arXiv subjects
Publications and source records attributed to M. A. Taylor.
We record two results in the theory of vector and Banach lattices related to order adherence. First, we give a negative answer to Gao and Leung's question on whether the $uo$-adherence of sublattices must be order closed. Second, we present a self-contained counterexample showing that a Banach lattice with a weakly Fatou norm need not admit any equivalent lattice norm with the Fatou property.
The Euclid Early Release Observations (ERO) programme targeted the Perseus galaxy cluster in its central region over 0.7deg$^2$. We combined the exceptional image quality and depth of the ERO-Perseus with FUV and NUV observations from GALEX and AstroSat/UVIT, as well as $ugrizHα$ data from MegaCam at the CFHT, to deliver FUV-to-NIR magnitudes of the 87 brightest galaxies within the Perseus cluster. We reconstructed the star-formation history (SFH) of 59 early-type galaxies (ETGs) within the sample, through the spectral energy distribution (SED) fitting code CIGALE and state-of-the-art stellar population (SP) models to reproduce the galactic UV emission from hot, old, low-mass stars (i.e. the UV upturn). In addition, for the six most massive ETGs in Perseus [stellar masses $\log_{10}(M_{\ast}/M_{\odot}) \geq 10.3$], we analysed their spatially resolved SP through a radial SED fitting. In agreement with our previous work on Virgo ETGs, we found that (i) the majority of ETGs needs the presence of an UV upturn to explain their FUV emission, with temperatures $\langle T_{\rm UV}\rangle$~33800 K; (ii) ETGs have grown their stellar masses quickly, with SF timescales $τ\lesssim 1500$ Myr. We found that all ETGs in the sample have formed more than about 30% of their stellar masses at z~5, up to ~100%. At z~5, the stellar masses of the most massive nearby ETGs, which have present-day stellar masses $\log_{10}(M_{\ast}/M_{\odot})\gtrsim 10.8$, are then found to be comparable to those of the red quiescent galaxies observed by JWST at similar redshifts (z>4.6). This study can be extended to ETGs in the 14000 deg$^2$ extragalactic sky that will soon be observed by Euclid, in combination with those from other major upcoming surveys (e.g. Rubin/LSST), and UV observations, to ultimately assess whether the nearby massive ETGs represent the progeny of the massive high-z JWST red quiescent galaxies.
We study the free Banach lattice $FBL^{(p,\infty)}[E]$ with upper $p$-estimates generated by a Banach space $E$. Using a classical result of Pisier on factorization through $L^{p,\infty}(μ)$ together with a finite dimensional reduction, it is shown that the spaces $\ell^{p,\infty}(n)$ witness the universal property of $FBL^{(p,\infty)}[E]$ isomorphically. As a consequence, we obtain a functional representation for $FBL^{(p,\infty)}[E]$. More generally, our proof allows us to identify the norm of any free Banach lattice over $E$ associated with a rearrangement invariant function space. After obtaining the above functional representation, we take the first steps towards analyzing the fine structure of $FBL^{(p,\infty)}[E]$. Notably, we prove that the norm for $FBL^{(p,\infty)}[E]$ cannot be isometrically witnessed by $L^{p,\infty}(μ)$ and settle the question of characterizing when an embedding between Banach spaces extends to a lattice embedding between the corresponding free Banach lattices with upper $p$-estimates. To prove this latter result, we introduce a novel push-out argument, which when combined with the injectivity of $\ell^p$ allows us to give an alternative proof of the subspace problem for free $p$-convex Banach lattices. On the other hand, we prove that $\ell^{p,\infty}$ is not injective in the class of Banach lattices with upper $p$-estimates, elucidating one of many difficulties arising in the study of $FBL^{(p,\infty)}[E]$.
Let $(Ω,Σ,μ)$ be a measure space, and $1\leq p\leq \infty$. A subspace $E\subseteq L_p(μ)$ is said to do stable phase retrieval (SPR) if there exists a constant $C\geq 1$ such that for any $f,g\in E$ we have $$ \inf_{|λ|=1} \|f-λg\|\leq C\||f|-|g|\|. $$ In this case, if $|f|$ is known, then $f$ is uniquely determined up to an unavoidable global phase factor $λ$; moreover, the phase recovery map is $C$-Lipschitz. Phase retrieval appears in several applied circumstances, ranging from crystallography to quantum mechanics. In this article, we construct various subspaces doing stable phase retrieval, and make connections with $Λ(p)$-set theory. Moreover, we set the foundations for an analysis of stable phase retrieval in general function spaces. This, in particular, allows us to show that Hölder stable phase retrieval implies stable phase retrieval, improving the stability bounds in a recent article of M. Christ and the third and fourth authors. We also characterize those compact Hausdorff spaces $K$ such that $C(K)$ contains an infinite dimensional SPR subspace.
We investigate the structure of the free $p$-convex Banach lattice $FBL^{(p)}[E]$ over a Banach space $E$. After recalling why such a free lattice exists, and giving a convenient functional representation of it, we focus our study on how properties of an operator $T:E\rightarrow F$ between Banach spaces transfer to the associated lattice homomorphism $\overline{T}:FBL^{(p)}[E]\rightarrow FBL^{(p)}[F]$. Particular consideration is devoted to the case when the operator $T$ is an isomorphic embedding, which leads us to examine extension properties of operators into $\ell_p$, and several classical Banach space properties such as being a G.T. space. A detailed investigation of basic sequences and sublattices of free Banach lattices is provided. In addition, we begin to build a dictionary between Banach space properties of $E$ and Banach lattice properties of $FBL^{(p)}[E]$. In particular, we characterize the existence of lattice copies of $\ell_1$ in $FBL^{(p)}[E]$ and show that $FBL[E]$ has an upper $p$-estimate if and only if $id_{E^*}$ is $(q,1)$-summing ($\frac{1}{p}+\frac{1}{q}=1$). We also highlight the significant differences between $FBL^{(p)}$-spaces depending on whether $p$ is finite or infinite. For example, we show that $FBL^{(\infty)}[E]$ is lattice isometric to $FBL^{(\infty)}[F]$ whenever $E$ and $F$ have monotone finite dimensional decompositions, while, on the other hand, when $p<\infty$ and $E^*$ is smooth, $FBL^{(p)}[E]$ determines $E$ isometrically.
Given a Schauder basic sequence $(x_k)$ in a Banach lattice, we say that $(x_k)$ is bibasic if the expansion of every vector in $[x_k]$ converges not only in norm, but also in order. We prove that, in this definition, order convergence may be replaced with uniform convergence, with order boundedness of the partial sums, or with norm boundedness of finite suprema of the partial sums. The results in this paper extend and unify those from the pioneering paper "Order Schauder bases in Banach lattices" by A.Gumenchuk et al. In particular, we are able to characterize bibasic sequences in terms of the bibasis inequality, a result they obtained under certain additional assumptions. We then embark on a deeper study of their properties. We show that they are independent of ambient space, stable under small perturbations, and preserved under sequentially uniformly continuous norm isomorphic embeddings. We consider several special kinds of bibasic sequences, including permutable sequences, i.e., sequences for which every permutation is bibasic, and absolute sequences, i.e., sequences where expansions remain convergent after we replace every term with its modulus. We provide several equivalent characterizations of absolute sequences, showing how they relate to bibases and to further modifications of the basis inequality. We further consider bibasic sequences with unique order expansions. We show that this property does generally depend on ambient space, but not for the inclusion of $c_0$ into $\ell_\infty$. We also show that small perturbations of bibases with unique order expansions have unique order expansions, but this is not true if "bibases" is replaced with "bibasic sequences". Finally, we consider uo-bibasic sequences, which are obtained by replacing order convergence with uo-convergence in the definition of a bibasic sequence. We show that such sequences are very common.
We study the intrinsic shapes of a sample of over 400 quiescent galaxies in the cores of the Virgo and Fornax clusters with luminosities $10^{6} \leq L_{g}/L_{\odot} \leq 10^{8}$. Similar to satellites of the Local Group and Centaurus A, these faint, low surface brightness cluster galaxies are best described as a family of thick ($C/A > 0.5$), oblate-triaxial spheroids. However, the large sample size allows us to show that the flattening of their stellar distributions depends both on luminosity and on the presence of a nuclear star cluster. Nucleated satellites are thicker at all luminosities compared to their non-nucleated counterparts, and fainter galaxies are systematically thicker as well, regardless of nucleation. Once nucleation is accounted for, we find no evidence that the environment the satellites live in plays a relevant role in setting their three-dimensional structure. We interpret both the presence of stellar nuclei and the associated thicker shapes as the result of preferential early and rapid formation, effectively making these faint nucleated galaxies the first generation of cluster satellites.
We present the analysis of 61 nucleated dwarf galaxies in the central regions ($<R_{\rm vir}/4$) of the Fornax galaxy cluster. The galaxies and their nuclei are studied as part of the Next Generation Fornax Survey (NGFS) using optical imaging obtained with the Dark Energy Camera (DECam) mounted at Blanco/CTIO and near-infrared data obtained with VIRCam at VISTA/ESO. We decompose the nucleated dwarfs in nucleus and spheroid, after subtracting the surface brightness profile of the spheroid component and studying the nucleus using PSF photometry.In general, nuclei are consistent with colors of confirmed metal-poor globular clusters, but with significantly smaller dispersion than other confirmed compact stellar systems in Fornax. We find a bimodal nucleus mass distribution with peaks located at $\log({\cal M_*}/M_\odot)\!\simeq\!5.4$ and $\sim\,6.3$. These two nucleus sub-populations have different stellar population properties, the more massive nuclei are older than $\sim\!2$ Gyr and have metal-poor stellar populations ($Z\leq0.02\,Z_\odot$), while the less massive nuclei are younger than $\sim\!2$ Gyr with metallicities in the range $0.02\!<\!Z/Z_\odot\!\leq\!1$. We find that the nucleus mass (${\cal M}_{\rm nuc}$) vs. galaxy mass (${\cal M}_{\rm gal}$) relation becomes shallower for less massive galaxies starting around $10^8\,M_\odot$ and the mass ratio $η_n\!=\!{\cal M}_{\rm nuc}/{\cal M}_{\rm gal}$ shows a clear anti-correlation with ${\cal M}_{\rm gal}$ for the lowest masses, reaching $10\%$. We test current theoretical models of nuclear cluster formation and find that they cannot fully reproduce the observed trends. A likely mixture of in-situ star formation and star-cluster mergers seem to be acting during nucleus growth over cosmic time.
We report the discovery of 271 previously undetected dwarf galaxies in the outer Fornax cluster regions at radii $r_{\rm vir}/4<\!r\!<r_{\rm vir}/2$ using data from the Next Generation Fornax Survey (NGFS) with deep coadded $u'$, $g'$ and $i'$ images obtained with Blanco/DECam at Cerro Tololo Interamerican Observatory. From the 271 dwarf candidates we find 39 to be nucleated. Together with our previous study of the central Fornax region, the new dwarfs detected with NGFS data are 392, of which 56 are nucleated. The total Fornax dwarf galaxy population from NGFS and other catalogs rises, therefore, to a total of 643 with 181 being nucleated, yielding an overall nucleation fraction of $28\%$. The absolute $i'$-band magnitudes for the outer NGFS dwarfs are in the range $-18.80\le\,M_{i'}\le\,-8.78$ with effective radii $r_{{\rm eff},i'}\,=\,0.18-2.22$ kpc and an average Sersic index $\langle n\rangle_{i'}\,=\,0.81$. Non-nucleated dwarfs are found to be fainter and smaller by $Δ\langle M_{i'}\rangle\!=\!2.25$ mag and $Δ\langle r_{{\rm eff},i'}\rangle\!=\!0.4$ kpc than the nucleated dwarfs. We demonstrate a significant clustering of dwarf galaxies on scales $\lesssim\!100$ kpc, and projected surface number density profile estimates, $Σ_N(r)$, show a concentration of dwarfs in the Fornax core region within $r\!\sim\!350$ kpc. $Σ_N(r)$ has a flat distribution up to $\sim\!350$ kpc, beyond which it declines for the non-nucleated dwarfs. The nucleated dwarfs have a steeper $Σ_N(r)$ distribution, being more concentrated towards NGC 1399 and decreasing rapidly outwards. This is the first time the transition from cluster to field environment has been established for the very faint dwarf galaxy population with robust sample statistics.
We present the results of a wide spectroscopic survey aimed at detecting extragalactic globular clusters (GCs) in the core of the Fornax cluster. About 4500 low resolution spectra (from 4800 to 10000 Å) were observed in 25 VLT/VIMOS masks covering the central 1 deg$^{2}$ around the dominant galaxy NGC 1399 corresponding to $\sim$175 kpc galactocentric radius. We describe the methodology used for data reduction and data analysis. We found a total of 387 unique physical objects (372 GCs and 15 ultra compact dwarfs) in the field covered by our observations. Most of these objects are associated with NGC 1399, with only 10% likely belonging to other giant galaxies. The new VIMOS dataset is complementary to the many GC catalogues already present in the literature and it brings the total number of tracer particles around NGC 1399 to more than 1130 objects. With this comprehensive radial velocity sample we have found that the velocity dispersion of the GC population (equally for red and blue GC populations) shows a relatively sharp increase from low velocity dispersion ($\sim250$-$350$ kms$^{-1}$) to high velocity dispersion ($\sim300$-$400$ kms$^{-1}$) at projected radius of $\approx10$ arcmin ($\sim60$ kpc) from the galaxy centre. This suggests that at a projected radius of $\approx60$ kpc both blue and red GC populations begin to be governed by the dominating Fornax cluster potential, rather than by the central NGC 1399 galaxy potential. This kinematic evidence corroborates similar results found using surface brightness analysis and planetary nebulae kinematics.
We report a detailed small-angle neutron scattering (SANS) study of the skyrmion lattice phase of MnSi under compressive and tensile strain. In particular, we demonstrate that tensile strain applied in the skyrmion lattice plane, perpendicular to the magnetic field, acts to destabilize the skyrmion lattice phase. This experiment was enabled by our development of a versatile strain cell, unique in its ability to select the application of either tensile or compressive strain in-situ by using two independent helium-actuated copper pressure transducers, whose design has been optimized for magnetic SANS on modulated long-period magnetic structures and vortex lattices, and is compact enough to fit in common sample environments, such as cryostats and superconducting magnets.
Sensors that are able to detect and track single unlabelled biomolecules are an important tool both to understand biomolecular dynamics and interactions at nanoscale, and for medical diagnostics operating at their ultimate detection limits. Recently, exceptional sensitivity has been achieved using the strongly enhanced evanescent fields provided by optical microcavities and nano-sized plasmonic resonators. However, at high field intensities photodamage to the biological specimen becomes increasingly problematic. Here, we introduce an optical nanofibre based evanescent biosensor that operates at the fundamental precision limit introduced by quantisation of light. This allows a four order-of-magnitude reduction in optical intensity whilst maintaining state-of-the-art sensitivity. It enable quantum noise limited tracking of single biomolecules as small as 3.5 nm, and surface-molecule interactions to be monitored over extended periods. By achieving quantum noise limited precision, our approach provides a pathway towards quantum-enhanced single-molecule biosensors.
A setup is proposed to enhance tracking of very small particles, by using optical tweezers embedded within a Sagnac interferometer. The achievable signal-to-noise ratio is shown to be enhanced over that for a standard optical tweezers setup. The enhancement factor increases asymptotically as the interferometer visibility approaches 100%, but is capped at a maximum given by the ratio of the trapping field intensity to the detector saturation threshold. For an achievable visibility of 99%, the signal-to-noise ratio is enhanced by a factor of 200, and the minimum trackable particle size is 2.4 times smaller than without the interferometer.
It is now believed that the scaling exponents of moments of velocity increments are anomalous, or that the departures from Kolmogorov's (1941) self-similar scaling increase nonlinearly with the increasing order of the moment. This appears to be true whether one considers velocity increments themselves or their absolute values. However, moments of order lower than 2 of the absolute values of velocity increments have not been investigated thoroughly for anomaly. Here, we discuss the importance of the scaling of non-integer moments of order between +2 and -1, and obtain them from direct numerical simulations at moderate Reynolds numbers (Taylor microscale Reynolds numbers $R_λ\le$ 450) and experimental data at high Reynolds numbers ($R_λ\approx$ 10,000). The relative difference between the measured exponents and Kolmogorov's prediction increases as the moment order decreases towards -1, thus showing that the anomaly that is manifest in high-order moments is present in low-order moments as well. This conclusion provides a motivation for seeking a theory of anomalous scaling as the order of the moment vanishes. Such a theory does not have to consider rare events--which may be affected by non-universal features such as shear--and so may be regarded as advantageous to consider and develop.