1,036 research outputs found
Spectroscopic Confusion: Its Impact on Current and Future Extragalactic HI Surveys
We present a comprehensive model to predict the rate of spectroscopic
confusion in HI surveys, and demonstrate good agreement with the observable
confusion in existing surveys. Generically the action of confusion on the HI
mass function was found to be a suppression of the number count of sources
below the `knee', and an enhancement above it. This results in a bias, whereby
the `knee' mass is increased and the faint end slope is steepened. For ALFALFA
and HIPASS we find that the maximum impact this bias can have on the Schechter
fit parameters is similar in magnitude to the published random errors. On the
other hand, the impact of confusion on the HI mass functions of upcoming medium
depth interferometric surveys, will be below the level of the random errors. In
addition, we find that previous estimates of the number of detections for
upcoming surveys with SKA-precursor telescopes may have been too optimistic, as
the framework implemented here results in number counts between 60% and 75% of
those previously predicted, while accurately reproducing the counts of existing
surveys. Finally, we argue that any future single dish, wide area surveys of HI
galaxies would be best suited to focus on deep observations of the local
Universe (z < 0.05), as confusion may prevent them from being competitive with
interferometric surveys at higher redshift, while their lower angular
resolution allows their completeness to be more easily calibrated for nearby
extended sources.Comment: Accepted to MNRAS, 14 pages, 9 figures, 2 table
When is Stacking Confusing?: The Impact of Confusion on Stacking in Deep HI Galaxy Surveys
We present an analytic model to predict the HI mass contributed by confused
sources to a stacked spectrum in a generic HI survey. Based on the ALFALFA
correlation function, this model is in agreement with the estimates of
confusion present in stacked Parkes telescope data, and was used to predict how
confusion will limit stacking in the deepest SKA-precursor HI surveys. Stacking
with LADUMA and DINGO UDEEP data will only be mildly impacted by confusion if
their target synthesised beam size of 10 arcsec can be achieved. Any beam size
significantly above this will result in stacks that contain a mass in confused
sources that is comparable to (or greater than) that which is detectable via
stacking, at all redshifts. CHILES' 5 arcsec resolution is more than adequate
to prevent confusion influencing stacking of its data, throughout its bandpass
range. FAST will be the most impeded by confusion, with HI surveys likely
becoming heavily confused much beyond z = 0.1. The largest uncertainties in our
model are the redshift evolution of the HI density of the Universe and the HI
correlation function. However, we argue that the two idealised cases we adopt
should bracket the true evolution, and the qualitative conclusions are
unchanged regardless of the model choice. The profile shape of the signal due
to confusion (in the absence of any detection) was also modelled, revealing
that it can take the form of a double Gaussian with a narrow and wide
component.Comment: 11 pages, 6 figures, accepted to MNRA
The Arecibo Legacy Fast ALFA Survey: VIII. HI Source Catalog of the Anti-Virgo Region at dec = +25 deg
We present a fourth catalog of HI sources from the Arecibo Legacy Fast ALFA
(ALFALFA) Survey. We report 541 detections over 136 deg2, within the region of
the sky having 22h < R.A. < 03h and 24 deg < Dec. < 26 deg . This complements a
previous catalog in the region 26 deg < Dec. < 28 deg (Saintonge et al. 2008).
We present here the detections falling into three classes: (a) extragalactic
sources with S/N > 6.5, where the reliability of the catalog is better than
95%; (b) extragalactic sources 5.0 < S/N < 6.5 and a previously measured
optical redshift that corroborates our detection; or (c) High Velocity Clouds
(HVCs), or subcomponents of such clouds, in the periphery of the Milky Way. Of
the 541 objects presented here, 90 are associated with High Velocity Clouds,
while the remaining 451 are identified as extragalactic objects. Optical
counterparts have been matched with all but one of the extragalactic objects.Comment: 26 pages, 5 figures, 1 table, accepted for publication in
Astrophysical Journal Supplement Serie
Galaxy Peculiar Velocities and Infall onto Groups
We perform statistical analyses to study the infall of galaxies onto groups
and clusters in the nearby Universe. The study is based on the UZC and SSRS2
group catalogs and peculiar velocity samples. We find a clear signature of
infall of galaxies onto groups over a wide range of scales 5 h^{-1} Mpc<r<30
h^{-1} Mpc, with an infall amplitude on the order of a few hundred kilometers
per second. We obtain a significant increase in the infall amplitude with group
virial mass (M_{V}) and luminosity of group member galaxies (L_{g}). Groups
with M_{V}<10^{13} M_{\odot} show infall velocities V_{infall} \simeq 150 km
s^{-1} whereas for M_{V}>10^{13} M_{\odot} a larger infall is observed,
V_{infall} \simeq 200 km s^{-1}. Similarly, we find that galaxies surrounding
groups with L_{g}<10^{15} L_{\odot} have V_{infall} \simeq 100 km s^{-1},
whereas for L_{g}>10^{15} L_{\odot} groups, the amplitude of the galaxy infall
can be as large as V_{infall} \simeq 250 km s^{-1}. The observational results
are compared with the results obtained from mock group and galaxy samples
constructed from numerical simulations, which include galaxy formation through
semianalytical models. We obtain a general agreement between the results from
the mock catalogs and the observations. The infall of galaxies onto groups is
suitably reproduced in the simulations and, as in the observations, larger
virial mass and luminosity groups exhibit the largest galaxy infall amplitudes.
We derive estimates of the integrated mass overdensities associated with groups
by applying linear theory to the infall velocities after correcting for the
effects of distance uncertainties obtained using the mock catalogs. The
resulting overdensities are consistent with a power law with \delta \sim 1 at r
\sim 10 h^{-1}Mpc.Comment: 25 pages, 10 figure
Evolution of physicochemical, morphological and aromatic characteristics of Italian PDO dry-cured hams during processing
The aim of this work was to follow the evolution of physicochemical (dry matter, NaCl concentration, pH, water activity), morphological (image analysis) and aromatic (e-nose) characteristics of the three main Italian PDOs during processing, from slaughtering to end of ripening. Main phenomena distinguishing the PDOs are NaCl concentration increase, which is higher in Toscano than in Parma and San Daniele hams, starting from the salting phase. Water activity values decrease during processing, and the lowest values are detected in Toscano ham. Changes in morphological parameters (area, shape) and in color progressively occur during processing and are more pronounced in Toscano ham. A clear evolution of aroma of the three PDOs has been observed by e-nose, and the complexity of the aromatic profile of the ripened hams is clearly highlighted
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