ancientstraits · December 6, 2023 18:03
diff --git a/abstracts_and_summaries b/abstracts_and_summaries
 Abstract: We present the first deep learning model for segmenting galactic spiral arms and bars. In a blinded assessment by expert astronomers, our predicted spiral arm masks are preferred over both current automated methods (99% of evaluations) and our original volunteer labels (79% of evaluations). Experts rated our spiral arm masks as `mostly good' to `perfect' in 89% of evaluations. Bar lengths trivially derived from our predicted bar masks are in excellent agreement with a dedicated crowdsourcing project. The pixelwise precision of our masks, previously impossible at scale, will underpin new research into how spiral arms and bars evolve.

 Summary: Scientists have introduced a groundbreaking deep learning model designed for accurately segmenting galactic spiral arms and bars, outperforming current automated methods and even original volunteer labels, according to expert astronomers in a blinded assessment. With 89% of evaluations rating the predicted spiral arm masks as 'mostly good' to 'perfect,' the model's pixelwise precision opens doors for unprecedented research into the evolution of spiral arms and bars in galaxies.


 Abstract: Recent studies have postulated that the presence of dark matter (DM) spikes around IMBHs could lead to observable dephasing effects in gravitational wave (GW) signals emitted by Intermediate Mass Ratio Inspirals (IMRIs). While prior investigations primarily relied on non-self-consistent analytic methods to estimate the influence of DM spikes on eccentric IMRIs, our work introduces the first self-consistent treatment of this phenomenon through N-body simulations. Contrary to previous studies, which suggested that dynamical friction (DF), a cumulative effect of two-body encounters, is the primary mechanism responsible for energy dissipation, we reveal that the slingshot mechanism, a three-body effect, plays a more significant role in driving the binary system's energy loss and consequent orbital shrinkage, similar to stellar loss cone scattering in Massive Black Hole (MBH) binaries. Furthermore, our work extends its analysis to include rotation in DM spikes, a factor often overlooked in previous studies. We find that binaries that counter-rotate with respect to the spike particles merge faster, while binaries that co-rotate merge slower, in opposition to the expectation from DF theory. While our models are idealistic, they offer findings that pave the way for a more comprehensive understanding of the complex interactions between DM spikes, IMRIs, GW emission, and the ability to constrain DM microphysics. Our work systematically includes Post-Newtonian (PN) effects until 2.5 order and our results are accurate and robust.

 Summary: Recent research delves into the cosmic dance of Intermediate Mass Ratio Inspirals (IMRIs) and their gravitational wave (GW) signals, challenging prior notions by presenting the first self-consistent treatment through N-body simulations. Contrary to previous beliefs about dynamical friction (DF) being the main player in energy dissipation, the study unveils the dominant role of the slingshot mechanism in driving binary system energy loss, with a twist—binaries counter-rotating with dark matter (DM) spikes merge faster, shaking up expectations and offering a more nuanced understanding of the intricate interplay between DM spikes, IMRIs, and GW emission.


 Abstract: Early expansion plays a fundamental role in the dynamical evolution of young star clusters. However, until very recently most of our understanding of cluster expansion was based only on indirect evidence or on statistically limited samples of clusters. Here we present a comprehensive kinematic analysis of virtually all known young (t<300 Myr) Galactic clusters based on the improved astrometric quality of the Gaia DR3 data. Such a large sample provides the unprecedented opportunity to robustly constrain the fraction of clusters and the timescale during which expansion has a prominent impact on the overall kinematics. We find that a remarkable fraction (up to 80%) of clusters younger than ∼30 Myr is currently experiencing significant expansion, whereas older systems are mostly compatible with equilibrium configurations. We observe a trend where the expansion speed increases with the clustercentric distance, suggesting that clusters undergoing expansion will likely lose a fraction of their present-day mass. Also, most young expanding clusters show large sizes, possibly due to the expansion itself. A comparison with a set of N-body simulations of young star clusters shows that the observed expansion pattern is in general qualitative agreement with that found for systems undergoing violent relaxation and evolving toward a final virial equilibrium state. However, we also note that additional processes likely associated with residual gas expulsion and mass loss due to stellar evolution are also likely to play a key role in driving the observed expansion.

 Summary: Revolutionizing our understanding of young star clusters, a groundbreaking study utilizes the enhanced astrometric precision of Gaia DR3 data to conduct a comprehensive kinematic analysis of virtually all known young Galactic clusters. Unveiling that a substantial fraction, reaching up to 80%, of clusters younger than approximately 30 million years are actively undergoing expansion, the research sheds light on the dynamics, revealing a trend where expansion speed rises with clustercentric distance and suggesting potential mass loss for expanding clusters.


 Abstract: Carbon monoxide (CO) is a poor tracer of H2 in the diffuse interstellar medium (ISM), where most of the carbon is not incorporated into CO molecules unlike the situation at higher extinctions. We present a novel, indirect method to constrain H2 column densities (NH2) without employing CO observations. We show that previously-recognized nonlinearities in the relation between the extinction, AV(H2), derived from dust emission and the HI column density (NHI) are due to the presence of molecular gas. We employ archival NH2 data, obtained from the UV spectra of stars, and calculate AV(H2) towards these sight lines using 3D extinction maps. We derive an empirical relation between AV(H2) and NH2, which we use to constrain NH2 in the diffuse ISM. We construct a NH2 map of our Galaxy and compare it to the CO integrated intensity (WCO) distribution. We find that the average ratio (XCO) between NH2 and WCO is approximately equal to 2×1020 cm−2 (K km s−1)−1, consistent with previous estimates. However, we find that the XCO factor varies by orders of magnitude on arcminute scales between the outer and the central portions of molecular clouds. For regions with NH2≳1020 cm−2, we estimate that the average H2 fractional abundance, fH2 = 2NH2/(2NH2 + NHI), is 0.25. Multiple (distinct) largely atomic clouds are likely found along high-extinction sightlines (AV≥1 mag), hence limiting fH2 in these directions. More than 50% of the lines of sight with NH2≥1020 cm−2 are untraceable by CO with a J = 1-0 sensitivity limit WCO=1 K km s−1.

 Summary: Breaking away from traditional methods, scientists unveil a novel approach to estimate molecular hydrogen (H2) column densities in the diffuse interstellar medium without relying on carbon monoxide (CO) observations. Utilizing archival data from ultraviolet spectra of stars and 3D extinction maps, the study establishes an empirical link between extinction and H2 column densities, generating a detailed H2 map of the Milky Way, revealing variations in the H2-to-CO ratio across molecular clouds and highlighting the limitations of CO in tracing high-extinction regions.
	Abstract: We present the first deep learning model for segmenting galactic spiral arms and bars. In a blinded assessment by expert astronomers, our predicted spiral arm masks are preferred over both current automated methods (99% of evaluations) and our original volunteer labels (79% of evaluations). Experts rated our spiral arm masks as `mostly good' to `perfect' in 89% of evaluations. Bar lengths trivially derived from our predicted bar masks are in excellent agreement with a dedicated crowdsourcing project. The pixelwise precision of our masks, previously impossible at scale, will underpin new research into how spiral arms and bars evolve.

	Summary: Scientists have introduced a groundbreaking deep learning model designed for accurately segmenting galactic spiral arms and bars, outperforming current automated methods and even original volunteer labels, according to expert astronomers in a blinded assessment. With 89% of evaluations rating the predicted spiral arm masks as 'mostly good' to 'perfect,' the model's pixelwise precision opens doors for unprecedented research into the evolution of spiral arms and bars in galaxies.


	Abstract: Recent studies have postulated that the presence of dark matter (DM) spikes around IMBHs could lead to observable dephasing effects in gravitational wave (GW) signals emitted by Intermediate Mass Ratio Inspirals (IMRIs). While prior investigations primarily relied on non-self-consistent analytic methods to estimate the influence of DM spikes on eccentric IMRIs, our work introduces the first self-consistent treatment of this phenomenon through N-body simulations. Contrary to previous studies, which suggested that dynamical friction (DF), a cumulative effect of two-body encounters, is the primary mechanism responsible for energy dissipation, we reveal that the slingshot mechanism, a three-body effect, plays a more significant role in driving the binary system's energy loss and consequent orbital shrinkage, similar to stellar loss cone scattering in Massive Black Hole (MBH) binaries. Furthermore, our work extends its analysis to include rotation in DM spikes, a factor often overlooked in previous studies. We find that binaries that counter-rotate with respect to the spike particles merge faster, while binaries that co-rotate merge slower, in opposition to the expectation from DF theory. While our models are idealistic, they offer findings that pave the way for a more comprehensive understanding of the complex interactions between DM spikes, IMRIs, GW emission, and the ability to constrain DM microphysics. Our work systematically includes Post-Newtonian (PN) effects until 2.5 order and our results are accurate and robust.

	Summary: Recent research delves into the cosmic dance of Intermediate Mass Ratio Inspirals (IMRIs) and their gravitational wave (GW) signals, challenging prior notions by presenting the first self-consistent treatment through N-body simulations. Contrary to previous beliefs about dynamical friction (DF) being the main player in energy dissipation, the study unveils the dominant role of the slingshot mechanism in driving binary system energy loss, with a twist—binaries counter-rotating with dark matter (DM) spikes merge faster, shaking up expectations and offering a more nuanced understanding of the intricate interplay between DM spikes, IMRIs, and GW emission.


	Abstract: Early expansion plays a fundamental role in the dynamical evolution of young star clusters. However, until very recently most of our understanding of cluster expansion was based only on indirect evidence or on statistically limited samples of clusters. Here we present a comprehensive kinematic analysis of virtually all known young (t<300 Myr) Galactic clusters based on the improved astrometric quality of the Gaia DR3 data. Such a large sample provides the unprecedented opportunity to robustly constrain the fraction of clusters and the timescale during which expansion has a prominent impact on the overall kinematics. We find that a remarkable fraction (up to 80%) of clusters younger than ∼30 Myr is currently experiencing significant expansion, whereas older systems are mostly compatible with equilibrium configurations. We observe a trend where the expansion speed increases with the clustercentric distance, suggesting that clusters undergoing expansion will likely lose a fraction of their present-day mass. Also, most young expanding clusters show large sizes, possibly due to the expansion itself. A comparison with a set of N-body simulations of young star clusters shows that the observed expansion pattern is in general qualitative agreement with that found for systems undergoing violent relaxation and evolving toward a final virial equilibrium state. However, we also note that additional processes likely associated with residual gas expulsion and mass loss due to stellar evolution are also likely to play a key role in driving the observed expansion.

	Summary: Revolutionizing our understanding of young star clusters, a groundbreaking study utilizes the enhanced astrometric precision of Gaia DR3 data to conduct a comprehensive kinematic analysis of virtually all known young Galactic clusters. Unveiling that a substantial fraction, reaching up to 80%, of clusters younger than approximately 30 million years are actively undergoing expansion, the research sheds light on the dynamics, revealing a trend where expansion speed rises with clustercentric distance and suggesting potential mass loss for expanding clusters.


	Abstract: Carbon monoxide (CO) is a poor tracer of H2 in the diffuse interstellar medium (ISM), where most of the carbon is not incorporated into CO molecules unlike the situation at higher extinctions. We present a novel, indirect method to constrain H2 column densities (NH2) without employing CO observations. We show that previously-recognized nonlinearities in the relation between the extinction, AV(H2), derived from dust emission and the HI column density (NHI) are due to the presence of molecular gas. We employ archival NH2 data, obtained from the UV spectra of stars, and calculate AV(H2) towards these sight lines using 3D extinction maps. We derive an empirical relation between AV(H2) and NH2, which we use to constrain NH2 in the diffuse ISM. We construct a NH2 map of our Galaxy and compare it to the CO integrated intensity (WCO) distribution. We find that the average ratio (XCO) between NH2 and WCO is approximately equal to 2×1020 cm−2 (K km s−1)−1, consistent with previous estimates. However, we find that the XCO factor varies by orders of magnitude on arcminute scales between the outer and the central portions of molecular clouds. For regions with NH2≳1020 cm−2, we estimate that the average H2 fractional abundance, fH2 = 2NH2/(2NH2 + NHI), is 0.25. Multiple (distinct) largely atomic clouds are likely found along high-extinction sightlines (AV≥1 mag), hence limiting fH2 in these directions. More than 50% of the lines of sight with NH2≥1020 cm−2 are untraceable by CO with a J = 1-0 sensitivity limit WCO=1 K km s−1.

	Summary: Breaking away from traditional methods, scientists unveil a novel approach to estimate molecular hydrogen (H2) column densities in the diffuse interstellar medium without relying on carbon monoxide (CO) observations. Utilizing archival data from ultraviolet spectra of stars and 3D extinction maps, the study establishes an empirical link between extinction and H2 column densities, generating a detailed H2 map of the Milky Way, revealing variations in the H2-to-CO ratio across molecular clouds and highlighting the limitations of CO in tracing high-extinction regions.