The evolution of extragalactic peaked-spectrum sources down to 54 megahertz

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Table 1.

Sample selection criteria.

Selection step	Selection criterion	Number of sources
0	The LoTSS DR2 catalog with optical identifications	4 116 934 radio sources
	The SDSS 16th quasar catalog	750 414 quasars
	The LoLSS DR1 catalog	42 463 radio sources
	The FIRST catalog	946 432 sources
1	LoTSS quasar samples (Find the SDSS counterparts of LoTSS samples within 5″)	64 464 quasars
2	LoTSS quasar samples with both LoLSS (within 5″) and FIRST (2″) detections	1187 quasars
2.1	Separate the extended and compact sources	232 extended sources, 955 compact sources
2.2	Separate the radio and optical quasar samples	1037 optical quasars, 150 radio quasars
2.3	$α_{54}^{144} \geq 0.1$ $\alpha_{54}^{144} \geq 0.1$ and $α_{144}^{1400} < 0$ $\alpha_{144}^{1400} < 0$	61 MPS sources
3	LoTSS quasar samples within LoLSS DR1 and with FIRST/LoLSS upper limits	14 106 quasars
3.1	$α_{54, u}^{144} > 0$ $\alpha_{54,u}^{144} > 0$ and $α_{144, u}^{1400} < 0$ $\alpha_{144,u}^{1400} < 0$	103 MPS sources

Notes. 1. The “u” in $α_{54, u}^{144}$ $\alpha_{54,u}^{144}$ and $α_{144, u}^{1400}$ $\alpha_{144,u}^{1400}$ indicates the use of upper-limit flux densities. 2. The radio quasars in this work are SDSS quasars with FIRST counterparts within 2″; see Sect. 2.3.2 for details.

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