CCAPP Cosmolunch

Background image with NGC 1097 from Legacy Survey (https://www.legacysurvey.org/ )

Organizers for 2023/2024:

CCAPP Cosmology Lunch meets on Wednesdays at 3:00 pm (EST) in a hybrid format!

Join our Benty-Fields page! https://www.benty-fields.com/join_jc?invited_jc=471

April 19, 2023

April 12, 2023

April 5, 2023

March 29, 2023

March 22, 2023

March 1, 2023

February 22, 2023

February 8, 2023

February 1, 2023

January 25, 2023

January 18, 2023

January 11, 2023

December 7, 2022

November 30, 2022

November 16, 2022

November 9, 2022

November 2, 2022

October 26, 2022

October 19, 2022

October 12, 2022

October 5, 2022

September 22, 2022

September 14, 2022

September 7, 2022

August 31, 2022

July 20, 2022

Title: Dynamical perturbations of extreme mass ratio inspirals near resonances

Abstract: Extreme mass ratio inspirals (EMRIs) are systems with a compact object orbiting a much more massive (e.g., galactic center) black hole. They are of interest both as a new probe of the environments of galactic nuclei, and their waveforms are a precision test of the Kerr metric. My work focuses on expanding what Makana and Chris recently published by generalizing the outer orbit. This will help create more physically realistic models of galactic centers and the gravitational waveforms they will produce.

July 6, 2022

June 8, 2022

June 1, 2022

May 18, 2022

May 4, 2022

April 27, 2022

April 20, 2022

Title: Dynamical perturbations of extreme mass ratio inspirals near resonances

Abstract: Extreme mass ratio inspirals (EMRIs) - systems with a compact object orbiting a much more massive (e.g., galactic center) black hole - are of interest both as a new probe of the environments of galactic nuclei, and their waveforms are a precision test of the Kerr metric. This work focuses on the effects of an external perturbation due to a third body around an EMRI system. This perturbation will affect the orbit most significantly when the inner body crosses a resonance with the outer body, and result in a change of the conserved quantities (energy, angular momentum, and Carter constant) or equivalently of the actions, which results in a subsequent phase shift of the waveform that builds up over time. We present a general method for calculating the changes in action during a resonance crossing, valid for generic orbits in the Kerr spacetime. We show that these changes are related to the gravitational waveforms emitted by the two bodies (quantified by the amplitudes of the Weyl scalar ψ4 at the horizon and at ∞) at the frequency corresponding to the resonance. This allows us to compute changes in the action variables for each body, without directly computing the explicit metric perturbations, and therefore we can carry out the computation by calling an existing black hole perturbation theory code. We plan to use this technique for future investigations of third-body effects in EMRIs and their potential impact on waveforms for LISA.

April 13, 2022

April 6, 2022

March 30, 2022

March 23, 2022

March 8, 2022

March 2, 2022

February 23, 2022

February 16, 2022

February 9, 2022

February 2, 2022

January 26, 2022

January 12, 2022

December 15, 2021

November 17, 2021

Title: AGN Variability and HEAN in the age of VRO

Abstract: Over the next ten years, the Vera C. Rubin Observatory (VRO) will observe 10 million active galactic nuclei (AGN) with a regular and high cadence. During this time, the intensities of most of these AGN will vary stochastically. Moreover, these fluctuations may also be connected to the high-energy astrophysical neutrino (HEAN) flux observed by IceCube. In this talk, I explore the prospects to quantify these fluctuations with VRO-measurements of AGN light curves and also evaluate the capacity of VRO, in tandem with various current and upcoming neutrino telescopes, to establish AGN as HEAN emitters.  I find that AGN variability measurements will be so precise as to allow the AGN to be separated into up to 10 different correlation-timescale bins. I also show that if the correlation time varies as some power of the luminosity, the normalization and power-law index of that relation will be determined to O(10^{−4}%).  Finally, I find that it may be possible to detect AGN contributions at the ~ 3\sigma level to the HEAN flux even if these AGN contribute only ~10% of the HEAN flux.

November 10, 2021

Title: Studying galaxy cluster morphological metrics with Mock-X

Abstract: Dynamically relaxed galaxy clusters have long played a role in galaxy cluster studies because it is thought their properties can be reconstructed more precisely and with less systematics. As relaxed clusters are desirable, there exist a plethora of criteria for classifying a galaxy cluster as relaxed. In this work, we examine 9 commonly used observational and theoretical morphological metrics extracted from 54,000 Mock-X synthetic X-ray images of galaxy clusters taken from the IllustrisTNG, BAHAMAS and MACSIS simulation suites. We find that the simulated criteria distributions are in reasonable agreement with the observed distributions. Many criteria distributions evolve as a function of redshift, cluster mass, numerical resolution and subgrid physics, limiting the effectiveness of a single relaxation threshold value. All criteria are positively correlated with each other, however, the strength of the correlation is sensitive to redshift, mass and numerical choices. Driven by the intrinsic scatter inherent to all morphological metrics and the arbitrary nature of relaxation threshold values, we find the consistency of relaxed subsets defined by the different metrics to be relatively poor. Therefore, the use of relaxed cluster subsets introduces significant selection effects that are non-trivial to resolve.

November 3, 2021

October 27, 2021

October 20, 2021

October 13, 2021

September 29, 2021

Title: The DESI Focal Plane: Joys and Complication

Abstract: The Dark Energy Spectroscopic Instrument (DESI) is undertaking the largest redshift survey in existence. In the next few years, DESI will collect the redshifts of as many as 35 million galaxies. No small part of this incredible achievement is due to DESI's robotic focal plane system. In this talk I will give a brief overview of DESI and its science goals. I will go in depth on the focal plane and some of its technical achievements. I will then talk about some of the challenges and solutions to those challenges, the focal plane introduces in clustering analysis. This will include some classic complications DESI shares with older surveys such as eBOSS as well as newer complications due to the robotic nature of DESI's focal plane.

September 22, 2021

September 15, 2021

September 8, 2021

September 1, 2021

August 25, 2021

August 18, 2021

August 4, 2021

July 14, 2021

June 30, 2021

June 23, 2021

June 2, 2021

May 26, 2021

May 12, 2021

April 28, 2021

April 21, 2021

April 14, 2021

April 7, 2021

March 24, 2021

March 17, 2021

March 10, 2021

March 3, 2021

February 24, 2021

Title:

Probing the Cosmic Inventory by Unlocking the Diffuse Light in Sky Surveys

Abstract:

The formation of stars, galaxies, and the large-scale structure in the Universe drives complex energy density flows over a wide range of scales from atomic nuclei to the Hubble length. The net effect could be summarized by a census of the density parameters, Ω, for different entries in the cosmic inventory over time. I will present my ongoing effort to probe the history of several key cosmic constituents, including stars, dust, thermal, and gravitational energy associated with the large-scale structure. To do so, we deproject the cosmic UV, IR, and the Sunyaev-Zeldovich effect backgrounds over redshift using a new tomographic intensity mapping approach. While the results are already pushing our understanding of the Universe, they represent only the beginning of a new chapter of cosmology and astrophysics using the entire radiation field without necessarily resolving individual galaxies. Looking forward, I will describe the infrastructure that we are building in facilitating a close synergy between galaxy surveys and intensity mapping. I will close by highlighting some exciting science opportunities in the next decade.

February 17, 2021

February 10, 2021

February 3, 2021

January 27, 2021

January 20, 2021

January 13, 2021

December 16, 2020

December 9, 2020

Abstract:

I will present new constraints on the growth rate parameter $f \sigma_8$ from modeling the anisotropic clustering in BOSS LOWZ. Compared to previous analyses, we extend the modeling into the highly non-linear regime down to scales $s \sim 0.5 \, \mathrm{Mpc} / h$. Extracting cosmological information from non-linear scales is made possible via a sophisticated, simulation-based modeling approach. We directly compare observational data against dark matter-only simulations populated via a Halo Occupation Distribution (HOD) framework. I will discuss the HOD model used, including the effects of observational incompleteness, galaxy assembly bias and galaxy velocity bias. I will also discuss tests on mock catalogs to ensure that our cosmological constraints are unbiased. Finally, I will present cosmological constraints from applying this analysis framework to two samples of $~70,000$ galaxies at redshifts $z \approx 0.25$ and $z \approx 0.40$. The derived cosmological constraints on $f \sigma_8$ are more stringent than any previous study targeting large linear scales only.

December 2, 2020

November 18, 2020

November 4, 2020

October 28, 2020

October 21, 2020

October 14, 2020

October 7, 2020

September 30, 2020

September 23, 2020

September 16, 2020

September 9, 2020

August 19, 2020

August 5, 2020

July 22, 2020

July 8, 2020

July 1, 2020

June 17, 2020

May 27, 2020

May 6, 2020

April 29, 2020

April 22, 2020

April 15, 2020

April 8, 2020

April 1, 2020

March 25, 2020

March 18, 2020

February 26, 2020

February 12, 2020

February 5, 2020

January 29, 2020

January 22, 2020

January 15, 2020

December 4, 2019

November 20, 2019

November 6, 2019

October 23, 2019

October 16, 2019

October 9, 2019

October 2, 2019

September 25, 2019

Xiao Fang: https://docs.google.com/presentation/d/1IT3nkyy93wSn4eHrr17ylK-8SVFvJBhMVexZ3dLGlb0/edit?usp=sharing

September 18, 2019

September 11, 2019

September 4, 2019

August 13, 2019

August 6, 2019

July 3, 2019

June 26, 2019

June 19, 2019

June 5, 2019

May 29, 2019

May 1, 2019

April 24, 2019

April 17, 2019

April 10, 2019

April 3  2019

March 27  2019

March 6  2019

February 27  2019

February 19  2019

February 13  2019

February 6  2019 

January 29  2019 -> canceled due to polar vortex

January 23  2019 

Abstract:

The acceleration of the Universe is one of the biggest puzzles in physics: is it due to a cosmological constant, dynamical dark energy, or modification of gravity?  Galaxy clusters provide a unique opportunity to answer this question.  In this talk, I will first introduce how we use large sky surveys of galaxy clusters to study cosmic acceleration.  In these surveys, a major challenge is to accurately infer the mass of clusters.  I will then present my research on using simulations to improve mass calibration methods — including galaxy dynamics, weak gravitational lensing, and X-ray observations.  These results not only mitigate the systematic errors in current cluster surveys but also help the optimization of future ground- and space-based missions.

January 16  2019

December 11,  2018

November 28,  2018 (special time -> 2:00 pm)

November 14,  2018

Abstract:

The North American Nanohertz Observatory for Gravitational Waves (NANOGrav) is well into a second decade of precisely timing an array of millisecond pulsars with the intent to detect and characterize gravitational waves (GWs) generated by, among other things, inspiraling supermassive black hole binaries (SMBHBs). I will discuss various aspects of the astrophysics of nanohertz gravitational waves, from the coupling of SMBHBs to their environments to cosmic superstrings to non-Einsteinian GW polarizations. I will also discuss how the anticipated features of the nanohertz GW landscape and the astrophysics of pulsars and the interstellar medium inform NANOGrav’s observing strategies

October 31,  2018

Abstract:

I will present new results on the relationship between central galaxies and dark matter halos inferred from observations of satellite kinematics in the Sloan Digital Sky Survey (SDSS) DR7. We employ an updated analysis framework that includes detailed mock catalogues to model observational effects in SDSS. Our results constrain the color-dependent conditional luminosity function (CLF) of dark matter halos, as well as the radial profile of satellite galaxies. Confirming previous results, we find that red central galaxies live in more massive halos than blue galaxies at fixed luminosity. Additionally, our results suggest that satellite galaxies have a radial profile less centrally concentrated than dark matter but not as cored as resolved subhalos in dark matter-only simulations. Compared to previous works using satellite kinematics by More et al. (2011), we find much more competitive constraints on the galaxy-halo connection, on par with those derived from a combination of galaxy clustering and galaxy-galaxy lensing. I will also compare our results on the galaxy-halo connection to other studies using galaxy clustering, galaxy-galaxy lensing and group catalogues, showing very good agreement between these different techniques. This resolves the tension between satellite kinematics results, as previously reported by More et al. (2011), and other probes.

October 24,  2018 

Abstract:

The Stellar Mass-Halo Mass (SMHM) relation provides insight into the galaxy-dark matter halo connection.  In Golden-Marx & Miller (2018), we incorporate the magnitude gap, the difference in brightness between the BCG and 4th brightest cluster member within 0.5 R200, into the cluster SMHM relation.  We observe that at fixed halo mass, clusters with larger magnitude gaps have larger central galaxy stellar masses.  We also see this in semi-analytic simulations, which suggests that it can be explained by the hierarchical growth of central galaxies.  Accounting for the magnitude gap significantly reduces the inferred intrinsic scatter to below 0.1 dex, thus strictly limiting the model space that can explain the stellar mass growth in centrals of massive halos.  Hierarchical growth also predicts that the central’s stellar mass and magnitude gap decrease with increasing lookback time.  However, the extent of the growth of the central’s stellar mass is dependent upon the aperture defined by the radial extent of the central galaxy.  We investigate the impact of aperture size on the slope of the SMHM relation and find that the slope is significantly steeper at larger aperture radii (~100 kpc).  Using this result, we test the prediction of hierarchical growth, and present our latest results using SDSS-redMaPPer.  Unlike prior studies we detect redshift evolution in the slope of the SMHM relation (measured at 100kpc aperture), which can be explained by recent merger activity. 

October 10,  2018 

October 3,  2018 

September 25,  2018 

September 19,  2018 

September 12,  2018 

September 6,  2018 

August 23,  2018 

August 16,  2018

July 19,  2018

Abstract:

Intrinsic alignments (IA), correlations between the intrinsic shapes and orientations of galaxies on the sky, are both a significant systematic in weak lensing and a probe of the effect of large-scale structure on galactic structure and angular momentum. In the era of precision cosmology, it is thus especially important to model IA with high accuracy. Efforts to use cosmological perturbation theory to model the dependence of IA on the large-scale structure have thus far been relatively successful; however, extant models do not consistently account for time evolution. In particular, advection of galaxies due to peculiar velocities alters the impact of IA, because galaxy positions when observed are generally different from their positions at the epoch when IA is believed to be set. In this work, we evolve the galaxy IA from the time of galaxy formation to the time at which they are observed, including the effects of this advection, and show how this process naturally leads to a dependence of IA on the velocity shear. We calculate the galaxy-galaxy-IA bispectrum to tree level (in the linear matter density) in terms of the evolved IA coefficients. We then discuss the implications for weak lensing systematics as well as for studies of galaxy formation and evolution. We find that considering advection introduces nonlocality into the bispectrum, and that the degree of nonlocality represents the memory of a galaxy's path from the time of its formation to the time of observation. We discuss how this result can be used to constrain the redshift at which IA is determined and provide Fisher estimation for the relevant measurements using the example of SDSS-BOSS.

July 5,  2018 

Abstract:

The small-scale structure problems of the universe can be solved by self-interacting dark matter that becomes strongly interacting at low energy. A particularly predictive model for the self-interactions is resonant short-range interactions with an S-wave scattering length that is much larger than the range. The velocity dependence of the cross section in such a model provides an excellent fit to selfinteraction cross sections inferred from dark-matter halos of galaxies and clusters of galaxies if the dark-matter mass is about 19 GeV and the scattering length is about 17 fm. Such a model makes definite predictions for the few-body physics of weakly bound clusters of the dark-matter particles. The formation of the two-body bound cluster is a bottleneck for the formation of larger bound clusters. We calculate the production of two-body bound clusters by three-body recombination in the early universe under the assumption that the dark matter particles are identical bosons, which is the most favorable case. If the dark-matter mass is 19 GeV and the scattering length is 17 fm, the fraction of dark matter in the form of two-body bound clusters can increase by as much as 4 orders of magnitude when the dark-matter temperature falls below the binding energy, but its present value remains less than 10−6 . The present fraction can be increased to as large as 10−3 by relaxing the constraints from small-scale structure and decreasing the mass of the dark matter particle. 

June 28,  2018

June 14,  2018

June 5,  2018

Abstract:

Cosmic voids, the emptiest regions in the Universe, are an increasingly active sector of galaxy clustering analysis. In this talk I will explain why voids are interesting tools for cosmology and what kind of void-related observables we can focus on. I will discuss the treatment of systematics and present some recent methods and results. Finally I will discuss what we can expect from current and upcoming surveys in term of constraining power.

  

May 24,  2018

May 10,  2018

Abstract:

In this talk I will give an overview of the Physics of the Accelerating Universe Survey (PAUS): a unique combination of a large field-of-view and 40 narrow-band (NB) filters (12.5nm FWHM) that span the wavelength range from 450nm to 850nm and that was commissioned successfully in June 2015 on the WHT. This exquisite wavelength sampling results in photometric redshifts with a precision that approaches that of spectroscopic measurements, while being able to cover large areas of sky. I will present the current photometric redshift performance comparing to the zCOSMOS spectroscopic sample and the new photo-z template-based code that we have developed to estimate photometric redshifts for a narrow band photometric survey.

May 3,  2018

April 26,  2018

April 19,  2018

    Abstract: Ultracompact minihalos (UCMHs) have attracted considerable interest as a probe of the primordial power spectrum at small scales.  However, previous treatments assumed that halos collapsing at early times possess an extremely steep r^-9/4 density profile.  We recently found that UCMHs actually develop shallower r^-3/2 or r^-1 inner profiles depending on the shape of the power spectrum, but these halos are still highly concentrated due to their early formation.  I will discuss these results and the factors that set the inner density profile of a dark matter halo.  I will also outline the process of deriving power spectrum constraints in this revised picture.  Since the formalism can now include halos that collapse at any time, our preliminary revised constraints turn out to be stronger than prior constraints from UCMHs.

April 5,  2018

    Abstract: Self-interacting Dark Matter (SIDM) has been proposed as a way to help reconcile small scale astrophysical observations with CDM predictions. We use N-body simulations to study the effect of SIDM on the morphology of disk galaxies falling into galaxy clusters. An effective drag force arises from dark matter scatterings and leads to offsets of the stellar disk with respect to its surrounding halo, causing distortions in the disk. We show that potentially observable warps, asymmetries, and thickening of the disk occur in simulations with currently allowed cross-sections. With further analysis of the potential systematic uncertainties of these novel probes, we believe it could be possible to constrain SIDM cross-sections with current and future observations.

March 29,  2018

March 22,  2018

March 15,  2018

                Abstract: A robust measurement of galaxy clustering relies on our understanding of imaging systematics such as Galactic Extinction, and how they introduce fluctuations in galaxy density. In this talk we will present the idea of using Artificial Neural Networks in modeling the dependence of galaxy density on imaging systematics. This method could be used for systematic mitigation and therefore is beneficial to ongoing and future galaxy surveys such as eBOSS and DESI.

March 8,  2018

March 1,  2018

February 22,  2018

February 15,  2018

February 8,  2018

February 1,  2018

January 18,  2018

January 9,  2018

November 29,  2017

November 8,  2017

November 1,  2017

October 25,  2017

October 11,  2017

October 4,  2017

Sep 27,  2017

Sep 20,  2017

Sep 13,  2017

Sep 6,  2017

Aug 23,  2017

Aug 2,  2017

Jul 26,  2017

Jul 19,  2017

Jul 12,  2017

Jul 05,  2017

Jun 28,  2017

Jun 21,  2017

Jun 7,  2017

May 31,  2017

May, 17  2017

May, 11  2017

April, 19  2017

April, 5  2017

March, 29  2017

March, 22  2017

March, 8  2017

March, 1  2017

February, 22  2017

February, 15  2017

February, 08  2017

February, 01  2017

January, 25  2017

January, 11  2017

December, 14  2016

December, 1  2016

November, 17 2016

    Special talk: 

    Michael Wilson

    University of Edinburgh

    

    "Geometric and growth rate tests of gravity with the linearised galaxy distribution"

    Abstract:

    This talk will outline the consistency of the VIPERS PDR-2 census of the galaxy distribution at z=0.8 with the expansion history and linear growth rate predicted by General Relativity and a Planck (2015) cosmology.  These may be inferred from the observed anisotropy of the galaxy power spectrum, which is sensitive to both the coherent infall of galaxies towards clusters (outflow from voids) and the assumption of an expansion history differing from the true one.

    I will then present the results of including a simple density transform prior to the analysis; this tackles the principal cause of non-linearity by down-weighting the most massive structures and extends the validity of theoretical models.  Moreover, this weighting would amplify signatures of modified gravity in ‘shielded’ models and represents a higher-order statistic, which contains information beyond that available to the power spectrum.

    Finally, the final data release of the VIPERS spectroscopic survey will be on Nov 18th (http://vipers.inaf.it).  I will detail the characteristics of the survey and describe the breadth of the accompanying clustering analyses.

November, 10  2016

November, 3  2016

October, 27 2016

    Special talk: 

    Patrick Breysse

    John Hopkins University

    

    "High-Redshift Astrophysics Using Every Photon"

    Abstract:

    Large galaxy surveys have dramatically improved our understanding of the complex processes which govern gas dynamics and star formation in the nearby universe. However, we know far less about the most distant galaxies, as existing high-redshift observations can only detect the very brightest sources. Intensity mapping surveys provide a promising tool to access this poorly-studied population. By observing emission lines with low angular resolution, these surveys can make use of every photon in a target line to study faint emitters which are inaccessible using traditional techniques. With upcoming carbon monoxide experiments in mind, I will demonstrate how an intensity map can be used to measure the luminosity function of a galaxy population, and in turn how these measurements will allow us to place robust constraints on the cosmic star formation history. I will then show how cross-correlating CO isotopologue lines will make it possible to study gas dynamics within the earliest galaxies in unprecedented detail.

October, 20  2016

October, 6  2016

September, 29  2016

September, 22  2016

September, 15  2016

September, 8  2016

September, 1  2016