View
219
Download
4
Category
Tags:
Preview:
Citation preview
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
Recommended