The Life Cycle of Early-Type Galaxies

Galaxies are vast collections of stars, gas, dust, and dark matter bound together by gravity. They come in different shapes and sizes. Some are spiral, like our Milky Way, while others are more rounded, known as Early-type Galaxies (ETGs). These ETGs include elliptical galaxies and lenticular galaxies, which are like the older, quieter relatives of naughty spiral galaxies.

#What Happens in Early-Type Galaxies?

In early-type galaxies, star formation can slow down or even come to a complete stop. When this occurs, we say that the galaxy has been "quenched." Imagine a hot water pot that runs out of water-you can't make tea without water! In galaxies, the water is the Interstellar Medium (Ism)-a mix of gas and dust that helps form new stars.

#How Does Star Formation Stop?

There are many reasons why star formation might slow down in a galaxy. One big reason is the removal of the cold ISM. If the gas is taken away or heated up, it can't form new stars. It's like emptying out a swimming pool and then trying to swim in it-there's just no water left!

Several things can remove the ISM from galaxies:

1. Supernovae: When massive stars explode, they blow a lot of gas away.
2. Active Galactic Nuclei (AGNS): These are supermassive black holes at the centers of galaxies that can also push gas out with their energy.
3. Turbulence and Mergers: When galaxies bump into each other, they can force gas out of them.

#The Mystery of the Missing Stars

In this study, we looked at 2,409 dusty early-type galaxies to see what's going on with their ISM. Using special techniques, we can classify galaxies and figure out who’s causing the gas to leave.

We checked out the emissions from the galaxies, which are like their voices. Just like people can sound different based on how loud they speak or if they whisper, galaxies have different emissions based on what's happening inside them. We listened carefully to these emissions to classify galaxies into different groups based on their main energy sources.

#Classifying Galaxies

We used two main classification methods to understand these galaxies better:

1. BPT Diagram: This method uses certain emissions from the galaxies to see if they are star-forming or if they have strong AGN activity.
2. WHAN Diagram: This new method can classify even more galaxies, including those that are harder to analyze.

The BPT and WHAN diagrams help us identify if a galaxy is mainly forming stars, is dominated by AGNs, or falls somewhere in between.

#Our Findings About AGNs

From our research, we found that strong AGNs play a big role in removing the ISM from younger galaxies. If a galaxy is less than a billion years old, the AGN has a strong influence. But as galaxies age, AGNs seem to take a backseat while other sources, like old stars, start to play a more significant role.

Think of it this way: a young galaxy is like a high-energy teenager who throws wild parties (AGNs), while an older galaxy becomes more like a quiet retiree who prefers peaceful evenings (old stars).

#The Role of Old Stars

In older galaxies, the younger stars have faded, and something else becomes important: heating and ionization caused by hot low-mass stars, known as HOLMES. These stars aren’t big party animals, but they still manage to affect the ISM, keeping things warm enough to influence star formation.

#Understanding the Impact of AGN Feedback

AGN feedback is when the energy or Outflows from the black hole affect the galaxy’s surroundings. In our findings, we discovered that AGN feedback is significant for young galaxies but decreases as the galaxy gets older.

This is like a rock band that starts off loud and energetic but eventually settles down to softer tunes as they age. While they might still have some energy left, it’s not as impactful as when they first started.

#What About the Environment?

We also took a peek at the environment around these galaxies. Some galaxies are nestled together in groups, while others are loners. We found that only a few of the galaxies in our study were part of a dense group. Most seem to do their own thing, which suggests that being around other galaxies doesn’t play a big role in removing their ISM.

#Dust and Temperature

Dust is an important part of the ISM, and we examined how temperature and the amount of dust changed as galaxies aged. It turns out that cold dust temperatures generally drop as galaxies get older. Think of it as grandma's warm blanket becoming less cozy over time!

However, the cold dust in AGN galaxies stays warmer than that in non-AGN galaxies when they are both young. The difference in temperature tells us a lot about what's happening there.

#Star Formation Rates

Star formation rates (SFRs) measure how many new stars a galaxy is creating. We found that SFRs are highest in younger galaxies, which makes sense since they are teeming with fresh gas ready to make stars. As galaxies grow older, their SFRs decline, like a library losing its new books over time.

#The Importance of Outflows

Another piece of the puzzle is how much gas is being expelled from these galaxies, known as outflows. We measured outflow rates and found that galaxies with AGNs likely have powerful outflows, especially when they are younger.

It’s like when you shake a soda can-once you pop the top, it sprays everywhere! Young galaxies with AGNs are the ones likely spraying their gas out, while older galaxies keep their gas a little more contained.

#Conclusion

In summary, we learned that early-type galaxies face many challenges in maintaining their star formation. The removal of the ISM plays a crucial role, and this process changes as galaxies age.

AGN feedback is significant in younger galaxies but not so much in older ones. Instead, older galaxies rely more on old stars to influence their ISM. The environment these galaxies find themselves in doesn’t seem to play a big role in this process, as most galaxies do their own thing.

Much like life, galaxies grow, change, and adapt, showing us just how dynamic the universe can be. Whether through loud AGN parties or the quiet presence of old stars, the journey of these galaxies is both complex and fascinating.