424 research outputs found
Early-Type Galaxies And Their Sometimes Not So Old Globular Clusters
The work presented here deals with the age structure in globular cluster systems of early-type galaxies and aims at further clues about the formation and evolution of these galaxies. Hereby we turn our attention mainly to the detection of age sub-populations within the globular cluster systems, which are a clear signature of multiple star
formation events and describe the major phases in the evolutionary history of the host galaxy. The basic ingredients to our semi-numerical approach are combined optical and near-infrared observations of various globular cluster systems and Single Stellar
Population models.
Besides the introduction and the test of our semi-numerical method of deriving the age structure in globular cluster systems we are also interested in investigating an extended galaxy sample, i.e. their globular cluster systems in order to find systematic dependencies of the age structure. Since Single Stellar Population models are crucial for our project and various of these models are available we also to
evcaluate the influence of our choice of SSP model on the final result
Confirmation of a cluster of galaxies hidden behind the Galactic bulge using the VVV Survey
Suzaku and Chandra X-ray observations detected a new cluster of galaxies,
Suzaku J1759-3450, at a redshift z=0.13. It is located behind the Milky Way,
and the high Galactic dust extinction renders it nearly invisible at optical
wavelengths. We attempt here to confirm the galaxy cluster with near-infrared
imaging observations, and to characterize its central member galaxies. Images
from the VVV survey were used to detect candidate member galaxies of Suzaku
J1759-3450 within the central region of the cluster, up to 350 kpc from the
X-ray peak emission. Color-magnitude and color-color diagrams and morphology
criteria allowed us to select the galaxies among the numerous foreground
sources. Fifteen candidate cluster members were found very close to a modeled
red-sequence at the redshift of the cluster. Five members are extremely bright,
and one is possibly a cD galaxy. The asymmetry in the spatial distribution of
the galaxies respect to the X-ray peak emission is an indicator of that this
cluster is still suffering a virialization process. Our investigation of Suzaku
J1759-3450 demonstrates the potential of the VVV Survey to study the hidden
population of galaxies in the Zone of Avoidance.Comment: 7 pages, 5 figures. Accepted for Publication in Astronomy &
Astrophysic
VLT Spectroscopy of Globular Cluster Systems, I. The Photometric and Spectroscopic Dataset
We present Lick line-index measurements of extragalactic globular clusters in
seven early-type galaxies (NGC 1380, 2434, 3115, 3379, 3585, 5846, and 7192)
with different morphological types (E-S0) located in field and group/cluster
environments. High-quality spectra were taken with the FORS2 instrument at
ESO's Very Large Telescope. About 50% of our data allow an age resolution dt/t
~ 0.3 and a metallicity resolution ~0.25-0.4 dex, depending on the absolute
metallicity. Globular cluster candidates are selected from deep B, V, R, I, K
FORS2/ISAAC photometry with 80-100% success rate inside one effective radius.
Using combined optical/near-infrared colour-colour diagrams we present a method
to efficiently reduce fore-/background contamination down to <10%. We find
clear signs for bi-modality in the globular cluster colour distributions of NGC
1380, 3115, and 3585. The colour distributions of globular clusters in NGC
2434, 3379, 5846, and 7192 are consistent with a broad single-peak
distribution. For the analysed globular cluster systems the slopes of projected
radial surface density profiles, of the form Sigma(R) ~ R^-Gamma, vary between
~0.8 and 2.6. Using globular clusters as a tracer population we determine total
dynamical masses of host galaxies out to large radii (~1.6 - 4.8 Reff). For the
sample we find masses in the range ~8.8*10^10 Msolar up to ~1.2*10^12 Msolar.
The line index data presented here will be used in accompanying papers of this
series to derive ages, metallicities and abundance ratios. A compilation of
currently available high-quality Lick index measurements for globular clusters
in elliptical, lenticular, and late-type galaxies is provided and will serve to
augment the current data set. [abridged]Comment: A&A accepted, 42 page
The Acs Survey of Globular Clusters. Xiii. Photometric Calibration in Comparison with Stetson Standards
In this study we compare the photometric data of 34 Milky Way globular clusters, observed within the Advanced Camera for Surveys (ACS) Treasury Program (PI: A. Sarajedini) with the corresponding ground-based data, provided by the Photometric Standard Field Catalogs of Stetson. We focus on the transformation between the Hubble Space Telescope/ACS F606W to V-band and F814W to I-band only. The goal is to assess the validity of the filter transformation equations by Sirianni et al. with respect to their dependence on metallicity, horizontal branch morphology, mass, and integrated (V – I) color of the various globular clusters. The transformation equations as recommended by Sirianni et al. are based on synthetic photometry, were mostly tested on NGC 2419, and may introduce additional uncertainties when applied to different stellar populations. Such a dependence is expected due to the fact that the transformation equations are based on the observations of only one globular cluster, i.e., NGC 2419. Surprisingly, the correlation between offset and metallicity is found to be weak, with a low level significance. The correlation between offset and horizontal branch structure, as well as total cluster mass is still weaker. Based on the available data we do not find the photometric offset to be linked to multiple stellar populations, e.g., as found in NGC 0288, NGC 1851, and NGC 5139. The results of this study show that there are small systematic offsets between the transformed ACS- and observed ground-based photometry, and that these are only weakly correlated, if at all, with various cluster parameters and their underlying stellar populations. As a result, investigators wishing to transform globular cluster photometry from the Sirianni et al. ground-based V, I system onto the Stetson system simply need to add –0.040 (±0.012) to the V magnitudes and –0.047 (±0.011) to the I magnitudes. This in turn means that the transformed ACS V – I colors match the ground-based values from Stetson to within ~0.01 mag
Extinction ratios in the inner Galaxy as revealed by the VVV survey
Accepted for publication in ApJ Letters, 10 pages, 3 Figures, 2 Tables © 2017 The American Astronomical Society. All rights reserved.Interstellar extinction towards the Galactic Center is large and significantly differential. Its reddening and dimming effects in red clump stars in the Galactic Bulge can be exploited to better constrain the extinction law towards the innermost Galaxy. By virtue of a deep and complete catalog of more than 30 million objets at and obtained from VVV survey observations, we apply the red clump method to infer the selective-to-total extinction ratios in the , , , and broadband near-infrared filters. The measured values are smaller than previously reported, and are not constant, with mean values, e.g., and . We also obtain a ratio :::: of 7.74:5.38:3.30:1.88:1.0, implying extinction towards the Galactic Center to follow a distribution as a function of wavelength steeper than previously reported, consistent with a power law in the near-infrared.Peer reviewedFinal Accepted Versio
Milky Way demographics with the VVV survey. IV. PSF photometry from almost one billion stars in the Galactic bulge and adjacent southern disk
Accepted for publication in a forthcoming issue of Astronomy & Astrophysics. Reproduced with permission from Astronomy & Astrophysics. © 2018 ESO.Context. The inner regions of the Galaxy are severely affected by extinction, which limits our capability to study the stellar populations present there. The Vista Variables in the Vía Láctea (VVV) ESO Public Survey has observed this zone at near-infrared wavelengths where reddening is highly diminished. Aims. By exploiting the high resolution and wide field-of-view of the VVV images we aim to produce a deep, homogeneous, and highly complete database of sources that cover the innermost regions of our Galaxy. Methods. To better deal with the high crowding in the surveyed areas, we have used point spread function (PSF)-fitting techniques to obtain a new photometry of the VVV images, in the ZY JHK s near-infrared filters available. Results. Our final catalogs contain close to one billion sources, with precise photometry in up to five near-infrared filters, and they are already being used to provide an unprecedented view of the inner Galactic stellar populations. We make these catalogs publicly available to the community. Our catalogs allow us to build the VVV giga-CMD, a series of color-magnitude diagrams of the inner regions of the Milky Way presented as supplementary videos. We provide a qualitative analysis of some representative CMDs of the inner regions of the Galaxy, and briefly mention some of the studies we have developed with this new dataset so far.Peer reviewe
The ACS survey of globular clusters. XIII. Photometric calibration in comparison with Stetson standards
In this study we compare the photometric data of 34 Milky Way globular
clusters, observed within the ACS Treasury Program (PI: Ata Sarajedini) with
the corresponding ground-based data, provided by the Photometric Standard Field
Catalogs of Stetson (2000, 2005). We focus on the transformation between the
HST/ACS F606W to V-band and F814W to I-band only. The goal is to assess the
validity of the filter transformation equations by Sirianni et al.(2005) with
respect to their dependence on metallicity, Horizontal Branch morphology, mass
and integrated (V-I) colour of the various globular clusters. Such a dependence
is expected due to the fact that the transformation equations are based on the
observations of only one globular cluster, i.e., NGC 2419. Surprisingly, the
correlation between offset and metallicity is found to be weak, with a low
level significance. The correlation between offset and Horizontal Branch
structure, as well as total cluster mass is still weaker. Based on the
available data we do not find the photometric offset to be linked to multiple
stellar populations, e.g., as found in NGC 0288, NGC 1851, and NGC 5139. The
results of this study show that there are small systematic offsets between the
transformed ACS- and observed ground based photometry, and that these are only
weakly correlated, if at all, with various cluster parameters and their
underlying stellar populations. As a result, investigators wishing to transform
globular cluster photometry from the Sirianni et al.(2005) ground-based V, I
system onto the Stetson (2000) system simply need to add 0.040 (+/-0.012) to
the V-band magnitudes and 0.047 (+/-0.011) to the I-band magnitudes. This in
turn means that the transformed ACS (V-I) colours match the ground-based values
from Stetson (2000) to within ~0.01 mag.Comment: 28 pages, 14 figures, accepted for publication in ApJ
- …