hard x-ray observations of extremely red objects

sabato 22 aprile 2023 GH2003 Workshop 1

Hard X-ray observations of Extremely Red Objects

Marcella BrusaDip. Astronomia, Universita’ di Bologna & INAF- Osservatorio Astr. Di

BolognaIn collaboration with:A. Comastri, M. Mignoli & the HELLAS2XMM teamL. Pozzetti, E. Daddi, A. Cimatti F. Civano


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

OLD ELLIPTICALS DUSTY STARBURSTS OBSCURED AGN


EROs and hard X-ray sourcesOptical follow-up of sources detected in deep and medium

deep hard X-ray samples EROs colors

Why X-ray detected EROsshould be AGN?

X-ray flux = 2x10-16

z=1 Observed 2-10 keV luminosity: L=1042


Observational results1) How many? -Fraction of EROs among X-ray sources -Fraction of X-ray emitters among EROs2) Optical to X-ray properties3) Spectroscopic identification4) Hard X-ray spectral properties & link with QSO25) Non AGN EROs: X-ray constraints


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)


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)

Going toward faint X-ray (and K) fluxes …


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


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=IDred= no ID


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)


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


Z-dist for hard X-ray EROs

SHADED: spectr. (15)

SOLID: phot.+spec

(44)


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=IDred= no ID

4) Hard X-ray properties of EROs


PKS0312_127 in the HELLAS2XMM sample

R=23.5, K=18.4 R-K=5.1

Brusa et al. 2003, A&A,sub

z=2.251

R band K band


PKS0312_127 in the HELLAS2XMM sample

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

Brusa et al. 2003, A&A,sub


The K20 CDF-S EROS sample

individual detection: ERO 524R=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

Brusa et al. 2002, ApJ,L89,581


ERO 524: hard X-ray properties

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

Brusa et al. 2002, ApJ,581,L89


#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)


#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


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)


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….


#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….no evidences for Fe line…

Spectra of 4 sources with I-K>4


#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)


Rest frame NH=3.2x1023

(@z=1.13)

Observed 2-10 keV luminosity

L(2-10)=1.3x1044

#48 in CDFN - Barger et al. 2003 catalog


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


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


blue=IDred= no ID

4) Hard X-ray properties of EROs


Non AGN EROs:The K20 CDFS EROS sample

21 EROs in a sub-area of CDFS (K20 survey)

Average spectrum of old passive galaxies: red and smooth continuum (8 objects)

Average spectrum of dusty systems: strong OII emission

(12 objects)

Cimatti et al. 2002, A&A,381,L68


The K20 CDFS EROS sample

X-ray Stacking Results DUSTY SAMPLEDUSTY 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

OLD SAMPLEOLD 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

X-ray properties ofStarburst galaxies(e.g. Ptak et al. 1999)

Consistent with emissionfrom ellipticals in the localUniverse (e.g. Pellegrini 1999)

(Brusa et al. 2002, ApJ,581,L89)

see also Alexander et al. 2002


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/yrLarge 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)

The K20 CDFS EROS sample Star Formation from the X-rays


Conclusions 1How 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


Conclusions 2

Dusty systems are Hard X-ray emitters at the Starburst level. Column density <1022 cm-2. “Unbiased” SFR estimate.

Passive EROs remain undetected in the X-ray band

How many EROs are AGN? 2-15% (depending on limiting fluxes)

hard x-ray observations of extremely red objects

Documents

xray flux

hard xray observations

hard xray erosshaded

soft xray band

msobserved xray luminosity

r band

flux limit

hellas2xmm sample brusa