[Paper Review] The ALPINE-ALMA [CII] survey

Yoshinobu Fudamoto, Pascal A. Oesch+35 more|arXiv (Cornell University)|Apr 22, 2020

Galaxies: Formation, Evolution, PhenomenaPhysics and Astronomy92 references10 citations

TL;DR

This study analyzes dust attenuation in 118 main-sequence star-forming galaxies at z ∼4.4–5.8 using ALMA [CII] and far-IR continuum data. It finds a steeper IRX–β relation and lower obscured star formation fractions than at z < 4, indicating rapid evolution in dust properties during cosmic reionization, with massive galaxies at z ∼5–6 showing ~45% obscured star formation despite a significant decline from higher redshifts.

ABSTRACT

We present dust attenuation properties of spectroscopically confirmed star forming galaxies on the main sequence at a redshift of ~4.4-5.8. Our analyses are based on the far infrared continuum observations of 118 galaxies at rest-frame 158μm obtained with the Atacama Large Millimeter Array (ALMA) Large Program to INvestigate [CII] at Early times (ALPINE). We study the connection between the ultraviolet (UV) spectral slope ($β$), stellar mass (M_*), and infrared excess (IRX=L_IR/L_UV). Twenty-three galaxies are individually detected in the continuum at &gt;3.5 sigma significance. We perform a stacking analysis using both detections and nondetections 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&lt;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&gt;4. Similarly, we find that our galaxies have lower IRX values, up to 1dex on average, at a fixed mass compared to previously studied IRX-M_* relations at z&lt;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&gt;4 are characterised by (i) a steeper attenuation curve than at z&lt;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 (log M_*/$M_\odot$&gt;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.

Motivation & Objective

• To measure dust attenuation properties in high-redshift star-forming galaxies at z ∼4.4–5.8 using far-IR continuum data.
• To investigate the evolution of the IRX–β and IRX–M⋆ relations beyond z ≲4, where such relations are well established.
• To quantify the obscured fraction of star formation in UV-selected galaxies at z ≳5, addressing uncertainties in SFR density estimates.
• To assess the reliability of standard dust correction methods (e.g., M99 relation) at z > 4, where they may overpredict IR luminosities by up to 1 dex.

Proposed method

• Utilized ALMA Large Program data to obtain rest-frame 158 µm dust continuum measurements for 118 spectroscopically confirmed star-forming galaxies at z ∼4.4–5.8.
• Performed individual detections and stacking analysis on both detected and non-detected sources to derive average dust attenuation properties.
• Constructed the IRX–β and IRX–M⋆ relations using UV spectral slope (β) and stellar mass (M⋆), with IRX defined as LIR/LUV.
• Fitted the UV attenuation curve slope to compare with local templates (e.g., M99, SMC) and assess dust geometry and grain properties.
• Calculated the obscured fraction of star formation (fobs) as fobs = LIR/(LIR + LUV) and compared it with lower-redshift relations.
• Used Chabrier initial mass function and cosmological parameters (Ωm=0.3, ΩΛ=0.7, h=0.7) for consistent photometric and SED modeling.

Experimental results

Research questions

• RQ1 How do the IRX–β and IRX–M⋆ relations at z ∼4.4–5.8 compare to those at z < 4?
• RQ2 What is the obscured fraction of star formation in massive UV-selected galaxies at z ∼5–6, and how does it evolve with redshift?
• RQ3 Is the standard M99 dust attenuation law valid for high-redshift galaxies, or is a steeper curve required?
• RQ4 To what extent do existing dust correction methods overestimate IR luminosities and SFRs in z > 4 galaxies?
• RQ5 What does the observed dust evolution imply about the dominant dust production mechanisms at z ≳5?

Key findings

• The IRX–β relation at z ∼5 is significantly steeper than the M99 relation, with average IRX values 0.5 dex lower for βUV > −1.5, indicating a steeper dust attenuation curve.
• The attenuation curve is consistent with or steeper than the Small Magellanic Cloud (SMC) extinction curve, suggesting distinct dust grain properties at z ≳5.
• The IRX–M⋆ relation at z ∼5.5 lies below all previously reported relations at z ≲3, with a ∼1 dex overprediction of IR luminosity for massive galaxies (log M⋆/M⊙ > 10).
• The obscured fraction of star formation (fobs) decreases from ∼65% at z ∼4.5 to ∼45% at z ∼5.5 in massive galaxies (M⋆ ∼1–3×10¹⁰ M⊙), indicating rapid evolution.
• Even among UV-selected galaxies, massive z ∼5–6 galaxies exhibit a substantial obscured fraction of ∼45%, implying rapid dust buildup during reionization.
• Standard dust correction methods calibrated at z < 4 overpredict IR luminosities and SFRs by up to 1 dex for red, massive galaxies at z > 4, necessitating revised calibration.