| 1. |
- Ranalli, P., et al.
(author)
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The 2-10 keV unabsorbed luminosity function of AGN from the LSS, CDFS, and COSMOS surveys
- 2016
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 590
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Journal article (peer-reviewed)abstract
- The XMM-Large scale structure (XMM-LSS), XMM-Cosmological evolution survey (XMM-COSMOS), and XMM-Chandra deep field south (XMM-CDFS) surveys are complementary in terms of sky coverage and depth. Together, they form a clean sample with the least possible variance in instrument effective areas and point spread function. Therefore this is one of the best samples available to determine the 2-10 keV luminosity function of active galactic nuclei (AGN) and their evolution. The samples and the relevant corrections for incompleteness are described. A total of 2887 AGN is used to build the LF in the luminosity interval 1042-1046 erg s-1 and in the redshift interval 0.001-4. A new method to correct for absorption by considering the probability distribution for the column density conditioned on the hardness ratio is presented. The binned luminosity function and its evolution is determined with a variant of the Page-Carrera method, which is improved to include corrections for absorption and to account for the full probability distribution of photometric redshifts. Parametric models, namely a double power law with luminosity and density evolution (LADE) or luminosity-dependent density evolution (LDDE), are explored using Bayesian inference. We introduce the Watanabe-Akaike information criterion (WAIC) to compare the models and estimate their predictive power. Our data are best described by the LADE model, as hinted by the WAIC indicator. We also explore the recently proposed 15-parameter extended LDDE model and find that this extension is not supported by our data. The strength of our method is that it provides unabsorbed, non-parametric estimates, credible intervals for luminosity function parameters, and a model choice based on predictive power for future data.
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| 2. |
- Rutkowski, Michael J., et al.
(author)
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LYMAN CONTINUUM ESCAPE FRACTION OF STAR-FORMING DWARF GALAXIES AT z similar to 1
- 2016
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In: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 819:1
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Journal article (peer-reviewed)abstract
- To date, no direct detection of Lyman continuum emission has been measured for intermediate-redshift (z similar to 1) star-forming galaxies. We combine Hubble Space Telescope grism spectroscopy with GALEX UV and ground-based optical imaging to extend the search for escaping Lyman continuum to a large (similar to 600) sample of z similar to 1 low-mass (log((M) over bar) similar or equal to 9.3M(circle dot)), moderately star-forming ((Psi) over bar less than or similar to 10M(circle dot) yr(-1)) galaxies selected initially on H alpha emission. The characteristic escape fraction of LyC from star-forming galaxies (SFGs) that populate this parameter space remains weakly constrained by previous surveys, but these faint (sub-L-star) SFGs are assumed to play a significant role in the reionization of neutral hydrogen in the intergalactic medium (IGM) at high redshift z > 6. We do not make an unambiguous detection of escaping LyC radiation from this z similar to 1 sample, individual non-detections to constrain the absolute Lyman continuum escape fraction, f(esc) < 2.1% (3 sigma). We measure an upper limit of f(esc) < 9.6% from a sample of SFGs selected on high H alpha equivalent width (EW > 200 angstrom), which are thought to be close analogs of high redshift sources of reionization. For reference, we also present an emissivity-weighted escape fraction that is useful for measuring the general contribution SFGs to the ionizing UV background. In the discussion, we consider the implications of these intermediate redshift constraints for the reionization of hydrogen in the IGM at high (z > 6) redshift. If we assume our z similar to 1 SFGs, for which we measure this emissivity-weighted f(esc), are analogs to the high redshift sources of reionization, we find it is difficult to reconcile reionization by faint (MUV less than or similar to -13) SFGs with a low escape fraction (f(esc) < 3%), with constraints from independent high redshift observations. If f(esc) evolves with redshift, reionization by SFGs may be consistent with observations from Planck.
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