Heidelberg, Germany
Heidelberg, Germany

Time filter

Source Type

News Article | May 11, 2017
Site: phys.org

Basic set-up of the quasar observations: Light from a quasar (right) is absorbed by gas. Absorption is much less in the quasar's proximity zone, which is shown in green for an older quasar, in yellow for a younger quasar. The extent of the proximity zone can be read off the spectrum (bottom). The quasar itself is a central black hole, surrounded by a disk of swirling matter, and possibly sending out particles in two tightly focussed jets (inset, top right). Credit: A. C. Eilers & J. Neidel, MPIA Quasars are luminous objects with supermassive black holes at their centers, visible over vast cosmic distances. Infalling matter increases the black hole mass and is also responsible for a quasar's brightness. Now, using the W.M. Keck observatory in Hawaii, astronomers led by Christina Eilers have discovered extremely young quasars with a puzzling property: these quasars have the mass of about a billion suns, yet have been collecting matter for less than 100,000 years. Conventional wisdom says quasars of that mass should have needed to pull in matter a thousand times longer than that – a cosmic conundrum. The results have been published in the May 2 edition of the Astrophysical Journal. Within the heart of every massive galaxy lurks a supermassive black hole. How these black holes formed, and how they have grown to be as massive as millions or even billions of suns, is an open question. At least some phases of vigorous growth are highly visible to astronomical observers: Whenever there are substantial amounts of gas swirling into the black hole, matter in the direct vicinity of the black hole emits copious amount of light. The black hole has intermittently turned into a quasar, one of the most luminous objects in the universe. Now, researchers from the Max Planck Institute for Astronomy (MPIA) have discovered three quasars that challenge conventional wisdom on black hole growth. These quasars are extremely massive, but should not have had sufficient time to collect all that mass. The discovery, which is based on observations at the W.M. Keck observatory in Hawaii, glimpses into ancient cosmic history: Because of their extreme brightness, quasars can be observed out to large distances. The astronomers observed quasars whose light took nearly 13 billion years to reach Earth. In consequence, the observations show these quasars not as they are today, but as they were almost 13 billion years ago, less than a billion years after the big bang. The quasars in question have about a billion times the mass of the sun. All current theories of black hole growth postulate that, in order to grow that massive, the black holes would have needed to collect infalling matter, and shine brightly as quasars, for at least a hundred million years. But these three quasars proved to be have been active for a much shorter time, less than 100,000 years. "This is a surprising result," explains Christina Eilers, a doctoral student at MPIA and lead author of the present study. "We don't understand how these young quasars could have grown the supermassive black holes that power them in such a short time." To determine how long these quasars had been active, the astronomers examined how the quasars had influenced their environment – in particular, they examined heated, mostly transparent "proximity zones" around each quasar. "By simulating how the light from quasars ionizes and heats gas around them, we can predict how large the proximity zone of each quasar should be," explains Frederick Davies, a postdoctoral researcher at MPIA who is an expert in the interaction between quasar light and intergalactic gas. Once the quasar has been "switched on" by infalling matter, these proximity zones grow very quickly. "Within a lifetime of 100,000 years, quasars should already have large proximity zones." Surprisingly, three of the quasars had very small proximity zones – indicating that the active quasar phase cannot have set in more than 100,000 years earlier. "No current theoretical models can explain the existence of these objects," says Professor Joseph Hennawi, who leads the research group at MPIA that made the discovery. "The discovery of these young objects challenges the existing theories of black hole formation and will require new models to better understand how black holes and galaxies formed." The astronomers have already planned their next steps. "We would like to find more of these young quasars," says Christina Eilers, "While finding these three unusual quasars might have been a fluke, finding additional examples would imply that a significant fraction of the known quasar population is much younger than expected." The scientists have already applied for telescope time to observe several additional candidates. The results, they hope, will constrain new theoretical models about the formation of the first supermassive black holes in the universe – and, by implication, help astronomers understand the history of the giant supermassive black holes at the center of present-day galaxies like our own Milky Way. Explore further: Why the discovery of a bevy of quasars will boost efforts to understand galaxies' origins More information: Anna-Christina Eilers et al. Implications of∼ 6 Quasar Proximity Zones for the Epoch of Reionization and Quasar Lifetimes, The Astrophysical Journal (2017). DOI: 10.3847/1538-4357/aa6c60


Artists' impression of the gas and dust disk around the planet-like object OTS44. First radio observations indicate that OTS44 has formed in the same way as a young star. Credit: Johan Olofsson (U Valparaiso & MPIA) First radio observations of the lonely, planet-like object OTS44 reveal a dusty protoplanetary disk that is very similar to disks around young stars. This is unexpected, given that models of star and planet formation predict that formation from a collapsing cloud, forming a central object with surrounding disk, should not be possible for such low-mass objects. Apparently, stars and planet-like objects are more similar than previously thought. The finding, by an international team led by Amelia Bayo and including several astronomers from the Max Planck Institute for Astronomy, has been published in Astrophysical Journal Letters. A new study of the lonely, planet-like object OTS44 has provided evidence that this object has formed in a similar way as ordinary stars and brown dwarfs – a surprising result that challenges current models of star and planet formation. The study by a group of astronomers, led by Amelia Bayo of the University of Valparaiso and involving several astronomers from the Max Planck Institute for Astronomy, used the ALMA observatory in Chile to detect dust from the disk surrounding OTS44. This detection yielded mass estimates for the dust contained in the disk, which place OTS44 in a row with stars and brown dwarfs (that is, failed stars with too little mass for sustained nuclear fusion): All these objects, it seems, have rather similar properties, including a similar ratio between the mass of dust in the disk and the mass of the central object. The findings supplement earlier research that found OTS44 is still growing by drawing matter from its disk onto itself – another tell-tale similarity between the object and young stars. Taken together, this is compelling evidence that OTS44 formed in the same way as stars and brown dwarfs, namely by the collapse of a cloud of gas and dust. But going by current models of star and planet formation, it should not be possible for an object as low-mass as OTS44 to form in this way. An alternative way, the formation of multiple objects in one go, with low-mass objects like OTS44 among them, is contradicted by the observations, which show no such companion objects anywhere near OTS44. The strength of the radiation received from the dust at millimetre wavelength also suggests the presence of large, millimetre sized dust grains. This, too, is surprising. Under the conditions in the disk of a low-mass object, dust is not expected to clump together to reach this size (or beyond). Instead, the OTS44 dust grains appear to be growing – and might even be on the way of forming a mini-moon around the object; another similarity with stars and their planetary systems. Amelia Bayo (University of Valparaiso), who led this research effort, says: "The more we know about OTS44, the greater its similarities with a young star. But its mass is so low that theory tells us it cannot have formed like a star!" Thomas Henning of the Max Planck Institute for Astronomy adds: "It is amazing how an observatory like ALMA allows us to see half an Earth mass worth of dust orbiting an object with ten times the mass of Jupiter at a distance of 500 light-years. But the new data also shows the limit of our understanding. Clearly, there is still a lot to learn about the formation of low-mass astronomical objects!" Explore further: Brown dwarfs, stars share formation process, new study indicates More information: Amelia Bayo et al. First Millimeter Detection of the Disk around a Young, Isolated, Planetary-mass Object, The Astrophysical Journal (2017). DOI: 10.3847/2041-8213/aa7046


Cosmic delivery room: The protoplanetary dust disk around the young star HL Tauri. Left: earlier observations with the ALMA Observatory, which showed bright areas separated by gaps. Right: the new VLA observations with the VLA, which make the additional structures of the inner rings visible. The object marked as a clump is most likely a planetary embryo - a region in which a planet is just being born. Credit: Carrasco-Gonzalez et al.; Bill Saxton, NRAO/AUI/NSF Observations using the VLA radio telescope array in New Mexico show the innermost portion of a planetary birthplace around the young star HL Tauri in unprecedented detail. Clearly visible is a lump of dust with 3 to 8 times the mass of the Earth, which represents the ideal conditions for the formation of a planet: a planetary nursery with sufficient building material for a planet somewhere between the mass of our own Earth and that of Neptune. The presence of a lump points towards a solution for a fundamental problem of planet formation: how planets can form on the limited time scale available for such processes. New observations using the Karl G. Jansky Very Large Array (VLA) in New Mexico have produced some of the sharpest radio images yet of the disk around the young star HL Tauri. Earlier images taken with the ALMA observatory had already shown a characteristic pattern of dust rings and gaps in the disk. The new image shows a massive lump of dust in the innermost bright ring, a dust concentration with a mass between 3 and 8 times that of the Earth. MPIA director and co-leader of the discover team Thomas Henning says: "This lump looks like a 'planetary embryo', which is likely to develop into a fully grown planet over the next millions of years." The new discovery has wider implications: It has long been known that the simplest models of planet formation have a problem with time scales. In these models, the protoplanetary disks made of gas and dust, which a newly born star, are smooth and homogeneous. All the action happens on small scales, with dust grains sticking to each other and forming ever larger objects, until at long last planets are formed. But this is a rather slow process - too slow, since time is limited: Over the course of ten million years or so, gas and dust in the disk are driven away by the young star's intense radiation. Without gas and dust as raw material, planet formation will stop altogether. If the star has not managed to form large planets by then, it never will. The new images appear to show a sped-up, ultra-fast mode of planet formation: Gas flow within the disk produces local concentrations of dust, and planet formation processes in these high-dust regions can proceed much more quickly than usual. Hubert Klahr, leader of the MPIA Planet and Star Formation Theory Group, explains: "Ten years ago, we found first indications of such ultra-fast planet formation processes in our simulations. This is the first time that observations have shown us the details: High density dust rings that appear to form lumpy fragments." Further studies and analyses are underway to model the HL Tauri disk in detail, and to show that the giant lump is indeed attracting nearby matter to grow ever larger. Thomas Henning concludes: "Highly detailed images such as this are raising planet formation research to a new level. Apparently, disk structures such as the lump that we discovered are necessary if we want to explain the formation of systems like our own Solar System." Explore further: Discovery of multiple ring-like gaps in a protoplanetary disk More information: The VLA view of the HL Tau Disk - Disk Mass, Grain Evolution, and Early Planet Formation. arxiv.org/abs/1603.03731


News Article | March 17, 2016
Site: phys.org

The star and its disk were studied in 2014 with the Atacama Large Millimeter/submillimeter Array (ALMA), which produced what astronomers then called the best image ever of planet formation in progress. The ALMA image showed gaps in the disk, presumably caused by planet-like bodies sweeping out the dust along their orbits. This image, showing in real life what theorists had proposed for years, was surprising, however, because the star, called HL Tau, is only about a million years old—very young by stellar standards. The ALMA image showed details of the system in the outer portions of the disk, but in the inner portions of the disk, nearest to the young star, the thicker dust is opaque to the short radio wavelengths received by ALMA. To study this region, astronomers turned to the VLA, which receives longer wavelengths. Their VLA images show that region better than any previous studies. The new VLA images revealed a distinct clump of dust in the inner region of the disk. The clump, the scientists said, contains roughly 3 to 8 times the mass of the Earth. "We believe this clump of dust represents the earliest stage in the formation of protoplanets, and this is the first time we've seen that stage," said Thomas Henning, of the Max Planck Institute for Astronomy (MPIA). "This is an important discovery, because we have not yet been able to observe most stages in the process of planet formation," said Carlos Carrasco-Gonzalez from the Institute of Radio Astronomy and Astrophysics (IRyA) of the National Autonomous University of Mexico (UNAM). "This is quite different from the case of star formation, where, in different objects, we have seen stars in different stages of their life cycle. With planets, we haven't been so fortunate, so getting a look at this very early stage in planet formation is extremely valuable," he added. Analysis of the VLA data indicates that the inner region of the disk contains grains as large as one centimeter in diameter. This region, the scientists said, is presumably where Earth-like planets would form, as clumps of dust grow by pulling in material from their surroundings. Eventually, the clumps would gather enough mass to form solid bodies that would continue to grow into planets. The VLA observations, made in 2014 and 2015, received radio waves with a wavelength of 7 millimeters. The earlier ALMA observations of HL Tau were made at a wavelength of 1 millimeter. The VLA images showed a similar level of detail as the ALMA images. "These VLA observations are the most sensitive and show the most detail of any yet made of HL Tau's disk at these longer wavelengths," said Claire Chandler, of the National Radio Astronomy Observatory (NRAO). "The VLA's ability to produce such high-quality images in this region is very important to advancing our understanding of these initial stages of planet formation," Chandler added. The scientists are reporting their findings in the Astrophysical Journal Letters. Explore further: VLA images 18 years apart show dramatic difference in young stellar system


News Article | March 18, 2016
Site: www.rdmag.com

New images of a young star made with the Karl G. Jansky Very Large Array (VLA) reveal what scientists think may be the very earliest stages in the formation of planets. The scientists used the VLA to see unprecedented detail of the inner portion of a dusty disk surrounding the star, some 450 light-years from Earth. The star and its disk were studied in 2014 with the Atacama Large Millimeter/submillimeter Array (ALMA), which produced what astronomers then called the best image ever of planet formation in progress. The ALMA image showed gaps in the disk, presumably caused by planet-like bodies sweeping out the dust along their orbits. This image, showing in real life what theorists had proposed for years, was surprising, however, because the star, called HL Tau, is only about a million years old—very young by stellar standards. The ALMA image showed details of the system in the outer portions of the disk, but in the inner portions of the disk, nearest to the young star, the thicker dust is opaque to the short radio wavelengths received by ALMA. To study this region, astronomers turned to the VLA, which receives longer wavelengths. Their VLA images show that region better than any previous studies. The new VLA images revealed a distinct clump of dust in the inner region of the disk. The clump, the scientists said, contains roughly 3 to 8 times the mass of the Earth. "We believe this clump of dust represents the earliest stage in the formation of protoplanets, and this is the first time we've seen that stage," said Thomas Henning, of the Max Planck Institute for Astronomy (MPIA). "This is an important discovery, because we have not yet been able to observe most stages in the process of planet formation," said Carlos Carrasco-Gonzalez from the Institute of Radio Astronomy and Astrophysics (IRyA) of the National Autonomous University of Mexico (UNAM).  "This is quite different from the case of star formation, where, in different objects, we have seen stars in different stages of their life cycle. With planets, we haven't been so fortunate, so getting a look at this very early stage in planet formation is extremely valuable," he added. Analysis of the VLA data indicates that the inner region of the disk contains grains as large as one centimeter in diameter. This region, the scientists said, is presumably where Earth-like planets would form, as clumps of dust grow by pulling in material from their surroundings. Eventually, the clumps would gather enough mass to form solid bodies that would continue to grow into planets. The VLA observations, made in 2014 and 2015, received radio waves with a wavelength of 7 millimeters. The earlier ALMA observations of HL Tau were made at a wavelength of 1 millimeter. The VLA images showed a similar level of detail as the ALMA images. "These VLA observations are the most sensitive and show the most detail of any yet made of HL Tau's disk at these longer wavelengths," said Claire Chandler, of the National Radio Astronomy Observatory (NRAO). "The VLA's ability to produce such high-quality images in this region is very important to advancing our understanding of these initial stages of planet formation," Chandler added. The VLA study of HL Tau was an international collaboration, involving the UNAM, the MPIA, the NRAO, and the Spanish Consejo Superior de Investigaciones Cientificas (CSIC). The project leaders were Carlos Carrasco Gonzalez (UNAM) and Thomas Henning (MPIA). The scientists are reporting their findings in the Astrophysical Journal Letters. The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.


The world's largest digital sky survey data have been released. The Dec. 19 release of the Panoramic Survey Telescope & Rapid Response System (Pan-STARRS) project digitally surveyed and cataloged three-fourths of the night sky and captured information about 3 billion stars, galaxies, and other spatial objects. Participated by astronomers from the Max Planck Institutes for Astronomy, Heidelberg and Garching's Extraterrestrial Physics institute among others, the vast data of the digital sky survey comprises 3 billion sources including stars and galaxies. It must be mentioned that the survey paid extreme attention to the Milky Way plane and disk. This was an area shunned in most surveys because of the complexity involved in mapping the dusty regions. The project started in May 2010 as the first Panoramic Survey Telescope & Rapid Response System digital mapping of the sky in visible and near infrared light. "For the past three years, we put much effort into checking the quality of the data and defining the most useful structure for the catalog," explained Roberto Saglia, who represented the sky survey from Max Planck Institute for Extraterrestrial Physics. The survey scanned the sky in five filters until 2014 and two years were spent on cataloging the data in such a way the astrophysics community must benefit immensely. Hans-Walter Rix, director of the Galaxies and Cosmology department of MPIA noted that Pan-STARRS survey is unique because it combines imaging depth and colors in highlighting distant quasars which are the earliest evidence of giant black holes having emerged at the centers of galaxies. The roll out is in two steps. The first phase pertaining to "Static Sky" analyses individual epochs with every object assigned an average value in terms of brightness, position, and colors. Objects also get a stack image in the observed colors. Galaxies are provided with information on brightness, aperture sizes and viewing conditions. In part two of data, to be released in 2017, information on individual epochs will allow people to access individual images in each observation run. Reflecting the benefits for astronomers, Thomas Henning, director, Planet and Star Formation Department at MPIA said the data offers a better characterization of low-mass star formation in stellar clusters. "Based on Pan-Starrs, researchers are able to measure distances, motions and special characteristics such as the multiplicity fraction of all nearby stars, brown dwarfs, and of stellar remnants like, for example, white dwarfs," added Henning. In a nut shell, the gains of the Pan-STARRS project can be summarized as successfully tracking fast-moving objects in the sky with the use of the 6-foot telescope at the top of the Haleakala volcano in Hawaii's Maui. With meticulous details backed by images of the sky in every 30 seconds, expectations are high that the map can offer new insights into dark energy as well. © 2017 Tech Times, All rights reserved. Do not reproduce without permission.


News Article | December 19, 2016
Site: phys.org

In May 2010, the first Panoramic Survey Telescope & Rapid Response System or Pan-STARRS observatory, a 1.8-meter telescope at the summit of Haleakalā, on Maui, embarked on a digital map of the sky in visible and near infrared light. This was the first survey whose goal was to observe the sky very rapidly over and over again, looking for moving objects and transient or variable objects, including asteroids that could potentially threaten the Earth. The survey took approximately four years to complete, and scanned the sky 12 times in five filters. The data comprise 3 billion separate sources, including stars, galaxies, and various other objects. The immense collection contains 2 petabytes of data, which is equivalent to 40 million four-drawer filing cabinets filled with single-spaced text. All this information had to be properly catalogued so that the astrophysics community can quickly access and exploit the data. "For the past three years, we put much effort into checking the quality of the data and defining the most useful structure for the catalogue," explains Dr. Roberto Saglia, who led the Pan-STARRS participation at the Max Planck Institute for Extraterrestrial Physics. "In more than 100 teleconferences we discussed and improved test results, such as for astrometry or photometry for selected sky regions that have been observed previously with other telescopes. We also thought a lot about how best to combine the individual observations and how to present the relevant information for each type of objects." "Based on Pan-Starrs, researchers are able to measure distances, motions and special characteristics such as the multiplicity fraction of all nearby stars, brown dwarfs, and of stellar remnants like, for example white dwarfs. This will expand the census of almost all objects in the solar neighbourhood to distances of about 300 light-years", says Thomas Henning, director of the Planet and Star Formation Department of MPIA. "The Pan Starrs data will also allow a much better characterization of low-mass star formation in stellar clusters. Furthermore, we gathered about 4 million stellar light curves to identify Jupiter-like planets in close orbits around cool dwarf stars in order to constrain the fraction of such extrasolar planetary systems." "We also monitored our nearest neighbour, the Andromeda galaxy, where we detected several microlensing events and many new Cepheids variables. This allowed us to better constrain compact dark matter in M31 and improve its distance accuracy," concludes Ralf Bender, director of MPE. But Pan-STARRS also reaches out to on astronomical objects beyond our cosmic neighbourhood. "Pan-STARRS1 mapped our home galaxy, the Milky Way, to a level of detail never achieved before. The survey provides, for the first time, a deep and global view of a significant fraction of the Milky Way plane and disk—an area usually avoided by surveys given the complexity of mapping these dense and dusty regions", explains Hans-Walter Rix, director of the Galaxies and Cosmology department of MPIA. "And Pan-STARRS1 goes far beyond that: its unique combination of imaging depth, area and colors allowed it to discover the majority of the most distant known quasars: these are the earliest examples in our universe that giant black holes had grown at the centers of galaxies". The roll-out of the data is being done in two steps. Today's release is the "Static Sky," which is the average of each of the individual epochs. For every object, there's an average value for its position, its brightness, and its colours. Furthermore, for each object it will be possible to get the stack image in each of the observed colours. For galaxies there is further information such as their brightness for various aperture sizes and the seeing conditions. In 2017, the second set of data will be released, providing this information for each individual epoch, and also allowing people to access the individual images for each observation run. The full database will include information on each of the individual snapshots that Pan-STARRS took of a given region of sky, and that will complete the full 2 petabytes of data. "Our next step then is to measure the redshifts - that means distances - of galaxies and other cosmological objects," explains Saglia. "We need this information to analyse the distribution of galaxies in all three dimensions. From this structure, we can then infer the geometry of the Universe and further constrain our standard cosmological model. With the data of the individual epochs, we can then even study variability in far-away, active galaxies." The redshift information will be added to the Pan-STARRS catalogue as well. The data can be accessed at panstarrs.stsci.edu . Explore further: Astronomers release largest digital survey of the visible Universe The Pan-STARRS1 Surveys K. C. Chambers et al arxiv.org/abs/1612.05560 The Pan-STARRS1 Database and Data Products H. A. Flewelling et al arxiv.org/abs/1612.05243


News Article | February 21, 2017
Site: www.eurekalert.org

A team led from the Instituto de Astrofísica de Canarias (IAC) has found the most precise way ever to measure the rate at which stars form in galaxies using their radio emission at 1-10 Gigahertz frequency range Almost all the light we see in the universe comes from stars which form inside dense clouds of gas in the interstellar medium. The rate at which they form (referred to as the star formation rate, or SFR) depends on the reserves of gas in the galaxies and the physical conditions in the interstellar medium, which vary as the stars themselves evolve. Measuring the star formation rate is hence key to understand the formation and evolution of galaxies. Until now, a variety of observations at different wavelengths have been performed to calculate the SFR, each with its advantages and disadvantages. As the most commonly used SFR tracers, the visible and the ultraviolet emission can be partly absorbed by interstellar dust. This has motivated the use of hybrid tracers, which combine two or more different emissions, including the infrared, which can help to correct this dust absorption. However, the use of these tracers is often uncertain because other sources or mechanisms which are not related to the formation of massive stars can intervene and lead to confusion. Now, an international research team led by the IAC astrophysicist Fatemeh Tabatabaei has made a detailed analysis of the spectral energy distribution of a sample of galaxies, and has been able to measure, for the first time, the energy they emit within the frequency range of 1-10 Gigahertz which can be used to know their star formation rates. "We have used" explains this researcher "the radio emission because, in previous studies, a tight correlation was detected between the radio and the infrared emission, covering a range of more than four orders of magnitude". In order to explain this correlation, more detailed studies were needed to understand the energy sources and processes which produce the radio emission observed in the galaxies. "We decided within the research group to make studies of galaxies from the KINGFISH sample (Key Insights on Nearby Galaxies: a Far-Infrared Survey with Herschel) at a series of radio frequencies", recalls Eva Schinnerer from the Max-Planck-Institut für Astronomie (MPIA) in Heidelberg, Germany. The final sample consists of 52 galaxies with very diverse properties. "As a single dish, the 100-m Effelsberg telescope with its high sensitivity is the ideal instrument to receive reliable radio fluxes of weak extended objects like galaxies", explains Marita Krause from the Max-Planck-Institut für Radioastronomie (MPIfR) in Bonn, Germany, who was in charge of the radio observations of those galaxies with the Effelsberg radio telescope. "We named it the KINGFISHER project, meaning KINGFISH galaxies Emitting in Radio." The results of this project, published today in The Astrophysical Journal, show that the 1-10 Gigahertz radio emission used is an ideal star formation tracer for several reasons. Firstly, the interstellar dust does not attenuate or absorb radiation at these frequencies; secondly, it is emitted by massive stars during several phases of their formation, from young stellar objects to HII regions (zones of ionized gas) and supernova remnants, and finally, there is no need to combine it with any other tracer. For these reasons, measurements in the chosen range are a more rigorous way to estimate the formation rate of massive stars than the tracers traditionally used. This study also clarifies the nature of the feedback processes occurring due to star formation activity, which are key in evolution of galaxies. "By differentiating the origins of the radio continuum, we could infer that the cosmic ray electrons (a component of the interstellar medium) are younger and more energetic in galaxies with higher star formation rates, which can cause powerful winds and outflows and have important consequences in regulation of star formation", explains Fatemeh Tabatabaei.


News Article | February 21, 2017
Site: phys.org

Almost all the light we see in the universe comes from stars which form inside dense clouds of gas in the interstellar medium. The rate at which they form (referred to as the star formation rate, or SFR) depends on the reserves of gas in the galaxies and the physical conditions in the interstellar medium, which vary as the stars themselves evolve. Measuring the star formation rate is hence key to understand the formation and evolution of galaxies. Until now, a variety of observations at different wavelengths have been performed to calculate the SFR, each with its advantages and disadvantages. As the most commonly used SFR tracers, the visible and the ultraviolet emission can be partly absorbed by interstellar dust. This has motivated the use of hybrid tracers, which combine two or more different emissions, including the infrared, which can help to correct this dust absorption. However, the use of these tracers is often uncertain because other sources or mechanisms which are not related to the formation of massive stars can intervene and lead to confusion. Now, an international research team led by the IAC astrophysicist Fatemeh Tabatabaei has made a detailed analysis of the spectral energy distribution of a sample of galaxies, and has been able to measure, for the first time, the energy they emit within the frequency range of 1-10 Gigahertz which can be used to know their star formation rates. "We have used" explains this researcher "the radio emission because, in previous studies, a tight correlation was detected between the radio and the infrared emission, covering a range of more than four orders of magnitude". In order to explain this correlation, more detailed studies were needed to understand the energy sources and processes which produce the radio emission observed in the galaxies. "We decided within the research group to make studies of galaxies from the KINGFISH sample (Key Insights on Nearby Galaxies: a Far-Infrared Survey with Herschel) at a series of radio frequencies", recalls Eva Schinnerer from the Max-Planck-Institut für Astronomie (MPIA) in Heidelberg, Germany. The final sample consists of 52 galaxies with very diverse properties. "As a single dish, the 100-m Effelsberg telescope with its high sensitivity is the ideal instrument to receive reliable radio fluxes of weak extended objects like galaxies", explains Marita Krause from the Max-Planck-Institut für Radioastronomie (MPIfR) in Bonn, Germany, who was in charge of the radio observations of those galaxies with the Effelsberg radio telescope. "We named it the KINGFISHER project, meaning KINGFISH galaxies Emitting in Radio." The results of this project, published today in The Astrophysical Journal, show that the 1-10 Gigahertz radio emission used is an ideal star formation tracer for several reasons. Firstly, the interstellar dust does not attenuate or absorb radiation at these frequencies; secondly, it is emitted by massive stars during several phases of their formation, from young stellar objects to HII regions (zones of ionized gas) and supernova remnants, and finally, there is no need to combine it with any other tracer. For these reasons, measurements in the chosen range are a more rigorous way to estimate the formation rate of massive stars than the tracers traditionally used. This study also clarifies the nature of the feedback processes occurring due to star formation activity, which are key in evolution of galaxies. "By differentiating the origins of the radio continuum, we could infer that the cosmic ray electrons (a component of the interstellar medium) are younger and more energetic in galaxies with higher star formation rates, which can cause powerful winds and outflows and have important consequences in regulation of star formation", explains Fatemeh Tabatabaei. Explore further: Forming stars in the early universe More information: F. S. Tabatabaei et al. The Radio Spectral Energy Distribution and Star-formation Rate Calibration in Galaxies, The Astrophysical Journal (2017). DOI: 10.3847/1538-4357/836/2/185


News Article | February 21, 2017
Site: spaceref.com

Almost all the light we see in the universe comes from stars which form inside dense clouds of gas in the interstellar medium. The rate at which they form (referred to as the star formation rate, or SFR) depends on the reserves of gas in the galaxies and the physical conditions in the interstellar medium, which vary as the stars themselves evolve. Measuring the star formation rate is hence key to understand the formation and evolution of galaxies. Until now, a variety of observations at different wavelengths have been performed to calculate the SFR, each with its advantages and disadvantages. As the most commonly used SFR tracers, the visible and the ultraviolet emission can be partly absorbed by interstellar dust. This has motivated the use of hybrid tracers, which combine two or more different emissions, including the infrared, which can help to correct this dust absorption. However, the use of these tracers is often uncertain because other sources or mechanisms which are not related to the formation of massive stars can intervene and lead to confusion. Now, an international research team led by the IAC astrophysicist Fatemeh Tabatabaei has made a detailed analysis of the spectral energy distribution of a sample of galaxies, and has been able to measure, for the first time, the energy they emit within the frequency range of 1-10 Gigahertz which can be used to know their star formation rates. "We have used" explains this researcher "the radio emission because, in previous studies, a tight correlation was detected between the radio and the infrared emission, covering a range of more than four orders of magnitude". In order to explain this correlation, more detailed studies were needed to understand the energy sources and processes which produce the radio emission observed in the galaxies. "We decided within the research group to make studies of galaxies from the KINGFISH sample (Key Insights on Nearby Galaxies: a Far-Infrared Survey with Herschel) at a series of radio frequencies", recalls Eva Schinnerer from the Max-Planck-Institut für Astronomie (MPIA) in Heidelberg, Germany. The final sample consists of 52 galaxies with very diverse properties. "As a single dish, the 100-m Effelsberg telescope with its high sensitivity is the ideal instrument to receive reliable radio fluxes of weak extended objects like galaxies", explains Marita Krause from the Max-Planck-Institut für Radioastronomie (MPIfR) in Bonn, Germany, who was in charge of the radio observations of those galaxies with the Effelsberg radio telescope. "We named it the KINGFISHER project, meaning KINGFISH galaxies Emitting in Radio." The results of this project, published today in The Astrophysical Journal, show that the 1-10 Gigahertz radio emission used is an ideal star formation tracer for several reasons. Firstly, the interstellar dust does not attenuate or absorb radiation at these frequencies; secondly, it is emitted by massive stars during several phases of their formation, from young stellar objects to HII regions (zones of ionized gas) and supernova remnants, and finally, there is no need to combine it with any other tracer. For these reasons, measurements in the chosen range are a more rigorous way to estimate the formation rate of massive stars than the tracers traditionally used. This study also clarifies the nature of the feedback processes occurring due to star formation activity, which are key in evolution of galaxies. "By differentiating the origins of the radio continuum, we could infer that the cosmic ray electrons (a component of the interstellar medium) are younger and more energetic in galaxies with higher star formation rates, which can cause powerful winds and outflows and have important consequences in regulation of star formation", explains Fatemeh Tabatabaei. Article: "The radio spectral energy distribution and star formation rate calibration in galaxies", by F. Tabatabaei et al. The Astrophysical Journal. Volume 836, Number 2. (DOI: 10.3847/1538-4357/836/2/185) Please follow SpaceRef on Twitter and Like us on Facebook.

Loading MPIA collaborators
Loading MPIA collaborators