Galaxy and Mass Assembly (GAMA) : halo formation times and halo assembly bias on the cosmic web
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We present evidence for halo assembly bias as a function of geometric environment (GE). By classifying GAMA galaxy groups as residing in voids, sheets, filaments or knots using a tidal tensor method, we find that low-mass haloes that reside in knots are older than haloes of the same mass that reside in voids. This result provides direct support to theories that link strong halo tidal interactions with halo assembly times. The trend with geometric environment is reversed at large halo mass, with haloes in knots being younger than haloes of the same mass in voids. We find a clear signal of halo downsizing - more massive haloes host galaxies that assembled their stars earlier. This overall trend holds independently of GE. We support our analysis with an in-depth exploration of the L-Galaxies semi-analytic model, used here to correlate several galaxy properties with three different definitions of halo formation time. We find a complex relationship between halo formation time and galaxy properties, with significant scatter. We confirm that stellar mass to halo mass ratio, specific star formation rate (SFR) and mass-weighed age are reasonable proxies of halo formation time, especially at low halo masses. Instantaneous SFR is a poor indicator at all halo masses. Using the same semi-analytic model, we create mock spectral observations using complex star-formation and chemical enrichment histories, which approximately mimic GAMA's typical signal-to-noise ratio and wavelength range. We use these mocks to assert how well potential proxies of halo formation time may be recovered from GAMA-like spectroscopic data.
Tojeiro , R , Eardley , E , Peacock , J A , Norberg , P , Alpaslan , M , Driver , S P , Henriques , B , Hopkins , A M , Kafle , P R , Robotham , A S G , Thomas , P , Tonini , C & Wild , V 2017 , ' Galaxy and Mass Assembly (GAMA) : halo formation times and halo assembly bias on the cosmic web ' , Monthly Notices of the Royal Astronomical Society , vol. 470 , no. 3 , pp. 3720-3741 . https://doi.org/10.1093/mnras/stx1466
Monthly Notices of the Royal Astronomical Society
Copyright © 2017, the Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. This work has been made available online in accordance with the publisher’s policies. This is the author created, accepted version manuscript following peer review and may differ slightly from the final published version. The final published version of this work is available at https://doi.org/10.1093/mnras/stx1466
DescriptionRT acknowledges support from the Science and Technology Facilities Council via an Ernest Rutherford Fellowship (grant number ST/K004719/1). VW and EE acknowledge support of the European Research Council via the award of a starting grant (SEDMorph; P.I. V. Wild). PAT (ORCID 0000-0001-6888-6483) acknowledges support from the Science and Technology Facilities Council (grant number ST/L000652/1).
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