225 research outputs found
Surface Photometry and Metallicity of the Polar Ring Galaxy A0136-0801
We present a photometric and spectroscopic study of the polar ring galaxy
A0136-0801 in order to constrain its formation history. Near-Infrared (NIR) and
optical imaging data are used to extract surface brightness and color profiles
of the host galaxy and the wide polar structure in A0136-0801. The host galaxy
dominates the light emission in all bands; the polar structure is more luminous
in the optical bands and is three times more extended than the main spheroid.
The average stellar population in the spheroid is redder than in the polar
structure and we use their (B-K) vs. (J-K) colors to constraint the ages of
these populations using stellar population synthesis models. The inferred ages
are 3-5 Gyrs for the spheroid and 1-3 Gyrs for the polar structure. We then use
long slit spectra along the major axis of the polar structure to derive the
emission line ratios and constrain the oxygen abundance, metallicity and star
formation rate in this component. We find 12+log(O/H) = 8.33 +- 0.43 and Z ~
0.32 Zsun, using emission line ratios. These values are used, together with the
ratio of the baryonic masses of the host galaxy and polar structure, to
constraint the possible models for the formation scenario. We conclude that the
tidal accretion of gas from a gas rich donor or the disruption of a gas-rich
satellite are formation mechanisms that may lead to systems with physical
parameters in agreement with those measured for A0136-0801.Comment: 17 pages, 9 figures. Accepted for publication in MNRA
Multiwavelength study of interacting and peculiar galaxies
I present a multiwavelength study of a sample of peculiar galaxies in order to constraint the physics of interacting objects, to study how the physical processes affect the
structure of galaxies, and to derive some hints on the formation and evolution history of such galaxies.
One of the major open issues in modern cosmology is to understand how galaxies formed and evolved. Its likely that the formation of galaxies was dominated by two processes: the assembly of luminous and dark matter through accretion and merger, and the conversion of baryonic and non-baryonic matter into stars. This is the reason why the study of galaxy interactions has received an increasing attention both on the observational and the theoretical sides. Several
theoretical works based on numerical simulations, have tested different plausible scenarios for the origin of peculiar galaxies, such as ``Tidal accretion'', ``Cold accretion'' and ``Merging''.
For this reason, the sample of galaxies to use was selected in order to reproduce all these mechanisms. The first peculiar object that I studied is the minor axis dust lane galaxy NGC1947. I performed a detailed study of the main properties of this galaxy (Spavone et al 2009). In NGC1947 are present components with different angular momentum, infact gas and dust rotate along the minor axis while stars rotate along the major one. This is a clear evidence that it cannot be the result of a single protogalactic cloud collapse, but rather the result of an interaction event. I performed a detailed study of the main properties of this galaxy and compared them with the prediction of simulations. Putting together all this evidences it was difficult to disentangle in a non ambiguous way the two possible scenarios, even though some aspects can help us in understanding. First of all, the galaxy does not present clear signs of interaction, such as tidal tails and so on, and this leads to the conclusion that the merger occurred about 10 Gyrs ago, a fact which is not consistent with the fact that, according to my estimate, the last burst of star formation occurred 1 Gyr ago. So I can say that the accretion scenario is favoured. The second object in my sample is the Polar Ring Galaxy (PRG) NGC4650A. I used high resolution NIR and optical spectroscopy along the North and South side of the polar disk, to measure the metallicity of the HII regions in the polar disk of this galaxy because, if it formed from the accretion of external cold gas from cosmic web filaments, we expect metallicities similar to those of late type galaxies, while if the metallicities are similar to those of early type galaxies, the accretion from a gas rich donor is favoured. I estimated the metallicity by using both direct and empirical methods, the Stellar Formation Rate (SFR), and the metallicity gradient along
the disk. The average metallicity for the polar disk of NGC4650A turned out to be , which is lower than the typical values found in spiral galaxies, and is instead consistent with the metallicities predicted for the formation of disks by cold accretion processes (), due to the accretion of pristine
gas in the cold streams. Moreover, also the absence of any metallicity gradient is consistent with the infall of metal-poor gas from outside which is still forming the disk (see Spavone et al 2010 for details). As a follow up of this work, I obtained observing time at the TNG telescope to observe the PRGs UGC7576 and UGC9796. I performed the study of the chemical abundances also for these galaxies in order to constrain their formation history (Spavone et al. submitted). Both PRGs have metallicities (respectively 0.4 and 0.1 ) lower than that observed in spiral galaxies of the same total luminosity and, given
their present star formation rate, this values is again consistent with the predictions of the cold accretion mechanism for disk formation. UGC7576 is an isolated galaxy and the absence of close companions led to exclude both the tidal accretion from a donor galaxy and the merging with another galaxy. UGC9796 is instead in a group and has 5
close companions with an amount of HI gas comparable with that of UGC9796. The merging scenario is however ruled out because in order to produce a massive polar disk such as those observed in UGC9796 is required a merging with high mass ratios (7:1 or 10:1) and this would destroy the ordered motion of the central galaxy, transforming it into an elliptical-like, not rotationally supported galaxy. In conclusion, for this object, both the tidal accretion and the cold accretion seem to be plausible scenarios. Finally, to analyze also another type of merging process, I am
studying the pair of interacting galaxies known as CSL-1. By using high resolution spectroscopy (FORS1@VLT) and imaging (HST) I am studying the morphology, light distribution and structural parameters of this system, to test the dry-merger scenario (cf. ``A prototype dry-merger caught in the act'', M. Paolillo , G. Covone, C. Nipoti, M. Spavone, M. Capaccioli, G. Longo, A.Cimatti, L. Ciotti, in preparation). In order to investigate also the minor merging processes I also studied the photometric and kinematical properties of a compact group of galaxies belonging to the Hickson's catalogue. The group analyzed
in this work was HCG62, one of the nearest group in the celestial Southern hemisphere, which was selected by cross correlating the available X-ray and optical data. Galaxies in compact groups are in a very dense configuration in the
sky, having a mean separation comparable with their dimensions and a very low velocity dispersion. Taking into account that theories on formation and evolution of galaxies predict that the intensity and frequency of interactions strongly depend on the density of the environment, compact groups may be considered the ideal place where to test interaction processes, such as dynamical
friction, tidal interaction, collisions, merging and so on.
The main goal of this part of my work was to derive some hints on the formation and evolutionary history of compact groups, in order to address the possible scenario for the formation of structure in the Universe, and to determine the evolutionary status of the studied objects. To this aim, I performed a detailed study of the kinematical
properties of HCG62, that revealed the presence of many
peculiarities in the dominant galaxy of the group, NGC4778, such as the presence of a kinematically decoupled and counter-rotating core (KDC), or kinematical profiles strongly perturbed, also in the outer regions of this galaxy. Moreover, I also performed an analysis of the photometric properties of the whole group, to look for correlations between kinematical and photometric peculiarities. The absence of such correlations in HCG62,
can be explained by stating that weak interactions do not perturb the rotation curves but produce morphological deformations in the outer regions, while the so called minor mergers perturb the rotation curves in the inner regions, without producing morphological peculiarities. The results obtained in this work are in good agreement with similar studies performed on the same group and with its observed X-ray properties (Spavone et al 2006). I was also Co-Investigator in two accepted proposals to observe, with the TNG telescope, a sample of Shakhbazian galaxy groups, with the aim of building a larger statistical sample and obtain redshift informations which are lacking for most Shakhbazian groups, and are needed to establish on firm grounds their physical nature. Groups of galaxies have been extensively studied in the past decades. Despite this effort, their evolution is yet not well understood. Loose groups are almost certainly still collapsing and are therefore crucial to uncover the formation processes shaping cosmic structures. As it was already mentioned, in compact groups a few member galaxies are compressed in a small volume of space with low relative velocities. Early theoretical studies suggested that in such high density environments the low velocity dispersion of compact galaxy groups would favor strong interactions and mergers, leading to rapid evolution (within yrs) into a single massive merger remnant. The best studied sample of compact groups to date is the one included in the Hickson catalogue; this sample however, is biased towards extremely high values of matter density and therefore it allows to investigate only the ``close-to-final'' stage of the complex dynamical evolution of groups. The density range bridging the field to these almost coalesced structures is still poorly explored, mainly due to the difficulties encountered in constructing reliable samples of `physically bound', low multiplicity groups. Shakhbazian Groups of galaxies (SHKGs) in spite of having been originally selected as ``compact groups of compact galaxies'', have been shown to sample a large range of spatial densities. To properly characterize the properties of these groups and their evolutionary path, I obtained more accurate redshift determination for a sample of 10 SHK, so almost doubling the sample of SHK groups, with detailed spectroscopic data. Main goals of this work are: i) obtain redshift estimates for groups without literature data, sampling the different sub-populations; ii) confirm the galaxy membership of the groups, which is currently based on photometric estimates for most of the objects; iii) study the dynamical status of the group and derive dynamical mass estimates; iv) study the stellar population of the member galaxies through comparison with population synthesis models, and the degree of activity from emission line measurements
A kinematically decoupled component in NGC4778
We present a kinematical and photometrical study of a member, NGC4778, of the
nearest (z=0.0137) compact group: Hickson 62. Our analysis reveals that Hickson
62a, also known as NGC4778, is an S0 galaxy with kinematical and morphological
peculiarities, both in its central regions (r < 5'') and in the outer halo. In
the central regions, the rotation curve shows the existence of a kinematically
decoupled stellar component, offset with respect to the photometric center. In
the outer halo we find an asymmetric rotation curve and a velocity dispersion
profile showing a rise on the SW side, in direction of the galaxy NGC4776.Comment: Proceedings of the first workshop of astronomy and astrophysics for
student
Metallicity of the polar disk in NGC4650A: constraints for cold accretion scenario
We used high resolution spectra in the optical and near-infrared wavelength
range to study the abundance ratios and metallicities of the HII regions
associated with the polar disk in NGC4650A, in order to put constraints on the
formation of the polar disk through cold gas accretion along a filament; this
might be the most realistic way by which galaxies get their gas. We have
compared the measured metallicities for the polar structure in NGC4650A with
those of different morphological types and we have found that they are similar
to those of late-type galaxies: such results is consistent with a polar disk
formed by accretion from cosmic web filaments of external cold gas.Comment: Proceeding of the conference "Hunting for the Dark: The Hidden Side
of Galaxy Formation", Malta, 19-23 Oct. 200
An Ultra diffuse Galaxy in the NGC 5846 group from the VEGAS survey
Many ultra diffuse galaxies (UDGs) have now been identified in clusters of
galaxies. However, the number of nearby UDGs suitable for detailed follow-up
remain rare. Our aim is to begin to identify UDGs in the environments of nearby
bright early-type galaxies from the VEGAS survey. Here we use a deep g band
image of the NGC 5846 group, taken as part of the VEGAS survey, to search for
UDGs. We found one object with properties of a UDG if it associated with the
NGC 5846 group, which seems likely. The galaxy, we name NGC 5846UDG1, has
an absolute magnitude of M = -14.2, corresponding to a stellar mass of
10 M. It also reveals a system of compact sources which are
likely globular clusters. Based on the number of globular clusters detected we
estimate a halo mass that is greater than 810 M for
UDG1.Comment: 5 pages, 4 figures, accepted for publication in A&
Deep Photometry of Galaxies in the VEGAS Survey: The Case of NGC 4472
The VST-VEGAS project is aimed at observing and studying a rich sample of nearby early-type galaxies in order to systematically characterize their properties over a wide baseline of sizes and out to the faint outskirts where data are rather scarce so far. The external regions of galaxies more easily retain signatures about the formation and evolution mechanisms which shaped them, as their relaxation time are longer, and they are more weakly influenced by processes such as mergers, secular evolution, central black hole activity, and supernova feedback on the ISM, which tend to level age and metallicity gradients. The collection of a wide photometric dataset of a large number of galaxies in various environmental conditions, may help to shed light on these questions. To this end VEGAS exploits the potential of the VLT Survey Telescope (VST) which provides high quality images of 1 deg2 field of view in order to satisfy both the requirement of high resolution data and the need of studying nearby, and thus large, objects. We present a detailed study of the surface photometry of the elliptical galaxy NGC4472 and of smaller ETGs in its field, performed by using new g and i bands images to constrain the formation history of this nearby giant galaxy, and to investigate the presence of very faint substructures in its surroundings
Mapping the inner regions of the polar disk galaxy NGC4650A with MUSE
[abridged] The polar disk galaxy NGC4650A was observed during the
commissioning of the MUSE at the ESO VLT to obtain the first 2D map of the
velocity and velocity dispersion for both stars and gas. The new MUSE data
allow the analysis of the structure and kinematics towards the central regions
of NGC4650A, where the two components co-exist. These regions were unexplored
by the previous long-slit literature data available for this galaxy. The
extended view of NGC~4650A given by the MUSE data is a galaxy made of two
perpendicular disks that remain distinct and drive the kinematics right into
the very centre of this object. In order to match this observed structure for
NGC4650A, we constructed a multicomponent mass model made by the combined
projection of two disks. By comparing the observations with the 2D kinematics
derived from the model, we found that the modelled mass distribution in these
two disks can, on average, account for the complex kinematics revealed by the
MUSE data, also in the central regions of the galaxy where the two components
coexist. This result is a strong constraint on the dynamics and formation
history of this galaxy; it further supports the idea that polar disk galaxies
like NGC~4650A were formed through the accretion of material that has different
angular momentum.Comment: 14 pages, 10 figures; accepted for publication in Astronomy &
Astrophysic
VEGAS: A VST Early-type GAlaxy Survey. III. Mapping the galaxy structure, interactions and intragroup light in the NGC 5018 group
Most of the galaxies in the Universe at present day are in groups, which are
key to understanding the galaxy evolution. In this work we present a new deep
mosaic of 1.2 x 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
analyse the structure of the group members and to estimate the intra-group
light. Taking advantage of the 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 into the intra-group 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 that have produced the HI tail. A minor merging event also
happened in the formation history of NGC 5018 that have perturbed the inner
structure of this galaxy.Comment: 21 pages, 15 figures. Accepted for publication in Ap
An X-ray investigation of Hickson 62
We studied the X-ray properties of the Hickson Compact Group HCG62, in order
to determine the properties and dynamic and evolutionary state of its hot
gaseous halo. Our analysis reveals that the X-ray diffuse halo has an extremely
complex morphological, thermal and chemical structure. Two deep cavities, due
to the presence of the AGN hosted by the central galaxy NGC 4778, are clearly
visible in the group X-ray halo. The cavities appear to be surrounded by ridges
of cool gas. The group shows a cool core associated with the dominant galaxy.
In the outer regions the temperature structure is quite regular, while the
metal abundance shows a more patchy distribution, with large Si/O and Si/Fe
ratios.Comment: Published in the Proceedings of the "I Workshop of Astronomy and
Astrophysics for Students", Eds. N.R. Napolitano & M. Paolillo, Naples, 19-20
April 2006 (astro-ph/0701577
VEGAS: a VST Early-type GAlaxy Survey. IV. NGC 1533, IC 2038 and IC 2039: an interacting triplet in the Dorado group
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 mag/arcsec and mag/arcsec and out to about . At such faint levels
the structure of NGC 1533 appear amazingly disturbed with clear structural
asymmetry between inner and outer isophotes in the North-East 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
advantages of deep images, we are able to detect the optical counterpart to the
HI 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 show that also the two less
luminous galaxies, IC 2038 and IC 2039, are probably interacting each-other
and, in the past, IC 2038 could have also interacted with NGC 1533, which
stripped away gas and stars from its outskirts. The new picture emerging from
this study is of an interacting triplet, where the brightest galaxy NGC 1533
has ongoing mass assembly in the outskirts.Comment: Accepted for publication in The Astronomical Journal. High-resolution
version of paper is available at the following link:
https://www.dropbox.com/preview/VEGAS_IV.pdf?role=persona
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