60,882 research outputs found
The continuous rise of bulges out of galactic disks
(abridged) This study revolves around dmB, a new distance- and
extinction-independent measure of the contribution by stellar populations older
than 9 Gyr to the mean r-band surface brightness of the bulge component in 135
late-type galaxies (LTGs) from the CALIFA survey, spanning a range of 2.6 dex
and 3 dex in total and bulge stellar mass (M*T~10^(8.9-11.5) M_solar and
M*B~10^(8.3-11.3) M_solar, respectively). The main insight from this study is
that LTG bulges form a continuous sequence of increasing dmB with increasing
M*T, M*B, stellar mass surface density S* and mass-weighted age and
metallicity: high-dmB bulges are the oldest, densest and most massive ones, and
vice versa. Furthermore, we find that the bulge-to-disk age and metallicity
contrast, as well as the bulge-to-disk mass ratio increase with M*T, raising
from, respectively, ~0 Gyr, 0 dex and 0.25 to ~3 Gyr, ~0.3 dex and 0.67 across
the mass range covered by our sample. Whereas gas excitation in lower-mass
bulges is invariably dominated by star formation (SF), LINER- and
Seyfert-specific emission-line ratios were exclusively documented in high-mass,
high-S* bulges. The continuity both in the properties of LTG bulges themselves
and in their age and metallicity contrast to their parent disks suggests that
these components evolve alongside in a concurrent process that leads to a
continuum of physical and evolutionary characteristics. Our results are
consistent with a picture where bulge growth in LTGs is driven by a
superposition of quick-early and slow-secular processes, the relative
importance of which increases with M*T. These processes, which presumably
combine in situ SF in the bulge and inward migration of material from the disk,
are expected to lead to a non-homologous radial growth of S* and a trend for an
increasing Sersic index with increasing galaxy mass.Comment: 24 pages, accepted for publication in A&
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
Data-driven pattern identification and outlier detection in time series
We address the problem of data-driven pattern identification and outlier
detection in time series. To this end, we use singular value decomposition
(SVD) which is a well-known technique to compute a low-rank approximation for
an arbitrary matrix. By recasting the time series as a matrix it becomes
possible to use SVD to highlight the underlying patterns and periodicities.
This is done without the need for specifying user-defined parameters. From a
data mining perspective, this opens up new ways of analyzing time series in a
data-driven, bottom-up fashion. However, in order to get correct results, it is
important to understand how the SVD-spectrum of a time series is influenced by
various characteristics of the underlying signal and noise. In this paper, we
have extended the work in earlier papers by initiating a more systematic
analysis of these effects. We then illustrate our findings on some real-life
data
The dependence of Galactic outflows on the properties and orientation of zCOSMOS galaxies at z ~ 1
We present an analysis of cool outflowing gas around galaxies, traced by MgII
absorption lines in the co-added spectra of a sample of 486 zCOSMOS galaxies at
1 < z < 1.5. These galaxies span a range of stellar masses (9.45<
log[M*/Msun]<10.7) and star formation rates (0.14 < log [SFR/Msun/yr] < 2.35).
We identify the cool outflowing component in the MgII absorption and find that
the equivalent width of the outflowing component increases with stellar mass.
The outflow equivalent width also increases steadily with the increasing star
formation rate of the galaxies. At similar stellar masses the blue galaxies
exhibit a significantly higher outflow equivalent width as compared to red
galaxies. The outflow equivalent width shows strong effect with star formation
surface density ({\Sigma}SFR) of the sample. For the disk galaxies, the outflow
equivalent width is higher for the face-on systems as compared to the edge-on
ones, indicating that for the disk galaxies, the outflowing gas is primarily
bipolar in geometry. Galaxies typically exhibit outflow velocities ranging from
-200 km/s to -300 km/s and on average the face-on galaxies exhibit higher
outflow velocity as compared to the edge-on ones. Galaxies with irregular
morphologies exhibit outflow equivalent width as well as outflow velocities
comparable to face on disk galaxies. These galaxies exhibit minimum mass
outflow rates > 5-7 Msun/yr and a mass loading factor ({\eta} = dMout/dt /SFR)
comparable to the star formation rates of the galaxies.Comment: 12 pages, 14 figures, ApJ submitte
Task-Specific Experience and Task-Specific Talent: Decomposing the Productivity of High School Teachers
We use administrative panel data to decompose worker performance into components relating to general talent, task-specific talent, general experience, and task-specific experience. We consider the context of high school teachers, in which tasks consist of teaching particular subjects in particular tracks. Using the timing of changes in the subjects and levels to which teachers are assigned to provide identifying variation, we show that much of the productivity gains to teacher experience estimated in the literature are actually subject-specific. By contrast, very little of the variation in the permanent component of productivity among teachers is subject-specific or level-specific. Counterfactual simulations suggest that maximizing the value of task-specific experience could produce nearly costless efficiency gains on the order of .02 test score standard deviations
High-resolution mass models of dwarf galaxies from LITTLE THINGS
We present high-resolution rotation curves and mass models of 26 dwarf galaxies from LITTLE THINGS. LITTLE THINGS is a high-resolution Very Large Array HI survey for nearby dwarf galaxies in the local volume within 11 Mpc. The rotation curves of the sample galaxies derived in a homogeneous and consistent manner are combined with Spitzer archival 3.6 micron and ancillary optical U, B, and V images to construct mass models of the galaxies. We decompose the rotation curves in terms of the dynamical contributions by baryons and dark matter halos, and compare the latter with those of dwarf galaxies from THINGS as well as Lambda CDM SPH simulations in which the effect of baryonic feedback processes is included. Being generally consistent with THINGS and simulated dwarf galaxies, most of the LITTLE THINGS sample galaxies show a linear increase of the rotation curve in their inner regions, which gives shallower logarithmic inner slopes alpha of their dark matter density profiles. The mean value of the slopes of the 26 LITTLE THINGS dwarf galaxies is alpha =-0.32 +/- 0.24 which is in accordance with the previous results found for low surface brightness galaxies (alpha = -0.2 +/- 0.2) as well as the seven THINGS dwarf galaxies (alpha =-0.29 +/- 0.07). However, this significantly deviates from the cusp-like dark matter distribution predicted by dark-matter-only Lambda CDM simulations. Instead our results are more in line with the shallower slopes found in the Lambda CDM SPH simulations of dwarf galaxies in which the effect of baryonic feedback processes is included. In addition, we discuss the central dark matter distribution of DDO 210 whose stellar mass is relatively low in our sample to examine the scenario of inefficient supernova feedback in low mass dwarf galaxies predicted from recent Lambda SPH simulations of dwarf galaxies where central cusps still remain.Peer reviewe
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