77 research outputs found
Post-rift uplift of the Dhofar margin (Gulf of Aden)
International audienceAn investigation of the sedimentation pattern along the Dhofar margin allows us to describe its late-stage evolution. After the accumulation of a thick post-rift sedimentary succession, two debris flow events occurred at the foot of the slope. The first event, affecting a wide area of the margin, marks a major change in sedimentation. The second event is associated with a shift of sedimentary deposition from the slope toward the basin. This latter debris flow was caused by an uplift phase, and highlights two distinct deformational styles in the eastern and western part of the Dhofar margin. Both events occurred very late in the history of the margin, at least 7.6 Ma after the end of the rifting phase (35-17.6 Ma)
Glucose-derived spiro-isoxazolines are anti-hyperglycemic agents against type 2 diabetes through glycogen phosphorylase inhibition
International audienceGlycogen phosphorylase (GP) is a target for the treatment of hyperglycaemia in the context of type 2 diabetes. This enzyme is responsible for the depolymerization of glycogen into glucose thereby affecting the levels of glucose in the blood stream. Twelve new d-glucopyranosylidene-spiro-isoxazolines have been prepared from O-peracylated exo-D-glucals by regio- and stereoselective 1,3-dipolar cycloaddition of nitrile oxides generated in situ by treatment of the corresponding oximes with bleach. This mild and direct procedure appeared to be applicable to a broad range of substrates. The corresponding O-unprotected spiro-isoxazolines were evaluated as glycogen phosphorylase (GP) inhibitors and exhibited IC50 values ranging from 1 to 800 μM. Selected inhibitors were further evaluated in vitro using rat and human hepatocytes and exhibited significant inhibitory properties in the primary cell culture. Interestingly, when tested with human hepatocytes, the tetra-O-acetylated spiro-isoxazoline bearing a 2-naphthyl residue showed a much lower IC50 value (2.5 μM), compared to that of the O-unprotected analog (19.95 μM). The most promising compounds were investigated in Zucker fa/fa rat model in acute and sub-chronic assays and decreased hepatic glucose production, which is known to be elevated in type 2 diabetes. This indicates that glucose-based spiro-isoxazolines can be considered as anti-hyperglycemic agents in the context of type 2 diabetes
Wide-field CO isotopologue emission and the CO-to-H factor across the nearby spiral galaxy M101
Carbon monoxide (CO) emission is the most widely used tracer of the bulk
molecular gas in the interstellar medium (ISM) in extragalactic studies. The
CO-to-H conversion factor, , links the observed CO
emission to the total molecular gas mass. However, no single prescription
perfectly describes the variation of across all environments
across galaxies as a function of metallicity, molecular gas opacity, line
excitation, and other factors. Using resolved spectral line observations of CO
and its isotopologues, we can constrain the molecular gas conditions and link
them to a variation in the conversion factor. We present new IRAM 30-m 1mm and
3mm line observations of CO, CO, and CO} across the nearby
galaxy M101. Based on the CO isotopologue line ratios, we find that selective
nucleosynthesis and opacity changes are the main drivers of the variation in
the line emission across the galaxy. Furthermore, we estimated using different approaches, including (i) the dust mass surface
density derived from far-IR emission as an independent tracer of the total gas
surface density and (ii) LTE-based measurements using the optically thin
CO(1-0) intensity. We find an average value of across the galaxy,
with a decrease by a factor of 10 toward the 2 kpc central region. In contrast,
we find LTE-based values are lower by a factor of 2-3 across the disk relative
to the dust-based result. Accounting for variations, we found
significantly reduced molecular gas depletion time by a factor 10 in the
galaxy's center. In conclusion, our result suggests implications for commonly
derived scaling relations, such as an underestimation of the slope of the
Kennicutt Schmidt law, if variations are not accounted for.Comment: Accepted for publication in A&A, 25 pages, 15 figure
A z=0 Multi-wavelength Galaxy Synthesis I: A WISE and GALEX Atlas of Local Galaxies
We present an atlas of ultraviolet and infrared images of ~15,750 local (d <
50 Mpc) galaxies, as observed by NASA's WISE and GALEX missions. These maps
have matched resolution (FWHM 7.5'' and 15''), matched astrometry, and a common
procedure for background removal. We demonstrate that they agree well with
resolved intensity measurements and integrated photometry from previous
surveys. This atlas represents the first part of a program (the z=0
Multi-wavelength Galaxy Synthesis) to create a large, uniform database of
resolved measurements of gas and dust in nearby galaxies. The images and
associated catalogs are publicly available at the NASA/IPAC Infrared Science
Archive. This atlas allows us estimate local and integrated star formation
rates (SFRs) and stellar masses (M) across the local galaxy population
in a uniform way. In the appendix, we use the population synthesis fits of
Salim et al. (2016, 2018) to calibrate integrated M and SFR estimators
based on GALEX and WISE. Because they leverage an SDSS-base training set of
>100,000 galaxies, these calibrations have high precision and allow us to
rigorously compare local galaxies to Sloan Digital Sky Survey results. We
provide these SFR and M estimates for all galaxies in our sample and
show that our results yield a "main sequence" of star forming galaxies
comparable to previous work. We also show the distribution of intensities from
resolved galaxies in NUV-to-WISE1 vs. WISE1-to-WISE3 space, which captures much
of the key physics accessed by these bands.Comment: 46 pages, 27 figures, published in ApJS
(https://ui.adsabs.harvard.edu/abs/2019ApJS..244...24L/abstract ). See that
version for full resolution figures and machine readable tables. Go download
data for your favorite nearby galaxy here:
https://irsa.ipac.caltech.edu/data/WISE/z0MGS/overview.html . The appendix
presents detailed analysis of translations to physical quantitie
PHANGS-JWST: Data-processing Pipeline and First Full Public Data Release
The exquisite angular resolution and sensitivity of JWST are opening a new window for our understanding of the Universe. In nearby galaxies, JWST observations are revolutionizing our understanding of the first phases of star formation and the dusty interstellar medium. Nineteen local galaxies spanning a range of properties and morphologies across the star-forming main sequence have been observed as part of the PHANGS-JWST Cycle 1 Treasury program at spatial scales of ∼5–50 pc. Here, we describe pjpipe, an image-processing pipeline developed for the PHANGS-JWST program that wraps around and extends the official JWST pipeline. We release this pipeline to the community as it contains a number of tools generally useful for JWST NIRCam and MIRI observations. Particularly for extended sources, pjpipe products provide significant improvements over mosaics from the MAST archive in terms of removing instrumental noise in NIRCam data, background flux matching, and calibration of relative and absolute astrometry. We show that slightly smoothing F2100W MIRI data to 0.″9 (degrading the resolution by about 30%) reduces the noise by a factor of ≈3. We also present the first public release (DR1.1.0) of the pjpipe processed eight-band 2–21 μm imaging for all 19 galaxies in the PHANGS-JWST Cycle 1 Treasury program. An additional 55 galaxies will soon follow from a new PHANGS-JWST Cycle 2 Treasury program
CI and CO in Nearby Spiral Galaxies -- I. Line Ratio and Abundance Variations at ~ 200 pc Scales
We present new neutral atomic carbon [CI](3P1-3P0) mapping observations
within the inner ~7 kpc and ~4 kpc of the disks of NGC3627 and NGC4321 at a
spatial resolution of 190 pc and 270 pc, respectively, using the ALMA Atacama
Compact Array (ACA). We combine these with the CO(2-1) data from PHANGS-ALMA,
and literature [CI] and CO data for two other starburst and/or active galactic
nucleus (AGN) galaxies (NGC1808, NGC7469), to study: a) the spatial
distributions of CI and CO emission; b) the observed line ratio RCICO =
I_[CI](1-0)/I_CO(2-1) as a function of various galactic properties; and c) the
abundance ratio of [CI/CO]. We find excellent spatial correspondence between CI
and CO emission and nearly uniform RCICO ~0.1 across the majority of the
star-forming disks of NGC3627 and NGC4321. However, RCICO strongly varies from
~0.05 at the centre of NGC4321 to >0.2-0.5 in NGC1808's starburst centre and
NGC7469's centre with an X-ray AGN. Meanwhile, RCICO does not obviously vary
with , similar to the prediction of PDR models. We also find a mildly
decreasing RCICO with an increasing metallicity over 0.7-0.85 solar
metallicity, consistent with the literature. Assuming various typical ISM
conditions representing GMCs, active star-forming regions and strong
starbursting environments, we calculate the LTE radiative transfer and estimate
the [CI/CO] abundance ratio to be ~0.1 across the disks of NGC3627 and NGC4321,
similar to previous large-scale findings in Galactic studies. However, this
abundance ratio likely has a substantial increase to ~1 and >1-5 in NGC1808's
starburst and NGC7469's strong AGN environments, respectively, in line with the
expectations for cosmic-ray dominated region (CRDR) and X-ray dominated region
(XDR) chemistry. Finally, we do not find a robust evidence for a generally
CO-dark, CI-bright gas in the disk areas we probed. (abbreviated)Comment: 23 pages, 13 figures and one table in total (17 pages and 9 figures
in main text). Accepted for publication in A&A. For associated data cubes and
moment maps, see
https://www.canfar.net/storage/vault/list/phangs/RELEASES/DZLIU_etal_202
Calibrating mid-infrared emission as a tracer of obscured star formation on HII-region scales in the era of JWST
Measurements of the star formation activity on cloud scales are fundamental
to uncovering the physics of the molecular cloud, star formation, and stellar
feedback cycle in galaxies. Infrared (IR) emission from small dust grains and
polycyclic aromatic hydrocarbons (PAHs) are widely used to trace the obscured
component of star formation. However, the relation between these emission
features and dust attenuation is complicated by the combined effects of dust
heating from old stellar populations and an uncertain dust geometry with
respect to heating sources. We use images obtained with NIRCam and MIRI as part
of the PHANGS--JWST survey to calibrate dust emission at 21, and the
emission in the PAH-tracing bands at 3.3, 7.7, 10, and 11.3 as
tracers of obscured star formation. We analyse 20000 optically selected
HII regions across 19 nearby star-forming galaxies, and benchmark their IR
emission against dust attenuation measured from the Balmer decrement. We model
the extinction-corrected H flux as the sum of the observed H
emission and a term proportional to the IR emission, with as the
proportionality coefficient. A constant leads to extinction-corrected
H estimates which agree with those obtained with the Balmer decrement
with a scatter of 0.1 dex for all bands considered. Among these bands,
21 emission is demonstrated to be the best tracer of dust
attenuation. The PAH-tracing bands underestimate the correction for bright HII
regions, since in these environments the ratio of PAH-tracing bands to 21 decreases, signalling destruction of the PAH molecules. For fainter HII
regions all bands suffer from an increasing contamination from the diffuse
infrared background.Comment: accepted for publication in A&
PHANGS-ML: Dissecting Multiphase Gas and Dust in Nearby Galaxies Using Machine Learning
The PHANGS survey uses Atacama Large Millimeter/submillimeter Array, Hubble Space Telescope, Very Large Telescope, and JWST to obtain an unprecedented high-resolution view of nearby galaxies, covering millions of spatially independent regions. The high dimensionality of such a diverse multiwavelength data set makes it challenging to identify new trends, particularly when they connect observables from different wavelengths. Here, we use unsupervised machine-learning algorithms to mine this information-rich data set to identify novel patterns. We focus on three of the PHANGS-JWST galaxies, for which we extract properties pertaining to their stellar populations; warm ionized and cold molecular gas; and polycyclic aromatic hydrocarbons (PAHs), as measured over 150 pc scale regions. We show that we can divide the regions into groups with distinct multiphase gas and PAH properties. In the process, we identify previously unknown galaxy-wide correlations between PAH band and optical line ratios and use our identified groups to interpret them. The correlations we measure can be naturally explained in a scenario where the PAHs and the ionized gas are exposed to different parts of the same radiation field that varies spatially across the galaxies. This scenario has several implications for nearby galaxies: (i) The uniform PAH ionized fraction on 150 pc scales suggests significant self-regulation in the interstellar medium, (ii) the PAH 11.3/7.7 μm band ratio may be used to constrain the shape of the non-ionizing far-ultraviolet to optical part of the radiation field, and (iii) the varying radiation field affects line ratios that are commonly used as PAH size diagnostics. Neglecting this effect leads to incorrect or biased PAH sizes
PHANGS-ML: dissecting multiphase gas and dust in nearby galaxies using machine learning
The PHANGS survey uses ALMA, HST, VLT, and JWST to obtain an unprecedented
high-resolution view of nearby galaxies, covering millions of spatially
independent regions. The high dimensionality of such a diverse multi-wavelength
dataset makes it challenging to identify new trends, particularly when they
connect observables from different wavelengths. Here we use unsupervised
machine learning algorithms to mine this information-rich dataset to identify
novel patterns. We focus on three of the PHANGS-JWST galaxies, for which we
extract properties pertaining to their stellar populations; warm ionized and
cold molecular gas; and Polycyclic Aromatic Hydrocarbons (PAHs), as measured
over 150 pc-scale regions. We show that we can divide the regions into groups
with distinct multiphase gas and PAH properties. In the process, we identify
previously-unknown galaxy-wide correlations between PAH band and optical line
ratios and use our identified groups to interpret them. The correlations we
measure can be naturally explained in a scenario where the PAHs and the ionized
gas are exposed to different parts of the same radiation field that varies
spatially across the galaxies. This scenario has several implications for
nearby galaxies: (i) The uniform PAH ionized fraction on 150 pc scales suggests
significant self-regulation in the ISM, (ii) the PAH 11.3/7.7 \mic~ band ratio
may be used to constrain the shape of the non-ionizing far-ultraviolet to
optical part of the radiation field, and (iii) the varying radiation field
affects line ratios that are commonly used as PAH size diagnostics. Neglecting
this effect leads to incorrect or biased PAH sizes.Comment: Main results in figures 6 and 12. Submitted to ApJ, and comments are
welcome
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