[Paper Review] Jellyfish galaxies with the IllustrisTNG simulations -- No enhanced population-wide star formation according to TNG50

Junia Göller, Gandhali D Joshi+3 more|arXiv (Cornell University)|Apr 18, 2023

Plant and animal studiesAgricultural and Biological Sciences3 citations

TL;DR

Using the high-resolution TNG50 cosmological simulation, this study investigates star formation in jellyfish galaxies—galaxies undergoing ram-pressure stripping. Despite frequent star formation in both galactic bodies and stripped tails, TNG50 finds no population-wide enhancement in star formation rates compared to matched control samples, indicating that observed enhancements in some observations may stem from selection biases rather than intrinsic population-level effects.

ABSTRACT

Due to ram-pressure stripping, jellyfish galaxies are thought to lose large amounts, if not all, of their interstellar medium. Nevertheless, some, but not all, observations suggest that jellyfish galaxies exhibit enhanced star formation compared to control samples, even in their ram pressure-stripped tails. We use the TNG50 cosmological gravity+magnetohydrodynamical simulation, with an average spatial resolution of 50-200 pc in the star-forming regions of galaxies, to quantify the star formation activity and rates (SFRs) of more than 700 jellyfish galaxies at $z=0-1$ with stellar masses $10^{8.3-10.8}\,\mathrm{M}_\odot$ in hosts with mass $10^{10.5-14.3}\,\mathrm{M}_\odot$. We extract their global SFRs, the SFRs within their main stellar body vs. within the tails, and we follow the evolution of the star formation along their individual evolutionary tracks. We compare the findings for jellyfish galaxies to those of diversely-constructed control samples, including against satellite and field galaxies with matched redshift, stellar mass, gas fraction and host halo mass. According to TNG50, star formation and ram-pressure stripping can indeed occur simultaneously within any given galaxy, and frequently do so. Moreover, star formation can also take place within the ram pressure-stripped tails, even though the latter is typically subdominant. However, TNG50 does not predict elevated population-wide SFRs in jellyfish compared to analog satellite galaxies with the same stellar mass or gas fraction. Simulated jellyfish galaxies do undergo bursts of elevated star formation along their history but, at least according to TNG50, these do not translate into a population-wide enhancement at any given epoch.

Motivation & Objective

• To determine whether jellyfish galaxies exhibit enhanced global star formation rates compared to control samples in a cosmological simulation.
• To investigate the coexistence of ram-pressure stripping and star formation in individual galaxies across cosmic time.
• To assess whether star formation in stripped tails contributes significantly to overall galaxy SFRs.
• To evaluate whether observed population-wide SFR enhancements in jellyfish galaxies are real or biased by selection effects.
• To compare jellyfish galaxies with matched satellite and field galaxies in terms of stellar mass, gas fraction, and host halo mass to isolate environmental effects.

Proposed method

• Utilized the TNG50 simulation, a large-scale gravity-magnetohydrodynamical cosmological simulation with 50–200 pc resolution in star-forming regions.
• Identified over 700 jellyfish galaxies at redshifts z = 0–1 based on morphology and gas tail features, independent of star formation tracers.
• Measured global, body, and tail-specific star formation rates (SFRs) for each jellyfish galaxy using time-resolved particle tracking.
• Constructed multiple control samples: matched satellite and field galaxies with similar stellar mass, gas fraction, and host halo mass.
• Tracked individual jellyfish galaxies through their evolutionary tracks to analyze SFR evolution during ram-pressure events.
• Compared median SFRs across populations at different redshifts (up to z ≈ 1) and assessed quenching fractions and starburst prevalence.

Experimental results

Research questions

• RQ1 Do jellyfish galaxies in TNG50 exhibit elevated global star formation rates compared to control samples with matched mass and gas fraction?
• RQ2 Is star formation in ram-pressure-stripped tails a significant contributor to the total SFR in jellyfish galaxies?
• RQ3 Do jellyfish galaxies experience enhanced SFRs during their evolution, and if so, do these bursts lead to a population-wide SFR increase?
• RQ4 How does the quenching fraction of jellyfish galaxies compare to that of randomly selected satellite galaxies in the same mass and environment?
• RQ5 To what extent do observational claims of population-wide SFR enhancement in jellyfish galaxies reflect selection biases rather than physical reality?

Key findings

• TNG50 shows that jellyfish galaxies are typically star forming despite severe ram-pressure stripping, with star formation occurring both in the main galactic body and in stripped tails.
• Star formation in the tails is subdominant, contributing significantly less to total SFR than in the main body, though it is physically plausible and observed in the simulation.
• Although 74% of jellyfish galaxies experience short-lived SFR bursts above the star-forming main sequence during pericentric passages, these do not result in a population-wide SFR enhancement.
• At any given epoch, the median SFR of jellyfish galaxies is below the star-forming main sequence and statistically indistinguishable from matched control samples of field and satellite galaxies.
• Jellyfish galaxies are less frequently quenched than the general satellite population due to their higher initial gas fractions, which is a selection bias in observational samples.
• The simulation reveals no evidence for a systematic, population-wide increase in star formation in jellyfish galaxies, challenging observational claims of enhanced SFRs in such systems.