X-rays from the first massive black holes

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Abstract

X-ray studies of high-redshift (z > 4) active galaxies have advanced substantially over the past few years, largely due to results from the new generation of X-ray observatories. As of this writing X-ray emission has been detected from nearly 60 high-redshift active galaxies. This paper reviews the observational results and their implications for models of the first massive black holes, and it discusses future prospects for the field.

Section snippets

Introduction and importance of high-redshift X-ray studies

Understanding of the X-ray emission from z > 4 active galactic nuclei (AGN) has advanced rapidly over the past few years. The high sensitivities of Chandra and XMM-Newton have allowed the efficient detection of many z > 4 AGN, and wide-field AGN surveys (e.g., the Sloan Digital Sky Survey, hereafter SDSS; York et al., 2000) have greatly enlarged the number of suitable X-ray targets. The number of X-ray detections at z > 4 has increased to 57 (see Fig. 1(a)).

X-ray observations

Most z > 4 X-ray detections to date have been obtained via moderate-depth [≈(1–20) × 10−15 erg cm−2 s−1 in the 0.5–2 keV band] follow-up observations of AGN discovered at other wavelengths (e.g., Kaspi et al., 2000, Vignali et al., 2001, Brandt et al., 2002a, Bechtold et al., 2003, Vignali et al., 2003a, Vignali et al., 2003c).

Conclusions and future prospects

From a general perspective, the main conclusions from the X-ray analyses reviewed above are the following:

  • 1.

    To the limits of current observation, AGN at z  4–6 and z  0–3 have reasonably similar X-ray and broad-band spectra (after controlling for luminosity effects upon the broad-band spectra). Specifically, the distributions of X-ray power-law photon index and αox appear consistent.

  • 2.

    The current X-ray data do not provide any hints for different accretion mechanisms at low and high redshift. The

Acknowledgements

We thank all of our collaborators on the work reviewed here. We thank G. Brunetti, S.C. Gallagher, D.A. Schwartz, and M.A. Strauss for useful discussions. We gratefully acknowledge the financial support of NASA LTSA grant NAG5-8107 (WNB, CV), NASA grant NAG5-9918 (WNB, CV, DPS), Chandra X-ray Center grant G02-3134X (WNB, CV, DPS), NSF grant AST99-00703 (DPS), Chandra X-ray Center grant G02-3187A (DMA, FEB), and NASA grant NAS 8-01128 (GPG).

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