Probing the Metal Enrichment of the Intergalactic Medium at $z=5-6$ Using the Hubble Space Telescope

Abstract

We test the galactic outflow model by probing associated galaxies of four strong intergalactic CIV absorbers at $z=5$--6 using the Hubble Space Telescope (HST) ACS ramp narrowband filters. The four strong CIV absorbers reside at $z=5.74$, $5.52$, $4.95$, and $4.87$, with column densities ranging from $N_{\mathrm{CIV}}=10^{13.8}$ cm${}^{-2}$ to $10^{14.8}$ cm${}^{-2}$. At $z=5.74$, we detect an i-dropout Ly$\alpha$ emitter (LAE) candidate with a projected impact parameter of 42 physical kpc from the CIV absorber. This LAE candidate has a Ly$\alpha$-based star formation rate (SFR${}_{\mathrm{Ly}\alpha }$) of 2 $M_{\odot }$ yr${}^{-1}$ and a UV-based SFR of 4 $M_{\odot }$ yr${}^{-1}$. Although we cannot completely rule out that this $i$-dropout emitter may be an [OII] interloper, its measured properties are consistent with the CIV powering galaxy at $z=5.74$. For CIV absorbers at $z=4.95$ and $z=4.87$, although we detect two LAE candidates with impact parameters of 160 kpc and 200 kpc, such distances are larger than that predicted from the simulations. Therefore we treat them as non-detections. For the system at $z=5.52$, we do not detect LAE candidates, placing a 3-$\sigma$ upper limit of SFR${}_{\mathrm{Ly}\alpha }\approx 1.5M_{\odot }$ yr${}^{-1}$. In summary, in these four cases, we only detect one plausible CIV source at $z=5.74$. Combining the modest SFR of the one detection and the three non-detections, our HST observations strongly support that smaller galaxies (SFR${}_{\mathrm{Ly}\alpha }\lesssim 2M_{\odot }$ yr${}^{-1}$) are main sources of intergalactic CIV absorbers, and such small galaxies play a major role in the metal enrichment of the intergalactic medium at $z\gtrsim 5$.

Accepted for Publications in ApJL

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• Evolution of Neutral Oxygen During the Epoch of Reionization and its Use in Estimating the Neutral Hydrogen Fraction
• Into the Lyα jungle: exploring the circumgalactic medium of galaxies at z ~ 4-5 with MUSE
• A [C II] 158$\mu$m Emitter Associated with an OI Absorber at the End of the Reionization Epoch
• The environments and hosts of metal absorption at z>5
• A SPectroscopic survey of biased halos In the Reionization Era (ASPIRE): JWST Discovers an Overdensity around a Metal Absorption-selected Galaxy at $z\sim 5.5$
• Searching for [CII] Emission from the First Sample of $z\sim 6$ OI Absorption-Associated Galaxies with ALMA
• A Global Census of Metals in the Universe