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Register a new userThe importance of the local density in shaping the galaxy stellar mass functions
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Benedetta Vulcani
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Exploiting the capabilities of four different surveys --- the Padova-Millennium Galaxy and Group Catalogue (PM2GC), the WIde-field Nearby Galaxy-cluster Survey (WINGS), the IMACS Cluster Building Survey (ICBS) and the ESO Distant Cluster Survey (EDisCS) --- we analyze the galaxy stellar mass distribution as a function of local density in mass-limited samples, in the field and in clusters from low (z>0.04) to high (z<0.8) redshift. We find that at all redshifts and in all environments, local density plays a role in shaping the mass distribution. In the field, it regulates the shape of the mass function at any mass above the mass limits. In clusters, it seems to be important only at low masses (log M_ast/M_sun <10.1 in WINGS and log M_ast/M_sun < 10.4 in EDisCS), otherwise it seems not to influence the mass distribution. Putting together our results with those of Calvi et al. and Vulcani et al. for the global environment, we argue that at least at $zleq 0.8$ local density is more important than global environment in determining the galaxy stellar mass distribution, suggesting that galaxy properties are not much dependent of halo mass, but do depend on local scale processes.
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[Abridged] With the first 10000 spectra of the flux limited zCOSMOS sample (I<=22.5) we study the evolution of environmental effects on galaxy properties since z=1.0, and disentangle the dependence among galaxy colour, stellar mass and local density (3D local density contrast `delta, computed with the 5th nearest neighbour approach). We confirm that within a luminosity-limited sample (M_B<=-20.5-z) the fraction of red (U-B>=1) galaxies f_red depends on delta at least up to z=1, with red galaxies residing mainly in high densities. This trend weakens for increasing z, and it is mirrored by the behaviour of the fraction of galaxies with D4000A break >=1.4. We also find that up to z=1 the fraction of galaxies with log(EW[OII]) >=1.15 is higher for lower delta, and also this dependence weakens for increasing z. Given the triple dependence among galaxy colours, stellar mass and delta, the colour-delta relation found in the luminosity-selected sample can be due to the broad range of stellar masses. Thus, we fix the stellar mass and we find that in this case the colour-delta relation is flat up to z=1 for galaxies with log(M/M_sun)>=10.7. This means that for these masses the colour-delta relation found in a luminosity-selected sample is the result of the combined colour-mass and mass-delta relations. In contrast, we find that for 0.1<=z<=0.5 and log(M/M_sun)<=10.7 f_red depends on delta even at fixed mass. In these mass and z ranges, environment affects directly also galaxy colours. We suggest a scenario in which the colour depends primarily on stellar mass, but for relatively low mass galaxies the local density modulates this dependence. These galaxies formed more recently, in an epoch when evolved structures were already in place, and their longer SFH allowed environment-driven physical processes to operate during longer periods of time.
Magnification changes the observed number counts of galaxies on the sky. This biases the observed tangential shear profiles around galaxies, the so-called galaxy-galaxy lensing (GGL) signal, and the related excess mass profile. Correspondingly, inference of physical quantities, such as the mean mass profile of halos around galaxies, are affected by magnification effects. We use simulated shear and galaxy data of the Millennium Simulation to quantify the effect on shear and mass estimates from magnified lens and source number counts. The former are due to the large-scale matter distribution in the foreground of the lenses, the latter are caused by magnification of the source population by the matter associated with the lenses. The GGL signal is calculated from the simulations by an efficient fast-Fourier transform that can also be applied to real data. The numerical treatment is complemented by a leading-order analytical description of the magnification effects, which is shown to fit the numerical shear data well. We find the magnification effect is strongest for steep galaxy luminosity functions and high redshifts. For a lens redshift of $z_mathrm{d}=0.83$, a limiting magnitude of $22,mathrm{mag}$ in the $r$-band and a source redshift of $z_mathrm{s}=0.99$, we find that a magnification correction changes the shear profile up to $45%$ and the mass is biased by up to $55 %$. For medium-redshift galaxies the relative change in shear and mass is typically a few percent. As expected, the sign of the bias depends on the local slope of the lens luminosity function $alpha_mathrm{d}$, where the mass is biased low for $alpha_mathrm{d}<1$ and biased high for $alpha_mathrm{d}>1$. Whereas the magnification effect of sources is rarely than more $1%$, the statistical power of future weak lensing surveys warrants correction for this effect.
The disk surface density of the nearby spiral galaxy M33 is estimated assuming that it is marginally stable against gravitational perturbations. For this purpose we used the radial profile of line-of-sight velocity dispersion of the disk planetary nebulae obtained by Ciardullo et al. (2004). The surface density profile we obtained is characterized by the radial scalelength which is close to the photometrical one and is in a good agreement with the rotation curve of M33 and with the mass-to-light ratio corresponding to the observed color indices. However at the galactocentric distance $r>7$ kpc the dynamical overheating of the disk remains quite possible. A thickness of the stellar disk of M33 should increase outwards. The dark halo mass exceeds the mass of the disk at $r>$ 7 kpc. The obtained radial profile of the disk surface density and the radial gradient of $O/H$ are used to calculate the effective oxygen yield $Y_{eff}$ in the frame of the instantaneous recycling approximation. It is shown that $Y_{eff}$ increases with radius which may indicate that the role of accretion of metal-poor gas in the chemical evolution of interstellar medium decreases outwards.
We investigate the impact of local environment on the galaxy stellar mass function (SMF) spanning a wide range of galaxy densities from the field up to dense cores of massive galaxy clusters. Data are drawn from a sample of eight fields from the Observations of Redshift Evolution in Large-Scale Environments (ORELSE) survey. Deep photometry allow us to select mass-complete samples of galaxies down to 10^9 Msol. Taking advantage of >4000 secure spectroscopic redshifts from ORELSE and precise photometric redshifts, we construct 3-dimensional density maps between 0.55<z<1.3 using a Voronoi tessellation approach. We find that the shape of the SMF depends strongly on local environment exhibited by a smooth, continual increase in the relative numbers of high- to low-mass galaxies towards denser environments. A straightforward implication is that local environment proportionally increases the efficiency of (a) destroying lower-mass galaxies and/or (b) growth of higher-mass galaxies. We also find a presence of this environmental dependence in the SMFs of star-forming and quiescent galaxies, although not quite as strongly for the quiescent subsample. To characterize the connection between the SMF of field galaxies and that of denser environments we devise a simple semi-empirical model. The model begins with a sample of ~10^6 galaxies at z_start=5 with stellar masses distributed according to the field. Simulated galaxies then evolve down to z_final=0.8 following empirical prescriptions for star-formation, quenching, and galaxy-galaxy merging. We run the simulation multiple times, testing a variety of scenarios with differing overall amounts of merging. Our model suggests that a large number of mergers are required to reproduce the SMF in dense environments. Additionally, a large majority of these mergers would have to occur in intermediate density environments (e.g. galaxy groups).
The metallicity and its relationship with other galactic properties is a fundamental probe of the evolution of galaxies. In this work, we select about 750,000 star-forming spatial pixels from 1122 blue galaxies in the MaNGA survey to investigate the global stellar mass - local stellar mass surface density - gas-phase metallicity ($M_*$ - $Sigma_*$ - $Z$ ) relation. At a fixed $M_*$, the metallicity increases steeply with increasing $Sigma_*$. Similarly, at a fixed $Sigma_*$, the metallicity increases strongly with increasing $M_*$ at low mass end, while this trend becomes less obvious at high mass end. We find the metallicity to be more strongly correlated to $Sigma_*$ than to $M_*$. Furthermore, we construct a tight (0.07 dex scatter) $M_*$ - $Sigma_*$ - $Z$ relation, which reduces the scatter in the $Sigma_*$ - $Z$ relation by about 30$%$ for galaxies with $7.8 < {rm log}(M_*/M_odot) < 11.0$, while the reduction of scatter is much weaker for high-mass galaxies. This result suggests that, especially for low-mass galaxies, the $M_*$ - $Sigma_*$ - $Z$ relation is largely more fundamental than the $M_*$ - $Z$ and $Sigma_*$ - $Z$ relations, meaning that both $M_*$ and $Sigma_*$ play important roles in shaping the local metallicity. We also find that the local metallicity is probably independent on the local star formation rate surface density at a fixed $M_*$ and $Sigma_*$. Our results are consistent with the scenario that the local metallicities in galaxies are shaped by the combination of the local stars formed in the history and the metal loss caused by galactic winds.
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