Where outflows meet inflows: gas kinematics in SSA22 Ly α blob 2 decoded by advanced radiative transfer modelling

Creators: Li, Zhihui; Steidel, Charles C.; Gronke, Max; Chen, Yuguang; Matsuda, Yuichi

Abstract

We present new spectroscopic observations of Ly α (Ly α) Blob 2 (z ∼ 3.1). We observed extended Ly α emission in three distinct regions, where the highest Ly α surface brightness (SB) centre is far away from the known continuum sources. We searched through the MOSFIRE slits that cover the high Ly α SB regions, but were unable to detect any significant nebular emission near the highest SB centre. We further mapped the flux ratio of the blue peak to the red peak and found it is anticorrelated with Ly α SB with a power-law index of ∼ –0.4. We used radiative transfer models with both multiphase, clumpy, and shell geometries and successfully reproduced the diverse Ly α morphologies. We found that most spectra suggest outflow-dominated kinematics, while 4/15 spectra imply inflows. A significant correlation exists between parameter pairs, and the multiphase, clumpy model may alleviate previously reported discrepancies. We also modelled Ly α spectra at different positions simultaneously and found that the variation of the inferred clump outflow velocities can be approximately explained by line-of-sight projection effects. Our results support the 'central powering + scattering' scenario, i.e. the Ly α photons are generated by a central powering source and then scatter with outflowing, multiphase H I gas while propagating outwards. The infalling of cool gas near the blob outskirts shapes the observed blue-dominated Ly α profiles, but its energy contribution to the total Ly α luminosity is less than 10 per cent, i.e. minor compared to the photoionization by star-forming galaxies and/or AGNs.

Additional Information

© 2022 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model). Accepted 2022 March 28. Received 2022 February 24; in original form 2021 April 21. Published: 08 April 2022. We thank the anonymous referee for carefully reading our manuscript and providing constructive feedback, which significantly improved the quality of this paper. We thank Phil Hopkins for providing computational resources. ZL, CCS, and YC acknowledge financial support by NSF grant AST-2009278. YM acknowledges support from JSPS KAKENHI Grant (17H04831, 17KK0098, 19H00697, and 20H01953). The data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. We are also grateful to the dedicated staff of the W.M. Keck Observatory who keep the instruments and telescopes running effectively. MG was supported by NASA through the NASA Hubble Fellowship grant HST-HF2-51409 awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555. Numerical calculations were run on the Caltech compute cluster 'Wheeler,' allocations from XSEDE TG-AST130039 and PRAC NSF.1713353 supported by the NSF and NASA HEC SMD-16-7592. This research made use of Montage. It is funded by the National Science Foundation under Grant Number ACI-1440620, and was previously funded by the National Aeronautics and Space Administration's Earth Science Technology Office, Computation Technologies Project, under Cooperative Agreement Number NCC5-626 between NASA and the California Institute of Technology. We also acknowledge the use of the following software packages: ASTROPY (Astropy Collaboration et al. 2018), the SCIPY and NUMPY system (Virtanen et al. 2020; Harris et al. 2020), seaborn (Waskom 2021) and QFitsView.24 Data Availability: The data underlying this article will be shared on reasonable request to the corresponding author.

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