High Surface Brightness Galaxies Research Articles

The properties of a large volume-limited sample of face-on low surface brightness disk galaxies

We select a large volume-limited sample of low surface brightness galaxies (LSBGs, 2021) to investigate in detail their statistical properties and their differences from high surface brightness galaxies (HSBGs, 3639). The distributions of stellar masses of LSBGs and HSBGs are nearly the same and they have the same median values. Thus this volume-limited sample has good completeness and is further removed from the effect of stellar masses on their other properties when we compare LSBGs to HSBGs. We found that LSBGs tend to have lower stellar metallicities and lower effective dust attenuations, indicating that they have lower dust than HSBGs. The LSBGs have relatively higher stellar mass-to-light ratios, higher gas fractions, lower star forming rates (SFRs), and lower specific SFRs than HSBGs. Moreover, with the decreasing surface brightness, gas fraction increases, but the SFRs and specific SFRs decrease rapidly for the sample galaxies. This could mean that the star formation histories between LSBGs and HSBGs are different, and HSBGs may have stronger star forming activities than LSBGs.

Low and high surface brightness galaxies at void walls

Abstract We study the relative fraction of low and high surface brightness galaxies (LSBGs and HSBGs) at void walls in the Sloan Digital Sky Survey (SDSS) Data Release 7. We focus on galaxies in equal local density environments. We assume that the host dark matter halo mass (for which we use SDSS group masses) is a good indicator of local density. This analysis allows us to examine the behaviour of the abundance of LSBGs and HSBGs at a fixed local density and distinguish the large-scale environment defined by the void geometry. We compare galaxies in the field and in the void walls; the latter are defined as the volume of void shells of radius equal to that of the void. We find a significant decrement, a factor of ∼4, of the relative fraction of blue, active star-forming LSBGs in equal-mass groups at the void walls and the field. This decrement is consistent with an increase of the fraction of blue, active star-forming HSBGs. In contrast, red LSBGs and HSBGs show negligible changes. We argue that these results are consistent with a scenario where LSBGs with blue colours and strong star formation activity at the void walls are fuelled by gas from the expanding void regions. This process could lead to LSBG to HSBG transformations.

On the general structure of giant low surface brightness galaxy Malin 2

AbstractWe carried out the multicolor surface photometry in BVR and griz filters parallel with stellar kinematic measurements from the long slit spectra for the low surface brightness galaxy Malin 2. The use of the multicolor surface photometry as well as the available HI rotation curve allowed us to construct the mass distribution model of the galaxy. Photometrical and dynamical mass estimates agree with the dark halo mass fraction of about 70% within four disc radial scalelengths (~ 70 kpc). We used our dynamical model to obtain radial profiles of the equilibrium disc volume density and gas pressure in the galaxy midplane based on the available HI and CO data. The observed molecular gas fraction appears to be much higher than in the high surface brightness galaxies for a similar gas pressure.

Stellar populations of bulges in galaxies with a low surface-brightness disc

AbstractThe radial profiles of the Hβ, Mg, and Fe line-strength indices are presented for a sample of eight spiral galaxies with a low surface-brightness stellar disc and a bulge. The correlations between the central values of the line-strength indices and velocity dispersion are consistent to those known for early-type galaxies and bulges of high surface-brightness galaxies. The age, metallicity, and α/Fe enhancement of the stellar populations in the bulge-dominated region are obtained using stellar population models with variable element abundance ratios. Almost all the sample bulges are characterized by a young stellar population, on-going star formation, and a solar α/Fe enhancement. Their metallicity spans from high to sub-solar values. No significant gradient in age and α/Fe enhancement is measured, whereas only in a few cases a negative metallicity gradient is found. These properties suggest that a pure dissipative collapse is not able to explain formation of all the sample bulges and that other phenomena, like mergers or acquisition events, need to be invoked. Such a picture is also supported by the lack of a correlation between the central value and gradient of the metallicity in bulges with very low metallicity. The stellar populations of the bulges hosted by low surface-brightness discs share many properties with those of high surface-brightness galaxies. Therefore, they are likely to have common formation scenarios and evolution histories. A strong interplay between bulges and discs is ruled out by the fact that in spite of being hosted by discs with extremely different properties, the bulges of low and high surface-brightness discs are remarkably similar.

Structure and dynamics of galaxies with a low surface-brightness disc - II. Stellar populations of bulges★

The radial profiles of the Hb, Mg, and Fe line-strength indices are presented for a sample of eight spiral galaxies with a low surface-brightness stellar disc and a bulge. The correlations between the central values of the line-strength indices and velocity dispersion are consistent to those known for early-type galaxies and bulges of high surface-brightness galaxies. The age, metallicity, and alpha/Fe enhancement of the stellar populations in the bulge-dominated region are obtained using stellar population models with variable element abundance ratios. Almost all the sample bulges are characterized by a young stellar population, on-going star formation, and a solar alpha/Fe enhancement. Their metallicity spans from high to sub-solar values. No significant gradient in age and alpha/Fe enhancement is measured, whereas only in a few cases a negative metallicity gradient is found. These properties suggest that a pure dissipative collapse is not able to explain formation of all the sample bulges and that other phenomena, like mergers or acquisition events, need to be invoked. Such a picture is also supported by the lack of a correlation between the central value and gradient of the metallicity in bulges with very low metallicity. The stellar populations of the bulges hosted by low surface-brightness discs share many properties with those of high surface-brightness galaxies. Therefore, they are likely to have common formation scenarios and evolution histories. A strong interplay between bulges and discs is ruled out by the fact that in spite of being hosted by discs with extremely different properties, the bulges of low and high surface-brightness discs are remarkably similar.

Bar pattern speed evolution over the last 7 Gyr

The tumbling pattern of a bar is the main parameter characterising its dynamics. From numerical simulations, its evolution since bar formation is tightly linked to the dark halo in which the bar is formed through dynamical friction and angular momentum exchange. Observational measurements of the bar pattern speed with redshift can restrict models of galaxy formation and bar evolution. We aim to determine, for the first time, the bar pattern speed evolution with redshift based on morphological measurements. We have selected a sample of 44 low inclination ringed galaxies from the SDSS and COSMOS surveys covering the redshift range 0 <z< 0.8 to investigate the evolution of the bar pattern speed. We have derived morphological ratios between the deprojected outer ring radius (R_{ring}) and the bar size (R_{bar}). This quantity is related to the parameter {\cal R}=R_{CR}/R_{bar} used for classifiying bars in slow and fast rotators, and allow us to investigate possible differences with redshift. We obtain a similar distribution of $R$ at all redshifts. We do not find any systematic effect that could be forcing this result. The results obtained here are compatible with both, the bulk of the bar population (~70%) being fast-rotators and no evolution of the pattern speed with redshift. We argue that if bars are long-lasting structures, the results presented here imply that there has not been a substantial angular momentum exchange between the bar and halo, as predicted by numerical simulations. In consequence, this might imply that the discs of these high surface-brightness galaxies are maximal.

Far-infrared colours of nearby late-type galaxies in theHerschelReference Survey

We study the far infrared (60-500 $\mu$m) colours of late-type galaxies in the $Herschel$ Reference Survey, a K-band selected, volume limited sample of nearby galaxies. The far infrared colours are correlated with each other, with tighter correlations for the indices that are closer in wavelength. We also compare the different colour indices to various tracers of the physical properties of the target galaxies, such as the surface brightness of the ionising and non-ionising stellar radiation, the dust attenuation and the metallicity. The emission properties of the cold dust dominating the far infrared spectral domain are regulated by the properties of the interstellar radiation field. Consistent with that observed in nearby, resolved galaxies, our analysis shows that the ionising and the non-ionising stellar radiation, including that emitted by the most evolved, cold stars, both contribute to the heating of the cold dust component. This work also shows that metallicity is another key parameter characterising the cold dust emission of normal, late-type galaxies. A single modified black body with a grain emissivity index $\beta$=1.5 better fits the observed SPIRE flux density ratios $S250/S350$ vs. $S350/S500$ than $\beta$=2, although values of $\beta$ $\simeq$ 2 are possible in metal rich, high surface brightness galaxies. Values of $\beta$ $\lesssim$ 1.5 better represent metal poor, low surface brightness objects. This observational evidence provides strong constraints for dust emission models of normal, late type galaxies.

Fitting dwarf galaxy rotation curves with conformal gravity

We continue our study of the application of the conformal gravity theory to galactic rotation curves. Previously we had studied a varied 111 spiral galaxy sample consisting of high surface brightness galaxies, low surface brightness galaxies and dwarf galaxies. With no free parameters other than galactic mass to light ratios, we had found that the theory is able to account for the systematics that is observed in the entire set of galactic rotation curves without the need for any dark matter whatsoever. In the present paper we extend our study to incorporate a further 27 galaxies of which 25 are dwarf galaxies and provide updated studies of 3 additional galaxies that had been in the original sample, and again without dark matter find fully acceptable fits, save only for just a few galaxies that we find to be somewhat troublesome. Our current study brings to 138 the number of rotation curves of galaxies that have been accounted for by the conformal gravity theory. Since one of the primary ingredients in the theory is a universal contribution to galactic motions coming from matter exterior to the galaxies, and thus independent of them, our study reinforces one of the central concepts of the conformal gravity studies, namely that invoking dark matter should be viewed as being nothing more than an attempt to describe global physics contributions in purely local galactic terms.

THE STABILITY OF LOW SURFACE BRIGHTNESS DISKS BASED ON MULTI-WAVELENGTH MODELING

To investigate the structure and composition of the dusty interstellar medium (ISM) of low surface brightness (LSB) disk galaxies, we have used multiwavelength photometry to construct spectral energy distributions for three low-mass, edge-on LSB galaxies. We use Monte Carlo radiation transfer codes that include the effects of transiently heated small grains and polycyclic aromatic hydrocarbon molecules to model and interpret the data. We find that unlike the high surface brightness galaxies previously modeled, the dust disks appear to have scale heights equal to or exceeding their stellar scale heights. This result supports the findings of previous studies that low mass disk galaxies have dust scale heights comparable to their stellar scale heights and suggests that the cold ISM of low mass, LSB disk galaxies may be stable against fragmentation and gravitational collapse. This may help to explain the lack of observed dust lanes in edge-on LSB galaxies and their low current star formation rates.

The dust distribution in late-type low surface brightness disks

AbstractLate-type low surface brightness (LSB) disk galaxies are common in the local universe and appear dynamically and chemically under evolved compared to their high surface brightness (HSB) counterparts. We have utilized multi-wavelength imaging and photometry of three edge-on, low-mass LSB disk galaxies to investigate the dust distribution in such systems. Through the use of Monte Carlo radiation transfer models to interpret the data, we find that the dust disk appears to have a vertical scale height similar to the stellar disk. This is in contrast to previous findings from HSB galaxies, where the dust is believed to be more concentrated in the galactic mid-plane. We believe the change in the relative scale heights of the dust and stellar disks is likely associated with the increased stability of the ISM against vertical collapse and the thin nature of the stellar disks.

Galactic rotation curves in brane world models

In the braneworld scenario the four dimensional effective Einstein equation has extra source terms, which arise from the embedding of the 3-brane in the bulk. These non-local effects, generated by the free gravitational field of the bulk, may provide an explanation for the dynamics of the neutral hydrogen clouds at large distances from the galactic center, which is usually explained by postulating the existence of the dark matter. In the present paper we consider the asymptotic behavior of the galactic rotation curves in the brane world models, and we compare the theoretical results with observations of both High Surface Brightness and Low Surface Brightness galaxies. For the chosen sample of galaxies we determine first the baryonic parameters by fitting the photometric data to the adopted galaxy model; then we test the hypothesis of the Weyl fluid acting as dark matter on the chosen sample of spiral galaxies by fitting the tangential velocity equation of the combined baryonic-Weyl model to the rotation curves. We give an analytical expression for the rotational velocity of a test particle on a stable circular orbit in the exterior region to a galaxy, with Weyl fluid contributions included. The model parameter ranges for which the $\chi^2$ test provides agreement (within 1$\sigma$ confidence level) with observations on the velocity fields of the chosen galaxy sample are then determined. There is a good agreement between the theoretical predictions and observations, showing that extra-dimensional models can be effectively used as a viable alternative to the standard dark matter paradigm.

LOW SURFACE BRIGHTNESS GALAXIES IN THE SDSS: THE LINK BETWEEN ENVIRONMENT, STAR-FORMING PROPERTIES, AND ACTIVE GALACTIC NUCLEI

Using the Sloan Digital Sky Survey (SDSS) data release 4 (DR 4), we investigate the spatial distribution of low and high surface brightness galaxies (LSBGs and HSBGs, respectively). In particular, we focus our attention on the influence of interactions between galaxies on the star formation strength in the redshift range $0.01 < z < 0.1$. With cylinder counts and projected distance to the first and fifth-nearest neighbor as environment tracers, we find that LSBGs tend to have a lack of companions compared to HSBGs at small scales ($<2$ Mpc). Regarding the interactions, we have evidence that the fraction of LSBGs with strong star formation activity increases when the distance between pairs of galaxies ($r_{p}$) is smaller than about four times the Petrosian radius ($r_{90}$) of one of the components. Our results suggest that, rather than being a condition for their formation, the isolation of LSBGs is more connected with their survival and evolution. The effect of the interaction on the star formation strength, measured by the average value of the birthrate parameter $b$, seems to be stronger for HSBGs than for LSBGs. The analysis of our population of LSBGs and HSBGs hosting an AGN show that, regardless of the mass range, the fraction of LSBGs having an AGN is lower than the corresponding fraction of HSBGs with an AGN. Also, we observe that the fraction of HSBGs and LSBGs having an AGN increases with the bulge luminosity. These results, and those concerning the star-forming properties of LSBGs as a function of the environment, fit with the scenario proposed by some authors where, below a given threshold of surface mass density, low surface brightness disks are unable to propagate instabilities, preventing the formation and evolution of massive black holes in the centers of LSBGs.

Multiwavelength study of nearly face-on low surface brightness disk galaxies

We study the ages of a large sample (1802) of nearly face-on disk low surface brightness galaxies (LSBGs) using the evolutionary population synthesis (EPS) model PEGASE with an exponentially decreasing star formation rate to fit their multiwavelength spectral energy distributions (SEDs) from far-ultraviolet (FUV) to near-infrared (NIR). The derived ages of LSBGs are 1–5 Gyr for most of the sample no matter if constant or varying dust extinction is adopted, which are similar to most of the previous studies on smaller samples. This means that these LSBGs formed the majority of their stars quite recently. However, a small part of the sample (∼2%–3%) has larger ages of 5–8 Gyr, meaning their major star forming process may have occurred earlier. At the same time, a large sample (5886) of high surface brightness galaxies (HSBGs) are selected and studied using the same method for comparisons. The derived ages are 1–5 Gyr for most of the sample (97%) as well. These results probably mean that these LSBGs have not much different star formation histories from their HSBGs counterparts. However, we should notice that the HSBGs are generally about 0.2 Gyr younger, which could mean that the HSBGs may have undergone more recent star forming activities than the LSBGs.

The distinguishing factor for gravity models: stellar population synthesis

Alternative gravitations of Milgrom (MOND), Moffat (MOG), and CDM scenarios all simulate rotation curves of spirals with reasonable details. They display significant disparities however in predicting the stellar mass-to-light (M∗/L) ratios of the galaxies. We maintain this feature could serve as a distinguishing factor between different alternative theories. We analyze the rotation curves of 46 low- and high-surface brightness galaxies and compare the resulting M∗/Ls with the predictions of the Stellar Population Synthesis (SPS) scheme. The color–M∗/L correlation obtained for MOND is consistent with predictions of SPS models. MOG does not show this consistency, and the M∗/Ls of CDM model shows large dispersions. Furthermore, M∗/L ratios of MOND with Bekenstein interpolating function favor Kroupa’s initial mass function (IMF) of the SPS scheme, while those of MOND with standard and simple interpolating functions are consistent with Salpeter’s IMF. Here is another indication to differentiate between different IMFs that are used in SPS context.

A large sample of low surface brightness disc galaxies from the SDSS - II. Metallicities in surface brightness bins

We study the spectroscopic properties of a large sample of Low Surface Brightness galaxies (LSBGs) (with B-band central surface brightness mu0(B)>22 mag arcsec^(-2)) selected from the Sloan Digital Sky Survey Data Release 4 (SDSS-DR4) main galaxy sample. A large sample of disk-dominated High Surface Brightness galaxies (HSBGs, with mu0(B)<22 mag arcsec^(-2)) are also selected for comparison simultaneously. To study them in more details, these sample galaxies are further divided into four subgroups according to mu0(B) (in units of mag arcsec^(-2)): vLSBGs (24.5-22.75),iLSBGs (22.75-22.0), iHSBGs (22.0-21.25), and vHSBGs (<21.25). The diagnostic diagram from spectral emission-line ratios shows that the AGN fractions of all the four subgroups are small (<9%). The 21,032 star-forming galaxies with good quality spectroscopic observations are further selected for studying their dust extinction, strong-line ratios, metallicities and stellar mass-metallicities relations. The vLSBGs have lower extinction values and have less metal-rich and massive galaxies than the other subgroups. The oxygen abundances of our LSBGs are not as low as those of the HII regions in LSBGs studied in literature, which could be because our samples are more luminous, and because of the different metallicity calibrations used. We find a correlation between 12+log(O/H) and mu0(B) for vLSBGs, iLSBGs and iHSBGs but show that this could be a result of correlation between mu0(B) and stellar mass and the well-known mass-metallicity relation. This large sample shows that LSBGs span a wide range in metallicity and stellar mass, and they lie nearly on the stellar mass vs. metallicity and N/O vs. O/H relations of normal galaxies. This suggests that LSBGs and HSBGs have not had dramatically different star formation and chemical enrichment histories.

KECK/LRIS SPECTROSCOPIC CONFIRMATION OF COMA CLUSTER DWARF GALAXY MEMBERSHIP ASSIGNMENTS

Keck/LRIS multi-object spectroscopy has been carried out on 140 of some of the lowest and highest surface brightness faint (19 < R < 22) dwarf galaxy candidates in the core region of the Coma Cluster. These spectra are used to measure redshifts and establish membership for these faint dwarf populations. The primary goal of the low surface brightness sample is to test our ability to use morphological and surface brightness criteria to distinguish between Coma Cluster members and background galaxies using high resolution HST/ACS images. Candidates were rated as expected members, uncertain, or expected background. From 93 spectra, 51 dwarf galaxy members and 20 background galaxies are identified. Our morphological membership estimation success rate is ~100% for objects expected to be members and better than ~90% for galaxies expected to be in the background. We confirm that low surface brightness is a very good indicator of cluster membership. High surface brightness galaxies are almost always background with confusion arising only from the cases of the rare compact elliptical galaxies. The more problematic cases occur at intermediate surface brightness. Many of these galaxies are given uncertain membership ratings, and these were found to be members about half of the time. Including color information will improve membership determination but will fail for some of the same objects that are already mis-identified when using only surface brightness and morphology criteria. Compact elliptical galaxies with B-V colors ~0.2 magnitudes redward of the red sequence in particular require spectroscopic follow-up. In a sample of 47 high surface brightness, UCD candidates, 19 objects have redshifts which place them in the Coma Cluster. Redshift measurements are presented and the use of indirect means for establishing cluster membership is discussed.

Self-consistent nonspherical isothermal halos embedding zero-thickness disks

Disk-halo decompositions of galaxy rotation curves are generally performed in a parametric way. We construct self-consistent models of nonspherical isothermal halos embedding a zero-thickness disk, by assuming that the halo distribution function is a Maxwellian. The method developed here can be used to study other physically-based choices for the halo distribution function and the case of a disk accompanied by a bulge. In a preliminary investigation we note the existence of a fine tuning between the scalelengths R_{\Omega} and h, respectively characterizing the rise of the rotation curve and the luminosity profile of the disk, which surprisingly applies to both high surface brightness and low surface brightness galaxies. This empirical correlation identifies a much stronger conspiracy than the one required by the smoothness and flatness of the rotation curve (disk-halo conspiracy). The self-consistent models are characterized by smooth and flat rotation curves for very different disk-to-halo mass ratios, hence suggesting that conspiracy is not as dramatic as often imagined. For a typical rotation curve, with asymptotically flat rotation curve at V_{\infty} (the precise value of which can also be treated as a free parameter), and a typical density profile of the disk, self-consistent models are characterized by two dimensionless parameters, which correspond to the dimensional scales (the disk mass-to-light ratio M/L and the halo central density) of standard disk-halo decompositions. We show that if the rotation curve is decomposed by means of our self-consistent models, the disk-halo degeneracy is removed and typical rotation curves are fitted by models that are below the maximum-disk prescription. Similar results are obtained from a study of NGC 3198. Finally, we quantify the flattening of the spheroidal halo, which is significant, especially on the scale of the visible disk.

Structure and dynamics of giant low surface brightness galaxies

Giant low surface brightness (GLSB) galaxies are commonly thought to be massive, dark matter dominated systems. However, this conclusion is based on highly uncertain rotation curves. We present here a new study of two prototypical GLSB galaxies: Malin 1 and NGC 7589. We re-analysed existing H I observations and derived new rotation curves, which were used to investigate the distributions of luminous and dark matter in these galaxies. In contrast to previous findings, the rotation curves of both galaxies show a steep rise in the central parts, typical of high surface brightness (HSB) systems. Mass decompositions with a dark matter halo show that baryons may dominate the dynamics of the inner regions. Indeed, a “maximum disk” fit gives stellar mass-to-light ratios in the range of values typically found for HSB galaxies. These results, together with other recent studies, suggest that GLSB galaxies are systems with a double structure: an inner HSB early-type spiral galaxy and an outer extended LSB disk. We also tested the predictions of MOND: the rotation curve of NGC 7589 is reproduced well, whereas Malin 1 represents a challenging test for the theory.

The large-scale environment of low surface brightness galaxies

The exact formation scenarios and evolutionary processes that led to the existence of the class of low surface brightness galaxies (LSBs) have not yet been understood completely. Since the environment of LSBs has been studied before only on small scales (below 2 Mpc), a study of the galaxy content in the vicinity of LSB galaxies on larger scales could add a lot to our understanding of the origin of this galaxy class. We used the spectroscopic main galaxy sample of the SDSS DR4 to investigate the environmental galaxy density of LSB galaxies compared to the galaxy density in the vicinity of high surface brightness galaxies (HSBs). The environment studies, divided into two redshift bins, show that both the low mass, and the more massive LSBs possess an environment with a lower galaxy density than HSBs. The differences in the galaxy density between LSBs and HSBs are significant on scales between 2 and 5 Mpc, the scales of groups and filaments. To quantify this, we have introduced for the first time the LSB-HSB Antibias. The obtained LSB-HSB Antibias parameter has a value of 10%-15%. From these results we conclude that LSBs formed in low-density regions of the initial universe and have drifted until now to the outer parts of the filaments and walls of the large-scale structure. Furthermore, our results, together with actual cosmological simulations, show that LSBs are caused by a mixture of nature and nurture.

Dark matter dominance at all radii in the superthin galaxy UGC 7321

We model the shape and density profile of the dark matter halo of the low surface brightness, superthin galaxy UGC 7321, using the observed rotation curve and the Hi scale height data as simultaneous constraints. We treat the galaxy as a gravitationally coupled system of stars and gas, responding to the gravitational potential of the dark matter halo. An isothermal halo of spherical shape with a core density in the range of 0.039–0.057M⊙pc-3 and a core radius between 2.5 and 2.9kpc, gives the best fit to the observations for a range of realistic gas parameters assumed. We find that the best-fit core radius is only slightly higher than the stellar disc scale length (2.1kpc), unlike the case of the high surface brightness galaxies where the halo core radius is typically 3–4 times the disc scale length of the stars. Thus our model shows that the dark matter halo dominates the dynamics of the low surface brightness, superthin galaxy UGC 7321 at all radii, including the inner parts of the galaxy.