We present the results of 325MHz Giant Metrewave Radio Telescope observations of a supercluster field, known to contain five Abell clusters at redshift z~0.2. We achieve a nominal sensitivity of 34uJy/beam towards the phase centre. We compile a catalogue of 3257 sources with flux densities in the range 183uJy-1.5Jy within the entire ~6.5deg^2^ field of view. Subsequently, we use available survey data at other frequencies to derive the spectral index distribution for a sub-sample of these sources, recovering two distinct populations - a dominant population which exhibit spectral index trends typical of steep-spectrum synchrotron emission, and a smaller population of sources with typically flat or rising spectra. We identify a number of sources with ultrasteep spectra or rising spectra for further analysis, finding two candidate high-redshift radio galaxies and three gigahertz-peaked-spectrum radio sources. Finally, we derive the Euclidean-normalized differential source counts using the catalogue compiled in this work, for sources with flux densities in excess of 223uJy. Our differential source counts are consistent with both previous observations at this frequency and models of the low-frequency source population. These represent the deepest source counts yet derived at 325MHz. Our source counts exhibit the well-known flattening at mJy flux densities, consistent with an emerging population of star-forming galaxies; we also find marginal evidence of a downturn at flux densities below 308uJy, a feature so far only seen at 1.4GHz.
We use a compilation of redshifts of rich clusters by Andernach, Tago and Stengler-Larrea (1996, in preparation) to determine superclusters of rich clusters up to a redshift of z=0.12. Superclusters were searched for with a clustering algorithm, using a neighbourhood radius of 24h^-1^Mpc (h is the Hubble constant in units of 100km/s/Mpc). The catalogue contains 220 superclusters of rich clusters, of which 90 superclusters have been determined for the first time. Table A2 gives the supercluster number, its multiplicity, centre coordinates, a list of member clusters and identifications with the catalogue by Einasto et al. (1994MNRAS.269..301E).
We present optical light curves, redshifts, and classifications for 365 spectroscopically confirmed Type Ia supernovae (SNe Ia) discovered by the Pan-STARRS1 (PS1) Medium Deep Survey. We detail improvements to the PS1 SN photometry, astrometry, and calibration that reduce the systematic uncertainties in the PS1 SN Ia distances. We combine the subset of 279 PS1 SNe Ia (0.03<z<0.68) with useful distance estimates of SNe Ia from the Sloan Digital Sky Survey (SDSS), SNLS, and various low-z and Hubble Space Telescope samples to form the largest combined sample of SNe Ia, consisting of a total of 1048 SNe Ia in the range of 0.01<z<2.3, which we call the "Pantheon Sample". When combining Planck 2015 cosmic microwave background (CMB) measurements with the Pantheon SN sample, we find {Omega}_m_=0.307+/-0.012 and w=-1.026+/-0.041 for the wCDM model. When the SN and CMB constraints are combined with constraints from BAO and local H_0_ measurements, the analysis yields the most precise measurement of dark energy to date: w_0_=-1.007+/-0.089 and w_a_=-0.222+/-0.407 for the w_0_w_a_CDM model. Tension with a cosmological constant previously seen in an analysis of PS1 and low-z SNe has diminished after an increase of 2x in the statistics of the PS1 sample, improved calibration and photometry, and stricter light-curve quality cuts. We find that the systematic uncertainties in our measurements of dark energy are almost as large as the statistical uncertainties, primarily due to limitations of modeling the low-redshift sample. This must be addressed for future progress in using SNe Ia to measure dark energy.
The Sagittarius dwarf spheroidal galaxy, the closest satellite galaxy of the Milky Way, has survived for many orbits about the Galaxy. Extent numerical calculations modeled this galaxy as a system with a centrally-concentrated mass profile, following the light, and found that it should lose more than one-half of its mass every 2-4 orbits and be completely disrupted long before now. Apparently the Sagittarius dwarf spheroidal, and by implication other dSph galaxies, do not have a centrally-concentrated profile for their dark matter. We develop a model in which the stars of the Sgr dwarf are embedded in a constant-density dark matter halo, representing the core of a tidally-limited system, and show that this is consistent with its survival. We present new photometric and kinematic observations of the Sagittarius dwarf spheroidal and show these data are consistent with this explanation for the continued existence of this galaxy. The Sagittarius dwarf is being tidally distorted and is tidally limited, but is not disrupted as yet. The corresponding minimum total mass is 10^9^M_{sun}_, while the central mass to visual light ratio is ~50 in Solar units. Our new photographic photometry allows the detection of main-sequence stars of the Sagittarius dwarf over an area of 22x8{deg}. The Sagittarius dwarf is prolate, with axis ratios ~3:1:1. For an adopted distance of 16+/-2kpc from the Galactic center on the opposite side of the Galaxy to the Sun, the major axis is >~9kpc long and is aligned approximately normal to the plane of the Milky Way Galaxy, roughly following the coordinate line l=5{deg}. The central velocity dispersion of giant stars which are members of the Sagittarius dwarf is 11.4+/-0.7km/s and is consistent with being constant over the face of the galaxy. The gradient in mean line-of-sight velocity with position along the major axis, dv/db, is ~0km/s/degree in the central regions and increases in amplitude to dv/db=-3km/s/degree over the outermost three degrees for which we have data. A first measurement of the proper motion of the Sagittarius dwarf determines the component of its space velocity parallel to its major axis to be 250+/-90km/s, directed towards the Galactic Plane. We model these kinematic data to determine the orbit of the Sagittarius dwarf. Our best fit model has an orbital period of <~1Gyr and has the Sagittarius dwarf spheroidal close to perigalacticon. This period is shorter, by about a factor of >~10, than the age of the bulk of its stellar population. (Copyright) 1997 American Astronomical Society.