New Species of Dwarf Galaxy in the Galaxy Cluster Ecosystem?

This Hubble Space Telescope image shows the spiral galaxy ESO 137-001, which has been transformed into a "jellyfish galaxy" trailing gaseous tentacles. Credit:NASA, ESA; Acknowledgements: Ming Sun (UAH), and Serge Meunier

Title: Dark-Matter-Free Dwarf Galaxy Formation at the Tips of the Tentacles of Jellyfish Galaxies
Authors: V. Lora et al.
First Author’s Institution: Institute of Nuclear Sciences, Mexico (UNAM)
Status: Published in ApJL

When Jellyfish Fly

Most galaxies are part of a galaxy cluster, which is exactly what it sounds like — a large collection of galaxies that are gravitationally bound to the larger cluster, much like how stars are gravitationally bound to a larger galaxy. In addition to the galaxies themselves, there is also gas between the galaxies in the cluster, referred to as the intracluster medium. When a disk-like galaxy moves through the intracluster medium in a galaxy cluster, some of the gas within the galaxy (the interstellar medium) gets stripped away from the galaxy. This creates long gaseous tails (or, if you will, tentacles), giving the galaxy an uncanny resemblance to a jellyfish!

Jellyfish galaxies, and their tentacles in particular, have been studied for decades. Astronomers have investigated how much of the gas in the tentacles comes from the intracluster medium versus the interstellar medium, as well as where and how star formation occurs within the tentacles. Interestingly, astronomers have found star-forming regions in the tentacles that have similar masses and sizes to ultra-compact dwarf galaxies. Today’s authors look to reproduce those results computationally and better understand how this dwarf galaxy formation channel works.

Hanging On by a Tentacle

The authors use data from the IllustrisTNG50 simulation, a cosmological simulation large enough to form dozens of galaxy clusters with enough resolution to accurately model features such as the arms of spiral galaxies. The authors identify a set of jellyfish galaxies within this simulation, then make additional cuts to:

• ensure the galaxies have obvious tentacles;
• find locations of star formation within the tentacles; and
• eliminate galaxies where tentacle-like features could be due to interactions with other galaxies.

These cuts leave only one galaxy with a mass of ~400 billion solar masses; compare this to the mass of the Milky Way, which is typically reported as ~1 trillion solar masses. (However, a 2023 study found that the Milky Way mass was closer to ~200 billion solar masses.)

The authors identify a star-forming site within one of the tentacles of this galaxy, highlighted in Figure 1. This both supports the observational evidence and suggests that this may be a new type of dwarf galaxy (more on this in a moment). Additionally, by tracking the galaxy’s history prior to the infall, they determine that the galaxy loses gas but not stars. This means that the gas in the tentacle came from the galaxy, but the stars are forming in the tentacle rather than being relocated from the galaxy. This is a consequence of ram-pressure stripping, the primary physical phenomenon that creates the tails of jellyfish galaxies. Another important finding about the dwarf galaxy candidate is that it lies well outside the dark-matter halo of the jellyfish galaxy, which has important ramifications for its status as a dwarf galaxy candidate.

Figure 1: Different visualizations of the selected galaxy. The top panel shows neutral gas (green), dark matter (white), and star formation (rainbow). The bottom panel shows the dark matter (white) and stellar mass (rainbow). The dwarf candidate is circled in magenta in both panels. Credit: Lora et al. 2024

Figure 2: Star formation rate (top panel) and oxygen abundance (proxy for metal concentration, bottom panel) of the ram-pressure-stripped candidate (magenta). Credit: Lora et al. 2024

Dark-Matter-Deficient Dwarfs

The authors perform additional analysis on the dwarf galaxy candidate. First, they determine that the gas and stars are gravitationally bound, meaning that they can be thought of as a single system much like how a galaxy is thought of as a single system. They also look at the dark-matter content of the dwarf galaxy candidate and find that none of it is gravitationally bound, making this a dark-matter-free dwarf galaxy. Furthermore, they estimate the mass and size of the dwarf galaxy candidate to be ~200 million solar masses and ~1–1.5 kiloparsecs. Based on these findings, the authors conclude that this system represents a new kind of dwarf galaxy, which they dub a ram-pressure-stripped dwarf galaxy; additionally, ram-pressure-stripped dwarf galaxies are unique among dwarf galaxies because they lack a dark-matter halo due to their creation via ram pressure stripping.

The authors also analyze the star formation and metallicity of the ram-pressure-stripped dwarf, shown in Figure 2. They find a high star formation rate compared to other star-forming regions created via ram pressure stripping. They also find that the ram-pressure-stripped dwarf is very metal rich compared to other dwarf galaxies of similar size and mass; this is because the jellyfish galaxy is also rich in metals, so the gas stripped into the tentacle to form stars has a higher concentration of metals.

Today’s authors have found evidence of a new type of dwarf galaxy, which they call a ram-pressure-stripped dwarf galaxy. These dwarf galaxies form via ram pressure stripping in the tentacles of jellyfish galaxies and are characterized as being gravitationally self-bound, hosting star formation, and lacking a dark-matter halo. The authors hope to continue studies of ram-pressure-stripped dwarf galaxies, noting that other cosmological simulations that can resolve smaller amounts of mass may lead to more discoveries of ram-pressure-stripped dwarfs with lower masses.

Original astrobite edited by Amaya Sinha

Source: American Astronomical Society/AAS-Nova

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About the author, Brandon Pries:

I am a graduate student in physics at Georgia Institute of Technology (Georgia Tech). I do research in computational astrophysics with John Wise, using machine learning to study the formation and evolution of supermassive black holes in the early universe. I’ve also done extensive research with the IceCube Collaboration as an undergraduate at Michigan State University, studying applications of neural networks to event reconstructions and searching for signals of neutrinos from dark matter annihilation.

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Editor’s Note: Astrobites is a graduate-student-run organization that digests astrophysical literature for undergraduate students. As part of the partnership between the AAS and astrobites, we occasionally repost astrobites content here at AAS Nova. We hope you enjoy this post from astrobites; the original can be viewed at astrobites.org.

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Dwarfs from ELVES: The structure of dwarf satellite galaxies

This composite image reveals electric blue ram pressure stripping streaks seen emanating from ESO 137-001, as well as a giant gas stream that can be seen extending towards the bottom of the frame in X-rays. Credit: NASA/ESA/CXC

Title: ELVES I: Structures of Dwarf Satellites of MW-like Galaxies; Morphology, Scaling Relations, and Intrinsic Shapes
Authors: Scott G. Carlsten et al.
First Author’s Institution: Princeton University

Status: Accepted to ApJ

Dwarf galaxies are thought to be incredibly suggestible; there has been a range of diverse dwarf galaxies observed in our universe, indicating that they are extremely sensitive to their surroundings. The observed differences in sizes, shapes, and colours of dwarf galaxies is believed to be at least in part due to differences in the environment they inhabit. All galaxies are thought to be surrounded by a halo of dark matter (see this astrobite for more details). Many dwarf galaxies are satellite galaxies, meaning that they are found in orbit within a larger host dark matter halo that also typically contains a larger central galaxy (for example, the Small and Large Magellanic Clouds are satellite galaxies, both in orbit of our own Milky Way).

Satellite galaxies are subject to many different interactions with their host dark matter halo. These interactions between a satellite galaxy and its host can have devastating effects on the satellite galaxy itself. For example, their gas content can become extremely disturbed (and sometimes completely removed) by ram pressure stripping, which can eventually bring star formation in the satellite to a halt (see this astrobite for a summary of the seminal paper on ram pressure stripping). Similarly, their stars are subject to tidal stripping, which arises due to differences in the gravitational potential of the satellite galaxy and its host.

Figure 1: Examples of dwarfs visually classified as early-type (ETG) and late-type (LTG). Late-type dwarfs are irregular, with apparent active star formation throughout the galaxy while early-types are smooth and featureless without any star-forming clumps.Credit: Carlsten et al. 2021

Despite the observed diversity of dwarf galaxies, they can broadly be classified into two morphological types: late-type and early-type (see Figure 1 for examples). Late-type galaxies are typically star-forming, whereas early-type galaxies lack star-forming regions and appear smoother than late-types. Today’s paper uses the ongoing Exploration of Local VolumE Satellites (ELVES) Survey to investigate how the structural properties of dwarf galaxies can change depending on the environment and morphology of the galaxy. The galaxies in the ELVES sample are all within the Local Volume (D < 12 Mpc), and are satellite galaxies in orbit of Milky Way-like halos.

Going from a Late-type to an Early-type?

The current picture of dwarf galaxy evolution suggests that early-type dwarfs are formed from late-type dwarfs interacting with a host halo. If this is the case, then early-type dwarfs can be thought of as dwarf galaxies in the last throes of their evolution, and any differences in characteristics of late-type and early-type galaxies could provide insights into the physical mechanisms behind this evolution (such as the removal of star-forming gas through ram pressure stripping).

Figure 2: Log effective radius vs. log stellar mass for the dwarf galaxies in the Local Volume sample. The upper panel displays points for each dwarf galaxy in the sample, with red indicating early-type and blue indicating late-type. The bottom panel shows average trends binned by stellar mass. The dashed lines show the mass-size relations for early-type (red) and late-type (blue) dwarf galaxies of higher stellar mass from the GAMA Survey. [Adapted from Carlsten et al. 2021]

To investigate whether there are any structural differences between early- and late-types, the authors plot the effective radius of the dwarf galaxies in their sample (essentially the galaxy’s size) by their stellar mass. It can be seen from Figure 2 that there is no significant difference between the early- and late-type galaxies at fixed stellar mass. This similarity between late-types and early-types suggests that the physical processes relevant in forming early-type galaxies (such as ram pressure stripping) do not necessarily induce any change in the galaxy’s size. These results indicate that the transformation process from late-type to early-type requires only the removal of the galaxy’s star-forming gas — significant structural change to the galaxy is not necessarily required. Also of note is the difference between the author’s results, where the sample is limited to dwarf galaxies with M_* < 10^8.5 M_⊙ and results for satellite galaxies with higher masses (indicated by the blue and red lines in the bottom panel of Figure 2). The authors suggest that this difference hints that there is a characteristic stellar mass scale, above which additional physical processes may be required to explain the sudden difference in sizes between early- and late-types.

Environmental Effects

The next question the authors aim to answer is: how does the mass of the dwarf galaxy’s host dark matter halo affect the evolution of the dwarf galaxy? To consider this, the authors again compare the sizes of dwarf galaxies. This time, a comparison is made between dwarf galaxies that are orbiting within larger cluster environments and the dwarf galaxies in their Local Volume environment.

Figure 3: The mass–size relations of the cluster (grey) and field (cyan) dwarf samples normalized to the full Local Volume sample (green). At fixed stellar mass, the cluster sample is offset to larger sizes, whereas the isolated field sample is offset to smaller sizes. Field galaxies are isolated dwarf galaxies that have been taken from an auxiliary sample, using additional observational data. Credit: Adapted from Carlsten et al. 2021

As can be seen in Figure 3, dwarf galaxies in cluster environments tend to be slightly larger than dwarf galaxies in the Local Volume at a fixed stellar mass. The authors argue that the observed increase in size is down to more intense tidal stripping and heating of galaxies in extreme cluster environments, which aligns with theoretical expectations. While an ~8% increase in sizes for the dwarfs in cluster environments is observed, the authors note the mass–size relation is strikingly similar between the two environments, especially since the mass of the host dark matter halos differ by a factor of 10. This is perhaps indicative that the exact environment plays a fairly small role in dwarf galaxy evolution — a somewhat surprising result!

In conclusion, today’s authors are able to gain insights into the physics of dwarf galaxy transformation from late-types to early-types, and how these processes vary between the Milky Way-like and cluster environments. The authors comment that a comparison with simulations will be useful in constraining the physics of how dwarf galaxies evolve. Their observational results have quantified the start and end points of the transformation, and simulations may now be able to tie them together to tell the middle part of the story!

Original astrobite edited by Luna Zagorac.

 By Astrobites

Editor’s note: Astrobites is a graduate-student-run organization that digests astrophysical literature for undergraduate students. As part of the partnership between the AAS and astrobites, we occasionally repost astrobites content here at AAS Nova. We hope you enjoy this post from astrobites; the original can be viewed at astrobites.org.

 By Astrobites

Source: American Astronomical Society - ASS NOVA

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A “Jellyfish” Galaxy Swims Into View of NASA’s Upcoming Webb Telescope

Galaxy ESO 137-001 (Visible)

The spiral galaxy ESO 137-001 is an example of a “jellyfish” galaxy, because blue tendrils of star formation stream away from it like jellyfish tentacles. NASA’s Webb Space Telescope will study those sites of star formation to learn more about conditions there. Credits: NASA, ESA

Galaxy ESO 137-001 (Visible and X-ray) 

This composite view of ESO 137-001 includes visible light from Hubble and X-ray light from the Chandra X-ray Observatory (in blue). It reveals a tail of hot gas that has been stripped from the galaxy.  Credits: NASA, ESA, CXC

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Webb will examine clumps of newly formed stars in the galaxy’s tail

As the spiral galaxy ESO 137-001 plunges into a galaxy cluster, gas is being pulled off of it as though it faced a cosmic headwind. Within that gas, stars are forming to create the appearance of giant, blue tentacle-like streamers. Astronomers, puzzled that stars could form within such tumult, plan to use Webb to study this galaxy and its stellar offspring.

If you look at the galaxy ESO 137-001 in visible light, you can see why it’s considered an example of a “jellyfish” galaxy. Blue ribbons of young stars dangle from the galaxy’s disk like cosmic tentacles. If you look at the galaxy in X-ray light, however, you will find a giant tail of hot gas streaming behind the galaxy. After launch, NASA’s James Webb Space Telescope will study ESO 137-001 to learn how the gas is being removed from the galaxy, and why stars are forming within that gaseous tail.

The newly forming stars in the tail are mysterious because processes common in large groups of galaxies should make it difficult for new stars to emerge. Most galaxies live in groups — for example, the Milky Way is a member of the Local Group, which also contains galaxies like Andromeda and the Triangulum spiral. Some galaxies reside in much larger gatherings of hundreds or even thousands of galaxies known as a galaxy cluster. The “jellyfish” galaxy ESO 137-001 is part of a cluster called Abell 3627.

A galaxy cluster isn’t just galaxies surrounded by empty space. The realm between the galaxies is filled with hot, tenuous gas. For galaxies living in the cluster or a wandering galaxy that gets pulled in by the cluster’s gravity, that gas acts like a headwind. That wind can remove gas and dust from the hapless galaxy in a process known as “ram pressure stripping.”

As a result, ram pressure stripping can slow star formation in the affected galaxy. Galaxies need gas to form stars. Eventually, all galaxies run out of gas and star formation stops. Ram pressure stripping can hasten that end.

This is one reason why galaxies in clusters stop forming new stars sooner than their relatives outside of clusters. But, the mechanisms involved are still mysterious.

“Both gas and dust are getting stripped off, but how much and what happens to the stripped material and the galaxy itself are still open questions,” said Stacey Alberts of the University of Arizona, a co-investigator on the project.

A star formation mystery

ESO 137-001 is a spiral galaxy similar in size to the Milky Way, and slightly less massive. Its tail extends across 260,000 light-years of space, almost three times the galaxy’s width. Galactic tails like this are difficult to spot because they are so tenuous. Surprisingly, stars seem to be forming in this tail.

Webb will target sites of star formation at different points along the tail: close to the galaxy, in the middle, and near the end of the tail. Since material at the tail’s end was removed before material close to the galaxy, astronomers can learn how the stripping process changed over time and how that affected conditions to form new stars.

Researchers aren’t sure how stars are able to form at all within the tail since the stripping process should have heated the gas. “We think it’s hard to strip off a molecular cloud that’s already forming stars because it should be tightly bound to the galaxy by gravity. Which means either we’re wrong, or this gas got stripped off and heated up, but then had to cool again so that it could condense and form stars,” explained Alberts.

“Telling these two scenarios apart is one of the things we want to get at,” she added.

Mid-infrared completes the puzzle

The team will examine ESO 137-001 using Webb’s Mid-Infrared Instrument (MIRI). MIRI observes infrared light at wavelengths of 5 to 28 microns, a range known as the mid-infrared. MIRI’s observations will provide 50 times more spatial detail and 20 times better spectral detail than previous work by other infrared observatories.

MIRI is sensitive to light emitted from hydrogen molecules as well as chemical elements like sulfur and oxygen. MIRI also will detect more complex, sooty molecules of carbon and hydrogen known as polycyclic aromatic hydrocarbons (PAHs), which are signposts of star formation. In addition to learning about the composition of gas and dust within these star-forming regions, astronomers will measure the physical conditions of the gas like temperature and density.

The team will combine the new Webb observations with existing data in visible light, X-rays, and at longer far-infrared wavelengths to get a more complete picture of ESO 137-001 and its environment. “Each different wavelength gives you a piece of the puzzle,” said Alberts.

Ultimately, astronomers want to learn more about how stars came to form in the tail. They also want to understand how gas is being stripped from the galaxy, how much is being stripped, and how efficiently it’s being removed. This will provide clues to the eventual fate of ESO 137-001 and the question of whether ram pressure stripping will shut down star formation, leaving behind a dead relic filled with aging, red stars.

The observations described here will be taken as part of Webb’s Guaranteed Time Observation (GTO) program. The GTO program provides dedicated time to the scientists who have worked with NASA to craft the science and instrument capabilities of Webb throughout its development.

The James Webb Space Telescope will be the world's premier space science observatory when it launches in 2021. Webb will solve mysteries of our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it. Webb is an international project led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.

What Is a Galaxy?

Galaxies are concentrations of stars, gas, dust, and dark matter. They come in a variety of shapes and sizes. Some are fated to collide, like the Milky Way and Andromeda. Credits: NASA, and J. Olmsted (STScI). Youtube

Source: NASA's James Webb Space Telescope/News

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MUSE Reveals True Story Behind Galactic Crash

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MUSE view of the ram-pressure stripped galaxy ESO 137-001

 

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MUSE view of the ram-pressure stripped galaxy ESO 137-001

 

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The galaxy ESO 137-001 in the constellation of Triangulum Australe

 

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Wide-field view of the sky around the galaxy ESO 137-001

 

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Hubble and Chandra composite of ESO 137-001

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Zooming in on ESO 137-001

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MUSE shows ESO 137-001 in three dimensions 

The new MUSE instrument on ESO’s Very Large Telescope (VLT) has provided researchers with the best view yet of a spectacular cosmic crash. The new observations reveal for the first time the motion of gas as it is ripped out of the galaxy ESO 137-001 as it ploughs at high speed into a vast galaxy cluster. The results are the key to the solution of a long-standing mystery — why star formation switches off in galaxy clusters.

A team of researchers led by Michele Fumagalli from the Extragalactic Astronomy Group and the Institute for Computational Cosmology at Durham University, were among the first to use ESO’s Multi Unit Spectroscopic Explorer (MUSE) instrument on the VLT. Observing ESO 137-001 — a spiral galaxy 200 million light-years away in the southern constellation of Triangulum Australe (The Southern Triangle) — they were able to get the best view so far of exactly what is happening to the galaxy as it hurtles into the Norma Cluster.

MUSE gives astronomers not just a picture, but provides a spectrum — or a band of colours — for each pixel in the frame. With this instrument researchers collect about 90 000 spectra every time they look at an object, and thereby record a staggeringly detailed map of the motions and other properties of the observed objects [1].

ESO 137-001 is being robbed of its raw materials by a process called ram-pressure stripping, which happens when an object moves at high speed through a liquid or gas. This is similar to how air blows a dog’s hair back when it sticks its head out of the window of a moving car. In this case the gas is part of the vast cloud of very thin hot gas that is enveloping the galaxy cluster into which ESO 137-001 is falling at several million kilometres per hour [2].

The galaxy is being stripped of most of its gas — the fuel needed to make the next generations of young blue stars. ESO 137-001 is in the midst of this galactic makeover, and is being transformed from a blue gas-rich galaxy to a gas-poor red one. Scientists propose that the observed process will help to solve a long-standing scientific riddle.

“It is one of the major tasks of modern astronomy to find out how and why galaxies in clusters evolve from blue to red over a very short period of time,” says Fumagalli. “Catching a galaxy right when it switches from one to the other allows us to investigate how this happens.”

Observing this cosmic spectacle, however, is no mean feat. The Norma Cluster lies close to the plane of our own galaxy, the Milky Way, so it is hidden behind copious amounts of galactic dust and gas.

With the help of MUSE, which is mounted on one of the VLT’s 8-metre Unit Telescopes at the Paranal Observatory in Chile, scientists could not only detect the gas in and around the galaxy, but were able to see how it moves. The new instrument is so efficient that a single hour of observing time was sufficient to obtain a high resolution image of the galaxy as well as the distribution and motion of its gas.

The observations show that the outskirts of ESO 137-001 are already completely devoid of gas. This is a result of the cluster gas — heated to millions of degrees — pushing the cooler gas out of ESO 137-001 as this drives towards the centre of the cluster. This happens first in the spiral arms where the stars and matter are more thinly spread than at the centre, and gravity has only a relatively weak hold over the gas. In the centre of the galaxy, however, the gravitational pull is strong enough to hold out longer in this cosmic tug-of-war and gas is still observed.

Eventually, all of the galactic gas will be swept away into bright streaks behind ESO 137-001 — telltale remnants of this dramatic robbery. The gas that is torn away from the galaxy is mixed with the hot cluster gas to form magnificent tails extending to a distance of over 200 000 light-years. The team had a closer look at these streams of gas to better understand the turbulence created by the interaction.

Surprisingly the new MUSE observations of this gas plume show that the gas continues to rotate in same way the galaxy does, even after being swept out into space. Furthermore, researchers were able to determine that the rotation of stars in ESO 137-001 remains unchanged. This provides further evidence for the cluster gas, not gravity, being responsible for stripping the galaxy [3].

Matteo Fossati (Universitäts-Sternwarte München and Max-Planck-Institut für extraterrestrische Physik, Garching, Germany) and a co-author of the paper concludes: “With the details revealed by MUSE we are getting closer to fully understanding the processes that go on in such collisions. We see the motions of the galaxy and the gas in detail — something that wouldn’t be possible without the new and unique MUSE instrument. These and future observations will help us develop a better idea of what is driving the evolution of galaxies.” 

Notes

[1] MUSE is the first large integral field spectrograph ever installed at an 8-metre telescope. As a comparison, previous studies of ESO 137-001 collected no more than 50 spectra.

[2] The NASA/ESA Hubble Space Telescope has provided a spectacular image of this object — but, unlike MUSE, cannot reveal the motions of the material.

[3] If gravity were to play a role in the stripping process, the researchers would have expected to see disruptions within the galaxy.

 

More Information

This research was presented in a paper entitled “MUSE sneaks a peek at extreme ram-pressure stripping events. I. A kinematic study of the archetypal galaxy ESO137-001” to appear in Monthly Notices of the Royal Astronomical Society on 10 November 2014.

The team is composed of Michele Fumagalli (Extragalactic Astronomy Group and Institute for Computational Cosmology, Durham University, United Kingdom), Matteo Fossati (Universitäts-Sternwarte München and Max-Planck-Institut für extraterrestrische Physik, Garching, Germany), George K. T. Hau (ESO, Santiago, Chile), Giuseppe Gavazzi (Università di Milano-Bicocca, Italy), Richard Bower (Extragalactic Astronomy Group and Institute for Computational Cosmology, Durham University, United Kingdom), Alessandro Boselli (Laboratoire d'Astrophysique de Marseille, France) and Ming Sun (Department of Physics, University of Alabama, USA).

ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 15 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning the 39-metre European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.  

Links

• Research paper
• Photos of the VLT
• Press release on first light of MUSE
• Hubble imaging of ESO 137-001

Contacts

Michele Fumagalli
Institute for Computational Cosmology, Durham University
Durham, United Kingdom
Tel: +44 191 334 3789
Email: michele.fumagalli@durham.ac.uk

Matteo Fossati
Universitäts-Sternwarte München and Max-Planck-Institut für extraterrestrische Physik
Munich, Germany
Tel: +49 89 30000 3890
Email: mfossati@mpe.mpg.de

Richard Hook
ESO education and Public Outreach Department
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Email: rhook@eso.org

Source: ESO

Spiral galaxy spills blood and guts

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New Hubble image of spiral galaxy ESO 137-001

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Hubble and Chandra composite of ESO 137-001

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Videos

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Hubblecast 72: Clues to a cosmic crime

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Zooming in on ESO 137-001

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Panning across ESO 137-001

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3D visualisation of ESO 137-001 (artist’s impression)

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Fade between Hubble and Chandra images of ESO 137-001

This new Hubble image shows spiral galaxy ESO 137-001, framed against a bright background as it moves through the heart of galaxy cluster Abell 3627. This cluster is violently ripping the spiral’s entrails out into space, leaving bright blue streaks as telltale clues to this cosmic crime.

This new Hubble image shows ESO 137-001, a galaxy located in the southern constellation of Triangulum Australe (The Southern Triangle) — a delicate and beautiful spiral galaxy, but with a secret.

This image not only captures the galaxy and its backdrop in stunning detail, but also something more dramatic — intense blue streaks streaming outwards from the galaxy, seen shining brightly in ultraviolet light.

These streaks are actually hot young stars, encased in wispy streams of gas that are being torn away from the galaxy by its surroundings as it moves through space. This violent galactic disrobing is due to a process known as ram pressure stripping — a drag force felt by an object moving through a fluid [1]. The fluid in question here is superheated gas, which lurks at the centres of galaxy clusters.

This image also shows other telltale signs of this process, such as the curved appearance of the disc of gas and dust — a result of the forces exerted by the heated gas. The cluster's drag may be strong enough to bend ESO 137-001, but in this cosmic tug-of-war the galaxy's gravitational pull is strong enough to hold on to the majority of its dust — although some brown streaks of dust displaced by the stripping are visible.

Studying ram pressure stripping helps astronomers to better understand the mechanisms that drive the evolution of galaxies. For example, it will leave this galaxy with very little of the cold gas that is essential for star formation, rendering the galaxy effectively incapable of forming new stars.

ESO 137-001 is part of the Norma Cluster, a cluster of galaxies near the centre of the Great Attractor, a region of space that earned its name by being so massive, and having a gravitational pull so strong, that it is pulling entire galaxy clusters towards it. This region is located around 200 million light-years from our galaxy, the Milky Way. Both our galaxy and its home group, the Local Group, are slowly being hauled towards this mysterious region. Hubble also imaged ESO 137-001's neighbour, ESO 137-002, which is also known to have a hot tail of gas extending outwards into space (potw1302).

Despite being relatively close by cosmic standards, catching even a glimpse of the Norma Cluster is no mean feat. Observed from Earth, the cluster lies close to the plane of the Milky Way and is obscured by a thick smog of cosmic dust. But Hubble is up to the challenge — using new data from Hubble's Wide Field Camera 3 (WFC3).

As with most images from Hubble, this is not just a pretty picture; it tells us a great deal about the harsh environment at the heart of a galaxy cluster, and the fate of galaxies like ESO 137-001 that find passage through it.

A version of this image was submitted to the Hubble's Hidden Treasures image processing competition by contestant Serge Meunier.

Notes

[1] A quick and simple analogy for this effect would be to imagine leaning out of a car window as it travelled quickly along a motorway, or walking within a swimming pool.

Notes for editors

The Hubble Space Telescope is a project of international cooperation between ESA and NASA.
The data for this image comes from HST project 12377, with prinicipal investigator Ming Sun.

More information

Image credit: NASA, ESA
Acknowledgements: Ming Sun (UAH), and Serge Meunier

Links

• Images of Hubble
• NASA release

Contacts

Georgia Bladon
Hubble/ESA
Garching bei München, Germany
Tel: +49-89-3200-6855
Email: gbladon@partner.eso.org

Source: ESA/HUBBLE - Space Telescope

ESO 137-001: Two Tails to Tell

Credit X-ray: NASA/CXC/UVa/M. Sun, et al;

H-alpha/Optical: SOAR (UVa/NOAO /UNC/CNPq-Brazil)/M.Sun et al.

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Two spectacular tails of X-ray emission have been seen trailing behind a galaxy using the Chandra X-ray Observatory. A composite image of the galaxy cluster Abell 3627 shows X-rays from Chandra in blue, optical emission in yellow and emission from hydrogen light -- known to astronomers as "H-alpha" -- in red. The optical and H-alpha data were obtained with the Southern Astrophysical Research (SOAR) Telescope in Chile.

At the front of the tail is the galaxy ESO 137-001. The brighter of the two tails has been seen before and extends for about 260,000 light years. The detection of the second, fainter tail, however, was a surprise to the scientists.

The X-ray tails were created when cool gas from ESO 137-001 (with a temperature of about ten degrees above absolute zero) was stripped by hot gas (about 100 million degrees) as it travels towards the center of the galaxy cluster Abell 3627. What astronomers observe with Chandra is essentially the evaporation of the cold gas, which glows at a temperature of about 10 million degrees. Evidence of gas with temperatures between 100 and 1,000 degrees Kelvin in the tail was also found with the Spitzer Space Telescope.

Galaxy clusters are collections of hundreds or even thousands of galaxies held together by gravity that are enveloped in hot gas. The two-pronged tail in this system may have formed because gas has been stripped from the two major spiral arms in ESO 137-001. The stripping of gas is thought to have a significant effect on galaxy evolution, removing cold gas from the galaxy, shutting down the formation of new stars in the galaxy, and changing the appearance of inner spiral arms and bulges because of the effects of star formation.

The H-alpha data shows evidence for star formation in the tails -- the first unambiguous evidence that star formation can occur when cold gas is stripped out of galaxies as they fall through clusters. The Chandra data also reveal an excess of luminous X-ray point sources around the X-ray tails. Some of them are considered to be young massive binary stars associated with nearby young star clusters, giving more evidence of star formation in the tails. The implication is that a large portion of stars between cluster galaxies can be formed in situ.

The X-ray data also reveal that there is little change in temperature of the hot gas in the tails, and also little change in width of the tails with distance from ESO 137-001. Both of these features present challenges to scientists doing simulations of the galaxy tails.

Fast Facts for ESO 137-001:

Scale: Image is 5 arcmin across
Category: Groups & Clusters of Galaxies
Coordinates: (J2000) RA 16h 13m 25.59s | Dec -60° 45' 43.10
Constellation: Norma
Observation Date: 6/12/2008
Observation Time: 39 hours
Obs. ID: 9518
Color Code: X-ray (Blue); Optical (Yellow); H-alpha (Red)
Instrument: ACIS
References: Sun, M., et al, 2010, ApJ 708 946
Distance Estimate: About 230 million light years