27 research outputs found
Birth, life and survival of Tidal Dwarf Galaxies
Advances on the formation and survival of the so-called Tidal Dwarf Galaxies
(TDGs) are reviewed. The understanding on how objects of the mass of dwarf
galaxies may form in debris of galactic collisions has recently benefited from
the coupling of multi-wavelength observations with numerical simulations of
galaxy mergers. Nonetheless, no consensual scenario has yet emerged and as a
matter of fact the very definition of TDGs remains elusive. Their real
cosmological importance is also a matter of debate, their presence in our Local
Group of galaxies as well. Identifying old, evolved, TDGs among the population
of regular dwarf galaxies and satellites may not be straightforward. However a
number of specific properties (location, dark matter and metal content) that
objects of tidal origin should have are reminded here. Examples of newly
discovered genuine old TDGs around a nearby elliptical galaxy are finally
presented.Comment: 9 pages, 5 figures, invited talk at JENAM 2010 symposium on "Dwarf
Galaxies", v2:reference and acknowledgements update
From Globular Clusters to Tidal Dwarfs: Structure Formation in the Tidal Tails of Merging Galaxies
Using V and I images obtained with WFPC2/HST, we investigate compact stellar
structures within tidal tails. Six regions of tidal debris in the four classic
``Toomre Sequence'' mergers: NGC 4038/39 (``Antennae''), NGC 3256, NGC 3921,
and NGC 7252 (``Atoms for Peace'') have been studied in order to explore how
the star formation depends upon the local and global physical conditions. These
mergers sample a range of stages in the evolutionary sequence and tails with
and without embedded tidal dwarf galaxies. The six tails are found to contain a
variety of stellar structures, with sizes ranging from those of globular
clusters up to those of dwarf galaxies. From V and I WFPC2 images, we measure
the luminosities and colors of the star clusters. NGC 3256 is found to have a
large population of blue clusters (0.2 < V-I < 0.9), particularly in its
Western tail, similar to those found in the inner region of the merger. In
contrast, NGC 4038/39 has no clusters in the observed region of the tail, only
less luminous point sources likely to be individual stars. A significant
cluster population is clearly associated with the prominent tidal dwarf
candidates in the eastern and western tails of NGC 7252. The cluster-rich
Western tail of NGC 3256 is not distinguished from the others by its dynamical
age or by its total HI mass. However, the mergers that have few clusters in the
tail all have tidal dwarf galaxies, while NGC 3256 does not have prominent
tidal dwarfs. We speculate that star formation in tidal tails may manifest
itself either in small structures like clusters along the tail or in large
structures such as dwarf galaxies, but not in both. Also, NGC 3256 has the
highest star formation rate of the four mergers studied, which may contribute
to the high number of star clusters in its tidal tails.Comment: Accepted to Astronomical Journal. 34 pages including 15 figures and 4
table
NGC 3256: Kinematic anatomy of a merger
We have used the Australia Telescope Compact Array to image the neutral
hydrogen in the merging system NGC 3256, to test the idea that globular
clusters (GC) form during the interactions and mergers of disk galaxies. We
compare our observations with hydrodynamical numerical simulations, from the
literature, to examine the hypothesis that the H I fragments with masses
greater than 10^{7\pm1} \mo are sites of GC formation. We appear to have
detected detached H I fragments in the vicinity of NGC 3256. These fragments,
with masses ~10^7 solar masses, may have little dark matter content which is
also a characteristic of globular clusters, and so our observations support the
hypothesis that globular clusters form in the type of interaction that resulted
in NGC 3256.Comment: Jpeg images; colour images are meant to only appear on monitors, not
printout. 25 pages, 9 figures, and 2 tables. To be published in Astronomical
Journal Mar. 200
Galaxy Collisions - Dawn of a New Era
The study of colliding galaxies has progressed rapidly in the last few years,
driven by observations with powerful new ground and space-based instruments.
These instruments have used for detailed studies of specific nearby systems,
statistical studies of large samples of relatively nearby systems, and
increasingly large samples of high redshift systems. Following a brief summary
of the historical context, this review attempts to integrate these studies to
address the following key issues. What role do collisions play in galaxy
evolution, and how can recently discovered processes like downsizing resolve
some apparently contradictory results of high redshift studies? What is the
role of environment in galaxy collisions? How is star formation and nuclear
activity orchestrated by the large scale dynamics, before and during merger?
Are novel modes of star formation involved? What are we to make of the
association of ultraluminous X-ray sources with colliding galaxies? To what do
degree do mergers and feedback trigger long-term secular effects? How far can
we push the archaeology of individual systems to determine the nature of
precursor systems and the precise effect of the interaction? Tentative answers
to many of these questions have been suggested, and the prospects for answering
most of them in the next few decades are good.Comment: 44 pages, 9 figures, review article in press for Astrophysics Update
Vol.
Star cluster formation and star formation: the role of environment and star-formation efficiencies
“The original publication is available at www.springerlink.com”. Copyright Springer. DOI: 10.1007/s10509-009-0088-5By analyzing global starburst properties in various kinds of starburst and post-starburst galaxies and relating them to the properties of the star cluster populations they form, I explore the conditions for the formation of massive, compact, long-lived star clusters. The aim is to determine whether the relative amount of star formation that goes into star cluster formation as opposed to field star formation, and into the formation of massive long-lived clusters in particular, is universal or scales with star-formation rate, burst strength, star-formation efficiency, galaxy or gas mass, and whether or not there are special conditions or some threshold for the formation of star clusters that merit to be called globular clusters a few billion years later.Peer reviewe
Star-formation in the HI bridge between M81 and M82
We present multi-wavelength observations of stellar features in the HI tidal
bridge connecting M81 and M82 in the region called Arp's Loop. We identify
eight young star-forming regions from Galaxy Evolution Explorer ultraviolet
observations. Four of these objects are also detected at H\alpha. We determine
the basic star formation history of Arp's Loop using F475W and F814W images
obtained with the Advanced Camera for Surveys on board the Hubble Space
Telescope. We find both a young (1 Gyr) stellar
population with a similar spatial distribution and a metallicity Z~0.004. We
suggest that the old stellar population was formed in the stellar disk of M82
and/or M81 and ejected into the intergalactic medium during a tidal passage (~
200-300 Myr ago), whereas the young UV-bright stars have formed in the tidal
debris. The UV luminosities of the eight objects are modest and typical of
small clusters or OB associations. The tidal bridge between M81-M82 therefore
appears to be intermediate between the very low levels of star formation seen
in the Magellanic bridge and actively star-forming tidal tails associated with
major galaxy mergers.Comment: Astronomical Journal accepte
Capillary Zone Electrophoresis–Electrospray Ionization-Tandem Mass Spectrometry for Top-Down Characterization of the <i>Mycobacterium marinum</i> Secretome
Capillary
zone electrophoresis (CZE) with an electrokinetically
pumped sheath-flow nanospray interface was coupled with a high-resolution
Q-Exactive mass spectrometer for the analysis of culture filtrates
from <i>Mycobacterium marinum</i>. We confidently identified
22 gene products from the wildtype <i>M. marinum</i> secretome
in a single CZE–tandem mass spectrometry (MS/MS) run. A total
of 58 proteoforms were observed with post-translational modifications
including signal peptide removal, N-terminal methionine excision,
and acetylation. The conductivities of aqueous acetic acid and formic
acid solutions were measured from 0.1% to 100% concentration (v/v).
Acetic acid (70%) provided lower conductivity than 0.25% formic acid
and was evaluated as low ionic-strength and a CZE–MS compatible
sample buffer with good protein solubility
Capillary Zone Electrophoresis–Electrospray Ionization-Tandem Mass Spectrometry for Top-Down Characterization of the <i>Mycobacterium marinum</i> Secretome
Capillary
zone electrophoresis (CZE) with an electrokinetically
pumped sheath-flow nanospray interface was coupled with a high-resolution
Q-Exactive mass spectrometer for the analysis of culture filtrates
from <i>Mycobacterium marinum</i>. We confidently identified
22 gene products from the wildtype <i>M. marinum</i> secretome
in a single CZE–tandem mass spectrometry (MS/MS) run. A total
of 58 proteoforms were observed with post-translational modifications
including signal peptide removal, N-terminal methionine excision,
and acetylation. The conductivities of aqueous acetic acid and formic
acid solutions were measured from 0.1% to 100% concentration (v/v).
Acetic acid (70%) provided lower conductivity than 0.25% formic acid
and was evaluated as low ionic-strength and a CZE–MS compatible
sample buffer with good protein solubility