Low Surface Brightness Research Articles

A Tale of NGC 3785: The formation of an ultra-diffuse galaxy at the end of the longest tidal tail

We present the discovery of an extended and faint tail observed in the isolated environment associated with galaxy NGC\,3785. This study additionally provides observational evidence supporting the formation of ultra-diffuse galaxies (UDGs) at the end of the tail. We utilized the Gnuastro software to detect and analyze the low surface brightness structures in the optical $g$- and $r$-bands using data from the Dark Energy Camera Legacy Survey. We created a detection map to identify the faint tail and measured its length using cubic spline fitting. Additionally, we found 84 star-forming clumps along the tail and performed photometric analysis on the tail portion after applying a significance threshold on the signal-to-noise ratio . We have measured the projected length of the tail, which is sim 390 kpc. We propose that this tail arises from the interaction of the NGC\,3785 with a gas-rich galaxy, which ends up as a UDG at the end of the tail.

Systematically Measuring Ultradiffuse Galaxies. VII. The H i Survey Overview

We present the results from the neutral hydrogen (H i) follow-up survey of 378 optically detected ultradiffuse galaxy (UDG) candidates from the Systematically Measuring Ultra-Diffuse Galaxies survey using the Robert C. Byrd Green Bank Telescope. We detect H i in 110 targets and determine 37 to be UDGs and 73 to be low-surface-brightness (LSB) dwarfs based on their effective radii and central surface brightnesses. In line with previous studies, we find that: (i) our H i detections have on average bluer g − r colors and more irregular morphologies than our H i nondetections, (ii) our H i detections populate the tail end of the star-forming main sequence from the ALFALFA catalog with marginally lower specific star formation rates, and (iii) H i detections are mostly in relatively isolated (i.e., field) environments, while most nondetections have at least one nearby neighbor in projection. We find that the H i mass to stellar mass ratios (i.e., gas richnesses) scale with the physical sizes for UDGs and LSB dwarfs alike, suggesting that mechanisms other than bursty star formation feedback may be at play for UDGs. However, we find a stronger trend between gas richnesses and physical sizes if we define UDGs using their effective surface brightness instead of their central surface brightness. We are in the process of using this unprecedented sample of UDG candidates to carry out detailed follow-up studies (i.e., star formation and environmental analysis, comparisons to simulations) and are obtaining resolved H i observations for several of them.

At First Sight! Zero-shot Classification of Astronomical Images with Large Multimodal Models

Abstract Vision-Language multimodal Models (VLMs) offer the possibility for zero-shot classification in astronomy: i.e., classification via natural language prompts, with no training. We investigate two models, GPT-4o and LLaVA-NeXT, for zero-shot classification of low-surface brightness galaxies and artifacts, as well as morphological classification of galaxies. We show that with natural language prompts these models achieved significant accuracy (above 80% typically) without additional training/fine tuning. We discuss areas that require improvement, especially for LLaVA-NeXT, which is an open source model. Our findings aim to motivate the astronomical community to consider VLMs as a powerful tool for both research and pedagogy, with the prospect that future custom-built or fine-tuned models could perform better.

Wide Area VISTA Extra-galactic Survey (WAVES): Unsupervised star-galaxy separation on the WAVES-Wide photometric input catalogue using UMAP and hdbscan

Abstract Star-galaxy separation is a crucial step in creating target catalogues for extragalactic spectroscopic surveys. A classifier biased towards inclusivity risks including high numbers of stars, wasting fibre hours, while a more conservative classifier might overlook galaxies, compromising completeness and hence survey objectives. To avoid bias introduced by a training set in supervised methods, we employ an unsupervised machine learning approach. Using photometry from the Wide Area VISTA Extragalactic Survey (WAVES)-Wide catalogue comprising 9-band u - Ks data, we create a feature space with colours, fluxes, and apparent size information extracted by ProFound. We apply the non-linear dimensionality reduction method UMAP (Uniform Manifold Approximation and Projection) combined with the classifier hdbscan to classify stars and galaxies. Our method is verified against a baseline colour and morphological method using a truth catalogue from Gaia, SDSS, GAMA, and DESI. We correctly identify 99.75% of galaxies within the AB magnitude limit of Z = 21.2, with an F1 score of 0.9971 ± 0.0018 across the entire ground truth sample, compared to 0.9879 ± 0.0088 from the baseline method. Our method’s higher purity (0.9967 ± 0.0021) compared to the baseline (0.9795 ± 0.0172) increases efficiency, identifying 11% fewer galaxy or ambiguous sources, saving approximately 70,000 fibre hours on the 4MOST instrument. We achieve reliable classification statistics for challenging sources including quasars, compact galaxies, and low surface brightness galaxies, retrieving 92.7%, 84.6%, and 99.5% of them respectively. Angular clustering analysis validates our classifications, showing consistency with expected galaxy clustering, regardless of the baseline classification.

Weak Gravitational Lensing around Low Surface Brightness Galaxies in the DES Year 3 Data

We present galaxy-galaxy lensing measurements using a sample of low surface brightness galaxies (LSBGs) drawn from the Dark Energy Survey Year 3 (Y3) data as lenses. LSBGs are diffuse galaxies with a surface brightness dimmer than the ambient night sky. These dark-matter-dominated objects are intriguing due to potentially unusual formation channels that lead to their diffuse stellar component. Given the faintness of LSBGs, using standard observational techniques to characterize their total masses proves challenging. Weak gravitational lensing, which is less sensitive to the stellar component of galaxies, could be a promising avenue to estimate the masses of LSBGs. Our LSBG sample consists of 23,790 galaxies separated into red and blue color types at g−i≥0.60 and g−i<0.60, respectively. Combined with the DES Y3 shear catalog, we measure the tangential shear around these LSBGs and find signal-to-noise ratios of 6.67 for the red sample, 2.17 for the blue sample, and 5.30 for the full sample. We use the clustering redshifts method to obtain redshift distributions for the red and blue LSBG samples. Assuming all red LSBGs are satellites, we fit a simple model to the measurements and estimate the host halo mass of these LSBGs to be . We place a 95% upper bound on the subhalo mass at . By contrast, we assume the blue LSBGs are centrals, and place a 95% upper bound on the halo mass at log(Mhost/M⊙)<11.84. We find that the stellar-to-halo mass ratio of the LSBG samples is consistent with that of the general galaxy population. This work illustrates the viability of using weak gravitational lensing to constrain the halo masses of LSBGs.

Dwarf galaxies in the MATLAS Survey: Hubble Space Telescope observations of the globular cluster systems of 74 ultra-diffuse galaxies

Ultra-diffuse galaxies (UDGs), characterised by their low surface brightness and large physical size, constitute a subclass of dwarf galaxies that challenge our current understanding of galaxy formation and evolution. In this paper, we probe the properties of 74 UDGs, identified in the MATLAS survey, based on a comprehensive study of their globular cluster (GC) populations. We obtained high-resolution HST imaging of these galaxies using the ACS F606W and F814W filters, which allowed us to select GCs on the basis of the colour and concentration index. After a background subtraction and completeness correction, we calculated an overall total of 387 GCs. The number of GCs per galaxy ranges from 0 to 38, with the majority (64%) having low counts (0 − 2 GCs). On average, the more massive UDGs tend to host a larger number of GCs. We find that our UDGs have specific frequencies (SN) ranging from 0 to 91, with a small population (9%) having SN > 30. The median SN of our sample is similar to the one for the Perseus cluster UDGs, despite the fact that our UDGs are found in lower density environments. The SN measurements for individual galaxies can extend beyond those found in Perseus, but remain below the values found for UDGs in the Virgo and Coma cluster. Based on a trending analysis of the SN values with the host galaxy properties, we find trends with host galaxy size, roundness, colour, and local density. For the UDGs with sufficiently high statistics, we studied 2D density maps of the GC distributions, which display a variety of appearances: symmetric, asymmetric, off-centre, and elongated. The UDGs with disturbed density maps also show disturbed stellar light morphologies. We further quantified the distribution by modelling it with a Sérsic profile, finding Re, GC/Re, gal ∼ 1.0, which indicates that the GCs follow the stellar light of the host galaxy.

The hot circumgalactic medium in the eROSITA All-Sky Survey

Context. The circumgalactic medium (CGM) provides the material needed for galaxy formation and influences galaxy evolution. The hot (T > 106K) CGM is poorly detected around galaxies with stellar masses (M*) lower than 3 × 1011 M⊙ due to the low surface brightness. Aims. We aim to detect the X-ray emission from the hot CGM around Milky Way-mass (MW-mass, log(M*/M⊙) = 10.5 − 11.0) and M31-mass (log(M*/M⊙) = 11.0 − 11.25) galaxies, in addition to measuring the X-ray surface brightness profile of the hot CGM. Methods. We applied a stacking technique to gain enough statistics to detect the hot CGM. We used the X-ray data from the first four SRG/eROSITA All-Sky Surveys (eRASS:4). We discussed how the satellite galaxies could bias the stacking and the method we used to carefully build the central galaxy samples. Based on the SDSS spectroscopic survey and halo-based group finder algorithm, we selected central galaxies with spectroscopic redshifts of zspec < 0.2 and stellar masses of 10.0 < log(M*/M⊙) < 11.5 (85 222 galaxies) – or halo masses of 11.5 < log(M200m/M⊙) < 14.0 (125,512 galaxies). By stacking the X-ray emission around galaxies, we obtained the mean X-ray surface brightness profiles. We masked the detected X-ray point sources and carefully modeled the X-ray emission from the unresolved active galactic nuclei (AGN) and X-ray binaries (XRB) to obtain the X-ray emission from the hot CGM. Results. We measured the X-ray surface brightness profiles for central galaxies of log(M*/M⊙) > 10.0 or log(M200m/M⊙) > 11.5. We detected the X-ray emission around MW-mass and more massive central galaxies extending up to the virial radius (Rvir). The signal-to-noise ratio (S/N) of the extended emission around MW-mass (M31-mass) galaxy is about 3.1σ (4.7σ) within Rvir. We used a β model to describe the X-ray surface brightness profile of the hot CGM (SX, CGM). We obtained a central surface brightness of log(SX,0[erg s−1 kpc−2]) = 36.7−0.4+1.4 (37.1−0.4+1.5) and β = 0.43−0.06+0.10 (0.37−0.02+0.04) for MW-mass (M31-mass) galaxies. For galaxies with log(M200m/M⊙) > 12.5, the extended X-ray emission is detected with S/N > 2.8σ and the SX, CGM can be described by a β model with β ≈ 0.4 and log(SX,0[erg s−1 kpc−2]) > 37.2. We estimated the baryon budget of the hot CGM and obtained a value that is lower than the prediction of ΛCDM cosmology, indicating significant gas depletion in these halos. We extrapolated the hot CGM profile measured within Rvir to larger radii and found that within ≈3Rvir, the baryon budget is close to the ΛCDM cosmology prediction. Conclusions. We measured the extended X-ray emission from representative populations of central galaxies around and above MW-mass out to Rvir. Our results set a firm footing for the presence of the hot CGM around such galaxies. These measurements constitute a new benchmark for galaxy evolution models and possible implementations of feedback processes therein.

ViCTORIA project: The LOFAR-MeerKAT view of active galactic nuclei in Virgo cluster early-type galaxies

Context. The evolution of active galactic nuclei (AGNs) is closely connected to their host galaxies and surroundings. Via feedback processes, AGNs can counteract the cooling of the intracluster medium (ICM) and suppress star formation in their host galaxies. Radio observations at low frequencies provide a glimpse into the history of AGN activity. The Virgo cluster is a substantial reservoir of nearby galaxies and provides an ideal laboratory for the study of AGNs as well as their feedback mechanisms. Aims. The aim of our work is to characterise the AGN population within the Virgo cluster down to low radio luminosities, constrain the AGN duty cycle, and investigate environmental feedback in cluster member galaxies. Methods. We analysed 144 MHz and 1.3 GHz radio observations of early-type galaxies from the ACS Virgo Cluster Survey (ACSVCS) taken with LOFAR and MeerKAT. Results. We detect 12 of these galaxies at 144 MHz, five of which show clearly extended radio emission. The radio luminosity shows a strong dependence on the stellar mass of the host galaxy, in agreement with previous results. As a notable outlier, the massive elliptical galaxy NGC 4365 (M* = 2.2 × 1011 M⊙) is not detected as compact source in the LOFAR observations. Instead, it is surrounded by diffuse, low-surface brightness emission, which hints towards a past phase of stronger nuclear activity. Furthermore, we find a cavity in NGC 4472 (=M 49) inflated by the wide-angle tail only visible in the LOFAR data, which implies that the cavity was created by a past outburst. The corresponding cavity power is of the same order of magnitude as the jet power in the present duty cycle of the AGN.

A Closer Look at the Extended Edge-on Low-surface Brightness Galaxies

To understand the origin of extended disks of low-surface brightness (LSB) galaxies, we studied in detail four such systems with large disks seen edge on. Two of them are edge-on giant LSB galaxies (gLSBGs) recently identified by our team. The edge-on orientation of these systems boosts their surface brightnesses that provided an opportunity to characterize stellar populations spectroscopically and yielded the first such measurements for edge-on gLSBGs. We collected deep images of one galaxy using the 1.4 m Milanković Telescope, which we combined with the archival Subaru Hyper Suprime-Cam and DESI Legacy Surveys data available for the three other systems, and measured the structural parameters of the disks. We acquired deep long-slit spectra with the Russian 6 m telescope and the 10 m Keck II telescope and estimated stellar population properties in the high-surface brightness and LSB regions as well as the gas-phase metallicity distribution. The gas metallicity gradients are shallow to flat in the range between 0 and −0.03 dex per exponential disk scale length, which is consistent with the extrapolation of the gradient–scale length relation for smaller disk galaxies. Our estimates of stellar velocity dispersion in the LSB disks as well as the relative thickness of the disks indicate the dynamical overheating. Our observations favor mergers as the essential stage in the formation scenario for massive LSB galaxies.

Low surface brightness dwarf galaxies and their globular cluster populations around the low-density environment of our closest S0 NGC 3115

Abstract Understanding faint dwarf galaxies is fundamental to the development of a robust theory of galaxy formation on small scales. Since the discovery of a population of ultra diffuse galaxies (UDGs) rich in globular clusters (GCs) in Coma, an increasing number of studies on low surface brightness dwarf galaxies (LSBds) have been published in recent years. The most massive LSBds have been observed predominantly in groups and clusters, with properties displaying dependence on the environment. In this work, we use deep DECam imaging to systematically identify LSBds and their GC populations around the low-density environment of NGC 3115. We carefully analyse the structure and morphology of 24 candidates, 18 of which are reported for the first time. Most candidates exhibit red colours suggesting a connection between their colour and distance to NGC 3115. We followed up with Gemini GMOS imaging 9 LSBds to properly identify their GC populations. We derive lower limits for the number of GCs associated with each galaxy. Our analysis reveals that they occur around of the same loci of Fornax LSB dwarf GC systems. The relationship between the number of GCs and total mass provides a tool in which, by counting the GCs in these galaxies, we estimate an upper limit for the total mass of these LSB dwarfs, obtaining the mean value of ∼3.3 × 1010 M⊙. Our results align with expectations for dwarf-sized galaxies, particularly regarding the distribution and specific frequency of their GC systems.

The PIPER survey. II. The globular cluster systems of low surface brightness galaxies in the Perseus cluster

ABSTRACT We present Hubble Space Telescope ACS/WFC and WFC3/UVIS imaging for a sample of 50 low-surface brightness (LSB) galaxies in the $\sim 10^{15}$ M$_{\odot }$ Perseus cluster, which were originally identified in ground-based imaging. We measure the structural properties of these galaxies and estimate the total number of globular clusters (GCs) they host. Around half of our sample galaxies meet the strict definition of an ultra-diffuse galaxy (UDG), while the others are UDG-like but are either somewhat more compact or slightly brighter. A small number of galaxies reveal systems with many tens of GCs, rivalling some of the richest GC systems known around UDGs in the Coma cluster. We find the sizes of rich GC systems, in terms of their half-number radii, extending to $\sim$1.2 times the half-light radii of their host galaxy on average. The mean colours of the GC systems are the same, within the uncertainties, as those of their host galaxy stars. This suggests that GCs and galaxy field stars may have formed at the same epoch from the same enriched gas. It may also indicate a significant contribution from disrupted GCs to the stellar component of the host galaxy as might be expected in the ‘failed galaxy’ formation scenario for UDGs.

How Does a Low Surface Brightness Galaxy Form Spiral Arms?

The formation and evolution of spiral arms in low surface brightness galaxies (LSBs) are not well understood. We study the dynamics of spiral arms in two prototypical LSBs, FGC 568-VI and FGC 568-01, using both analytical models and N-body + hydrodynamical simulations. We first consider the disk as a two-component system of gravitationally coupled stars and gas in the force field of a spherical dark matter halo, subjected to local, nonaxisymmetric perturbations. However, no local spirals are formed. We next assume the disk to be a one-component system of stars in the net gravitational potential of a galaxy with a spherical dark matter halo perturbed by a global m = 2 instability. In this case, the growth time for spiral formation was low, equal to 0.78 and 0.96 Gyr, respectively, corresponding to a few dynamical times of the galaxies. Finally, we simulate the LSBs using the N-body + hydrodynamical simulation code RAMSES. Our results show that a quadrupolar field associated with an oblate halo with an axial ratio of 0.7 is necessary to drive a long-lived global spiral in the LSB disks. Further, feedback corresponding to a supernova mass fraction of ∼0.05 is essential to comply with the observed stellar surface density. The simulated spirals survive for about 10 dynamical times and the average pattern speed lies between 10 and 15 km s−1 kpc−1. The spiral arms thus formed are therefore a transient global pattern driven by the tidal field of the oblate dark matter halo.

A Candidate Dark Matter Deficient Dwarf Galaxy in the Fornax Cluster Identified through Overluminous Star Clusters

Two low surface brightness (LSB) dwarf galaxies were identified recently as having little or no dark matter (DM), provoking widespread interest in their formation histories. These galaxies also host populous systems of star clusters that are on average larger and more luminous than typical globular clusters (GCs). We report an initial attempt to identify new candidate DM-deficient dwarfs via their unusual GC systems. Using a large catalog of LSB galaxies from the Dark Energy Survey, we inspect their Dark Energy Camera Legacy Survey (DECaLS) imaging and identify FCC 224 as a candidate found on the outskirts of the Fornax cluster. We analyze the GC system using DECaLS and archival Hubble Space Telescope WFPC2 imaging, and find an apparent population of overluminous GCs. More detailed follow-up of FCC 224 is in progress.

Gas-rich "ultra-diffuse" galaxies are consistent with the baryonic Tully-Fisher relation and with Milgromian dynamics

Some gas-rich ``ultra-diffuse'' galaxies (UDGs), which are extreme examples of low surface brightness (LSB) dwarf galaxies, have been reported to lack dark matter and to be offset from the baryonic Tully-Fisher relation (BTFR). If confirmed, these UDGs would represent a serious challenge for both Lambda CDM galaxy-formation models and Milgromian dynamics. Here I demonstrate that these conclusions are very dubious due to underestimated uncertainties on inclinations and/or distances. First, I show that UDGs are offset from the BTFR in the same way as usual face-on LSB dwarfs due to systematic biases at low inclinations. Next, I analyze the two UDGs with the best available rotation-curve data. The first (AGC\,242019) is ideally inclined for kinematic studies; MOND can fit the observed rotation curve with a distance of 12.5pm 0.6 Mpc, which is consistent with Virgocentric flow models. The second UDG (AGC\,114905) is close to face-on, so not ideal for kinematic studies; MOND can fit the observed rotation curve with a distance of 68pm 13 Mpc and inclination of circ circ $, which are consistent with existing data. In particular, I show that the disk inclination is more uncertain than previously estimated due to significant asymmetries (lopsidedness) in the stellar distribution. In conclusion, there is no strong evidence that gas-rich UDGs and gas-rich LSB dwarfs are distinct galaxy populations with different dynamical properties; instead, UDGs seem to be a subset of LSB dwarf galaxies biased toward face-on systems.

Ionized and Cold Gas Components in Low Surface Brightness Galaxy AGC 102004

Abstract We present the integral field spectroscopic observations of ionized gas (Hα and [N II]) using the PCWI, along with deep CO(2–1) observations by the ‵ U ¯ ‵ u ¯ receiver on JCMT for AGC 102004. The velocity field of Hα shows an anomalous distribution in the northwestern (NW) disk. The Hα spectrum is well-fitted by two Gaussian components, and the weak Gaussian component is dominated by the anomalous Hα in the NW disk. The Gaussian fit center of Hα emission is offset by +24.2 km s−1 from the systemic velocity obtained from the H i emission. We derive the gas-phase metallicity, 12+log(O/H), using [N II]λ6583/Hα ratio as a proxy. The mean value of 12+log(O/H) is 8.30 ± 0.19 over the whole galaxy. The metallicity in the outer disk is lower than the detection limit of 7.72, indicating the metallicity gradient exists in AGC 102004. We speculate a minor/mini-merger event could have happened to the NW disk. CO(2–1) emission has nondetection in AGC 102004, reaching a noise level of 0.33 mK smoothed to 30 km s−1. The upper limit of molecular gas mass in AGC 102004 is 2.1 × 107 M ⊙ with X CO = 3.02 × 1020 cm−2 (K km s−1)−1. The M H 2 /M H I corr of AGC 102004 is lower than 0.0037 and lower than that of normal galaxies.

3D-DASH: The Evolution of Size, Shape, and Intrinsic Scatter in Populations of Young and Old Quiescent Galaxies at 0.5 < z < 3

We present a study of the growth of the quiescent galaxy population between 0.5 < z < 3 by tracing the number density and structural evolution of a sample of 4518 old and 583 young quiescent galaxies with log(M ⋆/M ⊙) > 10.4, selected from the COSMOS2020 catalog with complementary Hubble Space Telescope F160W imaging from the 3D-DASH survey. Among the quiescent population at z ∼ 2, roughly 50% are recently quenched galaxies; these young quiescent galaxies become increasingly rare toward lower redshift, supporting the idea that the peak epoch of massive galaxy quenching occurred at z > 2. Our data show that while the effective half-light radius of quiescent galaxies generally increases with time, young quiescent galaxies are significantly smaller than their older counterparts at the same redshift. In this work we investigate the connection between this size difference and other structural properties, including axis ratio, color gradients, stellar mass, and the intrinsic scatter in effective radius. We demonstrate that the size difference is driven by the most massive subpopulation (log(M ⋆/M ⊙) > 11) and does not persist when restricting the sample to intermediate-mass galaxies (10.4 < log(M ⋆/M ⊙) < 11). Interestingly, the intrinsic scatter in physical size shows a strong coevolution over the investigated time period and peaks around z ∼ 2 for both populations, only diverging at z < 1. Taken together, and assuming we are not missing a significant population of lower surface brightness galaxies, while the formation and quenching mechanisms that dominate at higher redshifts yield compact remnants, multiple evolutionary pathways may explain the diverse morphologies of galaxies that quench at z < 1.

Environmental effects on low surface brightness galaxies in the IllustrisTNG simulation

ABSTRACT Employing the TNG100 run of the IllustrisTNG project, we characterize the environment of low surface brightness galaxies (LSBGs) across varying scales, from their associated dark matter haloes to their distribution within the broader cosmic structure. We find no significant differences in the halo concentration index $c_{200}$ between LSBGs and their high surface brightness galaxy (HSBG) counterparts, with LSBGs residing in haloes with higher spin parameter $\lambda$ and slightly more spherical shapes than HSBGs. LSBGs show a stronger alignment between the dark and stellar angular momentum vectors than their high surface brightness counterparts. The relative abundance of LSBGs within groups and clusters displays a central deficit, hinting at potential destruction upon reaching these core regions. Studying the density field, we find a preference for rotation-dominated LSBGs to reside in low-density environments, while dispersion-dominated LSBGs thrive in high-density regions where galaxy interactions govern their evolution, an observation corroborated by our analysis of the two-point correlation function $\xi (r)$. Our examination of the cosmic web reveals no significant differences in the distance to the closest large-scale structure, barring a few exceptions. This suggests a limited impact of large-scale spatial distribution on mechanisms driving LSBG evolution. All together, we conclude that the halo vicinity and local environment at the scale of galaxy clusters, where mechanisms such as galaxy mergers and tidal stripping, as well as stellar and gas accretion take place, is the most likely environment that favour the emergence of LSBGs with different morphologies, mostly driven by the presence or absence of important local interaction phenomena.

From traffic jams to roadblocks: The outer regions of TW Hya with ALMA Band 8

Current ALMA surveys often underestimate protoplanetary disk sizes as many disks have extended low surface-brightness regions that fall below ALMA's detection limits. To effectively capture faint millimeter continuum emission in these outer regions, increased sensitivity is required. In order to gain insights on the connection between disk structure and planet formation, we aim to uncover continuum emission in the outer regions of the disk around TW Hya. Additionally, we aim to investigate the evolution of this disk by studying its dust properties. We present Atacama Large Millimeter Array (ALMA) observations of TW Hya at 0.65 mm with sim 0.5 arcsecond angular resolution, together with high angular resolution archival observations at 0.87 mm, 1.3 mm, 2.1 mm and 3.1 mm. We constrain the outer disk emission with both image-plane retrieval, and visibility-plane modeling with non-parametric and parametric fitting tools. Our results confirm emission in the outer disk regions of TW Hya (60 au leq R leq 110 au) at 0.65 mm, 0.87 mm and 1.3 mm. With image-plane retrieval we resolve the new continuum gap and ring, namely D79 and B86, at 0.87 mm and 1.3 mm. With visibility-plane modeling we also detect this substructure at 0.65 mm in the form of a quasi-constant emission at the 1sigma level Furthermore, it has a high spectral index of 3.7, which may indicate dust grain sizes ll 1 mm. It may be a dust trap or a traffic jam, that has a flux density of sim 60 mJy and a mass (1.59 $M_ that accounts for up to 2&lt;!PCT!&gt; of the dust disk at 0.65 mm. We confirm the existence of a faint ring in the outer regions of TW Hya at multiple millimeter wavelengths. With visibility-plane modeling, we are able to set constrains that are 3 times better than the resolution of our Band 8 observations.

How does dark matter stabilize disc galaxies?

ABSTRACT The study presents a theoretical framework for understanding the role of dark matter on the stability of the galactic disc. We model the galaxy as a two-component system consisting of stars and gas in equilibrium with an external dark matter halo. We derive the equations governing the growth of perturbations and obtain a stability criterion that connects the potential of the dark matter halo and the gas fraction with the stability levels of the galaxy. We find that a two-component disc is more susceptible to the growth of gravitational instabilities than individual components, particularly as gas fractions increase. However, the external field, due to the dark matter halo, acts as a stabilizing agent and increases the net stability levels even in the presence of a cold gas component. We apply the stability criterion to models of the Milky Way, low surface brightness galaxies, and baryon-dominated cold rotating disc galaxies observed in the early universe. Our results show that the potential due to the dark matter halo plays a significant role in stabilizing nearby galaxies, such as the Milky Way, and low surface brightness galaxies, which would otherwise be prone to local gravitational instabilities. However, we find that the baryon-dominated cold disc galaxies observed in the early universe remain susceptible to the growth of local gravitational instabilities despite the stabilizing effect of the dark matter halo.

Automatic Search for Low-surface-brightness Galaxies from Sloan Digital Sky Survey Images Using Deep Learning

Low-surface-brightness (LSB) galaxies play a crucial role in our understanding of galaxy evolution and dark matter cosmology. However, efficiently detecting them in large-scale surveys is challenging, due to their dim appearance. In this study, we propose a two-step detection method based on deep learning to address this issue. First, an object detection model called GalCenterNet was designed to detect LSB galaxy candidates in astronomical images. The model was trained using a data set of 665 Sloan Digital Sky Survey (SDSS) images, which contained 667 LSB galaxies. On the test set, the model achieved an accuracy of 95.05% and a recall of 96.00%. Next, an anomaly detection technique known as Deep Support Vector Data Description was applied to identify abnormal sources, thus refining the LSB candidates. By applying the two-step detection method to SDSS images, we have obtained a sample of 37,536 LSB galaxy candidates. This wide-area sample contains diverse and abundant LSB galaxies, which are valuable for studying the properties of LSB galaxies and the role that the environment plays in their evolution. The proposed detection method enables end-to-end detection from the SDSS images to the final detection results. This approach will be further employed to efficiently identify objects in the upcoming Chinese Survey Space Telescope sky survey.