Friday, July 19, 2013

CANDELS Conquers the Vikings' Land: a Galaxy Evolution Tour in Northern Europe

Dear CANDELS followers,

Best greetings from Helsinki. I am waiting at the moment to take my flight back home to Scotland. Before that, I would like to to recap here for you the events that happened during the last couple of weeks involving our CANDELS collaboration in the land of northern Europe. These last words are important: northern Europe. Why? Because sometimes it is necessary to halt for a moment in order to realise the huge impact CANDELS is having all around the world. Our survey has become the "de facto" standard extragalactic observations of the distant Universe. Actually, I began my scientific career with Chris Conselice working on another galaxy survey utilizing the previous near infrared HST camera NICMOS. Just to give a flavour of how much things have improved let me remember those times when I was tired with my PhD work. At that time, I would open on my personal computer the images from the old HST camera and their beauty was such that everything made sense again. So now just imagine what a professional astronomer feels when contemplating the brand-new CANDELS images. I could give you here numbers about their superb resolution, or its large area and depth, but I do think recalling my previous experiences is more personal, more touching. Perhaps the best comparison might be a person watching the world from glasses that does not fit him or her any longer. When changing them, new unexpected details and features appear everywhere. I can tell I really feel privileged working on these breathtaking data.

Jumping back to the real world, two weeks ago I organized a parallel session in the National Astronomical Society meeting -- "national" in this context means "British" ;) -- in St. Andrews about the declining star formation of the Universe over cosmic time. Nowadays, it is fairly well established that the Universe peaked in its efficiency of creating stars some 10 billion years ago. Since then, it is slowly fading away, as it is running out of the gas that fuels its stars. The point is that when trying to explain how the Universe changes between its early stages and now... bang! CANDELS is one of the best tools available for these kind of studies. Afterwards, I flew this week to Finland to participate in the European Week of Astronomy and Space Science, where we discussed in a number of special sessions the consequences of galaxy evolution. I would like to highlight the symposia titled "The mystery of ellipticals" and "The co-evolution of black holes and galaxies", where several CANDELS members presented some awesome work and led the scientific discussion. And please, let me emphasize one more time that the quest of understanding the Universe does not only belong to a single group of people or nation; the CANDELS survey is a joint effort from a multinational group of people that has repercussions all around the world.

I guess you heard St. Andrews is not only about its destroyed cathedral
or high class university (where the Prince & Princess of Wales met)
but it is the so-called "home of golf", with multiple golf courses all
around surrounded by beautiful landscapes by the sea. Here I show
a photo from the  Royal and Ancient Golf Club and its famous
stone bridge. Image Credit

Diving a little bit deeper into what we have presented in the conferences, I will start by mentioning that you can find in this blog excellent previous posts about similar topics by friends like Romeel Davé, Tao Wang, Victoria Bruce and Guillermo Barro. However, our projects, although related to theirs, are slightly different. In the Scottish conference, we commenced by showing how the state-of-the-art astronomical simulations in the biggest computers in the world still struggle to produce realistic galaxies. Especially challenging is knowing how and when to switch on the Super Massive Black Holes (do not forget this link either) that are usually found in the centers of galaxies. Reproducing their behaviour accurately is mandatory in order to understand the most massive galaxies in the Universe, because without their energy and jets, we cannot explain how these galaxies stopped forming stars. The rationale is very easy: the bigger the galaxy is, the larger the amount of gas it contains. Unless we remove this gas, the galaxy would continue producing stars crazily, finishing up as a monster object which does not exist in the Universe. In fact, this was the second part of the meeting: the local Universe. And of course we concluded by connecting all the previous topics with the high redshift Universe. Several CANDELSiers (such Vivienne Wild, Caterina Lani and Victoria Bruce) presented very interesting results. The upshot of all this was that we have tested convincingly how galaxies (both the biggest and the big-ish, as the dwarf ones are elusive even in our galactic neighbourhood) change their morphologies, sizes, colours, and star formation over cosmic time/cosmic distance/redshift (choose your favourite term from the jargon) but thus far we have not identified how the mechanisms at play (the aforementioned black holes and galaxy mergers) contribute to this process.

M87 is, in many ways, the typical massive galaxy. Located at
the core of the Virgo galaxy cluster, it is red, devoid of young stars,
featureless and probably the most massive galaxy nearby in the
Universe. It hosts a huge supermassive black hole in its center,
which produces the jet of matter we see in the image. Many questions
arise from this picture: do massive galaxies always look the same
even in the primeval Universe? Is it indispensable to have a big black
hole in order to suppress the star formation of galaxies? Does
CANDELS show dead galaxies in the early Universe and what
can we learn from them? Image Credit

For the following week, I changed scenery. Now I am in Scandinavia, in a charming town (nice cathedral and castle, plus a river full of boats) called Turku, which is a communication point in between Sweden, the Baltic countries and St. Petersburg. This European meeting is, in many ways, similar to those of the American Astronomical Society (such as the one described in this post): crowded with people and with many special sessions.

Turku at night :) Astronomers just want to have fun
Image Credit:
I cannot give you a full account of what happened, but I will try to summarize the most relevant contributions related to our studies.  My presentation was focused on when is the crucial moment for the majority of the most massive galaxies of the Universe to transition into spheroidal, big and red elliptical galaxies, and whether the way stars move in these systems could shed some light into this problem. This second idea breaks many degeneracies, and it is based in a novel observational technique called 3D spectroscopy. One of the longstanding astronomical problems is how to infer properties of a 3D Universe which is projected in images of only two dimensions. The solution is based on the Doppler effect observed in the galaxy light. The parts of the galaxy which move in our line of sight appear bluer for the same physical principle as the sound of the ambulances have a higher pitch when it approaches closes to us; I am sure all of you are thinking of this. Combining the light wobbling with the images, my data suggested massive galaxies acquire their present appearance seven billion years ago approximately. Vivienne Wild, who was also in Scotland with me, explained her galaxy evolution ideas stressing the influence of the black holes in killing the galaxies' star formation. Elizabeth McGrath told us about a missing piece of evidence in this puzzle, which is the fact that CANDELS unveils many disk galaxies like our Milky Way in the distant Universe that seem to be "killed" as well, but without developing a spheroidal shape.

NGC1277 has been amply debated in both of our meetings. Seemingly, this galaxy hosts the largest observed supermassive black hole in comparison with its mass, cointaining half of it! Moreover, its size is tiny, roughly a third of our Milky Way. What are the secrets of its galaxy? Or is it just the astronomers are missing something? More questions yet to be answered, this galaxy is really mysterious. Credit: Hubble Space Telescope

As you can see, there are still many amazing discoveries for which we do not have yet a convincing explanation. The CANDELS project and astronomers are committed to investigating how our ever-changing Universe grew and behaved during its infancy. Surrounded by this awe-inspiring cosmos I can only refer you to words by the Spanish (like me) Roman philosopher Seneca "Nature does not reveal all her secrets at once" or more recently to our admired colleague Carl Sagan who said "Somewhere, something incredible is awaiting to be known".

(As this is the first time I am posting in English for an internet blog, I asked for help to two good friends of mine, Andrew Davis and Jeyhan Kartaltepe. A big thanks and a smile to both of them).

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