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Abstract We use medium- and high-resolution spectroscopy of close pairs of quasars to analyze the circumgalactic medium (CGM) surrounding 32 damped Ly α absorption systems (DLAs). The primary quasar sightline in each pair probes an intervening DLA in the redshift range 1.6 < z abs < 3.5, such that the secondary sightline probes absorption from Ly α and a large suite of metal-line transitions (including O i , C ii , C iv , Si ii , and Si iv ) in the DLA host galaxy’s CGM at transverse distances 24 kpc ≤ R ⊥ ≤ 284 kpc. Analysis of Ly α in the CGM sightlines shows an anticorrelation between R ⊥ and H i column density ( N HI ) with 99.8% confidence, similar to that observed around luminous galaxies. The incidences of C ii and Si ii with N > 10 13 cm −2 within 100 kpc of DLAs are larger by 2 σ than those measured in the CGM of Lyman break galaxies (C f ( N C II ) > 0.89 and C f ( N Si II ) = 0.75 − 0.17 + 0.12 ). Metallicity constraints derived from ionic ratios for nine CGM systems with negligible ionization corrections and N HI > 10 18.5 cm −2 show a significant degree of scatter (with metallicities/limits across the range − 2.06 ≲ log Z / Z ⊙ ≲ − 0.75 ), suggesting inhomogeneity in the metal distribution in these environments. Velocity widths of C iv λ 1548 and low-ionization metal species in the DLA versus CGM sightlines are strongly (>2 σ ) correlated, suggesting that they trace the potential well of the host halo over R ⊥ ≲ 300 kpc scales. At the same time, velocity centroids for C iv λ 1548 differ in DLA versus CGM sightlines by >100 km s −1 for ∼50% of velocity components, but few components have velocities that would exceed the escape velocity assuming dark matter host halos of ≥10 12 M ⊙ .
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Constraining the Size of the Circumgalactic Medium Using the Transverse Autocorrelation Function of C iv Absorbers in Paired Quasar Spectra
Abstract The circumgalactic medium (CGM) plays a vital role in the formation and evolution of galaxies, acting as a lifeline between galaxies and the surrounding intergalactic medium. In this study, we leverage a unique sample of quasar pairs to investigate the properties of the CGM with absorption line tomography. We present a new sample of medium-resolution Keck/ESI, Magellan/MagE, and VLT/XSHOOTER spectra of 29 quasar pairs at redshift 2 < z < 3. We supplement the sample with additional spectra of 32 pairs from the literature, creating a catalog of 61 quasar pairs with angular separations between 1.″7 and 132.″9 and projected physical separations ( r ⊥ ) between 14 kpc and 887 kpc. We construct a catalog of 906 metal-line absorption doublets of C iv ( λλ 1548, 1550) with equivalent widths ranging from 6 m Å ≤ W r ,1550 ≤ 2053 m Å. The best-fit linear model to the log-space equivalent width frequency distribution ( log f ( W r ) = m log ( W r ) + b ) of the sample yields coefficients of m = −1.44 ± 0.16 and b = −0.43 ± 0.16. To constrain the projected extent of C iv , we calculate the transverse autocorrelation function. The flattening of the autocorrelation function at low r ⊥ provides a lower limit for the coherence length of the metal enriched CGM—on the order of 200 h −1 comoving kpc. This physical size constraint allows us to refine our understanding of the metals in the CGM, where the extent of C iv in the CGM depends on gas flows, feedback, timescale of metal injection and mixing, and the mass of the host galaxies.
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- PAR ID:
- 10342172
- Publisher / Repository:
- AJ
- Date Published:
- Journal Name:
- The Astronomical Journal
- Volume:
- 164
- Issue:
- 2
- ISSN:
- 0004-6256
- Page Range / eLocation ID:
- 51
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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