1. The Starburst-AGN Connection Among COSMOS (U)LIRGs
Jeyhan Kartaltepe - NOAO
COSMOS Meeting – IfA, Honolulu, HI
2010 June 8
D. Sanders, V. Smolcic, L. Kewley,
M. Salvato, P. Capak, E. Le Floc’h,
H. Aussel, D. Frayer et al.

2. COSMOS 70 mm Sample Paper I Paper II Next…
SEDs  Kartaltepe et al. 2010, ApJ, 709, 572
Paper II
Morphology  re-submitted, should hear back any day
Next…
The Starburst-AGN Connection Among COSMOS (U)LIRGs
Focus on optical spectroscopy out to z~1

3. The Starburst-AGN Connection
Starburst/AGN activity are directly linked
Together may regulate black hole/bulge growth in galaxies
Luminous infrared galaxies have high luminosities due to dust enshrouded SF/AGN activity
Each contribute to the bolometric luminosity
How can we separate the two?
What can we do with existing optical spectroscopy?

4. COSMOS 70 mm Sample 1503 sources with 0 < z < 3
Spectroscopy for ~40%
zCOSMOS, DEIMOS, etc.
Eventual goal: correlate activity with luminosity/morphology
HyLIRGs
ULIRGs
log (LIR)
LIRGs
Redshift (z)

5. AGN Selection Methods X-ray luminosity Radio power
SED shape (i.e., Power-law)
IRAC colors
Infrared to optical ratio (e.g., Fiore et al. 2008, Dey et al. 2008)
Spectroscopic diagnostics

6. Fraction of Sources with AGN Signatures
100% for HyLIRGs
>70% for ULIRGs
AGN Fraction
5% at low LIR
log (LIR)

7. At low redshift….
At low redshift, can classify 135 galaxies using standard line diagnostics
0 < z < 0.5 (where Ha still observable, 18% of sample at these redshifts)
log(LIR) = 8.8 – 11.7, <log(LIR)> = 10.6

8. At low redshift…. 8 (6%) classified as AGN
34 (25%) classified as composite
93 (69%) classified as star forming
 Many more sources identified as AGN through spectroscopy than other selection methods

9. Use color as a proxy for [NII]/Ha?
AGN
380 sources (0 < z < 1)
8 sources selected
2 X-ray detected
Another 2 (z<0.5) have Ha
Both are Seyferts on all 3 low-z diagnostics
DEEP2: e.g., Montero-Dorta et al. 2009

10. Color
Correlation between rest-frame color and galaxy’s position on BPT diagram for radio selected sources
P1 ‘color’ (derived from modified Stromgren system for SDSS galaxies) correlates with metallicity and stellar population, P2 with dust
P1 > 0.15  AGN selection
Appears to work well at low z, results at high z are untested
Is there redshift evolution?
Can composites be separated?
Smolcic et al. 2006, 2008

11. [OII] EW vs. Hb EW 218 Sources (0 < z < 1) 22 sources selected
None are AGN by other methods
8 overlap with low-z sample
4 SF on all 3 diagrams
Other 4 are either Seyferts, LINERS, or composites on 2 out of 3
DEEP2: e.g.,Yan et al. 2006; Willmer et al. 2006; Montero-Dorta et al. 2009

12. Future Work Incorporate new spectra Further tests
DEIMOS, 20k sample, etc.
Further tests
Evolution of P1 with redshift
Lamareille et al. (2004, 2010) diagnostics
X-ray stacking
Compare diagnostics with SDSS in the local universe
z > 1 ?
NIR Spectroscopy (FMOS, MOSFIRE, MOIRCS, FLAMINGOS2, etc.)