937 research outputs found
On the robustness of the H Lick index as a cosmic clock in passive early-type galaxies
We examine the H Lick index in a sample of massive () and passive early-type galaxies extracted from SDSS at
z<0.3, in order to assess the reliability of this index to constrain the epoch
of formation and age evolution of these systems. We further investigate the
possibility of exploiting this index as "cosmic chronometer", i.e. to derive
the Hubble parameter from its differential evolution with redshift, hence
constraining cosmological models independently of other probes. We find that
the H strength increases with redshift as expected in passive evolution
models, and shows at each redshift weaker values in more massive galaxies.
However, a detailed comparison of the observed index with the predictions of
stellar population synthesis models highlights a significant tension, with the
observed index being systematically lower than expected. By analyzing the
stacked spectra, we find a weak [NII] emission line (not
detectable in the single spectra) which anti-correlates with the mass, that can
be interpreted as a hint of the presence of ionized gas. We estimated the
correction of the H index by the residual emission component exploiting
different approaches, but find it very uncertain and model-dependent. We
conclude that, while the qualitative trends of the observed H-z
relations are consistent with the expected passive and downsizing scenario, the
possible presence of ionized gas even in the most massive and passive galaxies
prevents to use this index for a quantitative estimate of the age evolution and
for cosmological applications.Comment: 20 pages, 11 figures, 1 table. Accepted for publication in MNRAS Main
Journa
Pure Luminosity Evolution models for faint field galaxy samples
We have examined a set of pure luminosity evolution (PLE) models in order to
explore up to what extent the rapidly increasing observational constraints from
faint galaxy samples can be understood in this simple framework. We find that a
PLE model, in which galaxies evolve mildly in time even in the rest frame UV,
can reproduce most of the observed properties of faint galaxies assuming an
open () universe. In particular, such a model is able to fit
reasonably well the number counts in the , and bands, as
well as the colour and redshift distributions derived from most of the existing
samples. The most significant discrepancy between the predictions of this model
and the data is the distribution of faint -selected galaxies.
Significantly worse fits are obtained with PLE models for the theoretically
attractive value of , although a simple number luminosity evolution
model with a significant amount of merger events fits the data also in this
cosmology.Comment: 15 pages, plain tex (insert encapsulated postscript figures), plus an
extra figure Fig3c.ps and the tex-macro mn.tex uuencoded, gzipp'ed tar file
-- accepted by MNRA
Extending higher dimensional quasi-cocycles
Let G be a group admitting a non-elementary acylindrical action on a Gromov
hyperbolic space (for example, a non-elementary relatively hyperbolic group, or
the mapping class group of a closed hyperbolic surface, or Out(F_n) for n>1).
We prove that, in degree 3, the bounded cohomology of G with real coefficients
is infinite-dimensional. Our proof is based on an extension to higher degrees
of a recent result by Hull and Osin. Namely, we prove that, if H is a
hyperbolically embedded subgroup of G and V is any G-module, then any n-quasi
cocycle on H with values in V may be extended to G. Also, we show that our
extensions detect the geometry of the embedding of hyperbolically embedded
subgroups, in a suitable sense.Comment: Minor revisions. This version has been accepted for publication by
the Journal of Topolog
Listening to galaxies tuning at z ~ 2.5 - 3.0: The first strikes of the Hubble fork
We investigate the morphological properties of 494 galaxies selected from the
GMASS survey at z>1, primarily in their optical rest frame, using HST images,
from the CANDELS survey. We propose that the Hubble sequence of galaxy
morphologies takes shape at redshift 2.5<z<3. The fractions of both ellipticals
and disks decrease with increasing lookback time at z>1, such that at redshifts
z=2.5-2.7 and above, the Hubble types cannot be identified, and most galaxies
are classified as irregular. The quantitative morphological analysis shows
that, at 1<z<3, morphological parameters are not as effective in distinguishing
the different morphological Hubble types as they are at low redshift. No
significant morphological k-correction was found to be required for the Hubble
type classification, with some exceptions. In general, different morphological
types occupy the two peaks of the rest-frame (U-B) colour bimodality of
galaxies: most irregulars occupy the blue peak, while ellipticals are mainly
found in the red peak, though with some level of contamination. Disks are more
evenly distributed than either irregulars and ellipticals. We find that the
position of a galaxy in a UVJ diagram is related to its morphological type: the
"quiescent" region of the plot is mainly occupied by ellipticals and, to a
lesser extent, by disks. We find that only ~33% of all morphological
ellipticals in our sample are red and passively evolving galaxies. Blue
galaxies morphologically classified as ellipticals show a remarkable structural
similarity to red ones. Almost all irregulars have a star-forming galaxy
spectrum. In addition, the majority of disks show some sign of star-formation
activity in their spectra, though in some cases their red continuum is
indicative of old stellar populations. Finally, an elliptical morphology may be
associated with either passively evolving or strongly star-forming galaxies.Comment: 27 pages, 16 figures, 5 tables. "Morphological atlas" in the
appendix. Revised version accepted for publication in A&
A new photometric technique for the joint selection of star-forming and passive galaxies at 1.4<z<2.5
A simple two color selection based on B-, z-, and K- band photometry is
proposed for culling galaxies at 1.4<z<2.5 in K-selected samples and
classifying them as star-forming or passive systems. The method is calibrated
on the highly complete spectroscopic redshift database of the K20 survey,
verified with simulations and tested on other datasets. Requiring
BzK=(z-K)-(B-z)>-0.2 (AB) allows to select actively star-forming galaxies at
z>1.4, independently on their dust reddening. Instead, objects with BzK<-0.2
and (z-K)>2.5 (AB) colors include passively evolving galaxies at z>1.4, often
with spheroidal morphologies. Simple recipes to estimate the reddening, SFRs
and masses of BzK-selected galaxies are derived, and calibrated on K<20
galaxies. Based on their UV (reddening-corrected), X-ray and radio
luminosities, the BzK-selected star-forming galaxies with K<20 turn out to have
average SFR ~ 200 Msun yr^-1, and median reddening E(B-V)~0.4. Besides missing
the passively evolving galaxies, the UV selection appears to miss some relevant
fraction of the z~2 star-forming galaxies with K<20, and hence of the
(obscured) star-formation rate density at this redshift. The high SFRs and
masses add to other existing evidence that these z=2 star-forming galaxies may
be among the precursors of z=0 early-type galaxies. Theoretical models cannot
reproduce simultaneously the space density of both passively evolving and
highly star-forming galaxies at z=2. In view of Spitzer Space Telescope
observations, an analogous technique based on the RJL photometry is proposed to
complement the BzK selection and to identify massive galaxies at 2.5<z<4.0.
These color criteria should help in completing the census of the stellar mass
and of the star-formation rate density at high redshift (abridged).Comment: 19 pages, 17 figures, to appear on ApJ (20 December 2004 issue
Time to be responsive in the process industry: a literature-based analysis of trends of change, solutions and challenges
The current uncertain and volatile business context is challenging firms worldwide, leading to the need to be responsive at a competitive cost. This trend is so substantial that it even affects industries traditionally competing in rather stable contexts, such as the process industry. Although the process industry includes multiple sectors with different technologies and processes, these share several aspects that make the industry as a whole distinctive to the discrete manufacturing industry. Based on a literature review, this study identifies and describes trends leading the process industry to the need for responsiveness, corresponding solutions to accommodate the need, and related challenges hindering the industrialization and diffusion of solutions in this industry. This study shows that trends, such as the uncertainty and volatility of market requirements, are challenging the process industry to develop reconfigurability solutions across multiple production levels. The development of reconfigurability solutions is hindered by modularity, integrability, co-ordination and collaboration challenges
On the Determination of Star Formation Rates in Evolving Galaxy Populations
The redshift dependence of the luminosity density in certain wavebands (e.g.
UV and H-alpha) can be used to infer the history of star formation in the
populations of galaxies producing this luminosity. This history is a useful
datum in studies of galaxy evolution. It is therefore important to understand
the errors that attend the inference of star formation rate densities from
luminosity densities. This paper explores the self-consistency of star
formation rate diagnostics by reproducing commonly used observational
procedures in a model with known galaxy populations, evolutionary histories and
spectral emission properties. The study reveals a number of potential sources
of error in the diagnostic processes arising from the differential evolution of
different galaxy types. We argue that multi-wavelength observations can help to
reduce these errors.Comment: 13 pages (including 5 encapsulated postscript figures), aastex,
accepted for publication in Ap
New Clues on the Nature of Extremely Red Galaxies
We present near-infrared VLT-UT1+ISAAC spectroscopy of a sample of 9
extremely red galaxies (ERGs) with R-K>5 and K<19.0. Neither strong emission
lines (F_lim<1-5 10^{-16} erg s^{-1}cm^{-2}) nor continuum breaks are detected.
From near-infrared spectrophotometry, complemented with broad-band optical
and near-IR photometry, we estimate ``spectro-photometric'' redshifts to be in
the range of 0.8<z_sphot<1.8. We derive upper limits on the star formation
rates in range of SFR<6-30h_50^{-2} M_solar yr^{-1}. Two of the observed ERGs
are dusty starburst candidates because they require strong dust reddening to
reproduce their global spectral energy distributions. The other ERGs are
consistent with being dustless old passively evolved spheroidals at z>0.8. We
discuss the general implications of our findings in relation with the problem
of the formation of early type galaxies.Comment: 6 pages, 2 figures. Astronomy & Astrophysics (Letters), in pres
LSD: Lyman-break galaxies Stellar populations and Dynamics. I: Mass, metallicity and gas at z~3.1
We present the first results of a project, LSD, aimed at obtaining
spatially-resolved, near-infrared spectroscopy of a complete sample of
Lyman-Break Galaxies at z~3. Deep observations with adaptive optics resulted in
the detection of the main optical lines, such as [OII], Hbeta and [OIII], which
are used to study sizes, SFRs, morphologies, gas-phase metallicities, gas
fractions and effective yields. Optical, near-IR and Spitzer/IRAC photometry is
used to measure stellar mass. We obtain that morphologies are usually complex,
with the presence of several peaks of emissions and companions that are not
detected in broad-band images. Typical metallicities are 10-50% solar, with a
strong evolution of the mass-metallicity relation from lower redshifts. Stellar
masses, gas fraction, and evolutionary stages vary significantly among the
galaxies, with less massive galaxies showing larger fractions of gas. In
contrast with observations in the local universe, effective yields decrease
with stellar mass and reach solar values at the low-mass end of the sample.
This effect can be reproduced by gas infall with rates of the order of the
SFRs. Outflows are present but are not needed to explain the mass-metallicity
relation. We conclude that a large fraction of these galaxies are actively
creating stars after major episodes of gas infall or merging.Comment: MNRAS, in pres
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