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Durham University

Department of Physics

Staff profile

Publication details for Professor Ian Smail

da Cunha, E., Walter, F., Smail, I. R., Swinbank, A. M., Simpson, J. M., Decarli, R., Hodge, J. A., Weiss, A., van der Werf, P. P., Bertoldi, F., Chapman, S. C., Cox, P., Danielson, A. L. R., Dannerbauer, H., Greve, T. R., Ivison, R. J., Karim, A. & Thomson, A. (2015). An ALMA Survey of Sub-millimeter Galaxies in the Extended Chandra Deep Field South: Physical Properties Derived from Ultraviolet-to-radio Modeling. The Astrophysical Journal 806(1): 110.

Author(s) from Durham

Abstract

The ALESS survey has followed up on a sample of 122 sub-millimeter sources in the Extended Chandra Deep Field
South at 870 μmwith the Atacama Large Millimeter Array (ALMA), allowing us to pinpoint the positions of submillimeter
galaxies (SMGs) to ∼0.3 arcsec and to find their precise counterparts at different wavelengths. This
enabled the first compilation of the multi-wavelength spectral energy distributions (SEDs) of a statistically reliable
survey of SMGs. In this paper, we present a new calibration of the MAGPHYS SED modeling code that is optimized to
fit these ultraviolet-to-radio SEDs of z > 1 star-forming galaxies using an energy balance technique to connect the
emission from stellar populations, dust attenuation, and dust emission in a physically consistent way. We derive
statistically and physically robust estimates of the photometric redshifts and physical parameters (such as stellar
masses, dust attenuation, star formation rates (SFRs), and dust masses) for the ALESS SMGs. We find that the
ALESS SMGs have median stellar mass = ± × ⊙ M* 8.9 0.1 1010 M , median SFR = ± ⊙
280 70 M yr−1, median
overall V-band dust attenuation AV = 1.9 ± 0.2 mag, median dust mass = ± × ⊙ Mdust (5.6 1.0) 10 M
8 , and median
average dust temperature Tdust ≃ 40 K.We find that the average intrinsic SED of the ALESS SMGs resembles that of
local ultra-luminous infrared galaxies in the infrared range, but the stellar emission of our average SMG is brighter
and bluer, indicating lower dust attenuation, possibly because they are more extended. We explore how the average
SEDs vary with different parameters (redshift, sub-millimeter flux, dust attenuation, and total infrared luminosity),
and we provide a new set of SMG templates that can be used to interpret other SMG observations. To put the ALESS
SMGs into context, we compare their stellar masses and SFRs with those of less actively star-forming galaxies at the
same redshifts. We find that at z ≃ 2, about half of the SMGs lie above the star-forming main sequence (with SFRs
three times larger than normal galaxies of the same stellar mass), while half are consistent with being at the highmass
end of the main sequence. At higher redshifts (z ≃ 3.5), the SMGs tend to have higher SFRs and stellar
masses, but the fraction of SMGs that lie significantly above the main sequence decreases to less than a third.