2018/6/7 @ galaxy evolution workshop 2018

Molecular gas and star formation
in bar regions of strongly barred galaxy

Fumiya Maeda ( Kyoto Univ. )K. Ohta (Kyoto Univ)Suppression of SF in bars
• HII regions are seen in spiral arms.
• In the bar regions, although the dark lane implies the presence of dust andmolecular clouds, there is no (massive) star formation.

NGC1300
NGC1300
HST
B, V, I - band
+ Hα filter

Hα

https://www.spacetelescope.org/images/opo0501a/2

What prevents star formation in bar regions?

3• The molecular clouds may be destroyed by shock due to the high velocity of thegases relative to the bar structure. (e.g., Tubbs 1982)• Strong shear motion in the bar region may prevent molecular cloud formation (e.g.,Athanassoula 1992).
• Combination of these (Reynaud & Downes 1998).
Recent studies• Molecular clouds in bar regions are gravitationally unbound (e.g., Sorai et al. 2012.)• The high-speed collision of the clouds in the bar region shortens a gas accretion
phase of the cloud cores formed, leading to suppression of core growth and massive
star formation (Takahira et al. 2014, 2018)• Most of the molecular gases may be diffuse in bar region.

→We must resolve molecular gas into clouds.

= High resolution CO imaging of barred galaxies is required.

Previous works : intermediate-type bar with SF

LAR NURSERIES

415SFE393
inof bar
CO (1–0) •imaging
M83regions is 2~3 times lower than
13 that in arm region.
• Too large angular resolution to detect clumps.
• Many of targets have an intermediate-type bar and do have star-forming regions
associated with the bar or bar-like region.
CHAPTER 1. INTRODUCTION

No. M83
1, 201039oWide-field 12 CO (1–0) imaging(a)(b)

NGC4303

nalo, 1994). The bar structure is likely responsible for feeding gas to the nuclear region
ArmM83
grenetal.,
2004a;
Fathietal.,2008).
Oﬀset
ridgesresidealong
thestellarbar,andthoseb).
are associated with shocked gas (Ondrechen, 1985).
nd
ere are many mapping observations in CO lines (WiklindBaret al., 1990; Handa et al., 1990;
omand Kenney, 1991; Kenney and Lord, 1991; Rand et al., 1999; Crosthwaite et al., 2002;
oto et al., 2004; Lundgren et al., 2004b; Muraoka et al., 2009a,b; Hirota et al., 2014).
ndmass of HI gas is 7.7 × 109 M⊙ (Huchtmeier and Bohnenstengel, 1981). Total mass of H207.
993.2 × 10 M⊙ (Crosthwaite et al., 2002) or 3.9 × 10 M⊙ (Lundgren et al., 2004b).

Hirota et al. 2014ation of spiral arm and bar structures

logΣSFRArm

1.3. Image of the barred spiral galaxy M83. This image is based on data acquired with the 1.5-metre Danishe at ESO’s La Silla Observatory in Chile, through three filters (B, V, R). Credit: ESO/IDA/Danish 1.5
endler, S. Guisard and C. Thone.

SFRR will1.3. GIANT MOLECULAR CLOUDS: STELLAR NURSSFE IN THE BARRED SPIRAL GALAXY
NGC 4303
No. ]NGC4303

BarFig. 14. (a, b) Pseudo color representation of the original
Hα image (a) and the background subtracted Hα image (b).
Both images share same color scaling. (c, d) Same as (a) and(b), but for 24µm images. (e) Image of SFR derived fromthe linear combinations of background subtracted Hα and24µm images based on the calibration of Calzetti et al. 2007.

Momose et al. 2010logΣemission removal here. In the subsequent analysis of SFR

rmation process of spiral arm structures has been well debated, but consensus has not
H2and SFE (§5.2), to make an independent
check, SFR will′′
eached yet. Oneof the10.
mostΣpopulartheories of spiral structure is the density wave theory
FigureatthescaleofKennicutt(1998)’sFigure
9. Right: the same as t
H2 vs. ΣSFR plot (KS plot). Left: ΣH2 vs. ΣSFR at the resolution of 6 (∼500 pc; color)be derived using the Hα alone in
the latersection.

Strongly barred galaxies : ideal lab
CO observations of strongly barred galaxies are important, because themechanism of the suppression is expected to be clearly seen in such bars.

NGC1300 is the nearest strongly barred

NGC1300 (d = 20 Mpc)

galaxy which has remarkable dark lanes inthe bar region without HII regions.
• GMCs (~ 50pc) are detectable with ALMA.

However...
• CO emission line has not been detected towards the bar regions.

5Before45-m
observationsØNGC 1300going to ALMA:ØNGC
5383• ビーム= 1.3
kpcNRO 45-m(2016/17)

野辺山45-m

6• ビーム = 2.1 kpc• 観測領域• beam size = 13.”5φ = 1.3 kpc • 観測領域
• Bar A, B Hαなし
• Bar A, B Hαなし
NRO 45-m• •onArmsource= 0.5 ~ 2.7hrs / point
A, BtimeHαあり

• Arm A, BHαあり

ArmC ~Hαなし• •rms=816 mK at 10 km/s bin

NGC5383:Hα---dustdustlanelane---

NGC1300:Hα
NGC1300:Hα40”

Declination (J2000)

領域• ビーム（HPBW） = 13.5”

Arm B-19°24’00”

Arm CArm A20”

40”

Bar A
3h19m40s

Bar Br = 1.5kpc

38s

36s

Right Ascension (J2000)

34s

Maeda et al. 2018 Sheth, et al. 2000, APJ, 632, 217より改変

7

Moleculargases exist in bar regions
観測領域
Maeda et al. 2018

Mmol (Msun) = 4.36 L’CO (K km/s pc2)

NGC 1300

Bar A

Arm B

Declination (J2000)

Intensity [mK]

40”

Arm B
-19°24’00”

Arm C

40”

Arm A

Bar B

20”

Bar A

velocity [km/s]
3h19m40s

Bar B

Intensity [mK]velocity [km/s]
38s

36s

Arm C

Right Ascension (J2000)

BarA = Bar1
BarB = Bar3

Bar End A = Bar End

velocity [km/s]

34s

Arm AArmA = Arm3
ArmB = Arm1

ArmC = Arm4

velocity [km/s]

velocity [km/s]

v
xi-kaRndlbFaau
S(Σlgntsesn.
8
1.4as.
aeaxosreiusi
H2nntgΣΣepflw
aooisti
ti
etel
∝s.
adar
bIRlaxllve)
eaer
Rnrrr
SaSµm
K
FRStiongΣ SFbi(SaKΣK
4lt2eononidheofthndl retm
Usingmcontinuum
subtracted
Hαimageatiandnyhsabeo2)
bct.
irorwtlaS2
VaoohU1.
ttrf
tigelaneags(sruFate
8cdfromHST, uwe
Sn derived SFEs on 1.3
ht Aof Armni kpc inv
1.4 of 1
gninoetene
foroiveKeuitld
1.2
ashpanisscale:s h . Figina ws tmthesnbamsee⌃SFR n a 1 atio 11) n a s com shoxi
αaflvoi0Hw (yr er)
SFE =)
ao2ga(asnmexpcm4bk⌃.
od.
oH
l0rol2nr
1fiel
75 ed ftaedonergeew
ifehtur
n
Arm
Btor
sau
agi
bnsu
su
ol
niu
Faosarow ly chioeteei.
hhtr)
umm1Sc• SFEs in Arm
toh- are; comparable.2 .
olrdeela A &igB
e0sr
tedBarBa−rr±eea8her0hs2w(1.
wetig dex
00hi
ntsshOs
22eTtfeHRΣCcoprevious observations
Finat spirals.
FRnv∝niSmRe t al.
t)2 ofSotiey C st-fi).
he ArmfroHFReatS
hl+8lI
Σde
0Tnr
He
beie
0er
Σg.
2hSuei( are• SFEs in bar
gw
KtimesB of NGC1300
aBar
as ~10vs.
.
reAt thelmaagalRmth.1e
SFancuetr
1Σhedlelcsmaller than thateo=w
twgie in earm.
omsioVnt
Bso-fif A nd sh)
tdgaosbse(t2anbH→ SF is remarkably
inulioa suppressedston
ecihr
ttintiluw
sexoeesret th dust
strongly bar regions.
laati : Arm , Blue : BartheaRedgdpsrarteehtoviawith w
Color regions by Bigiel et al. (2008)• The low SFE in Arm C is consistent
eperhetyng
show SFEs in 18 nearby spiral galaxies
heangiThc
the absent of HII regions there.
muw
on 0.75 kpc scale.
ass er law
pos
theu

very low SFEs in strongly bar region

9y studies

NGC5383
The very low SFEs are also seen in bar regions of strongly barred galaxy
NGC5383.
NGC 5383 (d = 32Mpc)

CO(1-0) observations with 45-m
Bar 1

Arm 1

Bar 2

Arm 2

5= +41d50m46

Arm 2

DSS gri image of NGC 5383. This is a strongly barred galaxy with very little star formationec
its two predominant straight dust lanes in the bar region.
1d50m40.9s
Bar 1Bar 2

1d50m23.3s

1d50m08.0s

beamsize = 2.1kpc

1d50m59.6s

1d51m24.3s

Arm 1

Continuum-subtracted Hα image (Sheth et al. 2000)

Maeda et al. 2018

10y studies

NGC5383
The very low SFEs are also seen in bar regions of strongly barred galaxy
NGC5383.
●：NGC 1300■：NGC 5383

NGC 5383 (d = 32Mpc)

Arm
5= +41d50m46

Bar

Arm 2

DSS gri image of NGC 5383. This is a strongly barred galaxy with very little star formationec
its two predominant straight dust lanes in the bar region.
1d50m40.9s
Bar 1Bar 2

1d50m23.3s

1d50m08.0s

beamsize = 2.1kpc

1d50m59.6s

1d51m24.3s

Arm 1Continuum-subtracted Hα image

Red : Arm , Blue : Bar
Color regions by Bigiel et al. (2008)
show SFEs in 18 nearby spiral galaxies
on 0.75 kpc scale.

(c)12CO(1-0)

11CO(1-0) observations with ALMA
ALMA Cycle 5 (2017.0.00248.S)(a) HαFoV ~ 54”φ = 3.2 kpc × 2 points (Arm & Bar)• beam size ~ 0.”42 × 0.”30 = 42pc × 30pc• on source time ~ 2.7hrs / pointHαALMA-Arm• rms = 0.7 mJy/beam at 2.0 km/s bin

Arm B(b) B,V,I,Hα

Arm C

Arm A

Bar B
Bar A

ALMA-BarCO imaging with ALMA

12(a) HαHαALMA-ArmWe detected the GMC-like gas clouds
in the Arm and Bar regions.

Arm B
Arm C

(b) B,V,I,Hα

Arm A

Bar B

Velocity integrated map (1550 - 1700 km/s)
Arm region

Bar region

beam

100pc
100pc
beam

3.2 kpc

Bar A

ALMA-Bar13Hα + CO map• Arm region : HII regions and GMC-like gas clouds are coexist (e.g., M51).
• Bar region : There are GMC-like gas clouds without HII regions.
→ A possibility that GMCs are formed but massive SFs are not occurred.

Bar region

Arm region

14

Comparison with 45-m observations
観測領域

NGC 1300

Bar A

Arm B

Declination (J2000)

40”

Arm B
-19°24’00”

Arm C

Arm A

Bar B

20”

Bar A

40”

100pc
Bar B

3h19m40s

38s

36s

Arm C

Right Ascension (J2000)

BarA = Bar1
BarB = Bar3

Bar End A = Bar End

ArmA = Arm3
ArmB = Arm1

ArmC = Arm4

34s

Arm A

Comparison with 45-m observations
We estimate the amount of diffuse emission distributed on the scale larger
than 400 pc ( = LAS of this ALMA observations).
L’co(45m)(K km/s pc2)

L’co(ALMA)(K km/s pc2)

fraction
(%)

Arm A

6.9×106

4.1×106

~40

Arm B

4.1×106

5.7×105~85

Arm C

4.6×106

3.4×105

~90

Bar A

3.9×106

1.1×106

~70

Bar B

6.7×106

1.8×106~70• In Arm A, ALMA has detected 40% of total-flux with NRO 45-m.
cf. M51: L’CO(PdBI) /L’CO(PdBI+30m) ~ 50 %(Pety et al 2013)• In Bar, Arm B & C, diffuse gases may be account for the most of total gases.
→This is the cause of the low SFE in bar regions?

15

Next Step : identification of GMCs
We are identifying GMCs in NGC1300 by using clumpfind/CPROPS.
Deriving the properties of GMCs
• Radius• velocity width• LCO → Mmol

→ Mvirvirial parameter• relative velocity distributions→ Investigation of the cause of SF suppression.
• Gravitationally unbound cloud in bar regions→ Large virial parameters of GMCs in bar regions• The high-speed collision of the clouds→ High relative velocity of GMCs in bar regions

16

17

Summary• Strongly barred galaxy, NGC1300 is one of the suitable targets to investigate thecause of star formation suppression in bar regions.
• However, CO emission line has not been detected towards the bar regions.
CO observations with the Nobeyama 45-m telescope• The molecular gases do exist in the bar regions without
associating clear HII regions.
• SFEs in bar of NGC1300 are ~10 times smaller thanthat in arm.
CO observations with the ALMA
• We detected the GMC-like gas clouds in the arm and bar.
• Molecular gas may be mostly distributed on scales larger
than 400 pc.
• We will identify GMCs and investigation of the cause ofSF suppression.

ArmBar