Star formation losses due to tidal debris in "hierarchical" galaxy formation

¹ Institut d'Astrophysique de Paris, 98bis Bld. Arago, 75014 Paris, France e-mail: ninin@iap.fr; devriend@iap.fr; bouchet@iap.fr; guider@iap.fr; gam@iap.fr
² Observatoire astronomique de Strasbourg, CNRS, 11 rue de l'Université, 67000 Strasbourg, France
³ Nicolaus Copernicus Astronomical Center, ul. Bartycka 18, 00-716 Warsaw, Poland
⁴ Inter-University Centre for Astronomy and Astrophysics, Post Bag 4, Ganeshkhind, Pune, 411 007, India
⁵ DAEC, Observatoire de Paris-Meudon, 5 place Jules Janssen, 92195 Meudon Cedex, France

Corresponding author: B. F. Roukema, boud.roukema@obspm.fr

Received: 27 January 2000
Accepted: 7 May 2001

Abstract

N-body studies have previously shown that the bottom-up hierarchical formation of dark matter haloes is not as monotonic as implicitly assumed in the Press-Schechter formalism. During and following halo mergers, matter can be ejected into tidal tails, shells or low density "atmospheres" outside of the successor haloes' virialisation radii (or group-finder outermost radii). The implications that the possible truncation of star formation in this tidal "debris" may have for observational galaxy statistics are examined here using the ArFus N-body plus semi-analytical galaxy modelling software for standard star formation hypotheses. In the N-body simulations studied, the debris typically remains close to the successor halo and falls back into the successor haloes given sufficient time. A maximum debris loss of around 16% is found for redshift intervals of around at with little dependence on the matter density parameter and the cosmological constant . Upper and lower bounds on stellar losses implied by a given set of N-body simulation output data can be investigated by choice of the merging/identity criterion of haloes between successive N-body simulation output times. A median merging/identity criterion is defined and used to deduce an upper estimate of possible star formation and stellar population losses. A largest successor merging/identity criterion is defined to deduce an estimate which minimises stellar losses. The losses for star formation and luminosity functions are strongest for low luminosity galaxies -a likely consequence of the fact that the debris fraction is highest for low mass haloes - and at intermediate redshifts . The losses in both cases are mostly around 10% -30% , have some dependence on and negligible dependence on This upper bound on likely losses in star formation rates and stellar populations is smaller than the uncertainties in estimates of corresponding observational parameters. Hence, it may not be urgent to include a correction for this in Press-Schechter based galaxy formation models, except when statistics regarding dwarf galaxies are under study.