Deceptively cold dust in the massive starburst galaxy GN20 at z ∼ 4 - Archive ouverte HAL Access content directly
Journal Articles Astronomy and Astrophysics - A&A Year : 2020

## Deceptively cold dust in the massive starburst galaxy GN20 at z ∼ 4

(1) , (1, 2) , (1) , (3) , (4) , (5) , (6) , (7) , (3) , (8) , (4) , (3) , (9) , (10) , (1) , (1)
1
2
3
4
5
6
7
8
9
10
Isabella Cortzen
• Function : Correspondent author
Francesco Valentino
• Function : Author
• PersonId : 837613
Daizhong Liu
Dimitra Rigopoulou
• Function : Author
Mark Sargent
Dominik Riechers
Diane Cormier
• Function : Author
Jacqueline A. Hodge
• Function : Author
Fabian Walter
David Elbaz
• Function : Author
Matthieu Béthermin
• Function : Author
Thomas R. Greve
• Function : Author
Vasily Kokorev
Sune Toft

#### Abstract

We present new observations, carried out with IRAM NOEMA, of the atomic neutral carbon transitions [C I]($^3$P$_1$–$^3$P$_0$) at 492 GHz and [C I]($^3$P$_2$–$^3$P$_1$) at 809 GHz of GN20, a well-studied star-bursting galaxy at $z$ = 4.05. The high luminosity line ratio [C I]($^3$P$_2$–$^3$P$_1$) /[C I]($^3$P$_1$–$^3$P$_0$) implies an excitation temperature of 48$^{+14}_{−9}$ K, which is significantly higher than the apparent dust temperature of $T_d$ = 33 $\pm$ 2 K ($\beta$ = 1.9) derived under the common assumption of an optically thin far-infrared dust emission, but fully consistent with $T_d$ = 52 $\pm$ 5 K of a general opacity model where the optical depth ($\tau$) reaches unity at a wavelength of $\lambda_0$ = 170 $\pm$ 23 $\mu$m. Moreover, the general opacity solution returns a factor of ∼2× lower dust mass and, hence, a lower molecular gas mass for a fixed gas-to-dust ratio, than with the optically thin dust model. The derived properties of GN20 thus provide an appealing solution to the puzzling discovery of starbursts appearing colder than main-sequence galaxies above $z$ $>$  2.5, in addition to a lower dust-to-stellar mass ratio that approaches the physical value predicted for starburst galaxies.

#### Domains

Physics [physics] Astrophysics [astro-ph]

### Dates and versions

cea-02496332 , version 1 (02-03-2020)

### Identifiers

• HAL Id : cea-02496332 , version 1
• DOI :

### Cite

Isabella Cortzen, Georgios E. Magdis, Francesco Valentino, Emanuele Daddi, Daizhong Liu, et al.. Deceptively cold dust in the massive starburst galaxy GN20 at z ∼ 4. Astronomy and Astrophysics - A&A, 2020, 634, pp.L14. ⟨10.1051/0004-6361/201937217⟩. ⟨cea-02496332⟩

### Export

BibTeX TEI Dublin Core DC Terms EndNote Datacite

46 View