Gas Re-Accretion Observed in Dying Galaxies for the First Time

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Filament Structures Left Behind by Ram Pressure Stripping NGC4921

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Shown here in composite view, ALMA information (red/orange) exposes filament structures left by ram pressure removing in a Hubble Space Telescope optical view of NGC4921. Scientists think that these filaments are formed as electromagnetic fields in the galaxy avoid some matter from being removed away. Credit: ALMA (ESO/NAOJ/NRAO)/S. Dagnello (NRAO), NASA/ESA/Hubble/K. Cook (LLNL), L. Shatz

ALMA information shows that ram pressure removing doesn’t spell an instant end for galaxies.

A brand-new research study from researchers utilizing the Atacama Large Millimeter/submillimeter Array (ALMA) recommends that formerly displaced gases can re-accrete onto galaxies, possibly decreasing the procedure of galaxy death brought on by ram pressure removing, and developing special structures more resistant to its results.

“Much of the previous work on ram pressure stripped galaxies is focused on the material that gets stripped out of galaxies. In this new work we see some gas that rather than being thrown out of the galaxy never to return is instead moving like a boomerang, being ejected out but then circling around and falling back to its source,” stated William Cramer, an astronomer at Arizona State University and the lead author on the brand-new research study. “By combining Hubble and ALMA data at very high resolution, we are able to prove that this process is happening.”

Zoomed in Composite NGC4921

Zoomed in view of an ALMA (red/orange) and Hubble Space Telescope (optical) composite of NGC4921. This composite highlights filament structures arising from the results of ram pressure removing. Ram pressure removing is a procedure understood to strip gas out of galaxies, leaving them without the product required to form brand-new stars. A brand-new research study shows that some product might not be removed away from the galaxy, and is rather, reaccreted, possibly with the aid of electromagnetic fields, decreasing the procedure of galaxy death. Credit: ALMA (ESO/NAOJ/NRAO)/S. Dagnello (NRAO), NASA/ESA/Hubble/K. Cook (LLNL), L. Shatz

Ram pressure removing describes the procedure that displaces gas from galaxies, leaving them without the product required to form brand-new stars. As galaxies move through their galaxy clusters, hot gas called the intra-cluster medium—or, the area in between—imitates a strong wind, pressing gases out of the taking a trip galaxies. Over time, this results in the hunger and “death” of once-active star-forming galaxies. Because ram pressure removing can accelerate the typical life process of galaxies and change the quantity of molecular gas within them, it is of specific interest to researchers studying the life, maturation, and death of galaxies.

“We’ve seen in simulations that not all of the gas being pushed by ram pressure stripping escapes the galaxy because it has to reach escape velocity in order to actually escape and not fall back. The re-accretion that we’re seeing, we believe is from clouds of gas that were pushed out of the galaxy by ram pressure stripping, and didn’t achieve escape velocity, so they’re falling back,” stated Jeff Kenney, an astronomer at Yale University, and the co-author on the research study. “If you’re trying to predict how fast a galaxy is going to stop forming stars over time and transform into a red, or dead galaxy, then you want to understand how effective ram pressure is at stripping the gas out. If you don’t know that gas can fall back onto the galaxy and continue to recycle and form new stars, you’re going to overpredict the quenching of the stars. Having proof of this process means more accurate timelines for the lifecycle of galaxies.”

Viewed face-on, Hubble Space Telescope (HST) exposes the circulation of young stars and dust in the spiral nebula NGC4921. The galaxy is under ram pressure from its galaxy cluster, the Coma Cluster. This procedure is removing gas far from the galaxy, changing its structure and the circulation of molecular gas, as traced by ALMA (seen here in red). Eventually, ram pressure can remove away adequate gas to stop the development of brand-new stars. The mix of information from HST and ALMA offers a 3-dimensional view of gas circulation and motion in NGC4921. Here we see that some clouds of molecular gas are really behind the galaxy and falling back towards the host, opposite the instructions of ram pressure. This re-accretion of gas can slow the strangulating result of ram pressure on the life of the galaxy. This is the very first observational proof of the fallback procedure. Credit: ALMA (ESO/NAOJ/NRAO)/S. Dagnello (NRAO), NASA/ESA/Hubble, K. Cook (LLNL), L. Shatz, W. Cramer et al (Yale)

The brand-new research study concentrates on NGC 4921—a disallowed spiral nebula and the biggest spiral nebula in the Coma Cluster—situated approximately 320 million light-years from Earth in the constellation Coma Berenices. NGC 4921 is of specific interest to researchers studying the results of ram pressure removing due to the fact that proof of both the procedure and its consequences is plentiful.

“Ram pressure triggers star formation on the side where it is having the greatest impact on the galaxy,” stated Cramer. “It’s easy to identify in NGC 4921 because there are many young blue stars on the side of the galaxy where it’s occurring.”

Kenney included that ram pressure removing in NGC 4921 has actually produced a strong, noticeable line in between where dust still exists in the galaxy and where it doesn’t. “There is a strong dust line present, and beyond that there’s almost no gas in the galaxy. We think that that part of the galaxy has been almost completely cleaned out by ram pressure.”

Side by Side Composite NGC4921

This side-by-side composite programs ALMA (red/orange) information laid over Hubble Space Telescope (optical) pictures of NGC4921. A brand-new research study of the spiral bar galaxy exposed filament structures comparable to the Pillars of Creation however considerably bigger. These structures are brought on by a procedure called ram pressure removing, which presses gas out of galaxies, leaving them without the product required to form brand-new stars. Credit: ALMA (ESO/NAOJ/NRAO)/S. Dagnello (NRAO), NASA/ESA/Hubble/K. Cook (LLNL), L. Shatz

Using ALMA’s Band 6 receiver, researchers had the ability to deal with carbon monoxide gas, the secret to “seeing” both those locations of the galaxy without gas, in addition to those locations where it is re-accreting. “We know that the majority of molecular gas in galaxies is in the form of hydrogen, but molecular hydrogen is very difficult to observe directly,” stated Cramer. “Carbon monoxide is commonly used as a proxy for studying molecular gas in galaxies because it is much easier to observe.”

The capability to see more of the galaxy, even at its faintest, revealed intriguing structures most likely produced in the procedure of gas displacement, and more unsusceptible to its results. “Ram pressure appears to form unique structures, or filaments in galaxies that are 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, although on a much more massive scale,” stated Cramer. “We think that they are supported by magnetic fields which are preventing them from being stripped away with the rest of the gas.”

Observations exposed that the structures are more than simply wisps of gas and dust; the filaments have mass and a great deal of it. “These filaments are heavier and stickier—they hold on to their material more tightly than the rest of the galaxy’s interstellar medium can do—and they seem to be connected to that big dust ridge both in space and in velocity,” stated Kenney. “They’re more like molasses than smoke. If you just blow on something that is smoke, the smoke is light, and it disperses and goes in all directions. But this is much heavier than that.”

Although a considerable advancement, the outcomes of the research study are just a beginning point for Cramer and Kenney, who took a look at one little part of simply one galaxy. “If we want to predict the death rate of galaxies, and the birthrate of new stars, we need to understand if and how much of the material that forms stars, originally lost to ram pressure, is actually recycled back,” stated Cramer. “These observations are of just one quadrant of NGC 4921. There is likely even more gas falling back into other quadrants. While we have confirmed that some stripped gas can ‘rain’ back down, we need more observations to quantify how much gas falls back and how many new stars form 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,” included Joseph Pesce, NRAO/ALMA program officer at the NSF. “Ram pressure stripping is an important phenomenon for galaxies in clusters, and understanding the process better allows us to understand galaxy evolution—and nature—better.”

The outcomes of the research study will be released in an approaching edition of The Astrophysical Journal.

Reference: “Molecular gas filaments and fallback in the ram pressure stripped Coma spiral NGC 4921” by William J. Cramer, Jeffrey D. P. Kenney, Stephanie Tonnesen, Rory Smith, Tony Wong, Pavel Jáchym, Juan R. Cortés, Paulo C. Cortés, Yu-Ting Wu, Accepted, The Astrophysical Journal.
arXiv: 2107.11731

About ALMA

The Atacama Large Millimeter/submillimeter Array (ALMA), a worldwide astronomy center, is a collaboration of the European Organisation for Astronomical Research in the Southern Hemisphere (ESO), the U.S. National Science Foundation (NSF) and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is moneyed by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the Ministry of Science and Technology (A LOT OF) and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI).

ALMA building and operations are led by ESO on behalf of its Member States; by the National Radio Astronomy Observatory (NRAO), handled by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) offers the unified management and management of the building, commissioning and operation of ALMA.