Molecules in G1.6-0.025 - 'Hot' Chemistry in the Absence of Star Formation at the Periphery of the Galactic Center Region

Abstract

We present molecular line mapping of the Giant Molecular Cloud G1.6-0.025, which is located at the high longitude end of the Central Molecular Zone of our Galaxy. We assess the degree of star formation activity in that region using several tracers and find very little. We made a large scale, medium (2') resolution map in the J = 2-1 transition of SiO for which we find clumpy emission over a ~0.8 x 0.3 degree-sized region stretching along the Galactic plane. Toward selected positions we also took spectra in the easy to excite J_k=2_k-1_k quartet of CH3OH and the CS 2-1 line. Throughout the cloud these \meth lines are, remarkably, several times stronger than, both, the CS and the SiO lines. The large widths of all the observed lines, similar to values generally found in the Galactic center, indicate a high degree of turbulence. Several high LSR velocity clumps that have 0-80 km/s higher velocities than the bulk of the molecular cloud appear at the same projected position as "normal" velocity material; this may indicate cloud-cloud collisions. Statistical equilibrium modeling of the CH3OH lines observed by us and others yield relatively high densities and moderate temperatures for a representative dual velocity position. We find 8 10^4 cm-3/30 K for material in the G1.6-0.025 cloud and a higher temperature (190 K), but a 50% lower density in a high velocity clump projected on the same location. Several scenarios are discussed in which shock chemistry might enhance the CH3OH and SiO abundances in G1.6-0.025 and elsewhere in the Central Molecular Zone.

51 pages incl. 9 figures and 6 Tables, ApJ (in press)

References in corpus (3)

• Formation of methyl formate and other organic species in the warm-up phase of hot molecular cores
• Organic Molecules in the Galactic Center. Hot Core Chemistry without Hot Cores
• Coupling the dynamics and the molecular chemistry in the Galactic center

Cited by in corpus (22)

• Dense gas in the Galactic central molecular zone is warm and heated by turbulence
• The Galactic Center Molecular Cloud Survey. I. A Steep Linewidth-Size Relation & Suppression of Star Formation
• Low-velocity shocks traced by extended SiO emission along the W43 ridges: witnessing the formation of young massive clusters
• Detection of Widespread Hot Ammonia in the Galactic Center
• The dynamics and star-forming potential of the massive Galactic centre cloud G0.253+0.016
• Online Database of Class I Methanol Masers
• The Galactic Center Molecular Cloud Survey. II. A Lack of Dense Gas & Cloud Evolution along Galactic Center Orbits
• A Comprehensive Survey of Hydrogen Chloride in the Galaxy
• Expanded VLA Detection of 36.2 GHz Class I Methanol Masers in Sagittarius A
• Expanded Very Large Array Detection of 44.1 GHz Class I Methanol Masers in Sagittarius A
• ALMA Observations of Massive Clouds in the Central Molecular Zone: Ubiquitous Protostellar Outflows
• ALCHEMI finds a "shocking" carbon footprint in the starburst galaxy NGC~253
• Living on the edge of the Central Molecular Zone: G1.3 is the more likely candidate for gas accretion into the CMZ
• The foot points of the Giant Molecular Loops in the Galactic center region
• CO-0.30-0.07: A Peculiar Molecular Clump with an Extremely Broad Velocity Width
• Investigations of the Class I methanol masers in NGC 4945
• Characterizing the chemical pathways for water formation -- A deep search for hydrogen peroxide
• A Multi-Line Ammonia Survey of the Galactic Center Region with the Tsukuba 32-m Telescope - I. Observations and Data
• Dancing with the stars: Stirring up extraordinary turbulence in Galactic center clouds
• ALMA observations of massive clouds in the central molecular zone: slim filaments tracing parsec-scale shocks
• Parabolic-like Trend in SiO Ratios throughout the Central Molecular Zone: Possible Signature of a Past Nuclear Activity in the Galactic Center
• Star Formation in the Galactic Center