arXiv subjects

Kirsten R. Hall

Publications and source records attributed to Kirsten R. Hall.

11 recordsLinked to original sources

arXiv2025

A flux-limited sample of dusty star-forming galaxies from the Atacama Cosmology Telescope: physical properties and the case for multiplicity

We report the modeling of the millimeter and far-infrared spectral energy distributions of 71 dusty star-forming galaxies (DSFGs) selected by the Atacama Cosmology Telescope (ACT) with a lower flux-density limit of 8 mJy at 220 GHz (1.4 mm). All sources were cross-identified with Herschel surveys at 500, 350, and 250 μm, and nineteen of our sources were observed at with the Submillimeter Array. A probabilistic cataloging algorithm, PCAT, favors multiple unresolved flux components in the Herschel data for the majority of ACT-selected DSFGs. We compare the derived physical properties of the DSFGs obtained from modeling the flux densities with those from similar studies of both lensed and unlensed DSFG populations. We find the median, 16th and 84th percentiles for the following model parameters: redshift zphot=3.3(+0.7)(-0.6), apparent size μd=5.2(+0.9)(-2.4) kpc, apparent dust mass log10(μMd/Msun)=9.14(+0.12)(-0.04) and cutoff temperature Tc=35.6(+4.8)(-1.6) K, and the corresponding apparent far-infrared luminosity log10(μLIR/Lsun)=13.6(+0.2)(-0.3), where μ is lensing magnification. While many of the properties broadly agree with those of samples of primarily lensed DSFGs, we exercise caution in interpreting them. ACT's lower flux limit, the PCAT decomposition, and the higher-resolution SMA observations all suggest that some fraction of these DSFGs are likely to be unlensed and possibly multiples. The SMA data indicate that at least fourteen out of nineteen sources are such, either via "missing" flux in comparison to the ensemble model or detection of additional sources in the fields. Additional high-resolution follow-up and targeted redshift observations are needed to better understand this flux-limited sample of DSFGs.

astro-ph.GA↗

arXiv2025

ASASSN-24fw: Candidate circumplanetary disk occultation of a main-sequence star

Dusty disks around planetary and substellar companions in outer reaches of exo-planetary systems can be detected as long-lasting occultations, provided the observer is close to the secondary's orbital plane. Here we report optical spectroscopy with KOSMOS (APO), MagE (Magellan) and GHOST (Gemini-S) of ASASSN-24fw (Gaia 07:05:18.97+06:12:19.4), a 4-magnitude dimming event of a main-sequence star which lasted 8.5 months. We discover multiple low-ionization metal emission lines with velocity dispersion $\lesssim 10$ km/s blue-shifted by 27 km/s with respect to the star, as well as kinematically complex Na D absorption. If associated with the occulter, these detections suggest that the occulter is gas-rich. Further, we detect blue-shifted and broad ($\sim 200$ km/s) H$α$ line, which likely originates in the inner circumstellar disk. We confirm the previously reported occultations in 1981 and 1937 seen in historic data, yielding a semi-major axis of the occulter's orbital motion around the star of 14 AU. If the occulter is a circumsecondary disk filling 30-100% of the Hill radius, we estimate the minimum mass of the secondary to be a few Jupiter masses and a disk mass of 1% of the mass of the Moon. Given the age of the star ($>2$ Gyr), the disk is unlikely to be a survivor of the planet formation stage and may be a result of a planetary collision. If Na D absorption and/or metal emission lines originate in the disk, the observations presented here are the first discovery of a circumsecondary disk wind or rotation.

astro-ph.EP↗

arXiv2024

The Atacama Cosmology Telescope: DR6 Gravitational Lensing Map and Cosmological Parameters

We present cosmological constraints from a gravitational lensing mass map covering 9400 sq. deg. reconstructed from CMB measurements made by the Atacama Cosmology Telescope (ACT) from 2017 to 2021. In combination with BAO measurements (from SDSS and 6dF), we obtain the amplitude of matter fluctuations $σ_8 = 0.819 \pm 0.015$ at 1.8% precision, $S_8\equivσ_8({Ω_{\rm m}}/0.3)^{0.5}=0.840\pm0.028$ and the Hubble constant $H_0= (68.3 \pm 1.1)\, \text{km}\,\text{s}^{-1}\,\text{Mpc}^{-1}$ at 1.6% precision. A joint constraint with CMB lensing measured by the Planck satellite yields even more precise values: $σ_8 = 0.812 \pm 0.013$, $S_8\equivσ_8({Ω_{\rm m}}/0.3)^{0.5}=0.831\pm0.023$ and $H_0= (68.1 \pm 1.0)\, \text{km}\,\text{s}^{-1}\,\text{Mpc}^{-1}$. These measurements agree well with $Λ$CDM-model extrapolations from the CMB anisotropies measured by Planck. To compare these constraints to those from the KiDS, DES, and HSC galaxy surveys, we revisit those data sets with a uniform set of assumptions, and find $S_8$ from all three surveys are lower than that from ACT+Planck lensing by varying levels ranging from 1.7-2.1$σ$. These results motivate further measurements and comparison, not just between the CMB anisotropies and galaxy lensing, but also between CMB lensing probing $z\sim 0.5-5$ on mostly-linear scales and galaxy lensing at $z\sim 0.5$ on smaller scales. We combine our CMB lensing measurements with CMB anisotropies to constrain extensions of $Λ$CDM, limiting the sum of the neutrino masses to $\sum m_ν < 0.13$ eV (95% c.l.), for example. Our results provide independent confirmation that the universe is spatially flat, conforms with general relativity, and is described remarkably well by the $Λ$CDM model, while paving a promising path for neutrino physics with gravitational lensing from upcoming ground-based CMB surveys.

astro-ph.CO↗

arXiv2024

The Atacama Cosmology Telescope: Extragalactic Point Sources in the Southern Surveys at 150, 220 and 280 GHz observed between 2008-2010

We present a multi-frequency, multi-epoch catalog of extragalactic sources. The catalog is based on 150, 220, and 280 GHz observations carried out in 2008, 2009, and 2010 using the Millimeter Bolometric Array Camera on the Atacama Cosmology Telescope. We also present and release 280 GHz maps from 2008 and 2010. The catalog contains 483 sources found in a sky area of ${\sim}600$ square degrees. It was obtained by cross-matching sources found in 11 sub-catalogs, one for each season and frequency band. We also include co-added data from ${\sim}150$ and ${\sim}160$ square degrees using two and three years of overlapping observations. We divide the sources into two populations, synchrotron and dusty emitters, based on their spectral behavior in the 150-280 GHz frequency range. We find 284 synchrotron sources and 183 dusty source candidates. Our cross-matching with catalogs from radio to X-ray results in 251 synchrotron sources (88%) and 92 dusty sources (51%) with counterparts and suggests that 91 dusty candidates are not in existing catalogs. We study the variability and number counts of each population. In the case of synchrotron sources, we find year-to-year variability, with a mean value around 35%. As expected, we find no evidence of dusty source variability. Our number counts generally agree with previous measurements and models, except for dusty sources at 280 GHz, where some models overestimate our results.

astro-ph.GA↗

arXiv2024

Ozone Anomalies in Dry Intrusions Associated with Atmospheric Rivers

As a result of their important role in weather and the global hydrological cycle, understanding atmospheric rivers' (ARs) connection to synoptic-scale climate patterns and atmospheric dynamics has become increasingly important. In addition to case studies of two extreme AR events, we produce a December climatology of the three-dimensional structure of water vapor and O3 (ozone) distributions associated with ARs in the northeastern Pacific from 2004-2014 using MERRA-2 reanalysis products. Results show that positive O3 anomalies reside in dry intrusions of stratospheric air due to stratosphere-to-troposphere transport (STT) behind the intense water vapor transport of the AR. In composites, we find increased excesses of O3 concentration, as well as in the total O3 flux within the dry intrusions, with increased AR strength. We find that STT O3 flux associated with ARs over the NE Pacific accounts for up to 13 percent of total Northern Hemisphere STT O3 flux in December, and extrapolation indicates that AR-associated dry intrusions may account for as much as 32 percent of total NH STT O3 flux. This study quantifies STT of O3 in connection with ARs for the first time and improves estimates of tropospheric ozone concentration due to STT in the identification of this correlation. In light of predictions that ARs will become more intense and/or frequent with climate change, quantifying AR-related STT O3 flux is especially valuable for future radiative forcing calculations.

physics.ao-ph↗

arXiv2023

Uncovering a Massive z~7.7 Galaxy Hosting a Heavily Obscured Radio-Loud QSO Candidate in COSMOS-Web

In this letter, we report the discovery of the highest redshift, heavily obscured, radio-loud AGN candidate selected using JWST NIRCam/MIRI, mid-IR, sub-mm, and radio imaging in the COSMOS-Web field. Using multi-frequency radio observations and mid-IR photometry, we identify a powerful, radio-loud (RL), growing supermassive black hole (SMBH) with significant spectral steepening of the radio SED ($f_{1.28 \mathrm{GHz}} \sim 2$ mJy, $q_{24μm} = -1.1$, $α_{1.28-3\mathrm{GHz}}=-1.2$, $Δα= -0.4$). In conjunction with ALMA, deep ground-based observations, ancillary space-based data, and the unprecedented resolution and sensitivity of JWST, we find no evidence of AGN contribution to the UV/optical/NIR data and thus infer heavy amounts of obscuration (N$_{\mathrm{H}} > 10^{23}$ cm$^{-2}$). Using the wealth of deep UV to sub-mm photometric data, we report a singular solution photo-z of $z_\mathrm{phot}$ = 7.7$^{+0.4}_{-0.3}$ and estimate an extremely massive host-galaxy ($\log M_{\star} = 11.4 -12\,\mathrm{M}_{\odot}$) hosting a powerful, growing SMBH (L$_{\mathrm{Bol}} = 4-12 \times 10^{46}$ erg s$^{-1}$). This source represents the furthest known obscured RL AGN candidate, and its level of obscuration aligns with the most representative but observationally scarce population of AGN at these epochs.

astro-ph.GA↗

arXiv2023

The Atacama Cosmology Telescope: Modeling the Gas Thermodynamics in BOSS CMASS galaxies from Kinematic and Thermal Sunyaev-Zel'dovich Measurements

The thermal and kinematic Sunyaev-Zel'dovich effects (tSZ, kSZ) probe the thermodynamic properties of the circumgalactic and intracluster medium (CGM and ICM) of galaxies, groups, and clusters, since they are proportional, respectively, to the integrated electron pressure and momentum along the line-of-sight. We present constraints on the gas thermodynamics of CMASS galaxies in the Baryon Oscillation Spectroscopic Survey (BOSS) using new measurements of the kSZ and tSZ signals obtained in a companion paper. Combining kSZ and tSZ measurements, we measure within our model the amplitude of energy injection $εM_\star c^2$, where $M_\star$ is the stellar mass, to be $ε=(40\pm9)\times10^{-6}$, and the amplitude of the non-thermal pressure profile to be $α_{\rm Nth}<0.2$ (2$σ$), indicating that less than 20% of the total pressure within the virial radius is due to a non-thermal component. We estimate the effects of including baryons in the modeling of weak-lensing galaxy cross-correlation measurements using the best-fit density profile from the kSZ measurement. Our estimate reduces the difference between the original theoretical model and the weak-lensing galaxy cross-correlation measurements in arXiv:1611.08606 by half but does not fully reconcile it. Comparing the tSZ measurements to cosmological simulations, we find that simulations underestimate the CGM pressure at large radii while they fare better in comparison with the kSZ measurements. This suggests that the energy injected via feedback models in the simulations that we compared against does not sufficiently heat the gas at these radii. We do not find significant disagreement at smaller radii. These measurements provide novel tests of current and future simulations. This work demonstrates the power of joint, high signal-to-noise kSZ and tSZ observations, upon which future cross-correlation studies will improve.

astro-ph.CO↗

arXiv2021

Merger or Not: Accounting for Human Biases in Identifying Galactic Merger Signatures

Significant galaxy mergers throughout cosmic time play a fundamental role in theories of galaxy evolution. The widespread usage of human classifiers to visually assess whether galaxies are in merging systems remains a fundamental component of many morphology studies. Studies that employ human classifiers usually construct a control sample, and rely on the assumption that the bias introduced by using humans will be evenly applied to all samples. In this work, we test this assumption and develop methods to correct for it. Using the standard binomial statistical methods employed in many morphology studies, we find that the merger fraction, error, and the significance of the difference between two samples are dependent on the intrinsic merger fraction of any given sample. We propose a method of quantifying merger biases of individual human classifiers and incorporate these biases into a full probabilistic model to determine the merger fraction and the probability of an individual galaxy being in a merger. Using 14 simulated human responses and accuracies, we are able to correctly label a galaxy as ''merger'' or ''isolated'' to within 1\% of the truth. Using 14 real human responses on a set of realistic mock galaxy simulation snapshots our model is able to recover the pre-coalesced merger fraction to within 10\%. Our method can not only increase the accuracy of studies probing the merger state of galaxies at cosmic noon, but also can be used to construct more accurate training sets in machine learning studies that use human classified data-sets.

astro-ph.GA↗

arXiv2019

Quantifying the Thermal Sunyaev-Zel'dovich Effect and Excess Millimeter Emission in Quasar Environments

In this paper we probe the hot, post-shock gas component of quasar-driven winds through the thermal Sunyaev-Zel'dovich (tSZ) effect. Combining datasets from the Atacama Cosmology Telescope, the $\textit{Herschel}$ Space Observatory, and the Very Large Array, we measure average spectral energy distributions (SEDs) of 109,829 optically-selected, radio quiet quasars from 1.4~GHz to 3000~GHz in six redshift bins between $0.3 1.91$, we measure the tSZ effect at $3.8σ$ significance with an amplitude corresponding to a total thermal energy of $3.1\times10^{60}$ ergs. If this energy is due to virialized gas, then our measurement implies quasar host halo masses are $\sim6\times10^{12}~h^{-1}$M$_\odot$. Alternatively, if the host dark matter halo masses are $\sim2\times10^{12}~h^{-1}$M$_\odot$ as some measurements suggest, then we measure a $>$90 per cent excess in the thermal energy over that expected due to virialization. If the measured SZ effect is primarily due to hot bubbles from quasar-driven winds, we find that $(5^{+1.2}_{-1.3}$) per cent of the quasar bolometric luminosity couples to the intergalactic medium over a fiducial quasar lifetime of 100 Myr. An additional source of tSZ may be correlated structure, and further work is required to separate the contributions. At $z\leq1.91$, we detect emission at 95 and 148~GHz that is in excess of thermal dust and optically thin synchrotron emission. We investigate potential sources of this excess emission, finding that CO line emission and an additional optically thick synchrotron component are the most viable candidates.

astro-ph.GA↗

arXiv2018

Downsizing of Star Formation Measured from the Clustered Infrared Background Correlated with Quasars

Powerful quasars can be seen out to large distances. As they reside in massive dark matter haloes, they provide a useful tracer of large scale structure. We stack Herschel-SPIRE images at 250, 350 and 500 microns at the location of 11,235 quasars in ten redshift bins spanning $0.5 \leq z \leq 3.5$. The unresolved dust emission of the quasar and its host galaxy dominate on instrumental beam scales, while extended emission is spatially resolved on physical scales of order a megaparsec. This emission is due to dusty star-forming galaxies clustered around the dark matter haloes hosting quasars. We measure radial surface brightness profiles of the stacked images to compute the angular correlation function of dusty star-forming galaxies correlated with quasars. We then model the profiles to determine large scale clustering properties of quasars and dusty star-forming galaxies as a function of redshift. We adopt a halo model and parameterize it by the most effective halo mass at hosting star-forming galaxies, finding $\log(M_\mathrm{eff}/M_{\odot}) = 13.8^{+0.1}_{-0.1}$ at $z=2.21-2.32$, and, at $z=0.5-0.81$, the mass is $\log(M_\mathrm{eff}/M_{\odot}) = 10.7^{+1.0}_{-0.2}$. Our results indicate a downsizing of dark matter haloes hosting dusty star-forming galaxies between $0.5 \leq z \leq 2.9$. The derived dark matter halo masses are consistent with other measurements of star-forming and sub-millimeter galaxies. The physical properties of dusty star-forming galaxies inferred from the halo model depend on details of the quasar halo occupation distribution in ways that we explore at $z>2.5$, where the quasar HOD parameters are not well constrained.

astro-ph.GA↗

arXiv2016

The RESOLVE Survey Atomic Gas Census and Environmental Influences on Galaxy Gas Reservoirs

We present the HI mass inventory for the RESOLVE survey, a volume-limited, multi-wavelength census of >1500 z=0 galaxies spanning diverse environments and complete in baryonic mass down to dwarfs of 10^9 Msun. This first 21cm data release provides robust detections or strong upper limits (1.4M_HI < 5 to 10% of stellar mass M_stars) for 94% of RESOLVE. We examine global atomic gas-to-stellar mass ratios (G/S) in relation to galaxy environment using several metrics: group dark matter halo mass M_h , central/satellite designation, relative mass density of the cosmic web, and distance to nearest massive group. We find that at fixed M_stars, satellites have decreasing G/S with increasing M_h starting clearly at M_h = 10^12 Msun, suggesting the presence of starvation and/or stripping mechanisms associated with halo gas heating in intermediate-mass groups. The analogous relationship for centrals is uncertain because halo abundance matching builds in relationships between central G/S, stellar mass, and halo mass, which depend on the integrated group property used as a proxy for halo mass (stellar or baryonic mass). On larger scales G/S trends are less sensitive to the abundance matching method. At fixed M_h < 10^12 Msun, the fraction of gas-poor centrals increases with large-scale structure density. In overdense regions, we identify a rare population of gas-poor centrals in low-mass (M_h < 10^11.4 Msun) halos primarily located within 1.5 times the virial radius of more massive (M_h > 10^12 Msun) halos, suggesting that gas stripping and/or starvation may be induced by interactions with larger halos or the surrounding cosmic web. We find that the detailed relationship between G/S and environment varies when we examine different subvolumes of RESOLVE independently, which we suggest may be a signature of assembly bias.

astro-ph.GA↗