Hard X-ray observations of Extremely Red Objects Marcella Brusa Dip. Astronomia, Universita’ di Bologna & INAF- Osservatorio Astr. Di Bologna In collaboration with: A. Comastri, M. Mignoli & the HELLAS2XMM team L. Pozzetti, E. Daddi, A. Cimatti F. Civano venerdì 30 novembre 2018 GH2003 Workshop

Extremely Red Objects Discovered serendipitously in optical and near-infrared surveys by colour selection (Elston et al. 1988) Sources with most of the emission in the near-infrared band: R-K>5; I-K>4: Faint optical magnitude (R>23) Redshift range: 0.8<z<3 DUSTY STARBURSTS OBSCURED AGN OLD ELLIPTICALS venerdì 30 novembre 2018 GH2003 Workshop

EROs and hard X-ray sources Optical follow-up of sources detected in deep and medium deep hard X-ray samples  EROs colors Why X-ray detected EROs should be AGN? X-ray flux = 2x10-16 z=1  Observed 2-10 keV luminosity: L=1042 venerdì 30 novembre 2018 GH2003 Workshop

Observational results How many? -Fraction of EROs among X-ray sources -Fraction of X-ray emitters among EROs 2) Optical to X-ray properties 3) Spectroscopic identification 4) Hard X-ray spectral properties & link with QSO2 5) Non AGN EROs: X-ray constraints venerdì 30 novembre 2018 GH2003 Workshop

1a) Fraction of EROs (R-K>5) among hard X-ray sources 35 ks XMM observation of a complete sample of 350 EROs (K<19.2, Daddi et al. 2000,A&A,361,565) Flux limit of 5x10-15 erg cm-2 s-1, 46 hard X-ray sources 5 EROs  12% of X-ray sources are EROs (Brusa et al. 2003, AN, 324, 113) venerdì 30 novembre 2018 GH2003 Workshop

Going toward faint X-ray (and K) fluxes … Lockman Hole (Mainieri et al. 2002) 13/53 24% (flux limit ~1e-15; BUT incomplete K coverage) CDFS Roche et al 2003: 14/73 20% (hard) Mainieri phD Thesis 2003: 80/346 23% (full) (flux limit ~4e-16; GOODS area, K<22) CDFN Barger et al. 2003: 70/325 21% (hard) (flux limit ~1e-16; complete (?) K cov in all the CDFN area, K=20-22) Alexander et al 2002: 8% (flux limit ~2e-16; complete K cov only in 70.6 arcmin2, K=20) venerdì 30 novembre 2018 GH2003 Workshop

1b) Fraction of X-ray emitters among optically selected EROS (R-K>5) “Daddi Field” Brusa et al. 2002 5/350 2% (flux limit = 5e-15; complete K cov over a large area 450 arcmin2 ELAIS Roche et al. 2002 1/34 3% (flux limit ~1.5e-15; K<19.5, small area, 38.7 arcmin2) CDFS Roche et al 2003: 14/172 8% (flux limit ~4e-16; GOODS area, K<22) CDFN Alexander et al 2002: 4/29 14% (flux limit ~2e-16; complete K cov only in 70.3 arcmin2, K<20.1) COMPLETENESS and LARGE AREA are needed venerdì 30 novembre 2018 GH2003 Workshop

2) X-ray to optical properties of AGN powered EROs AGN EROs populate a well-defined region (high X/O locus) in the R vs. Hard X-ray flux plane lg(X/O)=1+/-1 1 order of magnitude higher than BL AGN blue=ID red= no ID venerdì 30 novembre 2018 GH2003 Workshop

A15 in A2390 field: R>23.2, I>22.9 K=18.9, I-K>4 R-K>4.3 Optically obscured or … X-ray obscured? (an effect of the K-correction) A15 in A2390 field: R>23.2, I>22.9 K=18.9, I-K>4 R-K>4.3 venerdì 30 novembre 2018 GH2003 Workshop

3) Spectroscopic identifications status (hard X-ray selected) PUBLISHED Spectroscopic Redshifts (15) 8 in CDFN (Barger et al. 2003), 2 in Lockman Hole (Mainieri et al. 2002), 5 additional in other X-ray observations (1 in ELAIS, 2 in A2390, 1 in K20 survey, 1 in Hellas2XMM) Photometric Redshifts (29) 25 in CDFN, 3 in Lockman Hole, 1 in ELAIS venerdì 30 novembre 2018 GH2003 Workshop

Z-dist for hard X-ray EROs SHADED: spectr. (15) SOLID: phot.+spec (44) venerdì 30 novembre 2018 GH2003 Workshop

4) Hard X-ray properties of EROs PKS0312 #127 in the HELLAS2XMM sample (Brusa et al. 2003) ERO 524 in the K20 sample (Brusa et al. 2002) Lockman #25 (Mainieri et al. 2002) ELAIS N2_21 (Willott et al. 2002) A2390 #18 (Cowie et al. 2003) CDFN #122; #48 (Barger et al. 2003, Vignali et al. 2003) blue=ID red= no ID venerdì 30 novembre 2018 GH2003 Workshop

PKS0312_127 in the HELLAS2XMM sample Brusa et al. 2003, A&A,sub R=23.5, K=18.4 R-K=5.1 z=2.251 K band R band venerdì 30 novembre 2018 GH2003 Workshop

PKS0312_127 in the HELLAS2XMM sample Brusa et al. 2003, A&A,sub Hard X-ray source (HR=0.37)  @z=2.251 corresponds to rest frame NH>1023 X-ray spectral analysis (with Cash statistic): rest frame NH=1.7x1023 NH>1022 @90% Lx=3x1044 erg/s venerdì 30 novembre 2018 GH2003 Workshop

The K20 CDF-S EROS sample individual detection: ERO 524 Brusa et al. 2002, ApJ,L89,581 R=23.81, K=18.44, z=1.327 F2-10 = 6.4x10-16 erg cm-2 s-1; undetected in the soft X-ray band (1 Ms) Observed X-ray luminosity = 5x1042 erg s-1 venerdì 30 novembre 2018 GH2003 Workshop

ERO 524: hard X-ray properties Brusa et al. 2002, ApJ,581,L89 Hardness Ratio: HR>0.76  intrinsic NH>4x1023 cm-2 (at z=1.327) X-ray spectral analysis (Cash stat.) NH=2.5x1023 cm-2 (NH>7x1022 cm-2 @90%) Unabsorbed X-ray luminosity > 1043 erg s-1 venerdì 30 novembre 2018 GH2003 Workshop

#25 in Lockman Hole (Mainieri et al. 2002) R=25.5, K=19.3 R-K=6.2 z=2.71 (ph.) Rest frame NH=6.5x1023 cm-2 Lx>1045 erg/s ( see also Stevens et al. 2003) venerdì 30 novembre 2018 GH2003 Workshop

#21 in ELAIS_N2 (Willott et al. 2002) R=25.0, K=18.60 R-K=6.4 z=1.575 from infrared spectrum Rest frame NH=5x1021 cm-2 Lx=2x1044 erg s-1 venerdì 30 novembre 2018 GH2003 Workshop

A2390 #18 (Crawford et al. 2002, Cowie et al. 2001) R=23.86, K=16.49 R-K=7.37 z=1.467 (from optical spectrum) venerdì 30 novembre 2018 GH2003 Workshop

A2390 #18 (Crawford et al. 2002, Gandhi et al. 2002) Rest frame NH=2x1023 cm-2 Lx=2x1045 erg s-2 “…genuine X-ray Type II QSO…” Gandhi, Fabian & Crawford 2002 Excess @2.6 keV  rest-frame 6.4 keV line? too poor statistic…. venerdì 30 novembre 2018 GH2003 Workshop

#122 in CDFN - Barger et al. 2003 catalog (Alexander et al #122 in CDFN - Barger et al. 2003 catalog (Alexander et al. 2002, Vignali et al. 2002, astro-ph/0209415) R=25.5, HK=20.3 R-K=5.5 z=1.338 (from optical spectrum) Rest frame NH>1022 cm-2 Lx(obs)=1043 erg s-1 Spectra of 4 sources with I-K>4 ….no evidences for Fe line… venerdì 30 novembre 2018 GH2003 Workshop

#48 in CDFN - Barger et al. 2003 catalog R=23.7, I=22.2, HK=18.8  R-K=5.2 (I-K=3.7) NO spec z; phot z=0.86 … but BRIGHT X-ray source  F(2-10)=1.9x10-14 cgs, ~1000 cts in 2 Ms z=1.13 +/-0.05 @90% EW=255 eV (obs frame) venerdì 30 novembre 2018 GH2003 Workshop

#48 in CDFN - Barger et al. 2003 catalog Rest frame NH=3.2x1023 (@z=1.13) Observed 2-10 keV luminosity L(2-10)=1.3x1044 venerdì 30 novembre 2018 GH2003 Workshop

EROs and QSO2 AGN EROs are highly obscured X-ray sources (6/7 have NH>1022 cm-2) (>80% including also unid. sources and/or NH from HR) A significant fraction has LX>1044 erg s-1 IF WE DEFINE AN X-RAY TYPE 2 QSO any object with Lx>1044 erg/s and NH>1022 cm-2  Bright X-ray EROs are best candidates venerdì 30 novembre 2018 GH2003 Workshop

How many QSO2 among EROs? 30% have NH>22 & Lx>44 Search for QSO2: Select R-K>5 objects (good optical/NIR data)  high z @ bright X-ray fluxes (high X/O sources)  high NH venerdì 30 novembre 2018 GH2003 Workshop

4) Hard X-ray properties of EROs blue=ID red= no ID venerdì 30 novembre 2018 GH2003 Workshop

Non AGN EROs: The K20 CDFS EROS sample 21 EROs in a sub-area of CDFS (K20 survey) Cimatti et al. 2002, A&A,381,L68 Average spectrum of old passive galaxies: red and smooth continuum (8 objects) Average spectrum of dusty systems: strong OII emission (12 objects) venerdì 30 novembre 2018 GH2003 Workshop

The K20 CDFS EROS sample X-ray Stacking Results (Brusa et al. 2002, ApJ,581,L89) OLD SAMPLE 8 objects, zmean=1.145 Effective 7 Ms exposure X-ray emission remains undetected in all the adopted energy bands Upper limit on soft X-ray emission: L0.5-2<1041 erg s-1 DUSTY SAMPLE 12 objects, zmean=1.053 Effective 10 Ms exposure Positive detection (>3 sigma level) in the 0.5-8, 0.5-2 and 1-5 keV bands Rest-frame Hard X-ray luminosity L2-10=8.0x1040 erg s-1 Intrinsic X-ray absorption NH<1022 cm -2 Consistent with emission from ellipticals in the local Universe (e.g. Pellegrini 1999) X-ray properties of Starburst galaxies (e.g. Ptak et al. 1999) venerdì 30 novembre 2018 GH2003 Workshop see also Alexander et al. 2002

The K20 CDFS EROS sample Star Formation from the X-rays From the X-rays (Ranalli et al. 2002) SFR(X)=5-44 Msun/yr (similar predictions from Bauer et al. 2002, Nandra et al 2002 & Grimm et al. 2002 relations) From optical OII flux (Kennicutt 1998) + dereddening E(B-V)=0.5-0.8 SFR(OII)=35-110 Msun/yr Large uncertainties, but the X-ray emission suggests the lower E(B-V)~0.5 lower SFR (in agreement with Radio/Fir results; see Smail et al. 2002) venerdì 30 novembre 2018 GH2003 Workshop

Conclusions 1 How many AGN are EROs? 10-25% (depending on limiting fluxes) obscured in both X-ray and optical bands(X/O~10) high redshift (z=1-3) 30% are QSO2 venerdì 30 novembre 2018 GH2003 Workshop

2-15% (depending on limiting fluxes) Conclusions 2 How many EROs are AGN? 2-15% (depending on limiting fluxes) Passive EROs remain undetected in the X-ray band Dusty systems are Hard X-ray emitters at the Starburst level. Column density <1022 cm-2. “Unbiased” SFR estimate. venerdì 30 novembre 2018 GH2003 Workshop