On the Evidence for Molecular Outflows in High-redshift Dusty Star-forming Galaxies

Abstract

Galactic-scale outflows of molecular gas from star-forming galaxies constitute the most direct evidence for regulation of star formation. In the early universe ($z>4$), such outflows have recently been inferred from gravitationally-lensed dusty star-forming galaxies (DSFGs) based on ubiquitous detections of OH absorption extending to more blueshifted velocities than [CII] or CO emission in spatially-integrated spectra. Because these lines are redshifted to sub-mm wavelengths, such measurements require careful corrections for atmospheric absorption lines, and a proper accounting of sometimes large variations in measurement uncertainties over these lines. Taking these factors into consideration, we re-analyze OH and [CII] data taken with ALMA for the five sources where such data is available, of which four were categorised as exhibiting outflows. Based on their spatially-integrated spectra alone, we find statistically significant ($\ge 3\sigma$) OH absorption more blueshifted than [CII] emission in only one source. By contrast, searching channel maps for signals diluted below the detection threshold in spatially-integrated spectra, we find evidence for a separate kinematic component in OH absorption in all five sources in the form of: (i) more blueshifted OH absorption than [CII] emission and/or (ii) a component in OH absorption exhibiting a different spatio-kinematic pattern than [CII] emission, the latter presumably tracing gas in a rotating disc. Providing a more complete and accurate assessment of molecular outflows in gravitationally-lensed DSFGs, we suggest methods to better assess the precision of corrections for atmospheric absorption and to more accurately measure the source continuum in future observations.

arXiv comment18 pages, 8 figures, 2 tables

References in corpus (17)

• Astropy: A Community Python Package for Astronomy
• The Astropy Project: Building an inclusive, open-science project and status of the v2.0 core package
• The Astropy Project: Sustaining and Growing a Community-oriented Open-source Project and the Latest Major Release (v5.0) of the Core Package
• The Structure and Kinematics of the Circum-Galactic Medium from Far-UV Spectra of z~2-3 Galaxies
• Outflows in Infrared-Luminous Starbursts at z < 0.5. II. Analysis and Discussion
• Cool Outflows in Galaxies and their Implications
• Galaxies in a Simulated $\Lambda$CDM Universe II: Observable Properties and Constraints on Feedback
• Observations of the Lyman-$\alpha$ Universe
• Molecular outflows in local ULIRGs: energetics from multi-transition OH analysis
• Fast Molecular Outflow from a Dusty Star-Forming Galaxy in the Early Universe
• Feedback in low-mass galaxies in the early Universe
• Fast Outflows Identified in Early Star-Forming Galaxies at $z=5-6$
• Far-Infrared OH fluorescent emission in Sagittarius B2
• Ubiquitous Molecular Outflows in z > 4 Massive, Dusty Galaxies I. Sample Overview and Clumpy Structure in Molecular Outflows on 500pc Scales
• Ubiquitous Molecular Outflows in z > 4 Massive, Dusty Galaxies II. Momentum-Driven Winds Powered by Star Formation in the Early Universe
• Estimating the statistical uncertainty due to spatially correlated noise in interferometric images
• Tracking ALMA System Temperature with Water Vapor Data at High Frequency

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• The ALMA-CRISTAL Survey: Spatial extent of [CII] line emission in star-forming galaxies at $z=4-6$
• Starburst-Driven Galactic Outflows -- Unveiling the Suppressive Role of Cosmic Ray Halos