ISM evolution of M51 · 2014. 3. 4. · total flux in CARMA+45m data = 1100 Jy km/s ! only 6% of the total flux detected in B-array data ! 1σ=2.5x104 Msun; 5 σ C typical GMCs background:

ISM evolution of M51

Fumi Egusa（江草芙実） ISAS/JAXA

Feb. 18, 2014The Impact of Galactic Structure on Star Formation

1

Outline

Feb. 18, 2014Fumi Egusa (ISAS/JAXA)2

!  Molecular gas and star formation in M51 !  offset (~100pc) between CO and H-alpha

!  assuming the classical density waves !  star formation timescale = 7 Myr for arm1 !  results for other nearby galaxies

!  molecular gas evolution across a spiral arm !  from CARMA CO observations at 30pc scale

!  Interstellar dust properties of M51 from AKARI mid-infrared images !  ionization fraction of PAHs

!  systematically higher in both spiral arms

Molecular Gas Evolution in M51

F. Egusa, K. Kohno, Y. Sofue, H. Nakanishi, & S. Komugi (2009, ApJ, 697, 1870)

F. Egusa, J. Koda, & N. Scoville (2011, ApJ, 726, 85)


Molecular Gas & Star Formation


!  Offsets !  molecular clouds (CO, dust

lane): upstream !  HII regions: downstream !  up to ~500pc

!  Assuming density waves 1.  Star formation timescale

!  time needed for molecular clouds to form stars & HII regions

!  large streaming motions preventing to form stars (S. Meidt’s talk this morning)

2.  Pattern speed !  rotational speed of the

gravitational potential pattern !  can be different from rotational

velocity of gas & starsCO(1-0) of M51 by Koda et al. (2009)

red=H-alpha (HST)

rotational direction

Offset Method


!  Assumption !  rigid rotation of spiral pattern

!  ΩP=vP/R=const.

!  circular rotation of gas & stars !  at angular speed of Ω !  non-circular motions: a factor of 5--10

smaller than the circular velocity

!  constant star formation timescale (tSF)

!  Angular offset !  θ=d/R=(Ω-ΩP)tSF

!  known: θ, Ω !  unknown: ΩP, tSF -- can be derived by

the fit simultaneously

molecular arms at t=0 (dashed) and t=tSF (solid)

ΩP tSF

Ω (km/s/kpc)θ

(de

gree

)

Data & Result for M51


!  images+RC !  CO (Helfer et al. 2003), Ha (Martin & Kennicutt

2001), RC (Sofue et al. 1999) !  CO beamsize ~ 6’’ ~ 250pc

!  offset (θ) vs Ω !  different for arm1 & arm2!

!  fitting results (arm1) !  tSF = 7.1±0.5 Myr !  ΩP = 31±5 km/s/kpc → RCR = 2.9’ (~8kpc)

!  where Ω=ΩP (white ellipse)

arm1

arm2

CO contours on Ha image

Ω (km/s/kpc)

θ (

degr

ee)

Comparison with Preceding Studies


!  Star formation timescale !  this work: 7Myr for arm1

!  can be lower limit considering the non-circular orbit

!  Tosaki et al. (2002) !  assuming ΩP, tSF=7--15Myr

from 12CO(1-0) & 13CO(1-0) at one position in M51

!  Habe-san’s talk yesterday !  core forming timescale in

CCC ~ 0.5tFF ~ several Myr !  Chandar et al. (2010)

!  age of stellar clusters in M83: 1--10Myr from population synthesis models + optical data

!  Pattern speed/corotation !  this work: RCR = 2.9’ !  Tully (1974), Elmegreen et al.

(1992) !  RCR~2.2’ from optical

morphology !  offset reversal should be

apparent !  Oey et al. (2003)

!  RCR~5.0’ from isochrone fit !  Meidt et al. (2008)

!  using revised TW method !  multiple pattern speeds

decreasing with radius

Offset Method to Nearby Galaxies


!  5/12 Successful (C) !  tSF =4--30Myr

!  free-fall time: (Gn)-1/2~6Myr for n=100/cc

!  Corotation Resonance (CR) !  RCR/R25~0.4 !  RCR around or beyond the border of

CO data

!  Others !  2 no offsets (N)

!  not circular rotation due to the central bar?

!  no density waves? !  5 ambiguous (A)

!  negative tSF or large uncertainties

Recent Updates


!  No systematic offsets !  Foyle et al. (2011) !  gas: CO(2-1), HI !  star formation: 24um, FUV

!  Systematic offsets !  Louie, Koda, & Egusa (2013) !  gas: CO(1-0), HI !  star formation: Ha, 24um !  offset found with CO(1-0)

& Ha !  CO(2-1) & HI more closely

related to star formation

Molecular Gas Evolution


!  What is really happening during the star formation timescale?

!  Molecular cloud distribution !  Giant Molecular Clouds (GMCs)

!  105-6 Msun, ~40pc !  found everywhere

!  Giant Molecular Associations (GMAs) !  >107 Msun, >100pc !  only at spiral arms in external galaxies !  confusion of GMCs or discrete structure?

!  Evolutionary sequence !  GMCs -> GMAs in arms -> star formation

-> GMCs? !  need to resolve spiral arms at GMC scale

Molecular cloud distribution according to its mass (Koda et al. 2009)

CARMA CO Observations toward M51

Feb. 18, 2014 Fumi Egusa (ISAS/JAXA) 12

!  Observational details !  toward the brightest GMA in arm1

!  field of view = 1’

!  B-array in Nov. & Dec. 2008 !  5 tracks (34 hours) !  beamsize = 0.73” x 0.60” (31pc x 25pc) !  shortest baseline length = 8” or 300pc

!  sensitivity (1σ) !  12mJy/beam (dV=5.1km/s) or 2.5K !  2.5x104 Msun; 5σ typical GMCs

White circle = field of view of new CARMA obs.

Results


!  Cloud Distribution !  Clump find algorithm (William

et al. 1994) !  34 clumps detected

!  radius=10--60pc !  larger clumps on downstream &

smaller ones on upstream !  large clumps coincide with HII

regions = GMA cores? !  no clumps detected after passage

of the spiral arm !  more overlapping (interacting?)

clumps on downstream?

!  Molecular Gas Evolution Scenario !  GMCs (smaller clumps) ->

GMAs -> GMA cores (larger clumps) -> HII regions

CO on CO

clumps on CO

clumps on Paa

clumps on Ha

Results


!  Internal structure of GMAs !  only a few clouds detected in

each GMA → GMAs are not confusion of GMCs

!  Flux comparison !  total flux in B-array data = 67

Jy km/s !  total flux in CARMA+45m

data = 1100 Jy km/s !  only 6% of the total flux

detected in B-array data !  1σ=2.5x104 Msun; 5σ

typical GMCs

background: CARMA+45m data black circles: GMAs defined from the above data B-array data are not sensitive to extended (> 300pc) structures.

GMCs in MW (Solomon et al. 1987)

Large missing flux also indicates the smooth structure for GMAs.

core formation fraction in CCC

calculation ~ 10% (by Habe-san)

Summary


!  Gas Evolution & Star Formation Scenario 1.  GMCs colliding at spiral arms 2.  GMAs as smooth structures 3.  GMAs with cores 4.  star formation in GMA cores 5.  breaking up to (smaller) GMCs

Rough scenario with lower resolution data

0 1 5

tSF: from step2 to step5 ~ 10 Myr

HII regions next to spurs

Interstellar Dust Properties of M51 from AKARI Mid-infrared Images

F. Egusa, T. Wada, I. Sakon, T. Onaka, K. Arimatsu, & H. Matsuhara (2013, ApJ, 778, 1)


AKARI


!  Instruments !  68.5cm mirror !  IRC + FIS

!  1.8--26um + 50--180um !  continuous filter coverage

!  imaging & spectroscopy

!  Science observations !  2006 May -- 2010 Feb

!  2007 Aug 26, liquid He boil off

!  all sky survey + pointed observations

wavelength [um]

AKARI, Spitzer, WISE filter response curves

AKARI Products


!  IRC/FIS point source catalogues !  open to public !  1.3 million sources

!  IRC image map !  work in progress !  PAH distribution at 5’’

resolution !  FIS image map

!  work in progress !  cold dust distribution at 1’

resolution

90 um & 140 um

9 um

9 um, 18um, 90um

More AKARI Products


Product name Public Release

# of sources Description

Asteroid Catalogue Ver. 1 2011/10/14 5,120 Radius and albedo of asteroids distinguished in the IRC All-Sky Survey data.

LMC Point Source Catalogue Ver. 1 2012/11/13 660,286 Flux and position of sources located in the LMC region (~10 deg2).

LMC Near-IR Spectral Catalogue Ver. 1 2013/01/07 1757 Low-resolution spectra taken with the

objective prism on IRC/NIR camera. NEP-Wide Field Point Source Catalogue Ver. 1 2013/03/15 114,794 NEP-Deep Field Point Source Catalogue Ver. 1

NEP-Deep Field Point Source Catalogue Ver. 2 2013/10/16 27,770

Fluxes and positions of the infrared sources observed at 9 wavelengths (2, 3, 4, 7, 9, 11, 15, 18, 24 um) in the NEP-deep region (0.67 deg2).

Near-IR Diffuse Spectral Catalogue Ver. 1 2013/06/27 278

Low-resolution (R ~ 20) near-IR spectrum (1.8–5.3 um) of diffuse radiation at various positions in the sky.

available from AKARI observers page (http://www.ir.isas.jaxa.jp/ASTRO-F/Observation/) & more to come!

!  Interstellar dust !  Polycyclic Aromatic Hydrocarbon

(PAH) !  spectral features in MIR !  excited & ionized by UV

!  large grains !  modified blackbody spectra

!  InfraRed Camera (IRC) !  MIR

!  S7: ionized PAH !  S11: neutral PAH !  L15: hot dust + PAH !  L24: warm dust (~100K)

!  continuous coverage -> efficient to trace different dust conditions

Interstellar Dust & AKARI IRC


AKARI

Spitzer

WISE

AKARI Images of M51


!  Four MIR bands !  Earthshine light

!  removed for MIR-L !  PSF corrected

!  FWHM=7.4’’~300pc !  ghost of M51b

!  masked for MIR-S !  aligned

!  WCS registered !  North-up !  3.7’’/pix

!  flux calibrated !  Tanabe et al. (2008) !  unit: MJy/sr

S7 S11

L15 L24

Color Maps


!  S7/S11 !  Broad distribution, globally traces the spiral arms

!  L15/S11, L24/S11 !  Peak at individual HII regions

ArmInterarm

S7/S11


!  Previous works !  Sakon et al. (2007) found S7/S11

> 1 in the spiral arm of NGC6946.

!  high 7.7/11.3 ratio in spiral arms (Vogler et al. 2005, Galliano et al. 2008)

!  PAH ionization !  balance between ionization and

recombination: G0Tgas1/2/ne

!  S7/S11 not tightly correlated with L24 !  PAHs are ionized at the border of

HII regions but recombined inside due to high electron density?

!  smaller PAHs are destroyed within HII regions?

S7/S11

C 0.9 ± 0.1

A1 1.0 ± 0.1

A2 1.1 ± 0.1

I1 0.9 ± 0.1

I2 0.9 ± 0.1Arm1

Arm2

Color-color Plots


!  Draine & Li (2007; DL07) model !  middle 2 columns of the CC plot !  often used to interpret Spitzer

observations !  does not explain the observed

distribution !  PAH+WD Model

!  right 2 columns of the CC plot !  symbol size: p0

!  ionized PAH fraction: 0-70% !  symbol color: p1

!  WD/PAH increasing from blue to red: a factor of 16

!  DL07: PAH/dust (qPAH) increasing from red to blue

!  two parameters positively correlated !  more warm dust, more ionized

PAHs

DL07 PAH+WD

more ionized

PAHs

Summary


!  Molecular gas evolution in M51 !  from CO-Ha offset,

tSF=7Myr for arm1 !  for arm2, offsets are found

but not explained by the classical density waves

!  GMA cores detected downstream side of arm1

!  evolutionary sequence of molecular gas proposed

!  Interstellar dust properties in M51 !  S7/S11 systematically high

in spiral arms !  CC distribution cannot be

explained by DL07 model !  more PAHs ionized when

warm dust more abundant !  S11 is important!

!  Currently working on... !  comparison with

interstellar gas distribution

Documents

ISM evolution of M51 · 2014. 3. 4. · total flux in CARMA+45m data = 1100 Jy km/s ! only 6% of the total flux detected in B-array data ! 1σ=2.5x104 Msun; 5 σ C typical GMCs background: