An Ordered Bipolar Outflow from a Massive Early-Stage Core

2.9 MB·

by  Jonathan C. Tan

Draft version March 3, 2016
AN ORDERED BIPOLAR OUTFLOW FROM A MASSIVE EARLY-STAGE CORE
Jonathan C. Tan
Depts. ofAstronomy&Physics,UniversityofFlorida,Gainesville,Florida32611,USA
[email protected]
Shuo Kong
Dept. ofAstronomy,UniversityofFlorida,Gainesville,Florida32611,USA
Yichen Zhang
DepartamentodeAstronom´ıa,UniversidaddeChile,Casilla36-D,Santiago,Chile
Francesco Fontani
6
1 INAF-OsservatorioAstrofisicodiArcetri,I-50125,Florence,Italy
0
2
Paola Caselli

r MaxPlanckInstituteforExtraterrestrialPhysics(MPE),Giessenbachstr. 1,D-85748Garching,Germany
a
M
Michael J. Butler

2 MaxPlanckInstituteforAstronomy,K¨onigstuhl17,69117Heidelberg,Germany
Draft version March 3, 2016

]
A ABSTRACT
G We present ALMA follow-up observations of two massive, early-stage core candidates, C1-N & C1-S,
. in Infrared Dark Cloud (IRDC) G028.37+00.07, which were previously identified by their N2D+(3-2)
h
emission and show high levels of deuteration of this species. The cores are also dark at far infrared
p wavelengths up to 100µm. We detect 12CO(2-1) from a narrow, highly-collimated bipolar outflow
- ∼
o that is being launched from near the center of the C1-S core, which is also the location of the peak
r 1.3mmdustcontinuumemission. Thisprotostar,C1-Sa,hasassociateddensegastracedbyC18O(2-1)
t and DCN(3-2), from which we estimate it has a radial velocity that is near the center of the range
s
a exhibited by the C1-S massive core. A second outflow-driving source is also detected within the pro-
[ jected boundary of C1-S, but appears to be at a different radial velocity. After considering properties

of the outflows, we conclude C1-Sa is a promising candidate for an early-stage massive protostar and
2
as such it shows that these early phases of massive star formation can involve highly ordered outflow,
v
and thus accretion, processes, similar to models developed to explain low-mass protostars.
3
4 Keywords: stars: formation – ISM: clouds; jets and outflows
0
7
0 1. INTRODUCTION less, self-gravitating cores, but rather low-mass cores,
. Understanding how massive stars form is an impor- with most of the mass reservoir joining later from the
1 protocluster clump.
tant goal, since their radiative, mechanical and chemical
0
To try and distinguish between these theories we have
6 feedback play leading roles in regulating the interstellar
developed a method for searching for massive starless
1 medium, star formation activity and overall evolution of
and early-stage core candidates. We first identify tar-
: galaxies. CoreAccretion(e.g.,McKee&Tan2003,here-
v get regions in IRDCs using mid-infrared, i.e., 8 µm
after MT03) is one class of models for massive star for-
i Spitzer-IRAC, extinction (MIREX) mapping (Butler &
X mation, which involve initial conditions of a high-mass,
Tan 2009; 2012). We select regions that are peaks in
self-gravitating starless core, followed by relatively or-
r the resulting mass surface density, Σ, map. We fur-
a dered collapse to a central disk and protostar (see Tan
ther check that these regions are dark in 24µm (Spitzer-
et al. 2014 for a review). These models are scaled-up
MIPS) and 70 µm (Herschel-PACS) images. We then
from those developed for low-mass star formation (e.g.,
search for N D+(3-2) emission with ALMA, since the
Shuetal. 1987),but,inthecaseoftheMT03Turbulent 2
abundance of this species, i.e., the deuteration frac-
Core Model, involve nonthermal forms of pressure sup-
pcoorret,toi.eb.e, itnurabpuplreonxciemaantedpmreasgsnuerteicanfidelvdisr,iafloerqtuhileibirniiutmial. (tiTon<D2fNr0a2cHK+)≡, d[eNn2sDe+(n]/[N(cid:38)2H1+0]5icsmk−n3o)wcnontoditriiosensi,necspoled-
H
Alternatively, Competitive Accretion models (e.g., ciallywhenCOmoleculesarelargelyfrozen-outontodust
Bonnell et al. 2001; Wang et al. 2010) involve a mas- grainicemantlesandtheortho-to-pararatioofH drops
2
sivestargainingmostofitsmassbycompetitive,chaotic to low values (e.g., Kong et al. 2015a). N D+ is known
2
Bondi-Hoyle accretion in the center of a crowded proto- to be a good tracer of low-mass starless cores that are
cluster of mostly low-mass stars. In these models, the on the verge of collapse, i.e., pre-stellar cores (Caselli &
initial conditions of massive star formation, i.e., the gas Ceccarelli 2012), as well as early stage low-mass Class 0
immediately surrounding the protostar that is destined sources (Emprechtinger et al. 2009).
tobecomeahigh-massstar, donotinvolvemassivestar- We carried out a pilot search of 4 IRDC regions
2 Tan et al.
(C1,F1,F2,G2)withALMAinCycle0(compactconfig- of 12CO(2-1) emission with moderate velocity resolu-
uration, 2.3(cid:48)(cid:48) resolution), identifying 6N D+(3-2) cores tion. Note, ambient CO molecules in the core and
2
(Tan et al. 2013, hereafter T13) by projection of their even the wider scale IRDC are expected to be largely
3σl b vspaceN D+(3-2)contours. Thetwomostmas- frozen-out onto dust grain ice mantles (Hernandez et al.
2
sive−cor−eswereinIRDCG028.37+00.07(hereafterCloud 2011). However, 12CO(2-1) emission near ambient ve-
C) C1 region: we refer to these as C1 North and South locities is still likely to be very optically thick from this
(C1-N, C1-S). We estimated masses in two ways: (1) region. In our data the 9 channels closest to the ex-
fromtheMIREXmap,findingC1-Nhas61 30M(cid:12) and pected ambient velocity of C1-S have velocities centered
C1-S has 59 30M(cid:12) with 50% systematic±uncertainty at: 74.1,75.4,76.7,78.0,79.3,80.6,81.9,83.2,84.5kms−1.
± ∼
duetodistance(5 1kpc)anddustopacity( 30%)un- The other basebands were tuned to observe N D+(3-
± ∼ 2
certainties; (2) from mm dust continuum emission, find- 2), C18O(2-1), DCN(3-2), DCO+(3-2), SiO(v=1)(5-4)
ing C1-N has 16373 M(cid:12) and C1-S has 6312279 M(cid:12), with and CH3OHvt = 05(1,4) 4(2,2). These data will be
uncertainties mostly due to the adopted dust tempera- −
presentedandanalyzedinfullinafuturepaper,whilein
ture of T = 10 3K, together with distance and dust this Letter we focus mostly on the results of the broad
±
emissivity uncertainties. continuumbandandits12CO(2-1)line,alongwithsome
TheseALMAobservationsresolvethecoreswithabout results from C18O(2-1) and DCN(3-2) that help probe
three beam diameters. C1-S appears quite round,
denser gas of protostellar cores.
centrally-concentratedandmonolithic,whileC1-Nshows
evidence of multiple fragments. Given their high level
3. RESULTS
of deuteration (Kong et al. 2016) and their dark ap-
pearance in Herschel-PACS images, even at wavelengths Figure 1a presents the MIREX Σ map (Butler et
as long as 100 µm, C1-S, and perhaps also C1-N, are al. 2014) of the C1 region, together with contours of
amongst the best known candidates of massive starless N D+(3-2) integrated intensity (T13), which define C1-
2
or early-stage cores. S and C1-N. Also shown are locations of potential pro-
However, we note Wang et al. (2006) reported a water tostars defined by 1.3 mm dust continuum peaks de-
maser detection in this area (just outside C1-S’s low- tected in the ALMA Cycle 2 image (Fig.1b), which has
est N D+(3-2) contour), though at a different velocity been cleaned with natural weighting and had a primary
2
(59.5kms−1) and in single channel (0.66kms−1wide). beam correction applied. Figure 1b also shows inte-
This water maser was not detected in the more sensi- grated intensities of (continuum subtracted) 12CO(2-1)
tive observations of Chambers et al. (2009) and Wang with red contours tracing v = 85.8to124.8kms−1,
LSR
et al. (2012). We also note that Pon et al. (2015) have i.e., redshifted velocities up to 45.4 km s−1 with re-
detected CO(8-7) and (9-8) emission towards C1-N & S specttoC1-S’scentralvelocity,andbluecontourstracing
with Herschel-HIFI ( 20(cid:48)(cid:48) resolution) and argue that from 33.8to72.8kms−1, i.e., blueshifted velocities up to
∼
this emission results from turbulence dissipating in low 45.6kms−1fromC1-S.Figure1cshowsjusthighvelocity
velocity shocks, which could be either driven by large- outflow gas that is > 20 kms−1away from C1-S’s am-
scale turbulent motions from the surrounding cloud or
bient velocity. Figure 1d shows the integrated intensity
from protostellar outflow activity. of “ambient” 12CO(2-1), i.e., from 75.4to83.2kms−1.
Herewesearchforpotentialprotostarsandoutflowac-
tivity via 12CO(2-1) and other tracers using an ALMA Figures 1e and 1f show integrated intensities of C18O(2-
1) and DCN(3-2), respectively, both potentially helpful
Cycle 2 observation. Below we describe the observations
to identify dense gas associated with protostellar cores
( 2), present our results ( 3) and discuss their implica-
§ § (e.g., Pariseetal. 2009), andthustheirradialvelocities.
tions ( 4).
§ From these images we clearly identify two protostel-
2. OBSERVATIONS lar sources that are spatially overlapped with the C1-
S core (Table 1). We refer to the more central source
We use data from our ALMA Cycle 2 project
as C1-Sa and define its spatial position as the location
(2013.1.00248.S, PI:Tan), which observed the C1 region
of the 1.3 mm continuum peak. This peak, with flux
inacompactconfigurationon05-Apr-2015,yieldingsen-
density 11 mJy/beam, is 1.31(cid:48)(cid:48) from C1-S’s center as
sitivitytoscalesfrom 10(cid:48)(cid:48)to 1(cid:48)(cid:48)). Thepositionofthe
fieldcenterwasR.A.=∼18:42:46∼.5856,Dec.=-04:04:12.361 defined by N2D+(3-2) (T13). Recall that for an esti-
mated (kinematic) source distance of 5 1kpc, 1(cid:48)(cid:48) cor-
(FK5J2000system)(l=28.3230, b=+0.06750). Itwas
responds to 5000AU, i.e., 0.024pc, wit±h 20% uncer-
chosen to be between C1-N and C1-S, slightly closer to
∼
C1-S. Thus both cores are within the 27(cid:48)(cid:48) field of view. tainties. SothespatiallocationofC1-Saisquitecloseto
center of the C1-S core, which has a radius of 3.61(cid:48)(cid:48) (i.e.,
The spectral set-up included a continuum band cen-
0.0875pc;18,000AU).
tered at 231 GHz with width 1.875 GHz, i.e., from
230.0625GHz to 231.9375GHz. The achieved sensitiv- Figures 1g, 1h and 1i show the spectra of 12CO(2-1),
ity was 0.045mJy per 1.51(cid:48)(cid:48) 0.84(cid:48)(cid:48) beam. In this con- C18O(2-1) and DCN(3-2), also in comparison with the
tinuum band, each channel ×has width 1.129 MHz, i.e., T13 observation of N D+(3-2), towards the protostars.
2
velocity resolution 1.465 kms−1. The 12CO(2-1) line We estimate the radial velocity of the C1-Sa protostar
frequency is 230.538 GHz. C1-S’s radial velocity from from the C18O(2-1) and DCN(3-2) spectra towards the
its N D+(3-2) emission is +79.40 0.01kms−1with 1D continuumpeak. TheC18O(2-1)spectrumshowsamain
2
dispersion of 0.365kms−1(i.e., FW±HM= 0.860kms−1), peak at +79.01 0.12kms−1, while DCN(3-2) shows a
so the sky frequency of 12CO(2-1) from this source is single peak at +±79.8 0.2kms−1. Thus it seems very
230.477 GHz. Thus we are sensitive to the presence likely that C1-Sa is f±orming inside the C1-S N D+(3-
2
An Ordered Bipolar Outflow from a Massive Early-Stage Core 3
(a)color:MIREX;contour:N2D+(3-2) (b)color:1.3mmcontinuum;contour:CO(2-1) (c)color:1.3mmcontinuum;contour:HVCO(2-1)
0.1pc 0.72 0.1pc 0.0075 0.1pc 0.0075
C1b 0.64 C1b
+00.0700◦ C1a C1a 0.0060 0.0060
0.56
0.0045 0.0045
Latitude+00.0680◦ C1-N C1-Sa C1-S 00..4408 C1-Sa 0.0030 0.0030
Galactic 0.32 0.0015 0.0015
+00.0660◦ C1-Sb 0.24 C1-Sb
0.0000 0.0000
0.16
+00.0640◦ 0.08 −0.0015 −0.0015
28.3260◦ 28.3240◦ 28.3220◦ 28.3200◦ 28.3260◦ 28.3240◦ 28.3220◦ 28.3200◦ 28.3260◦ 28.3240◦ 28.3220◦ 28.3200◦
GalacticLongitude GalacticLongitude GalacticLongitude
(d)color:1.3mmcontinuum;contour:CO(2-1) (e)color:1.3mmcontinuum;contour:C18O(2-1) (f)color:1.3mmcontinuum;contour:DCN(3-2)
0.1pc 0.0075 0.1pc 0.0075 0.1pc 0.0075
+00.0700◦ 0.0060 0.0060 0.0060
0.0045 0.0045 0.0045
Latitude+00.0680◦ 0.0030 0.0030 0.0030
Galactic 0.0015 0.0015 0.0015
+00.0660◦
0.0000 0.0000 0.0000
+00.0640◦ −0.0015 −0.0015 −0.0015
28.3260◦ 28.3240◦ 28.3220◦ 28.3200◦ 28.3260◦ 28.3240◦ 28.3220◦ 28.3200◦ 28.3260◦ 28.3240◦ 28.3220◦ 28.3200◦
GalacticLongitude GalacticLongitude GalacticLongitude
(g)red:12CO(2-1);blue:N2D+(3-2) (h)red:C18O(2-1);blue:N2D+(3-2) (l)red:DCN(3-2);blue:N2D+(3-2)
1.2 0.30 0.30 0.30 0.06 0.30
1.0 0.25 0.25 0.25 0.05 0.25
0.8 0.20 0.20 0.20 0.04 0.20
m) 0.6 0.15 0.15 0.15 0.03 0.15
bea
/
y
(J 0.4 0.10 0.10 0.10 0.02 0.10
S
0.2 0.05 0.05 0.05 0.01 0.05
0.0 0.00 0.00 0.00 0.00 0.00
0.2 0.05 0.05 0.05 0.01 0.05
− 70 75 80 85 90− − 70 75 80 85 90− − 70 75 80 85 90−
v(kms−1) v(kms−1) v(kms−1)
Figure 1. (a) Top Left: MIREX Σ map (in gcm−2) of C1 region, also showing N2D+(3-2) emission (black contours) observed with
ALMA(Cycle0)(T13)(ALMAbeamisgreyellipseinlowerleft;SpitzerbeamthatsetsMIREXmapresolutionisinlowerright). N2D+(3-
2) contours are shown from 2, 3, 4σ..., with 1σ 10mJybeam−1kms−1. The C1-S core is prominent at center-right, while the more
fragmented C1-N core is center-left. Protostar ca(cid:39)ndidates (“+” symbols) are based on mm-continuum peaks (panel b). (b) Top Middle:
231GHzcontinuumemission(colorscaleinJy/beam)fromALMACycle2observationwith1.2(cid:48)(cid:48) beamshowninlowerleft. Redcontours
showintegratedintensityof12CO(2-1)fromvLSR=85.8to124.8kms−1;bluecontoursshowemissionfrom33.8to72.8kms−1 . Contour
levels start from 30, 60, 90σ..., where σ = 11.6mJybeam−1kms−1. Beam at line frequency is at lower right. (c) Top Right: Same as
(b),butnowonlyshowinghighvelocity(HV)gasthatis+20kms−1orgreater(redcontours)and 20kms−1orless(bluecontours)than
vLSR ofC1-S.Thecontourlevelsareshownfrom20, 30, 60, 90σ...,whereσ=9.3mJybeam−1km−s−1. (d) Center Left: As(b),butnow
contours show “ambient” 12CO(2-1) integrated intensity over velocities 75.4to83.2kms−1, ranging from 3, 10, 20, 30, 60, 90σ..., with
1σ=5.9mJybeam−1kms−1. (e) Center: As(b),butnowcontoursshowC18O(2-1)integratedintensityovervelocities74to84kms−1,
rangingfrom3, 5, 7, 9, 11, 13, 15, 18σ,with1σ=8.5mJybeam−1kms−1. (f) Center Right: As(b),butnowcontoursshowDCN(3-2)
integratedintensityovervelocities77to81kms−1,rangingfrom3, 4, 5, 6, 7, 8, 9σ,with1σ=3.8mJybeam−1kms−1. (g) Bottom Left:
Spectra of 12CO(2-1) (red solid lines) and N2D+(3-2) (dotted blue lines) extracted over 1 beam area towards C1-Sa (top, offset up) and
C1-Sb (bottom). (h) Bottom Middle: As (g), but showing C18O(2-1) and N2D+(3-2). (i) Bottom Right: As (g), but showing DCN(3-2)
andN2D+(3-2).
2) core, which has mean velocity of +79.4km s−1 and C1-Sa’s 12CO(2-1) outflow axis, which we define to
FWHM of 0.86kms−1. the blueshifted axis, is 155◦. The outflow
The Galactic coordinate frame position angle of is highly-collimated and is(cid:39)seen to extend 12(cid:48)(cid:48)
∼
4 Tan et al.
Table 1
CoresandProtostarsinC1Region
Name l(◦) b(◦) S1.3mm(mJy) vLSR(kms−1) P.A.outflow(◦)
C1-N 28.32503 0.06724 6.94 0.72 81.18 0.03a ...
C1-S 28.32190 0.06745 26.7±0.77 79.40±0.01a ...
C1-Sa 28.322093 0.067698664 19.5± 0.1 79.01±0.12b 155
C1-Sb 28.321752 0.066847223 2.7 ±0.1 81.36±0.42c 113
C1a 28.324765 0.069543149 3.6±0.1 80±.2d 150
C1b 28.323272 0.069987301 3.5±0.1 ... 150
±
a vLSRofC1-NandC1-SestimatedfromN2D+(3-2)(T13). vLSRofprotostarsestimatedfromstrongestC18O(2-1)peak,butseealsonotesbelow
forindividualsources.
b C1-Sa: vLSRestimatedfromstrongestC18O(2-1)peak. Secondarypeaksat75.08±0.05kms−1,81.08±0.03kms−1,whileDCN(3-2)hassingle
peakat79.8±0.2kms−1.
c C1-Sb: vLSR estimatedfromstrongestC18O(2-1)peak. Secondarypeakat78.16±0.05kms−1. DCN(3-2)istooweaktomeasurevLSR.
d C1a: vLSR tentativelyestimatedfromweakN2D+(3-2)emission(T13).
(60,000 AU, 0.3 pc), and is quite symmetric, i.e., P.A. ysis of lower intensity contours (down to 3σ) indicates
of the redshifted lobe is almost 180◦ greater than that a bunching close to the higher intensity contours. This
of the blueshifted lobe. Also the observed extent of the may indicate that, unlike for C1-Sa, we are seeing the
outflow is similar in each direction, although the high- full extent of C1-Sb’s outflow.
est velocity flow is more extended on the redshifted side. In Figure 1b we identify two more candidate proto-
The outflow can be traced down to 3σ above the noise stars that are away from the C1-S and C1-N cores.
level,withoutbunchingofthecontours,soweexpectthe C1a is located in a region with faint N D+(3-2) emis-
2
observedextentissimplyduetoobservationalsensitivity sion with radial velocity of 80.6 kms−1. There is rel-
and the actual extent could be much larger. atively faint 12CO(2-1) emission, which may be driven
We re-checked our ALMA Cycle 0 data, which in- fromthissourcewithP.A. 130◦. Thereisnosignificant
cluded a requested bandpass set to an intermediate fre- C18O(2-1)emissionassocia∼tedwiththissource,andonly
quency between DCN(3-2) and SiO(v =0)(5-4). How- a weak 3σ feature in the DCN(3-2) integrated intensity
ever, this frequency was later mistakenly shifted to be map. C1b is close to C1a and has a similar P.A. of its
closer to DCN(3-2) causing the SiO line center to be un- 12CO(2-1) emission of about 130◦. There is no signifi-
observed: only the potential blue wing up to vLSR = cant C18O(2-1) or N D+(3-2) emission at C1b, and only
+69 km s−1 was observed. For this reason, T13 did 2
a very weak feature in DCN(3-2). Note, the protostel-
not report detection of any SiO emission towards C1-
lar nature of C1a and C1b is uncertain, especially since
S. However, now we do see indications of the blue wing someoftheobserved12CO(2-1)featuresmaybeaffected
of SiO(v =0)(5-4) overlapping with the central part of
by side-lobe contamination from C1-Sa and C1-Sb.
the blue lobe of the 12CO(2-1) outflow and extending
Figure 2 shows nine channel maps of “ambient”
to vLSR +50kms−1. We conclude it is likely that the 12CO(2-1) emission from the C1 region, with high and
outflowf(cid:39)romC1-SaalsoemitsstronglyinSiO(v =0)(5-4) low velocity ends connecting with the “outflow” veloc-
across its full velocity range. ities plotted in Fig. 1b. The C1-Sa outflow lobes are
The second source, C1-Sb, has a much weaker 1.3mm visible in the low and high velocity channels. Fig. 2 also
continuum flux of 1.3 mJy/beam and is located 2.0(cid:48)(cid:48) suggests the C1-Sb outflow has a driving source with a
from the center of the C1-S N2D+(3-2) core and 3.3(cid:48)(cid:48) vLSR +81kms−1, since the blueshifted lobe is already
from C1-Sa. The C18O(2-1) spectrum towards C1-Sb appar(cid:39)entinthe79.3kms−1 channel,whiletheredshifted
shows a main peak at +81.36 0.42kms−1and a sec- lobe appears to vanish by the 81.9km s−1 channel.
ondary peak (with about half t±he equivalent width) at ThereareseveralotherstrikingfeaturesseeninFig.2.
+78.16 0.45kms−1. The DCN(3-2) spectrum shows First, there is a very elongated “filament” that peaks
no part±icularly strong features, although a 3σ peak is in the 76.7 and 78.0kms−1channels, but is visible from
seen in the integrated intensity map (Fig. 1f). We ten- 74.1to79.3kms−1. ThefilamentoverlapswiththeC1-Sa,
tatively assign C1-Sb’s radial velocity to be that of the C1-Sb and C1b protostars and its orientation is almost
main C18O(2-1) spectral feature. We discuss below that perpendicular to their outflows. The interpretation of
this assignment is potentially supported by examination this filament as an ambient gas feature, rather than as a
of the channel maps of the 12CO(2-1) “ambient” gas. collimated bipolar outflow, is discussed below consider-
If this radial velocity is correct, then it would suggest ing its position-velocity diagram. Second, there is a rel-
that C1-Sb is not physically associated with the C1-S atively weak, but still highly significant, quasi-spherical
N D+(3-2) core, and in fact may be part of a gas struc- “core” of gas seen in the 80.6 and 81.9kms−1channels.
2
turethatislinkedtotheC1-Ncore. However,wecannot Third, there is 12CO(2-1) emission in the vicinity of the
exclude the possibility that C1-Sb is also forming from C1-NN D+(3-2)core. Fourth,thereareadditionalemis-
2
the C1-S core. sion features on the periphery of the image.
The outflow from C1-Sb has a similar extent as that Figure 3 shows position-velocity diagrams of 12CO(2-
from C1-Sa and appears to have a wider opening an- 1) emission along the outflow axes of C1-Sa and C1-Sb
gle. It has a P.A.=113◦, and on its blueshifted side the and along the axis of the “ambient filament.” These are
outflow spatially overlaps with that from C1-Sa. Anal- defined by rectangular regions 3(cid:48)(cid:48) wide running length-
An Ordered Bipolar Outflow from a Massive Early-Stage Core 5
74.1km/s 0.1pc 75.4km/s 76.7km/s
+00.0700◦
Latitude+00.0680◦
Galactic
+00.0660◦
+00.0640◦
78.0km/s 79.3km/s 80.6km/s
+00.0700◦
Latitude+00.0680◦
Galactic
+00.0660◦
+00.0640◦
81.9km/s 83.2km/s 84.5km/s
+00.0700◦
Latitude+00.0680◦
Galactic
+00.0660◦
+00.0640◦
28.3260◦ 28.3240◦ 28.3220◦ 28.3200◦ 28.3260◦ 28.3240◦ 28.3220◦ 28.3200◦ 28.3260◦ 28.3240◦ 28.3220◦ 28.3200◦
GalacticLongitude GalacticLongitude GalacticLongitude
Figure 2. Channelmapsof12CO(2-1)emission,withcontoursstartingfrom3,5,7,10,20,30,60,90σ...,whereσ=2.1mJybeam−1kms−1.
Backgroundimageshows231GHzcontinuum(Fig.1b).
wise along the P.A. of each outflow or the filament. Sb, integrating from 45 < (v /kms−1) < 110 the
LSR
Theambientnatureofthefilamentisreadilyapparent blue/red lobes have masses 0.73/0.38M and momenta
(cid:12)
inthesefigures. Ithasaverynarrowvelocitydispersion, 8.5/3.5M kms−1, respectively. Note, the estimates for
(cid:12)
which is comparable to other ambient gas tracers, like each blueshifted lobe are affected by the overlap of the
C18O(2-1) and N2D+(3-2), and does not show a signifi- sources, leading to modest overestimation of their prop-
cantgradientinradialvelocity. Thelackofsuchagradi- erties, especially relative to the redshifted lobes. How-
ent could be explained by an outflow that was precisely ever,ingeneraltheabsolutevaluesoftheaboveestimates
aligned in the plane of the sky, but this would still be shouldbeviewedaslowerlimits,notonlybecauseofthe
expected to have a relatively broad velocity dispersion, choice of T = 17 K, but also because of inclination
ex
which the filament feature does not exhibit. effects (which boost momentum estimates by 1/cos(i),
Figure 4 shows 12CO(2-1) spectra and derived mass where i is the inclination of the outflow axis to the line
and momentum distributions of the C1-Sa and C1-Sb of sight, with random expectation value of i=60◦), and
outflows,extractedfromthesameregionsusedforFig.3. becauseofopticaldeptheffects(bothwithintheoutflow-
To derive the mass, one must assume an excitation tem- ing gas, which may boost momentum by factors of 6
perature, with values of Tex 10—50K typically being (Zhang et al. 2016), and due to foreground absorptio∼n).
used. Tex = 17K minimize(cid:39)s the mass estimate, while For C1-Sa, the mass-weighted mean velocities (vw =
50K increases this by a factor of 1.5. p /m ) of the blue/red lobes are v = 7.3/21kms−1,
w w w
For C1-Sa, integrating from 50 < (vLSR/kms−1) < while for C1-Sb they are 12/9.2kms−1. Assuming the
140 and assuming Tex = 17 K, the blue/red lobes length of all the outflows lobes are 12(cid:48)(cid:48) (60,000AU),
have masses m = 0.50/0.32 M and momenta p = (cid:39)
w (cid:12) w the dynamical times for the blue/red lobes of C1-Sa are
3.6/6.6 M(cid:12) kms−1, respectively. Similarly, for C1- tw =(3.9/1.3) 104yrandforC1-Sbare(2.4/3.1) 104yr.
× ×
6 Tan et al.
115
110
C1-Sa
105
100
95
)
1− 90 0.45
s 85
m 80
k 75
(
R 70 0.40
S 65
L
v 60
55
50
0.35
45
115
110
C1-Sb
105
100 0.30
95
)
1 90
−
s 85 m
m 80 0.25 a
(kR 7705 Jy/be
S 65
L
v 60 0.20
55
50
45
115 0.15
110
filament
105
100
) 95 0.10
1 90
−
s 85
m 80
k 75
( 0.05
R 70
S 65
L
v 60
55
50
45
40
-10” -5” 0” 5” 10”
positionaloffset
Figure 3. Position-velocity diagram of 12CO(2-1) emission along the axis of the C1-Sa outflow (top), C1-Sb outflow (middle) and the
ambient“filament”(bottom). Horizontallinesareincludedforreferenceat79.0kms−1forC1-Sa/filamentandat81.4kms−1forC1-Sb.
The correction factor for inclination is cos(i)/sin(i), i.e., the mass that has been swept-up by the primary out-
0.58 for i = 60◦. The mass outflow rates for the C1- flow). Models of massive protostar formation (Zhang
Sa blue/red lobes are (1.3/2.5) 10−5 M yr−1, and et al. 2014) based on the Turbulent Core Model
(cid:12)
for C1-Sb are (3.0/1.2) 10−5×M(cid:12) yr−1. The cor- (MT03) for cores of 60 M(cid:12) in a clump environment
rection factor for inclinat×ion is sin(i)/cos(i), i.e., 1.73 with Σ 0.4gcm−2 (relevant for C1-S) predict p˙ (cid:46)
cl w
for i = 60◦. Finally, the momentum injection rates 6 10−3M(cid:39) kms−1yr−1, when the protostellar mass is
(cid:12)
f1o0r−4thMe(cid:12)Ck1m-Ssa−1bylure−/1readndlofboresthaereC1p˙-wSb=blu(e0/.r9e/d5.l0o)be×s mm×∗ (cid:46)31M0M(cid:12),r.isiIntgitsoin∼te1r0e−st2iMng(cid:12)tkhmats−th1eyser−e1stbiymtahteestiamree
acorerre(c3t.5io/n1.f1a)ct×or1i0s−s4inM(i(cid:12))/ckoms2si−,1i.ey.r,−31.4.6Tfohreii=nc6li0n◦a.tAioln- acon∗md(cid:39)pCa1r-aSbbl.e(cid:12)Twhitihsstuhgegeosbtssetrhvaetd,ivfaClu1e-sSaofisp˙awmfraosmsivCe1p-rSoa-
lowingforamassunderestimationfactorof3andassum- tostarintheprocessofformation,thatitiscurrentlyata
ingi=60◦,theoverallestimatesofthetotalmomentum very early stage, i.e., has yet to accrete most of its mass.
fluxes are boosted by a factor of 10, i.e., totals for C1-Sa Thiswouldbebroadlyconsistentwiththeprotostarhav-
of p˙ 5.9 10−3 M kms−1 yr−1 and for C1-Sb of ing a relatively low luminosity such that it does not ap-
w (cid:12)
4.6 ∼10−3×M kms−1yr−1. pear yet as a MIR source. High angular resolution, high
(cid:12)
∼ × sensitivity MIR to FIR observations, e.g., with JWST,
are needed to measure the SED of the protostar, which
4. DISCUSSION
canthenalsoconstrainprotostellarmodels. Weconclude
Outflow momentum flux is expected to be the most thatwehavedetectedprotostarsofrelativelylowcurrent
reliable direct tracer of protostellar properties, since it masses. C1-Sa appears to be embedded within the C1-S
should be independent of the effects of ambient envi- massive, cold core, as defined by N D+(3-2) emission. It
2
ronment (unlike mass flux, which depends mostly on
An Ordered Bipolar Outflow from a Massive Early-Stage Core 7
pFriogtuorstear4s.an(da)alTigonpedroawlo:n1g2CthOe(o2u-1t)floswpeacxtreas.oTfChe1-eSsatim(leaftte)daanmdbCie1n-tSbve(lroicgihtite)s, eoafcthheexptrroatcotsetdarfsroamreash2o4w(cid:48)(cid:48)n×w3i(cid:48)t(cid:48)hadpoetrtteudrelicneenst.e(rbe)dSoencotnhde
row: Distributionofoutflowmass(seetext). (c) Third row: Distributionofoutflowmomentum(seetext). (d) Bottom row: Comparison
of mass distributions of blueshifted and redshifted outflows versus outflow velocity, voutflow, i.e., relative to the ambient velocity of each
protostar.
thus has a large mass reservoir from which to continue ration of protostellar activity. Given the symmetric and
to grow: we speculate it is destined to become a massive linear morphology of the outflow lobes, it appears that
star. C1-Sa (and C1-Sb) have not suffered significant dynam-
As traced by 12CO(2-1), C1-Sa’s bipolar outflow is ical disturbance from other nearby (proto)stars during
highly collimated and has velocities extending to the period they have been driving these outflows. This
50 kms−1. Similar (blueshifted) velocities are seen i∼n is consistent with assumptions of Core Accretion models
SiO(v=0)(5-4) emission. Using mass-weighted mean ve- and is a constraint on Competitive Accretion models.
locities, which are 10kms−1, the i = 60◦ inclination- For constant instantaneous star formation effi-
correctedoutflowti∼mescaleis 2 104yr. However,since ciency from the core, (cid:15)c, the fiducial Turbulent
∼ × Core Model predicts m = (cid:15) M (t/t )2, where
C1-Sa’s outflow is likely to extend to larger distances ∗ c c ∗f
the total star formation time is t 1.29
thanweobserve,thisisprobablyalowerlimitonthedu- ∗f
→ ×
105(M /60 M )1/4(Σ /1 gcm−2)−3/4 yr. So for the
c (cid:12) cl
8 Tan et al.
M =60M andΣ =0.4gcm−2case,thent>2 104yr AUI/NRAO and NAOJ.
c (cid:12) cl
implies m > 0.36M (assuming (cid:15) 1, expecte×d dur-
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