We present results from our investigation of galaxy evolution in dense cluster environments up to redshift z=1.3 based on high S/N ground-based spectroscopy and HST imaging of bulge-dominated galaxies: (1) An analysis of sizes, M/L ratios and line indices of galaxies in massive clusters out to z=1.3. The results are published in Jørgensen & Chiboucas (2013) and Jørgensen et al. (2014). (2) A preliminary analysis (Fig. 1) of absorption line indices, ages, metallicities and abundance ratios for galaxies in nine massive clusters out to z=0.9. New data cover three clusters at z=0.2-0.5.

A simple model for M51a is constructed to explore its evolutionary history by assuming its disk grows from continuous gas infall, which is shaped by a free parameter-the infall-peak time tp. By adopting a constant infall-peak time tp = 7.0Gyr, our model predictions can reproduce most of the observed constraints and still show that the disk of M51a forms inside-out. Our results also show that the current molecular gas surface density, the star-formation rate and the UV-band surface brightness are important quantities to trace the effect of recent interactions on galactic star-formation process.

We use the SDSS Stripe 82 to study the stellar-mass growth that is triggered by minor mergers in local disk galaxies. Since major mergers destroy disks and create spheroids, morphologically disturbed spirals are likely remnants of minor mergers (since the disk remains intact). Disturbed spirals exhibit enhanced specific star formation rates (SSFRs), with the enhancement increasing in galaxies with ‘later’ morphological type (that have larger gas reservoirs and smaller bulges). By combining the SSFR enhancements with the fraction of time spirals in various morphological classes spend in this ‘enhanced’ mode, we estimate that ~40% of the star formation activity in local spirals is directly triggered by minor mergers. Combining our results with the star formation in local early-type galaxies – which is almost completely driven by minor mergers – suggests that around half the star formation activity at the present day is likely to be triggered by the minor-merger process.

The X-ray light curve of Sw~J1644+57 indicates this event would be due to a tidal disruption. The lightcurve shows large amplitude fluctuation. As proposed by Lyubarskii (1997), the aperiodic variability observed in the Galactic X-ray binaries and active galactic nuclei is likely from the fluctuation of the viscous parameter in their disks. We explain the significant fluctuation of the late X-ray lightcurve (t>106 seconds) of Sw J1644+57 with this model. We assume the stochastic variations in the viscous parameter featuring as α(R,t) = α0 [1+β(R,t)], where the time-scale for varying β(R,t) is set as ten times of the dynamic time-scale for disk at the radius R (Janiuk & Misra 2012). Based on the simulation results of Lodato et al. (2009), we describe the fallback behavior of the tidal disruption as Ṁfb ∝ {[(t - tb)/tfb]κ n + [(t - tb)/tfb]5n/3}−1/n for t > tb and Ṁfb=0 for other situations, where κ=10.0, n=0.5, tfb=103τ, and tb=102τ in which τ=2π(Rf3/GMBH)1/2 and Rf=5rg is the pericentre distance. Figure 1 compare the power-density spectra (PDS) derived from the observed and our simulated lightcurves. It is found the our simulations are well consistent with the observations.

Based on the Sloan Digital Sky Survey DR 7, we investigate the environment, morphology, and stellar population of bulgeless low surface-brightness (LSB) galaxies in a volume-limited sample with redshift ranging from 0.024 to 0.04 and Mr ≤ −18.8. We find that, for bulgeless galaxies, the surface brightness does not depend on the environment. Irregular LSB galaxies have more young stars and are more metal-poor than regular LSB galaxies. These results suggest that the evolution of LSB galaxies may be driven by their dynamics, including mergers rather than by their large-scale environment.

We compare the host galaxies of 902 supernovae, including Type Ia, II and Ibc, which are selected by cross-matching the Asiago Supernova Catalog with the SDSS DR7. We further selected 213 galaxies by requiring the light fraction of spectral observations > 15%, which could represent well the global properties of the galaxies. The diagrams related to Dn(4000), HδA, stellar masses, SFRs and specific SFRs for the SNe hosts show that almost all SNe II and most of SNe Ibc occur in SF galaxies. A significant fraction of SNe Ia occurs in AGNs and Absorp galaxies. These results are compared with those of the 689 comparison galaxies where the SDSS fiber captures < 15% of the total light. These comparison galaxies appear biased towards higher 12+log(O/H) (~0.1dex) at a given stellar mass, suggesting the aperture effect should be kept in mind when the properties of the hosts for different types of SNe are discussed.

Massive luminous red galaxies (LRGs) are believed to be evolving passively and can be used as cosmic chronometers to estimate the Hubble constant (the differential age method). However, different LRGs may be located in different environments. We investigate the environmental and mass dependence of the formation of ‘quiescent’ LRGs by using the population synthesis software STARLIGHT. We derive the stellar populations in each LRG, and obtain the mean age distribution and the mean star formation history (SFH) of those LRGs. We find that there is no apparent dependence of the mean age and the SFH of quiescent LRGs on their environment, while the ages of these quiescent LRGs depend weakly on their mass. We also evaluate the possible uncertainties in estimating the Hubble constant by the differential age method when using LRGs as cosmic chronometers.

This work sketches how SDSS ugr colors and Kepler 2 in halo fields can identify red giants 50–100 kpc distant with minimal metallicity bias. For these mildly-reddened, metal-poor giants, (g-r)o yields the effective temperature Teff to 100 K. K2 can detect the p-mode oscillations of red giants and measure their frequency of maximum power νmax. This sets the luminosity Lbol and thus the distance, plus an estimate of metallicity [Fe/H].

The removal of ISM of disk galaxies through ram pressure stripping (RPS) has been extensively studied in numerous simulations (see Roediger 2009 and references therein). The models show that RPS has a significant impact on galaxy evolution (truncation of the ISM will lead to a decrease in star formation and a change in galaxy color). Nevertheless, the role of magnetic fields (MFs) on the dynamics of the gas in this process has not been sufficiently studied, although the influence of the MFs on the large scale structure is well established. This motivated us to perform a 3D MHD simulation of a disk galaxy with an isothermal, non-self gravitating and magnetized gaseous disk in equilibrium with a galaxy potential (Allen & Santillán, 1991). We model RPS on the galactic disk under the wind-tunnel approximation with the use of the RAMSES code (Teyssier, 2002) in order to understand the effects of MFs in RPS.

Stellar populations are fossil records of several physical processes which occur in galaxies and their distribution within these objects may provide important clues on how they form and evolve. By using parameters from image processing we have been developing a new approach to understand the spatial distribution of stellar populations and how this is correlated with the form and evolution of galaxies. In this work we present some results obtained with data from the CALIFA survey.

We show that redshift-space distortions of galaxy correlations have a strong effect on correlation functions with the signature of the Baryon Acoustic Oscillations (BAO). Near the line of sight, the features become sharper as a result of redshift-space distortions. We analyze the SDSS DR7 main-galaxy sample (MGS), splitting the sample into slices 2.5 deg on the sky in various rotations. Measuring 2D correlation functions in each slice, we do see a sharp bump along the line of sight. Using Mexican-hat wavelets, we localize it to (110 ± 10) h − 1 Mpc and estimate its significance at about 4σ.

We probe many kinds of approaches used for photometric redshift estimation of quasars, including KNN (K-nearest neighbor algorithm), Lasso (Least Absolute Shrinkage and Selection Operator), PLS (Partial Least Square regression), ridge regression, SGD (Stochastic Gradient Descent) and Extra-Trees.