Credit: ALMA (ESO/NAOJ/NRAO)/S. Dagnello (NRAO), NASA/ESA/Hubble/K. Cook (LLNL), L. Shatz
A new study by scientists using the Atacama Large Millimeter / Submillimeter Array (ALMA) suggests that previously displaced gases can be restored in galaxies, potentially slowing the galaxy death process caused by ram pressure and Creating unique structures that are more resistant to their effects.
“Much of the previous work on ram-stripped galaxies has focused on material stripped from galaxies. In this new work we see a gas that, instead of being ejected out of the galaxy, moves like a boomerang, is ejected, but then circles and returns to its source, ”said Arizona astronomer William Cramer. at Arizona State University and the lead author of the new study. “By combining data from Hubble and ALMA in very high resolution, we can show that this process is taking place.
Ram pressure stripping refers to the process of displacing gas from galaxies, leaving them without the material needed to form new stars. As galaxies move through their galaxy clusters, the hot gas known as the intracluster medium or space in between acts like a strong wind, pushing the gases out of the moving galaxies. Over time, this leads to starvation and the “death” of once active star-forming galaxies. Because ram pressure stripping can speed up the normal life cycle of galaxies & change the amount of molecular gas in them, it is of particular interest to scientists studying the life, maturation, and death of galaxies.
“We have seen in simulations that not all of the gas that is pushed out of the galaxy by the ram pressure stripping escapes because it has to reach the escape velocity speed in order to escape and not go back. We believe that the recretion we see comes from clouds of gas blown out of the galaxy by ram pressure stripping that have not reached an escape velocity, so they are fall-back, ”said Jeff Kenney, an astronomer at Yale University & co-author. “If you want to predict how quickly a galaxy will stop forming stars and turn into a red or dead galaxy over time, then you want to understand how effective the ram pressure is in removing gas. Unless you know that gas can fall back into the galaxy and continue to recycle and form new stars, You will overestimate the star extinction.. Evidence of this process means more accurate time-lines for the life cycle of galaxies.
The new study focuses on NGC 4921, a barred spiral galaxy and the largest spiral galaxy in the Coma Cluster, located about 320 million light years from Earth in the Coma Berenices constellation. NGC 4921 is of particular interest to scientists studying the effects of ram pressure stripping as there is ample evidence for both the process and its aftermath is ab-undant.
RAM Pressure triggers the formation of stars on the side where it has the greatest impact on the galaxy,” said Cramer. “It’s easy to identify in NGC 4921 because there are many young blue stars on the side of the galaxy where they occur.
Kenney added that the ram pressure stripping in NGC 4921 created a strong, visible line between places where dust is still present in the galaxy & places where it doesn’t. “There is a strong line of dust & far away from that, there is almost no gas in the galaxy. We believe that this part of the galaxy has been almost completely cleaned by the ram pressure.
With ALMA’s 6-band receiver, the scientists were able to re-solve carbon monoxide, the key to “seeing” both the gas-poor areas of the galaxy and the areas where it is being created. “We know that most of the molecular gas in galaxies is in the form of hydrogen, but molecular hydrogen is very difficult to observe directly,” said Cramer. “Carbon monoxide is often used as a substitute for studying molecular gas in galaxies because it is so much easier to observe.
The ability to see more of the galaxy, even in its faint-est, revealed interesting structures that are likely formed when the gas was displaced and are immune to its effects. “Ram pressure seems to form unique structures or filaments in galaxies that provide clues as to how a galaxy evolves under a ram pressure wind. In the case of NGC 4921, they bear a striking resemblance to the famous nebula, the Pillars of Creation, albeit on a much more massive scale, “Cramer said. “We believe they are supported by magnetic fields that prevent them from being stripped out with the rest of the gas.”
Observations revealed that the structures are more than just clouds of gas and dust; the filaments have mass & a lot. “These filaments are heavier and stickier, they adhere more firmly to their material than the rest of the interstellar medium in the galaxy, and they appear to be connected to this great ridge of dust both in space & in velocity” Kenney said. “They are more like molasses than smoke. If you just smoke a little, the smoke is light & it disperses and goes in all directions. But that’s a lot heavier than that.”
Although a significant step forward, the study results are just a starting point for Cramer and Kenney, who studied a small portion of 1 galaxy. “If we are to predict the death rate of galaxies and the birth rate of new stars, we need to understand whether and how much of the material that stars are made of that was originally lost-to ram pressure is actually recycled,” said Cramer. “These observations come from only one quadrant of NGC 4921. More gas is likely to fall into other quadrants. We have confirmed that some of the gas stripped can “rain” back-down, but we need more observations to quantify how much gas falls-back & how many new stars are created as a result.
“A fascinating study demonstrating the power of ALMA and the benefit of combining its observations with those of a telescope at other wavelengths,” added Joseph Pesce, NRAO / ALMA program officer in NSF. “The ram pressure stripping is an important phenomenon for galaxies in-clusters, and a better understanding of the process enables us to better understand the evolution of galaxies and nature.
The findings will be published in an upcoming edition of The Astrophysical Journal.
You Can get more information here Arxiv.
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