The Tail of the Stripped Gas that Cooled: HI, Halpha and X-ray Observational Signatures of Ram Pressure Stripping (0909.3097v1)

Abstract: Galaxies moving through the intracluster medium (ICM) of a cluster of galaxies can lose gas via ram pressure stripping. This stripped gas forms a tail behind the galaxy which is potentially observable. In this paper, we carry out hydrodynamical simulations of a galaxy undergoing stripping with a focus on the gas properties in the wake and their observational signatures. We include radiative cooling in an adaptive hydrocode in order to investigate the impact of a clumpy, multi-phase interstellar medium. We find that including cooling results in a very different morphology for the gas in the tail, with a much wider range of temperatures and densities. The tail is significantly narrower in runs with radiative cooling, in agreement with observed wakes. In addition, we make detailed predictions of H I, Halpha and X-ray emission for the wake, showing that we generally expect detectable H I and Halpha signatures, but no observable X-ray emission (at least for our chosen ram-pressure strength and ICM conditions). We find that the relative strength of the Halpha diagnostic depends somewhat on our adopted minimum temperature floor (below which we set cooling to zero to mimic physics processes not included in the simulation).

Analysis of Ram Pressure Stripping in Galaxy Clusters

This paper by Tonnesen and Bryan explores the hydrodynamical simulation of ram pressure stripping experienced by galaxies moving through the intracluster medium (ICM). The primary focus is on the formation and observational consequences of the tail of stripped gas that follows a galaxy during this process. The simulations incorporate radiative cooling in an adaptive hydrocode framework to facilitate the analysis of a multiphase interstellar medium (ISM), with particular emphasis on the morphological attributes of the gas tail and its observational signatures, specifically in H{\small I}, H$\alpha$, and X-ray regimes.

Major Findings and Observations

• Impact of Radiative Cooling: The inclusion of radiative cooling was found to significantly impact the morphology of the stripped tail, with the simulations yielding narrower and more structured tails in contrast to simulations where cooling was not included. The tails showed a wider range of temperatures and densities, resonating with actual observations such as narrower wakes in galaxies observed in clusters.
• H{\small I} and H$\alpha$ Detection: The simulations predict detectable H{\small I} and H$\alpha$ emissions from stripped galactic tails, aligning with empirical observations from Virgo and other clusters. However, the X-ray emissions were found to be negligible for the assumed ICM conditions and ram-pressure strength, challenging some observations which have detected X-ray bright tails.
• Velocity and Density Structure: The velocity distribution of the stripped gas was substantially different when cooling was considered. In scenarios with cooling, stripped gas does not accelerate to the velocity of the ICM wind, exhibiting differential stripping and acceleration behavior, which is consistent with observed features in certain galaxies where gas shows varied velocities and positions.

Implications and Future Directions

The insights from this paper underscore the importance of including radiative cooling in simulations for a realistic portrayal of ISM dynamics in cluster galaxies. The paper highlights potential areas for improvement and further exploration:

• Comparison with Observational Data: The paper's predictions concerning the detectability of H{\small I} and H$\alpha$ could motivate targeted observations using modern facilities with higher sensitivity, potentially revealing longer and more structured tails than previously obtained.
• Star Formation and Feedback: Future simulations should integrate star formation and related feedback processes to examine their impact on the evolution and emission characteristics of the stripped tails. This could help understand phenomena such as star formation within these tails, akin to observed trails of 'fireballs' aligned with stripped galaxy paths.
• Role of Magnetic Fields and Cosmic Rays: Incorporating the influence of magnetic fields and cosmic rays in subsequent models may provide further insight into the structural integrity and longevity of cool gas clouds within the tails, which might also influence observational diagnostics, including radio continuum observations.

The paper paves the way for enriching our comprehension of environmental interactions within galaxy clusters, demonstrating that nuanced hydrodynamic simulations that account for multi-phase ISM characteristics are crucial for forecasting observational signatures. Continued exploration, especially with more complex physical models, is necessary to fully understand the transformation and fate of galaxies influenced by ram pressure stripping in dense cluster environments.