Using NIR spectral features in an SDSS sample of early-type galaxies to constrain the low-mass Initial Mass Function

The stellar initial mass function (IMF) is a major component in galaxy formation theory, it describes the original distribution of stars as a function of mass at the epoch of formation of the population. To investigate the form and possible variation of the IMF at low stellar-masses, features are measured in spectra from the Sloan Digital Sky Survey DR7 for a sample of ∼2000, low-redshift (0.010 - 0.057) red sequence galaxies and in simple stellar population models that cover a range of elemental abundances and IMFs. Particular attention is paid to the calcium triplet (at ∼8600 Å) and the sodium doublet (at ∼8200 Å) which are characteristic of high-mass ( 8 M ) and low-mass ( 0.5 M ) stars respectively and the NaD (at 5895 Å) and CaI (at 4227 Å) features which show a strong response to their respective elemental abundances. The combination of these spectral features is a useful technique for separating the effects of elemental abundance and IMF on the size of the measured spectral features, allowing the form and variation of the IMF to be investigated individually. The sodium abundance is constrained from the NaD index, popularly disregarded as an abundance indicator due to the effect of interstellar absorption on this feature. In this work there is no strong evidence to suggest that interstellar absorption has a detrimental effect on the abundance constraints from the NaD index. Evidence is found for an increasing sodium abundance ([Na/Fe] ∝ σ 1.654±0.050 ) and marginally decreasing calcium abundance ([Ca/Fe] ∝ σ −0.19±0.12 ) with increasing galaxy mass. With these abundances taken into consideration, the IMF variation found is slightly shallower at higher masses but also consistent with zero; ∆x = -0.111±0.071 ∆ log σ (where x is the power-law index describing the slope of the IMF). Taking into consideration the average abundances, the best-fitting IMF is found to be approximately Chabrier-like, with outlying galaxies that correspond to more extreme environments including high sodium abundances and bottom-heavy IMFs

Equity and diversity in astronomy

`Why is there a black hole where women should be?' asked Member of Parliament Chi Onwurah during her plenary talk on women in science at EWASS 2018. Gender equity was among a variety of topics discussed in a day-long Special Session

Equality, diversity and inclusion perspectives

An overview of the developments arising from equality, diversity and inclusion events at this year’s National Astronomy Meeting, by Vinesh Maguire-Rajpaul on behalf of the organizers

MOPTOP: Multi-colour Optimised Optical Polarimeter

Polarimetric measurements are essential for the study of jetted sources associated with black holes, such as γ-ray bursts and blazars. The relativistic jets launched from regions close to the black hole are threaded with magnetic fields, which produce synchrotron emission, and can be studied with polarimetric measurements. The multi-colour, optimised, optical polarimeter (MOPTOP) is a multi-band imaging instrument designed for use on the Liverpool Telescope. By replacing the rotating polaroid with a half wave plate and beam splitter, the instrument utilises twice as much of the incoming beam of light from the telescope compared to its predecessor, Ringo3. MOPTOP also builds on the successful introduction of dichroic mirrors to perform simultaneous multi-waveband polarimetric and photometric analysis in Ringo3, and enhances the sensitivity of the instrument with sCMOS cameras to use all photons as efficiently as possible

Promise of persistent multi-messenger astronomy with the Blazar OJ 287

Successful observations of the seven predicted bremsstrahlung flares from the unique bright blazar OJ 287 firmly point to the presence of a nanohertz gravitational wave (GW) emitting supermassive black hole (SMBH) binary central engine. We present arguments for the continued monitoring of the source in several electromagnetic windows to firmly establish various details of the SMBH binary central engine description for OJ 287. In this article, we explore what more can be known about this system, particularly with regard to accretion and outflows from its two accretion disks. We mainly concentrate on the expected impact of the secondary black hole on the disk of the primary on 3 December 2021 and the resulting electromagnetic signals in the following years. We also predict the times of exceptional fades, and outline their usefulness in the study of the host galaxy. A spectral survey has been carried out, and spectral lines from the secondary were searched for but were not found. The jet of the secondary has been studied and proposals to discover it in future VLBI observations are mentioned. In conclusion, the binary black hole model explains a large number of observations of different kinds in OJ 287. Carefully timed future observations will be able to provide further details of its central engine. Such multi-wavelength and multidisciplinary efforts will be required to pursue multi-messenger nanohertz GW astronomy with OJ 287 in the coming decades

Promise of Persistent Multi-Messenger Astronomy with the Blazar OJ 287

Successful observations of the seven predicted bremsstrahlung flares from the unique bright blazar OJ 287 firmly point to the presence of a nanohertz gravitational wave (GW) emitting supermassive black hole (SMBH) binary central engine. We present arguments for the continued monitoring of the source in several electromagnetic windows to firmly establish various details of the SMBH binary central engine description for OJ 287. In this article, we explore what more can be known about this system, particularly with regard to accretion and outflows from its two accretion disks. We mainly concentrate on the expected impact of the secondary black hole on the disk of the primary on 3 December 2021 and the resulting electromagnetic signals in the following years. We also predict the times of exceptional fades, and outline their usefulness in the study of the host galaxy. A spectral survey has been carried out, and spectral lines from the secondary were searched for but were not found. The jet of the secondary has been studied and proposals to discover it in future VLBI observations are mentioned. In conclusion, the binary black hole model explains a large number of observations of different kinds in OJ 287. Carefully timed future observations will be able to provide further details of its central engine. Such multi-wavelength and multidisciplinary efforts will be required to pursue multi-messenger nanohertz GW astronomy with OJ 287 in the coming decades

Ringo2 Optical Polarimetry of Blazars

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Refining the prediction for OJ 287 next impact flare arrival epoch

The bright blazar OJ~287 routinely parades high brightness bremsstrahlung flares which are explained as being a result of a secondary supermassive black hole (SMBH) impacting the accretion disk of a primary SMBH in a binary system. We begin by showing that these flares occur at times predicted by a simple analytical formula, based on the Kepler equation, which explains flares since 1888. The next impact flare, namely the flare number 26, is rather peculiar as it breaks the typical pattern of two impact flares per 12 year cycle. This will be the third bremsstrahlung flare of the current cycle that follows the already observed 2015 and 2019 impact flares from OJ~287. Unfortunately, astrophysical considerations make it difficult to predict the exact arrival epoch of the flare number 26. In the second part of the paper, we describe our recent OJ~287 observations. They show that the pre-flare light curve of flare number 22, observed in 2005, exhibits similar activity as the pre-flare light curve in 2022, preceding the expected flare number 26 in our model. We argue that the pre-flare activity most likely arises in the primary jet whose activity is modulated by the transit of the secondary SMBH through the accretion disk of the primary. Observing the next impact flare of OJ~287 in October 2022 will substantiate the theory of disk impacts in binary black hole systems.Comment: 16 pages, 2 figure