# Presentation: 485453

## Modelling the Local Warm Bubble

- D. Breitschwerdt: LB and Beyond II

*                 **Dieter Breitschwerdt*
*Institut für Astronomie, Universit**ä**t Wien, A-1180 Wien, Austria *
- http://homepage.univie.ac.at/dieter.breitschwerdt/

- “*The History and Future of the Local *
*And Loop I bubbles*” – Breitschwerdt
- & Avillez 2006, A&A Letters **452**, 1

## In collaboration with:

- D. Breitschwerdt: LB and Beyond II

- Miguel de Avillez (University of Evora, Portugal)
- Michael Freyberg (MPE Garching)
- Burkhard Fuchs (ARI/ZAH Heidelberg)

## Overview

- D. Breitschwerdt: LB and Beyond II

- _Overview_

- Introduction
- Some important facts about the ISM
- Origin of the LB – Search for the Smoking Gun
- Moving groups
- Complete search of local volume
- Results: 3D AMR Simulations
- Summary & Conclusions

## 1. Introduction

- D. Breitschwerdt: LB and Beyond II

- _1. Introduction_

- Region of very low HI density
-  Local emission of soft X-rays
-  Low OVI column density
-  Low pressure of local cloud: P/k ~ 2000 K cm-3
-  Probably open toward NGP
-  Probably interacting with Loop I

- What do we know about the LB for sure?

## Sketch of LISM

- D. Breitschwerdt: LB and Beyond II

-  Solar System and
-   heliosphere embedded
-   in Local Cloud (LIC):
-   T  6700 K, R  2 pc,
-   n  0.1 cm-3
-  Local Bubble is our
-   cosmic interstellar
-   habitat:
-  T  106 K, R  100 pc,
-  n  5 10-3 cm-3 ???
-  bubbles are embedded
-   in a general SN driven
-   ISM!
-  LB is interacting with
-   an adjacent bubble

## Local Bubble & Loop I

- D. Breitschwerdt: LB and Beyond II

- LB and Loop I are interacting bubbles!

## 2. Some facts to remember about the ISM – how does it evolve?

- D. Breitschwerdt: LB and Beyond II

-  Low resolution: ISM appears
-   smooth and distributed into
-   distinct phases: molecular (MM),
-   cold (CNM), warm (WNM + WIM:
-   neutral + ionized), hot (HIM)
-  High resolution: ISM is frothy,
-   filamentary, fractal, not in pressure
-   equilibrium, turbulent (supersonic,
-   superalfvénic)

**Notes:**
Mass balance (cloud evaporation rate = dense shell condensation rate) and energy balance (SN shock input = radiation loss) provide existence of HIM
 ATCA = Australian Telescope Compact Array
Mass balance (cloud evaporation rate = dense shell condensation rate) and energy balance (SN shock input = radiation loss) provide existence of HIM

##  Reynolds Number is high:

- D. Breitschwerdt: LB and Beyond II

-  Reynolds Number is high:
-    i.e. 105 – 107 (Elmegreen & Scalo 2004); M=u/c ... Mach number

-  Possible driving sources:
-   stellar: HII regions, stellar winds, supernovae (SNe),
-                superbubbles (SBs)
-  galactic rotation
-  self-gravity
-  fluid instabilities: RT-, KH-, Parker instability, MRI etc.
-  MHD: streaming instability (cosmic rays)

**Notes:**
1SNu = 1 SN/100 yr (10^10 L_B/L_sun)

## Modeling a SN driven ISM

- D. Breitschwerdt: LB and Beyond II

- Things to remember:
-  choose a “representative” patch of the ISM
-  large enough to be not severely influenced by BC’s
-  small enough to put on a grid with sufficient resolution
-  choose a sufficiently large extension perpendicular to the
-    disk to capture disk-halo-disk circulation flows
-  Evolution time: results should not depend on initial set-up:
-    erase “memory effects”

- Philosophy: “bottom-up” model
-  include most important physical processes step by step
-  focus on the most important ones:
-    heating and cooling
-    gravitational potential by stars (self-gravity underway)
-    galactic magnetic field and its evolution

## High Resolution Simulations 

- D. Breitschwerdt: LB and Beyond II

- Solve full-blown HD/MHD equations on a
_***large grid: 1 kpc ***__***× 1kpc × ± 10 kpc***_ (Δx=0.625 pc)
- Type Ia,b/II SNe: random + clustered (~60%), IMF
- Background heating due to diffuse UV photon field
- SFR  local density/temp.: n >10 cm-3/T<100 K

- High Resolution Simulations_ _

-   Evolution of computational volume for  ~ 400 Myr

-  3D calculations on parallel processors with AMR

-  Galactic gravitational field by stars (Kuijken & Gilmore, 1989)

## HD Evolution of large/small scale structures of the ISM

- D. Breitschwerdt: LB and Beyond II

## 2D cuts through 3d data cube (disk cut)

- D. Breitschwerdt: LB and Beyond II

- _2D cuts through 3d data cube (disk cut)_

- σ

- n

- P/k

- T

## Distribution of WNM in the Galaxy

- D. Breitschwerdt: LB and Beyond II

- WNM in the unstable regime
- 102.8 ≤ T ≤103.2 K has
- filamentary structure
- opposite to MO model
- in agreement with
-    observations (Heiles 2001,
-    Heiles & Troland 2003)
- Turbulent diffusion can stabilize!

**Notes:**
631 K< T < 1584 K (2.8 < log(T) < 3.2

## Results

- D. Breitschwerdt: LB and Beyond II

-  P/k far from uniform: spatial structure even for high
-   SN rate (σ/σgal = 4)
-  <P/k> ~ 3000 for Milky Way, i.e. much less than
-    canonical values of  > 10,000
-   Reason: due to fountain flow, average disk pressure
-                 can be lowered
-  lots of small scale structure: filaments, shock
-   compressed layers  cloud formation
-  turbulence is a key element in ISM structure formation

## 3. Origin of the Local Bubble 

- D. Breitschwerdt: LB and Beyond II

- 3. Origin of the Local Bubble
-    - Search for the Smoking Gun

- Idea: Cavity AND X-ray emitting gas produced by
-          multiple supernova (SN) explosions
- BUT: No OB star cluster INSIDE Local Bubble !

- _Look for “Smoking Gun”:_
-  Moving group (subcluster) of Pleiades
-   found (Berghöfer & Breitschwerdt, 2001, 2002)
-   passing through the LB about 15 Myr ago
-  (s. also Maiz-Appelaniz 2001)
- BUT: can we be sure not to have missed stars???

-  Search for remnant star cluster in the whole
-   volume around the Sun  ( ~ 400 pc) using
-   parallactic distances from Hipparcos catalogue
-   and radial velocities from ARIVEL (ARI, HD

## a) Moving groups

- D. Breitschwerdt: LB and Beyond II

- Local moving groups (e.g. Pleiades)
- 1924 B-F-MS stars (kin.): *Hipparcos* + photometric ages (Asiain et al. 1999)
- Youngest SG B1: 27 B,
- Use evol. track (Schaller 1992):det. M* , IMF
-  Adjusting B1-IMF:

## b) Complete search of LISM

- D. Breitschwerdt: LB and Beyond II

- Selection Criteria I:
- B – V < - 0.05, parallaxes > 5 milliarcsec,
-     earlier than A0, R < 200 pc: 762 stars
- remove subdwarfs (only interested in young stars!)
- search in ARIVEL data base: 610 stars with radial velocities

**Notes:**
 parallaxes larger than 5 mas, because otherwise distances would be too inaccurate

## Young stars in the solar neighbourhood

- D. Breitschwerdt: LB and Beyond II

-  Positions of 610 stars from
-    Hipparcos and ARIVEL catalogues
-  clustering can be seen

##  Selection Criteria II:

- D. Breitschwerdt: LB and Beyond II

-  Selection Criteria II:

## Selection 

- D. Breitschwerdt: LB and Beyond II

- Selection
- criteria III:
-  larger size at
- t=30 Myr is due
- to distance errors
- increasing with
- time
-  overdense
-  region in past
-  with 302 stars:
-  spatial selection!

##  Selection Criteria IV:

- D. Breitschwerdt: LB and Beyond II

-  Selection Criteria IV:

##  Selection Criteria V:

- D. Breitschwerdt: LB and Beyond II

-  Selection Criteria V:

## Trajectory of youngest nearby cluster

- D. Breitschwerdt: LB and Beyond II

## ... same for meridional projections of trajectory

- D. Breitschwerdt: LB and Beyond II

- ... same for meridional projections of trajectory

-  NaI contours taken from
-   Lallement et al.(2003) for
-   present day LB extension
-  position of UCL and LCC
-   stars colour coded

_**Results:**_
-  stars exit LB today (at t=0 Myr)
-  stars INSIDE LB at t=5 & 10 Myr
-  stars entered LB at t=15 Myr (bottom right)

## IMF:                                                 (Massey et al. 1995)

Number of present day stars in the associations
             calibrating the IMF!

- D. Breitschwerdt: LB and Beyond II

- IMF:                                                 (Massey et al. 1995)
- Number of present day stars in the associations
-              calibrating the IMF!

- UCL + LCC

- How many supernovae created the LB?

## Number of supernovae = ``missing ́ ́ stars

Main sequence life time scales with mass as

Entry of the associations into present bubble
volume between 10 and 15 Myr ago:

- D. Breitschwerdt: LB and Beyond II

- Number of supernovae = ``missing ́ ́ stars
- Main sequence life time scales with mass as
- Entry of the associations into present bubble
- volume between 10 and 15 Myr ago:

- 14 SNe
- 20 SNe

- M?=15.4 Msol

- M?=26.6 Msol

## Numerical Modeling 

- D. Breitschwerdt: LB and Beyond II

- Solve full-blown hydrodynamic equations in a _***realistic environment!***_
- Local Bubble expands into ambient medium which was disturbed by SNe & Superbubbles at Galactic rate over ~ 100 Myrs
- Local Bubble & Cavity generated by 19 SNe according to IMF
- 3D calculations on parallel processors with adaptive mesh refinement (AMR)

- _Numerical Modeling _

## Disturbed background ambient medium 

- D. Breitschwerdt: LB and Beyond II

- Disturbed background ambient medium

## 3D AMR Simulations

- D. Breitschwerdt: LB and Beyond II

- _3D AMR Simulations_

- Density
- Cut through galactic plane
- LB originates at (x,y) = (200 pc, 400 pc)
- Loop I at (x,y) = (500 pc, 400 pc)

- _Results _
- Bubbles collided       ~ 3 Myr ago
- Interaction shell fragments in ~3Myrs_ _
- Bubbles dissolve in   ~ 10 Myrs

## The Local Bubble: Now and in the Future

- D. Breitschwerdt: LB and Beyond II

-  LB is extinct: last SN 0.5 Myr
-   ago
-  LB age: 14.4±0.7/0.5 Myr

-  Interaction shell LB/Loop I breaks
-  Overflow of gas into recombining
-    LB

## Comparison with UV-Observations

- D. Breitschwerdt: LB and Beyond II

-  OVI column densities from
-    simulations averaged over
-   91 L.O.S. towards Loop I
-  Direct Comparison with
-    FUSE satellite date

-  Previous models produced
-   too much OVI!

## OVI Column densities

- D. Breitschwerdt: LB and Beyond II

-  Crucial test for LB  models
-   (Cox 2003)

-  Reason: previous SNR and
-   SB models generate 10–100
-   times too much OVI in
-   absorption towards back-
-   ground stars

-  Possible solution:
-  LB is old and has complex
-     temperature structure

-  Hot gas highly turbulent

-  Ambient medium inhomogneous

## ... and OVII and OVIII

- D. Breitschwerdt: LB and Beyond II

- ... and OVII and OVIII

-  OVII traces hot gas during
-   ongoing SN activity

-  OVIII is post-supernova tracer
-  Loop I higher activity: more OVIII

## Coexistence of UV absorbing and X-ray 

- D. Breitschwerdt: LB and Beyond II

- Coexistence of UV absorbing and X-ray
- emitting gas

- LB in temperature filter 105 K < T < 106 K

## Summary & Conclusions

- D. Breitschwerdt: LB and Beyond II

-   Solar system embedded in void of HI filled with X-ray emitting gas

-   X-ray plasma does not fill Local Cavity completely
-      spectrum inconsistent with gas in CIE (cf. XQC, CHIPS ...)

- Huge pressure imbalance between LB (P/k ~ 15000, Snowden 1998)
-     and Local Cloud (P/k ~ 1700 - 2600, Lallement 1998) and other
-     clouds (P/k ~ 103 – 104, Jenkins 2002) inside the LB
- OVI absorption column density in previous models 10 times higher than observed  our simulations reproduce FUSE data

-  Fast adiabatically expanding plasma due to superbubble evolution
-  ionization and recombination are out of equilibrium
-  delayed recombination produces spectrum roughly in agreement
-  solar wind charge exchange may contribute as well

## Origin of the Local Bubble/Cavity probably solved! 

- D. Breitschwerdt: LB and Beyond II

- Origin of the Local Bubble/Cavity probably solved!
-  subgroups belonging now to Sco Cen association crossed LB
-    region ago 10 – 15 Myr
-  14 – 20 SN explosions created LB Cavity, X-ray and OVI emission
-  LB has age of 14.5 Myr
-  LB will dissolve in about 15 Myr
-  LB/Loop I interaction shell will fragment in 3 Myr
-  LIC and local clouds are relics from instability of interaction shell

- Which physical processes are at work in the Local Bubble?
-  Local Bubble (and Loop I) are typical objects in star
-   forming regions   LB is evolved and recombining superbubble
-                                Loop I evolution is still in full swing
-   LB breaks out into halo
-   LB radiates in UV and soft X-rays for some time
-   Turbulence is a key process for LB dynamics and evolution!

## 3 D AMR high resolution numerical simulations: 

- D. Breitschwerdt: LB and Beyond II

_**3 D AMR high resolution numerical simulations:**_
-  Modelling of LISM (LB+ Loop I) in realistic (SN modified)
-   background medium  good agreement of LB/LI extensions
-  pressure problem also solved: P/k ~ 2000 K cm-3!
-  especially useful for describing old bubbles with density
-   inhomogeneities and mass loading of entrained clouds
-  possible to reproduce OVI absorption column densities
-  generation of local cloudlets by RT instabilities

_**Future Work:**_
-  Numerical modelling of LB including full non-equilibrium
-   ionization (NEI) cooling and emission!
-  Model X-ray emission and compare to observations
-  Determine time-dependent cosmic ray flux during last 30 Myr

## - The End -

- D. Breitschwerdt: LB and Beyond II

## The OVI test: The General ISM

- D. Breitschwerdt: LB and Beyond II

- _The OVI test: The General ISM_

-  OVI traces (cooling down) HIM, not soft X-ray emitting gas!
-  OVI produced in conduction fronts? efficiency rather high!
-  our simulations show: OVI in turbulent mixing layers!

**Notes:**
OVI density distribution in midplane at t= 393 Myr; zoom is the bubble in position C

## N(OVI) through Local Bubble sight lines

- D. Breitschwerdt: LB and Beyond II

-  Temperature map at t=14.4 Myr

-  Sampling OVI in absorption

-  <N(OVI)> at l=200 pc: ~21013cm-2

-  Copernicus data: ~1.6 1013cm-2
-   (Shelton & Cox 1994)

##  FUSE & Copernicus data of 

- D. Breitschwerdt: LB and Beyond II

-  FUSE & Copernicus data of
-    OVI absorption lines towards
-    background stars
-  comparison with simulations
-   (run for t = 393 Myr): spatially
-   averaged (red triangles, blue
-   squares) and single LOS
-   N(OVI)
-  ISM has a pattern, repeating
-   on scales of a few 100 pc!
-  _**Note:**_ simulations were done
-   before data of Oegerle et al.
-   (2004) were published!
-   No “tuning” of results!

**Notes:**
averaged over all angles

## Local Bubble X-ray spectra

- D. Breitschwerdt: LB and Beyond II

- Where does
- Local Cavity
- come from?
-  Talk by Lallement!

- What produces
- X-ray emitting
- Plasma?

- _Supernovae_ could create
-   a local hole
_*Local Bubble!*_
- contribution by solar wind charge exchange

_**Local Bubble X-ray spectra**_

## When and where did the last 

- D. Breitschwerdt: LB and Beyond II

- When and where did the last
- Supernova close to Earth occur?

-  Measurement of 60Fe/Fe
-   concentration in deep sea
-   ferromanganese
-   crust (Knie et al. 2004)
-  dominant source of 60Fe is
-   explosive nucleosynthesis in
-   Type II SNe
-  significant increase at
-   t = 2.8 Myr