Surface Photometry Quantitative description of galaxy morphology. Hubble Sequence Qualitative description of galaxy morphology

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1 Hubble Sequence Qualitative description of galaxy morphology Surface Photometry Quantitative description of galaxy morphology Galaxy structure contains clues about galaxy formation and evolution

2 Point Spread Function (PSF) - blurring of a point source from telescope optics and atmosphere Ground-based image WFPC2 image

3 PSFs for seeing-limited observations vs. adaptive optics

4 AO not perfect correction Space-based observations provide most stable PSFs Accurate surface photometry requires knowing your PSF

5 devaucouleurs surface brightness of elliptical galaxy follows R 1/4 law

6 devaucouleurs surface brightness of spiral galaxy follows: -- R 1/4 law for spheroidal component -- exponential law for disk component Freeman 1970: dynamically hot stars in bulge -- puffy, large stellar velocity dispersions from Freeman 1970 dynamically cold stars in the disk -- flatter, rotationally supported

7 Both are special cases of Sersic (1968) profile: Σe is the pixel surface brightness at the effective radius re half the total flux contained within re κ is coupled to n (not a free parameter) n = 4: devaucouleurs profile n = 1: exponential profile n = 0.5: Gaussian profile large n = steep center and shallow wings Peng et al small n = shallow center and steep wings

8 Other Profiles Moffat (1969) - function that approximates an unresolved point source (star) on photographic emulsion WFPC2 PSF shows significant departures from Gaussian profile in wings

9 Moffat Profile Σ0 : central surface brightness n : concentration index similar to Gaussian but has strong wings Peng et al. 2010

10 Other Profiles spatially resolved globular clusters not well described by devaucouleurs R 1/4 law King (1966) - profile from theoretical description of self-gravitational stellar system (modified isothermal sphere)

11 King Profile Σ0 : central surface brightness rc : core radius rt : truncation radius (function = 0 outside of rt) standard King profile has α = 2 Peng et al. 2010

12 Other Profiles centers of nearby galaxies appear to depart from single powerlaw profiles Nuker profile introduced (Lauer et al. 1995) - double powerlaw profile

13 Nuker Profile rb : break radius Ib : intensity at rb γ : inner powerlaw slope β : outer powerlaw slope α : controls the sharpness of the transition change γ change β change α Peng et al. 2010

Surface brightness fits: 1-D vs 2-D Benefits of 1-D - Simple - Fast Gaussian in 1-D Benefits of 2-D - Uses all the information in an image - Avoids choice of major vs.

14 Surface brightness fits: 1-D vs 2-D Benefits of 1-D - Simple - Fast Gaussian in 1-D Benefits of 2-D - Uses all the information in an image - Avoids choice of major vs. minor axis cut - Allows independent determination of axis ratios and position angles for each galaxy component Gaussian in 2-D Do benefits of 2-D outweigh drawbacks?

15 2-D fits: Simple elliptical galaxy Left to Right: image + isophotes image - Nuker fit image - (Sersic + exp) fit points: data solid line: Nuker dashed lines: Sersic + exp Peng et al. 2002

16 2-D fits: Another simple elliptical galaxy Left to Right: image + isophotes image - Nuker fit image - (4 x Sersic) fit points: data solid line: Nuker dashed lines: 4 x Sersic Nuker profile proposed to fit centers of galaxies, but does less well in 2-D than 1-D Peng et al. 2002

17 2-D fits: How complicated should they be? As complicated as needed, but no more Start with simple fits then add increasing complexity Monitor quantities of interest to see magnitude of change Total galaxy magnitude Best fit: m = mag Traditional fit: m = mag Single component fit: m = mag Peng et al. 2010

18 Quantitative morphology Clues about formation and evolution Example: Quasar Host Galaxies Very difficult to separate quasar from host galaxy Jahnke et al Host galaxy colors are very blue, suggesting recent or ongoing episodes of intense star formation

Quantitative morphology Clues about formation and evolution Example: Core vs. Cuspy Ellipticals Cuspy Ellipticals: (Cuspy) - Lower luminosity, MV > -20.5.

19 Quantitative morphology Clues about formation and evolution Example: Core vs. Cuspy Ellipticals Cuspy Ellipticals: (Cuspy) - Lower luminosity, MV > May have formed from wet (gas-rich) mergers of ellipticals. Gas moves to center to form new stars, leaving a denser nucleus. Core Ellipticals: Lauer et al Luminous, MV < May have formed from dry (gas-poor) mergers of ellipticals Binary black holes "scour out" nucleus by flinging stars away.

20 Quantitative morphology Clues about formation and evolution Example: When is a bulge not a bulge? When it behaves like a disk instead Kormendy (1993) calls these pseudobulges

21 Pseudobulges show disk-like characteristics nuclear bar and/or spiral lots of gas, dust, star formation in nucleus (not from merger) NGC 4736

22 Pseudobulges show disk-like characteristics nuclear bar and/or spiral lots of gas, dust, star formation in nucleus (not from merger) flattened shape round bulge flat bulge very flat bulge (bar?) Late-type galaxies are more likely to have bulges that are as flat or flatter than their disks Kormendy 1993

in nucleus (not from merger) flattened shape rotation

circular flat Late-type galaxies are more likely to

23 Pseudobulges show disk-like characteristics nuclear bar and/or spiral lots of gas, dust, star formation in nucleus (not from merger) flattened shape rotation > random motions ordered prolate oblate random circular flat Late-type galaxies are more likely to have bulges that are rotationally dominated (dynamically cold )

24 Pseudobulges show disk-like characteristics nuclear bar and/or spiral lots of gas, dust, star formation in nucleus (not from merger) flattened shape rotation > random motions low Sersic index Revised Hubble Type -3 = S0 0 = S0/a 1 = Sa 3 = Sb 5 = Sc Late-type galaxies are more likely to have ~exponential bulges Andredakis et al. 1995

25 Pseudobulge interpretation Bulges are mini-ellipticals Created through major mergers

26 Pseudobulge interpretation Eris Simulation of Milky Way-like galaxy formation Pseudobulges are not built through mergers, but through angular momentum transport of gas from outer regions of galaxy to inner regions of galaxy Instabilities (e.g., bars, spirals) drive gas to center, puffs up inner galaxy

This week at Astro Lecture 06, Sep 13, Pick up PE#6. Please turn in HW#2. HW#3 is posted

This week at Astro Lecture 06, Sep 13, Pick up PE#6. Please turn in HW#2. HW#3 is posted This week at Astro 3303 Lecture 06, Sep 13, 2017 Pick up PE#6 Please turn in HW#2 HW#3 is posted Today: Introduction to galaxy photometry Quantitative morphology Elliptical galaxies Reading: Continue reading