Rapid Formation of New Stars in Distant Galaxies

Galaxies forming stars at extreme rates nine billion years ago were more efficient than average galaxies today, researchers find.
The majority of stars have been believed to lie on a “main sequence”, where the larger a galaxy’s mass, the higher its efficiency to form new stars. However, every now and then a galaxy will display a burst of newly-formed stars that shine brighter than the rest. A collision between two large galaxies is usually the cause of such starburst phases, where the cold gas residing in the giant molecular clouds becomes the fuel for sustaining such high rates of star formation.

The question astronomers have been asking is whether such starbursts in the early universe were the result of having an overabundant gas supply, or whether galaxies converted gas more efficiently.

A new study to be published in Astrophysical Journal Letters on October 14, led by John Silverman at the Kavli Institute for the Physics and Mathematics of the Universe, studied carbon monoxide (CO) gas content in seven starburst galaxies far away from when the Universe was a young four billion years old. This was feasible by the advent of Atacama Large Millimeter Array (ALMA), located on a mountaintop plateau in Chile, which works in tandem to detect electromagnetic waves at a wavelength range in the millimeter (pivotal for studying molecular gas) and a sensitivity level that is just starting to be explored by astronomers today.

The researchers found the amount of CO-emitting gas was already diminished even though the galaxy continued to form stars at high rates. These observations are similar to those recorded for starburst galaxies near Earth today, but the amount of gas depletion was not quite as rapid as expected. This led researchers to conclude there might be a continuous increase in the efficiency depending on how high above the rate of forming stars is from the main sequence.

This study relied on a variety of powerful telescopes available through the COSMOS survey. Only the Spitzer and Herschel Observatories could measure accurate rates of star formation, and the Subaru Telescope could confirm the nature and distance of these extreme galaxies using spectroscopy.

John Silverman’s comment

“These observations clearly demonstrate ALMA’s unique capability to measure with ease a critical component of high redshift galaxies thus indicative of the remarkable results to come from ALMA.”

Useful Links

All images can be seen and downloaded from this page: http://web.ipmu.jp/press//20151015-pacs867/

Paper details

Journal: Astrophysical Journal Letters
Title: A higher efficiency of converting gas to stars pushes galaxies at z~1.6 well-above the star-forming main sequence
Authors: J. D. Silverman (1), E. Daddi (2), G. Rodighiero (3), W. Rujopakarn (1,?4), M. Sargent (5), A. Renzini (6), D. Liu (2), C. Feruglio (7), D. Kashino (8), D. Sanders (9), J. Kartaltepe (10), T. Nagao (11), N. Arimoto (12), S. Berta (13), M. B ?ethermin (14), A. Koekemoer (15), D. Lutz (13), G. Magdis (16,17), C. Mancini (6), M. Onodera (18), G. Zamorani (19)

Author affiliations:
1 Kavli Institute for the Physics and Mathematics of the Universe (WPI), The University of Tokyo Insti- tutes for Advanced Study, The University of Tokyo, Kashiwa, Chiba 277-8583, Japan
2 Laboratoire AIM, CEA/DSM-CNRS-Universite Paris Diderot, Irfu/Service d’Astrophysique, CEA Saclay
3 Dipartimento di Fisica e Astronomia, Universita di Padova, vicolo Osservatorio, 3, 35122, Padova, Italy
4 Department of Physics, Faculty of Science, Chulalongkorn University, 254 Phayathai Road, Pathumwan, Bangkok 10330, Thailand
5 Astronomy Centre, Department of Physics and Astronomy, University of Sussex, Brighton, BN1 9QH, UK
6 Instituto Nazionale de Astrofisica, Osservatorio Astronomico di Padova, v.co dell’Osservatorio 5, I-35122, Padova, Italy, EU
7 IRAM – Institut de RadioAstronomie Millim ?etrique, 300 rue de la Piscine, 38406 Saint Martin d’H`eres, France
8 Division of Particle and Astrophysical Science, Graduate School of Science, Nagoya University, Nagoya, 464-8602, Japan
9 Institute for Astronomy, University of Hawaii, 2680 Woddlawn Drive, Honolulu, HI, 96822
10 National Optical Astronomy Observatory, 950 N. Cherry Ave., Tucson, AZ, 85719
11 Graduate School of Science and Engineering, Ehime University, 2-5 Bunkyo-cho, Matsuyama 790-8577, Japan
12 Subaru Telescope, 650 North A’ohoku Place, Hilo, Hawaii, 96720, USA
13 Max-Planck-Institut fu ?r extraterrestrische Physik, D-84571 Garching, Germany
14 European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany
15 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD, 21218, USA
16 Department of Physics, University of Oxford, Keble Road, Oxford OX1 3RH, UK
17 Institute for Astronomy, Astrophysics, Space Applications and Remote Sensing, National Observatory of Athens, GR-15236 Athens, Greece
18 Institute of Astronomy, ETH Zu ?rich, CH-8093, Zu ?rich, Switzerland
19 INAF Osservatorio Astronomico di Bologna, via Ranzani 1, I-40127, Bologna, Italy

DOI: 10.1088/2041-8205/812/2/L23
Paper: http://iopscience.iop.org/article/10.1088/2041-8205/812/2/L23 (Astrophysical Journal Letters)
Preprint: http://arxiv.org/abs/1505.04977 (arXiv.org archive website)