The Fornax Deep Survey (FDS) with VST XII: Low surface brightness dwarf galaxies in the Fornax cluster

Abstract

Context. Low surface brightness (LSB) dwarf galaxies in galaxy clusters are an interesting group of objects as their contribution to the galaxy luminosity function and their evolutionary paths are not yet clear. Increasing the completeness of our galaxy catalogs is crucial for understanding these galaxies, which have effective surface brightnesses below 23 mag arcsec −2 (in optical). Progress is continuously being made via the performance of deep observations, but detection depth and the quantification of the completeness can also be improved via the application of novel approaches in object detection. For example, the Fornax Deep Survey (FDS) has revealed many faint galaxies that can be visually detected from the images down to a surface brightness level of 27 mag arcsec −2 , whereas traditional detection methods, such as using Source Extractor (SE), fail to find them. Aims. In this work we use a max-tree based object detection algorithm (Max-Tree Objects, MTO) on the FDS data in order to detect previously undetected LSB galaxies. After extending the existing Fornax dwarf galaxy catalogs with this sample, our goal is to understand the evolution of LSB dwarfs in the cluster. We also study the contribution of the newly detected galaxies to the faint end of the luminosity function. Methods. We test the detection completeness and parameter extraction accuracy of MTO using simulated and real images. We then apply MTO to the FDS images to identify LSB candidates. The identified objects are fitted with 2D Sérsic models using GALFIT and classified as imaging artifacts, likely cluster members, or background galaxies based on their morphological appearance, colors, and structure.Results. With MTO, we are able to increase the completeness of our earlier FDS dwarf catalog (FDSDC) 0.5-1 mag deeper in terms of total magnitude and surface brightness. Due to the increased accuracy in measuring sizes of the detected objects, we also add many small galaxies to the catalog that were previously excluded as their outer parts had been missed in detection. We detect 265 new LSB dwarf galaxies in the Fornax cluster, which increases the total number of known dwarfs in Fornax to 821. Using the whole cluster dwarf galaxy population, we show that the luminosity function has a faint-end slope of α=-1.38±0.02. We compare the obtained luminosity function with different environments studied earlier using deep data but do not find any significant differences. On the other hand, the Fornax-like simulated clusters in the IllustrisTNG cosmological simulation have shallower slopes than found in the observational data. We also find several trends in the galaxy colors, structure, and morphology that support the idea that the number of LSB galaxies is higher in the cluster center due to tidal forces and the age dimming of the stellar populations. The same result also holds for the subgroup of large LSB galaxies, so-called ultra-diffuse galaxies.

The Exploration of Local VolumE Satellites (ELVES) Survey: A Nearly Volume-limited Sample of Nearby Dwarf Satellite Systems

“…Such sources are likely to get "shredded" (i.e., over-deblended). More advanced algorithms (e.g., Akhlaghi & Ichikawa 2015;Lang et al 2016;Melchior et al 2018;Robotham et al 2018;Haigh et al 2021) are being developed that demonstrate promise for LSB dwarf surveys (Venhola et al 2021). While our search algorithm is more complicated than simply using SExtractor, it still does make use of SExtractor in multiple "hotand-cold" runs (i.e., runs with high and low thresholds; see below) intermixed with aggressive masking.…”

“…Pushing to larger distances, deep surveys are starting to map the dwarf content of various galaxy groups (e.g., Greco et al 2018b;Zaritsky et al 2019;Habas et al 2020;Prole et al 2021;Tanoglidis et al 2021b). At the highest host mass end, nearby galaxy clusters are also being surveyed for dwarf satellites (Ferrarese et al 2012(Ferrarese et al , 2016(Ferrarese et al , 2020Muñoz et al 2015;Eigenthaler et al 2018;Venhola et al 2018Venhola et al , 2021La Marca et al 2022;Su et al 2021).…”

The Exploration of Local VolumE Satellites (ELVES) Survey: A Nearly Volume-Limited Sample of Nearby Dwarf Satellite Systems

“…More advanced algorithms (e.g. Akhlaghi & Ichikawa 2015;Lang et al 2016;Robotham et al 2018;Melchior et al 2018;Haigh et al 2021) are being developed that demonstrate promise for LSB dwarf surveys (Venhola et al 2021). While our search algorithm is more complicated than simply using SExtractor, it still does make use of SExtractor in multiple 'hot-and-cold' runs (i.e.…”

“…Greco et al 2018b;Zaritsky et al 2019;Habas et al 2020;Tanoglidis et al 2021;Prole et al 2021). At the highest host mass end, nearby galaxy clusters are also being surveyed for dwarf satellites (Ferrarese et al 2012(Ferrarese et al , 2016(Ferrarese et al , 2020Muñoz et al 2015;Eigenthaler et al 2018;Venhola et al 2018Venhola et al , 2021Su et al 2021;La Marca et al 2021).…”

Photometric properties of nuclear star clusters and their host galaxies in the Fornax cluster

“…Indeed, we find significant correlations for both nucleated and non-nucleated galaxies for 10 7 M ⊙ < M * ,galaxy < 10 8.5 M ⊙ . The trend between surface brightness and axial ratio is investigated in detail in Venhola et al (2021).…”