The Keck Baryonic Structure Survey: Using foreground/background galaxy pairs to trace the structure and kinematics of circumgalactic neutral hydrogen at z ∼ 2

Yuguang Chen*, Charles C. Steidel, Cameron B. Hummels, Gwen C. Rudie, Bili Dong, Ryan F. Trainor, Milan Bogosavljević, Dawn K. Erb, Max Pettini, Naveen A. Reddy, Alice E. Shapley, Allison L. Strom, Rachel L. Theios, Claude André Faucher-Giguère, Philip F. Hopkins, Dušan Kereš

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

5 Scopus citations

Abstract

We present newmeasurements of the spatial distribution and kinematics of neutral hydrogen in the circumgalactic and intergalactic medium surrounding star-forming galaxies at z ∼ 2. Using the spectra of ≃3000 galaxies with redshifts 〈z〉 = 2.3 ± 0.4 from the Keck Baryonic Structure Survey,we assemble a sample ofmore than 200 000 distinct foreground-background pairs with projected angular separations of 3-500 arcsec and spectroscopic redshifts, with 〈zfg〉 = 2.23 and 〈zbg〉 = 2.57 (foreground, background redshifts, respectively.) The ensemble of sightlines and foreground galaxies is used to construct a 2D map of the mean excess HI Ly α optical depth relative to the intergalactic mean as a function of projected galactocentric distance (20 ≲ Dtran/pkpc ≲ 4000) and line-of-sight velocity. We obtain accurate galaxy systemic redshifts, providing significant information on the line-of-sight kinematics of HI gas as a function of projected distance Dtran. We compare the map with cosmological zoom-in simulation, finding qualitative agreement between them. A simple two-component (accretion, outflow) analytical model generally reproduces the observed line-of-sight kinematics and projected spatial distribution of HI. The best-fitting model suggests that galaxy-scale outflows with initial velocity vout ≃ 600 km s-1 dominate the kinematics of circumgalactic HI out to Dtran ≃ 50 kpc, while HI at Dtran ≳100 kpc is dominated by infall with characteristic vin ≲circular velocity. Over the impact parameter range 80≲Dtran/pkpc ≲ 200, the HI line-of-sight velocity range reaches a minimum, with a corresponding flattening in the rest-frame Ly α equivalent width. These observations can be naturally explained as the transition between outflow-dominated and accretion-dominated flows. Beyond Dtran ≃ 300 pkpc (∼1 cMpc), the line-of-sight kinematics are dominated by Hubble expansion.

Original languageEnglish (US)
Pages (from-to)1721-1746
Number of pages26
JournalMonthly Notices of the Royal Astronomical Society
Volume499
Issue number2
DOIs
StatePublished - Dec 1 2020

Keywords

  • galaxies: ISM
  • galaxies: evolution
  • galaxies: high-redshift
  • galaxies: intergalatic medium

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Fingerprint

Dive into the research topics of 'The Keck Baryonic Structure Survey: Using foreground/background galaxy pairs to trace the structure and kinematics of circumgalactic neutral hydrogen at z ∼ 2'. Together they form a unique fingerprint.

Cite this