arXiv subjects

Stefanie Phleps

Publications and source records attributed to Stefanie Phleps.

7 recordsLinked to original sources

arXiv2013

The Pan-STARRS1 Medium-Deep Survey: The role of galaxy group environment in the star formation rate versus stellar mass relation and quiescent fraction out to $z \sim 0.8$

Using a large sample of field and group galaxies drawn from the Pan-STARRS1 Medium-Deep Survey, we present the specific star formation rate (SSFR) - stellar mass (M*) relation, as well as the quiescent fraction versus M* relation in different environments. We confirm that the fraction of quiescent galaxies is strongly dependent on environment at a fixed stellar mass, but that the amplitude and the slope of the star-forming sequence is similar between the field and groups: in other words, the SSFR-density relation at a fixed stellar mass is primarily driven by the change in the star-forming and quiescent fractions between different environments rather than a global suppression in the star formation rate for the star-forming population. However, when we restrict our sample to the cluster-scale environments ($M>10^{14}M_{solar}$), we find a global reduction in the SSFR of the star forming sequence of $17\%$ at 4$σ$ confidence as opposed to its field counterpart. After removing the stellar mass dependence of the quiescent fraction seen in field galaxies, the excess in the quiescent fraction due to the environment quenching in groups and clusters is found to increase with stellar mass. We argue that these results are in favor of galaxy mergers to be the primary environment quenching mechanism operating in galaxy groups whereas strangulation is able to reproduce the observed trend in the environment quenching efficiency and stellar mass relation seen in clusters. Our results also suggest that the relative importance between mass quenching and environment quenching depends on stellar mass -- the mass quenching plays a dominant role in producing quiescent galaxies for more massive galaxies, while less massive galaxies are quenched mostly through the environmental effect, with the transition mass around $1-2\times10^{10}M_{solar}$ in the group/cluster environment. (abridged)

astro-ph.CO↗

arXiv2013

More than just halo mass: Modelling how the red galaxy fraction depends on multiscale density in a HOD framework

The fraction of galaxies with red colours depends sensitively on environment, and on the way in which environment is measured. To distinguish competing theories for the quenching of star formation, a robust and complete description of environment is required, to be applied to a large sample of galaxies. The environment of galaxies can be described using the density field of neighbours on multiple scales - the multiscale density field. We are using the Millennium simulation and a simple HOD prescription which describes the multiscale density field of Sloan Digital Sky Survey DR7 galaxies to investigate the dependence of the fraction of red galaxies on the environment. Using a volume limited sample where we have sufficient galaxies in narrow density bins, we have more dynamic range in halo mass and density for satellite galaxies than for central galaxies. Therefore we model the red fraction of central galaxies as a constant while we use a functional form to describe the red fraction of satellites as a function of halo mass which allows us to distinguish a sharp from a gradual transition. While it is clear that the data can only be explained by a gradual transition, an analysis of the multiscale density field on different scales suggests that colour segregation within the haloes is needed to explain the results. We also rule out a sharp transition for central galaxies, within the halo mass range sampled.

astro-ph.CO↗

arXiv2012

A model of the anisotropic correlation function xi(rp, pi) in redshift space including redshift errors

With the advent of very large volume, wide-angle photometric redshift surveys like e.g. Pan-STARRS, DES, or PAU, which aim at using the spatial distribution of galaxies as a means to constrain the equation of state parameter of dark energy, w_DE, it has become extremely important to understand the influence of redshift inaccuracies on the measurement. We have developed a new model for the anisotropic two point large-scale (r > 64 h^-1 Mpc) correlation function xi(rp,pi), in which nonlinear structure growth and nonlinear coherent infall velocities are taken into account, and photometric redshift errors can easily be incorporated. In order to test its validity and investigate the effects of photometric redshifts, we compare our model with the correlation function computed from a suite of 50 large-volume, moderate-resolution numerical N-body simulation boxes, where we can perform the analysis not only in real- and redshift space, but also simulate the influence of a gaussian redshift error distribution with an absolute rms of sigma_z= 0.015, 0.03, 0.06, and 0.12, respectively. We conclude that for the given volume (V_box =2.4 h^-3 Gpc^3) and number density (n ~ 1.25 10^-4) of objects the full shape of xi(rp,pi) is modeled accurately enough to use it to derive unbiased constraints on the equation of state parameter of dark energy w_DE and the linear bias b, even in the presence of redshift errors of the order of sigma_z = 0.06.

astro-ph.CO↗

arXiv2012

Cosmological implications from the full shape of the large-scale power spectrum of the SDSS DR7 luminous red galaxies

We obtain cosmological constraints from a measurement of the spherically averaged power spectrum (PS) of the distribution of about 90000 luminous red galaxies (LRGs) across 7646 deg2 in the Northern Galactic Cap from the DR7 of the SDSS. The errors and mode correlations are estimated thanks to the 160 LasDamas mock catalogues, created in order to simulate the same galaxies and to have the same selection as the data. We apply a model, that can accurately describe the full shape of the PS with the use of a small number of free parameters. Using the LRG PS, in combination with the latest measurement of the temperature and polarisation anisotropy in the cosmic microwave background (CMB), the luminosity-distance relation from the largest available type 1a supernovae (SNIa) dataset and a precise determination of the local Hubble parameter, we obtain cosmological constraints for five different parameter spaces. When all the four experiments are combined, the flat LCDM model is characterised by Omega_M=0.259+-0.016, Omega_b=0.045+-0.001, n_s=0.963+-0.011, sigma_8=0.802+-0.021 and h=0.712+-0.014. When we consider curvature as a free parameter, we do not detect deviations from flatness: Omega_k=(1.6+-5.4)*10^{-3}, when only CMB and the LRG PS are used; the inclusion of the other two experiments do not improve this result. Considering the dark energy equation of state w_DE as time independent, we measure w_DE=-1.025+-0.065, for a flat geometry, w_DE=-0.981+-0.083 otherwise. When describing w_DE through a linear function of the scale factor, our results do not evidence any time evolution. In the next few years new experiments will allow to measure the clustering of galaxies with a precision much higher than achievable today. Models like the one used here will be a valuable tool in order to achieve the full potentials of the observations and obtain unbiased constraints on the cosmological parameters.

astro-ph.CO↗

arXiv2010

A new model for the full shape of the large-scale power spectrum

We present a new model for the full shape of large-scale the power spectrum based on renormalized perturbation theory. To test the validity of this prescription, we compare this model against power spectra measured in a suite of 50 large volume, moderate resolution N-body simulations. Our results indicate that this simple model provides an accurate description of the full shape of the power spectrum taking into account the effects of non-linear evolution, redshift-space distortions and halo bias for scales k < 0.15 h/Mpc, making it a valuable tool for the analysis of forthcoming galaxy surveys. Even though its application is restricted to large scales, this prescription can provide tighter constraints on the dark energy equation of state parameter w_{DE} than those obtained by modelling the baryonic acoustic oscillations signal only, where the information of the broad-band shape of the power spectrum is discarded. Our model is able to provide constraints comparable to those obtained by applying a similar model to the full shape of the correlation function, which is affected by different systematics. Hence, with accurate modelling of the power spectrum, the same cosmological information can be extracted from both statistics.

astro-ph.CO↗

arXiv2006

The merger rate of massive galaxies

We calculate the projected two point correlation function for samples of luminous and massive galaxies in the COMBO-17 photometric redshift survey, focusing particularly on the amplitude of the correlation function at small projected radii and exploring the constraints such measurements can place on the galaxy merger rate. For nearly volume-limited samples with 0.4 2.5e10 M_sun is 5+/-1%. Incorporating close pair fractions from the literature, the 2dFGRS and the SDSS, we find a fairly rapid evolution of the merger fraction of massive galaxies between z=0.8 and the present day. Assuming that the major merger timescale is of order the dynamical timescale for close massive galaxy pairs, we tentatively infer that ~50% (70%) of all galaxies with present-day masses M_*>5e10 M_sun (remnants of mergers between galaxies with M_*>2.5e10 M_sun) have undergone a major merger since z=0.8(1): major mergers between massive galaxies are a significant driver of galaxy evolution over the last eight billion years.

astro-ph↗

arXiv2006

Comment on ``General Relativity Resolves Galactic Rotation Without Exotic Dark Matter'' by F.I. Cooperstock & S. Tieu

The general relativistic model of Cooperstock & Tieu, which attempts to fit rotation curves of spiral galaxies without invoking dark matter, is tested empirically using observations of the Milky Way. In particular, predictions for the mass density in the solar neighbourhood and the vertical density distribution at the position of the Sun are compared with observations. It is shown that the model of Cooperstock & Tieu, which was so constructed that it gives an excellent fit of the observed rotation curve, singularly fails to reproduce the observed local mass density and the vertical density profile of the Milky Way.

astro-ph↗