Fakultäten » Mathematisch-naturwissenschaftliche Fakultät » Physik-Institut » Prof. Dr. Philippe Jetzer » Jetzer

Completed research project

Title / Titel Scaling relations and connections with star formation histories (2010)
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Summary / Zusammenfassung We examine correlations between the masses, sizes, and star formation histories for a large sample of low-redshift early-type galaxies (ETGs), using a simple suite of dynamical and stellar populations models [3]. We con rm an anti-correlation between size and stellar age, and survey for trends with the central content of dark matter (DM). An average relation between central DM density and galaxy size of hDMi / R��2 eff provides the rst clear indication of cuspy DM haloes in these galaxies akin to standard CDM haloes that have undergone adiabatic contraction. The DM density scales with galaxy mass as expected, deviating from suggestions of a universal halo pro le for dwarf and late-type galaxies. We introduce a new fundamental constraint on galaxy formation by nding that the central DM fraction decreases with stellar age. This result is only partially explained by the sizeage dependencies, and the residual trend is in the opposite direction to basic DM halo expectations. Therefore, we suggest that there may be a connection between age and halo contraction, and that galaxies forming earlier had stronger baryonic feedback which expanded their haloes, or else lumpier baryonic accretion that avoided halo contraction. An alternative explanation is a lighter initial mass function for older stellar populations.

Central dark matter trends in early-type galaxies from strong lensing, dynamics and stellar populations (Ph. Jetzer, C. Tortora) We analyze the correlations between central dark matter (DM) content of early-type galaxies and their sizes and ages, using a sample of intermediate-redshift (z  0:2) gravitational lenses from the SLACS survey, and by comparing them to a larger sample of 2 z  0 galaxies. We decompose the deprojected galaxy masses into DM and stellar components using combinations of strong lensing, stellar dynamics, and stellar populations modelling. For a given stellar mass, we nd that for galaxies with larger sizes, the DM fraction increases and the mean DM density decreases, consistently with the cuspy halos expected in cosmological formation scenarios. The DM fraction also decreases with stellar age, which can be partially explained by the inverse correlation between size and age. The residual trend may point to systematic dependencies on formation epoch of halo contraction or stellar initial mass functions. These results are similar for the lens and local galaxies, showing no evidence of galaxy evolution over the last  3 Gyr other than passive stellar ageing. The paper with our results has been accepted for publication in ApJ [14].

Dark matter scaling relations in intermediate z haloes (C. Tortora) We investigate scaling relations between the dark matter (DM) halo model parameters for a sample of intermediate redshift early-type galaxies (ETGs) resorting on a combined analysis of Einstein radii and aperture velocity dispersions. Modelling the dark halo with a Navarro-Frenk-White pro le and assuming a Salpeter initial mass function (IMF) to estimate stellar masses, we nd that the column density S and the Newtonian acceleration within the halo characteristic radius rs and e ective radius Reff are not universal quantities, but correlates with the luminosity LV , the stellar mass M? and the halo mass M200, contrarily to what is expected from recent claims in literature. We nally discuss a tight correlation among the DM mass MDM(Reff ) within the e ective radius Reff , the stellar mass M?(Reff ) and Reff itself. The slope of the scaling relations discussed here strongly depends, however, on the DM halo model and the IMF adopted so that these ingredients have to be better constrained in order to draw de nitive conclusions on the DM scaling relations for ETGs. The paper is accepted for publication in MNRAS [15].
Project leadership and contacts /
Projektleitung und Kontakte
Prof Philippe Jetzer (Project Leader)  
Dr Crescenzo Tortora  
Funding source(s) /
Unterstützt durch
Universität Zürich (position pursuing an academic career), SNF (Personen- und Projektförderung)
Duration of Project / Projektdauer Jan 2010 to Dec 2010