Surveys for high-redshift (z>6) AGN with AXIS (cf. Athena) James Aird. University of Cambridge (-> University of Leicester)

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1 Surveys for high-redshift (z>6) AGN with AXIS (cf. Athena) James Aird University of Cambridge (-> University of Leicester)

2 SMBH seed formation mechanisms Pop III star remnants MBH ~ 100 M z~20-30 Direct gravitational collapse MBH ~ 10 5 M z~15 Stellar cluster collapse MBH ~ 1000 M z~10 from Volonteri (2012) MBH ~ M z~6 and below Grow by merging and accretion

3 AGN at z>6 - the tip of the iceberg The known population of z > 6 consists of extremely luminous QSOs, identified in large area optical/near-infrared surveys (Fan et al. 2003, 2006, Mortlock et al. 2011, Banados et al. 2014, Venemans et al. 2015) Powered by SMBHs with MBH ~ 10 9 M, comparable to the most massive SMBHs in the local Universe, but when the age of the Universe was only <1Gyr

4 Building high redshift QSOs - constraints on growth rates and seed masses Assuming Eddington limited growth, black hole mass grows as: cosmic time Redshift (z) ULAS J seed mass radiative efficiency ~0.1 Eddington ratio ~1 The seed of ULAS J1120 (z=7.083, MBH 2 x 10 9 M ) could have formed by direct collapse at z~15, but requires growth at ~Eddington limit for entire lifetime Pop III seed requires super-eddington growth for substantial fraction of age of the Universe MBH/M N.B. extreme, rare object - not representative of bulk of early SMBHs and their growth Direct collapse PopIII remnant Age of the Universe (Myr) Cosmic Time

5 Science aims for a future X-ray observatory 1. Directly detect the population of seed SMBHs shortly after formation in the early universe => 10 5 Msun at z > 10 at best => LX 5x10 41 erg s (assuming accreting at the Eddington limit) (f0.5-2kev 4 x10-19 erg s -1 cm -2 ) 2. Track the subsequent growth of typical SMBHs during the early epoch of galaxy formation (i.e. Epoch of re-ionization: z=6-10) => detect+characterize populations of LX ~ erg s -1 => place constraints on different seed formation mechanisms

6 Evolution of AGN to high z Difficult to find z>6 AGN due to rapid decline in the space densities of AGN at z>3 for all luminosities (related to decreasing number density of galaxies?) Space density [Mpc 3 ] Redshift (z) < log L X < < log L X < < log L X < < log L X < log (1+z) Aird+15, Miyaji+15 (see also e.g. Brusa+09; Ueda+14; Vito+14,16; Georgakakis+15)

7 Surveys requirements for z>6 AGN To find typical luminosity AGN (LX= erg s -1 ) at z > 6 need to cover large areas of sky (>~1-10 sq. degrees) to depths comparable to deepest Chandra fields Area coverage to given flux limit required to yield >10 sources per 0.5 dex luminosity bin at indicated z (N.B. assuming one specific, but conservative, extrapolation of AGN LF) log f kev [erg s -1 cm -2 ] CDF-S (4Ms) AEGIS LX=10 43 erg s z=6 COSMOS Legacy XMM-LSS +XXL erosita SDSS QSOs z=6-7 z=7-8 z=8-10 LX=10 42 erg s z= Area [deg 2 ] Euclid QSOs 5" confusion limit 1.0" confusion limit 0.5" confusion limit

8 Athena survey capabilities Athena ~25Ms program (assuming 1.4m 2 eff. area) able to probe LX>10 43 erg s and LX~10 44 erg s -1 to z~8 N.B. Ultimately limited by ~5 confusion limit Does not directly detect seeds (~<10 5 Msun) at z>6, but is able to characterize the early growth log f kev [erg s -1 cm -2 ] CDF-S (4Ms) AEGIS COSMOS Legacy XMM-LSS +XXL erosita SDSS QSOs z=6-7 z=7-8 z=8-10 ATHENA (~25Ms) Area [deg 2 ] Euclid QSOs 5" confusion limit 1.0" confusion limit 0.5" confusion limit

9 AXIS survey capabilities Assuming: 01nov16 response matrix (0.5m 2 effective area) 12 x 12 field-of-view Moderate vignetting off-axis) PSF=0.5 across entire FOV log f kev [erg s -1 cm -2 ] CDF-S (4Ms) AEGIS COSMOS Legacy XMM-LSS +XXL erosita SDSS QSOs z=6-7 z=7-8 z=8-10 ATHENA (~25Ms) Euclid QSOs AXIS 320 x 50ks = 16Ms 5" confusion limit AXIS 80x200ks = 16Ms -18 AXIS 16x2Ms = 32Ms 1.0" confusion limit \ " confusion limit Area [deg 2 ]

10 AXIS survey capabilities Conclusions: Difficult to improve on Athena wide survey capabilities (complementary programs? e.g. AXIS follow-up of Athena z>6 candidates?) -14 XMM-LSS +XXL erosita SDSS QSOs A large (~80x200ks) =16Ms program is comparable to Athena deepest survey tier (~17x800ks) - but better PSF? Extremely large AXIS program (16x2Ms=32Ms) could probe a factor ~10 lower in Low-LX beyond AXIS capabilities Potential role for AXIS surveys, but difficult to make a strong case for transformative high-z science cf. Athena log f kev [erg s -1 cm -2 ] CDF-S (4Ms) AEGIS COSMOS Legacy z=6-7 z=7-8 z=8-10 ATHENA (~25Ms) Euclid QSOs AXIS 320 x 50ks = 16Ms 5" confusion limit AXIS 80x200ks = 16Ms AXIS 16x2Ms = 32Ms Other considerations: 1.0" confusion limit Larger field-of-view (e.g. 30 x 30 ) would significantly improve survey capability (assuming moderate vignetting) Only require ~1-2 PSF (N.B. reduces point source sensitivity; ideally want ~constant PSF over FOV) " confusion limit Area [deg 2 ]