187 research outputs found
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&
Embodied conversations: Performance and the design of a robotic dancing partner
This paper reports insights gained from an exploration of performance-based techniques to improve the design of relationships between people and responsive machines. It draws on the Emergent Objects project and specifically addresses notions of embodiment as employed in the field of performance as a means to prototype and develop a robotic agent, SpiderCrab, designed to promote expressive interaction of device and human dancer, in order to achieve ‘performative merging’.
The significance of the work is to bring further knowledge of embodiment to bear on the development of human-technological interaction in general. In doing so, it draws on discursive and interpretive methods of research widely used in the field of performance but not yet obviously aligned with some orthodox paradigms and practices within design research. It also posits the design outcome as an ‘objectile’ in the sense that a continuous and potentially divergent iteration of prototypes is envisaged, rather than a singular final product. The focus on performative merging draws in notions of complexity and user experience.
Keywords:
Embodiment; Performance; Tacit Knowledge; Practice-As-Research; Habitus.</p
AGN-Host Galaxy Connection: Morphology and Colours of X-ray Selected AGN at z < 2
The connection between AGN and their host galaxies has been widely studied
over recent years, showing it to be of great importance for providing answers
to some fundamental questions related with AGN fueling mechanisms, their
formation and evolution. Using X-ray and one of the deepest broad-band optical
data sets, we studied morphology and colours in relationship with X-ray
properties for sources at redshifts z < 2.0, using a sample of 262 AGN in the
Subaru/XMM-Newton Deep Survey (SXDS). Morphological classification was obtained
using the galSVM code, one of the new methods useful especially when dealing
with high-redshift sources and low-resolution data. Colour-magnitude diagrams
were studied in relationship with redshift, morphology, X-ray obscuration, and
X-ray-to-optical flux ratio. Finally, the significance of different regions was
analysed on colour-magnitude diagrams, relating the observed properties of AGN
populations with some models of their formation and evolution.Comment: 24 pages, 19 figures, accepted for publication in
Astronomy&Astrophysic
On the buildup of massive early-type galaxies at z<~1. I- Reconciling their hierarchical assembly with mass-downsizing
Several studies have tried to ascertain whether or not the increase in
abundance of the early-type galaxies (E-S0a's) with time is mainly due to major
mergers, reaching opposite conclusions. We have tested it directly through
semi-analytical modelling, by studying how the massive early-type galaxies with
log(M_*/Msun)>11 at z~0 (mETGs) would have evolved backwards-in-time, under the
hypothesis that each major merger gives place to an early-type galaxy. The
study was carried out just considering the major mergers strictly reported by
observations at each redshift, and assuming that gas-rich major mergers
experience transitory phases of dust-reddened, star-forming galaxies (DSFs).
The model is able to reproduce the observed evolution of the galaxy LFs at
z<~1, simultaneously for different rest-frame bands (B, I, and K) and for
different selection criteria on color and morphology. It also provides a
framework in which apparently-contradictory results on the recent evolution of
the luminosity function (LF) of massive, red galaxies can be reconciled, just
considering that observational samples of red galaxies can be significantly
contaminated by DSFs. The model proves that it is feasible to build up ~50-60%
of the present-day mETG population at z<~1 and to reproduce the observational
excess by a factor of ~4-5 of late-type galaxies at 0.8<z<1 through the
coordinated action of wet, mixed, and dry major mergers, fulfilling global
trends that are in general agreement with mass-downsizing. The bulk of this
assembly takes place during ~1 Gyr elapsed at 0.8<z<1. The model suggests that
major mergers have been the main driver for the observational migration of mass
from the massive-end of the blue galaxy cloud to that of the red sequence in
the last ~8 Gyr.(Abridged)Comment: Accepted for publication in Astronomy & Astrophysics; 21 pages, 8
figures. Minor corrections included, shortened title. Results and conclusions
unchange
Evolution along the sequence of S0 Hubble types induced by dry minor mergers. I - Global bulge-to-disk structural relations
Recent studies have argued that galaxy mergers are not important drivers for
the evolution of S0's, on the basis that mergers cannot preserve the coupling
between the bulge and disk scale-lengths observed in these galaxies and the
lack of correlation of their ratio with the S0 Hubble type. We investigate
whether the remnants resulting from collision-less N-body simulations of
intermediate and minor mergers onto S0 galaxies evolve fulfilling global
structural relations observed between the bulges and disks of these galaxies.
Different initial bulge-to-disk ratios of the primary S0 have been considered,
as well as different satellite densities, mass ratios, and orbits of the
encounter. We have analysed the final morphology of the remnants in images
simulating the typical observing conditions of S0 surveys. We derive bulge+disk
decompositions of the final remnants to compare their global bulge-to-disk
structure with observations. We show that all remnants present undisturbed S0
morphologies according to the prescriptions of specialized surveys. The dry
intermediate and minor mergers induce noticeable bulge growth (S0c --> S0b and
S0b --> S0a), but affect negligibly to the bulge and disk scale-lengths.
Therefore, if a coupling between these two components exists prior to the
merger, the encounter does not break this coupling. This fact provides a simple
explanation for the lack of correlation between the ratio of bulge and disk
scale-lengths and the S0 Hubble type reported by observations. These models
prove that dry intermediate and minor mergers can induce global structural
evolution within the sequence of S0 Hubble types compatible with observations,
meaning that these processes should not be discarded from the evolutionary
scenarios of S0's just on the basis of the strong coupling observed between the
bulge and disk scale-lengths in these galaxies (abridged).Comment: Accepted for publication in Astronomy & Astrophysics, 12 pages, 11
figures. Definitive version after proofs. Corrected typo in the legend of
Fig. 2. Definitive version of Fig. 7 (pending copyright implications in the
previous version). Added references and corrected typo
Clumpy galaxies at z~0.6: kinematics, stability, and comparison with analogs at other redshifts
Distant clumpy galaxies are thought to be Jeans-unstable disks, and an
important channel for the formation of local galaxies, as suggested by recent
spatially-resolved kinematic observations of z~2 galaxies. I study the
kinematics of clumpy galaxies at z~0.6, and compare their properties with those
of counterparts at higher and lower redshifts. I selected a sample of 11 clumpy
galaxies at z~0.6 from the representative sample of emission line,
intermediate-mass galaxies IMAGES. Selection was based on rest-frame UV
morphology from HST/ACS images, mimicking the selection criteria commonly used
at higher redshifts. Their spatially-resolved kinematics were derived in the
frame of the IMAGES survey, using the VLT/FLAMES-GIRAFFE multi-integral field
spectrograph. For those showing large-scale rotation, I derived the Toomre Q
parameter, which characterizes the stability of their gaseous and stellar
phases. I find that the fraction of UV-selected clumpy galaxies at z~0.6 is
20+/-12%. Roughly half of them (45+/-30%) have complex kinematics inconsistent
with Jeans-unstable disks, while those in the remaining half (55+/-30%) show
large-scale rotations. The latter reveal a stable gaseous phase, but the
contribution of their stellar phase makes them globally unstable to clump
formation. Clumpy galaxies appear to be less unstable at z~0.6 than at z~2,
which could explain why the UV clumps tend to vanish in rest-frame optical
images of z~0.6 clumpy galaxies, conversely to z~2 clumpy galaxies, in which
the stellar phase can substantially fragment. This suggests that the former
correspond to patchy star-formation regions superimposed on a smoother mass
distribution. A possible and widespread scenario for driving clump formation
relies on instabilities by cold streams penetrating the dark matter halos where
clumpy galaxies inhabit. While such a gas accretion process is predicted to be
significant in massive, z~2 haloes, it is also predicted to be strongly
suppressed in similar, z~0.6 haloes, which could explain why lowest-z clumpy
galaxies appear to be driven by a different mechanism. Instead, I found that
interactions are probably the dominant driver leading to the formation of
clumpy galaxies at z1 clumpy galaxies remains
more uncertain. While cold flows could be an important driver at z~2, I also
argue that the observed and cumulative merger fraction between z=2 and z=3 is
large enough so that every z~2 galaxy might be the result of a merger that
occurred within their past 1 Gyr. I conclude that it is premature to rule out
mergers as a universal driver for galaxy evolution from z~2 down to z=0.Comment: Accepted for publication in MNRAS. 14 pages, 2 figures
The role of major mergers in the size growth of intermediate-mass spheroids
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society. © 2014 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.We study of the role of ‘major’ mergers (mass ratios >1: 4) in driving size growth in high-redshift (1 1010.7 M⊙) SGs at z < 1, then major mergers are also likely to play an important role in the size growth of at least some massive SGs in this mass range.Peer reviewe
Introducing ICT in schools in England : rationale and consequences
This paper provides a critical perspective on the attempts to promote the use of information and communication technology (ICT) in teaching and learning in England. It describes the rationale given for the introduction of ICT in terms of its potential to impact on educational standards to contribute to developing a curriculum which has more vocational/social significance and, more generally, to provide a catalyst for curriculum reform. The introduction of ICT is underpinned by the argument that schools should show a higher degree of correspondence with a wider world where the use of technology is pervasive. However, the claims made for ICT display excessive optimism and a sense of “inevitability.” ICT has had only a modest impact on schools, though impact has to be considered in the context of what can realistically be expected: the contribution of ICT has not been negligible. Future development in the use of ICT should be more measured and adaptive, taking account of the multidimensional nature of technology
Optical frequency comb technology for ultra-broadband radio-frequency photonics
The outstanding phase-noise performance of optical frequency combs has led to
a revolution in optical synthesis and metrology, covering a myriad of
applications, from molecular spectroscopy to laser ranging and optical
communications. However, the ideal characteristics of an optical frequency comb
are application dependent. In this review, the different techniques for the
generation and processing of high-repetition-rate (>10 GHz) optical frequency
combs with technologies compatible with optical communication equipment are
covered. Particular emphasis is put on the benefits and prospects of this
technology in the general field of radio-frequency photonics, including
applications in high-performance microwave photonic filtering, ultra-broadband
coherent communications, and radio-frequency arbitrary waveform generation.Comment: to appear in Laser and Photonics Review
The importance of minor-merger-driven star formation and black-hole growth in disk galaxies
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society. © 2014 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.We use the SDSS Stripe 82 to empirically quantify the stellar-mass and black-hole growth triggered by minor mergers in local spiral (disk) galaxies. Since major mergers destroy disks and create spheroids, morphologically disturbed spirals are likely remnants of minor mergers. Disturbed spirals exhibit enhanced specific star formation rates (SSFRs), the enhancement increasing in galaxies of 'later' morphological type (which have more gas and smaller bulges). By combining the SSFR enhancements with the fraction of time spirals spend in this 'enhanced' mode, we estimate that ~40% of the star formation in local spirals is directly triggered by minor mergers. The disturbed spirals also exhibit higher nuclear-accretion rates, implying that minor mergers enhance the growth rate of the central black hole. However, the specific accretion rate shows a lower enhancement than that in the SSFR, suggesting that the coupling between stellar-mass and black-hole growth is weak in minor-merger-driven episodes. Given the significant fraction of star formation that is triggered by minor mergers, this weaker coupling may contribute to the large intrinsic scatter observed in the stellar vs. black-hole mass relation in spirals. Combining our results with the star formation in early-type galaxies -- which is minor-merger-driven and accounts for ~14% of the star formation budget -- suggests that around half of the star formation activity in the local Universe is triggered by the minor-merger process.Peer reviewedFinal Published versio
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