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3D spectroscopy of lensing cluster fields

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Galaxies as lenses to study more distant galaxies

Because gravity bends light, galaxies can act as giant lenses, magnifying more distant galaxies behind them and making their features clearer.

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The 3DLENS (3D spectroscopy of lensing cluster fields) project used observations recently taken with integral field spectroscopy instruments on the Very Large Telescope to study the resolved properties of lensed galaxies highly magnified by massive galaxy clusters. One of the main challenges was to correct for the effects of magnification to reach the smallest physical scales in distant galaxies (between 100 pc and 1 kpc) per spatial element of resolution. The team developed and published new algorithms to perform these corrections and measure the morphology and kinematics of the gas in distant lensed galaxies. This modelling relied on the spectroscopic measurement of multiple images in the same lensing clusters, which is feasible thanks to the large field of view and sensitivity of the instrument used, covering the full strong lensing region of the cluster. The measurements show that it is possible to measure well-ordered velocity fields in such distant galaxies. During the formation of isolated less massive galaxies early in the universe, the gas settled into disk-like structures, albeit more turbulent than the equivalent features in more local (and therefore older) galaxies. Dust and carbon monoxide (CO) molecular gas observations were obtained covering the high magnification region of two massive clusters. These allowed the detection of dust emission in highly magnified, distant low-mass galaxies, and high enough signal-to-noise to resolve the dust emission in the source plane. In addition, the team obtained the first detection of a dust continuum in an extremely distant galaxy. For the CO gas measurements, single-dish and interferometric millimetre observations allowed measurement of the molecular line transitions in distant low-mass galaxies, opening a new parameter space in far-infrared bright, magnified galaxies. This was possible thanks to the large collaboration supporting the project being able to make multi-wavelength follow-up observations of such galaxies. A study of the carbon properties in very distant galaxies has been initiated. A pilot study has shown that low-mass galaxies generally show reasonably strong carbon emission in the ultraviolet, extending the widely used Lyman-alpha study technique to a new spectroscopic probe. The first carbon detection of an extremely distant galaxy has been made.


Galaxies, 3DLENS, lensing cluster, Very Large Telescope, lensed galaxies

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