[Paper Review] High-redshift star formation in the ALMA era

Jacqueline Hodge, Elisabete da Cunha|arXiv (Cornell University)|Apr 2, 2020

Galaxies: Formation, Evolution, Phenomena636 references33 citations

TL;DR

ALMA dramatically advances the study of dust-obscured star formation at high redshift by delivering unprecedented resolution, sensitivity, and spectral capabilities, enabling precise localization, resolved ISM studies, and probing fainter galaxy populations beyond classical SMGs.

ABSTRACT

The Atacama Large Millimetre/submillimetre Array (ALMA) is currently in the process of transforming our view of star-forming galaxies in the distant ($z\gtrsim1$) universe. Before ALMA, most of what we knew about dust-obscured star formation in distant galaxies was limited to the brightest submillimetre sources$-$the so-called submillimetre galaxies (SMGs)$-$and even the information on those sources was sparse, with resolved (i.e., sub-galactic) observations of the obscured star formation and gas reservoirs typically restricted to the most extreme and/or strongly lensed sources. Starting with the beginning of early science operations in 2011, the last nine years of ALMA observations have ushered in a new era for studies of high-redshift star formation. With its long baselines, ALMA has allowed observations of distant dust-obscured star formation with angular resolutions comparable to$-$or even far surpassing$-$the best current optical telescopes. With its bandwidth and frequency coverage, it has provided an unprecedented look at the associated molecular and atomic gas in these distant galaxies through targeted follow-up and serendipitous detections/blind line scans. Finally, with its leap in sensitivity compared to previous (sub-)millimetre arrays, it has enabled the detection of these powerful dust/gas tracers much further down the luminosity function through both statistical studies of color/mass-selected galaxy populations and dedicated deep fields. We review the main advances ALMA has helped bring about in our understanding of the dust and gas properties of high-redshift ($z\gtrsim1$) star-forming galaxies during these first nine years of its science operations, and we highlight the interesting questions that may be answered by ALMA in the years to come.

Motivation & Objective

• Assess how ALMA’s capabilities transform observations of dust-obscured star formation in high-redshift galaxies (z > 1).
• Review progress on submillimeter-selected galaxies (SMGs) and strongly lensed systems with ALMA.
• Summarize statistical and resolved ISM properties of distant star-forming galaxies.
• Discuss how ALMA surveys and follow-ups extend the luminosity function and redshift coverage.

Proposed method

• Describe ALMA’s key capabilities: angular resolution, frequency coverage, bandwidth, and sensitivity.
• Explain how ALMA enables precise localization of SMGs and counterpart identification.
• Summarize approaches to resolving multiplicity and lensing effects in high-z sources.
• Outline how ALMA surveys (blind and targeted) constrain gas content and dust properties in distant galaxies.

Experimental results

Research questions

• RQ1 How has ALMA changed the ability to locate and identify counterparts of distant dusty star-forming galaxies identified in submillimetre surveys?
• RQ2 What have ALMA observations revealed about the ISM properties, gas fractions, and star formation laws in high-redshift galaxies?
• RQ3 To what extent do strongly lensed systems and blind surveys with ALMA alter our understanding of the high-z dusty galaxy population and cosmic gas density?
• RQ4 What defines the ALMA-era population of SMGs and how does it connect to color- and mass-selected high-z galaxies?

Key findings

• ALMA provides sub-arcsecond localization of SMGs, enabling precise counterpart identification and redshift estimation.
• ALMA resolves multiplicity in single-dish SMG sources, revealing multiple submillimetre galaxies within previous beams.
• The survey and follow-up capabilities of ALMA uncover dust/gas properties of high-z galaxies, including spatially resolved ISM and dynamics.
• Deep ALMA observations allow probing fainter galaxies, extending studies down the luminosity function beyond classical SMGs.
• ALMA’s spectral capabilities enable redshift confirmation and detailed ISM studies through multiple molecular and atomic lines.
• Lensing and source reconstruction techniques with ALMA improve measurements of high-z ISM physics and intrinsic source properties.