EVIDENCE FOR A POPULATION OF HIGH REDSHIFT SUBMILLIMETER GALAXIES Joshua D. Younger Harvard/CfA

P. Yamaguchi J. D. Younger, G. G. Fazio, J. Huang (CfA) M. S. Yun, G. Wilson, T. Perera, K. Scott, J. Austermann (U Mass) M. L. N. Ashby, M. A. Gurwell, K. Lai, A. B. Peck, G. Petitpas, D. Wilner (CfA) D. Iono, K. Kohno, R. Kawabe (NAOJ) D. Hughes, I. Aretzaga (INAOE), J. Lowenthal (Smith) T. Webb (McGill), A. Martinez-Sansigre, E. Schinnerer, V. Smolcic (MPIA) S. Kim (Sejong Univ)

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

Hughes et al. (1998) ~80% SF is obscured

INTRODUCTION Millimeter and submillimeter (submm) observations are critical to our understanding of galaxy birth and evolution in the early Universe. Studies of the diffuse far-IR and millimeter cosmic background radiation have shown this radiation is due to discrete sources dominated by luminous and ultraluminous infrared/submm galaxies at high redshift Multiwavelength studies of these galaxies have shown that they are massive, young objects in the process of formation, with very high star formation rates. However progress in understanding these galaxies has been hampered by their faintness at optical wavelengths and the poor angular resolution (~ 14 arcsec) of submm cameras. SMA and Spitzer Space Telescope (infrared) observations of these galaxies can provide new insight into the true nature of these sources.

SMG COUNTERPART IDENTIFICATION Radio continuum IRAC counterpart –Probability of association –N/MIR colors Redshifted PAH emission 1100  m 3.6  m

OBSERVATIONS AzTEC camera observations (1.1 mm wavelength; 18 arcsec resolution) on the JCMT of the COSMOS field (0.15 deg 2 ) detected 44 submm galaxies (SMGs) above 3.5 . SMA interferometric observations (890  m wavelength; 2 arcsec resolution) of the seven brightest AzTEC sources detected all seven SMGs and pinpointed their location to 0.2 arcsec. Follow-up observations by HST (ACS), SPITZER (IRAC and MIPS), and Very Large Array (VLA) revealed the detailed properties of these sources. The AzTEC/COSMOS Survey (Scott et al. 2007)

OVERVIEW OF RESULTS We detect all seven targets at high significance (>6  ) All seven SMA sources have IRAC 3.6mm counterparts Only a fraction (two/three) have optical counterparts For the five radio-dim sources, the submm, infrared and optical properties of these counterparts suggest higher redshift. –Higher submm/radio fluxes –Systematically low IRAC fluxes –No MIPS detection at 24  m AzTEC 1100  m ACS 814nm IRAC 3.6  m SMA 890  m

AzTEC1 AzTEC2 AzTEC3 AzTEC4 AzTEC5 AzTEC6 AzTEC7 890  m 20cm 24  m3.6  m0.8  m

ASTROMETRY OF SMA/AzTEC SOURCES

PHOTOMETRY OF SMA/AzTEC SOURCES

RADIO/SMM FLUX RATIOS Consistent with higher average/median redshift

IRAC COUNTERPARTS Consistent with higher average/median redshift

CONCLUSIONS From AzTEC and SMA observations, evidence for a population of SMGs that peak earlier in cosmic time (z > 3) –Constraints on galaxy formation and dust production models. From SMA imaging, brightest SMGs are single compact point-sources –Constraints on the physical mechanism driving far infrared emission and star formation Highlights the power of SMA to localize SMGs with sufficient accuracy for follow-up observations with HST and Spitzer Space Telescope. Younger, Fazio, et al. (2007) [astro-ph/ ]

HIGH-Z SMGs IN OTHER SAMPLES - SHADES We need bright high-significance targets targets (F 850  > 10 mJy or so) –wide areas –uniform coverage SHADES is a complete, unbiased large-area submm survey –~800 arcmin  m map of two fields (LH, SXDF) –Represents > 3 years of observations with SCUBA –Final map has rms ~ 2 mJy –Massive multiwavelength followup (VLA, Subaru, Spitzer, Keck, XMM, Chandra, …)

THE SHADES SURVEY Image Credit: J. Dunlop

THE TARGET: LH Brightest 850/1100  m source in the LH Two likely radio counterparts, one bright proximate MIPS source We detected LH at high significance (>6  ) with the SMA Compact, single point source singles out one radio counterpart Younger, Dunlop, Peck, Ivison et al. [in prep.]

MULTIWAVELENGTH COUNTERPARTS SMA 890  m POSITION R-band 3.6  m24  m 20cm

SEEMS TO BE PART OF SAME POPULATION

CONCLUSIONS (from a sample of 1) Clean illustration of problems with SMG counterpart identification Similar high-z SMG is also the brightest 850  m source in a wide-area blank field survey –High-z nature of sources likely related correlated more closely with brightness/luminosity than the wavelength in which they were selected –Brightest SMGs may be the most distant

WHAT TO DO NEXT? SMGs in a biased environment: MS0451 AzTEC sources (observing now) Further followup of AzTEC/COSMOS, (accepted for winter ‘09) Higher-resolution follow-up (accepted for winter ‘09) CARMA observations of AzTEC/COSMOS sources (submitted) CSO photometry at 350  m (submitted) SCUBA-2 Survey (both 450 and 850  m) Herschel Survey at  m