Arecibo L-band Feed Array Research Articles

Neutral Hydrogen Content of Dwarf Galaxies in Different Environments

Environments play an important role in galaxy formation and evolution, particularly in regulating the content of neutral gas. However, current H i surveys have limitations in their depth, which prevents them from adequately studying low H i content galaxies in high-density regions. In this study, we address this issue by employing the Five-hundred-meter Aperture Spherical radio Telescope with extensive integration times to complement the relatively shallow Arecibo Legacy Fast Arecibo L-band Feed Array H i survey. This approach allows us to explore the gas content of dwarf galaxies across various environments. We observe a positive relationship between H i mass and stellar mass in dwarf galaxies, with a well-defined upper boundary for H i mass that holds true in both observations and simulations. Furthermore, we find a decrease in the H i-to-stellar mass ratio (M H I/M *) as the density of the environment increases, irrespective of whether it is determined by the proximity to the nearest group or the projected number density. Comparing our observations to simulations, we note a steeper slope in the relationship, indicating a gradual gas-stripping process in the observational data. Additionally, we find that the scaling relation between the M H I/M * and optical properties can be improved by incorporating galaxy environments.

The kinematic structure of magnetically aligned H i filaments

ABSTRACT We characterize the kinematic and magnetic properties of H i filaments located in a high Galactic latitude region (165° < α < 195° and 12° < δ < 24°). We extract three-dimensional filamentary structures using fil3d from the Galactic Arecibo L-Band Feed Array H i (GALFA-H i) survey 21-cm emission data. Our algorithm identifies coherent emission structures in neighbouring velocity channels. Based on the mean velocity, we identify a population of local and intermediate velocity cloud (IVC) filaments. We find the orientations of the local (but not the IVC) H i filaments are aligned with the magnetic field orientations inferred from Planck 353 GHz polarized dust emission. We analyse position–velocity diagrams of the velocity-coherent filaments, and find that only 15 per cent of filaments demonstrate significant major-axis velocity gradients with a median magnitude of 0.5 km s−1 pc−1, assuming a fiducial filament distance of 100 pc. We conclude that the typical diffuse H i filament does not exhibit a simple velocity gradient. The reported filament properties constrain future theoretical models of filament formation.

Shear, writhe, and filaments: Turbulence in the high-latitude molecular cloud MBM 40

Context.Given the structural and thermodynamical complexity of the interstellar medium (ISM), the variety of governing processes, such as stellar feedback, poses challenges to the investigation. High-latitude molecular clouds (HLMCs) with no evidence of internal star formation, as in the case of MBM 40, are excellent sites for studying the chemistry and dynamic evolution of the cold neutral ISM.Aims.We used this high-latitude cloud as an exemplar for the dynamical and chemical processes in the diffuse interstellar medium.Methods.We analyzed new and archival12CO,13CO, CH, HCO+, CS, H2CO, and HCN data from Five College Radio Observatory (FCRAO), Onsala Space Observatory (OSO), Arizona Radio Observatory (ARO), andW. Gordontelescope (Arecibo) combined with the Galactic Arecibo L-band Feed Array H I(GALFA-HI) H I21 cm data set, to study the chemistry, thermal state, and dynamics of MBM 40. A new dynamical analytical approach was adopted by considering each line profile as a line-of-sight probability distribution function (PDF) of the turbulence weighted by gas emissivity.Results.The atomic and molecular gas are smoothly distributed in space and velocity. No steep transition is seen between circumcloud atomic and cloud molecular gas in either radial velocity or structure. We propose a topology of the cloud based on molecular tracers, as a contorted filamentary structure that is shaped by a broad embedding shear flow in the neutral atomic gas. A comparative examination of different molecular tracers shows that13CO, H2CO, and CS only arise from denser molecular cores, whereas12CO, CH, and HCO+trace diffuse gas with a broader range of dynamics.

H i Galaxy Detections in the Zone of Avoidance with FAST

The Zone of Avoidance (ZoA) is a region of low galactic latitude that is heavily obscured by the Milky Way. Observations with radio telescopes are basically unaffected by dust extinction and can unveil the structure behind it through the Milky Way. One of the scientific goals of the Five-hundred-meter Aperture Spherical radio Telescope (FAST) is to search for the neutral hydrogen and understand the large-scale physics to explore the origin and evolution of the universe. We take the 15,500 IRAS (the Infrared Astronomical Satellite) galaxies from PSCz (“Point Source Catalog”) survey to reconstruct the density field of the local universe, obtain the distribution of the relative density of galaxies in the ZoA region with a redshift z below 0.07, and the number of detectable galaxies with FAST is estimated by using the neutral hydrogen mass function of the ALFA (Arecibo L-band Feed Array) survey. We conclude that FAST can observe more than 2000 ZoA galaxies within a distance of 300 Mpc , and present preliminary results of the partial GPPS (the FAST Galactic Plane Pulsar Snapshot survey) data, compared with ALFA ZoA (The Arecibo L-band Feed Array Zone of Avoidance), show that FAST has a higher detection sensitivity to search for H i galaxies in the ZoA area.

A Generalist, Automated ALFALFA Baryonic Tully–Fisher Relation

The baryonic Tully–Fisher relation (BTFR) has applications in galaxy evolution as a test bed for the galaxy–halo connection and in observational cosmology as a redshift-independent secondary distance indicator. This analysis leverages the 31,000+ galaxy Arecibo Legacy Fast ALFA (Arecibo L-band Feed Array) Survey (ALFALFA) sample—which provides redshifts, velocity widths, and H i content for a large number of gas-bearing galaxies in the local universe—to fit and test an extensive local universe BTFR. The fiducial relation is fit using a 3000-galaxy subsample of ALFALFA, and is shown to be consistent with the full sample. This BTFR is designed to be as inclusive of ALFALFA and comparable samples as possible. Velocity widths measured via an automated method and M b proxies extracted from survey data can be uniformly and efficiently measured for other samples, giving this analysis broad applicability. We also investigate the role of sample demographics in determining the best-fit relation. We find that the best-fit relations are changed significantly by changes to the sample mass range and to second order by changes to mass sampling, gas fraction, different stellar mass and velocity width measurements. We use a subset of ALFALFA with demographics that reflect the full sample to measure a robust BTFR slope of 3.30 ± 0.06. We apply this relation and estimate source distances, finding general agreement with flow-model distances as well as average distance uncertainties of ∼0.17 dex for the full ALFALFA sample. We demonstrate the utility of these distance estimates by applying them to a sample of sources in the Virgo vicinity, recovering signatures of infall consistent with previous work.

Catching Tidal Dwarf Galaxies at a Later Evolutionary Stage with ALFALFA

We present deep optical imaging and photometry of four objects classified as “Almost-Dark” galaxies in the Arecibo Legacy Fast Arecibo L-band Feed Array (ALFALFA) survey because of their gas-rich nature and extremely faint or missing optical emission in existing catalogs. They have H i masses of 107–109 M ⊙ and distances of ∼9–100 Mpc. Observations with the WIYN 3.5 m telescope and One Degree Imager reveal faint stellar components with central surface brightnesses of ∼24–25 in the g band. We also present the results of H i synthesis observations with the Westerbork Synthesis Radio Telescope. These Almost-Dark galaxies have been identified as possible tidal dwarf galaxies (TDGs) based on their proximity to one or more massive galaxies. We demonstrate that AGC 229398 and AGC 333576 likely have the low dark matter content and large effective radii representative of TDGs. They are located much farther from their progenitors than previously studied TDGs, suggesting they are older and more evolved. AGC 219369 is likely dark matter dominated, while AGC 123216 has a dark matter content that is unusually high for a TDG, but low for a normal dwarf galaxy. We consider possible mechanisms for the formation of the TDG candidates such as a traditional major merger scenario and gas ejection from a high-velocity flyby. Blind H i surveys like ALFALFA enable the detection of gas-rich, optically faint TDGs that can be overlooked in other surveys, thereby providing a more complete census of the low-mass galaxy population and an opportunity to study TDGs at a more advanced stage of their life cycle.

Global Dynamic Scaling Relations of H i-rich Ultra-diffuse Galaxies

The baryonic Tully–Fisher relation (BTFR), which connects the baryonic mass of galaxies with their circular velocities, has been validated across a wide range of galaxies, from dwarf galaxies to massive galaxies. Recent studies have found that several ultra-diffuse galaxies (UDGs) deviate significantly from the BTFR, indicating a galaxy population with abnormal dynamical properties. However, such studies were still confined within a small sample size. In this study, we used the 100% complete Arecibo Legacy Fast Arecibo L-band Feed Array (ALFALFA) to investigate the BTFR of 88 H i-rich UDGs (HUDGs), which is the largest UDG sample with dynamical information. We found that the HUDGs form a continuous distribution in the BTFR diagram, with high-velocity galaxies consistent with normal dwarf galaxies at a 1σ level, and low-velocity galaxies deviating from the BTFR, in line with that reported in the literature. We point out that the observed deviation may be subject to various selection effects or systemic biases. Nevertheless, we found that the significance of the deviation of HUDGs from the BTFR and TFR are different, i.e., they either deviate from the BTFR or from the TFR. Our result indicates that a high gas fraction may play an important role in explaining the deviation of HUDGs from BTFR.

Discovery of a Filamentary Synchrotron Structure Connected to the Coherent Magnetic Field in the Outer Galaxy

Using data from the Galactic Arecibo L-band Feed Array Continuum Transit Survey, we report the discovery of two previously unidentified, very compressed, thin, and straight polarized filaments approximately centered at Galactic coordinates, (l, b) = (182.°5, − 4.°0), which we call G182.5–4.0. Using data from the Isaac Newton Telescope Galactic Plane Survey, we also find straight, long, and extremely thin Hα filaments coincident with the radio emission. These filaments are positioned in projection at the edge of the Orion-Eridanus superbubble and we find evidence indicating that the filaments align with the coherent magnetic field of the outer Galaxy. We find a lower limit on the total radio flux at 1.4 GHz to be 0.7 ± 0.3 Jy with an average linearly polarized fraction of . We consider various scenarios that could explain the origin of these filaments, including a shell-type supernova remnant (SNR), a bow shock nebula associated with a pulsar, or relic fragments from one or more supernova explosions in the adjacent superbubble, with a hybrid scenario being most likely. This may represent an example of a new class of objects that is neither an SNR nor a bow shock. The highly compressed nature of these filaments and their alignment with the Galactic plane suggests a scenario where this object formed in a magnetic field that was compressed by the expanding Orion-Eridanus superbubble, suggesting that the object is related to this superbubble and implying a distance of ∼400 pc.

The SPAN512 mid-latitude pulsar survey at the Nançay Radio Telescope

Context. The large number of ongoing surveys for pulsars and transients at various radio observatories is motivated by the science obtained from these sources. Timing and polarisation analysis of relativistic binaries can place strong constraints on theories of gravity. The observation of a growing number of millisecond pulsars (MSPs) spread over the celestial sphere may allow the detection of a stochastic gravitational wave background arising from supermassive black hole binaries. A more complete sample of young pulsars improves our knowledge of neutron star birth and evolution. Transients such as fast radio bursts can serve to probe the intergalactic medium. Aims. The SPAN512 pulsar survey covers intermediate Galactic latitudes using the L-band receiver of the Nançay Radio Telescope (NRT). The survey covers 224 sq. deg. of the sky for a total exposure time of 2200 h. Population syntheses predict the discovery of 3 to 19 new normal pulsars and a few MSPs. Methods. We present detailed modelling of the NRT beam with its L-band receiver and its sensitivity which we used to precisely assess the expected survey yield. We used the flexible Pulsar Arecibo L-band Feed Array data processing pipeline to search the 47 TB of SPAN512 data for pulsars and transients. Results. The SPAN512 survey discovered two new MSPs and one new middle-aged pulsar. We focus on the analysis of the 2.4-ms spin period pulsar J2205+6012 for which we also report the detection of gamma-ray pulsations. Its narrow pulse width (35µs at an observing frequency of 2.55 GHz) allows for sub-microsecond timing precision over 8 yr, with exciting prospects for pulsar timing array programs.

A Comparison of Multiphase Magnetic Field Tracers in a High Galactic Latitude Region of the Filamentary Interstellar Medium

Abstract Understanding how the Galactic magnetic field threads the multiphase interstellar medium (ISM) remains a considerable challenge, as different magnetic field tracers probe dissimilar phases and field components. We search for evidence of a common magnetic field shared between the ionized and neutral ISM by comparing 1.4 GHz radio continuum polarization and H i line emission from the Galactic Arecibo L-Band Feed Array Continuum Transit Survey (GALFACTS) and Galactic Arecibo L-Band Feed Array H i (GALFA-H i) survey, respectively. We compute the polarization gradient of the continuum emission and search for associations with diffuse/translucent H i structures. The polarization gradient is sensitive to changes in the integrated product of the thermal electron density and line-of-sight field strength (B ∥) in warm ionized gas, while narrow H i structures highlight the plane-of-sky field orientation in cold neutral gas. We identified one region in the high Galactic latitude Arecibo sky, G216+26 centered on (ℓ, b) ∼ (216°, +26°), containing filaments in the polarization gradient that are aligned with narrow H i structures roughly parallel to the Galactic plane. We present a comparison of multiphase observations and magnetic field tracers of this region, demonstrating that the warm ionized and cold neutral media are connected likely via a common magnetic field. We quantify the physical properties of a polarization gradient filament associated with Hα emission, measuring a line-of-sight field strength B ∥ = 6 ± 4 μG and a plasma beta β = 2.1 − 2.1 + 3.1 . We discuss the lack of widespread multiphase magnetic field alignments and consider whether this region is associated with a short-timescale or physically rare phenomenon. This work highlights the utility of multitracer analyses for understanding the magnetized ISM.

Study of 72 Pulsars Discovered in the PALFA Survey: Timing Analysis, Glitch Activity, Emission Variability, and a Pulsar in an Eccentric Binary

Abstract We present new discoveries and results from long-term timing of 72 pulsars discovered in the Pulsar Arecibo L-band Feed Array (PALFA) survey, including precise determination of astrometric and spin parameters, and flux density and scatter broadening measurements at 1.4 GHz. Notable discoveries include two young pulsars (characteristic ages ∼30 kyr) with no apparent supernova remnant associations, three mode-changing, 12 nulling and two intermittent pulsars. We detected eight glitches in five pulsars. Among them is PSR J1939+2609, an apparently old pulsar (characteristic age ∼1 Gy), and PSR J1954+2529, which likely belongs to a newly emerging class of binary pulsars. The latter is the only pulsar among the 72 that is clearly not isolated: a nonrecycled neutron star with a 931 ms spin period in an eccentric (e = 0.114) wide (P b = 82.7 days) orbit with a companion of undetermined nature having a minimum mass of ∼0.6 M ⊙. Since operations at Arecibo ceased in 2020 August, we give a final tally of PALFA sky coverage, and compare its 207 pulsar discoveries to the known population. On average, they are 50% more distant than other Galactic plane radio pulsars; PALFA millisecond pulsars (MSPs) have twice the dispersion measure per unit spin period than the known population of MSP in the plane. The four intermittent pulsars discovered by PALFA more than double the population of such objects, which should help to improve our understanding of pulsar magnetosphere physics. The statistics for these, rotating radio transients, and nulling pulsars suggest that there are many more of these objects in the Galaxy than was previously thought.

λ21-cm Interstellar HI Profiles, Critical Ionization Velocities, and Derived Electron Densities

Analysis of neutral hydrogen λ21-cm profiles at high northern and southern Galactic latitudes reveals unexpected properties, connects unanticipated associations, and confirms the fundamental parameters of the interstellar medium. Gaussian decomposition of profiles from the second data release of the Galactic Arecibo L-Band Feed Array (GALFA) confirms earlier results of a pervasive component with a linewidth of order 34 km s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> , consistent with the critical ionization velocity (CIV) of helium. The ratio of the column density of this component to the entire profile is proportional to the interstellar helium abundance. The results are comparable to the accepted value of the cosmic abundance, 0.085, in the southern Galactic hemisphere, but different for directions in the northern Galactic hemisphere. Normalizing to the cosmic abundance allows us to estimate how much HI is “missing” from the λ21-cm observations in the northern sky, confirming an asymmetry that has been known for decades. These CIV results also predict the volume density of interstellar electrons along different lines of site, which match values derived from pulsar dispersion measures and Hα observations. These results provide strong support for the hypothesis that interstellar λ21-cm HI profile linewidths are modulated by the CIV plasma phenomenon.

Extragalactic H i 21-cm absorption line observations with the Five-hundred-meter Aperture Spherical radio Telescope

ABSTRACT We present a pilot study of extragalactic H i 21-cm absorption lines using the Five-hundred-meter Aperture Spherical radio Telescope (FAST). We observed five continuum sources with H i absorption features first identified in the 40 per cent data release of the Arecibo Legacy Fast Arecibo L-Band Feed Array (ALFA) Survey (ALFALFA), including two systems later detected by the Westerbork Synthesis Radio Telescope (WSRT). Most of our observations were carried out during the FAST commissioning phase, and we have tested different observing modes, as well as data reduction methods, to produce the best spectra. Our observations successfully confirmed the existence of H i absorption lines in all these systems, including two sources that were marginally detected by ALFALFA. We fitted the H i profiles with single or double of Gaussian functions, and calculated the H i column densities of each source. The H i absorption profiles obtained by FAST show much higher spectral resolution and higher SNR ratio than the existing data in the literature, thus demonstrating the power of FAST in revealing detailed structures of H i absorption lines. Our pilot observations and tests have enabled us to develop a strategy to search for H i absorption sources using the data from the FAST extragalactic H i survey, which is one of the key projects undertaken at FAST. We expect that over 1500 extragalactic H i absorbing systems could be detected with survey data, based on sensitivity level that we achieved in pilot observations.

The Arecibo Ultra-Deep Survey

ABSTRACT The Arecibo Ultra-Deep Survey (AUDS) is a blind H i survey aimed at detecting galaxies beyond the local Universe in the 21-cm emission line of neutral hydrogen (H i). The Arecibo L-band Feed Array (ALFA) was used to image an area of 1.35 deg2 to a redshift depth of 0.16, using a total on-source integration time of over 700 h. The long integration time and small observation area makes it one of the most sensitive H i surveys, with a noise level of ∼75 μJy per 21.4 kHz (equivalent to 4.5 km s−1 at redshift z = 0). We detect 247 galaxies in the survey, more than doubling the number already detected in AUDS60. The mass range of detected galaxies is $\log (M_{\rm H\,{\small I}}~[h_{70}^{-2}\, {\rm M}_\odot ]) = 6.32\!-\!10.76$. A modified maximum likelihood method is employed to construct an H i mass function (HIMF). The best fitting Schechter parameters are low-mass slope α = −1.37 ± 0.05, characteristic mass $\log (M^*~[h_{70}^{-2}\, {\rm M}_\odot ]) = 10.15 \pm 0.09$, and density $\Phi _* = (2.41 \pm 0.57) \times 10^{-3} h_{70}^3$ Mpc−3 dex−1. The sample was divided into low- and high-redshift bins to investigate the evolution of the HIMF. No change in low-mass slope α was measured, but an increased characteristic mass M*, was noted in the higher redshift sample. Using Sloan Digital Sky Survey data to define relative galaxy number density, the dependence of the HIMF with environment was also investigated in the two AUDS regions. We find no significant variation in α or M*. In the surveyed region, we measured a cosmic H i density $\Omega _{\rm H\,{\small I}} = (3.55 \pm 0.30) \times 10^{-4}\, h_{70}^{-1}$. There appears to be no evolutionary trend in $\Omega _{\rm H\,{\small I}}$ above 2σ significance between redshifts of 0 and 0.16.

The Ursa Major association of galaxies – VI: a relative dearth of gas-rich dwarf galaxies

ABSTRACT We determined the H i mass function of galaxies in the Ursa Major association of galaxies using a blind Very Large Array (VLA) D-array survey, consisting of 54 pointings in a cross-pattern, covering the centre as well as the outskirts of the Ursa Major volume. The calculated H i mass function has best-fitting Schechter parameters θ* = 0.19 ± 0.11 Mpc−3, log $\mbox{$M^*_{\rm H\,{\small I}}$}\ /\mathrm{ M}_{\odot } = 9.8 \pm 0.8$, and α = −0.92 ± 0.16. The high-mass end is determined by a complementary, targeted Westerbork Synthesis Radio Telescope (WSRT) survey, and the low-mass end is determined by the blind VLA survey. The slope is significantly shallower than the slopes of the H i Parkes All Sky Survey (α = −1.37 ± 0.03 ± 0.05) and Arecibo Legacy Fast Arecibo L-band Feed Array (α = −1.33 ± 0.02) H i mass functions, which are measured over much larger volumes and cover a wider range of cosmic environments: There is a relative lack of low-H i mass galaxies in the Ursa Major region. This difference in the slope strongly hints at an environmental dependence of the H i mass function slope.

The ALFALFA-SDSS Galaxy Catalog

Abstract We present a H i optical catalog of ∼30,000 galaxies based on the 100% complete Arecibo Legacy Fast Arecibo L-band Feed Array (ALFALFA) survey combined with data from the Sloan Digital Sky Survey (SDSS). Our goal is to facilitate the public use of the completed ALFALFA catalog by providing carefully determined matches to SDSS counterparts, including matches for ∼10,000 galaxies that do not have SDSS spectra. These identifications can provide a basis for further crossmatching with other surveys using SDSS photometric IDs as a reference point. We derive absolute magnitudes and stellar masses for each galaxy using optical colors combined with an internal reddening correction designed for small- and intermediate-mass galaxies with active star formation. We also provide measures of stellar masses and star formation rates based on infrared and/or ultraviolet photometry for galaxies that are detected by the Wide-field Infrared Survey Explorer and/or the Galaxy Evolution Explorer. Finally, we compare the galaxy population in the ALFALFA-SDSS sample with the populations in several other publicly available galaxy catalogs and confirm that ALFALFA galaxies typically have lower masses and bluer colors.

The H i Structure of the Local Volume Dwarf Galaxy Pisces A

Abstract Dedicated H i surveys have recently led to a growing category of low-mass galaxies found in the Local Volume. We present synthesis imaging of one such galaxy, Pisces A, a low-mass dwarf originally confirmed via optical imaging and spectroscopy of neutral hydrogen (H i) sources in the Galactic Arecibo L-band Feed Array H i survey. Using H i observations taken with the Karl G. Jansky Very Large Array, we characterize the kinematic structure of the gas and connect it to the galaxy’s environment and evolutionary history. While the galaxy shows overall ordered rotation, a number of kinematic features indicate a disturbed gas morphology. These features are suggestive of a tumultuous recent history and represent % of the total baryonic mass. We find a total baryon fraction if we include these features. We also quantify the cosmic environment of Pisces A, finding an apparent alignment of the disturbed gas with nearby, large-scale filamentary structure at the edge of the Local Void. We consider several scenarios for the origin of the disturbed gas, including gas stripping via ram pressure or galaxy–galaxy interactions, as well as accretion and ram pressure compression. Though we cannot rule out a past interaction with a companion, our observations best support the suggestion that the neutral gas morphology and recent star formation in Pisces A are a direct result of its interactions with the intergalactic medium.

Detection of Radio Pulsars in Single-pulse Searches Within and Across Surveys

Pulsar detection using machine learning is a challenging problem as it involves extreme class imbalance and strong prioritization of high Recall. This paper is focused on automatic detection of astrophysical pulses in single-pulse searches, both within and across surveys. We use the output from the first stage of our previously developed two-stage Single-Pulse Event Group IDentification approach and focus on the second stage (i.e., classification of pulse candidates). Specifically, for the first time in time-domain single-pulse searches we (1) use boosting and deep learning algorithms for within-survey classification and (2) investigate cross-survey classification by using two transfer learning methods, trAdaBoost (instance-based) and fine-tuning (parameter-based). Our experimental results are based on two benchmark data sets, Green Bank Telescope Drift-scan (GBTDrift) and Pulsar Arecibo L-band Feed Array (PALFA)-extended, created from the GBTDrift survey and the PALFA survey. The main findings include: (1) Due to the emphasis on high Recall, F4 measure is more appropriate performance indicator than the balanced F1 measure. (2) For the GBTDrift benchmark, AdaBoost outperformed the other models with 98.5% Recall and F4 = 0.942. For the PALFA-extended benchmark, RandomForest performed the best, with 91.6% Recall and F4 = 0.890. (3) Models performance degraded significantly when they were used for pulsar classification across surveys. (4) Transfer learning improved cross-survey classification significantly when training data in the target data set were limited. When the GBTDrift benchmark was used as the target data set, fine-tuned SPEGnet models had the highest F4 measure, while trAdaBoost models had the highest F4 measure when PALFA-extended benchmark was used as the target data set. (5) Pulse classification was affected not only by the between-class imbalance (i.e., pulsar versus non-pulsar), but also by the within-class imbalance, which was more prominent in the case of the PALFA-extended benchmark due to the lack of labeled low signal-to-noise ratio pulsars.

Producing synthetic maps of dust polarization using a velocity channel gradient technique

ABSTRACT In modern cosmology, many efforts have been made to detect the primordial B-mode of cosmic microwave background polarization from gravitational waves generated during inflation. Considering the foreground dust contamination of microwave polarization maps, it is essential to obtain a precise prediction for polarization in dust emission. In this work, we show a new method to produce synthetic maps of dust polarization in the magnetized turbulent interstellar medium from more abundant high-resolution H i data. By using the velocity channel gradient technique, we are able to predict both the direction and degree of dust polarization by investigating spectroscopic H i information in position–position–velocity space. We apply our approach to the Galactic Arecibo L-band Feed Array H i data, and find a good correspondence between synthesized maps and Planck’s polarization measurements at 353 GHz.

The H i morphology and stellar properties of strongly barred galaxies: support for bar quenching in massive spirals

ABSTRACT Galactic bars are able to affect the evolution of galaxies by redistributing their gas, possibly contributing to the cessation of star formation. Several recent works point to ‘bar quenching’ playing an important role in massive disc galaxies. We construct a sample of six gas-rich and strongly barred disc galaxies with resolved H i observations. This sample of galaxies, which we call H i-rich barred galaxies, was identified with the help of Galaxy Zoo to find galaxies hosting a strong bar, and the Arecibo Legacy Fast Arecibo L-band Feed Array blind H i survey to identify galaxies with a high H i content. The combination of strong bar and high gas fraction is rare, so this set of six galaxies is the largest sample of its type with resolved H i observations. We measure the gas fractions, H i morphology and kinematics, and use archival optical data from the Sloan Digital Sky Survey to reveal star formation histories and bar properties. The galaxies with the lowest gas fractions (still very high for their mass) show clear H i holes, dynamically advanced bars, and low star formation rates, while those with the highest gas fractions show little impact from their bar on the H i morphology, and are still actively star-forming. These galaxies support a picture in which the movement of gas by bars can lead to star formation quenching. How these unusual galaxies came to be is an open question.