43 research outputs found
The Neon Gap: Probing Ionization with Dwarf Galaxies at z~1
We present measurements of [NeIII]{\lambda}3869 emission in z~1 low-mass
galaxies taken from the Keck/DEIMOS spectroscopic surveys HALO7D and DEEPWinds.
We identify 167 individual galaxies with significant [NeIII] emission lines,
including 112 "dwarf" galaxies with log(M_{\star}/M_{\odot}) < 9.5, with 0.3 <
z < 1.4. We also measure [NeIII] emission from composite spectra derived from
all [OII]{\lambda}{\lambda}3727,3729 line emitters in this range. This provides
a unique sample of [NeIII]-emitters in the gap between well-studied emitters at
z = 0 and 2 < z < 3. To study evolution in ionization conditions in the ISM
over this time, we analyze the
log([NeIII]{\lambda}3869/[OII]{\lambda}{\lambda}3727,3729) ratio (Ne3O2) as a
function of the stellar mass and of the
log([OIII]{\lambda}{\lambda}4959,5007/[OII]{\lambda}{\lambda}3727,3729) ratio
(O32). We find that the typical star-forming dwarf galaxy at this redshift, as
measured from the composite spectra, shares the Ne3O2-M_{\star} relation with
local galaxies, but have higher O32 at given Ne3O2. This finding implies that
the ionization and metallicity characteristics of the z~1 dwarf population do
not evolve substantially from z~1 to z=0, suggesting that the known evolution
in those parameter from z~2 has largely taken place by z~1. Individual
[NeIII]-detected galaxies have emission characteristics situated between local
and z~2 galaxies, with elevated Ne3O2 and O32 emission potentially explained by
variations in stellar and nebular metallicity. We also compare our dwarf sample
to similarly low-mass z > 7 galaxies identified in JWST Early Release
Observations, finding four HALO7D dwarfs with similar size, metallicity, and
star formation properties.Comment: Accepted to ApJL, 16.01.202
Dwarf galaxies show little ISM evolution from to : a spectroscopic study of metallicity, star formation, and electron density
We present gas-phase metallicity measurements for 583 emission line galaxies
at , including 388 dwarf galaxies with , and explore the dependence of the metallicity on the stellar mass and
star formation properties of the galaxies. Metallicities are determined through
the measurement of emission lines in very deep (7 hr exposure)
Keck/DEIMOS spectra taken primarily from the HALO7D survey. We measure
metallicity with three strong-line calibrations (O3H, R23, and O3O2) for
the overall sample, as well as with the faint [Ne III]3869 and [O
III]4363 emission lines for 112 and 17 galaxies where robust
detections were possible. We construct mass-metallicity relations (MZR) for
each calibration method, finding MZRs consistent with other strong-line results
at comparable redshift, as well as with galaxies. We quantify the
intrinsic scatter in the MZR as a function of mass, finding it increases with
lower stellar mass. We also measure a weak but significant correlation between
increased MZR scatter and higher specific star formation rate. We find a weak
influence of SFR in the fundamental metallicity relation as well, with an SFR
coefficient of . Finally, we use the flux ratios of the [O
II]3727,3729 doublet to calculate gas electron density in
1000 galaxies with as a function of
redshift. We measure low electron densities ( cm) for
galaxies, again consistent with conditions, but measure higher
densities ( cm) at . These results all suggest that
there is little evolution in star-forming interstellar medium conditions from
to , confirmed with a more complete sample of low-mass galaxies
than has previously been available in this redshift range.Comment: 22 pages, 10 figures, accepted to Ap
Spectrophotometric Redshifts In The Faint Infrared Grism Survey: Finding Overdensities Of Faint Galaxies
We improve the accuracy of photometric redshifts by including low-resolution
spectral data from the G102 grism on the Hubble Space Telescope, which assists
in redshift determination by further constraining the shape of the broadband
Spectral Energy Disribution (SED) and identifying spectral features. The
photometry used in the redshift fits includes near-IR photometry from
FIGS+CANDELS, as well as optical data from ground-based surveys and HST ACS,
and mid-IR data from Spitzer. We calculated the redshifts through the
comparison of measured photometry with template galaxy models, using the EAZY
photometric redshift code. For objects with F105W AB mag with a
redshift range of , we find a typical error of for the purely photometric redshifts; with the addition of FIGS spectra,
these become , an improvement of 50\%. Addition of
grism data also reduces the outlier rate from 8\% to 7\% across all fields.
With the more-accurate spectrophotometric redshifts (SPZs), we searched the
FIGS fields for galaxy overdensities. We identified 24 overdensities across the
4 fields. The strongest overdensity, matching a spectroscopically identified
cluster at , has 28 potential member galaxies, of which 8 have previous
spectroscopic confirmation, and features a corresponding X-ray signal. Another
corresponding to a cluster at has 22 members, 18 of which are
spectroscopically confirmed. Additionally, we find 4 overdensities that are
detected at an equal or higher significance in at least one metric to the two
confirmed clusters.Comment: 17 pages, 13 figures. To appear in Ap
Emission Line Metallicities From The Faint Infrared Grism Survey and VLT/MUSE
We derive direct measurement gas-phase metallicities of for 14 low-mass Emission Line Galaxies (ELGs) at
identified in the Faint Infrared Grism Survey (FIGS). We use deep slitless G102
grism spectroscopy of the Hubble Ultra Deep Field (HUDF), dispersing light from
all objects in the field at wavelengths between 0.85 and 1.15 microns. We run
an automatic search routine on these spectra to robustly identify 71 emission
line sources, using archival data from VLT/MUSE to measure additional lines and
confirm redshifts. We identify 14 objects with with measurable
O[III]4363 \AA\ emission lines in matching VLT/MUSE spectra. For these
galaxies, we derive direct electron-temperature gas-phase metallicities with a
range of . With matching stellar masses in the
range of , we construct a
mass-metallicity (MZ) relation and find that the relation is offset to lower
metallicities compared to metallicities derived from alternative methods
(e.g.,, O3N2, N2O2) and continuum selected samples. Using star
formation rates (SFR) derived from the emission line, we calculate
our galaxies' position on the Fundamental Metallicity Relation (FMR), where we
also find an offset toward lower metallicities. This demonstrates that this
emission-line-selected sample probes objects of low stellar masses but even
lower metallicities than many comparable surveys. We detect a trend suggesting
galaxies with higher Specific Star Formation (SSFR) are more likely to have
lower metallicity. This could be due to cold accretion of metal-poor gas that
drives star formation, or could be because outflows of metal-rich stellar winds
and SNe ejecta are more common in galaxies with higher SSFR.Comment: 14 pages, 11 figures, accepted in Ap
Median Surface Brightness Profiles of Lyman- Haloes in the MUSE Extremely Deep Field
We present the median surface brightness profiles of diffuse Ly
haloes (LAHs) around star-forming galaxies by stacking 155 spectroscopically
confirmed Ly emitters (LAEs) at 3<z<4 in the MUSE Extremely Deep Field
(MXDF), with median Ly luminosity . After correcting for a systematic surface brightness
offset we identified in the datacube, we detect extended Ly emission
out to a distance of 270 kpc. The median Ly surface brightness profile
shows a power-law decrease in the inner 20 kpc, and a possible flattening trend
at larger distance. This shape is similar for LAEs with different Ly
luminosities, but the normalisation of the surface brightness profile increases
with luminosity. At distances larger than 50 kpc, we observe strong overlap of
adjacent LAHs, and the Ly surface brightness is dominated by the LAHs
of nearby LAEs. We find no clear evidence of redshift evolution of the observed
Ly profiles when comparing with samples at 4<z<5 and 5<z<6. Our results
are consistent with a scenario in which the inner 20 kpc of the LAH is powered
by star formation in the central galaxy, while the LAH beyond a radius of 50
kpc is dominated by photons from surrounding galaxies.Comment: Submitted to A&
FIGS -- Faint Infrared Grism Survey: Description and Data Reduction
The Faint Infrared Grism Survey (FIGS) is a deep Hubble Space Telescope (HST)
WFC3/IR (Wide Field Camera 3 Infrared) slitless spectroscopic survey of four
deep fields. Two fields are located in the Great Observatories Origins Deep
Survey-North (GOODS-N) area and two fields are located in the Great
Observatories Origins Deep Survey-South (GOODS-S) area. One of the southern
fields selected is the Hubble Ultra Deep Field. Each of these four fields were
observed using the WFC3/G102 grism (0.8-1.15 continuous coverage)
with a total exposure time of 40 orbits (~ 100 kilo-seconds) per field. This
reaches a 3 sigma continuum depth of ~26 AB magnitudes and probes emission
lines to . This paper details the four
FIGS fields and the overall observational strategy of the project. A detailed
description of the Simulation Based Extraction (SBE) method used to extract and
combine over 10000 spectra of over 2000 distinct sources brighter than
m_F105W=26.5 mag is provided. High fidelity simulations of the observations is
shown to significantly improve the background subtraction process, the spectral
contamination estimates, and the final flux calibration. This allows for the
combination of multiple spectra to produce a final high quality, deep,
1D-spectra for each object in the survey.Comment: 21 Pages. 17 Figures. To appear in Ap
The Role of Properdin in Zymosan-and Escherichia coli-Induced Complement Activation
Properdin is well known as an enhancer of the alternative complement amplification loop when C3 is activated, whereas its role as a recognition molecule of exogenous pathogen-associated molecular patterns and initiator of complement activation is less understood. We therefore studied the role of properdin in activation of complement in normal human serum by zymosan and various Escherichia coli strains. In ELISA, microtiter plates coated with zymosan induced efficient complement activation with deposition of C4b and terminal complement complex on the solid phase. Virtually no deposition of C4b or terminal complement complex was observed with mannose-binding lectin (MBL)-deficient serum. Reconstitution with purified MBL showed distinct activation in both readouts. In ELISA, normal human serum-induced deposition of properdin by zymosan was abolished by the C3-inhibiting peptide compstatin. Flow cytometry was used to further explore whether properdin acts as an initial recognition molecule reacting directly with zymosan and three E. coli strains. Experiments reported by other authors were made with EGTA Mg 2+ buffer, permitting autoactivation of C3. We found inhibition by compstatin on these substrates, indicating that properdin deposition depended on initial C3b deposition followed by properdin in a second step. Properdin released from human polymorphonuclear cells stimulated with PMA did not bind to zymosan or E. coli, but when incubated in properdin-depleted serum this form of properdin bound efficiently to both substrates in a strictly C3-dependent manner, as the binding was abolished by compstatin. Collectively, these data indicate that properdin in serum as well as polymorphonuclear-released properdin is unable to bind and initiate direct alternative pathway activation on these substrates
FIGS: Spectral fitting constraints on the star formation history of massive galaxies since Cosmic Noon
We constrain the stellar population properties of a sample of 52 massive
galaxies, with stellar mass log Ms>10.5, over the redshift range 0.5<z<2 by use
of observer-frame optical and near-infrared slitless spectra from HST's ACS and
WFC3 grisms. The deep exposures (~100 ks) allow us to target individual spectra
of massive galaxies to F160W=22.5AB. Our spectral fitting approach uses a set
of six base models adapted to the redshift and spectral resolution of each
observation, and fits the weights of the base models, including potential dust
attenuation, via an MCMC method. Our sample comprises a mixed distribution of
quiescent (19) and star-forming galaxies (33). We quantify the width of the age
distribution (Dt) that is found to dominate the variance of the retrieved
parameters according to Principal Component Analysis. The population parameters
follow the expected trend towards older ages with increasing mass, and Dt
appears to weakly anti-correlate with stellar mass, suggesting a more efficient
star formation at the massive end. As expected, the redshift dependence of the
relative stellar age (measured in units of the age of the Universe at the
source) in the quiescent sample rejects the hypothesis of a single burst (aka
monolithic collapse). Radial colour gradients within each galaxy are also
explored, finding a wider scatter in the star-forming subsample, but no
conclusive trend with respect to the population parameters.Comment: 20 pages, 12+3 figures, 4+3 tables. MNRAS, in pres
The Dwarf Galaxy Population at z ∼ 0.7: A Catalog of Emission Lines and Redshifts from Deep Keck Observations
We present a catalog of spectroscopically measured redshifts over
and emission line fluxes for 1440 galaxies. The majority (65\%) of the
galaxies come from the HALO7D survey, with the remainder from the DEEPwinds
program. This catalog includes redshifts for 646 dwarf galaxies with
. 810 catalog galaxies did not have previously
published spectroscopic redshifts, including 454 dwarf galaxies. HALO7D used
the DEIMOS spectrograph on the Keck II telescope to take very deep (up to 32
hours exposure, with a median of 7 hours) optical spectroscopy in the
COSMOS, EGS, GOODS-North, and GOODS-South CANDELS fields, and in some areas
outside CANDELS. We compare our redshift results to existing spectroscopic and
photometric redshifts in these fields, finding only a 1\% rate of discrepancy
with other spectroscopic redshifts. We measure a small increase in median
photometric redshift error (from 1.0\% to 1.3\%) and catastrophic outlier rate
(from 3.5\% to 8\%) with decreasing stellar mass. We obtained successful
redshift fits for 75\% of massive galaxies, and demonstrate a similar 70-75\%
successful redshift measurement rate in
galaxies, suggesting similar survey sensitivity in this low-mass range. We
describe the redshift, mass, and color-magnitude distributions of the catalog
galaxies, finding HALO7D galaxies representative of CANDELS galaxies up to
\textit{i}-band magnitudes of 25. The catalogs presented will enable studies of
star formation (SF), the mass-metallicity relation, SF-morphology relations,
and other properties of the dwarf galaxy population.Comment: 23 pages, 19 Figures, updated to version accepted by ApJ