Ay 21 Slides - Jan 14

http://star-www.st-and.ac.uk/~spd3/Teaching/AS3011/AS3011_5.pdf

http://star-www.st-and.ac.uk/~spd3/Teaching/AS3011/AS3011_5.pdf

Problems With Traditional Galaxy Classification Appearance of galaxies is strongly dependent on whichwavelength the observations are made in.

X-ray UV Visible Near-IR Far-IRNote: large change in appearance between the UV and the near infrared images.

e.g., the nearby galaxy M81:

Galaxies look “clumpier” in the UV, and increasingly smoothas we go to the visible and longer wavelengths.

4

GalaxyLuminosityFunctionBingelli,Sandage,andTammann1988ARAA2650

Credit: NASA/STScI- Hubble Ultra-Deep Field

http://www.bo.astro.it/~eps/templates/ff06.jpg

GalaxySpectralEnergyDistributionsvs.HubbleType

Light from young stars

Kennicutt1992,ApJS79,255

CaH,K+“4000Abreak”

CH~4300A

MgI+molec.~5170A

NaI

Early-Type (E) Galaxies: integrated stellar light

ProminentNebularEmissionLines(rest-frameoptical)

[OII]3727,3729Ratiosensitivetoelectrondensity,strongathighmetallicity

[OIII]4959,5007Ratiofixed(1:3)but[OIII]/Hβsensitivetoionizingsource;strongestlineforZ<0.6Z◉

Hα/Hβ(6564/4861)Firstcountsionizingphotons,ratioshouldbe~2.9intheabsenceofreddening/extinction

[NII](6549,6585)Ratiooftwolinesfixed(1:3)but[NII]/Hαsensitivetometallicity

[SII](6717,6731)Ratiosensitivetoelectrondensity

Kennicutt1992,ApJS79,255

Hα+[NII](6564,6585)

[SII](6718,6732)

Balmerseriesabs

[OII]3727

Typical Spiral Galaxies (MW-like)

[SII]6717,6731

[OII]3727

Hβ,[OIII]4959,5007

Hα+[NII]

Irregular Galaxies- Strongly Star-Forming