1908.05765
The impact of the observed baryon distribution in haloes on the total matter power spectrum
Debackere, Schaye, Hoekstra
The interpretation of upcoming weak gravitational lensing surveys depends critically on our understanding of the matter power spectrum on scales $k < 10 h/\mathrm{Mpc}$, where baryonic processes are important. In this paper we study the impact of gas flows associated with galaxy formation on the matter power spectrum using a halo model that treats the stars and gas separately from the dark matter distribution. The baryonic components are constrained empirically: the hot gas using fits to X-ray observations of groups and clusters of galaxies, and the stellar component using a halo occupation distribution. Since X-ray observations cannot generally measure the hot gas content outside $r_\mathrm{500c}$, we vary the gas density profiles beyond this radius. Compared with dark matter only models, we find a total power suppression of $1\%$ ($5\%$) on scales $0.2-1 h/\mathrm{Mpc}$ ($0.5-2 h/\mathrm{Mpc}$), where lower baryon fractions result in stronger suppression. We show that groups of galaxies ($10^{13} < m_\mathrm{500c} / (M_\odot/h) < 10^{14}$) dominate the total power at all scales $k \lesssim 10 h/\mathrm{Mpc}$. We illustrate the importance of measuring accurate halo masses by comparing models that do and do not account for a hydrostatic bias of $1-b=0.7$ in the halo masses from X-ray observations. We find that using biased halo masses results in an underestimation of the power suppression of up to $4\%$ at $k=1 h/\mathrm{Mpc}$. Contrary to work based on hydrodynamical simulations, our conclusion that baryonic effects can no longer be neglected is not subject to uncertainties associated with our poor understanding of feedback processes. Our findings highlight the need for observations to probe the outskirts of groups and clusters since these observations are the most constraining for the power suppression on scales $k \lesssim 1 h/\mathrm{Mpc}$.
The impact of the observed baryon distribution in haloes on the total matter power spectrum
Debackere, Schaye, Hoekstra
The interpretation of upcoming weak gravitational lensing surveys depends critically on our understanding of the matter power spectrum on scales $k < 10 h/\mathrm{Mpc}$, where baryonic processes are important. In this paper we study the impact of gas flows associated with galaxy formation on the matter power spectrum using a halo model that treats the stars and gas separately from the dark matter distribution. The baryonic components are constrained empirically: the hot gas using fits to X-ray observations of groups and clusters of galaxies, and the stellar component using a halo occupation distribution. Since X-ray observations cannot generally measure the hot gas content outside $r_\mathrm{500c}$, we vary the gas density profiles beyond this radius. Compared with dark matter only models, we find a total power suppression of $1\%$ ($5\%$) on scales $0.2-1 h/\mathrm{Mpc}$ ($0.5-2 h/\mathrm{Mpc}$), where lower baryon fractions result in stronger suppression. We show that groups of galaxies ($10^{13} < m_\mathrm{500c} / (M_\odot/h) < 10^{14}$) dominate the total power at all scales $k \lesssim 10 h/\mathrm{Mpc}$. We illustrate the importance of measuring accurate halo masses by comparing models that do and do not account for a hydrostatic bias of $1-b=0.7$ in the halo masses from X-ray observations. We find that using biased halo masses results in an underestimation of the power suppression of up to $4\%$ at $k=1 h/\mathrm{Mpc}$. Contrary to work based on hydrodynamical simulations, our conclusion that baryonic effects can no longer be neglected is not subject to uncertainties associated with our poor understanding of feedback processes. Our findings highlight the need for observations to probe the outskirts of groups and clusters since these observations are the most constraining for the power suppression on scales $k \lesssim 1 h/\mathrm{Mpc}$.
1908.05785
OPTICAM: a triple-camera optical system designed to explore the fastest timescales in Astornomy
Castro, et al
We report the development of a high-time resolution, 3-colour, simultaneous optical imaging system for the 2.1 m telescope in San Pedro M\'artir Observatory, M\'exico. OPTICAM will be equipped with three Andor Zyla 4.2-Plus sCMOS cameras and a set of SDSS filters allowing optical coverage in the 320-1,100 nm range. OPTICAM will nominally allow sub-second exposures. Given its instrumental design, a wide range of fast-variability astrophysical sources can be targeted with OPTICAM including X-ray binaries, pulsating white dwarfs, accreting compact objects, eclipsing binaries and exoplanets. OPTICAM observations will be proprietary for only six months and will then be made publicly available for the astronomical community.
1908.05993
Ten years of all-sky neutrino point-source searches
Carver
These proceedings present the results of point-like neutrino source searches using ~10 yrs of IceCube data from Apr.~6, 2008 to Jul.~10, 2018. We evaluate the significance of an astrophysical signal from a point-like source looking for an excess of clustered neutrino events with energies above ~1 TeV among the background of atmospheric muons and neutrinos. We perform a full sky scan, a search based on a selected source catalog, and a catalog population study. The most significant location in the Northern hemisphere from the full-sky scan is compatible with the Seyfert galaxy NGC 1068. This object had also been identified in the source catalog search which finds a 2.9 $\sigma$ excess after accounting for statistical trials. The combination of this result along with excesses observed at the coordinates of three other sources, including TXS 0506+056, suggests that collectively correlations with sources in the Northern catalog are inconsistent with background at the level of 3.3 $\sigma$. These results motivate further interest in such point-like sources which should become observable or ruled out after accumulation of more data or with future detectors.
1908.06056
Astrometric planet search around southern ultracool dwarfs IV. Relative motion of the FORS2/VLT CCD chips
Lazorenko, Sahlmann
We present an investigation of the stability of the two chips in the FORS2 camera CCD mosaic on the basis of astrometric observations of stars in 20 sky fields, some of which were monitored for four to seven years. We detected a smooth relative shear motion of the chips along their dividing line that is well approximated by a cubic function of time with an amplitude that reaches ~0.3 pixels (px) or ~38 mas over seven years. In a single case, we detected a step change of ~0.06 px that occurred within four days. In the orthogonal direction that corresponds to the separation between the chips, the motion is a factor of 5-10 smaller. This chip instability in the camera significantly reduces the astrometric precision when the reduction uses reference stars located in both chips, and the effect is not accounted for explicitly. We found that the instability introduces a bias in stellar positions with an amplitude that increases with the observation time span. When our reduction methods and FORS2 images are used, it affects stellar positions like an excess random noise with an RMS of ~0.5 mas for a time span of three to seven years when left uncorrected. We demonstrate that an additional calibration step can adequately mitigate this and restore an astrometric accuracy of 0.12 mas, which is essential to achieve the goals of our planet-search program. These results indicate that similar instabilities could critically affect the astrometric performance of other large ground-based telescopes and extremely large telescopes that are equipped with large-format multi-chip detectors if no precautions are taken.
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