Difference between revisions of "Ew(Hα) of one star forming galaxy"
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(以“* Equivalent Width : EW(Hα) Recall EW(Hα) measures the relative strength of Hα to the continuum under the line It therefore acts like a long baseline color index...”为内容创建页面) |
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=== Equivalent Width : EW(Hα) === | |||
Recall EW(Hα) measures the relative strength of Hα to the continuum under the line | Recall EW(Hα) measures the relative strength of Hα to the continuum under the line | ||
It therefore acts like a long baseline color index UV(Hα)<--> λ6550 A | It therefore acts like a long baseline color index UV(Hα)<--> λ6550 A | ||
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http://www.astro.virginia.edu/class/whittle/astr553/Topic11/Lecture_11.html | http://www.astro.virginia.edu/class/whittle/astr553/Topic11/Lecture_11.html | ||
* | === Exercise: measure the Ew(Hα) of one SFing galaxy in the Lamost survey === | ||
*RA=169.02567, DEC=4.79585, z=0.02729 (Lamost) | |||
* SDSS image | |||
http://skyserver.sdss3.org/dr10/en/tools/explore/summary.aspx?id=1237654605329661983&spec=0&apid=#imaging | |||
* Lamost sepctrum | |||
[[文件:spec-55977-F5597703_sp10-191.ps]] | |||
* Calculation of the Ew(Hα) | |||
** ignore the stellar absorption (usually ~2A) and the dust distinction | |||
** central wavelength of this galaxy: 6563*(1+z)=6742 A | |||
** continuum (blue dashed line): linear fit of the wavelength range [6650,6850] (masked the emission line region [6710,6780]) | |||
** Ha emission (thick red solid line) | |||
** Ew(Hα)=area (between thick red line and blue dashed line)/strength of continuum = 67.95A | |||
Latest revision as of 02:02, 24 December 2013
Equivalent Width : EW(Hα)
Recall EW(Hα) measures the relative strength of Hα to the continuum under the line It therefore acts like a long baseline color index UV(Hα)<--> λ6550 A
Although it cannot be converted to a current SFR, it has another important use : It measures the ratio of the current SFR (from Hα) to the integrated past SF (from the continuum) Using synthesis models, this relation can be quantified, to give : EW(Hα)--> (current SFR) / (mean past SFR) ; written SFR/<SFR> or "b" http://www.astro.virginia.edu/class/whittle/astr553/Topic11/Lecture_11.html
Exercise: measure the Ew(Hα) of one SFing galaxy in the Lamost survey
- RA=169.02567, DEC=4.79585, z=0.02729 (Lamost)
- SDSS image
- Lamost sepctrum
文件:spec-55977-F5597703_sp10-191.ps
- Calculation of the Ew(Hα)
- ignore the stellar absorption (usually ~2A) and the dust distinction
- central wavelength of this galaxy: 6563*(1+z)=6742 A
- continuum (blue dashed line): linear fit of the wavelength range [6650,6850] (masked the emission line region [6710,6780])
- Ha emission (thick red solid line)
- Ew(Hα)=area (between thick red line and blue dashed line)/strength of continuum = 67.95A