More about CANDELS at the AAS

As mentioned by Liz McGrath in her recent blog post, the American Astronomical Society held its 223rd meeting  in early January. Altogether there were 37 presentations that had the word CANDELS somewhere in their title, author list, or abstract, and probably several others that used CANDELS under the radar. I thought it worth sharing a few highlights.

The meeting opened with the Kavli lecture by Bob Williams, the former director of the Space Telescope Science institute and president of the International Astronomical Union, who recounted the history of the original Hubble Deep Field and the science legacy that flowed from that first observation. One of the things he emphasized is how the making the data completely non-proprietary helped build the scientific momentum. Instead of observing separate spots in the sky and keeping the data to themselves, astronomers interested in the distant universe were suddenly much more willing to point telescopes to the same spot and share the data. CANDELS carries forward the legacy of this culture change; all of the Hubble data and most of the data from other telescopes are available to everyone.

A figure from Steve Finkelstein's talk, showing the number of galaxies found at redshifts
z=7 and 8 from the ultra-deep survey fields (blue) and CANDELS (red). Absolute magnitude
is a measure of brightness, with smaller numbers (more negative) indicating brighter galaxies.
CANDELS is great for finding brighter (rarer) galaxies, while the ultra-deep fields
excel at finding fainter (but more common) galaxies.

On Monday afternoon, the CANDELS and CLASH projects were featured in a special session. This was an opportunity for astronomers from both projects to give a top-level summary of the results. The CANDELS talks were given by Jeyhan Kartaltepe, Steve Finkelstein, Yu Lu and Steve Rodney. Jeyhan summarized the results on galaxy morphology, with particular attention to the CANDELS visual classifications and the evidence that ultraluminous infrared galaxies are associated with galaxy collisions and mergers, even at high redshift. Steve Finkelstein summarized the state of research on the most distant galaxies. He showed a nice diagram that helps to put into perspective the contributions of the "deep but narrow" fields (the Hubble Ultradeep field and associated parallel observations), and CANDELS. He also talked his discovery of what is currently the record-holder for the most distant spectroscopically confirmed galaxy, at redshift z=7.51. Yu Lu summarized the effort of part of the CANDELS theory group to compare semi-analytical models of galaxy formation. This is the most detailed side-by-side test of such models yet carried out and will be of great utility in helping us understand what we are learning from CANDELS. Finally, Steve Rodney partnered with Or Graur of the CLASH team to give a summary of the supernova program, including the first estimates of the evolution of supernova rates from both surveys.

A figure from Guillermo Barro's talk about the evolution of compact galaxies at high redshift.
The vertical axis shows how active the galaxy is in forming stars. Specifically, it shows
the ratio of each galaxy's star-formation rate, to its total stellar mass. The horizontal axis
shows how densely packed the stars are together. Dense galaxies are to the right,
diffuse galaxies are to the left. Guillermo is finding that galaxies tend to make the
transformation from being diffuse to being compact while they are still forming stars;
the quenching of star formation happens later.

The next day, CANDELS figured prominently in the Hieneman prize lecture given by Rachel Somerville. Rachel has been one of the leaders of the theory effort in CANDELS and recounted the progress in trying use the observations to get at the detailed physics of galaxy formation. One of the more recent results she showed in her talk was the success that she and Lauren Porter have had in matching the trends that Guillermo Barro and Christina Williams see in the evolution of compact galaxies. Both Guillermo and Christina spoke that morning in a session about galaxy surveys that was almost entirely populated by CANDELS talks.

In addition to the talks, there were quite a few posters. Posters are tacked to display boards in a big exhibition hall, and stay up all day. On the plus side, this gives people an opportunity to wander by and discuss the research, which is harder to do in a session packed with 5-minute talks. On the minus side, there are so many posters that it impossible to look at them all. CANDELS was very fortunate to have most of our posters on the first day located right near the entrance to the hall, so there was lots of opportunity for people to see them.

It was also great to see work by other groups using the CANDELS data. One of the press releases from the meeting was from Garth Illingworth, discussing finding some suprisingly bright galaxies in the CANDELS GOODS-N data that might be at redshift z>9. These are not yet spectroscopically confirmed, but if they are really at high redshift, then they indicate that star-formation was already proceeding vigorously when the universe was only 500 million years old.