38 research outputs found
Utilisation of probabilistic magnetotelluric modelling to constrain magnetic data inversion: proof-of-concept and field application
We propose, test and apply a methodology integrating 1DÂ magnetotelluric (MT) and magnetic data inversion, with a focus on the characterisation of
the coverâbasement interface. It consists of a cooperative inversion workflow relying on standalone inversion codes. Probabilistic information about
the presence of rock units is derived from MT and passed on to magnetic inversion through constraints combining structural constraints with
petrophysical prior information. First, we perform the 1DÂ probabilistic inversion of MT data for all sites and recover the respective probabilities
of observing the coverâbasement interface, which we interpolate to the rest of the study area. We then calculate the probabilities of observing the
different rock units and partition the model into domains defined by combinations of rock units with non-zero probabilities. Third, we combine these
domains with petrophysical information to apply spatially varying, disjoint interval bound constraints (DIBC) to least-squares magnetic data
inversion using the alternating direction method of multipliers (or ADMM). We demonstrate the proof-of-concept using a realistic synthetic model
reproducing features from the Mansfield area (Victoria, Australia) using a series of uncertainty indicators. We then apply the workflow to field
data from the prospective mining region of Cloncurry (Queensland, Australia). Results indicate that our integration methodology efficiently
leverages the complementarity between separate MT and magnetic data modelling approaches and can improve our capability to image the coverâbasement
interface. In the field application case, our findings also suggest that the proposed workflow may be useful to refine existing geological
interpretations and to infer lateral variations within the basement.</p
The crustal structure of the Cantabrian Mountains revealed by magnetotelluric soundings
EM Induction Workshop (24th, 2018, HelsingĂžr, Denmark
Structure of the mantle beneath the Alboran basin from magnetotelluric soundings
We present results of marine MT acquisition in the Alboran sea that also incorporates
previously acquired land MT from southern Spain into our analysis. The marine data
show complex MT response functions with strong distortion due to seafloor
topography and the coastline, but inclusion of high resolution topography and
bathymetry and a seismically defined sediment unit into a 3D inversion model has
allowed us to image the structure in the underlying mantle. The resulting resistivity
model is broadly consistent with a geodynamic scenario that includes subduction of
an eastward trending plate beneath Gibraltar, which plunges nearly vertically beneath
the Alboran. Our model contains three primary features of interest: a resistive body beneath the
central Alboran, which extends to a depth of ~150 km. At this depth, the mantle
resistivity decreases to values of ~100 Ohm-m, slightly higher than those seen in
typical asthenosphere at the same depth. This transition suggests a change in slab
properties with depth, perhaps reflecting a change in the nature of the seafloor
subducted in the past.
Two conductive features in our model suggest the presence of fluids released by the
subducting slab or a small amount of partial melt in the upper mantle (or both). Of
these, the one in the center of the Alboran basin, in the uppermost-mantle (20-30km
depth) beneath Neogene volcanics and west of the termination of the Nekkor Fault, is
consistent with geochemical models, which infer highly thinned lithosphere and
shallow melting in order to explain the petrology of seafloor volcanics
Structure of the mantle beneath the Alboran Basin from Magnetotelluric Soundings
We present results of marine MT acquisition in the Alboran sea that also incorporates previously acquired land MT from southern Spain into our analysis. The marine data show complex MT response functions with strong distortion due to seafloor topography and the coastline, but inclusion of high resolution topography and bathymetry and a seismically defined sediment unit into a 3âD inversion model has allowed us to image the structure in the underlying mantle. The resulting resistivity model is broadly consistent with a geodynamic scenario that includes subduction of an eastward trending plate beneath Gibraltar, which plunges nearly vertically beneath the Alboran. Our model contains three primary features of interest: a resistive body beneath the central Alboran, which extends to a depth of âŒ150 km. At this depth, the mantle resistivity decreases to values of âŒ100 Ohmâm, slightly higher than those seen in typical asthenosphere at the same depth. This transition suggests a change in slab properties with depth, perhaps reflecting a change in the nature of the seafloor subducted in the past. Two conductive features in our model suggest the presence of fluids released by the subducting slab or a small amount of partial melt in the upper mantle (or both). Of these, the one in the center of the Alboran basin, in the uppermostâmantle (20-30 km depth) beneath Neogene volcanics and west of the termination of the Nekkor Fault, is consistent with geochemical models, which infer highly thinned lithosphere and shallow melting in order to explain the petrology of seafloor volcanics
Galaxy morphology from z ~ 6 through the lens of JWST
Context: The James Webb Space Telescope's (JWST's) unprecedented combination of sensitivity, spatial resolution, and infrared coverage has enabled a new era of galaxy morphology exploration across most of cosmic history. Aims: We analyze the near-infrared (NIR ~ 0.8 -1 ÎŒm) rest-frame morphologies of galaxies with log Mâ/Mâ > 9 in the redshift range of 0 < z < 6, compare with previous HST-based results and release the first JWST-based morphological catalog of ~20 000 galaxies in the CEERS survey. Methods: We classified the galaxies in our sample into four main broad classes: spheroid, disk+spheroid, disk, and disturbed, based on imaging with four filters: F150W, F200W, F356W, and F444W. We used convolutional neural networks (CNNs) trained on HST/WFC3 labeled images and domain-adapted to JWST/NIRCam. Results: We find that ~90% and ~75% of galaxies at z < 3 have the same early and late and regular and irregular classification, respectively, in JWST and HST imaging when considering similar wavelengths. For small (large) and faint objects, JWST-based classifications tend to systematically present less bulge-dominated systems (peculiar galaxies) than HST-based ones, but the impact on the reported evolution of morphological fractions is less than ~10%. Using JWST-based morphologies at the same rest-frame wavelength ( ~0.8 -1 ÎŒm), we confirm an increase in peculiar galaxies and a decrease in bulge-dominated galaxies with redshift, as reported in previous HST-based works, suggesting that the stellar mass distribution, in addition to light distribution, is more disturbed in the early Universe. However, we find that undisturbed disk-like systems already dominate the high-mass end of the late-type galaxy population (log Mâ/Mâ > 10.5) at z ~ 5, and bulge-dominated galaxies also exist at these early epochs, confirming a rich and evolved morphological diversity of galaxies ~1 Gyr after the Big Bang. Finally, we find that the morphology-quenching relation is already in place for massive galaxies at z > 3, with massive quiescent galaxies (log Mâ/Mâ > 10.5) being predominantly bulge-dominated.</p
Galaxy morphology from z ~ 6 through the lens of JWST
Context: The James Webb Space Telescope's (JWST's) unprecedented combination of sensitivity, spatial resolution, and infrared coverage has enabled a new era of galaxy morphology exploration across most of cosmic history. Aims: We analyze the near-infrared (NIR ~ 0.8 -1 ÎŒm) rest-frame morphologies of galaxies with log Mâ/Mâ > 9 in the redshift range of 0 < z < 6, compare with previous HST-based results and release the first JWST-based morphological catalog of ~20 000 galaxies in the CEERS survey. Methods: We classified the galaxies in our sample into four main broad classes: spheroid, disk+spheroid, disk, and disturbed, based on imaging with four filters: F150W, F200W, F356W, and F444W. We used convolutional neural networks (CNNs) trained on HST/WFC3 labeled images and domain-adapted to JWST/NIRCam. Results: We find that ~90% and ~75% of galaxies at z < 3 have the same early and late and regular and irregular classification, respectively, in JWST and HST imaging when considering similar wavelengths. For small (large) and faint objects, JWST-based classifications tend to systematically present less bulge-dominated systems (peculiar galaxies) than HST-based ones, but the impact on the reported evolution of morphological fractions is less than ~10%. Using JWST-based morphologies at the same rest-frame wavelength ( ~0.8 -1 ÎŒm), we confirm an increase in peculiar galaxies and a decrease in bulge-dominated galaxies with redshift, as reported in previous HST-based works, suggesting that the stellar mass distribution, in addition to light distribution, is more disturbed in the early Universe. However, we find that undisturbed disk-like systems already dominate the high-mass end of the late-type galaxy population (log Mâ/Mâ > 10.5) at z ~ 5, and bulge-dominated galaxies also exist at these early epochs, confirming a rich and evolved morphological diversity of galaxies ~1 Gyr after the Big Bang. Finally, we find that the morphology-quenching relation is already in place for massive galaxies at z > 3, with massive quiescent galaxies (log Mâ/Mâ > 10.5) being predominantly bulge-dominated.</p
Extremely Red Galaxies at z = 5-9 with MIRI and NIRSpec:Dusty Galaxies or Obscured Active Galactic Nuclei?
We study a new population of extremely red objects (EROs) recently discovered by the James Webb Space Telescope (JWST) based on their NIRCam colors F277W â F444W > 1.5 mag. We find 37 EROs in the Cosmic Evolution Early Release Science Survey (CEERS) field with F444W < 28 mag and photometric redshifts between 5 < z < 7, with median z = 6.9 â 1.6 + 1.0 . Surprisingly, despite their red long-wavelength colors, these EROs have blue short-wavelength colors (F150W â F200W ⌠0 mag) indicative of bimodal spectral energy distributions (SEDs) with a red, steep slope in the rest-frame optical, and a blue, flat slope in the rest-frame UV. Moreover, all these EROs are unresolved, point-like sources in all NIRCam bands. We analyze the SEDs of eight of them with MIRI and NIRSpec observations using stellar population models and active galactic nucleus (AGN) templates. We find that dusty galaxies or obscured AGNs provide similarly good SED fits but different stellar properties: massive and dusty, log M â / M â ⌠10 and A V âł 3 mag, or low mass and obscured, log M â / M â ⌠7.5 and A V ⌠0 mag, hosting an obscured quasi-stellar object (QSO). SED modeling does not favor either scenario, but their unresolved sizes are more suggestive of AGNs. If any EROs are confirmed to have log M â / M â âł 10.5, it would increase the pre-JWST number density at z > 7 by up to a factor âŒ60. Similarly, if they are QSOs with luminosities in the L bol > 1045-46 erg sâ1 range, their number would exceed that of bright blue QSOs by more than three orders of magnitude. Additional photometry at mid-infrared wavelengths will reveal the true nature of the red continuum emission in these EROs and will place this puzzling population in the right context of galaxy evolution.</p
Spectroscopic verification of very luminous galaxy candidates in the early universe
During the first 500 million years of cosmic history, the first stars and
galaxies formed and seeded the cosmos with heavy elements. These early galaxies
illuminated the transition from the cosmic "dark ages" to the reionization of
the intergalactic medium. This transitional period has been largely
inaccessible to direct observation until the recent commissioning of JWST,
which has extended our observational reach into that epoch. Excitingly, the
first JWST science observations uncovered a surprisingly high abundance of
early star-forming galaxies. However, the distances (redshifts) of these
galaxies were, by necessity, estimated from multi-band photometry. Photometric
redshifts, while generally robust, can suffer from uncertainties and/or
degeneracies. Spectroscopic measurements of the precise redshifts are required
to validate these sources and to reliably quantify their space densities,
stellar masses, and star formation rates, which provide powerful constraints on
galaxy formation models and cosmology. Here we present the results of JWST
follow-up spectroscopy of a small sample of galaxies suspected to be amongst
the most distant yet observed. We confirm redshifts z > 10 for two galaxies,
including one of the first bright JWST-discovered candidates with z = 11.4, and
show that another galaxy with suggested z ~ 16 instead has z = 4.9, with strong
emission lines that mimic the expected colors of more distant objects. These
results reinforce the evidence for the rapid production of luminous galaxies in
the very young Universe, while also highlighting the necessity of spectroscopic
verification for remarkable candidates.Comment: Submitted to Natur
CEERS Key Paper IV: Galaxies at are Bluer than They Appear -- Characterizing Galaxy Stellar Populations from Rest-Frame micron Imaging
We present results from the Cosmic Evolution Early Release Survey (CEERS) on
the stellar-population parameters for 28 galaxies with redshifts using
imaging data from the James Webb Space Telescope (JWST) Mid-Infrared Instrument
(MIRI) combined with data from the Hubble Space Telescope and the Spitzer Space
Telescope. The JWST/MIRI 5.6 and 7.7 m data extend the coverage of the
rest-frame spectral-energy distribution (SED) to nearly 1 micron for galaxies
in this redshift range. By modeling the galaxies' SEDs the MIRI data show that
the galaxies have, on average, rest-frame UV (1600 \r{A}) -band colors
0.4 mag bluer than derived when using photometry that lacks MIRI. Therefore,
the galaxies have lower (stellar)-mass-to-light ratios. The MIRI data reduce
the stellar masses by dex at (a
factor of 1.8) and 0.37 dex at (a factor of 2.3). This also reduces the
star-formation rates (SFRs) by
dex at and 0.27 dex at . The MIRI data also improve constraints
on the allowable stellar mass formed in early star-formation. We model this
using a star-formation history that includes both a "burst' at and a
slowly varying ("delayed-") model. The MIRI data reduce the allowable
stellar mass by 0.6 dex at and by 1 dex at . Applying
these results globally, this reduces the cosmic stellar-mass density by an
order of magnitude in the early universe (). Therefore, observations
of rest-frame 1 m are paramount for constraining the stellar-mass
build-up in galaxies at very high-redshifts.Comment: Updated with accepted ApJ version. Part of the CEERS Focus Issue. 27
pages, many figures (4 Figure Sets, available upon reasonable request
CEERS Key Paper. V. Galaxies at 4 < z < 9 Are Bluer than They Appear-Characterizing Galaxy Stellar Populations from Rest-frame âŒ1 ÎŒm Imaging
We present results from the Cosmic Evolution Early Release Survey on the stellar population parameters for 28 galaxies with redshifts 4 < z < 9 using imaging data from the James Webb Space Telescope (JWST) Mid-Infrared Instrument (MIRI) combined with data from the Hubble Space Telescope and the Spitzer Space Telescope. The JWST/MIRI 5.6 and 7.7 ÎŒm data extend the coverage of the rest-frame spectral energy distribution to nearly 1 ÎŒm for galaxies in this redshift range. By modeling the galaxiesâ SEDs the MIRI data show that the galaxies have, on average, rest-frame UV (1600 Ă
)âI-band colors 0.4 mag bluer than derived when using photometry that lacks MIRI. Therefore, the galaxies have lower ratios of stellar mass to light. The MIRI data reduce the stellar masses by ă Î log M * ă = 0.25 dex at 4 < z < 6 and 0.37 dex at 6 < z < 9. This also reduces the star formation rates (SFRs) by ăÎlogSFRă = 0.14 dex at 4 < z < 6 and 0.27 dex at 6 < z < 9. The MIRI data also improve constraints on the allowable stellar mass formed in early star formation. We model this using a star formation history that includes both a âburstâ at z f = 100 and a slowly varying (âdelayed-Ïâ) model. The MIRI data reduce the allowable stellar mass by 0.6 dex at 4 < z < 6 and by â1 dex at 6 < z < 9. Applying these results globally, this reduces the cosmic stellar-mass density by an order of magnitude in the early Universe (z â 9). Therefore, observations of rest-frame âł1 ÎŒm are paramount for constraining the stellar-mass buildup in galaxies at very high redshifts.</p