Resolved Schmidt-Kennicutt relation in a binary hyperluminous infrared galaxy at $z=2.41$

TL;DR

This study uses high-resolution ALMA imaging to analyze the star formation laws in a binary hyperluminous infrared galaxy at z=2.41, revealing a steep Schmidt-Kennicutt relation and detailed gas properties during peak galaxy growth.

Contribution

First resolved imaging of a binary HyLIRG at z=2.41 with detailed gas kinematics and star formation relations, highlighting the steepness of the SK relation in extreme starburst systems.

Findings

Gas kinematics are rotation-dominated in both galaxies.

Resolved SK relation shows a steep slope of ~1.7.

Depletion times are 50-100 Myr in W and 100-500 Myr in T.

Abstract

Hyperluminous infrared galaxies (HyLIRGs; SFRs up to about 1000 Msun yr-1), though rare, provide key constraints on galaxy evolution. H-ATLAS J084933.4+021443, a z = 2.41 binary HyLIRG (galaxies W and T) with two additional luminous companions (C and M), offers an ideal laboratory for studying star formation during "cosmic noon". We use ALMA to obtain resolved imaging and kinematics of CO J:7-6, [C I] 2-1, H2O, and rest-frame 340-1160 GHz continuum emission in all four galaxies. Each system is spatially resolved within ~0.3 arcsec (2.5 kpc) apertures. Gas kinematics in W and T are rotation-dominated, with galaxy T showing emission extended along its kinematic minor axis due to lensing magnification. Spatially resolved SEDs indicate that W is well fitted by single-temperature greybody dust despite hosting a luminous AGN, while T requires an additional hot-dust component and extra millimetre emission. We confirm [C I] J:2-1 as a tracer of warm/dense molecular gas in these extreme systems, though its luminosity ratio with CO J:7-6 rises sub-linearly. We derive resolved (2.5 kpc-scale) Schmidt-Kennicutt (SK) relations for W and T using both cold and warm/dense gas, finding depletion times of about 50-100 Myr (W) and about 100-500 Myr (T). Both galaxies follow a steep SK relation with power-law index n ~ 1.7, significantly above the n ~ 1 observed in normal star-forming galaxies.