A greedy giant

NGC 1222

 Credit: ESA/Hubble & NASA

NGC 1222, seen in this image taken with the Wide Field Camera 3 on board the NASA/ESA Hubble Space Telescope (HST), is a galaxy with a rather eventful story to tell. NGC 1222 has been described as a peculiar example of a type of galaxy known as a lenticular galaxy. Typically, this kind of galaxy would present a rather smooth appearance on the sky and would consist mostly of old, reddish stars. A bit dull, perhaps.

But NGC 1222 is certainly not a typical member of its class — and it’s anything but dull.

Observations show the characteristic features of very recent star formation on a huge scale — an event known as a starburst. The reason for all this violent activity is caused by the fact that NGC 1222 is not alone. It actually contains three compact regions, each of which appears to be the central nucleus of a galaxy. Astronomers think that NGC 1222 is in the process of swallowing up two much smaller dwarf galaxies that strayed too close to it. It is likely that the encounter was the trigger for the starburst in NGC 1222, bringing in fresh supplies of gas that are now fuelling the burst of star formation.

Although its peculiarities were first seen in photographic images, these were not able to reveal the level of fine detail that can be recovered by Hubble. The image taken by Hubble allows us to see an astonishing amount of structure in this galaxy, emphasising its colourful history. Against the smooth background of old stars that was the original lenticular galaxy, we can clearly see dark filaments of dust and bright filaments of gas, both associated with the powerful star formation process.

Source: ESA/Hubble - Space Telescope/Images

Entire galaxies feel the heat from newborn stars

PR Image heic1308a

Artist's impression of a galaxy undergoing a starburst

 Videos

PR Video heic1308a

Probing a galactic halo with Hubble

PR Video heic1308b

Animation of a starburst galaxy (artist’s impression)

Bursts of star birth can curtail future galaxy growth 

Astronomers using the NASA/ESA Hubble Space Telescope have shown for the first time that bursts of star formation have a major impact far beyond the boundaries of their host galaxy. These energetic events can affect galactic gas at distances of up to twenty times greater than the visible size of the galaxy — altering how the galaxy evolves, and how matter and energy is spread throughout the Universe.

When galaxies form new stars, they sometimes do so in frantic episodes of activity known as starbursts. These events were commonplace in the early Universe, but are rarer in nearby galaxies.

During these bursts, hundreds of millions of stars are born, and their combined effect can drive a powerful wind that travels out of the galaxy. These winds were known to affect their host galaxy — but this new research now shows that they have a significantly greater effect than previously thought.

An international team of astronomers observed 20 nearby galaxies, some of which were known to be undergoing a starburst. They found that the winds accompanying these star formation processes were capable of ionising [1] gas up to 650 000 light-years from the galactic centre — around twenty times further out than the visible size of the galaxy. This is the first direct observational evidence of local starbursts impacting the bulk of the gas around their host galaxy, and has important consequences for how that galaxy continues to evolve and form stars.

“The extended material around galaxies is hard to study, as it’s so faint,” says team member Vivienne Wild of the University of St. Andrews. “But it’s important — these envelopes of cool gas hold vital clues about how galaxies grow, process mass and energy, and finally die. We’re exploring a new frontier in galaxy evolution!”

The team used the Cosmic Origins Spectrograph (COS) instrument [2] on the NASA/ESA Hubble Space Telescope to analyse light from a mixed sample of starburst and control galaxies. They were able to probe these faint envelopes by exploiting even more distant objects — quasars, the intensely luminous centres of distant galaxies powered by huge black holes. By analysing the light from these quasars after it passed through the foreground galaxies, the team could probe the galaxies themselves.

“Hubble is the only observatory that can carry out the observations necessary for a study like this,” says lead author Sanchayeeta Borthakur, of Johns Hopkins University. “We needed a space-based telescope to probe the hot gas, and the only instrument capable of measuring the extended envelopes of galaxies is COS.”

The starburst galaxies within the sample were seen to have large amounts of highly ionised gas in their halos — but the galaxies that were not undergoing a starburst did not. The team found that this ionisation was caused by the energetic winds created alongside newly forming stars.

This has consequences for the future of the galaxies hosting the starbursts. Galaxies grow by accreting gas from the space surrounding them, and converting this gas into stars. As these winds ionise the future fuel reservoir of gas in the galaxy’s envelope, the availability of cool gas falls — regulating any future star formation.

“Starbursts are important phenomena — they not only dictate the future evolution of a single galaxy, but also influence the cycle of matter and energy in the Universe as a whole,” says team member Timothy Heckman, of Johns Hopkins University. “The envelopes of galaxies are the interface between galaxies and the rest of the Universe — and we’re just beginning to fully explore the processes at work within them.”

The team's results will appear in the 1 May 2013 issue of The Astrophysical Journal.

 

Notes

[1] A gas is said to be ionised when its atoms have lost one or more electrons — in this case by energetic winds exciting galactic gas and knocking electrons out of the atoms within.

[2] Spectrographs are instruments that break light into its constituent colours and measure the intensity of each colour, revealing information about the object emitting the light — such as its chemical composition, temperature, density, or velocity.

 

More information

The Hubble Space Telescope is a project of international cooperation between ESA and NASA.

The research is presented in a paper entitled “The Impact of Starbursts on the Circumgalactic Medium”, published in the 1 May 2013 issue of The Astrophysical Journal.

The international team of astronomers in this study consists of: S. Borthakur (Johns Hopkins University, USA), T. Heckman (Johns Hopkins University, USA), D. Strickland (Johns Hopkins University, USA), V. Wild (University of St. Andrews, UK), D. Schiminovich (Columbia University, USA). 

Image credit: ESA, NASA, L. Calçada

 

Links

• Research paper
• Images of Hubble
• Hubble's Instruments: COS — Cosmic Origins Spectrograph

 

Contacts

Vivienne Wild
University of St Andrews
UK
Tel: +44 1334 461680
Email: vw8@st-andrews.ac.uk

Sanchayeeta Borthakur
Johns Hopkins University
Baltimore, Md., USA
Tel: +1 410 516 4737
Email: sanch@pha.jhu.edu

Nicky Guttridge
Hubble/ESA
Garching, Germany
Tel: +49-89-3200-6855
Email: nguttrid@partner.eso.org

Shedding Light on the Power of M 82's Superwinds

An international team of astronomers, led by Dr. Kazuya Matsubayshi (Kyoto University), has discovered that outflows of gas from starburst galaxy M 82 (see Note 1 for a reference figure) collide with a "cap" of gas clouds 40,000 light years away from the galactic disk. Shockwaves (Note 2) from M 82's central starburst region are the most likely source of the bright clouds within the cap. The large light-gathering power of Subaru Telescope's 8.2-m mirror and its ability to produce highly detailed images enabled the researchers to make these findings, which provide important clues about the wind's power.

The central regions of starburst galaxies are sites of immense star formation. They give birth to thousands of massive stars, which are dozens of times heavier than the Sun and then explode as supernovae when they die. Many supernovae explosions heat the gas around them to temperatures of more than a million degrees, and this hot gas flows out from the galaxy as galactic wind. These winds are so powerful that they may play an important role in the evolution of galaxies and the inter-galactic medium. However, galactic winds are usually diffuse and difficult to observe; therefore, it has been difficult to confirm their power. Nevertheless, it is possible to precisely estimate their energy level by measuring how far the galactic winds reach.

The current team tackled the issue of shedding light on the processes behind large-scale galactic winds by focusing their research on the "cap" of M 82, one of the closest starburst galaxies to Earth, about 12 million light years away. M 82 has large-scale galactic winds, so-called "superwinds", and its cap consists of gas clouds about 40,000 light years away from its galactic disk. Matsubayashi pinpointed the research question: "Why are there ionized gas clouds so far from the galactic disk? If we investigate the ionization source of the cap, we can confirm whether M 82's galactic winds reach it."

Two possibilities for ionization sources of M 82's cap are: 1) ultraviolet photons from massive stars in M 82's starburst regions and 2) shockwaves caused by the collision of M 82's galactic winds with gas clouds in the cap (Figure 1). The researchers reasoned, "Because we can estimate the intensity of ultraviolet photons from the starburst regions and the pressure of the galactic winds from past observational data, the morphology and H-alpha (Note 3) intensity of the cap region will reveal the answer."

Figure 1: Sketches of possible ionization sources of M 82's cap (Credit: NAOJ)
left: Ultraviolet photons from massive stars in the M 82 starburst region.
right: Ultraviolet photons from shockwaves caused by the collision between M 82's galactic winds and gas clouds.   
The team investigated the ionization source of M 82's cap by observing it with Kyoto 3DII mounted on the Subaru Telescope. They used the Fabry-Perot interferometer, which works as a narrow-band filter that researchers can tune for a desired wavelength. They obtained images of continuum and H-alpha emissions of the cap. (Figure 2)

Figure 2: Images of the cap of M 82 (Credit: NAOJ)

left: H-alpha image of M 82. The contours represent the intensity of X-rays. The brightest region at the lower left of the panel is M 82's center. The diffuse emission region at the upper right is the cap.

center: Continuum image that shows the background area of the cap. The objects in this panel are stars in the Milky Way Galaxy or distant galaxies. There is no detection of a continuum emission from the cap.

right: H-alpha image of the cap. This shows the detection of H-alpha emission from the cap. It also shows that the cap is clumpy rather than uniform. The typical size of clumps is 300 - 500 light years in diameter.   

If UV light from the M 82 starburst regions ionized the clumps of the cap, the H-alpha emission should be ten times weaker than what was observed. In contrast, the H-alpha intensity predicted by the shock model matches well with the measurement from the observations. Therefore, the team concluded that shockwaves from M 82's galactic winds ionized the gas clouds in the cap. This suggests that the galactic winds travel and have direct impacts on inter-galactic gas at least 40,000 light years away from the galactic disk.

The research raises another question: "Do galactic winds affect gas clouds at an even further distance from the galactic disk?" Matsubayashi remarked, "We would like to carry out observations to survey more distant gas clouds ionized by galactic winds."


References:

• The scientific results on which this release was based were published in the December 10, 2012 edition of The Astrophysical Journal: K. Matsubayashi et al., "Ionization Source of a Minor-Axis Cloud in the Outer Halo of M 82", 761:55 (8pp).

• For more information about M 82's galactic winds, refer to previous press releases from Subaru Telescope:

• "Red Light Flowing from Galaxy (M 82, NGC 3034)"

• "New Images of Starburst Galaxy M 82 Reveal Multiple Sources of Its Superwind"

Acknowledgements:
This research  was supported by the Japan Society for the Promotion of Science (Nos. 17253001, 1934006, 23244031, 23654068, 24103003)

Note:

1) This reference figure is an image of M 82 viewed edge-on and captured by FOCAS (Faint Object Camera and Spectrograph) mounted on the Subaru Telescope. The red filaments that expand perpendicular to the galactic disk are outflowing ionized gas from many supernovae in the galaxy. (Credit NAOJ)

2) A shockwave is a type of disturbance spreading at supersonic speed in a compressive medium, such as air. Immense explosions or supersonic flights can cause shockwaves.

3) An H-alpha emission is one of the emission lines from hydrogen atoms and results when ionized hydrogen and an electron recombine. The wavelength of H-alpha is 656 nm, and it is the brightest hydrogen emission line in the optical wavelength (400 - 750 nm)