- study z<0.5 environmental star-formation quenching

- test strangulation scenario of Maier, Kuchner, Ziegler

et al. (2016, A&A, 590, A108) using metallicity O/H of

cluster galaxies as a quenching tracer

- constrain quenching timescales by comparing the

observed fraction of star-forming galaxies as a function

of cluster-centric radius with simulations

Cluster star formation quenching probed by gas metallicity

Christian Maier1, B. L. Ziegler1, C. P. Haines2 & G. P. Smith3 Contact: christian.maier@univie.ac.at 1University of Vienna, Department of Astrophysics 2Osservatorio Astronomico Brera 3University of Birmingham

Goals

Z(M,SFR) observed vs. theory

Mass-metallicity relation (MZR) Phase-space diagram

- LoCuSS: Local Cluster Substructure Survey, Smith et

al. (2010, MNRAS, 409, 169)

- Seven selected clusters at 0.15<z<0.26

- 2700 spectroscopic members ACReS Hectospec/MMT

- [OII]λ3727, Hβ, [OIII]λ5007, Hα, [NII]λ6584 lines

- derived SFRs from extinction-corrected Hα

- derived O/Hs from emission lines with the O3N2

method used in Maier et al. (2016, A&A, 590, A108)

Observations

Quenching timescales

Slow-then-rapid quenching

Star-forming, with

O/H measured, non-

star forming galaxies

in seven LoCuSS

clusters

Mlow:

10≤log(M/Msun)<10.5

Mhigh:

10.5≤log(M/Msun)≤11

- Mlow median O/H higher at R<R200 than field & R>R200

Difference

between measured

O/Hs and expected

O/HLi13 at measured

(SFR, mass) from

bathtub model of

Lilly et al. (2013,

ApJ, 772, 119)

O/H ~ SFR/Ф * yield

If inflow Ф

decreases or stops

(strangulation),

O/H increases

Amendment of the Wetzel et al. (2013, MNRAS, 432, 336)

delayed-then-rapid scenario:

- slow quenching (strangulation) initiated when galaxies

first pass R200

- SFRs are hardly affected (slowly decline) during a “delay”

time of 1-2 Gyrs, but metallicities increase

- after the “delay” time: galaxies have travelled to more

inner and denser regions of cluster --> rapid decline in star

formation possibly intensified by ram-pressure stripping

- SSFR-mass median values (Mlow, Mhigh) similar for

star-forming field & cluster galaxies with O/H measured

- Higher metallicities of R<R200 galaxies indicate

strangulation (gas inflow stops, no dillution with

pristine gas of the ISM, higher O/H) when they pass R200

- Lower [OIII]/Hβ ratios (corresponding to higher O/Hs)

of R<R200 galaxies indicate they are in the act of being

quenched (Quai et al. 2018, MNRAS, 478, 3335)

Strangulation scenario

Observed fraction of SF galaxies vs. Millennium

simulation (curves): quenching times (delays) ~1-2Gyrs