|
| | | | |
| | | |
| Stat |
Members: 3645
Articles: 2'501'711
Articles rated: 2609
19 April 2024 |
|
| | | | |
|
Article overview
| |
|
|
Synchrotron spectral index and interstellar medium densities of star-forming galaxies | | Aritra Basu
; Rainer Beck
; Philip Schmidt
; Subhashis Roy
; | | Date: |
9 Mar 2015 | | Abstract: | The spectral index of synchrotron emission is an important parameter in
understanding the properties of cosmic ray electrons (CREs) and the
interstellar medium (ISM). We determine the synchrotron spectral index
($alpha_{
m nt}$) of four nearby star-forming galaxies, namely NGC 4736, NGC
5055, NGC 5236 and NGC 6946 at sub-kpc linear scales. The $alpha_{
m nt}$ was
determined between 0.33 and 1.4 GHz for all the galaxies. We find the spectral
index to be flatter ($gtrsim -0.7$) in regions with total neutral (atomic +
molecular) gas surface density, $Sigma_{
m gas} gtrsim
m 50~M_odot
pc^{-2}$, typically in the arms and inner parts of the galaxies. In regions
with $Sigma_{
m gas} lesssim
m 50~M_odot pc^{-2}$, especially in the
interarm and outer regions of the galaxies, the spectral index steepens sharply
to $<-1.0$. The flattening of $alpha_{
m nt}$ is unlikely to be caused due to
thermal free--free absorption at 0.33 GHz. Our result is consistent with the
scenario where the CREs emitting at frequencies below $sim0.3$ GHz are
dominated by bremsstrahlung and/or ionization losses. For denser medium
($Sigma_{
m gas} gtrsim
m 200~M_odot pc^{-2}$), having strong magnetic
fields ($sim 30~mu$G), $alpha_{
m nt}$ is seen to be flatter than $-0.5$,
perhaps caused due to ionization losses. We find that, due to the clumpy nature
of the ISM, such dense regions cover only a small fraction of the galaxy
($lesssim5$ percent). Thus, the galaxy-integrated spectrum may not show
indication of such loss mechanisms and remain a power-law over a wide range of
radio frequencies (between $sim 0.1$ to 10 GHz). | | Source: | arXiv, 1503.2420 | | Services: | Forum | Review | PDF | Favorites | |
|
|
No review found.
Did you like this article?
Note: answers to reviews or questions about the article must be posted in the forum section.
Authors are not allowed to review their own article. They can use the forum section.
browser Mozilla/5.0 AppleWebKit/537.36 (KHTML, like Gecko; compatible; ClaudeBot/1.0; +claudebot@anthropic.com)
|
| |
|
|
|
|
News, job offers and information for researchers and scientists:
| |
REGISTER