[Paper Review] Multi-Wavelength Properties of Barred Galaxies in the Local Universe: Environment and evolution across the Hubble sequence

Lea Giordano, Kim‐Vy Tran+2 more|arXiv (Cornell University)|Nov 7, 2011

Galaxies: Formation, Evolution, Phenomena3 citations

TL;DR

This study investigates bar fractions in disk galaxies across isolated and dense environments using H-band and optical imaging, finding no significant environmental dependence (30–35% bar fraction) but a strong morphological trend: early-type spirals (Sa–Sb) have ~50% bar fractions, twice that of late-type spirals (Sbc–Sm), suggesting secular evolution via bar-driven pseudo-bulge formation. The results support that bars form prior to cluster assembly and that S0 galaxies likely arise from disk transformation via harassment in dense environments.

ABSTRACT

We investigate possible environmental and morphological trends in the $z\sim0$ bar fraction using two carefully selected samples representative of a low-density environment (the isolated galaxies from the AMIGA sample) and of a dense environment (galaxies in the Virgo cluster). Galaxies span a stellar mass range from $10^8$ to $10^{12}$M$_{\odot}$ and are visually classified using both high-resolution NIR (H-band) imaging and optical exttt{rgb} images. We find that the bar fraction in disk galaxies is independent of environment suggesting that bar formation may occur prior to the formation of galaxy clusters. The bar fraction in early type spirals ($Sa-Sb$) is $\sim$50%, which is twice as high as the late type spirals ($Sbc-Sm$). The higher bar fraction in early type spirals may be due to the fact that a significant fraction of their bulges are pseudo-bulges which form via the buckling instability of a bar. i.e. a large part of the Hubble sequence is due to secular processes which move disc galaxies from late to early types. There is a hint of a higher bar fraction with higher stellar masses which may be due to the susceptibility to bar instabilities as the baryon fractions increase in halos of larger masses. Overall, the $S0$ population has a lower bar fraction than the $Sa-Sb$ galaxies and their barred fraction drops significantly with decreasing stellar mass. This supports the notion that $S0s$ form via the transformation of disk galaxies that enter the cluster environment. The gravitational harassment thickens the stellar disks, wiping out spiral patterns and eventually erasing the bar - a process that is more effective at lower galaxy masses.

Motivation & Objective

• To determine whether galaxy environment influences the bar fraction in disk galaxies at z ~ 0.
• To investigate how bar fraction varies with disk morphology across the Hubble sequence.
• To test whether the morphology-density relation is driven by environmental effects such as gravitational harassment.
• To assess the role of secular processes, such as bar-induced pseudo-bulge formation, in morphological evolution.
• To compare barred disk fractions in isolated field galaxies (AMIGA sample) and Virgo cluster galaxies using consistent, high-resolution visual classification.

Proposed method

• Utilized high-resolution H-band (UKIDSS) and optical (SDSS DR7) imaging to enable robust visual classification of bars, minimizing dust and star formation contamination.
• Selected two representative samples: isolated field galaxies from the AMIGA catalog and Virgo cluster galaxies, spanning stellar masses from 10⁸ to 10¹² M⊙ and Hubble types S0 to Sm.
• Classified galaxies visually using both H-band and RGB images to ensure accurate identification of bars and disk components.
• Divided disk galaxies into three morphological classes: S0–S0a (lenticulars), Sa–Sb (early-type spirals), and Sbc–Sm (late-type spirals) for comparative analysis.
• Measured bar fraction as the ratio of barred disks to total disk galaxies within each environment and morphological class.
• Validated results using an independent optically selected sample (NA10) to test robustness of bar fraction constancy across density regimes.

Experimental results

Research questions

• RQ1 Does the bar fraction in disk galaxies depend on local environment, such as isolated fields versus dense clusters?
• RQ2 How does the bar fraction vary across different morphological types (S0, Sa–Sb, Sbc–Sm) in both field and cluster environments?
• RQ3 Is the higher bar fraction in early-type spirals (Sa–Sb) due to intrinsic properties like baryon fraction or secular evolution processes?
• RQ4 To what extent does environmental harassment in clusters suppress or erase bars, particularly in low-mass galaxies?
• RQ5 Can the morphology-density relation be explained by environmental transformation of disk galaxies into S0s via bar destruction?

Key findings

• The barred disk fraction is remarkably constant at 30–35% in both isolated field galaxies and Virgo cluster galaxies, indicating no significant environmental dependence.
• Early-type spirals (Sa–Sb) have a bar fraction of ~50%, which is approximately twice that of late-type spirals (Sbc–Sm), whose bar fraction is less than 25%.
• Lenticular galaxies (S0–S0a) have a lower bar fraction than early-type spirals, with the barred fraction dropping below 10% in low-mass S0s, suggesting environmental disruption.
• The bar fraction in massive S0s (M⋆ > 10¹⁰ M⊙) is ~50%, similar to early-type spirals, but declines sharply in low-mass S0s, supporting a harassment-driven formation mechanism.
• The constancy of the bar fraction across environments implies that bars form prior to galaxy cluster assembly, consistent with the lack of strong evolution in bar fraction with redshift.
• The results support that secular processes, particularly bar-driven pseudo-bulge formation via buckling instabilities, play a key role in morphological evolution from late-type to early-type spirals.