{"article_processing_charge":"No","publication_identifier":{"issn":["0004-637X"]},"date_created":"2024-09-06T12:06:45Z","OA_place":"repository","oa":1,"intvolume":"       521","page":"L9-L12","date_updated":"2024-11-12T13:00:30Z","issue":"1","abstract":[{"lang":"eng","text":"It is currently unknown whether the universe was reionized by quasars or stars at z ≳ 5. We point out that quasars can be best distinguished from stellar systems by their X-ray emission. Based on a simple hierarchical CDM model, we predict the number counts and X-ray fluxes of quasars at high redshifts. The model is consistent with available data on the luminosity function of high-redshift quasars in the optical and soft X-ray bands. The cumulative contribution of faint, undetected quasars in our model is consistent with the unresolved fraction of the X-ray background. We find that the Chandra X-ray Observatory might detect ~10^2 quasars from redshifts z ≳ 5 per its 17' × 17' field of view at the flux threshold of ~2 × 10^-16 ergs s^-1 cm^-2. The redshifts of these faint point sources could be identified by follow-up infrared observations from the ground or with the Next Generation Space Telescope."}],"month":"08","day":"10","title":"X-ray emission from the first quasars","publication_status":"published","date_published":"1999-08-10T00:00:00Z","extern":"1","_id":"17827","year":"1999","type":"journal_article","arxiv":1,"doi":"10.1086/312177","user_id":"2DF688A6-F248-11E8-B48F-1D18A9856A87","language":[{"iso":"eng"}],"volume":521,"publication":"The Astrophysical Journal","OA_type":"green","main_file_link":[{"open_access":"1","url":"https://doi.org/10.48550/arXiv.astro-ph/9904340"}],"publisher":"American Astronomical Society","oa_version":"Preprint","author":[{"orcid":"0000-0003-3633-5403","full_name":"Haiman, Zoltán","last_name":"Haiman","first_name":"Zoltán","id":"7c006e8c-cc0d-11ee-8322-cb904ef76f36"},{"full_name":"Loeb, Abraham","last_name":"Loeb","first_name":"Abraham"}],"citation":{"short":"Z. Haiman, A. Loeb, The Astrophysical Journal 521 (1999) L9–L12.","chicago":"Haiman, Zoltán, and Abraham Loeb. “X-Ray Emission from the First Quasars.” <i>The Astrophysical Journal</i>. American Astronomical Society, 1999. <a href=\"https://doi.org/10.1086/312177\">https://doi.org/10.1086/312177</a>.","ama":"Haiman Z, Loeb A. X-ray emission from the first quasars. <i>The Astrophysical Journal</i>. 1999;521(1):L9-L12. doi:<a href=\"https://doi.org/10.1086/312177\">10.1086/312177</a>","apa":"Haiman, Z., &#38; Loeb, A. (1999). X-ray emission from the first quasars. <i>The Astrophysical Journal</i>. American Astronomical Society. <a href=\"https://doi.org/10.1086/312177\">https://doi.org/10.1086/312177</a>","mla":"Haiman, Zoltán, and Abraham Loeb. “X-Ray Emission from the First Quasars.” <i>The Astrophysical Journal</i>, vol. 521, no. 1, American Astronomical Society, 1999, pp. L9–12, doi:<a href=\"https://doi.org/10.1086/312177\">10.1086/312177</a>.","ista":"Haiman Z, Loeb A. 1999. X-ray emission from the first quasars. The Astrophysical Journal. 521(1), L9–L12.","ieee":"Z. Haiman and A. Loeb, “X-ray emission from the first quasars,” <i>The Astrophysical Journal</i>, vol. 521, no. 1. American Astronomical Society, pp. L9–L12, 1999."},"scopus_import":"1","external_id":{"arxiv":["astro-ph/9904340"]},"status":"public","quality_controlled":"1","article_type":"original"}