1. Extended IR Emission from LIRGs V. Charmandaris, T. Diaz-Santos, (Univ. of Crete) L. Armus & A. Petric (SSC/Caltech)

2. Heidelberg - 23 Feb 2010 VC MotivationMotivation  A number of the observational properties of SMGs such as:  cold infrared colors  energy production dominated by star formation ( > 100 Msun/yr)  mid-IR spectral features (ie PAH strength) … resemble those of local LIRGs rather than ULIRGs.  Kinematical evidence from ionized (Hα) and molecular (CO) gas are consistent the presence of extended (~5kpc) star forming disks  There is a “ broad ” connection between mid-IR emission and star formation rates (with some caveats … )  We wish to quantify the extended extranuclear emission in local LIRGs in the 5-15μm range to contribute additional evidence in the analogy between the physics of the ISM excitation in LIRGs and the conditions seen in SMGs at z>1.

3. Heidelberg - 23 Feb 2010 VC The Sample  The Sample is drawn from the Great Observatory Allsky LIRG Survey (GOALS; Armus et al. 2009) of 202 systems (181 of which are LIRGs)  All systems are observed with all four Spitzer/IRS modules (5-37μm)  Apply an upper limit on distance (<85 Mpc) in order for the IRS slit size to correspond to a projected distance < 1.5kpc (best case is 0.26kpc)  A total of 93 galaxies are selected.

4. Heidelberg - 23 Feb 2010 VC The Method  Use the 2D images of all LIRGs and re-extract total 5-15μm spectrum using the SSC pipeline algorithms  Use a standard star (HR7341) as our unresolved point source (PSF)  Scale the spatial profile of the standard star along the slit at every wavelength and subtract it from the corresponding profile of each source.  Define as fraction of Extended Emission (EE): Total LIRG flux (λ) - PSF (λ) Fraction of EE (λ) = Total LIRG flux (λ)

5. Heidelberg - 23 Feb 2010 VC Extended Emission Fraction Type (1) Follow the green curve… No Extended Emission

6. Heidelberg - 23 Feb 2010 VC Extended Emission Fraction Type (2) Constant Extended Emission Follow the green curve…

7. Heidelberg - 23 Feb 2010 VC PAHs [ArII] Extended Emission Fraction Type (3) Wavelength Depended Extended Emission

8. Heidelberg - 23 Feb 2010 VC Mean Fraction of mid-IR Extended Emission  For 90% of the sample, at least 20% of the mid-IR flux is extended  For more than 35% of the sample, the EE fraction is larger than 0.5 (= 50%)

9. Heidelberg - 23 Feb 2010 VC Fraction of mid-IR Extended Emission  LIRGs with EE fractions larger than 0.5 are detected up to 80 Mpc!  The EE fraction is not correlated with the IR luminosity => the most luminous LIRGS are not necessarily the most compact Limits to identifying a source with intrinsic EE=0.75 due to distance

10. Heidelberg - 23 Feb 2010 VC Are PAHs more extended than [NeII] ? (1)  “Neutral” PAHs such as the 11.3μm are… … possibly because they do not require a strong ionizing radiation field

11. Heidelberg - 23 Feb 2010 VC Are PAHs more extended than [NeII] ? (2)  “Ionized” PAHs such as the 6.2μm and 7.7μm are not…

12. Heidelberg - 23 Feb 2010 VC AGN dependence of mid-IR Extended Emission We can calculate the mid-IR AGN fraction using the EW of the 6.2μm PAH (Petric et al. 2010)… We find no obvious dependence of Extended Emission on mid-IR AGN strength

13. Heidelberg - 23 Feb 2010 VC Conclusions / Perspectives Even though the spatial resultion of IRS is ~3.6arcsecs..  LIRGs display large fraction of extended mid-IR emission in both continuum and 5-15μm features  For at least 90% of the sample more than 20% of the mid-IR flux originates outside the nuclear unresolved region.  For at least 35% of the sample more than 50% of the mid-IR flux is extranuclear (possibly also their star formation?)  The extended emission varies as a function of wavelength.  The 11.3μm PAH displays the larger extended emission, consistent with it being a “neutral” PAH.  No clear correlation between extended emission and mid-IR AGN classification nor IR luminosity  To do: - Explore the correlations with merging stage - Increase the range of IR luminosity to include some ULIRGs.