3-8 µm diagnostics of starbursts and AGNs in the local and high-z Universe Guido Risaliti INAF - Osservatorio Astrofisico di Arcetri & Harvard-Smithsonian Center for Astrophysics Eleonora Sani, Emanuele Nardini, S. Berta, V. Braito, R. Della Ceca, A. Franceschini, R. Maiolino, A. Marconi, M. Salvati, M. Imanishi in collaboration with: Bologna, 28/06/2007

Outline: -Why study ULIRGs in the 3-8  m band ? -IR diagnostics of AGN and SB in ULIRGs: - ISAAC/SUBARU observations of bright sources - Spitzer IRS spectra of local ULIRGs - The nature of LINER ULIRGs -Quantitative estimates of the relative AGN/SB fraction in ULIRGs - Application to high-z sources

Ultraluminous Infrared Galaxies: L IR > L sun (L IR ~L BOL ) Mostly interacting systems “Local” analogous to sub-mm sources dominating the high-z Universe Energy source: starburst (SB) or accretion on supermassive black holes (AGN)

ULIRGs: obscured AGNs or starbursts ? A) Optical/near IR spectroscopy. +++ narrow high ionization lines observable in faint sources (Ex: complete spectroscopy of 118 sources of the 1Jy sample (Veilleux et al. 1999) Poor estimate of relative AGN contribution; ~50% of the objects classified as LINERs

ULIRGs: obscured AGNs or starbursts ? B) X-ray imaging / spectroscopy +++ spatial resolution of active nuclei +++ Detection of the AGN hard X-ray emission +++ spectral decomposition of SB/AGN components Braito et al Komossa et al NGC 6240 Vignati et al Only possible with the ~15 brightest objects

Genzel et al ULIRGs: obscured AGNs or starbursts ? C) Mid-IR spectroscopy. +++ High ionization lines (AGN), PAH features (SB) Poor estimate of relative AGN contribution; Only for bright objects +++ Major improvements with Spitzer!!

ULIRGs: obscured AGNs or starbursts ? Armus et al. 2006

Farrah et al ULIRGs: obscured AGNs or starbursts ?

- - - ULIRGs: obscured AGNs or starbursts ? D) 3-8  m spectroscopy (Spitzer, Subaru, VLT) Huge background! L sky ~ 5/arcsec 2 M sky ~1.5/arcsec 2 L ULIRGs > Low dust extinction (A V /A L ~ 40) +++ Biggest differences between AGNs and SB (also in hard X-rays…) SB SED AGN SED

ULIRGs: obscured AGNs or starbursts ? OBSERVATIONS: -ISAAC-VLT (3-4  m and 3-5  m) -SUBARU (3-4  m) -Spitzer-IRS (low-RES) -15 Brightest ULIRGs sample (Genzel et al. 1998) -1 Jy ULIRGs Sample, z<0.15 (~68 sources) (Kim & Sanders 1998, Veilleux et al.1999)

ULIRGs: L-band spectroscopy Imanishi & Dudley 2000

ISAAC Spectroscopy: low absorption AGN

ISAAC Spectroscopy: heavily absorbed AGN

ISAAC Spectroscopy: NGC 6240

L-band spectra of starbursts

L-band diagnostics of SB/AGN contributions Pure SB ObscuredAGN Non-obscured AGN

Application to faint sources 1 Jy ULIRGs sample, z<0.15: 55 objects,~50% LINERs (Kim & Sanders 1998, Veilleux et al. 1999)

AGN/SB spectral deconvolution f =  f (SB)+(1-  )f (AGN)e -  ( ) Contribution to L BOL : ULIRGs: AGN 20%, SB 80% LINERs: AGN 20%, SB 80% Sources hosting AGNs: ULIRGs: ~60% LINERs: ~60%

Spitzer IRS spectra Imanishi et al. 2007

Spitzer IRS spectra: starbursts

AGN/SB spectral deconvolution f =  f (SB)+(1-  )f (AGN)e -  ( )

AGN/SB spectral deconvolution

AGN/SB spectral deconvolution: results

Summary of results for local ULIRGs : -Overall, 85-90% of ULIRGs luminosity due to starburst -AGNs present in ~2/3 of ULIRGs, but with significant contribution in ~30% of the sources -LINER ULIRGs are a composite class, with ~same proportions as the whole ULIRG class

Summary of method: - AGN intrinsically more luminous than SBs by factors of ~100 (3  m), ~30 (6  m) -Starburst spectra ~all the same in all sources -ULIRGs spectra dependent on two parameters only: relative AGN/SB contributions and AGN extintion -Three independent observational indicators: PAH, spectral slope, ratio to bolometric luminosity

Application to high-z sources Houck et al. 2005

z  2.5 Application to high-z sources