Star formation scaling relations at ∼100 pc from PHANGS: Impact of completeness and spatial scale

Ismael Pessa ,A Usero,J Pety,E Schinnerer,Simon C O Glover ,Adam K Leroy ,J M Diederik Kruijssen ,Andreas Schruba ,Kathryn Grasha ,Kathryn Kreckel ,María J Jiménez-Donaire ,Elizabeth J Watkins ,Eric W Koch ,I-Ting Ho ,Daniel A Dale ,Mélanie Chevance ,Francesco Belfiore ,Francesco Santoro ,Ralf S Klessen ,Guillermo A Blanc ,Miguel Querejeta ,Sharon E Meidt ,Daizhong Liu ,Enrico Congiu ,P Sánchez‐Blázquez ,Jiayi Sun ,Brent Groves ,Frank Bigiel ,Toshiki Saito ,Éric Emsellem ,Erik Rosolowsky ,Hsi-An Pan ,Christopher M Faesi ,Thomas G Williams

doi:10.1051/0004-6361/202140733

Abstract

Aims.The complexity of star formation at the physical scale of molecular clouds is not yet fully understood. We investigate the mechanisms regulating the formation of stars in different environments within nearby star-forming galaxies from the Physics at High Angular resolution in Nearby GalaxieS (PHANGS) sample.Methods.Integral field spectroscopic data and radio-interferometric observations of 18 galaxies were combined to explore the existence of the resolved star formation main sequence (Σstellarversus ΣSFR), resolved Kennicutt–Schmidt relation (Σmol. gasversus ΣSFR), and resolved molecular gas main sequence (Σstellarversus Σmol. gas), and we derived their slope and scatter at spatial resolutions from 100 pc to 1 kpc (under various assumptions).Results.All three relations were recovered at the highest spatial resolution (100 pc). Furthermore, significant variations in these scaling relations were observed across different galactic environments. The exclusion of non-detections has a systematic impact on the inferred slope as a function of the spatial scale. Finally, the scatter of the Σmol. gas + stellarversus ΣSFRcorrelation is smaller than that of the resolved star formation main sequence, but higher than that found for the resolved Kennicutt–Schmidt relation.Conclusions.The resolved molecular gas main sequence has the tightest relation at a spatial scale of 100 pc (scatter of 0.34 dex), followed by the resolved Kennicutt–Schmidt relation (0.41 dex) and then the resolved star formation main sequence (0.51 dex). This is consistent with expectations from the timescales involved in the evolutionary cycle of molecular clouds. Surprisingly, the resolved Kennicutt–Schmidt relation shows the least variation across galaxies and environments, suggesting a tight link between molecular gas and subsequent star formation. The scatter of the three relations decreases at lower spatial resolutions, with the resolved Kennicutt–Schmidt relation being the tightest (0.27 dex) at a spatial scale of 1 kpc. Variation in the slope of the resolved star formation main sequence among galaxies is partially due to different detection fractions of ΣSFRwith respect to Σstellar.

Highlights

In the current paradigm of evolution of galaxies, star formation occurs inside cold and dense molecular gas clouds
We recover all three scaling relations at a spatial scale of 100 pc and we explore how these relations change when the data are degraded to lower spatial resolutions
We present each relation when considering all available pixels from the full galaxy sample, and derived for each individual galaxy to study galaxy-to-galaxy variations

Summary

Introduction

In the current paradigm of evolution of galaxies, star formation occurs inside cold and dense molecular gas clouds. As a result of the interplay of such regulating mechanisms, different scaling relations at galactic scales arise between the total amount of star formation in a galaxy and the physical quantities that contribute to its regulation In this regard, the star formation main sequence (SFMS) is a tight (scatter of ∼0.3 dex) relation between the total star formation rate (SFR) of a galaxy and its total stellar mass. The star formation main sequence (SFMS) is a tight (scatter of ∼0.3 dex) relation between the total star formation rate (SFR) of a galaxy and its total stellar mass It consists of a power law, with a slope of ∼1, and it has been studied in the local Universe and at a higher redshift (Brinchmann et al 2004; Daddi et al 2007; Noeske et al 2007; Salim et al 2007; Lin et al 2012; Whitaker et al 2012; Speagle et al 2014; Saintonge et al 2016; Popesso et al 2019). It correlates the total SFR with the total amount of gas and is consistent with a power law of order unity, even though the methodology does have an impact on the specific quantitative description (Schmidt 1959; Kennicutt 1998; Wyder et al 2009; Genzel et al 2010, 2012; Tacconi et al 2010; Bigiel et al 2011; Schruba et al 2011)

Methods

Results

Discussion

Conclusion