The Arp 240 Galaxy Merger: A Detailed Look at the Molecular Kennicutt-Schmidt Star Formation Law on Subkiloparsec Scales
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Date
2025
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Publisher
IOP Publishing Ltd
Abstract
The molecular Kennicutt-Schmidt Law has been key for understanding star formation (SF) in galaxies across allredshifts. However, recent subkiloparsec observations of nearby galaxies reveal deviations from the nearly unityslop e(N) obtained with disk-averaged measurements. We study SF and molecular gas (MG) distribution in theearly-stage luminous infrared galaxy merger Arp 240(NGC 5257-8). Using Very Large Array radio continuum (RC) and Atacama Large Millimeter/submillimeter Array CO(2-1)observations at 500 pc scale, with a uniformgrid analysis, we estimate SF rates and MG surface densities (Sigma(SFR) and H-2, respectively). In Arp 240,Nissublinear at 0.52 +/- 0.17. For NGC 5257 and NGC 5258,Nis 0.52 +/- 0.16 and 0.75 +/- 0.15, respectively. Weidentify two SF regimes: high surface brightness (HSB) regions in RC with N similar to 1, and low surface brightness (LSB) regions with shallow N (ranging 0.15 +/- 0.09-0.48 +/- 0.04). Median CO(2-1) linewidth and MG turbulent pressure (P-turb) are 25 km s(-1) and 9 x 10(5) K cm(-3). No significant correlation was found between Sigma(SFR) and CO(2-1) linewidth. However, Sigma(SFR) correlates with P-turb, particularly in HSB regions (rho>0.60). In contrast, SF efficiency moderately anticorrelates with P-turb in LSB regions but shows no correlation in HSB regions. Additionally, we identify regions where peaks in SF and MG are decoupled, yielding a shallow N (<= 0.28 +/- 0.18). Overall, the range of N reflects distinct physical properties and distribution of both the SF and MG, which can be masked by disk-averaged measurements.