207 research outputs found
The 12 μm ISO-ESO-Sculptor and 24 μm Spitzer faint counts reveal a population of ULIRGs as dusty massive ellipticals: Evolution by types and cosmic star formation
Context. Multi-wavelength galaxy number counts provide clues to the nature of galaxy evolution. The interpretation per galaxy type of
the mid-IR faint counts obtained with ISO and Spitzer, consistent with the analysis of deep UV-optical-near IR galaxy counts, provide
new constraints on the dust and stellar emission. Discovering the nature of new populations, such as high redshift ultra-luminous
(≥10^(12) L_⊙) infrared galaxies (ULIRGs), is also crucial for understanding galaxy evolution at high redshifts.
Aims. We first present the faint galaxy counts at 12 μm from the catalogue of the ISO-ESO-Sculptor Survey (ISO-ESS) published in a
companion article (Seymour et al. 2007a, A&A, 475, 791). They go down to 0.31 mJy after corrections for incompleteness. We verify
the consistency with the existing ISO number counts at 15 μm. Then we analyse the 12 μm (ISO-ESS) and the 24 μm (Spitzer) faint
counts, to constrain the nature of ULIRGs, the cosmic star formation history and time scales for mass buildup.
Methods. We show that the “normal” scenarios in our evolutionary code PÉGASE, which had previously fitted the deep UV-opticalnear
IR counts, are unsuccessful at 12 μm and 24 μm. We thus propose a new ULIRG scenario adjusted to the observed cumulative
and differential 12 μm and 24 μm counts and based on observed 12 μm and 25 μm IRAS luminosity functions and evolutionary
optical/mid-IR colours from PÉGASE.
Results. We succeed in simultaneously modelling the typical excess observed at 12 μm, 15 μm (ISO), and 24 μm (Spitzer) in the
cumulative and differential counts by only changing 9% of normal galaxies (1/3 of the ellipticals) into ultra-bright dusty galaxies
evolving as ellipticals, and interpreted as distant ULIRGs. These objects present similarities with the population of radio-galaxy hosts
at high redshift. No number density evolution is included in our models even if minor starbursts due to galaxy interactions remain
compatible with our results.
Conclusions. Higher spectral and spatial resolution in the mid-IR, together with submillimeter observations using the future Herschel
observatory, will be useful to confirm these results
The 12 μm ISO-ESO-Sculptor and 24 μm Spitzer faint counts reveal a population of ULIRGs as dusty massive ellipticals: Evolution by types and cosmic star formation
Context. Multi-wavelength galaxy number counts provide clues to the nature of galaxy evolution. The interpretation per galaxy type of
the mid-IR faint counts obtained with ISO and Spitzer, consistent with the analysis of deep UV-optical-near IR galaxy counts, provide
new constraints on the dust and stellar emission. Discovering the nature of new populations, such as high redshift ultra-luminous
(≥10^(12) L_⊙) infrared galaxies (ULIRGs), is also crucial for understanding galaxy evolution at high redshifts.
Aims. We first present the faint galaxy counts at 12 μm from the catalogue of the ISO-ESO-Sculptor Survey (ISO-ESS) published in a
companion article (Seymour et al. 2007a, A&A, 475, 791). They go down to 0.31 mJy after corrections for incompleteness. We verify
the consistency with the existing ISO number counts at 15 μm. Then we analyse the 12 μm (ISO-ESS) and the 24 μm (Spitzer) faint
counts, to constrain the nature of ULIRGs, the cosmic star formation history and time scales for mass buildup.
Methods. We show that the “normal” scenarios in our evolutionary code PÉGASE, which had previously fitted the deep UV-opticalnear
IR counts, are unsuccessful at 12 μm and 24 μm. We thus propose a new ULIRG scenario adjusted to the observed cumulative
and differential 12 μm and 24 μm counts and based on observed 12 μm and 25 μm IRAS luminosity functions and evolutionary
optical/mid-IR colours from PÉGASE.
Results. We succeed in simultaneously modelling the typical excess observed at 12 μm, 15 μm (ISO), and 24 μm (Spitzer) in the
cumulative and differential counts by only changing 9% of normal galaxies (1/3 of the ellipticals) into ultra-bright dusty galaxies
evolving as ellipticals, and interpreted as distant ULIRGs. These objects present similarities with the population of radio-galaxy hosts
at high redshift. No number density evolution is included in our models even if minor starbursts due to galaxy interactions remain
compatible with our results.
Conclusions. Higher spectral and spatial resolution in the mid-IR, together with submillimeter observations using the future Herschel
observatory, will be useful to confirm these results
A Dynamic Discrete/Continuous Choice Model for Forward-Looking Agents Owning One or More Vehicles
During the last 40 years, a large number of studies have analyzed car holding and use behavior. Most of these ignore the dynamics of household and driver needs that very likely drive such decisions. Our work builds up on a disaggregate (compensatory) approach using revealed choices to address these dynamics. We develop a dynamic discrete/continuous choice model of car holding duration for forward-looking agents. We estimate this model using French panel survey data. Our findings indicate that a household’s time preference is a crucial element in car use and holding decisions
Assisted specification of discrete choice models
Determining appropriate utility specifications for discrete choice models is time-consuming and prone to errors. With the availability of larger and larger datasets, as the number of possible specifications exponentially grows with the number of variables under consideration, the analysts need to spend increasing amounts of time on searching for good models through trial-and-error, while expert knowledge is required to ensure these models are sound. This paper proposes an algorithm that aims at assisting modelers in their search. Our approach translates the task into a multi-objective combinatorial optimization problem and makes use of a variant of the variable neighborhood search algorithm to generate sets of promising model specifications. We apply the algorithm both to semi-synthetic data and to real mode choice datasets as a proof of concept. The results demonstrate its ability to provide relevant insights in reasonable amounts of time so as to effectively assist the modeler in developing interpretable and powerful models
Relative frequencies of supernovae versus properties of spiral hosts
In this work, we present an analysis of SNe number ratios in spiral galaxies
with different morphological subtypes, luminosities, sSFR, and metallicities,
to provide important information about the physical properties of the
progenitor populations.Comment: 2 pages, 1 figur
Supernovae and their host galaxies - II. The relative frequencies of supernovae types in spirals
We present an analysis of the relative frequencies of different supernova
(SN) types in spirals with various morphologies and in barred or unbarred
galaxies. We use a well-defined and homogeneous sample of spiral host galaxies
of 692 SNe from the Sloan Digital Sky Survey in different stages of
galaxy-galaxy interaction and activity classes of nucleus. We propose that the
underlying mechanisms shaping the number ratios of SNe types can be interpreted
within the framework of interaction-induced star formation, in addition to the
known relations between morphologies and stellar populations. We find a strong
trend in behaviour of the NIa/NCC ratio depending on host morphology, such that
early spirals include more Type Ia SNe. The NIbc/NII ratio is higher in a broad
bin of early-type hosts. The NIa/NCC ratio is nearly constant when changing
from normal, perturbed to interacting galaxies, then declines in merging
galaxies, whereas it jumps to the highest value in post-merging/remnant
galaxies. In contrast, the NIbc/NII ratio jumps to the highest value in merging
galaxies and slightly declines in post-merging/remnant subsample. The
interpretation is that the star formation rates and morphologies of galaxies,
which are strongly affected in the final stages of interaction, have an impact
on the number ratios of SNe types. The NIa/NCC (NIbc/NII) ratio increases
(decreases) from star-forming to active galactic nuclei (AGN) classes of
galaxies. These variations are consistent with the scenario of an
interaction-triggered starburst evolving into AGN during the later stages of
interaction, accompanied with the change of star formation and transformation
of the galaxy morphology into an earlier type.Comment: 14 pages, 9 figures, 16 tables, online dat
Supernovae and their host galaxies - IV. The distribution of supernovae relative to spiral arms
Using a sample of 215 supernovae (SNe), we analyze their positions relative
to the spiral arms of their host galaxies, distinguishing grand-design (GD)
spirals from non-GD (NGD) galaxies. We find that: (1) in GD galaxies, an offset
exists between the positions of Ia and core-collapse (CC) SNe relative to the
peaks of arms, while in NGD galaxies the positions show no such shifts; (2) in
GD galaxies, the positions of CC SNe relative to the peaks of arms are
correlated with the radial distance from the galaxy nucleus. Inside (outside)
the corotation radius, CC SNe are found closer to the inner (outer) edge. No
such correlation is observed for SNe in NGD galaxies nor for SNe Ia in either
galaxy class; (3) in GD galaxies, SNe Ibc occur closer to the leading edges of
the arms than do SNe II, while in NGD galaxies they are more concentrated
towards the peaks of arms. In both samples of hosts, the distributions of SNe
Ia relative to the arms have broader wings. These observations suggest that
shocks in spiral arms of GD galaxies trigger star formation in the leading
edges of arms affecting the distributions of CC SNe (known to have short-lived
progenitors). The closer locations of SNe Ibc vs. SNe II relative to the
leading edges of the arms supports the belief that SNe Ibc have more massive
progenitors. SNe Ia having less massive and older progenitors, have more time
to drift away from the leading edge of the spiral arms.Comment: 19 pages, 10 figures, 11 tables, resubmitted to MNRAS after
addressing referee's comment
Clustering of loose groups and galaxies from the Perseus--Pisces Survey
We investigate the clustering properties of loose groups in the
Perseus--Pisces redshift Survey (PPS). Previous analyses based on CfA and SSRS
surveys led to apparently contradictory results. We investigate the source of
such discrepancies, finding satisfactory explanations for them. Furthermore, we
find a definite signal of group clustering, whose amplitude exceeds the
amplitude of galaxy clustering (,
for the most significant case; distances are
measured in \hMpc). Groups are identified with the adaptive
Friends--Of--Friends (FOF) algorithms HG (Huchra \& Geller 1982) and NW
(Nolthenius \& White 1987), systematically varying all search parameters.
Correlation strenght is especially sensitive to the sky--link (increasing
for stricter normalization ), and to the (depth \mlim of the) galaxy
data. It is only moderately dependent on the galaxy luminosity function
, while it is almost insensitive to the redshift--link (both to
the normalization and to the scaling recipes HG or NW).Comment: 28 pages (LaTeX aasms4 style) + 5 Postscript figures ; ApJ submitted
on May 4th, 1996; group catalogs available upon request
([email protected]
Dinosaur tracks from the Kilmaluag Formation (Bathonian, Middle Jurassic) of Score Bay, Isle of Skye, Scotland, UK
Tracks of a juvenile theropod dinosaur with footprint lengths of between 2 and 9 cm as well as adults of the same ichnospecies with footprints of about 15–25 cm in length were found in the Bathonian (Middle Jurassic) Kilmaluag Formation of Score Bay, northwestern Trotternish Peninsula, Isle of Skye, Scotland, UK. Two footprint sizes occur together on the same bedding plane in the central portion of Score Bay, both in situ and on loose blocks. Another horizon containing footprints above this was also identified. The footprints from the lowest horizon were produced in a desiccated silty mud that was covered with sand. A close association of both adults and juveniles with similar travel direction indicated by the footprints may suggest post-hatching care in theropod dinosaurs. Other footprints, produced on a rippled sandy substrate, have been found on the slightly higher bedding plane at this locality. Loose blocks found 130 m to the northeast in the central part of Score Bay have not been correlated with any in situ sediments, but were preserved in a similar manner to those from the higher bedding plane. These tracks represent the youngest dinosaur remains yet found in Scotland
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