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The ALPINE-ALMA [CII] survey: Dust attenuation properties and obscured star formation at z ∼4.4-5.8

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Fudamoto, Y 
Oesch, PA 
Faisst, A 
Béthermin, M 
Ginolfi, M 


We present dust attenuation properties of spectroscopically confirmed star forming galaxies on the main sequence at redshift ~4.4-5.8. Our analyses are based on the far infrared continuum observations of 118 galaxies at rest-frame 158μm obtained with the ALMA large program ALPINE. We study the connection between the UV spectral slope (β), stellar mass (M), and infrared excess (IRX=LIR/LUV). Twenty-three galaxies are individually detected in the continuum at >3.5σ significance. We perform a stacking analysis using both detections and non-detections to study the average dust attenuation properties at z~4.4-5.8. The individual detections and stacks show that the IRX-β relation at z~5 is consistent with a steeper dust attenuation curve than typically found at lower redshifts (z<4). The attenuation curve is similar to or even steeper than that of the extinction curve of the Small Magellanic Cloud (SMC). This systematic change of the IRX-β relation as a function of redshift suggests an evolution of dust attenuation properties at z>4. Similarly, we find that our galaxies have lower IRX values up to 1 dex on average at fixed mass compared to previously studied IRX-M relations at z≲4, albeit with significant scatter. This implies a lower obscured fraction of star-formation than at lower redshifts. Our results suggest that dust properties of UV-selected star forming galaxies at z≳4 are characterised by (i) a steeper attenuation curve than at z≲4, and (ii) a rapidly decreasing dust obscured fraction of star formation as a function of redshift. Nevertheless, even among this UV-selected sample, massive galaxies (logM/M⊙>10) at z~5-6 already exhibit an obscured fraction of star formation of ∼45%, indicating a rapid build-up of dust during the epoch of reionization.



galaxies: high-redshift, galaxies: ISM, dust, extinction

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Astronomy and Astrophysics

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EDP Sciences


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Science and Technology Facilities Council (ST/M001172/1)
European Research Council (695671)