The radio-infrared correlation in galaxies

Proceedings of the International Astronomical Union 11/2009; DOI: 10.1017/S1743921310010057
Source: arXiv


The radio-infrared correlation was explained as a direct and linear
relationship between star formation and IR emission. However, one fact making
the IR-star formation linkage less obvious is that the IR emission consists of
at least two emission components, cold dust and warm dust. The cold dust
emission may not be directly linked to the young stellar population.
Furthermore, understanding the origin of the radio-IR correlation requires to
discriminate between the two main components of the radio continuum emission,
free-free and synchrotron emission. Here, we present a multi-scale study of the
correlation of IR with both the thermal and non-thermal (synchrotron)
components of the radio continuum emission from the nearby galaxies M33 and

Download full-text


Available from: Fatemeh Tabatabaei, Mar 20, 2014
3 Reads
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Context: As more and more data are collected by cosmic ray experiments such as the Pierre Auger Observatory and Telescope Array (TA), the search for the sources of the Ultra High Energy Cosmic Rays (UHECR) continues. Already we have some hints about the sources or type of sources involved and more work is required to confirm any of this. Aims: We intend to predict the UHECR fluxes and the maximal energies of particles from two complete samples of nearby active galaxies, selected at radio and far-infrared frequencies. Also, we investigate the magnetic scattering of the UHECR path in the intervening cosmic space. Methods: We propose here a new method of searching for the sources of the UHECR in three steps, first we model the activity of the type of sources and get the flux of UHECR and a maximal energy for particle acceleration, then we model the interaction and angle deflection in the intergalactic space and finally we simulate the distribution of the cosmic rays events that can be statistically compared with future data of the cosmic rays observatories. Results: We analyzed two classes of sources, gamma ray bursts (GRBs) and Radio Galaxies (RGs). Ordering by the UHECR flux, few RGs are viable candidates, as for GRB many sources are viable candidates, requiring less scattering of the particles along their path to Earth to interpret the presently observed sky distribution. Most of the flux from RGs comes from the Southern sky, and most of the flux of particles from GRB comes from the North, although the differences are so small as to require large statistics to confirm this. The intergalactic and Galactic magnetic fields may help to distinguish the two extreme cases, also pure protons from heavy nuclei at the same energy. As a consequence flat spectrum radio sources such as 3C279 should confirm the production of UHECR in this class of sources through energetic neutrinos.
  • [Show abstract] [Hide abstract]
    ABSTRACT: We present the first maps of NGC 3044 and NGC 4157 at λ 450 μm and λ 850 μm from the James Clerk Maxwell Telescope as well as the first maps at 617 MHz from the Giant Metrewave Radio Telescope. High-latitude emission has been detected in both the radio continuum and sub-mm for NGC 3044 and in the radio continuum for NGC 4157, including several new features. For NGC 3044, in addition, we find 617 MHz emission extending to the north of the major axis, beginning at the far ends of the major axis. One of these low-intensity features, more than 10 kpc from the major axis, has apparently associated emission at λ 20 cm and may be a result of in-disc activity related to star formation. The dust spectrum at long wavelengths required fitting with a two-temperature model for both galaxies, implying the presence of cold dust (Tc = 9.5 K for NGC 3044 and Tc = 15.3 K for NGC 4157). Dust masses are Md = 1.6 × 108 M⊙ and Md = 2.1 × 107 M⊙ for NGC 3044 and NGC 4157, respectively, and are dominated by the cold component. There is a clear correlation between the 617 MHz and λ 850 μm emission in the two galaxies. In the case of NGC 3044 for which the λ 850 μm data are strongly dominated by cold dust, this implies a relation between the non-thermal synchrotron emission and cold dust. The 617 MHz component represents an integration of massive star formation over the past 107-8 yr and the λ 850 μm emission represents heating from the diffuse interstellar radiation field (ISRF). The 617 MHz-λ 850 μm correlation improves when a smoothing kernel is applied to the λ 850 μm data to account for differences between the cosmic ray (CR) electron diffusion scale and the mean free path of an ISRF photon to dust. The best-fitting relation is L_{617_MHz} ∝ {L_{850μ m}}^{2.1 ± 0.2} for NGC 3044. If variations in the cold dust emissivity are dominated by variations in dust density, and the synchrotron emission depends on magnetic field strength (a function of gas density) as well as CR electron generation (a function of massive star formation rate and therefore density via the Schmidt law) then the expected correlation for NGC 3044 is L_{617_MHz} ∝ {L_{850μ m}}^{2.2}, in agreement with the observed correlation.
    Monthly Notices of the Royal Astronomical Society 07/2013; 433(4):1670-. DOI:10.1093/mnras/stt937 · 5.11 Impact Factor