92 research outputs found
Quantifying the energy balance between the turbulent ionised gas and young stars
We investigate the ionised gas morphology, excitation properties, and
kinematics in 19 nearby star-forming galaxies from the PHANGS-MUSE survey. We
directly compare the kinetic energy of expanding superbubbles and the turbulent
motions in the interstellar medium with the mechanical energy deposited by
massive stars in the form of winds and supernovae, with the aim to answer
whether the stellar feedback is responsible for the observed turbulent motions
and to quantify the fraction of mechanical energy retained in the superbubbles.
Based on the distribution of the flux and velocity dispersion in the H
line, we select 1484 regions of locally elevated velocity dispersion
((H)>45 km/s), including at least 171 expanding superbubbles.
We analyse these regions and relate their properties to those of the young
stellar associations and star clusters identified in PHANGS-HST data. We find a
good correlation between the kinetic energy of the ionised gas and the total
mechanical energy input from supernovae and stellar winds from the stellar
associations, with a typical efficiency of 10-20%. The contribution of
mechanical energy by the supernovae alone is not sufficient to explain the
measured kinetic energy of the ionised gas, which implies that pre-supernova
feedback in the form of radiation/thermal pressure and winds is necessary. We
find that the gas kinetic energy decreases with metallicity for our sample
covering Z=0.5-1.0 Zsun, reflecting the lower impact of stellar feedback. For
the sample of superbubbles, we find that about 40% of the young stellar
associations are preferentially located in their rims. We also find a slightly
higher (by ~15%) fraction of the youngest (1-2.5 Myr) stellar associations in
the rims of the superbubbles than in the centres, and the opposite for older
associations, which implies possible propagation or triggering of star
formation.Comment: 31 pages (including 5 pages in appendix), 19 figures, the abstract is
abridged; submitted to A&A (in mid May; awaiting report
Kinematics of Galactic Centre clouds shaped by shear-seeded solenoidal turbulence
The Central Molecular Zone (CMZ; the central ~ 500 pc of the Galaxy) is a
kinematically unusual environment relative to the Galactic disc, with high
velocity dispersions and a steep size-linewidth relation of the molecular
clouds. In addition, the CMZ region has a significantly lower star formation
rate (SFR) than expected by its large amount of dense gas. An important factor
in explaining the low SFR is the turbulent state of the star-forming gas, which
seems to be dominated by rotational modes. However, the turbulence driving
mechanism remains unclear. In this work, we investigate how the Galactic
gravitational potential affects the turbulence in CMZ clouds. We focus on the
CMZ cloud G0.253+0.016 (`the Brick'), which is very quiescent and unlikely to
be kinematically dominated by stellar feedback. We demonstrate that several
kinematic properties of the Brick arise naturally in a cloud-scale
hydrodynamics simulation that takes into account the Galactic gravitational
potential. These properties include the line-of-sight velocity distribution,
the steepened size-linewidth relation, and the predominantly solenoidal nature
of the turbulence. Within the simulation, these properties result from the
Galactic shear in combination with the cloud's gravitational collapse. This is
a strong indication that the Galactic gravitational potential plays a crucial
role in shaping the CMZ gas kinematics, and is a major contributor to
suppressing the SFR by inducing predominantly solenoidal turbulent modes.Comment: 7 pages, 8 figures; accepted to MNRAS (July 24th 2023
Surveying the Whirlpool at Arcseconds with NOEMA (SWAN)- I. Mapping the HCN and NH 3mm lines
We present the first results from "Surveying the Whirlpool at Arcseconds with
NOEMA" (SWAN), an IRAM Northern Extended Millimetre Array (NOEMA)+30m large
program that maps emission from several molecular lines at 90 and 110 GHz in
the iconic nearby grand-design spiral galaxy M~51 at cloud-scale resolution
(3\arcsec=125\,pc). As part of this work, we have obtained the first
sensitive cloud-scale map of NH(1-0) of the inner kpc of a normal star-forming galaxy, which we compare to HCN(1-0) and
CO(1-0) emission to test their ability in tracing dense, star-forming gas. The
average NH-to-HCN line ratio of our total FoV is , with
strong regional variations of a factor of throughout the disk,
including the south-western spiral arm and the center. The central kpc
exhibits elevated HCN emission compared to NH, probably caused by
AGN-driven excitation effects. We find that HCN and NH are strongly
super-linearily correlated in intensity (), with an
average scatter of dex over a span of dex in
intensity. When excluding the central region, the data is best described by a
power-law of exponent , indicating that there is more NH per unit
HCN in brighter regions. Our observations demonstrate that the HCN-to-CO line
ratio is a sensitive tracer of gas density in agreement with findings of recent
Galactic studies which utilize NH. The peculiar line ratios present
near the AGN and the scatter of the power-law fit in the disk suggest that in
addition to a first-order correlation with gas density, second-order physics
(such as optical depth, gas temperature) or chemistry (abundance variations)
are encoded in the NH/CO, HCN/CO and NH/HCN ratios.Comment: Accepted for publication in A&A. 6 pages, 3 figures (+ Appendix 4
pages, 2 figures
Fuelling the nuclear ring of NGC 1097
Galactic bars can drive cold gas inflows towards the centres of galaxies. The
gas transport happens primarily through the so-called bar ``dust lanes'', which
connect the galactic disc at kpc scales to the nuclear rings at hundreds of pc
scales much like two gigantic galactic rivers. Once in the ring, the gas can
fuel star formation activity, galactic outflows, and central supermassive black
holes. Measuring the mass inflow rates is therefore important to understanding
the mass/energy budget and evolution of galactic nuclei. In this work, we use
CO datacubes from the PHANGS-ALMA survey and a simple geometrical method to
measure the bar-driven mass inflow rate onto the nuclear ring of the barred
galaxy NGC~1097. The method assumes that the gas velocity in the bar lanes is
parallel to the lanes in the frame co-rotating with the bar, and allows one to
derive the inflow rates from sufficiently sensitive and resolved
position-position-velocity diagrams if the bar pattern speed and galaxy
orientations are known. We find an inflow rate of averaged over a time span of 40 Myr, which varies by a
factor of a few over timescales of 10 Myr. Most of the inflow appears to
be consumed by star formation in the ring which is currently occurring at a
rate of -, suggesting that the
inflow is causally controlling the star formation rate in the ring as a
function of time.Comment: Accepted in MNRA
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&
H α Emission and H ii Regions at the Locations of Recent Supernovae in Nearby Galaxies
We present a statistical analysis of the local, ≈50–100 pc scale, Hα emission at the locations of recent (≤125 yr) supernovae (SNe) in nearby star-forming galaxies. Our sample consists of 32 SNe in 10 galaxies that are targets of the PHANGS-MUSE survey. We find that 41% (13/32) of these SNe occur coincident with a previously identified H ii region. For comparison, H ii regions cover 32% of the area within ±1 kpc of any recent SN. Contrasting this local covering fraction with the fraction of SNe coincident with H ii regions, we find a statistical excess of 7.6% ± 8.7% of all SNe to be associated with H ii regions. This increases to an excess of 19.2% ± 10.4% when considering only core-collapse SNe (CCSNe). These estimates appear to be in good agreement with qualitative results from new, higher-resolution Hubble Space Telescope Hα imaging, which also suggests many CCSNe detonate near but not in H ii regions. Our results appear consistent with the expectation that only a modest fraction of stars explode during the first ≲5 Myr of the life of a stellar population when Hα emission is expected to be bright. Of the H ii region associated SNe, 85% (11/13) also have associated detected CO (2–1) emission, indicating the presence of molecular gas. The SNe associated with H ii regions have typical extinctions of A V ∼ 1 mag, consistent with a significant amount of pre-clearing of gas from the region before the SNe explode
The ALMOND Survey: Molecular cloud properties and gas density tracers across 25 nearby spiral galaxies with ALMA
We use new HCN(1-0) data from the ALMOND (ACA Large-sample Mapping Of Nearby
galaxies in Dense gas) survey to trace the kpc-scale molecular gas density
structure and CO(2-1) data from PHANGS-ALMA to trace the bulk molecular gas
across 25 nearby, star-forming galaxies. At 2.1 kpc scale, we measure the
density-sensitive HCN/CO line ratio and the SFR/HCN ratio to trace the star
formation efficiency in the denser molecular medium. At 150 pc scale, we
measure structural and dynamical properties of the molecular gas via CO(2-1)
line emission, which is linked to the lower resolution data using an
intensity-weighted averaging method. We find positive correlations (negative)
of HCN/CO (SFR/HCN) with the surface density, the velocity dispersion and the
internal turbulent pressure of the molecular gas. These observed correlations
agree with expected trends from turbulent models of star formation, which
consider a single free-fall time gravitational collapse. Our results show that
the kpc-scale HCN/CO line ratio is a powerful tool to trace the 150 pc scale
average density distribution of the molecular clouds. Lastly, we find
systematic variations of the SFR/HCN ratio with cloud-scale molecular gas
properties, which are incompatible with a universal star formation efficiency.
Overall, these findings show that mean molecular gas density, molecular cloud
properties and star formation are closely linked in a coherent way, and
observations of density-sensitive molecular gas tracers are a useful tool to
analyse these variations, linking molecular gas physics to stellar output
across galaxy discs.Comment: 48 pages, 40 figure
Recommended from our members
PHANGS-JWST First Results: Spurring on Star Formation: JWST Reveals Localized Star Formation in a Spiral Arm Spur of NGC 628
We combine JWST observations with Atacama Large Millimeter/submillimeter Array CO and Very Large Telescope MUSE Hα data to examine off-spiral arm star formation in the face-on, grand-design spiral galaxy NGC 628. We focus on the northern spiral arm, around a galactocentric radius of 3-4 kpc, and study two spurs. These form an interesting contrast, as one is CO-rich and one CO-poor, and they have a maximum azimuthal offset in MIRI 21 μm and MUSE Hα of around 40° (CO-rich) and 55° (CO-poor) from the spiral arm. The star formation rate is higher in the regions of the spurs near spiral arms, but the star formation efficiency appears relatively constant. Given the spiral pattern speed and rotation curve of this galaxy and assuming material exiting the arms undergoes purely circular motion, these offsets would be reached in 100-150 Myr, significantly longer than the 21 μm and Hα star formation timescales (both < 10 Myr). The invariance of the star formation efficiency in the spurs versus the spiral arms indicates massive star formation is not only triggered in spiral arms, and cannot simply occur in the arms and then drift away from the wave pattern. These early JWST results show that in situ star formation likely occurs in the spurs, and that the observed young stars are not simply the “leftovers” of stellar birth in the spiral arms. The excellent physical resolution and sensitivity that JWST can attain in nearby galaxies will well resolve individual star-forming regions and help us to better understand the earliest phases of star formation
PHANGS--JWST First Results: ISM structure on the turbulent Jeans scale in four disk galaxies observed by JWST and ALMA
JWST/MIRI imaging of the nearby galaxies IC 5332, NGC 628, NGC 1365 and NGC
7496 from PHANGS reveals a richness of gas structures that in each case form a
quasi-regular network of interconnected filaments, shells and voids. We examine
whether this multi-scale network of structure is consistent with the
fragmentation of the gas disk through gravitational instability. We use
FilFinder to detect the web of filamentary features in each galaxy and
determine their characteristic radial and azimuthal spacings. These spacings
are then compared to estimates of the most Toomre-unstable length (a few kpc),
the turbulent Jeans length (a few hundred pc) and the disk scale height (tens
of pc) reconstructed using PHANGS-ALMA observations of the molecular gas as a
dynamical tracer. Our analysis of the four galaxies targeted in this work
indicates that Jeans-scale structure is pervasive. Future work will be
essential for determining how the structure observed in gas disks impacts not
only the rate and location of star formation but also how stellar feedback
interacts positively or negatively with the surrounding multi-phase gas
reservoir.Comment: 15 pages, 4 figures. Accepted as part of a PHANGS-JWST ApJL Focus
Issu
Multiomics links global surfactant dysregulation with airflow obstruction and emphysema in COPD
RATIONALE: Pulmonary surfactant is vital for lung homeostasis as it reduces surface tension to prevent alveolar collapse and provides essential immune-regulatory and antipathogenic functions. Previous studies demonstrated dysregulation of some individual surfactant components in COPD. We investigated relationships between COPD disease measures and dysregulation of surfactant components to gain new insights into potential disease mechanisms. METHODS: Bronchoalveolar lavage proteome and lipidome were characterised in ex-smoking mild/moderate COPD subjects (n=26) and healthy ex-smoking (n=20) and never-smoking (n=16) controls using mass spectrometry. Serum surfactant protein analysis was performed. RESULTS: Total phosphatidylcholine, phosphatidylglycerol, phosphatidylinositol, surfactant protein (SP)-B, SP-A and SP-D concentrations were lower in COPD versus controls (log2 fold change (log2FC) -2.0, -2.2, -1.5, -0.5, -0.7 and -0.5 (adjusted p<0.02), respectively) and correlated with lung function. Total phosphatidylcholine, phosphatidylglycerol, phosphatidylinositol, SP-A, SP-B, SP-D, napsin A and CD44 inversely correlated with computed tomography small airways disease measures (expiratory to inspiratory mean lung density) (r= -0.56, r= -0.58, r= -0.45, r= -0.36, r= -0.44, r= -0.37, r= -0.40 and r= -0.39 (adjusted p<0.05)). Total phosphatidylcholine, phosphatidylglycerol, phosphatidylinositol, SP-A, SP-B, SP-D and NAPSA inversely correlated with emphysema (% low-attenuation areas): r= -0.55, r= -0.61, r= -0.48, r= -0.51, r= -0.41, r= -0.31 and r= -0.34, respectively (adjusted p<0.05). Neutrophil elastase, known to degrade SP-A and SP-D, was elevated in COPD versus controls (log2FC 0.40, adjusted p=0.0390), and inversely correlated with SP-A and SP-D. Serum SP-D was increased in COPD versus healthy ex-smoking volunteers, and predicted COPD status (area under the curve 0.85). CONCLUSIONS: Using a multiomics approach, we demonstrate, for the first time, global surfactant dysregulation in COPD that was associated with emphysema, giving new insights into potential mechanisms underlying the cause or consequence of disease
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