Sunday, February 28, 2021

North American Megafauna Extinction Driven Mostly By Younger Dryas

The evidence increasingly favors a larger role for the Younger Dryas climate event, and a smaller role for over hunting in North American megafauna extinctions. 

"Megafauna populations appear to have been increasing as North American began to warm around 14,700 years ago," states Stewart. "But we then see a shift in this trend around 12,900 years ago as North America began to drastically cool, and shortly after this we begin to see the extinctions of megafauna occur."

And while these findings suggest that the return to near glacial conditions around 12,900 years ago was the proximate cause for the extinctions, the story is likely to be more complicated than this.

"We must consider the ecological changes associated with these climate changes at both a continental and regional scale if we want to have a proper understanding of what drove these extinctions," explains group leader Huw Groucutt, senior author of the study. "Humans also aren't completely off the hook, as it remains possible that they played a more nuanced role in the megafauna extinctions than simple overkill models suggest."

Many researchers have argued that it is an impossible coincidence that megafauna extinctions around the world often happened around the time of human arrival. However, it is important to scientifically demonstrate that there was a relationship, and even if there was, the causes may have been much more indirect (such as through habitat modification) than a killing frenzy as humans arrived in a region.

From Science Daily.

The disappearance of many North American megafauna at the end of the Pleistocene is a contentious topic. While the proposed causes for megafaunal extinction are varied, most researchers fall into three broad camps emphasizing human overhunting, climate change, or some combination of the two. Understanding the cause of megafaunal extinctions requires the analysis of through-time relationships between climate change and megafauna and human population dynamics. To do so, many researchers have used summed probability density functions (SPDFs) as a proxy for through-time fluctuations in human and megafauna population sizes. SPDFs, however, conflate process variation with the chronological uncertainty inherent in radiocarbon dates. Recently, a new Bayesian regression technique was developed that overcomes this problem—Radiocarbon-dated Event-Count (REC) Modelling. 
Here we employ REC models to test whether declines in North American megafauna species could be best explained by climate changes, increases in human population densities, or both, using the largest available database of megafauna and human radiocarbon dates. Our results suggest that there is currently no evidence for a persistent through-time relationship between human and megafauna population levels in North America. There is, however, evidence that decreases in global temperature correlated with megafauna population declines.
Stewart, M., Carleton, W. C., Groucutt, H. S. "Climate change, not human population growth, correlates with Late Quaternary megafauna declines in North America." Nature Communications (February 16, 2021).  DOI: 10.1038/s41467-021-21201-8

Friday, February 26, 2021

Lepton Universality Not Violated In Top Quark Decays

Lepton universality is the Standard Model principle that electrons, muons, and tau leptons have identical properties except for mass. There have been some experimental anomalies in collider experiments that suggest that this principle is violated despite many other seemingly similar kinds of experiments where these anomalies are not seen.

An new analysis of top quark decays from ATLAS experiment data at the Large Hadron Collider (LHC)  is consistent with an absence of lepton universality violations. This further contributes to the difficulty of identifying any beyond the Standard Model physics that could give rise to the lepton universality anomalies observed in certain kinds of B meson decays, while not producing any signs of lepton universality violations in any other kinds of interactions.

About Newton

Everyone remembers Newton for his contributions to physics. 

But he made much of his fortune as the director of London's mint, making coins, and investing in businesses, after he got sick of being a professor at Cambridge, where he felt tormented as a Unitarian in a Trinitarian institution.

Wednesday, February 24, 2021

Ancient Cats


Luminous Matter Distribution Shape Predicts Stellar To Dark Matter Halo Mass Ratio

One of the core principle's of Alexandre Deur's efforts to explain dark matter and dark energy phenomena as due to the self-interaction of weak gravitational fields is that these phenomena disappear in truly spherically symmetric matter distributions, while growing stronger in the case for disk-like matter distributions and reaching their greatest extremes in matter distributions that approximate two point-like matter sources.

A new study confirms this observational result the the stellar-to-halo mass ratio is larger in more spherically symmetric galaxies (i.e. they have less inferred dark matter) and smaller in spiral galaxies (i.e. they have more inferred dark matter), while trying to explain it in a LambdaCDM dark matter particle paradigm (unconvincingly in my opinion). The main result of the paper is in the figure below in which the top of the chart involve systems with less dark matter relative to stellar mass and the bottom involves systems with more dark matter relative to stellar mass, the left of each chart involves lower masses and the right of each chart involves higher masses.

Fig. 3. SHMR in the form of the ratio f(*) ≡ M(*)/ f(b)M(h) as a function of stellar mass (left) or halo mass (right) for the sample of spiral galaxies in SPARC (blue diamonds, PFM19) and for the sample of ellipticals and lenticulars in SLUGGS (red circles, this work). The halo masses of late types are estimated from HI rotation curves, those of early types from the kinematics of the GC system. We compare to the SHMR from the abundance matching model by Moster et al. (2013, grey band).

The paper and its abstract are as follows (small print and original font retained in abstract to preserve formatting):

We derive the stellar-to-halo mass relation (SHMR), namely fM/Mh versus M and Mh, for early-type galaxies from their near-IR luminosities (for M) and the position-velocity distributions of their globular cluster systems (for Mh). Our individual estimates of Mh are based on fitting a dynamical model with a distribution function expressed in terms of action-angle variables and imposing a prior on Mh from the concentration-mass relation in the standard ΛCDM cosmology. 
We find that the SHMR for early-type galaxies declines with mass beyond a peak at M5×1010M and Mh1012M (near the mass of the Milky Way). This result is consistent with the standard SHMR derived by abundance matching for the general population of galaxies, and with previous, less robust derivations of the SHMR for early types. However, it contrasts sharply with the monotonically rising SHMR for late types derived from extended HI rotation curves and the same ΛCDM prior on Mh as we adopt for early types. The SHMR for massive galaxies varies more or less continuously, from rising to falling, with decreasing disc fraction and decreasing Hubble type. 
We also show that the different SHMRs for late and early types are consistent with the similar scaling relations between their stellar velocities and masses (Tully-Fisher and Faber-Jackson relations). Differences in the relations between the stellar and halo virial velocities account for the similarity of the scaling relations. 
We argue that all these empirical findings are natural consequences of a picture in which galactic discs are built mainly by smooth and gradual inflow, regulated by feedback from young stars, while galactic spheroids are built by a cooperation between merging, black-hole fuelling, and feedback from AGNs.

Lorenzo Posti, S. Michael Fall "Dynamical evidence for a morphology-dependent relation between the stellar and halo masses of galaxies" Accepted for publication in A&A. arXiv:2102.11282 [astro-ph.GA] (February 22, 2021). Per Wikipedia articles on the linked terms:
The Faber–Jackson relation provided the first empirical power-law relation between the luminosity and the central stellar velocity dispersion of elliptical galaxy, and was presented by the astronomers Sandra M. Faber and Robert Earl Jackson in 1976. 

with the index approximately equal to 4.


the Tully–Fisher relation (TFR) is an empirical relationship between the mass or intrinsic luminosity of a spiral galaxy and its asymptotic rotation velocity or emission line width. It was first published in 1977 by astronomers R. Brent Tully and J. Richard Fisher. The luminosity is calculated by multiplying the galaxy's apparent brightness by , where  is its distance from us, and the spectral-line width is measured using long-slit spectroscopy.

Several different forms of the TFR exist, depending on which precise measures of mass, luminosity or rotation velocity one takes it to relate. Tully and Fisher used optical luminosity, but subsequent work showed the relation to be tighter when defined using microwave to infrared (K band) radiation (a good proxy for stellar mass), and even tighter when luminosity is replaced by the galaxy's total baryonic mass (the sum of its mass in stars and gas). This latter form of the relation is known as the Baryonic Tully–Fisher relation (BTFR), and states that baryonic mass is proportional to velocity to the power of roughly 4.

The regularity of these relationships motivated and has been taken as evidence of Modified Newtonian Dynamics (MOND), some of the implications of which can be formulated as the empirical, descriptive and predictive Radial Acceleration Relation (RAR) which is diplomatically agnostic about the reason that it arises unlike MOND which provides a gravity modification mechanism that reproduces the RAR.

The body text of the new paper notes that:

The unit "dex" is a power of ten. Hence, a factor 0.8 dex is a factor of 6.3,  0.35 dex is a factor of 2.2, 0.27 dex is a factor of 1.86 and 0.08 dex is 20%.

So, pure disk galaxies in their proposed SHMR scheme have 6.3 times as much dark matter as pure spheroids in a galaxies with the same amount of ordinary matter from stars, and segregating disk galaxies from spheroid galaxies (which are much less common) reduces the overall scatter in the data by about 20%.

A difference in the SHMR for disk galaxies and elliptical and lenticular galaxies flows naturally and transparently from the self-interaction of gravitational fields in Deur's approach.

Footnote on Another Galaxy Scaling Relation

Another similar relationship not mentioned (because it isn't relevant here) is the

M–sigma (or M–σ) relation is an empirical correlation between the stellar velocity dispersion σ of a galaxy bulge and the mass M of the supermassive black hole at its center.

The M–σ relation was first presented in 1999 during a conference at the Institut d'astrophysique de Paris in France. The proposed form of the relation, which was called the "Faber–Jackson law for black holes", was 

where  is the solar mass. Publication of the relation in a refereed journal, by two groups, took place the following year. One of many recent studies, based on the growing sample of published black hole masses in nearby galaxies, gives 

Earlier work demonstrated a relationship between galaxy luminosity and black hole mass, which nowadays has a comparable level of scatter. The M–σ relation is generally interpreted as implying some source of mechanical feedback between the growth of supermassive black holes and the growth of galaxy bulges, although the source of this feedback is still uncertain.

Discovery of the M–σ relation was taken by many astronomers to imply that supermassive black holes are fundamental components of galaxies.

Other Works By The Authors

I'll provide below some cut and post arXiv paper summaries for other works by some of the same authors:

The impact of the halo spin-concentration relation on disc scaling laws

Galaxy scaling laws, such as the Tully-Fisher, mass-size and Fall relations, can provide extremely useful clues on our understanding of galaxy formation in a cosmological context. Some of these relations are extremely tight and well described by one single parameter (mass), despite the theoretical existence of secondary parameters such as spin and concentration, which are believed to impact these relations. In fact, the residuals of these scaling laws appear to be almost uncorrelated with each other, posing significant constraints on models where secondary parameters play an important role. 
Here, we show that a possible solution is that such secondary parameters are correlated amongst themselves, in a way that removes correlations in observable space. In particular, we focus on how the existence of an anti-correlation between the dark matter halo spin and its concentration -- which is still debated in simulations -- can weaken the correlation of the residuals of the Tully-Fisher and mass-size relations. Interestingly, using simple analytic galaxy formation models, we find that this happens only for a relatively small portion of the parameter space that we explored, which suggests that this idea could be used to derive constraints to galaxy formation models that are still unexplored.
Comments:Accepted for publication in A&A
Subjects:Astrophysics of Galaxies (astro-ph.GA); Cosmology and Nongalactic Astrophysics (astro-ph.CO)
Journal reference:A&A 644, A76 (2020)
Cite as:arXiv:2010.09727 [astro-ph.GA]

 [Submitted on 14 Sep 2020 (v1), last revised 1 Feb 2021 (this version, v3)]

The baryonic specific angular momentum of disc galaxies

(Abridged) Specific angular momentum is one of the key parameters that control the evolution of galaxies. We derive the baryonic specific angular momentum of disc galaxies and study its relation with the dark matter specific angular momentum. Using a combination of high-quality HI rotation curves and HI/near-IR surface densities, we homogeneously measure the stellar (j) and gas (jgas) specific angular momenta for a large sample of local disc galaxies. This allows us to determine the baryonic specific angular momentum (jbar) with high accuracy and across a very wide range of masses. 
The jM relation is an unbroken power-law from 7 log(M/M)11.5, with slope 0.54±0.02. For the gas component, we find that the jgasMgas relation is also an unbroken power-law from 6 log(Mgas/M)11, with a steeper slope of 1.02±0.04. Regarding the baryonic relation, our data support a correlation characterized by single power-law with slope 0.60±0.02. Our most massive spirals and smallest dwarfs lie along the same jbarMbar sequence. 
While the relations are tight and unbroken, we find internal correlations inside them: At fixed M, galaxies with larger j have larger disc scale lengths, and at fixed Mbar, gas-poor galaxies have lower jbar than expected. We estimate the retained fraction of baryonic specific angular momentum, finding it constant across our entire mass range with a value of 0.6, indicating that the jbar of present-day disc galaxies is comparable to the initial specific angular momentum of their dark matter haloes. These results set important constraints for hydrodynamical simulations and semi-analytical models aiming to reproduce galaxies with realistic specific angular momenta.
Comments:A&A, in press. Small changes w.r.t. previous version, see updated tables. Nature of results remains unchanged. The full version of the main table is available at this https URL and will be soon available at the CDS
Subjects:Astrophysics of Galaxies (astro-ph.GA); Cosmology and Nongalactic Astrophysics (astro-ph.CO)
Cite as:arXiv:2009.06645 [astro-ph.GA]

Massive disc galaxies in cosmological hydrodynamical simulations are too dark matter-dominated

We investigate the disc-halo connection in massive (Mstar/Msun>5e10) disc galaxies from the cosmological hydrodynamical simulations EAGLE and IllustrisTNG, and compare it with that inferred from the study of HI rotation curves in nearby massive spirals from the Spitzer Photometry and Accurate Rotation Curves (SPARC) dataset. 
We find that discrepancies between the the simulated and observed discs arise both on global and on local scales. Globally, the simulated discs inhabit halos that are a factor ~4 (in EAGLE) and ~2 (in IllustrisTNG) more massive than those derived from the rotation curve analysis of the observed dataset. We also use synthetic rotation curves of the simulated discs to demonstrate that the recovery of the halo masses from rotation curves are not systematically biased. 
We find that the simulations predict dark-matter dominated systems with stellar-to-total enclosed mass ratios that are a factor of 1.5-2 smaller than real galaxies at all radii. This is an alternative manifestation of the `failed feedback problem', since it indicates that simulated halos hosting massive discs have been too inefficient at converting their baryons into stars, possibly due to an overly efficient stellar and/or AGN feedback implementation.
Comments:10 pages, 6 figures, accepted by A&A
Subjects:Astrophysics of Galaxies (astro-ph.GA)
Journal reference:A&A 640, A70 (2020)
Cite as:arXiv:2005.01724 [astro-ph.GA]

Off the baryonic Tully-Fisher relation: a population of baryon-dominated ultra-diffuse galaxies

We study the gas kinematics traced by the 21-cm emission of a sample of six HIrich low surface brightness galaxies classified as ultra-diffuse galaxies (UDGs). Using the 3D kinematic modelling code 3DBarolo we derive robust circular velocities, revealing a startling feature: HIrich UDGs are clear outliers from the baryonic Tully-Fisher relation, with circular velocities much lower than galaxies with similar baryonic mass. 
Notably, the baryon fraction of our UDG sample is consistent with the cosmological value: these UDGs are compatible with having no "missing baryons" within their virial radii. Moreover, the gravitational potential provided by the baryons is sufficient to account for the amplitude of the rotation curve out to the outermost measured point, contrary to other galaxies with similar circular velocities. We speculate that any formation scenario for these objects will require very inefficient feedback and a broad diversity in their inner dark matter content.
Comments:Accepted for publication by The Astrophysical Journal Letters (ApJL). V2: Acknowledgments have been updated, and a typo has been corrected
Subjects:Astrophysics of Galaxies (astro-ph.GA); Cosmology and Nongalactic Astrophysics (astro-ph.CO)
Cite as:arXiv:1909.01363 [astro-ph.GA]

Galaxy disc scaling relations: A tight linear galaxy -- halo connection challenges abundance matching

In ΛCDM cosmology, to first order, galaxies form out of the cooling of baryons within the virial radius of their dark matter halo. The fractions of mass and angular momentum retained in the baryonic and stellar components of disc galaxies put strong constraints on our understanding of galaxy formation. 
In this work, we derive the fraction of angular momentum retained in the stellar component of spirals, fj, the global star formation efficiency fM, and the ratio of the asymptotic circular velocity (Vflat) to the virial velocity fV, and their scatter, by fitting simultaneously the observed stellar mass-velocity (Tully-Fisher), size-mass, and mass-angular momentum (Fall) relations. We compare the goodness of fit of three models: (i) where the logarithm of fjfM, and fV vary linearly with the logarithm of the observable Vflat; (ii) where these values vary as a double power law; and (iii) where these values also vary as a double power law but with a prior imposed on fM such that it follows the expectations from widely used abundance matching models. 
We conclude that the scatter in these fractions is particularly small (0.07 dex) and that the linear model is by far statistically preferred to that with abundance matching priors. This indicates that the fundamental galaxy formation parameters are small-scatter single-slope monotonic functions of mass, instead of being complicated non-monotonic functions. This incidentally confirms that the most massive spiral galaxies should have turned nearly all the baryons associated with their haloes into stars. We call this the failed feedback problem.
Comments:A&A in press (17 pages, 3 appendices)
Subjects:Astrophysics of Galaxies (astro-ph.GA); Cosmology and Nongalactic Astrophysics (astro-ph.CO)
Cite as:arXiv:1909.01344 [astro-ph.GA]

The dichotomy of dark matter fraction and total mass density slope of galaxies over five dex in mass

We analyse the mass density distribution in the centres of galaxies across five orders of magnitude in mass range. Using high-quality spiral galaxy rotation curves and infrared photometry from SPARC, we conduct a systematic study of their central dark matter fraction (fDM) and their mass density slope (α), within their effective radius. 
We show that lower-mass spiral galaxies are more dark matter dominated and have more shallow mass density slopes when compared with more massive galaxies, which have density profiles closer to isothermal. Low-mass (M1010M) gas-rich spirals span a wide range of \fdm\ values, but systematically lower than in gas-poor systems of similar mass. With increasing galaxy mass, the values of \fdm\ decrease and the density profiles steepen. In the most massive late-type gas-poor galaxies, a possible flattening of these trends is observed. 
When comparing these results to massive (M1010M) elliptical galaxies from SPIDER and to dwarf ellipticals from SMACKED, these trends result to be inverted. Hence, the values of both fDM and α, as a function of M, exhibit a U-shape trend. At a fixed stellar mass, the mass density profiles in dwarf ellipticals are steeper than in spirals. These trends can be understood by stellar feedback from a more prolonged star formation period in spirals, causing a transformation of the initial steep density cusp to a more shallow profile via differential feedback efficiency by supernovae, and by galaxy mergers or AGN feedback in higher-mass galaxies.
Comments:12 pages, 4 figures, MNRAS in press. Version updated according to the referee comments. Figures are also updated, other typos are corrected
Subjects:Astrophysics of Galaxies (astro-ph.GA); Cosmology and Nongalactic Astrophysics (astro-ph.CO)
Cite as:arXiv:1902.10158 [astro-ph.GA]

Mass and shape of the Milky Way's dark matter halo with globular clusters from Gaia and Hubble

We estimate the mass of the inner (<20 kpc) Milky Way and the axis ratio of its dark matter halo using globular clusters as tracers. At the same time, we constrain the phase-space distribution of the globular cluster system. We use the Gaia DR2 catalogue of 75 globular clusters' proper motions and recent measurements of the proper motions of another 20 distant clusters obtained with the Hubble Space Telescope. We describe the globular cluster system with a 2-component distribution function (DF), with a flat, rotating disc and a rounder, more extended halo. While fixing the Milky Way's disc and bulge, we let the mass and shape of the dark matter halo and we fit these two parameters, together with other six describing the DF, with a Bayesian method. 
We find the mass of the Galaxy within 20 kpc to be M(<20kpc)=1.91+0.180.17×1011M, of which MDM(<20kpc)=1.37+0.180.17×1011M is in dark matter, and the density axis ratio of the dark matter halo to be q=1.30±0.25. This implies a virial mass Mvia=1.3±0.3×1012M. 
Our analysis rules out oblate (q<0.8) and strongly prolate halos (q>1.9) with 99\% probability. Our preferred model reproduces well the observed phase-space distribution of globular clusters and has a disc component that closely resembles that of the Galactic thick disc. 
The halo component follows a power-law density profile ρr3.3, has a mean rotational velocity of Vrot14kms1 at 20 kpc, and has a mildly radially biased velocity distribution (β0.2±0.07, fairly constant outside 15 kpc). We also find that our distinction between disc and halo clusters resembles, although not fully, the observed distinction in metal-rich ([Fe/H]>0.8) and metal-poor ([Fe/H]0.8) cluster populations.
Comments:Accepted for publication in A&A
Subjects:Astrophysics of Galaxies (astro-ph.GA)
Journal reference:A&A 621, A56 (2019)
Cite as:arXiv:1805.01408 [astro-ph.GA]

The body text of this paper states in the conclusion that:
(iv) we measure the mass of the dark matter halo of the Galaxy within 20 kpc to be log10 M20,DM/M = 11.14 ± 0.05. This very accurate measurement implies a total virial mass for the Milky Way of Mvir = 1.3 ± 0.3 × 1012M after assuming a concentration-virial mass relation; 
(iv) we measure a flattening q = 1.22 ± 0.23, and find oblate halos with q < 0.7 to be ruled out by our analysis (with 99% probability) and spherical models to be disfavoured in comparison to prolate halos.
Oblate means a spheroid flattened at the poles. Prolate means lengthened in the direction of a polar diameter.

Angular Momentum and Galaxy Formation Revisited: Scaling Relations for Disks and Bulges

We show that the stellar specific angular momentum j_*, mass M_*, and bulge fraction beta_* of normal galaxies of all morphological types are consistent with a simple model based on a linear superposition of independent disks and bulges. In this model, disks and bulges follow scaling relations of the form j_*d ~ M_*d^alpha and j_*b ~ M_*b^alpha with alpha = 0.67 +/- 0.07 but offset from each other by a factor of 8 +/- 2 over the mass range 8.9 <= log M_*/M_Sun <= 11.8. Separate fits for disks and bulges alone give alpha = 0.58 +/- 0.10 and alpha = 0.83 +/- 0.16, respectively. This model correctly predicts that galaxies follow a curved 2D surface in the 3D space of log j_*, log M_*, and beta_*. We find no statistically significant indication that galaxies with classical and pseudo bulges follow different relations in this space, although some differences are permitted within the observed scatter and the inherent uncertainties in decomposing galaxies into disks and bulges. As a byproduct of this analysis, we show that the j_*--M_* scaling relations for disk-dominated galaxies from several previous studies are in excellent agreement with each other. In addition, we resolve some conflicting claims about the beta_*-dependence of the j_*--M_* scaling relations. The results presented here reinforce and extend our earlier suggestion that the distribution of galaxies with different beta_* in the j_*--M_* diagram constitutes an objective, physically motivated alternative to subjective classification schemes such as the Hubble sequence.
Comments:ApJ, in press; 17 pages, 4 figures; minor revisions to discussion of errors and final implications
Subjects:Astrophysics of Galaxies (astro-ph.GA)
Cite as:arXiv:1808.02525 [astro-ph.GA]

Relations Between the Sizes of Galaxies and their Dark Matter Halos at Redshifts 0<z<3

We derive relations between the effective radii Reff of galaxies and the virial radii R200c of their dark matter halos over the redshift range 0<z<3. For galaxies, we use the measured sizes from deep images taken with \emph{Hubble Space Telescope} for the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey; for halos, we use the inferred sizes from abundance matching to cosmological dark matter simulations via a stellar mass--halo mass (SMHM) relation. For this purpose, we derive a new SMHM relation based on the same selection criteria and other assumptions as for our sample of galaxies with size measurements. As a check on the robustness of our results, we also derive Reff--R200c relations for three independent SMHM relations from the literature. We find that galaxy Reff is proportional on average to halo R200c, confirming and extending to high redshifts the z=0 results of Kravtsov. Late-type galaxies (with low Sérsic index and high specific star formation rate [sSFR]) follow a linear Reff--R200c relation, with effective radii at 0.5<z<3 close to those predicted by simple models of disk formation; at z<0.5, the sizes of late-type galaxies appear to be slightly below this prediction. Early-type galaxies (with high Sérsic index and low sSFR) follow a roughly parallel Reff--R200c relation,  0.2--0.3 dex below the one for late-type galaxies. Our observational results, reinforced by recent hydrodynamical simulations, indicate that galaxies grow quasi-homologously with their dark matter halos.
Comments:This version is the same as the published ApJ paper, including a few minor corrections made in proof
Subjects:Astrophysics of Galaxies (astro-ph.GA)
Cite as:arXiv:1701.04001 [astro-ph.GA]