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تسجيل مستخدم جديدThe new class of FR0 radio galaxies
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Ranieri D. Baldi
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Are the FRI and FRII radio galaxies representative of the radio-loud (RL) AGN population in the local Universe? Recent studies on the local low-luminosity radio sources cast lights on an emerging population of compact radio galaxies which lack extended radio emission. In a pilot JVLA project, we study the high-resolution images of a small but representative sample of this population. The radio maps reveal compact unresolved or slightly resolved radio structures on a scale of 1-3 kpc. We find that these RL AGN live in red massive early-type galaxies, with large black hole masses ($gtrsim$10$^{8}$ M$_{odot}$), and spectroscopically classified as Low Excitation Galaxies, all characteristics typical of FRI radio galaxies which they also share the same nuclear luminosity with. However, they are more core dominated (by a factor of $sim$30) than FRIs and show a clear deficit of extended radio emission. We call these sources FR0 to emphasize their lack of prominent extended radio emission. A posteriori, other compact radio sources found in the literature fulfill the requirements for a FR0 classification. Hence, the emerging FR0 population appears to be the dominant radio class of the local Universe. Considering their properties we speculate on their possible origins and the possible cosmological scenarios they imply.
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We explore the low-frequency radio properties of the sources in the Fanaroff-Riley class 0 catalog (FR0CAT) as seen by the LOw Frequency ARray (LOFAR) observations at 150 MHz. This sample includes 104 compact radio active galactic nuclei (AGN) associ
ated with nearby (z<0.05) massive early-type galaxies. Sixty-six FR0CAT sources are in the sky regions observed by LOFAR and all of them are detected, usually showing point-like structures with sizes smaller than 3-6 kpc. However, 12 FR0s present resolved emission of low surface brightness which contributes between 5% and 40% of the total radio power at 150 MHz, usually with a jetted morphology extending between 15 and 50 kpc. No extended emission is detected around the other FR0s, with a typical luminosity limit of 5 x 10$^{22}$ W/Hz over an area of 100 kpc x 100 kpc. The spectral slopes of FR0s between 150 MHz and 1.4 GHz span a broad range (-0.7 < $alpha$ < 0.8) with a median value of $overlinealpha sim 0.1$; 20% of them have a steep spectrum ($alpha$ > 0.5), an indication of the presence of substantial extended emission confined within the spatial resolution limit. The fraction of FR0s showing evidence for the presence of jets, by including both spectral and morphological information, is at least ~40%. This study confirms that FR0s and FRIs can be interpreted as two extremes of a continuous population of jetted sources, with the FR0s representing the low end in size and radio power.
We present the results of a pilot JVLA project aimed at studying the bulk of the radio-emitting AGN population, unveiled by the NVSS/FIRST and SDSS surveys.We obtained A-array observations at the JVLA at 1.4, 4.5, and 7.5 GHz for 12 sources of the SD
SS/NVSS sample. The radio maps reveal compact unresolved or slightly resolved radio structures on a scale of 1-3 kpc, with only one exception of a FRI/FRII source extended over $sim$40 kpc. We isolate the radio core component in most of them. The sample splits into two groups. Four sources have small black hole (BH) masses (mostly $sim$10$^{7}$ M$_{odot}$) and are hosted by blue galaxies, often showing evidence of a contamination from star formation to their radio emission and associated with radio-quiet AGN. The second group consists in seven radio-loud AGN, which live in red massive ($sim10^{11}$ M$_{odot}$) early-type galaxies, with large BH masses ($gtrsim$10$^{8}$ M$_{odot}$), and spectroscopically classified as Low Excitation Galaxies, all characteristics typical of FRI radio galaxies. They also lie on the correlation between radio core power and [O III] line luminosity defined by FRIs. However, they are more core dominated (by a factor of $sim$30) than FRIs and show a deficit of extended radio emission. We dub these sources FR0 to emphasize their lack of prominent extended radio emission, the single distinguishing feature with respect to FRIs. The differences in radio properties between FR0s and FRIs might be ascribed to an evolutionary effect, with the FR0 sources undergoing to rapid intermittency that prevents the growth of large scale structures. In our preferred scenario the lack of extended radio emission in FR0s is due to their smaller jet Lorentz $Gamma$ factor with respect to FRIs, causing possible instabilities and their premature disruption.[abridged]
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.05$, with a radio size $lesssim$ 5 kpc, and with an optical spectrum characteristic of low-excitation galaxies. Their 1.4-GHz radio luminosities range $10^{38} lesssim u L_{1.4} lesssim 10^{40}$ erg/s. The FR0CAT hosts are mostly (86%) luminous ($-21 gtrsim M_r gtrsim -23$) red early-type galaxies with black hole masses $10^8 lesssim M_{rm BH} lesssim 10^9 M_odot$: similar to the hosts of FRI radio galaxies, but they are on average a factor $sim$1.6 less massive. The number density of FR0CAT sources is $sim$5 times higher than that of FRIs, and thus they represent the dominant population of radio sources in the local Universe. Different scenarios are considered to account for the smaller sizes and larger abundance of FR0s with respect to FRIs. An age-size scenario that considers FR0s as young radio galaxies that will all eventually evolve into extended radio sources cannot be reconciled with the large space density of FR0s. However, the radio activity recurrence, with the duration of the active phase covering a wide range of values and with short active periods strongly favored with respect to longer ones, might account for their large density number. Alternatively, the jet properties of FR0s might be intrinsically different from those of the FRIs, the former class having lower bulk Lorentz factors, possibly due to lower black hole spins. Our study indicates that FR0s and FRI/IIs can be interpreted as two extremes of a continuous population of radio sources that is characterized by a broad distribution of sizes and luminosities of their extended radio emission, but shares a single class of host galaxies.
We present the results of Karl G. Jansky Very Large Array (VLA) observations to study the properties of FR0 radio galaxies, the compact radio sources associated with early-type galaxies which represent the bulk of the local radio-loud AGN population.
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