2003.13575
The propermotiof of sub-populations in Omega Centauri
Sanna, et al
The galactic globular cluster Omega Centauri is the most massive of its kind, with a complex mix of multiple stellar populations and several kinematic and dynamical peculiarities. Different mean proper motions have been detected among the three main sub-populations, implying that the most metal-rich one is of accreted origin. This particular piece of evidence has been a matter of debate because the available data have either not been sufficiently precise or limited to a small region of the cluster to ultimately confirm or refute the result. Using astrometry from the second Gaia data release and recent high-quality, multi-band photometry, we are now in a position to resolve the controversy. We reproduced the original analysis using the Gaia data and found that the three populations have the same mean proper motion. Thus, there is no need to invoke an accreted origin for the most metal-rich sub-population.
2003.13643
The habitability of large elliptical galaxies
Whitmire
Based on numbers of stars, supernova rates, and metallicity, a prior study (Dayal et al. 2015) concluded that large elliptical galaxies contain up to 10,000 times more habitable planets than the Milky Way and are thus the "cradles of life". Using the results of their model and taking into account galactic number distributions and supernova rates I argue here that this result constitutes a violation of the Principle of Mediocrity as applied to the reference class of all extant technological species. Assuming that we are a typical technological species in the attribute of inhabiting a relatively large disk-dominated galaxy, I outline two hypotheses that could significantly limit the habitability of large elliptical galaxies: (1) massive galactic sterilization events associated with quasar/AGN activity and starburst supernovae that occurred when the antecedents of today's large elliptical galaxies were much more compact; and (2) the probability of habitable planet formation in large elliptical galaxies may be small since a disproportionately larger number of gaseous planets are expected to form as a result of the generally higher metallicity in large elliptical galaxies. Consequently, fewer habitable planets will accrete if the gaseous planets inward migrations are sufficiently slow. The sterilization events of Hypothesis (1) occurred at earlier epochs (z $\geq$ 1) and so they must be effectively permanent, implying two possible scenarios regarding the origin and evolution of life. In connection with one of these scenarios, independent applications of the Principle of Mediocrity suggest that M-dwarf stars are not significant hosts of technological life.
The propermotiof of sub-populations in Omega Centauri
Sanna, et al
The galactic globular cluster Omega Centauri is the most massive of its kind, with a complex mix of multiple stellar populations and several kinematic and dynamical peculiarities. Different mean proper motions have been detected among the three main sub-populations, implying that the most metal-rich one is of accreted origin. This particular piece of evidence has been a matter of debate because the available data have either not been sufficiently precise or limited to a small region of the cluster to ultimately confirm or refute the result. Using astrometry from the second Gaia data release and recent high-quality, multi-band photometry, we are now in a position to resolve the controversy. We reproduced the original analysis using the Gaia data and found that the three populations have the same mean proper motion. Thus, there is no need to invoke an accreted origin for the most metal-rich sub-population.
2003.13643
The habitability of large elliptical galaxies
Whitmire
Based on numbers of stars, supernova rates, and metallicity, a prior study (Dayal et al. 2015) concluded that large elliptical galaxies contain up to 10,000 times more habitable planets than the Milky Way and are thus the "cradles of life". Using the results of their model and taking into account galactic number distributions and supernova rates I argue here that this result constitutes a violation of the Principle of Mediocrity as applied to the reference class of all extant technological species. Assuming that we are a typical technological species in the attribute of inhabiting a relatively large disk-dominated galaxy, I outline two hypotheses that could significantly limit the habitability of large elliptical galaxies: (1) massive galactic sterilization events associated with quasar/AGN activity and starburst supernovae that occurred when the antecedents of today's large elliptical galaxies were much more compact; and (2) the probability of habitable planet formation in large elliptical galaxies may be small since a disproportionately larger number of gaseous planets are expected to form as a result of the generally higher metallicity in large elliptical galaxies. Consequently, fewer habitable planets will accrete if the gaseous planets inward migrations are sufficiently slow. The sterilization events of Hypothesis (1) occurred at earlier epochs (z $\geq$ 1) and so they must be effectively permanent, implying two possible scenarios regarding the origin and evolution of life. In connection with one of these scenarios, independent applications of the Principle of Mediocrity suggest that M-dwarf stars are not significant hosts of technological life.
2003.13694
Emergence of an ultra-red ultra-massive galaxy cluster core at $z=4$
Long, Cooray, et al
Recent simulations and observations of massive galaxy cluster evolution predict that the majority of stellar mass build up happens within cluster members by $z=2$, before cluster virialization. Protoclusters rich with dusty, star-forming galaxies (DSFGs) at $z>3$ are the favored candidate progenitors for these massive galaxy clusters at $z\sim0$. We present here the first study analyzing stellar emission along with cold dust and gas continuum emission in a spectroscopically confirmed $z=4.002$ protocluster core rich with DSFGs, the Distant Red Core (DRC). We combine new \textit{HST} and \textit{Spitzer} data with existing Gemini, \textit{Herschel}, and ALMA observations to derive individual galaxy-level properties, and compare them to coeval field and other protocluster galaxies. All of the protocluster members are massive ($>10^{10}$ M$_\odot$), but not significantly more so than their coeval field counterparts. Within uncertainty, all are nearly indistinguishable from galaxies on the star-forming vs. stellar mass main-sequence relationship. However, when placed on the star formation efficiency plane, DRC components exhibit starburst-like characteristics with SFRs 10-100$\times$ greater than the expected field value at a given molecular gas mass. Assuming no future major influx of fresh gas, we estimate that these gas poor (f$_\mathrm{gas}<25\%$) yet bursty DSFGs will deplete their gas reservoirs in $<30$ Myr. Using various methodologies, we derive a total $z=4$ halo mass of $\sim10^{14}$ M$_\odot$, and estimate that the DRC will evolve to become an ultra-massive cluster core of mass $\gtrsim10^{15}$ M$_\odot$ by $z=0$.
2003.13722
Defining the really habitable zone
Pedbost, et al
Since the discovery of the first confirmed exoplanet, observations have revealed a remarkable diversity of worlds. A wide variety of orbital and physical characteristics are detected in the exoplanet population, and much work has been devoted to deciding which of these planets may be suitable for life. Until now, though, little work has been devoted to deciding which of the potentially habitable planets might actually be \textit{worth} existing on. To this end, we present the Really Habitable Zone (RHZ), defined as the region around a star where acceptable gins and tonic are likely to be abundant. In common with much of the work in the field, we rely throughout on assumptions which are difficult if not impossible to test and present some plots which astronomers can use in their own talks, stripped of all caveats. We suggest that planets in the Really Habitable Zone be early targets for the JWST, because by the time that thing finally launches we're all going to need a drink. [April 1, 2020 post]
2003.13918
Resolving exa-continents with Einstein ring deconvolution
Madurowicz
["Please do not print this document" -- BW inverted PDF, April 1, 2020 post]
A mission to the focus of the solar gravitational lens could produce images with unprecedented angular resolution and sensitivity. In the context of trying to resolve the time variable thermal signature of continents on other Earth-like exoplanets, we develop an approach to improve the image reconstruction performance by using azimuthal variations in the Einstein Ring's intensity. In the first post-Newtonian approximation to General Relativity, an arbitrary disk intensity distribution in the source plane is mapped to a narrow annulus around the Einstein Ring, with each azimuthal element corresponding to a sector in the disk. A matrix-based linear measurement model at various fixed signal-to-noise ratios demonstrates that this extra information is useful in improving the reconstruction when the image is sparsely sampled, which could improve integration times and temporal errors. Various issues and future outlooks are discussed.
Large-scale magnetic fields in the Milky Way are thought to be created by an $\alpha\Omega$ dynamo, which implies that they should have opposite handedness North and South of the midplane of the Galactic disk. Here we attempt to detect this variation in handedness using polarization data from the Wilkinson Microwave Anisotropy Probe. Previous analyses of the parity-even and parity-odd constituents of linear polarization of the global dust and synchrotron emission have focused on quadratic correlations in spectral space of, and between, these two components. Here, by contrast, we analyze the parity-odd polarization of the magnetic field itself and show that it has opposite signs in Northern and Southern Galactic hemispheres. This is suggestive of the presence of magnetic helicity in the Galaxy and thereby an important diagnostic for Galactic dynamo models. Comparison with a Galactic mean-field dynamo model shows broad qualitative agreement. The observed hemispheric dependence for the azimuthally averaged parity-odd polarization is recovered if, in the model, the observer is placed sufficiently far away from the Galactic center.
Galaxy merger histories correlate strongly with stellar mass, largely regardless of morphology. Thus, at fixed stellar mass, spheroids and discs share similar assembly histories, both in terms of the frequency of mergers and the distribution of their mass ratios. Since mergers are the principal drivers of disc-to-spheroid morphological transformation, and the most massive galaxies typically have the richest merger histories, it is surprising that discs exist at all at the highest stellar masses (e.g. beyond the knee of the mass function). Using Horizon-AGN, a cosmological hydro-dynamical simulation, we show that extremely massive (M*> 10^11.4 MSun) discs are created via two channels. In the primary channel (accounting for ~70% of these systems and ~8% of massive galaxies) the most recent, significant merger (stellar mass ratio > 1:10) between a massive spheroid and a gas-rich satellite `spins up' the spheroid by creating a new rotational stellar component, leaving a massive disc as the remnant. In the secondary channel (accounting for ~30% of these systems and ~3% of massive galaxies), a system maintains a disc throughout its lifetime, due to an anomalously quiet merger history. Not unexpectedly, the fraction of massive discs is larger at higher redshift, due to the Universe being more gas-rich. The morphological mix of galaxies at the highest stellar masses is, therefore, a strong function of the gas fraction of the Universe. Finally, these massive discs have similar black-hole masses and accretion rates to massive spheroids, providing a natural explanation for why a minority of powerful AGN are surprisingly found in disc galaxies.
The significant increase in precision that will be achieved by Stage IV cosmic shear surveys means that several currently used theoretical approximations may cease to be valid. An additional layer of complexity arises from the fact that many of these approximations are interdependent; the procedure to correct for one involves making another. Two such approximations that must be relaxed for upcoming experiments are the reduced shear approximation and the effect of neglecting magnification bias. Accomplishing this involves the calculation of the convergence bispectrum; typically subject to the Limber approximation. In this work, we compute the post-Limber convergence bispectrum, and the post-Limber reduced shear and magnification bias corrections to the angular power spectrum for a Euclid-like survey. We find that the Limber approximation significantly overestimates the bispectrum when any side of the bispectrum triangle, $\ell_i<60$. However, the resulting changes in the reduced shear and magnification bias corrections are well below the sample variance for $\ell\leq5000$.
2003.14178
Hemispheric handedness in the Galactic synchrotron polarization foreground
Brandenburg, Brüggen
2004.00023
Why do extremely massive disc galaxies exist today?
Jackson, et al
2004.00170
Weak lensing clusters from HSC survey first-year data: mitigating the dilution effect of foreground and cluster member galaxies
Hamana, Shirasaki, Lin
We present weak lensing cluster search using Hyper Suprime-Cam Subaru Strategic Program (HSC survey) first-year data. We pay a special attention to the dilution effect of cluster member and foreground galaxies on weak lensing peak signal-to-noise ratios ($SN$s); we adopt the globally normalized weak lensing estimator which is least affected by cluster member galaxies, and we select source galaxies by using photometric redshift information to mitigate the effect of foreground galaxies. We produce six samples of source galaxies with different low-$z$ galaxy cuts, construct weak lensing mass maps for each of source sample, and search for high peaks in the mass maps that cover the effective survey area of $\sim$120 deg$^2$. We compile six catalogs of high peaks into the sample of cluster candidates which contains 124 high peaks with $SN\ge 5$. We cross-match the peak sample with the public optical cluster catalog constructed from the same HSC survey data to identify cluster counterparts of the peaks. We find that 107 out of 124 peaks have matched clusters within 5 arcmin from peak positions. Among them, we define a sub-sample of 64 secure clusters that we use to examine dilution effects on our weak lensing peak finding. We find that source samples with the low-$z$ galaxy cuts mitigate the dilution effect on peak $SN$s of high-$z$ clusters ($z > 0.3$), and thus combining multiple peak catalogs from different source samples improves the efficiency of weak lensing cluster searches.
2004.00439
Magnetic field evolution in solar-type stars
Brandenburg
We discuss selected aspects regarding the magnetic field evolution of solar-type stars. Most of the stars with activity cycles are in the range where the normalized chromospheric Calcium emission increases linearly with the inverse Rossby number [[Rossby number is the ratio of inertial force to Coriolis force; it characterizes the importance of Coriolis accelerations arising from planetary rotation]]. For Rossby numbers below about a quarter of the solar value, the activity saturates and no cycles have been found. For Rossby numbers above the solar value, again no activity cycles have been found, but now the activity goes up again for a major fraction of the stars. Rapidly rotating stars show nonaxisymmetric large-scale magnetic fields, but there is disagreement between models and observations regarding the actual value of the Rossby number where this happens. We also discuss the prospects of detecting the sign of magnetic helicity using various linear polarization techniques both at the stellar surface using the parity-odd contribution to linear polarization and above the surface using Faraday rotation.
2004.00680
Mergers do trigger AGNs out to z $\sim$ 0.6
Gao, et al
Aims. The fueling and feedback of Active Galactic Nuclei (AGNs) are important in understanding the co-evolution between black holes and host galaxies. Mergers are thought to have the capability to bring gas inwards and ignite nuclear activity, especially for more powerful AGNs. However, there is still significant ongoing debate on whether mergers can trigger AGNs and, if they do, whether mergers are a significant triggering mechanism. Methods. We select a low-redshift ($0.005<z<0.1$) sample from the Sloan Digital Sky Survey (SDSS) and a high-redshift ($0 < z < 0.6$) sample from the Galaxy And Mass Assembly (GAMA) survey. We take advantage of the convolutional neural network technique to identify mergers. We use mid-infrared (MIR) color cut and optical emission line diagnostics to classify AGNs. We also include Low Excitation Radio Galaxies (LERGs) to investigate the connection between mergers and low accretion rate AGNs. Results. We find that AGNs are more likely to be found in mergers than non-mergers, with an AGN excess up to $1.81\pm{0.16}$, suggesting that mergers can trigger AGNs. We also find the fraction of mergers in AGNs is higher than that in non-AGN controls, for both MIR and optically selected AGNs, as well as LERGs, with values between $16.40\pm{0.5}\%$ and $39.23\pm{2.10}\%$, implying a non-negligible to potentially significant role of mergers in triggering AGNs. This merger fraction in AGNs increases as stellar mass increases which supports the idea that mergers are more important for triggering AGNs in more massive galaxies. In terms of merger fraction as a function of AGN power we find a positive trend for MIR selected AGNs and a complex trend for optically selected AGNs, which we interpret under an evolutionary scenario proposed by previous studies. In addition, obscured MIR selected AGNs are more likely to be hosted in mergers than unobscured MIR selected AGNs.
2004.01666
The post-Limber weak lensing bispectrum, reduced shear correction, and magnification bias correction
Deshpande, Kitching
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