Central and Satellite Colors in Galaxy Groups: A Comparison of the Halo Model and SDSS Group Catalogs

Current analytic and semi-analytic dark matter halo models distinguish between the central galaxy in a halo and the satellite galaxies in halo substructures. Using a recent halo-model description of the color dependence of galaxy clustering (Skibba & Sheth 2008), we investigate the colors of central and satellite galaxies predicted by the model and compare them to those of two galaxy group catalogs constructed from the Sloan Digital Sky Survey (Yang et al. 2007, Berlind et al. 2006a). In the model, the environmental dependence of galaxy color is determined by that of halo mass, and the predicted color mark correlations were shown to be consistent with SDSS measurements. The model assumes that satellites tend to follow a color-magnitude sequence that approaches the red sequence at bright luminosities; the model's success suggests that bright satellites tend to be `red and dead' while the star formation in fainter ones is in the process of being quenched. In both the model and the SDSS group catalogs, we find that at fixed luminosity or stellar mass, central galaxies tend to be bluer than satellites. In contrast, at fixed group richness or halo mass, central galaxies tend to be redder than satellites, and galaxy colors become redder with increasing mass. We also compare the central and satellite galaxy color distributions, as a function of luminosity and as a function of richness, in the model and in the two group catalogs. Except for faint galaxies and small groups, the model and both group catalogs are in very good agreement.Comment: 9 pages, 7 figures, revised version submitted to MNRAS. Significant revisions were made, and figures were added showing the color distributions. Important correction: the model and both group catalogs now have consistent satellite colors--almost independent of group richnes

A Cross-Case Analysis of How Faculty Connect Learning in Hybrid Courses

This qualitative, multiple case study analysis found that faculty use hybrid courses to facilitate learning by creating a continuous learning loop between the in-person and online environments. Connecting learning in both environments helps students acquire and integrate new knowledge, extend and refine knowledge, and use knowledge meaningfully

Galaxy formation with cold gas accretion and evolving stellar initial mass function

The evolution of the galaxy stellar mass function is especially useful to test the current model of galaxy formation. Observational data have revealed a few inconsistencies with predictions from the $\Lambda {\rm CDM}$ model. For example, most massive galaxies have already been observed at very high redshifts, and they have experienced only mild evolution since then. In conflict with this, semi-analytical models of galaxy formation predict an insufficient number of massive galaxies at high redshift and a rapid evolution between redshift 1 and 0 . In addition, there is a strong correlation between star formation rate and stellar mass for star-forming galaxies, which can be roughly reproduced with the model, but with a normalization that is too low at high redshift. Furthermore, the stellar mass density obtained from the integral of the cosmic star formation history is higher than the measured one by a factor of 2. In this paper, we study these issues using a semi-analytical model that includes: 1) cold gas accretion in massive halos at high redshift; 2) tidal stripping of stellar mass from satellite galaxies; and 3) an evolving stellar initial mass function (bottom-light) with a higher gas recycle fraction. Our results show that the combined effects from 1) and 2) can predict sufficiently massive galaxies at high redshifts and reproduce their mild evolution at low redshift, While the combined effects of 1) and 3) can reproduce the correlation between star formation rate and stellar mass for star-forming galaxies across wide range of redshifts. A bottom-light/top-heavy stellar IMF could partly resolve the conflict between the stellar mass density and cosmic star formation history.Comment: 9 pages, 7 figures. Accepted for publication in Ap

Marked Statistics and the Environmental Dependence of Galaxy Formation

Many have used the two-point correlation function to study the clustering of galaxies as a function of their properties, such as luminosity, color, and stellar mass. We explore the technique of `marked' correlations, in which clustering is measured with galaxies weighted by a particular property or `mark'. Marked clustering statistics identify and quantify how galaxy properties are correlated with their environment. We present marked correlation analyses in the framework of the dark matter halo model, in which all environmental correlations are due to the correlation of the masses and formation histories of halos with their environment. We perform marked correlation analyses of galaxy luminosity, color, stellar mass, metallicity, and star formation rate in the Sloan Digital Sky Survey and the Millennium Run Simulation. We also analyze luminosity-marked correlations of galaxies in groups and clusters. Our measurements show that luminous, red, massive, metal-rich, and passively star forming galaxies tend to be located in denser environments than fainter, bluer, less massive, metal-poor, and actively star forming galaxies. Our marked correlation measurements also show how these environmental correlations vary as a function of scale. Our halo-model analyses show that the environmental dependence of luminosity and stellar mass of SDSS galaxies is primarily driven by the environmental dependence of halo mass

Preventive effect of non-mitogenic acidic fibroblast growth factor on diabetes-induced testicular cell death.

Fibroblast growth factor (FGF)-1 was found to protect the heart from oxidative damage, but clinically its long-term use was restricted for its undesirable proliferating activity on cells. Thus a cluster of amino acids responsible for the proliferation were deleted in the native FGF-1 to create a non-mitogenic FGF-1 (nmFGF-1). To assess whether nmFGF-1 protects male germ cells from diabetes-induced apoptotic death, the study employed a murine model of diabetes using multiple low-doses of streptozotocin, followed by nmFGF-1 treatment for 6 months. Diabetic mice showed a decrease in testicular weight and an increase in apoptotic cell death. Treatment with nmFGF-1 alleviated diabetic effects on testicular weight and apoptotic cell death. Mechanistically, nmFGF-1 alleviated diabetes-induced germ cell death by decreasing the BAX/Bcl-2 ratio, endoplasmic reticulum stress and associated cell death. Our results suggest that nmFGF-1 application prevents apoptotic cell death in testes of diabetic mice from mediation which was associated with Nrf-2 and AKT activation

Satellite Luminosities in Galaxy Groups

Halo model interpretations of the luminosity dependence of galaxy clustering assume that there is a central galaxy in every sufficiently massive halo, and that this central galaxy is very different from all the others in the halo. The halo model decomposition makes the remarkable prediction that the mean luminosity of the non-central galaxies in a halo should be almost independent of halo mass: the predicted increase is about 20% while the halo mass increases by a factor of more than 20. In contrast, the luminosity of the central object is predicted to increase approximately linearly with halo mass at low to intermediate masses, and logarithmically at high masses. We show that this weak, almost non-existent mass-dependence of the satellites is in excellent agreement with the satellite population in group catalogs constructed by two different collaborations. This is remarkable, because the halo model prediction was made without ever identifying groups and clusters. The halo model also predicts that the number of satellites in a halo is drawn from a Poisson distribution with mean which depends on halo mass. This, combined with the weak dependence of satellite luminosity on halo mass, suggests that the Scott effect, such that the luminosities of very bright galaxies are merely the statistically extreme values of a general luminosity distribution, may better apply to the most luminous satellite galaxy in a halo than to BCGs. If galaxies are identified with halo substructure at the present time, then central galaxies should be about 4 times more massive than satellite galaxies of the same luminosity, whereas the differences between the stellar M/L ratios should be smaller. Therefore, a comparison of the weak lensing signal from central and satellite galaxies should provide useful constraints. [abridged]Comment: 8 pages, 3 figures. Matches version accepted by MNRA

Using a Hybrid Instructional Model in Teaching and Learning

Hybrid courses allow for in-person learning communities combined with the convenience and reflective nature of online learning. This roundtable will provide an opportunity to share educators’ experiences and techniques in implementing the hybrid model to facilitate student learning

Autocorrelations of stellar light and mass in the low-redshift Universe

The final data release of the Sloan Digital Sky Survey (SDSS) provides reliable photometry and spectroscopy for about half a million galaxies with median redshift 0.09. Here we use these data to estimate projected autocorrelation functions w_p(r_p) for the light of galaxies in the five SDSS photometric bands. Comparison with the analogous stellar mass autocorrelation, estimated in a previous paper, shows that stellar luminosity is less strongly clustered than stellar mass in all bands and on all scales. Over the full nonlinear range 10 kpc/h < r_p < 10 Mpc/h our autocorrelation estimates are extremely well represented by power laws. The parameters of the corresponding spatial functions \xi(r) = (r/r_0)^\gamma vary systematically from r_0=4.5 Mpc/h and \gamma=-1.74 for the bluest band (the u band) to r_0=5.8 Mpc/h and \gamma=-1.83 for the reddest one (the z band). These may be compared with r_0=6.1 Mpc/h and \gamma=-1.84 for the stellar mass. Ratios of w_p(r_p) between two given wavebands are proportional to the mean colour of correlated stars at projected distance r_p from a randomly chosen star. The ratio of the stellar mass and luminosity autocorrelations measures an analogous mean stellar mass-to-light ratio (M*/L). All colours get redder and all mass-to-light ratios get larger with decreasing r_p, with the amplitude of the effects decreasing strongly to redder passbands. Even for the u-band the effects are quite modest, with maximum shifts of about 0.1 in u-g and about 25% in M*/L_u. These trends provide a precise characterisation of the well-known dependence of stellar populations on environment.Comment: 6 pages, 4 figures, accepted to MNRAS; three new paragraphs added: two at the end of Sec. 2 concerning cross-correlations between different bands and possible biases due to photometry errors, and one at the end of the paper discussing marked correlation function

Satellite Kinematics III: Halo Masses of Central Galaxies in SDSS

We use the kinematics of satellite galaxies that orbit around the central galaxy in a dark matter halo to infer the scaling relations between halo mass and central galaxy properties. Using galaxies from the Sloan Digital Sky Survey, we investigate the halo mass-luminosity relation (MLR) and the halo mass-stellar mass relation (MSR) of central galaxies. In particular, we focus on the dependence of these scaling relations on the colour of the central galaxy. We find that red central galaxies on average occupy more massive haloes than blue central galaxies of the same luminosity. However, at fixed stellar mass there is no appreciable difference in the average halo mass of red and blue centrals, especially for M* \lsim 10^{10.5} h^{-2} Msun. This indicates that stellar mass is a better indicator of halo mass than luminosity. Nevertheless, we find that the scatter in halo masses at fixed stellar mass is non-negligible for both red and blue centrals. It increases as a function of stellar mass for red centrals but shows a fairly constant behaviour for blue centrals. We compare the scaling relations obtained in this paper with results from other independent studies of satellite kinematics, with results from a SDSS galaxy group catalog, from galaxy-galaxy weak lensing measurements, and from subhalo abundance matching studies. Overall, these different techniques yield MLRs and MSRs in fairly good agreement with each other (typically within a factor of two), indicating that we are converging on an accurate and reliable description of the galaxy-dark matter connection. We briefly discuss some of the remaining discrepancies among the various methods.Comment: 19 pages, 14 figures, MNRAS submitted, comments welcom