Satellite galaxies and dwarfs in the Local Group

The local neighborhood surrounding the Milky Way and M31 is teeming with small satellite galaxies whose properties are of immense interest. In the past few years the number of dwarfs observed in the local group has nearly doubled, mostly due to increased sensitivity in observations. These observations have posed a number of challenges to the theoretical modeling of dwarf galaxies.

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Possible evidence for dark matter particles

Dark matter, the mysterious substance estimated to make up approximately more than one-quarter of the mass of the Universe, is crucial to the formation of galaxies, stars and even life but has so far eluded direct observation. At a recent UCLA symposium attended by 190 scientists from around the world, physicists presented several analyses that participants interpreted to imply the existence of a dark matter particle.

“The likely mass would be approximately 30 billion electron-volts“, said the symposium’s organizer, David Cline, a professor of physics in the UCLA College of Letters and Science and one of the world’s experts on dark matter. The physicists at the Feb. 26–28 event were in agreement that “there seems to be an excess in the available data that could be due to dark matter“, Cline said. “At this symposium, it was obvious that excitement is building in the fields of dark matter theory and, especially, detection“, said Cline, who noted that there are several ways dark matter can be observed and that all were discussed at the UCLA meeting. “Because dark matter makes up the bulk of the mass of galaxies and is fundamental in the formation of galaxies and stars, it is essential to the origin of life in the Universe and on Earth“, Cline said. The first evidence for dark matter was discovered in 1933 using the Mt. Wilson telescope outside of Los Angeles. More recently, various theoretical models and detector improvements have made it possible to search for dark matter particles at extremely sensitive levels, some of the most sensitive measurements made by any scientists in the world. One search technique involves using the vast amount of dark matter in our galaxy. The NASA Fermi Satellite Telescope, an international collaboration involving NASA, the Goddard Space Flight Center and the SLAC National Accelerator Laboratory, searches for gamma rays, very high-energy light particles, from this dark matter. There are models of dark matter that would allow a signal in the galactic dark matter consistent with the claims at the meeting and provide a small interaction consistent with the “null results” in the direct dark matter searches all over the world. Much larger direct dark matter detectors are being planned in the U.S., Italy, Canada and China (including Xenon 3 Ton, LUX-ZEPLIN 7 Ton and DarkSide, which will weigh five tons). “These larger detectors potentially could see a dark matter signal in the next few years“, Cline said.

Dark matter is widely thought to be a kind of massive elementary particle that interacts weakly with ordinary matter. Physicists refer to these particles as WIMPS, for weakly interacting massive particles, and think they originated from the Big Bang. WIMPs are thought to be streaming constantly through the solar system and the Earth.

Another search method is to look for an interaction of a WIMP with xenon or argon nuclei and others (like germanium) in very low-background laboratories deep underground in Italy, the U.S., Canada, China and other countries. While these experiments have seen no signal of a WIMP above 30 billion electron volts, “there is no incompatibility with the interesting excess in the FERMI data“, Cline said. “The discovery of the Higgs boson, which won the 2013 Nobel Prize in physics, plays a role in the search for dark matter“, Cline said, adding that this topic was discussed in detail at the meeting. “Dark matter“, he said, “could consist of axions, WIMPs or sterile neutrinos, all of which were discussed at the symposium” (post). The UCLA dark matter symposium is convened every two years; this was the 11th such meeting. Cline said he and his colleagues hope to clarify the dark matter puzzle at the 2016 symposium.

It was at this same dark matter symposium in 1998 that two groups of scientists reported that the Universe is accelerating, as well as expanding, a finding Cline described as “one of the greatest discoveries in the history of science”.

See more on last week’s conference.

UCLA: Possible evidence for dark matter particle presented at UCLA physics symposium

The Near-Field / Deep-Field Connection

The Southern California Center for Galaxy Evolution (CGE) and the University of California High-Performance AstroComputing Center (HiPACC) are bringing together theorists and observers for a three-day conference on the Near-Field Deep-Field Connection.

Topics of the workshop to be covered will include:

• local relics of reionization,
• connections between first stars and local metallicity,
• the evidence for and impact of IMF variation,
• the CGM of the Milky Way and beyond,
• dwarf galaxies at high and low z, and
• star-formation histories near and far.

 

Detected the most distant galaxy

Grazie alla tecnica della spettroscopia, un gruppo di ricercatori della Texas A&M University e della University of Texas ad Austin sono stati in grado di rivelare la galassia più distante formatasi quando l’Universo aveva una età di appena 700 milioni di anni dopo il Big Bang.

The research is published in the most recent edition of the journal Nature. “It’s exciting to know we’re the first people in the world to see this“, said Vithal Tilvi, a Texas A&M postdoctoral research associate and co-author of the paper. “It raises interesting questions about the origins and the evolution of the Universe”. The paper’s lead author is Steven Finkelstein, an assistant professor at the University of Texas at Austin and 2011 Hubble Fellow who previously was a postdoctoral research associate at Texas A&M under the mentorship of Texas A&M astrophysicist Casey Papovich, who is second author as well as current mentor to Tilvi. Ten other international institutions collaborated on the effort, from California to Massachusetts and Italy to Israel. The galaxy, known by its catalog name z8_GND_5296, fascinated the researchers.

Whereas our home, the Milky Way, creates about one or two Sun-like stars every year or so, this newly discovered galaxy forms around 300 a year and was observed by the researchers as it was 13 billion years ago.

That’s the time it took for the galaxy’s light to travel to Earth. Just how mind-boggling is that? A single light year, which is the distance light travels in a year, is nearly six trillion miles. Because the Universe has been expanding the whole time, the researchers estimate the galaxy’s present distance to be roughly 30 billion light years away. “Because of its distance we get a glimpse of conditions when the Universe was only about 700 million years old, only 5 percent of its current age of 13.8 billion years“, said Papovich, an associate professor in the Department of Physics and Astronomy and a member of the George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy since 2008. Papovich notes that researchers are able to accurately gauge the distances of galaxies by measuring a feature from the ubiquitous element hydrogen called the Lyman alpha transition, which emits brightly in distant galaxies. It’s detected in nearly all galaxies that are seen from a time more than one billion years from the Big Bang, but getting closer than that, the hydrogen emission line, for some reason, becomes increasingly difficult to see. “We were thrilled to see this galaxy“, Finkelstein said. “And then our next thought was, ‘Why did we not see anything else? We’re using the best instrument on the best telescope with the best galaxy sample. We had the best weather, it was gorgeous. And still, we only saw this emission line from one of our sample of 43 observed galaxies, when we expected to see around six. What’s going on?’” The researchers suspect they may have zeroed in on the era when the Universe made its transition from an opaque state in which most of the hydrogen is neutral to a translucent state in which most of the hydrogen is ionized. So it’s not necessarily that the distant galaxies aren’t there. It could be that they’re hidden from detection behind a wall of neutral hydrogen fog, which blocks the hydrogen emission signal. Tilvi notes this is one of two major changes in the fundamental essence of the Universe since its beginning, the other being a transition from a plasma state to a neutral state. He is leading the effort on a follow-up paper that will use a sophisticated statistical analysis to explore that transition further. “Everything seems to have changed since then“, Tilvi said. “If it was neutral everywhere today, the night sky that we see wouldn’t be as beautiful. What I’m working on is studying exactly why and exactly where this happened. Was this transition sudden, or was it gradual?” The Nature paper is the result of raw data gleaned from a powerful Hubble Space Telescope imaging survey of the distant Universe called CANDELS, or Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey. Using that data, the team was armed with 43 potential distant galaxies and set out to confirm their distances. On a crisp, clear April night, Tilvi, Finkelstein and his graduate student, Mimi Song, sat behind a panel of computers in the control room of the W.M. Keck Observatory, which is perched atop the summit of Hawaii’s dormant Mauna Kea volcano and houses the two largest optical and infrared telescopes in the world, each standing eight stories tall, weighing 300 tons and equipped with 10-meter-wide mirrors. They detected only one galaxy during their two nights of observation at Keck, but it turned out to be the most distant ever confirmed. It was at a redshift 7.51, or created about 13 billion years ago. Because the Universe is expanding, the space between galaxies also is increasing. And as objects move away, they become redder. In essence, the higher the redshift, the farther away the object. Only five other galaxies have ever been confirmed to have a redshift greater than 7, with the previous high being 7.215. Finkelstein credits technological advancements in recent years for allowing astronomers to probe deeper into space and closer to the Big Bang. For instance, a powerful new spectrometer called MOSFIRE (Multi-Object Spectrometer For Infra-Red Exploration) that is 25 times more light-sensitive than others of its kind was installed at Keck in 2012. And the Hubble Space Telescope is powered by a new near-infrared camera installed by astronauts aboard the Space Shuttle in 2009 that sees farther into the Universe. Finkelstein and Papovich’s collaboration to study distant galaxies and our cosmic evolution is one of several between Texas’ two public research giants in the realm of astronomy. Texas A&M, the University of Texas at Austin and other institutions are building the largest spectrograph in the world to be installed at the Hobby-Eberly Telescope in west Texas to shed light on the mysterious force dark energy that likely is driving the expansion of the universe. Perhaps the largest and most important collaboration between the two universities’ astronomy programs is on the Giant Magellan Telescope, which, when complete in 2020, will create images 10 times sharper than the Hubble Space Telescope and enable astronomers to see earlier into the universe than ever before. Texas A&M and the University of Texas at Austin are two of 10 international institutions that are founding partners on the project. “The Giant Magellan Telescope will revolutionize this research“, Papovich said. “We are pushing the current telescopes to their limits and only seeing the brightest galaxies at these redshifts. It is slow-going with current telescopes. The GMT will have about five times the light gathering power of the biggest telescopes we’re using now, and it will make the measurements we’re doing that much easier. It will probably take the GMT to really understand the conditions in the very early universe“. Nicholas Suntzeff, director of the Texas A&M astronomy program, said the University of Texas at Austin has been instrumental in helping to boost the College Station program’s international profile and providing access to telescopes and facilities. Suntzeff, who this year was appointed Texas A&M’s highest faculty rank, distinguished professor, himself serves as an adjunct professor at the University of Texas at Austin. “If we want to maintain Texas as one of the most important centers in the world for astronomy, we can no longer do it as individual universities“, Suntzeff said. “UT, Texas A&M and other universities must work together. Just as a strength of the University of California program is that its system is united, if we are going to be part of the biggest projects in the world, we must unite our forces. This is the only way we can rejoin the group of elite astronomical institutions that are doing the best science on the biggest telescopes. In Texas, we are on that path“.

TAMU: UT, Texas A&M Astronomers Discover Universe's Most Distant Galaxy

arXiv: A Rapidly Star-forming Galaxy 700 Million Years After the Big Bang at z=7.51

Multi-Spin Galaxies

Galaxies are the building blocks of the Universe: thus, in order to trace its evolution history one needs to understand how galaxies formed and evolved, in particular which are the main physical processes that have let to the observed structures.  The “classical” disk galaxies are made by stars, gas and dust which are distributed in a plane forming the disk: all these components co-rotating with the angular momentum vectors almost aligned.  A class of “peculiar” objects has also been observed, but significantly more rare than disk galaxies, that show a decoupled component of the angular momentum and so classified as “multi-spin galaxies” by V. Rubin in 1994. Up to date, this class of objects includes all galaxies with a kinematically distinct component of gas and/or stars, with several inclination angles and extensions with respect to the host galaxy: they are galaxies with extended polar rings/disks, inner polar disks, low-inclined rings, kinematically decoupled cores, and extended counter-rotating components. The observed phenomenon of warped gaseous and stellar disks is yet another example of misalignment between rotating components in a galaxy. Finally, recent findings show that even the Galaxy and M31  host a disk of satellites, possibly rationally supported, raising new questions and insights to the Λ-CDM models adopted in the “near-field cosmology.

Given that the decoupling of the angular momentum cannot be explained by the collapse of a single proto-galactic cloud, a “second event” need to be invoked in the formation history of the multi-spin galaxies, which could be galaxy-galaxy or galaxy-environment interactions. In the cold dark matter scenario for galaxy formation, such kind of gravitational interactions have played a fundamental role in defining the morphology of “normal” galaxies, in particular in the building up of spheroids: in this framework, the study of multi-spin galaxies, both at low and high redshift, can shed light on the main processes at work during galaxy interactions and on the influence of the environment. Moreover, the existence of two orthogonal components of the angular momentum in polar ring galaxies and the off-plane of gas in the warped disk galaxies, let these systems the ideal laboratory to study also the intrinsic shape of the dark matter halo. The question of the halo shape is important to constrain the dark matter models, through cosmological simulations which predict the distribution of the halo shapes and the universal radial mass density profile of the dark matter.

The conference will focus on the following topics:

1. PROPERTIES:

1. -Morphological and photometric properties of multi-spin systems: inner polar disks, polar rings/disks, warped host and inclined rings
2. -Kinematic signatures of extraplanar rings/disks along the Hubble sequence
3. -Relative frequency and the impact of environment
4. -Sizes, luminosities, chemical abundances and masses of the decoupled components
5. -Correlations of spin component properties
6. -The Milky Way as a multi-spin galaxy
7. -High z multi-spin systems

2. STRUCTURE & FORMATION:

1. -Density waves in counter-rotating stellar and gaseous disks
2. -Time-scales and evolutionary paths: can we recognise transient features? Can we measure growth rates?
3. -Warp structure & dynamics
4. -Extreme warping
5. -Star formation and stellar population of inclined and host rings/disks
6. -Constraints on dark halos using extraplanar disks
7. -Formation and evolution of inclined rings/disks

LSST@Europe: The Path to Science

The Large Synoptic Survey Telescope (LSST) project is now entering an exciting phase, moving towards the start of federal construction expected in 2014. With first light planned for 2019 and science operations to commence in 2021, it is now timely to consider the scientific opportunities of LSST in the era of major new European facilities, especially wide-field missions such as Gaia, eRosita and Euclid, and flagship ground based facilities such as ESO’s E-ELT.

This first LSST science meeting in Europe will bring together LSST scientists and European scientists involved in, or interested in, taking LSST forward. This will allow for discourse as to current key science, the role of LSST, and the role of European expertise and facilities in partnership with LSST, in driving forward the next astronomical science revolution into the 2020’s. The meeting will provide an opportunity to review the current status of the LSST, and the key science programmes which are underpinning its development. The conference will include presentations identifying current science challenges where a combination of LSST and leading new European facilities and expertise will result in major leaps in understanding. These topics will range from studies of our Solar System and the Milky Way, to the Universe at the largest scales.

Dig Sites of Stellar Archeology: Giant Stars in the Milky Way

Elemental abundances are the fingerprints of the stellar evolution; they provide critical information about the history of Galactic chemical evolution. Low and intermediate mass stars play the most important role in Galactic chemical enrichment and depending on many parameters such as initial mass, metallicity, and mass loss rate at red giant phase, age, helium abundance and rotation, they follow different paths on the HR-diagram.

Evolved giants (RHB and Red Clump stars), especially of lower masses than 2.5 M_☉, are the best laboratories to investigate the extra-mixing mechanisms observed right after the luminosity function bump of red giant branch. Carbon and nitrogen (C/N) and ¹²C/¹³C ratios are the best indicators of deep mixing. The results show different ratios depending on the initial mass, metallicity and the stellar evolutionary stages. However, unambiguous relationships among these parameters have not been found yet. New observational and theoretical efforts are needed to unveil the relation between extra-mixing processes and the observed elemental abundances. Such extra-mixing is not explained by standard stellar evolution and therefore brings new challenges in theoretical studies.

Other evolutionary stages that witness drastic chemical changes in stellar atmospheres are AGB and post-AGB. Such stars are of critical importance to understand the last evolutionary stages of low and intermediate mass stars. Because of their fairly fast evolution, not many are known to date; these stars are still largely shrouded in mystery. A major influence of the third dredge-up phenomenon takes place in the post-AGB atmospheres which mainly alters the chemical abundance of ¹³C at the surface. This phenomenon also triggers the slow neutron-capture reactions (the s-process) in the stellar interiors. Some post-AGB stars are known to be enriched by the s-process elements, although some others do not show a single sign. The variety of the Galactic post-AGB population especially in chemical domain makes them even more difficult objects to investigate. The linkage between the post-AGBs enriched and non-enriched by certain elements remains unknown.

Giant stars are the ideal objects to dig down the ancient history of the Milky Way. The aim of this workshop is to bring up the current struggles and new challenges in both observational and theoretical studies on chemical evolution of the evolved stars, and discuss the new observational and theoretical approaches to improve our understanding on the Galactic chemical evolution.

Topics will include:

• What happens after main sequence: the evolution of low and intermediate mass stars
• Abundance alterations in red giants: extra-mixing processes
• He-core burning stars in the field and stellar clusters: RHB vs. Red Clumps
• AGB and Post-AGB stars: the third dredge-up and the complex atmospheres

Milky Way gives birth to its most massive star

Gli astronomi hanno assistito, si fa per dire, alla nascita della stella più massiccia della Via Lattea, immersa in una nube scura che dista circa 10.000 anni-luce dalla Terra.

The team used the new ALMA (Atacama Large Millimetre/submillimetre Array) telescope in Chile, the most powerful radio telescope in the world, to view the stellar womb which, at 500 times the mass of the Sun and many times more luminous, is the largest ever seen in our galaxy. The researchers say their observations reveal how matter is being dragged into the centre of the huge gaseous cloud by the gravitational pull of the forming star, or stars, along a number of dense threads or filaments. “The remarkable observations from ALMA allowed us to get the first really in-depth look at what was going on within this cloud“, said lead author Nicolas Peretto, from Cardiff University. “We wanted to see how monster stars form and grow, and we certainly achieved our aim”.

One of the sources we have found is an absolute giant, the largest protostellar core ever spotted in the Milky Way! Even though we already believed that the region was a good candidate for being a massive star-forming cloud, we were not expecting to find such a massive embryonic star at its centre.

“This cloud is expected to form at least one star 100 times more massive than the Sun and up to a million times brighter. Only about one in 10,000 of all the stars in the Milky Way reach that kind of mass“. Different theories exist as to how these massive stars form but the team’s findings lend weight to the idea that the entire cloud core begins to collapse inwards, with material raining in towards the centre to form one or more massive stars. Co-author Professor Gary Fuller, from the University of Manchester, said: “Not only are these stars rare, but their births are extremely rapid and childhood short, so finding such a massive object so early in its evolution in our Galaxy is a spectacular result. Our observations reveal in superb detail the filamentary network of dust and gas flowing into the central compact region of the cloud and strongly support the theory of global collapse for the formation of massive stars“. Team member Ana Duarte-Cabral, from the Université de Bordeaux, said: “Matter is drawn into the centre of the cloud from all directions but the filaments are the regions around the star that contain the densest gas and dust and so these distinct patterns are generated“. Peretto added: “We managed to get these very detailed observations using only a fraction of ALMA’s ultimate potential. ALMA will definitely revolutionise our knowledge of star formation, solving some current problems, and certainly raising new ones“.

University of Manchester: Astronomers witness birth of Milky Way’s most massive star

ALMA: ALMA Prenatal Scan Reveals Embryonic Monster Star

arXiv: Global collapse of molecular clouds as a formation mechanism for the most massive stars

This video starts with a view of the Milky Way and closes in on the constellation of Norma and one of the richest parts of the sky. We see many star clusters and glowing nebulae, but many objects of great interest are hidden by thick clouds of dust and can only be seen at longer wavelengths. The final part of the video shows a new view of the dark cloud SDC 335.579-0.292 using ALMA, the Atacama Large Millimeter/submillimeter Array. These observations have given astronomers the best view yet of a monster star in the proces of forming. Credit: ESO/Nick Risinger (skysurvey.org), DSS, ALMA (ESO/NAOJ/NRAO), NASA/JPL-Caltech/GLIMPSE. Music: movetwo

Did the Milky Way and Andromeda already collide?

Gli scienziati ritengono che tra circa 3 miliardi di anni la Via Lattea si scontrerà con Andromeda e che tale evento sarà il primo di una serie di collisioni galattiche. Oggi, però, un gruppo di astronomi guidati da Hongsheng Zhao della University of St Andrews propone un nuovo scenario in cui viene ipotizzato che le due galassie si sono già scontrate una volta, circa 10 miliardi di anni fa, e che la nostra conoscenze sulla gravità sono fondamentalmente errate. In realtà, questa idea potrebbe spiegare non solo la struttura della nostra galassia e quella di Andromeda ma anche la presenza delle galassie satelliti.

The Milky Way, made up of about 200 billion stars, is part of a group of galaxies called the Local Group. Astrophysicists often theorise that most of the mass of the Local Group is invisible, made of so-called dark matter. Most cosmologists believe that across the whole Universe, this matter outweighs ‘normal’ matter by a factor of five.

The dark matter in both Andromeda and the Milky Way then makes the gravitational pull between the two galaxies strong enough to overcome the expansion of the cosmos, so that they are now moving towards each other at around 100 km per second, heading for a collision 3 billion years in the future.

But this model is based on the conventional model of gravity devised by Newton and modified by Einstein a century ago, and it struggles to explain some properties of the galaxies we see around us. Zhao and his team argue that at present the only way to successfully predict the total gravitational pull of any galaxy or small galaxy group, before measuring the motion of stars and gas in it, is to make use of a model first proposed by Prof. Mordehai Milgrom of the Weizmann Institute in Israel in 1983. This modified gravity theory (Modified Newtonian Dynamics or MOND) describes how gravity behaves differently on the largest scales, diverging from the predictions made by Newton and Einstein.

Zhao and his colleagues have for the first time used this theory to calculate the motion of Local Group galaxies. Their work suggests that the Milky Way and Andromeda galaxies had a close encounter about 10 billion years ago.

If gravity conforms to the conventional model on the largest scales then taking into account the supposed additional pull of dark matter, the two galaxies would have merged. “Dark matter would work like honey: in a close encounter, the Milky Way and Andromeda would get stuck together, figuratively speaking“, says team member Prof. Pavel Kroupa from Bonn University. “But if Milgrom’s theory is right“, says his colleague Benoit Famaey (Observatoire Astronomique de Strasbourg), “then there are no dark particles and the two large galaxies could have simply passed each other thereby drawing matter from each other into long thin tidal arms“. New little galaxies would then form in these arms, a process often observed in the present-day Universe. Zhao explains: “The only way to explain how the two galaxies could come close to each other without merging is if dark matter isn’t there. Observational evidence for a past close encounter would then strongly support the Milgromian theory of gravity”. Just such a signature might already have been found. Astronomers struggle to account for the distribution of dwarf galaxies in orbit around both the Milky Way and Andromeda.

The dwarf galaxies could be explained if they were born from gas and stars ripped out of the two parent galaxies during their close encounter. Pavel Kroupa sees this as the ‘smoking gun’ for the collision.

“Given the arrangement and motion of the dwarf galaxies, I can’t see how any other explanation works”, he comments. The team now plan to model the encounter using Milgromian dynamics and are developing a computer code at Bonn University for this purpose. In the new model, the Milky Way and Andromeda are still going to crash into each other again in the next few billion years, but it will feel like ‘deja vu’. And the team believes that their discovery has profound consequences for our current understanding of the Universe. Pavel Kroupa concludes, “If we are right, the history of the cosmos will have to be rewritten from scratch”.

RAS: Did Andromeda crash into the Milky Way 10 billion years ago?

arXiv: Local Group timing in Milgromian dynamics. A past Milky Way-Andromeda encounter at z>0.8

222° Meeting of the American Astronomical Society

One of the largest astronomy meetings of the year will open to the public for the first time in its history. More than 500 astronomers, journalists and guests will bring their cosmic know-how to Indianapolis next week for the 222nd meeting of the American Astronomical Society (AAS). The conference begins on Sunday (June 2) and runs through June 6 at the Indiana Convention Center; it is the second of two meetings held annually by the AAS. New findings about alien worlds, mysterious dark matter and the Milky Way will be discussed, and this year anyone can take part in the cosmic action. Several presentations on Monday and Tuesday will be geared toward amateurs that decide to pay the fee and attend. The presentations include information about the Hubble Space Telescope, nearby exoplanets, Pluto, and the formation of galaxies in the early universe. In addition to those talks, the society will also hold two free public events during the convention. Throughout the course of the conference, scientists will take part in town hall-style meetings about NASA, the National Science Foundation and other agencies. The latest findings from the badly damaged planet hunting Kepler Space Telescope will be presented as well. Twitter users can follow the conference using the hashtag #AAS222.