Transcript ALMA_BoJun605_Gruppioni

Normal/Starburst Galaxies
at Low/Intermediate-z
with ALMA
Bologna, 2005 June 6
WHY ALMA?
Strong limitation of Current mm Interferometers
In sensitivity (PdBI, the most sensitive)
In Ang. Res. (bs max = 2km for BIMA, ~500m others)
In Freq. Coverage (ALMA open sub-mm window)
In Imaging capability (6 to 10 antennas only)
 ALMA factor 10-100 better in resolution
 ALMA @1.3 mm vs. PdBI sensitivity
Continuum  factor 100 better (6 µ Jy/beam in 1 hr)
Spectral line  factor 30 better (1.1 mJy/beam in 10 hr)
Nobeyama Millimeter
Array
OVRO
IRAM
Primary Goals for ALMA in
Extragalactic Astronomy
The ability to detect spectral line emission
from CO or CI in a normal galaxy like the
Milky Way at a redshift of 3, in less than
24 hours of observation.
The ability to provide precise images at an
angular resolution of 0.1” or better (0.01”
at 650 GHz) to map the dust/molecular
clouds structure in distant galaxies
Detecting normal galaxies at z=3
CO emission now
detected in 25 z>2
objects. To date
only in luminous
AGN and/or
gravitationally
lensed in 1to 2 days
of total obs. time. Normal galaxies are
20 to 30 times fainter.
Detecting normal galaxies at z=3
• Total CO luminosity of Milky Way: L’co(1-0) = 3.7x108
K km s-1pc2 (Solomon & Rivolo 1989).
• COBE found slightly higher luminosities in higher
transitions (Bennett et al 1994) → adopt L’co =
5x108 K km s-1pc2.
• At z=3 → observe (3-2) or (4-3) transition in the
84-116 GHz atmospheric band → need to correct,
but also higher TCMB providing higher background
levels for CO excitation.
• Different models predict brighter or fainter higherorder transitions. Few measurements of CO rotational
transitions exist for distant quasars and ULIRGs, but
these are dominated by central regions.
• → Assume L’co(3-2) / L’co(1-0) = 1.
Detecting normal galaxies at z=3
• For ΛCDM cosmology, Δv=300
km/s, the expected peak CO(3-2)
flux density is 36 µJy.
• 5σ detection achievable with ALMA
in 12h on source (16h total time)
ALMA AS A REDSHIFT MACHINE
• >50% of the FIR/submm background are submm
galaxies.
• Trace heavily obscured star-forming galaxies.
• Optical/near-IR
identification very difficult.
• Optical spectroscopy:
<z>~2.4.
• Confirmation needed
with CO spectroscopy.
SCUBA image of the HDF-N
mm continuum contours + HST
optical image for the strongest
SCUBA source in the HDF-N
Hughes et al. 1998
Downes et al. 2000
ALMA AS A REDSHIFT MACHINE
ALMA will provide 0.1”
images of submm sources
found in bolometer
surveys (LABOCA/APEX,
SCUBA-2/JCMT) or with
ALMA itself.
• 3 frequency settings will
cover the entire 84-116
GHz band → at least one
CO line. (1h per source)
• Confirm with observation
of high/lower order CO
line. (1h per source)
•
PHOTOMETRIC REDSHIFTS
FROM FLUX RATIOS
• At z<1, the 1.4 GHz radio to 350 GHz submm
flux ratio can provide an estimate of the source
redshift (Carilli & Yun 1999)
NB: valid for SBs. In AGNs radio excess is possible
• At higher z, this flux ratio saturates
 one can use broad band SEDs obtained by
observing in different ALMA bands to constrain
the position of the redshifted 50-80 K hot dust
peak
Photometric methods not very accurate for single
gals but useful to determine global z distributions
THE EFFECT OF DUST ON THE
STAR FORMATION HISTORY
Cosmic SFR density evolution with z show a peak at
z = 1.5 – 3 (Blain et al. 2002)
BUT effect of dust unknown since current sub-mm obs.
limited to most extreme systems at such distances
ALMA sensitivities of 10’s of
to avoid confusion (plaguing
Single Dish obs.)
 normal star-forming gals
at high z
(SFR~10’s of MSun/yr)
µJy
+ sufficient resolution
PRECISE MAPPING OF SUB-MM SOURCES
•
Follow-up with ALMA:
High resolution CO imaging to determine
morphology (mergers?), derive rotation curves
→ Mdyn, density, temperature, ... (1h per
source)
• Observe sources in HCN to trace dense
regions of star-formation. (10h per source,
20 sources)
• Total: 12h per source, 170h for sample of 50
sources.
•
M51 Galaxy (Whirlpool, NGC5195)
Located at a distance of 37 million light-years from us, the famous M51 Galaxy (Sc type) was discovered in
1773 by Charles Messier.
Due to its orientation in space, it is seen "face-on".
Optical image of M51.
Left : Continuum
emission at 1.3
mm from the cold
dust (<20K) contained
in the spiral arms of
M51 as observed
with the 30m
telescope.
Right: Map of
the CO(2-1)
emission from
M51.
The pixel size in both images is 12 arc seconds. The continuum emission of cold dust closely follows the spiral pattern traced by the CO
emission and correlates poorly with the emission from neutral hydrogen HI clouds. Similar results have been obtained by mapping the
"edge-on" galaxy NGC 891, where the dust correlates well with the CO emission up to a radius of 25 thousand light-years from the center of
the galaxy.
Obscured galaxy formation: low redshift
(Meier & Turner 2004)
IC342
 distance = 2 Mpc
 M_gas = 4e7 M_sun
 SFR = 0.1 M_sun/yr
30” =
300pc
 Starburst age =
1e7 yrs
colors  OPTICAL
Grey contours  CO(1-0)
White contours  mm continuum
Nearby star forming Galaxies – Chemistry/Physics: IC342, D=2Mpc
Meier & Turner 2004
CO: all
gas
300pc
HC3N:
Dense
C2H:
PDRs
ALMA: Image with GMC resolution (50pc) to 250 Mpc
 Rich clusters: Virgo = 16 Mpc,
Coma = 100 Mpc
 ULIRGs: Arp 220 = 75 Mpc, Mrk 273 = 160 Mpc
Schinnerer et al., in prep.
Nearby Gals II: Dynamics: ‘feeding
the nucleus’ – NGC6946, D=5.5Mpc
PdBI 0.5” CO(2-1)
- Gas Lanes along Bar
- Streaming Motions
- Gas Disk w/ R <15pc
ALMA: extend to
Mrk 231 at 180 Mpc
Cygnus A at 240 Mpc
100 pc
Disentangling Nuclear Starbursts from
AGNs
 MAMBO survey of the cluster A2125 (Carilli et al. 2001) at 250 GHz
– Detected sources not associated
with cluster galaxies.
– Associated with mJy radio
sources (VLA)
– Mostly dusty star forming
galaxies at median redshift 2.5
- but also possible that heating
sources are AGN
Optically identified submm detected sources (only three so far)
Two of them have large molecular gas masses (seen through CO emission)
Dust continuum CO(3-2) emission
z = 2.81
AGN Type II
(Frayer & Scoville
1999)
z = 2.56
Starburst
0.1” res.  ~1 kpc at z~1
0.01” res. ~1 kpc at z~3
Power of IR Classification:
Edge-on Spiral NGC 5746
Optical
gri
2MASS
JHK
Frei al. 1996 (AJ, 111, 174) Jarrett et al. 2003 (AJ, 125, 525)
Spitzer/IRAC
3 -10 mm
Prominent dust lane in optical (and even near-IR)
prevents unambiguous classification
IR images demonstrate class "Sab" with ring
Star formation concentrated along ring and outside it
NGC 5128 - Centaurus A
Visible image
IRAC image
Keene et al. 2004