8 research outputs found
Structure and dynamics of galaxies with a low surface-brightness disc - II. Stellar populations of bulges
The radial profiles of the Hb, Mg, and Fe line-strength indices are presented
for a sample of eight spiral galaxies with a low surface-brightness stellar
disc and a bulge. The correlations between the central values of the
line-strength indices and velocity dispersion are consistent to those known for
early-type galaxies and bulges of high surface-brightness galaxies. The age,
metallicity, and alpha/Fe enhancement of the stellar populations in the
bulge-dominated region are obtained using stellar population models with
variable element abundance ratios. Almost all the sample bulges are
characterized by a young stellar population, on-going star formation, and a
solar alpha/Fe enhancement. Their metallicity spans from high to sub-solar
values. No significant gradient in age and alpha/Fe enhancement is measured,
whereas only in a few cases a negative metallicity gradient is found. These
properties suggest that a pure dissipative collapse is not able to explain
formation of all the sample bulges and that other phenomena, like mergers or
acquisition events, need to be invoked. Such a picture is also supported by the
lack of a correlation between the central value and gradient of the metallicity
in bulges with very low metallicity. The stellar populations of the bulges
hosted by low surface-brightness discs share many properties with those of high
surface-brightness galaxies. Therefore, they are likely to have common
formation scenarios and evolution histories. A strong interplay between bulges
and discs is ruled out by the fact that in spite of being hosted by discs with
extremely different properties, the bulges of low and high surface-brightness
discs are remarkably similar.Comment: 24 pages, 12 figures, 7 tables, accepted for pubblication on MNRA
Evolution of blue E/S0 galaxies from z~1: merger remnants or disk rebuilding galaxies?
Studying outliers from the bimodal distribution of galaxies in the color-mass
space, such as morphological early-type galaxies residing in the blue cloud,
can help to better understand the physical mechanisms that lead galaxy
migrations in this space. In this paper we study the evolution of the
properties of 210 M*/Msol>10^10 blue E/S0s between z~1.4 and z~0.2 in the
COSMOS field with confirmed spectroscopic redshifts from the zCOSMOS 10k
release. We first observe that the threshold mass, defined at z=0 in previous
studies as the mass below which the population of blue early-type galaxies
starts to be abundant relative to passive E/S0s, evolves from log(M*/Msol)~10.1
at z~0.3 to log(M*/Msol)~10.9 at z~1. Second, there seems to be a turn-over
mass in the nature of blue E/S0 galaxies. Above log(M*/Msol)~10.8 blue E/S0
resemble to merger remnants probably migrating to the red-sequence in a
time-scale of ~3 Gyr. Below this mass, they seem to be closer to normal
late-type galaxies as if they were the result of minor mergers which triggered
the central star-formation and built a central bulge component or were
(re)building a disk from the surrounding gas, suggesting that they are moving
back or staying in the blue-cloud. This turn-over mass does not seem to evolve
significantly from z~1 in contrast with the threshold mass and therefore does
not seem to be linked with the relative abundance of blue E/S0s.Comment: accepted for publication in A&
Stellar Populations of Bulges in 14 Cluster Disc Galaxies
‘The definitive version is available at www.blackwell-synergy.com.’ Copyright Blackwell Publishing / RAS. DOI: 10.1111/j.1365-2966.2008.13566.xPeer reviewe
The PN.S Elliptical Galaxy Survey: the dark matter in NGC 4494
We present new Planetary Nebula Spectrograph observations of the ordinary
elliptical galaxy NGC 4494, resulting in positions and velocities of 255 PNe
out to 7 effective radii (25 kpc). We also present new wide-field surface
photometry from MMT/Megacam, and long-slit stellar kinematics from VLT/FORS2.
The spatial and kinematical distributions of the PNe agree with the field stars
in the region of overlap. The mean rotation is relatively low, with a possible
kinematic axis twist outside 1 Re. The velocity dispersion profile declines
with radius, though not very steeply, down to ~70 km/s at the last data point.
We have constructed spherical dynamical models of the system, including Jeans
analyses with multi-component LCDM-motivated galaxies as well as logarithmic
potentials. These models include special attention to orbital anisotropy, which
we constrain using fourth-order velocity moments. Given several different sets
of modelling methods and assumptions, we find consistent results for the mass
profile within the radial range constrained by the data. Some dark matter (DM)
is required by the data; our best-fit solution has a radially anisotropic
stellar halo, a plausible stellar mass-to-light ratio, and a DM halo with an
unexpectedly low central density. We find that this result does not
substantially change with a flattened axisymmetric model.
Taken together with other results for galaxy halo masses, we find suggestions
for a puzzling pattern wherein most intermediate-luminosity galaxies have very
low concentration halos, while some high-mass ellipticals have very high
concentrations. We discuss some possible implications of these results for DM
and galaxy formation.Comment: 29 pages, 17 figures. MNRAS, accepte
In search of precision in absorptive capacity research: A synthesis of the literature and consolidation of findings
This paper addresses two fundamental problems in the absorptive capacity (AC) literature: conceptual ambiguity on what AC is and a lack of synthesized empirical findings showing how AC matters for firm outcomes. We take a two-pronged approach to address these problems: (1) conceptual distillation of the literature to discern the core AC dimensions, outcomes, and contingent external knowledge conditions and (2) meta-analysis of the empirical literature to synthesize the findings. For conceptual distillation, we identify three dimensions of AC: absorptive effort (i.e., the knowledge-building investments made by a firm), absorptive knowledge base (i.e., the current knowledge stock of a firm), and absorptive process (i.e., a firm’s internal procedures and practices related to knowledge diffusion). We develop these dimensions by explicating their theoretical roots, functions, mechanisms, and corresponding measures. Leveraging the conceptual distillation, we conduct meta-analyses of the empirical literature and synthesize key findings. We find that AC has a significant positive effect on firm outcomes and that the most commonly used dimension, absorptive effort, has the lowest mean effect size. We also find that knowledge acquisition and innovation generation fully mediate the effect of absorptive knowledge base but partially mediate the effects of absorptive effort and absorptive process on firm performance. Furthermore, AC’s effects on firm outcomes vary across external knowledge contingencies. Overall, this paper provides a strong theoretical and empirical basis to advance a dimensional approach in AC research and thereby facilitates a more rigorous research necessary for cumulative knowledge development on this important topic