Science, Mathematics, & Computing

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Analytic torsion and Faddeev-Popov ghosts
(2002) McIntyre, Andrew
The regularized determinant of the Laplacian on n-differentials on a hyperbolic Riemann surface is studied. The main result is an intrinsic characterization of the connection form for the determinant line bundle, endowed with the Quillen metric, over the Teichmüller space, in terms of the Green’s function of the Cauchy-Riemann operator. Further, an explicit series representation of that Green’s function, on a Schottky uniformization of the surface, is established. This is a rigorous version of physical heuristics due to Martinec and Verlinde & Verlinde, relating the determinant to the stress-energy tensor of Faddeev-Popov ghost fields on the Riemann surface. One corollary is a simpler proof of the rigorous hyperbolic Belavin-Knizhnik formula, due to Zograf and Takhtajan, which is an intrinsic characterization of the curvature form of the determinant line bundle with Quillen metric. Another corollary is a proof of an explicit holomorphic factorization formula for n = 1 and genus greater than 1, due to Zograf, which generalizes the well known formula for n = 1 and genus 1 relating the determinant of the Laplacian to the Dedekind eta function.
Holomorphic factorization of determinants of Laplacians on Riemann surfaces and a higher genus generalization of Kronecker’s first limit formula
(Springer Verlag, 2006-09) McIntyre, Andrew; Takhtajan, Leon A.
For a family of compact Riemann surfaces X_t of genus g>1 parametrized by the Schottky space S_g, we define a natural basis for the holomorphic n-differentials on X_t which varies holomorphically with t and generalizes the basis of normalized abelian differentials of the first kind for n=1. We introduce a holomorphic function F(n) on S_g which generalizes the classical product \prod(1-q^m)^2 appearing in the Dedekind eta function for n=1 and g=1. We prove a holomorphic factorization formula expressing the regularized determinant of the Laplacian as a product of |F(n)|^2, a holomorphic anomaly depending on the classical Liouville action (a Kahler potential of S_g), and the determinant of the Gram matrix of the natural basis. The factorization formula reduces to Kronecker's first limit formula when n=1 and g=1, and to Zograf's factorization formula for n=1 and g>1.
Holomorphic factorization of determinants of Laplacians using quasi-Fuchsian uniformization
(Springer Verlag, 2006) McIntyre, Andrew; Teo, Lee-Peng
For a quasi-Fuchsian group Γ with ordinary set Ω, and Δ_n the Laplacian on n-differentials on Γ\Ω, we define a notion of a Bers dual basis ϕ_1,…,ϕ_2_d for ker Δ_n. We prove that det Δ_n/det⟨ϕ_j,ϕ_k⟩, is, up to an anomaly computed by Takhtajan and the second author in (Commun. Math Phys 239(1-2):183–240, 2003), the modulus squared of a holomorphic function F(n), where F(n) is a quasi-Fuchsian analogue of the Selberg zeta function Z(n). This generalizes the D’Hoker–Phong formula det Δ_n=c_g,_nZ(n), and is a quasi-Fuchsian counterpart of the result for Schottky groups proved by Takhtajan and the first author in Analysis 16, 1291–1323, 2006.
Tau function and Chern–Simons invariant
(Elsevier, 2014) McIntyre, Andrew; Park, Jinsung
We define a Chern-Simons invariant for a certain class of infinite volume hyperbolic 3-manifolds. We then prove an expression relating the Bergman tau function on a cover of the Hurwitz space, to the lifting of the function F defined by Zograf on Teichmüller space, and another holomorphic function on the cover of the Hurwitz space which we introduce. If the point in cover of the Hurwitz space corresponds to a Riemann surface X, then this function is constructed from the renormalized volume and our Chern-Simons invariant for the bounding 3-manifold of X given by Schottky uniformization, together with a regularized Polyakov integral relating determinants of Laplacians on X in the hyperbolic and singular flat metrics. Combining this with a result of Kokotov and Korotkin, we obtain a similar expression for the isomonodromic tau function of Dubrovin. We also obtain a relation between the Chern-Simons invariant and the eta invariant of the bounding 3-manifold, with defect given by the phase of the Bergman tau function of X.
Strain localization on an oceanic detachment fault system, Atlantis Massif, 30 °N, Mid-Atlantic Ridge
(Wiley American Geophysical Union, 2004-11) Schroeder, Timothy; John, Barbara E.
Abstract: Microstructural observations, mineral chemistry, and the spatial distribution of deformation fabrics recorded in outcrop samples collected from Atlantis Massif, the active inside corner high at 30 °N, Mid- Atlantic Ridge, suggest that strain is localized near the subhorizontal domal surface hypothesized to be an exposed detachment fault. Deformation textures in peridotite and gabbro indicate that high-temperature (>500 °C) strain occurred via crystal-plastic flow and diffusive mass transfer. Low-temperature (<400 °C) shear zones containing brittle and semibrittle microboudinage textures in which tremolite, chlorite, and/or talc replace fractured serpentine or hornblende cut earlier formed high-temperature deformation fabrics in peridotite. Textures indicate strain was localized by cataclasis and reaction softening into zones of intense greenschist and subgreenschist grade metamorphism. Gabbro is only weakly deformed below amphibolite facies (<500° C), indicating that strain was partitioned into altered peridotite at low temperature. There is a clear relationship between deformation intensity and structural depth beneath the subhorizontal surface of the Massif. Discontinuous high-intensity crystal-plastic deformation fabrics are found at all structural depths (0–520 m) beneath the surface, indicating that high-temperature, granulite- and amphibolite-grade deformation was not localized in a single shear zone. In contrast, semibrittle and brittle low-temperature shear zones are concentrated less than 90 m structurally beneath the surface, and the most intensely brittlely deformed samples concentrated in the upper 10 m. Localization of brittle deformation fabrics near the upper surface of the massif supports the hypothesis that it is the exposed footwall of a detachment fault. The structural evolution of Atlantis Massif is therefore analogous to a continental metamorphic core complex. Strain was localized onto the fault by reaction-softening and fluid-assisted fracturing during greenschist- and subgreenschist-grade hydrothermal alteration of olivine, clinopyroxene, serpentine, and hornblende to tremolite, chlorite, and/or talc. Keywords: detachment fault; low-angle normal fault; megamullion; metamorphic core complex; oceanic core complex; slow-spreading ridges.
Nonvolcanic seafloor spreading and corner-flow rotation accommodated by extensional faulting at 15 °N on the Mid- Atlantic Ridge: A structural synthesis of ODP Leg 209
(Wiley American Geophysical Union, 2007-06) Schroeder, Timothy; Cheadle, Michael J.; Dick, Henry J. B.; Faul, Ulrich; Casey, John F.; Kelemen, Peter B.
Abstract: Drilling during ODP Leg 209, dredging, and submersible dives have delineated an anomalous stretch of the Mid-Atlantic Ridge north and south of the 15°20'N Fracture Zone. The seafloor here consists dominantly of mantle peridotite with gabbroic intrusions that in places is covered by a thin, discontinuous extrusive volcanic layer. Thick lithosphere (10–20 km) in this region inhibits magma from reaching shallow levels beneath the ridge axis, thereby causing plate accretion to be accommodated by extensional faulting rather than magmatism. The bathymetry and complex fault relations in the drill-core suggest that mantle denudation and spreading are accommodated by a combination of high-displacement, rolling-hinge normal faults and secondary lower-displacement normal faults. These extensional faults must also accommodate corner flow rotation (up to 90 °) of the upwelling mantle within the shallow lithosphere, consistent with remnant magnetic inclinations in denuded peridotite and gabbro from Leg 209 core that indicate up to 90 ° of sub-Curie-temperature rotation. Keywords: seafloor spreading; ocean drilling program; nonvolcanic mid-ocean ridges; extensional faulting.
Fluid circulation and carbonate vein precipitation in the footwall of an oceanic core complex, Ocean Drilling Program Site 175, Mid-Atlantic Ridge
(Wiley American Geophysical Union, 2015-10) Schroeder, Timothy; Bach, Wolfgang; Jöns, Niels; Jöns, Svenja; Monien, Patrick; Klügel, Andreas
Carbonate veins recovered from the mafic/ultramafic footwall of an oceanic detachment fault on the Mid-Atlantic Ridge record multiple episodes of fluid movement through the detachment and secondary faults. High-temperature ( ~75–175° C) calcite veins with elevated REE contents and strong positive Euanomalies record the mixing of up-welling hydrothermal fluids with infiltrating seawater. Carbonate precipitation is most prominent in olivine-rich troctolite, which also display a much higher degree of greenschist and sub-greenschist alteration relative to gabbro and diabase. Low-temperature calcite and aragonite veins likely precipitated from oxidizing seawater that infiltrated the detachment fault and/or within secondary faults late or post footwall denudation. Oxygen and carbon isotopes lie on a mixing line between seawater and Logatchev-like hydrothermal fluids, but precipitation temperatures are cooler than would be expected for isenthalpic mixing, suggesting conductive cooling during upward flow. There is no depth dependence of vein precipitation temperature, indicating effective cooling of the footwall via seawater infiltration through fault zones. One sample contains textural evidence of low-temperature, seawater-signature veins being cut by high-temperature, hydrothermal-signature veins. This indicates temporal variability in the fluid mixing, possibly caused by deformation-induced porosity changes or dike intrusion. The strong correlation between carbonate precipitation and olivine-rich troctolites suggests that the presence of unaltered olivine is a key requirement for carbonate precipitation from seawater and hydrothermal fluids. Our results also suggest that calcite-talc alteration of troctolites may be a more efficient CO2 trap than serpentinized peridotite.
Diverse Cellular Functions of the Hsp90 Molecular Chaperone Uncovered Using Systems Approaches
(Elsevier, 2007-10) McClellan, Amie J.; Xia, Yu; Deutschbauer, Adam M.; Davis, Ron W.; Gerstein, Mark; Frydman, Judith
A comprehensive understanding of the cellular functions of the Hsp90 molecular chaperone has remained elusive. Although Hsp90 is essential, highly abundant under normal conditions, and further induced by environmental stress, only a limited number of Hsp90 ‘‘clients’’ have been identified. To define Hsp90 function, a panelofgenome-wide chemical-genetic screens in Saccharomyces cerevisiae were combined with bioinformatic analyses. This approach identified several unanticipated functions of Hsp90 under normal conditions and in response to stress. Under normal growth conditions, Hsp90 plays a major role in various aspects of the secretory pathway and cellular transport; during environmental stress, Hsp90 is required for the cell cycle, meiosis, and cytokinesis. Importantly, biochemical and cell biological analyses validated several of these Hsp90-dependent functions, highlighting the potential of our integrated global approach to uncover chaperone functions in the cell.
Protein Quality Control: Chaperones Culling Corrupt Conformations
(Nature Publishing Group, 2005-08) McClellan, Amie J.; Tam, Stephen; Kaganovich, Daniel; Frydman, Judith
Achieving the correct balance between folding and degradation of misfolded proteins is critical for cell viability. The importance of defining the mechanisms and factors that mediate cytoplasmic quality control is underscored by the growing list of diseases associated with protein misfolding and aggregation. Molecular chaperones assist protein folding and also facilitate degradation of misfolded polypeptides by the ubiquitin–proteasome system. Here we discuss emerging links between folding and degradation machineries and highlight challenges for future research.
Folding and Quality Control of the VHL Tumor Suppressor Proceed through Distinct Chaperone Pathways
(Elsevier, 2005-06) McClellan, Amie J.; Scott, Melissa D.; Frydman, Judith
The mechanisms by which molecular chaperones assist quality control of cytosolic proteins are poorly understood. Analysis of the chaperone requirements for degradation of misfolded variants of a cytosolic protein, the VHL tumor suppressor, reveals that distinct chaperone pathways mediate its folding and quality control. While both folding and degradation of VHL require Hsp70, the chaperon in TRiC is essential for folding but is dispensable for degradation. Conversely, the chaperone Hsp90 neither participates in VHL folding nor is required to maintain misfolded VHL solubility but is essential for its degradation. The cochaperone HOP/Sti1p also participates in VHL quality control and may direct the triage decision by bridging the Hsp70-Hsp90 interaction. Our finding that a distinct chaperone complex is uniquely required for quality control provides evidence for active and specific chaperone participation in triage decisions and suggests that a hierarchy of chaperone interactions can control the alternate fates of a cytosolic protein.
Quality Control of Protein Folding in the Cytosol
(Wilvey, 2012-05) McClellan, Amie J.
In order to function properly, newly synthesised proteins must rapidly and efficiently attain their native conformations. If they fail to do so, the cell may be adversely affected due to loss of function or toxic gain of function effects of misfolded polypeptides. Effective quality control mechanisms to recognise and eliminate misfolded proteins are thus critical for cell viability.The primary means by which misfolded proteins are selectively removed from the cell is via the ubiquitin–proteasome system. Although much is known about regulated proteolysis, how any given protein,which could potentially misfold, is recognised and targeted for proteasome-mediated degradation has been challenging to decipher. Recent progress,much of it in yeast, has identified specific E3 ligases involved in this process,clarified or added to our knowledge of the roles of molecular chaperones,and identified multiple cellular locations where degradation, or failing that, aggregation, occurs.
Heterozygous Yeast Deletion Collection Screens Reveal Essential Targets of Hsp90
(Public Library of Science, 2011-11) Franzosa, Eric A.; Albanèse, Véronique; Frydman, Judith; Xia, Yu; McClellan, Amie J.
Hsp90 is an essential eukaryotic chaperone with a role in folding specific ‘‘client’’ proteins such as kinases and hormone receptors. Previously performed homozygous diploid yeast deletion collection screens uncovered broad requirements for Hsp90 in cellular transport and cell cycle progression. These screens also revealed that the requisite cellular functions of Hsp90 change with growth temperature. We present here for the first time the results of heterozygous deletion collection screens conducted at the hypothermic stress temperature of 15°C. Extensive bioinformatic analyses were performed on the resulting data in combination with data from homozygous and heterozygous screens previously conducted at normal (30°C) and hyperthermic stress (37°C) growth temperatures. Our resulting meta-analysis uncovered extensive connections between Hsp90 and (1) general transcription, (2) ribosome biogenesis and (3) GTP binding proteins. Predictions from bioinformatic analyses were tested experimentally, supporting a role for Hsp90 in ribosome stability. Importantly, the integrated analysis of the 15°C heterozygous deletion pool screen with previously conducted 30°C and 37°C screens allows for essential genetic targets of Hsp90 to emerge. Altogether, these novel contributions enable a more complete picture of essential Hsp90 functions.
The Stellar Population of Stripped Cluster Spiral NGC 4522: A Local Analog to K+A Galaxies?
(The American Astronomical Society, 2006-10) Crowl, Hugh H.; Kenney, Jeffrey D. P.
We present observations of the stripped Virgo Cluster spiral galaxy NGC 4522, a clear, nearby example of a galaxy currently undergoing interstellar medium-intracluster medium (ISM-ICM) stripping. Utilizing SparsePak integral field spectroscopy on the Wisconsin-Indiana-Yale-NOAO (WIYN) 3.5 m telescope and Galaxy Evolution Explorer (GALEX) UV photometry, we present an analysis of the outer disk (r>3 kpc) stellar population of this galaxy, beyond the H I and Hα truncation radius. We find that the star formation in the gas-stripped outer disk ceased very recently, ~100 Myr ago, in agreement with previous claims that this galaxy is currently being stripped. At the time of this stripping, data and models suggest that the galaxy experienced a modest starburst. The stripping is occurring in a region of the cluster well outside the cluster core, likely because this galaxy is experiencing extreme conditions from a dynamic ICM due to an ongoing subcluster merger. The outer disk has a spectrum of a K+A galaxy, traditionally observed in high-redshift cluster galaxies. In the case of NGC 4522, a K+A spectrum is formed by simple stripping of the interstellar gas by the hot intracluster medium. These data show K+A spectra can be created by cluster processes and that these processes likely extend beyond the cluster core.
Transformation of a Virgo Cluster Dwarf Irregular Galaxy by Ram Pressure Stripping: IC3418 and its Fireballs
(The American Astronomical Society, 2014-01-10) Kenney, Jeffrey D. P.; Geha, Marla; Jachym, Pavel; Crowl, Hugh H.; Dague, William; Chung, Aeree; van Gorkom, Jacqueline; Vollmer, Bernd
We present optical imaging and spectroscopy and H I imaging of the Virgo Cluster galaxy IC 3418, which is likely a "smoking gun" example of the transformation of a dwarf irregular into a dwarf elliptical galaxy by ram pressure stripping. IC 3418 has a spectacular 17 kpc length UV-bright tail comprised of knots, head-tail, and linear stellar features. The only Hα emission arises from a few H II regions in the tail, the brightest of which are at the heads of head-tail UV sources whose tails point toward the galaxy ("fireballs"). Several of the elongated tail sources have Hα peaks outwardly offset by ~80-150 pc from the UV peaks, suggesting that gas clumps continue to accelerate through ram pressure, leaving behind streams of newly formed stars which have decoupled from the gas. Absorption line strengths, measured from Keck DEIMOS spectra, together with UV colors, show star formation stopped 300 ± 100 Myr ago in the main body, and a strong starburst occurred prior to quenching. While neither Hα nor H I emission are detected in the main body of the galaxy, we have detected 4 × 10^7 M☉ of H I from the tail with the Very Large Array. The velocities of tail H II regions, measured from Keck LRIS spectra, extend only a small fraction of the way to the cluster velocity, suggesting that star formation does not happen in more distant parts of the tail. Stars in the outer tail have velocities exceeding the escape speed, but some in the inner tail should fall back into the galaxy, forming halo streams.
A Spectacular Hα Complex in Virgo: Evidence for a Collision between M86 and NGC 4438 and Implications for the Collisional ISM Heating of Ellipticals
(The American Astronomical Society, 2008-10) Kenney, Jeffrey D. P.; Tal, Tomer; Crowl, Hugh H.; Feldmeier, John; Jacoby, George H.
Deep wide-field Hα+[N II] imaging around the Virgo Cluster giant elliptical galaxy M86 reveals a highly complex and disturbed ISM/ICM. The most striking feature is a set of Hα filaments which clearly connect M86 with the nearby disturbed spiral NGC 4438 (23' = 120 kpc projected away), providing strong evidence for a previously unrecognized collision between them. Spectroscopy of selected regions shows a fairly smooth velocity gradient between M86 and NGC 4438, consistent with the collision scenario. Such a collision would impart significant energy into the ISM of M86, probably heating the gas and acting to prevent the gas from cooling to form stars. We propose that cool gas stripped from NGC 4438 during the collision and deposited in its wake is heated by shocks, ram pressure drag, or thermal conduction, producing most of the Hα filaments. Some Hα filaments are associated with the well-known ridge of bright X-ray emission to the NW of the nucleus, suggesting that the collision is responsible for peculiarities of M86 previously ascribed to other effects. M86 is radio-quiet; thus AGN heating is unlikely to play a significant role. The M86 system has implications for understanding the role of gravitational interactions in the heating of the ISM in ellipticals, and how collisions in clusters transform galaxies.
VLA Imaging of Virgo Spirals in Atomic Gas (VIVA).
(The American Astronomical Society, 2009-12) Chung, Aeree; Gorkom, J. H.; Kenney, Jeffrey D. P.; Crowl, Hugh H.; Vollmer, Bernd
We present the results of a new VLA H I Imaging survey of Virgo galaxies, the VLA Imaging survey of Virgo galaxies in Atomic gas (VIVA). The survey includes high-resolution H I data of 53 carefully selected late type galaxies (48 spirals and five irregular systems). The goal is to study environmental effects on H I gas properties of cluster galaxies to understand which physical mechanisms affect galaxy evolution in different density regions, and to establish how far out the impact of the cluster reaches. As a dynamically young cluster, Virgo contains examples of galaxies experiencing a variety of environmental effects. Its nearness allows us to study each galaxy in great detail. We have selected Virgo galaxies with a range of star formation properties in low to high density regions (at projected distances from M87, d 87 = 0.3-3.3 Mpc). Contrary to previous studies, more than half of the galaxies in the sample (~60%) are fainter than 12 mag in BT . Overall, the selected galaxies represent the late type Virgo galaxies (S0/a to Sd/Irr) down to mp <~ 14.6 fairly well in morphological type, systemic velocity, subcluster membership, H I mass, and deficiency. The H I observations were done in C short (CS) configuration of the VLA radio telescope, with a typical spatial resolution of 15'' and a column density sensitivity of ≈3-5 × 1019 cm-2 in 3σ per 10 km s-1 channel. The survey was supplemented with data of comparable quality from the NRAO archive, taken in CS or C configuration. In this paper, we present H I channel maps, total intensity maps, velocity fields, velocity dispersions, global/radial profiles, position-velocity diagrams and overlays of H I/1.4 GHz continuum maps on the optical images. We also present H I properties such as total flux (S H I ), H I mass (M H I ), linewidths (W 20 and W 50), velocity (V H I ), deficiency (def H I ), and size (D eff H I and D iso H I ), and describe the H I morphology and kinematics of individual galaxies in detail. The survey has revealed details of H I features that were never seen before. In this paper, we briefly discuss differences in typical H I morphology for galaxies in regions of different galaxy densities. We confirm that galaxies near the cluster core (d 87 <~ 0.5 Mpc) have H I disks that are smaller compared to their stellar disks (D H I /D 25 < 0.5). Most of these galaxies in the core also show gas displaced from the disk, which is either currently being stripped or falling back after a stripping event. At intermediate distances (d 87 ~ 1 Mpc) from the center, we find a remarkable number of galaxies with long one-sided H I tails pointing away from M87. In a previous letter, we argue that these galaxies are recent arrivals, falling into the Virgo core for the first time. In the outskirts, we find many gas-rich galaxies, with gas disks extending far beyond their optical disks. Interestingly, we also find some galaxies with H I disks that are smaller compared to their stellar disks at large clustercentric distances.
The Line-of-Sight Depth of Populous Clusters in the Small Magellanic Cloud
(The American Astronomical Society, 2001-07) Crowl, Hugh H.; Sarajedini, Ata; Piatti, Andrés E.; Geisler, Doug; Bica, Eduardo; Clariá, Juan J.; João, F. C. Santos, Jr.
We present an analysis of age, metal abundance, and positional data on populous clusters in the Small Magellanic Cloud (SMC) with the ultimate aim of determining the line-of-sight (LOS) depth of the SMC by using these clusters as proxies. Our data set contains 12 objects and is limited to clusters with the highest-quality data for which the ages and abundances are best known and can be placed on an internally consistent scale. We have analyzed the variation of the clustersÏ properties with position on the sky and with line-of-sight depth. Based on this analysis, we draw the following conclusions : (1) The observational data indicate that the eastern side of the SMC (facing the Large Magellanic Cloud) contains younger and more metal-rich clusters as compared with the western side. This is not a strong correlation because our data set of clusters is necessarily limited, but it is suggestive and warrants further study. (2) Depending on how the reddening is computed to our clusters, we find a mean distance modulus that ranges from (m-M)^0 = 18.71± 0.06 to 18.82 ± 0.05. (3) The intrinsic ±1 σ LOS depth of the SMC populous clusters in our study is between ~ 6 and ~ 12 kpc, depending primarily on whether we adopt the Burstein & Heiles reddenings or those from Schlegel et al. (4) Viewing the SMC as a triaxial galaxy with declination, right ascension, and LOS depth as the three axes, we find axial ratios of approximately 1:2:4. Taken together, these conclusions largely agree with those of previous investigators and underscore the utility of populous star clusters as probes of the structure of the Small Magellanic Cloud.
Dense Cloud Ablation and Ram Pressure Stripping of the Virgo Spiral NGC 4402
(The American Astronomical Society, 2005-07) Crowl, Hugh H.; Kenney, Jeffrey D. P.; van Gorkom, J. H.; Vollmer, Bernd
We present optical, H i, and radio continuum observations of the highly inclined Virgo Cluster Sc galaxy NGC 4402, which show evidence for ram pressure stripping and dense cloud ablation. Very Large Array H i and radio continuum maps show a truncated gas disk and emission to the northwest of the main disk emission. In particular, the radio continuum emission is asymmetrically extended to the north and skewed to the west. The H image shows numerous H ii complexes along the southern edge of the gas disk, possibly indicating star formation triggered by the intracluster medium (ICM) pressure. Our BVR images at 0B5 resolution obtained with the WIYN Tip-Tilt Imager show a remarkable dust lane morphology: at half the optical radius, the dust lane of the galaxy curves up and out of the disk, matching the H i morphology. Large dust plumes extend upward for 1.5 kpc from luminous young star clusters at the southeast edge of the truncated gas disk. These star clusters are very blue, indicating very little dust reddening, which suggests dust blown away by an ICM wind at the leading edge of the interaction. To the south of the main ridge of interstellar material, where the galaxy is relatively clean of gas and dust, we have discovered 1 kpc long linear dust filaments with a position angle that matches the extraplanar radio continuum tail; we interpret this angle as the projected ICM wind direction. One of the observed dust filaments has an H ii region at its head.We interpret these dust filaments as large, dense clouds that were initially left behind as the low-density interstellar medium was stripped but were then ablated by the ICM wind. These results provide striking new evidence on the fate of molecular clouds in stripped cluster galaxies.
The Stellar Populations of Stripped Spiral Galaxies in the Virgo Cluster
(The American Astronomical Society, 2008-10) Crowl, Hugh H.; Kenney, Jeffrey D. P.
We present an analysis of the stellar populations of the gas-stripped outer disks of ten Virgo cluster spiral galaxies, utilizing SparsePak integral field spectroscopy on the WIYN 3.5 m telescope and Galaxy Evolution Explorer (GALEX) UV photometry. The galaxies in our sample show evidence for being gas-stripped spiral galaxies, with star formation within a truncation radius and a passive population beyond the truncation radius. We find that all of the galaxies with spatially truncated star formation have outer-disk stellar populations consistent with star formation ending within the last 500 Myr. The synthesis of optical spectroscopy and GALEX observations demonstrate that star formation was relatively constant until the quenching time, after which the galaxies passively evolved. Large starbursts at the time of quenching are excluded for all galaxies, but there is evidence of a modest starburst in at least one galaxy. For approximately half of our galaxies, the timescales derived from our observations are consistent with galaxies being stripped in or near the cluster core, where simple ram-pressure estimates can explain the observed stripping. However, the other half of our sample galaxies were clearly stripped outside the cluster core. Such galaxies provide evidence that the intra-cluster medium is not static and smooth. For three of the most recently stripped galaxies, there are estimates for the stripping timescales from detailed gas-stripping simulations. For all three of these galaxies, our stripping timescales agree with those from the gas-stripping simulations, suggesting that star formation is quenched near the time of peak pressure. While the stripping of star-forming gas in the outer disk creates a passive population in our sample of galaxies, there is still normal star formation in the center of these galaxies. It may be that Virgo is not massive enough to completely strip these spiral galaxies and, in a more dynamically active cluster or a cluster with a higher density intracluster medium, such a process would lead to passive spirals and/or S0s.
Can Sea Urchins Beat the Heat? Sea Urchins, Thermal Tolerance and Climate Change
(PeerJ, 2015-06-09) Sherman, Elizabeth
The massive die-off of the long-spined sea urchin, Diadema antillarum, a significant reef grazer, in the mid 1980s was followed by phase shifts from coral dominated to macroalgae dominated reefs in the Caribbean.While Diadema populations have recovered in some reefs with concomitant increases in coral cover, the additional threat of increasing temperatures due to global climate change has not been investigated in adult sea urchins. In this study, I measured acute thermal tolerance of D. antillarum and that of a sympatric sea urchin not associated with coral cover, Echinometra lucunter, over winter, spring, and summer, thus exposing them to substantial natural thermal variation. Animals were taken from the wild and placed in laboratory tanks in room temperature water (∼22 ◦C) that was then heated at 0.16–0.3 ◦C min−1 and the righting behavior of individual sea urchins was recorded. I measured both the temperature at which the animal could no longer right itself (TLoR) and the righting time at temperatures below the TLoR. In all seasons, D. antillarum exhibited a higher mean TLoR than E. lucunter. The mean TLoR of each species increased with increasing environmental temperature revealing that both species acclimatize to seasonal changes in temperatures. The righting times of D. antillarum weremuch shorter than those of E. lucunter. The longer relative spine length of Diadema compared to that of Echinometra may contribute to their shorter righting times, but does not explain their higher TLoR. The thermal safety margin (the difference between the mean collection temperature and the mean TLoR) was between 3.07–3.66 ◦C for Echinometra and 3.79–5.67 ◦C for Diadema. While these thermal safety margins exceed present day temperatures, they are modest compared to those of temperate marine invertebrates. If sea temperatures increase more rapidly than can be accommodated by the sea urchins (either by genetic adaptation, phenotypic plasticity, or both), this will have important consequences for the structure of coral reefs.

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