The NuSTAR Extragalactic Survey: A 1st Look at the Distant High-Energy X-ray

Background

D.R. Ballantyne (Georgia Tech) on behalf of

M. Ajello, D. Alexander, R. Assef, M. Balokovic, F. Bauer, S. Boggs, K. Boydstun, C. Bridge, F. Christensen, W. Craig, G. Lansbury, A. Del Moro, P. Eisenhardt, A. Gonzalez, C. Hailey, F. Harrison, T.-N. Lu, D. Stern, W. Zhang and the rest of the NuSTAR Extragalactic Surveys Working Group

The X-ray Background: Current Status

~100% directly resolved at <6 keV and >50% at 6-10 keV by

Chandra & XMM

~1-2% directly resolved at 20-30 keV peak by

Swift-BAT/INTEGRAL etc

Goals for NuSTAR

• Composition of ~20-30 keV peak and resolving >30-50% of the X-ray background from direct detections and stacking Chandra/XMM sources

• Trace the evolution of AGNs and obscuration with redshift (NuSTAR AGN selection almost irrespective of obscuration)

• Measure to high precision the high-energy properties of local AGNs to better define the physical components and modelling of the XRB

DRB, Draper, Madsen, Rigby & Treister (2011)

NuSTAR

Deep: E-CDF-S (GOODS-S)Deep: E-CDF-S (GOODS-S)~200 ks/pointing over ~200 ks/pointing over

0.25 deg0.25 deg22

Medium: COSMOSMedium: COSMOS~25-50 ks/pointing over ~25-50 ks/pointing over

1-2 deg1-2 deg22

Large area: Large area: serendipitousserendipitousSerendipitous Serendipitous

detections, principally detections, principally 100 Swift-BAT AGNs (~16 100 Swift-BAT AGNs (~16 ks each) but also other ks each) but also other NuSTARNuSTAR targets to get targets to get ~3-4 deg~3-4 deg22 of coverage of coverage

Extragalactic surveys: three-tiered design

See poster 109.09 by F. Civano on 1st ECDF-S and COSMOS

results

Multi-wavelength properties of 3C382 serendipitous Multi-wavelength properties of 3C382 serendipitous sourcesource

Serendipitous Survey

NuSTAR A

NuSTAR B

XMM-Newton

Optical

3.4um WISE 12um WISE

Produced by: G. Lansbury, D. Produced by: G. Lansbury, D. Alexander, A. Del Moro, J. MullaneyAlexander, A. Del Moro, J. Mullaney

NuSTAR 3-24 keV image of 3C382 field

3C382

Serendipitous detection

Current statistics: 33 Current statistics: 33 serendipitous sources detected serendipitous sources detected by by NuSTARNuSTAR in in 64 fields - 20 have been 64 fields - 20 have been spectroscopically identified spectroscopically identified to date (including one known to date (including one known Galactic CV)Galactic CV)

Here, I report on the properties of the first 10 AGNs discovered in the serendipitous survey (Alexander et al. in prep).

First 10 serendips: optical spectra

Overall: 5 (~50%) are broad-line AGNs, 4 (~40%) are narrow-line AGNs, and 1 BL Lac

Example optical spectra: most of the serendipitous sources were not studied before and so we have been obtaining optical spectroscopic follow up.

z=0.020 narrow-line AGN (hosted in a dwarf galaxy)

z=2.923 broad-line AGN

z=0.891 narrow-line AGN

z=1.073 broad-line AGN

First 10 serendips: basic properties

NuSTAR is ~100x more sensitive than Swift-BAT for AGN in Burlon et al. (2011):• average redshift is z~0.8 (z~0.03 for Swift-BAT)• average X-ray luminosity is ~3x1044 erg/s (~3x1043 erg/s for Swift-BAT)X-ray band ratios suggest that AGNs are Compton thin with NH<5x1023 cm-2.

NLAGN

BLAGN

NLAGN

BLAGN

First 10 serendips: X-ray spectral fitting

Broad-band 0.5-30 keV spectral fitting (absorbed power law): need to use C statistics for the majority of the sources, which are faint.

Results: 5 AGNs (~50%) are obscured with NH~1022-1024 cm-2 (~1.8).

Broadly consistent with the Swift-BAT results of Burlon et al. (2011) but AGNs are ~10x more luminous.

Lack of Compton-thick AGNs at this early stage is consistent with the Swift-BAT sample and theoretical expectations.

Swift-XRT (or Chandra/XMM-Newton)

NuSTAR

First 10 serendips: joint rest-frame 10-40 keV

Joint spectral fitting of the rest-frame 10-40 keV data for all non-beamed sources with LX>1043 erg/s.

The best-fitting spectral slope and constraint on reflection (~1.9 and R<1.4) are consistent with local AGNs (see poster 109.02 by Ballantyne).

With these results we are starting to constrain models for the evolution in the properties of the obscuring region with redshift.

Summary

• All 3 NuSTAR extragalactic surveys underway

• Initial results show that, as advertised, NuSTAR will efficiently detect z<~ 2 Compton-thin AGNs regardless of the obscuring column-density

NuSTAR (launch in 9 days!!)

10

First 10 serendips: UV-mid-infrared SEDs

Key result: average stellar mass of z~0.8 NuSTAR AGNs is ~1011 solar masses, as compared to ~2x1010 solar masses for z~0.03 Swift-BAT AGNs (Koss et al. 2011) – “downsizing” in the AGN population.

Example UV-mid-IR SEDs for two sources. Model fitting performed by Roberto Assef following Assef et al. (2008) and constraints AGN and host galaxy components, including dust reddening (E(B-V)).