1. THE PHYSICAL SCALE OF THE FAR-IR IN THE MOST LUMINOUS SUBMM GALAXIES Joshua D. Younger Harvard University

2. J. D. Younger, G. G. Fazio, D. Wilner, J.-S. Huang (CfA) M. S. Yun, G. Wilson, T. Perera, K. Scott, J. Austermann (U Mass) M. L. N. Ashby, R. Blundell, M. A. Gurwell, K. Lai, G. Petitpas, M. Krips (CfA) A. B. Peck (ALMA/Chile) I. Smail, K. Coppin, J. Geach (Durham) R. J. Ivison, A. D. Biggs (UKATC/Edinburgh) J. S. Dunlop, E. L. Chapin (UBC) S. Dye (Cardiff) D. Iono, K. Kohno, R. Kawabe (NAOJ) D. Hughes, I. Aretzaga (INAOE) J. Lowenthal (Smith) T. Webb (McGill) A. Martinez-Sansigre, E. Schinnerer, T. Greve (MPIA) V. Smolcic (Caltech) S. Kim (Sejong Univ) D. Clements (Imperial)

4. 20-30% of FIRB Resolved Coppin et al. (2006)

5. Le Floc’h et al. (2005) low L IR LIRGS UIRGS

6. WHAT CAN WE LEARN FROM HIGH RESOLUTION IMAGING? COUNTERPART IDENTIFICATION SUBMILLIMETER SIZES SEDs “REDSHIFTS” SOURCE & NATURE OF FAR-IR CONSTRAINTS ON MODELS OF GALAXY FORMATION & EVOLUTION

7. THE AGN CONTRIBUTION TO SMGs Submm number counts suggest a significant fraction of high-z SF is obscured Question remains how much of the far-IR luminosity in SMGs is powered by AGN vs. SF This has important consequences for SAMs (e.g., Baugh et al. 2005; Swinbank et al. 2008) Several approaches: –FIR/radio SED (e.g., Kovacs et al. 2006) –N/MIR SED (e.g., Pope et al. 2008) –X-ray detections (e.g., Alexander et al. 2008) Hughes et al. (1998)

8. THE PHYSICAL SCALE OF THE FAR-IR The physical scale of the FIR is connected to the engine driving the emission Previous observations provide modest constraints on the apparent submm sizes of SMGs (Younger et al. 2007, 2008, in prep) High resolution radio imaging has found starbursts on scales of 1-8 kpc (median 5kpc; Chapman et al. 2004; Biggs & Ivison 2008) Preferable to image the rest frame FIR directly, via submm interferometry Followed up the two brightest sources known with existing COM configuration data in more extended configurations (EXT+VEX) –Higher resolution - 0.3-0.8” vs. ~2” previously –Measured the apparent sizes of both targets

9. THE TARGETS GN20 and AzTEC1 are brightest mm/submm sources in the HDFN and COSMOS Fields Unresolved in COM configuration (beam ~2”) Optical/NIR and submm/radio SEDs suggest comparable redshift z~4 AzTEC1 (15 mJy) Younger et al. (2007) GN20 (24 mJy) Iono et al. (2006)

10. THE SUBMILLIMETER ARRAY Submm interferometer atop Mauna Kea ALMA Pathfinding instrument Operates from 230-690 GHz Up to 8 movable antennas 6m across Three configurations with baselines from 8 to 500m

11. FOLLOWUP OBSERVATIONS COM (beam~2”) EXT (beam~1”) VEX (beam~0.3”)

12. RESULTS: IMAGES

13. RESULTS: GN20 GN20 is resolved in the EXT configuration Fit to visibility data indicates a source size of 0.6-1.0” (Gaussian vs. disk model) Corresponds to physical scales of 4-7 kpc at z~4 Test quasar confirms the phase transfer

14. RESULTS: AzTEC1 AzTEC1 is unresolved in EXT, but resolved in VEX Fit to visibility data indicates a source size of 0.3-0.4” (Gaussian vs. disk model) Corresponds to physical scales of 1.5-2.5 kpc at z~4 Test quasar confirms the phase transfer in EXT, and we use it to remove baseline errors in VEX (still extended relative to effective resolution limit)

15. ARE THE MOST LUMINOUS SMGs EDDINGTON LIMITED STARBURSTS? Radiation pressure from the opacity of dust to UV generated by ongoing star formation drives winds, sets a natural upper limit to the SFR density In the optically thin limit - optically thick clouds with low volume filling factor - the opacity of dust yields a maximum SFR of Our submm observations constrain the size scale of the dust directly Assuming an Arp220 template and typical potential depths of SMGs suggested by CO spectroscopy, both GN20 & AzTEC1 are possibly at or near their Eddington limit

16. SOME CAVEATS Deeper potential (strong scaling with  ); Daddi et al. recently found FWHM~700 km/s for GN20 In optically thick limit - high volume filling factor - the Eddington limit is an order of magnitude higher –Low brightness temperature suggests temperatures somewhat low compared to local and high-z systems of comparable luminosity –Possibly intermediate between the two regimes –See also D. Narayanan’s talk on need for additional obscuration in simulations of SMGs Can’t rule out multi-component source structure

17. CONCLUSIONS Our high resolution submm imaging provides a size measurement of the FIR directly. Most of the emission arises on kpc scales This suggests that an AGN is likely not contributing significantly to the FIR luminosity in the most luminous systems Under a series of simplifying assumptions, these scales are comparable to the Eddington limit for a starburst.

18. THE FUTURE Observations of two additional sources in EXT and VEX scheduled for this winter AzTEC & SCUBA2 will identify many promising (i.e., bright) targets for SMA eVLA offers fantastic sensitivity and resolution for spatially resolved studies of radio continuum and CO kinematics ALMA will do these kinds of measurements routinely

19. BACKUP SLIDES

20. SIZE MEASUREMENTS

21. EXT TRACKS: CALIBRATED VISIBILITIES