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CHAPTER 5: LUMINOSITY FUNCTION OF XMS SOURCES sources with intrinsic column densities up to N H < 10 24 cm −2 , although they are not energetic enough to escape from Compton-thick objects (N H > 1.5 × 10 24 cm −2 , for which the Compton-scattering optical depth σ T equals unity). Previous hard X-ray surveys in the 2-10 keV band ([32], [69], [79], [4]) have provided unbiased and highly complete samples of sources, many of them being obscured AGN. Notwithstanding this, an important fraction of the AGN detected in deep fields fail to provide good quality X-ray information, and their optical counterparts are far too faint to make reliable spectroscopic identifications of the totality of the samples. Previous works have studied the X-ray luminosity function (XLF, hereafter) of AGN, mainly in the 0.5-2 keV and 2-10 keV bands. For instance, [157] and [104] studied the the 0.5-2 keV XLF of AGN testing a variety of models. Their results seem to rule out both Pure Luminosity and Pure Density Evolution models in favour of a Luminosity Dependent Density Evolution model. This paper aims to confirm this results and to improve the accuracy of the determination of the model parameters by using a sample that contains ∼30% more AGN than the [157] sample and is comparable to that of [104]. [211] studied the XLF of high redshift AGN in the 2-8 keV band but they did not consider the intrinsic absorption of the sources due to the limited count statistics. Other works in the 2-10 keV band such as [224] and [130] have taken into account the N H distribution of the sources when calculating the XLF, but an important fraction of the N H values were derived from the hardness ratios of the sources rather than from a spectral analysis. This may introduce a certain degree of uncertainty since a template spectrum has to be assumed to compute the N H . The XLF of very hard sources (>5 keV) is almost unexplored so far with the exception of the work by [48], who studied the de-evolved (z = 0) luminosity function of absorbed and unabsorbed AGN in the 4.5-7.5 keV band but was unable to perform detailed evolutionary studies due to the low statistics. In this chapter we use the XMM-Newton Medium Survey (XMS, [12], see section 2.2), along with other highly complete deeper and shallower surveys, to compute the X-ray luminosity function (XLF, hereafter) in several energy bands. Furthermore, given the availability of high-quality X-ray spectral information in the XMS, we are able to model the intrinsic absorption of the hard sources (those detected in the 2-10 and 4.5-7.5 keV bands) as a function of the X-ray luminosity up to column densities of ∼ 10 24 cm −2 . These issues are key tools 116
CHAPTER 5: LUMINOSITY FUNCTION OF XMS SOURCES to probe the accretion history of the Universe across cosmic time. Thanks to the extremely high identification completeness of the XMS sample and the accompanying surveys we have assembled an overall sample of ∼1000 identified AGN in the 0.5-2 keV, ∼450 identified AGN in the 2-10 keV band, and ∼120 identified AGN in the 4.5-7.5 keV bands, leading to one of the largest and most complete sample up to date in all three energy bands. This chapter is organized as follows: in section 5.2 we study the absorbing column density distribution of the spectroscopically identified AGN detected in hard X-rays (>2 keV) and we model the intrinsic fraction of absorbed AGN as a function of both luminosity and redshift in the 2-10 and 4.5-7.5 keV bands. In section 5.3 we discuss the method used to compute the X-ray luminosity function of AGN in several energy bands using two methods: a modified version of the classic 1/V a method to construct binned luminosity functions, and a Maximum Likelihood fit technique to an analytical model using all the sources available without binning. In section 5.4 we discuss the results obtained and we compare them with those obtained in previous works. Finally, the conclusions extracted from this work are reported in section 5.5. Throughout this chapter we have assumed a cosmological framework with H 0 = 70 km s −1 Mpc −1 , Ω M = 0.3 and Ω Λ = 0.7 ([213]). 5.2 The N H function In this chapter we are pursuing to calculate the cosmological evolution of the X-ray luminosity function of all AGN (both Type-1 and Type-2) within our sample in three energy bands. This should be done by calculating the intrinsic (before absorption) luminosity and absorption (N H ) function in order to obtain purely observation-based results. Since hard X-ray photons are less affected by absorption, absorbed AGN are more likely to be detected at energies above 2 keV and hence we have applied such method to the hard (2-10 keV) and ultrahard (4.5-7.5 keV) sources, for which we have detailed spectral information (photon index Γ and instrinsic absorbing column densities N H ). The ultrahard sources are particularly interesting since we would expect to detect absorbed sources more easily in this band than in the softer ones. Around 25% of the XMS sources in the Hard and Ultrahard bands have been classified as Type-2 AGN, having most of them an intrinsic log N H > 22, which is the N H value 117
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Universidad de Cantabria Departamen
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A mis padres
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explicar las altas luminosidades de
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Además, una importante fracción (
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ealizar estudios de espectroscopía
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distribución diferencial que, al e
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materia sobre el agujero negro cent
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analizadas proviene de fuentes en t
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Haciendo uso del segundo catálogo
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With magic, you can turn a frog int
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Un capítulo aparte merecen mis com
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Summary Since its discovery more th
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xxxiv
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CONTENTS 1.6.1 The K-correction . .
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CONTENTS 5.3.2 Analytical model . .
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LIST OF FIGURES 4.6 Soft 1 − P µ
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Chapter 1 Introduction In the last
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CHAPTER 1: INTRODUCTION have confir
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CHAPTER 1: INTRODUCTION by this mis
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CHAPTER 1: INTRODUCTION Figure 1.2
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CHAPTER 1: INTRODUCTION [161], [242
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CHAPTER 1: INTRODUCTION tant contri
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CHAPTER 1: INTRODUCTION to-noise ra
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CHAPTER 1: INTRODUCTION Compton up-
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CHAPTER 1: INTRODUCTION ([142]). It
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CHAPTER 1: INTRODUCTION (NLR) and i
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CHAPTER 1: INTRODUCTION optically c
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CHAPTER 1: INTRODUCTION ber of AGN
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CHAPTER 1: INTRODUCTION Figure 1.5
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CHAPTER 1: INTRODUCTION 1.7.3 The X
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CHAPTER 1: INTRODUCTION AGN are ess
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CHAPTER 1: INTRODUCTION subjects ma
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CHAPTER 2: AGN SURVEYS WITH XMM-New
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R R OQP ONM 40 Table 2.1: Continued
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Chapter 3 Source counts of the AXIS
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CHAPTER 3: SOURCE COUNTS OF THE AXI
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61 Table 3.1 Maximum likelihood fit
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Page 206 and 207: REFERENCES [16] Barger, A. J., Cowi
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REFERENCES [107] Hawkins, M. R. S.
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REFERENCES [148] Matarrese, S., Col
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REFERENCES [190] Richstone, D., Ahj
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REFERENCES [236] Wisotzky, L., 1998
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