1505.05518
Galaxy and mass assembly (GAMA): trends in galaxy colors, morphology, and stellar populations with large scale structure, group, and pair environments
Alpaslan, et al
Explore trends in galaxy properties with Mpc-scale structures using catalogues of environment and LSS from GAMA. Existing GAMA catalogues of LSS, group and pair membership allow construction of galaxy stellar mass functions for different environmental types. To avoid simply extracting the known underlying correlations between galaxy properties and stellar mass, create a mass matched sample of galaxies with stellar masses between 9.6<log(M*/h2^-2 Msun) < 11 for each environmental population. Using these samples, show that mass normalised galaxies in different large scale environments have similar energy outputs, u-r colors, luminosities, and morphologies. Extending the analysis to group and pair environments, show galaxies that are not in groups or pairs exhibit similar characteristics to each other regardless of broader environment. For the mass controlled sample, fail to see a strong dependence of Sersic index or galaxy luminosity on halo mass, but do find that it correlates very strongly with color. Repeating the analysis for galaxies that have not been mass controlled introduces and amplifies trends in the properties of galaxies in pairs, groups, and LSS indicating that stellar mass is the most important predictor of the galaxy properties examined, as opposed to environmental classifications.
1505.06421
HDFITS: porting the FITS data model to HDF5
Price, Barsdell, Greenhill
The FITS data format has been the de factor data format for astronomy-related data products since its inception in the late 1970s. While the FITS file format is widely supported, it lakes many of the features of more modern data serialization, such as the HDF5 (Hierarchical Data Format). The HDF5 file format offers considerable advantages over FITS, such as improved I/O speed and compression, but has yet to gain widespread adoption within astronomy. One of the major holdbacks is that HDF5 is not well supported by data reduction SW packages and image viewers. Here, present a comparison of FITS and HDF5 as a format for storage of astronomy datasets. Show that the underlying data model of FITS can be ported to HDF5 in aa straightforward manner, and that by doing so the advantages of the HDF5 file format can be leveraged immediately. In addition, present a SW tool, fits2hdf, for converting between FITS and a new 'HDFITS' format, where data are stored in HDF5 in a FITS-like manner. Show that HDFITS allows after reading of data (up to 100x of FITS in some use cases), and improved compression (higher compression ratios and higher throughput). Finally, show that by only changing the import lines in Python-based FITS utilities, HDFITS formatted data can be presented transparently as an in-memory FITS equivalent.
1505.06211
Illuminated a dark lens: a type Ia supernova magnified by the frontier fields galaxy cluster able 2744
Rodney, et al
SN HFF14Tom is a Type Ia SN discovered at z=1.3457±0.0001 behind the galaxy cluster A2744 (z=0.308). In a cosmology-independent analysis, find that HFF14Tom is 0.77±0.15 mag brighter than unlensed Type Ia SNe at similar z, implying a lensing magnification of 2.03±0.29. This observed magnification provides a rare opportunity for a direct empirical test of galaxy cluster lens models. Test 17 models, 13 of which were generated before the SN magnification was known, qualifying as pure "blind tests". The models are collectively fairly accurate: 8 of the models deliver median magnifications tat are consistent with measured mu to within 1-sigma. However, there is a subtle systematic bias: the significant disagreements all involve models over predicting the magnification. Evaluate possible causes for this mild bias, and find no single physical or methodological explanation to account for it. Find that model accuracy can be improved to some extent with stringent quality cuts on multiply-imaged systems, such as requiring that a large fraction have spectroscopic redshifts. In addition to testing model accuracies as done here, Type Ia SN mags could also be used as inputs for future lens models of A2744 and other clusters, providing valuable constraints in regions where traditional strong- and weak-lensing information is unavailable.
1505.07454
Filaments from the galaxy distribution and from the velocity field in the local universe
Libeskind et al
Characterizing the cosmic web in many ways: e.g., large z surveys can be used in combination with point process algorithms to extract long curvilinear filaments in the galaxy distribution. Alternatively, given a full 3D reconstruction of the velocity field, kinematic techniques can be used to decompose the web into voids, sheets, filaments and knots. In this paper, look at how two such algorithms - the Bisous model and the velocity shear web - compare with each other in the local Universe (within 100 Mpc), finding good agreement. This is both remarkable and comforting, given that the two methods are radically different in ideology and applied to completely independent and different data sets. Unsurprisingly, the methods are in better agreement when applied to unbiased and complete data sets, like cosmological simulations, than when applied to observational samples. Conclude that more observational data is needed to improve on these methods, but that both methods are most likely properly tracing the underlying distribution of matter in the Universe.
1505.07465
The new Milky Way satellites: alignment with the VPOS and predictions for proper motions and velocity dispersions
Pawlowski, McGaugh, Jerjen
The evidence that stellar systems surrounding the MW are distribution in vast polar structure (VPOS) may be observationally biased by satellites detected in surveys of the northern sky. The recent discoveries of more than a dozen new systems in the southern hemisphere thus constitute a critical test of the VPOS phenomenon. Report that the new objects are located close to the original VPOS, with half of the sample having offsets lest than 20 kpc. The positions of the new satellite galaxy candidates are so well aligned that the orientation of the revised best-fitting VPOS structure is preserved to within 9 degrees and the VPOS flattening is almost unchanged (31 kpc height). Interestingly, the shortest distance of the VPOS plane from the MW center is now only 2.5 kpc, indicating that the new discoveries balance out the VPOS at the Galactic center. The vast majority of the NW satellites are thus consistent with sharing a similar orbital plane as the Magellanic Clouds, confirming a hypothesis proposed by Kunkel & Demers and Lynden-Bell almost 40 years ago. Predict the absolute proper motions of the new objects assuming they orbit within the VPOS. Independent of the VPOS results, also predict the velocity dispersions of the new systems under 3 distinct assumptions: that they (i) are DM-free star clusters obeying Newtonian dynamics, (ii) are dwarf satellites lying on empirical scaling relations of galaxies in DM haloes, and (iii) they obey MOND.
1505.07477
The effect of massive neutrinos on the BAO peak
Peloso, et al
Show that the evolution with z of the correlation function and its dependence on the neutrino masses is well reproduced in a simplified version of the Zel'dovich approximation, in which the mode-coupling contribution to the PS is neglected. While in linear theory the BAO peak decreases for increasing neutrino masses, the effect of NL structure formation goes in the opposite direction, since the peak broadening by LS flows is less effective. As a results of this combined effect, the peak decreases by ~0.6% for sum m_nu=0.15 eV and increases by ~1.2% for sum m_nu=0.3 eV, with respect to a massless neutrino cosmology with equal value of the other cosmological parameters. Extend the analysis to z space and to haloes, and confirm the agreement between simulations and the analytic formulae. Argue that all analytical approaches having the Zel'dovich propagator in their lowest order approximation should give comparable performances, irrespectively to their formulation in Lagrangian or in Eulerian space.
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