363 research outputs found
Seeking the Ultraviolet Ionizing Background at z~3 with the Keck Telescope
We describe the initial results of a deep long-slit emission line search for
redshifted (2.7<z<4.1) Lyman-alpha. These observations are used to constrain
the fluorescent Ly-alpha emission from the population of clouds whose
absorption produces the higher-column-density component of the Ly-alpha forest
in quasar spectra. We use the results to set an upper limit on the ultraviolet
ionizing background. Our spectroscopic data obtained with the Keck II telescope
at lambda/(Delta lambda FWHM)~2000 reveals no candidate Ly-alpha emission over
the wavelength range of 4500-6200 Ang along a 3 arcmin slit in a 5400 s
integration. Our 3 sigma upper bound on the mean intensity of the ionizing
background at the Lyman limit is J(nu 0) < 2E-21 erg/s/cm**2/Hz/sr for
2.7<z<3.1 (where we are most sensitive), assuming Lyman limit systems have
typical radii of 70 kpc (q_0=0.5, H_0=50 km/s/Mpc). This constraint is more
than an order of magnitude more stringent than any previously published direct
limit. However, it is still a factor of three above the ultraviolet background
level expected due to the integrated light of known quasars at z~3. This pilot
study confirms the conclusion of Gould \& Weinberg (1996) that integrations of
several hours on a 10-m class telescope should be capable of measuring J(nu 0)
at high redshift.Comment: 22 pages, 2 postscipt figures. Latex requires aaspp4.sty and epsf.sty
(included). Accepted for publication in the Astronomical Journal (Nov 1998
The First Dynamical Mass Measurement in the HR 8799 System
HR 8799 hosts four directly imaged giant planets, but none has a mass
measured from first principles. We present the first dynamical mass measurement
in this planetary system, finding that the innermost planet HR~8799~e has a
mass of . This mass results from combining
the well-characterized orbits of all four planets with a new astrometric
acceleration detection (5) from the Gaia EDR3 version of the
Hipparcos-Gaia Catalog of Accelerations. We find with 95\% confidence that
HR~8799~e is below , the deuterium-fusing mass limit. We
derive a hot-start cooling age of \,Myr for HR~8799~e that
agrees well with its hypothesized membership in the Columba association but is
also consistent with an alternative suggested membership in the
~Pictoris moving group. We exclude the presence of any additional
5- planets interior to HR~8799~e with semi-major axes
between 3-16\,au. We provide proper motion anomalies and a matrix
equation to solve for the mass of any of the planets of HR~8799 using only mass
ratios between the planets.Comment: Accepted to ApJ Letter
The stellar content of the halo of NGC 5907 from deep Hubble Space Telescope NICMOS imaging
We present H-band images obtained with NICMOS of a field 75'' (5kpc) above
the plane of the disk of the edge-on spiral galaxy NGC 5907. Ground-based
observations have shown that NGC 5907 has a luminous halo with a shallow radial
profile between 4 and 8 kpc that roughly traces the dark matter distribution of
the galaxy deduced from its rotation curve. Our NICMOS observations were
designed to resolve bright giants in the halo of NGC 5907 to constrain its
stellar composition with the goal of understanding its nature and origin. More
than 100 stars are expected in the NICMOS images if the dwarf-to-giant ratio in
the halo of NGC 5907 is consistent with that expected from standard stellar
initial mass functions, and if ground-based estimates of the distance to NGC
5907 and the integrated colors of its halo are correct. Instead we observe only
one candidate giant star. This apparent discrepancy can be resolved by assuming
either a significantly larger distance than suggested by several studies, or a
halo metallicity much lower than suggested by ground-based colors and as low as
metal-poor Galactic globular clusters. If previous distance and halo color
estimates for NGC 5907 are correct, our NICMOS results suggest that its
extended light is composed of stars that formed with an initial mass function
different than that observed locally, leading to a much higher ratio of dwarfs
to giants. We describe how these three possible explanations for the absence of
bright giants in our NICMOS images of the halo of NGC 5907 might be constrained
by future observations.Comment: Accepted for publication in the Astronomical Journal, 23 pages, 6
figure
The Nature of the Halo Population of NGC 5128 Resolved with NICMOS on the Hubble Space Telescope
We present the first infrared color-magnitude diagram (CMD) for the halo of a
giant elliptical galaxy. The CMD for the stars in the halo of NGC 5128
(Centaurus A) was constructed from HST NICMOS observations of the WFPC2 CHIP-3
field of Soria et al. (1996) to a 50% completeness magnitude limit of
[F160W]=23.8. This field is located at a distance of 08'50" (~9 kpc) south of
the center of the galaxy. The luminosity function (LF) shows a marked
discontinuity at [F160W]=20.0. This is 1-2 mag above the tip of the red giant
branch (TRGB) expected for an old population (~12 Gyr) at the distance modulus
of NGC 5128. We propose that the majority of stars above the TRGB have
intermediate ages (~2 Gyr), in agreement with the WFPC2 observations of Soria
et al. (1996). Five stars with magnitudes brighter than the LF discontinuity
are most probably due to Galactic contamination. The weighted average of the
mean giant branch color above our 50% completeness limit is
[F110W]-[F160W]=1.22+-0.08 with a dispersion of 0.19 mag. From our
artificial-star experiments we determine that the observed spread in color is
real, suggesting a real spread in metallicity. We estimate the lower and upper
bounds of the stellar metallicity range by comparisons with observations of
Galactic star clusters and theoretical isochrones. Assuming an old population,
we find that, in the halo field of NGC 5128 we surveyed, stars have
metallicities ranging from roughly 1% of solar at the blue end of the color
spread to roughly solar at the red end, with a mean of [Fe/H]=-0.76 and a
dispersion of 0.44 dex.Comment: Accepted for publication in AJ, 23 pages of text, 13 figures, uses
aastex v5.
Radial Velocity Survey for Planets around Young stars (RVSPY) A transiting warm super-Jovian planet around HD 114082, a young star with a debris disk
Aiming to detect planetary companions to young stars with debris disks via
the radial velocity method, we observed HD114082 during April 2018 - August
2022 as one of the targets of our RVSPY program (Radial Velocity Survey for
Planets around Young stars). We used the FEROS spectrograph, mounted to the
MPG/ESO 2.2 m telescope in Chile, to obtain high signal-to-noise spectra and
time series of precise radial velocities (RVs). Additionally, we analyzed
archival HARPS spectra and TESS photometric data. We used the CERES, CERES++
and SERVAL pipelines to derive RVs and activity indicators and ExoStriker for
the independent and combined analysis of the RVs and TESS photometry. We report
the discovery of a warm super-Jovian companion around HD114082 based on a
109.80.4 day signal in the combined RV data from FEROS and HARPS, and on
one transit event in the TESS photometry. The best-fit model indicates a
8.01.0 Mjup companion with a radius of 1.000.03 Rjup in an orbit with
a semi-major axis of 0.510.01 au and an eccentricity of 0.40.04. The
companions orbit is in agreement with the known near edge-on debris disk
located at about 28 au. HD114082b is possibly the youngest (156 Myr), and
one of only three younger than 100 Myr giant planetary companions for which
both their mass and radius have been determined observationally. It is probably
the first properly model-constraining giant planet that allows distinguishing
between hot and cold-start models. It is significantly more compatible with the
cold-start model.Comment: 10 pages, 9 figures, 5 tables; Accepted for publication in A&A
Letter
Characterization of Extragalactic 24micron Sources in the Spitzer First Look Survey
In this Letter, we present the initial characterization of extragalactic 24um
sources in the Spitzer First Look Survey (FLS) by examining their counterparts
at 8um and R-band. The color-color diagram of 24-to-8 vs. 24-to-0.7um is
populated with 18,734 sources brighter than the 3sigma flux limit of 110uJy,
over an area of 3.7sq.degrees. The 24-to-0.7um colors of these sources span
almost 4 orders of magnitudes, while the 24-to-8um colors distribute at least
over 2 orders of magnitudes. In addition to identifying ~30% of the total
sample with infrared quiescent, mostly low redshift galaxies, we also found
that: (1) 23% of the 24um sources (~1200/sq.degrees) have very red 24-to-8 and
24-to-0.7 colors and are probably infrared luminous starbursts with
L(IR)>3x10^(11)Lsun at z>1. In particular, 13% of the sample (660/sq.degrees)
are 24um detected only, with no detectable emission in either 8um or R-band.
These sources are the candidates for being ULIRGs at z>2. (2) 2% of the sample
(85/sq.degrees) have colors similar to dust reddened AGNs, like Mrk231 at
z~0.6-3. (3) We anticipate that some of these sources with extremely red colors
may be new types of sources, since they can not be modelled with any familiar
type of spectral energy distribution. We find that 17% of the 24um sources have
no detectable optical counterparts brighter than R limit of 25.5mag. Optical
spectroscopy of these optical extremely faint 24um sources would be very
difficult, and mid-infrared spectroscopy from the Spitzer would be critical for
understanding their physical nature (Abridged).Comment: Accepted for publication in ApJ (Spitzer Special Issue
Infrared Properties of Radio-Selected Submillimeter Galaxies in the Spitzer First Look Survey Verification Field
We report on submillimeter and infrared observations of 28 radio-selected
galaxies in the Spitzer First Look Survey Verification field (FLSV). All of the
radio-selected galaxies that show evidence for emission at 850um with SCUBA
have Spitzer counterparts at 24um, while only half of the radio-selected
galaxies without 850um emission have detectable counterparts at 24um. The data
show a wide range of infrared colors (S70/S24 < 5--30, S8/S3.6 < 0.3--4),
indicative of a mixture of infrared-warm AGN and cooler starburst dominated
sources. The galaxies showing 850um emission have Spitzer flux densities and
flux density ratios consistent with the range of values expected for
high-redshift (z=1--4) ultraluminous infrared galaxies.Comment: Accepted for Spitzer ApJS Special Edition, 12 pages including 4
figures and 1 tabl
Leptoquark pair production at the Fermilab Tevatron: Signal and backgrounds
We perform a Monte-Carlo simulation of scalar leptoquark pair production at
the Tevatron (energy =1.8 TeV and luminosity =100 pb^{-1}) with ISAJET. We also
investigate the dominant sources of Standard Model background: Z*jj, ZZ
production and heavy quark top-antitop. We find that the top-antitop background
is the most important except near the Z pole where the Z*jj background is
peaked. We also evaluate the signal-to-background ratio and find a discovery
reach of 130 GeV (170 GeV) for a branching ratio of B(LQ-> eq)=0.5 (B=1).Comment: 8 pages, 6 figures, latex (revtex
The Herschel Virgo Cluster Survey: VII. Dust in cluster dwarf elliptical galaxies
We use the Science Demonstration Phase data of the Herschel Virgo Cluster
Survey to search for dust emission of early-type dwarf galaxies in the central
regions of the Virgo Cluster as an alternative way of identifying the
interstellar medium.We present the first possible far-infrared detection of
cluster early-type dwarf galaxies: VCC781 and VCC951 are detected at the 10
sigma level in the SPIRE 250 micron image. Both detected galaxies have dust
masses of the order of 10^5 Msun and average dust temperatures ~20K. The
detection rate (less than 1%) is quite high compared to the 1.7% detection rate
for Hi emission, considering that dwarfs in the central regions are more Hi
deficient. We conclude that the removal of interstellar dust from dwarf
galaxies resulting from ram pressure stripping, harassment, or tidal effects
must be as efficient as the removal of interstellar gas.Comment: Letter accepted for publication in A&A (Herschel special issue
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