Star Formation in the Milky Way. Matthew S. Povich Guest Lecture, Astro November 2011

Size: px

Start display at page:

Download "Star Formation in the Milky Way. Matthew S. Povich Guest Lecture, Astro November 2011"

Gwendolyn Henry
7 years ago
Views:

1 Star Formation in the Milky Way Matthew S. Povich Guest Lecture, Astro November 2011

2 Why do spiral arms look like this?

Overview of Observational Star Formation Tracers in the Milky Way and External Galaxies Extragalactic (see Kennicutt 1998) Broadband UV/optical colors Optical/near-IR recombination lines (and

3 Overview of Observational Star Formation Tracers in the Milky Way and External Galaxies Extragalactic (see Kennicutt 1998) Broadband UV/optical colors Optical/near-IR recombination lines (and forbidden lines) IR continuum (alone or combined with Hα; Calzetti et al. 2007; Kennicutt et al. 2009) Galactic Thermal radio continuum (Smith, Biermann, & Mezger 1978; Schraml & Mezger 1982; Murray & Rahman 2010) Global IR continuum (Misiriotis et al. 2006) Supernova/nucleosynthesis rate (Diehl et al. 2006) Young stellar object counts (Robitaille & Whitney 2010, Davies et al. 2011) NGC 1566 optical NGC 1566 mid-ir

4 Why Is the Milky Way Hard to Study?

6 The Milky Way Galaxy: Our Best Guess

Molecular Gas: Raw Materials +30 +30 Beam +20 +10 +10 Galactic Latitude +20 0 0 10 10 20 20 30 30 180 170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 0 350 340 330 320 310 300 290 280 270

7 Molecular Gas: Raw Materials Beam Galactic Latitude Galactic Longitude Ursa Major CTA-1 G S212 W3 NGC7538 Cas A Tau-Per-Aur Complex a W51 f 120 r m ar Ri x p a r Carin a Ar m e r s FIG. 2. Velocity-integrated CO map of the Milky Way. The angular resolution is 9 over most of the map, including the entire Galactic plane, but is lower (15 or 30 ) in some regions out of the plane (see Fig. 1 & Table 1). The sensitivity varies somewhat from region to region, since each component survey was integrated individually using moment masking or clipping in order to display all statistically significant emission but little noise (see 2.2). A dotted line marks the sampling boundaries, given in more detail in Fig. 1. S i n g 1.0 log T mb dv (K km s 1 ) 180 ng e u +260 s A Vela r +240 m CMa OB1 Maddalena s Mon Gem Cloud OB1 OB1 Carina Tangent S Centaurus Tangent n d in g A rm 60 A R 240 P E r O u t e S. Ori Filament Gem OB1 Rosette λori Ori A & B 300 Fa ul c m A r 120 ec p 180 ol k e r s e u s W44 Aquila Rift Cyg X Cas A Mon R P W3 W51 W50 Gum Nebula Chamaeleon 0 Galactic Longitude Cyg OB7 Mon OB1 CMa OB1 Orion Complex 60 Lindblad Ring & Local Arm Vela Carina Nebula G317 4 R CrA M S235 Coal Sack Galactic Center Scutum Tangent Sagittarius Tangent S147 Maddalena s Cloud Lupus Aquila Rift t W44 Aquila South i R t Pegasus 180 LSR radial velocity ( km s 1 ) Hercules e Lacerta Per OB2 20 r Cyg OB7 Cyg X Disk S147 S235 0 Ophiuchus Nuclear Galactic Latitude Polaris Flare Cepheus Flare Cam Norma Tangent 0 Galactic Longitude Resolution LSR radial velocity ( km s 1 ) Galactic Longitude Galactic Longitude Dame, Hartmann, & Thaddeus (2001) log T mb db 0.0 (K arcdeg) FIG. 3. Longitude-velocity map of CO emission integrated over a strip ~4 wide in latitude centered on the Galactic plane (see 2.2) a latitude range adequate to include essentially all emission beyond the Local spiral arm (i.e., at v > 20 km s 1). The map has been smoothed in velocity to a resolution of 2 km s 1 and in longitude to a resolution of 12. The sensitivity varies somewhat over the map, since each component survey was integrated individually using moment masking at the 3-σ level (see 2.2)

8 Dust: The Galactic Bolometer 1.2 µm 2.2 µm 60 µm 100 µm 140 µm 240 µm Data: COBE/Diffuse Infrared Background Explorer Models: Misiriotis et al. (2006)

9 Ionized Gas: Counting Far-UV Photons H-alpha fails in the Galaxy thanks to high extinction. Thermal radio continuum observations trace free-free (Bremsstrahlung) emission from ionized gas, and hence Lyman continuum (<912 Å) photon rates. The conversion from Lyman continuum photon rates to star formation rates requires models of massive star properties and the stellar initial mass function (IMF). Beware of systematics! WMAP data, Murray & Rahman (2010)

11 OK, Since It s So Hard to Study the Milky Way, Why Bother?

12 It s the resolution, Stupid!

r 4 14 Narrow-band visual images by John Gleason, http://jpgleason.zenfolio.com/ ~2 x2 D ~ 2.3 kpc, 10 ~ 6.7 pc.

13 r 4 14 Narrow-band visual images by John Gleason, ~2 x2 D ~ 2.3 kpc, 10 ~ 6.7 pc. The Great Nebula in Carina Carina is a starburst region, an example of the large-scale star formation seen in starburst galaxies. Carina contains at least 200 O and early-b stars, including the prototype O2 I star, +WRs +Eta Car. 4

14 Hubble Space Telescope ~6 12 mosaic of the Great Nebula in Carina

15 Hubble Space Telescope image of Herbig-Haro jets and pillars in the Carina Nebula

16 A low-mass star like the Sun High-mass stars ionizing H II regions

17 The Initial Mass Function In star-forming galaxies, the light comes from massive stars but the mass is in low-mass stars! Chomiuk & Povich (2011) Published uncertainties of ~0.3 on the high-mass, power-law slope of the IMF translate into factors of ~2 uncertainty on star formation rates (SFRs).

18 Is the intermediate-mass IMF actually Salpeter s? 2 1 Γ Star-forming Field Clusters Associations Salpeter Kroupa (2002) Chabrier (2005) Stellar mass (M ) Bastian, Covey & Meyer (2010) ARA&A

19 Treat Galactic H II regions as single sources by extracting flux densities from IR survey images. Then measure IR luminosities (biggest uncertainty is the distance to each region). Plot SFR derived from X-ray + IR star counts against equivalent Spitzer/MIPS 24 µm luminosity. Note the significant, systematic discrepancy between this relation and the Calzetti et al. (2007) extragalactic calibration (dashed line). Chomiuk & Povich (2011)

20 The Future of Galaxy-Wide Star Formation Studies Link resolved stellar population studies to global star formation activity (Robitaille & Whitney 2010, Chomiuk & Povich 2011). Recent revival of interest in measuring starformation laws in the (very local) Milky Way (Heiderman et al. 2010, Lada et al. 2010).

NGUYEN LUONG QUANG. Président du jury: J. Le Bourlot Rapporteurs: H. Beuther, T. Moore Examinateurs: I. Bonnell, F. Boulanger, F. Combes, F.

NGUYEN LUONG QUANG. Président du jury: J. Le Bourlot Rapporteurs: H. Beuther, T. Moore Examinateurs: I. Bonnell, F. Boulanger, F. Combes, F. NGUYEN LUONG QUANG Supervisors: Frédérique Motte (CEA Saclay) Marc Sauvage (CEA Saclay) Président du jury: J. Le Bourlot Rapporteurs: H. Beuther, T. Moore Examinateurs: I. Bonnell, F. Boulanger, F. Combes,