Optical Astronomy: Towards the HST, VLT and Keck Era

Introduction & Overview Chris O’Dea Acknowledgements: Marc Postman, Jeff Valenti, & Bernard Rauscher

Aims for this lecture

 Historical overview  A brief history of optical astronomy  trends in aperture and detector size  CCD Detection  Observing Issues  Effect of the Atmosphere  Effect of the Space Environment

Aims for this lecture II.

 Optical Science   Pretty Pictures – HST – VLT  The synergy between optical and radio (real astrophysics) – The radio loud/quiet quasar transition – Time scales for fueling and activity in radio galaxies Current `big’ issues in optical astronomy

Atmospheric Transmission (300-1100 nm)

History

    Pre-history: mismatch between solar and lunar cycles required astronomical observations to calibrate calendars and predict times for natural and agricultural events  Newgrange, Ireland 3500 BC  Stonehenge, England 3000 BC First millenium BC – Greeks search for  Systematics of planetary motion  Geometric model for planetary motion Ptolemy’s Almagest (AD 145) presented robust geometric model of planetary motion 12 th century Islam- Need for more accurate measurements of positions led to first “observatories” – dedicated structures housing large, fixed instruments.

History

 1575 Tycho Brahe’s Uraniborg – prototype of modern observatory    1609 Galileo uses telescope for astronomy  Features on the moon  Sattelites of Jupiter  Stars remained unresolved Development of reflecting telescopes (enables larger collecting areas)  Gregory 1663, Newton 1668, Cassegrain 1672 Spectroscopy  1817 Fraunhofer combines narrow slit, prism and telescope to make first spectrograph and discovers spectrum of the sun  1859 Kirchoff shows that the solar spectrum reveals the chemical composition

History

 Photography  1845 daguerreotype of sun – Focault & Fizeau  1870’s - Improvements led to photography of faint stars and nebulae  1872 – Draper obtained photographic spectrum of Vega  1875-1900 Combination of Photography and Spectroscopy led to a shift of astronomy from positional measurements to astrophysics

History

 1970’s 4-m class telescopes become common  1980’s CCDs are developed  1990 HST launched  1990’s 10-m class telescopes become available

Newgrange Megalithic Passage Tomb

 Built ~3500 BC in County Meath, Ireland  On winter solstice sun shines down roof box and illuminates central 62-ft passage.

 Passage is illuminated for 17 min after dawn Dec 19-23

Tycho Brahe’s Uraniborg

 Built 1576-1580  Prototype of “modern” observatory  First “Big Science” – required 1% of Danish national budget!

 Dedicated to precision positional measurements (one arcmin) – made possible advances by Copernicus and Kepler

Telescopes in Time

1858: Lassell 48” First “Large” Reflector 1859: Clark 18.5” 1609 Galileo 1.75” 1672 Newton 1.5” 1897 Yerkes 40” Largest Refractor 1917 Hooker 100” 1948 Hale 200”

Edwin Hubble Hubble & Humason 1931, ApJ, 74, 43 H~560 km/sec/Mpc

Aperture vs Time

250 200 150 100 450 400 350 300

Keck

50

Galileo Newton

0 1500 1550 1600 1650 1700 1750

Year

1800 1850 1900 1950 2000

The Biggest Telescopes Today

10

Size Distribution of the 46 largest optical telescopes

8 6

HST

4 2 0

CCD Camera Development for Ground Applications: 1.E+10 1.E+09 1.E+08 1.E+07 2k 2

Luppino, 1998

DMT38k 2 WFHRI36k 2 OMEGA16k 2 CFH_MEGA18k 2 MMT_MEGA18k 2 18k x 18k UH4k 2 SDSS10kx12k CFH8kx12k UH8K 2 Macho 8k 2 EROS8k 2 NOAO4k 2 MOCAM4k 2 BTC4k 2 NOAO8k 2 DEIMOS8k 2 QUEST8k 2 MDM8k 2 MAGNUM8k 2 CTIO8k 2 ESO8k 2 UW12kx16k 8kx8k 4kx4k 2kx2k 8k x 8k 4k x 4k 2k x 2k 1.E+06 1990 1992 1994 1996 1998 Year 2000 2002 2004 2006

CCD Camera Development for Space Applications: 1.E+10 1.E+09 1.E+08 1.E+07 1.E+06 1990 WFPC1 4x0.8k

2 GEST 60 3kx6k SNAP 250x2k 2 18k x 18k GAIA136x2k 2 Fame 24 2kx4k Kepler 21x2k 2 8k x 8k 4k x 4k ACS 4kx4k WF3 4kx4k 2k x 2k WFPC2 4x0.8k

2 STIS 1kx1k 1995 2000 Year 2005 2010

Astronomy at the end of the 20 th Century    Questions about the universe have become progressively more sophisticated   From “Are there other galaxies? (ca. 1920)” structure in the universe?” to “What is the origin of From “How many planets in our solar system?

(Pluto discovered 1930)” to “How many extra-solar planetary systems lie within 100 light years of the sun?” … and are any inhabited?

The basics of cosmology (age & density of universe), detailed maps of the nearby galaxy dist’n, a basic theory of stellar evolution, and a census of the stars in the solar neighborhood exist (or will exist within 5 years).

Astronomers today rely heavily on joint observations from ground & space and data spanning large regions of the electromagnetic spectrum.

CCD Detection

MOS Capacitor:

Silicon Dioxide + Metal Electrode Depletion Region Silicon Substrate • • • • • CCDs are arrays of Metal Oxide Semiconductor (MOS) capacitors separated by channel stops (implanted potential barriers).

Application of positive voltage repels majority carriers (holes) from region underneath oxide layer, forming a potential well for electrons.

A photon produces an electron-hole pair: the hole is swept out of depletion region and electron is attracted to the positive electrode.

Photoexcited charge collects in “depletion region” at PN junction.

Collected charge is shifted to amplifier (CCD) or sensed in situ (IR).

Structure of a 3-Phase CCD Consider a 3-phase CCD.

•Columns are separated by non-conducting channel stops.

•Rows are defined by electrostatic potential. •Charge is physically moved within the detector during readout.

CCD Vertical Structure

 In the vertical direction, one sees a PN junction and control electrodes.  Depletion regions form under both the metal gate and at the PN junction.

 Charge is collected where these depletion regions overlap.

Charge

moves

in a CCD

  By changing electrode voltages, charge can be moved to the output amplifier.

This process is called charge transfer.

 In an IR array, this does not happen. Charge is sensed in place.

CCD Readout Amplifier:

CCD Readout Amplifier Packet of Q electrons is transferred through the output gate onto a storage capacitor, producing a voltage V=Q/C.

The Atmosphere

Atmospheric absorption versus airmass

 The amount of absorbed radiation depends upon the number of absorbers along the line of sight

AM=1 AM=2

Atmosphere

I

 

I

0 ,  10  

mag

/ 2 .

5 , 

mag where



is atm

.

extinction

 

AM

,

coefficien t

.

Atmospheric absorption versus altitude

 Particle number densities (n) for most absorbers fall off rapidly with increasing altitude.

I

 

I

0, 

e

   ,

where

 

is optical depth

,      

ndx

 

e



x

/

x

0

dx

x 0,H 2 0 ~ 2 km, x 0,CO 2 ~ 7 km, x 0,O 3 ~ 1530 km So, 95% of atmospheric water vapor is below the altitude of Mauna Kea.

Atmospheric Turbulence

 A diffraction-limited point spread function (PSF) has a full-width at half-maximum (FWHM) of:    

FW HM

 1 .

2  {

m

}

D

{

m

} {

radians

}  0 .

25  { m

m

}

D

{

m

} In reality, atmospheric turbulence smears the image: {" } 

FW HM

 0 .

25 

r

{ m

m

{

m

} } {" },

where r

0   6 / 5 .

0 At Mauna Kea, r 0 =0.2 m at 0.5 m m.

“Isoplanatic patch” is area on sky over which phase is relatively constant.

Atmospheric Turbulence

1.4

O seeing 0.5

O seeing no seeing!

Lick 3-m Figer 1995 PhD Thesis Keck I 10-m Serabyn, Shupe, & Figer Nature 1998, 394, 448 HST/NICMOS 2.4-m Figer et al. 1999 ApJ. 525, 750

Adaptive Optics: “Eye Glasses” for Ground-based Telescopes

Laser Guide Star Wave Front Sensor Adjust Mirror Shape

Adaptive Optics: “Eye Glasses” for Ground-based Telescopes

Where does NGST win?

    NGST should perform better than current 10m class ground-based telescopes.

In the mid-IR range (wavelengths  3 m ), NGST will produce better quality (higher S/N) images and spectra than a 50m AO corrected ground-based telescope. For surveying large fields of view – AO only works over a small field of view.

Sky is much darker in space in NGST’s wavelength range – better faint object detection.

Observing in Space

HST Facts

         Deployed 25 Apr 1990 Mass: 11600 kg Length: 13.1 m Primary diameter: 2.4 m Secondary: 0.34 m f/24 Ritchey-Chrétien 28 arcmin field-of-view 0.11 m m <  < 3 m m 0.043 arcsec FWHM at 5000 Å

HST Orbit:

     Height = 590 km Orbital period = 96.6 minutes Precessional period = 56 days Inclination = 28.5° Continuous viewing zones (CVZ) at   ±61.5°

Space Environment :

Magnetic Flux Tubes :

CCD Radiation Damage: ACS CCD 10 year dose

 Radiation damage  limits the science lifetime of a CCD Ionization damage - flat band shifts  Bulk damage – – Displacement of Si atoms in lattice produces traps Hot pixels created by electrons from silicon valence band jump to trapping centers and generate high dark current  Annealing  once a month to mitigate hot pixel accumulation. WFPC2 is warmed to +20 o C   STIS CCD is warmed -15 o C 80% of new hot pixels (>0.1 electron sec –1 pix –1 ) fixed

Losses Transferring Charge

SITe 1024  1024 CCD thinned backside NGC 6752, 8  20s, ‘D’ amp at the top

Courtesy R. Gilliland (STScI)

Degradation of Charge Transfer Efficiency

Optical Science

 Pretty Pictures  Astrophysics

Hubble Deep Field

There is a Synergy between High Resolution Optical and Radio Observations

The Radio Loud/Quiet Transition

 Overall SED is similar for RL and RQ quasars.

 Why the difference in radio power?

Sanders & Mirabel 1996, ARAA, 34, 749

Smooth Distribution in Radio Loudness

FIRST quasars. Solid line = all quasars, hatched region = newly discovered quasars . Traditionally, radio loud objects have log R ~3-4. Brinkmann etal 2000, A&A, 356, 445

Unimodal Distribution of Quasar Radio Luminosity

5 GHz luminosity of FIRST Bright Quasar Survey II. White etal. 2000, ApJS, 126, 133

Radio Luminosity – Optical Line Correlation.

There is a strong correlation between radio luminosity and optical emission line luminosity for both RL and RQ objects. (see also Baum & Heckman 1989) Xu etal 1999, AJ, 118, 1169

Emission Lines are Powered by Accretion Disk Luminosity.

There is a strong correlation between X-ray luminosity and optical emission line luminosity for both RL and RQ objects. Xu etal 1999, AJ, 118, 1169

The AGN Paradigm

Annotated by M. Voit

What Causes the RL – RQ Transition?

 Earlier data indicated a Bi-modal distribution of radio loudness suggesting that the transition was very abrupt. New data suggests a continuous distribution of radio loudness. Thus, there is a more gradual transition.  Previously it was thought that there was a correlation with host galaxy type – I.e., RQs are in Spirals and RLs in Elliptical hosts. New data suggests that Ellipticals host both RQ and RL quasars but only those with optically luminous nuclei.

Quasar Host Galaxy Observations

  Sample rest frame optical avoiding bright emission lines.

Match samples in optical luminosity at different z. Kukula et al. 2001, MNRAS, 326 1533

Properties of the Host Galaxies

 The surface brightness profiles are well fit by a r ¼ law; I.e. the host galaxies are bulge dominated.

Dunlop etal 2001, astroph

Properties of the Host Galaxies

  The more luminous nuclei live in galaxies which are more bulge dominated.

Disk-dominated hosts become increasingly rare with increasing nuclear power.

Relative contribution of the bulge to the total luminosity of the host galaxy. RLQs are open, RQQs are filled circles, * are X-ray selected AGN from Schade etal (2000). Dunlop etal 2001, astroph

BH Mass vs. Galaxy Bulge Mass

There is a relationship between BH mass and bulge luminosity. And an even tighter relationship with the bulge velocity dispersion. M(BH) ~ 10 -3 M(Bulge). Ferrarese & Merritt 2000, ApJ, 539, L9

Consistency Between Different Methods

 BH Mass vs bulge magnitude relation is similar for both active and quiescent galaxies. BH Mass vs bulge magnitude for quiescent galaxies, Seyferts and nearby quasars. Size of symbol for AGN is proportional to the Hβ FWHM. Merritt & Ferrarese 2001, astro-ph/0107134

BH Masses

    BH Masses tend to be high in these luminous quasars.

Estimates of BH mass from Hβ line widths and host spheroid luminosity are in rough agreement. RLQs tend to have higher BH mass than RQQs.

Assumes M bh = 0.0025 M sph Comparison between BH masses estimated from the host galaxy spheriod luminosity and the Hβ line-width by McLure & Dunlop (2001). The shaded area marks BH masses greater then 10 9 solar masses. RLQs are open, RQQs are filled circles. Dunlop etal 2001, astroph

What Fraction of Eddington Luminosity?

 RQQ and RLQs are radiating at 1-10% of their Eddington luminosity. Observed nuclear absolute magnitude vs that expected if the BH is emitting at the Eddington luminosity. RLQs are open, RQQs are filled circles. Solid, dashed, and dot-dashed are 100%, 10% and 1% of Eddington luminosity. Dunlop etal 2001, astroph

The Paradigm Shift

   Earlier data indicated a Bi-modal distribution of radio loudness suggesting that the transition was very abrupt. New data suggests a continuous distribution of radio loudness. Thus, there is a more gradual transition. Previously it was thought that there was a correlation with host galaxy type – I.e., RQs are in Spirals and RLs in Elliptical hosts. New data suggests that Ellipticals host both RQ and RL quasars but only those with optically luminous nuclei. This is consistent with a correlation between optically luminous nuclei and massive BHs and between BH mass and host galaxy bulge mass.

Is it BH Spin ?

 Possibilities include  BH Mass (but both RQs and RLs live in big bulges and thus have high BH Mass)  Mass accretion rate (but RQs and RLs have similar optical luminosities)  BH Spin

Time Scales for Gas Transport, Fueling, and AGN Activity

Double-Doubles -- “Born-again” Radio Sources

  5-10% of > 1 Mpc radio sources show double double structure.

Working hypothesis: the radio galaxy turned off and then turned back on - creating a new double propagating outwards amidst the relic of the previous activity.

Schoenmakers etal (2000)

Schematic of Supersonic Jet Model

Concept from Scheuer 1974, Blandford & Rees 1974. Illustration from Carvalho & O’Dea 2001.

Probing Time Scales of Activity

 The double-doubles allow us to probe the timescale of recurrent activity and the nature of the fuelling/triggering of the activity.

 Selection effects will limit the time scales which can be detected in the double-doubles  If the source tuns off for < 10 6 yr the effects on the larger source may not be noticable, and the younger source may not be resolved from the core.

 If the source turns off for > 10 8 yr, the larger source will fade.

3C236 - 4 Mpc Radio Source

The largest radio galaxy known. WSRT 92 cm image (55”x96”) Mack etal. 1997) overlayed on DSS image .

Inner 2 kpc double is well aligned with outer 4 Mpc double

The Inner 2 Kpc Double

Global VLBI 1.66 GHz image (Schilizzi etal 2001) superposed on HST WFPC2 V band image At z=0.1, and H o =75, 1 arcsec = 1.7 kpc O’Dea etal. 2001, AJ, 121, 1915

The Host Galaxy (in color)

• • • Note dust lane along major axis tilted inner disk blue knots along inner edge of dust lane 3-color image. STIS Near-UV MAMA (F25SRF2 2300Å) 1440s WFPC2 F555W (V) 600s WFPC2 F702W (R) 560s O’Dea etal. 2001, AJ, 121, 1915

STIS Near-UV Image

Note the 4 very blue regions in an arc along the inner edge of the dust lane ~0.5” (800 pc) from the nucleus, and perpendicular to the radio source axis.

Regions are resolved with sizes ~0.3” (500 pc) No strong emission lines in the F25SRF2 filter Most likely to be due to relatively young star formation Bruzual-Charlot population synthesis models are consistent with ages knots 2,4  5-10 Myr for knots 1,3 and ~100 Myr for STIS NUV image with global VLBI image (Schilizzi etal 2001) superposed. O’Dea etal. 2001, AJ, 121, 1915

Ages Estimated via Comparison with Stellar Population Models

(Top) UV-V color as a function of time for Bruzual-Charlot models with both constant star formation and an instantaneous burst.

(Bottom) Evolution in color color space of 3 models. Plotted are the colors of the 4 knots, the nucleus, and the older population in the host galaxy.

Knots 1, 3 are consistent with 5 10 Myr, and knots 2, 4 with ~100 Myr.

O’Dea etal. 2001, AJ, 121, 1915

Star Formation Properties

Time Scales

Dynamical Ages: Large radio source: t~7.8x10

8 (v/0.01c) yr (comparable to the age of the oldest blue knots) Small radio source: t~3.2x10

5 (v/0.01c) yr (much younger than the youngest blue knots) Dynamical time scale of the disk on the few hundred pc scale t~10 7 yr

Alignments and the Bardeen-Petterson effect

 The small and large scale radio source are aligned to within about 10 deg.

 The radio sources are aligned to within a few degrees of perpendicular to the “inner" (1 kpc) dust disk but are poorly aligned with the perpendicular to the larger dust lane.

 The Bardeen-Petterson effect will cause the black hole to swing its rotation axis into alignment with the rotation axis of the disk of gas (on scales of hundreds to thousands of Schwarzschild radii) which is feeding it; and conversely will keep the spin axis of the inner disk aligned with the BH spin (e.g., Bardeen & Petterson 1975; Rees 1978)  The combination of the long term stability of the jet ejection axis and the alignment of the jets with the inferred rotation axis of the inner kpc-scale dust disk suggests that the orientation of the inner dust disk has also been stable over the lifetime of the radio source.

 This also implies that the outer misaligned dust lane (which presumably feeds the disk) settles into the same preferred plane as the disk.

The Scenario

 The small and large radio sources are due to two different events of mass infall.  Spectral aging estimates in the hot spotes of the large source imply the radio source may have turned off for ~ 10 7 yr in between the two events.  The difference in the ages of the young and old star formation regions also implies two different triggers.

Implications

 The two episodes of radio activity and the two episodes of star formation are due to non-steady transport of gas in the disk.  If the young radio source and the young starburst (knots 1,3) are related by the same mass transport event, the gas must be transported from the hundreds of pc scale to the sub-pc scale on the dynamical time scale.

The Current Big Issues

Current `Big’ Issues for Optical Astronomy  Planet Formation & Evolution  When, where, & how frequently do planets form?

 How important is dynamical evolution in planet formation and consequent habitability?

 Answers will require powerful (high S/N, high res.) spectroscopic observations as 1 AU  0.002” at Orion ?

??

Current ‘Big’ Issues for Optical Astronomy  Star Formation & Evolution  Must have a more predictive and comprehensive theory for star formation & evolution  Will require studies of stellar systems in hundreds of other galaxies at (angular & spectral) resolutions comparable with the work done in our own Galaxy

Current ‘Big’ Issues in Optical Astronomy  Galaxy Formation & Evolution  When do the first stars and galaxies form?

 What processes trigger this formation and how do they affect a galaxy’s evolution?

 Develop a predictive theory of galaxy formation and evolution HST Deep Field Theory

Current ‘Big’ Issues for Optical Astronomy  Large-scale Structure     How are (proto) galaxies & clusters distributed at when universe was only 25% of it’s current age (z > 2)?

How do the distributions depend on the galaxy’s mass, morphology, or star formation rate in these early epochs?

How does structure evolve from the very smooth pattern when universe was only a few 100,000 years old (z ~ 1000) to the highly clumped and coherent pattern seen since last 6 billion years or so (z < 1)?

Answers will require large area telescope(s) with large FOV and (moderate resolution) spectrograph

The End