Survival of Massive Star-forming Galaxies in Cluster Cores Drives Gas-phase Metallicity Gradients: The Effects of Ram Pressure Stripping

Abstract

Recent observations of galaxies in a cluster at z = 0.35 show that their integrated gas-phase metallicities increase with decreasing cluster-centric distance. To test if ram pressure stripping (RPS) is the underlying cause, we use a semi-analytic model to quantify the "observational bias" that RPS introduces into the aperture-based metallicity measurements. We take integral field spectroscopy of local galaxies, remove gas from their outer galactic disks via RPS, and then conduct mock slit observations of cluster galaxies at z = 0.35. Our RPS model predicts a typical cluster-scale metallicity gradient of −0.03 dex/Mpc. By removing gas from the outer galactic disks, RPS introduces a mean metallicity enhancement of +0.02 dex at a fixed stellar mass. This gas removal and subsequent quenching of star formation preferentially removes low mass cluster galaxies from the observed star-forming population. As only the more massive star-forming galaxies survive to reach the cluster core, RPS produces a cluster-scale stellar mass gradient of −0.05 log(M * /M ⊙ )/Mpc. This mass segregation drives the predicted cluster-scale metallicity gradient of −0.03 dex/Mpc. However, the effects of RPS alone can not explain the higher metallicities measured in cluster galaxies at z = 0.35. We hypothesize that additional mechanisms including steep internal metallicity gradients and self-enrichment due to gas strangulation are needed to reproduce our observations at z = 0.35.

Chemical pre-processing of cluster galaxies over the past 10 billion years in the IllustrisTNG simulations

“…Observations show that environmental processes are mostly effective for galaxies with M * < 10 10 M ⊙ /h (Peng et al 2010). Gupta et al (2017) shows that star formation suppression in the galactic outskirts due to ram pressure stripping (RPS) can not directly produce a significant enhancement in the SFR-weighted metallicity. However, a relative increase in the metallicity of cluster galaxies compared to field galaxies due to suppression of pristine gas inflow by RPS can not be ruled out.…”

GASP. XV. A MUSE view of extreme ram-pressure stripping along the line of sight: physical properties of the jellyfish galaxy JO201

“…), and it is consistent with the mechanism of outside-inward stripping, whereby the most distant, lowest metallicity gas from the galaxy is stripped first, followed by subsequently higher metallicity gas closer to the centre. In fact, semianalytic models of galaxies in clusters (Gupta et al 2017) have invoked outside-in gas stripping to explain, at least partially, the cluster scale (integrated) metallicity gradients observed in galaxy clusters (see e.g. Ellison et al 2009).…”

Age and Metallicity of galaxies in different environments of the Coma supercluster

“…For galaxies in the Coma cluster ( = 0.023), Carter et al (2002) find a gradient in the Mg 2 and ⟨Fe⟩ indices, which they attribute to pressure confinement of the supernova ejecta by the ICM (also Pasquali et al, 2012). Their suggestion is loosely supported by the ram-pressure stripping (RPS) model of Gupta et al (2017), who show that gas removal by RPS will primarily remove lowmass cluster galaxies from the star-forming population, leading to a cluster-scale metallicity gradient of -0.03 dex Mpc −1 at = 0.35. Gupta et al (2017), therefore hypothesize that RPS is insufficient in explaining the observed Z gradient in = 0.35 cluster, which would require "self-enrichment due to gas strangulation".…”

“…Their suggestion is loosely supported by the ram-pressure stripping (RPS) model of Gupta et al (2017), who show that gas removal by RPS will primarily remove lowmass cluster galaxies from the star-forming population, leading to a cluster-scale metallicity gradient of -0.03 dex Mpc −1 at = 0.35. Gupta et al (2017), therefore hypothesize that RPS is insufficient in explaining the observed Z gradient in = 0.35 cluster, which would require "self-enrichment due to gas strangulation". In a study of galaxies in the nearby universe, Hughes et al (2013) came to similar conclusions by studying the oxygen abundances and HI gas mass and gas fraction in 260 star-forming galaxies.…”