What radio emission tells us about star formation in distant spiral galaxies
A team of astronomers led by Fatemeh Tabatabaei from the Instituto de Astrofisica de Canarias (IAC), including scientists from two Max Planck institutes (MPIfR, Bonn and MPIA, Heidelberg), has measured the radio emission for a large sample of galaxies with the Effelsberg 100-m radio telescope at different wavelengths. These galaxies were selected from the KINGFISH sample previously observed in the infrared with the Herschel satellite. This allows for the first time a comparative study of a total of 52 spiral galaxies. A reliable method could be established to determine the star formation rate exclusively from radio data without including other spectral regimes.
Almost all the light we see in the universe comes from stars which
form inside dense clouds of gas in the interstellar medium of galaxies.
The rate at which they form (referred to as star formation rate) depends
on the reserves of gas and its physical properties like density,
temperature, and magnetic field strength. To understand how star
formation works, measuring the star formation rate is a key task.
In order to derive the star formation rates, a variety of
observations at different wavelengths had been undertaken until now,
each with its advantages and disadvantages. The tracers used in the
visible and the ultraviolet can be partly absorbed by interstellar dust.
This led to the use of hybrid tracers, which combine two or more
different wavelength ranges, among them the infrared, which can help to
correct for the dust absorption. However, other emissions which are not
related to the formation of massive stars can intervene and lead to
confusion.
Now, an international research team made a detailed analysis of the
spectral energy distribution of a subsample of the KINGFISH galaxies
(Fig. 1). The scientists determined for the first time the emitted radio
energy which can be used as a tracer to calculate their star formation
rates. “We have used the radio emission at intermediate frequencies
between 1 and 10 GHz because a tight correlation between the radio and
the infrared emission was detected in previous studies, covering a total
range of more than four orders of magnitude,” says Fatemeh Tabatabaei
from the IAC (La Laguna, Tenerife), the leading author of the study. In
order to improve this relation, more precise studies were needed to
understand the energy sources and how radio emission from galaxies is
produced.
Spiral
Galaxy NGC 4725. Contour lines of radio continuum emission at a
frequency of 8.5 GHz, observed with the Effelsberg 100-m radio
telescope, overlayed onto an optical image of the galaxy. ©Ancor Damas-Segovia (radio map & combined image), Martin Pugh/martinpughastrophotography.id.au (optical image)
“We decided within the research group to make studies of galaxies
from the KINGFISH sample at a series of radio wavelengths”, recalls Eva
Schinnerer from the Max-Planck-Institut für Astronomie (MPIA) in
Heidelberg, Germany. The final sample consists of 52 galaxies with very
diverse properties. “As a single dish, the 100-m Effelsberg telescope
with its high sensitivity is the ideal instrument to receive reliable
radio fluxes of weak extended objects like galaxies”, explains Marita
Krause from the Max-Planck-Institut für Radioastronomie (MPIfR) in Bonn,
Germany, who was in charge of the radio observations of those galaxies
with the Effelsberg radio telescope. “We named it the KINGFISHER
project, meaning KINGFISH galaxies Emitting in Radio.” Fig. 2 shows the
radio emission of one galaxy from the sample (NGC 4725).
The results of this project, published today in The Astrophysical
Journal, show that the radio emission over the frequency range used is
an ideal tracer for calculating the star formation rate, for several
reasons. Firstly, the interstellar dust does not attenuate or absorb
radiation at this wavelength; secondly, it is emitted by massive stars
during several phases of their formation, from young stellar objects to
HII regions (zones of ionized gas) and supernova remnants, and finally,
there is no need to combine it with any other tracer. For these reasons,
measurements in the chosen range are a more rigorous way to measure the
formation rate of massive stars than the tracers traditionally used.
“Now we can apply this method to many more galaxies, using the
Effelsberg 100-m telescope”, concludes Rainer Beck from MPIfR, also a
co-author of the study.
The research team comprises F.S. Tabatabaei, E. Schinnerer, M.
Krause, G. Dumas, S. Meidt, A. Damas-Segovia, R. Beck, E.J. Murphy, D.D.
Mulcahy, B. Groves, A. Bolatto, D. Dale, M. Galametz, K. Sandstrom, M.
Boquien, D. Calzetti, R.C. Kennicutt, L.K. Hunt, I. de Looze and E.W.
Pellegrini. Co-authors from MPIfR are Marita Krause, Ancor Damas-Segovia
and Rainer Beck.
Fatemeh Tabatabaei started to investigate the radio and infrared
emission of galaxies as part of her PhD thesis at MPIfR, followed by
postdoc positions at MPIfR and MPIA. At present she is a researcher at
the Instituto de Astrofisica de Canarias (IAC), La Laguna.
KINGFISH (“Key Insights on Nearby Galaxies: a Far-Infrared Survey
with Herschel”) is a survey of 61 galaxies in the Nearby Universe. KINGFISHER
(“KINGFISH galaxies Emitting in Radio”) provides a subsample of these
galaxies north of -21 degrees declination. For 17 of these galaxies
radio data from the Effelsberg 100-m radio telescope at different
frequencies did already exist (see “Atlas of Galaxies” web page), 35
galaxies were newly observed with the Effelsberg telescope. Both data
sets with a total of 52 galaxies were used for the present study.
Original Paper
The radio spectral energy distribution and star formation rate calibration in galaxies
F. S. Tabatabaei et al., 2017, The Astrophysical Journal (21 February 2017)
Links
Cosmic Magnetism
Cosmic Magnetism, Research at MPIfR Bonn
Radio Telescope Effelsber
Effelsberg Radio Telescope
Atlas of Galaxies
Radio images of Galaxies, compiled by Maja Kierdorf and Rainer Beck (MPIfR Bonn)
KINGFISH
“Key Insights on Nearby Galaxies: a Far-Infrared Survey with Herschel” (KINGFISH)
IAC
Instituto de Astrofísica de Canarias (IAC)
Tune your radio: galaxies sing when forming stars
Parallel Press Release of the Instituto de Astrofisica de Canarias (IAC), La Laguna, Spain, 21 February 2017
MPIA
Max Planck Institute for Astronomy (MPIA), Heidelberg
Radio astronomers tune in to the star formation channel
Parallel Press Release of the Max Planck Institute for Astronomy (MPIA) Heidelberg, 21 February 2017
Radioastronomische Fundamentalphysik
Research Department "Fundamental Physics in Radio Astronomy" at MPIfR, Bonn, Germany
Local Contact
Dr. Marita Krause Phone:+49 228 525-312
Dr. Rainer Beck
Phone:+49 228 525-323
Email: rbeck@mpifr-bonn.mpg.de
Max-Planck-Institut für Radioastronomie, Bonn
Dr. Norbert Junkes Press and Public Outreach Phone:+49 228 525-399
Email: njunkes@mpifr-bonn.mpg.de
Max-Planck-Institut für Radioastronomie, Bonn
Links
Cosmic Magnetism
Cosmic Magnetism, Research at MPIfR Bonn
Radio Telescope Effelsber
Effelsberg Radio Telescope
Atlas of Galaxies
Radio images of Galaxies, compiled by Maja Kierdorf and Rainer Beck (MPIfR Bonn)
KINGFISH
“Key Insights on Nearby Galaxies: a Far-Infrared Survey with Herschel” (KINGFISH)
IAC
Instituto de Astrofísica de Canarias (IAC)
Tune your radio: galaxies sing when forming stars
Parallel Press Release of the Instituto de Astrofisica de Canarias (IAC), La Laguna, Spain, 21 February 2017
MPIA
Max Planck Institute for Astronomy (MPIA), Heidelberg
Radio astronomers tune in to the star formation channel
Parallel Press Release of the Max Planck Institute for Astronomy (MPIA) Heidelberg, 21 February 2017
Radioastronomische Fundamentalphysik
Research Department "Fundamental Physics in Radio Astronomy" at MPIfR, Bonn, Germany
Local Contact
Dr. Marita Krause Phone:+49 228 525-312
Dr. Rainer Beck
Phone:+49 228 525-323
Email: rbeck@mpifr-bonn.mpg.de
Max-Planck-Institut für Radioastronomie, Bonn
Dr. Norbert Junkes Press and Public Outreach Phone:+49 228 525-399
Email: njunkes@mpifr-bonn.mpg.de
Max-Planck-Institut für Radioastronomie, Bonn
