Star Formation Newsletter#356 30-37
Yusuke Aso (NAOJ, KASI)Stratiﬁed Distribution of Organic Molecules at the Planet-formation Scale in the HH 212
Disk Atmosphere1Chin-Fei Lee1,2, Claudio Codella3,4, Cecilia Ceccarelli4, and Ana López-Sepulcre4,5

Academia Sinica Institute of Astronomy and Astrophysics, P.O. Box 23-141, Taipei 106, Taiwan; cﬂee@asiaa.sinica.edu.tw
2
Graduate Institute of Astronomy and Astrophysics, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei 10617, Taiwan
3
INAF, Osservatorio Astroﬁsico di Arcetri, Largo E. Fermi 5, I-50125 Firenze, Italy
4
Univ. Grenoble Alpes, CNRS, Institut de Planétologie et d’Astrophysique de Grenoble (IPAG), F-38000 Grenoble, France
5
Institut de Radioastronomie Millimétrique (IRAM), 300 rue de la Piscine, F-38400 Saint-Martin d’Hères, France
Received 2022 May 8; revised 2022 August 22; accepted 2022 August 22; published 2022 September 16

Abstract
Formamide (NH2CHO) is considered an important prebiotic molecule because of its potential to form peptide
bonds. It was recently detected in the atmosphere of the HH 212 protostellar disk on the solar system scale whereplanets will form. Here we have mapped it and its potential parent molecules HNCO and H2CO, along with othermolecules CH3OH and CH3CHO, in the disk atmosphere, studying its formation mechanism. Interestingly, we ﬁnd
a stratiﬁed distribution of these molecules, with the outer emission radius increasing from ∼24 au for NH2CHOand HNCO, to 36 au for CH3CHO, to 40 au for CH3OH, and then to 48 au for H2CO. More importantly, we ﬁndthat the increasing order of the outer emission radius of NH2CHO, CH3OH, and H2CO is consistent with thedecreasing order of their binding energies, supporting that they are thermally desorbed from the ice mantle on dust
grains. We also ﬁnd that HNCO, which has much lower binding energy than NH2CHO, has almost the same spatial
distribution, kinematics, and temperature as NH2CHO, and is thus more likely a daughter species of desorbed
NH2CHO. On the other hand, we ﬁnd that H2CO has a more extended spatial distribution with different kinematics
from NH2CHO, thus questioning whether it can be the gas-phase parent molecule of NH2CHO.
Uniﬁed Astronomy Thesaurus concepts: Star formation (1569); Star forming regions (1565); Stellar accretion disks(1579); Astrochemistry (75); Interstellar molecules (849)
1. Introduction
Formamide (NH2CHO) is an interstellar complex organic
molecule (iCOM, referring to C-bearing species with six atoms
or more; Herbst & van Dishoeck 2009; Ceccarelli et al. 2017)and a key precursor of more complex organic molecules, thatcan lead to the origin of life, because of its potential to form
peptide bonds (Saladino et al. 2012; Kahane et al. 2013; LópezSepulcre et al. 2019). It has been detected in the gas phase in
hot corinos (Kahane et al. 2013; Coutens et al. 2016; Imai et al.
2016; López-Sepulcre et al. 2017; Bianchi et al. 2019; Hsu
et al. 2022), which are the hot (100 K) and compact (100au) regions immediately around low-mass (Sun-like) protostars(Ceccarelli et al. 2007). The formamide origin is still under
debate. In principle, formamide could be synthesized on thegrain surfaces or in the gas phase. Two routes have been
proposed in the ﬁrst case: the hydrogenation of HNCO
(Charnley & Rodgers 2008) and the combination of the HCO
and NH2 radicals, when they become mobile upon the warmingof the dust by the protostar. However, the ﬁrst route has been

NH3+CO in competition with the formamide (Enrique-Romero
et al. 2022). In the gas-phase formation theory, it has been
proposed that formamide is formed by the gas-phase reaction of
H2CO with NH2 (Kahane et al. 2013). This hypothesis waslater challenged by Song & Kastner (2016). Nonetheless, QM
computations (Vazart et al. 2016; Skouteris et al. 2017)
coupled with astronomical observations in shocked regions(Codella et al. 2017) support this hypothesis. In the same vein,
the observed deuterated isomers of formamide (including
NH2CDO, cis- and trans-NHDCHO; Coutens et al. 2016) ﬁt
well with the theoretical predictions of a gas-phase formationroute (Skouteris et al. 2017). On the other hand, the observedhigh deuterium fractionation of ∼2% for the three different
forms of formamide (NH2CDO, cis- and trans-NHDCHO)
could also be consistent with the formation in ice mantles on
dust grains.
The hot corino in the HH 212 protostellar system (Codella
et al. 2016) in Orion at a distance of ∼400 pc is particularlyinteresting because recent observations have spatially resolved

Stratiﬁed Distribution of Organic Molecules at the Planet-formation Scale in the HH 212
Disk AtmosphereChin-Fei Lee1,21, Claudio Codella3,4, Cecilia Ceccarelli4, and Ana López-Sepulcre4,5

Academia Sinica Institute of Astronomy and Astrophysics, P.O. Box 23-141, Taipei 106, Taiwan; cﬂee@asiaa.sinica.edu.tw
2
Graduate Institute of Astronomy and Astrophysics,
National Taiwan
University,
1, Sec.
4, September
Roosevelt Road,
The AstrophysicalJournal,937:10No.
(11pp),
2022
20 Taipei 10617, Taiwan
3
INAF, Osservatorio Astroﬁsico di Arcetri, Largo E. Fermi 5, I-50125 Firenze, Italy
4
Univ. Grenoble Alpes, CNRS, Institut de Planétologie et d’Astrophysique de Grenoble (IPAG), F-38000 Grenoble, France
5
Institut de Radioastronomie Millimétrique (IRAM), 300 rue de la Piscine, F-38400 Saint-Martin d’Hères, France
Received 2022 May 8; revised 2022 August 22; accepted 2022 August 22; published 2022 September 16

メタノールでLVG

Lee et al.

Abstract
Formamide (NH2CHO) is considered an important prebiotic molecule because of its potential to form peptide
bonds. It was recently detected in the atmosphere of the HH 212 protostellar disk on the solar system scale whereplanets will form. Here we have mapped it and its potential parent molecules HNCO and H2CO, along with othermolecules CH3OH and CH3CHO, in the disk atmosphere, studying its formation mechanism. Interestingly, we ﬁnd
a stratiﬁed distribution of these molecules, with the outer emission radius increasing from ∼24 au for NH2CHOand HNCO, to 36 au for CH3CHO, to 40 au for CH3OH, and then to 48 au for H2CO. More importantly, we ﬁndthat the increasing order of the outer emission radius of NH2CHO, CH3OH, and H2CO is consistent with the
The Astrophysical Journal, 937:10 (11pp), 2022 September 20
decreasing order of their binding energies, supporting that they are thermally desorbed from the ice mantle on dust
grains. We also ﬁnd that HNCO, which has much lower binding energy than NH2CHO, has almost the same spatial
distribution, kinematics, and temperature as NH2CHO, and is thus more likely a daughter species of desorbed
a more extended spatial distribution with different kinematics
NH2CHO. On the other hand, we ﬁnd that H2CO has 2
from NH2CHO, thus questioning whether it can be the gas-phase parent molecule of NH2CHO.
Uniﬁed Astronomy Thesaurus concepts: Star formation (1569); Star forming regions (1565); Stellar accretion disks(1579); Astrochemistry (75); Interstellar molecules (849)

The Astrophysical Journal, 937:10 (11pp), 2022 September 20

Lee et al.

Lee et

他はLTE
NH CHOとHNCOが同じ温度。

NH3+CO in competition with the formamide (Enrique-Romero
etal. 2022). In the gas-phase formation theory, it has beenFormamide (NH2CHO) is an interstellar complex organic
proposed
that formamide is formed by the gas-phase reaction ofmolecule (iCOM, referring to C-bearing species with six atoms
Figure 4. Rotation diagrams H
for2CO
molecular
lines
CH3CHO.
diagrams arewas
derived from the line intensities in the lower disk atmosphere
2CHO, HNCO,
withNHof2 NH
(Kahaneet al. and2013).
ThisThehypothesis
or more; Herbst & van Dishoeck 2009; Ceccarelli
al. 2017)
listed inetTable
1. The error bars show the uncertainty in our measurements, which are assumed to be 40% of the data values. The solid line is a linear ﬁt to the data.
later challenged by Song & Kastner (2016). Nonetheless, QM
Figure 3. Physical properties of CH OH toward the disk atmosphere. (a) and (b) show the results of the non-LTE LVG analysis using the lines with E < 200 K withand a key precursor
morecomplex organic molecules, that
2 with E > 200ofK. The
rotation diagram using the lines
line intensity is extracted from an The blended lines of NH2CHO are excluded from the diagram. The optically thick line of HNCO is marked with an open square and excluded from the ﬁtting. For
the GRELVG code (Ceccarelli et al. 2003), while (c) shows the result of the3plot.
Thebecause
contour representsaits
1σ potential
emission peak in the lower disk atmosphere, as marked by a blue circle in Figure1(j).lead(a) Density–Temperature
χ contour
temperatureiscomputations
ﬁxed at 100 K. (Vazart et al. 2016; Skouteris et al. 2017)
CH3CHO, the
can
to
the
origin
of
life,
of
to
form
conﬁdence level, assuming the best-ﬁt values of N(A-CH OH) and N(E-CH OH). The best-ﬁt solution is marked by the cross. (b) The ratio between the observed line
coupled with astronomical observations in shocked regions(c) Rotation(Saladino
diagram of CH OH
same symbols.
The solidet al. 2013; Lópezintensities (circles for
A-type and squares for E-type)with those of the best ﬁt as a peptide
function of E .bonds
et withal.the2012;
Kahane32line is a linear ﬁt to the data. The optically thick lines are marked with open squares and circles and excluded from the ﬁtting.
(Codella
the samebarriervein, at ∼44 au. More importantly, since water has
Sepulcre et al. 2019). It has been detected in the gas phase in
Tableet2 al. 2017) support this hypothesis. In
centrifugal
theobserved
deuterated
isomersofformamide(including
ColumnDensities
andAbundances
in
the
Lower
Disk
Atmosphere
supporting this possibility. The faint NH2CHO and CH3OH hot
thecorinos
disk (Figure5(b)), the etstratiﬁcationin thedistribution(Kahaneal. 2013;
Coutens
et ofal. 2016; Imai et al.
a BE similar to that of H2CO (see Table 3), it is likely thatemission detected in the midplane likely comes from the upper
these molecules could be related to their binding energy (BE;et al.like
2016)
ﬁt is also desorbed from the ice mantle on the
NH2CDO, cis- and trans-NHDCHO; Coutenswater,
López-Sepulcre et al. 2017; Bianchi et al. 2019; Hsu
H2CO,and lower disk atmospheres due to the beam convolution. 2016;
and thus sublimation temperature). Table 3 lists the recently
Excitation
well
with
the
theoreticalpredictions
formationh of a gas-phase
However, the H2CO emission in the midplane near the CB (see et computed
BE forwhichthese molecules.
consistentcomparison,al. 2022),
are theForhot(100K) andSpecies
compact (100
dust
grains.
Thus
the water snowline can be located around or
Temperature
Column Density
Abundance
Figure 1(g)) should be real detection because the optical depth
we adopt the values obtained from similar methods on−2
route(Skouterisetal.
2017).
On
the
other
hand,
the
observedslightly
outsidethecentrifugal barrier.
au)regions
immediatelyaroundlow-mass(Sun-like)
protostars
(K)
(cm
)
of the dust continuum decreases to smaller than 3 at the edge.
amorphous solid water ice (Ferrero et al. 2020; Ferrero &high +deuterium
fractionation
for the three different(Ceccarelli
et al.HNCO
2007).
The
formamide
originisGrieco 2022). Since
was not
includedin those studies,
astill under+48−2+4.2 of ∼2%
4.5
7
18
CH3OH
92
1.4 0.7 ´ 10
1.5-0.8 ´ 10 cm
we adoptIn
its value
from Song& Kastner (2016).
Noticedebate.
principle,
formamide
could
bethatsynthesized on221
the±-37132 forms
cis- and trans-NHDCHO)
of formamide (4.8(NH±-2CDO,
4.2. Distribution of Molecules and Binding Energy
different methods can result in different BE, e.g., HCOOH was NH2CHOb(5.2 ± 2.6) × 1015
2.4) × 10−10
2 earlier, a stratiﬁcation is seen in the distribution grain
4.3. Centrifugal
Barrier and H2CO and CH3OH
in ofthephase.
found surfaces
to have a BEor
valueless gasthan 5000
K on Twopure iceroutes
be× consistentwith
the× formationin ice mantles
on
As discussed
HNCOb have been
231 ± 100 could(1.8also± 0.5)
1016(1.7± 0.9)
10−9(Kruczkiewicz
et theal. 2021),
signiﬁcantly
lower
than thatof molecules in the disk atmosphere, with the outer disk radius proposed
c of HNCO
e
16
−9
in
ﬁrst
case:
the
hydrogenation
dust
grains.
60±20(1.4 ± 0.7) × 10
(1.3 ± 0.7) × 10
(with
The
high
deuterationof
H2CO
adopted here. As can be seen, the increasing order of the H2CO
decreasing from H2CO, to CH3OH, to CH3CHO, and then tod& radius
Rodgers
and theCHcombination
CHO/t-HCOOH,
observed outerof NH22008)
The
corinoHH
212× protostellar
system(Codella
NH2CHO/HNCO/HCOOH, as shown in Figure 5(b) together (Charnley(4.5 hot± 2.3)× 1016 in the(4.2± 2.1)
10−9
3OH, and H2CO of the HCO
CO]/[HCO]
0.053)
andmethanol
(with
[D
2
2
14
−11
the decreasingorder ofmobile
their BE, upon
H2CO
with the temperature structure of the dusty disk model (Lee andNHis consistentradicals,with
when
they become
H13COthe warming
60 ± 20e et al.
(9.02016)± 4.5) in× 104.2) × 10ofOrion
at(8.3a ±distance∼400 pc
particularly
DOH]/[CHOH]
et al.optical
2019)
thatlevels 1, 3, and 5[CHismap
indicating2 that these molecules are thermally desorbed from the 2
et al. 2021b). Similar stratiﬁcation of H2CO, CH3CHO, andFigure(black contours and3gray
image, ∼0.12;
same as Figure Lee
1(c)), continuum
depth (bluesupports
contours, with contourf15−10 5. (a) Continuum 2
D
CO
92
±
30
(2.4
±
1.2)
×
10
(2.2
±
1.1)
×
10
(red contours, same as Figure 1(a)) and CH OH (cyan contours, same as Figure 1(j)) total line intensity maps. (b) Stratiﬁcat
λ ∼ 1.33
mm (orspatially
226 GHz), NH CHO
of
the
dust
by
the
protostar.
However,
the
ﬁrst
route
has
been
ice mantle on dust grains. Notice that this does not necessarily 2
NH2CHO has been seen toward the bow shock region B1 in theinteresting because recent observations
haveboth areresolved
originally formed in ice. These ratios of
1. Introduction

ホルムアミド, CH OH, H COは半径と昇華温度が負の相関。
CH OHとH COはエンベロープダストから降着ショックで出た可能性も。
3

u

u

3

2

3

u

3

HNCOはホルムアミドと半径、速度、温度が同じ。
しかし昇華温度は低いのでガス相のホルムアミドからできた（起源ではない）。
H COは半径と速度が違うのでホルムアミドの起源かは不明。

2

3

The evolution of protoplanetary disc radii and disc masses in star-forming
regions‹†

Department of Physics and Astronomy, The University of Sheffield, Hicks Building, Hounsfield Road, Sheffield S3 7RH, UK

Accepted 2022 July 26. Received 2022 July 26; in original form 2022 May 11

Downloaded *+o, -../0122a3ade,435o6/53o,2,n+a02a+.43le2787292799:2;;7<=:9 >? @a.4onal A0.+ono,43al B>0e+Ca.o+? o* Da/an 60e+ on

Bridget Marchington and Richard J. Parker星の大部分が星団にいて、そんな環境では円盤や惑星軌道が削られる。光蒸発や粘性も質量を減らす。
ABSTRACT

Protoplanetary discs are crucial∝Fとし、係数は経験則。
to understanding how planets form and evolve, but these objects are subject to the vagaries of the
観測論文からMdustを引くか、M
dustbirth environments of their host stars. In particular, photoionizing radiation from massive stars has been shown to be an effective
agent in disrupting protoplanetary discs. External
leads to the inward evolution of the radii of discs, whereas the
10番目に近い星までの体積から局所的な𝜌。>5M̅ photoevaporation
sunの星からのFUVフラックスを<5M
sunの星の場所で計算。
internal viscous evolution of the disc causes the radii to evolve outwards. We couple N-body simulations of star-forming regionswith a post-processing analysis of disc evolution to determine how the radius and mass distributions of protoplanetary discs
evolve in young star-forming regions. To be consistent with observations, we find that the initial disc radii must be of the orderof 100 au, even though these discs are readily destroyed by photoevaporation from massive stars. Furthermore, the observed disc
3 densities (100 M! pc−3 ),radius distribution in the Orion Nebula Cluster (ONC) is more consistent with moderate initial stellar
sun
in tension with dynamical models that posit much higher initial densities for the ONC. Furthermore, we cannot reproduceDisc
the radii and masses in star-forming regions
').*
').(
!observed disc radius distribution in the Lupus star-forming region if its discs are subject to external photoevaporation. A moredetailed comparison is not possible due to the well-documented uncertainties in determining the ages of pre-main-sequence".$%⨀(disc-hosting) stars.

Starlab環境のKIRAを使って星形成領域の力学進化を計算。
N=1500 (ONC, λ Ori) or 150 (他)で、星密度は10-1000 M
!
".$%⨀

'$.(

1+

/pc 。

から0.1-50 Msunを抽出。

$+,!"#$

一方で粘性進化の式から円盤の拡大も計算。

Most stars form in groups with between 10 and 104 stellar siblings(Lada & Lada 2003; Gutermuth et al. 2009; Bressert et al. 2010).
Some of these groups coalesce to form long-lived bound star clusters(Kruijssen 2012) or unbound associations (Wright 2020; Wright et al.
2022). While the evolution and fate of star-forming regions is likely
to be more nuanced than this dichotomy, at early ages (<10 Myr) thestellar density in all of these regions significantly exceeds the stellar
density in the Milky Way’s disc by several orders of magnitude(Korchagin et al. 2003).
Planets are observed to be forming (Haisch, Lada & Lada 2001;
Richert et al. 2018), and in some cases are thought to have alreadyformed (Alves et al. 2020) when their host stars are still embeddedin these stellar groups, implying that the birth environment of stars

produce photoionizing extreme ultraviolet (EUV) and far-ultraviolet(FUV) radiation. EUV and FUV radiation readily evaporates the gas
component of protoplanetary discs (e.g. Johnstone, Hollenbach &Bally 1998; Störzer & Hollenbach 1999; Hollenbach, Yorke &Johnstone 2000; Scally & Clarke 2001; Adams et al. 2004; Fatuzzo &Adams 2008; Winter et al. 2018b; Nicholson et al. 2019; Parker,
1. The2021a
observational
we willuse to compare
withaoursimulations.
The blue lines in each panel are the initial conditions for our simulations. In
Nicholson &Figure
Alcock; anddatamanyothers),and tolesserextentpanel (a), these blue lines are a Gaussian fit to the ONC data (the red line). In each panel, the mint green dashed line represents the respective gas distribution,
the dust (Haworth
et al. 2018).
whereas solid lines represent the dust distributions. Dotted lines indicate an alternative dust radius in ρ Oph (orange line) and Lupus (mint green line).
In addition to external photoevaporation from EUV/FUV radiation
both thegas masses
dust masses
are shownfor Lupus(the
3 METHOD
produced byformassiv
e stars,
manandy other
processes
affectthe evolution
mint green lines; Ansdell et al. 2016). The initial mass distribution in
In this section, we describe the N-body simulations we use to modelof protoplanetary
discs,
includinginternal
photoev
aporationfromthe
all of our simulations (see the next section) is shown by the blue lines.
star-forming regions, the post-processing analysis we use to follow
host star, andWe
bothandexternal
X-ray-driv
will internal
compare oursimulateddisc populations
toen
the evaporation
observathe evolution of protoplanetary discs, and the observational data withdata atvarious ages.&Stellar
ages are2022
notoriously
difficultevento(Picogna et tionalal. 2019; Coleman
Haworth). Notably,
inwhich we will compare our simulations.
estimate (Bell et al. 2013), and many of the star-forming regions wethe absencewillof compare
external
effects, the disc is expected to evolve due
our data with have more than one age estimate, or a

Downloaded *+o, -../0122a3ade,435o6/53o,2,n+a02a+.43le2787292799:2;;7<=:9 >Key words: methods: numerical – protoplanetary discs – photodissociation region (PDR) – open clusters and associations:Mdisc=0.1M*。
general.
FUVによる質量損失をFRIEDで計算。
%!"#$
が保存するように円盤が縮小。
planet formation if these regions contain stars massive enough to
1 I N T RO D U C T I O N

5451

Disc radii and masses in star-forming regions

The evolution of protoplanetary disc radii and disc masses in star-forming
regions‹†

Department of Physics and Astronomy, The University of Sheffield, Hicks Building, Hounsfield Road, Sheffield S3 7RH, UK

結果）
Accepted 2022 July 26. Received 2022 July 26; in original form 2022 May 11
ONC, λ Oriは初期に100-1000 Msun/pc3、他は100 Msun/pc3のABSTRACTとき 𝜌とFUVフラックスが観測と合う。
̅Protoplanetary discs are crucial to understanding how planets form and evolve, but these objects are subject to the vagaries of the
光蒸発だけでは観測された円盤半径と円盤質量に合わない。
birth environments of their host stars. In particular, photoionizing radiation from massive stars has been shown to be an effective
agent in disrupting protoplanetary discs. External photoevaporation leads to the inward evolution of the radii of discs, whereas the
粘性も入れて初期にrdisc=100auのときモデルの円盤が少し軽い。
internal
viscous evolution of the disc causes the radii to evolve outwards. We couple N-body simulations of star-forming regions
withapost-processing
analysis of disc evolution to determine how the radius and mass distributions of protoplanetary discs
初期に10 auだと重く、小さくなる。
evolve in young star-forming regions. To be consistent with observations, we find that the initial disc radii must be of the orderof 100M
au,suneven/pc
though3thesediscs are readily
destroyed by photoevaporation from massive stars. Furthermore, the observed disc
N=1500で初期に1000だと0.5Myrで円盤が無くなる。
radius distribution in the Orion Nebula Cluster (ONC) is more consistent with moderate initial stellar densities (100 M pc ),ßガス無しダスト円盤ならokだが。
in tension with dynamical models that posit much higher initial densities for the ONC. Furthermore, we cannot reproduce thedisc radius
distribution in the Lupus star-forming region if its discs are subject to external photoevaporation. A more
N=1500で初期に100observed
Msun/pc3だとUpper
Scoは5 Myr, それ以外
detailed
comparison is not possible due to the well-documented uncertainties in determining the ages of pre-main-sequence(disc-hosting) stars.
はONCも含めて1 Myrで合う。
Key words: methods: numerical – protoplanetary discs – photodissociation region (PDR) – open clusters and associations:
N=150だとおよそ合うが、5Myrで小さい円盤が観測より多い。
general.
!

1 I N T RO D U C T I O N

planet formation if these regions contain stars massive enough to
produce photoionizing extreme ultraviolet (EUV) and far-ultraviolet(FUV) radiation. EUV and FUV radiation readily evaporates the gas
component of protoplanetary discs (e.g. Johnstone, Hollenbach &Bally 1998; Störzer & Hollenbach 1999; Hollenbach, Yorke &Johnstone 2000; Scally & Clarke 2001; Adams et al. 2004; Fatuzzo &Adams 2008; Winter et al. 2018b; Nicholson et al. 2019; Parker,
Nicholson & Alcock 2021a; and many others), and to a lesser extent
the dust (Haworth et al. 2018).
In addition to external photoevaporation from EUV/FUV radiation
produced by massive stars, many other processes affect the evolutionof protoplanetary discs, including internal photoevaporation from thehost star, and both internal and external X-ray-driven evaporation(Picogna et al. 2019; Coleman & Haworth 2022). Notably, even in
the absence of external effects, the disc is expected to evolve due

注意）
Most stars form in groups with between 10 and 10 stellar siblings(Lada & Lada 2003; Gutermuth et al. 2009; Bressert et al. 2010).
観測はダスト円盤だが、蒸発するのはガス円盤。
Some of these groups coalesce to form long-lived bound star clusters(Kruijssen 2012) or unbound associations (Wright 2020; Wright et al.
初期半径はもっと大きいかも。
2022). While the evolution and fate of star-forming regions is likely
to be more nuanced than this dichotomy, at early ages (<10 Myr) the
Lupusはどのモデルより大きい円盤が多いß隣りのOB
stellar density in all of these regions significantly exceeds the stellar
density in the Milky Way’s disc by several orders of magnitude
associationからの輻射のせいで薄く広がった放射。
(Korchagin et al. 2003).
4

Planets are observed to be forming (Haisch, Lada & Lada 2001;
Richert et al. 2018), and in some cases are thought to have alreadyformed (Alves et al. 2020) when their host stars are still embeddedin these stellar groups, implying that the birth environment of stars−3

Downloaded *+o, -../0122a3ade,435o6/53o,2,n+a02a+.43le2787292799:2;;7<=:9 >? @a.4onal A0.+ono,43al B>0e+Ca.o+? o* Da/an 60e+ on

Bridget Marchington and Richard J. Parker

5457

© 2022. The Author(s). Published by the American Astronomical Society.

The Molecular Composition of Shadowed Proto-solar Disk Midplanes Beyond the Water
Snowline
Shota Notsu1,61, Kazumasa Ohno2, Takahiro Ueda3,4, Catherine Walsh5, Christian Eistrup3, and Hideko Nomura4

Star and Planet Formation Laboratory, RIKEN Cluster for Pioneering Research, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan; shota.notsu@riken.jp
2
Department of Astronomy and Astrophysics, University of California, Santa Cruz, 1156 High Street, Santa Cruz, CA 95064, USA
3
Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg, Germany
4
National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
5
School of Physics and Astronomy, University of Leeds, Leeds, LS2 9JT, UK
Received 2022 May 10; revised 2022 July 25; accepted 2022 August 7; published 2022 September 14

惑星系の化学は分子雲からと円盤での温度に依る化学進化で決まる。
Abstract
木星では揮発性のNなどと他元素が同程度にリッチ。
disk midplane temperature is potentially affected by the dust traps/rings. The dust depletion beyond the water
ßN2スノーライン外>30The
auでできた？しかし移動が速すぎる。
snowline
will cast a shadow. In this study, we adopt a detailed gas-grain chemical reaction network, and investigate
the radial gas and ice abundance distributions of dominant carbon-, oxygen-, and nitrogen-bearing molecules in
スノーラインにダストが溜まると影を作るàNなども凍る。
disks with shadow structures beyond the water snowline around a proto-solar-like star. In shadowed disks, the dust

grains at r ∼ 3–8 au are predicted to have more than ∼5–10 times the amount of ices of organic molecules such as
H2CO, CH3OH, and NH2CHO, saturated hydrocarbon ices such as CH4 and C2H6, in addition to H2O, CO, CO2,
NH3, N2, and HCN ices, compared with those in non-shadowed disks. In the shadowed regions, we ﬁnd thathydrogenation (especially of CO ice) is the dominant formation mechanism of complex organic molecules. The
gas-phase N/O ratios show much larger spatial variations than the gas-phase C/O ratios; thus, the N/O ratio issun* be a useful tracer of the shadowed region. N2H+ line emission is a potential tracer of the shadowed
predicted toregion. We conclude that a shadowed region allows for the recondensation of key volatiles onto dust grains,provides a region of chemical enrichment of ices that is much closer to the star than within a non-shadowed disk,
and may explain to some degree the trapping of O2 ice in dust grains that formed comet 67P/Churyumovextends
out.does
Evennotin thecasetoofhavea smallvariationvast
in thethe degree of (cosmic-ray) ionization. In order to investigate
Gerasimenko. We discuss that, if formed in a shadowed
disk,farther
Jupiterneed
migrated
distances.

ガス-粒子化学反応網を使って影のあるTタウリ円盤の化学組成を調べる。
M*=1.0 Msun, R*=2.6 R , T =4300 K, 面密度冪3/5, 水のスノーライン
1.3 auより外は小ダスト（0.1-100 µm）密度f倍。
温度は、RADMC3Dで鉛直構造と無撞着に得られた過去論文の温度。
the effects of ionization on chemistry in the shadowed disk,
dust density proﬁle with f = 0.3, T is around 20 K lower thanwe adopt two values of radially constant ionization rates
Uniﬁed Astronomy Thesaurus concepts: Protoplanetary
Planet(1241);
that disks
in the (1300);
non-shadowed
diskformation
with f = 1.0.
For f Astrochemistry0.03, T is
ガス化学はUMIST Database/RATE12（光蒸発、光乖離、宇宙線含む）。
[s ] and 1.0 × 10
[s ] (e.g., Cleeves
ξ (r) = 1.0 × 10
<30 K(832);
at r ∼ 3–8
au, and <25
K at around (487);
the current
orbit of(75); Interstellar molecules (849); Interstellar abundances
Exoplanet
atmospheres
Planetaryetal.
2014b;
Eistrup
et
al.
2016,
2018).
The former highJupiter(∼5
au).
In
contrast,
thevalues
of
T
at
r
>
20
au
atmospheres (1244); Planetary system formation (1257)
ダスト粒子との反応は宇宙線と熱による乖離と吸着。表面反応はOSU。
ionization value includes contributions from the decay
increase with decreasing f, although the degree of increase isproducts of short-lived radionuclides (SLRs; Cleeves et al.
small and T is <35 K even for f = 0.003. We interpret that
1 Myrまで。
2013a, 2013b) and from cosmic-rays, originating externally to
reduced dust surface density beyond the water snowline allows
temperature T(r) in protoplanetary disks is determined by
1. Introduction
CR

−17

−1

−18

−1

the disk (e.g., Umebayashi & Nakano 2009; Padovani et al.
the reprocessed stellar radiation to enter the outer disk
2018),
whereas the latter low ionization value considers
midplaneheatingfrom thedue
uppertodisk
surface (Cleeves
2016).(onlyAt thein theviscousdissipation
innermostProtoplanetary disks are composed of bare and ice-coatedouter disk midplane (r > 20 au), the heating effect by suchcontribution
from the decay products of SLRs only. We noteregion) and the stellar irradiation grazing the disk surface(e.g.,
refractory grains, and gas, which are the ingredients ofradiation overcomes the cooling effect, which reduces as rthat, in reality, the ionization rate has radial dependence, since
et al. 2011; Mori et al. 2021).
Since inthetheamountheating from SLRs decreases as r increases (Cleevestheofcontribution
The disk temperature is expected to be
3 2011; Öbergincreases.Oka
2 higherplanetesimals and planets (e.g.,2Williams & Ciezaper (beyond
unit volume
from
both
of thesesourcesdecreases
with
et
al.
2013b)and that from cosmic-rays increases as r increases
outer
disk
r
>
20
au)
if
we
assumelower
surface& Bergin 2021). Disks are chemically active environments that(e.g.,disk,
Umebayashi& Nakano 2009; Padovani et al. 2018;diskchose.
radiusTher, values
in a smooth(non-shadowed)
thedensitiesincreasing
than we initiallyof disk masses
are
2
3
2
create simple and complex molecules, including organicdetermined by the density proﬁle in the outer region of the disk.
et al. 2021; Seifert et al. 2021; Fujii & Kimura 2022).
temperature monotonically decreases as the Aikawa
disk radiusmaterial. The physical and chemical conditions of protoplane-We note that we have adopted the surface densities following a
Using Equation (30) of Cleeves et al. (2013b) and our assumed
increases (Kusaka et al. 1970; Kenyon & Hartmann1987;
Σgas(r) proﬁle, the ionization rates for the contribution fromtary disks determine the properties of forming planets,single power-law proﬁle for the sake of simplicity (seeChiang&Goldreich
1997;
Oka
et
al.
2011).
Inside
the
water
SLRs
are
estimated to be ∼5 × 10−19 [s−1] at r ∼5 au andmass within 20 au and 40 au
including mass and chemical composition (e.g., Öberg et al.Equations (1)−2and 2). The disk gas −2−19snowline, H O ice evaporates from the dust grain surfaces[s−1] at r ∼1 au. Nonetheless, we assume a∼7 × 10 into
2011; Öberg & Bergin 2016, 2021; Madhusudhan et al. 2014;is ∼2.2 × 10 Me and2∼5.8 × 10 Me, respectively. Eistrup
constant
et al. (2016)a diskwhereas
surface density
proﬁlean outerout onto
the adopted
gas phase,outsideit with
is frozen
the value
dust of the ionization rate at all radii to clarify its
Pontoppidan et al. 2014; Eistrup et al. 2016, 2018; Cridlandexponential cutoff radius of rc = 20 au. If we include such an
impacts
the disk chemical evolution.
grain surfaces (Hayashi 1981). In addition, the coldouterondisk
et al. 2017; Booth & Ilee 2019; Notsu et al. 2020; Schneider &outer exponential cutoff with rc ∼20 au in the disk surface
is needed for the formation of various complex organic
Bitsch 2021; Turrini et al. 2021; Mollière et al. 2022). Indensity proﬁle, the total disk mass within 40 au will be aroundCalculation of the Disk Chemical Structure
molecules,
since cutoff.
the sequential
hydrogenationof CO 2.2.
on thehalfofthe value without
Recently, Trapman
et al.
addition, molecular abundances in comets and other primitive
cold (T(r)
10–30
dust
grain that
surfaces
leads
to
the
O lineobservations
the(2022) estimatedfrom∼HDand C18K)
We calculated the chemical evolution of the shadowed disk

影があると木星軌道5.3 auでは、H OやNH は変わらないが、COとN が凍り、表面反応で水素が付く（e.g, H CO, CH OH, NH CHO, HCN）。
粒子に飽和有機分子アイスが影無しの5-10倍。

small bodies in our solar system are determined by the

The Molecular Composition of Shadowed Proto-solar Disk Midplanes Beyond the Water
Snowline
Shota Notsu1,61, Kazumasa Ohno2, Takahiro Ueda3,4, Catherine Walsh5, Christian Eistrup3, and Hideko Nomura4

Star and Planet Formation Laboratory, RIKEN Cluster for Pioneering Research, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan; shota.notsu@riken.jp
2
Department of Astronomy and Astrophysics, University of California, Santa Cruz, 1156 High Street, Santa Cruz, CA 95064, USA
3
Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg, Germany
4
National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
5
School of Physics and Astronomy, University of Leeds, Leeds, LS2 9JT, UK
Received 2022 May 10; revised 2022 July 25; accepted 2022 August 7; published 2022 September 14

Abstract
The disk midplane temperature is potentially affected by the dust traps/rings. The dust depletion beyond the water
snowline will cast a shadow. In this study, we adopt a detailed gas-grain chemical reaction network, and investigate
the radial gas and ice abundance distributions of dominant carbon-, oxygen-, and nitrogen-bearing molecules indisks with shadow structures beyond the water snowline around a proto-solar-like star. In shadowed disks, the dust
grains at r ∼ 3–8 au are predicted to have more than ∼5–10 times the amount of ices of organic molecules such as
H2CO, CH3OH, and NH2CHO, saturated hydrocarbon ices such as CH4 and C2H6, in addition to H2O, CO, CO2,
NH3, N2, and HCN ices, compared with those in non-shadowed disks. In the shadowed regions, we ﬁnd thathydrogenation (especially of CO ice) is the dominant formation mechanism of complex organic molecules. The
gas-phase N/O ratios show much larger spatial variations than the gas-phase C/O ratios; thus, the N/O ratio ispredicted to be a useful tracer of the shadowed region. N2H+ line emission is a potential tracer of the shadowed
region. We conclude that a shadowed region allows for the recondensation of key volatiles onto dust grains,provides a region of chemical enrichment of ices that is much closer to the star than within a non-shadowed disk,
and may explain to some degree the trapping of O2 ice in dust grains that formed comet 67P/ChuryumovGerasimenko. We discuss that, if formed in a shadowed disk, Jupiter does not need to have migrated vast distances.
Uniﬁed Astronomy Thesaurus concepts: Protoplanetary disks (1300); Planet formation (1241); Astrochemistry(75); Interstellar molecules (849); Interstellar abundances (832); Exoplanet atmospheres (487); Planetaryatmospheres (1244); Planetary system formation (1257)
1. Introduction
Protoplanetary disks are composed of bare and ice-coatedrefractory grains, and gas, which are the ingredients ofplanetesimals and planets (e.g., Williams & Cieza 2011; Öberg
& Bergin 2021). Disks are chemically active environments thatcreate simple and complex molecules, including organic
material. The physical and chemical conditions of protoplanetary disks determine the properties of forming planets,
including mass and chemical composition (e.g., Öberg et al.
2011; Öberg & Bergin 2016, 2021; Madhusudhan et al. 2014;
Pontoppidan et al. 2014; Eistrup et al. 2016, 2018; Cridland
et al. 2017; Booth & Ilee 2019; Notsu et al. 2020; Schneider &Bitsch 2021; Turrini et al. 2021; Mollière et al. 2022). In
addition, molecular abundances in comets and other primitive
small bodies in our solar system are determined by the© 2022. The Author(s)Tracers of Dense Gas in the Outer Galaxy
Sudeshna Patra1
1, Neal J. Evans II2,3,4 , Kee-Tae Kim3,5 , Mark Heyer6 , Jens Kauffmann7
Manash R. Samal8 , and Swagat R. Das1

, Jessy Jose1,

Indian Institute of Science Education and Research (IISER) Tirupati, Rami Reddy Nagar, Karakambadi Road, Mangalam (P.O.), Tirupati 517507, India
inspire.sudeshna@gmail.com
2
Department of Astronomy, The University of Texas at Austin, 2515 Speedway, Stop C1400 Austin, Texas 78712-1205, USA
3
Korea Astronomy and Space Science Institute, 776 Daedeokdae-ro, Yuseong-gu Daejeon, 34055, Republic of Korea
4
Humanitas College, Global Campus, Kyung Hee University, Yongin-shi 17104, Republic of Korea
5
University of Science and Technology, Korea (UST), 217 Gajeong-ro, Yuseong-gu, Daejeon 34113, Republic of Korea
6
Department of Astronomy, University of Massachusetts Amherst, Amherst, MA 01003, USA
7
Haystack Observatory, MIT, 99 Milstone Road, Westford, MA 01886 USA
8Astronomy & Astrophysics Division, Physical Research Laboratory, Ahmedabad, 380009, State of Gujarat, India
Received 2022 April 4; revised 2022 July 6; accepted 2022 July 21; published 2022 September 7

Abstract
We have mapped HCN and HCO (J = 1 → 0) line emission toward a sample of seven star-forming regions (with12 + log [O H] ranging from 8.34 to 8.69) in the outer Milky Way (Galactocentric distance >9.5 kpc), using the
14 m radio telescope of the Taeduk Radio Astronomy Observatory. We compare these two molecular lines withother conventional tracers of dense gas, millimeter-wave continuum emission from dust and extinction thresholds(AV 8 mag), inferred from the 13CO line data. HCN and HCO+ correlate better with the millimeter emission thanwith the extinction criterion. A signiﬁcant amount of luminosity comes from regions below the extinction criterion
and outside the millimeter clump for all the clouds. The average fraction of HCN luminosity from within theregions with AV 8 mag is 0.343 ± 0.225; for the regions of millimeter emission, it is 0.478 ± 0.149. Based on acomparison with column density maps from Herschel, HCN and HCO+ trace dense gas in high column density
regions better than does 13CO. HCO+ is less concentrated than HCN for outer Galaxy targets, in contrast with theinner Galaxy sample, suggesting that metallicity may affect the interpretation of tracers of dense gas. The
conversion factor between the dense gas mass (Mdense) and line luminosities of HCN and HCO+, when integrated
over the whole cloud, is comparable to factors used in extragalactic studies.
+

Uniﬁed Astronomy Thesaurus concepts: Star forming regions (1565); Molecular clouds (1072)
1. Introduction
Detailed observation of molecular clouds in the Milky Way(Heiderman et al. 2010; Lada et al. 2010, 2012; Evans et al. 2014;
Vutisalchavakul et al. 2016) and studies of external galaxies (Gao& Solomon 2004a) have shown that star formation is moreaccurately predicted by the amount of dense molecular gas rather
than by the total amount of molecular gas. The molecules withhigh dipole moment and high critical density, such as HCN and
HCO+, are used as dense gas tracers. The pioneering studies by
Gao & Solomon (2004a, 2004b) revealed a tight linear correlation
between the luminosity of the HCN J = 1 → 0 transition (as atracer of the mass of dense molecular gas) and the far-infrared
luminosity, indicative of the star formation rate (SFR) for wholegalaxies. Later works extended this relation to resolved structuresin other galaxies (Jiménez-Donaire et al. 2019; Heyer et al. 2022)(Evans 1989). In reality, multilevel excitation effects and radiative
trapping effects all tend to lower the effective excitation density(neff), deﬁned as the density needed to detect a molecular line withintegrated intensity of 1 K km s−1 (Evans 1999; Shirley 2015). For
the low-J transitions the effective excitation densities are typically
1–2 orders of magnitude lower than the critical densities. The
values of neff for HCN and HCO+ are 4.5 × 103 cm−3 and5.3 × 102 cm−3 at 20 K, respectively (Shirley 2015). For modern
surveys with low rms noise, lines at the detection limits can beproduced by gas with density as low as 50–100 cm−3, explaining
the emission from extended translucent regions where the densityof gas is much lower than the critical densities of HCN and HCO+
(Evans et al. 2020).
Pety et al. (2017) found that only a small fraction of theluminosity of HCN (18%) and HCO+ (16%) arises from

3

University of Leiden, P.O. Box 9513, 2300 RA, Leiden, The Netherlands
Space Research Institute, Austrian Academy of Sciences, Schmiedlstrasse 6, A-8042 Graz, Austria
5
Centre for Exoplanet Science, University of St. Andrews, North Haugh, St. Andrews, KY16 9SS,UK
6
Circumplanetary
disk
ices
Max-Planck-Institut für extraterrestrische Physik,
Giessenbachstrasse 1,
85748
Garching, Germany

I. Ice formation vs. viscous evolution and grain drift
Received — accepted —N. Oberg1, 2 , I. Kamp1 , S. Cazaux2, 3 , P. Woitke4, 5 , and W.F.Thi6

1

Kapteyn Astronomical Institute, University of Groningen, P.O. Box 800, 9700 AV Groningen, The Netherlands
ABSTRACTe-mail: oberg@astro.rug.nl
2
Faculty of Aerospace Engineering, Delft University of Technology, Delft, The Netherlands
3
University of Leiden, P.O. Box 9513, 2300 RA, Leiden, The Netherlands
Context. The large icy
4 moons of Jupiter formed in a circumplanetary disk (CPD). CPDs are fed by vertically infalling circumstellar
Space Research Institute, Austrian Academy of Sciences, Schmiedlstrasse 6, A-8042 Graz, Austria
5
gas and dust which may
beforshock-heatedaccretion.
Accretedmaterial
is theneither incorporated into moons, falls into theCentreExoplanet Science,upon
Universityof St. Andrews,
North Haugh,
St. Andrews,
KY16 9SS,UK
6
Max-Planck-Institut
fürextraterrestrische
Physik,Giessenbachstrasse
1,85748
Garching,
Germany
planet, or is lost beyond the disk edge on relatively short timescales. If ices are sublimated during accretion onto the CPD we know

iv:2208.11053v1 [astro-ph.EP] 23 Aug 2022

:2208.11053v1 [astro-ph.EP] 23 Aug 2022

4

there must be sufficient time for them to recondense or moons such as Ganymede or Callisto could not form. The chemical timescale
Received — accepted —to form sufficiently icy
solids places a novel constraint on the dynamical behaviour and properties of CPDs.
Aims. We aim to explore the process of ice formation in CPDs to constrain which disk properties (such as the mass, viscosity, andABSTRACT
dust-to-gas ratio) are consistent with the formation of an icy moon system.
The large
icy moons of Jupiterformedin a circumplanetary
disk (CPD). CPDs
are fedby verticallyinfalling circumstellar
Methods. We use theContext.
radiation
thermochemical
code
ProDiMo(Protoplanetary
Disk
Model)
to analyze
how the radial ice abundancegas and dust which may be shock-heated upon accretion. Accreted material is then either incorporated into moons, falls into theevolves in CPDs. We planet,
considerdi↵erentchemicalofIftheto explore
consequences
ofknow
infalling material being
or is lost
beyond theinitial
disk edge
on relativelyconditions
short timescales.
ices disk
are sublimatedduringthe
accretion
onto the CPD we
there
must
be
sufficient
time
for
them
to
recondense
or
moons
such
as
Ganymedeor
Callisto
could
not
form.
The
chemicaltimescaleinherited from the circumstellar disk or being reset to atomic conditions by shock-heating. We contrast the timescales of ice formation
to form sufficiently icy solids places a novel constraint on the dynamical behaviour and properties of CPDs.
with disk viscous timescales
andto radial
dust
drift.
Aims. We aim
explore theprocessof ice formation in CPDs to constrain which disk properties (such as the mass, viscosity, anddust-to-gas
ratio)
areconsistentwiththe formationof an oficy moonsystem.
Results. We have derived the radial ice abundance
and rate
ice formation
in a small grid of model CPDs. Water ice can form very
Methods. We use the radiation thermochemical code ProDiMo (Protoplanetary Disk Model) to analyze how the radial ice abundance
efficiently in the CPDevolves
fromininitiallyatomicconditions,asasignificant
fractionis efficiently
re-depositedon dustCPDs. We consider di↵erent initial chemical conditions of the disk to explore
the consequencesof infalling material
being grains within < 1 yr.
inherited fromor being
resetthose
to atomicof
conditions
by shock-heating.
We contrast
timescales
ice formation
Radial grain drift timescales
aretheincircumstellar
general disk
longerthan
ice formation
on grains.
Icythegrains
ofofsizea < 3 mm retain their icy
with disk viscous timescales and radial dust drift.
mantles while crossing
an optically thin circumstellar disk gap at 5 au for L < 10 L .
Results. We have derived the radial ice abundance and rate of ice formation in ⇤a small grid of model CPDs. Water ice can form very
Conclusions. Three-bodyreactionsplayinitiallyan importantroleasinwater formationin thedense onmidplanecondition
efficiently
in the CPD fromatomic conditions,a significant
fraction is efficiently
re-deposited
dust grains within< 1 yr. of CPDs. The CPD
Radialgrain
drift
timescalesareingenerallonger
than
those
of
ice
formationon
grains.
Icy
grains
of
size
a
<
3
mm
retaintheir
midplane must be depleted
in dust relative to the circumstellar disk by a factor 10-50 to produce solids with icy
the ice to rock ratio of
mantles while crossing an optically thin circumstellar disk gap at 5 au for L⇤ < 10 L .
the icy Galilean satellites.
The Three-body
CPD snowline
is noterasedrole
byinradial
grain drift,
whichis consistent
with The
theCPD
compositional gradientConclusions.
reactions play
an importantwater formationin the dense
midplanecondition of CPDs.
midplane
mustprimordial.
be depleted in dust relative to the circumstellar disk by a factor 10-50 to produce solids with the ice to rock ratio ofof the Galilean satellites
being
the icy Galilean satellites. The CPD snowline is not erased by radial grain drift, which is consistent with the compositional gradientof the Galilean satellites being primordial.

Key words. Planets and satellites: formation – Planets and satellites: composition – Accretion, accretion disks, – Protoplanetary

Key words. Planets and satellites: formation – Planets and satellites: composition – Accretion, accretion disks, – Protoplanetarydisks, – Planets and satellites:
individual: Jupiter – Methods: numerical
CPDへの降着中にアイスが溶けるが、また固まる時間がある。この間の化学からCPDの質量
disks, – Planets and satellites: individual: Jupiter – Methods: numerical、粘性、g/dを制限する。

1. Introduction

1. Introduction

A general feature of regular satellite formation theory is that thecircumplanetary disk (CPD) consists of circumstellar material
A general feature of regularsatellite
formationthat theaccreted fromwithin thevicinity of theory
the planetis(Lubow
et al.

2013; Szulágyi et al. 2014) infalling gas spends only a limited
time
insideSzulágyi
the CPD before
being2014)
lost (Canup& Ward 2002).
2013;
et al.
infallinggas spends only a limited
The insidetimescaletheof radial
dust
drift in small
disks
is alsopretime
CPD
beforebeing
lost(Canup& Ward 2002).
dicted to be short (Pinilla et al. 2013; Shibaike et al. 2017; Rab

Max Planck Institut für Extraterrestrische Physik (MPE), Giessenbachstrasse 1, 85748 Garching, Germany
Université Paris-Saclay, CNRS, Institut d’Astrophysique Spatiale, 91405 Orsay, France
4
DARK, Niels Bohr Institute, University of Copenhagen, Jagtvej 128, 2200 Copenhagen, Denmark
5complex
Physics Institute, N-bearing
University of Bern,
Sidlerstrasseorganics
5, 3012 Bern,toward
Switzerlandhigh-mass protostars
6
INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy7
ratios pointing
to formationin Astronomy,
similar pre-stellar
acrossa Manchester,
Jodrell BankConstantCentre for Astrophysics,
Departmentof Physics andUniversity ofconditions
Manchester, Oxford
Road,large mass range
M13 9PL, UK
8
I. Physikalisches Institut,
Universität
zu
Köln,
Zülpicher
Str.77, 50937,
Köln, Germany
1
1
1
1
1, 2
3
4
3

P. Nazari , J. D. Meijerhof , M. L. van Gelder , A. Ahmadi , E. F. van Dishoeck , B. Tabone , D. Langeroodi , N. F.
W.YYY
Ligterink5 , J. Jaspers1 , M. T. Beltrán6 , G. A. Fuller7, 8 , Á. Sánchez-Monge8 , and P. Schilke8
Received XXX; accepted1

Xiv:2208.11128v1 [astro-ph.GA] 23 Aug 2022

Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, the Netherlands
ABSTRACTe-mail: nazari@strw.leidenuniv.nl
2
Max Planck Institut für Extraterrestrische Physik (MPE), Giessenbachstrasse 1, 85748 Garching, Germany
3
Université Paris-Saclay, CNRS, Institut d’Astrophysique Spatiale, 91405 Orsay, France
Context. Complex
organic species are known to be abundant toward low- and high-mass protostars. No statistical study of these
4
DARK, Niels Bohr Institute, University of Copenhagen, Jagtvej 128, 2200 Copenhagen, Denmark
species toward a 5large
samplehigh-mass
protostars
theBern,
Atacama
Large Millimeter/submillimeter Array (ALMA) has been
Physics
Institute,of
Universityof Bern,
Sidlerstrassewith
5, 3012
Switzerland
6
INAF-Osservatorio
AstrofisicodiArcetri,
Largo
E.
Fermi
5,
50125
Firenze,Italycarried out so far.7
Jodrell Bank Centre for Astrophysics, Department of Physics and Astronomy, University of Manchester, Oxford Road, Manchester,Aims. We aim to study
six N-bearing species: methyl cyanide (CH3 CN), isocyanic acid (HNCO), formamide (NH2 CHO), ethyl
M13 9PL, UK
8
cyanide (C2 H5 CN),vinyl
cyanide(C2 H
methylamine(CH50937,) in aGermany
large sample of line-rich high-mass protostars.
3 CN) and3 NH2Köln,
I. Physikalisches
Institut,
Universität
zu Köln,Zülpicher Str.77,

Methods. From the ALMA Evolutionary study of High Mass Protocluster Formation in the Galaxy survey, 37 of the most line-richReceived XXX; accepted YYY

hot molecular cores with ⇠100 angular resolution are selected. Next, we fit their spectra and find column densities and excitation
ABSTRACT
Context. Complex organic species are known to be abundant toward low- and high-mass protostars. No statistical study of these

species toward a large sample of high-mass protostars with the Atacama Large Millimeter/submillimeter Array (ALMA) has been
carried out so far.
Aims. We aim to study six N-bearing species: methyl cyanide (CH3 CN), isocyanic acid (HNCO), formamide (NH2 CHO), ethyl
cyanide (C2 H5 CN), vinyl cyanide (C2 H3 CN) and methylamine (CH3 NH2 ) in a large sample of line-rich high-mass protostars.
Methods. From the ALMA Evolutionary study of High Mass Protocluster Formation in the Galaxy survey, 37 of the most line-richhot molecular cores with ⇠100 angular resolution are selected. Next, we fit their spectra and find column densities and excitation
temperatures of the N-bearing species mentioned above, in addition to methanol (CH3 OH) to be used as a reference species. Finally,
we compare our column densities with those in other low- and high-mass protostars.
Results. CH3 OH, CH3 CN and HNCO are detected in all sources in our sample, whereas C2 H3 CN and CH3 NH2 are (tentatively)
detected in ⇠78% and ⇠32% of the sources. We find three groups of species when comparing their excitation temperatures: hot(NH2 CHO; T ex & 250 K), warm (C2 H3 CN, HN13 CO and CH13
3 CN; 100 K . T ex . 250 K) and cold species (CH3 OH and CH3 NH2 ;T ex . 100 K). This temperature segregation reflects the trend seen in the sublimation temperature of these molecules and validates
the idea that complex organic emission shows an onion-like structure around protostars. Moreover, the molecules studied here show
constant column density ratios across low- and high-mass protostars with scatter less than a factor ⇠3 around the mean.
Conclusions. The constant column density ratios point to a common formation environment of complex organics or their precursors,most likely in the pre-stellar ices. The scatter around the mean of the ratios, although small, varies depending on the species considered.
This spread can either have a physical origin (source structure, line or dust optical depth) or a chemical one. Formamide is most prone
to the physical e↵ects as it is tracing the closest regions to the protostars, whereas such e↵ects are small for other species. Assumingthat all molecules form in the pre-stellar ices, the scatter variations could be explained by di↵erences in lifetimes or physical conditionsof the pre-stellar clouds. If the pre-stellar lifetimes are the main factor, they should be similar for low- and high-mass protostars (withinfactors ⇠2 3).

Key words. Astrochemistry – Stars: massive – Stars: protostars – ISM: abundances – Techniques: interferometric – Stars: pre-main

sequence

I. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
Department of Astronomy, University of Florida, PO Box 112055 Gainesville, FL, USA
4
NRAO, 520 Edgemont Rd,
Charlottesville,
22903,
USA
The
physical VA
andchemicalstructure of Sagittarius B2
5
Agnes Scott College, 141 E. College Ave., Decatur, GA 30030, USA?
6
VI.Giessenbachstrasse
UCHII regions in1, Sgr
B2Garching,
Max Planck Institute for Extraterrestrial Physics,
85748
Germany
7
Max Planck Institute for Radio Astronomy,
Auf dem Hügel2 69, 531212 Bonn, Germany
1,2
3
4,5
3
3

F. Meng (), Á. Sánchez-Monge , P. Schilke , A. Ginsburg , C. DePree , N. Budaiev ,3
D. Jeff , A. Schmiedeke6 , A. Schwörer2 , V. S. Veena7 , and Th. Möller2

Received 30 March 2022 / Accepted 8 July 2022
1

University of Chinese Academy of Sciences, Beijing 100049, PR Chinae-mail: mengfanyi@ucas.ac.cn; meng@ph1.uni-koeln.de
2
I. Physikalisches Institut, Universität zu Köln, ZülpicherABSTRACT
Str. 77, 50937 Köln, Germany
3
Department of Astronomy, University of Florida, PO Box 112055 Gainesville, FL, USA
4
NRAO, 520 Edgemont Rd, Charlottesville, VA 22903, USA
5
Context. The giant molecular
B2Decatur,(hereafter
SgrUSAB2) is the most massive region with ongoing high-mass star formaAgnes Scott cloudCollege, Sagittarius
141 E. College Ave.,
GA 30030,
6
Max
PlanckInstitutefor
Extraterrestrial
Physics,
Giessenbachstrasse
1, 85748 in
Garching,
Germanytion in the Galaxy. Twoultra-compact HII (UCHII ) regions were identified
Sgr B2’scentral hot cores, Sgr B2(M) and Sgr B2(N).
7
Max Planck Institute for Radio Astronomy, Auf dem Hügel 69, 53121 Bonn, Germany

Aims. Our aim is to characterize the properties of the HII regions in the entire Sgr B2 cloud. Comparing the HII regions and the dust
Received 30 March 2022 / Accepted 8 July 2022
cores, we aim to depict
the evolutionary stages of different parts of Sgr B2.
Methods. We use the Very Large Array in its A, CnB, and D configurations, and in the frequency band C (⇠6 GHz) to observe thewhole Sgr B2 complex. Using ancillary VLA data at 22.4 GHzABSTRACT
and ALMA data at 96 GHz, we calculated the physical parameters ofContext.
giant molecular
cloud Sagittarius B2 (hereafter Sgr B2) is the most massive region with ongoing high-mass star formathe UCHII regions andtheirThedense
gas environment.
tion in the Galaxy. Two ultra-compact HII (UCHII ) regions were identified in Sgr B2’s central hot cores, Sgr B2(M) and Sgr B2(N).
Results. We identifyAims.
54 UCH
IIisregionsin the6 GHz image,of inwhich
areSgralso
detected
at 22.4of the 54 UCHII regions
Our aimto characterize
the propertiesof the HII 39
regions
the entire
B2 cloud.
Comparingthe HIIGHz.
regions Eightand the dust
cores,
weaim
todepicttheevolutionary
stagesofdifferent
parts
of
Sgr
B2.
are newly discovered. The UCHII regions have radii between 0.006 pc and 0.04 pc, and have emission measure between 106 pc cm 6
We use the Very Large Array in its A, CnB, and D configurations, and in the frequency band C (⇠6 GHz) to observe theand 109 pc cm 6 . TheMethods.
UCH
are ionized
by starsof types
found thea typical
gas densityof ⇠106 –109 cm 3
whole
SgrIIB2regions
complex. Using
ancillary VLA
data at 22.4
GHz andfrom
ALMAB0.5
data atto
96O6.
GHz, We
we calculated
physical parametersofthe UCHIIThe
regionspressure
and their dense
around the UCHII regions.
of gastheenvironment.
UCHII regions and the dense gas surrounding them are comparable. The expansion
Results. We identify 54 UCHII regions in the 6 GHz image,
39 of5 which are also detected at 22.4 GHz. Eight of the 54 UCHII regions
timescale of these UCH
IIregionsisdetermined
to be ⇠104 –10
yr. The percentage of the dust cores that are associated with HII
are newly discovered. The UCHII regions have radii between 0.006 pc and 0.04 pc, and have emission measure between 106 pc cm 69
69
regions are 33%, 73%,
forIISgr
B2(N),
SgrbyB2(M),
Sgr
B2(S),Sgr
B2(DS),
respectively.
Two-thirdsof the dust coresand 4%,
10 pc andcm . 1%The UCHregions
are ionizedstars of types
fromB0.5 to andO6. Wefound
a typical gas
density of ⇠106 –10
cm 3
aroundthe
UCH
II regions. The pressure of the UCH II regions and the dense gas surrounding them are comparable. The expansionin Sgr B2(DS) are associatedwith outflows.
timescale of these UCHII regions is determined to be ⇠104 –105 yr. The percentage of the dust cores that are associated with HIIConclusions. The electron
densitiesof andthe1%UCH
IIB2(N),regions
we identified
in agreement
thatofofthetypicalregions are 33%, 73%, 4%,
for Sgr
Sgr B2(M),Sgr B2(S), andare
Sgr B2(DS),respectively.with
Two-thirds
dust coresUCH II regions, whilein
Sgr
B2(DS)
areassociatedwithoutflows.
the radii are smaller Conclusions.
than thoseTheofelectron
the typical
UCHII regions. The dust cores in Sgr B2(M) are more evolved than in Sgr B2(N). The
densities of the UCHII regions we identified are in agreement with that of typical UCHII regions, while
dust cores in Sgr B2(DS)
are
inthe
Sgr
B2(M)
Sgr B2(N).
the radii
are younger
smaller thanthan
those oftypicalUCHIIorregions.
The dust cores in Sgr B2(M) are more evolved than in Sgr B2(N). The
dust cores in Sgr B2(DS) are younger than in Sgr B2(M) or Sgr B2(N).

Key words. stars: formationstars:
massive
radio– radio
continuum:
ISM– radio– radiolines:ISM– ISM:
individual
Key words. –stars:
formation– stars: –massivecontinuum: ISM
lines: ISM– ISM:
individual
objects:
Sgr B2 – objects: Sgr B2 –ISM: clouds

1. Introduction

ISM: clouds

1. Introduction

The giant molecular cloud Sagittarius B2 (Sgr B2) is the most
massive (⇠107 M ) region with ongoing high-mass star formain the Sagittarius
Galaxy (see e.g.,B2
Goldsmithal. 1990).
Sgr most
B2 hasThe giant moleculartion
cloud(Sgr etB2)
is thea higher density (>105 cm 3 ) and dust temperature (&50–70 K)
7
massive (⇠10 M ) region
high-mass
formacompared withto otherongoingstar forming
regions in thestar
Galacticplane

to study high-mass star formation in an extreme high-pressure
environment. Such an environment resembles nearby starburst
galaxies (Leroy et al. 2018). Understanding the structure of the
Sgr B2 molecular cloud complex is necessary to comprehend
the most massive star forming region in our Galaxy, which at
the same time provides a unique opportunity to study in detail thenearest counterpart of the extreme environments that dominate