[论文解读] The Fornax Deep Survey (FDS) with the VST: III. Low Surface Brightness (LSB) dwarfs and Ultra Diffuse Galaxies (UDGs) in the center of the Fornax cluster

A. Venhola, R. F. Peletier+17 more|arXiv (Cornell University)|Oct 12, 2017

Galaxies: Formation, Evolution, Phenomena参考文献 94被引用 66

一句话总结

This study identifies and analyzes a deep sample of low surface brightness galaxies in the Fornax cluster core using VST/FDS data, distinguishing LSB dwarfs from UDGs and comparing their properties.

ABSTRACT

Studies of low surface brightness (LSB) galaxies in nearby clusters have revealed a sub-population of extremely diffuse galaxies with central surface brightness $μ_{0,g'}$ > 24 mag arcsec$^{-2}$ and effective radius between 1.5 kpc < R$_{e}$ < 10 kpc. The origin of these Ultra Diffuse Galaxies (UDGs) is still unclear, although several theories have been suggested. We exploit the deep g', r' and i'-band images of the Fornax Deep Survey (FDS), in order to identify LSB galaxies in the center of the Fornax cluster. We identified visually all extended structures having r'-band central surface brightness of $μ_{0,r'}$ > 23 mag arcsec$^{-2}$. We classified the objects based on their appearance and performed 2D Sérsic model fitting with GALFIT. We analyzed their distribution and orientations in the cluster, and studied their colors and compared the LSB galaxies in Fornax with those in other environments. Our sample consists of 205 galaxies of which 196 are LSB dwarfs (with R$_e$ < 1.5kpc) and nine are UDGs (R$_e$ > 1.5 kpc). We show that the UDGs have g'-r' colors similar to those of LSB dwarfs. The largest UDGs in our sample appear different from the other LSB galaxies, in that they are significantly more elongated and extended, whereas the smaller UDGs differ from the LSB dwarfs only by their effective radii. We do not find clear differences between the structural parameters of the UDGs in our sample and those of UDGs in other galaxy environments. We find that the dwarf LSB galaxies in our sample are less concentrated in the cluster center than the galaxies with higher surface brightness, and that their number density drops in the core of the cluster. Our findings are consistent with the small UDGs forming the tail of a continuous distribution of less extended LSB galaxies. However, the elongated and distorted shapes of the large UDGs could imply that they are tidally disturbed galaxies.

研究动机与目标

• Identify and catalog LSB galaxies in the central Fornax fields using deep g', r', i' imaging.
• Distinguish Ultra Diffuse Galaxies (UDGs) from LSB dwarfs by effective radius criteria.
• Measure structural parameters via 2D Sérsic fits and analyze color, distribution, and orientation.
• Compare Fornax LSB populations with those in other environments (e.g., Centaurus group).
• Assess whether UDGs form a continuum with the broader LSB dwarf population.

提出的方法

• Visual identification of extended, low surface brightness sources with μ0,r' ≥ 23 mag/arcsec^2 and diameter d27 ≥ 10 arcsec.
• 2D Sérsic modeling with GALFIT to derive structural parameters of galaxies.
• Radial distribution and orientation analysis with respect to cluster center and member galaxies.
• Color analysis using g'−r' and r'−i' colors to compare LSB dwarfs and UDGs.
• Comparison of Fornax LSB properties with LSBs in other environments (e.g., Centaurus group).
• Data reduction includes dedicated background subtraction, illumination correction, and careful artifact masking.

实验结果

研究问题

• RQ1 Do UDGs form a continuum with the dwarf LSB population in Fornax?
• RQ2 What are the colors, sizes, and Sérsic profiles of Fornax LSB dwarfs and UDGs and how do they compare to other environments?
• RQ3 How does the radial distribution and cluster-centric concentration of LSB dwarfs differ from higher surface brightness galaxies?
• RQ4 Are the largest UDGs preferentially elongated or tidally disturbed, and what does this imply for their origin?

主要发现

• Final sample includes 205 galaxies: 196 LSB dwarfs (Re < 1.5 kpc) and 9 UDGs (Re ≥ 1.5 kpc).
• UDGs have g′−r′ colors similar to LSB dwarfs of the same luminosity.
• Largest UDGs (Re ≥ 3 kpc) tend to be more elongated and extended than other LSB galaxies.
• Smaller UDGs differ from LSB dwarfs mainly by slightly larger effective radii.
• No clear differences between the structural parameters of Fornax UDGs and UDGs in other environments.
• Dwarf LSB galaxies in Fornax are less concentrated toward the cluster center, with their number density dropping within 180 kpc of the center.
• Compared with Centaurus group LSB dwarfs, the smallest LSB dwarfs have similar colors, sizes, and Sérsic profiles; in Centaurus colors become bluer with fainter magnitudes, likely due to lower mass and environmental influence.