Sagittarius II, Draco II and Laevens 3: Three New Milky Way Satellites Discovered in the Pan-STARRS 1 3 Survey

We present the discovery of three new Milky Way satellites from our search for compact stellar overdensities in the photometric catalog of the Panoramic Survey Telescope and Rapid Response System 1 (Pan-STARRS 1, or PS1) 3π survey. The first satellite, Laevens 3, is located at a heliocentric distance of d = 67 ± 3 kpc. With a total magnitude of MV = −4.4 ± 0.3 and a half-light radius of rh = 7 ± 2 pc, its properties resemble those of outer halo globular clusters. The second system, Draco II/Laevens 4, is a closer and fainter satellite (d ~ 20 kpc, MV = −2.9 ± 0.8), whose uncertain size (${r}_{h}={19}_{-6}^{+8}\;\mathrm{pc}$) renders its classification difficult without kinematic information; it could either be a faint and extended globular cluster or a faint and compact dwarf galaxy. The third satellite, Sagittarius II/Laevens 5 (Sgr II), has an ambiguous nature, as it is either the most compact dwarf galaxy or the most extended globular cluster in its luminosity range (${r}_{h}={37}_{-8}^{+9}\;\mathrm{pc}$ and MV = −5.2 ± 0.4). At a heliocentric distance of 67 ± 5 kpc, this satellite lies intriguingly close to the expected location of the trailing arm of the Sagittarius stellar stream behind the Sagittarius dwarf spheroidal galaxy (Sgr dSph). If confirmed through spectroscopic follow up, this connection would locate this part of the trailing arm of the Sagittarius stellar stream that has so far gone undetected. It would further suggest that Sgr II was brought into the Milky Way halo as a satellite of the Sgr dSph

Globular cluster luminosity function as distance indicator

Globular clusters are among the first objects used to establish the distance scale of the Universe. In the 1970-ies it has been recognized that the differential magnitude distribution of old globular clusters is very similar in different galaxies presenting a peak at M_V ~ -7.5. This peak magnitude of the so-called Globular Cluster Luminosity Function has been then established as a secondary distance indicator. The intrinsic accuracy of the method has been estimated to be of the order of ~0.2 mag, competitive with other distance determination methods. Lately the study of the Globular Cluster Systems has been used more as a tool for galaxy formation and evolution, and less so for distance determinations. Nevertheless, the collection of homogeneous and large datasets with the ACS on board HST presented new insights on the usefulness of the Globular Cluster Luminosity Function as distance indicator. I discuss here recent results based on observational and theoretical studies, which show that this distance indicator depends on complex physics of the cluster formation and dynamical evolution, and thus can have dependencies on Hubble type, environment and dynamical history of the host galaxy. While the corrections are often relatively small, they can amount to important systematic differences that make the Globular Cluster Luminosity Function a less accurate distance indicator with respect to some other standard candles.Comment: Accepted for publication in Astrophysics and Space Science. Review paper based on the invited talk at the conference "The Fundamental Cosmic Distance Scale: State of the Art and Gaia Perspective", Naples, May 2011. (13 pages, 8 figures

Newly Discovered Globular Clusters in the Outer Halo of M31

Original paper can be found at: http://www.astrosociety.org/pubs/cs/309.html--Copyright Astronomical Society of the PacificWe present nine newly discovered globular clusters in the outer halo of M31, found by a semi-automated procedure from an INT Wide Field Camera survey of the region. The sample includes a candidate at the largest known projected galactocentric radius yet from M31

A tale of two GRB-SNe at a common redshift of z=0.54

none74We present ground-based and Hubble Space Telescope optical observations of the optical transients (OTs) of long-duration Gamma Ray Bursts (GRBs) 060729 and 090618, both at a redshift of z=0.54. For GRB 060729, bumps are seen in the optical light curves (LCs), and the late-time broad-band spectral energy distributions (SEDs) of the OT resemble those of local Type Ic supernovae (SNe). For GRB 090618, the dense sampling of our optical observations has allowed us to detect well-defined bumps in the optical LCs, as well as a change in colour, that are indicative of light coming from a core-collapse SN. The accompanying SNe for both events are individually compared with SN1998bw, a known GRB supernova, and SN1994I, a typical Type Ic supernova without a known GRB counterpart, and in both cases the brightness and temporal evolution more closely resemble SN1998bw. We also exploit our extensive optical and radio data for GRB 090618, as well as the publicly available Swift-XRT data, and discuss the properties of the afterglow at early times. In the context of a simple jet-like model, the afterglow of GRB 090618 is best explained by the presence of a jet-break at t − to > 0.5 d. We then compare the rest-frame, peak V-band absolute magnitudes of all of the GRB and X-Ray Flash (XRF)-associated SNe with a large sample of local Type Ibc SNe, concluding that, when host extinction is considered, the peak magnitudes of the GRB/XRF-SNe cannot be distinguished from the peak magnitudes of non-GRB/XRF SNe.noneZ. Cano; D. Bersier; C. Guidorzi; R. Margutti; K.M Svensson; S. Kobayashi; A. Melandri; K. Wiersema; A. Pozanenko; A.J. van der Horst; G. G. Pooley; A. Fernandez-Soto; A.J. Castro-Tirado; A. de Ugarte Postigo; M. Im; A.P. Kamble; D. Sahu; M. Alexander; Jorge Alonso-Lorite; G. Anupama; J. L. Bibby; M. J. Burgdorf; N. Clay; P.A. Curran; T. A. Fatkhullin; A. S. Fruchter; P. Garnavich; A. Gomboc; J. Gorosabel; J. F. Graham; U. Gurugubelli; J. Haislip; K. Huang; A. Huxor; M. Ibrahimov; Y. Jeon; Y-B. Jeon; K. Ivarsen; D. Kasen; E. Klunko; C. Kouveliotou; A. LaCluyze; A. J. Levan; V. Loznikov; P.A. Mazzali; C. Mottram; C. G. Mundell; P.E. Nugent; M. Nysewander; P. T. OBrien; W. -K. Park; V. Peris; E. Pian; D. Reichart; J. E. Rhoads; E. Rol; V. Rumyantsev; V. Scowcroft; D. Shakhovskoy; E. Small; R. J. Smith; V. V. Sokolov; R.L.C. Starling; I. Steele; R. Strom; N. R. Tanvir; Y. Tsapras; Y. Urata; O. Vaduvescu; A. Volnova; A. Volvach; R. A. M. J. Wijers; S. E. Woosley; D. R. YoungZ., Cano; D., Bersier; Guidorzi, Cristiano; R., Margutti; K. M., Svensson; S., Kobayashi; A., Melandri; K., Wiersema; A., Pozanenko; A. J., van der Horst; G. G., Pooley; A., Fernandez Soto; A. J., Castro Tirado; A., de Ugarte Postigo; M., Im; A. P., Kamble; D., Sahu; M., Alexander; Jorge Alonso, Lorite; G., Anupama; J. L., Bibby; M. J., Burgdorf; N., Clay; P. A., Curran; T. A., Fatkhullin; A. S., Fruchter; P., Garnavich; A., Gomboc; J., Gorosabel; J. F., Graham; U., Gurugubelli; J., Haislip; K., Huang; A., Huxor; M., Ibrahimov; Y., Jeon; Y. B., Jeon; K., Ivarsen; D., Kasen; E., Klunko; C., Kouveliotou; A., Lacluyze; A. J., Levan; V., Loznikov; P. A., Mazzali; C., Mottram; C. G., Mundell; P. E., Nugent; M., Nysewander; P. T., Obrien; W. K., Park; V., Peris; E., Pian; D., Reichart; J. E., Rhoads; E., Rol; V., Rumyantsev; V., Scowcroft; D., Shakhovskoy; E., Small; R. J., Smith; V. V., Sokolov; R. L. C., Starling; I., Steele; R., Strom; N. R., Tanvir; Y., Tsapras; Y., Urata; O., Vaduvescu; A., Volnova; A., Volvach; R. A. M. J., Wijers; S. E., Woosley; D. R., Youn