12 research outputs found
[OIII] Emission and Gas Kinematics in a Lyman-alpha Blob at z ~ 3.1
We present spectroscopic measurements of the [OIII] emission line from two
subregions of strong Lyman-alpha emission in a radio-quiet Lyman-alpha blob
(LAB). The blob under study is LAB1 (Steidel et al. 2000) at z ~ 3.1, and the
[OIII] detections are from the two Lyman break galaxies embedded in the blob
halo. The [OIII] measurements were made with LUCIFER on the 8.4m Large
Binocular Telescope and NIRSPEC on 10m Keck Telescope. Comparing the redshift
of the [OIII] measurements to Lyman-alpha redshifts from SAURON (Weijmans et
al. 2010) allows us to take a step towards understanding the kinematics of the
gas in the blob. Using both LUCIFER and NIRSPEC we find velocity offsets
between the [OIII] and Lyman-alpha redshifts that are modestly negative or
consistent with 0 km/s in both subregions studied (ranging from -72 +/- 42 --
+6 +/- 33 km/s). A negative offset means Lyman-alpha is blueshifted with
respect to [OIII], a positive offset then implies Lyman-alpha is redshifted
with respect to [OIII]. These results may imply that outflows are not primarily
responsible for Lyman alpha escape in this LAB, since outflows are generally
expected to produce a positive velocity offset (McLinden et al. 2011). In
addition, we present an [OIII] line flux upper limit on a third region of LAB1,
a region that is unassociated with any underlying galaxy. We find that the
[OIII] upper limit from the galaxy-unassociated region of the blob is at least
1.4 -- 2.5 times fainter than the [OIII] flux from one of the LBG-associated
regions and has an [OIII] to Lyman-alpha ratio measured at least 1.9 -- 3.4
times smaller than the same ratio measured from one of the LBGs.Comment: submitted to Ap
Galactic winds and stellar populations in Lyman emitting galaxies at z ~ 3.1
We present a sample of 33 spectroscopically confirmed z ~ 3.1
Ly-emitting galaxies (LAEs) in the Cosmological Evolution Survey
(COSMOS) field. This paper details the narrow-band survey we conducted to
detect the LAE sample, the optical spectroscopy we performed to confirm the
nature of these LAEs, and a new near-infrared spectroscopic detection of the [O
III] 5007 \AA\ line in one of these LAEs. This detection is in addition to two
[O III] detections in two z ~ 3.1 LAEs we have reported on previously (McLinden
et al 2011). The bulk of the paper then presents detailed constraints on the
physical characteristics of the entire LAE sample from spectral energy
distribution (SED) fitting. These characteristics include mass, age,
star-formation history, dust content, and metallicity. We also detail an
approach to account for nebular emission lines in the SED fitting process -
wherein our models predict the strength of the [O III] line in an LAE spectrum.
We are able to study the success of this prediction because we can compare the
model predictions to our actual near-infrared observations both in galaxies
that have [O III] detections and those that yielded non-detections. We find a
median stellar mass of 6.9 10 M and a median star
formation rate weighted stellar population age of 4.5 10 yr. In
addition to SED fitting, we quantify the velocity offset between the [O III]
and Ly lines in the galaxy with the new [O III] detection, finding that
the Ly line is shifted 52 km s redwards of the [O III] line,
which defines the systemic velocity of the galaxy.Comment: 38 pages, 27 figures, 4 tables, Accepted for publication in MNRA
The Dynamical Masses, Densities, and Star Formation Scaling Relations of Lyman Alpha Galaxies
We present the first dynamical mass measurements for Lyman alpha galaxies at
high redshift, based on velocity dispersion measurements from rest-frame
optical emission lines and size measurements from HST imaging, for a sample of
nine galaxies drawn from four surveys. These measurements enable us to study
the nature of Lyman alpha galaxies in the context of galaxy scaling relations.
The resulting dynamical masses range from 1e9 to 1e10 solar masses. We also fit
stellar population models to our sample, and use them to plot the Lyman alpha
sample on a stellar mass vs. line width relation. Overall, the Lyman alpha
galaxies follow well the scaling relation established by observing star forming
galaxies at lower redshift (and without regard for Lyman alpha emission),
though in 1/3 of the Lyman alpha galaxies, lower-mass fits are also acceptable.
In all cases, the dynamical masses agree with established stellarmass-linewidth
relation. Using the dynamical masses as an upper limit on gas mass, we show
that Lyman alpha galaxies resemble starbursts (rather than "normal" galaxies)
in the relation between gas mass surface density and star formation activity,
in spite of relatively modest star formation rates. Finally, we examine the
mass densities of these galaxies, and show that their future evolution likely
requires dissipational ("wet") merging. In short, we find that Lyman alpha
galaxies are low mass cousins of larger starbursts.Comment: Submitted to The Astrophysical Journal. 23 pp including three figures
and four table
First spectroscopic measurements of [OIII] emission from Lyman-alpha selected field galaxies at z ~ 3.1
We present the first spectroscopic measurements of the [OIII] 5007 A line in
two z ~ 3.1 Lyman-alpha emitting galaxies (LAEs) using the new near-infrared
instrument LUCIFER1 on the 8.4m Large Binocular Telescope (LBT). We also
describe the optical imaging and spectroscopic observations used to identify
these Lya emitting galaxies. Using the [OIII] line we have measured accurate
systemic redshifts for these two galaxies, and discovered a velocity offset
between the [OIII] and Ly-alpha lines in both, with the Lya line peaking 342
and 125 km/s redward of the systemic velocity. These velocity offsets imply
that there are powerful outflows in high-redshift LAEs. They also ease the
transmission of Lya photons through the interstellar medium and intergalactic
medium around the galaxies. By measuring these offsets directly, we can refine
both Lya-based tests for reionization, and Lya luminosity function measurements
where the Lya forest affects the blue wing of the line. Our work also provides
the first direct constraints on the strength of the [OIII] line in
high-redshift LAEs. We find [OIII] fluxes of 7 and 36 x 10^-17 erg s^-1 cm^-2
in two z ~ 3.1 LAEs. These lines are strong enough to dominate broad-band flux
measurements that include the line (in thiscase, K_s band photometry). Spectral
energy distribution fits that do not account for the lines would therefore
overestimate the 4000 A (and/or Balmer) break strength in such galaxies, and
hence also the ages and stellar masses of such high-z galaxies.Comment: Accepted by the Astrophysical Journal. 11 pages, 3 figures, 1 table
(emulateapj
The Hobby–Eberly Telescope Dark Energy Experiment (HETDEX) Survey Design, Reductions, and Detections
We describe the survey design, calibration, commissioning, and emission-line detection algorithms for the Hobby–Eberly Telescope Dark Energy Experiment (HETDEX). The goal of HETDEX is to measure the redshifts of over a million Lyα emitting galaxies between 1.88 < z < 3.52, in a 540 deg2 area encompassing a comoving volume of 10.9 Gpc3. No preselection of targets is involved; instead the HETDEX measurements are accomplished via a spectroscopic survey using a suite of wide-field integral field units distributed over the focal plane of the telescope. This survey measures the Hubble expansion parameter and angular diameter distance, with a final expected accuracy of better than 1%. We detail the project’s observational strategy, reduction pipeline, source detection, and catalog generation, and present initial results for science verification in the Cosmological Evolution Survey, Extended Groth Strip, and Great Observatories Origins Deep Survey North fields. We demonstrate that our data reach the required specifications in throughput, astrometric accuracy, flux limit, and object detection, with the end products being a catalog of emission-line sources, their object classifications, and flux-calibrated spectra
Airborne Emission Rate Measurements Validate Remote Sensing Observations and Emission Inventories of Western U.S. Wildfires
Carbonaceous emissions from wildfires are a dynamic mixture of gases and particles that have important impacts on air quality and climate. Emissions that feed atmospheric models are estimated using burned area and fire radiative power (FRP) methods that rely on satellite products. These approaches show wide variability and have large uncertainties, and their accuracy is challenging to evaluate due to limited aircraft and ground measurements. Here, we present a novel method to estimate fire plume-integrated total carbon and speciated emission rates using a unique combination of lidar remote sensing aerosol extinction profiles and in situ measured carbon constituents. We show strong agreement between these aircraft-derived emission rates of total carbon and a detailed burned area-based inventory that distributes carbon emissions in time using Geostationary Operational Environmental Satellite FRP observations (Fuel2Fire inventory, slope = 1.33 ± 0.04, r2 = 0.93, and RMSE = 0.27). Other more commonly used inventories strongly correlate with aircraft-derived emissions but have wide-ranging over- and under-predictions. A strong correlation is found between carbon monoxide emissions estimated in situ with those derived from the TROPOspheric Monitoring Instrument (TROPOMI) for five wildfires with coincident sampling windows (slope = 0.99 ± 0.18; bias = 28.5%). Smoke emission coefficients (g MJ–1) enable direct estimations of primary gas and aerosol emissions from satellite FRP observations, and we derive these values for many compounds emitted by temperate forest fuels, including several previously unreported species
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Causal and Associational Language in Observational Health Research: A Systematic Evaluation.
We estimated the degree to which language used in the high profile medical/public health/epidemiology literature implied causality using language linking exposures to outcomes and action recommendations; examined disconnects between language and recommendations; identified the most common linking phrases; and estimated how strongly linking phrases imply causality. We searched and screened for 1,170 articles from 18 high-profile journals (65 per journal) published from 2010-2019. Based on written framing and systematic guidance, three reviewers rated the degree of causality implied in abstracts and full text for exposure/outcome linking language and action recommendations. Reviewers rated the causal implication of exposure/outcome linking language as None (no causal implication) in 13.8%, Weak 34.2%, Moderate 33.2%, and Strong 18.7% of abstracts. The implied causality of action recommendations was higher than the implied causality of linking sentences for 44.5% or commensurate for 40.3% of articles. The most common linking word in abstracts was "associate" (45.7%). Reviewers' ratings of linking word roots were highly heterogeneous; over half of reviewers rated "association" as having at least some causal implication. This research undercuts the assumption that avoiding "causal" words leads to clarity of interpretation in medical research