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STScI March 24, 2004
Ebb & Flow: Molecular Gas and Star Formation
in Nearby Spirals
Michele ThornleyBucknell University/STScI
With grateful thanks to:M. Regan, D. Calzetti, M. Meyer, M. Mutchler, R. Kennicutt,
S.Vogel, T. Wong, T. Helfer, K. Sheth, C. Spohn-Larkins, R. Magee + the BIMA SONG & SINGS collaborations
To take away:
•Value of wide-field surveys
•Promise of CO studies with millimeter interferometers
•Promise of studying gas, dust and star formation with Spitzer
STScI March 24, 2004
CO as an H2 tracer
Open question: dependence of “X-factor” on metallicity, temperature, e.g. (an extremely abbreviated list…) • Maloney & Black 1988• Wilson 1995; Arimoto et al. 1996; Israel 1997• Regan 2000• Dame, Hartman, & Thaddeus 2001• Wei, Neininger, Huttemeister & Klein 2001• Boselli et al. 2002• Rosolowsky et al. 2003• Bolatto et al. 2003, Walter et al. 2003
(NGC 3627, BIMA SONG)
CO J =1-0 B-I B-K I -K J -KCO J =1-0CO J =1-0 B-IB-I B-KB-K I -KI -K J -KJ -K
STScI March 24, 2004
Molecular gas in the Milky Way
Dame, Hartmann, & Thaddeus 2001
STScI March 24, 2004
Questions to ask:
•Interaction of molecular and atomic gas?
•Distribution & population of molecular clouds?
•Dependence of star formation on large-scale dynamics?
•Variation between galaxies?
STScI March 24, 2004
Transitions between molecular & atomic gas
Crosthwaite & Turner (2001, 2002)
CO
HI
IC 342 M8310’ 5’
Pressure dependent cloud formation: e.g., Elmegreen 1993, Elmegreen & Parravano 1994, Elmegreen 1995, Sofue et al. 1995, Honma et al. 1995, Hidaka & Sofue 2002
STScI March 24, 2004
Local Group spirals
Dame et al 1993 (~1.7kpc resolution)
M31M31
Guelin 2000, Neininger et al 2001
(90 pc resolution)
Loinard et al 1999 (200 pc resolution)
STScI March 24, 2004
M31
Loinard et al 1999
Berman 2001, Berman & Loinard 2002Kinematics as constraints on bulge & disk distributions:fast rotating, triaxial bulge
thick H2 disk (or warping)?
z0~200-
500pc
STScI March 24, 2004
Zooming in on M31 clouds
Neininger et al 1998, Neininger et al. 2001
(~3-4 pc resolution)
STScI March 24, 2004
Local Group spirals
Engargiola et al. 2003 (50 pc resolution), Rosolowsky et al. 2003 (20 pc resolution)
M33M33
See also: Fukui et al. 2001, 2003 (LMC w/ NANTEN)
STScI March 24, 2004
M33
Kinematics and distribution provide constraints on cloud formation:cloud size, low angular momentumcorrelations in velocity gradients for separations < 500 pc
Engargiola et al. 2003, Rosolowsky et al. 2003
GalacticM33
STScI March 24, 2004
BIMA Survey of Nearby Galaxies (BIMA SONG)Regan et al. 2001, Helfer et al.
2003
(Das et al. 2003)
STScI March 24, 2004
BIMA SONG
Selection criteria:• Vsys < 2000 km sec-1
• BT< 11
• Sa-Sd
• i < 70o (>-20o,D25<70’)
93% of the sample detected Chosen 44 spirals include:
• 29 bars (SAB+SB) • 20 emission-line (Seyfert, LINER)• 19 grand-design spirals • 17 HII nuclei
Average distance 12 Mpc (H0=75 km s-1 Mpc-1)• Map out to R~5 kpc
ab b bc c cd d
(Hubble type)0
510
nu
mb
er
UnbarredBarred
STScI March 24, 2004
2
4
6
8
10
Sab/Sb Sbc Sc/Scd
Central excessNo central excess
(5)
(2)(3) (3)
(8)
(6)
Num
ber
12
15
3
6
9
SA SAB/SB
Central excessNo central excess
(5) (6)
(14)
(2)N
umbe
r
BIMA SONG Radial Profiles
Regan et al. 2001
Thornley et al. 2004 (in prep.)
(27 of 44 galaxies)
STScI March 24, 2004
Central concentrations
Central surface densities higher in barred spirals• Statistical support for bar-
induced inflow:• Sakamoto et al. 1999• Sheth et al. 2004
High nuc correlated with large surface mass density• Perhaps bar not necessary
for centrally peaked gas• Sofue et al.2003• (Thornley et al. 2004)
Sakamoto et al. 1999
STScI March 24, 2004
H2,HI, and the Schmidt law in SONG galaxies
Wong & Blitz 2002
(from Elmegreen 1989)
STScI March 24, 2004
Star Formation & Bars
Sheth et al. 2002
(CO)
(H)
STScI March 24, 2004
Measuring streaming motions(NGC 5055)
BIMA SONG CO velocity residuals (Thornley et al., 2004)
HI & H, (Thornley & Mundy 1997)
STScI March 24, 2004
The future of millimeter studies
CARMA (~2005)
Cedar Flat CARMA on Cedar Flat (simulated)
ALMA (~2008/2012)
Chajnantor
STScI March 24, 2004
Other tracers of gas and dust?CO J =1-0 B-I B-K I -K J -KCO J =1-0CO J =1-0 B-IB-I B-KB-K I -KI -K J -KJ -K
(BIMA SONG)
Dale & Helou 2002
IRACMIPS
IRS/MIPS
STScI March 24, 2004
Spitzer Infrared Nearby Galaxies Survey (SINGS)
PI: R. Kennicutt 75 nearby galaxies (d<30 Mpc)
• Range of Hubble type, luminosity, IR/optical Comprehensive database:
• IRAC/MIPS broadband imaging (3.6-160 m)
• IRS/MIPS SED strips (14-100 m)
• IRS spectral maps (5-37 m)• Nuclear & extranuclear
• Lots of ancillary data! (optical/NIR, UV, CO, HI,…)
SINGS website: http://sings.stsci.edu
STScI March 24, 2004
SINGS sample & plan
Kennicutt et al. 2003, PASP, 115, 928
IRAC
MIPS
MIPS SED
IRS (low)
IRS(S-high)
IRS(L-high)
STScI March 24, 2004
IRAC
MIPS
NGC 7331
Regan et al. 2004
STScI March 24, 2004
The ring in NGC 7331
Regan et al. 2004
+ ring* outside ring total
(Scale
d)
STScI March 24, 2004
Comparing gas, dust, and star formation
gas gasStar formation
? ?
STScI March 24, 2004
Spectroscopy with Spitzer
Nucleus
Short Low
Long HighJ.D. Smith et al. 2004
STScI March 24, 2004
M81: Early Release
http://www.spitzer.caltech.edu
NASA/JPL-Caltech/R. Hurt (SSC/Caltech)
STScI March 24, 2004
Summary
High spatial and spectral resolution observations of molecular gas in galaxies are becoming increasingly common.
We are now able to examine the relationship of gas, dust, stars, and galactic structure over a range of galaxy types.
We can address a wide variety of questions in a quantitative way:• Cloud formation (e.g., turbulence, HI H2)
• Star formation variations• Large- and small-scale kinematics