Inverse stellar population age gradients of post-starburst galaxies at z=0.8 with LEGA-C

D'Eugenio, Francesco and Wel, Arjen van der and Wu, Po-Feng and Barone, Tania M. and Houdt, Josha van and Bezanson, Rachel and Straatman, Caroline M. S. and Pacifici, Camilla and Muzzin, Adam and Gallazzi, Anna and Wild, Vivienne and Sobral, David and Bell, Eric F. and Zibetti, Stefano and Mowla, Lamiya and Franx, Marijn (2020) Inverse stellar population age gradients of post-starburst galaxies at z=0.8 with LEGA-C. Monthly Notices of the Royal Astronomical Society, 497 (1). 389–404. ISSN 0035-8711

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Abstract

We use deep, spatially resolved spectroscopy from the Large Early Galaxy Astrophysics Census Survey to study radial variations in the stellar population of 17 spectroscopically selected post-starburst (PSB) galaxies. We use spectral fitting to measure two Lick indices, H δA and Fe 4383 , and find that, on average, PSB galaxies have radially decreasing H δA and increasing Fe 4383  profiles. In contrast, a control sample of quiescent, non-PSB galaxies in the same mass range shows outwardly increasing H δA and decreasing Fe 4383 . The observed gradients are weak (≈−0.2 Å/Re), mainly due to seeing convolution. A two-SSP (simple stellar population) model suggests that intrinsic gradients are as strong as observed in local PSB galaxies (≈−0.8 Å/Re). We interpret these results in terms of inside-out growth (for the bulk of the quiescent population) versus star formation occurring last in the centre (for PSB galaxies). At z ≈ 0.8, central starbursts are often the result of gas-rich mergers, as evidenced by the high fraction of PSB galaxies with disturbed morphologies and tidal features (40 per cent). Our results provide additional evidence for multiple paths to quiescence: a standard path, associated with inside-out disc formation and with gradually decreasing star formation activity, without fundamental structural transformation, and a fast path, associated with centrally concentrated starbursts, leaving an inverse age gradient and smaller half-light radius.