1,640 research outputs found
Astrophysical constraints on the proton-to-electron mass ratio with FAST
That the laws of physics are the same at all times and places throughout the
Universe is one of the basic assumptions of physics. Astronomical observations
provide the only means to test this basic assumption on cosmological time and
distance scales. The possibility of variations in the dimensionless physical
constant {\mu} - the proton-to-electron mass ratio, can be tested by comparing
astronomical measurements of the rest frequency of certain spectral lines at
radio wavelengths with laboratory determinations. Different types of molecular
transitions have different dependencies on {\mu} and so observations of two or
more spectral lines towards the same astronomical source can be used to test
whether there is any evidence for either temporal or spatial changes in the
physical fundamental constants. {\mu} will change if the relative strength of
the strong nuclear force compared to the electromagnetic force varies.
Theoretical studies have shown that the rotational transitions of some
molecules which have transitions in the frequency range that will be covered by
FAST (e.g., CH3OH, OH and CH) are sensitive to changes in {\mu}. A number of
studies looking for possible variations in {\mu} have been undertaken with
existing telescopes, however, the greater sensitivity of FAST means it will
open new opportunities to significantly improve upon measurements made to date.
In this paper, we discuss which molecular transitions and sources (both in the
Galaxy and external galaxies) are likely targets for providing improved
constraints on {\mu} with FAST
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
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
A New 95 GHz Methanol Maser Catalog: I. Data
The Purple Mountain Observatory 13.7 m radio telescope has been used to
search for 95 GHz (8--7A) class I methanol masers towards 1020
Bolocam Galactic Plane Survey (BGPS) sources, leading to 213 detections. We
have compared the line width of the methanol and HCO thermal emission in
all of the methanol detections and on that basis we find 205 of the 213
detections are very likely to be masers. This corresponds to an overall
detection rate of 95 GHz methanol masers towards our BGPS sample of 20%. Of the
205 detected masers 144 (70%) are new discoveries. Combining our results with
those of previous 95 GHz methanol masers searches, a total of four hundred and
eighty-one 95 GHz methanol masers are now known, we have compiled a catalog
listing the locations and properties of all known 95 GHz methanol masers.Comment: 18 pages, 7 figures, 8 tables, accepted for publication in ApJ
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
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