# SDSS IV MaNGA: Bar pattern speed in Milky Way Analogue galaxies

**Authors:** Luis Garma-Oehmichen, Héctor Hernández-Toledo, Erik Aquino-Ortíz, Luis Martinez-Medina, Ivanio Puerari, Mariana Cano-Díaz, Octavio Valenzuela, José Antonio Vázquez-Mata, Tobias Géron, Luis Artemio Martínez-Vázquez, Richard Lane  
**arXiv:** [2210.11424](https://arxiv.org/abs/2210.11424)  
**Date:** 2022-10-20  
**Summary page:** https://www.summarizepaper.com/en/paper/2210.11424v1/

## Key points

- Stellar bars produce secular effects that depend on their pattern speed
- Pattern speed is the most difficult observational parameter to estimate
- Researchers measured bar pattern speed of 97 Milky-Way Analogue galaxies from the MaNGA survey using the Tremaine-Weinberg method
- Sample was selected by constraining stellar mass and morphological type
- Researchers improved measurements by weighting three independent estimates of disc position angle and fitting a kinematic model to H$_\alpha$ velocity maps while correcting for non-circular motions produced by the bar
- Complete sample had a smooth distribution of bar pattern speeds, corotation radius, and rotation rate
- Two sets of correlations were found between bar pattern speed, bar length, logarithmic stellar mass, disc circular velocity, and bar rotation rate
- Stronger correlations were observed when sample was constrained by inclination and relative orientation
- Fraction of ultra-fast bars reduced from 20% to 10% when sample was constrained
- A sub-sample of 25 Milky Way analogue galaxies with distributions in good agreement with current estimations for our Galaxy was obtained

## Summary

Stellar bars are known to produce secular effects that strongly depend on their pattern speed, which is also the most difficult observational parameter to estimate. In a recent study, published in Monthly Notices of the Royal Astronomical Society, a team of researchers led by Luis Garma-Oehmichen from the National Autonomous University of Mexico measured the bar pattern speed of 97 Milky-Way Analogue galaxies from the MaNGA survey using the Tremaine-Weinberg method. The sample was selected by constraining the stellar mass and morphological type. The researchers improved their measurements by weighting three independent estimates of the disc position angle and fitting a kinematic model to H$_\alpha$ velocity maps to recover the disc rotation curve while correcting for non-circular motions produced by the bar. The complete sample had a smooth distribution of bar pattern speeds ($\Omega_{Bar}=28.14^{+12.30}_{-9.55}$ km s$^{-1}$ kpc $^{-1}$), corotation radius ($R_{CR} = 7.82^{+3.99}_{-2.96}$ kpc), and rotation rate ($\mathcal{R} = 1.35^{+0.60}_{-0.40}$). The researchers found two sets of correlations: (i) between bar pattern speed, bar length, and logarithmic stellar mass; and (ii) between bar pattern speed, disc circular velocity, and bar rotation rate. When they constrained their sample by inclination within $30 \degree < i < 60 \degree$ and relative orientation $20\degree<|PA_{disc} - PA_{bar}|<70\degree$, they observed stronger correlations and reduced the fraction of ultra-fast bars from 20% to 10% of the sample. The study suggests that a significant fraction of ultra-fast bars in their sample could be associated with geometric limitations in the Tremaine-Weinberg method used for measuring pattern speeds. By further constraining bar size and disc circular velocity, they obtained a sub-sample of 25 Milky Way analogue galaxies with distributions $\Omega_{Bar}=30.48^{+10.94}_{−6.57 }$ km s${^−1 }$ kpc${^−1 }$, $R_{CR } = 6 .77 ^{ + 2 .32 } _{ − 1 .91 }$ kpc ,and $\mathcal { R } = 1 .45 ^{ + 0 .57 } _{ − 0 .43 }$, which were in good agreement with current estimations for our Galaxy .