The Extended [CII] under Construction? Observation of the brightest high-z lensed star-forming galaxy at z = 6.2

Abstract

We present results of [CII]$158\hat{\mathrm{I}}¼\mathrm{m}$ emission line observations, and report the spectroscopic redshift confirmation of a strongly lensed ($\hat{I}¼\sim 20$) star-forming galaxy, MACS0308-zD1 at $z=6.2078\pm 0.0002$. The [CII] emission line is detected with a signal-to-noise ratio $>6$ within the rest-frame UV bright clump of the lensed galaxy (zD1.1) and exhibits multiple velocity components; the narrow [CII] has a velocity full-width-half-maximum (FWHM) of $110\pm 20km/s$, while broader [CII] is seen with an FWHM of $230\pm 20km/s$. The broader [CII] component is blueshifted ($-80\pm 20km/s$) with respect to the narrow [CII] component, and has a morphology which extends beyond the UV-bright clump. We find that while the narrow [CII] emission is most likely associated with zD1.1, the broader component is possibly associated with outflowing gas. Based on the non-detection of $\hat{I}{»}_{158\hat{\mathrm{I}}¼\mathrm{m}}$ dust continuum, we find that MACS0308-zD1's star-formation activity occurs in a dust-free environment with the stringent upper limit of infrared luminosity $\lesssim 9\times 10^8{\mathrm{L}}_{\odot }$. Targeting this strongly lensed faint galaxy for follow-up ALMA and JWST observations will be crucial to characterize the details of typical galaxy growth in the early Universe.

10 pages, 6 figures, 1 table; submitted to ApJ