3 results
Search Results
Now showing 1 - 3 of 3
- ItemX-ray emission from a rapidly accreting narrow-line Seyfert 1 galaxy at z = 6.56(Les Ulis : EDP Sciences, 2023) Wolf, J.; Nandra, K.; Salvato, M.; Buchner, J.; Onoue, M.; Liu, T.; Arcodia, R.; Merloni, A.; Ciroi, S.; Di Mille, F.; Burwitz, V.; Brusa, M.; Ishimoto, R.; Kashikawa, N.; Matsuoka, Y.; Urrutia, T.; Waddell, S.G.H.The space density of X-ray-luminous, blindly selected active galactic nuclei (AGN) traces the population of rapidly accreting super-massive black holes through cosmic time. It is encoded in the X-ray luminosity function, whose bright end remains poorly constrained in the first billion years after the Big Bang as X-ray surveys have thus far lacked the required cosmological volume. With the eROSITA Final Equatorial-Depth Survey (eFEDS), the largest contiguous and homogeneous X-ray survey to date, X-ray AGN population studies can now be extended to new regions of the luminosity-redshift space (L2-10 keV > 1045 erg s-1 and z > 6). Aims. The current study aims at identifying luminous quasars at z > 5:7 among X-ray-selected sources in the eFEDS field in order to place a lower limit on black hole accretion well into the epoch of re-ionisation. A secondary goal is the characterisation of the physical properties of these extreme coronal emitters at high redshifts. Methods. Cross-matching eFEDS catalogue sources to optical counterparts from the DESI Legacy Imaging Surveys, we confirm the low significance detection with eROSITA of a previously known, optically faint z = 6:56 quasar from the Subaru High-z Exploration of Low-luminosity Quasars (SHELLQs) survey. We obtained a pointed follow-up observation of the source with the Chandra X-ray telescope in order to confirm the low-significance eROSITA detection. Using new near-infrared spectroscopy, we derived the physical properties of the super-massive black hole. Finally, we used this detection to infer a lower limit on the black hole accretion density rate at z > 6. Results. The Chandra observation confirms the eFEDS source as the most distant blind X-ray detection to date. The derived X-ray luminosity is high with respect to the rest-frame optical emission of the quasar.With a narrow Mgii line, low derived black hole mass, and high Eddington ratio, as well as its steep photon index, the source shows properties that are similar to local narrow-line Seyfert 1 galaxies, which are thought to be powered by young super-massive black holes. In combination with a previous high-redshift quasar detection in the field, we show that quasars with L2-10 keV > 1045 erg s-1 dominate accretion onto super-massive black holes at z _ 6.
- ItemMUSE observations towards the lensing cluster A2744: Intersection between the LBG and LAE populations at z ∼ 3–7(Les Ulis : EDP Sciences, 2020) de La Vieuville, G.; Pelló, R.; Richard, J.; Mahler, G.; Lévêque, L.; Bauer, F.E.; Lagattuta, D.J.; Blaizot, J.; Contini, T.; Guaita, L.; Kusakabe, H.; Laporte, N.; Martinez, J.; Maseda, M.V.; Schaerer, D.; Schmidt, K.B.; Verhamme, A.We present a study of the intersection between the populations of star forming galaxies selected as either Lyman break galaxies (LBGs) or Lyman-alpha emitters (LAEs) in the redshift range 2.9 − 6.7 and within the same volume of universe sampled by the Multi-Unit Spectroscopic Explorer (MUSE) behind the Hubble Frontier Fields lensing cluster A2744. We define three samples of star-forming galaxies: LBG galaxies with an LAE counterpart (92 galaxies), LBG galaxies without an LAE counterpart (408 galaxies), and LAE galaxies without an LBG counterpart (46 galaxies). All these galaxies are intrinsically faint because of the lensing nature of the sample (M1500 ≥ −20.5). The fraction of LAEs among all selected star-forming galaxies increases with redshift up to z ∼ 6 and decreases for higher redshifts, in agreement with previous findings. The evolution of LAE/LBG populations with UV magnitude and Lyα luminosity shows that the LAE selection is able to identify intrinsically UV faint galaxies with M1500 ≥ −15 that are typically missed in the deepest lensing photometric surveys. The LBG population seems to fairly represent the total population of star-forming galaxies down to M1500 ∼ −15. Galaxies with M1500 < −17 tend to have SFRLyα < SFRuv, whereas the opposite trend is observed within our sample for faint galaxies with M1500 > −17, including galaxies only detected by their Lyα emission, with a large scatter. These trends, previously observed in other samples of star-forming galaxies at high-z, are seen here for very faint M1500 ∼ −15 galaxies; that is, much fainter than in previous studies. The present results show no clear evidence for an intrinsic difference between the properties of the two populations selected as LBG and/or LAE. The observed trends could be explained by a combination of several phenomena, like the existence of different star-formation regimes, the dust content, the relative distribution and morphology of dust and stars, or the stellar populations.
- ItemAstraeus - VI. Hierarchical assembly of AGN and their large-scale effect during the Epoch of Reionization(Oxford : Oxford Univ. Press, 2022) Trebitsch, Maxime; Hutter, Anne; Dayal, Pratika; Gottlöber, Stefan; Legrand, Laurent; Yepes, GustavoIn this work, the sixth of a series, we use the seminumerical rAdiative tranSfer coupling of galaxy formaTion and Reionization in N-body dark-matter simUlationS (ASTRAEUS) framework to investigate the nature of the sources that reionized the Universe. We extend ASTRAEUS, which already couples a galaxy formation semi-analytical model with a detailed seminumerical reionization scheme, to include a model for black-hole formation, growth, and the production of ionizing radiation from associated active galactic nuclei (AGNs). We calibrate our fiducial AGN model to reproduce the bolometric luminosity function at z ≃ 5, and explore the role of the resulting AGN population in reionizing the Universe. We find that in all the models yielding a reasonable AGN luminosity function, galaxies dominate overwhelmingly the ionizing budget during the Epoch of Reionization, with AGN accounting for 1-10 per cent of the ionizing budget at z = 6 and starting to play a role only below z ≾ 5.