A Physical Approach to the Identification of High-z Mergers: Morphological Classification in the Stellar Mass Domain.
Abstract
At z ≳ 1, the distinction between merging and “normal” star-forming galaxies based on single band morphology is often hampered by the presence of large clumps which result in a disturbed, merger-like appearance even in rotationally supported disks. In this paper we discuss how a classification based on canonical, non-parametric structural indices measured on resolved stellar mass maps, rather than on single-band images, reduces the misclassification of clumpy but not merging galaxies. We calibrate the mass-based selection of mergers using the MIRAGE hydrodynamical numerical simulations of isolated and merging galaxies which span a stellar mass range of 109.8-1010.6 M⊙ and merger ratios between 1:1-1:6.3. These simulations are processed to reproduce the typical depth and spatial resolution of observed Hubble Ultra Deep Field (HUDF) data. We test our approach on a sample of real z≃ 2 galaxies with kinematic classification into disks or mergers and on ∼100 galaxies in the HUDF field with photometric/spectroscopic redshift between 1.5 ≤ z ≤ 3 and M > 109.4 M⊙. We find that a combination of the asymmetry AMASS and M20, MASS indices measured on the stellar mass maps can efficiently identify real (major) mergers with ≲20% contamination from clumpy disks in the merger sample. This mass-based classification cannot be reproduced in star-forming galaxies by H-band measurements alone, which instead result in a contamination from clumpy galaxies which can be as high as 50%. Moreover, we find that the mass-based classification always results in a lower contamination from clumpy galaxies than an H-band classification, regardless of the depth of the imaging used (e.g., CANDELS versus HUDF).
- Publication:
-
The Astrophysical Journal
- Pub Date:
- June 2015
- DOI:
- 10.1088/0004-637X/805/2/181
- arXiv:
- arXiv:1503.06220
- Bibcode:
- 2015ApJ...805..181C
- Keywords:
-
- galaxies: high-redshift;
- galaxies: interactions;
- galaxies: irregular;
- galaxies: structure;
- Astrophysics - Astrophysics of Galaxies;
- Astrophysics - Cosmology and Nongalactic Astrophysics
- E-Print:
- Accepted for publication in ApJ. The complete Table 1 can be found at this URL: http://www.phys.susx.ac.uk/~ac625/Table1_full.pdf