Studying the Host Galaxies of Quasars

Quasars are like the rock stars of the universe. They shine incredibly bright, and we can see them from very far away, even when they were young and the universe was still in its infancy. In the last twenty years, we have found a lot more of these bright objects, especially those that are very, very distant. These quasars have supermassive black holes in their centers, surrounded by gas that is already full of heavy elements.

While studying these quasars, we often focus on their host galaxies-the places where they live. But observing the light from these galaxies can be tricky because they are often overshadowed by the bright light from the quasar itself. Recently, fancy new telescopes like the James Webb Space Telescope have made it easier to see the starlight from these host galaxies. Instead of looking for light from the stars, scientists have been studying the cool gas and Dust in these galaxies using observations at different wavelengths.

We want to understand how the radio jets from quasars interact with their host galaxies. Radio-loud quasars are those that emit strong radio waves, and they tend to be surrounded by large amounts of gas and dust. This interaction is thought to be important for the growth and evolution of both the quasars and their host galaxies.

#Observations with ALMA

In this study, we used the Atacama Large Millimeter/submillimeter Array (ALMA) to observe the host galaxies of six radio-loud quasars. ALMA is a powerful tool that helps us see light emitted by cool gas and dust in the universe. We focused on two specific lines of light, the 158 um line and the underlying dust continuum.

For five of the quasars we studied, we were able to recover the 158 um line and the dust emission. However, one quasar didn't show any sign of these emissions. It's like going to a party and only five people showed up while one person just ghosted.

At the resolution we were working with-about 1 arcsecond-we didn’t see any signs of disturbed shapes or unusual motions that might indicate that some of these galaxies are merging with others.

#The Gas and Dust in These Galaxies

The host galaxies of the quasars are already holding vast amounts of gas. In fact, they contain millions of solar masses of gas, and they are forming stars at impressive rates. By looking at their radio and submillimeter emissions, we discovered that in four of the quasars, the emissions we detected were due to both synchrotron radiation and dust, with synchrotron contributing around 10% of what we observed at 300 GHz.

By assuming that the only source of our detected emissions was cold dust, we calculated infrared luminosities. We then decided to stack up what we found against a much larger set of radio-quiet quasars from past studies.

Interestingly, we saw a mild decrease in gas emission for radio-loud quasars, which could suggest that the radio jets are doing some damage by sweeping away the gas.

#Searching for Companions

When we looked closely at the areas around the five radio-loud quasars we observed, we didn’t find any companion galaxies, which was a bit surprising. In the past, researchers found companions around radio-quiet quasars, and our results didn’t show anything different.

To really get to the bottom of understanding these radio-loud quasars, future observations that are sharper and cover a broader range of frequencies will be key.

#The Life of Quasars

Quasars are among the brightest objects in the universe, emitting light in ways that can be seen from great distances. Over time, we’ve found more and more quasars at very high redshifts, which means they are very far away and we see them as they were not long after the Big Bang.

Supermassive black holes are often found at the center of these quasars and are accompanied by gas that’s rich in heavy elements. However, studying the light from the stars in these galaxies has been hard due to the overwhelming brightness from the quasars themselves.

Recent breakthroughs with the James Webb Space Telescope have allowed us to uncover this hidden stellar light in a few cases.

Observations of cool gas and dust in these galaxies have been more insightful. The 158 um line tells us a lot about the gas in a galaxy. It's a key way to measure how much energy a galaxy might be putting out.

Initial studies done on a handful of quasars used earlier telescopes, but with ALMA, we've been able to study many more quasars and get a better understanding of their host galaxies.

#The Profile of Radio-Loud Quasars

Some quasars are classified as radio-loud based on strong radio emission linked to powerful jets. These jets are thought to play a huge role in how both the black hole and host galaxy evolve together, sometimes even stifling star formation or promoting it through shockwaves.

Radio-loud quasars are found in rich environments, making them prime targets for exploring galaxy formation and evolution during the early universe.

Out of the 50 known radio-loud quasars, studies have only begun to scratch the surface of their host galaxies. Previous observations have provided some insights, yet the majority of findings are primarily for radio-quiet quasars.

#The New Observations

In this work, we present the results of our new observations of the host galaxies of six radio-loud quasars and one radio-quiet quasar. Our observations were conducted using the ALMA telescope. We report the methods we employed to derive various properties of these galaxies, including their gas masses, star formation rates, and the presence of any nearby companion galaxies.

Our new results provide a clearer picture of how the host galaxies of radio-loud quasars are behaving compared to radio-quiet quasars.

#Observing the Quasars

We targeted high-redshift radio-loud quasars, aiming to unveil the properties of their host galaxies. During this phase, we noted that one of the targets, J2053+0047, was originally thought to be radio-loud but was later classified as radio-quiet after deeper observations were made. We still included its results here to ensure completeness.

Our ALMA observations were carefully planned with a set configuration to ensure we captured the necessary data without losing crucial information.

#Extracting the Data

From the data we collected, we worked to derive key measurements for the properties of the galaxies. We focused on recovering the emissions we were interested in and fitted them to understand them better.

We managed to find the 158 um emission line in all targeted quasars, which tells us a lot about the conditions within those galaxies.

For some of the quasars, we had to be cautious in interpreting the results because the emissions were near the edge of detection limits.

#The Results

From our analysis of the light emitted from these galaxies, we created maps that highlight where this emission is coming from. The results showed that while we could recover the emissions, the shapes of the galaxies did not appear to be dramatically altered, which suggests no strong disruptions.

The follow-up on the dynamical structure of these galaxies indicated that they could be relatively stable and undisturbed.

#Conclusion of Findings

We derived various measurements related to the gas and dust properties of the galaxies. This information adds to our understanding of what these galaxies are made of and how they function.

When we compare these findings to the data from radio-quiet quasars, we found both similarities and differences in the luminosity and star formation rates.

Interestingly, radio-loud quasars seem to be systematically fainter in certain measurements than their radio-quiet counterparts.

The interaction between the jets from these quasars and their interstellar medium may play a role in shaping what we observe, but we concluded that more research is needed to fully grasp these interactions.

#Looking Ahead

As we aim for a deeper understanding of these galaxies, we anticipate that more advanced observations will provide the clarity we need regarding the relationships between quasars, their host galaxies, and the environments around them.

With newer technologies and telescopes on the horizon, we are excited to continue our exploration of these fascinating objects that serve as windows into the earlier universe.

In conclusion, our quest to understand the cosmos continues. We’re lucky to have powerful tools like ALMA to help us peel back the layers of the universe and reveal what lies beneath the bright surface of quasars. And who knows? Maybe one day we’ll find a quasar with a party of companion galaxies, all shining brightly together in the vast cosmos.