Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userLow-surface-brightness spheroidal galaxies as Milgromian isothermal spheres
66
0
0.0
(
0
)
Authors
R.H. Sanders
Ask ChatGPT about the research
No Arabic abstract
I consider a sample of eight pressure-supported low-surface brightness galaxies in terms of Milgroms modified Newtonian dynamics (MOND). These objects include seven nearby dwarf spheroidal galaxies -- Sextans, Carina, Leo II, Sculptor, Draco, Leo I, Fornax, and the ultra-diffuse galaxy DF44. The objects are modelled as Milgromian isotropic isothermal spheres characterised by two parameters that are constrained by observations: the constant line-of-sight velocity dispersion and the central surface density. The velocity dispersion determines the total mass, and, with the implied mass-to-light ratio, the central surface brightness. This then specifies the radial run of surface brightness over the entire isothermal sphere. For these objects the predicted radial distribution of surface brightness is shown to be entirely consistent with observations. This constitutes a success for MOND that is independent of the reduced dynamical mass.
rate research
Read More
Dwarf spheroidal galaxies (dSphs) are mostly investigated in the Local Group. DSphs are difficult targets for observations because of their small size and very low surface brightness. Here we measure spectroscopic and photometric parameters of three candidates for isolated dSphs, KKH65=BTS23, KK180, and KK227, outside the Local Group. The galaxies are found to be of low metallicity and low velocity dispersion. They are among the lowest surface brightness objects in the Local Universe. According to the measured radial velocities, metallicities, and structural and photometric parameters, KKH65 and KK227 are representatives of the ultra-diffuse quenched galaxies. KKH65 and KK227 belong to the outer parts of the groups NGC3414 and NGC5371, respectively. KK180 is located in the Virgo cluster infall region.
With the aim of assessing if low surface brightness galaxies host stellar bars, and study the dependence of the occurrence of bars as a function of surface brightness, we use the Galaxy Zoo 2 dataset to construct a large volume-limited sample of galaxies, and segregate the galaxies as low and high surface brightness in terms of their central surface brightness. We find that the fraction of low surface brightness galaxies hosting strong bars is systematically lower than the one found for high surface brightness galaxies. The dependence of the bar fraction on the central surface brightness is mostly driven by a correlation of the surface brightness with the spin and the gas-richness of the galaxies, showing only a minor dependence on the surface brightness. We also find that the length of the bars shows a strong dependence on the surface brightness, and although some of this dependence is attributed to the gas content, even at fixed gas-to-stellar mass ratio, high surface brightness galaxies host longer bars than their low surface brightness counterparts, which we attribute to an anticorrelation of the surface brightness with the spin.
The existence of galaxies with a surface brightness $mu$ lower than the night sky has been known since three decades. Yet, their formation mechanism and emergence within a $rmLambda CDM$ universe has remained largely undetermined. For the first time, we investigated the origin of Low Surface Brightness (LSB) galaxies with M$_{star}$$sim$10$^{9.5-10}$M$_{odot}$, which we are able to reproduce within hydrodynamical cosmological simulations from the NIHAO suite. The simulated and observed LSBs share similar properties, having large HI reservoir, extended star formation histories and effective radii, low S{e}rsic index and slowly rising rotation curves. The formation mechanism of these objects is explored: simulated LSBs form as a result of co-planar co-rotating mergers and aligned accretion of gas at early times, while perpendicular mergers and mis-aligned gas accretion result in higher $mu$ galaxies by $z$=0. The larger the merger, the stronger the correlation between merger orbital configuration and final $mu$. While the halo spin parameter is consistently high in simulated LSB galaxies, the impact of halo concentration, feedback-driven gas outflows and merger time only plays a minor-to-no role in determining $mu$. Interestingly, the formation scenario of such `classical LSBs differs from the one of less massive, M$_{star}$$sim$10$^{7-9}$M$_{odot}$, Ultra-Diffuse Galaxies, the latter resulting from the effects of SNae driven gas outflows: a M$_{star}$ of $sim$10$^9$M$_{odot}$ thus represents the transition regime between a feedback-dominated to an angular momentum-dominated formation scenario in the LSB realm. Observational predictions are offered regarding spatially resolved star formation rates through LSB discs: these, together with upcoming surveys, can be used to verify the proposed emergence scenario of LSB galaxies.
Our statistical understanding of galaxy evolution is fundamentally driven by objects that lie above the surface-brightness limits of current wide-area surveys (mu ~ 23 mag arcsec^-2). While both theory and small, deep surveys have hinted at a rich population of low-surface-brightness galaxies (LSBGs) fainter than these limits, their formation remains poorly understood. We use Horizon-AGN, a cosmological hydrodynamical simulation to study how LSBGs, and in particular the population of ultra-diffuse galaxies (UDGs; mu > 24.5 mag arcsec^-2), form and evolve over time. For M* > 10^8 MSun, LSBGs contribute 47, 7 and 6 per cent of the local number, mass and luminosity densities respectively (~85/11/10 per cent for M* > 10^7 MSun). Todays LSBGs have similar dark-matter fractions and angular momenta to high-surface-brightness galaxies (HSBGs; mu < 23 mag arcsec^-2), but larger effective radii (x2.5 for UDGs) and lower fractions of dense, star-forming gas (more than x6 less in UDGs than HSBGs). LSBGs originate from the same progenitors as HSBGs at z > 2. However, LSBG progenitors form stars more rapidly at early epochs. The higher resultant rate of supernova-energy injection flattens their gas-density profiles, which, in turn, creates shallower stellar profiles that are more susceptible to tidal processes. After z ~ 1, tidal perturbations broaden LSBG stellar distributions and heat their cold gas, creating the diffuse, largely gas-poor LSBGs seen today. In clusters, ram-pressure stripping provides an additional mechanism that assists in gas removal in LSBG progenitors. Our results offer insights into the formation of a galaxy population that is central to a complete understanding of galaxy evolution, and which will be a key topic of research using new and forthcoming deep-wide surveys.
We investigate the formation and properties of low surface brightness galaxies (LSBGs) with $M_{*} > 10^{9.5} mathrm{M_{odot}}$ 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 disks in EAGLE, which are comparable in size to observed giant LSBGs, are built up via mergers. These galaxies are found to inhabit dark matter halos with a higher spin in their inner regions ($<0.1r_{200c}$), even when excluding the effects of baryonic physics by considering matching halos from a dark matter only simulation with identical initial conditions.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
