Hard Xray observations of Extremely Red Objects

1
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

2
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-K5 I-K4
• Faint optical magnitude (R23)
• Redshift range 0.8

DUSTY STARBURSTS
OBSCURED AGN
OLD ELLIPTICALS
3
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
• z1
• ? Observed 2-10 keV luminosity L1042

4
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

5
1a) Fraction of EROs (R-K5)among hard X-ray
sources

• 35 ks XMM observation of a complete sample of 350
  EROs (K
• 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)

6
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
• CDFN
• Barger et al. 2003
  70/325 21 (hard)
• (flux limit 1e-16 complete (?) K cov in
  all the CDFN area, K20-22)
• Alexander et al 2002
  8
• (flux limit 2e-16 complete K cov only in
  70.6 arcmin2, K20)

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1b) Fraction of X-ray emitters among optically
selected EROS (R-K5)

• 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 Karea, 38.7 arcmin2)
• CDFS
• Roche et al 2003 14/172 8
• (flux limit 4e-16 GOODS area, K
• CDFN
• Alexander et al 2002 4/29
  14
• (flux limit 2e-16 complete K cov only in
  70.3 arcmin2, K
• COMPLETENESS and LARGE AREA are needed

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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

blueID red no ID
9
A15 in A2390 field R23.2, I22.9 K18.9,
I-K4 R-K4.3
Optically obscured or X-ray obscured? (an
effect of the K-correction)
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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

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• Z-dist for hard X-ray EROs
• SHADED
• spectr. (15)
• SOLID
• phot.spec (44)

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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)

blueID red no ID
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PKS0312_127 in the HELLAS2XMM sample
Brusa et al. 2003, AA,sub

• R23.5, K18.4 R-K5.1

z2.251
K band
R band
14
PKS0312_127 in the HELLAS2XMM sample
Brusa et al. 2003, AA,sub

• Hard X-ray source (HR0.37) ?
• _at_z2.251 corresponds to rest frame NH1023
• X-ray spectral analysis
• (with Cash statistic) rest frame NH1.7x1023
  
• NH1022 _at_90
• Lx3x1044 erg/s

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The K20 CDF-S EROS sample individual
detection ERO 524
Brusa et al. 2002, ApJ,L89,581

• R23.81, K18.44, z1.327
• 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

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ERO 524 hard X-ray properties
Brusa et al. 2002, ApJ,581,L89

• Hardness Ratio HR0.76
• ? intrinsic NH4x1023 cm-2 (at z1.327)
• X-ray spectral analysis (Cash stat.) NH2.5x1023
  cm-2
• (NH7x1022 cm-2 _at_90)
• Unabsorbed X-ray luminosity 1043 erg s-1
  
  

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25 in Lockman Hole (Mainieri et al. 2002)

• R25.5, K19.3
• R-K6.2
• z2.71 (ph.)
• Rest frame NH6.5x1023 cm-2
• Lx1045 erg/s

( see also Stevens et al. 2003)
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21 in ELAIS_N2 (Willott et al. 2002)

• R25.0, K18.60
• R-K6.4
• z1.575 from infrared spectrum
• Rest frame
• NH5x1021 cm-2
• Lx2x1044 erg s-1

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A2390 18 (Crawford et al. 2002, Cowie et
al. 2001)

• R23.86, K16.49
• R-K7.37
• z1.467 (from optical spectrum)

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A2390 18 (Crawford et al. 2002, Gandhi et al.
2002)

• Rest frame
• NH2x1023 cm-2
• Lx2x1045 erg s-2

genuine X-ray Type II QSO Gandhi, Fabian
Crawford 2002
Excess _at_2.6 keV ? rest-frame 6.4 keV line? too
poor statistic.
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122 in CDFN - Barger et al. 2003
catalog(Alexander et al. 2002, Vignali et al.
2002, astro-ph/0209415)

• R25.5, HK20.3
• R-K5.5
• z1.338 (from optical spectrum)
• Rest frame
• NH1022 cm-2
• Lx(obs)1043 erg s-1

Spectra of 4 sources with I-K4
.no evidences for Fe line
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48 in CDFN - Barger et al. 2003 catalog

• R23.7, I22.2, HK18.8 ? R-K5.2 (I-K3.7)
• NO spec z phot z0.86 but BRIGHT X-ray source
• ? F(2-10)1.9x10-14 cgs, 1000 cts in 2 Ms

z1.13 /-0.05 _at_90 EW255 eV (obs frame)
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48 in CDFN - Barger et al. 2003 catalog

• Rest frame NH3.2x1023
• (_at_z1.13)
• Observed 2-10 keV luminosity
• L(2-10)1.3x1044

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EROs and QSO2

• AGN EROs are highly obscured X-ray sources (6/7
  have NH1022 cm-2)
• (80 including also unid. sources and/or NH
  from HR)
• A significant fraction has LX1044 erg s-1
• IF WE DEFINE AN X-RAY TYPE 2 QSO any object
  with Lx1044 erg/s and NH1022 cm-2
• ? Bright X-ray EROs are best candidates

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EROs and QSO2

• AGN EROs are highly obscured X-ray sources (80
  have NH1022 cm-2)
• A significant fraction has LX1044 erg s-1
• QSO2 CANDIDATES
• Bright X-ray sources best candidates

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How many QSO2 among EROs?
30 have NH22 Lx44

• Search for QSO2
• Select R-K5 objects
• (good optical/NIR data)
• ? high z
• _at_ bright X-ray fluxes
• (high X/O sources)
• ? high NH

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4) Hard X-ray properties of EROs
blueID red no ID
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Non AGN EROsThe K20 CDFS EROS sample

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

Cimatti et al. 2002, AA,381,L68

• Average spectrum of old passive galaxies red and
  smooth continuum (8 objects)
• Average spectrum of dusty systems
  strong OII emission
• (12 objects)

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The K20 CDFS EROS sample X-ray Stacking
Results
(Brusa et al. 2002, ApJ,581,L89)

• OLD SAMPLE
• 8 objects, zmean1.145
• 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

• DUSTY SAMPLE
• 12 objects, zmean1.053
• 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 L2-108.0x1040
  erg s-1
• Intrinsic X-ray absorption NH

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)
see also Alexander et al. 2002
30
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)

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Conclusions 1

• How many AGN are EROs?
• 10-25 (depending on limiting fluxes)
• obscured in both X-ray and optical
  bands(X/O10)
• high redshift (z1-3)
• 30 are QSO2

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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 Unbiased SFR estimate.