Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userThe Zeeman Effect in the 44 GHz Class I Methanol Maser Line toward DR21(OH)
155
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We report the detection of the Zeeman effect in the 44 GHz Class I methanol maser line toward the star forming region DR21(OH). In a 219 Jy/beam maser centered at an LSR velocity of 0.83 km s$^{-1}$, we find a 20-$sigma$ detection of $zB_{text{los}} = 53.5 pm 2.7$ Hz. If 44 GHz methanol masers are excited at $n sim 10^{7-8}$ cm$^{-3}$, then the $B~vs.~n^{1/2}$ relation would imply from comparison with Zeeman effect detections in the CN($1-0$) line toward DR21(OH) that magnetic fields traced by 44 GHz methanol masers in DR21(OH) should be $sim$10 mG. Together with our detected $zB_{text{los}} = 53.5$ Hz, this would imply that the value of the 44 GHz methanol Zeeman splitting factor $z$ is $sim$5 Hz mG$^{-1}$. Such small values of $z$ would not be a surprise, as the methanol molecule is non paramagnetic, like H$_2$O. Empirical attempts to determine $z$, as demonstrated, are important because currently there are no laboratory measurements or theoretically calculated values of $z$ for the 44 GHz methanol transition. Data from observations of a larger number of sources are needed to make such empirical determinations robust.
rate research
Read More
We report the detection of the Zeeman effect in the 44 GHz Class I methanol maser line toward the high mass star forming region DR21W. There are two prominent maser spots in DR21W at the ends of a northwest-southeast linear arrangement. For the maser at the northwestern end (maser A), we fit three Gaussian components. In the strongest component, we obtain a significant Zeeman detection, with $zB_{rm los}=-23.4pm3.2$ Hz. If we use $z=-0.920$ Hz mG$^{-1}$ for the $F=5 rightarrow 4$ hyperfine transition, this corresponds to a magnetic field $|B_{rm los}|=25.4$ mG; $B_{rm los}$ would be higher if a different hyperfine was responsible for the 44 GHz maser, but our results also rule out some hyperfines, since fields in these regions cannot be hundreds of mG. Class I methanol masers form in outflows where shocks compress magnetic fields in proportion to gas density. Designating our detected $B_{rm los}=25$ mG as the magnetic field in the post-shock gas, we find that $B_{rm los}$ in the pre-shock gas should be 0.1-0.8 mG. Although there are no thermal-line Zeeman detections toward DR21W, such values are in good agreement with Zeeman measurements in the CN thermal line of 0.36 and 0.71 mG about $3.5$ away in DR21(OH) in gas of comparable density to the pre-shock gas density in DR21W. Comparison of our derived magnetic energy density to the kinetic energy density in DR21W indicates that magnetic fields likely play a significant role in shaping the dynamics of the post-shocked gas in DR21W.
We present a second epoch of observations of the 44 GHz Class I methanol maser line toward the star forming region OMC-2. The observations were carried out with the Very Large Array, and constitute one of the first successful Zeeman effect detections with the new WIDAR correlator. Comparing to the result of our earlier epoch of data for this region, we find that the intensity of the maser increased by 50%, but the magnetic field value has stayed the same, within the errors. This suggests that the methanol maser may be tracing the large-scale magnetic field that is not affected by the bulk gas motions or turbulence on smaller scales that is causing the change in maser intensity.
We have used the Australia Telescope Compact Array (ATCA) to search for emission from the $4_{-1} rightarrow 3_{0}E$ transition of methanol (36.2 GHz) towards the center of the nearby starburst galaxy NGC253. Two regions of emission were detected, offset from the nucleus along the same position angle as the inner spiral arms. The emission is largely unresolved on a scale of 5 arcsec, has a full-width half maximum (FWHM) line width of < 30 km s$^{-1}$, and an isotropic luminosity orders of magnitude larger than that observed in any Galactic star formation regions. These characteristics suggest that the 36.2 GHz methanol emission is most likely a maser, although observations with higher angular and spectral resolution are required to confirm this. If it is a maser this represents the first detection of a class I methanol maser outside the Milky Way. The 36.2 GHz methanol emission in NGC253 has more than an order of magnitude higher isotropic luminosity than the widespread emission recently detected towards the center of the Milky Way. If emission from this transition scales with nuclear star formation rate then it may be detectable in the central regions of many starburst galaxies. Detection of methanol emission in ultra-luminous infra-red galaxies (ULIRGs) would open up a new tool for testing for variations in fundamental constants (in particular the proton-to-electron mass ratio) on cosmological scales.
We present a (sub)millimeter line survey of the methanol maser outflow located in the massive star-forming region DR21(OH) carried out with the Submillimeter Array (SMA) at 217/227 GHz and 337/347 GHz. We find transitions from several molecules towards the maser outflow such as CH$_3$OH, H$_2$CS, C$^{17}$O, H$^{13}$CO$^+$ and C$^{34}$S. However, with the present observations, we cannot discard the possibility that some of the observed species such as C$^{17}$O, C$^{34}$S, and H$_2$CS, might be instead associated with the compact and dusty continuum sources located in the MM2 region. Given that most of transitions correspond to methanol lines, we have computed a rotational diagram with CASSIS and a LTE synthetic spectra with XCLASS for the detected methanol lines in order to estimate the rotational temperature and column density in small solid angle of the outflow where enough lines are present. We obtain a rotational temperature of $28pm 2.5$K and a column density of $6.0pm 0.9 times 10^{15}$ cm$^{-2}$. These values are comparable to those column densities/rotational temperatures reported in outflows emanating from low-mass stars. Extreme and moderate physical conditions to excite the maser and thermal emission coexist within the CH$_3$OH flow. Finally, we do not detect any complex molecules associated with the flow, e.g., CH3OCHO, (CH3)2CO, and CH$_3$CH$_2$CN.
We report the results of a search for class II methanol masers at 37.7, 38.3 and 38.5 GHz towards a sample of 70 high-mass star formation regions. We primarily searched towards regions known to show emission either from the 107 GHz class II methanol maser transition, or from the 6.035 GHz excited OH transition. We detected maser emission from 13 sources in the 37.7 GHz transition, eight of these being new detections. We detected maser emission from three sources in the 38 GHz transitions, one of which is a new detection. We find that 37.7 GHz methanol masers are only associated with the most luminous 6.7 and 12.2 GHz methanol maser sources, which in turn are hypothesised to be the oldest class II methanol sources. We suggest that the 37.7 GHz methanol masers are associated with a brief evolutionary phase (of 1000-4000 years) prior to the cessation of class II methanol maser activity in the associated high-mass star formation region.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
