203 research outputs found
The (black hole mass)-(color) relations for early- and late-type galaxies: red and blue sequences
[Abridged] Tight correlations between supermassive black hole (SMBH) mass
() and the properties of the host galaxy have useful implications
for our understanding of the growth of SMBHs and evolution of galaxies. Here,
we present newly observed correlations between and the host galaxy
total UV [3.6] color (, Pearson's r = )
for a sample of 67 galaxies (20 early-type galaxies and 47 late-type galaxies)
with directly measured in the GALEX/SG survey. The colors
are carefully measured in a homogeneous manner using the galaxies' FUV, NUV and
3.6 \micron magnitudes and their multi-component structural decompositions in
the literature. We find that more massive SMBHs are hosted by (early- and
late-type) galaxies with redder colors, but the relations for the two morphological types have slopes that differ at
level. Early-type galaxies define a red sequence in the diagrams, while late-type galaxies trace a blue
sequence. Within the assumption that the specific star formation rate of a
galaxy (sSFR) is well traced by , it follows that the
SMBH masses for late-type galaxies exhibit a steeper dependence on sSFR than
those for early-type galaxies. The and
relations for the sample galaxies reveal a
comparable level of vertical scatter in the log direction, roughly
more than the vertical scatter of the relation.
Our relations suggest different channels
of SMBH growth for early- and late-type galaxies, consistent with their
distinct formation and evolution scenarios.Comment: 27 pages, 8 figures, 6 tables, accepted for publication in Ap
Revisiting the Ceara Rise, equatorial Atlantic Ocean: isotope stratigraphy of ODP Leg 154 from 0 to 5Ma
Isotope stratigraphy has become the method of choice for investigating both past ocean temperatures and global ice volume. Lisiecki and Raymo (2005) published a stacked record of 57 globally distributed benthic δ18O records versus age (LR04 stack). In this study LR04 is compared to high-resolution records collected at all of the sites drilled during ODP Leg 154 on the Ceara Rise, in the western equatorial Atlantic Ocean. Newly developed software is used to check data splices of the Ceara Rise sites and better align out-of-splice data with in-splice data. Core images recovered from core table photos are depth and age scaled and greatly assist in the data analysis. The entire splices of ODP sites 925, 926, 927, 928 and 929 were reviewed. Most changes were minor although several were large enough to affect age models based on orbital tuning. A Ceara Rise composite record of benthic δ18O is out of sync with LR04 between 1.80 and 1.90Ma, where LR04 exhibits two maxima but Ceara Rise data contain only one. The interval between 4.0 and 4.5Ma in the Ceara Rise compilation is decidedly different from LR04, reflecting both the low amplitude of the signal over this interval and the limited amount of data available for the LR04 stack. A regional difference in benthic δ18O of 0.2‰ relative to LR04 was found. Independent tuning of Site 926 images and physical property data to the Laskar et al. (2004) orbital solution and integration of available benthic stable isotope data from the Ceara Rise provides a new regional reference section for the equatorial Atlantic covering the last 5 million years
Stellar Population Diagnostics of Elliptical Galaxy Formation
Major progress has been achieved in recent years in mapping the properties of
passively-evolving, early-type galaxies (ETG) from the local universe all the
way to redshift ~2. Here, age and metallicity estimates for local cluster and
field ETGs are reviewed as based on color-magnitude, color-sigma, and
fundamental plane relations, as well as on spectral-line indices diagnostics.
The results of applying the same tools at high redshifts are then discussed,
and their consistency with the low-redshift results is assessed. Most low- as
well as high-redshift (z~1) observations consistently indicate 1) a formation
redshift z>~3 for the bulk of stars in cluster ETGs, with their counterparts in
low-density environments being on average ~1-2 Gyr younger, i.e., formed at
z>~1.5-2, 2) the duration of the major star formation phase anticorrelates with
galaxy mass, and the oldest stellar populations are found in the most massive
galaxies. With increasing redshift there is evidence for a decrease in the
number density of ETGs, especially of the less massive ones, whereas existing
data appear to suggest that most of the most-massive ETGs were already fully
assembled at z~1. Beyond this redshift, the space density of ETGs starts
dropping significantly, and as ETGs disappear, a population of massive,
strongly clustered, starburst galaxies progressively becomes more and more
prominent, which makes them the likely progenitors to ETGs.Comment: To appear on Annual Review of Astronomy & Astrophysics, Vol. 44
(2006). 46 pages with 16 figures. Replaced version includes updated
references, few typos less, and replaces Fig. 11 and Fig. 16 which had been
skrewed u
Kinematics, Abundances, and Origin of Brightest Cluster Galaxies
We present kinematic parameters and absorption line strengths for three
brightest cluster galaxies, NGC 6166, NGC 6173 and NGC 6086. We find that NGC
6166 has a velocity dispersion profile which rises beyond 20 arcsec from the
nucleus, with a halo velocity dispersion in excess of 400 km/s. All three
galaxies show a positive and constant h4 Hermite moment. The rising velocity
dispersion profile in NGC 6166 thus indicates an increasing mass-to-light
ratio. Rotation is low in all three galaxies, and NGC 6173 and NGC 6086 show
possible kinematically decoupled cores. All three galaxies have Mg2 gradients
similar to those found in normal bright ellipticals, which are not steep enough
to support simple dissipative collapse models, but these could be accompanied
by dissipationless mergers which would tend to dilute the abundance gradients.
The [Mg/Fe] ratios in NGC 6166 and NGC 6086 are higher than that in NGC 6173,
and if NGC 6173 is typical of normal bright ellipticals, this suggests that cDs
cannot form from late mergers of normal galaxies.Comment: 21 pages, accepted for publication in MNRA
Gradients of absorption-line strengths in elliptical galaxies
© 1999. The American Astronomical Society. All rights reserved. This is the final published version of the work, which was originally published at https://doi.org/10.1086/308092We have restudied line-strength gradients of 80 elliptical galaxies. Typical metallicity gradients of elliptical galaxies are Delta[Fe/H]/Delta log r similar or equal to -0.3, which is flatter than the gradients predicted by monolithic collapse simulations. The metallicity gradients do not correlate with any physical properties of galaxies, including central and mean metallicities, central velocity dispersions sigma(0), absolute B magnitudes M-B, absolute effective radii R-e, and dynamical masses of galaxies. By using the metallicity gradients, we have calculated mean stellar metallicities for individual ellipticals. Typical mean stellar metallicities are [[Fe/H]] similar or equal to -0.3 and range from [[Fe/H]] similar or equal to -0.8 to +0.3, which is contrary to what Gonzalez & Gorgas claimed; the mean metallicities of ellipticals are not universal. The mean metallicities correlate well with sigma(0) and dynamical masses, though relations for M-B and R-e include significant scatters. We find fundamental planes defined by surface brightnesses SBe, [[Fe/H]], and R-e (or M-B), the scatters of which are much smaller than those of the [[Fe/H]]-R-e (or [[Fe/H]]-M-B) relations. The [[Fe/H]]-log sigma(0) relation is nearly parallel to the [Fe/H](0)-log sigma(0) relation but systematically lower by 0.3 dex; thus the mean metallicities are about one-half of the central values. The metallicity-mass relation or, equivalently, the color-magnitude relation of ellipticals holds not only for the central parts of galaxies but also for entire galaxies. Assuming that Mg-2 and Fe-1 give [Mg/H] and [Fe/H], respectively, we find [[Mg/Fe]] similar or equal to +0.2 in most of elliptical galaxies. [[Mg/Fe]] shows no correlation with galaxy mass tracers such as sigma(0), in contrast to what was claimed for the central [Mg/Fe]. This can be most naturally explained if the star formation had stopped in elliptical galaxies before the bulk of Type Ia supernovae began to occur. Elliptical galaxies can have significantly different metallicity gradients and [[Fe/H]], even if they have the same galaxy mass. This may result from galaxy mergers, but no evidence is found from presently available data to support the same origin for metallicity gradients, the scatters around the metallicity-mass relation, and dynamical disturbances. This may suggest that the scatters have their origin at the formation epoch of galaxies.Peer reviewe
Near-Infrared Imaging of Early-Type Galaxies IV. The Physical Origins of the Fundamental Plane Scaling Relations
The physical origins of the Fundamental Plane (FP) scaling relations are
investigated for early-type galaxies observed at optical and near-infrared
wavelengths. The slope for the FP is shown to increase systematically with
wavelength from the U-band through the K-band. A distance-independent
construction of the observables is described which provides an accurate
measurement of the change in the FP slope between any pair of bandpasses. The
variation of the FP slope with wavelength is strong evidence of systematic
variations in stellar content along the elliptical galaxy sequence. The
intercept of the diagnostic relationship between log(D_K/D_V) and log(sigma_0)
shows no significant dependence on environment within the uncertainties of the
Galactic extinction corrections, demonstrating the universality of the stellar
populations contributions at the level of Delta(V-K)=0.03 mag to the zero-point
of the global scaling relations.
Several other constraints on the properties of early-type galaxies --- the
slope of the Mg_2-sigma_0 relation, the effects of stellar populations
gradients, and deviations of early-type galaxies from a dynamically homologous
family --- are included to construct an empirical, self-consistent model which
provides a complete picture of the underlying physical properties which are
varying along the early-type galaxy sequence. This empirical approach
demonstrates that there are significant systematic variations in both age and
metallicity along the elliptical galaxy sequence, and that a small, but
systematic, breaking of dynamical homology (or a similar, wavelength
independent effect) is required. Predictions for the evolution of the slope of
the FP with redshift are described. [abriged]Comment: to appear in The Astronomical Journal; 40 pages, including 10
Postscript figures and 3 tables; uses AAS LaTeX style file
The epochs of early-type galaxy formation as a function of environment
The aim of this paper is to set constraints of the epochs of early-type
galaxy formation through the 'archaeology' of the stellar populations in local
galaxies. Using our models of absorption line indices that account for variable
abundance ratios, we derive the stellar population parameters of 124 early-type
galaxies in high and low density environments. We find that all three
parameters age, metallicity, and alpha/Fe ratio are correlated with velocity
dispersion. We further find evidence for an influence of the environment on the
stellar population properties. Massive early-type galaxies in low-density
environments appear on average ~2 Gyrs younger and slightly more metal-rich
than their counterparts in high density environments. No offsets in the
alpha/Fe ratios, instead, are detected. We translate the derived ages and
alpha/Fe ratios into star formation histories. We show that most star formation
activity in early-type galaxies is expected to have happened between redshifts
3 and 5 in high density and between redshifts 1 and 2 in low density
environments. We conclude that at least 50 per cent of the total stellar mass
density must have already formed at z 1, in good agreement with observational
estimates of the total stellar mass density as a function of redshift. Our
results suggest that significant mass growth in the early-type galaxy
population below z 1 must be restricted to less massive objects, and a
significant increase of the stellar mass density between redshifts 1 and 2
should be present caused mainly by the field galaxy population. The results of
this paper further imply vigorous star formation episodes in massive objects at
z 2-5 and the presence of evolved ellipticals around z 1, both observationally
identified as SCUBA galaxies and EROs.Comment: 20 pages, 10 figures, plus appendix, accepted by Ap
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