un:spiral-and-irregular-galaxies
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| un:spiral-and-irregular-galaxies [2026/02/09 06:24] – shuvo | un:spiral-and-irregular-galaxies [2026/02/10 00:14] (current) – [0.4 Surface Brightness Profile] shuvo | ||
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| Accurate determination of these profiles requires meticulous sky subtraction to account for the background sky brightness, which typically averages: | Accurate determination of these profiles requires meticulous sky subtraction to account for the background sky brightness, which typically averages: | ||
| - | $\mu_{sky} \approx 22 \ arcsec^{-2}$ | + | $\mu_{sky} \approx 22 \ mag \ arcsec^{-2}$ |
| The bulges of spiral galaxies and large elliptical galaxies are most frequently modeled using the de Vaucouleurs $r^{1/4}$ law. In units of magnitudes per arcsecond squared ($\text{mag arcsec}^{-2}$), | The bulges of spiral galaxies and large elliptical galaxies are most frequently modeled using the de Vaucouleurs $r^{1/4}$ law. In units of magnitudes per arcsecond squared ($\text{mag arcsec}^{-2}$), | ||
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| In this versatile model: (1) $n = 1$ yields the exponential disk profile, (2) $n = 4$ recovers the standard de Vaucouleurs law. | In this versatile model: (1) $n = 1$ yields the exponential disk profile, (2) $n = 4$ recovers the standard de Vaucouleurs law. | ||
| - | Finally, the **Holmberg radius** ($r_H$) and the isophotal radius $R_{25}$ (where the surface brightness reaches $25 \ arcsec^{-2}$ provide standardized benchmarks for comparing the physical extents of different galaxies regardless of their Hubble type. | + | Finally, the **Holmberg radius** ($r_H$) and the isophotal radius $R_{25}$ (where the surface brightness reaches $25 \ mag \ arcsec^{-2}$ provide standardized benchmarks for comparing the physical extents of different galaxies regardless of their Hubble type. |
un/spiral-and-irregular-galaxies.1770643487.txt.gz · Last modified: by shuvo