Cold gas and dust: Hunting spiral-like structures in early-type galaxies
Abstract
Context. Observations of neutral hydrogen (H I) and molecular gas show that 50% of all nearby early-type galaxies contain some cold gas. Molecular gas is always found in small gas discs in the central region of the galaxy, while neutral hydrogen is often distributed in a low-column density disc or ring typically extending well beyond the stellar body. Dust is frequently found in early-type galaxies as well.
Aims: The goal of our study is to understand the link between dust and cold gas in nearby early-type galaxies as a function of H I content.
Methods: We analyse deep optical g - r images obtained with the MegaCam camera at the Canada-France-Hawaii Telescope for a sample of 21 H I-rich and 41 H I-poor early-type galaxies.
Results: We find that all H I-rich galaxies contain dust seen as absorption. Moreover, in 57% of these H I-rich galaxies, the dust is distributed in a large-scale spiral pattern. Although the dust detection rate is relatively high in the H I-poor galaxies (∼59%), most of these systems exhibit simpler dust morphologies without any evidence of spiral structures. We find that the H I-rich galaxies possess more complex dust morphology extending to almost two times larger radii than H I-poor objects. We measured the dust content of the galaxies from the optical colour excess and find that H I-rich galaxies contain six times more dust (in mass) than H I-poor ones. In order to maintain the dust structures in the galaxies, continuous gas accretion is needed, and the substantial H I gas reservoirs in the outer regions of early-type galaxies can satisfy this need for a long time. We find that there is a good correspondence between the observed masses of the gas and dust, and it is also clear that dust is present in regions further than 3 Reff.
Conclusions: Our findings indicate an essential relation between the presence of cold gas and dust in early-type galaxies and offer a way to study the interstellar medium in more detail than what is possible with H I observations.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- April 2020
- DOI:
- 10.1051/0004-6361/201935090
- arXiv:
- arXiv:2001.08087
- Bibcode:
- 2020A&A...636A...8Y
- Keywords:
-
- galaxies: elliptical and lenticular;
- cD;
- galaxies: evolution;
- galaxies: ISM;
- galaxies: photometry;
- galaxies: stellar content;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 11 pages, 7 figures, 3 tables, and 4 appendices. Appendices contain dust masses and images of studied galaxies (62). The fits files will be uploaded into the CDS database. Figures in the appendices are of low quality. High-quality images are given in a separated folder. Accepted for publication in A&