This work makes available a further of the GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey, covering half of the accessible galactic plane, across 20 frequency bands sampling 72-231MHz, with resolution 4-2arcmin. Unlike previous GLEAM data releases, we used multi-scale CLEAN to better deconvolve large-scale galactic structure. For the galactic longitude ranges 345{deg}<l<67{deg}, 180{deg}<l<240{deg}, we provide a compact source catalogue of 22037 components selected from a 60-MHz bandwidth image centred at 200MHz, with RMS noise ~-10-20mJy/beam and position accuracy better than 2-arcsec. The catalogue has a completeness of 50% at ~120mJy, and a reliability of 99.86%. It covers galactic latitudes 1{deg}<=|b|<=10{deg} towards the galactic centre and |b|<=10{deg} for other regions, and is available from Vizier; images covering |b|<=10{deg} for all longitudes are made available on the GLEAM Virtual Observatory (VO).server and SkyView.
We present the South Galactic Pole (SGP) data release from the GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey. These data combine both years of GLEAM observations at 72-231MHz conducted with the Murchison Widefield Array (MWA) and cover an area of 5,113 deg^2^ centred on the SGP at 20h40m<RA<05h04m and -48{deg}<Dec<-2{deg}. At 216MHz, the typical rms noise is ~5mJy/beam and the angular resolution ~2 arcmin. The source catalogue contains a total of 108851 components above 5{sigma}, of which 77 per cent have measured spectral indices between 72 and 231MHz. Improvements to the data reduction in this release include the use of the GLEAM Extragalactic catalogue as a sky model to calibrate the data, a more efficient and automated algorithm to deconvolve the snapshot images, and a more accurate primary beam model to correct the flux scale. This data release enables more sensitive large-scale studies of extragalactic source populations as well as spectral variability studies on a one-year timescale.
The GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) is a radio continuum survey at 76-227MHz of the entire southern sky (Declination <+30{deg}) with an angular resolution of ~2arcmin. In this paper, we combine GLEAM data with optical spectroscopy from the 6dF Galaxy Survey to construct a sample of 1,590 local (median z~0.064) radio sources with S_200MHz_>55mJy across an area of ~16700deg^2^. From the optical spectra, we identify the dominant physical process responsible for the radio emission from each galaxy: 73 per cent are fuelled by an active galactic nucleus (AGN) and 27 per cent by star formation. We present the local radio luminosity function for AGN and star-forming galaxies at 200MHz and characterise the typical radio spectra of these two populations between 76MHz and ~1GHz. For the AGN, the median spectral index between 200MHz and ~1GHz, {alpha}, is -0.600+/-0.010 (where S proportional to {nu}^{alpha}^) and the median spectral index within the GLEAM band, {alpha}_low_, is -0.704+/-0.011. For the star-forming galaxies, the median value of {alpha}_high_ is -0.650+/-0.010 and the median value of {alpha}_low_ is -0.596+/-0.015. Among the AGN population, flat-spectrum sources are more common at lower radio luminosity, suggesting the existence of a significant population of weak radio AGN that remain core-dominated even at low frequencies. However, around 4 per cent of local radio AGN have ultra-steep radio spectra at low frequencies ({alpha}_low_<-1.2). These ultra-steep-spectrum sources span a wide range in radio luminosity, and further work is needed to clarify their nature.
Nearly 200 hours of observing with the Murchison Widefield Array (MWA) radio telescope during the Galactic and Extra-galactic All-sky MWA (GLEAM) survey were used to assemble images of ionospheric structure. These images cover a nearly 50 degree-wide area on the sky at a cadence of 10 minutes over many 5-7 hours-long observing runs. They are generated by tracking the apparent motions of ~200-800 cosmic radio sources caused by changes in the transverse gradient of the ionospheric total electron content. Spectral analysis of these images revealed that the dataset was dominated by three distinct signatures. The first is consistent with field-aligned structures within the topside ionosphere/lower plasmasphere previously imaged with the MWA. The second are structures that are relatively large and aligned nearly east/west. Regional weather data implies that these are preferentially detected when there is a noticeable shear within the sub- tropical jet stream, which passes near the MWA. This suggests that this signature may be related to gravity waves launched by jet stream shear. The final signature is consistent with the properties of so-call electro-buoyancy waves that are known to occur at midlatitudes at night. Detections of these were more common when regional sporadic-E was present, supporting a proposed connection between these waves and polarization electric fields that may arise within sporadic-E. We discuss the implications for future observations with the Square Kilometer Array.
We study the atomic neutral hydrogen (HI) content of ~1600 galaxies up to z~0.1 using stacking techniques. The observations were carried out with the Westerbork Synthesis Radio Telescope (WSRT) in the area of the SDSS South Galactic Cap (SSGC), where we selected a galaxy sample from the SDSS spectroscopic catalog. Multi-wavelength information is provided by SDSS, NVSS, GALEX, and WISE. We use the collected information to study HI trends with color, star-forming, and active galactic nuclei (AGN) properties. Using near-UV (NUV)-r colors, galaxies are divided into blue cloud, green valley and red sequence galaxies.
We report on a study of the 2300-2600 {AA} Fe II/Fe II* multiplets in the rest-UV spectra of star-forming galaxies at 1.0<z<2.6 as probes of galactic-scale outflows. We extracted a mass-limited sample of 97 galaxies at z~1.0-2.6 from ultra-deep spectra obtained during the GMASS spectroscopic survey in the GOODS South field with the Very Large Telescope and FORS2. We obtain robust measures of the rest equivalent width of the Fe II absorption lines down to a limit of W_r_>1.5 {AA} and of the Fe II* emission lines to W_r_>0.5 {AA}. Whenever we can measure the systemic redshift of the galaxies from the [O II] emission line, we find that both the Fe II and Mg II absorption lines are blueshifted, indicating that both species trace gaseous outflows. We also find, however, that the Fe II gas has generally lower outflow velocity relative to that of Mg II. We investigate the variation of Fe II line profiles as a function of the radiative transfer properties of the lines, and find that transitions with higher oscillator strengths are more blueshifted in terms of both line centroids and line wings. We discuss the possibility that Fe II lines are suppressed by stellar absorptions. The lower velocities of the Fe II lines relative to the Mg II doublet, as well as the absence of spatially extended Fe II* emission in two-dimensional stacked spectra, suggest that most clouds responsible for Fe II absorption lie close (3~4 kpc) to the disks of galaxies. We show that the Fe II/Fe II* multiplets offer unique probes of the kinematic structure of galactic outflows.
We determine the global star formation rate (SFR) density at 0.7<z<1.9 using emission-line-selected galaxies identified in Hubble Space Telescope-Near Infrared Camera and Multi-Object Spectrograph (HST-NICMOS) grism spectroscopy observations. Observing in a pure parallel mode throughout HST Cycles 12 and 13, our survey covers ~104arcmin^2^ from which we select 80 galaxies with likely redshifted H{alpha} emission lines. In several cases, a somewhat weaker [OIII] doublet emission is also detected.
Fifty-seven nearby low surface brightness dwarf galaxies (-10>~M_V_>~-16) were searched for globular cluster candidates (GCCs) using Hubble Space Telescope WFPC2 imaging in V and I. The sample consists of 18 dwarf spheroidal (dSph), 36 irregular (dIrr), and 3 "transition" type (dIrr/dSph) galaxies with angular sizes less than 3.7kpc situated at distances 2-6Mpc in the field and in the nearby groups: M 81, Centaurus A, Sculptor, Canes Venatici I cloud.
We present Hubble Space Telescope/Advanced Camera for Surveys (HST/ACS) g and z photometry and half-light radii R_h_ measurements of 360 globular cluster (GC) candidates around the nearby S0 galaxy NGC 3115. We also include Subaru/Suprime-Cam g, r, and i photometry of 421 additional candidates. The well-established color bimodality of the GC system is obvious in the HST/ACS photometry. We find evidence for a "blue tilt" in the blue GC subpopulation, wherein the GCs in the blue subpopulation get redder as luminosity increases, indicative of a mass-metallicity relationship. We find a color gradient in both the red and blue subpopulations, with each group of clusters becoming bluer at larger distances from NGC 3115. The gradient is of similar strength in both subpopulations, but is monotonic and more significant for the blue clusters. On average, the blue clusters have ~10% larger R_h_than the red clusters. This average difference is less than is typically observed for early-type galaxies but does match that measured in the literature for the Sombrero Galaxy (M104), suggesting that morphology and inclination may affect the measured size difference between the red and blue clusters. However, the scatter on the R_h_ measurements is large. We also identify 31 clusters more extended than typical GCs, which we term ultra-compact dwarf (UCD) candidates. Many of these objects are actually considerably fainter than typical UCDs. While it is likely that a significant number will be background contaminants, six of these UCD candidates are spectroscopically confirmed as NGC 3115 members. To explore the prevalence of low-mass X-ray binaries in the GC system, we match our ACS and Suprime-Cam detections to corresponding Chandra X-ray sources. We identify 45 X-ray-GC matches: 16 among the blue subpopulation and 29 among the red subpopulation. These X-ray/GC coincidence fractions are larger than is typical for most GC systems, probably due to the increased depth of the X-ray data compared to previous studies of GC systems.
We aim to explore the relationship between globular cluster total number, N_GC_, and central black hole mass, M_*_, in spiral galaxies, and compare it with that recently reported for ellipticals. We present results for the Sbc galaxy NGC 4258, from Canada-France-Hawaii Telescope data. Thanks to water masers with Keplerian rotation in a circumnuclear disk, NGC 4258 has the most precisely measured extragalactic distance and supermassive black hole mass to date. The globular cluster (GC) candidate selection is based on the (u*-i') versus (i'-Ks) diagram, which is a superb tool to distinguish GCs from foreground stars, background galaxies, and young stellar clusters, and hence can provide the best number counts of GCs from photometry alone, virtually free of contamination, even if the Galaxy is not completely edge-on. The mean optical and optical-near-infrared colors of the clusters are consistent with those of the Milky Way and M 31, after extinction is taken into account. We directly identify 39 GC candidates; after completeness correction, GC luminosity function extrapolation, and correction for spatial coverage, we calculate a total N_GC_=144+/-31_-36_^+38^ (random and systematic uncertainties, respectively). We have thus increased to six the sample of spiral galaxies with measurements of both M_*_ and N_GC_. NGC 4258 has a specific frequency S_N_=0.4+/-0.1 (random uncertainty), and is consistent within 2{sigma} with the N_GC_ versus M_*_ correlation followed by elliptical galaxies. The Milky Way continues to be the only spiral that deviates significantly from the relation.