88 research outputs found
Local Voids as the Origin of Large-angle Cosmic Microwave Background Anomalies: The Effect of a Cosmological Constant
We explore the large angular scale temperature anisotropies in the cosmic
microwave background (CMB) due to homogeneous local dust-filled voids in a flat
Friedmann-Robertson-Walker universe with a cosmological constant. In comparison
with the equivalent dust-filled void model in the Einstein-de Sitter
background, we find that the anisotropy for compensated asymptotically
expanding local voids can be larger because second-order effects enhance the
linear integrated Sachs-Wolfe (ISW) effect. However, for local voids that
expand sufficiently faster than the asymptotic velocity of the wall, the
second-order effect can suppress the fluctuation due to the linear ISW effect.
A pair of quasi-linear compensated asymptotic local voids with radius
(2-3)*10^2 ~h^{-1} Mpc and a matter density contrast ~-0.3 can be observed as
cold spots with a temperature anisotropy Delta T/T~O(10^{-5}) that might help
explain the observed large-angle CMB anomalies. We predict that the associated
anisotropy in the local Hubble constant in the direction of the voids could be
as large as a few percent.Comment: 23 pages, 5 figures, version accepted for publication in ApJ with
minor revisio
Delayed Recombination and Standard Rulers
Measurements of Baryonic Acoustic Oscillations in galaxy surveys have been
recognized as a powerful tool for constraining dark energy. However, this
method relies on the knowledge of the size of the acoustic horizon at
recombination derived from Cosmic Microwave Background Anisotropy measurements.
This estimate is typically derived assuming a standard recombination scheme;
additional radiation sources can delay recombination altering the cosmic
ionization history and the cosmological inferences drawn from CMB and BAO data.
In this paper we quantify the effect of delayed recombination on the
determination of dark energy parameters from future BAO surveys such as BOSS
and WFMOS. We find the impact to be small but still not negligible. In
particular, if recombination is non-standard (to a level still allowed by CMB
data), but this is ignored, future surveys may incorrectly suggest the presence
of a redshift dependent dark energy component. On the other hand, in the case
of delayed recombination, adding to the analysis one extra parameter describing
deviations from standard recombination, does not significantly degrade the
error-bars on dark energy parameters and yields unbiased estimates.Comment: 8 pages, 5 figure
Relativistic jet feedback - III. Feedback on gas discs
We study the interactions of a relativistic jet with a dense turbulent gaseous disc of radius ~2 kpc. We have performed a suite of simulations with different mean density, jet power, and orientation. Our results show that: (A) The relativistic jet couples strongly with the gas in the inner kpc, creating a cavity and launching outflows. (B) The high pressure bubble inflated by the jet and its back-flow compresses the disc at the outer edges, driving inflows within the disc. (C) Jets inclined towards the disc affect the disc more and launch sub-relativistic, wide-angled outflows along the minor axis. (D) Shocks driven directly by the jet and the jet-driven energy bubble raise the velocity dispersion throughout the disc by several times its initial value. (E) Compression by the jet-driven shocks can enhance the star formation rate in the disc, especially in a ring-like geometry close to the axis. However, enhanced turbulent dispersion in the disc also leads to quenching of star formation. Whether positive or negative feedback dominates depends on jet power, ISM density, jet orientation with respect to the disc, and the time-scale under consideration. Qualitatively, our simulations compare favourably with kinematic and morphological signatures of several observed galaxies such as NGC 1052, NGC 3079, 3C 326, and 3C 293.DMâs visit to JHU was supported by a Balzan
grant from New College, Oxford. AYW has been supported in part
by ERC Project No. 267117 (DARK) hosted by Universite Pierre ÂŽ
et Marie Curie (UPMC) â Paris 6, PI: J. Silk
Cosmic Star Formation, Reionization, and Constraints on Global Chemical Evolution
Motivated by the WMAP results indicating an early epoch of reionization, we
consider alternative cosmic star formation models which are capable of
reionizing the early intergalactic medium. We develop models which include an
early burst of massive stars (with several possible mass ranges) combined with
standard star formation. We compute the stellar ionizing flux of photons and we
track the nucleosynthetic yields for several elements: D, He4, C, N, O, Si, S,
Fe, Zn. We compute the subsequent chemical evolution as a function of redshift,
both in the intergalactic medium and in the interstellar medium of forming
galaxies, starting with the primordial objects which are responsible for the
reionization. We apply constraints from the observed abundances in the Lyman
alpha forest and in Damped Lyman alpha clouds in conjunction with the ability
of the models to produce the required degree of reionization. We also consider
possible constraints associated with the observations of the two extremely
metal-poor stars HE 0107-5240 and CS22949-037. We confirm that an early
top-heavy stellar component is required, as a standard star formation model is
unable to reionize the early Universe and reproduce the abundances of the very
metal-poor halo stars. A bimodal (or top-heavy) IMF (40 - 100 M_\odot) is our
preferred scenario compared to the extreme mass range (\ga 100 M_\odot) often
assumed to be responsible for the early stages of reionization. A mode of even
more extreme stellar masses in the range (\ge 270 M_\odot) has also been
considered. All massive stars in this mode collapse entirely into black holes,
and as a consequence, chemical evolution and reionization are de-correlated.
[Abstract abbreviated.]Comment: 45 pages, 18 eps figures, as accepted in Ap
Probing the evolution of early-type cluster galaxies through chemical enrichment
A simple chemical enrichment model for cluster early-type galaxies is
described in which the mechanisms considered in the evolutionary model are
infall of primordial gas, outflows and a possible variation in the star
formation efficiency. We find that - within the framework of our models - only
outflows can generate a suitable range of metallicities. The chemical
enrichment tracks can be combined with the latest population synthesis models
to simulate clusters over a wide redshift range, for a set of toy models. The
color-magnitude relation of local clusters is used as a constraint, fixing the
correlation between absolute luminosity and ejected fraction of gas from
outflows. It is found that the correlations between color or mass-to-light
ratios and absolute luminosity are degenerate with respect to most of the input
parameters. However, a significant change between monolithic and hierarchical
models is predicted for redshifts z\simgt 1. The comparison between predicted
and observed mass-to-light ratios yield an approximate linear bias between
total and stellar masses: in
early-type galaxies. If we assume that outflows constitute the driving
mechanism for the colors observed in cluster early type galaxies, the
metallicity of the intracluster medium (ICM) can be linked to outflows. The
color-magnitude constraint requires faint galaxies to eject 85%
of their gas, which means that most of the metals in the ICM may have
originated in these dwarf galaxies.Comment: Accepted for publication in ApJ. Uses emulateapj.sty. 12 pages with
10 embedded EPS figure
Cumulants as non-Gaussian qualifiers
We discuss the requirements of good statistics for quantifying
non-Gaussianity in the Cosmic Microwave Background. The importance of
rotational invariance and statistical independence is stressed, but we show
that these are sometimes incompatible. It is shown that the first of these
requirements prefers a real space (or wavelet) formulation, whereas the latter
favours quantities defined in Fourier space. Bearing this in mind we decide to
be eclectic and define two new sets of statistics to quantify the level of
non-Gaussianity. Both sets make use of the concept of cumulants of a
distribution. However, one set is defined in real space, with reference to the
wavelet transform, whereas the other is defined in Fourier space. We derive a
series of properties concerning these statistics for a Gaussian random field
and show how one can relate these quantities to the higher order moments of
temperature maps. Although our frameworks lead to an infinite hierarchy of
quantities we show how cosmic variance and experimental constraints give a
natural truncation of this hierarchy. We then focus on the real space
statistics and analyse the non-Gaussian signal generated by points sources
obscured by large scale Gaussian fluctuations. We conclude by discussing the
practical implementations of these techniques
Star formation in 30 Doradus
Using observations obtained with the Wide Field Camera 3 (WFC3) on board the
Hubble Space Telescope (HST), we have studied the properties of the stellar
populations in the central regions of 30 Dor, in the Large Magellanic Cloud.
The observations clearly reveal the presence of considerable differential
extinction across the field. We characterise and quantify this effect using
young massive main sequence stars to derive a statistical reddening correction
for most objects in the field. We then search for pre-main sequence (PMS) stars
by looking for objects with a strong (> 4 sigma) Halpha excess emission and
find about 1150 of them over the entire field. Comparison of their location in
the Hertzsprung-Russell diagram with theoretical PMS evolutionary tracks for
the appropriate metallicity reveals that about one third of these objects are
younger than ~4Myr, compatible with the age of the massive stars in the central
ionising cluster R136, whereas the rest have ages up to ~30Myr, with a median
age of ~12Myr. This indicates that star formation has proceeded over an
extended period of time, although we cannot discriminate between an extended
episode and a series of short and frequent bursts that are not resolved in
time. While the younger PMS population preferentially occupies the central
regions of the cluster, older PMS objects are more uniformly distributed across
the field and are remarkably few at the very centre of the cluster. We
attribute this latter effect to photoevaporation of the older circumstellar
discs caused by the massive ionising members of R136.Comment: 15 pages, 12 figures. Accepted for publication in The Astrophysical
Journa
Therapy with high-dose Interleukin-2 (HD IL-2) in metastatic melanoma and renal cell carcinoma following PD1 or PDL1 inhibition
Abstract
Background
Metastatic melanoma (mM) and renal cell carcinoma (mRCC) are often treated with anti-PD-1 based therapy, however not all patients respond and further therapies are needed. High dose interleukin-2 (HD IL-2) can lead to durable responses in a subset of mM and mRCC patients. The efficacy and toxicity of HD IL-2 therapy following anti-PD-1 or anti-PD-L1 therapy have not yet been explored.
Methods
Reports on mM and mRCC patients who had received HD IL-2 after PD-1 or PD-L1 inhibition were queried from the PROCLAIMSM database. Patient characteristics, toxicity and efficacy were analyzed.
Results
A total of 57 patients (40âmM, 17 mRCC) were treated with high dose IL-2 after PD-1 or PD-L1 inhibition and had data recorded in the PROCLAIM database. The best overall response rate to HD IL-2 was 22.5% for mM (4 complete response (CR), 5 partial responses (PRs)) and 24% for mRCC (2 CRs, 2 PRs). The toxicity related to HD IL-2 observed in these patients was similar to that observed in patients treated with HD IL-2 without prior checkpoint blockade. One patient who had received prior PD-L1 blockade developed drug induced pneumonitis with HD IL-2 requiring steroid therapy.
Conclusion
In this retrospective analysis, HD IL-2 therapy displayed durable antitumor activity in mM and mRCC patients who progressed following treatment with PD-1 and PD-L1 inhibition. The toxicities were generally manageable and consistent with expectations from HD IL-2 but physicians should watch for immune related toxicities such as pneumonitis. This analysis supports the development of randomized prospective trials to assess the proper sequencing and combination of immune checkpoint blockade and cytokine therapy.https://deepblue.lib.umich.edu/bitstream/2027.42/148134/1/40425_2019_Article_522.pd
Using H-alpha Morphology and Surface Brightness Fluctuations to Age-Date Star Clusters in M83
We use new WFC3 observations of the nearby grand design spiral galaxy M83 to
develop two independent methods for estimating the ages of young star clusters.
The first method uses the physical extent and morphology of Halpha emission to
estimate the ages of clusters younger than tau ~10 Myr. It is based on the
simple premise that the gas in very young (tau < few Myr) clusters is largely
coincident with the cluster stars, is in a small, ring-like structure
surrounding the stars in slightly older clusters (e.g., tau ~5 Myr), and is in
a larger ring-like bubble for still older clusters (i.e., ~5-10 Myr). The
second method is based on an observed relation between pixel-to-pixel flux
variations within clusters and their ages. This method relies on the fact that
the brightest individual stars in a cluster are most prominent at ages around
10 Myr, and fall below the detection limit (i.e., M_V < -3.5) for ages older
than about 100 Myr. These two methods are the basis for a new morphological
classification system which can be used to estimate the ages of star clusters
based on their appearance. We compare previous age estimates of clusters in M83
determined from fitting UBVI Halpha measurements using predictions from stellar
evolutionary models with our new morphological categories and find good
agreement at the ~95% level. The scatter within categories is ~0.1 dex in log
tau for young clusters (10 Myr) clusters. A
by-product of this study is the identification of 22 "single-star" HII regions
in M83, with central stars having ages ~4 Myr.Comment: 33 pages, 10 figures, 3 tables; published in March Ap
The HST Survey of BL Lacertae Objects. II. Host Galaxies
We have used the HST WFPC2 camera to survey 132 BL Lac objects comprising
seven complete radio-, X-ray-, and optically-selected samples. We obtained
useful images for 110 targets spanning the redshift range 0 < z < 1.3. In two
thirds of the BL Lac images, host galaxies are detected, including nearly all
for z < 0.5 (58 of 63). The highest redshift host galaxy detected is in a BL
Lac object at z=0.664. In 58 of the 72 resolved host galaxies, a de Vaucouleurs
profile is significantly preferred, at >99% confidence, over a pure exponential
disk; the two fits are comparable in the remaining 14 cases. These results
limit the number of disk systems to at most 8% of BL Lacs (at 99% confidence),
and are consistent with all BL~Lac host galaxies being ellipticals. The
detected host galaxies are luminous ellipticals with a median absolute
K-corrected magnitude of M_R= -23.7 +- 0.6 mag, at least one magnitude brighter
than M* and comparable to brightest cluster galaxies. The galaxy morphologies
are generally smooth and undisturbed, with small or negligible ellipticities
(<0.2). There is no correlation between host galaxy and observed nuclear
magnitude or estimated jet power corrected for beaming. If black hole mass is
correlated linearly with bulge mass in general, this implies a large range in
Eddington ratio. Present data strongly support the unification picture with FR
I galaxies constituting the bulk of the parent population of BL Lac objects.Comment: Accepted for publication on ApJ. 38 pages, 8 figure
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