6,015 research outputs found
Bar-induced central star formation as revealed by integral field spectroscopy from CALIFA
We investigate the recent star formation history (SFH) in the inner region of
57 nearly face-on spiral galaxies selected from the Calar Alto Legacy Integral
Field Area (CALIFA) survey. For each galaxy we use the integral field
spectroscopy from CALIFA to obtain two-dimensional maps and radial profiles of
three parameters that are sensitive indicators of the recent SFH: the 4000\AA\
break (D(4000)), and the equivalent width of H absorption
(EW(H)) and H emission (EW(H)). We have also
performed photometric decomposition of bulge/bar/disk components based on SDSS
optical image. We identify a class of 17 "turnover" galaxies whose central
region present significant drop in D(4000), and most of them
correspondingly show a central upturn in EW(H) and EW(H).
This indicates that the central region of the turnover galaxies has experienced
star formation in the past 1-2 Gyr, which makes the bulge younger and more
star-forming than surrounding regions. We find almost all (15/17) the turnover
galaxies are barred, while only half of the barred galaxies in our sample
(15/32) are classified as a turnover galaxy. This finding provides strong
evidence in support of the theoretical expectation that the bar may drive gas
from the disc inward to trigger star formation in galaxy center, an important
channel for the growth/rejuvenation of pseudobulges in disc galaxies.Comment: 19 pages, 10 figures, ApJ accepte
Coupling the valley degree of freedom to antiferromagnetic order
Conventional electronics are based invariably on the intrinsic degrees of
freedom of an electron, namely, its charge and spin. The exploration of novel
electronic degrees of freedom has important implications in both basic quantum
physics and advanced information technology. Valley as a new electronic degree
of freedom has received considerable attention in recent years. In this paper,
we develop the theory of spin and valley physics of an antiferromagnetic
honeycomb lattice. We show that by coupling the valley degree of freedom to
antiferromagnetic order, there is an emergent electronic degree of freedom
characterized by the product of spin and valley indices, which leads to
spin-valley dependent optical selection rule and Berry curvature-induced
topological quantum transport. These properties will enable optical
polarization in the spin-valley space, and electrical detection/manipulation
through the induced spin, valley and charge fluxes. The domain walls of an
antiferromagnetic honeycomb lattice harbors valley-protected edge states that
support spin-dependent transport. Finally, we employ first principles
calculations to show that the proposed optoelectronic properties can be
realized in antiferromagnetic manganese chalcogenophosphates (MnPX_3, X = S,
Se) in monolayer form.Comment: 6 pages, 5 figure
Conditional HI mass functions and the HI-to-halo mass relation in the local Universe
We present a new HI mass estimator which relates the HI-to-stellar mass ratio
to four galaxy properties: stellar surface mass density, color index ,
stellar mass and concentration index, with the scatter of individual galaxies
around the mean HI mass modeled with a Gaussian distribution. We calibrate the
estimator using the xGASS sample, including both HI detection and
non-detection, and constrain the model parameters through Bayesian inferences.
Tests with mock catalogs demonstrate that our estimator provides unbiased HI
masses for optical samples like the SDSS, thus suitable for statistical studies
of HI gas contents in galaxies and dark matter halos. We apply our estimator to
the SDSS spectroscopic sample to estimate the local HI mass function (HIMF),
the conditional HI mass function (CHIMF) in galaxy groups and the HI-halo mass
(HIHM) relation. Our HIMF agrees with the ALFALFA measurements at
, but with higher amplitude and a steeper
slope at lower masses. We show that this discrepancy is caused primarily by the
cosmic variance which is corrected for the SDSS sample but not for the ALFALFA.
The CHIMFs for all halo masses can be described by a single Schechter function,
and this is true for red, blue and satellite galaxies. For central galaxies the
CHIMFs show a double-Gaussian profile, with the two components contributed by
the red and blue galaxies, respectively. The total HI mass in a group increases
monotonically with halo mass. The HI mass of central galaxies in galaxy groups
increases rapidly with halo mass only at , while
the mass dependence becomes much weaker at higher halo masses. The observed
HI-halo mass relation is not reproduced by current hydrodynamic simulations and
semi-analytic models of galaxy formation.Comment: 10 figures, 2 tables, published in ApJ. : The version
published in ApJ has a typo. In the last paragraph of section 3.2, the
maximum posterior value of c_a should be c_a = 0.10 \pm 0.08, not c_a = 0.16
\pm 0.1
Semi-solid slurry of AZ91 magnesium alloy prepared by electromagnetic stirring near liquidus temperature
An electromagnetic stirring process near liquidus temperature was designed and demonstrated experimentally to produce semi-solid slurry of AZ91 magnesium alloy, in order to avoid not only contamination from mechanical stirring but also the inflammation of Mg alloy melt at elevated temperature. AZ91 alloy feedstock was isothermally heat treated at 600-610 for 20 min, and then stirred by electromagnetic field. Globular primary particle characteristic was observed optically in the castings. Mechanical properties were also studied
- …