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"Lee, Nicholas Y."
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A massive, dead disk galaxy in the early Universe
When the Universe was just 3 billion years old, half of the most massive galaxies had already ceased star formation, and such a galaxy has now been observed using gravitational lensing, unexpectedly turning out to be a compact, fast-spinning disk galaxy rather than a proto-bulge galaxy.
Dead disk galaxy formed by incoming gas
When the Universe was only three billion years old, half of the most massive galaxies were already 'dead', meaning that few new stars would form in them. It is believed that these galaxies grew into the massive local elliptical galaxies seen today. Sune Toft
et al
. report an analysis of a galaxy that has been strongly gravitationally lensed. This means that they can observe spatial scales that are far smaller than those accessible by any other means. They find that, surprisingly, the galaxy is a fast-spinning disk and that its stars formed
in situ
rather than in a nuclear starburst. They conclude that the gas out of which the stars formed was accreted from outside the galaxy in cold streams of gas.
At redshift
z
= 2, when the Universe was just three billion years old, half of the most massive galaxies were extremely compact and had already exhausted their fuel for star formation
1
,
2
,
3
,
4
. It is believed that they were formed in intense nuclear starbursts and that they ultimately grew into the most massive local elliptical galaxies seen today, through mergers with minor companions
5
,
6
, but validating this picture requires higher-resolution observations of their centres than is currently possible. Magnification from gravitational lensing offers an opportunity to resolve the inner regions of galaxies
7
. Here we report an analysis of the stellar populations and kinematics of a lensed
z
= 2.1478 compact galaxy, which—surprisingly—turns out to be a fast-spinning, rotationally supported disk galaxy. Its stars must have formed in a disk, rather than in a merger-driven nuclear starburst
8
. The galaxy was probably fed by streams of cold gas, which were able to penetrate the hot halo gas until they were cut off by shock heating from the dark matter halo
9
. This result confirms previous indirect indications
10
,
11
,
12
,
13
that the first galaxies to cease star formation must have gone through major changes not just in their structure, but also in their kinematics, to evolve into present-day elliptical galaxies.
Journal Article
A Massive Dead Disk Galaxy in the Young Universe
At z=2, when the Universe was just 3 Gyr old, half of the most massive galaxies were extremely compact and had already exhausted their fuel for star formation1–4. It is believed that they were formed in intense nuclear starbursts and that they ultimately grew into the most massive local elliptical galaxies seen today, through mergers with minor companions5,6, but validating this scenario requires higher resolution observations of their centers than currently possible, even from space. Magnification due to gravitational lensing offers a unique opportunity to resolve their inner regions, as demonstrated in a recent study of a z=2.6 compact spheroidal galaxy which revealed a bulge, rotating at velocities comparable to the fastest rotating local ellipticals7. Following the same approach, here we map the stellar populations and kinematics of a lensed z=2.1478 compact galaxy, which surprisingly turn out to be a fast spinning, rotationally supported disk galaxy. Rather than in a merger-driven nuclear starburst8, its stars must thus have formed in a disk, likely fed by streams of cold gas, which were able to penetrate the hot halo gas until they were cut off by shock heating from the dark matter halo9. This result unambiguously confirm indications from a growing body of indirect evidence10–13 that the first galaxies to cease star formation must go through major changes not just in their structure, but also in their kinematics to evolve into present day ellipticals.
Journal Article
A massive, dead disk galaxy in the early Universe
When the Universe was just 3 billion years old, half of the most massive galaxies had already ceased star formation, and such a galaxy has now been observed using gravitational lensing, unexpectedly turning out to be a compact, fast-spinning disk galaxy rather than a proto-bulge galaxy.
Journal Article
Tracing infrared galaxies throughout cosmic time
Infrared observations are crucial for a full understanding of galaxy formation and evolution, as they reveal the full luminosity of galaxies enshrouded by ubiquitous interstellar dust. Ultraviolet and optical radiation from young massive stars is absorbed by dust grains that heat up and reradiate the absorbed radiation at far-infrared wavelengths. A complete characterization of the galactic emission requires observations at infrared wavelengths. Using the recently launched Herschel Space Telescope, we analyze the deepest and most complete far-infrared surveys to characterize the dust-obscured star formation at high redshifts (z ∼ 0.5–3). We provide the first detailed characterization of the full spectral energy distribution of infrared luminous galaxies at high redshift. By calibrating SFR indicators using far-infrared derived values, we extend our analysis to the full population of star-forming galaxies and discover new star formation laws that have important implications for galaxy evolution.
Dissertation
A massive, dead disk galaxy in the early Universe
At redshift z = 2, when the Universe was just three billion years old, half of the most massive galaxies were extremely compact and had already exhausted their fuel for star formation(1-4). It is believed that they were formed in intense nuclear starbursts and that they ultimately grew into the most massive local elliptical galaxies seen today, through mergers with minor companions(5,6), but validating this picture requires higher-resolution observations of their centres than is currently possible. Magnification from gravitational lensing offers an opportunity to resolve the inner regions of galaxies(7). Here we report an analysis of the stellar populations and kinematics of a lensed z = 2.1478 compact galaxy, which surprisingly turns out to be a fast-spinning, rotationally supported disk galaxy. Its stars must have formed in a disk, rather than in a merger-driven nuclear starburst(8). The galaxy was probably fed by streams of cold gas, which were able to penetrate the hot halo gas until they were cut off by shock heating from the dark matter halo(9). This result confirms previous indirect indications(10-13) that the first galaxies to cease star formation must have gone through major changes not just in their structure, but also in their kinematics, to evolve into present-day elliptical galaxies.
Paper
SN 2008S: A Cool Super-Eddington Wind in a Supernova Impostor
We present visual-wavelength photometry and spectroscopy of supernova SN2008S. Based on the low peak luminosity for a SN of M_R = -13.9 mag, photometric and spectral evolution unlike that of low-luminosity SNe, a late-time decline rate slower than 56Co decay, and slow outflow speeds of 600-1000 km/s, we conclude that SN2008S is not a true core-collapse SN and is probably not an electron-capture SN. Instead, we show that SN2008S more closely resembles a \"SN impostor\" event like SN1997bs, analogous to the giant eruptions of LBVs. Its total radiated energy was 1e47.8 ergs, and it may have ejected 0.05-0.2 Msun in the event. We discover an uncanny similarity between the spectrum of SN 2008S and that of the Galactic hypergiant IRC+10420, which is dominated by narrow H-alpha, [Ca II], and Ca II emission lines formed in an opaque wind. We propose a scenario where the vastly super-Eddington wind of SN2008S partly fails because of reduced opacity due to recombination, as suggested for IRC+10420. The range of initial masses susceptible to eruptive LBV-like mass loss was known to extend down to 20-25 Msun, but estimates for the progenitor of SN2008S (and the similar NGC300 transient) may extend this range to around 15 Msun. As such, SN2008S may have implications for the progenitor of SN1987A.
Paper
The Relationship between Age and the Manifestations of and Mortality Associated with Severe Malaria
Background. The reported case-fatality rate associated with severe malaria varies widely. Whether age is an independent risk factor is uncertain. Methods. In a large, multicenter treatment trial conducted in Asia, the presenting manifestations and outcome of severe malaria were analyzed in relation to age. Results. Among 1050 patients with severe malaria, the mortality increased stepwise, from 6.1% in children (age, <10 years) to 36.5% in patients aged >50 years (P < .001). Compared with adults aged 21–50 years, the decreased risk of death among children (adjusted odds ratio, 0.06; 95% confidence interval, 0.01–0.23; P < .001) and the increased risk of death among patients aged 150 years (adjusted odds ratio, 1.88; 95% confidence interval, 1.01–3.52; P = .046) was independent of the variation in presenting manifestations. The incidence of anemia and convulsions decreased with age, whereas the incidence of hyperparasitemia, jaundice, and renal insufficiency increased with age. Coma and metabolic acidosis did not vary with age and were the strongest predictors of a fatal outcome. The number of severity signs at hospital admission also had a strong prognostic value. Conclusion. Presenting syndromes in severe malaria depend on age, although the incidence and the strong prognostic significance of coma and acidosis are similar at all ages. Age is an independent risk factor for a fatal outcome of the disease.
Journal Article
Evidence for several waves of global transmission in the seventh cholera pandemic
Source of current cholera epidemic
Cholera has affected human populations for centuries, and the agent responsible,
Vibrio cholerae
, continues to infect millions each year. Using whole genome phylogeny, it is now shown that the current seventh epidemic originated in the Bay of Bengal in the 1950s and has spread through the world in three independent waves.
Vibrio cholerae
is a globally important pathogen that is endemic in many areas of the world and causes 3–5 million reported cases of cholera every year. Historically, there have been seven acknowledged cholera pandemics; recent outbreaks in Zimbabwe and Haiti are included in the seventh and ongoing pandemic
1
. Only isolates in serogroup O1 (consisting of two biotypes known as ‘classical’ and ‘El Tor’) and the derivative O139 (refs
2
,
3
) can cause epidemic cholera
2
. It is believed that the first six cholera pandemics were caused by the classical biotype, but El Tor has subsequently spread globally and replaced the classical biotype in the current pandemic
1
. Detailed molecular epidemiological mapping of cholera has been compromised by a reliance on sub-genomic regions such as mobile elements to infer relationships, making El Tor isolates associated with the seventh pandemic seem superficially diverse. To understand the underlying phylogeny of the lineage responsible for the current pandemic, we identified high-resolution markers (single nucleotide polymorphisms; SNPs) in 154 whole-genome sequences of globally and temporally representative
V. cholerae
isolates. Using this phylogeny, we show here that the seventh pandemic has spread from the Bay of Bengal in at least three independent but overlapping waves with a common ancestor in the 1950s, and identify several transcontinental transmission events. Additionally, we show how the acquisition of the SXT family of antibiotic resistance elements has shaped pandemic spread, and show that this family was first acquired at least ten years before its discovery in
V. cholerae
.
Journal Article
Efficacy and safety of tirzepatide for treatment of overweight or obesity. A systematic review and meta-analysis
BackgroundRecent studies suggest that tirzepatide, a dual glucose-dependent insulinotropic-peptide (GIP) and glucagon-like peptide-1 receptor agonist (GLP-1 RA), has significant weight loss effects. This systematic review and meta-analysis aims to assess the efficacy and safety of tirzepatide for weight loss in patients with overweight or obesity.MethodsMedline, Embase and Cochrane CENTRAL were searched for randomized controlled trials (RCTs) on tirzepatide’s weight loss efficacy for these patients. A single arm meta-analysis of proportions estimated primary outcomes, ≥5%, ≥10%, and ≥15% weight loss, and adverse events (AEs); while meta-analysis of means estimated secondary outcomes. Comparative meta-analysis was conducted between tirzepatide and control arms where mean differences and odds ratios were estimated for continuous and dichotomous outcomes respectively.ResultsRCTs included in this study revealed that among 5800 patients, 78.22% (95% CI: 72.15% to 83.73%), 55.60% (95% CI: 46.54% to 64.47%), 32.28% (95% CI: 23.17% to 42.12%) achieved ≥5%, ≥10%, and ≥15% weight loss, respectively. Tirzepatide 5 mg demonstrated weight loss superiority relative to placebo (MD: −12.47 kg, 95% CI: −13.94 kg to −11.00 kg) and semaglutide (n = 1409, MD: −1.90 kg, 95% CI: −2.97 kg to −0.83 kg) with dose-dependent increase for 10 mg and 15 mg doses. The comparison between tirzepatide and semaglutide was examined in the SURPASS-2 trial that was included in this systematic review. For AEs, there was increase odds of experiencing gastrointestinal AEs with tirzepatide compared to placebo, but no significant difference with semaglutide.ConclusionTirzepatide has significant potential as a weight loss drug in patients with overweight and obesity, with little increase in AEs compared to other weight loss drugs. With its ability to concurrently target multiple aspects of metabolic syndrome, it should be considered as the next helm of weight loss therapies.
Journal Article