547 research outputs found
Confirmation of two extended objects along the line of sight to PKS1830-211 with ESO-VLT adaptive optics imaging
We report on new high-resolution near-infrared images of the gravitationally
lensed radio source PKS1830-211, a quasar at z=2.507. These adaptive optics
observations, taken with the Very Large Telescope (VLT), are further improved
through image deconvolution. They confirm the presence of a second object along
the line of sight to the quasar, in addition to the previously known spiral
galaxy. This additional object is clearly extended in our images. However, its
faint luminosity does not allow to infer any photometric redshift. If this
galaxy is located in the foreground of PKS1830-211, it complicates the modeling
of this system and decreases the interest in using PKS1830-211 as a means to
determine H0 via the time delay between the two lensed images of the quasar.Comment: Accepted in A&A Letter
Optical/Near-Infrared Observations of GRO J1744-28
We present results from a series of optical (g and r-band) and near-infrared
(K'-band) observations of the region of the sky including the entire XTE and
ROSAT error circles for the ``Bursting Pulsar'' GRO J1744-28. These data were
taken with the Astrophysical Research Consortium's 3.5-m telescope at Apache
Point Observatory and with the 2.2-m telescope at the European Southern
Observatory. We see no new object, nor any significant brightening of any known
object, in these error circles, with the exception of an object detected in our
8 February 1996 image. This object has already been proposed as a near-infrared
counterpart to GRO J1744-28. While it is seen in only two of our ten 8 February
frames, there is no evidence that this is an instrumental artifact, suggesting
the possibility of near-infrared flares from GRO J1744-28, similar to those
that have been reported from the Rapid Burster. The distance to the ``Bursting
Pulsar'' must be more than 2 kpc, and we suggest that it is more than 7 kpc.Comment: 21 pages, 5 JPEG plates, 2 postscript figures. This paper will appear
in the May 1, 1997 edition of the Astrophysical Journa
The properties of the brightest Lyα emitters at z ∼ 5.7
We use deep Very Large Telescope (VLT) optical and near-infrared spectroscopy and deep Spitzer/IRAC imaging to examine the properties of two of the most luminous Lyα emitters at z= 5.7. The continuum redward of the Lyα line is clearly detected in both objects, thus facilitating a relatively accurate measurement (10-20 per cent uncertainties) of the observed rest-frame equivalent widths, which are around 160 Å for both objects. Through detailed modelling of the profile of the Lyα line with a 3D Monte Carlo radiative transfer code, we estimate the intrinsic rest-frame equivalent width of Lyα and find values that are around 300 Å, which is at the upper end of the range allowed for very young, moderately metal-poor star-forming galaxies. However, the uncertainties are large and values as high as 700 Å are permitted by the data. Both Lyα emitters are detected at 3.6 m in deep images taken with the Spitzer Space Telescope. We use these measurements, the measurement of the continuum redward of Lyα and other photometry to constrain the spectral energy distributions of these very luminous Lyα emitters and to compare them with three similar Lyα emitters from the literature. The contribution from nebular emission is included in our models: excluding it results in significantly higher masses. Four of the five Lyα emitters have masses of the order of ∼109 M⊙ and fairly high specific star formation rates (≳10-100 Gyr−1). While our two Lyα emitters appear similar in terms of the observed Lyα rest-frame equivalent width, they are quite distinct from each other in terms of age, mass and star formation history. Evidence for dust is found in all objects, and emission from nebular lines often makes a dominant contribution to the rest-frame 3.6 m flux. Rich in emission lines, these objects are prime targets for the next generation of extremely large telescopes, the James Webb Space Telescope (JWST) and the Atacama Large Millimeter Array (ALMA
Faint K Selected Galaxy Correlations and Clustering Evolution
Angular and spatial correlations are measured for K-band--selected galaxies,
248 having redshifts, 54 with z>1, in two patches of combined area 27 arcmin^2.
The angular correlation for K<=21.5 mag is (theta/1.4+/-0.19 arcsec
e^{+/-0.1})^{-0.8}. From the redshift sample we find that the real-space
correlation, calculated with q_0=0.1, of M_K<=-23.5 mag galaxies (k-corrected)
is \xi(r) = (r/2.9e^{+/-0.12}1/h Mpc)^{-1.8} at a mean z= 0.34,
(r/2.0e^{+/-0.15}1/h Mpc)^{-1.8} at z= 0.62, (r/1.4e^{+/-0.15}1/h Mpc)^{-1.8}
at z= 0.97, and (r/1.0e^{+/-0.2}1/h Mpc)^{-1.8} at z= 1.39, the last being a
formal upper limit for a blue-biased sample. In general, these are more
correlated than optically selected samples in the same redshift ranges. Over
the interval 0.32 AB
mag, have \xi(r)=(r/2.4e^{+/-0.14}1/h Mpc)^{-1.8} whereas bluer galaxies, which
have a mean B of 23.7 mag and mean [OII] equivalent width W_{eq} = 41=\AA, are
very weakly correlated, with \xi(r)=(r/0.9e^{+/-0.22}1/h Mpc)^{-1.8}. For our
measured growth rate of clustering, this blue population, if non-merging, can
grow only into a low-redshift population less luminous than 0.4L_\ast. The
cross-correlation of low- and high-luminosity galaxies at z=0.6 appears to have
an excess in the correlation amplitude within 100/h kpc. The slow redshift
evolution is consistent with these galaxies tracing the mass clustering in low
density, Omega= 0.2, relatively unbiased, sigma_8=0.8, universe, but cannot yet
exclude other possibilities.Comment: to be published in the Aug 1 ApJ, 20 pages as a uuencoded postscript
file Postscript with all figures is available at
http://manaslu.astro.utoronto.ca/~carlberg/paper
K-Band Galaxy Counts in the South Galactic Pole Region
We present new K-band galaxy number counts from K=13 to 20.5 obtained from
-band surveys in the south galactic pole region, which cover 180.8
arcmin to a limiting magnitude of K=19, and 2.21 arcmin to K=21.
These are currently the most precise K-band galaxy counts at
because the area of coverage is largest among the existing surveys for this
magnitude range.
The completeness and photometry corrections are estimated from the recovery
of simulated galaxy and stellar profiles added to the obtained field image.
Many simulations were carried out to construct a probability matrix which
corrects the galaxy counts at the faint-end magnitudes of the surveys so the
corrected counts can be compared with other observations.
The K-band star counts in the south galactic pole region to are
also presented for use to constrain the vertical structure of the Galaxy.Comment: accepted for publication in ApJ. 26 pages with 4 figures, and 2
plates are not included. All documents and figures can be retrieved from
http://merope.mtk.nao.ac.jp/~minezaki/mine_paper.htm
The Wide Field Imager Lyman-Alpha Search (WFILAS) for Galaxies at Redshift ~5.7: II. Survey Design and Sample Analysis
Context: Wide-field narrowband surveys are an efficient way of searching
large volumes of high-redshift space for distant galaxies.
Aims: We describe the Wide Field Imager Lyman-Alpha Search (WFILAS) over 0.74
sq. degree for bright emission-line galaxies at z~5.7.
Methods: WFILAS uses deep images taken with the Wide Field Imager (WFI) on
the ESO/MPI 2.2m telescope in three narrowband (70 A), one encompassing
intermediate band (220 A) and two broadband filters, B and R. We use the novel
technique of an encompassing intermediate band filter to exclude false
detections. Images taken with broadband B and R filters are used to remove low
redshift galaxies from our sample.
Results: We present a sample of seven Lya emitting galaxy candidates, two of
which are spectroscopically confirmed. Compared to other surveys all our
candidates are bright, the results of this survey complements other narrowband
surveys at this redshift. Most of our candidates are in the regime of bright
luminosities, beyond the reach of less voluminous surveys. Adding our
candidates to those of another survey increases the derived luminosity density
by ~30%. We also find potential clustering in the Chandra Deep Field South,
supporting overdensities discovered by other surveys. Based on a FORS2/VLT
spectrum we additionally present the analysis of the second confirmed Lya
emitting galaxy in our sample. We find that it is the brightest Lya emitting
galaxy (1 x 10^-16 erg s^-1 cm^-2) at this redshift to date and the second
confirmed candidate of our survey. Both objects exhibit the presence of a
possible second Lya component redward of the line.Comment: 15 pages, accepted for publication in A&A Replaced with published
versio
Ground-based follow-up observations of TRAPPIST-1 transits in the near-infrared
The TRAPPIST-1 planetary system is a favorable target for the atmospheric
characterization of temperate earth-sized exoplanets by means of transmission
spectroscopy with the forthcoming James Webb Space Telescope (JWST). A possible
obstacle to this technique could come from the photospheric heterogeneity of
the host star that could affect planetary signatures in the transit
transmission spectra. To constrain further this possibility, we gathered an
extensive photometric data set of 25 TRAPPIST-1 transits observed in the
near-IR J band (1.2 m) with the UKIRT and the AAT, and in the NB2090 band
(2.1 m) with the VLT during the period 2015-2018. In our analysis of these
data, we used a special strategy aiming to ensure uniformity in our
measurements and robustness in our conclusions. We reach a photometric
precision of (RMS of the residuals), and we detect no significant
temporal variations of transit depths of TRAPPIST-1 b, c, e, and g over the
period of three years. The few transit depths measured for planets d and f hint
towards some level of variability, but more measurements will be required for
confirmation. Our depth measurements for planets b and c disagree with the
stellar contamination spectra originating from the possible existence of bright
spots of temperature 4500 K. We report updated transmission spectra for the six
inner planets of the system which are globally flat for planets b and g and
some structures are seen for planets c, d, e, and f.Comment: accepted for publication in MNRA
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