Modelling the photometric and morphological evolution of disc galaxies in the cluster environment

TL;DR

This work develops a simplified ΛCDM-based model linking ram-pressure stripping–driven quenching and a subsequent cluster-driven morphological transformation to the observed photometric and morphological evolution of disc galaxies in clusters. By fitting to color–$M_igstar$ distributions from OmegaWINGS at $z\approx0.055$ and EDisCS at $z\approx0.7$, it constrains the characteristic timescales $t_{ m s}$ and $t_{ m m}$ as functions of $M_igstar/M_{ m cl}$, finding $t_{ m s}$ typically in the range $0.1$–$1$ Gyr with a strong anti-correlation to the mass ratio and $t_{ m m}$ of a few Gyr with weak mass dependence; a maximum transformation probability $p_{ m max}\approx0.8$ is required. The results imply that spectrophotometric ageing after abrupt quenching is a key channel for spiral-to-S0 transformation in clusters, with orbit anisotropy offering a plausible explanation for the observed $t_{ m s}$–mass trend. The model reproduces the observed spirals and S0s distributions and supports a view in which environmental processes, rather than secular evolution alone, drive the recent morphological evolution of cluster galaxies in the last ~6–7 Gyr.

Abstract

Observations indicate that the disc population in galaxy clusters has undergone rapid evolution, transitioning from a dominance of blue spirals to red S0s over the past $\sim7$ Gyr. We build a simplified cluster evolutionary model in the $Λ$CDM framework to constrain the characteristic timescales of this transformation. In our model, field spirals joining the cluster are subject to ram-pressure stripping (RPS), which removes their gas reservoir leading to the quenching of their star formation on a timescale $t_{\rm s}$, and to an (initially) unspecified mechanism that transforms them into S0s on a timescale $t_{\rm m}$. We assume that $t_{\rm s}$ and $t_{\rm m}$ are independent and both power-law functions of $M_\star/M_{\rm cl}$, the galaxy-to-cluster mass ratio. We constrain our model using the observed distribution of spirals and S0s in a color-mass plane from the OmegaWINGS and EDisCS cluster surveys at $z\simeq0.055$ and $z\simeq0.7$. Our best-fit model reproduces the data remarkably well and predicts evolutionary trends for the main morphological fractions in agreement with previous studies. We find typical $t_{\rm s}$ between $0.1$ and $1$ Gyr, compatible with previous estimates. A surprisingly strong anti-correlation between $t_{\rm s}$ and $M_\star/M_{\rm cl}$ is required in order to suppress the formation of red, low-mass spirals at low redshift, which we interpret as driven by orbit anisotropy. Conversely, $t_{\rm m}$ depends very weakly on $M_\star/M_{\rm cl}$ and has typical values of a few Gyr. The inferred morphological evolution is compatible with that resulting from the ageing of the stellar populations in galaxies abruptly quenched by ram pressure stripping: we confirm spectrophotometric ageing as a key channel for the spiral-to-S0 transition in galaxy clusters, with secular evolution playing a secondary role.

Figures (11)

• Figure 1: Flowchart illustrating our method. White blocks show pre-existing dataset or software packages. Yellow blocks show the new products built for this study. The chart indicates also the Sections of the main text that provide details on a given part of the method.
• Figure 2: Evolutionary properties of our model cluster. Top panel: mass (solid black curve) and accretion rate (dashed grey curve) vs redshift for a cluster with $M_{\rm cl}\!=\!5\times10^{14}\,{\rm M}_\odot$ at $z\!=\!0.055$. The blue square and the red circle show the median $M_{\rm cl}$ and redshifts of the EDisCS and OmegaWINGS clusters, respectively, with the error bars corresponding to half the difference between the 84th and 16th percentiles of the galaxy distribution. Bottom panel: morphology fractions for field galaxies that join the cluster as a function of $z$, assumed to be independent of the galaxy $M_\star$.
• Figure 3: Photometric evolution and mass build-up of an idealised main-sequence galaxy with initial $M_\star\simeq2\times10^{10}\,{\rm M}_\odot$ that joins our cluster model at $z\!=\!1$, for stripping timescales of $0.5$ and $2.0\,{\rm Gyr}$ (dark-red and orange curves, respectively), and for a case without stripping (blue curve). Top panel: SFR as a function of the lookback time. For times larger than $\sim8\,{\rm Gyr}$ ($z>1$), the three models share a common SFH shown by the solid black curve. Bottom panel: galaxy evolution in the rest-frame ($B-V$) colour vs $M_\star$ plane. The white square shows the initial values at $z\!=\!1$, the coloured circles show the final ($z\!=\!0$) values for the three scenarios considered. The green dashed-line separates the red sequence from the blue cloud Vulcani+22.
• Figure 4: Comparison of our best-fit cluster model with the EDisCS data at $z=0.7$ (top six panels), and with the OmegaWINGS data at $z=0.055$ (bottom six panels). The data and the model are shown in the first and second row of each panel set, respectively. Panels in the leftmost (central) column show the distribution of spirals (S0s) in a colour-$M_\star$ plane, where the colour is the observed-frame ($V-I$) for EDisCS and the ($B-V$) for OmegaWINGS. The colour palette indicate the number of galaxies per bin. Cyan contours are drawn at $2$, $5$, $10$ and $15$ galaxies per bin in EDisCS and in the model at $z=0.7$, and at $2$, $10$, $30$ and $100$ galaxies per bin in OmegaWINGS and in the model at $z=0.055$. The total fraction of Spi and S0 galaxies with respect to the total disc (Spi+S0) population is indicated in the top-right corner of each panel. Panels in the rightmost column show the S0 fraction as a function of colour and $M_\star$, for bins that have at least $5$ galaxies in the data.
• Figure 5: Characteristic timescales for the ram-pressure stripping (blue) and for the cluster-driven morphological transformation (red) as a function of the galaxy-to-cluster mass ratio ($M_\star/M_{\rm cl}$) derived with our analysis (Equations \ref{['eq:ts']} and \ref{['eq:tm']}). The solid lines show the median trend, with the shaded regions showing the difference between the 16th and 84th percentiles. The dashed lines show the best-fit model. As a reference, in the horizontal axis on top we report the $M_\star$ scale for a fixed $\log_{10}(M_{\rm cl}/\,{\rm M}_\odot)=14.7$.