Uniform Silicon Isotope Ratios Across the Milky Way Galaxy

Abstract

We report the relative abundances of the three stable isotopes of silicon, ${}^{28}$Si, ${}^{29}$Si and ${}^{30}$Si, across the Galaxy using the $v=0,J=1\to 0$ transition of silicon monoxide. The chosen sources represent a range in Galactocentric radii ($R_{\mathrm{GC}}$) from 0 to 9.8 kpc. The high spectral resolution and sensitivity afforded by the GBT permit isotope ratios to be corrected for optical depths. The optical-depth-corrected data indicate that the secondary-to-primary silicon isotope ratios ${}^{29}\mathrm{Si}{/}^{28}\mathrm{Si}$ and ${}^{30}\mathrm{Si}{/}^{28}\mathrm{Si}$ vary much less than predicted on the basis of other stable isotope ratio gradients across the Galaxy. Indeed, there is no detectable variation in Si isotope ratios with $R_{\mathrm{GC}}$. This lack of an isotope ratio gradient stands in stark contrast to the monotonically decreasing trend with $R_{\mathrm{GC}}$ exhibited by published secondary-to-primary oxygen isotope ratios. These results, when considered in the context of the expectations for chemical evolution, suggest that the reported oxygen isotope ratio trends, and perhaps that for carbon as well, require further investigation. The methods developed in this study for SiO isotopologue ratio measurements are equally applicable to Galactic oxygen, carbon and nitrogen isotope ratio measurements, and should prove useful for future observations of these isotope systems.

arXiv comment18 pages, 12 figures, 2 tables. Published in The Astrophysical Journal, Volume 839, Issue 2

References in corpus (41)

• The Global Schmidt Law in Star Forming Galaxies
• Star Formation in the Milky Way and Nearby Galaxies
• The Star Formation Efficiency in Nearby Galaxies: Measuring Where Gas Forms Stars Effectively
• A computer program for fast non-LTE analysis of interstellar line spectra
• Galactic Chemical Evolution: Hydrogen Through Zinc
• Galactic chemical evolution: Carbon through Zinc
• How to Calculate Molecular Column Density
• The Evolution of Isotope Ratios in the Milky Way Galaxy
• An Accurate Flux Density Scale from 1 to 50 GHz
• The Type Ia Supernova Rate
• Radial migration in galactic disks caused by resonance overlap of multiple patterns: Self-consistent simulations
• HII Region Metallicity Distribution in the Milky Way Disk
• Using Cepheids to determine the galactic abundance gradient I. The solar neighbourhood
• First stars IX -Mixing in extremely metal-poor giants. Variation of the 12C/13C, [Na/Mg] and [Al/Mg] ratios
• Chemical Abundances of Luminous Cool Stars in the Galactic Center from High-Resolution Infrared Spectroscopy
• Using Cepheids to determine the galactic abundance gradient II. Towards the galactic center
• Using Cepheids to determine the galactic abundance gradient. III.First results for the outer disc
• Metallicity in the Galactic Center: The Quintuplet cluster
• On the metallicity gradient of the Galactic disk
• Galactic Evolution of Silicon Isotopes: Application to Presolar SiC Grains From Meteorites
• Warm SiO gas in molecular bullets associated with protostellar outflows
• A new formulation of the Type Ia SN rate and its consequences on galactic chemical evolution
• Si Isotopic Ratios in Mainstream Presolar SiC Grains Revisited
• On carbon and oxygen isotope ratios in starburst galaxies: New data from NGC253 and Mrk231 and their implications
• Multiple Jets from the High-Mass (Proto)stellar Cluster AFGL5142
• Galactic interstellar 18O/17O ratios - a radial gradient?
• HNCO abundances in galaxies: Tracing the evolutionary state of starbursts
• The chemical abundances in the Galactic Centre from the atmospheres of Red Supergiants
• Nova nucleosynthesis and Galactic evolution of the CNO isotopes
• SiO emission from low- and high-velocity shocks in Cygnus-X massive dense clumps
• A large 12C/13C isotopic ratio in M82 and NGC253
• An Extensive, Sensitive Search for SiO Masers in High- and Intermediate-Mass Star-Forming Regions
• The role of the Galactic bar in the chemical evolution of the Milky Way
• Radio Continuum and Methanol Observations of DR21(OH)
• Thermal SiO and H${}^{13}$CO${}^{+}$ Line Observations of the Dense Molecular Cloud G0.11$-$0.11 in the Galactic Center region
• Nature of W51e2: Massive Cores at Different Phases of Star Formation
• Decoding the message from meteoritic stardust silicon carbide grains
• Astronomical Oxygen Isotopic Evidence for Supernova Enrichment of the Solar System Birth Environment by Propagating Star Formation
• Galactic Chemical Evolution and the Oxygen Isotopic Composition of the Solar System
• HII Region Ionization of the Interstellar Medium: A Case Study of NGC 7538
• From dusty filaments to massive stars: The case of NGC 7538 S

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• The Bulge Asymmetries and Dynamical Evolution (BAaDE) SiO Maser Survey at 86 GHz with ALMA
• Spectral-line Survey of the Region of Massive Star Formation W51e1/e2 in the 4 mm Wavelength Range
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