53 10 9 430 45 6011 23. 5 40 .11901 .204 42.. ..0 ...... 24.2 0.42 0.52 0.14 149 5.31 02 34 +57 36.7 52 10 1 0 46 7091 34. 5 81 .71801 .200 551. . .. 7.0 18.5 25.5 0.00 0.42 0.18 148 8.77 16 28 +57 48.1 53 10 9 0 47 86791 22. 5 30 .61701 .800 411. 4.3 19.8 24.1 0.00 0.28 0.19 147 6.46 06 23 +57 20.2 52 10 9 607 48 09121 25. 5 85 .61800 .312 531. 3.4 11.9 15.3 1.25 0.33 0.05 138 1.36 59 28 +57 53.0 52 10 2 901 50 9091 11. 5 63 24 4 .503 .0...... 0.00 0.36 0.25 142 12.47 35 26 +57 11.8 51 10 9 0 49 24811 32. 5 81 .21202 .100 241. 3.6 18.8 22.4 0.00 0.41 0.24 132 5.62 19 28 +57 24.6 53 10 1 428 52 11 05 82+73 530 3 .702 .02. 95310 3.1 19.5 22.6 0.00 0.26 0.17 136 3.03 05 31 +57 28.2 52 10 1 18 51 33 05 96+72 499 3 .703 .02...... 21.3 0.00 0.33 0.27 130 9.96 04 21 +57 29.6 53 10 1 38 53 48411 31. 5 42 .81801 .800 271. 3.6 19.1 22.7 0.00 0.28 0.19 128 6.88 25 34 +57 12.4 53 10 1 804 54 6021 25. 5 20 .11501 .800 131. . 0. 4.5 16.8 21.3 0.00 0.28 0.16 125 3.41 00 32 +57 51.6 52 10 2 0 56 5091 41. 5 05 20 2 .103 .0...... 0.00 0.37 0.31 127 12.00 57 30 +57 10.9 54 10 9 0 55 73 05 57+72 262 2 .202 .02. 86391 3.9 18.6 22.5 0.00 0.27 0.22 125 6.22 02 23 +57 25.7 52 10 1 36 57 95 05 77+71 51.11202 .800 ...... 15.9 0.00 0.00 0.28 0.00 0.21 0.28 122 123 14.11 9.22 05 15 +57 34 07.7 37 53 +57 10 21.9 52 10 1 5 54 802 59 58 0031 24. 5 62 .01100 .211 79.. ..0 ...... 17.9 1.12 0.72 0.00 121 7.60 22 36 +57 47.6 52 10 3 0 60 3021 25. 5 13 .31600 .500 911. . .. 3.1 16.0 19.1 0.00 0.45 0.07 106 3.03 33 31 +57 52.1 52 10 2 0 63 2091 30. 5 50 40 1 .802 .0...... 0.00 0.28 0.18 113 14.03 00 15 +57 01.8 53 10 9 0 62 1091 24. 5 12 26 1 .502 .0...... 0.00 0.26 0.25 118 12.69 28 41 +57 48.5 52 10 9 0 61 4091 33. 5 51 .11401 .000 591. . .. 6.2 19.7 25.9 0.00 0.00 0.15 104 7.31 16 25 +57 30.5 53 10 9 0 64 5091 21. 5 20 .81200 .300 531. . .. 5.8 19.5 25.3 0.00 0.53 0.06 102 5.38 04 32 +57 11.1 52 10 9 0 65 68011 22. 5 25 .01101 .000 131. 3.5 17.8 21.3 0.00 0.00 0.18 101 6.40 51 22 +57 25.4 52 10 1 870 66 96411 31. 5 30 .69 .302 .02...... 23.2 .... 19.9 0.00 26.6 0.00 0.23 0.00 0.27 0.13 0.25 0.21 97 0.17 98 100 6.86 9.81 5.27 08 23 +57 13 25 +57 11.6 56 53 23 10 +57 50.8 53 10 58.2 52 10 1 4 4 634 128 34 69 68 67 0091 31. 5 45 .09 .405 .02. 9451... 5.1 19.4 24.5 0.00 0.53 0.04 95 5.90 51 24 +57 15.5 53 10 9 0 70 5091 14. 5 03 .89 .800 .02. 9264... 6.4 19.2 25.6 0.00 0.00 0.18 91 7.78 35 30 +57 46.6 51 10 9 0 75 18 05 23+72 654 401 .000 281. . 0. 3.8 19.0 22.8 0.00 0.00 0.14 94 5.41 06 25 +57 12.3 53 10 1 82 71 31 05 73+73 290 201 .400 221. . 0. ... 3.2 4.5 19.0 19.6 22.2 24.1 0.00 0.34 0.34 0.49 0.13 0.00 92 94 9.02 4.55 42 30 +57 30 24 +57 37.3 51 10 31.8 52 10 1 9 19 0 73 72 4091 24. 5 54 .79 .400 .0...... 0.00 0.00 0.14 91 6.97 46 35 +57 43.4 52 10 9 0 74 6091 15. 5 93 .59 .200 .02. 0443... 4.3 20.4 24.7 0.00 0.00 0.12 90 6.45 34 29 +57 55.3 51 10 9 0 76 88111 35. 5 92 01 901 .000 25...... 22.5 0.00 0.00 0.15 89 10.14 23 29 +57 58.3 53 10 1 861 78 7091 34. 5 35 .89 .100 .0...... 0.00 0.00 0.21 90 9.98 51 33 +57 47.1 53 10 9 0 77 0091 20. 5 41 .38 .202 .02...... 5.6 23.1 17.2 0.00 22.8 0.27 0.00 0.12 0.42 87 0.20 88 7.23 10.01 12 34 +57 07.2 18 52 35 10 +57 39.8 53 10 9 4 0 228 80 79 (continued) a ADcO-xscut Flux counts Off-axis Dec RA angle f 057 052 21][5-10] [2-10] [0.5-2] [0.5-7] b Flux b Flux b K R ′ R-K ...... 1.66 0.00 ...... 2.416 ...... 4 .01.84 0.00 1.843 . ′ .1 21.84 3.410 .4 21.43 2.340 .4 .02.21 0.00 2.949 .0 23.64 0.204 .4 20.34 1.145 .9 21.20 1.598 .1 .02.24 0.00 1.213 .4 ...... 21342.546 42.173 ...... 0.340 .0 .02.25 0.00 0.807 .3 ...... 97439.902 39.754 1.43 ...... 0.00 ...... 1.544 0.033 .5 ...... 38344.022 43.843 ...... 1.250 .. 21.95 ...... 19.90 ...... 20.52 ...... 19.92 ...... 20.75 ...... 20.51 ..... 1421.85 .164 9300 1.78 0.00 .993 5421.34 .524 1823.35 .118 9 23.55 792 6 21.41 664 6 .01.64 0.00 960 9 20.20 894 log(N z . 21.88 ... . 21.97 ... . .01.84 0.00 ... . 22.04 ... . .01.66 0.00 ... . .01.91 0.00 ...... 22.12 .. .00 1.96 0.00 ...... 00 1.63 0.00 .. 23 23 19 21 19 22 21 22 21 22 21 22 19 20 19 21 23 23 19 21 19 20 19 20 20 21 19 21 19 21 19 21 22 23 21 22 21 22 21 22 19 21 H ...... ) 31 80 76 75 76 32 95 83 28 55 56 16 76 85 76 00 37 82 76 73 76 60 76 00 00 84 76 65 76 34 76 15 82 71 40 39 65 42 63 54 76 64 c 2.00 1.89 1.84 1.75 1.51 1.83 1.52 1.91 2.97 1.77 2.18 2.34 1.81 2.56 1.65 2.08 2.69 1.74 1.74 1.77 1.68 Γ d 2 1 2 1 2 1 2 1 9 0 2 1 2 1 1 1 2 1 2 1 4 1 2 1 2 1 2 2 2 1 2 1 2 2 1 1 2 1 2 1 3 2 2 0 1 1 2 1 2 1 1 1 1 2 1 1 3 2 1 1 2 1 2 1 2 2 1 1 ...... 85 33 24 59 15 55 55 91 76 96 74 00 82 17 90 26 34 63 21 41 02 93 08 49 58 93 58 14 45 92 21 35 82 06 74 49 25 21 73 66 18 18 60 95 91 77 60 40 69 89 73 16 93 64 38 28 09 30 02 33 38 38 27 64 30 05 22 59 24343.613 42.413 40444.478 44.004 44944.651 44.439 10041.831 41.020 29243.198 42.952 10142.219 41.031 36644.061 43.626 35443.539 43.514 31843.256 43.108 25842.996 42.538 36443.640 43.604 41944.546 44.139 02841.566 40.228 27142.663 42.701 30243.471 43.022 25142.843 42.521 37544.007 43.725 052 [2-10] [0.5-2] L ...45.000 ...... 43.715 ...... X e L X e V. Mainieri et al.: XMM-Newton observation of the Lockman Hole 15 e d c a Type Rosat XID 2. Table g f b nuiso 10 of units In nrni bopini xest h aatcoe ( ones Galactic the to excess in absorption Intrinsic o fosre uioiyi h etfaebn,i nt o units in band, rest-frame the in luminosity observed of Log 71821 22. 5 33 .47 .900 .02. 84370 3.7 18.4 22.1 0.00 0.00 0.09 71 5.14 30 33 +57 27.8 52 10 2 108 97 8091 24. 5 03 .87 .700 .02. 0352... 5.2 20.3 25.5 0.00 0.00 0.07 70 1.88 39 30 +57 41.5 52 10 9 0 98 63 05 97+72 489 101 .000 172. . 3. 1.1 20.6 21.7 0.00 0.00 0.14 71 8.94 04 21 +57 09.7 52 10 1 39 96 2031 25. 5 33 .47 .000 .02. 90530.4 . 5.3 .... 19.0 .... 24.3 0.00 .... 0.00 0.00 0.00 0.10 0.12 72 73 5.24 11.22 35 33 +57 59 26 +57 58.6 52 10 20.6 51 10 3 9 0 0 92 91 44421 25. 5 25 .07 .300 .02. 80420 4.2 18.0 22.2 0.00 0.00 0.13 71 6.30 51 22 +57 58.4 52 10 2 434 94 5091 23. 5 50 .57 .002 .82. 9850... 5.0 .. 19.8 4.1 24.8 0.38 20.1 24.2 0.23 0.00 0.00 0.00 71 0.09 4.05 72 03 6.70 25 +57 31.5 52 10 43 30 +57 9 55.1 51 10 0 9 21 95 93 03 05 03+72 072 300 .003 221. . 0. 2.8 19.4 22.2 0.32 0.20 0.07 73 7.27 20 24 +57 00.3 52 10 1 33 90 9091 24. 5 91 .17 .802 .02. 9842... 0 4.2 .... 19.8 24.0 .... 0.00 17.5 0.00 0.20 0.00 0.08 0.15 73 73 0.41 9.36 11 29 +57 48 42.3 20 52 +57 10 19.0 53 10 9 4 0 41 89 88 7091 22. 5 53 .67 .900 .02. 9651... 5.1 19.6 24.7 0.00 0.00 0.09 75 4.16 32 25 +57 23.8 52 10 9 0 87 6091 34. 5 60 .17 .000 .92. 9636... 3.6 19.6 23.2 0.39 0.00 0.10 75 9.01 06 26 +57 46.9 53 10 9 0 86 4021 15. 5 52 .08 .703 .02. 74440.6 4.4 17.4 21.8 0.00 0.34 0.07 80 7.90 21 25 +57 50.1 51 10 2 0 84 5091 32. 5 14 .87 .002 .02. 9362... 6.2 19.3 25.5 0.00 0.27 0.10 78 5.98 48 31 +57 21.4 53 10 9 0 85 3091 33. 5 92 23 100 .406 ...... 0.61 0.64 0.00 81 12.39 23 39 +57 30.9 53 10 9 0 83 pcrlIdxad9%cndnerange. confidence 90% and Index Spectral 1091 25. 5 15 .48 .802 .32...... 22.9 0.33 0.28 0.08 87 3.44 51 31 +57 54.8 52 10 9 0 81 2091 23. 5 60 27 601 .000 ...... 0.00 0.00 0.15 86 12.77 03 16 +57 37.0 52 10 9 0 82 htmti esit seLhane l 2001a). al. et Lehmann (see redshifts Photometric pia lsicto:1Tp1AN =ye G,3 galaxy 3= AGN, 2=Type2 AGN, 1=Type1 classification: Optical narcmin. In (continued) − 14 r s erg a − 1 . ADcO-xscut Flux counts Off-axis Dec RA ∼ angle 5 . 7 × f 10 r s erg f 19 057 052 21][5-10] [2-10] [0.5-2] [0.5-7] cm =ru/lse,5sa,9uietfidsource 9=unidentified 5=star, 4=group/cluster, , − − 1 2 . n 0 ofiec range. confidence 90% and ) b Flux b Flux b K R ′ R-K ′ 6621.08 .696 30...... 4.3 42.279 42.336 ...... 340 7221.36 .762 ...... 22.04 ...... 00 1.98 0.00 .... 8 22.69 281 7 .00.67 0.00 974 log(N z . .01.89 0.00 ... . 21.71 ... .00 1.46 0.00 .. .22.28 .. .19.60 .. 720.97 17 .00 1.63 0.00 .. .00 2.00 0.00 .. .21.53 .. 621.97 76 22 23 19 22 19 22 20 21 20 22 19 21 20 21 21 22 21 22 20 22 H ...... ) 30 00 76 01 76 85 78 66 90 52 76 57 90 53 95 70 18 37 00 24 c 1.13 2.55 1.36 2.12 1.61 1.06 2.42 1.10 1.42 1.22 Γ 2 − d 1 1 3 2 2 0 1 0 2 1 2 2 1 1 1 0 2 1 3 1 4 1 1 0 2 0 2 1 1 0 . 0 31 ...... 51 21 20 00 33 78 37 20 90 30 56 53 69 10 65 68 37 26 03 52 39 47 80 40 23 83 24 71 98 39 . 06 20742.719 42.097 23943.115 42.309 28243.123 42.862 42.282 41.853 18042.901 41.890 052 [2-10] [0.5-2] L ...... 44.472 ...... X e L X e