Seeing Triple

SN H0pe

What at first appears to be a glowing strand of molten iron in the image above is something far wilder: a distant galaxy whose light has been stretched into galactic taffy by the immense gravity of an intervening galaxy cluster. This phenomenon, known as strong gravitational lensing, multiplies and magnifies images of faraway sources, allowing astronomers to use massive objects like galaxy clusters as natural telescopes. Look closely at the zoomed-in version of the image: three points of light stand out against the glow of the lensed galaxy. These three dots are multiple images of a single supernova cataloged as SN H0pe. Researchers plan to use this rare multiply imaged supernova to calculate the Hubble constant, which quantifies the universe’s expansion rate. Using observations from JWST, a team led by Justin Pierel (Space Telescope Science Institute) calculated the time delay of the light from the images, finding arrival times offset by 49 and 117 days. The value of the Hubble constant derived from these observations will be reported in a future publication. In the meantime, be sure to check out the details of these initial calculations in the article linked below.

Citation

“JWST Photometric Time-Delay and Magnification Measurements for the Triply Imaged Type Ia “SN H0pe” at z = 1.78,” J. D. R. Pierel et al 2024 ApJ 967 50. doi:10.3847/1538-4357/ad3c43

Source: American Astronomical Society/AAS-Nova

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A novel 3D technique to study the kinematics of lensed galaxies

This schematic view shows lensed images in the top row and the source plane in the bottom row. Lensed data are shown for three representative velocity channels of the data cube; the respective grid on the image plane is regular. For each velocity channel, the position of a pixel in the image plane corresponds to a position on the source plane (lower panel), determined by the lens equation. The points form the vertices of a triangular adaptive grid on the source plane. The source grid automatically adapts with the lensing magnification, so that there is a high pixel density in the high-magnification regions close to the caustics. © MPA

Gravitational lensing offers the possibility to study faint, far-away galaxies. MPA researchers have now developed the first three dimensional lens modelling method, which allows not only the reconstruction of the mass distribution of the foreground galaxy but also the kinematics of the background galaxy. Consequently, the matter content can now be studied also in young galaxies. 

In the standard model of cosmology, galaxies form as the baryonic gas cools at the centre of dark matter halos. They subsequently grow through accretion and mergers, leading to the hierarchical build-up of galaxy mass. While this general picture is well known, there are numerous physical mechanisms determining the relative contribution of baryons and dark matter within a galaxy and several open questions remain: What are the most important physical mechanisms that lead to the variety of galaxies we observe today? How do these mechanisms influence the matter content within galaxies? The answer to these questions is one of the significant challenges of modern astrophysics.

The study of galaxy kinematics has played a key role in this context. For example, in the local universe, the flatness of observed rotation curves is a well-established fact. The outer parts of the observed rotation curves cannot be explained by the mass predicted from the observed stellar and gas distribution and this discrepancy has been interpreted as evidence for the presence of a "dark matter" halo. Within high redshift galaxies, however, the relative content of baryons and dark matter is poorly known and also its evolution with cosmic time is not well understood. Neither current numerical simulations nor observational studies were able to produce consistent results on the fraction of dark matter within young galaxies.
 

 

Data and modelling for one simulated 3D dataset. The rows show three representative channel maps, corresponding to three velocities. Column 1 shows the input source, a rotating disc with its approaching (first row) and receding side (third row); the middle row shows the component which is at rest relative to the observer. Each row is then lensed forward to obtain the mock lensed data in Column 2. The model obtained with the 3D-lens modelling method is shown in column 3 and the residuals (difference of the data and the model) in column 4. From this model, both the source (column 5) and its kinematics (column 6) can be reconstructed. © MPA

The diverging results on the kinematics of high-redshift galaxies - and in consequence on their matter content - can be ascribed to the different methods used to overcome the observational limitations. The study of kinematics is mainly hampered by two factors: low spatial resolution and low signal-to-noise ratio.

These observational limitations can be successfully overcome by targeting galaxies for which the line of sight lies very close to a foreground galaxy. The gravitational field of the foreground galaxy then deflects the light from the distant background galaxy, producing distorted, magnified, and even multiple images of the background object. This effect is known as strong gravitational lensing and it offers the opportunity to study the background galaxies at high physical resolution and with good signal-to-noise. Furthermore, the magnifying power of gravitational lensing opens the possibility to study faint galaxies with low stellar masses, which are not easily accessible by surveys targeting unlensed galaxies.

The gravitational lensing group at MPA developed the first three dimensional lens modelling method (see Figure 1). This can be applied to 3D (IFU or radio) data, characterized by two spatial dimensions and one spectral dimension (velocity, frequency or wavelength), to simultaneously reconstruct both the mass distribution of the foreground galaxy and the kinematics of the background galaxy (see Figure 2).

For different mock background galaxies, these plots show the velocity fields (upper panels) and rotation curves (bottom panels). The velocity field is colour coded (see bar on the side) with red areas moving away from the observer and blue areas moving towards the observer. The original rotation curves are shown in blue and the best fit kinematic model is shown in red. The orange band shows the possible errors from uncertainties of the parameters that defined the rotation curves.  The mock data M1-M3 have input rotation curves described by functional forms, while for M4-M6 the rotation curves were taken from real galaxies. The rotation curves of M1 and M4 are typical of dwarf galaxies, the rotation curves of M2 and M5 are prototypes of spirals, while those of M3 and M6 are typical of massive spirals with a prominent bulge.© MPA

Our method represents a significant improvement over those used until now, since it does not require the use of high-resolution imaging data for the derivation of the lens parameters, as these are derived from the same 3D data used for the kinematics of the background galaxy. Moreover, the latter is not obtained by fitting on the source plane, but directly the lensed data. This is achieved in a hierarchical Bayesian fashion, where the kinematics on the source plane is essentially a hyper-parameter of the model (i.e. a parameter defining the prior). We are thus able to study the possible degeneracies between the lens and kinematic parameters and estimate the uncertainties consistently.

With our technique we are able to recover both the lens and the kinematics parameters with great accuracy under different observational conditions. Furthermore, we have successfully tested the capability of this new method in recovering a variety of rotation curves with shapes which are prototypes of different morphological galaxy types, from dwarf to massive spiral galaxies (see Figure 3).

Source: Max Planck Institute for Astrophysics

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Authors

Francesca Rizzo
PhD student
Phone: 2019
Email: frizzo@mpa-garching.mpg.de
Room: 107

Simona Vegetti
Scientific Staff
Phone: 2285
Email: svegetti@mpa-garching.mpg.de
Room: 105

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Original Publication

1. Rizzo F., Vegetti S., Fraternali F., Di Teodoro E.

A novel 3D technique to study the kinematics of lensed galaxies

Submitted to MNRAS in June 2018

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Hubble Captures Massive Dead Disk Galaxy that Challenges Theories of Galaxy Evolution

Galaxy Cluster MACS J2129-0741 and Lensed Galaxy MACS2129-1

Credits: Science: NASA, ESA, and S. Toft (University of Copenhagen)

Acknowledgment: NASA, ESA, M. Postman (STScI), and the CLASH team

Released images

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Young, Dead, Compact, Disk Galaxy Surprises Astronomers, Offers New Clues to How Modern-Day Elliptical Galaxies Formed

By combining the power of a "natural lens" in space with the capability of NASA's Hubble Space Telescope, astronomers made a surprising discovery—the first example of a compact yet massive, fast-spinning, disk-shaped galaxy that stopped making stars only a few billion years after the big bang.

Finding such a galaxy early in the history of the universe challenges the current understanding of how massive galaxies form and evolve, say researchers.

When Hubble photographed the galaxy, astronomers expected to see a chaotic ball of stars formed through galaxies merging together. Instead, they saw evidence that the stars were born in a pancake-shaped disk.

This is the first direct observational evidence that at least some of the earliest so-called "dead" galaxies — where star formation stopped — somehow evolve from a Milky Way-shaped disk into the giant elliptical galaxies we see today.

This is a surprise because elliptical galaxies contain older stars, while spiral galaxies typically contain younger blue stars. At least some of these early "dead" disk galaxies must have gone through major makeovers. They not only changed their structure, but also the motions of their stars to make a shape of an elliptical galaxy.

"This new insight may force us to rethink the whole cosmological context of how galaxies burn out early on and evolve into local elliptical-shaped galaxies," said study leader Sune Toft of the Dark Cosmology Center at the Niels Bohr Institute, University of Copenhagen, Denmark. "Perhaps we have been blind to the fact that early "dead" galaxies could in fact be disks, simply because we haven't been able to resolve them."

Previous studies of distant dead galaxies have assumed that their structure is similar to the local elliptical galaxies they will evolve into. Confirming this assumption in principle requires more powerful space telescopes than are currently available. However, through the phenomenon known as "gravitational lensing," a massive, foreground cluster of galaxies acts as a natural "zoom lens" in space by magnifying and stretching images of far more distant background galaxies. By joining this natural lens with the resolving power of Hubble, scientists were able to see into the center of the dead galaxy.

The remote galaxy is three times as massive as the Milky Way but only half the size. Rotational velocity measurements made with the European Southern Observatory's Very Large Telescope (VLT) showed that the disk galaxy is spinning more than twice as fast as the Milky Way.

Using archival data from the Cluster Lensing And Supernova survey with Hubble (CLASH), Toft and his team were able to determine the stellar mass, star-formation rate, and the ages of the stars.

Why this galaxy stopped forming stars is still unknown. It may be the result of an active galactic nucleus, where energy is gushing from a supermassive black hole. This energy inhibits star formation by heating the gas or expelling it from the galaxy. Or it may be the result of the cold gas streaming onto the galaxy being rapidly compressed and heated up, preventing it from cooling down into star-forming clouds in the galaxy's center.

But how do these young, massive, compact disks evolve into the elliptical galaxies we see in the present-day universe? "Probably through mergers," Toft said. "If these galaxies grow through merging with minor companions, and these minor companions come in large numbers and from all sorts of different angles onto the galaxy, this would eventually randomize the orbits of stars in the galaxies. You could also imagine major mergers. This would definitely also destroy the ordered motion of the stars."

The findings are published in the June 22 issue of the journal Nature. Toft and his team hope to use NASA's upcoming James Webb Space Telescope to look for a larger sample of such galaxies.

The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, Inc., in Washington, D.C.

The Very Large Telescope is a telescope facility operated by the European Southern Observatory on Cerro Paranal in the Atacama Desert of Northern Chile.

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Related Links

This site is not responsible for content found on external links

• The science paper by S. Toft et al.
• NASA's Hubble Portal
• CLASH Project Website
• Journal Nature

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Contacts

Ann Jenkins / Ray Villard
Space Telescope Science Institute, Baltimore, Maryland
410-338-4488 / 410-338-4514
jenkins@stsci.edu / villard@stsci.edu

Sune Toft
Dark Cosmology Center, Niels Bohr Institute,
University of Copenhagen, Copenhagen, Denmark
sune@dark-cosmology.dk

Source: HubbleSit

Sharpest View Ever of Star Formation in the Distant Universe

PR Image eso1522a

Montage of the SDP.81 Einstein Ring and the lensed galaxy

PR Image eso1522b

The lensed galaxy

PR Image eso1522c

The Einstein Ring SDP.81 seen with ALMA

PR Image eso1522d

Hubble image of the region around SDP.81

PR Image eso1522e

Montage of the SDP.81 Einstein Ring and the lensed galaxy (no annotations)

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Videos 

PR Video eso1522a

Gravitational lensing of distant star-forming galaxies (schematic)

PR Video eso1522b

Gravitational lensing of distant star-forming galaxies (schematic)

ALMA’s observation of Einstein Ring reveals extraordinary detail

ALMA’s Long Baseline Campaign has produced a spectacular image of a distant galaxy being gravitationally lensed. The image shows a magnified view of the galaxy’s star-forming regions, the likes of which have never been seen before at this level of detail in a galaxy so remote. The new observations are far sharper than those made using the NASA/ESA Hubble Space Telescope, and reveal star-forming clumps in the galaxy equivalent to giant versions of the Orion Nebula in the Milky Way. 

ALMA’s Long Baseline Campaign has produced some amazing observations, and gathered unprecedentedly detailed information about the inhabitants of the near and distant Universe. Observations made at the end of 2014 as part of the campaign targeted a distant galaxy called HATLAS J090311.6+003906, otherwise known as SDP.81. This light from this galaxy is a victim of a cosmic effect known as gravitational lensing. A large galaxy sitting between SDP.81 and ALMA [1] is acting as a lens, warping and magnifying the view of a more distant galaxy and creating a near-perfect example of a phenomenon known as an Einstein Ring [2].

At least seven groups of scientists [3] have independently analysed the ALMA data on SDP.81. This flurry of research papers has revealed unprecedented information about the galaxy, including details about its structure, contents, motion, and other physical characteristics.

ALMA acts as an interferometer. Simply speaking, the array’s multiple antennas work in perfect synchrony to collect light as an enormous virtual telescope [4]. As a result, these new images of SDP.81 have a resolution up to six times higher [5] than those taken in the infrared with the NASA/ESA Hubble Space Telescope.

The astronomers’ sophisticated models reveal fine, never-before-seen structure within SDP.81, in the form of dusty clouds thought to be giant repositories of cold molecular gas — the birthplaces of stars and planets. These models were able to correct for the distortion produced by the magnifying gravitational lens.

As a result, the ALMA observations are so sharp that researchers can see clumps of star formation in the galaxy down to a size of about 200 light-years, equivalent to observing giant versions of the Orion Nebula producing thousands of times more new stars at the far side of the Universe. This is the first time this phenomenon has been seen at such an enormous distance.

“The reconstructed ALMA image of the galaxy is spectacular,” says Rob Ivison, co-author of two of the papers and ESO’s Director for Science. “ALMA’s huge collecting area, the large separation of its antennas, and the stable atmosphere above the Atacama desert all lead to exquisite detail in both images and spectra. That means that we get very sensitive observations, as well as information about how the different parts of the galaxy are moving. We can study galaxies at the other end of the Universe as they merge and create huge numbers of stars. This is the kind of stuff that gets me up in the morning!”

Using the spectral information gathered by ALMA, astronomers also measured how the distant galaxy rotates, and estimated its mass. The data showed that the gas in this galaxy is unstable; clumps of it are collapsing inwards, and will likely turn into new giant star-forming regions in the future.

Notably, the modeling of the lensing effect also indicates the existence of a supermassive black hole at the centre of the foreground galaxy lens [6]. The central part of SDP.81 is too faint to be detected, leading to the conclusion that the foreground galaxy holds a supermassive black hole with more than 200–300 million times the mass of the Sun.

The number of papers published using this single ALMA dataset demonstrates the excitement generated by the potential of the array’s high resolution and light-gathering power. It also shows how ALMA will enable astronomers to make more discoveries in the years to come, also uncovering yet more questions about the nature of distant galaxies.

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Notes

[1] The lensed galaxy is seen at a time when the Universe was only 15 percent of its current age, just 2.4 billion years after Big Bang. The light has taken over twice the age of the Earth to reach us (11.4 billion years), detouring along the way around a massive foreground galaxy that is comparatively close at four billion light-years away from us.

[2] Gravitational lenses were predicted by Albert Einstein as part of his theory of general relativity. His theory tells us that objects bend space and time. Any light approaching this curved space-time will itself follow the curvatures created by the object. This enables particularly massive objects — huge galaxies and galaxy clusters — to act as cosmic magnifying glasses. An Einstein ring is a special type of gravitational lens, in which the Earth, the foreground lensing galaxy, and the background lensed galaxy are in perfect alignment, creating a harmonious distortion in the form of a ring of light. This phenomenon is illustrated in Video A.

[3] The science teams are listed below.

[4] ALMA’s ability to see the finest detail is achieved when the antennas are at their greatest separation, up to 15 kilometres apart. For comparison, earlier observations of gravitational lenses made with ALMA in a more compact configuration, with a separation of only around 500 metres, can be seen here.

[5] Details down to 0.023 arc-seconds, or 23 milli-arcseconds, can be measured in these data. Hubble observed this galaxy in the near-infrared, with a resolution of about 0.16 arc-seconds. Note, however, that when observing at shorter wavelengths, Hubble can reach finer resolutions, down to 0.022 arcseconds in the near-ultraviolet. ALMA’s resolution can be adjusted depending on the type of observations by moving the antennas further apart or closer together. For these observations, the widest separation was used, resulting in the finest resolution possible.

[6] The high-resolution ALMA image enables researchers to look for the central part of the background galaxy, which is expected to appear at the centre of the Einstein ring. If the foreground galaxy has a supermassive black hole at the centre, the central image becomes fainter. The faintness of the central image indicates how massive the black hole in the foreground galaxy is.

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More Information

This research was presented in eight papers to appear in the near future. The science teams are listed below.

http://arxiv.org/abs/1503.07605
Yoichi Tamura (The University of Tokyo), Masamune Oguri (The University of Tokyo), Daisuke Iono (National Astronomical Observatory of Japan/SOKENDAI), Bunyo Hatsukade (National Astronomical Observatory of Japan), Yuichi Matsuda (National Astronomical Observatory of Japan/SOKENDAI), and Masao Hayashi (National Astronomical Observatory of Japan).

http://arxiv.org/abs/1503.08720
Simon Dye (University of Nottingham), Christina Furlanetto (University of Nottingham; CAPES Foundation, Ministry of Education of Brazil, Brazil), Mark Swinbank (Durham University), Catherine Vlahakis (Joint ALMA Observatory, Chile; ESO, Chile), James Nightingale (University of Nottingham), Loretta Dunne (University of Canterbury, New Zealand; Institute for Astronomy [IfA], Royal Observatory Edinburgh), Steve Eales (Cardiff University), Ian Smail (Durham), Ivan Oteo-Gomez (IfA, Edinburgh; ESO, Germany), Todd Hunter (National Radio Astronomy Observatory, Charlottesville, Virginia, USA), Mattia Negrello (INAF, Osservatorio Astronomico di Padova, Vicolo Osservatorio, Padova, Italy), Helmut Dannerbauer (Universitat Wien, Vienna, Austria), Rob Ivison (IfA, Edinburgh; ESO, Germany), Raphael Gavazzi (Universite Pierre et Marie Curie, Paris), Asantha Cooray (California Institute of Technology, USA) and Paul van der Werf (Leiden University, The Netherlands).

http://arxiv.org/abs/1505.05148
Mark Swinbank (Durham University), Simon Dye (University of Nottingham), James Nightingale (University of Nottingham), Christina Furlanetto (University of Nottingham; CAPES Foundation, Ministry of Education of Brazil, Brazil), Ian Smail (Durham), Asantha Cooray (California Institute of Technology, USA), Helmut Dannerbauer (Universitat Wien, Vienna, Austria), Loretta Dunne (University of Canterbury, New Zealand; Institute for Astronomy [IfA], Royal Observatory Edinburgh), Steve Eales (Cardiff University), Raphael Gavazzi (Universite Pierre et Marie Curie, Paris), Todd Hunter (National Radio Astronomy Observatory, Charlottesville, Virginia, USA), Rob Ivison (IfA, Edinburgh; ESO, Germany), Mattia Negrello (INAF, Osservatorio Astronomico di Padova, Vicolo Osservatorio, Padova, Italy), Ivan Oteo-Gomez (IfA, Edinburgh; ESO, Germany), Renske Smit (Durham), Paul van der Werf (Leiden University, The Netherlands), and Catherine Vlahakis (Joint ALMA Observatory, Chile; ESO, Chile).

http://arxiv.org/abs/1503.05558
Kenneth C. Wong (Institute of Astronomy and Astrophysics, Academia Sinica (ASIAA), Taipei, Taiwan), Sherry H. Suyu (ASIAA, Taiwan), and Satoki Matsushita (ASIAA, Taiwan)

http://arxiv.org/abs/1503.07997
Bunyo Hatsukade (National Astronomical Observatory of Japan, Tokyo, Japan) Yoichi Tamura (Institute of Astronomy, University of Tokyo, Tokyo, Japan), Daisuke Iono (National Astronomical Observatory of Japan; The Graduate University for Advanced Studies [SOKENDAI], Tokyo, Japan), Yuichi Matsuda (National Astronomical Observatory of Japan), Masao Hayashi (National Astronomical Observatory of Japan), Masamune Oguri (Research Center for the Early Universe, University of Tokyo, Tokyo, Japan; Department of Physics, University of Tokyo, Tokyo, Japan; Kavli Institute for the Physics and Mathematics of the Universe [Kavli IPMU, WPI], University of Tokyo, Chiba, Japan)

http://arxiv.org/abs/1503.02652
The ALMA Partnership, C. Vlahakis (Joint ALMA Observatory [JAO]; ESO) , T. R. Hunter (National Radio Astronomy Observatory [NRAO]), J. A. Hodge (NRAO) , L. M. Pérez (NRAO) , P. Andreani (ESO), C. L. Brogan (NRAO) , P. Cox (JAO, ESO) , S. Martin (Institut de Radioastronomie Millimétrique [IRAM]) , M. Zwaan (ESO) , S. Matsushita (Institute of Astronomy and Astrophysic, Taiwan) , W. R. F. Dent (JAO, ESO), C. M. V. Impellizzeri (JAO, NRAO), E. B. Fomalont (JAO, NRAO), Y. Asaki (National Astronomical Observatory of Japan; Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency [JAXA]) , D. Barkats (JAO, ESO) , R. E. Hills (Astrophysics Group, Cavendish Laboratory), A. Hirota (JAO; National Astronomical Observatory of Japan), R. Kneissl (JAO, ESO), E. Liuzzo (INAF, Istituto di Radioastronomia), R. Lucas (Institut de Planétologie et d’Astrophysique de Grenoble) , N. Marcelino (INAF), K. Nakanishi (JAO, National Astronomical Observatory of Japan), N. Phillips (JAO, ESO), A. M. S. Richards (University of Manchester), I. Toledo (JAO), R. Aladro (ESO), D. Broguiere (IRAM), J. R. Cortes (JAO, NRAO), P. C. Cortes (JAO, NRAO), D. Espada (ESO, National Astronomical Observatory of Japan), F. Galarza (JAO), D. Garcia-Appadoo (JAO, ESO), L. Guzman-Ramirez (ESO), A. S. Hales (JAO, NRAO) , E. M. Humphreys (ESO) , T. Jung (Korea Astronomy and Space Science Institute) , S. Kameno (JAO, National Astronomical Observatory of Japan) , R. A. Laing (ESO), S. Leon (JAO,ESO) , G. Marconi (JAO, ESO) , A. Mignano (INAF) , B. Nikolic (Astrophysics Group, Cavendish Laboratory), L. A. Nyman (JAO, ESO), M. Radiszcz (JAO), A. Remijan (JAO, NRAO), J. A. Rodón (ESO), T. Sawada (JAO, National Astronomical Observatory of Japan), S. Takahashi (JAO, National Astronomical Observatory of Japan), R. P. J. Tilanus (Leiden University), B. Vila Vilaro (JAO, ESO), L. C. Watson (ESO), T. Wiklind (JAO, ESO), Y. Ao (National Astronomical Observatory of Japan) , J. Di Francesco (National Research Council Herzberg Astronomy & Astrophysics), B. Hatsukade (National Astronomical Observatory of Japan), E. Hatziminaoglou (ESO), J. Mangum (NRAO), Y. Matsuda (National Astronomical Observatory of Japan), E. Van Kampen (ESO), A. Wootten (NRAO), I. De Gregorio-Monsalvo (JAO, ESO), G. Dumas (IRAM), H. Francke (JAO), J. Gallardo (JAO), J. Garcia (JAO), S. Gonzalez (JAO), T. Hill (ESO), D. Iono (National Astronomical Observatory of Japan), T. Kaminski (ESO), A. Karim (Argelander-Institute for Astronomy), M. Krips (IRAM), Y. Kurono (JAO, National Astronomical Observatory of Japan) , C. Lonsdale (NRAO), C. Lopez (JAO), F. Morales (JAO), K. Plarre (JAO), L. Videla (JAO), E. Villard (JAO, ESO), J. E. Hibbard (NRAO), K. Tatematsu (National Astronomical Observatory of Japan)

http://arxiv.org/abs/1503.02025
M. Rybak (Max Planck Institute for Astrophysics), J. P. McKean (Netherlands Institute for Radio Astronomy; University of Groningen) S. Vegetti (Max Planck Institute for Astrophysics), P. Andreani (ESO) and S. D. M. White (Max Planck Institute for Astrophysics)

http://arxiv.org/abs/1506.01425
M. Rybak (Max Planck Institute for Astrophysics), S. Vegetti (Max Planck Institute for Astrophysics), J. P. McKean (Netherlands Institute for Radio Astronomy; University of Groningen), P. Andreani (ESO) and S. D. M. White (Max Planck Institute for Astrophysics)

The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of ESO, the US National Science Foundation (NSF) and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the National Science Council of Taiwan (NSC) and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI).

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

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 16 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile. 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 a major partner in ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre European Extremely Large Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”. ESO is a major partner in ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre European Extremely Large Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

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Links

Research papers;

• http://arxiv.org/abs/1503.07605
• http://arxiv.org/abs/1503.08720
• http://arxiv.org/abs/1505.05148
• http://arxiv.org/abs/1503.05558
• http://arxiv.org/abs/1503.07997
• http://arxiv.org/abs/1503.02652
• http://arxiv.org/abs/1503.02025
• http://arxiv.org/abs/1506.01425

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Contacts

Lars Lindberg Christensen
Head of ESO ePOD
Garching bei München, Germany
Tel: +49 89 3200 6761
Cell: +49 173 3872 621
Email: lars@eso.org

Source: ESO

Dusty substructure in a galaxy far far away

Fig. 1 The ALMA image of the continuum emission at 236 GHz of the lensed galaxy SDP.81 at two angular resolutions. The lensed system consists of four images with an extended, low-surface brightness Einstein ring. 

Fig. 2 The modelled sky-brightness distribution for the image in Fig. 1 (left) and the reconstructed surface brightness distribution (right) of the background galaxy. There are three areas with enhanced emission, which could indicate a disk galaxy seen edge-on. 

Fig. 3 This map shows the reconstructed star formation rate of the distant galaxy, which is actually quite small (as indicated by the length scale in light-years). The colour coding shows the amount of dust heated by radiation from the young stars.

Scientists at the Max Planck Institute for Astrophysics (MPA) have combined high-resolution images from the ALMA telescopes with a new scheme for undoing the distorting effects of a powerful gravitational lens in order to provide the first detailed picture of a young and distant galaxy, over 11 billion light-years from Earth. The reconstructed images show that star formation is heating interstellar dust and making it glow strongly in three distinct clumps embedded in a broader distribution, suggesting that object may be a rotating disk galaxy seen nearly edge-on.

Galaxies are constantly forming new stars within dense clouds of interstellar material. The star formation rate in today's galaxies is, however, much lower than it used to be. When the universe was about a quarter its current age, star formation was at its peak, and so astronomers are keen to learn about this period.

Looking back in time is possible because of the finite speed of light, but only by looking out to great distances, which in turn means that young galaxies appear very small and very faint. In addition, most of their new-born stars cannot be seen directly, because their radiation is absorbed by dust in the surrounding gas cloud and is re-emitted at far-infrared wavelengths.

As a result, star-forming regions in distant galaxies are one of the prime targets for the Atacama Large Millimetre/submillimetre Array. ALMA will consist of 66 high precision antennas, located on the Chajnantor plateau at 5000 meters altitude in northern Chile. The data from the individual antennas can be combined interferometrically, and the 15 kilometre span of the telescope provides resolution of better than a tenth of an arc-second. On its own, however, even this capability is not sufficient to make detailed pictures of young galaxies at the peak of their star formation.

"At a recent conference, ALMA scientists presented data they had used to verify the scientific capabilities of their array, among them an image of a strongly gravitationally lensed system, which immediately raised our interest", remembers Simona Vegetti, postdoctoral scientist at MPA. "Because of the lensing, the background galaxy is strongly magnified, by 17 times actually, which is why we can see it at all. Together with ALMA's unique angular resolution, this gave us the chance to try and see details in the distribution of dust in such a far-away galaxy for the first time."

Strong gravitational lensing happens when a background galaxy is closely aligned with a foreground mass concentration such as a cluster of galaxies, which bends light-rays from the source on their way to the observer. The foreground lens is, however, an imperfect optical system, leading to very large distortions (see Fig. 1). Nevertheless, from the properties of the lensed images, the mass distribution of the lensing system can be determined and a "true" (i.e. undistorted) image of the distant galaxy can be reconstructed. "Previous attempts to do this had assumed the background galaxies to be smooth and regular", explains Matus Rybak, who carried out the computer modelling at MPA. "This seems likely to be a very poor approximation to the structure of a strongly star-forming galaxy, and the raw ALMA images gave clear hints that this background source is complex. The new, more general approach we have developed is much better suited to irregular systems."

This intuition is borne out by the reconstructed image of the galaxy SDP.81 which shows star formation to be concentrated in three distinct regions (see Fig. 2). "This is the first time, that we can see structure in the dust emission of a z=3 galaxy on scales smaller than 150 light-years", points out Simona Vegetti. At this cosmic time, typical galaxies were forming stars at their peak rate, and indeed SDP.81 is forming about 300 solar masses of stars every year. (In our Milky Way, the star formation rate is about 3 solar masses per year.) The complex structure of the galaxy may indicate that it is a rotating disk with a central bulge that is seen (and lensed) edge-on; alternatively it may be a system which is undergoing a merger in which the separate components are still visible. To distinguish between these possibilities, data on the motions of gas within the galaxy are needed, so the next step for the MPA team together with their colleagues Paola Andreani at ESO and John McKean at the University of Groningen and the Netherlands Institute for Radio Astronomy (ASTRON) will be to analyse the molecular line observations of this system which ALMA has also obtained. 

Links:

Original publication
ALMA imaging of SDP.81 I. A pixelated reconstruction of the far-infrared continuum emission, M. Rybak, J. P. McKean, S. Vegetti, P. Andreani and S. D. M. White, submitted to MNRAS - ALMA

Contact:

Simona Vegetti
Max-Planck-Institut für Astrophysik
Phone: 089 30000-2285
Email: svegetti@mpa-garching.mpg.de

Hannelore Hämmerle
Press Officer
Max-Planck-Institut für Astrophysik
Tel. +49 89 30000-3980
E-mail: pr@mpa-garching.mpg.de

Source: Max Planck Institute for Astrophysics