Browsing by Author "Galaz, G"

Now showing 1 - 7 of 7
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    CG J1720 67.8: A detailed analysis of optical and infrared properties of a new ultracompact group of galaxies
    (2003) Temporin, S; Weinberger, R; Galaz, G; Kerber, F
    We present here optical spectroscopy and BVRJHK(s) photometry of the recently discovered ultracompact group of galaxies CG J1720-67.8. This work represents a considerable extension of the preliminary results we presented in a previous paper. Despite the complicated morphology of the group, a quantitative morphological classification of the three brightest members of the group is attempted based on photometric analysis. We find that one galaxy is consistent with a morphological type S0, while the other two are most probably late-type spiral galaxies that are already losing their identity because of the interaction process. Information on the star formation activity and dust content derived from both spectroscopic data and optical and near-infrared colors is complemented with a reconstruction of far-infrared maps from IRAS raw data. Enhanced star formation activity is revealed in all the group's members, including the early-type galaxy and the extended tidal tail, along which several tidal dwarf galaxy candidates are identified. The metallicity of the gaseous component is investigated, and photoionization models are applied to the three main galaxies of the group, while a detailed study of the tidal dwarf candidates will appear in a companion paper. Subsolar metal abundances are found for all the three galaxies, the highest values being shown by the early-type galaxy (Z similar to 0.5 Z(.)).
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    Investigating new planetary nebulae in the southern hemisphere
    (2000) Kerber, F; Furlan, E; Roth, M; Galaz, G; Chanamé, JC
    The major purpose of the investigation presented in this paper was to prove or disprove the nature of planetary nebula (PN) candidates in the southern hemisphere, selected from the third volume of the Atlas of Galactic Nebulae by Neckel & Vehrenberg. We present imaging and spectroscopic observations of seven PNe, five of them identified for the first time. An additional object probably is an H II region. All observed PNe represent evolved stages, their angular diameter ranging from 15 " to 170 ", and exhibit low surface brightnesses.
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    Sn 2005bf
    (2006) Folatelli, G; Contreras, C; Phillips, MM; Woosley, SE; Blinnikov, S; Morrell, N; Suntzeff, NB; Lee, BL; Hamuy, M; González, S; Krzeminski, W; Roth, M; Li, WD; Filippenko, AV; Foley, RJ; Freedman, WL; Madore, BF; Persson, SE; Murphy, D; Boissier, S; Galaz, G; González, L; McCarthy, PJ; McWilliam, A; Pych, W
    We present u'g'r'i'BV photometry and optical spectroscopy of the Type Ib/Ic SN 2005bf covering the first similar to 100 days following discovery. The u'g'BV light curves displayed an unprecedented morphology among Type Ib/Ic supernovae, with an initial maximum some 2 weeks after discovery and a second, main maximum about 25 days after that. The bolometric light curve indicates that SN 2005bf was a remarkably luminous event, radiating at least 6.3 x 10(42) ergs s(-1) at maximum light and a total of 2.1 x 10(49) ergs during the first 75 days after the explosion. Spectroscopically, SN 2005bf underwent a unique transformation from a Type Ic-like event at early times to a typical Type Ib supernova at later phases. The initial maximum in u'g'BV was accompanied by the presence in the spectrum of high-velocity (> 14,000 km s(-1)) absorption lines of Fe II, Ca II, and H I. The photospheric velocity derived from spectra at early epochs was below 10,000 km s(-1), which is unusually low compared with ordinary Type Ib supernovae. We describe one-dimensional computer simulations that attempt to account for these remarkable properties. The most favored model is that of a very energetic (2 x 10(51) ergs), asymmetric explosion of a massive ( 8.3 M-circle dot) Wolf-Rayet WN star that had lost most of its hydrogen envelope. We speculate that an unobserved relativistic jet was launched producing a two-component explosion consisting of ( 1) a polar explosion containing a small fraction of the total mass and moving at high velocity and ( 2) the explosion of the rest of the star. At first, only the polar explosion is observed, producing the initial maximum and the high-velocity absorption-line spectrum resembling a Type Ic event. At late times, this fast- moving component becomes optically thin, revealing the more slowly moving explosion of the rest of the star and transforming the observed spectrum to that of a typical Type Ib supernova. If this scenario is correct, then SN 2005bf is the best example to date of a transition object between normal Type Ib/Ic supernovae and gamma-ray bursts.
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    The Butcher-Oemler effect at z∼0.35
    (2006) Andreon, S; Quintana, H; Tajer, M; Galaz, G; Surdej, J
    In this paper we focus on the much debated Butcher-Oemler effect: the increase with redshift of the fraction of blue galaxies in clusters. Considering a representative cluster sample made of seven groups/clusters at z similar to 0.35, we have measured the blue fraction from the cluster core to the cluster outskirts and the field mainly using wide-field Cerro Tololo Inter-American Observatory images. This sample represents a random selection of a volume complete X-ray selected cluster sample, selected so that there is no physical connection with the studied quantity (blue fraction), to minimize observational biases. In order to statistically assess the significance of the Butcher-Oemler effect, we introduce the tools of Bayesian inference. Furthermore, we have modified the blue fraction definition in order to take into account the reduced age of the Universe at higher redshifts, because we should no longer attempt to reject an unphysical universe in which the age of the Universe does depend on redshift, whereas the age of its content does not. We have measured the blue fraction from the cluster centre to the field and we find that the cluster affects the properties of the galaxies up to two virial radii at z similar to 0.35. Data suggest that during the last 3 Gyr no evolution of the blue fraction, from the cluster core to the field value, is seen beyond that needed to account for the varying age with the redshift of the Universe and of its content. The agreement of the radial profiles of the blue fraction at z= 0 and z similar to 0.35 implies that the pattern infall did not change over the last 3 Gyr, or, at least, its variation has no observational effect on the studied quantity.
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    The multiwavelength survey by Yale-Chile (MUSYC)
    (2006) Gawiser, E; van Dokkum, PG; Herrera, D; Maza, J; Castander, FJ; Infante, L; Lira, P; Quadri, R; Toner, R; Treister, E; Urry, CM; Altmann, M; Assef, R; Christlein, D; Coppi, PS; Durán, MF; Franx, M; Galaz, G; Huerta, L; Liu, C; López, S; Méndez, R; Moore, DC; Rubio, M; Ruiz, MT; Toft, S; Yi, SK
    We present UBVRIz' optical images taken with MOSAIC on the CTIO 4 m telescope of the 0.32 deg(2) Extended Hubble Deep Field-South. This is one of four fields comprising the MUSYC survey, which is optimized for the study of galaxies at z=3, active galactic nucleus (AGN) demographics, and Galactic structure. Our methods used for astrometric calibration, weighted image combination, and photometric calibration in AB magnitudes are described. We calculate corrected aperture photometry and its uncertainties and find through tests that these provide a significant improvement upon standard techniques. Our photometric catalog of 62,968 objects is complete to a total magnitude of R-AB=25, with R-band counts consistent with results from the literature. We select z similar or equal to 3 Lyman break galaxy (LBG) candidates from their UVR colors and find a sky surface density of 1.4 arcmin(-2) and an angular correlation function w(theta) (2.3 +/- 1.0)theta(-0.8), consistent with previous findings that high-redshift Lyman break galaxies reside in massive dark matter halos. Our images and catalogs are available online.
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    The nature of blue cores in spheroids
    (2005) Menanteau, F; Martel, AR; Tozzi, P; Frye, B; Ford, HC; Infante, L; Benítez, N; Galaz, G; Coe, D; Illingworth, GD; Hartig, GF; Clampin, M
    We investigate the physical nature of blue cores in early-type galaxies through the first multiwavelength analysis of a serendipitously discovered field blue-nucleated spheroid in the background of the deep Hubble Space Telescope ACS/WFC griz multicolor observations of the cluster A1689. The resolved g - r, r - i, and i - z color maps reveal a prominent blue core identifying this galaxy as a "typical'' case study, exhibiting variations of 0.5 - 1.0 mag in color between the center and the outer regions, opposite to the expectations of reddened metallicity- induced gradients in passively evolved elliptical galaxies. From a Magellan-Clay telescope spectrum we secure the galaxy redshift at z = 0.624. We find a strong X-ray source coincident with the spheroid galaxy. Spectral features and a high X-ray luminosity indicate the presence of an active galactic nucleus (AGN) in the galaxy. However, a comparison of the X-ray luminosity to a sample derived from the Chandra Deep Field - South displays L-X to be comparable to type 1/QSO galaxies while the optical flux is consistent with a normal star-forming galaxy. We conclude that the galaxy's nonthermal component dominates at high-energy wavelengths, while we associate the spheroid blue light with the stellar spectrum of normal star-forming galaxies. We argue for a probable association between the presence of blue cores in spheroids and AGN activity.
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    The Type Ia supernova 1999aw
    (2002) Strolger, LG; Smith, RC; Suntzeff, NB; Phillips, MM; Aldering, G; Nugent, P; Knop, R; Perlmutter, S; Schommer, RA; Ho, LC; Hamuy, M; Krisciunas, K; Germany, LM; Covarrubias, R; Candia, P; Athey, A; Blanc, G; Bonacic, A; Bowers, T; Conley, A; Dahlén, T; Freedman, W; Galaz, G; Gates, E; Goldhaber, G; Goobar, A; Groom, D; Hook, IM; Marzke, R; Mateo, M; McCarthy, P; Méndez, J; Muena, C; Persson, SE; Quimby, R; Roth, M; Ruiz-Lapuente, P; Seguel, J; Szentgyorgyi, A; von Braun, K; Wood-Vasey, WM; York, T
    SN 1999aw was discovered during the first campaign of the Nearby Galaxies Supernova Search project. This luminous, slow-declining [Deltam(15)(B) = 0.81 +/- 0.03] Type Ia supernova was noteworthy in at least two respects. First, it occurred in an extremely low luminosity host galaxy that was not visible in the template images nor in initial subsequent deep imaging. Second, the photometric and spectral properties of this supernova indicate that it very likely was similar to the subclass of Type Ia supernovae whose prototype is SN 1999aa. This paper presents the BVRI and J(s)HK(s) light curves of SN 1999aw ( through similar to100 days past maximum light), as well as several epochs of optical spectra. From these data, we calculate the bolometric light curve and give estimates of the luminosity at maximum light and the initial Ni-56 mass. In addition, we present deep BVI images obtained recently with the Baade 6.5 m telescope at Las Campanas Observatory that reveal the remarkably low-luminosity host galaxy.