19 research outputs found
The GALEX Arecibo SDSS Survey. I. Gas Fraction Scaling Relations of Massive Galaxies and First Data Release
We introduce the GALEX Arecibo SDSS Survey (GASS), an on-going large program
that is gathering high quality HI-line spectra using the Arecibo radio
telescope for an unbiased sample of ~1000 galaxies with stellar masses greater
than 10^10 Msun and redshifts 0.025<z<0.05, selected from the SDSS
spectroscopic and GALEX imaging surveys. The galaxies are observed until
detected or until a low gas mass fraction limit (1.5-5%) is reached. This paper
presents the first Data Release, consisting of ~20% of the final GASS sample.
We use this data set to explore the main scaling relations of HI gas fraction
with galaxy structure and NUV-r colour. A large fraction (~60%) of the galaxies
in our sample are detected in HI. We find that the atomic gas fraction
decreases strongly with stellar mass, stellar surface mass density and NUV-r
colour, but is only weakly correlated with galaxy bulge-to-disk ratio (as
measured by the concentration index of the r-band light). We also find that the
fraction of galaxies with significant (more than a few percent) HI decreases
sharply above a characteristic stellar surface mass density of 10^8.5 Msun
kpc^-2. The fraction of gas-rich galaxies decreases much more smoothly with
stellar mass. One of the key goals of GASS is to identify and quantify the
incidence of galaxies that are transitioning between the blue, star-forming
cloud and the red sequence of passively-evolving galaxies. Likely transition
candidates can be identified as outliers from the mean scaling relations
between gas fraction and other galaxy properties. [abridged]Comment: 25 pages, 12 figures. Accepted for publication in MNRAS. Version with
high resolution figures available at
http://www.mpa-garching.mpg.de/GASS/pubs.ph
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
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
COLD GASS, an IRAM Legacy Survey of Molecular Gas in Massive Galaxies: II. The non-universality of the Molecular Gas Depletion Timescale
We study the relation between molecular gas and star formation in a
volume-limited sample of 222 galaxies from the COLD GASS survey, with
measurements of the CO(1-0) line from the IRAM 30m telescope. The galaxies are
at redshifts 0.025<z<0.05 and have stellar masses in the range
10.0<log(M*/Msun)<11.5. The IRAM measurements are complemented by deep Arecibo
HI observations and homogeneous SDSS and GALEX photometry. A reference sample
that includes both UV and far-IR data is used to calibrate our estimates of
star formation rates from the seven optical/UV bands. The mean molecular gas
depletion timescale, tdep(H2), for all the galaxies in our sample is 1 Gyr,
however tdep(H2) increases by a factor of 6 from a value of ~0.5 Gyr for
galaxies with stellar masses of 10^10 Msun to ~3 Gyr for galaxies with masses
of a few times 10^11 Msun. In contrast, the atomic gas depletion timescale
remains contant at a value of around 3 Gyr. This implies that in high mass
galaxies, molecular and atomic gas depletion timescales are comparable, but in
low mass galaxies, molecular gas is being consumed much more quickly than
atomic gas. The strongest dependences of tdep(H2) are on the stellar mass of
the galaxy (parameterized as log tdep(H2)= (0.36+/-0.07)(log M* -
10.70)+(9.03+/-0.99)), and on the specific star formation rate. A single
tdep(H2) versus sSFR relation is able to fit both "normal" star-forming
galaxies in our COLD GASS sample, as well as more extreme starburst galaxies
(LIRGs and ULIRGs), which have tdep(H2) < 10^8 yr. Normal galaxies at z=1-2 are
displaced with respect to the local galaxy population in the tdep(H2) versus
sSFR plane and have molecular gas depletion times that are a factor of 3-5
times longer at a given value of sSFR due to their significantly larger gas
fractions.Comment: Accepted for publication in MNRAS. 19 pages, 11 figure
The impact of interactions, bars, bulges, and AGN on star formation efficiency in local massive galaxies
Using observations from the GASS and COLD GASS surveys and complementary data
from SDSS and GALEX, we investigate the nature of variations in gas depletion
time observed across the local massive galaxy population. The large and
unbiased COLD GASS sample allows us to assess the relative importance of galaxy
interactions, bar instabilities, morphologies and the presence of AGN in
regulating star formation efficiency. Both the H2 mass fraction and depletion
time vary as a function of the distance of a galaxy from the main sequence in
the SFR-M* plane. The longest gas depletion times are found in below-main
sequence bulge-dominated galaxies that are either gas-poor, or else on average
less efficient than disk-dominated galaxy at converting into stars any cold gas
they may have. We find no link between AGN and these long depletion times. The
galaxies undergoing mergers or showing signs of morphological disruptions have
the shortest molecular gas depletion times, while those hosting strong stellar
bars have only marginally higher global star formation efficiencies as compared
to matched control samples. Our interpretation is that depletion time
variations are caused by changes in the ratio between the gas mass traced by
the CO(1-0) observations, and the gas mass in high density star-forming cores,
with interactions, mergers and bar instabilities able to locally increase
pressure and raise the ratio of efficiently star-forming gas to CO-detected
gas. Building a sample representative of the local massive galaxy population,
we derive a global Kennicutt-Schmidt relation of slope 1.18+/-0.24, and observe
structure within the scatter around this relation, with galaxies having low
(high) stellar mass surface densities lying systematically above (below) the
mean relation, suggesting that gas surface density is not the only parameter
driving the global star formation ability of a galaxy.Comment: 19 pages, 12 figures, accepted for publication in Ap
Molecular and atomic gas along and across the main sequence of star-forming galaxies
We use spectra from the ALFALFA, GASS and COLD GASS surveys to quantify
variations in the mean atomic and molecular gas mass fractions throughout the
SFR-M* plane and along the main sequence (MS) of star-forming galaxies.
Although galaxies well below the MS tend to be undetected in the Arecibo and
IRAM observations, reliable mean atomic and molecular gas fractions can be
obtained through a spectral stacking technique. We find that the position of
galaxies in the SFR-M* plane can be explained mostly by their global cold gas
reservoirs as observed in the HI line, with in addition systematic variations
in the molecular-to-atomic ratio and star formation efficiency. When looking at
galaxies within +/-0.4 dex of the MS, we find that as stellar mass increases,
both atomic and molecular gas mass fractions decrease, stellar bulges become
more prominent, and the mean stellar ages increase. Both star formation
efficiency and molecular-to-atomic ratios vary little for massive main sequence
galaxies, indicating that the flattening of the MS is due to the global
decrease of the cold gas reservoirs of galaxies rather than to bottlenecks in
the process of converting cold atomic gas to stars.Comment: 9 pages, 6 figures. Accepted for publication in MNRA
The RESOLVE Survey Atomic Gas Census and Environmental Influences on Galaxy Gas Reservoirs
We present the H i mass inventory for the REsolved Spectroscopy Of a Local VolumE (RESOLVE) survey, a volume-limited, multi-wavelength census of >1500 z = 0 galaxies spanning diverse environments and complete in baryonic mass down to dwarfs of ~109 . This first 21 cm data release provides robust detections or strong upper limits (1.4M H i 1012 ) halos, suggesting that gas stripping and/or starvation may be induced by interactions with larger halos or the surrounding cosmic web. We find that the detailed relationship between G/S and environment varies when we examine different subvolumes of RESOLVE independently, which we suggest may be a signature of assembly bias
Finishing the euchromatic sequence of the human genome
The sequence of the human genome encodes the genetic instructions for human physiology, as well as rich information about human evolution. In 2001, the International Human Genome Sequencing Consortium reported a draft sequence of the euchromatic portion of the human genome. Since then, the international collaboration has worked to convert this draft into a genome sequence with high accuracy and nearly complete coverage. Here, we report the result of this finishing process. The current genome sequence (Build 35) contains 2.85 billion nucleotides interrupted by only 341 gaps. It covers ∼99% of the euchromatic genome and is accurate to an error rate of ∼1 event per 100,000 bases. Many of the remaining euchromatic gaps are associated with segmental duplications and will require focused work with new methods. The near-complete sequence, the first for a vertebrate, greatly improves the precision of biological analyses of the human genome including studies of gene number, birth and death. Notably, the human enome seems to encode only 20,000-25,000 protein-coding genes. The genome sequence reported here should serve as a firm foundation for biomedical research in the decades ahead
In Vitro Activity of Twenty Commercially Available, Plant-Derived Essential Oils against Selected Dermatophyte Species
The in vitro activity of twenty chemically defined essential oils (EOs) obtained from Boswellia sacra, Citrus bergamia, C. limon, C. medica, Cinnamomum zeylanicum, Eucalyptus globulus, Foeniculum vulgare, Helichrysum italicum, Illicium verum, Litsea cubeba, Mentha spicata, Myrtus communis, Ocimum basilicum, Origanum majorana, O. vulgare, Pelargonium graveolens, Rosmarinus officinalis, Santalum album, Satureja montana, and Thymus serpyllum was assayed against clinical animal isolates of Microsporum canis, Trichophyton mentagrophytes, T. erinacei, T. terrestre and Microsporum gypseum, main causative agents of zoonotic and/or environmental dermatophytoses in humans. Single main components present in high amounts in such EOs were also tested. Different dermatophyte species showed remarkable differences in sensitivity. In general, more effective EOs were T. serpyllum (MIC range 0.025%-0.25%), O. vulgare (MIC range 0.025%-0.5%) and L. cubeba (MIC range 0.025%-1.5%). F. vulgare showed a moderate efficacy against geophilic species such as M. gypseum and T. terrestre. Among single main components tested, neral was the most active (MIC and MFC values ≤ 0.25%). The results of the present study seem to be promising for an in vivo use of some assayed EOs
Susceptibility of Microsporum canis arthrospores to a mixture of chemically defined essential oils: a perspective for environmental decontamination.
The zoophilic dermatophyte Microsporum canis has cats as natural reservoir, but it is able to infect a wide range of hosts, including humans, where different clinical features of the so-called ringworm dermatophytosis have been described. Human infections are increasingly been reported in Mediterranean countries. A reliable control program against M. canis infection in cats should include an antifungal treatment of both the infected animals and their living environment. In this article, a herbal mixture composed of chemically defined essential oils (EOs) of Litsea cubeba (1%), Illicium verum, Foeniculum vulgare, and Pelargonium graveolens (0.5% each) was formulated and its antifungal activity assessed against M. canis arthrospores which represent the infective environmental stage of M. canis. Single compounds present in higher amounts in the mixture were also separately tested in vitro. Litsea cubeba and P. graveolens EOs were most effective (minimum inhibitory concentration (MIC) 0.5%), followed by EOs of I. verum (MIC 2%) and F. vulgare (MIC 2.5%). Minimum fungicidal concentrations (MFC) values were 0.75% (L. cubeba), 1.5% (P. graveolens), 2.5% (I. verum) and 3% (F. vulgare). MIC and MFC values of the mixture were 0.25% and 0.5%, respectively. The daily spray of the mixture (200 μL) directly onto infected hairs inhibited fungal growth from the fourth day onwards. The compounds present in higher amounts exhibited variable antimycotic activity, with MIC values ranging from >10% (limonene) to 0.1% (geranial and neral). Thus, the mixture showed a good antifungal activity against arthrospores present in infected hairs. These results are promising for a further application of the mixture as an alternative tool or as an adjuvant in the environmental control of feline microsporosis