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The correlation of star formation quenching with internal galaxy properties and environment
Kimm, Taysun,Somerville, Rachel S.,Yi, Sukyoung K.,van den Bosch, Frank C.,Salim, Samir,Fontanot, Fabio,Monaco, Pierluigi,Mo, Houjun,Pasquali, Anna,Rich, R. M.,Yang, Xiaohu Blackwell Publishing Ltd 2009 MONTHLY NOTICES- ROYAL ASTRONOMICAL SOCIETY Vol.394 No.3
<P>ABSTRACT</P><P>We investigate the correlation of star formation quenching with internal galaxy properties and large-scale environment (halo mass) in empirical data and theoretical models. We make use of the halo-based group catalogue of Yang and collaborators, which is based on the Sloan Digital Sky Survey. Data from the Galaxy evolution explorer are also used to extract the recent star formation rate. In order to investigate the environmental effects, we examine the properties of ‘central’ and ‘satellite’ galaxies separately. For central galaxies, we are unable to conclude whether star formation quenching is primarily connected with halo mass or stellar mass, because these two quantities are themselves strongly correlated. For satellite galaxies, a nearly equally strong dependence on halo mass and stellar mass is seen. We make the same comparison for five different semi-analytic models based on three independently developed codes. We find that the models with active galactic nuclei feedback reproduce reasonably well the dependence of the fraction of central red and passive galaxies on halo mass and stellar mass. However, for satellite galaxies, the same models badly overproduce the fraction of red/passive galaxies and do not reproduce the empirical trends with stellar mass or halo mass. This <I>satellite overquenching problem</I> is caused by the too-rapid stripping of the satellites' hot gas haloes, which leads to rapid strangulation of star formation.</P>
Show and Tell : cell biology of pathogen invasion
Serry Koh,Shauna Somerville 한국작물학회 2007 한국작물학회 학술발표대회 논문집 Vol.2007 No.11
The powdery mildews are obligate biotrophic fungi and are one of the most economically important groups of plant pathogens (Agrios, 1997). As a family, the powdery mildews infect a broad range of plant species including barley, wheat, pea, apple, sugar beet, and grape (Braun, 1987). Powdery mildew pathogens uptake nutrients by forming a feeding structure, the haustorium, within 12‐18 hours after infection (hai) in their respective host plants. Because of the initial stages of these plant pathogen invasion are mostly confined to a limited number of host cells, it’s often too late to find out till the infections widely spread out. To identify the earliest and often transient responses to pathogen attack, there is considerable interest in monitoring the subcellular events that occur specifically in living host cells. Recent improvements in live cell imaging using fluorescent‐tagged markers have expanded the scope of experiments that can be performed. Changes in the subcellular distribution of organelles as well as fluorescently tagged proteins can be monitored in real time in living tissues during pathogen attack, and the dynamic nature of such changes across space and over time can be determined. The application of these sensitive imaging methods has extended earlier observations made with Nomarski microscopy or inferred from static transmission electron micrographs about the focal accumulation of subcellular organelles at sites of pathogen attack. In addition, recent experiments have demonstrated the focused accumulation and interaction of specific plant proteins at penetration sites, opening a new window on early host responses and raising questions about the underlying plant processes that sense and direct this marshalling of host resources to block pathogen entry.
Song, Mimi,Finkelstein, Steven L.,Ashby, Matthew L. N.,Grazian, A.,Lu, Yu,Papovich, Casey,Salmon, Brett,Somerville, Rachel S.,Dickinson, Mark,Duncan, K.,Faber, Sandy M.,Fazio, Giovanni G.,Ferguson, He American Astronomical Society 2016 The Astrophysical Journal Vol.825 No.1
<P>We present galaxy stellar mass functions (GSMFs) at z = 4-8 from a rest-frame ultraviolet (UV) selected sample of similar to 4500 galaxies, found via photometric redshifts over an area of similar to 280 arcmin(2) in the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS)/Great Observatories Origins Deep Survey (GOODS) fields and the Hubble Ultra Deep Field. The deepest Spitzer/IRAC data to date and the relatively large volume allow us to place a better constraint at both the low- and high-mass ends of the GSMFs compared to previous space-based studies from pre-CANDELS observations. Supplemented by a stacking analysis, we find a linear correlation between the rest-frame UV absolute magnitude at 1500 angstrom (M-UV) and logarithmic stellar mass (log M-*) that holds for galaxies with log(M-*/M-circle dot) less than or similar to 10. We use simulations to validate our method of measuring the slope of the log M-*-M-UV relation, finding that the bias is minimized with a hybrid technique combining photometry of individual bright galaxies with stacked photometry for faint galaxies. The resultant measured slopes do not significantly evolve over z = 4-8, while the normalization of the trend exhibits a weak evolution toward lower masses at higher redshift. We combine the log M-*-M-UV distribution with observed rest-frame UV luminosity functions at each redshift to derive the GSMFs, finding that the low-mass-end slope becomes steeper with increasing redshift from alpha = -1.55(-0.07)(+0.08) at z = 4 to alpha = -2.25(-0.35)(+0.72) at z = 8. The inferred stellar mass density, when integrated over M-* = 10(8)-10(13) M-circle dot, increases by a factor of 10(-2)(+30) between z = 7 and z = 4 and is in good agreement with the time integral of the cosmic star formation rate density.</P>
Mantha, Kameswara Bharadwaj,McIntosh, Daniel H,Brennan, Ryan,Ferguson, Henry C,Kodra, Dritan,Newman, Jeffrey A,Rafelski, Marc,Somerville, Rachel S,Conselice, Christopher J,Cook, Joshua S,Hathi, Nimish Oxford University Press 2018 MONTHLY NOTICES- ROYAL ASTRONOMICAL SOCIETY Vol.475 No.2
<P>The rate of major galaxy-galaxy merging is theoretically predicted to steadily increase with redshift during the peak epoch of massive galaxy development (1 <= z <= 3). We use close-pair statistics to objectively study the incidence of massive galaxies (stellar M1 > 2 x 10(10)M(circle dot)) hosting major companions (1 <= M-1/M-2 <= 4; i.e. <4: 1) at six epochs spanning 0 < z < 3. We select companions from a nearly complete, mass-limited (>= 5 x 10(9)M(circle dot)) sample of 23 696 galaxies in the five Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey fields and the Sloan Digital Sky Survey. Using 5-50 kpc projected separation and close redshift proximity criteria, we find that the major companion fraction f(mc)(z) based on stellar mass-ratio (MR) selection increases from 6 per cent (z similar to 0) to 16 per cent (z similar to 0.8), then turns over at z similar to 1 and decreases to 7 per cent (z similar to 3). Instead, if we use a major F160W flux-ratio (FR) selection, we find that f(mc)(z) increases steadily until z similar to 3 owing to increasing contamination from minor (MR > 4: 1) companions at z > 1. We show that these evolutionary trends are statistically robust to changes in companion proximity. We find disagreements between published results are resolved when selection criteria are closely matched. If we compute merger rates using constant fraction-to-rate conversion factors (C-merg,C-pair = 0.6 and T-obs,T-pair = 0.65 Gyr), we find that MR rates disagree with theoretical predictions at z > 1.5. Instead, if we use an evolving T-obs,T-pair(z) alpha (1 + z)- 2 from Snyder et al., our MR-based rates agree with theory at 0 < z < 3. Our analysis underscores the need for detailed calibration of C-merg,C-pair and T-obs,T-pair as a function of redshift, mass, and companion selection criteria to better constrain the empirical major merger history.</P>