1. An Initial Look at the FIR-Radio Correlation within Galaxies using Spitzer Eric Murphy (Yale) Co-Investigators George Helou (SSC/IPAC) Robert Braun (ASTRON) Lee Armus (SSC) Jeff Kenney (Yale) SINGS team Murphy et al. (2005)

2. Eric J. MurphyIsland Universes7/7/2005 FIR – Radio Correlation q ≡ log(FIR/3.75 x 10 -12 Hz/S ν ) (Helou et al. 1985) ► Spans 5 Orders of Magnitude in Luminosity ► Dispersion of ~0.2 dex (no AGN, IRAS confusion etc…) ► Found to Exist up to z~2 (Appleton et al. 2004) ► Thought to be driven by the Process of Massive Star Formation (Harwit & Pacini 1975)  FIR – Dust heated by Massive stars  Radio – CRe - accelerated by SNe in B-field  Wait a sec… How did they know before IRAS observations?

3. Eric J. MurphyIsland Universes7/7/2005 The First Signs…van der Kruit 1971 ► ~35 years later, and still trying to figure out why it works!

4. But… ► FIR affected by:  IMF  UV photon transport  Optical depth  Grain distribution/composition ► Radio affected by:  IMF  SNe & SNR  ISM shocks  Particle acceleration  Transport – diffusion & confinement  Magnetic Field ► How can FIR/Radio ratios of galaxies show such little scatter? Duric (1991)

5. Eric J. MurphyIsland Universes7/7/2005 IR and Radio Data ► Spitzer IR data:  MIPS maps at 24, 70, and 160μm ► FWHM of 70μm PSF ~17” ► WSRT Radio Continuum data:  Maps at 18 and 22cm ► FWHM of radio beam ~17” ► CLEAN data restored with MIPS 70μm PSF ► Galaxy Sample: 30 galaxy subset of SINGS Legacy Science Sample (Kennicutt et al. 2003) SINGS

6. Eric J. MurphyIsland Universes7/7/2005 Thesis Goals ► Improve the current physical picture of the FIR-Radio correlation:  Quantify variations in the correlation across galaxy disks.  Correlate observed variations with ancillary observations. ► e.g. mean star-formation age and strength  Derive a better understanding of what regulates the correlation on galaxy scales. ► Constrain CRe - diffusion and decay models from observations.

7. Eric J. MurphyIsland Universes7/7/2005 Paper Sample Galaxies ► Chosen due to proximity and low inclination. GalaxyTypeDistance(Mpc)Resolution(pc)SFR (M  /yr) q NGC 2403 SABcd3.53000.7722.50 NGC 3031 SAab3.53000.8572.45 NGC 5194 SABbc8.27506.062.09 NGC 6946 SABcd5.55004.052.28 SFRs are IRAS based using equation 5 from Bell (2003)

8. NGC 2403 (q 70 ) S 22cm I 70µm

9. NGC 3031 (q 70 ) S 22cm I 70µm

10. NGC 5194 (q 70 ) S 22cm I 70µm

11. NGC 6946 (q 70 ) S 22cm I 70µm

12. NGC 2403 NGC 3031 NGC 5194 NGC 6946 I 24µm I 70µm I 22cm

13. Eric J. MurphyIsland Universes7/7/2005 IR/Radio (q) Maps q λ  log(f ν (λ[μm])/f ν (22cm)) ► λ=24 and 70µm  At best common resolution w/ radio data

14. q 70 Maps

15. q 24 Maps

16. Eric J. MurphyIsland Universes7/7/2005 q λ Map Results Coincidence in IR and Radio Peaks  q 24 more strongly peaked than q 70 around HII regions  24µm emission traces hotter dust & more localized around HII regions IR/Radio Morphology  Higher along Arms & HII regions  Lower for inter-arms & outer-disk

17. Aperture Photometry ► ‘Critical’ Aperture Size  FWHM of 70μm PSF  Linearly Projected at: NGC 5194 0.75 kpc NGC 6946 0.5 kpc NGC 3031 0.3 kpc NGC 2403 0.3 kpc ► Regions  Nucleus: Cyan  Inner-Disk: Red  Arm: Blue  Inter-Arm: Green  Outer-Disk: Yellow

18. Radial Trends in q 70

19. q 70 vs. f ν (70μm)

20. Eric J. MurphyIsland Universes7/7/2005 Photometry Statistics Galaxy σ 70 σ 24 NGC 2403 2.240.2191.080.235 NGC 3031 2.200.2511.020.224 NGC 5194 1.900.1970.8560.231 NGC 6946 1.940.2030.9470.231 NOTE: Radial and Surface Brightness trends similar for q 24

21. Eric J. MurphyIsland Universes7/7/2005 Dispersion in q 70 vs. Aperture Diameter

22. q 70 within and among Galaxies (1.5 kpc apertures) σ g = 0.267 N = 1752 (Yun et al. 2002) σ w = 0.240 N = 282

23. Eric J. MurphyIsland Universes7/7/2005 Aperture Photometry Results General trend of increasing q 70 and q 24 with:  Increasing IR surface brightness (Opposite of global trend)  Decreasing Radius Dispersion at constant radius ~25% larger than at constant surface brightness.  SF sites more important in determining shape of IR/radio disk than exponential disks. Dispersion in q 70 within galaxies comparable to dispersion among galaxies

24. Eric J. MurphyIsland Universes7/7/2005 Cosmic Ray Diffusion Modeling ► Image Smearing Model of Bicay & Helou (1990) ► Assumption: Difference in IR and Radio morphology due to diffusion of CRe - ► Following work of Marsh & Helou (1995, 98)  But, we are using IR images at native resolution (unlike IRAS HiRes used by MH95, 98)

25. Eric J. MurphyIsland Universes7/7/2005 Image Smearing Technique ► IR image: I(r); Radio Image: R(r) ► Smeared IR Image: Ĩ(r) = I(r) * κ(r)  κ(r): kernel containing CRe - diffusion and decay physics ► Residual Image = log(Q -1 Ĩ(r)) – log(R(r))  Q = ∑Ĩ j (r) / ∑R j (r)

26. Eric J. MurphyIsland Universes7/7/2005 Residuals ► Minimize Residual Parameter: φ(Q,t,p,l) = ∑ [Q -1 Ĩ j - R j ] 2 / ∑ R j 2  t: type (Gaussian/exponential)  p: projection (sky/galaxy)  l: scale-length ► Normalize by radio image to account for variations in surface brightness

27. Residuals vs. Scale-length

28. Smearing Residual Maps

29. Eric J. MurphyIsland Universes7/7/2005 Improvements by Image Smearing (case: exponential kernel in plane of sky) Galaxy l (pc) Φ (pixels) σ 70 δ σ 70 (apertures) NGC 2403 900 0.075 (19%) 0.146 -0.073 (18%) NGC 3031 2500 0.31 (~2x) 0.230 -0.021 (5%) NGC 5194 500 0.29 (~2x) 0.160 -0.037 (9%) NGC 6946 300 0.17 (50%) 0.161 -0.042 (10%) Φ≡ log(φ(0)/min(φ)) :masked Φ ≡ log(φ(0)/min(φ)) :masked δ σ 70 ≡ σ 70 - σ 70 (smeared) :no mask

30. Eric J. MurphyIsland Universes7/7/2005 CRe - Diffusion Modeling Results Smearing technique works to improve the correlation  Reduces residuals by up to a factor of 2 Exponential kernels work marginally better than Gaussians (~15%)  Suggests CRe - evolution not well described by random-walk diffusion A single kernel does not work for entire disk.  Residual trends opposite for active & quiescent regions Quiescent galaxies have larger scale-lengths  Due to deficit of recent CRe - injection into ISM NGC 2403: Are we seeing two populations of CRe - ?

31. NGC 2403: A case for 2 CRe - populations? n ≥ 5 cm -3 l ~ 1 kpc τ ~ 5 x 10 7 yrs (Helou & Bicay (1993) NGC 6946: l = 300 pc NGC 2403: l 1 = ~200 pc l 2 = ~1 kpc

32. Eric J. MurphyIsland Universes7/7/2005 Future Goals Future Goals ► Perform same analysis on ~30 SINGS galaxies. ► More Detailed Modeling of CRe - Diffusion  Separate high spatial frequency components from disks  Compare observed smearing scale-lengths with models ► Include other data sets to  help constrain dependence of IR/radio ratio on HII region age and ISM properties.  gain more insight into CRe - physics: ► NIR [FeII] and Paβ imaging ► Dust Temperature Maps ► Radio spectral index maps ► 8/24μm colors ► IRS Spectroscopy