Outflows in Sodium Excess Objects
Abstract
Van Dokkum and Conroy revisited the unexpectedly strong Na i lines at 8200 Å found in some giant elliptical galaxies and interpreted them as evidence for an unusually bottom-heavy initial mass function. Jeong et al. later found a large population of galaxies showing equally extraordinary Na D doublet absorption lines at 5900 Å (Na D excess objects: NEOs) and showed that their origins can be different for different types of galaxies. While a Na D excess seems to be related to the interstellar medium (ISM) in late-type galaxies, smooth-looking early-type NEOs show little or no dust extinction and hence no compelling signs of ISM contributions. To further test this finding, we measured the Doppler components in the Na D lines. We hypothesized that the ISM would have a better (albeit not definite) chance of showing a blueshift Doppler departure from the bulk of the stellar population due to outflow caused by either star formation or AGN activities. Many of the late-type NEOs clearly show blueshift in their Na D lines, which is consistent with the former interpretation that the Na D excess found in them is related to gas outflow caused by star formation. On the contrary, smooth-looking early-type NEOs do not show any notable Doppler components, which is also consistent with the interpretation of Jeong et al. that the Na D excess in early-type NEOs is likely not related to ISM activities but is purely stellar in origin.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- August 2015
- DOI:
- 10.1088/0004-637X/809/1/91
- arXiv:
- arXiv:1507.03342
- Bibcode:
- 2015ApJ...809...91P
- Keywords:
-
- catalogs;
- galaxies: abundances;
- galaxies: elliptical and lenticular;
- cD;
- galaxies: evolution;
- galaxies: spiral;
- galaxies: stellar content;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 2015ApJ...809...91P