Difference between revisions of "Ew(Hα) of one star forming galaxy in LAMOST survey"
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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, S/N=12.89 | *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 | http://skyserver.sdss3.org/dr10/en/tools/explore/summary.aspx?id=1237654605329661983&spec=0&apid=#imaging | ||
[[file:image-55977-F5597703_sp10-191.jpg|800px]] | [[file:image-55977-F5597703_sp10-191.jpg|800px]] | ||
*A blue, compact, normal galaxy | |||
** blue: | |||
*** within R_50: ⟨μ_50,g⟩=20.1374, ⟨μ_50,r⟩=19.7729 → ⟨μ_50,g⟩ - ⟨μ_50,r⟩ =0.36 '''<''' 0.43 | |||
*** within R_90: ⟨μ_90,g⟩=21.1151, ⟨μ_90,r⟩=20.8108 → ⟨μ_90,g⟩ - ⟨μ_90,r⟩ =0.30 '''<''' 0.43 | |||
** compact: | |||
*** within R_50: 21.83-0.47(⟨μ_50,g⟩ - ⟨μ_50,r⟩) =21.66 '''>''' ⟨μ_50,g⟩ | |||
*** within R_50: 21.83-0.47(⟨μ_90,g⟩ - ⟨μ_90,r⟩) =21.69 '''>''' ⟨μ_90,g⟩ | |||
** not dwarf: | |||
*** z=0.02729 → D=119 Mpc → M_g= -19.1277, M_r= -19.4277 → M_g '''<''' -19.12+1.82(M_g-M_r)= -18.6040 | |||
=== Lamost sepctrum === | |||
[[file:spec-55977-F5597703_sp10-191.jpg|800px]] | [[file:spec-55977-F5597703_sp10-191.jpg|800px]] | ||
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** continuum (blue dashed line): linear fit of the wavelength range [6650,6850] (masked the emission line region [6710,6780]) | ** 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) | ** 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|800px]] | [[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 the 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]] | [[file:K98_fig3.jpg|600px]] | ||
Latest revision as of 01:48, 25 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
- A blue, compact, normal galaxy
- blue:
- within R_50: ⟨μ_50,g⟩=20.1374, ⟨μ_50,r⟩=19.7729 → ⟨μ_50,g⟩ - ⟨μ_50,r⟩ =0.36 < 0.43
- within R_90: ⟨μ_90,g⟩=21.1151, ⟨μ_90,r⟩=20.8108 → ⟨μ_90,g⟩ - ⟨μ_90,r⟩ =0.30 < 0.43
- compact:
- within R_50: 21.83-0.47(⟨μ_50,g⟩ - ⟨μ_50,r⟩) =21.66 > ⟨μ_50,g⟩
- within R_50: 21.83-0.47(⟨μ_90,g⟩ - ⟨μ_90,r⟩) =21.69 > ⟨μ_90,g⟩
- not dwarf:
- z=0.02729 → D=119 Mpc → M_g= -19.1277, M_r= -19.4277 → M_g < -19.12+1.82(M_g-M_r)= -18.6040
- blue:
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 the 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
