Search

Velocity offsets in the broad Balmer lines of quasars and their temporal variations serve as indirect evidence for bound supermassive black hole binaries (SBHBs) at sub-parsec separations. In this work, we test the SBHB hypothesis for 14 quasars with double-peaked broad emission lines using their long-term (14–41 yr) radial velocity curves. We improve on the previous work by (i) using elliptical instead of circular orbits for the SBHBs, (ii) adopting a statistical model for radial velocity jitter, (iii) employing a Markov chain Monte Carlo method to explore the orbital parameter space efficiently and build posterior distributions of physical parameters, and (iv) incorporating new observations. We determine empirically that jitter comprises approximately Gaussian distributed fluctuations about the smooth radial velocity curves that are larger than the measurement errors by factors of a few. We initially treat jitter by enlarging the effective error bars and then verify this approach via a variety of Gaussian process models for it. We find lower mass limits for the hypothesized SBHBs in the range 108–1011 M⊙. For seven objects, the SBHB scenario appears unlikely based on goodness-of-fit tests. For two additional objects, the minimum SBHB masses are unreasonably large (>1010 M⊙), strongly disfavouring the SBHB scenario. Using constraints on the orbital inclination angle (which requires some assumptions) makes the minimum masses of four more objects unreasonably large. We also cite physical and observational arguments against the SBHB hypothesis for nine objects. We conclude that the SBHB explanation is not the favoured explanation of double-peaked broad emission lines. [ABSTRACT FROM AUTHOR]

The effect of dust attenuation on a galaxy's light depends on a number of physical properties, such as geometry and dust composition, both of which can vary across the faces of galaxies. To investigate this variation, we continue analysis on star-forming regions in 29 galaxies studied previously. We analyse these regions using Swift /UV Optical Telescope and Wide-field Infrared Survey Explorer images, as well as Sloan Digital Sky Survey/Mapping Nearby Galaxies at Apache Point Observatory emission line maps to constrain the relationship between the infrared excess (IRX) and the ultraviolet spectral index, β, for each star-forming region. This relationship can be used to constrain which dust attenuation law is appropriate for the region. We find that the value of Dn (4000) for a region is correlated with both IRX and β, and that the gas-phase metallicity is strongly correlated with the IRX. This correlation between metallicity and IRX suggests that regardless of aperture, metal-rich regions have steeper attenuation curves. We also find that integrated galactic light follows nearly the same IRX–β relationship as that found for kpc-sized star-forming regions. This similarity may suggest that the attenuation law followed by the galaxy is essentially the same as that followed by the regions, although the relatively large size of our star-forming regions complicates this interpretation because optical opacity and attenuation curves have been observed to vary within individual galaxies. [ABSTRACT FROM AUTHOR]

Galaxy clusters enable unique opportunities to study cosmology, dark matter, galaxy evolution, and strongly lensed transients. We here present a new cluster-finding algorithm, CluMPR (Clusters from Masses and Photometric Redshifts), that exploits photometric redshifts (photo- z 's) as well as photometric stellar mass measurements. CluMPR uses a 2D binary search tree to search for overdensities of massive galaxies with similar redshifts on the sky and then probabilistically assigns cluster membership by accounting for photo- z uncertainties. We leverage the deep DESI Legacy Survey grzW1W2 imaging over one-third of the sky to create a catalogue of |$\sim 300\, 000$| galaxy cluster candidates out to z = 1, including tabulations of member galaxies and estimates of each cluster's total stellar mass. Compared to other methods, CluMPR is particularly effective at identifying clusters at the high end of the redshift range considered (z = 0.75–1), with minimal contamination from low-mass groups. These characteristics make it ideal for identifying strongly lensed high-redshift supernovae and quasars that are powerful probes of cosmology, dark matter, and stellar astrophysics. As an example application of this cluster catalogue, we present a catalogue of candidate wide-angle strongly lensed quasars in Appendix C. The nine best candidates identified from this sample include two known lensed quasar systems and a possible changing-look lensed QSO with SDSS spectroscopy. All code and catalogues produced in this work are publicly available (see Data Availability). [ABSTRACT FROM AUTHOR]

ABSTRACT We model the emission lines generated in the photoionized debris of a tidally disrupted horizontal branch (HB) star. We find that at late times, the brightest optical emission lines are [N ii] λλ6548, 6583 and [O iii] λλ4959, 5007. Models of a red clump HB star undergoing mild disruption by a massive (50-100 M⊙) black hole (BH) yield an emission-line spectrum that is in good agreement with that observed in the NGC 1399 globular cluster hosting the ultraluminous X-ray source CXOJ033831.8−352604. We make predictions for the ultraviolet emission-line spectrum that can verify the tidal disruption scenario and constrain the mass of the BH. [ABSTRACT FROM AUTHOR]

The attenuation of light from star-forming galaxies is correlated with a multitude of physical parameters including star formation rate, metallicity and total dust content. This variation in attenuation is even more evident on kiloparsec scales, which is the relevant size for many current spectroscopic integral field unit surveys. To understand the cause of this variation, we present and analyse Swift /UVOT near-UV (NUV) images and SDSS/MaNGA emission-line maps of 29 nearby (z < 0.084) star-forming galaxies. We resolve kiloparsec-sized star-forming regions within the galaxies and compare their optical nebular attenuation (i.e. the Balmer emission line optical depth, |$\tau ^{l}_{B}\equiv \tau _{\textrm {H}\beta }-\tau _{\textrm {H}\alpha }$|⁠) and NUV stellar continuum attenuation (via the NUV power-law index, β) to the attenuation law described by Battisti et al. We show the data agree with that model, albeit with significant scatter. We explore the dependence of the scatter of the β– |$\tau ^{l}_{B}$| measurements from the star-forming regions on different physical parameters, including distance from the nucleus, star formation rate and total dust content. Finally, we compare the measured |$\tau ^{l}_{B}$| and β values for the individual star-forming regions with those of the integrated galaxy light. We find a strong variation in β between the kiloparsec scale and the larger galaxy scale that is not seen in |$\tau ^{l}_{B}$|⁠. We conclude that the sightline dependence of UV attenuation and the reddening of β due to the light from older stellar populations could contribute to the scatter in the β– |$\tau ^{l}_{B}$| relation. [ABSTRACT FROM AUTHOR]

We have identified 55 candidate high-mass X-ray binaries (HMXBs) in M33 using available archival Hubble Space Telescope (HST) and Chandra imaging to find blue stars associated with X-ray positions. We use the HST photometric data to model the colour–magnitude diagrams in the vicinity of each candidate HMXB to measure a resolved recent star formation history (SFH), and thus a formation time-scale, or age for the source. Taken together, the SFHs for all candidate HMXBs in M33 yield an age distribution that suggests preferred formation time-scales for HMXBs in M33 of < 5 and ∼40 Myr after the initial star formation episode. The population at 40 Myr is seen in other Local Group galaxies, and can be attributed to a peak in formation efficiency of HMXBs with neutron stars as compact objects and B star secondary companions. This time-scale is preferred as neutron stars should form in abundance from ∼8 M⊙ core-collapse progenitors on these time-scales, and B stars are shown observationally to be most actively losing mass around this time. The young population at < 5Myr has not been observed in other Local Group HMXB population studies, but may be attributed to a population of very massive progenitors forming black holes very early on. We discuss these results in the context of massive binary evolution, and the implications for compact object binaries and gravitational wave sources. [ABSTRACT FROM AUTHOR]

We present observations of the double-peaked broad Hα profile emitted by the active nucleus of NGC7213 using the Gemini South Telescope in 13 epochs between 2011 September 27 and 2013 July 23. This is the first time that the double-peaked line profile of this nucleus - typical of gas emission from the outer parts of an accretion disc surrounding a supermassive black hole (SMBH) - is reported to vary. From the analysis of the line profiles we find two variability time-scales: (1) the shortest one, between 7 and 28 d, is consistent with the light travel time between the ionizing source and the part of the disc emitting the line; and (2) a longer one of≥3m corresponding to variations in the relative intensity of the blue and red sides of the profile, which can be identified with the dynamical time-scale of this outer part of the accretion disc. We modelled the line profiles as due to emission from a region between ≈300 and 3000 gravitational radii of a relativistic, Keplerian accretion disc surrounding the SMBH. Superposed on the disc emissivity, the model includes an asymmetric feature in the shape of a spiral arm with a rotation period of ≈21 m, which reproduces the variations in the relative intensity of the blue and red sides of the profile. Besides these variations, the rms variation profile reveals the presence of another variable component in the broad line, with smaller velocity width W68 (the width of the profile corresponding to 68 per cent of the flux) of∼2100 km s-1. [ABSTRACT FROM AUTHOR]

We report the discovery of a new 'changing-look' quasar, SDSS J101152.98+544206.4, through repeat spectroscopy from the Time Domain Spectroscopic Survey. This is an addition to a small but growing set of quasars whose blue continua and broad optical emission lines have been observed to decline by a large factor on a time-scale of approximately a decade. The 5100 Å monochromatic continuum luminosity of this quasar drops by a factor of >9.8 in a rest-frame time interval of <9.7 yr, while the broad Hα luminosity drops by a factor of 55 in the same amount of time. The width of the broad Hα line increases in the dim state such that the black hole mass derived from the appropriate single-epoch scaling relation agrees between the two epochs within a factor of 3. The fluxes of the narrow emission lines do not appear to change between epochs. The light curve obtained by the Catalina Sky Survey suggests that the transition occurs within a rest-frame time interval of approximately 500 d. We examine three possible mechanisms for this transition suggested in the recent literature. An abrupt change in the reddening towards the central engine is disfavoured by the substantial difference between the time-scale to obscure the central engine and the observed time-scale of the transition. A decaying tidal disruption flare is consistent with the decay rate of the light curve but not with the prolonged bright state preceding the decay; nor can this scenario provide the power required by the luminosities of the emission lines. An abrupt drop in the accretion rate on to the supermassive black hole appears to be the most plausible explanation for the rapid dimming. [ABSTRACT FROM AUTHOR]