2022A&A...657A..49K


Query : 2022A&A...657A..49K

2022A&A...657A..49K - Astronomy and Astrophysics, volume 657A, 49-49 (2022/1-1)

Exploring the physics behind the non-thermal emission from star-forming galaxies detected in γ rays.

KORNECKI P., PERETTI E., DEL PALACIO S., BENAGLIA P. and PELLIZZA L.J.

Abstract (from CDS):


Context. Star-forming galaxies emit non-thermal radiation from radio to γ rays. Observations show that their radio and γ-ray luminosities scale with their star formation rates, supporting the hypothesis that non-thermal radiation is emitted by cosmic rays produced by their stellar populations. However, the nature of the main cosmic-ray transport processes that shape the emission in these galaxies is still poorly understood, especially at low star formation rates.
Aims. Our aim is to investigate the main mechanisms of global cosmic-ray transport and cooling in star-forming galaxies. The way they contribute to shaping the relations between non-thermal luminosities and star formation rates could shed light onto their nature, and allow us to quantify their relative importance at different star formation rates.
Methods. We developed a model to compute the cosmic-ray populations of star-forming galaxies, taking into account their production, transport, and cooling. The model is parametrised only through global galaxy properties, and describes the non-thermal emission in radio (at 1.4 GHz and 150 MHz) and γ rays (in the 0.1-100 GeV band). We focused on the role of diffusive and advective transport by galactic winds, either driven by turbulent or thermal instabilities. We compared model predictions to observations, for which we compiled a homogeneous set of luminosities in these radio bands, and updated those available in γ rays.
Results. Our model reproduces reasonably well the observed relations between the γ-ray or 1.4 GHz radio luminosities and the star formation rate, assuming a single power-law scaling of the magnetic field (with index β = 0.3) and winds blowing either at Alfvenic speeds (∼tens of km/s, for ≥5 M/yr) or typical starburst wind velocities (∼hundreds of km/s, for ≥5 M/yr). Escape of cosmic rays is negligible for ≥30 M/yr. A constant ionisation fraction of the interstellar medium fails to reproduce the 150 MHz radio luminosity throughout the whole star formation rate range.
Conclusions. Our results reinforce the idea that galaxies with high star formation rates are cosmic-ray calorimeters, and that the main mechanism driving proton escape is diffusion, whereas electron escape also proceeds via wind advection. They also suggest that these winds should be cosmic-ray or thermally driven at low and intermediate star formation rates, respectively. Our results globally support that magneto-hydrodynamic turbulence is responsible for the dependence of the magnetic field strength on the star formation rate and that the ionisation fraction is strongly disfavoured to be constant throughout the whole range of star formation rates.

Abstract Copyright: © ESO 2022

Journal keyword(s): galaxies: starburst - galaxies: star formation - gamma rays: galaxies - radio continuum: galaxies

Simbad objects: 15

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Number of rows : 15
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2023
#notes
1 M 31 G 00 42 44.330 +41 16 07.50 4.86 4.36 3.44     ~ 12097 1
2 NGC 253 SyG 00 47 33.134 -25 17 19.68   8.03   6.94 8.1 ~ 3193 2
3 NAME SMC G 00 52 38.0 -72 48 01   2.79 2.2     ~ 10530 1
4 M 33 GiG 01 33 50.8965749232 +30 39 36.630403128 6.17 6.27 5.72     ~ 5603 1
5 M 77 GiP 02 42 40.7091669408 -00 00 47.859690204 9.70 9.61 8.87 10.1 9.9 ~ 4425 2
6 NAME Magellanic Clouds GrG 03 00 -71.0           ~ 6555 1
7 NAME LMC G 05 23 34.6 -69 45 22     0.4     ~ 16509 1
8 NGC 2146 SBG 06 18 37.710 +78 21 25.27 11.67 11.38 10.59     ~ 681 2
9 NGC 2403 AGN 07 36 51.3381434280 +65 36 09.650825640 9.31 8.84 8.38 8.19   ~ 1721 1
10 M 82 IG 09 55 52.430 +69 40 46.93 9.61 9.30 8.41     ~ 5677 6
11 NGC 3424 GiP 10 51 46.322 +32 54 02.44   13.2       ~ 145 1
12 NGC 3690 IG 11 28 31.326 +58 33 41.80   13.19 12.86     ~ 950 4
13 NGC 4945 Sy2 13 05 27.279 -49 28 04.44   9.31 14.40 7.55   ~ 1398 2
14 NAME Circinus Galaxy Sy2 14 13 09.906 -65 20 20.47   10.89 9.84 10.6 10.0 ~ 1127 2
15 IC 4553 SyG 15 34 57.22396 +23 30 11.6084   14.76 13.88     ~ 2872 4

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2023.01.31-01:16:49

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