Ram-pressure-induced star formation in low-mass galaxies infalling on-to the Coma cluster: insights from DESI

Abstract

Ram-pressure stripping is a key driver of galaxy morphological transformation in clusters, contributing to the formation of quenched, especially dwarf, populations. Ram-pressure compression can also induce a starburst prior to quenching and build up significant stellar mass in an initially gas-rich galaxy. The detailed physics of these processes remains poorly understood, especially in the low-mass regime. Here we demonstrate that the key factor for a ram-pressure induced starburst in a low-mass galaxy is its angular momentum within a host cluster. In this study, we select a sample of 41 post-starburst galaxies (PSGs) in the Coma cluster using the DESI EDR spectroscopic data, extending to low luminosities ($M_g < -14$). This sample is at least 90% complete down to $M_g \approx -14.8$, which enabled us a systematic analysis of their properties. For each galaxy, we use projected cluster-centric distances and line-of-sight velocities to constrain the normalized orbital angular momentum and a 3D radial coordinate to the cluster center, assuming zero orbital energy. The resulting probability distributions show that while star-forming galaxies are split into two populations favoring intermediate and high angular momentum, almost all PSGs prefer high angular momentum. Our analysis statistically demonstrates that ram-pressure-induced starbursts are more efficient on tangential orbits, where gas stripping proceeds slowly enough to allow substantial star formation before gas removal.

Figures (7)

• Figure 1: Position (yellow squares) of the post-starburst galaxies (PSGs) identified in Coma cluster with DESI EDR spectroscopic sample overlaid on a HSC $g$-band image and their color cutouts from Legacy Surveys with a name of a galaxy and a number in top left corner matching the yellow square on the map. Dashed cyan circle matches the virial radius of Coma ($R_\mathrm{vir}$) we adopted in this study.
• Figure 2: The projected phase space diagram of the Coma cluster members (grey points) based on DESI EDR redshift measurements with the position of the selected PSGs (magenta stars) and SFGs (open green circles). On this figure we also demonstrate a virial radius estimate, escape velocity, and line-of-sight velocity dispersion for the results of the modeling from 2003MNRAS.343..401L in a grey vertical dashed line, grey filled lines and red dashed lines respectively.
• Figure 3: Size -- luminosity 1977ApJ...218..333K and the surface brightness -- luminosity relations of early-type galaxies. With stars we show the position of the selected post-starburst galaxies, including those, previously identified with SDSS (2021NatAs...5.1308G, blue stars) and new objects, identified with DESI (pink stars). For a reference here we show samples of objects from 1992ApJ...399..462B2003AJ....126.1794G2005AA...438..491DChilingarian+08Chilingarian091944ApJ...100..137Byagi162012AJ....144....4M2007AJ....133.1722EChilingarian+111997ApJ...474L..19D2004ApJ...610..233M2014MNRAS.443.1151N2008MNRAS.385L..83C
• Figure 4: Assessment of the normalized total angular momentum ($\hat{L}$) and total cluster-centric distance ($r$) for the PSG GMP 3294. The grey-shaded region indicates the allowed values of $\hat{L}$ and $r$ based on the observed line-of-sight velocity ($v_z$) and projected distance to the cluster center ($r_\mathrm{\perp}$ = 0.447 Mpc), with the latter shown as a magenta line representing the minimal possible distance to the cluster center. The red dotted line marks the maximum 3D radius ($r$) for which $\hat{L}_\mathrm{max}$ = 1. The dashed and solid blue lines correspond to the Abel transform kernel multiplied by 0.1 and $f(r \mid d_\mathrm{\rm proj})$ for an NFW profile, respectively.
• Figure 5: Individual probability distribution functions (PDF, upper panels) and cumulative distribution functions (CDF, lower panels) for $\hat{L}$ values from 0 to 1 for the sample of PSGs (left) and SFGs (right), each line is a different galaxy.