PEARLS: NuSTAR and XMM-Newton Extragalactic Survey of the JWST North Ecliptic Pole Time-domain Field III

TL;DR

This paper presents the NuSTAR and XMM-Newton NEP-Time-Domain Field survey results for cycles 8+9, expanding the hard X-ray AGN census over 0.31 deg^2 with ~2.0 Ms of NuSTAR data and ~166 ks of XMM data. The authors implement extensive simulations to quantify reliability, completeness, and sensitivity, and construct detailed source catalogs in five NuSTAR bands along with an XMM-Newton catalog, achieving 75 NuSTAR detections and 274 XMM detections with robust multiwavelength crossmatches. They find a logN$-$logS slope in the 8–24 keV band consistent with Euclidean expectations within uncertainties, identify a substantial fraction of obscured AGN, and estimate a Compton-thick AGN fraction of about 9 extsuperscript{+18}_{-8} ext{%,} with ongoing follow-up to refine redshifts and spectral properties. The work demonstrates the value of joint hard X-ray and soft X-ray observations, complemented by JWST and other multiwavelength data, for probing AGN obscuration, evolution, and their contribution to the CXB in a time-domain context.

Abstract

The James Webb Space Telescope (JWST) North Ecliptic Pole (NEP) Time-Domain Field (TDF) has been monitored by NuSTAR and XMM-Newton with a regular cadence for five years starting in 2019. The survey has accumulated 3.5Ms of NuSTAR exposure and 228 ks quasi-simultaneous XMM-Newton observations covering 0.31 deg^2. This paper presents the results from the most recent two-years' 2Ms NuSTAR and 166 ks XMM observations in NuSTAR cycles 8 and 9. These observations reached a 20%-area flux of 2.20 x 10^-14 erg cm^-2 s^-1 in the 8-24 keV band. 75 NuSTAR sources and 274 XMM-Newton sources are detected at 99% reliability level. The logN-logS measured in cycles 8+9 are consistent with those measured in the previous cycle 5+6 NuSTAR NEP survey, but in a larger area (0.3 deg^2 compared with 0.19 deg^2). The slope of the cycles 8+9 8-24 keV logN-logS curve is flatter than other works (α89 = 1.13 +/- 0.46), but is consistent with the Euclidean value of α = 1.50. In addition, we found ~36% of the NuSTAR sources to be heavily obscured (NH >= 10^23 cm^-2). The Compton-thick (NH >= 10^24 cm^-2) (CT-) AGN fraction is 9+18-8% in the NEP-TDF, which is consistent with the measurements in previous surveys.

Figures (22)

• Figure 1: The cumulative area covered by the NuSTAR NEP TDF survey as a function of the FPMA+FPMB vignetting corrected exposure times. The cycle 5 curve is in red, cycle 6 (two year program) in blue, the combined cycles 5 and 6 in purple, cycle 8 in green, cycle 9 in cyan, and combined cycles 8 and 9 in orange. The 3$-$24 keV curve is plotted as a solid line, the 3$-$8 keV as a dotted line, and the 8$-$24 keV as a dashed line. The grey vertical lines enclose the five exposure bins used to determine the reliability of the cycles 8+9 survey (see Section \ref{['sec:rel_and_compl']}).
• Figure 2: The combined NuSTAR cycles 8+9 mosaic in the 3$-$24 keV band. All 75 detected sources are labeled. The green circles (25$\arcsec$ radius) represent the 48 sources with XMM-Newton counterparts from cycles 8+9, the magenta circles (25$\arcsec$ radius) represent the 5 sources with XMM-Newton counterparts from cycle 6, and the black squares (45$\arcsec$ width) represent the 22 NuSTAR sources without XMM-Newton counterparts. See Section \ref{['sec:xmm_nus_crossmatch']} for more details. Also plotted are footprints from the NuSTAR cycles 5+6 survey (black), the XMM-Newton cycle 6 survey (white), and the XMM-Newton cycles 8+9 survey (blue).
• Figure 3: The five plots display each of the five different time bins selected to measure the reliability and completeness of our cycle 8+9 simulations. These bins were selected to provide an equal amount of sources per bin, thus ensuring significant statistics could be measured for every bin. The left plots show the reliability as a function of DET_ML and the right plots show the completeness at a 99% reliability level as a function of flux. In all plots, the solid black line represents the 3$-$24 keV band, the dashed black the 3$-$8 keV, the dash-dot black line the 8$-$24 keV, the solid green the 8$-$16 keV, and the solid blue line the 16$-$24 keV. On the left, the 95% and 99% reliability levels are indicated with horizontal black dotted lines. Note: It is not correct to directly compare the curves from each different energy band. A conversion factor, dependent on the two bands in question, must be applied in order to do so.
• Figure 4: The sky coverage as a function of flux at a 99% reliability level for all five energy bands. The orange solid lines represent the cycles 8+9 curves while the purple dashed lines represent the cycles 5+6 curves. The vertical lines illustrate the half-area fluxes.
• Figure 5: The 8$-$24 keV sensitivity curves of the NEP TDF survey for cycles 8+9 (orange) and 5+6 (purple). Other NuSTAR surveys included for comparison are the: COSMOS Civano2015, ECDFS Mullaney2015, EGS (dash dot dotted line; Aird et al. in preparation), UDS Masini2018a, 40-month Serendipitous Lansbury2017, and the 80-month Serendipitous Greenwell2024.