arXiv subjects

Kelly Whalen

Publications and source records attributed to Kelly Whalen.

4 recordsLinked to original sources

arXiv2026

The Hunt for Red Dual AGNs I: Spatially-Resolved Mid-IR Dual AGNs in the DeCam Legacy Survey

Theoretical studies predict that dual AGNs are a critical stage of galaxy merger-driven supermassive black hole growth. Systematic searches for dual AGNs typically target late-stage mergers ($\leq10$ kpc nuclear separations) and select AGNs based on optical diagnostics. Yet, simulations predict that obscuration can occur early in the merger sequence, and that a significant fraction of dual AGNs can be found beyond $10$ kpc. Here, we report on a new sample of 157 spatially resolved mid-IR dual AGNs candidates selected based upon their mid-IR $W1-W2$ colors from the Wide-Field Infrared Survey Explorer and optically classified as galaxy merger candidates using imaging from the Dark Energy Camera Legacy Survey. Spectroscopic results are presented for approximately 2/3 of the sample. 76 candidates have been confirmed to reside in galaxy mergers; among these, 13 have been confirmed as bona fide mid-IR dual AGNs, while 63 represent strong dual AGN candidates that require further examination. 46 candidates have been rejected as non-merger contaminants (foreground-background AGNs, separations inconsistent with interacting galaxies, etc.). 35 candidates still await spectroscopic coverage. The confirmed and high confidence dual AGN candidates exhibit separations of 14.5-129 kpc; $>50$% reside at separations $>50$ kpc. Confirmed and high confidence candidates also exhibit a diversity of nuclear optical BPT classes. Seyfert-Seyferts and Seyfert-HIIs dominate the overall BPT pairs sample. 31% of confirmed mid-IR dual AGNs reside in multi-mergers involving three or more galaxies. The diversity in AGN properties and environments identified in this work highlights the importance of multiwavelength selection strategies and analyses in the quest to holistically understand dual AGNs as a population.

astro-ph.GA↗

arXiv2026

The Need for Ultra High Resolution X-ray Imaging

This paper discusses the broad science case for obtaining milliarcsecond to microarcsecond astronomical imaging resolution in the soft to medium-energy X-ray band (~0.5 to ~8 keV). Astronomy across much of the electromagnetic spectrum has been fundamentally transformed with a rapid increase in ground-based and space-based capabilities to examine celestial objects on small scales that relate directly to their relevant physical processes. X-ray imaging capabilities, however, have fallen far behind observations at longer wavelengths. As such, without decisive advances in X-ray imaging, we will be unable to uncover key phenomena on the smallest astrophysical scales, leaving entire classes of high-energy discoveries beyond our reach. Here we describe several science goals for which high quality X-ray imaging is crucial and the status of some current technologies or mission concepts that would be required for these advances. In particular, we discuss the Accretion Explorer, a mission architecture under current study for a dispersed aperture X-ray interferometer.

astro-ph.HE↗

arXiv2025

Deep Ultraviolet, Emission-Line Imaging of the Makani Galactic Wind

The OVI 1032, 1038 A line is a key probe of cooling gas in the circumgalactic medium (CGM) of galaxies, but has been observed to date primarily in absorption along single sightlines. We present deep HST ACS-SBC observations of the compact, massive starburst Makani. Makani hosts a 100 kpc, [OII]-emitting galactic wind driven by two episodes of star formation over 400 Myr. We detect OVI and Ly$α$ emission across the [OII] nebula with similar morphology and extent, out to r ~ 50 kpc. Using differential narrow-band imaging, we separate Ly$α$ and OVI and show that the OVI emission is comparable in brightness to [OII], with $L_{OVI} = 4\times10^{42}$ erg/s. The similar hourglass morphology and size of [OII] and OVI implicate radiative cooling at $T = 10^{5.5}$ K in a hot-cold interface. This may occur as the $T > 10^7$ K CGM -- or the hot fluid driving the wind -- exchanges mass with the $T \approx 10^4$ K clouds entrained in (or formed by) the wind. The optical/UV line ratios may be consistent with shock ionization, though uncertain attenuation and Ly$α$ radiative transfer complicate the interpretation. The detection of OVI in Makani lies at the bleeding edge of the UV imaging capabilities of HST, and provides a benchmark for future emission-line imaging of the CGM with a wide-area UV telescope.

astro-ph.GA↗

arXiv2024

The Intrinsic Sizes of Odd Radio Circles

A new class of radio source, the so-called Odd Radio Circles (ORCs), have been discovered by recent sensitive, large-area radio continuum surveys. The distances of these sources have so far relied on photometric redshifts of optical galaxies found at the centers of or near the ORCs. Here we present Gemini rest-frame optical spectroscopy of six galaxies at the centers of, or potentially associated with, the first five ORC discoveries. We supplement this with Legacy Survey imaging and Prospector fits to their griz+W1/W2 photometry. Of the three ORCs with central galaxies, all lie at distances (z = 0.27-0.55) that confirm the large intrinsic diameters of the radio circles (300-500 kpc). The central galaxies are massive ($M_*\sim10^{11}M_\odot$), red, unobscured ellipticals with old ($\gtrsim$1~Gyr) stellar populations. They have LINER spectral types that are shock- or AGN-powered. All three host low-luminosity, radio-quiet AGN. The similarity of their central galaxies are consistent with a common origin, perhaps as a blastwave from an ancient starburst. The other two ORCs are adjacent and have no prominent central galaxies. However, the z=0.25 disk galaxy that lies between them hosts a Type 2, moderate-luminosity AGN. They may instead be the lobes of a radio jet from this AGN.

astro-ph.GA↗