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This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited., We present Hubble Space Telescope imaging of 14 gas-rich, low-surface-brightness galaxies in the field at distances of 25–36 Mpc, with mean effective radii and g-band central surface brightnesses of 1.9 kpc and 24.2 mag arcsec−2. Nine meet the standard criteria to be considered ultra-diffuse galaxies (UDGs). An inspection of point-like sources brighter than the turnover magnitude of the globular cluster luminosity function and within twice the half-light radii of each galaxy reveals that, unlike those in denser environments, gas-rich, field UDGs host very few old globular clusters (GCs). Most of the targets (nine) have zero candidate GCs, with the remainder having one or two candidates each. These findings are broadly consistent with expectations for normal dwarf galaxies of similar stellar mass. This rules out gas-rich, field UDGs as potential progenitors of the GC-rich UDGs that are typically found in galaxy clusters. However, some in galaxy groups may be directly accreted from the field. In line with other recent results, this strongly suggests that there must be at least two distinct formation pathways for UDGs, and that this subpopulation is simply an extreme low surface brightness extension of the underlying dwarf galaxy population. The root cause of their diffuse stellar distributions remains unclear, but the formation mechanism appears to only impact the distribution of stars (and potentially dark matter), without strongly impacting the distribution of neutral gas, the overall stellar mass, or the number of GCs. © 2022. The Author(s). Published by the American Astronomical Society., This work is based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. These observations are associated with program # HST-SNAP-16758. Support for program # HST-SNAP-16758 was provided by NASA through a grant from the Space Telescope Science Institute. This work used images from the Dark Energy Camera Legacy Survey (DECaLS; Proposal ID 2014B-0404; PIs: David Schlegel and Arjun Dey). Full acknowledgment can be found at https://www.legacysurvey.org/acknowledgment/. D.J.S. acknowledges support from NSF grant Nos. AST-1821967 and 1813708. K.S. acknowledges support from the Natural Sciences and Engineering Research Council of Canada (NSERC). A.K. acknowledges financial support from the grant (SEV-2017-0709) funded by MCIN/AEI/10.13039/501100011033 and from the grant POSTDOC_21_00845 funded by the Economic Transformation, Industry, Knowledge and Universities Council of the Regional Government of Andalusia. L.L. acknowledges support from NSF grant No. AST-2045371., With funding from the Spanish government through the "Severo Ochoa Centre of Excellence" accreditation (CEX2021-001131-S).

We investigate the influence of active galactic nucleus (AGN) feedback on the galaxy cold gas content and its connection to galaxy quenching in three hydrodynamical simulations of Illustris, IllustrisTNG and SIMBA. By comparing to the observed atomic and molecular neutral hydrogen measurements for central galaxies, we find that Illustris over-predicts the cold gas masses in star-forming galaxies and significantly under-predicts them for quenched galaxies. IllustrisTNG performs better in this comparison than Illustris, but quenched galaxies retain too much cold gas compared with observations. SIMBA shows good agreement with observations, by depleting the global cold gas reservoir for quenched galaxies. We find that the discrepancies in IllustrisTNG are caused by its weak kinetic AGN feedback that only redistributes the cold gas from the inner disks to the outer regions and reduces the inner cold gas densities. It agrees with observations much better when only the cold gas within the stellar disk is considered to infer the star formation rates. From dependences of cold gas reservoir on the black hole mass and Eddington ratio, we find that the cumulative energy release during the black hole growth is the dominant reason for the cold gas depletion and thus the galaxy quenching. We further measure the central stellar surface density within 1 kpc ($\Sigma_1$) for the high-resolution run of IllustrisTNG and find a tight correlation between $\Sigma_1$ and black hole mass. It suggests that the observed decreasing trend of cold gas mass with $\Sigma_1$ is also a reflection of the black hole growth., Comment: 20 pages, 14 figures. Accepted by ApJ

Thin, lightweight, and durable broadband acoustic absorbers capable of absorbing sounds over a wide frequency range, especially below 1000 Hz, while also surviving harsh operational conditions such as exposure to sprays of liquid and solid debris and high temperatures are desired for many noise control applications. While today’s commercially available broadband acoustic liners are impressive, such as melamine foam and perforate-over-honeycomb structures, each style has its limitations. Motivated by the need to reduce aircraft engine noise pollution NASA has recently patented a broadband acoustic absorber that claims some benefit over existing acoustic liners. Inspired by nature, these structures resemble the geometry and acoustic absorption of bundles of natural reeds, slender grasses that grow in wetlands across the world. Proof-of-concept experiments have begun at NASA. This report summarizes the design, fabrication, and normal incidence impedance tube tests performed for assemblies of natural reeds and additively-manufactured plastic prototypes that resemble the irregular geometry of bundles of natural reeds. Some synthetic prototypes were tested with and without perforated face sheets. Results indicate that there are a number of synthetic designs that exhibit substantial acoustic absorption in the frequency range of 500 Hz to 3000 Hz, and especially below 1000 Hz, as compared to baseline acoustic absorbers of similar thicknesses and weights. Many of these prototypes have an average acoustic absorption coefficient greater than 0.6. Additionally, an annular prototype was designed and printed but not yet subjected to tests. This annular prototype of a multifunctional structure designed to transfer heat and absorb sound was developed to fit inside the NASA Glenn Research Center’s DGEN Aeropropulsion Research Turbofan engine testbed. This invention can be considered and developed for a variety of aerospace, automotive, industrial, and architectural noise control applications.

The emphasis on increased turbofan fuel efficiency requires advanced turbofan designs that will integrate higher engine bypass ratios and shorter nacelles. The resulting acoustic signature of these designs will have a more broadband character as well as a smaller available area for liner installation. This two-fold impact compels a need for an improvement in the state of the art in liner technology. Increasing the acoustic absorption efficacy over a broader frequency range is a means to address this need. NASA investigated over-the-rotor acoustic liners for turbofan applications as a potential solution. This type of liner represents a significant advance over traditional liners due to placement in close proximity to the rotor. An advantage of placing treatment in this region is a modification of the acoustic near field, thereby inhibiting noise generation mechanisms. This can result in higher attenuation levels than could be achieved by the conventional sound absorption means. In addition, there is potential to integrate the liner with fan rub-strip and containment components, reducing engine components and thus weight, enabling a systematic enhancement in noise reduction and engine performance. This article reviews the development and evaluation process of three unique over-the-rotor concepts focusing on the discrete tests conducted across the Technology Readiness Level span.

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited., We use panoramic optical spectroscopy obtained with the Very Large Telescope/MUSE to investigate the nature of five candidate extremely isolated low-mass star-forming regions (Blue Candidates; hereafter, BCs) toward the Virgo cluster of galaxies. Four of the five (BC1, BC3, BC4, and BC5) are found to host several H ii regions and to have radial velocities fully compatible with being part of the Virgo cluster. All the confirmed candidates have mean metallicity significantly in excess of that expected from their stellar mass, indicating that they originated from gas stripped from larger galaxies. In summary, these four candidates share the properties of the prototype system SECCO 1, suggesting the possible emergence of a new class of stellar systems, intimately linked to the complex duty cycle of gas within clusters of galaxies. A thorough discussion of the nature and evolution of these objects is presented in a companion paper, where the results obtained here from the MUSE data are complemented with Hubble Space Telescope (optical) and Very Large Array (Hi) observations. © 2022. The Author(s). Published by the American Astronomical Society., M.B. acknowledges the financial support of INAF—OAS Bologna, through the Ob. F. 1.05.01.01—Ricerca di Base funds. D.J.S. acknowledges support from NSF grants AST-1821967 and 1813708. A.K. acknowledges financial support from the State Agency for Research of the Spanish Ministry of Science, Innovation and Universities, through the "Center of Excellence Severo Ochoa" awarded to the Instituto de Astrofísica de Andalucía (SEV-2017-0709), and through the grant POSTDOC_21_00845, financed from budgetary program 54a Scientific Research and Innovation of the Economic Transformation, Industry, Knowledge and Universities Council of the Regional Government of Andalusia. E.A.K.A. is supported by the WISE research program, which is financed by the Dutch Research Council (NWO). R.R.M. gratefully acknowledges support from the ANID BASAL project FB210003. K.S. acknowledges support from the Natural Sciences and Engineering Research Council of Canada (NSERC). B.M.P. is supported by an NSF Astronomy and Astrophysics Postdoctoral Fellowship under award AST2001663. J.M.C., J.F., and J.L.I. are supported by NSF/AST grant 2009894. G.B. acknowledges support from the Agencia Estatal de Investigación del Ministerio de Ciencia en Innovación (AEI-MICIN) and the European Regional Development Fund (ERDF), under grants CEX2019-000920-S and PID2020-118778GB-I00/10.13039/501100011033.

The emphasis on increased turbofan fuel efficiency requires advanced turbofan designs that will integrate higher engine bypass ratios and shorter nacelles. The resulting acoustic signature of these designs will have a more broadband character as well as a smaller available area for liner installation. This two-fold impact compels a need for an improvement in the state of the art in liner technology. Increasing the acoustic absorption efficacy over a broader frequency range is a means to address this need. An acoustic liner development and optimization process was conceived and employed to achieve and demonstrate an improved broadband liner design concept. A series of increasing technology readiness level liner studies were conducted to enhance the optimization methodology while validating the concept. This progression spanned several NASA Aeronautics Research Mission Directorate programs/projects due to its relevance. This article reviews the development and evaluation process of the multi-degree-of-freedom liner technology concept from formation through simple experimental models to a flight test over an approximate 10-year period, focusing on the discrete tests comprising the development.

The attenuation of fan tones remains an important aspect of fan noise reduction for high bypass ratio turbofan engines. However, as fan design considerations have evolved, the simultaneous reduction of broadband fan noise levels has gained interest. Advanced manufacturing techniques have also opened new possibilities for the practical implementation of broadband liner concepts. To effectively address these elements, practical acoustic liner design methodologies must provide the capability to efficiently predict the acoustic benefits of novel liner configurations. This paper describes such a methodology to design and evaluate multiple candidate liner configurations using realistic, three dimensional geometries for which minimal source information is available. The development of the design methodology has been guided by a series of studies culminating in the design and flight test of a low drag, broadband inlet liner. The excellent component and system noise benefits obtained in this test demonstrate the effectiveness of the broadband liner design process. They also illustrate the value of the approach in concurrently evaluating multiple liner designs and their application to various locations within the aircraft engine nacelle. Thus, the design methodology may be utilized with increased confidence to investigate novel liner configurations in future design studies.

This paper presents results for five uniform and two multizone liners based on data acquired in the NASA Langley Grazing Flow Impedance Tube. Two methods, Prony and CHE, are used to educe the impedance spectra for each of these liners for many test conditions. The Prony method is efficient and generally provides accurate results for uniform liners, but is not well suited for multizone liners. The CHE method supports assessment of both uniform and multizone liners, but is much more computationally expensive. The results from these liners demonstrate the efficacy of both eduction methods, but also clearly demonstrate that sufficient attenuation is required to support accurate impedance eduction. For the liners considered in this study, the data indicate approximately 3 dB attenuation is needed for each zone of a multizone liner in order to ensure quality impedance eduction results. This study was conducted in response to two acoustic liner research challenges in support of a collaboration of multiple national laboratories under the International Forum for Aviation Research.

This paper presents the contribution from the German Aerospace Center (DLR) to the first liner benchmark challenge under the framework of the International Forum for Aviation Research (IFAR). Therefore, two sets of acoustically damping wall treatments, called ‘liner samples’, have been produced by additive manufacturing based on the design data provided by NASA coordinating this benchmark. These liner samples have been integrated and acoustically characterized in the liner flow test facility DUCT-R at DLR Berlin as well as in the liner flow test facility GFIT at NASA Langley. Besides the dissipation coefficients and the axial pressure profiles, the liner wall impedance was educed by first determining the axial wave numbers and then applying a straightforward method based on the one-dimensional Convected Helmholtz Equation. Finally, the comparison of the liner impedance values to the NASA results show a fairly good agreement.

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited., We report the discovery of Tucana B, an isolated ultra-faint dwarf galaxy at a distance of D = 1.4 Mpc. Tucana B was found during a search for ultra-faint satellite companions to the known dwarfs in the outskirts of the Local Group, although its sky position and distance indicate the nearest galaxy to be ∼500 kpc distant. Deep ground-based imaging resolves Tucana B into stars, and it displays a sparse red giant branch consistent with an old, metal-poor stellar population analogous to that seen in the ultra-faint dwarf galaxies of the Milky Way, albeit at fainter apparent magnitudes. Tucana B has a half-light radius of 80 ± 40 pc and an absolute magnitude of ${M}_{V}=-{6.9}_{-0.6}^{+0.5}$ mag (${L}_{V}=({5}_{-2}^{+4})\times {10}^{4}$ L⊙), which is again comparable to the Milky Way's ultra-faint satellites. There is no evidence for a population of young stars, either in the optical color–magnitude diagram or in GALEX archival ultraviolet imaging, with the GALEX data indicating $\mathrm{log}({\mathrm{SFR}}_{\mathrm{NUV}}/{M}_{\odot }\,{\mathrm{yr}}^{-1})\lt -5.4$ for star formation on ≲100 Myr timescales. Given its isolation and physical properties, Tucana B may be a definitive example of an ultra-faint dwarf that has been quenched by reionization, providing strong confirmation of a key driver of galaxy formation and evolution at the lowest mass scales. It also signals a new era of ultra-faint dwarf galaxy discovery at the extreme edges of the Local Group. © 2022. The Author(s). Published by the American Astronomical Society., D.J.S. acknowledges support from NSF grants AST-1821967 and 1813708. B.M.P. is supported by an NSF Astronomy and Astrophysics Postdoctoral Fellowship under award AST-2001663. Research by D.C. is supported by NSF grant AST-1814208. A.K. acknowledges financial support from the State Agency for Research of the Spanish Ministry of Science, Innovation and Universities through the "Center of Excellence Severo Ochoa" awarded to the Instituto de Astrofísica de Andalucía (SEV-2017-0709) and through the grant POSTDOC_21_00845 financed from the budgetary program 54a Scientific Research and Innovation of the Economic Transformation, Industry, Knowledge and Universities Council of the Regional Government of Andalusia. F.W. thanks the support provided by NASA through the NASA Hubble Fellowship grant #HF2-51448 awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555. A.C. is supported by a Brinson Prize Fellowship at UChicago/KICP. K.S. acknowledges support from the Natural Sciences and Engineering Research Council of Canada (NSERC).

We estimate the H i mass function (HIMF) of galaxies in groups based on thousands of ALFALFA (Arecibo Legacy Fast ALFA survey) H i detections within the galaxy groups of four widely used SDSS (Sloan Digital Sky Survey) group catalogues. Although differences between the catalogues mean that there is no one definitive group galaxy HIMF, in general we find that the low-mass slope is flat, in agreement with studies based on small samples of individual groups, and that the 'knee' mass is slightly higher than that of the global HIMF of the full ALFALFA sample. We find that the observed fraction of ALFALFA galaxies in groups is approximately 22 per cent. These group galaxies were removed from the full ALFALFA source catalogue to calculate the field HIMF using the remaining galaxies. Comparison between the field and group HIMFs reveals that group galaxies make only a small contribution to the global HIMF as most ALFALFA galaxies are in the field, but beyond the HIMF 'knee' group galaxies dominate. Finally, we attempt to separate the group galaxy HIMF into bins of group halo mass, but find that too few low-mass galaxies are detected in the most massive groups to tightly constrain the slope, owing to the rarity of such groups in the nearby Universe where low-mass galaxies are detectable with existing H i surveys.© 2020 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society, We acknowledge the work of the entire ALFALFA team for observing, flagging, and performing signal extraction. We thank the anonymous referee for their suggestions that helped to improve this paper. MGJ is supported by a Juan de la Cierva formacion´ fellowship (FJCI-2016-29685) from the Spanish Ministerio de Ciencia, Innovacion y Universidades (MCIU). MGJ and LVM ´ also acknowledge support from the grants AYA2015-65973-C3-1- R (MINECO/FEDER, UE) and RTI2018-096228-B-C31 (MCIU). The research of KMH is supported by the under the European Union’s Seventh Framework Programme (FP/2007-2013)/ERC Grant Agreement nr. 291531. EAKA is supported by the WISE research programme, which is financed by the Netherlands Organisation for Scientific Research (NWO). This work has been supported by the State Agency for Research of the Spanish MCIU through the ‘Centro de Excelencia Severo Ochoa’ award to the Instituto de Astrof´ısica de Andaluc´ıa (SEV-2017-0709). This research was supported by the Munich Institute for Astro- and Particle Physics (MIAPP) which is funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation)

Airborne noise with a dominant low-frequency content (

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited., The two sources AGC 226178 and NGVS 3543, an extremely faint, clumpy, blue stellar system and a low surface brightness dwarf spheroidal, are adjacent systems in the direction of the Virgo cluster. Both have been studied in detail previously, with it being suggested that they are unrelated normal dwarf galaxies or that NGVS 3543 recently lost its gas through ram pressure stripping and AGC 226178 formed from this stripped gas. However, with Hubble Space Telescope Advanced Camera for Surveys imaging, we demonstrate that the stellar population of NGVS 3543 is inconsistent with being at the distance of the Virgo cluster and that it is likely a foreground object at approximately 10 Mpc, whereas the stellar population of AGC 226178 is consistent with it being a very young (10–100 Myr) object in the Virgo cluster. Through a reanalysis of the original ALFALFA H i detection, we show that AGC 226178 likely formed from gas stripped from the nearby dwarf galaxy VCC 2034, a hypothesis strengthened by the high metallicity measured with MUSE VLT observations. However, it is unclear whether ram pressure or a tidal interaction is responsible for stripping the gas. Object AGC 226178 is one of at least five similar objects now known toward Virgo. These objects are all young and unlikely to remain visible for over ∼500 Myr, suggesting that they are continually produced in the cluster. © 2022. The Author(s). Published by the American Astronomical Society., This work is based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. These observations are associated with program No. HST-GO-15183. Support for program No. HST-GO-15183 was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. It is also based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO program 0101.B-0376A. This work used archival data from the Karl G. Jansky Very Large Array. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. The data were observed as part of program 13A-028 (PI: J. Cannon). The work used images from the Dark Energy Camera Legacy Survey (DECaLS; proposal ID 2014B-0404; PIs: David Schlegel and Arjun Dey). Full acknowledgment at https://www.legacysurvey.org/acknowledgment/. Funding for the SDSS and SDSS-II has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, the U.S. Department of Energy, the National Aeronautics and Space Administration, the Japanese Monbukagakusho, the Max Planck Society, and the Higher Education Funding Council for England. The SDSS website is http://www.sdss.org/. D.J.S. acknowledges support from NSF grants AST-1821967 and 1813708. M.B. acknowledges financial support of this research from INAF Main Stream grant 1.05.01.86.28 assigned to the program The Smallest Scale of the Hierarchy (SSH). K.S. acknowledges support from the Natural Sciences and Engineering Research Council of Canada (NSERC). B.M.P. is supported by an NSF Astronomy and Astrophysics Postdoctoral Fellowship under award AST-2001663. E.A.K.A. is supported by the WISE research program, which is financed by the Dutch Research Council (NWO). G.B. acknowledges financial support through grant (AEI/FEDER, UE) AYA2017-89076-P, as well as by the Ministerio de Ciencia, Innovación y Universidades through the state budget and by the Consejería de Economía, Industria, Comercio y Conocimiento of the Canary Islands Autonomous Community through the regional budget. J.S. acknowledges support from the Packard Foundation. M.P.H. acknowledges support from NSF/AST-1714828 and grants from the Brinson Foundation. J.M.C., J.F., and J.L.I. are supported by NST/AST 2009894. R.R.M. gratefully acknowledges support from project ANID PIA/BASAL FB210003. Research by D.C. is supported by NSF grant AST-1814208. AK acknowledges financial support from the State Agency for Research of the Spanish MCIU through the "Center of Excellence Severo Ochoa" award to the Instituto de Astrofísica de Andalucía (SEV-2017-0709).

We present neutral atomic hydrogen (H I) observations using the Robert C. Byrd Green Bank Telescope along the lines of sight to 49 confirmed or possible dwarf satellite galaxies around eight Local Volume systems (M104, M51, NGC 1023, NGC 1156, NGC 2903, NGC 4258, NGC 4565, and NGC 4631). We detect the H I reservoirs of two candidates (dw0934+2204 and dw1238−1122) and find them to be background sources relative to their nearest foreground host systems. The remaining 47 satellite candidates are not detected in H I, and we place stringent 5σ upper limits on their H I mass. We note that some (15/47) of our non-detections stem from satellites being occluded by their putative host’s H I emission. In addition to these new observations, we compile literature estimates on the H I mass for an additional 17 satellites. We compare the H I properties of these satellites to those within the Local Group, finding broad agreement between them. Crucially, these observations probe a ‘transition’ region between −10 ≳ MV ≳ −14 where we see a mixture of gas-rich and gas-poor satellites. While there are many gas-poor satellites within this region, some are gas-rich and this suggests that the transition towards predominantly gas-rich satellites occurs at LV ∼ 107L⊙, in line with simulations. The observations presented here are a key step toward characterizing the properties of dwarf satellite galaxies around Local Volume systems and future wide-field radio surveys with higher angular resolution (e.g. WALLABY) will vastly improve upon the study of such systems. © 2022 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society, AK acknowledges financial support from the State Agency for Research of the Spanish Ministry of Science, Innovation and Universities through the ‘Center of Excellence Severo Ochoa’ awarded to the Instituto de Astrofísica de Andalucía (SEV-2017-0709), from grant RTI2018-096228-B-C31 (MCIU/AEI/FEDER,UE) and through the grant POSTDOC_21_00845 financed from the budgetary program 54a Scientific Research and Innovation of the Economic Transformation, Industry, Knowledge and Universities Council of the Regional Government of Andalusia. KS acknowledges support from the Natural Sciences and Engineering Research Council of Canada (NSERC). BMP is supported by an NSF Astronomy and Astrophysics Postdoctoral Fellowship under award AST2001663. Research by DC is supported by NSF grant AST-1814208. DJS acknowledges support from NSF grants AST-1821967 and 1813708.

Full list of authors: Namumba, B.; Koribalski, B. S.; Józsa, G. I. G.; Lee-Waddell, K.; Jones, M. G.; Carignan, C.; Verdes-Montenegro, L.; Ianjamasimanana, R.; de Blok, W. J. G.; Cluver, M.; Garrido, J.; Sánchez-Expósito, S.; Ramaila, A. J. T.; Thorat, K.; Andati, L. A. L.; Hugo, B. V.; Kleiner, D.; Kamphuis, P.; Serra, P.; Smirnov, O. M.; Maccagni, F. M.; Makhathini, S.; Molnár, D. Cs.; Perkins, S.; Ramatsoku, M.; White, S. V.; Loi, F., We report the discovery of large amounts of previously undetected cold neutral atomic hydrogen (H I) around the core triplet galaxies in the nearby NGC 7232 galaxy group with MeerKAT. With a physical resolution of ∼1 kpc, we detect a complex web of low-surface-brightness H I emission down to a 4σ column density level of ∼1 × 1019 cm−2 (over 44 km s−1). The newly discovered H I streams extend over ∼20 arcmin corresponding to 140 kpc in projection. This is approximately three times the H I extent of the galaxy triplet (52 kpc). The H I debris has an H I mass of ∼6.6 × 109 M⊙, more than 50 per cent of the total H I mass of the triplet. Within the galaxy triplet, NGC 7233 and NGC 7232 have lost a significant amount of H I while NGC 7232B appears to have an excess of H I. The H I deficiency in NGC 7232 and NGC 7233 indicates that galaxy–galaxy interaction in the group concentrates on this galaxy pair while the other disc galaxies have visited them over time. In comparison to the AMIGA sample of isolated galaxies, we find that with regards to its total H I mass the NGC 7232/3 galaxy triplet is not H I-deficient. Despite the many interactions associated to the triplet galaxies, no H I seems to have been lost from the group (yet). © 2021 The Author(s)., The MeerKAT telescope is operated by the South African Radio Astronomy Observatory, which is a facility of the National Research Foundation, an agency of the Department of Science and Innovation. BN’s research is supported by the South African Radio Astronomy Observatory (SARAO). We acknowledge the Inter-University Institute for Data Intensive Astronomy (IDIA) for supporting us with the data intensive cloud for data processing. IDIA is a South African university partnership involving the University of Cape Town, the University of Pretoria, and the University of the Western Cape. BN acknowledges financial support from the CSIC Program of Scientific Cooperation for Development i-COOP+2019. The research of OS is supported by the South African Research Chairs Initiative of the Department of Science and Technology and National Research Foundation. PK is partially supported by the BMBF project 05A17PC2 for D-MeerKAT. LVM, MGJ, and BN acknowledge financial support from the State Agency for Research of the Spanish MCIU through the ‘Center of Excellence Severo Ochoa’ award to the Instituto de Astrofísica de Andalucía (SEV-2017-0709). BN acknowledges the discussion with the AMIGA team at IAA regarding data reduction and analysis. LVM, MJ, SSE, and JG acknowledge as well support from the grants AYA2015-65973-C3-1-R (MINECO/FEDER, UE) and RTI2018-096228-B-C31 (MCIU/AEI/FEDER,UE). MGJ fellowship was supported by a Juan de la Cierva formación fellowship. The work of WJGdB has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No. 882793/MeerGas). This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement no. 679627; project name FORNAX). MEC is a recipient of an Australian Research Council Future Fellowship (project No. FT170100273) funded by the Australian Government.

Results achieved with three acoustic liner configurations are used to evaluate the effects of recent modifications to the NASA Normal Incidence Tube and Grazing Flow Impedance Tube. These include a calibration liner, a wire mesh liner, and a perforate liner. The effects of source type, source level, and mean flow Mach number on the impedances educed with these liners are explored. Existing models are used to predict the impedance for each test condition and are compared with educed impedance spectra to determine their validity. The results suggest that educed impedances are similar for either a stepped sine or swept sine source. The predicted models are acceptable for the perforate liner and are quite good for the calibration and wire mesh liners.

Different methods of introducing CO2 to a heterogeneous mixture of water and 1-cyclohexylpiperidine are explored in order to generate a single-phase aqueous 1-cyclohexylpiperidinium bicarbonate solution. Membrane gas contacting was found to be an effective method for CO2 addition. This analysis varied solution temperature, gas pressure, solution pressure, solution flow rate, and membrane area to determine and minimize mass transport and chemical reaction limiting phenomena. Both mass transport limitations and chemical kinetic limitations were found for the industrially relevant membrane gas contacting process conditions explored in this study.

We quantitatively investigate the dependence of central galaxy HI mass (MHI) on the stellar mass (M*), halo mass (Mh), star formation rate (SFR), and central stellar surface density within 1 kpc (Σ1), taking advantage of the HI spectra stacking technique using both the Arecibo Fast Legacy ALFA Survey and the Sloan Digital Sky Survey. We find that the shapes of MHI–Mh and MHI–M* relations are remarkably similar for both star-forming and quenched galaxies, with massive quenched galaxies having constantly lower HI masses of around 0.6 dex. This similarity strongly suggests that neither halo mass nor stellar mass is the direct cause of quenching, but rather the depletion of the HI reservoir. While the HI reservoir for low-mass galaxies of M* < 1010.5 M☉ strongly increases with Mh, more massive galaxies show no significant dependence of MHI with Mh, indicating that the main effect of halo is to determine the smooth cold gas accretion. We find that the star formation and quenching of central galaxies are directly regulated by the available HI reservoir, with an average relation of SFR µ MH2.75I M*0.40 implying a quasi-steady state of star formation. We further confirm that galaxies are depleted of their HI reservoir, once they drop off the star formation main sequence and there is a very tight and consistent correlation between MHI and Σ1 in this phase, with MH I µ S1-2. This result is consistent with the compaction-triggered quenching scenario, with galaxies going through three evolutionary phases of cold gas accretion, compaction and post-compaction, and quenching. © 2021. The American Astronomical Society. All rights reserved., This work is supported by the National Key R&D Program of China (grant No. 2018YFA0404503), National SKA Program of China (grant No. 2020SKA0110100), National Science Foundation of China (Nos. 11922305, 11773049, 12073002, 11721303), and Spanish Science Ministry "Centro de Excelencia Severo Ochoa" program under grant SEV-2017-0709. M.G.J. was supported by a Juan de la Cierva formación fellowship (FJCI-2016-29685). M.G.J. also acknowledges support from the grants AYA2015-65973-C3-1-R and RTI2018-096228-B-C31 (MINECO/FEDER, UE). Funding for the SDSS and SDSS-ii has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, the U.S. Department of Energy, the National Aeronautics and Space Administration, the Japanese Monbukagakusho, the Max Planck Society, and the Higher Education Funding Council for England. The SDSS website is http://www.sdss.org/.

We compare the star-forming properties of satellites around Milky Way (MW) analogs from the Stage~II release of the Satellites Around Galactic Analogs Survey (SAGA-II) to those from the APOSTLE and Auriga cosmological zoom-in simulation suites. We use archival GALEX UV imaging as a star-formation indicator for the SAGA-II sample and derive star-formation rates (SFRs) to compare with those from APOSTLE and Auriga. We compare our detection rates from the NUV and FUV bands to the SAGA-II H$\alpha$ detections and find that they are broadly consistent with over $85\%$ of observed satellites detected in all three tracers. We apply the same spatial selection criteria used around SAGA-II hosts to select satellites around the MW-like hosts in APOSTLE and Auriga. We find very good overall agreement in the derived SFRs for the star-forming satellites as well as the number of star-forming satellites per host in observed and simulated samples. However, the number and fraction of quenched satellites in the SAGA-II sample are significantly lower than those in APOSTLE and Auriga below a stellar mass of $M_*\sim10^{8}\,M_{\odot}$, even when the SAGA-II incompleteness and interloper corrections are included. This discrepancy is robust with respect to the resolution of the simulations and persists when alternative star-formation tracers are employed. We posit that this disagreement is not readily explained by vagaries in the observed or simulated samples considered here, suggesting a genuine discrepancy that may inform the physics of satellite populations around MW analogs., Comment: Accepted for publication in ApJ Letters after minor changes to text