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Title: ENHANCED STAR FORMATION OF LESS MASSIVE GALAXIES IN A PROTOCLUSTER AT z = 2.5

Abstract

We investigate a correlation between star formation rate (SFR) and stellar mass for H α emission-line galaxies (HAEs) in one of the richest protoclusters ever known at z∼2.5, the USS 1558-003 protocluster. This study is based on a 9.7 hr narrowband imaging data with MOIRCS on the Subaru telescope. We are able to construct a sample in combination with additional H -band data taken with WFC3 on the Hubble Space Telescope , of 100 HAEs reaching the dust-corrected SFRs down to 3 M {sub ⊙} yr{sup −1} and the stellar masses down to 10{sup 8.0} M {sub ⊙}. We find that while the star-forming galaxies with ≳10{sup 9.3} M {sub ⊙} are located on the universal SFR-mass main sequence (MS) irrespective of the environment, less massive star-forming galaxies with ≲10{sup 9.3} M {sub ⊙} show a significant upward scatter from the MS in this protocluster. This suggests that some less massive galaxies are in a starburst phase, although we do not know yet if this is due to environmental effects.

Authors:
;  [1]; ;  [2]; ; ;  [3];  [4]
  1. Optical and Infrared Astronomy Division, National Astronomical Observatory, Mitaka, Tokyo 181-8588 (Japan)
  2. Subaru Telescope, National Astronomical Observatory of Japan, 650 North A’ohoku Place, Hilo, HI 96720 (United States)
  3. Department of Astronomical Science, SOKENDAI (The Graduate University for Advanced Studies), Mitaka, Tokyo 181-8588 (Japan)
  4. Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstrasse, D-85748 Garching (Germany)
Publication Date:
OSTI Identifier:
22654262
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal Letters; Journal Volume: 826; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; CORRELATIONS; DUSTS; EMISSION; ENVIRONMENTAL EFFECTS; GALAXIES; GALAXY CLUSTERS; MASS; SPACE; STARS; TELESCOPES

Citation Formats

Hayashi, Masao, Kodama, Tadayuki, Tanaka, Ichi, Koyama, Yusei, Shimakawa, Rhythm, Suzuki, Tomoko L., Yamamoto, Moegi, and Tadaki, Ken-ichi, E-mail: masao.hayashi@nao.ac.jp. ENHANCED STAR FORMATION OF LESS MASSIVE GALAXIES IN A PROTOCLUSTER AT z = 2.5. United States: N. p., 2016. Web. doi:10.3847/2041-8205/826/2/L28.
Hayashi, Masao, Kodama, Tadayuki, Tanaka, Ichi, Koyama, Yusei, Shimakawa, Rhythm, Suzuki, Tomoko L., Yamamoto, Moegi, & Tadaki, Ken-ichi, E-mail: masao.hayashi@nao.ac.jp. ENHANCED STAR FORMATION OF LESS MASSIVE GALAXIES IN A PROTOCLUSTER AT z = 2.5. United States. doi:10.3847/2041-8205/826/2/L28.
Hayashi, Masao, Kodama, Tadayuki, Tanaka, Ichi, Koyama, Yusei, Shimakawa, Rhythm, Suzuki, Tomoko L., Yamamoto, Moegi, and Tadaki, Ken-ichi, E-mail: masao.hayashi@nao.ac.jp. 2016. "ENHANCED STAR FORMATION OF LESS MASSIVE GALAXIES IN A PROTOCLUSTER AT z = 2.5". United States. doi:10.3847/2041-8205/826/2/L28.
@article{osti_22654262,
title = {ENHANCED STAR FORMATION OF LESS MASSIVE GALAXIES IN A PROTOCLUSTER AT z = 2.5},
author = {Hayashi, Masao and Kodama, Tadayuki and Tanaka, Ichi and Koyama, Yusei and Shimakawa, Rhythm and Suzuki, Tomoko L. and Yamamoto, Moegi and Tadaki, Ken-ichi, E-mail: masao.hayashi@nao.ac.jp},
abstractNote = {We investigate a correlation between star formation rate (SFR) and stellar mass for H α emission-line galaxies (HAEs) in one of the richest protoclusters ever known at z∼2.5, the USS 1558-003 protocluster. This study is based on a 9.7 hr narrowband imaging data with MOIRCS on the Subaru telescope. We are able to construct a sample in combination with additional H -band data taken with WFC3 on the Hubble Space Telescope , of 100 HAEs reaching the dust-corrected SFRs down to 3 M {sub ⊙} yr{sup −1} and the stellar masses down to 10{sup 8.0} M {sub ⊙}. We find that while the star-forming galaxies with ≳10{sup 9.3} M {sub ⊙} are located on the universal SFR-mass main sequence (MS) irrespective of the environment, less massive star-forming galaxies with ≲10{sup 9.3} M {sub ⊙} show a significant upward scatter from the MS in this protocluster. This suggests that some less massive galaxies are in a starburst phase, although we do not know yet if this is due to environmental effects.},
doi = {10.3847/2041-8205/826/2/L28},
journal = {Astrophysical Journal Letters},
number = 2,
volume = 826,
place = {United States},
year = 2016,
month = 8
}
  • Both observations and simulations show that major tidal interactions or mergers between gas-rich galaxies can lead to intense bursts of star formation. Yet, the average enhancement in star formation rate (SFR) in major mergers and the contribution of such events to the cosmic SFR are not well estimated. Here we use photometric redshifts, stellar masses, and UV SFRs from COMBO-17, 24 mum SFRs from Spitzer, and morphologies from two deep Hubble Space Telescope (HST) cosmological survey fields (ECDFS/GEMS and A901/STAGES) to study the enhancement in SFR as a function of projected galaxy separation. We apply two-point projected correlation function techniques,more » which we augment with morphologically selected very close pairs (separation <2'') and merger remnants from the HST imaging. Our analysis confirms that the most intensely star-forming systems are indeed interacting or merging. Yet, for massive (M{sub *} >= 10{sup 10} M{sub sun}) star-forming galaxies at 0.4 < z < 0.8, we find that the SFRs of galaxies undergoing a major interaction (mass ratios <=1:4 and separations <=40 kpc) are only 1.80 +- 0.30 times higher than the SFRs of non-interacting galaxies when averaged over all interactions and all stages of the interaction, in good agreement with other observational works. Our results also agree with hydrodynamical simulations of galaxy interactions, which produce some mergers with large bursts of star formation on approx100 Myr timescales, but only a modest SFR enhancement when averaged over the entire merger timescale. We demonstrate that these results imply that only approx<10% of star formation at 0.4 <= z <= 0.8 is triggered directly by major mergers and interactions; these events are not important factors in the build-up of stellar mass since z = 1.« less
  • We present high angular resolution Submillimeter Array and Karl G. Jansky Very Large Array observations of the massive protocluster G18.67+0.03. Previously targeted in maser surveys of GLIMPSE Extended Green Objects (EGOs), this cluster contains three Class I CH{sub 3}OH maser sources, providing a unique opportunity to test the proposed role of Class I masers as evolutionary indicators for massive star formation. The millimeter observations reveal bipolar molecular outflows, traced by {sup 13}CO(2-1) emission, associated with all three Class I maser sources. Two of these sources (including the EGO) are also associated with 6.7 GHz Class II CH{sub 3}OH masers; themore » Class II masers are coincident with millimeter continuum cores that exhibit hot core line emission and drive active outflows, as indicated by the detection of SiO(5-4). In these cases, the Class I masers are coincident with outflow lobes, and appear as clear cases of excitation by active outflows. In contrast, the third Class I source is associated with an ultracompact (UC) H II region, and not with Class II masers. The lack of SiO emission suggests that the {sup 13}CO outflow is a relic, consistent with its longer dynamical timescale. Our data show that massive young stellar objects (MYSOs) associated only with Class I masers are not necessarily young and provide the first unambiguous evidence that Class I masers may be excited by both young (hot core) and older (UC H II) MYSOs within the same protocluster.« less
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