Nearby Galaxies (mostly) at mm and IR wavelengths

1. Nearby Galaxies (mostly) at mm and IR wavelengths Adam Leroy (MPIA Heidelberg) Christof Buchbender (IRAM Granada) Liberally plundering .ppt by: Eric Bell, Hans-Walter Rix, James Graham

2. Topics A Broad Look at Nearby Galaxies Nearby Galaxies at Millimeter Wavelengths Mapping Nearby Galaxies With the IRAM 30m Working Group: Mapping the bulk distribution of molecular gas in a bright nearby spiral galaxy.

3. A Broad Look at Nearby Galaxies • Goal: Briefly survey the components of galaxies, how these are observed, how they relate to one another, and how mm and IR observations fit into the picture. • Gloss over: nuclei (S.G-B.), detailed phase balance (C.K.), B. Fields (C.T.) • Specific Topics: • Why study nearby galaxies? • Key components of a galaxy and its ISM? Which are observable from the 30m? • What does the zoomed out SED of a galaxy look like? Where do IR and mm fit in? • Scaling relations in nearby galaxies and their relation to IR and mm work. • Apologies in advance (but not really): I’ve tried to stay IR and mm focused, but I may drift a bit into other wavelengths in the interests of a more complete cartoon.

4. Why Study Nearby Galaxies? • Galactic Star Formation • Nearby galaxies give you: • wider range of environments • zoomed out view / statistics • no distance ambiguity • easier to isolate a particular environment • … compared to the Milky Way. • Cosmology • Nearby galaxies give you: • spatial resolution • sensitivity, wavelength coverage • input for simulations • baseline for comparison • … compared to high z / simulation.

5. NGC 3627 NGC 3351 NGC 7793 NGC 2976 SINGS IRAC HST view of M64 HST view of M51 GALEX view of M81 swiped from A.P.o.D. & NASA heritage websites

6. VLA (HI) view of NGC 2403 F. Walter Spitzer view of the SMC K. Gordon et al. 30m Map of M63 HST view of M51 30m Map of M51 K. Schuster et al.

7. Cartoon Anatomy of A Galaxy Dark Matter Halo Hot Ionized Halo Gas Warm Ionized Gas Atomic Gas Young stars Molecular Gas Stellar Bulge Dust Stellar Disk

8. How To Study the Cartoon Anatomy Dark Matter Halo: kinematics Hot Ionized Halo Gas: X-Rays, Absorption Warm Ionized Gas: line emission, radio/mm-cont Atomic Gas: 21cm line, UV and radio absorption Young stars: UV, optical cont Stellar Disk and Bulge: Optical, NIR Molecular Gas: mm lines, (especially CO), UV absorption, dust Dust: IR emission, opt/UV absorption

9. Galaxy Components Observable with the 30m Dark Matter Halo: using kinematics traced by line emission Warm Ionized Gas: via mm free-free continuum Molecular Gas: using millimeter lines andmillimeter dust continuum Dust: via the millimeter continuum

10. Cartoon Breakdown of the ISM * In addition to these diagnostics, absorption against background sources from the UV to the radio is an incredibly powerful diagnostic of physical conditions in the ISM.

11. Cartoon Breakdown of the ISM * In addition to these diagnostics, absorption against background sources from the UV to the radio is an incredibly powerful diagnostic of physical conditions in the ISM.

12. Spectral Energy Distribution of A Galaxy • Right: SED of a massive, metal-rich star-forming galaxy (like ours): • energy ~ half optical (stellar black body), half IR (dust black body) … • shape ~ mix of black bodies (broad), and narrow features (lines) … • other shape at very long  (synchrotron, thin free free) … • mm and radio emission is a footnote (useful as a tracer of conditions). swiped from E. Bell

13. Spectral Energy Distribution of A Galaxy UV Optical near-IR mid-IR far-IR sub-mm • NGC 6822: A star-forming, low metal, low dust, low mass Local Group dwarf: • high UV relative to IR • high UV relative to optical / near-IR • low IR relative to optical / near-IR • Dominated by young star-light. • NGC 7331: A star-forming, metal-rich, low dusty, spiral galaxy (like the Milky Way): • low UV relative to IR • low UV relative to optical / near-IR • high IR relative to optical / near-IR • Dominated by reprocessed young star-light. Flux (log  Fn) • NGC 4594: A very early-type spiral (almost elliptical). • comparable UV and IR • low UV relative to optical / near-IR • low IR relative to optical / near-IR • Dominated by old starlight. 0.1 1 10 100 1000 Remember: mm & radio don’t carry appreciable energy! Dale+ 2007 Wavelength (m)

14. Turning the SED into Physical Information Near-IR Continuum: Stellar Mass Absorption: Dust mass (hard) Lines: As optical Optical Continuum and Absorption: Stellar Mass, Age, Metallicity Emission Lines: Warm Ionized Medium UV Continuum: Young Stars UV Absorption: HI, H2, metals

15. Turning the SED into Physical Information Millimeter Continuum: Dust, Ionized Gas Lines: Molecular Mass, Dens., Temp. Radio Continuum: SN Remnants, B Field Lines: HI Column Mid-IR Continuum: Hot/small dust Band Features: PAH modes Far-IR Continuum: Dust Lines: Atomic ISM Cooling Same galaxy, axes, longer wavelength range (from NED)

16. Scaling Relations “How galaxies are” … … these are basic observational facts about galaxies. Drive science …… how do scaling relations evolve with z?… what physics cause them? Affect observations; e.g., …… low metals means less dust, less CO… high mass means high CO/HI, red means little SF

17. Scaling Relations: Starlight and Dark Matter Meyer+ 2008 following Tully & Fisher 1977 Stellar Luminosity (left: B band, right: K band) Maximum Rotation Velocity (from HI profile) The stellar luminosity of a spiral galaxy is tightly correlated circular velocity: Circular velocity driven by the mass of the dark matter halo hosting the galaxy. So halo mass and galaxy mass are intimately related. Considering all baryons (not just stars) needed to make it work for low-mass galaxies.

18. Scaling Relations: Starlight and Dark Matter Jorgensen+ 1996 After Faber & Jackson 1976 Face On Velocity Dispersion Edge On Stellar Luminosity Ellipticals also show basic relations between star light and dark matter: “Fundamental plane” or Faber Jackson relation. Best-fit relation for ellipticals has three (rather than two) parameters.

19. Scaling Relations: Starlight and Dark Matter • Relation to Millimeter and IR astronomy: • Millimeter lines can be used to trace galaxy kinematics (and thus the dark matter distribution). • If you know the mass / optical magnitude of a galaxy, you can guess its line width with reasonable accuracy.* • If you know the line width of a galaxy from line observations, you can estimate its distance or at least check for consistency.* • Ellipticals, more ambiguous… • * With the caveat that CO is more compact than HI and may not trace the whole potential.

20. Scaling Relations: Size and Luminosity/Mass Galaxy Size (Optical) Scatter About Relation Stellar Mass The size of a galaxy (here stellar half-light) is a clear function of its mass.

21. Scaling Relations: Size and Luminosity/Mass • Relation to Millimeter and IR astronomy: • The size of the molecular gas disk is fairly tightly coupled to the size of the stellar disk. So this is is also (roughly) a way to guess the distribution of H2. • Exceptions: LIRG/ULIRGs and ellipticals tend to have central molecular disks with scales of hundreds of parsecs, not matched to stellar disk. • Why? Related to ability to build a stellar disk.

22. Scaling Relations: The Galaxy CMD Salim+ 2007 (following lots of SDSS stuff, e.g., Kauffmann, Blanton, Hogg) Red Red Blue Optical/UV Color Blue The galaxy population is strongly bimodal: Most galaxies are either blue star formers or “red and dead” (with a less populated “green valley” in between).

23. Scaling Relations: Mass and Star Formation Salim+ 2007 Star Formers Non-star Formers Star Formation per Stellar Mass Stellar Mass Star formation is largely a function of the stellar mass of a galaxy: Low-mass galaxies show more star formation per unit mass. More massive are bimodal, a mixture of red non-star formers and star formers.

24. Scaling Relations: Mass and Star Formation • Relation to Millimeter and IR astronomy: • The millimeter continuum (free free) and infrared (dust) continuum both allow us to measure the amount of recently formed stars without worrying about dust. Infrared is absolutely key to many current star formation tracers. • Millimeter lines are the most straightforward way to trace the star-forming ISM. Although it isn’t in this plot directly, tracing the distribution and evolution of gas in galaxies is key to understanding why galaxy populations have this basic behavior.

25. Scaling Relations: Mass and Metallicity Tremonti+ 2004 Lee, Bell, and Somerville 2008-2009 Metal Abundance (Gas Phase) Metal Abundance (Stellar) Stellar Mass Stellar Mass Low mass galaxies have less heavy elements relative to their mass: There is a strong relationship between stellar mass and heavy element abundance (gas phase & stellar) spanning many orders of magnitude.

26. Scaling Relations: Mass and Metallicity • Relation to Millimeter and IR astronomy: • The infrared continuum is a key tracer of the distribution of dust and the dust-to-gas ratio is intimately related to heavy element enrichment (e.g., you need dust to see IR!). • Along similar lines, millimeter line tracers of the ISM are key to robustly measure the dust-to-gas ratio in large systems. • CO (and other molecules) are known to be suppressed relative to other galaxy components at low metallicity. A robust guess as to the metallicity is helpful to plan observations. • In reverse: the effect of metallicity on the ISM and star formation is of considerable interest. This relation allows one to readily guess metallicity from mass.

27. Scaling Relations: Gas and Star Formation Kennicutt 1998 Stars Formed per Area per Time Gas (HI + H2) per Area More gas means more star formation for actively star-forming galaxies: Averages over galaxy disks yield a tight correlation between star formation rate and gas content.

28. Scaling Relations: Gas and Star Formation Wong & Blitz 2002 Bigiel+ 2008 Kennicutt+ 2007 CO per Area CO per Area Stars Formed per Area per Time Blue: HI Black & Green: CO HI per Area HI per Area Inside galaxy disks star formation correlates with CO (H2) more clearly than HI

29. Scaling Relations: Gas and Star Formation Wu et al. 2005 Gao & Solomon 2004 Galaxies Infrared Luminosity ~ Star Formation Rate Infrared Luminosity ~ Star Formation Rate Milky Way Cores Emission From High Density Molecular Gas Emission From High Density Molecular Gas Emission from dense gas (HCN) shows a linear correlation with star formation Even where the correlation between CO and star formation is non-linear

30. Scaling Relations: Gas and Star Formation • Relation to Millimeter and IR astronomy: • Both axes… IR is key to trace recent star formation (and mm can help). • Millimeter lines almost the exclusive tracer of molecular gas distribution. • Combinations of lines (ideally up to the sub-mm) can give physical conditions (density, temp.) in the H2. • It’s almost impossible to study the relationship between gas and star formation without integrally involving the IR and millimeter lines.

31. Scaling Relations: Radio and FIR Emission Yun+ 2001 Condon 1992 1.4 GHz (mostly nonthermal) Continuum Luminosity Infrared Luminosity (IRAS Satellite) (Non-thermal) Radio continuum luminosity correlates very tightly with IR luminosity

32. Scaling Relations: Radio and FIR Emission • Relation to Millimeter and IR astronomy: • The IR part of the “radio-IR” correlation. • Cartoon of star formation, supernova, cosmic rays, synchrotron implies a connection to star forming gas (but beware “conspiracies”)… mm lines may help address “why?”

33. Scaling Relations: Stellar Mass and Gas Roberts & Haynes 1994 HI Mass (21cm) per Stellar Luminosty (B-band) S0 S0a Sa Sab Sb Sbc Sc Scd Sd Sm Im Hubble Type Low Mass High Mass Low mass galaxies have more HI relative to stellar mass than high mass galaxies

34. Scaling Relations: Stellar Mass and Gas CO per Stellar Luminosty (B-band) Stellar Luminosity [Magnitudes] The ratio of H2 to stellar mass does not vary strongly in relatively massive galaxies

35. Scaling Relations: Stellar Mass and Gas Star Formation per Area per Time CO per Stellar Luminosty (B-band) Stellar Luminosity [Magnitudes] CO per Unit Area The ratio of CO to stellar mass or star formation does vary strongly at low metallicity Red circles: low mass, low metallicity galaxies But is this because you have less CO or less H2? Mizuno+ 01; Wilke+ 03; Young+ 95; Kennicutt 98; Elfhag+ 96; Gondhalekar+ 98; Boker+ 01; Murgia+ 02; Taylor+ 98; Leroy+ 05

36. Scaling Relations: Stellar Mass and Gas • Relation to Millimeter and IR astronomy: • Obviously (again) millimeter lines are key tracers of molecular mass. • At the same time a warning that millimeter lines are not perfect tracers of H2. • Small galaxies have less CO/HI and more HI/stars, why?

37. Wrap Up Why are nearby galaxies interesting?Environment, Statistics, Perspective, (plus very pretty!) What are the major constituents of galaxies?Young/Old Stars, Gas (HII, HI, H2), Dark Matter What does the zoomed-out SED of a galaxy look like?Quiescent/Star-Forming, Embedded/Unobscured How do you pull physical information about #2 from #3?Radio/mm Lines & Continuum, Dust Emission, Starlight What are some of the basic galaxy scaling relations?Tully-Fisher, Mass-SFR, Mass-Metallicity, Gas-SFR, Mass-Gas