1,024 research outputs found
Building the red sequence through gas-rich major mergers
Understanding the details of how the red sequence is built is a key question
in galaxy evolution. What are the relative roles of gas-rich vs. dry mergers,
major vs. minor mergers or galaxy mergers vs. gas accretion? In Wild et al.
2009 we compare hydrodynamic simulations with observations to show how gas-rich
major mergers result in galaxies with strong post-starburst spectral features,
a population of galaxies easily identified in the real Universe using optical
spectra. Using spectra from the VVDS deep survey with z~0.7, and a principal
component analysis technique to provide indices with high enough SNR, we find
that 40% of the mass flux onto the red-sequence could enter through a strong
post-starburst phase, and thus through gas-rich major mergers. The deeper
samples provided by next generation galaxy redshift surveys will allow us to
observe the primary physical processes responsible for the shut-down in
starformation and build-up of the red sequence.Comment: 4 pages, 7 figures, proceedings of IAU symposium 262 "Stellar
populations, planning for the next decade
Are nuclear star clusters the precursors of massive black holes?
We present new upper limits for black hole masses in extremely late type
spiral galaxies. We confirm that this class of galaxies has black holes with
masses less than 10^6 Msolar, if any. We also derive new upper limits for
nuclear star cluster (NC) masses in massive galaxies with previously determined
black hole masses. We use the newly derived upper limits and a literature
compilation to study the low mass end of the global-to-nucleus relations. We
find the following (1) The M_BH-sigma relation cannot flatten at low masses,
but may steepen. (2) The M_BH-M_bulge relation may well flatten in contrast.
(3) The M_BH-Sersic n relation is able to account for the large scatter in
black hole masses in low-mass disk galaxies. Outliers in the M_BH-Sersic n
relation seem to be dwarf elliptical galaxies. When plotting M_BH versus M_NC
we find three different regimes: (a) nuclear cluster dominated nuclei, (b) a
transition region, and (c) black hole-dominated nuclei. This is consistent with
the picture, in which black holes form inside nuclear clusters with a very
low-mass fraction. They subsequently grow much faster than the nuclear cluster,
destroying it when the ratio M_BH/M_NC grows above 100. Nuclear star clusters
may thus be the precursors of massive black holes in galaxy nuclei.Comment: This version has a corrected value for Sersic n for NGC205, which got
mixed up in the original version. None of the conclusions chang
Conformal field theory, boundary conditions and applications to string theory
This is an introduction to two-dimensional conformal field theory and its
applications in string theory. Modern concepts of conformal field theory are
explained, and it is outlined how they are used in recent studies of D-branes
in the strong curvature regime by means of CFT on surfaces with boundary.Comment: 45 pages, LaTeX2
About the morphology of dwarf spheroidal galaxies and their dark matter content
The morphological properties of the Carina, Sculptor and Fornax dwarfs are
investigated using new wide field data with a total area of 29 square degrees.
The stellar density maps are derived, hinting that Sculptor possesses tidal
tails indicating interaction with the Milky Way. Contrary to previous studies
we cannot find any sign of breaks in the density profiles for the Carina and
Fornax dwarfs. The possible existence of tidal tails in Sculptor and of King
limiting radii in Fornax and Carina are used to derive global M/L ratios,
without using kinematic data. By matching those M/L ratios to kinematically
derived values we are able to constrain the orbital parameters of the three
dwarfs. Fornax cannot have M/L smaller than 3 and must be close to its
perigalacticon now. The other extreme is Sculptor that needs to be on an orbit
with an eccentricity bigger than 0.5 to be able to form tidal tails despite its
kinematic M/L.Comment: 9 pages, 7 figures, accepted by A&
Abundance patterns in early-type galaxies: is there a 'knee' in the [Fe/H] vs. [alpha/Fe] relation?
Early-type galaxies (ETGs) are known to be enhanced in alpha elements, in
accordance with their old ages and short formation timescales. In this
contribution we aim to resolve the enrichment histories of ETGs. This means we
study the abundance of Fe ([Fe/H]) and the alpha-element groups ([alpha/Fe])
separately for stars older than 9.5 Gyr ([Fe/H]o, [alpha/Fe]o) and for stars
between 1.5 and 9.5 Gyr ([Fe/H]i, [alpha/Fe]i). Through extensive simulation we
show that we can indeed recover the enrichment history per galaxy. We then
analyze a spectroscopic sample of 2286 early-type galaxies from the SDSS
selected to be ETGs. We separate out those galaxies for which the abundance of
iron in stars grows throughout the lifetime of the galaxy, i.e. in which
[Fe/H]o < [Fe/H]i. We confirm earlier work where the [Fe/H] and [alpha/Fe]
parameters are correlated with the mass and velocity dispersion of ETGs. We
emphasize that the strongest relation is between [alpha/Fe] and age. This
relation falls into two regimes, one with a steep slope for old galaxies and
one with a shallow slope for younger ETGs. The vast majority of ETGs in our
sample do not show the 'knee' in the plot of [Fe/H] vs. [alpha/Fe] commonly
observed in local group galaxies. This implies that for the vast majority of
ETGs, the stars younger than 9.5 Gyrs are likely to have been accreted or
formed from accreted gas. The properties of the intermediate-age stars in
accretion-dominated ETGs indicate that mass growth through late (minor) mergers
in ETGs is dominated by galaxies with low [Fe/H] and low [alpha/Fe]. The method
of reconstructing the stellar enrichment histories of ETGs introduced in this
paper promises to constrain the star formation and mass assembly histories of
large samples of galaxies in a unique way.Comment: 22 pages, 25 figures, accepted for publication by A&
An Accreting Black Hole in the Nuclear Star Cluster of the Bulgeless Galaxy NGC 1042
We present spectroscopic evidence for a low-luminosity, low-excitation active
galactic nucleus (AGN) in NGC 1042, powered by an intermediate-mass black hole.
These findings are significant in that the AGN is coincident with a compact
star cluster known to reside in the nucleus, thus providing an example where
the two types of central mass concentration coexist. The existence of a central
black hole is additionally remarkable in that NGC 1042 lacks a stellar bulge.
Objects such as NGC 1042 may have an important role in testing theories for the
genesis of massive black holes in galaxy nuclei, and the extent to which they
are in symbiosis with the larger stellar host.Comment: 15 pages, 6 figures, accepted for publication in Ap
Differential stellar population models: how to reliably measure [Fe/H] and [alpha/Fe] in galaxies
We present differential stellar population models, which allow improved
determinations of the ages, iron and alpha-element abundances of old stellar
populations from spectral fitting. These new models are calibrated at solar
abundances using the predictions from classical, semi-empirical stellar
population models. We then use the predictive power of fully synthetic models
to compute predictions for different [Fe/H] and [alpha/Fe]. We show that these
new differential models provide remarkably accurate fits to the integrated
optical spectra of the bulge globular clusters NGC6528 and NGC6553, and that
the inferred [Fe/H] and [alpha/Fe] agree with values derived elsewhere from
stellar photometry and spectroscopy. The analysis of a small sample of SDSS
early-type galaxies further confirms that our alpha-enhanced models provide a
better fit to the spectra of massive ellipticals than the solar-scaled ones.
Our approach opens new opportunities for precision measurements of abundance
ratios in galaxies.Comment: 5 pages, 5 figures, MNRAS in pres
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