# Multiwavelength Bulge-Disk Decomposition for the Galaxy M81 (NGC 3031). I. Morphology

**Authors:** Ye-Wei Mao, Jun-Yu Gong, Hua Gao, Si-Yue Yu  
**arXiv:** [2306.01605](https://arxiv.org/abs/2306.01605)  
**Date:** 2023-06-02  
**Summary page:** https://www.summarizepaper.com/en/paper/2306.01605v1/

## Key points

- Panchromatic investigation of the morphology of early-type spiral galaxy M81
- Bulge-disk decomposition performed at 20 different wavebands
- Morphological parameters derived for both bulge and disk
- Morphology of M81 varies with wavelength
- Sersic index and effective radius show variable-slope trend
- Position angle and axis ratio remain relatively constant in optical-NIR range
- Sersic index for bulge drops in UV bands, suggesting misidentification as pseudo-bulge or no bulge at high redshifts
- Future work includes studying spatially resolved spectral energy distributions (SEDs) for bulge and disk separately
- Importance of multiwavelength observations when studying galaxy morphology highlighted
- Findings have implications for understanding galaxy evolution over cosmic time and provide insights into structural properties.

## Summary

This paper presents a panchromatic investigation of the morphology of the early-type spiral galaxy M81. The authors perform a bulge-disk decomposition in M81 images at 20 different wavebands ranging from FUV to NIR, obtained with various telescopes including GALEX, Swift, SDSS, WIYN, 2MASS, WISE and Spitzer. They derive morphological parameters such as Sersic index, effective radius, position angle and axis ratio for both the bulge and the disk at all wavebands. This enables them to quantify the morphological K-correction for M81 and reproduce images of the bulge and disk at any waveband. The study reveals that the morphology of M81 varies with wavelength. The Sersic index and effective radius show a variable-slope trend with steeper variations at UV-optical bands and shallower variations at optical-NIR bands. On the other hand, the position angle and axis ratio remain relatively constant at least in the optical-NIR range. One interesting finding is that the Sersic index for the bulge reaches values of about 4-5 in optical and NIR bands but drops to around 1 in UV bands. This suggests that a classical bulge may be misidentified as a pseudo-bulge or no bulge when observed through rest-frame UV channels with optical telescopes at high redshifts. The authors plan to continue this work by studying spatially resolved spectral energy distributions (SEDs) for the bulge and disk separately. This will allow them to explore stellar population properties and investigate star formation/quenching history of M81's subsystems. Overall, this study highlights the importance of considering multiwavelength observations when studying galaxy morphology; its findings have implications for understanding how galaxies evolve over cosmic time and provide valuable insights into their structural properties.