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Discovering Milky Way HII Regions

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Discovering Milky Way HII Regions Discovering Milky Way HII Regions Tom Bania Institute for Astrophysical Research Department of Astronomy Boston University GBT HRDS Green Bank Telescope HII Region Discovery Survey AO HRDS AreciBo OBservatory HII Region Discovery Survey SHRDS Southern HII Region Discovery Survey Milky Way H II Regions HII regions are zones of ionizeD gas surrounDing O anD B type stars (Masses > 8 M¤ ) l Lifetimes <10 Myr → Trace star formation at present epoch Emit at radio wavelengths via Bremsstrahlung (free-free) continuum and radio recomBination line (RRL) emission → Thermal plasma emission mechanisms Emit at infrared (IR) due to presence of dust → The Brightest oBjects in the Galaxy at radio and IR wavelengths! The signature of HII regions is a high IR anD raDio flux H II Regions anD Galaxies The GBT Galactic H II Region Discovery Survey T.M. Bania (Boston University), L. D. Anderson (West Virginia University) Dana S. Balser (NRAO), and RoBert T. Rood (University of Virginia) GBT HRDS CollaBorators NormalizeD to Age 30 Tom Bania (Boston University) Dana Balser (NRAO) BoB RooD (University of Virginia) Loren Anderson (West Virginia University) H II Region Surveys Eagle NeBula NGC 6611 M 16 S 49 RCW 165 Gum 83 “Pillars of Creation” POSS RaDio Continuum Surveys Dwingeloo 25 m telescope 1390 MHz Westerhout (1958) RaDio RecomBination Lines (RRLs) H109α Antenna Temperature Antenna Frequency HoglunD & Mezger (1965) RaDio Wavelength Sky Surveys Continuum surveys Began in the 1950s Recombination line surveys Began in the 1960s MPIfR W43 100 m 4.875 GHz Altenhoff et al., 1979 H II Region Evolution Photo-Dissociation Region PDR Ionizing source (O7 star) Ionized gas fills interior H II Region Case StuDies RGB à 8, 4.5, 3.6 microns RGB à 24, 8, 3.6 microns Spitzer IR MAGPIS 20cm (white contour) GRS 13CO (green contour) GBT H II Region Discovery Survey Coincident 24µ m and 20 cm Flux > 100 mJy @ 20 cm -16o < ! < + 67 o and -1o < b < 1o H87α - H93 α (8-10 GHz) HPBW ~ 80 arcsec Δν = 12 kHz (Δ v = 0.4 km s1- ) All HII regions ionizeD By a single O-type star within the Solar orBit GBT HRDS RRL Composite Spectra 5' GBT HRDS RRL Composite Spectra 5' HRDS H II Regions Map of Milky Way H II Regions 0.80 5 0.60 50 50o 0 0.40 40 40o 30 30o Number of HII Regions 20 20o Distance from Galactic Center (kpc) -5 0.20 -10 0.00 0 2 4 6 8 10 12 0 2 4 6 8 10 12 Distance from Galactic Center (kpc) Figure 7: Galactic Distribution of H II regions. The left panel shows the location of individual H II regions; HRDS sources are shown with triangles and previously known H II regions with assigned distances with crosses. In the right panel these positions are binned into 0.25 0.25 × kpc pixels, and the resultant image smoothed with a 5 5 pixel Gaussian filter. The straight × lines show the longitude range of our sample, 18 ◦ 65 ◦. The solid half-circle indicates − the tangent-point distance while the dotted half-circle shows the Solar orbit. The peaks in Figure 6 appear as the two prominant arcs of sources. monthly telecons. The first WISE data release, available now, covers only 57% of the sky. This primary ∼ data release, however, covers 75% of the Galactic plane. The final data release is scheduled ∼ to be in the spring of 2012. We have taken this data release schedule into account when preparing the plan of work although a delay in the final data release would likely extend our schedule. There are two major milestones: (1) the creation of the WISE H II region catalog, and (2) completion of the aperture photometry measurements. We estimate that the creation of the WISE H II region catalog will take one and a half years. Minor milestones within this timeframe will be (1) downloading the WISE data (less than one month), (2) searching all 13 Southern HII Region Discovery Survey ATCA Australia Telescope Compact Array Trey Wenger University of Virginia SHRDS Guru ATCA + CABB-CX CAAB-CX Compact Array BroaDBanD BackenD • Two 2 GHz wiDe BanDs can Be placeD anywhere between 4.1 and 10.4 GHz • Within these can place 32 ‘zoom BanDs’ that can have widths of either 64 MHz or 1 MHz • Zoom Bands have 2048 channels each Simultaneously observe 20 RRLs with 2 orthogonal polarizations Stacking these improves SNR ~ 5 x SHRDS Last HII region survey of Southern Sky was Caswell & Haynes (1987) using Parkes SHRDS will Discover ~ 500 HII regions Most will Be locateD at great Distances on the far side of the Galactic Centre beyond the Solar Orbit Outer Scutum – Centarus Arm L – V Plots are not to Be feareD: DON’T PANIC ! Milky Way HII Regions 180 150 120 II 90 60 30 I 0 -30 -60 Galactic Longitude (deg) IV -90 -120 -150 III -180 -200 -100 0 100 200 LSR Velocity (km s-1) This is a cartoon. It is not a model. It is not a map. + Sun Benjamin & Hurt have a lot to answer for …… FINIS Resolving the KDA with H I Absorption HI Emission/Absorption (HI E/A): Absorption of H II region emission by foreground H I l HI absorption up to HII region velocity→ Near l HI absorption up to tangent point velocity → Far See Kuchar& Bania (1994), Kolpak et al. (2002), Anderson & Bania (2009) Resolving the Kinematic Distance AmBiguity Near! &&&& = 7.4 km/s Far! Anderson & Bania (2009) H II Region Electron Temperatures TL −1.15 ∝ T e TC RRL anD free-free continuum emission in LTE at 3 cm Shaver et al. (1983) Te is a proxy for the neBular metallicity Electron Temperature DistriBution has Azimuthal Structure ! Sample : GBT + 140 Foot 330o ≤ Az ≤ 60o Contours : Range : 6400 −11200 K Interval: 400 K.
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