43 research outputs found
Detection of HCN maser emission in NGC253
We report the detection of maser emission from the transition of
HCN at 36.4~GHz towards the nearby starburst galaxy NGC253. This is the
first detection of maser emission from this transition in either a Galactic or
extragalactic source. The HCN maser emission has a brightness temperature
in excess of 2500 K and is offset from the center of the galaxy by
approximately 18 arcsec (300 pc), but close to a previously reported class~I
methanol maser. Both the HCN and methanol masers appear to arise near the
interface between the galactic bar and the central molecular zone, where it is
thought that molecular gas is being transported inwards, producing a region of
extensive low-velocity shocks.Comment: Accepted for publication in ApJ Letters, 7 pages, 3 figure
The first high-resolution observations of 37.7-, 38.3- and 38.5-GHz methanol masers
We have used the Australia Telescope Compact Array (ATCA) to undertake the
first high angular resolution observations of 37.7-GHz ()
methanol masers towards a sample of eleven high-mass star formation regions
which host strong 6.7-GHz methanol masers. The 37.7-GHz methanol sites are
coincident to within the astrometric uncertainty (0.4 arcseconds) with the
6.7-GHz methanol masers associated with the same star formation region.
However, spatial and spectral comparison of the 6.7- and 37.7-GHz maser
emission within individual sources shows that the 37.7-GHz masers are less
often, or to a lesser degree co-spatial than are the 12.2-GHz and 6.7-GHz
masers. We also made sensitive, high angular resolution observations of the
38.3- and 38.5-GHz class II methanol transitions ( and
, respectively) and the 36.2-GHz () class
I methanol transition towards the same sample of eleven sources. The 37.7-,
38.3- and 38.5-GHz methanol masers are unresolved in the current observations,
which implies a lower limit on the brightness temperature of the strongest
masers of more than K. We detected the 38.3-GHz methanol transition
towards 7 sources, 5 of which are new detections and detected the 38.5-GHz
transition towards 6 sources, 4 of which are new detections. We detected
36.2-GHz class I methanol masers towards all eleven sources, 6 of these are new
detections for this transition, of which 4 sources do not have previously
reported class I methanol masers from any transition.Comment: Accepted for publication in MNRAS, 34 pages, 20 figure
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
Detection of a methanol megamaser in a major-merger galaxy
We have detected emission from both the 4_{-1}-3_{0} E (36.2~GHz) class I and
7_{-2}-8_{-1} E (37.7~GHz) class II methanol transitions towards the centre of
the closest ultra-luminous infrared galaxy Arp 220. The emission in both the
methanol transitions show narrow spectral features and have luminosities
approximately 8 orders of magnitude stronger than that observed from typical
class I methanol masers observed in Galactic star formation regions. The
emission is also orders of magnitude stronger than the expected intensity of
thermal emission from these transitions and based on these findings we suggest
that the emission from the two transitions are masers. These observations
provides the first detection of a methanol megamaser in the 36.2 and 37.7 GHz
transitions and represents only the second detection of a methanol megamaser,
following the recent report of an 84 GHz methanol megamaser in NGC1068. We find
the methanol megamasers are significantly offset from the nuclear region and
arise towards regions where there is Ha emission, suggesting that it is
associated with starburst activity. The high degree of correlation between the
spatial distribution of the 36.2 GHz methanol and X-ray plume emission suggests
that the production of strong extragalactic class I methanol masers is related
to galactic outflow driven shocks and perhaps cosmic rays. In contrast to OH
and H2O megamasers which originate close to the nucleus, methanol megamasers
provide a new probe of feedback (e.g. outflows) processes on larger-scales and
of star formation beyond the circumnuclear starburst regions of active
galaxies.Comment: Accepted for publication in ApJ
The Carina Nebula and Gum 31 molecular complex: II. The distribution of the atomic gas revealed in unprecedented detail
We report high spatial resolution observations of the HI 21cm line in the
Carina Nebula and the Gum 31 region obtained with the Australia Telescope
Compact Array. The observations covered 12 deg centred on , achieving an angular resolution of 35
arcseconds. The HI map revealed complex filamentary structures across a wide
range of velocities. Several "bubbles" are clearly identified in the Carina
Nebula Complex, produced by the impact of the massive star clusters located in
this region. An HI absorption profile obtained towards the strong extragalactic
radio source PMN J1032--5917 showed the distribution of the cold component of
the atomic gas along the Galactic disk, with the Sagittarius-Carina and Perseus
spiral arms clearly distinguishable. Preliminary calculations of the optical
depth and spin temperatures of the cold atomic gas show that the HI line is
opaque ( 2) at several velocities in the Sagittarius-Carina
spiral arm. The spin temperature is K in the regions with the highest
optical depth, although this value might be lower for the saturated components.
The atomic mass budget of Gum 31 is of the total gas mass. HI self
absorption features have molecular counterparts and good spatial correlation
with the regions of cold dust as traced by the infrared maps. We suggest that
in Gum 31 regions of cold temperature and high density are where the atomic to
molecular gas phase transition is likely to be occurring.Comment: 20 pages, 1 table, 16 Figures, Accepted for Publication in the
Monthly Notices of the Royal Astronomical Society Journa