Jack Baldwin’s work on

Quasars & the Early History of Galaxies

What we can directly observe about quasars:

• "Quasar" = "Quasi-stellar radio source"

  • Distant quasars look like points of light, just like stars.

  • Originally discovered through their radio emission.

    • But most quasars known today are not radio sources.

• Defining feature is their spectrum:

  • Strong "non-thermal" continuum spanning very large wavelength range.

  • Strong, broad emission lines.

    • Line-emitting gas has ~ 10,000 km/sec velocity spread.

• Relatively bright objects with large redshifts ==> extremely luminous.

  • Up to 1000x more luminous than an entire galaxy of 100,000,000,000 stars.

  • HST images show that they occur at centers of galaxies.

• Rapid continuum variability ==> continuum light comes from an extremely small volume.

  • Light-hours to light-days.

  • About same size as our solar system.

• Emission line variability indicates size of broad emission line region.

  • Light-weeks to light year, depending on continuum luminosity.

  • Lower ionization emission lines come from 10-20 times further out than high ionization lines.

• Many more quasars existed when galaxies were recently formed than exist now.

  • We know this from counts of quasar's space density as a function of redshift.

  • Redshift ==> distance ==> lookback time.

What we think they are:

• Gas from central region of surrounding host galaxy falls in to center of galaxy.

  • Mass density becomes high enough to generate a black hole at center.

  • Gas continues to fall in ==> black hole reaches 10⁶ - 10⁸ solar masses.

• Accretion disk forms around the black hole.

  • Gas can't fall straight in because of angular momentum.

  • Infalling gas hits material in accretion disk and heats it.

  • Source of continuum luminosity: gravitational potential energy of infalling gas.

• Continuum radiation from accretion disk then ionizes nearby gas.

  • This is the Broad Emission Line Region.

    •  Exact configuration of this gas not known.

    • Outflowing wind blown off accretion disk?

• Lots of gas fell into black hole early on, but then the gas was all used up.

  • So most quasars shut off early in the lives of galaxies.

  • But the black holes live on.

    • There is one in the center of our own Milky Way Galaxy.

Quasars as probes of the early evolution of massive galaxies:

• Use relative strengths of different broad emission lines to measure chemical composition of gas.

  • This is presumably gas that has fallen in from surrounding host galaxy.

  • It's chemical enrichment is due to processing through early generations of stars in host galaxy.

  • Our work shows this gas is often super-metal-rich ==> very vigorous star formation early in life of host galaxy.

• Relative line strengths also measure shape of ionizing continuum.

  • Depends on accretion rate & mass of central black hole.

  • Can show history of mass accretion rate at centers of young massive galaxies.

• Iron (Fe) abundance in quasars.

  • We expect Fe to be formed in Type Ia supernovae.

    • Stars must evolve for ~ 1 billion years before exploding as Type Ia SNe.

  • Hope is to quantitatively measure Fe abundance in quasar emission line regions.

    • Expect sudden jump in Fe abundance ~ 1 billion years after initial round of star formation.

  • Our recent work highlights how difficult it is to measure Fe abundances.

    • Strengths of many Fe II lines depend on parameters such as velocity gradient in gas as much as they do on Fe abundance.

  • MSU grad student Charles Kuehn is currently studying relative location of the Fe II - emitting region, using reverberation measurements.

    	Spectrum of the unusual QSO 0353-383 (with redshift z = 1.96), showing its extremely strong N IV] l1486 and N III] l1750 emisssion lines. The lighter line is the average of the spectra of many QSOs with the same luminosity as Q0353-383, for comparison.
    Rest Wavelength è

The Helium II conundrum.

• Preceeding work depends on interpreting broad emission lines as being produced by photionization from central continuum source.

• Variability ("reverberation") timescales of He II 1640 and 4686 lines do not seem to fit into this picture.

  • Should vary on same timescale as C IV 1549.

  • He II 1640 is reported to vary much more rapidly than C IV 1549.

• What's going on???

  • Thesis project for Aaron LaCluyze.

	Contours showing predicted emission line response to continuum variations, for C IV 1549, He II 1640 & 4686. From Bottorff et al. 2002 .

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My collaborators:

• Aaron LaCluyze (“Cluze”) MSU grad student  

• Neelam Dhanda.  MSU Grad student

• Charles Kuehn.  MSU Grad student

• Gary Ferland (Univ. of Kentucky)

• Kirk Korista (Western Michigan Univ.)

• Fred Hamann (Univ. of Florida)

• Mark Bottorff (Southwestern University)

• Brad Peterson (The Ohio State University)

• Ryan Porter (Univ. of Kentucky)

• Pat Osmer (The Ohio State University)

• Misty Bentz (The Ohio State University)

Some of our relevant papers:

• Kuehn, C.A., Baldwin, J.A., Peterson, B.M. & Korista, K.T. 2008, ApJ (in press) “On the Size of the Fe II Emitting Region in the AGN Akn 120”, http://xxx.lanl.gov/abs/0710.5248

• Dhanda, N., Baldwin, J.A., Bentz, M.C. & Osmer, P.S.2007, ApJ, 658, 804  "Quasars with Super Metal Rich Emission Line Regions" http://xxx.lanl.gov/abs/astro-ph/0612610

• Baldwin, J.A., Ferland, G., Korista, K.T., Hamann, F. & LaCluyzé, A. 2004, ApJ, 615, 610 “The Origin of Fe II Emission in AGN”   http://arXiv.org/abs/astro-ph/0407404

• P. J. Green, J. D. Silverman, R. A. Cameron, D. -W. Kim, B. J. Wilkes, A. LaCluyze, D. Morris, A. Mossman, H. Ghosh, J. P. Grimes, B. T. Jannuzi, H. Tananbaum, T. L. Aldcroft, J. A. Baldwin, F. H. Chaffee, A. Dey, A. Dosaj, N. R. Evans, X. Fan, C. Foltz, T. Gaetz, E. J. Hooper, V. L. Kashyap, S. Mathur, M. B. McGarry, M. G. Smith, P. S. Smith, R. C. Smith, G. Torres, A. Vikhlinin, and D. R. Wik  2004, ApJ Suppl., 150, 43,  “The Chandra Multiwavelength Project: Optical Followup of Serendipitous Chandra Sources” http://arxiv.org/abs/astro-ph/0308506

• Baldwin, J.A., Hamann, F., Korista,  K.T., Ferland, G.J., Dietrich, M. and Warner, C. 2003, ApJ, 583, 649 “Chemical Abundances in Broad Emission Line Regions: The “Nitrogen-Loud” QSO 0353-383”  http://arxiv.org/abs/astro-ph/0210153

• Baldwin, J.A., Ferland, G.J.,Korista,  K.T., Hamann, F. and Dietrich, M. 2003, ApJ, 582, 590 “The Mass of Quasar Broad Emission Line Regions” http://arXiv.org/abs/astro-ph/0209335

• Bottorff, M.C., Baldwin, J.A., Ferland, G.J., Ferguson, J.W. and Korista, K.T.  2002, ApJ , 581, 932 “HeII Reverberation in AGN Spectra”  pdf

• Hamann, F., Korista, K.T., Ferland, G.J., Warner, C. & Baldwin, J. 2002, ApJ. 564, 592, “Metallicities and Abundance Ratios from Quasar Broad Emission Lines”   http://xxx.lanl.gov/abs/astro-ph/0109006

Research grants currently supporting this work:

• HST grant AR-10932 "Hard Ionizing Photons at High Redshift --- A New Method for Measuring the QSO Continuum Shape".