HI Gas Research Articles

The role of active galactic nucleus feedback on the evolution of dwarf galaxies from cosmological simulations

Aims. Recent observational studies suggest that feedback from active galactic nuclei (AGNs) may play an important role in the formation and evolution of dwarf galaxies, an issue that has received little attention from a theoretical perspective. Methods. We investigated this using two sets of 12 cosmological magnetohydrodynamic simulations of the formation of dwarf galaxies (108.3M⊙ ≤ M* ≤ 109.8M⊙): one set using a version of the AURIGA galaxy formation physics model including AGN feedback and a parallel set with AGN feedback turned off. Results. We show that the full-physics AGN runs satisfactorily reproduce several scaling relations, including the black-hole-to-stellar mass (MBH-M⋆), the black-hole-to-sigma (MBH-σ⋆), and the baryonic Tully-Fisher relation. We find that the global star formation (SF) of galaxies run with an AGN is reduced compared to the one in which the AGN has been turned off, suggesting that AGN feedback is a viable way of suppressing SF in dwarf galaxies, even though none of our galaxies is completely quenched by z = 0. Furthermore, we find a tight correlation between the median SF rates and the MBH/M⋆ ratio in our simulated dwarfs. Star formation is suppressed due to gas heating in the vicinity of the AGN: less HI gas is available in AGN runs, though the total amount of gas is preserved across the two settings within each galaxy. This indicates that the main effect of AGN feedback in our dwarfs is to heat up and push the gas away from the galaxy’s centre rather than expelling it completely. Finally, we show that the two galaxies harbouring the largest supermassive black holes have suffered a considerable (up to ∼65%) reduction in their central dark matter density, pinpointing the role of AGNs in determining the final dark matter mass distribution within dwarf galaxies. This pilot paper highlights the importance of modelling AGN feedback at the lowest mass scales and the impact this can have on dwarf galaxy evolution.

Black holes regulate cool gas accretion in massive galaxies

The nucleus of almost all massive galaxies contains a supermassive black hole (BH)1. The feedback from the accretion of these BHs is often considered to have crucial roles in establishing the quiescence of massive galaxies2–14, although some recent studies show that even galaxies hosting the most active BHs do not exhibit a reduction in their molecular gas reservoirs or star formation rates15–17. Therefore, the influence of BHs on galaxy star formation remains highly debated and lacks direct evidence. Here, based on a large sample of nearby galaxies with measurements of masses of both BHs and atomic hydrogen (HI), the main component of the interstellar medium18, we show that the HI gas mass to stellar masses ratio (μHI = MHI/M⋆) is more strongly correlated with BH masses (MBH) than with any other galaxy parameters, including stellar mass, stellar mass surface density and bulge masses. Moreover, once the μHI–MBH correlation is considered, μHI loses dependence on other galactic parameters, demonstrating that MBH serves as the primary driver of μHI. These findings provide important evidence for how the accumulated energy from BH accretion regulates the cool gas content in galaxies, by ejecting interstellar medium gas and/or suppressing gas cooling from the circumgalactic medium.

Development of a hydrogen permselective silica membrane and its application to the thermochemical water splitting method

Abstract The thermochemical water splitting IS process is one of the hydrogen production method to use a heat directly. The temperature of the thermal decomposition of water (4000 K) can be reduced under 700 K by introducing I2 and SO2 as recycling catalysts. One of the problems in the IS process is that the conversion of the HI decomposition reaction is low at about 20%. If a membrane reactor with the H2 permselective membrane is applied to the HI decomposition reaction, the hydrogen can be extracted to improve the HI conversion. We focus on a counter diffusion CVD method for the preparation method of the membranes. Two reactants (e.g. silica precursor and oxidant) are provided at the opposite side of the porous substrates and hybrid silica is deposited inside the pore of the substrate. The pore sizes are controlled by introducing organic functional groups to silica precursor. In this study, the silica hybrid membrane with high H2 permeation performance and high H2/HI selectivity were developed by introducing organic functional groups. Effects of the organic functional groups were summarized by using a pore model. The HI gas and other inorganic gases permeation performance were tested through silica hybrid membranes.

Young Metal-Rich Stars in the Halo of M82: a tidal dwarf galaxy?

Abstract We present Hubble Space Telescope Advanced Camera for Surveys photometry of an arc structure of stars in the southern halo of M82. The structure is located at a projected height of ≈5 kpc from the disk of M82 but its stellar content exhibits a younger mean age than that of typical halo stars. We measured the distance, mean age, and peak metallicity of the stars in the arc and used them to determine the structure’s origin. The arc color-magnitude diagram yields a tip of red giant branch (RGB) distance of 3.63 ± 0.08 Mpc, similar to that of M82, confirming its association with the galaxy. The color-magnitude diagram also reveals a population of predominantly young stars with a mean age of ≈100 - 160 Myr, which is similar to that of the young stars formed in the tidal debris between M81, M82, and NGC 3077. We derived the mean metallicity of the halo stars surrounding the arc to be [Fe/H] ≈ -1.0, similar to that of the RGB population of the halo of M81. The RGB stars in the arc, while they are slightly more metal-rich than the halo RGB, show no spatial correlation with the young stars, suggesting that the arc is consist of mainly young stellar population. Furthermore, the observed age gradient along the structure of the arc indicates that the arc began forming from the closer side to M82, then moving outward. Taken together, the results suggest that the formation of the young stars which gives rise to the arc structure could have been triggered by the interactions between M82’s southern outflow and the HI gas clouds surrounding it, representing a snapshot of a tidal dwarf galaxy in the process of forming.

Exploring extreme conditions for star formation: A deep search for molecular gas in the Leo ring

Aims. We carried out sensitive searches for the 12CO J = 1–0 and J = 2–1 lines in the giant extragalactic HI ring in Leo to investigate the star formation process within environments where gas metallicities are close to solar, but physical conditions are different than those typical of bright galaxy disks. Our aim is to check the range of validity of known scaling relations. Methods. We used the IRAM-30 m telescope to observe 11 regions close to HI gas peaks or where sparse young massive stars have been found. For all pointed observations we reached spectral noise between 1 and 5 mK for at least one of the observed frequencies at 2 km s−1 spectral resolution. Results. We marginally detect two 12CO J = 1–0 lines in the star-forming region Clump 1 of the Leo ring, whose radial velocities are consistent with those of Hα lines, but whose line widths are much smaller than observed for virialized molecular clouds of similar mass in galaxies. The low signal-to-noise ratio, the small line widths, and the extremely low number densities inferred by virialized cloud models suggest that a more standard population of molecular clouds, still undetected, might be in place. Using upper limits to the CO lines, the most sensitive pointed observations show that the molecular gas mass surface density is lower than expected from the extrapolation of the molecular Kennicutt–Schmidt relation established in the disk of galaxies. The sparse stellar population in the ring, possibly forming ultra diffuse dwarf galaxies, might then be the result of a short molecular gas depletion time in this extreme environment.

A Virgo Environmental Survey Tracing Ionised Gas Emission (VESTIGE)

Using a compilation of Hα fluxes for 384 star-forming galaxies detected during the Virgo Environmental Survey Tracing Ionised Gas Emission (VESTIGE), we study several important scaling relations linking the star formation rate, specific star formation rate, stellar mass, stellar mass surface density, and atomic gas depletion timescale for a complete sample of galaxies in a rich environment. The extraordinary sensitivity of the narrow-band imaging data allows us to sample the whole dynamic range of the Hα luminosity function, from massive galaxies (Mstar ≃ 1011 M⊙) to dwarf systems (Mstar ≃ 106 M⊙), where the ionised gas emission is due to the emission of single O-early B stars. This extends previous works to a dynamic range in stellar mass and star formation rate (10−4 ≲ SFR ≲ 10 M⊙ yr−1) that has never been explored so far. The main-sequence relation derived for all star-forming galaxies within one virial radius of the Virgo cluster has a slope comparable to that observed in other nearby samples of isolated objects, but its dispersion is about three times larger (∼1 dex). The dispersion is tightly connected to the available amount of HI gas, with gas-poor systems located far below objects of similar stellar mass, but with a normal HI content. When measured on unperturbed galaxies with a normal HI gas content (HI-def ≤ 0.4), the relation has a slope a = 0.92 ± 0.06, an intercept b = −1.57 ± 0.06 (at a pivot point of log Mstar = 8.451 M⊙), and a scatter σ ≃ 0.40, and it has a constant slope in the stellar mass range 106 ≲ Mstar ≲ 3 × 1011 M⊙. The specific star formation rate of HI-poor galaxies is significantly lower than that of HI-rich systems of similar stellar mass, while their atomic gas consumption timescale τHI is fairly similar, in particular, for objects of stellar mass 107 ≲ Mstar ≲ 109 M⊙. We compare these observational results to the prediction of models expressly tuned to reproduce the effects induced by the interaction of galaxies with their surrounding environment. The observed scatter in the main-sequence relation can be reproduced only after a violent and active stripping process such as ram-pressure stripping that removes gas from the disc (outer parts first) and quenches star formation on short (< 1 Gyr) timescales. This rules out milder processes such as starvation. This interpretation is also consistent with the position of galaxies of different star formation activity and gas content within the phase-space diagram. We also show that the star-forming regions that formed in the stripped material outside perturbed galaxies are located well above the main-sequence relation drawn by unperturbed systems. These extraplanar HII regions, which might be at the origin of ultra-compact dwarf galaxies (UCDs) and other compact sources typical in rich environments, are living a starburst phase lasting only ≲50 Myr. They later become quiescent systems.

Observations of decameter carbon radio recombination lines in several galactic directions. Part 1. Experimental study

Subject and Purpose. Since decameter carbon radio recombination lines (RRLs) were detected for the first time more than forty years ago, they have significantly extended our knowledge of the physics, kinematics and chemistry of the cold rarefied interstellar medium (ISM). A large number of these lines have been observed towards various Galactic radio sources. The present paper describes our studies of decameter carbon RRLs in such Galactic directions as the sight-lines to the S140 emission nebula and to the large volume of cold neutral hydrogen known as the GSH 139-03-69 super shell. Methods and Methodology. Observations within a 1-MHz frequency band centered at 26 MHz were performed using the UTR-2 radio telescope and a multi-channel digital correlator. The UTR-2 is still the world largest and the most sensitive low-frequency radio telescope. Results.We report the detection of decameter carbon RRL series C627α – C637α from the medium lying towards the S140 nebula. The extents of RRL forming regions have been estimated. It is suggested that RRLs in the S140 direction are formed in the local ISM lying along the line of sight. The RRL-forming region is probably associated with omnipresent diffuse neutral HI gas in the Galactic plane rather than with S140 nebula itself. Toward the GSH 139-03-69 super shell, decameter RRLs have been detected as well. Likewise, they apparently originate from the local medium lying along the sight-line. Yet, the spectrum contains a RRL component corresponding to the absorption of the cold gas of the GSH 139-03-69 itself in the ISM. Conclusions. The obtained results indicate great possibilities of decameter carbon RRLs not only for cold ISM probing but also for making a good auxiliary tool for studying large complexes of extremely cold hydrogen HI in the Galaxy.

First look at the multiphase interstellar medium using synthetic observations from low-frequency Faraday tomography

Faraday tomography of radio polarimetric data below 200 MHz from the LOw Frequency ARray (LOFAR) has been providing new perspectives on the diffuse and magnetized interstellar medium (ISM). One aspect of particular interest is the unexpected discovery of Faraday-rotated synchrotron polarization associated with structures of neutral gas, as traced by atomic hydrogen (HI) and dust. Here, we present the first in-depth numerical study of these LOFAR results. We produced and analyzed comprehensive synthetic observations of low-frequency synchrotron polarization from magneto-hydrodynamical (MHD) simulations of colliding super shells in the multiphase ISM from the literature. Using an analytical approach to derive the ionization state of the multiphase gas, we defined five distinct gas phases over more than four orders of magnitude in gas temperature and density, ranging from hot, and warm fully ionized gas to a cold neutral medium. We focused on establishing the contribution of each gas phase to synthetic observations of both rotation measure and synchrotron polarized intensity below 200 MHz. We also investigated the link between the latter and synthetic observations of optically thin HI gas. We find that it is not only the fully ionized gas, but also the warm partially ionized and neutral phases that strongly contribute to the total rotation measure and polarized intensity. However, the contribution of each phase to the observables strongly depends on the choice of the integration axis and the orientation of the mean magnetic field with respect to the shell collision axis. A strong correlation between the HI synthetic data and synchrotron polarized intensity, reminiscent of the LOFAR results, is obtained with lines of sight perpendicular to the mean magnetic field direction. Our study suggests that multiphase modeling of MHD processes is needed in order to interpret observations of the radio sky at low frequencies. This work is a first step toward understanding the complexity of low-frequency synchrotron emission that will be soon revolutionized thanks to large-scale surveys with LOFAR and the Square Kilometre Array.

The molecular gas resolved by ALMA in the low-metallicity merging dwarf galaxy Haro 11

Context.The physical mechanisms driving starbursts and quenching in less massive (M* ≤ 1010 M⊙) galaxies are unclear. The merger is one of the inescapable processes referred to as both starburst and quenching in massive galaxies. However, the effects of the merger on star formation in dwarf galaxies and their evolution are still uncertain.Aims.We aim to explore how star formation in dwarf galaxies is both triggered and quenched by studying metal-poor gas-rich dwarf mergers based on multi-band observations at a spatial resolution of ∼460 pc.Methods.We use archival data of Atacama Large Millimetre Array (Band 3 and 8) and Very Large Telescope/Multi Unit Spectroscopic Explorer to map CO(J = 1–0), [CI](3P1–3P0), and Hαemission in one of the most extreme merging starburst dwarf galaxies, Haro 11.Results.We find the molecular gas is assembled around the central two star-forming regions (knots B and C). The molecular and ionized gas and stellar components show complex kinematics, indicating that the gas is probably at a combined stage of collision of clouds and feedback from star formation. The peak location and distribution of [CI](1–0) closely coincide with the CO(1–0) emission, meaning that it might trace the same molecular gas as CO in such a dwarf merger starburst galaxy. The enhancement of line ratios (∼0.5) of [CI]/CO around knot C is probably generated by the dissociation of CO molecules by cosmic rays and far-ultraviolet photons. Globally, Haro 11 and its star-forming regions share similar star formation efficiency (SFE) to the high-zstarburst galaxies or the clumps in nearby ultraluminous infrared galaxies.Conclusions.Given the high SFE, the high specific star formation rate, small stellar mass, low metallicity, and deficient HI gas, Haro 11 could be an analog of a high-zdwarf starburst and the potential progenitor of the nearby less massive elliptical galaxies. The significantly smaller turbulent pressure and viral parameter is probably triggering the intense starbursts. We predict that Haro 11 will quench atM* ≤ 8.5 × 109 M⊙.

HI observations of the MATLAS dwarf and ultra-diffuse galaxies

The presence of HI gas in galaxies is inextricably linked to their morphology and evolution. This paper aims to understand the HI content of the already identified 2210 dwarfs located in the low-to-moderate density environments of the Mass Assembly of early-Type GaLAxies with their fine Structures (MATLAS) deep imaging survey. We combined the HI observations from the ATLAS3Dsurvey, with the extragalactic HI sources from the Arecibo Legacy Fast ALFA survey, to extract the HI line width, velocity, and mass of the MATLAS dwarfs. From the 1773 dwarfs in our sample with available HI observations, 8% (145) have an HI line detection. The majority of the dwarfs show an irregular morphology, while 29% (42) are ellipticals, which is the largest sample of HI-bearing dwarf ellipticals (dEs) to date. Of the HI dwarf sample, 2% (three) are ultra-diffuse galaxies (UDGs), 12% have a transition-type morphology, 5% are tidal dwarf candidates, and 10% appear to be disrupted objects. In our optically selected sample, 9.5% of the dEs, 7% of the UDGs, and 10% of the classical dwarfs are HI-bearing. The HI-bearing dwarfs have, on average, bluer colors than the dwarfs without detected HI. We find relations between the stellar and HI masses, gas fraction, color, and absolute magnitude to be consistent with previous studies of dwarfs probing similar masses and environments. For 79% of the dwarfs identified as satellites of massive early-type galaxies, we find that the HI mass increases with the projected distance to the host. Using the HI line width, we estimate dynamical masses and find that 5% (seven) of the dwarfs are dark matter deficient.

Off-centering of the disk in the halo potential and the kinematic lopsidedness in the dwarf irregular galaxy WLM

In this work, to investigate the dynamical nature of the kinematic asymmetry in the isolated gas-rich dwarf irregular galaxy W LM in the Local Group, we consider that the dark matter halo and the disk do not have the same center of mass (i.e., the disk lies off-center in the potential of the extended dark matter halo), which is one of the possible physical explanations for the kinematic lopsidedness. To do so, we generate a lopsided halo potential by considering two dark matter mass density models, ISO and Burkert, and we add up the contribution to the rotation curve of a perturbation term [Formula: see text] in the gravitational potential, which arises from the offset between the disk and the dark matter halo. We show that such an m = 1 perturbation improves the rotation curve modeling when compared to a non-perturbed potential and the shape of the HI gas rotation curves is fitted better in the approaching side if the perturbation term in the halo potential is taken into account for this galaxy dynamics. In fact, displacing the disk center by 0.1 kpc from the halo center is sufficient to provide such an improvement in modeling the rotation curve.

The dark matter haloes of HI selected galaxies

ABSTRACT We present the neutral hydrogen mass (MHI) function (HIMF) and velocity width (w50) function (HIWF) based on a sample of 7857 galaxies from the 40 per cent data release of the ALFALFA survey (α.40). The low mass (velocity width) end of the HIMF (HIWF) is dominated by the blue population of galaxies whereas the red population dominates the HIMF (HIWF) at the high mass (velocity width) end. We use a deconvolution method to estimate the HI rotational velocity (Vrot) functions (HIVF) from the HIWF for the total, red, and blue samples. The HIWF and HIVF for the red and blue samples are well separated at the knee of the function compared to their HIMFs. We then use recent stacking results from the ALFALFA survey to constrain the halo mass (Mh) function of HI-selected galaxies. This allows us to obtain various scaling relations between MHI−w50−Vrot−Mh, which we present. The MHI−Mh relation has a steep slope ∼2.10 at small masses and flattens to ∼0.34 at masses larger than a transition halo mass, $\log _{10}(M_{\rm{ht}}h_{70}^2/M_{\odot })=10.62$. Our scaling relation is robust and consistent with a volume-limited sample of α.40. The MHI−Mh relation is qualitatively similar to the Mstar−Mh relation but the transition halo mass is smaller by ∼1.4 dex compared to that of the Mstar−Mh relation. Our results suggest that baryonic processes like heating and feedback in larger mass haloes suppress HI gas on a shorter time-scale compared to star formation.

Fabrication, permeation, and corrosion stability measurements of silica membranes for HI decomposition in the thermochemical iodine–sulfur process

In this study, a corrosion-stable silica membrane was developed to be used in H2 purification during the hydrogen iodide decomposition (2HI → H2 + I2), which is a new application of the silica membranes. From a practical perspective, the membrane separation length was enlarged up to 400 mm and one end of the membrane tubes was closed to avoid any thermal variation along the membrane length and sealing issues. The silica membranes consisted of a three-layer structure comprising a porous α-Al2O3 ceramic support, an intermediate layer, and a top silica layer. The intermediate layer was composed of γ-Al2O3 or silica, and the top silica layer that is H2 selective was prepared via counter-diffusion chemical vapor deposition of a hexyltrimethoxysilane.To the best of our knowledge, this is the first report of 400-mm-long closed-end silica membranes supported on Si-formed α-Al2O3 tubes produced via chemical vapor deposition method. A 400-mm-long closed-end membrane using a Si-formed α-Al2O3 tube exhibited a higher H2/SF6 selectivity of 1240 but lower H2 permeance of 1.4 × 10−7 mol Pa−1 m−2 s−1 with compared with the membrane using a γ-Al2O3-formed α-Al2O3 tube (907 and 5.6 × 10−7 mol Pa−1 m−2 s−1, respectively). The membrane using the Si-formed α-Al2O3 tube was more stable in corrosive HI gas than a membrane with a γ-Al2O3-formed α-Al2O3 tube after 300 h of stability tests. In conclusion, the developed silica membranes using the Si-formed α-Al2O3 tubes seem suitable for membrane reactors that produce H2 on large scale using HI decomposition in the thermochemical iodine–sulfur process.

The HI gas and star formation in star-forming galaxies selected from ALFALFA

This paper presents the results of Hα imaging of 169 galaxies randomly selected from the α.40 - SDSS catalog. The sample has excluded all low surface brightness galaxies (LSBGs) whose central surface brightness in B band (μ0(B)) fainter than 22.5 mag arcsec−2. It can be used as the counterparts sample to LSBGs. We observed their Hα and R band images by using the 2.16 m telescope at the Xinglong Observatory of the National Astronomical Observatories, Chinese Academy of Sciences (NAOC). The main goal of this work is to present the properties of those galaxies, together with Hα flux and star formation-, gas-, stellar mass- surface density. In addition, we confirm the correlations among HI content, stellar mass and star formation in ALFALFA galaxies. The HI mass increases with stellar mass, and the slope slows down at the higher stellar mass. The overall trend was that the specific star formation rate (sSFR) decreases with stellar mass, and the sSFR dropped sharply when the stellar mass is close to 1010.3 ∼ 1010.5 M ⊙. The weak correlation between SFR/MHI and M HI implies the HI contribute little to star formation. Our sample, which are mostly star-forming galaxies, follows the revisited Kennicutt-Schmidt law as well as the Kennicutt-Schmidt law.

A Virgo Environmental Survey Tracing Ionised Gas Emission (VESTIGE)

Context. The evolution of galaxies depends on their interaction with the surrounding environment. Ultra-diffuse galaxies (UDGs) have been found in large numbers in clusters. We detected a few star-forming blobs in the VESTIGE survey, located at ∼5 kpc from a UDG, namely NGVS 3543, in association with an HI gas cloud AGC 226178, suggesting a recent interaction between this low-surface-brightness system and the surrounding cluster environment. Aims. We use a complete set of multi-frequency data including deep optical, UV, and narrow-band Hα imaging and HI data to understand the formation process that gave birth to this peculiar system. Methods. For this purpose, we measured (i) the multi-wavelength radial surface brightness profiles of NGVS 3543 and compared them to the predictions of spectro-photometric models of galaxy evolution in rich clusters; and (ii) the aperture photometry of the blue regions in the vicinity of NGVS 3543 in order to determine their age and stellar mass. Results. Comparisons of the observations with evolutionary models indicate that NGVS 3543 has undergone a ram-pressure stripping that peaked ∼100 Myr ago, transforming a blue gas-rich UDG into a red gas-poor UDG. Star formation has taken place in the ram pressure stripped gas, the mass of which is ∼108 M⊙, forming star complexes with a typical age of ∼20 Myr and a stellar mass of ∼104 M⊙. Conclusions. These results suggest that we are observing for the first time the ongoing transformation of a gas-rich UDG into a red and quiescent UDG under the effect of a ram-pressure stripping event. The same process could explain the lack of star-forming UDGs in rich environments observed in several nearby clusters.

FUV and NIR size of the HI selected low surface brightness galaxies

How low surface brightness galaxies (LSBGs) form stars and assemble stellar mass is one of the most important questions related to understanding the LSBG population. We select a sample of 381 HI bright LSBGs with both far ultraviolet (FUV) and near infrared (NIR) observations to investigate the star formation rate (SFR) and stellar mass scales, and the growth mode. We measure the FUV and NIR radii of our sample, which represent the star-forming and stellar mass distribution scales respectively. We also compare the FUV and H band radius-stellar mass relation with archival data, to identify the SFR and stellar mass structure difference between the LSBG population and other galaxies. Since galaxy HI mass has a tight correlation with the HI radius, we can also compare the HI and FUV radii to understand the distribution of HI gas and star formation activities. Our results show that most of the HI selected LSBGs have extended star formation structure. The stellar mass distribution of LSBGs may have a similar structure to disk galaxies at the same stellar mass bins, but the star-forming activity of LSBGs happens at a larger radius than the high surface density galaxies, which may help to identify the LSBG sample from the wide-field deep u band image survey. The HI is also distributed at larger radii, implying a steeper (or not) Kennicutt-Schmidt relation for LSBGs.

Star Formation Activity of Galaxies Undergoing Ram Pressure Stripping in the Virgo Cluster

We study galaxies undergoing ram pressure stripping in the Virgo cluster to examine whether we can identify any discernible trend in their star formation activity. We first use 48 galaxies undergoing different stages of stripping based on HI morphology, HI deficiency, and relative extent to the stellar disk, from the VIVA survey. We then employ a new scheme for galaxy classification which combines HI mass fractions and locations in projected phase space, resulting in a new sample of 365 galaxies. We utilize a variety of star formation tracers, which include g - r, WISE [3.4] - [12] colors, and starburstiness that are defined by stellar mass and star formation rates to compare the star formation activity of galaxies at different stripping stages. We find no clear evidence for enhancement in the integrated star formation activity of galaxies undergoing early to active stripping. We are instead able to capture the overall quenching of star formation activity with increasing degree of ram pressure stripping, in agreement with previous studies. Our results suggest that if there is any ram pressure stripping induced enhancement, it is at best locally modest, and galaxies undergoing enhancement make up a small fraction of the total sample. Our results also indicate that it is possible to trace galaxies at different stages of stripping with the combination of HI gas content and location in projected phase space, which can be extended to other galaxy clusters that lack high-resolution HI imaging.

Ternary-source vapor-phase deposition of CH3NH3PbI3 polycrystalline thin films using CH3NH2 and HI gas sources with PbI2 solid source

We have investigated reaction processes of vacuum deposition of CH3NH3PbI3 using CH3NH3I and PbI2 solid sources. CH3NH3I decomposes to CH3NH2 and HI at around 100 °C under usual vacuum deposition conditions. Therefore, CH3NH3I solid source can be replaced with CH3NH2 and HI gas sources. We have demonstrated that high-quality CH3NH3PbI3 polycrystalline thin films can be fabricated by ternary-source vacuum deposition using CH3NH2 and HI gas sources combined with PbI2 solid source. The newly developed ternary-source vapor-phase deposition technique is useful because of its high stability and controllability in deposition rates.

The multiphase and magnetized neutral hydrogen seen by LOFAR

Faraday tomography of polarimetric observations at low frequency in the radio is a unique tool for studying the structure of the magneto-ionic diffuse interstellar medium (ISM) based on Faraday depth. LOFAR data below 200 MHz have revealed a plethora of features in polarization, whose origin remains unknown. Previous studies have highlighted the remarkable association of such features with tracers of the magnetized-neutral ISM, such as interstellar dust and atomic hydrogen (HI). However, the physical conditions responsible for the correlation between magneto-ionic and neutral media have not been clarified yet. In this Letter we further investigate the correlation between LOFAR data and the HI spectroscopic observations at 21 cm from the Effelsberg-Bonn HI Survey (EBHIS). We focus on the multiphase properties of the HI gas. We present the first statistical study on the morphological correlation between LOFAR tomographic data and the cold (CNM), lukewarm (LNM), and warm (WNM) neutral medium HI phases. We use the Regularized Optimization for Hyper-Spectral Analysis approach to decompose the HI phases based on a Gaussian decomposition of the HI spectra. We study four fields of view – Fields 3C196, A, B, and C – and find, in at least the first two, a significant correlation between the LOFAR and EBHIS data using the histograms of oriented gradients (HOG) feature. The absence of a correlation in Fields B and C is caused by a low signal-to-noise ratio in polarization. The observed HOG correlation in Fields 3C196 and A is associated with all HI phases and it is surprisingly dominant in the CNM and LNM phases. We discuss possible mechanisms that would explain the correlation between CNM, LNM, and WNM with polarized emission at Faraday depths up to 10 rad m−2. Our results show how the complex structure of the ionic medium seen by the LOFAR tomographic data is tightly related to phase transition in the diffuse and magnetized neutral ISM traced by HI spectroscopic data.

Compressed magnetized shells of atomic gas and the formation of the Corona Australis molecular cloud

We present the identification of the previously unnoticed physical association between the Corona Australis molecular cloud (CrA), traced by interstellar dust emission, and two shell-like structures observed with line emission of atomic hydrogen (HI) at 21 cm. Although the existence of the two shells had already been reported in the literature, the physical link between the HI emission and CrA had never been highlighted until now. We used both Planck and Herschel data to trace dust emission and the Galactic All Sky HI Survey (GASS) to trace HI. The physical association between CrA and the shells is assessed based both on spectroscopic observations of molecular and atomic gas and on dust extinction data with Gaia. The shells are located at a distance between ~140 and ~190 pc, which is comparable to the distance of CrA, which we derived as (150.5 ± 6.3) pc. We also employed dust polarization observations from Planck to trace the magnetic-field structure of the shells. Both of them show patterns of magnetic-field lines following the edge of the shells consistently with the magnetic-field morphology of CrA. We estimated the magnetic-field strength at the intersection of the two shells via the Davis-Chandrasekhar-Fermi (DCF) method. Despite the many caveats that are behind the DCF method, we find a magnetic-field strength of (27 ± 8) μG, which is at least a factor of two larger than the magnetic-field strength computed off of the HI shells. This value is also significantly larger compared to the typical values of a few μG found in the diffuse HI gas from Zeeman splitting. We interpret this as the result of magnetic-field compression caused by the shell expansion. This study supports a scenario of molecular-cloud formation triggered by supersonic compression of cold magnetized HI gas from expanding interstellar bubbles.