1,176 research outputs found
Old and young bulges in late-type disk galaxies
ABRIDGED: We use HSTACS and NICMOS imaging to study the structure and colors
of a sample of nine late-type spirals. We find: (1) A correlation between bulge
and disks scale-lengths, and a correlation between the colors of the bulges and
those of the inner disks. Our data show a trend for bulges to be more
metal-enriched than their surrounding disks, but otherwise no simple
age-metallicity connection between these systems; (2) A large range in bulge
stellar population properties, and, in particular, in stellar ages.
Specifically, in about a half of the late-type bulges in our sample the bulk of
the stellar mass was produced recently. Thus, in a substantial fraction of the
z=0 disk-dominated bulged galaxies, bulge formation occurs after the
formation/accretion of the disk; (3) In about a half of the late-type bulges in
our sample, however, the bulk of the stellar mass was produced at early epochs;
(4) Even these "old" late-type bulges host a significant fraction of stellar
mass in a young(er) c component; (5) A correlation for bulges between stellar
age and stellar mass, in the sense that more massive late-type bulges are older
than less massive late-type bulges. Since the overall galaxy luminosity (mass)
also correlates with the bulge luminosity (mass), it appears that the galaxy
mass regulates not only what fraction of itself ends up in the bulge component,
but also "when" bulge formation takes place. We show that dynamical friction of
massive clumps in gas-rich disks is a plausible disk-driven mode for the
formation of "old" late-type bulges. If disk evolutionary processes are
responsible for the formation of the entire family of late-type bulges, CDM
simulations need to produce a similar number of initially bulgeless disks in
addition to the disk galaxies that are observed to be bulgeless at z=0.Comment: ApJ in press; paper with high resolution figures available at
http://www.exp-astro.phys.ethz.ch/carollo/carollo1_2006.pdf; B, I, and H
surface brightness profiles published in electronic tabular for
The Hubble Sequence in Groups: The Birth of the Early-Type Galaxies
The physical mechanisms and timescales that determine the morphological
signatures and the quenching of star formation of typical (~L*) elliptical
galaxies are not well understood. To address this issue, we have simulated the
formation of a group of galaxies with sufficient resolution to track the
evolution of gas and stars inside about a dozen galaxy group members over
cosmic history. Galaxy groups, which harbor many elliptical galaxies in the
universe, are a particularly promising environment to investigate morphological
transformation and star formation quenching, due to their high galaxy density,
their relatively low velocity dispersion, and the presence of a hot intragroup
medium. Our simulation reproduces galaxies with different Hubble morphologies
and, consequently, enables us to study when and where the morphological
transformation of galaxies takes place. The simulation does not include
feedback from active galactic nuclei showing that it is not an essential
ingredient for producing quiescent, red elliptical galaxies in galaxy groups.
Ellipticals form, as suspected, through galaxy mergers. In contrast with what
has often been speculated, however, these mergers occur at z>1, before the
merging progenitors enter the virial radius of the group and before the group
is fully assembled. The simulation also shows that quenching of star formation
in the still star-forming elliptical galaxies lags behind their morphological
transformation, but, once started, is taking less than a billion years to
complete. As long envisaged the star formation quenching happens as the
galaxies approach and enter the finally assembled group, due to quenching of
gas accretion and (to a lesser degree) stripping. A similar sort is followed by
unmerged, disk galaxies, which, as they join the group, are turned into the
red-and-dead disks that abound in these environments.Comment: 12 pages, 12 Figures, 1 Table, accepted for publication in AP
Geometric phases and criticality in spin systems
A general formalism of the relation between geometric phases produced by
circularly evolving interacting spin systems and their criticality behavior is
presented. This opens up the way for the use of geometric phases as a tool to
study regions of criticality without having to undergo a quantum phase
transition. As a concrete example a spin-1/2 chain with XY interactions is
presented and the corresponding geometric phases are analyzed. The
generalization of these results to the case of an arbitrary spin system
provides an explanation for the existence of such a relation.Comment: 12 pages, 4 figure
On the relation between sSFR and metallicity
In this paper we present an exact general analytic expression
linking the gas metallicity Z to the specific
star formation rate (sSFR), that validates and extends the approximate relation
put forward by Lilly et al. (2013, L13), where is the yield per stellar
generation, is the instantaneous ratio between inflow and star
formation rate expressed as a function of the sSFR, and is the integral of
the past enrichment history, respectively. We then demonstrate that the
instantaneous metallicity of a self-regulating system, such that its sSFR
decreases with decreasing redshift, can be well approximated by the first term
on the right-hand side in the above formula, which provides an upper bound to
the metallicity. The metallicity is well approximated also by the L13 ideal
regulator case, which provides a lower bound to the actual metallicity. We
compare these approximate analytic formulae to numerical results and infer a
discrepancy <0.1 dex in a range of metallicities and almost three orders of
magnitude in the sSFR. We explore the consequences of the L13 model on the
mass-weighted metallicity in the stellar component of the galaxies. We find
that the stellar average metallicity lags 0.1-0.2 dex behind the gas-phase
metallicity relation, in agreement with the data. (abridged)Comment: 14 pages, 6 figures, MNRAS accepte
Large stellar disks in small elliptical galaxies
We present the rotation velocities V and velocity dispersions sigma along the
principal axes of seven elliptical galaxies less luminous than M_B= -19.5.
These kinematics extend beyond the half-light radii for all systems in this
photometrically selected sample. At large radii the kinematics not only confirm
that rotation and "diskiness" are important in faint ellipticals, as was
previously known, but also demonstrate that in most sample galaxies the stars
at large galactocentric distances have (V/sigma)_max of about 2, similar to the
disks in bona-fide S0 galaxies. Comparing this high degree of ordered stellar
motion in all sample galaxies with numerical simulations of dissipationless
mergers argues against mergers with mass ratios <=3:1 as an important mechanism
in the final shaping of low-luminosity ellipticals, and favors instead the
dissipative formation of a disk.Comment: 11 pages LaTex with 4 Postscript figure
Evolution of field early-type galaxies: The view from GOODS/CDFS
(Abridged) We explore the evolution of field early-type galaxies on a sample
extracted from GOODS/CDFS. The galaxies are selected by means of a
non-parametric analysis followed by visual inspection. We exclude those
galaxies which are not consistent with an evolution into the Kormendy relation.
The final set comprises 249 galaxies with a median redshift z=0.7. The
distribution of number counts versus apparent magnitude suggests a substantial
decrease of the comoving number density with redshift. The majority of the
galaxies feature passively evolving old stellar populations. One third of those
in the upper half of the redshift distribution have blue colors, in contrast to
only 10% in the lower redshift subsample. An adaptive binning of the color maps
is performed to explore the internal color distribution. We find that most blue
galaxies in our sample feature blue cores whereas most of the red early-types
are passively evolving stellar populations with red cores. The color gradients
and scatter do not evolve with redshift and are compatible with the
observations at z=0 assuming a radial dependence of the metallicity within each
galaxy. This work emphasizes the need for a careful sample selection, as we
found that most of those galaxies which were visually classified as early types
-- but then rejected based on the Kormendy relation -- feature blue colors
characteristic of recent star formation.Comment: 14 pages, 16 figures. Uses emulateapj. Accepted for publication in
ApJ. Some figures in low resolutio
Oxygen Gas Abundances at 0.4<z<1.5: Implications for the Chemical Evolution History of Galaxies
We report VLT-ISAAC and Keck-NIRSPEC near-infrared spectroscopy for a sample
of 30 0.47<z<0.92 CFRS galaxies and five [OII]-selected, M_B,AB<-21.5, z~1.4
galaxies. We have measured Halpha and [NII] line fluxes for the CFRS galaxies
which have [OII], Hbeta and [OIII] line fluxes available from optical
spectroscopy. For the z~1.4 objects we measured Hbeta and [OIII] emission line
fluxes from J-band spectra, and Halpha line fluxes plus upper limits for [NII]
fluxes from H-band spectra. We derive the extinction and oxygen abundances for
the sample using a method based on a set of ionisation parameter and oxygen
abundance diagnostics, simultaneously fitting the [OII], Hbeta, [OIII], Halpha
and [NII] line fluxes. Our most salient conclusions are: a) the source of gas
ionisation in the 30 CFRS and in all z~1.4 galaxies is not due to AGN activity;
b) about one third of the 0.47<z<0.92 CFRS galaxies in our sample have
substantially lower metallicities than local galaxies with similar luminosities
and star formation rates; c) comparison with a chemical evolution model
indicates that these low metallicity galaxies are unlikely to be the
progenitors of metal-poor dwarf galaxies at z~0, but more likely the
progenitors of massive spirals; d) the z~1.4 galaxies are characterized by the
high [OIII]/[OII] line ratios, low extinction and low metallicity that are
typical of lower luminosity CADIS galaxies at 0.4<z<0.7, and of more luminous
Lyman Break Galaxies at z~3.1, but not seen in CFRS galaxies at 0.4<z<1.0; e)
the properties of the z~1.4 galaxies suggest that the period of rapid chemical
evolution takes place progressively in lower mass systems as the universe ages,
and thus provides further support for a downsizing picture of galaxy formation,
at least from z~1.4 to today.Comment: Proceedings contribution for "The Fabulous Destiny of Galaxies;
Bridging Past and Present", Marseille, 200
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