A Predicted Correlation Between Age Gradient and Star Formation History in FIRE Dwarf Galaxies

We explore the radial variation of star formation histories in dwarf galaxies simulated with Feedback In Realistic Environments (FIRE) physics. The sample contains 9 low-mass field dwarfs with M_ star = 10^5 - 10^7 M_sun from previous FIRE results, and a new suite of 17 higher mass field dwarfs with M_star = 10^7 - 10^9 M_sun introduced here. We find that age gradients are common in our dwarfs, with older stars dominant at large radii. The strength of the gradient correlates with overall galaxy age such that earlier star formation produces a more pronounced gradient. The relation between formation time and strength of the gradient is driven by both mergers and star-formation feedback. Mergers can both steepen and flatten the age gradient depending on the timing of the merger and star formation history of the merging galaxy. In galaxies without significant mergers, early feedback pushes stars to the outskirts at early times. Interestingly, among galaxies without mergers, those with large dark matter cores have flatter age gradients because these galaxies have more late-time feedback. If real galaxies have age gradients as we predict, stellar population studies that rely on sampling a limited fraction of a galaxy can give a biased view of its global star formation history. We show that central fields can be biased young by a few Gyrs while outer fields are biased old. Fields positioned near the 2D half-light radius will provide the least biased measure of a dwarf galaxy's global star formation history.Comment: 13 pages, 8 figures. Submitted to MNRAS, comments welcom

Formation of proto-globular cluster candidates in cosmological simulations of dwarf galaxies at z>4z>4

We perform cosmological hydrodynamical simulations to study the formation of proto-globular cluster candidates in progenitors of present-day dwarf galaxies $(M_{\rm vir} \approx 10^{10}\, {\rm M}_\odot$ at $z=0$) as part of the "Feedback in Realistic Environment" (FIRE) project. Compact ($r_{1/2}<30$ pc), relatively massive ($0.5 \times 10^5 \lesssim M_{\star}/{\rm M}_\odot \lesssim 5\times10^5$), self-bound stellar clusters form at $11\gtrsim z \gtrsim 5$ in progenitors with $M_{\rm vir} \approx 10^9\,{\rm M}_\odot$. Cluster formation is triggered when at least $10^7\,{\rm M}_\odot$ of dense, turbulent gas reaches $\Sigma_{\rm gas} \approx 10^4\, {\rm M}_\odot\, {\rm pc}^{-2}$ as a result of the compressive effects of supernova feedback or from cloud-cloud collisions. The clusters can survive for $2-3\,{\rm Gyr}$; absent numerical effects, they would likely survive substantially longer, perhaps to $z=0$. The longest-lived clusters are those that form at significant distance -- several hundreds of pc -- from their host galaxy. We therefore predict that globular clusters forming in progenitors of present-day dwarf galaxies will be offset from any pre-existing stars within their host dark matter halos as opposed to deeply embedded within a well-defined galaxy. Properties of the nascent clusters are consistent with observations of some of the faintest and most compact high-redshift sources in \textit{Hubble Space Telescope} lensing fields and are at the edge of what will be detectable as point sources in deep imaging of non-lensed fields with the \textit{James Webb Space Telescope}. By contrast, the star clusters' host galaxies will remain undetectable.Comment: 14 pages, 5 figures, submitted to MNRA

Fire in the field: simulating the threshold of galaxy formation

We present a suite of 15 cosmological zoom-in simulations of isolated dark matter haloes, all with masses of M_(halo) ≈ 10^(10) M_⊙ at z = 0, in order to understand the relationship among halo assembly, galaxy formation and feedback's effects on the central density structure in dwarf galaxies. These simulations are part of the Feedback in Realistic Environments (FIRE) project and are performed at extremely high resolution (m_(baryon) = 500 M_⊙, m_(dm) = 2500 M_⊙). The resultant galaxies have stellar masses that are consistent with rough abundance matching estimates, coinciding with the faintest galaxies that can be seen beyond the virial radius of the Milky Way (M_*/M_⊙ ≈ 10^5 − 10^7). This non-negligible spread in stellar mass at z = 0 in haloes within a narrow range of virial masses is strongly correlated with central halo density or maximum circular velocity V_(max), both of which are tightly linked to halo formation time. Much of this dependence of M_* on a second parameter (beyond M_(halo)) is a direct consequence of the M_(halo) ∼ 10^(10) M_⊙ mass scale coinciding with the threshold for strong reionization suppression: the densest, earliest-forming haloes remain above the UV-suppression scale throughout their histories while late-forming systems fall below the UV-suppression scale over longer periods and form fewer stars as a result. In fact, the latest-forming, lowest-concentration halo in our suite fails to form any stars. Haloes that form galaxies with M_⋆ ≳ 2 × 10^6 M_⊙ have reduced central densities relative to dark-matter-only simulations, and the radial extent of the density modifications is well-approximated by the galaxy half-mass radius r_(1/2). Lower-mass galaxies do not modify their host dark matter haloes at the mass scale studied here. This apparent stellar mass threshold of M_⋆ ≈ 2 × 10^6 − 2 × 10^(−4) M_(halo) is broadly consistent with previous work and provides a testable prediction of FIRE feedback models in Λcold dark matter

IRE1β negatively regulates IRE1α signaling in response to endoplasmic reticulum stress

IRE1β is an ER stress sensor uniquely expressed in epithelial cells lining mucosal surfaces. Here, we show that intestinal epithelial cells expressing IRE1β have an attenuated unfolded protein response to ER stress. When modeled in HEK293 cells and with purified protein, IRE1β diminishes expression and inhibits signaling by the closely related stress sensor IRE1α. IRE1β can assemble with and inhibit IRE1α to suppress stress-induced XBP1 splicing, a key mediator of the unfolded protein response. In comparison to IRE1α, IRE1β has relatively weak XBP1 splicing activity, largely explained by a nonconserved amino acid in the kinase domain active site that impairs its phosphorylation and restricts oligomerization. This enables IRE1β to act as a dominant-negative suppressor of IRE1α and affect how barrier epithelial cells manage the response to stress at the host–environment interface

Comparison of Pond Production of Phase-III Sunshine Bass Fed 32-, 36-, and 40%-Crude-Protein Diets with Fixed Energy : Protein Ratios

We stocked phase-III sunshine bass (white bass Morone chrysops ♀ × striped bass M. saxatilis ♂) at a rate of 6,188 fingerlings/ha into twelve 0.04-ha earthen ponds supplied with continuous aeration. Three dietary treatments were randomly assigned to quadruplicate ponds. Sunshine bass were fed to apparent satiation once daily after average initial weight (mean ± SE = 214 ± 5 g) and total length (245 ± 1.6 mm) were determined. Diets were formulated to conserve the estimated digestible energy:crude protein (CP) ratio (9.3 kcal/g protein) and represented the following CP and energy values fed to fish: 32% CP (3,000 kcal/kg), 36% CP (3,360 kcal/kg), and 40% CP (3,760 kcal/kg). Harvest data suggest that nutrient density is a variable that can be manipulated to optimize production and reduce production costs. Production rates (mean ± SE) were 2,851 ± 600 kg/ha for the 32%-CP diet, 2,895 ± 341 kg/ha for the 36%-CP diet, and 2,953 ± 142 kg/ha for the 40%-CP diet; production rates were not significantly different among dietary treatments. Survival was excellent and did not appear to be related to dietary treatment. Dressed (gilled and gutted) fish averaged 80% of whole-fish weight, and the dressed percentage did not vary as a function of nutrient density. Feed conversion ratios of 3.0 ± 0.4, 2.8 ± 0.2, and 2.6 ± 0.1 were obtained for the fish fed 32-, 36-, and 40%-CP diets, respectively. Protein conversion ratios (mean = 1.0) were not significantly influenced by dietary treatment. Feed cost increased with increasing dietary CP level; costs were US$0.447 per kilogram for the 32$0.493 per kilogram for the 36%-CP diet, and $0.541 per kilogram for the 40$1.34, $1.38, and$1.41 per kilogram of gain for the 32-, 36-, and 40%-CP diets, respectively. A savings of $0.16 per kilogram produced, or approximately$450 per hectare, was realized as a result of feeding either of the two lower-CP, lower-energy diets. Accordingly, we suggest that phase-III sunshine bass can be more economically produced by feeding diets as low as 32% CP with a minimum energy:protein ratio of 9.3 kcal/g CP

Star formation at the edge of the Local Group: a rising star formation history in the isolated galaxy WLM

We present the star formation history (SFH) of the isolated (D~970 kpc) Local Group dwarf galaxy WLM measured from color-magnitude diagrams constructed from deep Hubble Space Telescope imaging. Our observations include a central (0.5 $r_h$) and outer field (0.7 $r_h$) that reach below the oldest main sequence turnoff. WLM has no early dominant episode of star formation: 20% of its stellar mass formed by ~12.5 Gyr ago (z~5). It also has an SFR that rises to the present with 50% of the stellar mass within the most recent 5 Gyr (z<0.7). There is evidence of a strong age gradient: the mean age of the outer field is 5 Gyr older than the inner field despite being only 0.4 kpc apart. Some models suggest such steep gradients are associated with strong stellar feedback and dark matter core creation. The SFHs of real isolated dwarf galaxies and those from the the Feedback In Realistic Environment suite are in good agreement for $M_{\star}(z=0) \sim 10^7-10^9 M_{\odot}$, but in worse agreement at lower masses ($M_{\star}(z=0) \sim 10^5-10^7 M_{\odot}$). These differences may be explainable by systematics in the models (e.g., reionization model) and/or observations (HST field placement). We suggest that a coordinated effort to get deep CMDs between HST/JWST (crowded central fields) and WFIRST (wide-area halo coverage) is the optimal path for measuring global SFHs of isolated dwarf galaxies.Comment: 13 pages, 13 Figures, 4 Tables. Re-submitted to MNRAS after addressing the referee's comment

Analysis of baseline parameters in the HALT polycystic kidney disease trials

HALT PKD consists of two ongoing randomized trials with the largest cohort of systematically studied patients with autosomal dominant polycystic kidney disease to date. Study A will compare combined treatment with an angiotensin-converting inhibitor and receptor blocker to inhibitor alone and standard compared with low blood pressure targets in 558 early-stage disease patients with an eGFR over 60ml/min per 1.73m2. Study B will compare inhibitor-blocker treatment to the inhibitor alone in 486 late-stage patients with eGFR 25–60ml/min per 1.73m2. We used correlation and multiple regression cross-sectional analyses to determine associations of baseline parameters with total kidney, liver, or liver cyst volumes measured by MRI in Study A and eGFR in both studies. Lower eGFR and higher natural log-transformed urine albumin excretion were independently associated with a larger natural log–transformed total kidney volume adjusted for height (ln(HtTKV)). Higher body surface area was independently associated with a higher ln(HtTKV) and lower eGFR. Men had larger height-adjusted total kidney volume and smaller liver cyst volumes than women. A weak correlation was found between the ln(HtTKV) and natural log–transformed total liver volume adjusted for height or natural log liver cyst volume in women only. Women had higher urine aldosterone excretion and lower plasma potassium. Thus, our analysis (1) confirms a strong association between renal volume and functional parameters, (2) shows that gender and other factors differentially affect the development of polycystic disease in the kidney and liver, and (3) suggests an association between anthropomorphic measures reflecting prenatal and/or postnatal growth and disease severity