THE STAR FORMATION NEWSLETTER

An electronic publication dedicated to early stellar/planetary evolution and molecular clouds

No. 244 7 April 2013 Editor: Bo Reipurth (reipurth@ifa.hawaii.edu)

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The Star Formation Newsletter

Editor: Bo Reipurthreipurth@ifa.hawaii.edu

Technical Editor: Eli Bresserteli.bressert@csiro.au

Technical Assistant: Hsi-Wei Yenhwyen@asiaa.sinica.edu.tw

Editorial Board

Joao AlvesAlan Boss

Jerome BouvierLee Hartmann

Thomas HenningPaul Ho

Jes JorgensenCharles J. Lada

Thijs KouwenhovenMichael R. MeyerRalph Pudritz

Luis Felipe RodrguezEwine van DishoeckHans Zinnecker

The Star Formation Newsletter is a vehicle forfast distribution of information of interest for as-tronomers working on star and planet formationand molecular clouds. You can submit materialfor the following sections: Abstracts of recentlyaccepted papers (only for papers sent to refereedjournals), Abstracts of recently accepted major re-views (not standard conference contributions), Dis-sertation Abstracts (presenting abstracts of newPh.D dissertations), Meetings (announcing meet-ings broadly of interest to the star and planet for-mation and early solar system community), NewJobs (advertising jobs specifically aimed towardspersons within the areas of the Newsletter), andShort Announcements (where you can inform or re-quest information from the community). Addition-ally, the Newsletter brings short overview articleson objects of special interest, physical processes ortheoretical results, the early solar system, as wellas occasional interviews.

Newsletter Archivewww.ifa.hawaii.edu/users/reipurth/newsletter.htm

List of Contents

Interview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

My Favorite Object . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Perspective . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Abstracts of Newly Accepted Papers . . . . . . . . . . 13

Abstracts of Newly Accepted Major Reviews . 40

Dissertation Abstracts . . . . . . . . . . . . . . . . . . . . . . . . 41

New Jobs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

New and Upcoming Meetings . . . . . . . . . . . . . . . . . 44

Cover Picture

A view of the central part of the Carina complex,from a near-infrared JHK mosaic of HAWK-I im-ages obtained at ESOs VLT. The bright clusterto the upper left is Trumpler 14; this is the second-richest cluster in the region after Trumpler 16 whichis associated with Eta Carinae. The large clusterto the right in the image is pointing towards Trum-pler 14, while the other cloud structure face Trum-pler 16 outside the image and towards the lowerleft. Courtesy ESO/T.Preibisch.

High resolution jpg files of the entire Carina clusterregion can be downloaded fromhttp://www.eso.org/public/images/eso1208a/

Submitting your abstracts

Latex macros for submitting abstractsand dissertation abstracts (by e-mail toreipurth@ifa.hawaii.edu) are appended toeach Call for Abstracts. You can alsosubmit via the Newsletter web inter-face at http://www2.ifa.hawaii.edu/star-formation/index.cfm

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My Favorite ObjectThe Carina Nebula Complex

Thomas Preibisch

Most stars form in rich stellar clusters or associations, andtherefore close to high-mass (M > 20M) stars. Evenour solar system seems to have formed in such an envi-ronment, where nearby massive stars had an importantimpact on the early evolution of the solar nebula. The hotand luminous O-type stars in massive star-forming regionsprofoundly influence their environments by creating HIIregions, generating wind-blown bubbles, and exploding assupernovae. This feedback can disperse a large fractionof the original molecular clouds, out of which the starsformed, and thus may terminate the star formation pro-cess. On the other hand, cloud compression provided byionization fronts and expanding wind bubbles may alsotrigger the formation of new generations of stars in thecompressed clouds. The detailed balance of these two op-posing processes determines the global evolution, i.e. thestar formation history and the resulting star formation ef-ficiency. However, the involved physical processes are notyet well understood and it is still debated whether themassive star feedback is more or less important than theprimordial turbulence in the clouds, and how efficient thetriggering of star formation can actually be. These ques-tions are also of fundamental importance for understand-ing the star formation process in (extragalactic) starburstregions, where the number of very massive stars is (much)higher than in the largest Galactic star forming regions.

A major observational problem for studies of massive starfeedback results from the fact that the nearby star formingregions, which can be easily studied at high spatial resolu-tion, host (at most) very small numbers of high-mass stars;therefore, the level of feedback is orders of magnitudessmaller than in extragalactic starburst regions. Regionshosting significant numbers of very massive (M 50M)stars (which dominate the feedback) are usually too faraway to allow detailed studies of small-scale cloud struc-tures or to detect their full stellar populations.

The Carina Nebula is an ideal target in this respect: ata moderate and well known distance of 2.3 kpc, it rep-resents the nearest southern region with a large enoughpopulation of massive stars ( 70 O-type and WR stars)to sample the top of the IMF. Most of the massive starsin the Carina Nebula reside in one of several loose clusterswith ages ranging from

mation about stellar properties. Deep near-infrared dataare essential for a determination of individual stellar (andcircumstellar) parameters, but such data existed only fora few selected small parts in the inner Carina Nebula re-gion; a deep and comprehensive wide-field near-infraredsurvey was obviously missing.

When the Chandra Carina Complex Project was planned,the new near-infrared wide-field imager HAWK-I for theESO 8m Very Large Telescope was just being commis-sioned. From discussions with Hans Zinnecker and MarkMcCaughrean I realized that HAWK-I would be the per-fect instrument to obtain the required deep wide-field sur-vey data. Our proposal for observing time was successfuland in January 2008 a mosaic of 24 contiguous HAWK-I fields was observed as part of the scientific verificationprogram. Our HAWK-I survey of the Carina Nebula (seePreibisch et al. 2011c for a detailed description and theESO Photo Release1 for images) covered a total area of1280 square-arcminutes. All data were processed and cali-brated by the Cambridge Astronomical Survey Unit. Witha detection limit of J 23, H 22, and Ks 21our HAWK-I data represent the largest and deepest near-infrared survey of the Carina Nebula obtained so far. Morethan 600 000 point sources were detected, about 20 timesmore than the number of 2MASS sources in the same area.

Our HAWK-I images are deep enough to detect all starsin the Carina Nebula down to masses of 0.1M for agesup to 3 Myr and extinctions of AV = 15 mag. The verygood seeing conditions during our observations (FWHM 0.5) and the 0.106 pixel scale of HAWK-I resulted ina superb image quality and revealed numerous interest-ing cloud structures in unprecedented detail. One partic-ularly notable detection was an embedded young stellarobject with a circumstellar disk seen almost edge-on (seeFig. 1). As described in Preibisch et al. (2011b), our ra-diative transfer modeling showed that the central youngstellar object must be rather massive, most likely in therange 10 15M. The surrounding disk and envelope isvery large (with a diameter of about 7000 AU) and mas-sive ( 2M), and constitutes an interesting target forfurther detailed studies. Our modeling of another pecu-liar nebulosity is described in Ngoumou et al. (2013).

Matching the HAWK-I point-sources to the Chandra X-ray source catalog yielded infrared counterparts for 6636X-ray sources. This strongly increased the number ofknown infrared counterparts to the Chandra sources (inthe common field-of-view), from just 33.9% based on 2MASSto 88.8% with HAWK-I. It provided the basis for a de-tailed characterization of the X-ray selected population ofyoung stars, as described in Preibisch et al. (2011a). Wefound that the number of X-ray detected low-mass starsis at least as high as expected from the number of known

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Figure 1: RGB composite image of the disk object in theCarina Nebula, constructed from the Ks-, H-, and J-bandHAWK-I images. The bright bluish point-source left of thecenter is an unrelated (foreground?) star. See Preibischet al. (2011b) for further information.

high-mass stars and scaling by the field star IMF. Thisimplies that there is clearly no deficit of low-mass stars inthe Carina Nebula Complex. Our analysis of the K-bandluminosity function of the X-ray selected Carina membersalso showed that (at least down to the X-ray detectionlimit around 0.5M) the shape of the IMF in the CarinaNebula is consistent with that in the field IMF. This is rel-evant because some observational studies of massive starforming or starburst regions (including earlier studies ofthe Carina Nebula) had claimed to see a truncated IMFand a corresponding deficit of low-mass stars; our datashow no indication of such an effect.

We also found that the fraction of near-infrared excesssources (i.e. a proxy of disk-bearing young stars) in theindividual clusters in the Carina Nebula is considerablylower than typical for nearby, less massive clusters of sim-ilar age. This suggests that the process of circumstellardisk dispersal proceeds on a faster timescale in the CarinaNebula than in the more quiescent regions, and is mostlikely the consequence of the very high level of massivestar feedback in the Carina Nebula.

Further important information about the young stars inthe Carina Nebula was obtained in the analysis of Spitzerobservations of the complex (Smith et al. 2010b; Povichet al. 2011). In combination, these X-ray, near-, and mid-infrared surveys have strongly boosted our knowledge ofthe young stellar populations in the Carina Nebula Com-plex (see also Preibisch 2011).

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In order to investigate the interaction of the stars and thesurrounding clouds, detailed information on the structureand the physical properties of the clouds is needed. Whilethe available Spitzer and MSX maps showed the surfacestructure of the clouds and traced the warm gas, the bulkof the cloud mass is inside denser and colder structures,and can only be observed at longer wavelengths. All far-infrared/sub-mm or radio data sets existing at that timehad either too poor angular resolution to reveal detailsin the cloud structure, or covered only small parts of thelarge Carina Nebula Complex. Therefore, we performedcomprehensive wide-field surveys of the clouds in the far-infrared and sub-mm regime as another major part of ourmulti-wavelength project.

As a first step to meaningfully complement the extraor-dinary quality of the recent X-ray, optical, and infrareddata sets, I started a collaboration with Karl Menten andFrederic Schuller from the Max Planck Institute for Ra-dio Astronomy in Bonn to obtain a deep wide-field sub-mm survey with LABOCA at the APEX telescope. Our1.21.2 LABOCA map provided an unprecedented viewof the cold, dense clouds in the Carina Nebula Complexat an angular resolution of 18, corresponding to phys-ical scales of 0.2 pc. An impressive comparison of thesub-mm and optical appearance of the cloud complex canbe seen in an ESO Photo Release2. Our analysis of theLABOCA data (see Preibisch et al. 2001d) showed thatthe cold dust in the complex is distributed in a wide va-riety of structures, from the very massive ( 15 000M)and dense cloud to the west of the stellar cluster Tr 14,over several clumps of a few hundred solar masses, to nu-merous small clumps containing only a few solar massesof gas and dust. Most clouds show clear indications thattheir structure is shaped by the very strong ionizing radi-ation and possibly the stellar winds of the massive stars.The total mass of the dense clouds to which LABOCAis sensitive was found to be 60 000M. There is thusclearly still a large reservoir of dense clouds available forfurther star formation. An analysis of the clump massspectra is described in Pekruhl et al. (2013).

While LABOCA was the perfect instrument to map thedense and cold cloud clumps, it is less sensitive to thesomewhat warmer and more diffuse gas at the surfaces ofthe irradiated clouds and in the inner regions of the Ca-rina Nebula, where the original clouds have already beenlargely destroyed by the feedback of the massive stars.The Herschel observatory is ideally suited to map thefar-infrared emission from this slightly warmer gas and toprovide a complete inventory of the cloud structures. Wetherefore used SPIRE and PACS onboard of Herschel tomap the full spatial extent (more than 5 square-degrees)of the entire Carina Nebula Complex at wavelengths be-

2http://www.eso.org/public/news/eso1145/

Figure 2: Color composite of a 2.5 2.7 re-gion of our Herschel 70m (blue), 160m (green),and 250m (red) maps. This image was createdfor the ESA Science & Technology website releasesci.esa.int/science-e/www/object/index.cfm?fobjectid=50414.The bubble-like cloud complex in the upper right part isthe Gum 31 region.

tween 70m and 500m. Our Herschel maps (see Fig. 2)revealed the small-scale structure of the clouds in unprece-dented details and allowed us to determine the temper-atures and column densities (see Preibisch et al. 2012).A detailed study of the physical parameters of individ-ual cloud structures and the cloud mass budget was re-cently completed (Roccatagliata et al. 2013). We foundthat most clouds have temperatures ranging from about20 K (in the dense clumps) up to 35 40 K (for cloudsclose to massive stars). The total cloud mass above theAV 1 mag threshold is about 500 000M. Consideringthat the strong feedback from massive stars is dispersingthe cloud complex since several Myr, this a remarkablylarge value. We could also quantify the level of the ra-diative feedback from the hot stars and found that theintensity of the FUV irradiation at most cloud surfacesis at least about 1000 times stronger than the galacticaverage value (the so-called Habing field). This level ofirradiation is very similar to the observed FUV intensitiesin the 30 Dor region or in the starburst nucleus of M82.

The Herschel maps furthermore revealed over 600 point-like sources, most of which are embedded protostars. Ouranalysis (see Gaczkowski et al. 2013) of their luminosi-

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ties and masses (estimated from radiative transfer simula-tion of the observed spectral energy distributions) yieldedthe remarkable result that all these objects seem to below- or intermediate-mass protostars (M 10 15M);no highly luminous (L 10

4L), i.e. high-mass (M 20M) young stellar objects are seen in our maps. Thisabsence of high-mass protostars is remarkable, given thepresence of large numbers ( 70) of high-mass stars in the(few Myr old) optically visible young stellar population inthe Carina Nebula.

Our analysis of the spatial distribution of the Herschel -detected protostars showed that they are strongly concen-trated along the edges of irradiated clouds. A very similarresult had been found in our previous investigation of jet-driving protostars (Ohlendorf et al. 2012). This suggeststhat the currently forming generation of stars in the Ca-rina Nebula Complex is predominantly triggered by thefeedback from the numerous massive stars in the severalMyr old generation. These findings provide strong obser-vational support for the model of triggered star formationin the irradiated pillars that was suggested by Smith etal. (2010b). The current star formation activity is thuslargely restricted to the surfaces of the numerous individ-ual pillars.

As the sample of Herschel detected protostars traces theyoungest generation of currently forming stars in the Ca-rina Nebula, we could also estimate the current star forma-tion rate in the complex. The value of 0.017M/yearwe derived is very similar to the average star formationrate over the last few Myr, that was determined by Povichet al. (2011). This shows that the Carina Nebula Complexalone is responsible for as much as about 1 percent of thetotal star formation rate of our entire Galaxy, emphasizingonce again the importance of this star forming region.

Numerous further interesting aspects of the Carina NebulaComplex still remain to be explored. We have recently be-gun to extend our studies of the young stellar populationsto the Gum 31 HII region at the north-western edge of theCarina Nebula (see Fig. 2); first results are presented inOhlendorf et al. (2013). We also have performed new X-ray and infrared observations to improve the spatial com-pleteness of our studies of the young stellar population.

Detailed observations of the small-scale structure of indi-vidual cloud pillars constitute another current topic of ourongoing work. The direct comparison of these data withsophisticated numerical models (see, e.g., Gritschneder etal. 2010; Ercolano et al. 2012) will provide new insight intothe formation and evolution of pillars and their gravita-tional collapse into stars and stellar clusters. To conclude,the Carina Nebula will certainly keep us busy for the nextseveral years.

I would like to thank several colleagues for discussions andadvice that was important for the success of this project,particularly Hans Zinnecker, Mark McCaughrean, KarlMenten, Frederic Schuller, and Silvia Leurini. I also wouldlike to name the Postdocs, PhD- and Master-students inmy group at the University of Munich who have been(or are still) contributing to the different analysis steps:Thorsten Ratzka, Veronica Roccatagliata, Stephanie Pekruhl,Henrike Ohlendorf, Judith Ngoumou, Benjamin Gaczkowski,Max Mehlhorn, Peter Zeidler, Caroline Hebinck, TiagoGehring, and Benjamin Kuderna.

Finally, I want to acknowledge funding for various aspectsof this project by the German Science Foundation (DFGPR569/9-1). The analysis of the Herschel data was fundedby the German Federal Ministry of Economics and Tech-nology through the DLR grant number 50 OR 1109. Addi-tional support came from funds from the Munich Clusterof Excellence: Origin and Structure of the Universe.

References:

Broos, P., Townsley, L., Feigelson, E.D., et al. 2011, ApJS, 194, 2Ercolano, B., Dale, J. E., Gritschneder, M., et al. 2012, MNRAS,420, 141Feigelson, E.D., Getman, K.V., Townsley, L., et al. 2011, ApJS, 194,9Gaczkowski, B., Preibisch, T., Ratzka, T., Roccatagliata, V., Ohlen-dorf, H., Zinnecker, H., 2013, A&A, 549, A67Gritschneder, M., Burkert, A., Naab, T. et al. 2010, ApJ, 723, 971Ngoumou, J., Preibisch, T., Ratzka, T., Burkert, A., 2013, ApJ,submittedOhlendorf, H., Preibisch, H., Gaczkowski, B., Ratzka, T., Grell-mann, R., McLeod, A., 2012, A&A, 540, A81Ohlendorf, H., Preibisch, T., Gaczkowski, B., Ratzka, T., Ngoumou,J., Roccatagliata, V., Grellmann, R., 2013, A&A, 552, A14Pekruhl, S., Preibisch, T., Schuller, F., Menten, K., 2013, A&A, 550,A29Povich, M.S., Smith, N., Majewski, S.R., et al. 2011, ApJS 194, 14Preibisch, T., 2011, Reviews in Modern Astronomy, (ed. R. vonBerlepsch), Vol. 23, p. 223Preibisch, T., Hodgkin, S., Irwin, M., et al. 2011a, ApJS, 194, 10Preibisch, T., Ratzka, T., Gehring, T. et al. 2011b, A&A, 530, A40Preibisch, T., Ratzka, T., Kuderna, B., et al. 2011c, A&A, 530, A34Preibisch, T., Schuller, F., Ohlendorf, H., Pekruhl, S., Menten, K.M.,Zinnecker, H., 2011d, A&A, 525, A92Preibisch, T., Roccatagliata, V., Gaczkowski, B., Ratzka, T., 2012,A&A, 541, A133Roccatagliata, V., Preibisch, T., Ratzka, T., Gaczkowski, B., 2013,A&A, submitted (arXiv:1303.5201)Smith, N., & Brooks, K. J. 2008, Handbook of Star Forming Re-gions, (ed. B. Reipurth), Volume II, 138Smith, N. 2006, MNRAS, 367, 763Smith, N., Egan, M.P., Carey, s., et al. 2000, ApJ 532, L145Smith, N., Bally, J., & Walborn, N.R. 2010a, MNRAS, 405, 1153Smith, N., Povich, M. S., Whitney, B. A., et al. 2010b, MNRAS,406, 952Townsley, L., Broos, P., Corcoran, M.F., et al. 2011, ApJS, 194, 1

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