What made discy galaxies giant?

Abstract

I studied giant discy galaxies with optical radii more than 30 kpc. The comparison of these systems with discy galaxies of moderate sizes revealed that they tend to have higher rotation velocities, B-band luminosities, H masses and dark-to-luminous mass ratios. The giant discs follow the trend log(M HI )(R 25 ) found for normal size galaxies. It indicates the absence of the peculiarities of evolution of star formation in these galaxies. The H mass to luminosity ratio of giant galaxies appears not to differ from that of normal size galaxies, giving evidences in favor of similar star formation efficiency. I also found that the bars and rings occur more frequently among giant discs. I performed mass-modelling of the subsample of 18 giant galaxies with available rotation curves and surface photometry data and constructed χ 2 maps for the parameters of their dark matter haloes. These estimates indicate that giant discs tend to be formed in larger more massive and rarified dark haloes in comparison to moderate size galaxies. However giant galaxies do not deviate significantly from the relations between the optical sizes and dark halo parameters for moderate size galaxies. These findings can rule out the catastrophic scenario of the formation of at least most of giant discs, since they follow the same relations as normal discy galaxies. The giant sizes of the discs can be due to the high radial scale of the dark matter haloes in which they were formed.

A Malin 1 ‘cousin’ with counter-rotation: internal dynamics and stellar content of the giant low surface brightness galaxy UGC 1922

“…They concluded that the gLSB disc of Malin 2 could have been formed because of unusual properties of the dark halo of the galaxy, namely, its large radial scale and low central density. Saburova (2018) came to a similar conclusion for a sample of giant disc HSB galaxies.…”

Observational insights on the origin of giant low surface brightness galaxies

“…The question of the gLSBGs formation remains open (Kasparova et al 2014;Galaz et al 2015;Hagen et al 2016;Boissier et al 2016;Saburova 2018;Saburova et al 2021) despite their importance as a "stress test" for the ΛCDM cosmology. An in-plane major merger of two giant spiral galaxies with fine-tuned orbital parameters can end-up in a system resembling a gLSBG (Saburova 2018). So does a triple major merger with two gas-rich galaxies when a host's hot halo gas cooling is triggered by the cold gas supply from the infalling systems and later forms a giant extended disc (Zhu et al 2018).…”

“…Only a couple of dozens gLSBGs were found since the discovery of the prototypical galaxy Malin 1 in the 80s by Bothun et al (1987) so they are considered extremely rare. The question of the gLSBGs formation remains open (Kasparova et al 2014;Galaz et al 2015;Hagen et al 2016;Boissier et al 2016;Saburova 2018;Saburova et al 2021) despite their importance as a "stress test" for the ΛCDM cosmology. An in-plane major merger of two giant spiral galaxies with fine-tuned orbital parameters can end-up in a system resembling a gLSBG (Saburova 2018).…”

“…We performed spectral long-slit observations at the 6-m BTA telescope of SAO RAS using SCORPIO and SCORPIO-2 spectrographs (Afanasiev & Moiseev 2005, 2011. The details of the data reduction and analysis could be found in Saburova (2018); Saburova et al (2019Saburova et al ( , 2021. The most prominent result of these observations is the discovered kinematically decoupled components in UGC 1922 and UGC 1382.…”

UGC 1378 – a Milky Way sized galaxy embedded in a giant low surface brightness disc

“…Our deep imaging reveals the complex E-mail:saburovaann@gmail.com structure of UGC 1378, including a high-surface brightness (HSB) bulge and disc, and a gLSB disc. In common with other gLS-BGs, UGC 1378 has prominent spiral arms (like Malin 1, Malin 2, UGC 1922, UGC 1382, Boissier et al 2016Galaz et al 2015;Hagen et al 2016;Kasparova et al 2014;Saburova 2018), resembling the Milky Way immersed in a gLSB disc.…”