447 research outputs found
Diamonds on the Hat: Globular Clusters in The Sombrero Galaxy (M104)
Images from the HST ACS are used to carry out a new photometric study of the
globular clusters (GCs) in M104, the Sombrero galaxy. The primary focus of our
study is the characteristic distribution function of linear sizes (SDF) of the
GCs. We measure the effective radii for 652 clusters with PSF-convolved King
and Wilson dynamical model fits. The SDF is remarkably similar to those
measured for other large galaxies of all types, adding strong support to the
view that it is a "universal" feature of globular cluster systems.
We develop a more general interpretation of the size distribution function
for globular clusters, proposing that the shape of the SDF that we see today
for GCs is strongly influenced by the early rapid mass loss during their star
forming stage, coupled with stochastic differences from cluster to cluster in
the star formation efficiency (SFE) and their initial sizes. We find that the
observed SDF shape can be accurately predicted by a simple model in which the
protocluster clouds had characteristic sizes of pc and SFEs of
. The colors and luminosities of the M104 clusters show the
clearly defined classic bimodal form. The blue sequence exhibits a
mass/metallicity relation (MMR), following a scaling of heavy-element abundance
with luminosity of very similar to what has been found in most
giant elliptical galaxies. A quantitative self-enrichment model provides a good
first-order match to the data for the same initial SFE and protocluster size
that were required to explain the SDF. We also discuss various forms of the
globular cluster Fundamental Plane (FP) of structural parameters, and show that
useful tests of it can be extended to galaxies beyond the Local Group.Comment: In press for MNRA
Are the hosts of VLBI selected radio-AGN different to those of radio-loud AGN?
Recent studies have found that radio-AGN selected by radio-loudness show
little difference in terms of their host galaxy properties when compared to
non-AGN galaxies of similar stellar mass and redshift. Using new 1.4~GHz VLBI
observations of the COSMOS field we find that approximately 49\% of
high-mass (M 10 M), high luminosity (L
10 W~Hz) radio-AGN possess a VLBI detected counterpart. These
objects show no discernible bias towards specific stellar masses, redshifts or
host properties other than what is shown by the radio-AGN population in
general. Radio-AGN that are detected in VLBI observations are not special, but
form a representative sample of the radio-loud AGN population.Comment: 6 pages, 4 figures, lette
In Vitro Demonstration of Delayed Hypersensitivity in Patients with Berylliosis
To clarify immunopathological mechanisms in granulomatous hypersensitivity (GHR) to beryllium (Be), migration inhibitory factor (MIF) was assayed. Blood lymphocytes from three patients with GHR to Be and two normal persons were isolated and cultured with and without BeO or other antigens. Cell-free supernatants removed daily were dialyzed, lyophilized and assayed for MIF by measuring the area of migration of normal guinea pig peritoneal exudate cells out of capillary tubes within 24 hours after exposure to the supernatant. BeO added to sensitized lymphocytes produced supernatant that decreased migration, in contrast to supernatant from non-sensitized lymphocytes, indicating that BeO-sensitized lymphocytes cultured with Be elaborate a soluble factor, MIF, which correlates with delayed hypersensitivity and may play a role in granuloma formation. It may also prove useful in diagnosis of berylliosis
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
The Most Luminous z~9-10 Galaxy Candidates yet Found: The Luminosity Function, Cosmic Star-Formation Rate, and the First Mass Density Estimate at 500 Myr
[abridged] We present the discovery of four surprisingly bright (H_160 ~ 26 -
27 mag AB) galaxy candidates at z~9-10 in the complete HST CANDELS WFC3/IR
GOODS-N imaging data, doubling the number of z~10 galaxy candidates that are
known, just ~500 Myr after the Big Bang. Two similarly bright sources are also
detected in a systematic re-analysis of the GOODS-S data set. Three of the four
galaxies in GOODS-N are significantly detected at 4.5-6.2sigma in the very deep
Spitzer/IRAC 4.5 micron data, as is one of the GOODS-S candidates. Furthermore,
the brightest of our candidates (at z=10.2+-0.4) is robustly detected also at
3.6 micron (6.9sigma), revealing a flat UV spectral energy distribution with a
slope beta=-2.0+-0.2, consistent with demonstrated trends with luminosity at
high redshift. The abundance of such luminous candidates suggests that the
luminosity function evolves more significantly in phi_* than in L_* at z>~8
with a higher number density of bright sources than previously expected.
Despite the discovery of these luminous candidates, the cosmic star formation
rate density for galaxies with SFR >0.7 M_sun/yr shows an order-of-magnitude
increase in only 170 Myr from z ~ 10 to z ~ 8, consistent with previous
results. Based on the IRAC detections, we derive galaxy stellar masses at z~10,
finding that these luminous objects are typically 10^9 M_sun. The cosmic
stellar mass density at z~10 is log10 rho_* = 4.7^+0.5_-0.8 M_sun Mpc^-3 for
galaxies brighter than M_UV~-18. The remarkable brightness, and hence
luminosity, of these z~9-10 candidates highlights the opportunity for deep
spectroscopy to determine their redshift and nature, demonstrates the value of
additional search fields covering a wider area to understand star-formation in
the very early universe, and highlights the opportunities for JWST to map the
buildup of galaxies at redshifts much earlier than z~10.Comment: 20 pages, 12 figures, changed to match resubmitted version to Ap
Pulsar Searches with the SKA
The Square Kilometre Array will be an amazing instrument for pulsar
astronomy. While the full SKA will be sensitive enough to detect all pulsars in
the Galaxy visible from Earth, already with SKA1, pulsar searches will discover
enough pulsars to increase the currently known population by a factor of four,
no doubt including a range of amazing unknown sources. Real time processing is
needed to deal with the 60 PB of pulsar search data collected per day, using a
signal processing pipeline required to perform more than 10 POps. Here we
present the suggested design of the pulsar search engine for the SKA and
discuss challenges and solutions to the pulsar search venture.Comment: 4 pages, 1 figure. To be published in Proceedings of IAU Symposium
337: Pulsar Astrophysics - The Next 50 Year
The repeating Fast Radio Burst FRB 121102: Multi-wavelength observations and additional bursts
We report on radio and X-ray observations of the only known repeating Fast
Radio Burst (FRB) source, FRB 121102. We have detected six additional radio
bursts from this source: five with the Green Bank Telescope at 2 GHz, and one
at 1.4 GHz at the Arecibo Observatory for a total of 17 bursts from this
source. All have dispersion measures consistent with a single value (
pc cm) that is three times the predicted maximum Galactic value. The
2-GHz bursts have highly variable spectra like those at 1.4 GHz, indicating
that the frequency structure seen across the individual 1.4 and 2-GHz
bandpasses is part of a wideband process. X-ray observations of the FRB 121102
field with the Swift and Chandra observatories show at least one possible
counterpart; however, the probability of chance superposition is high. A radio
imaging observation of the field with the Jansky Very Large Array at 1.6 GHz
yields a 5 upper limit of 0.3 mJy on any point-source continuum
emission. This upper limit, combined with archival WISE 22-m and IPHAS
H surveys, rules out the presence of an intervening Galactic HII
region. We update our estimate of the FRB detection rate in the PALFA survey to
be 1.1 FRBs sky day (95% confidence)
for peak flux density at 1.4 GHz above 300 mJy. We find that the intrinsic
widths of the 12 FRB 121102 bursts from Arecibo are, on average, significantly
longer than the intrinsic widths of the 13 single-component FRBs detected with
the Parkes telescope.Comment: 18 pages, 5 figures. Accepted for publication in Ap
Consistent dynamical and stellar masses with potential light IMF in massive quiescent galaxies at using velocity dispersions measurements with MOSFIRE
We present the velocity dispersion measurements of four massive
quiescent galaxies at based on deep H and
Kband spectra using the Keck/MOSFIRE near-infrared spectrograph. We find
high velocity dispersions of order km/s based on strong
Balmer absorption lines and combine these with size measurements based on
HST/WFC3 F160W imaging to infer dynamical masses. The velocity dispersion are
broadly consistent with the high stellar masses and small sizes. Together with
evidence for quiescent stellar populations, the spectra confirm the existence
of a population of massive galaxies that formed rapidly and quenched in the
early universe . Investigating the evolution at constant velocity
dispersion between and , we find a large increase in
effective radius dex and in dynamical-to-stellar mass ratio
of 0.33$\pm0.08$ dex, with low expected
contribution from dark matter. The dynamical masses for our $z\sim3.5$ sample
are consistent with the stellar masses for a Chabrier initial mass function
(IMF), with the ratio =
-0.130.10 dex suggesting an IMF lighter than Salpeter may be common for
massive quiescent galaxies at . This is surprising in light of the
Salpeter or heavier IMFs found for high velocity dispersion galaxies at
and cores of present-day ellipticals, which these galaxies are thought
to evolve into. Future imaging and spectroscopic observations with resolved
kinematics using the upcoming James Webb Space Telescope could rule out
potential systematics from rotation, and confirm these results.Comment: 11 pages, 3 figures. Accepted to ApJ Letter
On the Lack of Correlation Between [OIII]/[OII] and Lyman-Continuum Escape Fraction
We present the first results of our pilot study of 8 photometrically selected
Lyman continuum (LyC) emitting galaxy candidates from the COSMOS field and
focus on their optical emission line ratios. Observations were performed in the
H and K bands using the Multi-Object Spectrometer for Infra-Red Exploration
(MOSFIRE) instrument at the Keck Observatory, targeting the [OII], H,
and [OIII] emission lines. We find that photometrically selected LyC emitting
galaxy candidates have high ionization parameters, based on their high
[OIII]/[OII] ratios (O32), with an average ratio for our sample of 2.50.2.
Preliminary results of our companion Low Resolution Imaging Spectrometer (LRIS)
observations, targeting LyC and Ly, show that those galaxies with the
largest O32 are typically found to also be Ly emitters. High O32
galaxies are also found to have tentative non-zero LyC escape fractions
() based on band photometric detections. These results are
consistent with samples of highly ionized galaxies, including confirmed LyC
emitting galaxies from the literature. We also perform a detailed comparison
between the observed emission line ratios and simulated line ratios from
density bounded H regions modeled using the photoionization
code MAPPINGS V. Estimates of for our sample fall in the range
from 0.0-0.23 and suggest possible tension with published correlations between
O32 and , adding weight to dichotomy of arguments in the
literature. We highlight the possible effects of clumpy geometry and mergers
that may account for such tension.Comment: 21 pages, 11 figures, 3 tables, accepted for publication in MNRA
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