Cold gas stripping in satellite galaxies: from pairs to clusters (1611.00896v2)

Abstract: In this paper we investigate environment driven gas depletion in satellite galaxies, taking full advantage of the atomic hydrogen (HI) spectral stacking technique to quantify the gas content for the entire gas-poor to -rich regime. We do so using a multi-wavelength sample of 10,600 satellite galaxies, selected according to stellar mass (log M${\star}$/M${\odot}$ $\geq$ 9) and redshift (0.02 $\leq$ z $\leq$ 0.05) from the Sloan Digital Sky Survey, with HI data from the Arecibo Legacy Fast ALFA (ALFALFA) survey. Using key HI-to-stellar mass scaling relations, we present evidence that the gas content of satellite galaxies is, to a significant extent, dependent on the environment in which a galaxy resides. For the first time, we demonstrate that systematic environmental suppression of gas content at both fixed stellar mass and fixed specific star formation rate (sSFR) in satellite galaxies begins in halo masses typical of the group regime (log M${h}$/M${\odot}$ < 13.5), well before galaxies reach the cluster environment. We also show that environment driven gas depletion is more closely associated to halo mass than local density. Our results are then compared with state-of-the-art semi-analytic models and hydrodynamical simulations and discussed within this framework, showing that more work is needed if models are to reproduce the observations. We conclude that the observed decrease of gas content in the group and cluster environments cannot be reproduced by starvation of the gas supply alone and invoke fast acting processes such as ram-pressure stripping of cold gas to explain this.

Cold Gas Stripping in Satellite Galaxies: Implications and Models

The research paper titled "Cold gas stripping in satellite galaxies: from pairs to clusters" by Toby Brown et al. explores the multifaceted effects of environmental processes on the cold gas content of satellite galaxies, utilizing a sample from the Sloan Digital Sky Survey (SDSS) and the Arecibo Legacy Fast ALFA (ALFALFA) survey. The paper focuses on the mechanisms leading to gas depletion in satellites as they traverse varying cosmic environments, from small pairs to massive clusters, providing insights that extend our understanding of galaxy evolution.

Main Findings and Highlights

The authors employ atomic hydrogen ($\text{H I}$) spectral stacking to investigate the gas content across a diverse sample of 10,600 satellite galaxies. They quantify the relationship between gas content and environmental factors, including dark matter (DM) halo mass and local galaxy density. This paper stands out as it bridges the gap between small-scale pair interactions and the large-scale influences of galaxy clusters.

1. Gas Fraction Dependence on Halo Mass:
   • The paper reveals that satellite galaxies exhibit a systematic decline in gas content with increasing halo mass, starting at halo masses around $\log M_{\rm h}/M_\odot < 13.5$. This depletion occurs well before the galaxies enter the cluster environment, signifying that environment-induced gas loss begins in the group halo regime.
2. Halo Mass vs. Local Density:
   • The paper distinguishes the role of halo mass from local density. While both parameters influence $\text{H I}$ content, halo mass emerges as the dominant factor in dictating gas depletion. This suggests that hydrodynamical processes within the halo, potentially ram-pressure stripping, are effective in large group environments.
3. Comparison with Models:
   • The paper scrutinizes the efficacy of current theoretical models. It compares the observations with predictions from semi-analytic models (GP14 and GP14+GRP) and hydrodynamical simulations. The findings indicate that these models typically predict excessive gas depletion, failing to match the observed gas fractions, particularly at fixed stellar mass and specific star formation rate (sSFR).

Theoretical and Practical Implications

The results have profound implications for understanding the environmental mechanisms influencing galaxy evolution:

• Hydrodynamical Processes: The observed gas depletion patterns suggest that fast-acting processes such as ram-pressure stripping are primary mechanisms acting in group and cluster environments. This provides a contextual framework for interpreting gas content variations with host halo dynamics.
• Modeling Challenges: The discrepancies between observed gas fractions and model predictions underscore the need for improved methodologies in semi-analytic and hydrodynamical models. Enhancing the treatment of gas dynamics and interactions within these models could lead to more accurate predictions of satellite galaxy evolution.
• Observational Strategy: The adoption of $\text{H I}$ spectral stacking has demonstrated significant utility in circumventing the sensitivity limits of individual detections, offering a template for future large-scale surveys with next-generation radio telescopes.

Future Developments

The research opens avenues for further exploration of environmental effects on satellite galaxies using advanced simulations and observational technologies:

• Enhanced Simulation Techniques: Incorporation of refined SPH formulations and better resolution of fluid dynamics could help reconcile model outputs with empirical data.
• Deep Surveys and Instrumentation: Upcoming facilities like the Square Kilometer Array (SKA) will allow more precise observations of $\text{H I}$ distribution in galaxies across varied environments, potentially unraveling subtle processes undetectable by current techniques.

In summary, the paper by Brown et al. forms a cornerstone in the ongoing investigation of environmental influences on satellite galaxies, providing essential insights that challenge existing models and set a direction for future astrophysical research.