Browsing by Author "Hilker, Michael"

Now showing 1 - 8 of 8
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    Astroinformatics-based search for globular clusters in the Fornax Deep Survey
    (2019) Angora, Giuseppe; Brescia, Massimo; Cavuoti, Stefano; Paolillo, M.; Longo, Giuseppe; Cantiello, M.; Capaccioli, M.; D'Abrusco, Raffaele; D'Ago, Giuseppe; Puzia, Thomas H.; Hilker, Michael; Iodice, Enrichetta; Mieske, Steffen; Napolitano, Nicola R.; Peletier, R.; Pota, Vincenzo; Riccio, Giuseppe; Spavone, Marilena
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    Dynamical versus stellar masses of ultracompact dwarf galaxies in the Fornax cluster☆
    (2011) Chilingarian, Igor V.; Mieske, Steffen; Hilker, Michael; Infante, Leopoldo
    The origin of ultracompact dwarf (UCD) galaxies, compact extragalactic stellar systems, is still a puzzle for present galaxy formation models. We present the comprehensive analysis of high-resolution multi-object spectroscopic data for a sample of 24 Fornax cluster UCDs obtained with VLT with Fibre Large Array Multi Element Spectrograph (FLAMES). It comprises previously published data for 19 objects which we re-analysed, including 13 with available Hubble Space Telescope (HST) photometric data. Using Virtual Observatory technologies we found archival HST images for two more UCDs and then determined their structural properties. For all objects we derived internal velocity dispersions, stellar population parameters and stellar mass-to-light ratios (M/L)(*) by fitting individual simple stellar population (SSP) synthetic spectra convolved with a Gaussian against the observed spectra using the NBursts full spectral fitting technique. For 14 objects we estimated dynamical masses suggesting no dark matter (DM) in 12 of them and no more than 40 per cent DM mass fraction in the remaining two, in contrast to findings for several UCDs in the Virgo cluster. Some Fornax UCDs even have too high values of (M/L)(*) estimated using the Kroupa stellar initial mass function (IMF) resulting in negative formally computed DM mass fractions. The objects with too high (M/L)(*) ratios compared to the dynamical ones have relatively short dynamical relaxation time-scales, close to the Hubble time or below. We therefore suggest that their lower dynamical ratios (M/L)(dyn) are caused by low-mass star depletion due to dynamical evolution. Overall, the observed UCD characteristics suggest at least two formation channels: tidal threshing of nucleated dwarf galaxies for massive UCDs (similar or equal to 108 M-circle dot), and a classical scenario of red globular cluster formation for lower-mass UCDs (less than or similar to 107 M-circle dot).
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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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    Galaxy populations in the Hydra I cluster from the VEGAS survey I. Optical properties of a large sample of dwarf galaxies
    (2022) La Marca, Antonio; Peletier, Reynier; Iodice, Enrichetta; Paolillo, Maurizio; Challapa, Nelvy Choque; Venhola, Aku; Forbes, Duncan A.; Cantiello, Michele; Hilker, Michael; Rejkuba, Marina; Arnaboldi, Magda; Spavone, Marilena; D'Ago, Giuseppe; Raj, Maria Angela; Ragusa, Rossella; Mirabile, Marco; Rampazzo, Roberto; Spiniello, Chiara; Mieske, Steffen; Schipani, Pietro
    Context. Due to their relatively low stellar mass content and diffuse nature, the evolution of dwarf galaxies can be strongly affected by their environment. Analyzing the properties of the dwarf galaxies over a wide range of luminosities, sizes, morphological types, and environments, we can obtain insights about their evolution. At similar to 50 Mpc, the Hydra I cluster of galaxies is among the closest cluster in the z similar or equal to 0 Universe, and an ideal environment to study dwarf galaxy properties in a cluster environment.
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    Galaxy populations in the Hydra I cluster from the VEGAS survey II. The ultra-diffuse galaxy population
    (2022) La Marca, Antonio; Iodice, Enrichetta; Cantiello, Michele; Forbes, Duncan A.; Rejkuba, Marina; Hilker, Michael; Arnaboldi, Magda; Greggio, Laura; Spiniello, Chiara; Mieske, Steffen; Venhola, Aku; Spavone, Marilena; D'Ago, Giuseppe; Raj, Maria Angela; Ragusa, Rossella; Mirabile, Marco; Rampazzo, Roberto; Peletier, Reynier; Paolillo, Maurizio; Challapa, Nelvy Choque; Schipani, Pietro
    In this work, we extend the catalog of low-surface brightness (LSB) galaxies, including ultra-diffuse galaxy (UDG) candidates, within approximate to 0.4R(vir) of the Hydra I cluster of galaxies based on deep images from the VST Early-type GAlaxy Survey (VEGAS). The new galaxies were found by applying an automatic detection tool and carrying out additional visual inspections of g and r band images. This led to the detection of 11 UDGs and 8 more LSB galaxies. For all of them, we assessed the cluster membership using the color-magnitude relation derived for early-type giant and dwarf galaxies in Hydra I. The UDGs and new LSB galaxies found in Hydra I span a wide range of central surface brightness (22.7 less than or similar to mu(0.g) less than or similar to 26.5 mag arcse(-2)), effective radius (0.6 less than or similar to R-e less than or similar to 4.0 kpc), and color (0.4 <= g-r <= 0.9 mag), and have stellar masses in the range similar to 5 x 10(6)-2 x 10(8) M-circle dot. The 2D projected distribution of both galaxy types is similar to the spatial distribution of dwarf galaxies, with over-densities in the cluster core and north of the cluster center. They have similar color distribution and comparable stellar masses to the red dwarf galaxies. Based on photometric selection, we identify a total of nine globular cluster (GC) candidates associated to the UDGs and four to the LSB galaxies, with the highest number of candidates in an individual UDG being three. We find that there are no relevant differences between dwarfs, LSB galaxies, and UDGs: the structural parameters (i.e., surface brightness, size, color, and n-index) and GC content of the three classes have similar properties and trends. This finding is consistent with UDGs being the extreme LSB tail of the size-luminosity distribution of dwarfs in this environment.
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    The Fornax Cluster VLT Spectroscopic Survey III. Kinematical characterisation of globular clusters in the Fornax galaxy cluster
    (2022) Chaturvedi, Avinash; Hilker, Michael; Cantiello, Michele; Napolitano, Nicola R.; van de Ven, Glenn; Spiniello, Chiara; Fahrion, Katja; Paolillo, Maurizio; Gatto, Massimiliano; Puzia, Thomas
    The Fornax cluster provides an unparalleled opportunity of investigating the formation and evolution of early-type galaxies in a dense environment in detail. We aim at kinematically characterising photometrically detected globular cluster (GC) candidates in the core of the cluster. We used spectroscopic data from the Visible Multi Object Spectrograph at Very Large Telescope (VLT/VIMOS) from the FVSS survey in the Fornax cluster, covering one square degree around the central massive galaxy NGC 1399. We confirm a total of 777 GCs, almost doubling previously detected GCs, using the same dataset as was used before. Combined with previous literature radial velocity measurements of GCs in Fornax, we compile the most extensive spectroscopic GC sample of 2341 objects in this environment. We found that red GCs are mostly concentrated around major galaxies, while blue GCs are kinematically irregular and are widely spread throughout the core region of the cluster. The velocity dispersion profiles of blue and red GCs show a quite distinct behaviour. Blue GCs exhibit a sharp increase in the velocity dispersion profile from 250 to 400 km s(-1) within 5 arcmin (similar to 29 kpc/similar to 1 r(eff) of NGC 1399) from the central galaxy. The velocity dispersion profile of red GCs follows a constant value between 200 and 300 km s(-1) until 8 arcmin (similar to 46 kpc/similar to 1.6 r(eff)), and then rises to 350 km s(-1) at 10 arcmin (similar to 58 kpc/similar to 2 r(eff)). Beyond 10 arcmin and out to 40 arcmin (similar to 230 kpc/ similar to 8 r(eff)), blue and red GCs show a constant velocity dispersion of 300 +/- 50 km s(-1), indicating that both GC populations trace the cluster potential. We kinematically confirm and characterise the previously photometrically discovered overdensities of intra-cluster GCs. We found that these substructured intra-cluster regions in Fornax are dominated mostly by blue GCs.
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    The Next Generation Fornax Survey (NGFS). III. Revealing the Spatial Substructure of the Dwarf Galaxy Population Inside Half of Fornax's Virial Radius
    (2018) Órdenes Briceño, Yasna; Eigenthaler, Paul; Taylor, Matthew A.; Puzia, Thomas H.; Alamo-Martinez, Karla; Ribbeck, Karen X.; Munoz, Roberto P.; Zhang, Hongxin; Grebel, Eva K.; Ángel Ángel, Simón Andrés; Cote, Patrick; Ferrarese, Laura; Hilker, Michael; Lancon, Ariane; Mieske, Steffen; Miller, Bryan W.; Rong, Yu; Sanchez-Janssen, Ruben
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    The Next Generation Fornax Survey (NGFS). IV. Mass and Age Bimodality of Nuclear Clusters in the Fornax Core Region
    (2018) Órdenes Briceño, Yasna; Puzia, Thomas H.; Eigenthaler, Paul; Taylor, Matthew A.; Munoz, Roberto P.; Zhang, Hongxin; Alamo-Martinez, Karla; Ribbeck, Karen X.; Grebel, Eva K.; Ángel Ángel, Simón Andrés; Cote, Patrick; Ferrarese, Laura; Hilker, Michael; Lancon, Ariane; Mieske, Steffen; Miller, Bryan W.; Rong, Yu; Sanchez-Janssen, Ruben