43 research outputs found
Dynamics of embedded bars and the connection with AGN. I. ISAAC/VLT stellar kinematics
We present new stellar kinematical profiles of four galaxy hosts of active galactic nuclei, using the CO bandhead around 2.3 micron with the ISAAC/VLT spectrograph. We find that the nuclear bars or discs, embedded in large-scale primary bars, have all a decoupled kinematics, in the sense that the maximum of the rotational velocity occurs in the nuclear region. In three cases (NGC 1097, NGC 1808 and NGC 5728), the velocity dispersion displays a significant drop at the nucleus, a rarely observed phenomenon. We also detect kinematical asymmetries (m=1 mode) along the nuclear bar major-axis of NGC 1808 and NGC 5728, dynamical counterparts of corresponding asymmetries in the surface brightness. We have derived simple dynamical models in an attempt to fit the kinematics of each galaxy and reconstruct the full velocity field. For all four targets, the fits are good, and confirm the presence of the decoupled nuclear components. These models cannot however reproduce the observed central drop in the dispersion. We suggest that this drop is due to a transient cold nuclear disc, fuelled by gas inflow along the bar, that has recently formed new stars
The Nearby Supernova Factory
The Nearby Supernova Factory (SNfactory) is an ambitious project to find and
study in detail approximately 300 nearby Type Ia supernovae (SNe~Ia) at
redshifts 0.03<z<0.08. This program will provide an exceptional data set of
well-studied SNe in the nearby smooth Hubble flow that can be used as
calibration for the current and future programs designed to use SNe to measure
the cosmological parameters. The first key ingredient for this program is a
reliable supply of Hubble-flow SNe systematically discovered in unprecedented
numbers using the same techniques as those used in distant SNe searches. In
2002, 35 SNe were found using our test-bed pipeline for automated SN search and
discovery. The pipeline uses images from the asteroid search conducted by the
Near Earth Asteroid Tracking group at JPL. Improvements in our subtraction
techniques and analysis have allowed us to increase our effective SN discovery
rate to ~12 SNe/month in 2003.Comment: 7 pages, 3 figures to be published in New Astronomy Review
A companion to a quasar at redshift 4.7
There is a growing consensus that the emergence of quasars at high redshifts
is related to the onset of galaxy formation, suggesting that the detection of
concentrations of gas accompanying such quasars should provide clues about the
early history of galaxies. Quasar companions have been recently identified at
redshifts up to . Here we report observations of Lyman-
emission (a tracer of ionised hydrogen) from the companion to a quasar at
=4.702, corresponding to a time when the Universe was less than ten per cent
of its present age. We argue that most of the emission arises in a gaseous
nebula that has been photoionised by the quasar, but an additional component of
continuum light -perhaps quasar light scattered from dust in the companion
body, or emission from young stars within the nebula- appears necessary to
explain the observations. These observations may be indicative of the first
stages in the assembly of galaxy-sized structures.Comment: 8 pages, 4 figures, plain LaTeX. Accepted for publication in Natur
Atmospheric extinction properties above Mauna Kea from the Nearby Supernova Factory spectro-photometric data set
We present a new atmospheric extinction curve for Mauna Kea spanning
3200--9700 \AA. It is the most comprehensive to date, being based on some 4285
standard star spectra obtained on 478 nights spread over a period of 7 years
obtained by the Nearby SuperNova Factory using the SuperNova Integral Field
Spectrograph. This mean curve and its dispersion can be used as an aid in
calibrating spectroscopic or imaging data from Mauna Kea, and in estimating the
calibration uncertainty associated with the use of a mean extinction curve. Our
method for decomposing the extinction curve into physical components, and the
ability to determine the chromatic portion of the extinction even on cloudy
nights, is described and verified over the wide range of conditions sampled by
our large dataset. We demonstrate good agreement with atmospheric science data
obtain at nearby Mauna Loa Observatory, and with previously published
measurements of the extinction above Mauna Kea.Comment: 22 pages, 24 figures, 6 table
Standardizing Type Ia Supernova Absolute Magnitudes Using Gaussian Process Data Regression
We present a novel class of models for Type Ia supernova time-evolving
spectral energy distributions (SED) and absolute magnitudes: they are each
modeled as stochastic functions described by Gaussian processes. The values of
the SED and absolute magnitudes are defined through well-defined regression
prescriptions, so that data directly inform the models. As a proof of concept,
we implement a model for synthetic photometry built from the spectrophotometric
time series from the Nearby Supernova Factory. Absolute magnitudes at peak
brightness are calibrated to 0.13 mag in the -band and to as low as 0.09 mag
in the blueshifted -band, where the dispersion includes
contributions from measurement uncertainties and peculiar velocities. The
methodology can be applied to spectrophotometric time series of supernovae that
span a range of redshifts to simultaneously standardize supernovae together
with fitting cosmological parameters.Comment: 47 pages, 15 figures, accepted for publication by Astrophysical
Journa
Evidence of Environmental Dependencies of Type Ia Supernovae from the Nearby Supernova Factory indicated by Local H{\alpha}
(Abridged) We study the host galaxy regions in close proximity to Type Ia
supernovae (SNe Ia) to analyze relations between the properties of SN Ia events
and environments most similar to where their progenitors formed. We focus on
local H\alpha\ emission as an indicator of young environments. The Nearby
Supernova Factory has obtained flux-calibrated spectral timeseries for SNe Ia
using integral field spectroscopy, allowing the simultaneous measurement of the
SN and its immediate vicinity. For 89 SNe Ia we measure H\alpha\ emission
tracing ongoing star formation within a 1 kpc radius around each SN. This
constitutes the first direct study of the local environment for a large sample
of SNe Ia also having accurate luminosity, color and stretch measurements. We
find that SNe Ia with local H\alpha\ emission are redder by 0.036+/-0.017 mag,
and that the previously-noted correlation between stretch and host mass is
entirely driven by the SNe Ia coming from passive regions. Most importantly,
the mean standardized brightness for SNe Ia with local H\alpha\ emission is
0.094+/-0.031 mag fainter than for those without. This offset arises from a
bimodal structure in the Hubble residuals, that also explains the
previously-known host-mass bias. We combine this bimodality with the cosmic
star-formation rate to predict changes with redshift in the mean SN Ia
brightness and the host-mass bias. This change is confirmed using high-redshift
SNe Ia from the literature. These environmental dependences point to remaining
systematic errors in SNe Ia standardization. The observed brightness offset is
predicted to cause a significant bias in measurements of the dark energy
equation of state. Recognition of these effects offers new opportunities to
improve SNe Ia as cosmological probes - e.g. SNe Ia having local H\alpha\
emission are more homogeneous, having a brightness dispersion of 0.105+/-0.012
mag.Comment: accepted for publication in Section 3. Cosmology of A&A (The official
date of acceptance is 30/08/2013
Nearby Supernova Factory Observations of SN 2007if: First Total Mass Measurement of a Super-Chandrasekhar-Mass Progenitor
We present photometric and spectroscopic observations of SN 2007if, an
overluminous (M_V = -20.4), red (B-V = 0.16 at B-band maximum), slow-rising
(t_rise = 24 days) type Ia supernova in a very faint (M_g = -14.10) host
galaxy. A spectrum at 5 days past B-band maximum light is a direct match to the
super-Chandrasekhar-mass candidate SN Ia 2003fg, showing Si II and C II at
~9000 km/s. A high signal-to-noise co-addition of the SN spectral time series
reveals no Na I D absorption, suggesting negligible reddening in the host
galaxy, and the late-time color evolution has the same slope as the Lira
relation for normal SNe Ia. The ejecta appear to be well mixed, with no strong
maximum in I-band and a diversity of iron-peak lines appearing in
near-maximum-light spectra. SN2007 if also displays a plateau in the Si II
velocity extending as late as +10 days, which we interpret as evidence for an
overdense shell in the SN ejecta. We calculate the bolometric light curve of
the SN and use it and the \ion{Si}{2} velocity evolution to constrain the mass
of the shell and the underlying SN ejecta, and demonstrate that SN2007 if is
strongly inconsistent with a Chandrasekhar-mass scenario. Within the context of
a "tamped detonation" model appropriate for double-degenerate mergers, and
assuming no host extinction, we estimate the total mass of the system to be 2.4
+/- 0.2 solar masses, with 1.6 +/- 0.1 solar masses of nickel-56 and with
0.3-0.5 solar masses in the form of an envelope of unburned carbon/oxygen. Our
modeling demonstrates that the kinematics of shell entrainment provide a more
efficient mechanism than incomplete nuclear burning for producing the low
velocities typical of super-Chandrasekhar-mass SNeIa.Comment: 23 pages, 13 figures, 4 tables, emulateapj format; v2 fixed some
typos and added a reference; v3 included minor copy-editing changes + fixed
typos in Figure 9, Table 4; accepted to Ap
OASIS integral-field spectroscopy of the central kpc in 11 Seyfert 2 galaxies
We map narrow-line regions (NLRs) of 11 nearby Seyfert 2 galaxies with the
optical integral-field spectrograph OASIS mounted at CFHT. We model
emission-line profiles of 5 forbidden-line doublets and 2 Balmer lines,
correcting for the underlying stellar absorption by reconstructing stellar
spectra with synthetic evolutionary stellar population models. For each of the
11 targets, we present 2D maps of surface brightness in the observed emission
lines, diagnostic line intensity ratios, gas kinematics (mean line-of-sight
velocity and velocity dispersion), electron density, and interstellar
reddening, and we plot spatially resolved spectral-diagnostic diagrams. The
stellar data are represented by maps of mean line-of-sight (LOS) velocities and
of the relative mass fractions of the young stellar populations. The gas
velocity fields in 80% of the sample exhibit twisted S-shaped isovelocity
contours, which are signatures of non-circular orbits and indicate
non-axisymmetric gravitational potentials, gas motions out of the galactic
plane, or possible outflows and inflows. Based on the kinematic measurements,
we identified a possible nuclear ring or radial gas flow in NGC 262 (Mrk 348),
not reported before. Eight of the eleven observed objects exhibit strongly
asymmetric or multi-component emission-line profiles, in most cases confined to
an elongated region passing through the galactic centre, perpendicular to the
major axis of emission.Comment: 40 pages, 25 figure
SCALA: In situ calibration for integral field spectrographs
International audienceThe scientific yield of current and future optical surveys is increasingly limited by systematic uncertainties in the flux calibration. This is the case for Type Ia supernova (SN Ia) cosmology programs, where an improved calibration directly translates into improved cosmological constraints. Current methodology rests on models of stars. Here we aim to obtain flux calibration that is traceable to state-of-the-art detector-based calibration. We present the SNIFS Calibration Apparatus (SCALA), a color (relative) flux calibration system developed for the SuperNova Integral Field Spectrograph (SNIFS), operating at the University of Hawaii 2.2 m (UH 88) telescope. By comparing the color trend of the illumination generated by SCALA during two commissioning runs, and to previous laboratory measurements, we show that we can determine the light emitted by SCALA with a long-term repeatability better than 1%. We describe the calibration procedure necessary to control for system aging. We present measurements of the SNIFS throughput as estimated by SCALA observations. The SCALA calibration unit is now fully deployed at the UH\,88 telescope, and with it color-calibration between 4000 {\AA} and 9000 {\AA} is stable at the percent level over a one-year baseline
The ESO/VLT 3rd year Type Ia supernova data set from the Supernova Legacy Survey
We present 139 spectra of 124 Type Ia supernovae (SNeIa) that were observed
at the ESO/VLT during the first three years of the Canada-France-Hawai
Telescope (CFHT) Supernova Legacy Survey (SNLS). This homogeneous data set is
used to test for redshift evolution of SNeIa spectra, and will be used in the
SNLS 3rd year cosmological analyses.
Spectra have been reduced and extracted with a dedicated pipeline that uses
photometric information from deep CFHT Legacy Survey (CFHT-LS) reference images
to trace, at sub-pixel accuracy, the position of the supernova on the
spectrogram as a function of wavelength. It also separates the supernova and
its host light in 60% of cases. The identification of the supernova candidates
is performed using a spectrophotometric SNIa model.
A total of 124 SNeIa, roughly 50% of the overall SNLS spectroscopic sample,
have been identified using the ESO/VLT during the first three years of the
survey. Their redshifts range from z=0.149 to z=1.031. The average redshift of
the sample is z=0.63+/-0.02. This constitutes the largest SNIa spectral set to
date in this redshift range. The spectra are presented along with their
best-fit spectral SNIa model and a host model where relevant. In the latter
case, a host subtracted spectrum is also presented. We produce average spectra
for pre-maximum, maximum and post-maximum epochs for both z=0.5
SNeIa. We find that z<0.5 spectra have deeper intermediate mass element
absorptions than z>= 0.5 spectra. The differences with redshift are consistent
with the selection of brighter and bluer supernovae at higher redshift.Comment: Accepted for publication in Astronomy and Astrophysics, 103 pages, 11
main figures (+139 figures of VLT spectra