217 research outputs found
Galaxy / Halo Assembly from z=10 to z=0
No full textI discuss new methods to combine multiple datasets to maximally constrain galaxy evolution and the galaxy—dark matter halo connection, and show how these methods have already changed our understanding of galaxy formation physics (including why galaxies stop forming stars)
Antenna and pulse selection for colocated MIMO radar
No full textMultiple input multiple output (MIMO) radar is known for its superiority over conventional radar due to its antenna and waveform diversity. However, the increased hardware cost (due to multiple transmitters and receivers), power consumption (due to multiple transmitters and pulses), and computational complexity (due to numerous pulses) form the drawbacks of MIMO radar. On one hand, a higher estimation accuracy is required, but on the other hand, a lower number of active antennas/pulses is desirable. Therefore, in this paper, by proposing a convex optimization approach for the general case of transmitter-receiver-pulse selection, we will minimize the total number of active antennas/pulses in order to guarantee a prescribed performance accuracy. The performance measure we will optimize is the Cramer-Rao lower bound (CRLB) for the angle and velocity estimation accuracy of two targets, which provides a trade-off between the main beamwidth and the sidelobe level (SLL) of the ambiguity function.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Signal Processing System
Recoiling supermassive black hole escape velocities from dark matter haloes
No full textInternational audienceWe simulate recoiling black hole trajectories from z = 20 to z = 0 in dark matter haloes, quantifying how parameter choices affect escape velocities. These choices include the strength of dynamical friction, the presence of stars and gas, the accelerating expansion of the Universe (Hubble acceleration), host halo accretion and motion, and seed black hole mass. Lambda cold dark matter halo accretion increases escape velocities by up to 0.6 dex and significantly shortens return time-scales compared to non-accreting cases. Other parameters change orbit damping rates but have subdominant effects on escape velocities; dynamical friction is weak at halo escape velocities, even for extreme parameter values. We present formulae for black hole escape velocities as a function of host halo mass and redshift. Finally, we discuss how these findings affect black hole mass assembly as well as minimum stellar and halo masses necessary to retain supermassive black holes
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Dynamics of Local Group Satellite Galaxies in the Era of Precision Astrometry
No full textHigh-precision astrometric data from the {\em Hubble Space Telescope} (HST) and {\em Gaia} are revolutionizing our ability to study galaxies in the Local Group (LG) in unprecedented detail. Recent breakthroughs, such as high accuracy proper motion (PM) measurements for Andromeda (M31), Triangulum (M33), and many of the dwarf galaxies orbiting the Milky Way (MW) and M31 now make it possible to analyze the interaction histories between satellite galaxies and their hosts. In this dissertation, I explore how the combination of astrometric data with high-resolution cosmological simulations can be used to improve our classical understanding of the LG's dynamical history.
Using PMs from HST and the \textit{Very Long Baseline Array} and independently measured PMs with \textit{Gaia}, I show that the most plausible orbital history for M31's most massive satellite galaxy, M33, is a first infall scenario where M33 enters M31's halo in the last 2-4 Gyr, arriving at its closest position relative to M31 today. I also demonstrate that this orbital history is consistent with those of M33 analogs in M31-mass systems in \textit{Illustris-1-Dark}. M33's new orbital history is contrary to its classical orbit (developed before M31's PM was measured) where M33 has a close ( 100 kpc), recent ( 3 Gyr) tidal interaction with M31, resulting in M33's curious morphology. If on first infall into M31's halo, M33 is expected to retain its infall mass and any associated satellite galaxies. Here, I quantify the predicted satellite galaxy population of M33 in a CDM paradigm, which may provide an alternative explanation for M33's warped morphology and can be directly tested with existing observatories.
In the remaining chapters, I develop innovative methods to statistically constrain the precise masses of the MW and M31 by comparing the kinematic and dynamical properties of their satellite galaxies to the properties of simulated analogs in \textit{Illustris-1-Dark}. I show that the orbital angular momenta of satellite galaxies is the most reliable estimator of host halo mass over time. Using the angular momenta of multiple satellites simultaneously narrows the current uncertainty in the MW’s mass by 25\%, showing promise for improved constraints on the mass of M31 and ultimately the LG
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Host Galaxies of Extragalactic Transients
No full textHost galaxy properties of extragalactic transients provide valuable insights into the nature of their progenitors. This dissertation focuses on the automated identification of transient host galaxies, the systematic difference in host properties and rate dependencies across supernova subtypes, and the demographics and cosmic environments of supernovae without host galaxies detected.Chapter 1 presents a brief overview of transient-host connections.
Chapter 2 describes a novel machine learning-based algorithm to identify transient host galaxies with high accuracy (above 97%). Based on this algorithm, we develop software pipelines to identify transient host galaxies, collect their measured properties across multiple sky surveys, and assemble the largest-ever value-added database of host galaxies.
Chapter 3 compares host galaxy physical properties (stellar mass, star formation rate, metallicity) and photometric properties (absolute magnitude, rest-frame color) across supernova subtypes and characterizes how supernova rates depend on galaxy properties.
We find subtle but statistically significant differences in host properties across several core-collapse supernova (CC SN) subtypes. Contrary to common belief, CC SN rates are not proportional to their host star formation rates -- either a fraction of long-lived progenitors or a metallicity-dependent supernova production efficiency better interpret the observed host properties. SN Ia subtypes feature heterogeneous host properties attributable to the dramatic contrast of progenitor ages.
Chapter 4 presents the analysis of a supernova sample without hosts detected. There are more interacting and superluminous (especially hydrogen-deficient) subtypes among hostless supernovae than in a typical transient sample. Wide-field galaxy surveys put rigorous limits on their host luminosities -- the faintest ones are close to the typical luminosity of dwarf spheroidal galaxies or even globular clusters. The lack of spatial association with galaxy clusters and the excess of slowly-declining SN Ia imply a population of star-forming dwarf hosts in the field.
Finally, Chapter 5 summarizes the main results and provides a future outlook
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The Effect of the Large Magellanic Cloud on the Dark Matter Halo of the Milky Way
No full textThe Large Magellanic Cloud (LMC), the most massive satellite of the Milky Way(MW), is perturbing the dynamics and equilibrium of the MW. Understanding the
nature and time evolution of these perturbations remains one of the most important
challenges to the interpretation of 6D phase space measurements of tracers (satel-
lites, streams, halo stars) of the dark matter (DM) distribution and assembly history
of the MW. Using results from 8 high-resolution N-body simulations, I will describe
the main perturbations caused by the LMC: the DM wake, the barycenter displace-
ment, and the reflex motion. I show that these perturbations can be detected in
both the kinematics and densities of the stellar halo beyond 50 kpc. Furthermore,
I will illustrate how the present-day MW–LMC system can be modeled analytically
using Basis Function Expansions. I maximize the physical signal in the representa-
tion through a comprehensive noise analysis. As a result, the simulations of 10 8 DM
particles representing the distorted MW(MW+LMC) system can be described by≈
236(2067) coefficients. We find that the LMC induces asymmetric perturbations to
the MW’s halo, which are inconsistent with oblate, prolate, or triaxial halos. The
presence of the LMC also complicates efforts to recover the underlying shape of the
MW’s halo. I also discuss how the LMC induces clustering of orbital poles of objects
in orbit about the MW. By tracking the evolution of orbital poles for initially ran-
dom, steady-state dark matter particles, I find that, after the infall of the LMC, the
present-day orbital poles of particles , at Galactocentric distances beyond ≥50kpc,
cluster near the present-day orbital pole of the LMC. This clustering can be up to a
factor of ≈1.3 times higher than the density of orbital poles in an isolated MW halo
and is most pronounced after the recent, close (≈50 Myr ago, 49 kpc) passage of the
LMC. Given our location within the disk, particles in the simulation are observed
from a non-inertial reference frame relative to the outer halo leading to an appar-16
ent alignment in their orbital poles. The DM wake induced by the LMC changes
the kinematics of particles in the Southern Hemisphere. Observations of satellites
selected within spatial planes also suffer from a bias, such that measuring orbital
poles in a great circle in the sky enhances the probability of their orbital poles being
clustered. I expect this scenario to be ubiquitous among hosts that have captured a
massive satellite (at least ≈1:10 mass ratio) making a recent (≤ 1 Gyr) pericentric
approach, where the massive satellite will cluster orbital poles of halo tracers
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The Phase-Space Distribution of Galaxy Clusters
No full textWe provide the modeling framework to enable a proposed new measurement of the Hubble constant, using the radial extent of galaxy clusters as a standard ruler. Observationally, we plan to measure the angular extent of the cluster and the velocity of galaxies around the cluster. More massive clusters have galaxies that orbit faster, so we can use the velocity of galaxies within clusters to estimate an effective cluster mass. To enable this, we have calibrated the relation between line-of-sight galaxy velocity and cluster mass using cosmological simulations. With an estimate of halo mass now in hand, we can infer the radius of the dark matter halo containing it. To enable this, we have also calibrated the relationship between halo mass and radius with simulations. We find that a halo whose mass is has a physical radius of kPc/h, better than precision. Comparing the halo radius inferred from galaxies' velocities to their angular extent allows us to estimate the distance to the cluster, which in turn can be used to assemble a Hubble diagram for galaxy clusters. The high level of precision in the halo radius needed to establish this measurement is founded on a recent insight in halo modeling: galaxies in halos can be split into two populations: those orbiting their host dark matter halo, and those falling into the host for the first time. Here, we present an algorithm that uses the galaxies' accretion history to distinguish between them. We use our split catalog to generate fits for the orbiting and infalling galaxy phase space densities. Importantly, each can be described as depending on a single fundamental scale, the halo radius . Both the orbiting and density profiles can be described with 5 accuracy using as the length scale. In velocity space, we show that the infalling velocity distribution has a bimodal appearance due to the impact of the Hubble flow on galaxy velocities. Our model of the distribution of galaxy line-of-sight velocities is also 5\% accurate. Finally, to prepare the calibration for application to galaxy clusters, we characterize the impact of cluster selection effects the phase space distribution of galaxies. To do so, we select clusters based on the galaxy counts in cylinders of height 20 h~Mpc and 60 h~Mpc along the line of sight. The distributions of line-of-sight velocities for both orbiting and infalling galaxies are robust to cluster selection; so is the projected orbiting surface density. The projected surface density of the infalling population, however, exhibits a strong scale-dependent bias, where the scale is set by the aperture used in the process of cluster selection. Finally, we suggest the next steps needed to characterize the dependence of the halo radius on the assumed cosmology, as well as the possible influence of baryonic processes on it. As a coda, we also include work on the broadband emission of galaxy clusters, and examine the possible detection of extra-solar neutrinos (via the ICECUBE and Auger experiments) from the Coma cluster of galaxies, as well as for -ray-bright clusters
MultiDark-Galaxies:data release and first results
No full textWe present the public release of the MULTIDARK-GALAXIES: three distinct galaxy catalogues derived from one of the Planck cosmology MULTIDARK simulations (i.e. MDPL2, with a volume of (1 h-1 Gpc)3 and mass resolution of 1.5 × 109 h-1 M☉) by applying the semi-analytic models GALACTICUS, SAG, and SAGE to it. We compare the three models and their conformity with observational data for a selection of fundamental properties of galaxies like stellar mass function, star formation rate, cold gas fractions, and metallicities - noting that they sometimes perform differently reflecting model designs and calibrations. We have further selected galaxy subsamples of the catalogues by number densities in stellar mass, cold gas mass, and star formation rate in order to study the clustering statistics of galaxies. We show that despite different treatment of orphan galaxies, i.e. galaxies that lost their dark-matter host halo due to the finite-mass resolution of the N-body simulation or tidal stripping, the clustering signal is comparable, and reproduces the observations in all three models - in particular when selecting samples based upon stellar mass. Our catalogues provide a powerful tool to study galaxy formation within a volume comparable to those probed by ongoing and future photometric and redshift surveys. All model data consisting of a range of galaxy properties - including broad-band SDSS magnitudes - are publicly available.Fil: Knebe, Alexander. Universidad Autónoma de Madrid; EspañaFil: Stoppacher, Doris. Universidad Autónoma de Madrid; EspañaFil: Prada, Francisco. Instituto de Astrofísica de Andalucía; EspañaFil: Behrens, Christoph. Universität Göttingen; AlemaniaFil: Benson, Andrew. Carnegie Observatories; ChileFil: Cora, Sofia Alejandra. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; ArgentinaFil: Croton, Darren J.. Swinburne University Of Technology; AustraliaFil: Padilla, Nelson David. Pontificia Universidad Católica de Chile; Chile. Universidad Católica de Chile; ChileFil: Ruiz, Andrés Nicolás. Observatorio Astronomico de la Universidad Nacional de Cordoba; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; ArgentinaFil: Sinha, Manodeep. Swinburne University Of Technology; AustraliaFil: Stevens, Adam R. H.. University of Western Australia; Australia. Swinburne University Of Technology; AustraliaFil: Vega Martínez, Cristian Antonio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; ArgentinaFil: Behroozi, Peter. University of California at Berkeley; Estados UnidosFil: Gonzalez Perez, Violeta. University Of Portsmouth; Reino UnidoFil: Gottlöber, Stefan. Leibniz Institute For Astrophysics Potsdam; AlemaniaFil: Klypin, Anatoly A.. New Mexico State University Las Cruces; Estados UnidosFil: Yepes, Gustavo. Universidad Autónoma de Madrid; EspañaFil: Enke, Harry. Leibniz Institute For Astrophysics Potsdam; AlemaniaFil: Libeskind, Noam I.. Leibniz Institute For Astrophysics Potsdam; AlemaniaFil: Riebe, Kristin. Leibniz Institute For Astrophysics Potsdam; AlemaniaFil: Steinmetz, Matthias. Leibniz Institute For Astrophysics Potsdam; Alemani
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The Rest-Frame Ultraviolet Spectra of Galaxies in the Reionization-Era
No full textRecent studies have revealed detections of UV metal emission lines (CIII], OIII], CIV) in three of the first galaxies observed at z>6,
providing the first spectroscopic insight into the nature of early star forming galaxies. The equivalent widths (EWs) of these lines are more than an order of magnitude stronger than what is typical at lower redshifts, potentially indicating significant differences in the ionizing spectrum of galaxies in the reionization era. The origin of the high ionization lines remains unclear, likely requiring either a low metallicity stellar population or AGN. However owing to the limited number of z>6 sources with deep spectroscopy and limited number of analogs at lower redshifts, it has proven difficult to generalize and interpret the initial results. In the first part of my thesis, I have undertaken a comprehensive Keck, LBT and VLT spectroscopic campaign to characterize the EW distribution of UV metal lines at z>6. My results present new constraints on the fraction of strong CIII] and CIV emitting galaxies at z>6 and indicate that ionizing spectrum from stellar population at z>6 could be significantly harder than systems at a lower redshift. In the second part of my thesis, I have developed a new strategy to identify and characterize analogs of the strong UV metal line emitters at lower redshift. This has resulted in a new sample of extreme CIII] emitters at z~2. Using spectroscopic tools, I have shown that large equivalent width CIII] emission lines tend to be those with moderately low gas-phase oxygen abundance, low stellar metallicity, large ionization parameter, and very little dust extinction. My results will guide surveys with current and future facilities (Spitzer, JWST, WFIRST) providing optimal strategy to target UV metal lines in the reionization epoch
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