Mass-to-light versus colour relations (MLCRs), derived from stellar population synthesis models, are widely used to estimate galaxy stellar masses (M$_*$) yet a detailed investigation of their inherent biases and limitations is still lacking. We quan
tify several potential sources of uncertainty, using optical and near-infrared (NIR) photometry for a representative sample of nearby galaxies from the Virgo cluster. Our method for combining multi-band photometry with MLCRs yields robust stellar masses, while errors in M$_*$ decrease as more bands are simultaneously considered. The prior assumptions in ones stellar population modelling dominate the error budget, creating a colour-dependent bias of up to 0.6 dex if NIR fluxes are used (0.3 dex otherwise). This matches the systematic errors associated with the method of spectral energy distribution (SED) fitting, indicating that MLCRs do not suffer from much additional bias. Moreover, MLCRs and SED fitting yield similar degrees of random error ($sim$0.1-0.14 dex) when applied to mock galaxies and, on average, equivalent masses for real galaxies with M$_* sim$ 10$^{8-11}$ M$_{odot}$. The use of integrated photometry introduces additional uncertainty in M$_*$ measurements, at the level of 0.05-0.07 dex. We argue that using MLCRs, instead of time-consuming SED fits, is justified in cases with complex model parameter spaces (involving, for instance, multi-parameter star formation histories) and/or for large datasets. Spatially-resolved methods for measuring M$_*$ should be applied for small sample sizes and/or when accuracies less than 0.1 dex are required. An Appendix provides our MLCR transformations for ten colour permutations of the $grizH$ filter set.
We present an extenstive literature compilation of age, metallicity, and chemical abundance pattern information for the 41 Galactic globular clusters (GGCs) studied by Schiavon et al. (2005). Our compilation constitutes a notable improvement over pre
vious similar work, particularly in terms of chemical abundances. Its primary purpose is to enable detailed evaluations of and refinements to stellar population synthesis models designed to recover the above information for unresolved stellar systems based on their integrated spectra. However, since the Schiavon sample spans a wide range of the known GGC parameter space, our compilation may also benefit investigations related to a variety of astrophysical endeavours, such as the early formation of the Milky Way, the chemical evolution of GGCs, and stellar evolution and nucleosynthesis. For instance, we confirm with our compiled data that the GGC system has a bimodal metallicity distribution and is uniformly enhanced in the alpha-elements. When paired with the ages of our clusters, we find evidence that supports a scenario whereby the Milky Way obtained its globular clusters through two channels, in situ formation and accretion of satellite galaxies. The distributions of C, N, O, and Na abundances and the dispersions thereof per cluster corroborate the known fact that all GGCs studied so far with respect to multiple stellar populations have been found to harbour them. Finally, using data on individual stars, we also confirm that the atmospheres of stars become progressively polluted by CN(O)-processed material after they leave the main sequence and uncover evidence which suggests the alpha-elements Mg and Ca may originate from more than one nucleosynthetic production site. [abridged]
We present stellar age profiles for 64 Virgo cluster disk galaxies whose analysis poses a challenge for current galaxy formation models. Our results can be summarized as follows: first, and contrary to observations of field galaxies, these cluster ga
laxies are distributed almost equally amongst the three main types of disk galaxy luminosity profiles (I/II/III), indicating that the formation and/or survival of Type II breaks is suppressed within the cluster environment. Second, we find examples of statistically-significant
We use a combination of deep optical (gri) and near-infrared (H) photometry to study the radially-resolved colours of a broad sample of 300 Virgo cluster galaxies. For most galaxy types, we find that the median g-H colour gradient is either flat (gas
-poor giants and gas-rich dwarfs) or negative (i.e., colours become bluer with increasing radius; gas-poor dwarfs, spirals, and gas-poor peculiars). Later-type galaxies typically exhibit more negative gradients than early-types. Given the lack of a correlation between the central colours and axis ratios of Virgo spiral galaxies, we argue that dust likely plays a small role, if at all, in setting those colour gradients. We search for possible correlations between galaxy colour and photometric structure or environment and find that the Virgo galaxy colours become redder with increasing concentration, luminosity and surface brightness, while no dependence with cluster-centric radius or local galaxy density is detected (over a range of ~2 Mpc and ~3-16 Mpc^-2, respectively). However, the colours of gas-rich Virgo galaxies do correlate with neutral gas deficiency, such that these galaxies become redder with higher deficiencies. Comparisons with stellar population models suggest that these colour gradients arise principally from variations in stellar metallicity within these galaxies, while age variations only make a significant contribution to the colour gradients of Virgo irregulars. A detailed stellar population analysis based on this material is presented in Roediger et al (2011b; arXiv:1011.3511).
We use a combination of deep optical and near-infrared light profiles for a morphologically diverse sample of Virgo cluster galaxies to study the radially-resolved stellar populations of cluster galaxies over a wide range of galaxy structure. We find
that, in the median, the age gradients of Virgo galaxies are either flat (lenticulars and Sa-Sb spirals) or positive (ellipticals, Sbc+Sc spirals, gas-rich dwarfs, and irregulars), while all galaxy types have a negative median metallicity gradient. Comparison of the galaxy stellar population diagnostics (age, metallicity, and gradients thereof) against structural and environmental parameters also reveals that the ages of gas-rich systems depend mainly on their atomic gas deficiencies. Conversely, the metallicities of Virgo gas-poor galaxies depend on their concentrations, luminosities, and surface brightnesses. The stellar population gradients of all Virgo galaxies exhibit no dependence on either their structure or environment. We interpret these stellar population data for Virgo galaxies in the context of popular formation and evolution scenarios, and suggest that gas-poor giants grew hierarchically (through dissipative starbursts), gas-poor dwarfs have descended from at least two different production channels (e.g., environmental transformation and merging), while spirals formed inside-out, but with star formation in the outskirts of a significant fraction of the population having been quenched due to ram pressure stripping. (Abridged)
