The ATLAS3D project - XXII. Low-efficiency star formation in early-type galaxies: hydrodynamic models and observations

Martig, Marie; Crocker, Alison F.; Bournaud, Frédéric; Emsellem, Eric; Gabor, Jared M.; Alatalo, Katherine; Blitz, Leo; Bois, Maxime; Bureau, Martin; Cappellari, Michele; Davies, Roger L.; Davis, Timothy A.; Dekel, Avishai; de Zeeuw, P. T.; Duc, Pierre-Alain; Falcón-Barroso, J.; Khochfar, Sadegh; Krajnović, Davor; Kuntschner, Harald; Morganti, Raffaella; McDermid, Richard M.; Naab, Thorsten; Oosterloo, Tom; Sarzi, Marc; Scott, Nicholas; Serra, Paolo; Griffin, Kristen Shapiro; Teyssier, Romain; Weijmans, Anne-Marie; Young, Lisa M.
Bibliographical reference

Monthly Notices of the Royal Astronomical Society, Volume 432, Issue 3, p.1914-1927

Advertised on:
7
2013
Number of authors
30
IAC number of authors
1
Citations
106
Refereed citations
100
Description
We study the global efficiency of star formation in high-resolution hydrodynamical simulations of gas discs embedded in isolated early-type and spiral galaxies. Despite using a universal local law to form stars in the simulations, we find that the early-type galaxies are offset from the spirals on the large-scale Kennicutt relation, and form stars two to five times less efficiently. This offset is in agreement with previous results on morphological quenching: gas discs are more stable against star formation when embedded in early-type galaxies due to the lower disc self-gravity and increased shear. As a result, these gas discs do not fragment into dense clumps and do not reach as high densities as in the spiral galaxies. Even if some molecular gas is present, the fraction of very dense gas (typically above 104 cm-3) is significantly reduced, which explains the overall lower star formation efficiency. We also analyse a sample of local early-type and spiral galaxies, measuring their CO and H I surface densities and their star formation rates as determined by their non-stellar 8 μm emission. As predicted by the simulations, we find that the early-type galaxies are offset from the Kennicutt relation compared to the spirals, with a twice lower efficiency. Finally, we validate our approach by performing a direct comparison between models and observations. We run a simulation designed to mimic the stellar and gaseous properties of NGC 524, a local lenticular galaxy, and find a gas disc structure and global star formation rate in good agreement with the observations. Morphological quenching thus seems to be a robust mechanism, and is also consistent with other observations of a reduced star formation efficiency in early-type galaxies in the COLD GASS survey. This lower efficiency of star formation is not enough to explain the formation of the whole red sequence, but can contribute to the reddening of some galaxies.
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Traces of Galaxy Formation: Stellar populations, Dynamics and Morphology
We are a large, diverse, and very active research group aiming to provide a comprehensive picture for the formation of galaxies in the Universe. Rooted in detailed stellar population analysis, we are constantly exploring and developing new tools and ideas to understand how galaxies came to be what we now observe.
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