Transcript 2007_spitzer_lecture_series_kennicutt_talk3

Demographics of Local Star-Forming
Galaxies and Starbursts
M82: Spitzer/CXO/HST
Primary Datasets
• Spitzer Infrared Nearby Galaxies Survey (SINGS)
– resolved UV  radio mapping of 75 galaxies
– selection: maximize diversity in type, mass, IR/optical
• 11 Mpc Ha/Ultraviolet Survey (11HUGS)
– resolved Ha, 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 Ha, 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)
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/Ha/IR census of local volume
• HST ANGST sample to 3.5 Mpc
• GALEX 11HUGS sampel to 11 Mpc
The Starburst Bestiary
GEHRs
nuclear starbursts
SSCs
circumnuclear starbursts
HII galaxies
clumpy irregular galaxies
ELGs
Ly-a galaxies
CNELGs
E+A galaxies
W-R galaxies
K+A galaxies
BCGs
LBGs
BCDs
DRGs
LIGs, LIRGs
EROs
ULIGs, ULIRGs
SCUBA galaxies
LUVGs, UVLGs
extreme starbursts
Demographics of Star-Forming Galaxies
Baseline: 11 Mpc Ha + 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:
• absolute SFR (Mo/yr)
– from Ha corrected for [NII], dust
• SFR density, intensity (Mo/yr/kpc2)
– defined as SFR/pR2SF
– 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
11HUGS/LVL Sample
R = 100 pc
1 kpc
10 kpc
11HUGS Sample + HaGS + Goldmine Virgo Sample
(James et al. 2003; Gavazzi et al. 2003)
SFR* ~5 Mo/yr
Gronwall 1998
LIGs, ULIGs (Dopita et al., Soifer et al, Scoville et al)
merger-driven
inflows, starbursts
Martin 2005, ApJ, 619, L59
1 O5V/3_Myr
Mgas/tHubble Mgas/tdyn
Meurer limit
Sgas/tHubble
Scrit
Lecture 4 Begins Here
Contributions to the global star formation budget
IR-luminous: ~5-8%
circumnuclear: ~3-4%
BCGs, ELGs: ~5-8%
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
Kennicutt 1998, ARAA, 36, 189
Brinchmann et al. 2004, MNRAS, 351, 1151
• spectra best fitted with IMF ~ Salpeter for M* > 1 Mo
• SF is ubiquitous when cold gas is present
- <4% S-Irr non-detects in Ha, 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
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 y(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
M82
NGC 3034
Lo et al. 1987, ApJ, 312, 574
IR-luminous galaxies
ELS limit
normal galaxies
Kennicutt 1998, ARAA, 36, 189
Circumnuclear Star Formation - Trends with Type
ellipticals too?!
Yi et al. 2005,
ApJ, 619, L111
Ho et al. 1997, ApJ, 487, 595
Borne et al. 2000, ApJ, 529, L77
Contributions to the global star formation budget
IR-luminous: ~5-8%
circumnuclear: ~3-4%
BCGs, ELGs: ~5-8%
Total fraction ~10-20%
total
IR-luminous
starbursts
L’Floch et al. 2005, ApJ, 632, 169
The Star Formation Law
starbursts
normal galaxies
Kennicutt 1998, ApJ, 498, 541
Gao, Solomon 2004, ApJ, 606, 271
Basic Observations
• 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
Scaling Laws
starbursts
normal galaxies
Kennicutt 1998, ApJ, 498, 541
Gao, Solomon 2004, ApJ, 606, 271
Crothswaite et al. 2003
Martin & Kennicutt 2001, ApJ, 555, 301
SFR surface density
starburst galaxies
normal galaxies
HI+H2 mass surface density
NGC 1291
Blue: Carnegie Atlas
Sandage & Bedke 1994
Ha + R: SINGG survey
Meurer et al. 2006
Questions: Schmidt Law
• 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?
“Schmidt law”:
SFR vs gas density power law
“Silk law”:
SFR vs gas density/dynamical time
Questions
• 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: Thresholds
• Do the observed Ha 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?
The Global Schmidt Law Revisited
• analyze galaxies with spatiallymapped star formation (Ha, Pa,
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
Kennicutt 1998, ApJ, 498, 541
metal-poor dwarf galaxies
The Spatially Resolved Star Formation Law in M51
Kennicutt et al. 2007, ApJ, submitted
FUV, Ha, 24mm
- 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 Ha + Pa and
Ha + 24 mm emission to correct for
extinction in SFR measurements
- Probe scales from 300 - 1850 pc
(IR/HII regions to unbiased
sampling of the disk)
Calzetti et al. 2005, ApJ, 633, 871
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 mm
Ha + R
MIPS 24 mm
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 = y0/<y(t)>)
• 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 mm)
Kennicutt 1989, ARAA, 36, 189
Michigan Spectral Catalog
Vols 1-3
Kron 1982, Vistas Astron,
26, 37
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 3177 Sb
NGC 7690 Sab
NGC 5806 Sb
Examples of pseudobulges:
NGC 986 SBb
NGC 4030 Sbc
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