16 research outputs found
Revisiting the fossil group candidates UGC 842 and NGC 6034
We present a new insight on NGC 6034 and UGC 842, two groups of galaxies
previously reported in the literature as being fossil groups. The study is
based on optical photometry and spectroscopy obtained with the CTIO Blanco
telescope and Sloan Digital Sky Survey archival data. We find that NGC 6034 is
embedded in a large structure, dominated by three rich clusters and other small
groups. Its first and next four ranked galaxies have magnitude differences in
the r band and projected distances which violate the optical criteria to
classify it as a fossil group. We confirm that the UGC 842 group is a fossil
group, but with about half the velocity dispersion that is reported in previous
works. The velocity distribution of its galaxies reveals the existence of two
structures in its line of sight, one with sigmaV ~ 223 km/s and another with
sigmaV ~ 235 km/s, with a difference in velocity of ~820 km/s. The main
structure is dominated by passive galaxies, while these represent ~60% of the
second structure. The X-ray temperature for the intragroup medium of a group
with such a velocity dispersion is expected to be kT ~0.5-1 keV, against the
observed value of kT ~1.9 keV reported in the literature. This result makes UGC
842 a special case among fossil groups because (1) it represents more likely
the interaction between two small groups, which warms the intragroup medium
and/or (2) it could constitute evidence that member galaxies lost energy in the
process of spiraling toward the group center, and decreased the velocity
dispersion of the system. As far as we know, UGC 842 is the first low-mass
fossil group studied in detail.Comment: 18 pages, 8 figures, published in A
Millimagnitude Photometry for Transiting Extrasolar Planetary Candidates IV: The Puzzle of the Extremely Red OGLE-TR-82 Primary Solved
We present precise new V, I, and K-band photometry for the planetary transit
candidate star OGLE-TR-82. Good seeing V-band images acquired with VIMOS
instrument at ESO VLT allowed us to measure V=20.6+-0.03 mag star in spite of
the presence of a brighter neighbour about 1" away. This faint magnitude
answers the question why it has not been possible to measure radial velocities
for this object. One transit of this star has been observed with GMOS-S
instrument of GEMINI-South telescope in i and g-bands. The measurement of the
transit allows us to verify that this is not a false positive, to confirm the
transit amplitude measured by OGLE, and to improve the ephemeris. The transit
is well defined in i-band light curve, with a depth of A_i=0.034 mag. It is
however, less well defined, but deeper (A_g=0.1 mag) in the g-band, in which
the star is significantly fainter. The near-infrared photometry obtained with
SofI array at the ESO-NTT yields K=12.2+-0.1 and V-K=8.4+-0.1, so red that it
is unlike any other transit candidate studied before. Due to the extreme nature
of this object, we have not yet been able to measure velocities for this star,
but based on the new data we consider two different possible configurations:(1)
a nearby M7V star, or (2) a blend with a very reddened distant red giant. The
nearby M7V dwarf hypothesis would give a radius for the companion of
R_p=0.3+-0.1 R_J, i.e. the size of Neptune. Quantitative analysis of near-IR
spectroscopy finally shows that OGLE-TR-82 is a distant, reddened metal poor
early K giant. This result is confirmed by direct comparison with stellar
templates that gives the best match for a K3III star. Therefore, we discard the
planetary nature of the companion. Based on all the new data, we conclude that
this system is a main-sequence binary blended with a background red giant.Comment: 26 pages, 9 figures, ApJ accepte
Star formation outside the elliptical galaxy NGC2865
We have searched for young stellar complexes\ud
around the elliptical galaxy NGC2865.\ud
We find them in a ring of HI around the\ud
galaxy. Using the Multi-Slit Imaging Spectroscopy\ud
Technique (MSIS), we detected a total\ud
of seven Hα emitters in the south part of\ud
the tidal tail of the galaxy NGC2865. These\ud
regions are young sources with stellar masses\ud
in the range 4x103M⊙ to 2x106 M⊙, overlapping\ud
the location of the low density intergalactic\ud
HI gas, where the probability to form stars\ud
is expected to be low. For one of the intergalactic\ud
HII regions we estimated a solar oxygen\ud
abundance, 12 + log(O/H) ∼ 8.7. Given\ud
these proprieties, the regions are considered\ud
young star forming regions, born in-situ from\ud
a pre-enriched gas which has been removed\ud
from the host galaxies in a merger event
Gemini multi-conjugate adaptive optics system review II: Commissioning, operation and overall performance
The Gemini Multi-conjugate Adaptive Optics System - GeMS, a facility
instrument mounted on the Gemini South telescope, delivers a uniform, near
diffraction limited images at near infrared wavelengths (0.95 microns- 2.5
microns) over a field of view of 120 arc seconds. GeMS is the first sodium
layer based multi laser guide star adaptive optics system used in astronomy. It
uses five laser guide stars distributed on a 60 arc seconds square
constellation to measure for atmospheric distortions and two deformable mirrors
to compensate for it. In this paper, the second devoted to describe the GeMS
project, we present the commissioning, overall performance and operational
scheme of GeMS. Performance of each sub-system is derived from the
commissioning results. The typical image quality, expressed in full with half
maximum, Strehl ratios and variations over the field delivered by the system
are then described. A discussion of the main contributor to performance
limitation is carried-out. Finally, overheads and future system upgrades are
described.Comment: 20 pages, 11 figures, accepted for publication in MNRA
Gemini Frontier Fields: Wide-field Adaptive Optics Ks-band Imaging of the Galaxy Clusters MACS J0416.1-2403 and Abell 2744
International audienceWe have observed two of the six Frontier Fields galaxy clusters, MACS J0416.1-2403 and Abell 2744, using the Gemini Multi-Conjugate Adaptive Optics System (GeMS) and the Gemini South Adaptive Optics Imager (GSAOI). With 0." 08-0." 10 FWHM our data are nearly diffraction-limited over a 100\prime\prime × 100\prime\prime wide area. GeMS/GSAOI complements the Hubble Space Telescope (HST) redwards of 1.6 mum with twice the angular resolution. We reach a 5sigma depth of {{K}s}˜ 25.6 mag (AB) for compact sources. In this paper, we describe the observations, data processing, and initial public data release. We provide fully calibrated, co-added images matching the native GSAOI pixel scale as well as the larger plate scales of the HST release, adding to the legacy value of the Frontier Fields. Our work demonstrates that even for fields at high galactic latitude where natural guide stars are rare, current multi-conjugated adaptive optics technology at 8 m telescopes has opened a new window on the distant universe. Observations of a third Frontier Field, Abell 370, are planned
Gemini Frontier Fields: Wide-field Adaptive Optics Ks-band Imaging of the Galaxy Clusters MACS J0416.1-2403 and Abell 2744
International audienceWe have observed two of the six Frontier Fields galaxy clusters, MACS J0416.1-2403 and Abell 2744, using the Gemini Multi-Conjugate Adaptive Optics System (GeMS) and the Gemini South Adaptive Optics Imager (GSAOI). With 0." 08-0." 10 FWHM our data are nearly diffraction-limited over a 100\prime\prime × 100\prime\prime wide area. GeMS/GSAOI complements the Hubble Space Telescope (HST) redwards of 1.6 mum with twice the angular resolution. We reach a 5sigma depth of {{K}s}˜ 25.6 mag (AB) for compact sources. In this paper, we describe the observations, data processing, and initial public data release. We provide fully calibrated, co-added images matching the native GSAOI pixel scale as well as the larger plate scales of the HST release, adding to the legacy value of the Frontier Fields. Our work demonstrates that even for fields at high galactic latitude where natural guide stars are rare, current multi-conjugated adaptive optics technology at 8 m telescopes has opened a new window on the distant universe. Observations of a third Frontier Field, Abell 370, are planned