Stellar Explosions and Cosmic Chemistry

Excerpts from the ALCHEMI atlas of the center of NGC 253. The different colors represent the distribution of molecular gas (blue), shocked regions (red), relatively high-density regions (orange), young starbursts (yellow), developed starbursts (magenta), and molecular gas affected by cosmic-ray ionization (cyan). Credit: ALMA (ESO/NAOJ/NRAO), N. Harada et al. Hi-Res File

(Top) Spectra from the ALCHEMI survey. (Bottom) A schematic image of the center of the starburst galaxy, NGC 253, describing locations where various tracer molecular species are enhanced according to the ALCHEMI survey. Credit: ALMA (ESO/NAOJ/NRAO), N. Harada et al. Hi-Res File

Artist’s impression of the center of the starburst galaxy NGC 253

Credit: NRAO/AUI/NSF. Hi-Res File

---

Unveiling the Secrets of Starburst Galaxies with ALMA

Astronomers have discovered the secrets of a starburst galaxy producing new stars at a rate much faster than our Milk Way. This research revealed many different molecules, more than ever seen before in a galaxy like this.

This international research team used the Atacama Large Millimeter/submillimeter Array (ALMA) to observe the center of starburst galaxy NGC 253. Through ALMA’s high sensitivity and angular resolution, the team detected over one hundred molecular species in NGC 253, far more than previously observed in galaxies beyond the Milky Way.

This research was assembled from several papers from the ALMA Comprehensive High-resolution Extragalactic Molecular Inventory (ALCHEMI),a large program led by Sergio Martín of the European Southern Observatory/Joint ALMA Observatory, Nanase Harada of the National Astronomical Observatory of Japan, and Jeff Mangum of the National Radio Astronomy Observatory.

The astronomers found that the center of NGC 253 has a lot of dense gas, which helps make stars. This molecular gas is more than ten times as dense as the gas found in the center of our own Milky Way galaxy. Astronomers also discovered an abundance of complex organic molecules around regions of active star formation. When clouds of gas collide, they create shock waves that make certain molecules easier to see with telescopes like ALMA. The ALCHEMI survey expanded the molecular species atlas outside the Milky Way, doubling the number of identified species.

By employing machine learning, astronomers identified molecules effectively tracing various stages of star formation. This research also observed enhanced species like H3O+ and HOC+ in developed starburst regions, indicating energy output from massive stars, which could inhibit future star formation. NGC 253 has had a lot of stars explode as supernovae, and these powerful bursts of energy make it harder for gas to come together to form new stars.

The ALCHEMI survey provided an atlas of 44 molecular species. By applying a machine-learning technique to this atlas, the researchers were able to identify which molecules are present at specific stages of star formation. Identifying tracers can help guide future ALMA observations, particularly with the anticipated wideband sensitivity upgrade. This upgrade, outlined in the ALMA 2030 Development roadmap, will allow for the simultaneous tracking of multiple tracer molecules, further advancing astronomers understanding of how stars form.

Links

• Read more at ALMA

Source: National Radio Astronomy Observatory (NRAO)/News

---

Featured Image: A Rare X-ray Binary in a Starburst Galaxy

An X-ray view of the dwarf starburst galaxy NGC 4214 created from Chandra X-ray Observatory Data
Credit:Adapted from Lin et al. 2023

Ten million light-years from Earth, a tiny galaxy that glitters with new stars houses a rare kind of binary system. The binary, cataloged as CXOU J121538.2+361921 and referred to simply as X-1, is the brightest X-ray point source in its home galaxy. The system’s bright X-ray light is the result of a star having its atmosphere stolen by a compact companion, like a black hole or a neutron star, creating an extremely hot accretion disk. In a recent research article, a team led by Zikun Lin (Key Laboratory of Optical Astronomy, Chinese Academy of Sciences; University of Chinese Academy of Sciences) used data from the Chandra X-ray Observatory and the Hubble Space Telescope to learn more about this unusual system. The Chandra data, shown to the right, allowed the team to confirm that the binary components eclipse each other every 3.6 hours. The Hubble data, shown above, allowed them to identify the optical counterpart of the X-ray binary for the first time: a blazingly hot blue star that is likely a massive, evolved star with powerful winds and a metal-rich atmosphere. In some tens of millions of years, this star and its companion — the team suspects a black hole, though a neutron star can’t yet be ruled out — will lose their orbital energy to gravitational waves and coalesce in a spectacular cosmic explosion.

By Kerry Hensley

Citation

“On the Short-period Eclipsing High-mass X-Ray Binary in NGC 4214,” Zikun Lin et al 2023 ApJ 954 46. doi:10.3847/1538-4357/ace770

Source: American Astronomical Society/AAS-Nova

---

Featured Image: Outflows from the Silver Coin Galaxy

NGC 253

The Silver Coin Galaxy, also known as NGC 253, is one of the nearest examples of a starburst galaxy — one that forms new stars faster than typical galaxies. In visible light, the nearly edge-on Silver Coin looks like a bright, narrow ellipse mottled with dark dust clouds. X-ray data tell a different story, though, as the image above shows. While the optical emission (H-alpha; green) is confined to the galaxy’s tilted disk, the X-ray emission (blue) extends perpendicular to the disk, tracing immense outflows powered by the galaxy’s fervent star formation. Millimeter emission (red) rounds out the three-color image. Using images and spectra from the Chandra X-ray Observatory, Sebastian Lopez (The Ohio State University) and collaborators investigated the physical properties of the galaxy’s outflows, finding that the galactic winds expel roughly 6 solar masses of gas each year. Spectral analysis revealed that the innermost region of the outflows are chemically enriched, providing a potential source for the metals found in the sparse gas between the Milky Way and its galactic neighbors. For more details about this windy starburst galaxy, be sure to check out the full article linked below!

By Kerry Hensley

Citation

“X-Ray Properties of NGC 253’s Starburst-Driven Outflow,” Sebastian Lopez et al 2023 ApJ 942 108. doi:10.3847/1538-4357/aca65e

Source: American Astronomical Society - AAS Nova

---

The Early Cooling of our Universe

Fig. 1: The Cosmic Microwave Background (left) was released 380,000 years after the Big Bang, and it acts as a background to all galaxies in the Universe. The starburst galaxy HFLS3 is embedded in a large cloud of cold water vapour (middle, indicated in blue), and is observed 880 million years after the Big Bang. Because of its low temperature, the water casts a dark shadow on the Microwave background (zoom-in panel on the left), corresponding to a contrast about 10,000 times stronger than its intrinsic fluctuations of only 0.001% (light/dark spots). © Telescope picture: IRAM/MPIA; galaxy illustration: ESA; microwave background image: ESA and the Planck collaboration; zoom-in panel: Dominik Riechers, Universität zu Köln; image composition: Martina Markus, Universität zu Köln.

Shadow of cosmic water cloud reveals the temperature of the young Universe

An international group of astrophysicists including Axel Weiß from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has developed a new method of measuring the cosmic microwave background temperature of the young Universe only 880 million years after the Big Bang. It is the first time that the temperature of the cosmic microwave background radiation – a relic of the energy released by the Big Bang – has been measured at such an early epoch of the Universe. The prevailing cosmological model assumes that the Universe has cooled off since the Big Bang – and still continues to do so. The model also describes how the cooling process should proceed, but so far it has been directly confirmed only for relatively recent cosmic epochs. The discovery not only sets a very early milestone in the development of the cosmic background temperature, but could also have implications for the enigmatic dark energy.

The result is published in this week’s issue of “Nature”.

The scientists used the NOEMA (Northern Extended Millimeter Array) observatory in the French Alps, the most powerful radio telescope in the Northern Hemisphere, to observe HFLS3, a galaxy showing a massive burst of star formation in a distance corresponding to an age of only 880 million years after the Big Bang. They discovered a screen of cold water gas that casts a shadow on the cosmic microwave background radiation. The shadow appears because the colder water absorbs the warmer microwave radiation on its path towards Earth, and its darkness reveals the temperature difference. As the temperature of the water can be determined from other observed properties of the starburst, the difference indicates the temperature of the Big Bang’s relic radiation, which at that time was about six times higher than in the Universe today.

“Other than proof for cooling, this discovery also shows us that the Universe in its infancy had some quite specific physical characteristics that no longer exist today”, says lead author Prof. Dominik Riechers from the University of Cologne’s Institute of Astrophysics. “Quite early, about 1.5 billion years after the Big Bang, the cosmic microwave background was already too cold for this effect to be observable. We have therefore a unique observing window that opens up to a very young Universe only”, he continues. In other words, if a galaxy with otherwise identical properties as HFLS3 were to exist today, the water shadow would not be observable because the required contrast in temperatures would no longer be available.

“This important milestone not only confirms the expected cooling trend for a much earlier epoch than has previously been possible, but could also have direct implications for the nature of the elusive dark energy”, says Dr Axel Weiß from the Max Planck Institute for Radio Astronomy (MPIfR) in Bonn, the second author of the study. He further explains: “That is to say, an expanding Universe in which the density of dark energy does not change.” Dark energy is thought to be responsible for the accelerated expansion of the Universe over the past few billion years, but its properties remain poorly understood because it cannot be directly observed with the currently available facilities and instruments. However, its properties influence the evolution of cosmic expansion, and hence the cooling rate of the Universe over cosmic time. Based on this experiment, the properties of dark energy remain – for now - consistent with those of Einstein’s ’cosmological constant’.

Having discovered one such cold water cloud, the team is now setting out to find many more across the sky. Their aim is to map out the cooling of the Big Bang echo within the first 1.5 billion years of cosmic history. ‘This new technique provides important new insights into the evolution of the Universe, including the properties of dark energy, which are very difficult to constrain otherwise at such early epochs,’ Riechers said.

‘Our team is already following this up with NOEMA by studying the surroundings of other galaxies”, says co-author and NOEMA project scientist Dr Roberto Neri. “With the expected improvements in precision from studies of larger samples of water clouds, it remains to be seen if our current, basic understanding of dark energy holds.’

Fig. 2: Antennas of the NOEMA observatory in the French Alps (MPG/Germany, CNRS/France, IGN/Spain). Using their unique resolving power, astronomers probed the early Universe and found a new method for measuring the cosmic microwave background’s temperature. © IRAM, A. Rambaud

Background information:

NOEMA, the “NOrthern Extended Millimeter Array”, is the most powerful radio telescope in the Northern Hemisphere. The observatory operates at over 2500 meters above sea level on one of the most extended European high-altitude sites, the Plateau de Bure in the French Alps.

The telescope is operated by the Institut de Radioastronomie Millimétrique (IRAM) and is financed by the Max-Planck Society (Germany), the Centre National de Recherche Scientifique (France) and the Instituto Geografico Nacional (Spain).

Dominik Riechers (University of Cologne) conducted the study together with his colleagues Axel Weiß (Max Planck Institute for Radio Astronomy, MPIfR), Fabian Walter (Max Planck Institute for Astronomy, MPIA), Christopher L. Carilli (National Radio Astronomy Observatory, NRAO), Pierre Cox (Centre National de Recherche Scientifique, CNRS), Roberto Decarli (INAF -Osservatorio di Astrofisica e Scienza dello Spazio), and Roberto Neri (Institut de RadioAstronomie Millimétrique, IRAM).

The study has been funded by the US National Science Foundation (NSF), the Alexander von Humboldt Foundation (AvH), the Max-Planck-Society (MPG), Centre national de la recherche scientifique (CNRS), and Instituto Geográfico Nacional (IGN).

---

Contact:

Dr. Axel Weiß
tel: +49 228 525-273
Max-Planck-Institut für Radioastronomie, Bonn

Prof. Dr. Dominik Riechers
tel: +49 221 470-76027
Astrophysik, I. Physik, Universität zu Köln

Dr. Norbert Junkes
Press and Public Outreach
tel: +49 228 525-399
Max Planck Institute for Radio Astronomy, Bonn

Original Paper:

Microwave Background Temperature at Redshift 6.34 from H2O Absorption

D. Riechers et al., 2022, Nature, 3. Februar 2022 (DOI: 10.1038/s41586-021-04294-5), after the embargo expires. Requests under embargo to press@nature.com

Source: Max Planck for Radio Astronomy/Press Releases

---

A new type of supernova illuminates an old mystery

Figure 1: Las Cumbres Observatory and the Hubble Space Telescope color composite of the electron-capture supernova 2018zd (the large white dot on the right) and the host starburst galaxy NGC 2146 (towards the left). (Credit: NASA/STScI/J. DePasquale; Las Cumbres Observatory)

Figure 2: Artist impressions of a super-asymptotic giant branch star (left) and its core (right) made up of oxygen (O), neon (Ne), and magnesium (Mg). A super-asymptotic giant branch star is the end state of stars in a mass range of around 8-10 solar masses, whose core is pressure supported by electrons (e-). When the core becomes dense enough, neon and magnesium start to eat up electrons (so called electron-capture reactions), reducing the core pressure and inducing a core-collapse supernova explosion. (Credit: S. Wilkinson; Las Cumbres Observatory)

A worldwide team of researchers has discovered the first convincing evidence for a new type of stellar explosion, theorized 40 years ago by Kavli Institute for the Physics and Mathematics Senior Scientist Ken’ichi Nomoto; the new study was published in Nature Astronomy on June 28.

Electron-capture supernovae Nomoto theorized in the early 1980s are thought to arise from the explosions of massive super-asymptotic giant branch (SAGB) stars, for which there has also been scant evidence. The new discovery sheds light on the thousand-year mystery of the supernova from 1054AD that was seen all over the world in the daytime, before eventually becoming the Crab Nebula.

"I am very pleased that the electron-capture supernova has finally been discovered, which my colleagues and I predicted to exist, and connected to the Crab Nebula, 40 years ago. I very much appreciate the great efforts of observations that confirmed the old theoretical predictions, which is a wonderful example of the combination between observation and theory," said Nomoto.

Historically, there have been two main supernova types. One is the thermonuclear supernova - the explosion of a white dwarf star that gains matter in a binary system. These white dwarfs are the dense cores of ash that remain after a low-mass star (one up to about 8 times the mass of the Sun) reaches the end of its life. Another main supernova type is a core-collapse supernova where a massive star, one more than about 10 times the mass of the Sun, runs out of nuclear fuel and has its iron core collapse, creating a black hole or neutron star. The electron-capture supernovae are in between these two types of supernovae. They push the boundary of core-collapse supernovae down to about 8 solar masses and explode by a different mechanism.

While gravity is always trying to crush a star, what keeps most stars from collapsing is that you can’t pack the atoms in their cores any tighter. But in an electron-capture supernova, the star is so massive that some of the electrons in atoms in the core get smashed into their atomic nuclei, called an electron capture. This causes the core of the star to buckle under its own weight and collapse, resulting in an electron-capture supernova.

Using recently updated electron-capture rates, Nomoto and collaborators had been able to reconfirm their theoretical predictions.

Over the decades, theorists including Nomoto have formulated predictions of what to look for in an electron-capture supernova and their SAGB star progenitors. The stars should have a lot of mass, lose much of it before exploding, and this mass near the dying star should be on an unusual chemical composition. Then the electron-capture supernova should be weak, have little radioactive fallout, and have neutron-rich elements in the core.

The new study, led by Daichi Hiramatsu, a graduate student at the University of California, Santa Barbara, and Las Cumbres Observatory, and a core member of the Global Supernova Project, a worldwide team of researchers using dozens of telescopes around and above the globe. The team found that the supernova SN 2018zd had many unusual characteristics, some of which were seen for the first time in a supernova.

It helped that the supernova was relativity nearby, only 31 million light-years away, in the galaxy NGC 2146. This allowed the team to examine archival images taken prior to the explosion from the Hubble Space telescope and to detect the likely progenitor star before it exploded. The observations were consistent with another recently identified SAGB star in the Milky Way, but inconsistent with models of the progenitors of normal core-collapse supernovae, red supergiants.

The study looked through all published data on supernovae, and found that while some supernovae had a few of the indicators predicted for electron capture supernovae, only SN 2018zd had all six – an apparent SAGB progenitor, strong pre-supernova mass loss, an unusual stellar chemical composition, a weak explosion, little radioactivity, and a neutron-rich core.

The leader of the study, Daichi Hiramatsu said, “We started by asking ‘what’s this weirdo?’ Then we examined every aspect of SN 2018zd and realized that all of them can be explained in the electron-capture scenario.”

The new discoveries also illuminate some mysteries of the most famous supernova of the past. In 1054 AD a supernova happened in the Milky Way 

Galaxy, and according to Chinese and Japanese records was so bright that it could be seen in the daytime for 23 days, and at night nearly for two years. The resulting remnant, the Crab Nebula, has been studied in great detail. It was previously the best candidate for an electron-capture supernova, but this was uncertain partly because the explosion happened nearly a thousand years ago. The new result increases the confidence that SN 1054 was an electron-capture supernova. It also explains why that supernova was relatively bright compared to the models. Its luminosity was probably artificially enhanced by the supernova ejecta colliding with material cast off by the progenitor star as was seen in SN 2018zd.

---

Paper details
Journal: Nature Astronomy
Title: The electron-capture origin of supernova 2018zd

Authors: 

Daichi Hiramatsu (1,2), D. Andrew Howell (1,2), Schuyler D. Van Dyk (3), Jared A. Goldberg (2), Keiichi Maeda (4,5), Takashi J. Moriya (6,7), Nozomu Tominaga (8, 5, 6), Ken’ichi Nomoto (5), Griffin Hosseinzadeh (9), Iair Arcavi (10,11), Curtis McCully (1,2), Jamison Burke (1,2), K. Azalee Bostroem (12), Stefano Valenti (12), Yize Dong (12), Peter J. Brown (13), Jennifer E. Andrews (14), Christopher Bilinski (14), G. Grant Williams (14,15), Paul S. Smith (14), Nathan Smith (14), David J. Sand (14), Gagandeep S. Anand (16,17), Chengyuan Xu (18), Alexei V. Filippenko (19,20), Melina C. Bersten (21,22, 5), Gastón Folatelli (21,22, 5), Patrick L. Kelly (23), Toshihide Noguchi (24) and Koichi Itagaki (25)

Author affiliations:

1. Las Cumbres Observatory, Goleta, CA, USA.
2. Department of Physics, University of California, Santa Barbara, CA, USA.
3. Caltech/Spitzer Science Center, Caltech/IPAC, Pasadena, CA, USA.
4. Department of Astronomy, Kyoto University, Kyoto, Japan.
5. Kavli Institute for the Physics and Mathematics of the Universe (WPI), The University of Tokyo Institutes for Advanced Study, The University of Tokyo, Kashiwa, Japan.
6. National Astronomical Observatory of Japan, National Institutes of Natural Sciences, Mitaka, Japan.
7. School of Physics and Astronomy, Faculty of Science, Monash University, Clayton, Victoria, Australia.
8. Department of Physics, Faculty of Science and Engineering, Konan University, Hyogo, Japan.
9. Center for Astrophysics ∣ Harvard & Smithsonian, Cambridge, MA, USA.
10. The School of Physics and Astronomy, Tel Aviv University, Tel Aviv, Israel.
11. CIFAR Azrieli Global Scholars program, CIFAR, Toronto, Ontario, Canada.
12. Department of Physics, University of California, Davis, CA, USA.
13. Mitchell Institute for Fundamental Physics and Astronomy, Texas A&M University, College Station, TX, USA.
14. Steward Observatory, University of Arizona, Tucson, AZ, USA.
15. MMT Observatory, Tucson, AZ, USA.
16. Infrared Processing and Analysis Center, California Institute of Technology, Pasadena, CA, USA.
17. Institute for Astronomy, University of Hawai‘i, Honolulu, HI, USA.
18. Media Arts and Technology, University of California, Santa Barbara, CA, USA.
19. Department of Astronomy, University of California, Berkeley, CA, USA.
20. Miller Institute for Basic Research in Science, University of California, Berkeley, CA, USA.
21. Instituto de Astrofísica de La Plata (IALP), CONICET, Argentina.
22. Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata, La Plata, Argentina.
23. School of Physics and Astronomy, University of Minnesota, Minneapolis, MN, USA.
24. Noguchi Astronomical Observatory, Katori, Japan.
25. Itagaki Astronomical Observatory, Yamagata, Japan.

DOI: https://doi.org/10.1038/s41550-021-01384-2 (Posted on June 28, 2021)

Preprint (arXiv.org page)
Paper abstract (Nature Astronomy)

Research contact 

Ken’ichi Nomoto 
Senior Scientist
Kavli Institute for the Physics and Mathematics of the Universe, University of Tokyo
E-mail: nomoto@astron.s.u-tokyo.ac.jp

Media contact

Motoko Kakubayashi
Press officer 
Kavli Institute for the Physics and Mathematics of the Universe, The University of Tokyo
E-mail: press@ipmu.jp
TEL: 080-4056-2767

 Source:Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU)

---

It Isn’t Gatorade Quenching This Galaxy

This Hubble image of the Antennae galaxies provides an example of a starburst: a galaxy undergoing a sudden burst of intense star formation. [NASA/ESA/Hubble Heritage Team/B. Whitmore/James Long]

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.

Title: Stellar and Molecular Gas Rotation in a Recently Quenched Massive Galaxy at z ∼ 0.7
Authors: Qiana Hunt et al.
First Author’s Institution: Princeton University
Status: Published in ApJL

We know that as they age, galaxies transition from blue, star-forming disks to red, quiescent ellipticals, but the stages of evolution and the process of stopping star formation (often called quenching) are still mysterious. One clue to answering these questions may be post-starburst galaxies, or galaxies that recently experienced a period of intense star formation and are now calm and quiet. The authors of today’s paper explore the properties of the stars and gas in a post-starburst galaxy to explain what mechanisms may have stopped the star formation.

The Starting Line-Up

Post-starburst galaxies are generally full of A-type stars. This means their period of star formation must have stopped a few billion years ago, within the lifetime of main sequence A-type stars. The quenching mechanism for star formation (basically, whatever turns it off) is thought to leave a signature, but that signature deteriorates over time, so it is essential to look at galaxies right after their star formation stops.

SDSS J0912+1523 is a recent and unusual post-starburst galaxy. Its molecular gas mass is around 30% of the stellar mass, much higher than other similar galaxies, which makes it an interesting target. Figure 1 shows the galaxy. On the left is the flux map, which shows the brightest portions of the galaxy in green. There are two main peaks at the center of the galaxy, which might indicate that the galaxy has two cores. On the right is the galaxy separated into spatial bins, with different shaded grey regions representing different bins that will be used later. The flux contours are overlaid to again show the brightest portion, and the rightmost squiggly line shows the combination of flux and noise across the galaxy.

Figure 1: Left: The flux map of SDSS J0912+1523, a post-starburst galaxy. Green represents higher flux, while dark blue represents lower flux. The two central peaks in the flux represent two possible cores. Right: The galaxy sectioned into bins (differing shades of grey) with flux contours overlaid in the same colors as in the left plot. The purple line on the right side shows the combination of flux and noise across the galaxy. [Hunt et al. 2020] 

Moving As A Team

The authors of today’s paper used spectroscopy from Gemini Observatory to look at the properties of stars in the galaxy. They looked for oxygen emission lines that generally indicate star formation and found none, which is to be expected for a quenched galaxy. The authors did, however, find lots of hydrogen Balmer absorption lines, because A-type stars have very strong Balmer lines in their spectra. The depth of those lines can actually be used as a proxy for stellar age. The deeper the absorption line, the more recent the star formation episode.

To quantify how deep the Balmer lines were in each spectra, the authors used an equivalent width. When an absorption line dips below the continuum, there is a certain area between the curve and the continuum. The equivalent width is how much of the continuum (in this case in Angstroms) it would take to make a rectangle with that same area underneath. The equivalent widths in the center of the galaxy can be seen in the top row of Figure 2. On the left, the figure shows the values for the equivalent width with position in the galaxy, while on the right it shows the equivalent width with distance from the center of the galaxy. The equivalent width doesn’t change much within the inner part of the galaxy, which means that all the stars are probably from a common population that formed at the same time.

The spectra were also used to find velocities and velocity dispersions, as shown in the second and third rows of Figure 2. The velocity map and trend with distance from the center of the galaxy shows that the galaxy is clearly rotating, as one side is moving away from us and one side is moving towards us. The consistency in the velocity dispersion indicates that the two cores (the two peaks in intensity that we saw above) are the same galaxy rotating as a single object. The authors suggest the two cores might be remnants of a galaxy merger or a single core with a lane of dust obscuring part of it.

Figure 2: Top row: The first column shows the equivalent width of the hydrogen Balmer absorption line for bins in the center region of the galaxy. Larger values correspond to more recent star formation. The second column shows the equivalent width with distance from the center of the galaxy, color-coded by signal-to-noise. Middle row: Velocity within binned regions of the galaxy and velocity with distance from the center. The galaxy is clearly rotating, with one side blueshifted and the other redshifted. Bottom row: The same as seen in the other rows, but for velocity dispersion. [Hunt et al. 2020]

Subbing In A New Player

The authors of today’s paper also compared their findings to ALMA data that shows the galaxy’s molecular gas content. Figure 3 shows the comparison of stellar (left) to molecular gas (right) velocities. The stellar velocities very closely resemble the molecular gas velocity, so the stars and gas are likely rotating together.

Figure 3. The velocity map for stellar velocity from this paper (the same as in Figure 2) compared to cold molecular gas in the galaxy (from ALMA data). The similarity indicates that the stars and the gas are rotating together. [Hunt et al. 2020]

Hydrating A Galaxy

So what does this information tell us about the star-formation quenching mechanism? There are a lot of ideas about what might stop star formation. Galaxy mergers might heat up gas and prevent it from collapsing into stars. Gas might fall to the center of galaxies, creating star formation there but leaving an empty outer part of the galaxy, or it might get ejected altogether in an outflow. Each of these scenarios is expected to result in a certain amount of velocity dispersion and cold molecular gas. And this galaxy? Because of its large molecular gas content and stable velocity dispersion, it doesn’t fit well with any of these scenarios. Today’s authors suggest that something else might be at play — a type of quenching where the disk of a galaxy stabilizes itself from collapse, the very thing that causes star formation.

This target is a very interesting example of the transition from star-forming to quiescent galaxies. Continuing to study subjects like it will allow astronomers to determine how galaxies become red and dead.

About the author, Ashley Piccone: 

I am a second year PhD student at the University of Wyoming, where I use polarimetry and spectroscopy to study the magnetic field and dust around bowshock nebulae. I love science communication and finding new ways to introduce people to astronomy and physics. In addition to stargazing at the clear Wyoming skies, I also enjoy backpacking, hiking, running and skiing.

Related Journal Articles

• Massive Quenched Galaxies at z ∼ 0.7 Retain Large Molecular Gas Reservoirs doi: 10.3847/2041-8213/aa85dc
• Spatially Resolved Stellar Kinematics from LEGA-C: Increased Rotational Support in z ∼ 0.8 Quiescent Galaxies doi: 10.3847/1538-4357/aabc55
• Molecular Gas Contents and Scaling Relations for Massive, Passive Galaxies at Intermediate Redshifts from the LEGA-C Survey doi: 10.3847/1538-4357/aac438
• Caught in the Act: Gas and Stellar Velocity Dispersions in a Fast Quenching Compact Star-Forming Galaxy at z~1.7 doi: 10.3847/0004-637X/820/2/120
• Resolving Quiescent Galaxies at z ≳ 2. II. Direct Measures of Rotational Support doi: 10.3847/1538-4357/aacd4f

 By Susanna Kohler

Source: American Astronomical Society (AAS) Nova

---

The Detection of a Molecular Outflow in a Primeval Starburst Galaxy

Figure 1: Absorption profile of the two water transitions observed towards the far-infrared continuum emission of the distant starburst galaxy (SPT 0346-52).

Figure 2. Molecular outflow rate (Ṁ) as a function of star formation rate (SFR) for galaxies with detected molecular outflows. Outflows driven by AGNs are shown by diamonds, while those driven by starbursts are shown by star symbols. Each object is coloured according to its redshift. The range and average of best-fit outflow rates of our object (SPT 0346-52) are shown. The molecular outflow detected in this work is in the most powerful starburst. Additional data include both low-redshift (z~1.5-5.3) sources. A representative uncertainty for all low-redshift sources (±0.3 dex) is shown for one such source.

Using the Atacama Large Millimeter/submillimeter Array, a team led by scientists from the Kavli Institute have observed two water absorption lines towards a starburst galaxy (i.e., forming stars at a rate ~4000x faster than the Milky Way) in the early Universe, or about one billion years after the Big Bang, finding evidence for outflowing gas (Figure 1).

The distinct shape of these blueshifted water lines, in addition to the extremely hot and dense environments required for their detection, indicates that they originate from a massive nuclear outflow.

When the outflow rate and star formation rate of this object are compared to those of local galaxies and other high-redshift objects (see Figure 2), it is apparent that the outflow detected here is at the highest redshift and originates from the object with the highest star formation rate. However, the outflow rate is much less than the star formation rate, suggesting that this outflow does not represent a dominant form of mass loss in this system. Thus, the galaxy is likely undergoing a period of runaway star formation.

This work was led by Gareth Jones, a postdoctoral research associate at the Kavli Institute and the results has been published in Astronomy & Astrophysics Letters:

• Online paper: https://www.aanda.org/articles/aa/abs/2019/12/aa36989-19/aa36989-19.html
• arxiv link: https://arxiv.org/abs/1911.09967

Source: Kavli Institute for Cosmology, Cambridge (KICC)/News

---

Galactic Wind Provides Clues to Evolution of Galaxies

The magnetic field lines of the the Cigar Galaxy (also called M82) appear in this composite image. The lines follow the bipolar outflows (red) generated by exceptionally high rates of star formation. Credit: NASA/SOFIA/E. Lopez-Rodiguez; NASA/Spitzer/J. Moustakas et al.  › Full image and caption

The Cigar Galaxy (also known as M82) is famous for its extraordinary speed in making new stars, with stars being born 10 times faster than in the Milky Way. Now, data from the Stratospheric Observatory for Infrared Astronomy, or SOFIA, have been used to study this galaxy in greater detail, revealing how material that affects the evolution of galaxies may get into intergalactic space.

Researchers found, for the first time, that the galactic wind flowing from the center of the Cigar Galaxy (M82) is aligned along a magnetic field and transports a very large mass of gas and dust - the equivalent mass of 50 million to 60 million Suns. 

"The space between galaxies is not empty," said Enrique Lopez-Rodriguez, a Universities Space Research Association (USRA) scientist working on the SOFIA team. "It contains gas and dust - which are the seed materials for stars and galaxies. Now, we have a better understanding of how this matter escaped from inside galaxies over time." 

Besides being a classic example of a starburst galaxy, which means it is forming an extraordinary number of new stars compared with most other galaxies, M82 also has strong winds blowing gas and dust into intergalactic space. Astronomers have long theorized that these winds would also drag the galaxy's magnetic field in the same direction, but despite numerous studies, there has been no observational proof of the concept.

Researchers using the airborne observatory SOFIA found definitively that the wind from the Cigar Galaxy not only transports a huge amount of gas and dust into the intergalactic medium, but also drags the magnetic field so it is perpendicular to the galactic disc. In fact, the wind drags the magnetic field more than 2,000 light-years across - close to the width of the wind itself.

"One of the main objectives of this research was to evaluate how efficiently the galactic wind can drag along the magnetic field," said Lopez-Rodriguez. "We did not expect to find the magnetic field to be aligned with the wind over such a large area." 

These observations indicate that the powerful winds associated with the starburst phenomenon could be one of the mechanisms responsible for seeding material and injecting a magnetic field into the nearby intergalactic medium. If similar processes took place in the early universe, they would have affected the fundamental evolution of the first galaxies.

The results were published in January 2019 in the Astrophysical Journal Letters.

SOFIA's newest instrument, the High-resolution Airborne Wideband Camera-Plus, or HAWC+, uses far-infrared light to observe celestial dust grains, which align along magnetic field lines. From these results, astronomers can infer the shape and direction of the otherwise invisible magnetic field. Far-infrared light provides key information about magnetic fields because the signal is clean and not contaminated by emission from other physical mechanisms, such as scattered visible light.

"Studying intergalactic magnetic fields - and learning how they evolve - is key to understanding how galaxies evolved over the history of the universe," said Terry Jones, professor emeritus at the University of Minnesota, in Minneapolis, and lead researcher for this study. "With SOFIA's HAWC+ instrument, we now have a new perspective on these magnetic fields."

The HAWC+ instrument was developed and delivered to NASA by a multi-institution team led by the Jet Propulsion Laboratory. JPL scientist and HAWC+ Principal Investigator Darren Dowell, along with JPL scientist Paul Goldsmith, were part of the research team using HAWC+ to study the Cigar Galaxy.

SOFIA, the Stratospheric Observatory for Infrared Astronomy, is a Boeing 747SP jetliner modified to carry a 106-inch diameter telescope. It is a joint project of NASA and the German Aerospace Center, DLR. NASA's Ames Research Center in California's Silicon Valley manages the SOFIA program, science and mission operations in cooperation with the Universities Space Research Association headquartered in Columbia, Maryland, and the German SOFIA Institute (DSI) at the University of Stuttgart. The aircraft is maintained and operated from NASA's Armstrong Flight Research Center Hangar 703, in Palmdale, California.

News Media Contact

Calla Cofield
Jet Propulsion Laboratory, Pasadena, Calif.
626-808-2469
calla.e.cofield@jpl.nasa.gov

Written by Kassandra Bell and Arielle Moullet, USRA SOFIA Science Center

Source: JP-Caltech/News

---

Stuck in the middle

NGC 2655
Credit: ESA/Hubble & NASA, A. Fillipenko

This pretty, cloud-like object may not look much like a galaxy — it lacks the well-defined arms of a spiral galaxy, or the reddish bulge of an elliptical — but it is in fact something known as a lenticular galaxy. Lenticular galaxies sit somewhere between the spiral and elliptical types; they are disc-shaped, like spirals, but they no longer form large numbers of new stars and thus contain only ageing populations of stars, like ellipticals. 

NGC 2655’s core is extremely luminous, resulting in its additional classification as a Seyfert galaxy: a type of active galaxy with strong and characteristic emission lines. This luminosity is thought to be produced as matter is dragged onto the accretion disc of a supermassive black hole sitting at the centre of NGC 2655. The structure of NGC 2655’s outer disc, on the other hand, appears calmer, but it is oddly-shaped. The complex dynamics of the gas in the galaxy suggest that it may have had a turbulent past, including mergers and interactions with other galaxies.

NGC 2655 is located about 80 million light-years from Earth in the constellation of Camelopardalis (The Giraffe). Camelopardalis contains many other interesting deep-sky objects, including the open cluster NGC 1502, the elegant Kemble’s Cascade asterism, and the starburst galaxy NGC 2146.

Source: ESA/Hubble/Potw

A double discovery

IC 39, NGC 178

Credit: ESA/Hubble & NASA

NGC 178 may be small, but it packs quite a punch. Measuring around 40 000 light-years across, its diameter is less than half that of the Milky Way, and it is accordingly classified as a dwarf galaxy. Despite its diminutive size, NGC 178 is busy forming new stars. On average, the galaxy forms stars totalling around half the mass of the Sun per year — enough to label it a starburst galaxy.

The galaxy’s discovery is an interesting, and somewhat confusing, story. It was originally discovered by American astronomer Ormond Stone in 1885 and dubbed NGC 178, but its position in the sky was recorded incorrectly — by accident the value for the galaxy’s right ascension (which can be thought of as the celestial equivalent of terrestrial longitude) was off by a considerable amount.

In the years that followed NGC 178 was spotted again, this time by French astronomer Stéphane Javelle. As no catalogued object occupied that position in the sky, Javelle believed he had discovered a new galaxy and entered it into the expanded Index Catalogue under the name IC 39. Later, American astronomer Herbert Howe also observed the object and corrected Stone’s initial mistake.

Many years later, astronomers finally noticed that NGC 178 and IC 39 were actually the same object!

This image of NGC 178 comprises data gathered by the Wide Field Planetary Camera 2 aboard the NASA/ESA Hubble Space Telescope.

Source: ESA/Hubble/Potw

A distorted duo Credit: ESA/Hubble & NASA

IC 1727, UGC 1249

Credit:  ESA/Hubble & NASA

Gravity governs the movements of the cosmos. It draws flocks of galaxies together to form small groups and more massive galaxy clusters, and brings duos so close that they begin to tug at one another. This latter scenario can have extreme consequences, with members of interacting pairs of galaxies often being dramatically distorted, torn apart, or driven to smash into one another, abandoning their former identities and merging to form a single accumulation of gas, dust, and stars.

The subject of this NASA/ESA Hubble Space Telescope image, IC 1727, is currently interacting with its near neighbour, NGC 672 (which is just out of frame). The pair’s interactions have triggered peculiar and intriguing phenomena within both objects — most noticeably in IC 1727. The galaxy’s structure is visibly twisted and asymmetric, and its bright nucleus has been dragged off-centre. 

In interacting galaxies such as these, astronomers often see signs of intense star formation (in episodic flurries known as starbursts) and spot newly-formed star clusters. They are thought to be caused by gravity churning, redistributing, and compacting the gas and dust. In fact, astronomers have analysed the star formation within IC 1727 and NGC 672 and discovered something interesting — observations show that simultaneous bursts of star formation occurred in both galaxies some 20 to 30 and 450 to 750 million years ago. The most likely explanation for this is that the galaxies are indeed an interacting pair, approaching each other every so often and swirling up gas and dust as they pass close by.

Source: ESA/Hubble/Potw

A galaxy fit to burst

NGC 3125

Credit: ESA/Hubble & NASA

Acknowledgement: Judy Schmidt (Geckzilla)

This NASA/ESA Hubble Space Telescope image reveals the vibrant core of the galaxy NGC 3125. Discovered by John Herschel in 1835, NGC 3125 is a great example of a starburst galaxy — a galaxy in which unusually high numbers of new stars are forming, springing to life within intensely hot clouds of gas.

Located approximately 50 million light-years away in the constellation of Antlia (The Air Pump), NGC 3125 is similar to, but unfathomably brighter and more energetic than, one of the Magellanic Clouds.    Spanning 15 000 light-years, the galaxy displays massive and violent bursts of star formation, as shown by the hot, young, and blue stars scattered throughout the galaxy’s rose-tinted core. Some of these clumps of stars are notable — one of the most extreme Wolf–Rayet star clusters in the local Universe, NGC 3125-A1, resides within NGC 3125.

Despite their appearance, the fuzzy white blobs dotted around the edge of this galaxy are not stars, but globular clusters. Found within a galaxy’s halo, globular clusters are ancient collections of hundreds of thousands of stars. They orbit around galactic centres like satellites — the Milky Way, for example, hosts over 150 of them.

Source: ESA/Hubble - Space Telescope

A lonely birthplace

MCG+07-33-027 

Credit: ESA/Hubble & NASA and N. Grogin (STScI)

This image was taken by the NASA/ESA Hubble Space Telescope’s Advanced Camera for Surveys (ACS), and shows a starburst galaxy named MCG+07-33-027. This galaxy lies some 300 million light-years away from us, and is currently experiencing an extraordinarily high rate of star formation — a starburst. Normal galaxies produce only a couple of new stars per year, but starburst galaxies can produce a hundred times more than that! As MCG+07-33-027 is seen face-on, the galaxy’s spiral arms and the bright star-forming regions within them are clearly visible and easy for astronomers to study. 

In order to form newborn stars, the parent galaxy has to hold a large reservoir of gas, which is slowly depleted to spawn stars over time. For galaxies in a state of starburst, this intense period of star formation has to be triggered somehow — often this happens due to a collision with another galaxy. 

MCG+07-33-027, however, is special; while many galaxies are located within a large cluster of galaxies, MCG+07-33-027 is a field galaxy, which means it is rather isolated. Thus, the triggering of the starburst was most likely not due to a collision with a neighbouring or passing galaxy and astronomers are still speculating about the cause.

Source: ESA/Hubble - Space Telescope

Bursting at the seams

NGC 1569

Credit: ESA/Hubble & NASA, Aloisi, Ford
Acknowledgement: Judy Schmidt (Geckzilla)

This NASA/ESA Hubble Space Telescope image reveals the iridescent interior of one of the most active galaxies in our local neighbourhood — NGC 1569, a small galaxy located about eleven million light-years away in the constellation of Camelopardalis (The Giraffe).

This galaxy is currently a hotbed of vigorous star formation. NGC 1569 is a starburst galaxy, meaning that — as the name suggests — it is bursting at the seams with stars, and is currently producing them at a rate far higher than that observed in most other galaxies. For almost 100 million years, NGC 1569 has pumped out stars over 100 times faster than the Milky Way!

As a result, this glittering galaxy is home to super star clusters, three of which are visible in this image — one of the two bright clusters is actually  the superposition of two massive clusters. Each containing more than a million stars, these brilliant blue clusters reside within a large cavity of gas carved out by multiple supernovae, the energetic remnants of massive stars.

In 2008, Hubble observed the galaxy's cluttered core and sparsely populated outer fringes. By pinpointing individual red giant stars, Hubble’s Advanced Camera for Surveys enabled astronomers to calculate a new — and much more precise — estimate for NGC 1569’s distance. This revealed that the galaxy is actually one and a half times further away than previously thought, and a member of the IC 342 galaxy group.

Astronomers suspect that the IC 342 cosmic congregation is responsible for the star-forming frenzy observed in NGC 1569. Gravitational interactions between this galactic group are believed to be compressing the gas within NGC 1569. As it is compressed, the gas collapses, heats up and forms new stars.

Source: ESA/Hubble - Space Telescope

Starburst cycles in galaxies

Figure 1: The distribution of model galaxies, where the specific star formation rate is plotted versus the strength of the 4000-Angstrom-break. Model galaxies that have experienced continuous star formation histories are coloured in green, those that are currently undergoing bursts are coloured in blue and those that have experienced bursts in the past are coloured in red. One can clearly distinguish the three groups, even if there is some overlap. Plots of the specific star formation rate versus the Balmer absorption or emission line features show a similar picture. 

Figure 2: Postage stamp images of some of the low mass galaxies in the SDSS that are currently undergoing strong bursts. 

While it is well known that galaxies reside in halos of dark matter, there has been disagreement about the detailed distribution of dark matter between cosmological simulations and observations: the so-called "cuspy halo problem". Astrophysicists at the MPA have now used spectral features in a number of SDSS galaxies to show that strong starbursts occur frequently enough in low mass galaxies flatten the inner mass profiles of these systems, explaining why the theoretically predicted "cusps" are not observed. 

Cosmological simulations of the evolution of cold dark matter (CDM) show that the dark matter in galaxy halos forms cuspy distributions - with inner profiles that are too steep compared with observations. This is commonly referred to as the "cuspy halo problem". One solution to this problem, that was proposed early on, is as a galaxy loses mass in the form of explosions this can lead to an irreversible expansion of the orbits of stars and dark matter near the centre of the halo. The very dense cusps would then be spread out over a wider area. These conclusions, however, were based on simple analytic arguments and it was not clear whether this mechanism could in fact produce central density profiles in close agreement with observations. Later gas-dynamical simulations of dwarf galaxies indeed demonstrated that repeated gas outflows during bursts of star formation could in principle transfer enough energy to the dark matter component to flatten 'cuspy' central dark matter profiles. 

Nevertheless, it has remained unclear whether the energy requirements for flattening cuspy profiles are in line with the actual stellar populations and star formation histories of real low mass galaxies. In order to estimate how frequently starbursts occur as well as the amplitude range in star formation during a burst, it is necessary to analyze a large sample of galaxies that are intrinsically similar. 

High quality spectra provide a number of stellar features that are extremely useful as diagnostics of the star formation history of a galaxy. A primary feature is the strong break at 4000 Angstroms, caused by the blanket absorption of high energy radiation from metals in stellar atmospheres. This break becomes strong once young, hot, blue stars have evolved off the Main Sequence. In addition, absorption lines from the Balmer series, which are strongest in stars of spectral type A-F, are a diagnostic of the contribution of stars of intermediate ages to the total luminosity of the galaxy. 

Finally, Balmer emission lines arise in large, low-density clouds of gas where very recently formed stars emit copious amounts of ultraviolet light that ionize the surrounding gas (predominantly hydrogen). 

Used in concert, Kauffmann (2014) found that these spectral features allow one to clearly separate galaxies in three groups: those that are currently undergoing a burst of star formation, those that have formed their stars continuously and those that have experienced a burst in the past (Fig. 1). Applied to a large sample of galaxies from the Sloan Digital Sky Survey, the scientists were able to constrain the fraction of galaxies that were experiencing current starbursts, the mass of stars typically formed in these bursts, as well the duration of the starbursts. One could then investigate whether the burst frequency depended on the mass of the galaxy and whether starbursts were associated with changes in the internal structure of galaxies. 

The analysis showed that the fraction of the total star formation rate in galaxies with ongoing bursts was a strong function of stellar mass, declining from 0.85 for the smallest galaxies in the sample to 0.25 for galaxies with masses close to that of the Milky Way. Also the burst mass fraction, the half-mass formation times and the burst amplitudes and durations could be constrained. Finally, the scientists found that the central stellar densities in bursting low mass galaxies are reduced compared to their quiescent counterparts. 

These results are in remarkably good agreement with predictions of some of the recent hydrodynamical simulations and give further credence to the idea that the cuspy halo problem can be solved by energy input from multiple starbursts over the lifetime of the galaxy.

Guinevere Kauffmann

References:

Guinevere Kauffmann, Quantitative constraints on starburst cycles in galaxies with stellar masses in the range 10⁸-10¹⁰ M_sun, MNRAS (2014) 441 (3): 2717-2724

Source: Max Planck Institute for Astrophysics

Starburst to Star Bust

PR Image eso1334a

Three-dimensional view of ALMA observations 
of the outflows from NGC 253

PR Image eso1334b

The starburst galaxy NGC 253 seen with the VISTA and ALMA

PR Image eso1334c

The galaxy NGC 253 in the constellation of Sculptor

PR Image eso1334d

Wide-field view of NGC 253 from the VLT Survey Telescope

   

Videos

PR Video eso1334a

Three-dimensional view of ALMA observations  o
f the outflows from NGC 253 

PR Video eso1334b

Three-dimensional view of ALMA observations 
of the outflows from NGC 253

ALMA Sheds Light on Mystery of Missing Massive Galaxies

New observations from the ALMA telescope in Chile have given astronomers the best view yet of how vigorous star formation can blast gas out of a galaxy and starve future generations of stars of the fuel they need to form and grow. The dramatic images show enormous outflows of molecular gas ejected by star-forming regions in the nearby Sculptor Galaxy. These new results help to explain the strange paucity of very massive galaxies in the Universe. The study is published in the journal Nature on 25 July 2013.

Galaxies — systems like our own Milky Way that contain up to hundreds of billions of stars — are the basic building blocks of the cosmos. One ambitious goal of contemporary astronomy is to understand the ways in which galaxies grow and evolve, a key question being star formation: what determines the number of new stars that will form in a galaxy?

The Sculptor Galaxy, also known as NGC 253, is a spiral galaxy located in the southern constellation of Sculptor. At a distance of around 11.5 million light-years from our Solar System it is one of our closer intergalactic neighbours, and one of the closest starburst galaxies [1] visible from the southern hemisphere. 

Using the Atacama Large Millimeter/submillimeter Array (ALMA) astronomers have discovered billowing columns of cold, dense gas fleeing from the centre of the galactic disc.

“With ALMA’s superb resolution and sensitivity, we can clearly see for the first time massive concentrations of cold gas being jettisoned by expanding shells of intense pressure created by young stars,” said Alberto Bolatto of the University of Maryland, USA lead author of the paper. “The amount of gas we measure gives us very good evidence that some growing galaxies spew out more gas than they take in. We may be seeing a present-day example of a very common occurrence in the early Universe.”

These results may help to explain why astronomers have found surprisingly few high-mass galaxies throughout the cosmos. Computer models show that older, redder galaxies should have considerably more mass and a larger number of stars than we currently observe. It seems that the galactic winds or outflow of gas are so strong that they deprive the galaxy of the fuel for the formation of the next generation of stars [2].

“These features trace an arc that is almost perfectly aligned with the edges of the previously observed hot, ionised gas outflow,” noted Fabian Walter, a lead investigator at the Max Planck Institute for Astronomy in Heidelberg, Germany, and a co-author of the paper. “We can now see the step-by-step progression of starburst to outflow.”

The researchers determined that vast quantities of molecular gas — nearly ten times the mass of our Sun each year and possibly much more — were being ejected from the galaxy at velocities between 150 000 and almost 1 000 000 kilometres per hour [3]. The total amount of gas ejected would add up to more gas than actually went into forming the galaxy’s stars in the same time. At this rate, the galaxy could run out of gas in as few as 60 million years.

“For me, this is a prime example of how new instruments shape the future of astronomy. We have been studying the starburst region of NGC 253 and other nearby starburst galaxies for almost ten years. But before ALMA, we had no chance to see such details,” says Walter. The study used an early configuration of ALMA with only 16 antennas. “It’s exciting to think what the complete ALMA with 66 antennas will show for this kind of outflow!” Walter adds.

More studies with the full ALMA array will help determine the ultimate fate of the gas carried away by the wind, which will reveal whether the starburst-driven winds are recycling or truly removing star forming material.

Notes

[1] Starburst galaxies are producing stars at an exceptionally high rate. As NGC 253 is one of the closest such extreme objects it is an ideal target to study the effect of such growth frenzy on the galaxy hosting it.

[2] Previous observations had shown hotter, but much less dense, gas streaming away from NGC 253’s star-forming regions, but alone this would have little, if any, impact on the fate of the galaxy and its ability to form future generations of stars. This new ALMA data show the much more dense molecular gas getting its initial “kick” from the formation of new stars and then being swept along with the thin, hot gas on its way to the galactic halo.

[3] Although the velocities are high, they may not be high enough for the gas to be ejected from the galaxy. It would get trapped in the galactic halo for many millions of years, and could eventually rain back on the disk, causing new episodes of star formation.

More information

This research was presented in a paper “The Starburst-Driven Molecular Wind in NGC 253 and the Suppression of Star Formation”, by Alberto D. Bolatto et al., to appear in Nature on 25 July 2013.

The team is composed of A. D. Bolatto (Department of Astronomy, Laboratory for Millimeter-wave Astronomy, and Joint Space Institute, University of Maryland, USA), S. R. Warren (University of Maryland), A. K. Leroy (National Radio Astronomy Observatory, Charlottesville, USA), F. Walter (Max-Planck Institut für Astronomie, Heidelberg, Germany), S. Veilleux (University of Maryland), E. C. Ostriker (Department of Astrophysical Sciences, Princeton University, USA), J. Ott (National Radio Astronomy Observatory, New Mexico, USA), M. Zwaan (European Southern Observatory, Garching, Germany), D. B. Fisher (University of Maryland), A. Weiss (Max-Planck-Institut für Radioastronomie, Bonn, Germany), E. Rosolowsky (Department of Physics, University of Alberta, Canada) and J. Hodge (Max-Planck Institut für Astronomie, Heidelberg, Germany).

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
• More about ALMA
• Photos of ALMA
• Press release at NRAO
• Press release at MPIA

Contacts

Alberto Bolatto
University of Maryland
USA
Tel: +49 6221 528 493
Email: bolatto@astro.umd.edu

Martin Zwaan
ESO
Garching bei München, Germany
Tel: +49 89 3200 6834
Email: mzwaan@eso.org

Fabian Walter
Max-Planck Institut für Astronomie
Heidelberg, Germany
Tel: +49 6221 528 225
Email: walter@mpia.de

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