The Star Formation Rate–Radius Connection: Data and Implications for Wind Strength and Halo Concentration

Lin Lin,Viraj Pandya,Guillermo Barro,Mauro Stefanon,Bahram Mobasher,Hooshang Nayyeri,Aaron A Dutton,Avishai Dekel,S M Faber,Anton M Koekemoer,Jerome J Fang,Joel R Primack,David C Koo,Aldo Rodríguez-Puebla,Norman A Grogin,Lei Hao,Samir Salim,Rachel S Somerville,Zhu Chen,Henry C Ferguson,Fangzhou Jiang,Arjen Van Der Wel ,Y Guo ,Susan Kassin ,Christoph T Lee ,T Dahlén ,Yunli Luo ,P Santini ,A Galametz

doi:10.3847/1538-4357/aba755

Abstract

Abstract This paper is one in a series that explores the importance of radius as a second parameter in galaxy evolution. The topic investigated here is the relationship between star formation rate (SFR) and galaxy radius ( ) for main-sequence star-forming galaxies. The key observational result is that, over a wide range of stellar mass and redshift in both CANDELS and SDSS, there is little correlation between SFR and at fixed stellar mass. The Kennicutt–Schmidt law, or any similar density-related star formation law, then implies that smaller galaxies must have lower gas fractions than larger galaxies (at fixed ), and this is supported by observations of gas in local star-forming galaxies. We investigate the implications by adopting the equilibrium “bathtub” model: the ISM gas mass is assumed to be constant over time, and the net SFR is the difference between the accretion rate of gas onto the galaxy from the halo and the outflow rate due to winds. To match the observed null correlation between SFR and radius, the bathtub model requires that smaller galaxies at fixed mass have weaker galactic winds. Our hypothesis is that galaxies are a two-parameter family whose properties are set mainly by halo mass and concentration. These determine the radius and gas accretion rate, which in turn predict how wind strength needs to vary with to keep the SFR constant.

Highlights

Understanding how galaxies grow their stellar mass is one of the central questions in galaxy formation
It is well known that star formation rate (SFR) for green valley galaxies are systematically overestimated by 24μm data according to several studies reviewed by Fang et al (2018), and the same trend is seen here
These are not a concern since our goal is the relative ranking of objects within the star-forming main-sequence” (SFMS), which is not disturbed by a zero-point shift

Summary

Introduction

Understanding how galaxies grow their stellar mass is one of the central questions in galaxy formation. The global star formation rates of starforming galaxies are observed to be well correlated with their stellar masses, a relation that has been termed the “star-forming main-sequence” (SFMS) (Noeske et al 2007; Elbaz et al 2007, 2011; Daddi et al 2007; Whitaker et al 2012; Speagle et al 2014). Data show that this empirical relation has existed since z ≥ 2 with a scatter of only 0.3 dex at fixed stellar mass (Whitaker et al 2012). A negative correlation is expected between residuals in sSFR and SMA relative to the sSFR-mass and size-mass relations at fixed mass

Objectives

Results

Discussion

Conclusion