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Published August 20, 2015 | Submitted + Published
Journal Article Open

The Quasar-LBG Two-point Angular Cross-correlation Function at z~4 in the COSMOS Field


In order to investigate the origin of quasars, we estimate the bias factor for low-luminosity quasars at high redshift for the first time. In this study, we use the two-point angular cross-correlation function (CCF) for both low-luminosity quasars at -24 < M_(1450) < -22 and Lyman-break galaxies (LBGs). Our sample consists of both 25 low-luminosity quasars (16 objects are spectroscopically confirmed low-luminosity quasars) in the redshift range 3.1 < z < 4.5 and 835 color-selected LBGs with z'_(LBG) < 25.0 at z ~ 4 in the COSMOS field. We have performed our analysis for the following two quasar samples: (1) the spectroscopic sample (the 16 quasars confirmed by spectroscopy), and (2) the total sample (the 25 quasars including 9 quasars with photometric redshifts). The bias factor for low-luminosity quasars at z ~ 4 is derived by utilizing the quasar-LBG CCF and the LBG auto-correlation function. We then obtain the 86% upper limits of the bias factors for low-luminosity quasars, which are 5.63 and 10.50 for the total and the spectroscopic samples, respectively. These bias factors correspond to the typical dark matter halo masses, log (M_(DM)/(h^(-1)M⊙)) = 12.7 and 13.5, respectively. This result is not inconsistent with the predicted bias for quasars that is estimated by the major merger models.

Additional Information

© 2015 The American Astronomical Society. Received 2014 August 21; accepted 2015 July 13; published 2015 August 18. We would like to thank the Subaru staff for their invaluable help and all members of the COSMOS team. We thank Philip Hopkins for providing the data of the predicted bias factor, which are calculated by his models. We also thank the referee for useful suggestions and comments that helped us to improve this paper. This work was financially supported in part by the Japan Society for the Promotion of Science (JSPS; grant Nos. 23244031 and 25707010), and also by the Yamada Science Foundation. T.M. is supported by UNAM-DGAPA grant PAPIIT IN104113 and CONACyT Grant Científica Básica 179662. H.I. and K.M. are financially supported by the JSPS through the JSPS Research Fellowship.

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Published - Ikeda_2015.pdf

Submitted - 1507.05292v2.pdf


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August 20, 2023
October 25, 2023