arXiv subjects

Hannah Bish

Publications and source records attributed to Hannah Bish.

5 recordsLinked to original sources

arXiv2026

Hot off the Stacks: X-rays in Romulus25, Part I - Comparisons to Observations from eRosita

Recent observations from the from Spectrum Roentgen Gamma (SRG)/eROSITA all-sky survey data have helped to illuminate the hot circumgalactic medium (CGM) around galaxies at Milky Way-masses and above. In our study, we explore the hot X-ray emitting (T \textgreater 10$^6$ K) component of the CGM in over 750 galaxies from the Romulus25 cosmological simulation (Tremmel et al. 2017) between 10.0 < log(M$_*/M_{\odot}$) < 11.5. We forward-model soft X-ray [0.5 - 2.0] keV observations of our simulated galaxies using pyXSIM and SIXTE to measure the X-ray surface brightness (SB) profiles of the hot CGM. We then compare the average X-ray surface brightness profiles of six stellar-mass selected sub-samples to compare to the observational results from Chadayammuri et al. (2022a) and Zhang et al. 2024a. Broadly, we find that our stacked SB profiles are too bright compared to observations from Chadayammuri et al. (2022a) and Zhang et al.(2024a) particularly in the inner CGM. Additionally, we calculate the X-ray luminosity (L$_χ$) of the hot CGM for each galaxy and compare the average L$_χ$ across stellar mass to observations from Zhang et al. (2024b) as well as measurements from the EAGLE, TNG, SIMBA simulations. Across stellar mass, the average L$_χ$ of galaxies from Romulus25 are brighter than observations except at the lower, Milky Way-mass end where we are in relative agreement with both observations and most other simulations. We also consider a zero-metallicity emission model, because Romulus25 does not have metal-line cooling, finding the average L$_χ$ decreases by nearly an order-of-magnitude, which better matches observations particularly in the Milky Way-mass regime.

astro-ph.GA↗

arXiv2026

Extra! Extra! X-ray Emission!: X-rays in Romulus25, Part II - Physical Drivers of X-ray Emission in the CGM

Characterizing the hot (T ~ 10$^{6}$ K) circumgalactic medium (CGM) around Milky Way-mass (MW-mass) galaxies is critical to a full understanding of galaxy evolution. In this second paper of the "X-rays in Romulus25" series, we unpack the specific physical processes giving rise to the presence of hot X-ray emitting gas in the halos of galaxies from the Romulus25 (R25) simulation, focusing on L$_{*}$ galaxies. We determine that a strong correlation appears between the mass of hot CGM gas, M$_{gas, T > 10^{5.5} K}$, and the X-ray emissivity, $ε_χ$, measured in the first paper of this series, (Sanchez et al. 2026a, submitted). There is also a secondary correlation between M$_{gas, T > 10^{5.5} K}$ and $ε_χ$ with the average metallicity of the hot CGM gas, $\bar{Z}_{gas, T > 10^{5.5} K}$. We use the well-studied PIONEER simulations from Sanchez et al. (2019), a set of zoom-in MW-mass galaxies run with the genetic modification technique of Roth et al. (2016) and the same physics as R25, to interpret these correlations. We determine that the presence of hot X-ray emitting gas is determined by two key processes: 1) the quantity of hot gas mass in the CGM, M$_{gas, T > 10^{5.5} K}$, is set by the combined total energy injection of $both$ stellar and AGN feedback, and 2) together the average temperature and metallicity of the hot CGM changes the soft X-ray spectrum of the gas resulting in brighter metal-rich CGM and dimmer metal-poor CGM for the same quantity of M$_{gas, T > 10^{5.5} K}$. These results indicate, for the first time, that metal-rich gas halos may bias X-ray observations of MW-mass galaxies.

astro-ph.GA↗

arXiv2025

The Plane Quasar Survey: An Ionized Extension of the Magellanic Stream on the Northern Side of the Galactic Plane

The Magellanic Stream (MS) is a vast gaseous structure in the Milky Way halo, containing most of its mass in ionized form and tracing the interaction between the Large and Small Magellanic Clouds and the Galaxy. Using HST/COS G160M spectra from the Plane Quasar Survey, we detect C IV absorbers likely associated with the MS, extending to the northern side of the Galactic plane, approximately 60$^\circ$ beyond its previously known ionized extent. These absorbers exhibit position and kinematic alignment and show consistent ionization trends with previously studied MS sight lines. The non-detection of low ions such as Al II and Si II, and the detection of C IV (and Si IV in some sightlines), indicates a highly ionized gas phase. The observed Si IV/C IV column density ratios suggest a gas temperature of $T \sim 10^{5.3}$~K and favor collisional ionization over photoionization. We estimate the newly detected extension increases the previous ionized gas mass of the MS, and its coherent kinematics suggest that it was stripped within the past few hundred Myr and has not yet mixed with the Milky Way halo. The existence of highly-ionized MS gas at a location above the Galactic Plane may constrain the orbital direction of the Magellanic Clouds.

astro-ph.GA↗

arXiv2024

The Plane Quasar Survey: First Data Release

We present a sample of 305 QSO candidates having $|b| < 30^{\circ}$, the majority with GALEX magnitudes NUV < 18.75. To generate this sample, we apply UV-IR color selection criteria to photometric data from the Ultraviolet GAlactic Plane Survey (UVGAPS) as part of GALEX-CAUSE, the Million Quasars Catalog, Gaia DR2, and Pan-STARRS DR1. 165 of these 305 candidate UV-bright AGN (54%) have published spectroscopic redshifts from 45 different surveys, confirming them as AGN. We further obtained low-dispersion, optical, longslit spectra with the APO 3.5-m, MDM 2.4-m, and MDM 1.3-m telescopes for 84 of the candidates, and confirm 86% (N = 72) as AGN, generally with z < 0.6. These sources fill a gap in the Galactic latitude coverage of the available samples of known UV-bright QSO background probes. Along with a description of the confirmed QSO properties, we provide the fully-reduced, flux and wavelength-calibrated spectra of 84 low-latitude QSOs through the Mikulski Archive for Space Telescopes. Future HST/COS spectroscopy of these low-Galactic-latitude QSOs has the potential to transform our view of the Milky Way and Local Group circumgalactic medium.

astro-ph.GA↗

arXiv2013

To Stack or Not to Stack: Spectral Energy Distribution Properties of Lya-Emitting Galaxies at z=2.1

We use the Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey (CANDELS) GOODS-S multi-wavelength catalog to identify counterparts for 20 Lya Emitting (LAE) galaxies at z=2.1. We build several types of stacked Spectral Energy Distributions (SEDs) of these objects. We combine photometry to form average and median flux-stacked SEDs, and postage stamp images to form average and median image-stacked SEDs. We also introduce scaled flux stacks that eliminate the influence of variation in overall brightness. We use the SED fitting code SpeedyMC to constrain the physical properties of individual objects and stacks. Our LAEs at z = 2.1 have stellar masses ranging from 2x10^7 Msun - 8x10^9 Msun (median = 3x10^8 Msun), ages ranging from 4 Myr to 500 Myr (median =100 Myr), and E(B-V) between 0.02 and 0.24 (median = 0.12). We do not observe strong correlations between Lya equivalent width (EW) and stellar mass, age, or E(B-V). The Lya radiative transfer (q) factors of our sample are predominantly close to one and do not correlate strongly with EW or E(B-V), implying that Lya radiative transfer prevents Lya photons from resonantly scattering in dusty regions. The SED parameters of the flux stacks match the average and median values of the individual objects, with the flux-scaled median SED performing best with reduced uncertainties. Median image-stacked SEDs provide a poor representation of the median individual object, and none of the stacking methods captures the large dispersion of LAE properties.

astro-ph.CO↗