We investigate the stellar populations for a sample of 24 quiescent galaxies at 1.5 < z < 2.5 using deep rest-frame optical spectra obtained with Keck MOSFIRE. By fitting templates simultaneously to ...the spectroscopic and photometric data and exploring a variety of star formation histories, we obtain robust measurements of median stellar ages and residual levels of star formation. After subtracting the stellar templates, the stacked spectrum reveals the H and N ii emission lines, providing an upper limit on the ongoing star formation rate of 0.9 0.1 M yr−1. By combining the MOSFIRE data with our sample of Keck LRIS spectra at lower redshift, we analyze the quiescent population at 1 < z < 2.5 in a consistent manner. We find a tight relation (with a scatter of 0.13 dex) between the stellar age and the rest-frame U − V and V − J colors, which can be used to estimate the age of quiescent galaxies, given their colors. Applying this age-color relation to large photometric samples, we are able to model the number density evolution for quiescent galaxies of various ages. We find evidence for two distinct quenching paths: a fast quenching that produces compact post-starburst systems and a slow quenching of larger galaxies. Fast quenching accounts for about a fifth of the growth of the red sequence at z ∼ 1.4 and half at z ∼ 2.2. We conclude that fast quenching is triggered by dramatic events, such as gas-rich mergers, while slow quenching is likely caused by a different physical mechanism.
Abstract
We present new determinations of the rest-UV luminosity functions (LFs) at
z
= 2–9 to extremely low luminosities (>−14 mag) from a sample of >2500 lensed galaxies found behind the Hubble ...Frontier Fields (HFF) clusters. For the first time, we present faint-end slope results from lensed samples that are fully consistent with blank-field results over the redshift range
z
= 2–9, while reaching to much lower luminosities than possible from the blank-field studies. Combining the deep lensed sample with the large blank-field samples allows us to set tight constraints on the faint-end slope
α
of the
z
= 2–9 UV LFs and its evolution. We find a smooth flattening in
α
from −2.28 ± 0.10 (
z
= 9) to −1.53 ± 0.03 (
z
= 2) with cosmic time (
dα
/
dz
= −0.11 ± 0.01), fully consistent with dark matter halo buildup. We utilize these new results to present new measurements of the evolution in the
UV
luminosity density
ρ
UV
brighter than −13 mag from
z
∼ 9 to
z
∼ 2. Accounting for the star formation rate (SFR) densities to faint luminosities implied by our LF results, we find that unobscured star formation dominates the SFR density at
z
≳ 4, with obscured star formation dominant thereafter. Having shown we can quantify the faint-end slope
α
of the LF accurately with our lensed HFF samples, we also quantify the apparent curvature in the shape of the UV LF through a curvature parameter
δ
. The constraints on the curvature
δ
strongly rule out the presence of a turn-over brighter than −13.1 mag at
z
∼ 3, −14.3 mag at
z
∼ 6, and −15.5 mag at all other redshifts between
z
∼ 9 and
z
∼ 2.
We report on the detailed analysis of a gravitationally lensed Y-band dropout, A2744_YD4, selected from deep Hubble Space Telescope imaging in the Frontier Field cluster Abell 2744. Band 7 ...observations with the Atacama Large Millimeter/submillimeter Array (ALMA) indicate the proximate detection of a significant 1 mm continuum flux suggesting the presence of dust for a star-forming galaxy with a photometric redshift of . Deep X-SHOOTER spectra confirms the high-redshift identity of A2744_YD4 via the detection of Ly emission at a redshift z = 8.38. The association with the ALMA detection is confirmed by the presence of O iii 88 m emission at the same redshift. Although both emission features are only significant at the 4 level, we argue their joint detection and the positional coincidence with a high-redshift dropout in the Hubble Space Telescope images confirms the physical association. Analysis of the available photometric data and the modest gravitational magnification ( ) indicates A2744_YD4 has a stellar mass of ∼2 × 109 , a star formation rate of ∼20 yr−1 and a dust mass of ∼6 × 106 . We discuss the implications of the formation of such a dust mass only after the onset of cosmic reionization.
ABSTRACT We present deep near-infrared spectra for a sample of 24 quiescent galaxies in the redshift range obtained with the MOSFIRE spectrograph at the W. M. Keck Observatory. In conjunction with a ...similar data set we obtained in the range with the LRIS spectrograph, we analyze the kinematic and structural properties for 80 quiescent galaxies, the largest homogeneously selected sample to date spanning 3 Gyr of early cosmic history. Analysis of our Keck spectra together with measurements derived from associated Hubble Space Telescope images reveals increasingly larger stellar velocity dispersions and smaller sizes to redshifts beyond . By classifying our sample according to Sérsic indices, we find that among disk-like systems the flatter ones show a higher dynamical to stellar mass ratio compared to their rounder counterparts, which we interpret as evidence for a significant contribution of rotational motion. For this subset of disk-like systems, we estimate that , the ratio of the circular velocity to the intrinsic velocity dispersion, is a factor of two larger than for present-day disky quiescent galaxies. We use the velocity dispersion measurements also to explore the redshift evolution of the dynamical to stellar mass ratio, and to measure for the first time the physical size growth rate of individual systems over two distinct redshift ranges, finding a faster evolution at earlier times. We discuss the physical origin of this time-dependent growth in size in the context of the associated reduction of the systematic rotation.
The contemporary discoveries of galaxies and gamma ray bursts (GRBs) at high redshift have supplied the first direct information on star formation when the universe was only a few hundred million ...years old. Using an extensive sample of 112 GRBs above a fixed luminosity limit drawn from the Second Swift Burst Alert Telescope catalog and accounting for uncertainty in their redshift distribution by considering the contribution of "dark" GRBs, we compare the cumulative redshift distribution N(<z) of GRBs with the star formation density p*(z) measured from UV-selected galaxies over 0 < z <4. While some previous studies of the GRB-SFR connection have concluded that GRB-inferred star formation at high redshift would be sufficient to maintain cosmic reionization over 6< z <9 and reproduce the observed optical depth of Thomson scattering to the cosmic microwave background, we show that such a star formation history would overpredict the observed stellar mass density at z > 4 measured from rest-frame optical surveys.
We discuss the rest-frame optical emission line spectra of a large (∼50) sample of z ∼ 3.1 Ly emitting galaxies (LAEs) whose physical properties suggest such sources are promising analogs of galaxies ...in the reionization era. Reliable Lyman continuum (LyC) escape fractions have now been determined for a large sample of such LAEs from the LymAn Continuum Escape Survey (LACES) undertaken via deep Hubble Space Telescope imaging in the SSA22 survey area reported in Fletcher et al. Using new measures of O ii emission secured from Keck MOSFIRE spectra we re-examine, for a larger sample, earlier claims that LyC leakages may correlate with the nebular emission line ratio O iii/O ii as expected for density-bound H ii regions. We find that a large O iii/O ii line ratio is indeed a necessary condition for LyC leakage, strengthening earlier claims made using smaller samples at various redshifts. However, not all LAEs with large O iii/O ii line ratios are leakers and leaking radiation appears not to be associated with differences in other spectral diagnostics. This suggests the detection of leaking radiation is modulated by an additional property, possibly the viewing angle for porous H ii regions. We discuss our new results in the context of the striking bimodality of LAE leakers and non-leakers found in the LACES program and the implications for the sources of cosmic reionization.
We use the largest sample of galaxies to date from the first four Hubble Frontier Fields clusters to set constraints on the shape of the luminosity functions (LFs) to fainter than mag. We quantify, ...for the first time, the impact of magnification uncertainties on LF results and thus provide more realistic constraints than other recent work. Our simulations reveal that, for the highly magnified sources, the systematic uncertainties can become extremely large fainter than −14 mag, reaching several orders of magnitude at 95% confidence at approximately −12 mag. Our new forward-modeling formalism incorporates the impact of magnification uncertainties into the LF results by exploiting the availability of many independent magnification models for the same cluster. One public magnification model is used to construct a mock high-redshift galaxy sample that is then analyzed using the other magnification models to construct an LF. Large systematic errors occur at high magnifications ( ) because of differences between the models. The volume densities we derive for faint ( −17 mag) sources are ∼3-4× lower than one recent report and give a faint-end slope , which is 3.0-3.5 shallower (including or not including the size uncertainties, respectively). We introduce a new curvature parameter δ to model the faint end of the LF and demonstrate that the observations permit (at 68% confidence) a turn-over at in the range of −15.3 to −14.2 mag, depending on the assumed lensing model. The present consideration of magnification errors and new size determinations raise doubts about previous reports regarding the form of the LF at . We discuss the implications of our turn-over constraints in the context of recent theoretical predictions.
We present the results of a new search for galaxies at redshift z ≃ 9 in the first two Hubble Frontier Fields with completed HST WFC3/IR and ACS imaging. To ensure robust photometric redshift ...solutions, and to minimize incompleteness, we confine our search to objects with H
160 < 28.6 (AB mag), consider only image regions with an rms noise σ160 > 30 mag (within a 0.5-arcsec diameter aperture), and insist on detections in both H
160 and J
140. The result is a survey covering an effective area (after accounting for magnification) of 10.9 arcmin2, which yields 12 galaxies at 8.4 < z < 9.5. Within the Abell-2744 cluster and parallel fields, we confirm the three brightest objects reported by Ishigaki et al., but recover only one of the four z > 8.4 sources reported by Zheng et al. In the MACSJ0416.1−240 cluster field, we report five objects, and explain why each of these eluded detection or classification as z ≃ 9 galaxies in the published searches of the shallower CLASH data. Finally, we uncover four z ≃ 9 galaxies from the MACSJ0416.1−240 parallel field. Based on the published magnification maps, we find that only one of these 12 galaxies is likely boosted by more than a factor of 2 by gravitational lensing. Consequently, we are able to perform a fairly straightforward reanalysis of the normalization of the z ≃ 9 UV galaxy luminosity function as explored previously in the HUDF12 programme. We conclude that the new data strengthen the evidence for a continued smooth decline in UV luminosity density (and hence star formation rate density) from z ≃ 8 to 9, contrary to recent reports of a marked drop-off at these redshifts. This provides further support for the scenario in which early galaxy evolution is sufficiently extended to explain cosmic reionization.
Effect of abuse-deterrent formulation of OxyContin Cicero, Theodore J; Ellis, Matthew S; Surratt, Hilary L
New England journal of medicine/The New England journal of medicine,
2012-Jul-12, Volume:
367, Issue:
2
Journal Article
Low-cost sensing strategies hold the promise of denser air quality monitoring networks, which could significantly improve our understanding of personal air pollution exposure. Additionally, low-cost ...air quality sensors could be deployed to areas where limited monitoring exists. However, low-cost sensors are frequently sensitive to environmental conditions and pollutant cross-sensitivities, which have historically been poorly addressed by laboratory calibrations, limiting their utility for monitoring. In this study, we investigated different calibration models for the Real-time Affordable Multi-Pollutant (RAMP) sensor package, which measures CO, NO2, O3, and CO2. We explored three methods: (1) laboratory univariate linear regression, (2) empirical multiple linear regression, and (3) machine-learning-based calibration models using random forests (RF). Calibration models were developed for 16–19 RAMP monitors (varied by pollutant) using training and testing windows spanning August 2016 through February 2017 in Pittsburgh, PA, US. The random forest models matched (CO) or significantly outperformed (NO2, CO2, O3) the other calibration models, and their accuracy and precision were robust over time for testing windows of up to 16 weeks. Following calibration, average mean absolute error on the testing data set from the random forest models was 38 ppb for CO (14 % relative error), 10 ppm for CO2 (2 % relative error), 3.5 ppb for NO2 (29 % relative error), and 3.4 ppb for O3 (15 % relative error), and Pearson r versus the reference monitors exceeded 0.8 for most units. Model performance is explored in detail, including a quantification of model variable importance, accuracy across different concentration ranges, and performance in a range of monitoring contexts including the National Ambient Air Quality Standards (NAAQS) and the US EPA Air Sensors Guidebook recommendations of minimum data quality for personal exposure measurement. A key strength of the RF approach is that it accounts for pollutant cross-sensitivities. This highlights the importance of developing multipollutant sensor packages (as opposed to single-pollutant monitors); we determined this is especially critical for NO2 and CO2. The evaluation reveals that only the RF-calibrated sensors meet the US EPA Air Sensors Guidebook recommendations of minimum data quality for personal exposure measurement. We also demonstrate that the RF-model-calibrated sensors could detect differences in NO2 concentrations between a near-road site and a suburban site less than 1.5 km away. From this study, we conclude that combining RF models with carefully controlled state-of-the-art multipollutant sensor packages as in the RAMP monitors appears to be a very promising approach to address the poor performance that has plagued low-cost air quality sensors.
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