We investigate the stellar population of star-forming galaxies at z \sim 4 by focusing on their slope of rest-frame ultraviolet ( UV ) continuum , \beta where f _ { \lambda } \propto \lambda ^ { \beta } .
We investigate the sample of bright Lyman Break Galaxies ( LBGs ) with i ’ \leq 26.0 in the Subaru/XMM-Newton Deep Survey field by using the SED fitting analysis .
We find that the apparently redder ( \beta _ { \mathrm { obs } } > -1.73 ) LBGs tend to be dusty ( \mathrm { Av } > 1.0 ) , have the young stellar population ( \beta _ { \mathrm { int } } < -2.42 ) , and the intrinsically active star-forming galaxies ( SFR \gtrsim a few \times 10 ^ { 2 } \mathrm { M _ { \solar } } \ > \mathrm { yr ^ { -1 } } ) .
It means that a significant fraction of the UV–selected LBGs at z \sim 4 is on-going active and dust obscured star-forming galaxies .
We compare the IR to UV luminosity ratio assuming the dust attenuation laws with the sub-millimeter observations from previous works .
The result suggests that the Calzetti-like dust attenuation law is preferable for the active and dusty star-forming LBGs at z = 4 .
We also find that an extrapolation of the \beta _ { \mathrm { int } } – M _ { \mathrm { UV,int } } relation toward the fainter magnitude range below our sample magnitude limit intersects the \beta _ { \mathrm { obs } } – M _ { \mathrm { UV,obs } } relation previously obtained in the deeper narrow-area observations at M _ { \mathrm { UV } } = -18.9 and \beta = -1.94 , which coincides with the break point of \beta _ { \mathrm { obs } } – M _ { \mathrm { UV,obs } } relation observed so far .
The coincidence suggest that we see the almost dust-free population at M _ { \mathrm { UV,obs } } \gtrsim - 18.9 .