DECam and Gemini South Discover Three Tiny ‘Stellar-Ghost-Town’ Galaxies

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Sculptor Galaxies

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Sculptor A

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Sculptor B

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Sculptor C

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Videos

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Cosmoview Episode 93: DECam and Gemini South Discover Three Tiny ‘Stellar-Ghost-Town’ Galaxies

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Cosmoview Episodio 93: DECam y Gemini Sur descubren tres diminutas ciudades fantasmas

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The Sculptor galaxies relative to NGC 300 (3D Visualization)

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Panning across the Sculptor galaxies

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Rare ultra-faint dwarf galaxies beyond the influence of other galaxies show evidence that star formation was stifled long ago

By combining data from the DESI Legacy Imaging Surveys and the Gemini South telescope, astronomers have investigated three ultra-faint dwarf galaxies that reside in a region of space isolated from the environmental influence of larger objects. The galaxies, located in the direction of NGC 300, were found to contain only very old stars, supporting the theory that events in the early Universe cut star formation short in the smallest galaxies.

Ultra-faint dwarf galaxies are the faintest type of galaxy in the Universe. Typically containing just a few hundred to a thousand stars — compared with the hundreds of billions that make up the Milky Way — these small diffuse structures usually hide inconspicuously among the many brighter residents of the sky. For this reason, astronomers have previously had the most luck finding them nearby, in the vicinity of our own Milky Way Galaxy.

But this presents a problem for understanding them; the Milky Way’s gravitational forces and hot corona can strip away the dwarf galaxies’ gas and interfere with their natural evolution. Additionally, further out beyond the Milky Way, ultra-faint dwarf galaxies increasingly become too diffuse and unresolvable for astronomers and traditional computer algorithms to detect.

That’s why a manual, by-eye search by University of Arizona astronomer David Sand was needed to discover three faint and ultra-faint dwarf galaxies located in the direction of spiral galaxy NGC 300 and the Sculptor constellation. “It was during the pandemic,” recalls Sand. “I was watching TV and scrolling through the DESI Legacy Survey viewer, focusing on areas of sky that I knew hadn't been searched before. It took a few hours of casual searching, and then boom! They just popped out.”

The images uncovered by Sand were taken for the DECam Legacy Survey (DECaLS), one of three public surveys, known as the DESI Legacy Imaging Surveys [1], that jointly imaged 14,000 square degrees of sky to provide targets for the ongoing Dark Energy Spectroscopic Instrument (DESI) Survey. DECals was conducted using the 570-megapixel Department of Energy-fabricated Dark Energy Camera (DECam), mounted on the U.S. National Science Foundation (NSF) Víctor M. Blanco 4-meter Telescope at Cerro Tololo Inter-American Observatory (CTIO) in Chile, a Program of NSF NOIRLab.

The Sculptor galaxies, as they are referred to in the paper, are among the first ultra-faint dwarf galaxies found in a pristine, isolated environment free from the influence of the Milky Way or other large structures. To investigate the galaxies further, Sand and his team used the Gemini South telescope, one half of the International Gemini Observatory, partly funded by the NSF and operated by NSF NOIRLab. The results from their study are presented in a paper appearing in The Astrophysical Journal Letters, as well as at a press conference at the AAS 245 meeting in National Harbor, Maryland.

Gemini South’s Gemini Multi-Object Spectrograph (GMOS) captured all three galaxies in exquisite detail. An analysis of the data showed that they appear to be empty of gas and contain only very old stars, suggesting that their star formation was stifled a long time ago. This bolsters existing theories that ultra-faint dwarf galaxies are stellar ‘ghost towns’ where star formation was cut off in the early Universe.

This is exactly what astronomers would expect for such tiny objects. Gas is the crucial raw material required to coalesce and ignite the fusion of a new star. But ultra-faint dwarf galaxies just have too little gravity to hold onto this all-important ingredient, and it is easily lost when they are buffeted by the dynamic Universe they are part of.

But the Sculptor galaxies are far from any larger galaxies, meaning their gas could not have been removed by giant neighbors. An alternative explanation is an event called the Epoch of Reionization — a period not long after the Big Bang when high-energy ultraviolet photons filled the cosmos, potentially boiling away the gas in the smallest galaxies. Another possibility is that some of the earliest stars in the dwarf galaxies underwent energetic supernova explosions, emitting ejecta at up to 35 million kilometers per hour (about 20 million miles per hour) and pushing the gas out of their own hosts from within.

If reionization is responsible, these galaxies would open a window into studying the very early Universe. “We don’t know how strong or uniform this reionization effect is,” explains Sand. “It could be that reionization is patchy, not occurring everywhere all at once. We’ve found three of these galaxies, but that isn’t enough. It would be nice if we had hundreds of them. If we knew what fraction was affected by reionization, that would tell us something about the early Universe that is very difficult to probe otherwise.”

“The Epoch of Reionization potentially connects the current day structure of all galaxies with the earliest formation of structure on a cosmological scale,” says Martin Still, NSF program director for the International Gemini Observatory. “The DESI Legacy Surveys and detailed follow-up observations by Gemini allow scientists to perform forensic archeology to understand the nature of the Universe and how it evolved to its current state.”

To speed up the search for more ultra-faint dwarf galaxies, Sand and his team are using the Sculptor galaxies to train an artificial intelligence system called a neural network to identify more. The hope is that this tool will be able to automate and accelerate discoveries, offering a much vaster dataset from which astronomers can draw stronger conclusions.

Source: NSF’s National Optical-Infrared Astronomy Research Laboratory (NOIRLab)/News.

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Notes

[1] The DESI Legacy Imaging Surveys data are served to the astronomical community via the Astro Data Lab at NSF NOIRLab’s Community Science and Data Center (CSDC).

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More information

This research was presented in a paper entitled “Three Quenched, Faint Dwarf Galaxies in the Direction of NGC 300: New Probes of Reionization and Internal Feedback” to appear in The Astrophysical Journal Letters. DOI: 10.3847/2041-8213/ad927c

The team is composed of David J. Sand (University of Arizona), Burçin Mutlu-Pakdil (Dartmouth College), Michael G. Jones (University of Arizona), Ananthan Karunakaran (University of Toronto), Jennifer E. Andrews (International Gemini Observatory/NSF NOIRLab), Paul Bennet (Space Telescope Science Institute), Denija Crnojević (University of Tampa), Giuseppe Donatiello (Unione Astrofili Italiani), Alex Drlica-Wagner (Fermi National Accelerator Laboratory, Kavli Institute for Cosmological Physics, University of Chicago), Catherine Fielder (University of Arizona), David Martínez-Delgado (Unidad Asociada al CSIC), Clara E. Martínez-Vázquez (International Gemini Observatory/NSF NOIRLab), Kristine Spekkens (Queen’s University), Amandine Doliva-Dolinsky (Dartmouth College, University of Tampa), Laura C. Hunter (Dartmouth College), Jeffrey L. Carlin (AURA/Rubin Observatory), William Cerny (Yale University), Tehreem N. Hai (Rutgers, the State University of New Jersey), Kristen B.W. McQuinn (Space Telescope Science Institute, Rutgers, the State University of New Jersey), Andrew B. Pace (University of Virginia), and Adam Smercina (Space Telescope Science Institute)

NSF NOIRLab, the U.S. National Science Foundation center for ground-based optical-infrared astronomy, operates the International Gemini Observatory (a facility of NSF, NRC–Canada, ANID–Chile, MCTIC–Brazil, MINCyT–Argentina, and KASI–Republic of Korea), NSF Kitt Peak National Observatory (KPNO), NSF Cerro Tololo Inter-American Observatory (CTIO), the Community Science and Data Center (CSDC), and NSF–DOE Vera C. Rubin Observatory (in cooperation with DOE’s SLAC National Accelerator Laboratory). It is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with NSF and is headquartered in Tucson, Arizona.

The scientific community is honored to have the opportunity to conduct astronomical research on I’oligam Du’ag (Kitt Peak) in Arizona, on Maunakea in Hawai‘i, and on Cerro Tololo and Cerro Pachón in Chile. We recognize and acknowledge the very significant cultural role and reverence of I’oligam Du’ag (Kitt Peak) to the Tohono O’odham Nation, and Maunakea to the Kanaka Maoli (Native Hawaiians) community.

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Links

• Read the paper: Three Quenched, Faint Dwarf Galaxies in the Direction of NGC 300: New Probes of Reionization and Internal Feedback
• DESI Legacy Imaging Surveys
• Photos of the Gemini South telescope
• Videos of the Gemini South telescope
• Images taken with GMOS-S
• Images of GMOS-S
• Photos of the Víctor M. Blanco 4-meter Telescope
• Videos of the Víctor M. Blanco 4-meter Telescope
• Photos of DECam
• Images taken by DECam
• Check out other NOIRLab Science Releases

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Contacts:

David Sand
Professor & Astronomer
University of Arizona/Steward Observatory
Email: dsand@arizona.edu

Josie Fenske
Jr. Public Information Officer
NSF NOIRLab
Email: josie.fenske@noirlab.edu

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The Whole Picture of Distant Supercluster in Three Dimensions

Figure 1: The 3-D and 2-D maps of the number density of galaxies associated with the supercluster. In the 2-D map, the large-scale structures of galaxies located in the slice at about 7.3 billion years ago are shown. The white areas show the structures already known from previous studies, and the yellow areas show the structures newly discovered by this study. The structures marked by the dotted ellipses are to be confirmed by future works. The white vertical line in the figure corresponds to a distance of about 30 million light-years (i.e., 10 Mpc). (Credit: NAOJ)

Using the Subaru Telescope and Gemini-North Telescope, a team of astronomers has revealed that the supercluster CL1604, a distant supercluster located about 7.3 billion light-years away, is a large-scale 3-D structure extending over about 160 million light-years in the north-south direction. This is more than two times more extended than what was already known. Until now, we saw merely the “tip of the iceberg” of the supercluster. The wide-field capability of the Subaru Telescope enabled us to survey the whole of the supercluster and the Gemini-North Telescope played a critical role in confirming the structures. This is the outcome of the good synergy of the telescopes of the Maunakea observatories.

Galaxies are distributed inhomogeneously in the Universe. It is well-known that nearby galaxies are strongly influenced by their environment, e.g., whether they are located in dense areas called galaxy clusters or less dense areas called voids. However, how galaxies form and evolve along with the growth of the cosmic web structures is one of the hot topics of astronomy. A wide-field survey of the distant Universe allows us to witness what actually happened with galaxies in the early phase of structure formation in the Universe. Among the few superclusters currently known, one of the best targets for study is the supercluster CL1604. Based on previous studies, its extent is 80 million light-years and its era is 7.3 billion years ago.

The uniqueness of the data taken by Hyper Suprime-Cam (HSC) on the Subaru Telescope is the deep imaging data over a field wide enough to fully cover the known supercluster and the surrounding area. A team led by Masao Hayashi and Yusei Koyama from NAOJ estimated the distances of individual galaxies from the galaxy colors using a technique called “photometric redshift.” Then, the three dimensional picture of the large-scale structures appears, which consists of several galaxy clusters newly discovered in the north-south direction as well as the structures already known (Figure 1). 

Figure 2: The distribution of redshift (i.e., distance in the depth direction) of the galaxies confirmed by our spectroscopic observations. In each area, the histogram is color-coded by the distance of the galaxies. The same color for the histograms means that the galaxy clusters are located at the same distance in the depth direction irrespective of the location on the sky. (Credit: NAOJ)

Furthermore, the team used the Faint Object Camera and Spectrograph (FOCAS) on the Subaru Telescope and the Gemini Multi-Object Spectrograph (GMOS) on Gemini-North to confirm the precise distances of 137 galaxies associated with the galaxy clusters revealed by HSC (Figure 2). It is found that the supercluster is a complex large-scale structure not only over the vast projected area but also along the line-of-sight direction in 3D. The galaxies spread over the 160 million light-years seem to be independent due to the vast area, however, the spectroscopic observations tell us that the galaxies formed simultaneously and then evolve along with the growth of large-scale structures. 

Our Galaxy is a member of Local Group on the outskirts of Virgo Galaxy Cluster. A team led by an astronomer from the University of Hawaii recently revealed that the Virgo Cluster is a member of a more extended enormous large-scale structure named the Laniakea Supercluster. "The supercluster we discovered 7.3 billion years ago may grow to be a huge large-scale structure similar to Laniakea where we live" said Hayashi. 

These results were published in Publications of the Astronomical Society of Japan (Hayashi et al., "The whole picture of the large-scale structure of the CL1604 supercluster at z∼0.9"). A preprint is available here.

Links

• Gemini Helps Map Larger than Expected Structure of Ancient Supercluster (Press Release from Gemini Observatory) 

Source: Subaru Telescope

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Gemini Observatory Captures Multicolor Image of First-ever Interstellar Comet

Gemini Observatory two-color composite image of C/2019 Q4 (Borisov) which is the first interstellar comet ever identified. This image was obtained using the Gemini North Multi-Object Spectrograph (GMOS) from Hawaii’s Maunakea. The image was obtained with four 60-second exposures in bands (filters) r and g. Blue and red dashes are images of background stars which appear to streak due to the motion of the comet. Composite image by Travis Rector. Image Credit: Gemini Observatory/NSF/AURA. download JPG 230 KB | TIFF 23 MB

The first-ever comet from beyond our Solar System has been successfully imaged by the Gemini Observatory in multiple colors. The image of the newly discovered object, denoted C/2019 Q4 (Borisov), was obtained on the night of 9-10 September using the Gemini Multi-Object Spectrograph on the Gemini North Telescope on Hawaii’s Maunakea.

“This image was possible because of Gemini’s ability to rapidly adjust observations and observe objects like this, which have very short windows of visibility,” said Andrew Stephens of Gemini Observatory who coordinated the observations. “However, we really had to scramble for this one since we got the final details at 3:00 am and were observing it by 4:45!”

The image shows a very pronounced tail, indicative of outgassing, which is what defines a cometary object. This is the first time an interstellar visitor to our Solar System has clearly shown a tail due to outgassing. The only other interstellar visitor studied in our Solar System was ‘Oumuamua which was a very elongated asteroid-like object with no obvious outgassing.

The Gemini observations used for this image were obtained in two color bands (filters) and combined to produce a color image. The observations were obtained as part of a target of opportunity program led by Piotr Guzik and Michal Drahus at the Jagiellonian University in Krakow (Poland). The research team has submitted a paper for publication.

C/2019 Q4 is currently close to the apparent position of the Sun in our sky and is consequently difficult to observe due to the glow of twilight. The comet’s hyperbolic path, which is evidence of its origin beyond our Solar System, will bring it to more favorable observing conditions over the next few months.

C/2019 Q4 was discovered by Russian amateur astronomer Gennady Borisov on 30 August, 2019.

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Contacts:

Peter Michaud
Gemini Observatory, Hilo HI
Email: pmichaud@gemini.edu
Cell: (808) 936-6643
Desk: (808) 974-2510

Michal Drahus
Jagiellonian University, Krakow (Poland)
Email: drahus@oa.uj.edu.pl

Andy Stephens
Gemini Observatory
Email: astephens@gemini.edu

Source: Gemini Observatory

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Science Public/Images About Careers Contact Change page style: Making Good Use of Bad Weather: Finding Metal-poor Stars Through the Clouds

Figure 1. Equatorial and Galactic coordinate distribution of the stars observed with Gemini North and Gemini South in poor weather conditions.

The Gemini telescopes helped identify low-metallicity stars by gathering medium-resolution spectroscopic GMOS data for 666 bright stars under poor weather conditions. These data provide a unique opportunity to explore the chemical evolution of the Milky Way and look at the enrichment of star-forming gas clouds in the early Universe. 

 

Note: Below are highlights from an article published in the April 2019 issue of GeminiFocus by Principal Investigator Vinicius Placco of the University of Notre Dame. The original papers were published in The Astrophysical Journal and The Astronomical Journal. 

Low-metallicity stars (stars with less than 1% of the elements heavier than Hydrogen and Helium than the Sun contains) are the Rosetta Stones of stellar astrophysics. Encoded in the atmosphere of these low-mass, long-lived relics are the signatures of the processes by which the first chemical elements were cooked up, perhaps as early as a few tens of millions of years after the Big Bang. These stars are believed to be the direct descendants of the first stars to be born in the Universe, which were massive and short-lived. Hence, second-generation, low-metallicity stars are the artifacts which help us write the ancient chemical history of the Universe.

In particular, the Extremely Metal-Poor stars (EMP - with iron abundances of 1/1,000 of the solar value) are believed to carry in their atmospheres the chemical fingerprints of the evolution of as few as one first-generation massive star. EMP stars are intrinsically rare (less than 30 stars identified to date with iron abundances of 1/10,000 of the solar value) and the majority (more than 60%) show a very strong molecular carbon signature in their optical spectrum. The low-metallicity and strong carbon also affect the colors of these stars in optical wavelengths. Taking advantage of this, we were able to preselect bright candidates from two public stellar databases — the RAdial Velocity Experiment (RAVE) and the Best & Brightest Survey (B&B). We then used the Gemini Multi-Object Spectrograph (GMOS; North and South) with the B600 gratings and 1-arcsecond slits to obtain the spectra of 666 stars (see Figure 1).

In total, seven GMOS Poor Weather programs were executed (three in the North and four in the South) spanning four semesters (from 2015A to 2016B). Those programs had 310 hours of allocated time, and, assuming the 666 targets took 222 hours of observing time, the efficiency was around 72%, meaning that only 28% of the already poor weather was lost, which is a great accomplishment for the program and the Observatory.

The spectra gathered at Gemini/GMOS are of sufficient quality (signal-to-noise ratios and spectral resolution) to allow for the determination of stellar atmospheric parameters: effective temperature, surface gravity, metallicity, and carbon abundance. A subset of these stars were then re-observed in higher-resolution, so it was possible to determine their full chemical abundance pattern. There is already a study published based on the extremely metal-poor star J2005-3057, first identified at Gemini (Cain et al., 2018). We are also gathering high-resolution data for the most carbon-enhanced stars identified by Gemini and the results are also promising. In the near future, such bright stars will be perfect targets for high-resolution spectroscopic follow-up with GHOST, which will be a great asset in pushing these efforts forward.

Source: Gemini Observatory

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Shining Light on Dim Galactic Neighbors

On sky distribution of all known Milky Way satellite candidates with respect to the Magellanic Clouds and the neutral hydrogen gas of the Magellanic stream. For more details we refer to Nidever et al. (2010). The three candidates discussed in this study are highlighted in cyan.

False color RGB image of DES1 which is the small overdensity of stars in the centre of this field. The arrows in the lower right corner have a length of 15 arcseconds.

By measuring the brightness of about a dozen stars, lingering just outside of our galaxy, a team of astronomers believe they have solved a nearby intergalactic mystery. The researchers exposed the identities of three ultra-faint dwarf galaxy candidates using the Gemini South telescope. The team reports that the objects appear to be loose clusters of stars, not dwarf galaxies as some had previously believed. This finding has profound ramifications on the quantity of cold dark matter around our Milky Way and, by implication, other galaxies.

Using the Gemini Multi-Object Spectrograph (GMOS) at the Gemini South telescope in Chile, an international research team led by Dr. Blair C. Conn of the Australian National University studied three ultra-faint dwarf galaxy candidates, and found they were not as expected.

The three ultra-faint dwarf galaxy suspects, DES1, Eridanus III, and Tucana V, located in the vicinity of the Magellanic Clouds, were studied using a wide array of classification techniques. For each, fundamental properties including age, mass, luminosity, metallicity (ratio of heavier elements) and distance were determined. Based upon these parameters, the objects have instead been classified as star clusters.

While the brightness and metallicity are consistent with that of ultra-faint dwarf galaxies, their size and structure reveal their true nature. DES1 and Eri III are, according to the researchers, old, small, and highly elliptical stellar populations with very low metallicity.  Tuc V displays a low-level excess of stars at various locations across the GMOS field without a well-defined center. This suggests that Tuc V is either a star cluster in a late stage of dissolution, or a grouping of stars associated with the Small Magellanic Cloud (SMC) halo.

Classification of these faint objects as star clusters implies that they are not dominated by dark matter, as dwarf galaxies typically are, “and so we are still trying to define ultra-faint dwarf galaxies. Where are these smallest galaxies, what are their properties and how many are there? Answering these questions will help complete the census of Milky Way satellites and let us understand the history of our galaxy.”, says Conn.

Conn and his team are looking into the “Missing Satellites” problem which was originally identified almost two decades ago. Based on what is called the hierarchical formation scenario, many astronomers expected a large number of dwarf satellite galaxies, each containing a high fraction of dark matter, surrounding larger galaxies like our Milky Way. However, too few such satellites have been found to account for the expected amounts of dark matter.  Thus, classifying these ultra-faint objects is crucial to our understanding of dark matter in the Universe.

Watch for a feature article on this result in the April issue of GeminiFocus.

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Abstract:

"We use deep Gemini/GMOS-S g,r photometry to study the three ultra-faint dwarf galaxy candidates DES1, Eridanus III (Eri III) and Tucana V (Tuc V). Their total luminosities, MV(DES1) =−1.42±0.50 and MV(Eri III) =−2.07±0.50, and mean metallicities, [Fe/H] =−2.38+0.21−0.19 and [Fe/H] =−2.40+0.19−0.12, are consistent with them being ultra-faint dwarf galaxies as they fall just outside the 1-sigma confidence band of the luminosity-metallicity relation for Milky Way satellite galaxies. However, their positions in the size-luminosity relation suggests that they are star clusters. 

Interestingly, DES1 and Eri III are at relatively large Galactocentric distances with DES1 located at DGC=74±4 kpc and Eri III at DGC=91±4 kpc. In projection both objects are in the tail of gaseous filaments trailing the Magellanic Clouds and have similar 3D-separations from the Small Magellanic Cloud (SMC): ΔDSMC,DES1 = 31.7 kpc and ΔDSMC,EriIII = 41.0 kpc, respectively. It is plausible that these stellar systems are metal-poor SMC satellites. Tuc V represents an interesting phenomenon in its own right. Our deep photometry at the nominal position of Tuc V reveals a low-level excess of stars at various locations across the GMOS field without a well-defined centre. A SMC Northern Overdensity-like isochrone would be an adequate match to the Tuc V colour-magnitude diagram, and the proximity to the SMC (12.1∘; ΔDSMC,TucV=13 kpc) suggests that Tuc V is either a chance grouping of stars related to the SMC halo or a star cluster in an advanced stage of dissolution."

Source: Gemini Observatory

Korean Astronomers Dissect a Fragmented Asteroid

Figure 1. Rotational light curve of the largest fragment of P/2010 A2. Time-series g’-band photometry over two nights (upper panel) and phase based on the best-fit double-peaked period of 11.36 hr (lower panel). A sine curve with a period of 11.36 hr was plotted in the upper panel (gray line). 

Figure 2. Composite image of asteroid P/2010 A2 constructed from data from the Gemini Multi-Object Spectrograph on Gemini North. The team used this data to compare against models of the object’s structure and dynamics.

A team of Korean astronomers uses imaging from the Gemini Multi-Object Spectrograph (GMOS) on Gemini North to characterize the rotation of active asteroid P/2010 A2’s largest fragment. The observations show that this faint and tiny (about the size of an American football field) asteroid, which underwent a mass ejection episode, is slowly rotating, indicative of an impact fragmentation rather a rotational breakup.

In January 2017, the active and fragmented main belt asteroid P/2010 A2 (hereafter A2) made its closest approach to the Earth after its 2010 discovery, when it exhibited a mysterious comet-like dust trail. Prior to this year’s passage, the fragments had not yet been characterized, due to the extremely small size (~120 meters in diameter) and faintness of this object. A Korean team, led by Yoonyoung Kim of Seoul National University, received time on Gemini North to observe the object’s 2017 close passage when the fragments and associated debris swarm were just over one astronomical unit away. 

According to Kim, a variety of hypotheses have been suggested to explain the history of this body, including rotational breakup, impact cratering, or shattering. The team determined a rotation period ~11.36 hours for the largest fragment. If the fragment’s spin period has been constant after the mass ejection, which Kim says is reasonable to believe, then it fails to meet the critical spin rate for rotational breakup. The observations also reveal that the largest fragment has a highly-elongated shape with about a 2:1 ratio. Looking at the size distributions of the ejecta and other fragments, the team concludes that the body likely underwent impact shattering in order to produce the observed morphology. 

The study’s light curve is shown in Figure 1 and presents the largest fragment’s double-peaked period of 11.36 +/- 0.02 hours. Figure 2 presents a composite from the imaging data revealing the array of fragments and debris used to determine the mass of the largest fragment is about 80% of the system’s mass with the other fragments and ejecta making up the remaining 20%. All figures are from the accepted paper scheduled for publication in The Astrophysical Journal Letters. A preprint is available here. 

Paper Abstract:
 

We report new observations of the active asteroid P/2010 A2 taken when it made its closest approach to the Earth (1.06 au in 2017 January) after its first discovery in 2010. Despite a crucial role of the rotational period in clarifying its ejection mechanism, the rotational property of P/2010 A2 has not yet been studied due to the extreme faintness of this tiny object (∼120 m in diameter). Taking advantage of the best observing geometry since the discovery, we succeed in obtaining the rotational light curve of the largest fragment with Gemini/GMOS-N. We find that (1) the largest fragment has a double-peaked period of 11.36±0.02 hr spinning much slower than its critical spin period; (2) the largest fragment is a highly elongated object (a/b⩾1.94) with an effective radius of 61.9^+16.8_−9.2 m; (3) the size distribution of the ejecta follows a broken power law (the power indices of the cumulative size distributions of the dust and fragments are 2.5±0.1 and 5.2±0.1, respectively); (4) the mass ratio of the largest fragment to the total ejecta is around 0.8; and (5) the dust cloud morphology is in agreement with the anisotropic ejection model in Kim et al. These new characteristics of the ejecta obtained in this work are favorable to the impact shattering hypothesis. 

Source: Gemini Observatory

Planetoid Pairs Reveal "A Kinder, Gentler Neptune"

Artist’s conception of a loosely tethered binary planetoid pair like those studied by Fraser et al. in this work which led to the conclusion that Neptune’s shepherding of them to the Kuiper Belt as gradual and gentle in nature. Credit: Gemini Observatoryy/AURA, artwork by Joy Pollard.  Full resolution JPEG | TIFF

The Gemini North telescope (foreground, right) with the Canada-France-Hawaii Telescope in background (left). Image obtained during observations for Col-OSSOS and both telescopes are pointing at the same target.Credit: Gemini Observatory/AURA, photo by Joy Pollard.  Full resolution JPEG | TIFF

"It’s a kinder, gentler Neptune," says Gemini astronomer Meg Schwamb in describing a new result that leaves little doubt about how Neptune gently swept a class of planetoid pairs into the outer Solar System. 

The study focused on a type of loosely bound pairs of planetoids in the outer reaches of our Solar System that scientists say were likely shepherded by Neptune’s gravitational nudges into their current orbits in the distant Kuiper Belt. The paper is published in the April 4th issue of the journal Nature Astronomy (subscription required). 

The research team, led by Wes Fraser of Queen’s University in Belfast, UK, used data collected from the Gemini North Frederick C. Gillett Telescope and Canada-France Hawaii Telescope (CFHT) both on Maunakea in Hawai‘i. The team measured the colors of peculiar new Cold Classical Kuiper Belt Object (CCKBO) pairs as part of the Colours of the Outer Solar System Origins Survey (Col-OSSOS). 

The objects are among a category of bodies known as "blue binaries" which are oddball pairs in the Kuiper Belt because they don’t share the very red color that distinguishes most of the other CCKBO’s surfaces. The Kuiper Belt is a huge swarm of icy small planetoids well beyond the orbit of Neptune, and left-over from the formation of our Solar System. 

It is believed that the blue binaries migrated from more inward parts of the Solar System out to the present-day Kuiper Belt. It is thought that this migration occurred several billion years ago during profound changes to the orbits of the outer planets Jupiter, Saturn, Uranus and Neptune. 

"The red CCKBOs are thought to have formed at the location in the outer Solar System where they currently reside. The blue binaries, on the other hand, are interlopers from closer in hiding out in the Kuiper belt today," says Schwamb, who is also a coauthor on the study. 

Fraser and his team compared the observed properties of the blue binaries to models of Neptune’s migration. Fraser found that although these blue binaries have such a tenuous gravitational embrace, these pairs can survive Neptune’s smoothly pushing them over a distance of at least four AU (four times the distance between the Earth and Sun) as the giant planet migrated outward. "The blue binaries are fossils from the long gone planetary disk that our planets formed from. These objects give us a unique new window into the history of the our Solar System," Schwamb adds.

"This research has opened the window to new aspects of understanding the early stages of planet growth,” concludes Fraser. “We now have a solid handle on how and where these blue binaries originated." 

Chris Davis, Program Officer at the U.S. National Science Foundation, one of the five partner organizations which support Gemini operations, notes that "This is another great example of the successful use of one of Gemini’s many versatile observing modes. The observatory’s Large and Long Program has allowed the team to find and study these enigmatic objects in amongst a sea of millions of other Kuiper Belt Objects." 

The Gemini/CFHT observations help address ongoing questions and debates among scientists about Neptune’s migration from its primordial formation orbital location to its current locale. The team found and characterized the peculiar blue binary objects thanks to CFHT MEGACAM data and confirmed by follow-up observations with the Gemini Multi-Object Spectrograph (GMOS) which was part of an ongoing Large and Long Program at Gemini to study the outer reaches of our Solar System. 

The observations required significant coordination between Gemini and CFHT. "Like synchronized swimming, Gemini North and the Canada-France-Hawaii telescopes aligned their movements to observe the Col-OSSOS Kuiper Belt objects at nearly the same time," said Schwamb. "This choreographed ballet on Maunakea allowed us to measure the light from the same side of the Kuiper Belt object, removing one of the main challenges in studying Solar System bodies that rotate." 

"Facilitating the simultaneous observations with the Col-OSSOS team and Gemini Observatory was challenging, but paved the way for a greater understanding of the origins of these blue binaries," said Todd Burdullis, Queued Service Operations Specialist at CFHT who helped to coordinate the observations. "In tandem, the two facilities observed all the colors of the outer solar system for the Col-OSSOS team." 

Queen's University Belfast's press release can be found here. 

Science Contacts:

• Wesley Fraser
  Col-OSSOS Principal Investigator
  Queen's University, Belfast, UK
  Email: wes.fraser@qub.ac.uk
  Office: +44 (0) 74 02 46 21 34
  Cell: +44 074 024 621 34


• Meg Schwamb
  Gemini Observatory
  Hilo, Hawai‘i
  Email: mschwamb@gemini.edu
  Office: 808 074-2593
  Cell: 808 315-8014


• Michele Bannister
  Col-OSSOS collaborator
  OSSOS Core member
  Queen's University Belfast
  Email: m.bannister@qub.ac.uk
  Phone: +44 074 555 471 79


• JJ Kavelaars
  Col-OSSOS collaborator
  OSSOS Co-PI
  Herzberg Institute, Victoria, BC, Canada
  Email: jjk@uvic.ca
  Phone: +1 778 677 3131

Media Contact:

•  
  • Peter Michaud
    Public Information and Outreach Manager
    Gemini Observatory
    Hilo, Hawai‘i
    Email: pmichaud@gemini.edu
    Desk: 808 974-2510
    Cell: 808 936-6643
  
  
  • Mary Beth Laychak
    Outreach Manager
    Canada-France-Hawaii Telescope
    Email: mary@cfht.hawaii.edu
    Phone: 808 885-3121
  
  
  • Emma Gallagher
    Communications Officer
    Queen's University, Belfast, UK
    Email: emma.gallagher@qub.ac.uk
    Phone: 028 9097 5384
  
  
  
  
  Source: Gemini Observatory

First evidence of rocky planet formation in Tatooine system

A disc of rocky debris from a disrupted planetesimal surrounds white dwarf plus brown dwarf binary star. The white dwarf is the burned-out core of a star that was probably similar to the Sun, the brown dwarf is only ~60 times heavier than Jupiter, and the two stars go around each other in only a bit over two hours. Credit: Mark Garlick, UCL, University of Warwick and University of Sheffield.  Full resolution JPEG
 

Using the Gemini Multi-Object Spectrograph (GMOS) on Gemini South, a team led by Jay Farihi (University College London) found, for the first time, a dust and debris disk surrounding a binary star with a white dwarf as a substellar companion. To date, almost all of the known planetary systems which include a white dwarf are single stars. Using GMOS spectra Farihi et al. identified critical metal features in the spectrum as well as the higher Balmer lines. From the Gemini data the team estimated a surface temperature of 21,800 Kelvin (about 3.5 times hotter than the Sun) and a mass of ~0.4 solar masses for the white dwarf star and a mass of ~0.063 solar masses for the companion. 

The research is published in the February 27th online issue of Nature Astronomy.

The following text is provided verbatim from the University College London press release: 

Evidence of planetary debris surrounding a double sun, ‘Tatooine-like’ system has been found for the first time by a UCL-led team of researchers.

Published today in Nature Astronomy and funded by the Science and Technology Facilities Council and the European Research Council, the study finds the remains of shattered asteroids orbiting a double sun consisting of a white dwarf and a brown dwarf roughly 1000 light-years away in a system called SDSS 1557.

The discovery is remarkable because the debris appears to be rocky and suggests that terrestrial planets like Tatooine – Luke Skywalker’s home world in Star Wars – might exist in the system. To date, all exoplanets discovered in orbit around double stars are gas giants, similar to Jupiter, and are thought to form in the icy regions of their systems.

In contrast to the carbon-rich icy material found in other double star systems, the planetary material identified in the SDSS 1557 system has a high metal content, including silicon and magnesium. These elements were identified as the debris flowed from its orbit onto the surface of the star, polluting it temporarily with at least 1017 g (or 1.1 trillion US tons) of matter, equating it to an asteroid at least 4 km in size.

Lead author, Dr Jay Farihi (UCL Physics & Astronomy), said: “Building rocky planets around two suns is a challenge because the gravity of both stars can push and pull tremendously, preventing bits of rock and dust from sticking together and growing into full-fledged planets. With the discovery of asteroid debris in the SDSS 1557 system, we see clear signatures of rocky planet assembly via large asteroids that formed, helping us understand how rocky exoplanets are made in double star systems."

In the Solar System, the asteroid belt contains the leftover building blocks for the terrestrial planets Mercury, Venus, Earth, and Mars, so planetary scientists study the asteroids to gain a better understanding of how rocky, and potentially habitable planets are formed. The same approach was used by the team to study the SDSS 1557 system as any planets within it cannot yet be detected directly but the debris is spread in a large belt around the double stars, which is a much larger target for analysis.

The discovery came as a complete surprise, as the team assumed the dusty white dwarf was a single star but co-author Dr Steven Parsons (University of Valparaíso and University of Sheffield), an expert in double star (or binary) systems noticed the tell-tale signs. "We know of thousands of binaries similar to SDSS 1557 but this is the first time we've seen asteroid debris and pollution. The brown dwarf was effectively hidden by the dust until we looked with the right instrument", added Parsons, "but when we observed SDSS 1557 in detail we recognised the brown dwarf's subtle gravitational pull on the white dwarf."

The team studied the binary system and the chemical composition of the debris by measuring the absorption of different wavelengths of light or ‘spectra’, using the Gemini Observatory South telescope and the European Southern Observatory Very Large Telescope, both located in Chile. 

Co-author Professor Boris Gänsicke (University of Warwick) analysed these data and found they all told a consistent and compelling story. "Any metals we see in the white dwarf will disappear within a few weeks, and sink down into the interior, unless the debris is continuously flowing onto the star. We'll be looking at SDSS 1557 next with Hubble, to conclusively show the dust is made of rock rather than ice."

Notes to Editors
 

For more information or to speak to the researchers involved, please contact Dr Rebecca Caygill, UCL press office. T: +44 (0)20 3108 3846 / +44 (0)7733 307 596, E: r.caygill@ucl.ac.uk

J. Farihi, S. G. Parsons, B. T. Gansicke, ‘A circumbinary debris disk in a polluted white dwarf system’ will be published by Nature Astronomy at 1600 London time / 1100 US Eastern Time on 27 February 2017 and is under a strict embargo until then. DOI: 10.1038/s41550-016-0032.

About UCL (University College London)
 

UCL was founded in 1826. We were the first English university established after Oxford and Cambridge, the first to open up university education to those previously excluded from it, and the first to provide systematic teaching of law, architecture and medicine. We are among the world's top universities, as reflected by performance in a range of international rankings and tables. UCL currently has over 38,000 students from 150 countries and over 12,000 staff. Our annual income is more than £1 billion.

www.ucl.ac.uk | Follow us on Twitter @uclnews | Watch our YouTube channel  YouTube.com/UCLTV

 

About the University of Warwick
 
The University of Warwick is consistently ranked in the top 10 universities in the UK and top 100 in the world. It is one of the UK's leading universities, with an acknowledged reputation for excellence in research, teaching and innovation, alongside pioneering links with business and industry.

About the University of Sheffield
 

With almost 27,000 of the brightest students from over 140 countries, learning alongside over 1,200 of the best academics from across the globe, the University of Sheffield is one of the world’s leading universities.

A member of the UK’s prestigious Russell Group of leading research-led institutions, Sheffield offers world-class teaching and research excellence across a wide range of disciplines.

Unified by the power of discovery and understanding, staff and students at the university are committed to finding new ways to transform the world we live in.

Sheffield is the only university to feature in The Sunday Times 100 Best Not-For-Profit Organisations to Work For 2016 and was voted number one university in the UK for Student Satisfaction by Times Higher Education in 2014. In the last decade it has won four Queen’s Anniversary Prizes in recognition of the outstanding contribution to the United Kingdom’s intellectual, economic, cultural and social life.

Sheffield has six Nobel Prize winners among former staff and students and its alumni go on to hold positions of great responsibility and influence all over the world, making significant contributions in their chosen fields.

Global research partners and clients include Boeing, Rolls-Royce, Unilever, AstraZeneca, Glaxo SmithKline, Siemens and Airbus, as well as many UK and overseas government agencies and charitable foundations.

About the Science and Technology Facilities Council (STFC)
 
The Science and Technology Facilities Council is keeping the UK at the forefront of international science and tackling some of the most significant challenges facing society such as meeting our future energy needs, monitoring and understanding climate change, and global security. The Council has a broad science portfolio including supporting UK work in space and ground-based astronomy technologies and research. http://www.stfc.ac.uk/

Source: Gemini Observatory 

First evidence of rocky planet formation in Tatooine system

A disc of rocky debris from a disrupted planetesimal surrounds white dwarf plus brown dwarf binary star. The white dwarf is the burn-out core of a star that was probably similar to the Sun, the brown dwarf is only ~60 times heavier than Jupiter, and the two stars go around each other in only a bit over two hours. Credit: Mark Garlick, UCL, University of Warwick and University of Sheffield. Full resolution JPEG

 

Using the Gemini Multi-Object Spectrograph (GMOS) on Gemini South, a team led by Jay Farihi (University College London) found, for the first time, a dust and debris disk surrounding a binary star with a white dwarf as a substellar companion. To date, almost all of the known planetary systems which include a white dwarf are single stars. Using GMOS spectra Farihi et al. identified critical metal features in the spectrum as well as the higher Balmer lines. From the Gemini data the team estimated a surface temperature of 21,800 Kelvin (about 3.5 times hotter than the Sun) and a mass of ~0.4 solar masses for the white dwarf star and a mass of ~0.063 solar masses for the companion. 

The research is published in the February 27th online issue of Nature Astronomy. 

The following text is provided verbatim from the University College London press release:
 

Evidence of planetary debris surrounding a double sun, ‘Tatooine-like’ system has been found for the first time by a UCL-led team of researchers.

Published today in Nature Astronomy and funded by the Science and Technology Facilities Council and the European Research Council, the study finds the remains of shattered asteroids orbiting a double sun consisting of a white dwarf and a brown dwarf roughly 1000 light-years away in a system called SDSS 1557.

The discovery is remarkable because the debris appears to be rocky and suggests that terrestrial planets like Tatooine – Luke Skywalker’s home world in Star Wars – might exist in the system. To date, all exoplanets discovered in orbit around double stars are gas giants, similar to Jupiter, and are thought to form in the icy regions of their systems.

In contrast to the carbon-rich icy material found in other double star systems, the planetary material identified in the SDSS 1557 system has a high metal content, including silicon and magnesium. These elements were identified as the debris flowed from its orbit onto the surface of the star, polluting it temporarily with at least 1017 g (or 1.1 trillion US tons) of matter, equating it to an asteroid at least 4 km in size.

Lead author, Dr Jay Farihi (UCL Physics & Astronomy), said: “Building rocky planets around two suns is a challenge because the gravity of both stars can push and pull tremendously, preventing bits of rock and dust from sticking together and growing into full-fledged planets. With the discovery of asteroid debris in the SDSS 1557 system, we see clear signatures of rocky planet assembly via large asteroids that formed, helping us understand how rocky exoplanets are made in double star systems."

In the Solar System, the asteroid belt contains the leftover building blocks for the terrestrial planets Mercury, Venus, Earth, and Mars, so planetary scientists study the asteroids to gain a better understanding of how rocky, and potentially habitable planets are formed. The same approach was used by the team to study the SDSS 1557 system as any planets within it cannot yet be detected directly but the debris is spread in a large belt around the double stars, which is a much larger target for analysis.

The discovery came as a complete surprise, as the team assumed the dusty white dwarf was a single star but co-author Dr Steven Parsons (University of Valparaíso and University of Sheffield), an expert in double star (or binary) systems noticed the tell-tale signs. "We know of thousands of binaries similar to SDSS 1557 but this is the first time we've seen asteroid debris and pollution. The brown dwarf was effectively hidden by the dust until we looked with the right instrument", added Parsons, "but when we observed SDSS 1557 in detail we recognised the brown dwarf's subtle gravitational pull on the white dwarf."

The team studied the binary system and the chemical composition of the debris by measuring the absorption of different wavelengths of light or ‘spectra’, using the Gemini Observatory South telescope and the European Southern Observatory Very Large Telescope, both located in Chile. 

Co-author Professor Boris Gänsicke (University of Warwick) analysed these data and found they all told a consistent and compelling story. "Any metals we see in the white dwarf will disappear within a few weeks, and sink down into the interior, unless the debris is continuously flowing onto the star. We'll be looking at SDSS 1557 next with Hubble, to conclusively show the dust is made of rock rather than ice."

Notes to Editors
 

For more information or to speak to the researchers involved, please contact Dr Rebecca Caygill, UCL press office. T: +44 (0)20 3108 3846 / +44 (0)7733 307 596, E: r.caygill@ucl.ac.uk

J. Farihi, S. G. Parsons, B. T. Gansicke, ‘A circumbinary debris disk in a polluted white dwarf system’ will be published by Nature Astronomy at 1600 London time / 1100 US Eastern Time on 27 February 2017 and is under a strict embargo until then. DOI: 10.1038/s41550-016-0032.

About UCL (University College London)
 

UCL was founded in 1826. We were the first English university established after Oxford and Cambridge, the first to open up university education to those previously excluded from it, and the first to provide systematic teaching of law, architecture and medicine. We are among the world's top universities, as reflected by performance in a range of international rankings and tables. UCL currently has over 38,000 students from 150 countries and over 12,000 staff. Our annual income is more than £1 billion.

www.ucl.ac.uk | Follow us on Twitter @uclnews | Watch our YouTube channel YouTube.com/UCLTV
 
About the University of Warwick
 

The University of Warwick is consistently ranked in the top 10 universities in the UK and top 100 in the world. It is one of the UK's leading universities, with an acknowledged reputation for excellence in research, teaching and innovation, alongside pioneering links with business and industry.

About the University of Sheffield
 

With almost 27,000 of the brightest students from over 140 countries, learning alongside over 1,200 of the best academics from across the globe, the University of Sheffield is one of the world’s leading universities.

A member of the UK’s prestigious Russell Group of leading research-led institutions, Sheffield offers world-class teaching and research excellence across a wide range of disciplines.

Unified by the power of discovery and understanding, staff and students at the university are committed to finding new ways to transform the world we live in.

Sheffield is the only university to feature in The Sunday Times 100 Best Not-For-Profit Organisations to Work For 2016 and was voted number one university in the UK for Student Satisfaction by Times Higher Education in 2014. In the last decade it has won four Queen’s Anniversary Prizes in recognition of the outstanding contribution to the United Kingdom’s intellectual, economic, cultural and social life.

Sheffield has six Nobel Prize winners among former staff and students and its alumni go on to hold positions of great responsibility and influence all over the world, making significant contributions in their chosen fields.

Global research partners and clients include Boeing, Rolls-Royce, Unilever, AstraZeneca, Glaxo SmithKline, Siemens and Airbus, as well as many UK and overseas government agencies and charitable foundations.

About the Science and Technology Facilities Council (STFC)
 

The Science and Technology Facilities Council is keeping the UK at the forefront of international science and tackling some of the most significant challenges facing society such as meeting our future energy needs, monitoring and understanding climate change, and global security. The Council has a broad science portfolio including supporting UK work in space and ground-based astronomy technologies and research.   http://www.stfc.ac.uk/

Source: Gemini Observatory

Gemini Images Galaxy That Is 99.99 Percent Dark Matter

The dark galaxy Dragonfly 44. The image on the left is a wide view of the galaxy taken with the Gemini North telescope using the Gemini Multi-Object Spectrograph (GMOS). The close-up on the right is from the same very deep image, revealing the large, elongated galaxy, and halo of spherical clusters of stars around the galaxy’s core, similar to the halo that surrounds our Milky Way Galaxy. Dragonfly 44 is very faint for its mass, and consists almost entirely of Dark Matter. Credit: Pieter van Dokkum, Roberto Abraham, Gemini, Sloan Digital Sky Survey. PNG image

MAUNAKEA, Hawaii — Using the world's most powerful telescopes, an international team of astronomers has discovered a massive galaxy that consists almost entirely of Dark Matter. Using the W. M. Keck Observatory and the Gemini North telescope – both on Maunakea, Hawaii – the team found a galaxy whose mass is almost entirely Dark Matter. The findings are being published in The Astrophysical Journal Letters today.

Even though it is relatively nearby, the galaxy, named Dragonfly 44, had been missed by astronomers for decades because it is very dim. It was discovered just last year when the Dragonfly Telephoto Array observed a region of the sky in the constellation Coma. Upon further scrutiny, the team realized the galaxy had to have more than meets the eye: it has so few stars that it quickly would be ripped apart unless something was holding it together.

To determine the amount of Dark Matter in Dragonfly 44, astronomers used the DEIMOS instrument installed on Keck II to measure the velocities of stars for 33.5 hours over a period of six nights so they could determine the galaxy’s mass. The team then used the Gemini Multi-Object Spectrograph (GMOS) on the 8-meter Gemini North telescope on Maunakea in Hawaii to reveal a halo of spherical clusters of stars around the galaxy’s core, similar to the halo that surrounds our Milky Way Galaxy.

“Motions of the stars tell you how much matter there is, van Dokkum said. “They don’t care what form the matter is, they just tell you that it’s there. In the Dragonfly galaxy stars move very fast. So there was a huge discrepancy: using Keck Observatory, we found many times more mass indicated by the motions of the stars, then there is mass in the stars themselves.”

The mass of the galaxy is estimated to be a trillion times the mass of the Sun – very similar to the mass of our own Milky Way galaxy. However, only one hundredth of one percent of that is in the form of stars and "normal" matter; the other 99.99 percent is in the form of dark matter. The Milky Way has more than a hundred times more stars than Dragonfly 44.

Finding a galaxy with the mass of the Milky Way that is almost entirely dark was unexpected. "We have no idea how galaxies like Dragonfly 44 could have formed,” Roberto Abraham, a co-author of the study, said. "The Gemini data show that a relatively large fraction of the stars is in the form of very compact clusters, and that is probably an important clue. But at the moment we're just guessing."

“This has big implications for the study of Dark Matter,” van Dokkum said. “It helps to have objects that are almost entirely made of Dark Matter so we don’t get confused by stars and all the other things that galaxies have. The only such galaxies we had to study before were tiny. This finding opens up a whole new class of massive objects that we can study.

“Ultimately what we really want to learn is what Dark Matter is,” van Dokkum said. “The race is on to find massive dark galaxies that are even closer to us than Dragonfly 44, so we can look for feeble signals that may reveal a Dark Matter particle.”

Additional co-authors are Shany Danieli, Allison Merritt, and Lamiya Mowla of Yale, Jean Brodie of the University of California Observatories, Charlie Conroy of Harvard, Aaron Romanowsky of San Jose State University, and Jielai Zhang of the University of Toronto.

The W. M. Keck Observatory operates the largest, most scientifically productive telescopes on Earth. The two, 10-meter optical/infrared telescopes near 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 spectrographs and world-leading laser guide star adaptive optics systems.

DEIMOS (DEep Imaging Multi-Object Spetrograph) boasts the largest field of view (16.7 arcmin by 5 arcmin) of any of the Keck Observatory instruments, and the largest number of pixels (64 Mpix). It is used primarily in its multi-object mode, obtaining simultaneous spectra of up to 130 galaxies or stars. Astronomers study fields of distant galaxies with DEIMOS, efficiently probing the most distant corners of the universe with high sensitivity.

Keck Observatory is a private 501(c) 3 non-profit organization and a scientific partnership of the California Institute of Technology, the University of California and NASA.

---

Science Contact:

Pieter van Dokkum
Yale University
New Haven, Connecticut, USA
Tel: +1-203-432-3000
E-mail: pieter.vandokkum@yale.edu 

Media Contact:

Steve Jefferson
W. M. Keck Observatory
(808) 881-3827
sjefferson@keck.hawaii.edu

Source:   W.M. Keck Observatory

Could Gravitational Wave Events Flash in Visible Light?

Figure 1. Spectra of PS15dpn from the combined GMOS, PESSTO and SNIFS campaign. The vertical dashed green lines refer to He I and He II lines, while the blue (only shown on left) refer to Hα and Hβ. Right panel refers to restframe days after peak. 

Figure 2. Artist's conception of gravitational wave event showing possible emmission of visible light. 

Image Credit: LIGO.

Gemini explores the possibility of short-lived optical emission (visible light) from the violent events that produce gravitational waves.

Even before the announcement of the first gravitational wave detection by the Laser Interferometer Gravitational-Wave Observatory (LIGO) in February of this year, theorists wondered if the extreme energy required to produce strong gravitational waves might also produce a detectable optical flash.

Currently the most widely accepted explanation for gravitational wave events is the collision of black holes. The impact would send gravitational waves rippling through space at the speed of light. Thanks to LIGO the existence of gravitational waves is now confirmed, but unknown is the extent to which they might be accompanied by the emission of optical light or radiation at higher energies such as x-ray or gamma-rays.

A recent study headed by Stephen Smartt at Queen’s University in Belfast and Ken Chambers from University of Hawai‘i could help answer this question. “We were looking for the perverbial needle in the haystack,” says Chambers. “The area of sky was about 290 square degrees, and while we found several potential sources, in the end none could be associated with the LIGO discovery source.”

Smartt adds that the coordination of observations between wide-field telescopes like Pan-STARRS1 and deep spectroscopic follow-ups with Gemini were critical to the research which ultimately proved the concept for future gravitational wave events. “With this effort we’ve demonstrated that we can tile out the big sky area that LIGO thinks the source originated, find anything that is transient or variable to quite deep limits and then trigger a range of other powerful facilities like Gemini,” said Smartt. “It’s a big team project and I’m very excited about it’s potential. We have the tools to discover the sources in the next couple of years.”

The paper, titled: “A Search for an Optical Counterpart to the Gravitational Wave Event GW151226” has been accepted for publication in The Astrophysical Journal Letters and is also on astro-ph.

The Gemini Observatory followup observations – to provide spectroscopic classifications of transient sources – were made with the Gemini Multi-Object Spectrograph (GMOS) on the Gemini North telescope on Maunakea in Hawai‘i. One interesting source is a supernova that occurred at roughly the same time as (within a few days of) the gravitational wave source, but it is too distant to be the counterpart. Data were also provided by Pan-STARRS1, the University of Hawai‘i’s 2.2-meter telescope, the ATLAS survey telescope, the Public ESO Spectroscopic Survey of Transient Objects (PESSTO), and an additional observation using the Hubble Space Telescope.

Paper Abstract

We present a search for an electromagnetic counterpart of the gravitational wave source GW151226. Using the Pan-STARRS1 telescope we mapped out 290 square degrees in the optical iP1 filter starting 11.5hr after the LIGO information release and lasting for a further 28 days. The first observations started 49.5hr after the time of the GW151226 detection. We typically reached sensitivity limits of iP1 = 20.3 ± 20.8 and covered 26.5% of the LIGO probability skymap. We supplemented this with ATLAS survey data, reaching 31% of the probability region to shallower depths of m≅19. We found 49 extragalactic transients (that are not obviously AGN), including a faint transient in a galaxy at 7Mpc (a luminous blue variable outburst) plus a rapidly decaying M-dwarf flare. Spectral classification of 20 other transient events showed them all to be supernovae. We found an unusual transient, PS15dpn, with an explosion date temporally coincident with GW151226 which evolved into a type Ibn supernova. The redshift of the transient is secure at z=0.1747 ± 0.0001 and we find it unlikely to be linked, since the luminosity distance has a negligible probability of being consistent with that of GW151226. In the 290 square degrees surveyed we therefore do not find a likely counterpart. However we show that our survey strategy would be sensitive to NS-NS mergers producing kilonovae at D ≤ 100 Mpc which is promising for future LIGO/Virgo searches.

Source: Gemini Observatory