## News and Views on "New estimates of scale heights and spiral structures for non-edge-on spiral galaxies"

(News & views on the paper by Hu & Peng, RAA, 2014, vol.14, 869-874)
**Xi-Wei Liu**

*(Department of Physics, Huazhong
Agricultural University)*

Disk galactic diameters are far larger than their scale heights. Thus the scale height is usually omitted in studies and the galactic disk is assumed to be a 2-dimensional plane. Whether this assumption about 2-dimensions is good or not has been controversial for many years (Binney & Tremaine 1987; Peng 1988). The scale height is a key parameter for determining a model describing the 3-dimensional structure of spiral galaxies. Estimating the scale height would shed light on understanding the dynamics and evolution of galaxies. An estimate of the scale height of edge-on spiral galaxies has been well established (van der Kruit & Searle 1981a, 1981b; 1982a, 1982b). However, it has been challenging to measure the scale height of non-edge-on spiral galaxies for many years. Peng (1988) presented a mathematical method for determining the scale heights of non-edge-on spiral galaxies. This is the only method for determining scale heights of non-edge-on spiral galaxies until now.

Peng’s method is based on measuring parameters of spiral structure. The forbidden radius (i.e. spiral arms could not appear in the region r

**References**

- Binney, J., Tremaine, S., 1987, Galactic Dynamics, Princeton University Press ADS
- Peng Q. H., 1988, A&A, 206, 18 ADS
- van der Kruit, P. C., Searle, L., 1981a, A&A, 95, 105 ADS
- van der Kruit, P. C., Searle, L., 1981b, A&A, 95, 116 ADS
- van der Kruit, P. C., Searle, L., 1982a, A&A, 110, 61 ADS
- van der Kruit, P. C., Searle, L., 1982b, A&A, 110, 79 ADS