arXiv subjects

Patricio Gallardo

Publications and source records attributed to Patricio Gallardo.

At least 37 records · Page 2Linked to original sources

arXiv2020

Comparing complex impedance and bias step measurements of Simons Observatory transition edge sensors

The Simons Observatory (SO) will perform ground-based observations of the cosmic microwave background (CMB) with several small and large aperture telescopes, each outfitted with thousands to tens of thousands of superconducting aluminum manganese (AlMn) transition-edge sensor bolometers (TESs). In-situ characterization of TES responsivities and effective time constants will be required multiple times each observing-day for calibrating time-streams during CMB map-making. Effective time constants are typically estimated in the field by briefly applying small amplitude square-waves on top of the TES DC biases, and fitting exponential decays in the bolometer response. These so-called "bias step" measurements can be rapidly implemented across entire arrays and therefore are attractive because they take up little observing time. However, individual detector complex impedance measurements, while too slow to implement during observations, can provide a fuller picture of the TES model and a better understanding of its temporal response. Here, we present the results of dark TES characterization of many prototype SO bolometers and compare the effective thermal time constants measured via bias steps to those derived from complex impedance data.

astro-ph.IM↗

arXiv2020

Applications of the moduli continuity method to log K-stable pairs

The 'moduli continuity method' permits an explicit algebraisation of the Gromov-Hausdorff compactification of Kähler-Einstein metrics on Fano manifolds in some fundamental examples. In this paper, we apply such method in the 'log setting' to describe explicitly some compact moduli spaces of K-polystable log Fano pairs. We focus on situations when the angle of singularities is perturbed in an interval sufficiently close to one, by considering constructions arising from Geometric Invariant Theory. More precisely, we discuss the cases of pairs given by cubic surfaces with anticanonical sections, and of projective space with non-Fano hypersurfaces, and we show ampleness of the CM line bundle on their good moduli space (in the sense of Alper). Finally, we introduce a conjecture relating K-stability (and degenerations) of log pairs formed by a fixed Fano variety and pluri-anticanonical sections to certain natural GIT quotients.

math.AG↗

arXiv2020

Geometric interpretation of toroidal compactifications of moduli of points in the line and cubic surfaces

It is known that some GIT compactifications associated to moduli spaces of either points in the projective line or cubic surfaces are isomorphic to Baily-Borel compactifications of appropriate ball quotients. In this paper, we show that their respective toroidal compactifications are isomorphic to moduli spaces of stable pairs as defined in the context of the MMP. Moreover, we give a precise mixed-Hodge-theoretic interpretation of this isomorphism for the case of eight labeled points in the projective line.

math.AG↗

arXiv2019

The CCAT-Prime Submillimeter Observatory

The Cerro Chajnantor Atacama Telescope-prime (CCAT-prime) is a new 6-m, off-axis, low-emissivity, large field-of-view submillimeter telescope scheduled for first light in the last quarter of 2021. In summary, (a) CCAT-prime uniquely combines a large field-of-view (up to 8-deg), low emissivity telescope (< 2%) and excellent atmospheric transmission (5600-m site) to achieve unprecedented survey capability in the submillimeter. (b) Over five years, CCAT-prime first generation science will address the physics of star formation, galaxy evolution, and galaxy cluster formation; probe the re-ionization of the Universe; improve constraints on new particle species; and provide for improved removal of dust foregrounds to aid the search for primordial gravitational waves. (c) The Observatory is being built with non-federal funds (~ \$40M in private and international investments). Public funding is needed for instrumentation (~ \$8M) and operations (\$1-2M/yr). In return, the community will be able to participate in survey planning and gain access to curated data sets. (d) For second generation science, CCAT-prime will be uniquely positioned to contribute high-frequency capabilities to the next generation of CMB surveys in partnership with the CMB-S4 and/or the Simons Observatory projects or revolutionize wide-field, sub-millimetter line intensity mapping surveys.

astro-ph.IM↗

arXiv2019

Moduli of cubic surfaces and their anticanonical divisors

We consider the moduli space of log smooth pairs formed by a cubic surface and an anticanonical divisor. We describe all compactifications of this moduli space which are constructed using Geometric Invariant Theory and the anticanonical polarization. The construction depends on a weight on the divisor. For smaller weights the stable pairs consist of mildly singular surfaces and very singular divisors. Conversely, a larger weight allows more singular surfaces, but it restricts the singularities on the divisor. The one-dimensional space of stability conditions decomposes in a wall-chamber structure. We describe all the walls and relate their value to the worst singularities appearing in the compactification locus. Furthermore, we give a complete characterization of stable and polystable pairs in terms of their singularities for each of the compactifications considered.

math.AG↗

arXiv2018

On the neighborliness of dual flow polytopes of quivers

In this note we investigate under which conditions the dual of the flow polytope (henceforth referred to as the `dual flow polytope') of a quiver is k-neighborly, for generic weights near the canonical weight. We provide a lower bound on k, depending only on the edge connectivity of the underlying graph, for such weights. In the case where the canonical weight is in fact generic, we explicitly determine a vertex presentation of the dual flow polytope. Finally, we specialize our results to the case of complete, bipartite quivers where we show that the canonical weight is indeed generic, and are able to provide an improved bound on k. Hence, we are able to produce many new examples of high-dimensional, k-neighborly polytopes.

math.CO↗

arXiv2018

Weak-Lensing Mass Calibration of ACTPol Sunyaev-Zel'dovich Clusters with the Hyper Suprime-Cam Survey

We present weak-lensing measurements using the first-year data from the Hyper Suprime-Cam Strategic Survey Program on the Subaru telescope for eight galaxy clusters selected through their thermal Sunyaev-Zel'dovich (SZ) signal measured at 148 GHz with the Atacama Cosmology Telescope Polarimeter experiment. The overlap between the two surveys in this work is 33.8 square degrees, before masking bright stars. The signal-to-noise ratio of individual cluster lensing measurements ranges from 2.2 to 8.7, with a total of 11.1 for the stacked cluster weak-lensing signal. We fit for an average weak-lensing mass distribution using three different profiles, a Navarro-Frenk-White profile, a dark-matter-only emulated profile, and a full cosmological hydrodynamic emulated profile. We interpret the differences among the masses inferred by these models as a systematic error of 10\%, which is currently smaller than the statistical error. We obtain the ratio of the SZ-estimated mass to the lensing-estimated mass (the so-called hydrostatic mass bias $1-b$) of $0.74^{+0.13}_{-0.12}$, which is comparable to previous SZ-selected clusters from the Atacama Cosmology Telescope and from the {\sl Planck} Satellite. We conclude with a discussion of the implications for cosmological parameters inferred from cluster abundances compared to cosmic microwave background primary anisotropy measurements.

astro-ph.CO↗

arXiv2018

Compactifications of the moduli space of plane quartics and two lines

We study the moduli space of triples $(C, L_1, L_2)$ consisting of quartic curves $C$ and lines $L_1$ and $L_2$. Specifically, we construct and compactify the moduli space in two ways: via geometric invariant theory (GIT) and by using the period map of certain lattice polarized $K3$ surfaces. The GIT construction depends on two parameters $t_1$ and $t_2$ which correspond to the choice of a linearization. For $t_1=t_2=1$ we describe the GIT moduli explicitly and relate it to the construction via $K3$ surfaces.

math.AG↗

arXiv2018

The LABOCA/ACT Survey of Clusters at All Redshifts: multi-wavelength analysis of background submillimeter galaxies

We present a multi-wavelength analysis of 48 submillimeter galaxies (SMGs) detected in the LABOCA/ACT Survey of Clusters at All Redshifts, LASCAR, which acquired new 870 $μ$m and ATCA 2.1 GHz observations of ten galaxy clusters detected through their Sunyaev-Zel'dovich effect (SZE) signal by the Atacama Cosmology Telescope. Far-infrared observations were also conducted with the PACS (100/160 $μ$m) and SPIRE (250/350/500 $μ$m) instruments on $Herschel$ for sample subsets of five and six clusters. LASCAR 870 $μ$m, maps were reduced using a multi-scale iterative pipeline that removes the SZE increment signal, yielding point-source sensitivities of $σ\sim2\rm{\,mJy\,beam}^{-1}$. We detect in total 49 sources at the $4σ$ level, and conduct a detailed multi-wavelength analysis considering our new radio and far-IR observations plus existing near-IR and optical data. One source is identified as a foreground galaxy, 28 SMGs are matched to single radio sources, 4 have double radio counterparts, and 16 are undetected at 2.1 GHz but tentatively associated in some cases to near-IR/optical sources. We estimate photometric redshifts for 34 sources with secure (25) and tentative (9) matches at different wavelengths, obtaining a median $z=2.8^{+2.1}_{-1.7}$. Compared to previous results for single-dish surveys, our redshift distribution has a comparatively larger fraction of sources at $z>3$ and the high-redshift tail is more extended. This is consistent with millimeter spectroscopic confirmation of a growing number of high-$z$ SMGs and relevant for testing of cosmological models. Analytical lens modeling is applied to estimate magnification factors for 42 SMGs at cluster-centric radii $>1.2$'; with the demagnified flux densities and source-plane areas, we obtain integral number counts that agree with previous submillimeter surveys.

astro-ph.GA↗

arXiv2018

Results from the Atacama B-mode Search (ABS) Experiment

The Atacama B-mode Search (ABS) is an experiment designed to measure cosmic microwave background (CMB) polarization at large angular scales ($\ell>40$). It operated from the ACT site at 5190~m elevation in northern Chile at 145 GHz with a net sensitivity (NEQ) of 41 $μ$K$\sqrt{\rm s}$. It employed an ambient-temperature sapphire half-wave plate rotating at 2.55 Hz to modulate the incident polarization signal and reduce systematic effects. We report here on the analysis of data from a 2400 deg$^2$ patch of sky centered at declination $-42^\circ$ and right ascension $25^\circ$. We perform a blind analysis. After unblinding, we find agreement with the Planck TE and EE measurements on the same region of sky. We marginally detect polarized dust emission and give an upper limit on the tensor-to-scalar ratio of $r<2.3$ (95% cl) with the equivalent of 100 on-sky days of observation. We also present a new measurement of the polarization of Tau A and introduce new methods associated with HWP-based observations.

astro-ph.CO↗

arXiv2017

Modular interpretation of a non-reductive Chow quotient

The space of n distinct points and a disjoint parameterized hyperplane in projective d-space up to projectivity---equivalently, configurations of n distinct points in affine d-space up to translation and homothety---has a beautiful compactification introduced by Chen-Gibney-Krashen. This variety, constructed inductively using the apparatus of Fulton-MacPherson configuration spaces, is a parameter space of certain pointed rational varieties whose dual intersection complex is a rooted tree. This generalizes $\overline{M}_{0,n}$ and shares many properties with it. In this paper, we prove that the normalization of the Chow quotient of $(\mathbb{P}^d)^n$ by the diagonal action of the subgroup of projectivities fixing a hyperplane, pointwise, is isomorphic to this Chen-Gibney-Krashen space $T_{d,n}$. This is a non-reductive analogue of Kapranov's famous quotient construction of $\overline{M}_{0,n}$, and indeed as a special case we show that $\overline{M}_{0,n}$ is the Chow quotient of $(\mathbb{P}^1)^{n-1}$ by an action of a semidirect product of the additive and multiplicative group.

math.AG↗

arXiv2017

Families of elliptic curves in $\mathbb{P}^3$ and Bridgeland Stability

We study wall crossings in Bridgeland stability for the Hilbert scheme of elliptic quartic curves in three dimensional projective space. We provide a geometric description of each of the moduli spaces we encounter, including when the second component of this Hilbert scheme appears. Along the way, we prove that the principal component of this Hilbert scheme is a double blow up with smooth centers of a Grassmannian, exhibiting a completely different proof of this known result by Avritzer and Vainsencher. This description allows us to compute the cone of effective divisors of this component.

math.AG↗

arXiv2017

Variations of geometric invariant quotients for pairs, a computational approach

We study the GIT compactifications of pairs formed by a hypersurface and a hyperplane. We provide a general setting to characterize all polarizations which give rise to different GIT quotients. Furthermore, we describe a finite set of one-parameter subgroups sufficient to determine the stability of any GIT quotient. We characterize all maximal orbits of non stable and strictly semistable pairs, as well as minimal closed orbits of strictly semistable pairs. Our construction gives natural compactifications of the space of log smooth pairs for Fano and Calabi-Yau hypersurfaces.

math.AG↗

arXiv2017

A Generic Slice of the Moduli Space of Line Arrangements

We study the compactification of the locus parametrizing lines with a fixed intersection to a given line, inside the moduli space of line arrangements in the projective plane constructed for weight one by Hacking-Keel-Tevelev and Alexeev for general weights. We show that this space is smooth, with normal crossing boundary, and that it has a morphism to the moduli space of marked rational curves which can be understood as a natural continuation of the blow up construction of Kapranov. In addition, we prove that it is isomorphic to a closed subvariety inside a non-reductive Chow quotient. The parametrized objects are surfaces with broken lines, whose dual graphs are rooted trees with possibly repeated markings.

math.AG↗

arXiv2017

Wonderful compactifications of the moduli space of points in affine and projective space

We introduce and study smooth compactifications of the moduli space of n labeled points with weights in projective space, which have normal crossings boundary and are defined as GIT quotients of the weighted Fulton-MacPherson compactification. We show that the GIT quotient of a wonderful compactification is also a wonderful compactification under certain hypotheses. We also study a weighted version of the configuration spaces parametrizing n points in affine space up to translation and homothety. In dimension one, the above compactifications are isomorphic to Hassett's moduli space of rational weighted stable curves.

math.AG↗

arXiv2016

The Atacama Cosmology Telescope: Two-Season ACTPol Lensing Power Spectrum

We report a measurement of the power spectrum of cosmic microwave background (CMB) lensing from two seasons of Atacama Cosmology Telescope Polarimeter (ACTPol) CMB data. The CMB lensing power spectrum is extracted from both temperature and polarization data using quadratic estimators. We obtain results that are consistent with the expectation from the best-fit Planck LCDM model over a range of multipoles L=80-2100, with an amplitude of lensing A_lens = 1.06 +/- 0.15 (stat.) +/- 0.06 (sys.) relative to Planck. Our measurement of the CMB lensing power spectrum gives sigma_8 Omega_m^0.25 = 0.643 +/- 0.054; including baryon acoustic oscillation scale data, we constrain the amplitude of density fluctuations to be sigma_8 = 0.831 +/- 0.053. We also update constraints on the neutrino mass sum. We verify our lensing measurement with a number of null tests and systematic checks, finding no evidence of significant systematic errors. This measurement relies on a small fraction of the ACTPol data already taken; more precise lensing results can therefore be expected from the full ACTPol dataset.

astro-ph.CO↗

arXiv2016

The Atacama Cosmology Telescope: Two-Season ACTPol Spectra and Parameters

We present the temperature and polarization angular power spectra measured by the Atacama Cosmology Telescope Polarimeter (ACTPol). We analyze night-time data collected during 2013-14 using two detector arrays at 149 GHz, from 548 deg$^2$ of sky on the celestial equator. We use these spectra, and the spectra measured with the MBAC camera on ACT from 2008-10, in combination with Planck and WMAP data to estimate cosmological parameters from the temperature, polarization, and temperature-polarization cross-correlations. We find the new ACTPol data to be consistent with the LCDM model. The ACTPol temperature-polarization cross-spectrum now provides stronger constraints on multiple parameters than the ACTPol temperature spectrum, including the baryon density, the acoustic peak angular scale, and the derived Hubble constant. Adding the new data to planck temperature data tightens the limits on damping tail parameters, for example reducing the joint uncertainty on the number of neutrino species and the primordial helium fraction by 20%.

astro-ph.CO↗

arXiv2016

On the GIT Quotient Space of Quintic Surfaces

We describe the GIT compactification for the moduli space of smooth quintic surfaces in projective space. In particular, we show that a normal quintic surface with at worst an isolated double point or a minimal elliptic singularity is stable. We also describe the boundary of the GIT quotient, and we discuss the stability of the non-normal surfaces.

math.AG↗