English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Tools annual

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools monthly

Global: Zendy Plus monthly

Presents the access of premium content as premium feature

Premium Content

Global: Zendy Plus annual

Global: Zendy Free Plan

Using the 4 Ms Chandra Deep Field-South (CDF-S) survey, we have identified asample of 6845 X-ray undetected galaxies that dominates the unresolved ~ 20-25%of the 6-8 keV cosmic X-ray background (XRB). This sample was constructed byapplying mass and color cuts to sources from a parent catalog based onGOODS-South HST z-band imaging of the central 6'-radius area of the 4 Ms CDF-S.The stacked 6-8 keV detection is significant at the 3.9 sigma level, but thestacked emission was not detected in the 4-6 keV band which indicates theexistence of an underlying population of highly obscured active galactic nuclei(AGNs). Further examinations of these 6845 galaxies indicate that the galaxieson the top of the blue cloud and with redshifts of 1 < z < 3, magnitudes of 25< z_850 < 28, and stellar masses of 2E8 < M_star/M_sun < 2E9 make the majoritycontributions to the unresolved 6-8 keV XRB. Such a population is seeminglysurprising given that the majority of the X-ray detected AGNs reside in massive(> ~1E10 M_sun) galaxies. We discuss constraints upon this underlying AGNpopulation, supporting evidence for relatively low-mass galaxies hosting highlyobscured AGNs, and prospects for further boosting the stacked signal.

Tracking Down the Source Population Responsible for the Unresolved Cosmic 6-8 keV Background