18,492 research outputs found
The UNAM-KIAS Catalog of Isolated Galaxies
A new catalog of isolated galaxies from The Sloan Digital Sky Survey (DR5) is
presented. 1520 isolated galaxies were found in 1.4 steradians of sky. The
selection criteria in this so called UNAM-KIAS catalog was implemented from a
variation on the criteria developed by Karachentseva 1973 including full
redshift information. Through an image processing pipeline that takes advantage
from the high resolution (~ 0.4 ''/pix) and high dynamic range of the SDSS
images, a uniform g band morphological classification for all these galaxies is
presented. We identify 80% (SaSm) spirals (50% later than Sbc types) on one
hand, and a scarce population of early-type E(6.5%) and S0(8%) galaxies
amounting to 14.5% on the other hand. This magnitude-limited catalog is ~ 80%
complete at 16.5, 15.6, 15.0, 14.6 and 14.4 magnitudes in the ugriz bands
respectively. Some representative physical properties including SDSS magnitudes
and color distributions, color-color diagrams, absolute magnitude-color, and
concentration-color diagrams as a function of morphological type are presented.
The UNAM-KIAS Morphological Atlas is also released along with this paper. For
each galaxy of type later than Sa, a mosaic is presented that includes: (1) a
g-band logarithmic image, (2) a g band filtered-enhanced image where a Gaussian
kernel of various sizes was applied and (3) an RGB color image from the SDSS
database. For E/S0/Sa galaxies, in addition to the images in (1), (2) and (3),
plots of r band surface brightness and geometric profiles (ellipticity,
Position Angle PA and A4/B4 coefficients of the Fourier series expansions of
deviations of a pure ellipse) are provided...Comment: 40 pages, 17 figures and 3 table
The UNAM-KIAS Catalog of Isolated Galaxies
A new catalog of isolated galaxies from The Sloan Digital Sky Survey (DR5) is
presented. 1520 isolated galaxies were found in 1.4 steradians of sky. The
selection criteria in this so called UNAM-KIAS catalog was implemented from a
variation on the criteria developed by Karachentseva 1973 including full
redshift information. Through an image processing pipeline that takes advantage
from the high resolution (~ 0.4 ''/pix) and high dynamic range of the SDSS
images, a uniform g band morphological classification for all these galaxies is
presented. We identify 80% (SaSm) spirals (50% later than Sbc types) on one
hand, and a scarce population of early-type E(6.5%) and S0(8%) galaxies
amounting to 14.5% on the other hand. This magnitude-limited catalog is ~ 80%
complete at 16.5, 15.6, 15.0, 14.6 and 14.4 magnitudes in the ugriz bands
respectively. Some representative physical properties including SDSS magnitudes
and color distributions, color-color diagrams, absolute magnitude-color, and
concentration-color diagrams as a function of morphological type are presented.
The UNAM-KIAS Morphological Atlas is also released along with this paper. For
each galaxy of type later than Sa, a mosaic is presented that includes: (1) a
g-band logarithmic image, (2) a g band filtered-enhanced image where a Gaussian
kernel of various sizes was applied and (3) an RGB color image from the SDSS
database. For E/S0/Sa galaxies, in addition to the images in (1), (2) and (3),
plots of r band surface brightness and geometric profiles (ellipticity,
Position Angle PA and A4/B4 coefficients of the Fourier series expansions of
deviations of a pure ellipse) are provided...Comment: 40 pages, 17 figures and 3 table
Dependence of the Star Formation Efficiency on the Parameters of Molecular Cloud Formation Simulations
We investigate the response of the star formation efficiency (SFE) to the
main parameters of simulations of molecular cloud formation by the collision of
warm diffuse medium (WNM) cylindrical streams, neglecting stellar feedback and
magnetic fields. The parameters we vary are the Mach number of the inflow
velocity of the streams, Msinf, the rms Mach number of the initial background
turbulence in the WNM, and the total mass contained in the colliding gas
streams, Minf. Because the SFE is a function of time, we define two estimators
for it, the "absolute" SFE, measured at t = 25 Myr into the simulation's
evolution (sfeabs), and the "relative" SFE, measured 5 Myr after the onset of
star formation in each simulation (sferel). The latter is close to the "star
formation rate per free-fall time" for gas at n = 100 cm^-3. We find that both
estimators decrease with increasing Minf, although by no more than a factor of
2 as Msinf increases from 1.25 to 3.5. Increasing levels of background
turbulence similarly reduce the SFE, because the turbulence disrupts the
coherence of the colliding streams, fragmenting the cloud, and producing
small-scale clumps scattered through the numerical box, which have low SFEs.
Finally, the SFE is very sensitive to the mass of the inflows, with sferel
decreasing from ~0.4 to ~0.04 as the the virial parameter in the colliding
streams increases from ~0.15 to ~1.5. This trend is in partial agreement with
the prediction by Krumholz & McKee (2005), since the latter lies within the
same range as the observed efficiencies, but with a significantly shallower
slope. We conclude that the observed variability of the SFE is a highly
sensitive function of the parameters of the cloud formation process, and may be
the cause of significant scatter in observational determinations.Comment: 19 pages, submitted to MNRA
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