424 research outputs found
Starburst-driven Starbursts in the Heart of Ultraluminous Infrared Galaxies
There is increasing evidence for the presence of blue super star clusters in
the central regions of ultraluminous infrared galaxies like Arp 220.
Ultraluminous galaxies are thought to be triggered by galaxy mergers, and it
has often been argued that these super star clusters may form during violent
collisions between gas clouds in the final phase of the mergers. We now
investigate another set of models which differ from previous ones in that the
formation of the super star clusters is linked directly to the very intense
starburst occurring at the very center of the galaxy. Firstly we show that a
scenario in which the super star clusters form in material compressed by shock
waves originating from the central starburst is implausible because the objects
so produced are much smaller than the observed star clusters in Arp 220. We
then investigate a scenario (based on the Shlosman-Noguchi model) in which the
infalling dense gas disk is unstable gravitationally and collapses to form
massive gaseous clumps. Since these clumps are exposed to the external high
pressure driven by the superwind (a blast wave driven by a collective effect of
a large number of supernovae in the very core of the galaxy), they can collapse
and then massive star formation may be induced in them. The objects produced in
this kind of collapse have properties consistent with those of the observed
super star clusters in the center of Arp 220.Comment: 13 pages, 1 figure, ApJ (Letters) in pres
New Probable Dwarf Galaxies in Northern Groups of the Local Supercluster
We have searched for nearby dwarf galaxies in 27 northern groups with
characteristic distances 8-15 Mpc based on the Second Palomar Sky Survey
prints. In a total area of about 2000 square degrees, we have found 90
low-surface-brightness objects, more than 60% of which are absent from known
catalogs and lists. We have classified most of these objects (~80%) as
irregular dwarf systems. The first 21-cm line observations of the new objects
with the 100-m Effelsberg radio telescope showed that the typical linear
diameters (1-2 kpc), internal motions (30 km/s), and hydrogen masses
(~2*10^7M_sun) galaxies correspond to those expected for the dwarf population
of nearby groups.Comment: 8 pages, 1 fugur
A SAURON study of dwarf elliptical galaxies in the Virgo Cluster: kinematics and stellar populations
Dwarf elliptical galaxies (dEs) are the most common galaxy type in nearby
galaxy clusters; even so, many of their basic properties have yet to be
quantified. Here we present the results of our study of 4 Virgo dwarf
ellipticals obtained with the SAURON integral field unit on the William
Herschel Telescope (La Palma, Spain). While traditional long-slit observations
are likely to miss more complicated kinematic features, with SAURON we are able
to study both kinematics and stellar populations in two dimensions, obtaining a
much more detailed view of the mass distribution and star formation histories.
What is visible even in such a small sample is that dEs are not a uniform
group, not only morphologically, but also as far as their kinematic and stellar
population properties are concerned. We find the presence of substructures,
varying degrees of flattening and of rotation, as well as differences in age
and metallicity gradients. We confirm that two of our galaxies are
significantly flattened, yet non-rotating objects, which makes them likely
triaxial systems. The comparison between the dwarf and the giant groups shows
that dEs could be a low-mass extension of Es in the sense that they do seem to
follow the same trends with mass. However, dEs as progenitors of Es seem less
likely as we have seen that dEs have much lower abundance ratios.Comment: 8 pages, 6 figures; to appear in the proceedings of the JENAM 2010
Symposium on Dwarf Galaxies (Lisbon, September 9-10, 2010); minor edits and
references adde
Photometric Properties of the Arp 220 Super Star Clusters
We investigate the photometric properties of six super stellar clusters
(SSCs) seen in both the optical and near-infrared Hubble Space Telescope images
of the local ultraluminous starburst galaxy Arp 220. Three of the SSCs are
located in the central 0.5 kpc region. The remaining three are in the
circumnuclear region between 0.5 kpc and 2.5 kpc from the centre. Comparing the
observed spectral energy distributions (SEDs) of the SSCs with the Starburst99
models of Leitherer et al., we confirm that all the three nuclear SSCs are
heavily obscured ( mag). Considering the results from this
comparison in conjunction with measurements of the near-infrared CO absorption
index and of millimetre CO line widths and luminosities, we estimate the ages
of the nuclear SSCs to be yrs. The bolometric luminosity of the
three nuclear SSCs is at most one-fifth of the total bolometric luminosity of
Arp 220. On the other hand, the circumnuclear SSCs have little internal
extinction ( 1 mag). These contribute negligibly to the total
bolometric luminosity.Comment: 8 pages, 5 figures. Accepted for publication in MNRA
Using participatory and creative methods to facilitate emancipatory research with people facing multiple disadvantage: a role for health and care professionals
Participatory and creative research methods are a powerful tool for enabling active engagement in the research process of marginalised people. It can be particularly hard for people living with multiple disadvantage, such as disabled people from ethnic minority backgrounds, to access research projects that are relevant to their lived experience. This article argues that creative and participatory methods facilitate the co-researchers’ engagement in the research process, which thus becomes more empowering. Exploring the congruence of these methods with their professional ethos, health and care professionals can use their skills to develop them further. Both theory and practice examples are presented
The Near-Infrared Number Counts and Luminosity Functions of Local Galaxies
This study presents a wide-field near-infrared (K-band) survey in two fields;
SA 68 and Lynx 2. The survey covers an area of 0.6 deg., complete to
K=16.5. A total of 867 galaxies are detected in this survey of which 175 have
available redshifts. The near-infrared number counts to K=16.5 mag. are
estimated from the complete photometric survey and are found to be in close
agreement with other available studies. The sample is corrected for
incompleteness in redshift space, using selection function in the form of a
Fermi-Dirac distribution. This is then used to estimate the local near-infrared
luminosity function of galaxies. A Schechter fit to the infrared data gives:
M, and Mpc (for H Km/sec/Mpc and q). When
reduced to , this agrees with other available estimates of the local
IRLF. We find a steeper slope for the faint-end of the infrared luminosity
function when compared to previous studies. This is interpreted as due to the
presence of a population of faint but evolved (metal rich) galaxies in the
local Universe. However, it is not from the same population as the faint blue
galaxies found in the optical surveys. The characteristic magnitude
() of the local IRLF indicates that the bright red galaxies ( mag.) have a space density of Mpc and hence,
are not likely to be local objects.Comment: 24 pages, 8 figures, AASTEX 4.0, published in ApJ 492, 45
Barred Galaxies in the Coma Cluster
We use ACS data from the HST Treasury survey of the Coma cluster (z~0.02) to
study the properties of barred galaxies in the Coma core, the densest
environment in the nearby Universe. This study provides a complementary data
point for studies of barred galaxies as a function of redshift and environment.
From ~470 cluster members brighter than M_I = -11 mag, we select a sample of
46 disk galaxies (S0--Im) based on visual classification. The sample is
dominated by S0s for which we find an optical bar fraction of 47+/-11% through
ellipse fitting and visual inspection. Among the bars in the core of the Coma
cluster, we do not find any very large (a_bar > 2 kpc) bars. Comparison to
other studies reveals that while the optical bar fraction for S0s shows only a
modest variation across low-to-intermediate density environments (field to
intermediate-density clusters), it can be higher by up to a factor of ~2 in the
very high-density environment of the rich Coma cluster core.Comment: Proceedings of the Bash symposium, to appear in the Astronomical
Society of the Pacific Conference Series, eds. L. Stanford, L. Hao, Y. Mao,
J. Gree
Disturbed isolated galaxies: indicators of a dark galaxy population?
We report the results of our search for disturbed (interacting) objects among
very isolated galaxies. The inspections of 1050 northern isolated galaxies from
KIG and 500 nearby, very isolated galaxies situated in the Local Supercluster
yielded five and four strongly disturbed galaxies, respectively. We suggest
that the existence of "dark" galaxies explains the observed signs of
interaction. This assumption leads to a cosmic abundance of dark galaxies (with
the typical masses for luminous galaxies) that is less than ~1/20 the
population of visible galaxies.Comment: 5 pages, 1 figure. Astronomy and Astrophysics, accepte
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