Title: X-ray clues on the nature of sub-mm galaxies
1X-ray clues on the nature of sub-mm galaxies
- I.Georgantopoulos INAF/OABO
- A Comastri INAF/OABO
- E. Rovilos MPE
-
2Outline
- 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).
-
3Questions 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 ?
4SMG 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
5SMGs 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) -
6SMG Introduction
The median luminosity is 1013 Lsolar Spitzer
IRS spectra show star-forming spectra (Pope08)
Smail98
7X-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)
8The 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
9X-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
10X-ray properties spectra and Lx
Galaxies
Galaxies are sources with low luminosity and
soft spectra eg Georgakakis06
11Yet another check Lx vs LFIR
Ranalli03 Lx-Lfir relation Star-forming
Galaxies
Open circles denote the X-ray classified Galaxies
12AGN 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
13Non-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
14AGN absorption
- Significant absorption among the AGN
Hash upper limits
15What is the power mechanism ?
Hopkins07 Bolometric correction
Star-formation is the dominant power mechanism
16Example SED
Total
A torus is needed in most cases at 24 µm but the
IR luminosity is dominated by the SFR component
Torus
Arp220
17Summary
- 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