We present a new survey of HCN(1-0) emission, a tracer of dense molecular gas, focused on the little-explored regime of normal star-forming galaxy disks. Combining HCN, CO, and infrared (IR) ...emission, we investigate the role of dense gas in star formation, finding systematic variations in both the apparent dense gas fraction (traced by the HCN-to-CO ratio) and the apparent star formation efficiency of dense gas. The latter may be unexpected, given the recent popularity of gas density threshold models to explain star formation scaling relations. Our survey used the IRAM 30 m telescope to observe HCN(1-0), CO(1-0), and several other emission lines across 29 nearby disk galaxies whose CO(2-1) emission has previously been mapped by the HERACLES survey. We detected HCN in 48 out of 62 observed positions. We explore one such model in which variations in the Mach number drive many of the trends within galaxy disks, while density contrasts drive the differences between disk and merging galaxies.
ABSTRACT We analyze the velocity dispersions of individual H i and CO profiles in a number of nearby galaxies from the high-resolution HERACLES CO and THINGS H i surveys. Focusing on regions with ...bright CO emission, we find a CO dispersion value = 7.3 1.7 km s−1. The corresponding H i dispersion = 11.7 2.3 km s−1, yielding a mean dispersion ratio = 1.4 0.2, independent of radius. We find that the CO velocity dispersion increases toward lower peak fluxes. This is consistent with previous work where we showed that when using spectra averaged ("stacked") over large areas, larger values for the CO dispersion are found, and a lower ratio = 1.0 0.2. The stacking method is more sensitive to low-level diffuse emission, whereas individual profiles trace narrow-line, GMC-dominated, bright emission. These results provide further evidence that disk galaxies contain not only a thin, low velocity dispersion, high density CO disk that is dominated by GMCs, but also a fainter, higher dispersion, diffuse disk component.
We present the Atacama Large Millimeter/submillimeter Array survey of CO(2-1) emission from the 1/5 solar metallicity, Local Group dwarf galaxy NGC 6822. We achieve high ( pc) spatial resolution ...while covering a large area: four 250 pc × 250 pc regions that encompass of NGC 6822's star formation. In these regions, we resolve compact CO clumps that have small radii (∼2-3 pc), narrow line width ( km s−1), and low filling factor across the galaxy. This is consistent with other recent studies of low-metallicity galaxies, but here shown with a larger sample. At parsec scales, CO emission correlates with emission better than with emission and anticorrelates with H , so that polycyclic aromatic hydrocarbon emission may be an effective tracer of molecular gas at low metallicity. The properties of the CO clumps resemble those of similar-size structures in Galactic clouds except of slightly lower surface brightness and with CO-to-H2 ratio ∼1-2× the Galactic value. The clumps exist inside larger atomic-molecular complexes with masses typical for giant molecular clouds. Using dust to trace H2 for the entire complex, we find the CO-to-H2 ratio to be the Galactic value, but with strong dependence on spatial scale and variations between complexes that may track their evolutionary state. The H2-to-H i ratio is low globally and only mildly above unity within the complexes. The ratio of star formation rate to H2 is higher in the complexes than in massive disk galaxies, but after accounting for the bias from targeting star-forming regions, we conclude that the global molecular gas depletion time may be as long as in massive disk galaxies.
We present the Heterodyne Receiver Array CO Line Extragalactic Survey, an atlas of CO emission from 18 nearby galaxies that are also part of The H I Nearby Galaxy Survey and the Spitzer Infrared ...Nearby Galaxies Survey. We used the HERA multipixel receiver on the IRAM 30-m telescope to map the CO J = 2 -> 1 line over the full optical disk (defined by the isophotal radius r 25) of each target, at 13'' angular resolution and 2.6 km s-1 velocity resolution. Here we describe the observations and reduction of the data and show channel maps, azimuthally averaged profiles, integrated intensity maps, and peak intensity maps. The implied H2 masses range from 7 X 106 to 6 X 109 M , with four low metallicity dwarf irregular galaxies yielding only upper limits. In the cases where CO is detected, the integrated H2-to-H I ratios range from 0.02 to 1.13 and H2-to-stellar mass ratios from 0.01 to 0.25. Exponential scale lengths of the CO emission for our targets are in the range 0.8-3.2 kpc, or 0.2 ± 0.05r 25. The intensity-weighted mean velocity of CO matches that of H I very well, with a 1s scatter of only 6 km s-1. The CO J = 2 -> 1/J = 1 -> 0 line ratio varies over a range similar to that found in the Milky Way and other nearby galaxies, ~0.6-1.0, with higher values found in the centers of galaxies. The typical line ratio, ~0.8, could be produced by optically thick gas with an excitation temperature of ~10 K.
We present Karl G. Jansky Very Large Array observations of the CO(2-1) emission in the z = 4.05 submillimeter galaxy (SMG) GN20. These high-resolution data allow us to image the molecular gas at 1.3 ...kpc resolution just 1.6 Gyr after the big bang. The data reveal a clumpy, extended gas reservoir, 14 + or - 4 kpc in diameter, in unprecedented detail. A dynamical analysis shows that the data are consistent with a rotating disk of total dynamical mass 5.4 + or - 2.4 x 10 super(11) M sub(middot in circle). We use this dynamical mass estimate to constrain the CO-to-H sub(2) mass conversion factor ( alpha sub(CO)), finding alpha sub(CO) = 1.1 + or - 0.6 M sub(middot in circle)(K km s super(-1) pc super(2)) super(-1). We identify five distinct molecular gas clumps in the disk of GN20 with masses a few percent of the total gas mass, brightness temperatures of 16-31K, and surface densities of >3200-4500 x ( alpha CO/0.8) M sub(middot in circle) pc super(-2). Virial mass estimates indicate they could be self-gravitating, and we constrain their CO-to-H sub(2) mass conversion factor to be <0.2-0.7 M sub(middot in circle)(K km s super(-1) pc super(2)) super(-1). A multiwavelength comparison demonstrates that the molecular gas is concentrated in a region of the galaxy that is heavily obscured in the rest-frame UV/optical. We investigate the spatially resolved gas excitation and find that the CO(6-5)/CO(2-1) ratio is constant with radius, consistent with star formation occurring over a large portion of the disk. We discuss the implications of our results in the context of different fueling scenarios for SMGs.
Selective digestive tract decontamination (SDD) and selective oropharyngeal decontamination (SOD) are infection-prevention measures used in the treatment of some patients in intensive care, but ...reported effects on patient outcome are conflicting.
We evaluated the effectiveness of SDD and SOD in a crossover study using cluster randomization in 13 intensive care units (ICUs), all in The Netherlands. Patients with an expected duration of intubation of more than 48 hours or an expected ICU stay of more than 72 hours were eligible. In each ICU, three regimens (SDD, SOD, and standard care) were applied in random order over the course of 6 months. Mortality at day 28 was the primary end point. SDD consisted of 4 days of intravenous cefotaxime and topical application of tobramycin, colistin, and amphotericin B in the oropharynx and stomach. SOD consisted of oropharyngeal application only of the same antibiotics. Monthly point-prevalence studies were performed to analyze antibiotic resistance.
A total of 5939 patients were enrolled in the study, with 1990 assigned to standard care, 1904 to SOD, and 2045 to SDD; crude mortality in the groups at day 28 was 27.5%, 26.6%, and 26.9%, respectively. In a random-effects logistic-regression model with age, sex, Acute Physiology and Chronic Health Evaluation (APACHE II) score, intubation status, and medical specialty used as covariates, odds ratios for death at day 28 in the SOD and SDD groups, as compared with the standard-care group, were 0.86 (95% confidence interval CI, 0.74 to 0.99) and 0.83 (95% CI, 0.72 to 0.97), respectively.
In an ICU population in which the mortality rate associated with standard care was 27.5% at day 28, the rate was reduced by an estimated 3.5 percentage points with SDD and by 2.9 percentage points with SOD. (Controlled Clinical Trials number, ISRCTN35176830.)
We combine data from The H I Nearby Galaxy Survey and the GALEX Nearby Galaxy Survey to study the relationship between atomic hydrogen (H I) and far-ultraviolet (FUV) emission outside the optical ...radius (r 25) in 17 spiral and 5 dwarf galaxies. In this regime, H I is likely to represent most of the interstellar medium (ISM) and FUV emission to trace recent star formation with little bias due to extinction, so that the two quantities closely trace the underlying relationship between gas and star formation rate (SFR). The azimuthally averaged H I and FUV intensities both decline with increasing radius in this regime, with the scale length of the FUV profile typically half that of the H I profile. Despite the mismatch in profiles, there is a significant spatial correlation (at 15'' resolution) between local FUV and H I intensities; near r 25 this correlation is quite strong, in fact stronger than anywhere inside r 25 (where H I is not a good tracer for the bulk of the ISM), and shows a decline toward larger radii. The star formation efficiency (SFE)--defined as the ratio of FUV/H I and thus the inverse of the gas depletion time--decreases with galactocentric radius across the outer disks, though much shallower than across the optical disks. On average, we find the gas depletion times to be well above a Hubble time (~1011 yr). We observe a clear relationship between FUV/H I and H I column in the outer disks, with the SFE increasing with increasing H I column. Despite observing systematic variations in FUV/H I, we find no clear evidence for step-function-type star formation thresholds, though we emphasize that it may not be realistic to expect them. When compared with results from inside r 25, we find outer disk star formation to be distinct in several ways: it is extremely inefficient (depletion times of many Hubble times which are also long compared to either the free fall or orbital timescale) with column densities and SFRs lower than found anywhere inside the optical disks. It appears that the H I column is one of the key environmental factors--perhaps the key factor--in setting the SFR in outer galaxy disks.
ABSTRACT
We report the detection of a bright fast radio burst, FRB 191108, with Apertif on the Westerbork Synthesis Radio Telescope. The interferometer allows us to localize the FRB to a narrow 5 ...arcsec × 7 arcmin ellipse by employing both multibeam information within the Apertif phased-array feed beam pattern, and across different tied-array beams. The resulting sightline passes close to Local Group galaxy M33, with an impact parameter of only 18 kpc with respect to the core. It also traverses the much larger circumgalactic medium (CGM) of M31, the Andromeda Galaxy. We find that the shared plasma of the Local Group galaxies could contribute ∼10 per cent of its dispersion measure of 588 pc cm−3. FRB 191108 has a Faraday rotation measure (RM) of +474 $\pm \, 3$ rad m−2, which is too large to be explained by either the Milky Way or the intergalactic medium. Based on the more moderate RMs of other extragalactic sources that traverse the halo of M33, we conclude that the dense magnetized plasma resides in the host galaxy. The FRB exhibits frequency structure on two scales, one that is consistent with quenched Galactic scintillation and broader spectral structure with Δν ≈ 40 MHz. If the latter is due to scattering in the shared M33/M31 CGM, our results constrain the Local Group plasma environment. We found no accompanying persistent radio sources in the Apertif imaging survey data.
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