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Science with ALMA: a new era for Astrophysics 13 - 17 November 2006 Madrid, Spain. Fig.1. Fig.2. 24 m m 70 m m. Fig.3. 24 m m 70 m m. 70 m m 24 m m. Fig.5. Fig.4. 70 m m 24 m m. 70 m m 24 m m. Resolving the dust emission in the Vela Molecular Ridge

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slide1

Science with ALMA: a new era for Astrophysics

13 - 17 November 2006

Madrid, Spain

Fig.1

Fig.2

24 mm

70 mm

Fig.3

24 mm

70 mm

70 mm

24 mm

Fig.5

Fig.4

70 mm

24 mm

70 mm

24 mm

Resolving the dust emission in the Vela

Molecular Ridge

M. De Luca(1,2),T. Giannini(2), D. Lorenzetti(2), D. Elia(3), G. Fazio(4),

M. Marengo(4), F. Massi(5), B. Nisini(2), H. A. Smith(4)

(1)Dipart. di Fisica - Università di Roma "Tor Vergata", (2)INAF - Oss. Astronomico di Roma, (3) Dipart. di Fisica - Università di Lecce, (4)Harvard Smithsonian Center for Astrophysics - MA (USA), (5)INAF - Oss. Astrofisico di Arcetri

Unresolved peaks

The Vela Molecular Cloud - D, located in the Vela Molecular Ridge (VMR-D, at 700 pc[1]), is a region characterized by high efficiency in producing both young embedded clusters and

Figures: 24(blue) and 70(red)mmimages of some unresolved dust peaks with overlaid contours of 1.2 mm emission (in green, from 3sin steps of 3s). The positions of IRAS and MSX point sources (cyan 3suncertainty ellipses) and a new 10.4 mm detection (magenta diamond in Fig.3, Timmi2-ESO) are shown as well.

and isolated stars and constitutes one of the best southern hemisphere sites to investigate low- to intermediate-mass star formation.

Our observations of the dust continuum emission (1.2 mm) of about 1 square degree with the SIMBA (SEST) bolometer array (24" HPBW), reveals a clumpy structure with 29 resolved (q > 24") and 26 unresolved (q < 24") peaks [2]. The majority of these latter (hereafter: umms), present clear signs of star formation activity, such as association with: (i) far infrared point sources (IRAS [3] -MSX [4]); (ii) near infrared sources with intrinsic excess evidenced by two colour diagrams; (iii) jet-like H2 emission (this topic is

is discussed in Giannini et al., this conference).

Therefore such peaks might represent real detections of faint compact mm emission and, hence, suitable candidates of low-mass star forming sites. As such, they deserve further investigation.

To better improve both sensitivity and resolution in the mid- far-infrared and to reconstruct the spectral energy distributions,

distributions, we observed these unresolved dust peaks with Spitzer-MIPS: here we present some interesting cases where point-like far infrared counterparts have been revealed.

Tab.1

Association of unresolved dust peaks with far infrared point sources

(IRAS, MSX point source catalogs and MIPS images).

  • What we learn from Spitzer-MIPS data
  • The association of IRAS and MSX point sources with 30% of the unresolved dust peaks (Tab.1) indicates the possible occurrence within them of star formation activity.
  • The MIPS observations highly increase (by a factor of 3) the dust peaks with associated counterpart (Tab.1). This should be taken into account when considering the percentage of dust peaks with associations reported in the literature (for our data the 1s sensitivity level is ~200 mJy at 24 mm, about 100 times bigger than the IRAS sensitivity).
  • - Occurrence of far infrared point sources within a radius

of 12" from the dust peak (SIMBA HPBW)

  • -Occurrence of far infrared point sources within a radius

of 24" from the dust peak (2 x SIMBA HPBW)

  • (?) - Uncertain association (bold faced if inside the SIMBA HPBW)
  • diff.- Diffuse emission (bold faced if inside the SIMBA HPBW)
  • When investigated with Spitzer, some IRAS objects have been revealed as multiple (Fig.1) or diffuse (Fig.2, 3), with major consequences in the ILF estimates.

References

[1] Liseau R., Lorenzetti D., Nisini B. et al. 1992 A&A 265, 577

[2] Massi F., De Luca M., Elia D. et al. 2006 A&A, submitted 399,14

[3]C.A. Beichman et al. 1988, Infrared Astronomical Satellite (IRAS)

Catalogs and Atlases, vol. 1, Explanatory Supplement

[4] Price, S.D.et al. 2001 AJ 121, 2819

  • The map resolution of the dust emission (24" corresponds to 0.08 pc at the estimated Vela distance) is not enough to determine both sizes and masses of these small structures. Higher resolution (sub-arcsec scale) and more sensitive millimeter maps of the reported peaks could be performed since the beginning of operation of ACA-ALMA,with a resulting significant improvement in the knowledge of the star formation picture of this region.
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