Tag Archives: paper

New Paper: Mocking the First Galaxies for JWST

Yesterday, PhD candidate Kirk Barrow submitted his first (!) paper (arXiv), titled “First Light: Exploring the Spectra of High-Redshift Galaxies in the Renaissance Simulations”. Correlations between physical and observational properties of the first galaxies are imperative to determine before JWST launches in October 2018. We have examined two of the most massive galaxies in detail in mock spectra, imaging, and photometry and then searched for any trends in the ~1,600 galaxies in the sample. There is very high variability in the smallest galaxies (like the ultra faint dwarfs around the Milky Way), but the trends settle into various relationships above 1 million solar masses in stars when star formation occurs on a more regular basis. We also found that viewing angle can account for a 3-fold difference in emergent flux due to the absorption of intervening gas in the galaxy.

New Paper: Early X-ray Background

About a month ago, we submitted a new paper on the build-up of the X-ray radiation background. Here we used the Renaissance Simulations to estimate the number density of high-mass X-ray binaries from the first metal-free (Population III) stars. We found that these binaries produce about 6 eV of energy in the X-rays per hydrogen atom, potentially pre-heating the intergalactic medium to about 1000 K. These effects are important to consider when deciphering future 21-cm observations of the early universe that can tell us the last cosmic phase transition, reionization.

New Paper: Early Magnetic Field Amplification

My graduate student, Daegene Koh, submitted his first paper to MNRAS two months ago, titled “Amplification of Magnetic Fields in a Primordial HII Region and Supernova”. Late last week, we resubmitted the paper after making revisions after a favorable referee report, and posted it on arXiv today. Here we run a suite of three simulations, focusing on the amplification of magnetic fields during the generation of the ionized region and in the aftermath of its supernova. We find that through small-scale dynamo action the magnetic field grows primarily when the supernova blastwave can cool efficiently, fragments, and becomes turbulent. On average, the fields are amplified by a factor of 100 in the remnant shell and up to a factor of 106 within the shock. These strengthened fields will propagate into the first generations of galaxies, possibly affecting the nature of their star formation.

Congratulations, DK, on your first 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

New paper: The remnants of the first stars

There is building evidence that the first stars are not as massive as previously thought and that they are merely typical massive stars on the order of tens of solar masses instead of behemoths up to 300 solar masses.  Furthermore, a non-negligible fraction of this population form in binary systems. These stellar systems can leave behind stellar-mass black holes, chemically enriched regions from their supernovae, and X-ray binaries if the companion star overflows onto the black hole during its giant phase. All of this depends on the initial mass function of the first stars, which is highly uncertain at the moment, but luckily it’s an active area of research!

To determine the evolution and impact of these remnants, we must know where they migrate after their progenitor star dies.  This week, Hao Xu, Michael Norman at UCSD and I submitted a paper that focuses on exactly this point. Continue reading New paper: The remnants of the first stars

“The Birth of a Galaxy” Published

High-z dwarf galaxy
High-redshift disk dwarf galaxy

In late November, our paper, “The Birth of a Galaxy: Primordial Metal Enrichment and Stellar Populations”, was accepted for publication in The Astrophysical Journal. It was recently published in the January 20th issue.

In this paper, we followed the formation of over 300 Population III (metal-free) stars and accurately modeled the radiative feedback from their main sequence and studied the chemical enrichment from their supernovae. Our methods allowed us to follow a natural transition from Population III to Population II star formation, leading to the formation of 38 high-redshift dwarf galaxies with the most massive having M = 109 solar masses. We found that they produce a metallicity floor of 10-3 of solar metallicity in the vicinity (5-10 kpc) of their host halos. At redshift 7, about 14% of the cosmic mass is enriched above 10-6 of solar metallicity. This gives some clues on the origin of an observed metallicity floor of 10-3 in damped Lyman alpha absorbers.