Understanding the Shift from Star-Forming to Non-Star-Forming Galaxies

One interesting topic in the study of galaxies is how they change from being blue and filled with stars to red and not forming stars. Recent surveys have allowed scientists to see how both star-forming and Non-star-forming galaxies have changed over time, even in the distant past. Once a galaxy turns red and becomes non-star-forming, it tends to stay that way, which leads to an overall increase in non-star-forming galaxies.

However, we still do not fully understand what makes star-forming galaxies stop making stars. This process of stopping star formation is called Quenching. There are various theories about how this might happen, either from outside the galaxy, like losing gas because of pressure from other galaxies, or from inside, like feedback from active galactic nuclei (AGN).

One way to study quenching is to look at how many galaxies there are with different amounts of stars over time. This helps us see how galaxies are formed and how they change. For example, massive galaxies had a lot of star formation around a period called "cosmic noon," when they formed a huge part of their stars. Evidence shows that many of the largest non-star-forming galaxies were already in place by that time. Some studies found that the number of non-star-forming galaxies grew significantly over various Masses, and that the smaller non-star-forming galaxies became more common over time.

Quenching can be divided into two main types: one related to the mass of the galaxy and another related to its environment. Research showed that the effects of mass and environment on quenching could be separated until a certain point, and they could explain how both blue and red galaxy populations evolved over time. They found that the efficiency of mass quenching is related to the rate of star formation, while environmental quenching depends on the density of galaxies in the area. However, some studies have suggested that this separation may not hold true in different circumstances.

In looking at these issues, studying galaxies that are undergoing transitions might help us understand how quenching works. One specific category is post-starburst galaxies, which are thought to have recently experienced a significant burst of star formation followed by rapid quenching. These galaxies have distinctive traits in their light and are rare, but studies have shown that they might make up a sizable fraction of non-star-forming galaxies.

#Goals of the Study

In this study, we investigate how the mass of galaxies and their environment contribute to the growth of non-star-forming galaxies over time. We will look at how various factors, like stellar mass and environment, influence this change. Using data from the UKIDSS Ultra-Deep Survey (UDS), we can explore typical galaxies and analyze their properties in relation to their environment.

We present our findings in the following way: we first describe the data and methods used, then present results on quenching rates in different Environments, and finally, we explore how post-starburst galaxies contribute to the growth of the non-star-forming population.

#Data and Methods

#The Ultra-Deep Survey

The UDS is a very deep near-infrared survey that allows us to see very faint galaxies. We use data from the latest UDS release, which captures a wide range of light in different bands, allowing for a comprehensive view of the galaxies. This survey helps us analyze thousands of galaxies and their redshifts, which tell us how far away they are.

To gather this information, we use various advanced techniques to compute the brightness of galaxies and their distances using light from different bands. We also analyzed thousands of galaxies with secure distance measurements to improve the accuracy of our findings.

#Classifying Galaxies

To categorize the galaxies, we use a method that combines different traits of their light, called principal component analysis (PCA). This technique helps us understand the different types of galaxies, such as star-forming, non-star-forming, and post-starburst. With the analysis, we can determine how each galaxy fits into one of these categories based on how bright it is and the age of its stars.

#Measuring Environment

We measure the environment of each galaxy by calculating how many other galaxies are nearby. We look at a specific area around each galaxy and see how many they have within that region. This tells us about the density of galaxies in that area, allowing us to classify galaxies into categories based on their environment: high, medium, and low density.

#Results

#Growth of Non-Star-Forming Galaxies

Our analysis shows that a greater number of non-star-forming galaxies are found in regions with a higher density of galaxies across all types of masses. We also observe a notable increase in low-mass non-star-forming galaxies in crowded environments, which suggests that these galaxies are more likely to stop forming stars when surrounded by other galaxies.

#Quenching Rates

We find that the rate at which galaxies become non-star-forming is significantly higher in crowded environments at all redshifts (distance in time) and masses. There is a clear trend that as galaxy mass increases, the chance of a star-forming galaxy becoming non-star-forming also rises. For the most massive galaxies, they are about 1.7 times more likely to stop forming stars in the densest environments compared to the least dense environments.

#Contribution of Post-Star-Burst Galaxies

Post-star-burst galaxies are crucial to understanding the growth of the non-star-forming population. Our findings indicate that these galaxies can account for a considerable fraction of the increase in non-star-forming galaxies, especially at higher masses. At lower masses, the contribution might be even more significant.

#Discussion

#Summary of Findings

This study highlights the complex relationship between quenching processes, mass, and environmental factors. Our results indicate that denser regions significantly influence the quenching rates of galaxies. This suggests that environmental factors play a crucial role in shaping the evolution of galaxies over time.

#Importance of Future Studies

As we explore deeper into the universe, it becomes essential to understand the different pathways through which galaxies transition from star-forming to non-star-forming. Future studies using advanced imaging and analysis techniques will allow us to investigate these trends further and refine our understanding of the mechanisms behind galaxy evolution.

#Conclusion

In conclusion, our research sheds light on the factors that contribute to the growth of non-star-forming galaxies over time. We demonstrate that both stellar mass and environment play significant roles in these processes. Our findings lay the groundwork for future exploration into the complex relationships between galaxy formation, quenching, and the environment. By continuing to study these aspects, we hope to uncover more about the underlying processes that govern how galaxies evolve and change throughout the universe.