Duality in spatially resolved star formation relations in local LIRGs

¹ Centro de Astrobiología (CSIC/INTA), Ctra de Torrejón a Ajalvir, km 4, 28850 Torrejón de Ardoz, Madrid, Spain
e-mail: mariasg@cab.inta-csic.es
² Observatorio Astronómico Nacional (OAN-IGN)-Observatorio de Madrid, Alfonso XII, 3, 28014 Madrid, Spain
³ Centro de Astrobiología (CAB, CSIC-INTA), ESAC Campus, 28692 Villanueva de la Cañada, Madrid, Spain
⁴ Department of Physics, General Studies, College of Engineering, Nihon University, 1 Nakagawara, Tokusada, Tamuramachi, Koriyama, Fukushima 963-8642, Japan
⁵ National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
⁶ Department of Physics, University of Crete, 71003 Heraklion, Greece
⁷ Institute of Astrophysics, Foundation for Research and Technology-Hellas, Heraklion 70013, Greece
⁸ Instituto de Astrofísica de Andalucía (IAA-CSIC), Apdo. 3004, 18008 Granada, Spain
⁹ Telespazio UK for the European Space Agency (ESA), ESAC, Spain

Received: 5 August 2021
Accepted: 30 October 2021

Abstract

We analyse the star formation (SF) relations in a sample of 16 nearby luminous infrared galaxies (LIRGs) with more than 2800 regions defined on scales of 90 to 500 pc. We used ALMA to map the distribution of the cold molecular gas traced by the J = 2–1 line of CO and archival Paα HST/NICMOS imaging to trace the recent SF. In four objects we find two different branches in the Kennicutt-Schmidt relation at 90 pc scales, suggesting the existence of a duality in this relation. The two branches correspond to two different dynamical environments within each galaxy. One branch, which corresponds to the central region of these galaxies (90% of the regions are located at radii < 0.85 kpc), shows higher gas and SF rate surface densities with higher velocity dispersion. The other branch, which shows lower molecular gas and SF rate surface densities, corresponds to the more external disk regions (r ∼ 1 kpc). Despite the scatter, the SF efficiency of the galaxies with dual behaviour increases with increasing boundedness as measured by the b parameter (b≡ Σ_H2/σ² ∝ α_vir⁻¹). At larger spatial scales (250 and 500 pc), the duality disappears. The rest of the sample does not show evidence of this dual behaviour at any scale.