101 research outputs found
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
Recommended from our members
Aligning Practice to Policies: Changing the Culture to Recognize and Reward Teaching at Research Universities
Recent calls for improvement in undergraduate education within STEM (science, technology, engineering, and mathematics) disciplines are hampered by the methods used to evaluate teaching effectiveness. Faculty members at research universities are commonly assessed and promoted mainly on the basis of research success. To improve the quality of undergraduate teaching across all disciplines, not only STEM fields, requires creating an environment wherein continuous improvement of teaching is valued, assessed, and rewarded at various stages of a faculty member’s career. This requires consistent application of policies that reflect well-established best practices for evaluating teaching at the department, college, and university levels. Evidence shows most teaching evaluation practices do not reflect stated policies, even when the policies specifically espouse teaching as a value. Thus, alignment of practice to policy is a major barrier to establishing a culture in which teaching is valued. Situated in the context of current national efforts to improve undergraduate STEM education, including the Association of American Universities Undergraduate STEM Education Initiative, this essay discusses four guiding principles for aligning practice with stated priorities in formal policies: 1) enhancing the role of deans and chairs; 2) effectively using the hiring process; 3) improving communication; and 4) improving the understanding of teaching as a scholarly activity. In addition, three specific examples of efforts to improve the practice of evaluating teaching are presented as examples: 1) Three Bucket Model of merit review at the University of California, Irvine; (2) Evaluation of Teaching Rubric, University of Kansas; and (3) Teaching Quality Framework, University of Colorado, Boulder. These examples provide flexible criteria to holistically evaluate and improve the quality of teaching across the diverse institutions comprising modern higher education
Prediction of peptide and protein propensity for amyloid formation
Understanding which peptides and proteins have the potential to undergo amyloid formation and what driving forces are responsible for amyloid-like fiber formation and stabilization remains limited. This is mainly because proteins that can undergo structural changes, which lead to amyloid formation, are quite diverse and share no obvious sequence or structural homology, despite the structural similarity found in the fibrils. To address these issues, a novel approach based on recursive feature selection and feed-forward neural networks was undertaken to identify key features highly correlated with the self-assembly problem. This approach allowed the identification of seven physicochemical and biochemical properties of the amino acids highly associated with the self-assembly of peptides and proteins into amyloid-like fibrils (normalized frequency of β-sheet, normalized frequency of β-sheet from LG, weights for β-sheet at the window position of 1, isoelectric point, atom-based hydrophobic moment, helix termination parameter at position j+1 and ΔGº values for peptides extrapolated in 0 M urea). Moreover, these features enabled the development of a new predictor (available at http://cran.r-project.org/web/packages/appnn/index.html) capable of accurately and reliably predicting the amyloidogenic propensity from the polypeptide sequence alone with a prediction accuracy of 84.9 % against an external validation dataset of sequences with experimental in vitro, evidence of amyloid formation
The Evolution of Ly-alpha Emitting Galaxies Between z = 2.1 and z = 3.1
We describe the results of a new, wide-field survey for z=3.1 Ly-alpha
emission-line galaxies (LAEs) in the Extended Chandra Deep Field South
(ECDF-S). By using a nearly top-hat 5010 Angstrom filter and complementary
broadband photometry from the MUSYC survey, we identify a complete sample of
141 objects with monochromatic fluxes brighter than 2.4E-17 ergs/cm^2/s and
observers-frame equivalent widths greater than ~ 80 Angstroms (i.e., 20
Angstroms in the rest-frame of Ly-alpha). The bright-end of this dataset is
dominated by x-ray sources and foreground objects with GALEX detections, but
when these interlopers are removed, we are still left with a sample of 130 LAE
candidates, 39 of which have spectroscopic confirmations. This sample overlaps
the set of objects found in an earlier ECDF-S survey, but due to our filter's
redder bandpass, it also includes 68 previously uncataloged sources. We confirm
earlier measurements of the z=3.1 LAE emission-line luminosity function, and
show that an apparent anti-correlation between equivalent width and continuum
brightness is likely due to the effect of correlated errors in our
heteroskedastic dataset. Finally, we compare the properties of z=3.1 LAEs to
LAEs found at z=2.1. We show that in the ~1 Gyr after z~3, the LAE luminosity
function evolved significantly, with L* fading by ~0.4 mag, the number density
of sources with L > 1.5E42 ergs/s declining by ~50%, and the equivalent width
scale-length contracting from 70^{+7}_{-5} Angstroms to 50^{+9}_{-6} Angstroms.
When combined with literature results, our observations demonstrate that over
the redshift range z~0 to z~4, LAEs contain less than ~10% of the
star-formation rate density of the universe.Comment: 39 pages, 12 figures, Accepted to Ap
Dopamine neurons modulate neural encoding and expression of depression-related behaviour
Major depression is characterized by diverse debilitating symptoms that include hopelessness and anhedonia1. Dopamine neurons involved in reward and motivation are among many neural populations that have been hypothesized to be relevant, and certain antidepressant treatments, including medications and brain stimulation therapies, can influence the complex dopamine system. Until now it has not been possible to test this hypothesis directly, even in animal models, as existing therapeutic interventions are unable to specifically target dopamine neurons. Here we investigated directly the causal contributions of defined dopamine neurons to multidimensional depression-like phenotypes induced by chronic mild stress, by integrating behavioural, pharmacological, optogenetic and electrophysiological methods in freely moving rodents. We found that bidirectional control (inhibition or excitation) of specified midbrain dopamine neurons immediately and bidirectionally modulates (induces or relieves) multiple independent depression symptoms caused by chronic stress. By probing the circuit implementation of these effects, we observed that optogenetic recruitment of these dopamine neurons potently alters the neural encoding of depression-related behaviours in the downstream nucleus accumbens of freely moving rodents, suggesting that processes affecting depression symptoms may involve alterations in the neural encoding of action in limbic circuitry
A novel a-L-Arabinofuranosidase of Family 43 Glycoside Hydrolase (Ct43Araf ) from Clostridium thermocellum
Articles in International JournalsThe study describes a comparative analysis of biochemical, structural and functional properties of two recombinant
derivatives from Clostridium thermocellum ATCC 27405 belonging to family 43 glycoside hydrolase. The family 43 glycoside
hydrolase encoding a-L-arabinofuranosidase (Ct43Araf) displayed an N-terminal catalytic module CtGH43 (903 bp) followed
by two carbohydrate binding modules CtCBM6A (405 bp) and CtCBM6B (402 bp) towards the C-terminal. Ct43Araf and its
truncated derivative CtGH43 were cloned in pET-vectors, expressed in Escherichia coli and functionally characterized. The
recombinant proteins displayed molecular sizes of 63 kDa (Ct43Araf) and 34 kDa (CtGH43) on SDS-PAGE analysis. Ct43Araf
and CtGH43 showed optimal enzyme activities at pH 5.7 and 5.4 and the optimal temperature for both was 50uC. Ct43Araf
and CtGH43 showed maximum activity with rye arabinoxylan 4.7 Umg21 and 5.0 Umg21, respectively, which increased by
more than 2-fold in presence of Ca2+ and Mg2+ salts. This indicated that the presence of CBMs (CtCBM6A and CtCBM6B) did
not have any effect on the enzyme activity. The thin layer chromatography and high pressure anion exchange
chromatography analysis of Ct43Araf hydrolysed arabinoxylans (rye and wheat) and oat spelt xylan confirmed the release of
L-arabinose. This is the first report of a-L-arabinofuranosidase from C. thermocellum having the capacity to degrade both pnitrophenol-
a-L-arabinofuranoside and p-nitrophenol-a-L-arabinopyranoside. The protein melting curves of Ct43Araf and
CtGH43 demonstrated that CtGH43 and CBMs melt independently. The presence of Ca2+ ions imparted thermal stability to
both the enzymes. The circular dichroism analysis of CtGH43 showed 48% b-sheets, 49% random coils but only 3% a-helices
- …