arXiv subjects

Mary Putman

Publications and source records attributed to Mary Putman.

At least 19 recordsLinked to original sources

arXiv2026

The Multi-phase HI of the Milky Way and Nearby Galaxies

Atomic hydrogen (HI) is the dominant baryonic component of the interstellar medium (ISM) in Milky Way-like galaxies and the reservoir from which molecular clouds and stars ultimately form. The condensation of diffuse HI into cold structures is governed by a complex interplay between radiative cooling, turbulence, magnetic fields, stellar feedback, and galactic dynamics, acting over scales ranging from astronomical units to kiloparsecs. Understanding how these processes regulate the thermal structure of the HI, the formation of cold clouds, and the transfer of matter and energy across scales is essential for connecting the small-scale physics of the ISM to the evolution of galaxies. Recent advances from SKA precursors have transformed our view of the atomic ISM, revealing a highly structured and filamentary cold medium, increasing the density of HI absorption measurements by orders of magnitude, and enabling new approaches to infer the thermodynamic and magnetic properties of the gas from spectral-line datasets. SKA-mid will provide the first comprehensive characterization of HI as a multi-phase, turbulent, and magnetized medium across the Milky Way and nearby galaxies. Its combination of sensitivity, angular resolution, spectral resolution, and survey speed will enable matched emission-absorption studies, dense optical-depth grids, and detailed mapping of the atomic-to-molecular transition over a broad range of environments. Combined with polarization, Zeeman, recombination-line, and multi-wavelength observations, SKA-mid will establish a unified observational framework to study the evolution of diffuse matter in galaxies, in connection with star formation, from the Solar neighborhood to galactic scales.

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arXiv2026

Identifying signatures of inflow onto face-on galaxies using the Balmer decrement

Isolated star-forming galaxies require inflows of fresh gas from the surrounding medium to sustain episodes of star formation over time. However, there are very few direct detections of accretion onto external galaxies. Studies in absorption can only observe along limited sightlines, while those in emission can have difficulty distinguishing inflowing gas in the foreground of the galactic disk from similarly Doppler-shifted outflowing gas in the background. We explore the possibility of using the Balmer decrement (H$\alpha$/H$\beta$) in low-inclination systems as a diagnostic for disentangling the flow geometry in disk-like galaxies. We leverage mock spatial-spectral observations of an isolated Milky Way-mass galaxy simulated using the radiation-hydrodynamics code AREPO-RT and post-processed with the Monte Carlo radiative transfer code COLT. We find that gas components located in front of the disk exhibit systematically lower Balmer decrements than gas embedded in or behind the disk, with a mean front-back offset of $\Delta(\text{H}\alpha/\text{H}\beta) \approx -0.14$. The ability to differentiate between the disk and far-side components is limited by the extremely clumpy, multiphase dust distribution along the line of sight introducing substantial scatter. Overall, the results provide a useful observational diagnostic of inflow and outflow in dusty face-on galaxies.

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arXiv2025

TiNy Titans HI: Discovering Satellites via HI Gas in an Isolated, Compact Group of Dwarf Galaxies

We report on the HI content of an isolated, compact group of 6 dwarf galaxies at a distance of 145 Mpc. The distribution and kinematics of the HI, including multiple gaseous bridges, indicate the group is a gravitationally bound system. The HI maps further reveal two newly discovered dwarf satellites easily identified by their gas but only barely visible in optical images. The four dwarf group members previously identified in SDSS have 9.06 < log(Mstar/Msun) < 9.43 and 9.42 < log(MHI/Msun) < 9.73. The two newly discovered dwarf satellites have log(Mstar/Msun) = 6.10 with log(MHI/Msun) = 8.71 and log(Mstar/Msun) = 7.07 with log(MHI/Msun) = 9.18. New Gemini optical spectra link the HI detections and their optical counterparts. The group's 3D velocity dispersion (188 km/s), mass-to-light ratio (M_L/B ~44), dynamical-to-baryonic mass ratio (Mdyn/Mbary ~ 21), size (69 kpc), and gas fraction (0.56) are all consistent with the compact dwarf groups in the TNG50 simulation. The group has a top-heavy satellite mass function that is inconsistent with predictions for LMC-sized hosts and may instead be two or more groups coming together. A Voronoi tessellation reveals the group resides in a tendril outside the intersection of two filaments. These intermediate density environments within large scale structure provide the conditions needed for groups of star forming, gas-rich dwarf galaxies to form and eventually merge. Our results further show that it is possible to uncover fainter dwarf satellites around dwarf galaxy hosts via HI maps.

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arXiv2025

Baryonic Masses and Properties of Gaseous Satellite Galaxies

We present a sample of 127 gas-bearing dwarf galaxies around 56 late-type host galaxies within 30 Mpc using 21-cm HI data from the WALLABY, MHONGOOSE, and ALFALFA surveys. We characterize the environment of each dwarf galaxy based on its host galaxy halo and derive optical properties using the DESI Legacy Surveys for 110. The gaseous satellites span $\log (M_{\rm HI}/M_{\odot}) = 5.8-9.7$ and $\log (M_{\star}/M_{\odot}) = 5.6-10.0$, with a median velocity line-width of $W_{50}=40$ km/s, comparable to the Local Group gaseous dwarf galaxies. We assess the HI mass sensitivity of the data by injecting model dwarf galaxies and find $M_{\rm HI,lim} \approx 10^{6.7} M_{\odot}$ for WALLABY and $M_{\rm HI,lim} \approx 10^{5.4} M_{\odot}$ for MHONGOOSE at 10 Mpc. Our sample has lower average atomic gas fractions ($M_{\rm HI}/M_{\star}$) than previous gaseous dwarf samples in field and satellite environments, although this offset partly reflects differences in HI sensitivity. The abundance of gaseous satellites per host is low and increases with host mass: $0-2$ for dwarf centrals and $0-5$ for Milky Way-mass spiral hosts. These numbers are consistent with the Milky Way, M31, and star-forming satellite abundances from recent deep optical surveys. The inferred quenched fractions and gas-depleted satellites indicate that environmental quenching is effective in Milky Way-mass hosts, likely driven by gas stripping processes.

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arXiv2025

The MDW H{\alpha} Sky Survey: Data Release 1

The Mittelman-di Cicco-Walker (MDW) H$\alpha$ Sky Survey is an autonomously-operated all-sky narrow-band (3nm) H$\alpha$ imaging survey. The survey was founded by amateur astronomers and the northern sky (Decl. $\geq$ 0$^\circ$) is presented here in its second stage of refinement for academic use. Each 3.6$\times$3.6 sq. deg MDW field has 12 20-minute individual exposures with a pixel scale of 3.6", a typical PSF of 6", and a stack point source depth of 16-17 magnitudes. The northern MDW Survey Data Release 1 (DR1) includes: calibrated and raw mean and individual images, star-removed mean fields, and point source catalogs for all images matched to Data Release 1 of the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS1) and the INT Galactic Plane Survey (IGAPS). Our initial study of H$\alpha$ filament widths finds a typical FWHM of 30-45" in the Lyra region. The matched catalogs (with a median match distance of ~0.5"), combined with our distinctive narrow-band photometry, are used to identify H$\alpha$ variable and excess sources. These initial studies highlight some of the many scientific uses of the MDW H$\alpha$ survey.

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arXiv2025

Caught in the Cosmic Web: Evidence for Ram-Pressure Stripping of a Low-Mass Galaxy by the Cosmic Web

We present interferometric radio observations of the neutral atomic gas in AGC 727130, a low-mass, gas-rich, field galaxy lacking significant star-formation. The atomic gas in AGC 727130 displays a pronounced asymmetry, extending well beyond the stellar disk in one direction while remaining relatively undisturbed in the other. Despite proximity to a pair of interacting dwarfs, tidal analysis suggests these neighboring galaxies are not responsible for this pronounced asymmetry. Instead, using a topological cosmic web filament finder on spectroscopic catalogue data, we find AGC 727130 lies at the intersection of several large-scale cosmic web filaments, environments predicted to host diffuse, shock-heated gas. We propose that an interaction with this ambient medium is stripping gas from the galaxy via cosmic web ram-pressure stripping. This mechanism, supported by recent simulations, may quench low-mass galaxies outside of massive halos, and must be accounted for when comparing observed numbers of dwarf galaxies to theoretical predictions.

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arXiv2025

The Karl G. Jansky Very Large Array Local Group L-band Survey (LGLBS)

We present the Local Group L-Band Survey (LGLBS), a Karl G. Jansky Very Large Array (VLA) survey producing the highest quality 21-cm and 1-2 GHz radio continuum images to date for the six VLA-accessible, star-forming, Local Group galaxies. Leveraging the VLA's spectral multiplexing power, we simultaneously survey the 21-cm line at high 0.4 km/s velocity resolution, the 1-2 GHz polarized continuum, and four OH lines. For the massive spiral M31, the dwarf spiral M33, and the dwarf irregular galaxies NGC6822, IC10, IC1613, and the Wolf-Lundmark-Melotte Galaxy (WLM), we use all four VLA configurations and the Green Bank Telescope to reach angular resolutions of $< 5''$ ($10{-}20$~pc) for the 21-cm line with $<10^{20}$~cm$^{-2}$ column density sensitivity, and even sharper views ($< 2''$; $5{-}10$~pc) of the continuum. Targeting these nearby galaxies ($D\lesssim1$ Mpc) reveals a sharp, resolved view of the atomic gas, including 21-cm absorption, and continuum emission from supernova remnants and HII regions. These datasets can be used to test theories of the abundance and formation of cold clouds, the driving and dissipation of interstellar turbulence, and the impact of feedback from massive stars and supernovae. Here, we describe the survey design and execution, scientific motivation, data processing, and quality assurance. We provide a first look at and publicly release the wide-field 21-cm HI data products for M31, M33, and four dwarf irregular targets in the survey, which represent some of the highest physical resolution 21-cm observations of any external galaxies beyond the LMC and SMC.

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arXiv2025

Simulating High-Velocity Clouds in the Observational Plane: An Initial Study with the Smith Cloud

High-velocity clouds (HVCs) may fuel future star formation in the Milky Way, but they must first survive their passage through the hot halo. While recent work has improved our understanding of the survival criterion for cloud-wind interactions, few observational comparisons exist that test this criterion. We therefore present an initial comparison of simulations with the Smith Cloud (SC; $d=$ 12.4 kpc, $l, b = 40^{\circ}, -13^{\circ}$) as mapped with the GALFA-HI survey. We use the Smith Cloud's observed properties to motivate simulations of comparable clouds in wind tunnel simulations with Enzo-E, an MHD code. For both observations and simulations, we generate moment maps, characterize turbulence through a projected first-order velocity structure function (VSF), and do the same for HI column density with a normalized autocovariance function. We explore how initial cloud conditions (such as radius, metallicity, thermal pressure, viewing angle, and distance) affect these statistics, demonstrating that the small-scale VSF is sensitive to cloud turbulence while large scales depend on cloud bulk velocity and viewing angle. We find that some simulations reproduce key observational features (particularly the correlation between column density and velocity dispersion) but none match all observational probes at the same time (the large scales of the column density autocovariance is particularly challenging). We find that the simulated cloud (cloud C) showing growth via a turbulent radiative mixing layer (TRML) is the best match, implying the importance of TRML-mediated cooling for Milky Way HVCs. We conclude by suggesting improvements for simulations to better match observed HVCs.

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arXiv2025

Introducing the Descriptive Parametric Model: Gaseous Profiles for Galaxies, Groups, and Clusters

We develop and present the Descriptive Parametric Model (DPM), a tool for generating profiles of gaseous halos (pressure, electron density, and metallicity) as functions of radius, halo mass, and redshift. The model assumes single-phase, spherically symmetric, volume-filling warm/hot gas. The DPM framework enables mock observations of the circumgalactic medium (CGM), group halos, and clusters across a number of wavebands including X-ray, sub-millimeter/millimeter, radio, and ultraviolet (UV). We introduce three model families calibrated to reproduce cluster profiles while having different extrapolations to the CGM -- (i) self-similar halos, (ii) a reduced gas model for lower halo masses, and (iii) a model with shallower radial slopes at lower masses. We demonstrate how our z=0.0-0.6 models perform when applied to stacked and individual X-ray emission profiles, measurements of the thermal and kinetic Sunyaev-Zel'dovich Effect, electron dispersion measures from fast radio bursts, O VI absorption, and UV-derived pressures. Our investigation supports models that remove baryons from halos more effectively and have shallower profiles at lower halo mass. We discuss biases and systematics when modelling observables using consistent hot gaseous halo models for all wavebands explored. We release the DPMhalo code to encourage the use of our framework and new formulations in future investigations. Included with the DPMhalo distribution is a set of recent observations that allow the reproduction of most plots in this paper.

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arXiv2024

A Search for 3-mm Molecular Absorption Line Transitions in the Magellanic Stream

The Magellanic Stream, a tidal tail of diffuse gas falling onto the Milky Way, formed by interactions between the Small and Large Magellanic Clouds, is primarily composed of neutral atomic hydrogen (HI). The deficiency of dust and the diffuse nature of the present gas make molecular formation rare and difficult, but if present, could lead to regions potentially suitable for star formation, thereby allowing us to probe conditions of star formation similar to those at high redshifts. We search for HCO$^+$, HCN, HNC, and C$_2$H using the highest sensitivity observations of molecular absorption data from the Atacama Large Millimeter Array to trace these regions, comparing with HI archival data to compare these environments in the Magellanic Stream to the HI column density threshold for molecular formation in the Milky Way. We also compare the line of sight locations with confirmed locations of stars, molecular hydrogen, and OI detections, though at higher sensitivities than the observations presented here. We find no detections to a 3$\sigma$ significance, despite four sightlines having column densities surpassing the threshold for molecular formation in the diffuse regions of the Milky Way. Here we present our calculations for the upper limits of the column densities of each of these molecular absorption lines, ranging from $3 \times 10^{10}$ to $1 \times 10^{13}$ cm$^{-2}$. The non-detection of HCO$^+$ suggests that at least one of the following is true: (i) $X_{HCO^+, \mathrm{MS}}$ is significantly lower than the Milky Way value; (ii) that the widespread diffuse molecular gas observed in the Milky Way's diffuse ISM does not have a direct analog in the MS; (iii) the HI-to-H$_2$ transition occurs in the MS at a higher surface density in the MS than in the LMC or SMC; or (iv) molecular gas exists in the MS, but only in small, dense clumps.

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arXiv2024

The MDW H{\alpha} Sky Survey: Data Release 0

The Mittelman-di Cicco-Walker (MDW) H$\alpha$ Sky Survey is an autonomously-operated and ongoing all-sky imaging survey in the narrowband H$\alpha$ wavelength. The survey was founded by amateur astronomers, and is presented here in its first stage of refinement for rigorous scientific use. Each field is exposed through an H$\alpha$ filter with a 3nm bandwidth for a total of four hours, with a pixel scale of 3.2 arcsec. Here, we introduce the first Data Release of the MDW H$\alpha$ Survey (Data Release 0, or DR0), spanning 238 fields in the region of Orion (~3100 deg$^2$). DR0 includes: calibrated mean fields, star-removed mean fields, a point source catalog matched to Data Release 1 of the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS1) and the INT Galactic Plane Survey (IGAPS), and mosaics.

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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.

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arXiv2024

Braving the Storm: Quantifying Disk-wide Ionized Outflows in the Large Magellanic Cloud with ULLYSES

The Large Magellanic Cloud (LMC) is home to many HII regions, which may lead to significant outflows. We examine the LMC's multiphase gas ($T\sim10^{4-5}$ K) in HI, SII, SiIV, and CIV using 110 stellar sight lines from the HST's Ultraviolet Legacy Library of Young Stars as Essential Standards (ULLYSES) program. We develop a continuum fitting algorithm based on the concept of Gaussian Process regression and identify reliable LMC interstellar absorption over $v_{\rm helio}=175-375$ km s$^{-1}$. Our analyses show disk-wide ionized outflows in SiIV and CIV across the LMC with bulk velocities of $|v_{\rm out, bulk}|\sim20-60$ km s$^{-1}$, which indicates that most of the outflowing mass is gravitationally bound. The outflows' column densities correlate with the LMC's star formation rate surface densities ($\Sigma_{\rm SFR}$), and the outflows with higher $\Sigma_{\rm SFR}$ tend to be more ionized. Considering outflows from both sides of the LMC as traced by CIV, we conservatively estimate a total outflow rate of $\dot{M}_{\rm out}\gtrsim 0.03~M_\odot {\rm yr}^{-1}$ and a mass loading factor of $\eta\gtrsim 0.15$. We compare the LMC's outflows with those detected in starburst galaxies and simulation predictions, and find a universal scaling relation of $|v_{\rm out, bulk}|\propto \Sigma_{\rm SFR}^{0.23}$ over a wide range of star-forming conditions ($\Sigma_{\rm SFR}\sim10^{-4.5}-10^{2}~M_\odot {\rm yr}^{-1} {\rm kpc}^{-2}$). Lastly, we find that the outflows are co-rotating with the LMC's young stellar disk and the velocity field does not seem to be significantly impacted by external forces; we thus speculate on the existence of a bow shock leading the LMC, which may have shielded the outflows from ram pressure as the LMC orbits the Milky Way.

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arXiv2021

Investigating the Baryon Cycle in Interacting Dwarfs with the Very Large Array and Pan-STARRS

We present resolved HI synthesis maps from the Very Large Array (VLA) of three interacting dwarf systems: the NGC 3664 dwarf pair, the NGC 3264 dwarf pair, and the UGC 4638 dwarf triplet. All three dwarf systems are captured at various stages of interaction and span a range of environments. We detect clear hallmarks of tidal interactions through the presence of HI bridges, and diffuse HI extensions that surround the dwarfs. We overlay the HI data on Pan-STARRS r-band images and find further evidence of tidal interactions through coincident distorted HI and tidal stellar features in NGC 3264 and UGC 4638, and an unwound spiral arm pointing towards its smaller companion in NGC 3264. In UGC 4638, both the gas and diffuse stars are extended to similar radii east of the primary, which could indicate that the smaller dwarf in the system has already completed one pass through the primary. We additionally find that our three systems, and those from the Local Volume TiNy Titans survey, are not HI deficient and thus the interaction has not resulted in a loss of gas from the systems. A comparison with non-interacting dwarf galaxies shows that the interactions have a significant impact on the kinematics of the systems. Our new resolved HI kinematics, combined with detailed stellar and HI morphologies, provide crucial constraints for future dynamical modelling of hierarchical mergers and the baryon cycle at the low-mass scale.

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arXiv2020

Discovery of Magellanic Stellar Debris in the H3 Survey

We report the discovery of 15 stars in the H3 survey that lie, in projection, near the tip of the trailing gaseous Magellanic Stream (MS). The stars have Galactocentric velocities $< -155$ km s$^{-1}$, Galactocentric distances of $\approx 40$ to 80 kpc (increasing along the MS), and [Fe/H] consistent with that of stars in the Small Magellanic Cloud. These 15 stars comprise 94% (15 of 16) of the H3 observed stars to date that have $R_{GAL} > 37.5$ kpc, $-$350 km s$^{-1} < V_{GSR} < -155$ km s$^{-1}$, and are not associated with the Sagittarius Stream. They represent a unique portion of the Milky Way's outer halo phase space distribution function and confirm that unrelaxed structure is detectable even at radii where H3 includes only a few hundred stars. Due to their statistical excess, their close association with the MS and H I compact clouds in the same region, both in position and velocity space, and their plausible correspondence with tidal debris in a published simulation, we identify these stars as debris of past Magellanic Cloud encounters. These stars are evidence for a stellar component of the tidal debris field far from the Clouds themselves and provide unique constraints on the interaction.

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arXiv2020

The QuaStar Survey: Detecting Hidden Low-Velocity Gas in the Milky Way's Circumgalactic Medium

From our position embedded within the Milky Way's interstellar medium (ISM), we have limited ability to detect gas at low relative velocities in the extended Galactic halo because those spectral lines are blended with much stronger signals from dense foreground gas. As a result, the content of the Milky Way's circumgalactic medium (CGM) is poorly constrained at $|v_{\rm LSR}|$ $\lesssim$ 150 km s$^{-1}$. To overcome this complication, the QuaStar Survey applies a spectral differencing technique using paired quasar-star sightlines to measure the obscured content of the Milky Way's CGM for the first time. We present measurements of the CIV doublet ($\lambda\lambda$ 1548 \r{A}, 1550 \r{A}), a rest-frame UV metal line transition detected in HST/COS spectra of 30 halo-star/quasar pairs evenly distributed across the sky at Galactic latitudes $|b|>30^\circ$. The 30 halo stars have well-constrained distances (d$\approx$5-14 kpc), and are paired with quasars separated by $<$ 2.8$^\circ$. We argue that the difference in absorption between the quasar and stellar sightlines originates primarily in the Milky Way's extended CGM beyond $\sim$10 kpc. For the Milky Way's extended, low velocity CGM ($|v|<$150 km/s), we place an upper limit on the mean CIV column density of $\rm \Delta logN_{LVCGM} < 13.39$ and find a covering fraction of $f_{\rm CIV,LVCGM} (\rm logN>13.65)=$ 20% [6/30], a value significantly lower than the covering fraction for star-forming galaxies at low redshift. Our results suggest either that the bulk of Milky Way's CIV-traced CGM lies at low Galactic latitudes, or that the Milky Way's CGM is lacking in warm, ionized material compared to low-redshift ($z < 0.1$) star-forming galaxy halos.

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arXiv2019

Group pre-processing versus cluster ram-pressure stripping: the case of ESO156-G029

We report on observations of ESO156-G029, member of a galaxy group which is positioned at the virial radius of cluster Abell 3193. ESO156-G029 is located ~ 1.4 Mpc in projected distance from the brightest cluster galaxy NGC1500. We show that ESO156-G029 has disturbed gas kinematics and a highly asymmetric neutral hydrogen (HI) distribution, which are consequences of group pre-processing, and possibly of ram-pressure. Based on the current data we propose a scenario in which ESO156-G029 had a minor gas-rich merger in the past and now starts to experience ram-pressure. We infer that the galaxy will undergo rapid evolution once it gets closer to the cluster centre (less than 0.5 Mpc) where ram-pressure is strong enough to begin stripping the HI from the galaxy.

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arXiv2019

A Correlated Search for Local Dwarf Galaxies in GALFA-HI and Pan-STARRS

In recent years, ultrafaint dwarf (UFD) galaxies have been found through systematic searches of large optical surveys. However, the existence of Leo T, a nearby gas-rich dwarf, suggests that there could be other nearby UFDs that are optically obscured but have gas detectable at nonoptical wavelengths. With this in mind, we perform a search of the full Galactic Arecibo $L-$band Feed Array HI (GALFA-HI) survey, a radio survey which covers one-third of the sky at velocities $-650 < V_{\rm{LSR}} < +650 \; \rm{km} \; \rm{s^{-1}}$, for neutral hydrogen sources. We are able to probe regions of the sky at lower Galactic latitudes and smaller $|V_{LSR}|$ compared to previous explorations. We use the Source Finding Application (SoFiA) on GALFA-HI and select all sources with similar properties to Leo T and other local dwarf galaxies. We find 690 dwarf galaxy candidates, one of which is particularly promising and likely a new galaxy near the Galactic plane ($b=-8^{\circ}$) that is comparable in velocity width and HI-flux to other recently discovered local volume galaxies. We find we are sensitive to Leo T-like objects out to $1 \; \rm{Mpc}$ at velocities clear from background HI emission. We check each candidate's corresponding optical fields from Pan-STARRS and fit stars drawn from isochrones, but find no evidence of stellar populations. We thus find no other Leo T-like dwarfs within $500 \; \rm{kpc}$ of the Milky Way in the one-third of the sky covered by the GALFA-HI footprint and discuss our nondetection in a cosmological context.

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