Towards direct observation of large samples of intergalactic filaments in the early universe

One quasar of the sample embedded into extended Lyman alpha emission (cyan), which reaches the edge of the circumgalactic medium of its host galaxy. The uncovered filamentary structure is stretched in the direction of the second quasar of the pair (not shown). Multiple further sources are visible in this field, which are not physically associated with the quasar pair; these lie between Earth and the observed quasar. © MPA

This plot shows the alignment of the Lyman alpha nebulae with the quasar pair direction. An angle of zero degrees corresponds to perfect alignment. In the sample studied, all large nebulae (extending into the circumgalactic medium by more than 200,000 light years) trace the quasar pair direction. This trend is not driven by the quasar luminosity (colour of the points) or the distance between the quasar pairs (size of the dots). This shows that the Lyman alpha nebulae indeed trace the cosmic web filaments. © MPA

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The distribution of matter in the universe is predicted by supercomputer simulations to occur in a network of filaments, known as the "cosmic web", where galaxies form and evolve. The vast majority of this intricate structure is in the form of diffuse hydrogen gas, so rarefied that it is extremely challenging to observe it directly. A collaboration led by MPA researchers has targeted the active supermassive black holes of galaxy pairs at close separations to reveal the connecting filamentary structures of the cosmic web in the early universe. The results are promising and unveil evidence for such structures stretching between the observed pairs, ultimately providing excellent targets for future ultra-deep observations.

Galaxies are embedded in large reservoirs of gas bound to them by gravity, the so-called 'circumgalactic medium'. Like all gas in the universe, it mainly consists of hydrogen and helium with traces of other elements that are produced in stars and ejected from the galaxy disks in bubbles of hot gas or fast winds expanding into the circumgalactic medium. In turn, cool gas is funneled back into the galaxy in streams and can form new stars or feed the supermassive black hole at the galactic centre. Galaxies are not hermits though: large filamentary gas structures connect galaxies to their neighbours. This overall skeleton is called 'cosmic web' (see Monthly Highlight of June 2024), and galaxies can accrete additional material from its filaments to rejuvenate and grow. While simulations have explored this process very well, observational evidence of the filamentary cosmic web is sparse and mainly indirect, e.g. inferred from the observed position of galaxies in the local universe or by how the cosmic web absorbs light from bright background sources.

The areas where multiple filaments of the cosmic web intersect are called 'nodes', typically inhabited by the most massive galaxies. In the early universe, 11.5 billion years ago, these massive galaxies are commonly pinpointed by quasars – a brief phase in these galaxies’ life cycle, when matter falling onto their central supermassive black holes powers exceptionally luminous events that easily outshine all stars in their host galaxy. Therefore quasars can act as powerful natural 'cosmic flashlights': Their radiation can reach far into the circumgalactic medium and the surrounding cosmic web, lighting up the hydrogen gas at a specific ultraviolet colour, the Lyman alpha wavelength.

Researchers from MPA have now observed a sample of quasar pairs, i.e. two massive active galaxies in direct vicinity to each other, to unveil the Lyman alpha emission in their circumgalactic medium and in-between the galaxies (commonly referred to as 'Lyman alpha nebulae'). Extended emission is detected in most targeted systems (see example in Fig. 1) and the emission is preferentially aligned with the pair direction (see Fig. 2). These results are in line with expectations, if a cosmic web filament connects the two quasars and cool gas gets funneled directly from the filament through the circumgalactic medium down to the galactic disk.

Compared to other massive galaxies at this epoch, quasar pairs are embedded in smaller reservoirs of cool gas. Their circumgalactic medium actually resembles that of galaxies at a cosmic time one billion years later. Such an accelerated evolution might be caused by the rich environment inhabited by quasar pairs and/or by highly energetic processes connected to the accreting supermassive black holes, which could heat up the gas surrounding the galaxy and counteract the gas accretion.

This sample of quasar pair observations is the largest to date and represents the best collection of promising targets for directly studying the emission of the cosmic web in the early universe with future ultra-deep observations. More and more observations of the intricate web of cosmic filaments will become available in the near future.

Source: Max Planck Institute for Astrophysics/News

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Author:

Eileen Herwig
PhD student
tel:2344
eherwig@mpa-garching.mpg.de

Original publication

Eileen Herwig
Arrigoni Battaia, Fabrizio;
González Lobos, Jay; et al.
QSO MUSEUM: II. Search for extended Lyα emission around eight z ∼ 3 quasar pairs
A&A, 691, A210 (2024)

Source | DOI

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Astronomers Spot Distant Galaxy Group Driving Ancient Cosmic Makeover

EGS77 is the farthest galaxy group identified to date. It dates back to a time when the universe was only 680 million years old, or less than 5 percent of its current age of 13.8 billion years.  Credit: Nasa's Goddard Space Flight Center 

Maunakea, Hawaii – An international team of astronomers funded in part by NASA has found the farthest galaxy group identified to date. With the help of W. M. Keck Observatory on Maunakea, Hawaii, the team confirmed the trio of galaxies called EGS77 dates to a time when the universe was only 680 million years old, or less than 5% of its current age of 13.8 billion years. 

More significantly, observations show the galaxies are participants in a sweeping cosmic makeover called reionization. The era began when light from the first stars changed the nature of hydrogen throughout the universe in a manner akin to a frozen lake melting in the spring. This transformed the dark, light-quenching early cosmos into the one we see around us today.

“The young universe was filled with hydrogen atoms, which so attenuate ultraviolet light that they block our view of early galaxies,” said James Rhoads at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, who presented the findings on Jan. 5 at the 235th meeting of the American Astronomical Society in Honolulu. “EGS77 is the first galaxy group caught in the act of clearing out this cosmic fog.” 

While more distant individual galaxies have been observed, EGS77 is the farthest galaxy group to date showing the specific wavelengths of far-ultraviolet light revealed by reionization. This emission, called Lyman alpha light, is prominent in all members of EGS77.

In its infancy, the universe was a hot, opaque plasma. After expanding and cooling for about 380,000 years, the universe formed the first atoms — more than 90% of them hydrogen. Hundreds of millions of years later, this gas formed the first stars and galaxies. But the very presence of this abundant gas poses challenges for spotting galaxies in the early universe.  

In its earliest phase, the universe was a glowing plasma of particles, including electrons, protons, atomic nuclei, and light. Atoms could not yet exist. The universe was in an ionized state, similar to the gas inside a lighted neon sign or fluorescent tube.

This illustration of the EGS77 galaxy group shows the galaxies surrounded by overlapping bubbles of hydrogen ionized by ultraviolet light from their stars. By transforming light-quenching hydrogen atoms to ionized gas, UV starlight is thought to have formed such bubbles throughout the early universe, gradually transitioning it from opaque to completely transparent. Credit: Nasa's Goddard Space Flight Center

After the universe expanded and cooled for about 380,000 years, electrons and protons combined into the first atoms — more than 90% of them hydrogen. Hundreds of millions of years later, this gas formed the first stars and galaxies. But the very presence of this abundant gas poses challenges for spotting galaxies in the early universe. 

Hydrogen atoms readily absorb and quickly re-emit far-ultraviolet light known as Lyman alpha emission, which has a wavelength of 121.6 nanometers. When the first stars formed, some of the light they produced matched this wavelength. Because Lyman alpha light easily interacted with hydrogen atoms, it couldn’t travel far before the gas scattered it in random directions.  

“Intense light from galaxies can ionize the surrounding hydrogen gas, forming bubbles that allow starlight to travel freely,” said team member Vithal Tilvi, a researcher at Arizona State University in Tempe. “EGS77 has formed a large bubble that allows its light to travel to Earth without much attenuation. Eventually, bubbles like these grew around all galaxies and filled intergalactic space, reionizing the universe and clearing the way for light to travel across the cosmos.”

EGS77 was discovered as part of the Cosmic Deep And Wide Narrowband (Cosmic DAWN) survey, for which Rhoads serves as principal investigator. The team imaged a small area in the constellation Boötes using a custom-built filter on the National Optical Astronomy Observatory’s Extremely Wide-Field InfraRed Imager (NEWFIRM), which was attached to the 4-meter Mayall telescope at Kitt Peak National Observatory near Tucson, Arizona.

This animation shows EGS77’s place in cosmic history, flies to the galaxies, and illustrates how ultraviolet light from their stars create bubbles of ionized hydrogen around them.  Credit: Nasa's Goddard Space Flight Center 

Because the universe is expanding, Lyman alpha light from EGS77 has been stretched out during its travels, so astronomers actually detect it at near-infrared wavelengths. We can’t see these galaxies in visible light now because that light started out at shorter wavelengths than Lyman alpha and was scattered by the fog of hydrogen atoms.

To help select distant candidates, the researchers compared their images with publicly available data of the same region taken by NASA’s Hubble and Spitzer space telescopes. Galaxies appearing brightly in near-infrared images were tagged as possibilities, while those appearing in visible light were rejected as being too close.  

The team confirmed the distances to EGS77’s galaxies by using the Multi-Object Spectrometer for Infra-Red Exploration (MOSFIRE) on the Keck I telescope at the W. M. Keck Observatory on Maunakea, Hawaii. The three galaxies all show Lyman alpha emission lines at slightly different wavelengths, reflecting slightly different distances. The separation between adjacent galaxies is about 2.3 million light-years, or slightly closer than the distance between the Andromeda galaxy and our own Milky Way. 

A paper describing the findings, led by Tilvi, has been submitted to The Astrophysical Journal.

“While this is the first galaxy group identified as being responsible for cosmic reionization, future NASA missions will tell us much more,” said co-author Sangeeta Malhotra at Goddard. “The upcoming James Webb Space Telescope is sensitive to Lyman alpha emission from even fainter galaxies at these distances, and may find more galaxies within EGS77.” 

Astronomers expect that similar reionization bubbles from this era will be rare and hard to find. NASA’s planned Wide Field Infrared Survey Telescope (WFIRST) may be able to uncover additional examples, further illuminating this important transition in cosmic history.

Source:  W.M. Keck Observatory/News

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About MOSFIRE

MOSFIRE (Multi-Object Spectrograph for Infrared Exploration) is a highly-efficient instrument that can take images or up to 46 simultaneous spectra. Using a sensitive state-of-the-art detector and electronics system, MOSFIRE obtains observations fainter than any other near infrared spectrograph. MOSFIRE is an excellent tool for studying complex star or galaxy fields, including distant galaxies in the early Universe, as well as star clusters in our own Galaxy. MOSFIRE obtained first light in April 2012 and was made possible by funding provided by the National Science Foundation and astronomy benefactors Gordon and Betty Moore. It is currently the most in-demand instrument at the W. M. Keck Observatory.


About W. M. Keck Observatory

The W. M. Keck Observatory telescopes are among the most scientifically productive on Earth. The two, 10-meter optical/infrared telescopes on the summit of Maunakea on the Island of Hawaii feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectrometers, and world-leading laser guide star adaptive optics systems.

Some of the data presented herein were obtained at Keck Observatory, which is a private 501(c) 3 non-profit organization operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. 

The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.
The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the Native Hawaiian community.  We are most fortunate to have the opportunity to conduct observations from this mountain.

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Cool dense hydrogen gas around the first quasars

Figure 1: An atlas of the extended Ly-Alpha halos detected at around z~6 quasars (i.e., when the Universe is only 1/15th of its current age). The black dot at the center marks the quasar location. See also an animated 3D-version for P308-21 at the end of the page. © MPA

Quasars are amongst the brightest non-transient sources in the sky. Thanks to their high luminosity, they can be observed even at early cosmic times, where – surprisingly – these first quasars appear as already evolved systems: with black holes with masses exceeding one billion solar masses hosted by massive and heavily star forming galaxies. To explain such rapid growth, theorists believe these systems must reside in peculiarly dense environments, where huge gas reservoirs favour efficient inflow of material onto seed super-massive black holes. An international team of astronomers has recently found the first clear observational evidence that this is indeed the case. The new “panoramic” spectrograph called MUSE unveiled, for the first time, the almost ubiquitous presence of large amounts of cool gas in close proximity to the first quasars. This pristine fuel will fall on the primordial galaxies and sustain their growth in both stellar and black hole mass.

A prime objective of observational astrophysics is to peer deep into the young Universe and study how the first stars, galaxies, and black holes formed. For decades, astronomers exploited the brightness of quasars to study galaxy formation and evolution at all cosmic times, both as silhouettes against the luminous quasars, and in emission around them. Despite significant progress, we still do not understand the detailed processes whereby super-massive black holes with masses a billion times larger than the Sun assemble their mass in less than one billion years after the Big Bang, a small fraction of the current Universe age (13.7 billion years).

Hydro-dynamical cosmological simulations and analytical arguments suggest that to grow such massive systems in such a short time scale, the host galaxies of the first quasars need a continuous replenishment of fresh fuel. This gas has to be provided by cold filamentary streams from the so-called intergalactic medium down to the quasar's host galaxy and/or by mergers with other gas rich galaxies. While a merger is a violent short episode, the aforementioned filaments should be present around each quasar.

Emission from this large-scale gas is, however, typically too faint to be detected unless it is illuminated by the intense radiation from the quasar. In this case, the hydrogen in the gas reprocesses the incident radiation and shines as an extended "fuzz" of Ly-Alpha emission, now detectable with top-notch facilities. Recently, a team of astronomers from Garching, Heidelberg, and Santa Barbara took advantage of this boosted emission and embarked on a large survey aimed at uncovering the presence of this fuzz around more than 30 luminous quasars in the young Universe.

Figure 2: In the past years, several studies showed that quasars at the so-called cosmic noon (2-3 billion years after the Big Bang) are embedded in large Ly-Alpha nebulae. This plot illustrates how the average Ly-Alpha emission becomes fainter with increasing distance from the center of the dark matter halo where these quasars reside. The three different colors correspond to studies at different cosmic times. Surprisingly, while the shape of this drop remains similar, the earliest supermassive black holes (this study, red) appears to be surrounded by larger gas masses. © MPA

An investment of more than 50 hours with the panoramic integral-field spectrograph MUSE on the Very Large Telescope revealed that around 40% of first quasars are embedded in Ly-Alpha halos (see Figure 1) with a total extent of up to a hundred thousand light years. These halos are directly tracing the presence of cool dense hydrogen gas around the first quasars. In particular, the researchers discovered that this gas is bound within the dark matter halo of the quasar host galaxies and that it is abundant enough to maintain both the observed high-rate of gas consumption of the central supermassive black holes and their highly star forming host galaxies.

The presence of these extended nebulae is an important piece of the puzzle that astronomers are building to picture the formation of large cosmic structures more than 12 billion years ago. By providing detailed constraints on the fuel supply, these new observations can be used to test current theories and models for the growth of massive galaxies and black holes from the Big Bang to the present (see Figure 2). While additional observations are already planned to fully capture the physical status of the gas, current data already pose new challenges to theoretical models. They indicate that, rather than being smooth, "Lyman-alpha" nebulae take on the consistency of a mist comprising an enormous number of tiny droplets. Reproducing the structure of these clouds may prove to be a key challenge for the next generation of theoretical models of galaxy evolution.

3D visualization of the extended Ly-Alpha halo around the quasar P308-21 at z=6.23. The “hole” at the center represents the quasar location, which has been removed so as not to contaminate the measurement with light coming from the central black hole. The gas appears to be in a relatively quiescent motion, suggesting that it is moving within the dark matter halo where the central quasar resides.

Source: Max Planck Institute for Astrophysics

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Authors

Emanuele Paolo Farina
MPIA, Heidelberg, and MPA, Garching

Thales Gutcke, Dr.
Postdoc
Tel.: 2205
email: thales@mpa-garching.mpg.de

Tiago Costa, Dr.
Postdoc
Tel.: 2033
email: tcosta@mpa-garching.mpg.de

Dr. Fabrizio Arrigoni Battaia
Postdoc 
Tel.: 2288
email: arrigoni@mpa-garching.mpg.de

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More Information:

The Requiem Survey

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Studying Lyman-α-galaxies with strong gravitational lensing

Images by the Hubble Space telescope of all gravitational lens systems. The surface brightness scale is in electrons per second. The lensing morphologies are quite varied, from nearly complete Einstein rings to very compact 2-image systems. © MPA

These images show the lens model of one of the systems in the sample showing the actual data, the model, normalized residuals, and the reconstruction of the source (from left). Critical curves and caustics are plotted in grey. © MPA

The star-formation rate intensity of the objects from Fig. 1, based on the source reconstructions from the grid-based gravitational lens modelling. The colour-scale for each object is in units of solar masses per year in a square with 1 kiloparsec on the side. (The reconstruction of the object J0201+3228 was not included as this presented strong residuals.) © MPA

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Strong gravitational lensing is an extremely powerful tool to go beyond the current limits in angular resolution and to investigate the high-redshift, i.e. distant Universe. Scientists at MPA take advantage of this phenomenon to perform a detailed study of 17 Lyman-α-galaxies and present an analysis of the sizes and star formation rates of their reconstructed ultra-violet (UV) continuum emission.

Lyman-α-emitting (LAE) galaxies represent a unique probe of the young Universe, about 1 to 2 billion years after the Big Bang. Typical LAEs are characterised by high-ionisation and strong star formation with low metallicity (i.e. few elements heavier than hydrogen and in general a low mass. The Lyman-α emission is produced when electrons recombine with the ionized hydrogen atoms and the properties cited above, combined with low dust content, allow for the escape of a significant fraction of these photons. While this emission is thought to have had a crucial role in the reionisation of the young Universe, very little is known about the detailed structure of these galaxies and, most importantly, about the mechanism that leads to the production of these high-energy photons.

So far the study of these high-redshift objects has been limited to quantifying the properties of their strong optical lines. Alternatively, many efforts have been spent to identify local analogues, i.e. nearby galaxies presenting similar physical and morphological characteristics. Both these approaches, however, require significant investment in telescope time.

Another resource to study these galaxies lies in high-resolution imaging studies that so far have been very useful to reveal their structure. LAEs are found to be quite compact objects and there is no evidence that they change their size as they evolve. Moreover they are surrounded by a large Lyman-α-emitting halo which is on average 10 times more extended than the UV continuum emitting region. Also this halo does not show an evolution in size with redshift. However, such studies are currently limited by the angular resolution of the observations and struggle to reveal the detailed structure of these objects.

Strong gravitational lensing can be used to overcome these limits. The first statistically significant sample of LAEs at z~2.5 strongly lensed by early type galaxies at z~0.5, has recently been revealed by observations with the Hubble Space Telescope. Due to the lensing magnification by a factor of about 20, we can access and probe the detailed structure of these galaxies at scales around 100 pc (some 300 light-years).

We have studied the intrinsic properties of the UV-continuum emission of these LAEs and we found that they have a median star formation rate of 1.4 solar masses per year with peaks of up to 54 solar masses per year. (This is actually a lower limit as we could not correct for dust attenuation.) We have found these galaxies to be quite compact, with a median size of about 500 pc and a range of radii from 200 to 1800 pc – our Milky Way with about 60 000 pc is gigantic compared to these LAE. Interestingly, they show quite complex morphologies with several compact and diffuse components, while in some cases they appear to be interacting. In two cases (14 percent of 17?) the galaxies seem to have off-axis components that may be associated with mergers.

Most interestingly, our LAEs are found to be quite elliptical, with a mean axis-ratio of about 0.5. This morphology is consistent with disk-like structures of star-formation for three-quarters of our sample, which would rule out models where the Lyman-α-emission is only seen perpendicular to the disk to favour instead clumpy models. Our results are in agreement with the studies of non-lensed LAEs at similar redshifts, but are more robust given the improved angular resolution of our analysis and given that no stacking techniques are needed.

With 200 pc, our lower limit on the intrinsic size of these objects is a factor of two smaller than what is achieved in non-lensed LAEs studies. In general our analysis further promotes gravitational lensing as a powerful tool to analyse and resolve the detailed structure of high-redshift galaxies, allowing the study of their physical and morphological properties at a resolution otherwise only achievable with nearby targets.

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Authors

Ritondale, Elisa Ritondale, Elisa PhD student
Phone: 2233
Email: elisa@mpa-garching.mpg.de
Room: 252

Vegetti, Simona Vegetti, Simona
Scientific Staff
Phone: 2285
Email: svegetti@mpa-garching.mpg.de
Room: 107

Source: Max Planck Institute for Astrophysics

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Studying Lyman-α-galaxies with strong gravitational lensing

Images by the Hubble Space telescope of all gravitational lens systems. The surface brightness scale is in electrons per second. The lensing morphologies are quite varied, from nearly complete Einstein rings to very compact 2-image systems. © MPA

Strong gravitational lensing is an extremely powerful tool to go beyond the current limits in angular resolution and to investigate the high-redshift, i.e. distant Universe. Scientists at MPA take advantage of this phenomenon to perform a detailed study of 17 Lyman-α-galaxies and present an analysis of the sizes and star formation rates of their reconstructed ultra-violet (UV) continuum emission.

Lyman-α-emitting (LAE) galaxies represent a unique probe of the young Universe, about 1 to 2 billion years after the Big Bang. Typical LAEs are characterised by high-ionisation and strong star formation with low metallicity (i.e. few elements heavier than hydrogen and in general a low mass. The Lyman-α emission is produced when electrons recombine with the ionized hydrogen atoms and the properties cited above, combined with low dust content, allow for the escape of a significant fraction of these photons. While this emission is thought to have had a crucial role in the reionisation of the young Universe, very little is known about the detailed structure of these galaxies and, most importantly, about the mechanism that leads to the production of these high-energy photons.

So far the study of these high-redshift objects has been limited to quantifying the properties of their strong optical lines. Alternatively, many efforts have been spent to identify local analogues, i.e. nearby galaxies presenting similar physical and morphological characteristics. Both these approaches, however, require significant investment in telescope time.

These images show the lens model of one of the systems in the sample showing the actual data, the model, normalized residuals, and the reconstruction of the source (from left). Critical curves and caustics are plotted in grey. © MPA

Another resource to study these galaxies lies in high-resolution imaging studies that so far have been very useful to reveal their structure. LAEs are found to be quite compact objects and there is no evidence that they change their size as they evolve. Moreover they are surrounded by a large Lyman-α-emitting halo which is on average 10 times more extended than the UV continuum emitting region. Also this halo does not show an evolution in size with redshift. However, such studies are currently limited by the angular resolution of the observations and struggle to reveal the detailed structure of these objects.

Strong gravitational lensing can be used to overcome these limits. The first statistically significant sample of LAEs at z~2.5 strongly lensed by early type galaxies at z~0.5, has recently been revealed by observations with the Hubble Space Telescope. Due to the lensing magnification by a factor of about 20, we can access and probe the detailed structure of these galaxies at scales around 100 pc (some 300 light-years).

The star-formation rate intensity of the objects from Fig. 1, based on the source reconstructions from the grid-based gravitational lens modelling. The colour-scale for each object is in units of solar masses per year in a square with 1 kiloparsec on the side. (The reconstruction of the object J0201+3228 was not included as this presented strong residuals.) © MPA

We have studied the intrinsic properties of the UV-continuum emission of these LAEs and we found that they have a median star formation rate of 1.4 solar masses per year with peaks of up to 54 solar masses per year. (This is actually a lower limit as we could not correct for dust attenuation.) We have found these galaxies to be quite compact, with a median size of about 500 pc and a range of radii from 200 to 1800 pc – our Milky Way with about 60 000 pc is gigantic compared to these LAE. Interestingly, they show quite complex morphologies with several compact and diffuse components, while in some cases they appear to be interacting. In two cases (14 percent of 17?) the galaxies seem to have off-axis components that may be associated with mergers.

Most interestingly, our LAEs are found to be quite elliptical, with a mean axis-ratio of about 0.5. This morphology is consistent with disk-like structures of star-formation for three-quarters of our sample, which would rule out models where the Lyman-α-emission is only seen perpendicular to the disk to favour instead clumpy models. Our results are in agreement with the studies of non-lensed LAEs at similar redshifts, but are more robust given the improved angular resolution of our analysis and given that no stacking techniques are needed.

With 200 pc, our lower limit on the intrinsic size of these objects is a factor of two smaller than what is achieved in non-lensed LAEs studies. In general our analysis further promotes gravitational lensing as a powerful tool to analyse and resolve the detailed structure of high-redshift galaxies, allowing the study of their physical and morphological properties at a resolution otherwise only achievable with nearby targets.

Authors

Ritondale, Elisa
PhD student
Phone: 2233
Email: elisa@mpa-garching.mpg.de
Room: 252

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

Source: Max Planck Institute for Astrophysics

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Gemini Confirms the Most Distant Radio Galaxy

Top: Two-dimensional GMOS spectrum of the strong emission line observed in the radio galaxy TGSS J1530+1049. The size of the emission region is a bit less than one arcsec. Bottom: One-dimensional profile of the observed emission line. The asymmetry indicates that the line is Lyman-α at redshift of z = 5.72, making TGSS J1530+1049 the most distant radio galaxy known to date.

Using the Gemini North telescope in Hawai`i, an international team of astronomers from Brazil, Italy, the Netherlands, and the UK has discovered the most distant radio galaxy to date, at 12.5 billion light years, when the Universe was just 7% of its current age.

The team used spectroscopic data from the Gemini Multi-Object Spectrograph (GMOS-N) to measure a redshift of z = 5.72 for the radio galaxy identified as TGSS J1530+1049. This is the largest redshift of any known radio galaxy. The redshift of a galaxy tells astronomers its distance because galaxies at greater distances move away from us at higher speeds, and this motion causes the galaxy's light to shift farther into the red. Because light has a finite speed and takes time to reach us, more distant galaxies are also seen at earlier times in the history of the Universe.

The study was led by graduate students Aayush Saxena (Leiden Observatory, Netherlands) and Murilo Marinello (Observatório Nacional, Brazil), and the observations were obtained through Brazil's participation in Gemini. "In the Gemini spectrum of TGSS J1530+1049, we found a single emission line of hydrogen, known as the Lyman alpha. The observed shift of this line allowed us to estimate the galaxy's distance," explains Marinello.

The relatively small size of the radio emission region in TGSS J1530+1049 indicates that it is quite young, as expected at such early times. Thus, the galaxy is still in the process of assembling. The radio emission in this kind of galaxy is powered by a supermassive black hole that is sucking in material from the surrounding environment. This discovery of the most distant radio galaxy confirms that black holes can grow to enormous masses very quickly in the early Universe.

The measured redshift of TGSS J1530+1049 places it near the end of the Epoch of Reionization, when the majority of the neutral hydrogen in the Universe was ionized by high-energy photons from young stars and other sources of radiation. "The Epoch of Reionization is very important in cosmology, but it is still not well understood," said Roderik Overzier, also of Brazil's Observatorio Nacional, and the Principal Investigator of the Gemini program. "Distant radio galaxies can be used as tools to find out more about this period."

The research has been published by Monthly Notices of the Royal Astronomical Society. A preprint of the paper is available at astro-ph.

Source: Gemini Observatory

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Distant Galaxies ‘Lift the Veil’ on the End of the Cosmic Dark Ages

False color image of a 2 square degree region of the LAGER survey field, created from images taken in the optical at 500 nm (blue), in the near-infrared at 920 nm (red), and in a narrow-band filter centered at 964 nm (green). The last is sensitive to hydrogen Lyman alpha emission at z ~ 7. The small white boxes indicate the positions of the 23 LAEs discovered in the survey. The detailed insets (yellow) show two of the brightest LAEs; they are 0.5 arcminutes on a side, and the white circles are 5 arcseconds in diameter. Image Credit: Zhen-Ya Zheng (SHAO) & Junxian Wang (USTC).

Milestones in the history of the Universe (not to scale). The intergalactic gas was in a neutral state from about 300,000 years after the Big Bang until light from the first generation of stars and galaxies began to ionize it. The gas was completely ionized after 1 billion years. The LAGER study takes a close look at the state of the Universe at 800 million years (yellow box) to investigate when and how this transformation occurred. Image Credit: NAOJ.

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Astronomers studying the distant Universe have found that small star-forming galaxies were abundant when the Universe was only 800 million years old, a few percent of its present age. The results suggest that the earliest galaxies, which illuminated and ionized the Universe, formed at even earlier times.

Long ago, about 300,000 years after the beginning of the Universe (the Big Bang), the Universe was dark. There were as yet no stars and galaxies, and the Universe was filled with neutral hydrogen gas. At some point the first galaxies appeared, and their energetic radiation ionized their surroundings, the intergalactic gas, illuminating and transforming the Universe.

While this dramatic transformation is known to have occurred sometime in the interval between 300 million years and 1 billion years after the Big Bang, determining when the first galaxies formed is a challenge. The intergalactic gas, which is initially neutral, strongly absorbs and scatters the ultraviolet light emitted by the galaxies, making them difficult to detect.

To home in on when the transformation occurred, astronomers take an indirect approach. Using the demographics of small star-forming galaxies to determine when the intergalactic gas became ionized, they can infer when the ionizing sources, the first galaxies, formed. If star forming galaxies, which glow in the light of the hydrogen Lyman alpha line, are surrounded by neutral hydrogen gas, the Lyman alpha photons are readily scattered, much like headlights in fog, obscuring the galaxies. When the gas is ionized, the fog lifts, and the galaxies are easier to detect.

A new study taking this approach has discovered 23 candidate Lyman alpha emitting galaxies (LAEs) that were present 800 million years after the Big Bang (at a redshift of z~7), the largest sample detected to date at that epoch. The study, “Lyman-Alpha Galaxies in the Epoch of Reionization” (LAGER), was carried out by an international team of astronomers from China, the US, and Chile using the Dark Energy Camera (DECam) on the CTIO 4-m Blanco telescope.

While the study detected many LAEs, it also found that LAEs were 4 times less common at 800 million years than they were a short time later, at 1 billion years (at a redshift of z~5.7). The results imply that the process of ionizing the Universe began early and was still incomplete at 800 million years, with the intergalactic gas about half neutral and half ionized at that epoch. The low incidence rate of LAEs at 800 million years results from the suppression of their Lyman alpha emission by neutral intergalactic gas.

The study shows that “the fog was already lifting when the universe was 5% of its current age”, explained Sangeeta Malhotra (Goddard Space Flight Center and Arizona State University), one of the co-leads of the survey.

Junxian Wang (USTC), the organizer of the study, further explained, “Our finding that the intergalactic gas is 50% ionized at z ~ 7 implies that a large fraction of the first galaxies that ionized and illuminated the universe formed early, less than 800 million years after the Big Bang.”

For Zhenya Zheng (Shanghai Astronomical Observatory, CAS), the lead author of the paper describing these results, “800 million years is the current frontier in reionization studies.” While hundreds of LAEs have been found at later epochs, only about two dozen candidate LAEs were known at 800 million years prior to the current study. The new results dramatically increase the number of LAEs known at this epoch.

“None of this science would have been possible without the widefield capabilities of DECam and its community pipeline for data reduction,” remarked coauthor James Rhoads. “These capabilities enable efficient surveys and thereby the discovery of faint galaxies as well as rare, bright ones.”

To build on these results, the team is “continuing the search for distant star forming galaxies over a larger volume of the Universe”, said Leopoldo Infante (Pontificia Catolica University of Chile and the Carnegie Institution for Science), “to study the clustering of LAEs.” Clustering provides unique insights into how the fog lifts. The team is also investigating the nature of these distant galaxies.

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Reference: 

“First Results from the Lyman Alpha Galaxies in the Epoch of Reionization (LAGER) Survey: Cosmological Reionization at z ~ 7,” Zhenya Zheng et al. 2017, Astrophysical Journal Letters, 842, 22.

Preprint: https://arxiv.org/abs/1703.02985

Cerro Tololo Inter-American Observatory is managed by the National Optical Astronomy Observatory, which is operated by the Association of Universities for Research in Astronomy Inc. (AURA) under a cooperative agreement with the National Science Foundation.

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Science Contacts

Dr. Junxian Wang
Department of Astronomy
University of Science and Technology of China
96 Jinzhai Road Hefei, Anhui 230026 China
Email: jxw@ustc.edu.cn

Dr. Sangeeta Malhotra
ASU School of Earth and Space Exploration
and
Astrophysics Science Division,
Goddard Space Flight Center
8800 Greenbelt Road
Greenbelt, Maryland 20771
Email: sangeeta.malhotra@asu.edu

Source: National Optical Astronomy Observatory>