Spectral Slope Sample Clauses

Spectral Slope. By measuring the radio spectral slope, Fν ∝ να, in the sources it is possible to consider the origin of their radio emission. A steeper slope is associated with non- thermal, or synchrotron, emission, while a flat spectrum is indicative of thermal radio emission arising from thermal electrons in HII regions. Emission associated with AGN and their jets can span a wide range of spectral indices. A total of ten of our targets were observed at 5.5 GHz with ATCA [Stanway & Xxxxxx, log(ΣSF R [M⊙/yr/kpc2]) 0 −1 −2 −3 −4 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 log(Stellar Mass Density [M⊙/pc2]) Figure 3.4: Lower limits on stellar mass density and the star formation rate density for our sample using the radio-derived SFRs. Since the sources are unresolved in both the optical and radio observations, the true sizes are likely smaller than the ones used here, and hence the derived densities are lower limits (the arrow in the top left corner of the figure indicates the direction in which the sample would move with decreasing size). The underlying grey-scale represents the local galaxy population as sampled by the SDSS in the same redshift range as our sample, and clearly separates into passive (low ΣSF R) and star forming galaxies. The blue dotted line indicates the criterion of 0.1 M⊙ yr−1 kpc−2, suggested by Xxxxxxx [2002] as indicating the onset of starburst-driven galactic winds, or superwinds (see section 3.4.3). 2014]. Of these, three reported fluxes have a signal-to-noise ratio < 3, and are thus likely to represent upper limits, rather than robust detections. An additional three sources were detected at 3 <SNR< 5. Given the extended beam of ATCA at this frequency for objects at these declinations, these detections might also be suspect in a blind field survey in which the false detection rate rises rapidly as signal-to- noise ratios fall below 5. However, Xxxxxxx & Xxxxxx [2014] inspected each source and found it to be coincident with the targeted optical galaxy, decreasing the likeli- hood of a false positive detection for the sources described here. The 5.5 GHz fluxes for these targets were also consistent with, or deficient relative to, the expected ultraviolet-inferred star formation rate in each case. If the low signal-to-noise detec- tion, in fact, represents a misclassification of background noise, then the deficiency in radio flux seen in both the Stanway & Xxxxxx [2014] sample and the observations discussed here, is more dramatic still. In the following, so...