Dark matter free dwarf galaxy formation at the the tips of the tentacles of jellyfish galaxies

Abstract: When falling into a galaxy cluster, galaxies experience a loss of gas due to ram pressure stripping. In particular, disk galaxies lose gas from their disks and very large tentacles of gas can be formed. Because of the morphology of these stripped galaxies they have been referred to as Jellyfish galaxies. It has been found that star formation is triggered not only in the disk, but also in the tentacles of such Jellyfish galaxies. The observed star forming regions located in the tentacles of those galaxies have been found to be as massive as $3\times10^7$ M${\odot}$ and with sizes $> 100$ pc. Interestingly, these parameters in mass and size agree with those of dwarf galaxies. In this work we make use of the state of the art magneto-hydrodynamical cosmological simulation Illustris TNG-50, to study massive jellyfish galaxies with long tentacles. We find that, in the tentacles of TNG-50 Jellyfish galaxies, the star formation regions (gas+stars) formed could be as massive as $\sim2\times10^8$ M${\odot}$. A particular star forming region was analyzed. This region has a star formation rate of $0.04$ M$_{\odot}$/yr, it is metal rich, has an average age of $0.46$ Gyr, and has a half mass radius of $\sim1$ kpc, typical of standard dwarf galaxies. Most importantly, this region is gravitationally self-bound. All and all, we identify a new type of dwarf galaxy being born from the gas tentacles of jellyfish galaxies, that by construction lacks a dark matter (hereafter DM) halo.

• The paper demonstrates that ram pressure stripping in jellyfish galaxies can produce self-gravitating dwarf galaxy candidates devoid of dark matter.
• It utilizes the Illustris TNG-50 simulation to identify massive galaxies undergoing RPS, analyzing detailed baryonic mass and star formation metrics.
• The findings refine galaxy formation models by highlighting hydrodynamic forces in cluster environments, prompting further observational and simulation studies.

Dark Matter-Free Dwarf Galaxy Formation at the Tips of the Tentacles of Jellyfish Galaxies

Introduction

This paper investigates the phenomenon of star formation within the tentacles of so-called "Jellyfish galaxies" through the Illustris TNG-50 cosmological simulation. Jellyfish galaxies, characterized by their extended gas tentacles formed via ram pressure stripping (RPS) when they plunge into the denser intra-cluster medium, have been observed to host star forming regions along these tentacles, bearing similar mass and size parameters to conventional dwarf galaxies. The objective of this research is to analyze whether these star forming regions can evolve into self-gravitating objects without dark matter content, thus resembling a new subtype of dwarf galaxies formed purely through hydrodynamic interactions.

Methods and Sample Selection

The paper describes the utilization of the TNG-50 simulation, part of the larger Illustris-TNG project, to identify potential candidates for dark matter-free dwarf galaxy formation within the tentacles of jellyfish galaxies. By imposing selection criteria focused on massive galaxies experiencing significant RPS and possessing extended gas distributions beyond their stellar disks, the authors refine their analysis to a sample where the effects of RPS-induced star formation could be most evident.

Findings

The analysis reveals the existence of an object within a massive tentacle of a jellyfish galaxy, displaying characteristics akin to conventional dwarf galaxies — a total baryonic mass of $\approx 2\times10^8 M_{\odot}$, self-gravitation, and the absence of a dark matter halo. Further investigation into this object indicates a vigorous star formation rate, high metallicity, and a structural profile that can be fitted by Plummer's sphere model. This profile, along with its size and mass, situates the object comfortably within the parameters observed for known dwarf galaxies, despite its extraordinary formation mechanism and lack of dark matter.

Implications and Theoretical Underpinnings

The identification of this dark matter-free dwarf galaxy candidate validates the hypothesis that ram pressure stripping in jellyfish galaxies can lead to the formation of new dwarf galaxies in the cluster environment. These findings also suggest a broader mechanism of galaxy formation and evolution within clusters, emphasizing hydrodynamic effects besides gravitational dynamics commonly associated with dark matter. The results can help refine galaxy formation models by incorporating the role of RPS in spawning new galaxies within the dense environments of galaxy clusters.

Future Outlook

The study opens avenues for further inquiries into the formation of dwarf galaxies through non-traditional pathways. It prompts a reevaluation of the role of hydrodynamical forces in shaping galaxy properties and distributions in cluster environments. Moreover, with the advancement of simulation resolutions and observational techniques, it will be possible to explore the prevalence and characteristics of these RPS-induced dwarf galaxies across different environments and epochs, potentially revealing a ubiquitous mechanism contributing to the dwarf galaxy population observed in the universe.

Conclusion

In conclusion, this paper presents compelling evidence for the formation of dark matter-free dwarf galaxies at the tips of the tentacles of jellyfish galaxies, a process facilitated by ram pressure stripping. This discovery highlights the diversity of galaxy formation processes and underscores the significant role of the intracluster medium in influencing galaxy evolution. Future investigations, both observational and through simulations, are vital to further understand the properties, prevalence, and contributions of these objects to the overall galaxy population and dynamics within clusters.