Quantitative and statistical analysis of the molecular gas
morphology in the nearby star-forming galaxies

Credit: F. Santoro & A. Leroy/PHANGS/ALMA

Credit: ALMA (ESO/NAOJ/NRAO), A. Marinkovic/X-Cam

Takashi Yamamoto (University of Tsukuba)
Daisuke Iono (NAOJ), Toshiki Saito (NAOJ), Nario Kuno (University of Tsukuba)Tomonaga Center for the History of the Universe

December 18, 2023

Introduction

The process of galaxy evolution remains unresolved.
z∼0
Cimatti, A. et al., 2020

1<z<3

The Hubble classification of galaxy morphology

The Age of JWST in Astronomy

2Madau & Dickinson 2015

The process of galaxy evolution remains unresolved.
Introduction

Star-forming galaxies

Non-barred spiral galaxies
Barred spiral galaxies

Passive galaxies

3Introduction

The diverse shapes of the galaxy tell a lot of information.
Arp 248

Non-barred spiral galaxies

Star-forming galaxies
Passive galaxies
Barred spiral galaxies
Credit:
ESA/Hubble & NASA, Dark Energy Survey/DOE/FNAL/
DECam/CTIO/NOIRLab/NSF/AURA, J. Dalcanton

Qualitative morphology is not sufficient to explore galaxy evolution.
Quantitative morphology is needed.

> We want to understand how galaxy populations are related to each other andto their formation histories (right panel).

4

Introduction

Can we classify them more quantitatively?

> Quantitative analysis of the morphology of galaxies using optical and infrared
data has been extensively studied by Conselice (2003) and others.

> On the other hand, quantitative analysis of the distribution morphology ofmolecular gas in nearby galaxies using radio data essential for the study of galaxy
evolution has not been sufficiently carried out due to the lack of spatial resolution.
>However, with the operation of ALMA, a large amount of high-resolution
molecular gas observation data has been accumulated. This has made it possible todo equivalent to Conselice’s research in radio astronomy.
5Introduction

We want to obtain clues to the evolutionary process of nearby galaxies.
For this purpose, quantitative classification of morphology by molecular gas isessential.
This is because star formation is a principal factor in the formation and evolutionof galaxies, and molecular gas is the material for star formation.
NGC 3627
NGC 628

SA(s)cCredit: F. Santoro & A. Leroy/PHANGS/ALMA

6SAB(s)bMethod

The CAS Parameters

By C. J. Conselice(2003).

Many attempts have been presented in the literature to define the quantitative method.
The CAS physical morphology parameters have been the most widely used among them.
Concentration ( C )Asymmetry ( A )r80%
C = 5 × log( r20% )|I − R|
A=I
σ

Clumpiness( S )10 × (I − I )S=I

σ = 0.3 × r (η = 0.2)
r : Petrosian radius
7

Method

Modified CAS (Conselice 2003) parameters
Concentration ( C )r90%
C = 5 × log( r10% )Central concentration of molecular gas

Asymmetry ( A )|I − R|
A=2I

Distortion of molecular gas distribution
σClumpiness( S )10 × (I − I )S=I

σ = 0.3 × Re

The ratio of GMAs in molecular gas
GMAs; The Giant Molecular cloud Associations
8

Data
73 galaxies
From PHANGS-ALMA
Archive data
The Physics at High Angular resolution
in Nearby Galaxies (PHANGS)

Leroy et al., 2021a

Credit: F. Santoro & A. Leroy/PHANGS/ALMA

Spatial resolution∼ 180 pc

9Querejeta et al. 2021
10ResultThis is the first study to examine molecular gas distribution using all threemodel-independent CAS parameters from Conselice (2003).
As a result of this analysis, we made several important
findings, as shown in the figure below.
The clear correlation between
Asymmetry(A) and Clumpiness(S)The bar structure increases the central
concentration of molecular gas.

Barred spiral galaxies, non-barredspiral galaxies, and lenticular galaxies
are plotted in characteristic positions
on the CAS space.

Barred spirals
Non barred spirals

S0 galaxies

11ResultThis is the first study to examine molecular gas distribution using threemodel-independent CAS parameters from Conselice (2003).
As a result of this analysis, we made several importantfindings, as shown in the figure below.
The clear correlation between
Asymmetry(A) and Clumpiness(S)The bar structure increases the central
concentration of molecular gas.

Barred spiral galaxies, non-barredspiral galaxies, and lenticular galaxies
are plotted in characteristic positions
on the CAS space.

Barred spirals
Non barred spirals

S0 galaxies

12Result & Discussion

The correlation between Asymmetry(A) and Clumpiness(S)(1) One of the results is that Clumpiness (S) and Asymmetry (A) showed a clearcorrelation. It suggests that galaxies with a more distorted distribution of molecular gas
are more likely to form GMAs.

Spearman's rank correlation coefficient is 0.62, with the associated p-value of 4 × 10−913Result & Discussion

Asymmetric galaxies affected by past interactions are more likely to form giant
molecular cloud associations due to repeated collisions between gas clouds
caused by perturbations of molecular gas clouds.

NGC 1546

NGC 4731

Symmetric galaxies, such as S0 galaxies, have an extended distribution of molecular
gas in the galactic bulge and are less likely to form GMAs.
14

Result

This is the first study to examine molecular gas distribution using threemodel-independent CAS parameters from Conselice (2003).
As a result of this analysis, we made several important
findings, as shown in the figure below.
The clear correlation between
Asymmetry(A) and Clumpiness(S)The bar structure increases the central
concentration of molecular gas.

Barred spiral galaxies, non-barredspiral galaxies, and lenticular galaxies
are plotted in characteristic positions
on the CAS space.

Barred spirals
Non barred spirals

S0 galaxies

15

Result & Discussion

The bar structure increases the central concentration of molecular gas.

We used the Kolmogorov-Smirnov (KS) test for twosamples, SA galaxies and SB+SAB galaxies.
KS probability value is 1.46 × 10−416Result & Discussion

The bar structure increases the central concentration of molecular gas.

Concentration(C) vs.Clumpiness(S)Concentration(C) vs.Asymmetry(A)17Result & Discussion

The bar structure increases the central concentration of molecular gas.
The mean C value for all galaxy samples inthis analysis is 4.9. The mean C value forbarred spiral galaxies is 5.4, while the mean
C value for non-barred spiral galaxies is 3.9.
This is consistent with the results ofprevious studies (e.g., Sakamoto et al. 1999;
Sheth et al. 2005; Kuno et al. 2007).
It is also consistent with many previous
theoretical studies on the physicalprocesses that cause molecular gas to fall
into the center of galaxies due to bar
structures (e.g., Wada et al. 1995; Baba etal. 2022).
18Result & Discussion

However, barred spiral galaxies have awide range of C values 3.0 ≤ C ≤ 7.7.
This study found that 25% of barredspiral galaxies with C values are lower
than the average C value of non-barredspiral galaxies. What is the cause of thisdifference in C values?
Wide range!

19

Result & Discussion

A positive correlation was found between C and Bar length (Rbar /R25), as
shown in this figure.
Here, Lang et al., 2020 was cited for the calculation.

Spearman's rank correlation coefficient is 0.63 with the associated p − value of 3.8 × 10−5)20Result & Discussion

This result is consistent with Kuno et al., 2007, whichshowed that the bar structure efficiently transports
molecular gas within the length of the bar toward thecenter while the role in bringing gas in from the outerparts of the disks is small.

Mechanism of efficient concentrationof molecular gas to the galactic center

NGC 1433; ALMA, CO (2-1)

Although the quantitative relationship between the concentration ofmolecular gas at the Galactic center and the length of the bar structure has
not been clarified in Kuno et al., 2007, This study provides quantitative
results of this relationship between the two.
21

Result

This is the first study to examine molecular gas distribution using threemodel-independent CAS parameters from Conselice (2003).
As a result of this analysis, we made several important
findings, as shown in the figure below.
The clear correlation between
Asymmetry(A) and Clumpiness(S)The bar structure increases the central
concentration of molecular gas.

Barred spiral galaxies, non-barredspiral galaxies, and lenticular galaxies
are plotted in characteristic positions
on the CAS space.

Barred spirals
Non barred spirals

S0 galaxies

22Result & Discussion

The three populations of galaxies, barred spiral galaxies (SB+SAB), non-barred spiralgalaxies (SA), and lenticular galaxies (S0), are plotted in characteristic positions on theCAS space.

23

Result & Discussion

The three populations of galaxies, barred spiral galaxies (SB+SAB), non-barred spiralgalaxies (SA), and lenticular galaxies (S0), are plotted in characteristic positions on theCAS space.

Bershady et al. 2000

24

Result & Discussion

SA

The most significant result of this study is the history of the distribution
morphology of molecular gas in nearby disk galaxies.

CCThe three populations of galaxies, barred spiral galaxies (SB+SAB), non-barred spiral galaxies (SA), andlenticular galaxies (S0), are plotted in characteristic positions on the CAS space.
25

Summary✔︎ Applying CAS methods of quantitative morphometric analysis to the PHANGS-ALMA
CO(2-1) data yielded several significant results.
✔︎ One of the results is that Clumpiness (S) and Asymmetry (A) showed a clear correlation.
It suggests that galaxies with a more distorted distribution of molecular gas are more likelyto form GMAs.
✔︎ The results of this analysis indicate that barred spiral galaxies have high central
concentrations of molecular gas. This is consistent with the results of previous studies.
Our new finding is a positive correlation between C and bar length (Rbar /R25).
✔︎ In this study, we make a remarkable classification of non-barred spiral galaxies andbarred spiral galaxies, taking advantage of the characteristics of the CO(2-1) emission line
data. Quantitatively and statistically analyzing molecular gas morphology in nearby disk
galaxies for the first time classified barred spiral galaxies (SB+SAB), non-barred spiralgalaxies (SA), and lenticular galaxies (S0) on CAS space.
26