368 research outputs found
The Physical Model in Action: Quality Control for X-Shooter
The data reduction pipeline for the VLT 2nd generation instrument X-Shooter
uses a physical model to determine the optical distortion and derive the
wavelength calibration. The parameters of this model describe the positions,
orientations, and other physical properties of the optical components in the
spectrograph. They are updated by an optimisation process that ensures the best
possible fit to arc lamp line positions. ESO Quality Control monitors these
parameters along with all of the usual diagnostics. This enables us to look for
correlations between inferred physical changes in the instrument and, for
example, instrument temperature sensor readings.Comment: 9 pages, 8 figures, style files included, Proc. of Observatory
Operations: Strategies, Processes, and Systems III, eds. D.R. Silva, A.B.
Peck, B.T. Soifer, SPIE 7737, 1
Optical and near-IR spectroscopy of candidate red galaxies in two z~2.5 proto-clusters
We present a spectroscopic campaign to follow-up red colour-selected
candidate massive galaxies in two high redshift proto-clusters surrounding
radio galaxies. We observed a total of 57 galaxies in the field of MRC0943-242
(z=2.93) and 33 in the field of PKS1138-262 (z=2.16) with a mix of optical and
near-infrared multi-object spectroscopy.
We confirm two red galaxies in the field of PKS1138-262 at the redshift of
the radio galaxy. Based on an analysis of their spectral energy distributions,
and their derived star formation rates from the H-alpha and 24um flux, one
object belongs to the class of dust-obscured star-forming red galaxies, while
the other is evolved with little ongoing star formation. This result represents
the first red and mainly passively evolving galaxy to be confirmed as companion
galaxies in a z>2 proto-cluster. Both red galaxies in PKS1138-262 are massive,
of the order of 4-6x10^11 M_Sol. They lie along a Colour-Magnitude relation
which implies that they formed the bulk of their stellar population around z=4.
In the MRC0943-242 field we find no red galaxies at the redshift of the radio
galaxy but we do confirm the effectiveness of our JHK_s selection of galaxies
at 2.3<z<3.1, finding that 10 out of 18 (56%) of JHK_s-selected galaxies whose
redshifts could be measured fall within this redshift range. We also
serendipitously identify an interesting foreground structure of 6 galaxies at
z=2.6 in the field of MRC0943-242. This may be a proto-cluster itself, but
complicates any interpretation of the red sequence build-up in MRC0943-242
until more redshifts can be measured.Comment: 17 pages, 14 figures, accepted for publication in Astronomy and
Astrophysic
Sensing and control of segmented mirrors with a pyramid wavefront sensor in the presence of spiders
The segmentation of the telescope pupil (by spiders & the segmented M4)
create areas of phase isolated by the width of the spiders on the wavefront
sensor (WFS), breaking the spatial continuity of the wavefront. The poor
sensitivity of the Pyramid WFS (PWFS) to differential piston leads to badly
seen and therefore uncontrollable differential pistons. In close loop
operation, differential pistons between segments will settle around integer
values of the average sensing wavelength. The differential pistons typically
range from one to ten times the sensing wavelength and vary rapidly over time,
leading to extremely poor performance. In addition, aberrations created by
atmospheric turbulence will contain large amounts of differential piston
between the segments. Removing piston contribution over each of the DM segments
leads to poor performance. In an attempt to reduce the impact of unwanted
differential pistons that are injected by the AO correction, we compare three
different approaches. We first limit ourselves to only use the information
measured by the PWFS, in particular by reducing the modulation. We show that
using this information sensibly is important but will not be sufficient. We
discuss possible ways of improvement by using prior information. A second
approach is based on phase closure of the DM commands and assumes the
continuity of the correction wavefront over the entire unsegmented pupil. The
last approach is based on the pair-wise slaving of edge actuators and shows the
best results. We compare the performance of these methods using realistic
end-to-end simulations. We find that pair-wise slaving leads to a small
increase of the total wavefront error, only adding between 20-45 nm RMS in
quadrature for seeing conditions between 0.45-0.85 arcsec. Finally, we discuss
the possibility of combining the different proposed solutions to increase
robustness.Comment: 12 pages, 15 figures, AO4ELT5 Proceedings, Adaptive Optics for
Extremely Large Telescopes 5, Conference Proceeding, Tenerife, Canary
Islands, Spain, June 25-30, 201
Polarization and kinematics in Cygnus A
From optical spectropolarimetry of Cygnus A we conclude that the scattering
medium in the ionization cones in Cygnus A is moving outward at a speed of
170+-34 km/s, and that the required momentum can be supplied by the radiation
pressure of an average quasar. Such a process could produce a structure
resembling the observed ionization cones, which are thought to result from
shadowing by a circumnuclear dust torus. We detect a polarized red wing in the
[O III] emission lines arising from the central kiloparsec of Cygnus A. This
wing is consistent with line emission created close to the boundary of the
broad-line region.Comment: 5 pages, accepted for publication in MNRAS letter
The Dragonfly Galaxy. III. Jet-brightening of a High-redshift Radio Source Caught in a Violent Merger of Disk Galaxies
The Dragonfly Galaxy (MRC 0152-209), the most infrared-luminous radio galaxy
at redshift z~2, is a merger system containing a powerful radio source and
large displacements of gas. We present kpc-resolution data from ALMA and the
VLA of carbon monoxide (6-5), dust, and synchrotron continuum, combined with
Keck integral-field spectroscopy. We find that the Dragonfly consists of two
galaxies with rotating disks that are in the early phase of merging. The radio
jet originates from the northern galaxy and brightens when it hits the disk of
the southern galaxy. The Dragonfly Galaxy therefore likely appears as a
powerful radio galaxy because its flux is boosted into the regime of high-z
radio galaxies by the jet-disk interaction. We also find a molecular outflow of
(1100 550) M/yr associated with the radio host galaxy, but not
with the radio hot-spot or southern galaxy, which is the galaxy that hosts the
bulk of the star formation. Gravitational effects of the merger drive a slower
and longer lived mass displacement at a rate of (170 40) M/yr,
but this tidal debris contain at least as much molecular gas mass as the much
faster outflow, namely M(H2) = (3 1) x 10 (alpha(CO)/0.8)
M. This suggests that both the AGN-driven outflow and mass transfer
due to tidal effects are important in the evolution of the Dragonfly system.
The Keck data show Ly emission spread across 100 kpc, and CIV and HeII
emission across 35 kpc, confirming the presence of a metal-rich and extended
circumgalactic medium previously detected in CO(1-0).Comment: Accepted for publication in ApJ (15 pages, 9 figures
Redshifts of Emission-Line Objects in the Hubble Ultra Deep Field
We present redshifts for 115 emission-line objects in the Hubble Ultra Deep Field identified through the Grism ACS Program for Extragalactic Science (GRAPES) project using the slitless grism spectroscopy mode of the Advanced Camera for Surveys on the Hubble Space Telescope (HST). The sample was selected by an emission-line search on all extracted one-dimensional GRAPES spectra. We identify the emission lines using line wavelength ratios where multiple lines are detected in the grism wavelength range (5800 Å ≲ λ ≲ 9600 Å), and using photometric redshift information where multiple lines are unavailable. We then derive redshifts using the identified lines. Our redshifts are accurate to δz ≈ 0.009, based on both statistical uncertainty estimates and comparison with published ground-based spectra. Over 40% of our sample is fainter than typical magnitude limits for ground-based spectroscopy (with i_(AB) > 25 mag). Such emission lines would likely remain undiscovered without our deep survey. The emission-line objects fall into three categories: (1) most are low- to moderate-redshift galaxies (0 ≤ z ≤ 2), including many actively star-forming galaxies with strong H II regions; (2) nine are high-redshift (4 ≤ z ≤ 7) Lyα emitters; and (3) at least three are candidate active galactic nuclei
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