38 research outputs found
Gender disparities in colloquium speakers at top universities
Colloquium talks at prestigious universities both create and reflect academic researchers' reputations. Gender disparities in colloquium talks can arise through a variety of mechanisms. The current study examines gender differences in colloquium speakers at 50 prestigious US colleges and universities in 2013-2014. Using archival data, we analyzed 3,652 talks in six academic disciplines. Men were more likely than women to be colloquium speakers even after controlling for the gender and rank of the available speakers. Eliminating alternative explanations (e.g., women declining invitations more often than men), our follow-up data revealed that female and male faculty at top universities reported no differences in the extent to which they (i) valued and (ii) turned down speaking engagements. Additional data revealed that the presence of women as colloquium chairs (and potentially on colloquium committees) increased the likelihood of women appearing as colloquium speakers. Our data suggest that those who invite and schedule speakers serve as gender gatekeepers with the power to create or reduce gender differences in academic reputations
CANDELS: The progenitors of compact quiescent galaxies at z~2
We combine high-resolution HST/WFC3 images with multi-wavelength photometry
to track the evolution of structure and activity of massive (log(M*) > 10)
galaxies at redshifts z = 1.4 - 3 in two fields of the Cosmic Assembly
Near-infrared Deep Extragalactic Legacy Survey (CANDELS). We detect compact,
star-forming galaxies (cSFGs) whose number densities, masses, sizes, and star
formation rates qualify them as likely progenitors of compact, quiescent,
massive galaxies (cQGs) at z = 1.5 - 3. At z > 2 most cSFGs have specific
star-formation rates (sSFR = 10^-9 yr^-1) half that of typical, massive SFGs at
the same epoch, and host X-ray luminous AGN 30 times (~30%) more frequently.
These properties suggest that cSFGs are formed by gas-rich processes (mergers
or disk-instabilities) that induce a compact starburst and feed an AGN, which,
in turn, quench the star formation on dynamical timescales (few 10^8 yr). The
cSFGs are continuously being formed at z = 2 - 3 and fade to cQGs by z = 1.5.
After this epoch, cSFGs are rare, thereby truncating the formation of new cQGs.
Meanwhile, down to z = 1, existing cQGs continue to enlarge to match local QGs
in size, while less-gas-rich mergers and other secular mechanisms shepherd
(larger) SFGs as later arrivals to the red sequence. In summary, we propose two
evolutionary scenarios of QG formation: an early (z > 2), fast-formation path
of rapidly-quenched cSFGs that evolve into cQGs that later enlarge within the
quiescent phase, and a slow, late-arrival (z < 2) path for SFGs to form QGs
without passing through a compact state.Comment: Submitted to the Astrophysical Journal Letters, 6 pages, 4 figure
Keck-I MOSFIRE Spectroscopy of Compact Star-Forming Galaxies at \u3cem\u3ez\u3c/em\u3e ≳ 2: High Velocity Dispersions in Progenitors of Compact Quiescent Galaxies
We present Keck-I MOSFIRE near-infrared spectroscopy for a sample of 13 compact star-forming galaxies (SFGs) at redshift 2 ≤ z ≤ 2.5 with star formation rates of SFR ~ 100 M ☉ yr–1 and masses of log(M/M ☉) ~10.8. . . .
For the remainder of the abstract, please visit:
http://dx.doi.org/10.1088/0004-637X/795/2/14
CEERS Key Paper VII: Emission Line Ratios from NIRSpec and NIRCam Wide-Field Slitless Spectroscopy at z>2
We use James Webb Space Telescope Near-Infrared Camera Wide Field Slitless
Spectroscopy (NIRCam WFSS) and Near-Infrared spectrograph (NIRSpec) in the
Cosmic Evolution Early Release survey (CEERS) to measure rest-frame optical
emission-line of 155 galaxies at z>2. The blind NIRCam grism observations
include a sample of galaxies with bright emission lines that were not observed
on the NIRSpec masks. We study the changes of the Ha, [OIII]/Hb, and
[NeIII]/[OII] emission lines in terms of redshift by comparing to lower
redshift SDSS and CLEAR samples. We find a significant (>3) correlation
between [OIII]/Hb with redshift, while [NeIII]/[OII] has a marginal (2)
correlation with redshift. We compare [OIII]/Hb and [NeIII]/[OII] to stellar
mass and Hb SFR. We find that both emission-line ratios have a correlation with
Hb SFR and an anti-correlation with stellar mass across the redshifts 0<z<9.
Comparison with MAPPINGS~V models indicates that these trends are consistent
with lower metallicity and higher ionization in low-mass and high-SFR galaxies.
We additionally compare to IllustriousTNG predictions and find that they
effectively describe the highest [OIII]/Hb ratios observed in our sample,
without the need to invoke MAPPINGS models with significant shock ionizionation
components.Comment: 16 pages, 11 figure
CEERS Spectroscopic Confirmation of NIRCam-Selected z > 8 Galaxy Candidates with JWST/NIRSpec: Initial Characterization of their Properties
We present JWST NIRSpec spectroscopy for 11 galaxy candidates with
photometric redshifts of and newly
identified in NIRCam images in the Cosmic Evolution Early Release Science
(CEERS) Survey. We confirm emission line redshifts for 7 galaxies at
using spectra at m either with the NIRSpec prism or
its three medium resolution gratings. For photometric candidates, we
achieve a high confirmation rate of 90\%, which validates the classical
dropout selection from NIRCam photometry. No robust emission lines are
identified in three galaxy candidates at , where the strong [OIII] and
H lines would be redshifted beyond the wavelength range observed by
NIRSpec, and the Lyman- continuum break is not detected with the
current sensitivity. Compared with HST-selected bright galaxies
() that are similarly spectroscopically confirmed at
, these NIRCam-selected galaxies are characterized by lower star
formation rates (SFR~yr) and lower stellar masses
(), but with higher [OIII]+H equivalent widths
(1100), and elevated production efficiency of ionizing photons
() induced by young stellar
populations (~Myrs) accounting for of the galaxy mass,
highlighting the key contribution of faint galaxies to cosmic reionization.
Taking advantage of the homogeneous selection and sensitivity, we also
investigate metallicity and ISM conditions with empirical calibrations using
the [OIII]/H ratio. We find that galaxies at have higher SFRs
and lower metallicities than galaxies at similar stellar masses at ,
which is generally consistent with the current galaxy formation and evolution
models.Comment: 21 pages, 11 figures, 2 tables. Submitted to ApJL Focus Issu
The Physical Conditions of Emission-Line Galaxies at Cosmic Dawn from JWST/NIRSpec Spectroscopy in the SMACS 0723 Early Release Observations
We present rest-frame optical emission-line flux ratio measurements for five
galaxies observed by the JWST Near-Infared Spectrograph (NIRSpec) in the
SMACS 0723 Early Release Observations. We add several quality-control and
post-processing steps to the NIRSpec pipeline reduction products in order to
ensure reliable relative flux calibration of emission lines that are closely
separated in wavelength, despite the uncertain \textit{absolute}
spectrophotometry of the current version of the reductions. Compared to
galaxies in the literature, the galaxies have similar
[OIII]5008/H ratios, similar [OIII]4364/H
ratios, and higher (0.5 dex) [NeIII]3870/[OII]3728
ratios. We compare the observations to MAPPINGS V photoionization models and
find that the measured [NeIII]3870/[OII]3728,
[OIII]4364/H, and [OIII]5008/H emission-line
ratios are consistent with an interstellar medium that has very high ionization
(, units of cm~s), low metallicity (), and very high pressure (, units of
cm). The combination of [OIII]4364/H and
[OIII](4960+5008)/H line ratios indicate very high electron
temperatures of , further implying metallicities of
with the application of low-redshift calibrations for
``-based'' metallicities. These observations represent a tantalizing new
view of the physical conditions of the interstellar medium in galaxies at
cosmic dawn.Comment: Accepted for publication in AAS Journals. 14 pages, 6 figures, 3
table
CEERS Key Paper V: A triality on the nature of HST-dark galaxies
The new capabilities that JWST offers in the near- and mid-infrared (IR) are
used to investigate in unprecedented detail the nature of optical/near-IR
faint, mid-IR bright sources, HST-dark galaxies among them. We gather JWST data
from the CEERS survey in the EGS, jointly with HST data, and analyze spatially
resolved optical-to-mid-IR spectral energy distributions (SEDs) to estimate
both photometric redshifts in 2 dimensions and stellar populations properties
in a pixel-by-pixel basis. We select 138 galaxies with F150W-F356W>1.5 mag,
F356W<27.5 mag. The nature of these sources is threefold: (1) 71% are dusty
star-forming galaxies at 2<z<6 with masses 9<log M/M_sun<11 and a variety of
specific SFRs (100 Gyr^-1); (2) 18% are quiescent/dormant (i.e., subject
to reignition and rejuvenation) galaxies at 3<z<5, masses log M/M_sun~10 and
post-starburst stellar mass-weighted ages (0.5-1 Gyr); and (3) 11% are strong
young starbursts with indications of high-EW emission lines (typically,
[OIII]+Hbeta) at 6<z<7 and log M/M_sun~9.5. The sample is dominated by
disk-like galaxies with a remarkable compactness for XELG-z6 (effective radii
smaller than 0.4 kpc). Large attenuations in SFGs, 2<A(V)<5 mag, are found
within 1.5 times the effective radius, approximately 2 kpc, while QGs present
A(V)~0.2 mag. Our SED-fitting technique reproduces the expected dust emission
luminosities of IR-bright and sub-millimeter galaxies. This study implies high
levels of star formation activity between z~20 and z~10, where virtually 100%
of our galaxies had already formed 10^8 M_sun of their stellar content, 60% of
them had assembled 10^9 M_sun, and 10% up to 10^10 M_sun (in situ or ex situ).
(abridged)Comment: Published in CEERS ApJL Focus Issue, ApJL 946, L1
Evaluation of individual and ensemble probabilistic forecasts of COVID-19 mortality in the United States
Short-term probabilistic forecasts of the trajectory of the COVID-19 pandemic in the United States have served as a visible and important communication channel between the scientific modeling community and both the general public and decision-makers. Forecasting models provide specific, quantitative, and evaluable predictions that inform short-term decisions such as healthcare staffing needs, school closures, and allocation of medical supplies. Starting in April 2020, the US COVID-19 Forecast Hub (https://covid19forecasthub.org/) collected, disseminated, and synthesized tens of millions of specific predictions from more than 90 different academic, industry, and independent research groups. A multimodel ensemble forecast that combined predictions from dozens of groups every week provided the most consistently accurate probabilistic forecasts of incident deaths due to COVID-19 at the state and national level from April 2020 through October 2021. The performance of 27 individual models that submitted complete forecasts of COVID-19 deaths consistently throughout this year showed high variability in forecast skill across time, geospatial units, and forecast horizons. Two-thirds of the models evaluated showed better accuracy than a naïve baseline model. Forecast accuracy degraded as models made predictions further into the future, with probabilistic error at a 20-wk horizon three to five times larger than when predicting at a 1-wk horizon. This project underscores the role that collaboration and active coordination between governmental public-health agencies, academic modeling teams, and industry partners can play in developing modern modeling capabilities to support local, state, and federal response to outbreaks
The United States COVID-19 Forecast Hub dataset
Academic researchers, government agencies, industry groups, and individuals have produced forecasts at an unprecedented scale during the COVID-19 pandemic. To leverage these forecasts, the United States Centers for Disease Control and Prevention (CDC) partnered with an academic research lab at the University of Massachusetts Amherst to create the US COVID-19 Forecast Hub. Launched in April 2020, the Forecast Hub is a dataset with point and probabilistic forecasts of incident cases, incident hospitalizations, incident deaths, and cumulative deaths due to COVID-19 at county, state, and national, levels in the United States. Included forecasts represent a variety of modeling approaches, data sources, and assumptions regarding the spread of COVID-19. The goal of this dataset is to establish a standardized and comparable set of short-term forecasts from modeling teams. These data can be used to develop ensemble models, communicate forecasts to the public, create visualizations, compare models, and inform policies regarding COVID-19 mitigation. These open-source data are available via download from GitHub, through an online API, and through R packages