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X-ray clues on the nature of sub-mm galaxies. I.Georgantopoulos INAF/OABO A Comastri INAF/OABO E. Rovilos MPE. Outline. What are the sub-mm galaxies SMGs ? What can the X-ray observations tell us about SMGs? (Alexander et al claim that sub-mm galaxies present a phase of co-eval

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x ray clues on the nature of sub mm galaxies

X-ray clues on the nature of sub-mm galaxies

I.Georgantopoulos INAF/OABO

A Comastri INAF/OABO

E. Rovilos MPE

outline
Outline
  • What are the sub-mm galaxies SMGs ?
  • What can the X-ray observations tell us about SMGs?

(Alexander et al claim that sub-mm galaxies present a phase of co-eval

growth of black holes and star-formation).

questions to be addressed
Questions to be addressed
  • Fraction of AGN among sub-mm galaxies

2. Level of Obscuration

3. What is the major power-mechanism that produces the Bolometric luminosity ?

smg an introduction
SMG: an Introduction
  • SCUBA detector (850micron) on JCMT gave a boost to sub-mm Cosmology
  • The negative K-correction plays a major role making high-redshift galaxies easier to detect

850μm

smgs an introduction
SMGs: an Introduction
  • It is expected many SMG are at high redshift z>2
  • Of course the identification is very very difficult because of

Large PSF and associated uncertainties in source position 8 arcsec

(see reviews by Maiolino 2008, Blain+02)

Chapman+05 did a breakthrough observing radio positions of SMGs and then observing counterparts with Keck z=2-3

(altough Daddi+09, Capak+08 find counterparts even at z=4-5)

smg introduction
SMG: Introduction

The median luminosity is ~1013 Lsolar

Spitzer IRS spectra show star-forming spectra (Pope+08)

Smail+98

x ray observations cdfn
X-ray observations CDFN
  • Alexander+05 find that a large fraction 70% of SMGs are X-ray sources and thus AGN. Many of these appear to be highly obscured
  • Co-evolution of black hole growth and star-formation

under a veil of dust ?

  • Laird+09 criticise the sample selection

(a mixture of SMGs with radio positions and

Radio sources with sub-mm detection)

Laird et al find instead a lower fraction of X-ray detections

among ‘true’ SMGs while they claim that many of the X-ray sources are normal galaxies (not AGN)

the cdfs laboca observations
The CDFS LABOCA observations

Here we attempt to address anew these issues in the CDFS

Which is the field with the deepest X-ray observations ever.

(2 MS Chandra + another 2Ms starting in June)

(4 Chandra 200ksec observations around the CDFS)

(3 Ms of XMM observations)

Spitzer IRAC and MIPS observations

Sub-mm observations at 870 μm LABOCA camera APEX telescope.

128 sources detected in the area of the eCDFS

x ray sub mm associations
X-ray/sub-mm associations

Background: R

Contours: MIPS

Circle: sub-mm

Blue: X-ray

Maximum-Likelihood Method for the association between MIPS and LABOCA

13 associations

x ray properties spectra and lx
X-ray properties: spectra and Lx

Galaxies

Galaxies are sources

with low luminosity and

soft spectra

eg Georgakakis+06

yet another check lx vs l fir
Yet another check: Lx vs LFIR

Ranalli+03

Lx-Lfir relation

Star-forming

Galaxies

Open circles denote

the X-ray classified

Galaxies

agn fraction
AGN fraction
  • eCDFS+CDFS AGN fraction : 9/128 (7%)
  • Considering only the CDFS: 7/38 (18+/-7 %)

very close to the estimates of Laird et al.

IMPLYING THAT THE MAJORITY OF SMGs ARE STARFOMING

non x ray detected sources stacking analysis
Non-X-ray detected sources: stacking analysis

Hardness Ratio -0.40 corresponding to Γ~1.4 (or NH~1022 cm-2)

This suggests that most of the undetected SMGs are galaxies

agn absorption
AGN absorption

Significant absorption among the AGN

Hash= upper limits

what is the power mechanism
What is the power mechanism ?

Hopkins+07

Bolometric correction

Star-formation is the

dominant power mechanism

example sed
Example SED

Total

A torus is needed in most cases at

24 μm but the IR luminosity is

dominated by the SFR component

Torus

Arp220

summary
Summary
  • 13 X-ray detections out of 128 LABOCA SMGs in the eCDFS

and CDFS

  • In the CDFS the AGN fraction is only 18+/-7 %

in agreement with Laird+09 in the CDFN

  • Stacking analysis for the undetected SMGs gives a signal in the soft band 2x10-17 cgs or Lx=5x1041 cgs Suggesting that most are normal galaxies.
  • Even among the AGN SMGs, the contribution of the AGN is small suggesting that the major contributor to their luminosities (all but one are ULIRGs) is star-formation