37 research outputs found
Detection of 84-GHz class I methanol maser emission towards NGC 253
We have investigated the central region of NGC 253 for the presence of
84.5-GHz (E) methanol emission using the Australia
Telescope Compact Array. We present the second detection of 84.5-GHz class~I
methanol maser emission outside the Milky Way. This maser emission is offset
from dynamical centre of NGC 253, in a region with previously detected emission
from class~I maser transitions (36.2-GHz E and 44.1-GHz
A methanol lines) . The emission features a narrow
linewidth (12 km s) with a luminosity approximately 5 orders of
magnitude higher than typical Galactic sources. We determine an integrated line
intensity ratio of between the 36.2 GHz and 84.5-GHz class I
methanol maser emission, which is similar to the ratio observed towards
Galactic sources. The three methanol maser transitions observed toward NGC 253
each show a different distribution, suggesting differing physical conditions
between the maser sites and that observations of additional class~I methanol
transitions will facilitate investigations of the maser pumping regime.Comment: Accepted into ApJL 12 October 2018. 10 pages, 3 Figures and 2 Table
Search for ionized jets towards high-mass young stellar objects
We are carrying out multi-frequency radio continuum observations, using the
Australia Telescope Compact Array, to systematically search for collimated
ionized jets towards high-mass young stellar objects (HMYSOs). Here we report
observations at 1.4, 2.4, 4.8 and 8.6 GHz, made with angular resolutions of
about 7, 4, 2, and 1 arcsec, respectively, towards six objects of a sample of
33 southern HMYSOs thought to be in very early stages of evolution. The objects
in the sample were selected from radio and infrared catalogs by having positive
radio spectral indices and being luminous (L_bol > 20,000 L_sun), but
underluminous in radio emission compared to that expected from its bolometric
luminosity. This criteria makes the radio sources good candidates for being
ionized jets. As part of this systematic search, two ionized jets have been
discovered: one previously published and the other reported here. The rest of
the observed candidates correspond to three hypercompact hii regions and two
ultracompact hii regions. The two jets discovered are associated with two of
the most luminous (70,000 and 100,000 Lsun) HMYSOs known to harbor this type of
objects, showing that the phenomena of collimated ionized winds appears in the
formation process of stars at least up to masses of ~ 20 M_sun and provides
strong evidence for a disk-mediated accretion scenario for the formation of
high-mass stars. From the incidence of jets in our sample, we estimate that the
jet phase in high-mass protostars lasts for 40,000 yr.Comment: Accepted for publication in the Astrophysical Journal. (53 pages, 22
Figures) (Color figures were degraded to comply with arXiv requirements
MALT-45: A 7mm survey of the southern Galaxy - II. ATCA follow-up observations of 44GHz class I methanol masers
We detail interferometric observations of 44 GHz class I methanol masers detected by MALT-45 (a 7 mm unbiased auto-correlated spectral-line Galactic-plane survey) using the Australia Telescope Compact Array. We detect 238 maser spots across 77 maser sites. Using high-resolution positions, we compare the class I CH3OH masers to other star formation maser species, including CS (1–0), SiO v = 0 and the H53 α radio-recombination line. Comparison between the cross- and auto-correlated data has allowed us to also identify quasi-thermal emission in the 44 GHz class I methanol maser line. We find that the majority of class I methanol masers have small spatial and velocity ranges (<0.5 pc and <5 km s−1), and closely trace the systemic velocities of associated clouds. Using 870 μm dust continuum emission from the ATLASGAL survey, we determine clump masses associated with class I masers, and find that they are generally associated with clumps between 1000 and 3000 M⊙. For each class I methanol maser site, we use the presence of OH masers and radio recombination lines to identify relatively evolved regions of high-mass star formation; we find that maser sites without these associations have lower luminosities and preferentially appear towards dark infrared regions
WALLABY Early Science - I. The NGC 7162 Galaxy Group
We present Widefield ASKAP L-band Legacy All-sky Blind Survey (WALLABY) early
science results from the Australian Square Kilometre Array Pathfinder (ASKAP)
observations of the NGC 7162 galaxy group. We use archival HIPASS and Australia
Telescope Compact Array (ATCA) observations of this group to validate the new
ASKAP data and the data reduction pipeline ASKAPsoft. We detect six galaxies in
the neutral hydrogen (HI) 21-cm line, expanding the NGC 7162 group membership
from four to seven galaxies. Two of the new detections are also the first HI
detections of the dwarf galaxies, AM 2159-434 and GALEXASC J220338.65-431128.7,
for which we have measured velocities of and km s,
respectively. We confirm that there is extended HI emission around NGC 7162
possibly due to past interactions in the group as indicated by the
offset between the kinematic and morphological major axes for NGC 7162A, and
its HI richness. Taking advantage of the increased resolution (factor of
) of the ASKAP data over archival ATCA observations, we fit a tilted
ring model and use envelope tracing to determine the galaxies' rotation curves.
Using these we estimate the dynamical masses and find, as expected, high dark
matter fractions of for all group members. The
ASKAP data are publicly available.Comment: 20 pages, 11 figures, accepted for publication in MNRA
MALT-45: a 7 mm survey of the southern Galaxy - I. Techniques and spectral line data
We present the first results from the MALT-45 (Millimetre Astronomer's Legacy Team-45 GHz) Galactic Plane survey. We have observed 5 square degrees (l = 330°–335°, b = ±0 ∘ . 5) for spectral lines in the 7 mm band (42–44 and 48–49 GHz), including CS (1–0), class I CH3OH masers in the 7(0,7)–6(1,6) A+ transition and SiO (1–0) v = 0, 1, 2, 3. MALT-45 is the first unbiased, large-scale, sensitive spectral line survey in this frequency range. In this paper, we present data from the survey as well as a few intriguing results; rigorous analyses of these science cases are reserved for future publications. Across the survey region, we detected 77 class I CH3OH masers, of which 58 are new detections, along with many sites of thermal and maser SiO emission and thermal CS. We found that 35 class I CH3OH masers were associated with the published locations of class II CH3OH, H2O and OH masers but 42 have no known masers within 60 arcsec. We compared the MALT-45 CS with NH3 (1,1) to reveal regions of CS depletion and high opacity, as well as evolved star-forming regions with a high ratio of CS to NH3. All SiO masers are new detections, and appear to be associated with evolved stars from the Spitzer Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE). Generally, within SiO regions of multiple vibrational modes, the intensity decreases as v = 1, 2, 3, but there are a few exceptions where v = 2 is stronger than v = 1
Deep ATLAS radio observations of the CDFS-SWIRE field
We present the first results from the Australia Telescope Large Area Survey
(ATLAS), which consist of deep radio observations of a 3.7 square degree field
surrounding the Chandra Deep Field South, largely coincident with the infrared
Spitzer Wide-Area Extragalactic (SWIRE) Survey. We also list
cross-identifications to infrared and optical photometry data from SWIRE, and
ground-based optical spectroscopy. A total of 784 radio components are
identified, corresponding to 726 distinct radio sources, nearly all of which
are identified with SWIRE sources. Of the radio sources with measured
redshifts, most lie in the redshift range 0.5-2, and include both star-forming
galaxies and active galactic nuclei (AGN). We identify a rare population of
infrared-faint radio sources which are bright at radio wavelengths but are not
seen in the available optical, infrared, or X-ray data. Such rare classes of
sources can only be discovered in wide, deep surveys such as this.Comment: Accepted by A