This week at Astro 3303

Transcription

1 This week at Astro 3303 First, we have the in-class presentations Then I will return the test I will collect HW#5 HW#6 is posted and due next Wednesday Includes elements from the test Soon, we will get working on final projects! Today: The BPT diagram as a diagnostic tool Intro to quasars; the discovery of 3C273 Relativistic Doppler formula and why we need cosmology Reading: For next week: Chapter 4; start looking at Chapter 5

2 Set#2!" $" #" %"

3 Garden variety of AGN galaxies

4 BPT diagrams Baldwin, Phillips & Terlevich 1981, PASP 93, 5 The question: What line ratios will allow us to identify AGN, starburst galaxies (and won t be confused with galactic objects like planetary nebulae)? As we (now) realize, ratios of lines can discriminate AGN from starbursts because the strength/width of a spectra line depends on the ionization sources/mechanisms.

5 Emission-Line AGN [OIII] H!" Classification AGN vs. SF: emission-line ratios [OIII]5007 as AGN tracer because it is usually the strongest AGN line and has much less contribution from SF

6 SDSSid! Rest! OVI_ Ly!_ NV_ OI_ CII_ SiIV_ SiIV_OIV CIV_ HeII_ OIII_ AlIII_ CIII_ CII_ NeIV_ MgII_ NeV_ NeVI_ OII_ OII_ H'_ Oy_ HeI_ K_ H_ SDSS spectral lines SDSSid! Rest! H#_ SII_ H$_ G_ H%_ OIII_ H&_ OIII_ OIII_ OIII_ Mg_ Na_ OI_ OI_ NI_ NII_ H!_ NII_ Li_ SII_ SII_ CaII_ CaII_ CaII_

7 SDSS emission line diagnostics Kewley et al red line shows extreme starburst, dashed line is classification division LINER: low ionization nuclear emission region

8 Kewley et al OI (6302Å) OII (3739 Å) OIII (5007 Å) H! (6565 Å) - [OIII]/[OII] is sensitive to ionization parameter (how ionized the gas is) - [OI]/H! is sensitive to hardness of radiation field Based on Baldwin, Phillips & Terlevich 1981, PASP 93, 5

9 Classifications (1) Morphology (2) Color (3) Spectral Features Early-type Red AGN vs no AGN AGN rel. importance of AGN Seyfert Late-type Blue HII LINER Park & Choi (2005)! Early-type galaxies! Late-type galaxies Lee et al. (2006)! Red galaxies! Blue galaxies Kauffmann et al. (2003) Kewley et al. (2006)! Passive, HII! Seyfert, LINER ((g-i) is the color difference between the region with R<0.5R p and the region 0.5R p < R < R p - dominance of emission lines - dominance of AGN lines

10 &'()*"!" #" z=1.8 quasar z=0.6 quasar Quasars: bright, so the first objects we could ID out to cosmological distances

11 Discovery of First Quasars Hazard et al. (1963) detected strong radio emission from a stellar object. This source, 3C273, had very strange optical emission lines. Maarten Schmidt realized this was redshifted hydrogen (z=0.16). brighntess Quasars: Quasi-stellar radio source QSO s: Quasi-stellar object wavelength H& emission line (rest wavelength=4863å) observed redshifted at 5673Å => z = 0.16

12 Discovery of First Quasars Hazard et al. (1963) detected strong radio emission from a stellar object. This source, 3C273, had very strange optical emission lines. Maarten Schmidt realized this was redshifted hydrogen (z=0.16). Flux density Quasars: Quasi-stellar radio source QSO s: Quasi-stellar object wavelength H& emission line (rest wavelength=4863å) observed redshifted at 5673Å => z = 0.16

13 SMBH at center of galaxy Normal supermassive black hole (SMBH) => AGN Ultraluminous SMBH => quasar

14 Quasars and Active Galactic Nuclei The most distant quasar known today has a redshift of (ULAS_J ; June 2011) That redshift corresponds to a look back time of 12.9 Gyr (12.9 billion years), or an epoch of only 776 Myr) after the Big Bang occurred. In order to interpret distances, times, sizes, etc, we must understand the geometry of the universe. The SMBH in the MW (SgrA*) has a mass of 3 x 10 6 M " Quasar SMBHs can be up to M "

15 Looking out is looking back Light year: the distance light travels in one year We are able to observe the universe at earlier times because it takes light time to travel from there (there and then) to here (here and now). How long it takes for light to reach us depends on: 1. How far away the emitting object is. 2. The path light travels through space-time from there to here. more soon. The most distant objects we can observe in the universe today include the quasars, which are extremely luminous so they can be seen even very far away. Quasars are very active supermassive black holes at the centers of distant galaxies.

16 Looking out is looking back The time it takes light to travel from a distant object to us depends on the geometry of the universe longer path shorter path In order to know the light travel time, we must know the geometry The geometry depends on the amount of matter (baryonic and dark) and (as we will see ) dark energy

17 What is the Geometry of cosmic space?! It depends on the density of its matter+energy contents A high density Universe has POSITIVE curvature A low density Universe has NEGATIVE curvature A Universe with zero curvature, said to be FLAT, has critical density

18 History and Fate of the Universe Hot Big Bang Model 13.7 billion years ago, the universe was much hotter and much denser than it is today. A tremendous release of energy took place: the Big Bang event. Since then, the universe has been expanding. Will the universe keep expanding? Or will the expansion halt? The attractive force of gravity of all the mass in the universe should be acting to slow the expansion or so we would expect

19 Universal Expansion 1664 Newton s Theory of Gravitation He realizes the Universe must be infinite to prevent collapse and that equilibrium is unstable 1917 Einstein obtains new set of equations of gravitational field (ToGR)! unstable Universe (rel. to steady-state), unless a cosmological constant ) term is introduced Friedmann obtains set of expanding solutions of Einstein s equations. They are independently obtained by Lemaitre in Hubble discovers universal expansion: v = H o d He determines H o to be ~500 km/s/mpc! universal age ~ 2 Gyr Einstein declares introduction of " his greatest mistake ever late 1940s Gamow, Alpher and Hermann postulate existence of cosmic radiation background with T ~ 5 K early 1960s Quasars are shown to be at cosmological distances 1964 Hoyle and Tayler show that He abundance can be explained by primordial nucleosynthesis 1965 Penzias and Wilson detect Cosmic Microwave Background radiation 1992 COBE detects fluctuations in the CMB (teams of Smoot and Mather) 1998 Observations of SNeIa reveal that the universal expansion is accelerating (teams of Perlmutter, Schmidt and Riess) 2003 WMAP accurately determines main cosmological parameters 2013 Planck provides a more accurate description of cosmology

20 Evidence for the Big Bang Model 1. Olber s paradox: Why is the sky dark at night? 2. Hubble s Law and the expansion of the universe More distant galaxies receding faster 3. Cosmic Microwave Background (CMB) radiation 4. Primordial nucleosynthesis Hydrogen, helium (light ones only) and in right proportions 5. Large scale distribution of galaxies today (the way galaxies cluster) Any alternative theory of cosmology would have to explain these critical observational facts.

21 Evidence for the Big Bang Model Olber s paradox: (Heinrich Olbers: 1823) Why is the sky dark at night? If the universe were infinite, then every line of sight would eventually intercept a star (or galaxy) and hence the whole night sky should look like the surface of a star. Solution: universe must be finite in space, in age or both Remember: the concept of galaxy is < 100 years old.

22 Edwin Hubble ~ Hubble s Law Discovered first Cepheids in M31 and M33 VERY DISTANT Measured distances to 18 galaxies for which Doppler shifts also measured. The further away a galaxy is from us, the faster it is moving away from us. Velocity away from us Hubble s Law Distance from us

23 Discovery of the Microwave Background

24 NASA Animation Cosmic Microwave Background Radiation After the Big Bang, the universe cooled as it expanded. About 300,000 years after the Big Bang, protons and electrons combined to form hydrogen => and the cosmic background radiation photons were emitted This radiation is called the Cosmic Microwave Background Radiation or the 3-degree Background Radiation

25 A Serendipitous Discovery - noise feature all over the sky, like radio or TV station - First suspect: antenna issues - white dielectric substance? (pigeon-related) Winning a Nobel Prize may involve some dirty work!

26 Today The Bell Labs Horn Antenna In Crawford Hill, NJ

27 Cosmic Microwave Background Radiation The Cosmic Microwave Background photons were emitted about 300,000 years after the Big Bang at z ~ 1000 Photons emitted when thermal plasma in universe was ~3000 degrees K. Spectrum then redshifted by factor of 1000 Appears as spectrum with temp ~ 3 degrees Kelvin A more perfect BB than we can make in the lab => thermal

28 Big Bang Nucleosynthesis Any successful model of the early universe must explain the timescale on which the temperature and density of the universe drops as the universe expands. Hot Big Bang Model: about 3 minutes after the Big Bang, the temperature and density were hot and dense enough to allow formation of stable protons and neutrons. Hydrogen nuclei formed Some H nuclei fused to form He nuclei A tiny bit of Lithium, Beryllium and Boron were produced. Quickly though, as the universe expanded, the temperature density dropped so that no more fusion could take place => no more He 90% of atoms are hydrogen ~9+% of nuclei are helium Trace amounts of Li, Be, B Nothing heavier than that!

29 Large Scale Structure Our cosmological model must explain how the structure developed to look this way (and not something else) and it has to do it in 13.7 billion years (not earlier, not later) Smoother earlier on Time => Galaxies, clusters, superclusters and voids today CMB

30 Evidence for the Big Bang Model Olber s paradox: (Heinrich Olbers: 1823) The sky is dark at night. Hubble s Law & the expansion of the Universe (Edwin Hubble: 1927) If the universe is finite in space and time and is expanding, it must have been smaller in the past. The Cosmic Microwave Background (CMB) Radiation (Arno Penzias and Robert Wilson: 1965) Thermal spectrum with equivalent temperature of 3 degrees => 3 degree blackbody radiation = CMB Abundance of the elements via primordial nucleosynthesis The large scale structure of the universe: the way galaxies are seen today to cluster into groups, clusters and super-clusters.