Tag Archives: featured

New Paper: The First Metal-Enriched Stars

Today, we have submitted a new paper on the formation of the first metal-enriched stars. We concentrate on the scenario where an external supernova blastwave enriches a nearby halo to 1/30,000th of the solar metallicity, sparking the gravitational collapse of the gas that can cool through molecular hydrogen formation on newly-formed dust grains. See the movie below for a full tour of the simulation’s evolution.

The First Pop II Star from Britton Smith on Vimeo.

This work significantly improves on previous efforts that only considered non-cosmological simulations or a uniformly enriched medium. Our simulations include coupled radiative feedback from Population III massive stars and their supernova, following the metal enrichment from the explosion site to the subsequent star forming region. We find that cooling through dust grains enhances fragmentation during the collapse, suggesting that the most metal-poor stars are the result of incomplete mixing. For more images and details, see Britton Smith’s webpage on the paper.

New Paper: 21cm Signal from the First Galaxies

In a companion paper to our X-ray binary paper, we calculated the expected 21-cm signal (Wikipedia) from a strongly clustered group of galaxies at redshift 15 when the universe was only 300 Myr old. Here we make predictions for the SKA radio observatory, which could possibly probe the heating and ionization caused by UV and X-ray sources within the first galaxies. In this paper, we show that in some circumstances it will be possible to determine from SKA observations whether X-ray sources had a significant impact on the surrounding intergalactic medium, constraining the earliest population of stars and their remnants in the first galaxies.

Image credit: SKA

New paper: Heating the IGM from Pop III Binaries

We have submitted a new paper to the Astrophysical Journal that focuses on the effects of massive metal-free stellar binaries in the early universe. This is the second paper that uses the “Rarepeak” simulation that consumed over 10 million core-hours to reach a redshift of 15 (280 million years after the Big Bang), following more than 10,000 Population III stars and 3,000 galaxies with nearly 2 billion computational elements. We expect several more papers to come from this rich dataset, exploring the properties of the first galaxies and their role during the Universe’s re-emergence from the Dark Ages. Continue reading New paper: Heating the IGM from Pop III Binaries

New paper: The Birth of a Galaxy – III

We have finally finished the finale in the The Birth of a Galaxy trilogy, where we further analyzed the data first presented in the second paper of the trilogy. In this paper, we convincingly demonstrate that the faintest galaxies play an important role during reionization, which contribute nearly 30% of the ionizing photon budget. This is important because previous studies of reionization usually ignored the smallest galaxies because they are easily suppressed by external and internal feedback. However, we find that they indeed do form at very high redshifts (z > 10), only to be suppressed as the universe is gradually heated and ionized by galaxies. Continue reading New paper: The Birth of a Galaxy – III

Atlanta Science Festival

Today marks the beginning of the first Atlanta Science Festival, a week-long celebration of science and technology with dozens of activities happening around metro Atlanta. Members from the CRA will be leading a few events in the next week.

  • Tech Talks (Monday, March 24, 2014 – 6:30pm to 8:00pm; Georgia Tech Scheller College of Business Rm. 100): Atlanta science’s version of TedTalks with a competitive edge! Local science students battle one another through sharing short talks that communicate their research to public audiences.
  • Galaxy Collider: Come see the merger of galaxies unfold before your eyes! Throw galaxies at others and see them collide!
  • Spark Chamber: Did you know that there are tiny particles zipping through you all of the time at nearly the speed of light? Use our device to detect these particles and see the paths that they take.

The last two events will be a part of the Exploration Expo at Centennial Olympic Park on Saturday, March 29th, 11-4. Most of my group will be at the Galaxy Collider.  Come and join the fun!

Daegene Koh receives the EAPSI Fellowship!

Graduate student Daegene Koh has received the EAPSI (East Asian and Pacific Summer Institutes) Fellowship for Summer 2014. Congratulations! He will be working in Chosun University in Korea with Prof. Kyung-jin Ahn. They will be investigating the contribution from the first stars and galaxies to the cosmic near-infrared background, using massively parallel radiative transfer simulations. The product of this research will secure additional observational constraints on the nature of galaxy formation during the first billion years of the Universe, probing the faintest galaxies that are otherwise individually undetectable with current facilities. However, their cumulative luminosity may leave an imprint in the cosmic near-infrared background, which can be disentangled from galaxies that form closer to home, when utilizing theoretical models of galaxy formation.

New paper: On the contribution of active galactic nuclei to reionization

Reionization is an extended process where the whole universe transitions from neutral to ionized between 300 and 1,000 million years after the Big Bang. While it has been established that galaxies are the main drivers of reionization and that active galactic nuclei (AGN) are unimportant during this process, very few have made an effort to quantify the exact contribution to the reionization history. In our paper, we find that AGN only increases the optical depth to Thomson scattering by ~2% under the most optimal conditions, thus strengthening the need for other sources beyond observed AGN and galaxies to match the observed optical depth by WMAP and Planck. This paper was primarily written by Rachel Grissom, who is a 2nd year graduate student at the CRA, and it is her first paper. Congratulations!

Public Talk in Hokkaido University

Last month, I was in Hokkaido University, giving an Enzo users’ workshop with a few of my colleagues. While I was there, I agreed to give a public talk about the first galaxies, titled “Baby Galaxies: The First Steps to the Milky Way”. Elizabeth Tasker graciously wrote a post about my talk. I thought it was a success with standing room only during the last half of my talk, even with a dying typhoon off the coast of Japan lashing cold rain and wind throughout Hokkaido.

For those at Georgia Tech, I will be giving a similar public talk as a part of the Inquiring Minds series (PDF flyer) in two weeks on Monday, November 18th at 6pm in CULC.  Be sure to make it!