We investigate the physical properties of a sample of six submillimeter galaxies ( SMGs ) in the COSMOS field , spectroscopically confirmed to lie at redshifts z > 4 .
While the redshifts for four of these SMGs have been previously known , we present here two newly discovered z _ { \mathrm { spec } } > 4 SMGs .
For our analysis we employ the rich ( X-ray to radio ) COSMOS multi-wavelength datasets .
In particular , we use new Giant Meterwave Radio Telescope ( GMRT ) 325 MHz and 3 GHz Jansky Very Large Array ( VLA ) data to probe the rest-frame 1.4 GHz emission at z = 4 , and to estimate the sizes of the star-forming regions of these sources , respectively .
We find that only one SMG is clearly resolved at a resolution of 0 \aas@@fstack { \prime \prime } 6 \times 0 \aas@@fstack { \prime \prime } 7 at 3 GHz , two may be marginally resolved , while the remaining three SMGs are unresolved at this resolution .
Combining this with sizes from high-resolution ( sub- ) mm observations available in the literature for AzTEC 1 and AzTEC 3 we infer a median radio-emitting size for our z > 4 SMGs of ( 0 \aas@@fstack { \prime \prime } 63 \pm 0 \aas@@fstack { \prime \prime } 12 ) \times ( 0 % \aas@@fstack { \prime \prime } 35 \pm 0 \aas@@fstack { \prime \prime } 05 ) or 4.1 \times 2.3 kpc ^ { 2 } ( major \times minor axis ; assuming z = 4.5 ) or lower if we take the two marginally resolved SMGs as unresolved .
This is consistent with the sizes of star-formation regions in lower-redshift SMGs , and local normal galaxies , yet higher than the sizes of star-formation regions of local ULIRGs .
Our SMG sample consists of a fair mix of compact and more clumpy systems with multiple , perhaps merging , components .
With an average formation time of \sim 280 Myr , as derived through modeling of the UV-infrared ( IR ) spectral energy distributions ( SEDs ) , the studied SMGs are young systems .
The average stellar mass , dust temperature , and IR luminosity we derive are M _ { \star } \sim 1.4 \times 10 ^ { 11 } M _ { \sun } , T _ { dust } \sim 43 K , and L _ { IR } \sim 1.3 \times 10 ^ { 13 } L _ { \sun } , respectively .
The average L _ { IR } is up to an order of magnitude higher than for SMGs at lower redshifts .
Our SMGs follow the correlation between dust temperature and IR luminosity as derived for Herschel -selected 0.1 < z < 2 galaxies .
We study the IR-radio correlation for our sources and find a deviation from that derived for z < 3 ULIRGs ( \langle q _ { \mathrm { IR } } \rangle = 1.95 \pm 0.26 for our sample , compared to q \approx 2.6 for IR luminous galaxies at z < 2 ) .
In summary , we find that the physical properties derived for our z > 4 SMGs put them at the high end of the L _ { IR } – T _ { dust } distribution of SMGs , and that our SMGs form a morphologically heterogeneous sample .
Thus , further in-depth analyses of large , statistical samples of high-redshift SMGs are needed to fully understand their role in galaxy formation and evolution .