Testing the universalityof the star formation efficiency
in dense molecular gas

submittedto A&A

Y. SHIMAJIRI (CEA), Ph. André (CEA), J. Braine (Bordeaux Univ.), V. Könyves, S. Bontemps,(Bordeaux Univ.), N. Schneider (Cologne Univ.), B. Ladjelate, A. Roy, (CEA),
Y. Gao (Chinese Academy of Science), H. Chen (Nanjing Univ.)
Herschel

1. Introduction+ Filaments and Dense gas+ Universality of the relation between SFR and Mdense

2. Observations (IRAM, MOPRA, Nobeyama)
3. Results

MOPRA+Comparison among obtained maps
+Estimate of Mdense
IRAM30m

4. Discussions+Variations in αHCN+Star Formation Rate in observed clouds+Calibration of Mdense in external gal.
+Universality of relation between SFE and Mdense

NRO 45m

STARFICH

5. Summary
6. 南極望遠鏡による観測

Summary
Corrected Mdense of extra gal.
based on our results of obs. toward nearby clouds.

We foundconstant SFE on a wide range of the scale from ~1-10pc to > 10 kpc

Introduction:
Herschel Gould Belt Survey Result

Ubiquitous offilamentary structuresin molecular clouds

Andre et al. 2010, 2014, Molinari et al. 2010, Arzoumanian et al. 2011

0.1pc-width filaments

Arzoumanian+11

Palmeirim+13

Structure inside filament
13CO(1-0)

ArTeMiS+SPIRE

C18O(1-0)

2pc-12.0 ~ -11.0km/s-10.4 ~ -9.6km/s

Hacar+13

André et al. 2016

0.1pc-width filaments

Arzoumanian+11

Palmeirim+13

Structure inside filament
13CO(1-0)

ArTeMiS+SPIRE
ALMA N2H+C18O(1-0)

2pc-12.0 ~ -11.0km/s-10.4 ~ -9.6km/s

Hacar+13

Shimajiri +in prep.

Give restrictions on
theoretical filamentstudies

Mass accretion

12CO(1-0):6.6-7.4km/s
13CO(1-0):5.6-6.4km/s(b)(b)τ(CO)Model(a) Observations

12CO(1-0):4.2-5.5km/s

1pc

Accretion by gravity
feeds filament.
viewsky(c) Model Palmeirim+13 (d) Schematic
Shimajiri+in prep.

RinitFilaments to cores

Routθ

0.14

Velocity Structure Function

0.12

Modeled filament
with fragmentation

Sv1/2(km/s)

0.1

Gravity causes
fragmentation
into cores

0.08
0.06

our H 13 CO+ centroid velocity

0.04
0.02

Modeled filament
without fragmentation

000.1

0.2

0.3

0.4

0.5

0.6

0.7l (pc)

Konyves+15

Shimajiri +in prep.

Introduction:
Mass budget in the Aquila cloud complex
Number of pixels per bin: ΔN/ΔlogNH2

Column Density Probability Density Function

AquilaFilaments dominate
at high column densities(see also Schisano+2014)~ 85% ofcloudmassFilam

en
ts:

>50-7
5%ofmaAv~ 7Av~7Column density, NH2 (cm-2)

ssPDF
after subtracting cores
PDF
after subtracting cores &filaments(Könyves et al. 2015)●Below Av ~ 7: ~10-20% of the mass in the form in filaments,<1% in prestellar cores●Above Av ~ 7: >50-75%of the mass in the form of filaments,
fpre~15±5% in prestellar cores

Introduction:
Density threshold for star formation●Critical (thermal) mass per unit length: Mline,crit=2cs2/G(Stodolkiewicz 1963, Ostriker 1964)●Thermally supercritical filament with Mline > Mline,crit:
Unstable for radial collapse and gravitational fragmentation(Inustuka & Miyama 1992, 1997)●Mline,crit ~ 16 Msun/pc @10K!

●Mline,crit/Wfil ~ 160 Msun/pc2
which is corresponding to AV ~ 8mag!

●Mline,crit/Wfil2 ~ 1600 Msun/pc3
which is corresponding ton(H2) ~ 2.3×10-4 cm-3.

W(width)L(Filament length)

Mline = M / LIntroduction:
Universality of the relation between SFR and Mdense
SFR directly proportional to the mass of dense gas (≧104 cm-3)
SFR-Mdense relation

galaxies[External galaxies]
SFR=1.8×10-8 Msun/yr × (Mdense/Msun)(Gao&Solomon 2004)[Nearby clouds]
SFR=4.6×10-8 Msun/yr × (Mdense/Msun)(Lada et al. 2010,12)

nearby clouds(also see Andre et al. 2014)

The similar SFR-Mdense relation has been foundin the nearby galactic clouds and external galaxies.
May be a universal “star formation law” converting the dense gas into stars

Mdense in external galaxies are larger than Mdense expectedfrom the SFR-Mdense relation in the nearby clouds.

Introduction:
Universality of the relation between SFR and Mdense
SFR directly proportional to the mass of dense gas (≧104 cm-3)
SFR-Mdense relation

galaxies

nearby clouds
extinction

Mdense = αHCN × LHCN
*αHCN = 10

Different tracers were used to estimate Mdense.
→Observations in the same tracer are required.

Introduction:
Selection of molecular lines
Mline,crit~16Msun/pc — n=2.3×104cm-3 HCN(1-0) — 8.4×103cm-3

Effective excitation densities at 10K H13CN(1-0)— 3.5×105cm-3(Shirley 2015)
HCO+(1-0)—9.5×102cm-3*Density results in a spectral line with 1 K km/s.
H13CO+(1-0)—3.9×104cm-3●Detectable in extra gal.
●Many HCN studies in extra gal.
■Chin et al. 1997 (LMC)■Chin et al. 1998 (SMC)■Gao & Solomon 2004 (LIGs, ULIGs)■Brouillet et al. 2005 (M31)■Buchbender et al. 2013 (M33)■Chen et al. 2015, 2016 (M51)
etc…

Molecular line observations
AquilaW40

Serp. S

Aquila/coldHCN(1-0)
H13CN(1-0)
HCO+(1-0)
H13CO+(1-0)
Oph.

θ~28” (~0.04pc)

IRAM30m

Amap=0.42deg2(~8.7pc2)

Orion Bθ~19” (~0.04pc)
NGC2071
NGC2068
Amap=0.14deg2(~6.8pc2)

Oph/main (L1688)
NGC2024

Oph/coldAmap=0.21deg2(~1.2pc2)

θ~39” (~0.03pc)

MOPRA22m

NRO45m
NGC2023

Results: Maps in Aquila
Herschel N(H2)

H13CO+(1-0)

H13CN(1-0)

Distributions of H13CO+ & H13CN
are similar to that of Herschel N(H2).
→Good tracers of “dense” Herschel filaments

Results: Maps in Aquila
Herschel N(H2)

HCO+(1-0)

HCN(1-0)

Serp SW40

FUV field strength
From 70µm+100µm

Stronger HCO+ & HCN
around HII region.
→ Dependence of HCO+ & HCN
on FUV radiation
PDR model also predicts this dependence(Meijrink et al. 2007)

Discussion:Variations in αHCN
Estimate αHerschel-HCN in our observed clouds as below:
map>8magαHerschel-HCN = MHerschel/LHCN●Range of αHerschel-HCN : 50-3800●Much larger than αHerschel-HCN used in other studies(e.g. 10:Gao & Solomon, 7±2: Wu et al. 2005)●Large variations are recognized
Possible reason:+ FUV radiation(correlation coefficient = -0.82→ strong correlation)
αHerschel-HCN = MHerschel / LHCN = 496×G0-0.24

Discussion:
Star Formation Rate in observed clouds
AquilaStar formation rate (SFR)

contour:8mag

Lifetime of Class II: 2 Myrs
Median mass : 0.5 Msun
(Covey+10, Dunham+15, Muench+07)

Classification of protostars
Class II: -1.6 ≦ α < -0.3(Greene et al. 1994)

Spitzer YSO catalogs:
Dunham et al. 2015 for Oph and Aquila
Megeath et al. 2012 for Orion B

Oph(main)Oph(cold)

W40Serp

Aquila(cold)

N(ClassII)

5905454

7829

420

SFR
(M

14.8×10—

13.5×10

13.5×10

1.8×10

2.0×109.0×10

1.0×10

5.0×10

NGC2023 NGC2024 NGC2068 NGC2071

Discussion:
Calibration of Mdense in external gal.
HCN survey toward etragal.

HGBS N(H2)

HCN(1-0)■Chin et al. 1997 (LMC)■Chin et al. 1998 (SMC)■Gao & Solomon 2004 (LIGs, ULIGs)■Brouillet et al. 2005 (M31)■Buchbender et al. 2013 (M33)■Chen et al. 2015, 2016 (M51)
etc…

Beam size for external gal.
is much larger.
(θbeam = 9 pc — 36kpc)

̶ Av=8mag

Pety+16

98% of HCN flux arises
from Av>2 area (Pety+16)

Need calibration of the contamination from lower Av area.

Discussion:
Calibration of Mdense in external gal.

Column Density
Probability Density Function

Dependence of effective excitation
densities on Temperature

Orion BAquila
Orion B + Aquila

Könyves et al. 2015, Könyves et al. in prep.

cf. Shirley 2015
Assumptions:Tdust ∝ G0.2
01NH2 ∝ ρ1− α (α = 1.75 ± 0.25)

0.056±0.0120.43)∝GLHCN,Av=2 ∝ (nHCN0eﬀ−0.34±0.08+0.06−0.095±0.02
fitfit′× αHerschel−HCN ∝ G0
αHerschel−HCN ≈ 0.13−0.06 × G0

Discussion:
Relation between SFR and Mdense
Corrected SFR-Mdense relation

Linear relation between SFR and Mdense

Discussion:
Relation between SFE and Mdense
Corrected SFE-Mdense relation

Universal “star formation law”
converting the dense gas into starsConstant SFE on a wide range of the scale from ~1-10pc to > 10 kpc

Summary•

We conducted a wide field mappingin HCN, HCO+, H13CN, and H13CO+
toward Aquila, Oph., and Orion B.

•H13CO+ and H13CN:
Good tracers of “dense” Herschel filaments.

•

Larger variations in αHCN (=Mdense/LHCN)
conversion factor.
→ αHCN decreases as G0 increases(αHCN∝G0-0.24).

•Corrected Mdense for the external galaxies
Constant SFE on a wide range of the scalefrom ~1-10 pc to > 10 kpc.

南極望遠鏡によるHCN観測
HCH(1-0) — optically thickContamination from lower Av area

●Obs. in higher-J HCN or its isotope
toward nearby clouds and etragal.

●Wide field mapping toward nearby
clouds to evaluate the contamination.
●Obs. in continuum are also required
to estimate Mdense.
HGBS N(H2)̶ Av=8mag

HCN(1-0)

Pety+16

南極望遠鏡による連続波観測

AzTEC@ASTE
1.1mm

NIKA2@IRAM30m
1mm + 2mm (+pol.)ArTéMiS@APEX
350µm+450µm

南極望遠鏡による連続波観測
AzTEC/ASTE
2007

PCA
(no extended emission)

Shimajiri et al. 2011,2015aIntensity profiles around strong sources- - - - - - PCA——— FRUIT

南極望遠鏡による連続波観測
AzTEC/ASTE
2010

Intensity profiles around strong sources- - - - - - PCA——— FRUIT

FRUIT(extended emission)

Shimajiri et al. 2011,2015a

Reconstructing extended emission is crucialfor star formation studies

南極望遠鏡による連続波観測
ArTeMiS/APEX

Andre et al. 2016

ESO news letter (14 Junes 2016)

http://www.eso.org/sci/publications/announcements/sciann16034.html

Combined APEX/ArTeMiS image with Herschel/SPIRE image.

Thank you