22 research outputs found
The Millennium Galaxy Catalogue: Dynamically Close Galaxy Pairs and the Global Merger Rate
We derive the number of dynamically close companions per galaxy () and
their total luminosity () for galaxies in the Millennium Galaxy Catalogue:
is similar to the fraction of galaxies in close pairs and is directly
related to the galaxy merger rate. We find and
for galaxies with and , for galaxies with , with
. The integrated merger rate to for both samples is about 20
%, but this depends sensitively on the fraction of kinematic pairs that are
truly undergoing a merger (assumed here to be 50%), the evolution of the merger
rate (here as ) and the adopted timescale for mergers (0.2 and 0.5 Gyr
for each sample, respectively). Galaxies involved in mergers tend to be
marginally bluer than non-interacting galaxies and show an excess of both
early-type and very late-type objects and a deficiency of intermediate-type
spirals. This suggests that interactions and mergers partly drive the star
formation and morphological evolution of galaxies.Comment: 26 pages, 3 figures, AJ accepted for publicatio
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
The VST Early-type GAlaxy Survey: Exploring the Outskirts and Intra-cluster Regions of Galaxies in the Low-surface-brightness Regime
The VST Early-type GAlaxy Survey (VEGAS) is a deep, multi-band (u, g, r, i)
imaging survey, carried out with the 2.6-metre VLT Survey Telescope (VST) at
ESO's Paranal Observatory in Chile. VEGAS combines the wide (1-square-degree)
OmegaCAM imager and long integration times, together with a specially designed
observing strategy. It has proven to be a gold mine for studies of features at
very low surface brightness, down to levels of mu_g~27-30 magnitudes
arcsec^(-2), over 5-8 magnitudes fainter than the dark sky at Paranal. In this
article we highlight the main science results obtained with VEGAS observations
of galaxies across different environments, from dense clusters of galaxies to
unexplored poor groups and in the field.Comment: Published in The Messenger, vol. 183, p. 25-2
Galaxy populations in the Hydra i cluster from the VEGAS survey:I. Optical properties of a large sample of dwarf galaxies
At ~50 Mpc, the Hydra I cluster of galaxies is among the closest cluster in
the z=0 Universe, and an ideal environment to study dwarf galaxy properties in
a cluster environment. We exploit deep imaging data of the Hydra I cluster to
construct a new photometric catalog of dwarf galaxies in the cluster core,
which is then used to derive properties of the Hydra I cluster dwarf galaxies
population as well as to compare with other clusters. Moreover, we investigate
the dependency of dwarf galaxy properties on their surrounding environment. The
new Hydra I dwarf catalog contains 317 galaxies with luminosity between
-18.5<<-11.5 mag, a semi-major axis larger than ~200 pc (a=0.84 arcsec),
of which 202 are new detections, previously unknown dwarf galaxies in the Hydra
I central region. We estimate that our detection efficiency reaches 50% at the
limiting magnitude =-11.5 mag, and at the mean effective surface
brightness =26.5 mag/. We present the standard
scaling relations for dwarf galaxies and compare them with other nearby
clusters. We find that there are no observational differences for dwarfs
scaling relations in clusters of different sizes. We study the spatial
distribution of galaxies, finding evidence for the presence of substructures
within half the virial radius. We also find that mid- and high-luminosity
dwarfs (<-14.5 mag) become on average redder toward the cluster center,
and that they have a mild increase in with increasing clustercentric
distance, similar to what is observed for the Fornax cluster. No clear
clustercentric trends are reported with surface brightness and S\'ersic index.
Considering galaxies in the same magnitude-bins, we find that for high and
mid-luminosity dwarfs (<-13.5 mag) the g-r color is redder for the
brighter surface brightness and higher S\'ersic n index objects.Comment: Accepted for publication in A&A. 25 pages, 21 figure
Making space for shellfish farming along the Adriatic coast
This work focuses on the selection of new areas for shellfish farming along the coast of the Northern Adriatic Sea (Italy). Shellfish site suitability was assessed by means of a methodology based on Spatial Multi-Criteria Evaluation (SMCE), which provided the framework to combine mathematical models and operational oceanography products. Intermediate level criteria considered in the analysis included optimal growth conditions, environmental interactions, and socio-economic evaluation (e.g. organic carbon deposition; distance to harbour). Results showed that the whole coastal area comprised within 0 and 3 nm is highly suitable for farming of mussel, while the area comprised between 3 and 12 nm is divided between a highly suitable northern part, and a less suitable southern one. Seven different scenarios of development of shellfish aquaculture industry were explored. The introduction of a new species, and the assessment of the exposure to storm events are specific aspects taken into account in development scenarios. Results show that the degree of suitability for shellfish aquaculture in this area would not change dramatically with the introduction of oyster farming. Furthermore, results highlight that: (i) the growth potential in this area is high; (ii) the space with suitability index >0.5 increases when prioritizing the optimal growth condition criteria, and (iii) the socio-economic is the most restrictive Intermediate Level Criteria. Results were discussed by deriving general lessons concerning the use of SMCE in aquaculture space allocation, from the specific application in the Northern Adriatic Sea. Challenges and opportunities related to the proposed methodological framework, with particular reference to the use of resources provided by remote sensing and operational oceanography by means of mathematical models, were also discussed. Results can support a science-based identification of allocated zones for aquaculture in order to avoid conflicts, and promote sustainable aquaculture in the Mediterranean Sea, where the space for these activities is becoming increasingly limited
Temporal variability and effect of environmental variables on airborne bacterial communities in an urban area of Northern Italy
Despite airborne microorganisms representing a relevant
fraction of atmospheric suspended particles, only a small
amount of information is currently available on their abundance
and diversity and very few studies have investigated the environmental
factors influencing the structure of airborne bacterial
communities. In this work, we used quantitative PCR and Illumina
technology to provide a thorough description of airborne
bacterial communities in the urban area of Milan (Italy). Forty
samples were collected in 10-day sampling sessions, with one
sessionper season.Themeanbacterialabundancewasabout104
ribosomal operons perm3 of air andwas lower inwinter than in
the other seasons. Communitieswere dominated by Actinobacteridae,
Clostridiales, Sphingobacteriales and fewproteobacterial
orders (Burkholderiales, Rhizobiales, Sphingomonadales
andPseudomonadales).Chloroplastswere abundant in all samples.
Ahigher abundanceof Actinobacteridae,which are typical
soil-inhabiting bacteria, and a lower abundance of chloroplasts in samples collected on cold days were observed. The variation
in community composition observed within seasons was comparable
to that observed between seasons, thus suggesting that
airborne bacterial communities showlarge temporal variability,
even between consecutive days. The structure of airborne bacterial
communities therefore suggests that soil and plants are the
sources which contribute most to the airborne communities of
Milan atmosphere, but the structure of the bacterial community
seems to depend mainly on the source of bacteria that predominates
in a given period of time
The New Boundaries of the Galaxy Concept
In Chapter 6 we outlined the research strategies implemented for the studies of high
redshift galaxies, briefly addressed their structures, morphologies and star formation,
discussed the ancestor problem and touched the theme of the origin of the first
galaxies. With this Chapter we certainly enter in the modern view of galaxies, as
members of a big society. Up to now we have essentially described and characterized
the properties of nearby isolated galaxies, that are sufficiently relaxed to show
their almost unperturbed properties. However the history of this society, not differently
from the man society, is full of conflicts and battles for surviving. The present
knowledge of the cosmic web, of the hierarchical nature of the structures in the Universe,
and of the galaxy components have clearly demonstrated that gravitational
interactions, gas accretion and outflows, as well as merging events and gravitational
interactions are the true past history of galaxies. Galaxies change their structure and
morphology across the Hubble time and many of their observed properties today
depend on their past history, as well as in many cases on the environment in which
they evolved.
The title of this Chapter reflects our tentative effort of looking at galaxies along
this viewpoint. What are the current boundaries of the galaxy concept? In other
words, to what extent the structures we see today were present in the past and what
are their limits in mass, luminosity, size, stellar populations and chemical enrichment
across the Hubble time? What is the role of the dark matter? In which way the energetic phenomena observed in the galaxy nuclei and in SNe have changed
the properties of galaxies? The suspect is that we have built the concept of galaxies
looking only at their mature appearance and not at their whole life. Can we speak
of man describing only its adult phase and not considering his interaction with the
whole society?
The following interviews will clarify several things connected to this new point
of view. We start in Sec. 7.2 with a nice review of the effects of gravitational interactions
and merging that will highlight the progresses done by simulations since
the early Toomre’ pioneering work. We then address in Sec. 7.3 the problem of the
disk assembling and the remarkable extended UV disks found in many galaxies.
The current limits in the mass function of galaxies, from dwarfs to giants, are discussed
in Sec. 7.4. The various effects of the presence of an AGN at the center of
galaxies are analyzed in Sec. 7.5, while the activity of SNe is addressed in Sec. 7.6.
Finally, Sec. 7.7 provide the different point of views on the role and nature of the
dark matter
Architecture, connectivity and transmitter receptors of human extrastriate visual cortex: comparison with nonnhuman primates.
Just after WWII Astronomy started to live its \u201cGolden Age\u201d, not differently to many other sciences and human activities, especially in the west side countries. The improved resolution of telescopes and the appearance of new efficient light detectors (e.g. CCDs in the middle eighty) greatly impacted the extragalactic researches. The first morphological analysis of galaxies were rapidly substituted by \u201canatomic\u201d studies of their structural components, star and gas content, and in general by detailed investigations of their properties. As for the human anatomy, where the final goal was that of understanding the functionality of the organs that are essential for the life of the body, galaxies were dissected to discover their basic structural components and ultimately the mystery of their existence
The Milky Way and the Local Group
The beauty and the charm of the Milky May (MW) have been celebrated by countless poets and writers of many Countries along the centuries (see e.g. the beautiful anthology of Piero Boitani 2012 ). The stellar nature of the MW was firstly observed by Galileo. In 1610 in the Sidereus Nuncius ( Galilei 1993 ) Galileo wrote that the MW is “nient’altro che una congerie di innumerevoli Stelle, disseminate a mucchi; chè in qualunque regione di essa si diriga il cannocchiale, subito una ingente folla di Stelle si presenta alla vista, delle quali parecchi si vedono abbastanza grandi e molto distinte; ma la moltitudine delle piccole è del tutto inesplorabile”. In the same paragraph, Galileo remarked that observations with his telescope, for the first time, wipe out centuries of philosophical discussions about the nature of the MW. Three more centuries have been necessary to complete a second radical Copernican Revolution that displaces the solar system from being roughly at the center of the MW and project this latter in the vast Universe populated by billions of similar spiral galaxies (see Chap. 1)