The cosmic ray ionization rate (CRIR) is a key parameter in understanding the
physical and chemical processes in the interstellar medium. Cosmic rays are a
significant source of energy in star ...formation regions, which impacts the
physical and chemical processes which drive the formation of stars. Previous
studies of the circum-molecular zone (CMZ) of the starburst galaxy NGC 253 have
found evidence for a high CRIR value; $10^3-10^6$ times the average cosmic ray
ionization rate within the Milky Way. This is a broad constraint and one goal
of this study is to determine this value with much higher precision. We exploit
ALMA observations towards the central molecular zone of NGC 253 to measure the
CRIR. We first demonstrate that the abundance ratio of H$_3$O$^+$ and SO is
strongly sensitive to the CRIR. We then combine chemical and radiative transfer
models with nested sampling to infer the gas properties and CRIR of several
star-forming regions in NGC 253 due to emission from their transitions. We find
that each of the four regions modelled has a CRIR in the range
$(1-80)\times10^{-14}$ s$^{-1}$ and that this result adequately fits the
abundances of other species that are believed to be sensitive to cosmic rays
including C$_2$H, HCO$^+$, HOC$^+$, and CO. From shock and PDR/XDR models, we
further find that neither UV/X-ray driven nor shock dominated chemistry are a
viable single alternative as none of these processes can adequately fit the
abundances of all of these species.
The effectiveness of two commercial bee attractants, Bee-Scent and Beeline, for enhancing pollination of cucumber (Cucumis sativus L.) and watermelon Citrullus lanatus (Thunb.) Matsum. and Nakai was ...evaluated by counting the number of bee visitations to blossoms of cucumber and watermelon and their effect(s) on fruit quality, yield, and crop profitability. In 1989, Bee-Scent was tested in a commercial pickling cucumber field. In 1990, watermelon plots were sprayed with Bee-Scent and Beeline and compared with a nontreated control. The compounds did not improve bee visitations for either pickling cucumbers or watermelons. There was no significant improvement in cucumber or watermelon yield or monetary returns
Molecular abundances are sensitive to UV-photon flux and cosmic-ray ionization rate. In starburst environments, the effects of high-energy photons and particles are expected to be stronger. We ...examine these astrochemical signatures through multiple transitions of HCO\(^+\) and its metastable isomer HOC\(^+\) in the center of the starburst galaxy NGC 253 using data from the ALMA large program ALCHEMI. The distribution of the HOC\(^+\)(1-0) integrated intensity shows its association with "superbubbles", cavities created either by supernovae or expanding HII regions. The observed HCO\(^+\)/HOC\(^+\) abundance ratios are \(\sim 10-150\), and the fractional abundance of HOC\(^+\) relative to H\(_2\) is \(\sim 1.5\times 10^{-11} - 6\times 10^{-10}\), which implies that the HOC\(^+\) abundance in the center of NGC 253 is significantly higher than in quiescent spiral-arm dark clouds in the Galaxy and the Galactic center clouds. Comparison with chemical models implies either an interstellar radiation field of \(G_0\gtrsim 10^3\) if the maximum visual extinction is \(\gtrsim 5\), or a cosmic-ray ionization rate of \(\zeta \gtrsim 10^{-14}\) s\(^{-1}\) (3-4 orders of magnitude higher than that within clouds in the Galactic spiral-arms) to reproduce the observed results. From the difference in formation routes of HOC\(^+\), we propose that a low-excitation line of HOC\(^+\) traces cosmic-ray dominated regions, while high-excitation lines trace photodissociation regions. Our results suggest that the interstellar medium in the center of NGC 253 is significantly affected by energy input from UV-photons and cosmic rays, sources of energy feedback.
The cosmic ray ionization rate (CRIR) is a key parameter in understanding the physical and chemical processes in the interstellar medium. Cosmic rays are a significant source of energy in star ...formation regions, which impacts the physical and chemical processes which drive the formation of stars. Previous studies of the circum-molecular zone (CMZ) of the starburst galaxy NGC 253 have found evidence for a high CRIR value; \(10^3-10^6\) times the average cosmic ray ionization rate within the Milky Way. This is a broad constraint and one goal of this study is to determine this value with much higher precision. We exploit ALMA observations towards the central molecular zone of NGC 253 to measure the CRIR. We first demonstrate that the abundance ratio of H\(_3\)O\(^+\) and SO is strongly sensitive to the CRIR. We then combine chemical and radiative transfer models with nested sampling to infer the gas properties and CRIR of several star-forming regions in NGC 253 due to emission from their transitions. We find that each of the four regions modelled has a CRIR in the range \((1-80)\times10^{-14}\) s\(^{-1}\) and that this result adequately fits the abundances of other species that are believed to be sensitive to cosmic rays including C\(_2\)H, HCO\(^+\), HOC\(^+\), and CO. From shock and PDR/XDR models, we further find that neither UV/X-ray driven nor shock dominated chemistry are a viable single alternative as none of these processes can adequately fit the abundances of all of these species.
