Low accretion rates at the AGN cosmic downsizing epoch
Context: X-ray surveys of Active Galactic Nuclei (AGN) indicate `cosmic downsizing', with the comoving number density of high-luminosity objects peaking at higher redshifts (z about 2) than low-luminosity AGN (z<1). Aims: We test whether downsizing is caused by activity shifting towards...
| Main Authors: | , , , , , |
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| Format: | Journal article |
| Language: | English |
| Published: |
2007
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| _version_ | 1826261574603505664 |
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| author | Babic, A Miller, L Jarvis, M Turner, T Alexander, D Croom, S |
| author_facet | Babic, A Miller, L Jarvis, M Turner, T Alexander, D Croom, S |
| author_sort | Babic, A |
| collection | OXFORD |
| description | Context: X-ray surveys of Active Galactic Nuclei (AGN) indicate `cosmic downsizing', with the comoving number density of high-luminosity objects peaking at higher redshifts (z about 2) than low-luminosity AGN (z<1). Aims: We test whether downsizing is caused by activity shifting towards low-mass black holes accreting at near-Eddington rates, or by a change in the average rate of accretion onto supermassive black holes. We estimate the black hole masses and Eddington ratios of an X-ray selected sample of AGN in the Chandra Deep Field South at z<1, probing the epoch where AGN cosmic downsizing has been reported. Methods: Black hole masses are estimated both from host galaxy stellar masses, which are estimated from fitting to published optical and near-infrared photometry, and from near-infrared luminosities, applying established correlations between black hole mass and host galaxy properties. Both methods give consistent results. Comparison and calibration of possible redshift-dependent effects is also made using published faint host galaxy velocity dispersion measurements. Results: The Eddington ratios in our sample span the range 10^{-5} to 1, with median log(L_bol/L_Edd)=-2.87, and with typical black hole masses about 10^{8} solar masses. The broad distribution of Eddington ratios is consistent with that expected for AGN samples at low and moderate luminosity. We find no evidence that the CDF-S AGN population is dominated by low-mass black holes accreting at near-Eddington ratios and the results suggest that diminishing accretion rates onto average-sized black holes are responsible for the reported AGN downsizing at redshifts below unity. |
| first_indexed | 2024-03-06T19:23:31Z |
| format | Journal article |
| id | oxford-uuid:1aec1a56-cd61-4a41-a036-f3213608a2b9 |
| institution | University of Oxford |
| language | English |
| last_indexed | 2024-03-06T19:23:31Z |
| publishDate | 2007 |
| record_format | dspace |
| spelling | oxford-uuid:1aec1a56-cd61-4a41-a036-f3213608a2b92022-03-26T10:57:26ZLow accretion rates at the AGN cosmic downsizing epochJournal articlehttp://purl.org/coar/resource_type/c_dcae04bcuuid:1aec1a56-cd61-4a41-a036-f3213608a2b9EnglishSymplectic Elements at Oxford2007Babic, AMiller, LJarvis, MTurner, TAlexander, DCroom, SContext: X-ray surveys of Active Galactic Nuclei (AGN) indicate `cosmic downsizing', with the comoving number density of high-luminosity objects peaking at higher redshifts (z about 2) than low-luminosity AGN (z<1). Aims: We test whether downsizing is caused by activity shifting towards low-mass black holes accreting at near-Eddington rates, or by a change in the average rate of accretion onto supermassive black holes. We estimate the black hole masses and Eddington ratios of an X-ray selected sample of AGN in the Chandra Deep Field South at z<1, probing the epoch where AGN cosmic downsizing has been reported. Methods: Black hole masses are estimated both from host galaxy stellar masses, which are estimated from fitting to published optical and near-infrared photometry, and from near-infrared luminosities, applying established correlations between black hole mass and host galaxy properties. Both methods give consistent results. Comparison and calibration of possible redshift-dependent effects is also made using published faint host galaxy velocity dispersion measurements. Results: The Eddington ratios in our sample span the range 10^{-5} to 1, with median log(L_bol/L_Edd)=-2.87, and with typical black hole masses about 10^{8} solar masses. The broad distribution of Eddington ratios is consistent with that expected for AGN samples at low and moderate luminosity. We find no evidence that the CDF-S AGN population is dominated by low-mass black holes accreting at near-Eddington ratios and the results suggest that diminishing accretion rates onto average-sized black holes are responsible for the reported AGN downsizing at redshifts below unity. |
| spellingShingle | Babic, A Miller, L Jarvis, M Turner, T Alexander, D Croom, S Low accretion rates at the AGN cosmic downsizing epoch |
| title | Low accretion rates at the AGN cosmic downsizing epoch |
| title_full | Low accretion rates at the AGN cosmic downsizing epoch |
| title_fullStr | Low accretion rates at the AGN cosmic downsizing epoch |
| title_full_unstemmed | Low accretion rates at the AGN cosmic downsizing epoch |
| title_short | Low accretion rates at the AGN cosmic downsizing epoch |
| title_sort | low accretion rates at the agn cosmic downsizing epoch |
| work_keys_str_mv | AT babica lowaccretionratesattheagncosmicdownsizingepoch AT millerl lowaccretionratesattheagncosmicdownsizingepoch AT jarvism lowaccretionratesattheagncosmicdownsizingepoch AT turnert lowaccretionratesattheagncosmicdownsizingepoch AT alexanderd lowaccretionratesattheagncosmicdownsizingepoch AT crooms lowaccretionratesattheagncosmicdownsizingepoch |