A3COSMOS: The dust attenuation of star-forming galaxies at z = 2.5 − 4.0 from the COSMOS-ALMA Archive

Yoshinobu Fudamoto, P. A. Oesch, B. Magnelli, E. Schinnerer, D. Liu, P. Lang, E. F. Jiménez-Andrade, B. Groves, S. Leslie, M. T. Sargent

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We present an analysis of the dust attenuation of star forming galaxies at z = 2.5 − 4.0 through the relationship between the UV spectral slope (β), stellar mass (M) and the infrared excess (IRX= LIR/LUV) based on far-infrared continuum observations from the Atacama Large Millimeter/sub-millimeter Array (ALMA). Our study exploits the full ALMA archive over the COSMOS field processed by the A3COSMOS team, which includes an unprecedented sample of ∼ 1500 galaxies at z ∼ 3 as primary or secondary targets in ALMA band 6 or 7 observations with a median continuum sensitivity of 126 µJy/beam (1σ). The detection rate is highly mass dependent, decreasing drastically below log(M/M ) = 10.5. The detected galaxies show that the IRX-β relationship of massive (log M/M > 10) main sequence galaxies at z = 2.5 − 4.0 is consistent with that of local galaxies, while starbursts are generally offset by ∼ 0.5 dex to larger IRX values. At the low mass end, we derive upper limits on the infrared luminosities through stacking of the ALMA data. The combined IRX-M relation at log (M/M) > 9 exhibits a significantly steeper slope than reported in previous studies at similar redshifts, implying little dust obscuration at log M/M < 10. However, our results are consistent with early measurements at z ∼ 5.5, indicating a potential redshift evolution between z ∼ 2 and z ∼ 6. Deeper observations targeting low mass galaxies will be required to confirm this finding.

Original languageEnglish
JournalUnknown Journal
Publication statusPublished - 2019 Oct 28
Externally publishedYes


  • Galaxies: evolution
  • Galaxies: ISM
  • Galaxies: star formation
  • Submillimetre: ISM

ASJC Scopus subject areas

  • General

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