The diffuse molecular component in the nuclear bulge of the Milky Way

Abstract

Context: The bulk of the Molecular gas in the Central Molecular Zone (CMZ) of the Galactic center region shows warm kinetic temperatures, ranging from $>20$ K in the coldest and densest regions (n$\sim 10^{4-5}$ cm${}^{-3}$) up to more than 100 K for densities of about n$\sim 10^3$ cm${}^{-3}$. Recently, a more diffuse, hotter ($n\sim 100$ cm${}^{-3}$, $T\sim 250$ K) gas component was discovered through absorption observations of H${}_3^{+}$. This component may be widespread in the Galactic center, and low density gas detectable in absorption may be present even outside the CMZ along sightlines crossing the extended bulge of the Galaxy. Aims: We aim to observe and characterize diffuse and low density gas using observations of 3-mm molecular transitions seen in absorption. Methods: Using the Atacama Large (sub)Millimeter Array (ALMA) we observed the absorption against the quasar J1744-312, which is located towards the Galactic bulge region at $(l,b)=(-2{}^{\circ }.13,-1{}^{\circ }.0)$, but outside the main molecular complexes. Results: ALMA observations in absorption against the J1744-312 quasar reveal a rich and complex chemistry in low density molecular and presumably diffuse clouds. We detected three velocity components, at $\sim$ 0, $-153$, and $-192$ km s${}^{-1}$. The component at $\sim 0$ km s${}^{-1}$ could represent gas in the Galactic disk while the velocity components at $-153$, and $-192$ km s${}^{-1}$ likely originate from the Galactic bulge. We detected 12 molecules in the survey, but only 7 in the Galactic bulge gas.

arXiv commentAccepted for publication in A&A

References in corpus (34)

• The Nuclear Bulge of the Galaxy. III. Large-Scale Physical Characteristics of Stars and Interstellar Matter
• Complex organic molecules in the interstellar medium: IRAM 30 m line survey of Sagittarius B2(N) and (M)
• Dense gas in the Galactic central molecular zone is warm and heated by turbulence
• Spatial distribution of interstellar gas in the innermost 3 kpc of our Galaxy
• Hot and Diffuse Clouds near the Galactic Center Probed by Metastable H3+
• Spectral imaging of the Central Molecular Zone in multiple 3-mm molecular lines
• Molecules at z=0.89: A 4-mm-rest-frame absorption line survey toward PKS 1830-211
• SiO emission from the Galactic Center Molecular Clouds
• The thermal state of molecular clouds in the Galactic Center: evidence for non-photon-driven heating
• Comparative Chemistry of Diffuse Clouds II: CN, HCN, HNC, CH3CN & N2H+
• A New Spiral Arm of the Galaxy: The Far 3-Kpc Arm
• Hyperstrong Radio-Wave Scattering in the Galactic Center. II. A Likelihood Analysis of Free Electrons in the Galactic Center
• Molecular absorption lines toward star-forming regions : a comparative study of HCO+, HNC, HCN, and CN
• Absorption Line Survey of H3+ toward the Galactic Center Sources II. Eight Infrared Sources within 30 pc of the Galactic Center
• Physical conditions in the central molecular zone inferred by H3+
• HCO mapping of the Horsehead : Tracing the illuminated dense molecular cloud surfaces
• An ALMA Early Science survey of molecular absorption lines toward PKS1830-211 -- Analysis of the absorption profiles
• Absorption Line Survey of H3+ toward the Galactic Center Sources I. GCS 3-2 and GC IRS3
• Chemical Features in the Circumnuclear Disk of the Galactic Center
• Phase Correction for ALMA with 183 GHz Water Vapour Radiometers
• Infrared H3+ and CO Studies of the Galactic Core: GCIRS 3 and GCIRS 1W
• A survey of the Galactic center region in HCO+, H13CO+ and SiO
• The kinetic temperature of a molecular cloud at redshift 0.9: Ammonia in the gravitational lens PKS1830-211
• Tracing gas accretion in the Galactic center using isotopic ratios
• Two New and Remarkable Sightlines through the Galactic Center's Molecular Gas
• HCO, c-C3H and CF+ : three new molecules in diffuse, translucent and "spiral-arm'' clouds
• The Celestial Reference Frame at 24 and 43 GHz. II. Imaging
• The detection of the (J,K)=(18,18) line of NH3
• OH+ and H2O+ absorption toward PKS1830-211
• 3 mm spectral line survey of two lines of sight toward two typical cloud complexes in the Galactic Center
• Submillimeter water and ammonia absorption by the peculiar z~0.89 interstellar medium in the gravitational lens of the PKS 1830-211 system
• New Detections of Galactic Molecular Absorption Systems toward ALMA Calibrator Sources
• ALMA hints at the existence of an unseen reservoir of diffuse molecular gas in the Galactic bulge
• The foot points of the Giant Molecular Loops in the Galactic center region

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• A molecular absorption line survey toward the AGN of Hydra-A
• Molecular Gas and Dark Neutral Medium in the Outskirts of Chamaeleon
• Revealing The CO X-factor In Dark Molecular Gas through Sensitive ALMA Absorption Observations
• Unusual Galactic HII Regions at the Intersection of the Central Molecular Zone and the Far Dust Lane
• Discovery of CO absorption at z=0.05 in G0248+430
• ALMA observations of molecular absorption in four directions toward the Galactic bulge
• CO+ as a probe of the origin of CO in diffuse interstellar clouds
• Self-modulation of cosmic rays in molecular clouds: Imprints in the radio observations