Conferencias y seminarios
Jueves 17 de Mayo de 2018
Sala de Conferencias Federico Ristenpart (Camino El Observatorio 1515, Departamento de Astronomía, Edificio Central, piso 3, Las Condes, Santiago, Chile)
Dr. Konstantina Boutsia
Carnegie Observatories, Las Campanas Observatory
Looking for the sources of reionization
The source population responsible for the reionization of the Universe is still elusive. So far, it has been attributed to high redshift star-forming galaxies but recent studies fail to detect enough ionizing radiation, escaping these sources, to sustain the entire process. Very bright QSOs are able to ionize their surrounding medium but their volume density is too low to provide the required UV background. A significant contribution by faint AGN at z>4 could solve the problem. Recently, we measured an HI ionizing escape fraction greater than 70% in 16 faint (L>0.5L*) AGN at 3.5<z<4.2 with deep spectroscopy.
The Lyman Continuum escape fraction of our faint AGN sample does not show any dependence on absolute luminosities or observed colors. This indicates that the faint AGN population can contribute substantially (36-73%) to the ionizing background at z~4. In order to better constraint such AGN contribution, it is thus mandatory to accurately measure also the luminosity function of AGN at high-z and at faint magnitudes (L~0.01-1.0 L*). At this aim, we performed extensive searches for z>4 AGN in the deep CANDELS survey and in the wide COSMOS field. In particular, we used the wide field spectrograph IMACS on the 6.5m Baade Magellan Telescope to spectroscopically confirm a sample of L~L* z>4 AGN candidates in the COSMOS field.
The spectroscopically confirmed sources, coupled with the AGN at L~0.01-0.1L* found in the CANDELS survey, allow us to better constraint the slope at the faint end of the AGN luminosity function and the break magnitude. The resulting space density of faint AGN at z>4 seems to indicate that they could give a substantial contribution to the reionization process.
Rene A. Mendez
Comunicaciones DAS - FCFM