235 research outputs found
Gemini Planet Imager Observational Calibrations VI: Photometric and Spectroscopic Calibration for the Integral Field Spectrograph
The Gemini Planet Imager (GPI) is a new facility instrument for the Gemini
Observatory designed to provide direct detection and characterization of
planets and debris disks around stars in the solar neighborhood. In addition to
its extreme adaptive optics and corona graphic systems which give access to
high angular resolution and high-contrast imaging capabilities, GPI contains an
integral field spectrograph providing low resolution spectroscopy across five
bands between 0.95 and 2.5 m. This paper describes the sequence of
processing steps required for the spectro-photometric calibration of GPI
science data, and the necessary calibration files. Based on calibration
observations of the white dwarf HD 8049B we estimate that the systematic error
in spectra extracted from GPI observations is less than 5%. The flux ratio of
the occulted star and fiducial satellite spots within coronagraphic GPI
observations, required to estimate the magnitude difference between a target
and any resolved companions, was measured in the -band to be in laboratory measurements and using
on-sky observations. Laboratory measurements for the , , and
filters are also presented. The total throughput of GPI, Gemini South and the
atmosphere of the Earth was also measured in each photometric passband, with a
typical throughput in -band of 18% in the non-coronagraphic mode, with some
variation observed over the six-month period for which observations were
available. We also report ongoing development and improvement of the data cube
extraction algorithm.Comment: 15 pages, 6 figures. Proceedings of the SPIE, 9147-30
Metallicity gradients in local field star-forming galaxies: Insights on inflows, outflows, and the coevolution of gas, stars and metals
We present metallicity gradients in 49 local field star-forming galaxies. We
derive gas-phase oxygen abundances using two widely adopted metallicity
calibrations based on the [OIII]/Hbeta, [NII]/Halpha and [NII]/[OII] line
ratios. The two derived metallicity gradients are usually in good agreement
within +/-0.14 dex/R25 (R25 is the B-band iso-photoal radius), but the
metallicity gradients can differ significantly when the ionisation parameters
change systematically with radius. We investigate the metallicity gradients as
a function of stellar mass (8<log(M*/Msun)<11) and absolute B-band luminosity
(-16 > MB > -22). When the metallicity gradients are expressed in dex/kpc, we
show that galaxies with lower mass and luminosity, on average, have steeper
metallicity gradients. When the metallicity gradients are expressed in dex/R25,
we find no correlation between the metallicity gradients, and stellar mass and
luminosity. We provide a local benchmark metallicity gradient of field
star-forming galaxies useful for comparison with studies at high redshifts. We
investigate the origin of the local benchmark gradient using simple chemical
evolution models and observed gas and stellar surface density profiles in
nearby field spiral galaxies. Our models suggest that the local benchmark
gradient is a direct result of the coevolution of gas and stellar disk under
virtually closed-box chemical evolution when the stellar-to-gas mass ratio
becomes high (>>0.3). These models imply low current mass accretion rates
(<0.3xSFR), and low mass outflow rates (<3xSFR) in local field star-forming
galaxies.Comment: 25 pages, 21 figures, accepted to MNRA
The M 31 double nucleus probed with OASIS and HST. A natural m=1 mode?
We present observations with the adaptive optics assisted integral field
spectrograph OASIS of the M 31 double nucleus at a spatial resolution better
than 0.5 arcsec FWHM. These data are used to derive the two-dimensional stellar
kinematics within the central 2 arcsec. Archival WFPC2/HST images are revisited
to perform a photometric decomposition of the nuclear region. We also present
STIS/HST kinematics obtained from the archive. The luminosity distribution of
the central region is well separated into the respective contributions of the
bulge, the nucleus including P1 and P2, and the so-called UV peak. We then show
that the axis joining P1 and P2, the two local surface brightness maxima, does
not coincide with the kinematic major-axis, which is also the major-axis of the
nuclear isophotes (excluding P1). We also confirm that the velocity dispersion
peak is offset by ~ 0.2 arcsec from the UV peak, assumed to mark the location
of the supermassive black hole. The newly reduced STIS/HST velocity and
dispersion profiles are then compared to OASIS and other published kinematics.
We find significant offsets with previously published data. Simple parametric
models are then built to successfully reconcile all the available kinematics.
We finally interpret the observations using new N-body simulations. The nearly
keplerian nuclear disk of M31 is subject to a natural m=1 mode, with a very
slow pattern speed (3 km/s/pc for M_BH = 7 10^7~\Msun), that can be maintained
during more than a thousand dynamical times. The resulting morphology and
kinematics of the mode can reproduce the M~31 nuclear-disk photometry and mean
stellar velocity, including the observed asymmetries. It requires a central
mass concentration and a cold disk system representing between 20 and 40% of
its mass. Abridged..Comment: 21 pages. accepted for publication in A&
Axisymmetric dynamical models for SAURON and OASIS observations of NGC 3377
We present a unique set of nested stellar kinematical maps of NGC 3377
obtained with the integral-field spectrographs OASIS and SAURON. We then
construct general axisymmetric dynamical models for this galaxy, based on the
Schwarzschild numerical orbit superposition technique applied to these
complementary measurements. We show how these two datasets constrain the mass
of the central massive object and the overall mass-to-light ratio of the galaxy
by probing the inner and outer regions respectively. The simultaneous use of
both datasets leads us to confirm the presence of a massive black hole with a
mass of M_{BH} = 7_{-5}^{+4} 10^{7} M_\sun (99.7% confidence level), with a
best-fit stellar mass-to-light ratio (for an assumed
edge-on inclination).Comment: 15 pages, 14 figures. Accepted for publication in A&A (original fig.
layout, letterpaper
On-sky speckle nulling demonstration at small angular separation with SCExAO
This paper presents the first on-sky demonstration of speckle nulling, which
was achieved at the Subaru Telescope in the context of the Subaru Coronagraphic
Extreme Adaptive Optics (SCExAO) Project. Despite the absence of a high-order
high-bandwidth closed-loop AO system, observations conducted with SCExAO show
that even in poor-to-moderate observing conditions, speckle nulling can be used
to suppress static and slow speckles even in the presence of a brighter dynamic
speckle halo, suggesting that more advanced high-contrast imaging algorithms
developed in the laboratory can be applied to ground-based systems.Comment: 5 figures, accepted for publication by PAS
Gas accretion as the origin of chemical abundance gradients in distant galaxies
It has recently been suggested that galaxies in the early Universe can grow
through the accretion of cold gas, and that this may have been the main driver
of star formation and stellar mass growth. Because the cold gas is essentially
primordial, it has a very low abundance of elements heavier than helium
(metallicity). As it is funneled to the centre of a galaxy, it will lead the
central gas having an overall lower metallicity than gas further from the
centre, because the gas further out has been enriched by supernovae and stellar
winds, and not diluted by the primordial gas. Here we report chemical
abundances across three rotationally-supported star-forming galaxies at z~3,
only 2 Gyr after the Big Bang. We find an 'inverse' gradient, with the central,
star forming regions having a lower metallicity than less active ones, opposite
to what is seen in local galaxies. We conclude that the central gas has been
diluted by the accretion of primordial gas, as predicted by 'cold flow' models.Comment: To Appear in Nature Oct 14, 2010; Supplementary Information included
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A Magnified View of the Kinematics and Morphology of RCSGA 032727-132609: Zooming in on a Merger at z=1.7
We present a detailed analysis of multi-wavelength HST/WFC3 imaging and
Keck/OSIRIS near-IR AO-assisted integral field spectroscopy for a highly
magnified lensed galaxy at z=1.70. This young starburst is representative of
UV-selected star-forming galaxies (SFG) at z~2 and contains multiple individual
star-forming regions. Due to the lensing magnification, we can resolve spatial
scales down to 100pc in the source plane of the galaxy. The velocity field
shows disturbed kinematics suggestive of an ongoing interaction, and there is a
clear signature of a tidal tail. We constrain the age, reddening, SFR and
stellar mass of the star-forming clumps from SED modelling of the WFC3
photometry and measure their H-alpha luminosity, metallicity and outflow
properties from the OSIRIS data. With strong star formation driven outflows in
four clumps, RCSGA0327 is the first high redshift SFG at stellar mass <10^10
M_sun with spatially resolved stellar winds. We compare the H-alpha
luminosities, sizes and dispersions of the star-forming regions to other high-z
clumps as well as local giant HII regions and find no evidence for increased
clump star formation surface densities in interacting systems, unlike in the
local Universe. Spatially resolved SED modelling unveils an established stellar
population at the location of the largest clump and a second mass concentration
near the edge of the system which is not detected in H-alpha emission. This
suggests a picture of an equal-mass mixed major merger, which has not triggered
a new burst of star formation or caused a tidal tail in the gas-poor component.Comment: 22 pages, 16 figures, accepted to Ap
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