The Local Interstellar Medium:Reconstructing our Interstellar Past

Seth Redfield(University of Texas at Austin)

Adapted from Mewaldt & Liewer (2001)

• Nearest environment to study general ISM phenomena.

• Interaction of Sun (stars) with the surrounding LISM (ISM) has implications for a LISM-Earth (ISM-planet) connection.

• Chemical evolution and mixing, distance indicator, star formation indicator and trigger, etc.

Why study the LISM?

Other ISM Bubbles

Kim et al. (1998)

LMC HI mosaic

Density contours based on NaI abs.

Lallement, Welsh, et al. (2003)

in situ

He I emission Ulysses (Witte et al. 1996)ISM dust w/ Stardust (Brownlee et al. 2003)Voyager 1 in pristine ISM in only 45 years!

Absorption Line Spectroscopy

Most transitions lie in FUV (900-

1200Å), UV (1200-3000Å), and

optical (3000-10000Å)

How do we measure properties of the LISM?

LISM

Lyman-α

CaII H and K

MgIISiIICIIFeIIOI

Targets within 100 pc observed at high and moderate resolution that may contain LISM absorption lines (~60% taken for other purposes).

HST Sample

Observational Diagnostics

1 ion, 1 sightline Velocity, Column Density

multiple ions, 1 sightline

Temperature, Turbulence, Volume Density, Abundances, Depletion, Ionization Fraction

Redfield & Linsky 2004

Observational Diagnostics

1 ion, 1 sightline Velocity, Column Density

multiple ions, 1 sightline

multiple ions, multiple sightlines

Temperature, Turbulence, Volume Density, Abundances, Depletion, Ionization Fraction

Global Morphology, Global Kinematics, Intercloud Variation

The Morphology of the Local Interstellar Cloud

Redfield & Linsky 2000

Observational Diagnostics

1 ion, 1 sightline Velocity, Column Density

multiple ions, 1 sightline

multiple ions, multiple sightlines

Temperature, Turbulence, Volume Density, Abundances, Depletion, Ionization Fraction

Global Morphology, Global Kinematics, Intercloud Variation

Origin and Evolution, Interaction of LISM Phases

Zank & Frisch (1999)

Increase the density of the surrounding LISM by only a factor of 50 (nH from 0.2 to 10 cm-3) and the termination shock shrinks from 100 AU to 10 AU.

How large of a density increase is needed to significantly alter the

structure of the heliosphere?

nH(LISM) = 10 cm-3

nH(LISM) = 0.2 cm-3

Müller (2004)

What are the consequences of a compressed heliosphere?

(1) Cosmic rays flux modulated by magnetized solar wind: CR ionization in lower atmosphere, leads to cloud nucleation, increase in planetary albedo

(Marsh & Svensmark 2000, Carslaw et al. 2002)

Lightning triggered by CR secondaries (Gurevich & Zybin 2005)

CR increase NO and NO2 production, alters ozone layer chemistry (Randall et al. 2005)

CR source DNA mutation; current dose: 31 millirem/yr, legal dose: 5 rem/yr (EPA), @ 10-100 MeV FLISM = 102-103 F1AU (Reedy et al. 1983)

(2) Direct deposition of ISM material onto planetary atmosphere:

Dust deposition through GMC could trigger “snowball” Earth episode (Pavlov et al. 2005)

Create mesospheric ice clouds, increase in planetary albedo (McKay & Thomas 1978)

Tracing the Historical Path of the SunLong history of speculating about the link between our interstellar environment and our climate

H. Shapley (1921): “Note on a Possible Factor in Changes of Geological Climate”F. Hoyle & R.A. Lyttleton (1939): “The Effect of Interstellar Matter on Climatic Variation”H. Shapley (1949): “Galactic Rotation and Cosmic Seasons”H.J. Fahr (1968): “On the Influence of Neutral Interstellar Matter on the Upper Atmosphere”W.H. McCrea (1975): “Ice Ages and the Galaxy”M.C. Begelman & M.J. Rees (1976): “Can Cosmic Clouds Cause Climatic Catastrophes?”R.J. Talbot et al. (1976): “Climatic Effects during Passage of the Solar System through Interstellar Clouds”C.P. McKay & G.E. Thomas (1978): “Consequences of a Past Encounter of the Earth with an Interstellar Cloud”D.M. Butler et al. (1978): “Interstellar Cloud Material: Contribution to Planetary Atmospheres”D.A. Russell (1979): “The Enigma of the Extinction of the Dinosaurs”P. Thaddeus (1986): “Molecular Clouds and Periodic Events in the Geologic Past”M. Bzowski, H.J. Fahr, & D. Rucinski (1996): “Interplanetary Neutral Particle Fluxes Influencing the Earth’s Atmosphere

and the Terrestrial Environment”P.C. Frisch (1998): “Galactic Environments of the Sun and Cool Stars”G.P. Zank & P.C. Frisch (1999): “Consequences of a Change in the Galactic Environment of the Sun”N.J. Shaviv (2003): “The Spiral Structure of the Milky Way, Cosmic Rays, and Ice Age Epochs on Earth”A.A. Pavlov et al. (2003): “Passing through a Giant Molecular Cloud – Snowball Glaciations Produced by Interstellar Dust”D.R. Gies & J.W. Helsel (2005): “Ice Age Epochs and the Sun’s Path Through the Galaxy”P.C. Frisch (2006): “Introduction: Paleoheliosphere Versus Paleolism”

Reconstructing the Solar Historical LISM

Collaborators: J. Scalo and D. Smith

Measure ISM along the historical solar path out to 500 pc, which, given the solar velocity, corresponds to ~ 40 Myr.

Observed 50 stars between 25 and 500 pc.

Median Δd ~ 5 pc, which corresponds to Δt ~ 0.3 Myr

Time (Myr)

Reconstructing the Solar Historical LISM

Zachos et al. (2001)

(1) Reconstruct density profile for last ~50 Myr.

(2) Calculate the heliospheric response: radiushelio, FCR(1AU)/FCR(LISM)

(3) Compare with geologic tracers. Direct: cosmogenic nuclides (10Be). Indirect: climate

Conclusions

(1) High-resolution spectroscopy from the FUV to the optical is required to fully sample the structures in the LISM

(2) Low column density of LISM has been a challenge, but means several interesting problems remain to be solved: morphology, origins, evolution, ionization structure, relationship between warm and hot gas.

(3) LISM provides an opportunity to study general ISM phenomena in detail and in three dimensions.

(4) LISM also interacts with stellar and planetary systems: new way to measure weak solar-like winds, LISM drives CR flux on planetary atmospheres, test if LISM variations correlate with geological indicators of CR flux, extrapolate to other nearby planetary systems, perhaps with weaker stellar winds or surrounded by denser ISM environments.