arXiv subjects

Alister W. Graham

Publications and source records attributed to Alister W. Graham.

At least 37 records · Page 2Linked to original sources

arXiv2023

Massive Black Hole Binaries as LISA Precursors in the Roman High Latitude Time Domain Survey

With its capacity to observe $\sim 10^{5-6}$ faint active galactic nuclei (AGN) out to redshift $z\approx 6$, Roman is poised to reveal a population of $10^{4-6}\, {\rm M_\odot}$ black holes during an epoch of vigorous galaxy assembly. By measuring the light curves of a subset of these AGN and looking for periodicity, Roman can identify several hundred massive black hole binaries (MBHBs) with 5-12 day orbital periods, which emit copious gravitational radiation and will inevitably merge on timescales of $10^{3-5}$ years. During the last few months of their merger, such binaries are observable with the Laser Interferometer Space Antenna (LISA), a joint ESA/NASA gravitational wave mission set to launch in the mid-2030s. Roman can thus find LISA precursors, provide uniquely robust constraints on the LISA source population, help identify the host galaxies of LISA mergers, and unlock the potential of multi-messenger astrophysics with massive black hole binaries.

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arXiv2023

Resequencing the Hubble sequence and the quadratic (black hole mass)-(spheroid stellar mass) relation for elliptical galaxies

One of the most protracted problems in astronomy has been understanding the evolution of galaxy morphology. Much discussion has surrounded how lenticular galaxies may form a bridging population between elliptical and spiral galaxies. However, with recourse to a galaxy's central black hole mass, accretion-built spiral galaxies have emerged as the bridging population between low-mass lenticular galaxies and the dusty merger-built lenticular galaxies contiguous with elliptical galaxies and `brightest cluster galaxies' in the black hole/galaxy mass diagram. Spiral galaxies, including the Milky Way, appear built from gas accretion and minor mergers onto what were initially lenticular galaxies. These connections are expressed as a new morphology sequence, dubbed the `Triangal', which subsumes elements of the Hubble sequence and the van den Bergh trident and reveals the bridging nature of the often overlooked ellicular galaxies. Furthermore, a quadratic black hole/galaxy mass relation is found to describe ordinary elliptical galaxies. The relation is roughly parallel to the quadratic-like relations observed for the central spheroidal component of spiral galaxies, dust-rich lenticular galaxies, and old dust-poor lenticular galaxies. The brightest cluster galaxies are offset according to expectations from an additional major merger. The findings have implications for feedback from active galactic nuclei, mapping morphology into simulations, and predicting gravitational wave signals from colliding supermassive black holes. A new galaxy speciation model is presented. It disfavours the `monolithic collapse' scenario for spiral, dusty lenticular, and elliptical galaxies. It reveals substantial orbital angular momentum in the Universe's first galaxies and unites dwarf and ordinary `early-type' galaxies.

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arXiv2023

Splitting the lentils: Clues to galaxy/black hole coevolution from the discovery of offset relations for non-dusty versus dusty (wet-merger-built) lenticular galaxies in the $M_{\rm bh}$-$M_{\rm *,spheroid}$ diagram

This work advances the (galaxy morphology)-dependent (black hole mass, $M_{\rm bh}$)-(spheroid/galaxy stellar mass, $M_*$) scaling relations by introducing `dust bins' for lenticular (S0) galaxies. Doing so has led to the discovery of $M_{\rm bh}$-$M_{\rm *,sph}$ and $M_{\rm bh}$-$M_{\rm *,gal}$ relations for dusty S0 galaxies - built by major wet mergers and comprising half the S0 sample - offset from the distribution of dust-poor S0 galaxies. The situation is reminiscent of how major dry mergers of massive S0 galaxies have created an offset population of ellicular and elliptical galaxies. For a given $M_{\rm bh}$, the dust-rich S0 galaxies have 3 to 4 times higher $M_{\rm *,sph}$ than the dust-poor S0 galaxies, and the steep distributions of both populations in the $M_{\rm bh}$-$M_{\rm *,sph}$ diagram bracket the $M_{\rm bh} \propto M_{\rm *,sph}^{2.27+/-0.48}$ relation defined by the spiral galaxies, themselves renovated through minor mergers. The new relations offer refined means to estimate $M_{\rm bh}$ in other galaxies and should aid with: (i) constructing (galaxy morphology)-dependent black hole mass functions; (ii) estimating the masses of black holes associated with tidal disruption events; (iii) better quantifying evolution in the scaling relations via improved comparisons with high-$z$ data by alleviating the pickle of apples versus oranges; (iv) mergers and long-wavelength gravitational wave science; (v) simulations of galaxy/black hole coevolution and semi-analytic works involving galaxy speciation; plus (vi) facilitating improved extrapolations into the intermediate-mass black hole landscape. The role of the galaxy's environment is also discussed, and many potential projects that can further explore the morphological divisions are mentioned.

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arXiv2023

Reading the tea leaves in the $M_{\rm bh}$-$M_{\rm *,sph}$ and $M_{\rm bh}$-$R_{\rm e,sph}$ diagrams: dry and gaseous mergers with remnant angular momentum

We recently revealed that bulges and elliptical galaxies broadly define distinct, super-linear relations in the $M_{\rm bh}$-$M_{\rm *,sph}$ diagram, with the order-of-magnitude lower $M_{\rm bh}/M_{\rm *,sph}$ ratios in the elliptical galaxies due to major (disc-destroying, elliptical-building) dry mergers. Here we present a more nuanced picture. Galaxy mergers, in which the net orbital angular momentum does not cancel, can lead to systems with a rotating disc. This situation can occur with either wet (gas-rich) mergers involving one or two spiral galaxies, e.g., NGC~5128, or dry (relatively gas-poor) collisions involving one or two lenticular galaxies, e.g., NGC~5813. The spheroid and disc masses of the progenitor galaxies and merger remnant dictate the shift in the $M_{\rm bh}$-$M_{\rm *,sph}$ and $M_{\rm bh}$-$R_{\rm e,sph}$ diagrams. We show how this explains the (previously excluded merger remnant) Sersic S0 galaxies near the bottom of the elliptical sequence and core-Sersic S0 galaxies at the top of the bulge sequence, neither of which are faded spiral galaxies. Different evolutionary pathways in the scaling diagrams are discussed. We also introduce two ellicular (ES) galaxy types, explore the location of brightest cluster galaxies and stripped `compact elliptical' galaxies in the $M_{\rm bh}$-$M_{\rm *,sph}$ diagram, and present a new merger-built $M_{\rm bh}$-$M_{\rm *,sph}$ relation which may prove helpful for studies of nanohertz gravitational waves. This work effectively brings into the fold many systems previously considered outliers with either overly massive or undermassive black holes relative to the near-linear $M_{\rm bh}$-$M_{\rm *,sph}$ `red sequence' patched together with select bulges and elliptical galaxies.

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arXiv2022

Disc cloaking: Establishing a lower limit to the number density of local compact massive spheroids/bulges and the potential fate of some high-z red nuggets

The near-absence of compact massive quiescent galaxies in the local Universe implies a size evolution since $z\sim2.5$. It is often theorised that such `red nuggets' have evolved into today's elliptical (E) galaxies via an E-to-E transformation. We examine an alternative scenario in which a red nugget develops a rotational disc through mergers and accretion, say, at $1\lesssim z\lesssim2$, thereby cloaking the nugget as the extant bulge/spheroid component of a larger, now old, galaxy. We have performed detailed, physically-motivated, multi-component decompositions of a volume-limited sample of 103 massive ($M_*/\rm M_{\odot} \gtrsim 1\times 10^{11}$) galaxies within 110\,Mpc. Among our 28 galaxies with existing elliptical classifications, we found that 18 have large-scale discs, and two have intermediate-scale discs, and are reclassified here as lenticulars (S0) and elliculars (ES). The local spheroid stellar mass function, size-mass diagram and bulge-to-total ($B/T$) flux ratio are presented. We report lower-limits for the volume number density of compact massive spheroids, $n_\mathrm{c,Sph}\sim (0.17$-$1.2) \times 10^{-4}\,\rm Mpc^{-3}$, based on different definitions of `red nuggets' in the literature. Similar number densities of local compact massive bulges were reported by de la Rosa et al. using automated two-component decompositions and their existence is now abundantly clear with our multi-component decompositions. We find disc-cloaking to be a salient alternative for galaxy evolution. In particular, instead of an E-to-E process, disc growth is the dominant evolutionary pathway for at least low-mass ($1\times10^{10}<M_*/\rm M_{\odot} \lessapprox 4 \times 10^{10}$) red nuggets, while our current lower-limits are within an alluring factor of a few of the peak abundance of high-mass red nuggets at $1\lesssim z\lesssim2$.

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arXiv2022

The size--mass and other structural parameter ($n, μ_z, R_z$) relations for local bulges/spheroids from multicomponent decompositions

We analyse the bulge/spheroid size-(stellar mass), $R_{\rm e,Sph}-M_{\rm *,Sph}$, relation and spheroid structural parameters for 202 local (predominantly $\lesssim 110~\rm Mpc$) galaxies spanning $ M_*\sim 3\times10^{9}-10^{12}~\rm M_{\odot}$ and $ 0.1 \lesssim R_{\rm e, Sph}\lesssim32~\rm kpc$ from multicomponent decomposition. The correlations between the spheroid Sérsic index ($n_{\rm Sph}$), central surface brightness ($μ_{\rm 0, Sph}$), effective half-light radius ($R_{\rm e, Sph}$), absolute magnitude ($\mathfrak{M}_{\rm Sph}$) and stellar mass ($M_{\rm *,Sph}$) are explored. We also investigate the consequences of using different scale radii, $R_{z,\rm Sph}$, encapsulating a different fraction ($z$, from 0 to 1) of the total luminosity. The correlation strengths for projected mass densities, $Σ_z$ and $\langle Σ\rangle_z$, vary significantly with the choice of $z$. Spheroid size ($R_{\rm z, Sph}$) and mass ($M_{\rm *,Sph}$) are strongly correlated for all light fractions $z$. We find: $\log(R_{\rm e,Sph}/\rm kpc) = 0.88\log(M_{\rm *,Sph}/\rm M_{\odot})-9.15$ with a small scatter of $Δ_{rms} = 0.24~\rm dex$. This result is discussed relative to the \textit{curved} size-mass relation for early-type galaxies due to their discs yielding larger galaxy radii at lower masses. Moreover, the slope of our spheroid size-mass relation is a factor of $\sim3$, steeper than reported bulge size-mass relations, and with bulge sizes at $M_{\rm *,sph}\sim 3\times10^9~M_\odot$ which are 2 to 3 times smaller. Finally, we show that the local spheroids align well with quiescent galaxies at $z\sim1.25$--$2.25$. In essence, local spheroids and high-$z$ quiescent galaxies appear structurally similar, likely dictated by the virial theorem.

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arXiv2022

Galaxy And Mass Assembly: Galaxy Morphology in the Green Valley, Prominent rings and looser Spiral Arms

Galaxies broadly fall into two categories: star-forming (blue) galaxies and quiescent (red) galaxies. In between, one finds the less populated ``green valley". Some of these galaxies are suspected to be in the process of ceasing their star-formation through a gradual exhaustion of gas supply or already dead and are experiencing a rejuvenation of star-formation through fuel injection. We use the Galaxy And Mass Assembly database and the Galaxy Zoo citizen science morphological estimates to compare the morphology of galaxies in the green valley against those in the red sequence and blue cloud. Our goal is to examine the structural differences within galaxies that fall in the green valley, and what brings them there. Previous results found disc features such as rings and lenses are more prominently represented in the green valley population. We revisit this with a similar sized data set of galaxies with morphology labels provided by the Galaxy Zoo for the GAMA fields based on new KiDS images. Our aim is to compare qualitatively the results from expert classification to that of citizen science. We observe that ring structures are indeed found more commonly in green valley galaxies compared to their red and blue counterparts. We suggest that ring structures are a consequence of disc galaxies in the green valley actively exhibiting characteristics of fading discs and evolving disc morphology of galaxies. We note that the progression from blue to red correlates with loosening spiral arm structure.

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arXiv2022

Invoking the virial theorem to understand the impact of (dry) mergers on the $M_{\rm bh}$-$σ$ relation

While dry mergers can produce considerable scatter in the (black hole mass, $M_{\rm bh}$)-(spheroid stellar mass, $M_{\rm *,sph}$) and $M_{\rm bh}$-(spheroid half-light radius, $R_{\rm e,sph}$) diagrams, the virial theorem is used here to explain why the scatter about the $M_{\rm bh}$-(velocity dispersion, $σ$) relation remains low in the face of such mergers. Its small scatter has been claimed as evidence of feedback from active galactic nuclei (AGNs). However, it is shown that galaxy mergers also play a significant role. The major merger of two S0 galaxies with $M_{\rm *,sph}\sim10^{11}$ M$_\odot$ advances a system along a slope of $\sim$5 in the $M_{\rm bh}$-$σ$ diagram. However, a major E$+$E galaxy merger moves a system (slightly) along a trajectory with a slope of $\sim$9, while mergers of lower-mass S0 galaxies with $M_{\rm *,sph}\sim10^{10}$ M$_\odot$ move (slightly) along a trajectory with a slope of $\sim$3. This produces a steeper distribution for the E (and Es,e) galaxies in the $M_{\rm bh}$-$σ$ diagram, reported here to have a slope of 7.27$\pm$0.91, compared to the S0 galaxies which have a slope of 5.68$\pm$0.60. This result forms an important complement to the AGN feedback models like that from Silk and Rees, providing a more complete picture of galaxy/(black hole) coevolution. It also has important implications for nanohertz gravitational wave research. Abridged.

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arXiv2022

Quashing a suspected selection bias in galaxy samples having dynamically-measured supermassive black holes

Local early-type galaxies with directly-measured black hole masses, $M_{\rm bh}$, have been reported to represent a biased sample relative to the population at large. Such galaxies with Spitzer Space Telescope imaging have been purported to possess velocity dispersions, $σ$, at least $\sim$0.1 dex larger for a given galaxy stellar mass, $M_{\rm *,gal}$, than is typically observed among thousands of early-type galaxies imaged by the Sloan Digital Sky Survey. This apparent offset led Shankar et al. to reduce the normalisation of the observed $M_{\rm bh} \propto σ^5$ relation by at least $\sim$0.5 dex to give their "intrinsic relations", including $σ$-based modifications to the $M_{\rm bh}$-$M_{\rm *,gal}$ relation. These modifications were based on the untested assumption that the stellar masses had been derived consistently between the two samples. Here, we provide the necessary check using galaxies common to the Spitzer Survey of Stellar Structure in Galaxies (S$^4$G) and the Sloan Digital Sky Survey (SDSS). We find that the stellar masses of galaxies with and without directly measured black holes had appeared offset from each other due to the use of inconsistent stellar mass-to-light ratios, $Υ_*$, for the optical and infrared data. We briefly discuss the "intrinsic relations" and why some of these will at times appear to have had partial success when applied to data based on similarly inconsistent values of $Υ_*$. Finally, we reiterate the importance of the $\upsilon$ (lower-case $Υ$) term, which we previously introduced into the $M_{\rm bh}$-$M_{\rm *}$ relations to help avoid $Υ_*$-related mismatches.

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arXiv2022

Appreciating mergers for understanding the non-linear $M_{\rm bh}$-$M_{\rm ,spheroid}$ and $M_{\rm bh}$-$M_{\rm ,galaxy}$ relations, updated herein, and the implications for the (reduced) role of AGN feedback

We present revised (black hole mass)-(spheroid stellar mass) and (black hole mass)-(galaxy stellar mass) scaling relations based on colour-dependent stellar mass-to-light ratios. Our 3.6 micron luminosities were obtained from multicomponent decompositions, which accounted for bulges, discs, bars, ansae, rings, nuclear components, etc. The lenticular galaxy bulges (not associated with recent mergers) follow a steep M_bh~M_{*,bulge}^{1.53+/-0.15} relation, offset by roughly an order of magnitude in black hole mass from the M_bh~M_{*,ellip}^{1.64+/-0.17} relation defined by the elliptical (E) galaxies which, in Darwinian terms, are shown to have evolved by punctuated equilibrium rather than gradualism. We use the spheroid, i.e., bulge and elliptical, size-mass relation to reveal how disc-galaxy mergers explain this offset and the dramatically lower M_bh/M_{*,sph} ratios in the elliptical galaxies. The popular but deceptive near-linear M_bh-M_{*,sph} `red sequence', followed by neither the bulge population nor the elliptical galaxies, is shown to be an artefact of sample selection, combining bulges and elliptical galaxies from disparate M_bh-M_{*,sph} sequences. Moreover, both small bulges with `undermassive' black holes and big lenticular galaxies (including relic `red nuggets') with `overmassive' black holes - relative to the near-linear M_bh-M_{*,sph} sequence - are no longer viewed as outliers. We confirm a steep M_bh~M_{*,bulge}^{2.25+/-0.39} relation for spiral galaxies and discuss numerous implications of this work, including how mergers, rather than (only) feedback from active galactic nuclei, have shaped the high-mass end of the galaxy mass function. We also explain why there may be no useful M_bh-M_{*,sph}-R_{e,sph} plane due to M_{*,sph} scaling nearly linearly with R_{e,sph}.

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arXiv2022

Galaxy And Mass Assembly (GAMA): Bulge-disk decomposition of KiDS data in the nearby universe

We derive single Sérsic fits and bulge-disk decompositions for 13096 galaxies at redshifts z < 0.08 in the GAMA II equatorial survey regions in the Kilo-Degree Survey (KiDS) g, r and i bands. The surface brightness fitting is performed using the Bayesian two-dimensional profile fitting code ProFit. We fit three models to each galaxy in each band independently with a fully automated Markov-chain Monte Carlo analysis: a single Sérsic model, a Sérsic plus exponential and a point source plus exponential. After fitting the galaxies, we perform model selection and flag galaxies for which none of our models are appropriate (mainly mergers/Irregular galaxies). The fit quality is assessed by visual inspections, comparison to previous works, comparison of independent fits of galaxies in the overlap regions between KiDS tiles and bespoke simulations. The latter two are also used for a detailed investigation of systematic error sources. We find that our fit results are robust across various galaxy types and image qualities with minimal biases. Errors given by the MCMC underestimate the true errors typically by factors 2-3. Automated model selection criteria are accurate to > 90 % as calibrated by visual inspection of a subsample of galaxies. We also present g-r component colours and the corresponding colour-magnitude diagram, consistent with previous works despite our increased fit flexibility. Such reliable structural parameters for the components of a diverse sample of galaxies across multiple bands will be integral to various studies of galaxy properties and evolution. All results are integrated into the GAMA database.

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arXiv2022

Galaxy And Mass Assembly (GAMA): Data Release 4 and the z < 0.1 total and z < 0.08 morphological galaxy stellar mass functions

In Galaxy And Mass Assembly Data Release 4 (GAMA DR4), we make available our full spectroscopic redshift sample. This includes 248682 galaxy spectra, and, in combination with earlier surveys, results in 330542 redshifts across five sky regions covering ~250deg^2. The redshift density, is the highest available over such a sustained area, has exceptionally high completeness (95 per cent to r_KIDS=19.65mag), and is well suited for the study of galaxy mergers, galaxy groups, and the low redshift (z<0.25) galaxy population. DR4 includes 32 value-added tables or Data Management Units (DMUs) that provide a number of measured and derived data products including GALEX, ESO KiDS, ESO VIKING, WISE and Herschel Space Observatory imaging. Within this release, we provide visual morphologies for 15330 galaxies to z<0.08, photometric redshift estimates for all 18million objects to r_KIDS~25mag, and stellar velocity dispersions for 111830 galaxies. We conclude by deriving the total galaxy stellar mass function (GSMF) and its sub-division by morphological class (elliptical, compact-bulge and disc, diffuse-bulge and disc, and disc only). This extends our previous measurement of the total GSMF down to 10^6.75 M_sol h^-2_70 and we find a total stellar mass density of rho_*=(2.97+/-0.04)x10^8 M_sol h_70 Mpc^-3 or Omega_*=(2.17+/-0.03)x10^-3 h^-1_70. We conclude that at z<0.1, the Universe has converted 4.9+/-0.1 per cent of the baryonic mass implied by Big Bang Nucleosynthesis into stars that are gravitationally bound within the galaxy population.

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arXiv2022

A Chandra Virgo cluster survey of spiral galaxies. I. Introduction to the survey and a new ULX sample

We present an analysis of the ultraluminous X-ray source (ULX) population in 75 Virgo cluster late-type galaxies, including all those with a star formation rate >~ 1 M_{sun}/yr and a representative sample of the less star-forming ones. This study is based on 110 observations obtained over 20 years with the Chandra X-ray Observatory Advanced Camera for Imaging Spectroscopy. As part of a Large Chandra Program, new observations were obtained for 52 of these 75 galaxies. The data are complete to a sensitivity of about 10^{39} erg/s, with a typical detection limit of about 3 x 10^{38} erg/s for the majority of the sources. The catalogue contains about 80 ULXs (0.3-10 keV luminosity >10^{39} erg/s), and provides their location, observed flux, de-absorbed luminosity, and (for the 25 most luminous ones) simple X-ray spectral properties. We discuss the ULX luminosity function in relation to the mass and star formation rate of the sample galaxies. We show that recent models of low-mass plus high-mass X-ray binary populations (scaling with stellar mass and star formation rate, respectively) are mostly consistent with our observational results. We tentatively identify the most luminous X-ray source in the sample (a source in IC 3322A with L_{X} ~ 6 x 10^{40} erg/s) as a recent supernova or its young remnant. The properties of the sample galaxies (morphologies, stellar masses, star formation rates, total X-ray luminosities from their point-source population) are also summarised.

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arXiv2021

Central X-ray point-sources found to be abundant in low-mass, late-type galaxies predicted to contain an intermediate-mass black hole

Building upon three late-type galaxies in the Virgo cluster with both a predicted black hole mass of less than $\sim$10$^5$ M$_{\odot}$ and a centrally-located X-ray point-source, we reveal 11 more such galaxies, more than tripling the number of active intermediate-mass black hole candidates among this population. Moreover, this amounts to a 36$\pm$8% X-ray detection rate (despite the sometimes high, X-ray-absorbing, HI column densities), compared to just 10$\pm$5% for (the largely HI-free) dwarf early-type galaxies in the Virgo cluster. The expected contribution of X-ray binaries from the galaxies' inner field stars is negligible. Moreover, given that both the spiral and dwarf galaxies contain nuclear star clusters, the above inequality appears to disfavor X-ray binaries in nuclear star clusters. The higher occupation, or rather detection, fraction among the spiral galaxies may instead reflect an enhanced cool gas/fuel supply and Eddington ratio. Indeed, four of the 11 new X-ray detections are associated with known LINERs or LINER/HII composites. For all (four) of the new detections for which the X-ray flux was strong enough to establish the spectral energy distribution in the Chandra band, it is consistent with power-law spectra. Furthermore, the X-ray emission from the source with the highest flux (NGC 4197: $L_X \approx 10^{40}$ erg s$^{-1}$) suggests a non-stellar-mass black hole if the X-ray spectrum corresponds to the `low/hard state'. Follow-up observations to further probe the black hole masses, and prospects for spatially resolving the gravitational spheres-of-influence around intermediate-mass black holes, are reviewed in some detail.

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arXiv2021

Potential Black Hole Seeding of the Spiral Galaxy NGC 4424 via an Infalling Star Cluster

Galaxies can grow through their mutual gravitational attraction and subsequent union. While orbiting a regular high-surface-brightness galaxy, the body of a low-mass galaxy can be stripped away. However, the stellar heart of the infalling galaxy, if represented by a tightly-bound nuclear star cluster, is more resilient. From archival Hubble Space Telescope images, we have discovered a red, tidally-stretched star cluster positioned ~5 arcseconds (~400 pc in projection) from, and pointing toward the center of, the post-merger spiral galaxy NGC 4424. The star cluster, which we refer to as `Nikhuli', has a near-infrared luminosity of (6.88+/-1.85)x10^6 L_{solar,F160W} and likely represents the nucleus of a captured/wedded galaxy. Moreover, from our Chandra X-ray Observatory image, Nikhuli is seen to contain a high-energy X-ray point source, with L_{0.5-8 keV} = 6.31^{+7.50}_{-3.77}x10^{38} erg/s (90% confidence). We argue that this is more likely to be an active massive black hole than an X-ray binary. Lacking an outward-pointing comet-like appearance, the stellar structure of Nikhuli favors infall rather than the ejection from a gravitational-wave recoil event. A minor merger with a low-mass early-type galaxy may have sown a massive black hole, aided an X-shaped pseudobulge, and be sewing a small bulge. The stellar mass and the velocity dispersion of NGC 4424 predict a central black hole of (0.6-1.0)x10^5 M_solar, similar to the expected intermediate-mass black hole in Nikhuli, and suggestive of a black hole supply mechanism for bulgeless late-type galaxies. We may potentially be witnessing black hole seeding by capture and sinking, with a nuclear star cluster the delivery vehicle.

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arXiv2021

Galaxy and Mass Assembly (GAMA): The Weak Environmental Dependence of Quasar Activity at 0.1<z<0.35

Understanding the connection between nuclear activity and galaxy environment remains critical in constraining models of galaxy evolution. By exploiting extensive catalogued data from the Galaxy and Mass Assembly (GAMA) survey, we identify a representative sample of 205 quasars at 0.1 < z < 0.35 and establish a comparison sample of galaxies, closely matched to the quasar sample in terms of both stellar mass and redshift. On scales <1 Mpc, the galaxy number counts and group membership of quasars appear entirely consistent with those of the matched galaxy sample. Despite this, we find that quasars are ~1.5 times more likely to be classified as the group center, indicating a potential link between quasar activity and cold gas flows or galaxy interactions associated with rich group environments. On scales of ~a few Mpc, the clustering strength of both samples are statistically consistent and beyond 10 Mpc we find no evidence that quasars trace large scale structures any more than the galaxy control sample. Both populations are found to prefer intermediate-density sheets and filaments to either very high- or very low- density environments. This weak dependence of quasar activity on galaxy environment supports a paradigm in which quasars represent a phase in the lifetime of all massive galaxies and in which secular processes and a group-centric location are the dominant trigger of quasars at low redshift.

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arXiv2021

The (Black Hole Mass)-(Spheroid Stellar Density) Relations: $M_{\rm BH}$--$μ$ (and $M_{\rm BH}$--$Σ$) and $M_{\rm BH}$--$ρ$

This paper is the fourth in a series presenting (galaxy morphology, and thus galaxy formation)-dependent black hole mass, $M_{\rm BH}$, scaling relations. We have used a sample of 119 galaxies with directly-measured $M_{\rm BH}$ and host spheroid parameters obtained from multi-component decomposition of, primarily, $3.6\,μ$m Spitzer images. Here, we investigate the correlations between $M_{\rm BH}$ and the projected luminosity density $μ$, the projected stellar mass density $Σ$, and the deprojected (internal) stellar mass density $ρ$, for various spheroid radii. We discover the predicted $M_{\rm BH}$--$μ_{\rm 0,sph}$ relation and present the first $M_{\rm BH}$--$μ_{\rm e, sph}$ and $M_{\rm BH}$--$ρ_{\rm e,int, sph}$ diagrams displaying slightly different (possibly curved) trends for early- and late-type galaxies (ETGs and LTGs) and an offset between ETGs with (fast-rotators, ES/S0) and without (slow-rotators, E) a disk. The scatter about various $M_{\rm BH}$--$\langleΣ\rangle_{\rm R,sph}$ (and $\langleρ\rangle_{\rm r,sph}$) relations is shown to systematically decrease as the enclosing aperture (and volume) increases, dropping from 0.69~dex when using the spheroid \enquote{compactness}, $\langleΣ\rangle_{\rm 1kpc,sph}$, to 0.59~dex when using $\langleΣ\rangle_{\rm 5kpc,sph}$. We also reveal that $M_{\rm BH}$ correlates with the internal density, $ρ_{\rm soi,sph}$, at the BH's sphere-of-influence radius, such that core-Sérsic (high Sérsic index, $n$) and (low-$n$) Sérsic galaxies define different relations with total rms scatters 0.21~dex and 0.77~dex, respectively.(Abridged)

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arXiv2021

The Weak Lensing Radial Acceleration Relation: Constraining Modified Gravity and Cold Dark Matter theories with KiDS-1000

We present measurements of the radial gravitational acceleration around isolated galaxies, comparing the expected gravitational acceleration given the baryonic matter with the observed gravitational acceleration, using weak lensing measurements from the fourth data release of the Kilo-Degree Survey. These measurements extend the radial acceleration relation (RAR) by 2 decades into the low-acceleration regime beyond the outskirts of the observable galaxy. We compare our RAR measurements to the predictions of two modified gravity (MG) theories: MOND and Verlinde's emergent gravity. We find that the measured RAR agrees well with the MG predictions. In addition, we find a difference of at least $6σ$ between the RARs of early- and late-type galaxies (split by Sérsic index and $u-r$ colour) with the same stellar mass. Current MG theories involve a gravity modification that is independent of other galaxy properties, which would be unable to explain this behaviour. The difference might be explained if only the early-type galaxies have significant ($M_{gas} \approx M_*$) circumgalactic gaseous haloes. The observed behaviour is also expected in $Λ$CDM models where the galaxy-to-halo mass relation depends on the galaxy formation history. We find that MICE, a $Λ$CDM simulation with hybrid halo occupation distribution modelling and abundance matching, reproduces the observed RAR but significantly differs from BAHAMAS, a hydrodynamical cosmological galaxy formation simulation. Our results are sensitive to the amount of circumgalactic gas; current observational constraints indicate that the resulting corrections are likely moderate. Measurements of the lensing RAR with future cosmological surveys will be able to further distinguish between MG and $Λ$CDM models if systematic uncertainties in the baryonic mass distribution around galaxies are reduced.

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