Extended extragalactic radio sources have traditionally been classified into Fanaroff & Riley (FR) I and II types, based on the ratio rs of the separation S between the brightest regions on either ...sides of the host galaxy and the total size T of the radio source (rs = S/T). In this paper, we examine the distribution of various physical properties as a function of rs of 1040 luminous (L L *) extended radio galaxies (RGs) at z < 0.3 selected with well-defined criteria from the SDSS, NVSS, and FIRST surveys. About 2/3 of the RGs are lobe dominated (LD) and 1/3 have prominent jets. If we follow the original definition of the FR types, i.e., a division based solely on rs , FR I and FR II RGs overlap in their host galaxy properties. However, the rare LD sources with rs 0.8 and O III Delta *l5007 line luminosity >106 L are markedly different on average from the rest of the RGs, in the sense that they are hosted in lower mass galaxies, live in relatively sparse environments, and likely have higher accretion rates onto the central supermassive black hole (SMBH). Thus, these high emission line luminosity, high-rs LD RGs, and the rest of RGs form a well-defined dichotomy. Motivated by the stark differences in the nuclear emission line properties of the RG subsamples, we suggest that the accretion rate onto the SMBH may play the primary role in creating the different morphologies. At relatively high accretion rates, the accretion system may produce powerful jets that create the 'classical double' morphology (roughly corresponding to the LD sources with rs 0.8 and emission lines); at lower accretion rates, the jets from a radiatively inefficient accretion flow generate radio lobes without apparent 'hot spots' at the edge (corresponding to the majority of LD sources). At slightly lower accretion rates and in galaxies with dense galactic structure, sources with prominent jets result. It is possible that while the high accretion rate systems could affect sub-Mpc scale environments, the jets from lower accretion rate systems may efficiently suppress activity within the host galaxies.
Type II supernovae (SNe) stem from the core collapse of massive (>8 M ) stars. Due to their short lifespan, we expect a very low rate of such events in elliptical hosts, where the star formation rate ...is low, and which are mostly comprised of an old stellar population. SN 2016hil (iPTF16hil) is an SN II located in the extreme outskirts of an elliptical galaxy at z = 0.0608 (projected distance 27.2 kpc). It was detected near peak (Mr ∼ −17 mag) 9 days after the last non-detection. The event has some potentially peculiar properties: it presented an apparently double-peaked light curve, and its spectra suggest low metallicity content (Z < 0.4 Z ). We place a tentative upper limit on the mass of a potential faint host at using deep optical imaging from Keck/LRIS. In light of this, we discuss the possibility of the progenitor forming locally and other more exotic formation scenarios such as a merger or common-envelope evolution causing a time-delayed explosion. Further observations of the explosion site in the UV are needed in order to distinguish between the cases. Regardless of the origin of the transient, observing a population of such seemingly hostless SNe II could have many uses, including an estimate the amount of faint galaxies in a given volume, and tests of the prediction of a time-delayed population of core-collapse SNe in locations otherwise unfavorable for the detection of such events.
ABSTRACT
We present a nuclear transient event, PS1-13cbe, that was first discovered in the Pan-STARRS1 survey in 2013. The outburst occurred in the nucleus of the galaxy SDSS J222153.87+003054.2 at ...z = 0.123 55, which was classified as a Seyfert 2 in a pre-outburst archival Sloan Digital Sky Survey (SDSS) spectrum. PS1-13cbe showed the appearance of strong broad H α and H β emission lines and a non-stellar continuum in a Magellan spectrum taken 57 d after the peak of the outburst that resembled the characteristics of a Seyfert 1. These broad lines were not present in the SDSS spectrum taken a decade earlier and faded away within 2 yr, as observed in several late-time MDM spectra. We argue that the dramatic appearance and disappearance of the broad lines and a factor of ∼8 increase in the optical continuum are most likely caused by variability in the pre-existing accretion disc than a tidal disruption event, supernova, or variable obscuration. The time-scale for the turn-on of the optical emission of ∼70 d observed in this transient is among the shortest observed in a ‘changing-look’ active galactic nucleus.
We present optical and near-infrared observations of SN 2012au, a slow-evolving supernova (SN) with properties that suggest a link between subsets of energetic and H-poor SNe and superluminous SNe. ...SN 2012au exhibited conspicuous Type-Ib-like He I lines and other absorption features at velocities reaching approximate2 x 10 super(4) km s super(-1) in its early spectra, and a broad light curve that peaked at M sub(B) = -18.1 mag. Models of these data indicate a large explosion kinetic energy of ~1052 erg and super(56)Ni mass ejection of M sub(Ni) approximate 0.3 M sub(middotincircle) on par with SN 1998bw. SN 2012au's spectra almost one year after explosion show a blend of persistent Fe II P-Cyg absorptions and nebular emissions originating from two distinct velocity regions. These late-time emissions include strong FeII, CaII, OI, Mg I, and Na I lines at velocities > ~4500 km s super(-1) as well as O I and Mg I lines at noticeably smaller velocities <, ~2000 km s super(-1) Many of the late-time properties of SN 2012au are similar to the slow-evolving hypernovae SN 1997dq and SN 1997ef, and the superluminous SN 2007bi. Our observations suggest that a single explosion mechanism may unify all of these events that span -21 <, ~ M sub(B) <, ~ -17 mag. The aspherical and possibly jetted explosion was most likely initiated by the core collapse of a massive progenitor star and created substantial high-density, low-velocity Ni-rich material.
The use of standard rulers, such as the scale of the baryonic acoustic oscillations (BAOs), has become one of the more powerful techniques employed in Cosmology to probe the entity driving the ...accelerating expansion of the Universe. In this paper, the topology of large-scale structure (LSS) is used as one such standard ruler to study mysterious 'dark energy'. By following the redshift evolution of the clustering of luminous red galaxies as measured by their 3D topology (counting structures in the cosmic web), we can chart the expansion rate and extract information about the equation of state of dark energy. Using the technique first introduced in Park & Kim, we evaluate the constraints that can be achieved using 3D topology measurements from next-generation LSS surveys, such as the Baryonic Oscillation Spectroscopic Survey. In conjunction with the information that will be available from the Planck satellite, we find a single topology measurement on three different scales is capable of constraining a single dark energy parameter to within 5-10 per cent when dynamics are permitted. This offers an alternative use of the data available from redshift surveys and serves as a cross-check for BAO studies.
The use of standard rulers, such as the scale of the baryonic acoustic oscillations (BAOs), has become one of the more powerful techniques employed in Cosmology to probe the entity driving the ...accelerating expansion of the Universe. In this paper, the topology of large-scale structure (LSS) is used as one such standard ruler to study mysterious 'dark energy'. By following the redshift evolution of the clustering of luminous red galaxies as measured by their 3D topology (counting structures in the cosmic web), we can chart the expansion rate and extract information about the equation of state of dark energy. Using the technique first introduced in Park & Kim, we evaluate the constraints that can be achieved using 3D topology measurements from next-generation LSS surveys, such as the Baryonic Oscillation Spectroscopic Survey. In conjunction with the information that will be available from the Planck satellite, we find a single topology measurement on three different scales is capable of constraining a single dark energy parameter to within 5-10 per cent when dynamics are permitted. This offers an alternative use of the data available from redshift surveys and serves as a cross-check for BAO studies.
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