Dwarf galaxies are thought to host the remnants of the early Universe seed black holes (BHs) and to be dominated by supernova feedback. However, recent studies suggest that BH feedback could also strongly impact their growth. We report the discovery of 35 dwarf galaxies hosting radio AGN out to redshift $\sim$3.4, which constitutes the highest-redshift sample of AGN in dwarf galaxies. The galaxies are drawn from the VLA-COSMOS 3 GHz Large Project and all are star-forming. After removing the contribution from star formation to the radio emission, we find a range of AGN radio luminosities of $L^\mathrm{AGN}_\mathrm{1.4 GHz} \sim 10^{37}$-$10^{40}$ erg s$^{-1}$. The bolometric luminosities derived from the fit of their spectral energy distribution are $\gtrsim 10^{42}$ erg s$^{-1}$, in agreement with the presence of AGN in these dwarf galaxies. The 3 GHz radio emission of most of the sources is compact and the jet powers range from $Q_\mathrm{jet} \sim 10^{42}$ to 10$^{44}$ erg s$^{-1}$. These values, as well as the finding of jet efficiencies $\geq 10$ \% in more than 50\% of the sample, indicate that dwarf galaxies can host radio jets as powerful as those of massive radio galaxies whose jet mechanical feedback can strongly affect the formation of stars in the host galaxy. We conclude that AGN feedback can also have a very strong impact on dwarf galaxies, either triggering or hampering star formation and possibly the material available for BH growth. This implies that those low-mass AGN hosted in dwarf galaxies might not be the untouched relics of the early seed BHs, which has important implications for seed BH formation models.

Radio jets from AGNs in dwarf galaxies in the COSMOS survey: mechanical feedback out to redshift ∼3.4

The Duke storage ring is a dedicated driver for the storage ring based oscillator free-electron lasers (FELs), and the High Intensity Gamma-ray Source (HIGS). It is operated with a beam current ranging from about 1 mA to 100 mA per bunch for various operations and accelerator physics studies. High performance operations of the FEL and γ-ray source require a stable electron beam orbit, which has been realized by the global orbit feedback system. As a critical part of the orbit feedback system, the electron beam position monitors (BPMs) are required to be able to precisely measure the electron beam orbit in a wide range of the single-bunch current. However, the high peak voltage of the BPM pickups associated with high single-bunch current degrades the performance of the BPM electronics, and can potentially damage the BPM electronics. A signal conditioning method using low pass filters is developed to reduce the peak voltage to protect the BPM electronics, and to make the BPMs capable of working with a wide range of single-bunch current. Simulations and electron beam based tests are performed. The results show that the Duke storage ring BPM system is capable of providing precise orbit measurements to ensure highly stable FEL and HIGS operations.

http://iopscience.iop.org/article/10.1088/1674-1137/38/10/107003/pdf

Conditioning of BPM pickup signals for operations of the Duke storage ring with a wide range of single-bunch current

The Duke storage ring is a dedicated driver for the storage ring based oscillator free-electron lasers (FELs), and the High Intensity Gamma-ray Source (HIGS). It is operated with a beam current ranging from about 1 mA to 100 mA per bunch for various operations and accelerator physics studies. High performance operations of the FEL and gamma-ray source require a stable electron beam orbit, which has been realized by the global orbit feedback system. As a critical part of the orbit feedback system, the electron beam position monitors (BPMs) are required to be able to precisely measure the electron beam orbit in a wide range of the single-bunch current. However, the high peak voltage of the BPM pickups associated with high single-bunch current degrades the performance of the BPM electronics, and can potentially damage the BPM electronics. A signal conditioning method using low pass filters is developed to reduce the peak voltage to protect the BPM electronics, and to make the BPMs capable of working with a wide range of single-bunch current. Simulations and electron beam based tests are performed. The results show that the Duke storage ring BPM system is capable of providing precise orbit measurements to ensure highly stable FEL and HIGS operations.

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Conditioning of BPM pickup signals for operations of the Duke storage ring with a wide range of single-bunch current

Conditioning of BPM pickup signals for operations of the Duke storage ring with a wide range of single-bunch current