Browsing by Author "Gullieuszik, Marco"

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    Formation of an ultra-diffuse galaxy in the stellar filaments of NGC 3314A: Caught in the act?
    (2021) Iodice, Enrichetta; La Marca, Antonio; Hilker, Michael; Cantiello, Michele; D'Ago, Giuseppe; Gullieuszik, Marco; Rejkuba, Marina; Arnaboldi, Magda; Spavone, Marilena; Spiniello, Chiara; Forbes, Duncan A.; Greggio, Laura; Rampazzo, Roberto; Mieske, Steffen; Paolillo, Maurizio; Schipani, Pietro
    The VEGAS imaging survey of the Hydra I cluster has revealed an extended network of stellar filaments to the south-west of the spiral galaxy NGC 3314A. Within these filaments, at a projected distance of similar to 40 kpc from the galaxy, we discover an ultra-diffuse galaxy (UDG) with a central surface brightness of mu(0,g) similar to 26 mag arcsec(-2) and effective radius R-e similar to 3.8 kpc. This UDG, named UDG 32, is one of the faintest and most diffuse low-surface-brightness galaxies in the Hydra I cluster. Based on the available data, we cannot exclude that this object is just seen in projection on top of the stellar filaments and is thus instead a foreground or background UDG in the cluster. However, the clear spatial coincidence of UDG 32 with the stellar filaments of NGC 3314A suggests that it might have formed from the material in the filaments, becoming a detached, gravitationally bound system. In this scenario, the origin of UDG 32 depends on the nature of the stellar filaments in NGC 3314A, which is still unknown. The stellar filaments could result from ram-pressure stripping or have a tidal origin. In this letter we focus on the comparison of the observed properties of the stellar filaments and of UDG 32 and speculate on their possible origin. The relatively red colour (g - r=0.54 +/- 0.14 mag) of the UDG, similar to that of the disk in NGC 3314A, combined with an age older than 1 Gyr and the possible presence of a few compact stellar systems, points towards a tidal formation scenario.
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    Looking for the Building Blocks of the Galactic Halo: Variable stars in the Fornax, Bootes I, Canes Venatici II Dwarfs and in NGC2419
    (2009) Greco, Claudia; Clementini, Gisella; Held, Enrico E.; Poretti, Ennio; Catelan, Márcio; Federici, Luciana; Gullieuszik, Marco; Maio, Marcella; Ripepi, Vincenzo; Dall'Ora, Massimo; di Fabrizio, Luca; Kinemuchi, Karen; di Criscienzo, Marcella; Marconi, Marcella; Musella, Ilaria; Rest, Armin; de Lee, Nathan; Pritzl, Barton J.; Smith, Horace
    Looking for the building blocks of the Galactic Halo we have investigated and compared the properties of the RR Lyrae stars in a number of different stellar systems inside and outside the Milky Way.
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    Variable stars in the fornax dsph galaxy. I. The globular cluster fornax
    (2007) Greco, Claudia; Clementini, Gisella; Catelan, Marcio; Held, Enrico V.; Poretti, Ennio; Gullieuszik, Marco; Maio, Marcella; Rest, Armin; De Lee, Nathan; Smith, Horace A.; Pritzl, Barton J.
    Variable stars have been identified for the first time in Fornax 4, the globular cluster located near the center of the Fornax dwarf spheroidal galaxy. By applying the image-subtraction technique to B and V time series photometry obtained with the MagIC camera of the 6.5m Magellan Clay telescope and with the wide field imager of the 4 m Blanco CTIO telescope, we detected 27 RR Lyrae stars (22 fundamental-mode, 3 first-overtone, and 2 double-mode pulsators) in a 2.4' x 2.4' area centered on Fornax 4. The average and minimum periods of the ab-type RR Lyrae stars, < Pab > = 0: 594 days and P(ab,min) = 0.5191 days, respectively, as well as the revised position of the cluster in the horizontal branch type-metallicity plane, all consistently point to an Oosterhoff-intermediate status for the cluster, unlike what is seen for the vast majority of Galactic globular clusters, but in agreement with previous indications for the other globular clusters in Fornax. The average apparent magnitude of the RR Lyrae stars located within 3000 from the cluster center is < V(RR)> = 21.43 +/- 0.03 mag (sigma = 0.10 mag, average of 12 stars), leading to a true distance modulus of mu(0) = 20.64 +/- 0.09 mag or mu(0) = 20.53 +/- 0.09 mag, depending on whether a low ([Fe/H] = -2.0) or a moderately high ([Fe/H] = -1: 5) metallicity is adopted.