[Paper Review] Missing Giants: Predictions on Dust-Obscured Galaxy Stellar Mass Assembly Throughout Cosmic Time

Arianna S. Long, Caitlin M. Casey+6 more|arXiv (Cornell University)|Nov 3, 2022

Stellar, planetary, and galactic studies4 citations

TL;DR

This study develops a numerical model using empirical data on dust-obscured, star-forming galaxies (DSFGs) to predict their stellar mass assembly across cosmic time. It finds that massive DSFGs contribute 50–100% of all star-forming galaxies with M ≥ 10¹¹ M⊙ at z > 1, and their quiescent descendants explain the observed number density of massive passive galaxies, indicating they are a sufficient ancestral population for high-redshift massive galaxies.

ABSTRACT

Due to their extremely dust-obscured nature, much uncertainty still exists surrounding the stellar mass growth and content in dusty, star-forming galaxies (DSFGs) at $z>1$. In this work, we present a numerical model built using empirical data on DSFGs to estimate their stellar mass contributions across the first $\sim$10 Gyr of cosmic time. We generate a dust-obscured stellar mass function that extends beyond the mass limit of star-forming stellar mass functions in the literature, and predict that massive DSFGs constitute as much as $50-100\%$ of all star-forming galaxies with M $\ge10^{11}$M$_\odot$ at $z>1$. We predict the number density of massive DSFGs and find general agreement with observations, although more data is needed to narrow wide observational uncertainties. We forward model mock massive DSFGs to their quiescent descendants and find remarkable agreement with observations from the literature demonstrating that, to first order, massive DSFGs are a sufficient ancestral population to describe the prevalence of massive quiescent galaxies at $z>1$. We predict that massive DSFGs and their descendants contribute as much as $25-60\%$ to the cosmic stellar mass density during the peak of cosmic star formation, and predict an intense epoch of population growth during the $\sim1$ Gyr from $z=6$ to 3 during which the majority of the most massive galaxies at high-$z$ grow and then quench. Future studies seeking to understand massive galaxy growth and evolution in the early Universe should strategize synergies with data from the latest observatories (e.g. JWST and ALMA) to better include the heavily dust-obscured galaxy population.

Motivation & Objective

• To quantify the role of dust-obscured, star-forming galaxies (DSFGs) in stellar mass assembly across cosmic time, particularly at z > 1.
• To address the bias in UV/optical-based galaxy evolution models that exclude heavily dust-attenuated systems.
• To test whether massive DSFGs can account for the observed number density of massive quiescent galaxies at high redshift.
• To estimate the contribution of DSFGs and their descendants to the cosmic stellar mass density during peak star formation.
• To guide future observations by identifying key synergies between JWST and ALMA for resolving DSFG properties.

Proposed method

• The authors construct a dust-obscured stellar mass function (SMF) by extending UV/optical-based SMFs with empirical data on DSFGs, incorporating IR luminosity functions and dust attenuation models.
• They model the high-mass end of the SMF with a power-law extension beyond the characteristic mass, using conservative assumptions to minimize bias.
• The model incorporates uncertainties in IR luminosity functions and SED fitting, marginalizing over DSFG properties such as star-formation efficiency and gas depletion timescales.
• They forward model mock massive DSFGs through evolutionary tracks to predict their quiescent descendants, comparing predicted number densities with observed passive galaxies.
• The model uses redshift-dependent IR luminosity functions and dust-attenuation prescriptions calibrated from deep submillimeter and far-IR surveys.
• They validate predictions against observational constraints, including number densities of massive DSFGs and passive galaxies at z > 1, while accounting for observational depth and selection biases.

Experimental results

Research questions

• RQ1 To what extent do dust-obscured, star-forming galaxies (DSFGs) dominate the stellar mass assembly of massive galaxies at z > 1?
• RQ2 Can massive DSFGs alone account for the observed number density of massive quiescent galaxies at z > 1?
• RQ3 What fraction of the cosmic stellar mass density at z ~ 2 is contributed by DSFGs and their quiescent descendants?
• RQ4 How does the inclusion of DSFGs resolve discrepancies between integrated star formation rate density and directly measured stellar mass density?
• RQ5 What observational strategies, particularly with JWST and ALMA, are needed to better constrain the DSFG population?

Key findings

• Massive DSFGs (M ≥ 10¹¹ M⊙) constitute 50–100% of all star-forming galaxies at z > 1, indicating they are not a minor population but a dominant driver of high-mass growth.
• The model-predicted number density of massive DSFGs shows general agreement with observations, though uncertainties remain large at z > 4 due to limited stellar mass measurements.
• Forward modeling of DSFGs to their quiescent descendants yields excellent agreement with observed number densities of massive passive galaxies at z > 1, supporting their role as the primary progenitors.
• DSFGs and their quiescent descendants contribute 25–60% to the cosmic stellar mass density during the peak of star formation at z ~ 2, significantly closing the gap between inferred and observed mass densities.
• An intense 1 Gyr growth and quenching phase occurs between z = 6 and z = 3, during which the majority of the most massive galaxies form and transition to quiescence.
• The majority (>75%) of galaxies in the high-mass end of the dust-obscured SMF (M ≥ 10¹⁰.⁵ M⊙) have LIRG-like or ULIRG-like luminosities (L_IR ≥ 10¹¹ L⊙), with most exceeding 10¹² L⊙.