[Paper Review] The ALPINE-ALMA [CII] Survey: The nature, luminosity function and star formation history of dusty galaxies up to z~6

C. Gruppioni, M. Béthermin+31 more|SPIRE - Sciences Po Institutional REpository|Jun 8, 2020

Galaxies: Formation, Evolution, PhenomenaPhysics and Astronomy136 references19 citations

TL;DR

This study presents the first far-IR luminosity function and star formation rate density (SFRD) measurements for dusty galaxies up to z ≈ 6 using serendipitous ALMA [CII] survey sources. It reveals a flat infrared luminosity function with little evolution from z ≈ 2.5 to z ≈ 6, and finds that dusty, optically dark galaxies contribute ~17% of the SFRD at z ≈ 5, challenging UV-based SFR estimates and current galaxy formation models.

ABSTRACT

We present the detailed characterisation of a sample of 56 sources serendipitously detected in ALMA band 7, as part of the ALMA Large Program to INvestigate CII at Early Times (ALPINE) in COSMOS and ECDFS. These sources have been used to derive the total infrared luminosity function (LF) and to estimate the cosmic star formation rate density (SFRD) up to z=6. We have looked for counterparts in all the available multi-wavelength and photometric redshift catalogues, and in deeper near- and mid-IR source lists and maps, to identify optically dark sources with no matches in the public catalogues. Our ALMA blind survey allows us to push further the study of the nature and evolution of dusty galaxies at high-z, identifying luminous and massive sources to redshifts and faint luminosities never probed before by any far-infrared surveys. The ALPINE data are the first ones to sample the faint-end of the infrared LF, showing little evolution from z=2.5 to z=6, and a flat slope up to the highest redshifts. The SFRD obtained by integrating the luminosity function remains almost constant between z=2 and 6, and significantly higher than the optical/UV derivations, showing an important contribution of dusty galaxies and obscured star formation up to high-z. About 14 per cent of the ALPINE serendipitous continuum sources are optically+near-IR dark (six show a counterpart only in the mid-IR and no HST or near-IR identification, while two are detected as [CII] emitters at z=5). The six HST and near-IR dark galaxies with mid-IR counterpart contribute for about 17 per cent of the total SFRD at z=5 and dominate the high-mass end of the stellar mass function at z>3.

Motivation & Objective

• To characterize the nature and evolution of dusty galaxies at high redshift (z ≈ 6) using serendipitously detected ALMA continuum sources.
• To derive the total infrared luminosity function (LF) and cosmic star formation rate density (SFRD) from z ≈ 0.5 to z ≈ 6, filling the faint-end gap in far-IR surveys.
• To quantify the contribution of optically and near-IR dark galaxies—especially those detected only in mid-IR or [CII]—to the total SFRD and stellar mass function at high redshift.
• To test the consistency of ALPINE results with existing Herschel and SCUBA-2 LFs and to assess discrepancies with UV-based SFRD estimates.
• To evaluate the implications of high SFRD and massive dusty galaxies at z > 3 for current galaxy formation models and simulations.

Proposed method

• Identified 56 serendipitous ALMA band 7 continuum sources in COSMOS and ECDFS fields with 860 μm fluxes between ~0.3–12.5 mJy.
• Cross-identified sources with multi-wavelength catalogs (HST, VLA, UltraVISTA, Spitzer) and deeper maps to detect optically dark galaxies.
• Estimated photometric redshifts and derived rest-frame 250 μm and total infrared (8–1000 μm) luminosities from SED fitting.
• Constructed rest-frame 250 μm and total IR luminosity functions (LFs) in redshift bins from z ≈ 0.5 to z ≈ 6 using ALPINE data.
• Integrated the IR LF to compute the cosmic star formation rate density (SFRD) across redshifts, comparing with UV-based estimates.
• Quantified the contribution of HST and near-IR dark galaxies (with or without mid-IR counterparts) to the total SFRD and stellar mass function.

Experimental results

Research questions

• RQ1 How does the far-IR luminosity function of dusty galaxies evolve from z ≈ 0.5 to z ≈ 6, and does it show significant evolution in shape or normalization?
• RQ2 What fraction of the cosmic star formation rate density (SFRD) at z ≈ 5 is contributed by optically and near-IR dark galaxies?
• RQ3 How do the SFRD estimates from the ALPINE far-IR survey compare with those derived from UV-observed galaxies at z > 3?
• RQ4 To what extent do current galaxy formation models reproduce the observed number density and mass function of massive, dusty galaxies at z > 3?
• RQ5 What is the role of dust-obscured star formation in the cosmic noon (z ≈ 1–3) and beyond, and why is it missed by UV surveys?

Key findings

• The ALPINE survey samples the faint end of the infrared luminosity function (LF) with no significant evolution from z ≈ 2.5 to z ≈ 6, showing a flat slope across the entire redshift range.
• The total infrared luminosity function remains nearly constant in normalization and shape from z ≈ 0.5 to z ≈ 6, with no drop at high luminosities, indicating sustained dusty star formation activity.
• The cosmic star formation rate density (SFRD) derived from the ALPINE IR LF is nearly flat from z ≈ 2 to z ≈ 6, significantly higher than UV-based estimates, which differ by a factor of ~10 at z ≈ 6.
• Approximately 14% of ALPINE serendipitous sources are optically and near-IR dark (to Ks ~24.9 mag), with six detected only in the mid-IR and two confirmed as [CII] emitters at z ≈ 5.
• HST and near-IR dark galaxies with mid-IR counterparts contribute about 17% of the total SFRD at z ≈ 5 and dominate the high-mass end of the stellar mass function at z > 3.
• The number density of massive, dusty galaxies (M* > 10^10.7 M⊙) at z > 3 is comparable to that of more massive quiescent galaxies, challenging current semi-analytical and hydrodynamic simulations.