2021A&A...648A...9M

Query : 2021A&A...648A...9M

2021A&A...648A...9M - Astronomy and Astrophysics, volume 648A, 9-9 (2021/4-1)

The best of both worlds: Combining LOFAR and Apertif to derive resolved radio spectral index images.

MORGANTI R., OOSTERLOO T.A., BRIENZA M., JURLIN N., PRANDONI I., ORRU E., SHABALA S.S., ADAMS E.A.K., ADEBAHR B., BEST P.N., COOLEN A.H.W.M., DAMSTRA S., DE BLOK W.J.G., DE GASPERIN F., DENES H., HARDCASTLE M., HESS K.M., HUT B., KONDAPALLY R., KUTKIN A.M., LOOSE G.M., LUCERO D.M., MAAN Y., MACCAGNI F.M., MINGO B., MOSS V.A., MOSTERT R.I.J., NORDEN M.J., OOSTRUM L.C., ROTTGERING H.J.A., RUITER M., SHIMWELL T.W., SCHULZ R., VERMAAS N.J., VOHL D., VAN DER HULST J.M., VAN DIEPEN G.M., VAN LEEUWEN J. and ZIEMKE J.

Abstract (from CDS):

Super massive black holes at the centres of galaxies can cycle through periods of activity and quiescence. Characterising the duty cycle of active galactic nuclei (AGN) is crucial for understanding the impact of the energy they release on the host galaxy. For radio AGN, this can be done by identifying dying (remnant) and restarted radio galaxies from their radio spectral properties. Using the combination of the images at 1400 MHz produced by Apertif, the new phased-array feed receiver installed on the Westerbork Synthesis Radio Telescope, and images at 150 MHz provided by LOFAR, we have derived resolved spectral index images (at a resolution of ∼15arcsec) for all the sources within an approximately 6deg2 area of the Lockman Hole region. In this way, we were able to select 15 extended radio sources with emission (partly or entirely) characterised by extremely steep spectral indices (steeper than 1.2). These objects represent cases of radio sources in the remnant or the restarted phases of their life cycle. Our findings confirm that these objects are not as rare as previously thought, suggesting a relatively fast cycle. They also show a variety of properties that can be relevant for modelling the evolution of radio galaxies. For example, the restarted activity can occur while the remnant structure from a previous phase of activity is still visible. This provides constraints on the duration of the "off" (dying) phase. In extended remnants with ultra-steep spectra at low frequencies, the activity likely stopped a few hundred megayears ago, and they correspond to the older tail of the age distribution of radio galaxies, in agreement with the results of simulations of radio source evolution. We find remnant radio sources with a variety of structures (from double-lobed to amorphous), possibly suggesting different types of progenitors. The present work sets the stage for exploiting the powerful tool of low-frequency spectral index studies of extended sources by taking advantage of the large areas common to the LOFAR and the Apertif surveys.

Abstract Copyright: © ESO 2021

Journal keyword(s): radio continuum: galaxies - galaxies: active

VizieR on-line data: <Available at CDS (J/A+A/648/A9): list.dat fits/*>

Nomenclature: Figs 6-7, Table 1: [MOB2021] JHHMMSS+DDMMSS N=15.

Simbad objects: 21

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Number of rows : 21
N Identifier Otype ICRS (J2000)
RA 		ICRS (J2000)
DEC 		Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2024 		#notes
1 ICRF J054236.1+495107 Sy1 05 42 36.13789710 +49 51 07.2337139   18.45 17.80 17.210   ~ 1492 1
2 IC 2476 LIN 09 27 52.8290410824 +29 59 08.744484660   14.5       ~ 95 0
3 NAME Lockman Hole reg 10 45 00.0 +58 00 00           ~ 840 0
4 [MOB2021] J104618+581421 Rad 10 46 18.0 +58 14 21           ~ 1 0
5 [MOB2021] J104806+573035 Rad 10 48 06.0 +57 30 35           ~ 1 0
6 [MOB2021] J104842+585326 Rad 10 48 42.0 +58 53 26           ~ 2 0
7 [MOB2021] J104913+575008 Rad 10 49 13.0 +57 50 08           ~ 1 0
8 [MOB2021] J104959+570715 Rad 10 49 59.0 +57 07 15           ~ 1 0
9 [MOB2021] J105034+564539 Rad 10 50 34.0 +56 45 39           ~ 1 0
10 [MOB2021] J105123+582801 Rad 10 51 23.0 +58 28 01           ~ 1 0
11 [MOB2021] J105221+585054 Rad 10 52 21.0 +58 50 54           ~ 1 0
12 [MOB2021] J105233+585451 Rad 10 52 33.0 +58 54 51           ~ 1 0
13 [MOB2021] J105554+563537 Rad 10 55 54.0 +56 35 37           ~ 1 0
14 [MOB2021] J105723+565938 Rad 10 57 23.0 +56 59 38           ~ 1 0
15 ACO 1132 ClG 10 58 32.05 +56 47 14.2           ~ 129 1
16 [MOB2021] J110135+580653 Rad 11 01 35.0 +58 06 53           ~ 1 0
17 [MOB2021] J110201+583122 Rad 11 02 01.0 +58 31 22           ~ 1 0
18 [MOB2021] J110255+585740 Rad 11 02 55.0 +58 57 40           ~ 1 0
19 [MOB2021] J110317+573757 Rad 11 03 17.0 +57 37 57           ~ 1 0
20 ICRF J181935.0-634548 Sy2 18 19 35.00241 -63 45 48.1926   16.80 14.40 13.4   ~ 146 1
21 3C 388.0 SyG 18 44 02.3840387736 +45 33 29.628672300   16.91 15.56     ~ 325 1

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