Two Conditions for Galaxy Quenching: Compact Centres and Massive Haloes

Joanna Woo; Avishai Dekel; S. M. Faber; David C. Koo

doi:10.1093/mnras/stu2755

paper

Two Conditions for Galaxy Quenching: Compact Centres and Massive Haloes

arXiv:1406.5372 · doi:10.1093/mnras/stu2755

Abstract

We investigate the roles of two classes of quenching mechanisms for central and satellite galaxies in the SDSS ( $z < 0.075$ ): those involving the halo and those involving the formation of a compact centre. For central galaxies with inner compactness $Σ_{1kpc} \sim 1 0^{9 - 9.4} M_{⊙} kpc^{- 2}$ , the quenched fraction $f_{q}$ is strongly correlated with $Σ_{1kpc}$ with only weak halo mass $M_{h}$ dependence. However, at higher and lower $Σ_{1kpc}$ , sSFR is a strong function of $M_{h}$ and mostly independent of $Σ_{1kpc}$ . In other words, $Σ_{1kpc} \sim 1 0^{9 - 9.4} M_{⊙} kpc^{- 2}$ divides galaxies into those with high sSFR below and low sSFR above this range. In both the upper and lower regimes, increasing $M_{h}$ shifts the entire sSFR distribtuion to lower sSFR without a qualitative change in shape. This is true even at fixed $M_{*}$ , but varying $M_{*}$ at fixed $M_{h}$ adds no quenching information. Most of the quenched centrals with $M_{h} > 1 0^{11.8} M_{⊙}$ are dense ( $Σ_{1kpc} > 1 0^{9} M_{⊙} kpc^{- 2}$ ), suggesting compaction-related quenching maintained by halo-related quenching. However, 21% are diffuse, indicating only halo quenching. For satellite galaxies in the outskirts of halos, quenching is a strong function of compactness and a weak function of host $M_{h}$ . In the inner halo, $M_{h}$ dominates quenching, with $\sim 90%$ of the satellites being quenched once $M_{h} > 1 0^{13} M_{⊙}$ . This regional effect is greatest for the least massive satellites. As demonstrated via semi-analytic modelling with simple prescriptions for quenching, the observed correlations can be explained if quenching due to central compactness is rapid while quenching due to halo mass is slow.

16 pages, 11 figures, MNRAS accepted

Two Conditions for Galaxy Quenching: Compact Centres and Massive Haloes

Abstract

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