Strong Mg II and Fe II Absorbers at 2.2 < z < 6.0

Abstract

We present a study of strong intervening absorption systems in the near-IR spectra of 31 luminous quasars at $z>5.7$. The quasar spectra were obtained with {\it Gemini} GNIRS that provide continuous wavelength coverage from $\sim$0.9 to $\sim$2.5 $\mu$m. We detect 32 strong Mg II doublet absorbers with rest-frame equivalent width $W_r$ ($\lambda 2796$) $>1.0$ Åat $2.2<z<6.0$. Each Mg II absorber is confirmed by at least two associated Fe II absorption lines in the rest-frame wavelength range of $\sim 1600-2600$ Å. We find that the comoving line density ($dN/dX$) of the strong Fe II-bearing Mg II absorbers decreases towards higher redshift at $z>3$, consistent with previous studies. Compared with strong Mg II absorbers detected in damped Ly$\alpha$ systems at 2 $<z<$ 4, our absorbers are potentially less saturated and show much larger rest-frame velocity widths. This suggests that the gas traced by our absorbers are potentially affected by galactic superwinds. We analyze the {\it Hubble Space Telescope} near-IR images of the quasars and identify possible associated galaxies for our strong absorbers. There are a maximum of two galaxy candidates found within 5" radius of each absorber. The median F105W-band magnitude of these galaxy candidates is 24.8 mag, which is fainter than the $L^{\ast }$ galaxy luminosity at $z\sim$ 4. By using our observed $dN/dX$ of strong Mg II absorbers and galaxy candidates median luminosity, we suggest that at high redshift, strong Mg II absorbers tend to have a more disturbed environment but smaller halo size than that at $z<$ 1.

16 pages, 12 figures, 4 tables. Accepted for publication in ApJ

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• Spectral variability studies in Active Galactic Nuclei: Exploring continuum and emission line regions in the age of LSST and JWST
• Searching for [CII] Emission from the First Sample of $z\sim 6$ OI Absorption-Associated Galaxies with ALMA
• Interstellar and Circumgalactic Properties of an Unseen $z=6.84$ Galaxy: Abundances, Ionization, and Heating in the Earliest Known Quasar Absorber