27 research outputs found
Star Clusters in the Tidal Tails of Interacting Galaxies: Cluster Populations Across a Variety of Tail Environments
We have searched for compact stellar structures within 17 tidal tails in 13
different interacting galaxies using F606W- and F814W- band images from the
Wide Field Planetary Camera 2 (WFPC2) on the Hubble Space Telescope (HST). The
sample of tidal tails includes a diverse population of optical properties,
merging galaxy mass ratios, HI content, and ages. Combining our tail sample
with Knierman et al. (2003), we find evidence of star clusters formed in situ
with Mv < -8.5 and V-I < 2.0 in 10 of 23 tidal tails; we are able to identify
cluster candidates to Mv = -6.5 in the closest tails. Three tails offer clear
examples of "beads on a string" star formation morphology in V-I color maps.
Two tails present both tidal dwarf galaxy (TDG) candidates and cluster
candidates. Statistical diagnostics indicate that clusters in tidal tails may
be drawn from the same power-law luminosity functions (with logarithmic slopes
~ -2 - -2.5) found in quiescent spiral galaxies and the interiors of
interacting systems. We find that the tail regions with the largest number of
observable clusters are relatively young (< 250 Myr old) and bright (V < 24 mag
arcsec^(-2)), probably attributed to the strong bursts of star formation in
interacting systems soon after periapse. Otherwise, we find no statistical
difference between cluster-rich and cluster-poor tails in terms of many
observable characteristics, though this analysis suffers from complex,
unresolved gas dynamics and projection effects.Comment: Accepted for publication in the Astrophysical Journal. 27 pages, 8
figure
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.
NGC6240: Merger-Induced Star Formation & Gas Dynamics
We present spatially resolved integral field spectroscopic K-band data at a
resolution of 0.13" (60pc) and interferometric CO(2-1) line observations of the
prototypical merging system NGC6240. Despite the clear rotational signature,
the stellar kinematics in the two nuclei are dominated by dispersion. We use
Jeans modelling to derive the masses and the mass-to-light ratios of the
nuclei. Combining the luminosities with the spatially resolved Br-gamma
equivalent width shows that only 1/3 of the K-band continuum from the nuclei is
associated with the most recent star forming episode; and that less than 30% of
the system's bolometric luminosity and only 9% of its stellar mass is due to
this starburst. The star formation properties, calculated from typical merger
star formation histories, demonstrate the impact of different assumptions about
the star formation history. The properties of the nuclei, and the existence of
a prominent old stellar population, indicate that the nuclei are remnants of
the progenitor galaxies' bulges.Comment: 18 pages, 14 figures. Accepted for publication in A&
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
Quantitative measurement of intact alpha-synuclein proteoforms from post-mortem control and Parkinson's disease brain tissue by intact protein mass spectrometry
A robust top down proteomics method is presented for profiling alpha-synuclein species from autopsied human frontal cortex brain tissue from Parkinson's cases and controls. The method was used to test the hypothesis that pathology associated brain tissue will have a different profile of post-translationally modified alpha-synuclein than the control samples. Validation of the sample processing steps, mass spectrometry based measurements, and data processing steps were performed. The intact protein quantitation method features extraction and integration of m/z data from each charge state of a detected alpha-synuclein species and fitting of the data to a simple linear model which accounts for concentration and charge state variability. The quantitation method was validated with serial dilutions of intact protein standards. Using the method on the human brain samples, several previously unreported modifications in alpha-synuclein were identified. Low levels of phosphorylated alpha synuclein were detected in brain tissue fractions enriched for Lewy body pathology and were marginally significant between PD cases and controls (p = 0.03)