Main Sequence Scatter is Real: The Joint Dependence of Galaxy Clustering on Star Formation and Stellar Mass

TL;DR

This study demonstrates that galaxy clustering depends on both stellar mass and specific star formation rate, revealing that the scatter in the star-forming main sequence is physically linked to the large-scale cosmic density field, with implications for galaxy evolution models.

Contribution

It provides new measurements of galaxy clustering as a joint function of stellar mass and sSFR at low redshift, confirming the physical connection between main sequence scatter and cosmic density.

Findings

Galaxy clustering is more strongly dependent on sSFR than on stellar mass at fixed stellar mass.

Galaxies above the star-forming main sequence are less clustered than those below at the same stellar mass.

Increased correlation between SFR and halo accretion rate improves model agreement with SDSS data.

Abstract

We present new measurements of the clustering of stellar mass-complete samples of $\sim40,000$ SDSS galaxies at $z\sim0.03$ as a joint function of stellar mass and specific star formation rate (sSFR). Our results confirm what Coil et al. (2017) find at $z\sim0.7$: galaxy clustering is a stronger function of sSFR at fixed stellar mass than of stellar mass at fixed sSFR. We also find that galaxies above the star-forming main sequence (SFMS) with higher sSFR are less clustered than galaxies below the SFMS with lower sSFR, at a given stellar mass. A similar trend is present for quiescent galaxies. This confirms that main sequence scatter, and scatter within the quiescent sequence, is physically connected to the large-scale cosmic density field. We compare the resulting galaxy bias versus sSFR, and relative bias versus sSFR ratio, for different galaxy samples across ${0<z<1.2}$ to mock galaxy catalogs based on the empirical galaxy evolution model of Behroozi et al. (2019). This model fits PRIMUS and DEEP2 clustering data well at intermediate redshift, but agreement with SDSS is not as strong. We show that increasing the correlation between galaxy SFR and halo accretion rate at $z\sim0$ in the model substantially improves agreement with SDSS data. Mock catalogs suggest that central galaxies contribute substantially to the dependence of clustering on sSFR at a given stellar mass and that the signal is not simply an effect of satellite galaxy fraction differences with sSFR. Our results are highly constraining for galaxy evolution models and show that the stellar-to-halo mass relation (SHMR) depends on sSFR.