2,383 research outputs found
Resolving the age bimodality of galaxy stellar populations on kpc scales
Galaxies in the local Universe are known to follow bimodal distributions in
the global stellar populations properties. We analyze the distribution of the
local average stellar-population ages of 654,053 sub-galactic regions resolved
on ~1-kpc scales in a volume-corrected sample of 394 galaxies, drawn from the
CALIFA-DR3 integral-field-spectroscopy survey and complemented by SDSS imaging.
We find a bimodal local-age distribution, with an old and a young peak
primarily due to regions in early-type galaxies and star-forming regions of
spirals, respectively. Within spiral galaxies, the older ages of bulges and
inter-arm regions relative to spiral arms support an internal age bimodality.
Although regions of higher stellar-mass surface-density, mu*, are typically
older, mu* alone does not determine the stellar population age and a bimodal
distribution is found at any fixed mu*. We identify an "old ridge" of regions
of age ~9 Gyr, independent of mu*, and a "young sequence" of regions with age
increasing with mu* from 1-1.5 Gyr to 4-5 Gyr. We interpret the former as
regions containing only old stars, and the latter as regions where the relative
contamination of old stellar populations by young stars decreases as mu*
increases. The reason why this bimodal age distribution is not inconsistent
with the unimodal shape of the cosmic-averaged star-formation history is that
i) the dominating contribution by young stars biases the age low with respect
to the average epoch of star formation, and ii) the use of a single average age
per region is unable to represent the full time-extent of the star-formation
history of "young-sequence" regions.Comment: 17 pages, 11 figures, MNRAS accepte
Fitonematoides associados Ă cultura de soja na regiĂŁo serrana do estado de Santa Catarina, Brasil.
Analysis of IL2/IL21 Gene Variants in Cholestatic Liver Diseases Reveals an Association with Primary Sclerosing Cholangitis
Background/Aims: The chromosome 4q27 region harboring IL2 and IL21 is an established risk locus for ulcerative colitis (UC) and various other autoimmune diseases. Considering the strong coincidence of primary sclerosing cholangitis (PSC) with UC and the increased frequency of other autoimmune disorders in patients with primary biliary cirrhosis (PBC), we investigated whether genetic variation in the IL2/IL21 region may also modulate the susceptibility to these two rare cholestatic liver diseases. Methods: Four strongly UC-associated single nucleotide polymorphisms (SNPs) within the KIAA1109/TENR/IL2/IL21 linkage disequilibrium block were genotyped in 124 PBC and 41 PSC patients. Control allele frequencies from 1,487 healthy, unrelated Caucasians were available from a previous UC association study. Results: The minor alleles of all four markers were associated with a decreased susceptibility to PSC (rs13151961: p = 0.013, odds ratio (OR) 0.34; rs13119723: p = 0.023, OR 0.40; rs6822844: p = 0.031, OR 0.41; rs6840978: p = 0.043, OR 0.46). Moreover, a haplotype consisting of the four minor alleles also had a protective effect on PSC susceptibility (p = 0.0084, OR 0.28). A haplotype of the four major alleles was independently associated with PSC when excluding the patients with concomitant inflammatory bowel disease (p = 0.033, OR 4.18). Conclusion: The IL2/IL21 region may be one of the highly suggestive but so far rarely identified shared susceptibility loci for PSC and UC. Copyright (C) 2011 S. Karger AG, Base
Gravitational stability and dynamical overheating of stellar disks of galaxies
We use the marginal stability condition for galactic disks and the stellar
velocity dispersion data published by different authors to place upper limits
on the disk local surface density at two radial scalelengths .
Extrapolating these estimates, we constrain the total mass of the disks and
compare these estimates to those based on the photometry and color of stellar
populations. The comparison reveals that the stellar disks of most of spiral
galaxies in our sample cannot be substantially overheated and are therefore
unlikely to have experienced a significant merging event in their history. The
same conclusion applies to some, but not all of the S0 galaxies we consider.
However, a substantial part of the early type galaxies do show the stellar
velocity dispersion well in excess of the gravitational stability threshold
suggesting a major merger event in the past. We find dynamically overheated
disks among both seemingly isolated galaxies and those forming pairs. The ratio
of the marginal stability disk mass estimate to the total galaxy mass within
four radial scalelengths remains within a range of 0.4---0.8. We see no
evidence for a noticeable running of this ratio with either the morphological
type or color index.Comment: 25 pages, 5 figures, accepted to Astronomy Letter
A simplified approach for reliability evaluation and component allocation in three-state series and parallel systems composed of non-identical components
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