Lens Model and Source Reconstruction Reveal the Morphology and Star Formation Distribution in the Cool Spiral LIRG SGAS J143845.1$+$145407

Abstract

We present $HubbleSpaceTelescope$ ($HST$) imaging and grism spectroscopy of a strongly lensed LIRG at $z=0.816$, SGAS 143845.1$+$145407, and use the magnification boost of gravitational lensing to study the distribution of star formation throughout this galaxy. Based on the $HST$ imaging data, we create a lens model for this system; we compute the mass distribution and magnification map of the $z=0.237$ foreground lens. We find that the magnification of the lensed galaxy ranges between $2$ and $10$, with a total magnification (measured over all the images of the source) of $\mu =11.8_{-2.4}^{+4.6}$. We find that the total projected mass density within $\sim 34$ kpc of the brightest cluster galaxy is $6.0_{-0.7}^{+0.3}\times 10^{12}{M}_{\odot }$. Using the lens model we create a source reconstruction for SGAS 143845.1$+$145407, which paired with a faint detection of H$\alpha$ in the grism spectroscopy, allows us to finally comment directly on the distribution of star formation in a $z\sim 1$ LIRG. We find widespread star formation across this galaxy, in agreement with the current understanding of these objects. However, we note a deficit of H$\alpha$ emission in the nucleus of SGAS 143845.1$+$145407, likely due to dust extinction.

7 pages, 8 figures, 2 tables

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