Difference between revisions of "Ew(Hα) of one star forming galaxy in LAMOST survey"
Jump to navigation
Jump to search
Line 13: | Line 13: | ||
* SDSS image | * SDSS image | ||
http://skyserver.sdss3.org/dr10/en/tools/explore/summary.aspx?id=1237654605329661983&spec=0&apid=#imaging | http://skyserver.sdss3.org/dr10/en/tools/explore/summary.aspx?id=1237654605329661983&spec=0&apid=#imaging | ||
[[file:image-55977-F5597703_sp10-191.jpg]] | [[file:image-55977-F5597703_sp10-191.jpg|800px]] | ||
* Lamost sepctrum | * Lamost sepctrum | ||
[[file:spec-55977-F5597703_sp10-191.jpg| | [[file:spec-55977-F5597703_sp10-191.jpg|800px]] | ||
* Calculation of the Ew(Hα) | * Calculation of the Ew(Hα) | ||
** ignore the stellar absorption (usually ~2A) and the dust distinction | ** ignore the stellar absorption (usually ~2A) and the dust distinction | ||
Line 22: | Line 26: | ||
** Ha emission (thick red solid line) | ** Ha emission (thick red solid line) | ||
** Ew(Hα)=area (between thick red line and blue dashed line)/strength of continuum = 67.95A | ** Ew(Hα)=area (between thick red line and blue dashed line)/strength of continuum = 67.95A | ||
[[file:EwHa.jpg| | [[file:EwHa.jpg|800px]] | ||
* From Fig.3 of Kennicutt (1998, ARA&A, 36,189), it implies that the b= SFR/<SFR> is larger than 5 | |||
* From Fig.3 of '''Kennicutt (1998, ARA&A, 36,189)''', it implies that the b= SFR/<SFR> is larger than 5 | |||
[[file:K98_fig3.jpg|600px]] | |||
* '''Schaerer et al. (2013, A&A, 549, A4):''' Properties of z ∼ 3–6 Lyman break galaxies I. Testing star formation histories and the SFR-mass relation with ALMA and near-IR spectroscop | |||
[[file:Schaerer13 fig2425.jpg|800px]] |
Revision as of 07:42, 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, S/N=12.89
- SDSS image
http://skyserver.sdss3.org/dr10/en/tools/explore/summary.aspx?id=1237654605329661983&spec=0&apid=#imaging
- Lamost sepctrum
- 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
- From Fig.3 of Kennicutt (1998, ARA&A, 36,189), it implies that the b= SFR/<SFR> is larger than 5
- Schaerer et al. (2013, A&A, 549, A4): Properties of z ∼ 3–6 Lyman break galaxies I. Testing star formation histories and the SFR-mass relation with ALMA and near-IR spectroscop