5214

36

Megan Reiter ,1,2‹
Omnarayani Nayak,33 Margaret Meixner3,4
and Olivia Jones
1,2‹
3,4
1MeganOmnarayani
Nayak,Margaret
Meixner
Jones
Department Reiterof Astronomy, ,Universityof Michigan, 311 West
Hall, 1085 South
University Avenue,
Ann Arbor, MIand48109,Olivia
USA

2
2

21 UK Astronomy Technology Centre, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK
Department of Astronomy, University of Michigan, 311 West Hall, 1085 South University Avenue, Ann Arbor, MI 48109, USA
32 Department of Physics & Astronomy, Johns Hopkins University, 3400 N. Charles St., Baltimore, MD 21218, USA
UK Astronomy Technology Centre, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK

43 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
Department of Physics & Astronomy, Johns Hopkins University, 3400 N. Charles St., Baltimore, MD 21218, USA
4 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA

Accepted 2018 November 27. Received 2018 November 27; in original form 2018 August 31
Accepted 2018 November 27. Received 2018 November 27; in original form 2018 August 31

LMCとSMCの大質量YSO（6天体）に対し、ABSTRACTABSTRACTAs nearby neighbours to the Milkywith
Way, the Large
and Small（R=4800）
Magellanic Clouds (LMC and近赤外中分散分光観測
FIRE
As nearbyneighbours
to opportunity
the Milky Way,
the Large
and SmallinMagellanic
Clouds
(LMC
and
SMC)
providea uniqueto study
star formation
the context
of theirgalactic

10-12

10-14

SMC) provide
a unique ofopportunity
to study
starformation
the characterized
context of theirecosystems.
Thousands
young stellar
objects(YSOs)
have inbeen
withgalactic
largeecosystems.
Thousandsof surveys.
young stellar
objectshave
beencharacterizedwith oflargescale
Spitzerand Herschel
In thispaper, (YSOs)
we
present
newnear-IR
spectroscopy
fiveMC
candidatehigh-mass
YSOs:
near-IR
spectra5217
Figure 2. Approximate location of the YSOs targeted in this programme shown on three-colour Spitzer images of the Large (left; Meixner et al. 2006) andscale Spitzer
and inHerschelsurveys.
Ininthis
new near-IR
spectroscopyof fivehigh-mass
YSOs
the LMCand onethepaper,
SMC.weWepresent
detect multiplehydrogenrecombination
Small (right; Gordon et al. 2011) Magellanic Clouds. White boxes and labels indicate the regions targeted for near-IR spectroscopy. Most regions contain one
high-mass
YSOs
in
the
LMC
and
one
in
the
SMC.
We
detectmultiplehydrogenrecombinationlines, as well as He I 2.058 µm, H2 , [Fe II], and [S III] in these highly excited sources. We
object, except for N159 where we target three YSOs.
2.058 µm,ofHeachII], and
III] thatin thesehighly excitedsources.
lines, as thewellinternal
as He Iextinction
2 , [Feestimatesourceand[Sfind
it is highest
for sources
with Wetheestimate theinternal extinctionof eachUsing
sourceline
andratios,
find thatis highest
for sourcesexcitation
with theyoungest
evolutionaryclassifications.
weitassessthe dominant
Table 3. FIRE observations of high-mass star-forming regions in the LMC and SMC.
youngest evolutionaryline ratios,
assess the dominant excitation
mechanismin the threeclassifications.
sources whereUsing
we detectboth Hwe2 2.12 µm and [Fe II] 1.64 µm. Inµm we
anddetect[Fe II]CO
1.64µm. Inmechanismin the three sourceswhereweshock
detectexcitation.
both H2 2.12
eachcase, photoexcitation
dominates
overFinally,
bandhead
TargetRegion
RA
Dec.
Ka
tint
J2000
J2000
[mag]
[s]
each case, photoexcitation
dominates
overWhileshockthisexcitation.
Finally,
we detect COabsorption
in one of our LMC
sources.
feature isoften associatedwithbandhead
evolvedabsorption
in oneisoflikely
our LMC
While
this feature
is oftenassociated withevolvedstars,
this object
youngsources.
with strong
polycyclicaromatichydrocarbons(PAHs)
andJ84.703995–69.079110
LMC/30 Dor
05h 38m 48.s 96–69◦ 04′ 44.′′ 8
14.07
4 × 60stars, this object
is likely
young
with
polycyclicaromatichydrocarbons
andJ72.971176–69.391112
LMC/N79
04h 51m 53.s 08–69◦ 23′ 28.′′ 0
12.39
4 × 60detected
at longer
wavelengths.(PAHs)
Comparedfine-structure
emissionlines
tracing
an strong
H II region
J84.906182–69.769472
LMC/N15905h 39m 37.s 53–69◦ 46′ 09.′′ 8
12.57
4 × 300
detected
longer wavelengths.
Comparedfine-structure
emissionlines
tracingour
an sources
H II regiontohigh-mass YSOs
in theGalaxy,havehigher atbolometricand line luminosities,
J84.923542–69.769963
LMC/N15905h 39m 41.s 89–69◦ 46′ 11.′′ 9
12.16
4 × 600
to high-mass
YSOs
the Galaxy,
our ofsourceshave higher
bolometricand andlineSMC.
luminosities,
consistentwiththeirinselection
as somethe brightest
sourcesin the LMC
J85.018918–69.743288
LMC/N15905h 40m 04.s 54–69◦ 44′ 35.′′ 8
11.73
4 × 300
consistent with their selection as some of the brightest sources in the LMC and SMC.
J16.280250–71.995194
SMC/N7601h 05m 07.s 26–71◦ 59′ 42.′′ 7
14.12
5 × 600
Key words: stars: formation – stars: massive – stars: pre-main-sequence – stars: protostars.
5218
M. Reiter
et al.– stars: massive – stars: pre-main-sequence – stars: protostars.
Note.a K magnitudes from Kato et al. (2007).
Key words:
stars: formation

全てで多数の水素再結合線（とHe I 2.058 µm）を示す

比Paβ/Brγを使って、internal減光量を見積もった：1 <= Av <= 12 mag
Table 5. Extinction estimates.
of ionizing radiation precedes the end of accretion (e.g. Klaassen
To improve the signal in these cases, we bin the data to a spectral

resolution R ≈ 1200 to improve line identification and fitting. All
et al. 2011, 2018). Therefore, theetpresenceof LMCemissionlines
frommany sources at a uniform
al. 2016). The
and SMC
providelines detected with ≥3σ
are rγlisted in Table
4. V)
1 I N T RO D U C T I O N
NamePa β/B
E(B −
AV a
et
al.
2016).
The
LMC
and
SMC
providemany
sourcesatauniform(∼50 kpc,
Pietrzyński
et al. 2013 and ∼60 kpc, Scowcroftnecessarily
signalthat accretionan emerging H II region does notdistance
1 I N T RO D U C T I O N
distance(∼50
kpc, Pietrzyński
et al.galaxies
2013 and∼60
kpc, Scowcroft
The formation and evolution ofhas
high-mass
stars remains an openetal. 2016,
respectively)in irregularwithfavourable
orienfinished.
30
DorandYSO
4.24 ± 0.41 0.72 ± 0.16
2.46 ± 0.57
The
formationand evolutionof high-mass
remainsplane
an openet al. 2016,
respectively)in irregularlaboratories,
galaxies withorienquestionin astrophysics.
The recent
explosionstarsof Galactic
surtations.
Unlikeother extragalactic
thefavourable
LMC
SMC
5 S P E C T R A L F E AT U R E S-16dominatetheother
spectra,likelytrac10veys
1.56 ± 0.01 3.09 ± 0.05
10.5 ± 0.15
questionastrophysics.
The recentHydrogen
explosionof recombination
Galacticofplanesur- lines aretations.
extragalacticlaboratories,
theH72.97–69.39
LMC and SMC
has inprovidedan unprecedented
view of thousands
activelycloseUnlike
enoughto resolve
individual
high-mass
star-forming
reBinnedand smoothed
spectraare shown
3. The most
II Multi-wavelength
regions.
Most
sourcesalso
ing
emissiontheassociatedveys has provided
unprecedented
view ofactivelyareHcloseenough toresolve
individual
high-mass
star-forming
restar-forming
cloudsanthroughout
the planeof thousands
thefrom
Milky ofWay
(e.g.
gions.
surveysparticularly
with J84.906182–69.769472
Spitzerand Her5.18± 0.230.25in±Fig.
0.05
0.84 promi± 0.15
nent emission lines in each source are hydrogen recombination
star-forming
cloudsthroughout
the
plane
the etMilky
WayMoli(e.g.
gions.
Multi-wavelength
surveys
Spitzer
HerHoareet al. 2005;
Urquhart
et al.
2008;
Schulleral. 2009;
schel
have
uncovereda wealth
ofparticularly
candidate withyoung
stellarand
objects
Iofemission(fiveout of six).
Hard
UV
photons
are required
haveHe
J84.923542–69.769963
1.40 ± 0.38 3.34 ± 0.59
11.4 ± 2.05
and higher excitation species are seen in a few
Hoare
et al.
2005;
Urquhartal.
Schulleral.
2009; obserMolischelhigh-luminosity
have
uncovereda wealthof candidate
stellar objects
nari
et al.
2010;
Aguirreet al.et2011).
Unlikeprevioustargeted(YSOs)
in bothgalaxies(e.g.
Meixner
et al. young
2006;
Whitney
et lines,
al. although rarer3.20
hinting thatsourcesmay
to2008;
exciteHe I etemission,
Papillon
YSO± 0.31 1.39 ± 0.16
4.73 ± 0.56
nari et al.these
2010;surveys
Aguirredid
et al.
previous targeted
obser(YSOs)Meixner
in both etgalaxies(e.g.
Meixneral. 2006;
Whitney
et cases.
al. Lines detected in each source are listed in Table 4. We briefly
vations,
not2011).
selectUnlike
for a particularstar-formation2008;
al. 2013;
Sewiłoet al.et2013;
Seale
et al. 2014).
N76
YSO
0.88
± 0.65
4.43± below.
0.11 12.13 ± 0.30
excitetheline.
However,
there
does
not
appeartobealuminosity
describetherelevant
featuresofeach
objectvations,these
surveysdid
notselectforaparticularstar-formation
2008;
Meixner
et
al.
2013;
Sewiło
et
al.
2013;
Seale
et
al.
2014).
indicator, instead providing an unbiased sample. This large populaHundreds of candidate YSOs have been targeted for follow-up ob-18
a Assuming
YSOs(Cooperthresholdfor
He I in Galactic
indicator,
insteadan unbiased
This large
populaHundredshigh-massofcandidate
YSOsInfraRed
have
beenSpectrographtargeted forfollow-up
ob- RV = 3.41 and RV = 2.74 for the LMC and SMC, respecof clumps
hasproviding
enabled construction
ofsample.
an required
evolutionary
sequenceservations
withthe Spitzer(Spitzer
IRS;
10tionNote.
tion massof clumps
has enabledconstructionof anSvoboda
evolutionary
servations
the around
Spitzeret InfraRed
Spectrograph(SpitzerIRS;
andfunctionfor high-mass
al.sequence2016).
Oliveira
et withal. 2009;
Sealeal.
2009;and
Oliveira et tively.
al. 2011;
Woods
in emission
lowetstars
al. (e.g.
2013)
and etindeedHe I is seen
5.1 30 Dor YSO
andGalaxy-widemass function
for high-massstarsthose(e.g. Svoboda
al.
2016).
Oliveira
et al.
2009;Seale
al. Fischer
2009;
Oliveiraal. 2011;
surveys,particularlythat targetetgalaxies
ex- Edwards
etal. 2011;
Oliveira
et 2006;
al.et2013;
Ruffleet al. et2015;
JonesWoods
et al.
intermediate-mass
stars
(e.g.
et
al.
2003,
Galaxy-wide
surveys,thosethat target
exet al. 2011;
Oliveira etal.reveal
2013;absorption
Ruffle et al.
Jones etices
al. most massive and luminous YSOs in the LMC reside in the
ternalto the MilkyWay, particularly
allow detailed
studiesof thegalaxies
association
2017).
Spectroscopic
data
due2015;
to molecularThe
etdetailedal. 2008;
Cauley&galaxies
Johns-Krulland
2014;
Reiteret al.
Inprotostars
H II due
Our targets
haveof internal
extinction
ternal to star
the formation
Milky Way,
studiesof closest
the association
2017).
Spectroscopic
data2018).
reveal absorption
to molecularices
betweenandallowenvironment.
Twoof thesilicate
dust in theyoungestwhile
more
evolved
R136
SSCa atrange
the heartof 30 Dor.
The YSOvalues.
that weTwo
targetofinthe
regions
as of
well
as
low-mass
photoexcibetween
star formationand environment.
Twothe closest
galaxiesand silicate
in stars,
the youngest
protostars
while
moreheavily
evolvedtothe Milky
Way, the Large
andSmall Magellanic
Clouds(LMC pre-main-sequencesources
showdust
fine-structure
emissionlines andUV-pumped
poly! 5) also
have theevomostthisextincted
programmeobjects
lies ∼11(ApcV outside
the central
SSCyoungest
where strong
to-20
the
MilkyareWay,
the Largeprime
and
Small
Magellanic
Cloudssourcesaromaticshow
fine-structure
emission
andtypically
UV-pumped
polySMC),
particularly
for observational
scrutiny(LMC(e.g. collisional
cyclichydrocarbons(PAHs) linesthat areexcitedinwinds
and turbulencefrom R136 impact ongoingtationlikelydominates
overexcitation(see Osterbrock10andv
lutionaryclassifications(J84.923542–69.769963
andstartheformation.
N76 YSO;and SMC),
are2008;
particularly
for observational(e.g.Fischer
cyclicaromatichydrocarbons(PAHs)that
that are typically excitedJ84.703995–69.079110,
in
II regions.
Whitney
et al.
Dobbs etprime
al.&2010;
Louie,2006;
Koda &scrutiny
Egusa 2013;
H
which we refer to as the 30 Dor YSO, isFerland
Kwan
&
2011,
respectively).
Given
see Table 1). Our extinction estimate
for the N76 YSO is intermediregions.
Whitneyetetal.al.
2008;Choi
Dobbs
et al.
2010;
Louie,
Koda& Egusa
2013; 2.0
H IINew
observations with2.5
the Atacama Large Millimeter/subSewiło
2013;
et al.
2015;
Lewis
et al.
2015;
Ochsendorf
the most massive YSO within the footprint of ALMA observations
1.0
1.5
I
emission
is
seen
in
young
embeddedsources
(e.g.
Covey
et
al.
He
ate
betweenthevaluesdetermined
Ward
al. (2017)
whoinfoundNew observations
with provide
the Atacama
Sewiło et al. 2013; Choi et al. 2015; Lewis et al. 2015; Ochsendorf
millimeter
Array (ALMA)
maps Largeof the Millimeter/subcontinuum andof 30 Dor (Nayak et al. 2016).byThis
sourceetremains
embeddedits
λ [µm]
2011; Connelley& Greene 2014)molecular
as well as
more
evolvedregions,
millimeter
Array(ALMA)
providemapsof theandemissionwithcomparable
sensitivity
to= 0.81and± 0.35
maggas,(optical)
and
AV =
± by
9.3fitting
magthe(KAcontinuum
natal
molecular
with a massof ∼24M⊙19.5(derived
V resolution⋆ E-mail: megan.reiter@stfc.ac.uk
molecular
with comparable
andtoemission
observationsof evolutionary
Galactic
clouds.stage.
For sensitivity
the first time,itresolution
is using
possible
Robitailleet al.
2006
modelsto theSED;
see Nayak
et al. 2016).
it is not clearly an indicator of source
massemission
or
band)
line
ratioswiththe
Galactic
extinction
curve⋆ E-mail: megan.reiter@stfc.ac.uk
observationsof Galactic
clouds.sources
For the first time, it is possibleThe spectrum of the 30 Dor YSO shows a few of the brighter
We
detectalargernumberofnear-IRemission
lines
from
=
3.1.
(Cardelli,
Clayton&Mathis
1989)
and
R
⃝
V
C 2019 The Author(s)hydrogen recombination lines (Paβ, Brγ) as well as He I emission at
II classification.
two sources in the LMC with the
⃝
with
the H
C 2019 The
PublishedbyAuthor(s)Oxford University Presson behalfof theRoyal AstronomicalThe
Society
We detect both the 1.26 µm and 1.64 µm lines of [Fe II] in
Published by Oxford University Presson behalfof theRoyal Astronomical
Society
fewestlines
detectedalso havethe lowest luminosities (see Table 3).
two sources, the H72.97–69.39 candidate SSC and J84.906182–
MNRAS 483, 5211–5222 (2019)
J84.923542–69.769963 has the youngest source classification of our
69.769472. These two [Fe II] lines originate from the same uppersources in the LMC, YSO2, and is the only source with rising conlevel, so a deviation of their observed flux compared to the intrinsic
tinuum in the near-IR spectrum. Deeper integrations would provide
value (1.49; see Smith & Hartigan 2006) provides an independent
better signal-to-noise data, allowing for more line detections, andestimate of the reddening. Following the same procedure as for

高いA を持つ天体：

2.058 µm. We also detect high ionization lines like [S III] 0.9533 µm
in the 30 Dor YSO spectrum.
The 30 Dor YSO is the only source in the sample that shows theCO bandhead in absorption. Molecules readily form in the cooler
envelopes of evolved stars, making CO bandhead absorption a usefulprobe of their extended atmospheres (e.g. Förster Schreiber 2000;
Bieging, Rieke & Rieke 2002). In young sources, CO bandhead
emissionhas been shown to trace circumstellar discs in some highmass young stellar objects (e.g. Ilee et al. 2013). The CO bandhead
has been seen in absorption in a few lower-mass stars, particularly
those with high accretion rates (typically members of the FU Orionis
class of objects; see e.g. Calvet et al. 1991; Hartmann & Kenyon
1996; Connelley & Reipurth 2018).

Downloaded from https://academic.oup.com/mnras/article-abstrac

Flux + offset [erg s-1 cm-2 A-1]

10-10

M. Reiter et al.

Downloadedfromhttps://academic.oup.com/mnras/article-abstract/483/4/5211/5284997
National
AstronomicalObservatory,
Japan
user
February
2019
Downloadedfromhttps://academic.oup.com/mnras/article-abstract/483/4/5211/5284997
by byNational
AstronomicalObservatory,
Japan
user
on on
27 27
February
2019

Unveiling the nature of candidate high-mass young stellar objects in theUnveiling the nature of candidate high-mass young stellar objects in the
Magellanic Clouds with near-IR spectroscopy
Magellanic Clouds with near-IR spectroscopy

5.2 Super star cluster H72.97–69.39 in N79
H72.97–69.39 is a young SSC candidate located in the N79 regionof the LMC. It is the most luminous site of star formation in the
LMC, with physical characteristics that suggest that it is a younger
analogue of the R136 SSC in the heart of 30 Dor (see Ochsendorf
et al. 2017). ALMA observations of H72.97–69.39 suggest that thesource is young as it is still associated with a significant amountof dense molecular gas. At the same time, the mass of ionized gas
is small compared to other YSOs in the LMC, suggesting that thehighest-mass sources are just beginning to ionize the surrounding

他の天体よりも若い進化分類になり、星形成の初期フェーズを意味

3つ：[Fe II] 1.64 µm emissionを示す
4つ：H2 2.12 µm emissionを示す

両輝線：ショックのトレーサーと見なされるが、HII領域に付随しているので強いUVによる光励起
かも[Fe II]と水素再結合の比 <1：３天体全てで、光励起が卓越していることを示す
しかしながら、
0.01 <= H2/Brγ <= 1.3：４天体のうち２天体の励起にショックが寄与していることを示す
H2/Brγが高い天体は若い進化分類を持ち、その内部のsourceは降着・アウトフロー
を駆動していることを意味する

30 Dor YSO：CO bandhead 吸収を検出
若いはず
Spitzer IRS：PAHの特徴やHII領域で励起される典型的なemission lineを示す
ALMA：母分子雲に付随していることを示す
銀河系内の大質量YSOsでの検出の多くはemissionでのCO bandheadを示す（Cooper+13）
30 Dor YSOでのCO bandhead吸収の起源はよくわからない

The Astrophysical Journal Letters, 871:L12 (5pp), 2019 January 20

40

Evidence
Evidence ofof Hubble
Hubble Flow-like
Flow-like Motion
Motion ofof Young
Young Stellar
StellarPopulations
away
from
the
Perseus
Populations away from the Perseus ArmArmperpendicular to the plane of thprescription of Gaia Collaboration etan expansion center at (l, b ) =Section 3), located near the young
We then derived a new set of opositions ( xp , yp), and proper motion
center. Assuming that rotation and
PsAm are negligible, the variation
motions as a function of the projectwill only keep the bulk motion compline of sight: ¶mx ¶x » ¶my ¶y »to either of the m xp versus xp or m yp v
ﬁrst order, a direct estimate ofcorrection. In our case, thecml, b » 5.4 (xp , yp) mas yr-1, applie
projected positions, which we ﬁnallyproper motions. This accounts forcorrection by the unknown line of sNow, it is important to consider tdata, it is impossible to determin
expansion is due to purely persp
effects. In order to quantify this, w
and Wright & Mamajek (2018; theira system in linear expansion withpredict the required radial velocitie
velocities measured from the sy
expansion age term8 kd = (1.0227t
routine, we found that for stars w
Section 3), the expected distribution
peak around 100 km s−1. We are a
distribution by providing our sample
in the range -15 < vR < -65 km
standard of rest velocity for the W34
1998; Bieging & Peters 2011). We
distribution when we increased theover 100 km s−1. Radial velocity
physically unreasonable as a solely
fore, we can safely consider our sam
expansion.
Finally, we applied the same csamples within the same cone: one (flimited to sources with distances d<the PsAm) and a second one (cocontaining stars in the same distan
older population dominated by ﬁ
(BP - RP ) < 2.4. The resultant s
2468 stars, respectively. The purpos
is to apply a similar analysis to t
observed behavior (see Section 3
candidates in the PsAm is not a datain the whole Gaia DR2 sample in th

1,2
2,3
1,2
Carlos
Tapia
Carlos G.
G. Román-Zúñiga
Román-Zúñiga1,2 ,,1Alexandre
Alexandre Roman-Lopes
Roman-Lopes2,3 ,, Mauricio
Mauricio
Tapia1,2 ,,
11
1
Jesús
Jesús Hernández
Hernández ,, andand Valeria
Valeria Ramírez-Preciado
Ramírez-Preciado

11Instituto
Institutode
deAstronomía,
Astronomía,Universidad
UniversidadNacional
NacionalAutónoma
AutónomadedeMéxico,
México,Unidad
UnidadAcadémica
Académicaen
enEnsenada,
Ensenada,Ensenada
Ensenada22860
22860Mexico;
Mexico;croman@astro.unam.mx
croman@astro.unam.mx
2
2Programa de Estancias de Investigación (PREI), DGAPA-UNAM, Mexico
Programa de Estancias de Investigación (PREI), DGAPA-UNAM, Mexico
33

Departamento
Departamentode
deFísica
FísicayyAstronomía,
Astronomía,Universidad
UniversidadLa
LaSerena,
Serena,La
LaSerena,
Serena,Chile
Chile
Received
Received2018
2018AugustAugust19;
19;revised
revised2018
2018December
December12;
12;accepted
accepted2018
2018December
December26;
26;publishedpublished2019
2019January
January22
22

Abstract
Abstract
In
In thisthis Letter
Letter we
we present
present evidence
evidence ofof thethe coherent
coherent outward
outward motion
motion ofof aa sample
sample ofof young
young stars
stars (t(t<<3030Myr)
Myr) inin thethePerseus
W3/W4/W5
PerseusArm,
Arm,whose
whoseapparent
apparentorigin
originisislocatedlocatedin
inthe
thevicinity
vicinityof
ofthe
the
W3/W4/W5complex.
complex.Using
Usingastrometricastrometricand
and◦◦photometricradius ﬁeld
ﬁeld centeredcentered near
near W4,
W4, wewe selected
selected aa
photometric data
data fromfrom thethe Gaia
Gaia Data
Data Release
Release 22 catalog
catalog ofof anan 88 radius
samplesample ofof young
young intermediateintermediate- toto high-mass
high-mass star
star candidates.
candidates. The
The sample
sample isis limited
limited toto sources
sources with
with parallax
parallax
uncertainties
uncertainties below
below 20%
20% andand Bayesian
Bayesian distancedistance estimatesestimates within
within 1800
1800 andand 3100
3100pc.
pc. TheThe selection
selection includes
includesembeddedembedded stellar
stellar populations
populations as
as wellwell asas young
young open
open clusters.
clusters. Projected
Projected velocities
velocities derived
derived fromfrom perspectiveperspectivecorrected
corrected proper
proper motions
motions clearlyclearly suggest
suggest thatthat thethe youngyoung star
star population
population emerged
emerged fromfrom thethe Perseus
Perseus Arm,Arm, with
with aapossiblezone
possible convergence
convergencezone near
near W3/W4/W5
W3/W4/W5 region,
region, tracing
tracing aa front
front thatthat expands
expands away
away atat aa rate
rate of
of
1
1
about
15km
kmss-1kpc
kpc-1..
about15
Key
Key words:
words: Galaxy:
Galaxy: kinematics
kinematics andand dynamics
dynamics –– open
open clusters
clusters andand associations:associations: generalgeneral –– stars:
stars: kinematics
kinematics andanddynamics
dynamics –– stars:
stars: massive
massive

W3/W4/W5領域のGaia DR2 dataを使用
W4付近から半径8 カタログ

若い（<30 Myr）中・大質量候補天体をセレクト
HHIIII regions
regions (W4(W4 andand W5),W5), aa massive
massive molecularmolecular ridge
ridge with
with
activeactiveformation
formation(W3),(W3),andandseveral
severalembedded
embeddedstar
starclusters
clusters(e.g.,(e.g.,
Carpenter
et
al.
2000;
Koenigetal.
2008;
Román-Zúñiga
etCarpenter et al. 2000; Koenig et al. 2008; Román-Zúñiga etal.
al.
2015;
2015; Jose
Jose etet al.
al. 2016;
2016; Sung
Sung etet al.
al. 2017)
2017) possibly
possibly hosting
hosting aa
large
large number
number ofof OB
OB stars.
stars. AroundAround W345,
W345, this
this region
region ofof thethe
PsAm
PsAm hosts
hosts several
several OB
OB associations
associations like
like PerPer OB1,
OB1, which
which
contains
contains thethe open
open clusters
clusters NGC
NGC 884884 andand 869,
869, andand thethe
Cassiopeia
Cassiopeia OB8,
OB8, which
which includes
includes thethe cluster
cluster NGC
NGC 663.
663. HereHerewe
we show
show thatthat aa sample
sample ofof intermediateintermediate- toto high-mass
high-mass young
young
stars
stars in
inW345
W345 andand nearby
nearby associations
associations traces
traces what
what looks
looks like
like aacoherent
expanding
front
of
young
(t
<
30
Myr)
stars
coherent expanding front of young (t < 30 Myr) stars andandclusters,
clusters, likely
likely born
born atat thethe PsAm
PsAm close
close toto thethe W345
W345 region.
region.

1.1. Introduction
IntroductionStar
clusters
areformedStar clusters are formed within
within giant
giant molecularmolecular clouds
clouds(GMCs)(GMCs) with
with aa large
large diversity,
diversity, likely
likely related
related toto thethe early
earlyorganization
organization ofof thethe clouds
clouds andand environmental
environmental factors
factors (Lada(Lada &&
Lada
Lada 2003;
2003; Longmore
Longmore etet al.
al. 2014).
2014). In
In aa recent
recent review,
review,
Gouliermis
Gouliermis(2018,(2018,and
andreferencesreferencestherein)
therein)discussed
discussedthe
thecasecaseofofgravitationallygravitationally unboundunbound young
young stellar
stellar systems,
systems, representing
representing
GMC
GMC complex-scaled
complex-scaled multiplex
multiplex associations
associations thatthat may
may bebeconsidered
considered to
to bebe thethe open
open end
end ofof an
an intricate,
intricate, hierarchicalhierarchicalprocess
process thatthat scales
scales down
down toto thethe formation
formation ofof compact,
compact, boundboundclusters.
clusters.In
Inthatthatscenario,
scenario,large
largeGMC
GMCcomplexes
complexesmay
mayproduce
produceaa
large
large number
number ofof starstar clusters
clusters born
born with
with aa variety
variety ofof energy
energydistributions
distributions(Blaauw(Blaauw1964)1964)that,
that,ininmostmostcases:
cases:(a)(a)expandexpandandanddisperse,
disperse, (b)(b) cancan bebe tracedtraced throughthrough their
their massive
massive (OB)(OB)
members,
and
(c)
may
containcrucialinformation
about
their
members, and (c) may contain crucial information about theirformationformation process.
process. In
In general,
general, thethe expansion
expansion andand dispersal
dispersal ofof
young
young star
star systems
systems may
may bebe related
related toto complex
complex dynamical
dynamical
interactions
interactions between
between clusters
clusters andand sub-clusters
sub-clusters during
during their
theirformationformation process,process, andand also
also toto thethe rapid
rapid removal
removal ofof gasgas duedue totomassivemassive star
star winds
winds andand moremore violent
violent events
events like
like Wolf–Rayet
Wolf–Rayetoutbursts
orsupernova
explosions.
The
current
availabilityofoutbursts or supernova explosions. The current availability of
precisepreciseastrometricastrometricparametersparameters(distances,(distances,proper
propermotions)motions)from
from
the
theGaia
Gaiasatellite
satelliteData
DataRelease
Release22(DR2;(DR2;see
seeGaia
GaiaCollaboration
Collaboration
etet al.
al. 2016,
2016, 2018)2018) allows
allows thethe exploration
exploration ofof starstar kinematics
kinematics ininthisthis context,
context, andand itit has
has provided
provided evidence
evidence ofof coherent
coherent motion
motionandand expansion
expansion ofof stellar
stellar populations
populations inin certain
certain stellar
stellar systems,
systems,fromfrom star-forming
star-forming complexes
complexes (e.g.,(e.g., Kounkel
Kounkel etet al.
al. 2018;
2018; Kuhn
Kuhn
etet al.
al. 2019)
2019) toto moremore evolved
evolved young
young cluster
cluster associations
associations (e.g.,(e.g.,
WrightWright && Mamajek
Mamajek 2018)2018) andand OBOB associations
associations with
with driven
drivenexpansion
expansion (e.g.,(e.g., Cantat-Gaudin
Cantat-Gaudin etet al.
al. 2019).
2019).
The
The goal
goal ofof thisthis Letter
Letter isis toto report
report aa discovery
discovery about
about thetheglobalglobalpicture
pictureof
ofstar
starcluster
clusterevolution
evolutionin
inaaregion
regionof
ofthe
thePerseus
PerseusArm(hereafterPsAm),
aroundthe
W3/W4/W5
complexArm (hereafter PsAm), around the W3/W4/W5 complex(hereafter(hereafter W345).
W345). W345,
W345, locatedlocated onon thethe Galactic
Galactic plane,
plane, isis aa
well-studied
well-studied massive
massivestar-forming
star-forming region,
region,containing
containing two
twogiant
giant

2.2. Data
Data Sample
Sample Selection
Selection andand Analysis
Analysis
Our
main
goal
is
to
study
the
kinematics
Our main goal is to study the kinematics ofof intermediate
intermediate totomassivemassive(OB)(OB)stars
starsasastracers
tracersof
ofthe
theyoung
youngstellar
stellarpopulation
populationinin
W345
W345 andand its
its surroundings.
surroundings. Using
Using thethe Gaia
Gaia Table
Table Access
AccessProtocolProtocol (TAP)(TAP) services
services andand 4catalog
catalog extraction
extraction tool
tool atat
Astronomisches
we retrieved
retrieved aa catalog
catalog
Astronomisches Rechen-Institut,
Rechen-Institut,4 wecomprising
comprising all
all DR2DR2 entries
entries within
within an
an 8°-radius
8°-radius5conecone centeredcenteredon
The catalog
catalogon thethe W345
W345 complex
complex atat (α,(α, δ)=(40°,δ)=(40°, 61°).
61°).5 The
contains
and RRpp magnitudes)
magnitudes)contains aa full
full set
set ofof photometricphotometric (G,(G, BBpp,, and,parallaxes,ϖandparallax
andastrometric(propermotions,μand astrometric (proper motions, μPP, parallaxes, ϖ and parallax
errors,parameters. This
Thisconeconeextends
extendsroughlyroughlyfrom
from250
250totoerrors, σσϖϖ))parameters.
420
420pc
pc (depending(depending on
on distance)
distance) inin eacheach direction
direction fromfrom thethe
W345
W345complex,
complex,covering
coveringthe
theprojected
projectedwidth
widthof
ofthe
thePsAm
PsAmandandprovidingproviding aa good
good sampling
sampling ofof thethe populations
populations formed
formed atat GMC
GMC
complexes
complexes inin thethe region.
region.
The
The TAPTAP tool
tool also
also provides
provides distancedistance estimatesestimates forfor eacheach starstar
byby using
using aa Galactic
Galactic stellar
stellar density
density model
model priorprior thatthat varies
varies with
with
each
position(l,b)(Bailer-Jones
et
al.
2018)
and
provideseach position (l, b) (Bailer-Jones et al. 2018) and provides
conﬁdence
conﬁdence intervals,
intervals, deﬁned
deﬁned byby lower
lower andand upper
upper limits,
limits, ddlow
low44
http://gaia.ari.uni-heidelberg.de/
http://gaia.ari.uni-heidelberg.de/55

Figure 1. Gaia color-absolute magnitude diagram showing the selection of asample containing OB stars. Gray symbols are Gaia sources in the main catalog
with parallax errors under 20%. Green symbols indicate the PsAm sample.
Yellow and cyan symbols show the control samples. The color/brightness
constraints (Section 2) are indicated with dotted lines. The solid color lines are
3 Myr isochrones from the PARSEC 1.2 s models (Bressan et al. 2012; Tanget al. 2014).

and dhigh. We extracted sources within 1.8 < (d kpc) < 3.1,
which we deﬁne as a “full” sample expected to contain sources
across the entire girth of the PsAm. We limited the sample tosources with sv v < 0.2 parallax accuracy6 and contained
within a distance range deﬁned by (dhigh - dlow ) < 1.2d + 20 .
As shown in Figure 1, using the MRP versus BP - RP Gaia
color-absolute magnitude diagram, we selected a locus
containing sources brighter than 1.547 ´ (BP - RP ) - 1.2(the slope follows the reddening vector using the extinction
coefﬁcients from Evans et al. 2018) and colors within
0.3 < BP - RP < 1.2 mag. This locus minimizes contamination from ﬁeld giant and dwarf stars, and is expected to containmostly bright intermediate to massive members of young stellar
groups with average extinctions within AV=1 and 3 mag. We
estimate around 10% of contamination in this sample due toﬁeld stars with anomalous colors, with a distribution affectedby patchy extinction. Finally, we also restricted the projected
raw velocity moduli to vl2 + vb2 = ∣v∣ < 60 km s-1. The total
number of sources in this restricted PsAm sample is 1100.
From the distances and proper motions, we calculated
projected velocities over the plane of the sky on galactic
coordinates as vl, b = 4.74dml, b , where ml and μb are directlytransformed from the μα and μδ values provided in the DR2.7
The angular size of the region of study is quite large, thus
requiring a correction by perspective expansion/contraction(Brown et al. 1997) to take into account the effect of the motion

3. Results

In Figure 2 we show the persp
velocities vl,pc, vb, pc (scaled to unit
Gaia DR2 stars present in the full dithat traces star-forming regions, as
molecular and neutral gas near W345
well as H I and CO integrated intens
we use an orientation parameter byWe
Weconﬁrmed
conﬁrmedthat
thataalarger
largeropening
openingdoes
doesnot
notalteralterourourresults
resultssigniﬁcantly.
signiﬁcantly.

11

6

A tighter constraint of σϖ/ϖ0.1 does not signiﬁcantly alter our results.
All proper motions and velocities are expressed units of mas yr−1 andkm s−1, respectively.
782

between the corrected projected velocity, vl,pc , and a purely

Plus a redshift/blueshift correction, which

For instance, the Gaia DR2 parallaxes provide distances thatare still uncertain in the 102 pc scale for the PsAm, impeding an
accurate analysis of the distribution of young stellar populations within this part of the Arm. Also, the lack of radial
velocity measurements for most of the stars in our sample
prevents a full six-dimensional position–velocity analysis at
this Galactic region. From the observed expanding motion andthe available theories in the literature, we propose threepossible scenarios.

ベクトルを戻すとW345近くの収束領域に行き着く
現在は1.5 Myrの若い埋もれたpopulationがある

1. The presence of the HB-3 supernova (SN) remnant nearW3, along with the presence of tens of OB stars in theW345 complex (see the top panel Figure 2), suggest thatSN explosions could be one possible driving mechanism in
the region, which could transfer the mechanical energy to
the cluster-gas systems. Indeed, it is known that a single SN
can imprint momentum of the order of 10 5M: km s-1 (Kim
& Ostriker 2015), providing up to 1050 erg in 10 Myr(Thornton et al. 1998). Super-bubble-type expansions via
SN often pierce and surpass the disk, depending on thehomogeneity of the local medium (Mac Low et al. 1989).
Also, most of the mechanical energy from SN events andmassive star winds is carried by ionizing radiation, which
could provide impulse for the stellar system expansion.
Gaia DR2 data could provide evidence of a champagneﬂow-type expansion of gas layers (Tenorio-Tagle 1979),
with the stars moving along with the gas.
2. Recently, Tchernyshyov et al. (2018) presented detailed gas
velocity maps and compared them to the Stationary Density
Wave model of the Milky Way spiral structure (Lin &Shu 1964), particularly near the PsAm. The study suggeststhat a spiral arm can be fed from one side by diffuse gas
causing a net outward ﬂow toward its trailing edge. The
main effect is a concentration of the dense gas where ﬂows
converge, and a dissipation of those centers after starformation, forming a divergence of the velocity ﬁeld. Thismechanism can provide a direct explanation of theobserved effect in our sample. Moreover, if gas and stars
are expelled away from the arm, aided by this mechanism,
then we should expect a net torque in the arm. If this is true,
our study presents actual evidence of the action of spiraldensity waves near the co-rotation radius in the PsAm.
3. Another possibility is that all the groups that we areconsidering are all part of a much larger association of2clusters that is expanding away as a massive unboundyoung stellar system with an age spread of about 30 Myr(considering the estimated ages of the older clusters in thesample). The driving mechanisms behind the expansion
could be directly related to the star formation process,along with gas dispersal and the dynamic evolution of thesystem, similar to what is observed in star-forming
complexes like Orion, Vela OB2, or Scorpio–Centaurus.
However, it would be necessary to determine how toadjust such proposed scenarios to the spiral arm widthscale that we report in this Letter.

結果の解釈＆現在受け入れられている銀河系での星形成シナリオへの影響：(l, b ) = (137.8, 1.3), which was estimated by projecting
backwards the vl , vb vectors of candidate members of known
open clusters, (deﬁned as sources within a small vicinity
around published centers and distances and limited tosv v < 0.1). We can see how the corrected velocity moduli
for most of the sources are in the range of 10–20 km s−1, which
is signiﬁcantly larger than the typical expansion velocities forunbound groups in other systems (e.g., Cantat-Gaudin et al.
2019; Kuhn et al. 2019; Wright & Mamajek 2018). It is clearthat the young stellar population is actually expanding away fromthe Galactic plane: a linear ﬁt to the data suggests a (projected)
Hubble-type expansion of about 15.4 km s-1 kpc-1. The
additional panel of the Figure 4 shows the equivalent plot forthe control sample, where we conﬁrm a null expansion trend,with a correlation coefﬁcient near zero. The results for the codistant control sample are equivalent, with a null expansion trend
and little or no coherence in the dot-vector plot.

=> このレターの範囲を超えている（より正確なデータが必要なので）例えば・・・

Gaia DR2の視差は10 pc scaleで不確定性が未だあり、正確な分布解析が難しい

また、radial velocityの測定がないため、6次元の位置速度解析ができていない
4. Discussion and Summary

今回観測された広がる動きと現在ある理論から、可能性のある３つシナリオを提案
The analysis of the Gaia DR2 data described above reveals ascenario where young stellar populations are moving awayfrom a location in the PsAm. Tracing back the (v , v ) vectors

While eloquent, our analysis is just a starting point. Future

1：W3付近のHB-3超新星残骸の存在：超新星爆発が駆動メカニズム
力学的エネルギーを星団-ガス系へ移す
実際、単一SNは105 Msun km s-1の運動量（Kim&Ostriker 15）、
最大1050 erg in 10 Myrを与える（Thompson+98）
SNによるSuper-bubbleタイプの膨張は、ディスクを貫く（Mac Low+89）
また、SNと大質量星風からの力学的エネルギーの多くは、
ionizing radiatoinによって運ばれ、恒星系膨張への要因となる
Gaia DR2 dataはシャンパン流型のガス層の膨張の証拠（Tenorio-Tagle 79）であり、星はガスに沿って動いている。
2：Tchernyshyov+18：
詳細なガスの速度マップを示し、銀河系spiral構造の密度波モデル（Lin & Shu 64）と比較を行なっている（特にPrAm付近の）。
主な効果は高密度ガスの集中（そこに流れが収束）と、星形成後の中心ガスの散逸。
それが速度場の発散を生み出している
今回の観測結果はこのメカニズムによるものと解釈できる

更に、このメカニズムによって星とガスがarmから追い出されるとすると、armでのnet torqueを
これが本当ならば我々の研究は、PsAmでのspiral密度波の作用の実際の証拠を与えている。
3：全てのグループが、かなり大きな星団アソシエーションである可能性。
約30Myrで広がっている、巨大なunboundな若い恒星系のような膨張をしている
膨張の駆動メカニズム：ガスの散逸・系の力学的進化の変化による星形成過程と直接関係している（OrionやVela OB2、Scorpio-Centaurusのような星形成領域で観測されるものと似ている）=> But このシナリオをspiral armスケールにどのように適合させるかが問題である

Advance Access publication 2018 December 6

39 Evolution of Hubble wedges in episodic protostellar outflows
1

and D.

1 I. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, D-50937 Köln, Germany
2 School of Physics and Astronomy, Cardiff University, Cardiff CF24 3AA, UK

3 Universitäts-Sternwarte München, Scheinerstraße 1, D-81679 München, Germany

Accepted 2018 November 30. Received 2018 November 30; in original form 2018 August 23

ABSTRACT

Young low-mass protostars undergo short phases of high accretion and outburst activity leading
to lumpy outflows. Recent observations have shown that the position–velocity and mass–
velocity diagrams of such outflows exhibit individual bullet-like features; some of these bullets
subscribe to a ‘Hubble Law’ velocity relation, and others are manifest as ‘Hubble wedges’.
In order to explore the origin of these features, we have developed a new episodic outflow
model for the SPH code GANDALF, which mimics the accretion and ejection behaviour of
FU-Ori-type stars. We apply this model to simulations of star formation, invoking two typesof initial conditions: spherically symmetric cores in solid-body rotation with ρ ∝ r−2 , andspherically symmetric turbulent cores with density proportional to the density of an Bonnor–
Ebert sphere. For a wide range of model parameters, we find that episodic outflows lead to
self-regulation of the ejected mass and momentum, and we achieve acceptable results, evenwith relatively low resolution. Using this model, we find that recently ejected outflow bullets
produce a ‘Hubble wedge’ in the position–velocity relation. However, once such a bullet hits
the leading shock front, it decelerates and aligns with older bullets to form a ‘Hubble-law’.
Bullets can be identified as bumps in the mass–velocity relation, which can be fit with a−1.5.
power-law, dM/dυRAD ∝ υRAD
Key words: stars: formation – stars: protostars – stars: winds, outflows.

1 I N T RO D U C T I O N
In the core accretion scenario for star formation, collapsing dense
cores form protostars, and these protostars are usually surroundedby accretion discs (e.g. Shu & Adams 1987; Tan et al. 2014, andreferences therein). However, the observed luminosities of suchprotostars, and therefore by implication also their accretion rates,
are typically much lower than one would expect, given their masses
and formation time-scales, and assuming steady accretion; this mismatch is called ‘the luminosity problem’ (Kenyon et al. 1990, 1994;
Kenyon & Hartmann 1995). The luminosity problem can be mitigated if the accretion from the disc onto the protostar is episodic,
with a large fraction of the accretion occuring in short intense events
called outbursts (Offner & McKee 2011; Dunham & Vorobyov
2012; Cesaroni et al. 2018; Hsieh et al. 2018; Ibryamov, Semkov &Peneva 2018; Kuffmeier et al. 2018). Such outbursts are observedin FU-Orionis-type stars (FUors), which undergo a rapid increasein accretion rate, from ∼ 10−7 M⊙ yr−1 to ∼10−4 M⊙ yr−1 , for aperiod of order 10 years (Herbig 1966; Hartmann & Kenyon 1985;⋆ E-mail: rohde@ph1.uni-koeln.de (PFR); seifired@ph1.uni-koel.de (SW)

Hartmann et al. 1989; Audard et al. 2014; Safron et al. 2015; Fehér
et al. 2017). The cause of this behaviour is still debated, but one
possibility is the interplay of gravitational and magnetorotational
instabilities (MRI; Balbus & Hawley 1991) in the disc (e.g. Zhu,
Hartmann & Gammie 2009a; Zhu et al. 2010a; Stamatellos, Whitworth & Hubber 2011b; Kuffmeier et al. 2018). Using a large ensemble of Smoothed Particle Hydrodynamics (SPH) simulations
Lomax, Whitworth & Hubber (2016a,b) conclude that episodic accretion is necessary to reproduce the observed stellar initial massfunction and the ratio of brown dwarfs to hydrogen-burning stars.
Most, possibly all, forming protostars launch fast bipolar outflows (see, e.g., the reviews of Arce et al. (2007); Frank et al. (2014);
Bally (2016), or the recent results from Samal et al. (2018)). The
inference is that, during the collapse, gravitational energy is converted into kinetic and magnetic energy, which then drives andcollimates the outflow, either through magnetic pressure or magnetocentrifugal forces (Blandford & Payne 1982; Lynden-Bell 2003;
Pudritz et al. 2007; Machida, Inutsuka & Matsumoto 2008; Seifried
et al. 2012; Frank et al. 2014; Bally 2016). The outflow removes
a significant fraction of the angular momentum from the star–discsystem, enabling the gas in the accretion disc to reach the central
protostar (Konigl & Pudritz 2000; Pudritz et al. 2007). Since the⃝C 2018 The Author(s)Published by Oxford University Press on behalf of the Royal Astronomical Society

Downloaded from https://academic.oup.com/mnras/article-abstract/483/2/2563/5232391 by National Astronomical Observatory of Japan user on 27 February 2019

P. F. Rohde,1‹ S. Walch,1‹ D. Seifried ,1 A. P. Whitworth,2 S. D. Clarke
A. Hubber3

1. Rotating setup
一時的な降着とprotostarからのアウトフローの効果を調査
安定した、剛体回転の球対称コア（ρr-2）の中心で形成
Hubble wedges in protostellar outflows
2569
2570
P. F. Rohde et al.
Table 2. Parameters for the runs performed with the Rotating Setup (Section 2.4). Reading left to right, the columns give the run number, the run ID, thefeedback mechanism, the number of particles in the core (NCORE ), the sink formation density (ρSINK ), the wind opening angle (θWIND ), the launching radius(rLAUNCH ), the jet opening angle (θJET ), the fraction of the gas accreted by a protostar that is ejected in bipolar outflows (fEJECT ), the minimum radius at which
the SPH particles representing the outflow are injected (rMIN ), and the Shakura–Sunyaev viscosity parameter for MRI viscosity (αMRI ).

2573

Hubble wedges in protostellar outflows

Run

Feedback

NCORE
103

ρSINK
g cm−3

θWIND
radianrLAUNCH
AU

θJET
radianfEJECT

rMIN
AU

αMRI

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22

CONT:100
CONT:200
CONT:400
EPISODIC:25
EPISODIC:50
EPISODIC:100
EPISODIC:200
EPISODIC:400
RHOSINK:11
RHOSINK:12
THETAWIND:0.6
THETAWIND:0.2
RLAUNCH:14
RLAUNCH:047
THETAJET:0.05
THETAJET:0.005
FEJECT:0.2
FEJECT:0.05
RMIN:30
RMIN:10
ALPHAMRI:0.2
ALPHAMRI:0.05

Continuous
Continuous
Continuous
Episodic
Episodic
Episodic
Episodic
Episodic
Episodic
Episodic
Episodic
Episodic
Episodic
Episodic
Episodic
Episodic
Episodic
Episodic
Episodic
Episodic
Episodic
Episodic

100
200
400
25
50
100
200
400
100
100
100
100
100
100
100
100
100
100
100
100
100
100

10−10
10−10
10−10
10−10
10−10
10−10
10−10
10−10
10−11
10−12
10−10
10−10
10−10
10−10
10−10
10−10
10−10
10−10
10−10
10−10
10−10
10−10

0.4
0.4
0.4
0.4
0.4
0.4
0.4
0.4
0.4
0.4
0.6
0.2
0.4
0.4
0.4
0.4
0.4
0.4
0.4
0.4
0.4
0.4

0.07
0.07
0.07
0.07
0.07
0.07
0.07
0.07
0.07
0.07
0.07
0.07
0.14
0.047
0.07
0.07
0.07
0.07
0.07
0.07
0.07
0.07

0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.05
0.005
0.01
0.01
0.01
0.01
0.01
0.01

0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.2
0.05
0.1
0.1
0.1
0.1

20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
30
10
20
20

0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.2
0.05

3.2 Comparison between episodic and continuous outflows

Here, we compare and contrast episodic outflow feedback with
continuous outflow feedback. The continuous feedback runs (Runs
1–3, Table 2) equate the accretion rate onto the protostar (dM⋆ /dt)
to the accretion rate onto the sink particle (dMSINK /dt) – rather
than using the sub-grid model of Stamatellos, Hubber & Whitworth(2011a) and obtaining episodic accretion rate onto the protostar;
we reiterate that in the episodic approach particles are only ejectedduring an outburst (see Section 2.3). The continuous feedback runs
use NCORE ≃ 105 (Run 1), NCORE ≃ 2 × 105 (Run 2), and NCORE ≃4 × 105 (Run 3); all other parameters have their default values. The
results are compared with the episodic accretion Runs 6 and 7.
Fig. 5 shows the evolution of MSINK (t) and MTOTAL (t) (top panel),and POUTFLOW (t) and PTOTAL (t) (bottom panel), obtained with continuous and episodic outflows. There is no evidence that the runs
with continuous outflows have converged with increasing NCORE –particularly as regards the momentum carried away from the core
(blue, , and black lines on the bottom panel of Fig. 5) – and therefore we cannot safely draw any conclusions regarding the physics
of continuous outflows. The reason for non-convergence is that thecontinuous outflows are not properly resolved.
To be properly resolved, the SPH particles near the axis of theoutflow must have neighbour-lists which contain exclusively SPH
particles that are also in the outflow (and all SPH particles in theoutflow must have neighbour-lists which contain at least a significant fraction of SPH particles that are also in the outflow). In otherwords, the SPH particles in the outflow must interact hydrodynamically with one another. With continuous outflow, the rate at which
outflow SPH particles are launched may be so low that this requirement is not met; successively ejected outflow SPH particles may
be too far apart. The SPH particles in the outflow will only interacthydrodynamically with one another if they have very low-mass, andtherefore are very numerous, specificallyṀ⋆ fEJECT (4π/3) rMIN
2 υ
4 N̄NEIB πθJETLAUNCHRUN11以下で、パラメータを一つだけ

Figure 3. False-colour images of the column-density in run EPISODIC:400 at times t = 2.4 kyr, t = 4 kyr and t = 16 kyr. The spatial scale increases from top
to bottom, and the circle in the bottom panel shows the initial radius of the dense core (0.015 pc). The first panel shows the outflow cavity shortly after the first
outflow event. In the second panel, the outflow breaks outHubbleof the wedges
dense core.
Multipleoutflows
bullets forming
in protostellar
2573 a chain of Herbig–Haro-like objects are seen in the third
panel.

In Runs 6, 9 and 10 (see Table 2), the number of SPH particles in
the core is held constant (at NCORE = 105 ; hence mSPH = 10−5 M⊙
and MRES = 10−3 M⊙ ) and the sink creation density is decreased
from ρSINK = 10−10 g cm−3 (Run 6) through ρSINK = 10−11 g cm−3
(Run 9) to ρSINK = 10−12 g cm−3 (Run 10). Along this sequence, thesink radius increases from rSINK = 0.9 AU (Run 6) through rSINK =2.0 AU (Run 9) to rSINK = 4.3 AU (Run 10).
Fig. 4 shows the evolution of MSINK (t) and MTOTAL (t) (top righthand panel), and POUTFLOW (t) and PTOTAL (t) (bottom right-handpanel), obtained with different ρSINK . There are some systematicchanges with increasing ρSINK , and the results are therefore notstrictly converged, even at the highest ρSINK . In particular, the downtime between outbursts is longer with lower ρSINK . However, theoverall behaviour is not strongly dependent on ρSINK . (i) At all
times, the mass of the sink particle, MSINK (t) varies by less thana few per cent. (ii) In all the simulations, the downtime between
successive outburst events increases with time. (iii) At late times(t ! 30 kyr), as ρSINK changes by a factor of 100, the total mass

escaping from the core and its envelope, MTOTAL (t), varies by atmost 10 per cent; and the total momentum escaping, PTOTAL (t), byat most 20 per cent.

3.1.3 Synopsis

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3.1.2 Sink creation

変化させた

mSPH << 7 × 10−6 M⊙!

Ṁ⋆
10−6 M⊙ yr−1"!

υLAUNCH
100 km s−1

"−1

.

(41)

(42)

To obtain the second expression, we have substituted the default values for fEJECT = 0.1, rMIN = 20 AU, and θJET = 0.01 rad. The factor
4 in the denominator derives from the fact that we launch outflow
SPH particles in groups of four. N̄NEIB is the mean number of neighbours, and we have substituted N̄NEIB = 50. In the runs with continuous outflow, Ṁ⋆ is usually much smaller than 10−6 M⊙ yr−1 , andthe launch speed, υLAUNCH is usually ! 100 km s−1 . Consequently,
convergence requires NCORE ! 106 SPH particles per M⊙ .
A further issue affecting the runs with continuous outflow is thatthe high velocity of the launched SPH particles greatly reduces thetime-step for these particles and for all those with which they interact, even indirectly – in particular, those that get entrained in theoutflow early on. Even though the code uses individual particle time
steps, many particles have short time steps, throughout the simulation, and hence the computing requirements are very demanding.
In contrast, the runs with episodic outflow only require these shorttimesteps for brief periods during and immediately after an outburst.

主要なproperty（protostarの成長速度・アウトフローに

Low NCORE means not having to follow so many SPH particles(but at the price of coarser mass resolution), and low ρSINK means
not having to follow the SPH particles to such high densities, andhence with such short timesteps (but at the price of excising thedetailed dynamics at these high densities). On both counts this reduces computing requirements. Since our outburst model produces
approximately converged results with low NCORE and low ρSINK –modulo slightly longer downtimes between outburst events – weconclude that it can be used in larger scale simulations of star formation (e.g. Clarke et al. 2017), where the computing requirementswith higher NCORE and/or higher ρSINK = 10−10 g cm−3 might not be
feasible.

よって運ばれる質量や運動量）は、数値パラメータにほとんど依存しないMNRAS 483, 2563–2580 (2019)

MNRAS 483, 2563–2580 (2019)

3.3 Varying the physical parameters
The Outflow Feedback Model involves six physical parameters, andtheir values are poorly constrained by observation or theory. In thissection, we explore how the results change when these parameters
are increased or decreased from their default values (i.e. those in thefiducial Run 6, EPISODIC:100: θWIND = 0.4 rad, rLAUNCH = 0.07 AU,

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2. Turbulent Setup
一時的な降着とprotostarからのアウトフローの効果を調査
turbulentで球対称なコア（Bonnor-Ebert球に比例する密度proﬁle）の中心付近で誕生
Hubble wedges in protostellar outflows
2575
2576
P. F. Rohde et al.

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Figure 9. Evolution of the accretion rates onto the sink particle, ṀSINK (t) (green), and the protostar, Ṁ⋆ (t) (blue). The labels, A–F, correspond to the outflow
bullets formed in the individual outbursts (see Figs. 8 and 10). Note that the time resolution in this figure is too coarse to fully resolve the very short outbursts.

(2001); Tafalla et al. (2004); Santiago-Garcı́a et al. (2009); Wanget al. (2014), we construct PV-diagrams, i.e. false-colour plots of"MPIXEL =d 2M"r "υRADdr dυRAD(46)

on the (r, υRAD ) plane. Here, r is radial distance, and υRAD is radial
velocity, both measured from the centre of mass. For the velocity
axis we take 180 bins with a width of "υRAD = 0.56 km s−1 . For
the spatial axis, we take 180 spherically symmetric shells aroundthe centre of mass with a width of "r = 0.0056 pc and consider
only particles with radial outflow velocities larger than the escapevelocity (equation (37)). Note that in this case MTOTAL = 3.9 M⊙ ,so the escape velocity at 0.1 pc is 0.58 km s−1 . This effectively
constrains our analysis to the outflow cones. As a final step, we use
a kernel density estimator to compute "MPIXEL , with a smoothinglength obtained using ”Scott’s Rule” (Scott 1992).
Fig. 10 (right-hand side) shows PV diagrams for the left lobe of
Figure 8. Column density images of the Turbulent Setup, at t = 115, 117, 120 and 122 kyr. The circle indicates the initial radiusof the core,andsamethe viewing
the outflow
at thetimes as shown on Fig. 8. Features associatedangle is chosen so that the outflow axis is approximately horizontal. The bullets are labelled AL/R through EL/R for the corresponding
left and rightlobe, arein marked A, B, C, etc., in both figures.
with the individualbulletsorder of increasing age (see Fig. 9). The time series, from top to bottom, shows the end of a cycle of a bullet, here bullet DL , when
it
hits
the
leading
shock
The PV-diagram at 115
kyr is shown in the top right-hand panel
front. Bullet DL hits the leading shock front with high velocity, overtakes the older bullets and decelerates. In the last panel, theofnewly
ejectedbulletE
isinaL
Fig. 10. At this stage,bullets
A, B, and C define the Hubble
comparable position as former bullet DL in the first frame.
Law. The oldest bullet, A, moves slowest, at ∼25 km s−1 and has
only reached ∼0.3 pc. Bullets B and C appear merged, but are in−5
The first two bullets interact with the collapsing dense core material∼2 × 10and B moves outwards faster than A, at
t = 150 kyr. ṀSINK is relatively constant,factbetween
kinematicallyseparate.
−1
and are thus not visible in Fig. 8. The timespan from 115 kyr to 122
tends
todecreaseovertime. ∼0.46 pc. C moves outwards faster∼5 × 10−6 M⊙ yr−1 . The accretion rate∼30
km s , and has reached−1
kyr is chosen to capture the end of a cycle of an outflow bullet, here
It drops briefly, following an outburst, because
outburst
thehas reached ∼0.52 pc. Bullet D moves, andthan B, theat ∼40km sheats−1 ofbullet D, when it hits the leading shock front. This cycle happens
accretion disc (cf. Lomax et al. 2014, outwards2015). The, but has only been going for ∼6 kyr, so it
at accretion∼80 km srate−1−7
in a similar fashion for all other bullets, except the first bullet A.
10hit
M, butshock and been decelerated. Bullet E
the protostar is low in the quiescent phase,⊙ yr
has Ṁ
notyettheleading⋆ =This is the first bullet that breaks out of the core and survives as a
Notethelaunched,time res- within the last ∼1 kyr; the outburst at
approaches 10−3 M⊙ yr−1 during an outburst.
has only
justthatbeen
coherent structure. Bullets B and C have higher velocity and haveolution in Fig. 9 is too coarse to resolve ∼114
the verykyrshortthat outbursts.
launches EThecan be seen on Fig. 9.

4.2 Mass–velocity Relation
The left-hand panels of Fig. 10 show MV-diagrams for the left lobeof the simulated outflow, i.e. plots of
"M =

dM
"υRAD
dυRAD

(47)

against υRAD , at the same times as the PV-diagrams in the righthand panels. Each point represents the mass in a radial velocity
interval "υRAD = 2 km s−1 , and only points that correspond to ≥22
SPH articles (≥ 10−4 M⊙ ) are considered. At low velocities, υRAD !
80 km s−1 , the plots can be fitted well with a single shallow powerlaw,

一時的アウトフロー：
pcスケールの長いS字型のbulletのchain
を生む

dM
−γ
∝ υRAD
,
dυRAD

(48)

with γ ≃ 1.5, in good agreement with observed and simulated values(Kuiper et al. 1981; Lada & Fich 1996; Bachiller & Tafalla 1999;
Richer et al. 2000; Keegan & Downes 2005; Arce et al. 2007; Liuet al. 2017; Li et al. 2018).
Some observers have reported a knee, at high velocities, above
which the slope abruptly becomes much steeper. We find no evi-=> HH天体と同一であると見なした

Hubble wedges in protostellar outflows

2577

bulletのPV図は２つの特徴を示す：
・初期に排出されたbulletは低視線速度で放出、
leading shockで減速されている。bulletはradial
distanceに比例するradial velocityを持つ（ハッブル則に従う）
・最近に放たれたbulletは速い視線速度を持ち、shock frontで未だに減速していない。
bulletsはハッブルwedgeを形作る

アウトフロー中のガスの質量-速度の関係（左図）：dM/dvRAD

vRAD-1.5でだいたいﬁtできる=> 観測値によく合う。
個々のbullet：この関係に従う小さなbumpとして現れる

Department of Earth and Planetary Sciences, Tokyo Institute of Technology, 2-12-1, Ookayama, Meguro-ku, Tokyo 152-8551, Japan
4
Graduate School of Natural Sciences, Nagoya City University, Yamanohata 1, Mizuho-cho, Mizuho-ku, Nagoya 467-8501, Japan
Received 2018 August 21; revised 2018 October 31; accepted 2018 December 9; published 2019 January 25© 2019.©The
AmericanAstronomical
Society. Society.
All rights
2019.
The American
Astronomical
Allreserved.
rights reserved.

Planetesimals
Perturbed
by abyGiant
Planetin ainGas
Disk
Shock-generating
Planetesimals
Perturbed
a Giant
Planeta Gas
Disk
33Shock-generating
1

1
2
2
3
3
4
M. Nagasawa, 1K. K.
, H.2Tanaka, H.2Nomura, 3T. Nakamoto, and3, H.
M. Nagasawa, K.Tanaka
K. Tanaka, H. Tanaka, H. Nomura, T. Nakamoto
andMiura
H. Miura4
Abstract1
Departmentof Physics,
SchoolSchoolof Medicine,
KurumeUniversity,
67 Asahi-machi,
Kurume-city,
Fukuoka
830-0011,
Japan;Japan;
nagasawa_makiko@med.kurume-u.ac.jp
Departmentof Physics,of Medicine,
KurumeUniversity,
67 Asahi-machi,
Kurume-city,
Fukuoka
830-0011,
nagasawa_makiko@med.kurume-u.ac.jp
22
AstronomicalInstitute,
TohokuUniversity,
6-3 Aramaki,
Aoba-ku
Sendai,
MiyagiMiyagi
980-8578,
Japan Japan
AstronomicalInstitute,
TohokuUniversity,
6-3 Aramaki,
Aoba-ku
Sendai,
980-8578,
33Departmentof Earthand Planetary
Sciences,TokyoTokyo
Instituteof Technology,
2-12-1,2-12-1,
Ookayama,
Meguro-ku,
TokyoTokyo
152-8551,
Japan Japan
Departmentof Earthand Planetary
Sciences,
Instituteof Technology,
Ookayama,
Meguro-ku,
152-8551,
4
4Graduate
SchoolSchoolof Natural
Sciences,
NagoyaCity University,
Yamanohata
1, Mizuho-cho,
Mizuho-ku,
Nagoya467-8501,
Japan Japan
Graduateof Natural
Sciences,
NagoyaCity University,
Yamanohata
1, Mizuho-cho,
Mizuho-ku,
Nagoya467-8501,
Received
2018
August21;
revised2018
October
31;
accepted
2018
December
9;
published
2019
January
25
Received 2018 August 21; revised 2018 October 31; accepted 2018 December 9; published 2019 January 25

We examined the excitations of planetesimals caused by the resonances of a giant planet in a protoplanetary gas
disk. The highly excited planetesimals generate bow shocks, the mechanism of which results in chondrule
formation, crystallization of silicate dust, and evaporation of icy planetesimals. The planetesimals beyond 2:1
Abstract
Abstract
resonance
migrateowing caused
to causedthegasdrag andobtaintheinmaximum
eccentricity around 3:1 resonance, which is
We examinedthe excitationsof planetesimals
by theof a giant
planetplanet
in a protoplanetarygas gasWe examinedthe excitationsof planetesimals
byresonances
the resonancesof a gianta protoplanetary
locatedat excited
approximately
half
theshocks,
planetary
distance.
Theeccentricity
depends on the parameters of the
disk. disk.
Thehighlyexcitedplanetesimals
generate
bow bow
shocks,the mechanismof which
results
in chondruleThehighlyplanetesimals
generate
the mechanismof which
results
in chondrule
formation,
crystallizationof silicate
dust, dust,
and evaporationof icyof planetesimals.
The Theplanetesimals
beyond
2:1 2:1
formation,
crystallizationof silicate
and evaporation
icy planetesimals.
planetesimals
beyondplanetesimals
andtheJovianplanet,
such
as
size
and
location,
and
the
gas
density of the disk. The maximum
resonance
migrateowing
to thetogas
and obtainthe maximum
eccentricity
around3:1 resonance,
whichwhich
is isresonance
migrateowing
the draggas dragand obtainthe maximum
eccentricity
around3:1 resonance,−1locatedat approximately
half ofthe aplanetary
distance.
Theeccentricity
depends
onrespectthethein the case of
relative
velocity
100
km
sized
planetesimalwiththeofgas
locatedat approximately
halftheplanetary
distance.
Theeccentricity
depends
on parameters
the toparametersof disk
the reaches up to ∼12 km splanetesimals
andtheJovianplanet,
such
as
size
and
location,
and
the
gas
density
of
the
disk.
The
maximum
planetesimals and the Jovian planet, such as size and location, and the gas density of the disk. The maximum
Jupitertosecularresonance,
occursbecausethethedisk’s
gravity. We ﬁnd that if a Jovian-mass planet
relative
velocity
ofowinga 100planetesimalwith withrespect
towhichthetogas
up toup
∼12
kmof
s−1
incasethe ofcase ofrelative
velocityof akm100sized
km sizedplanetesimal
respect
thediskgas reaches
disk reaches
to ∼12
kmins−1
Jupiterowing
to secularresonance,whichoccursbecauseof theofdisk’s
gravity.
We ﬁndthat
a100
Jovian-massplanetplanet
Jupiterowing
to secularresonance,whichoccursbecausethe disk’s
gravity.
Weﬁndifthat
if a Jovian-massislocatedwithin10 au,
theplanetesimals
largerthan
km gainsufﬁcient velocity to cause the melting ofis locatedwithin10 au,10thelargerlarger
than than
100 kmsufﬁcientvelocity
to cause
the meltingof ofis locatedwithinau, planetesimals
the planetesimals
100gainkm gainsufﬁcientvelocity
to cause
the melting
chondruleprecursors
andcrystallizationofthesilicate.
Themaximum
is higher for large planetesimals andchondruleprecursors
andcrystallizationof theofsilicate.
The maximum
velocityishigherfor large
planetesimals
and velocity
chondruleprecursors
and crystallization
the silicate.
The maximum
velocity
is higher
for large
planetesimals
andeccentric
planets.
Planetesimals
arePlanetesimals
trappedtemporarily
intheintrappedresonancesandcontinue
to havehighspeed
over overeccentric
planets.
Planetesimals
are trapped
temporarily
the resonancesand continue
toinhavespeed
eccentric
planets.
aretemporarily
thehighresonancesand continue to have high speed over
1 Myrafter after
the formationof a of
Jovianplanet.
This Thisdurationﬁts into
the timescaleof chondrule
formation
1 Myrthe formationa Jovianplanet.
durationﬁts into
the timescaleof chondrule
formation
1byMyrformation
ofplanetesimals
Jovianplanet.
This
duration
ﬁts
into the timescale of chondrule formationsuggested
thedata.theThe evaporationof icyof
occurswhenwhena Jovianplanetis locatedwithinsuggestedbyisotopic
theafterisotopicdata.
The
evaporation
icyaplanetesimals
occursa Jovianplanetis locatedwithin15 au.15This
mechanism
can benewindicatorof planet
formation
in exosystems
if somemolecules
ejectedfromoccurs
au. Thismechanismcana bea new
indicatorof planet
formation
in exosystems
if somemolecules
ejectedfromsuggestedbytheisotopicdata.
The
evaporationoficy
planetesimals
when a Jovian planet is located within
icy planetesimals
are detected.
icy planetesimals
are detected.
15
au.
This
mechanism
can
be
a
new
indicatorofplanetformationinexosystems
if some molecules ejected from
Key words:
meteorites,
meteors,
meteoroids– minorplanets,
asteroids:
general– planets
and satellites:
dynamical
Key words:
meteorites,
meteors,
meteoroids– minorplanets,
asteroids:
general– planets
and satellites:
dynamical
icy
planetesimals
aredetected.
evolutionand stability– planets
and satellites:
formation– shock
waves
evolutionand stability– planets
and satellites:
formation– shockwaves
Key words: meteorites, meteors, meteoroids – minor planets, asteroids: general – planets and satellites: dynamical
1. Introduction
system,whichwhich
is normallysimilarto theto rotational
speedspeedof of
1. Introduction
system,is normallysimilarthe rotational
evolutionand stability – planets andsatellites:
formation–it allows
shock
the ascending
nodesnodesof planets,
it allows
the inclinationof theof thetheascendingof planets,
the wavesinclination

The observationof anofasteroid
belt shows
depletionor piling
The observation
an asteroid
belt shows
depletionor pilingasteroid
to oscillatewith withlargelarge
amplitude.
The inner
boundary
asteroid
to oscillate
amplitude.
The inner
boundary
up ofupmaterials
dependingon theof planet
resonances.
of materials
dependingonlocation
the locationof planet
resonances.
of thebelt beltof current
asteroids(∼2 au)of mainthe mainof current
asteroids(∼2 isau) mainly
is mainly
The Theresonanceswith with
Jupiterare especially
noticeable.
Asterresonances
Jupiterare especially
noticeable.
Asterdeterminedby theresonances
relatedto theto rotation
determinedby secular
the secularresonances
relatedthe rotation
oids oids
betweenthe Jovian
2:1 resonance(3.3 (3.3au) and
betweenthe Jovian
2:1 resonanceau) Jupiterand Jupiterof theperiastronand andascendingnodesystem,of Saturncausedby isbynormally similar to the rotational speed of
1.
Introduction
which
of
the
periastronascendingnodeofSaturncaused(5.2 au)have
currently
dispersed
exceptforobjects
trappedin(5.2 au) have currently dispersed except for objects trapped in
Jupiter.
WhenWhenthe primordialgas disk
the eigenfrequenJupiter.
the primordialgas exists,
disk exists,
the eigenfrequenresonances(e.g.,(e.g.,
Trojansand Hildas).
Migrationof asteroids
resonances
Trojansand Hildas).
Migrationof asteroids
theascendingnodes of planets, it allows the inclination of theoftheofsystemcoincidewith withthe rotational
speedsof ofcies
the system
almostcoincide
the rotational
speedsThe observationof draganasteroid
belt
shows
depletion
oralmost
piling(planetesimals)causedby gasaccounts
for the(planetesimals)causedby draggas
accounts
forloss
the from
loss
from cies
theperiastraofplanets
causedbygravity
of
the
disk.
In
such
a
the
periastraofplanets
causedbygravity
of
the
disk.
In
such
a with large amplitude. The inner boundary
asteroidtooscillatetheup
regionbeyond2:1 resonanceif theifprotoplanetary
disk disk
is isof planet resonances.
theof
regionbeyond
2:1
resonancetheprotoplanetary
materials
dependingonof
thelocation
67
the resonancerelatedto Jupiteris mosteffectivein in
7
situation,
the resonancerelatedto Jupiteris mosteffective
yr afterthe formation
Jupiter(Ida &
preserved
for 10yr afterthe formationof Jupiter(Ida & situation,
preserved
for–10
106–10
ofof asteroids.
the mainof current asteroids (∼2 au) is mainly
excitationof theeccentricitiesof theThe Thediskbelt
the excitation
ofAsterthe eccentricities
the asteroids.
disk
resonances
with
Jupiterareespecially
LinThe1996;
Marzari
et al.et1997;
Weidenschilling
et al.
Lin 1996;
Marzarial.
1997;
Weidenschillinget1998;al. 1998; thenoticeable.
shouldnot bewhen
we consider
the theself-gravity
shouldnotneglected
be neglectedwhen
we consider
the secular resonances related to the rotation
determinedby
Marzari& Weidenschilling2002).
Duringthe migration,
the the self-gravity
Marzari&Weidenschilling2002).
Duringthemigration,oids
betweenthe
Jovian2:1
resonance(3.3 evolutionau)ofand
Jupiterplanetesimals
experiencing
gas drag.
Nagasawaof planetesimals
experiencing
gas drag.
Nagasawa
planetesimals
pass passthroughmanymany
Jovianresonances,whichwhich evolution
planetesimals
through
Jovianresonances,etal.
(2014)
showedthat thesecularresonance,
whichwhichetal.
(2014)
showedthat
the Jovian
secularresonance,
excitetheau)
eccentricitiesof theTheseTheseeccentri(5.2currently
dispersed
exceptfor objects trappedin Jovianexcitethe haveeccentricitiesof planetesimals.
the planetesimals.
eccentriowing
to thetogas
gravity,excitesthe 300owing
the diskgas diskgravity,excites
the km300sized
km sized
citiescities
are further
boostedat theatlocationof 2:1ofresonance,
and and arisesarises
are further
boostedthe location
2:1 resonance,
resonances(e.g.,
Trojans
andHildas).
Migration
ofupasteroids
toup
vrelto20
km s−11). 1).
planetesimals
vrel20
km(Figures−1 (Figuretheynormally
reachreachas highase∼0.3–0.6
at approximately
theynormally
as highas e∼0.3–0.6
at approximately planetesimals
supersonicplanetesimals,
whichwhichappearfollowing
the thesupersonicplanetesimals,
appearfollowing
kmdrag
s−1
2–3
au,
they
obtainacausedvelocity
ofby
vrelof8
kmrelatives−1
relative The
2–3thatau,is,
thatis, theyobtaina velocity
vrel8(planetesimals)gasaccounts
forThe
the
loss
from
of a of
Jovianplanet,causecause
severalinteresting
effects.
formationa Jovianplanet,severalinteresting
effects.
to the(Marzari& Weidenschilling2002).
Secularto gasthe diskgas disk(Marzari& Weidenschilling2002).
Secular formationtheregionbeyond
2:1
resonance
if asteroidal
the protoplanetarydisk
is thebyplanetesimals
The shockwavewavegeneratedbyis wellknown
The shockgenerated
the planetesimals
is wellknown
resonance
is known
to havea strong
effecteffecton theresonance
is known
to havea strong
on asteroidal
the7
theofformation
mechanismsof chondrules,
whichwhich
are areas ofone
the formation
mechanismsof chondrules,
orbit
in thegas6–10disk(e.g.,
Heppenheimer
1980;1980; as one
orbit
in primordial
the primordialgas disk
Heppenheimer
yr(e.g.,after
the formationofJupiter(Ida&
preserved
for 10mm sized
spherical
grainsgrains
commonly
foundfoundin primitive
mm sized
spherical
commonlyin primitive
WardWard
1981;1981;
LecarLecar& Franklin
1997).
The secularresonances& Franklin
1997).
The secularresonances 0.1–10.1–1
1996;
Marzari
1997;
Weidenschilling
et
al.
1998;
In thebelt regionof themeteorites.
In asteroid
theasteroid
belt regionof minimum-mass
the minimum-mass
areLinrelatedto thetomotionsof theofet
pericenterand theare relatedthemotions
theal.
pericenterandascending
the ascending meteorites.
−10
(∼10
cm−3
), −3
athe
of 10km s−1be be
disk(∼10g−10g cm),velocity
a velocityof 10km would
s−1 would
nodesof thePeriastra
and andnodesnodesof2002).
objects
rotatenodes
of objects.
thePeriastraof objects
rotate disk
Marzari& objects.
Weidenschilling
Duringthenecessary
migration,
for themeltingof 1 mmsizedsized
dust dust(Iida (Iidafor complete
the complete
meltingof 1 mmowing
to thetogravity
of otherplanets
and theWhenWhen
the the necessary
owing
the gravity
of otherplanets
anddisk.
the disk.
planetesimals
passthroughal.et2001).
In Figure
1, we1,show
the conditions
requiredto to
al. 2001).
In which
Figurewe show
the conditions
requiredrotational
speedspeedof theof anofasteroid
is closeto to etresonances,rotationalof periastronthe periastronan many
asteroidisJovianclose
the meltingof chondrule
precursors(1900(1900
K) andthe meltingof chondrule
precursorsK) theand thetheexcite
eigenfrequenciesof theofsystem,
whichwhich
is normallysimilarto to causecause
the eigenfrequencies
the system,
is normallysimilartheeccentricitiesoftheplanetesimals.
These
eccentrirequired
for theinitiationof vaporizationof ofthe rotational
speedspeedof theofperiastraof planets,
the eccentricity
conditions
required
for theinitiationof vaporization
the rotational
the periastraof planets,
the eccentricity conditions
areoscillates
furtherat the2:1chondrules
resonance,(2100(2100K) (see
Section4). In4).theIn outerregion,the theof cities
theofasteroid
withboosted
largelarge
amplitude.
It corresponds
to of
K)and
(see
Sectionthe outerregion,the asteroid
oscillates
withamplitude.
Itlocation
corresponds
to chondrules
velocities
becomehigherbecausethe gasis isthetheytransferof themomentumof theplanetto thevelocities
becomehigherbecausethe density
gas density
the transfer
of angular
the angularmomentumofasthee∼0.3–0.6
planetto the required
normally
reach
as high
atrequired
approximately
The Themaximum
relative
velocitiesof 300asteroid.
Similarly,
whenwhen
the rotational
speedspeedof theofascending
relative
velocitiesof km
300 sized
km sizedasteroid.
Similarly,
the rotational
the ascending small.small.
−1 maximum
km s excited
relative
2–3
that
is,
they
velocityof ofplanetesimals
by Jupiterare indicatedby circles.
To To
node
of au,
anofasteroid
is close
toobtainthetheplanetesimals
excitedby Jupiterare indicatedby circles.
node
anasteroid
is closeto eigenfrequencies
the aeigenfrequencies
ofvtherel8

to the gas disk (Marzari & Weidenschilling2002). Secular
1 1
resonance is known to have a strong effect on the asteroidal
orbit in the primordial gas disk (e.g., Heppenheimer 1980;
Ward 1981; Lecar & Franklin 1997). The secular resonancesINAF-Osservatorio Astroﬁsico di Arcetri, Largo Enrico Fermi 5, I-50125, Firenze, Italia; rivilla@arcetri.astro.it
Departamento de Astronomía, Universidad de Chile, Camino el Observatorio 1515, Las Condes, Santiago, Chile; gejixing666@gmail.com
Received 2018
February
2; revisedtoward2018 December
accepted 2018 December 5; published 2019 February 5
ALMA Observationsof Ethyl
FormateOrion4;KL© 2019. The American Astronomical Society. All rights reserved.

4

35

ALMA Observations of Ethyl Formate toward Orion KL
1,2
Yaping Peng
Peng1,2
YapingV. M.
M. Rivilla
Rivilla33,, Li
Li Zhang
Zhang11
,, V.

1,2
J. X.
X. Ge
Ge44,, andand Bing
Bing Zhou
Zhou1,2,, J.
Abstract11
Department of Astronomy, Yunnan University, and Key Laboratory of Astroparticle Physics of Yunnan Province, Kunming, 650091, Peopleʼs Republic of China

Department of Astronomy, Yunnan University, and Key Laboratory of Astroparticle Physics of Yunnan Province, Kunming, 650091, Peopleʼs Republic of China
pyp893@163.com, lizhang@ynu.edu.cn,
lizhang@ynu.edu.cn, bingzhoukm@126.com
bingzhoukm@126.com
pyp893@163.com,
2
2
College ofof Science,
Science, Yunnan
Yunnan Agricultural
Agricultural University,
University, Kunming,
Kunming, 650201,
650201, Peopleʼs
Peopleʼs Republic
Republic ofof China
China
College
3
3 INAF-Osservatorio Astroﬁsico di Arcetri, Largo Enrico Fermi 5, I-50125, Firenze, Italia; rivilla@arcetri.astro.it
INAF-Osservatorio Astroﬁsico di Arcetri, Largo Enrico Fermi 5, I-50125, Firenze, Italia; rivilla@arcetri.astro.it
44
Departamento dede Astronomía,
Astronomía, Universidad
Universidad dede Chile,
Chile, Camino
Camino elel Observatorio
Observatorio 1515,
1515, Las
Las Condes,
Condes, Santiago,
Santiago, Chile;
Chile; gejixing666@gmail.com
gejixing666@gmail.com
Departamento
Received 20182018 February
February 2;
2; revised
revised 20182018 December
December 4;4; accepted
accepted 20182018 December
December 5;5; publishedpublished 20192019 February
February 55
Received

Orion KL is one of the prime templates of astrochemical and prebiotic chemical studies. We wish to explore moreorganic molecules with increasing complexity in this region. In particular, we have searched for one of the mostcomplex organic molecules detected in space so far, ethyl formate (C2H5OCHO). This species is the next step inchemical complexity afterAbstract
the simplest member of esters (methyl formate, CH3OCHO). The mechanisms leading to
Abstract
formation
are ofstill
poorly andknown.
havestudies.
usedWehighresolution (∼1 5) ALMA observations covering
Orion KL
KL is
is oneoneitsof thetheprime templates
templatesofastrochemical
andprebioticWe
chemicalstudies.
We
wish angular
to explore
explore more
more
Orion
of
prime
astrochemical
prebiotic
chemicalwish
toorganic molecules
molecules
with increasing
increasing
complexity
in thisthisregion.
In particular,
particular,
wehavesearched
for oneone ofoftheunblended
mostorganicwithcomplexity
inregion.
In
wehavesearched
for
the
most
a
large
bandwidth
from
214
to
247
GHz.
We
have
detected
82
lines of C2H5OCHO (49 and 33 of the
H55OCHO).
OCHO). This
This species
species isis thethe next
next step
step inincomplex organicorganic molecules
molecules detected
detected inin space
space soso far,far, ethyl
ethyl formate
formate (C(C22H
complextransandgauche-conformers,
respectively).
The
line
imagesshowedthat
C2H5OCHO arises mainly from theOCHO).
The
mechanisms
leadingtochemicalcomplexity
after
the
simplest
memberofesters(methylformate,CH3chemical complexity after the simplest member of esters (methyl formate, CH3OCHO). The mechanisms leading to5) ALMA
ALMA observations
observations
coveringrotational temperatures and column densities
its formation
formation are
arecompact
still poorly
poorly known.
known.
We
havetheused hothigh angularangularresolution (∼1(∼1 regions.
5)covering
its
still
have
used
high
resolution
ridgeWeandcore-southwest
The derived
H55OCHOOCHO (49(49 andand 3333 ofof thethelarge bandwidth
bandwidth fromfrom 214
214 toto 247247 GHz.
GHz. WeWe have detected
detected 82
82 unblended
unblendedlines of
of C
C22H
16
−2lines16−2
aa large
cmthathotcore-SW,andfor theare 122±34
K, (0.9have± 0.3)×10
H55theOCHO
arisesmainly fromfromthe 103±13 K, (0.6 ± 0.3)×10 cm
trans- andand gauche-conformers,
gauche-conformers,
respectively).
Theline images
images showed
showedthat for
C22H
OCHO
arisesmainlythetransrespectively).
The
line
C
compact ridge
ridge andandthe hot
hot core-southwest
core-southwest
regions.
The derived
derivedrotationaltemperaturesand column
columndensities
compact
ridge.
The
comparisonofspatialdistribution
andabundance
ratioswithchemicallyrelatedmolecules
compact
theregions.
The
rotationaltemperatures
anddensities
16
−2
16
−2
cm−2
for thethe hot
hot core-SW,
core-SW, andand 103±13103±13 K,
K, (0.6(0.6 ±± 0.3)×100.3)×1016
cm−2
for thetheare 122±34
122±34 K,
K, (0.9(0.9 ±± 0.3)×100.3)×1016
cm
for
cm
for
are
OCHO
is likely formed on the surface of dust grains
formate,ethanol,andacid)
thatrelated
C2H
5molecules
compact ridge.
ridge. (methyl
The comparison
comparisonof spatial
spatialdistribution
andformic
abundance
ratiosindicateswith chemicallychemicallyrelatedmolecules
compact
Theof
distribution
andabundance
ratioswith
MNRAS 482, 5349–5361 (2019)
doi:10.1093/mnras/sty2901
H
OCHO
is
likelyformedonthesurfaceof
dust
grains(methyl formate,formate,ethanol,andformicacid)
indicatesthatC
tofunctional-groupradicals(CH
OCHO)
derivedfrom methyl formate (CH3OCHO).
byaddition
of
CH
2
5
H
OCHO
is
likelyformedonthesurfaceof
dust
grains(methylethanol,andformicacid)
indicatesthat
C
3 October 29 2 52Advance Access publication 2018
to functional-groupfunctional-group radicals
radicals (CH(CH22OCHO)OCHO) derived
derived fromfrom methyl
methyl formate
formate (CH(CH33OCHO).
OCHO).
by addition
addition ofof CH
CH33 tobyKeywords:
ISM:
abundances– ISM:(Orion
Key words:
words: ISM:
ISM:
abundances
ISM:
individual
objects (Orion(OrionKL) –– individual
ISM: molecules
moleculesobjects
radio lines:
lines:
ISM –– KL)stars: – ISM: molecules – radio lines: ISM – stars:
Keyabundances–– ISM:
individual
objects
KL)
ISM:–– radioISM
stars:
formationformationformation
Supporting material:material: ﬁgure
ﬁgure sets,
sets, machine-readable
machine-readable tables
tablesSupporting

A 6.7 GHz methanol maser survey of the central molecular zone
Supporting material: ﬁgure sets, machine-readable tables
Matthew Rickert,1,2‹ F. Yusef-Zadeh1‹ and J. Ott2

11.
Introduction
OCHO,
hereafterMF),
which isis USA
relatively
methyl formate
formate(CH
CIERA
and Department of Physics and Astronomy, Northwestern
University,(CH214533OCHO,
Sheridan Rd,
Evanston,
IL 60208-3112,
1.
Introduction
hereafter
MF),
which
relatively
methyl2 National Radio Astronomy Observatory, 1003 Lopezville Rd, Socorro, NM 87801, USAabundant inin many
many high-mass
high-mass (e.g.,(e.g., Favre
Favre etet al.
al. 2011;
2011; Rivilla
Rivilla etet al.
al.
abundant
Almost200
molecules
have
been
detectedintheinterstellar
Almost 200 molecules have been detected 1.
in theinterstellar
Introduction
methylformate2017a, 2017b)
2017b) andand low-mass
low-mass star-forming
star-forming regions
regions(e.g.,
Cazaux (CH3OCHO, hereafter MF), which is relatively
2017a,(e.g.,
Cazauxmedium (ISM)(ISM) andand circumstellar
circumstellar environments,
environments, ofof whichwhich more
more
mediumet al.
al. 2003).
2003). Ethyl
Ethyl formate
formate (C(C22H
H55OCHO,
OCHO, hereafter
hereafterEF) isis the
the
next
et
EF)
abundantin next
many high-mass (e.g., Favre et al. 2011; Rivilla et al.
than 65
65 areare considered
considered complex
complex organicorganic molecules
molecules (COMs),(COMs),
than
Accepted
2018
October 18. Received
2018 been
October 11;
insteporiginal
form
2018
11
Almost200
molecules
have
inchemical
theAugustinterstellar
stepin thethechemicalcomplexityof esters,
esters, with
with 11
11 atoms.
atoms. EF
EF hashas
incomplexityofmolecules with
with 66 atoms
atoms containing
containing carbon.
carbon. The
The formation
formation ofof detected
molecules
2017a,
2017b) and low-mass star-forming regions (e.g., Cazaux
two conformers:
conformers:thetrans-conformer(also called
calledanti-conformer)
twothetrans-conformer(also
anti-conformer)
these COMs
COMs medium
in thethe ISMISM isis(ISM)
still poorly
poorlyandunderstoodand isis subject
subjectenvironments,ofcircumstellar
of
which
more
these
in
still
understoodandofwhere thethe heavy
heavy atoms
atoms C-C-O-C=O
C-C-O-C=O form
form etplanarzigzag chain,chain,
al. 2003).
Ethyl formate (C2H5OCHO, hereafter EF) is the next
where
aa planar
zigzagintense debate.
debate.
Two 65generaltheories
have been
been complex
proposed: gasgasintenseTwogeneralhave
proposed:than
are theories
consideredmolecules(COMs),and thethegauche-conformer
produced byby anan out-of-plane
out-of-plane rotation
rotation ofof
A2015;B S Torganic
R A C Tandgauche-conformer
producedphasechemistry(e.g.,
Millaretal.
1991;
Balucanietal.
phase chemistry (e.g., Millar et al. 1991; Balucani et al. 2015;
step
in
the
chemicalcomplexity of esters, with 11 atoms. EF has◦
the ethyl
ethyl The
group(CMZ)(C22H
H55))spansaroundthe
O-Cbondpc(Medvedev(Medvedev
et Galaxy.
al.
The
centralmolecular
zone
the
inner
∼450
(∼3
)
of
our
This region
the
group
(C
around
the
O-C
bond
et
al.
molecules
with
6
atoms
containing
carbon.
formationofTaquetetal.
2016),
and
dust
grain
surfacechemistry(e.g.,
GarrodTaquet et al. 2016), and dust grain surface chemistry (e.g., Garrod2009).
The formation
formationroutesof EF
EF arearestillpoorlyknown.
Severaltwo
conformers:thetrans-conformer (also called anti-conformer)2009).
The
routesofstillpoorlyknown.
Severalisdefinedbyitsenhancedmolecularemissionandcontains
5
per
cent
of
the
entireGalaxy’s&
Herbst2006;
Fedoseev
et
al.
2015;
Chuangetal.
2016).
& Herbst 2006;
Fedoseev
et al.in2015;
et al.
2016).
theseCOMs
theChuang
ISM isstill
poorly understoodand is havesubjectofchemicalpathwayshavebeen proposed,
proposed,
includingreactions
ontowards the CMZ
pathways
been
includingreactions
Orion KLKL is
is aa high-mass
high-mass star-forming
star-forming region
region thatthat provides
providesmolecular
gaschemical
mass. However,thenumberof detected
star-forming
siteson
where
the
heavy
atoms
C-C-O-C=O form a planar zigzag chain,Orionaa
the surface
surfaceofproposed:
dust grains
grains andandgasreactions inin the gas
gas phase.
phase. On
On oneone
intensedebate. Two
generaltheorieshave
beenofdust
reactionssuperb template
templatefor constraining
constraining
the chemicalchemicalmodels(e.g.,
superbforthemodels(e.g.,
may
be low thefor the amountof molecular
gas that is thepresent,
andgauche-conformer
improved
surveys of starproduced by an out-of-plane rotation of
and
the
hand,
Charnleyetal.
(1995)
usedgas-phasereactionsstarting
with
hand,Charnleyet etal. (1995)
usedgas-phasestarting
Brouillet et
et al.
al.
2013; Crockett
Crockett
et al.
al. 2015;
2015;
FengMillar
et al.
al. 2015;
2015;
Carrollphase
chemistry(e.g.,
etformational. 1991;
Balucanial. this.
2015;
Brouillet
2013;
et
Feng
et
Carrollindicators
canHhelp
With
Karlreactions
G.EF.
JanskyVerywith
Large
Array (VLA),
ethanol (C(COH,clarify
hereafterET)
tothe
produce
Recently,the (C
2H5
5OH,
ethanolhereafterET)
toproduceEF.ethyl
Recently,theet al.
al. 2017;
2017; Favre
Favre etet al.
al. 2017;
2017; FriedelFriedel && Looney
Looney 2017).
2017). Orion
Orion KL
KL
2
the
group
the O-C bond (Medvedev et al.
et2Hinner5) aroundOH)
masersspanning
the3◦
we conductedablindsurveyof
6.7GHz
methanol(CH
Taquetetal.
2016),
and
dust
grain
surfacechemistry(e.g.,
Garrod3
formation ofof EF
EF hashas been
been included
included inin aa newnew gas-phase
gas-phase chemicalchemicalformation
consistsofdifferent
spatialandchemicalcomponentsy:
thehotconsists of different spatial and chemical componentsy: thehotarcmin (450 pc × 100 pc) of the Galaxy. We detected2009).
The
formationroutesofEFare still poorly known. Several
×
40
43
CH
OH
maserstowards
network (Taquet(Taquetal. 2016),
2016), inin whichwhich formic
formic acidacid (HCOOH)(HCOOH)3andand
networkal.
core, thethe compact
compact
ridge, 2006;
the extended
extendedridge, andandtheplateau& Herbst
Fedoseev
et theal.plateau
2015; Chuang
et al. etet2016).
core,
ridge,
theridge,
28 locations,∼16 of whicharenewdetections.
Thevelocities
of
most
of
these
masersareammonia
(NH
)
favor
the
formation
of
EF.
On
the
other
hand,
3
ammonia
(NH
)
favor
the
formation
of
EF.
On
the
other
hand,
(Blakeetal.
1987).
In
particular,
tworegions,
the
hot
core
and
the
chemicalpathwayshave
been
proposed,
including reactions on
3(Blake et al. 1987).
In particular,
the hot core
and the
Orion
KLspecial
istwoaregions,high-mass
star-forming
regionprovidesGarrodetlocatedal.that(2008)
proposedana Aalternative
scenario
based onon
consistent
beingetwithinthe CMZ.
majority scenarioof the detected
CH3 OH masers are
Garrodal.
(2008)
proposedanalternative
based
compact ridge,
ridge, have
have received
received special
attention because
because they
they
are withcompact
attentionaresurfacedust
grains and reactions in the gas phase. On one
grain-surface
chemistry,
inlongitudes,which
EF cancanbetheformedfrom ET
ETofandthetemplate
foretet al.
chemicalmodels(e.g.,EFvery richrich inin superb
organic species
species(e.g., Blake
Blake
al.constraining
1987; Favre
Favre
et al.
al.the towards
grain-surface
chemistry,whichbeformedfromanddistributed
positive
Galacticin
similarto two-thirdsofmolecular gas
very
organic(e.g.,
1987;
et
MF at
viapositive
cosmic Galactic
ray-induced
photodissociation.
hand,
Charnleyetal.
(1995) used gas-phase reactions starting with2011; Wang
WangBrouillet
et al.
al. 2011).
2011). et
While
the
hot
core
is
rich
in
nitrogenMF
via
cosmicray-induced
photodissociation.
OH
maser
is
an
exclusive
mass
distributed
longitudes.
The
6.7
GHz
CH
2011;
et
While
the
hot
core
is
rich
in
nitrogen3
al.2013,
2013;
Crockett
etal.al.
2015; Fenget al. 2015;
Carrollproposed should be compared
The different
different chemicalchemical routes proposed
2017; Pagani
Pagani etet al.
2017; of high-mass
bearing molecules
molecules (Peng(Peng etet al.
al. 2013,
Theshouldbe compared
2017;
2017;
bearing
formation, withnew detections
indicatingsites of ET) to produce EF. Recently, theindicator(> 8 M⊙ ) starroutes
ethanol(C
H
OH,
hereafter
2
5
et al.the
2017;
Favre
etricheral. 2017;
Friedel& Looney2017).
KLits
with observations
observationsofOrionEF andandits chemicallychemically related
related species.
species.
Rizzo etet al.
al. 2017),
2017),
thecompact
ridge isisricherin oxygen-bearing
oxygen-bearing
with
of
EF
Rizzo
compactridgeinmassive star formationin the CMZ.
However,
because
EF
is
a
very
complexmolecule
that
therefore
formation
of
EF
has
been
included in a new gas-phase chemical
species(Blakeetal.
1987;
Beuther
et
al.
2005;
Friedel&SnyderHowever,
because
EF
is
a
very
complexmolecule
that
therefore
species (Blake
et al. 1987;ofBeuther
et al. 2005;
Friedeland& Snyderconsists
different
spatialchemicalhascomponentsy:
thesohot
low abundance,
abundance,
it– Galaxy:has sofarcent16
been detected
detected
only
towardfour
Key bywords: hascatalogues– surveys it(e/Tc48(o)
440
er)
TcOcleuys– al.
e(Gala5(d)-17in)-1(iBTo)-07in
Tf-: acid (HCOOH) and2008; Gong
Gong etet al.
al. 2015).
2015). The
The hot
hot corecore region
region may
may bebe heatedheatedbyaa low
has
far
been
only
towardfour
2008;
network(Taquetet2016),
in which
formiccompact
ridge,
the orridge, theandplateausources:thethreethemassivestar-forming regions
regions Sgr
Sgr B2(N)B2(N)
shocks fromfrom core,source IIthe
outﬂow(e.g., Goddi
Goddi
et al.
al. 2011)
2011)
orextendedby anansources:threemassivestar-forming
shockssourceoutﬂow(e.g.,
etbyammonia(Bellocheal. 2009),
2009),
W51
e2the(Rivilla etet al.
al.
2017b), andand(NH
Orion3) favor the formation of EF. On the other hand,
explosive event
event
that occurredoccurredaround500In
yr agoago(e.g., Bally
Ballytwo
et al.
al. regions,(Bellocheal.
(Rivilla
2017b),
Orion(Blakeet al.around1987).
particular,
theetethot
coreW51
ande2
explosive
that
500
yr
(e.g.,etKL (Tercero(Tercero etet al.
al. 2013,
2013, 2015),
2015), andand thethe low-mass
low-massstar-forming
2011, 2017;2017; Zapata
Zapata etet al.
al. 2011;
2011; Rivilla
Rivilla etet al.
al. 2013;
2013; Wright
Wright &&KLstar-forming
2011,
Garrodetal.
(2008) proposed an alternative scenario based oncompact
ridge,
have received
specialattention
becausethey etetareregion Barnard
Barnard1b (Marcelino(Marcelino
al. 2018).
2018). Belloche
Belloche etet al.
al. (2009),(2009),
Plambeck 2017).
2017). Whether
Whether this
this explosive
explosive event
event impacted
impacted thetheregion1bal.
Plambeckgrain-surface
chemistry,in which EF can be formed from ET and
Terceroal. (2013),(2013),
and Rivilla
Rivillaet al.
al. (2017b)(2017b) all
all used
used single-dishsingle-dishvery molecules
rich in into
organic(e.g.,
Blake Tercero
et al. etet1987;
Favre
et al.
release ofof complex
complexmolecules
into
the gasgas species
phase isis underunder
debateal.
andetreleasethephasedebate
IRAM
30
m
data.
Single-dishobservations
give
the
line
intensity(e.g.,
Favre
et
al.
2017;
Friedel&Looney2017).
MF
via
cosmicray-induced
photodissociation.
IRAM
30
m
data.
Single-dishobservations
give
the
line
intensity(e.g., Favre etal. 2017;
Friedel et& Looney2017). While the hot core is rich in nitrogen2011;Wangal.
2011).
integrated over
over aa large
large beam
beam area
area andand dodo notnot provide
provide thethe spatial
spatialThe ester
ester familyfamily ofof molecules
molecules isis essential
essential forfor many
many prebiotic
prebiotic
integrated
The
The
different
chemicalroutesproposed should be compared
Paganibearing
et al.molecule
2013, 2017;
distributionof EF,
EF,etnornoral.
do 2017;
they provide
provide anan accurate
accurate value
value ofof thetheprocesses. The
The
simplestmolecules
representative (Pengis thethe 8-atom
8-atommolecule
distribution
of
do
they
processes.
simplest
representativeis

Rizzo et al. 2017), the compact ridge is richer in oxygen-bearing
11
species (Blake et al. 1987; Beuther et al.
2005; Friedel & Snyder
2008; Gong et al. 2015). The hot core region may be heated byshocks from source I outﬂow (e.g., Goddi et al. 2011) or by an
explosive event that occurred around 500 yr ago (e.g., Bally et al.

with observations of EF and its chemically related species.
However, because EF is a very complex molecule that therefore
has a low abundance, it has so far been detected only toward four
sources: the three massive star-forming regions Sgr B2(N)(Belloche et al. 2009), W51 e2 (Rivilla et al. 2017b), and Orion