Late-type Low Surface Brightness Galaxies Research Articles

Abundance gradients in low surface brightness spirals: clues on the origin of common gradients in galactic discs

We acquired spectra of 141 HII regions in ten late-type low surface brightness galaxies (LSBGs). The analysis of the chemical abundances obtained from the nebular emission lines shows that metallicity gradients are a common feature of LSBGs, contrary to previous claims concerning the absence of such gradients in this class of galaxies. The average slope, when expressed in units of the isophotal radius, is found to be significantly shallower in comparison to galaxies of high surface brightness. This result can be attributed to the reduced surface brightness range measured across their discs, when combined with a universal surface mass density-metallicity relation. With a similar argument we explain the common abundance gradient observed in high surface brightness galaxy (HSBG) discs and its approximate dispersion. This conclusion is reinforced by our result that LSBGs share the same common abundance gradient with HSBGs, when the slope is expressed in terms of the exponential disc scale length.

How does the surface density and size of disc galaxies measured in hydrodynamic simulations correlate with the halo spin parameter?

Late-type low surface brightness galaxies (LSBs) are faint disc galaxies with central maximum stellar surface densities below 100 M⊙ pc−2. The currently favoured scenario for their origin is that LSBs have formed in fast-rotating haloes with large angular momenta. We present the first numerical evidence for this scenario using a suite of self-consistent hydrodynamic simulations of a 2.3 × 1011 M⊙ galactic halo, in which we investigate the correlations between the disc stellar/gas surface densities and the spin parameter of its host halo. A clear anticorrelation between the surface densities and the halo spin parameter λ is found. That is, as the halo spin parameter increases, the disc cutoff radius at which the stellar surface density drops below 0.1 M⊙ pc−2 monotonically increases, while the average stellar surface density of the disc within that radius decreases. The ratio of the average stellar surface density for the case of λ = 0.03 to that for the case of λ = 0.14 reaches more than 15. We demonstrate that the result is robust against variations in the baryon fraction, confirming that the angular momentum of the host halo is an important driver for the formation of LSBs.

EFFECTS OF CHAMELEON SCALAR FIELD ON ROTATION CURVES OF THE GALAXIES

We investigate the effects of chameleon scalar field to the effective density and pressure of a dark matter (DM) halo. The pressure is generated from the chameleonic fifth force on the matter. We demonstrate that the thick-shell nonsingular boundary condition which forbids singular point, leads to extremely stringent constraint on the matter-chameleon coupling when applied to galaxy. We argue that chameleon profile with central singularity is more likely to develop in general physical situation. The chameleonic fifth force from the chameleon profile with central singularity experienced by DM could significantly modify the rotation curve of galaxies. The chameleonic fifth force could generate steeper cusp to the rotation curves in any DM profiles starting from the Navarro–Frenk–White (NFW) to the pseudo-isothermal (ISO) profile. Upper limits on the coupling constant between the chameleon and DM are estimated from observational data of the late-type low surface brightness galaxies (LSB). It is in the order of β < 10-3.

Late-type dwarf irregular galaxies in the Virgo cluster -- I. H and red continuum data

We present H-alpha and red continuum observations for a sample of late-type low surface brightness (LSB) dwarf irregular galaxies(DIGs), consisting of all the m_B<17.2 ImIV and V galaxies in the Virgo cluster (VC), and compare them with a representative sample of VC high surface brightness (HSB) DIGs. Line fluxes and equivalent widths are listed for individual HII regions and total H-alpha emission is measured for the entire DIG. The HII regions we identified do not produce all the line emission. For LSBs with line emission we find star formation rates (SFR) of 6.9-43.0 10^{-3} M_sol/yr, ~10x weaker than for HSB objects. About 2 HII regions are detected per LSB galaxy; they are smaller and fainter than in HSB galaxies in the VC, have line equivalent widths ~50% of those in HSBs, and cover similar fractions of the galaxies. The line-emitting regions of LSB galaxies are preferentially located at the periphery of a galaxy, while in HSBs they tend to be central. The line strength of an HII region is correlated with the red continuum light underneath the region. No fundamental differences were identified in the star formation properties of the LSB and HSB dwarf galaxies we studied and infer that these galaxies must be similar, with the difference being the intensity of the present star-formation burst.

Are Low Surface Brightness Disks Young?

We reconsider the problem of the age of the stellar disks of late-type low surface brightness galaxies (LSBs) by making use of a new IMF recently derived from numerical fluid dynamics simulations (Padoan, Nordlund, & Jones 1997), and a new synthetic stellar population code, based on Jimenez & MacDonald (1997) evolutionary tracks and Kurucz atmospheric models (Kurucz 1992).

H I observations of low surface brightness galaxies: probing low-density galaxies

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.

An optical and H I study of late-type low surface brightness galaxies

An optical and H I study of late-type low surface brightness galaxies