NuSTAR and the Cosmic X-ray Background

The cosmic X-ray background (CXB) was first discovered in the early 1960's, several years before the detection of the cosmic microwave background (CMB). However, unlike the CMB, it appears that the CXB is dominated by the emission from high-energy distant point sources: Active Galactic Nuclei (AGNs), the sites of intense black-hole growth that reside at the centres of galaxies. A key goal of high-energy astrophysics is to determine the composition of the CXB.

Huge strides in revealing the composition of the CXB have been made over the past decade, with sensitive surveys undertaken by the Chandra and XMM-Newton observatories, revealing a plethora of obscured and unobscured AGNs out to z~5-6. However, Chandra and XMM-Newton are only sensitive to sources emitting at ~0.5-10 keV, far from the peak of the CXB at ~20-30 keV. Previous generation observatories have only resolved ~1-2% of the CXB at the 20-30 keV peak and therefore provide a very limited view of the source populations that dominate the CXB.

The great breakthrough in resolving the peak of the CXB is NuSTAR. NuSTAR was successfully launched on June 13th 2012 and is the first >10 keV observatory with focusing optics. The focusing optics on NuSTAR provide a ~1-2 orders of magnitude improvement in sensitivity and angular resolution over previous-generation >10 keV observatories, a genuine leap forward in performance. One of the primary tasks of NuSTAR is to complete a sensitive extragalactic survey and identify the source populations that produce the peak of the CXB.

NuSTAR Extragalactic Survey

The NuSTAR extragalactic survey is comprised of three components (see Table~6 of Harrison et al. 2013): a deep small-area survey in the Extended Chandra Deep Field-South (E-CDF-S), a medium wider-area survey in the Cosmic Evolution Survey (COSMOS) and a large area (typically shallow) serendipitous survey conducted in the fields of other NuSTAR targets, including ~100 Swift-BAT identified AGNs.

Durham is leading the execution of the deep E-CDF-S survey, is leading the shallow serendipitous survey, and is making significant contributions to the execution of the medium COSMOS survey. Durham is responsible for providing the NuSTAR data products and data catalogues for the E-CDF-S and serendipitous surveys within the NuSTAR extragalactic survey team.

Publications for the extragalactic survey:

1. - THE NUSTAR EXTRAGALACTIC SURVEY: A FIRST LOOK AT THE DISTANT HIGH-ENERGY COSMIC X-RAY BACKGROUND POPULATION; Alexander, D.M., Stern, D., Del Moro, A., Lansbury, G.B., Assef, R.J., Aird, J., Ajello, M., Ballantyne, D.R., Bauer, F.E., Boggs, S.E., Brandt, W.N., Christensen, F.E., Civano, F., Comastri, A., Craig, W.W., Elvis, M., Grefenstette, B.W., Hailey, C.J., Harrison, F.A., Hickox, R.C., Luo, B., Madsen, K.K., Mullaney, J.R., Perri, M., Puccetti, S., Saez, C., Treister, E., Urry, C.M., Zhang, W.W., Bridge, C.R., Eisenhardt, P.R.M., Gonzalez, A.H., Miller, S.H., Tsai, C.W. 2013, ApJ, 773, 125.


2. - NUSTAR J033202-2746.8: DIRECT CONSTRAINTS ON THE COMPTON REFLECTION IN A HEAVILY OBSCURED QUASAR AT Z~2; Del Moro, A., Mullaney, J.R., Alexander, D.M., Comastri, A., Bauer, F.E., Treister, E., Stern, D., Civano, F., Ranalli, P., Vignali, C., Aird, J.A., Ballantyne, D.R., Balokovic, M., Boggs, S.E., Brandt, W.N., Christensen, F.E., Craig, W.W., Gandhi, P., Gilli, R., Hailey, C.J., Harrison, F.A., Hickox, R.C., LaMassa, S.M., Lansbury, G.B., Luo, B., Puccetti, S., Urry, C.M., Zhang, W.W. 2014, 786, 16.


3. - THE NUSTAR EXTRAGALACTIC SURVEY: EXTENDED CHANDRA DEEP FIELD SOUTH CATALOGS; J. Mullaney et al., in prep.


4. - THE NUSTAR EXTRAGALACTIC SURVEY: COSMIC EVOLUTION SURVEY CATALOGS; F. Civano et al., in prep.

















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