Stars Are Exploding in Dusty Galaxies. We Just Can’t Always See Them (Planetary Science)

Exploding stars generate dramatic light shows. Infrared telescopes like Spitzer can see through the haze and to give a better idea of how often these explosions occur.

You’d think that supernovae – the death throes of massive stars and among the brightest, most powerful explosions in the universe – would be hard to miss. Yet the number of these blasts observed in the distant parts of the universe falls way short of astrophysicists’ predictions.

A new study using data from NASA’s recently retired Spitzer Space Telescope reports the detection of five supernovae that, going undetected in optical light, had never been seen before. Spitzer saw the universe in infrared light, which pierces through dust clouds that block optical light – the kind of light our eyes see and that unobscured supernovae radiate most brightly.

Download this free poster from NASA, which commemorates the retired Spitzer Space Telescope. Available in English and Spanish. Credit: NASA/JPL-Caltech

To search for hidden supernovae, the researchers looked at Spitzer observations of 40 dusty galaxies. (In space, dust refers to grain-like particles with a consistency similar to smoke.) Based on the number they found in these galaxies, the study confirms that supernovae do indeed occur as frequently as scientists expect them to. This expectation is based on scientists’ current understanding of how stars evolve. Studies like this are necessary to improve that understanding, by either reinforcing or challenging certain aspects of it.

“These results with Spitzer show that the optical surveys we’ve long relied on for detecting supernovae miss up to half of the stellar explosions happening out there in the universe,” said Ori Fox, a scientist at the Space Telescope Science Institute in Baltimore, Maryland, and lead author of the new study, published in the Monthly Notices of the Royal Astronomical Society. “It’s very good news that the number of supernovae we’re seeing with Spitzer is statistically consistent with theoretical predictions.”

The “supernova discrepancy” – that is, the inconsistency between the number of predicted supernovae and the number observed by optical telescopes – is not an issue in the nearby universe. There, galaxies have slowed their pace of star formation and are generally less dusty. In the more distant reaches of the universe, though, galaxies appear younger, produce stars at higher rates, and tend to have higher amounts of dust. This dust absorbs and scatters optical and ultraviolet light, preventing it from reaching telescopes. So researchers have long reasoned that the missing supernovae must exist and are just unseen.

“Because the local universe has calmed down a bit since its early years of star-making, we see the expected numbers of supernovae with typical optical searches,” said Fox. “The observed supernova-detection percentage goes down, however, as you get farther away and back to cosmic epochs where dustier galaxies dominated.”

Detecting supernovae at these far distances can be challenging. To perform a search for supernovae shrouded within murkier galactic realms but at less extreme distances, Fox’s team selected a local set of 40 dust-choked galaxies, known as luminous and ultra-luminous infrared galaxies (LIRGs and ULIRGs, respectively). The dust in LIRGs and ULIRGs absorbs optical light from objects like supernovae but allows infrared light from these same objects to pass through unobstructed for telescopes like Spitzer to detect.

The researchers’ hunch proved correct when the five never-before-seen supernovae came to (infrared) light. “It’s a testament to Spitzer’s discovery potential that the telescope was able to pick up the signal of hidden supernovae from these dusty galaxies,” said Fox.

“It was especially fun for several of our undergraduate students to meaningfully contribute to this exciting research,” added study co-author Alex Filippenko, a professor of astronomy at the University of California, Berkeley. “They helped answer the question, ‘Where have all the supernovae gone?’”

The types of supernovae detected by Spitzer are known as “core-collapse supernovae,” involving giant stars with at least eight times the mass of the Sun. As they grow old and their cores fill with iron, the big stars can no longer produce enough energy to withstand their own gravity, and their cores collapse, suddenly and catastrophically.

The intense pressures and temperatures produced during the rapid cave-in forms new chemical elements via nuclear fusion. The collapsing stars ultimately rebound off their ultra-dense cores, blowing themselves to smithereens and scattering those elements throughout space. Supernovae produce “heavy” elements, such as most metals. Those elements are necessary for building up rocky planets, like Earth, as well as biological beings. Overall, supernova rates serve as an important check on models of star formation and the creation of heavy elements in the universe.

“If you have a handle on how many stars are forming, then you can predict how many stars will explode,” said Fox. “Or, vice versa, if you have a handle on how many stars are exploding, you can predict how many stars are forming. Understanding that relationship is critical for many areas of study in astrophysics.”

Next-generation telescopes, including NASA’s Nancy Grace Roman Space Telescope and the James Webb Space Telescope, will detect infrared light, like Spitzer.

“Our study has shown that star formation models are more consistent with supernova rates than previously thought,” said Fox. “And by revealing these hidden supernovae, Spitzer has set the stage for new kinds of discoveries with the Webb and Roman space telescopes.”

More About the Mission

NASA’s Jet Propulsion Laboratory in Southern California conducted mission operations and managed the Spitzer Space Telescope mission for the agency’s Science Mission Directorate in Washington. Science operations were conducted at the Spitzer Science Center at Caltech in Pasadena. Spacecraft operations were based at Lockheed Martin Space in Littleton, Colorado. Data are archived at the Infrared Science Archive housed at IPAC at Caltech. Caltech manages JPL for NASA.

More information about Spitzer is available at:

https://www.nasa.gov/mission_pages/spitzer/main

Featured image: The image shows galaxy Arp 148, captured by NASA’s Spitzer and Hubble telescopes. Specially processed Spitzer data is shown inside the white circle, revealing infrared light from a supernova hidden by dust. Credit: NASA/JPL-Caltech

---

Reference: Ori D Fox et al, A Spitzer survey for dust-obscured supernovae, Monthly Notices of the Royal Astronomical Society (2021). DOI: 10.1093/mnras/stab1740

---

Provided by NASA JPL

Astronomers May Have Discovered Largest Filament Known To Date Or A New Spiral Arm (Cosmology)

Using the Five-hundred-meter Aperture Spherical radio Telescope (FAST), a team of international astronomers detected a giant filamentary H I structure “Cattail”, which is possibly the furthest (Rgc∼22 kpc) and largest (∼1.1 kpc) filament to date. Their study recently appeared in Arxiv.

Gas filaments are the largest known structures in the universe, consisting of walls of gravitationally bound galaxy superclusters. The largest elongated molecular cloud structures are called giant molecular filaments with length greater than 10 pc. Compared to gaint molecular filaments, H I filaments are not well studied. Most of the H I filaments are aligned with the Galactic plane, which is similar to the situation of giant molecular filaments. The H I filaments are normally cold with a typical excitation temperature Tex∼50 K and often associated with CO dark molecular gas. However, detailed physical properties of H I filaments, as well as their distribution in the Galaxy, are not well characterized.

Now, a team of international astronomers led by Keping Qiu, with the help of FAST, observed the sky region of Right Ascension of 307°.7 < α < 311°.0 and Declination of 40°.9 < δ < 43°.4 on 2019 August 24. This sky region covers the main part of the Cygnus-X North molecular cloud, which has a velocity range of – 30 km s¯¹ to 20 km s¯¹ and is located 1.4 kpc away from the Sun.

Table 1: Physical Parameters of Cattail © Keping Qui et al.

They detected a gaint filamentary H I structure having a velocity between –170 km s¯¹ to –130 km s¯¹, and a mean velocity of – 150 km s¯¹ at a Galactocentric distance of 22 kpc.

This has a length of 1.1 kpc, which appears to be so far the furthest and largest giant filament in the Galaxy. They named it Cattail. Its mass is calculated to be 6.5 × 10⁴ M and the linear mass density is 60 M pc¯¹. Its width is 207 pc, corresponding to an aspect ratio of 5:1.

Cattail possesses a small velocity gradient (0.02 km s¯¹ pc¯¹) along its major axis. Together with the HI4PI data, they found that Cattail could have an even larger length, up to 5 kpc. They also identified another new elongated structure to be the extension into the Galactic first quadrant of the Outer Scutum-Centaurus (OSC) arm, and Cattail appears to be located far behind the OSC.

“Based on the above analysis, we suggest two possible explanations for Cattail: it is a giant filament with a length of ∼5 kpc, or part of a new arm in the Extreme Outer Galaxy (EOG) ”

— they wrote.

---

The question about how such
a huge filament is produced at the extreme Galactic location remains open. Alternatively, Cattail might be part of a
new arm beyond the OSC, though it is puzzling that the structure does not fully follow the warp of the Galactic disk.

Featured image: Artist’s conception view of the Milky Way (R. Hurt: NASA/JPL-Caltech/SSC) . The new part of the OSC and the Cattail identified in this work are indicated with the green and blue dashed line, respectively. © Keping Qiu et al.

---

Reference: Chong Li, Keping Qiu, Bo Hu, Yue Cao, “The discovery of the largest gas filament in our Galaxy, or a new spiral arm?”, Arxiv, 2021. https://arxiv.org/abs/2108.01905

---

Note for editors of other websites: To reuse this article fully or partially kindly give credit either to our author/editor S. Aman or provide a link of our article

New Findings On The Evolution Of Galaxies (Cosmology)

Emirati national Aisha Al Yazeedi, a research scientist at the NYU Abu Dhabi (NYUAD) Center for Astro, Particle, and Planetary Physics, has published her first research paper, featuring some key findings on the evolution of galaxies.

Galaxies eventually undergo a phase in which they lose most of their gas, which results in a change into their properties over the course of their evolution. Current models for galaxy evolution suggest this should eventually happen to all galaxies, including our own Milky Way; Al Yazeedi and her team are delving into this process.

Commenting on the findings, Al Yazeedi said: “The evolution of galaxies is directly linked to the activity of their central supermassive blackhole (SMBH). However, the connection between the activity of SMBHs and the ejection of gas from the entire galaxy is poorly understood. Observational studies, including our research, are essential to clarify how the central SMBH can influence the evolution of its entire host galaxy and prove key theoretical concepts in the field of astrophysics.”

Titled “The impact of low luminosity AGN on their host galaxies: A radio and optical investigation of the kpc-scale outflow in MaNGA 1-166919,” the paper has been published in the Astronomical Journal. Its findings outline gas ejection mechanisms, outflow properties, and how they are related to the activity of the supermassive blackhole (SMBH) at the center of the host galaxy.

Superposition of optical z-band MzLS imageisophotes (gray color) and our highest spatial resolution radio image in S band (in blue). Optical image has a spatial resolution of 0:0084, while S-band radio data { 0:009. Credit: NYU Abu Dhabi

To that end, the paper presents a detailed optical and radio study of the MaNGA 1-166919 galaxy, which appears to have an Active Galactic Nucleus (AGN). Radio morphology shows two lobes (jets) emanating from the center of the galaxy, a clear sign of AGN activity that could be driving the optical outflow. By measuring the outflow properties, the NYUAD researchers documented how the extent of the optical outflow matches the extent of radio emission.

Al Yazeedi is a member of NYUAD’s Kawader program, a national capacity-building research fellowship that allows outstanding graduates to gain experience in cutting-edge academic research. The three-year, individually tailored, intensive program is designed for graduates considering a graduate degree or a career in research.

The above figure is a GMOS outflow map with radio contours overlaid in black. The outflow velocities show a clear spatial separation of “red” and “blue” components. It strongly suggests a biconical outflow and nicely shows the correspondence between the optical outflow and radio emission. Credit: NYU Abu Dhabi

Her paper adds to the growing body of UAE space research and activities. The UAE has sent an Emirati into space, a spacecraft around Mars and recently announced plans to send a robotic rover to the Moon in 2022, ahead of the ultimate goal to build a city on Mars by 2117.

Emirati women are playing a key role in the research and development behind these projects. The Mars Hope probe science team, which is 80 percent female, was led by Sarah Al Amiri, Minister of State for Advanced Sciences and chairperson of the country’s space agency.

Featured image: Composite RGB image of the Blob Source extracted from the DESI Legacy Imaging Surveys (Dey et al.(2019), legacysurvey.org). MaNGA _eld of view is shown in orange. Gray box corresponds to the GMOS _eld of view. Credit: Dey et al.(2019), legacysurvey.org

---

Reference: Aisha Al Yazeedi et al, The impact of low luminosity AGN on their host galaxies: A radio and optical investigation of the kpc-scale outflow in MaNGA 1-166919, Astronomical Journal (2021), arXiv:2105.07335v1 [astro-ph.GA] arxiv.org/abs/2105.07335

---

Provided by New York University

The Magnetic Field in the Galactic Outflow of M82 (Cosmology)

Messier 82 (M82) is a luminous infrared galaxy about twelve million light-years away from the Milky Way. Its burst of star formation powers the radiation and drives a bipolar superwind that originates near the core of the galaxy. The wind extends perpendicular to the galactic plane out into the halo and intergalactic medium; ionized gas in the wind traces a continuous structure that is about thirty-four thousand light-years long. Astronomers think that star formation along the superwind is exciting the gas and also generating X-ray emission, the latter produced by associated shocks.

M82 is not unique among galaxies in having an outflowing wind although because it is relatively nearby and seen nearly edge-on, its outflow is easier to study. A key question relates to the material flowing in the wind. If it escapes and is deposited into the space between galaxies, it enriches the intergalactic medium, but if it recirculates back onto the galaxy it will redistribute the material and can stimulate star formation in outer regions. The magnetic field in the wind both drives and helps to shape the outcome. Details depend on whether the field lines spread and “open” into space or are “closed,” curling or looping around the galaxy and staying more tightly confined. To date, the magnetic fields in galactic outflows have been studied using the polarized radiation emitted at radio wavelengths by electrons moving in the ionized flow. In M82, previous studies have indeed found magnetic fields stretching from the central region and extending perpendicularly to the disk, but the interpretation is complex and these studies differ on whether or not the field lines are open or closed.

CfA astronomer Mahboubeh Asgari-Targhi was part of a team that recognized that scattered infrared radiation from dust grains aligned by these magnetic fields could resolve the debate. They used the High-resolution Airborne Wideband Camera-plus (HAWC+) on NASA’s Stratospheric Observatory for Infrared Astronomy (SOFIA) to map the magnetic fields in M82, and combined their results with a modified technique more commonly used by solar astronomers who are studying the Sun’s magnetic fields. The novel approach extrapolates the measured field with some reasonable approximations about the electrical currents present; the scientists complete the picture with other polarization data from the literature. They show clearly, for the first time, that in M82 the field lines are open, and also that the energy in turbulent motions is comparable to that in the magnetic field. The results indicate that the outflow winds associated with starburst phenomena in galaxies inject enriched material into the intergalactic medium.

Featured image: An optical image of the luminous infrared superwind galaxy M82.  The image highlights in red the wind emission in the radiation from filaments of ionized hydrogen. Some of the gas in the superwind, enriched in heavy elements forged in massive stars, will eventually escape into intergalactic space. Astronomers used Stratospheric Observatory for Infrared Astronomy (SOFIA) to map the magnetic field that drives this wind in M82. © Alentejo Remote Observatory, Team ARO

---

Reference:

“The Strength and Structure of the Magnetic Field in the Galactic Outflow of Messier 82,” Enrique Lopez-Rodriguez, Jordan A. Guerra, Mahboubeh Asgari-Targhi, and Joan T. Schmelz, The Astrophysical Journal 914, 24, 2021.

---

Provided by Harvard-Smithsonian Center for Astrophysics

Scientists Observe Gas Re-accretion in Dying Galaxies for the First Time (Cosmology)

ALMA data proves that ram pressure stripping doesn’t spell an immediate end for galaxies

A new study from scientists using the Atacama Large Millimeter/submillimeter Array (ALMA) suggests that previously displaced gases can re-accrete onto galaxies, potentially slowing down the process of galaxy death caused by ram pressure stripping, and creating unique structures more resistant to its effects.  

“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,” said William Cramer, an astronomer at Arizona State University and the lead author on the new study. “By combining Hubble and ALMA data at very high resolution, we are able to prove that this process is happening.”

Ram pressure stripping refers to the process that displaces gas from galaxies, leaving them without the material needed to form new stars. As galaxies move through their galaxy clusters, hot gas known as the intra-cluster medium—or, the space between—acts like a forceful wind, pushing gases out of the traveling galaxies. Over time, this leads to the starvation and “death” of once-active star-forming galaxies. Because ram pressure stripping can speed up the normal life cycle of galaxies and alter the amount of molecular gas within them, it is of particular interest to scientists 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,” said Jeff Kenney, an astronomer at Yale University, and the co-author on the 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.”

The new study focuses on NGC 4921—a barred spiral galaxy and the largest spiral galaxy in the Coma Cluster—located roughly 320 million light-years from Earth in the constellation Coma Berenices. NGC 4921 is of particular interest to scientists studying the effects of ram pressure stripping because evidence of both the process and its aftermath is abundant.

“Ram pressure triggers star formation on the side where it is having 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 it’s occurring.”

Kenney added that ram pressure stripping in NGC 4921 has created a strong, visible line 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.”

Using ALMA’s Band 6 receiver, scientists were able to resolve carbon monoxide, the key to “seeing” both those areas of the galaxy devoid of gas, as well as those areas 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,” said Cramer. “Carbon monoxide is commonly used as a proxy for studying molecular gas in galaxies because it is much easier to observe.”

The ability to see more of the galaxy, even at its faintest, unveiled interesting structures likely created in the process of gas displacement, and further immune to its effects. “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,” said 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 revealed that the structures are more than just wisps of gas and dust; the filaments have mass and a lot 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,” said 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 significant breakthrough, the results of the study are only a starting point for Cramer and Kenney, who examined one small part of just 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,” said 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,” added 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 results of the study will be published in an upcoming edition of The Astrophysical Journal.

Featured image: NGC 4921 © Credit: ALMA (ESO/NAOJ/NRAO)/S. Dagnello (NRAO), NASA/ESA/Hubble/K. Cook (LLNL), L. Shatz

---

Resource
“Molecular gas filaments and fallback in the ram pressure stripped Coma spiral NGC 4921,” W. Cramer et al, ApJ, preview [https://arxiv.org/abs/2107.11731]

---

A Restless Triplet Of Galaxies (Cosmology)

The Hubble Space Telescope has captured Arp 195, a fantastic triplet of interacting galaxies featured in Halton Arp’s Atlas of Peculiar Galaxies. The image represents a bonus snapshot, obtained between one scheduled observation and another, so as not to waste even a moment of the precious space telescope time

Thanks to NASA and ESA’s Hubble Space Telescope , astronomers have captured this fantastic triplet of interacting galaxies. The system, known as Arp 195 (or Ugc 4653), is one of those present in the Atlas of Peculiar Galaxies : an astronomical catalog of some of the strangest and most wonderful galaxies in the universe, compiled by Halton Arp and published in 1966 by California Institute of Technology . Arp 195 is found in the Lynx constellation , a northern constellation so faint that its name derives from the fact that it takes the eyes of a lynx to see it.

The observation time of the Hubble Space Telescope is extremely precious and astronomers do not want to waste even a second. The Hubble observing schedule is calculated using a computer algorithm that allows the satellite to occasionally collect “bonus” snapshots between longer observations. This image of the triplet of interacting galaxies in Arp 195 is one such snapshot. Extra observations like these do more than provide spectacular images – they also help identify promising targets to observe with other telescopes, such as the upcoming James Webb Space Telescope , Jwst.

Watch the video on the youtube channel HubbleEsa (Credits: Esa / Hubble & Nasa, J. Dalcanton)

Featured image: The triplet of interacting galaxies Arp 195 as seen by the Hubble Space Telescope. Credits: Esa / Hubble & Nasa, J. Dalcanton

---

Provided by INAF

Play Of Light And Shadow From the Core of the Galaxy (Cosmology)

Ic 5063 is located 156 million light years from us. It is an active galaxy (Agn) pervaded by a fascinating play of light and shadow generated by the supermassive and extremely ravenous black hole in the center. Light rays and shadow beams extend across the galaxy for about 36,000 light years

Taken by the Hubble Space Telescope’s Wide Field Camera 3 and Advanced Camera for Surveys on March 7 and November 25, 2019, this image reveals the appearance of the heart of the active galaxy Ic 5063 , 156 million light-years away. The galaxy is pervaded by a mixture of light rays and dark shadows emanating from the “flaming” core, home to a supermassive black hole.

Ic 5063 belongs to the class of active galactic nuclei : galaxies in which the central black hole is intensely growing and which therefore, seen through the telescope, show an enormously brighter central area than what happens in “normal” galaxies. 

Analyzing this photograph, astronomers suggest that a ring of dusty material surrounding the black hole may be casting its shadow into space around the galaxy. What happens? Light and shadow interact when the light emitted by the immense and ravenous black hole hits the ring of dust, which is buried within the core. The light “escapes” through the cracks in the ring, creating the bright rays visible in the image (like the setting Sun whose rays peek out of the clouds). However, denser areas in the disk block out much of the light, casting long dark shadows across the galaxy.

This play of light and shadow extends across the galaxy for about 36,000 light years.

Featured image: The galaxy Ic 5063. Credits: Nasa, Esa, STScI and WP Maksym (CfA)

---

Provided by INAF

What Is The Mass Of Large Magellanic Cloud? (Cosmology)

By using stellar streams, Nora Shipp and colleagues measured the mass of Large Magellanic Cloud (LMC). They found that the mass of the LMC to be ~ 1.8 × 10¹¹ M. Their study recently appeared in Arxiv.

The mass of the Large Magellanic Cloud (LMC), the Milky Way’s largest satellite galaxy, has proven notoriously difficult to measure. Many researchers tried to directly measure the mass of the LMC from the dynamics of its star clusters and rotation curve. But, such direct dynamical tracers are only measuring the central region of a much more massive LMC halo. Another, direct dynamical tracer called stellar streams, the remnants of recently disrupted dwarf galaxies and globular clusters, measure the mass of the LMC at much larger distances.

The interaction geometry between a stream and the LMC. The blue dotted line represents a stream within an orbital plane traced by the solid black oval. The black dashed line represents the vector between the stream and the LMC at closest approach. They decompose this vector into components aligned with the angular momentum vector of the stream’s orbit (Lˆ), the radial vector between the stream and the Galactic center (ˆr), and a third perpendicular vector tangential to the stream’s orbit (Lˆ × rˆ). © Authors

Recently, a large number of stellar streams in the southern hemisphere were discovered by Dark Energy Survey (DES). Gaia then provided unprecedented measurements of proper motions of greater than 1 billion Milky Way stars, enabling the measurement of the proper motions of the DES streams. Many of these streams are close in projection to the LMC, suggesting the exciting opportunity to probe the mass of the LMC at large radii with multiple direct dynamical tracers. Such a measurement was proposed by Erkal et al., who predicted the effect of the LMC on the Tucana III (Tuc III) stream and found that the LMC could induce a substantial proper motion perpendicular to the track of the stream on the sky. They further argued that the size of this offset could be used to measure the mass of the LMC.

Now, Nora Shipp and colleagues measured the LMC mass with five streams in the Southern Galactic hemisphere, combining observations from the Southern Stellar Stream Spectroscopic Survey (S5), Gaia EDR3, and the Dark Energy Survey (DES). They found that the mass of the LMC to be ~ 1.8 × 10¹¹ M.

Table 1: LMC mass measurements and parameters of the last closest approach © authors

“This mass is compatible with previous measurements, showing that a consistent picture is emerging of the LMC’s influence on structures in the Milky Way.”

— they said.

---

Finally, they examined the LMC’s impact on their sample of streams. They found that the LMC’s effect depends on the relative orientation of the stream and LMC at their point of closest approach. To better understand this, they presented a simple model based on the impulse approximation and showed that the LMC’s effect depends both on the magnitude of the velocity kick imparted to the stream and the direction of this kick.

“Further study of the complexity of the Milky Way and LMC potential with a large population of stellar streams will build upon this work to reveal a more complete picture of the effect of the Milky Way’s largest satellite on our Galaxy.”

— they concluded.

---

Reference: Nora Shipp, Denis Erkal, Alex Drlica-Wagner, Ting S. Li, Andrew B. Pace, Sergey E. Koposov, Lara R. Cullinane, Gary S. Da Costa, Alexander P. Ji, Kyler Kuehn, Geraint F. Lewis, Dougal Mackey, Jeffrey D. Simpson, Zhen Wan, Daniel B. Zucker, Joss Bland-Hawthorn, Peter S. Ferguson, Sophia Lilleengen, S5 Collaboration, “Measuring the Mass of the Large Magellanic Cloud with Stellar Streams Observed by ${S}^5$”, Arxiv, pp. 1-23, 2021. https://arxiv.org/abs/2107.13004

---

Note for editors of other websites: To reuse this article fully or partially kindly give credit either to our author/editor S. Aman or provide a link of our article

Scientists Capture Most-detailed Radio Image Of Andromeda Galaxy To Date (Cosmology)

‘Disk of galaxy’ identified as region where new stars are born

Scientists have published a new, detailed radio image of the Andromeda galaxy – the Milky Way’s sister galaxy – which will allow them to identify and study the regions of Andromeda where new stars are born.

Sofia Fatigoni © UBC

The study – which is the first to create a radio image of Andromeda at the microwave frequency of 6.6 GHz – was led by University of British Columbia physicist Sofia Fatigoni, with colleagues at Sapienza University of Rome and the Italian National Institute of Astrophysics. It was published online in Astronomy and Astrophysics.

“This image will allow us to study the structure of Andromeda and its content in more detail than has ever been possible,” said Fatigoni, a PhD student in the department of physics and astronomy at UBC. “Understanding the nature of physical processes that take place inside Andromeda allows us to understand what happens in our own galaxy more clearly – as if we were looking at ourselves from the outside.”

Prior to this study, no maps capturing such a large region of the sky around the Andromeda Galaxy had ever been made in the microwave band frequencies between one GHz to 22 GHz. In this range, the galaxy’s emission is very faint, making it hard to see its structure. However, it is only in this frequency range that particular features are visible, so having a map at this particular frequency is crucial to understanding which physical processes are happening inside Andromeda.

In order to observe Andromeda at this frequency, the researchers required a single-dish radio telescope with a large effective area. For the study, the scientists turned to the Sardinia Radio Telescope, a 64-metre fully steerable telescope capable of operating at high radio frequencies, located in Italy.

The Sardinia Radio Telescope, located in Sardinia, Italy. Credit: S. Fatigoni et al (2021)

It took 66 hours of observation and consistent data analysis for the researchers to map the galaxy with high sensitivity.

They were then able to estimate the rate of star formation within Andromeda, and produce a detailed map that highlighted the ‘disk of the galaxy,’ as the region where new stars are born.

“By combining this new image with those previously acquired, we have made significant steps forward in clarifying the nature of Andromeda’s microwave emissions and allowing us to distinguish physical processes that occur in different regions of the galaxy,” said Dr. Elia Battistelli, a professor in the department of physics at Sapienza and coordinator of the study.

“In particular, we were able to determine the fraction of emissions due to thermal processes related to the early stations of new star formation, and the fraction of radio signals attributable to non-thermal mechanisms due to cosmic rays that spiral in the magnetic field present in the interstellar medium,” Fatigoni said.

Final image of the Andromeda galaxy after averaging over the whole bandwidth at 6.6 GHz. Credit: S. Fatigoni et al (2021)

For the study, the team also developed and implemented software that allowed them to test new algorithms to identify never-before-examined lower emission sources in the field of view around Andromeda at a frequency of 6.6 GHz.

From the resulting map, researchers were able to identify a catalog of about 100 ‘point sources’ including stars, galaxies and other objects in the background of Andromeda.

Featured image: Radio image of Andromeda galaxy at 6.6 GHz (inset), captured using the Sardinia Radio Telescope in Italy. Credit: S. Fatigoni et al. (2021)

---

Reference: S. Fatigoni et al, Study of the thermal and nonthermal emission components in M 31: the Sardinia Radio Telescope view at 6.6 GHz, Astronomy & Astrophysics (2021). DOI: 10.1051/0004-6361/202040011

---

Provided by UBC