Large Scale Flows from Orion-South

0.8 MB·English

by  W. J. Henney

Draftversion February5,2008
PreprinttypesetusingLATEXstyleemulateapjv.10/09/06
LARGE SCALE FLOWS FROM ORION-SOUTH1,2,3
W. J. Henney,4 C. R. O’Dell,5 Luis A. Zapata,4 Ma. T. Garc´ıa-D´ıaz,4,6 Luis F. Rodr´ıguez,4
and Massimo Robberto7
Draft versionFebruary 5, 2008
ABSTRACT
Multiple optical outflows are known to exist in the vicinity of the active star formation region
calledOrion-South(Orion-S).We havemappedthe velocityoflowionizationfeaturesinthe brightest
part of the Orion Nebula, including Orion-S, and imaged the entire nebula with the Hubble Space
Telescope. These new data, combined with recent high resolution radio maps of outflows from the
7
Orion-Sregion,allow us to trace the originofthe opticaloutflows. It is confirmedthatHH 625arises
0
from the blueshifted lobe of the CO outflow from 136–359 in Orion-S while it is likely that HH 507
0
2 arises from the blueshifted lobe of the SiO outflow from the nearby source 135–356. It is likely that
redshifted lobes are deflected within the photon dominated region behind the optical nebula. This
n
leadstoapossibleidentificationofanewlargeshocktothesouthwestfromOrion-Sasbeingdrivenby
a
the redshifted CO outflow arising from 137–408. The distant object HH 400 is seen to have two even
J
further components and these all are probably linked to either HH 203, HH 204, or HH 528. Distant
2
shocks on the west side of the nebula may be related to HH 269. The sources of multiple bright
2
blueshifted Herbig-Haroobjects (HH 202,HH 203,HH 204,HH 269,HH 528)remain unidentified, in

spite ofearlierclaimed identifications. Some of this lackof identificationmay arise fromthe fact that
1
deflection in radial velocity can also produce a change in direction in the plane of the sky. The best
v
4 way to resolve this open question is through improved tangential velocities of low ionization features
1 arising where the outflows first break out into the ionized nebula.
6 Subject headings: H II regions—ISM: jets and outflows—ISM: Herbig-Haro objects—ISM: individual
1 (Orion Nebula, HH 528, Orion-S, OMC-1S, Orion South, M42)—stars: pre-main
0
sequence
7
0
h/ 1. INTRODUCTION x-ray, and radio observations to tell what is happening
p As the nearest region of star formation that includes among the optically obscured cluster stars lying beyond
- young massive stars, the Orion Nebula and its epony- the H II region, which constitute roughly half of the to-
o tal cluster membership (Hillenbrand 1997). In the case
mous cluster attract considerable attention from stu-
r
of the highly embedded (about 0.2 pc behind the neb-
t dentsofstarformation. Theclusteris displacedtowards
s ula) BN-KL region, one only sees a few optical features
a the observer from the remainder of the host molecular
resultingfromstellaroutflowatthetipsoftheAllenand
: star and the visible nebula is a relatively thin, irregu-
v Burton fingers (1993). However, in the region known as
lar, concave layer of ionized gas on the observer’s side
i Orion-South (Orion-S, also known as Orion Molecular
X of the molecular cloud. Numerous optical shocks and
Cloud 1 South or OMC-1S), lying 1′ to the southwest
jets (O’Dell 2001) reveal the presence of collimated and
r from the dominant ionizing star θ1Ori C, the embed-
a broadoutflows fromthose stars that lie in the photoion-
ded sources lie near the surface of the nebula and we
izedportionofthisregion;butonemustrelyoninfrared,
see numerous Herbig-Haro (HH) objects there. This is
Electronicaddress: [email protected] the third region of star formation in the vicinity of the
1Based on observations obtained at the Observatorio As- Orion nebula and is in a local bump in the surface of
trono´mico Nacional, San Pedro Ma´rtir, Baja California, Mex- the nebula (Wen & O’Dell 1995), where the expanding
ico, which is operated by the Universidad Nacional Auto´noma de
HIIregionhasbeenslowedbecauseofthehigherdensity
M´exico.
2BasedonobservationsobtainedattheKittPeakNationalOb- of gas there. There have been numerous recent papers
servatory, whichisoperated bytheAssociationofUniversitiesfor that try to relate the moving optical features to the ob-
ResearchinAstronomy,Inc.,underaCooperativeAgreementwith scuredsourcesofthe outflows,but wereassessthe situa-
theNationalScienceFoundation.
3Based on observations with the NASA/ESA Hubble Space tionherebecauseoftherecentavailability(Zapata et al.
Telescope,obtainedattheSpaceTelescopeScienceInstitute,which 2005, 2006) of high spatial resolution maps of CO and
is operated by the Association of Universities for Research in As- SiO outflows from Orion-S. We present new results ob-
tro4nComenyt,rIoncd.e,uRndaderioNasAtrSoAnoCmo´ınatryactANstor.ofN´ısAicSa,5-U26n5iv5e5r.sidad Na- tained spectroscopically and with imaging in § 2, sum-
marize what we know about the optical features in § 3,
cionalAuto´nomadeM´exico,ApartadoPostal3-72,58090Morelia,
Michaoaca´n, M´exico presenta combinedpicture ofthe opticalfeaturesin § 4,
5DepartmentofPhysicsandAstronomy,VanderbiltUniversity, and discuss their relation to the CO and SiO outflows
Box1807-B,Nashville,TN37235
6Instituto de Astronom´ıa, Universidad Nacional Auto´noma de in § 5. Throughout this paper we will adopt a distance
M´exico, Apartado Postal 877, 22800 Ensenada, Baja California, of 460 pc, after Bally, O’Dell, & McCaughrean (2000),
M´exico henceforth BOM.
7SpaceTelescopeScienceInstitute,3700SanMartinDrive,Bal-
timore,MD21218
2 Henney et al.
a b subtracting18.1km s−1. Allpositionsinthissectionare
given in arcseconds, (x, y), with respect to θ1Ori C, the
100
brightestoftheTrapeziumstarsandtheprincipalsource
of ionizing photons in the nebula. Some artifacts are
50 present in the data, principally due to variations in sky
arcsec)arcsec) 0 binritghhetnimesas,gewsh.icThhemsaenairfeesmt tohsetmnsoetlivceesabalsevwerhteircealtshterispiegs-
((
offsetoffset nemalisissioinntr(isnhsoicwanllyaswreeadk,insuFchig.as1ain) athnedbalrueesfhuirfttheedr[dOisI-]
DecDec −50 cussed in GH07, Section 2.
Thedifferenceintheemissiondistributionbetweenthe
−100 three lines is due primarily to changes in ionization: the
[SIII] line is emitted only by fully ionized gas, whereas
−150 V⊙=−02kms−1 V⊙=+10kms−1 the [OI] line comes from a thin layer of partially ionized
gasat the ionizationfrontor fromshocks in neutralgas.
c d
The [SII] line comes from both the ionization front (IF)
100 and from the fully ionized gas that is close to it. In
addition, collisional deexcitation causes the [SII] line to
50 saturateinthehighestdensityregions. Sincetheelectron
arcsec)arcsec) 0 dceenntseitryofshtohwesnaebguelan,ertahledoeuctlienrepwaritths odfistthaencmeafprohmavtehae
ffset(ffset( gwrheielne tthinegien,ninerdipcaarttivsevoafryreflraotmiveplyinsktrtoongbl[uSeI,I]deempeinssdioinng,
oo
DecDec −50 onwhetherlow-orhigh-ionizationemissionisdominant.
The emission in the most blueshifted channel that we
−100 show, centered on V⊙ = −2 km s−1, is dominated by a
broad band of high-ionization gas known as the Big Arc
(O’Dell et al.1997a),whichcrossesthesouthoftheneb-
−150 V⊙=+22kms−1 V⊙=+34kms−1 ula from east to west. One also sees emission from the
low-velocity wings of the highly blue-shifted HH objects
−100 −50 0 50 −100 −50 0 50
(O’Dell et al. 1997b): HH 203/204around (−90, −100);
RRAAooffffsseett((aarrccsseecc)) RRAAooffffsseett((aarrccsseecc))
HH 202 around (70, 30); and the low-ionization HH 201
Fig. 1.— Multiline isovelocity maps of the Orion Nebula in at (75, 90). As one passes to more redshifted channels,
whichtheemissionin[OI],[SII],and[SIII]isshowninred,green,
andblue,respectively. Eachpanel showsemissionina12kms−1 these features fade away to be replaced by the systemic
widechannelcenteredontheheliocentricvelocityindicatedinthe nebular emission, which in low-ionization lines is domi-
lower-leftcorners. Theintensityscalingsvarybetweenthedifferent nated by linear bar-like features (O’Dell & Yusef-Zadeh
channels and different lines. Position offsets are measured with 2000), of which the Bright Bar (in the lower-left of the
respecttoθ1OriC.
images)ismerelythemostprominentexample(seeGH07
2. OBSERVATIONS for a more detailed discussion). In this paper we discuss
only the data around HH 528 out of the rich body of in-
InthissectionwepresentnewobservationsoftheOrion
formation of this data-set because this is the lowest ion-
Nebula. Thefirstresultsarefromaprogramofmapping
ization object among the many HH objects in the Orion
the radialvelocity acrossthe Huygens regionofthe neb-
Nebula.
ula, the second are results from imaging an even wider
region with the Hubble Space Telescope. 2.1.1. Radial Velocity Measurements of HH 528’s Jet
HH 528 is a long, collimated outflow along a position
2.1. HH 528
angle ≃ 150◦, which originates around 30′′ south of the
We have constructed isovelocity channel maps of the Trapeziumasabroadjetandendsinadiffusebowshock
coreoftheOrionNebula,basedonechellelongslitobser- where it interacts with the Bright Bar.
vations in the optical emission lines of [SII]6716,6731˚A, The HH 528 jet can be best seen in our channel map
[OI]6300˚A, and [SIII]6312˚A. Full details of the ob- centered on V⊙ = 10 km s−1 (Figure 1) as an elongated
servations and data reduction process are given in (20′′×7′′) pink-orange region, centered on (0, −72). It
Garc´ıa-D´ıaz& Henney (2006, henceforth GH07) . The can also be seen at more blueshifted velocities, where it
data were obtained primarily with the Manchester is superimposed on the higher ionization Big Arc South,
EchelleSpectrometer(Meaburn et al.2003)onthe2.1m andmore redshifted velocities,where it is seento be cut
telescope of the Observatorio Astron´omico Nacional at in two by a dark extinction feature.
San Pedro Martir, B.C., Mexico, while part of the [SII] In [OI], the jet appears to have two components: a
datasetwasobtainedwiththe4mtelescopeatKittPeak spatiallybroad,smoothcomponent,whichisalsoseenin
National Observatory (Doi, O’Dell, & Hartigan 2004, [SII],plusaseriesofcompactknotsalongitseasternside
henceforth DOH04) . Figure 1 shows images of selected at (−2, −67), (−4, −71), and (−3, −75). These knots
channelmaps,with[OI]6300˚Ashowninred,[SII]6731˚A are more blueshifted than the smooth component, being
shown in green, and [SIII]6312˚A shown in blue. All ve- most visible in the +6 km s−1 channel. Further south,
locitiesinthissectionaregivenintheheliocentricframe, we can identify two more knots of blueshifted emission
andcanbetransformedtotheLocalStandardofRestby in both [SII] and [OI] at (−18, −92) and (−14, −89),
Large Scale Flows from Orion-South 3
NorthBG −−33 3000
mm
1.25 SouthBG cc 2000
BG-subtractedjet y,y,
1 Gaussianfit sitsit 1000
y nn
nsit 0.75 DeDe 0
e
nt
I 0.5
Line 15 HH528peak
0.25 HH528wing
BrightBar
0
yy 10
0 10 20 30 40 50 tt
sisi
HeliocentricVelocity,kms−1 nn
ee
tt
Fig. 2.—Background-subtractedprofileoftheHH528jetinthe inin
[OI] line (black symbols with error bars), together with adjacent ee
nn
nebular background profiles (gray symbols). The continuous line LiLi
shows a Gaussian fit to the jet profile. The error bars in the jet 5
profile are a combination of the observational noise with the un-
certainty in the estimated nebular background at the jet position
(seetext).
whichshowthe highestcontrastagainstthe surrounding
nebula in the +14 km s−1 channel. No [SIII] emission is 0
seen from the jet.
The visibility of the jet in a given channel is strongly −10 0 10 20 30 40 50
affected by the brightness and velocity of the surround-
ing nebular emission and so is not a reliable guide to HHeelliioocceennttrriicc vveelloocciittyy,, kkmm ss−−11
the jet’s radial velocity. Therefore, we have extracted
Fig. 3.—[SII]lineprofilesoftheHH528bowshockfroma70µm
one dimensional [OI] spectra from 5′′-long samples of slit(instrumentalwidth: 6kms−1). Thetoppanelshowselectron
the slit, which cover the jet and two adjoining back- densitiescalculatedfromthedoubletratio,whilethebottompanel
ground regions. We have fitted a Gaussian profile to showstheintensityofthelongercomponent.
thebackground-subtractedjetprofile,assumingthatthe
nebular emission in the jet sample can be linearly inter- straight line to the southwest. There is also blueshifted
polated from the two background samples (see Fig. 2). emission, strongest in [OI], extending about 40′′ south-
Althoughthepeakvelocityandshapeofthebackground west along the Bar, which seems to be a wing of the
nebular line is relatively stable in the vicinity of the jet, bowshock. Weaker blueshifted emission also extends a
its brightness shows substantial variation along the slit, similar distance to the east and north east, which may
and this is the primary contribution to the uncertainty represent the opposite wing of the bowshock.
inthejetprofileonitsredwardside(wehaveusedacon- Figure3showsprofilesofthe[SII]6731˚Alinefromtwo
servative estimate of one half of the difference between positions in the bowshock and for an adjoining undis-
the two background samples). The derived jet velocity turbed region of the Bright Bar at (−65, −90). The
from the Gaussian fit is V⊙([OI])=+15.9±1.8 km s−1, bulk of the bowshock emission is blueshifted with re-
where the uncertainty is given by the formal standard spect to the systemic velocity, peaking at V⊙ = +16 to
error in the fitting parameters. +18 km s−1, as opposed to +24 km s−1 for the undis-
We followed a similar procedure for [SII] but this turbedbar. Notethatitisimpossibletoreliablysubtract
was complicated by the presence of blueshifted emis- thebackgroundnebularemissionfromthebowshockpro-
sion from the Big Arc at the same position as the jet. file,aswasdoneforthejetprofileabove. Thisisbecause
Nonetheless, we determine a jet velocity of V⊙([SII]) = the nebular emission shows extreme brightness fluctu-
+16±3km s−1,whichisconsistentwiththemoreprecise ations that preclude the possibility of interpolating its
[OI] value. The electron density in the jet is determined value from adjacent regions. In particular, the emission
tobe1900±500cm−3,whichisverysimilartothevalue from the Bright Bar is significantly depressed at the po-
in the surrounding nebula. sitionofthebowshock,ascanbeseenfromFigure3. On
the other hand, the bowshock component is so strong
2.1.2. Radial Velocity Measurements of HH 528’s Bowshock that its velocity can be reliably estimated even without
The terminal bowshock of HH 528 is also visible as a backgroundsubtraction.
blue-shifted feature in our maps, showing the greatest In addition to the blueshifted peak, the bowshock
contrastin the same channels as for the jet. Although it profiles also show weak red wings, extending out to
is strongest in the low-ionization lines, it is also present +50 km s−1, which are lacking in the Bar profile. The
in [SIII]. The brightest part of the bowshock is a diffuse weaklow density componentaround0 km s−1 is present
clump, of roughly 10′′ in diameter, centered on (−25, in all the profiles and is an unrelated general feature of
−105). It is displaced about 10′′ towards the Trapezium thispartofthenebula(GH07). Thesurfacebrightnessof
from where one would expect to find the Bright Bar, the bowshock emission is very similar to that of the rest
assuming that the northeastern portion continued in a ofthe bar,asis the electrondensity (upper panelofFig-
4 Henney et al.
ure 3) at 2500 to 3000 cm−3. The bowshock also shows withOrion-Sandinthenextsectioninvestigatewhether
the same ionization stratification as the bar, with the there are common sources for them.
emission from more highly ionized lines becoming pro- For each object we will identify the discovery paper
gressivelymore diffuse and shifted towards the direction (when possible, sometimes there were multiple steps in
of the Trapezium. On the other hand, the [OI] emission recognition of the nature of the object), the values of
is not as thin as in the Bar proper. the most accurate tangential and radial velocities, de-
Roughly15′′tothesouthofthebowshockliesacurious rived velocity vectors, and any major papers that dis-
zoneoflow-ionization,low-brightness,scallopedemission cuss the object. Since we are interested in the motions
featureswhicharemostvisibleinthe velocityrange+25 relativeto the hostregion,we convertheliocentricradial
to +40 km s−1. Electron density channel maps (GH07) velocities to velocities relative to Orion (VOMC) by as-
show a narrow ridge of enhanced density that is contin- suming the velocity of Orion Molecular Cloud to be 28
uous between these features and the eastern portion of km s−1(O’Dell 2001). When motions in the plane of the
the Bright Bar. sky (tangential motions, V ) are available, these can be
T
combined with the V values to give spatial motions
2.2. An HST Survey of the full Orion Nebula OMC
(V ) and in all cases we will report the angle (θ) of that
S
The new Hubble Space Telescope (HST) images used velocityvectorwith respectto the plane ofthe sky(pos-
inthisstudywereobtainedaspartofprogramGO10246, itive values are towards the observer) and the direction
with Massimo Robberto serving as the Principal Inves- by the Position Angle (PA) measured counter clockwise
tigator. This program imaged the Huygens region of with respect to north. It is worth noting that referring
the Orion Nebula and its periphery using 104 pointings. the angle of the velocity vector to the plane of the sky
The Advanced Camera for Surveys (ACS) was the pri- is in contrastwith earlier work (DOH04), where the ori-
mary instrument and the pointings were chosen so as entation was given with respect to the line of sight. The
to provide a continuous mosaic across the nebula. Par- objectswillbesummarizedinorderoftheirPAasviewed
allel observations were made with the Wide Field and from Orion-S.
PlanetaryCamera(WFPC2),andtheNICMOSinfrared The forms and locations of the objects discussed are
instrument, althoughthose data arenotused inthe cur- presented in Figures 5 and 6. The richness of fea-
rentstudy. TheprimaryscientificthrustofprogramGO tures in the Orion Nebula means that drawings like
10246 is to study the properties of the Orion Nebula this are the best method for isolating objects within a
Clusterstarsandthisdrovetheselectionofthefiltersem- given class. Figure 5 shows a 450′′ square field near
ployed; however, a complete mosaic was made with the the Trapezium stars (group of four circles). Numbers
F658N filter (characteristic exposure time 340 s), which indicate the HH object number. The red arrows and
is equally sensitive to both hydrogen Hα (6563 ˚A) and open square indicate the HH objects associated with
[NII](6583˚A)emission. Theother filtersemployedand deeply embedded BN-KL region. The H2 symbols indi-
cate the position of compact H objects in the survey of
their characteristic exposure times were F435W (420 s), 2
Stanke, McCaughrean, & Zinnecker (2002). The dashed
F555W(385s),F775W(385s),andF850LP(385s). The
yellow line traces the path of the HH 625 components
observations were made in two observing campaigns, in
and the dashed black line traces the faint outer features
October, 2004 and April, 2005. The wealth of images
beyondHH 203-HH204-HH528. The open ellipse is the
were combined and rendered into a seamless mosaic.
position of the Optical Outflow Source (OOS) identified
TheresultingpicturefromthissurveyisshowninFig-
by O’Dell & Doi (2003, henceforth OD03). Figure 6
ure 4, which is the combined image from all the filters,
depicts a 1650′′×1825′′ field around the Orion Nebula.
including those dominated by continuum, rather than
Theirregularouterboundaryshowstheedgesofthecov-
emissionlines. Theoutlineofthefieldcoveredbythesur-
eragewith the HST ACSsurvey andthe dashedbox the
veyisshowninFigure6andtheouterpartsofthisimage
field covered in Figure 5. A few major features within
havebeenfilled-inbyimagesmadebyMassimoRobberto
thenebulaarelabeledandthesymbolsemployedarethe
with the ESO La Silla 2.2 meter telescope. The color
same as in Figure 5. Also shown are outer shock fea-
coding is red (F850LP+F775W,dominated by scattered
tures that are newly discovered in the ACS survey and
starlightwithsome[SIII]emission),red/orange(F658N,
which are discussed in more detail in Section 5.4 below.
dominatedbyHα+[N II]), green(F555W,dominatedby
Inthiscasethe featuresoutsideHH203-HH204-HH528
[OIII]andscatteredstarlight),andblue(F435W,domi-
are drawn as solid blue lines for clarity.
nated about equally by hydrogenBalmer lines and scat-
tered starlight). 3.1. HH 529
3. PROPERTIESOFTHEHHOBJECTSASSOCIATED The high ionization shock features now called HH 529
WITHTHEORION-SREGION were visible in the first HST images (O’Dell & Wong
There are two regions of large scale outflows in the 1996), their similar and high velocities were noted in a
Orion Nebula: one centered about 55′′ to the southwest lowvelocityresolutionstudybyO’Delletal. (1997),and
from the brightest Trapezium star (θ1Ori C) and the they were designated as a single system by BOM. The
other centered on the BN-KL sources to the northwest. shocksareeasilyvisiblein[OIII]andHα,butarefaintin
The two regions are clearly independent of one another [NII]. They become broader and larger in the eastward
and in this paper we’ll address only the outflows asso- directionofapparentpropagation. Thefactthattheyare
ciated with the southwest Orion-S region. As we shall oflowerionizationtowardsthewestisdiscussedindetail
see, it is likely that there are multiple sources in this by Blagrave,Martin, & Baldwin (2006), who also note
region. In this section we will summarize the character- thatthereareerrorsinthe[OI]datainBOM’sFigure6.
isticsoftheopticaloutflowsthatappeartobeassociated Theemissioninthefiltermeanttoisolatethe[OI]lineat
Large Scale Flows from Orion-South 5
200"
Fig. 4.—Thecoreof this30′×30′ imageof theOrionNebulawas preparedfromHST ACSimages. Theirregularoutlineshows most
of thefield covered bythe ACSsurveyindicated inFigure6. Outsidethe boundaries of thissurvey, groundbased images wereused. The
colorcodingisdescribedinthetext.
6300˚Aismostlikelydominatedbythe[SIII]6312˚Aline multiple components of this HH object, we will desig-
and the spectrum given for [OI] is an accidental repro- nate eachaccordingto the position-basedsystemfor the
duction of the [OIII] spectrum. The interpretation that Orion Nebula introduced by O’Dell & Wen (1994). We
these are shocks located within the ionized layer of the willadopttheradialvelocitiesfromDOH04andthetan-
Orion Nebula (O’Dell et al. 1997a) is strengthened from gentialvelocitiesofOD03astheyhavealongertime-base
the study of their spectra (Blagrave,Martin, & Baldwin thanDoi, O’Dell, & Hartigan(2002,henceforthDOH02)
2006). Componentsofthissystemwereoriginallyidenti- and BOM. The heliocentric velocities of the features
fied by their high radial velocities (Lee 1969; Castan˜eda near150–352,158–353,and165–358are−44±4km s−1,
1988; Massey & Meaburn 1995) and BOM measured −35±9km s−1,and−26±2km s−1 respectively,which
someofthecomponentswiththeKeckHIRESwithgood yields values of V = −72, −63, and −54 km s−1.
OMC
spatial and velocity resolution. DOH04 mapped the en- The V values of these features are 88 ± 20 km s−1,
T
tire object in Hα, [OIII], and [NII] in their slit study of 46±16 km s−1, and101±16 km s−1 towardsPAvalues
the Huygens regionof the OrionNebula. Because of the
6 Henney et al.
of98◦±8◦,110◦±23◦,and96◦±26◦. Theresultantval-
ues of V are 114 km s−1, 78 km s−1, and 115 km s−1,
100" S
with θ = 39◦, 54◦, and 29◦. Since the errors in the ve-
locities that are used to derive θ are significant and the
201,205-7
209-10 calculatedanglesarecorrespondinglyuncertain,itisnot
601-4 clearifthesethreefeaturesaremovingatdifferentangles
or along a common average angle of about 41◦. In the
discussion in § 4, we shall assume the latter.
3.2. HH 203
.
HH 203 was first recorded by Mu¨nch & Wilson (1962)
2 andhasbeenthesubjectofnumeroussubsequentstudies
0
2 of its appearance in different ions (O’Dell et al. 1997b),
itselectrondensity(Walsh1982),radialvelocity(O’Dell,
Wen,&Hu1993,DOH04),andtangentialmotions(Cud-
H25 0H72 269 H2 worth & Stone 1977, Hu 1996, DOH02). Because of its
529 proximitytoθ2OriAMu¨nch&Taylor(1974)interpreted
530
theobjectastheresultoftheinteractionofastellarwind
with the ambient nebular gas, but the symmetry of the
8
203 52 shockandthepresenceofahighvelocityjetleadingtoit
2 0 4 (O’Dell et al. 1997a, Rosado et al. 2001, DOH04) indi-
cate that it is a jet driven shock. Henney (1996) argues
that its asymetry in brightness can be explained by the
Fig. 5.— This drawing of a 450′′ square field in the center jetstrikingdenserambientmaterialatgrazingincidence.
of the Orion Nebula depicts only the brighter stars and the HH The tip of this feature is a series of well defined shocks.
objects. Thecodingofthesymbols,letters,andlinesisexplained
inthetext. Thedominantionizingstarθ1OriCisshownasafilled Originally,O’Delletal. (1997b)arguedthattheshockis
circle. formed when the driving jet strikes the foreground Veil
ofneutralmaterialthatliesinfrontofthenebula(O’Dell
2001), but a more accurate knowledge of the position of
theVeil(Abel et al.2004)andanimprovedknowledgeof
the shock’s trajectory allowed DOH04 to establish that
HH203ariseswherethedrivingjetstrikesdensernebular
material where the ionization front of the Orion Nebula
M 43 tilts up. This tilt is what gives rise to the Bright Bar
feature that runs from northeast to southwest, passing
H20210,6920-0115-0-4 7 NoSrhtohcwkesst vnVeeTlaorhceiθt2yr=Oafdr−oiira7Al4Hv.Heklmo2c0ist−3y1om.faT−ph4oe6ftD±aOn1gH5e0nk4tmiaylise−vlde1ls,oawcihhtyeiclihsotcumedneytarnoicsf
OMC
Dark Bay 202 DOH02 gives a value of V = 73±23 km s−1 towards
204 522039 528 HH55H03270 269 H2 WSehHsotcekrsn PVSA==110344k±m1s7−◦.1Tanhdisθm=ea4Tn5s◦.that the spatial velocity is
ShSoocukthwest 3.3. HH 204
400 Bright Bar H2 stuHdHied20a4t itsheclsoasme eintipmoesitaisonHHto2H0H3 in20t3heanpdrehvaiosubseienn-
H2 vestigations. It extends slightly further from the center
H2
oftheOrionNebulaandisquite differentinappearance,
400-S H2 H2H2 H2 200" theheadoftheparabolicshockformbeinghighlyfloccu-
lentinappearance,ratherthanhavingthemultiplesmall
H2 H2 shocks present in HH 203. It has extended [O III] emis-
sion within the parabolic shock form, which is a strong
400-SS H2
indicationthatitisanobjectthatisbeingphotoionized,
H2 possiblyeitherbyθ2OriAormorelikelybyθ1OriC.The
presence of low ionization lines in its tip indicate that it
Fig. 6.—Thisdrawingofa1650′′×1825′′fieldaroundtheOrion too is striking a dense, low ionization region of the neb-
NebulashowstheHHobjectsintheouterpartsofthenebula. The ula, like HH 203, or, alternatively, that the compression
segmented linedepicts the boundaryof thesurveymadewiththe of the ionized gas by the shock leads to the trapping of
HSTACS,whichhasledtothediscoveryofmanyoftheseshocks. the ionization front.
Thecodeofthesymbols,letters,andlinesisexplainedinthetext.
TheradialvelocitymapofDOH04yieldsaheliocentric
The dashed box shows the central field shown in Fig. 5, while
theredrectangularboxshowstheregionmappedspectroscopically velocity for HH 204 of −18±18 km s−1, which means
thatisshowninFig.1. V = −46 km s−1. The tangential velocity study of
OMC
DOH02 gives a value of V = 92±10 km s−1 towards
T
Large Scale Flows from Orion-South 7
PA= 137◦±7◦. This means that the spatial velocity is nebula,andtherearenotangentialvelocitiesforHH400,
V =103 km s−1 and θ =27◦. it is impossible to derive its spatial motion. However,
S
Bally et al. (2001) argue from the shape of the HH 400
3.4. HH 528 shocks that it is moving almost in the plane of the sky.
TangentialvelocitiesintheHH528jethavebeenmea- 3.7. HH 530
sured for individual knots in the [OI] (BOM) and [SII]
(DOH02) lines. Three of these coincide with knots for HH 530 was first identified in BOM, where it is de-
which we have measured radial velocities. Taking the picted in their Figure 22. OD03 improved the measure-
vector mean of the proper motion measurements of the ments of the tangentialmotions and questionedwhether
knots gives a tangential velocity of V = 25±6 km s−1 the shock at 108–430 is part of this outflow (since it
T
atapositionangleofPA=139±15◦,whichisconsistent may be associated with the silhouette proplyd 114–
426). OD03 measured the components 105–416 and
with the orientation of the line between the jet and the
bowshock(PA=148±5◦)andthemajoraxisofthejetas 105–417, which are parts of a well defined shock ori-
Omuearsufirtesdtforomtheoujret[OcIo]mchpaonnneenltminapsth(ePA[O=I]15a0n±d 1[0S◦I)I]. eVnTte=d2a8lm±o5stkmduse−w1etsotw. aTrhdesyPAha=ve2a4n4◦a±ve2r6a◦g.eTmhoetrioenisoaf
line profiles give V⊙ = 17 ± 2 km s−1, implying that nearby3′′ featureorientedalmosteast-west(PA=260◦)
and may be an associated jet. This latter feature was
VOMC = 11 ± 3 km s−1, in which the uncertainty in- found to be moving at V = 63 ± 7 km s−1 towards
cludes the effect of the 2 km s−1 velocity dispersion of PA=255◦±4◦. ThereareTno published radialvelocities
stars in the Trapezium cluster (Jones & Walker 1988).
of this outflow.
Therefore θ =24◦±8◦ for the jet.
Tangentialvelocitieshavealsobeenmeasuredforknots 3.8. HH 269
in the bowshock of HH 528 (BOM; DOH02), although
thedispersioninmagnitudeanddirectionisratherlarge. HH 269 was first identified as an HH object in
Taking the vector mean of the 6 measured knots gives (Walter et al. 1995), following earlier observations of its
V =21±8 km s−1 at a PA of 206±24 ◦. The highest peculiar form (Feibelman 1976) and density enhance-
T
velocity (33 km s−1 at PA = 176◦) is seen in knot 182– ments in this region (Walter 1994). It is composed
of a series of shock structures oriented towards the
513 at (−25, −109), which lies at the very nose of the
west. Although some [O III] emission is seen, the object
bowshock. Our [SII] spectra of the bowshock (Figure 3)
is brightest in low ionization lines (Walter et al. 1995)
show peak velocities of V⊙ =16–18km s−1, very similar and there are associated H features in the images of
to that of the jet, implying VOMC ∼ 11 km s−1. Given Stanke, McCaughrean, & Zin2necker(2002). Thetangen-
the uncertainties involved,the data are therefore consis- tial velocities of the tip of the east shock were measured
tent with the jet and bowshock sharing the same space byOD03tobe 40±26km s−1 towardsPA=283◦±12◦.
velocity.8
The heliocentric radial velocity of the east shock is
(Walter et al. 1995) 13 km s−1 (V = −15 km s−1).
3.5. Features possibly related to HH 203-204-528 These values yield V =43 km s−1OwMiCth θ =21◦.
S
Figure 7 shows faint, high-ionization emission to the
south-east of the Bright Bar. The morphology of the 3.9. HH 507
emission is reminiscent of a bowshock shape, which may
HH 507 was first identified in BOM, where it is de-
representan outer shock related to the HH 203/204sys-
picted well in their Figures 22 and 23. It lies along the
tem. Alternatively, we cannot rule out that it may be
axis of HH 269, but is clearly separate as it has its own
associated with HH 528. Superimposed on this feature
characteristic velocities while features to the east and
is a faint arc of relatively high-density gas, identified in
westhavethecommonmotionofHH269. Ithastheform
[SII] channel maps by GH07. ofawest-northwestorientedparabola. OD03foundthat
V = 27±12 km s−1 towards PA = 298◦±41◦. BOM
3.6. HH 400 T
pointoutthatthereis a linearfeaturealongthe symme-
HH 400 was discovered by Bally et al. (2001) on Hα try axis of this shock and has PA = 296◦. If associated
and[SII]imagesoftheOrionNebulaandtheyalsoreport with HH 507, this means that the driving jet is not the
on velocity mapping of the southern part of the nebula nearbyproplyd117–352asitisnotalignedwiththatob-
in the [SII] lines. This is the largest of the known HH ject. BOMhypothesizethatHH507isdrivenbyoutflow
objectsintheOrionNebula,beingagroupoflargeshocks fromsourceFIR4(Mezger et al.1990),althoughamore
with the furthest tip extending 633′′ from Orion-S with completediscussionispresentedinour§5. Thereareno
PA = 146◦. In Figures 5 and 6 we see that there are published radial velocities of HH 507.
even larger shocks extending to 789′′ at PA = 147◦ and
the shock features at 970′′ at PA = 160◦ may also be 3.10. HH 625
associatedif the curvature continues. Bally et al.(2001)
HH625wasidentifiedinOD03andisunlikeanyofthe
give only radial velocities relative to the local region of
other HH objects in the Orion Nebula. It has a peculiar
the nebula, finding it redshifted by 8–20 km s−1. Since dark feature lying 76′′ at PA = 267◦ from θ1Ori C and
there areno published[SII]velocities for this partofthe that feature has a brightrimon its northwestboundary,
the feature being oriented towards PA = 325◦. OD03
8 Note that our results are inconsistent with the claim of
measuredthetangentialvelocityofthe associatedbright
Smithetal. (2004), based on unpublished Fabry-Perot observa-
tions,thatHH528isredshifted. features to be moving at VT = 26±4 km s−1 towards
8 Henney et al.
Fig. 7.—DeepHST WFPC2imagesoftheregionsouth-eastoftheBrightBarin[NII](upper-left)and[OIII](upper-right). Theseare
shownasnegative grayscales thathave beentuned toemphasizefaintfeatures, withtheresultthattheemissionfromthe innernebulais
saturated. Alsoshownisthe[OIII]/[NII]ratio(lower-right,withblacksignifyinghigherionization),andacartoon(lower-left)showingthe
principalfeatures.
PA=304◦±12◦. There are associated H features seen sured by Meaburn (1986), Clayton & Meaburn (1994),
2
in Subaru images (Kaifu et al. 2000) and in the H sur- O’Dell, Wen, & Hester (1991), and DOH04. The north-
2
vey of the regionby Stanke, McCaughrean, & Zinnecker west tip of the object is extremely complex in both im-
(2002). ThesmallH knotsseeninthelatterstudybegin agesmadeindifferentionicemissionandinlong-slitspec-
2
with a linear alignment close to PA = 313◦, then curve troscopy. Thebrightestpartisnearthistipandiscalled
slightlyclockwise,reachingadistanceofabout204′′from HH 202-S. The extended emission in [OIII] within the
their point of origin that is discussed in § 5. parabolicenvelopearguesthatlikeHH204,thisshockis
There are no published radial velocities of the optical photoionized from the rear, in this case almost certainly
features in this outflow. However, if one adopts a value by θ1Ori C.
ofV =80km s−1,assuggestedbytheCOmolecular DOH04 give a heliocentric velocity of −39±2 km s−1
OMC
outflow(Zapata et al.2005)thatis the drivingsourceof for the bright HH 202-S complex, which corresponds
thisHHobject(asdiscussedin§5),thenV =84km s−1 to V = −67 km s−1, and OD03 give V = 53 ±
S OMC T
and this part of the object has θ =73◦. 14km s−1 towardsPA=332◦±13◦ forthe sameregion.
These values yield V =85 km s−1 and θ =52◦.
S
3.11. HH 202
HH 202 was one of the first HH objects identi- 4. THECOMBINEDPROPERTIESOFTHEHHOBJECTS
fied in the Orion Nebula (Canto´ et al. 1980). The In the case where we can determine spatial velocity
best imaging study was carried out with the HST vectors (PA, V , and θ are known) and have at least an
T
(O’Dell et al. 1997b), where it was revealed that there approximate idea of the place of origin, we can depict
are a series of fine scale structures near the tip these flows in a manner that illuminates what is hap-
of a broad parabolic envelope. Tangential veloci- pening. Figure 8 shows the central region of the nebula
ties have been measured by Cudworth & Stone (1977), in three dimensions. For simplicity, we have assumed in
DOH02, and OD03. Radial velocities have been mea- calculating the position along the vertical axis that the
Large Scale Flows from Orion-South 9
A process for deflection of a redshifted componenthas
been proposed and modeled by Canto´ & Raga (1996).
They establishtheoretically that a jet passingthrougha
density gradient will be deflected towards the direction
of the lower density. This is extremely attractive for
explaining what we see in the Orion Nebula because we
know that there is a strong density gradient away from
the IF, being lower towards the observer (O’Dell 2001)
and theoretical models indicate that the density in the
neutral PDR should rise as one passes the IF. Whether
ornotabeamisdeflectedbyorpenetratesthePDRwill
be dependent upon many factors, including geometry,
magnitude of the density gradient, mass flux of the jet,
so that one cannot make an accurate prediction of what
will occur.
This means that redshifted flow from a source located
within the ionized zone of the nebula will eventually
reach the IF. If it is deflected sufficiently it can become
a blueshifted flow and if it passes through or remains in
Fig. 8.—Themotionsofthe cataloged HHobjects intheHuy-
the PDR then it will be optically invisible.
gens region of the Orion Nebula are shown superimposed on an
early mosaic of WFPC2 images (O’Dell&Wong 1996). The po- If the source is obscured by extinction (embedded),
sitionof thedominant ionizingstar (θ1OriC)withrespect tothe then the conversion of a redshifted into a blueshifted
ionization front is shown as a sphere while the location of O’Dell component means that the source must lie close enough
& Doi’s (2003) Optical Outflow Source is shown as an ellipse. behind the PDR so that there is still an increase of den-
The ionization front is actually an irregular, concave (as viewed
sity away from the observer. There is some evidence
by the observer) surface. The observer is located at an extension
of the vertical axis in this figure. When both radial and tangen- that this is the case for the flow from the OOS source
tial velocities are known, their velocity vectors are shown (all are since OD03 calculated that the source was only a few
blue-shifted)whilethoseobjectswithonlytangentialvelocitiesare
hundredths of a parsec beyond the IF.
drawnas being inthe plane of the figure. The lines drawn inthe
Unfortunately, the Canto´ & Raga mechanism can also
planeofthefigureindicatethesymmetryaxisofeachshock.
makeitmoredifficulttoidentifythelocationofasource.
objectsalloriginatefromthecenteroftheOOS.Thisas- This is because if a jet strikes a region with a tilted
sumptioniscertainlynotvalidforalltheHHobjects,but density gradient not only will there be the potential of
affectsonly little the generalpicture ofwhatis goingon. changinga redshift into a blueshift, but, the directionin
Ineachcasethedirectionofthevelocityvectoristhatde- the plane of the sky can be changed. However, one ex-
rivedfromV andθ. Itshouldberecalledthattheinner pectsthatthisalterationwillbe lessimportantsincethe
T
regionoftheOrionNebulahasbeenmappedinthreedi- concavity of the IF is not great except in the region of
mensionsbyWen & O’Dell(1995),whodeterminedthat the Bright Bar. This mechanism may be what produces
the surface is concave (as viewed by the observer), with the curvature of the path of the components of HH 625,
θ1Ori C lying about 0.2 pc (90′′) in front of the ioniza- whichOD03argueisaflowgrazingalongjustbehindthe
tion frontandthere is a local riseof about 0.05pc (22′′) IF.
at Orion-S. The last feature indicates that Orion-S is a There is another mechanism that complicates identi-
denserregionwithinthehostOrionMolecularCloudand fication of a source of an outflow by extrapolating back
thatthe ionizationfronthasnotpenetratedas farthere. in the plane of the sky and that is deviations in the di-
ThefirststrikingthingaboutFigure8isthatallofthe rection of the flow caused by a wind blowing on the jet.
optical objects are blueshifted. This indicates that the This mechanism has been invoked by Masciadri & Raga
sourcesfortheseHHobjectslieinthe backgroundofthe (2001) to explain the bent small-scale bipolar jets that
visible nebula or even in the optically obscured region one sees in the OrionNebula, the object associatedwith
beyond the IF. One would expect the optical extinction LL Orionis being the best example (BOM). The side
to increase significantly as one begins to penetrate the wind is most likely to be the flow of gas away from the
Photon Dominated Region (PDR) because the density bright central region of the nebula. It may be that the
jumps there. If a source were close to the IF, its red- welldefinedcurvaturenecessarytoconnectHH203+HH
shifted component would quickly disappear, unless the 204 to HH 400 and its southernmost components is
flow was diverted into being blueshifted. caused by such a wind.
The fact that several flows seem to be paired (e.g., The second striking thing about Figure 8 is that the
HH 529 and HH 269, HH 203/204 and HH 202) has led backwardsprojectionofthevelocityorsymmetryvectors
multiple authors to posit that these are bipolar flows crossinarelativelysmallarea,closetoOrion-S.In§5we
from a single source, with the originally redshifted com- will discuss the probable sources that lie in this region,
ponent being altered into having a blueshift without a putting special emphasis on identification of infrared or
significant change in the orientation on the plane of the radiocompactsourcesandthe molecularflowsknownto
sky (O’Dell et al. 1997a; Bally et al. 2001; Rosado et al. exist there.
2001, OD03). This argument is especially attractive for
theHH529-HH269pairingbecauseoneseesthe compo-
nents moving in opposite directions in the plane of the
sky, leaving a gap only in the OOS region (OD03). 5. DISCUSSION
10 Henney et al.
2
0
2
H 5
H 2
6
H
H
5 0 7
H H
HH 529
HH 269
t
e
0 3 J HH 530
2
H
H
8
2
Fig. 9.—TheCO(brightblueandred)andSiO(pinkandpale- 5
blue) emission in a 44′′ square region around Orion-S is shown H
H
superimposedonacompositeofHSTWFPC2imagesasdescribed
inthetext. ThewhiteellipseindicatestheOpticalOutflowSource
regionidentifiedbyOD03astheregionofthesourceofHH269and
HH529. Thesquaresandcirclesrepresentthepositionsofvarious
radioandinfraredcompactsources,withthewhitecirclerepresent- Fig. 10.— The features of Figure 9 (inner box) are shown on
ing the 1.6 µm and 2.2 µm source from Hillenbrand & Carpenter a 143′′×168′′ field within the Orion Nebula compiled from HST
2000, redcirclesthe10and20 µm MAXstudyofRobbertoetal. WFPC2withthesamecolorcodingasFigure9. Thefieldcovered
(2005)withthebrightestsourcefilled-in,theblacksquaresthe1.3 inFigure9isoutlinedinred. ThelocationofvariousHHobjectsis
cmsourcesofZapataetal.(2004),theredsquaresthesourcesseen indicated. ThinyellowlinesindicateH2 emissionfromtheSubaru
atboth1.3cmand1.3mm,andthebluesquaresthesourcesseen images(Kaifuetal. 2002)andthecontoursindicatehighvelocity
only at 1.3 mm (Zapataetal. 2005). FIR 4 is the 1.3 mm source features delineated by enhanced HeI 10830 emission as described
ofMezgeretal.(1990)andCS3isfromMundyetal.(1986). inthetext.
the vicinity ofOrion-S,as discussedlater in this section,
5.1. Comparison of the Optical Objects with the in addition to the Optical Outflow Source of OD03.
Embedded Molecular Outflows A wider field around Orion-S is shown in Figure 10,
Significant progresshas been made recently in the un- wherewehaveaddedtotheinnerregiondataofFigure9
derstanding of molecular outflow from the Orion-S re- theouteropticalobjects(designatedbytheirHHcatalog
gion. The most important recent contributions are the numbers), and H2 emission indicated on the Subaru im-
studies of CO (Zapata et al. 2005) and SiO (Zapata et ages(Kaifu et al.2000). Highlyblueshiftedopticalemis-
al. 2006), which exceed in sensitivity and angular reso- sionisshownbyclosedcontoursofthinyellowlines. The
lution the previous investigations of this region. These locationofthecompactandnarrowhighvelocitycompo-
two studies are summarized in Figures 9 and 10. nents are best delineated in DOH04, but we have shown
InFigure9theCOresultsareshownascontoursofthe the contours of HeI emission from Takami et al. (2002).
redshifted (red) and blueshifted (blue) components. For This is useful because the HeI 10830 ˚A line is optically
simplicity we have drawn only the outermost brightness thick because its lower state is metastable. Differences
contours and a few of the inner. Zapata et al. (2005) ofradialvelocityshiftthelineoutsidethecoreoftheab-
show that the flow aligned along PA = 306◦ reaches sorption and allow that radiation to selectively escape.
maximum values of ±80 km s−1. SiO emission in the
5.2. A Well Defined Connection between the CO
outflows from this region far exceed the normal nebu-
Outflow, its Infrared Source, and HH 625
lar abundance and must arise from destruction of grains
withinthemolecularcloudorthePDRlyingimmediately The new high spatial resolution CO images of the
beyondthenebula’sIF(Zapataetal. 2006). Theresults Orion-Sregionhaveprovidedthenecessaryingredientsto
ofthe SiOstudy areshowninFigure 9ina similarman- firmlyestablishthatHH 625is drivenby the blueshifted
ner to the CO results, except that redshifted emission outflowfromtheembeddedsource136–359aspreviously
is depicted as pink and blueshifted as pale-blue. The suggested in OD03. It is likely that the beam of molec-
primary emission occurs along an axis of PA=284◦and ular gas remains very confined and is grazing along the
reaches velocities of V =-90 km s−1 and V =75 PDR, occasionally breaking through the irregular and
OMC OMC
km s−1. These radio results are shown displayed on an concave IF. In this way one can reconcile the CO, H ,
2
HST WFPC2 optical image with the color coding [S II]- and optical observations.
red, [N II]-green, and [O III]-blue. In addition, we show It is natural to look for optical features corresponding
the positions of compact radio and infrared sources in totheredshiftedCOoutflow. Thedeflectionofthebeam