25 research outputs found
SiO Outflows as Tracers of Massive Star Formation in Infrared Dark Clouds
To study the early phases of massive star formation, we present ALMA
observations of SiO(5-4) emission and VLA observations of 6 cm continuum
emission towards 32 Infrared Dark Cloud (IRDC) clumps, spatially resolved down
to pc. Out of the 32 clumps, we detect SiO emission in 20
clumps, and in 11 of them the SiO emission is relatively strong and likely
tracing protostellar outflows. Some SiO outflows are collimated, while others
are less ordered. For the six strongest SiO outflows, we estimate basic outflow
properties. In our entire sample, where there is SiO emission, we find 1.3 mm
continuum and infrared emission nearby, but not vice versa. We build the
spectral energy distributions (SEDs) of cores with 1.3 mm continuum emission
and fit them with radiative transfer (RT) models. The low luminosities and
stellar masses returned by SED fitting suggest these are early stage
protostars. We see a slight trend of increasing SiO line luminosity with
bolometric luminosity, which suggests more powerful shocks in the vicinity of
more massive YSOs. We do not see a clear relation between the SiO luminosity
and the evolutionary stage indicated by . We conclude that as a protostar
approaches a bolometric luminosity of , the shocks in
the outflow are generally strong enough to form SiO emission. The VLA 6 cm
observations toward the 15 clumps with the strongest SiO emission detect
emission in four clumps, which is likely shock ionized jets associated with the
more massive ones of these protostellar cores.Comment: 42 pages, 18 figures, accepted to Ap
Discovery of a Photoionized Bipolar Outflow towards the Massive Protostar G45.47+0.05
Massive protostars generate strong radiation feedback, which may help set the
mass they achieve by the end of the accretion process. Studying such feedback
is therefore crucial for understanding the formation of massive stars. We
report the discovery of a photoionized bipolar outflow towards the massive
protostar G45.47+0.05 using high-resolution observations at 1.3 mm with the
Atacama Large Millimeter/Submillimeter Array (ALMA) and at 7 mm with the Karl
G. Jansky Very Large Array (VLA). By modeling the free-free continuum, the
ionized outflow is found to be a photoevaporation flow with an electron
temperature of 10,000 K and an electron number density of ~1.5x10^7 cm^-3 at
the center, launched from a disk of radius of 110 au. H30alpha hydrogen
recombination line emission shows strong maser amplification, with G45 being
one of very few sources to show such millimeter recombination line masers. The
mass of the driving source is estimated to be 30-50 Msun based on the derived
ionizing photon rate, or 30-40 Msun based on the H30alpha kinematics. The
kinematics of the photoevaporated material is dominated by rotation close to
the disk plane, while accelerated to outflowing motion above the disk plane.
The mass loss rate of the photoevaporation outflow is estimated to be
~(2-3.5)x10^-5 Msun/yr. We also found hints of a possible jet embedded inside
the wide-angle ionized outflow with non-thermal emissions. The possible
co-existence of a jet and a massive photoevaporation outflow suggests that, in
spite of the strong photoionization feedback, accretion is still on-going.Comment: Accepted to ApJL. 16 pages, 5 figures, 3 appendix figure
The White Mountain Polarimeter Telescope and an Upper Limit on CMB Polarization
The White Mountain Polarimeter (WMPol) is a dedicated ground-based microwave
telescope and receiver system for observing polarization of the Cosmic
Microwave Background. WMPol is located at an altitude of 3880 meters on a
plateau in the White Mountains of Eastern California, USA, at the Barcroft
Facility of the University of California White Mountain Research Station.
Presented here is a description of the instrument and the data collected during
April through October 2004. We set an upper limit on -mode polarization of
14 (95% confidence limit) in the multipole range
. This result was obtained with 422 hours of observations of a 3
sky area about the North Celestial Pole, using a 42 GHz
polarimeter. This upper limit is consistent with polarization predicted
from a standard -CDM concordance model.Comment: 35 pages. 12 figures. To appear in ApJ
The Evolutionary Map of the Universe Pilot Survey
We present the data and initial results from the first pilot survey of the Evolutionary Map of the Universe (EMU), observed at 944 MHz with the Australian Square Kilometre Array Pathfinder (ASKAP) telescope. The survey covers 270 deg2 of an area covered by the Dark Energy Survey, reaching a depth of 25–30 μJy beam−1 rms at a spatial resolution of ∼11–18 arcsec, resulting in a catalogue of ∼220 000 sources, of which ∼180 000 are single-component sources. Here we present the catalogue of single-component sources, together with (where available) optical and infrared cross-identifications, classifications, and redshifts. This survey explores a new region of parameter space compared to
previous surveys. Specifically, the EMU Pilot Survey has a high density of sources, and also a high sensitivity to low surface brightness emission. These properties result in the detection of types of sources that were rarely seen in or absent from previous surveys. We present some of these new results here
Localization and broadband follow-up of the gravitational-wave transient GW 150914
A gravitational-wave (GW) transient was identified in data recorded by the Advanced Laser Interferometer Gravitational-wave Observatory (LIGO) detectors on 2015 September 14. The event, initially designated G184098 and later given the name GW150914, is described in detail elsewhere. By prior arrangement, preliminary estimates of the time, significance, and sky location of the event were shared with 63 teams of observers covering radio, optical, near-infrared, X-ray, and gamma-ray wavelengths with ground- and space-based facilities. In this Letter we describe the low-latency analysis of the GW data and present the sky localization of the first observed compact binary merger. We summarize the follow-up observations reported by 25 teams via private Gamma-ray Coordinates Network circulars, giving an overview of the participating facilities, the GW sky localization coverage, the timeline, and depth of the observations. As this event turned out to be a binary black hole merger, there is little expectation of a detectable electromagnetic (EM) signature. Nevertheless, this first broadband campaign to search for a counterpart of an Advanced LIGO source represents a milestone and highlights the broad capabilities of the transient astronomy community and the observing strategies that have been developed to pursue neutron star binary merger events. Detailed investigations of the EM data and results of the EM follow-up campaign are being disseminated in papers by the individual teams
The EMU view of the Large Magellanic Cloud: Troubles for sub-TeV WIMPs
We present a radio search for WIMP dark matter in the Large Magellanic Cloud
(LMC). We make use of a recent deep image of the LMC obtained from observations
of the Australian Square Kilometre Array Pathfinder (ASKAP), and processed as
part of the Evolutionary Map of the Universe (EMU) survey. LMC is an extremely
promising target for WIMP searches at radio frequencies because of the large
J-factor and the presence of a substantial magnetic field. We detect no
evidence for emission arising from WIMP annihilations and derive stringent
bounds on the annihilation rate as a function of the WIMP mass, for different
annihilation channels. This work excludes the thermal cross section for masses
below 480 GeV and annihilation into quarks.Comment: 23 pages, 14 figures. v2: presentation improved, discussion expanded,
accepted for publication in JCA
Multiwavelength view of SPT-CL J2106-5844
Context. SPT-CL J2106-5844 is among the most massive galaxy clusters at z > 1 yet discovered. While initially used in cosmological tests to assess the compatibility with Λ Cold Dark Matter cosmology of such a massive virialized object at this redshift, more recent studies indicate SPT-CL J2106-5844 is undergoing a major merger and is not an isolated system with a singular, well-defined halo.
Aims. We use sensitive, high spatial resolution measurements from the Atacama Large Millimeter/Submillimeter Array (ALMA) and Atacama Compact Array (ACA) of the thermal Sunyaev-Zeldovich (SZ) effect to reconstruct the pressure distribution of the intracluster medium in this system. These measurements are coupled with radio observations from the pilot survey for the Evolutionary Map of the Universe, using the Australian Square Kilometre Array Pathfinder (ASKAP), and the Australia Telescope Compact Array (ATCA) to search for diffuse nonthermal emission. Further, to better constrain the thermodynamic structure of the cluster, we complement our analysis with reprocessed archival Chandra observations.
Methods. We jointly fit the ALMA and ACA SZ data in uv-space using a Bayesian forward modeling technique. The ASKAP and low-frequency ATCA data are processed and imaged to specifically highlight any potential diffuse radio emission.
Results. In the ALMA and ACA SZ data, we reliably identify at high significance two main gas components associated with the mass clumps inferred from weak lensing. Our statistical test excludes at the ∼9.9σ level the possibility of describing the system with a single SZ component. While the components had been more difficult to identify in the X-ray data alone, we find that the bimodal gas distribution is supported by the X-ray hardness distribution. The EMU radio observations reveal a diffuse radio structure ∼400 kpc in projected extent along the northwest-southeast direction, indicative of strong activity from the active galactic nucleus within the brightest cluster galaxy. Interestingly, a putative optical star-forming filamentary structure detected in the HST image is in an excellent alignment with the radio structure, albeit on a smaller scale