DEEP IMAGING SURVEYS OF STAR-FORMING CLOUDS. IV. THE MEEK AND THE MIGHTY: OUTFLOWS FROM YOUNG STARS IN CHAMAELEON I

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1 The Astronomical Journal, 132: , 2006 November # The American Astronomical Society. All rights reserved. Printed in U.S.A. DEEP IMAGING SURVEYS OF STAR-FORMING CLOUDS. IV. THE MEEK AND THE MIGHTY: OUTFLOWS FROM YOUNG STARS IN CHAMAELEON I John Bally Center for Astrophysics and Space Astronomy, University of Colorado, CB 389, Boulder, CO 80309; bally@casa.colorado.edu Josh Walawender Institute for Astronomy, University of Hawaii, 640 North Aohoku Place, Hilo, HI 96720; joshw@ifa.hawaii.edu Kevin L. Luhman Pennsylvania State University, University Park, PA 16802; kluhman@astro.psu.edu and Giovanni Fazio Center for Astrophysics, Cambridge, MA 02138; gfazio@cfa.harvard.edu Received 2006 June 5; accepted 2006 July 8 ABSTRACT We present a survey of shocks and outflows in the Chamaeleon I star-forming complex using H,[S ii], and SDSS i 0 images obtained from the ground, an i 0 image obtained with the Hubble Space Telescope, and 4.5 m images obtained with the Infrared Array Camera (IRAC) on the Spitzer Space Telescope. We find new Herbig-Haro (HH) objects and extensions to the previously cataloged shocks that trace parts of at least 20 distinct outflows from young stars. Some HH objects mark the presence of giant outflows, the largest of which is powered by Cha-MMS1 and associated with HH 49/50 near the Ced 110 region. Other large flows are powered by Cha-MMS2 in the Ced 112 region and the IRN in the Ced 111 region. Although some shocks exhibit infrared emission in the IRAC bands, most notably HH 49/50 (the tornado ), most outflows in the Cha I clouds are not detected in the Spitzer IRAC bands. This result is consistent with the general lack of extensive 2.12 m H 2 emission from Cha I. Key words: ISM: clouds ISM: individual (Chamaeleon I, HH 49/50) stars: formation 1. INTRODUCTION Protostellar outflows and jets inject momentum and energy into their environment. Their shocks dissociate molecules, ionize atoms, and sputter grains and their ice mantles. Thus, outflows can dramatically alter the physical and chemical state of the surrounding star-forming cloud. They represent a major feedback mechanism for the self-regulation of star formation in low-mass star-forming environments (e.g., Walawender et al. 2005). Deep imaging surveys in narrowband filters transmitting the emission lines of commonly excited species in shocks can be used to measure the area filling factor of shocks and the rate at which they reprocess the impacted cloud. This is the fourth in a series of papers presenting visual wavelength narrowband surveys of nearby star-forming clouds (e.g., NGC 2264, Reipurth et al. 2004; Perseus, Walawender et al. 2004, 2005). In this paper we present deep narrowband ground-based H and [S ii], Hubble Space Telescope (HST ) i 0,andSpitzer Space Telescope near-infrared images that trace shocks, outflows, and their source stars in the Chamaeleon I (Cha I) cloud complex. The Cha I dark cloud complex, located at the periphery of the Scorpius-Centaurus OB association near the south celestial pole, is one of the nearest regions of active star formation with a distance of about pc (Knude & Hog 1998; Luhman 2006). The Lower Centaurus Crux subgroup of Sco-Cen is located approximately (70 pc) north of the Cha I clouds. The massive stars in this subgroup of the Sco-Cen association provide external UV illumination of Cha I and may be responsible for the large-scale cometary morphology of these clouds. Interactions with radiation and expanding supernova-propelled debris from the OB association may have triggered star formation here The Cha I region contains over 150 low-mass young stellar objects ( YSOs) and a few moderate-mass stars with spectral type B9 or later; the total mass of the young stars is about 120 M (Mizuno et al. 1999; Kenyon & Gómez 2001; Carpenter et al. 2002; Comerón et al. 2004; Luhman 2004; Feigelson & Lawson 2004). The median age of the Cha I stars is about 2 Myr (Baraffe et al. 1998; Chabrier 2000; Luhman 2004). The cloud has a total mass of about 1000 M, of which roughly 230 M is located in cores traced by C 18 O (Luhman 2006; Haikala et al. 2005). Cha I contains three centers of ongoing star formation along the roughly north-south ridge of a filamentary molecular cloud. The northern center ( Figs. 1 3) contains the reflection nebula Ced 112 (Cederblad 1946), a bipolar molecular outflow possibly associated with the B9 V star HD or the nearby star HM 23 (Mattila 1989), and several dozen YSOs and infrared sources ( Haikala et al. 2005). This region contains at least one millimeterwavelength continuum source, Cha-MMS2 (Reipurth et al. 1996a). A second center of active star birth is located about 0N8 south and is associated with the bright reflection nebula Ced 110 (top of Fig. 4). This region contains the bright millimeter source Cha-MMS1 ( Reipurth et al. 1996b), several IRAS sources, and a north-south bipolar outflow associated with Cha-MMS1 ( Mattila et al. 1989; Lehtinen et al. 2001). Schwartz (1977) discovered a pair of bright Herbig-Haro (HH) objects known as HH 49/50 about 10 0 south of Ced 110. Subsequently, Schwartz et al. (1984) measured the proper motions of these HH objects, demonstrating that they are moving toward the south, away from the Ced 110 region. Cha-MMS1, located near the center of the CO bipolar outflow, may be the driving source for these HH objects. A third center of star formation activity is located about 0N3 south of Ced 110 near the reflection nebula Ced 111 (bottom of Fig. 4). This region

2 1924 BALLY ET AL. Fig. 1. H + [S ii] image showing the locations of HH objects in the Ced 112 region. Numbers associated with lines in this and subsequent figures correspond to the flow numbers given in the first column of Table 2. contains a number of IRAS sources; a bright near-infrared reflection nebula known as the IRN, which is bifurcated by a nearly edge-on disk shadow (Cohen & Schwartz 1984); and several moderate-mass stars with spectral types A and B. The structure of the Cha 1 cloud has been extensively mapped in C18O with 10 resolution (Haikala et al. 2005). The cloud has also been mapped at resolution in the more abundant 12CO species (Boulanger et al. 1998; Mizuno et al. 1998, 1999, 2001). However, higher resolution 12CO maps (10 or better) have only been obtained in small regions. Thus, the distribution of CO outflows is only poorly understood. Fig. 2. H [S ii] difference image showing the Ced 112 region that has been binned to reveal very low surface brightness features. H -dominated features are black, while [S ii]-dominated features are white. Vol. 132 Fig. 3. Spitzer IRAC band 2 (4.5 m) image showing the Ced 112 region. A large north-facing bow associated with HH 912 may be driven by the giant outflow from Cha-MMS1 (see text). HH 912 and 51 are the only HH objects with detected IRAC counterparts. Recently, Wang & Henning (2006) discovered several dozen shock-excited HH objects in the Cha I cloud. In this paper we present deep ground-based CCD images of the entire Cha I complex in H, [S ii], and SDSS i 0 and a survey of the Cha I region with the Infrared Array Camera ( IRAC; Fazio et al. 2004) on Spitzer (Werner et al. 2004). We report dozens of new, even fainter HH objects and dim extensions to the previously cataloged shocks. In addition, we show that many HH objects trace giant outflows, the largest of which is powered by Cha-MMS1 and associated with HH 49/50. Although some shocks exhibit infrared emission in the IRAC bands, most notably HH 49/50 (the tornado ), most outflows in the Cha I clouds are not detected in the Spitzer Fig. 4. H image showing the locations of HH objects in the Ced 110 and Ced 111 regions.

3 No. 5, 2006 DEEP IMAGING SURVEYS OF STAR-FORMING CLOUDS. IV IRAC bands. This result is consistent with the general lack of extensive 2.12 m emission from Cha I reported by Gómez et al. (2004). 2. OBSERVATIONS 2.1. CTIO Images were obtained on the nights of 2003 May with the NOAO Mosaic2 camera at the f/3.1 prime focus of the 4 m Blanco telescope at the Cerro Tololo Inter-American Observatory (CTIO). The Mosaic camera is 8192 ; 8192 pixels (consisting of eight 2048 ; 4096 pixel CCD chips) with a pixel scale of 0B26 pixel 1 and a field of view 35A4 on a side. We used narrowband filters centered on 6569 and , both with a FWHM of 80 8, for our H and [S ii] observations, respectively. For our continuum image we used the SDSS i 0 filter, which is centered on with a FWHM of Images were overscanned, trimmed, bias-subtracted, and flatfielded (using dome flats) in the standard manner using the MSCRED package in IRAF. Cosmic rays were removed using CRNEBULA. 1 Because we used single exposures in much of the survey, the images may contain a small number of cosmic rays that were not eliminated by the CRNEBULA task; however, we can safely distinguish the cosmic rays from the objects by their morphology: cosmic rays have sharp edges and are often only 1 pixel in extent. We used the procedures MSCCMATCH, MSCIMAGE, and MSCIMATCH to remove relative distortions, generate a singleextension FITS image, and match the sky background between images. For the pointings for which we obtained multiple images in each filter in a dither pattern, we used the MSCSTACK procedure to combine all images in each filter into a single image that eliminates the gaps between CCD chips. Registered H and [S ii] images were subtracted from each other to remove contamination by extensive reflection nebulosity. The resulting images were boxcar-smoothed and resampled to several pixel scales to search for low surface brightness extended H and/or [S ii] emission. The estimated 3 sensitivity of the narrowband images is about 3 ; ergs s 1 cm 2 arcsec 2 (3 ; Wm 2 arcsec 2 ) when the data are resampled to binned 1B0 pixels Spitzer Space Telescope Near-infrared images at 3.6, 4.5, 6, and 8 m were obtained with Spitzer as part of the Guaranteed Time Observations allocated to the IRAC team (PI: Fazio) between 2004 February 19 and September 2. For a description of the Spitzer IRAC observations, see Luhman et al. (2005b) Hubble Space Telescope The Advanced Camera for Surveys (ACS) on-board the HST was used to obtain images of HH 49/50 in the F775W (i 0 )and F850LP (z) filters on 2005 February 15 using exposure times of 1700 and 700 s for the F775W and F850LP filters, respectively ( Luhman et al. 2005a). The standard pipeline-processed data were used for the analysis presented here. 1 The CRNEBULA task removes cosmic rays from a region with fine nebular structure that can be misidentified by more traditional cosmic-ray rejection routines. The routine uses box and ring median filters to distinguish fine nebular structure from cosmic rays. For a detailed discussion of how this procedure works, see the IRAF CRNEBULA help page (available at crnebula). 3. RESULTS The Mosaic CCD survey of Cha covers about 2 deg 2 and includes the three major centers of star formation activity associated with Ced 112 in the north, Ced 110 in the central part of the complex, and Ced 111 in the southern part of the cloud. Table 1 lists the positions of the HH objects. Table 2 lists candidate outflows and their position angles (measured in degrees from north to east, etc.), lengths, and possible driving sources. Figures 1, 2, and 4 show the locations of the HH objects and the possible orientations of the outflows they trace. In the following sections, we first discuss the major new outflows, followed by smaller outflows and new HH objects. Previously detected HH objects that are not part of the newly recognized flows are discussed in the Appendix The Ced 112 Region: The Northern Complex The 10 0 region surrounding the reflection nebula Ced 112 in the north contains a small cluster of several dozen YSOs evident in Figure 3. A diffuse halo of additional YSOs extends over a roughly 1 deg 2 region surrounding the subcluster core (Luhman 2006). This portion of the Cha I cloud contains HH 51 and HH 912 to HH 917, recently detected by Wang & Henning (2006) Large Flows Giant outflows originating near WW Cha and Cha-MMS2. Cha-MMS2 is a bright millimeter source embedded in the Ced 112 region (Reipurth et al. 1996b). Mattila et al. (1989) found a bipolar molecular outflow with a roughly east-west orientation centered near this embedded protostar. The star WW Cha, located within a few arcseconds of the millimeter-wavelength source, illuminates a bright reflection nebula that opens toward the southeast. The bright star HD 97300, located about 2 0 south of WW Cha and Cha-MMS2, illuminates a somewhat redder reflection nebula that opens toward the southwest. These two stars and their reflection nebulae dominate scattered light in the Ced 112 region. Wang & Henning (2006) identified HH 915, a jetlike HH object located about southeast of WW Cha with an orientation of P:A: 130. Our images reveal a large flow propagating toward the southeast from near WW Cha and Cha-MMS2. A dim, nearly 5 0 long and 3 0 wide H-dominated bow shock, HH 931, is located 13 0 southeast of WW Cha and Cha-MMS2. This feature is best seen in the H [S ii] difference images (Fig. 2), which remove to first order the extensive reflection nebulosity surrounding Ced 112. This giant bow lies at P:A: 120 with respect to Cha-MMS2, similar to the position angle of HH 915. A faint chain of diffuse H emission extends from the brightest part of this bow to the southern rim of the reflection nebula that appears to be illuminated by WW Cha. The orientation of the reflection nebula is consistent with an outflow cavity opening toward the southeast. The outflow from WW Cha is listed as flow 1 in Table 2. HH 933 and 934 are two very faint H-dominated HH objects northwest of the Ced 112 nebula. These objects are near the detection limit and are found in the smoothed H [S ii] images. This chain may originate from the star HM 23 (IRAS ). The reflection nebula associated with HM 23 opens toward P:A: 135, exactly opposite the line connecting HM 23 to HH 933 and 934. It is likely that these faint HH objects trace a redshifted flow that emerges from behind the Ced 110 region. No obvious shocks are located on the axis of the reflection nebula to the southeast, although the position angle of the HM 23 reflection nebula and the HH 933/934 chain only differs by 15 from the

4 TABLE 1 HH Objects in Cha I Object R.A. (J2000.0) Decl. (J2000.0) IRAC a Comments b Ced 112 Region HH Y Bright, compact knot 13 0 N of Ced 112 HH N WH06; compact [S ii] knot, NW of disk shadow HH N WH06; [S ii] knot, counterflow to HH 913? HH Y WH06; diffuse [S ii] knot NW of Ced 112 HH 917A N WH06; diffuse [S ii] HH 917B N WH06; compact H knot HH 917C N WH06; W-facing H bow HH N WH06; [S ii] filament, P:A: 135 HH N 1 0 long H filament, P.A. 75 /255,6 0 SSE of Ced 112 HH 928A N NW part of H bow 12 0 SW of Ced 112, P:A: 40 HH 928B N SE part of bow HH 928C N Jet from CW Cha Star Y W Cha HH N Crescent of [S ii] NWW of Ced 112 HH N Dim H bow SE of Ced 112 HH N Dim H tube E of Ced 112 HH N Dim H knot NW of Ced 112 HH N Dim H knot NW of Ced 112 Ced 110 Region HH Y H-dominated HH Y [S ii]-dominated HH 906A Y WH06; bright shock in HH 49/50 flow HH 906B N WH06; faint shock at base of HH 49/50/906 lobe HH 925A N E rim of extended HH 49/50 H bow HH 925B N Pair of filaments in extended HH 49/50 bow HH 925C N SE rim of extended HH 49/50 bow HH 925D N S tip of extended HH 49/50 H bow HH 924A N N-facing bow, NE of Ced 110 HH 924B N Faint, diffuse H at cloud edge HH N WH06; 2 0 filament in Ced 110 cavity HH 911N Y WH06; N part of double shock HH 911S Y WH06; S part of double shock HH N Double jet in Ced 110 cavity HH N [S ii]-dominated, faint, S-facing bow HH N Faint, H bow SW of Ced 110 HH Y Large partial bow in IRAC Ced 111 Region IRN Y Infrared reflection nebula HH 909A Y WH06; knot W of IRN HH 909B Y WH06; partial bow W of IRN HH 909C Y WH06; faint knot W of IRN HH Y Bow in E lobe of IRN HH N SSW of DI Cha ( IRAS ) HH 920A N N from HM 16 ( Persi 2001) HH 920B N N from HM 16 ( Persi 2001) HH 921A N E of SAO ( HD 97048) HH 921B N E-facing bow from SAO HH N WH06; [S ii] knot HH 910A N Faint H knot S of IRN HH 910B N Faint H arc HH 910C N Faint H knot HH 910D N W side of faint bow HH 910E N WH06; compact, bright H bow, S of IRN HH 922ctr N Center of radius H ring HH 922A N W edge of H ring HH 922B N...

5 TABLE 1 Continued Object R.A. (J2000.0) Decl. (J2000.0) IRAC a Comments b HH 922C N S tip HH 922D N... HH 922E N E edge HH Y Faint H knot, 2 0 N of IRN axis HH Y Bright H bow shock, 2 0 N of IRN axis Note. Units of right ascension are hours, minutes, and seconds, and units of declination are degrees, arcminutes, and arcseconds. a Refers to the detection (or nondetection) of band 2 emission from shocks. b WH06: Wang & Henning (2006). DEEP IMAGING SURVEYS OF STAR-FORMING CLOUDS. IV orientation of flow 1. This outflow from HM 23 is listed as flow 2 in Table 2. A faint chain of nebulosity extends from the bottom of Figures 1 and 2 through HH 912 to HH 51 and may trace a giant flow emerging from Cha-MMS1 in the Ced 110 region. This flow is discussed in x Smaller Flows and New HH Objects Flow from WZ Cha: HH 932. A very low surface brightness object, HH 932, extends 5 0 east of the m R ¼ 13 mag, spectral type M1e star WZ Cha at P:A: (Figs. 1 and 2). This dim H feature is a limb-brightened tube about wide that extends into a cavity located east of Ced 112 that is rendered visible by reflected light in Figure 1. HH 932 may be a counterflow to the much brighter HH 917, located about west of WZ Cha. HH 917 is a [S ii]-dominated shock listed as HH 917A in Table 1. The H [S ii] difference image reveals that there are two additional H knots located on the axis connecting WZ Cha to HH 917. HH 917B is midway between HH 917A and WZ Cha, while HH 917C is a small, west-facing bow located a few arcseconds west of HH 917A. HH 932 may be propagating into the lowdensity interior of a cavity, while HH 917 may trace a shock where the outflow from WZ Cha rams dense gas associated with the Ced 112 region. This is flow 3 in Table 2. HH 930. HH 930 is an arcminute-scale crescent of [S ii] emission located 9A5 west-northwest of Ced 112 (near the right edge of Figs. 1 and 2). The crescent faces southeast, and there is a faint star at the point of symmetry of the crescent at R:A: ¼ 11 m 07 h 10: s 7, decl: ¼ (J2000.0). The closest known YSO is the variable H emission-line star UZ Cha (spectral type M0.5e) located at R:A: ¼ 11 m 07 h 12: s 09, decl: ¼ (J2000.0), about 1 0 north of HH 930. The morphology of HH 930 does not indicate any direct connection to UZ Cha. It is also possible that this HH object is powered by one of the protostars in Ced 112. This is flow 4 in Table 2. HH 928. Located almost 3 0 northeast of the m R ¼ 15:0 mag variable star CW Cha (lost in the glare of the brighter star CV Cha in Figs. 1 3), this HH flow consists of a partial H bow shock. Component A is the brighter, northwestern part of the shock, while component B is a fainter arc of emission along the southeastern side. A long filament of H emission at P:A: 40 from CW Cha (HH 928C) may trace a one-sided jet. However, the jet points north of HH 928A. A large but faint envelope of reflection nebulosity surrounds CV Cha, an m R ¼ 11:0 mag star located about west of the jet source, CW Cha. The structure of this nebula is consistent with the illumination of dust located in a plane orthogonal to the HH 928 jet axis. This is flow 5 in Table 2. TABLE 2 Suspected Outflows in Cha I Flow HH Objects P.A. (deg) Length ( pc) Source Comments / / WW Cha /Cha-MMS2 Large, diffuse, with filaments / / HM 23/Cha-MMS2 Receding lobe from HM 23? /917 H 80/260? WZ Cha NE of Ced ??? Near UZ Cha / CW Cha Jet + bow / ? ESO H 569 Faint filaments / / ISO Cha I 225 Along axis of disk shadow /50/906/922/924/ / Cha-MMS1 Tornado S of Ced CHXR 15? SW of Ced H 2 bow/ Ced 110 IRS 4 Large IRAC bow NE of Ced ??? 21 0 SE of Ced /918 95/ IRN IRN in Ced /926 90/270 >0.5 VW Cha Parallel to IRN flow, 1 0 N / >0.5 Sz 26? Axis passes 1 0 W of IRN /285 >0.2 CU Cha C-symmetric E-W flow >0.1 HM 16 N-facing >0.05 DI Cha S-facing jet in refl. neb A 100/ HH 48IR First jet B 170/ HH 48IR Secondary jet in binary? / / Ced 110IR Along axis of Ced 110 cavity Note. A question mark implies that the position angle cannot be determined, since the source location or direction of the flow is not known.

6 1928 BALLY ET AL. Fig. 5. H [S ii] difference image showing the giant outflow lobe extending south from Cha-MMS1 that contains HH 49/50/906/925/922. The east-west outflow from the IRN crosses horizontally from HH 909A to 909C. HH 919. This HH object is the brightest part of a dim, several arcminute long filament of H emission located about 70 south-southeast of Ced 112. This filament appears to protrude from the dark cloud located several arcminutes west of the quoted position. There are no bright infrared sources along the apparent axis of the filament. However, a faint star, DENIS J ( ESO H 569, spectral type K7e, mr 17:7 mag; Comero n et al. 2004) located northeast of the HH object exhibits a northeast-southwest-oriented H filament that may trace a several arcsecond long microjet aimed toward HH 919. This is flow 6 in Table 2. HH 913 from ISO Cha I 225. The star ISO Cha I 225 is surrounded by a disk shadow, indicating a nearly edge-on disk. Two shocks, HH 913 to the northwest and HH 916 to the southeast, are located close to the axis of the disk. This outflow is listed as flow 7 in Table 2. The Spitzer image shows many YSOs in the core of the Ced 112 region between ISO Cha I 225 in the north and HD Vol. 132 Fig. 6. Spitzer IRAC band 2 (4.5 m) image showing the Ced 110 region near Cha-MMS1 and the giant outflow it drives, including HH 49/50, the tornado. in the south. This region contains many individual shocks and reflection nebulae. However, the association of individual shocks with specific sources is rendered difficult by source confusion. Future radial velocity and proper-motion measurements will be needed to resolve source confusion The Ced 110 Region: The Central Complex The central part of the Cha I cloud is dominated by the bright reflection nebula Ced 110. The reflection nebula is located at the southeastern end of a large and transparent cavity in the molecular cloud that opens toward the northwest at P:A: 310. Two previously known HH objects and several new ones are located in this part of the cloud Large Flows The tornado: HH 49/50. Schwartz (1977) detected a pair of objects, HH 49/50, south of Ced 110 that are the brightest shocks in the Cha I cloud (Figs. 5 8). Our images show that they trace the brightest part of a giant double bow-shock structure associated

7 No. 5, 2006 DEEP IMAGING SURVEYS OF STAR-FORMING CLOUDS. IV Fig. 7. H image showing a close-up of HH 49, 50, 906, and 925. with a north-south outflow from the vicinity of Ced 110. This flow is discussed in this subsection, followed by a discourse on other flows near Ced 110. A bright H and [S ii] knot located midway between Ced 110 and HH 49/50 is designated HH 906. The southern edge of this shock is nearly as bright as HH 49/50. A pair of fainter H filaments separated by about sweeps back toward the north. HH 49/50 and HH 906 are embedded within a giant, highly elongated (10 0 long by 1 0 wide) bow-shock complex oriented toward P:A: 190 (Figs. 5 and 7). A lattice of faint H filaments extends from the eastern rim of this bow to 5 0 east. This large bubble, which can be traced at least 12 0 south of Cha-MMS1, is collectively labeled HH 925. Several of the brightest features are designated HH 925A to 925D in Table 1. The eastern rim of this structure contains continuous filaments of faint H extending from HH 925A, through HH 925C, to HH 925D, which marks the southern end of this outflow complex, located several arcminutes south of HH 49/50. HH 925B marks the center of a pair of arcminute-long parallel filaments separated by about from each other and located about 2 0 west of HH 925A. The emission from HH 49/50/906/925 traces a giant outflow lobe emerging from a 1.3 mm source known as Cha-MMS1, located about 10 0 north of HH 49/50 (Reipurth et al. 1996b). An IRAS source, IRAS , and a small cluster of nearinfrared sources located about 1 0 north of Cha-MMS1 are embedded in a C 18 O and CS core (Mattila et al. 1989). Prusti et al. (1991) found a small CO outflow centered on the millimeter source, Cha-MMS1, whose redshifted lobe is aimed directly toward HH 49/50. Assuming that Cha-MMS1 is the driving source, HH 49/50/906 is propagating toward the south at P:A: 190, consistent with the orientation of the walls of the outflow cavity and the proper-motion vectors. Schwartz found that HH 49/50 is redshifted, which further strengthens the association of HH 49/50 with the outflow from Cha-MMS1. The Spitzer images (Figs. 6 and 8) show a striking infrared nebula associated with the brightest part of HH 49/50. The nebula is brightest in IRAC band 2 (4.5 m), where it consists of a pair of intertwined, twisting, helical filaments that widen from south to north. The peculiar morphology suggests the name tornado. The southern tip of the tornado is associated with the southern end of HH 49/50. A faint red star is visible in all IRAC bands about south of the southern tip of HH 49/50 and the base of the tornado at R:A: ¼ 11 h 05 m 53: s 8, decl: ¼ (J2000.0). This star is centered on a dim circular nebula about in diameter in the 3.6, 4.5, and 6.0 m images; at 8 m, the outer rim of this disk becomes a partial circle or crescent of emission facing northeast with a clear gap between it and the central star. HSTACS images (Fig. 9) show that the star is surrounded by a compact subarcsecond-diameter reflection nebula opening toward the southeast, indicating that the star is embedded in the Cha I cloud. Two aspects of the IRAC images make this star and its circumstellar nebula unusual: (1) its proplyd-like appearance, suggesting illumination from the north or east, and (2) its location at the southern tip of HH 49/50, the brightest shocks in Cha I. Although the morphology might be taken as an indication that the tornado emerges from this star as an outflow moving north, multiple lines of evidence suggest that HH 49/50, its giant H envelope HH 925, and the tornado are driven from the north, probably by Cha-MMS1. The location of this star at the southern end of the H 2 emission associated with HH 49/50 is either a coincidence or an indication that the Cha-MMS1 outflow is impacting the envelope of a young star in the Cha cloud complex. The impact of a supersonic flow on a small cloud core that contains the IRAC source would readily produce strong shocks, which would radiate unusually strong visual wavelength and near-infrared emission from this part of the HH 49/50/Cha-MMS1 outflow. The cloud core would severely decelerate the outflow, and if the medium contains molecules, the resulting shocks should be bright in H 2, thereby explaining the 4.5 m emission. Proper motions of HH 49/50 provide a crucial test of this hypothesis. Indeed, the proper-motion data indicate that the HH 49/50 complex is moving toward the south with V km s 1 toward P:A: (Schwartz et al. 1984). Outflow-cloud collisions have been observed in other starforming regions. A classic case is the impact of the HH 270 jet on a small cloud core in Orion, an interaction that produces HH 110 (Reipurth et al. 1996b; Raga et al. 2002; López Martí et al. 2005). Another example is the impact of the HH 280 flow on the L1451 cloud in Perseus, which produces HH 493 (Walawender et al. 2004). The 8 m crescent may be a photon-dominated region (PDR) illuminated from the east by UV or from the west by the star located close to its center. Illumination from the Sco-Cen OB association would produce many other irradiated features in the Cha clouds. However, none are seen in the Spitzer IRAC data. Thus, it is more likely that the red star in the center of the crescent is the illuminator. The IRAC source may be a T Tauri star whose UV excess produces a small reflection nebula and a PDR in the cavity wall where polycyclic aromatic hydrocarbons (PAHs) might produce the infrared crescent. As discussed below, it is likely that the brightness of the tornado in the Spitzer and visual wavelength images, and its location at the point of intersection of the faint

8 1930 BALLY ET AL. Vol. 132 Fig. 8. Spitzer IRAC image of the tornado ( HH 49/50) showing the emission in bands 1 (3.6 m; blue), 2 (4.5 m; green), 3 (6.0 m; orange), and 4 (8.0 m; red ). double bow consisting of HH 925 on the east and HH 49/50/906 on the west, is due to the collision of this flow with the envelope of the faint star. HH 922. HH 922 is a remarkable, nearly circular ring of faint H emission about 5 0 in diameter located southwest of the IRN in Ced 111. This semicircular filament is only a few arcseconds wide and nearly constant in brightness along its arc length. The ring is located slightly east of the axis of the tornado flow from Cha- MMS1, which contains the giant bow HH 925 and HH 49/50 (flow 8). HH 922 lies close to the axis of an outflow (HH 927, discussed below) from LkH , located 10 0 north of HH 922. The H [S ii] difference image shows that HH 49/50/906/ 925 and HH 922 share a very faint envelope of H emission that extends from a few arcminutes south of Cha-MMS1 to the southern end of HH 922, about 25 0 south. Thus, HH 922 is likely to be a giant, limb-brightened bow shock and part of the HH 49/50/ 906/925 flow powered by Cha-MMS1. HH 924, the northern lobe of the outflow from Cha-MMS1. This is a faint bow shock located northeast of Ced 110. No H 2 emission is seen in the IRAC images. This HH object is approximately the same distance from Cha-MMS1 as HH 49/50 but lies in the opposite direction. Thus, it is likely that HH 924 traces the counterflow associated with HH 49/50/906/925 driven by Cha- MMS1. However, this shock is much fainter than HH 49/50/906, perhaps because the density of the medium with which the counterflow is interacting is much lower. The extinction in this region appears to be low, as HH 924 lies beyond the projected edge of the Ced 110 cloud, where background galaxies can be seen. If this HH object is powered by Cha-MMS1, then this flow is at least 22 0, or about 1 pc in length. The HH 49/50/906/922/925/924 outflow, the tornado, is listed as flow 8 in Table 2.

9 No. 5, 2006 DEEP IMAGING SURVEYS OF STAR-FORMING CLOUDS. IV Fig. 9. HST ACS i 0 image showing the star located at the southern tip of HH 49. The image of the star is slightly extended when compared to the binary star in the right portion of the image. Note the faint reflection nebula opening toward the southeast. Fig. 10. Spitzer IRAC band 2 (4.5 m) image showing the large IRACdetected bow shock located northeast of Ced 110, HH 929. CHXR 15: The source of HH 906 and HH 936? HH 936 is a very faint and diffuse H feature located in the cloud due south of the southern edge of the cavity associated with Ced 110, about 4 0 southwest-west from Ced 110IR. A line drawn from HH 936 to HH 906 contains a YSO, CHXR 15 (BYB 22, spectral type M6), which is a young, low-mass red dwarf (López Martí etal. 2004; Luhman 2004). The morphology of HH 906 is consistent with it being powered by CHXR 15. The long diagonal filament associated with HH 925B in the center of HH 925 also lies on an axis that passes through HH 906, CHXR 15, and HH 936. It is possible that CHXR 15 is the source of a collimated outflow whose southeastern lobe is superposed on the giant outflow lobe from Cha-MMS1. The presence of HH 906 at the location where the two flows cross suggests that these two outflows are interacting. This is flow 9 in Table Smaller Flows and New HH Objects HH 929. The Spitzer IRAC images reveal a several arcminute long partial bow located about 11 0 north-northeast of the Ced 110 reflection nebula just north of the northern edge of the molecular cloud (Fig. 10). This feature contains a very dim H and [S ii] counterpart, indicating that it either is obscured or has very low density and produces only faint visual wavelength forbidden emission lines. This feature traces a shock in a flow propagating toward the north or northeast. This flow may be associated with one of the roughly north-south flows emerging from the Ced 111 region. Possible candidates include flow 15 from CU Cha and flow 17 from DI Cha. It is also possible that this shock traces an independent flow. Due to these uncertainties, it is listed as flow 10 in Table 2. HH 935. This faint, south-facing, roughly diameter bow shock located due east of HH 49/50 is visible only in [S ii]. It is embedded in an extensive network of faint filamentary reflection nebulosity centered on an 11 mag star about 1A5 southeast. The bow orientation suggests that this feature traces a flow moving south from the cluster of infrared sources east of Ced 110. This is listed as flow 11 in Table The Ced 111 Region: The Southern Complex One of the most spectacular disk shadows and reflection nebulae in the sky, the IRN, is located in the southeastern part of the Ced 111 complex (Figs. 11 and 12). The axis of the disk (and nebula) is almost exactly east-west, with the east-facing lobe being larger and brighter than the west-facing lobe. The reflection nebula and disk shadow are prominent from visual wavelengths to IRAC bands 1 and 2 (3.6 and 4.5 m). At longer wavelengths the reflection nebula becomes faint and light from the central star overwhelms the disk shadow. A chain of HH objects, HH 909 and 918, delineates a parsec-scale outflow along the axis of the IRN Large Flows A parsec-scale flow from the IRN: HH 909/918. Three HH objects lie along the axis of the IRN to the west (perpendicular to the disk) and are designated HH 909A, 909B, and 909C. HH 909A is an H-dominated knot located inside the western lobe of the IRN, about west of the disk center. HH 909B is an arcminute-long filament of H-dominated emission located slightly north of the IRN axis and several arcminutes west of the disk shadow. This feature is also prominent in IRAC band 2 (4.5 m), indicating the presence of shock-excited H 2. HH 909C is a compact and faint H knot about 10 0 from the IRN on its axis. HH 918 is a well-defined, H-dominated bow shock located about 15 0 east of the IRN. The orientation of this bow and its location along the axis defined by the IRN and HH 909 indicate that it is part of a giant outflow from the YSO embedded in the IRN s disk. A line drawn from HH 918 to HH 909C has an orientation of P:A: 95. HH 909/918 traces the western and eastern lobes of a giant outflow from the YSO embedded in the IRN (designated flow 12 in Table 2). About 1 2 pc west of the IRN, the Cha I cloud exhibits a pronounced west-facing kink on the axis of the IRN outflow. Although there are no HH objects here, it is possible that flow 12 from the IRN, and possibly flow 13 from VW Cha, have collectively impacted this portion of the molecular cloud and produced a bow-shaped dent of dust and molecular gas. If this interpretation is correct, the CO emission may exhibit a small radial velocity perturbation in this portion of the cloud. Outflow from VW Cha: HH 923/926. Two shocks lie on a line parallel to the IRN flow but about 1 0 north. HH 923 is a very faint H feature, while HH 926 is a prominent H bow shock about 1 0 east of HH 923. Both shocks are visible in the IRAC band 2 (4.5 m) images, with HH 926 being much brighter than HH 923. A line drawn through this pair of shocks and extended

10 1932 BALLY ET AL. Vol. 132 Fig. 11. H [S ii] difference image showing compact bow shocks east of the IRN. to the west passes very close to the m V ¼ 12:3 mag K5 star VW Cha, located northwest of the IRN, that is a likely source for this pair of HH objects. HH 909C in flow 10 from the IRN (discussed above) also lies on this axis but about 8 0 west of VW Cha. Thus, rather than being part of the IRN outflow, HH 909C may trace a counterflow to HH 923/926. The flow from VW Cha is listed as flow 13 in Table 2. Fig. 12. H [S ii] difference image showing HH 920, 921, and 927 north and west of the IRN and the first pair of shocks in the western lobe of the IRN outflow, HH 909. South-facing flow south of the IRN: HH 908/910. A faint chain of H knots, filaments, and bow shocks extends south from near the IRN along an axis that intersects the IRN outflow about 1 0 west of its source star. This chain of HH objects can be traced for at least 7 0 south from HH 910A to HH 910E. The latter feature consists of a bright, compact, south-facing H bow shock embedded within the eastern rim of a much fainter arcminutescale bow. The orientation of this chain is P:A: 177.This is flow 14 in Table Smaller Flows and New HH Objects Bent bipolar jet from CU Cha: HH 921. This is a compact flow propagating east at P:A: 100 from the m V ¼ 8:5 mag spectral type B9e star HD (CU Cha), a companion, or an unrelated star in its vicinity. The flow contains two faint compact H bows east of the star and some fainter emission features farther east. Several faint knots are also visible west of CU Cha. A pair of H filaments traces either small bows or possibly limbbrightened cavities on both the eastern and western sides of CU Cha. Overall, this chain of H features forms a bent, several arcminute long, C-symmetric outflow from CU Cha. This flow deflection indicates either that CU Cha is moving toward the north or that the cloud is flowing past the star and its outflow is toward the south. This is flow 15 in Table 2. North-facing flow from HM 16: HH 920. This is a compact north-south flow emerging from HM 16, an embedded YSO surrounded by a compact reflection nebula and a large infrared excess. This is flow 16 in Table 2. Jet from DI Cha: HH 927. HH 927, located a few arcseconds south of LkH (DI Cha, IRAS ; m V ¼ 10:9 mag, spectral type G1 Iab:pe), is a north-south oriented filament embedded in a south-facing parabolic cone of reflection nebulosity. Apparently, this star is surrounded by a large cavity opening to the south. This is flow 17 in Table DISCUSSION 4.1. The Large-Scale Environment of Cha I The Cha I complex is located on the outskirts of the Lower Centaurus Crux subgroup of the Sco-Cen OB association and may have been influenced by energy released by its massive stars.

11 No. 5, 2006 DEEP IMAGING SURVEYS OF STAR-FORMING CLOUDS. IV During the last 10 Myr, UV radiation, stellar winds, and supernovae in Sco-Cen inflated a 100 diameter superbubble visible in 21 cm H i (Blaauw 1991; Hartmann & Burton 1997). The Cha I clouds are embedded in the interior of the H i shell about 10 from their projected edge. The major axis of the Cha I clouds is aimed roughly toward the center of the Lower Centaurus Crux subgroup of Sco-Cen (Blaauw 1991), and their cometary morphology may have been sculpted by the winds and radiation fields of the massive stars powering the shell. Recent star formation occurred at the northern ends of the Cha I filaments, consistent with triggering from the north by interaction with the OB association. The long axes of the filaments in the Cha I cloud complex are approximately orthogonal to the nearby portion of the Sco-Cen supershell, as traced by 21 cm H i emission. In addition, the average orientation of the magnetic field threading the clouds is roughly parallel to the supershell walls and orthogonal to the Cha I clouds (Whittet et al. 1994; McGregor et al. 1994). This largescale magnetic field may have influenced the orientations of some outflows emerging from this cloud Multiple Outflows in Cha I The visual and near-infrared images presented here provide evidence for multiple outflows in the Cha I star-forming region. The northern cluster of YSOs near Ced 112 drives at least seven distinct outflows. The central cluster near Ced 110 contains at least five distinct outflows, including the spectacular HH 49/50/ 924/906/925/922 system powered by Cha-MMS1. The brightest shocks in this flow are traced by HH 49/50, whose morphology in the Spitzer IRAC images suggests the name tornado. The southern cluster associated with Ced 111 and the IRN contains at least five distinct outflows, including the giant flow from the IRN. Thus, HH objects and shock-excited H 2 emission reveal the presence of at least 20 distinct outflows, which contain over 30 numbered HH objects and over 40 distinct shocks. Table 2 lists these proposed outflows and their likely driving sources. These outflow identifications are based on alignments; it is possible that the actual number of flows is considerably greater. Some shocks may be chance alignments from unrelated outflows. Deeper imaging, radial velocity, and proper-motion measurements are needed to confirm these proposed flows or to identify additional ones. Table 2 reveals an unusually large number of outflow candidates oriented southeast-northwest (P:A: or ; we do not know the outflow Doppler shifts, so the position angle of the blueshifted lobe is ambiguous by 180 ). Polarization orientation vectors measured by Whittet et al. (1994) and McGregor et al. (1994) indicate that the average magnetic field in Cha I is oriented approximately southeast-northwest (see Fig. 8 in Haikala et al. 2005). It is possible that the large-scale magnetic field may have influenced the direction of cloud collapse, the orientations of circumstellar disks, and the propagation directions of outflows. Outflow activity in the Cha I star-forming complex can be compared with other cluster-forming regions, such as NGC 1333 and IC 348 in the Perseus molecular cloud complex or the Oph region, which contain a similar number of YSOs within a factor of 2. Of these clusters, the Oph region has a much larger column density of molecular gas, and its stars and outflows are much more obscured and embedded than Cha I. IC 348 is older, with an age of about 2 4 Myr, and contains very little dust and few shocks in either visible or near-infrared wavelength images. However, Walawender et al. (2005) recently identified extensive outflow activity and recent star formation in a cloud core containing the well-known HH 211 jet and Flying Ghost Nebula, which are located southwest of IC 348. With an age of 1 Myr or less, NGC 1333 is currently the most active site of recent and ongoing star formation in the Perseus cloud. Of these complexes, NGC 1333 may provide the best comparison to Cha I. However, it differs in several respects. NGC 1333 contains 150 YSOs, somewhat less than Cha I. Yet NGC 1333 contains many more HH objects, and most of these are bright in the IRAC band 2 (4.5 m) images. NGC 1333 contains over 100 distinct H and/or [S ii] shocks, whose area covering factor is larger than 10%. In contrast, Cha I contains several dozen, mostly very faint, visual wavelength shocks. NGC 1333 is laced with bright emission from jets, outflows, and associated shocks in the IRAC band 2 images. Cha I contains little IRAC band 2 nebulosity; only a few of the brightest HH objects, such as HH 49/50 (the tornado), are detected. While Spitzer IRAC images in NGC 1333 reveal many shocks that have no visual-wavelength counterparts, only one shock in Cha I was first identified in the IRAC images. The area covering factor of band 2 (H 2 ) emission is much lower in Cha I than in NGC In addition, the amount of molecular gas and the extinction in Cha I is less than in NGC These differences are consistent with a greater age and a relatively more evolved state of Cha I compared to NGC Many Cha I outflows are weak and probably interact with mostly atomic gas. Only a few shocks in Cha I contain H 2 ; most produce faint visual wavelength emission. The faint and sparsely spaced emission from these flows indicates that, on average, they are much weaker than the outflows in younger regions such as NGC Electron Density Estimation The H surface brightness, I(H), can be used to make a rough estimate of the electron density. In a fast shock propagating into a mostly neutral medium, hydrogen will recombine following collisional ionization, and the emission measure, EM, in units of cm 6 pc is related to I(H) by Z EM ¼ n 2 e dl n e 2 L ¼ 4:9 ; I(H); where I(H) is in units of ergs s 1 cm 2 arcsec 2 and the path length of the emitting region along the line of sight (LOS), L,isin parsecs. The numerical value assumes a temperature of 10 4 K(see Spitzer 1978, eqs. [3] [36]). The electron density in the compressed postshock region is then given by n e (EM/L) 1/2 cm 3. In dim features, such as the H bubble HH 922, I(H) ð3 30Þ ; ergs s 1 cm 2 arcsec 2 so that EM 1:5 15 cm 6 pc. Using Figure 5, the LOS path length through the postshock layer of the limb-brightened rim of this H ring is about 10 4 AU (0.05 pc), corresponding to 1 0 on the plane of the sky. Thus, n e 5 17 cm 3. Bright features, such as HH 49/50, have estimated peak electron densities of order cm The Giant HH 49/50/906/925/922 Outflow Lobe from Cha-MMS1 The HH 49/50/906/925/922 outflow lobe from Cha-MMS1 in the Ced 110 region is the largest outflow at visual wavelengths in H and [S ii]. It can be traced for at least 27 0 (1.3 pc) from Cha- MMS1 to HH 922, a semicircular ring of H emission over 5 0 in diameter. The first segment of this outflow extends south from Cha-MMS1 to about HH 49/50 and contains the bright and compact knot HH 906 and the large, diffuse bubble of H emission HH 925. The outflow continues 17 0 farther south to HH 922. Some very low surface brightness filaments and patches of H emission located midway between HH 925 and 922 may mark additional shocks in this flow.

12 1934 BALLY ET AL. Vol. 132 The first segment of the Cha-MMS1 outflow consists of two distinct parts: a collimated lobe containing HH 49/50 and 906, near the western rim of the lobe, and a diffuse bubble located to the east, designated HH 925. HH 49/50 and 906 mark the brightest portions of a collimated lobe connected by two nearly parallel walls of fainter H and [S ii] emission separated by less than 1 0. These walls can be traced from 2 0 south of Cha-MMS1 to the southern tip of HH 49/50, where IRAC band 2 emission from the tornado peaks about 8 0 south of Cha-MMS1. The faint filamentary network associated with the HH 925 diffuse bubble extends 3 0 east of the lobe containing HH 49/50/906 and 10 0 south of Cha-MMS1. The diffuse bubble is traced by a network of faint H filaments. This morphology may be explained by two models. First, while HH 49/50/906 is powered by Cha-MMS1, HH 925 may be powered by another source. There is evidence that HH 906 and HH 925B may be powered by a crossing flow from CHXR 15, a spectral type M6 red dwarf star. However, most of HH 925 appears to be powered by a flow from near Cha-MMS1. Second, HH 925 may be powered by sideways splashing of the Cha-MMS1 flow resulting from the collision with the envelope of the IRAC star at the southern end of the tornado. That HH 925D is located several arcminutes south of the IRAC star at the base of the tornado indicates that the outflow from Cha-MMS1 has propagated past the IRAC star and enveloped this region. If the first model is correct, then the leading edge of the Cha-MMS1 flow is just now impacting the environment of the IRAC star, and the tornado marks the terminal working surface of this flow. The HH 925 diffuse bubble has propagated past the IRAC star, either in the foreground or the background. If the second model is correct, the leading edge of the eruption responsible for HH 49/50 is currently located near HH 925D, or possibly farther south. In this case, HH 49/50 marks the location of an internal working surface where relatively young ejecta from Cha-MMS1 are impacting the environment of the IRAC star. The impacts of older/prior ejecta would have splashed off the eastern side of the circumstellar environment of the IRAC star to inflate the diffuse bubble consisting of HH 925. Future radial velocity and proper-motion measurements may be able to distinguish between these models HH 49/50: The Tornado HH 49/50 is made up of the brightest shocks in both visual wavelengths and the near-infrared, as traced by the Spitzer IRAC images. Previous work has shown that these shocks are redshifted. The bright HH 49/50 shock exhibits several remarkable traits. First, the brightest emission is located at the apparent intersection of two large bow shocks traced by filaments of H emission. Thus, the emitting region may have been compressed by converging shocks. Furthermore, this part of the flow may be interacting with the dense, circumstellar envelope of the IRAC star. Thus, the emission measure of this region may be unusually large. Second, the Spitzer IRAC images show a color gradient from the southern tip of this bow to the northern tail. The tip is relatively brighter at short wavelengths (3.6 and 4.5 m), while the bow-shock wings are relatively brighter in the long-wavelength (8 m) images. This color gradient can be readily understood as an excitation effect. The shocked emission in the IRAC bands is likely to be dominated by the pure rotational transitions of H 2, including the 0 0 S(4) 8.0 m to 0 0 S(13) 3.8 m transitions, which lie 3400 to more than 15,000 K above the ground state. Shocks become more oblique and weaker as one moves from the tip to the wings. Thus, the shorter wavelength bands probe the upper rotational states, which require progressively higher postshock temperatures for excitation. Third, the IRAC images exhibit a remarkable set of filaments that run diagonally across the face of the shock from the southeast to the northwest, giving the impression of a helical twist. The impact of a north-to-south flow on an east-west density gradient may have triggered an instability resulting in the formation of diagonal filaments. Alternatively, a skewed magnetic field may have imposed this filament orientation. Polarization orientation vectors measured by Whittet et al. (1994) and McGregor et al. (1994) indicate that the average magnetic field near HH 49/50 is oriented southeast-northwest, roughly parallel to the IRAC filaments. Thus, the apparent twist in the shocks may be a consequence of the interaction of the flow with the magnetic field. The eastern rim of this bow shock is brighter than the western rim in H and [S ii]. This can be readily explained by the magnetic field orientation in the context of the models of Smith (1991). In this geometry the flow vectors are relatively close to parallel to the field lines on the eastern side of the shock but roughly perpendicular on the western side. On the eastern side gas can slide along the field lines and pass through a hard shock on collision with slower moving material without compressing the magnetic field. A strong radiative shock will result in large compressions, relatively high excitation, and large emission measures. On the western side the magnetic field is compressed, resulting in weaker shocks and lower excitation conditions and emission measures. The northern lobe of the Cha-MMS1 outflow, which must be blueshifted, only contains two faint HH objects, the north-facing bow shocks HH 924A and 924B, located on the opposite side of HH 49/50 with respect to Cha-MMS1. The absence of H 2 emission and the low surface brightness of HH 924 may indicate that outflowing material is interacting only with very low density gas in the northern blueshifted outflow from Cha-MMS1. 5. DOES THE CHA-MMS1 FLOW EXTEND FARTHER? It is interesting to note that HH 907, located 1 south of Cha- MMS1 (Wang & Henning 2006), and HH 51, located 1 north, lie within 3 of a straight line running through Cha-MMS1. HH 912 near Ced 112 also lies within 1 of this line. HH 933 also lies close to a line connecting Cha-MMS1, HH 912, and HH 51. The binned difference images show that HH 912 has a faint trail of H emission extending south along this line. Furthermore, the morphology of HH 912 is consistent with a bow shock moving toward the north, parallel to this line. The Spitzer IRAC band 2 (4.5 m) images show a pronounced north-facing bow shock a few arcseconds north of HH 912. This emission is probably generated by shock-excited H 2. The morphology of HH 912 is consistent with a north-moving, lowdensity flow plowing into a higher density molecular medium. In this interpretation, the IRAC band 2 emission traces a lowvelocity forward shock where H 2 is excited. The reverse shock, where the lower density flow is decelerated in a fast shock, is traced by H and [S ii] emission. This shock structure, combined with the very faint H trail extending south, requires that the driving source of HH 912 be located to the south. The most likely location is in the Ced 110 region. If HH 907 and 912 are part of a giant outflow from Cha-MMS1, this flow would be 2 (5.8 pc) in extent as seen in projection. Assuming an average proper motion of 100 km s 1, the dynamical age of this giant flow would be about 2:8 ; 10 4 yr, somewhat longer than the canonical age of a typical Class 0 protostar but less that the duration of the Class I phase. If these objects are indeed part of one giant flow, HH 912 and 51 are predicted to be blueshifted and HH 907 is predicted to be redshifted. Future spectroscopy and proper-motion measurements will provide a test for this giant outflow hypothesis.