A SPectroscopic survey of biased halos In the Reionization Era (ASPIRE): JWST Discovers an Overdensity around a Metal Absorption-selected Galaxy at $z\sim 5.5$

Abstract

The launch of $JWST$ opens a new window for studying the connection between metal-line absorbers and galaxies at the end of the Epoch of Reionization (EoR). Previous studies have detected absorber-galaxy pairs in limited quantities through ground-based observations. To enhance our understanding of the relationship between absorbers and their host galaxies at $z>5$, we utilized the NIRCam Wide Field Slitless Spectroscopy (WFSS) to search for absorber-associated galaxies by detecting their rest-frame optical emission lines (e.g., [OIII] + H$\beta$). We report the discovery of a MgII-associated galaxy at $z=5.428$ using data from the $JWST$ ASPIRE program. The MgII absorber is detected on the spectrum of quasar J0305--3150 with a rest-frame equivalent width of 0.74$\mathring{A}$. The associated galaxy has an [OIII] luminosity of $10^{42.5}\mathrm{erg}{\mathrm{s}}^{-1}$ with an impact parameter of 24.9 proper kiloparsecs (pkpc). The joint $HST$-$JWST$ spectral energy distribution (SED) implies a stellar mass and star-formation rate of ${\mathrm{M}}_{\ast }\approx 10^{8.8}$ ${\mathrm{M}}_{\odot }$, $\mathrm{SFR}\approx 10{\mathrm{M}}_{\odot }\mathrm{y}{\mathrm{r}}^{-1}$. Its [OIII] equivalent width and stellar mass are typical of [OIII] emitters at this redshift. Furthermore, connecting the outflow starting time to the SED-derived stellar age, the outflow velocity of this galaxy is $\sim 300\mathrm{km}{\mathrm{s}}^{-1}$, consistent with theoretical expectations. We identified six additional [OIII] emitters with impact parameters of up to $\sim 300$ pkpc at similar redshifts ($|dv|<1000\mathrm{km}{\mathrm{s}}^{-1}$). The observed number is consistent with that in cosmological simulations. This pilot study suggests that systematically investigating the absorber-galaxy connection within the ASPIRE program will provide insights into the metal-enrichment history in the early universe.

Accepted for publication in ApJL. Main text 8 pages, 4 figures. For more information of the JWST ASPIRE program please check https://aspire-quasar.github.io/index.html

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