Observations of diffuse starlight in the outskirts of galaxies are thought to be a fundamental source of constraints on the cosmological context of galaxy assembly in the Λ CDM model. Such ...observations are not trivial because of the extreme faintness of such regions. In this work, we investigated the photometric properties of six massive early-type galaxies (ETGs) in the VST Elliptical GAlaxies Survey (VEGAS) sample (NGC 1399, NGC 3923, NGC 4365, NGC 4472, NGC 5044, and NGC 5846) out to extremely low surface brightness levels with the goal of characterizing the global structure of their light profiles for comparison to state-of-the-art galaxy formation models. We carried out deep and detailed photometric mapping of our ETG sample taking advantage of deep imaging with VST/OmegaCAM in the g and i bands. By fitting the light profiles, and comparing the results to simulations of elliptical galaxy assembly, we have identified signatures of a transition between relaxed and unrelaxed accreted components and can constrain the balance between in situ and accreted stars. The very good agreement of our results with predictions from theoretical simulations demonstrates that the full VEGAS sample of ∼ 100 ETGs will allow us to use the distribution of diffuse light as a robust statistical probe of the hierarchical assembly of massive galaxies.
The Fornax Deep Survey with the VST Venhola, Aku; Peletier, Reynier; Laurikainen, Eija ...
Astronomy and astrophysics (Berlin),
12/2018, Letnik:
620
Journal Article
Recenzirano
Odprti dostop
Context.
The Fornax Deep Survey (FDS), an imaging survey in the
u
′,
g
′,
r
′, and
i
′-bands, has a supreme resolution and image depth compared to the previous spatially complete Fornax Cluster ...Catalog (FCC). Our new data allows us to study the galaxies down to
r
′-band magnitude
m
r
′
≈ 21 mag (
M
r
′
≈ −10.5 mag), which opens a new parameter regime to investigate the evolution of dwarf galaxies in the cluster environment. After the Virgo cluster, Fornax is the second nearest galaxy cluster to us, and with its different mass and evolutionary state, it provides a valuable comparison that makes it possible to understand the various evolutionary effects on galaxies and galaxy clusters. These data provide an important legacy dataset to study the Fornax cluster.
Aims.
We aim to present the Fornax Deep Survey (FDS) dwarf galaxy catalog, focusing on explaining the data reduction and calibrations, assessing the quality of the data, and describing the methods used for defining the cluster memberships and first order morphological classifications for the catalog objects. We also describe the main scientific questions that will be addressed based on the catalog. This catalog will also be invaluable for future follow-up studies of the Fornax cluster dwarf galaxies.
Methods.
As a first step we used the SExtractor fine-tuned for dwarf galaxy detection, to find galaxies from the FDS data, covering a 26 deg
2
area of the main cluster up to its virial radius, and the area around the Fornax A substructure. We made 2D-decompositions of the identified galaxies using GALFIT, measure the aperture colors, and the basic morphological parameters like concentration and residual flux fraction. We used color–magnitude, luminosity–radius and luminosity–concentration relations to separate the cluster galaxies from the background galaxies. We then divided the cluster galaxies into early- and late-type galaxies according to their morphology and gave first order morphological classifications using a combination of visual and parametric classifications.
Results.
Our final catalog includes 14 095 galaxies. We classify 590 galaxies as being likely Fornax cluster galaxies, of which 564 are dwarfs (
M
r
′
> −18.5 mag) consisting our Fornax dwarf catalog. Of the cluster dwarfs we classify 470 as early-types, and 94 as late-type galaxies. Our final catalog reaches its 50% completeness limit at magnitude
M
r
′
= −10.5 mag and surface brightness
μ¯
e,
r
′
= 26 mag arcsec
−2
, which is approximately three magnitudes deeper than the FCC. Based on previous works and comparison with a spectroscopically confirmed subsample, we estimate that our final Fornax dwarf galaxy catalog has ≲10% contamination from the background objects.
Most of the galaxies in the universe today are in groups, which are key to understanding their evolution. In this work we present a new deep mosaic of 1.2 × 1.0 square degrees of the group of ...galaxies centered on NGC 5018, acquired at the ESO VLT Survey Telescope. We use u, g, r images to analyze the structure of the group members and to estimate the intragroup light. Taking advantage of deep and multiband photometry and of the large field of view of the VST telescope, we studied the structure of the galaxy members and the faint features leading into the intragroup space, and we give an estimate of the intragroup diffuse light in the NGC 5018 group of galaxies. We found that ∼41% of the total g-band luminosity of the group is in the form of intragroup light (IGL). The IGL has a (g - r) color consistent with those of other galaxies in the group, indicating that the stripping leading to the formation of IGL is ongoing. From the study of this group we can infer that there are at least two different interactions involving the group members: one between NGC 5018 and NGC 5022, which generates the tails and ring-like structures detected in the light, and another between NGC 5022 and MCG-03-34-013, which has produced the H i tail. A minor merging event also happened in the formation history of NGC 5018 that perturbed the inner structure of this galaxy.
The Fornax Deep Survey (FDS) with VST Venhola, Aku; Peletier, Reynier; Laurikainen, Eija ...
Astronomy and astrophysics (Berlin),
05/2019, Letnik:
625
Journal Article
Recenzirano
Odprti dostop
Context
. Dwarf galaxies are the most common type of galaxies in galaxy clusters. Due to their low mass, they are more vulnerable to environmental effects than massive galaxies, and are thus optimal ...for studying the effects of the environment on galaxy evolution. By comparing the properties of dwarf galaxies with different masses, morphological types, and cluster-centric distances we can obtain information about the physical processes in clusters that play a role in the evolution of these objects and shape their properties. The Fornax Deep Survey Dwarf galaxy Catalog (FDSDC) includes 564 dwarf galaxies in the Fornax cluster and the in-falling Fornax A subgroup. This sample allows us to perform a robust statistical analysis of the structural and stellar population differences in the range of galactic environments within the Fornax cluster.
Aims
. By comparing our results with works concerning other clusters and the theoretical knowledge of the environmental processes taking place in galaxy clusters, we aim to understand the main mechanisms transforming galaxies in the Fornax cluster.
Methods
. We have exploited the FDSDC to study how the number density of galaxies, galaxy colors and structure change as a function of the cluster-centric distance, used as a proxy for the galactic environment and in-fall time. We also used deprojection methods to transform the observed shape and density distributions of the galaxies into the intrinsic physical values. These measurements are then compared with predictions of simple theoretical models of the effects of harassment and ram pressure stripping on galaxy structure. We used stellar population models to estimate the stellar masses, metallicities and ages of the dwarf galaxies. We compared the properties of the dwarf galaxies in Fornax with those in the other galaxy clusters with different masses.
Results
. We present the standard scaling relations for dwarf galaxies, which are the size-luminosity, Sérsic
n
-magnitude and color-magnitude relations. New in this paper is that we find a different behavior for the bright dwarfs (−18.5 mag <
M
r
′
< −16 mag) as compared to the fainter ones (
M
r
′
> −16 mag): While considering galaxies in the same magnitude-bins, we find that, while for fainter dwarfs the
g
′−
r
′ color is redder for lower surface brightness objects (as expected from fading stellar populations), for brighter dwarfs the color is redder for the higher surface brightness and higher Sérsic
n
objects. The trend of the bright dwarfs might be explained by those galaxies being affected by harassment and by slower quenching of star formation in their inner parts. As the fraction of early-type dwarfs with respect to late-types increases toward the central parts of the cluster, the color-surface brightness trends are also manifested in the cluster-centric trends, confirming that it is indeed the environment that changes the galaxies. We also estimate the strength of the ram-pressure stripping, tidal disruption, and harassment in the Fornax cluster, and find that our observations are consistent with the theoretically expected ranges of galaxy properties where each of those mechanisms dominate. We furthermore find that the luminosity function, color–magnitude relation, and axis-ratio distribution of the dwarfs in the center of the Fornax cluster are similar to those in the center of the Virgo cluster. This indicates that in spite of the fact that the Virgo is six times more massive, their central dwarf galaxy populations appear similar in the relations studied by us.
Context. Globular clusters (GCs) are key to our understanding of the Universe, as laboratories of stellar evolution, fossil tracers of the past formation epoch of the host galaxy, and effective ...distance indicators from local to cosmological scales. Aim. We analyze the properties of the sources in the NGC 253 with the aim of defining an up to date catalog of GC candidates in the galaxy. Given the distance of the galaxy, GCs in NGC 253 are ideal targets for resolved color-magnitude diagram studies of extragalactic GCs with next-generation diffraction limited ground-based telescopes. Methods. Our analysis is based on the science verification data of two ESO survey telescopes, VST and VISTA. Using ugri photometry from VST and JKs from VISTA, GC candidates were selected using as reference the morpho-photometric and color properties of spectroscopically confirmed GCs available in the literature. The strength of the results was verified against available archival HST/ACS data from the GHOSTS survey: all but two of the selected GC candidates appear as star clusters in HST footprints. Results. The adopted GC selection leads to the definition of a sample of ∼350 GC candidates. At visual inspection, we find that 82 objects match all the requirements for selecting GC candidates and 155 are flagged as uncertain GC candidate; however, 110 are unlikely GCs, which are most likely background galaxies. Furthermore, our analysis shows that four of the previously spectroscopically confirmed GCs, i.e., ∼20% of the total spectroscopic sample, are more likely either background galaxies or high-velocity Milky Way stars. The radial density profile of the selected best candidates shows the typically observed r1∕4-law radial profile. The analysis of the color distributions reveals only marginal evidence of the presence of color bimodality, which is normally observed in galaxies of similar luminosity. The GC luminosity function does not show the typical symmetry, mainly because of the lack of bright GCs. Part of the bright GCs missing might be at very large galactocentric distances or along the line of sight of the galaxy dusty disk. As an alternative possibility, we speculate that a fraction of low luminosity GC candidates might instead be metal-rich, intermediate age clusters, but fall in a similar color interval of old, metal-poor GCs. Conclusions. Defining a contaminant-free sample of GCs in extragalactic systems is not a straight forward exercise. Using optical and near-IR photometry we purged the list of GCs with spectroscopic membership and photometric GC candidates in NGC 253. Our results show that the use of either spectroscopic or photometric data only does not generally ensure a contaminant-free sample and a combination of both spectroscopy and photometry is preferred.
The Fornax Deep Survey with VST Cantiello, Michele; Venhola, Aku; Grado, Aniello ...
Astronomy and astrophysics (Berlin),
07/2020, Letnik:
639
Journal Article
Recenzirano
Odprti dostop
Context.
A possible pathway for understanding the events and the mechanisms involved in galaxy formation and evolution is an in-depth investigation of the galactic and inter-galactic fossil ...sub-structures with long dynamical timescales: stars in the field and in stellar clusters.
Aims.
This paper continues the Fornax Deep Survey (FDS) series. Following previous studies dedicated to extended Fornax cluster members, we present the catalogs of compact stellar systems in the Fornax cluster, as well as extended background sources and point-like sources.
Methods.
We derived
ugri
photometry of ∼1.7 million sources over the ∼21 square degree area of FDS centered on the bright central galaxy NGC 1399. For a wider area, of ∼27 square degrees extending in the direction of NGC 1316, we provided
gri
photometry for ∼3.1 million sources. To improve the morphological characterization of sources, we generated multi-band image stacks by coadding the best-seeing
gri
-band single exposures with a cut at full width at half maximum (
FWHM
) ≤ 0.″9. We used the multi-band stacks as master detection frames, with a FWHM improved by ∼15% and a FWHM variability from field to field reduced by a factor of ∼2.5 compared to the pass-band with the best FWHM, namely the
r
-band. The identification of compact sources, in particular, globular clusters (GC), was obtained from a combination of photometric (e.g., colors, magnitudes) and morphometric (e.g., concentration index, elongation, effective radius) selection criteria, also taking as reference the properties of sources with well-defined classifications from spectroscopic or high-resolution imaging data.
Results.
Using the FDS catalogs, we present a preliminary analysis of GC distributions in the Fornax area. The study confirms and extends further previous results that were limited to a smaller survey area. We observed the inter-galactic population of GCs, a population of mainly blue GCs centered on NGC 1399, extending over ∼0.9 Mpc, with an ellipticity
ϵ
∼ 0.65 and a small tilt in the direction of NGC 1336. Several sub-structures extend over ∼0.5 Mpc along various directions. Two of these structures do not cross any bright galaxy; one of them appears to be connected to NGC 1404, a bright galaxy close to the cluster core and particularly poor in GCs. Using the
gri
catalogs, we analyze the GC distribution over the extended FDS area and do not find any obvious GC sub-structure bridging the two brightest cluster galaxies, namely, NGC 1316 and NGC 1399. Although NGC 1316 is more than twice as bright of NGC 1399 in optical bands, using
gri
data, we estimate a GC population that is richer by a factor of ∼3−4 around NGC 1399, as compared to NGC 1316, out to galactocentric distances of ∼40′ or ∼230 kpc.
This paper focuses on NGC 1533 and the pair IC 2038 and IC 2039 in Dorado a nearby, clumpy, still un-virialized group. We obtained their surface photometry from deep OmegaCAM@ESO-VST images in g and ...r bands. For NGC 1533, we map the surface brightness down to g 30.11 mag arcsec−2 and r 28.87 mag arcsec−2 and out to about 4 Re. At such faint levels, the structure of NGC 1533 appears amazingly disturbed with clear structural asymmetry between inner and outer isophotes in the northeast direction. We detect new spiral arm-like tails in the outskirts, which might likely be the signature of a past interaction/merging event. Similarly, IC 2038 and IC 2039 show tails and distortions indicative of their ongoing interaction. Taking advantage of deep images, we are able to detect the optical counterpart to the H i gas. The analysis of the new deep data suggests that NGC 1533 had a complex history made of several interactions with low-mass satellites that generated the star-forming spiral-like structure in the inner regions and are shaping the stellar envelope. In addition, the VST observations also show that the two less luminous galaxies, IC 2038 and IC 2039, are probably interacting each other and IC 2038 could have also interacted with NGC 1533 in the past, which stripped away gas and stars from its outskirts. The new picture emerging from this study is that of an interacting triplet, where the brightest galaxy, NGC 1533, has ongoing mass assembly in the outskirts.
We analyze the globular cluster (GC) systems in two very different galaxies, NGC 3115 and NGC 1399. With the papers of this series, we aim at highlighting common and different properties in the GC ...systems in galaxies covering a wide range of parameter space. We compare the GCs in NGC 3115 and NGC 1399 as derived from the analysis of one square degree
u
-,
g
-, and
i
-band images taken with the VST telescope as part of the VST early-type galaxy survey (VEGAS) and Fornax deep survey (FDS). We selected GC candidates using as reference the morpho-photometric and color properties of confirmed GCs. The surface density maps of GCs in NGC 3115 reveal a morphology similar to the light profile of field stars; the same is true when blue and red GCs are taken separately. The GC maps for NGC 1399 are richer in structure and confirm the existence of an intra-cluster GC component. We confirm the presence of a spatial offset in the NGC 1399 GC centroid and find that the centroid of the GCs for NGC 3115 coincides well with the galaxy center. Both GC systems show unambiguous color bimodality in (
g
−
i
) and (
u
−
i
); the color–color relations of the two GC systems are slightly different with NGC 3115 appearing more linear than NGC 1399. The azimuthal average of the radial density profiles in both galaxies reveals a larger spatial extent for the total GCs population with respect to the galaxy surface brightness profile. For both galaxies, the red GCs have radial density profiles compatible with the galaxy light profile, while the radial profiles for blue GCs are shallower. As for the specific frequency of GCs,
S
N
, we find it is a factor of two higher in NGC 1399 than for NGC 3115; this is mainly the result of extra blue GCs. By inspecting the radial behavior of the specific frequency,
S
N
(<
r
), for the total, blue, and red GCs, we find notable similarities between the trends for red GCs in the two targets. In spite of extremely different host environments, the red GCs in both cases appear closely linked to the light distribution of field stars. Blue GCs extend to larger galactocentric scales than red GCs, marking a significant difference between the two galaxies: the blue/red GCs and field stellar components of NGC 3115 appear well thermalized with each other and the blue GCs in NGC 1399 appear to fade into an unrelaxed intra-cluster GC population.
PDF
