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

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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 ... – PowerPoint PPT presentation

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


1
X-ray clues on the nature of sub-mm galaxies
  • I.Georgantopoulos INAF/OABO
  • A Comastri INAF/OABO
  • E. Rovilos MPE

2
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).

3
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 ?

4
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
5
SMGs an Introduction
  • It is expected many SMG are at high redshift zgt2
  • 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, Blain02)
  • Chapman05 did a breakthrough observing radio
    positions of SMGs and then observing counterparts
    with Keck z2-3
  • (altough Daddi09, Capak08 find counterparts
    even at z4-5)

6
SMG Introduction
The median luminosity is 1013 Lsolar Spitzer
IRS spectra show star-forming spectra (Pope08)
Smail98
7
X-ray observations CDFN
  • Alexander05 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 ?
  • Laird09 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)

8
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

9
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
10
X-ray properties spectra and Lx
Galaxies
Galaxies are sources with low luminosity and
soft spectra eg Georgakakis06
11
Yet another check Lx vs LFIR
Ranalli03 Lx-Lfir relation Star-forming
Galaxies
Open circles denote the X-ray classified Galaxies

12
AGN fraction
  • eCDFSCDFS 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

13
Non-X-ray detected sources stacking analysis
sample No Counts 0.5-2 keV Flux
eCDFS 100 61 (5.6s) 2.3x10-17
CDFS 21 28 (2.5s) 2x10-17
Hardness Ratio -0.40 corresponding to G1.4 (or
NH1022 cm-2) This suggests that most of the
undetected SMGs are galaxies
14
AGN absorption
  • Significant absorption among the AGN

Hash upper limits
15
What is the power mechanism ?
Hopkins07 Bolometric correction
Star-formation is the dominant power mechanism
16
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
17
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 Laird09 in the CDFN
  • Stacking analysis for the undetected SMGs gives a
    signal in the soft band 2x10-17 cgs or Lx5x1041
    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
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