54 research outputs found
The star formation properties of disk galaxies: Halpha imaging of galaxies in the Coma supercluster
We present integrated H alpha measurements obtained from imaging observations
of 98 late-type galaxies, primarily selected in the Coma supercluster. These
data, combined with H alpha photometry from the literature, include a magnitude
selected sample of spiral (Sa to Irr) galaxies belonging to the "Great Wall"
complete up to mp=15.4, thus composed of galaxies brighter than Mp=-18.8
(H0=100 km Mpc^-1 s^-1). The frequency distribution of the H alpha E.W.,
determined for the first time from an optically complete sample, is
approximately gaussian peaking at E.W. ~25 A. We find that, at the present
limiting luminosity, the star formation properties of spiral+Irr galaxies
members of the Coma and A1367 clusters do not differ significantly from those
of the isolated ones belonging to the Great Wall. The present analysis confirms
the well known increase of the current massive star formation rate (SFR) with
Hubble type. Moreover perhaps a more fundamental anticorrelation exists between
the SFR and the mass of disk galaxies: low-mass spirals and dwarf systems have
present SFRs ~50 times higher than giant spirals. This result is consistent
with the idea that disk galaxies are coeval, evolve as "closed systems" with
exponentially declining SFR and that the mass of their progenitor protogalaxies
is the principal parameter governing their evolution. Massive systems having
high initial efficiency of collapse, or a short collapse time-scale, have
retained little gas to feed the present epoch of star formation. These findings
support the conclusions of Gavazzi & Scodeggio (1996) who studyed the
color-mass relation of a local galaxy sample and agree with the analysis by
Cowie et al. (1996) who traced the star formation history of galaxies up to
z>1.Comment: 13 pages (LateX) + 24 figures + 4 tables. To appear in Astronomical
Journal, April 1998 issu
Composition of Volatile Fraction from Inflorescences and Leaves of Dendrobium moschatum (Orchidaceae)
The volatile fractions from fresh inflorescences and leaves of Dendrobium moschatum (Buchanan-Hamilton) Swartz (Orchidaceae) were isolated by steam distillation with a yield of 0.498% and 0.041% (weight/fresh weight basis), respectively. From GC/FID and GC/MS analyses, coumarin was identified to be the most abundant constituent and quantified as 48.8% and 47.8% of the total volatiles from inflorescences and leaves, respectively. Hydrocarbons, ketones, esters, acids and aldehydes were also detected. Long chain mono unsaturated hydrocarbons were quantified in higher amount in leaves and their structures were elucidated by GC/MS of their dimethyl disulfide derivatives. These compounds together with long chain ethyl esters and methyl ketones may represent a particular feature of this plant species and can play a critical role in the interaction with pollinator insect
The lymphatic drain of below-knee malignant melanoma. Is the popliteal fossa a ghost station?
Sentinel lymph node biopsy is fundamental in the staging of primary cutaneous melanoma (PCL), but reported lymphoscintigraphic patterns are very heterogeneous. In this systematic review, we evaluated the role of the popliteal station in below-knee PCL. A systematic search of literature through was conducted on the electronic databases PubMed, SCOPUS and Web of Science (WOS) to identify eligible studies. A total of 22 studies (n=5,673 patients) were included. The average Breslow thickness of PCL was 2.86 mm. During the analysis of the included articles, it was not possible to classify patients into the 3 Menes popliteal drainage pattern, obtained by lymphoscintigraphy. The analysis of lymphatic drainage in patients undergoing lymphoscintigraphy for melanoma of the lower extremities below the knee was reported in 5,637 patients and the lymphatic popliteal drainage was reported only in 5.64% (320 patients). The rate of popliteal lymph nodes melanoma metastases was 1.48%: they were located exclusively at the popliteal level in 0.60%, at the popliteal and inguinal levels in 0.39%, at the popliteal and iliac level in 0.02% and at the groin level in 0.48%. In conclusion, the most common lymphoscintigraphic pattern is represented by popliteal nodes in-transit or interval nodes, so metastases from below-knee melanomas commonly transit through popliteal nodes stations and arrive to inguinal nodes stations. The popliteal nodes are the primary station in about 5.64% of cases. Larger studies are needed to corroborate these findings
COLD GASS, an IRAM legacy survey of molecular gas in massive galaxies: I. Relations between H2, HI, stellar content and structural properties
We are conducting COLD GASS, a legacy survey for molecular gas in nearby
galaxies. Using the IRAM 30m telescope, we measure the CO(1-0) line in a sample
of ~350 nearby (D=100-200 Mpc), massive galaxies (log(M*/Msun)>10.0). The
sample is selected purely according to stellar mass, and therefore provides an
unbiased view of molecular gas in these systems. By combining the IRAM data
with SDSS photometry and spectroscopy, GALEX imaging and high-quality Arecibo
HI data, we investigate the partition of condensed baryons between stars,
atomic gas and molecular gas in 0.1-10L* galaxies. In this paper, we present CO
luminosities and molecular hydrogen masses for the first 222 galaxies. The
overall CO detection rate is 54%, but our survey also uncovers the existence of
sharp thresholds in galaxy structural parameters such as stellar mass surface
density and concentration index, below which all galaxies have a measurable
cold gas component but above which the detection rate of the CO line drops
suddenly. The mean molecular gas fraction MH2/M* of the CO detections is
0.066+/-0.039, and this fraction does not depend on stellar mass, but is a
strong function of NUV-r colour. Through stacking, we set a firm upper limit of
MH2/M*=0.0016+/-0.0005 for red galaxies with NUV-r>5.0. The average
molecular-to-atomic hydrogen ratio in present-day galaxies is 0.3, with
significant scatter from one galaxy to the next. The existence of strong
detection thresholds in both the HI and CO lines suggests that "quenching"
processes have occurred in these systems. Intriguingly, atomic gas strongly
dominates in the minority of galaxies with significant cold gas that lie above
these thresholds. This suggests that some re-accretion of gas may still be
possible following the quenching event.Comment: Accepted for publications in MNRAS. 32 pages, 25 figure
Mycelium-based biomaterials as smart devices for skin wound healing
Introduction: Recently, mycelia of Ganoderma lucidum and Pleurotus ostreatus, edible fungi, have been characterized in vitro as self-growing biomaterials for tissue engineering since they are constituted of interconnected fibrous networks resembling the dermal collagen structure.Aim: This work aims to investigate the biopharmaceutical properties of G. lucidum and P. ostreatus mycelia to prove their safety and effectiveness in tissue engineering as dermal substitutes.Methods: The mycelial materials were characterized using a multidisciplinary approach, including physicochemical properties (morphology, thermal behavior, surface charge, and isoelectric point). Moreover, preclinical properties such as gene expression and in vitro wound healing assay have been evaluated using fibroblasts. Finally, these naturally-grown substrates were applied in vivo using a murine burn/excisional wound model.Conclusions: Both G. lucidum and P. ostreatus mycelia are biocompatible and able to safely and effectively enhance tissue repair in vivo in our preclinical model
The GALEX Arecibo SDSS Survey II: The Star Formation Efficiency of Massive Galaxies
We use measurements of the HI content, stellar mass and star formation rates
in ~190 massive galaxies with stellar masses greater than 10^10 Msun, obtained
from the Galex Arecibo SDSS Survey (GASS) described in Paper I (Catinella et
al. 2010) to explore the global scaling relations associated with the
bin-averaged ratio of the star formation rate over the HI mass, which we call
the HI-based star formation efficiency (SFE). Unlike the mean specific star
formation rate, which decreases with stellar mass and stellar mass surface
density, the star formation efficiency remains relatively constant across the
sample with a value close to SFE = 10^-9.5 yr^-1 (or an equivalent gas
consumption timescale of ~3 Gyr). Specifically, we find little variation in SFE
with stellar mass, stellar mass surface density, NUV-r color and concentration.
We interpret these results as an indication that external processes or feedback
mechanisms that control the gas supply are important for regulating star
formation in massive galaxies. An investigation into the detailed distribution
of SFEs reveals that approximately 5% of the sample shows high efficiencies
with SFE > 10^-9 yr^-1, and we suggest that this is very likely due to a
deficiency of cold gas rather than an excess star formation rate. Conversely,
we also find a similar fraction of galaxies that appear to be gas-rich for
their given specific star-formation rate, although these galaxies show both a
higher than average gas fraction and lower than average specific star formation
rate. Both of these populations are plausible candidates for "transition"
galaxies, showing potential for a change (either decrease or increase) in their
specific star formation rate in the near future. We also find that 36+/-5% of
the total HI mass density and 47+/-5% of the total SFR density is found in
galaxies with stellar mass greater than 10^10 Msun. [abridged]Comment: 18 pages, 11 figures. Accepted for publication in MNRAS. GASS
publications and released data can be found at
http://www.mpa-garching.mpg.de/GASS/index.ph
VERTICO VI: Cold-gas asymmetries in Virgo cluster galaxies
We analyze cold-gas distributions in Virgo cluster galaxies using resolved
CO(2-1) (tracing molecular hydrogen, H2) and HI observations from the Virgo
Environment Traced In CO (VERTICO) and the VLA Imaging of Virgo in Atomic Gas
(VIVA) surveys. From a theoretical perspective, it is expected that
environmental processes in clusters will have a stronger influence on diffuse
atomic gas compared to the relatively dense molecular gas component, and that
these environmental perturbations can compress the cold interstellar medium in
cluster galaxies leading to elevated star formation. In this work we
observationally test these predictions for star-forming satellite galaxies
within the Virgo cluster. We divide our Virgo galaxy sample into HI-normal,
HI-tailed, and HI-truncated classes and show, unsurprisingly, that the
HI-tailed galaxies have the largest quantitative HI asymmetries. We also
compare to a control sample of non-cluster galaxies and find that Virgo
galaxies, on average, have HI asymmetries that are 40 +/- 10 per cent larger
than the control. There is less separation between control, HI-normal,
HI-tailed, and HI-truncated galaxies in terms of H2 asymmetries, and on
average, Virgo galaxies have H2 asymmetries that are only marginally (20 +/- 10
per cent) larger than the control sample. We find a weak correlation between HI
and H2 asymmetries over our entire sample, but a stronger correlation for those
specific galaxies being strongly impacted by environmental perturbations.
Finally, we divide the discs of the HI-tailed Virgo galaxies into a leading
half and trailing half according to the observed tail direction. We find
evidence for excess molecular gas mass on the leading halves of the disc. This
excess molecular gas on the leading half is accompanied by an excess in star
formation rate such that the depletion time is, on average, unchanged.Comment: 15 pages, 8 figures, 1 table, accepted for publication in A&
VERTICO VII: Environmental quenching caused by suppression of molecular gas content and star formation efficiency in Virgo Cluster galaxies
We study how environment regulates the star formation cycle of 33 Virgo
Cluster satellite galaxies on 720 parsec scales. We present the first resolved
star-forming main sequence for cluster galaxies, dividing the sample based on
their global HI properties and comparing to a control sample of field galaxies.
HI-poor cluster galaxies have reduced star formation rate (SFR) surface
densities with respect to both HI-normal cluster and field galaxies (0.5 dex),
suggesting that mechanisms regulating the global HI content are responsible for
quenching local star formation. We demonstrate that the observed quenching in
HI-poor galaxies is caused by environmental processes such as ram pressure
stripping (RPS) simultaneously reducing molecular gas surface density and star
formation efficiency (SFE), compared to regions in HI-normal systems (by 0.38
and 0.22 dex, respectively). We observe systematically elevated SFRs that are
driven by increased molecular gas surface densities at fixed stellar mass
surface density in the outskirts of early-stage RPS galaxies, while SFE remains
unchanged with respect to the field sample. We quantify how RPS and starvation
affect the star formation cycle of inner and outer galaxy discs as they are
processed by the cluster. We show both are effective quenching mechanisms with
the key difference being that RPS acts upon the galaxy outskirts while
starvation regulates the star formation cycle throughout disc, including within
the truncation radius. For both processes, the quenching is caused by a
simultaneous reduction in molecular gas surface densities and SFE at fixed
stellar mass surface density.Comment: 17 pages, 1 table, 5 figures, accepted for publication in Ap
Estimating the H I gas fractions of galaxies in the local Universe
We use a sample of 800 galaxies with H I mass measurements from the HyperLeda
catalogue and optical photometry from the fourth data release of the Sloan
Digital Sky Survey to calibrate a new photometric estimator of the H I
to-stellar mass ratio for nearby galaxies. Our estimator, which is motivated by
the Kennicutt-Schmidt star formation law, is log(G_{HI}/S) = -1.73238(g-r) +
0.215182mu_i - 4.08451, where mu_i is the i-band surface brighteness and g-r is
the optical colour estimated from the g- and r-band Petrosian apparent
agnitudes. This estimator has a scatter of sigma = 0.31 dex in log(G_{HI}/S),
compared to sigma ~ 0.4 dex for previous estimators that were based on colour
alone. We investigate whether the residuals in our estimate of log(G_{HI}/S)
depend in a systematic way on a variety of different galaxy properties. We find
no effect as a function of stellar mass or 4000A break strength, but there is a
systematic effect as a function of the concentration index of the light. We
then apply our estimator to a sample of 10^5 emission-line galaxies in the SDSS
DR4 and derive an estimate of the H I mass function, which is in excellent
agreement with recent results from H I blind surveys. Finally, we re-examine
the well-known relation between gas-phase metallicity and stellar mass and ask
whether there is a dependence on H I-to-stellar mass ratio, as predicted by
chemical evolution models. We do find that gas-poor galaxies are more metal
rich at fixed stellar mass. We compare our results with the semi-analytic
models of De Lucia & Blaizot, which include supernova feedback, as well as the
cosmological infall of gas.Comment: 12 pages, 9 figures, accepted for publication in MNRA
FAST-ASKAP Synergy: Quantifying Coexistent Tidal and Ram-Pressure Strippings in the NGC 4636 Group
Combining new HI data from a synergetic survey of ASKAP WALLABY and FAST with
the ALFALFA data, we study the effect of ram-pressure and tidal interactions in
the NGC 4636 group. We develop two parameters to quantify and disentangle these
two effects on gas stripping in HI-bearing galaxies: the strength of external
forces at the optical-disk edge, and the outside-in extents of HI-disk
stripping. We find that gas stripping is widespread in this group, affecting
80% of HI-detected non-merging galaxies, and that 34% are experiencing both
types of stripping. Among the galaxies experiencing both effects, the strengths
(and extents) of ram-pressure and tidal stripping are independent of each
other. Both strengths are correlated with HI-disk shrinkage. The tidal strength
is related to a rather uniform reddening of low-mass galaxies
() when tidal stripping is the dominating effect. In
contrast, ram pressure is not clearly linked to the color-changing patterns of
galaxies in the group. Combining these two stripping extents, we estimate the
total stripping extent, and put forward an empirical model that can describe
the decrease of HI richness as galaxies fall toward the group center. The
stripping timescale we derived decreases with distance to the center, from
around to
near the center. Gas-depletion happens
since crossing for HI-rich galaxies,
but much quicker for HI-poor ones. Our results quantify in a physically
motivated way the details and processes of environmental-effects-driven galaxy
evolution, and might assist in analyzing hydrodynamic simulations in an
observational way.Comment: 44 pages, 22 figures, 5 tables, accepted for publication in ApJ.
Tables 4 and 5 are also available in machine-readable for
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