A comprehensive archive of Australian rainfall and climate data has been constructed from ground-based observational data. Continuous, daily time step records have been constructed using spatial ...interpolation algorithms to estimate missing data. Datasets have been constructed for daily rainfall, maximum and minimum temperatures, evaporation, solar radiation and vapour pressure. Datasets are available for approximately 4600 locations across Australia, commencing in 1890 for rainfall and 1957 for climate variables. The datasets can be accessed on the Internet at http://www.dnr.qld.gov.au/silo. Interpolated surfaces have been computed on a regular 0.05° grid extending from latitude 10°S to 44°S and longitude 112°E to 154°E. A thin plate smoothing spline was used to interpolate daily climate variables, and ordinary kriging was used to interpolate daily and monthly rainfall. Independent cross validation has been used to analyse the temporal and spatial error of the interpolated data. An Internet based facility has been developed which allows database clients to interrogate the gridded surfaces at any desired location.
Aims. The aim is to investigate the star-formation and LINER (low ionization nuclear emission line region) activity within the central kiloparsec of the galaxy NGC 1614. In this paper the radio ...continuum morphology, which provides a tracer of both nuclear and star-formation activity, and the distribution and dynamics of the cold molecular and atomic gas feeding this activity, are studied. In particular, the nature of an R ≈ 300 pc nuclear ring of star-formation and its relationship to the LINER activity in NGC 1614 is addressed. Methods. A high angular resolution, multi-wavelength study of the LINER galaxy NGC 1614 has been performed. Deep observations of the CO 1–0 spectral line were performed using the Owens Valley Radio Observatory (OVRO). These data have been complemented by extensive multi-frequency radio continuum and Hi absorption observations using the Very Large Array (VLA) and Multi-Element Radio Linked Interferometer Network (MERLIN). Results. Toward the center of NGC 1614, we have detected a ring of radio continuum emission with a radius of 300 pc. This ring is coincident with previous radio and Paα observations. The dynamical mass of the ring based on Hi absorption is 3.1 × 109 $M_{\odot}$. The peak of the integrated CO 1–0 emission is shifted by 1” to the north-west of the ring center. An upper limit to the molecular gas mass in the ring region is ~1.7 × 109 $M_{\odot}$. Inside the ring, there is a north to south elongated 1.4 GHz radio continuum feature, with a nuclear peak. This peak is also seen in the 5 GHz radio continuum and in the CO. Conclusions. We suggest that the R = 300 pc star forming ring represents the radius of a dynamical resonance – as an alternative to the scenario that the starburst is propagating outwards from the center into a molecular ring. The ring-like appearance is probably part of a spiral structure. Substantial amounts of molecular gas have passed the radius of the ring and reached the nuclear region. The nuclear peak seen in 5 GHz radio continuum and CO is likely related to previous star formation, where all molecular gas was not consumed. The LINER-like optical spectrum observed in NGC 1614 may be due to nuclear starburst activity, and not to an active galactic nucleus (AGN). Although the presence of an AGN cannot be excluded.
ABSTRACT
A key characteristic of many active galactic nuclei (AGNs) is their variability, but its origin is poorly understood, especially in the radio domain. Williams et al. (2017) reported a ...∼50 per cent increase in peak flux density of the AGN in the Seyfert galaxy NGC 4151 at 1.5 GHz with the e-MERLIN array. We present new high-resolution e-MERLIN observations at 5 GHz and compare these to archival MERLIN observations to investigate the reported variability. Our new observations allow us to probe the nuclear region at a factor three times higher resolution than the previous e-MERLIN study. We separate the core component, C4, into three separate components: C4W, C4E, and X. The AGN is thought to reside in component C4W, but this component has remained constant between epochs within uncertainties. However, we find that the Eastern-most component, C4E, has increased in peak flux density from 19.35 ± 1.10 to 37.09 ± 1.86 mJy beam−1, representing an 8.2σ increase on the MERLIN observations. We attribute this peak flux density increase to continue interaction between the jet and the emission line region (ELR), observed for the first time in a low-luminosity AGNs such as NGC 4151. We identify discrete resolved components at 5 GHz along the jet axis, which we interpret as areas of jet–ELR interaction.
The galaxy NGC 4418 contains one of the most compact obscured nuclei within a luminous infrared galaxy (LIRG) in the nearby Universe. This nucleus contains a rich molecular gas environment and an ...unusually high ratio of infrared-to-radio luminosity. The compact nucleus is powered by either a compact starburst or an active galactic nucleus (AGN). The aim of this study is to constrain the nature of the nuclear region (starburst or AGN) within NGC 4418 via very high-resolution radio imaging. Brightness temperatures >10sup 4.8 K indicate that these compact features cannot be HII-regions. The compact features could be super star clusters with intense star formation, and their associated free-free absorption could then naturally explain both their inverted radio spectrum and the low radio-to-IR ratio of the nucleus. The required star formation area density is extreme, however, and close to the limit of what can be observed in a well-mixed thermal/non-thermal plasma produced by star formation, and is also close to the limit of what can be physically sustained.
We present the results from multi-wavelength observations of a transient discovered during an intensive follow-up campaign of S191213g, a gravitational wave (GW) event reported by the LIGO-Virgo ...Collaboration as a possible binary neutron star merger in a low latency search. This search yielded SN 2019wxt, a young transient in a galaxy whose sky position (in the 80% GW contour) and distance (∼150 Mpc) were plausibly compatible with the localisation uncertainty of the GW event. Initially, the transient’s tightly constrained age, its relatively faint peak magnitude (
M
i
∼ −16.7 mag), and the
r
-band decline rate of ∼1 mag per 5 days appeared suggestive of a compact binary merger. However, SN 2019wxt spectroscopically resembled a type Ib supernova, and analysis of the optical-near-infrared evolution rapidly led to the conclusion that while it could not be associated with S191213g, it nevertheless represented an extreme outcome of stellar evolution. By modelling the light curve, we estimated an ejecta mass of only ∼0.1
M
⊙
, with
56
Ni comprising ∼20% of this. We were broadly able to reproduce its spectral evolution with a composition dominated by helium and oxygen, with trace amounts of calcium. We considered various progenitor channels that could give rise to the observed properties of SN 2019wxt and concluded that an ultra-stripped origin in a binary system is the most likely explanation. Disentangling genuine electromagnetic counterparts to GW events from transients such as SN 2019wxt soon after discovery is challenging: in a bid to characterise this level of contamination, we estimated the rate of events with a volumetric rate density comparable to that of SN 2019wxt and found that around one such event per week can occur within the typical GW localisation area of O4 alerts out to a luminosity distance of 500 Mpc, beyond which it would become fainter than the typical depth of current electromagnetic follow-up campaigns.
We present observations made with the Australia Telescope Compact Array (ATCA), the Jansky Very Large Array (JVLA) and the Giant Metre-Wave Telescope of the radio source within the galaxy WISE ...J071634.59-190039.2, claimed to be host of FRB 150418 by Keane et al. We have established a common flux density scale between the ATCA and JVLA observations, the main result of which is to increase the flux densities obtained by Keane et al. At a frequency of 5.5 GHz, the source has a mean flux density of 140 mu Jy and is variable on short time-scales with a modulation index of 0.36. Statistical analysis of the flux densities shows that the variations seen are consistent with the refractive interstellar scintillation of the weak active galactic nucleus at the centre of the galaxy. It may therefore be the case that the fast radio burst (FRB) and the galaxy are not associated. However, taking into account the rarity of highly variable sources in the radio sky, and our lack of knowledge of the progenitors of FRBs as a class, the association between WISE J071634.59-190039.2 and FRB 150418 remains a possibility.
We present interferometric CO observations of 12 z∼ 2 submillimetre-faint, star-forming radio galaxies (SFRGs) which are thought to be ultraluminous infrared galaxies (ULIRGs) possibly dominated by ...warmer dust (T
dust ≳ 40 K) than submillimetre galaxies (SMGs) of similar luminosities. Four other CO-observed SFRGs are included from the literature, and all the observations are taken at the Plateau de Bure Interferometer (PdBI) in the compact configuration. 10 of the 16 SFRGs observed in CO (63 per cent) are detected at >4σ with a mean inferred molecular gas mass of ∼2 × 1010 M⊙. SFRGs trend slightly above the local ULIRG L
FIR-L′CO relation. Since SFRGs are about two times fainter in radio luminosity but exhibit similar CO luminosities to SMGs, this suggests SFRGs are slightly more efficient star formers than SMGs at the same redshifts. SFRGs also have a narrow mean CO linewidth, 320 ± 80 km s−1. Many SMGs have similarly narrow CO linewidths, but very broad features (∼900 km s−1) are present in a few SMGs and are absent from SFRGs. SFRGs bridge the gap between properties of very luminous >5 × 1012 L⊙ SMGs and those of local ULIRGs, and are consistent with intermediate-stage major mergers. We suspect that more moderate luminosity SMGs, not yet surveyed in CO, would show similar molecular gas properties to SFRGs. The active galactic nucleus (AGN) fraction of SFRGs is consistent with SMGs and is estimated to be 0.3 ± 0.1, suggesting that SFRGs are observed near the peak phase of star formation activity and not in a later, post-SMG enhanced AGN phase. The excitation analysis of one SFRG is consistent with the CO excitation observed in SMGs turning over beyond 12CO(J= 4→3). This CO survey of SFRGs serves as a pilot project for the much more extensive survey of Herschel and SCUBA-2 selected sources which only partially overlap with SMGs. Better constraints on the CO properties of a diverse high-z ULIRG population are needed from ALMA to determine the evolutionary origin of extreme starbursts, and what role ULIRGs serve in catalyzing the formation of massive stellar systems in the early Universe.
We present high spatial resolution (0.4 arcsec, approximately equal to 3.5 kpc) Plateau de Bure Interferometer interferometric data on three ultraluminous infrared galaxies (ULIRGs) at z similar to ...2: two submillimetre galaxies (SMGs) and one submillimetre faint star-forming radio galaxy. The three galaxies have been robustly detected in CO rotational transitions, either 12CO (J = 4 arrow right 3) or 12CO (J = 3 arrow right 2), allowing their sizes and gas masses to be accurately constrained. These are the highest spatial resolution observations observed to date (by a factor of 62) for intermediate-excitation CO emission in z similar to 2 ULIRGs. The galaxies appear extended over several resolution elements, having a mean radius of 3.7 kpc. High-resolution (0.3 arcsec) combined Multi-Element Radio-Linked Interferometer Network-Very Large Array observations of their radio continua allow an analysis of the star formation behaviour of these galaxies, on comparable spatial scales to those of the CO observations. This 'matched beam' approach sheds light on the spatial distribution of both molecular gas and star formation, and we can therefore calculate accurate star formation rates and gas surface densities: this allows us to place the three systems in the context of a Kennicutt-Schmidt (KS)-style star formation law. We find a difference in size between the CO and radio emission regions, and as such we suggest that using the spatial extent of the CO emission region to estimate the surface density of star formation may lead to error. This size difference also causes the star formation efficiencies within systems to vary by up to a factor of 5. We also find, with our new accurate sizes, that SMGs lie significantly above the KS relation, indicating that stars are formed more efficiently in these extreme systems than in other high-z star-forming galaxies.
ABSTRACT
The results of an extremely deep, 8‐d long observation of the central kpc of the nearby starburst galaxy M82 using Multi‐Element Radio Linked Interferometer Network (MERLIN) at 5 GHz are ...presented. The 17 μJy beam−1 rms noise level in the naturally weighted image makes it the most sensitive high‐resolution radio image of M82 made to date. Over 50 discrete sources are detected, the majority of which are supernova remnants, but with 13 identified as H ii regions. Sizes, flux densities and radio brightnesses are given for all of the detected sources, which are all well resolved with a majority showing shell or partial shell structures. Those sources within the sample which are supernova remnants have diameters ranging from 0.3 to 6.7 pc, with a mean size of 2.9 pc.
From a comparison with previous MERLIN 5‐GHz observations made in 1992 July, which gives a 9.75‐yr timeline, it has been possible to measure the expansion velocities of 10 of the more compact sources, eight of which have not been measured before. These derived expansion velocities range between 2200 and 10 500 km s−1.
RC J0311+0507 is one of the most luminous objects in the high-redshift Universe having L ≥ 3 × 1029 W Hz−1 at a 500 MHz rest frequency. A very steep radio spectrum and an indication of a ...Fanaroff-Riley type II (FR II) structure from early Very Large Array (VLA) maps suggested the presence of a supermassive black hole inside the parent galaxy. Multi-Element Radio-Linked Interferometer Network and European Very Long Baseline Interferometer Network maps (intensity and polarization) of this object at 1.7 and 5 GHz with an order of magnitude better resolution than that of the VLA are presented. Also included are further optical observations with the Russian 6-m telescope and infrared K-band observations with the United Kingdom Infra-Red Telescope, which indicate the object to be a galaxy. The new radio observations now confirm the source's structure to be that of an FR II, but with a high degree of asymmetry in the flux densities of the source components.
PDF
