On the properties of compact groups identified in different photometric bands

Taverna, Antonela; Díaz-Giménez, Eugenia; Zandivarez, Ariel; Joray, Francisco; Kanagusuku, María José

doi:10.1093/mnras/stw1383

Cited by 13 publications

(14 citation statements)

References 25 publications

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“…The slight differences are caused by the wavebands, lightcones, and galaxy blending method. Similarly, the fraction of Real CGs found by Díaz-Giménez & Zandivarez (2015) (DGZ15) and Taverna et al (2016) (TDGZ16) were slightly higher than what we find here, but this is because we only compare here to our modified algorithm, which produces a lower fraction of Real CGs. Also, the fraction of Real CGs found with the GII SAM was higher in Díaz-Giménez et al…”

Section: Effects Of the Other Parameterscontrasting

confidence: 50%

“…Moreover, DGM10 found that the frequency (space density) of CGs was roughly 10 times higher in the simulations than observed, suggesting that the HCG sample was 90 per cent incomplete, mainly in groups dominated by a single galaxy (as previously noted by Prandoni et al 1994). In subsequent studies by our team (Díaz-Giménez et al 2012;Díaz-Giménez & Zandivarez 2015;Taverna et al 2016;Díaz-Giménez et al 2018), CGs were extracted from the public outputs of different SAMs based on different physics or from those of older SAMs run on the dark matter haloes extracted from cosmological simulations run with different cosmological parameters. These studies led to different fractions of physically dense groups.…”

Section: Introductionmentioning

confidence: 52%

“…We worked in two different wavebands, and therefore these values vary accordingly. For catalogues in the SDSS-r band, we adopted µ lim = 26.33, while the equivalent value for the sample identified in the Ks band is µ lim = 23.6 (for a full description, see Taverna et al 2016). The limiting magnitudes, m lim , are quoted in Table 2. Until recently, Hickson-like CGs have been usually identified in two steps: first, groups were identified in projection in the plane of sky; and second, a velocity filter was applied to the projected groups.…”

Section: The Compact Group Samplesmentioning

confidence: 99%

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Compact groups from semi-analytical models of galaxy formation – I. A comparative study of frequency and nature

Díaz-Giménez

Taverna

Zandivarez

et al. 2019

Monthly Notices of the Royal Astronomical Society

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Compact groups (CGs) of galaxies are defined as isolated and dense galaxy systems that appear to be a unique site of multiple galaxy interactions. Semi-analytical models of galaxy formation (SAMs) are a prime tool to understand CGs. We investigate how the frequency and the three-dimensional nature of CGs depends on the SAM and its underlying cosmological parameters. Extracting 9 lightcones of galaxies from 5 different SAMs and selecting CGs as in observed samples, we find that the frequency and nature of CGs depends strongly on the cosmological parameters. Moving from the WMAP1 to the WMAP7 and Planck cosmologies (increasing density of the Universe and decreasing normalisation of the power spectrum), the space density of CGs is decreased by a factor 2.5, while the fraction of CGs that are physically dense falls from 50 to 35 percent. The lower σ 8 leads to fewer dense groups, while the higher Ω m causes more chance alignments. However, with increased mass and spatial resolution, the fraction of CGs that are physically dense is pushed back up to 50 percent. The intrinsic differences in the SAM recipes also lead to differences in the frequency and nature of CGs, particularly those related to how SAMs treat orphan galaxies. We find no dependence of CG properties on the flux limit of the mock catalogues nor on the waveband in which galaxies are selected. One should thus be cautious when interpreting a particular SAM for the frequency and nature of CGs.

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Section: Effects Of the Other Parameterscontrasting

confidence: 50%

Section: Introductionmentioning

confidence: 52%

Section: The Compact Group Samplesmentioning

confidence: 99%

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Compact groups from semi-analytical models of galaxy formation – I. A comparative study of frequency and nature

Díaz-Giménez

Taverna

Zandivarez

et al. 2019

Monthly Notices of the Royal Astronomical Society

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“…1983;Nolthenius & White e.g. 1987; see also Table 5 in Díaz-Giménez et al 2012, Taverna et al 2016 and references therein). Here we invoke an algorithm with a set of tunable parameters that allows us to investigate how the demographics of a CG sample depend on individual parameters.…”

Section: Identification Of Cgs In the Millennium Simulation Galaxy Camentioning

confidence: 99%

The Occurrence of Compact Groups of Galaxies through Cosmic Time

Wiens

Wenger

Tzanavaris

et al. 2019

ApJ

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We use the outputs of a semianalytical model of galaxy formation run on the Millennium Simulation to investigate the prevalence of 3D compact groups (CGs) of galaxies from z = 11 to 0. Our publicly available code identifies CGs using the 3D galaxy number density, the mass ratio of secondary+tertiary to the primary member, mass density in a surrounding shell, the relative velocities of candidate CG members, and a minimum CG membership of three. We adopt "default" values for the first three criteria, representing the observed population of Hickson CGs at z = 0. The percentage of nondwarf galaxies (M > 5 × 10 8 h −1 M ) in CGs peaks near z ∼ 2 for the default set and in the range of z ∼ 1-3 for other parameter sets. This percentage declines rapidly at higher redshifts (z 4), consistent with the galaxy population as a whole being dominated by low-mass galaxies excluded from this analysis. According to the most liberal criteria, 3% of nondwarf galaxies are members of CGs at the redshift where the CG population peaks. Our default criteria result in a population of CGs at z < 0.03 with number densities and sizes consistent with Hickson CGs. Tracking identified CG galaxies and merger products to z = 0, we find that 16% of nondwarf galaxies have been CG members at some point in their history. Intriguingly, the great majority (96%) of z = 2 CGs have merged to a single galaxy by z = 0. There is a discrepancy in the velocity dispersions of Millennium Simulation CGs compared to those in observed CGs, which remains unresolved.

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“…The surveys have different apparent magnitude limits, different wavebands, and may or may not have spectroscopic information. Galaxies selected in different wavebands will form groups with different physical characteristics (Taverna et al 2016). In addition, the limits imposed in the criteria are arbitrary and can change depending on the identifier.…”

Section: Introductionmentioning

confidence: 99%

Compact groups from semi-analytical models of galaxy formation -- III: purity and completeness of Hickson-like catalogues

Taverna,

Diaz-Gimenez,

Zandivarez

et al. 2022

Preprint

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Many catalogues of isolated compact groups of galaxies (CGs) have been extracted using Hickson's criteria to identify isolated, dense systems of galaxies, with at least three or four galaxies concordant in magnitude and redshift. But is not clear to what extent the catalogues of CGs are complete and reliable, relative to 3D truly isolated, dense groups. Using five different semi-analytical models of galaxy formation (SAMs), we identify isolated dense groups in 3D real space, containing at least three galaxies. We then build mock redshift space galaxy catalogues and run a Hickson-like CG finder. We find that the Hickson-like algorithm in redshift space is poor at recovering 3D CGs of at least 3 galaxies, with a purity of ∼ 10% and a completeness of ∼ 22%. Among the ∼ 90% of spurious systems, typically 60% are dense structures that failed the 3D isolation criteria, while the remaining 40% are chance alignments of galaxies along the line of sight, nearly all of which are within regular groups, with some variation with the SAM used for the analysis. In other words, while only 10% of CGs are isolated dense groups, as intended, half are dense structures embedded within larger groups, and one-third are chance alignments within larger groups. The low completeness of the extracted CG sample is mainly due to the flux limits of the selection criteria. Our results suggest that a new observational algorithm to identify compact groups in redshift space is required to obtain dense isolated galaxy systems.

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On the properties of compact groups identified in different photometric bands

Cited by 13 publications

References 25 publications

Compact groups from semi-analytical models of galaxy formation – I. A comparative study of frequency and nature

Compact groups from semi-analytical models of galaxy formation – I. A comparative study of frequency and nature

The Occurrence of Compact Groups of Galaxies through Cosmic Time

Compact groups from semi-analytical models of galaxy formation -- III: purity and completeness of Hickson-like catalogues

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