ALMA observation of12CO(J=3-2) & 13CO(J=3-2) in merging ULIRGs
Misaki Ando (SOKENDAI/NAOJ), D. Iono, T. Michiyama(SOKENDAI/NAOJ), T. Saito(MPIA), J. Ueda(CfA)

Abstract
Galaxy mergers play an important role in the evolutionary process of galaxies, as it changes the physical/chemical
condition of the ISM, and intensiﬁes the starburst activity as seen in the frequent occurrence of mergers in Ultra/
Luminous Infrared Galaxies (U/LIRGs). We present here the preliminary results of 12CO(J=3-2) and 13CO(J=3-2)
observations obtained toward merging ULIRGs with ALMA. We took ratio maps of 12CO/13CO and found that theratios are typically lower at the central dust strong regions than the outer regions. We reveal that the trend of thehigh 12CO/13CO ratio in previous studies is due to the gas from the extended regions rather than the central gas. For
further investigation, we are analyzing additional data such as 12CO(J=1-0).

Introduction

Aalto+95

12CO(1-0)/13CO(1-0)

Interaction of galaxy change morphology, and physics andchemistry of molecular gas. These activities sometimes occur
intense starburst and nuclear activity. During these process,galaxy change their properties dramatically. It is therefore
important to quantify the properties of gas in such merging
galaxies in order to investigate the evolutionally scenario ofgalaxy.
One of the previous study of molecular gas in merging
galaxies shows the trend of the 12CO/13CO line intensity. The
ratio values are higher in luminous merging galaxies than innormal spirals, though the exact reason still unknown. ALMA
data can oﬀer clues of conditions causing this trend.

Our previous study:

ﬁlled symbols:
luminousmergers

Spatially resolved 12CO/13CO(2-1)
line ratio maps with ALMA
Merging galaxy:NGC 1614Open symbols:
normal spiral galaxies

colderf60/f100

Ando et al. in prepwarmer

12CO/13CO(3-2) line ratio maps

Six mergers of The brightest ULIRGs＊ULIRGs: LIR > 1012 L¤in the local universe

IRASF12112+0305

Used data hereØ 12CO(3-2)Ø 13CO(3-2)Ø Dust cont.

Results
Integrated Intensity

IRAS13120

IRASF05189

IRAS17207

ESO286

ESO148

IRASF12112

12CO(3-2)

13CO(3-2)

Ø The structures are spatially resolvedØ The distributions of 12CO are more extended than 13CO=> Making ratio maps from these twoVel. Dispersion Velocity Field

IRAS13120-5453

IRASF05189-2524

IRASF17207-0014

ESO286-IG019

ESO148-IG002

The ratio values for each galaxy
12CO/13CO

IRAS13120

low

Next step is to increase the sample

Most sources have lower
regions at the center, comperingto the outer region.
The global mean ratio in thewhole region is about 20, which
is typical for luminous mergers
and higher than normal spiralgalaxies.
Ratio values measured at thedust continuum peak are around
13.5, and typically lower than
the whole averaged values.
The typical values at the outerregion are about 40.
=> The high global ratio known
from the previous studies is due
to extended (~kpc) gas.

IRASF17207 ESO286 ESO148-0014-IG019 -IG002

IRAS17207

IRASF05189

ESO286

ESO148

IRASF12112

ratio values
Average(Whole region)
Ratio at the SFpeak

Possibly due to gas
inﬂow to the central
star forming region~620 pcDiscussion

Ø ALMA cycle 3-4Ø Band7 observations
Ø Typical spatial resolution: ~ 200pc

Contrary to expectations,the 12CO/13CO ratio islow at the central region~2”

Samples & Observations

IRAS13
IRASF05120-5453 189-2524

highIRAS IRAS IRASF ESO
13120 17207 05189 286

ESO148

IRASF Spiral12112 galaxies

21

171422

22

21

22

8

11

12

15

13~11

IRASF12112+0305

White contour:
Dust thermal continuum=> Star formation tracer

Possible reasons change the isotopic ratio in one galaxy
1. Opacity

12CO(3-2)

Ø Rotational motions are seen in most sourcesØ Complex velocity ﬁeld are also seen in some sources=> outﬂow, inﬂow or tidal motion caused by merging events?

12CO(3-2)

Ø Velocity dispersions are highest around the center of galaxies

Opacity of gas in merging galaxies may change because of somereasons such as large velocity dispersion and/or highly excitedconditions. This may cause the variation of 12CO/13CO line ratio values.
e.g. Aalto et al. 1991

2. Gradients in relative abundance
The variation of intrinsic abundance ratio is also reported. For example,[12CO]/[13CO] abundance ratio diﬀer between the center and the outerregions in Arp 220, which is a merging starburst.
Sliwa et al. 2017

Constrain the conditions by solving radiative transfer in future!