Scholarly Work - Physics
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Item Dynamical tides during the inspiral of rapidly spinning neutron stars: Solutions beyond mode resonance(American Physical Society, 2024-07) Yu, Hang; Arras, Phil; Weinberg, Nevin N.We investigate the dynamical tide in a gravitational wave (GW)-driven coalescing binary involving at least one neutron star (NS). The deformed NS is assumed to spin rapidly, with its spin axis antialigned with the orbit. Such an NS may exist if the binary forms dynamically in a dense environment, and it can lead to a particularly strong tide because the NS f-mode can be resonantly excited during the inspiral. We present a new analytical solution for the f-mode resonance by decomposing the tide into a resummed equilibrium component varying at the tidal forcing frequency and a dynamical component varying at the f-mode eigenfrequency that is excited only around mode resonance. This solution simplifies numerical implementations by avoiding the subtraction of two diverging terms as was done in previous analyses. It also extends the solution’s validity to frequencies beyond mode resonance. When the dynamical tide back reacts on the orbit, we demonstrate that the commonly adopted effective Love number is insufficient because it does not capture the tidal torque on the orbit that dominates the back reaction during mode resonance. An additional dressing factor originating from the imaginary part of the Love number is therefore introduced to model the torque. The dissipative interaction between the NS and the orbital mass multipoles is computed including the dynamical tide and shown to be subdominant compared to the conservative energy transfer from the orbit to the NS modes. Our study shows that orbital phase shifts caused by the 𝑙=3 and 𝑙=2 f-modes can reach 0.5 and 10 radians at their respective resonances if the NS has a spin rate of 850 Hz and direction antialigned with the orbit. Because of the large impact of the 𝑙=2 dynamical tide, a linearized analytical description becomes insufficient, calling for future developments to incorporate higher-order corrections. After mode excitation, the orbit cannot remain quasicircular, and the eccentricity excited by the 𝑙=2 dynamical tide can approach nearly 𝑒≃0.1, leading to nonmonotonic frequency evolution which breaks the stationary phase approximation commonly adopted by frequency domain phenomenological waveform constructions. Lastly, we demonstrate that the GW radiation from the resonantly excited f-mode alone can be detected with a signal-to-noise ratio exceeding unity at a distance of 50 Mpc with the next-generation GW detectors.Item Corrosion Resistance of Atomically Thin Graphene Coatings on Single Crystal Copper(MDPI AG, 2024-05) Mahmudul Hasan, Md; Devadig, Ramesh; Sigdel, Pawan; Lipatov, Alexey; Avci, Recep; Jasthi, Bharat K.; Gadhamshetty, VenkataramanaDesigning minimally invasive, defect-free coatings based on conformal graphene layers to shield metals from both abiotic and biotic forms of corrosion is a persistent challenge. Single-layer graphene (SLG) grown on polycrystalline copper (PC-Cu) surfaces often have inherent defects, particularly at Cu grain boundaries, which weaken their barrier properties and worsen corrosion through grain-dependent mechanisms. Here, we report that an SLG grown via chemical vapor deposition (CVD) on Cu (111) single crystal serves as a high-performance coating to lower corrosion by nearly 4–6 times (lower than bare Cu (111)) in abiotic (sulfuric acid) and microbiologically influenced corrosion (MIC) environments. For example, the charge transfer resistance for SLG/Cu (111) (3.95 kΩ cm2) was 2.5-fold higher than for bare Cu (111) (1.71 kΩ cm2). Tafel analysis corroborated a reduced corrosion current (42 ± 3 µA cm−2) for SLG/Cu (111) compared to bare Cu (111) (115 ± 7 µA cm−2). These findings are consistent with the results based on biofilm measurements. The SLG/Cu (111) reduced biofilm formation by 3-fold compared to bare Cu (111), increasing corrosion resistance, and effectively mitigating pitting corrosion. The average depths of the pits (3.4 ± 0.6 µm) for SLG/Cu (111) were notably shallower than those of bare Cu (111) (6.5 ± 1.2 µm). Surface analysis of the corrosion products corroborated these findings, with copper sulfide identified as a major component across both surfaces. The absence of grain boundaries in Cu (111) resulted in high-quality SLG manifesting higher barrier properties compared to SLG on PC-Cu. Our findings show promise for using the presented strategy for developing durable graphene coatings against diverse forms of corrosion.Item Tracing field lines that are reconnecting, or expanding, or both(Frontiers Media SA, 2024-07) Qiu, JiongThe explosive release of energy in the solar atmosphere is driven magnetically, but the mechanisms that trigger the onset of the eruption remain controversial. In the case of flares and coronal mass ejections (CMEs), ideal or non-ideal instabilities usually occur in the corona, but it is difficult to obtain direct observations and diagnostics there. To overcome this difficulty, we analyze observational signatures in the upper chromosphere or transition region, particularly brightening and dimming at the base of coronal magnetic structures. In this paper, we examine the time evolution of spatially resolved light curves in two eruptive flares and identify a variety of tempo-spatial sequences of brightening and dimming, such as dimming followed by brightening and dimming preceded by brightening. These brightening–dimming sequences are indicative of the configuration of energy release in the form of plasma heating or bulk motion. We demonstrate the potential of using these analyses to diagnose the properties of magnetic reconnection and plasma expansion in the corona during the early stages of the eruption.Item An Outflow-driven Water Maser Associated with Positive Black Hole Feedback in the Dwarf Galaxy Henize 2–10(American Astronomical Society, 2024-07) Gim, Hansung B.; Reines, Amy E.; Momjian, Emmanuel; Darling, JeremyHenize 2–10 is a dwarf galaxy experiencing positive black hole (BH) feedback from a radio-detected low-luminosity active galactic nucleus. Previous Green Bank Telescope (GBT) observations detected a H2O "kilomaser" in Henize 2–10, but the low angular resolution (33'') left the location and origin of the maser ambiguous. We present new Karl G. Jansky Very Large Array observations of the H2O maser line at 22.23508 GHz in Henize 2–10 with ∼2'' resolution. These observations reveal two maser sources distinct in position and velocity. The first maser source is spatially coincident with the known BH outflow and the region of triggered star formation ∼70 pc to the east. Combined with the broad width of the maser (W50 ∼ 66 km s−1), this confirms our hypothesis that part of the maser detected with the GBT is produced by the impact of the BH outflow shocking the dense molecular gas along the flow and at the interface of the eastern star-forming region. The second maser source lies to the southeast, far from the central BH, and has a narrow width (W50 ∼ 8 km s−1), suggesting a star formation–related origin. This work has revealed the nature of the H2O kilomaser in Henize 2–10 and illustrates the first known connection between outflow-driven H2O masers and positive BH feedback.Item Tracing field lines that are reconnecting, or expanding, or both(Frontiers Media SA, 2024-07) Qiu, JiongThe explosive release of energy in the solar atmosphere is driven magnetically, but the mechanisms that trigger the onset of the eruption remain controversial. In the case of flares and coronal mass ejections (CMEs), ideal or non-ideal instabilities usually occur in the corona, but it is difficult to obtain direct observations and diagnostics there. To overcome this difficulty, we analyze observational signatures in the upper chromosphere or transition region, particularly brightening and dimming at the base of coronal magnetic structures. In this paper, we examine the time evolution of spatially resolved light curves in two eruptive flares and identify a variety of tempo-spatial sequences of brightening and dimming, such as dimming followed by brightening and dimming preceded by brightening. These brightening–dimming sequences are indicative of the configuration of energy release in the form of plasma heating or bulk motion. We demonstrate the potential of using these analyses to diagnose the properties of magnetic reconnection and plasma expansion in the corona during the early stages of the eruption.Item A dependable distance estimator to black hole low-mass X-ray binaries(Oxford University Press, 2024-03) Abdulghani, Y.; Lohfink, A. M.; Chauhan, J.Black Hole Low Mass X-ray Binaries (BH-LMXBs) are excellent observational laboratories for studying many open questions in accretion physics. However, determining the physical properties of BH-LMXBs necessitates knowing their distances. With the increased discovery rate of BH-LMXBs, many canonical methods cannot produce accurate distance estimates at the desired pace. In this study, we develop a versatile statistical framework to obtain robust distance estimates soon after discovery. Our framework builds on previous methods where the soft spectral state and the soft-to-hard spectral state transitions, typically present in an outbursting BH-LMXB, are used to place constraints on mass and distance. We further develop the traditional framework by incorporating general relativistic corrections, accounting for spectral/physical parameter uncertainties, and employing assumptions grounded in current theoretical and observational knowledge. We tested our framework by analyzing a sample of 50 BH-LMXB sources using X-ray spectral data from the Swift/XRT, MAXI/GSC, and RXTE/PCA missions. By modeling their spectra, we applied our framework to 26 sources from the 50. Comparison of our estimated distances to previous distance estimates indicates that our findings are dependable and in agreement with the accurate estimates obtained through parallax and H i absorption methods. Investigating the accuracy of our constraints, we have found that estimates obtained using both the soft and transition spectral information have a median uncertainty (1σ) of 20%, while estimates obtained using only the soft spectral state spectrum have a median uncertainty (1σ) of around 50%. Furthermore, we have found no instrument-specific biases.Item The ALMA View of Positive Black Hole Feedback in the Dwarf Galaxy Henize 2–10(American Astronomical Society, 2024-03) Gim, Hansung B.; Reines, Amy E.Henize 2–10 is a dwarf starburst galaxy hosting a ∼106M⊙ black hole (BH) that is driving an ionized outflow and triggering star formation within the central ∼100 pc of the galaxy. Here, we present Atacama Large Millimeter/submillimeter Array continuum observations from 99 to 340 GHz, as well as spectral line observations of the molecules CO (1–0, 3–2), HCN (1–0, 3–2), and HCO+ (1–0, 3–2), with a focus on the BH and its vicinity. Incorporating centimeter-wave radio measurements from the literature, we show that the spectral energy distribution of the BH is dominated by synchrotron emission from 1.4 to 340 GHz, with a spectral index of α ≈ − 0.5. We analyze the spectral line data and identify an elongated molecular gas structure around the BH with a velocity distinct from the surrounding regions. The physical extent of this molecular gas structure is ≈130 pc × 30 pc and the molecular gas mass is ∼106M⊙. Despite an abundance of molecular gas in this general region, the position of the BH is significantly offset from the peak intensity, which may explain why the BH is radiating at a very low Eddington ratio. Our analysis of the spatially resolved line ratio between CO J = 3–2 and J = 1–0 implies that the CO gas in the vicinity of the BH is highly excited, particularly at the interface between the BH outflow and the regions of triggered star formation. This suggests that the cold molecular gas is being shocked by the bipolar outflow from the BH, supporting the case for positive BH feedback.Item Six More Ultra-faint Milky Way Companions Discovered in the DECam Local Volume Exploration Survey(American Astronomical Society, 2023-07) Cerny, W.; Martínez-Vázquez, C. E.; Drlica-Wagner, A.; Pace, A. B.; Mutlu-Pakdil, B.; Li, T. S.; Riley, A. H.; Crnojević, D.; Bom, C. R.; Carballo-Bello, J. A.; Carlin, J. L.; Chiti, A.; Choi, Y.; Collins, M. L. M.; Darragh-Ford, E.; Ferguson, P. S.; Geha, M.; Martínez-Delgado, D.; Massana, P.; Mau, S.; Medina, G. E.; Muñoz, R. R.; Nadler, E. O.; Noël, N. E. D.; Olsen, K. A. G.; Pieres, A.; Sakowska, J. D.; Simon, J. D.; Stringfellow, G. S.; Tollerud, E. J.; Vivas, A. K.; Walker, A. R.; Wechsler, R. H.We report the discovery of six ultra-faint Milky Way satellites identified through matched-filter searches conducted using Dark Energy Camera (DECam) data processed as part of the second data release of the DECam Local Volume Exploration (DELVE) survey. Leveraging deep Gemini/GMOS-N imaging (for four candidates) as well as follow-up DECam imaging (for two candidates), we characterize the morphologies and stellar populations of these systems. We find that these candidates all share faint absolute magnitudes (MV ≥ −3.2 mag) and old, metal-poor stellar populations (τ > 10 Gyr, [Fe/H] < −1.4 dex). Three of these systems are more extended (r1/2 > 15 pc), while the other three are compact (r1/2 < 10 pc). From these properties, we infer that the former three systems (Boötes V, Leo Minor I, and Virgo II) are consistent with ultra-faint dwarf galaxy classifications, whereas the latter three (DELVE 3, DELVE 4, and DELVE 5) are likely ultra-faint star clusters. Using data from the Gaia satellite, we confidently measure the proper motion of Boötes V, Leo Minor I, and DELVE 4, and tentatively detect a proper-motion signal from DELVE 3 and DELVE 5; no signal is detected for Virgo II. We use these measurements to explore possible associations between the newly discovered systems and the Sagittarius dwarf spheroidal, the Magellanic Clouds, and the Vast Polar Structure, finding several plausible associations. Our results offer a preview of the numerous ultra-faint stellar systems that will soon be discovered by the Vera C. Rubin Observatory and highlight the challenges of classifying the faintest stellar systems.Item Electrically tunable magnetic fluctuations in multilayered vanadium-doped tungsten diselenide(Springer Science and Business Media LLC, 2023-08) Nguyen, Lan-Anh T.; Jiang, Jinbao; Nguyen, Tuan Dung; Kim, Philip; Joo, Min-Kyu; Duong, Dinh Loc; Lee, Young HeeFluctuations are ubiquitous in magnetic materials and can cause random telegraph noise. Such noise is of potential use in systems such as spiking neuron devices, random number generators and probability bits. Here we report electrically tunable magnetic fluctuations and random telegraph noise in multilayered vanadium-doped tungsten diselenide (WSe2) using vertical tunnelling heterostructure devices composed of graphene/vanadium-doped WSe2/graphene and magnetoresistance measurements. We identify bistable magnetic states through discrete Gaussian peaks in the random telegraph noise histogram and the 1/f2 features of the noise power spectrum. Three categories of fluctuation are detected: small resistance fluctuations at high temperatures due to intralayer coupling between the magnetic domains; large resistance changes over a wide range of temperatures; and persistent large resistance changes at low temperatures due to magnetic interlayer coupling. We also show that the bistable state and cut-off frequency of the random telegraph noise can be modulated with an electric bias.Item Confident detection of doubly ionized thorium in the extreme Ap star CPD-62° 2717(Oxford University Press, 2023-05) Chojnowski, S Drew; Hubrig, Swetlana; Nidever, David L; Niemczura, Ewa; Labadie-Bartz, Jonathan; Mathys, Gautier; Hasselquist, StenDespite the Universe containing primordial thorium (Th) of sufficient abundance to appear in stellar spectra, detection of Th has to date been tentative and based on just a few weak and blended lines. Here, we present convincing evidence not only for the first Th detection in a magnetic chemically peculiar Ap star but also for the first detection of Th iii in a stellar spectrum. CPD-62° 2717 was initially recognized as a highly magnetized Ap star due to resolved magnetically split lines captured in H-band spectra from the SDSS/APOGEE survey. The star was subsequently pinpointed as extraordinarily peculiar when careful inspection of the H-band line content revealed the presence of five lines of Th iii, none of which are detected in the other ∼1500 APOGEE-observed Ap stars. Follow-up with the VLT + UVES confirmed a similarly peculiar optical spectrum featuring dozens of Th iii lines, among other peculiarities. Unlike past claims of Th detection, and owing to high-resolution observations of the strong (∼8–12 kG) magnetic field of CPD-62° 2717, the detection of Th iii can in this case be supported by matches between the observed and theoretical magnetic splitting patterns. Comparison of CPD-62° 2717 to stars for which Th overabundances have been previously reported (e.g. Przybylski’s Star) indicates that only for CPD-62° 2717 is the Th detection certain. Along with the focus on Th iii, we use time series measurements of the magnetic field modulus to constrain the rotation period of CPD-62° 2717 to ∼4.8 yr, thus establishing it as a new example of a superslowly rotating Ap star.Item The Role of Magnetic Shear in Reconnection-Driven Flare Energy Release(Cornell University, 2023-08) Qiu, J.; Alaoui, M.; Antiochos, S. K.; Dahlin, J. T.; Swisdak, M.; Drake, J. F.; Robison, A.; DeVore, C. R.; Uritsky, V. M.Using observations from the Solar Dynamics Observatory's Atmosphere Imaging Assembly and the Ramaty High Energy Solar Spectroscopic Imager, we present novel measurements of the shear of post-reconnection flare loops (PRFLs) in SOL20141218T21:40 and study its evolution with respect to magnetic reconnection and flare emission. Two quasi-parallel ribbons form adjacent to the magnetic polarity inversion line (PIL), spreading in time first parallel to the PIL and then mostly in a perpendicular direction. We measure magnetic reconnection rate from the ribbon evolution, and also the shear angle of a large number of PRFLs observed in extreme ultraviolet passbands (≲1 MK). For the first time, the shear angle measurements are conducted using several complementary techniques allowing for a cross-validation of the results. In this flare, the total reconnection rate is much enhanced before a sharp increase of the hard X-ray emission, and the median shear decreases from 60∘-70∘ to 20∘, on a time scale of ten minutes. We find a correlation between the shear-modulated total reconnection rate and the non-thermal electron flux. These results confirm the strong-to-weak shear evolution suggested in previous observational studies and reproduced in numerical models, and also confirm that, in this flare, reconnection is not an efficient producer of energetic non-thermal electrons during the first ten minutes when the strongly sheared PRFLs are formed. We conclude that an intermediate shear angle, ≤40∘, is needed for efficient particle acceleration via reconnection, and we propose a theoretical interpretation.Item Origins of the Evil Eye: M64's Stellar Halo Reveals the Recent Accretion of an SMC-mass Satellite(American Astronomical Society, 2023-06) Smercina, Adam; Bell, Eric F.; Price, Paul A.; Bailin, Jeremy; Dalcanton, Julianne J.; de Jong, Roelof S.; D’Souza, Richard; Gozman, Katya; Jang, In Sung; Monachesi, Antonela; Nidever, David; Slater, Colin T.M64, often called the "Evil Eye" galaxy, is unique among local galaxies. Beyond its dramatic, dusty nucleus, it also hosts an outer gas disk that counter-rotates relative to its stars. The mass of this outer disk is comparable to the gas content of the Small Magellanic Cloud (SMC), prompting the idea that it was likely accreted in a recent minor merger. Yet, detailed follow-up studies of M64's outer disk have shown no evidence of such an event, leading to other interpretations, such as a "flyby" interaction with the distant diffuse satellite Coma P. We present Subaru Hyper Suprime-Cam observations of M64's stellar halo, which resolve its stellar populations and reveal a spectacular radial shell feature, oriented ∼30° relative to the major axis and along the rotation axis of the outer gas disk. The shell is ∼45 kpc southeast of M64, while a similar but more diffuse plume to the northwest extends to >100 kpc. We estimate a stellar mass and metallicity for the southern shell of M⋆ = 1.80 ± 0.54 × 108M⊙ and [M/H] = −1.0, respectively, and a similar mass of 1.42 ± 0.71 × 108M⊙ for the northern plume. Taking into account the accreted material in M64's inner disk, we estimate a total stellar mass for the progenitor satellite of M⋆,prog ≃ 5 × 108M⊙. These results suggest that M64 is in the final stages of a minor merger with a gas-rich satellite strikingly similar to the SMC, in which M64's accreted counter-rotating gas originated, and which is responsible for the formation of its dusty inner star-forming disk.Item JWST’s PEARLS: TN J1338–1942 – I. Extreme jet-triggered star formation in a z = 4.11 luminous radio galaxy(Oxford University Press, 2023-04) Duncan, Kenneth J; Windhorst, Rogier A; Koekemoer, Anton M; Röttgering, Huub J A; Cohen, Jansen; Summers, Jake; Tompkins, Scott; Hutchison, Taylor A; Conselice, Christopher J; Driver, Simon P; Yan, Haojing; Adams, Nathan J; Cheng, Cheng; Coe, Dan; Diego, Jose M; Dole, Hervé; Frye, Brenda; Gim, Hansung B; Grogin, Norman A; Holwerda, Benne W; Lim, Jeremy; Marshall, Madeline A; Nonino, Mario; Pirzkal, Nor; Robotham, Aaron; Ryan, Russell E; Willmer, Christopher N AWe present the first JWST observations of the z = 4.11 luminous radio galaxy TN J1338–1942, obtained as part of the ‘Prime Extragalactic Areas for Reionization and Lensing Science’ (‘PEARLS’) project. Our NIRCam observations, designed to probe the key rest-frame optical continuum and emission line features at this redshift, enable resolved spectral energy distribution modelling that incorporates both a range of stellar population assumptions and radiative shock models. With an estimated stellar mass of log10(M/M⊙) ∼ 10.9, TN J1338–1942 is confirmed to be one of the most massive galaxies known at this epoch. Our observations also reveal extremely high equivalent-width nebular emission coincident with the luminous AGN jets that is best fit by radiative shocks surrounded by extensive recent star formation. We estimate the total star-formation rate (SFR) could be as high as ∼1600M⊙yr−1 , with the SFR that we attribute to the jet induced burst conservatively ≳500M⊙yr−1 . The mass-weighted age of the star-formation, tmass < 4 Myr, is consistent with the likely age of the jets responsible for the triggered activity and significantly younger than that measured in the core of the host galaxy. The extreme scale of the potential jet-triggered star-formation activity indicates the potential importance of positive AGN feedback in the earliest stages of massive galaxy formation, with our observations also illustrating the extraordinary prospects for detailed studies of high-redshift galaxies with JWST.Item Structure of the Plasma near the Heliospheric Current Sheet as Seen by WISPR/Parker Solar Probe from inside the Streamer Belt(IOP Publising, 2023-05) Liewer, Paulett C.; Vourlidas, Angelos; Stenborg, Guillermo; Howard, Russell A.; Qiu, Jiong; Penteado, Paulo; Panasenco, Olga; Braga, Carlos R.Parker Solar Probe (PSP) crossed the heliospheric current sheet (HCS) near the perihelion on encounters E8 and E11, enabling the Wide-field Imager for Solar Probe (WISPR) to image the streamer belt plasma in high resolution while flying through it. With perihelia of 16 R⊙ and 13 R⊙ for E8 and E11, respectively, WISPR images enable investigation of the structure of density encasing the HCS at much higher resolution than reported previously. As PSP flies closer to the Sun, fine-scale structures are resolved within the coronal rays of the streamer belt. Near the HCS, WISPR observes a fan of rays of various sizes and brightnesses, indicating large density variations in the HCS plasma sheet transverse to the radial direction. Near the perihelion, when PSP's speed exceeds the solar corotation speed, some rays exhibit large changes in apparent latitude as the HCS is encountered, and rays pass over and under the spacecraft. The multiple viewpoints provided during the HCS crossing enable us to extract the coordinates of a few rays in a heliocentric frame. The rays were found to lie near the HCS from a PFSS model. We compare their locations to the location of the streamers as seen in synoptic maps from the Large Angle and Spectrometric Coronagraph, and find that the rays generally fall within the bright streamer bands seen in these maps, which confirms that they are features of the streamer belt plasma. We speculate that the density variations in the helmet streamer plasma result from continuous interchange reconnection along the coronal hole boundaries.Item The Imprint of Clump Formation at High Redshift. II. The Chemistry of the Bulge(American Astronomical Society, 2023-04) Debattista, Victor P.; Liddicott, David J.; Gonzalez, Oscar A.; Beraldo e Silva, Leandro; Amarante, João A. S.; Lazar, Ilin; Zoccali, Manuela; Valenti, Elena; Fisher, Deanne B.; Khachaturyants, Tigran; Nidever, David L.; Quinn, Thomas R.; Du, Min; Kassin, SusanIn Paper I, we showed that clumps in high-redshift galaxies, having a high star formation rate density (ΣSFR), produce disks with two tracks in the [Fe/H]–[α/Fe] chemical space, similar to that of the Milky Way's (MW's) thin+thick disks. Here we investigate the effect of clumps on the bulge's chemistry. The chemistry of the MW's bulge is comprised of a single track with two density peaks separated by a trough. We show that the bulge chemistry of an N-body + smoothed particle hydrodynamics clumpy simulation also has a single track. Star formation within the bulge is itself in the high-ΣSFR clumpy mode, which ensures that the bulge's chemical track follows that of the thick disk at low [Fe/H] and then extends to high [Fe/H], where it peaks. The peak at low metallicity instead is comprised of a mixture of in situ stars and stars accreted via clumps. As a result, the trough between the peaks occurs at the end of the thick disk track. We find that the high-metallicity peak dominates near the mid-plane and declines in relative importance with height, as in the MW. The bulge is already rapidly rotating by the end of the clump epoch, with higher rotation at low [α/Fe]. Thus clumpy star formation is able to simultaneously explain the chemodynamic trends of the MW's bulge, thin+thick disks, and the splash.Item Ambipolar Heating of Magnetars(American Astronomical Society, 2023-03) Tsuruta, Sachiko; Kelly, Madeline J.; Nomoto, Ken’ichi; Mori, Kanji; Teter, Marcus; Liebmann, Andrew C.Magnetars, neutron stars thought to be with ultrastrong magnetic fields of 1014–15 G, are observed to be much hotter than ordinary pulsars with ∼1012 G, and additional heating sources are required. One possibility is heating by the ambipolar diffusion in the stellar core. This scenario is examined by calculating the models using the relativistic thermal evolutionary code without making the isothermal approximation. The results show that this scenario can be consistent with most of the observed magnetar temperature data.Item NuSTAR Observations of a Heavily X-Ray-obscured AGN in the Dwarf Galaxy J144013+024744(American Astronomical Society, 2023-01) Ansh, Shrey; Chen, Chien-Ting J.; Brandt, W. N.; Hood, Carol E.; Kammoun, E. S.; Lansbury, G.; Paltani, Stéphane; Reines, Amy E.; Ricci, C.; Swartz, Douglas A.; Trump, Jonathan R.; Vito, F.; Hickox, Ryan C.We present a multiwavelength analysis of the dwarf Seyfert 2 galaxy J144013+024744, a candidate obscured active galactic nucleus (AGN) thought to be powered by an intermediate-mass black hole (IMBH, M • ≈ 104−106 M ⊙) of mass M • ∼ 105.2 M ⊙. To study its X-ray properties, we targeted J144013+024744 with NuSTAR for ≈100 ks. The X-ray spectrum was fitted with an absorbed power law, Pexmon, and a physical model (RXTorus). A Bayesian X-ray analysis was performed to estimate the posteriors. The phenomenological and the physical models suggest the AGN to be heavily obscured by a column density of N H = (3.4–7.0) × 1023 cm−2. In particular, the RXTorus model with a subsolar metallicity suggests the obscuring column to be almost Compton-thick. We compared the 2–10 keV intrinsic X-ray luminosity with the inferred X-ray luminosities based on empirical scaling relations for unobscured AGNs using L [Oiv] 25.89 μm, L [Oiii] λ5007, and L 6μm and found that the high-excitation [Oiv] line provides a better estimate of the intrinsic 2–10 keV X-ray luminosity ( L 2 – 10 int ∼ 10 41.41 erg s−1). Our results suggest that J144013+024744 is the first type 2 dwarf galaxy that shows X-ray spectroscopic evidence for obscuration. The column density that we estimated is among the highest measured to date for IMBH-powered AGNs, implying that a typical AGN torus geometry might extend to the low-mass end. This work has implications for constraining the BH occupation fraction in dwarf galaxies using X-ray observations.Item Multiwavelength scrutiny of X-ray sources in dwarf galaxies: ULXs versus AGNs(Oxford University Press, 2023-01) Thygesen, Erica; Plotkin, Richard M; Soria, Roberto; Reines, Amy E; Greene, Jenny E; Anderson, Gemma E; Baldassare, Vivienne F; Owens, Milo G; Urquhart, Ryan T; Gallo, Elena; Miller-Jones, James C A; Paul, Jeremiah D; Rollings, Alexandar POwing to their quiet evolutionary histories, nearby dwarf galaxies (stellar masses M⋆≲3×109M⊙) have the potential to teach us about the mechanism(s) that ‘seeded’ the growth of supermassive black holes, and also how the first stellar mass black holes formed and interacted with their environments. Here, we present high spatial resolution observations of three dwarf galaxies in the X-ray (Chandra), the optical/near-infrared (Hubble Space Telescope), and the radio (Karl G. Jansky Very Large Array). These three galaxies were previously identified as hosting candidate active galactic nuclei on the basis of lower resolution X-ray imaging. With our new observations, we find that X-ray sources in two galaxies (SDSS J121326.01+543631.6 and SDSS J122111.29+173819.1) are off-nuclear and lack corresponding radio emission, implying they are likely luminous X-ray binaries. The third galaxy (Mrk 1434) contains two X-ray sources (each with LX ≈ 1040 erg s−1) separated by 2.8 arcsec, has a low metallicity [12 + log(O/H) = 7.8], and emits nebular He ii λ4686 line emission. The northern source has spatially coincident point-like radio emission at 9.0 GHz and extended radio emission at 5.5 GHz. We discuss X-ray binary interpretations (where an ultraluminous X-ray source blows a ‘radio bubble’) and active galactic nucleus interpretations (where an ≈4×105M⊙ black hole launches a jet). In either case, we find that the He ii emission cannot be photoionized by the X-ray source, unless the source was ≈30–90 times more luminous several hundred years ago.Item Auger electron spectroscopy mapping of lithium niobate ferroelectric domains with nano-scale resolution(Optica Publishing Group, 2022-12) McLoughlin, Torrey; Babbitt, Wm. Randall; Nakagawa, WataruThe +/−Z ferroelectric domains in periodically poled lithium niobate are characterized with Auger electron spectroscopy. The -Z domains have a higher Auger O-KLL transition amplitude than the +Z domains. Based on this, Auger electron spectroscopy mapping can be used on the O-KLL peak to image the +/-Z domain structure. This new characterization technique is confirmed with HF etching, and compared to SEM imaging. Spatial resolution down to 68 nm is demonstrated.Item First Flight of the EUV Snapshot Imaging Spectrograph (ESIS)(American Astronomical Society, 2022-10) Parker, Jacob D.; Smart, Roy T.; Kankelborg, Charles; Winebarger, Amy; Goldsworth, NelsonThe Extreme-ultraviolet Snapshot Imaging Spectrograph (ESIS) launched on a sounding rocket from White Sands Missile Range on 2019 September 30. ESIS is a computed tomography imaging spectrograph (CTIS) designed to map emission line profiles across a wide field of view, revealing the structure and dynamics of small-scale transient events that are prevalent at transition region temperatures. In this paper, we review the ESIS instrument, mission, and data captured. We demonstrate how this unique data set can be interpreted qualitatively and further present some initial quantitative inversions of the data. Using a multiplicative algebraic reconstruction technique, we combine information from all four ESIS channels into a single spatial–spectral cube at every exposure. We analyze two small explosive events in the O v 629.7 Å spectral line with jets near ±100 km s−1 that evolve on 10 s timescales and vary significantly over small spatial scales. Intriguingly, each of these events turns out to be a bimodal (red+blue) jet with outflows that are asymmetric and unsynchronized. We also present a qualitative analysis of a small jetlike eruption captured by ESIS and draw comparisons to previously observed mini-filament eruptions. In 5 minutes of observing time, ESIS captured the spatial and temporal evolution of tens of these small events across the ∼11.′5 field of view, as well as several larger extended eruptions, demonstrating the advantage of CTIS instruments over traditional slit spectrographs in capturing the spatial and spectral information of dynamic solar features across large fields of view.