Demographics of Local Star-Forming Galaxies and Starbursts

M82: Spitzer/CXO/HST

• Spitzer Infrared Nearby Galaxies Survey (SINGS) – resolved UV radio mapping of 75 galaxies

– selection: maximize diversity in type, mass, IR/optical

• 11 Mpc H/Ultraviolet Survey (11HUGS)– resolved H, UV imaging, integrated/resolved IR of 400 galaxies

– selection: volume-complete within 11 Mpc (S-Irr)

• Survey for Ionization in Neutral-Gas Galaxies (SINGG)– resolved H, UV imaging, integrated/resolved IR of 500 galaxies

– selection: HI-complete in 3 redshift slices

• Integrated Measurements– Ha flux catalogue (+IR, UV) for >3000 galaxies within 150 Mpc

- integrated spectra (+IR, UV) for ~600 galaxies in same volume (Moustakas & Kennicutt 2006, 2007)

Primary Datasets

Thanks to: S. Akiyama, J. Lee, C. Tremonti, J. Moustakas, C. Tremonti (Arizona), J. Funes (Vatican), S. Sakai (UCLA), L. van Zee (Indiana) + The SINGS Team: RCK, D. Calzetti, L. Armus, G. Bendo, C. Bot, J. Cannon, D. Dale, B. Draine, C. Engelbracht, K. Gordon, G. Helou, D. Hollenbach, T. Jarrett, S. Kendall, L. Kewley, C. Leitherer, A. Li, S. Malhotra, M. Meyer, E. Murphy, M. Regan, G. Rieke, M. Rieke, H. Roussel, K. Sheth, JD Smith, M. Thornley, F. Walter

Spitzer Local Volume Legacy

• UV/H/IR census of local volume• HST ANGST sample to 3.5 Mpc• GALEX 11HUGS sampel to 11 Mpc

The Starburst Bestiary

GEHRs

SSCs

HII galaxies

ELGs

CNELGs

W-R galaxies

BCGs

BCDs

LIGs, LIRGs

ULIGs, ULIRGs

LUVGs, UVLGs

nuclear starbursts

circumnuclear

starbursts

clumpy irregular

galaxies

Ly- galaxies

E+A galaxies

K+A galaxies

LBGs

DRGs

EROs

SCUBA galaxies

extreme starbursts

Demographics of Star-Forming Galaxies

• absolute SFR (Mo/yr)– from H corrected for [NII], dust

• SFR density, intensity (Mo/yr/kpc2)– defined as SFR/R2

SF

– correlates strongly with gas density, SF timescale

• normalized SFR/mass; birthrate parameter b – ratio of present SFR to average past SFR– defined here globally – integrated over galaxy– primary evolutionary variable along Hubble sequence

Baseline: 11 Mpc H + Ultraviolet Survey (11HUGS) - all known galaxies w/gas within 11 Mpc + Ursa Major cluster - companion GALEX Legacy survey coming…

Quantify SF properties in terms of 3 observables:

R = 100 pc

1 kpc

10 kpc

11HUGS/LVL Sample

11HUGS Sample + HGS + Goldmine Virgo Sample (James et al. 2003; Gavazzi et al. 2003)

Gronwall 1998

SFR* ~5 Mo/yr

LIGs, ULIGs (Dopita et al., Soifer et al, Scoville et al)

merger-driven inflows, starbursts

Martin 2005, ApJ, 619, L59

Mgas/Hubble

gas/Hubble

Mgas/dyn

crit

1 O5V/3_Myr

0.5” @ 4 M

pc

Meurer limit

Lecture 4 Begins Here

IR-luminous: ~5-8%circumnuclear: ~3-4%BCGs, ELGs: ~5-8%

Contributions to the global star formation budget

Total fraction ~10-20%

108 109 1010

1011 Mo

11MPC + BCGs (Gil de Paz et al. 2003)

Disk SF – Global Trends

Kennicutt 1998, ARAA, 36, 189 Bendo et al. 2002, AJ, 124, 1380

Kennicutt, Tamblyn, Congdon 1994, ApJ, 435, 22

Sandage 1986, A&A, 161, 89

Kennicutt 1998, ARAA, 36, 189

Bell, de Jong 2000,MNRAS, 312, 497

SFR increase reflects an increase in frequency of SF events, and a shift in the mass spectrum of single events

• Gas consumption– typical timescales for

depletion ~few Gyr– stellar recycling of gas

is significant factor!

Brinchmann et al. 2004, MNRAS, 351, 1151

blue sequence red sequence

Kauffmann et al. 2003, MNRAS, 341, 54

Lee & Kennicutt,in preparation

Disk SFRs: Main Results

• spectra best fitted with IMF ~ Salpeter for M* > 1 Mo

• SF is ubiquitous when cold gas is present - <4% S-Irr non-detects in H, nearly all show trace SF in UV

• average SFR/mass increases by 5-10x per type bin (S0 - Sa - Sb, etc)– proportional changes in disk SF history with type- changes in frequency and characteristic mass of SF events

• large residual variation in SFR within a given type– most variation in disk SFR vs B/D ratio– more strongly correlated with mean gas density– temporal SFR variations (bursts)

• strong bimodality seen in SFR/mass vs galaxy mass– extension to dwarfs shows evidence for third mode

• radial gradients in disk age and metallicity

Kennicutt 1998, ARAA, 36, 189Brinchmann et al. 2004, MNRAS, 351, 1151

Janice Lee, PhD thesis

Disk Star Formation Rates and Histories

• evolutionary synthesis of integrated colors

Tinsley 1968, ApJ, 151, 547 Searle et al. 1973, ApJ, 179, 427 Larson, Tinsley 1978, ApJ, 219, 46

• results – disk colors consistent

with sequence of constant age, IMF, Z, and variable SF history (t)

– best fit for ~Salpeter IMF

– spectra fit with similar model sequence

Kennicutt 1983, ApJ, 272, 54

Bruzual, Charlot 1993, ApJ, 405, 538

starburst duty cycle in dwarf galaxies (Lee 2006)

see poster by Lee et al.

Application to Starburst Duty Cycles

• bursts produce 20-40% of present-day SF in dwarfs• fraction of bursting dwarfs in same sample is 5-10%

• the galaxies are bursting 5-10% of the time

• average burst amplitude is ~4-8x the background SFR

• typical burst durations are 10-100 Myr (e.g., Gallagher, Harris, Calzetti, Zaritsky, Hunter…)

- a typical burst lasts for 0.1-1% of Hubble time

• a typical galaxy bursts ~10-20 times over a Hubble time, each time producing a few percent of its stars (every 500-1000 Myr)

NGC 1512 (HST)

NGC 1512 (GALEX FUV/NUV)

Kormendy & Kennicutt 2004, ARAA, 42, 603 Sakamoto et al. 1999, ApJ, 525, 691

M82NGC 3034

Lo et al. 1987, ApJ, 312, 574

Kennicutt 1998, ARAA, 36, 189

ELS limit

normal galaxies

IR-luminous galaxies

Circumnuclear Star Formation - Trends with Type

Ho et al. 1997, ApJ, 487, 595

ellipticals too?!

Yi et al. 2005, ApJ, 619, L111

Borne et al. 2000, ApJ, 529, L77

IR-luminous: ~5-8%circumnuclear: ~3-4%BCGs, ELGs: ~5-8%

Contributions to the global star formation budget

Total fraction ~10-20%

L’Floch et al. 2005, ApJ, 632, 169

total

IR-luminous starbursts

Kennicutt 1998, ApJ, 498, 541 Gao, Solomon 2004, ApJ, 606, 271

The Star Formation Law

normal galaxies

starbursts

• Galaxies exhibit an immense diversity in star

formation properties, varying by >107 in absolute SFR,

SFR/mass and SFR/area.

• Over this range the SFR/area is correlated with gas

surface density, following a truncated Schmidt power

law with index N = 1.4 +-0.1

– the correlation of with dense gas (e.g., HCN) is roughly linear

• The Schmidt law shows a turnover below a threshold

surface density that varies between galaxies.

– in gas-rich, actively star-forming galaxies this transition is

seen as a radial transition in the SFR/area

– some gas-poor disks reside in the threshold regime at all radii

Basic Observations

Kennicutt 1998, ApJ, 498, 541 Gao, Solomon 2004, ApJ, 606, 271

Scaling Laws

normal galaxies

starbursts

Crothswaite et al. 2003

Martin & Kennicutt 2001, ApJ, 555, 301

normal galaxies

starburst galaxies

HI+H2 mass surface density

SFR

su

rface d

en

sit

y

NGC 1291

Blue: Carnegie Atlas Sandage & Bedke 1994

H + R: SINGG survey Meurer et al. 2006

• Is the Schmidt law correlation really this good?

– do all galaxies follow the same Schmidt law?

– is the scatter driven by a second parameter?

• Is the global Schmidt law the result of a more

fundamental underlying SF scaling law?

– over what range of physical scales is the law valid?

• Is the SFR correlated more strongly with the total

(atomic + molecular) surface density or with the

molecular surface density alone?

• What is the physical origin of the relation?

Questions: Schmidt Law

“Schmidt law”: SFR vs gas density power law

“Silk law”: SFR vs gas density/dynamical time

• Is the correlation really this good?

– do all galaxies follow the same Schmidt law?

– is the scatter driven by a second parameter?

• Is the Schmidt law the result of a more

fundamental underlying SF scaling law?

– over what range of physical scales is the law valid?

• Is the SFR correlated more strongly with the total

(atomic + molecular) surface density or with the

molecular surface density alone?

• What is the physical origin of the relation?

Questions

• Do the observed H edges of galaxies trace

proportional changes in the SFR/area?

• Does the SFR in the sub-threshold regime follow

a (modified) Schmidt law? Or is it triggered

entirely by local compression events?

• What is the physical nature of the threshold?

Questions: Thresholds

The Global Schmidt Law Revisited

• analyze galaxies with spatially-mapped star formation (H, P, FIR), HI, and CO

• enlarged, diversified samples – normal galaxy sample 3x larger– larger ranges in gas and SFR

densities– large subsamples of

circumnuclear starbursts, low-metallicity galaxies incorporated

• densities averaged within active SF regions

• explicit corrections for [NII], extinction

• point-by-point analysis of SINGS + BIMA SONG galaxies

Work in progress!

Kennicutt 1998, ApJ, 498, 541

metal-poor dwarf galaxies

The Spatially Resolved Star Formation Law in M51 Kennicutt et al. 2007, ApJ, submitted

FUV, H, 24m

Calzetti et al. 2005, ApJ, 633, 871

- Use spatially-resolved measures of CO, HI, and SFR to characterize SFR vs gas surface density relation on a point-by-point basis

- Use combinations of H + P and H + 24 m emission to correct for extinction in SFR measurements

- Probe scales from 300 - 1850 pc (IR/HII regions to unbiased sampling of the disk)

M51: BIMA SONG Survey Helfer et al. 2003

NGC 6946– THINGS VLA HI Survey F. Walter et al.

Scoville et al. 2000, AJ, 122, 3017

GALEX FUV + NUV (1500/2500 A)

IRAC 8.0 m MIPS 24 m

H + R

Local Schmidt Law in M51

Kennicutt et al. 2006, in prep

Tentative Conclusions

• The disk-averaged Schmidt law in galaxies is rooted in

a local relationship that persists to scales of <500 pc

• In M51 the SF density is tightly coupled to the local H2

surface density, and not with HI density

• A kinematic star formation law does not seem to

extend as well to local scales

• The disk-averaged SF law is confirmed with

more/better observations. Some metal-poor galaxies

lie systematically above the mean relation.

Extra Slides

Star Formation Rates and Histories• synthesis models mainly sensitive to ratio of main

sequence to red giant stars --> ratio of current star formation rate (SFR) to average past rate (b = 0/<(t)>)

Kennicutt 1989, ARAA, 36, 189

• most sensitive measurements from spectral features that directly trace young population, combined with color constraints

- UV continuum fluxes

- nebular recombination lines (--> ionizing stellar continuum)

- thermal dust emission (10-200 m)

Kron 1982, Vistas Astron,26, 37

Michigan Spectral CatalogVols 1-3

Kennicutt 1992, ApJS, 79, 255

30 Doradus

Sbc, Sc, Scd, Sd

S0/a, Sa, Sab, Sb

bar-driven inflows, circumnuclear starbursts

Sdm, Sm, Im, I0 + BCGs (Gil de Paz et al. 2003)

NGC 1365 (HST)

NGC 3885 Sa NGC 7690 Sab NGC 986 SBb

NGC 3177 Sb NGC 5806 Sb NGC 4030 Sbc

Examples of pseudobulges: Kormendy & Kennicutt 2004, ARAA, 42, 603

Example: completeness of z=0 prism surveys (UCM)

Early results suggest that prism surveys miss 40-55% of local SF