The IR Compactness of Dusty Galaxies Sets Star Formation and Dust Properties at z ∼ 0–2

Abstract

The surface densities of gas, dust, and stars provide a window into the physics of star formation that, until the advent of high-resolution far-IR/submillimeter observations, has been historically difficult to assess among dusty galaxies. To study the link between IR surface densities and dust properties, we leverage the Atacama Large Millimetre/Submillimetre Array archive to measure the extent of cold dust emission in 15 z ∼ 2 IR-selected galaxies selected on the basis of having available mid-IR spectroscopy from Spitzer. We use the mid-IR spectra to constrain the relative balance between dust heating from star formation and active galactic nuclei (AGNs), and to measure emission from polycylic aromatic hydrocarbons (PAHs), small dust grains that play a key role in the photoelectric heating of gas. In general, we find that dust-obscured star formation at high IR surface densities exhibits similar properties at low and high redshift, namely, local luminous IR galaxies (LIRGs) have comparable PAH luminosity to total dust mass ratios as high-z galaxies, and star formation at z ∼ 0–2 is more efficient at high IR surface densities despite the fact that our sample of high-z galaxies is closer to the main sequence than local LIRGs. High star formation efficiencies are coincident with a decline in the PAH-to-IR luminosity ratio reminiscent of the deficit observed in far-IR fine-structure lines. Changes in the gas and dust conditions arising from high star formation surface densities might help drive the star formation efficiency up. This could help explain the high efficiencies needed to reconcile star formation and gas volume densities in dusty galaxies at cosmic noon.

COSMOS-Web: Intrinsically Luminous z ≳ 10 Galaxy Candidates Test Early Stellar Mass Assembly

“…This may suggest that, as observed, these galaxies could be viable progenitors of elliptical galaxy cores with similar densities. The star formation surface densities are very similar to those seen in some z > 7 bright LBGs (e.g., Bowler et al 2017), some local starbursts (e.g., the Great Observatories All-sky Luminous Infrared Galaxy Survey sample; Armus et al 2009;McKinney et al 2023b) and highredshift submillimeter galaxies (Hodge et al 2016;Burnham et al 2021), though the latter systems tend to be much larger (R eff > 1 kpc) with higher SFRs.…”

“…In addition, we overplot the measured sizes and surface densities of the compact z ∼ 8 sources first discovered by and whose sizes were analyzed in Baggen et al (2023). The star formation surface densities are on par with other z > 7 bright LBGs (Bowler et al 2017), local starbursts (Armus et al 2009;McKinney et al 2023b), and submillimeter galaxies with measured sizes (with R eff > 1 kpc; Burnham et al 2021). The sources from our sample are colored by subsample as in Figure 5.…”

The Interplay between the Initial Mass Function and Star Formation Efficiency through Radiative Feedback at High Stellar Surface Densities

“…However, it has become increasingly evident that this is not the case for GMCs typical of high interstellar medium (ISM) pressure environments (P/k B  10 8 K cm −3 ), for which both models (Fall et al 2010;Thompson & Krumholz 2016) and numerical simulations (Grudić et al 2018;Fukushima & Yajima 2021;Lancaster et al 2021a;Menon et al 2022aMenon et al , 2023Polak et al 2023) suggest efficiencies ò *  80% because the energy/momentum deposition rate of feedback in this regime is unable to counteract gravity. Such pressures correspond to GMCs with surface densities (Σ  Σ crit = 10 3 M ☉ pc −2 )-2-3 orders of magnitude higher than typical of GMCs in the local Universe-which are the likely sites of so-called super star cluster formation (e.g., McCrady et al 2005;Portegies Zwart et al 2010;Turner et al 2015;Smith et al 2020); observational estimates seem to be consistent with a high value of ò * for these conditions (Turner et al 2017;Emig et al 2020;Rico-Villas et al 2020;Smith et al 2020;Costa et al 2021;He et al 2022;McKinney et al 2023;Sun et al 2024). The environments that host these conditions are relatively rare in the local Universelimited to scenarios such as nuclear starbursts (e.g., Leroy et al 2018;Emig et al 2020;Levy et al 2021), merging luminous infrared (IR)-bright galaxies (e.g., Johnson et al 2015;Finn et al 2019;Inami et al 2022), and localized starbursts in dwarf galaxies (e.g., Ochsendorf et al 2017;Oey et al 2017; Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence.…”