1. The SEDs of Interacting Galaxies Lauranne Lanz Nicola Brassington, Andreas Zezas, Howard A. Smith, Matthew L. N. Ashby, Elisabete da Cunha, Christopher Klein, Patrik Jonsson, Chris Hayward Lars Hernquist, Giovanni Fazio Harvard-Smithsonian Center for Astrophysics llanz@cfa.harvard.edu NGC 520: NUV, 3.6 µm, & 8.0 µm L. Lanz, Harvard-CFA, SED2011 Sept. 6, 2011

2. Outline What is Spitzer Interacting Galaxy Survey (SIGS)? SED shapes SED fitting sSFR comparisons Trends with interaction stage N3226-N3227 3.6 µm, 4.5 µm, & 8 µm L. Lanz, Harvard-CFA, SED2011 Sept. 6, 2011

3. Sample Selection Keel-Kennicutt (Keel et al. 1985) “complete” and “Arp” samples: – Selected based on association likelihood – Require |Δv|< 600 km s -1 to remove non-associated pairs Imposed distance constraint cz < 4000 km s -1 Resulting sample: 111 galaxies in 50 systems NGC 2976: NUV, 3.6 µm, & 8.0 µm L. Lanz, Harvard-CFA, SED2011 Sept. 6, 2011

4. Observations Complete Spitzer coverage: – IRAC, MIPS, and nuclear IRS spectra Almost complete GALEX coverage Some Herschel coverage Ancillary data – WISE coverage – Some Chandra/XMM coverage – Hα fluxes M51 NUV, IRAC 3.6 µm, & SPIRE 250 µm L. Lanz, Harvard-CFA, SED2011 Sept. 6, 2011

5. Sample Selection and Observation Set Benefits Not morphologically selected: large range of interaction parameters Not infrared selected: less active systems included Not based on optical line diagnostics UV and IR coverage gives complete SFR NGC 470 & NGC 474: FUV, 3.6 and 4.5 µm, & 8.0 µm NGC 520: NUV, 3.6 µm, & 8.0 µm L. Lanz, Harvard-CFA, SED2011 Sept. 6, 2011

6. Example: M51 and NGC 3430/3424 SPIRE 250 µm IRAC 3.6 µm, 4.5 µm, 8 µm GALEX FUV NUV 2MASS J, H, Ks L. Lanz, Harvard-CFA, SED2011 Sept. 6, 2011

7. Photometry S-Extractor used to determine NUV and 3.6 µm apertures SPIRE 250 µm IRAC 3.6 µm, 4.5 µm, 8 µm GALEX FUV NUV 2MASS J, H, Ks L. Lanz, Harvard-CFA, SED2011 Sept. 6, 2011

8. Photometry S-Extractor used to determine NUV and 3.6 µm apertures Fluxes determined in larger aperture in all bands Uncertainty: Calibration and Poisson SPIRE 250 µm IRAC 3.6 µm, 4.5 µm, 8 µm GALEX FUV NUV 2MASS J, H, Ks L. Lanz, Harvard-CFA, SED2011 Sept. 6, 2011

9. SED shapes Log( νL ν / L  ) M51 A NGC 3424NGC 3430 M51 B L. Lanz, Harvard-CFA, SED2011 Sept. 6, 2011

10. Two blackbodies + β=1.5 graybody 4367 K 356.2 K 28.6 K 4058 K 357.1 K 25.8 K 3572 K 303.5 K 29.2 K 3307 K 339.5 K 25.2 K Log( νL ν / L  ) M51 A NGC 3424NGC 3430 M51 B L. Lanz, Harvard-CFA, SED2011 Sept. 6, 2011

11. MagPhys SED-fitting Code Optical stellar from Bruzual & Charlot 2003 and infrared dust from da Cunha, Charlot, & Elbaz 2008 spectral libraries Energy absorbed in UV/optical is re-emitted in IR No AGN contribution considered Likelihood distributions constructed for model parameters to determine best fit SED Elisabete da Cunha’s talk this afternoon L. Lanz, Harvard-CFA, SED2011 Sept. 6, 2011

12. Fit SEDs Log( λL λ / L  ) sSFR T warm T cold sSFR T warm T cold L. Lanz, Harvard-CFA, SED2011 Sept. 6, 2011

13. Fit SEDs Log( λL λ / L  ) sSFR T warm T cold sSFR T warm T cold L. Lanz, Harvard-CFA, SED2011 Sept. 6, 2011

14. Fit comparisons FIR β=1.5 gray-body temperature falls between SED-fitted warm and cold temperatures The integrated 8-1000 µm 3-component fit agrees well with the dust luminosity determined from fitting the SED. Log( L Dust, SED / L  ) Frac. Difference Log( L 8-1000µm, 3part / L  ) T Warm T Cold T Graybody / K T SED / K L. Lanz, Harvard-CFA, SED2011 Sept. 6, 2011

15. Log(sSFR/yr -1 ) SED Fitting Log(sSFR/yr -1 ) Prescription Comparison of Specific Star Formation Rates M51A N 3430 L. Lanz, Harvard-CFA, SED2011 Sept. 6, 2011

16. Trends with Interaction Stage L. Lanz, Harvard-CFA, SED2011 Sept. 6, 2011

17. Trends with Interaction Stage L. Lanz, Harvard-CFA, SED2011 Sept. 6, 2011

18. Trends with Interaction Stage L. Lanz, Harvard-CFA, SED2011 Sept. 6, 2011

19. Summary SIGS will provide a sample of interacting galaxies from first pass to coalescence with a range of interaction parameters. IC 1801 and NGC 935 NUV, 3.6 and 4.5 µm, & 8.0 µm L. Lanz, Harvard-CFA, SED2011 Sept. 6, 2011

20. Summary With the first 10 groups with SPIRE data, we: – find a range of SED shapes, especially in the ratio of MIR to optical/UV. – measured sSFR and temperatures using the MagPhys (da Cunha et al. 2008) SED-fitting code. – find an increase in warm component temperature with interaction stage, but no significant change in sSFR. M81: NUV, 8.0 µm, & 250 µm L. Lanz, Harvard-CFA, SED2011 Sept. 6, 2011

21. Thank you for the attention and stay tuned for more: 40 more interacting groups Nuclear activity Comparison with simulated systems N3448 – U6016: FUV, 3.6 µm, 4.5 µm, & 8 µm M101: NUV, 3.6 µm, & 8 µm Cox et al. 2006 L. Lanz, Harvard-CFA, SED2011 Sept. 6, 2011