1306.6330
The Sloan digital sky survey data release 7 spectrsoscopic m dwarf catalog iii: the spatial dependence of magnetic activity in the galaxy
Pineda, West, Bochanski, Burgasser
Analyze the magnetic activity of 59k M dwarfs from DR7. This analysis explores the spatial distribution of M dwarf activity as a function of both vertical distance from the Galactic plane (Z) and planar distance from the Galactic center (R). Confirm the established trends of decreasing magnetic activity (as measured by H-alpha emission) with increasing distance from the mid-plane of the disk and find evidence for a trend in Galactocentric radius. Measure a non-zero radial gradient in the activity fraction in the analysis of stars with spectral types dM3 and dM4. The activity fraction increases with R and can be explained by a decreasing mean stellar age with increasing distance from the Galactic center. [I guess it's the M stars that are responsible for Galactic-scale magnetic activity? Not clearly stated in the abstract, but seems to imply so. I guess they are abundant (low mass).]
1306.6332
The (galaxy-wide) IMF in giant elliptical galaxies: from top to bottom
Weidner, Ferraras, Vazdekis, La Barbera
Based on spectral line strengths and dynamical modeling, evidence of a non-universal stellar IMF emerges, implying an excess of low-mass stars in the most massive elliptical galaxies. Show that a time-independent bottom-heavy IMF is compatible neither with the observed metal-rich populations found in giant ellipticals nor with the number of stellar remnants observed within these systems. Suggest a two-stage formation scenario involving a time-dependent IMF to reconcile these observational constraints. In this model, an early strong star-bursting stage with a top-heavy IMF is followed by a more prolonged stage with a bottom-heavy IMF. Such model is physically motivated by the fact that a sustained high star formation will bring the interstellar medium to a state of pressure, temperature and turbulence that can drastically alter the fragmentation of the gaseous component into small clumps, promoting the formation of low-mass stars. This toy model is in good agreement with the different observational constraints on massive elliptical galaxies, such as age, metallicity, alpha-enhancement, M/L, or the mass fraction of the stellar component in low-mass stars.
1306.6333
Chronos: a NIR spectroscopic galaxy survey. From the formation of galaxies to the peak of activity
Ferraras, ... Conselice, et al
Chronos is a response to ESA's call for white papers to define the science for the future L2, L3 missions. Targets the formation and evolution of galaxies, by collecting the deepest NIR spectroscopic data, from the formation of the first galaxies at z~10 to the peak of formation activity at z~1-3. The strong emission from the atmospheric background makes this type of survey impossible from a ground-based observatory. The spectra of galaxies represent the equivalent of DNA fingerprint [OK,], containing information about the past history of SF and chemical enrichment. The proposed survey will allow us to dissect the formation process of galaxies including the timescales of quenching triggered by SF or AGN activity, the effect of environment, the role of infall/outflow processes, or the connection between the galaxies and their underlying dark matter haloes. To provide these data, the mission requires a 2.5m space telescope optimized for a campaign of very deep NIR spectroscopy. A combination of a high multiplex and very long integration times will result in the deepest, largest, high-quality spectroscopic dataset of galaxies from z=1 to 12, spanning the history of the Universe, from 400 million to 6 billion years after the big bang, i.e. covering the most active half of cosmic history.
1306.6334
The mass-metallicity relation of a z~2 protocluster with MOSFIRE
Kulas, ... Shapley, Steidel, ... et al
MOSFIRE observations of the role of environment in the formation of galaxies at z~2. Use K-band spectroscopy of Ha and [NII] emission lines; analyze the metallicities of galaxies within and around a z=2.3 protocluster discovered in the HS1700+643 field. Main sample consists of 23 protocluster and 20 field galaxies with estimates of stellar masses and gas-phase metallicities based on the N2 strong-line metallicity indicator. With these data, examine the mass-metallicity relation (MZR) wth respect to environment at z~2. Find that field galaxies follow the well-established trend between stellar mass and metallicity, such that more massive galaxies have larger metallicities. The protocluster galaxies, however, do not exhibit a dependence of metallicity on mass, with the low-mass protocluster galaxies showing an enhancement in metallicity compared to field galaxies spanning the same mass range. A comparison with galaxy formation models suggests that the mass-dependent environmental trend observed can be qualitatively explained in the context of the recycling of "momentum-driven" galaxy wind material. Accordingly, winds are recycled on a shorter timescale in denser environments, leading to an enhancement in metallicity at fixed mass for all but the most massive galaxies. Future hydrodynamical simulations of z~2 overdensities matching the one in the HS1700 field will be crucial for understanding the origin of the observed environmental trend in detail.
1306.6336
Measuring the gas clumping in Abell 133
Morandi, Cui
Developing a non-parametric method to measure inhomogeneities in the gas distribution from X-ray observations of galaxy clusters. Apply method to Chandra X-ray observations of A133 and present the determination of gas clumping factor from X-ray cluster data. Find that the gas clumping factor in A133 increases with radius and reaches ~2-3 at R_200. This is in good agreement with the predictions of hydrodynamical simulations and the previous determination, but at odds with several recent Suzaku studies. Then observe a general trend of steepening in the radial profiles of the gas density beyond 0.3 R_200, with a logarithmic slope of ~2.6 at R_200. The observed density profiles appear to be flatter compared to simulations, but in agreement with previous observational findings. In addition, observe that the measured temperature decreases steadily with radius toward the outskirts of A133, while the entropy increases monotonically with radius, gently flattening in the outer volumes. With respect to theoretical predictions from pure gravitational collapse, the results presented here point to an entropy excess in the central regions, which extends out to large radii. These results suggest that gas inhomogeneities should be treated properly when interpreting X-ray measurements in the envelope of galaxy clusters. Finally, discuss how the brightness distribution keeps a recored of the large-scale structures formation scenario, providing a snapshot of the 'melting pot' in the virialization region.
1306.6339
A lithium depletion boundary age of 22 Myr for NGC 1960
Jeffries et al
Deep Cousins RI photometric survey of open cluster NCD 1960, complete to R_C~22, I_C~21, that is used to select a sample of very low-mass cluster candidates. Gemini spectroscopy of a subset of these is used to confirm membership and locate the age-dependent "lithium depletion boundary" (LDB), the luminosity at which Li remains unburned in its low-mass stars. The LDB implies a cluster age of 22pm4 Myr and is quite insensitive to choice of evolutionary model. NGC 1960 is the youngest cluster for which a LDB age has been estimated and possesses a well populated upper main sequence and a rich low-mass pre-main sequence. The LDB age determined here agrees well with precise age estimates made for the same cluster based on isochrone fits to its high- and low-mass populations. The concordance between these three age estimation techniques, that rely on different facets of stellar astrophysics at very different masses, is an important step towards calibrating the absolute ages of young open clusters and lends confidence to ages determined using any one of them. [the three are: cluster MS population evolution, LDB, and isochrone fits? what's the difference between cluster MS population evolution and isochrone fits?----isochrone fits are fits to the color, which evolve over age, apparently.]
1306.6359
Clipping the cosmos II: cosmological information from non-linear scales
Simpson, Heavens, Heymans
A method for suppressing contributions from higher-order terms in perturbations theory, greatly increasing the amount of information which may be extracted from the matter PS. In an evolved cosmological density field, the highest density regions are responsible for the bulk of the NL power. By suitable down-weighting these problematic regions, find that the one- and two-loop terms are typically reduced in amplitude by ~70% and ~95% respectively, relative to the linear PS. This greatly facilitates modeling the shape of the galaxy power spectrum, potentially increasing the number of useful Fourier modes by more than two orders of magnitude. Provide a demonstration of how this technique allows the galaxy bias and the amplitude of linear matter perturbations sigma_8 to be determined from the PS on conventionally NL scales, 0.1<k<0.7 h/Mpc.
1306.6423
Exploring the systematic uncertainties of Type Ia supernovae as cosmological probes
Wang, Wang
No z-evolution with alpha or beta, the stretch-luminosity parameter.
1306.6466
Intrinsic alignments and 3d weak gravitational lensing
Merkel, Schaefer
Show how IA can be incorporated consistently in the formalism of 3d weak lensing. [What is 3d WL? 3d mass reconstruction? WL tomography?....no, apparently to "completely account for the 3-dimensional character of WL by maintaining the radial dependence of the lensing potential throughout the whole analysis (with the aid of photo-z, I presume).] Use two different descriptions of the intrinsic galaxy ellipticities, the so-called linear and quadratic model, respectively. For both models derive the covariance matrix of the intrinsic alignment signal (II-alginments) and GI-alignments (the cross correlation of intrinsic and lensing-induced ellipticities). Evaluating the covariance matrices for the linear model numerically and comparing the results to the cosmic shear signal, find that for a low redshift survey the total covariance matrix is dominated by the contributions of the II-alignments. For a Euclid-like survey II-alignments still dominated over GI-alignments, but they are more than one order of magnitude smaller than the lensing signal. THe shape of the ellipticity covariance matrices is quite different in the k-k'-plane for cosmic shear on the one hand and IA on the other hand. In comparison to lensing both alignment types tend to be rather elongated along the diagonal k=k'. Moreover, for high multipoles (l~100) IA are strongly concentrated along that diagonal.
1306.6468
AGN feedback works both ways
Zinn et all
Simulations of galaxy growth need to invoke strong negative feedback from AGN to suppress the formation of stars and thus prevent the over-production of very massive systems. While some observations provide evidence for such negative feedback, other studies find either no feedback, or even positive feedback, with increased SF associated with higher AGN luminosities. Report an analysis of several 100 AGN and their host galaxies in the CDFS using X-ray and radio data for sample selection. Combined with archival FIR data as a reliable tracer of SF activity in the AGN host galaxies, find that AGN with pronounced radio jets exhibit a much higher SFR than the purely X-ray selected ones, even at the same X-ray luminosities. This difference implies that positive AGN feedback plays an important role, too, and therefore has to be accounted for in all future simulation work. Interpret this to indicate that the enhanced SFR of radio-selected AGN arises because of jet-induced SF, as is hinted by the different jet powers among the AGN samples, while the suppressed SFR of X-ray selected AGN is caused by heating and photo-dissociation of molecular gas by the hot AGN accretion disc.
1306.6552
The nature of extremely red galaxies in the local universe
Sodré, da Silva, Santos
Investigate the nature of extremely red galaxies (ERGs), objects whose colors are redder than those found in the red sequence present in color-magnitude diagrams of galaxies. Selected from SDSS DR7 a volume-limited sample of such galaxies in 0.010<z<0.030, brighter than M_r=-17.8 (magnitudes dereddened, corrected for the MW extinction) and with (g-r) colors larger than those of galaxies in the red sequence. This sample contains 416 ERGs, which were classified visually. Classification was cross-checked with other classifications available in the literature. Found from visual classification that the majority of objects in sample are edge-on spirals (73%). OTher spirals correspond to 13%, whereas elliptical galaxies comprise only 11% of the objects. After comparing the morphological mix and the distributions of Ha Hb and axial ratios of ERGs and objects in the red sequence, suggest that dust, more than stellar population effects, is the driver of the red colors found in these extremely red galaxies.
1306.6565
The chemical case for no winds in dwarf irregular galaxies
Gavilán et al
Argue that isolated gas-rich dwarf galaxies (in particular dIrr) do not necessarily undergo significant gas loss. Aim is to investigate whether the observed properties of isolated, gas-rich dwarf galaxies, not affected by external environmental processes, can be reproduced by self-consistent chemo-photometric infall models with continuous SFH and no mass or metal loss. This model is characterized by the total mass of primordial gas available to the object, its characteristic collapse timescale, and a constant SF efficiency. A grid of 144 such models has been computed by varying these parameters, and their predictions (elemental abundances, stellar and gas masses, photometric colors) have been compared with a set of observations of dIrr galaxies obtained from the literature. It is found that the models with moderate to low efficiency are able to reproduce most of the observational data, including the relative abundances of nitrogen and oxygen.
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