Low Surface Brightness Galaxies Research Articles

The first detection of ultra-diffuse galaxies in the Hydra I cluster from the VEGAS survey

In this paper, we report the discovery of 27 low-surface brightness galaxies, of which 12 are candidates for ultra-diffuse galaxies (UDG) in the Hydra I cluster, based on deep observations taken as part of the VST Early-type Galaxy Survey (VEGAS). This first sample of UDG candidates in the Hydra I cluster represents an important step in our project that aims to enlarge the number of confirmed UDGs and, through study of statistically relevant samples, constrain the nature and formation of UDGs. This study presents the main properties of this class of galaxies in the Hydra I cluster. For all UDGs, we analysed the light and colour distribution, and we provide a census of the globular cluster (GC) systems around them. Given the limitations of a reliable GC selection based on two relatively close optical bands only, we find that half of the UDG candidates have a total GC population consistent with zero. Of the other half, two galaxies have a total population larger than zero at 2σ level. We estimate the stellar mass, the total number of GCs, and the GC specific frequency (SN). Most of the candidates span a range of stellar masses of 107 − 108 M⊙. Based on the GC population of these newly discovered UDGs, we conclude that most of these galaxies have a standard or low dark matter content, with a halo mass of ≤1010 M⊙.

Self-consistent Color–Stellar Mass-to-light Ratio Relations for Low Surface Brightness Galaxies

Abstract The color–stellar mass-to-light ratio relation (CMLR) is a widely accepted tool for estimating the stellar mass (M *) of a galaxy. However, an individual CMLR tends to give distinct M * for a same galaxy when it is applied in different bands. Examining five representative CMLRs from the literature, we find that the difference in M * predicted in different bands from optical to near-infrared by a CMLR is 0.1 ∼ 0.3 dex. Based on a sample of low surface brightness galaxies that covers a wide range of color and luminosity, we therefore recalibrated each original CMLR in r, i, z, J, H, and K bands to give internally self-consistent M * for a same galaxy. The g–r is the primary color indicator in the recalibrated relations, which show little dependence on red (r–z) or near-infrared (J–K) colors. Additionally, the external discrepancies in the originally predicted γ * by the five independent CMLRs have been greatly reduced after recalibration, especially in the near-infrared bands, implying that the near-infrared luminosities are more robust in predicting γ *. For each CMLR, the recalibrated relations provided in this work could produce internally self-consistent M * from divergent photometric bands, and are extensions of the recalibrations from the Johnson–Cousin filter system by the pioneering work of McGaugh & Schombert to the filter system of the Sloan Digital Sky Survey.

Nuclear X-Ray Activity in Low-surface-brightness Galaxies: Prospects for Constraining the Local Black Hole Occupation Fraction with a Chandra Successor Mission

Abstract About half of nearby galaxies have a central surface brightness ≥1 mag below that of the sky. The overall properties of these low-surface-brightness galaxies (LSBGs) remain understudied, and in particular we know very little about their massive black hole population. This gap must be closed to determine the frequency of massive black holes at z = 0 as well as to understand their role in regulating galaxy evolution. Here we investigate the incidence and intensity of nuclear, accretion-powered X-ray emission in a sample of 32 nearby LSBGs with the Chandra X-ray Observatory. A nuclear X-ray source is detected in four galaxies (12.5%). Based on an X-ray binary contamination assessment technique developed for normal galaxies, we conclude that the detected X-ray nuclei indicate low-level accretion from massive black holes. The active fraction is consistent with that expected from the stellar mass distribution of the LSBGs, but not their total baryonic mass, when using a scaling relation from an unbiased X-ray survey of normal galaxies. This suggests that their black holes co-evolved with their stellar population. In addition, the apparent agreement nearly doubles the number of galaxies available within ∼100 Mpc for which a measurement of nuclear activity can efficiently constrain the frequency of black holes as a function of stellar mass. We conclude by discussing the feasibility of measuring this occupation fraction to a few percent precision below ≲1010 M ⊙ with high-resolution, wide-field X-ray missions currently under consideration.

The formation of ultradiffuse galaxies in the RomulusC galaxy cluster simulation

ABSTRACT We study the origins of 122 ultradiffuse galaxies (UDGs) in the Romulus c zoom-in cosmological simulation of a galaxy cluster (M200 = 1.15 × 1014 M⊙), one of the only such simulations capable of resolving the evolution and structure of dwarf galaxies (M⋆ < 109 M⊙). We find broad agreement with observed cluster UDGs and predict that they are not separate from the overall cluster dwarf population. UDGs in cluster environments form primarily from dwarf galaxies that experienced early cluster in-fall and subsequent quenching due to ram pressure. The ensuing dimming of these dwarf galaxies due to passive stellar evolution results in a population of very low surface brightness galaxies that are otherwise typical dwarfs. UDGs and non-UDGs alike are affected by tidal interactions with the cluster potential. Tidal stripping of dark matter, as well as mass-loss from stellar evolution, results in the adiabatic expansion of stars, particularly in the lowest mass dwarfs. High-mass dwarf galaxies show signatures of tidal heating while low-mass dwarfs that survive until z = 0 typically have not experienced such impulsive interactions. There is little difference between UDGs and non-UDGs in terms of their dark matter haloes, stellar morphology, colours, and location within the cluster. In most respects cluster UDG and non-UDGs alike are similar to isolated dwarf galaxies, except for the fact that they are typically quenched.

Massive low-surface-brightness galaxies in the eagle simulation

ABSTRACT We investigate the formation and properties of low surface brightness galaxies (LSBGs) with M* > 109.5 M⊙ in the eagle hydrodynamical cosmological simulation. Galaxy surface brightness depends on a combination of stellar mass surface density and mass-to-light ratio (M/L), such that low surface brightness is strongly correlated with both galaxy angular momentum (low surface density) and low specific star formation rate (high M/L). This drives most of the other observed correlations between surface brightness and galaxy properties, such as the fact that most LSBGs have low metallicity. We find that LSBGs are more isolated than high-surface-brightness galaxies (HSBGs), in agreement with observations, but that this trend is driven entirely by the fact that LSBGs are unlikely to be close-in satellites. The majority of LSBGs are consistent with a formation scenario in which the galaxies with the highest angular momentum are those that formed most of their stars recently from a gas reservoir co-rotating with a high-spin dark matter halo. However, the most extended LSBG discs in EAGLE, which are comparable in size to observed giant LSBGs, are built up via mergers. These galaxies are found to inhabit dark matter haloes with a higher spin in their inner regions (<0.1r200c), even when excluding the effects of baryonic physics by considering matching haloes from a dark-matter-only simulation with identical initial conditions.

An expanded catalogue of low surface brightness galaxies in the Coma cluster using Subaru/Suprime-Cam

ABSTRACT We present a catalogue of low surface brightness (LSB) galaxies in the Coma cluster obtained from deep Subaru/Suprime-Cam V- and R-band imaging data within a region of $\mathord {\sim }4$ deg2. We increase the number of LSB galaxies presented in Yagi et al. (2016) by a factor of $\mathord {\sim }3$ and report the discovery of 29 new ultradiffuse galaxies (UDGs). We compile the largest sample of UDGs with colours and structural parameters in the Coma cluster. While most UDGs lie along the red-sequence relation of the colour–magnitude diagram, $\mathord {\sim }16$ per cent are outside (bluer or redder) the red-sequence region of Coma cluster galaxies. Our analyses show that there is no special distinction in the basic photometric parameters between UDGs and other LSB galaxies. We investigate the clustercentric colour distribution and find a remarkable transition at a projected radius of $\mathord {\sim }0.6$ Mpc. Within this cluster core region and relative to the red-sequence of galaxies, LSB galaxies are on average redder than co-spatial higher surface brightness galaxies at the 2σ level, highlighting how vulnerable LSB galaxies are to the physical processes at play in the dense central region of the cluster. The position of the transition radius agrees with expectations from recent cosmological simulation of massive galaxy clusters within which ancient infalls are predicted to dominate the LSB galaxy population.

A Sample of Edge-on H i-rich Low Surface Brightness Galaxy Candidates in the 40% ALFALFA Catalog

Low-surface-brightness galaxies(LSBGs) are defined as galaxies that are fainter than dark night sky and are important for studying our universe. Particularly, edge-on galaxies are useful for the study of rotational velocity and dynamical properties of galaxies. Hence here we focus on searching for edge-on LSBGs. In order to find these edge-on dim galaxies, a series of effects caused by inclination, including the surface brightness profile, internal extinction, and scale length, have been corrected. In this work, we present a catalog of 281 edge-on LSBG candidates, which are selected from the cross-match between SDSS DR7 and the 40% ALFALFA catalog. We also present the properties of these edge-on LSBG candidates including absolute magnitude, central surface brightness, B-V color, scale length, and relative thickness. Our result suggests that the correction of inclination effects is very important for obtaining a complete sample of LSBGs.

Observational constraints on Rastall gravity from rotation curves of low surface brightness galaxies * * Supported by National Natural Science Foundation of China (11503078, 11573060, 11847310, 11661161010)

Rastall gravity is a modification of Einstein's general relativity in which the energy-momentum conservation is not satisfied and depends on the gradient of the Ricci curvature. It is currently in dispute whether Rastall gravity is equivalent to general relativity (GR). In this work, we constrain the theory using the rotation curves of low surface brightness (LSB) spiral galaxies. By fitting the rotation curves of LSB galaxies, we obtain parameter of the Rastall gravity. The values of LSB galaxies satisfy the weak energy condition (WEC) and strong energy condition (SEC). Combining the values of type Ia supernovae and the gravitational lensing of elliptical galaxies on Rastall gravity, we conclude that Rastall gravity may be equivalent to general relativity.

Dark matter cores and cusps in spiral galaxies and their explanations

We compare proposed solutions to the core vs cusp issue of spiral galaxies, which has also been framed as a diversity problem, and demonstrate that the cuspiness of dark matter halos is correlated with the stellar surface brightness. We compare the rotation curve fits to the SPARC sample from a self-interacting dark matter (SIDM) model, which self-consistently includes the impact of baryons on the halo profile, and hydrodynamical N-body simulations with cold dark matter (CDM) . The SIDM model predicts a strong correlation between the core size and the stellar surface density, and it provides the best global fit to the data. The CDM simulations without strong baryonic feedback effects fail to explain the large dark matter cores seen in low surface brightness galaxies. On the other hand, with strong feedback, CDM simulations do not produce galaxy analogs with high stellar and dark matter densities, and therefore they have trouble in explaining the rotation curves of high surface brightness galaxies. This implies that current feedback implementations need to be modified. We also explicitly show how the concentration-mass and stellar-to-halo mass relations together lead to a radial acceleration relation (RAR) in an averaged sense, and reiterate the point that the RAR does not capture the diversity of galaxy rotation curves in the inner regions. These results make a strong case for SIDM as the explanation for the cores and cusps of field galaxies.

Baryon-Interacting Dark Matter: heating dark matter and the emergence of galaxy scaling relations

The empirical scaling relations observed in disk galaxies remain challenging for models of galaxy formation. The most striking among these is the Mass Discrepancy-Acceleration Relation (MDAR), which encodes both a tight baryonic Tully-Fisher relation (BTFR) and the observed diversity of galaxy rotation curves through the central surface density relation (CSDR) . Building on our earlier work [1], we propose here that the MDAR is the result of interactions between baryons and `Baryon-Interacting Dark Matter' (BIDM), which heat up the dark matter. Following a bottom-up, hydrodynamical approach, we find that the MDAR follows if: i) the BIDM equation of state approximates that of an ideal gas; ii) the BIDM relaxation time is order the Jeans time; iii) the heating rate is inversely proportional to the BIDM density. Remarkably, under these assumptions the set of hydrodynamical equations together with Poisson's equation enjoy an anisotropic scaling symmetry. In the BIDM-dominated regime, this gives rise to an enhanced symmetry which fully captures the low-acceleration limit of the MDAR . We then show that, assuming a cored pseudo-isothermal profile at equilibrium, this set of equations gives rise to parameters reproducing the MDAR . Specifically, in the flat part of the rotation curve the asymptotic rotational velocity matches the parametric dependence of the BTFR . Moreover, in the central region of high-surface brightness galaxies, the profile reproduces the CSDR . Finally, by studying the time-dependent approach to equilibrium, we derive a global combination of the BTFR and CSDR, which matches the expectations in low surface-brightness galaxies. The form of the heating rate also makes model-independent predictions for various cosmological observables. We argue that our scenario satisfies existing observational constraints, and, intriguingly, offers a possible explanation to the EDGES anomaly.

Robust H i kinematics of gas-rich ultra-diffuse galaxies: hints of a weak-feedback formation scenario

ABSTRACTWe study the gas kinematics of a sample of six isolated gas-rich low surface brightness galaxies, of the class called ultra-diffuse galaxies (UDGs). These galaxies have recently been shown to be outliers from the baryonic Tully–Fisher relation (BTFR), as they rotate much slower than expected given their baryonic mass, and to have a baryon fraction similar to the cosmological mean. By means of a 3D kinematic modelling fitting technique, we show that the H i in our UDGs is distributed in ‘thin’ regularly rotating discs and we determine their rotation velocity and gas velocity dispersion. We revisit the BTFR adding galaxies from other studies. We find a previously unknown trend between the deviation from the BTFR and the exponential disc scale length valid for dwarf galaxies with circular speeds ≲ 45 km s−1, with our UDGs being at the extreme end. Based on our findings, we suggest that the high baryon fractions of our UDGs may originate due to the fact that they have experienced weak stellar feedback, likely due to their low star formation rate surface densities, and as a result they did not eject significant amounts of gas out of their discs. At the same time, we find indications that our UDGs may have higher-than-average stellar specific angular momentum, which can explain their large optical scale lengths.

First spectroscopic study of ionised gas emission lines in the extreme low surface brightness galaxy Malin 1

Context. Malin 1 is the largest known low surface brightness (LSB) galaxy, the archetype of so-called giant LSB galaxies. The structure and origin of such galaxies are still poorly understood, especially because of the lack of high-resolution kinematics and spectroscopic data. Aims. We use emission lines from spectroscopic observations of Malin 1 aiming to bring new constraints on the internal dynamics and star formation history of Malin 1. Methods. We extracted a total of 16 spectra from different regions of Malin 1 and calculated the rotational velocities of these regions from the wavelength shifts and star formation rates from the observed Hα emission line fluxes. We compared our data with existing data and models for Malin 1. Results. For the first time we present the inner rotation curve of Malin 1, characterised in the radial range r < 10 kpc by a steep rise in the rotational velocity up to at least ∼350 km s−1 (with a large dispersion), which had not been observed previously. We used these data to study a suite of new mass models for Malin 1. We show that in the inner regions dynamics may be dominated by the stars (although none of our models can explain the highest velocities measured) but that at large radii a massive dark matter halo remains necessary. The Hα fluxes derived star formation rates are consistent with an early-type disc for the inner region and with the level found in extended UV galaxies for the outer parts of the giant disc of Malin 1. We also find signs of high metallicity but low dust content for the inner regions.

The formation of ultradiffuse galaxies in clusters

ABSTRACT We use the IllustrisTNG cosmological hydrodynamical simulation to study the formation of ultradiffuse galaxies (UDGs) in galaxy clusters. We supplement the simulations with a realistic mass–size relation for galaxies at the time of infall into the cluster, as well as an analytical model to describe the tidally induced evolution of their stellar mass, velocity dispersion, and size. The model assumes ‘cuspy’ NFW haloes and, contrary to recent claims, has no difficulty reproducing the observed number of UDGs in clusters. Our results further suggest that the UDG population consists of a mixture of ‘normal’ low surface brightness galaxies such as those found in the field (‘born’ UDGs, or B-UDGs), as well as a distinct population that owe their large size and low surface brightness to the effects of cluster tides (‘tidal’, or T-UDGs). The simulations indicate that T-UDGs entered the cluster earlier and should be more prevalent than B-UDGs near the cluster centres. T-UDGs should also have, at given stellar mass, lower velocity dispersion, higher metallicities, and lower dark matter content than B-UDGs. Our results suggest that systems like DF-44 are consistent with having been born as UDGs, while others such as DF2, DF4, and VLSB-D are possibly extreme T-UDG examples.

One Hundred SMUDGes in S-PLUS: Ultra-diffuse Galaxies Flourish in the Field

Abstract We present the first systematic study of the stellar populations of ultra-diffuse galaxies (UDGs) in the field, integrating the large area search and characterization of UDGs by the SMUDGes survey with the twelve-band optical photometry of the S-PLUS survey. Based on Bayesian modeling of the optical colors of UDGs, we determine the ages, metallicities, and stellar masses of 100 UDGs distributed in an area of ∼330 deg2 in the Stripe 82 region. We find that the stellar masses and metallicities of field UDGs are similar to those observed in clusters and follow the trends previously defined in studies of dwarf and giant galaxies. However, field UDGs have younger luminosity-weighted ages than do UDGs in clusters. We interpret this result to mean that field UDGs have more extended star formation histories, including some that continue to form stars at low levels to the present time. Finally, we examine stellar population scaling relations that show that UDGs are, as a population, similar to other low surface brightness galaxies.

Stellar Mass and Stellar Mass-to-light Ratio–Color Relations for Low Surface Brightness Galaxies

Abstract We estimate the stellar mass for a sample of low surface brightness galaxies (LSBGs) by fitting their multiband spectral energy distributions (SEDs) to the stellar population synthesis model. The derived stellar masses (log M */M ⊙) span from 7.1 to 11.1, with a mean of log M */M ⊙ = 8.5, which is lower than that for normal galaxies. The stellar mass-to-light ratio (γ*) in each band varies little with the absolute magnitude but increases with higher M *. This trend of γ* with M * is even stronger in bluer bands. In addition, the γ* for our LSBGs slightly declines from the r band to the longer-wavelength bands. The log (j = g, r, i, and z) have relatively tight relations with optical colors of g − r and g − i. Compared with several representative γ*–color relations (MLCRs) from the literature, our MLCRs based on LSBG data are consistently among those literature MLCRs previously defined on diverse galaxy samples, and the existing minor differences between the MLCRs are caused by the differences in the SED model ingredients (including initial mass function, star formation history, and stellar population model), line fitting techniques, galaxy samples, and photometric zero-point, rather than the galaxy surface brightness itself, which distinguishes LSBGs from high surface brightness galaxies. Our LSBGs would be very likely to follow those representative MLCRs previously defined in diverse galaxy populations, if those main ingredients were taken into account.

Modification of the laws of gravity in the DGP model by the presence of a second DGP brane

We investigate how the laws of gravity change in the DGP model, if we add a second, parallel 3-brane, endowed with a localized gravitational curvature term. We calculate the gravitational potential energy between two static point sources localized on different branes. We discover a new length scale, which is equal to the geometric mean of the DGP cross-over scale and the separation of the two branes in the extra dimension. For distances, which are larger than this new length scale, we recover the original DGP result, but for smaller distances the gravitational potential is weaker. Furthermore, a region emerges, where a 4-dimensional observer measures a distance independent force. We discuss a possible application of the present scenario for deriving rotation curves of low surface brightness galaxies. Using the Kaluza-Klein description, we observe a curious pattern, in which even and odd KK-modes contribute to the attractive and repulsive parts of the gravitational potential, respectively. Finally, since this setup allows for the existence of a sector of particle species that are interacting arbitrarily weakly with “our” sector, we discuss the implications of this phenomenon for black holes and the bound on the number of species. We find that the behavior is qualitatively different from theories with a normalizable zero-mode graviton.

A recent starbust in the low surface brightness galaxy UGC 628

ABSTRACT We present the star-formation history of the low surface brightness (LSB) galaxy UGC 628 as part of the MUSCEL program (MUltiwavelength observations of the Structure, Chemistry, and Evolution of LSB galaxies). The star-formation histories of LSB galaxies represent a significant gap in our knowledge of galaxy assembly, with implications for dark matter / baryon feedback, IGM gas accretion, and the physics of star formation in low metallicity environments. Our program uses ground-based IFU spectra in tandem with space-based UV and IR imaging to determine the star-formation histories of LSB galaxies in a spatially resolved fashion. In this work we present the fitted history of our first target to demonstrate our techniques and methodology. Our technique splits the history of this galaxy into 15 semilogarithmically spaced time-steps. Within each time-step the star-formation rate of each spaxel is assumed constant. We then determine the set of 15 star-formation rates that best recreate the spectra and photometry measured in each spaxel. Our main findings with respect to UGC 628 are: (i) the visible properties of UGC 628 have varied over time, appearing as a high surface brightness spiral earlier than 8 Gyr ago and a starburst galaxy during a recent episode of star formation several tens of Myr ago, (ii) the central bar/core region was established early, around 8–10 Gyr ago, but has been largely inactive since, and (iii) star formation in the past 3 Gyr is best characterized as patchy and sporadic.

Constraining dark matter annihilation with HSC low surface brightness galaxies

Searches for dark matter annihilation signals have been carried out in a number of target regions such as the Galactic Center and Milky Way dwarf spheroidal galaxies (dSphs), among a few others. Here we propose low surface brightness galaxies (LSBGs) as novel targets for the indirect detection of dark matter emission. In particular, LSBGs are known to have very large dark matter contents and be less contaminated by extragalactic γ-ray sources (e.g., blazars) compared to star forming galaxies. We report on an analysis that uses eight LSBGs (detected by Subaru Hyper Suprime-Cam survey data) with known redshifts to conduct a search for γ-ray emission at the positions of these new objects in Fermi Large Area Telescope data. We found no excesses of γ-ray emission and set constraints on the dark matter annihilation cross-section. We exclude (at the 95% C.L.) dark matter scenarios predicting a cross-section higher than ∼ 10−23 [cm3/s] for dark matter particles of mass 10 GeV self-annihilating in the bb̄ channel. Although this constraint is weaker than the ones reported in recent studies using other targets, we note that in the near future, the number of detections of new LSBGs will increase by a few orders of magnitude. We forecast that with the use of the full catalog of soon-to-be-detected LSBGs the constraint will reach cross-section sensitivities of ∼ 3× 10−25 [cm3/s] for dark matter particles with masses ≲ 10 GeV.

The M101 Satellite Luminosity Function and the Halo–Halo Scatter among Local Volume Hosts

Abstract We have obtained deep Hubble Space Telescope (HST) imaging of 19 dwarf galaxy candidates in the vicinity of M101. Advanced Camera for Surveys HST photometry for two of these objects showed resolved stellar populations and tip of the red giant branch derived distances (D ∼ 7 Mpc) consistent with M101 group membership. The remaining 17 were found to have no resolved stellar populations, meaning they are either part of the background NGC 5485 group or are distant low surface brightness (LSB) galaxies. It is noteworthy that many LSB objects that had previously been assumed to be M101 group members based on projection have been shown to be background objects, indicating the need for future diffuse dwarf surveys to be very careful in drawing conclusions about group membership without robust distance estimates. In this work we update the satellite luminosity function of M101 based on the presence of these new objects down to M V = −8.2. M101 is a sparsely populated system with only nine satellites down to M V ≈ −8, as compared with 26 for M31 and 24.5 ± 7.7 for the median host in the Local Volume. This makes M101 by far the sparsest group probed to this depth, although M94 is even sparser to the depth at which it has been examined (M V = −9.1). M101 and M94 share several properties that mark them as unusual compared with the other Local Volume galaxies examined: they have a very sparse satellite population but also have high star-forming fractions among these satellites; such properties are also found in the galaxies examined as part of the Satellites around Galactic Analogs survey. We suggest that these properties appear to be tied to the wider galactic environment, with more isolated galaxies showing sparse satellite populations that are more likely to have had recent star formation, while those in dense environments have more satellites that tend to have no ongoing star formation. Overall, our results show a level of halo-to-halo scatter between galaxies of similar mass that is larger than is predicted in the lambda cold dark matter model.

Star Formation in Low Surface Brightness Galaxies

Star Formation in Low Surface Brightness Galaxies