Whittle : EXTRAGALACTIC ASTRONOMY


 
     
 
1 : Preliminaries   6 :   Dynamics I 11 : Star Formation  16 : Cosmology
2 : Morphology   7 :   Ellipticals 12 : Interactions 17 : Structure Growth 
3 : Surveys 8 :   Dynamics II 13 : Groups & Clusters  18 : Galaxy Formation 
4 : Lum. Functions  9 :   Gas & Dust   14 : Nuclei & BHs 19 : Reionization & IGM  
5 : Spirals 10 : Populations    15 : AGNs & Quasars 20 : Dark Matter



 

11.   STAR FORMATION & STARBURST GALAXIES


 
         

   

(1) Introduction

First some preliminaries :

     

(2) Definitions and Abbreviations

SF Star Formation
SFR Star Formation Rate, in M yr-1
SFR surface SFR rate, in M yr-1kpc-2
gas surface density of gas, in M pc-2
SF-History time dependence of SFR (eg declining exponential; burst; constant; etc)
C-Nuc Circumnuclear 100 - 1000 pc
IRAS Infrared Astronomical Satellite (1983): S12 etc = fluxes at 12; 25; 60; 100 µ (in Jy)
PSC & FSC Point (& Faint) Source Catalogs from IRAS all sky survey
FIR Far-Infrared :   40 - 500 microns, depends on usage
NIR & Mid-IR Near-IR (1-5µ) & Mid-IR (5-20µ)
FUV & NUV Far (ionizing) UV & Near (1500-2800) UV
FFIR FIR flux (40 - 500µ) = 1.26×10-14(2.58S60 + S100) W m-2
FIR IR flux (8 - 1000µ) = 1.8×10-14(13.5S12 + 5.2S25 + 2.58S60 + S100) W m-2
LFIR & LIR Luminosities corresponding to FFIR & FIR
Lcm Radio luminosity at cm wavelengths (eg 5 GHz), mostly synchrotron
CR Cosmic Rays associated with synchrotron radio emission
SN & SNR Supernova & Supernova Remnant
SB Starburst
LIG Luminous Infrared Galaxy (LFIR > 1011L)
ULIG Ultra-Luminous Infrared Galaxy (LFIR > 1012L)
LINER Low Ionization Nuclear Emission Line Region (low luminosity AGN)
EW(Ha) Equivalent width of Ha = f(Ha) / f(cont)   Angstroms
IMF Initial Mass Function, usually PL :   N(M) M-x (eg x = 2.35 = Salpeter IMF)
Mlow & Mup lower and upper mass cut-off for the IMF

     

(3) Emission From Star Formation Regions

(a) Relevant Observables

Star formation yields an IMF with high mass stars dominating the luminosity
These yield, directly or indirectly, to a wide range of emission [image]

(b) Empirical Relations

     

(4) Measurements of Current SFR

(a) Synthesis Models to Calibrate SFR Relations

To calibrate the SFR (in M yr-1) we need synthesis models (eg refs) :

  1. evaluate evolutionary tracks Lbol & Te & R* as functions of Mass and Age
  2. add stellar atmospheres (Te & g) spectra (or UBV etc)
  3. Sum over an IMF isochrone spectrum (or UBV)
  4. Sum over a chosen star formation history current spectrum

Free parameters : SF-History; IMF; Metallicity.
in practice, main parameters are : burst age and/or e-folding decay; plus fraction of old pop

(b) Conversion Relations to find SFR

     

(5) Factors Affecting the SFR

(a) Preliminaries

It is clearly important to understand the origin of the enormous spread in SFRs found amongst galaxies.
Before considering the various factors, there are a few preliminaries :

(b) Hubble Type

(c) Arm Structure

Dividing galaxies into Grand Design and Flocculant :

(d) Bars

(e) Interactions

Overall, interactions have a dramatic impact on star formation rates

(f) Gas Surface Density

It is useful to consider properties expressed per unit area
eg SFR in M yr-1kpc-2 and gas in M pc-2.

(g) Summary of Star Formation in Disks and Nuclei

Here is Table 1 from Kennicutt 1998 ARAA 36 189 :

     

(6) SF Threshold & Toomre's Q Parameter

not yet typed up

     

(7) Starburst Galaxies

(a) Overview

(b) Samples of SB galaxies

(c) Luminosity Function

(d) Spectral Energy Distributions (SEDs)

Fig 2 from SM96 shows 0.1-1000µ spectra for galaxies spanning a wide range in IR luminosity

(e) Cause of Starbursts

(f) Compact Super-Star Clusters

Star formation is not uniform in starburst galaxies: It occurs in compact star clusters
consider M82 as example:

(g) Galactic Scale Superwinds

What is the effect of all this energy release on the ISM of the starburst galaxy ?

(h) Cosmological Implications of Starbursts

(i) Starburst Relics