Abstract
We report the discovery of a molecular wind signature from a massive intensely star-forming clump of a few 109 M⊙, in the strongly gravitationally lensed submillimeter galaxy “the Emerald” (PLCK_G165.7+49.0) at z = 2.236. The Emerald is amongst the brightest high-redshift galaxies on the submillimeter sky, and was initially discovered with the Planck satellite. The system contains two magnificient structures with projected lengths of 28.5″ and 21″ formed by multiple, near-infrared arcs, falling behind a massive galaxy cluster at z = 0.35, as well as an adjacent filament that has so far escaped discovery in other wavebands. We used HST/WFC3 and CFHT optical and near-infrared imaging together with IRAM and SMA interferometry of the CO(4–3) line and 850 μm dust emission to characterize the foreground lensing mass distribution, construct a lens model with LENSTOOL, and calculate gravitational magnification factors between 20 and 50 in most of the source. The majority of the star formation takes place within two massive star-forming clumps which are marginally gravitationally bound and embedded in a 9 × 1010 M⊙, fragmented disk with 20% gas fraction. The stellar continuum morphology is much smoother and also well resolved perpendicular to the magnification axis. One of the clumps shows a pronounced blue wing in the CO(4–3) line profile, which we interpret as a wind signature. The mass outflow rates are high enough for us to suspect that the clump might become unbound within a few tens of Myr, unless the outflowing gas can be replenished by gas accretion from the surrounding disk. The velocity offset of –200 km s−1 is above the escape velocity of the clump, but not that of the galaxy overall, suggesting that much of this material might ultimately rain back onto the galaxy and contribute to fueling subsequent star formation.
Highlights
Rapid, intense star formation that occurs in dusty star-forming galaxies at z ∼ 1–4 (Casey et al 2014) is expected to dominate the cosmic star-formation rate density at these epochs (e.g., Dole et al 2006) and corresponds to the early growth phase of giant ellipticals seen in high-density regions of the local Universe (e.g., Lilly et al 1999; Swinbank et al 2006)
A significantly lower ratio, R4,1 = 0.25 ± 0.10, is found if we use the integrated CO(4–3) line luminosity we measured with the IRAM 30-m telescope, μLCO(4−3) = (46.0 ± 3.1) × 1010 K km s−1 pc2 (Cañameras et al 2018), and the CO(1–0) line luminosity from Harrington et al (2018), who recently detected this line with the Green Bank Telescope (GBT) for a few lens candidates drawn from the Planck allsky survey, including five Gravitationally Enhanced subMillimeter Sources (GEMS)
If we subtract the wings of the CO(1–0) line from the GBT spectrum, and correct for missing flux in our Plateau de Bure Interferometer (PdBI) spectrum spatially-integrated over the arc, we find R4,1 0.45, comparable to the typical values found by Spilker et al (2014) and Danielson et al (2011)
Summary
Intense star formation that occurs in dusty star-forming galaxies at z ∼ 1–4 (Casey et al 2014) is expected to dominate the cosmic star-formation rate density at these epochs (e.g., Dole et al 2006) and corresponds to the early growth phase of giant ellipticals seen in high-density regions of the local Universe (e.g., Lilly et al 1999; Swinbank et al 2006). To further characterize this source, we obtained CFHT and Spitzer optical and near-infrared imaging, as well as subarcsecond submillimeter and millimeter interferometry of the dust and CO(4–3) line emission with the Submillimeter Array (SMA) and the IRAM Plateau de Bure Interferometer (PdBI) We used these data to characterize the foreground lensing potential, a hitherto unknown massive galaxy cluster at z = 0.348 with an adjacent filament, to calculate a strong lensing model with Lenstool, and to characterize the gas kinematics and spatially resolved dust and star formation properties of the background source.
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