3,259 research outputs found
Quantified HI Morphology VII: star-formation and tidal influence on local dwarf HI morphology
Scale-invariant morphology parameters applied to atomic hydrogen maps (HI) of
galaxies can be used to quantify the effects of tidal interaction or
star-formation on the ISM. Here we apply these parameters, Concentration,
Asymmetry, Smoothness, Gini, M20, and the GM parameter, to two public surveys
of nearby dwarf galaxies, the VLA-ANGST and LITTLE-THINGS survey, to explore
whether tidal interaction or the ongoing or past star-formation is a dominant
force shaping the HI disk of these dwarfs.
Previously, HI morphological criteria were identified for ongoing
spiral-spiral interactions. When we apply these to the Irregular dwarf
population, they either select almost all or none of the population. We find
that only the Asymmetry-based criteria can be used to identify very isolated
dwarfs (i.e., these have a low tidal indication). Otherwise, there is little or
no relation between the level of tidal interaction and the HI morphology. We
compare the HI morphology to three star-formation rates based on either Halpha,
FUV or the resolved stellar population, probing different star-formation
time-scales.
The HI morphology parameters that trace the inequality of the distribution,
the Gini, GM, and M20 parameters, correlate weakly with all these
star-formation rates. This is in line with the picture that local physics
dominates the ISM appearance and not tidal effects. Finally, we compare the
SDSS measures of star-formation and stellar mass to the HI morphological
parameters for all four HI surveys. In the two lower-resolution HI surveys
(12"), there is no relation between star-formation measures and HI morphology.
The morphology of the two high-resolution HI surveys (6"), the Asymmetry,
Smoothness, Gini, M20, and GM, do show a link to the total star-formation, but
a weak one.Comment: 26 figures, 4 tables, two appendices. Third appendix (HI maps of all
galaxies) omitted. Accepted by MNRA
A Cone Jet-Finding Algorithm for Heavy-Ion Collisions at LHC Energies
Standard jet finding techniques used in elementary particle collisions have
not been successful in the high track density of heavy-ion collisions. This
paper describes a modified cone-type jet finding algorithm developed for the
complex environment of heavy-ion collisions. The primary modification to the
algorithm is the evaluation and subtraction of the large background energy,
arising from uncorrelated soft hadrons, in each collision. A detailed analysis
of the background energy and its event-by-event fluctuations has been performed
on simulated data, and a method developed to estimate the background energy
inside the jet cone from the measured energy outside the cone on an
event-by-event basis. The algorithm has been tested using Monte-Carlo
simulations of Pb+Pb collisions at TeV for the ALICE detector at
the LHC. The algorithm can reconstruct jets with a transverse energy of 50 GeV
and above with an energy resolution of .Comment: 13 pages, 7 figure
A2626 and Friends:Large- And Small-scale Structure
New MMT/Hectospec spectroscopy centered on the galaxy cluster A2626 and
covering a area out to more than
doubles the number of galaxy redshifts in this region. The spectra confirm four
clusters previously identified photometrically. A2625, which was previously
thought to be a close neighbor of A2626, is in fact much more distant. The new
data show six substructures associated with A2626 and five more associated with
A2637. There is also a highly collimated collection of galaxies and galaxy
groups between A2626 and A2637 having at least three and probably four
substructures. At larger scales, the A2626--A2637 complex is not connected to
the Pegasus--Perseus filament.Comment: 18 pages, 13 figures, accepted for publication in the Astronomical
Journa
Comparison of Hi and optical redshifts of galaxies - The impact of redshift uncertainties on spectral line stacking
Accurate optical redshifts will be critical for spectral co-adding techniques used
to extract detections from below the noise level in ongoing and upcoming surveys for
Hi, which will extend our current understanding of gas reservoirs in galaxies to lower
column densities and higher redshifts. We have used existing, high quality optical and
radio data from the SDSS and ALFALFA surveys to investigate the relationship be-
tween redshifts derived from optical spectroscopy and neutral hydrogen (Hi) spectral
line observations.We find that the two redshift measurements agree well, with a negli-
gible systematic offset and a small distribution width. Employing simple simulations,
we determine how the width of an ideal stacked Hi profile depends on these redshift
offsets, as well as larger redshift errors more appropriate for high redshift galaxy sur-
veys. The width of the stacked profile is dominated by the width distribution of the
input individual profiles when the redshift errors are less than the median width of
the input profiles, and only when the redshift errors become large, 150 kms−1, do
they significantly affect the width of the stacked profile. This redshift accuracy can
be achieved with moderate resolution optical spectra. We provide guidelines for the
number of spectra required for stacking to reach a specified mass sensitivity, given tele-
scope and survey parameters, which will be useful for planning optical spectroscopy
observing campaigns to supplement the radio data.Web of Scienc
Quantified Morphology of HI Disks in the Universe
he upcoming new perspective of the high redshift Universe in the 21 cm line
of atomic hydrogen opens possibilities to explore topics of spiral disk
evolution, hitherto reserved for the optical regime. The growth of spiral gas
disks over Cosmic time can be explored with the new generation of radio
telescopes, notably the SKA, and its precursors, as accurately as with the
Hubble Space Telescope for stellar disks. Since the atomic hydrogen gas is the
building block of these disks, it should trace their formation accurately.
Morphology of HI disks can now equally be quantified over Cosmic time. In
studies of HST deep fields, the optical or UV morphology of high-redshift
galaxy disks have been characterized using a few quantities: concentration (C),
asymmetry (A), smoothness (S), second-order-moment (M20), the GINI coefficient
(G), and Ellipticity (E). We have applied these parameters across wavelengths
and compared them to the HI morphology over the THINGS sample. NGC 3184, an
unperturbed disk, and NGC 5194, the canonical 3:1 interaction, serve as
examples for quantified morphology. We find that morphology parameters
determined in HI are as good or better a tracer of interaction compared to
those in any other wavelength, notably in Asymmetry, Gini and M20. This opens
the possibility of using them in the parameterization pipeline for SKA
precursor catalogues to select interacting or harassed galaxies from their HI
morphology. Asymmetry, Gini and M20 may be redefined for use on data-cubes
rather than HI column density image.Comment: 6 pages, 3 figures, proceeding of the conference "Panoramic Radio
Astronomy: Wide-field 1-2 GHz research on galaxy evolution", June 02 - 05
2009, Groningen, update after small edit
A simple model for global H i profiles of galaxies
Context. Current and future blind surveys for H i generate large catalogs of spectral lines for which automated characterisation would be convenient
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