139 research outputs found
Surface Brightness Fluctuations from archival ACS images: a stellar population and distance study
We derive Surface Brightness Fluctuations (SBF) and integrated magnitudes in
the V- and I-bands using Advanced Camera for Surveys (ACS) archival data. The
sample includes 14 galaxies covering a wide range of physical properties:
morphology, total absolute magnitude, integrated color. We take advantage of
the latter characteristic of the sample to check existing empirical
calibrations of absolute SBF magnitudes both in the I- and V-passbands.
Additionally, by comparing our SBF and color data with the Teramo-SPoT simple
stellar population models, and other recent sets of population synthesis
models, we discuss the feasibility of stellar population studies based on
fluctuation magnitudes analysis. The main result of this study is that
multiband optical SBF data and integrated colors can be used to significantly
constrain the chemical composition of the dominant stellar system in the
galaxy, but not the age in the case of systems older than 3 Gyr.
SBF color gradients are also detected and analyzed. These SBF gradient data,
together with other available data, point to the existence of mass dependent
metallicity gradients in galaxies, with the more massive objects showing a
non--negligible SBF versus color gradient. The comparison with models suggests
that such gradients imply more metal rich stellar populations in the galaxies'
inner regions with respect to the outer ones.Comment: ApJ Accepte
Detection of Radial Surface Brightness Fluctuation and Color Gradients in elliptical galaxies with ACS
We study surface brightness fluctuations (SBF) in a sample of 8 elliptical
galaxies using Advanced Camera for Surveys (ACS) Wide Field Channel (WFC) data
drawn from the Hubble Space Telescope (HST) archive. SBF magnitudes in the
F814W bandpass, and galaxy colors from F814W, F435W, and F606W images -- when
available -- are presented. Galaxy surface brightness profiles are determined
as well. We present the first SBF--broadband color calibration for the ACS/WFC
F814W bandpass, and (relative) distance moduli estimates for 7 of our galaxies.
We detect and study in detail the SBF variations within individual galaxies
as a probe of possible changes in the underlying stellar populations.
Inspecting both the SBF and color gradients in comparison to model predictions,
we argue that SBF, and SBF-gradients, can in principle be used for unraveling
the different evolutionary paths taken by galaxies, though a more comprehensive
study of this issue would be required. We confirm that the radial variation of
galaxy stellar population properties should be mainly connected to the presence
of radial chemical abundance gradients, with the outer galaxy regions being
more metal poor than the inner ones.Comment: 47 pages, 13 figures, ApJ, accepte
Intracluster Planetary Nebulae in Virgo: Photometric selection, spectroscopic validation and cluster depth
We have imaged an empty area of 34'x34' one and a half degree north of the
Virgo cluster core to survey for intracluster planetary nebula candidates. We
have implemented and tested a fully automatic procedure for the selection of
emission line objects in wide-field images, based on the on-off technique from
Ciardullo and Jacoby. Freeman et al. have spectroscopically confirmed a sample
of intracluster planetary nebulae in one Virgo field. We use the photometric
and morphological properties of this sample to test our selection procedure. In
our newly surveyed Virgo field, 75 objects were identified as best candidates
for intracluster PNe.
The luminosity function of the spectroscopically confirmed PNe shows a
brighter cut-off than the planetary nebula luminosity function for the inner
regions of M87. Such a brighter cut-off is also observed in the newly surveyed
field and indicates a smaller distance modulus, implying that the front end of
the Virgo cluster is closer to us by a significant amount: 14% closer (2.1 Mpc)
than M87 for the spectroscopic field, using the PN luminosity function distance
of 14.9 Mpc to M87, and 19% closer (2.8 Mpc) than M87 for the newly surveyed
field. Independent distance indicators (Tully-Fisher relation for Virgo spirals
and surface brightness fluctuations for Virgo ellipticals) agree with these
findings.
From these two Virgo cluster fields there is no evidence that the surface
luminosity density for the diffuse stellar component in the cluster decreases
with radius. The luminosity surface density of the diffuse stellar population
is comparable to that of the galaxies.Comment: 30 pages, 8 figures, accepted for pubblication in A
The SAMI-Fornax Dwarfs Survey I: sample, observations, and the specific stellar angular momentum of dwarf elliptical galaxies
Dwarf ellipticals are the most common galaxy type in cluster environments,
however the challenges associated with their observation mean their formation
mechanisms are still poorly understood. To address this, we present deep
integral field observations of a sample of 31 low-mass ( M M) early-type galaxies in the Fornax cluster with the SAMI
instrument. For 21 galaxies our observations are sufficiently deep to construct
spatially resolved maps of the stellar velocity and velocity dispersion - for
the remaining galaxies we extract global velocities and dispersions from
aperture spectra only. From the kinematic maps we measure the specific stellar
angular momentum of the lowest mass dE galaxies to date. Combining
our observations with early-type galaxy data from the literature spanning a
large range in stellar mass, we find that decreases towards lower
stellar mass, with a corresponding increase in the proportion of slowly
rotating galaxies in this regime. The decrease of with mass in our
sample dE galaxies is consistent with a similar trend seen in somewhat more
massive spiral galaxies from the CALIFA survey. This suggests that the degree
of dynamical heating required to produce dEs from low-mass starforming
progenitors may be relatively modest, and consistent with a broad range of
formation mechanisms.Comment: 13 pages, 10 figures and an additional 10 pages of appendices.
Accepted for publication in MNRA
Probing the Formation and Evolution of the Galactic Halo with Strega@VST
STREGA (STRucture and Evolution of the Galaxy) is an ongoing VLT Survey Telescope Guaranteed Time survey, aimed at investigating the mechanisms of formation and evolution of the Galactic Halo on an area of about 150 square degrees. The main programme searches for the signatures of interaction between selected stellar systems and the Galactic Halo. We present the results obtained for a number of Galactici Globular Clusters (Omega Cen, NGC6752, Pal 12 and Pal3) and discuss future perspectives
Supplement: "Localization and broadband follow-up of the gravitational-wave transient GW150914" (2016, ApJL, 826, L13)
This Supplement provides supporting material for Abbott et al. (2016a). We briefly summarize past electromagnetic (EM) follow-up efforts as well as the organization and policy of the current EM follow-up program. We compare the four probability sky maps produced for the gravitational-wave transient GW150914, and provide additional details of the EM follow-up observations that were performed in the different bands
Extragalactic Planetary Nebulae as Mass Tracers in the Outer Halos of Early-Type Galaxies
DATA REDUCTION AND ASTROMETRY STRATEGIES FOR WIDE-FIELD IMAGES: AN APPLICATION TO THE CAPODIMONTE DEEP FIELD
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