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  • richardmitnick 9:04 pm on February 14, 2014 Permalink | Reply
    Tags: , , , CANDELS, ,   

    From CANDELS: “Breaking the Galaxy Distance Record” 

    Hubble Candles

    Thursday, February 13, 2014

    Steven Finkelstein

    In this loooong overdue post, I’m going to talk about what happened following the events of my previous post. In that post, I talked about how my research team and I used the Keck 10 meter telescope to obtain spectroscopy of 43 distant galaxies. To briefly recap, my group and I have been using CANDELS images to search for very distant galaxies (those that we see as they were within one billion years of the Big Bang, which gives them a redshift greater than 6). In a few previous posts, I’ve talked about some of the exciting things we’ve been learning in the distant universe, including how these galaxies get redder with time (as they build up their heavy elements; i.e. planet-making material), and whether galaxies can account for the reionization of the universe (yes! we think).

    In this previous post, we talked about how we use images to find these galaxies – essentially, since they are so far away, they are moving very quickly away from us, thus their light is redshifted due to the Doppler effect. Ideally, you would take a spectrum of every galaxy to search for redshifted emission lines to measure your redshift. However, this is impractical for samples of hundreds or thousands of galaxies. On the bright side, we can get a rough estimate of the redshift using imaging alone, and this technique has been well-documented over the past ~20 years.

    The downside of this is that 1) the redshift is only approximate, and that makes everything else you learn a little more uncertain; and 2) its possible that some galaxies you think are really distant are actually close by galaxies that just happen to be very red. To get around this, we typically try to take spectra of a small portion of our sample, to verify that our contamination is small. Fast forward, and this is why we went to Keck, to try to measure the redshifts for many of our distant galaxy candidates.

    As I looked at the data we took at Keck, we found a very bright emission line from one of our distant galaxy candidates before we even left Hawaii. This left me feeling very optimistic! However, as we continued to analyze our data, we found that the first line we saw would be the only line we would see – out of the 43 observed galaxies, we detected an emission line from only a single one. This may seem like a failure, but lets examine our detected galaxy a little more closely.

    candels good
    This image shows a region of the CANDELS GOODS-North field, just above the handle of the Big Dippler. Highlighted is z8_GND_5296, the most distant spectroscopically confirmed galaxy in the universe. The galaxy looks very red in this image, as it is so distant (and thus moving so quickly away from us), that it is only detected in Hubble’s reddest filters. Image Credit: V. Tilvi, S. Finkelstein, C. Papovich, A. Koekemoer, CANDELS and STScI/NASA.

    The emission line we saw was the Lyman alpha line from hydrogen. This line is emitted in the ultraviolet, but we saw it all the way in the infrared, meaning that it has a very high redshift. In fact, the measured redshift of this galaxy is 7.5, making it the highest redshift spectroscopically confirmed galaxy*** (the previous record was at 7.2). That’s exciting in itself, but the galaxy had more in store for us. Using how bright it is in the CANDELS imaging, we can measure how fast this galaxy is converting hydrogen gas into new stars, and we found that its “star-formation rate” is an insane 300 solar masses per year; this is 150 times faster than the Milky Way!!! From what we (thought we) knew at high redshift, if you found a random redshift seven galaxy, you would have expected it to be forming stars at around 10 solar masses per year, so this galaxy is forming stars 30 times faster than its peers.

    graph
    Our spectrum from the MOSFIRE spectrograph on the Keck 10 meter telescope.
    The white blob in the top panel shows Lyman alpha emission from z8_GND_5296.
    At the observed wavelength, this corresponds to a redshift of 7.5078. The bottom
    panel shows a cross-cut of the top spectrum (what we call a one-dimensional spectrum),
    which shows the galaxy’s flux versus wavelength. You can see the peak
    corresponding to Lyman-alpha emission (highlighted by the red line).
    There are a number of other peaks too, which all correspond to the position of emission
    lines from our own atmosphere. These are very bright, and we try to subtract
    them out, so what you see here are residuals. The lines are difficult to
    subtract completely, because their intensity changes rapidly with time.

    Not only has this level of star factory not been seen at these redshifts before, but it was also a complete surprise to theorists, who do not see such galaxies in their models. While this galaxy could just be a weirdo, we don’t think thats the case. The previous record redshift holder I mentioned, at z=7.2, has a star-formation rate of 100 solar masses per year. Smaller, yes, but still very high. And, it is located in the same region of the sky as our galaxy. What are the odds?!? What we think we’re learning is that these extreme star factories are much more common in the early universe than previously thought, so now we need to get with our theorist friends and try to figure out why that is.

    As for the other 42 galaxies we didn’t see? The jury is still out. It may be that the gas between galaxies is becoming neutral (as would happen if we’re entering the epoch of reionization), and this neutral gas “fog” is screening us from seeing the Lyman alpha photons. Or, it could be that these distant galaxies are becoming increasingly rich in gas themselves, preventing these Lyman alpha photons from escaping. Only time and further study will tell, but we’re hot on the trail! If you’re interested in all the details, you can see our paper, which has been published in Nature, here, and our official press release, which is here.

    ***Often in the news there are articles about the most distant galaxies in the universe – some of these are spectroscopically confirmed like our galaxy here, while others are candidate galaxies, meaning that their redshifts have not been verified. While many of these candidates turn out to be real, measuring the redshift spectroscopically is the gold standard for galaxy distance measurements. A case in point is our recent blog post, which mentions a galaxy with a redshift of close to 11 from the CLASH survey. This galaxy has not been spectroscopically confirmed (though Hubble will try to do it in a few months). However, in the particular case of this galaxy, I think its highly likely that its real, as not only are its colors that expected of such a distant galaxy, but the positions of the lensed images are what you would expect for a galaxy at the estimated redshift. Hopefully Hubble will measure a redshift, and, if not, then we’ll have to wait a few years for the next generation of telescopes.

    See the full article here.

    About the CANDELS blog

    In late 2009, the Hubble Space Telescope began an ambitious program to map five carefully selected areas of the sky with its sensitive near-infrared camera, the Wide-Field Camera 3. The observations are important for addressing a wide variety of questions, from testing theories for the birth and evolution of galaxies, to refining our understanding of the geometry of the universe.

    This is a research blog written by people involved in the project. We aim to share some of the excitement of working at the scientific frontier, using one of the greatest telescopes ever built. We will also share some of the trials and tribulations of making the project work, from the complications of planning and scheduling the observations to the challenges of trying to understand the data. Along the way, we may comment on trends in astronomy or other such topics.

    CANDELS stands for the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey. It builds on the legacy of the Hubble Deep Field, as well as the wider-area surveys called GOODS, AEGIS, COSMOS, and UKIDSS UDS. The CANDELS observations are designed to search for galaxies within about a billion years of the big bang, study galaxies at cosmic high-noon about 3 billion years after the big bang – when star-formation and black hole growth were at their peak intensity – and discover distant supernovae for refining our understanding of cosmic acceleration. You can find more details, and download the CANDELS data, from the CANDELS website.

    You can also use the Hubble Legacy Archive to view the CANDELS images.


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  • richardmitnick 7:29 pm on February 5, 2014 Permalink | Reply
    Tags: , , , CANDELS, ,   

    From CANDELS: “CLASH : the Cluster Lensing And Supernova search with Hubble” 

    Hubble Candles

    Wednesday, February 5, 2014
    Steve Rodney

    In 2010 the Hubble Space Telescope launched three bold new initiatives that came to be called the Multi-Cycle Treasury programs. One was the CANDELS program, the parent of this blog. Another was the Panchromatic Hubble Andromeda Treasury program (PHAT), a deep and detailed study of the nearby galaxy M31 [Andromeda Galaxy], led by Julianne Dalcanton of the University of Washington.

    m31
    M31 Andromeda

    The third program was called CLASH: the Cluster Lensing And Supernova survey with Hubble (tortured acronyms were a prerequisite for approval of the HST time). The CLASH team (not to be confused with The Clash) is led by Marc Postman from the Space Telescope Science Institute, and includes about 50 astronomers at some 25 institutions around the world. This survey is in many ways a close sister to the CANDELS program, and indeed there is significant overlap across the two groups, especially in the supernova search component, which has been a joint CLASH+CANDELS effort.

    macs
    Galaxy cluster MACS J1206.2-0847 (or MACS 1206 for short) as viewed
    through Hubble in the CLASH program. Credit: NASA, ESA,
    M. Postman (STScI), and the CLASH Team

    The CLASH program takes a deep look at 25 massive galaxy clusters. These are collections of galaxies (a few hundred in each), hot gas (heated to above 10 million degrees), and dark matter (more on that mysterious stuff below). The clusters in the CLASH sample sit at redshifts between about 0.2 and 0.9, so we are seeing them at a fairly recent epoch in terms of cosmic history (the universe was already more than 6 billion years old when the light we see left these clusters). Several of these clusters have been studied in great detail, but the CLASH program has opened up a new window to look in at one of the great mysteries of the universe: the nature of dark matter.

    When Hubble looks at a galaxy cluster in the CLASH survey, it captures the ultraviolet, optical, and infrared light emitted by billions upon billions of stars in the many galaxies that live within the cluster. Astronomers have long known, however, that these stars make up only a small fraction of the total contents of these clusters. Far more important is the hot gas in the Intra-Cluster Medium (ICM). This superheated gas (mostly Hydrogen and Helium) has been stripped away from the galaxies by tidal gravitational forces and the effects of ram pressure. The gas is so hot that it emits x-ray radiation, which can be observed using x-ray observatories like Chandra and XMM-Newton. The mass of gas in a typical galaxy cluster is almost 10 times greater than the total mass of all the stars in all the member galaxies. However, even after counting up all of the stars and gas, we still have only captured about 10% of the total mass of the galaxy cluster. The other 90% is (presumably) in the form of dark matter.

    “Dark matter” is the name we assign to all the mass in the universe that does not emit any light. There are a number of theories as to what this dark matter could be, and the most promising idea right now seems to be that it is some form of elementary particle that does not interact with other matter — except through the force of gravity. In galaxy clusters, we have two primary lines of evidence that reveal the presence of a large concentration of dark matter. First, the motions of the galaxies in the cluster show that there must be a large central mass pulling the galaxies in and through the cluster (more mass than we can account for in stars and gas). Second, we see the effect of the dark matter on background galaxies through gravitational lensing.

    Einstein’s theory of relativity tells us that the force of gravity is in fact a warping of spacetime. This distortion of the fabric of our universe affects all forms of matter — as we see in the motions of planets, stars and galaxies — and it also affects light itself. In the CLASH clusters, the warping is sufficiently strong to bend the pathway of light rays passing through the cluster. This results in a lensing effect, as light rays are distorted and redirected such that they focus on our location here in the Milky Way. We see the extraordinary evidence for this lensing in the form of absurdly stretched galaxies, long arcs, and impossibly bright background sources that have been distorted and magnified by the cluster’s gravitational lens.

    The principal aim of the CLASH program is to use these lensing artifacts to construct detailed models of the matter content of each of the 25 clusters. The cluster models are built by piecing together these distorted background sources to make a map of the dark matter that Hubble cannot see. Adding in evidence from the star light and the x-ray gas emission provides a complete picture of all the content in the cluster. With all of this information, the CLASH team has been able to improve our understanding of how these clusters are formed, and even to put new constraints on the nature of the dark matter fluid that dominates the cluster.

    blob
    The tiny red blob (just a fraction of the size of our Milky Way) is among
    the most distant galaxies ever observed. The object is observed just
    420 million years after the big bang, and is only visible to the Hubble
    Space Telescope due to the magnification from the massive galaxy
    cluster MACS0647, which lies in between us and the distant
    proto-galaxy. Credit: NASA, ESA, M. Postman and D. Coe (STScI),
    and the CLASH Team

    The gravitational lenses in the CLASH clusters also provide a powerful tool for looking back into the very early universe. The CLASH team has twice discovered objects behind the gravitational clusters that are among the most distant galaxies ever seen, first in April 2012, and then again in November 2012. These very distant background sources would normally be far too faint for even Hubble to see, but the intervening cluster acts like a natural telescope, focusing the light from the far-off galaxies so that Hubble can just barely detect them.

    The science work of the CLASH team is still in progress, and we expect many more exciting discoveries are yet to come. Hubble is not done with deep galaxy cluster surveys, either, as the new Frontier Fields initiative has already begun to follow in the footsteps of CLASH.

    See the full article here.

    About the CANDELS blog

    In late 2009, the Hubble Space Telescope began an ambitious program to map five carefully selected areas of the sky with its sensitive near-infrared camera, the Wide-Field Camera 3. The observations are important for addressing a wide variety of questions, from testing theories for the birth and evolution of galaxies, to refining our understanding of the geometry of the universe.

    This is a research blog written by people involved in the project. We aim to share some of the excitement of working at the scientific frontier, using one of the greatest telescopes ever built. We will also share some of the trials and tribulations of making the project work, from the complications of planning and scheduling the observations to the challenges of trying to understand the data. Along the way, we may comment on trends in astronomy or other such topics.

    CANDELS stands for the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey. It builds on the legacy of the Hubble Deep Field, as well as the wider-area surveys called GOODS, AEGIS, COSMOS, and UKIDSS UDS. The CANDELS observations are designed to search for galaxies within about a billion years of the big bang, study galaxies at cosmic high-noon about 3 billion years after the big bang – when star-formation and black hole growth were at their peak intensity – and discover distant supernovae for refining our understanding of cosmic acceleration. You can find more details, and download the CANDELS data, from the CANDELS website.

    You can also use the Hubble Legacy Archive to view the CANDELS images.


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  • richardmitnick 4:38 pm on September 6, 2013 Permalink | Reply
    Tags: , , , CANDELS, ,   

    From CANDELS: “”In Search of the First Galaxies” 

    Hubble Candles

    September 6, 2013
    V. Tilvi

    The quest for finding the first galaxies is motivated by at least two main goals: 1) these galaxies are likely the building blocks for present-day galaxies, and 2) they are responsible for making the Universe transparent to light, a period commonly referred to as the reionization epoch. This epoch is one of the most important periods in the history of the universe because it was when most of the neutral hydrogen in the Universe was evaporated. This event dramatically changed the Universe forever. Before diving into the method of searching first galaxies, here is a brief summary of what the Universe was like during the early stage of its lifetime.

    univ
    Color composite image of the three newly discovered galaxy candidates at redshift ~7 (at this redshift the age of the universe is merely 800 million years). These galaxies were selected using a medium-band imaging survey called the Fourstar Galaxy Evolution Survey

    Immediately after the Big Bang the Universe was too hot and chaotic for electromagnetic radiations to escape. It was only after about 400,000 years that the Universe expanded and cooled enough (to about 3000 Kelvin) for free electrons to be able to combine with protons to form neutral hydrogen. Due to this attraction of electrons to protons, enough empty was created for light to escape and travel to large distances (and eventually reaching us) without bouncing back and forth, for the first time. This is what we see today as the microwave background radiation (light emitted in the microwave part of the electromagnetic spectrum). Even by this time there were no stars and no galaxies in the Universe. The Universe went into the “Dark ages” during which it was full of neutral hydrogen and we would have to wait until about 100-500 Myrs after the Big Bang for the first stars and first galaxies to form.

    The intense radiation from the first stars and galaxies likely ionized the neutral hydrogen and the Universe changed from an opaque to a transparent Universe. This important milestone is referred to as the “reionization epoch” which most likely occurred between 100 – 1000 Myrs after the Big Bang. Searching for the first galaxies and understanding how and exactly when did this dense fog of neutral hydrogen evaporate are among the frontiers of modern observational cosmology.

    See the full very interesting article here.

    About the CANDELS blog

    In late 2009, the Hubble Space Telescope began an ambitious program to map five carefully selected areas of the sky with its sensitive near-infrared camera, the Wide-Field Camera 3. The observations are important for addressing a wide variety of questions, from testing theories for the birth and evolution of galaxies, to refining our understanding of the geometry of the universe.

    This is a research blog written by people involved in the project. We aim to share some of the excitement of working at the scientific frontier, using one of the greatest telescopes ever built. We will also share some of the trials and tribulations of making the project work, from the complications of planning and scheduling the observations to the challenges of trying to understand the data. Along the way, we may comment on trends in astronomy or other such topics.

    CANDELS stands for the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey. It builds on the legacy of the Hubble Deep Field, as well as the wider-area surveys called GOODS, AEGIS, COSMOS, and UKIDSS UDS. The CANDELS observations are designed to search for galaxies within about a billion years of the big bang, study galaxies at cosmic high-noon about 3 billion years after the big bang – when star-formation and black hole growth were at their peak intensity – and discover distant supernovae for refining our understanding of cosmic acceleration. You can find more details, and download the CANDELS data, from the CANDELS website.

    You can also use the Hubble Legacy Archive to view the CANDELS images.


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