Impact of Molecular Gas on the Mass Models of Nearby Galaxies

Transcription

1 Netherlands Institute for Radio Astronomy Impact of Molecular Gas on the Mass Models of Nearby Galaxies Frank, de Blok, Walter, Leroy and Carignan, 2015 submitted* PHISCC 2015 ASTRON is part of the Netherlands Organisation for Scientific Research (NWO) 1 *finally XP

2 Multiwavelength studies of the ISM in Nearby Galaxies Wishlist #11 What are the prospects for synergy between HI surveys and blind surveys of other ISM tracers (e.g., dust continuum and CO line emission)? Focus on resolved studies of Nearby Galaxies HI: THINGS (VLA), Walter et al CO: HERACLES (IRAM 30m), Leroy et al Stars/Dust SINGS (Spitzer), Kennicutt et al KINGFISH (Herschel), Kennicutt et al Environment, Star Formation, X-Factor, Dynamics The first comprehensive set of mass models inclusive of molecular gas

3

4 THINGS/HERACLES From Erwin de Blok s Talk THINGS: The HI Nearby Galaxy Survey (Walter et al. 2008) VLA B, C & D 1.4 GHz, δv ~ 5km/s, θ ~ galaxies, various morphologies; 19 Galaxies - Dynamical Analysis (de Blok et al. 2008) HERACLES: HEterodyne Receiver Array CO Line Extragalactic Survey (Leroy et al. 2009) IRAM 30m Dish at Pico Veleta, HERA Multipixel Feed CO (J=2-1), 230 GHz, δv = 2.6 km/s, θ = Galaxies; 12 Galaxies Overlap with THINGS for Dynamical Analysis (present work)

5 Velocity Fields IWM her 3 CO-3.6μm HI-CO

6 Profiles vs Rotation Curves

7 The Molecular Gas Mass Surface Density and αco Molecular Gas Mass Surface Density M pc 2 H2 = CO I CO CO Luminosity Kkms 1 Conversion Factor for CO J=2 1 line Milky Way: Sandstrom et al Use KINGFISH, HERACLES and THINGS data to calculate radial conversion factor D2G Also includes correction for Helium MW =6.3 M pc 2 (K km s 1 ) 1

8 Solving for DGR and α Dust? D Atomic Gas Leroy et al. 2011, Sandstrom et al Assumptions Dust and gas is well mixed Dust to Gas Ratio (DGR) is not a function of atomic/molecular phase Fraction of ionized gas is negligable ΣD - Dust mass surface density Draine 2007, Draine & Li 2007, SINGS, KINGFISH ΣHI - HI mass surface density THINGS DGR = HI + CO I CO? Molecular Gas ICO - CO Intensity HERACLES Sandstrom et al doi: / x/777/1/5

9 Radially Varying αco NGC 4736 Dust HERSCHEL KINGFISH HI VLA-THINGS CO IRAM- HERACLES D DGR = HI + CO I CO Sandstrom et al doi: / x/777/1/5

10 Radially Varying αco H2 = CO I CO

11 Molecular Gas Surface Density vs Stars vs HI HI is flat, depression in the centre. Stars: 1- or 2-component mass surface distribution. Molecular gas distributed similar to stars. Choice of α CO makes a substantial difference to H 2 mass surface density. Stars H 2 with α D2G H 2 with α MW NGC 3198 HI

12 Mass Models V 2 obs = V 2 g,a + V 2 g,m + V 2 + V 2 halo Observed Atomic Gas Predicted (HI, THINGS) Stars Predicted (3.6μm, SINGS) Molecular Gas Predicted (H 2, HERACLES) Dark Matter Fitted Rotation Curves from Dark Matter Models ISO NFW V (R) = apple 4 G 0 R 2 c 1 apple ln(1 + cx) V (R) =V 200 x[ln(1 + c) R c R arctan R R c cx/(1 + cx) c/(1 + c)] 1/2 1/2

13 NGC 3521: Mass Models

14 NGC 5055: Mass Models

15 NGC 3521 and NGC 5055

16 Mass Models Parameters ISO NFW

17 Conclusions Resolved studies of nearby galaxies with THINGS, HERACLES, SINGS and KINGFISH: Determine a radial dependent X-factor for each galaxy. CO can fill in the inner part of the rotation curve. Molecular gas can make a substantial contribution to the mass budget. Need a larger sample to reduce uncertainty in X-factor High inclination, overestimation of α CO, so molecular gas contribution is maximized. Outer parts of galaxies: α CO poorly constrained Also subject to uncertainties in M/L (yipes!) Assumed a Kroupa IMF What are the prospects for synergy between HI surveys and blind surveys of other ISM tracers (e.g., dust continuum and CO line emission)? Prospects are good, but multiwavelength synergies are essential for understanding the ISM and evolution of galaxies. Nearby galaxies are the important laboratory for studying the ISM and dynamics.