The astrophysical origin of gravitational wave (GW) events is one of the most timely problems in the wake of the LIGO/Virgo discoveries. In active galactic nuclei (AGN), binaries form and evolve efficiently by dynamical interactions and gaseous dissipation. Previous studies have suggested that binary black hole (BBH) mergers in AGN disks can contribute significantly to BBH mergers observed by GW interferometers. Here we examine the distribution of the effective spin parameter $\chi_\mathrm{eff}$ of this GW source population. We extend our semi-analytical model of binary formation and evolution in AGN disks by following the evolution of the binary orbital angular momenta and black hole (BH) spins. BH spins change due to gas accretion and BH mergers, while the binary orbital angular momenta evolve due to gas accretion and binary-single interactions. We find that the distribution of $\chi_\mathrm{eff}$ predicted by our AGN model is similar to the distribution observed during LIGO/Virgo O1 and O2. On the other hand, if radial migration of BHs is inefficient, $\chi_\mathrm{eff}$ is skewed toward higher values compared with the observed distribution, because of the paucity of scattering events that would randomize spin directions relative to the orbital plane. We suggest that high binary masses and the positive correlation between binary mass and the standard deviation of $\chi_\mathrm{eff}$ for chirp masses up to $\approx 20$ $\mathrm{M}_\odot$, can be possible signatures for mergers originating in AGN disks. Finally, hierarchical mergers in AGN disks naturally produce properties of the recent GW event GW190412, including a low mass ratio, a high primary BH spin, and a significant spin component in the orbital plane.

Spin Evolution of Stellar-mass Black Hole Binaries in Active Galactic Nuclei

https://iopscience.iop.org/article/10.3847/1538-4357/aba2cc/pdf

It has been known for a decade that hot stars with hot Jupiters tend to have high obliquities. Less is known about the degree of spin-orbit alignment for hot stars with other kinds of planets. Here, we re-assess the obliquities of hot Kepler stars with transiting planets smaller than Neptune, based on spectroscopic measurements of their projected rotation velocities (vsini). The basis of the method is that a lower obliquity -- all other things being equal -- causes sini to be closer to unity and increases the value of vsini. We sought evidence for this effect using a sample of 150 Kepler stars with effective temperatures between 5950 and 6550K and a control sample of 101 stars with matching spectroscopic properties and random orientations. The planet hosts have systematically higher values of vsini than the control stars, but not by enough to be compatible with perfect spin-orbit alignment. The mean value of sini is 0.856 +/- 0.036, which is 4-sigma away from unity (perfect alignment), and 2-sigma away from pi/4 (random orientations). There is also evidence that the hottest stars have a broader obliquity distribution: when modeled separately, the stars cooler than 6250K have = 0.928 +/- 0.042, while the hotter stars are consistent with random orientations. This is similar to the pattern previously noted for stars with hot Jupiters. Based on these results, obliquity excitation for early-G and late-F stars appears to be a general outcome of star and planet formation, rather than being exclusively linked to hot Jupiter formation.

/pdf/hot-stars-with-kepler-planets-have-high-obliquities-39sw480jkj.pdf

Hot Stars with Kepler Planets Have High Obliquities

Feedback from active galactic nuclei (AGN) is thought to be key in shaping the life cycle of their host galaxies by regulating star-formation activity. Therefore, to understand the impact of AGN on star formation, it is essential to trace the molecular gas out of which stars form. In this paper we present the first systematic study of the CO properties of AGN hosts at z  ≈ 2 for a sample of 27 X-ray selected AGN spanning two orders of magnitude in AGN bolometric luminosity (log L bol / erg s−1 = 44.7 − 46.9) by using ALMA Band 3 observations of the CO(3-2) transition (∼1″ angular resolution). To search for evidence of AGN feedback on the CO properties of the host galaxies, we compared our AGN with a sample of inactive (i.e., non-AGN) galaxies from the PHIBSS survey with similar redshift, stellar masses, and star-formation rates (SFRs). We used the same CO transition as a consistent proxy for the gas mass for the two samples in order to avoid systematics involved when assuming conversion factors (e.g., excitation corrections and α CO ). By adopting a Bayesian approach to take upper limits into account, we analyzed CO luminosities as a function of stellar masses and SFRs, as well as the ratio (a proxy for the gas fraction). The two samples show statistically consistent trends in the and planes. However, there are indications that AGN feature lower CO(3-2) luminosities (0.4–0.7 dex) than inactive galaxies at the 2–3σ level when we focus on the subset of parameters where the results are better constrained (i.e., L FIR  ≈ 1012.2 L ⊙ and M *  > 1011 M ⊙ ) and on the distribution of the mean log( ). Therefore, even by conservatively assuming the same excitation factor r 31 , we would find lower molecular gas masses in AGN, and assuming higher r 31 would exacerbate this difference. We interpret our result as a hint of the potential effect of AGN activity (such as radiation and outflows), which may be able to heat, excite, dissociate, and/or deplete the gas reservoir of the host galaxies. Better SFR measurements and deeper CO observations for AGN as well as larger and more uniformly selected samples of both AGN and inactive galaxies are required to confirm whether there is a true difference between the two populations.

/pdf/super-iv-co-j-3-2-properties-of-active-galactic-nucleus-5aj17humz2.pdf

SUPER - IV. CO(J = 3–2) properties of active galactic nucleus hosts at cosmic noon revealed by ALMA

Previous studies based on the 'Quantal Model' for synaptic transmission suggest that neurotransmitter release is mediated by a single release site at individual synaptic contacts in the neocortex. However, recent studies seem to contradict this hypothesis and indicate that multi-vesicular release (MVR) could better explain the synaptic response variability observed in vitro. In this study we present a novel method to estimate the number of release sites per synapse, also known as the size of the readily releasable pool (NRRP), from paired whole-cell recordings of connections between layer 5 thick tufted pyramidal cell (L5_TTPC) in the juvenile rat somatosensory cortex. Our approach extends the work of Loebel et al. (2009) by leveraging a recently published data-driven biophysical model of neocortical tissue. Using this approach, we estimated NRRP to be between two to three for synaptic connections between L5_TTPCs. To constrain NRRP values for other connections in the microcircuit, we developed and validated a generalization approach using published data on the coefficient of variation (CV) of the amplitudes of post-synaptic potentials (PSPs) from literature and comparing them against in silico experiments. Our study predicts that transmitter release at synaptic connections in the neocortex could be mediated by MVR and provides a data-driven approach to constrain the MVR model parameters in the microcircuit.

/pdf/estimating-the-readily-releasable-vesicle-pool-size-at-24u358rl36.pdf

Estimating the Readily-Releasable Vesicle Pool Size at Synaptic Connections in the Neocortex.

/pdf/kolmogorov-smirnov-test-for-two-dimensional-data-2n6s8ptru8.pdf

Kolmogorov-Smirnov test for two-dimensional data

Longtime readers of Computers in Physics may remember us as the editors/authors of the Numerical Recipes column that ran from 1988 through 1992. At that time, with the publication of the second edition of our Numerical Recipes (NR) books in C and Fortran, we took a sabbatical leave from column writing, a leave that became inadvertently permanent. Now, as a part of CIP's Tenth Anniversary celebration, we have been invited back to offer some observations about the past of scientific computing, including the educational niche occupied by our books, and to make some prognostications about where the field is going.

/pdf/numerical-recipes-does-this-paradigm-have-a-future-5ai8d7kme2.pdf

Wiliam H. Press

Papers

Kolmogorov-Smirnov test for two-dimensional data

Numerical recipes: does this paradigm have a future?