12CO and 13CO observation of the low-metallicity dwarf galaxy DDO 154

Abstract

The conversion factor from carbon monoxide (CO) intensity to molecular gas mass is a source of large uncertainty in understanding gas and its relation to star formation in galaxies. In particular, the conversion factor in low metallicity environments have remained elusive, as currently only two galaxies have been detected in any CO isotopes in environments with 12+log (O/H) < 8.0. Here we report 12CO(J=1-0) and 13CO(J=1-0) observations towards a star forming region in DDO 154, a low metallicity dwarf irregular galaxy at 12+log (O/H) = 7.67. This is a re-observation of a previous non-detection at higher angular and velocity resolution. No significant emission was detected. By estimating the molecular gas mass from associated star formation, we find that DDO 154 has a conversion factor of more than 10^3 times the Milky Way. Alternatively, if we estimate molecular mass using dust continuum emission, the conversion factor is at least 2 orders of magnitude larger than the Milky Way. These estimates signify a large amount of CO-dark molecular gas in this galaxy.

arXiv comment7 pages, 2 figures, published in Publications of the Astronomical Society of Japan (PASJ)

References in corpus (46)

• The CO-to-H2 Conversion Factor
• THINGS: The HI Nearby Galaxy Survey
• SINGS: The SIRTF Nearby Galaxies Survey
• Mass models of the Milky Way
• Metallicities of 0.3<z<1.0 Galaxies in the GOODS-North Field
• The CO-to-H2 Conversion Factor and Dust-to-Gas Ratio on Kiloparsec Scales in Nearby Galaxies
• The CO-to-H2 Conversion Factor From Infrared Dust Emission Across the Local Group
• The Evolving Interstellar Medium of Star Forming Galaxies Since z=2 as Probed by Their Infrared Spectral Energy Distributions
• The Resolved Properties of Extragalactic Giant Molecular Clouds
• An H-alpha Imaging Survey of Galaxies in the Local 11 Mpc Volume
• KINGFISH -- Key Insights on Nearby Galaxies: A Far-Infrared Survey with Herschel: Survey Description and Image Atlas
• The ACS Nearby Galaxy Survey Treasury VIII. The Global Star Formation Histories of 60 Dwarf Galaxies in the Local Volume
• Toward a Unification of Star Formation Rate Determinations in the Milky Way and Other Galaxies
• The Metallicity Dependence of the CO-to-H${}_2$ Conversion Factor from Observations of Local Group Galaxies
• Herschel Far-Infrared and Sub-millimeter Photometry for the KINGFISH Sample of Nearby Galaxies
• Giant Molecular Clouds in M33 -- II. High Resolution Observations
• Planck intermediate results. XVII. Emission of dust in the diffuse interstellar medium from the far-infrared to microwave frequencies
• Outside-in Shrinking of the Star-forming Disk of Dwarf Irregular Galaxies
• Mapping the cold dust temperatures and masses of nearby Kingfish galaxies with Herschel
• GALEX Ultraviolet Imaging of Dwarf Galaxies and Star Formation
• Converting H$\alpha$ Luminosities into Star Formation Rates
• A Mapping Survey of the 12CO and 13CO Emission in Galaxies
• Vindicating single-T modified blackbody fits to Herschel SEDs (Research Note)
• Determining Star Formation Timescale and Pattern Speed in Nearby Spiral Galaxies
• Dense cloud cores revealed by CO in the low metallicity dwarf galaxy WLM
• Digital Spectro-Correlator System for the Atacama Compact Array of the Atacama Large Millimeter/submillimeter Array
• Dust, CO and [CI]: Cross-calibration of molecular gas mass tracers in metal-rich galaxies across cosmic time
• The ${}^{12}$CO/${}^{13}$CO ratio in turbulent molecular clouds
• Unusual CO Line Ratios and kinematics in the N83/N84 Region of the Small Magellanic Cloud
• Carbon Monoxide Clouds at Low-Metallicity in the WLM Galaxy
• The Herschel-ATLAS Data Release 2, Paper I. Submillimeter and Far-infrared Images of the South and North Galactic Poles: The Largest Herschel Survey of the Extragalactic Sky
• Offsets between H-alpha and CO arms of a spiral galaxy NGC 4254: A New Method for Determining the Pattern Speed of Spiral Galaxies
• Central molecular zones in galaxies: 12CO-to-13CO ratios, carbon budget, and X factors
• Carbon monoxide in an extremely metal-poor galaxy
• Systematic variation of the 12CO/13CO ratio as a function of star-formation rate surface density
• Star Formation in the Extreme Outer Galaxy: Digel Cloud 2 Clusters
• Dust emissivity and absorption cross section in DustPedia late-type galaxies
• The CO content of the Local Group dwarf irregular galaxies IC5152, UGCA438, and the Phoenix dwarf
• The Carbon-to-H${}_2$, CO-to-H${}_2$ Conversion Factors and Carbon Abundance on Kiloparsec Scales in Nearby Galaxies
• Over-sized gas clumps in an extremely-metal-poor molecular cloud revealed by ALMA's pc-scale maps
• Relationships between the Stellar, Gaseous, and Star Formation Disks in LITTLE THINGS Dwarf Irregular Galaxies: Indirect Evidence for Substantial Fractions of Dark Molecular Gas
• A Search for CO in the Local Group Dwarf Irregular Galaxy WLM
• Deep CO Observations and the CO-to-H_2 Conversion Factor in DDO 154, a Low Metallicity Dwarf Irregular Galaxy
• Temperature Variations of the Cold Dust in the Triangulum Galaxy M33
• Gas, dust, and the CO-to-molecular gas conversion factor in low-metallicity starbursts
• Spatially resolved dust emission of extremely metal poor galaxies

Cited by in corpus (3)

• Metallicity dependence of the CO-to-H${}_2$ and the [CI]-to-H${}_2$ conversion factors in galaxies
• ALMA FACTS. II. Large Scale Variations in the 12CO(J=2-1) to 12CO(J=1-0) Line Ratio in Nearby Galaxies
• The CHIMERA Survey: The first CO detection in Leo T, the lowest mass known galaxy still hosting cold molecular gas