Properties of simulated Milky Way-mass galaxies in loose group and field environments

Abstract

Aims. We test the validity of comparing simulated field disk galaxies with the empirical properties of systems situated within environments more comparable to loose groups, including the Milky Way's Local Group. Methods. Cosmological simulations of Milky Way-mass galaxies have been realised in two different environment samples: in the field and in loose groups environments with similar properties to the Local Group. Apart from the differing environments of the galaxies, the samples are kept as homogeneous as possible with equivalent ranges in last major merger time, halo mass and halo spin. Comparison of these two samples allow for systematic differences in the simulations to be identified. A kinematic decomposition is employed to objectively quantify the spheroid-to-disk ratio and to isolate the disk-star population. Metallicity gradients, disk scale lengths, colours, magnitudes and age-velocity dispersion relations are studied for each galaxy in the suite and the strength of the link between these and environment of the galaxies is studied. Results. Metallicity gradients are consistent with observations of HII regions in spiral galaxies and, in agreement with observations, correlate with total galaxy mass. The bulge-to-disk ratio of the galaxies show that these galaxies are less spheroid dominated than many other simulated galaxies in literature with the majority of both samples being disk dominated. We find that secular evolution and mergers dominate the spread of morphologies and metallicity gradients with no visible differences between the two environment samples. In contrast with this consistency in the two samples there is tentative evidence for a systematic difference in the velocity dispersion-age relations of galaxies in the different environments. Loose group galaxies appear to have more discrete steps in their velocity dispersion-age relations, if this is true it suggests that impulsive heating is more efficient in the stars of galaxies in denser environment than in the field. We conclude that at the current resolution of cosmological galaxy simulations field environment galaxies are sufficiently similar to those in loose groups to be acceptable proxies for comparison with the Milky Way provided that a similar assembly history is considered.

The CALIFA survey across the Hubble sequence

“…Negative radial metallicity gradients are expected, as the classical models predict. This assumption is a natural outcome of the mass, momentum, and energy conservation laws imposed in the simulations of disks in a cosmological context (Brook et al 2011(Brook et al , 2012Few et al 2012;Pilkington et al 2012a,b;Gibson et al 2013). Pilkington et al (2012a) examined a set of 25 simulations, from several groups, using different codes and initial conditions (Stinson et al 2010;Rahimi et al 2011;Kobayashi & Nakasato 2011;Few et al 2012) to predict the present-day metallicity gradient in MW-like galaxies and its evolution.…”

“…This assumption is a natural outcome of the mass, momentum, and energy conservation laws imposed in the simulations of disks in a cosmological context (Brook et al 2011(Brook et al , 2012Few et al 2012;Pilkington et al 2012a,b;Gibson et al 2013). Pilkington et al (2012a) examined a set of 25 simulations, from several groups, using different codes and initial conditions (Stinson et al 2010;Rahimi et al 2011;Kobayashi & Nakasato 2011;Few et al 2012) to predict the present-day metallicity gradient in MW-like galaxies and its evolution. Although the evolution of the simulated metallicity gradients depends strongly on the choice of the subgrid physics employed, most of the simulated galaxies tend to a similar present-day gradient of ∼−0.05 dex kpc −1 , in agreement with the Chiappini et al (2001) and Mollá & Díaz (2005) models for normal galaxies as the MW.…”

“…To compare the RaDES simulated galaxies (Few et al 2012) with our results, 19 galaxies of the Pilkington et al (2012a) sample, have been analyzed, measuring the HLR and the gradients in a similar way as we have done with the CALIFA galaxies (Ruiz-Lara, in prep. ; Ruiz-Lara et al, priv.…”

“…Recently, a new set of cosmological hydrodynamic simulations have started to predict how the spatially resolved information of the properties of stellar populations in galaxies can constrain the complex interplay between gas infall, outflows, stellar migration, radial gas flows, and star formation efficiency, in driving the inside-out growth of galactic disks (Brook et al 2012;Gibson et al 2013;Few et al 2012;Pilkington et al 2012a;Minchev et al 2014). Radiative cooling, star formation, feedback from supernovae, and chemical enrichment are also included in simulations to predict radial metallicity gradients as a function of merging history.…”

Where do galaxies end? Comparing measurement techniques of hydrodynamic-simulation galaxies’ integrated properties

“…We note techniques beyond what we have listed exist in the literature as well (e.g. Doménech-Moral et al 2012;Few et al 2012, who decompose the galaxy into disc and bulge particles). The aperture choices listed in Table 1 can be broken into categories of an optical limit (R25), fixed aperture (comoving or physically fixed), and fraction of the virial radius.…”