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We present HI observations of four giant low surface brightness (GLSB) galaxies UGC 1378, UGC 1922, UGC 4422 and UM 163 using the Giant Meterwave Radio Telescope (GMRT). We include HI results on UGC 2936, UGC 6614 and Malin 2 from literature. HI is detected from all the galaxies and the extent is roughly twice the optical size; in UM 163, HI is detected along a broken disk encircling the optical galaxy. We combine our results with those in literature to further understand these systems. The main results are the following: (1) The peak HI surface densities in GLSB galaxies are several times 10^21 cm^{-2} . The HI mass is between 0.3 - 4 x 10^10 M_Sun/yr, dynamical mass ranges from a few times 10^11 M_Sun/yr to a few times 10^12 M_Sun/yr. (2) The rotation curves of GLSB galaxies are flat to the outermost measured point with rotation velocities of the seven GLSB galaxies being between 225 and 432 km s^{-1}. (3) Recent star formation traced by near-ultraviolet emission in five GLSB galaxies in our sample appears to be located in rings around the galaxy centre. We suggest that this could be due to a stochastic burst of star formation at one location in the galaxy being propagated along a ring over a rotation period. (4) The Hi is correlated with recent star formation in five of the seven GLSB galaxies.
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How does the low surface brightness galaxies (LSBGs) form stars and assemble the stellar mass is one of the most important questions to understand the LSBG population. We select a sample of 381 HI bright LSBGs with both Far Ultraviolet (FUV) and Near Infrared (NIR) observation to investigate the star formation rate (SFR) and stellar mass scales, and the growth mode. We measure the UV and NIR radius of our sample, which represent the star-forming and stellar mass distribution scales. We also compare the UV and H band radius-stellar mass relation with the archive 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 UV radii to understand the distribution of the 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 as the disk galaxies at the same stellar mass bins, while the star-forming activity of LSBGs happens at a larger radius than the high surface density galaxies, which may help to select the LSBG sample from the wide-field deep u band image survey. The HI also distributed at a larger radius, implying a steeper (or no) Kennicutt-Schmidt relation for LSBGs.
We present a study of the HI and optical properties of nearby ($z$ $le$ 0.1) Low Surface Brightness galaxies (LSBGs). We started with a literature sample of $sim$900 LSBGs and divided them into three morphological classes: spirals, irregulars and dwarfs. Of these, we could use $sim$490 LSBGs to study their HI and stellar masses, colours and colour magnitude diagrams, and local environment, compare them with normal, High Surface Brightness (HSB) galaxies and determine the differences between the three morphological classes. We found that LSB and HSB galaxies span a similar range in HI and stellar masses, and have a similar $M_{rm HI}$/$M_{star}$--$M_{star}$ relationship. Among the LSBGs, as expected, the spirals have the highest average HI and stellar masses, both of about 10$^{9.8}$ $M_odot$. The LSGBs ($g$--$r$) integrated colour is nearly constant as function of HI mass for all classes. In the colour magnitude diagram, the spirals are spread over the red and blue regions whereas the irregulars and dwarfs are confined to the blue region. The spirals also exhibit a steeper slope in the $M_{rm HI}$/$M_{star}$--$M_{star}$ plane. Within their local environment we confirmed that LSBGs are more isolated than HSB galaxies, and LSB spirals more isolated than irregulars and dwarfs. Kolmogorov-Smirnov statistical tests on the HI mass, stellar mass and number of neighbours indicates that the spirals are a statistically different population from the dwarfs and irregulars. This suggests that the spirals may have different formation and HI evolution than the dwarfs and irregulars.
We present Very Large Array ({sc vla}) and Westerbork Synthesis Radio Telescope ({sc wsrt}) 21-cm H{sc i} observations of 19 late-type low surface brightness (LSB) galaxies. Our main findings are that these galaxies, as well as having low surface brightnesses, have low H{sc i} surface densities, about a factor of $sim 3$ lower than in normal late-type galaxies. We show that LSB galaxies in some respects resemble the outer parts of late-type normal galaxies, but may be less evolved. LSB galaxies are more gas-rich than their high surface brightness counterparts. The rotation curves of LSB galaxies rise more slowly than those of HSB galaxies of the same luminosity, with amplitudes between 50 and 120~km~s$^{-1}$, and are often still increasing at the outermost measured point. The shape of the rotation curves suggests that LSB galaxies have low matter surface densities. We use the average total mass surface density of a galaxy as a measure for the evolutionary state, and show that LSB galaxies are among the least compact, least evolved galaxies. We show that both $M_{rm HI}/L_B$ and $M_{rm dyn}/L_B$ depend strongly on central surface brightness, consistent with the surface brightness--mass-to-light ratio relation required by the Tully-Fisher relation. LSB galaxies are therefore slowly evolving galaxies, and may well be low surface density systems in all respects.
Giant Low Surface Brightness (GLSB) galaxies are amongst the most massive spiral galaxies that we know of in our Universe. Although they fall in the class of late type spiral galaxies, their properties are far more extreme. They have very faint stellar disks that are extremely rich in neutral hydrogen gas but low in star formation and hence low in surface brightness. They often have bright bulges that are similar to those found in early type galaxies. The bulges can host low luminosity Active Galactic Nuclei (AGN) that have relatively low mass black holes. GLSB galaxies are usually isolated systems and are rarely found to be interacting with other galaxies. In fact many GLSB galaxies are found under dense regions close to the edges of voids. These galaxies have very massive dark matter halos that also contribute to their stability and lack of evolution. In this paper we briefly review the properties of this unique class of galaxies and conclude that both their isolation and their massive dark matter halos have led to the low star formation rates and the slower rate of evolution in these galaxies.
Giant low surface brightness galaxies (GLSBs) have flat discs extending up to ~100 kpc. Their formation is a puzzle for cosmological simulations in the cold dark matter scenario. We suggest that GLSBs might be the final product of the evolution of collisional ring galaxies. In fact, our simulations show that, approximately 0.5-1.5 Gyr after the collision which led to the formation of the ring galaxy, the ring keeps expanding and fades, while the disc becomes very large (~100 kpc) and flat. At this stage, our simulated galaxies match many properties of GLSBs (surface brightness profile, morphology, HI spectrum and rotation curve).
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